US20100163197A1

US20100163197A1 - Tissue With Improved Dispersibility

Info

Publication number: US20100163197A1
Application number: US12/344,854
Authority: US
Inventors: Kristina Fries Smits; Michael Alan Hermans
Original assignee: Kimberly Clark Worldwide Inc
Current assignee: Kimberly Clark Worldwide Inc
Priority date: 2008-12-29
Filing date: 2008-12-29
Publication date: 2010-07-01
Also published as: GB2478491A; WO2010076686A3; WO2010076686A2; GB201111298D0; MX2011007044A

Abstract

Soft tissue sheets, such as bath tissues, are provided with increased dispersibility and fiber opacity efficiency, while maintaining suitable strength, by the addition of acid-treated seed fibers to the fiber furnish.

Description

BACKGROUND OF THE INVENTION

Most consumers want bath tissue that is not only sufficiently strong for cleaning purposes, but they also want the comfort of mind that the tissues will disperse when flushed down the toilet so that they do not clog sewer or septic lines. While commercially-available bath tissues do disperse, there is room for improvement. Unfortunately, increased dispersibility usually comes with a decrease in strength, which is undesirable. Therefore there is a need for bath tissues having adequate strength with increased dispersibility, while at the same time exhibiting good opacity for perceived hand protection in use.

SUMMARY OF THE INVENTION

It has now been discovered that soft tissues, such as bath tissue, can be made with improved dispersibility and strength as compared to currently available commercial bath tissue products. In addition, the fiber opacity efficiency (hereinafter defined) can also be improved.
Hence in one aspect, the invention resides in a soft tissue having a bone dry basis weight from about 15 to about 35 grams per square meter, a geometric mean tensile strength from about 500 to about 1000 grams per 3 inches of width and a Dispersibility (hereinafter defined) of about 1.5 cycles or less.
In another aspect, the invention resides in a soft tissue having a bone dry basis weight from about 15 to about 35 grams per square meter and from about 0.5 to about 5 dry weight percent of an Enhanced Fiber Additive (hereinafter defined), said tissue having a geometric mean tensile strength from about 500 to about 1000 grams per 3 inches of width and a Dispersibility of about 1.5 cycles or less.
For purposes herein, a “soft tissue” is sheet of cellulosic papermaking fibers suitable for use as a bath tissue. Such soft tissue sheets are characterized by a relatively high bulk and low stiffness (as measured by the geometric mean slope). More specifically, the soft tissue sheet bulk can be about 3 cubic centimeters or greater per gram of fiber, more specifically from about 4 to about 20 cubic centimeters per gram of fiber (cc/g), and still more specifically from about 5 to about 10 cc/g. The geometric mean slope of the soft tissue sheet can be from about 1 to about 10 kilograms, more specifically from about 1.5 to about 8 kilograms, and still more specifically from about 2 to about 6 kilograms.
For purposes herein, an “Enhanced Fiber Additive” is a known seed-based fiber additive, such as fibers derived from corn or soybeans, which have been modified by acid treatment. The acid treatment may optionally be followed by a mild acid chlorite solution, a peroxide solution, or a combination of both. The resulting Enhanced Fiber Additive is high in hemicellulose, which increases fiber-to-fiber bonding, and is normally used as a strength agent in high density papers. The production and uses of Enhanced Fiber Additives is disclosed in U.S. Pat. No. 6,902,649 B1 entitled “Enhanced Fiber Additive; and Use”, issued Jun. 7, 2005 to Satyavolu et al., which is hereby incorporated by reference in its entirety. A commercially available line of Enhanced Fiber Additive is available from Cargill, Incorporated, Minneapolis, Minn., under the trade name HemiForce™. For purposes of this invention, the amount of Enhanced Fiber Additive in the soft tissue can be from about 0.5 to about 5 dry weight percent, more specifically from about 0.5 to about 4 dry weight percent, and still more specifically from about 1 to about 3 dry weight percent.
The bone dry basis weight of the soft tissues of this invention can be from about 15 to about 15 to about 35 grams per square meter (gsm), more specifically from about 15 to about 30 gsm, and more specifically from about 15 to about 25 gsm.
The geometric mean tensile strength (GMT) of the soft tissues of this invention can be from about 500 to about 1000 grams per 3 inches of width, more specifically from about 500 to about 900 grams per 3 inches of width, and still more specifically from about 550 to about 650 grams per 3 inches of width. For purposes of simplicity, the GMT is sometimes reported as “grams”.
The Dispersibility of the soft tissues of this invention can be about 1.5 cycles or less, more specifically from about 0.5 to about 1.5 cycles, more specifically from about 0.5 to about 1.0 cycle, and still more specifically about 1.0 cycle.
The opacity of the soft tissues of this invention can be from about 42.0 to about 47.0 percent, more specifically from about 42.0 to about 46.5 percent, and still more specifically from about 42.5 to about 46.5 percent.
The fiber opacity efficiency for the tissues of this invention, which is the ratio of the opacity divided by the bone dry basis weight and is a measure of the efficiency of the fibers in providing opacity to the tissue sheet, can be about 2.5 percent/gsm or greater, more specifically from about 2.5 to about 3.0 percent/gsm , and still more specifically from 2.56 to 2.70 percent/gsm.
Suitable papermaking fibers particularly include, without limitation, softwood and hardwood fibers. As used herein, the term “furnish” means the papermaking fibers, such as the softwood and hardwood fibers, used to make the tissue, excluding other furnish components or additives, such as EFA. The amount of softwood fibers in the furnish can be from about 5 to about 40 dry weight percent, more specifically from about 10 to about 40 percent, more specifically from about 10 to about 30 percent, and still more specifically from about 10 to about 20 percent. Similarly, the amount of hardwood fibers in the furnish can be from about 60 to about 95 dry weight percent, more specifically from about 60 to about 90 dry weight percent, more specifically from about 70 to about 90 percent, and still more specifically from about 80 to about 90 dry weight percent. Relatively speaking, higher amounts of softwood fibers will increase tensile strength, while higher levels of hardwood fibers will increase surface softness and opacity.
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. Similarly, a disclosure in this specification of a range from 0.1 to 0.5 shall be considered to support claims to any of the following ranges: 0.1-0.5; 0.1-0.4; 0.1-0.3; 0.1-0.2; 0.2-0.5; 0.2-0.4; 0.2-0.3; 0.3-0.5; 0.3-0.4; and 0.4-0.5. 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”.

Test Methods

As used herein, sheet “bulk” is calculated as the quotient of the sheet “caliper” (hereinafter defined), expressed in microns, divided by the basis weight, expressed in grams per square meter. The resulting sheet bulk is expressed in cubic centimeters per gram. More specifically, the sheet caliper is the representative thickness of a single sheet measured in accordance with TAPPI test methods T402 “Standard Conditioning and Testing Atmosphere For Paper, Board, Pulp Handsheets and Related Products” and T411 om-89 “Thickness (caliper) of Paper, Paperboard, and Combined Board” with Note 3 for stacked sheets. The micrometer used for carrying out T411 om-89 is an Emveco 200-A Tissue Caliper Tester available from Emveco, Inc., Newberg, Oreg. The micrometer has a load of 2 kilo-Pascals, a pressure foot area of 2500 square millimeters, a pressure foot diameter of 56.42 millimeters, a dwell time of 3 seconds and a lowering rate of 0.8 millimeters per second.
As used herein, the “geometric mean tensile strength” is the square root of the product of the machine direction tensile strength multiplied by the cross-machine direction tensile strength. The “machine direction (MD) tensile strength” is the peak load (grams-force) per 3 inches (76.2 mm) 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 (76.2 mm) of sample width when a sample is pulled to rupture in the cross-machine direction. The “stretch” is the percent elongation of the sample at the point of rupture during tensile testing. The procedure for measuring tensile strength is as follows.
Samples for tensile strength testing are prepared by cutting a 3 inches (76.2 mm) wide by 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 11S, 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 direction of the sample being tested. At least six (6) representative specimens are tested for each product or sheet, taken “as is”, and the arithmetic average of all individual specimen tests is either the MD or CD tensile strength for the product or sheet.
The “geometric mean slope” (GM Slope) is the square root of the product of the machine direction tensile slope and the cross-machine direction tensile slope. The tensile slope is the least squares regression slope of the load/elongation curve described above measured over the range of 70-157 grams (force). The slope is in kilograms per unit elongation (i.e. 100% strain) for a 76.2 mm (3 inches) wide sample, but for purposes of simplicity sometimes reported herein as “kilograms”.
As used herein, “Dispersibility” is a measure of the propensity of a tissue product to break apart when placed in water under mild agitation. It is determined by placing a sample of the product into a slosh box and observing the dynamic break-up of the sample as the slosh box tips (cycles) back and forth. For rolls of bath tissue, the sample to be tested is a single “sheet” which, for purposes herein and well understood within the tissue industry, is the segment of the bath tissue sheet located between consecutive lines of perforation. It can consist of one or more plies. Such sheets are typically about 4 inches square. The actual size, however, is not particularly important since the size of the slosh box is sufficiently large to accommodate any known tissue sheets. For purposes of testing tissue sample basesheets, which have not been converted into actual final product, a 4 inches-by-4 inches sample is sufficient.
The slosh box used for the dynamic break-up of the sample consists of a plastic box having inside dimensions measuring 18 inches wide (as viewed from the front), 12 inches deep (front to back) and 6.5 inches high. It is constructed from 0.5 inch thick Plexiglas® and is provided with a tightly fitting lid. The slosh box rests securely on a rocking platform and rocks back and forth from short side (12 inch end) to short side (opposite 12 inch end). The underside of the platform is attached to a reciprocating cam. In operation, the rotational movement of the cam cyclically raises one side of the platform and thereby also lowers the corresponding side of the slosh box, pivoting at the center of the box. The amplitude of the rocking motion of the one side of the slosh box is ±2 inches (a range of 4 inches from the top to the bottom of the rocking cycle). The rotational speed of the cam is set to a constant speed of 26 revolutions per minute (±2 revolutions per minute), which results in 43 slosh cycles per minute. For purposes herein, a “cycle” consists of one “up and down” motion of the slosh box.
Prior to testing, the slosh box is filled with 2000 ml±20 ml of a soak solution. The soak solution consists of distilled water mixed with 0.25 teaspoon of sodium bicarbonate in order to keep the pH of the soak solution higher than 7. The temperature of the soak solution is maintained at 23° C.±3° C. Solution is drained and the box chamber is rinsed and refilled between each specimen characterization. To carry out the test, the tissue sample is placed flat on the surface of the water in the slosh box and the slosh box is started immediately. The break-up of the sample in the slosh box is visually observed and the number of complete cycles required to separate the sample into two distinct pieces is recorded. (For multi-ply products, ply separation does not constitute separation of the sample into two distinct pieces for purposes of this test. Instead, at least one of the plies must separate into two distinct pieces.) Five replicates of the tissue sample are tested. The observed number of cycles needed to break up the test samples is averaged to achieve a Dispersibility value (in “cycles”) for the product sample.
As used herein, “opacity” is measured using a Technibrite Micro TB-1C tester, which is well known in the paper industry, available from Technidyne Corporation, 100 Quality Avenue, New Albany, Ind., USA. The Technibrite Micro TB-1C tester, which is a dual beam optical system, is a fully automatic microprocessor-controlled instrument that provides brightness, color, opacity and fluorescence in conformance with ISO and other international standards. Tests are conducted in a standard laboratory atmosphere (23° C.±1° C. and 50%±2% humidity) following the instructions for the instrument. For measuring tissue opacity, the QC routine is used with the black body cup and with the Y (green) filter in the active position. When taking measurements, the operator should avoid taking readings in areas of the sample which contain printing or perforations. Measurements should be taken on the outside of the sheet (the side of the sheet that consumers would see). Fifteen representative samples should be tested and the results averaged to obtain a value for the particular product. The measurement values represent reflectance and are expressed as a percent.

EXAMPLES

In order to further illustrate this invention, a number of tissues were produced using conventional creped, wet-pressed technology, such as the method disclosed in U.S. Pat. No. 6,368,454 entitled “Method of Making Soft Bulky Single Ply Tissue” issued Apr. 9, 2002, to Dwiggins et al. (without embossing), which is hereby incorporated by reference. Unless stated otherwise, the particular tissue making method used is not critical.

Example 1 (Invention)

Single-ply bath tissue basesheet was produced in a conventional manner on a pilot scale tissue machine. More particularly, a tissue web was formed on a forming fabric, transferred to a felt, and thereafter transferred to a Yankee dryer in a conventional manner. The tissue web was dried to approximately 95 percent consistency on the Yankee dryer and creped using standard creping technology. The resulting creped tissue sheet was wound into a parent roll for testing.
The tissue furnish was a blended furnish comprising eucalyptus hardwood (HW) fibers and refined northern softwood kraft (SW) fibers. Prior to formation of the web, the northern softwood fibers were pulped for 30 minutes at 2.5 percent consistency, while the eucalyptus hardwood fibers were pulped at 2 percent consistency. The northern softwood fibers were refined for 5 minutes. The pulp mix (expressed as bone dry weight percent) was 39.2 percent SW, 58.8 percent HW, and 2 percent Cargill HemiForce™ Enhanced Fiber Additive (EFA). The EFA was diluted to below 2 percent consistency and allowed to mix in the blended stock chest for 20 minutes before starting formation of the tissue web. The tissue machine speed (the speed of the Yankee dryer) was 50 feet per minute (fpm).

Example 2 (Invention)

A single-ply bath tissue was made as described in Example 1, except the pulp mix was 19.8 percent SW, 79.2 percent HW and 1 percent EFA.

Example 3 (Invention)

A single-ply bath tissue was made as described in Example 1, except the pulp mix was 9.7 percent SW, 87.3 percent HW and 3 percent EFA.

Example 4 (Control 1)

A single-ply bath tissue was made as described in Example 1, except the softwood fibers were not refined and the pulp mix was 40 percent SW and 60 percent HW. No EFA was added to the pulp mix.

Example 5 (Control 2)

A single-ply bath tissue was made as described in Example 1, except the softwood fibers were refined for 9 minutes and the pulp mix was 40 percent SW and 60 percent HW. No EFA was added to the pulp mix.

Example 6 (Control 3)

A single-ply bath tissue was made as described in Example 1, except the pulp mix was 40 percent SW and 60 percent HW. No EFA was added to the pulp mix.

Example 7 (Control 4)

A single-ply bath tissue was made as described in Example 1, except the pulp mix was 39.6 percent SW, 59.4 percent HW and 1 percent EFA.

Examples 8-16 (Commercial)

A number of commercially-available bath tissue samples were collected and tested for various properties. The furnish compositions are not known.
All of the tissues were measured for bone dry basis weight, geometric mean tensile strength, Dispersibility (slosh box cycles) and opacity. The Invention 1 and 2 samples and the Control 3 and 4 samples were also ranked for panel softness. These samples were chosen for softness testing since they all had approximately the. same geometric mean tensile strength. The tissue samples were given to a trained panel which ranked the tissue samples for surface softness on a relative scale. A ranking of “A” is considered relatively softer than a ranking of “B”. The results are presented below in Table 1.

TABLE 1

	Basis		EFA					Surface
	Weight	Furnish	(weight	GMT	Dispersibility	Opacity	Opacity/Basis	Softness
Example	(gsm)	(% SW/% HW)	percent)	(grams)	(Cycles)	(Percent)	Weight Ratio	(Grouping)

1-Invention 1	15.69	39.2/58.8	2	651	1	42.332	2.70	B
2-Invention 2	18.06	19.8/79.2	1	554	1	46.276	2.56	A
3-Invention 3	17.00	9.7/87.3	3	637	1	46.008	2.71
4-Control 1	18.17	40/60	0	311	1	45.44	2.50
5-Control 2	18.54	40/60	0	894	6.4	46.108	2.52
6-Control 3	18.73	40/60	0	586	2.6	46.158	2.46	B
7-Control 4	17.10	39.6/59.4	1	597	1.8	43.478	2.54	B
8-Marcal	16.30	—		942	5	46.76	2.87
9-Kroger	15.57	—		601	5	40.24	2.58
10-Scott 1000	17.22	—		773	6	44.63	2.59
11-Albertson's	17.68	—		684	2	44.29	2.51
12-Pert	16.39	—		419	3	44.04	2.69
13-Walgreen's	19.16	—		800	4	52.95	2.76
14-CVS	16.39	—		419	3	44.04	2.69
16-Homelife	17.43	—		895	7	41.31	2.37

The results show, with regard to softness, that the Invention 2 sample had the highest surface softness (95% confidence level) among the tissues tested. The other inventive sample tested (Invention 1) was judged to have surface softness similar to that of the controls. This data indicates that the inventive tissues were at least as soft as the control codes.
The results further show that the tissues of this invention have an improved Dispersibility and better opacity (as measured by the ratio of the opacity divided by the basis weight) at a fixed geometric mean tensile strength. Obtaining the desired combination of softness, tensile strength, Dispersibility and fiber opacity efficiency required furnish and chemistry manipulation. As the data of Table 1 indicates, the Control 1 sample had very good Dispersibility (1 cycle) by not refining the softwood fibers in the furnish. However, that sample also had a very low geometric mean tensile strength of 311 grams. On the other hand, the Control 4 sample, which included 1 dry weight percent EFA in the fiber furnish, had a good geometric mean tensile strength of 597 grams, but a higher Dispersibility (1.8 cycles), which was only somewhat better than the best of the commercially available bath tissues (2 cycles for the Albertson's product). Therefore, to further improve the Dispersibility, the furnish was adjusted for the inventive samples to include additional hardwood fiber and/or EFA. For the Invention 1 sample, the EFA content of the furnish was increased to 2 dry weight percent. For the Invention 2 and 3 samples, the hardwood portion of the furnish was increased to approximately 80 percent and 90 percent, respectively. In all cases, the Dispersibility was 1 cycle and the geometric mean tensile strength was above 550 grams.
Without being bound by theory, it is believed the increase in the hardwood portion of the furnish increased the Dispersibility of the product (i.e. reduced the number of cycles) and increased the opacity of the product. This is thought to be due to the higher fiber count and reduced fiber length associated with the substitution of hardwood fiber for a portion of the softwood fiber. The higher fiber count of the hardwood pulp is thought to have increased the opacity and the lower fiber length is thought to have increased the product Dispersibility. However, the increase in hardwood fiber content also decreased the tensile strength of the product, perhaps reducing it below the required strength level. This was countered, where necessary, by further increasing the level of EFA as the EFA provided improved strength and fiber opacity efficiency as well as good Dispersibility.
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.

Claims

1. A soft tissue having a bone dry basis weight from about 15 to about 35 grams per square meter, from about 5 to about 40 dry weight percent softwood fibers and from about 60 to about 95 dry weight percent hardwood fibers, a geometric mean tensile strength from about 500 to about 1000 grams per 3 inches of width and a Dispersibility of about 1.5 cycles or less.

2. The tissue of claim 1 having a Dispersibility from about 0.5 to about 1.5 cycles.

3. The tissue of claim 1 having a Dispersibility from about 0.5 to 1.0 cycles.

4. The tissue of claim 1 having a Dispersibility of about 1 cycle.

5. The tissue of claim 1 having a ratio of opacity divided by bone dry basis weight of about 2.5 percent/gsm or greater.

6. The tissue of claim 1 having a ratio of opacity divided by bone dry basis weight from about 2.5 to about 3.0 percent/gsm.

7. The tissue of claim 1 having a ratio of opacity divided by bone dry basis weight from 2.56 to 2.70 percent/gsm.

8. The tissue of claim 1 consisting of a single ply.

9. The tissue of claim 1 having from about 10 to about 20 dry weight percent softwood fibers and from about 80 to about 90 dry weight percent hardwood fibers.

10. A soft tissue having a bone dry basis weight from about 15 to about 35 grams per square meter, from about 5 to about 40 dry weight percent softwood fibers and from about 60 to about 95 dry weight percent hardwood fibers, and from about 0.5 to about 5 dry weight percent of an Enhanced Fiber Additive, said tissue having a geometric mean tensile strength from about 500 to about 1000 grams per 3 inches of width and a Dispersibility of about 1.5 cycles or less.

11. The tissue of claim 10 having from about 0.5 to about 4 dry weight percent of an Enhanced Fiber Additive.

12. The tissue of claim 10 having from about 1 to about 3 dry weight percent of an Enhanced Fiber Additive.

13. The tissue of claim 10 having a Dispersibility from about 0.5 to 1.5 cycles.

14. The tissue of claim 10 having a Dispersibility of about 1 cycle.

15. The tissue of claim 10 having a ratio of opacity divided by bone dry basis weight of about 2.5 percent/gsm or greater.

16. The tissue of claim 10 having a ratio of opacity divided by bone dry basis weight from about 2.5 to about 3.0 percent/gsm.

17. The tissue of claim 10 having a ratio of opacity divided by bone dry basis weight from 2.56 to 2.70 percent/gsm.

18. The tissue of claim 10 consisting of a single ply.

19. The tissue of claim 10 having from about 10 to about 20 dry weight percent softwood fibers and from about 80 to about 90 dry weight percent hardwood fibers.