Print dot drying device, print dot drying method, and printing system

Abstract

To provide a device, a method, and a system that can evaporate a print dot immediately while suppressing deterioration such as deformation of a product due to heat.SOLUTION: A print dot drying device 100 including a drying device for drying a print dot formed on an article includes: a blower device 50 for blowing air to the print dot; a temperature sensor 12 for detecting temperature of an article (product); and a control device 70 for controlling temperature of the air blown by the blower device. The control device 70 controls air temperature of the blower device so as to be equal to or lower than a storage temperature at which the article is stored.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a print dot drying device, a print dot drying method, and a printing system. [Background technology]

[0002] Ink dot printers, which print by ejecting ink dots (ink particles) onto the surface of a target object (item), are widely used in industrial applications, such as printing product names and manufacturing dates on products on production lines. Charge-controlled inkjet printers (continuous inkjet printers) or dot-on-demand (DOD) inkjet printers are commonly used for such industrial inkjet printers. The ink used for printing in such inkjet printers is liquid and generally contains a solvent.

[0003] The solvents used in inks for charge-controlled inkjet printers are often ketone solvents such as 2-butanone, acetone, and 3-methyl-2-butanone, or alcohol solvents such as ethanol, methanol, and 2-propanol. These evaporate more easily than water, but when the solvent evaporates from the surface of the printed dot, a film made of the solid components of the ink forms on the surface of the printed dot, which prevents the solvent from evaporating further, so it takes a considerable amount of time for the solvent to evaporate completely. On the other hand, the solvents used in inks for DOD inkjet printers are often water or cellosolve-based high-boiling point solvents.

[0004] Dots forming characters or the like printed on an article solidify and become stable (fixed) after printing as the solvent contained in the printed dots evaporates. Herein, "printed dots" refer to dot-shaped ink particles printed on an article that form information (characters, symbols, etc.). Immediately after printing, the ink is liquid, and over time, the solvent contained in the ink evaporates (volatilizes) and the dots become fixed. Because this solvent evaporation takes a certain amount of time, careful handling is required, such as not touching the printed area until a certain amount of time has passed. For example, if a certain amount of time has not passed since printing, the quality of the information printed on the article will deteriorate.

[0005] In particular, when the printed item is made of a substrate such as a resin film, resin plate, metal, or glass, complete evaporation takes a considerable amount of time. For example, the substrate of items such as packaging bags and containers for chilled and frozen foods is primarily a resin film. The top surface of the substrate is made of polypropylene (PP) or polyethylene (PE), and underneath is primarily polyethylene terephthalate (PET), on which the product name, photo, etc. are printed. The bottom layer is typically made of PP or PE. In recent years, many products have a thin aluminum film formed by vapor deposition between the PET layer and the bottom PP or PE layer to prevent deterioration due to light such as sunlight, indoor light, and lighting inside storage facilities.

[0006] When ink particles land on the surface of these substrates to form print dots, the solvent evaporates (volatilizes) from the surface of the print dots and gradually solidifies. After a certain amount of time, the solvent on the surface of the print dots and their surrounding areas evaporates, leaving the surface dry and preventing the ink from sticking to hands when touched. However, liquid ink remains inside the print dots, and the contained solvent slowly evaporates from the surface over a long period of time. Therefore, if a heavy object is placed on top of the print dots, the print dots may be crushed, causing the wet, highly viscous ink inside the print dots to spill out and adhere to the heavy object. Furthermore, if the print dots are rubbed against other substrates or human hands or fingers, not only will the insufficiently dried portions of the surface peel off, reducing print quality, but the wet, highly viscous ink inside the print dots may also adhere to the rubbed substrate, hands, or fingers.

[0007] Since faster evaporation of the solvent improves the operating rate of the production line, it is preferable to evaporate the solvent contained in the printed dots as quickly as possible. For this reason, inkjet printers equipped with drying devices have been proposed to accelerate the drying of the ink (evaporation of the solvent) in the printed dots.

[0008] For example, Japanese Patent Application Laid-Open Publication No. 2020-114658 (Patent Document 1) discloses an inkjet printer equipped with a drying unit (printed dot drying device) for drying printed dots. The drying unit introduces methods such as using a heater to heat and dry an object, air drying using hot air, or a combination of these. It also discloses a method of applying ultrasonic vibrations to an object while heating and drying it with a heater. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Japanese Patent Publication No. 2020-114658 Summary of the Invention [Problem to be solved by the invention]

[0010] By using a drying device such as that described in the above-mentioned Patent Document 1, the drying of the printed dots can be accelerated, thereby shortening the drying time.

[0011] However, if the object to be printed (printed material) is a product such as chilled food, excessive heating with a heater or high-temperature hot air to accelerate (promote) the drying process may cause the quality of the product (stored food) to be altered by the heat, or may cause deterioration such as spoilage during subsequent storage. In other words, simply heating the product to promote drying can be problematic for products such as food.

[0012] Therefore, the present invention aims to provide a print dot drying device, a print dot drying method, and a printing system that can quickly evaporate the solvent in the print dots while suppressing deterioration such as thermal denaturation of the printed product. [Means for solving the problem]

[0013] In order to solve the above problems, the present invention provides, as an example, a print dot drying device having a drying device that dries print dots formed on an object, the drying device comprising a blower that blows air onto the object, a temperature sensor that detects the temperature of the object or its vicinity, and a control device that inputs the temperature detected by the temperature sensor and controls the blower so that the temperature of the air is below the storage temperature of the object.

[0014] Another example of the present invention is a method for drying printed dots that are printed on an article using ink containing a solvent by an inkjet printer, the method comprising detecting the temperature at or near the printed dots and using the detected temperature to blow air onto the printed dots that has been adjusted to a temperature equal to or lower than the storage temperature of the article.

[0015] Furthermore, another example of the present invention is a printing system including a printer that prints by spraying dots of ink onto an object being transported, and a drying device that dries the printed dots on the object, wherein the drying device is equipped with a blower that blows air onto the object, a temperature sensor that detects the temperature at or near the object, and a control device that inputs the temperature detected by the temperature sensor and controls the blower so that the temperature of the air is below the storage temperature of the object. [Effects of the Invention]

[0016] According to the present invention, it is possible to provide a print dot drying device, a print dot drying method, and a printing system that are capable of evaporating the solvent in the print dots while minimizing the heating of the printed product. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 10 is a diagram showing the proportion of residual solvent in a printed dot. [Figure 2] 1 is a diagram illustrating a system configuration of a printer according to a first embodiment of the present invention. [Figure 3] 1 is a diagram showing the structure of a Peltier element and fins according to a first embodiment. FIG. [Figure 4] 10A and 10B are diagrams for explaining the process of solvent evaporation of print dots. [Figure 5] FIG. 1 is a diagram showing the absorption spectrum of 2-butanone in the infrared region. [Figure 6] FIG. 1 is a diagram showing the absorption spectrum of ethanol in the infrared region. [Figure 7] FIG. 1 is a diagram showing the absorption spectrum of propylene glycol monomethyl ether acetate in the infrared region. [Figure 8] FIG. 1 is a diagram showing a mechanism for irradiating light onto print dots using a semiconductor laser. [Figure 9] FIG. 2 is a diagram showing print dots and semiconductor lasers emitting light corresponding to the print dots. [Figure 10]FIG. 10 is a diagram showing the light irradiation range when light is irradiated onto print using an LED or a lamp. [Figure 11] FIG. 10 is a diagram illustrating a system configuration of a printer according to a second embodiment of the present invention. [Figure 12] FIG. 10 is a diagram showing a system configuration of a printer according to a third embodiment of the present invention. [Figure 13] FIG. 1 is a diagram showing the cross-sectional structure of a food bag having an aluminum vapor deposition layer. [Figure 14] FIG. 10 is a diagram showing a system configuration of a printer according to a fourth embodiment of the present invention. [Figure 15] FIG. 10 is a diagram showing a print dot drying device using reduced pressure. [Figure 16] FIG. 10 is a diagram showing a system configuration of a printer according to a fifth embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0018] Hereinafter, embodiments of the present invention (hereinafter referred to as "embodiments") will be described in detail with reference to the accompanying drawings.

[0019] First, before describing specific examples, a description will be given of points to be noted when promoting evaporation (volatilization) of a solvent contained in print dots that form printed information.

[0020] To prevent denaturation due to heat, chilled and frozen foods are printed with expiration dates after production and then quickly placed in an environment with the desired storage temperature. It is preferable to place the product in the storage environment within a few to 10 seconds after printing.

[0021] Figure 1 shows how the solvent contained in the printed dots evaporates over time. In Figure 1, a shows the case of ink whose solvent is 2-butanone. In Figure 1, b shows the case of ink whose solvent is ethanol.

[0022] As shown in Figure 1, although the amount of solvent in the printed dots varies depending on the solvent, when the solvent is 2-butanone at 20°C, approximately 40% of the solvent remains even 10 seconds after printing. When placed in a 5°C chilled food storage environment in this state, approximately 25% of the solvent remains even after one week. When placed in a frozen food storage environment, approximately 25% of the solvent remains even after one month. When stored at 20°C without being moved to a low-temperature environment, the solvent decreases to approximately 25% one minute after printing. After a further 10 minutes, it decreases to approximately 20%. When rubbed with a finger in this state, the printed dots extend in the direction of the rub, and some peel off from the object. After leaving it for one day, the solvent finally decreases to approximately 10%, and the printed dots are no longer destroyed by rubbing with a finger. When the solvent is ethanol, the solvent remaining rate is even higher, so it takes even longer for the physical strength of the printed dots to improve.

[0023] To obtain the data shown in Figure 1, we used a PX-R inkjet printer manufactured and sold by Hitachi Industrial Equipment Systems Co., Ltd. The ink used was also manufactured by the same company, with ink named JP-K72 used when the solvent was 2-butanone and ink named JP-K112 used when the solvent was ethanol.

[0024] As mentioned above, chilled and frozen foods are usually preferably placed in an environment with the desired storage temperature within a few seconds to a dozen seconds after printing. Therefore, leaving these foods at 20°C for a day to dry the printed dots printed on the product packaging is not practical, as it would cause the food to spoil or degenerate. If solvent remains in the printed dots, the physical strength of the printed dots will be insufficient, which is a problem for printing expiration dates and other information that must be as indestructible as possible.

[0025] Therefore, in the embodiments of the present invention described below, we will explain devices and methods that can promote the evaporation (volatilization) of solvent contained in the printing dots that form the printed information while suppressing deterioration of the printed object.

[0026] It should be noted that the present invention should not be construed as being limited to the description of the embodiments described below. Furthermore, in the configurations of the embodiments described below, the same devices and parts having similar operations and functions are designated by the same reference numerals. This may result in redundant explanations being omitted. Furthermore, the position, size, shape, range, etc. of each component shown in the drawings are simplified to facilitate understanding of the present invention, and do not represent the actual position, size, shape, range, etc. of each component.

[0027] [Example 1] First, the configuration of the first embodiment of the present invention will be described in detail with reference to Fig. 2 and Fig. 3. Fig. 2 is a diagram showing the system configuration of the printer in the first embodiment. Fig. 3 is a diagram showing the structure of the Peltier element and fins.

[0028] In Figure 2, a product 2, which is the object to be printed in this example, is placed on a conveying device 4, such as a conveyor belt, that moves in the X direction and is conveyed. As shown in the figure, an inkjet recording device 80 for printing predetermined information on the product 2 and a drying device 100 for drying the printed dots 1 on the product 2 downstream of the inkjet recording device 80 in the X direction are provided along the conveying device 4. Note that although the inkjet recording device 80 and the drying device 100 are shown as separate entities in Figure 2, they may also be integrated and housed in a single housing.

[0029] The inkjet recording device 80 comprises a main body 81 for supplying ink, a supply cable 82, and a print head 83 that performs inkjet printing using the ink supplied from the main body. An electrostatic inkjet printer or a DOD inkjet printer is used as the inkjet recording device 80. In this example, an electrostatic inkjet printer is used. The configuration and operation of the electrostatic inkjet recording device 80 are well known, so a detailed description will be omitted here.

[0030] The drying device 100 is equipped with a heating device 60 for heating the printed portion of the product 2 (printed dots and their vicinity), and air blowers 50 on both sides of the heating device in the conveyance direction (X direction) for blowing temperature-controlled air (cool air) onto the product 2. Furthermore, in this Example 1, the drying device 100 is equipped with two temperature sensors 12 for detecting the temperature of the product in a non-contact manner. However, the number of temperature sensors 12 may be one.

[0031] The drying device 100 also has a control device 70 that inputs the temperature detected by the temperature sensor 12 and controls the temperature of the air blown by the blower device 50 (air blown onto the items) using the temperature detected by the temperature sensor so that it is below the storage temperature of the items 2.

[0032] A typical computer can be used as the control device 70. Although the configuration of the control device 70 is not shown, it includes a ROM (read-only memory) that stores a control program for executing this embodiment, and a RAM (random access memory) that stores information and data necessary for control (such as the temperature detected by the temperature sensor and the temperature setting). The control device 70 also includes an arithmetic processing unit (such as an MPU: microprocessing unit) that calculates control signals for appropriately controlling the temperature and strength of the air blown by the air blower 50 in accordance with the control program stored in the ROM. The control device 70 also includes an input / output unit for inputting data and information used in arithmetic processing and outputting the control signals calculated by the arithmetic processing unit to the air blower 50, and a bus communication path for exchanging data and information between the devices that make up the control device 70.

[0033] The signal cable 14 is a communication cable for communicating various information (data, etc.) between an external device (not shown) (for example, an inkjet recording device 80 or a production management system) and the drying device 100 (control device 70). The light heating device, which will be described later, controls the light emission intensity and light emission time of the LED elements 9. To control the irradiation position, the control device 70 obtains printing information from the inkjet recording device 80 that formed the print dots, such as "what was printed," i.e., "where the dots landed," as well as information from the device driving the transport device 4, such as "at what speed the transport is being performed," and controls the light irradiation position based on this information.

[0034] In this embodiment, the drying device 100 includes an upstream air blower 50 and a downstream air blower 50 for blowing cool air onto the product 2 to dry it, and a heating device 60 for heating the printed area (printed dots and their surroundings) is located between these two air blowers 50 to promote drying of the printed dots. The air blower 50 blows temperature-controlled air over the entire product 2 to dry it, while the heating device 60 heats and dries the printed dots in the printed area by concentrating heat on them rather than the entire product 2. Therefore, the heating area of ​​the heating device 60 is limited, and the heated printed area of ​​the product 2 is cooled by the air from the air blower 50. This minimizes or eliminates any impact on the quality of the product 2 even if it is heated. As a result, drying by air blowing and drying by heating the printed area are effectively performed, minimizing damage to the product and achieving rapid drying of the ink.

[0035] Next, a specific configuration of the air blower 50 in this embodiment will be described. The air blower 50 in FIG. 1 includes a fan 8 for blowing air and a cooling mechanism that cools the blown air and delivers it to the products 2. The cooling mechanism in this example is composed of a Peltier element 7 and fins 6 that receive cooling energy from the Peltier element 7 and cool the air passing through. The fins 6 are made of aluminum, which has high thermal conductivity. The configuration of the Peltier element 7 and fins 6 is shown in FIG. 3. The upper diagram in FIG. 3 is a cross-sectional view seen from the side, and the lower diagram is a top view seen from above. As can be seen from FIG. 3, multiple fins 6 are connected to the Peltier element 7. As air passes between the fins 6 cooled by the Peltier element 7, the air is cooled and reaches the products 2 as cool air.

[0036] With this configuration, the air generated by the fan 8 is cooled as it passes through the gaps between the fins 6 cooled by the Peltier elements 7. The cooled air (cold air) exits the fins 6 and reaches the product 2, where it reaches the printed dots. This cool air (temperature-controlled air) dries the printed dots while suppressing a rise in the product temperature. In this embodiment, the air blowers 50 are installed on both sides of the heating device 60. Therefore, cooling occurs before and after heating by the heating device 60. Note that the air temperature before and after heating by the heating device may be controlled to different temperatures. Because the temperature of the product increases slightly due to heating of the printing section, it is also effective to control the air temperature of the downstream air blower 50 so that the air temperature after heating is lower than before heating. This air temperature control reliably prevents an abnormal rise in the temperature around the printed dots on the product 2.

[0037] When blowing cool air onto the products 2, it is advisable to direct the cool air perpendicular or nearly perpendicular to the products 2. If the air is blown at an angle, the wind may move the products 2 on the conveyor 4, and in some cases there is a risk of them falling off the conveyor 4. Furthermore, the Peltier elements 7 and fins 6 are positioned perpendicular or nearly perpendicular to the conveyor 4 so that the cool air blows onto the products 2 as perpendicularly as possible.

[0038] However, the fan 8 is positioned so that it blows air at a slightly different angle from perpendicular to the fins 6. This is because if it were positioned perpendicular, the air would not hit the surfaces of the fins 6 cooled by the Peltier elements 7, and would instead hit the products at room temperature at a higher rate. Therefore, by slightly changing the angle from perpendicular to the fins 6, the air blown by the fan 8 hits the cooled surfaces of the fins 6 and is sufficiently cooled. As a result, sufficiently cooled air hits the products, resulting in high efficiency. Note that while the air blower 50 in FIG. 1 is realized by a fan, Peltier elements, and fins, the configuration is not limited to this. Any air blower that can adjust the temperature of the air blown to the products will be acceptable.

[0039] Next, the temperature sensor 12 will be described. In this embodiment, the temperature sensor 12 measures the amount of infrared energy emitted from the printed dots and their vicinity, and measures the temperature of the product 2, particularly the printed dots and their vicinity. The infrared energy is obtained by a temperature measurement element (temperature sensor 12) with a measurement unit. Note that the temperature sensor 12 is not limited to a temperature sensor that uses infrared rays, and any sensor that can detect temperature without coming into contact with the printed portion (printed dots) of the product 2 will do.

[0040] In this embodiment, two temperature sensors 12 are provided, and are positioned to measure the temperature before and after heating the printed portion of the product. By outputting these detected temperatures to the control device 70 (the control device 70 inputs the detected temperatures), the control device 70 can optimally control the air blower 50 so that the printed dots and their vicinity are not overheated and so that the temperature of the product is kept below the storage temperature of the product.

[0041] Next, the specific configuration of the heating device 60 in this embodiment will be described. The heating device 60 in the embodiment of FIG. 1 will be described below as an "optical heating device" that uses light for heating. The light used for optical heating uses not only visible light but also wavelengths in the infrared region. As will be described later, in a preferred embodiment, heating is performed using infrared light. Therefore, in this specification, "light" includes not only light in the visible light region but also invisible light with longer wavelengths.

[0042] The heating device 60 (hereinafter referred to as the optical heating device) in this embodiment comprises an LED element 9 that generates light for optical heating, a light-collecting element 10 that collects and irradiates the generated light toward the print dots, and a power supply 11 that sends a current of an appropriate voltage to the LED element 9. Note that although an LED element is used as the light source here, a semiconductor laser can also be used as long as it can irradiate light of an appropriate wavelength with an appropriate output, or a mercury lamp or xenon lamp that is used in conjunction with a filter that transmits light of an appropriate wavelength can also be used.

[0043] The light heating device (heating device 60) controls the light emission intensity, light emission time, etc. of the LED elements 9. In order to control the irradiation position, the control device 70 receives print information from the inkjet recording device 80 that formed the print dots via a signal cable 14. It also receives conveyance speed information from the device that drives the conveyance device 4. This information makes it possible to control the light irradiation position. Note that, although the explanation here assumes that heating is performed by the heating device 60, in the case of products that are very sensitive to heat, it is also possible to dry them using only cool air controlled to below the storage temperature without heating by a heating device.

[0044] In this Example 1, the drying device 100 is installed adjacent to the inkjet recording device 80, and is positioned so that drying can be performed by the drying device 100 immediately after printing on the product 2. This is for the following reason: in order to volatilize the solvent after printing and before placing the product in the storage cabinet, it is easier for the solvent to evaporate if the product is irradiated with light as soon as possible after printing. This will be explained with reference to Figure 4.

[0045] Figure 4 is a schematic diagram showing the solvent evaporation process of a printed dot 1. Figure 4(a) shows the state immediately after printing. After printing, the solvent first evaporates from the portion of the printed dot that is in contact with the air, and (b) shows the state in which a film 17 begins to form on the surface. As the solvent evaporates, the thickness of this film 17 gradually increases, as shown in (c), until the printed dot 1 is finally dried. Since this film acts as a barrier that prevents the internal solvent from evaporating, it is desirable to evaporate the solvent before it becomes too thick. Irradiating the surface with light of a wavelength highly absorbed by solvent molecules can evaporate the internal solvent before the film forms. Furthermore, when this occurs, solvent molecules come into contact with part of the film and dissolve, thinning the film and facilitating the rapid evaporation of the solvent. In either case, it is desirable to irradiate the film while it is still thin, i.e., as soon as possible after printing. In the case of ink using 2-butanone as shown in FIG. 1a, it is desirable to irradiate within about 30 seconds after printing, while at least 30% of the solvent (2-butanone) remains.

[0046] Next, we will explain the wavelength of light used in the optical heating device. Each solvent used in ink has its own unique absorption characteristics, so by irradiating it with light of a wavelength that matches the absorption wavelength, it is possible to heat only the solvent and volatilize it quickly. In terms of light source, it is preferable to use LEDs that irradiate infrared light, which is cheaper than elements that emit ultraviolet or visible light, in order to reduce costs. In addition, infrared light has a lower absorption rate for components of air than ultraviolet or visible light, so it is also preferable in that it reaches the print dots with high efficiency. For this reason, infrared light is preferable as the irradiated light.

[0047] Next, we will explain the wavelength of the infrared light irradiated by the optical heating device. Figures 5, 6, and 7 show the absorption spectra in the infrared region of the main solvents used in ink. Figure 6 shows the absorption spectrum of 2-butanone in the infrared region. Ink contains organic compounds such as solvents, resins, and dyes, and most of these compounds have a wavenumber of approximately 3100 to 2700 cm. -1 (Kaiser) absorption due to the CH stretching vibration of hydrocarbons.

[0048] When the wave numbers shown here are expressed in terms of wavelength, the wavelength is 3200 to 3700 nm, as shown by A1 in Figure 5. Many products to be printed are also made up of organic matter, and therefore have absorption derived from CH stretching vibrations. When irradiated with light of this wavelength, i.e., light of 3200 to 3700 nm, many organic matter absorbs the light, converting the light energy into thermal energy and generating heat. In the present invention, it is desirable to minimize heat generation in products, so it is desirable not to irradiate with light in this range.

[0049] Furthermore, as shown in Figure 5A2, 2-butanone exhibits absorption due to the CO stretching vibration of the carbonyl group in the 1800-1600 Kaiser range, or 5500-6250 nm wavelength range. This absorption is characteristic of ketone-based solvents such as acetone and 3-methyl-2-butanone, in addition to 2-butanone. While organic materials such as resins also exhibit this absorption, the intensity of the absorption is generally weaker than the CH stretching vibration absorption described above. Therefore, in the case of an infrared heating device, irradiation with infrared light of this wavelength makes it possible to heat primarily ketone-based solvents in the printed dots. In other words, for inks containing 2-butanone, using light (infrared) in the 5500-6250 nm wavelength range is preferable, as it minimizes the impact on the product.

[0050] Next, Figure 6 shows the infrared absorption spectrum of ethanol. Ethanol exhibits absorption due to the OH stretching vibration of its hydroxyl group in the 3600-3200 Kaiser range, or 2780-3130 nm wavelength range (as shown in Figure 6, B1). This absorption is characteristic of alcohol-based solvents such as methanol and 2-propanol, in addition to ethanol. While organic materials such as resins also exhibit this absorption, the intensity of the absorption is generally weaker than the CH stretching vibration absorption described above. However, the end of the OH stretching absorption extends to around 3000 Kaiser, and this region overlaps with the CH stretching absorption. Therefore, by irradiating the ink with light in the 3600-3200 Kaiser range, or 2780-3130 nm wavelength range, which barely overlaps with the CH stretching absorption, it is possible to heat the alcohol-based solvent in the printed dots. In other words, for inks containing ethanol, irradiation with light (infrared) with a wavelength of 2780-3130 nm is preferred because it minimizes damage to the product. In addition, since light of this wavelength also absorbs the OH stretching vibration of water, it is also useful for inks that contain water as a solvent component.

[0051] Next, Figure 7 shows the infrared absorption spectrum of propylene glycol monomethyl ether acetate, a cellosolve-based organic solvent. Like ketone-based solvents, this solvent also exhibits absorption due to the CO stretching vibration of the carbonyl group in the 1800-1600 Kaiser range, or 5500-6250 nm wavelength range, as shown in Figure 7 C1. Therefore, like ketone-based solvents, irradiation with infrared light of this wavelength makes it possible to heat primarily the cellosolve-based solvent in the printed dots. In other words, using light (infrared light) with a wavelength of 5500-6250 nm is preferable because it has less impact on the product.

[0052] Next, we will explain the infrared light irradiation method. When printing expiration dates, serial numbers, etc., the size of the print dots formed on products is approximately 350 to 450 μm. When using a semiconductor laser as the light source, the minimum spot diameter is approximately twice the wavelength by passing the light through an optical lens adjusted to the appropriate shape and distance from the print dot.

[0053] When using ink with a 2-butanone solvent, the infrared light wavelength is 5500-6250 nm, resulting in a spot diameter of approximately 11-12.5 μm. When products are packaged in bags, handling can cause slight deformation during transport, resulting in a slight change in the distance between the semiconductor laser and the printed dots on the product. As a result, the spot diameter increases somewhat, but remains within a few tens of μm. This is a fraction to a few tens of μm smaller than the printed dot diameter. Therefore, by setting the laser spot diameter to be smaller than the printed dot size and aligning it so that it does not extend beyond the printed dot, it is possible to apply heat only to the printed dot, thereby minimizing thermal damage to the product. While the exposure time varies depending on the laser power, a short exposure time that does not extend beyond the printed dot allows for light to be applied only to the printed dot.

[0054] Figure 8 shows a light irradiation mechanism that uses a semiconductor laser as a light source. Figure 8 (A) is a side view of the light irradiation mechanism, and (B) is a view from below. In Figure 8, a laser diode 18, which consists of a light-emitting element and an optical lens and emits light with a small semiconductor spot diameter, is bonded to a power supply board 19. This light source corresponds to the printing of characters that are 7 x 5 dots in length and width, and 10 characters in total. To correspond to the number of dots to be printed, 7 laser diodes are bonded vertically and 5 laser diodes are bonded horizontally, and if this is considered one unit, a total of 10 units are bonded to the power supply board.

[0055] If the printed characters formed by the print dots 1 are "■1234■1234" as shown in (A) of Figure 9, the emitting laser diode 20 irradiates light onto the print dots representing "■1234■1234" as shown in (B) of Figure 9. The emitting laser diode 20 and the non-emitting laser diode 21 are controlled by the control device 70 in Figure 1. Also, when a semiconductor laser is installed in the drying device 100 of Figure 2, the LED element 9, the condensing element 10, and the power supply 11 are replaced by the laser diode 18 and the power supply board 19 if a semiconductor laser is used.

[0056] Here, we will explain the amount of light irradiation. When printing expiration dates, etc., an inkjet printer from Hitachi Industrial Equipment Systems Co., Ltd. is used, and the nozzle diameter is set to 65 μm and the number of ink droplets ejected is set to 68,900 droplets / second, the printed dot has a diameter of approximately 400 μm and an average thickness after drying of approximately 1 μm. The amount of solvent per ink droplet that forms one dot is approximately 4 × 10 -7 g. The solvent in most inks is 2-butanone, which has a boiling point of 80°C, a specific heat of 2.1 J / g·°C, and a latent heat of vaporization of 444 J / g. Assuming the ambient temperature during printing is 20°C, the amount of heat required to volatilize 2-butanone in one drop of ink is: 4×10 -7 ×{2.1×(80‐20)+444}≒5×10 -5 J This is about 5 × 10 -5 J of heat is required.

[0057] If the product transport speed is 1 m / s and the diameter of the print dot is 400 μm, the irradiation time is 4 × 10 -4 It will be seconds.

[0058] If the laser output is 1 mW, then 5 × 10 -5 Since irradiation for 1 second provides the energy required for the printing dot, if the printing dot and the laser irradiation position are aligned, it is possible to irradiate only the printing dot.

[0059] When using a light source with a wide light irradiation range, such as an LED element, mercury lamp, or xenon lamp, it is desirable to use an optical system, such as a range or mirror, to control the light so that it is irradiated only on the printed dots and their vicinity. Specifically, "proximity" refers to a level that allows simple control with an optical system, and corresponds to within 10 mm above, below, left, and right of the print size, and specifically, irradiation area 23, as shown in Figure 10, is desirable. Note that when drying printed dots printed on products that are very sensitive to heat, it is sufficient to dry them using only cold air without using light irradiation with a heating device.

[0060] According to the first embodiment of the present invention described above, it is possible to volatilize the solvent in the printed dots without heating the printed product as much as possible. That is, according to the first embodiment, the printed product is cooled by blowing controlled (adjusted) air below the product's storage temperature to air-dry the printed dots, and a heating device is used to heat and dry the printed dots. This makes it possible to quickly evaporate the solvent in the printed dots while suppressing deterioration of the product, such as denaturation due to heat. Furthermore, in this embodiment, air blowers are located upstream and downstream of the heating device in the conveying direction, thereby reliably preventing the product from overheating.

[0061] [Example 2] Next, a second embodiment of the present invention will be described with reference to Fig. 11. Fig. 11 is a diagram showing the system configuration of a printer in the second embodiment. First, this embodiment 2 has almost the same system configuration as the above-mentioned embodiment 1 (FIG. 2), and performs the same operations, so the description of the configuration and operations that have already been explained will be omitted, and the description will focus on the parts that are different from embodiment 1. Furthermore, in the description of embodiment 2, the description of the above-mentioned FIGS. 3 to 10 will also be omitted.

[0062] In Fig. 11, the drying device 100 includes a dehumidifying section 15 and an introduction path 16 that supplies dehumidified air to the fan 8 side. The other configurations are the same as those in Fig. 2. Example 2 shown in Fig. 11 has a configuration that adds a function of drying air to be supplied to the input side of the fan 8 of the air blower 50. The configuration with this additional function differs from that of Example 1 (Fig. 2).

[0063] For example, if the ink solvent is a hydrophilic solvent such as ethanol, moisture in the cold air may get mixed in, causing the moisture to seep into the printed dots and hinder their drying. Therefore, air dried by the dehumidifier 15 is introduced into the fan 8 via the inlet 16, making it possible to blow dry cold air onto the printed dots on the product. When the relative humidity of the cold air falls below approximately 50%, moisture tends to hardly get mixed into the printed dots, so the self-dehumidifying mechanism is activated to dehumidify the air to as low as possible.

[0064] According to the second embodiment of the present invention, the same effects as those of the first embodiment can be obtained, and drier air can be blown onto the products, so that the drying speed can be further increased.

[0065] [Example 3] Next, a third embodiment of the present invention will be described with reference to FIG. 12. FIG. 12 is a diagram showing the system configuration of a printer in the third embodiment. The basic configuration of this third embodiment is similar to that of the first and second embodiments already described. Therefore, in the third embodiment as well, the description of the matters already described in the first and second embodiments will be omitted, and the description will focus on the differences from the first and second embodiments.

[0066] In Fig. 12, the heating device 60 of the drying device 100 uses electromagnetic wave induction heating. Other details are the same as those in Examples 1 and 2. That is, the heating device 60 in Fig. 12 includes a heating coil 24 and a power supply unit that supplies current to the heating coil.

[0067] The product is heated by passing an alternating current through the heating coil 24 using the power supply unit 25. This heating device 60 can be used when the inside of a container such as a food bag that constitutes the product 2 is coated with a metal such as aluminum by vapor deposition.

[0068] For example, food bags and other containers with aluminum vapor-deposited on the inside generally have a cross-sectional structure as shown in Figure 13. In Figure 13, starting from surface 26 in contact with the outside air, there is a polypropylene layer 27, on the inside of which is a polyethylene terephthalate layer 28, and on the inside of that is an aluminum layer 29. Further inside is a polypropylene layer 30, the surface of which forms surface 31 in contact with the contents. Information to be shown to customers, such as the product name and ingredients, is printed on the surface of polyethylene terephthalate layer 28 opposite the aluminum layer.

[0069] When the printed portion of such a food bag reaches the vicinity of the heating coil 24 by the conveyor 4, the power supply unit 25 applies an alternating current to the heating coil 24, creating a magnetic field that induces a current in the aluminum layer of the food bag. This generates eddy currents in the aluminum layer, generating Joule heat according to the metal's electrical resistance, causing the aluminum layer to heat. This heat heats the polyethylene terephthalate layer 28 and the polypropylene layer 27, heating the printed dots above them and volatilizing the solvent inside. A surface film on the air layer of the printed dots forms immediately after printing, preventing the solvent from volatilizing. The substrate-side interface of the printed dots is the region with the highest solvent retention rate. Heating this area with the heat generated by the aluminum layer vaporizes the remaining solvent, slightly dissolving the film on the surface of the printed dots as it volatilizes. This reduces the interference of the film with solvent volatilization, allowing the solvent to volatilize more rapidly.

[0070] According to the third embodiment of the present invention, when a metal layer is used for the member for packaging the product, the same effects as those of the first and second embodiments described above can be obtained.

[0071] [Example 4] Next, a fourth embodiment of the present invention will be described with reference to Fig. 14. Fig. 14 is a diagram showing the system configuration of a printer in the fourth embodiment. In the case of this fourth embodiment, the basic configuration is similar to that of the first to third embodiments already described. Therefore, in the fourth embodiment as well, the description of the matters already described in the first to third embodiments will be omitted, and the description will focus on the differences from those embodiments.

[0072] In Fig. 14, a heating device 60 of a drying apparatus 100 utilizes a heating method using microwaves. The other configurations are the same as those of the other embodiments. The heating device 60 in Fig. 14 is composed of a high-voltage transformer 32 that generates a high voltage, a magnetron 33 that emits microwaves using high-voltage current, a microwave output unit 34, and a waveguide 35 that guides the microwaves.

[0073] When the product 2 reaches the position of the heating device 60 after printing, a high-voltage current is output from the high-voltage transformer 32 and supplied to the magnetron 33, causing microwaves to be emitted from the microwave output unit 34. The emitted microwaves pass through a waveguide 35 and are irradiated onto the print dots 1 on the product 2. As in the third embodiment, containers that can be heated include food bags and the like with aluminum vapor-deposited on the inside.

[0074] After passing through the polypropylene layer 27 and polyethylene terephthalate layer 28 shown in Figure 13, the microwaves are reflected by the aluminum layer 29 and do not reach the polypropylene layer 30 underneath. This prevents the microwaves from reaching the food or other contents inside the container, preventing them from heating up. The microwaves used have a wavelength of 2.45 GHz, which is permitted for use under the Radio Wave Control Act. Furthermore, because microwaves can interfere with communications between surrounding electronic devices, it is desirable to block the microwaves by installing a metal partition or other such measure around the conveyor device 4.

[0075] [Example 5] Next, a fifth embodiment of the present invention will be described with reference to Fig. 15. Fig. 15 is a schematic explanatory diagram of a mechanism for reducing the pressure in a printing portion including print dots.

[0076] While the above-described embodiments of the present invention were configured with a blower 50 and a heater 60, this embodiment differs in that it uses a blower and a pressure reduction mechanism instead of a heater. That is, this embodiment employs a method of reducing the pressure of the print dots to lower the boiling point of the solvent and volatilize the solvent in the print dots.

[0077] The other configurations are the same as those in the embodiment of the present invention already described, and therefore a description of the configurations already described will be omitted.

[0078] In this Example 5, specifically, as shown in Figure 15, a rubber cup 36 is pressed against the periphery of the printed dots on the product, and the pressure inside the cup is reduced. At the end of a hose 37 attached to the cup 36 is a decompression pump (not shown), which reduces the pressure inside the cup. This lowers the boiling point of the solvent, making it easier for the solvent to volatilize.

[0079] In this Example 5 of the present invention, it is possible to quickly volatilize the solvent in the print dots while suppressing deterioration such as thermal denaturation of the printed product. In particular, according to this Example 5, unlike the above-mentioned Examples 1 to 4, no heating process is performed, so it is possible to reliably prevent deterioration and denaturation of the product due to heat.

[0080] [Example 6] Next, a sixth embodiment of the present invention will be described with reference to FIG. 16. FIG. 16 is a diagram showing the system configuration of the sixth embodiment of the present invention. The embodiment shown in FIG. 16 also has a similar system configuration to the first embodiment already described, but differs in that an integrated control device 90 is provided for integrated control of the inkjet recording device 80 and the drying device 100. The drying device 100 must operate quickly after printing by the inkjet recording device 80, and must also accurately irradiate the print position with infrared light or the like. For this reason, the integrated control device 90 is provided for integrated control of the drying device 100 and the inkjet recording device 80, rather than controlling them individually.

[0081] In Figure 16, the control units of the drying device 100, inkjet recording device 80, and conveying device 4 are all connected to an integrated control device 90. When printing is performed on a product from the print head 83 of the inkjet recording device 80, a signal indicating that printing has been performed is sent to the integrated control device 90. Information on the product conveying speed is also sent to the integrated control device 90. From this information, the integrated control device 90 estimates the point at which the printed dots will arrive near the installation positions of the air blower and heating device, and sends that information signal to the drying device 100. The drying device 100 operates the air blower and heating device in accordance with the passage of product 2 (printed dot 1). This allows the solvent in the printed dots to volatilize quickly while suppressing deterioration such as denaturation of the printed product due to heat.

[0082] [Experimental Example] Next, an experimental example in which the above-described embodiment of the present invention is applied will be described. The inkjet printer used in this experiment is the PX-R inkjet printer manufactured by Hitachi Industrial Equipment Systems Co., Ltd. The product was printed on sample A, a food product packaged in a polypropylene bag. The ink used for printing was ink 4136K manufactured by Hitachi Industrial Equipment Systems Co., Ltd.

[0083] Within 1 second after printing, a drying device such as that shown in Example 2 in FIG. 11 was used to irradiate the printed dots with 5×10 laser light having a wavelength of 5500 nm and an output of 1 mW. -5 The sample was then placed on top of the print and rubbed once with a 500g load. Within 3 seconds of printing, the sample was placed in a frozen food storage cabinet at -20°C.

[0084] On the other hand, for another food sample B, the example of the present invention was not used, and the same type of food sample was placed on top of the print and rubbed once with a load of 500 g. Within 3 seconds of printing, the food sample was stored in a frozen food storage cabinet at -20°C.

[0085] After this experiment, Sample A and Sample B were taken out of the freezer and the state of the print was observed. As a result, Sample A, which was applied with Example 2 of the present invention, showed almost no change in the state of the print. On the other hand, Sample B had so much of the print dots that they were unrecognizable, and the print was completely unreadable.

[0086] The same experiment as above was also conducted, but with the ink changed from 4136K to 4146K. As a result, the printed dots of Sample C, which used Example 2 of the present invention, remained almost unchanged. On the other hand, Sample D, which was stored without implementing the present invention, retained a few more printed dots than the 4136K ink, but the printed content was still unreadable.

[0087] In this way, it was confirmed that by using the drying device according to the embodiment of the present invention, printed dots with high physical strength can be obtained in a short time.

[0088] [Other Examples] Although several embodiments (examples) have been described above, the present invention is not limited to the above-described embodiments and various modifications are possible. The above-described embodiments are provided as examples to facilitate understanding of the present invention, and are not necessarily limited to those including all of the configurations described. Furthermore, it is possible to replace part of the configuration of one embodiment with the configuration of another embodiment, or to add the configuration of another embodiment to the configuration of one embodiment. Furthermore, it is possible to delete part of the configuration of each embodiment, or to add or replace other configurations. [Explanation of symbols]

[0089] 1...printed dot, 2...product, 4...conveyor device, 6...fin, 7...peltier element, 8...fan, 9...LED element, 10...light-collecting element, 11...power supply, 12...temperature sensor, 14...communication cable, 15...dehumidifying section, 16...inlet path, 17...film, 18...laser diode, 19...power supply board, 22...printed content, 23...irradiation area, 24...heating coil, 25...power supply unit, 26...surface in contact with outside air, 27...polypropylene layer, 28...polyethylene tape phthalate layer, 29...aluminum layer, 30...polypropylene layer, 31...surface in contact with contents, 32...high voltage transformer, 33...magnetron, 34...microwave output unit, 35...waveguide, 36...cup, 37...hose, 50...blower, 60...heating device, 70...control device, 80...inkjet printer, 81...main body, 82...cable, 83...print head, 90...integrated control device, 100...print dot drying device, 200...light irradiation mechanism

Claims

1. A print dot drying device having a drying device for drying print dots formed on an article, The drying device is a blower that blows air onto the object; a temperature sensor for detecting the temperature of the item or its vicinity; a control device that receives the temperature detected by the temperature sensor and controls the air blower so that the temperature of the air is equal to or lower than the storage temperature of the item; Equipped with the drying device includes a heating device that heats the print dots, separate from the air blowing device; the heating device is an optical heating device that irradiates the print dots with light to heat them, the solvent of the ink that forms the print dots is a ketone solvent; The light is infrared light, and in the case of the ketone-based solvent, the wavelength is 5500 to 6250 nm.

2. In an inkjet printer equipped with an inkjet recording device and a print dot drying device, 2. An inkjet printer, wherein the print dot drying device is the print dot drying device according to claim 1.

3. A method for drying printed dots that are printed on an article using ink containing a solvent by an inkjet printer, comprising: Detecting a temperature at or near the item; Using the temperature, air adjusted to a temperature equal to or lower than the storage temperature of the item is blown onto the item; Furthermore, the printing dots are heated by a heating device, the heating is optical heating in which light is irradiated onto the print dots; the solvent of the ink that forms the print dots is a ketone solvent; The light is infrared light, and in the case of the ketone solvent, the wavelength is 5500 to 6250 nm.

4. A printing system including a printer that prints by ejecting ink dots onto an object, and a drying device that dries the print dots printed on the object, The drying device is a blower that blows air onto the object; a temperature sensor for detecting a temperature at or near the item; a control device that receives the temperature detected by the temperature sensor and controls the air blower so that the temperature of the air is equal to or lower than the storage temperature of the item; Equipped with the drying device includes a heating device that heats the print dots, separate from the air blowing device; the heating device is an optical heating device that irradiates the print dots with light to heat them, the solvent of the ink that forms the print dots is a ketone solvent; A printing system in which the light is infrared light, and in the case of the ketone-based solvent, the wavelength is 5500 to 6250 nm.

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