Image forming method, image forming apparatus, image and inkjet ink

Abstract

The objective is to provide an image forming method, an image forming apparatus, an image, and an inkjet ink that can improve the varnishability of the formed image. [Solution] An image forming method comprising the steps of: applying an inkjet ink containing wax and a polymerizable compound to a substrate from an inkjet head; and irradiating the substrate to which the ink has been applied with an active ray to form an image, wherein the adhesion force distribution image Y obtained by measuring the force curve of the image surface using a scanning probe microscope is divided into two regions based on the magnitude of the adhesion force in a predetermined procedure, the region with low adhesion force is designated as region A, and the region with high adhesion force is designated as region B, and the area S of region A A The ratio S of the sum of the areas of region A and region B. A An image forming method that satisfies the condition / S is 0.70 or less.

Description

Technical Field

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

Background Art

[0002] The inkjet recording method is used in various printing fields because it can form an image simply and at low cost. As an ink used in the inkjet recording method, an inkjet ink (hereinafter referred to as inkjet ink) that is cured by an active ray and has a polymerizable compound (hereinafter referred to as polymerizable compound) that is polymerized by an active ray as a liquid component is known. When the active ray-curable inkjet ink is irradiated with an active ray, it is cured by the polymerization of the active ray-polymerizable compound, and the coloring material is firmly adhered to the base material. By forming this cured film, a desired image can be formed.

[0003] As one type of inkjet ink, an inkjet ink containing a gelling agent (wax) is known.

[0004] For example, Patent Document 1 discloses a radiation-curable inkjet ink composition containing a first ester compound and a second ester compound. In Patent Document 1, it is said that by gelling the ink, excessive wet spread of the ink droplets can be suppressed (pinning property can be enhanced).

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] In inkjet inks containing wax as a gelling agent, the wax is dissolved by heating the inkjet ink during ejection, and then the wax crystallizes as the liquid temperature drops upon impact with the substrate, causing the inkjet ink to gel. By sufficiently increasing the gelling properties of the inkjet ink, the inkjet ink thickens sufficiently upon cooling after impact with the substrate, making it easier to improve the pinning properties of the inkjet ink.

[0007] On the other hand, with inkjet inks containing wax, varnish is sometimes applied to the resulting image. Images obtained using such inkjet technology sometimes exhibited poor wettability or adhesion to the varnish layer (i.e., poor varnishability) when varnished.

[0008] According to the inventors' research, there was a problem with the poor varnishability of images obtained from the inkjet ink described in Patent Document 1.

[0009] The present invention has been made in view of the above circumstances, and aims to provide an image forming method, an image forming apparatus, an image, and an inkjet ink that can improve the varnishability of the formed image. [Means for solving the problem]

[0010] One aspect of the present invention, for solving the above problems, relates to the image forming methods described below [1] to [4].

[0011] [1] A step of applying an inkjet ink containing wax and a polymerizable compound to a substrate from an inkjet head, The process involves irradiating a substrate coated with the aforementioned inkjet ink with an active ray to form an image, An image forming method including, The adhesion force distribution image Y obtained by measuring the force curve of the image surface using a scanning probe microscope is subjected to Otsu's binarization process to determine the adhesion force threshold. The image is then divided into two regions based on the magnitude of the adhesion force relative to the threshold, with the region with low adhesion force designated as region A and the region with high adhesion force designated as region B. The area S of region A is then defined. A The ratio S of the sum of the areas of region A and region B. A / S satisfies 0.70 or less. Image forming method.

[0012] [2] The inkjet ink contains two or more types of wax, The total mass of the two or more waxes is 1.0% to 10.0% by mass relative to the total mass of the inkjet inks. In the case where, among the two or more waxes mentioned above, the wax with the highest mass content and the wax with the second highest mass content are designated as the high-melting-point wax and the wax with the low-melting-point wax, The melting point of the high-melting-point wax is 5°C or more higher than the melting point of the low-melting-point wax. The mass content of the high-melting-point wax is 1.0% to 10.0% by mass relative to the mass content of the low-melting-point wax. The image formation method described in [1].

[0013] [3] The HSP distance between the high melting point wax and the polymerizable compound and the HSP distance between the low melting point wax and the polymerizable compound are both within the range of 2.5 to 6.5. The image formation method described in [2].

[0014] [4] The melting point of the high-melting-point wax is 10°C or more higher than the melting point of the low-melting-point wax. The mass content of the high-melting-point wax is 2.0% to 6.0% by mass relative to the mass content of the low-melting-point wax. The HSP distance between the high-melting-point wax and the polymerizable compound, and the HSP distance between the low-melting-point wax and the polymerizable compound are 3.5 to 5.5. The image formation method described in [3].

[0015] One aspect of the present invention, for solving the above problems, relates to the image forming apparatus described in [5] below.

[0016] An image forming apparatus used in any of the image forming methods described in [5][1] to [4], A storage section for storing the aforementioned inkjet ink, An inkjet head that applies the aforementioned inkjet ink to a substrate, An irradiation unit that irradiates with the aforementioned active ray, An image forming apparatus, including one.

[0017] One aspect of the present invention, for solving the above problems, relates to the image shown in [6] below.

[0018] An image formed by any of the image forming methods described in [6][1] to [4].

[0019] One aspect of the present invention, for solving the above problems, relates to the inkjet inks described in [7] to

[10] below.

[0020] [7] An inkjet ink that hardens by irradiation with an active ray, containing a wax and a polymerizable compound, The aforementioned inkjet ink is applied to high-quality coated paper at a substrate temperature of 40°C at a rate of 11 g / m². 2 The coating obtained by applying it was subjected to an integrated light intensity of 400 mJ / m 2 In the image obtained by curing with ultraviolet irradiation, The adhesion force distribution image Y' obtained by measuring the force curve of the image surface using a scanning probe microscope is used to determine the adhesion force threshold by Otsu's binarization process. The image is then divided into two regions based on the magnitude of the adhesion force relative to the threshold, with the region with low adhesion force designated as region A' and the region with high adhesion force designated as region B'. The area S of region A is then defined. AThe ratio S' of the sum of the areas of region A' and region B'. A ' / S' satisfies 0.70 or less, Inkjet ink.

[0021] [8] The inkjet ink contains two or more types of wax, The total mass of the two or more waxes is 1.0% to 10.0% by mass relative to the total mass of the inkjet inks. In the case where, among the two or more waxes mentioned above, the wax with the highest mass content and the wax with the second highest mass content are designated as the high-melting-point wax and the wax with the low-melting-point wax, The melting point of the high-melting-point wax is 5°C or more higher than the melting point of the low-melting-point wax. The mass content of the high-melting-point wax is 1.0% to 10.0% by mass relative to the mass content of the low-melting-point wax. [7] The inkjet ink described below.

[0022] [9] The HSP distance between the high melting point wax and the polymerizable compound and the HSP distance between the low melting point wax and the polymerizable compound are both within the range of 2.5 to 6.5. [8] The inkjet ink described above.

[0023]

[10] The melting point of the high-melting-point wax is 10°C or more higher than the melting point of the low-melting-point wax. The mass content of the high-melting-point wax is 2.0% to 6.0% by mass relative to the mass content of the low-melting-point wax. The HSP distance between the high-melting-point wax and the polymerizable compound, and the HSP distance between the low-melting-point wax and the polymerizable compound are 3.5 to 5.5. [9] The inkjet ink described below. [Effects of the Invention]

[0024] According to the present invention, it is possible to provide an image forming method, an image forming apparatus, an image, and an inkjet ink that can improve the varnishability of the formed image. [Brief explanation of the drawing]

[0025] [Figure 1A] Figure 1A shows an example of an adhesion force distribution image obtained by measuring the force curve of an image surface using a scanning probe microscope. [Figure 1B] Figure 1B is an example of an image obtained by image processing the adhesion force distribution image from Figure 1A using Otsu's binarization process. [Figure 2] Figure 2 is a schematic diagram showing the configuration of an image forming apparatus capable of carrying out the image forming method according to this embodiment. [Modes for carrying out the invention]

[0026] The embodiments of the present invention will be described in detail below. However, the present invention is not limited to the following embodiments.

[0027] In this specification, numerical ranges represented using "~" mean a range that includes the numbers written before and after "~" as the lower and upper limits, respectively.

[0028] Furthermore, in this specification, "(meth)acrylate" means either acrylate or methacrylate, or both, and "(meth)acrylic" means either acrylic or methacrylic, or both.

[0029] 1. Image forming method The image forming method according to this embodiment is: A process of applying an inkjet ink containing wax and a polymerizable compound to a substrate from an inkjet head, The process involves irradiating a substrate coated with the aforementioned inkjet ink with an active ray to form an image, An image forming method including, Regarding the adhesion force distribution image Y obtained by the force curve measurement of the image surface using a scanning probe microscope, the threshold value of the adhesion force is determined by Otsu's binarization process, and the adhesion force is divided into two regions based on the magnitude of the adhesion force with respect to the threshold value. When the region with a small adhesion force is defined as region A and the region with a large adhesion force is defined as region B, the area S of region A A and the ratio S of the area of region A to the total area S of the areas of region A and region B A / S satisfies 0.70 or less, It is preferably an image forming method.

[0030] The above adhesion force distribution image Y is obtained by measuring an image with a scanning probe microscope (Dimension iCON, manufactured by BRUKER) in a measurement range of 30 μm (resolution: 256 pix) in the PeakForce QNM (Quantitative nanoscale mechanical characterization) mode.

[0031] Also, the above Otsu's binarization process can be performed using known image processing software. Examples of known image processing software include image J, Fiji, Image Pro, WinROOF, and Python.

[0032] Hereinafter, the procedure for calculating the above S A / S will be described using FIGS. 1A and 1B.

[0033] FIG. 1A shows an example of an adhesion force distribution image Y obtained by force curve measurement of an image formed by the image forming method according to the present embodiment using the above scanning probe microscope. In FIG. 1A, the shading of the color indicates the magnitude of the adhesion force at each measurement point, and the dark-colored part indicates a location with a small adhesion force, and the light-colored part indicates a location with a large adhesion force.

[0034] Furthermore, Figure 1B is obtained by converting the adhesion force distribution image Y shown in Figure 1A into an 8-bit grayscale image, performing histogram equalization, and then dividing it into two regions based on the magnitude of the adhesion force using Otsu's binarization process. The region with high adhesion force (region B) is shown in black, and the region with low adhesion force (region A) is shown in white. In Figure 1B, the respective areas S of region A and region B. A S B S is calculated, A And, S B The sum of these two areas is equal to the total area S of the area of ​​region A and the area of ​​region B.

[0035] S is calculated from the area of ​​region A and region B calculated in this way. A / S can be an indicator of the wax coverage of an image for the following reasons:

[0036] Wax readily forms a sea-island structure on the image surface, and areas with high and low wax coverage exhibit different adhesive forces. We found that the reason for the difference in adhesive forces obtained by force curve measurement between areas with high and low wax coverage is due to the difference between the adhesive forces of polymerizable compounds and wax. The adhesive force measured by force curve measurement corresponds to the force acting between the probe of a scanning probe microscope and the measurement surface. The force acting between the probe and the measurement surface depends on the surface energy and hardness of the measurement surface. In other words, adhesive forces tend to be greater in areas with high surface energy (high hydrophilic areas).

[0037] Generally, polymerizable compounds that impart reactive curability to inkjet inks include highly polar compounds such as acrylates and methacrylates. Furthermore, since wax needs to be compatible with polymerizable compounds when heated and crystallize when cooled, it is often modified to introduce less polar functional groups, such as long-chain hydrocarbon groups, to reduce its compatibility with polymerizable compounds to a certain extent. Therefore, areas with a high amount (uneven distribution) of wax tend to have lower hydrophilicity and weaker adhesion (region A). Conversely, areas with a low amount (uneven distribution) of wax tend to have higher hydrophilicity and stronger adhesion (region B). For these reasons, S A We found that / S can be an indicator of the wax coverage rate in an image.

[0038] S identified by the method described above A The reason why varnish suitability tends to improve when an image formation method is used that results in a / S of 0.70 or less is not entirely clear, but it can be considered as follows.

[0039] Generally, polymerizable compounds that impart curability to inkjet inks using active rays include highly polar compounds such as acrylates and methacrylates. Furthermore, since waxes need to be compatible with polymerizable compounds when heated and crystallize when cooled, they are often modified to have a somewhat lower compatibility with polymerizable compounds by introducing less polar functional groups, such as long-chain hydrocarbon groups.

[0040] Varnish, like the polymerizable compounds mentioned above, may contain highly polar compounds such as acrylates and methacrylates. Therefore, the compatibility between polymerizable compounds and components in the varnish tends to be high, while the compatibility between wax and components in the varnish tends to be relatively low. Consequently, images obtained by image forming methods that reduce the wax coverage on the image surface are less likely to repel when varnish is applied, and adhesion to the varnish layer tends to improve.

[0041] Based on the above, it is thought that the suitability for varnishing will be increased.

[0042] S A To achieve a / S of 0.70 or less, adjust the ink formula as described below. A To make ' / S' smaller (for example, S A Examples of configurations that adjust the temperature ( / S) to ≤ 0.70, or by incorporating a wipe process or post-heating process as described later, are possible, but the method is not limited to these.

[0043] S A The upper limit of / S is 0.70 or less, and preferably 0.63 or less. Setting it to 0.63 or less makes it easier to improve varnish wettability. From the viewpoint of making it easier to improve varnish adhesion, 0.55 or less is even more preferable.

[0044] S A The lower limit of / S is preferably 0.25 or higher. Setting it to 0.25 or higher suppresses adhesion between images and to the paper surface due to the wax deposited on the image surface, thus improving blocking properties. From a similar viewpoint, 0.35 or higher is more preferable, and 0.45 or higher is even more preferable.

[0045] The inkjet ink according to this embodiment, based on the above findings, will be described in more detail below.

[0046] 1-1. Inkjet ink The inkjet ink according to this embodiment comprises a wax and a polymerizable compound, and may also contain other components such as a colorant, a pigment dispersant, a polymerization initiator, a polymerization inhibitor, and a surfactant.

[0047] Furthermore, the inkjet ink according to this embodiment is The aforementioned inkjet ink is applied to high-quality coated paper at a substrate temperature of 40°C at a rate of 11 g / m². 2 The coating obtained by applying it was subjected to an integrated light intensity of 400 mJ / m 2 In the image obtained by curing with ultraviolet irradiation, The adhesion force distribution image Y' obtained by measuring the force curve of the image surface using a scanning probe microscope is used to determine the adhesion force threshold by Otsu's binarization process. The image is then divided into two regions based on the magnitude of the adhesion force relative to the threshold, with the region with low adhesion force designated as region A' and the region with high adhesion force designated as region B'. The area S of region A is then defined. A The ratio S' of the sum of the areas of region A' and region B'. A ' / S' satisfies 0.70 or less, Inkjet ink is preferred.

[0048] The image formation process to obtain the adhesion force distribution image Y' is specifically carried out as follows: Inkjet ink is introduced into the HA1024 inkjet head (manufactured by Konica Minolta) of a line-type inkjet recording device (manufactured by Konica Minolta). The inkjet head is then applied to high-quality coated paper at a substrate temperature of 40°C at a rate of 11 g / m². 2 The coating obtained by applying each ink was subjected to an integrated light intensity of 400 mJ / m 2 The images were formed by curing the material with ultraviolet light. The inkjet head temperature was 80°C, and the substrate was OK Topcoat+ 127g / m². 2 (Manufactured by Oji Paper Co., Ltd.) was used. In addition, a solid 5cm x 5cm image was printed to form the image, and an LED lamp (395nm, water-cooled LED, manufactured by Phoseon Technology) placed downstream of the recording device was used to measure 400mJ / m³. 2 The ink is cured by UV irradiation. A piezo head is used for the inkjet head, and the ejection conditions are such that the volume of one drop is 9.0 pl, and the liquid is ejected at a liquid velocity of approximately 6 m / s, recording at a resolution of 1200 dpi × 1200 dpi. The recording speed was set to 500 mm / s. Image formation was performed in an environment of 23°C and 55% RH, and as mentioned above, the temperature of the substrate at the time of inkjet ink impact was adjusted to 40°C.

[0049] The adhesion force distribution image Y' is obtained using the same measuring device and conditions as the adhesion force distribution image Y described above.

[0050] Furthermore, the Otsu binarization process performed on the adhesion force distribution image Y' is carried out using the same method as the process performed on the adhesion force distribution image Y described above.

[0051] For the adhesion force distribution image Y', the adhesion force threshold is determined by Otsu's binarization process, and it is divided into two regions, region A' and region B', S A The procedure for calculating ' / S' is as follows: For the adhesion force distribution image Y described above, the adhesion force threshold is determined by Otsu's binarization process, and the image is divided into two regions, region A and region B, and S is calculated. A The procedure is the same as the procedure for calculating / S.

[0052] S is calculated from the area of ​​region A' and region B' calculated in this way. A ' / S' can serve as an indicator of the wax coverage rate of an image obtained by a certain image forming method using the inkjet ink according to this embodiment.

[0053] S A Examples of ink configurations that result in ' / S' being 0.70 or less include configurations in which the wax and / or polymerizable compound are in the preferred embodiments described later.

[0054] S A The upper limit of ' / S' is 0.70 or less, and preferably 0.63 or less. Setting it to 0.63 or less makes it easier to improve the wettability of the varnish. Furthermore, from the viewpoint of making it easier to improve the adhesion of the varnish, it is more preferable to set it to 0.55 or less.

[0055] S A The lower limit of ' / S' is preferably 0.25 or higher. Setting it to 0.25 or higher suppresses adhesion between images and to the paper surface due to the wax deposited on the image surface, thus improving the blocking properties. From a similar viewpoint, 0.35 or higher is more preferable, and 0.45 or higher is even more preferable.

[0056] 1-1-1. Wax Wax is a compound that dissolves in polymerizable compounds contained in inkjet ink when the inkjet ink containing it is heated (e.g., to 80°C). Furthermore, wax is a compound that crystallizes in the inkjet ink and gels it when the liquid temperature drops (e.g., to 40°C) as the inkjet ink is ejected from the inkjet head and lands on the surface of the substrate.

[0057] The aforementioned wax preferably contains two or more types of wax to enhance its varnishability. Furthermore, among the two or more types of wax, the wax with the highest mass content and the wax with the second highest mass content are designated as the high-melting-point wax and the wax with the lower melting-point wax. In this case, each wax satisfies the following requirements 1-2 and 3-2, which is important for S A It is preferable to lower the ' / S' value to make it easier to improve varnishability. Furthermore, it is even preferable that each wax satisfies all of the following requirements 1-1 to 3-2, as this also makes it easier to improve the pinning and ejection properties of the inkjet ink. (Requirement 1-1) The total mass of the two or more types of wax is 1.0% by mass or more of the total mass of the inkjet ink. (Requirement 1-2) The total mass of the two or more types of wax is 10.0% by mass or less of the total mass of the inkjet ink. (Requirement 2) The melting point of the high-melting-point wax is 5°C or higher than the melting point of the low-melting-point wax. (Requirement 3-1) The mass content of the high-melting-point wax is 1.0% by mass or more relative to the mass content of the low-melting-point wax. (Requirement 3-2) The mass content of the high-melting-point wax is 10.0% by mass or less relative to the mass content of the low-melting-point wax.

[0058] The reason why the varnishability of the formed image is more likely to improve when the two or more waxes satisfy the above-mentioned preferred embodiments is thought to be as follows.

[0059] As mentioned above, the wax is formulated to have a relatively low compatibility with polymerizable compounds, including highly polar compounds.

[0060] Among waxes, high-melting-point waxes tend to have worse compatibility with polymerizable compounds compared to low-melting-point waxes. For example, they may have a higher molecular weight due to the increased number of hydrocarbon groups introduced, or their polarity may be reduced due to the elongated chain length of the hydrocarbon groups. Therefore, when using two or more types of waxes, increasing the proportion of high-melting-point wax tends to increase the wax coverage of the image during image formation.

[0061] Therefore, in order to satisfy (Requirement 1-2), the total amount of wax in the inkjet ink is adjusted so as not to be too large, and in order to satisfy (Requirement 3-2), the addition ratio of high-melting-point wax, which has relatively low compatibility with polymerizable compounds, is reduced relative to low-melting-point wax, thereby improving the wax coverage of the image during image formation (S A The ' / S' factor is reduced, making it easier to further improve varnishability.

[0062] Furthermore, the reason why the two or more waxes described above satisfy the more preferable embodiments makes it easier to improve the pinning and ejection properties of the formed inkjet ink is thought to be as follows.

[0063] Furthermore, by adjusting the total amount of wax in the inkjet ink so that it does not become too low in order to satisfy (Requirement 1-1), the gelling properties of the inkjet ink can be easily improved. Then, by adjusting the melting point (structure) and addition ratio of the high-melting-point wax in order to satisfy (Requirement 2) and (Requirement 3-1), a small amount of high-melting-point wax with a different structure from the low-melting-point wax can be used to prevent the low-melting-point wax from becoming too densely aggregated when it crystallizes into a plate-like form, thus making it easier to create voids (three-dimensional spaces). This makes it easier to form a structure (cardhouse structure) that contains polymerizable compounds, making it easier for the inkjet ink to thicken, and thus making it easier to improve the pinning and ejection properties of the inkjet ink.

[0064] Furthermore, by satisfying requirements 2 and 3-2, even when the addition ratio of high-melting-point wax is low, the high-melting-point wax crystallizes first as the temperature of the low-inkjet ink decreases, acting as a seed crystal and promoting the crystallization of the low-melting-point wax. Therefore, even with a relatively small amount of high-melting-point wax added, the gelation temperature of the inkjet ink can be sufficiently raised, improving the gelability of the inkjet ink and making it easier to improve the pinning and ejection properties of the inkjet ink.

[0065] Based on the above, it is considered that by having two or more of the above-mentioned waxes satisfy the more preferred embodiments, it becomes easier to achieve both the pinning properties of the inkjet ink and the varnishability of the formed image.

[0066] Examples of waxes include aliphatic ketones, aliphatic esters, glycerol compounds, pentaerythritol compounds, petroleum waxes, plant waxes, animal waxes, mineral waxes, hydrogenated castor oil, modified waxes, higher fatty acids, higher alcohols, hydroxystearic acid, fatty acid amides including N-substituted fatty acid amides and special fatty acid amides, higher amines, esters of sucrose fatty acids, synthetic waxes, dibenzylidene sorbitol, dimer acid, and dimer ol. Of these, from the viewpoint of increasing solubility in polymerizable compounds at high temperatures and increasing crystallinity in polymerizable compounds at low temperatures, the wax is preferably aliphatic ketone, aliphatic ester, higher fatty acid, and higher alcohol, with aliphatic ketone and aliphatic ester being more preferred.

[0067] Examples of aliphatic ketones include, Dibehenyl ketone, diheptadecyl ketone (stearone), distearyl ketone, dieicosyl ketone, dipalmytil ketone, dilauryl ketone, dimyristyl ketone, myristylpalmytil ketone, and palmitylstearyl ketone This includes, etc.

[0068] Examples of aliphatic esters include, Behenyl behenate, eicosyl eicosanoate, stearyl stearate, palmityl stearate, behenyl stearate, myristyl myristate, cetyl myristate, oleyl palmitate, cetyl palmitate, and other monoalcohol fatty acid esters. Fatty acid esters of polyhydric alcohols such as glycerin fatty acid esters, sorbitan fatty acid esters, propylene glycol fatty acid esters, ethylene glycol fatty acid esters, polyoxyethylene fatty acid esters, and pentaerythritol fatty acid esters. It includes.

[0069] Examples of pentaerythritol fatty acid esters include pentaerythritol tetrastearate, pentaerythritol distearate, and pentaerythritol tetrapalmitate.

[0070] Examples of higher fatty acids include behenic acid, arachidic acid, stearic acid, palmitic acid, myristic acid, lauric acid, oleic acid, and erucic acid.

[0071] Examples of higher alcohols include stearyl alcohol and behenyl alcohol.

[0072] From the viewpoint of enhancing gelatinization, it is preferable that at least one of the two carbon chains flanking the ketone group or ester group in the aliphatic ketone and aliphatic ester has 12 to 22 carbon atoms. From the same viewpoint, it is more preferable that both carbon chains have 12 to 22 carbon atoms. When the number of carbon atoms is 12 or more, the crystallinity of the wax tends to increase, and more space tends to be created in the cardhouse structure. As a result, polymerizable compounds tend to be sufficiently encapsulated in the space, and the pinning properties of the inkjet ink tend to increase. Furthermore, when both carbon chains have 12 to 22 carbon atoms, the crystallinity tends to increase even further, and the pinning properties tend to increase even more. Also, when the number of carbon atoms is 22 or less, the solubility of the wax tends to increase, and the suitability for varnishing tends to improve.

[0073] Furthermore, the hydrocarbon chains contained in aliphatic ketones and aliphatic esters are preferably straight-chain hydrocarbon chains. When the hydrocarbon chains are straight-chain, the polarity of the wax can be reduced, which tends to decrease its compatibility with polymerizable compounds and increases the crystallinity of the wax.

[0074] Examples of aliphatic ketones containing hydrocarbon chains with 12 to 22 carbon atoms include dibehenyl ketone (21-22 carbon atoms), diheptadecyl ketone (stearone) (17-17 carbon atoms), distearyl ketone (17-18 carbon atoms), dieicosyl ketone (19-20 carbon atoms), dipalmityl ketone (15-16 carbon atoms), dimyristyl ketone (13-14 carbon atoms), dilauryl ketone (11-12 carbon atoms), and lauryl myristyl ketone. This includes lucetones (11-14 carbon atoms), lauryl palmityl ketones (11-16 carbon atoms), myristyl palmityl ketones (13-16 carbon atoms), myristyl stearyl ketones (13-18 carbon atoms), myristyl behenyl ketones (13-22 carbon atoms), palmityl stearyl ketones (15-18 carbon atoms), palmityl behenyl ketones (15-22 carbon atoms), and stearyl behenyl ketones (17-22 carbon atoms), etc. The carbon numbers in parentheses above represent the number of carbon atoms in each hydrocarbon chain bonded to the carbon atom of the carbonyl group.

[0075] Examples of aliphatic esters containing hydrocarbon chains with 12 to 22 carbon atoms include behenyl behenate (21-22 carbon atoms), eicosyl eicosanoate (19-20 carbon atoms), stearyl stearate (17-18 carbon atoms), palmityl stearate (17-16 carbon atoms), lauryl stearate (17-12 carbon atoms), behenyl stearate (17-22 carbon atoms), cetyl palmitate (15-16 carbon atoms), stearyl palmitate (15-18 carbon atoms), and myristate. This includes stil (13-14 carbon atoms), cetyl myristate (13-16 carbon atoms), octyldodecyl myristate (13-20 carbon atoms), stearyl oleate (17-18 carbon atoms), stearyl erucate (21-18 carbon atoms), stearyl linoleate (17-18 carbon atoms), behenyl oleate (18-22 carbon atoms), arachidyl linoleate (17-20 carbon atoms), pentaerythritol tetrastearate (17-17-17-17 carbon atoms), etc. The carbon numbers in parentheses above represent the number of carbon atoms in the hydrocarbon chain bonded to the carbon and oxygen atoms of the ester group.

[0076] The lower limit of the wax content is preferably 1.00% by mass or more, more preferably 2.00% by mass or more, and even more preferably 3.00% by mass or more, relative to the total mass of the inkjet ink. The upper limit of the wax content is preferably 10.00% by mass or less, more preferably 8.00% by mass or less, relative to the total mass of the inkjet ink. Furthermore, the upper limit of the wax content is even more preferably 6.00% by mass or less, and most preferably 4.00% by mass or less, relative to the total mass of the inkjet ink. Setting the wax content to 1.00% by mass or more makes it easier to improve the pinning and ejection properties of the inkjet ink. Setting it to 2.00% by mass or more makes it easier to improve the gelling properties of the inkjet ink, and thus improves the pinning properties of the ink. Setting it to 3.00% by mass or more makes it even easier to improve the pinning properties of the ink. Setting it to 10.00% by mass or less makes it easier to reduce the wax coating rate of the image, and thus improves the suitability for varnishing. By setting the amount to 8.00% by mass or less, the amount of wax near the surface of the image during image formation is reduced, which improves varnishability. By setting it to 6.00% by mass or less, varnishability is further improved. Furthermore, by setting it to 4.00% by mass or less, the amount of wax added, which is relatively difficult to dissolve in polymerizable compounds, is reduced, making it less likely for wax to precipitate near the nozzle during or before dispensing, thus improving injection performance. When two or more types of wax are included, the preferred range for the total mass of the wax is the same as the preferred range for the content mass of the wax.

[0077] The melting point of the wax is preferably 105°C or lower, more preferably 89°C or lower, and even more preferably 82°C or lower. When the melting point is 105°C or lower, the wax dissolves more easily with polymerizable compounds, the wax coverage of the image tends to decrease, and the suitability for varnishing tends to increase. Furthermore, when the melting point is 89°C or lower, the suitability for varnishing tends to increase even further, the crystallization rate of the gelling agent slows down, a stronger cardhouse structure is more easily formed, and the viscosity of the inkjet ink tends to increase. Furthermore, the melting point of the wax is preferably 30°C or higher, and more preferably 40°C or higher. When the melting point is 30°C or higher, the crystallinity of the wax can be further increased, making it easier to improve gelability. When two or more types of wax are included, it is preferable that the melting points of all waxes fall within the above ranges. The melting points of each wax were obtained using a differential scanning calorimeter "Diamond DSC" (manufactured by PerkinElmer). The melting point is measured under the following conditions (heating and cooling conditions): a first heating process where the temperature is raised from room temperature (25°C) to 110°C at a heating rate of 10°C / min and held isothermally at 110°C for 5 minutes; a cooling process where the temperature is cooled from 110°C to 0°C at a cooling rate of 10°C / min and held isothermally at 0°C for 5 minutes; and a second heating process where the temperature is raised from 0°C to 110°C at a heating rate of 10°C / min. The above measurement is performed by sealing 3.0 mg of the sample in an aluminum pan and setting it in the sample holder of a differential scanning calorimeter "Diamond DSC". An empty aluminum pan is used as a reference. In the above measurement, analysis is performed on the endothermic curve obtained during the first heating process, and the top temperature of the endothermic peak (full width at half maximum within 15°C) derived from the crystalline polyester resin is taken as the melting point (Tm) of the wax.

[0078] When two or more types of wax are included, the melting point of the high-melting-point wax is preferably 5°C or more higher than the melting point of the low-melting-point wax, more preferably 10°C or more higher, and even more preferably 10°C to 45°C higher. A melting point 5°C or more higher allows sufficient precipitation (seed crystals) of the high-melting-point wax to occur at the time of precipitation of the low-melting-point wax, thereby increasing gelatinization properties. By keeping the difference in melting points to 45°C or less, it is possible to suppress excessive crystallization of the high-melting-point wax at the time of precipitation of the low-melting-point wax, which can lead to excessively large seed crystals, thus increasing interaction with the low-melting-point wax.

[0079] When two or more types of wax are included, with regard to (Requirement 2), the following methods can be used to obtain a wax with a melting point 5°C or higher: increasing the number of hydroxyl groups (number of functional groups) of the alcohol used as a raw material for the aliphatic ester, and increasing the number of carbon atoms in the hydrocarbon chain contained in the aliphatic ketone and aliphatic ester.

[0080] When two or more types of wax are included, with respect to (Requirement 3), the lower limit of the mass content of high-melting-point wax is preferably 1.0% by mass or more relative to the mass content of low-melting-point wax. It is more preferably 2.0% by mass or more, and even more preferably 3.5% by mass or more. The upper limit of the mass content of high-melting-point wax is preferably 10.0% by mass or less, more preferably 6.0% by mass or less, and even more preferably 5.5% by mass or less, relative to the mass content of low-melting-point wax. Setting it to 1.0% by mass or more makes it easier to form the cardhouse structure described above, makes it easier for the inkjet ink to thicken, and makes it easier to improve the pinning and ejection properties of the inkjet ink. Setting it to 10.0% by mass or less reduces the addition ratio of high-melting-point wax, which is relatively difficult to dissolve in polymerizable compounds, making it easier for the wax coating rate of the image to decrease and making it easier to improve varnishability. Setting it to 6.0% by mass or less reduces the addition ratio of high-melting-point wax, which is relatively difficult to dissolve in polymerizable compounds, making it less likely for wax to precipitate on the image surface and making it easier to improve varnishability. Furthermore, by keeping the wax content below 6.0% by mass, wax is less likely to precipitate near the nozzle during or before dispensing, thus improving injection performance.

[0081] The inkjet ink may contain three or more types of wax, but it is preferable to have two types in order to easily achieve the effects of the present invention. If there are three or more types, the total mass of the two waxes consisting of the wax with the highest mass content and the wax with the second highest mass content is preferably 85% to 100% by mass, more preferably 90% to 100% by mass, and even more preferably 95% to 100% by mass, relative to the total mass of wax contained in the inkjet ink.

[0082] The wax may or may not have polymerizable groups within its molecule. Specifically, the wax may or may not be polymerizable by activated radiation.

[0083] When the wax contains polymerizable groups, the number of polymerizable groups is preferably 1 to 3. From the viewpoint of making it easier to form linear molecules of the wax and thereby further improving the crystallinity of the wax, the number of polymerizable groups is more preferably 1 to 2.

[0084] Examples of polymerizable groups include (meth)acryloyl groups, vinyl groups, and ethynyl groups. Of these, (meth)acryloyl groups are preferred.

[0085] The weight-average molecular weight of the gelling agent is preferably 150 to 1300, and more preferably 450 to 1000. The above molecular weight can be measured using gel permeation chromatography.

[0086] 1-1-2.Polymerizable compound Polymerizable compounds are components not found in waxes and are compounds that polymerize and crosslink upon irradiation with active rays. Preferably, the polymerizable compound is a radical polymerizable compound.

[0087] Furthermore, the polymerizable compound is preferably liquid at 30°C, from the viewpoint of adjusting the viscosity of the inkjet ink at or near room temperature and improving its ejection performance.

[0088] Examples of the active rays mentioned above include electron beams, ultraviolet rays, alpha rays, gamma rays, and X-rays. Of these, ultraviolet rays and electron beams are preferred, with ultraviolet rays being more preferred.

[0089] Radical polymerizable compounds are compounds (monomers, oligomers, polymers, or mixtures thereof) that have ethylenically unsaturated bonds that can be radically polymerized. Radical polymerizable compounds may be used alone or in combination of two or more types.

[0090] Examples of compounds having ethylenically unsaturated bonds that can be radically polymerized include unsaturated carboxylic acids and their salts, unsaturated carboxylic acid ester compounds, unsaturated carboxylic acid urethane compounds, unsaturated carboxylic acid amide compounds and their anhydrides. Other examples of compounds having ethylenically unsaturated bonds that can be radically polymerized include acrylonitrile, unsaturated polyesters, unsaturated polyethers, unsaturated polyamides, and unsaturated urethanes. Examples of unsaturated carboxylic acids include (meth)acrylic acid, itaconic acid, crotonic acid, isocrotonic acid, and maleic acid.

[0091] The radical polymerizable compound is preferably an unsaturated carboxylic acid ester compound, and among these, it is more preferably a (meth)acrylate from the viewpoint of facilitating the dissolution of the gelling agent in the ink.

[0092] Examples of monofunctional (meth)acrylates include isoamyl (meth)acrylate, stearyl (meth)acrylate, lauryl (meth)acrylate, octyl (meth)acrylate, decyl (meth)acrylate, isomirsutyl (meth)acrylate, isostearyl (meth)acrylate, 2-ethylhexyl-diglycol (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 2-(meth)acryloyloxyethylhexahydrophthalic acid, butoxyethyl (meth)acrylate, ethoxydiethylene glycol (meth)acrylate, methoxydiethylene glycol (meth)acrylate, and methoxypolyethyl This includes ethylene glycol (meth)acrylate, methoxypropylene glycol (meth)acrylate, phenoxyethyl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, isobornyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxy-3-phenoxypropyl (meth)acrylate, 2-(meth)acryloyloxyethyl succinic acid, 2-(meth)acryloyloxyethyl phthalic acid, 2-(meth)acryloyloxyethyl-2-hydroxyethyl phthalic acid, and t-butylcyclohexyl (meth)acrylate.

[0093] Examples of polyfunctional (meth)acrylates include triethylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, 1,4-butanediol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, 1,10-decanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, tricyclodecanedimethanol di(meth)acrylate, and neopentyl glycol hydroxypivalate. This includes difunctional (meth)acrylates comprising di(meth)acrylate, polytetramethylene glycol di(meth)acrylate, polyethylene glycol diacrylate, and tripropylene glycol diacrylate, as well as trifunctional or more (meth)acrylates comprising trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, glycerin propoxy tri(meth)acrylate, and pentaerythritol ethoxytetra(meth)acrylate.

[0094] The polymerizable compound preferably does not have a linear hydrocarbon chain with 12 or more carbon atoms. This configuration makes it easier to increase the crystallinity of the wax and improve the pinning properties of the inkjet ink.

[0095] Furthermore, the polymerizable compound preferably contains a (meth)acrylate having at least one (meth)acroyl group, and preferably contains a polymerizable compound having two or more (meth)acryloyl groups. It is preferable that the polymerizable compound does not contain a polymerizable compound having 10 or more (meth)acroyl groups. When there are two or more (meth)acrylate groups, the polarity of the polymerizable compound tends to increase, the crystallinity of the wax tends to increase, and the pinning properties of the inkjet ink tend to increase. By not containing a polymerizable compound having 10 or more (meth)acrylate groups, a moderate cross-linked structure is formed, which increases the toughness of the image, suppresses cohesive breakdown between the image and the varnish layer when varnish is applied, and tends to increase varnish adhesion.

[0096] On the other hand, from the viewpoint of improving compatibility with waxes and further enhancing the solubility of waxes, it is preferable that the radical polymerizable compound contains a (meth)acrylate having an ethylene oxide (EO) group or a propylene oxide (PO) group. Generally, (meth)acrylates have ester groups and tend to be highly polar. On the other hand, EO groups or PO groups have lower polarity compared to ester groups, and thus tend to have higher compatibility with relatively low-polarity waxes, such as those having long-chain alkyl groups.

[0097] The number of EO groups or PO groups contained in the (meth)acrylate having an EO group or PO group is preferably 1 to 14, and more preferably 2 to 12.

[0098] Examples of (meth)acrylates having an EO group or a PO group include polyethylene glycol diacrylate, EO-modified 1,6-hexanediol di(meth)acrylate, EO-modified nonylphenol (meth)acrylate, EO-modified cresol (meth)acrylate, EO-modified pentaerythritol tetraacrylate, EO-modified dipentaerythritol pentaacrylate, EO-modified dipentaerythritol hexaacrylate, EO-modified bisphenol A diacrylate, EO-modified ditrimethylolpropane tetraacrylate, EO-modified trimethylolpropane tri(meth)acrylate, PO-modified nonylphenol (meth)acrylate, PO-modified neopentyl glycol diacrylate, PO-modified trimethylolpropane tri(meth)acrylate, and PO-modified bisphenol A diacrylate.

[0099] The radical polymerizable compound may include modified acrylates such as urethane-modified acrylate, epoxy-modified acrylate, and polyester acrylate. Furthermore, the radical polymerizable compound may also include oligomers such as polyester oligomers.

[0100] Polymerizable compounds may include cationic polymerizable compounds. Examples of cationic polymerizable compounds include epoxy compounds, vinyl ether compounds, and oxetane compounds.

[0101] It is preferable that the HSP distance between the high-melting-point wax and the polymerizable compound, and the HSP distance between the low-melting-point wax and the polymerizable compound, are both within the range of 2.5 to 6.5. Furthermore, it is more preferable that the HSP distances are both within the range of 3.0 to 6.5, even more preferable that they are both between 3.5 to 5.5, and most preferable that they are both between 4.0 to 5.5. When the HSP distances are both 2.5 or greater, the compatibility between the wax and the polymerizable compound can be lowered, making it easier for crystallization to occur during cooling and improving pinning properties. When the HSP distances are both 3.5 or greater, the compatibility with the polymerizable compound is moderately low, making it easier for the wax to crystallize, and as a result of reduced wax mobility, uneven distribution of the wax on the image surface is suppressed, thus improving varnishability. When the HSP distances are both 4.0 or greater, the compatibility is moderate, making it easier for the wax to crystallize during cooling, and as a result of reduced wax mobility, it becomes less likely to precipitate near the image surface, thus further improving varnishability. When the HSP distance is 6.5 or less for all waxes, the compatibility between each wax and the polymerizable compound increases, making it less likely for the wax to precipitate and thus improving its varnishing properties. In addition, by moderately increasing compatibility, the wax becomes more viscous due to crystallization, which improves injection molding and pinning properties.

[0102] The HSP distance between each wax and the polymerizable compound is calculated as follows.

[0103] First, the HSP values ​​(Hansen solubility parameters: dispersion term (dD), polarity term (dP), and hydrogen bonding term (dH)) for each wax and polymerizable compound are calculated using the computer software Hansen Solubility Parameters in Practice 5th Edition 5.0.13 (HSPiP, manufactured by Tegara Co., Ltd.) by inputting the chemical structural formula into the software. The HSP value is based on the idea that "two substances with similar intermolecular interactions readily dissolve in each other" (as described in "Chemical Industry Co., Ltd., Chemical Industry, March 2010 issue, Hiroshi Yamamoto, Steven Abbott, Charles M. Hansen"). The HSP value consists of the following three parameters, and these three parameters can be considered as coordinates in three-dimensional space (also called "Hansen space"). The distance between these coordinates of two substances is called the HSP distance, and the closer the HSP distance, the higher the affinity and the more readily the substances dissolve in each other. δD: Energy due to intermolecular dispersion forces δP: Energy due to intermolecular dipole interactions δH: Energy due to intermolecular hydrogen bonding

[0104] The HSP distance between a high-melting-point wax or low-melting-point wax and a polymerizable compound (or a mixture of polymerizable compounds if multiple polymerizable compounds are included) is calculated using the following formula. In the following formula, the dispersion, polarity, and hydrogen bonding terms of one component of the wax and polymerizable compound (or mixture thereof) for which the HSP distance is calculated are denoted as dD, dP, and dH, respectively. The dispersion, polarity, and hydrogen bonding terms of the other component are denoted as dD', dP', and dH', respectively. If multiple polymerizable compounds are included, the parameters (dD, dP, and dH) of the polymerizable compound mixture are obtained by multiplying each parameter (dD, dP, and dH) of each polymerizable compound by the molar ratio of each compound in the inkjet ink and adding these values ​​together. HSP distance = (4 × (dD - dD') 2 +(dP-dP') 2 +(dH-dH') 2 ) 1 / 2

[0105] The polymerizable compound content is preferably 1% to 97% by mass, and more preferably 30% to 95% by mass, based on the total mass of the inkjet ink. Furthermore, the polymerizable compound content is even more preferably 50% to 95% by mass, and most preferably 70% to 95% by mass, based on the total mass of the inkjet ink.

[0106] 1-1-3. Other ingredients 1-1-3-1. Colorants In this embodiment, the inkjet ink may contain a colorant as needed.

[0107] The coloring agent is either a dye or a pigment, but pigments are preferred because they have good dispersibility with the components of inkjet ink and excellent weather resistance. Depending on the colors of the image to be formed, the pigment can be selected from, for example, yellow pigment, red or magenta pigment, blue or cyan pigment, black pigment, and white pigment.

[0108] Examples of yellow pigments include CIPigment Yellow (hereinafter also simply referred to as "PY") 1, PY3, PY12, PY13, PY14, PY17, PY34, PY35, PY37, PY55, PY74, PY81, PY83, PY93, PY94, PY95, PY97, PY108, PY109, PY110, PY137, PY138, PY139, PY153, PY154, PY155, PY157, PY166, PY167, PY168, PY180, PY185, and PY193, among others.

[0109] Examples of red or magenta pigments include CIPigment Red (hereinafter also simply referred to as "PR") 3, PR5, PR19, PR22, PR31, PR38, PR43, PR48:1, PR48:2, PR48:3, PR48:4, PR48:5, PR49:1, PR53:1, PR57:1, PR57:2, PR58:4, PR63:1, PR81, PR81:1, PR81:2, PR81:3, PR81:4, PR88, PR104, PR108, PR112, PR122, PR123, PR144, PR146, PR149, PR166, PR168, PR169, PR170, PR177, PR178, PR179, PR184, PR185, PR208, PR216, PR226, and PR257, CIPigment This includes Violet (hereinafter also simply referred to as "PV") 3, PV19, PV23, PV29, PV30, PV37, PV50, and PV88, as well as CIPigment Orange (hereinafter also simply referred to as "PO") 13, PO16, PO20, and PO36, etc.

[0110] Examples of blue or cyan pigments include CIPigment Blue (hereinafter also simply referred to as "PB") 1, PB15, PB15:1, PB15:2, PB15:3, PB15:4, PB15:6, PB16, PB17-1, PB22, PB27, PB28, PB29, PB36, and PB60, among others.

[0111] Examples of green pigments include CIPigment Green (hereinafter also simply referred to as "PG") 7, PG26, PG36, and PG50.

[0112] Examples of black pigments include CIPigment Black (hereinafter simply referred to as "PBk"). This includes 7, PBk26, and PBk28, etc.

[0113] The white pigment can be any pigment that causes the cured film formed by the hardening of white ink to exhibit a white color. Examples of white pigments include inorganic pigments such as titanium dioxide, zinc oxide, calcium carbonate, barium sulfate, and aluminum hydroxide. Of these, titanium dioxide is preferred.

[0114] The crystalline form of the titanium dioxide described above may be rutile, anatase, or blue kite. From the viewpoint of making it easier to reduce the particle size of the white pigment, the anatase type, which has a lower specific gravity, is preferred, and from the viewpoint of further improving the opacity of the formed image, the rutile type, which has a higher refractive index in the visible light region, is preferred.

[0115] The colorant content is preferably 0.1% to 10.0% by mass, and more preferably 1.0% to 5.0% by mass, relative to the total mass of the inkjet ink. If a white pigment is included, the white pigment content is preferably 3.0% to 8.0% by mass.

[0116] 1-1-3-2. Pigment Dispersant The above inkjet ink may contain a pigment dispersant for dispersing the pigment.

[0117] Examples of pigment dispersants include hydroxyl group-containing carboxylic acid esters, salts of long-chain polyaminoamides and high molecular weight acid esters, salts of high molecular weight polycarboxylic acids, salts of long-chain polyaminoamides and polar acid esters, high molecular weight unsaturated acid esters, polymer copolymers, modified polyurethanes, modified polyacrylates, polyether ester-type anionic surfactants, naphthalene sulfonic acid formalin condensate salts, aromatic sulfonic acid formalin condensate salts, polyoxyethylene alkyl phosphate esters, polyoxyethylene nonylphenyl ether, and stearylamine acetate. Examples of commercially available pigment dispersants include the Azisper series (manufactured by Ajinomoto Fine Techno Co., Ltd.).

[0118] The pigment dispersant content is preferably 10% to 200% by mass, and more preferably 20% to 100% by mass, relative to the total mass of the pigment. When the dispersant content is 10% or more by mass relative to the total mass of the pigment, the dispersion stability of the pigment is enhanced, and when the dispersant content is 200% or less by mass relative to the total mass of the pigment, the ink ejection performance from the inkjet head becomes more stable.

[0119] 1-1-3-3. Polymerization Initiators The inkjet ink according to this embodiment may contain an active ray polymerization initiator (hereinafter simply referred to as "polymerization initiator"). The polymerization initiator should be capable of initiating the polymerization of the active ray polymerizable compound described above by irradiation with an active ray. For example, when the inkjet ink contains a radical polymerizable compound, the polymerization initiator can be a radical polymerization initiator. Also, for example, when the inkjet ink contains a cationic polymerizable compound, the polymerization initiator can be a cationic polymerization initiator (photoacid generator). Note that when the inkjet ink can be sufficiently cured without a polymerization initiator, such as when curing the inkjet ink by electron beam irradiation, the polymerization initiator is not necessary.

[0120] Radical polymerization initiators include intramolecular bond cleavage type radical polymerization initiators and intramolecular hydrogen abstraction type radical polymerization initiators.

[0121] Examples of intramolecular bond cleavage type radical polymerization initiators include: Acetophenone-based initiators including diethoxyacetophenone, 2-hydroxy-2-methyl-1-phenylpropan-1-one, benzyldimethylketal, 1-(4-isopropylphenyl)-2-hydroxy-2-methylpropan-1-one, 4-(2-hydroxyethoxy)phenyl-(2-hydroxy-2-propyl)ketone, 1-hydroxycyclohexyl-phenylketone, 2-methyl-2-morpholino(4-methylthiophenyl)propan-1-one, and 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butanone, etc. Benzoin compounds, including benzoin, benzoin methyl ether, and benzoin isopropyl ether, Acylphosphine oxide initiators, including phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide (product name: Omnirad 819, manufactured by IGM Resins BV), Furthermore, it includes benzyl and methylphenylglyoxyester, among others.

[0122] Examples of intramolecular hydrogen abstraction type radical polymerization initiators include: Benzophenone-based initiators including benzophenone, o-methyl benzoylbenzoate, 4-phenylbenzophenone, 4,4'-dichlorobenzophenone, hydroxybenzophenone, 4-benzoyl-4'-methyl-diphenyl sulfide, acrylic benzophenone, 3,3',4,4'-tetra(t-butylperoxycarbonyl)benzophenone, and 3,3'-dimethyl-4-methoxybenzophenone, Thioxanthone-based initiators including 2-isopropylthioxanthone, 2,4-dimethylthioxanthone, 2,4-diethylthioxanthone, 2,4-dichlorothioxanthone, etc. Aminobenzophenone-based initiators including Michler ketone and 4,4'-diethylaminobenzophenone, This includes 10-butyl-2-chloroacridone, 2-ethylanthraquinone, 9,10-phenanthrenequinone, and camphorquinone, among others.

[0123] Examples of cationic polymerization initiators include photoacid generators. B(C6F5)4 aromatic onium compounds, including diazonium, ammonium, iodonium, sulfonium, and phosphonium. - PF6 - AsF6 - SbF6 - CF3SO3 - salt, etc. Sulfonates that produce sulfonic acid, Hydrogen halides are photocatalytic halides. and iron allene complexes, etc. It includes.

[0124] The content of the polymerization initiator is not particularly limited, as long as the inkjet ink is sufficiently cured by irradiation with active rays (e.g., ultraviolet light) without reducing its applicability to the substrate surface. For example, the content of the polymerization initiator is preferably 0.1% to 20% by mass, and more preferably 1% to 10% by mass, based on the total mass of the inkjet ink.

[0125] 1-1-3-4. Polymerization inhibitors In this embodiment, the inkjet ink may contain a polymerization inhibitor.

[0126] Examples of polymerization inhibitors include (alkyl)phenol, hydroquinone, catechol, resorcinol, p-methoxyphenol, t-butylcatechol, t-butylhydroquinone, pyrogallol, 1,1-picrylhydrazyl, phenothiazine, p-benzoquinone, nitrosobenzene, 2,5-di-t-butyl-p-benzoquinone, dithiobenzoyl disulfide, picric acid, cuperone, aluminum N-nitrosophenylhydroxylamine, tri-p-nitrophenylmethyl, N-(3-oxyanilino-1,3-dimethylbutylidene)aniline oxide, dibutylcresol, cyclohexanone oxime cresol, guaiacol, o-isopropylphenol, butyraldoxime, methyl ethyl ketoxime, and cyclohexanone oxime.

[0127] The content of the polymerization inhibitor is not particularly limited, but is preferably 0.1% to 10% by mass relative to the total mass of the inkjet ink.

[0128] 1-1-3-5. Surfactants In this embodiment, the inkjet ink may contain a surfactant for adjusting the surface tension.

[0129] Examples of surfactants include, Anionic surfactants including dialkyl sulfosuccinates, alkylnaphthalene sulfonates, and fatty acid salts, Nonionic surfactants including polyoxyethylene alkyl ethers, polyoxyethylene alkyl allyl ethers, acetylene glycols, and polyoxyethylene / polyoxypropylene block copolymers, Cationic surfactants containing alkylamine salts and quaternary ammonium salts, It contains silicone-based surfactants as well as fluorine-based surfactants.

[0130] Examples of commercially available silicone-based surfactants include KF-351A, KF-352A, KF-353, KF-354L, and KF-355A (all manufactured by Shin-Etsu Chemical Co., Ltd.).

[0131] The surfactant content is not particularly limited, but is preferably 0.001% to 10% by mass, and more preferably 0.001% to 1.0% by mass, relative to the total mass of the inkjet ink.

[0132] In this embodiment, the inkjet ink may, in addition to the above components, optionally contain a fixing resin, viscosity modifier, resistivity modifier, film-forming agent, ultraviolet absorber, antioxidant, fade inhibitor, mold inhibitor, rust inhibitor, and the like.

[0133] 1-1-4. Physical properties of inkjet inks The viscosity of the inkjet ink at 80°C is preferably 3 mPa·s to 20 mPa·s, and more preferably 5 mPa·s to 15 mPa·s. This improves the ejection performance when the inkjet ink is heated and ejected in the inkjet head.

[0134] The viscosity can be measured using a rheometer. For example, the pre-coating agent is heated to 100°C, and the viscosity is measured using a stress-controlled rheometer (Anton Paar, Physica MCR301 (cone plate diameter: 75 mm, cone angle: 1.0°)). The inkjet ink is cooled to 20°C under conditions of a shear rate of 11.7 (1 / s) and a cooling rate of 0.1°C / s to obtain a viscosity temperature dependence curve. The viscosity can then be determined by reading the viscosity at 80°C from the obtained temperature dependence curve.

[0135] Furthermore, the viscosity of the above inkjet ink at 35°C is preferably 3 Pa·s or more, more preferably 10 Pa·s or more, and even more preferably 15 Pa·s or more. The upper limit of the viscosity is not particularly limited, but for example, it is 300 Pa·s. The viscosity can be determined by reading the viscosity at 35°C from the temperature change curve described above.

[0136] 1-1-5. Method for preparing inkjet ink Inkjet ink can be prepared by mixing the aforementioned wax, polymerizable compound, and any other components under heating. It is preferable to filter the resulting mixture through a predetermined filter. When preparing an ink containing a pigment, it is preferable to prepare a pigment dispersion containing the pigment and an activated polymerizable compound, and then mix the pigment dispersion with the other components. The pigment dispersion may further contain a dispersant.

[0137] The above-mentioned pigment dispersion can be prepared by dispersing a pigment in a polymerizable compound. Pigment dispersion can be performed using, for example, a ball mill, sand mill, attritor, roll mill, agitator, Henschel mixer, colloid mill, ultrasonic homogenizer, pearl mill, wet jet mill, or paint shaker. A dispersant may also be added at this time.

[0138] Furthermore, when using multiple polymerizable compounds, the polymerizable compounds may be mixed first to prepare a polymerizable composition, and then the polymerizable composition, wax, and any other components may be mixed under heating.

[0139] 1-2. Image forming method The image forming method according to this embodiment is: A process of applying an inkjet ink containing wax and a polymerizable compound to a substrate from an inkjet head, The process involves irradiating a substrate coated with the aforementioned ink with an active ray to form an image, Includes, A scraping step is performed in which the surface of the image formed after the hardening step is scraped with a scraping member, A post-heating step is performed on the image formed through the curing step, The process involves coating the image formed on the aforementioned image surface with varnish, It may include.

[0140] Makes it easier to improve varnish suitability (S A From the viewpoint of making it easier to reduce S, it is preferable to include the above-mentioned scraping step and / or post-heating step. A From the viewpoint of making it easier to reduce / S, it is even more preferable to include a scraping step, and from the viewpoint of making it easier to achieve both varnishability and blocking properties (making it easier to widen the margin for conditions that achieve both varnishability and blocking properties), it is even more preferable to include a post-heating step.

[0141] 1-2-1. Inkjet Ink Application Process In this process, the aforementioned inkjet ink is ejected from the inkjet head and applied to the surface of the substrate (at a position corresponding to the image to be formed).

[0142] The inkjet head can use either an on-demand or continuous ejection method.

[0143] On-demand inkjet heads are Electromechanical conversion methods such as single-cavity type, double-cavity type, bender type, piston type, shear mode type, and sheared wall type, Furthermore, electrical-to-thermal conversion methods such as thermal inkjet type and bubble jet ("bubble jet" is a registered trademark of Canon Inc.) type. Any of the above is acceptable. Furthermore, the inkjet head can be either a scanning type or a line-type inkjet head.

[0144] Since inkjet ink droplets are ejected in a heated, sol-like state, it is preferable to set the temperature of the inkjet ink during inkjet head loading to be between the gelation temperature of the inkjet ink + 10°C and 30°C. When the temperature of the inkjet ink inside the inkjet head is 10°C or higher than the gelation temperature, a decrease in ejection performance due to ink gelation inside the inkjet head or on the nozzle surface is less likely to occur. On the other hand, when the temperature of the ink inside the inkjet head is 30°C or lower than the gelation temperature, degradation of components due to high temperature is less likely to occur. The gelation temperature of the inkjet ink is measured by the following method: The inkjet ink is heated to 100°C, and its viscosity is measured using a stress-controlled rheometer, Physica MCR301 (cone plate diameter: 75 mm, cone angle: 1.0°), manufactured by Anton Paar. The ink is cooled to 20°C under conditions of a shear rate of 11.7 (1 / s) and a cooling rate of 0.1°C / s to obtain a viscosity temperature dependence curve. The gelation temperature is defined as the temperature at which the viscosity changes to 200 mPa·s in the viscosity temperature dependence curve.

[0145] The method for heating inkjet ink is not particularly limited. For example, at least one of the ink supply system, such as the ink tank (housing section) that makes up the head carriage, the supply pipe and the pre-chamber ink tank (housing section) immediately before the head, the filtered piping and the piezo head, can be heated with a panel heater, ribbon heater and warm water, etc.

[0146] From the viewpoint of further improving recording speed and image quality, the amount of inkjet ink droplets ejected is preferably between 2 pL and 20 pL.

[0147] The base material is not particularly limited and can be ordinary uncoated paper, coated paper, synthetic paper YUPO ("YUPO" is a registered trademark of YUPO Corporation), various plastics used in flexible packaging, and their films. Examples of various plastic films include PP film, PET film, OPS film, OPP film, ONy film, PVC film, PE film, and TAC film. Other plastics that can be used include polycarbonate, (meth)acrylic resin, ABS, polyacetal, PVA, and rubbers.

[0148] The substrate temperature at the time of inkjet ink deposition is preferably 1°C to 25°C lower than the gelation temperature of the inkjet ink, more preferably 5°C to 25°C lower, and even more preferably 10°C to 25°C lower. By setting the substrate temperature within this range, it becomes easier to achieve both the pinning properties of the inkjet ink and the varnishability of the image obtained from the inkjet ink.

[0149] 1-2-2.Curing process In this process, the droplets of inkjet ink applied to the substrate in the application step are irradiated with an active ray to cure the droplets. This forms an image consisting of a cured film of the inkjet ink.

[0150] The active ray can be selected from, for example, electron beams, ultraviolet rays, alpha rays, gamma rays, and X-rays, but ultraviolet rays or electron beams are preferred. The ultraviolet ray is preferably light having a peak wavelength of 360 nm to 410 nm. Furthermore, the ultraviolet ray is preferably irradiated from an LED light source. LEDs emit less radiant heat compared to conventional light sources (e.g., metal halide lamps). Therefore, when irradiated with an active ray, LEDs make it less likely for the ink to melt and less likely to cause uneven gloss.

[0151] 1-2-3. Rubbing process In this process, the surface of the image formed through the curing process is rubbed by a scraping member. As a result, some of the components of the inkjet ink present on the image surface are removed, and the image surface may be modified.

[0152] As mentioned above, waxes are formulated to have a relatively low compatibility with polymerizable compounds. For example, waxes with low-polarity functional groups, such as long-chain hydrocarbon groups, tend to be unevenly distributed on the image surface, easily forming a wax-uneven layer. By rubbing an image covered with such a wax-uneven layer, some of the components of the image surface, including the wax-uneven layer, are removed, making it easier to expose layers with a higher proportion of polymerizable compounds. This reduces the wax coverage and improves the suitability for varnishing.

[0153] Examples of abrasive members include: Natural fibers such as cotton (cellulose fiber), silk, and wool; Synthetic fibers such as nylon, rayon, polyurethane, polyester, and acrylic resin; Or woven, knitted, nonwoven, gauze, and felt fabrics made from composite fibers combining these; In addition to regular uncoated paper and coated paper, synthetic paper; Various plastics (PP, PET, OPS, OPP, ONy, PVC, PE, TAC, polycarbonate, (meth)acrylic resin, ABS, polyacetal, PVA, rubbers) and films made from them; These may be used. Among these, cotton is preferred, and cotton No. 3-1 is particularly preferred.

[0154] From the viewpoint of suppressing scratches on the image surface and easily achieving both varnishability and blocking properties, it is preferable that the abrasive material contains a solvent that does not easily dissolve the various components of the inkjet ink. Suitable solvents that do not easily dissolve the various components of the inkjet ink are solvents with relatively high hydrophilicity, such as methanol, ethanol, 1-propanol, 1-butanol, and other alcohols. Among these solvents, ethanol is preferred from the viewpoint of safety.

[0155] The rubbing may be performed continuously or in a batch format.

[0156] Examples of processes involving continuous friction include: A method in which a rotating abrasive roller is brought into contact with the surface of an image formed through the hardening process, using an abrasive roller around which the above-mentioned abrasive member is wrapped, A method of bringing a sheet-shaped abrasive member into contact with the surface of an image formed through the hardening process, using the sheet-shaped abrasive member described above. These are some examples.

[0157] For example, a process that involves scraping in a batch format is: A method of changing the relative position with respect to a substrate by bringing a rotating abrasive roller or a sheet-like abrasive member into contact with the image surface formed through the above curing process. These are some examples.

[0158] The degree to which the image surface is modified can be controlled by factors such as the material of the abrasive member, the relative movement speed of the abrasive member with respect to the substrate, the pressure applied by the abrasive member to the image surface, and the number of times the image is abraded by the abrasive member. For example, when using an abrasive roller, it can also be controlled by factors such as the rotation speed of the abrasive roller and the overlap angle of the substrate with respect to the abrasive roller.

[0159] The pressing pressure of the abrasive member against the image surface is not particularly limited and can be appropriately selected depending on the purpose, but 1 Pa to 5 Pa is preferred, and 2 Pa to 3 Pa is more preferred.

[0160] The speed at which the relative position of the abrasive member with respect to the base material is changed is not particularly limited and can be appropriately selected depending on the purpose, but 240 m / h to 540 m / h is preferred, and 300 m / h to 420 m / h is more preferred.

[0161] There are no particular restrictions on the number of times the image is rubbed by the abrasive member, and it can be appropriately selected depending on the purpose, but 40 to 100 times is preferred, and 60 to 80 times is more preferred.

[0162] 1-2-4. Post-heating process In this process, the image formed through the curing process is subjected to heat treatment. This increases the mobility of each component of the inkjet ink present on the image surface. For example, if the components have high compatibility, mixing of the components will progress, or if the components have low compatibility, aggregation of identical components will progress, or phase separation will progress among the components. As a result, the components of the inkjet ink present on the image surface change before and after the post-heating process, and the image surface may be modified.

[0163] As mentioned above, waxes are adjusted to have a relatively low compatibility with polymerizable compounds. For example, waxes with low-polarity functional groups such as long-chain hydrocarbon groups tend to be unevenly distributed on the image surface, easily forming a layer of unevenly distributed wax. When such images are heat-treated, the waxes tend to aggregate. At this time, the aggregated waxes tend to aggregate into a spherical shape to reduce the contact area with the polymerizable compounds. When the unevenly distributed wax layer that was covering the image in layers changes to a spherical state, the distribution changes to accumulate in the thickness direction, making it easier to expose layers with a high proportion of polymerizable compounds. As a result, the wax coverage rate tends to decrease, and the suitability for varnishing tends to increase.

[0164] The means for the aforementioned heating treatment are not particularly limited as long as they can uniformly heat the recording surface of the recording medium, and can be appropriately selected according to the purpose. Examples of heating means include hot air heating by blowing hot air onto the printing surface, drum heating by heating a drum roller in contact with the substrate, and heater heating by placing a nichrome wire heater, halogen heater, ceramic heater, carbon heater, etc., near the image.

[0165] There are no particular restrictions on the heating temperature in the aforementioned post-heating step, and it can be appropriately selected according to the purpose, but 75°C to 120°C is preferred, and 90°C to 100°C is more preferred. If the heating temperature is 75°C or higher, surface modification will proceed sufficiently, and the suitability for varnishing will tend to improve. If the heating temperature is 120°C or lower, changes in gloss due to surface modification can be suppressed.

[0166] There are no particular restrictions on the heating time in the aforementioned post-heating step, and it can be appropriately selected according to the purpose, but 2 to 80 minutes is preferred, 4 to 12 minutes is more preferred, and 4 to 7 minutes is even more preferred. If the heating time is 2 minutes or more, surface modification will proceed sufficiently and varnishability will be easily improved. If the heating time is 80 minutes or less, high productivity can be achieved. Furthermore, if the heating time is 10 minutes or less, even higher productivity can be achieved, and if the heating time is 7 minutes or less, even higher productivity can be achieved.

[0167] 1-2-5. Process of applying varnish to the image In the process of applying varnish to the image layer, varnish is applied to the image formed by the image forming method for aesthetic and protective purposes. If drying is not required with the inkjet ink, varnish can be applied immediately after image formation.

[0168] Varnishing is a technique that involves coating the surface of an image with varnish. It is performed to give the image surface a glossy finish, thereby enhancing the quality of the recording, and to improve the scratch resistance and chemical resistance of the image surface.

[0169] Commercially available varnishes can be used, including: Digital Printing Varnish PL-LV, KM-EP Varnish KM-2, KM-3, UV Roll Coat Varnish RI-13, RI-13-K2, RI-16, RI-FX-3, RI-XG33, CX-1, CX-2, CX-3, UV Coat Varnish AT-B, UV VECTA Coat Varnish PC-3KW2 (manufactured by T&K TOKA), UV Gloss Varnish ULTRASHEEN UV-9021A (manufactured by ACTEGA), UV Matte Varnish 5070E, Soft Touch ULTRASHEEN UV-XT3037 (manufactured by KUSTOM&GROU), Plus Size (registered trademark) OP-5267, OP-5275 (manufactured by Go-O Chemical Co., Ltd.), FD Clear Coat PC, C-YS (manufactured by Toyo Ink Co., Ltd.), Brightone (registered trademark) TUV (manufactured by Sakata Inx Co., Ltd.), and DC POD Clear UV. Examples include SP-001~003 (manufactured by DIC Corporation).

[0170] In particular, from the standpoint of adhesion, an oil-based varnish is preferable. Specific examples of oil-based varnishes include UV VECTA Coat Varnish PC-3KW2 (manufactured by T&K TOKA), Plus Size (registered trademark) OP-5267, OP-5275 (manufactured by Go-o Chemical Co., Ltd.), and FD Clear Coat C-YS (manufactured by Toyo Ink Co., Ltd.).

[0171] The method of applying the varnish is not particularly limited and may be by inkjet or other methods. Methods other than inkjet include bar coating, spray coating, curtain coating, roll coating, screen printing, offset printing, gravure printing, methods using plates such as letterpress and intaglio plates, and other methods that do not use plates. Among these, screen printing, offset printing, gravure printing, or bar coating are preferred from the viewpoint of ease of work and uniform application.

[0172] From the standpoint of simplifying the apparatus configuration and reducing the cost of image formation, the method for applying the varnish is particularly preferably an inkjet method.

[0173] Furthermore, if the varnish is an active-ray curing type varnish, after applying the varnish to the image layer, the varnish is irradiated with active rays to cure it. From the viewpoint of simplifying the setup of the device and efficiently forming images, it is preferable that the conditions for irradiating the varnish with active rays be the same as the conditions for irradiating the inkjet ink with active rays.

[0174] The varnishing process may be performed using different machines for the image formation process and the varnishing process on the image layer, or it may be performed at different locations on the same machine. A step of transporting the substrate on which the image layer has been formed may be included between the image formation process and the varnishing process on the image layer. From the viewpoint of high speed, the transport speed of the substrate is preferably in the range of 30 to 120 m / min.

[0175] 2. Image forming apparatus The following describes an image forming apparatus 100 capable of performing the image forming method described above.

[0176] Figure 2 is a schematic diagram showing the configuration of an image forming apparatus 100 according to this embodiment. As shown in Figure 2, the image forming apparatus 100 has an inkjet head 110, a transport unit 120, and an irradiation unit 130, and may also have a heating unit 140 and a friction unit (not shown). Note that in Figure 2, the arrows indicate the transport direction of the substrate, and the dimensional ratios in the drawing are exaggerated for illustrative purposes and may differ from the actual ratios.

[0177] The inkjet head 110 has a nozzle surface 113 on which the nozzle 111 ejection ports are located, which faces the transport unit 120 when forming an image, and ejects inkjet ink onto the substrate 200 transported by the transport unit 120. From the viewpoint of improving the ejection performance of the inkjet ink, the inkjet head 110 may have a temperature adjustment means for adjusting the ink temperature to lower the viscosity of the ink. Examples of temperature adjustment means include a panel heater, a ribbon heater, and a heating means using warm water.

[0178] The inkjet head 110 may be a scanning type inkjet head whose width in the direction perpendicular to the substrate transport direction is smaller than the substrate 200, or it may be a line type inkjet head whose width in the direction perpendicular to the substrate transport direction is larger than the substrate 200.

[0179] The nozzle 111 has an outlet on the nozzle surface 113. The number of nozzles 111 can be equal to or greater than the number of inks used for image formation (e.g., 4).

[0180] The transport unit 120 transports the substrate 200 so that, when forming an image, the substrate 200 facing the inkjet head 110 moves directly below the inkjet head 110 in the vertical direction. For example, the transport unit 120 has a drive roller 121, a driven roller 122, and a transport belt 123.

[0181] The irradiation unit 130 irradiates the upper surface of the transport unit 120 with an active ray. This irradiates the inkjet ink droplets that have landed on the transported substrate 200 with the active ray, thereby curing the droplets. The irradiation unit 130 can be positioned downstream of the inkjet head 110 and directly above the transport unit 120.

[0182] The heating unit 140 heats the transport unit 120 from above. This heats the image that has been cured by the irradiation unit 130 and formed on the substrate 200, thereby modifying the image surface. The heating unit 140 can be positioned downstream of the irradiation unit 130. In Figure 2, the heating unit 140 is shown positioned directly above the transport unit 120, but the heating unit 140 may also be positioned on the underside of the transport unit (the side opposite to the inkjet-applied surface of the substrate).

[0183] The image forming apparatus 100 may also have a friction section (not shown) in addition to the above configuration. When the friction process is performed continuously from the inkjet ink application process and the curing process, for example, a friction roller with a friction member wrapped around it can be arranged downstream of the irradiation unit 130 and directly above the transport unit 120, at a position where the rotating friction roller contacts the image surface. A sheet-like friction member may also be arranged as the friction section, downstream of the irradiation unit 130 and directly above the transport unit 120, at a position where the sheet-like friction member contacts the image surface.

[0184] Furthermore, the image forming apparatus 100 may also have, in addition to the above configuration, a storage section (not shown) for storing inkjet ink before ejection, and an ink channel (not shown) that allows inkjet ink to flow between the storage section and the inkjet head 110. The image forming apparatus 100 may also have a control unit (not shown) that controls the operation of the inkjet head 110, the transport section 120, and the irradiation section 130.

[0185] The image forming apparatus 100 is shown as having a configuration in which the inkjet ink application process, curing process, and post-heating process are carried out in succession, but the scraping process and post-heating process may be carried out by a separate apparatus.

[0186] The image forming apparatus 100 may include an intermediate transfer body and a transfer unit (neither of which are shown). In this case, the inkjet head 110 ejects inkjet ink onto the intermediate transfer body, causing it to land on the surface of the intermediate transfer body, and forms an intermediate image on the surface of the intermediate transfer body, which is made up of aggregated droplets of inkjet ink. Subsequently, the transfer unit transfers the intermediate image from the surface of the intermediate transfer body to the surface of the substrate. Then, the irradiation unit 130 irradiates the intermediate image transferred to the surface of the substrate with an active ray to harden the droplets of inkjet ink. [Examples]

[0187] The present invention will be described below with reference to examples. The scope of the present invention is not to be limited by the examples.

[0188] 1. Preparation / Synthesis of Materials The materials used to prepare the inkjet ink are listed below.

[0189] 1-1. Wax Stearyl stearate (melting point: 50.0℃) Cetyl palmitate (melting point: 40.0℃) Behenyl behenate (melting point: 79.0°C) Stearon (melting point: 62.0℃) Behenyl stearate (melting point: 67.0°C) Pentaerythritol tetrastearate (melting point: 64.0℃)

[0190] The melting points of each wax were obtained using a differential scanning calorimeter "Diamond DSC" (manufactured by PerkinElmer). The melting point was measured under the following conditions (heating and cooling conditions): a first heating process where the temperature was raised from room temperature (25°C) to 110°C at a heating rate of 10°C / min and held isothermally at 110°C for 5 minutes; a cooling process where the temperature was cooled from 110°C to 0°C at a cooling rate of 10°C / min and held isothermally at 0°C for 5 minutes; and a second heating process where the temperature was raised from 0°C to 110°C at a heating rate of 10°C / min. The above measurements were performed by sealing 3.0 mg of the sample in an aluminum pan and setting it in the sample holder of the differential scanning calorimeter "Diamond DSC". An empty aluminum pan was used as a reference. In the above measurement, analysis was performed on the endothermic curve obtained during the first heating process, and the top temperature of the endothermic peak (full width at half maximum within 15°C) originating from the crystalline polyester resin was defined as the melting point (Tm) of the wax.

[0191] 1-2.Polymerizable compound 3EO-modified trimethylolpropane triacrylate Tricyclodecane dimethanol dimethacrylate 1,10-Decanediol dimethacrylate Tricyclodecanedimethanol diacrylate Neopentyl glycol diacrylate Lauryl acrylate

[0192] 1-3. Other ingredients 1-3-1. Pigment dispersion 9 parts by mass of pigment dispersant (Ajisper PB824, manufactured by Ajinomoto Fine Techno Co., Ltd.) and 71 parts by mass of tripropylene glycol diacrylate were placed in a stainless steel beaker and heated on a hot plate at 65°C for 1 hour while stirring. After cooling to room temperature, 20 parts by mass of Pigment Black 7 (#52, manufactured by Mitsubishi Chemical Corporation) were added to the stirred stainless steel beaker, and then the mixture was placed in a glass bottle with 200 g of zirconia beads (0.3 mm in diameter, manufactured by Nikkatoh Co., Ltd.) and sealed tightly. This pigment-containing solution was dispersed using a paint shaker, and then the zirconia beads were removed to obtain a pigment dispersion. The dispersion treatment time was 4 hours.

[0193] 1-3-2. Polymerization Initiators Polymerization initiator: Omnirad 819 (manufactured by IGM Resins BV)

[0194] 1-3-3. Polymerization inhibitors, surfactants Polymerization inhibitor: Irgasutab UV-10 (manufactured by BASF) Surfactant: KF-352A (manufactured by Shin-Etsu Chemical Co., Ltd.)

[0195] 1-4. Preparation of inkjet inks Wax, polymerizable compound, pigment dispersion, polymerization initiator, and other additives were placed in a stainless steel beaker to achieve the composition shown in Table 1, and the mixture was stirred at 105°C for 45 minutes. Inkjet inks 1-12 were then obtained by filtering the mixture through an ADVANTEC Teflon® 3μm membrane filter.

[0196] 1-5. Calculation of HSP distance The HSP values ​​(dispersion term (dD), polarity term (dP), and hydrogen bonding term (dH)) for each wax and polymerizable compound were calculated using the computer software Hansen Solubility Parameters in Practice 5th Edition 5.0.13 (HSPiP, manufactured by Tegara Co., Ltd.) by inputting the chemical structural formula into the software. When multiple polymerizable compounds were included, the parameters (dD, dP, and dH) for each polymerizable compound were multiplied by the molar ratio of each compound in the inkjet ink and added together to obtain the parameters (dD, dP, and dH) for the polymerizable compound mixture.

[0197] The HSP distance between a high-melting-point wax or low-melting-point wax and a polymerizable compound (or a mixture of polymerizable compounds if multiple polymerizable compounds are included) was calculated using the following formula. In the following formula, the dispersion, polarity, and hydrogen bonding terms of one component of each wax and polymerizable compound (or mixture thereof) were denoted as dD, dP, and dH, respectively, while the dispersion, polarity, and hydrogen bonding terms of the other component were denoted as dD', dP', and dH', respectively. HSP distance = (4 × (dD - dD') 2 +(dP-dP') 2 +(dH-dH') 2 ) 1 / 2

[0198] Table 1 shows the HSP distance between the high-melting-point wax or low-melting-point wax and the polymerizable compound (or mixture thereof) in each inkjet ink.

[0199] 1-6. Gelation temperature For inkjet inks 1-12, the viscosity was measured after heating to 100°C using a stress-controlled rheometer, Physica MCR301 (cone plate diameter: 75 mm, cone angle: 1.0°), manufactured by Anton Paar. The ink was cooled to 20°C under conditions of a shear rate of 11.7 (1 / s) and a cooling rate of 0.1°C / s to obtain a viscosity temperature dependence curve. The gelation temperature was determined as the temperature at which the viscosity reached 200 mPa·s in the viscosity temperature dependence curve. The gelation temperatures for each inkjet ink are shown in Table 1.

[0200] 1-7.S A Calculation of ' / S' 1-7-1. Image formation for each ink Inkjet inks 1 through 12 were introduced into the HA1024 inkjet head (manufactured by Konica Minolta) of a line-type inkjet recording device (manufactured by Konica Minolta). The inkjet head was applied to high-quality coated paper at a substrate temperature of 40°C at a rate of 11 g / m². 2 The coating obtained by applying each ink was subjected to an integrated light intensity of 400 mJ / m 2 The images were formed by curing the material with ultraviolet light. The inkjet head temperature was 80°C, and the substrate was OK Topcoat+ 127g / m². 2 Using a 5cm x 5cm solid image (manufactured by Oji Paper Co., Ltd.), a 400mJ / m³ solid image is printed. After the image is formed, an LED lamp (Phoseon Technology, 395nm, water-cooled LED) placed downstream of the recording device is used to generate 400mJ / m³. 2 The ink was cured by UV irradiation. A piezo head was used for the inkjet head, and the ejection conditions were set so that the volume of one drop was 9.0 pl, and the liquid was ejected at a liquid velocity of approximately 6 m / s, and recorded at a resolution of 1200 dpi x 1200 dpi. The recording speed was set to 500 mm / s. Image formation was performed in an environment of 23°C and 55% RH, and the substrate temperature was adjusted to 40°C at the time of inkjet ink impact. dpi represents the number of dots per inch (2.54 cm).

[0201] 1-7-2. Measurement of force curve in images, S A Calculation of ' / S' For each ink-formed image, a scanning probe microscope (Dimension iCON, BRUKER) was used to measure the force curve of the image surface in a measurement range of 30 μm (resolution: 256 pixels) and PeakForce QNM (Quantitative nanoscale mechanical characterization) mode, obtaining the adhesion force distribution image Y' for each image.

[0202] The obtained adhesion force distribution image Y' is used to determine the adhesion force threshold using Otsu's binarization process. The image is then divided into two regions based on the magnitude of the adhesion force relative to the threshold. The region with low adhesion force is designated as region A', and the region with high adhesion force is designated as region B'. The area S of region A is then defined. A The ratio S' of the sum of the areas of region A' and region B'. A ' / S' was calculated for each image. S for each inkjet ink A ' / S' is shown in Table 1.

[0203] The binarization process described above by Otsu was performed by first converting each adhesion force distribution image Y' into an 8-bit grayscale image, then equalizing the histograms, and finally using the image processing software ImageJ.

[0204] [Table 1]

[0205] 2. Image formation in Examples 1-1 to 1-9 and Comparative Examples 1-1 to 1-3 The above "1-7.S" A Images for Examples 1-1 to 1-9 and Comparative Examples 1-1 to 1-3 were obtained in the same manner as described in "Calculation of ' / S'", except that the type of ink was changed as shown in Table 2.

[0206] 3. Image formation in Example 2-1 Images were obtained in the same manner as in Comparative Examples 1-3 above, except that the substrate temperature at the time of inkjet impact was changed from 40°C to 50°C. Then, a cotton fabric of type 3-1 as specified in JIS L 0803:2011 was used as the abrasive material, and a 25cm abrasive material was attached to the abrasive material. 2 Ethanol was impregnated into the material so that the mass of ethanol was 1.5 g per unit area. The image for Example 2-1 was obtained by setting the pressing pressure of the wiping member to 2 Pa, the relative speed of the rubbing member with respect to the substrate to 360 m / h, and the number of rubbing cycles to 120. Note that the number of rubbing cycles was counted as one back-and-forth motion.

[0207] 4. Image formation in Examples 2-2 to 2-5, 3-1 to 3-5, and Comparative Examples 2-1, 2-2, and 3-1. Images for Examples 2-2 to 2-5, 3-1 to 3-5, and Comparative Examples 2-1, 2-2, and 3-1 were formed in the same manner as in Example 2-1, except that the substrate temperature at inkjet impact and the number of rubs were changed as shown in Tables 3 and 4.

[0208] 5. Image formation in Example 4-1 After obtaining an image in the same manner as in Comparative Example 1-1, the image of Example 4-1 was formed by heating the image in a constant-temperature drying oven (forced circulation type) (MOV-112F(U) manufactured by Sanyo Electric Co., Ltd.) for 10 minutes so that the film surface temperature (heating temperature) of the image reached 75°C.

[0209] 6. Image formation in Examples 4-2 to 4-12 and Comparative Examples 4-1 to 4-3 Images for Examples 4-2 to 4-12 and Comparative Examples 4-1 to 4-3 were formed in the same manner as in Example 4-1, except that the heating temperature and heating time in the post-heating step were changed as shown in Tables 5 to 6.

[0210] 7. Evaluation 7-1.S A Calculation of / S Using a scanning probe microscope (Dimension iCON, BRUKER) with a measurement range of 30 μm (resolution: 256 pixels) and PeakForce QNM (Quantitative nanoscale mechanical characterization) mode, force curve measurements were performed on the image surface to obtain adhesion force distribution images Y for each image.

[0211] The obtained adhesion force distribution image Y is used to determine the adhesion force threshold using Otsu's binarization process. The image is then divided into two regions based on the magnitude of the adhesion force relative to the threshold. The region with low adhesion force is designated as region A, and the region with high adhesion force is designated as region B. The area S of region A is then defined as the area of ​​region A. A The ratio S of the sum of the areas of region A and region B. A The S value of the images obtained from each image formation method was calculated. A The values ​​for / S are shown in Tables 2-6.

[0212] The binarization process described above by Otsu was performed by first converting each adhesion force distribution image Y into an 8-bit grayscale image, then equalizing the histograms, and finally using the image processing software ImageJ.

[0213] 7-2. Blocking properties On the image above, a blank OK Topcoat (manufactured by Oji Paper Co., Ltd.) is placed on top, sandwiched between two 10cm square glass plates, and then 10g / cm² is applied from above. 2 The samples were subjected to a load and left for 24 hours under environmental conditions of 60°C and 10% RH. After that, they were left at room temperature (25°C) for 2 hours, the applied OK topcoat was peeled off, and the peeling was visually observed and evaluated according to the evaluation criteria below. In all evaluation results, the level was at a level that was practically usable, but a higher number indicated a more desirable level.

[0214] 4: No peeling has occurred on the image. 3: The area of ​​peeling is less than 5% of the total area of ​​the image. 2: The area where peeling occurs is between 5% and 10% of the total area of ​​the image. 1: The area where peeling occurs is 10% or more of the total area of the image.

[0215] 7-3. Varnish Coating On the above image, as varnish, DC POD Clear UV SP-001 (manufactured by DIC Corporation) was applied to a thickness of 10 μm using a wire bar. Exposure and curing (output 120 W / min, cold mirror condenser type, irradiation distance 100 mm, conveyor line speed 15 m / min, maximum illuminance 220 mW / cm2, light quantity 300 mJ) were performed with a conveyor-equipped UV irradiator (manufactured by Iwasaki Electric Co., Ltd.) to obtain an image coated with varnish.

[0216] 7-4. Varnish Wettability Regarding the obtained image coated with varnish, the wettability of the varnish was magnified 100 times and observed. A level of 3 or more was regarded as usable in practice.

[0217] 4: There is no repelling in the image and no streaks are generated. 3: The area where repelling occurs is less than 1% of the total area of the image. 2: The area where repelling occurs is 1% or more and less than 10% of the total area of the image. 1: The area where repelling occurs is 10% or more of the total area of the image.

[0218] 7-5. Varnish Adhesion Regarding the obtained image coated with varnish, Nichiban brand cellophane tape (width 18 mm) ( "Cellophane Tape" is a registered trademark of Nichiban Co., Ltd.) was attached to the varnish surface, and the operation of quickly peeling it off was performed 3 times in total by changing the evaluation location, and the number of times varnish peeling occurred was evaluated. A level of 3 or more was regarded as usable in practice.

[0219] 4: No peeling occurs. 3: Peeling occurred in 1 test out of 3 tests. 2: Peeling occurred in 2 tests out of 3 tests. 1: Peeling occurred in 3 tests out of 3 tests.

[0220] 7-6. Injectability Inkjet recording devices were used to eject ink, and the presence or absence of nozzle defects and misaligned ejection was visually observed. Each inkjet ink was evaluated according to the following criteria. While all evaluation results were at a level suitable for practical use, a higher number indicated a more desirable level.

[0221] 4. No nozzle failures were observed at all. 3: Of the 1024 nozzles tested, 1 to 5 nozzles were found to be missing. 2: Out of a total of 1024 nozzles, nozzle defects were found in 6 to 9 nozzles. 1: Out of a total of 1024 nozzles, more than 10 nozzles were found to be defective.

[0222] 7-7. Pinning properties Dots were printed using the image formation method described above, with inks 1 to 12. When the 400 formed dots were observed using an optical microscope, it was confirmed that the active-ray polymerizable compound seeped out from the outer edge of the dots. Here, the longest distance from the center of the dot to the outer edge of the area where the active-ray polymerizable compound seeped out was defined as the "outer diameter" of the dot, and the distance from the center of the dot to the outer edge of the dot body (the part where the active-ray polymerizable compound begins to seep out) was defined as the "inner diameter" of the dot. The percentage of dots in which the difference between the outer diameter and the inner diameter was 10% or more relative to the inner diameter was determined, and the pinning properties were evaluated according to the following evaluation criteria. In all evaluation results, the level was at a practically usable level, but a larger number was preferable.

[0223] 4: The above quantity percentage was between 0 and 5. 3: The above percentage was between 6 and 10 percent. 2: The above percentage was between 11 and 20 percent. 1: The above percentage of droplets was 21% or more, confirming that adjacent droplets had merged.

[0224] The evaluation results are shown in Tables 2-6.

[0225] [Table 2]

[0226] [Table 3]

[0227] [Table 4]

[0228] [Table 5]

[0229] [Table 6]

[0230] As shown in Tables 2 to 6, the image formed by the image forming method in which S A / S is 0.70 or less was found to have improved varnish suitability (varnish wettability, varnish adhesion).

Industrial Applicability

[0231] According to the image forming method of the present invention, the varnish suitability of the formed image can be improved. Therefore, the present invention is useful in the field of image formation.

Explanation of Signs

[0232] 100 Image forming apparatus 110 Inkjet head 120 Conveying unit 130 Irradiating unit 140 Heating unit

Claims

1. A process of applying an inkjet ink containing wax and a polymerizable compound to a substrate from an inkjet head, The process involves irradiating a substrate coated with the aforementioned inkjet ink with an active ray to form an image, An image forming method including, The adhesion force distribution image Y obtained by measuring the force curve of the image surface using a scanning probe microscope is subjected to Otsu's binarization process to determine the adhesion force threshold. The image is then divided into two regions based on the magnitude of the adhesion force relative to the threshold, with the region with low adhesion force designated as region A and the region with high adhesion force designated as region B. The area S of region A is then defined. Ａ The ratio S of the total area S of region A and region B. Ａ / S satisfies 0.70 or less, Image forming method.

2. The aforementioned inkjet ink contains two or more types of wax, The total mass of the two or more waxes is 1.0% by mass to 10.0% by mass relative to the total mass of the inkjet inks. In the case where, among the two or more types of wax mentioned above, the wax with the highest mass content and the wax with the second highest mass content are designated as the high-melting-point wax and the wax with the low-melting-point wax, The melting point of the high-melting-point wax is 5°C or more higher than the melting point of the low-melting-point wax. The mass content of the high-melting-point wax is 1.0% to 10.0% by mass relative to the mass content of the low-melting-point wax. The image forming method according to claim 1.

3. The HSP distance between the high-melting-point wax and the polymerizable compound, and the HSP distance between the low-melting-point wax and the polymerizable compound, are both within the range of 2.5 to 6.

5. The image forming method according to claim 2.

4. The melting point of the high-melting-point wax is 10°C or more higher than the melting point of the low-melting-point wax. The mass content of the high-melting-point wax is 2.0% to 6.0% by mass relative to the mass content of the low-melting-point wax. The HSP distance between the high-melting-point wax and the polymerizable compound, and the HSP distance between the low-melting-point wax and the polymerizable compound are 3.5 to 5.

5. The image forming method according to claim 3.

5. An image forming apparatus used in the image forming method according to any one of claims 1 to 4, A storage section for storing the aforementioned inkjet ink, An inkjet head that applies the aforementioned inkjet ink to a substrate, An irradiation unit that irradiates with the aforementioned active ray, An image forming apparatus, including one.

6. An image formed by the image forming method according to any one of claims 1 to 4.

7. An inkjet ink that hardens upon irradiation with an active ray, containing a wax and a polymerizable compound, The aforementioned inkjet ink is applied to high-quality coated paper at a substrate temperature of 40°C at a rate of 11 g / m². ２ The coating obtained by applying it was subjected to an integrated light intensity of 400 mJ / m ２ In the image obtained by curing with ultraviolet irradiation, The adhesion force distribution image Y' obtained by measuring the force curve of the image surface using a scanning probe microscope is used to determine the adhesion force threshold by Otsu's binarization process. The image is then divided into two regions based on the magnitude of the adhesion force relative to the threshold, with the region with low adhesion force designated as region A' and the region with high adhesion force designated as region B'. The area S of region A is then defined. Ａ The ratio S' of the sum of the areas of region A' and region B'. Ａ The condition that ' / S' is 0.70 or less, Inkjet ink.

8. The aforementioned inkjet ink contains two or more types of wax, The total mass of the two or more waxes is 1.0% to 10.0% by mass relative to the total mass of the inkjet inks. In the case where, among the two or more types of wax mentioned above, the wax with the highest mass content and the wax with the second highest mass content are designated as the high-melting-point wax and the wax with the low-melting-point wax, The melting point of the high-melting-point wax is 5°C or more higher than the melting point of the low-melting-point wax. The mass content of the high-melting-point wax is 1.0% to 10.0% by mass relative to the mass content of the low-melting-point wax. The inkjet ink according to claim 7.

9. The HSP distance between the high-melting-point wax and the polymerizable compound, and the HSP distance between the low-melting-point wax and the polymerizable compound, are both within the range of 2.5 to 6.

5. The inkjet ink according to claim 8.

10. The melting point of the high-melting-point wax is 10°C or more higher than the melting point of the low-melting-point wax. The mass content of the high-melting-point wax is 2.0% to 6.0% by mass relative to the mass content of the low-melting-point wax. The HSP distance between the high-melting-point wax and the polymerizable compound, and the HSP distance between the low-melting-point wax and the polymerizable compound are 3.5 to 5.

5. The inkjet ink according to claim 9.

Images