Patent Application
20090242154
In the field of tissue products, tissues have long been made using a process known as “wet pressing”, which refers to the manner in which the newly-formed tissue wet tissue web is mechanically dewatered prior to final drying. More specifically, the wet web, while in contact with a papermaking felt, is pressed against and transferred to a hot drying cylinder, known as a Yankee dryer. During the pressing step, free water within the wet web is expressed and absorbed by the felt. The tissue is then final dried on the Yankee dryer and creped to soften the resulting tissue sheet. While this process is effective, the wet compression of the web prior to final drying densifies the sheet and is therefore detrimental to the ultimate softness and bulk properties of the final product.
More recently, throughdrying has become a popular method of drying tissue webs. Throughdrying avoids the extreme level of compaction associated with wet pressing and relies on hot air passing through the wet web to accomplish drying. Throughdried sheets are inherently less dense (greater bulk) than wet-pressed sheets and are therefore softer. While the ultimate product properties are desirable, throughdrying is more energy intensive and therefore more expensive to operate. Also, there are a great number of existing wet pressing tissue machines in operation and converting them to throughdrying entails a high capital expense, which may not be feasible.
Therefore there is a need for wet-pressed tissue products, particularly single-ply wet-pressed tissue products, that exhibit a level of softness previously associated with throughdried tissues.
It has now been discovered that a soft, layered, single-ply, wet-pressed tissue can be made with a softness equivalent to that of throughdried tissues.
Hence in one aspect, the invention resides in a layered, single-ply, wet-pressed tissue having two outer layers and one or more inner layers, wherein one or both outer layers contains polysiloxane-treated eucalyptus pulp fibers, said tissue having an Objective Softness Value (hereinafter defined) from about 60 to about 90 or greater, more specifically from about 70 to about 90, and still more specifically from about 75 to about 85.
In another aspect, the invention resides in a layered, single-ply, wet-pressed tissue having two outer layers and one or more inner layers, wherein one or both outer layers contains polysiloxane-treated eucalyptus pulp fibers, said tissue having an Objective Softness Value (OSV) as calculated by the following equation:
OSV≧110−2 BW,
where “BW” is the tissue bone dry basis weight, expressed in grams per square meter. More specifically, the OSV can also be about 90 or less.
In another aspect, the invention resides in a layered, single-ply, wet-pressed tissue having two outer layers and one or more inner layers, wherein one or both outer layers contains polysiloxane-treated eucalyptus pulp fibers, said tissue having an Objective Softness Value (OSV) as calculated by the following equation:
OSV≧100−160 SSC,
where “SSC” is the tissue single-sheet caliper expressed in millimeters. More specifically, the OSV can also be about 90 or less.
The tissues of this invention can be embossed or unembossed (not embossed).
Suitable methods for making the tissue products of this invention include those processes that utilize a combination of a felt, a transfer belt and a texturizing fabric. Suitable examples of such methods include U.S. Pat. No. 6,287,426 issued Sep. 11, 2001 to Edwards et al. and co-pending Ser. No. 11/588,652 filed Oct. 27, 2006, by Beuther et al. and entitled “Molded Wet-Pressed Tissue”, both of which are hereby incorporated by reference. A particularly suitable method comprises: (a) forming a layered wet tissue web having two outer layers, one or both outer layers comprising polysiloxane-treated eucalyptus fibers, and one or more inner layers of conventional papermaking fibers, the tissue web having a basis weight of about 20 grams or more per square meter; (b) carrying the wet tissue web to a dewatering pressure nip while supported by or otherwise in contact with a papermaking felt; (c) compressing the wet tissue web between the papermaking felt and a transfer belt, whereby the wet tissue web is dewatered to a consistency of about 30 percent or greater and transferred to the surface of the transfer belt; (d) transferring the dewatered web from the transfer belt to a texturizing fabric, with the aid of vacuum, to mold the dewatered web to the surface contour of the fabric; (e) pressing the web against the surface of a Yankee dryer while supported by a texturizing fabric and transferring the web to the surface of the Yankee dryer; and (f) drying and creping the web to produce a creped tissue sheet.
Suitable fibers for the two outer layers include conventional eucalyptus pulp fibers and/or polysiloxane-treated eucalyptus pulp fibers, such as disclosed in U.S. Pat. No. 6,582,560 B2 entitled “Method For Using Water Insoluble Chemical Additives With Pulp and Products Made By Said Method”, issued to Runge et al. Jun. 24, 2003, which is hereby incorporated by reference. In the one or both outer layers in which polysiloxane-treated eucalyptus fibers are present, the amount of polysiloxane-treated eucalyptus pulp fibers can independently be from 0 to about 100 dry weight percent, more specifically from about 10 to about 100 dry weight percent, more specifically from about 25 to about 80 dry weight percent, and still more specifically from about 40 to about 60 dry weight percent. It can be advantageous to provide the “air side” outer layer (the outer layer of the tissue web not in contact with the Yankee dryer surface during creping) with a greater amount of polysiloxane-treated pulp fibers than the “dryer side” outer layer (the outer layer of the tissue web in contact with the Yankee dryer surface during creping). Particularly suitable polysiloxanes include polydimethylsiloxanes and modified polydimethylsiloxanes, such as amino-functional polydimethylsiloxanes, alkylene oxide-modified polydimethylsiloxanes, organo-modified polydimethylsiloxanes, and the like.
Suitable fibers for the one or more inner layers include any papermaking fibers which provide sufficient tensile strength to the tissue for its intended purpose. Such papermaking fibers include conventional cellulosic papermaking fibers, such as hardwood and softwood fibers, bleached and unbleached fibers, virgin and recovered or recycled fibers, and fibers that have been mechanically pulped (e.g., groundwood), chemically pulped (including but not limited to the kraft and sulfite pulp processes), thermomechanically pulped, chemithermomechanically pulped, and the like. Mixtures of any subset of the above-mentioned fiber types or related fiber classes can also be used to provide the desired basis weight, strength and bulk.
The “basis weight” of the tissue webs of this invention can be about 20 grams or more per square meter (gsm), more specifically from about 20 to about 35 gsm, more specifically from about 25 to about 35 gsm, and still more specifically from about 25 to about 30 gsm. As used herein, “basis weight” refers to the amount of “bone dry” fiber in the finished tissue product.
The single-sheet caliper of the tissue sheets of this invention can be from about 0.20 to about 0.35 millimeters, more specifically from about 0.25 to about 0.30 millimeters.
The bulk of the tissue sheets produced by the method of this invention (finished product) can be about 5 cubic centimeters or greater per gram of fiber (cc/g), more specifically from about 5 to about 20 cc/g, still more specifically from about 7 to about 15 cc/g.
The geometric mean tensile strength of the tissue sheets of this invention can be about 500 grams or greater per 3 inches of sample width (g/3 inches), more specifically from about 500 to about 700 g/3 inches, still more specifically from about 500 to about 650 g/3 inches.
As described above and used herein, the term “wet-pressed” means that the web is mechanically dewatered by a compression nip while the wet web is in contact with a papermaking felt and thereafter dried without the aid of a throughdryer. The water expressed from the wet web during compression is absorbed and carried away by the felt. Commonly, the compression nip is formed between a press roll and the surface of a drying cylinder, such as a Yankee dryer. In all cases, wet pressing densifies the fiber structure of the wet web and normally has a detrimental effect on the softness of the resulting tissue sheet. Particularly suitable wet-pressed tissue products in accordance with this invention are mechanically dewatered, final-dried on a Yankee dryer and once-creped. Particularly suitable press loads for purposes of this invention can have a peak pressure of about 1.4 MPa or greater, more specifically from about 4 to about 8 MPa, and still more specifically from about 4 to about 6 MPa.
The wet tissue web can be dewatered to a consistency of about 30 percent or greater, more specifically about 40 percent or greater, more specifically from about 40 to about 50 percent, and still more specifically from about 45 to about 50 percent. As used herein and well understood in the art, “consistency” refers to the bone dry weight percent of the web based on fiber.
As used herein, a “felt” is an absorbent papermaking fabric designed to absorb water and remove it from a tissue web. Papermaking felts of various designs are well known in the art.
As used herein, a “transfer belt” is a water impermeable, or substantially water impermeable, belt having a relatively smooth surface. Examples of such transfer belts are described in the above-mentioned Edwards et al. patent, the above-mentioned co-pending U.S. patent application Ser. No. 11/588,652 to Beuther et al., and U.S. Pat. No. 5,298,124 issued Mar. 29, 1994 to Eklund et al. and entitled “Transfer Belt in a Press Nip Closed Draw Transfer”, which is hereby incorporated by reference. Particularly suitable transfer belts include a G3 TRANSBELT® and a LA TRANSBELT®, both from Albany International Corp.
As used herein, a “texturizing fabric” is a papermaking fabric, particularly a woven papermaking fabric, having a topographical or three-dimensional surface that can impart bulk to the final tissue sheet. Examples of such fabrics suitable for purposes of this invention include, without limitation, those disclosed in U.S. Pat. No. 5,672,248 to Wendt et al., U.S. Pat. No. 5,429,686 to Chiu et al., U.S. Pat. No. 5,832,962 to Kaufman et al., U.S. Pat. No. 6,998,024 B2 to Burazin et al., US 2005/0236122 A1 by Mullally et al. and commonly-owned co-pending application Ser. No. 11/588,652 to Beuther et al., all of which are herein incorporated by reference.
A particularly suitable texturizing fabric is a three-dimensional papermaking fabric, particularly a woven papermaking fabric, which has a topography that can form the ridges and valleys in the tissue sheet when the dewatered sheet is molded to conform to its surface. Such a fabric is illustrated herein in
The level of vacuum used to effect the transfer of the tissue web from the transfer belt to the texturizing fabric will depend upon the nature of the texturizing fabric. In general, the vacuum can be about 5 kPa or greater, more specifically from about 20 to about 60 kPa, still more specifically from about 30 to about 50 kPa. The vacuum at the pick-up (vacuum transfer roll) plays a much more important role for transferring light weight tissue webs from the transfer belt to the texturizing fabric than it does for heavier paper grades. Because the wet web tensile strength is so low, the transfer must be 100 percent complete before the belt and fabric separate—otherwise the web will be damaged. On the other hand, for heavier weight paper webs there is sufficient wet strength to accomplish the transfer, even over a short micro-draw, with modest vacuum (20 kPa). For light weight tissue webs, the applied vacuum needs to be much stronger in order to cause the vapor beneath the tissue to expand rapidly and push the web away from the belt and transfer the web to the fabric prior to fabric separation. On the other hand, the vacuum cannot be so strong as to cause excessive pinholes in the sheet after transfer.
To further effect transfer and molding of the web into the texturizing fabric, the vacuum transfer roll may contain a second vacuum holding zone.
The transfer of the web to the texturizing fabric can include a “rush” transfer or a “draw” transfer. Rush transfers are transfers where the receiving fabric (downstream fabric) is traveling at a machine speed that is lower than the machine speed of the upstream fabric. Draw transfers are the opposite, i.e. the receiving fabric is traveling at a machine speed that is higher than the upstream fabric. Depending upon the nature of the texturizing fabric, rush transfer can aid in creating higher sheet caliper. When used, the level of rush transfer can be about 5 percent or less.
In the interests of brevity and conciseness, any ranges of values set forth in this specification contemplate all values within the range and are to be construed as written description support for claims reciting any sub-ranges having endpoints which are whole number or otherwise of like numerical values within the specified range in question. By way of a hypothetical illustrative example, a disclosure in this specification of a range of from 1 to 5 shall be considered to support claims to any of the following ranges: 1-5; 1-4; 1-3; 1-2; 2-5; 2-4; 2-3; 3-5; 3-4; and 4-5. In addition, any values prefaced by the word “about” are to be construed as written description support for the value itself. By way of example, a range of “from about 1 to about 5” is to be interpreted as also disclosing and providing support for a range of “from 1 to 5”, “from 1 to about 5” and “from about 1 to 5”.
Referring to
All samples are conditioned in accordance with TAPPI test method T402 sp-03 “Standard Conditioning and Testing Atmosphere For Paper, Board, Pulp Handsheets and Related Products” before performing the test methods described below.
As used herein, “bulk” is calculated as the quotient of the sheet “caliper” (hereinafter defined) of a tissue sheet, expressed in microns, divided by the bone dry basis weight, expressed in grams per square meter. The bone dry weight of the sample is determined by placing the sample in a commercial oven (e.g. Blue M Industrial Ovens serial #10089811 from Thermal Product Solutions or equivalent) and maintained at 105±2° C. for 60±5 minutes before weighing. The resulting sheet bulk is expressed in cubic centimeters per gram (cc/g).
More specifically, the tissue sheet “caliper” is the representative thickness of a single tissue sheet measured in accordance with TAPPI test method T411 om-89 “Thickness (caliper) of Paper, Paperboard, and Combined Board” with modifications to the size of the pressure foot and the amount of pressure applied to the sample. In particular, the micrometer used for carrying out the caliper measurement is an Emveco 200-A Electronic Microgage available from Emveco, Inc., Newberg, Oreg., having a circular pressure foot area of 2500 square millimeters and a diameter of 56.42 millimeters. The dwell time is 3 seconds, the lowering rate is 0.8 millimeters per second and the applied pressure is 2 kilo-Pascals.
As used herein, the “machine direction (MD) tensile strength” is the peak load per 3 inches of sample width when a sample is pulled to rupture in the machine direction. Similarly, the “cross-machine direction (CD) tensile strength” is the peak load per 3 inches of sample width when a sample is pulled to rupture in the cross-machine direction. The percent elongation of the sample prior to breaking is the “stretch”.
The procedure for measuring tensile strength and stretch is as follows. Samples for tensile strength testing are prepared by cutting a 3 inches (76.2 mm) wide by 4 inches (102 mm) long strip in either the machine direction (MD) or cross-machine direction (CD) orientation using a JDC Precision Sample Cutter (e.g. Thwing-Albert Instrument Company, Philadelphia, Pa., Model No. JDC 3-10 or equivalent). The instrument used for measuring tensile strengths is a Constant-Rate-of-Extension (CRE) tensile tester (e.g. MTS Sintech 500/S or equivalent). The data acquisition software is MTS TestWorks® for Windows Ver. 4.08B from MTS Systems Corporation, Eden Prairie, Minn. 55344-2290. The load cell is 50 Newtons from MTS Systems Corporation such that the majority of peak load values fall between 10-90% of the load cell's full scale value. The gauge length between jaws is 2±0.04 inches (51±1 mm). The jaws are operated using pneumatic-action and are rubber coated. The minimum grip face width is 3 inches (76.2 mm), and the approximate height of a jaw is 0.5 inches (12.7 mm). The rate of separation of the jaws is 10±0.4 inches/min (254±10 mm/min). The preload preferably is less than 15 grams with 25 grams as the maximum allowable preload. The sample is placed in the jaws of the instrument, centered both vertically and horizontally. The test is then started and ends when the specimen breaks. The peak load is recorded as either the “MD tensile strength” or the “CD tensile strength” of the specimen depending on direction of the sample being tested. At least ten (10) representative specimens are tested for each tissue sheet and the arithmetic average of all individual specimen tests is either the MD or CD tensile strength for the tissue.
“Geometric Mean” (GM) values for any measurements having a machine direction value and a cross-machine direction value (such as tensile strength, stretch and slope) are calculated as the square root of the product obtained by multiplying the machine direction value and the cross-machine direction value.
As used herein, the “Objective Softness Value” (OSV) of a tissue sheet is determined by the following equation:
OSV=−43.043−132.52*Log10(GM13 MMD)−68.002*Log10(GM_Slope A)
This equation has been determined by correlating overall softness evaluations determined by trained sensory panelists with certain objective measurements that are generally accepted as components of softness, namely surface friction and stiffness. The surface friction softness component is designated “MMD” (hereinafter described). The stiffness softness component is represented by “Slope A” expressed in kg, which is determined when measuring tensile strength as described above, and is the average slope of the tensile curve between a load of 70 and 157 grams per 3 inches (or between 9.2 and 20.6 grams per centimeter). For purposes of measuring the OSV, both softness components are calculated and expressed as geometric mean (GM) values. Ten (10) repeat tests per sample code are conducted in MD and CD respectively and an average is performed to generate one number (a single “GM_SlopeA” for each sample code).
The surface softness component of the OSV can be measured using a KES Surface Tester (model KES-SE) manufactured by Kato Tech Co, LTD in Japan. In carrying out this measurement, a U-shaped probe of a single stainless steel wire having a diameter of 0.5 millimeter (mm) and a width of 5 millimeters at the base is used with a contact force of 5 grams. The test speed is set at 1 millimeter per second. “SENS”, which is the sensitivity setting, is set at “H”. “FRIC” is set at “GU” for simultaneous friction and roughness measurement. Samples are selected that are free from all folds, wrinkles, crimp lines, perforations, of any distortions that would make these samples abnormal from the rest of the sample. The sample size is approximately 10 cm×10 cm. Samples are marked to denote the MD and CD directions as well as the air side and dryer side surfaces. During one test run, while the probe is fixed at one location, the sample is secured on a plate which moves at 1 millimeter per second. The plate is 140 mm×80 mm. The sample is laid flat and placed underneath a stainless steel frame of 80 mm×60 mm with 10 mm in width and 5 mm in height and a weight of 97.9 g. The plate moves in one direction (i.e. forward pass) for 30 millimeters and then is reversed in the other direction (i.e. backward pass) for 30 millimeters. The initial and last 5 millimeters data in each pass is excluded from the calculation. The averaged results of forward and backward passes are used to generate three test parameters. The data is acquired using KES-FB System Measurement Program Ver. 7.07E/ For Win 98/2000/XP by Kato Tech Co., LTD with selections of “Testers”=FB4, “Measure”=Optional Condition, “Static Load” for “Friction”=5 g, for “Roughness”=5 g, “Friction Sens”=2X5 and “Roughness Sens”=2X5. The definition of each test parameter is as follows.
The three test parameters generated by this test are: the coefficient of friction (MIU); the mean deviation of MIU (MMD); and surface roughness (SMD).
where:
Each of the tissue sheet samples is tested for MMD in the machine direction (MD) and the cross-machine direction (CD) for both outer surfaces of the tissue (air side and dryer side). Geometric averages from the MD and CD measurements are obtained by taking the square root of the product of the two, i.e. Geometric Mean (GM)=(MD mean*CD mean)̂½. Five repeat tests per sample code are conducted and an overall average of the air side surfaces and the dryer side surfaces is performed to generate one number (a single “GM_MMD” for each tissue sheet sample code).
For purposes of comparison, the following data table provides various physical properties for commercially available tissue products in 2004, specifically including: the country; the brand name; the number of plies; the technology used to produce the product (wet pressed or creped through-air-dried (CTAD)); the GM_MMD value; the GM_SlopeA value; the OSV; the bone dry basis weight (BDBW); the single sheet caliper; the geometric mean tensile strength (GMT); and whether or not the product was embossed.
A three-layer single-ply tissue paper basesheet was made as illustrated in
The machine speed was 600 m/min with a 20% crepe: ((Yankee speed−reel speed)/Yankee speed=20%). The press load was 400 kN/m using an Albany G3 transfer belt. A 3% rush transfer was applied between the transfer belt and the texturizing fabric. The sheet was transferred to and molded into a texturizing fabric with 40 kilo-Pascals (kPa) vacuum. Some additional molding was gained by using 32 kPa vacuum on the holding zone. An additional molding slot in the molding box after the transfer of the sheet to the texturizing fabric. The molding box had two slots supplied with vacuum. One slot was 10 mm wide and the other 15 mm wide (as measured in the machine direction). The transfer and molding vacuum were both 40 kPa.
The resulting basesheet was converted into rolls of toilet paper on 43 mm diameter cores using a Perini winder at 106 m/min speed with a calendering loading of 2.5 kN/m on a steel-rubber calender. (In the data tables below, the basesheet is designated as “Code 271” and the converted product is designated as “Code 271L”).
Similar to Example 1, except that the calendering load was increased to 5 kN/m. (In the data tables below, the basesheet is designated as “Code 271” and the converted product is designated as “Code 271H”).
Same as Example 1, except using a 2% rush transfer and 32 kPa vacuum at the transfer and molding box. (In the data tables below, the basesheet is designated as “Code 272” and the converted product is designated as “Code 272L”).
Same as Example 3, except that the calendering was increased to 5 kN/m. (In the data tables below, the basesheet is designated as “Code 272” and the converted product is designated as “Code 272H”).
Same as Example 1, except that the debonder was removed and the basis weight increased to 32 gsm. (In the data tables below, the basesheet is designated as “Code 273” and the converted product is designated as “Code 273L”).
Same as Example 5, except that the calendering was increased to 5 kN/m. (In the data tables below, the basesheet is designated as “Code 273” and the converted product is designated as “Code 273H”).
The properties of the basesheets and converted products produced by the foregoing Examples are summarized in Tables 1, 2 and 3 below.
Table 1 lists the following: the Code; the percent rush transfer at the transfer belt/texturizing fabric transfer (R/T); the geometric mean tensile strength (GMT) measured on a 4-inch span; the bone dry basis weight (BDBW); the vacuum in the pick-up zone of the transfer roll (VacP); the vacuum in the molding box (VacM); the vacuum in the holding zone of the transfer roll (VacH); the single sheet caliper; the amount of starch added to the center layer fibers; the amount of debonder added to the air-side layer; and the amount of debonder added to the dryer-side layer.
Table 2 below lists the following: the Code; the calendering load; the bone dry basis weight (BDBW); the geometric mean tensile strength (GMT) measured on a 2-inch span; caliper; and “In Hand Ranking” (IHR) softness as measured by a trained sensory panel.
Table 3 below lists the surface softness parameters derived from the KES surface testing. In particular, listed are the Code; the geometric mean of mean deviation of the coefficient of friction (GM_MMD) for 5 representative samples; the geometric mean of the tensile slope (GM_SlopeA); and the Objective Softness Value.
The foregoing examples illustrate the ability of the process to make a wide range of products of high bulk at high rate of production on the paper machine and at a reduced energy usage for drying the paper.
It will be appreciated that the foregoing description and examples, given for purposes of illustration, are not to be construed as limiting the scope of this invention, which is defined by the following claims and all equivalents thereto.
