Abstract:
Pitch and sticky accumulation on papermaking fabric is reduced by applying a solution or dispersion of a cationic composition to the fabric. The cationic composition includes a cationic polymer, a nonionic surfactant and an anionic surfactant and retains a net cationic charge. Preferably, this is continuously applied during the papermaking process.

Description:
FIELD OF THE INVENTION  
       [0001]     During the manufacture of paper, a web of paper fibers derived from wood sources and also from recycled paper sources is typically formed on the surface of a fabric mesh which is used to drain excess water from the web. The drained web of fibers is then introduced into a series of rolls, some of which are covered by continuous belts of fabric or felt. As the paper web is fed through the rolls and between the layers of felt, pressure is applied to the paper web which forces water from the web.  
         [0002]     The fabrics are composed of various types of polyester or polyamide filaments of varying diameters or denier. The fabrics may be woven together into a mesh or needled into a mesh base to form a batt. It is highly desirable that these fabrics remain clean during their service lives. A clean fabric will facilitate proper drainage of water from the paper web. Proper drainage of water from the paper web will allow the paper web to attain optimum strength and allow it to be dried more easily in subsequent paper manufacturing operations. Improved paper strength results in fewer paper breaks, allowing for uninterrupted machine operation and is a desired characteristic of the final paper product.  
         [0003]     The paper fiber web, which is carried by the forming fabric and press fabrics, often contains undesirable contaminants. These include materials that may come from recycled fiber sources and include: inks, resins, hot melt and pressure sensitive adhesives, styrene butadiene, polystyrene, vinyl acrylates, rubber, waxes, and polyethylene. These materials are commonly known as stickies. Contaminants may also come from natural fiber sources and include: fatty acids salts and their esters, and abietic acid salts and their esters. These materials are commonly known as pitch. Finally, some contaminants are introduced during processing and include: wet strength resins, latexes, vinyl acrylates and paper sizing agents. These contaminants are also known as white pitch. These materials may contaminate the fabrics used to carry the paper web. They may coat the fabrics, impeding drainage and uniform paper formation, or they may completely obstruct the fabric in certain areas causing the appearance of light spots or holes in the paper web which greatly detract from the aesthetic and functional properties of the paper as well as causing the paper to break more easily from that point onward.  
         [0004]     Typically, these contaminants are removed after deposition. Cleaning chemicals and solvents are often used, either continuously or intermittently during the production of paper, or when the papermaking equipment is not in production. These materials have varying degrees of success depending on the nature of the contaminant and the cleaning method employed. In many cases, powerful solvents and caustic materials are needed to remove the contaminants. These negatively impact paper mill wastewater treatment facilities, as well as requiring more stringent occupational health and safety precautions.  
         [0005]     Applying cationic polymers to the surface of papermaking fabrics prevents the accumulation of deposits. Further, anionic surfactants as well as cationic polymers may be separately applied to a papermaking fiber slurry or directly to papermaking surfaces to prevent contamination, as described in Driesbach U.S. Pat. No. 5,556,510. This patent does not disclose the method for making a stable product from a combination of cationic polymer and anionic surfactant, the residual charge on the cationic polymer or the nature of the hydrophilic moieties on the anionic surfactant. In addition, it has been postulated that when cationic polymers alone are applied to a papermaking surface that the cationic polymers adsorb onto the papermaking surface and also attract anionic surfactants from the aqueous component of the fiber slurry or paper web (D. T. Nguyen, TAPPI June 1998). These methods also present problems. Applying an anionic surfactant along with a cationic polymer, as described by Driesbach, presents stability problems. These materials are typically incompatible and will not form a stable mixture. This makes the application of this mixture difficult when applied as either a single product or when the cationic polymer and anionic surfactant are applied separately.  
         [0006]     When only a cationic polymer is applied to a papermaking fabric the efficacy of the polymer is dependent on the nature of the anionic species in the papermaking furnish. This furnish will vary and may diminish the effectiveness of the polymer. According to generally accepted theories, the cationic polymer should nave some cationic nature to ensure that it is suitably attracted to the anionic surface of a papermaking fabric.  
         [0007]     Hence, it would be beneficial for ease of application to have a stable product with a balanced cationic charge that could be applied to a papermaking surface, which would incorporate both a cationic polymer and anionic surfactant with the specific properties needed to impart optimum contaminant resistant properties to the papermaking fabric.  
       SUMMARY OF THE INVENTION  
       [0008]     The present invention is premised on the realization that cationic polymer and anionic surfactants interact to form a hydrophilic layer on a negatively charged surface such as that found in papermaking. By applying such a product to a papermaking surface such as a felt or forming fabric, it is possible to impart a deposition resistance to that surface. This deposition resistance may be achieved by continuously coating the surface of the fabric with a liquid mixture including a cationic polymer, a non-ionic surfactant and an anionic surfactant. The amount of the anionic surfactant relative to the cationic polymer is such that the cationic polymer retains a substantial portion of its positive charge, generally 1.0%-50%.  
         [0009]     More preferably, the cationic polymer is a polydiallyldimethylammonium chloride and the anionic surfactant is a carboxylated linear alcohol, although a wide variety of other polymers and surfactants can be employed. The ability to apply a single stable product with specially selected anionic surfactants is a benefit in terms of ease of application and uniformity of the anionic surfactants which are complexed by the cationic polymer. Without limiting the generality of this invention, it has been discovered that anionic surfactants which contain a hydrophilic portion and, more specifically, a portion of the molecule which consists of ethylene oxide monomer adducts, is particularly well suited for the purposes of the invention. Alternatively, a sulfo oxo moiety may be used in the surfactant to achieve similar results.  
         [0010]     The invention will be further appreciated in light of the following detailed description. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]     The FIGURE is a diagrammatic of a papermaking process. 
     
    
     DETAILED DESCRIPTION  
       [0012]     The present invention is a method of improving the deposition resistance of papermaking fabric. This is accomplished by applying the composition of the present invention directly to the papermaking fabric by spraying or with applicator rolls. The composition of the present invention comprises a cationic polymer in combination with a non-ionic surfactant and an anionic surfactant.  
         [0013]     A wide of variety of cationic polymers can be used in the present invention. In general, these cationic polymers must be water soluble and are formed from cationic monomer units or both cationic and non-ionic monomer units. By the term cationic, it is meant that the monomer unit includes a group that either carries a positive charge or that has basic properties and can be protonated under mild acidic conditions.  
         [0014]     Suitable polymers include cationic addition and condensation polymers. The polymer will generally be composed partially of vinyl addition polymers of cationic and optionally non-ionic vinyl monomers.  
         [0015]     One preferred class is the quaternary ammonium polymers. These quaternary ammonium polymers are generally derived from ethylenically unsaturated monomers containing a quaternary ammonium group or obtained by reaction between an epihalohydrin and one or more amines such as those obtained by reaction between a polyalkylene polyamine and epichlorohydrin or by reaction between epichlorohydrin, dimethyl amine and either ethylenediamine or polyalkylene polyamine.  
         [0016]     Cationic polymers are disclosed in U.S. Pat. No. 5,368,694 the disclosure of which is incorporated herein by reference. Generally, with all these, the molecular weight must be such that the polymer is water soluble or dispersible.  
         [0017]     Other suitable cationic polymers include cationized polyacrylamides including polyacrylamides cationized with dimethylsulfate or methyl chloride by the Mannich reactions to varying degrees to achieve varying degrees of cationicity, polymers derived from quaternized dimethyl aminoethylacrylate, dicyanamide-formaldehyde condensates using one or both of formic acid and ammonium chloride as reactants, cationic cellulose starch compounds, carboxylated starch, xanthan gum, guar gum and polyacrylic acid. One preferred cationic polymer is polydiallyldimethylammonium chloride.  
         [0018]     A wide variety of non-ionic surfactants can be used in the present invention. These include ethoxylated fatty alcohols which are either linear or branched and which may have a carbon chain length of anywhere from 8 to 22 carbons. The degree of ethoxylation may vary from 3 moles to 22 moles of ethylene oxide per mole of alcohol. These would include the Rexonic® and Neodol® line of linear alcohol ethoxylates. Ethoxylated adducts of alkyl phenols as well as ethoxylated polyhydric alcohols including sorbitols or sorbitan esters may be used. Additional non-ionic surfactants include polyethylene oxide/polypropylene oxide block copolymers which would include the Pluronic® line of surfactants as well as ethoxylated versions of fatty acids and polyethylene glycol esters of phosphates, polyethylene glycol esters of fatty acids including esters derived from one mole of polyethylene glycol and one or two moles of fatty acids, tristyrylphenol ethoxylates and alkylpolyglycosides.  
         [0019]     Generally the HLB of these surfactants will be from 7 to 18 with a preferred range being from about 11 to 13. Preferred nonionics include Rexonic® N23-6.5 and Neodol™ N23-6.5.  
         [0020]     The third component of the present invention is an anionic surfactant. Suitable anionic surfactants include water soluble or water dispersible alkylarylsulfonates, sulfonated amines and amides, carboxylated alcohol ethoxylates, diphenylsulfonate derivatives, lignin and lignin derivatives, phosphate esters, soaps of process rosin, sulfates and sulfonates of ethoxylated alkyl phenols, sulfates of ethoxylated alcohol, sulfonates of napthalene and alkylnapthalene, polyethoxy carboxylic acid alcohols from the Neodox™ or Sandopan™ line of products, alky ether sulfates, alkyl benzene sulfonates, alkyl sulfonates, alkyl phosphates, alkyl sulfates, alpha olefin sulfonates, diphenyloxide disulfonates sulfosucinnates, ethoxylated sulfosucinnates and succinamates. One preferred surfactant of the present invention is a carboxylic acid capped ethoxylated tridecyl alcohol. A surfactant which incorporates a polyoxytheylene component in addition to an anionic component is particularly suited for this invention in that it allows a stable product to be more easily formulated as well as conferring a hydrophillic property to the papermaking surfaces on which it is applied in conjunction with a cationic polymer.  
         [0021]     Preferably, the composition comprises polydiallyidimethylammonium chloride in combination with trideceth (7) carboxylic acid and linear alcohol ethoxylate such as Rexonic® N23-6.5 or Neodol® N23-6.5. Alternatively, a secondary alkane sulfonate sodium salt based on n-paraffin sodium (C14-C16 Alkyl Sec Sulfonate) such as Hostapur SAS 60 may be used as the anionic surfactant.  
         [0022]     The amount of anionic surfactant to cationic polymer should be established so that the cationic polymer retains a significant portion of its cationic charge. Generally from 10%-80% of its positive charge should be maintained after the addition of the anionic surfactant.  
         [0023]     With only the above three components, the composition will be very acidic. The pH of the composition can be raised by the addition of water soluble bases such as sodium or potassium hydroxide, sodium or potassium carbonate, ammonia, organic amines such as triethanolamine, diethanolamine, monoethanolamine, or morpholine as well as other compatible bases. Sufficient base can be added to establish a desired pH of from about 3 up to about 10 depending on preference for the particular papermaking operation.  
         [0024]     The composition of the present invention will generally include 2% to 20% by weight cationic polymer, 2% to 40% by weight nonionic surfactant, 0.5% to 10% anionic surfactant 0% to 5% base with the remainder water.  
                                                       One preferred formulation is as follows:               Agefloc WT 40HB (40% active)     5%           Rexonic N23-6.5 (100% active)   7.4%           Sandopan DTC Acid (90% active) or   1.1%           Hostapur SAS 60 (60% active)                      
 
 with the remainder water. This is further diluted to obtain the desired application or use concentration. Generally, the use concentration will be 2-10,000 ppm (actives) and, preferably, 30 to 100 ppm actives. 
 
         [0025]     The FIGURE is a diagrammatic depiction of a press felt system for use in the present invention. The press felt system  10  includes an upper press felt run  12 . As shown in the drawing, the paper travels in the direction of arrow  14 .  
         [0026]     Low pressure fan shower  16  and high pressure needle showers  18  apply the treatment agent of the present invention to the return runs  22  of the upper and lower press felt runs. Alternately, coating rollers can be employed. This, of course, is a diagrammatic depiction of a press felt run and is intended merely for use in explaining the present invention.  
         [0027]     The present invention will be further appreciated in light of the following detailed example.  
       EXAMPLE 1  
       [0000]     Mill Type: Linerboard  
         [0000]     Furnish: 100% OCC  
         [0000]     Application Location: Bottom of former before the first sheet side return roll.  
         [0028]     Problem: Stickies would accumulate on the forming fabric usually within 6-24 hours of having been cleaned. These stickies originated from the old corrugated cardboard furnish that was being used. These stickies manifested themselves as large diameter “patches” on the surface of the wire, severely impeding the drainage of the paper slurry on the forming fabric and decreasing sheet quality. The only way to clean them was through the use of an aliphatic solvent cleaner. Other methods which had been tried as traditional passivation chemistry using cationic polymers alone or traditional cleaners either did not work or caused the deposition to occur in other places on the machine. The cost of the program was becoming prohibitive and required an excessive amount of solvent.  
         [0029]     The above preferred formulation was applied to a shower just slightly ahead of where the solvent was being applied at the rate of 100 ml/min and optimized to 60 ml/min. The deposition problem diminished dramatically in an unexpected way such that the solvent cleaning frequency has been reduced to only once per week rather than 2-3 times per day. This has resulted in a solvent use reduction of 90% and a cost reduction of approximately 10%.  
         [0030]     This method is a radical departure from the typical solvent cleaning methods previously used to deal with pitch and stickies. Instead of dissolving the pitch and stickies, this method prevents deposition. This, in turn, reduces the use of solvents, which is desirable in itself. It also reduces cost and improves efficiency.  
         [0031]     This has been a description of the present invention along with the preferred method of practicing the present invention. However, the invention itself should be defined by the appended claims WHEREIN