Paper making and fiber liberation – Processes of chemical liberation – recovery or purification... – With chemical or physical modification of liberated fiber
Reexamination Certificate
1999-06-16
2001-06-05
Chin, Peter (Department: 1731)
Paper making and fiber liberation
Processes of chemical liberation, recovery or purification...
With chemical or physical modification of liberated fiber
C162S100000, C162S111000, C162S112000, C162S113000, C162S125000, C162S127000, C162S129000, C162S130000, C162S158000, C162S182000
Reexamination Certificate
active
06241850
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a soft tissue product and a method for making a soft tissue product which exhibits improved resistance to linting while maintaining physical strength integrity.
BACKGROUND OF THE INVENTION
Tissue paper products are linked by common consumer demand for a generally conflicting set of physical properties: a pleasing tactile impression (i.e.; softness) while at the same time having strength and a resistance to linting and dusting. Research and development efforts have been directed to the improvement of each of these attributes without negatively impacting the others.
Strength is the ability of the product and its constituent webs to maintain physical integrity and to resist tearing, bursting, and shredding under use conditions.
Softness is the tactile sensation perceived by the consumer as the consumer holds a particular product, rubs it across his/her skin, or crumples it within his/her hand. This tactile sensation is provided by a combination of several physical properties including the stiffness, the surface smoothness, and the lubricity of the paper web from which the product is made. Stiffness, in turn, is usually considered to be directly dependent upon the dry tensile strength of the web and the stiffness of the fibers which make up the web.
Linting and dusting refers to the tendency of a fibrous product and its constitutent web to release unbound or loosely bound fibers during handling or use. Lint resistance is the ability of the fibrous product, and its constituent web, to bind together under use conditions. In other words, the higher the lint resistance, the lower the propensity of the web to lint.
It is well known in the art that hardwood pulp fibers tend to be shorter fibers than softwood fibers. It is also well known in the art that hardwood pulp fibers tend to provide more softness and have less tensile strength than softwood pulp fibers. Additionally, it is well known that hardwood pulp fibers have more of a tendency to lint than softwood pulp fibers.
Though consumers prefer a soft tissue, transfer of lint from the tissue to the user's skin and clothing is deemed undesirable. Furthermore, a tissue, which falls apart during use by the consumer is deemed undesirable.
Hence, it would be desirable to have a tissue which is soft and exhibits resistance to lint while maintaining physical strength integrity.
U.S. Pat. No. 3,554,863 issued to Hervey et al. on Jan. 12, 1971 purports to teach a cellulose pulp sheet impregnated with a cationic long chain fatty alkyl debonding agent. Hervey et al. teaches that addition of the debonding agent reduces the tensile strength of the pulp sheet.
U.S. Pat. No. 4,144,122 issued to Emanuelson et al. on Mar. 13, 1979 purports to teach a process for treating cellulose pulp fibers to reduce interfiber bonding and impart a low degree of mechanical strength to the web formed therefrom.
In light of the prior art, one would expect to find that the addition of debonding agents to the pulp fiber increases softness while negatively impacting lint formation and the physical strength integrity of the tissue. Hence, it is unexpected to find that the present invention allows for the addition of large amounts of debonding agent to the pulp fibers to produce a soft tissue without any appreciable loss of tensile strength or increases in lint formation.
It is also unexpected to find that large amounts of debonding agent can be added to hardwood pulp to increase the softness of the tissue without a detrimental increase in lint formation and without any appreciable loss of tissue physical strength integrity. This allows for larger percentages of hardwood fibers to be utilized in the consumer contacting areas of the tissue (i.e.; outer layers and/or outer plies of the tissue).
SUMMARY OF THE INVENTION
The present invention relates to a process for making soft tissue wherein the process comprises providing an aqueous slurry of papermaking fibers. The aqueous papermaking fibers may include hardwood fibers such as but not limited to eucalyptus fibers. The aqueous slurry of papermaking fibers is debonded and mechanically treated.
The debonding agent is added to the papermaking fibers in an amount from about 13 pounds per ton to 30 pounds per ton of the debonding agent by weight of dry papermaking fibers. The papermaking fibers are mechanically treated such that the Canadian Standard Freeness after mechanical treatment is at least about 1.5% less than the Canadian Standard Freeness of the papermaking fibers prior to mechanical treatment. The papermaking fibers are then formed into a tissue web and dried.
Suitable debonding agents include but are not limited to quaternary ammonium compounds and tertiary amines. The quaternary ammonium compound may have the following formula:
(R
1
)
4-m
—N
+
—[R
2
]
m
X
−
wherein
m is 1 to 3;
each R
1
is a C
1
-C
8
alkyl group, hydroxyalkyl group, hydrocarbyl or substituted hydrocarbyl group, alkoxylated group, benzyl group, or mixtures thereof;
each R
2
is a C
9
-C
41
alkyl group, hydroxyalkyl group, hydrocarbyl or substituted hydrocarbyl group, alkoxylated group, benzyl group, or mixtures thereof; and X
−
is any softener-compatible anion.
The quaternary ammonium compound may be a dialkyldimethylammonium salt wherein the dialkyldimethylammonium salt is dialkyldimethylammonium chloride, ditallowdimethylammonium methyl sulfate, di(hydrogenated)tallow dimethyl ammonium chloride, or mixtures thereof.
The quaternary ammonium compound may also be a biodegradable ester-functional quaternary ammonium compound having the formula:
(R)
4-m
—N
+
—[(CH
2
)
n
—Y—R
2
]
m
X
−
wherein
each Y=—O—(O)C—, or —C(O)—O—;
m=1 to 3;
each n=1 to 4;
each R substituent is a short chain C
1
-C
6
alkyl group, hydroxyalkyl group, hydrocarbyl group, benzyl group or mixtures thereof; each R
2
is a long chain, C
11
-C
23
hydrocarbyl, or substituted hydrocarbyl substituent and X
−
is any softener-compatible anion.
An optional wet strength agent may be added to the papermaking fibers in an amount from about 0.1 pound per ton to 60 pounds per ton by weight of the dry papermaking fibers. An optional dry strength agent may also be added to the papermaking fibers in an amount from about 0.1 pound per ton to 60 pounds per ton by weight of the dry papermaking fibers. A suitable dry strength agent for this purpose includes but is not limited to carboxymethylcellulose.
A tissue web is formed. The tissue web may be through air dried or conventionally wet pressed. The tissue web may be comprised of one or more layers. The tissue web includes at least one outer layer comprised of at least about 30% hardwood fiber. The tissue product may also be comprised of one or more plies.
The present invention also relates to a process for making soft tissue wherein the process comprises providing an aqueous slurry of hardwood papermaking fibers. The hardwood papermaking fibers are debonded with a debonding agent. The debonding agent is added to the hardwood papermaking fibers in an amount from about 13 pounds per ton to 30 pounds per ton of the debonding agent by weight of dry hardwood papermaking fibers. A tissue web is formed. The tissue web is comprised of an outer layer and an inner layer. The outer layer of the tissue web is hardwood fiber.
REFERENCES:
patent: 3414459 (1968-12-01), Wells
patent: 3554862 (1971-01-01), Hervey et al.
patent: 3554863 (1971-01-01), Hervey et al.
patent: 3755220 (1973-08-01), Freimark et al.
patent: 3812000 (1974-05-01), Salvucci, Jr. et al.
patent: 3817827 (1974-06-01), Benz et al.
patent: 3844880 (1974-10-01), Meisel, Jr. et al.
patent: 3867225 (1975-02-01), Nystrand
patent: 3974025 (1976-08-01), Ayers
patent: 3994771 (1976-11-01), Morgan, Jr. et al.
patent: 4144122 (1979-03-01), Emanuelsson et al.
patent: 4191609 (1980-03-01), Trokhan
patent: 4191756 (1980-03-01), Masi et al.
patent: 4196045 (1980-04-01), Ogden
patent: 4225382 (1980-09-01), Kearney et al.
patent: 4300981 (1981-11-01), Carstens
patent: 4351699 (198
Chin Peter
Glazer Julia A.
Rosnell Tara M.
The Procter & Gamble & Company
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