MXPA00002118A - Meltblown nonwoven web and process for making the same - Google Patents

Abstract

An improved process for producing nonwoven meltblown webs is disclosed. In particular, the meltblown web are made from a metallocene catalyzed thermoplastic polymer. For instance, in one application, the metallocene catalyzed polymer is polypropylene having a melt flow of less then 1,000 grams per 10 minutes and a relatively narrow molecular weight distribution range. The meltblown webs can be used in a variety of applications and are particularly well suited for use in the construction of laminates. For example, in one embodiment, the meltblown web can be combined with at least one spunbond web to form a nonwoven fabric laminate useful for wipers, towels, garments, liquid absorbent products and the like.

Description

NON-WOVEN FABRIC BLOWED WITH FUSION AND PROCESS TO MANUFACTURE THE SAME Field of the Invention The present invention is generally directed to meltblown nonwoven fabrics, laminates containing a meltblown nonwoven fabric, and a process for weaving. More particularly, the present invention is directed to a meltblown web made from a metallocene-catalyzed polymer. For example, in one embodiment, the metallocene catalyst polymer is polypropylene having a melt flow of less than 1000 g / 10 min and a molecular weight distribution of less than 3.0.

Background of the Invention Non-woven fabric laminates are useful for a wide range of applications. For example, such non-woven fabric laminates are useful for wipes, towels, industrial dresses, medical gowns, medical covers, the like. In heavier weights, laminates are used and recreational applications such as tents and as car covers. Laminated disposable fabrics have achieved especially widespread use in hospital operating rooms for covers, gowns, towels, foot covers, sterilization wraps, and the like. The non-woven fabrics have also been incorporated into other products such as diapers, feminine hygiene products, and the like.

Such non-woven fabric laminates are typically made by combining at least one spunbonded material with a fabric meltblown material. For example, in an embodiment, a melt blown fabric is placed between outer layers of spin-linked fabrics. The woven fabrics linked by spinning fabrics provide durability while the blown fabric with internal fusion provides a sweeping layer that is porous but inhibits the transfer of fluids or the penetration of bacteria from the outside of the laminated fabric to the interior.

Particular examples of non-woven laminates such as those described above are disclosed in United States of America Patent No. 4,041,203 issued to Brock et al., In United States of America No. 4,766.02 to Brock et al. , in U.S. Patent No. 5,464,688 issued to Timmons et al., and in U.S. Patent No. 5,607,798 issued Kobylivker and others which are all incorporated herein by reference in their entirety.

Currently, the meltblown non-woven fabrics used in the above-described laminates are made with a polypropylene resin having an initial melt flow ranging from 400 g / 10 min to 800 g / 10 min. Co is used herein, the melt flow refers to a viscosity measurement of the polymer and is expressed as the weight of material flowing from a capillary of known dimensions under the specified load or shear force rate for a measured period of time. time and is measured in g / 10 min according to, for example, according to the ASTM 1238 test. The initial polymer is synthesized according to the Ziegler-Natta method in which the propylene is polymerized with a catalyst that includes a transition metal salt. and an alkali metal. Polymers made according to this method typically have a wide molecular weight distribution and a low melt flow, which can create problems when the polymer is formed in a co-melt blown fabric.

To reduce the polymer molecular weight distribution and to increase the melt flow, the polypropylene is then coated with from about 500 parts per million to about 750 parts per million of peroxide. When the polymer is added to the extruder and melted, the peroxide reacts with the polymer to produce a final melt flow of between 1200 g / 10 min at about 1800 g / 10 min. The addition of peroxide has greatly improved the process of blowing with polymer fusion in a fabric.

The peroxide reaction, however, can create variability in the system based on the quality of the peroxide dispersed in the polymer. This variability in the resin can result in problems of basic weight uniformity and difference in the size of the fibers. Thus, a need still persist for a process that produces a more uniform product of blown with fusion. In particular, there is a need for a polymer to be used in a meltblown process that is uniform in melt flow and has a very narrow molecular weight distribution range.Synthesis of the Invention The present invention recognizes and points out the aforementioned disadvantages, and others of prior art construction and methods.

Accordingly, one purpose of the present invention is to provide a non-woven blow fabric with improved melting.

Another purpose of the present invention is to provide an improved process for producing a co-melt blown fabric.

It is another purpose of the present invention to provide a meltblown fabric that is made of a metallocene catalyzed polymer.

Another purpose of the present invention is to provide an improved laminate containing a meltblown non-woven fabric made of a metallocene-catalyzed polymer.

Still another object of the present invention is to provide a process for making a melt blown web using a metallocene catalyzed polymer having a melt flow of less than 1000 g / 10 min and having a relatively high molecular weight distribution. low.

It is another purpose of the present invention to provide a method for producing various laminated fabrics such as wipes, dresses, medical covers, diapers, feminine hygiene products, and the like incorporating a meltblown nonwoven fabric made of a catalysed polymer. with metallocene.

These and other purposes of the present invention are obtained by providing a process for forming a woven fabric of a meltblown polymer. The process includes l steps to extrude a polymer catalyzed by metallocene filaments. The metallocene catalyzed polymer has a melt flow of less than 1000 g / 10 min, particularly around 650 g / 10 min to about 850 g / 10 min, and in a preferred embodiment has a melt flow of about 700 g. /10 minutes.

Once formed, the filaments are placed in contact with a gas stream, such as high velocity hot air. The gas stream breaks the filaments and fibers. The fibers are spread out forming a surface where they form a non-woven fabric.

Preferably, the metallocene-catalyzed polymer used in the process of the present invention has a molecular weight distribution of less than 2.5, and in one embodiment, less than 2.1. As used herein, the molecular weight distribution of a polymer (or polydispersity index) is determined by dividing the average weight of the molecular weight. Thus a polymer with a low molecular weight distribution contains a low molecular weight range. Conversely, a polymer that has high fluctuations in molecular weight will have a high number of molecular weight distribution.

The metallocene-catalyzed polymers qu can be used in the process of the present invention to form the non-woven fabric include polyolefin homopolymers and copolymers. In a preferred embodiment, the metallocene-catalyzed polymer is polypropylene or is a copolymer d polypropylene.

As described above, meltblown filaments are attenuated and broken into fibers by a gas. The fibers that are typically produced have an average diameter of about 0.5 microns to about 10 microns. In one embodiment, the fibers have an average diameter of about 1 micron to 3 microns.

The basis weight of non-woven fabrics made according to the present invention may vary and will generally depend on the particular application for which the fabrics will be used. For most applications, the fabric will have a basis weight of approximately 0.35 ounces / yard to about 0.6 ounces / yard.

Non-woven fabrics blown with melting d made according to the process described above have many uses and applications. For example, in an embodiment, meltblown non-woven tel can be incorporated into a laminate. The laminate can include a meltblown bonded fabric with at least one woven spunbonded material. For example, the meltblown woven material can be placed between the first outer fabric bonded by spinning and a second outer fabric linked by spinning.

The laminates made according to the present invention can be incorporated into various products including cleaning cloths, towels, industrial dresses, medical dress, medical covers, diapers, feminine hygiene products, tents, car covers, as well as other various products. .

Other purposes, features and aspects of the present invention will be discussed in more detail below.

Brief Description of the Drawing A complete and possible description of the present invention, including the best known one thereof, to one of ordinary skill in the art, is set forth below particularly in the remainder of the specification, including reference to the accompanying figure, which represents a cross section view of an incorporation of a laminate made in accordance with the present invention.

Detailed Description of Preferred Additions It should be understood by a person with ordinary technical skill in the art that the present discussion is a description of exemplary incorporations only, and that it does not attempt to limit the broad aspects of the present invention whose broad aspects are incorporated in the exemplary construction.

In general, the present invention is directed to improving the melt blown nonwoven fabric and a process for making the fabric. The melt blown fabrics are particularly suitable for use in laminates that are used to make products such as dresses, cloth cleaners, diapers, feminine hygiene products, and the like. Compared to fabrics made according to prior art processes, blown fabrics with fusion of the present invention have improved property barriers at equivalent base weights In other words, the non-woven fabrics of the present invention are more impervious to pervious liquid than the constructions of the prior art.

As will be discussed hereinafter, the meltblown non-woven fabrics of the present invention also have fibers with larger size uniformity and improved base weight uniformity. In addition, the fabrics have a low flush level and contain fewer defects.

In general, the improvements and advantages described above are achieved by constructing the meltblown fabric with a polymer having a uniform melt flow index having a uniform molecular weight. In particular, according to the present invention, the meltblown fabrics are formed of a metallocene-catalyzed thermoplastic resin such as metallocene-catalyzed polypropylene.

In order to form non-woven fabrics, the metallocene-catalyzed polymer is fed to a melt blowing process. In general, the process for forming a non-woven fabric through meltblowing involves extruding the melted polymeric material, such as a thermoplastic resin, through a filament-forming matrix. As the filaments exit the matrix, high pressure fluid, such as hot air or steam, attenuates and breaks the discontinuous fiber filaments of smaller diameter. The fibers are randomly deposited in a grid with holes, drum or in a layer of material to form the fabric. The fabric possesses integrity due to the entanglement of the individual fibers in the fabric as well as a thermal or self-bonding between the fibers particularly when harvesting is only a short distance after extrusion.

In general, the fibers that are produced during the melt blowing process and that are used to form the non-woven fabric have an average diameter of about 0.5 microns about 50 microns. More particularly, for most applications, the fibers have an average diameter of about 0. microns to about 10 microns. For example, in a preferred embodiment, the fibers have an average diameter of about 1 micron about 3 microns.

The average weight of non-woven fabrics made according to the process of the present invention will vary depending on the particular application. When a laminated fabric is incorporated, meltblown fabric can have a basis weight of about 0.35 ounces / square yard to 0.60 ounces / square yard. More particularly, for most applications the base weight of the fabric will be about 0.5 ounces / square yard. It should be recognized, however, that for other applications, the base weight of the fabric can be much higher. For example, in other additions, the base weight can be as high as 10 ounces / square yard and even higher.

As described above, the present invention is directed to the use of metallocene-catalyzed thermoplastic polymers. As used herein, a metallocene catalyst refers to a metal derived from cyclopentadiene and can be described as a single homogenous site or constricted geometrical catalysis. A metallocene is a neutral compound, metal d transition stabilizer auxiliary ligand and may have the following general formula: i \ / ^? where: Lx is a cyclopentadienyl or a substituted cyclopentadienyl mite attached to the target through n-5 linkage L2 is an organic half, which may or may not be a cyclopentadienyl half, strongly bound to the metal that remains attached to the metal during polymerization B is an optional bridging group that restricts the movement of Lx and L2 and that modifies the angle between Lx and L2 M is such a metal, for example, as titanium zirconium X and are halides or other organic halides such as methyl groups.

For example, in an embodiment, the metallocen may be as follows: The metallocene is a catalyst that initiates the polymerization of a monomer to form a polymer. For example, in order to form a metallocene-catalyzed polymer, a liquid monomer, such as propylene, is combined with metallocene under constant stirring and heat. A number of controlled hydrogen gas are then fed to the mixture causing the polymer to form. In general, the amount of hydrogen gas fed to the reactor determines the melt flow of the resulting polymer.

According to the present invention, the metallocene-catalyzed polymer used to form the meltblown fabric should have a melt flow of about 500 g / 1 min to about 1,000 g / 10 min, and particularly about 650 g / 10 ml. at about 850 g / 10 min. For example, in a preferred embodiment of the present invention, a metallocene polypropylene catalyzed polymer having a melt flow of about 700 g / 10 min is used.

It has been discovered that many benefits and advantages are achieved by using metallocene-catalyzed polymers having a melt flow within the range described above which is an unexpected result in view of previous art teachings. In particular, in the past, in order to improve the characteristics of a meltblown fabric, the melt flow of the polymer used to make the fabric was increased. The present inventors have found that increasing the melt flow of metallocene-catalyzed polymers to conventional levels, on the other hand, does not provide similar advantages.

For example, the problems encountered in the form of blown fabrics with melting of metallocene-catalyzed polymers having a melt flow greater than 1,500 g / 1 min. As described above, the melt flow is a measure of the viscosity of the polymer and is related to the molecular weight of the polymer. It was discovered that metallocene catalyzed polymers that have a high melt flow (which have a low molecular weight) have poor melt elasticity characteristic for use in meltblowing processes. In particular, the filaments produced by these polymers tend to break and form buds, which are imperfections contained in the fabric. Unexpectedly and contrary to conventional teachings, it was discovered that metallocene catalyzed polymers of low melt flow actually produce more uniform nonwoven fabrics with fewer defects.

In addition to the melt flow, another important feature of the metallocene catalysed polymers used in the process of the present invention is the molecular weight distribution. It has been discovered that metallocene-catalyzed polymers have uniform molecular weight and thus a narrow range of molecular weight distribution. Because the polymer chains are all of about the same size without large fluctuations, metallocene-catalyzed polymers have a greater ability to produce more uniform fibers and thus, more uniform non-woven fabrics when used in meltblowing processes . It has also been found that by having a low molecular weight distribution in combination with a particular melt flow, the polymer produces non-woven fabrics with fewer defects.

In particular, the metallocene catalyzed polymers used in the present invention should have a molecular weight distribution of less than 3.0, and particularly less than 2.5. For example, in one embodiment, the polymer has a molecular weight distribution of about 1.9 to about 2.1 The thermoplastic polymer that is synthesized using the catalyst with metallocene for use in the present invention is preferably a homopolymer or a copolymer of a polyolefin. For example, in a preferred embodiment, the polymer is polypropylene or a polypropylene copolymer. An example of a copolymer, for example, is polypropylene polyethylene random copolymer.

When using a metallocene-catalyzed thermoplastic polymer according to the present invention to form a meltblown fabric, it has been found that it is preferable that the polymer, when being meltblown, is heated to a temperature of less than 450 °. F, and particularly about 350 ° F to 425 ° F. More uniform fabrics are produced when the polymer processing temperature is lower than 450 ° F. At higher temperatures, the fluid permeability levels of the fabric may start to decline .

One available commercial polymer that has been found particularly convenient for use in the present invention is the metallocen-catalyzed polypropylene sold by Exxon. This polymer resin has a melt flow of about 700 g / 10 min and a molecular weight distribution of about 1.9 to about 2.1.

The meltblown fabrics made according to the present invention can be used in a wide range of applications. For example, meltblown fabrics can be combined with other fabric materials to form a laminate. In one embodiment, for example, the meltblown fabric of the present invention can be combined with one more spunbonded fabrics to form a laminate having many commercial applications.

An example of such a laminate 10 is generally illustrated in the figure. As shown, the laminate 10 included a meltblown non-woven fabric 12 made in accordance with the present invention spaced between a first outer fabric bonded by spinning 14 and a second outer woven fabric spun 16. In this embodiment, the blown fabric with melt 1 acts as a barrier layer between bonded layers by spin 14 and 16.

As used herein, a spin-blown fabric refers to a fabric made of continuous filaments. The process to produce fabrics linked by spinning includes the continuous extrusion of a polymer through a row to form discrete filaments. Thereafter, the filaments are either mechanically or pneumatically attracted without breaking to molecularly orient the polymer filaments and achieve tenacity. The continuous filaments are then deposited in a substantially random manner on a conveyor belt or forming surface to form a fabric.

A multilayer laminate as illustrated in the figure may be formed by a different number of techniques including but not limited to the use of adhesives, sewing, ultrasonic uni, thermal calendering and any other method known in the art. In one embodiment, such a laminate can sequentially deposit on a first mobile conveyor or forming wire a layer of fabric linked by spinning, then a layer of meltblown fabric, and, if applicable, another layer bonded by spinning. Once the different layers have been assembled, the layers can be bonded together as described above. Alternatively, the fabric layers can be made individually, collected rolls, and combined in a separate joining step.

The laminates illustrated in the Figure are useful for a wide variety of applications. For example, such laminates can be incorporated into cleansing wipes, industrial gown towel, medical covers, medical footwear gowns, sterilizing wraps, diapers, feminine hygiene product, in addition to various other products.

The present invention may be better understood with reference to the following example.

EXAMPLE The following example was carried out in order to demonstrate that meltblown fabrics made according to the processes of the present invention have an improved uniformity and are more permeable to fluids than fabrics made according to prior art methods. The following test was also performed in order to determine the effects of the polymer on varying the temperature of the process when weaves of the present invention are formed.

The polypropylene resins synthesized according to the Ziegler-Natta method and reacted with peroxide as described above were melt blown nonwoven fabrics compared to wovens formed according to the present invention using a metallocene catalyzed polypropylene having a melt flow rate of 700. g / 10 min. Polypropylene resins made according to the Ziegler-Natta method had variable melt flows. The Ziegler-Natta catalyzed polymers were all blown with melt in filaments at a temperature of 470 ° F. The polymer process temperature of the metallocene-catalyzed polymers, however, was varied.

Three different melt blown fabrics were constructed of polymers made according to the Ziegler Natta method, while four different fabrics were constructed by the metallocene catalyzed polymer. All tissues had a basis weight of about 0.42 ounces / yard to about 0.4 ounces / yard.

Once formed, each of the tissues was then exposed to a hydrostatic test in order to determine the permeability of the tissues to the liquids. In particular, a sample of each of the weaves was placed in contact with a stream of water. The pressure of the water against the tissue was then increased until the water penetrated and flowed through the tissue. The water pressure was recorded once three drops of water were observed on the opposite side of tissue from the current flow. The following results were obtained: Table 1: Comparisons of Fluid Permeability between Polypropylene Blown and Blown Fabrics made using Ziegler-Natta Catalyzed Polymers and Metallocene Catalyzed Polymers As shown above, except for the metallocene-catalyzed polymer processed at 450 ° F, the fabrics made of metallocene-catalyzed polypropylene were more impervious to the fluid than the fabrics made of the Ziegler-Natta catalyzed polymer at about the same basis weight. As also shown, when a blown fabric is formed with melting of a metallocene catalyzed polymer, improved permeability results are obtained when the polymer is processed at a temperature of less than 450 ° F. Thus, metallocene-catalyzed polymers are preferably processed at lower temperatures than the polymers used in the past, which provides an additional advantage when using the polymers of the present invention.

These and other modifications and variations to the present invention can be practiced by those with ordinary experience in the art, without departing from the spirit scope of the present invention, which is more particularly set forth in the appended claims. Additionally, it should be understood that the aspects of the various incorporations can both be exchanged in full or in part. Furthermore, those with ordinary experience in the art will appreciate that the foregoing description is only exemplary only, and that it does not have the intention to limit the invention thus described in such appended claims.

Claims (26)

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

1. A process for forming a non-woven fabric is a meltblown polymer comprising the steps of: extruding a metallocene-catalyzed thermoplastic polymer into filaments, said metallocene-catalyzed polymer has a melt flow of about 500 g / 10 min about 1000 g / 10 min; contacting said filaments with a gas stream that breaks said filaments into fibers; Y forming said fibers in a non-woven fabric.

2. A process as claimed in clause 1, characterized in that said metallocene-catalyzed polymer has a melt flow of about 650 g / 10 min about 850 g / 10 min.

3. A process as claimed in clause 1, characterized in that said metallocene-catalyzed polymer has a melt flow of about 700 g / 10 min.

4. A process as claimed in clause 1, characterized in that said co-metallocene-catalyzed polymer has a molecular weight distribution of minus 3.0.

5. A process as claimed in clause 1, characterized in that said metallocene-catalyzed polymer has a molecular weight distribution of less than 2.1.

6. A process as claimed in clause 1, characterized in that said metallocene-catalyzed polymer consists of a polyolefin homopolymer or copolymer.

7. A process as claimed in clause 1, characterized in that said metallocene catalyst polymer consists of polypropylene or a copolymer containing polypropylene.

8. A process as claimed in clause 1, characterized in that said non-woven fabric has a basis weight of about 0.35 ounces / square yard to about 0. ounces / square yard.

9. A process as claimed in clause 1, characterized in that said fibers formed in a non-woven fabric have an average diameter of about 0.5 microns about 10 microns.

10. A process as claimed in clause 1, characterized in that said metallocene-catalyzed thermoplastic polymer is extruded at a temperature of at least 450 ° F.

11. A laminate consisting of at least one yarn-bound sheet adhered to a co-meltblown non-woven fabric, said meltblown fabric is made of a metallocene-catalyzed thermoplastic polymer having a melt flow of about 500g / 10min at about 1000 g / 10 min.

12. A laminate as claimed in clause 11, characterized in that said metallocene-catalyzed thermoplastic polymer has a melt flow of about 650 g / 10 min to about 850 g / 10 min.

13. A laminate as claimed in clause 11, characterized in that said metallocene-catalyzed thermoplastic polymer consists of polypropylene or a copolymer containing polypropylene.

14. A laminate as claimed in clause 12, characterized in that said metallocene-catalyzed thermoplastic polymer has a molecular weight distribution of less than 3.0.

15. A laminate as claimed in clause 14, characterized in that said metallocene-catalyzed thermoplastic polymer has a molecular weight distribution of less than 2.1.

16. A laminate as claimed in clause 11, characterized in that said melt blown non-woven fabric has a basis weight of about 0.35 ounces / square yard to about 0.6 ounces / square yard.

17. A laminate as claimed in clause 11, characterized in that said laminate first includes an external fabric linked by spinning and a second external fabric linked by spinning, said non-woven fabric blown with a melt being located between said first external fabric linked by spinning and said second outer fabric in linked by spinning.

18. A laminate as claimed in clause 11, characterized in that said laminate includes a garment.

19. A laminate as claimed in clause 11, characterized in that said laminate includes a cleaning cloth product.

20. A laminate as claimed in clause 11, characterized in that said laminate comprises a diaper or a feminine hygiene product.

21. A non-woven fabric comprising fibers made of a meltblown polymer, said co-meltblown polymer includes a metallocene-catalyzed polypropylene, metallocene-catalyzed polypropylene has a melt flow of about 650 g / 10min to about 850 g / l. min and a molecular weight distribution of less than 3.0.

22. A non-woven fabric as claimed in clause 21, characterized in that said metallocene-catalyzed polypropylene has a molecular weight distribution of less than 2.5.

23. A non-woven fabric as claimed in clause 21, characterized in that said fabric has a basis weight of about 0.35 ounces / square yard to about 0.6 ounces / square yard.

24. A non-woven fabric as claimed in clause 21, characterized in that said fibers have an average diameter of about 0.5 microns to about 10 microns.

25. A non-woven fabric as claimed in clause 21, characterized in that said metallocene-catalyzed polypropylene comprises a copolymer.

26. A non-woven fabric as claimed in clause 21, characterized in that said metallocene-catalyzed polypropylene is melt blown into said fiber at a temperature of about 350 ° F to about 425 ° F.