EP2240327A1

EP2240327A1 - Inkjet printer with drop catcher

Info

Publication number: EP2240327A1
Application number: EP09711419A
Authority: EP
Inventors: Menno Cornelis Bouhuijs; Jorrit Fedde Bloemhof; Robert Janson
Original assignee: OSIRIS TECHNOLOGY BV
Current assignee: Xennia Holland BV
Priority date: 2008-02-13
Filing date: 2009-02-13
Publication date: 2010-10-20
Anticipated expiration: 2029-02-13
Also published as: WO2009102208A1; NL2002534A1; EP2240327B1; DK2240327T3; ES2535456T3; NL2002534C2; PT2240327E

Abstract

An apparatus for printing a web of material by means of ink jet heads comprises removing means for catching and removing floating ink droplets by electrostatic means. Added for this purpose to each group of heads is a plate which is charged with an electrical voltage relative thereto and which during operation electrically attracts the floating ink droplets. Present between the conveyor belt for transporting a substrate for printing along the inkjet heads and the relevant head or heads is a transport member, for instance an endless conveyor belt, which transport member, in a collecting position, collects ink droplets attracted by the plate, is subsequently guided to a cleaning station for removal of collected ink from the transport member, and then guided back again to its collecting position.

Description

INKJET PRIKTER WITH DROP CATCHER

The invention relates to an apparatus for printing a web of material or substrate, for instance paper or textile, which apparatus is of the continuous or the discontinuous type and comprises: a main frame; an endless conveyor belt which is guided over a driven roller and a reversing roller disposed substantially parallel thereto and which is driven by- motor means at a chosen constant speed; glue dispensing means for applying a glue layer upstream of the active upper part of the conveyor belt for temporary light adhesion of the textile web to this active part such that this web is fixed non-movably relative to the conveyor belt; optional washing means placed downstream relative to the active part for removing glue from the conveyor belt; supply and feed means for feeding a textile web from a supply to the active part of the conveyor belt; printing means for printing the passing textile web in the zone of the active part of the conveyor belt; and discharge and storage means for removing the printed textile web from the conveyor belt and subsequent storage thereof; wherein the printing means comprise a number of, for instance 2-8, frame beams extending in transverse direction above said active part at determined mutual longitudinal distances along the direction of transport, each of which frame beams carries an array of fixedly disposed inkjet heads or one or more movable inkjet heads; control means are present which fulfil at least the following functions of: storing a chosen printing pattern, for instance a uniform printing, by means of inputting pattern information, for instance from a scanner; energizing the inkjet heads, also in relation to the chosen set speed of the conveyor belt and the mutual distances in the direction of transport between successive inkjet heads, such that each head sprays droplets of ink of the relevant colour onto the web at the positions on the web determined by the control means; the discharge means comprise drying means for drying the ink applied to the textile web. Such an apparatus is known from for instance the earlier European patent application of applicant, EP-A-I 591 258.

It is noted that "ink" is also understood to mean other liquids, for instance dye, conditioning liquids and other liquids intended for the purpose of printing and/or treating textile.

When the ink is applied from the ink-jet heads there occurs ink-splashing, i.e. scattering of droplets of ink into already applied ink. It is hereby not possible to prevent the surrounding area, in particular the substrate for printing but also the lower surface of the ink-jet heads, being contaminated with ink. Splashes are generally clearly visible on for instance a part of the textile which has not been printed or printed with another colour, or in other colour areas, which are visible up to a distance of more than 5 cm. This unwanted scattering of the ink has the further adverse consequence that a printed pattern, for instance on papβ± ui textile, is contaminated and blurring and colour contamination occur. This is particularly visible in the case of colours applied in large quantities. This problem is even so far-reaching that the unintentionally applied ink is clearly visible to the naked eye. This is highly undesirable, for instance for fine textile materials such as printed fashion fabrics. The described unwanted splashing often makes a printed product completely unusable.

It is known to use a certain suction by means of a suction fan or the like, with which ink droplets floating in the air are removed from the critical zone by means of an airflow. Such a solution has been found not to be very effective.

The invention has for its object to substantially improve the effectiveness of catching floating ink droplets.

The apparatus according to the invention comprises for this purpose removing means for catching and removing floating ink droplets which, after being sprayed toward the web of material by an inkjet head, are not or not fully absorbed by the material but splash for instance into already applied ink and subsequently undergo a displacement in a direction with a component having an orientation opposite that of the spraying direction, or cause already applied ink to undergo such a displacement, which removing means are of electrostatic type, and comprise: a plate which is added to each head, or to a group of heads, or to all heads and which is charged with an electrical voltage, for instance in the order of 5 kV, relative to the head or heads and which during operation electrically attracts the floating ink droplets; and a transport member which is present between the conveyor belt and the relevant head or heads and which in a collecting position collects ink droplets attracted by the plate, is subsequently guided to a cleaning station for removal of collected ink from the transport uteiiibeL, ctnd is then guided back again to its collecting position.

The appended claims describe various possibilities and options within the basic framework of the invention.

Use can preferably be made of pairs of endless conveyor belts which run below the row of nozzles and leave a space clear between them for spraying ink droplets to the substrate for printing.

The unintentionally upward splashing ink is attracted electrostatically by the electrically charged plate. The active part of the conveyor belt is guided with its underside along this plate. The return part is guided back again via another route, for instance over the upper side of the plate.

Relative to the frame, and in particular the inkjet heads, the plate has a high voltage, for instance in the order of 5 kV.

The active part of the endless conveyor belt which has left the contamination zone in the area of the nozzles is preferably guided through a rinsing bath, is there cleaned of adhering ink, leaves the bath, is dried, for instance by an airflow and/or heat or by being scraped dry with a doctor blade of for instance a rubber elastic material, such as a rubber, a synthetic rubber or a polyurethane, and once again enters the zone of the heads in order to resume its operation for catching the floating droplets.

The conveyor belt is not conductive. The electrostatic field is therefore not disrupted by the conveyor belt .

The conveyor belt need not lie against the plate charged with electrical voltage, although it is recommended to keep this distance as small as possible.

In a preferred embodiment the invention has the special feature that a transport member is a conveyor belt, which conveyor belt comprises two mutually parallel parts driven at equal speeds.

According to a specific aspect of the invention, the apparatus has the special feature that the conveyor belt is reciprocally displaceable.

Recommended is an embodiment in which the conveyor belt is of the endless type.

Cleaning of the conveyor belt can take place in any suitable manner.

According to a determined aspect of the invention, the apparatus has the special feature that the cleaning station comprises a bath with rinsing liquid.

This latter apparatus preferably comprises drying means for removing rinsing liquid from the cleaned transport member to be returned to the collecting position. A simple embodiment possibly to be recommended has the special feature that the cleaning station comprises a doctor blade pressing against the conveyor belt.

This latter embodiment can for instance have the feature that the doctor blade consists of a rubber elastic material, for instance a natural rubber, a synthetic rubber or a polyurethane .

According to a subsequent aspect of the invention, an apparatus has the feature that the or each plate has an electrically insulating cover layer, for instance an epoxy layer with a thickness in the order of 0.5 mm.

According to a following aspect of the invention, the apparatus has the special feature that the conveyor belt consists mainly of a TPO (thermoplastic olefin) , for instance Habileen®, or the belt is of the Transilon© type from the manufacturer Siegling.

According to yet another aspect of the invention, the apparatus has the special feature that on the side remote from the side collecting ink droplets the belt is provided with a layer enhancing the tensile strength and optionally roughness, for instance a rough-profiled layer of polyester.

The apparatus can also have the feature that on its side collecting ink droplets the belt has at least an outer layer with hydrophilic, ink-dispersing properties such that droplet formation is prevented. In this variant there is a negligible risk of ink droplets forming on the belt which could drop off the belt. Even when there is serious splashing of ink, this risk is wholly negligible due to this aspect of the invention.

Inexpensive, strong and reliable is an embodiment in which the apparatus has the feature that the or each plate consists substantially of metal, for instance steel, in particular stainless steel. Alternatively, the invention can have the special feature that the or each plate consists substantially of a plastic plate, for instance of PU (polyurethane) , which is sufficiently wear-resistant and which is electrically conductive to at least some extent. The invention will now be elucidated on the basis of the accompanying drawings. Herein: figure 1 shows a cut-away schematic perspective view of an apparatus according to EP-A-I 591 258; figure 2 is a schematic side view of the apparatus according to figure 1; figure 3 is a schematic side view of a conveyor, the active upper part of which is straight; figure 4 is a view corresponding to figure 3 of a conveyor, the active upper part of which has a generally curved form; figure 5 shows a more detailed side view of the conveyor according to figure 4 ; figure 6 is a schematic perspective view of the conveyor according to figures 4 and 5; figure 7 is a front view along the direction of transport of a U-shaped frame which can be moved in and out of the apparatus; figure 8 is a schematic front view of an apparatus according to the invention; figure 9 is a side view on enlarged scale of the apparatus according to figure 8; figure 10 is a perspective view of a part of the apparatus according to the invention in the area of the rinsing bath; figure 11 is a perspective view of a part of the apparatus on the other side; figure 12 shows part of another exemplary embodiment in which the endless conveyor belt comprises an upper and a lower part, these parts being held by rollers at a small iiiuLUdl distance, and in which the part or the conveyor belt contaminated by ink is cleaned by a doctor blade; figure 13A is an example shown in grey tones of a piece of textile printed with an ink pattern in which it is apparent that the light surfaces have been highly contaminated by floating ink droplets; and figure 13B shows by way of comparison a piece of textile printed with an apparatus according to the invention.

In the figures to be described below corresponding elements and components are always designated with the same reference numerals. Figure 1 shows an apparatus 1 for printing a textile web 2 (see also figure 2} . The apparatus comprises a main frame 3 placed on the ground or a shop floor.

As is particularly apparent from figures 3, 4, 5 and 6, apparatus 1 comprises an endless conveyor belt 6 which is guided over a driven roller 4 and a reversing roller 5 disposed substantially parallel thereto and which is driven by motor means (not shown) at a chosen constant speed as according to arrow 7. The apparatus further comprises glue dispensing means 8 for applying a glue layer upstream of the active upper part 9 of conveyor belt 6 for temporary light adhesion of textile web 2 to this active part 9 such that web 2 is fixed non-movably relative to the conveyor belt during transport by said upper part 9.

A washing apparatus 10 shown in figure 5 comprises sponge means 11 and a scraper 12 for removing glue residues from conveyor belt 9. These washing means 10 are placed downstream of the active part 9. Figure 2 shows a supply and feed unit and a pressure roller 15 which co-acts with roller 4 and which provides an intimate and adhering contact between the active upper part 9 and textile web 2.

A printing unit 16 comprises eight U-shaped frames 17, 18, 19, 20, 21, 22, 23, 24, which are each adapted to generate, under the control of a control unit (not shown) , a very small droplet of coloured ink at any point in time determined by the control unit by means of an inkjet head unit added to each frame, one colour tor each frame. Printing means 16 are operative in the zone of the active part 9 of the conveyor belt. The printing takes place in accordance with an adjustable pattern to be selected.

Connecting onto printing unit 16 is a dryer 25 which is finally followed by a discharge and storage unit 26 in which the dried web, otherwise than in the infeed unit 13, is not rolled up onto a roll but, swinging back and forth as according to arrow 27 in per se known manner, comes to lie under its own weight in layers of the now printed textile web 28 on a stack 29. The printing means, of which frames 17-24 form part, comprise frame beams which are added to the respective frames and supported thereby, and each of which carries an array of inkjet heads. During operation each of these arrays is immobile relative to the upper surface defined by the active part.

As shown in figure 3, conveyor belt 6 is supported over active part 9 by support surfaces, drawn in this case as rollers 31, 32, 33, 34, 35, 36, 37, 38, where the support positions for the conveyor belt correspond with the zones of the inkjet arrays situated thereabove. Rollers 31-38 are incorporated in the structure such that during operation they have a substantial difference in speed from that of conveyor belt 6. The rollers can for instance be driven or braked or, in the simplest case, be fixed.

Figures 4, 5 and 6 show an embodiment in which the rollers are ordered in an arc such that active part 9 of conveyor belt 6 is deflected by each roller through an angle in the order of 1°.

Conveyor belt 6 is arranged under tensile stress over rollers 4 and 5.

Figure 7 shows U-shaped frame 22 which can be displaced laterally out of apparatus 1 in the manner shown in figure 1. The U-shape leaves clear an opening 41 such that with a lateral displacement as according to arrow 42 the frame 22 can be moved to the right in the drawing without disrupting the operation of the rest of the apparatus. During normal operation with seven colours for instance one beam corresponding to a colour not in use can thus be removed for service lines.

The upper leg of the U bears a beam 43 which carries an inkjet array in a manner not shown. Beam 43 can be positioned very precisely relative to lower leg 44 by means of respective recesses and protrusions.

Reference numeral 71 designates a supply station for coloured ink. As shown particularly clearly in figure 2, this station contains two containers 72, 73, each with its own colour, between which it is possible to switch, or with the same colour for continuation of the printing process when one container is completely empty. Figures 8, 9, 10, 11 and 12 show the aspects added according to the invention to the known apparatus according to figures 1-7.

In these figures the reference numerals have the following designations:

101: inkjet heads

102: driven roller or reversing roller for the conveyor belt for the purpose of transporting the substrate of paper or textile for printing

103: drive motor for the endless cleaning conveyor belt according to the invention

104: stainless steel plate provided with a 0.5 mm thick epoxy coating, this plate being provided with a gap or free space 110 for passage of ink droplets 111. Electrical breakdown and sparking from the electrode to the surrounding area, particularly to the chassis parts of the drive, are prevented by this epoxy coating. This earlier occurring phenomenon was made worse when no coating was present because the belt became wet and therefore transmitted the electric voltage further into the mechanism. The epoxy layer is applied by powder- coating. This insulating cover layer has the further important advantage that there are substantially no electrified parts with which users and operatives can come into contact. This is an important aspect in terms of safety.

105: the active upper part of the cleaning conveyor consisting of two parallel parts

106: the lower return part of the cleaning conveyor

107: deflecting roller, one on each side, tensioned with draw springs for the purpose of holding the endless cleaning conveyor belt under tension 108: an electrical connection for the high voltage on electrode plate 104

109: the bath with rinsing liquid

110: the gap or free space between the two parts of the conveyor

111: the paths of the ink droplets, indicated schematically with straight lines

112: the direction of transport of the active upper part 105

113: the direction of displacement of the lower return part 106.

It is noted that, as shown particularly in figures 8 and 11, cleaning conveyor 105, 106 is disposed such that the gap or intermediate space 110 is situated in the zone in which the nozzles, lying in one line, of the inkjet heads are active. Cleaning conveyor 105, 106 thus extends in transverse direction relative to the direction of displacement 7 of endless conveyor belt 6 with which the textile web for printing is guided through the apparatus.

Not shown are drying means for removing rinsing liquid from the cleaning conveyor after it leaves bath 9. Figure 12 shows a detail of an embodiment in which parts 105 and 106 are held at small mutual distance by sets of rollers 211 which are situated both at the shown end and at the other end of cleaning conveyor 105, 106. This construction achieves that cleaning conveyor 105, 106 is situated a small distance from electrode plate

104. The number of rollers is kept as low as possible in order to limit as far as possible contamination and the occurrence of mechanical resistance.

Other than in the embodiment of figure 11, in which use is made of bounding flanges 232 on deflecting rollers 107 in order to prevent lateral displacement, in the embodiment of figure 12 use is made of a number of fixedly disposed guide plates 212 which guide the two parts 105, 106 of the cleaning conveyor and prevent lateral displacement. This prevents a high mechanical load on the side edges of the conveyors.

The embodiment according to figure 12 further comprises a cleaning mechanism in which use is not made of a rinsing bath but of a doctor blade 213 which scrapes dry the outer side of the conveyor by removing ink residues. In this embodiment the doctor blade 213 consists of a polyurethane and is pressed against the conveyor by means of spring means (not shown) . The ink droplets 210 removed by doctor blade 213 are collected and discharged in suitable manner. The excess ink can for instance drop onto the pressure belt of the apparatus adjacently of the textile web. This is possible in some circumstances because the pressure belt is for instance 60 cm or more wider than the overall printing width. The pressure belt is washed repeatedly such that the excess ink carried along by the pressure belt is always washed off.

The unit shown in figure 12 consists entirely of an electrically insulating material, for instance an epoxy composite material or other GRP (Glassfibre Reinforced Plastic) . Parts 105 and 106 also take a form which is entirely electrically insulating.

Owing to the described choices of material the leakage of voltage, electrical breakdown and spark-over can be effectively prevented. Figure 13A shows a piece of textile 214 printed with a prior art apparatus. The light zones are shown to be highly contaminated with ink. This ink consists of deposited, unintentionally floating ink droplets. Figure 13B shows a piece of textile 215 which largely corresponds to the textile 214 of figure 13A but which differs therefrom in the sense that the non- printed or light-coloured zones are free of unintentionally deposited floating ink droplets.

Claims

1. Apparatus for printing a web of material, for instance paper or textile, which apparatus is of the continuous or the discontinuous type and comprises: a main frame; an endless conveyor belt which is guided over a driven roller and a reversing roller disposed substantially parallel thereto and which is driven by motor means at a chosen constant speed; glue dispensing means for applying a glue layer upstream of the active upper part of the conveyor belt for temporary light adhesion of the textile web to this active part such that this web is fixed non-movably relative to the conveyor belt; optional washing means placed downstream relative to the active part for removing glue from the conveyor belt; supply and feed means for feeding a textile web from a supply to the active part of the conveyor belt; printing means for printing the passing textile web in the zone of the active part of the conveyor belt; and discharge and storage means for removing the printed textile web from the conveyor belt and subsequent storage thereof; wherein the printing aiβαiis comprise s number of_r for instance 2-8, frame beams extending in transverse direction above said active part at determined mutual longitudinal distances along the direction of transport, each of which frame beams carries an array of fixedly disposed inkjet heads or one or more movable inkjet heads ; control means are present which fulfil at least the following functions of: storing a chosen printing pattern, for instance a uniform printing, by means of inputting pattern information, for instance from a scanner; energizing the inkjet heads, also in relation to the chosen set speed of the conveyor belt and the mutual distances in the direction of transport between successive inkjet heads, such that each head sprays droplets of ink of the relevant colour onto the web at the positions on the web determined by the control means ; the discharge means comprise drying means for drying the ink applied to the textile web, characterized by removing means for catching and removing floating ink droplets which, after being sprayed toward the web of material by an inkjet head, are not or not fully absorbed by the material but splash for instance into already applied ink and subsequently undergo a displacement in a direction with a component having an orientation opposite that of the spraying direction, or cause already applied ink to undergo such a displacement, which removing means are of electrostatic type, and comprise: a plate which is added to each head, or to a group of heads, or to all heads and which is charged with an electrical voltage, for instance in the order of 5 kV, relative to the head or heads and which during operation electrically attracts the floating ink droplets; and a transport member which is present between the conveyor belt and the relevant head or heads and which in a collecting position collects ink droplets attracted by the plate, is subsequently guided to a cleaning station for removal of collected ink from the transport member, and is then guided back again to its collecting position.

2. Apparatus as claimed in claim 1, wherein a transport member is a conveyor belt, which conveyor belt comprises two mutually parallel parts driven at equal speeds.

3. Apparatus as claimed in claim 2, wherein the conveyor belt is reciprocally displaceable.

4. Apparatus as claimed in claim 2 or 3, wherein the conveyor belt is of the endless type.

5. Apparatus as claimed in claim 1, wherein the cleaning station comprises a bath with rinsing liquid.

6. Apparatus as claimed in claim 5, comprising drying means for removing rinsing liquid from the cleaned transport member to be returned to the collecting position.

7. Apparatus as claimed in claim 1, wherein the cleaning station comprises a doctor blade pressing against the conveyor belt.

8. Apparatus as claimed in claim 7, wherein the doctor blade consists of a rubber elastic material, for instance a natural rubber, a synthetic rubber or a polyurethane .

9. Apparatus as claimed in any of the foregoing claims, wherein the or each plate has an electrically insulating cover layer, for instance an epoxy layer with a thickness in the order of 0.5 mm.

10. Apparatus as claimed in any of the claims 2, 3 and 4, wherein the conveyor belt consists mainly of a

TPO (thermoplastic olefin) , for instance Habileen®.

11. Apparatus as claimed in any of the claims 2, 3 and 4, wherein on the side remote from the side collecting ink droplets the belt is provided with a layer enhancing the tensile strength and optionally roughness, for instance a rough-profiled layer of polyester.

12. Apparatus as claimed in any of the claims 2, 3 and 4, wherein on its side collecting ink droplets the belt has at least an outer layer with hydrophilic, ink- dispersing properties such that droplet formation is prevented.

13. Apparatus as claimed in any of the foregoing claims, wherein the or each plate consists substantially of metal, for instance steel, in particular stainless steel.

14. Apparatus as claimed in any of the claims 1-12, wherein the or each plate consists substantially of a plastic plate, for instance of PU (polyurethane) , which is sufficiently wear-resistant and which is electrically conductive to at least some extent.

15. Apparatus as claimed in any of the foregoing claims_/ wherein the transport member consists of one or more electrically insulating materials.