Abstract:
A process that can utilize current paper manufacturing facilities by adding consecutive spray apparatuses that can make and/or enhance the manufacture of a multitude of specific paper products on-line, or improve the properties of already formed paper products with consequent spraying steps on-line or off-line.

Description:
FIELD OF THE INVENTION  
       [0001]     This invention relates to paper manufacturing process itself and to paper and board surface enhancement in the paper and board manufacturing processes.  
       BACKGROUND OF THE INVENTION  
       [0002]     The paper is conventionally formed from a suspension of about 0.4% to 1.2% fiber solids (fibers) through a so called head box by spreading the suspension on a moving rotating wire, or a nip, formed by two rotating wires, followed by removing the suspension water as much as possible in consequent process steps through vacuum, pressing and drying.  
         [0003]     During paper web forming process or immediately thereafter, web interior and surfaces will require treatments to bring paper properties to acceptable level. These properties include printability, rigidity, strength and chemical penetration that are achieved through chemical treatment, filling and coating materials, and mechanical doctoring processes, some of which are specific for different paper and board grades.  
         [0004]     To increase paper whiteness and paper printing properties, the first approach is to add fillers, such as kaolin, and mix them together with around 1% fiber solution to reach filler contents typically from 5% to 35% in the final paper or board. However, up to 40% of these fillers go through the forming paper web on a moving wire, ending into recirculation.  
         [0005]     The so called ply-bond between two paper layers is currently achieved by excessive refining of the fibers or by spraying a dilute 2% starch on wire section between the layers. The low solids content is currently needed to minimize aerosol formation and nozzle plugging.  
         [0006]     Paper surface strength and rigidity are accomplished by surface sizing during the paper drying process. The size is typically added by immersing the sheet into the size solution at around 8% solids, or by applying size films with a two roller nip on dry paper sheet surfaces at 8% to 10% consistency. The low consistency causes considerable amount of paper rewetting requiring re-drying. The sheet must be fully dry at the application points as it can not otherwise withstand the mechanical forces around these processes.  
         [0007]     Paper is coated by adding up to 90% excess coating solution on the paper side and doctoring the excess solution to recirculation system. The coating solutions have typically high viscosity with solids from about 45% to 65%. The paper must be fully dry before first coating is applied and must also be dried between the consequent coating solution applications. Wet paper can not withstand the mechanical forces that are higher than with sizing. In this process the coating solution, often at zero initial machine speed, hits the paper web moving at speed up to 1800 meters per minute, accelerates to this speed, and comes to a full stop when up to 90% excess is doctored away for the desired coat weight on the paper or board surface.  
         [0008]     Most of the paper grades are re-moisturized during the drying process to correct for the continuously changing CD moisture profile resulting from the shifting imbalances in the dryer section and slowly changing mechanical conditions on the machine.  
         [0009]     The existing paper making, filling, sizing and coating methods lack the ability to apply a precise amount of material on the sheet to a specific position and can not as such provide means for cross directional (CD) profiling. Among these the paper making process itself has had a best CD profiling capability through a somewhat flexible metal lip opening in the so called Head Box that distributes the flow on a moving wire or wire nip. The lip opening is narrowed or widened through automated mechanical screws or thermally expanding metal bars. Unfortunately the total dynamics of this process at around 1% solids is difficult to master as every move has an impact elsewhere around it. Industry developed several computer algorithms to master the process but this was not enough. The next step was a so called dilution Head Box, where the individual Head Box sections are diluted with r circulating water to achieve the desired material amount to a specific position. This was a major improvement for the industry but it still lacks the ability to fully control the process especially against the still shifting fiber orientation that will at the end impair the product quality.  
         [0010]     This invention of paper fiber spraying allows complete control over the fiber orientation at any position, and additionally it allows a precise spray layer based engineering of the paper sheet in such a way that none of the current methods can do and provides the first time the ability to make fully engineered paper utilizing the variety of raw materials maximally.  
         [0011]     The use of original spraying technology for paper re-moisturizing turned to a huge success with advancement of computer technology in early 70&#39;s. Spraying of other materials has periodically been tested e.g. for paper surfacing but the results were largely unsuccessful. Even the latest applicator methods as presented in the U.S. Pat. No. 4,944,960 with improvements shown in the European Patent EP 0682571 still lack their first commercial application. The paper manufacturing itself has also been tried with gap sprayer technology but so far without success. One of the key components for fiber spraying is the nozzle shown in the recent U.S. patent application Ser. No. 10/455,194 by Kangas.  
         [0012]     For spraying the nozzle must be energy efficient, the spraying direction must essentially be downwards with gravity when other liquids than water are sprayed, the aerosols must be controlled, the spray pattern must be stable at varying nozzle flow rates for CD profiling, and in some cases the spray fog that has attached onto the substrate has to be doctored with a specific doctoring device according to this invention. The systems are illustrated in  FIGS. 12, 13 ,  14  and  15 .  
         [0013]     The benefits of this invention can be summarized as follows: 
        All paper and board filling, sizing, coating, and barrier surfacing can be accomplished in a simple and efficient way using this spraying process.     All paper and board grades can be manufactured using this spraying process leading to sizeable savings in the energy consumption of their manufacturing.     Paper and board can now be engineered through spray-layer approach according to this invention.     The system poses no limitations to the paper machine operating speed and is a major improvement in paper machine operating efficiency and productivity.     Lower strength and other raw materials can be utilized more efficiently throughout the paper making process.     The aerosol release to work environment is eliminated. Aerosols are formed whenever material is sprayed in room air environment and in film splitting typically found in size presses and similar paper pigmenting process.        
 
       OBJECTS OF THE INVENTION  
       [0020]     An object of the invention is to provide a process using current paper manufacturing facilities and consecutive spray apparatuses that enhance the manufacture of a multitude of specific paper products on-line, or improve the properties of already formed paper products with consequent spraying steps.  
       BRIEF SUMMARY OF THE INVENTION  
       [0021]     According to this invention, one spray apparatus with one or several consecutive separately supplied rows of nozzles applies a continuous seamless and fully controllable spray mist and particle mat on a moving wire or paper web using a battery of nozzles that use steam and other gases as a propellant that can be hot or cold, and are sometimes made wet with water or chemicals.  
         [0022]     One spray unit is generally a closed, but bottomless box, with ventilation option to capture aerosols and excess gases to the purification and material recirculation, as desired. This box is located so that its opening faces, in close proximity, the receiving surface, that is typically a moving paper manufacturing cloth, called wire, or paper web, or a nip where two of these wires are combined together from opposite sides, a combination nip of a wire and a already formed paper web, or a fully formed paper web. A complete paper manufacturing line can have several of these units after each other in various positions, in vertical to horizontal locations, but generally above the web, in the paper machine to fulfill the required material additions in paper manufacturing and surfacing processes that are needed to complete a specific paper or board product that is being made. Each spray box can have its own cross directional and machine directional control systems that can be integrated to a centralized paper machine control system.  
         [0023]     The formed spray is directed towards the opening from inside the box and further towards the mowing wire of paper web in close proximity of it. In case that the receiving element is a wire, the fineness of this wire is selected to capture most of the sprayed materials like paper manufacturing fibers. Only a few of the first fibers originating from the first spray unit that are sprayed on the wire have a change passing through the wire to the recirculation system while the rest will accumulate on a already formed fiber mat. In later spray units all materials and chemicals are accumulating on the moving paper web. The accumulation can sometimes be assisted with a vacuum applied on the opposite side of the wire or web but that is not the requirement.  
         [0024]     Each nozzle row forms a new consecutive layer of evenly distributed material or chemical on top of the previous layer starting from the original substrate that can be a paper web or a forming wire. This allows for a complete engineering of all paper products to maximize their most desired properties. This can be done to a precision that is far above the capabilities of current technology.  
         [0025]     The spraying environment inside the box, as described in this invention, prevents the viscous materials from solidifying inside this apparatus. The box can also be sealed both mechanically and/or dynamically to prevent the ambient air from entering the box and the potential aerosols from exiting the box. The optimal spray environment is generated by maintaining about 100% humidity inside the box and preventing or balancing the external air from entering the box. This semi condensing environment is generated and controlled by the humidity and water content in the propellant gas, and the amount of exhaust from the box into the gas purification system. A layered approach with temperature controlled liquid inside the box walls is needed for some applications, where the inner wall of the box might be chrome or Teflon coated, or have a specific liquid repelling inner surface built e.g. the way silica particles are positioned on a surface and affixed in exacting sub-millimeter positions. Additionally steam and gas/air blades and mechanical seals can be used in securing the open areas to prevent air from entering and aerosols from escaping the box. Chemical aerosols are harmful to people and equipment, especially electronics.  
         [0026]     The typical operating conditions for the current paper manufacturing unit processes in Table 1 are compared to the same after spray retrofitting:  
                                               TABLE 1                           Unit Operating Consistencies in       Percent with Current or this Spray Technology                Current   Spray Technology            Unit Process   Technology   Range   Typical               Paper Web Forming   0.4-1.5%   0.4-15%   3-8%       Ply-Bond (starch spray   1.5-4%   1.5-18%   5-18%       between web layers)       Sizing on Wire Section (or before)   0.4-1.5%   0.4-18%   5-18%       Filling on Wire Section (or before)   0.4-1.5%   0.4-50%   10-50%       Sizing on Dryer Section   8-10%   8-18%   12-18%       Pigmenting/Pre-coating on Dryer   8-10%   8-45%   12-45%       Section       Coating on Dryer Section   45-65%   45-65%   45-65%       Coating on Off Machine Coater   45-65%   45-65%   45-65%       Specialties, including   10-65%   10-65%   10-65%       microcapsules &amp; barriers       Sheet Re-Moisturizing   Water   Water   Water                  
 
         [0027]     The lower the solids at application the higher the amount of material and water is re-circulating in the system resulting to material losses, or when application is done on formed paper web the more-water has to be removed by mechanical means or evaporated. Regardless of the case the current manufacturing methods are low in productivity, waste raw materials, consume unnecessarily large amount of energy and are environmentally unfriendly.  
         [0028]     The system is controlled with generally commercially available technology. However, as some applications operate at elevated temperature areas the associated electronics and motors are protected through a separate compartment that can be insulated and cooled by blowing air or by installing cooling pipes. Each nozzle has a double control/information collection feature that allows the operator to know the status of the nozzle without actually seeing it. This feature is achieved by the excessive information process steps: The sprayed material is taken from the pressure controlled main distribution line into nozzle line through a specific orifice; Line pressure is measured again after the orifice; Step-motors with position indicators control the liquid valves leading to the nozzles. The humidity or liquid into the motive gas line of the nozzle are controlled separately as needed.  
         [0029]     According to this invention the paper surface doctoring without removing any material is a very important step especially with coating, and is done by specially designed doctors or rollers as shown in  FIGS. 4, 5 ,  6  and  7 . The main feature of these doctors is their ability to secure touching of the paper web, applying minimum loading to the web, and allowing the applied material to pass by without removing any, only allowing the material to shift around slightly. This non-metering effect is impossible to achieve with any the current doctoring devices with solid backing devices that form rigid gaps. In this invention the hydrodynamic balance between the applied force from the doctoring device and the existing viscous liquid layer are carefully tuned to maximize the evenness in this layer without destroying it. In essence all the above doctoring devices are hydroplaning, supported by this balance, and push any excess liquid into any valleys while escaping the contact with the underlying solid paper web.  
         [0030]     The drying of the paper can be done with the current technology and practices in the industry. Sometimes the spray unit can be followed by special Teflon or chrome coated cylinders enforced with infrared dryers before them, followed by high speed air dryers, or any of the multitudes of drying systems used by the paper industry. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0031]      FIG. 1  is a spray box unit containing four spray nozzle rows  
         [0032]      FIG. 2  is a vertical installation alternative for a spray unit  
         [0033]      FIG. 3  is another vertical installation alternative for a spray unit  
         [0034]      FIG. 4  is a gas jet based doctoring device  
         [0035]      FIG. 5  is a non-metering doctor blade with two examples shown  
         [0036]      FIG. 6  is a hydroplaning roll with web support from the back side  
         [0037]      FIG. 7  is a another hydroplaning roll alternative without web support from back side  
         [0038]      FIG. 8  is a schematic of a nozzle control system  
         [0039]      FIG. 9  is a schematic showing a spray liquid supply system  
         [0040]      FIG. 10  is a schematic for motive gas supply and mixing gases like e.g. air and steam  
         [0041]      FIG. 11  is an excess gas washer  
         [0042]      FIG. 12  is a schematic showing paper web forming examples by spraying  
         [0043]      FIG. 13  is a schematic showing examples of ply-bonding followed by web surfacing  
         [0044]      FIG. 14  is a schematic showing web surfacing examples on dryer section  
         [0045]      FIG. 15  is a schematic showing web surfacing examples below the dryer section 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0046]      FIG. 1  comprises of a Spray Box Unit consisting of four distinct spray sections that include the spray area  3000 , spraying equipment with nozzle bodies  3100 , space for control systems  3200 , and an attachment  7  for collecting the excess gases  23 . The outer housing for sections  3100  and  3200  is case dependent and they are not shown in further Figures. The spray area  3000  is limited by the substrate  1  to be sprayed generally a paper web or fine mesh wire, a generally adjustable gap  21  on incoming side, adjustable gap  22  that is modified by a separate closure mechanism  4 ,  5 ,  6 , or  7 , the inner wall  2  that is generally specially coated with materials including i.e. Teflon but can include a double wall cooled construction, and an opening allowing the excess gases  23  to be removed from the box parallel and in close proximity of the wall containing the tips of the spray nozzles  3 . The spraying equipment section  3100  contains the nozzles  3 , spray material distribution piping  31 , motive gas distribution pipe  370  and connecting tubing and control valves generally as shown in details in  FIG. 8 . The separated section  3200  that is cooled with coolants including air houses all electronic control and communication means including e.g. the step motors for control valves  35  in  FIG. 8 . The excess gases combined in a manifold type piping  7  and led through the transport piping  71 , aided by pressurized gas driven valve  73  controlled ejector  72  to a separate gas washing  74  system shown in  FIG. 11 .  
         [0047]      FIG. 2  comprises of a system that applies spray onto vertically running paper web  1 , supported by roller  13  creating high quality paper surface required in most demanding paper and board coating applications by evening the coated surface in two consequent doctoring steps  4 ,  5 , and  7 . The first step is achieved with a hydroplaning, rotating sweat-roll  6  that is internally cooled  611 ,  612  or heated to desired temperature, generally between 10 and 80 degrees C. The second step is done with various specially designed doctoring devices as shown in FIGS.  4  to  7  separately. The gap  600  doses the hydroplaning roll inside the spray area. The backing wire  111  supported by rollers  11 , and sometimes aided by vacuum  112  will allow for the most flexible doctoring pressure utilization of the hydroplaning roll  6 . An Infrared dryer  10  is shown here as an example of a typical first drying apparatus after a coating station to solidify the coating layer before further drying with heated cylinders.  
         [0048]      FIG. 3  comprises a generally similar system as in  FIG. 2  but now the spraying itself is performed more downwards as may be needed in some cases.  
         [0049]      FIG. 4  comprises of a non touch cold/hot, or moist gas  40  driven controllable  41  doctoring device  4  and roller  11  that are not used to remove material from the surface of the web  1  and doctoring device  4  can either precede or trail roller  11 . The doctoring effect only shifts material in a small scale laterally on the surface. The soft touch is further enforced by a gap  42  that with backing roller  11  prevents the hard solid nip doctoring effect, created by hard backing devices used in the air knife coaters in the paper industry. However, if the non-metering doctoring device  4  is installed on paper machine wire section roller  11  can be omitted as the system is used in this specific area mainly to prevent aerosols from escaping the spray box.  
         [0050]      FIG. 5  comprises of two examples of solid blade non-metering devices  5  and roller  11 , and  5  and table  12  that are different from conventional industry doctors as they can not remove material from the web  1  surface but can shit it laterally in a small scale. This inability to remove material is secured as there is no solid backing device as would be needed. The material shifting power is controlled by the gap of  52  that together with web tension impacts the material shifting capability of this doctoring device. The non-metering device consists of a replaceable blade  501  that can be either rigid or soft and easily bending, support mechanism  502 ,  507  and  508  and load changing system  504 , steam, air or wet gas  40  injection distributor  505  used when needed. When wet gas like steam is injected it condenses immediately as a thin solid layer on the top of the coating improving further the quality of paper surfacing. However, if the sprayed materials are temperature sensitive, like paper coatings, this distributor  505  can also be fed with stable water mist generated by ultrasonic mist generator  400  and then ducted  401  to this distributor. It may sometimes also be desirable to replace the typical doctor shower nozzles, not shown, with fine water mist provided through a separate mist distributor  402  to secure wetting of the tip of the non-metering doctor blade  501 .  
         [0051]      FIGS. 6 and 7  show the rotating temperature controlled hydroplaning sweat/hot rollers  6  and their backing devices  11 ,  111 ,  12  located behind the moving paper web  1 . The hydroplaning of a roller starts when its speed is lowered about 10% below the speed of the paper web. At this critical balance point all film splitting and aerosols will disappear. However, when installed according to  FIGS. 2 and 3  the rollers can also operate as normal rollers pressing the sprayed liquid into the web as needed, and the following non-metering devices  4 ,  5 , or  7  will be sufficient to even the additional liquid ribbon structures forming after these rollers. The desired surface temperature of the hydroplaning roller  6  is controlled as desired by pumping temperature controlled water or oil through, as practiced in different applications in the industry. The cold temperature causes the roll to sweat, or initiate condensation, preventing materials like coatings from sticking on its surface, and when heated materials like starches become fluid and will not solidify like they do on cold surfaces. Sweat roll  6  can be adjusted both horizontally  62  and vertically  61  allowing the maximum control for its loading. In case a backing wire  111  is used the web  1  itself is released from most of the stresses caused by the hydroplaning effect, and in some cases a slight vacuum under the wire  111  will secure that the sheet is not negatively impacted. In case a solid backing device or backing table  12  is utilized a gas flow  40  will prevent any friction load to web  1  caused by the said backing device.  
         [0052]      FIG. 8  comprise control logic of an individual nozzle  3  when combined in this invention with a position sensing step motor, driving control valve  35 , and when connected to a computer the system can do internal nozzle flow diagnostics without operator input. In this illustration the tube  37  provides the motive gas, and  38  illustrates the spray pattern out of nozzle. The spray liquid  32  is brought in by main distribution pipe  31  and liquid is taken to the nozzle line through a restriction or orifice  331  and further via tubing  33  to the control valve. The pressure sensor  34  determines together with pressure sensor in the main distribution pipe the flow into the nozzle  3 . As the valve characteristics, step motor position and pressure sensor  34  already determine the flow a rising discrepancy initiates a self cleaning process and warns the operator of a potential impending problem. Tubing  36  takes the fluid into nozzle, and this line can include another restrictor or orifice  332  depending on the nozzle type.  
         [0053]      FIG. 9  comprises of a spray storage and supply arrangements into the nozzles  3  in  FIG. 8 . The system starts from storage tank  39  that is supplied through a feed line  391 . From the tank the liquid is pumped by pump  394  through line  392  to two parallel filters  395  and continuation of line  292  to the nozzle distribution header  31  and excess returned back to the storage tank through continuation of line  392 . A constant pressure is maintained in the nozzle distribution header  31  and the pressure and flow are measured and controlled with related valves  313  and pressure  311  and flow  312  sensors. The system is cleaned with wash water  393  and flushed clean through the lines  390 . In case that paper making fibers are sprayed the distribution header can be equipped with a mixing device  333 , in its simplest form a helical screw, but can include other mechanical mixers and ultrasound to keep the fiber suspension fluidized and the intake restrictors in tubing  33  clear,  FIG. 8 . In this latter case the filters  395  are replaced with appropriate screens.  
         [0054]      FIG. 10  comprises the motive gas header  370  and mixing  372  of two gases  377  and  376  including the potential condensate removal  375  arrangements. Both incoming gas lines are monitored for incoming pressure  311 , condensate is removed when needed and flow is controlled with valve with a check valve preventing the backflow to these separate systems. After mixing the resulting gas is monitored for temperature and pressure in line  371  leading into the distribution header that is providing the motive gas for individual nozzles  3  through lines  37 .  
         [0055]      FIG. 11  comprises of a excess gas washer  74  and cleaning system. The gas cleaning starts from the spray box unit extraction manifold  7  and continues through the air piping  71  and gas ejector pump  72  to excess gas cleaning cyclone where the gases are cleaned by washing showers  30  and then released to the atmosphere through duct  76 . The washing water is collected at the bottom of the cyclone and recycled  740  by pumping  741  to initial washing in the manifold collection tube  30 , and washing liquid in the cyclone  742 . Excess  75  will be released from the process to effluent treatment only during process start-ups and shut downs.  
         [0056]      FIG. 12  comprises of exemplary spray units  20  in paper manufacturing using rotating fine mesh wires  2011 ,  2031  as substrate to spray fibers to form the initial web  1 . After this further fiber spraying is done on already formed web covering the wire. Various rollers  201 ,  202 , and  203  accommodate the movement of the rotating wire while the cleaning showers  30  keep the wire mesh clean for the new fiber mat. The finished web is then transferred to the dryer section with a vacuum aided roller  204  and felt  2041  pressing against the roller  201  and picking up the web.  
         [0057]      FIG. 13  comprises of exemplary spray units  20  surfacing the already existing paper web in the machine wire  2031 ,  2011  section. The machines can have one or several wire units depending on how they were built at the time. This featured machine is making a two ply paper and the top and the bottom plies are manufactured the conventional way using standard Head Boxes  200  to manufacture the top and bottom web layers. The manufactured two web layers are then glued together with a spray unit  20  just before the webs get together between the roller  203  and wire  2011 . After that another spray unit  20  adds i.e. a white mineral layer on top of the combined sheet preparing the sheet for further treatments like coating.  
         [0058]      FIG. 14  comprises of exemplary spray units  20  first (from left to right) sizing the paper web in a two sided sizing and then finishing it by two sided coating. The infrared dryer units  10  are followed each spray unit to solidify the sprayed material onto the surface. Roller  101  turns the web for sizing/treating facing the other side before drying on cylinders  100 . The rollers  202  turn the sheet for coating facing the other side before final drying on the drying cylinders  100 .  
         [0059]      FIG. 15  comprises of exemplary spray units  20  first used in the machine basement if there is no possibilities to install the units on the dryer section itself. The floors of the building are marked as  2000 . The system can be built a myriad of ways on existing and new paper machines based on concepts shown in  FIGS. 1, 2  and  3  and each case has to be assessed separately.