Classifications

• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
  • D21H23/00—Processes or apparatus for adding material to the pulp or to the paper
  • D21H23/02—Processes or apparatus for adding material to the pulp or to the paper characterised by the manner in which substances are added
  • D21H23/22—Addition to the formed paper
  • D21H23/46—Pouring or allowing the fluid to flow in a continuous stream on to the surface, the entire stream being carried away by the paper
  • D21H23/48—Curtain coaters
• • 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
  • B05C5/007—Slide-hopper coaters, i.e. apparatus in which the liquid or other fluent material flows freely on an inclined surface before contacting the work
  • B05C5/008—Slide-hopper curtain coaters
• • 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
  • B05C9/00—Apparatus or plant for applying liquid or other fluent material to surfaces by means not covered by any preceding group, or in which the means of applying the liquid or other fluent material is not important
  • B05C9/06—Apparatus or plant for applying liquid or other fluent material to surfaces by means not covered by any preceding group, or in which the means of applying the liquid or other fluent material is not important for applying two different liquids or other fluent materials, or the same liquid or other fluent material twice, to the same side of the work

Definitions

• the present invention relates to a paper/board web coating apparatus, comprising a nozzle unit which includes at least two adjacent nozzle parts, said nozzle unit housing at least one feeding chamber extending in a longitudinal direction of the coating apparatus, into which a coating paste is delivered by supply means, said nozzle unit being provided with at least one equalizing chamber, which is defined by a boundary surface between the nozzle parts and is in flow communication with the feeding chamber and which likewise extends in the longitudinal direction of the coating apparatus, and said nozzle unit comprising a nozzle slot between the nozzle parts, which is in flow communication with said at least one feeding chamber by way of said at least one equalizing chamber and which also extends in the longitudinal direction of the coating apparatus and into which a coating paste is delivered from the feeding chamber through the equalizing chamber across the entire width of the nozzle slot and is further conveyed from an outlet opening of the nozzle slot.
• curtain coaters can be categorized as slot-fed or slide-fed coaters.
• the coating is fed by means of a nozzle unit onto an inclined plane, the coating flowing therealong towards the edge of the plane to form a curtain as the coating drips from the edge of the plane.
• the coating is pumped via a manifold chamber into a narrow vertical slot, the curtain forming at its lip and drips onto a web.
• the coating can be applied in one or several layers.
• the curtain thus formed is guided by means of an edge guide, which, as suggested by its name, is located at the edge of a feed slot/feed lip.
• the current curtain coaters for a coating paste are hampered by several problems, all having an adverse effect on the manageability of a cross-profile in the coating paste.
• the nozzle slot In curtain coating, the nozzle slot must have its width strictly within certain size limits for feeding a proper amount of coating paste onto the top surface of a nozzle unit and further onto a web to be coated. In practice, this has called for highly precise machining, as well as a careful management of thermal loads applied to the nozzle unit.
• the currently available nozzle units constitute a part of a support structure. Being clamped together, the nozzle units provide a single solid supporting unit by means of external bracing. Such a construction causes certain problems in manufacturing.
• the supply ducts for a coating paste are all machined in a nozzle part, which comprises a single, integral, solid bar-shaped block and, hence, in the process of machining supply ducts it is also necessary to consider structural strength aspects.
• a coexisting problem is also the limited size of supply ducts, and the problem of managing the size of a flow slot resulting partly therefrom.
• the system of supply ducts is subjected to certain limits regarding both size and shape, thus curtailing options for sizing the ducts to provide optimal flow conditions for a coating paste.
• cross-profile is also problematic in varying applications when using a curtain coater of the prior art. This applies partial- larly to a slide-fed coater.
• the shape of supply ducts which can have an effect on overall profile, is determined in the process of designing an applicator block/beam. As the coating paste varies in terms of its properties and/or supply rate, the latter have a distinct effect on cross-profile, which can no longer be corrected.
• one important objective of the present invention is to provide an improved curtain coater, which firstly enables a consistent supply of coating paste across the entire width of a nozzle unit and thereby an improved man- agement over the cross-profile of the amount of coating, and secondly provides substantially less demanding requirements in terms of manufacturing technique and is thereby more attractive in terms of its manufacturing costs, as well.
• a coating apparatus of the invention is characterized in that the feeding chamber is defined entirely within one of the nozzle parts in a position substantially offset relative to the nozzle slot and the equalizing chamber, such that the delivery of a coating paste from the feeding chamber into the equalizing chamber is effected by way of a flow passage provided inside the nozzle part.
• An applicator is characterized in that the feeding chamber is designed to be convergent in its lengthwise direction from the inlet end of supplied substance towards the opposite end, and that at least one of the feeding chamber's walls is adjustable for setting the feeding chamber's convergence as desired.
• Fig. 1 shows in a schematic perspective view one nozzle unit for a slide- fed curtain coater, which can be implemented according to the invention
• fig. 2 shows in a schematic cross-sectional view one nozzle unit of the prior art for a multiple curtain coater
• fig. 3 shows in a schematic cross-sectional view one embodiment for nozzle parts containing a feeding chamber and a nozzle slot in the nozzle unit of a coater as shown in fig. 2,
• fig. 4 shows in a schematic cross-sectional view another embodiment for a nozzle part in the nozzle unit of a curtain coater as shown in fig. 2.
• Fig. 1 shows in general view one applicator beam 1 for a slide-fed curtain coater.
• the beam can be constructed also according to the present invention.
• the applicator beam comprises nozzle parts 3, 3a, and 32, which are mounted on top of bearers 2 providing a support structure and which to- gether establish a nozzle unit with three nozzle slots 30 to enable multiple coating.
• feeder pipes 4 for a coating paste to be fed which open into feeding chambers 12 (fig. 2).
• the substance be- ing fed passes along the feeding chamber towards the opposite end, which is optionally provided with a by-pass. While advancing in the feeding chamber, the substance to be fed moves at each point over the length of the feeding chamber to the equalizing chamber 13 and thence further to a nozzle slot 30 over the entire width of the nozzle slot 30 (fig. 2).
• the nozzle parts 3 and 32 are arranged in a movable manner on top of the bearers 2.
• the applicator block includes a fixed support 5 resting on the bearers 2, on one side of which, between the rearward nozzle part 32 and the fixed support 5, is a closing tube 6 and on the opposite side of the fixed support is an opening tube 7, whereby the closing tube 6 can be pressurized for shift- ing the nozzle parts 3, 32 towards the immobile nozzle part 3a to close the nozzle unit and pressure can be released from the closing tube 6 and the opening tube 7 can be pressurized for shifting the movable nozzle parts 3, 32 away from the fixed nozzle part 3a to open the nozzle unit, e.g.
• the figure also indicates the directions mentioned in this application, i.e. a longitudinal direction W of the coating apparatus, a height of the nozzle parts and at the same time a longitudinal direction L of the nozzle slot 30, and a lateral direction D of the nozzle slot.
• Fig. 2 depicts schematically a general construction for the nozzle unit of one prior known slide-fed multiple curtain coater.
• the nozzle unit comprises nozzle parts 3, 3a, and 32, each of which, except for the last-mentioned one, has a feeding chamber 12 and a equalizing chamber 13, as well as a nozzle slot 30.
• the outermost nozzle part 3a has its edge 33 forming a feed lip, over which is delivered a coating paste emerging from outlet openings 31 of the nozzle slots 30 and flowing along a top surface of the nozzle unit for producing a coating curtain and guiding the same by means of edge guides (not shown) onto the surface of a paper/board web to be coated, which progresses beneath the coater.
• Fig. 2 indicates also a so-called unsupported height H for the nozzle. It has an essential significance regarding the consistency of a feeding rate of the nozzle. In a nozzle unit with this type of construction, the unsupported height H extends from a bottom edge of the feeding chamber 12 all the way to an outer edge 31 of the nozzle slot 30.
• the feeding chamber's bottom edge constitutes the highest possible point of support, i.e. the height H represents a distance over which the adjacent nozzle parts do not provide support for each other.
• the height H has a value of about 75 mm.
• the width of the nozzle slot 30 depends both on the shape of surfaces in nozzle parts and on thermal expansions occurring in nozzle parts, caused by temperature differences due to thermal loads carried by the coating paste. Such a construction sets high precision requirements in terms of manufacturing technique, particularly as the beam size increases.
• the feeding rate of a coating paste varies quite linearly as a function of the slot width as far as typically employed slot widths are concerned.
• the objective is to allow a coating profile to have a maximum fluctua- tion of one percent in the amount of coating
• the accuracy of a 0,5 mm slot in the direction D must have an accuracy of 0,005 mm.
• Fig. 3 illustrates one nozzle unit configured in accordance with the invention, wherein the feeding chambers 12 are provided completely inside the nozzle units. The coating paste is now fed from the feeding chamber 12 in a substantially lateral direction D directly into the equalizing chamber 13 and thence further to the nozzle slot 30 in its extending direction L.
• the unsupported height H of a nozzle part is substantially reduced, thus relaxing substantially the precision requirements imposed on surfaces of the nozzle part with regard to manufacturing technique.
• the unsupported height is only 37 mm or 50% shorter than in a typical state-of-the art solution depicted in fig. 2.
• a nozzle part is able to retain its integrity without external bracing. All elements constituting a nozzle unit can be preferably welded to each other comprehensively prior to installation in the actual coating apparatus, pro- vided that the feeding chamber 12 is made entirely immobile. If, for example, the feeding chamber has its lower wall made movable, it is possible to provide packings (not shown) between sections 42 constituting the bottom part of a nozzle part. With regard to the nozzle unit of fig. 3, for example, the nozzle part may have its upper sections 40 preferably secured to each other by welding. The nozzle parts can be preferably clamped against each other by means of bolts 41 to provide a nozzle unit. The fastening of a bottom section 43 is also preferably obtainable by a screw attachment (not shown).
• a principal advantage gained by the novel construction is that the unsupported height remains unchanged regardless of the chamber size.
• the inventive solution also enables the construction of a considerably larger chamber with the same external dimensions and coating paste flow rates, and at the same time facilitates the management of a coating paste flow profile.
• the feeding chamber of fig. 2 has a cross-sectional area of 1330 mm 2 .
• the nozzle unit of fig. 3 is provided with an equally high construction (in this case 120 mm), the feeding chamber will have a cross-sectional area of 2325 mm 2 or 75% larger than the construction of fig. 2.
• fig. 3 depicts one solution of the invention for a nozzle part, wherein a space 17 extending longitudinal of the nozzle part encloses the feeding chamber from above and below, as well as from the side opposite relative to the equalizing chamber 13,
• the space 17 can be used for equalizing temperature differences resulting from thermal loads created by a coating paste (and other factors).
• the construction has material thicknesses which are highly consistent and the coating paste provides its heating or cooling effect over a very large area, whereby the deformations or strains due to temperature differences remain insignificant as compared with the prior art solution.
• the feeding chamber 12 is designed to be convergent in its longitudinal direction from the inlet end of supplied material towards the opposite end, and that at least one of the feeding chamber's walls is adjustable for setting the feeding chamber's convergence as desired. In a particularly preferred case, it is the feeding chamber's 12 bottom wall which is made adjustable.
• the solution enables further facilitating the optimization of coating paste flow rates and thereby provides an even more substance material profile for the coating paste flowing out of an outlet opening 31 of the nozzle slot 30. This provides benefits, especially in situations in which the feeding amounts are highly fluctuating. This is the case, particularly when it is desired to apply coating by using both multiple technique and single-layer technique.
• the coating paste discharging from a nozzle slot has the adjustment of its profile automated, whereby a crosswise profiling can be effected even during a run, which is not possible in currently known solutions.
• inventive solution can be further applied even in a more general sense in applicators intended for spreading various fibrous or other liquids or pastes in a paper/board or pulp machine environment, such as, for example, in the headbox of a paper machine.
• inventive construction is also conceivable for use in the blade coating of a fibrous web, in connection with so-called jet application feed.

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• Coating Apparatus (AREA)
• Paper (AREA)

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• 2003
  • 2003-09-10 FI FI20035150A patent/FI114726B/sv not_active IP Right Cessation
• 2004
  • 2004-09-02 DE DE112004001570T patent/DE112004001570B4/de active Active
  • 2004-09-02 WO PCT/FI2004/050124 patent/WO2005024133A1/en active Application Filing
  • 2004-09-02 JP JP2006525850A patent/JP4403179B2/ja active Active

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