GB2023494A - Absorbent facing and method for making the same - Google Patents

Abstract

An absorbent facing having a significant one-way valve characteristics for aqueous fluids is produced by a process which comprises the steps of: (a) superimposing a thin polymer film 10 and a first web 14 comprising absorbent fibers; (b) heating the assembly to a temperature such that the polymer film is in a formable state; (c) while the said assembly web is so heated, simultaneously applying shearing and compressive forces thereto to form said polymer film into a coating comprising a fine pattern of continuous areas which lie between and interconnect discontinuous areas, wherein the polymer in the continuous areas comprises a continuous or substantially continuous coating on the surface of said first web, and wherein most of the polymer in the discontinuous areas is coated on individual fibers; and (d) cooling the coated web thus formed to cool the polymer below its forming temperature, the process being effected using heated roller 18 co- operating with roller 20 having a resilient hill and dale surface. The product may be used in sanitary goods. <IMAGE>

Description

SPECIFICATION Absorbent facing and method for making the same The invention relates to an absorbent facing and to a process for producing the same.

Field of the invention Absorbent facings are often employed in such articles as disposable diapers, dressings, bandages, incontinent pads, sanitary products, and the like. An ideal absorbent facing would permit liquid to pass through it from a source to the absorbent material behind the facing, but would prevent liquid from flowing in the reverse direction. To state this desirable property in another way, it would be desirable to have an absorbent facing exhibit "one-way valve" characteristics to aqueous liquids.

Description of the PriorArt A number of approaches have been employed to impart one-way valve characteristics to the facings of absorbent materials. One such method is described by Kozak, in U.S. Patent No.

3,814,101, in which the absorbent material is faced with a polymeric film having a repeating pattern of indentations or dimples and slits in the film.

In Surowitz, U.S. Patent No. 3,307,545, a nonadherent dressing is described in which an absorbent material is faced with a polymer film having a pattern of depressions therein, with the depressions having openings to the absorbent material. The stated purpose of the facing of Surowitz is to prevent a dressing from adhering to a wound.

Summary of the Invention Broadly, the process for producing an absorbent facing material that is provided by this invention comprises the steps of: (a) superimposing a thin polymer film and a first web comprising absorbent fibers, to form a second web having said thin polymer film on one face and said first web on the other face; (b) heating said second web to a temperature such that said polymer film is formable;; (c) while said second web is so heated, simultaneously applying shearing and compressive forces to said second web to form said polymer film into a coating on said first web, said coating comprising a fine pattern of continuous areas which lie between and inter-connect discontinuous areas, wherein the polymer in the continuous areas comprises a continuous or substantially continuous coating on the surface of said first web, and wherein most of the polymer in the discontinuous areas is coated on individual fibers; and (d) cooling the coated web thus formed to cool the polymer below its forming temperature.

Brief Description of the Drawings Fig. 1 is a schematic view in elevation of one type of apparatus that can be employed to carry out the process of the invention; Fig. 2 is a scanning electron micrograph of one type of absorbent facing material of the invention, shown at a magnification of 75X; Fig. 3 is a scanning electron micrograph of another type of absorbent facing material of the invention, shown at a magnification of 1 40X: Fig. 4 is a scanning electron micrograph of a facing made in accordance with Surowitz, U.S.

Patent No. 3,307,545, shown at a magnification of 70X; Fig. 5 is a further enlarged scanning electron micrograph of a portion of the facing of Fig. 4, shown at a magnification of 1 70X; Fig. 6 is a perspective view of a sanitary napkin which utilizes the absorbent facing material of the . invention; and Fig. 7 is a perspective view of a disposable diaper which utilizes the absorbent facing material of the invention.

Description of the Preferred Embodiments Referring to Fig. 1, there is shown an apparatus that can be employed to carry out the process of the invention. In carrying out the process, a polymer film 10 and a fibrous web 14 composed principally of absorbent fibers are taken off suitable supply rolls 12, 16, which are mounted for rotation on bearings 13, 17 mounted in suitable framing F. The film 10 and fibrous web 14 are superimposed and are passed through the nip of a pair of counter-rotating rolls 1 8, 20. The rolls are mounted for rotation on bearings 19, 23 mounted in suitable framing F, and are driven by suitable drive mechanisms 21 , 25. The bottom roll 18 that is in contact with the fibrous web 14 has a smooth, uniform surface. Said bottom roll 18 is heated.The top roll 20 that is in contact with the polymer film 10 has a resilient surface that has a pattern of continuously arranged recessed areas (grooves) and discontinuously arranged raised areas disposed uniformly over the surface of the roll 20. As a general rule, the grooves will usually be from about 0.002 inch to about 0.05 inch wide, and from about 0.001 inch to about 0.035 inch deep. Preferably, the resilient roll 20 is moving at a peripheral speed slightly higher than the peripheral speed of the smooth roll 18. Peripheral speed ratios of from about 1.1:1 to 1.5:1 are suitable.After passing through the nip of the rolls 18, 20, the polymer film is formed into a coating on the fibrous web, with the coating comprising a fine pattern of continuous areas which lie between and interconnect discontinuous areas, wherein the polymer in the continuous areas comprises a continuous or substantially continuous coating on the surface of the fibrous web, and wherein the polymer in the discontinuous areas is coated on individual fibers.

The apparatus that can be employed to carry out the process of this invention is similar to the apparatus disclosed by Kalwaites, in U.S. Patent No. 3,881,381.

A wide variety of thin films can be employed in the invention. The preferred films are made from olefin polymers, such as polyethylene, both high and low density, polypropylene, ethylene copoloymers such as ethylene/vinyl acetate, ethylene/ethyl acrylate, and others such as ethylene/methyl acrylate. It is desirable to employ a film having a thickness of from about 1/4-mil to about 1-1/4 mils. In one preferred aspect, a corona-treated polyethylene film is used in order to achieve improved adhesion between the film and the fibrous web.

The fibrous web employed in the invention is composed predominately of absorbent fibers. (By "absorbent fibers" is meant those fibers that have an affinity for aqueous liquids.) The web can contain cellulosic fibers such as wood pulp, cotton, and rayon, or other hydrophilic fibers such as polyvinyl alcohol fibers or normally hydrophobic fibers such as polyester or polypropylene that have been treated by known methods to make them hydrophilic. It is generally preferred that the web be composed mostly of short or papermaking fibers, although textile length fibers can be employed. Minor amounts of non-absorbent fibers can be employed if desired. The web can be a loosely formed dry layed product, or it can be wet layed. If desired, the fibrous web can be lightly bonded.The binder can be viscose or other hydrophilic binder, it can be an acrylic binder, polyvinyl acetate, ethylene-vinyl acetate copolymer, SBR rubber, or the like. If desired, the binder can be crosslinkable. The binders that can be employed are well known in the art. The web can be overall saturated with binder, or it can be print or spot bonded. The web can contain a small proportion of thermoplastic fibers', which can be used as binding means by calendering, or the like.

While it is generally preferred to employ rather light weight webs (of the order of 1/2 to 2-1/2 ounces per square yard), the invention can be employed with heavier webs.

The temperature of the heated roll 18 is sufficient to increase the temperature of the film 10 to at least the forming temperature of the polymer in the film 10. The precise temperature employed in particular cases will depend upon factors such as the nature of the polymer in the film 10, the speed of the webs in passing through the nip, the thickness or weight of the fibrous web 14, the pattern of engraving on the resilient roll 20, and similar factors. As an illustration, when 1/2-mil low density polyethylene film is employed, the peripheral speed of the smooth roll 1 8 is about 6 feet per minute, and the peripheral speed of the resilient roll 20 is about 8 feet per minute, a temperature of from about 2600 to about 3900F.

in the smooth roll 18 has been found to be useful.

Preferably, the temperature in the smooth roll 18 is from about 2750 to about 3700F. in this case.

The resilient roll 20 is usually at a temperature below the forming temperature of the polymer in the film 10. Again, this will vary from one polymer to another, speed of the web, and the like, but for the conditions stated above using the 1/2mil polyethylene film and the speeds stated above, a temperature in the resilient roll 20 of from about 1 300 to about 2200 F. has been found useful.

Preferably, the temperature in the resilient roll 20 is from about 1700 to 21 50F. for these conditions.

As is seen from the breadth of the temperature ranges indicated above, the exact temperature employed has not been found to be narrowly critical. The important factors are to heat the film to its forming temperature, and to avoid sticking of the film to the resilient roll. It is well within the ordinary skill of the art to determine optimum temperatures in particular cases.

The resilient roll will ordinarily have a Durometer Shore A hardness of from about 45 to about 90. The surface of this roll can be of rubber; either hydro-carbon rubber or silicone rubber would be suitable. The surface of the resilient roll is engraved with a regular pattern of lines. As a general rule, the engraved pattern would be such as to provide from about 100 to about 10,000 openings (i.e., raised areas) per square inch of surface.

Pressure is maintained on the two rolls 1 8, 20 in order to provide a pressure at the nip of from about 5 to about 90 pounds per linear inch. The pressure can be provided by suitable hydraulic means such as those that are well known in the art.

After the coated web 26 passes through the nip of the rolls 1 8, 20, the polymer coating cools below the forming temperature of the polymer.

The coated web 26 is collected on a suitable wind-up 28, that is mounted for rotation on bearings 30 mounted on suitable framing F, and driven by a suitable drive mechanism 32.

In some cases, such as when operating at relatively high speeds, it may be desirable to preheat the fibrous web 14. This can be done by passing the web 14 around a preheating roll 22, which is mounted for rotation on bearings 27 mounted on suitable framing F. The web 14 passes around idler rolls 24a, 24b before and after the preheating roll 22.

The invention is further illustrated by the following examples: Example 1 Using an apparatus substantially as shown in Fig. 1 (without the preheating roll), an absorbent facing was made from 1/2-mii polyethylene film (density: 0.92 to 0.923, melt index: 5 to 7) and a fibrous web composed of 75 weight per cent wood pulp ("Alphanier F", from the Rayonier Corporation) and 25 weight per cent rayon (1 9/1 6 inch, 1.5 Denier), overall saturation bonded with Hycar 2600 x 120 (an acrylic latex containing a small amount of polymerized Nmethylolacrylamide cross-linker). The web weighed about 1-1/4 ounces per square yard, and was made in accordance with the procedure described in Example IV of Liloia et al., U.S. Patent No. 3,663,348.

The resilient roll had a silicone rubber surface with a Durometer Shore A hardness of about 60, and was engraved with a continuous pattern of recessed lines 0.020 inch wide and 0.018 inch deep, with 16 lines per inch running in the longitudinal direction (i.e., parallel to the longitudinal axis of the roll) and 20 lines per inch in the transverse direction. The smooth roll had a steel surface. The surface of the smooth roll was maintained at about 2850F., and the surface of the resilient roll reached an equilibrium temperature of about 1800 F., by appropriate heat exchange means. The pressure at the nip was about 40 pounds per linear inch. The periphery of the smooth roll was moving at a speed of 6 feet per minute, and the periphery of the resilient roll was moving at a speed of 8 feet per minute.

A A scanning electron micrograph (at about 75X) of the absorbent facing made in this Example 1 is shown in Fig. 2. The absorbent facing product 33 has a fine pattern oicontinuous areas 34 wherein the polyethylene is present as a continuous coating on the surface of the web. These continuous areas 34 correspond to the pattern of recessed lines engraved on the surface of the resilient roll. in between the continuous areas 34 are discontinuous areas 36 wherein most of the polyethylene is present as a coating on individual fibers.

Aqueous fluids readily pass through the coated surface of this absorbent facing product 33 to the absorbent fibers beneath the surface, but the fluids do not readily flow in the reverse direction.

Example 2 An absorbent facing was made using the same materials as those described in Example 1, and using substantially the same procedure except that the resilient roll had a pattern of 100 recessed lines per inch engraved in both the longitudinal and transverse directions. The lines were 0.00255 inch wide and 0.00118 inch deep. The surface temperature of the heated smooth roll was about 3600 F., and the resilient roll had a surface temperature of about 2000 F. A scanning electron micrograph (at about 140X) of the absorbent facing product 38 is shown in Fig. 3. The product 38 has a fine pattern of continuous areas 40 in which the polyethylene is present as a substantially continuous coating on the surface of the web. These continuous areas 40 correspond to the pattern of engraved recessed lines on the surface of the resilient roll.In between the continuous areas 40 are discontinuous areas 42 in which most of the polyethylene is coated on the surface of individual fibers.

Aqueous liquids readily flow through this absorbent facing from the polymer-coated side, but do not readily flow in the reverse direction.

Con trol Example 1 The process of Example 1 was repeated except that the resilient roll employed had a smooth surface. The resulting product was simply a web of fibers having a continuous film of polyethylene loosely adhered to the surface thereof. Thus, the surface could not be penetrated by aqueous liquids.

Control Example 2 When an open net of polyethylene is calendered to the surface of the fibrous web described in Example 1, no one-way valve characteristics are obtained. Aqueous fluid flows readily in both directions.

Control Example 3 Scanning electron micrographs of a product made in accordance with the teachings of Surowitz in U.S. Patent No. 3,307,545 are shown in Figs. 4 and 5. It is seen that the product has a substantially continuous coating 44 of plastic film, with a plurality of recesses 46. One of the recesses 46a is shown in greater magnification in Fig. 5. It is seen that in the recess, the plastic film is present as a substantially continuous coating 48 containing a pattern of holes or openings 50. The holes 50 are concentrated in the central (lowest) portion of the recesses 46.

In Fig. 6 there is shown a sanitary napkin 52 which utilizes the absorbent facing material of the invention. The napkin 52 contains an absorbent core 54, which may comprise absorbent fibrous material such as comminuted wood pulp fibers, cotton linters, rayon fibers, cotton staple, and the like. The core 54 of the napkin 52 is enveloped by a a layer 56 of the absorbent facing material of the invention. The napkin 52 will also normally contain a fluid impervious layer (not shown) on the side normally worn away from the body.

In Fig. 7, there is shown a disposable diaper 58 which employs the facing material of the invention. The diaper 58 comprises an absorbent core 60, a fluid impervious layer 62, and a layer 64 of the absorbent facing of the invention.

While a sanitary napkin and a disposable diaper have been shown, there are various other types of absorbent products in which the absorbent facing of the invention can be employed. These include tampons, underpads, surgical dressings or bandages, and the like. The absorbent facing of the invention is particularly useful as a surgical dressing or bandage because body fluids pass through it quite readily, but the facing has excellent non-sticking or wound-release properties.

Example 3 An absorbent facing was made using the same materials as those described in Example 2, and using the same equipment and substantially the same procedure except that the resilient roll was heated instead of the smooth roll and the pressure at the nip was about 60 pounds per linear inch.

The temperature of the resilient roll was about 2450F., and the smooth roll reached a temperature of about 2000 F. Excellent absorbent facings were made which had one-way valve characteristics with respect to aqueous liquids, using both 1/3-mil and 1/2-mil polyethylene film.

Example 4 Example 3 was repeated using a pressure at the nip of about 5 pounds per linear inch. A good absorbent facing was made.

Example 5 Example 4 was repeated except that the fibrous web was a polypropylene fiber web weighing about 4 ounces per square yard, which had been treated to make the fibers hydrophilic. A good absorbent facing was produced.

In Examples 3-5, wherein the resilient roll instead of the smooth roll is heated, lower temperatures than those set forth above in the specification can be used because the heat does not have to pass through the fibrous web.

Claims (25)

1. Process for producing an absorbent facing material, which process comprises: (a) superimposing a thin polymer film and a first web comprising absorbent fibers, to form a second web having said thin polymer film on one face and said first web on the other face; (b) heating said second web to a temperature such that said polymer film is formable; (c) while said second web is so heated, simultaneously applying shearing and compressive forces to said second web to form said polymer film into a coating on said first web, said coating comprising a fine pattern of continuous areas which lie between and interconnect discontinuous areas, wherein the polymer in the continuous areas comprises an at least substantially continuous coating on the surface of said first web, and wherein most of the polymer in the discontinuous areas is coated on individual fibers; and (d) cooling the coated web thus formed to cool said polymer below its forming temperature.

2. Process of claim 1 wherein step (b) includes contacting said other face with a heated, continuously moving, uniform surface.

3. Process of claims 1 or 2 wherein step (c) includes contacting said one face with a continuously moving resilient surface having a pattern of continuously arranged recessed areas and discontinuously arranged raised areas disposed uniformly over said resilient surface.

4. Process of claim 1 wherein said process includes passing said second web through the nip between a pair of counter-rotating rolls, the first roll of said pair being in contact with said one face and having a resilient surface that has a pattern of continuously arranged recessed areas and discontinuously arranged raised areas disposed uniformly over said resilient surface, and the second roll of said pair being in contact with said other face, wherein said second roll has a smooth, uniform surface, and wherein at least one of said rolls is heated.

5. The process of claim 4 wherein said first roll is moving at a slightly higher peripheral speed than said second roll.

6. The process of claims 4 or 5 wherein the pressure at said nip is within the range of from about 5 to about 90 pounds per linear inch.

7. The process of claim 4 wherein the polymer is an olefin polymer.

8. The process of claim 7 wherein the polymer film has a thickness of from about 1/4-mil to about 1-1/4 mils.

9. The process of claim 4 wherein the first web comprises absorbent papermaking fibers.

10. The process of claim 7 wherein the first web comprises absorbent papermaking fibers.

11. The absorbent facing material produced by the process of claims 1 or 4.

12. An absorbent facing material comprising a web of absorbent fibers having a polymer film coating on one surface thereof, wherein said coating comprises a fine pattern of continuous areas which lie between and interconnect discontinuous areas, wherein the polymer in said continuous areas comprises an at least substantially continuous coating on the surface of said web, and wherein most of the polymer in the discontinuous areas is coated on individual fibers of said web.

13. The absorbent facing material of claim 12 wherein the polymer is an olefin polymer.

14. The absorbent facing material of claim 13 wherein the olefin polymer is polyethylene.

1 5. The absorbent facing material of claim 12 wherein the absorbent fibers comprise absorbent papermaking fibers.

1 6. The absorbent facing material of claims 12 or 13 wherein the absorbent fibers comprise a mixture of wood pulp and rayon.

17. An absorbent product having an absorbent core and an absorbent facing material, wherein said absorbent facing material is the absorbent facing of claim 11.

18. An absorbent product having an absorbent core and an absorbent facing material, wherein said absorbent facing material is the absorbent facing of claim 12.

19. The absorbent product of claim 18 wherein said product is a surgical dressing.

20. The absorbent product of claim 17 wherein said product is a surgical dressing.

21. The absorbent product of claim 18 wherein said product is a sanitary napkin.

22. The absorbent product of claim 17 wherein said product is a sanitary napkin.

23. The absorbent product of claim 18 wherein said product is a disposable diaper.

24. The absorbent product of claim 17 wherein said product is a disposable diaper.

25. Process according to Claim 1 substantially as described with reference to the accompanying drawings.