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

• This invention relates to an arrangement in a curtain coater for a paper/board web for precluding the drying of a coating mix on a lip portion of the application bar.
• Solutions in relation to coating methods of a paper/board web, which apply curtain coating, have been described e.g. in publications WO 01/16427 Al, US 5,773,093 and US 5,885,659.
• curtain coating provides obvious advantages over other methods used for coating a paper/board web.
• a curtain coater is particularly conceivable as a replacement for air-brush coating.
• Curtain coating provides a coverage comparable with air-brush coating, and it further enables much higher coating speeds.
• there is no waste of mix in curtain coating as the coating agent is not sprayed the same way as in air-brush or spray coating.
• the web is subjected to a much lesser stress by curtain coating, which thus causes less downtime from breaks of the paper web and, hence, results in a better runnability.
• Curtain coating is not able to provide a smoothness equal to blade coating, yet the coverage achieved thereby is better than that obtained by blade coating.
• the problem with a curtain coater thus far has been the drying of a coating mix on a lip portion of the application bar.
• the lip portion is formed by the edges of a coating mix discharge opening, while in a slide-fed curtain coater the lip portion is formed by a feeding lip of the outermost nozzle element, from which the coating mix disengages and forms a coating curtain.
• the flowing rate of a coating mix being low at a lip portion, the mix has a tendency to dry along the lip portion's edge. Drying occurs particularly in the proximity of a static contact point, at which the coating mix disengages from the lip portion.
• cooling channels are intended for cooling a lip, such that ambient moisture condenses on the lip and prevents the mix from drying.
• a problem in such a method is, however, that cooling water has to be kept quite cold, which in turn affects the opening size of a feeding slot and, thus, the coating profile.
• the object is fulfilled with an arrangement, which is characterized in that the arrangement comprises means for feeding steam and/or moist air at a desired temperature and moisture to the proximity of the lip portion and a down-flowing coating curtain, whereby the moisture content and/or temperature of air surrounding the lip portion and the coating curtain are/is adjustable for controlling the drying of the mix.
• the coating curtain is fed from a slot, said steam or moist air feeding means being located in the vicinity of the feeding slot's lip portion, most preferably on either side of the coating curtain.
• the coating curtain is fed from an inclined platform established by nozzle elements, said steam or moist air feeding means being located in a space between the coating curtain and the outermost nozzle element underneath a lip portion.
• the coating curtain is provided with shield elements on either side thereof, by means of which the coating curtain can be surrounded with a confined working space, said feeding means being located thereinside.
• the inventive arrangement offers substantial benefits.
• a supply of steam or moist air in the proximity of a coating curtain and the lip portion of a feeding slot, the moisture content and temperature of ambient air can be preferably increased, and in a readily regulable fashion at that.
• the drying of a coating mix on the lip portion of an application bar can be precluded for thus eliminating the defects caused thereby in a coating curtain.
• the temperature of a lip portion and a coating curtain is brought by means of the inventive arrangement to become lower than the temperature of the ambient space, the condensation of ambient moisture preventing the coating mix from drying.
• the coating curtain by providing the coating curtain with a working space surrounding the same and containing steam or moist air, the effect of surface tension, and hence the stability of a coating curtain, can be more effectively controlled.
• Fig. 1 shows a slot-fed curtain coater in cross-section
• Fig. 2 shows a slide-fed curtain coater in cross-section.
• Fig. 1 depicts a curtain coater 1 of the invention, wherein the application of a coating onto a paper web 35 is effected from a feeding slot 20 arranged laterally of the paper web 35.
• Coating mix is delivered into the feeding slot 20 generally by means of pressure.
• the boundary surface between a lip portion 13, formed by a lower section of the feeding slot 20, and the coating mix develops static contact points 8, whereat the coating mix assumes the form of a coating curtain 32.
• the coating curtain flows under gravity towards the paper web 35 moving in the direction indicated by the arrow in fig. 1.
• the point of application between the coating curtain 32 and the paper web 35 develops a second boundary surface, i.e. a dynamic contact point 9, whereat the coating curtain spreads as a coating layer 34 on top of the paper web 35.
• Steam or moist air feeding means 3 are located near the lip portion 13 of the feeding slot 20 and exist in this embodiment preferably on either side of the coating curtain 32, the static contact point 8 also developing on either side of the coating curtain 32.
• a preferred embodiment of the invention shown in fig. 1 further includes shield elements 2 and 2a for stabilizing the coating curtain 32 and provided on either side of the coating curtain 32, which enable confining a working space, said feeding means 3 being located thereinside and said shield elements 2 and 2a facilitating the supply of steam or moist air into the working space.
• the injection of steam or moist air is also preferably achievable by not applying it directly to the coating curtain 32 in order not to disturb its stability thereby.
• the shield panels 2 and 2a are not necessary. There may also be a shield panel 2 on just one side of the coating curtain 32.
• the moisture content and temperature of ambient air can be increased as desired.
• the temperature of cooling water used for cooling the vicinity of the lip portion 13 need not be low.
• cooling and cooling elements, designated by numeral 4 in fig. 1 for illustrative purposes, are not absolutely necessary at all.
• Fig. 2 shows another preferred embodiment of the invention, wherein the curtain coater comprises a slide-fed curtain coater. It has nozzle elements 11 and an outermost nozzle element 12 together constituting a nozzle block, a coating mix layer 15 delivered by way of its feeding slots 20 being run along an inclined platform established by the nozzle block's top surface and the coating curtain 32 forming as the coating mix is falling under gravity towards the paper web 35 from the lip portion 13 formed by the final nozzle element 12.
• the steam or moist air feeding means 3 are located in a space between the down-flowing coating curtain 32 and the outermost nozzle element 12 underneath the feeding lip 13.
• the feeding means 3 are located to the left of the coating curtain 32, the static contact point 8 developing in this case at only a single point in a boundary surface between the lip portion 13 of the outermost nozzle element 12 and the coating curtain 32.

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• Coating Apparatus (AREA)
• Paper (AREA)

Priority Applications (1)

Applications Claiming Priority (2)

Publications (1)

Family

ID=8564614

Family Applications (1)

Country Status (3)

Cited By (3)

Citations (2)

• 2002
  • 2002-09-20 FI FI20021677A patent/FI20021677A/fi not_active Application Discontinuation
• 2003
  • 2003-09-17 WO PCT/FI2003/000678 patent/WO2004027153A1/en not_active Application Discontinuation
  • 2003-09-17 AU AU2003262603A patent/AU2003262603A1/en not_active Abandoned

Patent Citations (2)

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