GB2315221A - Absorbent Articles - Google Patents

Abstract

A core comprising water absorbent material and suitable for use in an absorbent article, said core having a hard upper surface formed by either spraying water or a binder e.g. latex onto one side of the core and thereafter treating the core e.g. by calendering and / or heating. The hard surface is believed to retard the speed at which fluid penetrates the core and thus allows it to spread more evenly over the surface thereby reducing the risk of localised pooling.

Description

Absorbent Articles The present invention relates to absorbent articles such as sanitary napkins and pads, incontinence garments and disposable diapers. In addition, the present invention relates to a water-absorbing layer for an absorbent article.

As used herein, the term "water" when used alone or in the phrases "waterabsorbing", "water-absorbent" and "water-swellable" is understood to mean not only water but also aqueous media such as, in particular, electrolyte solutions such as body fluids.

Sanitary napkins, pads, incontinence garments and disposable diapers have been known for many years and much effort has been made to improve the functional efficiency of such articles to make them more absorbent, more comfortable to wear and less obtrusive to the wearer.

In general, such products have a core which includes a water-absorbent layer. This water-absorbent layer may be formed from any suitable water-absorbent material including wood pulp, rayon, tissue or any of the water-absorbing polymer compositions known as superabsorbent polymers.

A number of absorbent compositions have been developed which exhibit the capacity to be water-absorbing. Known compositions may be in any suitable form including particles and fibers. U.S. Patent numbers 3,954,721 and 3,983,095, which are incorporated herein by reference, disclose preparations for derivatives of copolymers of maleic anhydride with at least one vinyl monomer in fibrous form. The fibrous copolymers are rendered hydrophillic and water-swellable by reaction with ammonia or an alkali metal hydroxide. U.S. Patent No. 3,810,468, which is incorporated herein by reference, discloses lightly cross-linked olefin-maleic anhydride copolymers prepared as substantially linear copolymers and then reacted with a diol or a diamine to introduce cross-linking. The resultant lightly cross-linked copolymers are treated with ammonia or an aqueous or alcohol solution of an alkali metal hydroxide. U.S.

Patent No. 3,980,663, which is incorporated herein by reference, describes water swellable absorbent articles made from carboxylic polyelectrolytes via cross-linking with glycerine diglycidyl ether.

European Published Application No. 0 268 498 (incorporated herein by reference) describes a water-absorbent composition formed by causing a substantially linear polymer of water-soluble ethylenically unsaturated monomer blends comprising carboxylic and hydroxylic monomers to cross-link internally.

Further examples of water-absorbent compositions are those produced from a copolymer of an QB unsaturated monomer having at least one pendant unit selected from a carboxylic acid group and derivatives thereof and a copolymerisable monomer.

A proportion of the pendant units are present in the final copolymer as the free acid and a proportion as the salt of the acid. These copolymers are capable of being cross linked, either internally or with a variety of cross-linking agents, to form the water swellable composition. Examples of water-swellable compositions of this type can be found in U.S. Patent Nos 4,616,063, 4,705,773, 4,731,067, 4,743,244, 4,788,237, 4,813,945, 4,880,868 and 4,892,533 and European Patent Nos 0 272 074 and 0 264 208 and European Published Application No. 0 436 514 which are incorporated herein by reference.

Derivatives of carboxylic acid groups include carboxylic acid salt groups, carboxylic acid amide groups, carboxylic acid imide groups, carboxylic acid anhydride groups and carboxylic acid ester groups.

Other examples of water-absorbent compositions can be found in US 4,798,861, WO 93/17066, WO 93/255735, WO 93/24684, WO 93/12275, European Published Application Nos 0 401 044, 0 269 393, 0 326 382, 0 227 305, 0 101 253, 0 213 799, 0 232 121, 0 342 919, 0 233 014, 0 268 498 and 0 397 410, British Patent Application Nos 2 082 614, 2 022 505, 2 270 030, 2 269 602 and 2 126 591, U.S.

Patent Nos 4,418,163, 4,418,163, 3,989,586, 4,332,917, 4,338,417, 4,420,588 and 4,155,957 and French Patent Application No. 2 525 121 which are all incorporated herein by reference.

Water-absorbent material of the kinds referred to in the above-mentioned patents and applications may be in any suitable form including powder, granular and fibers; the fibers may be straight or may be curled and/or crimped. Details of such curly/crimped fibers may be found in US 4,822,453, 4,888,453 5,462,793 and 4,898,462 which are incorporated herein by reference. In one alternative material, the water-absorbent polymer may be coated onto the whole or a part of the surface of other materials such as non-water-absorbent fibers. Details of one type of fibers of this type may be found in WO 96/15307 which is incorporated herein by reference.

Other kinds of water-absorbent materials may be used including naturally occurring water-absorbent material. One such water-absorbent material is the as starchy material such as that proposed by the US Department of Agriculture in 1969-1970.

Peat moss may also be used a water-absorbent material. In this connection, reference may be made to US 5,477,627 5,429,242 5,374,260 4,992,324 4,676,871 4,573,988 4,560,372 4,540,454 4,537,590 and 4,226,237 which are incorporated herein by reference. Alginates have also been proposed as suitable water-absorbent material.

An example of the use of such alginates are those suggested by Beghin/Kayserberg.

Whatever material is used for the absorbent layer, the core is generally backed by a fluid-impervious backing sheet to protect clothing and the surrounding area from soiling and to prevent leakage of the body fluid which would cause embarrassment to the user. Any suitable backing material may be used.

The article generally has a water-permeable non-woven type cover-sheet which defines the surface of the article which will, in use, be in contact with the user. The cover sheet is intended to insulate the wearer from contact with water that has been absorbed into the core, thus the cover sheet should allow water to pass through it into the core but remain dry and soft to the touch. Any suitable material may be used as thee cover-sheet. One example of a suitable cover-sheet is described in US 5257982 which is incorporated herein by reference.

As there is often a discharge of a substantial volume of water in a short time, the core may additionally include a distribution layer which is generally located above the water-absorbent layer. This distribution layer serves to wick the water away from the point of initial contact with the article and transport it to other parts of the waterabsorbent layer. The use of a distribution layer of this type is advantageous in addressing the problem of pooling if a substantial volume of water is discharged in a short time and thereby gives the user a feeling of dryness. Examples of distribution layers of this type include those described in EP 0 565 606, GB 2 266 465 and GB 2 278 371 which are incorporated herein by reference.

As the distribution layer serves to wick the water away from the point of initial contact, it is accepted that the water should be transported in the plane of the layer as quickly as possible and thus, distribution layers are generally made of hydrophillic material. The concept of speeding up the rate at which water is transported in the plane of the distribution layer is discussed in detail in EP 0 565 606 assigned to The Procter & Gamble Company in which the distribution layer forms part of the multiple layer absorbent core.

Whilst the use of distribution layers of this type go some way to reducing the effects of pooling, they do not satisfactorily overcome the problems of rewet once the water has been absorbed into the water-absorbent layer. Rewet is a measure of how dry the articles feel to the touch after water-absorption. This is generally measured under load of approximately 3-5kPa. Rewet is of particular importance in the applications to which the absorbent articles of the present invention are directed as if the article feels damp the user will feel damp and uncomfortable.

The problem of rewet is particularly acute where the water-absorbent layer is formed from or includes the water-absorbent polymers described above, in particular from fast absorbing water-absorbent polymers. Although the water-absorbent polymers described above can absorb a large volume of water and absorption can take place in a short time period, in some circumstances, the water-absorbent may become locally saturated because of the fast absorbency of the water-absorbent and may thereby feel damp to the touch.

We have now discovered that some of the benefits previously obtained by the use of a distribution layer may be obtained by providing the water-absorbent core with an upper surface that is harder than has been utilised heretofore. Without wishing to be bound by any theory it is believed that the hard surface serves to reduce the rate at which the water penetrates the core and thus allows for it to spread over the surface.

It is believed that the hard surface retards the speed at which water enters the core.

The hard surface may be provided by increasing the density of the core at its surface.

In one alternative arrangement, the hard surface is obtained by the provision of a smooth surface.

Thus in accordance with the present invention there is provided a core suitable for use in an absorbent article having a hard upper surface.

The core may be formed from any suitable material. Suitable materials from which the core may be formed from any suitable water-absorbent material including wood pulp, rayon and tissue. Additionally, or alternatively the layer may comprise the water-absorbing polymer compositions commonly known as superabsorbent polymers.

The polymers may be in any configuration. In particular, the polymers may be in the form of powders, particles, granules and fibers.

The core may formed by any suitable method including air laying and wet laying.

The core is preferably in the form of a non-woven fibrous bat.

The hard surface may be formed after the core has itself been formed. Any suitable means of forming the surface on the core may be utilised.

In one arrangement, water may be sprayed onto one side of the core which is then compressed, preferably by calendering and allowed to dry. When the compressive force is removed from the core, the surface of the core to which water was applied will remain compressed thereby forming the "hard surface". Without wishing to be bound by any theory, it is believed that the material from which the core is made, for example wood fluff becomes limp when it is sprayed with water becomes limp and when it dries it does not spring back.

Where the core includes water-absorbent material such as superabsorbent polymeric material, the water may activate the water-absorbent material causing it to swell. On The activated water-absorbent polymeric material may then act to bind the fibers.

Without wishing to be bound by any theory it is believed that as the water-absorbent material becomes swollen, it softens, and the other fibers of the core may be driven into the water-absorbent material. As the water evaporates, the water-absorbent material dries and the fibers are retained in the water-absorbent material.

In one arrangement, one surface of the core may be sprayed with a binder, such as latex, and then compressed, preferably by calendering. The core is then heated whilst under compression to allow the binder to cure thereby forming the hard surface.

In one arrangement, the binder, such as latex, is sprayed onto the surface of the core.

The core is then heated to cure the binder. The core is then compressed such as by calendering. After compression, the hard surface is formed.

In one arrangement, the core is compressed and, whilst in the state of compression, one side is sprayed with a binder, such as latex, or water. Where a binder is used, it may be allowed to cure before the compressive force is removed. When the compressive force is removed from the core, the surface of the core to which binder was applied will remain compressed thereby forming the "hard surface".

The hard surface may be formed as the core is produced. For example, where the core is formed using air laying techniques, as the fibers are laid to form the core, the apparatus can be arranged such that one surface of the core has increased density over the remainder of the core. This may be achieved by the use of a binder and compressive forces or by any other suitable means.

As described above, the core will commonly be used in conjunction with a waterpermeable non-woven type cover-sheet which defines the surface of the article which will, in use, be in contact with the user. In order to reduce manufacturing costs, the cover sheet may be applied to the core at the same time as the hard surface is formed.

For example, where the hard surface is formed after the core is formed, the cover sheet may be laid onto the upper surface of the core before or after it is sprayed with the binder and the whole is then compressed. The binder will then serve not only to form the hard surface but also to bind the cover-sheet to the core. Similarly, where the hard surface is formed simultaneously with the production of the core, the coversheet may be applied to the core and bound thereto simultaneously.

The core of the first aspect of the present invention may be used in an absorbent article. Thus, according to a further aspect of the present invention, there is provided an absorbent article comprising a liquid pervious cover sheet, a liquid impervious backsheet and a multi-layered water-absorbent core described in the above second aspect wherein the cover sheet is joined to the backsheet to enclose the waterabsorbent core.

Whilst the present invention has been described with reference to sanitary napkins and pads, incontinence garments and disposable diapers it will be understood that the invention is equally applicable to other products which require high water-absorption capability such as pant liners, training pads, tampons, adult incontinence pads, bandages, patient underpads (for example pads of the type described in US 3,814,101 US 4,342,314 and EP 0 052 403 which are incorporated herein by reference), mortuary pads, casket liners, forensic examination pads, meat trays, soaker pads for food use, medical tray pads, fenestration drapes, other medical related articles, seed germination pads, capillary mats, baby bibs, desiccant strips for anti-rust use, bath mats, packaging, sorbents, clothing, breast pads, underarm pads, surgical and dental sponges, bandages, industrial wipes, domestic wipes, wipes, filters, cable wrap, food preservation articles, roofing materials, automotive trim, furniture, gasket, sealants, pond liners, bedding, clothing, cement, household pet litter, soil modifiers, wound covers and the like.

Claims (1)

1. CLAIM:

   1. A core comprising water-absorbent material and suitable for use in an absorbent article, said core having a hard upper surface.