Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05C—APPARATUS FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05C5/00—Apparatus in which liquid or other fluent material is projected, poured or allowed to flow on to the surface of the work
  • B05C5/005—Curtain coaters

Definitions

• the invention relates to a coating head for applying a coating composition to a moving medium, in particular a coating head for the curtain coating method for forming a liquid curtain from coating composition which is to be applied to a continuously moving, web-shaped medium, the use of the coating head according to the invention and a Coating process using the coating head according to the invention.
• Coating heads of this type are known, for example, from EP 0 812 237 B1 or, in one embodiment as a horizontally operating extrusion coating head, from EP 0 673 684 B1 and essentially have a first and an adjacent second coating head half, between which one Gap is formed, the gap being connected to an ink chamber for accommodating the coating composition, and the coating composition being dispensed to the medium to be coated through the gap and a nozzle representing the outside end of the gap.
• the two protective rights EP 0 812 237 B1 and EP 0 673 684 B1 listed above attempt to solve the problem of achieving a uniform coating thickness without fluctuations, particularly in the case of thin coating jobs.
• the coating composition is free of trapped air in the form of air bubbles or foam, since each of such air bubbles leads to defects in the coating.
• DE 40 32 833 A1 proposes a complete casting application device for highly viscous products with a casting head, storage container, return channel and pump, with the proviso that the flow of the product has to take place in a laminar manner without the formation of bubbles.
• This document thus formulates less an invention than the knowledge that turbulent movements of the product in the feed to the coating head cause blistering. Thanks to the use of pumps, necessary ink mass filters and long, partially curved lines, the idealized conditions of only laminar flows in the coating material feed to the application head can never be fully realized.
• WO 84/02859 A 1 proposes a degassing container into which the coating composition is pumped from a storage container.
• the overflow mass containing foam and air bubbles is returned to the storage container from an overflow of this degassing container.
• the coating material discharged from the degassing container in the lower area is fed to a coating head and should then no longer have any foam or air bubbles.
• the new unit should be simple in construction, so that it is both inexpensive to buy and later to maintain. From the outset, it is also part of the catalog of requirements that the unit to be proposed can be used for the technology of applying coating compound by means of a liquid curtain.
• a coating head with a first half and an adjoining second half, between which a gap is formed with a gap length L and a gap width B oriented at right angles to the gap length L, the gap with at least one of the two coating head halves trained ink chamber is connected and the ink chamber is provided for accommodating a coating material through the gap and the outside of the gap end Representing nozzle is to be dispensed to the medium to be coated, characterized in that the ink chamber is provided with one or more bulges tapering upward, which open into ventilation openings.
• the paint chamber of the coating head according to the invention is preferably filled with coating material from a storage container via an intermediate degassing unit, residual foam from coating material with enclosed air bubbles collects in the bulges tapering upwards due to the lower specific mass of the coating material-air mixture contaminated with air bubbles. This mixture emerges from the ventilation openings and is ideally fed back to the storage container, for example via a vacuum vent.
• a variant is preferred in which a negative pressure is applied to the ventilation openings.
• the degassing performance of the coating head according to the invention can be increased considerably by means of such a preferably controllable suction device.
• the degassed coating compound is fed to a gap which ends in a nozzle as the outside end of the gap and releases the coating compound onto the medium to be coated.
• the gap width B corresponds to the desired curtain thickness
• the gap length L corresponds to the curtain width. In many cases, this is chosen to be wider than the medium to be coated, so that part of the liquid curtain falls past the medium into a collecting tray, from where the coating material is returned to the storage container.
• the compensation chamber is designed as an expansion of the gap in its width over the entire gap length L in a limited area between the nozzle and the ink chamber.
• the compensation chamber is connected to the paint chamber, for example via individual downpipes or connecting pipes or preferably via an intermediate gap between the compensation chamber and the paint chamber.
• the coating material is preferably supplied by means of a lateral inlet opening in the paint chamber, which is connected to the reservoir as far as possible via an intermediate degassing unit.
• the ink chamber has also via an outlet opening, which is embedded in the opposite side of the ink chamber and is connected to a bypass coating material discharge. Excess coating material is fed back into the storage container via the bypass. Numerous tests have shown that a ratio of coating material supplied to coating material returned by bypass in a range from 1: 0.2 to 1: 2 can be regarded as particularly advantageous.
• the present invention also includes the use of the coating head according to the invention for the application, in particular, of heat-sensitive coating compositions.
• Air bubble inclusions in heat-sensitive coatings lead to defective coatings and thus to the loss of the imaging function. Since the manufacturers of heat-sensitive recording materials are obliged to give a guarantee that the recording material is fully functional over its entire surface, incomplete coating can cause complaints to a large extent. against this background it becomes clear why the structurally simple possibility of a particularly effective and error-free, integrated degassing coating head according to the present invention is particularly suitable for heat-sensitive coating compositions.
• Coating compositions of this type contain dye precursors of active substance and preferably organic color acceptors which react with them to form a color under the influence of heat.
• other common additives in the heat-sensitive coating compositions include resins, waxes and stabilizers.
• the coating head according to the invention can be operated both with other coating systems and in a multiple arrangement, so that wet-on-wet coatings are made possible. It is also conceivable to change the design of the proposed coating head in such a way that it is suitable for simultaneous multiple coating. In this case, several ink chambers with tapering bulges opening into ventilation openings, possibly several compensation chambers and several gaps, which are arranged one behind the other in the same orientation, are used within a multiple coating head.
• the coating composition is preferably taken from a storage container via an intermediate degassing unit of the dyeing chamber of the coating head according to the invention supplied. If there are air pockets in the coating material, foam collects in the bulges of the ink chamber that taper upwards. This foam is removed by means of a preferably controllable suction device. For example, by means of vacuum deaerators, the coating mass fraction can be pulled out of the foam and returned to the storage container.
• the coating composition not drawn off as foam from the ink chamber is fed to the nozzle of the coating head according to the invention.
• the coating composition forms a liquid curtain below the nozzle, which falls along a forming - dynamic - wetting line onto the web-shaped medium which is continuously moving relative to the coating head.
• the coating composition is heat-sensitive, for which purpose it contains dye precursors and color acceptors which react with them to form a color under the influence of heat.
• a paper web is preferred as the medium.
• Another preferred method variant is the formation of a protective layer on the previously applied heat-sensitive coating.
• Both heat-sensitive and the protective layer covering them can be applied with the coating head according to the invention. This can be done with a time delay or simultaneously with a multi-coating head.
• Figure 1 shows a first variant of the coating head (3) according to the invention with a first half (1) and a second half (2), which is constructed mirror-inverted to the first half (1).
• the two coating head halves (1, 2) adjoin one another precisely along a straight contact line K.
• a tubular ink chamber (5) is formed, which is oriented parallel to the contact line K and half of which is formed in the two coating head halves (1, 2).
• the ink chamber (5) is expanded at the top with conical bulges (7).
• the bulges (7) taper upwards and open into ventilation openings (8), each half along the contact line K. are formed in the two coating head halves (1, 2).
• the ink chamber (5) is slotted down the entire length of the tube and connected via the slit to a gap (4), half of which is formed in each of the two coating head halves (1, 2).
• the gap (4) has a gap length L with the same orientation as the contact line K and a gap width B perpendicular to the gap length L.
• the gap width B is thus determined by the distance between the two coating head halves (1, 2) in their lower region in accordance with their respective shapes.
• the gap (4) is bounded at the top by the slot in the ink chamber (5) and at the bottom by a nozzle (6), which represents the gap end at the lower end of the coating head (3).
• the nozzle (6) runs parallel to the contact line K.
• the ink chamber (5) like the gap (4), is sealed laterally by closure means, not shown in FIG. 1.
• An opening (9, 10) is let into each of these closing means in the lateral extension of the ink chamber (5), one opening (9) for supplying the coating material and the other opening (10) for removing the coating material.
• a liquid curtain is shown, which runs vertically downwards along the nozzle (6) and in the lower region through the wetting line (13) as the cutting line of the liquid curtain with the medium to be coated (12 ) is limited.
• the wetting line (13) runs parallel to the contact line K.
• the direction of movement of the medium (12) runs at right angles to the wetting line (13) and parallel to the gap width B.
• FIG. 2 shows a further variant of the coating head (3 ' ) according to the invention.
• an additional tubular compensation chamber (11) is formed below the ink chamber (5), which is oriented parallel to the contact line K and half of which is formed in the two coating head halves (1, 2).
• the ink chamber (5) is slotted down over the entire length of the tube.
• the ink chamber (5) is connected via this slot to an intermediate gap (14), half of which is formed in each of the two coating head halves (1, 2).
• the intermediate gap (14) opens into an upper opening slot of the compensation chamber (11), which extends over the entire length of the tube.
• This has a second slot at the bottom over the entire length of the tube and is connected via this second slot to a slot (4) which, as already described for FIG. 1, opens into the nozzle (6).
• closure means which, in addition to the ink chamber (5) and the gap (4), now also laterally seal the compensation chamber (11) and the intermediate gap (14).
• FIG. 3 shows a simplified installation situation of the coating head (3, 3 ' ) according to the invention without possible pumps and / or further degassing units.
• a storage container (17) contains a coating material which is supplied from the storage container (17) via the coating material supply (15) to the coating head (3, 3 ' ) and further via the inlet opening (9) (not shown) to the paint chamber (5).
• FIG. 4 shows an overall coating curtain (18) formed by a multiple coating head.
• a multiple coating head comprises a plurality, in the case on which FIG. 4 is based, three individual coating heads.
• the nozzles of the three individual coating heads are combined so that the total coating curtain (18) has the same width the individual coating curtain widths and with a thickness corresponding to the sum of all individual coating curtain thicknesses.

Landscapes

• Coating Apparatus (AREA)
• Magnetic Heads (AREA)

Applications Claiming Priority (3)

Publications (2)

Family

ID=29796263

Family Applications (1)

Country Status (5)

Families Citing this family (2)

Family Cites Families (6)

• 2002
  • 2002-07-10 DE DE10231276A patent/DE10231276B4/de not_active Expired - Fee Related
• 2003
  • 2003-07-02 DE DE50302079T patent/DE50302079D1/de not_active Expired - Lifetime
  • 2003-07-02 AT AT03740402T patent/ATE314154T1/de not_active IP Right Cessation
  • 2003-07-02 AU AU2003281149A patent/AU2003281149A1/en not_active Abandoned
  • 2003-07-02 EP EP03740402A patent/EP1521643B1/fr not_active Expired - Lifetime
  • 2003-07-02 WO PCT/EP2003/007050 patent/WO2004007091A1/fr not_active Application Discontinuation

Non-Patent Citations (1)

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