Paper making and fiber liberation – Processes and products – Plural fiber containing
Reexamination Certificate
1999-12-29
2001-06-26
Chin, Peter (Department: 1731)
Paper making and fiber liberation
Processes and products
Plural fiber containing
C162S156000, C162S168300, C162S183000
Reexamination Certificate
active
06251224
ABSTRACT:
TECHNICAL FIELD AND INDUSTRIAL APPLICABILITY OF THE INVENTION
This invention relates generally to bicomponent mats and their method of manufacture. In particular, the invention relates to a method of making a bi-component mat of glass fibers and pulp fibers using a pulp surface treatment and a compatible dispersion system and the mats formed by this method.
BACKGROUND OF THE INVENTION
The present invention relates to a fibrous mat and its method of manufacture. Several types of fibrous mats and their method of manufacture are known. For example, one conventional method of making a nonwoven fabric is known as a dry process, which involves the bonding of fibers by heat. European Patent Application No. 0 070 164 to Fakete et al. (Fakete) generally involves such a method. The fabric in Fakete relates to a blend of bicomponent fiber and natural or synthetic fiber. Fakete generally involves a low density, thermobonded, nonwoven fabric comprising a staple length polyester/polyethylene bicomponent fiber and a short length natural cellulose fiber. The thermal bonding is at a temperature sufficient to fuse the polyethylene component without fusing the polyester component, while the web is maintained under little or no compression.
U.S. Pat. No. 4,160,159 to Samejima (Samejima) generally involves an absorbent fabric containing wood pulp combined with short-length, heat fusible fibers. Although Samejima generally involves the use of the combination of bicomponent fibers and cellulose fibers, the disclosure is not directed to a wet lay application.
Some conventional processes use cellulosic fibers, such as wood pulp, as the sole fibrous component in a mat or sheet. However, sheets incorporating only cellulose fibers are often dimensionally unstable. Depending on the application, swelling will often occur in the sheet and in any subsequent laminated surface covering into which the sheet is incorporated. This swelling can result in the buckling of the laminated sheet such that the borders may curl, sometimes resulting in the delamination of the backing sheet from the surface coverings.
Recently, nonwoven textile fabrics have been manufactured through the use of wet forming techniques on conventional or modified paper making or similar machines. Such manufacturing techniques have much higher production rates and are also suitable for very short fibers such as wood pulp fiber. Unfortunately, difficulties are often encountered in the use of textile length fibers in such wet forming manufacturing techniques.
Several problems arise in attempting to incorporate a heat fusible fiber such as a bicomponent fiber into a wet lay fibrous web. Problems encountered in attempting to incorporate a heat fusible fiber such as a bicomponent fiber into a wet lay process include, for example, attaining uniform dispersion of the bicomponent fiber as well as attaining a thermally bonded web with sufficient strength such that the thermally bonded web is usable. It has been found in the past that bicomponent fibers containing a sheath of high density polyethylene (HDPE) and a core of polyester are difficult to uniformly disperse in wet lay solutions. When such dispersion of fibers were attained, fibrous webs produced therefrom were found to lack the desired strength.
Nonwoven textile fabrics are normally manufactured by laying down one or more fibrous layers or webs of textile length fibers by dry textile carding techniques which normally align the majority of the individual fibers more or less generally in the machine direction. The individual textile length fibers of these carded fibrous webs are then bonded by conventional bonding (heating) techniques, such as, by point pattern bonding, whereby a unitary, self-sustaining nonwoven textile fabric is obtained.
Conventional manufacturing techniques for nonwoven textile fabrics are relatively slow and manufacturing processes having greater production rates are desired. Dry textile carding and bonding techniques are normally applicable only to fibers having a textile cardable length of at least about {fraction (1/2 )}inch and preferably longer. Such techniques are not generally applicable to short fibers such as wood pulp fibers which have very short lengths from about {fraction (1/6 )}inch down to about {fraction (1/25 )}inch or less.
Another conventional thermally bonded fibrous wet laid web containing a specific bicomponent fiber is generally taught in U.S. Pat. No. 5,167,765 to Nielsen et al. The bicomponent fiber consists essentially of a first component consisting of polyester or polyamide and a second component consisting of linear low density polyethylene and grafted high density polyethylene grafted with maleic acid or maleic anhydride. The thermally bonded fibrous wet laid web may further include a matrix fiber selected from a group consisting of cellulose paper making fibers, cellulose acetate fibers, glass fibers, polyester fibers, ceramic fibers, metal fibers, mineral wool fibers, polyamide fibers, and other naturally occurring fibers.
In the previous processes of making wet laid webs or paper from fibers of whatever source, it is customary to suspend previously beaten fibers, or what is generally known as pulp, in an aqueous medium for delivery to a sheet-forming device, such as a Fourdrinier wire. This fiber containing aqueous dispersion is commonly referred to in the art as a furnish. One drawback at this stage of making wet laid fibrous webs is the tendency for the fibers to clump, coagulate or settle in the aqueous tank or container. This condition is generally referred to as flocculation. Flocculation causes a nonuniform distribution of fibers in the resulting paper product. Typically, the end product has a mottled, uneven appearance and has very poor physical properties as tear, burst, and tensile strength. Another problem in making wet laid fibrous webs is a tendency of the fibers to float to the surface of the furnish.
For the manufacture of fibrous wet laid webs from conventionally used fibers such as cellulose, methods are known for attaining uniform dispersion of the fibers and reducing and preventing the occurrence of flocculation. One of the more effective means has been to add a small amount of karaya gum to the fiber furnish. However, this has not proven entirely satisfactory. Other agents such as carboxymethyl cellulose or polyacrylamide have been used to attain the desired result of the cellulose in the furnish.
Fibrous wet laid webs may also be made from other natural or synthetic fibers in addition to wood cellulose paper-making fibers. A water furnish of the fibers is generally made with an associative thickener and a dispersant. The cellulose pulp is dispersed in water prior to adding the dispersant. A thickener is added in an amount in the range up to 150 pounds per ton of dry fiber making up the water furnish. Then natural and/or synthetic fibers are added and dispersed in the mixture. Finally, the dispersion of mixed fibers in the water is diluted to a desired consistency and dispensed onto the forming wire of a conventional paper-making machine. An anti-foam agent may be added to the dispersion to prevent foaming, if necessary, and a wetting agent may be employed to assist in wetting the fibers. A bonded fibrous web may be formed from the fiber furnish on a high speed conventional Fourdrinier paper making machine to produce a fibrous wet laid web.
In prior art wet lay processes using polyester fibers as the textile staple fibers, water-based binders are generally added to the process to insure adhesion between the cellulose fibers and the polyester fibers. Generally, from about 4% to about 35% binder material is employed. One of the problems encountered with a water based binder is the binder leaches out of the resultant web in such applications as filters. Also, the addition of binders increases cost and results in environmental problems. Furthermore, latex binders have a short shelf life and require special storage conditions. Also, the latex binders may be sensitive to the condition of the water employed.
Another known thermal
Chin Peter
Eckert Inger H.
Owens Corning Fiberglass Technology, Inc.
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