FELT TREATMENT - INORGANIC DEPOSIT PREVENTION BY SPRAY TREATMENT

Abstract: This invention relates to an improved press felt conditioning treatment which controls the deposition of particulate substances in papermachine felts. The treatment comprises applying to the felt during paper production an effective inhibiting amount of an aqueous solution containing a pH control agent and a nonionic or anionic surfactant. The surfactant is preferably selected from the group consisting of dodecyl benzene sulfonates, lauryl ether sulfates, octyl phenol ethoxylates, nonyl phenol ethoxylates, dodecyl phenol ethoxylates, primary alcohol ethoxylates, secondary alcohol ethoxylates, ethoxylated polyoxypropylene glycols, dialkyl phenol ethoxylates, polyoxyethylene sorbitan monoester, linear alkylbenzene sulfonic acids, sodium xylene sulfonate, linear olefin sulfonates, fatty amine oxides, phosphate esters, fatty imidazoles, carboxylated derivatives of fatty imidazoles, sulfonated derivatives of fatty imidazoles, fatty amidobetanes, fatty sulphoamido-betanes and mixtures thereof.

Description: FELT TREATMENT - INORGANIC DEPOSIT PREVENTION BY SPRAY TREATMENT FIELD OF THE INVENTION The present invention relates to a method for inhibiting the deposition of particulate materials onto papermachine felts. More particularly, the present invention relates to a novel felt conditioner and method of use thereof to inhibit or prevent the deposition of particulate materials onto papermachine felts in paper grades having an incorporation of filter material such as fine or writing papermaking systems. BACKGROUND OF THE INVENTION The manufacture of paper involves the processing of an aqueous fiber suspension to produce a uniform dry paper sheet. Papermaking operations are always concerned with the problem of controlling deposits, particularly in the sheet pressing stage where the paper web is passed through presses covered with the porous press felts to extract retained water from the web. It is important to extract as much water from the paper web prior to its entering the dryer section since the mechanical removal of water through the press felts is much more cost effective method to dry the paper web than providing steam for dryers. Modern press felts are no longer made of natural woolen materials, but are made of synthetic fibers such as nylon and polyester blends. Among the desirable features of a press felt are the following: freedom from plugging; resistance to matting; permeability for water movement; non-compressible base to provide void volume; - smooth surface to avoid surface imperfections on the paper. A clean felt, having fine pores which are relatively open, is particularly desirable for effective paper manufacture since this allows efficient removal of water from the paper sheets without leaving marks or other imperfections on the paper. However, felts in the press section become filled or plugged with contaminants and require frequent, periodic shutdown and treatment with caustic solutions (i.e. boil-out) or eventual replacement. Felt plugging has become a major problem in modern papermaking operations due to the increased use of recycled water and increased use of recycled paper and a desire to reduce poor size to minimize felt marking. Contaminants which plug felts primarily include inorganic fillers such as clays, precipitated calcium carbonate, ground calcium carbonate, and titanium dioxides. In addition, ionically charged, relatively high molecular weight, water soluble polymers which are employed to enhance retention of cellulosic fibers, fines, and inorganic fillers, form flocculated particulate materials which can be transferred from the surface of the sheet to the press felts. The flocculated particles cannot pass through the fine, porous structure of the modern press felt and become entrapped therein. Particles of latex coating binders such as, polyvinyl acetate or styrene-butadiene rubber are also often found in plugged press felts. Other types of contaminants can include starches, natural wood pitch (fatty esters, fatty and resin acids/salts) cellulosic fiber fines, microbiological contaminants and absorbants, such as talc or bentonite, oil-based defoamers sizing agents and insoluble metal hydroxides. All of these contaminants can be present to some degree based on a variety of factors, such as, the paper machine system temperature, the wood fiber and water sources, time of year, grade of material produced, type and quantity of system additives, pulp production methods and equipment designs and capacities. If not controlled by adequate felt conditioning practices, these inorganic fillers and agglomerated particulate substances can severely impair the ability of the press felts to absorb water thereby reducing production rates and shortening the useful life of the felts. Processes to inhibit the deposition of contaminants in papermaking felts are known in the art. U.S. Patent No. 4,715,931 to Schellhamer et al. discloses a process for inhibiting aluminum hydroxide deposition in papermaking systems which comprises adding to the felts a hydroxylated carboxylic acid. The use of the carboxylic acid in combination with surfactants, such as octyl phenol ethoxylates, nonyl phenol ethoxylates and others listed therein inhibit aluminum hydroxide deposition and associated organic contaminants. U.S. Patent No. 4,861,429 to Barnett et al discloses a process for inhibiting white pitch deposition in felts by treating the felts with an organic, anionic polyelectrolyte. SUMMARY OF THE INVENTION It is an object of this invention to provide a method of treating papermachine felts to inhibit the deposition of particulate contaminants therein and thereby maintain porosity of the the felt. It is another object of this invention to eliminate or reduce off-line felt cleaning (boil-out) with damaging caustic or acid solutions. It is another object of this invention to provide a method of treating papermachine felts to inhibit the deposition of inorganic particles derived from fillers used in the manufacture of fine paper and/or writing paper. It is a further object of this invention to provide a method to inhibit or eliminate the deposition of inorganic particles derived from waste paper containing filler particles. In accordance with the present invention, there has been provided a method for treating papermachine felts to inhibit the deposition of particulate contaminants and to maintain the porosity of the felts comprising contacting the felts in a continuous or intermittant manner during the paper production with an aqueous solution of a pH control agent and a nonionic or anionic surfactant wherein the pH control agent is added to the aqueous solution in an amount sufficient to provide a pH in the range 9 to 13, and wherein the surfactant is present in the aqueous solution in a concentration range 0.01 to 5% on a weight basis. DETAILED DESCRIPTION The present invention relates to an improved press felt conditioning treatment which inhibits or prevents the deposition of particulate substances into press felts. The press felt conditioning treatments of the present invention maintain felt porosity, i.e., they inhibit compaction of the felts, reduce the loss of caliper of the felts which is otherwise caused by wear and compression and thus reduce the frequency of off-line cleaning procedures. More particularly, the present invention relates to the use of an aqueous solution of one or more water soluble nonionic or anionic surfactants in combination with certain pH control agents, which, when applied to papermachine press felts, control or inhibit the deposition of particulate contaminants into the press felts. Suitable surfactants generally include any anionic or nonionic surfactants which are water-soluble at the use concentration and which provide effective wetting at a pH in the range 9 to 13. The surfactants of the present invention which have been found to provide unexpected efficacy when combined with the pH control agents of the invention include, dodecyl benzene sulfonates, lauryl ether sulfates, sodium xylene sulfonate, linear olefin sulfonates, fatty amine oxides, phosphate esters, and mixtures thereof. Other suitable surfactants include, but are not limited to, octyl phenol ethoxylates, nonyl phenol ethoxylates, dodecyl phenol ethoxylates, primary alcohol ethoxylates, secondary alcohol ethoxylates, ethoxylated polyoxypropylene glycols, dialkyl phenol ethoxylates, polyoxyethylene sorbitan monoester, and linear alkybenzene sulfonic acids. These are more fully disclosed in U.S. Patent No. 4,861,429 which is incorporated herein in its entirety. Suitable surfactants also include amphoteric surfactants such as fatty imidazoles and their carboxylated and sulfonated derivatives, fatty amidobetanes. fatty sulphoamido-betanes. While these surfactants are cationic under acid pH conditions, they are anionic under normal papermaking conditions. Suitable pH control agents include, but are not limited to meta-silicateε, phosphates, carbonates, and the like, and mixtures thereof. Preferred pH control agents include sodium meta-silicate, sodium phosphate and sodium carbonate, and is most preferably sodium meta-silicate. The aqueous felt conditioner solutions of the present invention are prepared by diluting the surfactants in water to a final concentration in the range of 100 to 2000 pp and then adding the pH control agents in an amount effective to provide a pH in the range 9 to 13, preferably 10 to 12, and most preferably 11 to 12. Alternatively, the surfactant and pH control agent can be premixed in a ratio to give the desired pH and surfactant concentration by dilution with water. Fresh water may be used to prepare the aqueous felt treatment solution or optionally, recycled white water may be used. The aqueous felt conditioner solution generally contains between 30 ppm to 2000 ppm surfactant, preferably 50 ppm to 1500 ppm. The felt conditioners of the invention may optionally include a solubilizing agent to aid in wetting and/or one or more chelants for facilitating use in high hardness waters. Suitable solubilizing agents include glycols such as e.g., hexylene glycol or diethylene glycol, glycol ethers such as e.g., ethylene glycol mono-butyl ether. Suitable chelants are those capable of stabilizing calcium ion under high pH conditions and include, but are not limited to, ethylenediamine tetraacetic acid (EDTA) , nitrilo triacetic acid (NTA) , diethylenetriamine pentaacetic acid (DTPA) , and the like. The present invention also relates to a method for inhibiting the deposition of various organic and inorganic contaminants in a felt in a press section of the papermaking system wherein the felt is prone to such deposition. In accordance with the present invention, the felt conditioners of the present invention are applied by metering or spraying the press felts into the fresh water shower system, preferable a low pressure shower. These felt conditioners are generally applied to the sheet side of the felts, preferably with a fan shower. The felt conditioners are preferably sprayed at low pressures, i.e., in the range 2 to 7 kg/cm 2 , preferably 3 to 5 kg/cm 2 . It is considered an important feature of the present invention that the felt conditioners of the present invention are applied by metering into one or more fresh water showers which are directed onto the press felt on its run the point where the felt no longer contacts the paper sheet and the suction box, preferably between the press nip and the suction (Uhle) box which is utilized for dewatering the felt. The application of an aqueous solution of a pH control agent and one or more nonionic or anionic surfactants onto press felts in this area has been found to produce felt conditioning effectiveness which is unexpected based upon the conditioning effects of these felt conditioners in other areas or of the individual components. For typical papermaking processes, the felt conditioners of this invention can be sprayed or metered intermittently during the paper making operation, typically 2 to 3 times per day, at an actives concentration of 1 to 5 percent on a weight basis. Alternatively, the felt conditioners can be sprayed or metered continuously at an actives concentration of 0.01% to 0.2%, preferably at an active concentration of 0.1% on a weight basis. The total dosage amount of aqueous felt treatment applied to the felts is also considered an important feature of the present invention. In general, best results have been obtained when at least 6 liters of felt treatment is applied per square meter of felt per minute (l/m 2 /min) , preferably between 6 to 10 l/m 2 /min. The felt conditioners of this invention are particularly useful for treating felts used in the manufacture of paper grades having an incorporation of filler materials such as e.g., fine paper or writing paper. These paper grades typically contain large quantities of inorganic fillers such as clay, calcium carbonate, titanium dioxide, and the like. The felt conditioners of this invention are also effective in papermaking systems using thermomechanical pulp (TMP) which typically has a high level of fines which are known to plug press felts. The following examples are provided to illustrate the present invention in accordance with the principles of this invention, but are not to be construed as limiting the invention in any way except as indicated in the appended claims. All parts and percentages are by weight unless otherwise indicated. Example 1 This example demonstrates the effectiveness of the felt conditioning treatments of the present invention for maintaining the porosity of felts in the press section of a paper making machine which manufactured printing grade paper. The paper machine in this example used 100% kraft pulp furnish. The furnish contained a relatively high dosage amount of clay as filler. Before contacting the paper, the openness of the paper machine felts is measured by passing the felt over a vacuum box to remove excessive water. The vacuum readings which are necessary to draw air through the felts are representative of the openness of the paper machine felts. Typical vacuum readings for a clean felt are normally about 12 inches of Hg. Vacuum readings of greater than 16 inches Hg generally indicate that caustic cleaning of the felts is necessary. An aqueous felt conditioning solution was prepared containing 4.5% sodium meta-silicate, 14.5% of a mixture of anionic surfactants (sodium dodecylbenzene sulfonic acid and lauryl ether sulfate) , 6% chelant (EDTA) and 4% wetting agent (diethylene glycol) . The felt conditioner was metered into a spray bar prior to the first Uhle box at a pressure of 2-4 kg/cm 2 and a water flow of 40 liters/min. Conditions Prior to the Treatment Program Prior to treatment with the present felt conditioners, the paper machine was shut down, on average, every two to three days for caustic batch cleaning of the felt for clay removal. The average production loss per shut down for caustic cleaning was 12 tons. Conditions After Treatment Program The initial trial period was 20 days during which three shut downs were required for caustic cleaning. Two of the shut downs were as a direct result of the interruption of the spray application of the felt conditioners of the invention. An 18 day period was realized without any shut downs with continuous spray application of the present felt conditioners. Uhle box vacuums remained below 16 inches Hg throughout the 18 day period. All other paper machine and sheet standards remained constant. Scanpro testing involves determining the water content of the felts in grams H 2 0/m 2 of felt. A higher measure of water content in the felt is indicative of higher felt porosity. In addition, the Scanpro testing is a measure of the uniformity of water content across the entire cross- section of the felt. It is considered important that press felts have a uniform water content profile across the felt. Scanpro testing was conducted on the treated felts and were compared to previous results of other untreated felts and indicated that the treated felts had not only a higher water content, i.e., a significant porosity improvement over the previous untreated felts, but also indicated a more uniform water content profile across the felt than the previous untreated felts. At the time the felt was changed, the felt was reported to be in good condition. Example 2 This example demonstrates the effectiveness of the felt conditioning solutions of the present invention for maintaining felt porosity of press felts in paper machines used to manufacture directory grade paper. The furnish comprised 40% stone groundwood pulp, 50% thermomechanical pulp (TMP) and 10% Kraft pulp. Paper additives include talc and starch. The procedure in Example 1 was repeated in this example. Conditions Prior to Treatment Program This paper machine experienced downtime, on average, 437 hours per year for caustic washing of the felts to remove fines, thus requiring the consumption of about 10,000 kg per year of caustic chemicals. At an average production rate of 125 tons per day (TPD) , this amount of downtime results in considerable loss of production. In addition to downtime production losses, approximately 250 tons per year (TPY) of production loss was attributable to irregular moisture profiles across the felts. High pressure showers (8 to 12 kg/cm 2 ) were required for felt cleaning to remove fines. The average felt life for the previous 13 felts was 36.5 days. Conditions After Treatment Program Treatment of the papermachine felts with the conditioning agents of this invention resulted in a complete elimination of unscheduled downtime for caustic cleaning. The caustic cleaning of the felts at the second press section was reduced 50%. The vacuum box readings remained constant throughout the entire trial period, and Scanpro results indicated uniform water content profiles resulting in no lost paper production. The pressure of the high pressure showers was reduced to 8 kg/cm 2 . The felt life was increased to 57 days.

Claims: CLAIMS: 1. A method for treating papermachine felts which continuously circulate between a paper sheet contact stage and a suction box stage to maintain the porosity of the felts comprising contacting the felts during papermaking operations with a felt conditioner which further comprises an aqueous solution of a pH control agent and a nonionic or anionic surfactant wherein the pH control agent is present in an amount sufficient to provide a pH in the range 9 to 13, and wherein the surfactant is present in a concentration range of 30 ppm to 2000 ppm on a weight basis and wherein the felts are contacted with the felt conditioner at a point after the felt no longer contacts the paper sheet and at a point before the felt enters the suction box stage. 2. A method according to Claim 1 wherein the surfactant is selected from the group consisting of dodecyl benzene sulfonates, lauryl ether sulfates, octyl phenol ethoxylates, nonyl phenol ethoxylates, dodecyl phenol ethoxylates, primary alcohol ethoxylates, secondary alcohol ethoxylates, ethoxylated polyoxypropylene glycols, dialkyl phenol ethoxylates, polyoxyethylene sorbitan monoester, linear alkybenzene sulfonic acids, sodium xylene sulfonate, linear olefin sulfonates, fatty amine oxides, phosphate esters, fatty imidazoles, carboxylated derivatives of fatty imidazoles, sulfonated derivatives of fatty imidazoles, fatty amidobetanes, fatty sulphoamido-betanes and mixtures thereof. 3. A method according to Claim 1 wherein the pH control agent is selected from the group consisting of meta- silicates, phosphates, carbonates, and mixtures thereof. 4. A method according to Claim 3 wherein the pH control agent is selected from the group consisting of sodium meta- silicate, sodium carbonate and sodium phosphate. 5. A method according to Claim 1 wherein the pH is in the range 10 to 12. 6. A method according to Claim 1 wherein the pH is in the range 11 to 12. 7. A method according to Claim 1 wherein the aqueous solution is applied to the felts during paper production in an intermittent spray, two to three times per day at an actives concentration of 1 to 5 percent on a weight basis. 8. A method according to Claim 1 wherein the aqueous solution is applied to the felts in a continuous spray at an actives concentration of 0.01 to 0.2 percent on a weight basis. 9. A method according to Claim 7 wherein the aqueous solution is sprayed at a rate of at least 6 liters per square meter of felt per minute. 10. A method according to Claim 8 wherein the aqueous solution is sprayed at a rate of at least 6 liters per square meter of felt per minute.

Inventors: DUFFY ROBERT JAMES, KERSHAW PHILIP, DUFFY, ROBERT, JAMES, KERSHAW, PHILIP
Applicants: GRACE W R & CO, W.R. GRACE & CO.-CONN.
Application year: 1995
Main classification: D21F1
IPC codes: D21F1, D21F7