Slip resistant nonwoven

Details Slip resistant nonwoven Slip resistant nonwoven

2002-02-19

2004-08-10

Juska, Cheryl A. (Department: 1771)

Fabric (woven, knitted, or nonwoven textile or cloth, etc.)

Coated or impregnated woven, knit, or nonwoven fabric which...

Coating or impregnation intended to function as an adhesive...

C442S101000, C442S149000, C442S393000, C442S417000, C428S343000, C428S402200, C036S00900A, C036S00710R

Reexamination Certificate

active

06774063

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to slip resistant nonwoven materials especially those useful in surgical or clean room environments. More particularly, the invention relates to nonwovens useful for forming disposable protective articles such as drapes and footwear for health care and clean room environments.
2. Description of Related Art
Nonwovens are generally understood to be random-oriented fibrous webs which are produced by a variety of fibrous web manufacturing technologies generally utilizing substantial levels of synthetic fibers, though natural fibers can also be incorporated.
In nonwoven manufacturing, web forming is often done “dry”. Wet laid nonwoven manufacturing however is also known as are air laid processes which often use natural wood pulp fibers.
Fibrous webs are manufactured by at least three general processes: the wet papermaking processes; the nonwovens web making processes; and the woven textile web making processes. These three overlap each other in cost and performance. Papermaking is the lowest cost, and the products produced are the less durable. Some low end nonwovens compete with high end papers. On the other hand, woven textiles are very durable and comparably very expensive. Some high end nonwovens compete with low end woven textiles. Nonwovens may be considered as the webs which lie in between paper webs and textile webs.
Nonwovens web forming technologies include carding, air laid, spunbond, meltblown, and wet laid. Examples of additional nonwovens technologies include DRC (double recrepe), co-forming, and film aperturing.
Carding:
Carding is the oldest nonwoven technology. The easiest way to describe to the carding process is to consider the process of brushing a dog's hair. As the pet is brushed, some fibers are pulled out and gather in the bristles of the brush. Occasionally it is necessary to “reverse brush” and remove the fibers from the brush. This is somewhat like carding. In the carding process, synthetic fibers of, typically approximately 40 mm in length, are brushed out of a bale of fibers (The actual term used in the industry is “combing”.) The fibers which stick in the comb are then reverse brushed to pull them out of the comb and reorient them. At the same time they are reoriented, the fibers are laid down on a carrier screen to form a web. Orientation of these fibers is typically linear because the barbs on the rolls which do the combing are fixed in place. Thus virtually all of the fibers are lined up with the machine direction of the web. The cross direction orientation can be increased by additional processes such as randomizing and crosslapping. Because nonwoven carded webs have a high fiber orientation, it is generally necessary to do some type of additional bonding beyond that which occurs naturally with fiber entangling. Bonding may be done through chemical bonding, thermal bonding, or mechanical entanglement. Carded products utilize synthetic fibers, but also natural fibers like cotton and wool.
A limitation to the use of natural fibers in carding is that carding requires relatively long fibers to work well. Since carding occurs in air, it is also sometimes referred to as an air laid product or a dry laid product.
Air Laid:
Air laid web forming is more typically characterized by the fibers actually being deposited from an air stream onto a carrier fabric to form the nonwoven web. Webs formed by this process have high loft and high pore volume. Wood pulp fibers are the predominant fibers used in air laid manufacturing, and they are typically 2-3 mm in length. Longer, synthetic fibers can be added with lengths up to about 12 mm, but the most common usage is at about 4-6 mm due to machine handling considerations. The use of longer fibers is desirable in that they entangle better than wood pulp, and are generally stronger than wood pulp. Air laid webs are typically chemically bonded by spraying an emulsion polymer on both sides of the web. Bonding can also be achieved by the incorporation of synthetic fibers and the use of thermal bonding. Multi-bonding is used to describe air laid webs which have primary internal thermal bonding, and then a chemical topcoat to tie down loose fibers. Synthetic fibers are finding increased usage in these nonwovens.
Spunbond:
The spunbond process is characterized by the use of molten polymers, extruded through fine orifices to form essentially continuous fibers. Moving orifices and/or directed air streams cause the fibers to twirl around and overlap one another as they deposit on a moving carrier screen. The nonwoven web thus formed may be bonded by a degree of mechanical fiber entanglement; it may be bonded through final solidification of the molten fibers occurring after the web is formed and the fibers contact one another; it may be bonded through additional thermal treatments; or it may be bonded through chemical treatments. Nonwoven webs produced by the spunbond process are usually very strong, but have a high synthetic handfeel.
Meltblown:
The meltblown process is very similar to the spunbond process except for three major differences: 1) In the making of meltblown fibers, the air attenuation process used in fiber drawing causes the fibers to break with much shorter fiber lengths than in the spunbond process. 2) In the meltblown process, the design of the air flow used to draw the fibers out from the extrusion orifices also causes the fiber diameters to be much smaller than those found in the spunbond process, and 3) The fiber attenuation airflow used in the meltblown process occurs much closer to the extrusion orifice, and therefor it forms and cools the fibers before the extruded polymer has had a chance to molecularly orient itself. This creates fibers which are weaker than those found in the spunbond process. Because the meltblown process has shorter fiber lengths, there is more natural entanglement in the final nonwoven web, and some meltblown webs require no further bonding. Generally, however, thermal bonding via heated emboss rolls is the bonding method of preference.
Wetlaid:
The wetlaid nonwovens processes are basically just adaptations on regular papermaking machines. The manufacture of wet laid nonwovens utilizes three key variables compared to papermaking: 1) some synthetic fibers and/or longer other naturally occurring fibers (e.g. hemp) are included in the furnish; 2) selective chemical additives are used to properly disperse and suspend the synthetic fibers in the water slurry; and 3) the papermaking machine is redesigned and altered to allow better fiber handling and water drainage. The use of synthetic fibers in combination with wood pulp fibers in the wet laid process is limited by the degree to which the synthetic fibers can be kept suspended in water similar to the way this is done with wood pulp fiber. This suspendability, in turn, is affected by the density of the synthetic fibers, the surface wetting characteristics of the synthetic fibers, and the length of the synthetic fibers. Machine handling limitations in wet laid nonwovens generally rely on synthetic fiber lengths of about 8 mm or less. A high degree of bonding occurs through the normal entanglement of the fibers in the web forming process. Significant additional strength is sometimes generated by utilization of the bonding technology known as hydroentanglement.
DRC:
In the DRC (double re-crepe) process, a deliberately designed very weak sheet of paper is chemically bonded by design printing an emulsion polymer on one side of the sheet. The wet side of this sheet is immediately stuck to a large cylindrical dryer where the drying process begins. The drying process causes the sheet to stick to the dryer, and it is necessary to crepe the sheet in order to release it. The same sheet is then printed on the other side and dried and creped again. The resulting nonwoven product is far more durable than the original base sheet of paper, and the creping steps soften the hand feel and increase the absorbent characteristics of the sheet.
Co-Forming:
Co-forming is a process

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