US2833283A - Nonwoven fabric and absorbent products - Google Patents

Description

May 6, 1958 R. J. sPAHR ErAL NoNwovEN FABRIC AND ABsoRBENT lPRODUCTS Filed nec. 28, 1954 i Il n.:

ATTORNEY ilnited States Patent O NONWOVEN FABRIC AND ABSORBENT PRODUCTS Raymond J. Spain', Granbury, .lohn K. Sumner, Plainfield, and Elmer l. Yetllick, Westfield, N. J., assignors to Chicopee Manufacturing Corporation, a corporation of Massachusetts Application December 28, i954, Serial No. 477,982 7 Claims. (Cl. 12S- 290) The present invention relates to nonwoven fabrics, i. e., fabrics produced directly from fibers without the use of conventional spinning, weaving, or knitting operations, more particularly to such fabrics formed by bonding together the fibers of a loosely assembled web or webs of overlapping, intersecting fibers, and absorbent products covered therewith.

Bonded nonwoven fabrics have been formed by printing, impregnating, or otherwise depositing an adhesive bonding material uniformly throughout a base web of the type which may be formed by carding, garnetting, air laying, etc. of relatively long fibers including those of textile length. Generally speaking, it has been an aim to retain the fibrous nature of the web as much `as possible in order that the fabric will be soft and textile like in nature. For this reason, the bonding material employed should be capable of forming strong bonds with the fibers in the web to assure a maximum of strength with a minimum of binder. This is also important from a cost standpoint. Binders based upon polyvinyl acetate resins are known to be capable of forming strong bonds with textile fibers, particularly with cellulosic fibers, as well as to have good mechanical 'and chemical stability. Unfortunately, polyvinyl acetate tends to be quite brittle, which means it must be softened or plasticized in some way if it is to be used in the formation of textile-like fabrics wherein drape, flexibility, and softness are important qualities. In lthe past polyvinyl acetate resins have been softened for this purpose by the addition of external plasticizers such `as dibutyl phthalate to the resin emulsion before application to lthe web. These plasticizers, while improving the softness or hand of the fabric, tend to detract seriously from strength, particularly wet strength, to the extent that the resulting fabrics have either been lacking in strength, on the one extreme,

or softness on the other.

The present invention contemplates a fabric bonded with `an internally plasticized polyvinyl acetate, wherein the internal plasticization softens the acetate and yet does not detract seriously from its strength and bonding ability. This internal plasticization is in the nature of a modification by polymerization with another resin. The preferred resin modifier may be chosen from alkyl ,acrylates or alkyl methacrylates with the resulting internally plasticized polyvinyl acetate resin in the form of a copolymer of vinyl acetate and an alkyl acrylate, a copolymer of vinyl acetate and an alkyl methacrylate, or a tripolymer of vinyl acetate, an alkyl acrylate and an alkyl methacrylate. However, other modifiers such as copolymers of vinyl acetate and vinyl stearate may be used. Alkyl acrylates and methacrylates comprising lower alkyl radicals containing less than nine carbon atoms Iare preferred. The preferred acrylates may be defined by the following general formula:

ICC

where Ris an alkyl radical containing less than nine carbon atoms. The preferred methacrylates likewise may be defined by the following general formula:

where R is as defined above. Generally speaking, the copolymer or tripolymer should comprise predominantly or moreV than 50 percent vinyl acetate, based upon the weight of the total monomers. It is preferred that the copolymer or tripolymer comprise at least about percent vinyl acetate, on the same basis, and excellent results have been obtained with copolymers of vinyl acetate and alkyl acrylates comprising less than 15 percent acrylate based upon the weight of the total monomers.

Nonwoven fabrics bonded with Ithe above-described resins, not only are strong and soft, but `also possess unexpectedly high wet strength yand wet abrasion resistance. They also are capable of resisting heat and can be sterilized without becoming tacky or weakening thebonds between fibers during the sterilization process. The resulting liber-binder combination also is substantially nonionic and in this sense creates a favorable environment for use with anionic or cationic bactericides, odor preventatives, etc., which will not detract seriously from the effectiveness of even small quantities of these agents deposited in the fabric.

Due to the above and other qualities, the fabric of this invention is particularly adaptable for use in covers for sanitary napkins and dressings, disposable diapers, -bed pads, wiping cloths, towelling, filter materials, and many other applications.

Webs suitable for conversion into fabrics of this invention may be formed by cal-ding, garnetting, by air deposition using techniques such as described in U. S. Patent Nos. 2,676,363 and 2,676,364, and other methods. The bers it contains may be oriented predominantly in one direction as in a card web Aor a card web laminate, or the web may be substantially isotropic where equivalent strength in all directions is desired. For napkin covering and related uses the web may be fairly thin land weigh between 15() and 400 grains per square yard. Uniformity of fiber ldistribution is an important characteristic, particularly in thin fabrics which must nevertheless possess a substantial :amount of strength and be free of Weak spots due to lack of uniformity. Uniform webs may be produced by carding, in which case it is advantageous to use fibers which have good carding characteristics and can -be blended into a uniform carded web with facility. Fibers of viscose rayon and cotton are both satisfactory in this respect. An advantageous liber blend may comprise approximately 75 percent of substantially 1.5 denier viscose rayon ibers and the remainder substantially 1.5 denier bleached cotton fibers, both of textile length. However, it should be understood that almost any kind of a textile fiber may be employed in forming a fabric of this invention depending upon the intended end use. -For instance, the base web may comprise natural fibers, such as cotton, jute, ramie, or wool; artificial fibers of vis-cose rayon, cuprammoniurn, cellulose acetate, etc.; or synthetic fibers of materials, such as nylon, Saran, polyethylene, and others; alone or in combination with one another.

The binder may be deposited in the web by printing, spraying, impregnating, or by other techniques wherein i the amount of binder may be metered and the binder satisfactory for use in covers for sanitary napkins, may

ferred tothe web by contact therewith to` distribute Ithe binder in the web in spaced areas thereof. The` bonding material in the binder areas mayform'bon'ds ywiththose` portions of the fibers passing through the areas and the spaces between binder areas may be limited to assure that substantially -all of the fibers in the web are adequately bound. Since there is a corresponding pattern of unboundiber areas, extending between the arcas of binder deposition, a soft and flexible fabric niayresult wherein the binder which is deposited in the web is subje'cnt maximum utilization. In a pattern ,bonded fabric offthi'sV type, it is particularly important that the binder foi'n strong bonds with those portions of the bers passing through the binder areas.

`Examples of pattern bonded nonwoven fabrics and products illustrating certain Vuses of fabrics of this inve'ntion are shown in the attached drawings wherein: v

Fig. 1 is a plan view of one embodiment of a fabric according to this invention;

Fig. 2 is a plan View of another embodiment;

Fig. 3 is an isometric view of a sanitary napkin covered with a fabric of this invention;

Fig. V4 is an enlarged sectional view along the o'f Fig. 3";

Fig. 5 is an isometric `view of a diaper or absorbent pad covered with afabrie of this invention; Y

Fig. 6 is Aan 'enlarged fragmental sectional view along the line 6-6 of Fig. 5.

line 4 4 As shown in Fig. l, an adhesive bonding material may` binder. 1 referably, the binder areas are located close.

enough together to intersect and Vbind most Vof the fibers in the web even thoughsubstantial portions of the lengths of these fibers ',areifree of binder. The pattern of Fig. '1 is 'illustrative of fone Vtypeo'f an open pattern which may be used. Fig. 2 illustrateslanothertypeof pattern. In this figurethe binder is distributed Ain intersecting courses of spaced lines or strips 15 defining square or diagonal web areas 16` relatively freeA of binder between them. It will beobvious to one skilled jin the art thatY there are many variations of patternsfwhich may be used to deposit ftlie binder 1in spaced 'areas `in the web to provide a lfabric comprising an intermittent 'arrangement of soft `"areas relatively "free of binder fand areas lwhere the binder is deposited as if by impregnation to bind the'tbers together.

Figs. 3 fand vl 4illustrate a sanitary 'napkin A17 covered with a soft Vnonwoven'fabric '1.8 taccording'to this invention wherein the binder isdepdsitedfin apatternof spaced rings or atolls `19 such as isshown in" Fig. l. 'lfhe fabric is'wrapped` around an absonbentinner body 21 which may bedesigned to distributevuids as uniformly as possible throughout its length. VIt is extremely importantthatthe nonwoven napkin coverjremain vquitesoft while at the Sametime retaining its web-like integrity to` prevent-roping and chang during use. Thus, the binder must be relatively softxand flexible, wet and dry, and possessfrelatively highlwet and dry strengths to asurethat theliberswill remain bonded in use and'that'the'fabric will'vbe abrasionand 2 tend to be highly permeabledue'to the "high per-` basiswith the range of to 25 percent preferred for napkin cover use. Y

Figs. 5 and 6 illustrate a diaper or Iabsorbent pad 22 covered with a nonwoven fabric 23 according to this invention wherein the binder is deposited in a diagonal pattern of spaced strips 24 such as is shown in Fig. 2. The nonwoven facing fabric 23 covers an absorbent inner layer 25 which in turn may comprise `a number of sheets eoveragebe no greater than about 35 percent onian area 75 vthat will be readily apparent to the skilled artisan.

Ofcreped cellulose or an absorbent material such as fluled woodpulp. The pad may include a relatively waterproof or water-impermeable backing sheet 2.6 on one face of the diaper. The nonwoven -facing sheet 23 will be in contact with the wearer in the case of a diaper, for instance, and therefore must be quite soft and durable. As in the case of the sanitary napkin cover, described hereinbefore, the `diaper facing must retain its softness, permeability and strength, wet and dry, and rmust be capable of considerable resistance to abrasion when wet. yIn fact, ability to resist wet abrasion may be one of the most important requirements for a diaper cover of this type.

An illustrative fabric of this invention may be formed by printing a laminate of ve or six card webs with an aqueous dispersion of an adhesive binder comprising a copolymer of vinyl acetate and approximately l5 percent ethyl acrylate based upon the weight of rthe total monomers. The web may weigh approximately 170 grains per square yard and comprise approximately percent of substantially 1.5 denier viscose rayon staple fibers averaging about 2 inches in length and 25 percent of substantially 1.5 denier bleached absorbent cotton bers of textile length. The binder may be deposited in a pattern similar to that of Fig. l with the result that the binder deposited in the fabric weighs about 35 grains per square yard on a dry basis. The resulting fabric will be soft and strong, wet and dry. lt also will be flexible and highly extensible. The copolymer of vinyl acetate and ethyl acrylate, described, will form particularly good bonds with the rayon and cotton bers in the web with the result that the fabric .will be capable of resisting a good deal of abrasion and stretching when wet without serious loss of bond integrity. This fabric also will be capable of resisting quantities of heat, such as maybe necessary for sterilization, without deterioration or appreciable loss of bond integrity.

The binder dispersion may be applied to the fabric by bringing 'the card web laminate into contact with an engraved roll'carrying the binder, such as is generally described in U. S. Patent No. 2,545,952 to YE. R. Goldman. In the above example, the binder dispersion may comprise approximately 50 percent resins solids, a small amount o f a dispersing agent such as carboxymethylcellulose, a small amount of an anti-foaming agent such as the product soldas Anti-Foam A by the Dow Corning Corportion, and other conventional agents to assistin processing. The resulting fabric is substantially nouionic and therefore will provide afavorable environment for anionic and cationicagents. For instance, the fabric may be impregnated with a relativelysmall amount of a cationic bactericide or odor preventative such as a quaternary ammonium compound, and the compound will remain effective for this purpose for a relatively long period of time despite the small quantity employed.

Having now described the invention in specific detail and indicated the manner' in which it may be 'carried in to practice, it will be readily apparent to those skilled p in the art that innumerable variations, applications, modifications and extensions of the basic principles involved may be made without Vdeparting from its spirit orscope. Thus, thefabrics of the present invention may be laminated with other fabrics or employed in a host ofways lt should also be apparent that for uses wherein extreme softness is desired the binder employed may be softened further by the addition of a conventional external plasticizer for the binder in an amount calculated to effect the desired result. We therefore intend to be limited only in accordance with the appended patent claims.

The invention claimed is:

1. A relatively soft, strong and sterilizable nonwoven fabric comprising a loosely assembled web of overlapping, intersecting fibers, and a binder material distributed intermittently throughout the web in adhesive contact with the fibers therein and forming longitudinally and transversely spaced heat resistant bonds between the individual fibers, the distribution of the binder material being such as to retain the iibrous textile-like qualities of the original web to a large extent, said binder comprising a material selected from the group consisting of copolymers of vinyl acetate and an alkyl acrylate, copolymers of vinyl acetate and an alkyl methacrylate and tripolymers of vinyl acetate, an alkyl acrylate, and an alkyl methacrylate and said bonds being strong and capable of resisting abrasion when wet, said acrylates having the following structural formula: l

\G=JJC o 0 R H and said methacrylates having the following structural' formula:

' H on,

C=o o 0 Ry and wherein R is an alkyl radical containing less than nine carbon atoms, said 'binder material comprising at least about 70 percent of vinyl acetate based upon the weight of the total monomers.

2. A relatively soft, strong and sterilizable nonwoven fabric according to claim l wherein said binder material is a copolymer of vinyl acetate and an alkyl acrylate comprising less than l5 percent acrylate based upon the weight of the total monomers. v

3. A relatively soft, strong and .sterilizable nonwoven fabric according to claim 2 wherein said acrylate is ethyl acrylate. v

4. A relatively soft, strong and sterilizable nonwoven fabric comprising a loosely assembled web of overlapping, intersectingbers and a binder material distributed in a pattern defining alternate binder-free and binder-containing areas in the web, said binder being in adhesive contact with the bers in said binder containing areas and forming heat resistant bonds between .individual fibers therein, said binder containing areas comprising less than about 35 percent of the total fabric area, said binder comprising a material selected from the group consisting of copolymers of vinyl acetate and an alkyl acrylate, copolymersA of vinyl acetate and an alkyl methacrylate and tripolymers of vinyl acetate, an alkyl acrylate, and an alkyl methacrylate and said bonds being strong and capable of resisting abrasion when wet, said binder material comprising at least about 70 percent of vinyl acetate based upon the weight of the total monomers.

5. A relatively soft, strong and sterilizable nonwoven fabric comprising a loosely assembled web of overlapping, intersecting fibers, said web weighing between about 150 and 400 grains per square yard, and a binder material distributed in a pattern deiining `alternate binderfree and binder-containing areas in the web, said binder being in adhesive contact with the fibers in said binder containing areas and forming heat resistant bonds between individual iibers therein, said binder containing areas comprising less than about 35 percent of the total fabric area, rsaid binder comprising a material sellected from the group consisting of copolymers of vinyl acetate and an alkyl acrylate, copolymers of vinyl acetate and an alkyl methacrylate and tripolymers of vinyl acetate, an alkyl acrylate, and an alkyl methacrylate and said bonds being strong and capable of resisting abrasion when wet, said binder material comprising at least about percent of vinyl acetate based upon the weight of the total monomers.

6. A sterilizable absorbent pad comprising an inner absorbent layer and a relatively soft and Istrong nonwoven fabric covering at least the inner face thereof, and said nonwoven fabric comprising a loosely assembled web of overlapping, intersecting bers and a binder material distributed in a pattern defining alternate binder-free and binder-containing areas in the web, said binder being in adhesive contact with the fibers in said binder containing areas and forming heat resistant bonds between individual iibers therein, said binder containing areas comprising less than about 35 percent of the total fabric area, said binder comprising a material selected from the -group consisting of copolymers of vinyl acetate and an alkyl acrylate, copolymers of vinyl acetate and an alkyl methacrylate and tripolymers of vinyl acetate, an alkyl acrylate, and an alkyl methacrylate and said bonds being strong and capable of resisting abrasion when wet, said binder material lcomprising at least about 70 percent of vinyl acetate based upon the weight of the total monomers.

7. A sterilizable sanitary napkin comprising an inner absorbent layer and a relatively soft and strong nonwoven fabric covering at least the inner face thereof, comprising a loosely assembled web of overlapping, intersecting fibers, and a binder material distributed intermittently throughout the web in adhesive contact with the fibers therein and forming longitudinally and transversely spaced heat resistant bonds between the individual Vfibers, the distribution of the binder material being such as to retain the fibrous textile-like qualities of the original web to a large extent, said binder comprising a material selected from the group consisting of copolymers of vinyl acetate and an alkyl acrylate, copolymers of vinyl acetate and an alkyl methacrylate and tripolymers of vinyl acetate, an alkyl acrylate, and an alkyl methacrylate and said bonds being strong Iand capable of resisting abrasion when wet, -said acrylates having the following structural formula:

and said methacrylates having the following structur formula:

H CHa \C=ccoo1z and wherein R is an alkyl radical containing less than nine carbon atoms, said binder material comprising at least about 70 percent of vinyl acetate based upon the weight of the total monomers.

References Cited in the le of this patent UNITED STATES PATENTS 2,067,706 Fikentscher Jan. 12, 1937 2,431,745 Flanagan Dec. 2, 1947 2,705,497 Johnson et al. Apr. 5, 1955 2,705,686 Ness et al. Apr. 5, 1955

Claims (1)

1. A RELATIVELY SOFT, STRONG AND STERILIZABLE NONWOVEN FABRIC COMPRISING A LOOSELY ASSEMBLED WEB OF OVERLAPPING, INTERSECTING FIBER, AND A BINDER MATERIAL DISTRIBUTED INTERMITTENTLY THROUGHOUT THE WEB IN ADHESIVE CONTACT WITH THE FIBERS THEREIN AND FORMING LONGITUDINALLY AND TRANSVERSELY SPACED HEAT RESISTANT BONDS BETWEEN THE INVIDIDUAL FIBERS, THE DISTRIBUTION OF THE BINDER MATERIAL BEING SUCH AS TO RETAIN THE FIBROUS TEXTILE-LIKE QUALITIES OF THE ORIGINAL WEB TO A LARGE EXTENT, SAID BINDER COMPRISING A MA-

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