MXPA98004241A - Dielectric electretes of non-woven fabric with superfi treatment - Google Patents

Abstract

A nonwoven fabric having improved particulate barrier properties are supplied. A surface treatment having a faulty voltage not as great as 13 KV direct of current use is present on the non-woven fabric. The particulate barrier properties are improved by subjecting said treated non-woven fabric surface treatment or chorus discharge.

Description

ELECTRETOS DIELÉCTRICOS DE TELA NO TEJIDA WITH SURFACE TREATMENTS Field of the Invention The present invention relates to fabrics useful for forming protective garments. More particularly, the present invention relates to non-woven fabrics and surface coatings for such non-woven fabrics.

Background of the Invention There are many types of disposable limited-use or protective garments designed to provide barrier properties. Protective clothing must resist penetration by both liquids and / or particles. For a variety of reasons, it is undesirable that liquids and pathogens that can be carried by liquids pass through the garment to make contact with people who work in an environment where pathogens are present.

Similarly, it is highly desirable to isolate people from harmful substances which may be present in a workplace or accident site. To increase the likelihood that the protective garment will be worn correctly thereby reducing the opportunity for exposure, workers will benefit from wearing a protective garment that is relatively impervious to liquids and / or particles and that is durable, but will still be comfortable so that it does not reduce the worker's functioning. After use, it is usually very costly to decontaminate a protective garment that has been exposed to a harmful or dangerous substance. Therefore, it is important that a protective garment be cost effective to be disposable.

One type of protective garment are the disposable protective covers. The coverings can be used to effectively isolate a user from a damaging environment so that protective or open-style protective garments such as drapes, gowns and the like are unable to do so. Therefore, the covers can have many applications where the isolation of a user is desirable.

Disposable protective garments also include disposable surgical garments such as drapes and disposable surgical gowns. As is generally known, surgical gowns and drapes are designed to greatly reduce, if not prevent, transmission through the surgical garment of liquids and biological contaminants which could be carried there. In surgical procedure environments, such sources of fluid include the wearer's sweat of the gown, the patient's fluids, such as blood, sage, sweat and life supporting fluids such as plasma and salt water.

Many surgical garments were originally made of cotton or linen and were sterilized before use in the operating room. These surgical garments however, allowed the transmission through the same or the "transfer" of many of the liquids found in the surgical procedures. These surgical garments were undesirable, if not unsatisfactory, because such "handover" establishes a direct path for the transmission of bacteria and other contaminants to and from the user of the surgical garment. In addition, the garments were expensive and, of course, the procedures and sterilization were required before re-use.

Disposable surgical garments have greatly replaced linen surgical gowns. Because many surgical procedures generally require a high degree of liquid repellency to prevent transfer, the disposable surgical garments for use under these conditions are, for the most part, made entirely of liquid repellent fabrics.

Therefore, generally speaking, it is desirable that disposable protective garments be made from fabrics that are relatively impervious to liquids and / or particulates. These barrier type fabrics may also be suitable for the manufacture of protective clothing at such a low cost that it makes the disposal of garments economical after a single use.

Examples of disposable protective garments which are generally manufactured from non-woven fabric laminates to ensure that they are effectively cost-effective are the surgical drapes, robes, and surgical drapes sold by Kimberly-Clark Corporation. Many of the disposable protective garments sold by Kimberly-Clark Corporation are manufactured from a three-layer non-woven fabric laminate. The two outer layers are formed of spun-bonded polypropylene-based fibers and the inner layer is formed of melt-blown polypropylene-based fibers. The outer layers of spunbonded provide durable and strong abradability surfaces. The inner layer is not only water repellent but also acts as a breathable filter barrier allowing air and moisture vapor to pass through the fabric volume while filtering out many harmful particles.

In some cases the material forming the protective garments may include a film layer or a film laminate. Although the formation of protective garments of a film can improve the particle barrier properties of the protective garment, such a film or laminated film materials can also inhibit or prevent the passage of air and moisture vapor through them. . Generally, protective garments formed of materials which do not allow a sufficient passage of air and a moisture vapor through them become uncomfortable to be used correctly for extended periods of time.

Therefore, although in some cases, film or film laminate materials can provide improved particulate barrier properties compared to non-woven laminated fabrics, non-woven laminated fabrics generally provide comfort to the larger user. Therefore, there is a need for inexpensive disposable protective garments, and more particularly, inexpensive disposable protective garments formed of a nonwoven fabric which provides the improved particulate barrier properties while also being breathable and therefore comfortable to wear correctly. for extended periods of time.

Synthesis of the Invention The present invention provides a non-woven fabric having improved particulate barrier properties.

In one embodiment the non-woven fabric may include at least one layer formed of fibers subjected to corona discharge. The fibers subjected to corona discharge may include a surface treatment having a breaking voltage of no more than 13 thousand volts (KV) of direct current (DC) and desirably a breaking voltage not greater than 8 KV DC and more desirably a voltage of breakage not greater than 5 KV DC and more desirably a breaking voltage between 1 KV DC and 5 KV DC. The nonwoven fabric may also include fibers formed from a mixture of polypropylene and polybutylene. Desirably, polybutylene is present in the mixture in a range of from 0.5 to 20% by weight of the mixture. Another surface treatment having a breaking voltage greater than 13 KV DC may be present on the fibers subjected to the corona discharge or on fibers not subjected to corona discharge or both.

In another embodiment, the non-woven fabric can include at least one layer formed of spunbonded fibers and at least one layer formed of meltblown fibers. The fibers of at least one of the layers can be corona discharge and include a surface treatment having a breaking voltage of not more than 13 KV DC and desirably a breaking voltage not greater than 8 KV DC and more desirably a breakage not greater than 5 KV DC and more desirably a breaking voltage between 1 KV DC and 5 KV DC. The nonwoven fabric may also include fibers formed from a mixture of polypropylene and polybutylene. Desirably, polybutylene is present in the mixture in a range of from 0.5 to 20% by weight of the mixture. Another surface treatment having a breaking voltage greater than 13 KV DC may be present on the fibers subjected to corona discharge or on fibers not subjected to corona discharge or both.

In another embodiment, the non-woven fabric can include at least two layers formed of spunbonded fibers and at least one layer formed of meltblown fibers. The layer formed of meltblown fibers is placed between the two layers formed of fibers joined with yarn. The fibers of at least one of the layers may be subjected to corona discharge and include a surface treatment having a breaking voltage not greater than 13 KV DC, and desirably a breaking voltage not greater than 8 KV DC and more desirably a breaking voltage not greater than 5 KV DC and more desirably a breaking voltage between 1 KV DC and 5 KV DC. The nonwoven fabric may also include fibers formed from a mixture of polypropylene and polybutylene. Desirably, polybutylene is present in the mixture in a range of from 0.5 to 20% by weight of the mixture. Another surface treatment having a breaking voltage greater than 13 KV DC may be present on the fibers subjected to corona discharge or on fibers not subjected to corona discharge or both.

In another embodiment, the non-woven fabric may include at least two layers formed of spunbonded fibers and at least one layer formed of meltblown fibers wherein the layer formed of meltblown fibers is between the two layers. of spunbonded fibers, and wherein the fibers forming at least one of the layers are subjected to corona discharge. At least one of the spunbonded fiber layers may include a surface treatment having a breaking voltage not greater than 13 KV DC, and desirably a breaking voltage not greater than 8 KV DC and more desirably a breaking voltage not greater than 5 KV DC and more desirably a breaking voltage between 1 KV DC and 5 KV DC. The layer formed of meltblown fibers includes a surface treatment having a voltage no greater than 13 KV DC and desirably a breaking voltage no greater than 8 KV DC and more desirably a breaking voltage no greater than 5 KV DC and more Desirably a breaking voltage of between 1 KV DC and 5 KV DC. The meltblown layer can also be further formed from fibers which are formed of a mixture of polypropylene and polybutylene, and more particularly, polybutylene is present in the mixture in a range of from 0.5 to 20% by weight of the mixture. . Another surface treatment having a breaking voltage greater than 13 KV DC may be present on the fibers subjected to corona discharge or on fibers not subjected to corona discharge or both.

In another embodiment, the non-woven fabric includes at least two layers formed of spunbonded fibers and at least one layer formed of meltblown fibers wherein the formed layer formed of meltblown fibers is between two formed layers. of fibers joined with spinning. The fibers forming at least one of the layers include a surface treatment having a breaking voltage not greater than 13 KV DC, and wherein the fibers forming the other layer include another surface treatment having a higher breakdown voltage than 13 KV DC. Each layer formed of the fibers that includes a surface treatment is subjected to corona discharge. Spunbond fibers from one of the layers may include a surface treatment having a breaking voltage not greater than 13 KV DC and desirably a breaking voltage not greater than 8 KV DC and more desirably a breaking voltage not greater than 5. KV DC and more desirably a breaking voltage between 1 KV DC and 5 KV DC. Spunbonded fibers of another layer include a surface treatment having a breaking voltage greater than 13 KV DC. The layer formed of meltblown fibers may include a surface treatment having a breakdown voltage either not greater than 13 KV DC or greater than 13 KV DC or both.

Detailed description of the invention As used herein, the term "dielectric" means, according to the McGraw-Hill Encyclopedia of Science and Technology, Seventh Edition, Rights Reserved 1992, a material, such as a polymer, which is an electrical insulator or which An electric field can be sustained with a minimum energy dissipation. A solid material is a dielectric if its valence band is complete and is separated from the conduction band by at least 3 eV.

As used herein, the term "breakdown voltage" means the voltage at which the electrical fault occurs when a potential difference is applied to an electrically insulating material. The breakdown voltage reported for the various materials tested was determined by the ASTM Test Method for dielectric breakdown voltage (D 877-87).

As used herein, the term "electret" means a dielectric body having permanent or semi-permanent electrical poles of opposite sign.

As used herein, the term "surface treatment" means a material, for example a surfactant, which is present on the surface of another material, for example a shaped polymer such as a non-woven surface treatment can be applied topically The topical application methods include, for example, spraying, embedding or otherwise coating the polymer formed with the surface treatment. which are added to a melted or semi-melted polymer can be referred to as "internal additives." Internal additives suitable for use in the present invention are generally non-toxic and have a low volatility Desirably, these internal additives must be thermally stable at temperatures up to 300 ° C, and sufficiently soluble in the melted or semi-dripped polymer They must also be sufficiently separated from the phase so that said additive migrates from the volume of the shaped polymer to a surface thereof upon cooling of the shaped polymer.

As used herein, the term "constriction", "stretch with constriction" or "constriction and stretch" refer interchangeably to a method of elongating a fabric, generally in the machine direction, to reduce its width in a controlled manner to a desired amount. The controlled stretching can take place under cold, ambient or higher temperatures and is limited to an increase in the general direction in the direction that is being stretched to the elongation required to break the fabric, which in many cases is about 1.2. to 1.4 times the original unstretched direction. When it relaxes, the fabric retracts to its original dimensions. Such a process is described, for example, in U.S. Patent No. 4,443,513 issued to Mainer and Notheis, and in U.S. Patents Nos. 4,965,122, 4,981,747 and 5,114,781 issued to Morman, which all they are incorporated here by reference.

As used herein, the terms "smoothing with constriction" or "constriction and smoothing" means a stretch with constriction carried out without the addition of heat to the material as it is stretched, for example, at room temperature. In stretch with narrowing or softening, a fabric is mentioned, for example as being stretched by 20%.

As used herein, the term "non-woven fabric" refers to a fabric having a structure of individual fibers or filaments which are interleaved, but not in an identifiable repetitive manner.

As used herein, the term "spunbonded fibers" refers to fibers which are formed by extruding melted thermoplastic material as filaments from a plurality of usually circular and thin capillaries of a spinner with the diameter of the extruded filaments. then being quickly reduced as established for example, in U.S. Patent No. 4,340,563 issued to Appel et al., and in U.S. Patent No. 3,692,618 issued to Dorschner et al., U.S. Patent No. 3,802,817 issued to Matsuki et al., US Pat. Nos. 3,338,992 and 3,341,394 issued to Kinney, US Pat. Nos. 3,502,763 and 3,909,009 issued to Levy, and United States of America Patent No. 3,542,615 granted to Dobo and others which are incorporated herein by reference. Spunbonded fibers are generally continuous and in some cases have a larger average diameter of 7 microns.

As used herein, the term "meltblown fibers" means fibers formed by extruding a melted thermoplastic material through a plurality of capillaries, usually circular and thin, such as melted threads or filaments into gas streams (eg. example, air) usually heated and at high speed which attenuate the filaments of melted thermoplastic material to reduce its diameter. Then, the meltblown fibers are carried by the high velocity gas stream and are deposited on a collecting surface to form a meltblown fabric randomly discharged. Meltblowing is described, for example, in US Pat. No. 3,849,241 issued to Butin, in United States Patent No. 4,307,143 to Meitner et al., And in the patent of the United States of America. United States of America No. 4,707,398 issued to Wisneski and others which are all incorporated herein by reference. In some cases, meltblown fibers can generally have a smaller average diameter than 10 microns.

Polymers, and polyolefin polymers in particular, are well suited for the formulation of fibers or filaments used to form non-woven fabrics which are useful in the practice of the present invention. Non-woven fabrics can be made from a variety of processes, including but not limited to air-laying processes, wet laying processes, hydroentangling processes, melt-blown suspension or bonding, carding and short fiber bonding. , and spinning of solution.

The present invention provides a non-woven fabric which can include at least one layer formed of fibers subjected to corona discharge. The non-woven fabric may be formed of meltblown fibers or spunbonded fibers or both. Fibers subjected to corona discharge may include a surface treatment having a breaking voltage of no more than 13,000 volts (KV) of direct current (DC) and desirably a breaking voltage not greater than 8 KV DC and more desirably a breaking voltage not greater than 5 KV DC and more desirably a breaking voltage of between 1 KV DC and 5 KV DC. The nonwoven fabric may also include fibers formed from a mixture of polypropylene and polybutylene.

Desirably, polybutylene is present in the mixture in a range of from about 0.5 to 20% by weight of the mixture.

Other surface treatments also having a breaking voltage greater than 13 KV DC may be present on the fibers that are subjected to the corona discharge or on the fibers not subjected to corona discharge or both.

In another embodiment, the non-woven fabric can include at least one layer formed of spunbonded fibers and at least one layer formed of meltblown fibers. The fibers of at least one of the layers and desirably the layer formed of meltblown fibers can be subjected to corona discharge and include a surface treatment having a breaking voltage not greater than 13 KV DC, and desirably a voltage breakage not greater than 8 KV DC and more desirably a breakdown voltage not greater than 5 KV DC more desirably a breakdown voltage between 1 KV DC and 5 KV DC. The non-woven fabric may also include fibers, and desirably meltblown fibers, formed of a mixture of polypropylene and polybutylene. Desirably, polybutylene is present in the mixture in a range of from 0.5 to 20% by weight of the mixture. Another surface treatment having a breaking voltage greater than 13 KV DC may be present on the fibers subjected to corona discharge or on the fibers not subjected to corona discharge or both.

In another embodiment, the non-woven fabric can include at least two layers formed of spunbonded fibers and at least one layer formed of meltblown fibers. The layer formed of meltblown fibers can be placed between the two layers formed of fibers joined with yarn. The fibers of at least one of the layers, and desirably the layer formed of meltblown fibers, may be corona discharge and includes a surface treatment having a breaking voltage not greater than 13 KV DC and desirably a breaking voltage not greater than 8 KV DC and more desirably a breaking voltage not greater than 5 KV DC and more desirably a breaking voltage between 1 KV DC and 5 KV DC. The non-woven fabric may also include fibers, and desirably meltblown fibers, formed of a mixture of polypropylene and polybutylene. Desirably, polybutylene is present in the mixture in a range of from 0.5 to 20% by weight of the mixture. Another surface treatment having a breaking voltage greater than 13 KV DC may be present on the fibers subjected to corona discharge or on the fibers not subjected to corona discharge or both.

In another embodiment, the non-woven fabric can include at least two layers formed of spunbonded fibers and at least one layer formed of meltblown fibers wherein the layer formed of meltblown fibers can be placed between the layers. two layers formed of fibers joined with spinning, and wherein the fibers forming at least one of the layers are subjected to the corona discharge. At least one of the layers formed of the spunbonded fibers may include a surface treatment having a breaking voltage not greater than 13 KV DC and desirably a breaking voltage not greater than 8 KV DC and more desirably a breaking voltage. not greater than 5 KV DC and more desirably a breaking voltage between 1 KV DC and 5 KV DC. The layer formed of meltblown fibers includes a surface treatment having a breaking voltage not greater than 13 KV DC, and desirably a breaking voltage not greater than 8 KV DC and more desirably a breaking voltage not greater than 5 KV DC and more desirably a breaking voltage of between 1 KV DC and 5 KV DC. The meltblown layer may furthermore be formed of fibers which are formed of a mixture of polypropylene and polybutylene, and more particularly, polybutylene is present in the mixture in a range of 0.5 to 20% by weight of the mixture. Another surface treatment having a breaking voltage greater than 13 KV DC may be present on the fibers subjected to corona discharge or on fibers not subjected to corona discharge or both.

In another embodiment, the non-woven fabric includes at least two layers formed of spunbonded fibers and at least one layer formed of meltblown fibers wherein the layer formed of meltblown fibers can be placed between the two layers. formed of fibers joined with yarn. The fibers forming at least one of the layers includes a surface treatment having a breaking voltage of no greater than 13 KV DC, and wherein the fibers forming the other layer include another surface treatment having a higher breakdown voltage. of 13 KV DC. Each layer formed of fibers which include a surface treatment is subjected to a corona discharge. Spunbonded fibers from one of the layers may include a surface treatment having a breaking voltage not greater than 13 KV DC and desirably a breaking voltage not greater than 8 KV DC and more desirably a breaking voltage not greater than 5. KV DC and more desirably a breaking voltage between 1 KV and 5 KV DC. The spunbonded fibers of the other layer may include a surface treatment having a breakdown voltage greater than 13 KV DC. The layer formed of melt blown fibers may include a surface treatment having a treatment voltage either not greater than 13 KV DC or greater than 13 KV DC or both.

As described in more detail below, the full thickness of the non-woven fabric laminate can be corona discharge. Alternatively, the individual nonwoven layers which, when combined, form the nonwoven fabric laminate, may be separately subjected to corona discharge. When the full thickness of the nonwoven laminate is corona discharge, the fibers forming at least one of the nonwoven layers are desirably formed of a variety of dielectric polymers including, but not limited to polyesters, polyolefins, nylon and copolymer of these materials. The fibers forming the other non-woven layers can be formed from a variety of non-dielectric polymers, including, but not limited to cellulose, glass, wool and protein polymers.

When one or more individual nonwoven layers are separately subjected to corona discharge, the fibers forming these non-woven layers are desirably formed of the dielectric polymers described above. Those individual nonwoven layers which are not subjected to corona discharge can be formed from the non-dielectric polymers described above.

It has been found that the non-woven fabrics formed from the thermoplastic-based fibers and particularly the polyolefin-based fibers are particularly suitable for the aforementioned applications. Examples of such fibers include spunbonded fibers and meltblown fibers. Examples of the non-woven fabrics formed of such fibers are the non-woven polypropylene fabrics produced by the registration assignee, Kimberly-Clark Corporation.

As previously described, one embodiment of the present invention may include a nonwoven fabric laminate. For example, the non-woven fabric laminate includes at least one layer formed of spunbonded fibers and another layer formed of meltblown fibers, such as a non-woven laminate bonded with melt spinning / blowing (S / M) In another embodiment the non-woven fabric laminate may include at least one layer formed of meltblown fibers which is sandwiched between two layers formed of spunbonded fibers, such as the non-woven laminate bonded with spinning / blowing. with melting / bonding with spinning (S / M / S). Examples of non-woven fabric laminates are described in United States Patent No. 4,041,203 to Brock, et al., In United States Patent No. 5,169,706 to Collier et al. U.S. Patent No. 4,374,888 issued to Bornslaeger, all of which are incorporated herein by reference. More particularly, the yarn-bound fibers can be formed of polypropylene. Suitable polypropylenes for the spunbonded layers are commercially available as PD-9355 from Exxon Chemical Company of Baytown, Texas.

More particularly, the melt blown fibers can be formed of polyolefin polymers, and more particularly a mixture of polypropylene and polybutylene. Examples of such meltblown fibers are contained in U.S. Pat. Nos. 5,165,979 and 5,204,174 which are incorporated herein by reference. Still more particularly, meltblown fibers can be formed of a polypropylene and polybutylene blend wherein the polybutylene is present in the mixture in a range of from 0.5 to 20 percent by weight of the blend. One such suitable polypropylene is designated as 3746-G by Exxon Chemical Company, of Baytown, Texas. One such suitable polybutylene is available from DP-8911 from Shell Chemical Company, of Houston, Texas. The meltblown fibers may also contain a modified polypropylene according to U.S. Patent No. 5,213,881 which is incorporated herein by reference.

The non-woven fabric laminate S / M / S can be made by sequentially depositing on a moving forming web first a layer of spunbonded fabric, then a melted blown fabric layer on the top of the first spunbonded fabric and then another layer of fabric spunbonded on top of the meltblown fabric layer and then bonding the laminate in a manner described below. Alternatively, the layers can be made individually, collected in rolls, and combined in separate bonding step. S / M / S non-woven fabric laminates usually have an average basis weight of from about 0.1 to 12 ounces per square yard (osy) of 3 to 400 grams per square meter (gsm)) or more particularly around 0.75 to about ounces per square yard (25 to 170 grams per square meter) and even more particularly from about 0.75 to about 3 ounces per square yard (25 to 100 grams per square meter).

Methods for subjecting non-woven fabrics to corona discharge are well known to those skilled in the art. Briefly, crown discharge is achieved by the application of a sufficient direct current (DC) voltage to an electric field initiation structure (EFIS) in the vicinity of an electric field receiving structure (EFRS). The voltage must be high enough so that the ions are generated in the electric field initiation structure and flow from the electric field initiation structure to the electric field receiving structure. Both the electric field initiation structure and the electric field reception structure are desirably formed of conductive materials. Suitable conductive materials include copper, tungsten, stainless steel and aluminum.

A particular technique for subjecting non-woven fabrics to corona discharge is the technique described in U.S. Patent No. 5,401,446 which has been assigned to the University of Tennessee, and is incorporated herein by reference. This technique involves subjecting the non-woven fabric to a pair of electric fields in which the electric fields have opposite polarities. Each electric field forms a corona discharge.

In those cases where the non-woven fabric is a non-woven fabric laminate, the full thickness of the non-woven fabric laminate can be subjected to corona discharge.

In other cases, one or more of the individual layers which form the nonwoven fabric laminate or the fibers forming such individual layers may be separately subjected to corona discharge and then combined with other layers in a juxtaposed relationship to form the fabric laminate. non-woven In some cases, the electric charge on the nonwoven fabric laminate surface prior to corona discharge can be essentially the same as the electric charge on the surface of the corona discharge treated fabric. In other words, the nonwoven fabric laminate surface may not generally exhibit a higher electrical charge after subjecting the fabric to the corona discharge that the electrical charge presents on the surface of the fabric before subjecting it to corona discharge.

The non-woven fabric laminates can be generally bonded in some way as they are produced in order to give them sufficient structural integrity to withstand the rigors of further processing in a finished product. The bond can be achieved in a number of ways such as hydroentanglement, perforation, ultrasonic bonding, adhesive bonding and thermal bonding.

The ultrasonic bonding is carried out, for example, by passing the non-woven fabric laminate between a sonic horn and an anvil roll as illustrated in U.S. Patent No. 4,374,888 issued to Bornslaeger.

The thermal bonding of the nonwoven fabric laminate can be achieved by passing it between the rollers of a calendering machine. At least one of the rollers of the calender is heated and at least one of the rollers, not necessarily the same as the heated one, has a pattern which is printed on the laminate as it passes between the rollers. When passing the fabric between the rollers this is subjected to pressure as well as heat. The combination of heat and pressure applied in a particular pattern results in the creation of fused bonding areas in the non-woven fabric laminate where the joints thereon correspond to the pattern of bonding points on the calendering roll.

Several patterns have been developed for the calendering rollers. An example is the Hansen-Pennings pattern with between about 10 to 25 percent of bound area with about 100 to 500 joints / square inch as taught in U.S. Patent No. 3,855,046 issued to Hansen and Pennings. Another common pattern is a diamond pattern with slightly off-center and repetitive diamonds.

The exact calendering temperature and pressure for bonding the non-woven fabric laminate depends on the thermoplastics from which the non-woven fabric is made. Generally for non-woven fabric laminates formed of polyolefins, the desirable temperatures are between 150 and 350oF (66 and 177oC) and the pressure is between 300 and 1000 pounds per linear inch. More particularly, for polypropylene the desired temperatures are between 270 and 320oF (132 and 160oC) and the pressure is between 400 and 800 pounds per linear inch.

In those cases where the non-woven fabric is used in or around flammable materials and electrical discharge is a concern, the non-woven fabric can be treated with any number of antistatic materials. In these cases, the antistatic material can be applied to the non-woven fabric by any number of techniques including, but not limited to the embedding of the nonwoven in a solution containing the antistatic material or by spraying the nonwoven with a solution containing the antistatic material. In some cases the antistatic material can be applied to both the outer surfaces of the nonwoven and / or the nonwoven volume. In other cases, the antistatic material may be applied to parts of the nonwoven, such as a surface or selected surfaces thereof.

Of particular utility is the antistatic material known as ZELEC®, a phosphate alcohol salt product from Du Pont Corporation. The non-woven fabric can be treated with the antistatic material either before or after subjecting the fabric to the load. In addition, some or all of the layers of material can be treated with the antistatic material. In those cases where only some of the layers of material are treated with antistatic material, the untreated layer or layers can be subjected to the load before or after combining with the antistatic layer or layers.

Additionally, in those cases where the non-woven fabric is used around the alcohol, the non-woven fabric can be treated with an alcohol-repellent material. In these cases, the alcohol repellent material can be applied to the nonwoven fabric by any number of techniques including, but not limited to, embedding or spraying the non-woven fabric with a solution containing the alcohol repellent material.

In some cases the alcohol repellent material can be applied to both the outer surfaces of the non-woven fabric and the volume of the non-woven fabric. In other cases, the alcohol repellent material can be applied to parts of the non-woven fabric, such as the surface or selected surfaces thereof.

Of particular utility are the alcohol repellent materials formed of fluorinated urethane derivatives, or example of which includes FX-1801. The FX-1801, formerly called L-10307, is available from St. Paul, Minnesota. The FX-1801 has a melting point of around 130 to 138oC. The FX-1801 can be added to any the spunbonded and / or meltblown layer in an amount from about 0.1 to about 2.0 percent by weight, or more particularly from between about 0.25 and 1.0 percent. by weight. The FX-1801 can be applied topically or can be applied internally by adding the FX-1801 to the fiber-forming polymer before fiber formation.

Generally, internal additives, such as the alcohol repellent additive FX-1801, suitable for use in the present invention should not be toxic and should have low volatility. Additionally, the internal additive should be thermally stable at temperatures up to 300 ° C, and sufficiently soluble in the semi-melted or melted fiber-forming polymer. The internal additive must also be sufficiently phase separated so that the additive migrates from the volume of the polymer fiber towards the surface of the polymer fiber upon cooling of the fibers without requiring the addition of heat.

The layers of the fabric of this invention may also contain fire retardants for increased fire resistance, pigments to give each layer the same or different colors and / or chemicals such as amines hindered to provide improved ultraviolet light resistance. Fire retardants and pigments for meltblown and meltblown thermoplastic polymers are known in the art and can be internal additives. A pigment, if used, is generally present in an amount of less than 5 percent by weight of the layer.

EXAMPLES To demonstrate the attributes of the present invention, various surface treatments were combined with non-woven fabrics of various average basis weights and polymer blends as listed in TABLE 1.

TABLE 1 TREATMENT OF FLOOR SURFACE OF QUANTITY APPLIED TYPE OF NO INDUSTRIAL DESIGNATION CHEMICAL DESCRIPTION OF THE WOVEN SURFACE 1. Y- 12488 Modified Polyalkylene Oxide% and 1% 1.5 osy M Polydimethylsiloxane Union Carbide Corporation HYPERMER A409 Polyester Surfactant 4% 1.5 osy M Modified 98%; Xylene 2%, ICI America Inc. 3. FC1802 86-89% C8 Fluorinated Alkyl Alkoxylate; 9-10% Fluorinated C8 Alkyl Sulfonamide; 2- Alkyl Alkoxylate 2.48% 1.5 osy M Fluorinated C7; 0.2-1% C7 Fluorinated Alkyl Sulfonamide; 3M Corp. 4.FX 1801 Urethane Fouro 1% "16.6 osy S / M / S Derivative - 100% - 3M Corp. (contained 0.03% ZELEC) 5. TEGOPREN 5830 Polyether Copolymer 4% 1.5 osy M Polysiloxane - Goldschmidt Corp 6. TRITON XI02 Octylphenoxypolyethoxy Ethanol 2% 1.5 osy M having 12-13 Ethylene Oxide Groups - Rohm &Haas Co. 7. ZELEC S / M / S Phosphate Alcohol Alcohol, 03% "* 2.2 osy & Mixed Alkyl Phosphates KIMGUARD * S / M / S Neutralized-Du Pont 1.6 osy 8. FC808 S / M / S Ester Fluoroalfático Polymer .95% 1.8 osy 3M Corp. KLEENGUARD * 9. MASIL SF19 Silicon surfactant PPG 2.% 1.5 osy M 10 GEMTREX SM33 Sodium sulfosuccinate Dioctyl .3% 1.5 osy M Anionic Based; Finetex Corp.

S / M / S Fabric Laminate Joined with Yarn / Blown with Fusion / Joined with Yarn.

S Non-woven Fabric Joined with Yarn M Non Woven Blown Fabric with Fusion * All surface treatments applied topically except as noted.

** Melt polymer applicator. It bloomed to the surface of M.

*** Applied topically to a layer S.

For samples 1-3, 5, 6, 9, and 10, the respective surface treatments were applied to a meltblown nonwoven fabric having an average basis weight of about 1.5 ounces per square yard (osy). These fabrics were made of Himont PF105.

For sample 4 and a portion of the non-woven fabrics used in sample 7, the respective surface treatments were applied to an S / M / S laminate having an average basis of about 1.6 ounces per square yard. These samples included a meltblown layer having an average basis weight of about 0.5 ounces per square yard between the two layers of the yarn bonded material, each layer bonded with yarn having an average basis weight of about 0.55 ounces per square yard. The spunbonded layers were made of propylene copolymer designated PD-9355 by Exxon Chemical Company. The meltblown layer was made of polypropylene designated 3746 G from Exxon Chemical and polybutylene (10 weight percent) designated DP-8911 from Shell. The samples were narrowed and smoothed by 8 percent at room temperature. The ZELEC surface treatment was present on one of the spun bonded surfaces in an amount of from about 0.03% by weight of the spun bonded layer. The FX-1801 was present in the meltblowing layer of each of the aforementioned samples.

For the remaining part of the non-woven fabrics used in sample 7, the ZELEC surface treatment was applied to an S / M / S laminate having an average basis weight of about 2.2 ounces per square yard. Both layers bonded with yarn had an average basis weight of about 0.85 ounces per square yard and the meltblowing layer had an average basis weight of about 0.5 ounces per square yard. One of the spin-bonded layers of this sample contained 0.03% by weight of the spun bonded layer of the ZELEC surface treatment.

For sample 8, the respective surface treatment was applied to S / M / S laminate of 1.8 ounces per square yard. Spunbond layers were formed from polypropylene resins - Exxon PD-3445 and Himont PF-301. The dark blue and white pigments, Ampacet 41438 (Ampacet Inc., New York) and SCC 4402 (Strandrige Color Inc., Georgia), respectively, were added to the polypropylene resins to form one of the spin-bonded layers. The other spin-bonded layer was formed from these polypropylene resins without pigments. The meltblown layer was formed from the Himont polypropylene resin PF-015 without pigments.

The meltblown layer had an average weight of about 0.45 ounces per square yard and each layer bonded by spinning had an average basis weight of about 0.675 ounces per square yard. The solution was prepared by adding 0.5% hexanol, 2.95% FC808 and about 96.5% water. The FC808 solution was applied to one of the layers joined by spinning. FC808 is an alcohol repellent surface treatment consisting of a polymeric fluoroaliphatic ester (20%), water (80%) and ethyl acetate (400 parts / million).

A part of each of the non-woven fabrics treated with surface treatment described in Table 1 (samples 1-10) was removed and not subjected to corona discharge. The rest of each of the non-woven fabric samples treated with surface treatment (1-10) was subjected to corona discharge. Corona discharge occurred by using a 50/60 Hz reversible polarity energy unit Model No.

P / N 25A of 120 volts (from Simco Corporation, of Hatfield, Pennsylvania), which was connected to the electric field initiation structure, and a 50/60 Hz power unit, Model P16V 102 Vs, 25A (from Simco Corporation, of Hartfield, Pennsylvania), which was connected to the electric field receiving structure. The electric field initiation structure was a Charge Master RC-3 charge bar (from Simco, Corporation) and the electric field receiver structure was a 3-inch solid diameter aluminum roller. The environment of the corona discharge was generally around 71oF and 53% relative humidity. As described in the above-mentioned US patent No. 5,401,446, two sets of electric field initiation structure / electric field reception structure were used. The voltage applied to the first set of electric field initiation structure / electric field reception structure was 15 KV DC / 0.0 KV DC, respectively. The voltage applied to the second set of electric field initiation structure / electric field reception structure was 25 KV DC / 7.5 KV DC, respectively. The separation between the electric field initiation structure and the electric field reception structure for each set was one inch.

The filtration efficiency was analyzed for both samples of the corona treated and non-corona treated non-woven fabric. The particular filtration test used to evaluate the particular filtration properties of these nonwovens is generally known as the NaCl filter efficiency test (hereinafter referred to as the "NaCl test"). The NaCl test was carried out on an automated filter tester, Certitest Model Mark # 8110, which is available from TSI Inc., of St. Paul, Minnesota. The particulate filtration efficiency of the test cloth was reported as "% penetration". The "% penetration" was calculated by the following formula - 100 x (upstream particles / downstream particles). The upstream particles represent the total amount of approximately 0.1 μra of NaCl aerosol particles which were introduced into the tester. The downstream particles are those particles which have been introduced into the tester and which have been passed through the volume of the test cloth. Thus, the value of "% penetration" reported in Tables I-V is a percentage of the total amount of particles introduced into a controlled air flow inside the tester that passes through the volume of the test fabric. The size of the test cloth was 4.5 inches in diameter. The air flow was constant or varied. Around 32 liters per minute of air flow, a pressure difference of between 4 and 5 mm of Water Gage develops between the atmosphere on the upstream side of the test cloth compared to the atmosphere on the downstream side of the test cloth. The results of filtration efficiency for samples 1-6 and 8-10 are reported in Table 2. The results of filtration efficiency for sample 7, non-woven fabrics treated with ZELEC surface treatment, were not reported in the Table 2 TABLE 2 FILTRATION EFFICIENCY% PENETRATION 0.1 μ NaCl TREATMENT OF TREATED WITH TREATED WITHOUT SURFACE CORONA CROWN 1. And 12488 (1%) 66.3 70.6 1. And 12488 (4%) 54.3 55.2 2. A409 10.0 46.0 3. FC 1802 51.0 53.7 4. ZELEC + 1801 2.57 33.2 . 5830 57.5 57.7 6. TRITON 102 1.30 51.3 8 FC 808 62.4 63.0 9. SF19 45.5 80.9 . GEMTEX SM33 6.30 71.2 In view of Table 2, it was concluded that in those cases where there was a substantial increase in the filtration efficiency of the non-woven fabric treated with surface treatment between the non-corona treated and the corona treated, the non-woven fabric treated with a crown formed an electret. Based on the filtration efficiency results reported in Table 2, four selected liquid surface treatments were selected for the breaking voltage analysis. Filtration efficiency data for two of the liquid surface treatments, Y 12488 and TEGOPREN 5830, generally indicated an insignificant difference in filtration efficiency between corona treatment and corona treatment. The filtration efficiency data for the other two liquid surface treatments, Triton 102 and SF19, generally indicated a substantial improvement in filtration efficiency between a corona treatment and a corona treatment.

The breaking voltages for these surface treatments with liquid are reported in Table 3. The breaking voltage for each liquid surface treatment was determined by using a Hipot Tester, model No Hipotronics 100, having a range of 0-25 KV DC and an accuracy of +/- 2%. The electrodes were bronze electrodes one inch in diameter separated by 0.100 inches apart. The electrodes were submerged in a net amount of the respective liquid surface treatments. The voltage for the electrodes was increased from 0 KV DC to a rate of approximately 3 KV DC / second until the break occurred. The electrodes and the test container were thoroughly washed, rinsed with distilled water, dried in the air before testing the next surface treatment.

TABLE 3 BREAKING VOLTAGES * BREAKING VOLTAGE MATERIAL (DC) And 12488 24 KV MASIL SF19 4.8 KV TEGOPREN 5830 15 KV TRITÓN X-102 1.8 KV 'THE CURRENT TO VOLTAGE OF VARIOUS BREAKDOWN FROM 3.5 iliamps (MA) TO 4.9 MA.

For both of the liquid surface treatments, Y 12488 and TEGOPREN 5830, which generally indicated an insignificant difference in filtration efficiency between corona and non-corona treatment, the breakdown voltages were 24 KV DC and 15 KV DC, respectively. For the two liquid surface treatments, TRITON 102 and SF19, which generally indicated a substantial improvement in filtration efficiency between corona and non-corona treatment; the breaking voltages were 1.8 KV DC and 4.8 KV DC, respectively.

Although the invention has been described in detail with respect to the specific embodiments thereof, it will be appreciated by those skilled in the art to achieve an understanding of the foregoing, that alterations, variations and equivalents for such modalities can easily be conceived. Therefore, the scope of the present invention should be established as that of the appended claims and any equivalents thereof.

Claims (20)

R E I V I N D I C A C I O N S

1. A nonwoven fabric comprising: at least one layer formed of fibers, wherein the fibers subjected to corona discharge include a surface treatment having a breaking voltage not greater than 13 KV direct current.

2. The non-woven fabric as claimed in clause 1, characterized in that the fibers forming the layer are formed of a mixture of polypropylene and polybutylene.

3. The non-woven fabric as claimed in clause 2, characterized in that the fibers subjected to corona discharge include another surface treatment having a breaking voltage greater than 13 KV of direct current.

4. The non-woven fabric as claimed in clause 1, characterized in that the breaking voltage of the surface treatment is less than 8 KV of direct current.

5. The non-woven fabric as claimed in clause 2, characterized in that the polybutylene is present in the mixture in a range of from 0.5 to 20 percent by weight of the mixture.

6. A non-woven fabric comprising: at least two layers formed of fibers joined by spinning and at least one layer formed of meltblown fibers, wherein the layer formed of meltblown fibers is between the two layers formed of spunbonded fibers, and wherein the fibers of at least one of the layers are subjected to corona discharge; Y wherein the fibers subjected to corona discharge include a surface treatment having a breaking voltage not greater than 13 KV of direct current.

7. The non-woven fabric as claimed in clause 6, characterized in that the meltblown fibers are formed from a mixture of polypropylene and polybutylene.

8. The non-woven fabric as claimed in clause 7, characterized in that the polybutylene is present in the mixture in a range of from 0.5 to 20 percent by weight of the mixture.

9. The non-woven fabric as claimed in clause 6, characterized in that the average basis weight of the non-woven fabric is about 1.8 ounces per square yard.

10. The non-woven fabric as claimed in clause 6, characterized in that the fibers subjected to corona discharge include another surface treatment having a breaking voltage greater than 13 KV of direct current.

11. The non-woven fabric as claimed in clause 6, characterized in that the meltblown fibers are subjected to corona discharge.

12. A nonwoven fabric comprising: at least two layers formed of fibers joined by spinning and at least one layer formed of meltblown fibers, wherein the layer formed of meltblown fibers is between the two layers formed of spunbonded fibers, and wherein the fibers forming at least one of the layers are subjected to corona discharge; Y wherein at least one of the layers formed of the fibers joined by spinning includes a surface treatment having a breaking voltage not greater than 13 KV direct current and wherein the layer formed of meltblown fibers includes a surface treatment having a breaking voltage not greater than 13 KV direct current.

13. The non-woven fabric as claimed in clause 12, characterized in that the meltblown fibers are formed from a mixture of polypropylene and polybutylene.

14. The non-woven fabric as claimed in clause 13, characterized in that the polybutylene is present in the mixture in a range of from 0.5 to 20 percent by weight of the mixture.

15. The non-woven fabric as claimed in clause 12, characterized in that the breaking voltage of the surface treatment of the fibers bonded by spinning is less than 8 KV direct current.

16. The non-woven fabric as claimed in clause 12, characterized in that the breaking voltage of the surface treatment of the meltblown fibers is less than 8 KV of direct current.

17. The non-woven fabric as claimed in clause 12, characterized in that the meltblown fibers are subjected to corona discharge.

18. A nonwoven fabric comprising: at least two layers formed of fibers joined by spinning and at least one layer formed of meltblown fibers wherein the layer formed of meltblown fibers is between the two layers formed of fibers joined by spinning, and wherein the fibers forming at least one of the layers includes a surface treatment having a breaking voltage not greater than 13 KV direct current, and wherein the fibers forming the other layer include another surface treatment having a breaking voltage greater than 13 KV direct current; and wherein each layer formed of fibers including a surface treatment is subjected to a corona discharge.

19. The non-woven fabric, as claimed in clause 18, characterized in that the fibers joined by spinning of one of the layers includes a surface treatment having a breaking voltage not greater than 13 KV direct current, and wherein fibers joined by spinning of another layer include a surface treatment having a breaking voltage greater than 13 KV direct current.

20. The non-woven fabric, as claimed in clause 18, characterized in that the meltblown fibers include at least one surface treatment. SUMMARY A nonwoven fabric having improved particulate barrier properties is provided. A surface treatment has a breaking voltage not greater than 13 KV direct current is present on the nonwoven fabric. The particulate barrier properties are improved by subjecting said treated non-woven fabric with surface treatment to a corona discharge.