WO2000037736A2

WO2000037736A2 - Method of coating hydrophobic polymer fibers with poly(vinyl alcohol)

Info

Publication number: WO2000037736A2
Application number: PCT/US1999/029701
Authority: WO
Inventors: Ning Wei
Original assignee: Kimberly-Clark Worldwide, Inc.
Priority date: 1998-12-18
Filing date: 1999-12-15
Publication date: 2000-06-29
Also published as: WO2000037736A3; AR021732A1; PE20001253A1; AU2709300A

Abstract

A method of coating hydrophobic polymer fibers with a poly(vinyl alcohol), which method involves providing hydrophobic polymer fibers, preparing a solution of the poly(vinyl alcohol) in water, and treating the hydrophobic polymer fibers with the poly(vinyl alcohol) solution under conditions sufficient to deposit the poly(vinyl alcohol) on the surfaces of the fibers. In some embodiments, the hydrophobic polymer fibers are polyolefin fibers. For example, the polyolefin fibers may be polypropylene or polyethylene fibers. The poly(vinyl alcohol) is that which generally is referred to as hot water-soluble poly(vinyl alcohol). Such material is highly hydrolyzed, having a degree of hydrolysis of at least about 98 percent. The molecular weight of the poly(vinyl alcohol) typically will be at least about 10,000, which corresponds approximately to a degree of polymerization of 200. The present invention also provides a method of coating hydrophobic polymer fibers with a poly(vinyl alcohol). The method involves providing hydrophobic polymer fibers, dissolving the poly(vinyl alcohol) in water at a temperature of at least about 60°C to obtain a poly(vinyl alcohol) solution, and treating the hydrophobic polymer fibers with the poly(vinyl alcohol) solution under conditions sufficient to deposit the poly(vinyl alcohol) on the surfaces of the fibers. The hydrophobic polymer fibers may be polyolefin fibers, such as polypropylene or polyethylene fibers.

Description

METHOD OF COATING HYDROPHOBIC POLYMER FIBERS WITH POLY(VINYL ALCOHOL)

Background of the Invention

The present invention relates to coated fibers. More particularly, the present invention relates to coated hydrophobic polymer fibers.

Polymers are used extensively to make a variety of products which include blown and cast films, extruded sheets, injection molded articles, foams, blow molded articles, extruded pipe, monofilaments, and nonwoven webs. Some of such polymers, such as polyolefins, are naturally hydrophobic, and for many uses this property is either a positive attribute or at least not a disadvantage.

There are a number of uses for hydrophobic polymers, however, where their hydro- phobic nature either limits their usefulness or requires some effort to modify the surface characteristics of articles made therefrom. By way of example, polyolefins, such as polyethylene and polypropylene, are used to manufacture polymeric fabrics which are employed in the construction of such disposable absorbent articles as diapers; incontinent care products; feminine care products, such as sanitary napkins and tampons; filter elements; wipes; surgical gowns and drapes; protective pads; wound dressings, such as bandages; and the like. Such polymeric fabrics often are nonwoven webs prepared by, for example, such processes as meltblowing, coforming, and spunbonding. Frequently, such polymeric fabrics need to be wettable by water. Wettability can be obtained by spraying or otherwise coating (i.e., surface treating or topically treating) the fabric with a surfactant solution during or after its formation, and then drying the web. Some of the more common topically applied surfactants are nonionic surfactants, such as polyethoxylated octylphenols and condensation products of propylene oxide with propylene glycol, by way of illustration only. These surfactants are effective in rendering normally hydrophobic polymeric fabrics wettable. However, the surfactant is readily removed from the fabric, often after only a single exposure to an aqueous liquid. Alternatively, a surfactant can be included in the polymer which is to be melt- processed, as disclosed in U.S. Pat. Nos. 3,973,068 and 4,070,218 to Weber. In this case, however, the surfactant must be forced to the surface of the fibers from which the web is formed. This typically is done by heating the web on a series of steam-heated rolls or "hot cans". This process, called "blooming", is expensive and still has the disadvantage of ready removal of the surfactant by aqueous media. Moreover, the surfactant has a tendency to migrate back into the fiber which adversely affects shelf life, particularly at high storage temperatures. In addition, it is not possible to incorporate in the polymer levels of surfactant much above 1 percent by weight because of severe processability problems; surfactant levels at the surface appear to be limited to a maximum of about 0.33 percent by weight. Most importantly, the blooming process results in web shrinkage in the cross-machine direction and a significant loss in web tensile strength.

Other methods of imparting wettability to, or otherwise affecting the surface characteristics of, shaped articles made from polyolefins and other hydrophobic polymers are known. Such methods include, by way of example only, the use of internal melt additives (U.S. Pat. No. 4,578,414 to Sawyer and Knight, and U.S. Pat. Nos. 4,923,914, 5,057,262, and 5,120,888 to Nohr and MacDonald), the polymerization of vinyl monomers on the surfaces of the polymer substrate (U.S. Pat. No. 4,672,005 to Dyer), and the modification of polymeric surfaces by means of a block copolymer (U.S. Pat. No. 4,698,388 to Ohmura et al.).

Poly(vinyl alcohol) has interesting physical and chemical properties which are associated with its affinity for water. Crosslinked and noncrosslinked hydrogels of the polymer are used in numerous devices such as contact lenses (U.S. Pat. No. 4,696,037 to Ofstead), composite glass (U.S. Pat. No. 5,367,015 to Gutweiler et al.), and synthetic papers (U.S. Pat. Nos. 3,560,318 to Miller et al.; 4,002,796 to Baldi et al.; 4,152,317 to Agouri et al.; and 4,510,185 to Chiolle et al.). In the synthetic paper references, coatings of poly(vinyl alcohol) are described as being formed by deposition of aqueous emulsions of the polymer on hydrophobic substrates which most typically are fibrils of high density polyethylene. In addition, the surface modification of polyamides has been described, wherein poly(vinyl alcohol) has been partially esterified with polycarboxylic acids. The partially esterified material is bound to the polyamide surface via free carboxylate function- alities and reactive groups on the polyamide surface (U.S. Pat. No. 3,050,418 to Mendelsohn et al.). A composite material formed from poly(vinyl alcohol), a modified starch, and water-soluble cellulose has found utility as an aqueous-based size for cotton and cotton/polyester yarns (U.S. Pat. No. 5,420,180 to Kayayama et al.).

Finally, poly(vinyl alcohol) as a coating on hydrophobic polymer surfaces is known. Such coating was achieved by first treating the polymer surfaces with a nonaqueous solution of a hydrophobic vinyl polymer, such as poly(vinyl trifluoroacetate), having readily hydrolyzable pendant groups. Such pendant groups then were hydrolyzed under mild conditions after deposition of the hydrophobic vinyl polymer on the substrate to give a coating of poly(vinyl alcohol) on the surfaces of the polymer substrate (U.S. Pat. No. 5,733,603 to Turkevich et al.). There is, therefore, a need for a simple, one-step methodology which will permit the uniform coating of hydrophobic polymer surfaces directly with a poly(vinyl alcohol) in order to render such surfaces hydrophilic.

Summary of the Invention

The present invention addresses some of the difficulties and problems discussed above by providing a method of coating hydrophobic polymer fibers with a poly(vinyl alcohol). The method involves providing hydrophobic polymer fibers, preparing a solution of the poly(vinyl alcohol) in water, and treating the hydrophobic polymer fibers with the poly(vinyl alcohol) solution under conditions sufficient to deposit the poly(vinyl alcohol) on the surfaces of the fibers. In some embodiments, the hydrophobic polymer fibers are polyolefin fibers. For example, the polyolefin fibers may be polypropylene or polyethylene fibers. The poly(vinyl alcohol) useful in the present invention is that which generally is referred to as hot water-soluble poly(vinyl alcohol). In general, the poly(vinyl alcohol) will have a degree of hydrolysis of at least about 88 percent. For example, such material may be highly hydrolyzed, having a degree of hydrolysis of at least about 98 percent. Desirably, the poly(vinyl alcohol) will have a degree of hydrolysis of 99 percent or greater. The molecular weight of the poly(vinyl alcohol) typically will be at least about 10,000, which corresponds approximately to a degree of polymerization of 200.

The present invention also provides a method of coating hydrophobic polymer fibers with a poly(vinyl alcohol). In this instance, the method involves providing hydrophobic polymer fibers, dissolving the poly(vinyl alcohol) in water at a temperature of at least about 60°C to obtain a poly(vinyl alcohol) solution, and treating the hydrophobic polymer fibers with the poly(vinyl alcohol) solution under conditions sufficient to deposit the poly(vinyl alcohol) on the surfaces of the fibers. The hydrophobic polymer fibers may be polyolefin fibers, such as polypropylene or polyethylene fibers.

Finally, the present invention provides coated fibers, composed of a hydrophobic polymer, in which the fibers have on the surfaces thereof a coating of a poly(vinyl alcohol) applied by a method of the present invention. Detailed Description of the Invention

The term "hydrophobic polymer" is used herein to mean any polymer resistant to wetting, or not readily wet, by water, i.e., having a lack of affinity for water. A hydrophobic polymer typically will have a surface free energy of about 40 dynes/cm (10⁵ newtons/cm or N/cm) or less. Examples of hydrophobic polymers include, by way of illustration only, polyolefins, such as poylethylene, poly(isobutene), poly(isoprene), poly(4-methyl-1-pentene), polypropylene, ethylene-propylene copolymers, and ethylene-propylene-hexadiene copolymers; ethylene-vinyl acetate copolymers; styrene polymers, such as poly(styrene), poly(2-methylstyrene), styrene-acrylonitrile copolymers having less than about 20 mole- percent acrylonitrile, and styrene-2,2,3,3,-tetrafluoropropyl methacrylate copolymers; halogenated hydrocarbon polymers, such as poly(chloro-trifluoroethylene), chlorotrifluoroethylene-tetrafluoroethylene copolymers, poly(hexa-fluoropropylene), poly(tetrafluoroethylene), tetrafluoroethylene-ethylene copolymers, poly(trifluoroethylene), poly(vinyl fluoride), and poly(vinylidene fluoride); vinyl polymers, such as poly(vinyl butyrate), poly(vinyl decanoate), poly(vinyl dodecanoate), poly(vinyl hexadecanoate), poly(vinyl hexanoate), poly(vinyl propionate), poly(vinyl octanoate), poly(heptafluoroisopro- poxyethylene), 1-heptafluoroisopropoxy-methylethylene-maleic acid copolymers, poly(heptafluoroisopropoxypropylene), poly(methacrylonitrile), poly-(vinyl alcohol), poly(vinyl butyral), poly(ethoxyethylene), poly(methoxyethylene), and poly(vinyl formal); acrylic polymers, such as poly(n-butyl acetate), poly(ethyl acrylate), poly[(1-chlorodifluoromethyl)- tetrafluoroethyl acrylate], poly[di(chlorofluoromethyl)fluoromethyl acrylate], poly(1 ,1- dihydroheptafluorobutyl acrylate), poly(1 ,1-dihydropenta-fluoroisopropyl acrylate), poly(1 ,1- dihydropentadecafluorooctyl acrylate), poly(hepta-fluoroisopropyl acrylate), poly[5- (heptafluoroiospropoxy)pentyl acrylate], poly[11-(heptafluoroiospropoxy)undecyl acrylate], poly[2-(heptafluoropropoxy)ethyl acrylate], and poly(nonafluoroisobutyl acrylate); methacrylic polymers, such as poly(benzyl methacrylate), poly(t7-butyl methacrylate), poly(isobutyl methacrylate), poly(f-butyl methacrylate), poly(f-butylaminoethyl methacrylate), poly(dodecyl methacrylate), poiy(ethyl methacrylate), poly(2-ethylhexyl methacrylate), poly(n-hexyl methacrylate), poly(dimethylaminoethyl methacrylate), poly(hydroxyethyl methacrylate), poly(phenyl methacrylate), poly(n-propyl methacrylate), poly(octadecyl methacrylate), poly(1 ,1-dihydropentadecafluorooctyl methacrylate), poly(heptafluoroisopropyl methacrylate), poly(heptadecafluorooctyl methacrylate), poly(1-hydrotetrafluoroethyl methacrylate), poly(1 ,1-dihydrotetrafluoropropyl methacrylate), poly(1- hydrohexafluoroisopropyl meth-acrylate), and poly(f-nonafluorobutyl methacrylate); polyethers, such as poly(chloral), poly(oxybutene)diol, poly(oxyisobutene)diol, poly(oxydecamethylene), poly(oxyethyl-ene)-dimethyl ether polymers having molecular weights below about 1 ,500, poly(oxyhexamethylene)diol, poly(oxypropylene)diol, poly(oxypropylene)-dimethyl ether, and poly(oxytetramethylene); polyether copolymers, such as poly(oxyethylene)-poly(oxypropylene)-poly(oxyethylene) block copolymers, oxyethylene-oxypropylene copolymers having greater than about 20 mole percent oxy- propylene, oxytetra-methylene-oxypropylene copolymers, and block copolymers having oxyethylene-oxypropylene copolymer blocks separated by a poly(oxydimethylsilylene) block; polyamides, such as poly[imino(1-oxodecamethylene)], poly[imino(1-oxododeca-methylene)] or nylon 12, poly[imino(1-oxohexamethylene)] or nylon 6, poly[imino(1-oxotetramethylene)] or nylon 4, poly(iminoazelaoyliminononamethylene), poly(imino- sebacoyliminodecamethylene), and poly(iminosuberoyliminooctamethylene); polyimines, such as poly[(benzoylimino)ethylene], poly[(butyrylimino)ethylene], poly[(dodecanoylimino)- ethylene], (dodecanoylimino)ethylene-(acetyleimino)trimethylene copolymers, poly[(heptanoylimino)ethylene], poly[(hexanoylimino)ethylene], poly{[(3-methyl)butyryl- imino]ethylene}, poly[(pentadecafluorooctadecanoylimino)ethylene], and poly[(pentanoyl- imino)ethylene]; polyurethanes, such as those prepared from methylenediphenyl diisocyanate and butanediol poly(oxytetramethylene)diol, hexamethylene diisocyanate and triethylene glycol, and 4-methyl-1 ,3-phenylene diisocyanate and tripropylene glycol; polysiloxanes, such as poly(oxydimethylsilylene) and poly(oxymethylphenylsilylene); and cellulosics, such as amylose, amylopectin, cellulose acetate butyrate, ethyl cellulose, hemicellulose, and nitrocellulose.

The hydrophobic polymer fibers desirably will be fibers prepared from thermoplastic polyolefins, or mixtures thereof. Examples of thermoplastic polyolefins include polyethylene, polypropylene, poly(l-butene), poly(2-butene), poly(l-pentene), poly(2-pentene), poly(3- methyl-1-pentene), poly(4-methyl-1-pentene), and the like. In addition, the term "polyolefins" is meant to include blends of two or more polyolefins and random and block copolymers prepared from two or more different unsaturated monomers. Because of their commercial importance, the most desirable polyolefins are polyethylene and polypropylene.

Poly(vinyl alcohol) is manufactured commercially by the hydrolysis of poly(vinyl acetate). The physical properties of poly(vinyl alcohol) largely are a function of the degree of hydrolysis and molecular weight. The poly(vinyl alcohol) useful in the present invention is that which typically is referred to as hot water-soluble poly(vinyl alcohol). In general, the poly(vinyl alcohol) will have a degree of hydrolysis of at least about 88 percent. For example, such material may be highly hydrolyzed, having a degree of hydrolysis of at least about 98 percent. Desirably, the poly(vinyl alcohol) will have a degree of hydrolysis of 99 percent or greater. The molecular weight of the poly(vinyl alcohol) typically will be at least about 10,000, which corresponds approximately to a degree of polymerization of 200. As a rule, the lower the degree of hydrolysis, the higher must be the molecular weight of the polymer. Similarly, a lower molecular weight material requires a higher degree of hydrolysis. Correct combinations of degree of hydrolysis and molecular weight may be determined readily by those having ordinary skill in the art without the need for undue experimentation.

The resistance of poly(vinyl alcohol) to water, including its solubility characteristics, are functions of both the molecular weight of the polymer and the degree of hydrolysis. At a constant degree of hydrolysis, increases in molecular weight also increase the water resistance of the polymer. At a constant molecular weight, however, increases in the degree of hydrolysis increase the adhesion of the polymer to hydrophilic surfaces while increasing water resistance; this means that the adhesion to hydrophobic surfaces must decrease with increases in the degree of hydrolysis. Thus, the ability of a poly(vinyl alcohol) having a high degree of hydrolysis to durably adhere to hydrophobic polymer fibers is unexpected.

In general, the hydrophobic polymer fibers are treated with the poly(vinyl alcohol) solution under conditions sufficient to deposit the poly(vinyl alcohol) on the surfaces of the fibers. Such conditions typically involve passing the poly(vinyl alcohol) solution around the hydrophobic polymer fibers under shear stress conditions so that at least a portion of the poly(vinyl alcohol) is adsorbed onto at least some of the hydrophobic polymer fibers. Accordingly, the poly(vinyl alcohol) solution may be passed around the hydrophobic polymer fibers by any means known to those having ordinary skill in the art. For example, the solution may be "pulled" past the fibers by reducing the pressure on the side of the fibers which is opposite the side against which the solution has been applied. Alternatively, the solution may be forced past the fibers by the application of pressure. Additionally, the solution may be spayed onto the fibers which then are passed through a nip to remove excess solution.

The present invention is further described by the examples which follow. Such examples, however, are not to be construed as limiting in any way either the spirit or the scope of the present invention.

Example 1

Two layers of 1.875-inch (about 4.8-cm) diameter regular polypropylene meltblown discs, each having a basis weight of about 1 ounce per square yard or osy (about 34 grams per square meter or gsm) were placed in a Nalgene filter holder (250-ml capacity, Nalgene # 300-4000, Nalge Nunc International, Naperville, Illinois). Two hundred ml of a 0.1 percent by weight aqueous solution of poly(vinyl alcohol) (Elvanol^® 7006, Dupont Chemical Company, Wilmington, Delaware) was placed on top of the layers and then passed through the layers over a period of ten seconds by reducing the pressure on the opposite side. The treated meltblown discs were air dried. The contact angles of treated and untreated (control) samples were measured by means of a Goniometer. The treated samples had a contact angle of 0 degrees compared to a 135-degree contact angle for the untreated samples.

The treated samples were put in contact with deionized water for one minute to determine their water uptake. The wetted filters were air dried and then put into contact with water again. This dry-wet cycle was repeated several times to demonstrate the durability of the coating. The results are summarized in Table 1.

Table 1 Coating Durability Tests

Example 2

A single layer of a 1.875-inch (about 4.8-cm) diameter polypropylene spunbond- meltblown-spunbond (SMS) disc, prepared essentially as described in U.S. Patent No. 4,041 ,203 to Brock et al., which patent is incorporated herein by reference in its entirety, and having a basis weight of about 4 osy (about 136 gsm), was treated with a 0.1 percent aqueous poly(vinyl alcohol) solution as described in Example 1. Water uptake of the dried, treated disc was determined as described in Example 1; the results are summarized in Table 2. Table 2 Coating Durability Tests

Example 3

The procedure of Example 2 was repeated, except that the polypropylene SMS disc was replaced with a polypropylene spunbond disc having a basis weight of about 3 osy (about 102 gsm). Water uptake of the dried, treated disc was determined as described in Example 1 ; the results are summarized in Table 3.

Table 3 Coating Durability Tests

Example 4

A single piece of a regular polypropylene meltblown fabric, seven inches (about 18 cm) on each side, was dipped for one minute into 100 ml of a 0.3 percent by weight aqueous solution of a poly(vinyl alcohol) prepared as described in the previous examples; the solution also contained 30 percent by volume of isopropyl alcohol (99.5%, HPLC grade, Aldrich Chemical Company, Inc., Milwaukee, WI). The poly(vinyl alcohol) was obtained from Aldrich (Catalog No. 18,934-0, Aldrich Chemical Company, Milwaukee, Wisconsin, 88 percent hydrolyzed and having a weight-average molecular weight of 96,000). The web was removed from the solution and air dried. When the dried web was put in contact with water, it was wet in seconds. The wet web was air dried and put in contact with water again. This dry and wet cycle was repeated ten times without a noticeable decrease in wettability.

While the specification has been described in detail with respect to specific embodiments thereof, it will be appreciated that those skilled in the art, upon attaining an understanding of the foregoing, may readily conceive of alterations to, variations of, and equivalents to these embodiments. Accordingly, the scope of the present invention should be assessed as that of the appended claims and any equivalents thereto.

Claims

WHAT IS CLAIMED IS:

1. A method of coating hydrophobic polymer fibers with a poly(vinyl alcohol), the method comprising: providing hydrophobic polymer fibers; preparing a solution of the poly(vinyl alcohol) in water; and treating the hydrophobic polymer fibers with the poly(vinyl alcohol) solution under conditions sufficient to deposit the poly(vinyl alcohol) on the surfaces of the fibers.

2. The method of claim 1 , in which the hydrophobic polymer fibers are polyolefin fibers.

3. The method of claim 2, in which the polyolefin fibers are polypropylene or polyethylene fibers.

4. The method of claim 1 , in which the poly(vinyl alcohol) has a degree of hydrolysis of at least about 88 percent.

5. The method of claim 4, in which the poly(vinyl alcohol) has a degree of hydrolysis of at least about 98 percent.

6. The method of claim 5, in which the poly(vinyl alcohol) has a degree of hydrolysis of 99 percent or greater.

7. The method of claim 1 , in which the poly(vinyl alcohol) has a molecular weight of at least about 10,000.

8. A method of coating hydrophobic polymer fibers with a poly(vinyl alcohol), the method comprising: providing hydrophobic polymer fibers; dissolving the poly(vinyl alcohol) in water at a temperature of at least about 60°C to obtain a poly(vinyl alcohol) solution; and treating the hydrophobic polymer fibers with the solution under conditions sufficient to deposit the poly(vinyl alcohol) on the surfaces of the fibers.

9. The method of claim 8, in which the hydrophobic polymer fibers are polyolefin fibers.

10. The method of claim 9, in which the polyolefin fibers are polypropylene or polyethylene fibers.

11. The method of claim 8, in which the poly(vinyl alcohol) has a degree of hydrolysis of at least about 88 percent.

12. The method of claim 11 , in which the poly(vinyl alcohol) has a degree of hydrolysis of at least about 98 percent.

13. The method of claim 12, in which the poly(vinyl alcohol) has a degree of hydrolysis of 99 percent or greater.

14. The method of claim 8, in which the poly(vinyl alcohol) has a molecular weight of at least about 10,000.

15. Coated fibers, comprised of a hydrophobic polymer, said fibers having on the surfaces thereof a coating of a poly(vinyl alcohol) applied by the method of claim 1.

16. Coated fibers, comprised of a hydrophobic polymer, said fibers having on the surfaces thereof a coating of a poly(vinyl alcohol) applied by the method of claim 2.

17. Coated fibers, comprised of a hydrophobic polymer, said fibers having on the surfaces thereof a coating of a poly(vinyl alcohol) applied by the method of claim 8.

18. Coated fibers, comprised of a hydrophobic polymer, said fibers having on the surfaces thereof a coating of a poly(vinyl alcohol) applied by the method of claim 9.