Note: Descriptions are shown in the official language in which they were submitted.
CA 022~217 1998-12-21
METHOD AND APPARATUS FOR MAKING A SOFTER, MORE
ABSORBENT NO PRESS, NO CREPE TOWEL
Technical Field
This invention relates generally to an absorbent web, such as tissues towels
and wipes, and to a method for preparing the absorbent web. More particularly, the
invention relates to a softer, more absorbent cellulosic web or cellulosic sheet.
1 0 Background
Cellulosic web-based products, such as hand towels, wipers, and the like, are
widely manufactured in the paper making industry. Each product has unique
characteristics requiring appropriate attributes. The proper attributes ensure that the
product is suitable for its intended purpose.
During manufacture of many cellulosic webs, the web is pressed or creped
during or after drying in order to impart tensile strength. This pressing or creping
can detrimentally influence the softness and absorbency of the web, and requires an
additional manufacturing step or steps that can add complexity and cost to the
formation of the webs. The pressing and creping can increase stiffness of the web,
and take away from absorbency.
For many products, high tensile strength and high water absorbency are
important properties. Tensile strength of cellulosic webs is often measured under
dry conditions to determine "dry-tensile strength", and under wet conditions to
determine "wet-tensile strength". Wet-tensile strength and dry-tensile strength are
often closely related. Products having high dry-tensile strength frequently have high
wet-tensile strength. The relationship between dry-tensile strength and wet-tensile
CA 022~217 1998-12-21
strength occurs, in part, because certain manufacturing processes enhance both
properties. For example, pressing a cellulosic web under high pressure often imparts
increased dry-tensile and wet-tensile strengths. As noted above, the pressing of the
web under high pressure can be disadvantageous if it reduces the absorbency of the
5 web or makes the web stiffer.
A cellulosic web must have adequate dry-tensile strength and adequate wet-
tensile strength. However, since cellulosic webs often deteriorate and lose strength
when wet, wet-tensile strength is normally significantly lower than dry-tensile
strength. Thus, many cellulosic webs have inadequate wet-tensile strength, even
10 though they have adequate dry-tensile strength.
While a hand towel must have some dry-tensile strength, high dry-tensile
strength can be disadvantageous because it correlates closely with stiffness and stiff
webs. Hand towels manufactured from stiff webs are received with disfavor by
consumers, since the towels do not have the soft feel of traditional cotton hand
15 towels. In contrast, consumers desire high wet-tensile strength, because it allows
more vigorous use of the hand towel to pick up spills and scrub wet soiled surfaces.
The relationship between wet-tensile and dry-tensile is often expressed as a
tensile strength ratio in which wet-tensile strength is divided by dry-tensile strength
to get the wet/dry tensile ratio (wet-tensile value in numerator, dry-tensile value in
20 denominator). The wet/dry tensile ratio is normally less than 0.3, since the wet-
tensile strength is usually significantly less than the dry-tensile strength. The ratio is
preferably greater than 0.8, greater than or as close to 1 as possible, since this
CA 022~217 1998-12-21
indicates a high wet-tensile strength relative to dry-tensile strength. Cellulosic webs
with high wet/dry tensile ratios are soft, yet strong.
Therefore, a need exists for an improved cellulosic web that has sufficient
strength and absorbency, but is not pressed or creped so as to m~int~in softness.
Summary of the Invention
The present invention provides an improved method for making a cellulosic
web, as well as a web made using the improved method. The method includes
forming a finished cellulosic web without pressing or creping. A debonder and a
10 wetting agent, or a debonding wetting agent, are added to the papermaking furnish or
the web prior to drying. The finished web has improved absorbency and
advantageous wet-strength to dry-strength ratios.
A specific implementation of the method of the invention includes providing
a papermaking furnish containing a cellulosic material and water. An effective
amount of between 0.25 and 2.0 weight percent of a wet-strength resin is added to
the cellulosic material based on the dry-weight of the cellulosic material. In
addition, an effective amount, between 0.1 percent and 1.0 percent, of a debonder is
added based on the dry-weight of the cellulosic material; and between 0.1 and 1.0
percent of a hydroscopic wetting agent is added to the paperm~king furnish. A
20 cellulosic web is formed from the paperm:~king furnish and dried without pressing
and crepmg.
In another implementation, the cellulosic web is formed by adding a wet-
strength resin to a paperm~king furnish containing a cellulosic material and water.
CA 022~217 1998-12-21
A hydroscopic cationic wetting agent having debonding properties is added to thepaperm~king furnish, which in turn is dewatered and formed into a cellulosic webthat is dried without pressing or creping to form an improved web having
advantageous wet-strength and absorbency properties.
The above summary of the present invention is not intended to describe each
discussed embodiment of the present invention. While the invention is susceptible
to various modifications and alternative forms, specifics thereof will be described in
detail. It should be understood, however, that the intention is not to limit theinvention to particular embodiments described. On the contrary, the intention is to
cover modifications, equivalents, and alternatives falling within the spirit and scope
of the invention as defined by the appended claims.
Detailed Description of the Invention
The present invention is directed to an improved method for making a
cellulosic web, as well as a web made using the improved method. The method
includes addition of surfactant and wet strength resin to a paperm~king furnish. The
resulting paperm~king furnish is formed into a cellulosic web. A debonder and a
wetting agent are added to the paperm~king furnish or the web prior to drying.
Alternatively, a wetting agent having debonding properties is added to the furnish or
web prior to drying. The finished web has improved absorbency and advantageous
wet-strength to dry-strength ratios.
A specific implementation of the method of the invention includes providing
a papermaking furnish cont~ining a cellulosic material and water. Between about
CA 022~217 1998-12-21
0.25 and 2 weight percent of wet-strength resin is added to the cellulosic material
based on the dry-weight of the cellulosic material. In addition, between about 0.1
percent and 1 percent of a debonder is added based on the dry-weight of the
cellulosic material. Between about 0.1 and 1 percent of a hydroscopic wetting agent
5 is also added to the paperm~king furnish. A cellulosic web is formed from the
paperm~king furnish and dried without pressing and creping.
In another implementation, the cellulosic web is formed by adding between
about 0.25 and 2 percent by weight of a wet-strength resin to a paperm~king furnish
containing a cellulosic material and water. A hydroscopic cationic wetting agent
10 having debonding properties is added at between about 0.1 and 2 weight percent to
the paperm~king furnish, which in turn is dewatered and formed into a cellulosic
web that is dried without pressing or creping to form an improved web having
advantageous wet-strength and absorbency properties. This web is subsequently
dried in accordance with conventional paper making methods, including drying
15 without pressure and without creping. The finished web has improved strength
properties, for example, improved wet-tensile strength and an improved wet-tensile
strength to dry-tensile strength ratio (wet/dry tensile ratio).
The method includes providing a paperm~king furnish cont~ining a cellulosic
material and water. The cellulosic material is, for example, Northern Soft Wood
20 Kraft (NSWK), chemi-thermo-mechanical pulp (CTMP), natural redwood (RW),
Mobile Pine (MP), or a recycled wood fiber, such as bleached recycled office waste
fiber.
CA 022~217 1998-12-21
While the present invention is not limited to a specific hydroscopic wetting
agent, appropriate ones include any hydropohillic anionic, nonionic or cationic
wetting agent such as an anionic sulfonate, Witco 5175-26A, manufactured by the
Witco Chemical Co., nonionic polyethylene glycols (PEGs), quaternary ammonium
compounds, Incroquat AQ, and Glucoquat 125. Appropriate PEGs include PEG
300, PEG 400, and PEG 600. Witco 5175-26A includes a significant sulfonate
component, and certain appropriate hydroscopic wetting agents include an anionicalkyl sulfate or anionic alkyl sulfonate component. Other acceptable hydroscopicwetting agents include Witco EP-5327-97 and EP-5293-150, also manufactured by
the Witco Chemical Co. In addition to the anionic alkyl sulfate or anionic alkylsulfonate component, the hydroscopic wetting agent may include other wetting
agents to improve water compatibility and absorbency on the fiber.
The wet-strength resin is preferably water soluble. Suitable resins include
polyamide-epichlorohydrin resins such as those sold by Hercules Incorporated of
Wilmington, Delaware, under the brand name Kymene 557H and Kymene 2064.
These resins include low molecular weight polymers having reactive functional
groups, including epoxy and amino groups. In certain implementations, the wet-
strength resin is added at a rate of between about 5.0 and 30 pounds per ton of
cellulosic material.
The resulting cellulosic web has improved wet-tensile strength as well as an
improved ratio of wet-tensile strength to dry-tensile strength . Referring now to the
tables produced below, example formulations of cellulosic webs constructed in
accordance with the present invention are shown.
CA 022~217 1998-12-21
Example 1
Furnish = 40% Mobile Wet Lap Pine, 30% recycled fiber, 30% CTMP, and 0.8%
Kymene 557H.
Additive = none
Basis Weight (BW): 25.9
Machine Direction Tensile (MDT): 54
Machine Direction Strength (MDS): 13
Cross Directional Tensile (CDT): 31
Cross Directional Strength (CDS): 6
Cured Cross Direction Wet Tensile (CCDWT): 8.9
Balk / Basis Weight (BLK/B.W.): 15.2
XY Wick: 0.17
Wet/Dry: 28.6
Example 2
Furnish = 40% Mobile Wet Lap Pine, 30% recycled fiber, 30% CTMP, and 0.8%
Kymene 557H.
Additive = 0.7% Witco 5175-26A added to the wet end.
Basis Weight (BW): 28.4
Machine Direction Tensile (MDT): 40
Machine Direction Strength (MDS): 12
Cross Directional Tensile (CDT): 23
Cross Directional Strength (CDS): 5
Cured Cross Direction Wet Tensile (CCDWT): 7.4
Balk / Basis Weight (BLK/B.W.): 14.1
XY Wick: 0.19
Wet/Dry: 32.3
CA 022~217 1998-12-21
Example 3
Furnish = 40% Mobile Wet Lap Pine, 30% recycled fiber, 30% CTMP, and 0.8%
Kymene 557H.
Additive = 0.7% Witco 5175-26A added to the wet end and 0.3% Witco 5175-26A
added at the through dried wire.
Basis Weight (BW): 27.4
Machine Direction Tensile (MDT): 34
Machine Direction Strength (MDS): 12
Cross Directional Tensile (CDT): 22
Cross Directional Strength (CDS): 5
Cured Cross Direction Wet Tensile (CCDWT): 7.3
Balk / Basis Weight (BLK/B.W.): 16
XY Wick: .22
Wet/Dry: 33 3
Example 4
Furnish = 40% Mobile Wet Lap Pine, 30% recycled fiber, 30% CTMP, and 0.8%
Kymene 557H.
Additive = 0.7% Glucoquat 125 added to the wet end and 0.3% Glucoquat 125 added at
the through dried wire.
Basis Weight (BW): 26.2
Machine Direction Tensile (MDT): 42
Machine Direction Strength (MDS): 11
Cross Directional Tensile (CDT): 27
Cross Directional Strength (CDS): 5
Cured Cross Direction Wet Tensile (CCDWT): 8.2
Balk / Basis Weight (BLK/B.W.): 15
XY Wick: 0.22
Wet/Dry: 30.2
Example 1 shows a mixed pulp furnish with Kymene 557H wet strength resin
containing polyamide epichlorohydrin resins, but no other
debonders
,
CA 022~217 1998-12-21
or hydroscopic wetting agents. Examples 2, 3, and 4 show the mixed pulp furnish with
Kymene 557H wet strength resin along with hydroscopic wetting agent additives, and
indicate a reduction in dry tensile, measured as machine direction tensile (MDT), of 37
percent, with only a 7 to 17 percent loss in wet tensile measured as cured cross direction
5 wet tensile (CCDWT). In addition, a wicking speed increase of 30 percent is obtained,
along with improvements in the wet/dry tensile ratio. The sample from Example 3
shows a noticeably softer and more absorbent cellulosic web with small changes to the
wet strength. The methods of examples 2, 3, and 4 allow production of a soft towel by a
no press, no crepe (NPNC) or no press, no crepe (NPNC)/restrained drying technique.
10 A permanent pattern may be imparted onto the web by using a coarse through-dried
wire for formation of the cellulosic web.
Example 5
Furnish = 40% Mobile Wet Lap Pine, 30% recycled fiber, 30% CTMP, and 1.0%
Kymene 557H.
Additive = none.
Basis Weight (BW): 25.8
Machine Direction Tensile (MDT): 59
Machine Direction Strength (MDS): 11
Cross Directional Tensile (CDT): 31
Cross Directional Strength (CDS): 6
Cured Cross Direction Wet Tensile (CCDWT): 10.7
Balk / Basis Weight (BLK/B.W.): 15.6
XY Wick: 0.16
Wet/Dry: 34 9
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Example 6
Furnish = 40% Mobile Wet Lap Pine, 30% recycled fiber, 30% CTMP, and 1.0%
Kymene 557H.
Additive = 0.7% Witco 5175-26A added to the wet end and 0.3% Witco 5175-26A
added at the through dried wire.
Basis Weight (BW): 26.1
Machine Direction Tensile (MDT): 50
Machine Direction Strength (MDS): 13
Cross Directional Tensile (CDT): 27
Cross Directional Strength (CDS): 6
Cured Cross Direction Wet Tensile (CCDWT): 9.5
Balk / Basis Weight (BLK/B.W.): 15.1
XY Wick: 0.21
Wet/Dry: 36.0
Example 7
Furnish = 40% Mobile Wet Lap Pine, 30% recycled fiber, 30% CTMP, and 1.0%
Kymene 557H.
Additive = 0.7% Incroquat AQ added to the wet end and 0.3% Incroquat AQ added atthe through dried wire.
Basis Weight (BW): 25.5
Machine Direction Tensile (MDT): 50
Machine Direction Strength (MDS): 13
Cross Directional Tensile (CDT): 32
Cross Directional Strength (CDS): 5
Cured Cross Direction Wet Tensile (CCDWT): 11.7
Balk / Basis Weight (BLK/B.W.): 15.5
XY Wick: 0.21
Wet/Dry: 36.7
CA 022~217 1998-12-21
Example 8
Furnish = 40% Mobile Wet Lap Pine,30% recycled fiber,30% CTMP, and 1.0%Kymene 557H.
Additive = 0.2% Aerosurf PA-801 debonder added at the wet end.
Basis Weight (BW): 32.6
Machine Direction Tensile (MDT): 57
Machine Direction Strength (MDS): 14
Cross Directional Tensile (CDT): 37
Cross Directional Strength (CDS): 5
Cured Cross Direction Wet Tensile (CCDWT): 14.0
Balk / Basis Weight (BLK/B.W.): 14.0
XY Wick: 0.11
Wet/Dry: 38.1
Examples 6 and 7 show significant improvements in wicking speeds while
reducing tensile and improving the wet/dry ratio.
Example 9
Furnish = 40% NSWK,30% CTMP,30% Eucalyptus, and 0.6% Kymene 557H.
Additive = 0.3% polyethylene glycol 300 added at the through dried wire.
Basis Weight (BW): 25.9
Machine Direction Tensile (MDT): 60
Machine Direction Strength (MDS): 17
Cross Directional Tensile (CDT): 28
Cross Directional Strength (CDS): 5
Cured Cross Direction Wet Tensile (CCDWT): 10.0
Balk / Basis Weight (BLK/B.W.): 16.0
XY Wick: 0.10
Wet/Dry: 34.7
CA 022~217 1998-12-21
Example 10
Furnish = 40% NSWK, 30% CTMP, 30% Eucalyptus, and 0.6% Kymene 557H.
Additive = 0.4% of Arosurf PA801 was added to the paper furnish and 0.3%
polyethylene glycol was added to the web at the through-dried wire.
Basis Weight (BW): 26.9
Machine Direction Tensile (MDT): 25
Machine Direction Strength (MDS): 14
Cross Directional Tensile (CDT): 14
Cross Directional Strength (CDS): 5
Cured Cross Direction Wet Tensile (CCDWT): 6.6
Balk / Basis Weight (BLK/B.W.): 15.6
XY Wick: 0.14
Wet/Dry: 43. 1
Examples 9 and 10 show a combination of debonder and post-formed addition of
polyethylene glycol 300 reduces dry tensile by over 60%, while wet tensile was reduced
only 34%. The wet/dry ratio increased to 43%, giving a significantly softer towel.
While the present invention has been described with reference to several
particular implementations, those skilled in the art will recognize that many changes
may be made hereto without departing form the spirit and scope of the present
invention.
