Patent Application
20110146924
Toweling for automatic dispensers similar to those disclosed in U.S. Pat. No. 6,766,977 must reconcile several competing requirements—it must be reasonably lightweight and low in caliper yet feel substantial and reasonably soft when used for hand drying. As disclosed in United States Patent Application 2006/0289133 an MD bending length of at least about 3.5 cm may be required for the most reliable dispensing. It should provide sufficient absorbency and absorbent rate that most users will be satisfied to dry their hands with a single sheet as by far the most important requirement is that it have a low cost in use. Accordingly, cost constraints strongly encourage the use of recycle fiber which adds immense difficulties in obtaining a satisfactory combination of properties as recycled fibers not only contain higher proportions of fines but are also often more ribbonlike than cylindrical, the ease with which ribbonlike fibers bond strongly to each other tending to result in an undesirably strong sheet, compromising the softness of the sheet, but more importantly, making it difficult to attain satisfactorily high values of absorbency and wipe dry properties. After all, if users typically require several sheets to achieve satisfactory dryness, the raison d'etre of the automated dispenser is entirely defeated, at least from the point of view of the customer who is typically very sensitive to cost in use. To further aggravate matters, rather than employing through drying techniques, which typically imply both higher operating costs and higher capital costs, it is highly desirable economically to dry the sheets, particularly those containing recycle fibers, on a Yankee cylinder; but, again, this often conflicts with obtaining the desired absorbency. Accordingly sheets dried on a Yankee are usually creped to open up the sheet, adding softness and absorbency to what otherwise would be largely unsatisfactory for absorbent purposes. Traditionally, toweling grades have either been creped wet or dry, with dry creping often being conducted at consistencies of 95% and more while wet creping is more typically conducted at consistencies of between around 50% to 80%. When sheets are creped from Yankee cylinders, adhesive is typically used to secure the web to the Yankee. Typically, creping is accomplished using any of a variety of combinations of a very wide variety of adhesives and additives including but far from limited to polyacrylamide, polyaminoamide, polyvinylalcohol or polyamide epichlorohydrin resins along with release agents to carefully modulate the degree of adhesion between the web and the Yankee (see for example, U.S. Pat. No. 6,511,579). Similarly, a wide variety of creping configurations have been suggested.
The present inventors have discovered that toweling with surprisingly high absorbency can be attained using a furnish comprising a major proportion of recycle furnish if that furnish is creped:
More particularly, the present invention relates to a method of moist creping absorbent paper base sheet by: forming a nascent web comprising at least a major portion, on a length-weighted basis, of flattened ribbonlike cellulosic fibers (as observed in the dry state); applying a creping adhesive coating comprising an admixture of polyvinyl alcohol and a polyamide crosslinked with epichlorohydrin to a Yankee dryer; passing the nascent web through a nip defined between a suction pressure roll and said Yankee dryer; adhering the nascent web to said Yankee dryer with a pressure controlled by controlling the loading between said suction pressure roll and said Yankee dryer; drying the nascent web on said Yankee dryer to a moisture content corresponding to a sheet temperature (immediately prior to the creping blade) of between 225° F. and 255° F. (107° C. and 124° C.) preferably ranging from about 230° F. up to about 250° F. (110° C. to 121° C.); creping the nascent web sheet at a sheet temperature (immediately prior to the creping blade) of between 225° F. and 255° F. (107° C. and 124° C.) from said Yankee dryer with an undulatory creping blade bearing against said Yankee dryer to form a moist biaxially undulatory web, the contact area between said undulatory creping blade and said Yankee dryer defining an undulatory ribbon shape across the width of said Yankee dryer; and thereafter drying said moist biaxially undulatory web to form a sheet having a geometric mean breaking length of from about 900 m to about 1350 m. Preferably, the steam pressure within said Yankee dyer, the hood parameters, the Yankee speed, creping adhesive composition and the pressure with which the suction pressure roll bears against the Yankee dryer are controlled such that: the geometric mean breaking length of the resulting web is between 1000 m and 1250 m, the basis weight of the dry biaxially undulatory web is less than 30 lbs/3000 ft2; the caliper of the web exceeds 48 mils per 8 sheets; for unbleached toweling, the specific SAT absorbency (also known as WAC, water absorbent capacity) of the biaxially undulatory base sheet is at least 2.20 g/g and the WAR (“water absorbency rate”) is less than 50 seconds; while for sheets having an ash content exceeding 1.5% such as for bleached towels or white toweling, the SAT is at least 2.0 g/g and the WAR is less than 55 seconds. For best dispensing in connection with an automatic dispenser, it is preferred that the MD bending length of the resulting web is at least 3.0 cm. In a more preferred embodiment, the specific SAT absorbency of the unbleached biaxially undulatory base sheet is at least 2.3 g/g, the basis weight of the dry biaxially undulatory web is between 24 and 30 lbs/3000 ft2; the caliper of the web exceeds 50 mils per 8 sheets; and the WAR is less than 45 seconds. For good anti-tabbing performance, it is preferred that the CD wet tensile measured by the Finch cup method is at least 650 g/3″, preferably at least about 700 g/3″, more preferably 750 g/3″, most preferably 800 g/3″. In the most economical embodiments, the web comprises at least about 75%, more preferably at least about 90%, on a length-weighted basis of flattened ribbonlike fibers.
Another preferred embodiment relates to a method of moist creping absorbent paper base sheet comprising the steps of: forming a nascent web comprising at least a major portion, on a length-weighted basis, of flattened ribbonlike cellulosic fibers; applying a creping adhesive coating comprising an admixture of polyvinyl alcohol and a polyamide crosslinked with epichlorohydrin to a Yankee dryer; passing the nascent web through a nip defined between a suction pressure roll and said Yankee dryer; adhering the nascent web to said Yankee dryer with a controlled pressure between said suction pressure roll and said Yankee; drying the nascent web on said Yankee dryer to a moisture content corresponding to a sheet temperature (immediately prior to the creping blade) between 225° F. and 255° F. (107° C. and 121° C.), preferably ranging from about 230° F. (110° C.) up to about 250° F. (121° C.); creping the nascent web from said Yankee dryer at a sheet temperature between 225° F. and 255° F. (107° C. and 124° C.), preferably ranging from about 230° F. (110° C.) up to about 250° F. (121° C.) with a creping blade bearing against said Yankee dryer to form a moist web, and thereafter drying said moist web to form a sheet having a geometric mean breaking length of from about 900 m to about 1350 m. Still more preferably, the geometric mean breaking length of the toweling is from about 950 m to about 1300 m. Most preferably the creping temperature is from about 235° F. (113° C.) to about 245° F. (118° C.) and the geometric mean breaking length of the toweling is from about 1100 m to about 1250 m.
Another preferred embodiment relates to a method of moist creping absorbent paper base sheet comprising the steps of: forming a nascent web comprising at least a major portion of flattened ribbonlike cellulosic fibers; applying a creping adhesive coating to a Yankee dryer; passing the nascent web through a nip defined between a suction pressure roll and said Yankee dryer; adhering the nascent web to said Yankee dryer with a pressure controlled by controlling the loading between said suction pressure roll and said Yankee; drying the nascent web on said Yankee dryer to a moisture content corresponding to a sheet temperature (immediately prior to the creping blade) of between 230° F. and 250° F. (110° C. and 121° C.); creping the nascent web at a sheet temperature of between 230° F. and 250° F. (110° C. and 121° C.) from said Yankee dryer with an undulatory creping blade bearing against said Yankee dryer to form a moist biaxially undulatory web, the contact area between said undulatory creping blade and said Yankee dryer defining an undulatory ribbon shape across the width of said Yankee dryer; and thereafter drying said moist biaxially undulatory web.
Another preferred embodiment relates to a method of moist creping absorbent paper base sheet comprising the steps of: forming a nascent web comprising at least a major portion of cellulosic fibers; applying a creping adhesive coating comprising an admixture of polyvinyl alcohol and a polyamide crosslinked with epichlorohydrin to a Yankee dryer; passing the nascent web through a nip defined between a suction pressure roll and said Yankee dryer; adhering the nascent web to said Yankee dryer with a controlled pressure loading between said suction pressure roll and said Yankee; drying the nascent web on said Yankee dryer to a moisture content corresponding to a sheet temperature (immediately prior to the creping blade) of between 230° F. and 250° F. (110° C. and 121° C.); creping the nascent web at a sheet temperature of between 230° F. and 250° F. (110° C. and 121° C.) from said Yankee dryer with an undulatory creping blade bearing against said Yankee dryer to form a moist biaxially undulatory web, the contact area between said undulatory creping blade and said Yankee dryer defining an undulatory ribbon shape across the width of said Yankee dryer; and thereafter drying said moist biaxially undulatory web and recovering a web comprising at least about 1.5% ash by weight and at least about 10% non-hardwood fibers having an average fiber length of less than about 0.2 mm on a length-weighted basis.
Another preferred embodiment relates to a method of moist creping absorbent paper base sheet comprising the steps of: forming a nascent web comprising at least a major portion of recycled cellulosic fibers; applying a creping adhesive coating comprising an admixture of polyvinyl alcohol and a polyamide crosslinked with epichlorohydrin to a Yankee dryer; passing the nascent web through a nip defined between a suction pressure roll and said Yankee dryer; adhering the nascent web to said Yankee dryer with a pressure controlled by controlling the loading between said suction pressure roll and said Yankee; drying the nascent web on said Yankee dryer to a moisture content corresponding to a sheet temperature (immediately prior to the creping blade) of between 230° F. and 250° F. (110° C. and 121° C.); creping the nascent web at a sheet temperature of between 230° F. and 250° F. (110° C. and 121° C.) from said Yankee dryer with a creping blade bearing against said Yankee dryer to form a moist web; thereafter drying said moist web; and recovering an web comprising at least about 1.5% ash by weight and at least about 10% non-hardwood fibers having an average fiber length of less than about 0.2 mm on a weight weighted basis.
Another preferred embodiment relates to a method of moist creping absorbent paper basesheet comprising the steps of forming a nascent web comprising at least a major portion of recycled cellulosic fibers; applying a creping adhesive coating to a Yankee dryer; passing the nascent web through a nip defined between a suction pressure roll and said Yankee dryer; adhering the nascent web to said Yankee dryer with a pressure controlled by controlling the loading between said suction pressure roll and said Yankee; drying the nascent web on said Yankee dryer to a moisture content corresponding to a sheet temperature (immediately prior to the creping blade) of between 230° F. and 250° F. (110° C. and 121° C.); creping the nascent web at a sheet temperature of between 230° F. and 250° F. (110° C. and 121° C.) from said Yankee dryer with an undulatory creping blade bearing against said Yankee dryer to form a moist biaxially undulatory web, the contact area between said undulatory creping blade and said Yankee dryer defining an undulatory ribbon shape across the width of said Yankee dryer; thereafter drying said moist biaxially undulatory web; and recovering a web comprising at least about 1.5% ash by weight and at least about 10% non-hardwood fibers having an average fiber length of less than about 0.2 mm on a weight weighted basis.
The present invention relates to an extremely economical method of forming paper toweling from a very low cost furnish comprising at least a major proportion of recycled fiber, more preferably at least about 75% recycled fiber as determined on a length-weighted basis and most preferably over 90% recycled fiber. In general, recycled fiber has only one attribute recommending it for use in making absorbent toweling—low cost. Recycled fibers generally become rather flattened and ribbonlike making it quite easy to form overly strong, relatively nonporous sheets which are less than ideally-suited for toweling as they tend to have low absorbency and low softness. Further, recycled furnishes tend to have large proportions of fines and typically include a considerable amount of ash. Fines also contribute to excessive strength in the sheet, while the presence of ash is thought by many to, in some instances, interfere with drainage of water from the furnish during the sheet forming process. Inasmuch as the drainage length on most paper machines is fixed, reduction in the use of sufficient water to ensure good formation often contributes to a “papery feel”. We are able to counter this papery feel, at least in part, by use of an undulatory creping blade. Further, those recycled papers containing large amounts of ash are generally sold at a discount relative to lower ash sources. As shown hereinafter, the method of the present invention ameliorates these undesirable qualities of recycled furnish making it possible to achieve levels of absorbency and softness equaling or surpassing that of many previously known grades of toweling made from recycled fiber.
Terminology used herein is given its ordinary meaning consistent with the exemplary definitions set forth immediately below; mg refers to milligrams and m2 refers to square meters and so forth. Unless otherwise specified, test specimens are prepared under standard TAPPI conditions, that is, conditioned in an atmosphere of 23°±1.0° C. (73.4°±1.8° F.) at 50% relative humidity for at least about 2 hours.
Throughout this specification and claims, when we refer to a nascent web having an apparently random distribution of fiber orientation (or use like terminology), we are referring to the distribution of fiber orientation that results when known forming techniques are used for depositing a furnish on the forming fabric. When examined microscopically, the fibers give the appearance of being randomly oriented even though, depending on the jet to wire speed, there may be a significant bias toward machine direction orientation making the machine direction tensile strength of the web exceed the cross-direction tensile strength.
Unless otherwise specified, “basis weight”, BWT, bwt and so forth refers to the weight of a 3000 square foot ream of product. Consistency refers to percent solids of a nascent web, for example, calculated on a bone dry basis. “Air dry” means including residual moisture, by convention up to about 6% for paper. A nascent web having 30 percent water and 70 percent bone dry pulp has a consistency of 70 percent.
The term “cellulosic”, “cellulosic sheet” and the like is meant to include any product incorporating papermaking fiber having cellulose as a major constituent. “Papermaking fibers” include virgin pulps or recycle (secondary) cellulosic fibers or fiber mixes comprising cellulosic fibers. Fibers suitable for making the webs of this invention include: nonwood fibers, such as cotton fibers or cotton derivatives, abaca, kenaf, sabai grass, flax, esparto grass, straw, jute hemp, bagasse, milkweed floss fibers, and pineapple leaf fibers; and wood fibers such as those obtained from deciduous and coniferous trees, including softwood fibers, such as northern and southern softwood kraft fibers; hardwood fibers, such as hardwood, maple, birch, aspen, or the like. Papermaking fibers can be liberated from their source material by any one of a number of chemical pulping processes familiar to one experienced in the art including sulfate, sulfite, polysulfide, soda pulping, etc. The pulp can be bleached if desired by chemical means including the use of chlorine, chlorine dioxide, oxygen, alkaline peroxide and so forth. The products of the present invention may comprise a blend of conventional fibers (whether derived from virgin pulp or recycle sources) and high coarseness lignin-rich tubular fibers, such as bleached chemical thermomechanical pulp (BCTMP). “Furnish” and like terminology refers to aqueous compositions including papermaking fibers, optionally wet strength resins, debonders and the like for making paper products.
Throughout this specification and claims where the term “recycle fiber” is used, we are referring to fiber having the typical characteristics of recycled fiber, that at least a major portion, preferably over 60%, more preferably over 70%, and most preferably over 80% of the fibers, as determined on a length-weighted basis, exhibit the flattened ribbon like configuration typical of fibers that have been reused. In some cases, sheets made from recycle fibers can be recognized as such based on the presence of at least 10%, as determined on a length-weighted basis, of non-hardwood fines under 0.2 mm in length and at least about 1.5% ash in the finished sheet. In most cases, all three criteria will be satisfied; but percentage of flattened ribbonlike fiber and/or percent fines should be considered controlling for the purposes of this application as indicated by the context. Unless otherwise indicated, “major portion”, “over X %” and like terminology as used herein refers to length-weighted fiber length distribution of the pulp. Unless otherwise specified, the OpTest Fiber Quality Analyzer (FQA) from OpTest Equipment, Hawkesbury, Ontario, Canada, Model No. Code LDA 96, should be utilized to determine fiber length distribution. The analyzer is operated at standard settings, that is, the settings are for fibers 0.4 mm to 10 mm in length with curl indices from 0.5 to 10. The FQA measures individual fiber contour and projected lengths by optically imaging fibers with a CCD camera and polarized infrared light.
Calipers and or bulk reported herein may be measured at 8 or 16 sheet calipers as specified. The sheets are stacked and the caliper measurement taken about the central portion of the stack. Preferably, the test samples are conditioned in an atmosphere of 23°±1.0° C. (73.4°±1.8° F.) at 50% relative humidity for at least about 2 hours and then measured with a Thwing-Albert Model 89-II-JR or Progage Electronic Thickness Tester with 2-in (50.8-mm) diameter anvils, 539±10 grams dead weight load, and 0.231 in/sec descent rate. For finished product testing, each sheet of product to be tested must have the same number of plies as the product as sold. For testing in general, eight sheets are selected and stacked together. For base sheet testing off of winders, each sheet to be tested must have the same number of plies as produced off the winder. For base sheet testing off of the papermachine reel, an assemblage of single plies must be used. Sheets are stacked together aligned in the MD. Bulk may also be expressed in units of volume/weight by dividing caliper by basis weight.
MD bending length (cm) is determined in accordance with ASTM test method D 1388-96, cantilever option. Reported bending lengths refer to MD bending lengths unless a CD bending length is expressly specified. The MD bending length test was performed with a Cantilever Bending Tester available from Research Dimensions, 1720 Oakridge Road, Neenah, Wis., 54956 which is substantially the apparatus shown in the ASTM test method, item 6. The instrument is placed on a level stable surface, horizontal position being confirmed by a built in leveling bubble. The bend angle indicator is set at 41.5° below the level of the sample table. This is accomplished by setting the knife edge appropriately. The sample is cut with a one inch JD strip cutter available from Thwing-Albert Instrument Company, 14 Collins Avenue, W. Berlin, N.J. 08091. Six (6) samples are cut 1 inch×8 inch (2.54 cm×20.32 cm) machine direction specimens. Samples are conditioned at 23°±1° C. (73.4° F.±1.8° F.) at 50% relative humidity for at least two hours. For machine direction specimens the longer dimension is parallel to the machine direction. The specimens should be flat, free of wrinkles, bends or tears. The Yankee side of the specimens are also labeled. The specimen is placed on the horizontal platform of the tester aligning the edge of the specimen with the right hand edge. The movable slide is placed on the specimen, being careful not to change its initial position. The right edge of the sample and the movable slide should be set at the right edge of the horizontal platform. The movable slide is displaced to the right in a smooth, slow manner at approximately 5 inch/minute (12.7 cm/minute) until the specimen touches the knife edge. The overhang length is recorded to the nearest 0.1 cm. This is done by reading the left edge of the movable slide. Three specimens are preferably run with the Yankee side up and three specimens are preferably run with the Yankee side down on the horizontal platform. The MD bending length is reported as the average overhang length in centimeters divided by two to account for bending axis location. Bending length refers to MD bending length unless specified otherwise.
Absorbency of the inventive products is measured with a simple absorbency tester. The simple absorbency tester is a particularly useful apparatus for measuring the hydrophilicity and absorbency properties of a sample of tissue, napkins, or towel. In this test a sample of tissue, napkins, or towel 2.0 inches (5.08 cm) in diameter is mounted between a top flat plastic cover and a bottom grooved sample plate. The tissue, napkin, or towel sample disc is held in place by a ⅛ inch (0.32 cm) wide circumference flange area. The sample is not compressed by the holder. De-ionized water at 73° F. (23° C.) is introduced to the sample at the center of the bottom sample plate through a 1 mm diameter conduit. This water is at a hydrostatic head of minus 5 mm. Flow is initiated by a pulse introduced at the start of the measurement by the instrument mechanism. Water is thus imbibed by the tissue, napkin, or towel sample from this central entrance point radially outward by capillary action. When the rate of water imbibation decreases below 0.005 gm water per 5 seconds, the test is terminated. The amount of water removed from the reservoir and absorbed by the sample is weighed and reported as grams of water per square meter of sample or grams of water per gram of sheet. In practice, an M/K Systems Inc. Gravimetric Absorbency Testing System is used. This is a commercial system obtainable from M/K Systems Inc., 12 Garden Street, Danvers, Mass., 01923. WAC or water absorbent capacity, also referred to as SAT, is actually determined by the instrument itself. WAC is defined as the point where the weight versus time graph effectively has a “zero” slope, i.e., the sample has stopped absorbing. The termination criteria for a test are expressed in maximum change in water weight absorbed over a fixed time period. This is basically an estimate of zero slope on the weight versus time graph. The program uses a change of 0.005 g over a 5 second time interval as termination criteria; unless “Slow SAT” is specified in which case the cut off criteria is 1 mg in 20 seconds.
Water absorbency rate or WAR, is measured in seconds and is the time it takes for a sample to absorb a 0.1 gram droplet of water disposed on its surface by way of an automated syringe. The test specimens are preferably conditioned at 23°±1° C. (73.4±1.8° F.) at 50% relative humidity. For each sample, four 3×3 inch (7.62×7.62 cm) test specimens are prepared. Each specimen is placed in a sample holder such that a high intensity lamp is directed toward the specimen. 0.1 ml of water is deposited on the specimen surface and a stop watch is started. When the water is absorbed, as indicated by lack of further reflection of light from the drop, the stopwatch is stopped and the time recorded to the nearest 0.1 seconds. The procedure is repeated for each specimen and the results averaged for the sample. WAR is measured in accordance with TAPPI method T-432 cm-99.
Dry tensile strengths (MD and CD), stretch, ratios thereof, modulus, break modulus, stress and strain are measured with a standard Instron test device or other suitable elongation tensile tester which may be configured in various ways, typically using 3 or 1 inch (7.62 or 2.54 cm) wide strips of tissue or towel, conditioned in an atmosphere of 23°±1° C. (73.4°±1° F.) at 50% relative humidity for 2 hours. The tensile test is run at a crosshead speed of 2 in/min (5.08 cm/min). Tensile strength is sometimes referred to simply as “tensile”.
GM Break Modulus is expressed in grams/3 inches/% strain. % strain is dimensionless and units need not be specified. Tensile values refer to break values unless otherwise indicated. Tensile strengths are reported in g/3″ at break. GM Break Modulus is thus:
[(MD tensile/MD Stretch at break)×(CD tensile/CD Stretch at break)]½
Tensile ratios are simply ratios of the values determined by way of the foregoing methods. Unless otherwise specified, a tensile property is a dry sheet property.
The wet tensile of the tissue of the present invention is measured using a three-inch wide strip of tissue that is folded into a loop, clamped in a special fixture termed a Finch Cup, then immersed in a water. The Finch Cup, which is available from the Thwing-Albert Instrument Company of Philadelphia, Pa., is mounted onto a tensile tester equipped with a 2.0 pound (0.91 kg) load cell with the flange of the Finch Cup clamped by the tester's lower jaw and the ends of tissue loop clamped into the upper jaw of the tensile tester. The sample is immersed in water that has been adjusted to a pH of 7.0±0.1 and the tensile is tested after a 5 second immersion time using a crosshead speed of 2 in./min (5.08 cm/min). Values are divided by two, as appropriate, to account for the loop.
Wet/dry tensile ratios are expressed in percent by multiplying the ratio by 100.
PLI or pli means pounds force per linear inch.
Sheet temperature is the indicated readout of temperature taken of the sheet on the Yankee immediately prior to the creping blade using a Raynger ST infra-red thermometer with the emissivity setting of the IR thermometer set at 0.95. It should be noted that our data does not agree precisely with the suggested relationship between sheet temperature and moisture content alluded to in U.S. Pat. Nos. 5,494,554 and 5,377,428. We believe that the discrepancy may be explained by the difference in the weight of the web on the Yankees and the furnish composition as those patents concern making tissue (bath or facial) weight sheets from virgin furnish while we are concerned with making towel weight (25-30 lbs/3000 sq. ft. ream) from recycle fiber which may mask the underlying Yankee from the IR thermometer more effectively than in U.S. Pat. No. 5,494,554. It should also be noted that we are making our measurements in the falling rate portion of the drying curve in which the rate of loss of moisture is slowed.
The pulp can be mixed with strength adjusting agents such as wet strength agents, dry strength agents and debonders/softeners and so forth. Suitable wet strength agents are known to the skilled artisan. A comprehensive but non-exhaustive list of useful strength aids include ureaformaldehyde resins, melamine formaldehyde resins, glyoxylated polyacrylamide resins, polyamide-epichlorohydrin resins and the like. Thermosetting polyacrylamides are produced by reacting acrylamide with diallyl dimethyl ammonium chloride (DADMAC) to produce a cationic polyacrylamide copolymer which is ultimately reacted with glyoxal to produce a cationic cross-linking wet strength resin, glyoxylated polyacrylamide. These materials are generally described in U.S. Pat. No. 3,556,932 to Coscia et al. and U.S. Pat. No. 3,556,933 to Williams et al., both of which are incorporated herein by reference in their entirety. Resins of this type are commercially available under the trade name of PAREZ 631 NC by Bayer Corporation. Different mole ratios of acrylamide/DADMAC/glyoxal can be used to produce cross-linking resins, which are useful as wet strength agents. Furthermore, other dialdehydes can be substituted for glyoxal to produce thermosetting wet strength characteristics. Of particular utility are the polyamide-epichlorohydrin wet strength resins, an example of which is sold under the trade names Kymene 557LX and Kymene 557H by Hercules Incorporated of Wilmington, Del. and Amres® from Georgia-Pacific Resins, Inc. These resins and the process for making the resins are described in U.S. Pat. Nos. 3,700,623 and 3,772,076 each of which is incorporated herein by reference in its entirety. An extensive description of polymeric-epihalohydrin resins is given in Chapter 2: Alkaline Curing Polymeric Amine-Epichlorohydrin by Espy in Wet Strength Resins and Their Application (L. Chan, Editor, 1994), herein incorporated by reference in its entirety. A reasonably comprehensive list of wet strength resins is described by Westfelt in Cellulose Chemistry and Technology Volume 13, p. 813, 1979, which is incorporated herein by reference.
Suitable temporary wet strength agents may likewise be included, particularly in special applications where disposable towel with permanent wet strength resin is to be avoided. A comprehensive but non-exhaustive list of useful temporary wet strength agents includes aliphatic and aromatic aldehydes including glyoxal, malonic dialdehyde, succinic dialdehyde, glutaraldehyde and dialdehyde starches, as well as substituted or reacted starches, disaccharides, polysaccharides, chitosan, or other reacted polymeric reaction products of monomers or polymers having aldehyde groups, and optionally, nitrogen groups. Representative nitrogen containing polymers, which can suitably be reacted with the aldehyde containing monomers or polymers, includes vinyl-amides, acrylamides and related nitrogen containing polymers. These polymers impart a positive charge to the aldehyde containing reaction product. In addition, other commercially available temporary wet strength agents such as PAREZ 745, manufactured by Bayer, can be used, along with those disclosed, for example in U.S. Pat. No. 4,605,702.
The temporary wet strength resin may be any one of a variety of water-soluble organic polymers comprising aldehydic units and cationic units used to increase dry and wet tensile strength of a paper product. Such resins are described in U.S. Pat. Nos. 4,675,394; 5,240,562; 5,138,002; 5,085,736; 4,981,557; 5,008,344; 4,603,176; 4,983,748; 4,866,151; 4,804,769 and 5,217,576. Modified starches sold under the trademarks CO-BOND® 1000 and COBOND® 1000 Plus, by National Starch and Chemical Company of Bridgewater, N.J. may be used. Prior to use, the cationic aldehydic water soluble polymer can be prepared by preheating an aqueous slurry of approximately 5% solids maintained at a temperature of approximately 240° F. (116° C.) and a pH of about 2.7 for approximately 3.5 minutes. Finally, the slurry can be quenched and diluted by adding water to produce a mixture of approximately 1.0% solids at less than about 130° F. (54° C.).
Other temporary wet strength agents, also available from National Starch and Chemical Company are sold under the trademarks CO-BOND® 1600 and CO-BOND® 2300. These starches are supplied as aqueous colloidal dispersions and do not require preheating prior to use.
Temporary wet strength agents such as glyoxylated polyacrylamide can be used. Temporary wet strength agents such glyoxylated polyacrylamide resins are produced by reacting acrylamide with diallyl dimethyl ammonium chloride (DADMAC) to produce a cationic polyacrylamide copolymer which is ultimately reacted with glyoxal to produce a cationic cross-linking temporary or semi-permanent wet strength resin, glyoxylated polyacrylamide. These materials are generally described in U.S. Pat. No. 3,556,932 to Coscia et al. and U.S. Pat. No. 3,556,933 to Williams et al., both of which are incorporated herein by reference. Resins of this type are commercially available under the trade name of PAREZ 631 NC, by Bayer Industries. Different mole ratios of acrylamide/DADMAC/glyoxal can be used to produce cross-linking resins, which are useful as wet strength agents. Furthermore, other dialdehydes can be substituted for glyoxal to produce wet strength characteristics.
Suitable dry strength agents include starch, guar gum, polyacrylamides, carboxymethyl cellulose and the like. Of particular utility is carboxymethyl cellulose, an example of which is sold under the trade name Hercules CMC, by Hercules Incorporated of Wilmington, Del. According to one embodiment, the pulp may contain from about 0 to about 15 lb/ton (0 to 7.5 kg/tonne) of dry strength agent. According to another embodiment, the pulp may contain from about 1 to about 5 lbs/ton (0.5 to 2.5 kg/tonne) of dry strength agent.
Suitable debonders are likewise known to the skilled artisan. Debonders or softeners may also be incorporated into the pulp or sprayed upon the web after its formation. The present invention may also be used with softener materials including but not limited to the class of amido amine salts derived from partially acid neutralized amines. Such materials are disclosed in U.S. Pat. No. 4,720,383. Evans, Chemistry and Industry, 5 Jul. 1969, pp. 893-903; Egan, J. Am. Oil Chemist's Soc., Vol. 55 (1978), pp. 118-121; and Trivedi et al., J. Am. Oil Chemist's Soc., June 1981, pp. 754-756, incorporated by reference in their entirety, indicate that softeners are often available commercially only as complex mixtures rather than as single compounds. While the following discussion will focus on the predominant species, it should be understood that commercially available mixtures would generally be used in practice.
In many cases, a suitable softener material may be derived by alkylating a condensation product of oleic acid and diethylenetriamine. Synthesis conditions using a deficiency of alkylation agent (e.g., diethyl sulfate) and only one alkylating step, followed by pH adjustment to protonate the non-ethylated species, result in a mixture consisting of cationic ethylated and cationic non-ethylated species. A minor proportion (e.g., about 10%) of the resulting amido amine cyclize to imidazoline compounds. Since only the imidazoline portions of these materials are quaternary ammonium compounds, the compositions as a whole are pH-sensitive. Therefore, in the practice of the present invention with this class of chemicals, the pH in the head box should be approximately 6 to 8, more preferably 6 to 7 and most preferably 6.5 to 7.
Quaternary ammonium compounds, such as dialkyl dimethyl quaternary ammonium salts are also suitable particularly when the alkyl groups contain from about 10 to 24 carbon atoms. These compounds have the advantage of being relatively insensitive to pH.
Biodegradable softeners can be utilized. Representative biodegradable cationic softeners/debonders are disclosed in U.S. Pat. Nos. 5,312,522; 5,415,737; 5,262,007; 5,264,082; and 5,223,096, all of which are incorporated herein by reference in their entirety. The compounds are biodegradable diesters of quaternary ammonia compounds, quaternized amine-esters, and biodegradable vegetable oil based esters functional with quaternary ammonium chloride and diester dierucyldimethyl ammonium chloride which are representative biodegradable softeners.
In some embodiments, a particularly preferred debonder composition includes a quaternary amine component as well as a nonionic surfactant.
In
We have found that we can correlate the absorbency of web 118 closely with the creping temperature and the geometric mean breaking length of web 118 which is in turn strongly influenced by the pressure or pressures applied to web 118 as it is adhered to and passes around Yankee 124. If the degree of compaction is such that the geometric mean breaking length of web 118 exceeds about 1350 meters, we find that absorbency suffers greatly. In particular, we control the geometric mean breaking length of web 118 to between about 1000 and 1300 meters by controlling the level of compaction applied to web 118 along with the amount type of wet strength agents refining applied to the furnish. Preferably the geometric mean breaking length of web 118 after it is dried ranges from about 1050 meters up to about 1250 meters with a particular “sweet spot” ranging from about 1100 meters and about 1250 meters. By controlling geometric mean breaking length and sheet temperature to fall with the ranges described while using a PVOH/epichlorohydrin cross-linked polyamide creping adhesive and an undulatory blade, we are able to obtain over 20% improvement in specific SAT absorbency as compared to an otherwise comparable wet creping process. By way of comparison, a competitive wet creped brown towel exhibits a GM breaking length of 1393 meters and a specific SAT absorbency of 2.14 g/g while a competitive bleached or white towel exhibits a specific SAT of 1.82 g/g at a breaking length of 1802 meters.
After removal from Yankee, moist web 118 is preferably enveloped in sandwich 142 formed between two fabrics so that residual moisture therein can be removed as sandwich 142 passes around internally heated cans 144, 146, 148, 150 and 152 before being wound onto reel 154. Often a very large number of cans may be used; oftentimes over a dozen or more cans will be used. It is not strictly necessary to envelope moist web 118 in a sandwich as it passes around the array of dryer cans. In some cases, the sheet itself may be unsupported as it passes around each can in the array or the sheet may be carried on a single fabric and therefore contact alternate cans in configurations well known in the prior art.
Because we are able to decrease the dry strength more than is generally practicable with wet creping, we are able to increase the wet strength of the sheet while still maintaining comparable softness to stronger wet creped products enabling us to achieve increases in wet strength which are perceivable by the user at the same time as we achieve user perceptible increases in absorbency.
The creping adhesive used in the present invention comprises an aqueous admixture of polyvinyl alcohol and a polyamide crosslinked with an epihalohydrin such as epichlorohydrin. Suitable creping adhesives comprise an aqueous solution of polyvinyl alcohol, and a thermosetting cationic polyamide resin. In the practice of this invention, we carefully monitor sheet temperature prior to creping to ensure that sufficient moisture remains in the sheet at the time of creping to obviate the need for a plasticizer which would otherwise typically be used in the case of dry creping. The creping adhesive is typically applied as a solution containing from about 0.1 to about 1 percent solids, the balance being water. The suitable thermosetting cationic polyamide resins are the water-soluble polymeric reaction product of an epihalohydrin, preferably epichlorohydrin, and a water-soluble polyamide having secondary amine groups derived from polyalkylene polyamine and a saturated aliphatic dibasic carboxylic acid containing from about 3 to 10 carbon atoms. The amount of polyvinyl alcohol can be from about 1 to about 80 weight percent, more specifically from about 20 to about 60 weight percent on a solids basis. The water soluble polyamide contains recurring groups of the formula:
—NH(C″H2nHN)x—CORCO—
where n and x are each 2 or more and R is the divalent hydrocarbon radical of the dibasic carboxylic acid. An important characteristic of these resins is that they are phase compatible with polyvinyl alcohol. Suitable materials of this type are commercially available under the trademarks KYMENE® (Hercules, Inc.) and CASCAMID® (Borden) and are more fully described in U.S. Pat. No. 2,926,116 issued to Gerald Keim on Feb. 23, 1960, U.S. Pat. No. 3,058,873 issued to Gerald Keim et al. on Oct. 16, 1962, and U.S. Pat. No. 4,528,316 issued to Dave Soerens on Jul. 9, 1985, all of which are herein incorporated by reference. The creping adhesive includes polyvinyl alcohol. The amount of the thermosetting cationic polyamide resin in the creping composition, on a solids weight percent basis, can be from about 10 to about 80 percent, more specifically from about 20 to about 60 percent. Suitable plasticizers include quaternized polyamino amides and sorbitol, although the plasticizing mechanism of sorbitol is likely different than that of the quaternized polyamino amides. A significant amount of this moisture is desirably included in the sheet to plasticize adhesive as it hits the crepe blade in order to reduce the risk that the tissue sheet will wrap around the dryer and to prevent substantially build up of fibers on the dryer surface. Suitable amounts of water are retained in the creping adhesive composition when the sheet temperature at the crepe blade is from about 230° F. (110° C.) to about 250° F. (121° C.). More preferably the sheet temperature is controlled to from about 235° F. (113° C.) to about 245° F. (118° C.).
As illustrated in
When the most preferred undulatory creping blades of the patented undulatory blade are formed as shown in
Bleached and un-bleached toweling base sheet was manufactured on a commercial scale machine having the layout shown in
The furnish blends indicated in Table 2 were used targeting a basis weight of 29 #/rm using an undulatory crepe blade. To control the sheet moisture to fall in the range of from 6 to 9% at the crepe blade, the Yankee steam pressure was increased to 70 psi and the hood temperature to 780° F. while maintaining reel moisture at less than 3%. Buckman 385 absorbency aid was added as needed to achieve the WAR target of 30 sec. Similarly, wet strength resin as added to achieve the wet tensile strength target of 950 g/3″. Dry strength targets as listed in Table 2 were achieved by adding either Parez 631 or Varisoft de-bonder as needed. Comp U and Comp BL are competitive products offered in the market believed to be made from recycle fiber using a wet crepe process.
The furnish blend consists of 40% SFK PCW (post consumer waste) fiber, 32% SW BCTMP and 28% Peace River SWK. The basis weight was targeted at 27 #/rm using an undulatory blade (10 tpi/0.035″ depth). Yankee steam pressure was increased to 70 psi and the hood temperature to 780° F. while Yankee speed was cut as needed to control sheet moisture at the crepe blade to fall in the 6-9% range while maintain reel moisture at less than 3%. Buckman 385 absorbency aid was added to achieve the WAR target of 20 sec. The amount of wet strength resin was controlled to achieve wet tensile strength target as set forth in Table 2 while either Parez 631 or Varisoft GP-C debonder were added as needed to achieve the dry strength targets.
Samples of toweling produced according to Examples 3C, 5 and 7 as well as competitive samples were subjected to consumer testing by the assignee of the present application. The results indicated a directional overall preference for the towels of the present invention as compared to the prior art sample of Example 3C accompanied by parity ratings for softness and thickness but statistically significant preference in not shredding/falling apart, speed of absorbency and amount absorbed as indicated below in Table 4.
While the invention has been described in connection with several examples and embodiments, modifications to those examples and embodiments within the spirit and scope of the invention will be readily apparent to those of skill in the art. In view of the foregoing discussion, relevant knowledge in the art and references including co-pending applications discussed above in connection with the Background and Detailed Description, the disclosures of which are all incorporated herein by reference, further description is deemed unnecessary.
This non-provisional application is based upon U.S. Provisional Patent Application Ser. No. 61/283,648, of the same title, filed Dec. 7, 2009. The priority of U.S. Provisional Patent Application Ser. No. 61/283,648 is hereby claimed and the disclosure thereof is incorporated into this application by reference.
| Number | Date | Country | |
|---|---|---|---|
| 61283648 | Dec 2009 | US |
