JP7618213B2 - Inkjet printer - Google Patents

Description

The present invention relates to a continuous inkjet printer, and more specifically to preventing smearing and transfer caused by wet ink.

Inkjet printers have a problem where the ink printed on the substrate before drying rubs against the printed substrate, causing the ink to smudge or transfer, resulting in poor print quality.

To solve the above problems, conventionally, air is pumped out using a pump and then blown onto the wet printing surface to promote drying of the ink (see, for example, Patent Document 1).

However, the above-mentioned drying acceleration method requires a pump to deliver air and a mechanism to blow air onto the substrate, which increases the cost of the inkjet printer.

Inkjet printers, on the other hand, are broadly divided into continuous and on-demand types based on the printing method they use. Of these, continuous type inkjet printers use a pump to eject ink from a nozzle while vibrating the ink, and charge the ink droplets with a charging electrode at the point where the ink separates into droplets. They then use a deflection electrode to deflect the trajectory of the ink droplets, causing them to collide with a specified position on the printing surface, forming ink dots.

JP 2001-328253 A JP 2018-83369 A

The continuous inkjet printers mentioned above use quick-drying ink, so there are almost no problems with smearing or transfer caused by wet ink.

However, recently, due to the Organic Solvent Law and user needs to avoid the smell of solvents, there has been a trend to avoid the solvents with short drying times that were previously used, and instead, solvents with long drying times that are not subject to the Organic Solvent Law have come to be chosen. As a result, problems of smearing and transfer caused by undried ink have become apparent.

On the other hand, in continuous-type inkjet printers, the print head is covered with a case and a positive pressure is maintained inside the case to prevent dirt on the components caused by the ink mist generated by the ejected ink and to prevent dust from being sucked in through the gutter and clogging the pipes, which could cause breakdowns (see Patent Document 2).

By maintaining a positive pressure inside the cover using the pressurizing means, it is possible to slow the progression of contamination of the head components caused by ink mist, and also to prevent foreign matter such as dust from entering the ink circulation system.

The present invention aims to provide an inkjet printer that can accelerate the drying of printed ink at minimal cost by utilizing the standard air pressurization means that creates positive pressure inside the print head cover.

In order to achieve the above object, the inkjet printer according to the present invention comprises:
A gun that applies a constant period of vibration to the ink being ejected to generate continuous ink droplets;
a charging electrode for charging the ink droplets by applying a step-shaped voltage synchronized with a period of the ink droplets;
a deflection electrode for deflecting the charged ink droplets vertically or horizontally according to the degree of charge, so that the ink droplets land on a printing surface of a substrate;
a cylindrical case in which the gun, a charging electrode and a deflection electrode are housed in a hollow portion and in which a slit is formed through which the charged ink droplets pass;
An inkjet printer that causes ink droplets ejected from the print head to land on a printing substrate that moves relatively in a horizontal or vertical direction, and forms characters with multiple rows of printing dots,
Air compressed by a single compressor is branched, one of the air flows is supplied to a cavity in the case to maintain the cavity at a positive pressure, and the other air flow is blown onto a printing surface of the printing material to promote drying of the ink ;
As a means for blowing air onto the printing surface, an air nozzle that blows air from a small diameter hole is used,
The air nozzle is attached by wrapping a band around the outer circumferential surface of the case, and the position of the air nozzle can be adjusted by changing the attachment position of the band.

Further, the inkjet printer according to the present invention comprises:
A gun that applies a constant period of vibration to the ink being ejected to generate continuous ink droplets;
a charging electrode for charging the ink droplets by applying a step-shaped voltage synchronized with a period of the ink droplets;
a deflection electrode for deflecting the charged ink droplets vertically or horizontally according to the degree of charge, so that the ink droplets land on a printing surface of a substrate;
a cylindrical case in which the gun, a charging electrode and a deflection electrode are housed in a hollow portion and in which a slit is formed through which the charged ink droplets pass;
An inkjet printer that causes ink droplets ejected from the print head to land on a printing substrate that moves relatively in a horizontal or vertical direction, and forms characters with multiple rows of printing dots,
Air compressed by a single compressor is branched, one of the air flows is supplied to a cavity in the case to maintain the cavity at a positive pressure, and the other air flow is blown onto a printing surface of the printing material to promote drying of the ink;
As a means for blowing air onto the printing surface, an air nozzle that blows air from a small diameter hole is used ,
A regulator that keeps the air pressure constant is attached to the tube that supplies one of the air streams to the hollow portion of the case, and a throttle valve that adjusts the amount of air is attached to the tube that supplies the other of the air streams to the air nozzle.

In this invention, a compressor installed to create positive pressure inside the print head case is used as a means of blowing air onto the ink on the printing surface, thereby reducing the cost of the printer while preventing smearing and transfer caused by wet ink, eliminating deterioration of print quality.

1 is a perspective view showing the appearance of a print head according to the present invention incorporating an ink drying acceleration function. 2 is a partial cross-sectional front view showing a schematic configuration of a continuous-type ink-jet printer according to an embodiment of the present invention, including the print head of FIG. 1; 3 is a diagram illustrating an operation when printing on a printing substrate using the inkjet printer of FIG. 2. FIG. FIG. 1 is a piping diagram of an air supply system. FIG. 13 is a diagram showing examples of printing in which air is blown onto the printed surface to promote drying of the ink, and then the printed surface is rubbed with a wiper (a), and in which the printed surface is rubbed with a wiper without blowing air (b).

The following describes an inkjet printer according to an embodiment of the present invention with reference to the drawings.

Figure 1 is a perspective view showing the appearance of a print head 1 incorporating an ink drying promotion function, and Figure 2 is a partially sectional front view showing the general configuration of a continuous ink jet printer (hereinafter referred to as "IJP") 10 according to this embodiment, including the print head 1. Figure 3 is a diagram explaining the operation when printing on a substrate using the IJP 10 in Figure 2.

The components of the IJP10 according to this embodiment are broadly divided into components related to supplying ink to the print head 1 to perform printing (hereinafter, these will be referred to as the "ink supply system") and components related to supplying pressurizing air and air for promoting drying of the ink to the print head 1 (hereinafter, these will be referred to as the "air supply system"). First, the components of the ink supply system that supplies ink to the print head 1 to perform printing will be described.

<Ink supply system>
2, the IJP 10 is composed of a print head 1, an ink tank 2, and pumps 3a and 3b. Of these, the print head 1 is composed of a gun 12, a charging electrode 13, a detection electrode 14, a deflection electrode 15, a gutter 16, and pipes 17a and 17b, and these members are housed in a cylindrical case 11.

The gun 12 and other components that make up the print head 1 are actually arranged in close contact with the hollow portion 110 of the case 11, but in Figure 2, a rough layout is shown to clearly explain the function of each component.

The gun 12 sprays ink droplets ID toward the side of the printing substrate (see FIG. 3, for example, a box in which a product is packaged) 4, and is composed of a gun body 121, an ultrasonic vibrator 122, and a nozzle 123. Ink is pumped from the ink tank 2 by the pump 3a and supplied to the gun body 121 through the pipe 17a, and is sprayed from the hole of the nozzle 123 while being vibrated by the ultrasonic vibrator 122.

The ink column IP ejected from the nozzle 123 is separated into individual ink droplets ID by the vibration applied by the ultrasonic vibrator 122, and is then charged by the charging electrode 13. Only the ink droplets ID required for printing are deflected by the deflection electrode 15 according to the amount of charge, passing through the slit 111 formed in the front part of the case 11 and landing on the printing surface of the substrate 4.

Figure 3 shows a cosmetic box 4 moving at a constant speed on a belt conveyor (not shown) in the direction indicated by the arrow. Note that for ease of viewing, the case 11 of the print head 1, which is not related to the printing operation, is omitted from Figure 3.

The surface of the decorative box 4, which is the substrate to be printed, is coated with a film made of polyethylene or polypropylene. After the food or other items are packed into the box, the manufacturing number, expiry date, etc. are printed on the film to form the final product.

As shown in FIG. 3, when the cosmetic box 4 is moving in a direction perpendicular to the flight direction of the ink droplet ID, the position of the ink droplet ID that lands on the side of the cosmetic box 4 changes by changing the deflection amount of the ink droplet ID, and by repeatedly deflecting the ink droplet ID in synchronization with the movement of the cosmetic box 4, a character ("A" in the figure) is printed.

On the other hand, ink droplets ID that are not charged and ink droplets ID that are charged but are not used for printing are not deflected and jump directly into the gutter 16 for ink recovery and are recovered in the ink tank 2. The ink recovered by the gutter 16 is transferred by the pump 3b through the pipe 17b to the ink tank 2 and is reused.

The operation of the IJP 10 is controlled by a controller (not shown). The controller is composed of a CPU, memory (ROM, RAM, etc.), a timer, and a display, and controls the operation of the ultrasonic transducer 122 of the gun 12, the pulse power supply 131 of the charging electrode 13, the detection electrode 14, the DC power supply 151 of the deflection electrode 15, and the pumps 3a and 3b.

Specifically, the controller drives the pump 3a to apply pressure to the ink contained in the ink tank 2 and supply it to the gun body 121. The controller also controls the timing of the pulse voltage applied from the pulse power supply 131 to the charging electrode 13 based on the signal detected by the detection electrode 14, thereby adjusting the number and timing of the ink droplets ID to be charged. Furthermore, the controller adjusts the deflection amount of the ink droplets ID deflected by the deflection electrode 15 by controlling the voltage of the DC power supply 151.

<Air supply system>
Next, the air supply system of the IJP 10 will be described with reference to the above-mentioned Figures 1 to 3 and newly added Figure 4. Figure 4 is a piping diagram of the air supply system 5. Before describing the air supply system, the features of the present invention will be described.

The distinctive feature of this invention is that it uses a single compressor to achieve two air-related functions. Specifically, it utilizes the compressor that supplies pressurized air to the print head, which is a standard feature of continuous-type IJP, to achieve the function of promoting the drying of ink that has landed on the printed material, without adding a new compressor.

At food production sites, compressors are installed to drive air cylinders and the like. Air is supplied from the compressor through an air tube (hereafter simply called "tube") 51, and first passes through a drain catch 52 to remove excess moisture, and then through a mist separator 53 to remove oil mist. These processes are performed to prevent equipment driven by air from breaking down due to moisture or oil mist.

The air AR then branches into two, and the air AR that passes through tube 54a is supplied to the print head 1 and is used to create positive pressure inside the case 11. On the other hand, the air AR that branches into tube 54b is used to promote the drying of the ink that has landed on the printing substrate 4.

The function of the air branched off into tube 54a will now be explained. A regulator 55 is attached midway through tube 54a to reduce the pressure of the air compressed by the compressor to an appropriate value, and the air AR whose pressure has been adjusted by regulator 55 is supplied to the case 11 of the print head 1.

As shown in FIG. 2, the lid 112 that seals the rear of the cavity 110 of the case 11 has holes through which the tubes 54a and 54b pass, and the tip of the tube 54a is open to the cavity 110 of the case 11. The cavity 110 is sealed except for the slit 111 through which the ink droplets ID are ejected, and most of the air AR (indicated by the white arrow) supplied through the tube 54a remains within the case and increases the air pressure.

In a continuous-type IJP, some of the ink ejected from the nozzle 123 floats in the surrounding atmosphere as ink mist and adheres to the surfaces of the components, causing stains, so it is necessary to periodically clean the components inside the case 11. In addition, dust can enter the ink circulation system through the gutter and cause pipes to become clogged, resulting in malfunctions.

For this reason, the main components of the print head 1 are housed in the case 11, and the inside of the case 11 is kept under positive pressure, which promotes the discharge of ink mist to the outside and prevents dust from entering the case 11 from the outside. These measures make it possible to extend the frequency of cleaning the components and prevent clogging of pipes, etc., due to dust.

Next, the function of the air supplied to the air nozzle 57 through the tube 54b will be described. As shown in FIG. 4, the air AR branched to the tube 54b is supplied to the air nozzle 57 after the flow rate is adjusted by the throttle valve 56.

As shown in FIG. 2 above, the tube 54b is inserted into the hollow portion 110 of the case 11 and passes through a hole formed in a fixed block 61 attached to the outer periphery of the case 11. As shown in FIG. 1, the air AR taken out from the air outlet 62 passes through the tube 54b again and is supplied to the air nozzle 57, where it is sprayed onto the printing surface of the printing material 4.

The reason why the tube 54b is first inserted into the hollow portion 110 of the case 11 and then reconnected to the tube 54b through a hole in the fixed block 61 is to integrate the air nozzle 57 with the print head 1. This configuration makes it easier to handle the air nozzle 57 during maintenance and inspection.

As shown in FIG. 1, the air nozzle 57 is attached to the tip of the attachment 63, which is further fixed to the outer circumferential surface of the case 11 by a metal band 64.

If the air nozzle 57 is attached to the outer periphery of the case 11 using a band 64, the front-to-back and up-to-down positions of the air nozzle 57 can be easily changed by loosening the mounting fixture 63, making it easy to adjust the position of the air nozzle 57 relative to the printing surface.

Figure 3 mentioned above shows the state in which air AR blown out from the air nozzle 57 is blown onto the ink that has landed on the printing substrate 4. In the experiment, the ink used was a 3-methyl-2-butanone solvent (75-90%) to which chromium complex salt (5-15%) was added as a black dye, and to which a small amount of m,p-cresyl glycidyl ether (1-10%) was added. The above-mentioned ink was then used to print on the side of a decorative box 4, the surface of which was coated with a film.

As a result of the experiment, it was found that by using a small-diameter air nozzle 57 with a hole diameter of about 0.5 mm and spraying air at a rate of 0.5 to 3 liters/min with the tip of the air nozzle 57 positioned about 45 mm away from the printing surface, the ink can be dried to a degree that does not cause rubbing on the printing surface within 0.5 seconds after printing.

For reference, Figure 5 shows examples of printing in which air AR is blown onto the printing surface to accelerate the drying of the ink, and the printing surface is rubbed with a wiper 0.5 seconds after printing (a), and printing is performed without blowing air, and the printing surface is rubbed with a wiper 0.5 seconds after printing (b).

In the print example of Figure 5(a), the tip of the air nozzle 57 was placed about 45 mm away from the print surface, and air was sprayed at a rate of about 1.2 l/min. The temperature during printing was 26°C and the humidity was 60%.

As shown in Figure 5(b), when air is not blown onto the printing surface, the ink smudges and the characters become unreadable. In contrast, as shown in Figure 5(a), when air is blown onto the printing surface to promote drying of the ink, the ink dries and no smudges occur.

As explained above, by using the IJP of the present invention, air can be blown onto the ink that has landed on the printing surface, accelerating the drying of the ink and preventing the ink from smudging or transferring. As a result, deterioration of print quality caused by wet ink can be eliminated.

In addition, this invention achieves the ink drying promotion function without the need for a new air supply source by branching off the air that maintains positive pressure inside the print head case, which is a standard feature of continuous-type IJP. This makes it possible to keep the increase in IJP costs associated with adding new functions to a minimum.

In the above embodiment, a cylindrical case is used as the case for the print head, and the main components are housed in the hollow portion of the case, but the shape of the case is not limited to being cylindrical. A case with a square or hexagonal cross section may be used depending on the shape and arrangement of the components.

In the above embodiment, the case where printing is performed on a substrate moving in a horizontal direction has been described, but the direction of movement of the substrate is not limited to this, and it is possible to introduce the ink drying promotion function even if the substrate moves in a vertical direction, for example. In that case, the ink droplets are deflected in the horizontal direction, and the air nozzle is positioned above or below the print head.

AR air 1 Print head 2 Ink tank 3a, 3b Pump 4 Printing material 5 Air supply system 10 Inkjet printer 11 Case 12 Gun 13 Charging electrode 14 Detection electrode 15 Deflection electrode 16 Gutter 17a, 17b Pipe 51, 54a, 54b Tube 52 Drain catch 53 Mist separator 55 Regulator 56 Throttle valve 57 Air nozzle 61 Fixing block 63 Mounting fixture 64 Band 110 Hollow portion 111 Slit 112 Lid

Claims (2)

A gun that applies a constant period of vibration to the ink being ejected to generate continuous ink droplets;
a charging electrode for charging the ink droplets by applying a step-shaped voltage synchronized with a period of the ink droplets;
a deflection electrode for deflecting the charged ink droplets vertically or horizontally according to the degree of charge, so that the ink droplets land on a printing surface of a substrate;
a cylindrical case in which the gun, a charging electrode and a deflection electrode are housed in a hollow portion and in which a slit is formed through which the charged ink droplets pass;
An inkjet printer that causes ink droplets ejected from the print head to land on a printing substrate that moves relatively in a horizontal or vertical direction, and forms characters with multiple rows of printing dots,
Air compressed by a single compressor is branched, one of the air flows is supplied to a cavity in the case to maintain the cavity at a positive pressure, and the other air flow is blown onto a printing surface of the printing material to promote drying of the ink ;
As a means for blowing air onto the printing surface, an air nozzle that blows air from a small diameter hole is used,
The air nozzle is attached to an outer peripheral surface of the case by wrapping a band around the case, and the position of the air nozzle can be adjusted by changing the attachment position of the band . A gun that applies a constant period of vibration to the ink being ejected to generate continuous ink droplets;
a charging electrode for charging the ink droplets by applying a step-shaped voltage synchronized with a period of the ink droplets;
a deflection electrode for deflecting the charged ink droplets vertically or horizontally according to the degree of charge, so that the ink droplets land on a printing surface of a substrate;
a cylindrical case in which the gun, a charging electrode and a deflection electrode are housed in a hollow portion and in which a slit is formed through which the charged ink droplets pass;
An inkjet printer that causes ink droplets ejected from the print head to land on a printing substrate that moves relatively in a horizontal or vertical direction, and forms characters with multiple rows of printing dots,
Air compressed by a single compressor is branched, one of the air flows is supplied to a cavity in the case to maintain the cavity at a positive pressure, and the other air flow is blown onto a printing surface of the printing material to promote drying of the ink;
As a means for blowing air onto the printing surface, an air nozzle that blows air from a small diameter hole is used,
an inkjet printer characterized in that a regulator that keeps the air pressure constant is attached to a tube that supplies one of the air streams to a hollow portion of the case, and a throttle valve that adjusts the amount of air is attached to a tube that supplies the other of the air streams to the air nozzle .

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