Disposable Diaper

Abstract

Improvements in disposable diapers of the type having moisture-absorbing cellulosic material sandwiched between a waterproof backing sheet and a cover fabric worn next to the body. The cover fabric is a light-weight apertured nonwoven of unbonded polyester fibers hydraulically entangled into a strong fabric having durability in use, rapid transmission of fluid to the absorbing layer without wicking, and a dry feeling when the absorbing layer is wet.

Description

BACKGROUND OF THE INVENTION

The invention relates to disposable diapers which are discarded after a single use.

One of the major problems in using diapers is the wetting of clothes either by leaking or by wicking from the wet moisture-absorbing layer through the cover fabric. It has been proposed to seal the moisture-absorbing layer and the cover fabric with an extension of the waterproof backing sheet, but such contact of the body and the backing sheet is undesirable and can cause a rash. The use of a margin of cover fabric beyond the moisture-absorbing layer can reduce the wicking from the layer, but conventional cover fabrics of cellulose fibers, such as wood pulp or rayon, wick liquid fairly readily.

Papers used as cover sheets may lack integrity so as to leave loose fibers on the body, generally have an unpleasant papery feeling and usually wick liquids readily.

Another requirement of a satisfactory diaper is rapid transmission of fluid from the cover fabric to the absorbing layer so that the fluid does not leak from the diaper area. This has been conventionally attained by the use of moisture-absorbing fibers such as wood pulp, cotton, or rayon. However, the use of such fibers causes the surface of the diaper to feel wet when the absorbing layer is wet.

DEFINITION OF THE INVENTION

A preferred product of the present invention is a diaper comprising in combination:

1. a waterproof backing sheet of rectangular shape;

2. a moisture-absorbing layer of cellulosic material which is smaller in length and width than the backing sheet and is centrally disposed on it and covered by

3. an apertured, nonwoven cover fabric of unbonded staple fibers having an entanglement completeness of at least 0.5, the fabric weighing about 0.5 to 1.0 oz./yd..sup.2, having dimensions substantially the same as the backing sheet; and consisting of 75-100 percent of polyester fibers and from 0 to 25 percent of cellulosic fibers. Preferably the cover fabric contains less than about 10 percent cellulosic fibers and has an elongation at the break of less than about 90 percent.

Preferably the product has a waistband (the two shorter edges) which is reinforced and stiffened by film tapes secured to the backing sheet, or is reinforced and stiffened by a fold of the backing sheet that is secured directly to the backing sheet by an adhesive or by fusion.

Both side edges of the rectangular diaper are infolded and then outfolded along lines substantially parallel to the center longitudinal axis of the diaper to provide a pair of double folds which are secured in place with adhesive.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of a contoured diaper with a portion of the cover fabric broken away.

FIG. 2 is a cross-sectional view taken along line 2--2 of FIG. 1.

FIG. 3 is a plan view of a reinforced diaper with a portion of the cover fabric broken away.

FIG. 4 is a plan view of a rectangular diaper with a portion of the cover fabric broken away.

FIG. 5 is an illustration of a folded rectangular diaper.

DETAILED DESCRIPTION OF THE DRAWINGS

Referring to FIGS. 1 and 2, the illustrated diaper contains a moisture-absorbing layer 12 that rests upon waterproof backing sheet 14 and is covered by cover fabric 10. Moisture-absorbing layer 12 is smaller than the backing sheet and the cover fabric, and is centrally disposed between them so that a margin 18 and 18' is formed around the entire periphery of the diaper. This arrangement, in combination with the low wicking properties of the cover fabric, prevents the transmission of urine from the layer 12 to the infant's clothes. The same or slightly larger dimensions of the cover fabric 10 assures contact of the soft, nonwoven fabric with the body at all points of contact to avoid rash caused by the contact of the backing sheet and the body.

The concave lateral edges of the diaper 20 and 20' afford a better fit with the crotch. The edges may be cut in various shapes. A sine curve s conveniently used as the layers can be cut by a rotating cutter to give two or more row of fabric blanks with a minimum of waste.

The assembly is conveniently held together by a line of attachment between the cover fabric and backing sheet around the edges of the moisture-absorbing layer.

FIG. 3 illustrates a reinforced diaper wherein a reinforcing strip of fabric 16 having the same low-wicking properties of the cover fabric is added to the ends of the diaper where it is pinned about the waist of the infant.

FIG. 4 shows a diaper which is folded for use, wherein the backing sheet and cover fabric are of rectangular shape.

As illustrated in FIG. 5, one diaper of the invention is made by placing the unfolded diaper of FIG. 4 with cover fabric 10 upward. Each of the side edges 28 and 28' are then folded towards the center of the diaper. This provides a first fold 21 running along each side of the folded diaper substantially parallel to a center imaginary line. The infolded edges 28 and 28' are then folded back on themselves to where the edges 28 and 28' substantially coincide with the first folds. This provides two first folds 21 and two second folds 22 both extending lengthwise of the diaper. The second folds 22 may touch or be spaced from each other so as to leave a portion 26 of the center part of the diaper open and not covered by the folded-in sides. The cover fabric between folds 21 and 22 is secured to its opposite cover fabric. This is preferably done at fold 22 by an adhesive 24 placed substantially midway between the ends of the diaper.

COVER FABRIC

The cover fabric can be made by subjecting a web of fibers supported on an apertured plate or screen to the action of fine columnar streams of liquid as taught in U.S. Pat. No. 3,485,706 dated Dec. 23, 1969. The treatment results in the interentangling of the fibers to give a strong, integral fabric-like product. The appearance of the product depends upon the nature of the supporting plate, the weight of the web, and the intensity of the treatment. When using screens of 40 percent or less open area and up to 40 mesh, products may be prepared with actual visible holes corresponding to the screen pattern when products are of low weight, e.g., 1 ounce/square yard (oz./yd..sup.2) or less. With weights of 2 oz./yd..sup.2 the screen should be 30 mesh or coarser to give the desired apertured products. The cover fabrics of this invention are preferably made on a 20 .times. 20 mesh or finer screen.

The more preferred products have a slightly fuzzy surface (this is used on the outer face of the diaper next to the skin) due to fiber ends being driven through the fabric in its preparation.

The energy (E) expended during one passage under a manifold in the preparation of a given nonwoven fabric, in horsepower-hours per pound (HP-hrs./lb.) of fabric, may be calculated from the formula:

E = 0.125 (YPG/sb)

where:

Y = number of orifices per linear inch of manifold,

P = pressure of liquid in the manifold in psig.,

G = volumetric flow in cu.ft./min./orifice,

s = speed of passage of the web under the streams, in ft./min., and

b = the weight of the fabric produced, in oz./yd..sup.2

It has been observed that the entanglement of the fibers is related to the product of the energy (E) of the treatment and the impact force (I) (in pounds) of the hydraulic stream.

I = PAK

where P is the pressure on the orifice in psi., A is the area of a single orifice in square inches and K is the orifice discharge coefficient (approximately 0.64).

The polyester fibers used in the cover fabric should preferably have a denier no greater than about 2.5 and more preferably about 1.5. Any convenient fiber length can be used, e.g., up to 3 inch. The average length should not be much less than 0.75 inch as the tensile strength decreases with shorter lengths for a given entangling treatment.

The length of any cellulosic staple fiber used is not critical but is preferably about 0.75 to 1.5 inch. When rayon is used, a relatively low denier in the range of 1 to 2 is preferred. The cellulosic staple should comprise no more than about 25 percent of the weight of the blend with polyester and preferably less than about 10 percent.

MOISTURE-ABSORBING LAYER

Suitable moisture-absorbing layers are well known. A high absorbency of water or body fluids is required. Generally, this layer has a low order of wet strength and integrity. The layer may comprise layers of a paper, wood pulp crepe wadding, a layer of wood fluff, an embossed wood pulp pad or various combinations of such cellulosic products. Wood fluff is preferred.

Fluid distribution means known in the art may be incorporated in this layer.

WATERPROOF BACKING SHEET

Suitable backing sheets are well known in the art. It can be a thin plastic sheet such as polyethylene or the like, or a liquid repellant layer of a hydrophobic polymer on the bottom face of a nonwoven fabric.

ADHESIVES

The various components of the diaper can be secured in any desired manner as by stitching or cementing. Suitable adhesives include produces sold under the trademarks "Thermogrip" Hot Melt Adhesive No. 1313, which is a formulated polyethylene base adhesive sold by the B. B. Chemical Division of United Shoe Machinery Corp. of Cambridge, Mass., and "Sobo" which is a polyvinyl acetate/water emulsion sold by Solomon Laboratories of Long Island City, N.Y. Adhesive transfer tape (double-faced) is also suitable

TESTING PROCEDURES

Water-Retention Test

Diapers are assembled using the various nonwoven fabrics as the cover fabric and the moisture-absorbing layer and plastic film backing sheet of a commercial disposable diaper ("Newborn Pampers" made by Proctor and Gamble Co. of Cincinnati, Ohio). The moisture-absorbing layer comprises seven layers of 1 oz./yd..sup.2 crepe wadding (10 .times. 13.5 inch) embossed together in a pattern. The cover fabric is placed with the surface that faced the screen during entangling as the outer face (skin-contacting) of the diaper.

The water retention of each diaper cover is tested by placing the diaper flat on a surface with the cover fabric up, adding 100 ml. of water to the diaper through the cover fabric, covering with a plastic film, and pressing with an aluminum plate loaded to give 0.1 psi. pressure on the diaper for 30 minutes. The damp cover fabric is then removed from the moisture-absorbing layer and weighed. Water retention is the weight in grams of the water retained by the 10 .times. 13.5-inch cover fabric. The higher the water retention, the less desirable is the fabric due to the wet feeling.

Fluid Run-Off Test

Another important function of a diaper assembly is its ability to quickly absorb liquid. This is measured by a fluid run-off test wherein 30 ml. of water is added from a burette at a rate of 4 ml./second to a 6 .times. 6-inch portion of a diaper assembly of the cover fabric and the above commercial moisture-absorbing layer. The diaper assembly is supported at a 15.degree. angle to the horizontal, and the fluid that runs off the surface of the cover fabric is measured.

In use, the cover fabric may be wet with baby oil, lotions, etc., from the babies' skin, so the test is also run on a diaper section that has had 1 gram of baby oil (Johnson's Baby Oil) spread evenly over its surface by transfer from a plastic sheet. Strip tensile strength and elongation at break are measured on an Instron Tester at 70.degree.F. and 65 percent relative humidity using 1.0-inch wide samples with a 2-inch distance between jaws and elongating at 50 percent per minute. The results are given in pounds/inch (lb./in.) for machine direction (MD) and cross direction (XD) as MD/XD.

Wickability Test

The wickability of a fabric is determined by fastening the ends of a 2 .times. 5.5-inch strip to a perforated metal plate with rubber bands, resting the end of the plate under about 0.5 inch of distilled water at about 25.degree.C. at an angle of 25.degree. to the level of the water and noting the time in minutes and distance in inches at which the sample wicks. The wicking should be measured on samples cut in 2 directions at 90.degree. to each other (machine and cross directions) and the results averaged. A soluble dye may be added to the water to assist in determination of the level on the fabric.

A typical commercial nonwoven fabric of resin-bonded rayon fibers (Item G of Example I) has a wickability of 1.5 inches in 20 minutes. An entangled nonwoven fabric of rayon staple fibers (Item B of Example I) has a wickability of about 4 inches in 4 minutes.

ENTANGLEMENT COMPLETENESS TEST

In this test, nonwoven fabrics are characterized according to the completeness of the fiber entanglement in non-bonded fabric, as determined from strip tensile breaking data using an "Instron" tester.

Entanglement completeness is a measure of the proportion of fibers that break (rather than slip out) when a long and wide strip is tested. It is related to the development of fabric strength. Durable non-bonded products have an entanglement completeness of at least 0.5

Entanglement completeness is calculated from strip tensile breaking data, using strips of the following sizes: ---------------------------------------------------------------------------

Strip Strip "Instron" Gauge Elongation Rate Width Width (in.) Length (in.) (in./min.) Symbol __________________________________________________________________________ w.sub.o 0.8 0 0.5 w.sub.1 0.3 1.5 5 w.sub.2 1.9 1.5 5 __________________________________________________________________________

In cutting the strips from fabrics having a repeating pattern of ridges or lines of high and low basis weight, integral numbers of repeating units are included in the strip width, always cutting through the low basis weight portion and attempting in each case to approximate the desired widths (w.sub.o, w.sub.1, w.sub.2) closely. Ten or more specimens are tested a w.sub.1, and five or more at w.sub.2 and w.sub.o using an "Instron" tester with standard rubber coated, flat jaw faces and the gauge lengths and elongation rates listed above. Average tensile breaking forces for each width (w.sub.o, w.sub.1 and w.sub.2) are correspondingly reported as T.sub.o, T.sub.1, and T.sub.2. From these a value (c) is calculated as follows:

c = (T.sub.2 - T.sub.1)/(w.sub.2 - w.sub.1) .multidot. w.sub.o T.sub.o

For patterned fabrics, strips are cut in two directions: (a) in the direction of pattern ridges or lines of highest basis weight (i.e., weight per unit area), and (b) in the direction at 90.degree. to the direction specified in (a). For unpatterned fabrics any two directions at 90.degree. will suffice. The value (c) is determined separately for each direction and the arithmetic means of the values for both directions, (c) is calculated. The value (c) is called the entanglement completeness.

EXAMPLE 1

Random webs of staple fibers are made by the air deposition of polyester fibers (1.5 dpf. and 1.5-inch length), or rayon fibers (1.5 dpf. and 0.75-inch length), or blends of these fibers.

Each web is hydraulically entangled into an integral, strong, nonwoven fabric by passing it while supported on a 24 .times. 24 mesh screen (16 percent open area) under rows of fine columnar streams of water jetted under pressure from rows of orifices in manifolds located about 12 mm. above the web. The orifices are similar to those shown in FIG. 3 of U.S. Pat. No. 3,403,862 to Dworjanyn, have an upper cylindrical section of 0.005-inch diameter with a lower frusto-conical section as an exit, and are spaced 40 per inch in each row.

The compositions of the webs and the entangling conditions are given in Table I. Items A, C, D, and E are products useful in this invention. Items A through F are entangled nonwovens. Item G, a cover fabric used in a commercial diaper and made by resin bonding of a carded web of rayon fibers, is included for comparison.

Diapers are assembled from the various fabrics and tested as described in the section on Testing Procedures. It is noted in Table II that entangled rayon fabric (Item B) and the commercial fabric have relatively high water retentions as compared to the fabrics containing polyester fibers and display a very wet hand.

From the results in Table II, it can be seen that the preferred cover fabrics of polyester fibers with a minor proportion of cellulose fibers and having an adequate degree of entanglement as judged by c (Items C, D, and E) have relatively low values of fluid run-off on plain or oiled fabrics. These fabrics are further characterized by patterns of distinct apertures and by the presence of fiber ends (substantially all polyester fibers) that project from about 0.5 to 1 mm. beyond the downstream face of the fabric (the face of the fabric next to the screen during formation).

Item F is unacceptable as a cover fabric because an excessive amount of loose fibers are left on the infant's skin in use, and it is also readily stretched out of shape in use. These deficiencies are presumably due to the low c and high elongation-at-the-break of Item F.

The thickness of the fabrics are given in Table II is measured under about 0.16 pound per square inch load with a plunger of about 0.75-inch diameter (Federal Gauge made by Federal Products Corp. of Providence, R.I.). It is considered that the superior dry hand of the diapers of this invention is due in part to the thickness of the entangled nonwoven fabrics. The fabrics will preferably have a thickness of at least 10 mils, and more preferably at least 15 mils, even at the lowest fabric weights. ##SPC1## ##SPC2##

EXAMPLE 2

Fabric A of Example 1 is used as a cover fabric for a diaper. The fabric has a wickability of less than 0.1 inch in 20 minutes.

ASSEMBLY OF A DIAPER

Diapers are assembled as shown in FIG. 4 using the above nonwoven fabric as the cover fabric, polyethylene film (about 1.0 to 1.5 mils thick) as the waterproof backing sheet and plies of a composite moisture-absorbing layer consisting of one layer of wood fluff (4 or 6 ounces/square yard as indicated below) with two layers of crepe wadding (1 ounce/square yard per layer) on each face, which has been embossed together with a grid pattern. Typical dimensions of width (W) and length (L) in inches are given below: ##SPC3##

When assembling a given type, the larger of the moisture-absorbing layers is centered on the film, the smaller absorbing layer is centered on top of that. A strip of 0.75-inch wide transparent adhesive plastic tape is placed at each end of and adjacent to the two shorter edges of the larger layer running for the entire width of the diaper as reinforcement and the nonwoven fabric is placed on top of the assembly with the fuzzy (downstream) face up. The cover fabric is secured to the film in a line around the perimeter of the moisture-absorbing layer by strips of 0.25-inch wide adhesive transfer tape.

Claims

We claim:

1. A disposable diaper comprising in combination a waterproof backing sheet of rectangular shape, a moisture-absorbing layer of cellulosic material which is smaller in length and width than the backing sheet, and an apertured, nonwoven cover fabric of unbonded staple fibers having an entanglement completeness of at least 0.5, the cover fabric weighing about 0.5 to 1.0 oz./yd..sup.2, having dimensions substantially the same as the backing sheet, and consisting of 80 to 90 percent of polyester fibers and from 20 to 10 percent cellulosic fibers, both side edges of the rectangular diaper being infolded and then outfolded along lines substantially parallel to the center longitudinal axis of the diaper to provide a pair of double folds which are secured in place with adhesive.

2. A diaper as defined in claim 1 wherein said polyester fibers are about 1.5 denier and about 0.75 to 3 inches in length.