Paper making and fiber liberation – Processes and products – Non-uniform – irregular or configured web or sheet
Reexamination Certificate
1997-11-14
2001-08-21
Chin, Peter (Department: 1731)
Paper making and fiber liberation
Processes and products
Non-uniform, irregular or configured web or sheet
C162S112000, C162S125000, C162S127000, C162S129000, C162S130000, C162S134000, C162S135000, C162S146000
Reexamination Certificate
active
06277241
ABSTRACT:
FIELD OF THE INVENTION
The present invention is generally directed to abrasion resistant and strong base webs that have good liquid absorption properties. The base web is generally made from a combination of pulp fibers and synthetic fibers. In one embodiment, the base web is used as a wiping product.
BACKGROUND OF THE INVENTION
Liquid absorbent products such a paper towels, industrial wipers, food service wipers, napkins, medical pads, and other similar products are designed to include several important properties. For example, the products should have good bulk, a soft feel and should be highly absorbent. The products should also have good strength even when wet and should resist tearing. Further, the products should also have good stretch characteristics, should be abrasion resistant, and should not deteriorate in the environment in which they are used.
In the past, many attempts have been made to enhance and increase certain physical properties of such products. Unfortunately, however, when steps are taken to increase one property of these products, other characteristics of the products may be adversely affected. For instance, the softness of paper wiping products can be increased by several different methods, such as by selecting a particular fiber type, or by reducing cellulosic fiber bonding within the product. Increasing softness according to one of the above methods, however, may adversely affect the strength of the product. Conversely, steps normally taken to increase the strength of a fibrous web typically have an adverse impact upon the softness or the absorbency of the web.
One particular process that has proven to be very successful in producing paper towels and other wiping products is disclosed in U.S. Pat. No. 3,879,257 to Gentile, et al., which is incorporated herein by reference in its entirety. In Gentile, et al., a process is disclosed for producing soft, absorbent, single ply fibrous webs having a laminate-like structure that are particularly well suited for use as wiping products.
The fibrous webs disclosed in Gentile, et al. are formed from an aqueous slurry of principally lignocellulosic fibers under conditions which reduce inner fiber bonding. A bonding material, such as a latex elastomeric composition, is applied to a first surface of the web in a spaced-apart pattern. In particular, the bonding material is applied so that it covers from about 50% to about 60% of the surface area of the web. The bonding material provides strength to the web and abrasion resistance to the surface. Once applied, the bonding material can penetrate the web preferably from about 10% to about 40% of the thickness of the web.
The bonding material can then be similarly applied to the opposite side of the web for further providing additional strength and abrasion resistance. Once the bonding material is applied to the second side of the web, the web can be brought into contact with a creping surface. Specifically, the web will adhere to the creping surface according to the pattern to which the bonding material was applied. The web is then creped from the creping surface with a doctor blade. Creping the web greatly disrupts the fibers within the web, thereby increasing the softness, absorbency, and bulk of the web.
In one of the preferred embodiments disclosed in Gentile, et al., both sides of the paper web are creped after the bonding material has been applied. Gentile, et al. also discusses the use of chemical debonders to treat the fibers prior to forming the web in order to further reduce innerfiber bonding and to increase softness and bulk.
Although the processes disclosed in Gentile, et al. have provided great advancements in the art of making disposable wiping products, the present invention is directed to further improvements in fibrous base webs. In particular, the present invention is directed to a fibrous base web having an improved combination of abrasion resistance, strength, and wipe dry properties. These and other advantages will be made apparent from the following description.
SUMMARY OF THE INVENTION
As stated above, the present invention is directed to further improvements in prior art constructions and methods, which are achieved by providing an abrasion resistant, liquid absorbent base web. The base web may include a first outer fibrous layer defining a first side of the web and a second and opposing outer fibrous layer defining a second side of the web. The first and second outer layers may contain synthetic staple fibers either alone or in combination with pulp fibers. An intermediate fibrous layer may be positioned between the first outer layer and the second outer layer. The intermediate layer may contain pulp fibers.
Desirably, a bonding material is applied to at least one side of the base web. In particular, the bonding material may be applied to the web according to a predetermined pattern, such as a geometric pattern. After the bonding material is applied to at least one side of the web, the web may be creped. For instance, in one embodiment, the bonding material may be applied to both sides of the base web and both sides of the web may then be creped.
The synthetic staple fibers contained within the base web of the present invention can be made from one or more polymers including polyester, nylon, polypropylene and rayon. The fibers can have a length of at least 0.25 inches and can have a denier of less than about 2.5, and particularly less than 1.5. The synthetic fibers can be added to the base web in an/amount up to about 50% by weight and particularly from about 5% to about 15% by weight. Further, each outer layer containing the synthetic fibers can comprise from about 15% to about 40% of the total weight of the web, and particularly from about 25% to about 35% of the weight of the web.
In order to increase softness and the liquid absorbent properties of the base web, the intermediate fibrous layer can contain short pulp fibers having a low coarseness, which create a pore size gradient between the outer layers and the inner layer. It is believed that by creating a pore size gradient, the base web has improved wicking properties. Short fibers having a low coarseness that may be included in the intermediate layer include hardwood fibers, such as eucalyptus fibers or eucalyptus-like fibers. For instance, the fibers can have a length of less than about 2.0 millimeters and a coarseness of less than about 10. The hardwood fibers can be present within the base web in an amount from about 10% to about 40% by weight.
Other fibers that may be incorporated into the intermediate fibrous layer in order to improve the wipe dry properties of the base web include highly liquid absorbent and highly wettable fibers. For instance, such fibers can include highly extracted pulp fibers, such as mercerized alpha pulp fibers. The alpha pulp can be made from softwood fibers or hardwood fibers and can be present in the intermediate layer either alone or in combination with the above-described fibers.
The bonding material applied to the base web can be applied in a pattern that covers from about 10% to about 60%, and more particularly from about 20% to about 50% of the surface area of each side of the web. The bonding material can be applied to each side of the web in an amount up to about 10% by weight, and particularly from about 5% to about 8% by weight. Once applied, the bonding material can penetrate the web in an amount from about 15% to about 50% of the total thickness of the web.
The preselected pattern used to apply the bonding material can be, in one embodiment, a reticular interconnected design. Alternatively, the preselected pattern can comprise a succession of discrete dots. The bonding material can be for instance, a latex, such as an ethylene vinyl acetate copolymer cross-linked with N-methyl acrylamide groups. Copolymers of vinyl acrylics with cross-linking capability are also useful.
Once formed, the base web of the present invention can have a basis weight of from about 20 pounds per ream to about 80 pounds per ream, depending upon the particular applic
Anderson Ralph L.
Garneski Charles J.
Hurst Stephen A.
Merker Joseph F.
Saffel Thomas C.
Chin Peter
Dority & Manning P.A.
Kimberly--Clark Worldwide, Inc.
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