Paper making and fiber liberation – Processes and products – Non-fiber additive
Reexamination Certificate
2001-05-29
2003-05-06
Nguyen, Dean T. (Department: 3629)
Paper making and fiber liberation
Processes and products
Non-fiber additive
C162S199000, C106S002000
Reexamination Certificate
active
06558513
ABSTRACT:
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention relates to improving release of a paper web from the surface of equipment used in paper making processes. The invention also relates to decreasing the force necessary to remove the paper web from such equipment surfaces and to decreasing deposition of undesirable contaminants on such surfaces. The method of the invention comprises continuously or intermittently applying to such a surface non-aqueous, non-curing hydrocarbon polymer compositions. Preferred non-curing hydrocarbon polymers are polybutenes. The principal use of the present invention is on the surface of rolls used in the press section of the paper making process where application of the non-aqueous, non-curing hydrocarbon polymer compositions also has the advantage of eliminating the need for the large amounts of water typically used. Additionally, the invention could be used on other equipment surfaces of papermaking or paper converting processes where web release or deposition prevention is important. Examples of such equipment surfaces include lump-breaker rolls, couch rolls, uhle box covers, dryer cans, calender rolls, corrugating fluting rolls, papermaking fabrics including those used in through air dryers, fabric carrier rolls, and printing presses.
(2) Discussion of the Background
In the papermaking process, paper is formed into a continuous wet web which is then drained of water in the press section and dried in the dryer section. The web leaves the forming section and enters the press section containing, by weight, roughly 80% water. It exits the press section and enters the dryer section at approximately 60%, by weight, water.
The press section consists of one or more press nips formed between two rotating press rolls that squeeze the sheet as it passes through. Often one of the press rolls forming the nip will be felted and the other will be a relatively hard surface made of ceramic, granite, or a synthetic composite. As the web exits the nip it has a tendency to adhere to the hard, relatively smooth surface of the non-felted press roll. This adhesion requires the paper maker to apply force to the web by running subsequent operations at a higher speed in order to separate the web from the roll surface. Because the wet paper web is of limited strength, the adhesion to the roll can force the web to stretch to the point of causing breaks that disrupt the paper making operation.
The web adhesion to the roll can also cause unwanted materials such as fiber, inorganic fillers, or sticky contaminants to remain as a deposit on the roll surface. This deposit is often referred to as press picking or dusting. Doctor blades are commonly used to mechanically remove the material that has deposited on the roll surface. Doctor blades also protect the press section (felt and rolls) from damage resulting from large wads of paper from web breaks or other matter entering the nip area. It is common practice to directly spray water onto the press rolls prior to the doctor blade to provide lubrication to the roll so that the doctor blades do not cause premature wear of the roll cover. The disadvantage of such water shower is that they bring additional moisture to the web of paper at the press nip, when the goal is to remove water from the web. Additionally, they generate large amounts of waste water requiring treatment.
Roll manufacturers have attempted to improve web release from rolls by imparting some combination of permanent hydrophilic and hydrophobic properties to the roll surface. Such permanent hydrophilic and hydrophobic properties are used to increase release by interrupting the water film at the interface between the roll and the sheet. There are many examples in the patent literature where hydrophobic release agents are permanently added to press rolls. For example, Snellman (CA 2093829) teaches that a ceramic press roll cover can be partially coated with a cured fluoropolymer such as Teflon® to impart release characteristics.
Even with these roll cover modifications, chemical additives are often needed to control deposition or improve release. These chemicals are usually added to the water showers. For example, Murano (JP 11323766) teaches the use of water-soluble cationic polymers added to the shower water before the doctor blade to inhibit press roll dusting or picking. Ichihara (JP 08337988) also teaches the use of a cationic polymer in combination with a cationic surfactant to inhibit pitch deposition by spraying onto paper machine parts.
Some silicone-based materials are also known for preventing press roll adhesion. In one example, U.S. Pat. No. 4,704,776 to Watanabe teaches that the pores of a ceramic press roll cover can be impregnated with a silicone oil, a silicone plastic, or a fluoroplastic to impart release. In another example, U.S. Pat. No. 4,028,172 to Mazzarella teaches a method of controlling picking on wet press rolls through addition of polysiloxane polymers to the paper feed stock before sheet formation or by spraying on the wet web prior to pressing. Two specific types of polysiloxane polymers are taught: a water soluble polydimethylsiloxane polyoxyalkylene ether (a silicone surfactant) copolymer or an aqueous emulsion of polydimethyl siloxane (silicone oil). Silicone specialties manufacturer OSi (brochure 50-001-00, 1995) recommends certain of its silicone oils for anti-blocking applications in paper manufacture and certain of its silicone surfactants and silicone oil emulsions for preventing paper from sticking to rollers and dryers during paper manufacture. However, silicones have the disadvantage of being relatively expensive and have not eliminated the need for water showers on press rolls and the like.
Certain hydrophobic chemicals, typically in the form of aqueous emulsions, are also applied to paper machine equipment such as press rolls to control adhesion. For example, U.S. Pat. No. 5,658,374 to Glover teaches that an oil-in-water emulsion containing an alcohol, a fatty acid or an oil, and lecithin emulsified with a water-soluble or water-dispersible surfactant can be used to control sticky deposition on the surfaces of press rolls, yankee rolls and couch rolls surfaces in papermaking. In another example, U.S. Pat. No. 5,863,385 to Siebott et. al. teaches a process for cleaning and preventing deposition on paper machine parts, including the press section, by treating the surface with an oil-in-water emulsion. The oil phase can be any of several compounds including saturated hydrocarbons, fatty alcohols, fatty acids, fatty acid esters, paraffin oil, mineral oil or poly-alpha-olefins. The concentration of the oil-in-water emulsion in aqueous dilution is preferably 1-25%-weight relative to the aqueous dilution. It is applied at a rate of 20-500 L per hour per meter of the machine's working width. In another example, U.S. Pat. No. 6,139,911 to Vanhecke et. al. teaches the use of aqueous microemulsions for improving the release properties of press rolls where the oil phase is selected from oils, water insoluble surfactants, water insoluble polymers, and waxes. The microemulsion is applied by first diluting it with excess water or by applying it directly in the presence of excess water. When the microemulsion is applied to the press roll in either diluted manner, the emulsion breaks up, causing the release components to deposit on the roll surface as larger macroemulsion size (or greater) particles, which are more efficient at affecting release.
However, such hydrophobic release agents have the disadvantage that they contain surfactants necessary for their preparation. These same surfactants are well known to increase wetting and therefore will tend to increase the hydrophilic nature of the roll surface. Because the web of paper in the press section contains 60-80% water, increasing the hydrophilic nature of the press roll surface will promote adhesional wetting of the paper web to the roll. Thus, when the web is separated from the roll, the separation point will more likely occur within the water layer from t
Hendriks William A.
Pease Jacqueline K.
Hercules Incorporated
Nguyen Dean T.
Samuels Gary A.
LandOfFree
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