WO2006004543A1

WO2006004543A1 - Absorbent layer structure

Info

Publication number: WO2006004543A1
Application number: PCT/SE2005/001112
Authority: WO
Inventors: Ted Guidotti
Original assignee: Sca Hygiene Products Ab
Priority date: 2004-07-02
Filing date: 2005-07-04
Publication date: 2006-01-12
Also published as: US7888548B2; PL1765239T3; JP2008504866A; AU2005260153B2; CA2569929A1; MXPA06014759A; CN1976658B; CN1976658A; US20070112319A1; RU2361557C2; EP1765239A1; EP1765239B1; EP1765239A4; WO2006004464A1; RU2006143447A; JP4903137B2; AU2005260153A1

Abstract

An absorbent layer structure for use as an absorbent body in an absorbent article. The absorbent structure comprises a first surface layer consisting mainly of cellulose fluff pulp, a second surface layer consisting mainly of cellulose fluff pulp, and an inner layer arranged between the surface layers consisting of a mixture of cellulose fluff pulp and 5-90 % by weight superabsorbent material, the cellulose fluff pulp in the surface layers having a mat strength which is lower than the mat strength in the inner layer by at least 1 N measured at a weight per unit area of 300 g/m2 and a bulk of 4.5 cm3/g or less and preferably a mat strength which is lower than the mat strength in the inner layer by at least 2 N measured at a weight per unit area of 300 g/m2 and a bulk of 4.5 cm3/g or less.

Description

ABSORBENT LAYER STRUCTURE

TECHNICAL FIELD

The invention relates to an absorbent layer structure for use as an absorbent body in an absorbent article. The invention also relates to an absorbent hygiene article, such as a diaper, an incontinence pad or a sanitary towel.. The invention can also be applied to absorbent articles such as meat tray liners, bed protectors, chair protectors or the like.

BACKGROUND ART

Absorbent articles such as diapers, incontinence pads, sanitary towels or the like are gradually becoming thinner and thinner. Thin articles are in most cases more flexible and more discreet to wear and are therefore seen as something positive by users. Moreover, they are more compact, which is of course an advantage for transport and storage.

In order for it to be possible to offer thin absorbent articles with retained functioning as far as absorption capacity and leakage security are concerned, the use of different types of highly absorbent materials, what are known as superabsorbents, has become common. Such materials are polymers which are available in the form of particles, fibres or granules and are advantageously incorporated into a fibrous structure, in most cases comprising cellulose fluff pulp.

When superabsorbents are incorporated into a cellulose fibrous structure, however, a number of problems arise.

In order to retain the superabsorbent in the cellulose fluff structure, it is necessary for this to be compressed to a high density of the order of 0.1- 0.5 g/cm³. Such highly compressed structures feel hard and uncomfortable when they are used in an absorbent article.

Furthermore, fibres attach themselves to rollers and other machine parts during manufacture of the fibrous structures, which results in operational problems.

Moreover, liquid reception and liquid-spreading in a highly compressed material are very slow, which is a particular problem in absorbent articles intended to receive and absorb large quantities of liquid in a short period of time. For example, articles intended for incontinent adults must be capable of taking up several hundred ml of liquid which is discharged at great pressure in the course of ten seconds or so. Instead of being absorbed by the absorbent article, it therefore sometimes happens that the liquid instead flows out over the surface and runs out of the article along the edges and causes leakage. In practice, such an absorbent article may therefore have an actual absorption capacity which is considerably lower than might have been expected from theoretical calculations based on the absorption capacity of the component materials. In order to remedy this problem, use is often made of special liquid-receiving and/or spreading layers. However, such layers increase the thickness of the articles and contribute to a higher production cost owing to greater material consumption and a more complicated manufacturing process.

A modified cellulose fluff pulp produced by means of an oxidation process using nitroxide is previously known from EP 1 245 722. The process increases the degree of "self-cross-linking" between adjacent cellulose fibres and within one and the same cellulose fibre. In this way, an improved network for superabsorbents which are mixed with the modified cellulose fluff pulp is obtained in relation to conventionally cross-linked cellulose fluff pulps. WO 00/66833 describes another type of modified cellulose fluff pulp where the fibres are provided with a coating of bentonite which prevents bonds between the fibres and reduces the number of fibre knots in the material.

However, a major problem with the treated cellulose fluff pulps is that fibre webs produced from such cellulose fluff pulps have much too low a mat strength to be capable of being handled in continuous manufacturing processes. Moreover, their capacity for retaining superabsorbent particles is still inadequate.

There is therefore a need to produce an absorbent structure with good processability, a high absorption capacity, a good liquid-receiving capacity and great softness and flexibility. Another object of the invention is to offer an absorbent structure with a fibre network of cellulose fibres, which absorbent structure has a good capacity for retaining superabsorbents and for spreading liquid in the absorbent structure.

DISCLOSURE OF INVENTION

In accordance with the invention, an absorbent structure of the kind referred to in the introduction has now been produced. An absorbent structure according to the invention is characterized primarily in that it comprises a first surface layer consisting mainly of cellulose fluff pulp, a second surface layer consisting mainly of cellulose fluff pulp, and an inner layer arranged between the surface layers consisting of a mixture of cellulose fluff pulp and 5-90% by weight superabsorbent material, the cellulose fluff pulp in the surface layers having a mat strength which is lower than the mat strength in the inner layer by at least 1 N measured at a weight per unit area of 300 g/m² and a bulk of 4.5 cm³/g or less and preferably a mat strength which is lower than the mat strength in the inner layer by at least 2 N measured at a weight per unit area of 300 g/m² and a bulk of 4.5 cm³/g or less. By combining two layers with different types of cellulose fluff pulp, it is possible according to the invention to produce surprisingly improved experienced softness of the absorbent structure. An absorbent structure in accordance with the invention moreover has extremely good processability with regard to both mat strength and reduced fibre adhesion to rollers and other machine parts during manufacture of the absorbent structure.

Moreover, the absorbent structure offers a fibre network for a superabsorbent material which functions extremely well. The fibrous structure according to the invention provides a compact inner fibre network with a good retaining capacity for a mixed-in superabsorbent even at high superabsorbent contents, up to 90% by weight of the inner layer, and a good liquid-spreading capacity, and also soft outer surfaces with only a slight tendency to adhere to machine parts when the structure is handled in a manufacturing process.

In order to achieve these advantages, only very thin layers, of the order of 0.1-2 mm, of the treated cellulose fluff pulp are required.

DESCRIPTION OF FIGURES

The invention will be described in greater detail below with reference to the figures shown in accompanying drawings, in which:

Figure 1 shows an absorbent layer structure according to the invention;

Figure 2 shows a diaper comprising a layer structure according to the invention;

Figure 3 shows a sanitary towel comprising a layer structure according to the invention;

Figure 4 shows measuring equipment for determining mat strength, and Figure 5 shows a section through a part of the measuring equipment in Figure 4.

DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The absorbent layer structure 1 shown in Figure 1 comprises a first surface layer 2 consisting of cellulose fluff pulp, a second surface layer 3 consisting of cellulose fluff pulp, and an inner layer 4 arranged between the surface layers 2, 3 and consisting of a mixture of cellulose fluff pulp and 5-80% by weight superabsorbent material. The mixture is preferably an essentially homogeneous mixture, so that the superabsorbent material is uniformly distributed in the inner layer 4.

The superabsorbent material is preferably present in particle form, but granules, flakes or fibres can also be used within the scope of the invention. Superabsorbent materials are polymers with a capacity for absorbing several times their own weight of water or body fluid while forming an aqueous gel. The superabsorbent material can be of one single type or consist of a mixture of two or more superabsorbents which differ as far as absorption rate, particle size, gel strength, chemical composition or other properties are concerned. For example, there are superabsorbents with different absorption capacity at different temperatures or at different pH values.

The cellulose fluff pulp in the inner layer 4 is suitably untreated chemical cellulose fluff pulp (CP) with a bulk (excluding the superabsorbent material) of at most 4.5 cm³/g. The inner layer 4 suitably has a thickness of 0.3-5 mm, preferably 0.5-2 mm and most preferably roughly 1.2-1.6 mm.

The two surface layers 2, 3 can consist of the same or different cellulose fluff pulps. The cellulose fluff pulp in the surface layers 2, 3 is suitably a chemical cellulose fluff pulp which has been treated in order to reduce fibre-fibre bonds in the material. Such treatment can be brought about by coating the fibres with a debonding substance, such as various types of inorganic salts, for example aluminium salt, or mineral fillers such as clay, lime, carbonate, talc or microparticles of bentonite in accordance with WO 00/66833. Fibres treated in the way described in EP 1 245 722, that is to say by means of an oxidation process using nitroxide, can also be used for the surface layers. 6. Further exaples of useful debonders are found in US 3 844 880, US 4 432 833 and WO 98/19012. The debonders mentioned in these documents include quartemary ammonium compounds, bis-imidazolinium compounds, di-quartemary ammonium compounds, polyammonium compounds, phospholipids, silicone quarternaries, organoreactive polysiloxanes and silicone glycols.

The surface layers 2, 3 suitably have a bulk of 3 cm³/g or more and a thickness of 0.05-1.0 mm, preferably 0.1-0.5 mm and most preferably 0.2- 0.3 mm.

The entire absorbent structure suitably has a thickness of at most 8 mm, preferably at most 5 mm and most preferably at most 2 mm. The weight per unit area of the absorbent structure is 300-2000 g/m², preferably 500- 1500 g/m² and most preferably 800-1200 g/m².

Figure 2 shows a diaper 200 of fairly simple construction. It is of course possible to use additional components, such as raised leakage barriers, shape-stabilizing elements, liquid-receiving layers or the like. The diaper 200 shown in Figure 2 comprises a first, liquid-permeable surface layer 205, a second, liquid-impermeable surface layer 206, and an absorbent body 207 arranged between the surface layers 205, 206. The two surface layers 205, 206 extend beyond the absorbent body 207 around its entire periphery. The surface layers 205, 206 are interconnected within the extending portions 208 by gluing, or welding using heat or ultrasound. The liquid-permeable surface layer 205 can consist of any material known for the purpose such as a layer of non-woven material, perforated plastic film, net material or the like. The surface layer 205 can of course also consist of a laminate of two or more layers of the same material or different materials.

The liquid-impermeable surface layer 206 can consist of a liquidtight plastic film, a non-woven layer which has been coated with a liquid-blocking material, a laminate of non-woven and plastic film or another flexible material capable of resisting liquid penetration. It may be an advantage, however, if the liquid-impermeable surface layer 206 has a certain breathability, that is to say allows water vapour to pass through the layer 206.

The diaper 200 has an elongate shape, with wider front and rear portions 209, 210 and a narrower, intermediate crotch portion 211. The front portion

209 is that part of the diaper 200 which is intended to face forwards on the wearer when the diaper is being used, and the rear portion 210 is that part of the diaper 200 which faces backwards on the wearer. The diaper 200 also has two longitudinal, inwardly curved side edges 212, 213, a front edge 214 and a rear edge 215.

The diaper 200 is of the kind which is fastened together when it is used, so that it surrounds the lower part of the abdomen of the wearer in a pant-like manner. For this purpose, a fastening tab 217, 218 is arranged projecting from each side edge 212, 213, close to the rear edge 215 of the diaper. The fastening tabs 217, 218 are intended to interact with a receiving area 219 arranged on the liquid-impermeable surface layer 206 on the front portion 209 of the diaper 200. Such a receiving area 219 is arranged so as to interact with fastening elements on the fastening tabs 217, 218. Commonly used fastening elements are hook and loop surfaces or self-adhesive glue. In the first case, hook elements are in most cases arranged on the fastening tabs 217, 218, while the receiving area 219 comprises some form of loop element, for example non-woven. In the second case, the adhesive on the fastening tabs 217, 218 is arranged so as to adhere to a usually reinforced plastic surface on the outside of the diaper 200. It is of course possible to use alternative fastening elements, such as buttons and buttonholes, hooks and eyes, press studs or the like.

The diaper 200 is also provided with longitudinal elastic elements 220, 221 , applied in a pretensioned state, along the side edges 212, 213 of the diaper. The elastic elements 220, 221 are arranged so as to curve the diaper 200 according to the body of the wearer during use and at the same time constitute the leg elastic of the diaper. In this way, the elastic elements 220, 221 serve to hold the side edges 212, 213 of the diaper in sealing contact with the legs of the wearer so as to counteract gaps appearing between the diaper and the body of the wearer during use, through which body fluid can leak out of the diaper.

The absorbent body 207 consists of an hourglass-shaped layer of the absorbent structure according to the invention. The absorbent body 207 therefore consists of a laminate consisting of two thinner layers of treated cellulose fluff pulp which are arranged on each side of an inner layer of untreated, greatly compressed cellulose fluff pulp with 5-80% superabsorbent and preferably 15-35% superabsorbent mixed in.

The construction shown provides an absorbent article which functions well for many applications, with a good absorption capacity, great flexibility and a high degree of experienced softness. As the absorbent structure according to the invention can be made very thin, with a suitable thickness around roughly

2 mm, this means that a diaper according to the invention, with the simple construction shown in Figure 2, can have a total thickness which is less than 2.5 mm. If further absorption capacity is required, the absorbent structure can be made thicker, or alternatively a number of absorbent structures according to the invention can be placed one on another. The absorbent structure according to the invention can also be combined with other absorbent layers. For example, it may be desirable to place a layer with a very great absorption capacity and liquid-retaining capacity below the absorbent structure according to the invention, that is to say on that side of the absorbent structure which faces the liquid-impermeable surface layer 206. It may also be desirable to arrange a liquid-receiving layer immediately inside the liquid- permeable surface layer 205, between it and the absorbent body 207. Such a liquid-receiving layer is usually a layer of bonded or unbonded fibre wadding, a latex-bonded cellulose material or the like.

The invention can of course be applied to other variants of diapers, such as pant diapers, belted diapers or the like, and also to all kinds of incontinence pad. A pant diaper means a diaper which is supplied to the user in the form of assembled absorbent pants. A belted diaper is a diaper which is supported by a separate or integrated waist belt. Here, incontinence pads mean absorbent articles intended to be supported in the crotch portion of a pair of briefs.

The sanitary towel 300 shown in Figure 3 is shown from the side which is intended to face the underwear of the wearer when the towel is being worn. The sanitary towel 300 comprises a liquid-permeable surface layer 305, arranged on that side of the sanitary towel 300 which is intended to face the wearer during use, a liquid-impermeable surface layer 306, arranged on that side of the sanitary towel 300 which is intended to face away from the wearer during use, and an absorbent body 307 enclosed between the two surface layers 305, 306.

The material of the liquid-permeable surface layer 305 can be, for example, a perforated plastic film, a net made of plastic or textile material, a non-woven material or a laminate consisting of, for example, a perforated plastic layer and a non-woven layer. The plastic is usually a thermoplastic, such as polyethylene or polypropylene. Suitable non-woven materials can be made of natural fibres, such as cellulose or cotton, or of synthetic fibres, such as polyethylene, polypropylene, polyester, polyurethane, nylon or regenerated cellulose. It is of course also possible to use non-woven materials made from fibre mixtures.

It is not necessary for the liquid-permeable surface layer 305 actually to consist of a separate material layer. For example, the liquid-permeable covering layer can constitute an integrated part of the absorbent body 307.

Use can therefore be made of an absorbent non-woven material, which can be included as a component in the absorbent body 307 and at the same time constitute a liquid-permeable surface layer. Such constructions are not uncommon in very thin towels and panty liners.

The liquid-impermeable surface layer 306 consists of a liquid-impermeable material. Thin, liquidtight plastic films are suitable for the purpose. However, it is also possible to use materials which are originally liquid-permeable but have been provided with a coating of plastic, resin or other sealing material. In this way, leakage of liquid from the underside of the absorbent article is prevented. The liquid-impermeable surface layer 306 can therefore consist of any material which is skin-friendly and meets the liquid-impermeability criterion. Examples of materials suitable as a barrier layer are plastic films, non-woven materials and various types of laminate. Plastic films which can be used are, for example, those made of polyethylene, polypropylene or polyester. Alternatively, the liquid-impermeable surface layer 306 can consist of a laminate made of a liquid-impermeable plastic layer facing the absorbent body and a non-woven layer facing the underwear of the wearer. Such a construction provides a leakproof barrier layer with a textile feel. The two surface layers 305, 306 are interconnected outside the absorbent body 307 and form an extending edge 308 around the entire periphery of the sanitary towel 300. The surface layers can be joined together in any suitable way, such as by adhesive, sewing or welding using heat or ultrasound.

The sanitary towel 300 is essentially hourglass-shaped and has two end portions 309, 310 and an intermediate narrower crotch portion 311 intended to be arranged between the legs of the wearer. The sanitary towel 300 also has two inwardly curved side edges 312, 313 and two outwardly curved end edges 314, 315.

The sanitary towel 300 is provided with an adhesive fastening element 317 in the form of a strand of adhesive which is attached in the crotch portion of the briefs of the wearer when the towel 300 is worn. Before use, the fastening element 317 is protected in a conventional way by a detachable protective strip which is removed when the adhesive is to be exposed for fastening. The fastening element 317 shown is only an example of the design of an adhesive fastening element. Other patterns and positionings of fastening element are of course possible.

As in the case of the diaper 200 shown in Figure 2, the absorbent body 307 consists of an hourglass-shaped layer of an absorbent structure according to the invention. The absorbent body 307 therefore consists of a laminate consisting of two thinner layers of treated cellulose fluff pulp arranged one on each side of an inner layer of untreated, greatly compressed cellulose fluff pulp with 5-80% superabsorbent and preferably 15-35% superabsorbent mixed in.

In most cases, sufficient absorption capacity is provided with a single layer of the absorbent structure according to the invention. The resultant sanitary towel 300 has great flexibility and a high degree of experienced softness.

Sanitary towel development has moved towards thinner and thinner products which can be attached inside the briefs of the wearer in a conformable way and provide great discreetness and comfort when worn. As the absorbent structure according to the invention can be made very thin, with a suitable thickness around roughly 2 mm, this means that a sanitary towel according to the invention, with the simple construction shown in Figure 3, can have a total thickness which is less than 2.5 mm.

If further absorption capacity is required, the absorbent structure can be made thicker, or alternatively a number of absorbent structures according to the invention can be placed one on another. The absorbent structure according to the invention can also be combined with further absorbent layers. It may also be desirable to arrange a liquid-receiving layer immediately inside the liquid-permeable surface layer 305, between it and the absorbent body 307.

The invention can of course be applied to other absorbent articles intended to be attached inside the briefs of a wearer, such as incontinence pads and panty liners. Such sanitary towels, incontinence pads and panty liners can of course comprise other components apart from those described above, such as fastening wings, raised portions, textile edges, side edge barriers or the like.

TEST METHOD

Determining mat strength

Mat strength means the strength of an absorbent body made of defibred pulp. The idea behind the measurement is to determine the force required for a bursting body to pass through the pulp specimen at a constant speed. The apparatus is as shown in Figures 4 and 5 and comprises:

a bursting body 230

a specimen holder 231

a balance 232 with measuring accuracy of 0.01 g

a thickness gauge with a measuring foot of 50 cm² and a force of 2.5 N (0.5 kPa)

a punch with an 80 x 80 mm punching tool

a ruler with 1 mm measuring accuracy

Specimen preparation:

Number of specimens measured for each determination was five (5).

A specimen of a size of 80 x 80 mm was punched out of the pulp mat tested.

The thickness (t) of the specimen was determined with an accuracy of 0.01 cm.

The weight (m) of the specimen was determined with an accuracy of 0.1 g.

The specimen was handled carefully with the aid of a thin plate.

Determination of weight, thickness and bursting strength of the specimen is to be carried out directly after taking the specimen. From the values obtained, the values for bulk, weight per unit area and density can then be calculated. The measurements were performed on specimens conditioned at 23⁰C and maximum air humidity of 50%.

Procedure:

The specimen was fastened in the specimen holder 231. The specimen holder 231 and the bursting body 230 were mounted in the apparatus (see Figure 1). The test was started. The maximum force (F) on bursting was recorded.

Calculation and presentation of results:

Specimen thickness t (cm)

Specimen weight m (g)

Specimen area A (dm²)

Specimen length I (cm)

Specimen width w (cm)

Mat strength F (N)

Mat strength bulk B (cm³/g)

Bursting factor BF (N dm²/g)

B = A x 100 x t = I x w x t (cm³/g) m m BF = F x A = F x l x t (N dm²/g) m m x 100

The report indicates: mean value maximum value minimum value Accuracy: Mat strength 0.1 N

Bursting strength 0.01 N dm²/g

Mat strength bulk 0.5 cm³/g

Example 1

Cellulose fluff pulp from Weyerhaeuser. American Southern Pine, untreated pulp with designation NB416.

Example 2

American Southern Pine cellulose fluff pulp treated as indicated in EP 1 245 722.

Example 3

Cellulose fluff pulp from Weyerhaeuser. American Southern Pine, pulp with designation TR934A, treated in accordance with the invention.

The results of the measurements conducted on specimens according to Examples 1-3 at four different bulk values (3 crrrVg, 4.5 cm³/g, 6 cm³/g, and 10 cm³/g) are presented in Tables 1-3. Table 1 (Example 1 )

Table 2 (Example 2)

Table 3 (Example 3)

As emerges from the measurement results in the tables, there is a great difference in the mat strength of cellulose fluff pulp layers according to example 1 in comparison with examples 2 and 3 at low bulk/high density. This means that cellulose fluff pulp according to examples 2 and 3 has a poor cohesive capacity even after great compression and is thus difficult to process and has a poor capacity for retaining superabsorbents in the fibrous structure.

Claims

1. An absorbent layer structure for use as an absorbent body in an absorbent article, characterized in that the absorbent structure comprises a first surface layer consisting mainly of cellulose fluff pulp, a second surface layer consisting mainly of cellulose fluff pulp, and an inner layer arranged between the surface layers consisting of a mixture of cellulose fluff pulp and 5-90% by weight superabsorbent material, the cellulose fluff pulp in the surface layers having a mat strength which is lower than the mat strength in the inner layer by at least 1 N measured at a weight per unit area of 300 g/m² and a bulk of 4.5 cm³/g or less and preferably a mat strength which is lower than the mat strength in the inner layer by at least 2 N measured at a weight per unit area of 300 g/m² and a bulk of 4.5 cm³/g or less.

2. An absorbent layer structure according to Claim 1 , the cellulose fluff pulp in the surface layers having a mat strength which is lower than the mat strength in the inner layer by at least 1 N measured at a weight per unit area of 300 g/m² and a bulk of 3 cm³/g or less and preferably a mat strength which is lower than the mat strength in the inner layer by at least 2 N measured at a weight per unit area of 300 g/m² and a bulk of 3 cm³/g or less.

3. An absorbent layer structure according to Claim 1 or 2, the cellulose fibres in at least one of the surface layers having a coating of a substance which reduces the number of fibre-fibre bonds in the cellulose fluff pulp.

4. An absorbent layer structure according to Claim 3, the substance being an inorganic salt, preferably aluminium salt.

5. An absorbent layer structure according to Claim 3, the substance being a mineral filler such as clay, lime, carbonate, talc or microparticles of bentonite.

6. An absorbent layer structure according to Claim 3, the substance being a debonder chosen from the group including quarternary ammonium compounds, bis-imidazolinium compounds, di-quarternary ammonium compounds, polyammonium compounds, phospholipids, silicone quartemaries, organoreactive polysiloxanes and silicone glycols.

7. An absorbent layer structure according to Claim 1 or 2, the cellulose fibres in at least one of the surface layers having undergone oxidation, preferably by means of an oxidation process using nitroxide.

8. An absorbent layer structure according to any one of the preceding claims, the cellulose fluff pulp in the inner layer being a chemically produced cellulose fluff pulp (CP).

9. An absorbent layer structure according to any one of the preceding claims, the absorbent structure having a thickness of at most 8 mm, preferably at most 5 mm and most preferably at most 2 mm.

10. An absorbent layer structure according to any one of the preceding claims, the absorbent structure having a weight per unit area of 300-2000 g/m², preferably 500-1500 g/m² and most preferably 800-1200 g/m².

11. An absorbent layer structure according to any one of the preceding claims, the inner layer consisting of a mixture of cellulose fluff pulp and 30-90% by weight superabsorbent material, preferably 50-90% superabsorbent material.

12. An absorbent layer structure according to any one of the preceding claims, the structure having a compression pattern.

13. An absorbent article, characterized in that it comprises the absorbent structure according to any one of Claims 1-12.

14. An absorbent article according to Claim 13, the absorbent article being a diaper.

15. An absorbent article according to Claim 13, the absorbent article being a sanitary towel.