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
  • D21H23/50—Spraying or projecting
• • 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
  • B05C5/02—Apparatus in which liquid or other fluent material is projected, poured or allowed to flow on to the surface of the work the liquid or other fluent material being discharged through an outlet orifice by pressure, e.g. from an outlet device in contact or almost in contact, with the work
  • B05C5/0283—Flat jet coaters, i.e. apparatus in which the liquid or other fluent material is projected from the outlet as a cohesive flat jet in direction of the work
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05B—SPRAYING APPARATUS; ATOMISING APPARATUS; NOZZLES
  • B05B1/00—Nozzles, spray heads or other outlets, with or without auxiliary devices such as valves, heating means
  • B05B1/26—Nozzles, spray heads or other outlets, with or without auxiliary devices such as valves, heating means with means for mechanically breaking-up or deflecting the jet after discharge, e.g. with fixed deflectors; Breaking-up the discharged liquid or other fluent material by impinging jets
  • B05B1/262—Nozzles, spray heads or other outlets, with or without auxiliary devices such as valves, heating means with means for mechanically breaking-up or deflecting the jet after discharge, e.g. with fixed deflectors; Breaking-up the discharged liquid or other fluent material by impinging jets with fixed deflectors
  • B05B1/267—Nozzles, spray heads or other outlets, with or without auxiliary devices such as valves, heating means with means for mechanically breaking-up or deflecting the jet after discharge, e.g. with fixed deflectors; Breaking-up the discharged liquid or other fluent material by impinging jets with fixed deflectors the liquid or other fluent material being deflected in determined directions
• • 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
  • B05C11/00—Component parts, details or accessories not specifically provided for in groups B05C1/00 - B05C9/00
  • B05C11/02—Apparatus for spreading or distributing liquids or other fluent materials already applied to a surface ; Controlling means therefor; Control of the thickness of a coating by spreading or distributing liquids or other fluent materials already applied to the coated surface
  • B05C11/04—Apparatus for spreading or distributing liquids or other fluent materials already applied to a surface ; Controlling means therefor; Control of the thickness of a coating by spreading or distributing liquids or other fluent materials already applied to the coated surface with blades
• • 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
  • D21H25/00—After-treatment of paper not provided for in groups D21H17/00 - D21H23/00
  • D21H25/08—Rearranging applied substances, e.g. metering, smoothing; Removing excess material
  • D21H25/10—Rearranging applied substances, e.g. metering, smoothing; Removing excess material with blades

Definitions

• the present invention relates to a coater according to the preamble of claim 1 and a coating method according to the preamble of claim 8.
• the coating mix is applied to the surface of a moving web of paper from an applicator chamber which is filled with the coating mix and is located upstream from the doctor blade on the web travel.
• the rear end of the applicator chamber is formed by the doctor blade mounted on a blade support beam, while the front end is formed by a so-called meter- ing strip.
• Supportedly running on a backing roll the paper web to be coated forms the third side of the applicator chamber.
• the coating mix adheres to the surface of the moving web when the web travels over the application zone that begins at the metering strip and ends at the doctor blade.
• the width of the application zone is defined by the end seals of the applicator chamber.
• the coating mix is introduced into the applicator chamber via an infeed slit adapted to the bottom of the chamber.
• the amount of the return flow is about 95 % of the overall volumetric flow of the coating mix pumped into the applicator chamber.
• the purpose of the reverse-direction flow is to curtail the entry of the boundary air layer traveling on the web surface into the application zone, assure even distribution of the coating mix flow and a sufficiently high coat replacement rate in the applicator chamber and keep the outflow gap between the metering strip and the web free from obstructions.
• the amount of return flow can be adjusted by way of controlling the distance of the metering strip from the paper web. Also the construction of the applicator chamber may be varied in order to modify the flow conditions within the chamber.
• runnability of a shor -dwell coater is superior in regard to other coater types, thus making it highly preferred particularly in on-machine application. Its good runnability is based on a low application pressure and a short dwell time and zone length, the latter terms referring to the time from the instant of coating mix applica- tion to the instant of doctoring and, respectively, to the web travel from the point of application to the point of doctoring.
• the coating mix layer applied to the web surface contains solids slurried in water. After application, the coat applied to the web surface develops a superficial layer having a higher solids content. The relative thickness of this high-solids layer increases when the water of the applied coating mix is absorbed after application into the fiber of the underlying sheet of the base web. With a higher solids content of the applied coat and the resultant reduced flowability of the same, the force required for doctoring the applied coat increases. Respectively, the higher the solids content of the applied coat on the web, the greater will be the thickness of the coat remaining on the web surface after doctoring.
• doctoring is performed by means of, e.g., a zero-angle doctor blade immediately after application, the solids content of the coating mix layer on the web surface is initially low, which means that the coat thickness on the web remains small after doctoring.
• the coating mix and the water of the slur ⁇ ed mix do not have much time to soak deep into the fiber of the base web and the mterfiber crevices thereof, whereby the degradation of web strength properties due to the wetting of the base web remains minimal.
• the doctoring force required for leveling the applied coating mix layer is smaller than what is needed in most other application methods, because the solids content of the coat applied to the web is still low during the doctoring step.
• An additional benefit of a short-dwell-time coater is that it is readily adaptable for application of thin coatings.
• the short dwell time causes postswell- mg of base web fiber that occurs only after the doctoring of the applied coat, whereby the surface pro- file of a short-dwell -time coated paper is coarser than that rendered by a great number of other types of coaters .
• the use of the short-dwell-time application technique is limited by streakiness of the coated web surface and inferior cross-machine profile quality of the applied coat.
• wetting line is used for making reference to the cross- machine line along which the base web meets the coating mix being applied.
• Jet application is also hampered by the frequent plugging of the narrow slit of the jet nozzle and the air pocket that develops under the doctor blade, both of these factors tending to degrade the quality of the applied coat. In some cases it may be complicated to arrange the jet nozzle beam sufficiently close to the doctor blade holder beam. Due to the above- described reasons, it is difficult to manufacture a flawlessly functional short-dwell jet applicator.
• the goal of the invention is achieved by virtue of applying the coating mix to the web surface with the help of fan nozzles that have a fanned and vertically flattened spraying pattern and are placed in front of the doctor blade upstream on the travel of the web.
• the operating pressure of nozzles is kept relatively low and, resultingly, the spraying pattern of the nozzles is homogeneous, whereby the flow of coat leaving the nozzles is not atomized in contrast to what takes place in conventional spraying nozzles, for instance.
• nozzles there are disposed a plurality of nozzles over the cross-machine width of the web and the nozzles are mounted on a feed tube which is aligned to extend over the width of the web to be coated and is adapted to supply the coating mix to the nozzles. Also in the machine direction, there may a number of nozzle arrays operating in succession.
• the coater according to the invention is characterized by what is stated in the characterizing part of claim 1.
• the coating method according to the invention is characterized by what is stated in the characterizing part of claim 8.
• the invention offers significant benefits,
• a coater according to the invention has no closed applicator chamber as is conventional in a short-dwell-time applicator, thus allowing the coater to provide a smooth coat even at the highest web speeds exceeding 2000 m/min. Further, the coater according to the invention has an extremely simple construction, which makes it essentially less costly than the conventional jet applicator de- scribed above.
• the nozzle operating pressure of the coater according to the invention is low and thus there is no need for a supply of atomizing air, whereby also the nozzle structure design can be substantially simpler than that of conventional spraying nozzles, for instance.
• the volumetric supply rates and pressures of the coating mix are distributed in a relatively uniform manner between the individual nozzles, whereby also the profile of the coat applied to the web surface becomes uniform.
• the nozzles can be brought closer to the doctor blade than what would be possible for a narrow-slit jet applicator beam, thus permitting the present embodiment to use a short dwell travel if so required.
• the nozzle orifice has a larger diameter than the gap width of a narrow-slit jet nozzle, whereby the plugging tendency of the nozzles is reduced in regard to the performance of a conventional jet applicator nozzle.
• the dwell travel of the web in the coater is readily adjustable. Further, the replacement and cleaning of nozzles is easy, since the entire lightweight feed tube with its nozzles is detachable from the coater station. Also the cleaning of nozzles can be automated if so desired.
• the embodiment according to the invention does not need any straightness compensation for the feed tube inasmuch the line of application from a cross-machine array need not be as straight as is required in a conventional jet applicator, for instance.
• FIG. 1 shows schematically a sectional view of an embodiment of coater according to the invention.
• FIG. 2 shows a linear nozzle array of a coater according to the invention aligned in the cross-machine direction over the web.
• a paper web 1 to be coated which is supported by a backing roll 2, is shown running in the direction indicated by arrow 7.
• a doctor blade 3 is mounted on a blade holder beam 4.
• Nozzles 6 for coating mix application are mounted in a parallel disposition on a coating mix feed tube 5 that is aligned to extend over the width of the web 1.
• the jets 8 exiting the nozzles 6 has a fan-shaped and vertically flattened pattern, thus making the pattern of the jet 8 leaving the nozzle 6 to widen most substantially in the width direction of the web 1.
• the jet 8 emitted from the nozzles 6 is dense, because it is not atomized with the help of a separate atomizing-air supply as is the case in conventional spraying nozzles, for instance.
• the pattern of the jet 8 substantially thin in the travel direction of the web 1 as compared with the broadness of the jet in the width direction of the web 1.
• linear nozzle array refers to a line of at least two nozzles 6 in a parallel disposition in the width direction of the web 1, whereby the nozzles need not necessarily be located at identical distances from the doctoring member 3.
• the number of nozzles 6 needed in the applicator is dependent on such factors as the fan angle of the jet 8 emitted by the nozzles 6 and the distance of the nozzles 6 from the web 1.
• the mutual disposition of the nozzles 6 of a linear array is advantageously about 20-200 mm.
• the feed pressure of the nozzles 6 is relatively low, advantageously less than 10 bar, typically about 0.3- 6 bar.
• the fan angle of the jet 8 leaving the nozzle 6 in the width direction of the web 1 is typically about 15- 150°.
• the required fan angle is determined, among other things, by the feed pressure of the nozzle 6.
• the dwell travel defined as the distance from the point of incidence on the web 1 of the jet emitted by the nozzle 6 to the tip of the doctor blade 3 is advantageously about 20-800 mm.
• the coating mix jet is directed in the travel direction of the web 1 so that the angle between the tangent of the backing roll 2 and the fanned jet at the point of incidence of the jet on the web 1 is advantageously about 20- 90°.
• the distance of the coating mix feed tube 5, with the nozzles 6 mounted thereon, from the surface of the web 1 to be coated can be varied. Additionally, the angle of incidence on the web 1 of the jets 8 emitted by the nozzles 6 can be adjusted by rotating the feed tube 5.
• Coating mix is pumped along the feed tube 5 to the nozzles 6, wherefrom the coating mix is further applied to the surface of the web 1 moving supported on the backing roll 2.
• the excess coating mix is removed from the blade-side surface of the web 1 and the surface of the applied coat is leveled by means of a doctoring member such as a doctor blade 3 mounted on a blade holder beam 4.
• the excess coating mix doctored away from the surface of the web 1 can be returned back to the coating mix circulation.
• the thickness of the applied coat remaining after doctoring can be affected by varying the dwell time.
• the dwell time is made short, the water entrained in the coating mix layer applied to the surface of the web 1 has rather no time to soak into the fiber of the base web, thus making the thickness of the applied coat thin, particularly if a zero-angle doctor blade is used for leveling. If the dwell time is extend- ed, a proportionally larger portion of the water contained in the applied coating mix has time to soak into the base web fiber, whereby also the coating layer remaining particularly after zero-angle doctoring is respectively thicker.
• the doctoring member 3 can be a doctoring bar or air-knife doctor.
• the coating mix can be applied if so desired to an unsupported web or to a web running on a support belt or wire.

Landscapes

• Application Of Or Painting With Fluid Materials (AREA)
• Paper (AREA)
• Coating Apparatus (AREA)

Priority Applications (3)

Applications Claiming Priority (2)

Publications (1)

Family

ID=8555009

Family Applications (1)

Country Status (5)

Cited By (2)

Citations (6)

• 1999
  • 1999-07-01 FI FI991512A patent/FI111911B/sv not_active IP Right Cessation
• 2000
  • 2000-06-19 AU AU54090/00A patent/AU5409000A/en not_active Abandoned
  • 2000-06-19 BR BR0012151-7A patent/BR0012151A/pt not_active Withdrawn
  • 2000-06-19 EP EP00938845A patent/EP1189703A1/en not_active Withdrawn
  • 2000-06-19 WO PCT/FI2000/000547 patent/WO2001002097A1/en not_active Application Discontinuation

Patent Citations (6)

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