JP2023031676A - Manufacturing method of printed matter - Google Patents

Abstract

To provide a manufacturing method of a printed matter which can form an ink layer with high definition without color unevenness and stripe unevenness.SOLUTION: A manufacturing method of a printed material includes a printing step of forming an ink layer by applying a plurality of types of active energy ray-curable type ink to a metallic recording medium and photo-curing the ink with a serial type ink jet printer that has a carriage in which a plurality of ink jet heads respectively having a plurality of nozzles and a plurality of LED light sources are alternately arranged along the main-scanning direction. The printing step includes a scan step of causing the ink jet head to apply the ink while causing the carriage scan in the main-scanning direction, and causing the LED light source adjacent in the travel direction rear side to the ink jet head to emit light to the ink applied by the ink jet head. The scan steps are performed two or more times to the same region of the metallic recording medium by displacing the carriage in the sub-scanning direction.SELECTED DRAWING: None

Description

The present invention relates to a printed matter manufacturing method using an inkjet printing apparatus.

2. Description of the Related Art In recent years, there has been a demand for forming coating films of various colors on various absorbable recording media such as metals. There is also a demand for on-demand formation of a coating film according to needs.

The active energy ray-curable ink is cured by irradiation with active energy. Therefore, it is possible to form an image even on a metal recording medium that does not absorb solvents. In addition, the inkjet method does not require a plate during printing, and ejects ink only in the required area to form an image directly on the substrate to be printed. The cost advantage is high in the case of For example, Patent Literature 1 describes forming an ink layer by applying an active energy ray-curable ink to the surface of a siding by an inkjet method.

Here, there are a serial method and a line method as printing methods by the inkjet printing apparatus. In the serial method, the step of scanning the inkjet head in the width direction of the recording medium (herein also referred to as the "main scanning direction"), and moving the inkjet head and the recording medium in the direction perpendicular to the main scanning direction (herein referred to as the "main scanning direction"). and the step of relatively moving in the sub-scanning direction) are alternately repeated. On the other hand, in the line method, an inkjet head (line head) arranged to cover the recording medium in the width direction continuously forms an image while relatively moving the inkjet head and the recording medium.

JP 2010-112073 A

Here, according to the serial method, the length of the inkjet head (hereinafter also referred to as "head") can be relatively short, so the cost of the inkjet device (hereinafter also simply referred to as "printing device") can be reduced. 1A and 1B show an example of the configuration of a conventional serial printing apparatus for active energy ray-curable ink printing. FIG. 1A is a plan view of a partial configuration of printing apparatus 900, and FIG. 1B is a side view of the configuration. As shown in FIGS. 1A and 1B, the active energy ray-curable ink printing apparatus usually includes a head 911 for ejecting ink and a light source 912 for curing the ink ejected from the head 911. , which are mounted on the carriage 910 . As the carriage 910 moves in the main scanning direction X, the ink is applied and cured.

The head 911 usually includes a plurality of heads (a head 911K for black, a head 911C for cyan, a head 911M for magenta, and a head 911Y for yellow in FIG. 1) respectively corresponding to inks of a plurality of colors. Each head 911 has a nozzle (not shown) for ejecting ink, and ejects ink from the nozzle. On the other hand, only one light source 912 is arranged behind the plurality of heads 911 in the traveling direction, and collectively cures the inks of a plurality of colors applied from the heads 911 .

As a result of extensive studies by the present inventors, streaky unevenness (sometimes referred to as "banding phenomenon") and color unevenness occur along the main scanning direction when an ink layer is formed using a conventional serial printing apparatus. It became clear. The reason is as follows. In the printing apparatus 900 described above, the positions of the nozzles (not shown) may slightly deviate from the desired positions due to manufacturing errors of the head 911 and errors in attaching the head 911 to the carriage 910 . Then, the landing positions of the droplets (ink) ejected from the nozzles are all deviated from the desired locations. As a result, white streaks occur in portions where the distance to adjacent rows is long, and color unevenness occurs in portions where the distance to adjacent rows is short.

In addition, when all the inks of the respective colors are applied and then cured together as in the conventional printing apparatus 900, the time from application to curing is long, and the inks are merged before curing. In particular, when the amount of uncured ink is large, the inks tend to coalesce. When such coalescence occurs, the ink does not spread sufficiently in the width direction (sub-scanning direction Y), and the distance between adjacent dots increases in that direction. As a result, stripe unevenness occurs along the main scanning direction X. FIG.

Furthermore, the conventional printing apparatus 900 also has a problem that it is difficult to form a high-definition image. As described above, in the conventional printing apparatus 900, after each color ink is applied, the inks are collectively photo-cured. Therefore, there is a difference between the time it takes for the previously applied ink (black ink in FIG. 1A) to cure and the time it takes for the later applied ink (yellow ink in FIG. 1) to cure. Therefore, the farther the color is from the light source, the larger the dot diameter, which tends to blur and tends to cause deterioration in image quality.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for producing a printed matter that can form an ink layer with high definition without color unevenness or stripe unevenness.

The present invention relates to a serial-type printer having a carriage in which a plurality of inkjet heads each including a plurality of nozzles arranged along the sub-scanning direction and a plurality of LED light sources are alternately arranged along the main scanning direction. A method for producing a printed matter, comprising a printing step of forming an ink layer by applying a plurality of types of active energy ray-curable inks to a metal recording medium and photo-curing them by an inkjet printing apparatus, wherein the printing step includes the above-described printing step. While the carriage is scanned in the main scanning direction, the ink jet head applies the ink, and the LED light source adjacent to the ink jet head behind the ink jet head in the traveling direction irradiates the ink applied by the ink jet head with light. and a scanning step, wherein the scanning step is performed twice or more on the same area of the metal recording medium while shifting the carriage in the sub-scanning direction.

According to the method for producing a printed matter of the present invention, it is possible to produce a printed matter on which an ink layer is formed with high definition without color unevenness or stripe unevenness.

FIG. 1A is a plan view schematically showing the configuration of a conventional inkjet printer, and FIG. 1B is a side view of the configuration. FIG. 2A is a plan view schematically showing the configuration of an inkjet printing apparatus used in the printed matter manufacturing method of the present invention, and FIG. 2B is a side view of the configuration. 3A and 3B are plan views schematically showing the position of the carriage in the printed matter manufacturing method of the present invention.

In the present invention, an inkjet printing apparatus having a specific carriage is used to produce prints. Therefore, an inkjet printing apparatus will be described first, and then a method for manufacturing a printed matter using the inkjet printing apparatus will be described.

(inkjet printer)
An example of the configuration of the inkjet printing apparatus 100 is shown in FIGS. 2A and 2B. 2A is a plan view of a partial configuration of the printing apparatus 100, and FIG. 2B is a side view of the configuration.

The printing apparatus 100 has a serial carriage 110 . The carriage 110 includes a plurality of inkjet heads 111K, 111C, 111M, and 111Y (hereinafter collectively referred to as "heads 111" when there is no need to distinguish between them) and a plurality of LED light sources 112K, 112C, and 112M. , 112Y (hereinafter also collectively referred to as “LED light sources 112” when there is no need to distinguish between them). In the carriage 110 , multiple heads 111 and multiple LED light sources 112 are alternately arranged along the main scanning direction X of the carriage 110 .

Here, the number of heads 111 and the number of LED light sources 112 arranged on the carriage 110 are not particularly limited, and are appropriately selected according to the number of types of ink to be applied. A carriage 110 of the printing apparatus 100 shown in FIG. 2A is provided with heads 111 and LED light sources 112 corresponding to four types of ink. Specifically, a black head 111K, a black LED light source 112K, a cyan head 111C, a cyan LED light source 112C, a magenta head 111M, a magenta LED light source 112M, a yellow head 111Y, and a yellow LED light source 112Y. arranged in this order.

Each head 111 is a member for applying each color ink to a metal recording medium (hereinafter, also referred to as a "recording medium"), and includes an ink tank (not shown) for storing the ink and a head for ejecting the ink. It has a nozzle (not shown) for printing, a flow path connecting the nozzle and the ink tank, and the like. These structures are not particularly limited, and have structures similar to ink tanks, nozzles, and flow paths of known inkjet heads.

Each head 111 has a plurality of nozzles arranged at substantially equal intervals along the sub-scanning direction Y. As shown in FIG. The nozzle density of the head is preferably 200 nozzles/inch or more and 1600 nozzles/inch or less, more preferably 300 nozzles/inch or more and 1440 nozzles/inch or less. The wider the width of the head (total head width when multiple heads are connected in the sub-scanning direction), the greater the number of droplets that can be ejected in one scan of the carriage 110 (head 111). can be manufactured. Further, as will be described in detail later, in the method of manufacturing a printed matter according to the present embodiment, the carriage 110 is shifted in the sub-scanning direction Y and the same area is scanned a plurality of times by the carriage 110 . Therefore, the greater the number of nozzles, the finer the carriage 110 can be moved to apply ink to the same area a plurality of times. The number of nozzles of each head 111 and the distance between the nozzles may be different, but they are usually the same.

Further, in the printing apparatus 100, the head 111 is arranged such that the distance between the nozzles and the recording medium 10 is 0.5 to 10 mm. More preferably, the distance between the nozzle and the recording medium 10 is 0.5 to 5 mm. When the distance between the nozzle and the recording medium is within this range, the light emitted from the LED light source 112 is less likely to reach between the head 111 (nozzle) and the recording medium 10 during scanning of the carriage 110, and the Curing of the ink can be suppressed.

On the other hand, the LED light source 112 is a member for applying light to the active energy ray-curable ink that has landed on the recording medium 10 to photo-cure the ink. The LED light source 112 may include not only LEDs but also lenses, covers, mirrors, etc. for condensing light and reflecting it in desired directions.

Each LED light source 112 may have a structure capable of irradiating light onto all regions where ink is ejected from the nozzles of the corresponding head 111. It may have structures arranged side by side. Also, multiple types of LEDs may be combined. Each light source 112 may be capable of emitting the same wavelength of light with the same intensity, or may be capable of emitting light of different wavelengths or different intensities.

The wavelength of the light emitted from each LED light source 112 is appropriately selected according to the type of ink to be applied, but is preferably ultraviolet light or visible light, with a peak wavelength of preferably 350 to 420 nm, more preferably 380 to 410 nm. When the peak wavelength is within this range, the ink can be efficiently cured.

In addition, the intensity of the light emitted from each LED light source 112 may be an intensity capable of completely curing the ink, or may be an intensity sufficient to temporarily cure the ink. The intensity of light is, for example, preferably 0.5 to 25 W/cm ² , more preferably 2 to 15 W/cm ² . Within this range, it is possible to efficiently cure the ink while moving the carriage 110 in the scanning direction X.

In the printing apparatus 100, each LED light source 112 is preferably arranged such that the distance between the recording medium 10 side end of each LED light source 112 and the recording medium 10 is 5 to 15 mm. is more preferably 7 to 12 mm. When the distance between the LED light source 112 and the recording medium 10 is within this range, the ink can be cured with good energy efficiency.

The distance between each head 111 and the corresponding LED light source 112 (LED light source 112 adjacent in the rearward direction of travel) is not particularly limited, but the shorter the distance, the more ink ejected from the head 111. It can be allowed to harden before it can be wet spread. Also, the shorter these distances are, the more advantageous it is that the carriage 110 can be made smaller. The distance between the end of the nozzle located on the rearmost side in the main scanning direction X of each head 111 and the end on the front side in the main scanning direction X of the LED light source 112 is preferably about 20 to 60 mm. When the distance is 20 mm or more, it is difficult for light to flow between the head 111 (nozzle) and the recording medium 10, and curing of the ink in the vicinity of the nozzle can be suppressed. On the other hand, if the distance is 60 mm or less, the carriage 110 can be made compact. Since the LED light source 112 generates little heat, the distance is 60 mm or less, and the head 111 and the ink inside it are hardly affected. Also, such an LED light source 112 can be turned ON/OFF frequently.

Here, the method of attaching each head 111 and each LED light source 112 to the carriage 110 is not particularly limited. Not limited.

Further, in this embodiment, the carriage 110 is attached to a rail 120 extending in the main scanning direction X, and the carriage 110 moves along the rail 120 .

In addition to the carriage 110 and the rail 120, the inkjet printing apparatus 100 also has a transport mechanism (not shown) for relatively moving the recording medium 10 and the carriage 110 in the sub-scanning direction Y, and the like. The transport mechanism may be similar to a transport mechanism of a general serial printing apparatus. In addition to the above, the inkjet printing apparatus 100 may have various configurations within a range that does not impair the purpose and effect of the present embodiment.

Here, the recording medium that can be used in the printed matter manufacturing method using the printing apparatus 100 is not particularly limited as long as it contains metal, and may be combined with other materials. When the recording medium is a metal base material to be printed, which will be described later, the adhesion between the recording medium and the ink layer can be particularly enhanced, but the recording medium is not limited to the metal base material to be printed, which will be described later.

In addition, the ink used in the printing apparatus 100 is not particularly limited as long as it can be cured by irradiation with active energy rays, more specifically, by light emitted from the LED light source 112. It is appropriately selected according to the type and the intended use of the resulting printed matter. Examples of active energy rays in this specification include electron beams, ultraviolet light, visible light, alpha rays, gamma rays, X-rays, etc., and the ink can be cured by ultraviolet light or visible light. preferable.

The ink may be cationic polymerization ink or radical polymerization ink. Radical polymerization type ink is easier to cure with the LED light source, and is preferable from the viewpoint of cost and the like.

The composition of the radical polymerizable ink is not particularly limited, and usually contains a radical polymerizable compound and a radical polymerization initiator. The radically polymerizable compound may have a photopolymerizable functional group, and a compound having a (meth)acrylate group is particularly preferable. The compound having a (meth)acrylate group is not particularly limited, and known monofunctional or higher functional (meth)acrylate monomers can be used. As used herein, (meth)acrylate refers to methacrylate, acrylate, or both.

Moreover, the radical polymerization initiator is not particularly limited as long as it generates radicals by the light from the LED light source 112 and initiates the polymerization of the radically polymerizable compound. A known compound can be used as the radical polymerization initiator. Examples of radical polymerization initiators include acylphosphine oxide compounds, thioxanthone compounds, aromatic ketones, aromatic onium salt compounds, organic peroxides, thio compounds (such as thiophenyl group-containing compounds), α-aminoalkylphenones. compounds, hexaarylbiimidazole compounds, ketoxime ester compounds, borate compounds, azinium compounds, metallocene compounds, active ester compounds, compounds having a carbon-halogen bond, and alkylamine compounds.

In addition, the ink may contain components other than those described above. Examples include coloring materials such as pigments and dyes; various additives such as inhibitors, polymerization inhibitors and chelating agents;

(Manufacturing method of printed matter)
The method for producing a printed matter according to the present embodiment includes a printing step of forming an ink layer by applying a plurality of types of active energy ray-curable inks to a metal recording medium and photocuring the inks using the inkjet printing apparatus described above. In the printing process, the ink is applied by the ink jet head while the carriage is scanned in the main scanning direction, and the LED light source adjacent to the ink jet head behind the ink jet head emits light to the ink applied by the ink jet head. irradiating, including a scanning step; Further, in the ink layer forming step, the scanning step is performed twice or more on the same area of the metal recording medium while shifting the carriage in the sub-scanning direction. A detailed description will be given below.

In the scanning process, first, as shown in FIG. 3A, the carriage 110 is placed at a specific position (usually the edge of the recording medium 10). While moving the carriage 110 in the main scanning direction X, the ink from the head 111 is ejected onto the recording medium, and the ink that has landed on the recording medium is cured by light from the LED light source 112 . At this time, ejection and curing of ink are performed for each ink.

For example, when the carriage 110 of the printing apparatus 100 shown in FIG. 2A is used to apply all colors to a specific region, black ink is applied from the black head 111K and the black ink is cured by the black LED light source 112K. . Subsequently, cyan ink is applied to the area from the cyan head 111C, and the cyan ink is cured by the cyan LED light source 112C. Further, magenta ink is applied to the area from the magenta head 111M, and the magenta ink is cured by the magenta LED light source 112M. Then, the yellow ink is applied to the area from the yellow head 111Y, and the yellow ink is cured by the yellow LED light source 112Y. By applying and curing each ink in this manner, the dot diameter of each ink can be made uniform, and a high-definition ink layer can be easily obtained. Further, when an ink layer is formed by this method, it is difficult for uncured inks to coalesce on a recording medium, and streaky unevenness and color unevenness are less likely to occur in the resulting ink layer.

Here, the amount of ink to be applied while the carriage is scanned once in the main scanning direction X and the application pattern are determined by how many times the scanning process is performed for the same area. For example, if two scanning steps are performed on the same area, half the amount of ink required to form the desired pattern is applied in each scanning step. The pattern in which the ink is applied is not particularly limited, but it is preferable to print every other dot, for example. By coating in this manner, not only can the amount of ink be halved, but also streak unevenness and color unevenness are very inconspicuous in the resulting ink layer.

On the other hand, when scanning the same area four times, 1/4 of the amount of ink required to form a desired pattern is applied in each scanning process. Although there are no particular restrictions on the pattern in which the ink is applied, it is preferable to print every three dots. In this case as well, not only can the amount of ink be reduced to 1/4, but also streak unevenness and color unevenness become very inconspicuous in the resulting ink layer.

Subsequently, while shifting the carriage 110 in the sub-scanning direction, the scanning process is performed again on the area scanned by the carriage 110 . The width by which the carriage 110 is shifted (the distance indicated by W in FIG. 3) is determined by how many times the scanning process is performed for the same area. For example, when scanning the same area twice, the width W is half the length of the carriage in the sub-scanning direction Y. As shown in FIG. Further, when scanning the same area four times, the width W is set to 1/4 of the length of the carriage in the sub-scanning direction Y. As shown in FIG.

By shifting the carriage 110 and then performing the scanning process on the same area in this way, the nozzles used when performing the first scanning process can be made different from the nozzles used when performing the second and subsequent scanning processes. can be done. As a result, even if there is an installation error or the like in one nozzle, dot misalignment is less noticeable, and streak unevenness and color unevenness are less likely to occur.

In the second and subsequent scanning processes, it is preferable to apply ink so as to fill the gaps between the dots formed in the previous process.

Here, the number of times the scanning process is performed on the same region may be two or more, preferably two to eight. The larger the number of times, the longer it takes to produce printed matter, but the resulting ink layer is less prone to streak unevenness and color unevenness. In addition, when the color of the ink layer to be formed is dark, streak unevenness is particularly conspicuous. Therefore, the number of scanning processes may be set to be less in areas where the color of the ink layer is light, and the number of scanning processes may be increased in areas where the color of the ink layer is dark.

The size of each dot formed in each scanning step is appropriately selected according to the amount of ink ejected from the nozzles. It is preferably 115 μm or more, and more preferably 115 μm or more.

Here, in a general printing method, in order to improve productivity, printing may be performed in each of the reciprocating directions of a serial type carriage. However, if printing is performed in the forward and backward directions in this way, the printing order of black, cyan, magenta, and yellow will change between the outward and return passes. As a result, the color tone changes and the designability deteriorates. Therefore, in this embodiment, it is preferable to apply and cure the ink when the carriage 110 is moved in only one direction (the main scanning direction X). In other words, unidirectional printing is preferable.

Here, after the above-described printing step, that is, after forming a desired ink layer on the recording medium 10 using the printing apparatus 100, a step of further irradiating light as necessary (hereinafter, also referred to as a “post-curing step”). ) may be performed. Thereby, the curability of the ink layer can be further enhanced, and an ink layer with high strength can be obtained.

The wavelength of the light irradiated in the post-curing step is not particularly limited, and may be, for example, ultraviolet light, visible light, infrared light, or the like. It is appropriately selected according to the type of ink. Moreover, the light source is not particularly limited, and may be an LED light source or a general light source such as a halogen lamp. In addition, the atmosphere of the space in which the light is irradiated preferably has an oxygen concentration of 5% by volume or less, more preferably 1% by volume or less, in order to prevent a decrease in the degree of surface curing due to inhibition of oxygen in the ink layer.

The intensity of the light irradiated in the post-curing step is not particularly limited, and is preferably 0.5 to 25 W/cm ² , more preferably 10 to 25 W/cm ² . Within this range, the curability of the ink tends to be favorable.

Further, in the present embodiment, after the printing process, a process of relaxing the distortion generated in the ink layer in the printing process, that is, the distortion generated when the ink is cured by heating (hereinafter also referred to as a "distortion relaxation process"). may be further performed. By performing the strain relaxation process, the adhesion of the ink layer to the recording medium is enhanced.

The heating temperature in the strain relaxation step is not particularly limited, but is usually preferably 80 to 270°C, more preferably 100 to 230°C. The heating time is preferably about 0.5 to 60 minutes, more preferably about 1 to 20 minutes. When the heating temperature and time are within the above ranges, the strain can be relaxed without damaging the recording medium or the ink layer.

(effect)
As described above, in the carriage of the conventional serial type inkjet printing device, only one light source is arranged for a plurality of inkjet heads. For this reason, multiple types of ink are discharged from each inkjet head and then cured all at once, which tends to cause problems such as streak unevenness and color unevenness as described above. Furthermore, in the obtained ink layer, the dot diameter differs for each color, and there is also the problem that the image quality tends to deteriorate.

On the other hand, in the printing apparatus used in the printed matter manufacturing method of the present embodiment, an LED light source is arranged for each head, and ink is ejected and cured for each ink. Therefore, the amount of ink to be cured at one time is small, and it is difficult for the inks that have landed on the recording medium to coalesce. As a result, the landed ink can be sufficiently wetted and spread in the sub-scanning direction, and the interval between dots can be kept constant.

Further, in the above-described printed matter manufacturing method, the ink layer is formed by scanning the same region at least twice with the carriage of the inkjet printing device. Also, at this time, ink is applied from different nozzles in the first scan and the second scan. Therefore, even if there is an error or the like when attaching to the nozzles of the inkjet head, dot misalignment is less noticeable, and streak unevenness and color unevenness are less likely to occur.

Further, as described above, when applying a plurality of types of ink, the ink is ejected and cured for each type. Therefore, the dot diameter of each type of ink in the obtained ink layer can be made uniform. Therefore, a highly precise ink layer can be formed. According to the above method, the maximum dot diameter and the minimum dot diameter on the recording medium can each be kept within ±20% of the average dot diameter, and should be kept within ±10%. is also possible. The dot diameter of ink is the diameter of a main dot excluding satellite components when observed with a microscope, and the maximum and minimum values in a specific direction are specified for each dot. And let these average values be the dot diameter of each dot.

(preferred recording medium)
The type of metal recording medium used in the above-described method for producing a printed matter is not particularly limited. and a printed layer. In general, it is difficult to improve the adhesion of an ink layer, which is a cured product of an active energy ray-curable composition, and peeling is likely to occur at the interface between these layers when the thickness of the ink layer is particularly thick. The reason for this is that the shrinkage of the ink during curing is large, and residual stress is generated in the ink layer after curing, and stress is generated at the interface between the metal substrate and the ink layer during curing. It is thought that peeling of the film occurs.

On the other hand, the layer to be printed contains an alcohol structural unit derived from a polyhydric alcohol and a carboxylic acid structural unit derived from a polycarboxylic acid, and contains a polyester resin having a number average molecular weight of 4000 to 12000 and a melamine resin. and the ratio of the amount of the structural unit derived from a trihydric or higher alcohol to the total amount of the alcohol structural unit and the carboxylic acid structural unit is 20 mol% or less. Adhesion between the ink layer formed by the method for manufacturing printed matter and the recording medium (metal base material for printing) is likely to be greatly improved.

The reasons are as follows. The cured product of the paint for metal has an appropriate cross-linking density and is relatively flexible. When an ink layer is formed on such a layer to be printed by the method described above, the layer to be printed can relieve stress even if shrinkage occurs during curing of the ink. That is, the stress remaining in the ink layer is reduced. In addition, since the layer to be printed is relatively flexible, the layer to be printed can follow and deform according to the curing shrinkage of the ink. Therefore, stress is less likely to act between the layer to be printed and the ink layer, and the adhesion between them can be enhanced. In addition, since the layer to be printed has an appropriate crosslinking density, it has sufficiently high weather resistance. Therefore, it is also possible to use the printed matter described above outdoors.

Hereinafter, the metal paint for forming the print layer of the metal base material to be printed will be described, and then the metal base material to be printed that is formed using the metal paint will be described.

(metal paint)
The metal paint should only contain a polyester resin having a specific structure and molecular weight and a melamine resin, and if necessary, other components such as catalysts, amines, extender pigments and coloring pigments. good.

A polyester resin is a resin having a plurality of ester structures in its molecular chain, and is a resin containing a carboxylic acid structural unit derived from a polyhydric carboxylic acid and an alcohol structural unit derived from a polyhydric alcohol. The polyester resin can usually be prepared by polymerizing a polyhydric carboxylic acid and a polyhydric alcohol.

Here, examples of polyvalent carboxylic acids include aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, phthalic acid, 2,6-naphthalenedicarboxylic acid and 2,7-naphthalenedicarboxylic acid, and their anhydrides; succinic acid; , adipic acid, azelaic acid, sebacic acid, dodecanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid and other aliphatic dicarboxylic acids and their anhydrides; γ-butyrolactone, ε-caprolactone and other lactones; trimellitic acid, trimedine trivalent or higher polyvalent carboxylic acids such as acids and pyromellitic acid; The polyester resin may contain only one type of carboxylic acid structural unit derived from the polyvalent carboxylic acid, or may contain two or more types thereof. In the polyester resin, the ratio of the amount of structural units derived from trivalent or higher polyvalent carboxylic acid to the total amount of alcohol structural units derived from polyhydric alcohol and carboxylic acid structural units derived from polyvalent carboxylic acid is It is preferably 5 mol % or less, more preferably 2 mol % or less, so as not to excessively increase the crosslink density of the film.

On the other hand, examples of polyhydric alcohols include ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 1, 2-pentanediol, 1,4-pentanediol, 1,5-pentanediol, 2,3-pentanediol, 1,4-hexanediol, 2,5-hexanediol, 1,5-hexanediol, 1,6 -hexanediol, 3-methyl-1,5-pentanediol, 2-methyl-1,3-propanediol, diethylene glycol, triethylene glycol, 1,2-dodecanediol, 1,2-octadecanediol, neopentyl glycol, Glycols such as 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol, bisphenol A alkylene oxide adduct, bisphenol S alkylene oxide adduct; Trimethylolpropane, glycerin, trihydric or higher polyhydric alcohols such as pentaerythritol etc. are included. The polyester resin may contain only one type of alcohol structural unit derived from the polyhydric alcohol, or may contain two or more types thereof.

However, the ratio of structural units derived from trihydric or higher alcohol to the total amount of carboxylic acid structural units and alcohol structural units in the polyester resin contained in the metal paint is 20 mol % or less. The proportion of structural units derived from the trihydric or higher alcohol is more preferably 15 mol % or less, still more preferably 10 mol % or less. If the amount of the structural unit derived from a trihydric or higher alcohol exceeds 20 mol %, the three-dimensional crosslinked structure increases when the polyester resin is crosslinked with the melamine resin described below. As a result, the printed layer to be obtained tends to be hard, and the adhesion to the ink layer tends to be low. When the polyester resin contains a structural unit derived from a trivalent or higher alcohol, it preferably contains a structural unit derived from trimethylolpropane. When the polyester resin contains an alcohol structural unit derived from trimethylolpropane, the cross-linking density of the coating film becomes more stable, and adhesion to the ink layer can be easily obtained.

The polyester resin has a number average molecular weight of 4,000 to 12,000, preferably 5,000 to 11,000. The number average molecular weight of the polyester resin is a styrene conversion value specified by gel permeation chromatography (GPC). When the number average molecular weight of the polyester resin is 4,000 or more, the strength of the printed layer to be obtained tends to increase, and the weather resistance and workability of the printed layer tend to be improved. On the other hand, when the polyester resin has a number average molecular weight of 12,000 or less, the adhesion between the layer to be printed and the ink layer tends to be good.

Moreover, the hydroxyl value of the polyester resin is preferably 5 to 100 mgKOH/g, more preferably 10 to 70 mgKOH/g. A hydroxyl value is specified by a potentiometric titration method defined in JIS K0070 using a 0.5 mol/L KOH alcohol solution. When the hydroxyl value of the polyester resin is within this range, the OH groups on the surface of the metal substrate and the OH groups in the polyester resin (printed layer) are likely to form hydrogen bonds, etc., and adhesion between the metal substrate and the printed layer is enhanced. sexuality increases. Similarly, the OH groups in the polyester resin (printing layer) are more likely to form hydrogen bonds with the hydrophilic groups in the ink layer, further increasing their adhesion.

Further, the glass transition temperature of the polyester resin is preferably 0 to 100°C, more preferably 20 to 70°C. When the glass transition temperature of the polyester resin is within the above range, the processability of the resulting printed layer is improved.

On the other hand, the melamine resin contained in the paint for metal is not particularly limited, but includes methylated melamine resins such as methylolmelamine methyl ether; butylated melamine resins such as methylolmelamine butyl ether; and mixed etherified melamine resins of methyl and n-butyl. included. The paint for metal may contain only one type of melamine resin, or may contain two or more types. Among the above, methylated melamine resins, butylated melamine resins, and combinations thereof are preferred, and methylated melamine resins are particularly preferred. If the butylated melamine resin is excessively added, the crosslink density of the surface layer of the coating film may become excessive.

The ratio (mass ratio) of the polyester resin and the melamine resin contained in the paint for metal is preferably 90:10 to 60:40, more preferably about 85:15 to 65:35. When the mass ratio of the polyester resin and the melamine resin is within this range, a printed layer having excellent weather resistance and impact resistance can be obtained.

The total amount of the polyester resin and the melamine resin is preferably 30 to 80 parts by mass, more preferably 50 to 70 parts by mass, based on 100 parts by mass of the solid content of the paint for metal. When the total amount of the polyester resin and the melamine resin is within this range, the strength of the printed layer obtained from the paint for metal tends to be sufficiently increased. Furthermore, the adhesion between the layer to be printed and the ink layer tends to be good.

The metal paint may further contain a catalyst. Examples of catalysts include dodecylbenzenesulfonic acid, paratoluenesulfonic acid, benzenesulfonic acid, and the like. The amount of the catalyst to be used is preferably 0.1 to 8% by mass based on the total solid content of the metal paint.

Additionally, the metal coating may further comprise an amine. Amines are compounds for neutralizing catalytic reactions, examples of which include triethylamine, dimethylethanolamine, dimethylaminoethanol, monoethanolamine, isopropanolamine, and the like. The amount of amine to be used is not particularly limited, but is preferably 50 mol % or more of the acid (catalyst) equivalent.

In addition, the metal paint may further contain an extender pigment (including beads), a color pigment, and the like. Examples of extender pigments include silica, calcium carbonate, barium sulfate, aluminum hydroxide, talc, mica, resin beads, glass beads, and the like. Examples of resin beads include acrylic resin beads, polyacrylonitrile beads, polyethylene beads, polypropylene beads, polyester beads, urethane resin beads, epoxy resin beads and the like.

These resin beads may be produced using a known method, or may be commercially available. Examples of commercially available acrylic resin beads include “Toughtic AR650S (average particle size 18 μm)”, “Tufftic AR650M (average particle size 30 μm)”, “Tufftic AR650MX (average particle size 40 μm)”, “Tufftic AR650MZ” manufactured by Toyobo Co., Ltd. (average particle size 60 μm)”, “TUFTIC AR650ML (average particle size 80 μm)”, “TUFTIC AR650L (average particle size 100 μm)” and “TUFTIC AR650LL (average particle size 150 μm)”. Examples of commercially available polyacrylonitrile beads include Toyobo Co., Ltd. "Toughtic A-20 (average particle size 24 μm)", "Toughtic YK-30 (average particle size 33 μm)", "Toughtic YK-50 (average particle size diameter 50 μm)” and “Tuftic YK-80 (average particle diameter 80 μm)”. The metal paint may contain only one of these, or may contain two or more.

On the other hand, examples of coloring pigments include carbon black, titanium oxide, iron oxide, yellow iron oxide, phthalocyanine blue, cobalt blue and the like. The amount of pigment is appropriately selected according to the type of pigment, particle size, and the like. The metal paint may contain only one of these, or may contain two or more.

The paint for metal may further contain a solvent as needed. The solvent is not particularly limited as long as it can sufficiently dissolve the polyester resin and melamine resin and can uniformly disperse the extender pigment and coloring pigment. Examples of solvents include toluene, xylene, Solvesso® 100 (trade name, manufactured by ExxonMobil), Solvesso® 150 (trade name, manufactured by ExxonMobil), Solvesso® 200 (trade name). name, manufactured by Exxon Mobil); ketone solvents such as methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, and isophorone; ester solvents such as ethyl acetate, butyl acetate, and ethylene glycol monoethyl ether acetate; methanol, isopropyl Alcohol solvents such as alcohol and n-butyl alcohol; Ether alcohol solvents such as ethylene glycol monoethyl ether and diethylene glycol monobutyl ether; The metal paint may contain only one of these, or may contain two or more. Among these, xylene, Solvesso (registered trademark) 100, Solvesso (registered trademark) 150, cyclohexanone, and n-butyl alcohol are preferred from the viewpoint of compatibility with polyester resins and melamine resins.

The method for preparing the metal paint is not particularly limited, and the polyester resin, the melamine resin, and, if necessary, other components may be mixed by a known method.

(Metal substrate for printing)
The metal base material to be printed has a metal base material and a to-be-printed layer, which is a cured product of the metal coating material described above, disposed on the metal base material.

- Metal substrate The metal substrate is not particularly limited as long as it has a structure capable of forming a layer to be printed by applying the above metal paint, and the shape thereof is not particularly limited. For example, it may be tabular or have a three-dimensional structure. Also, the metal substrate may be strip-shaped or the like. The thickness of the metal substrate is not particularly limited, and is appropriately selected according to the intended use of the coated metal material.

In addition, the material of the metal substrate is not particularly limited, and hot-dip Zn-plated steel sheet, hot-dip Zn-55% Al alloy-plated steel sheet, hot-dip Zn-Al-Mg alloy-plated steel sheet, hot-dip Al-plated steel sheet, electro-Zn-plated steel sheet, electro-Cu Plated steel sheets such as plated steel sheets; steel sheets such as ordinary steel sheets and stainless steel sheets; aluminum sheets; copper sheets, and the like. The metal substrate may have a chemical conversion treatment film, an undercoat film, or the like formed on its surface within a range that does not impair the effects of the present invention. Furthermore, the metal base material may be subjected to uneven processing such as embossing or draw forming within a range that does not impair the effects of the present invention.

The type of chemical conversion treatment for forming the chemical conversion film is not particularly limited. Examples of chemical conversion treatments include chromate treatments, chromium-free treatments, phosphate treatments, and the like. The amount of the chemical conversion coating applied is not particularly limited as long as it is within a range effective for improving corrosion resistance.

Further, the undercoat film is a layer that is formed directly on the metal substrate or on the chemical conversion film to improve the adhesion of the printed layer or improve the corrosion resistance of the metal substrate.

The undercoat film is formed, for example, by applying an undercoat paint containing a resin to the surface of a metal substrate or a chemical conversion treatment film and drying (or curing) it. The type of resin contained in the undercoat is not particularly limited. Examples of resins include polyesters, epoxy resins, acrylic resins, and the like. Epoxy resins are particularly preferred because of their high polarity and good adhesion to metal substrates. The thickness of the undercoat film is appropriately selected according to the application and type of the final printed material (coated metal material), and is, for example, about 5 μm.

- To-be-printed layer The to-be-printed layer is a layer containing a cured product of the above-described metal coating material, and is formed by applying the above-described metal coating material onto the above-described metal base material and curing the coating material. Although the layer composed of the cured product of the metal paint may be used as the printed layer as it is, it is more preferable to use a layer obtained by further subjecting the layer to flame treatment or corona discharge treatment as the printed layer. By performing the flame treatment or the corona discharge treatment, the adhesion of the ink layer, which will be described later, is remarkably improved, and even if a thick ink layer is formed, it becomes difficult to peel off. Among these, a layer to be printed that has undergone frame treatment is particularly preferable from the viewpoint of adhesion of the ink layer and the like.

The method of applying the above-described metal paint onto a metal substrate is not particularly limited, and is appropriately selected according to the shape of the metal substrate, the pattern of the printed layer to be formed, the area of the printed layer to be formed, and the like. be. Examples of coating methods include inkjet printing, gravure printing, offset printing, screen printing, roll coating, bar coating, spin coating, air spraying, airless spraying, immersion and lifting, and the like. included. Two or more of these methods may be combined when applying the metal coating.

After applying the metal paint onto the metal substrate, the metal paint is cured by heating (hereinafter also referred to as "baking"). The baking method is not particularly limited, but it is preferable to heat the metal substrate so that the plate temperature reached is within the range of 150 to 250°C.

When the layer to be printed is to be subjected to flame treatment after baking the metal paint, the metal substrate on which the layer to be printed is formed is placed on a carrier such as a belt conveyor. Then, while moving in a fixed direction, a flame treatment burner is used to radiate a flame onto the layer to be printed.

Here, the frame processing amount is preferably 100 to 600 kJ/m ² . As used herein, the term "flame throughput" refers to the amount of heat per unit area of the metal base calculated on the basis of the amount of combustion gas such as LP gas supplied. The amount of flame treatment can be adjusted by adjusting the distance between the burner head of the flame treatment burner and the surface of the layer to be printed, the transport speed of the layer to be printed, and the like. When the flame treatment amount is 100 kJ/m ² or more, the entire surface of the layer to be printed is likely to be uniformly treated. On the other hand, when the flame treatment amount is 600 kJ/m ² or less, the printed layer is less likely to turn yellow.

In addition, preheating may be performed by heating the surface of the layer to be printed to 40° C. or higher before the flame treatment. When the print layer formed on the surface of a metal substrate having a high thermal conductivity (for example, a metal substrate having a thermal conductivity of 10 W/mK or more) is irradiated with a flame, water vapor generated by combustion of the combustible gas is cooled. becomes water and temporarily accumulates on the surface of the printed layer. Then, the water absorbs the energy during the flame treatment and becomes water vapor, which may hinder the flame treatment. In contrast, by preheating the surface of the layer to be printed, the generation of water during flame irradiation can be suppressed.

The means for preheating the layer to be printed is not particularly limited, and is appropriately selected according to the shape of the metal substrate. For example, a heating device commonly called a drying oven can be used. For example, a batch-type drying furnace (also referred to as a "safe furnace") can be used. automatic discharge dryer (model ATO-101) manufactured by Tojo Thermal Engineering Co., Ltd., and simple explosion-proof dryer (model TNAT-1000) manufactured by Tojo Thermal Engineering.

On the other hand, when performing the corona discharge treatment on the printed layer, the metal substrate on which the printed layer is formed is placed between an insulated electrode and a grounded counter electrode dielectric roll. A high frequency and high voltage of 1 to 600 KHz and 5 to 30 KV are applied between them to generate corona discharge. As a corona discharge treatment apparatus, there are a spark gap system, a vacuum tube system, a solid state system, etc., and any of them can be used. The corona discharge treatment conditions are preferably 200 w/m ² /min or more, more preferably 200 to 800 w/m ² /min. If it is less than 200 w/m ² /min, the corona discharge treatment amount may be insufficient, and if it exceeds 800 w/m ² /min, the treatment will be excessive, which is not economically preferable.

Here, the thickness of the layer to be printed is not particularly limited, but is preferably 10 to 40 μm, more preferably 12 to 25 μm. When the thickness of the layer to be printed is 10 μm or more, the durability of the layer to be printed tends to be good. In addition, the layer to be printed tends to become flexible, and the adhesiveness of the ink layer, which will be described later, tends to increase. On the other hand, when the thickness is 40 μm or less, popping is less likely to occur during the heating, and the surface condition tends to be good. Furthermore, when the surface condition of the layer to be printed is good, the active energy ray-curable composition to be described later tends to spread evenly, and the adhesion between the resulting ink layer and the layer to be printed tends to increase.

Here, the ratio of the amount of O atoms to the amount of C atoms when the surface of the layer to be printed is analyzed by X-ray electron spectroscopy (hereinafter also referred to as XPS method) is preferably 0.6 or more. The ratio of the amount of O atoms to the amount of C atoms is more preferably 0.8 or more. The ratio of the amount of O atoms to the amount of C atoms measured by the XPS method can be adjusted by the flame treatment or corona discharge treatment described above. When the flame treatment or corona discharge treatment described above is performed, the organic groups on the surface of the layer to be printed are partially decomposed and OH groups are introduced. As a result, the amount of O atoms increases compared to the case where no flame treatment or corona discharge treatment is performed. That is, the ratio of the amount of O atoms to the amount of C atoms is increased. Then, the OH group is likely to form a hydrogen bond with the hydrophilic group in the ink layer formed on the layer to be printed, and the adhesion between the layer to be printed and the ink layer is likely to be high.

Analysis of the composition (the amount of C atoms and O atoms) of the surface of the layer to be printed by the XPS method can be the same as analysis by a general XPS method using AlKα as the X-ray source. For example, the measurement can be performed using the following measurement equipment and measurement conditions.
(Measuring device and measurement conditions)
Measuring device: AXIS-NOVA scanning X-ray photoelectron spectrometer manufactured by KRATOS X-ray source: AlKα 1486.6 eV
Analysis area 700×300 μm
Analysis room vacuum: 1.0 × 10 ^-7 Pa

As described above, both flame treatment and corona discharge treatment can increase the ratio of the amount of O atoms to the amount of C atoms. However, treating the surface of the layer to be printed with flame treatment can more uniformly hydrophilize the surface (increase the amount of O atoms uniformly) than treating the surface of the layer to be printed with corona treatment. can increase the adhesion of.

Whether or not the surface of the layer to be printed is uniformly hydrophilized can be evaluated by the following methylene iodide sliding angle. For example, when the methylene iodide sliding angle of the layer to be printed is 15° or more and 45° or less, it can be said that the surface is uniformly hydrophilized. Note that the falling angle of methylene iodide is more preferably 35° or less.

The methylene iodide sliding angle tends to fall within the above range when the surface of the layer to be printed is sufficiently hydrophilic or when the surface of the layer to be printed is rough. However, if the hydrophilicity of the printed layer is non-uniform, the methylene iodide sliding angle will be higher than 45°. For example, when the surface is treated by corona treatment, the methylene iodide sliding angle tends to exceed 45°. On the other hand, when flame treatment is performed, the surface is uniformly hydrophilized, and the methylene iodide sliding angle is 45° or less.

The reason why the falling angle of methylene iodide becomes larger than 45° when the hydrophilicity of the surface of the layer to be printed becomes non-uniform due to corona discharge treatment or the like is considered as follows. It is assumed that there are two types of coating films each having the same number of hydrophilic groups and hydrophobic groups on the surface, one has no bias in the distribution of the hydrophilic groups and hydrophobic groups, and the other has a bias in the distribution of the hydrophilic groups and the hydrophobic groups. Assume. At this time, the static contact angles of both are hardly influenced by the distribution of the hydrophilic group and the hydrophobic group, and are substantially the same. On the other hand, the dynamic contact angles (methylene iodide sliding angles) of the two are influenced by the distribution of hydrophilic groups and hydrophobic groups and have different values. When the methylene iodide slid angle is measured, if the distribution of the hydrophilic groups and the hydrophobic groups is non-uniform, the methylene iodide droplets will be adsorbed to the portion with high density of the hydrophilic groups. In other words, if the distribution of the hydrophilic groups and the hydrophobic groups is biased, the methylene iodide droplets are more difficult to move than when there is no uneven distribution, resulting in a large falling angle. Therefore, when a large number of hydrophilic groups are introduced to the surface of the printing layer as in corona discharge treatment, but the distribution thereof is uneven, the methylene iodide sliding angle exceeds 45°.

The methylene iodide slid angle is a value measured as follows. First, 2 μl of methylene iodide is dropped onto the layer to be printed. After that, using a contact angle measuring device, the inclination angle of the printed layer (the angle between the plane perpendicular to gravity and the printed layer) is increased at a speed of 2 degrees/second. At this time, the droplet of methylene iodide is observed with a camera attached to the contact angle measuring device. Then, the inclination angle at the moment when the droplet of methylene iodide falls is specified, and the average value of five times is taken as the methylene iodide sliding angle of the layer to be printed. The moment when the methylene iodide droplet falls is the moment when both the end point of the methylene iodide (droplet) in the downward direction of gravity and the end point in the upward direction of gravity start to move.

(Painted metal material)
A coated metal material can be manufactured by forming an ink layer on a metal base material to be printed by the method for manufacturing a printed matter described above. The coated metal material may have the above-described metal base material to be printed and an ink layer disposed on the layer to be printed of the metal base material to be printed. It may be arranged in the entire area where the printing layer is formed, or may be arranged only in a part of the area where the layer to be printed is formed.

Furthermore, the thickness of the ink layer is preferably about 5 to 150 μm, more preferably about 10 to 100 μm. As described above, in general, the thicker the ink layer, the greater the curing shrinkage during curing, and the easier it is for the resulting ink layer to peel off. However, the metal substrate for printing (especially when it has a printing layer subjected to frame treatment) has high adhesion between the printing layer and the ink layer, and an ink layer having a thickness of, for example, 40 μm or more is formed. peeling is unlikely to occur even if

The ink layer may be formed so that the thickness of the cured ink layer changes continuously or intermittently. When printing layers with different thicknesses are formed on a general printing layer, the adhesion changes between the areas where the ink layer is thick and the areas where the ink layer is thin. Sometimes. On the other hand, in the metal base material for printing (especially when it has a layer to be printed that has undergone frame treatment), the ink layer and high adhesion to the printed layer. Therefore, even if an ink layer with a varying thickness is formed, peeling is unlikely to occur.

The ink for forming the ink layer to be applied on the layer to be printed may be any ink that can be applied by a printing apparatus, and may be a radical curing ink or a cationic curing ink. These can be known compositions conventionally used for printing on metal plates.

(Uses of painted metal materials)
The application of the above-mentioned coated metal material is not particularly limited, and it can be used for a wide variety of members and applications that use a metal base material. Examples of applications include interior decorative building materials such as partitions, doors, ceiling materials, floor materials, elevator doors, and interior panels for elevators; various residential equipment such as range hoods and bathroom interior materials; desks, chairs, lockers, and shelves. furniture such as refrigerator outer panels, microwave oven outer panels, personal computer housings, air conditioner housings and other household appliances; vehicle parts such as passenger car interiors and railway vehicle interiors. However, the application of the coated metal material is not limited to these.

Hereinafter, the present invention will be described in detail with reference to examples, but the present invention is not limited by these examples.

1. Preparation of recording media (metal base material for printing) (Preparation of metal base material)
A hot-dip Zn-55% Al alloy plated steel sheet of A4 size with a plate thickness of 0.27 mm and a coating amount per side of 90 g/m ² was used. After alkaline degreasing, the metal plate was treated with coating type chromate (manufactured by Nippon Paint Co., Ltd.: NRC300NS, coating amount of 50 mg/m ² as Cr). Furthermore, as a primer layer, a commercially available epoxy resin-based primer paint (manufactured by Nippon Paint Industrial Coatings: 715P) was applied with a roll coater so that the dry film thickness was 5 μm. After that, it was baked so that the maximum plate temperature reached 215°C.

(Formation of printed layer)
Thereafter, the polyhydric carboxylic acids and polyhydric alcohols shown in Table 1 were each polymerized by a conventional method to prepare polyester resins P1 to P4. Table 1 shows the number average molecular weight and hydroxyl value of each polyester resin, and the amount (% by mol) of structural units derived from a trihydric or higher alcohol with respect to the total amount of carboxylic acid structural units and alcohol structural units in the polyester resin.

After preparing the polyester resin, the polyester resin and the melamine resin were mixed. As the melamine resin, a methylated melamine resin (Nihon Cytec Industries Co., Ltd.: Cymel 303) and/or a butylated melamine resin (Nihon Cytec Industries Co., Ltd.: Cymel 325) was used. Table 2 shows the combination and mixing ratio of the polyester resin and the melamine resin.

A paint for metal was prepared by further adding the following ingredients to the mixture of the above polyester resin and melamine resin. The amount of each component is a value relative to the total solid content of the paint for metal. The remainder of the solids is a mixture of the polyester resin and the melamine resin.

Titanium oxide with an average particle size of 0.28 μm (Taika: JR-603) 40% by mass, mica with an average particle size of 10 μm (Yamaguchi Mica: SJ-010) 9% by weight, hydrophobic with an average particle size of 5.5 μm 6 mass % of hydrophobic silica (manufactured by Fuji Silysia Chemical Co., Ltd.: Cysilia 456) and 2 mass % of hydrophobic silica (manufactured by Fuji Silysia Chemical Ltd.: Cysilia 476) having an average particle diameter of 12 μm were used. Furthermore, dodecylbenzenesulfonic acid was used as a catalyst in an amount of 1% by mass based on the solid content of the above resin. As the amine, dimethylaminoethanol was used in an amount of 1.25 times as the amine equivalent with respect to the acid equivalent of dodecylbenzenesulfonic acid.

Then, one side of the metal substrate having the primer layer was coated with the metal paint by a roll coater so that the dry film thickness of the metal paint was 18 μm. After that, it was baked for 60 seconds so that the maximum board temperature reached 225° C. to form a layer to be printed on the metal substrate.

(frame processing)
The above-mentioned layer to be printed was subjected to flame treatment under the following conditions, if necessary. The metal substrate having the printed layer formed thereon was placed on a carrier, and the printed layer was subjected to flame treatment. F-3000 manufactured by Flynn Burner (USA) was used as a flame treatment burner. As the combustible gas, a mixed gas (LP gas:clean dry air (volume ratio)=1:25) obtained by mixing LP gas (combustion gas) and clean dry air with a gas mixer was used. The flow rate of each gas was adjusted to 1.67 L/min for LP gas (combustion gas) and 41.7 L/min for clean dry air per 1 cm ² of the flame port of the burner. The length of the flame port of the burner head in the conveying direction of the layer to be printed was set to 4 mm. On the other hand, the length of the flame port of the burner head in the direction perpendicular to the conveying direction was 450 mm. Furthermore, the distance between the flame port of the burner head and the surface of the layer to be printed was set to 50 mm according to the desired flame throughput. Furthermore, the frame throughput was adjusted to 212 kJ/m ² by setting the transport speed of the layer to be printed to 30 m/min.

2. Preparation of ink (active energy ray-curable composition) As an inkjet ink (active energy ray-curable composition), the following radical polymerizable inorganic ink of DNT Digital Coating System manufactured by Dai Nippon Toryo Co., Ltd. was used.
Cyan ink: NS-inorganic cyan 002
Magenta ink: NS-inorganic magenta 002
Yellow ink: NS-Inorganic Yellow 002
Black ink: NS-Black 002

3. Scanning process (Example 1)
A head for black, an LED light source for black, a head for cyan, an LED light source for cyan, a head for magenta, an LED light source for magenta, a head for yellow, and an LED light source for yellow were arranged in this order on the carriage of the inkjet printing apparatus. Each head used Kyocera KJ4A-TA (2656 nozzles, effective recording width 108.25 mm). For each LED light source, a UV-LED light source (peak wavelength: 395 nm, FE410, maximum UV output: 7.0 W/cm ² ) manufactured by Foseon Technology Japan was used. The distance between the nozzle of each head and the corresponding LED light source was 40 mm. Also, the output of the LED light source was set to 70% of the maximum output. Furthermore, the ink droplet volume from each nozzle of each head was set to 14 pl. Also, the ejection frequency was set so as to form an image of 600 dpi at a speed of about 45 m/min.

Then, while scanning the carriage in the main scanning direction at about 45 m/min, the ink was applied to the metal base material to be printed and the light was irradiated for each color. The print pattern at this time was appropriately selected according to the evaluation method described later. In Example 1, since the scanning process is performed twice (two passes) for the same area, ink was applied to the desired pattern every other dot in the first scanning process. Then, the relative positions of the carriage and the recording medium were shifted by 1/2 of the head width (the total head width when a plurality of heads are connected in the sub-scanning direction). Then, a second scanning step was performed in the same manner as above to obtain a desired ink layer. Also in the second scanning process, ink was applied to every other dot (where dots were not formed in the first scanning process).

After that, the ink layer was further irradiated with light (post-curing step) while moving the obtained print at a speed of 3 m/min. Light irradiation was performed in an atmosphere with an oxygen concentration of 5% by volume or less. Irradiation of light was performed using a UV-LED light source unit (Foseon Technology Japan, FL400, maximum UV output: 24 W/cm ² ) with a peak wavelength of 395 nm. The output at this time was 70% (16.8 W/cm ² ) of the maximum output. After that, heat treatment was performed by putting it in a heating furnace (manufactured by Takeda Rika Kogyo Co., Ltd.) at 230° C. for 1 minute to relax the shrinkage strain of the ink layer.

(Examples 2-8)
A coated metal plate was obtained in the same manner as in Example 1, except that the type of the metal substrate to be printed was changed as shown in Table 3.

(Examples 9-16)
Coated metal sheets were obtained in the same manner as in Examples 1 to 8, except that the same region was scanned four times each. In the second and subsequent scanning processes, the relative position between the carriage and the recording medium is shifted by 1/4 of the head width (the total head width when multiple heads are connected in the sub-scanning direction) from the initial position. went. Furthermore, in each scanning process, ink was applied to the desired pattern every three dots.

(Comparative Examples 1 to 8)
Coated metal sheets were obtained in the same manner as in Examples 1 to 8, except that the ink layer was formed in one scanning step.

(Comparative Examples 9-16)
A painted metal plate was prepared in the same manner as in Examples 9 to 16, except that a head for black, a head for cyan, a head for magenta, a head for yellow, and a common LED light source were arranged on the carriage, and the inks of each color were cured together. got

4. Evaluation Evaluation of ink adhesion to a recording medium (metal to be printed), evaluation of dot diameter, and evaluation of image quality were performed by the following methods.

<Evaluation of Dot Diameter (Wetting and Spreading of Ink)>
Dot printing was performed with black ink. At this time, the distance between adjacent dots was set to 500 μm so that the dots would not overlap each other. The dot diameter was measured using a scanning confocal laser microscope LEXT OLS3000 manufactured by Olympus. The dot diameters of 8 dots were measured by magnifying them so that only one dot was visible (200 times), and the average value is shown. When the spread of the dots was close to an ellipse, the average value of the major and minor diameters was taken as the dot diameter and evaluated as follows. △ or more was set as the pass.
◎: Dot diameter is 115 μm or more and less than 160 μm ○: Dot diameter is 95 μm or more and less than 115 μm △: Dot diameter is 75 μm or more and less than 95 μm ×: Dot diameter is less than 75 μm

<Evaluation of Ink Adhesion>
A color patch of 3.5 cm×10 cm and 300% density was prepared by the above printing method. It should be noted that the density refers to the ink adhesion area with respect to the area of the color patch. 300% means that the cyan, magenta, yellow, and black inks are evenly layered so that the total area of the cyan, magenta, yellow, and black inks is three times the area of the color patch. state.

A cross-cut test was performed on the color patch according to JIS K5600-5-6. Specifically, the surface of the ink layer was cut into base meshes so that 25 squares were formed at intervals of 2 mm, and a tape was attached to the cuts. After peeling off the tape, the residual rate of the coating film was observed. Evaluation was performed according to the following criteria. An evaluation of △ or more was regarded as a pass.
○: The peeling area of the ink layer is 0%
△: Peeling area is more than 0% and within 20% ×: Peeling area is more than 20%

<Color unevenness (bleed) evaluation>
By the above printing method, color patches were prepared in which the density was changed from 0% to 300% in increments of 30%. Then, it was observed from a distance of 50 cm to visually check whether there was color unevenness (bleed) inside the patch in the highlight portion (density 30%), medium density portion (density 90%), and high density portion (density 180%). It was observed and evaluated according to the following criteria. Ten persons were evaluated, and the evaluation value was the average of the ten persons. An evaluation point of △ or higher is acceptable.
○: No bleeding △: Slight bleeding ×: Much bleeding

<Evaluation of muscle unevenness>
A color patch was prepared in the same manner as in the color unevenness (bleed) evaluation. Then, the color patch is observed from a distance of 50 cm, and periodic streak-like unevenness (streak unevenness) is observed in the highlight portion (density 30%), medium density portion (density 90%), and high density portion (density 180%). ) was evaluated in the following five stages. Ten persons were evaluated, and the evaluation value was obtained by rounding off the average evaluation score of the ten persons. A rating of 3 or higher is acceptable.
5: No streak unevenness is observed.
4: Streak unevenness is slightly observed, but is unnoticeable.
3: Streak unevenness is observed, but acceptable.
2: I am concerned about muscle unevenness.
1: Streak unevenness is very worrisome.

5. Results The evaluation results are shown below.

As shown in Table 3 above, the ink was applied and cured for each ink type (color), and the same region was scanned a plurality of times while the carriage position was shifted (Example 1). 16), streaky unevenness and color unevenness were less likely to occur than in the case where all the inks were cured together (Comparative Examples 9 to 16).

Even if the ink was applied and cured for each type (color) of ink, when the ink layer was formed by performing the scanning process only once, streaky unevenness was likely to occur (Comparative Examples 1 to 8). It is thought that the state of the nozzles of the inkjet head was greatly affected.

According to the method for producing a printed matter of the present invention, it is possible to form a high-definition image on various recording media without color unevenness or stripe unevenness. Therefore, it is possible to manufacture various products with high designability.

100, 900 inkjet printer 110, 910 carriage 111, 111K, 111M, 111C, 111Y, 911, 911K, 911M, 911C, 911Y inkjet head 112, 112K, 112M, 112C, 112Y LED light source 113 holder 120 rail 912, 912K, 912M, 912C, 912Y light source

Claims (9)

By a serial inkjet printing device having a carriage in which a plurality of inkjet heads each including a plurality of nozzles arranged along the sub-scanning direction and a plurality of LED light sources are alternately arranged along the main scanning direction , A method for producing a printed matter, which has a printing step of applying multiple types of active energy ray-curable inks to a metal recording medium and photocuring to form an ink layer,
In the printing step, the ink is applied by the inkjet head while the carriage is scanned in the main scanning direction, and the LED light source adjacent to the inkjet head on the rear side in the traveling direction is coated by the inkjet head. including a scanning step of irradiating the ink with light;
performing the scanning step twice or more on the same area of the metal recording medium while shifting the carriage in the sub-scanning direction;
A method for producing printed matter. while shifting the carriage in the sub-scanning direction, performing the scanning step eight times or less on the same area of the metal recording medium;
The method for producing a printed matter according to claim 1. further comprising a step of irradiating the ink layer formed by the printing step with light;
3. The method for producing a printed matter according to claim 1 or 2. The metal recording medium is a metal base material for printing, which has a metal base material and a print layer for printing the ink disposed on the metal base material,
The printed layer is
A polyester resin containing an alcohol structural unit derived from a polyhydric alcohol and a carboxylic acid structural unit derived from a polycarboxylic acid and having a number average molecular weight of 4000 to 12000, and a melamine resin, and the alcohol structural unit and the carboxylic acid A cured product of a metal paint, wherein the ratio of the amount of structural units derived from a trihydric or higher alcohol to the total amount of acid structural units is 20 mol% or less.
A method for producing a printed matter according to any one of claims 1 to 3. The polyester resin contains a structural unit derived from trimethylolpropane,
The method for producing a printed matter according to claim 4. The ratio of the amount of O atoms to the amount of C atoms is 0.6 or more when the surface of the printed layer is analyzed by X-ray electron spectroscopy using AlKα rays as an X-ray source.
6. The method for producing a printed matter according to claim 4 or 5. The surface of the layer to be printed has a methylene iodide sliding angle of 15° or more and 45° or less.
A method for producing a printed matter according to any one of claims 4 to 6. Before performing the printing process,
A polyester resin containing an alcohol structural unit derived from a polyhydric alcohol and a carboxylic acid structural unit derived from a polycarboxylic acid and having a number average molecular weight of 4000 to 12000 and a melamine resin on a metal substrate, and forming a layer to be printed by applying a paint for metal in which the ratio of the amount of structural units derived from a trihydric or higher alcohol to the total amount of the alcohol structural units and the carboxylic acid structural units is 20 mol% or less;
flame treatment or corona discharge treatment of the layer to be printed;
having
A method for producing a printed matter according to any one of claims 1 to 3. The ink layer has a thickness of 40 μm or more.
A method for producing a printed matter according to any one of claims 1 to 8.

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