Patent Application
20070131367
Tissue products, which include facial tissue, bath tissue, paper towels, table napkins and the like, typically derive their strength from naturally-occurring hydrogen bonds that form between cellulose fibers upon removal of water. In most cases, this bonding is uniform throughout the structure. Most tissue making processes incorporate the use of multiple fabrics on the tissue machine to facilitate water removal and movement of the tissue web. Typically, flat fabrics with a very small average pore size are used in the forming section. The topography, pore sizes, and composition of subsequent fabrics differ by product and the manufacturer. For example, in producing uncreped throughdried (UCTAD) tissue products as described in U.S. patent application Ser. No. 10/745,184 to Hada et al., a series of fabrics following the forming fabric may be used, such as a topographic transfer fabric and a second topographic throughdrying (TAD) fabric. The particular topography pattern of each fabric is designed to impart the desired physical and aesthetic properties to the final tissue product.
One physical property that is believed to be necessary for the production of high quality tissue is good stretch. Broken into its directional components, stretch is typically defined as machine direction (MD) stretch and cross-machine direction (CD) stretch. Unmodified tissues made with fabrics having no topography inherently have MD stretch values of about 4 percent and CD stretch values of about 2 percent. Tissue with such low stretch values is known to not perform well in-use. Therefore, tissue manufacturers use various means to impart the stretch necessary for in-use durability. MD stretch is typically imparted by creping or rush transfer. These methods are well known in the art. CD stretch development, on the other hand, is a bit more complex. Methods of making UCTAD tissue as described in the above-mentioned Hada et al. patent, for example, utilize topographical transfer fabrics or topographical throughdrying fabrics to make tissue with acceptable CD stretch. By increasing the CD path length (molding into MD-aligned ripples), CD stretch is typically increased by more than 100 percent over a comparable un-molded tissue. One disadvantage of this approach is the inseparable tie between the finished product topographical appearance and the finished product CD stretch. For instance, if certain consumers prefer tissue with a flat surface or textural features other than MD ripples, another method to impart CD stretch into the product is necessary.
Therefore there is a need for a method of imparting CD stretch to tissue sheets that does not rely on a highly topographical texture in the final tissue product.
It has now been discovered that the topographical texture of a tissue sheet can be independent of the degree of CD stretch in the sheet. More specifically, a method is disclosed that is capable of producing a relatively flat tissue product with stretch values similar to tissue products which have been molded into a more topographical pattern. This is achieved by producing a new tissue sheet structure that contains a pattern of substantially MD-oriented alternating high and low basis weight regions resulting from z-direction buckling of the sheet during manufacture.
Hence, in one aspect the invention resides in a method of making a tissue or towel sheet comprising: (a) forming a wet tissue web by depositing an aqueous suspension of papermaking fibers onto a forming fabric; (b) transferring the wet tissue web to a molding fabric which imparts a three-dimensional contour to the web, said contour having spaced-apart elongated elevated regions aligned in the machine direction; (c) removing the wet molded web from the molding fabric; and (d) flattening the molded web, wherein elongated machine direction-oriented buckled regions are created, said buckled regions having a basis weight that is higher than the average basis weight of the web.
In another aspect, the invention resides in a tissue or towel sheet having a pattern of spaced-apart, elongated, substantially machine direction-oriented buckled regions having a basis weight greater than the average basis weight of the sheet.
As used herein, the terms “tissue sheet” or “tissue web” include any relatively low density paper sheet or web useful for making or for use as facial tissue, bath tissue, paper towels, table napkins and the like.
As used herein, a “buckled region” is an area of the sheet which is or has been folded upon itself. Buckled regions are visible to naked eye and appear on one side of the sheet as creases or severe elongated indentations and appear on the other side of the sheet as elongated bumps or ridges. Structurally similar features are commonly present in creped tissues in the form of crepe folds, except such structures are oriented in the cross-machine direction of the sheet. The nature of the buckled regions can be quantified by the “buckled tissue index” as hereinafter described. The tissue sheets of this invention can have a buckled tissue index of about −0.05 or less, more specifically from about −0.05 to about −0.40, more specifically from about −0.10 to about −0.35.
As used herein, “substantially machine direction-oriented” means the orientation is less than 45 degrees from the machine direction of the sheet, more specifically less than 25 degrees, more specifically less than 15 degrees, and still more specifically less than 5 degrees from the machine direction of the sheet.
As used herein, a “three-dimensional contour” of sheets or fabrics refers to their z-direction surface height variation, more specifically the distance between the low and high points on the sheet or the web-facing side of the fabric. Height variations may be measured by any standard surface topography quantification method known in the art. Three-dimensional fabrics that are able to impart buckles can have z-direction surface height variations from about 0.5 millimeters to about 5 millimeters or greater, more specifically from about 1 millimeter about 4 millimeters.
The moisture content of the “wet” molded web prior to being flattened can be from about 15 to about 80 percent, more specifically from about 20 to about 70 percent, and still more specifically from about 25 to about 50 percent. If the web is too wet, buckles are not formed due to fiber rearrangement. If the web is too dry, buckles are not formed because of the lack of hydrogen bonds formed in the buckled region. However, the latter case may be mitigated by the surface application of adhesive or bonding agents to hold the buckles in place. In this case, a substantially dry web may be buckled. An example of buckling a dry web is provided herein for towel product.
“Flattening” of the three-dimensionally-contoured molded web can be achieved by transferring the wet web to a fabric or other surface having a relatively flat contour. Such relatively flat fabrics have a z-directional topographical surface height variation of about 0.3 millimeters or less.
The average basis weight of the tissue sheets in accordance with this invention can be from about 15 to about 80 grams per square meter (gsm), more specifically from about 20 to about 60 gsm and still more specifically from about 20 to about 40 gsm. The average basis weight will depend upon the particular product form, such as facial tissue, bath tissue, paper towel, etc. and the number of tissue sheets (plies) in the product.
The ratio of the basis weight of the machine direction-oriented buckled regions relative to the average basis weight of the sheet can be about 1.5 or greater, more specifically from about 1.5 to about 3, and still more specifically from about 2 to about 2.5.
The CD stretch of the tissue sheets of this invention can be about 5 percent or greater, more specifically from about 5 to about 25 percent, more specifically from about 5 to about 20 percent, more specifically from about 10 to about 20 percent. Factors influencing the level of CD stretch include the level and type of buckling, fiber length, and tissue manufacturing and processing variables.
The CD TEA of the tissue sheets of this invention, which is indicative of the overall durability of a tissue sheet, can be about 3 grams-centimeter per square centimeter (g-cm/cm2) or greater, more specifically from about 3 to about 30 g-cm/cm2, more specifically from about 4 to about 25 g-cm/cm2, and still more specifically from about 5 to about 25 g-cm/cm2. Factors affecting CD TEA are similar to those that influence CD stretch.
The CD Slope of the tissue sheets of this invention, which is indicative of the softness or stiffness of the sheet, will depend on the particular product and the process conditions. More specifically, the CD Slope can be from about 3 to about 15 grams per 3 inches of sample width, more specifically from about 3 to about 10 grams per 3 inches of sample width, and still more specifically from about 3 to about 8 grams per 3 inches of sample width.
In the interests of brevity and conciseness, any ranges of values set forth in this specification are to be construed as written description support for claims reciting any sub-ranges having endpoints which are whole number values within the specified range in question. By way of a hypothetical illustrative example, a disclosure in this specification of a range of 1-5 shall be considered to support claims to any of the following sub-ranges: 1-4; 1-3; 1-2; 2-5; 2-4; 2-3; 3-5; 3-4; and 4-5.
Referring to
As shown in
Referring to
The wet web, which is relatively flat, is then transferred from the forming fabric to a transfer fabric 20 to effect treatment #1. Advantageously, the transfer fabric can be traveling at a slower speed than the forming fabric in order to impart increased stretch into the web. This is commonly referred to as a “rush” transfer. The relative speed difference between the two fabrics can be from 0 to about 60 percent, more specifically from about 15 to about 45 percent. Transfer is preferably carried out with the assistance of a vacuum shoe 22, suitably such that the forming fabric and the transfer fabric simultaneously converge and diverge at the leading edge of the vacuum slot. Suitably, in order to provide the three-dimensional molding of the web while in a relatively wet state, the transfer fabric can contain high and long impression knuckles or spaced-apart ridges and valleys running in the machine direction of the web. For example, the transfer fabric can have about from about 5 to about 300 impression knuckles per square inch which are raised at least about 0.005 inches above the plane of the fabric. The height profile of such fabrics, when viewed from a cross-machine direction perspective, is sinusoidal in nature. Suitable three-dimensional transfer fabrics are well known in the art, such as those known typically used as highly-contoured throughdrying fabrics, such as those described in U.S. Pat. No. 5,429,686 issued to Chiu et al. and U.S. Pat. No. 5,672,248 issued to Wendt, et al., both of which are herein incorporated by reference. Additional topographical fabrics with MD dominant features which can be utilized are described in U.S. Patent Application No. 2003/0084953 A1 published on May 8, 2003 to Burazin et al., herein incorporated by reference.
The web is then transferred from the transfer fabric to a relatively flat throughdrying fabric 24 (treatment #2) with the aid of a vacuum transfer roll 26 or a vacuum transfer shoe. This transfer causes the three-dimensional machine directions ridges to buckle and create the machine direction-oriented regions of higher basis weight as described above. The throughdrying fabric can be traveling at about the same speed or a different speed relative to the transfer fabric. If desired, the throughdrying fabric can be run at a slower speed to further increase machine direction stretch. Transfer can be carried out with vacuum assistance to ensure deformation of the sheet to conform to the throughdrying fabric without in-plane expansion. The level of vacuum used for the web transfers can be from about 3 to about 15 inches of mercury (75 to about 380 millimeters of mercury), preferably about 5 inches (125 millimeters) of mercury. The vacuum shoe (negative pressure) can be supplemented or replaced by the use of positive pressure from the opposite side of the web to blow the web onto the next fabric in addition to or as a replacement for sucking it onto the next fabric with vacuum. Also, a vacuum roll or rolls can be used to replace the vacuum shoe(s).
While supported by the throughdrying fabric, the web is final dried to a consistency of about 94 percent or greater by the throughdryer 28 to set the new structure with hydrogen bonding.
After drying the dried web 32 is transferred to a carrier fabric 30 and transported to the reel 34 using carrier fabric 30 and an optional carrier fabric 36. An optional pressurized turning roll 38 can be used to facilitate transfer of the web from carrier fabric 30 to fabric 36. In either case, the web 40 is wound into a roll for subsequent converting operations to produce the final product form. Suitable carrier fabrics for this purpose are Albany International 84M or 94M, Asten 959, 934, or 937, and Voith Fabrics 2164 and 44GST, all of which are relatively smooth fabrics having a fine pattern. Although not shown, reel calendering or subsequent off-line calendering can be used to improve the smoothness and softness of the basesheet.
Referring to
As shown, dried paper sheet 41 can be made according to a process as generally illustrated in
Sheet 41 is then contacted with a heated roll 52 after passing a roll 54. The heated roll 52 serves to partially dry the sheet. In general, the sheet can be heated to any temperature sufficient to dry the sheet and evaporate water. Besides the heated roll 52, any suitable heating device can be used to dry the sheet, such as an infra-red heater or any suitable convective oven or microwave oven, for example.
From the heated roll 52, the sheet 41 can be advanced by pull rolls 56 to an optional second bonding material application station. Station 58 includes a transfer roll 60 in contact with a rotogravure roll 62, which is in communication with a reservoir 64 containing a second bonding material 66. Similar to station 42, second bonding material 66 is applied to the opposite side of sheet 41 in a pre-selected pattern. Once the second bonding material is applied, sheet 41 is adhered to a creping roll 78 by a relatively flat press roll 70. At this point, any topography of the sheet 41 is flattened and turned into buckles. Sheet 41 is carried on the surface of the creping drum 78 for a distance and dried to lock in the structure of the buckled regions. The dried sheet is then dislodged from the creping drum by the action of a creping blade 72. The creping blade 72 performs a controlled pattern creping operation on the second side of the paper web.
Once creped, creped paper sheet 73 is pulled through a drying station 74. Drying station 74 can include any form of a heating unit, such as an oven energized by infrared heat, microwave energy, hot air or the like. Drying station 74 may be necessary in some applications to completely dry the sheet and/or further cure the first and second bonding materials. Depending upon the bonding agents selected, however, in other applications drying station 74 may not be needed.
The bonding materials applied to each side of the paper sheet are selected not only for assisting in creping the sheet but also for adding dry strength, wet strength, stretchability and tear resistance to the paper. Particular bonding materials that may be used include latex compositions, such as acrylates, vinyl acetates, vinyl chlorides and methacrylates. Some water-soluble bonding materials may also be used including polyacrylamides, polyvinyl alcohols and cellulose derivatives such as carboxymethyl cellulose. In one embodiment, the bonding materials comprise an ethylene vinyl acetate copolymer. In particular, the ethylene vinyl acetate copolymer can be cross-linked with N-methyl acrylamide groups using an acid catalyst. Suitable acid catalysts include ammonium chloride, citric acid and maleic acid.
More specifically, shown is the papermaking headbox 100 that injects or deposits an aqueous suspension of papermaking fibers between first and second forming fabrics 105 and 106 of a twin wire former to form a wet web 110. Desirably, while the web 110 is sandwiched between the forming fabrics 105 and 106, the web is transported through an air press 115 comprising an air plenum and a collection device, such as a vacuum box, in order to non-compressively dewater the web. The web 110 may also be carried over one or more vacuum or suction boxes (not shown) prior to the air press.
The wet web 110 is thereafter transported by the second forming fabric 106 to a transfer fabric 120. A vacuum pickup roll 125 is used to transfer the wet web 110 from the transfer fabric 120 onto a three-dimensional throughdrying fabric 130. The throughdrying fabric is arranged to carry the web over two throughdryers 135 and 140. As illustrated, a separate transfer fabric 145 sandwiches the web against the throughdrying fabric 130 for transport between the two throughdryers. The web 110 is desirably dried to greater than 35 percent dryness on the second throughdryer 140.
After the second throughdryer 140, a vacuum roll 150 is used to remove the web from the throughdrying fabric 130, whereupon the web is sandwiched between a relatively flat impression fabric 165 and a transfer fabric 170. The web is then pressed onto the surface of a drying cylinder, such as a Yankee dryer 175, with a pressure roll 176. The dried web 180 is desirably removed from the drying cylinder using a creping blade 177 to impart stretch and is then wound into a roll. Of course, the number and arrangement of throughdryers and fabrics may be varied from that shown.
Basis Weight Profile
Quantification of the increased basis weight in the buckled regions of the sheet is measured using image analysis techniques as described below. More specifically, a series of basis weight line profiles are taken on tissue at 0 percent, 2 percent, 5 percent, and 7 percent CD strain. The percentage of pixels with intensity values less than 2 times the standard deviation of the profile was plotted at each level of stretch. Finally, the slope of the linear trend line obtained from the number of values less than two times the standard deviation at each stretch level, plotted against tissue strain, is the buckled index. For purposes herein, tissue webs having a buckled index less than zero (0) have buckled regions in accordance with this invention. On the other hand, tissue webs having a buckled index of zero (0) or greater do not have buckled regions.
More specifically, the apparatus and set-up for determining the gray-level profile of tissue sheets will now be described. The test method involves retaining the products, from which samples will be cut, at room temperature of between 68° F. to 72° F. for a time period of 24 hours. After the products have been acclimated, a sample is cut of each product using scissors. The sample is normally cut into a rectangular shape to approximately 120 mm by 120 mm in size. The minimum size sample that can be cut will be approximately 60 mm by 60 mm in size and have a field of view size defined by the dimensions of approximately 48 mm by approximately 37 mm. The sample should be oriented so that the buckled regions are aligned vertically in the image.
The sample may have different textured surfaces due to processing of the material. Ideally, the sample surface facing the camera should also be the surface that best exhibits any buckling effects.
The sample is then clamped into a tissue stretching apparatus (see
Referring to
The video camera used was a SONY® video camera (Model DXC-930P) with synchronization and timing option (commonly called PAL format) and the red color channel was used. The adjustable 35-millimeter Nikon lens was mounted on the video camera via 1:1 relay adaptor #C20047 (Century Optics, USA). The 35-millimeter Nikon lens had an f-stop setting of 2.8. The video camera was mounted on a Polaroid MP-4 Land Camera (Polaroid Resource Center, Cambridge, Miss.) standard support. The support was attached to a KREONITE macro-viewer purchased from Kreonite, Inc., (Wichita, Kans.). The auto-stage was placed on the upper surface of the KREONITE macro-viewer, although it could be placed on an equivalent or similar apparatus. The auto stage was used as a spacer between the Chroma Pro 45 and the sample/stretching apparatus.
The distance D1 represents the distance between the upper surface of the sample and the bottom of the lens. The distance D1 was set to be approximately 21 centimeters (cm). The distance D2 represents the vertical distance between the macro-viewer and the auto-stage top surface. The distance D2 was approximately 16 cm. The sample was illuminated by the Chroma Pro 45 (Zeiss model no. 01-21628-01) which is distributed by Circle S, Inc. (Tempe, Ark.). It was placed just underneath a ¼″ sheet of transparent plexi-glass which sat on top of the macro-viewer as shown if
The image analysis system used to generate the gray-level profiles was a Quantimet 600 Image Analysis System available from Leica Microsystems, having an office in Wetzlar, Germany. The system was controlled and run by QWIN Version 1.06A software. The image analysis program ‘TISBW4’ was used to acquire, process and measure images using Quantimet User Interactive Programming System (QUIPS) language. Alternatively, the TISBW4 program could be used with a Quantimet 500 IW Image Analysis System which runs QWIN Version 2.4 software. The custom image analysis program is shown below.
Calibrate (CALVALUE CALUNITS$ per pixel)
CONTINUE:
Graphics (Inverted Grid, GRAPHNX×GRAPHNY Lines, Grid Size GRAPHWID×GRAPHHGHT, Origin GRAPHORGX×GRAPHORGY, Thickness GRAPHTHIK, Orientation GRAPHORNT, to GRAPHOUT Cleared)
Measure feature (plane Binary0, 8 ferets, minimum area: 16, grey image: Image0)
Feature Expression (UserDef1 (all features), title XLocation=(PXCENTROID(FTR)−108)*CALVALUE)
Feature Expression (UserDef2 (all features), title YLocation=(PYCENTROID(FTR)−230)*CALVALUE)
Feature Expression (UserDef3 (all features), title Basis Wt.=2.71828**((PMEANGREY(FTR)+175.04)/86.217))
File Feature Results (channel #1)
Feature Histogram #1 (Y Param Number, X Param UserDef3, from 0. to 100, linear, 20 bins)
GRAPHORGX=GRAPHORGX+GRAPHWID
Next (FIELD)
Profile Results Window (0, 638, 512, 256)
Profile Window (2, 671, 576, 256)
Prior to testing the first sample, shading correction was performed using the QWIN software and a blank field of view that was illuminated using the Chroma Pro and the translucent plexi-glass. The shading correction was performed using the ‘live’ mode. The system was also accurately calibrated using the QWIN software and a standard ruler with metric markings. The calibration was performed in the horizontal dimension of the video camera image.
After calibrating the system, the QUIPS routine TISBW4 was executed via the QWIN software and this initially prompts the analyst to place the sample within the field-of-view of the video camera. After positioning the sample in the stretching apparatus so the primary buckled region direction is parallel to the vertical direction in the image, the analyst will then be prompted to adjust the light level setting (via the POWERSTAT variable auto transformer) to register between Gray-Level readings of 186-188. During this process of light adjustment, the QUIPS routine TISBW4 will automatically display the current gray-level value on the Quantimet 600 video screen.
After the light has been properly adjusted, the QUIPS routine TISBW4 will then automatically acquire process and measure the gray-level profile of the image. The gray-level scale used on the Quantimet 600 system, or equivalent, is 8-bit and ranges from 0 to 255 (0 represents ‘black’ and 255 represents ‘white’). For gray-level measurements, the entire gray scale will be used.
The QUIPS routine TISBW4 will then measure the gray-level profile and export the data directly to an EXCEL®) spreadsheet. The profile generated at each point was based on the average of the corresponding pixel column of 86 pixels that ran vertically both below and above the central horizontal profile pixel line (172 total pixels). Thus, it is important to align the sample such that any buckling phenomenon is oriented vertically in the image.
After collecting the gray-level profile with 0% stretch of the sample, the analyst will then carefully use the stretching apparatus to stretch the tissue an additional 2 percent beyond its original size based on the dimensions within the stretching apparatus clamps. Again, stretching will be performed in. a direction orthogonal to the buckles orientation.
The whole image analysis and data collection process is again repeated for the collection of the strained tissue. After the 2 percent stretch data is collected, the stretching and image analysis steps are again repeated for 5 percent and 7 percent levels of stretch.
Tensile Strength.
Samples for tensile strength testing are prepared by cutting a 3 inches (76.2 mm) wide×5 inches (127 mm) long strip in either the machine direction (MD) or cross-machine direction (CD) orientation using a JDC Precision Sample Cutter (Thwing-Albert Instrument Company, Philadelphia, Pa., Model No. JDC 3-10, Serial No. 37333). The instrument used for measuring tensile strengths is an MTS Systems Sintech 11 S, Serial No. 6233. The data acquisition software is MTS TestWorks® for Windows Ver. 3.10 (MTS Systems Corp., Research Triangle Park, N.C.). The load cell is selected from either a 50 Newton or 100 Newton maximum, depending on the strength of the sample being tested, 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 4+/−0.04 inches (101.6+/−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 crosshead speed is 10+/−0.4 inches/min (254+/−1 mm/min), and the break sensitivity is set at 65%. 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 the sample being tested. At least six (6) representative specimens are tested for each product and the arithmetic average of all individual specimen tests, either in the MD or CD, is the tensile strength for the product.
Stretch.
“Stretch”, in either the MD or CD, is the average percent elongation of the sample at the breaking point when measuring the tensile strength as described above.
CD TEA.
In addition to measuring the tensile strength and stretch, the cross-machine direction tensile energy absorbed (CD TEA) is also reported by the MTS TestWorks® for Windows Ver. 3.10 program for each sample tested for CD tensile strength. The CD TEA is reported in the units of grams-centimeters/centimeters squared (g-cm/cm2) and is defined as the integral of the force produced by a specimen with its elongation up to the defined break point (65% drop in peak load) divided by the face area of the specimen.
CD Slope.
The “CD Slope” is the average slope of the load/elongation curve described above measured over the range of 0-20 grams (force). The slope is 20 grams (force)/centimeter divided by the strain value corresponding to a load of 20 grams (force)/centimeter when the width of the sample is 1 inch (2.54 cm).
(Bath Tissue).
To further illustrate the invention, bath tissue Examples 1-12 were produced using a pilot uncreped throughdried tissue machine was configured similarly to that illustrated in
The machine chest furnish was diluted to approximately 0.1 percent consistency and delivered to a forming fabric using a three-layered headbox. The layer fiber weight split was 33 percent/34 percent/33 percent, with 100 percent eucalyptus fiber in the two outer layers and 100 percent softwood in the middle layer. The Voith Fabrics 2164 forming fabric speed was approximately 62 feet per minute (fpm). The resulting web was then transferred to a transfer fabric traveling at 50 fpm using a vacuum shoe to assist the transfer. At a second vacuum shoe assisted transfer, the web was delivered onto a throughdrying fabric. The web was dried with a throughdryer operating at a temperature of 375° C.
The resulting bath tissue basesheet was produced with an oven-dry basis weight of approximately 26 grams per square meter (gsm). The resulting product was equilibrated for at least 4 hours in TAPPI standard conditions (73° F., 50% relative humidity) before tensile testing. All testing was performed on basesheet from the pilot machine without further processing.
Examples 1-3 represent control tissues sheets made with different levels of rush transfer using the same, relatively flat, fabric in the transfer fabric and the throughdrying (TAD) fabric position. The fabric used was a 2164. Examples 4-12 are examples in accordance with this invention in which the tissue sheets are made with a topographic transfer fabric and a relatively flat TAD fabric. More specifically, the transfer fabric (labeled Jetson), which served as the molding fabric for Examples 4-6, had a three-dimensional contour having an MD-dominant design of approximately 5 MD raised elements per centimeter and which were approximately 1 millimeter deep. A CD line trace of this fabric would have the approximate structure of a sine wave with amplitude of 1 millimeter and a frequency of 2 millimeters.
The transfer fabric (labeled Quickdraw), which served as the molding fabric for Examples 7-9, had a three-dimensional contour having an MD-dominant design of approximately 2 MD raised elements per centimeter and which were approximately 2 millimeters deep. A CD line trace of this fabric would have the approximate structure of a sine wave with amplitude of 2 millimeters and a frequency of 5 millimeters.
The transfer fabric (labeled IMv1.0), which served as the molding fabric for Examples 10-12, had a three-dimensional contour having an MD-dominant design of approximately 2 MD raised elements per centimeter and which were approximately 3 millimeters deep. A CD line trace of this fabric would have the approximate structure of a sine wave with amplitude of 3 millimeters and a frequency of 5 millimeters. The approximate 5 millimeters frequency of the basis weight spikes depicted for Example 10 in
Conversely, the throughdrying fabric, which was a 2164 manufactured by Voith Fabrics, was relatively flat and served to flatten the web. Relative to the schematic method depicted in
The results of these Examples are summarized in Table 1. For purposes herein, the 2164 fabric is considered to be a flat fabric which is not sufficiently contoured for use as a molding fabric in accordance with this invention. All of the other fabrics listed as part of this example are sufficiently three-dimensionally contoured to mold the tissue web and impart machine direction oriented buckled regions in accordance with this invention.
As the data show, on average, imparting machine direction oriented buckled regions in accordance with this invention increased CD stretch by nearly 300 percent. Such high increases in CD stretch while using a relatively flat TAD fabric were unexpected because, traditionally, the TAD fabric topography is the primary driver for CD stretch development. It was also unexpected because the abundance of water in the sheet while in its molded state (on the transfer fabric) prevents the formation of hydrogen bonds. Without bonding in the molded state, it was expected that any buckles created from subsequent placement onto a flat TAD fabric would have little or no effect on tissue properties. Therefore, if the molded tissue were to be dried sufficiently to allow for hydrogen bonds to be formed before the molded sheet was flattened, it is expected that the durability of the buckled regions in the final product could be improved, thereby further enhancing the CD stretch and other related properties.
The data also show that, as a result of the increased CD stretch, the CD slope was significantly decreased and the CD TEA was increased when buckles were added to the tissue. Both of these changes are highly desirable.
MD stretch was not affected by the fabric topographies used in this study. It would be expected that if fabrics were designed to impart buckled regions with a cross-machine direction orientation or an orientation having at least a significant cross-machine direction component, MD stretch would be similarly affected by those buckles. However, as previously stated, sufficient MD stretch can easily be developed by other means, such as rush transfer.
(Towels).
Examples 13 (control) and 14-15 (this invention) are paper towel sheets made using a pilot uncreped throughdried tissue machine that was configured similarly to
The machine chest furnish was diluted to approximately 0.1 percent consistency and delivered to a forming fabric using a single layer headbox. A Voith Fabrics 2164 forming fabric was used and which had a speed of approximately 62 fpm. The resulting web was then transferred to a transfer fabric traveling at 56 fpm using a vacuum shoe to assist the transfer. At a second vacuum shoe assisted transfer, the web was delivered onto a throughdrying fabric. The web was dried with a throughdryer operating at a temperature of 400° C. The resulting basesheet was produced with an oven-dry basis weight of approximately 45 gsm.
In Example 13, a 10 percent rush-transferred web was molded onto the surface of a flat TAD fabric (934). In Example 14, the same web was molded onto the surface of a three-dimensional TAD fabric (Jetson), which served as treatment #1 illustrated in
The physical testing results from these materials are summarized in Table 2 below.
Note the greater CD stretch and lower CD slope for the Jetson and Ironman buckled towel sheets of this invention. The unbuckled towel had a greater CD TEA, which is primarily because its CD tensile strength was greater.
(Facial Tissue).
The facial tissue sheets of Examples 16 and 17 were produced generally in accordance with the process illustrated in
The machine chest furnish was diluted to approximately 0.1 percent consistency and delivered to a forming fabric using a three-layered headbox. The layer fiber weight split was 33 percent/34 percent/33 percent, with 100 percent eucalyptus fiber in the two outer layers and 100% softwood in the middle layer. The Voith Fabrics 2164 forming fabric speed was approximately 62 fpm. The resulting web was then transferred to a transfer fabric traveling at 56 fpm using a vacuum shoe to assist the transfer. At a second vacuum shoe assisted transfer, the web was delivered onto a throughdrying fabric. The web was partially dried with a throughdryer operating at a temperature of 175° C. The basesheet was produced with an oven-dry basis weight of approximately 15 gsm.
The primary differences between Examples 16 and 17 and the previous Examples 4-12′was that Treatment #1 in this case was conducted on the TAD fabric (as opposed to the transfer fabric for Examples 4-12) and Treatment #2 was conducted upon molding into the carrier fabric and to some extent in the impression nip during application of the web to the moving dryer.
As previously defined, the Asten 852 and Voith Fabrics 44GST are flat fabrics. The fabrics used in Example 17 were a three-dimensional TAD fabric (Jetson) and a flat impression fabric (852). Normally, the function of a three-dimensional TAD fabric in a process of this type is to pre-strain the sheet for improved molding into the impression fabric. However, when the impression fabric is extremely flat, as is the 852 fabric, very little molding can occur due to the lack of topography in the impression (or carrier) fabric. Consequently, the excess sheet path-length created by the pre-straining step is translated into buckled regions as depicted in
As shown, compared to a sheet made with a relatively flat TAD fabric (44GST), the micro-buckled sheet of this invention has significantly more CD stretch while maintaining a fairly flat appearance. In this example, buckled regions were produced at web consistencies of 40 percent or greater due to the pre-drying effect of the through-dryer.
It will be appreciated that the foregoing 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.
