Stock material or miscellaneous articles – Coated or structually defined flake – particle – cell – strand,... – Rod – strand – filament or fiber
Reexamination Certificate
2000-05-18
2003-02-18
Morris, Terrel (Department: 1771)
Stock material or miscellaneous articles
Coated or structually defined flake, particle, cell, strand,...
Rod, strand, filament or fiber
C428S393000, C428S407000, C442S417000, C442S157000, C442S164000
Reexamination Certificate
active
06521339
ABSTRACT:
FIELD OF THE INVENTION
This invention concerns polymeric and non-polymeric binders for particles and the use of such binders in binding particles to fibers. The fibers and bound particles may be easily densified by external application of pressure. The binders are reactivatable, and maybe applied to particles, which thereafter may be bound to fibers on a wet-laid fiber sheet manufacturing line. In particular embodiments, the invention concerns binding superabsorbent particles to cellulosic fibers which may then be used, for example, to make absorbent fibers that are densified and incorporated into absorbent products. In other embodiments, the invention concerns the reactivation and use of binder coated particles, preferably at an article manufacturing plant, at a location remote from a pulp-sheet manufacturing line to bind superabsorbent and/or other particles to cellulosic fibers which may then be used, for example, as absorbent fibers incorporated into absorbents products.
BACKGROUND OF THE INVENTION
Superabsorbent polymers have been developed in recent years that are capable of absorbing many times their own weight of liquid. These polymers, which are also known as water insoluble hydrogels, have been used to increase the absorbency of sanitary products such as diapers and sanitary napkins. Superabsorbent polymers are often provided in the form of particulate powders, granules, or fibers that are distributed throughout absorbent cellulosic products to increase the absorbency of the product. Superabsorbent particles are described, for example, in U.S. Pat. Nos. 4,160,059; 4,676,784; 4,673,402; 5,002,814; and 5,057,166. Products such as diapers that incorporate absorbent hydrogels are shown in U.S. Pat. Nos. 3,669,103 and 3,670,731.
One problem with the use of superabsorbents is that the superabsorbent material can be physically dislodged from the cellulosic fibers of an absorbent product. Separation of the superabsorbent from its substrate reduces the absorbency of the product and diminishes the effectiveness of the superabsorbent material. This problem was addressed in European Patent Application 442 185 A1, which discloses use of a polyaluminum chloride binder to bind an absorbent polymer to a fibrous substrate. The polyaluminum binder, however, suffers from the drawback of being an inorganic product that is not readily biodegradable. Moreover, that European patent does not offer any guidance for selecting binders other than polyaluminum chloride that would be useful in binding absorbent particles.
A method of immobilizing superabsorbents is disclosed in U.S. Pat. No. 4,410,571 in which a water swellable absorbent polymer is converted to a non-particulate immobilized confluent layer. Polymer particles are converted to a coated film by plasticizing them in a polyhydroxy organic compound such as glycerol, ethylene glycol, or propylene glycol. The superabsorbent assumes a non-particulate immobilized form that can be foamed onto a substrate. The individual particulate identity of the superabsorbent polymer is lost in this process. The confluent nature of the superabsorbent material can also result in gel blocking, in which absorption is diminished as the water swollen polymers block liquid passage through the film layer.
U.S. Pat. Nos. 4,412,036 and 4,467,012 disclose absorbent laminates in which a hydrolyzed starch polyacrylonitrile graft copolymer and glycerol mixture is laminated between two tissue layers. The tissue layers are laminated to each other by applying external heat and pressure. The reaction conditions form covalent bonds between the tissue layers that firmly adhere the tissue layers to one another.
Numerous other patents have described methods of applying binders to fibrous webs. Examples include U.S. Pat. Nos. 2,757,150; 4,584,357; and 4,600,462. Such binders are not described as being useful in binding particulates, such as superabsorbent particles, to fibers. Yet other patents disclose crosslinking agents such as polycarboxylic acids that form covalent intrafiber bonds with individualized cellulose fibers, as in European Patent Application 440 472 A1; European Patent Application 427 317 A2; European Patent Application 427 316 A2; and European Patent Application 429 112 A2. The covalent intrafiber bonds are formed at elevated temperatures and increase the bulk of cellulose fibers treated with the crosslinker by forming intrafiber ester crosslinks. Crosslinking must occur under acidic conditions to prevent reversion of the ester bonds. The covalent bonds within the fibers produce a pulp sheet that is more difficult to compress to conventional pulp sheet densities than in an untreated sheet. Covalent crosslink bonds may also form between the fibers and particles, and occupy functional groups that would otherwise be available for absorption, hence absorption efficiency is decreased.
A particular disadvantage of forming covalent ester intrafiber crosslinks is that the resulting fiber product resists densification. Energy requirements for making densified absorbent products are increased because very high compression pressures must be used to densify the absorbent product. It would be advantageous to provide a method of enhancing densification of crosslinked fibers by reducing energy requirements for densification.
Many different types of particles other than superabsorbents may be added to fibers for different end uses. Antimicrobials, zeolites and fire retardants are but a few examples of particles that are added to fibers. It would be advantageous to provide a method of attaching particles that could be accommodated to the many different particle needs of end users. Moreover, it would be advantageous to reduce particulate waste in the attachment process, and simplify shipment of fiber products that require particulate addition. It would be further advantageous to bind particulates to fibers without requiring the shipment of bulk fibers with adhered particulates because shipping and excessive handling of these fibers subject them to mechanical impact which can dislodge some particles from the fibers. It would also be advantageous under some circumstances to incorporate binder coated particles onto fibers during the initial pulp sheet manufacturing process so that the fibers with particles are ready for use at a remote product manufacturing location. However, the particles are then subject to dislodgement during the subsequent manufacturing processes.
It has previously been important that particles added to cellulose products be insoluble in liquids such as water or liquid binders. It has been thought that liquid insolubility (particularly water insolubility) was an essential characteristic for particles bound to cellulose fibers because soluble particles would be dissolved by a water containing binder. Although the particle could eventually resolidify as the binder evaporated, dissolution of the particle in the binder would cause the particle to diffuse to areas of the product where it was not needed or desired. Water soluble particles have therefore not been used for particles that were to be bound to fibers using a binder.
SUMMARY OF THE INVENTION
The foregoing and other problems have been overcome by providing fibers with hydrogen bonding functional sites, and binders that have a volatility less than water. The binder has a functional group that forms a hydrogen bond with the fibers, and a functional group that is also capable of forming a hydrogen bond or a coordinate covalent bond with particles that have a hydrogen bonding or coordinate covalent bonding functionality. The binder is applied to the particles to at least partially coat the particles. The binder containing particles, when combined with the fibers, are bonded to the fibers by a bond that has been found to be resistant to mechanical disruption. A significant advantage of these binders is that the binder and particle together on the fiber have been found to reduce the pressure required to densify the fibers. This is particularly true for superabsorbent particles, and preferably comprises using s
Hansen Michael R.
Young, Sr. Richard H.
Christensen O'Connor Johnson & Kindness PLLC
Morris Terrel
Torres Norca L.
Weyerhaeuser Company
LandOfFree
Diol treated particles combined with fibers does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Diol treated particles combined with fibers, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Diol treated particles combined with fibers will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3165029