Image, image forming method, and image forming apparatus

Abstract

An object of the present disclosure is to provide an image in which occurrence of streaks is suppressed, and an image forming method and an image forming apparatus capable of suppressing occurrence of streaks.SOLUTION: An image having a region formed by printing from a plurality of inkjet heads, wherein a core part level height Sk of a surface roughness parameter measured within a range of a reference length of 120 μm set on a surface of the image is in a range of 0.1 to 0.2 μm, and a skewness Ssk of the surface roughness parameter is in a range of - 2.0 to 2.0.SELECTED DRAWING: Figure 7

Description

[Technical Field]

[0001] The present disclosure relates to an image, an image forming method, and an image forming apparatus, and more particularly to an image in which the occurrence of streaks is suppressed. [Background technology]

[0002] In an inkjet printing apparatus, when an image of a certain resolution is formed, there are areas in the image that are formed by printing from a plurality of inkjet heads.

[0003] Due to the characteristics of various printing methods used in image formation, some of the above-mentioned areas may appear as streaks in the formed image, causing image defects, and therefore techniques have been disclosed to improve this.

[0004] For example, the technology disclosed in Patent Document 1 suppresses the occurrence of streaks in the formed image and improves image quality by irradiating an ink composition containing a specific monomer with ultraviolet light within a specific range.

[0005] Furthermore, the technology disclosed in Patent Document 2 detects defective nozzles among multiple nozzles, controls the amount of ink droplets from nozzles adjacent to the defective nozzle, and compensates for the amount of ink droplets ejected from the defective nozzle, thereby suppressing the occurrence of white streaks and improving image quality.

[0006] However, even with these techniques, there is still room for improvement in order to prevent streaks from occurring in the formed image and improve image quality. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 2020-128038 [Patent Document 2] Japanese Patent Application Laid-Open No. 2017-109480 Summary of the Invention [Problem to be solved by the invention]

[0008] The present disclosure has been made in consideration of the above problems and circumstances, and the problem to be solved is to provide an image in which the occurrence of streaks is suppressed, and an image forming method and image forming apparatus that can suppress the occurrence of streaks. [Means for solving the problem]

[0009] Recent printing methods for recording media include single-pass and multi-pass printing. These printing methods tend to produce visible streaks in printed areas caused by joints between multiple heads or in printed areas of an image containing ink ejected to compensate for the amount of ink ejected from a head nozzle that has experienced an ejection failure. Such streaks are particularly likely to cause degradation of image quality with single-pass printing.

[0010] FIG. 1 is an example of a schematic diagram for explaining joints between heads when a plurality of heads are arranged in the transport direction of a recording medium.

[0011] In Figure 1, "H" stands for head, and "C H " represents the joint between the heads, "TD" represents the transport direction of the recording medium, and "WD" represents the width direction of the recording medium.

[0012] In order to avoid problems such as the printing area being interrupted, a printing device usually has a connecting portion C between the heads H when multiple heads H are arranged as shown in Figure 1. H will be established.

[0013] Joint C H This is advantageous in that ink is ejected to compensate for discontinuities in the printing area, but this can cause the ink to overlap in some areas of the recording medium, making streaks more likely to occur in those areas.

[0014] 2, 3, 4, 5, and 6 are examples of simplified diagrams for explaining compensation of ink amount when ink ejection is defective when multiple heads are arranged in the transport direction of the recording medium.

[0015] Figure 2 is a simplified diagram of an example of the arrangement of multiple heads relative to the transport direction of the recording medium. In Figure 2, "HM1" is a head module, "H1a," "H1b," and "H1c" are heads located upstream in the transport direction of the recording medium, and "H2a" and "H2b" are heads located downstream in the transport direction of the recording medium. First, inks "1a," "1b," and "1c" are ejected from "H1a," "H1b," and "H1c" onto the recording medium P, and then inks "2a" and "2b" are ejected from "H2a" and "H2b."

[0016] 2, 3, 4, 5, and 6, the printing range of the head located upstream in the transport direction of the recording medium is indicated as "area 1," and the printing range of the head located downstream in the transport direction of the recording medium is indicated as "area 2." The transport direction of the recording medium is indicated as "TD," and the width direction is indicated as "WD."

[0017] Figure 3 is a schematic diagram showing the size of ink droplets from each head when no ink ejection defects occur, and Figure 4 is a schematic diagram showing the size and spread of ink dots on a recording medium after passing through each head when no ink ejection defects occur.

[0018] Figure 5 is a schematic diagram showing the size of ink droplets from each head when ink ejection failure occurs, and Figure 6 is a schematic diagram showing the size and spread of ink dots on a recording medium after passing through each head when ink ejection failure occurs.

[0019] When forming an image, if no ink ejection defects occur, a fixed amount of ink is ejected from heads "H1a," "H1b," and "H1c," and a fixed amount of ink is ejected from heads "H2a" and "H2b."

[0020] In normal printing, if an ink ejection failure occurs in head "H1b" and the desired amount of ink is not ejected from head "H1b," image formation is performed by ejecting extra ink from heads "H2a" and "H2b" to make up for the amount of ink not ejected from head "H1b."

[0021] In such cases, the amount of ink in the final image is the same, but the ink ejection process is different, which can result in areas where the ink overlaps in an unintended manner in the image, making streaks more likely to occur.

[0022] As described above, there remains the problem of streaks occurring in overlapping ink areas formed due to connections between multiple heads arranged in the width direction, and in image areas formed by adjusting the amount of ink to compensate for poor ejection of some of the multiple heads arranged in the transport direction.

[0023] In order to solve the above problem, the present inventors have investigated the causes of the above problem and have found that the above problem can be solved by setting the core level height Sk and the deviation Ssk of the surface roughness parameters measured within a reference length of 120 μm set on the surface of the image within a certain range, thereby leading to the present disclosure. That is, the above-mentioned problems related to the present disclosure are solved by the following means.

[0024] 1. An image having an area formed by printing from multiple inkjet heads, The core level height Sk of the surface roughness parameter measured within a reference length of 120 μm set on the surface of the image is within the range of 0.1 to 0.2 μm, and the bias Ssk of the surface roughness parameter is within the range of -2.0 to 2.0. An image characterized by:

[0025] 2. The minimum autocorrelation length Sal of the surface roughness parameter is within the range of 0.3 to 5.0 μm. 2. The image according to claim 1,

[0026] 3. The image has an area where the edges of the printing ranges of a plurality of inkjet heads arranged in the width direction of the paper overlap, and The overlapping area of ​​the print area edges is within a range of 0.5 to 20 mm. 2. The image according to claim 1,

[0027] 4. The image is formed by ink ejected from a plurality of inkjet heads arranged in the paper transport direction. 2. The image according to claim 1,

[0028] 5. An image forming method for forming the image according to item 1, the image is formed by ink ejected from a plurality of inkjet heads arranged in the width direction of the paper, The overlap of the printing area edges of the inkjet heads is within a range of 0.5 to 20 mm. An image forming method comprising:

[0029] 6. An image forming method for forming the image according to item 1, The image is formed by ink ejected from a plurality of inkjet heads arranged in the paper transport direction. An image forming method comprising:

[0030] 7. A single-pass image forming apparatus in which multiple inkjet heads are arranged, A means for ejecting ink onto a substrate to form an image is provided, The core level height Sk of the surface roughness parameter measured within a reference length of 120 μm set on the surface of the image is within the range of 0.1 to 0.2 μm, and the bias Ssk of the surface roughness parameter is within the range of -2.0 to 2.0. An image forming apparatus characterized by:

[0031] 8. The minimum autocorrelation length Sal of the surface roughness parameter is within the range of 0.3 to 5.0 μm. 8. The image forming apparatus according to claim 7,

[0032] 9. An inkjet image forming apparatus that forms an image by ejecting ink from an inkjet head, When an image is formed on 0.11 mm thick coated paper at a resolution of 1200 dpi x 1200 dpi, the core level height Sk of the surface roughness parameter measured within a reference length of 120 μm on the surface of the image is within the range of 0.1 to 0.2 μm, and the deviation Ssk of the surface roughness parameter is within the range of -2.0 to 2.0. An image forming apparatus characterized by:

[0033] 10. An inkjet image forming method for forming an image by ejecting ink from an inkjet head, When an image is formed on 0.11 mm thick coated paper at a resolution of 1200 dpi x 1200 dpi, the core level height Sk of the surface roughness parameter measured within a reference length of 120 μm on the surface of the image is within the range of 0.1 to 0.2 μm, and the deviation Ssk of the surface roughness parameter is within the range of -2.0 to 2.0. An image forming method comprising: [Effects of the Invention]

[0034] The above-described means of the present disclosure can provide an image in which the occurrence of streaks is suppressed, and an image forming method and image forming apparatus capable of suppressing the occurrence of streaks. [Brief explanation of the drawings]

[0035] [Figure 1] An example of a schematic diagram showing a joint between heads when multiple heads are arranged in the conveyance direction of a recording medium. [Figure 2] An example of a simplified diagram of the arrangement of multiple heads in the conveyance direction of a recording medium. [Figure 3]Schematic diagram showing the size of ink droplets ejected from each head when there is no ink ejection failure [Figure 4] A schematic diagram showing the size and spread of ink dots on a recording medium after passing through each head when no ink ejection defects occur. [Figure 5] Schematic diagram showing the size of ink droplets ejected from each head when ink ejection failure occurs [Figure 6] A schematic diagram showing the size and spread of ink dots on a recording medium after passing through each head when ink ejection failure occurs. [Figure 7] FIG. 3 is a schematic diagram for explaining a printing range in a head. [Figure 8] A diagram to explain how one head compensates for the missing injection part with another head. [Figure 9] An example diagram for explaining exposure and nitrogen gas spraying. [Figure 10] An example diagram for explaining exposure and embossing DETAILED DESCRIPTION OF THE INVENTION

[0036] The present disclosure, its components, and embodiments for carrying out the disclosure will be described in detail below. In this application, the symbol "to" is used to mean that the numerical values ​​before and after it are included as lower and upper limits.

[0037] However, advantages and features provided by one or more embodiments of the present disclosure will be more fully understood from the following detailed description and the accompanying drawings, which are for illustrative purposes only and are not intended to define the limits of the present disclosure.

[0038] 1. Images The image disclosed herein is an image having an area formed by printing from multiple inkjet heads, characterized in that the core level height Sk of the surface roughness parameter measured within a reference length of 120 μm set on the surface of the image is within the range of 0.1 to 0.2 μm, and the bias Ssk of the surface roughness parameter is within the range of -2.0 to 2.0.

[0039] The material of the recording medium for recording the images of the present disclosure is not particularly limited, but examples include plastics such as polyvinyl chloride, polyethylene terephthalate, polypropylene, polyethylene, polycarbonate, cellulose diacetate, cellulose triacetate, cellulose propionate, cellulose butyrate, cellulose acetate butyrate, cellulose nitrate, polyethylene terephthalate, polyethylene, polystyrene, polypropylene, polycarbonate, and polyvinyl acetal, as well as plastics with treated surfaces, glass, paper, metal, and wood.

[0040] The form of the recording medium is not particularly limited, and examples include film, board, cloth, etc.

[0041] (1.1) Image Surface The images disclosed herein are formed with surface roughness parameters within a specific range, which are determined by a surface roughness evaluation method defined in accordance with ISO 25178 Surface Texture (Surface Roughness Measurement).

[0042] While "JIS B 0671-1 / ISO 13565-1 Line Roughness Measurement" is a standard that assumes evaluation using a stylus-type roughness meter, "ISO 25178 Surface Texture" is a standard that corresponds to two evaluation methods: contact (stylus) and non-contact (optical probe).

[0043] Furthermore, "ISO 25178 Surface Texture" is an evaluation method that does not suffer from the problems that arise with line roughness measurement, such as "variation in results depending on the measurement location" and "variation in results depending on the scanning direction."

[0044] First, an example will be described in which images 1 and 2, whose average surface roughness values ​​Sa of the images are not significantly different, are compared.

[0045] The above "Sa" is the arithmetic mean height, which is a parameter that extends Ra (arithmetic mean height of a line) to a surface, and is a parameter that is generally used when evaluating surface roughness.

[0046] Even if Sa is not significantly different between image 1 and image 2, differences in the trends of the core level height Sk of the surface roughness parameter, the bias Ssk of the surface roughness parameter, and the minimum autocorrelation length Sal may be observed, and this is thought to have an effect as streaks on the image surface.

[0047] The following description will focus on the portions of images 1 and 2 where irregularities are formed.

[0048] For example, an image with many relatively flat areas on its surface, but with a prominent protruding area on one side, would be designated Image 1, while an image with a protruding area on its surface, but with uniform unevenness overall, would be designated Image 2.

[0049] When comparing image 1 and image 2 as shown above, streaks are noticeable in image 1, which has many relatively flat areas, whereas streaks are not noticeable in image 2, which has uniform unevenness overall.

[0050] However, in the above images 1 and 2, Sa is the same, and adjusting Sa does not solve the streaking problem.

[0051] (Core level height Sk) The surface roughness parameter core level height Sk is the average of the absolute values ​​of the differences in height at each point between the peaks and valleys formed on the surface of an image when the surface of the image is measured, and is a parameter commonly used when evaluating surface roughness. Sk is also called core level height and is the height of the part excluding protruding peaks and valleys.

[0052] The smaller Sk is, the flatter the image surface is, and the larger Sk is, the less flat the image surface is.

[0053] For example, an image with Sk less than 0.1 μm and many flat portions is designated as image 1, and an image with Sk in the range of 0.1 to 0.2 μm and with appropriate unevenness is designated as image 2.

[0054] When comparing image 1 and image 2 as shown above, any streaks in image 1 are noticeable, but any streaks in image 2 are not noticeable.

[0055] (bias Ssk) The deviation Ssk of the surface roughness parameter is the deviation (skewness) value of the histogram of the height distribution of each point in the peaks and valleys formed on the surface of the image when the surface of the image is measured.

[0056] "Ssk" is also known as "skewness." When Ssk is 0, the unevenness formed on the image surface is considered to be uniform and symmetrically distributed.

[0057] When Ssk is a value less than 0, it can be determined that the unevenness formed on the image surface is distributed with an upward bias, and when it is a value greater than 0, it can be determined that the unevenness formed on the image surface is distributed with an upward bias.

[0058] For example, an image with Ssk greater than 2.0 and many flat areas is designated as image 1, and an image with Ssk in the range of -2.0 to 2.0 and with appropriate unevenness is designated as image 2.

[0059] When comparing image 1 and image 2 as shown above, any streaks in image 1 are noticeable, but any streaks in image 2 are not noticeable.

[0060] (Minimum autocorrelation length Sal) The irregularities formed on the image surface must be fine within a certain range, at least sufficiently smaller than the ink dots, otherwise a sense of incongruity will arise between them and the irregularities of the streaks, or if the irregularities are too fine, the effect of making the irregularities of the streaks less visible will be weak.

[0061] The "minimum autocorrelation length Sal" represents the horizontal distance in the direction in which the autocorrelation function decays most rapidly to a specific value s (default is 0.2), and conforms to the parameters of surface roughness (ISO 25178). Sal determines the distance at which the autocorrelation decays most rapidly, making it possible to determine whether there are any areas in the image surface where the height changes suddenly. If Image 1 has a smaller Sal than Image 2, this means that the height of the image surface changes suddenly even with the same surface roughness, and there are more height changes, meaning the image is finer.

[0062] In image processing, the autocorrelation is a measure of how well an image matches with a shifted image. If the shift amount is small, the overlapping area is large, and the autocorrelation is also large. On the other hand, if the shift amount is large, the overlapping area is small, and the autocorrelation is also small.

[0063] If the image surface has a sharp step, even a small shift will cause a large change in shape, causing the autocorrelation function to decay quickly. On the other hand, if the image surface has only a gentle slope, the shape will not change unless the shift is large, so the autocorrelation function will not decay easily.

[0064] For example, an image with Sal greater than 5.0 μm and many flat areas will be designated as Image 1, and an image with Sal in the range of 0.3 to 5.0 μm and with appropriate unevenness will be designated as Image 2.

[0065] When comparing image 1 and image 2 as shown above, any streaks in image 1 are noticeable, but any streaks in image 2 are not noticeable.

[0066] [Measurement method] In this specification, Sk, Ssk, and Sal are values ​​measured within a reference length of 120 μm. Sk, Ssk, and Sal are measured in accordance with ISO 25178-2 based on the three-dimensional parameters of the shape of the target image.

[0067] In this specification, "within a range of a reference length of 120 μm" means "within a range surrounded by a square of 120 μm×120 μm."

[0068] The three-dimensional parameters are information representing the shape of an object obtained by scanning the image surface with a laser, etc. The measurement method may be contact or non-contact.

[0069] Typically, an OLYMPUS non-contact laser microscope "OLS5100" with an objective lens MPLAPON100xLEXT is used. At a magnification of 100x, five locations within a 120 μm x 120 μm square are selected from a solid image area on a specific print.

[0070] From the five selected points, the maximum and minimum two points are removed and the average of the remaining three points is taken, allowing the surface roughness parameters to be measured.

[0071] Alternatively, the image surface can be observed using a KEYENCE laser microscope "VK-X250" with an objective lens at 150x magnification, and measurements can be taken in the same way.

[0072] Before calculating Sk, Ssk, and Sal, the height data is corrected for noise and waviness using a 10 μm low-pass filter (filtering out irregularities of 10 μm or more, Gaussian filter type).

[0073] Both are calculated based on ISO25178.

[0074] (1.2) Surface roughness control method Here is an example of a method for controlling the surface roughness of an image, with the core level height Sk in the range of 0.1 to 0.2 μm, the bias Ssk in the range of -2.0 to 2.0, and the minimum autocorrelation length Sal in the range of 0.3 to 5.0 μm. For example, the ink formulation, the pressure applied to the image surface by physical means after ink ejection, or printing conditions such as ink temperature, recording medium temperature, printing speed, suction force from the back surface of the recording medium, and curing method, as well as the thickness of the recording medium can be adjusted, either individually or in combination. Specific examples include the following methods (1) to (4).

[0075] (1) Method for adjusting the wax concentration in the ink (2) A method using the uneven shape of the filler in the ink (3) A method of forming an image with any concave and convex shape using an embossing roller (4) A method in which a specific polymer is mixed in advance with the photopolymerizable compound in the ink

[0076] (1.2.1) Method for adjusting wax concentration in ink For example, a case will be described in which an image is formed by ejecting ink containing wax at 80°C onto a recording medium whose temperature is in the range of 30 to 50°C and landing the ink thereon.

[0077] When the ink hits a recording medium that is cooler than the ink, the ink cools, causing the wax dissolved in the ink to crystallize and precipitate. The wax crystals then form a house-of-cards structure within the image, and the uneven shape is reflected on the surface of the image.

[0078] The term "house of cards structure" refers to a structure formed by combining playing cards like a tower. Although the bonds between wax crystals are not actually regular structures like a tower of playing cards, the structure that creates physical gaps is similar, so this wax bond structure is also called a house of cards structure.

[0079] The higher the wax concentration in the ink, the more house-of-card structures are formed, and the surface of the image formed on the recording medium becomes uneven, making streaks less noticeable. However, if the wax concentration is too high, the leveling of the ink dots formed on the recording medium cannot be maintained within an appropriate range for image formation. Therefore, by keeping the wax concentration at a certain concentration or below, the leveling of the ink dots can be maintained within an appropriate range for image formation.

[0080] Therefore, in order to impart a desired surface roughness to an image without noticeable streaks, it is preferable to adjust the wax concentration in the ink to a high level within a range that allows the ink dot leveling to be maintained within an appropriate range for image formation.

[0081] (Surface roughness control during image formation by high-speed printing) It takes a certain amount of time for the wax crystals in the ink to precipitate on the image surface. For example, if the printing speed during image formation is increased to 1600 mm / s, which is faster than usual, the ink will harden before the amount of wax crystals precipitated is sufficient. This may result in the image surface not forming the appropriate texture.

[0082] In the above cases, the wax is covered with ink, improving the smoothness of the image surface, and it is not possible to impart sufficient roughness to the image surface to make streaks less noticeable, and the card house structure is not properly formed. Thus, even when the printing speed during image formation is high, it is possible to impart sufficient surface roughness to the image, i.e., to form a proper card house structure, for example, by the following method.

[0083] When the ink hardens, the acrylate monomer, which is a solvent component in the ink, hardens directly on the recording medium, and solidifies while covering the house-of-cards structure formed by the wax crystals.

[0084] Naturally, the smoothness of the image surface is increased and streaks are more noticeable when the above-mentioned acrylate monomer is in a hardened state and covers the wax crystals, rather than when only card-house-structured wax crystals are present on the recording medium.

[0085] However, when the recording medium is sucked from the back side and brought into close contact with the conveying member during image formation, the acrylate monomer is more likely to penetrate and be absorbed when the ink lands on the recording medium if the recording medium is thin paper. Since the ink ejected onto the recording medium is sucked from the back side of the recording medium, the degree of penetration and absorption is adjusted by adjusting the thickness of the recording medium and the suction force.

[0086] Therefore, by using thinner paper than usual as the recording medium during image formation, the area of ​​the wax covered by the acrylate monomer is reduced, making it easier to expose the house-of-cards structure of the image surface formed by the wax crystals.

[0087] During image formation, a suction mechanism is often used to tightly hold the recording medium against the conveying device when transporting the recording medium. Therefore, for relatively thin paper, such as paper with a thickness of 0.1 mm or less, a stronger suction mechanism than usual can be used to improve the penetration and absorption of the acrylate monomer into the recording medium. The pressure of the suction mechanism is preferably between -60 kPa and -40 kPa.

[0088] (1.2.2) Method using the uneven shape of the filler in the ink The method of utilizing the uneven shape of the filler in the ink is as follows: First, ink whose surface hardening properties have been deliberately reduced by reducing the amount of initiator is used, and the ink is then deposited on a recording medium, after which the first stage of exposure processing is carried out in air.

[0089] At this time, the curing shrinkage is relatively more rapid inside the coating film, causing the ink components to shrink toward the substrate, which reflects the uneven shape of the filler on the coating film surface in a more emphasized form.

[0090] At this stage, the surface has already consumed some of the initiator that was originally reduced, and is still uncured, making it difficult to completely cure, so the second exposure process is carried out under nitrogen to completely cure the image surface, thereby forming the appropriate uneven shape on the image surface.

[0091] In inks containing general acrylate monomers, the acrylate monomers cure and shrink during image formation. When scaly fillers are added to such inks, an uneven shape reflecting the scaly fillers is formed on the surface of the image after image formation. The uneven shape imparts a roughness to the surface of the image that makes streaks less noticeable.

[0092] It is known that the cure shrinkage of acrylate monomers correlates with the molecular weight per acrylic group, called the "acrylic equivalent." The lower the acrylic equivalent, the stronger the cure shrinkage, and the higher the acrylic equivalent, the weaker the cure shrinkage.

[0093] The average acrylic equivalent weight of the acrylate monomer in the ink used to form the image of the present disclosure is preferably 250 or less, and more preferably 150 or less.

[0094] After the ink lands on the recording medium, the scaly filler particles are oriented somewhat randomly on the image surface, but if the scaly filler particles are too small, the formation of unevenness will not progress, and the image surface will not have sufficient roughness.

[0095] Therefore, the scaly filler particles must be relatively large, and specifically, the average particle diameter of the scaly filler particles is preferably 20% or more of the thickness of the ink coating film formed on a recording medium by the ink. The average particle diameter is preferably 1.5 μm or more, and from the viewpoint of ejection properties, preferably 5.0 μm or less.

[0096] However, if the scaly filler particles are too large, they tend to be oriented parallel to the ink coating surface, which simply causes the entire ink coating film to shrink upon curing, making it difficult to produce an appropriate uneven shape on the image surface.

[0097] If the acrylate monomer in the ink is susceptible to curing inhibition by oxygen in the atmosphere, curing will proceed first on the recording medium side of the ink coating, causing curing shrinkage and ink flow toward the recording medium side within the ink coating.

[0098] This causes the scaly filler particles to tilt in the ink in a direction perpendicular to the coating film, making it easier for the uneven shape reflecting the scaly filler particles to appear on the surface of the ink coating film.

[0099] The ink coating does not completely harden on its own, so it is finally exposed to light under nitrogen to completely harden the surface, thereby completely fixing the uneven shape of the image surface.

[0100] (1.2.3) A method of forming an image with any concave and convex shape using an embossing roller When an arbitrary uneven shape is to be formed in an image using an embossing roller, the image needs to be in a state close to plasticity. For example, when an actinic radiation curable ink is used as the ink, the ink can be applied to a recording medium, and then the amount of actinic radiation used to cure the ink can be adjusted to semi-cure the ink, thereby bringing the image into a state close to plasticity.

[0101] By pressing the semi-cured ink coating film, which has reached a state close to plasticity, with a micro-fabricated embossing roller, any desired uneven shape can be imparted, and the uneven shape can be completely fixed by further irradiating it with actinic rays.

[0102] It is desirable to use ink that hardens faster on the surface of the image than in the interior, for example by adjusting the type and amount of polymerization initiator used. If ink with poor surface hardening properties is used, unhardened ink will adhere more readily to the embossing roller, making it difficult to form a stable surface roughness on the image.

[0103] As a method for microfabrication of the embossing roller, various known metal etching processes or fine abrasives can be used. It is desirable to use fine abrasives with a ds-50% (particle diameter at the 50% cumulative height fraction) of 3 μm or less. From the viewpoint of realizing the effects of the present disclosure, i.e., making streaks in the image less noticeable, the pressure applied by the embossing roller is preferably within the range of 10 to 30 kgf / cm.

[0104] (1.2.4) Method of mixing a specific polymer with a photopolymerizable compound in ink Generally, actinic radiation-curable inks contain a photopolymerizable compound. In actinic radiation-curable inks, if a polymer is mixed into the photopolymerizable compound of the ink in advance, phase separation can be intentionally induced upon UV irradiation, resulting in the formation of unevenness on the image surface.

[0105] At this time, the polymer to be mixed in advance in the photopolymerizable compound is set to a certain molecular weight, and the difference in solubility parameter between the photopolymerizable compound and the polymer is set to 1.0 (cal / cm 3 ) 1 / 2 ~3.0(cal / cm 3 ) 1 / 2 This causes phase separation between the polymer portion and the monomer portion when the entire ink is cured, forming minute irregularities on the surface of the ink droplets that land on a recording medium.

[0106] In particular, by setting the ink ejection temperature to 70°C or higher and the recording medium temperature to 30°C or lower, the ink that has landed on the surface cools rapidly, resulting in the formation of finer, more pronounced irregularities on the image surface, where the seam structure, in which polymer portions exist in islands among monomer portions, becomes finer.

[0107] Examples of the polymer to be mixed in advance in the photopolymerizable compound include urethane polymers and urethane acrylic polymers having a molecular weight in the range of 2,000 to 15,000.

[0108] 2. Image forming method The method for forming an image according to the present disclosure is not particularly limited, but may be, for example, a single-pass method using a line head or a multi-pass method using a serial head.

[0109] In single-pass scanning, a head having a width equal to or greater than the recording width of the recording medium is fixed to the recording device, and while the recording medium is moved in the transport direction, ink droplets are ejected from the nozzles of the fixed head in conjunction with this movement onto the recording medium to record an image.

[0110] In multi-pass scanning, for example, a head is mounted on a carriage that can move in the width direction of the recording medium. The carriage is then moved along the main scanning direction (width direction), and ink droplets are ejected from the nozzles of the head onto the recording medium in conjunction with this movement, recording an image. Note that reading in a direction perpendicular to the direction in which the recording medium is moving is also called "main scanning."

[0111] The image forming method may, for example, include the following steps: Note that although the ink used in the present disclosure is not limited to actinic radiation-curable inkjet ink, the following description will be given assuming that actinic radiation-curable inkjet ink is used as the ink.

[0112] (1) A process of landing ink droplets on a recording medium (2) A process in which the ink droplets are irradiated with actinic rays to harden them.

[0113] (2.1) The process of landing ink droplets on a recording medium The amount of ink ejected from each nozzle of the inkjet head depends on the image resolution, but is preferably in the range of 0.5 to 50 pL, more preferably in the range of 0.5 to 10 pL, and even more preferably in the range of 0.5 to 5.0 pL, for forming high-resolution images.

[0114] The ink used for image formation is not particularly limited, and may be, for example, an actinic radiation-curable inkjet ink. The actinic radiation-curable inkjet ink is a composition that contains at least a photopolymerizable compound and can be ejected from a nozzle by an inkjet method. The ink may further contain a colorant, a photopolymerization initiator, and other components.

[0115] (Ink components) [Photopolymerizable compound] The photopolymerizable compound is a compound that crosslinks or polymerizes when irradiated with actinic rays. Examples of actinic rays include electron beams, ultraviolet rays, α rays, γ rays, and X-rays. Among these, ultraviolet rays are preferred as actinic rays. The photopolymerizable compound may be a radical polymerizable compound or a cation polymerizable compound.

[0116] The radical polymerizable compound is a compound having a radically polymerizable ethylenically unsaturated bond. The compound may be a monomer, an oligomer, a polymer, or a mixture thereof. The radical polymerizable compound may be used alone or in combination of two or more.

[0117] Examples of compounds having a radically polymerizable ethylenically unsaturated bond include unsaturated carboxylic acids and their salts, unsaturated carboxylic acid ester compounds, unsaturated carboxylic acid urethane compounds, unsaturated carboxylic acid amide compounds, and anhydrides thereof. Other examples include acrylonitrile, styrene, 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.

[0118] Among the above, the radical polymerizable compound is preferably an unsaturated carboxylic acid ester compound, and more preferably a (meth)acrylate compound.

[0119] The (meth)acrylate compound may be not only a monomer as described below, but also an oligomer, a mixture of a monomer and an oligomer, a modified product, an oligomer having a polymerizable functional group, or the like.

[0120] Here, "(meth)acrylate" refers to either or both of "acrylate" and "methacrylate," and "(meth)acrylic" refers to either or both of "acrylic" and "methacrylic."

[0121] Examples of the (meth)acrylate compound include monofunctional monomers, difunctional monomers, and trifunctional or higher polyfunctional monomers.

[0122] Examples of monofunctional monomers include isoamyl (meth)acrylate, stearyl (meth)acrylate, lauryl (meth)acrylate, octyl (meth)acrylate, decyl (meth)acrylate, isomylstyryl (meth)acrylate, isostearyl (meth)acrylate, 2-ethylhexyl-diglycol (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 2-(meth)acryloyloxyethyl hexahydrophthalic acid, butoxyethyl (meth)acrylate, ethoxydiethylene glycol (meth)acrylate, methoxydiethylene glycol (meth)acrylate, and methoxypolyethylene. 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 succinate, 2-(meth)acryloyloxyethyl phthalate, 2-(meth)acryloyloxyethyl-2-hydroxyethyl-phthalate, and t-butylcyclohexyl (meth)acrylate.

[0123] Examples of bifunctional monomers 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, neopentyl glycol di(meth)acrylate, dimethylol-tricyclodecane di(meth)acrylate, bisphenol A PO adduct di(meth)acrylate, hydroxypivalic acid neopentyl glycol di(meth)acrylate, and polytetramethylene glycol di(meth)acrylate.

[0124] Examples of trifunctional or higher polyfunctional monomers include trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, and pentaerythritol tetra(meth)acrylate. Further examples include dipentaerythritol hexa(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, glycerin propoxy tri(meth)acrylate, and pentaerythritol ethoxy tetra(meth)acrylate.

[0125] The (meth)acrylate compound may be a modified product. Examples of the modified (meth)acrylate compound include an ethylene oxide-modified (meth)acrylate compound, a caprolactone-modified (meth)acrylate compound, and a caprolactam-modified (meth)acrylate compound.

[0126] Examples of the ethylene oxide-modified (meth)acrylate compound include ethylene oxide-modified trimethylolpropane tri(meth)acrylate and ethylene oxide-modified pentaerythritol tetraacrylate.

[0127] Examples of the caprolactone-modified (meth)acrylate compound include caprolactone-modified trimethylolpropane tri(meth)acrylate.

[0128] Examples of the caprolactam-modified (meth)acrylate compound include caprolactam-modified dipentaerythritol hexa(meth)acrylate.

[0129] Commercially available ethylene oxide-modified (meth)acrylate compounds include, for example, 4EO-modified hexanediol diacrylate CD561 and 3EO-modified trimethylolpropane triacrylate SR454 manufactured by Sartomer, as well as 6EO-modified trimethylolpropane triacrylate SR499 and 4EO-modified pentaerythritol tetraacrylate SR494 manufactured by the same company.

[0130] Other examples include Shin-Nakamura Chemical Co., Ltd.'s polyethylene glycol diacrylate NK Ester A-400, polyethylene glycol diacrylate NK Ester A-600, polyethylene glycol dimethacrylate NK Ester 9G, polyethylene glycol dimethacrylate NK Ester 14G, 1,10-decanediol dimethacrylate NK Ester DOD-N, tricyclodecane dimethanol diacrylate NK Ester A-DCP, and tricyclodecane dimethanol dimethacrylate NK Ester DCP.

[0131] Other examples include tetraethylene glycol diacrylate V#335HP manufactured by Osaka Organic Chemical Industry Co., Ltd., and 3PO-modified trimethylolpropane triacrylate Photomer 4072 manufactured by Cognis, etc. Other examples include trimethylolpropane PO-modified triacrylate Miramer M360 manufactured by Miwon, etc.

[0132] The (meth)acrylate compound may be a polymerizable oligomer. Examples of the (meth)acrylate compound that is a polymerizable oligomer include epoxy (meth)acrylate oligomers and aliphatic urethane (meth)acrylate oligomers. Other examples include aromatic urethane (meth)acrylate oligomers, polyester (meth)acrylate oligomers, and linear (meth)acrylic oligomers.

[0133] When a cationically polymerizable compound is used as the photopolymerizable compound, examples of the cationically polymerizable compound that can be used include epoxy compounds, vinyl ether compounds, and oxetane compounds. The cationically polymerizable compounds may be used alone or in combination of two or more.

[0134] The epoxy compound is an aromatic epoxide, an alicyclic epoxide, an aliphatic epoxide, etc. From the viewpoint of enhancing curability, the epoxy compound is preferably an aromatic epoxide or an alicyclic epoxide.

[0135] The aromatic epoxide may be a di- or polyglycidyl ether obtained by reacting a polyhydric phenol or its alkylene oxide adduct with epichlorohydrin. Examples of the polyhydric phenol or its alkylene oxide adduct to be reacted include bisphenol A or its alkylene oxide adduct. The alkylene oxide in the alkylene oxide adduct may be ethylene oxide, propylene oxide, or the like.

[0136] The alicyclic epoxide may be a cycloalkane oxide-containing compound obtained by epoxidizing a cycloalkane-containing compound with an oxidizing agent such as hydrogen peroxide or a peracid. The cycloalkane in the cycloalkane oxide-containing compound may be cyclohexene or cyclopentene.

[0137] The aliphatic epoxide may be a di- or polyglycidyl ether obtained by reacting an aliphatic polyhydric alcohol or its alkylene oxide adduct with epichlorohydrin. Examples of the aliphatic polyhydric alcohol include alkylene glycols such as ethylene glycol, propylene glycol, and 1,6-hexanediol. The alkylene oxide in the alkylene oxide adduct may be ethylene oxide, propylene oxide, or the like.

[0138] Examples of the vinyl ether compound include a monovinyl ether compound, a divinyl ether compound, and a trivinyl ether compound.

[0139] Examples of monovinyl ether compounds include ethyl vinyl ether, n-butyl vinyl ether, isobutyl vinyl ether, octadecyl vinyl ether, cyclohexyl vinyl ether, hydroxybutyl vinyl ether, 2-ethylhexyl vinyl ether, cyclohexanedimethanol monovinyl ether, n-propyl vinyl ether, isopropyl vinyl ether, isopropenyl ether-o-propylene carbonate, dodecyl vinyl ether, diethylene glycol monovinyl ether, and octadecyl vinyl ether.

[0140] Examples of di- or trivinyl ether compounds include ethylene glycol divinyl ether, diethylene glycol divinyl ether, and triethylene glycol divinyl ether. Also included are propylene glycol divinyl ether and dipropylene glycol divinyl ether. Furthermore, examples of divinyl ether compounds include butanediol divinyl ether, hexanediol divinyl ether, cyclohexanedimethanol divinyl ether, and trimethylolpropane trivinyl ether.

[0141] Among the monovinyl ether compounds, divinyl ether compounds and trivinyl ether compounds, di- or trivinyl ether compounds are preferred in consideration of curability, adhesion and the like.

[0142] The oxetane compound is a compound having an oxetane ring. Examples of the oxetane compound include the oxetane compounds described in JP-A Nos. 2001-220526, 2001-310937, and 2005-255821.

[0143] Among these, there are mentioned compounds represented by general formula (1) described in paragraph 0089 of JP-A No. 2005-255821, compounds represented by general formula (2) described in paragraph 0092 of the same publication, and compounds represented by general formula (7) described in paragraph 0107. Further examples include compounds represented by general formula (8) described in paragraph 0109 and compounds represented by general formula (9) described in paragraph 0116.

[0144] The content of the photopolymerizable compound in the actinic radiation-curable inkjet ink is preferably within a range of 1 to 97% by mass, more preferably within a range of 10 to 95% by mass, and even more preferably within a range of 30 to 95% by mass, relative to the total mass of the ink.

[0145] When the photopolymerizable compound contains a (meth)acrylate compound, the content of the (meth)acrylate compound is preferably 10% by mass or more relative to the total mass of the ink, and the upper limit of the content of the (meth)acrylate compound can be 95% by mass, as described above.

[0146] [Colorant] The actinic radiation-curable inkjet ink may contain a colorant. The colorant may be a dye or a pigment, but a pigment is preferred because it is easier to obtain images with good weather resistance. The pigment is not particularly limited, and may be, for example, an organic pigment or an inorganic pigment having the following numbers listed in the Color Index.

[0147] Examples of red pigments or magenta pigments include Pigment Red 3, 5, 19, 22, 31, 38, 43, 48:1, 48:2, 48:3, 48:4, 48:5, 49:1, 53:1, 57:1, 57:2, 58:4, 63:1, 81, 81:1, 81:2, 81:3, 81:4, 88, 104, 108, 112, 122, 123, 144, 146, 149, 166, 168, 169, 170, 177, 178, 179, 184, 185, 208, 216, 226, and 257; Pigment Violet 3, 19, 23, 29, 30, 37, 50, and 88; and Pigment Orange. Examples include 13, 16, 20, and 36.

[0148] Examples of blue pigments or cyan pigments include Pigment Blue 1, 15, 15:1, 15:2, 15:3, 15:4, 15:6, 16, 17-1, 22, 27, 28, 29, 36, and 60.

[0149] Examples of green pigments include Pigment Green 7, 26, 36, and 50.

[0150] Examples of yellow pigments include Pigment Yellow 1, 3, 12, 13, 14, 17, 34, 35, 37, 55, 74, 81, 83, 93, 94, 95, 97, 108, 109, 110, 120, 137, 138, and 139. Other examples include Pigment Yellow 153, 154, 155, 157, 166, 167, 168, 180, 185, and 193.

[0151] Examples of black pigments include Pigment Black 7, 28, and 26.

[0152] The average particle size of the pigment is preferably within the range of 0.08 to 0.5 μm, and the maximum particle size of the pigment is preferably within the range of 0.3 to 10 μm, and more preferably within the range of 0.3 to 3 μm.

[0153] By adjusting the particle size of the pigment, clogging of the nozzles of the inkjet head can be suppressed, and the storage stability, ink transparency, and curing sensitivity of the ink can be maintained.

[0154] The content of the pigment is preferably within a range of 0.1 to 20% by mass, and more preferably within a range of 0.4 to 10% by mass, based on the total mass of the actinic radiation-curable inkjet ink.

[0155] When the content of the pigment is within the above range, the resulting image has sufficient color development and good ejection properties.

[0156] The pigment is preferably dispersed so that the average particle size of the pigment particles falls within the above-mentioned range. The pigment dispersion is adjusted by selecting the pigment, pigment dispersant, and dispersion medium. The pigment dispersion conditions, filtration conditions, etc. are also adjusted.

[0157] For dispersing the pigment, it is preferable to use, for example, a ball mill, a sand mill, an attritor, a roll mill, an agitator, a Henschel mixer, a colloid mill, an ultrasonic homogenizer, a pearl mill, a wet jet mill, a paint shaker, or the like.

[0158] [Pigment dispersant] The actinic radiation-curable inkjet ink may further contain a pigment dispersant to improve the dispersibility of the pigment.

[0159] 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, naphthalenesulfonic acid formalin condensate salts, aromatic sulfonic acid formalin condensate salts, polyoxyethylene alkyl phosphate esters, polyoxyethylene nonylphenyl ether, and stearylamine acetate.

[0160] The content of the dispersant in the actinic radiation curable inkjet ink is preferably within the range of 1 to 50% by mass relative to the pigment.

[0161] [Photopolymerization initiator] The actinic radiation-curable inkjet ink may contain a photopolymerization initiator. When the photopolymerizable compound is a compound having a radically polymerizable functional group, the photopolymerization initiator contains a photoradical initiator. When the photopolymerizable compound is a compound having a cationically polymerizable functional group, the photopolymerization initiator contains a photoacid generator.

[0162] The ink may contain only one type of photopolymerization initiator, or may contain two or more types of photopolymerization initiators. The photopolymerization initiator may be a combination of both a photoradical initiator and a photoacid generator.

[0163] Examples of the photoradical initiator include a cleavage type radical initiator and a hydrogen abstraction type radical initiator.

[0164] Examples of cleavage-type radical initiators include acetophenone-based initiators such as diethoxyacetophenone, 2-hydroxy-2-methyl-1-phenylpropan-1-one, benzyl dimethyl ketal, 1-(4-isopropylphenyl)-2-hydroxy-2-methylpropan-1-one, 4-(2-hydroxyethoxy)phenyl-(2-hydroxy-2-propyl)ketone, 1-hydroxycyclohexyl-phenyl ketone, 2-methyl-2-morpholino(4-thiomethylphenyl)propan-1-one, and 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butanone. Benzoin-based initiators include benzoin, benzoin methyl ether, and benzoin isopropyl ether. Acylphosphine oxide-based initiators include 2,4,6-trimethylbenzoindiphenylphosphine oxide, benzyl, and methylphenyl glyoxylate.

[0165] Examples of the hydrogen abstraction type radical initiator include benzophenone-based initiators, thioxanthone-based initiators, aminobenzophenone-based initiators, and other initiators.

[0166] Benzophenone initiators include, for example, benzophenone, o-benzoylmethylbenzoate-4-phenylbenzophenone, 4,4'-dichlorobenzophenone, and hydroxybenzophenone, as well as 4-benzoyl-4'-methyl-diphenyl sulfide, acrylated benzophenone, 3,3',4,4'-tetra(t-butylperoxycarbonyl)benzophenone, and 3,3'-dimethyl-4-methoxybenzophenone.

[0167] Examples of thioxanthone initiators include 2-isopropylthioxanthone, 2,4-dimethylthioxanthone, 2,4-diethylthioxanthone, and 2,4-dichlorothioxanthone.

[0168] Examples of the aminobenzophenone initiator include Michler's ketone and 4,4'-diethylaminobenzophenone.

[0169] Other initiators include, for example, 10-butyl-2-chloroacridone, 2-ethylanthraquinone, 9,10-phenanthrenequinone, and camphorquinone.

[0170] Examples of photoacid generators include triarylsulfonium hexafluorophosphate salts and iodonium (4-methylphenyl)(4-(2-methylpropyl)phenyl)hexafluorophosphate, as well as triarylsulfonium hexafluoroantimonate and 3-methyl-2-butenyltetramethylenesulfonium hexafluoroantimonate.

[0171] The content of the photopolymerization initiator in the actinic radiation-curable inkjet ink varies depending on the type of light irradiated during ink curing and the type of photopolymerizable compound, but is preferably in the range of 0.1 to 10% by mass, and more preferably in the range of 2 to 8% by mass.

[0172] 〔wax〕 The actinic radiation-curable inkjet ink may contain wax. Wax is an organic substance that is solid at room temperature but becomes liquid when heated, thereby causing the white ink to undergo a sol-gel phase transition in response to a change in temperature.

[0173] The content of the wax is preferably in the range of 0.3 to 10.0% by mass, and more preferably in the range of 3.0 to 8.0% by mass, relative to the total mass of the ink.

[0174] The wax preferably crystallizes in the ink at a temperature equal to or lower than the gelling temperature of the ink, which is the temperature at which the ink undergoes a phase transition from sol to gel when the ink, which has been converted into a sol or liquid by heating, is cooled, causing a sudden change in the viscosity of the ink.

[0175] Specifically, the ink that has been solated or liquefied is cooled while measuring its viscosity using, for example, a rheometer MCR300 (manufactured by Anton Paar), and the temperature at which the viscosity suddenly increases can be determined as the gelation temperature of the ink.

[0176] Furthermore, in order to stably eject ink droplets from an inkjet recording device, it is necessary that the radical polymerizable compound and the wax have good compatibility in the sol-state ink (at high temperatures, for example, about 80°C).

[0177] When the wax crystallizes in the ink, a structure may be formed in which the actinic radiation-polymerizable compound is encapsulated in a three-dimensional space formed by the wax crystallized into plates (such a structure will be referred to as a "house of cards structure" hereinafter).

[0178] When a house-of-cards structure is formed, the liquid actinic radiation-polymerizable compound is retained within the space, making it more difficult for the ink dots formed by the ink to wet and spread, and improving the ink pinning ability. When the ink pinning ability is improved, it becomes more difficult for the ink dots formed by the ink adhering to the recording medium to coalesce with each other.

[0179] Examples of the waxes suitable for forming the house-of-card structure include aliphatic ketone compounds, aliphatic ester compounds, fatty acid amides, N-substituted fatty acid amides, special fatty acid amides, and higher amines.

[0180] The wax preferably contains a linear or branched hydrocarbon group having 9 to 25 carbon atoms, from the viewpoint of facilitating the formation of the aforementioned "house of cards structure."

[0181] Among these, aliphatic ketones having a structure represented by the following general formula (G1) and aliphatic esters having a structure represented by the following general formula (G2) are particularly preferred.

[0182] General formula (G1): R1-CO-R2 General formula (G2): R3-COO-R4

[0183] In the above general formula (G1) or (G2), R1 to R4 each independently represent a linear or branched hydrocarbon group having a carbon number in the range of 9 to 25. The hydrocarbon group is preferably an alkyl group.

[0184] In general formula (G1), the hydrocarbon groups represented by R1 and R2 are not particularly limited, but are preferably linear or branched hydrocarbon groups having a carbon number of 9 to 25. Furthermore, linear or branched hydrocarbon groups having a carbon number of 12 to 25 are more preferred. The hydrocarbon groups having a carbon number of 9 to 25 and 12 to 25 are more preferably linear or branched alkyl groups.

[0185] Examples of the aliphatic ketone compound represented by the general formula (G1) include 18-pentatriacontanone (C17-C17), dilignoceryl ketone (C24-C24), dibehenyl ketone (C22-C22), distearyl ketone (C18-C18), dieicosyl ketone (C20-C20), dipalmityl ketone (C16-C16), dimyristyl ketone (C14-C14), dilauryl ketone (C12-C12), These include lauryl myristyl ketone (C12-C14), lauryl palmityl ketone (C12-C16), myristyl palmityl ketone (C14-C16), myristyl stearyl ketone (C14-C18), myristyl behenyl ketone (C14-C22), palmityl stearyl ketone (C16-C18), palmityl behenyl ketone (C16-C22), stearyl behenyl ketone (C18-C22), etc. The number of carbon atoms in the parentheses above indicates the number of carbon atoms in each of the two hydrocarbon groups separated by the carbonyl group.

[0186] Commercially available examples of the compound represented by general formula (G1) include 18-Pentatriacontanone (manufactured by Alfa Aeser), Hentriacontan-16-one (manufactured by Alfa Aeser), Kaowax T1 (manufactured by Kao Corporation), etc. The ink may contain only one type of aliphatic ketone compound, or a mixture of two or more types.

[0187] In general formula (G2), the hydrocarbon groups represented by R3 and R4 are not particularly limited, but are preferably linear or branched hydrocarbon groups having 9 to 25 carbon atoms, and more preferably linear or branched hydrocarbon groups having 12 to 25 carbon atoms. The hydrocarbon groups having 9 to 25 carbon atoms and 12 to 25 carbon atoms are more preferably linear or branched alkyl groups.

[0188] Examples of the aliphatic ester compound represented by general formula (G2) include behenyl behenate (C21-C22), icosanoic acid icosyl (C19-C20), stearyl stearate (C17-C18), palmityl stearate (C17-C16), lauryl stearate (C17-C12), cetyl palmitate (C15-C16), stearyl palmitate (C15-C18), myristyl myristate, (C13-C14), cetyl myristate (C13-C16), octyldodecyl myristate (C13-C20), stearyl oleate (C17-C18), stearyl erucate (C21-C18), stearyl linoleate (C17-C18), behenyl oleate (C18-C22), myricyl cerate (C25-C16), arachidyl linoleate (C17-C20), etc. The number of carbon atoms in the parentheses above indicates the number of carbon atoms in each of the two hydrocarbon groups separated by the ester group.

[0189] Examples of commercially available aliphatic ester compounds represented by general formula (G2) include Unistar M-2222SL (manufactured by NOF Corporation), Unistar M-9796 (manufactured by NOF Corporation), Exeparl SS (manufactured by Kao Corporation), EMALEX CC-18 (manufactured by Nippon Emulsion Co., Ltd.), Amreps PC (manufactured by Kokyu Alcohol Kogyo Co., Ltd.), Exeparl MY-M (manufactured by Kao Corporation), Sperm Acetate (manufactured by NOF Corporation), EMALEX CC-10 (manufactured by Nippon Emulsion Co., Ltd.), etc. These commercially available products are often mixtures of two or more types, and therefore may be separated and purified as necessary.

[0190] Examples of the fatty acid amides include lauric acid amide, stearic acid amide, behenic acid amide, oleic acid amide, erucic acid amide, ricinoleic acid amide, and 12-hydroxystearic acid amide (for example, the Nikkaamide series manufactured by Nippon Kasei Chemical Co., Ltd., the ITOWAX series manufactured by Ito Oil Mills, and the FATTYAMID series manufactured by Kao Corporation).

[0191] Examples of the N-substituted fatty acid amides include N-stearyl stearic acid amide and N-oleyl palmitic acid amide.

[0192] Examples of the special fatty acid amides include N,N'-ethylenebisstearylamide, N,N'-ethylenebis-12-hydroxystearylamide, and N,N'-xylylenebisstearylamide.

[0193] Examples of the higher amines include dodecylamine, tetradecylamine, and octadecylamine.

[0194] The wax contained in the ink may be a mixture of two or more types.

[0195] [Other ingredients] The actinic radiation-curable inkjet ink may further contain, as necessary, a photopolymerization initiator aid, a polymerization inhibitor, a surfactant, a leveling additive, a matting agent, an ultraviolet absorber, an infrared absorber, an antibacterial agent, etc. In addition, the actinic radiation-curable inkjet ink may further contain a basic compound, other resins, a gelling agent, etc. to improve the storage stability of the ink.

[0196] The photopolymerization initiator aid may be a tertiary amine compound, and is preferably an aromatic tertiary amine compound.

[0197] Examples of aromatic tertiary amine compounds include N,N-dimethylaniline, N,N-diethylaniline, N,N-dimethyl-p-toluidine, and N,N-dimethylamino-p-benzoic acid ethyl ester. Other examples include N,N-dimethylamino-p-benzoic acid isoamyl ethyl ester, N,N-dihydroxyethylaniline, triethylamine, and N,N-dimethylhexylamine.

[0198] Among the above aromatic tertiary amine compounds, N,N-dimethylamino-p-benzoic acid ethyl ester and N,N-dimethylamino-p-benzoic acid isoamyl ethyl ester are preferred, and only one of these compounds may be contained, or two or more types may be contained.

[0199] Examples of polymerization inhibitors include (alkyl)phenols, 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, cupferron, aluminum N-nitrosophenylhydroxylamine, tri-p-nitrophenylmethyl, N-(3-oxyanilino-1,3-dimethylbutylidene)aniline oxide, dibutyl cresol, cyclohexanone oxime cresol, guaiacol, o-isopropylphenol, butyraldoxime, methyl ethyl ketoxime, and cyclohexanone oxime.

[0200] Examples of the basic compound for enhancing the storage stability of the ink include basic alkali metal compounds, basic alkaline earth metal compounds, and basic organic compounds such as amines.

[0201] Examples of the other resins include resins for adjusting the physical properties of the cured film. Examples of such resins include polyester resins, polyurethane resins, vinyl resins, acrylic resins, and rubber resins. The amount of ink applied during image formation is 7 to 14 g / m. 2 In this case, the thickness of the ink coating film after curing will be in the range of approximately 7 to 14 μm.

[0202] (2.2) A process of irradiating the impacted ink droplets with actinic rays to harden them. By irradiating the ink droplets that have landed on the recording medium with actinic rays, the photopolymerizable compound contained in the ink droplets is polymerized, thereby hardening the droplets.

[0203] The light source of the actinic rays can be a light source capable of irradiating actinic rays, such as an LED or a halogen lamp. The peak irradiance of the actinic rays on the surface of the recording medium and the amount of light irradiated onto the surface of the substrate can be set arbitrarily within known ranges for forming an image.

[0204] The ink droplets are irradiated with actinic rays preferably within 10 seconds after landing on the recording medium, more preferably within 0.001 to 5 seconds, and even more preferably within 0.01 to 2 seconds.

[0205] The irradiation of actinic light is preferably carried out after ink droplets have been ejected from all of the inkjet heads housed in the head carriage.

[0206] (2.3) Specific embodiment of image forming method One embodiment of the image forming method of the present disclosure is the following image forming method.

[0207] An inkjet image forming method in which an image is formed by ejecting ink from an inkjet head, characterized in that when an image is formed on coated paper of 0.11 mm thickness at a resolution of 1200 dpi x 1200 dpi, the surface roughness parameter core level height Sk measured within a reference length of 120 μm on the surface of the image is within the range of 0.1 to 0.2 μm, and the surface roughness parameter bias Ssk is within the range of -2.0 to 2.0.

[0208] In this image forming method, Sk and Ssk are defined when an image is formed on coated paper having a thickness of 0.11 mm at a resolution of 1200 dpi x 1200 dpi.

[0209] When forming a normal image, a recording medium is selected from a variety of thicknesses and types, and the resolution is also adjusted to match the desired image.

[0210] In this embodiment, this refers to an image forming method in which, when an image is formed on coated paper with a thickness of 0.11 mm at a resolution of 1200 dpi x 1200 dpi, the core level height Sk of the surface roughness parameter measured within a reference length of 120 μm is within the range of 0.1 to 0.2 μm, and the bias Ssk of the surface roughness parameter is within the range of -2.0 to 2.0.

[0211] 3. Image forming equipment The image forming apparatus of the present disclosure is a single-pass type image forming apparatus with a plurality of inkjet heads arranged therein, and is equipped with a means for ejecting ink onto any substrate to create an image, and is characterized in that the core level height Sk of the surface roughness parameter measured within a reference length of 120 μm set on the surface of the image is within the range of 0.1 to 0.2 μm, and the bias Ssk of the surface roughness parameter is within the range of -2.0 to 2.0.

[0212] It is preferable that the minimum autocorrelation length Sal of the surface roughness parameters is within the range of 0.3 to 5.0 μm, from the viewpoint of making streaks less noticeable.

[0213] The image forming apparatus includes an inkjet head that ejects inkjet ink, an ink tank that stores ink to be supplied to the inkjet head, and an irradiation unit that irradiates ink droplets ejected from the inkjet head with actinic light rays.

[0214] The image forming apparatus may include a pretreatment liquid application unit that applies a pretreatment liquid, a heating unit that heats the landed ink droplets, a cooling unit that cools the landed ink droplets, etc. The "pretreatment liquid" is a liquid composition that fixes (pins) the ink on the recording medium before the ink lands on the recording medium, or that aggregates or thickens the ink by coming into contact with the ink.

[0215] Inkjet image forming apparatuses include single-pass and multi-pass types. The type may be selected depending on the required image resolution and image formation speed. However, from the viewpoint of high-speed image formation and from the viewpoint of more pronounced effects of the present disclosure, the single-pass type is preferred as it is prone to streak problems. The method is preferred.

[0216] (Specific Example of Image Forming Apparatus) One aspect of the image forming apparatus of the present disclosure is the following image forming apparatus.

[0217] An inkjet image forming apparatus that forms an image by ejecting ink from an inkjet head, characterized in that when an image is formed on coated paper of a thickness of 0.11 mm at a resolution of 1200 dpi x 1200 dpi, the core level height Sk of the surface roughness parameter measured within a reference length of 120 μm on the surface of the image is within the range of 0.1 to 0.2 μm, and the bias Ssk of the surface roughness parameter is within the range of -2.0 to 2.0.

[0218] In this device, Sk and Ssk are defined when an image is formed on coated paper with a thickness of 0.11 mm at a resolution of 1200 dpi x 1200 dpi.

[0219] This device may be capable of using recording media of other thicknesses and types, and may also be capable of forming images at other resolutions. This refers to an image forming device in which, when an image is formed on coated paper of 0.11 mm thickness at a resolution of 1200 dpi x 1200 dpi, the core level height Sk of the surface roughness parameter measured within a reference length of 120 μm is within the range of 0.1 to 0.2 μm, and the bias Ssk of the surface roughness parameter is within the range of -2.0 to 2.0. [Example]

[0220] The present disclosure will be specifically described below with reference to examples, but the present disclosure is not limited thereto. In the examples, the terms "parts" and "%" are used, but unless otherwise specified, they represent "parts by mass" or "% by mass."

[0221] [1] Preparation of ink materials The ink used to form the images in the examples was prepared by mixing the following pigment dispersion liquid [K], polymerization initiator, polymerization inhibitor, wax, and urethane polymer [U AB Other compounds containing ] were used. Brief information on these compounds is shown in Table I. In the following explanation, the product names and synonyms of the products listed in Table I may be abbreviated.

[0222] [Table 1]

[0223] (Preparation of pigment dispersion [K] and urethane polymer [U AB ]) <Preparation of pigment dispersion liquid [K]> 10 parts by mass of a pigment dispersant "EFKA7701" manufactured by BASF and 70 parts by mass of a photopolymerizable compound "APG-100" manufactured by Shin-Nakamura Chemical Co., Ltd. were placed in a stainless steel beaker and heated and stirred to prepare a solution [1].

[0224] After cooling the solution [1], 20 parts by mass of BASF's "SPECIAL BLACK 250" was added to it, and the mixture was placed in a glass bottle together with zirconia beads with a diameter of 0.5 mm, sealed, and dispersed. The zirconia beads were then removed to prepare a black pigment dispersion [K].

[0225] <Urethane polymer [U AB 〕 Preparation "ETERNACOLL UH-100" (ETERNACOLL is a registered trademark of Ube Industries) and norbornene methane isocyanate were mixed in a molar ratio of 1:1, and toluene and a tin catalyst were added, followed by heating to 70°C. This produced a mixed solution [1]. "ETERNACOLL UH-100" is a polypropylene glycol with a weight-average molecular weight of approximately 1000.

[0226] Hydroxyethyl acrylate was prepared as a reaction terminator [1] in an amount such that the molar ratio to polycarbonate diol was 4:1. After leaving the mixed solution [1] at room temperature for 3 hours, the reaction terminator [1] was added to the mixed solution [1] and left to stand for 2 hours. This produced urethane polymer [A]. The weight average molecular weight of the urethane polymer [A] was 3,000 and the functional group equivalent was 2.

[0227] Urethane polymer [B] was prepared in the same manner as urethane polymer [A], except that reaction terminator [1] was changed to ethanol. The weight-average molecular weight of urethane polymer [B] was 3,000 and the functional group equivalent was 0.

[0228] The urethane polymer [A] and the urethane polymer [B] were mixed in a molar ratio of 1:1 to prepare the urethane polymer [U AB ] was prepared. AB The weight average molecular weight of the copolymer was 3,000 and the functional group equivalent was 1.

[0229] [2] Preparation of ink [2-1] Ink [K1], [K1-2], [K3], [K3-2] The following materials were mixed in the amounts shown below and stirred at 80°C to prepare a solution [k1]. The solution [k1] was filtered through a Teflon (registered trademark) 3 μm membrane filter manufactured by ADVATEC. In this way, an ink [K1] was prepared. ·Pigment dispersion [K] 12.5 parts by mass NK Ester A-400 (photopolymerizable compound) 22.0 parts by mass ·"APG-100" (photopolymerizable compound) 20.0 parts by mass ·“SR454” (photopolymerizable compound) 21.3 parts by mass ·"MIRAMER M1602" (photopolymerizable compound) 10.0 parts by mass "DAROCURE TPO" (polymerization initiator) 7.0 parts by mass "UV10" (polymerization inhibitor) 0.2 parts by mass "EMALEX CC-18" (wax) 7.0 parts by weight

[0230] Ink [K1-2] was prepared in the same manner as ink [K1], except that 7.0 parts by mass of "EMALEX CC-18" was changed to 6.0 parts by mass of "WEP-11" and 3.0 parts by mass of "WEP-3."

[0231] Ink [K3] was prepared in the same manner as ink [K1], except that the amount of "SR454" was changed to 22.3 parts by mass, the amount of "EMALEX CC-18" was reduced from 7.0 parts by mass to 3.0 parts by mass, and 2.0 parts by mass of "SpeedCure2-ITX" was further added as a polymerization initiator.

[0232] Ink [K3-2] was prepared in the same manner as ink [K3], except that the amount of "SR454" was reduced from 22.3 parts by mass to 11.3 parts by mass and the amount of polymerizable compound "MIRAMER M1602" was increased from 10.0 parts by mass to 22.0 parts by mass.

[0233] [2-2] Ink [K2] The following materials were mixed in the amounts shown below and stirred at 80° C. to prepare a solution [k2]. The solution [k2] was filtered through a Teflon (registered trademark) 3 μm membrane filter manufactured by ADVATEC. ·Pigment dispersion [K] 12.5 parts by mass NK Ester A-200 (photopolymerizable compound) 17.0 parts by mass ·"APG-100" (photopolymerizable compound) 22.0 parts by mass ·“SR454” (photopolymerizable compound) 30.0 parts by mass ·“SR339A” (photopolymerizable compound) 8.3 parts by mass "DAROCURE TPO" (polymerization initiator) 5.0 parts by mass "UV10" (polymerization inhibitor) 0.2 parts by mass

[0234] Then, 5.0 parts by mass of "Somasif MEE" manufactured by Katakura Co-op Agri Co., Ltd. was mixed at 80°C to prepare ink [K2]. "Somasif MEE" is a scaly mica particle with a particle diameter of approximately 3 μm. At this time, the acrylic equivalent of the acrylic monomer that makes up ink [K2] was 142.0.

[0235] [2-3] Ink [K2-2] The following materials were mixed in the amounts shown below and stirred at 80° C. to prepare a solution [k2-2]. The solution [k2-2] was filtered through a Teflon (registered trademark) 3 μm membrane filter manufactured by ADVATEC. ·Pigment dispersion [K] 12.5 parts by mass NK Ester A-400 (photopolymerizable compound) 19.0 parts by mass ·"APG-100" (photopolymerizable compound) 22.0 parts by mass ·“SR454” (photopolymerizable compound) 21.3 parts by mass ·"MIRAMER M1602" (photopolymerizable compound) 15.0 parts by mass "DAROCURE TPO" (polymerization initiator) 5.0 parts by mass "UV10" (polymerization inhibitor) 0.2 parts by mass

[0236] Then, 5.0 parts by mass of "Somasif MEE" manufactured by Katakura Co-op Agri Co., Ltd. was mixed at 80°C to prepare ink [K2-2]. "Somasif MEE" is a scaly mica particle with a particle diameter of approximately 3 μm. At this time, the acrylic equivalent of the acrylic monomer that makes up ink [K2-2] was 211.4.

[0237] [2-4] Ink composition summary 1 The ink compositions described above are summarized in Table II.

[0238] [Table 2]

[0239] [2-5] Ink [K4] The following materials were mixed in the amounts shown below and stirred at 80°C to prepare a solution [k4]. The solution [k4] was filtered through a Teflon (registered trademark) 3 μm membrane filter manufactured by ADVATEC. In this way, an ink [K4] was prepared. ·Pigment dispersion [K] 12.5 parts by mass Urethane polymer (U AB ] 15.0 parts by mass ·"APG-200" (photopolymerizable compound) 12.5 parts by mass "N,N-dimethylacrylamide" (photopolymerizable compound) 53.8 parts by mass "DAROCURE TPO" (polymerization initiator) 6.0 parts by mass "UV10" (polymerization inhibitor) 0.2 parts by mass

[0240] [2-6] Ink [K4-2] The following materials were mixed in the amounts shown below and stirred at 80°C to prepare a solution [k4-2]. The solution [k4-2] was filtered through a 3 μm Teflon (registered trademark) membrane filter manufactured by ADVATEC. Ink [K4-2] was thus prepared. ·Pigment dispersion [K] 12.5 parts by mass Urethane polymer (U AB ] 15.0 parts by mass ·"APG-200" (photopolymerizable compound) 12.5 parts by mass ·“SR454” (photopolymerizable compound) 10.0 parts by mass "N,N-dimethylacrylamide" (photopolymerizable compound) 43.8 parts by mass "DAROCURE TPO" (polymerization initiator) 6.0 parts by mass "UV10" (polymerization inhibitor) 0.2 parts by mass

[0241] [2-7] Ink [K2-3] A solution [k2-3] was prepared by mixing the following materials in the amounts shown below and stirring at 80° C. The solution [k2-3] was filtered through a Teflon (registered trademark) 3 μm membrane filter manufactured by ADVATEC. ·Pigment dispersion [K] 12.5 parts by mass NK Ester A-600 (photopolymerizable compound) 27.0 parts by mass ·"APG-100" (photopolymerizable compound) 22.0 parts by mass ·“SR454” (photopolymerizable compound) 10.0 parts by mass ·"MIRAMER M1602" (photopolymerizable compound) 18.3 parts by mass "DAROCURE TPO" (polymerization initiator) 5.0 parts by mass "UV10" (polymerization inhibitor) 0.2 parts by mass

[0242] Then, 5.0 parts by mass of "Somasif MEE" manufactured by Katakura Co-op Agri Co., Ltd. was mixed at 80°C to prepare ink [K2-3]. "Somasif MEE" is a scaly mica particle with a particle diameter of approximately 3 μm. At this time, the acrylic equivalent of the acrylic monomer that makes up ink [K2-2] was 262.8.

[0243] [2-8] Ink [K5] The following materials were mixed in the amounts shown below and stirred at 80°C to prepare a solution [k5]. The solution [k5] was filtered through a Teflon (registered trademark) 3 μm membrane filter manufactured by ADVATEC. In this way, an ink [K5] was prepared. ·Pigment dispersion [K] 12.5 parts by mass NK Ester A-400 (photopolymerizable compound) 22.0 parts by mass ·"APG-100" (photopolymerizable compound) 20.0 parts by mass ·“SR454” (photopolymerizable compound) 24.3 parts by mass ·"MIRAMER M1602" (photopolymerizable compound) 10.0 parts by mass "DAROCURE TPO" (polymerization initiator) 7.0 parts by mass "UV10" (polymerization inhibitor) 0.2 parts by mass "T-1" (wax) 2.0 parts by weight "WEP-11" (wax) 2.0 parts by weight

[0244] [2-9] Ink [K6] Ink [K6] was prepared in the same manner as ink [K3], except that the amount of "MIRAMER M1602" was 13.0 parts by mass, the amount of polymerizable compound "SR454" was increased from 22.3 parts by mass to 24.8 parts by mass, and 0.5 parts by mass of polymerizable compound "tetrazole compound BHT-2NH3" was added.

[0245] [2-10] Ink composition summary 2 The ink compositions described above are summarized in Table III.

[0246] [Table 3]

[0247] [3] Image creation [3-1] Preparation for printing (ink supply) The prepared ink was supplied to the ink supply system of an inkjet recording device. The ink supply system was composed of an ink tank, a supply pipe, a sub-ink tank immediately before the head, a pipe with a filter, and a piezo head (recording head), all connected in this order. The recording head was an inkjet head manufactured by Konica Minolta and had 1,776 nozzles.

[0248] (Various settings) Figure 7 is a schematic diagram illustrating the printing range of the head. The applied voltage and the ink temperature inside the head were adjusted so that the appropriate amount of droplets would be ejected to form a solid image, and head modules each equipped with two heads were arranged in a staggered pattern, with two head modules arranged in the width direction (WD) as shown in Figure 7. Note that a "solid image" here refers to a state in which the ink dots cover the substrate without any gaps.

[0249] At this time, the head module HM1 was placed on the upstream side, and the head module HM2 was placed on the downstream side. In addition, they were placed so that the overlap E of the printing range ends of the heads was 3 mm.

[0250] 7, the printing range of head H1 is represented as "area1," the printing range of head H2 is represented as "area2," the printing range of head H3 is represented as "area3," and the printing range of head H4 is represented as "area4." Note that head H1, head H2, head H3, and head H4 are not shown in FIG.

[0251] In this specification, the case where the overlapping portion E at the end of the printing range of the head is visible on the image is referred to as a "joint line."

[0252] "Printing range of the head" refers to the area where ink ejected from the head can land on the recording medium, and does not include areas where ink is ejected and lands in unexpected locations due to nozzle defects in the head, etc.

[0253] "End of printing range in head" refers to the overlapping part of the printing ranges of multiple heads, which is set to prevent the printing range of the image from being interrupted due to some of the ink ejected from the heads not landing on the recording medium due to poor ejection of the heads, etc.

[0254] In addition, if there is a portion f (ejection defect f) where ink is not ejected in head H1 or head H3 located upstream in the paper transport direction TD within each head module, a process is set to complement the ejection defect f.

[0255] Figure 8 is a diagram for explaining how a missing injection of one head is complemented by another head. Figure 8 shows an example of the process in which head H2 complements the missing injection of head H1. The same applies to the process in which head H4 complements the missing injection of head H3.

[0256] The process of filling the missing ejection f was carried out by using the multi-drop method from the nozzles on both sides adjacent to the missing ejection f in the downstream heads H2 and H4 to fill the missing ejection f by ejecting droplets in an amount twice the amount ejected in the single-drop method.

[0257] Similarly, when this complemented portion is visible on the image, it is called a "defect correction streak."

[0258] In the following image production, ink is ejected onto paper and then the ink is cured by exposure to light to produce an image. The image before the ink on the paper is cured by the exposure process will be referred to as the "solid image before curing," and the image after curing will be simply referred to as the "image."

[0259] [3-2] Images [K1], [K1-2], [K1-3] (Examples 1 and 2) When producing image [K1], ink [K1] containing the most wax among the prepared inks was used, thinner paper was used than for the other images, and the pump suction was strengthened to produce the image at high speed.

[0260] When producing image [K1-2], ink [K1-2] with the highest wax content was used among the prepared inks, and the image was produced at high speed using thinner paper than the other images and with stronger pump suction.

[0261] The printing paper used to create the images was "Aurora Coat," a 0.06 mm thick coated printing paper manufactured by Nippon Paper Industries Co., Ltd., which is thinner than the paper normally used for printing. Furthermore, the paper transport speed during printing was set at 1600 mm / s, which is faster than normal. Details are shown in Table IV.

[0262] Finally, solid images of the image [K1] and the image [K1-2] before curing were formed on printing paper at a resolution of 1200 dpi x 600 dpi, where "dpi" represents the number of dots per 2.54 cm.

[0263] At this time, two fine holes of φ1.0 mm are placed on the paper transport belt per cm. 2 The printing paper was sucked by pump suction at a pressure of -50 kPa. The temperature of the printing paper was adjusted within the range of 30 to 40°C so that the droplets would level within an appropriate range.

[0264] After forming the pre-cured solid images of the image [K1] and the image [K1-2], an LED lamp was placed downstream of the inkjet recording device to illuminate the ink at 4 W / cm. 2 , 600mJ / cm 2 This caused the ink components constituting the pre-cured solid images of the image [K1] and the image [K1-2] to cure.

[0265] The LED lamp is an LED irradiator (8W / cm) manufactured by Phoseon Technology. 2 , 395 nm, air-cooled unit) was used.

[0266] This produced images [K1] and [K1-2], the details of which are shown in Table IV.

[0267] (Comparative Example 1) Image [K1-3] was produced in the same manner as Image [K1], except that ink [K1], which had the highest wax content among the prepared inks, was used and the pump suction pressure was set to -30 kPa. Details are shown in Table IV.

[0268] [Table 4]

[0269] [3-3] Images [K2], [K2-2], [K2-3] (Examples 3 and 4) To produce image [K2], ink [K2] containing scaly filler was used, and two-stage exposure was performed in a system with strong cure shrinkage.

[0270] To produce the image [K2-2], ink [K2-2] was used and two-stage exposure was carried out in a system with strong cure shrinkage.

[0271] Then, pre-curing solid images of image [K2] and image [K2-2] were formed in the same manner as the pre-curing solid image of image [K1], except for the following conditions. Printing paper: Oji Paper's 0.11mm thick coated printing paper "OK ​​Topcoat" Conveying speed: 800mm / s Pump suction pressure: -30kPa Resolution: 1200dpi x 1200dpi

[0272] Fig. 9 is an example diagram for explaining the exposure and nitrogen gas spraying. After forming the pre-cured solid images of image [K2] and image [K2-2], exposure was performed using the first LED lamp located downstream of the inkjet recording device as shown in Fig. 9.

[0273] After that, the second LED lamp was used to expose the solid image while nitrogen gas was blown through a 1 mm thick slit upstream of the second LED lamp. This cured the ink components that made up the solid image, producing images [K2] and [K2-2]. Details are shown in Table V.

[0274] 9, "LED1" represents the first LED lamp, "LED2" represents the second LED lamp, and "N" represents nitrogen gas.

[0275] The first LED lamp exposure was performed using a Phoseon Technology LED irradiator (2 W / cm 2 , 395 nm, air-cooled unit) at 4 W / cm 2 300mJ / cm 2 The experiment was carried out under the following conditions.

[0276] Nitrogen gas N was sprayed at a flow rate of 15 kPa.

[0277] The exposure to the second LED lamp was performed using a Phoseon Technology LED irradiator (8 W / cm 2 , 395 nm, air-cooled unit) at 4 W / cm 2 300mJ / cm 2 The experiment was carried out under the following conditions.

[0278] (Comparative Example 2) Image [K2-3] was produced using ink [K2-3] containing scaly filler. This ink [K2-3] has a high acrylic equivalent and is less likely to shrink upon curing, and was subjected to two-stage exposure. Except for this, image [K2-3] was produced using the same exposure method as image [K2]. Details are shown in Table V.

[0279] [Table 5]

[0280] [3-4] Images [K3], [K3-2], [K3-3] (Examples 5 and 6) To produce image [K3], ink [K3] was used, to which 2-isopropylthioxanthone was further added as a polymerization initiator to improve surface hardening. The ink was semi-hardened in the first exposure step, and after forming unevenness with an embossing roller, the ink was exposed to light in the second step.

[0281] Then, a pre-curing solid image of image [K3] was formed in the same manner as the pre-curing solid image of image [K2], except that the conveying speed was set to 100 mm / s.

[0282] Figure 10 is an example diagram illustrating the exposure and embossing process. After forming a solid image, the ink constituting the solid image was exposed to light using a first LED lamp located downstream of the inkjet recording device as shown in Figure 10, and the ink constituting the solid image was semi-cured. Then, while applying a pressure of 20 kgf / cm using the pressure roller RP, the embossing roller RE formed irregularities on the surface of the semi-cured solid image. The embossing roller used had been blasted with alumina WA abrasive fine powder F1500 (JIS R 6001-2, ds-50%: 2 μm).

[0283] Then, a second LED lamp emits 6W / cm 2 500mJ / cm 2 The ink was then fully cured under the conditions shown in Table VI to produce image K3.

[0284] To produce image [K3-2], ink [K3-2] was used, the ink was semi-cured in the first exposure step, and after forming concaves and convexes with an embossing roller RE, a second exposure step was carried out. Then, a pre-cured solid image of image [K3-2] was formed in the same manner as the pre-cured solid image of image [K2], except that the conveying speed was set to 300 mm / s.

[0285] After forming the solid image, an image [K3-2] was prepared in the same manner as image [K3], except that the pressure applied to the semi-cured solid image by the pressure roller RP was 30 kf / cm. Details are shown in Table VI.

[0286] (Comparative Example 3) To produce image [K3-3], ink [K3] was used, the ink was semi-cured in the first exposure step, and after forming unevenness with an embossing roller RE, a second exposure step was carried out. Then, a pre-cured solid image of image [K3-3] was formed in the same manner as the pre-cured solid image of image [K2], except that the conveying speed was set to 100 mm / s.

[0287] After forming the solid image, an image [K3-3] was prepared in the same manner as image [K3], except that the pressure applied to the semi-cured solid image by the pressure roller RP was set to 5 kgf / cm. Details are shown in Table VI.

[0288] Example 7 To produce the image [K3-4], the ink [K3] was used, and the ink was semi-cured in the first exposure step, and after forming the unevenness with an embossing roller, the ink was exposed to light in the second step.

[0289] Then, a pre-curing solid image of image [K3-4] was formed in the same manner as the pre-curing solid image of image [K2], except that the conveying speed was set to 100 mm / s.

[0290] After forming the solid image, the ink constituting the solid image was semi-cured by exposure to light from a first LED lamp located downstream of the inkjet recording device, as shown in Figure 10. Then, while applying a pressure of 20 kgf / cm using the pressure roller RP, the surface of the semi-cured solid image was textured using the embossing roller RE. The embossing roller used had been blasted with alumina WA abrasive fine powder F360 (JIS R 6001-2, ds-50%, 22.8 μm).

[0291] Then, a second LED lamp emits 6W / cm 2 500mJ / cm 2 The ink was then fully cured under the conditions shown in Table VI to produce an image [K3-4].

[0292] [Table 6]

[0293] [3-5] Images [K4], [K4-2], [K4-3] (Examples 8 and 9) Ink [K4] was used to prepare image [K4]. Furthermore, while the temperature of the printing paper was adjusted within a range of 30-40°C for the pre-cured solid image of image [K2], the temperature of the printing paper was adjusted within a range of 20-30°C for the pre-cured solid image of image [K4]. Otherwise, the pre-cured solid image of image [K4] was prepared in the same manner as the pre-cured solid image of image [K2]. Details are shown in Table VII.

[0294] After the solid image was formed, exposure was carried out in the same manner as in the image [K1] to harden the ink constituting the solid image, thereby producing an image [K4].

[0295] Image [K4-2] was produced using ink [K4-2]. Image [K4-2] was produced in the same manner as image [K4], except that the ink temperature in the head was increased and readjusted to prevent phase separation of the resin in the head.

[0296] Comparative Example 4 Ink [K4] was used to produce image [K4-3]. Furthermore, for the pre-curing solid image of image [K4], the printing paper temperature was adjusted within a range of 20 to 30°C, whereas for the pre-curing solid image of image [K4-3], the printing paper temperature was adjusted within a range of 30 to 40°C. Otherwise, the pre-curing solid image of image [K4-3] was formed in the same manner as the pre-curing solid image of image [K4].

[0297] After forming the solid image, exposure was carried out in the same manner as in image [K4] to cure the ink constituting the solid image, thereby producing image [K4-3], the details of which are shown in Table VII.

[0298] [Table 7]

[0299] [3-6] Creation of images [K5] and [K6] (Comparative Examples 5, 6, and 7) Ink [K5] was used to produce image [K5]. Furthermore, while the printing paper temperature was adjusted within a range of 30 to 40°C for the pre-curing solid image of image [K1], the printing paper temperature was adjusted within a range of 40 to 50°C for the pre-curing solid image of image [K5]. Otherwise, the pre-curing solid image of image [K5] was formed in the same manner as the pre-curing solid image of image [K1].

[0300] After forming the solid image, the ink constituting the solid image was cured by exposure in the same manner as in image [K1] to form image [K5], the details of which are shown in Table VIII.

[0301] Ink [K5] was used to produce image [K5-2]. Furthermore, for the pre-curing solid image of image [K1], the printing paper temperature was adjusted within a range of 30 to 40°C, whereas for the pre-curing solid image of image [K5-2], the printing paper temperature was adjusted within a range of 20 to 30°C. Otherwise, the pre-curing solid image of image [K5-2] was formed in the same manner as the pre-curing solid image of image [K1].

[0302] After the solid image was formed, the ink constituting the solid image was cured by exposure in the same manner as in image [K1] to form image [K5-2], the details of which are shown in Table VIII.

[0303] Ink [K6] was used to prepare image [K6]. Except for this, the pre-curing solid image of image [K6] was formed in the same manner as the pre-curing solid image of image [K1].

[0304] After forming the solid image, the ink constituting the solid image was cured by exposure in the same manner as in image [K1] to form image [K6], the details of which are shown in Table VIII.

[0305] [Table 8]

[0306] [4] Evaluation Surface roughness parameters were measured by arbitrarily selecting five points from the image area using an OLYMPUS laser microscope "OLS5100" with an objective lens MPLAPON100xLEXT.

[0307] When extracting Sk, Ssk, and Sal, the slope was removed and a low-pass filter of 10 μm (irregularities of 10 μm or more were filtered out, the filter type was Gaussian) was applied, and the average value of the values ​​excluding the top and bottom two points out of the five measurement points was used.

[0308] Furthermore, for each image from which Sk, Ssk, and Sal had been extracted, the presence of joint streaks and missing correction streaks was visually inspected, and the streak appearance was evaluated according to the following evaluation criteria: A and B in the following evaluation criteria were considered acceptable, and C and D were considered unacceptable.

[0309] (Evaluation criteria) A: No visible streaks (pass). B: Slight streaks are visible (pass). C: Streaks are visible (failure). D: Streaks are clearly visible (failure).

[0310] [Table 9]

[0311] [5] Consideration [5-1] About the Examples The images in the examples all have a surface roughness parameter core level height Sk in the range of 0.1 to 0.2 μm and a deviation Ssk in the range of -2.0 to 2.0, which suggests that the entire image surface is uneven with few smooth areas.The examples also show better evaluation results than the comparative examples.

[0312] An inkjet device with two head modules was used to form the image, and it is thought that the unevenness would be particularly severe in the connecting stripes that are printed at different times by the two head modules and the defect correction stripes that are printed locally with large droplets. However, even if the image surface has an uneven shape with few smooth areas, it is thought that the uneven shape spreads over the entire image surface, making the stripes in the image less visible.

[0313] Examples 1 and 2 The image [K1] in Example 1 received an evaluation result of A.

[0314] In contrast, in the image [K1-2] in Example 2, the evaluation result did not reach A, but the values ​​of the core level height Sk and the bias Ssk, which are surface roughness parameters, are acceptable.

[0315] However, since the ink [K1-2] used to create the image [K1-2] contained an excessive amount of wax, the ink droplets did not level well, and the streaks caused by poor ejection were emphasized, making the streaks somewhat more visible.

[0316] Examples 3 and 4 The image [K2] in Example 3 received an evaluation result of A.

[0317] In contrast, the image [K2-2] in Example 4 did not achieve an evaluation result of A, but the ink [K2-2] used to create the image [K2-2] had an ink formula with a slightly higher acrylic equivalent than the ink [K2] used to create the image [K2].

[0318] For this reason, the ink coating film formed by ink [K2-2] shrinks less on hardening than the ink coating film formed by ink [K2], and therefore the uneven structure of the scale-like filler contained in both inks is reflected less on the image surface.

[0319] This is thought to be why the core level height Sk in the image [K2-2] is smaller than the core level height Sk in the image [K2], making the streaks slightly more visible.

[0320] Examples 5 and 6 The image [K3] in Example 5 received an evaluation result of A.

[0321] However, even if no streaks are visible in the image [K3], an embossing roller is used when forming the image [K3], which means that the conveyance speed of the printing paper during image formation is slower than when forming other images.

[0322] Therefore, from the viewpoint of increasing the image printing speed and improving productivity, it may be preferable to form images by controlling the surface roughness parameters other than using an embossing roller, but it is also possible to improve productivity even when using an embossing roller.

[0323] In the image [K3-2] in Example 6, the evaluation result was A even though the image was formed by controlling the surface roughness parameters of the embossing roller, and the printing speed was improved.

[0324] In Example 6, in order to improve the printing speed, the ink composition of the ink [K3-2] used to produce the image [K3-2] is formulated to be more susceptible to plastic deformation than the ink composition of the ink [K3] used to produce the image [K3]. Furthermore, the roller pressure is also increased to maintain the embossing effect when forming irregularities on the image surface. This allows for improved productivity even when using an embossing roller.

[0325] Example 7 The image [K3-4] in Example 7 was rated B, but because a coarse embossing roll was used to form the unevenness, Sal was large, and as a result, streaks were slightly more visible than in the other Examples.

[0326] Examples 8 and 9 The image [K4] in Example 8 received an evaluation result of A.

[0327] In the image [K4-2] of Example 9, the ink [K4-2] used to produce the image [K4-2] was formulated with an acrylic monomer that had increased hydrophobicity, which made the resin more susceptible to phase separation, and this resulted in a larger core level height Sk, a surface roughness parameter.

[0328] In order to suppress phase separation of the resin in the ink [K4-2] head, it is necessary to set the ink temperature in the head high. This tends to slightly increase the risk of thermal polymerization in the head. It is thought that the image [K4-2] in Example 8 was evaluated as an A because these conditions were adjusted.

[0329] [5-2] Comparative Examples The images listed as Comparative Examples have a surface roughness parameter core level height Sk of less than 0.1 or a deviation Ssk of less than -2, which suggests that although there are irregularities across the entire image surface, there are many smooth areas. This makes the difference between the smooth areas across the entire image surface and the streaky areas more noticeable and easily visible, which is why the Comparative Examples are considered to have poorer evaluation results than the Examples.

[0330] (Comparative Example 1) In the image [K1-3] in Comparative Example 1, the pump suction pressure during the image creation process was insufficient, which is thought to have made it difficult for the wax to form a card-house structure on the image surface, and the surface roughness parameters did not fall within the appropriate range.

[0331] (Comparative Example 2) In the image [K2-3] of Comparative Example 2, the acrylic equivalent of the ink [K2-3] containing the scaly filler used was higher than the acrylic equivalent of the ink K [2-2] used in the process of producing the image K [2-2], and it is thought that the cure shrinkage was insufficient. Therefore, it is thought that the uneven structure of the scaly filler was less easily reflected on the image surface, and the surface roughness parameter did not fall within the appropriate range.

[0332] (Comparative Example 3) In the image [K3-3] in Comparative Example 3, the pressure applied by the embossing roller and pressure roller during the semi-curing of the ink in the image formation process was insufficient, which is thought to have made it difficult for the unevenness of the embossing roller to be transferred to the image surface, and as a result, the core level height Sk and the bias Ssk, which are surface roughness parameters, were both too small.

[0333] Comparative Example 4 The image [K4-3] in Comparative Example 4 was not affected by phase separation of the ink when it hardened during the image formation process. However, it is believed that the value of the bias Ssk was too small because phase separation was insufficient due to the difference between the temperature at the time of ink ejection and the temperature of the paper.

[0334] (Comparative Example 5) The ink [K5] used to produce the image [K5] in Comparative Example 5 contains less wax than the ink [K1] used to produce the image [K1], and because the paper thickness during the image production process is not particularly thin, the penetration of the acrylic monomer into the paper by pump suction is not significant. For this reason, it is thought that the wax house-of-cards structure is less likely to form on the image surface, resulting in a smaller bias degree Ssk.

[0335] (Comparative Example 6) The image [K5-2] in Comparative Example 6 uses ink [K5] containing wax when forming the image, but it is thought that because the wax crystals were precipitated at a low temperature, the wax crystals became extremely fine, resulting in a decrease in Sal.

[0336] (Comparative Example 7) The image [K6] in Comparative Example 7 was formed using ink [K6] containing the "tetrazole compound BHT-2NH3." The "tetrazole compound BHT-2NH3" releases a large amount of nitrogen gas when it decomposes by absorbing heat or ultraviolet light. The fine nitrogen gas bubbles generated during decomposition form on the image surface, creating moderate irregularities. However, in areas where no bubbles are generated, the surface shape of the image remains flat. This is thought to be why the surface roughness parameters core level height Sk and bias Ssk both decrease, making streaks more visible.

[0337] [6] Overall Review From the above, it can be seen that the occurrence of streaks is suppressed in the images formed in the examples compared to the images formed in the comparative examples.

[0338] While embodiments of the present disclosure have been described and illustrated in detail above, the disclosed embodiments are made for purposes of illustration and example only, and not limitation. The scope of the present disclosure should be construed by the terms of the appended claims. [Explanation of symbols]

[0339] H, H1, H2, H1a, H1b, H1c, H2a, H2b head 1a, 1b, 1c, 2a, 2b inks C H Joint between heads TD transport direction, paper transport direction WD Width direction P Recording medium HM1, HM2 head modules E Print area edge overlap in head f Missing launch LED1 First LED lamp LED2 Second LED lamp N nitrogen gas RP pressure roller RE Embossing Roller

Claims

1. An image having an area formed by printing from a plurality of inkjet heads, The core level height Sk of the surface roughness parameter measured within a reference length of 120 μm set on the surface of the image is within a range of 0.1 to 0.2 μm, and the bias Ssk of the surface roughness parameter is within a range of −2.0 to 2.

0. An image characterized by:

2. The minimum autocorrelation length Sal of the surface roughness parameter is within the range of 0.3 to 5.0 μm.

2. The image of claim 1 .

3. the image has an area where the edges of the printing ranges of a plurality of inkjet heads arranged in the width direction of the paper overlap each other, and The overlapping area of ​​the print area edges is within a range of 0.5 to 20 mm.

2. The image of claim 1 .

4. The image is formed by ink ejected from a plurality of inkjet heads arranged in the paper transport direction.

2. The image of claim 1 .

5. 10. An image forming method for forming the image according to claim 1, comprising: the image is formed by ink ejected from a plurality of inkjet heads arranged in the width direction of the paper, The overlap of the printing area edges of the inkjet heads is within a range of 0.5 to 20 mm. An image forming method comprising:

6. 10. An image forming method for forming the image according to claim 1, comprising: The image is formed by ink ejected from a plurality of inkjet heads arranged in the paper transport direction. An image forming method comprising:

7. A single-pass image forming apparatus in which a plurality of inkjet heads are arranged, A means for ejecting ink onto a substrate to form an image is provided, The core level height Sk of the surface roughness parameter measured within a reference length of 120 μm set on the surface of the image is within a range of 0.1 to 0.2 μm, and the bias Ssk of the surface roughness parameter is within a range of −2.0 to 2.

0. An image forming apparatus characterized by:

8. The minimum autocorrelation length Sal of the surface roughness parameter is within the range of 0.3 to 5.0 μm.

8. The image forming apparatus according to claim 7,

9. In an inkjet image forming apparatus that forms an image by ejecting ink from an inkjet head, When an image is formed on coated paper having a thickness of 0.11 mm at a resolution of 1200 dpi x 1200 dpi, the core level height Sk of the surface roughness parameter measured within a reference length of 120 μm on the surface of the image is within the range of 0.1 to 0.2 μm, and the bias Ssk of the surface roughness parameter is within the range of -2.0 to 2.

0. An image forming apparatus characterized by:

10. In an inkjet image forming method for forming an image by ejecting ink from an inkjet head, When an image is formed on coated paper having a thickness of 0.11 mm at a resolution of 1200 dpi x 1200 dpi, the core level height Sk of the surface roughness parameter measured within a reference length of 120 μm on the surface of the image is within the range of 0.1 to 0.2 μm, and the bias Ssk of the surface roughness parameter is within the range of -2.0 to 2.

0. An image forming method comprising:

Images