GB2560539A

GB2560539A - Continuous ink jet (CIJ) printhead

Info

Publication number: GB2560539A
Application number: GB1704072.6A
Authority: GB
Inventors: Lecheheb Ammar; Marcin Zaba Jerzy
Original assignee: MATRICODE Ltd
Current assignee: MATRICODE Ltd
Priority date: 2017-03-14
Filing date: 2017-03-14
Publication date: 2018-09-19
Anticipated expiration: 2037-03-14
Also published as: GB2560539B; GB201704072D0

Abstract

A continuous ink jet printhead comprising a plastic moulded gutter block 4a that is overmolded around at least one gutter return tube 6, 7 wherein one end of the tube acts as an inlet for the recycled ink drops and the other end is connected to the ink gutter return path. The return tube may comprise two sections of tube that are inserted into each other wherein one of the tubes has a smaller diameter than the other. When the two tubes are assembled the overmoulding of the gutter block forms a hermetically sealed gutter tube assembly. The two tube sections may be L-shaped, when connected together they form a U-shaped tube.

Description

(54) Title of the Invention: Continuous inkjet (CM) printhead Abstract Title: Continuous inkjet print head gutter block (57) A continuous inkjet printhead comprising a plastic moulded gutter block 4a that is overmolded around at least one gutter return tube 6, 7 wherein one end of the tube acts as an inlet for the recycled ink drops and the other end is connected to the ink gutter return path. The return tube may comprise two sections of tube that are inserted into each other wherein one of the tubes has a smaller diameter than the other. When the two tubes are assembled the overmoulding of the gutter block forms a hermetically sealed gutter tube assembly. The two tube sections may be L-shaped, when connected together they form a U-shaped tube.

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TITLE: CONTINUOUS INKJET (ClJ) PRINTHEAD

Background to the invention

The invention relates to industrial coding, marking and product identification employing printers operating under the so-called Continuous Ink Jet or CIJ principle described above. These are high speed, non contact, industrial printers used mainly to mark and code individual products on a moving production line. They code moving products “on the fly” and without coming into contact with these. They print on these products variable information such as “expiry dates”, “best before date”, barcodes, logos, batch code and serial numbers for product tracking and tracing purposes. The requirements on these printers are, amongst others, the ability to operate reliably and with low or no downtime in sometimes harsh factory environments. These include damp environment such as in beverage filling production lines, food canning and filling factory as well as dusty and oily environment, such as in the coding of automotive parts or in cement and bakeries packing or printing factories. Some of these factories operate 24 hours per day, sometimes 7 days per week. As a result, high machinery uptime and hence high productivity are important factors for these industrial applications, Downtime is very costly to factory owners in terms of lost productivity and even penalties in late deliveries.

More specifically, the invention relates to the printhead subsystem part of a CIJ printer system. A continuous inkjet (CIJ) printhead comprises a cover housing a printhead chassis itself supporting a print module. Assembled onto the top surface of the print module are the functional components of the CIJ printhead. The functional components include the following:

• Drop Generator chamber • Piezoelectric simulator transducer • The ink jet nozzle plate and orifice • The charge electrode • The charge synchronisation electrode • The droplet defection plates • The gutter and gutter ink return path • The fluid controlling electromagnetic solenoid valves

In use a pump supplies ink, under pressure (3 to 6 bars), to the drop generator in the printhead via a small plastic pipe (typically 1.6mm diameter). This pump is housed in a 3m to 6m umbilical connecting the main printer enclosure to the printhead. The pump supplies the ink to the drop generator from a small ink tank or reservoir housed in the printer enclosure. The drop generator breaks the jet of ink into droplets. Some of these are charged and then deflected to print onto moving substrates. The majority of the drops though are uncharged and are directed to a gutter for recycling back to the main ink tank.

Most of the root causes of downtime associated with these CIJ printers are related to faults or sudden malfunction of one or more of the functional components of the printhead subassembly. As a result, design, manufacture and assembly of these functional printhead components are challenging as they require multidisciplinary knowledge, expertise and experience involving electronics, mechanical, chemical, physics and fluids dynamics engineering.

Prior art

Over the years experts in the field of CIJ have encountered several stubborn technical problems associated with operating CIJ printhead. To date, one such stubborn problem still causes the most of CIJ printer downtime problems. It manifests itself as dried ink build up on the edge of the gutter tube inlet leading to the eventual formation of a string of dried ink between this gutter edge and one of the live deflector plates. When this occurs, the deflector plate is shorted to ground as the gutter tube is of necessity connected to the printhead earth. Therefore, printer fault and printer emergency shutdown ensue leading to operator intervention and printer downtime whilst the printhead is being cleaned, dried and printer system restarted.

The applicant has found that the root cause of this ink build up and subsequent printer malfunction is due to the way the non printing droplets impact the inside of the gutter. More specifically the issue is due to how and where the uncharged droplets strike the inside surface of the gutter tube. It is related to the drops impact angle and to the impact position and region of the droplets inside the gutter inlet tube surface.

To date the design and assembly of the gutter inlet tube has been variable. Therefore, the angle and region of impact of the uncharged drops vary within the same printer system and between the same printers over operating time and operators’ skills.

In use, more often than not, maintenance and service engineers use pliers and other tools to bend the inlet of the gutter tube. This is to adjust the gutter inlet to compensate for a jet of ink that cannot be adjusted into the inlet tube of the gutter. This practice is often because the operator finds it easier and quicker to bend the gutter rather than adjust the inkjet nozzle from which exits the jet of ink. By using such practices, the jet impact angle and the jet impact region within the inside of the gutter can be significantly and detrimentally altered from the original designer intention. As a result of the ensuing unfavourable impact region and impact angle, the ink spray from the droplet impact flies outside of the gutter tube and strikes other critical parts of the printhead. Eventually forming a dried ink connection between a high voltage part and ground potential such as gutter tube, ground deflector plate or printhead chassis or a combination of all these. It also results in the narrowing of the gutter inlet tube leading to decrease in entrained air and to loss of gutter suction and gutter effectiveness in recycling the ink not used for printing.

Objective of the present invention

Thus there exists a need for a CIJ printhead that provide a fixed, non-adjustable, tamper proof gutter tube. There also exists a need to provide a CIJ gutter tube that yields consistent, reliable ink recycling operation. There further exists a need to provide a gutter that ensures the resultant ink spray from the recycled drops hitting the inside surface of the gutter tube is contained within the inside of the gutter. This is so as to prevent ink spray from the droplet impact, reaching other critical parts of the printhead and producing build up of dried ink on the gutter tube opening edge or worse still on the deflector plates.

Summary of the invention

In accordance with a first aspect of the present invention, there is provided a continuous inkjet (CIJ) printhead comprising: a drop generator chamber or cavity which fitted on one end with a nozzle whose diameter ranges from typically 35 micro metres to 75 micro metres. Under pressure, the ink exits this nozzle in the form of a continuous stream of ink. This is then broken into a stream of equal and equidistant droplets by surface tension and by a piezoelectric transducer that continuously imparts ultrasound waves to the drop generator chamber at the rate of typically between 60 KHz and 128 KHz. The jet of droplets then passes through a charging tunnel or slot, through a pair of high voltage deflector plates to a gutter tube for recycling. The droplets entering the gutter tube are sucked back by a pump and are recycled back to the main ink supply reservoir.

In use, some of the ink stream droplets are inductively and selectively charged as they form in the charging electrode tunnel or slot. The charge imparted on each drop is controlled by the electronics and is variable depending on the desired image to be printed. These individual charged ink drops then separate from the main stream as they enter the deflection field formed between the deflector plates. The electrostatic charges on each drop determine their vertical flight (or deflection) to form the characters printed on the package or product. Only a small fraction of the drops of the ink stream are charged and deflected to print on moving substrates. The majority of ink droplets (about 95%) continue their un-deflected flight to the recycling gutter pick up or inlet tube

In one arrangement of the continuous inkjet (ClJ) printhead, the pick up or inlet gutter tube is designed in the form of a “U” shape so that one end is the inlet for the recycled drops and the other end is in direct communication with the gutter return channel of the printhead channel plate. At least the pickup end of the “U” tube is over moulded onto the gutter block so as to provide a finished, fixed, non-adjustable, hermetically sealed and tamper proof CIJ gutter pick up tube assembly.

In one arrangement of the continuous inkjet (CIJ) printhead, the gutter “U” tube is made of two L shaped tubes formed out of stainless where one of these L tubes is made to slide inside the other with small clearance. We have found that this arrangement overcomes the difficulties that are encountered when forming a unitary “U” tube out of stainless steel. The forming process of a unitary stainless “U” tube is not accurate enough to ensure repeatable distance between the two legs of the “U” tube. Furthermore, the forming of a unitary stainless steel tube results in a “U” tube whose two legs are not parallel to each but rather are at an angle to each other. This leads to the recycled drops impacting the inlet of the inside top surface of the gutter tube at an inclined angle of about 3 degrees. This would result in ink spray from drop impact flying outside of the gutter tube and hitting other printhead functional components.

In one preferred arrangement of the continuous ink jet (CIJ) printhead, the two “L” shaped tubes forming the gutter tube are manufactured and assembled into a unitary gutter tube by plastic overmoulding of the two “L” shaped stainless tubes. During the plastic moulding manufacturing process of the gutter block or gutter module of the printhead, these two “L” tubes are assembled together then loaded into a removable insert of the moulding tool, ensuring that the distance and angle between the two legs can be easily and repeatedly set. The moulding tool insert with the assembled tubes is then loaded into the moulding tool and overmoulded with plastic. This preferred method of manufacturing process allows for very low cost and precise location of the resulting unitary gutter tube within the gutter block. Thus, the finished gutter block incorporates a “unitary”, hermetically sealed gutter tube assembly with two fixed and parallel legs. This gutter tube assembly ensures that ink pray back from droplets impact is contained inside the gutter pick up or inlet tube. Thus avoiding dried ink building up on the gutter inlet tube edge and preventing contamination of other printhead critical components.

In one arrangement, the two gutter “L” shaped tubes can be loaded into a removable insert of the moulding tool and adjusted relative to each other within the moulding insert tool to set accurately and repeatedly the desired distance as well as the angle between the legs of the two “L” shaped tubes. Thereafter, the moulding insert with the assembled “L” shaped tubes is loaded into the moulding tool and overmoulded with plastic. This method of manufacturing process allows for very low cost, adjustable and precise location and manufacture of the resulting unitary “U” gutter tube within the gutter block.

Brief description of the drawings

Figure 1 shows a cylindrical cover housing a CIJ printhead of the present invention. It also shows the umbilical which connects the printhead to the main CIJ printer enclosure.

Figure 2 depicts a CIJ printhead of the present invention with the printhead cover removed.

Figure 3 shows an exploded view of the CIJ printhead gutter block or gutter module in accordance with the present invention.

Figure 4 shows an exploded view of the gutter block or gutter module of the present invention

Figure 5 depicts a plan view of the CIJ printhead gutter block and a section view A-A showing the overmoulded “U” shaped gutter tube of the present invention

Figure 6 shows the gutter block with views showing the inlet and outlet of the “U” shaped gutter tube overmouded onto the CIJ printhead gutter block

Figure 7 shows front and side views of the “L” shaped gutter tubes before insertion into each other to form a unitary “U” shaped gutter tube

Figure 8 shows plan and side views of the fully assembled printhead according to the present invention. This figure depicts the printhead active component and the umbilical housing the ink, solvent and air pipes as well as the electrical leads. The umbilical is connected to the printer cabinet that houses the ink, solvent and air supply as well the main controlling and driving electronics boards and associated software and firmware.

Detailed descriptions of the drawings

Figure 1 shows a continuous ink jet printhead of the present invention. It shows the printhead with the assembled cylindrical printhead cover (1) housing the CIJ printhead module and associated printhead functional components. It also shows the printhead umbilical on the right hand side of the figure and the printhead gutter block or gutter module the left hand side of the figure. The Umbilical connects the printhead to the printer enclosure (not shown). The umbilical length is typically 2 to 6 m in length.

Figure 2 depicts the CIJ printhead with the printhead cover removed. The figure shows the Cl J printhead chassi (2), the print module (3) and the gutter block (4).

Figure 4 shows a front exploded view of the gutter block or module. It shows fixing screws or bolts (5) used to fix the stainless steel gutter block ground plate (4b) onto the main plastic moulded gutter block (4a). The gutter block (4a) needs to be grounded (at ground potential) to prevent any electrostatic charge build up on the main gutter block which would occur as a result of partially charged recycled ink droplets.

Figure 5 depicts a plan view of the CIJ printhead gutter block (4a) with its printing slot 8. The printing slot is to allow charged and deflected drops to fly out of the printhead towards the moving product to be marked. This figure also shows a section view A-A showing the two legs (6 and 7) of the overmoulded “U” shaped gutter tube assembled together. The smaller diameter leg (7) of the “U” shaped tube is the gutter inlet or pick up tube where the unprinted drops enter the gutter. The larger diameter leg (6) of the “U” shaped gutter tube is in communication with the gutter channel which is formed in the printhead channel plate. The gutter return channel is itself in communication with a gutter plastic pipe housed in the umbilical and connected to a vacuum or gutter pump located in the main printer enclosure (not shown).

Figure 6 shows the fully assembled and overmoulded gutter block (4a) with views showing the inlet (7) and outlet (6) of the “U” shaped gutter tube overmouded onto the CIJ printhead gutter block.

Figure 7 shows front (7a) and side views (7b and 7c) of the “L” shaped gutter tubes before insertion into each other to form a unitary “U” shaped gutter tube (7c). This method of manufacture and assembly allows the two “L” shaped gutter tubes to be loaded into a removable insert of the moulding tool and adjusted relative to each other within the moulding insert tool to set accurately and repeatedly the desired distance as well as the angle between the legs of the two “L” shaped tubes. Thereafter, the moulding insert with the assembled “L” shaped tubes is loaded into the moulding tool and overmoulded with plastic. This method of manufacturing process allows for very low cost, adjustable and precise location and manufacture of the resulting unitary “U” gutter tube within the gutter block.

Figure 8 shows plan and side views of the fully assembled printhead according to the present invention showing the gutter block or gutter module (4). This figure also depicts the printhead active components and the umbilical (18) housing the ink, solvent and air pipes as well as the electrical leads. The umbilical (18) is connected to the printer cabinet that houses the ink, solvent and air supply as well the main controlling and driving electronics boards and associated software and firmware. The main active components of the printhead of the present invention shown in figure 8 are print module (3) comprising electromagnetic solenoids valves (9, 10, 11, and 12). These are normally closed and are for controlling the closing or opening of the supply channel to the drop generator bleed, gutter return, ink supply and cleaning solvent respectively. Figure 8 also shows the drop generator assembly (13) whose components parts are the nozzle plate, the drop generator chamber and piezoelectric transducer used to impart ultrasonic pressure waves (typically at a frequencies between 60 and 120 Khz) to break the continuous ink jet into uniform equidistant droplets (these components parts of the drop generator are not shown here). Also shown in figure 8 is the charging electrode (14) which inductively and selectively charges the individual droplets as these pass through the charging electrode slot. The droplet charging voltages are determined by the driving and controlling electronics software in accordance with the operator entered and desired image (s) to be printed. Figure 8 depicts the droplets charging detection and synchronisation electrode sometimes called the phasing electrode (15) too.

Similarly, figure 8 shows active drop deflector plate components (16 and 17).

Claims

1. A Continuous Ink Jet (ClJ) printhead compromising:

A plastic moulded gutter block incorporating at least one overmoulded gutter return tube with one end of the tube being the inlet for the recycled ink jet drops and the other end

5 being in direct communication with the gutter ink return path.

2. A continuous inkjet (Cl J) printhead according to claim 1 wherein the gutter tube is made out of two tubes inserted into each other. One tube being of smaller diameter than the other.

3. A continuous inkjet (ClJ) printhead according to claim 2, wherein at least one of the two

10 tubes is overmoulded into the plastic gutter block.

4. A continuous inkjet (CIJ) printhead according to claim 2, wherein the two tubes are assembled together then overmoulded into the plastic gutter block to form a hermitically sealed gutter tube assembly

5. A continuous inkjet (CIJ) printhead according to claim 4, wherein the two tubes are in the

15 form of an “L” shape.

6. A continuous inkjet (CIJ) printhead according to claim 5, wherein the two “L” tubes are assembled together then overmoulded into the plastic gutter block to form a hermitically sealed gutter tube assembly.

7. A continuous inkjet (CIJ) printhead according to the preceding three claims, wherein the

20 two “L” tubes are assembled together then overmoulded into the plastic gutter block to form a hermetically sealed “U” shaped tube gutter assembly.

Intellectual

Property

Office

Application No: GB1704072.6 Examiner: Mr Christopher Saul