WO2006071159A1

WO2006071159A1 - Absorbent article comprising a uv-curing adhesive and method for its production

Info

Publication number: WO2006071159A1
Application number: PCT/SE2004/002054
Authority: WO
Inventors: Annika Dahl; Jonas ÖBORN
Original assignee: Sca Hygiene Products Ab
Priority date: 2004-12-30
Filing date: 2004-12-30
Publication date: 2006-07-06

Abstract

The present invention concerns an absorbent article (1), such as sanitary napkin, a panty liner or an incotinence guard, which absorbent article (1) comprises a liguid-permeable topsheet (2), a liquid-impermeable backsheet (3) and an absorbent structure (4) arranged between the topsheet (2) and the backsheet (3). The absorbent article (1) has an essentially elongated shape, a longitudinal direction (x), a transverse direction (y), two essentially transverse end edges (6, 7) and two essentially longitudinal side edges (8, 9). The backsheet (3) comprises an outer fibrous material layer (3a) having an outer surface (13) intended to lie againts a user’s undergarment. An adhesive (14) is applied at least partly to the outer surface (13) and at least partly in the outer fibrous material layer (3a). The adhesive (14) is a UV-curable adhesive, which has been exposed to UV-radiation. The present invention also concerns a method for production of such an absorbent article.

Description

Absorbent article comprising a UV-curing adhesive and method for producing the same

Field of the invention The present invention concerns an absorbent article, such as a sanitary napkin, a panty liner or an incontinence protector, which absorbent article comprises a liquid-permeable topsheet, a liquid-impermeable backsheet and an absorbent structure arranged between the topsheet and the backsheet, and which absorbent article has an essentially elongated shape, a longitudinal direction, a transverse direction, two essentially transverse end edges and two essentially longitudinal side edges, wherein the backsheet comprises an outer fibrous material layer having an outer surface intended to lie against a user's undergarment, wherein an adhesive is applied at least partly to the outer surface and at least partly in the outer fibrous material layer. The present invention further concerns a method for production of the absorbent article.

Background to the invention

A variety of absorbent articles, such as sanitary napkins, panty liners and incontinence protectors are found on the market today, with differing shapes and dimensions. Such absorbent articles are designed to absorb and retain bodily fluids and, in use, are intended to be placed in the crotch portion of a user's undergarment. To prevent the absorbent article from moving substantially relative to the undergarment and to reduce the risk of leakage, the majority of today's absorbent articles can be fastened in the undergarment. Many of today's absorbent articles can be attached to an undergarment by means of an adhesive which is arranged to adhere to an undergarment in use. The surface of an absorbent article which is intended to lie against the undergarment of a user is therefore at least partly provided with an adhesive.

The adhesive which is used for adhering an absorbent article to an undergarment may for example be a hot melt type adhesive. Hot melt adhesives are solid at room temperature, but transform into a fluid or melt form upon heating to a certain temperature. Furthermore, hot melt adhesives are thermoplastic compositions, so that the transformation from solid form to fluid form is reversible. When a hot melt adhesive is to be applied to an absorbent article, the hot melt adhesive is first heated to a temperature at which it takes a fluid form, after which it can be applied to the backsheet of the absorbent article. After application to the absorbent article, the hot melt adhesive transforms into solid form as it cools. During cooling, bonding takes place to the absorbent article.

l Furthermore, the adhesive which is used for adhesion of an absorbent article to an undergarment may also be a pressure-sensitive type adhesive. A pressure-sensitive adhesive applied to an absorbent article may be made to attach and thereby bond to an undergarment via application of pressure, i.e. activation with heat or other means is not required to achieve bonding to an undergarment.

Today, it is common to utilize an adhesive which is both pressure-sensitive and a hot melt type adhesive, i.e. an adhesive which is a pressure-sensitive hot melt adhesive, for attachment to an undergarment. The pressure-sensitive hot melt adhesive is thereby bonded to the backsheet of an absorbent article upon application, as described above for hot melt adhesives, and the pressure-sensitive hot melt adhesive can thereafter in use be fastened to an undergarment via application of pressure, as described above for pressure-sensitive adhesives.

An adhesive of an absorbent article for adhesion to an undergarment exhibits an adhesive capacity (stickiness or "tackiness"). Such an adhesive further exhibits an adhesive strength ("peel-strength") to a material to which it adheres. The adhesive strength of an adhesive to a given material to which it adheres is completely dependent on the adhesive capacity (stickiness or "tackiness") of that adhesive. The adhesive strength to a certain material is therefore an indirect measure of the adhesive capacity (stickiness) of the adhesive. The adhesive strength of an adhesive is, however, different from material to material.

Many known absorbent articles comprise an adhesive intended for adhesion to an undergarment which is applied in e.g. one or more strands, stripes, points or similar, as well as in different positions on that surface of the absorbent article which is intended to lie against an undergarment. Such articles are known through e.g. US 3 888 255, WO

03/072004 and WO 00/37015. Furthermore, it is known through e.g. CA 2 126 252 to apply an adhesive for adhesion to an undergarment in a pattern over the surface of the absorbent article which is intended to lie against an undergarment, and it is known through e.g. WO 97/12572 to apply an adhesive as a complete coating.

In order for an absorbent article of the above-mentioned type to be as user-friendly as possible, it is inter alia important that the absorbent article does not substantially affect an undergarment to which it attaches in a negative manner. To this end, it is for example important that an adhesive for adhesion to an undergarment does not substantially leave residues behind on the undergarment after use of the absorbent article or does not substantially contribute to residues of both adhesive and backsheet material of the absorbent article being left behind on the undergarment after use. To obtain a high user-friendliness, it is therefore desirable that an adhesive for adhesion to an undergarment is substantially reliably anchored to the absorbent article.

Many of today's absorbent articles of the above-mentioned type have a backsheet which is constituted by, or comprises, an outer fibrous material layer. A fibrous material layer does not have a unitary, even outer surface to which an adhesive for adhesion to an undergarment can be reliably anchored. Reliable anchorage of an adhesive to a fibrous material layer requires that - upon application to the fibrous material layer - the adhesive at least partly penetrates into the fibrous material layer. One property which at least partly influences the penetration of the adhesive into the fibrous material layer is the viscosity of the adhesive upon application. If - upon application - the adhesive for adhesion to an undergarment does not penetrate into an outer fibrous material layer of a backsheet so that reliable anchorage can be obtained, there is a risk that the adhesive unsticks from the outer fibrous material layer and fastens to the undergarment. Furthermore, there is also the risk that the outer fibrous material layer breaks loose, so that residues of both fibrous material and adhesive fasten to the undergarment.

The possibility of obtaining reliable anchorage of an adhesive in an outer fibrous material layer of a backsheet, which adhesive is intended for adhesion to an undergarment, also depends upon the cohesion of the adhesive, i.e. its internal coherency. A cohesion which is too low means that there is a risk that the layer of adhesive does not hold together in use, but rather breaks apart so that residues of the layer of adhesive end up in the undergarment. To avoid the layer of adhesive breaking apart during use, it is important that the cohesive strength of the adhesive is as high as possible, and at least higher than the adhesive strength to the undergarment.

The penetration of an adhesive for adhesion to an undergarment into an outer fibrous material layer of a backsheet of an absorbent article, and the cohesion of the adhesive are parameters which have great influence over user-friendliness of the absorbent article, as - according to the above - they influence whether a reliable anchorage is achieved and whether residues of adhesive and fibrous material layer in the undergarment can be avoided.

The standard pressure-sensitive hot melt adhesives which are used today in production of absorbent articles as adhesives for adhesion to an undergarment have a sufficiently high viscosity that they do not substantially penetrate into an outer fibrous material layer, so that reliable anchorage can be obtained. Pressure-sensitive hot melt adhesives with low viscosity are also found on the market today, which are adapted for penetration into fibrous material layers. However, these adhesives with low viscosity have low cohesion, i.e. a low internal coherency of the adhesive.

There is accordingly a need for a simple way of providing a substantially reliable anchorage of an adhesive (which is intended for adhesion to an undergarment) to an outer fibrous material layer of a backsheet of an absorbent article.

Summary of the invention One object of the present invention is to provide an absorbent article, such as a sanitary napkin, a panty liner or an incontinence protector, with an outer fibrous material layer of a backsheet, to which an adhesive for adhesion to an undergarment is substantially reliably anchored.

This object is achieved by an absorbent article such as a sanitary napkin, a panty liner or an incontinence protector, said absorbent article comprising a liquid-permeable topsheet, a liquid-impermeable backsheet and an absorbent structure arranged between the topsheet and the backsheet, said absorbent article having an essentially elongated shape, a longitudinal direction, a transverse direction, two essentially transverse end edges and two essentially longitudinal side edges, wherein the backsheet comprises an outer fibrous material layer having an outer surface intended to lie against a user's undergarment, wherein an adhesive is applied at least partly to the outer surface and at least partly in the outer fibrous material layer, and wherein the adhesive is a UV-curable adhesive, which has been exposed to UV-radiation.

According to one aspect of the present invention, the adhesive has penetrated in between the fibres in said outer fibrous material layer.

According to another aspect of the present invention, the adhesive has penetrated through at least substantial amounts of the thickness of the outer fibrous material layer and preferably through the whole of the outer fibrous material layer.

In one embodiment, the outer fibrous material layer is a laminate which comprises at least two fibrous component layers, wherein the adhesive has penetrated through at least one of the fibrous component layers, preferably through at least two of the fibrous component layers. In a variant, the outer fibrous material layer is a laminate which comprises at least two fibrous component layers, wherein the adhesive has penetrated through all fibrous component layers in the fibrous material layer.

In one embodiment, the outer fibrous material layer is a laminate which comprises at least two fibrous component layers, wherein the laminate is an SM-laminate, SMS- laminate, SMMS-laminate, SMM-laminate or SMSM-laminate.

According to one aspect of the present invention, the adhesive is a pressure-sensitive adhesive.

According to a further aspect of the present invention, the adhesive is a hot melt adhesive.

In one embodiment, the adhesive is a UV-curable adhesive, which exhibits an adhesive capacity which depends on the dose of UV-radiation to which it has been exposed.

According to one aspect of the present invention, said outer surface and said outer fibrous material layer of the absorbent article are at least partly provided with the adhesive in at least two areas of the absorbent article, wherein the adhesive capacity of the adhesive differs between at least two of said areas in that the dose of UV-radiation to which the adhesive has been exposed differs between the at least two of said areas.

According to another aspect of the present invention, the absorbent article has at least one transverse fold line, wherein the absorbent article is intended to be folded along the at least one transverse fold line in its packaged state, and wherein the absorbent article is divided into at least two portions in its longitudinal direction, substantially defined by the at least one transverse fold line.

In a variant, each of said at least two portions comprises one of said at least two areas.

In one embodiment, the absorbent article has two transverse fold lines, wherein the absorbent article is intended to be folded along the two transverse fold lines in its packaged state, and wherein the absorbent article is divided into a first end portion, a second end portion and a centre portion situated between the end portions, substantially defined by the two transverse fold lines, and that the adhesive capacity of the adhesive in said end portions is higher than the adhesive capacity of the adhesive in said centre portion. According to one aspect of the invention, the adhesive capacity of the adhesive is such that the adhesive strength of the adhesive to an undergarment material lies in the range 2.0 -3.0 N/product for the end portions and in the range 1.5 - 2.5 N/product for the centre portion.

In a variant, the adhesive capacity of the adhesive in said first end portion is higher than the adhesive capacity of the adhesive in said second end portion.

In a further variant, the adhesive capacity of the adhesive in said second end portion is higher than the adhesive capacity of the adhesive in said first end portion.

Another object of the present invention is to provide a method for production of an absorbent article such as a sanitary napkin, a panty liner or an incontinence protector with an outer fibrous material layer of a backsheet, to which an adhesive for adhesion to an undergarment is substantially reliably anchored.

This object is achieved through a method for production of an absorbent article, comprising application of an adhesive in the form of a UV-curable adhesive in a non-UV- cured state at least partly to the outer surface and in the outer fibrous material layer, and, after application, exposing the adhesive to UV-curing by UV-radiation.

In one embodiment, application of the adhesive occurs directly to the outer surface and in the outer fibrous material layer.

In another embodiment, application of the adhesive occurs by transfer coating, whereby the adhesive is first applied to a protective layer intended to be placed at least partly over the outer surface of the absorbent article and is then transferred to the outer surface and the outer fibrous material layer through application of the protective layer on the outer surface.

According to one aspect of the present invention, application of the adhesive occurs to the outer surface and in the outer fibrous material layer in at least two areas of the absorbent article, wherein the outer surface and the outer fibrous material layer at least partly are provided with the adhesive in said at least two areas, and that at least two of said areas are exposed to different doses of UV-radiation. Further features of the present invention will become apparent from the following detailed description, which shall be interpreted with the help of the appended drawings. It should, however, be noted that the drawings are provided for the purpose of illustration only, and that they do not limit the invention. Neither are the drawings necessarily drawn to scale, and - unless otherwise stated - illustrate only conceptually the structures and procedures described herein.

Brief description of the drawings In the drawings, similar reference numbers denote similar elements throughout the different figures, and

Fig. Ia is a plan view of a first embodiment of an absorbent article according to the present invention, in which an outer surface of a backsheet is shown, which surface is intended to lie against a user's undergarment,

Fig. Ib is a cross-sectional view according to line II-II in Fig. 1,

Fig. Ic is a schematic, enlarged partial view in cross-section of an SMMS-material which constitutes the backsheet in the first embodiment,

Fig. 2 is a schematic, enlarged partial view in cross-section of an outer fibrous material layer in the backsheet in an embodiment in which the outer fibrous material layer is an SMS-laminate and in which an adhesive has penetrated down between the fibres in the outer fibrous material layer,

Fig. 3 is a plan view similar to that in Figure 1, but showing a variant of the first embodiment of the invention,

Fig. 4 is a plan view similar to that in Figure 1, but showing a further variant of the first embodiment of the invention,

Fig. 5a is a plan view of a second embodiment of an absorbent article according to the present invention, in which an upper surface is shown, which is intended to face the body of a user;

Fig. 5b is a plan view of the absorbent article in Fig. 5a after a first folding, Fig. 5c is a plan view of the absorbent article in Fig. 5a after a second folding, and

Fig. 6 is a plan view similar to that in Fig. 1, but showing a third embodiment of the invention.

Fig. 7 shows the results of viscosity experiments for three different adhesives.

Fig. 8 shows the results of penetration experiments for three different adhesives.

Fig. 9 shows the results of cohesion experiments for three different adhesives.

Detailed description of the invention

Figure Ia and Figure Ib show a plan view and a cross-sectional view, respectively, of a first embodiment of an absorbent article 1, such as a sanitary napkin, a panty liner or an incontinence protector, according to the present invention. The absorbent article 1 has a conventional construction and comprises a liquid-permeable topsheet 2, a liquid- impermeable backsheet 3 and an absorbent structure 4 arranged between the topsheet 2 and the backsheet 3. In use, the liquid-permeable topsheet 2 is intended to face a user, and the liquid-impermeable backsheet 3 is intended to face a user's undergarment.

Usually, the liquid-permeable topsheet 2 and the liquid-impermeable backsheet 3 extend out from the edges of the absorbent structure 4 and protruding portions 5 of the topsheet 2 and the backsheet 3 are thereby joined to one another around the periphery of the absorbent structure 4, e.g. by gluing, sewing or by welding with heat or ultrasound.

The absorbent article 1 has a conventional, essentially elongated shape, and is defined in the plane by two essentially transverse end edges 6, 7 as well as two essentially longitudinal side edges 8, 9 running between these. Furthermore, the absorbent article 1 has a longitudinal direction x and a transverse direction y. In the longitudinal direction x, the absorbent article 1 has a first and a second end part 10, 11 as well as a centre part 12 lying between the end parts 10, 11. The so-called wetting area, which is the area of an absorbent article which is intended to first receive exuded bodily fluid, is usually located within the centre part 12 (also called the crotch part). The various parts 10-12 do not, however, usually border each other clearly. In Figure Ia, the end parts 10, 11 are completely symmetric, whereby whichever of the two end parts 10, 11 can face forwards on a user when worn. Both the size and position of the various parts 10-12 in the longitudinal direction x are thereby first determined upon use. In alternative embodiments, however, the end parts 10, 11 can be asymmetrically shaped. For example, the first end part 10 can be longer than the second end part 11, whereby the first end part 10 is intended to face rearwards on a user when worn, and the second end part 11 forwards.

The material in the liquid-permeable topsheet 2 may be of any suitable type, and can for instance comprise a non-woven material, e.g. spunbond, meltblown, carded material, hydroentangled material, wet-laid material etc. Suitable non-woven materials can be composites of natural fibres, cotton fibres, artificial fibres such as polyester, polyethylene, polypropylene, viscose etc., or a mixture of natural and artificial fibres. Furthermore, the material in the liquid-permeable topsheet 2 may a comprise a material of tow fibres, which can be bound to each other in a bonding pattern, as described in EP- A-I 035 818. Further examples of materials which are suitable for the liquid-permeable topsheet 2 are perforated plastic films, nets and open-cell or perforated foam materials. Different types of laminates, e.g. laminates of non-woven material and plastic film may also be used. Materials which are suitable to use for the liquid-permeable topsheet 2 should be soft and non-irritating to the skin, and should be readily penetrated by bodily fluids, e.g. urine and menstrual fluid. However, it is not necessary that the liquid- permeable topsheet 2 is a separate material layer, but rather this topsheet 2 can instead be an integrated portion of the absorbent structure 4. Furthermore, the topsheet 2 can be different in different portions of the absorbent article 1. Often, for example, a material especially intended for admission of fluid is arranged centrally, and a specially soft and comfortable material is arranged along the longitudinal side edges 8, 9 of the article 1.

The liquid-impermeable backsheet 3 of the absorbent article 1 according to the invention comprises an outer fibrous material layer 3a having an outer surface 13 which is intended to lie against a user's undergarment. Examples of different types of materials which may be used for the liquid impermeable backsheet 3 are a non-woven material which has been made liquid-impermeable through coating or treatment with a liquid- impermeable material, a hydrophobic non-woven material which resists liquid penetration or a laminate of a plastic film and a non-woven material. In order that the absorbent article 1 should feel airy and comfortable to wear, the liquid-impermeable backsheet 3 suitably allows air and water vapour to be transported out from the absorbent structure 4. Examples of materials which are breathable and which are suitable for use as the liquid-impermeable backsheet 3 are laminates of non-woven materials, laminates of porous polymer films and non-woven materials. The liquid-impermeable backsheet 3 can be elastic or inelastic. The non-woven material can be spunbond (S), meltblown (M), carded, hydroentangled materials or the like. Preferred materials for the non-woven material are polyethylene, polypropylene and the like, although other compositions of natural or synthetic material may also be used. If the liquid-impermeable backsheet 3 is a laminate of nonwoven-materials, it can for example be an SM-laminate, i.e. a laminate comprising one component layer of spunbond and one component layer of meltblown, an SMS-laminate, i.e. a laminate comprising two component layers of spunbond and one component layer of meltblown placed between the two component layers of spunbond, an SMMS-laminate, i.e. a laminate comprising two component layers of spunbond and two component layers of meltblown placed between the two component layers of spunbond, an SMM-laminate, i.e. a laminate with the spunbond-meltblown-meltblown configuration, or an SMSM-laminate, i.e. a laminate with the spunbond-meltblown- spunbond-meltblown configuration.

In the first embodiment shown in Figures Ia and Ib, the liquid impermeable backsheet 3 is constituted by the outer fibrous material layer 3a. The outer fibrous material layer 3a is herein an SMMS-laminate, the construction of which is shown in a schematic, enlarged partial view in cross-section in Figure Ic. In accordance with the above examples of materials which may be used for the liquid impermeable backsheet 3, the backsheet 3 can in alternative embodiments, however, comprise at least one further material layer other than the outer fibrous material layer 3a. The further material layer may thereby be fibrous or a film-material, or similar.

Furthermore, an adhesive 14 is applied at least partly to the outer surface 13 and at least partly in the outer fibrous material layer 3a of the absorbent article 1 according to the invention. The adhesive 14 is intended to adhere to a user's undergarments in use.

As previously mentioned, parameters which influence the anchoring of an adhesive to an outer fibrous material layer of a backsheet, which adhesive is intended for adhesion to an undergarment, are the penetration of the adhesive into the outer fibrous material layer as well as the cohesion of the adhesive. If the adhesive does not exhibit sufficient penetration such that reliable anchorage can be obtained, there is a risk that the adhesive unsticks from the outer fibrous material layer and fastens to the undergarment. There is also the risk that the outer fibrous material layer breaks loose, so that residues of both fibrous material and adhesive fasten to the undergarment.

A cohesion which is too low means that there is a risk that the layer of adhesive does not hold together in use, but rather breaks apart so that residues of the layer of adhesive stick fast in the undergarment. To avoid the layer of adhesive breaking apart in use, it is important that the cohesive strength of the adhesive is as high as possible, and at least higher than the adhesive strength to the undergarment.

In accordance with the invention, the adhesive 14 is a UV-curable adhesive, which in the finished absorbent article 1 has been exposed to UV-radiation. The adhesive 14 is applied during production of the absorbent article 1 in a non-UV-cured state, at least partly on the outer surface 13, i.e. at least within certain areas of the outer surface 13. To obtain substantially reliable anchorage of the adhesive 14 to the outer fibrous material layer 3a, the adhesive 14 is a UV-curable adhesive which in a non-UV-cured state has the ability to penetrate at least partly into the outer fibrous material layer 3a. Upon application of the UV-curable adhesive 14 in a non-UV-cured state, it therefore penetrates into at least parts of the areas of the outer fibrous material layer 3a. Accordingly, upon application of the UV-curable adhesive 14 to the outer surface 13, penetration of the UV-curable adhesive 14 occurs also at least partly into the inner parts of the outer fibrous material layer 3a.

After application of the UV-curable adhesive 14 at least partly to the outer surface 13 and at least partly in the outer fibrous material layer 3a, the adhesive 14 is exposed to UV- curing via UV-radiation with one or more UV-lamps. In a non-UV-cured state, UV-curable adhesives have a low cohesion, i.e. a low inner coherency. Upon UV-curing of a UV- curable adhesive, its cohesion increases. The adhesive 14 in the absorbent article 1 according to the present invention is a UV-curable adhesive, the cohesion of which increases during UV-curing so that a reliable anchorage of the adhesive 14 with respect to the cohesive properties of the adhesive 14 is obtained.

Application of the adhesive 14 may take place directly upon the outer surface 13 and in the outer fibrous material layer 3a by e.g. spray application, contact application by means of a slot nozzle or rotating drums. Alternatively, application of the adhesive 14 may take place via so-called "transfer coating" in which the adhesive 14 is first applied to a protective layer intended to be placed at least partly over the outer surface 13 of the absorbent article 1 and afterwards transferred to the outer surface 13 and the outer fibrous material layer 3a through application of the protective layer to the outer surface 13.

UV-curable adhesives which before UV-curing have the ability to penetrate into an outer fibrous material layer suitable for use as a backsheet of an absorbent article, and which have a cohesion which increases upon curing so that a reliable anchorage with regard to cohesive properties may be obtained, are commercially available. Examples of such UV- curable adhesives will be given below and the experimentally-determined viscosity profile, the penetration into fibrous material layers and the cohesion of such a UV-curable adhesive will be provided in the experimental section.

In order to avoid as far as possible that the backsheet 3 breaks apart during use of the absorbent article 1 so that its residues stick fast in an undergarment, the adhesive 14 preferably does not penetrate only into the outer fibrous material layer 3a, but also down between the fibres in the outer fibrous material layer 3a upon application of the adhesive 14. The adhesive 14 preferably penetrates through at least substantial amounts of the thickness of the outer fibrous material layer 3a and even more preferably through the whole of the outer fibrous material layer 3a.

In accordance with the examples given above for materials of the backsheet 3, the outer fibrous material layer 3a may be a laminate which comprises at least two fibrous component layers. Examples of laminates which comprise at least two fibrous component layers are SM-laminates, SMM-laminates, SMMS-laminates, SMS-laminates and SMSM-laminates. In embodiments in which the outer fibrous material layer 3a is constituted by a laminate which comprises at least two fibrous component layers, it is preferred that the adhesive 14 has penetrated through at least one of the fibrous component layers, preferably through at least two of the fibrous component layers and even more preferably, the adhesive 14 has penetrated through all of the fibrous component layers in the fibrous material layer 3a. This is so as to avoid as much as possible that the backsheet 3 breaks apart in use of the absorbent article 1 so that its residues end up in an undergarment. Figure 2 shows a schematic, enlarged partial view in cross-section of the outer fibrous material layer 3a in an embodiment in which the fibrous material layer 3a is an SMS-laminate and in which the adhesive 14 has penetrated in between the fibres in the outer fibrous material layer 3a.

The UV-curable adhesive 14 is preferably a pressure-sensitive adhesive, or a hot melt adhesive. Even more preferably, the UV-curable adhesive 14 is a pressure-sensitive hot melt adhesive.

Preferred UV-curable adhesives may for example be acrylic-based or rubber-based.

In the first embodiment shown in Figure Ia and Figure Ib, the adhesive 14 is arranged such that it is anchored to the liquid-impermeable backsheet 3 in a continuous strand 15 substantially in the longitudinal direction x of the absorbent article 1. However, in alternative embodiments, the adhesive 14 can be arranged in two or more strands 15 substantially in the longitudinal direction x of the absorbent article 1, in one or more strands 16 substantially in the transverse direction y of the absorbent article 1 (Figure 3) or in both one or more strands 15 substantially in the longitudinal direction x, and in one or more strands 16 substantially in the transverse direction y. Furthermore, the strands 15 substantially in the longitudinal direction and/or the strands 16 substantially in the transverse direction may also each be divided into a series of intermittent areas or zones, or the adhesive 14 may be arranged in any other suitable pattern.

A strand 15 arranged substantially in the longitudinal direction x of the absorbent article 1 can extend over substantially the entire length of the absorbent article 1, or only portions thereof. Likewise, a strand 16 arranged substantially in the transverse direction y of the absorbent article 1 may extend over substantially the entire width of the absorbent article 1, or only portions thereof. The width of a strand 15 can be the same or different from strand 15 to strand of an absorbent article 1, and can also differ when different absorbent articles 1 are compared. If an absorbent article 1 comprises more than one strand 15, the distance between the strands 15 can be the same or different when different absorbent articles 1 are compared. If an absorbent article 1 comprises more than two strands 15, the distance between two strands 15 may be the same or different for each pair of strands 15. Similarly, the width of a strand 16 can be the same or different from strand 16 to strand of an absorbent article 1, and can also differ when different absorbent articles 1 are compared. If an absorbent article 1 comprises more than one strand 16, the distance between the strands 16 can be the same or different when different absorbent articles 1 are compared. If an absorbent article 1 comprises more than two strands 16, the distance between two strands 16 may be the same or different for each pair of strands 16.

Figure 3 shows a variant of the first embodiment of the absorbent article 1 according to the invention, in which the adhesive 14 is arranged in three strands 16 substantially in the transverse direction y. Figure 4 shows a further variant of the first embodiment of the absorbent article 1, in which the adhesive 14 is arranged as an entire coating on the backsheet 3. An area of the outer surface 13 is shown in Figure 4 without adhesive 14.

Further alternative embodiments correspond to any of the above-described embodiments, but possess the further advantage that the UV-curable adhesive 14 is a UV-curable adhesive 14, which exhibits an adhesive capacity which depends on the dose of UV-radiation to which it has been exposed. As mentioned in the introduction, the adhesive strength of an adhesive of an absorbent article to a material to which it adheres is completely dependent on the adhesive capacity (stickiness or "tackiness") of the adhesive. In this way, the adhesive strength is therefore an indirect measure of the adhesive capacity (stickiness) of the adhesive. The value of the adhesive strength (or "peel-strength") of an adhesive is given herein as the force which is required to separate an area of a carrier material from another material after adhesion, said area being substantially coated with the adhesive. The adhesive strength differs, however, from material to material. To reduce the risk of remnants of the adhesive 14 being left behind on the undergarment after use, it is, however, important that the adhesive 14 exhibits a higher adhesive strength to the liquid- impermeable backsheet 3 than to an undergarment.

The adhesive strength of the adhesive 14 to an undergarment is a parameter which also has great influence on how user-friendly the absorbent article 1 is. A certain adhesive strength is required so that the absorbent article 1 shall remain in place in a user's undergarment. If the absorbent article 1 does not retain its position due to an adhesive strength which is too low, the risk of leakage arises. Furthermore, the absorbent article 1 can thereby partly or wholly loosen from the undergarment and instead fasten to e.g. the user's body, causing discomfort.

A number of factors influence the adhesive strength of the adhesive 14 to an undergarment that is required for secure placement of the absorbent article 1. Examples of such factors are the shape, dimensions and materials of the absorbent article 1. As absorbent articles 1 belonging to different product categories, such as sanitary napkins, panty liners and incontinence protectors, have different designs, the adhesive strength of the adhesive 14 to an undergarment which is required for secure placement can be different for absorbent articles 1 belonging to different product categories. However, the adhesive strength required for secure placement can also vary for absorbent articles 1 which have different designs within the same product category.

Furthermore, neither is it user-friendly if the adhesive strength of the adhesive 14 to an undergarment is as high as possible. Adhesive strengths which are too high can lead to difficulties with removing the absorbent article 1 from the undergarment after use. This can possibly also lead to the undergarment being negatively affected, e.g. by colour or material of the undergarment being removed with the absorbent article 1 when it is removed from the undergarment. The problems of excessively high and excessively low adhesive strengths of the adhesive 14 must often be weighed against one another, with the aim of finding a level of adhesive capacity of the adhesive 14 which is as optimal for a given absorbent article 1 as possible. In most cases, it is desirable that the adhesive 14 exhibits an adhesive strength which provides secure placement, but which is not higher than that required for secure placement so that the problems of excessively high adhesive strength are avoided as far as possible.

Examples of ranges in which the optimal adhesive strength of an adhesive to an undergarment material lie are 1.5-3.0 N/product for sanitary napkins, panty liners and incontinence protectors, i.e. the optimal adhesive capacity of the adhesive is such that the adhesive strength of the adhesive to an undergarment material lies in the range 1.5- 3.0 N/product.

In the further alternative embodiments of the absorbent articles 1, in which the UV- curable adhesive is an adhesive - the adhesive capacity of which depends on the dose of UV-radiation to which it has been exposed - the adhesive capacity of the adhesive 14 can be controlled to one or more desired levels by controlling the dose of UV-radiation which is applied to the adhesive 14 upon curing. A given desired level of adhesive capacity of the adhesive 14 is thereby produced during curing of the adhesive 14 through application of a suitable dose of UV-radiation, which produces the desired level of adhesive capacity. In that the absorbent article 1 comprises a UV-curable adhesive 14, the adhesive capacity of which has been controlled to one or more levels during curing, the absorbent article 1 exhibits one or more levels of adhesive strength to an undergarment material.

The expression "dose of UV-radiation" is used herein to indicate the amount of radiation energy which is applied to the adhesive [mJ/m²]. The dose of UV-radiation which is applied to the adhesive 14 can be controlled by adjustment of the intensity of the UV- lamp or UV-lamps which is/are used, by the number of UV-lamps which the adhesive passes and/or by adjustment of the web speed of the web on which the absorbent article 1 is produced (see also the examples given in the experimental section), whereby the exposure time of the adhesive to the UV-lamp is controlled.

Furthermore, the UV-curable adhesive 14 whose adhesive capacity depends on the dose of UV-radiation to which it has been exposed, is a UV-curable adhesive which does not substantially cure afterwards, i.e. when curing is completed during the production, the adhesive capacity is substantially set at a given level. In this way, the adhesive capacity of such an adhesive 14 is not significantly affected by ageing, and the adhesive 14 thereby exhibits an adhesive capacity which is stable over time. Furthermore, the UV- curable adhesive 14, whose adhesive capacity depends on the dose of UV-radiation to which it has been exposed, is preferably a UV-curable adhesive which is cured with UVC- light (light with wavelength between 200 and 280 nm). The adhesive capacity of the adhesive 14 is thus not affected by sunlight, as this consists of UVB-light (light with wavelength between 280 and 320 nm) and UVA-light (light with wavelength between 320 and 400 nm).

Sanicare UV 4101 (obtainable from Henkel KGaA, Dϋsseldorf, Germany) and Ecomelt UV Nl (obtainable from Henkel KGaA, Dϋsseldorf, Germany) are examples of preferred acrylic-based UV-curable pressure-sensitive hot melt adhesives whose adhesive capacity can be controlled by the dose of UV-radiation to which they are exposed. Ecomelt UV N4

(obtainable from Henkel KGaA, Dϋsseldorf, Germany) is an example of a preferred rubber-based adhesive whose adhesive capacity can be controlled by the dose of UV- radiation to which it is exposed.

In variants of the further alternative embodiments, in which the adhesive 14 is a UV- curable adhesive, the adhesive capacity of which depends on the dose of UV-radiation to which it has been exposed, said outer surface 13 and said outer fibrous material layer 3a of the absorbent article 1 are at least partly provided with the adhesive 14 in at least two areas of the absorbent article 1, wherein the adhesive capacity of the adhesive 14 differs between at least two of said areas through that the dose of UV-radiation to which the adhesive 14 has been exposed differs between the at least two of said areas. Such an area can be constituted by e.g. a portion of the absorbent article 1 in the longitudinal direction x, a portion of the absorbent article 1 in the transverse direction y, a strand 15 substantially in the longitudinal direction x, a strand 16 substantially in the transverse direction y, or a point.

In other further alternative embodiments, each of which corresponds to any of the above-mentioned embodiments, except that the absorbent article 1 also has at least one transverse fold line, which extends substantially in the transverse direction y, whereby the absorbent article 1 is intended to be folded along the at least one transverse fold line in its packaged state, so as to minimize the space required for storage and supply of a convenient product. Thereby, the absorbent article 1 is divided into at least two portions in its longitudinal direction x, substantially defined by the at least one transverse fold line. In variants of the other further alternative embodiments, each of the at least two portions comprises one of the above-mentioned at least two areas. The adhesive 14 thereby exhibits different adhesive capacity in at least two of the portions in which the at least one fold line divides the absorbent article 1.

A second embodiment of the absorbent article 1, shown in Figures 5a, 5b and 5c, corresponds to the first embodiment, except that in the second embodiment, the adhesive 14 is specifically a UV-curable adhesive, the adhesive capacity of which depends on the dose of UV-radiation to which it has been exposed and that the absorbent article 1 further has two transverse fold lines; a first transverse fold line 17 and a second transverse fold line 18, which extend substantially in the transverse direction y. The absorbent article 1 is thereby intended to be folded along the two transverse fold lines

17, 18 in its packaged state and the absorbent article 1 is divided into a first and a second end portion 19, 20 and a centre portion 21 lying between the end portions 19,20 in its longitudinal direction x, substantially defined by the two transverse fold lines 17,

18. In the second embodiment, the first and second end portions 19, 20 substantially coincide with the first and second end parts 10, 11, respectively, and the centre portion

21 coincides substantially with the centre part 12. In an alternative embodiment, however, the first and second end portions 19, 20 do not coincide with the first and second end parts 10, 11 respectively, and the centre portion 21 does not coincide with the centre part 12.

Figure 5b shows the second embodiment of the absorbent article 1 after a first fold. The second end portion 20 has thereby been folded along the second transverse fold line 18, in the direction towards the topsheet 2 of the absorbent article, so that the topsheet 2 in the second end portion 20 lies at least partly against the topsheet 2 in the centre portion 21.

Figure 5c shows the second embodiment of the absorbent article 1 after a second, final fold. The first end portion 19 has thereby been folded in along the first transverse fold line 17 in the direction towards the first folded-in second end portion 20, so that the topsheet 2 in the first end portion 19 at least partly lies against the backsheet 3 in the second end portion 20. In such a folded state, the absorbent article 1 can be packed in a packaging wrapper so that a unit packed product is produced. Alternatively, the absorbent article 1 can be placed on a packaging wrapper before being folded together, whereby the folding of the absorbent article 1 occurs completely or partly together with the packaging wrapper.

As mentioned above, a number of factors are of importance as to the level of adhesive capacity of the adhesive 14 which is optimal for avoiding the problems with excessively high or excessively low adhesive strength of a given absorbent article 1 to an undergarment as much as possible. However, the optimal level of adhesive capacity of the adhesive 14 can also differ between different portions of an absorbent article 1.

Folding of the absorbent article 1 according to the second embodiment according to Figs. 5a-c along the two transverse fold lines 17, 18 gives rise to residual stress in the end portions 19, 20, which implies that the end portions 19,20 tend to fall back to (or towards) the positions they had when the absorbent article 1 was folded. To produce a reliable fastening, it is therefore desirable to have a stronger fastening of the end portions 19,20 than of the centre portion 21, i.e. a higher adhesive strength and thereby a higher adhesive capacity of the adhesive 14 in the end portions 19,20 than in the centre portion 21 is desirable.

To compensate for the tendency of the end portions 19,20 to loosen from the undergarment and return to the respective configuration they had when the absorbent article 1 was folded, it is therefore a desirable property that the adhesive 14 exhibits a higher adhesive capacity in the end portions 19,20 of the absorbent article 1 than in the centre portion 21.

In the second embodiment of the absorbent article 1, the adhesive 14 therefore exhibits a substantially higher adhesive capacity in the end portions 19, 20 than in the centre portion 21, which provides an advantage over traditional absorbent articles in which one usually compromises on adhesive capacity. Such a compromise involves that one has adjusted the adhesive capacity so that the centre portion 21 has obtained an adhesive capacity which is slightly too high and the end portions 19, 20 an adhesive capacity which is slightly too low. The result of such an adjustment is that the fastening of the end portions 19,20 is not completely reliable, while the problem readily occurs that the centre portion 21 sticks too strongly to the undergarment.

As the adhesive 14 in the second embodiment is a UV-curable adhesive, whose adhesive capacity can be controlled by the dose of UV-radiation which is applied to the adhesive 14 during production of the absorbent article 1, the dose of UV-radiation which has been applied to the adhesive 14 has thus been controlled in such a way in the second embodiment so as to provide a higher adhesive capacity of the adhesive 14 in the two end portions 19, 20 than in the centre portion 21.

Examples of ranges in which the optimal adhesive strength of a "three-folded" absorbent article 1 lies are 2.0-3.0 N/product for the rear and front portions, and 1.5-2.5 N/product for the centre portion, i.e. the optimal adhesive capacity of the adhesive is such that the adhesive strength of the adhesive to an undergarment material lies in the range 2.0-3.0 N/product for the rear and front portions, and 1.5-2.5 N/product for the centre portion.

In a variant of the second embodiment of the absorbent article l, the adhesive capacity of the adhesive 14 of the two end portions 19,20 is essentially the same. In a further variant of the second embodiment of the absorbent article 1, the adhesive capacity of the adhesive 14 in the first end portion 19 is higher than the adhesive capacity of the adhesive 14 in the second end portion 20, while in yet another variant of the second embodiment, the adhesive capacity of the adhesive 14 in the second end portion 20 is higher than the adhesive capacity of the adhesive 14 in the first end portion 19.

In alternative embodiments, each of which corresponds to any of the above-described embodiments, the absorbent article 1 also comprises at least one fastening flap 22, also called "wing", at each side edge 8,9. Each of the fastening flaps 22 is intended to be folded around an edge of a leg-opening of a user's undergarment, towards the outside of the undergarment. A fastening flap 22 is designed in any known way, and comprises the topsheet 2 and the backsheet 3 with the outer fibrous material layer 3a. Furthermore, each of the fastening flaps 22 are provided with the adhesive 14 at least partly on the outer surface 13 and in the outer fibrous material layer 3a, whereby the fastening flaps 22 are intended to be attached against the outside of a user's undergarment via the adhesive 14. The fastening flaps 22 help to securely position the absorbent article 1 in the undergarment of a user, as well as to reduce the risk of leakage via the side edges.

Figure 6 shows a third embodiment of the absorbent article 1, which corresponds to the first embodiment, except that in the third embodiment, the adhesive 14 is specifically a UV-curable adhesive, the adhesive capacity of which depends on the dose of UV-radiation to which it has been exposed, and that the absorbent article 1 further comprises a fastening flap 22 at each side edge 8, 9.

The adhesive capacity of the adhesive 14 which is applied to the fastening flaps 22 can differ from the adhesive capacity which is required of the adhesive 14 of the other parts of the absorbent article 1 in order to obtain optimal placement of the absorbent article 1.

As the adhesive 14 in the third embodiment is a UV-curable adhesive whose adhesive capacity can be controlled by the dose of UV-radiation which is applied to the adhesive 14, the adhesive capacity of the adhesive 14 of the fastening flaps 22 can be controlled during curing (hardening) by means of the dose of UV-radiation to which it is exposed. In a variant of the third embodiment, the adhesive 14 of each fastening flap 22 exhibits an adhesive capacity which is substantially different from the adhesive capacity of the adhesive 14 applied to the outer surface 13 and in the outer fibrous material layer 3a in the two end parts 10, 11 and the centre part 12. In a further variant of the third embodiment, the adhesive 14 of each fastening flap 22 exhibits an adhesive capacity which is substantially the same as the adhesive capacity of the adhesive 14 applied to the outer surface 13 and in the outer fibrous material layer 3a in the two end parts 10, 11 and the centre part 12.

An example of the range in which the optimal adhesive strength lies for the fastening flaps 22 is 1.5 - 3.0 N/product, i.e. the optimal adhesive capacity of the adhesive is such that the adhesive strength of the adhesive 14 of the fastening flaps 22 to an undergarment material lies in the range 1.5 - 3.0 N/product.

A fourth embodiment of the absorbent article 1 (not shown) is a combination of the second embodiment shown in Figures 5a, 5b and 5c, and the third embodiment shown in Figure 6. According to the fourth embodiment, the absorbent article 1 thus has two transverse fold lines 17, 18, whereby the absorbent article 1 is divided into a first and a second end portion 19,20, as well as a centre portion 21 which is located between the end portions 19,20, and comprises a fastening flap 22 on each side edge 8,9. In a variant of the fourth embodiment, the adhesive 14 of each fastening flap 22 exhibits an adhesive capacity which is different from the adhesive capacity of the adhesive 14 in all of the first and second end portions 19,20 and the centre portion 21. In a further variant of the fourth embodiment, the adhesive 14 of each fastening flap 22 exhibits an adhesive capacity which is substantially the same as the adhesive capacity of the adhesive 14 in at least one of the first and second end portions 19, 20 and the centre portion 21.

A fifth embodiment of the absorbent article 1 (not shown) corresponds to any of the previously-mentioned embodiments, except that at least one protective layer is further arranged over the adhesive 14, which protective layer has at least one surface which has been treated with a release substance and which lies detachably against the adhesive 14. The protective layer is formed from e.g. paper or similar which has been treated with a release substance, and is intended to function as protection against the adhesive 14 becoming dirty or undesirably adhering to other objects during transport and storage. Furthermore, the protective layer is intended to prevent the adhesive 14 from drying out before use. In a variant of the fifth embodiment, in which the absorbent article 1 has fastening flaps 22, the absorbent article 1 comprises a protective layer which covers the adhesive 14 of the two end parts 10,11 and of the fastening flaps 22. In another variant of the fifth embodiment, in which the absorbent article 1 has fastening flaps 22, the absorbent article 1 comprises a protective layer for the adhesive 14 of the two end parts 10,11 and the centre part 12, and a protective layer for the adhesive 14 of each fastening flap 22. In other variants of the fifth embodiment, the at least one protective layer is constituted by a packaging wrapper, which, as well as being a protective layer is intended to be a package in which the absorbent article 1 is packed.

The packaging wrapper can, for example, be a sheet of e.g. paper, plastic or other flexible material, which has been treated with a release substance in order to provide removable attachment. Such a treatment with a release substance usually comprises a silicone coating. The release substance treatment can be applied over the entire surface of the packaging wrapper which faces the absorbent article 1, or be selectively applied within those areas which lie against the adhesive 14 of the absorbent article 1.

Experimental

One of the above-mentioned preferred UV-curable adhesives, the adhesive capacity of which depends on the dose of UV-radiation to which it has been exposed, was subjected to experiments to determine its viscosity, penetration and cohesion properties. In the viscosity, penetration and cohesion experiments, two normally used adhesives were also tested; one with low viscosity and one with high viscosity, for comparison with the UV- curable adhesive. Furthermore, an example was carried out in order to illustrate an embodiment of the present invention in which the adhesive is a UV-curable adhesive, the adhesive capacity of which depends on the dose of UV-radiation to which it has been exposed.

The UV-curable adhesive which was used was Sanicare UV 4101 (may be obtained from Henkel KgaA, Dϋsseldorf, Germany), which is a pressure-sensitive UV-curable hot melt adhesive with an adhesive capacity which depends on the dose of UV-radiation to which it has been exposed. Sanicare UV 4101 cures upon irradiation with UVC-light (light with wavelength between 200 and 280 nm) and its adhesive capacity is thereby not affected by sunlight, as this consists of UVB-light (light with wavelength between 280 and 320 nm) and UVA-light (light with wavelength between 320 and 400 nm). The adhesive capacity of Sanicare UV 4101 is not affected by ageing and therefore exhibits a stable adhesive capacity over time. Furthermore, Sanicare UV 4101 is solvent-free, has a viscosity in the uncured state of 33000 ± 10000 mPa.s at 140⁰C, shows no irritation according to OECD-404 and ISO EN 10993-5 and provides a transparent, colourless adhesive film. The adhesive Lunatack D6312 (may be obtained from H. B. Fuller, Lϋneburg, Germany) and the adhesive Ecomelt H 145NA (may be obtained from Collano AG, Sempach-Station, Switzerland) were also used in the comparative experiments.

Viscosity and penetration experiments

The viscosity profiles for Sanicare UV 4101, Ecomelt H145NA and Lunatack D6312 were determined in a viscosity experiment. The Brookfield -viscosity was determined with Brookfield-models DVH, DV-II or DV-II. An appropriate spindle size and sample size of each adhesive was chosen in accordance with the instructions of the manufacturer of the viscometer. Each sample of adhesive was melted in the thermocel at the temperature at which the viscosity was to be measured. The spindle was lowered into the molten sample of adhesive. The motor was started and set at the lowest speed, and the corresponding torque reading was displayed. The speed was increased until the torque reading stabilised and the viscosity measurement was recorded after 30 minutes. The viscosity for each adhesive was tested within the temperature interval 120-180⁰C. The results of the viscosity experiments are shown in Fig. 7.

The penetration of Sanicare UV 4101, Ecomelt H145NA and Lunatack D6312 into a test material comprising 32 layers of Sawabond 4302 (Sandler AG, Schwarzenbach, Germany), which is an SMMS-material with a basis weight of 19 g/m², was investigated in a penetration experiment. A penetration test was carried out for each of the three adhesives. A sample of the test material was placed on a flat balance. A penetration tube of aluminium with a diameter of 25 mm was placed on the sample. A glue pistol (serial number LU 95070087 from Meltex/Nordson AB, Luneburg, Germany) was filled with each adhesive and the temperature was set at 170 ⁰C. With the help of the glue pistol, the penetration tube was then filled with 10 g of each adhesive at an air pressure of approximately 3 bar, whereby each adhesive was applied on a surface of about 4.9 cm² on the sample. Weight measurement was performed using the balance. After application of each adhesive, cooling to room temperature was allowed and the number of layers penetrated of each adhesive was recorded by peeling the sample material loose layer by layer from below until a layer was reached which was bonded via the adhesive to the other remaining layers. The number of penetrated layers was then recorded visually. The results of the penetration experiments are shown in Fig. 8.

The results of the viscosity and penetration experiments show that the UV-curable adhesive, Sanicare UV 4101, certainly shows a higher viscosity in the tested temperature interval and especially shows a higher viscosity at the temperature used in the penetration experiments (170⁰C) than Ecomelt H145NA and Lunatack D6312. However, the results of the penetration test show that Sanicare UV 4104 still shows a more than adequate penetration. In this penetration test, Sanicare UV 4101 penetrated 4 layers of Sawabond. As each layer of Sawabond is a layer of an SMMS-laminate, each layer consists of 4 component layers. Sanicare UV 4101 therefore penetrated a total of 16 component layers. As mentioned above, it is preferred that an adhesive for adhesion to an undergarment penetrates through an outer fibrous material layer so that it is substantially completely penetrated through, which, according to the present penetration experiment, Sanicare UV4101 ought to do. Lunatack D6312 penetrated 9 layers of Sawabond and Ecomelt H145NA penetrated 2 layers of Sawabond.

Cohesion experiments

In a cohesion experiment, the cohesion of uncured Sanicare UV 4101, cured Sanicare UV 4101, Ecomelt H145NA and Lunatack D6312 was investigated. The cohesion was investigated in a shear modulus experiment. It is well known that the cohesion properties of an adhesive can be indirectly derived from the shape of the shear modulus curve for the adhesive over a wide temperature range (e.g. from room temperature and up to 15O⁰C). The flatter the shear modulus curve for an adhesive is over a wide temperature range, the more stable the adhesive is, and the higher cohesion the adhesive has.

Cohesion experiments were carried out using a Rheometrics Dynamic Analyser RDAII (software: Rhios version V4.2.3) with a final tension of 0.01. The parallel plates which were used had a diameter of 25 mm and a gap of 1-1.5 mm. The thickness of the samples which were used was therefore 1-1.5 mm. The instrument was set at a frequency of 1 Hz. The cohesion was tested within the temperature range 30-150⁰C and a temperature change of 5°C/minute was carried out within this temperature range. Other parameters were as in ASTM D4440-01.

Samples of cured Sanicare UV4101 were prepared by pre-cured Sanicare UV4101 (cured with a dose of UV-radiation of 27 mJ/m²) being adhered to a polyethene film with the name Me 1148 (may be obtained from Trioplanex International AB; Landskrona, Sweden) was peeled off the polyethene film. Only small pieces of the cured adhesive could be peeled off at a time. The combined small pieces were then pressed together to a film with a thickness of 1.5 mm. A sample with a diameter of 25 mm was punched out of this film and placed in the rheometer. The rheometer was heated to 9O⁰C to provide good contact and adhesion between the parallel plates and the sample of adhesive. The equipment was then cooled to room temperature and then the test was carried out as described above. The results of the cohesion experiments are shown in Figure 9. As shown in Figure 9, the cured UV-curable adhesive exhibits a substantially flat shear modulus curve, which, according to that given above, means that it has a high cohesion. The results also show that the uncured UV-curable adhesive has a substantially sloping shear modulus curve, wherein there is a large difference between the shear modulus curves for the uncured and cured UV-curable adhesive and wherein the cohesion substantially increases during UV-curing. The shear modulus curves for Ecomelt H145NA and Lunatack D6312 show that these have a lower cohesion than the cured UV-curable adhesive.

Exemplified experiment

In a first test, Sanicare UV 4101 was applied to an SMMS-layer (spunbond-meltblown- meltblown-spunbond-layer), from Corovin GmbH, Peine, Germany with a basis weight of 30 g/m². Application of the adhesive was carried out in the same way as is usually carried out for corresponding application during production of absorbent articles such as e.g. sanitary napkins. A paper strip (Loparex ESP 43 from Loparex Oy, Finland) treated with a release substance was coated with a continuous strand of the adhesive, whereupon the adhesive was transferred to the SMMS-layer. Coating and transferring were carried out immediately after one another in a continuous operation. Application was carried out at a temperature of 150⁰C. The strand of adhesive had a width of 30mm and a coat weight of 24.7g/m². After 30 minutes storage at room temperature, the continuous material web comprising the release substance coated paper strip, the strands of adhesive and the SMMS-layer was cut into discrete lengths. The paper strip was removed, and UV-curing of the test samples was subsequently carried out in a separate process.

The adhesive was UV-cured on a total of 10 samples, of which half were cured with a UV- radiation dose of 27 mJ/m², and the other half were cured with a UV-radiation dose of 9 mJ/m². Irradiation was carried out with a standard mercury lamp (Fusion F 600) with an intensity of 30 mW/cm² and with UV-light with a wavelength of 250 nm (UVC-light). The samples were loaded onto a transport web with the adhesive oriented away from the material web. The transport web with the samples passed the mercury lamp, whereby the UV-radiation was set by adjusting the speed of the material web. At a web speed of 50 m/min, the dose of UV-radiation was 9 mJ/m² and at a web speed of 30 m/min, the dose was 27 mJ/m².

The adhesive strength on cotton cloth for the 10 samples was then measured. Measurement of the adhesive strength was carried out on cotton cloth no. 460 from Test Fabrics (previously Cromocol), USA. Measurements were carried out one week after UV- curing had taken place, but as the adhesive does not change after curing, measurements could well have taken place earlier. The cotton cloth, which is identical on both sides, was applied to the adhesive on the samples, after which a controlled compression was carried out via a roller with a hard rubber surface weighing 2 kilos and having a width of 50 mm. The roller was passed twice (over and back) over the cotton cloth and the sample comprising the surface with adhesive, at a speed of 1500 mm/min. One minute after compression was complete, the sample was placed in a tensile tester (Instron 4301) to determine the adhesive strength between the cotton cloth and the SMMS-layer comprising the adhesive. The tensile tests were carried out in the longitudinal direction of the adhesive strand, and measure the average force when a peel force perpendicular to the adhesive joint is applied to the sample, which gradually opens the joint. The sample is inserted into the tensile tester, with a flap of cotton cloth fastened in one fastening clamp of the tensile tester and a flap of the SMMS-layer in the other fastening clamp of the tensile tester so that the material layers are gradually separated in the longitudinal direction of the adhesive joint during the tensile test. During the tensile test, the portions of the SMMS-layer and the cotton cloth which are not yet separated from one another should be held substantially perpendicular to the pull-direction of the tensile tester. A computer program with the settings: clamping length 50 mm, pull-speed 500 mm/min and pull-length 140 mm was used in the tensile tester. The computer program also calculates the average force for the current tensile test.

The following results were obtained:

As the results show, different initial adhesive strengths were obtained upon application of various doses of UV-radiation to the adhesive. A low dose of UV-radiation gave a higher initial adhesive strength than a high dose of UV-radiation.

As the adhesive was coated with the same amount per unit area on all 10 samples in this test, a substantially uniform curing upon UV-irradiation with the two respective doses should have been obtained, and the adhesive strength does not therefore depend on deviations in the curing. The results for the two different doses of UV-radiation can thus be directly compared, and the differences in adhesive strength are due to the two different doses of UV-radiation giving rise to different adhesive capacities.

As mentioned above, the adhesive strength of an adhesive to a given material depends completely on the adhesive capacity (tackiness) of the adhesive, so that the measure of the adhesive strength is an indirect measure of the adhesive capacity. The results obtained in this test can also be expressed as that a low dose of UV-radiation gave a higher initial adhesive capacity (tackiness) of the adhesive than a high dose of UV- radiation.

After removal of the SMMS-film from the cotton cloth, there were no visible residues of adhesive or parts of the SMMS-film left on the cotton cloth in any of the 10 samples.

Through this embodiment, it has thus been demonstrated that a UV-curable adhesive can be reliably anchored to an outer fibrous material layer of a backsheet. Furthermore, it has been demonstrated that the adhesive capacity of a UV-curable adhesive, the adhesive capacity of which depends on the dose of UV-radiation to which it has been exposed, can be controlled during production to desired levels through application of different doses of UV-radiation.

Fundamental new features of the invention as applied to a preferred embodiment thereof have been shown and described and pointed out herein, although it should be understood that different omissions and replacements and amendments in the form and details of the illustrated articles, and in their use, can be made by those skilled in the art without departing from the spirit of the invention. For example, it is expressly intended that all combinations of those elements and/or method steps which carry out essentially the same function in essentially the same way to obtain the same result fall within the scope of the invention. Furthermore, it should be understood that structures and/or elements and/or method steps which are shown and/or described in connection with a disclosed form or embodiment of the invention may be incorporated in any other form or embodiment which is shown, described or indicated, as a general matter of design choice. It is the intention, therefore, to be limited only as indicated by the scope of the claims appended hereto.

For example, the absorbent article can comprise other UV-curable adhesives or other fibrous material layers in the backsheet than those given above. Furthermore, the number of fold lines can differ from the numbers given, the number of strands of adhesive can differ from those numbers given, or the adhesive may be applied in a pattern other than those given. Furthermore, the optimal values of adhesive capacity can vary from those which are given.

Claims

1. An absorbent article (1), such as a sanitary napkin, a panty liner or an incontinence protector, said absorbent article (1) comprising a liquid-permeable topsheet (2), a liquid- impermeable backsheet (3) and an absorbent structure (4) arranged between the topsheet (2) and the backsheet (3), said absorbent article (1) having an essentially elongated shape, a longitudinal direction (x), a transverse direction (y), two essentially transverse end edges (6, 7) and two essentially longitudinal side edges (8, 9), wherein the backsheet (3) comprises an outer fibrous material layer (3a) having an outer surface (13) intended to lie against a user's undergarment, wherein an adhesive (14) is applied at least partly to the outer surface (13) and at least partly in the outer fibrous material layer (3a), characterised in that the adhesive (14) is a UV-curable adhesive, which has been exposed to UV-radiation.

2. An absorbent article (1) according to claim 1, characterised in that the adhesive (14) has penetrated in between the fibres in said outer fibrous material layer (3a).

3. An absorbent article (1) according to claim 1 or 2, characterised in that the adhesive (14) has penetrated through at least substantial amounts of the thickness of the outer fibrous material layer (3a) and preferably through the whole of the outer fibrous material layer (3a).

4. An absorbent article (1) according to claim 1 or 2, characterised in that the outer fibrous material layer (3a) is a laminate which comprises at least two fibrous component layers, wherein the adhesive (14) has penetrated through at least one of the fibrous component layers, preferably through at least two of the fibrous component layers.

5. An absorbent article (1) according to claim 4, characterised in that the adhesive (14) has penetrated through all fibrous component layers (3a) in the fibrous material layer

(3a).

6. An absorbent article (1) according to claim 4 or 5, characterised in that the laminate is an SM-laminate, SMS-laminate, SMMS-laminate, SMM-laminate or SMSM-laminate.

7. An absorbent article (1) according to any of the preceding claims, characterised in that the adhesive (14) is a pressure-sensitive adhesive.

8. An absorbent article (1) according to any of the preceding claims, characterised in that the adhesive (14) is a hot melt adhesive.

9. An absorbent article (1) according to any of the preceding claims, characterised in that the adhesive (14) is a UV-curable adhesive, which exhibits an adhesive capacity which depends on the dose of UV-radiation to which it has been exposed.

10. An absorbent article (1) according to claim 9, characterised in that said outer surface (13) and said outer fibrous material layer (3a) of the absorbent article (1) are at least partly provided with the adhesive (14) in at least two areas of the absorbent article (1), and that the adhesive capacity of the adhesive (14) differs between at least two of said areas in that the dose of UV-radiation to which the adhesive (14) has been exposed differs between the at least two of said areas.

11. An absorbent article (1) according to any of the preceding claims, characterised in that the absorbent article (1) has at least one transverse fold line (17; 18), wherein the absorbent article (1) is intended to be folded along the at least one transverse fold line (17,18) in its packaged state, and wherein the absorbent article (1) is divided into at least two portions (19; 20; 21) in its longitudinal direction (x), substantially defined by the at least one transverse fold line (17; 18).

12. An absorbent article (1) according to claim 10 and 11, characterised in that each of said at least two portions comprises one of said at least two areas.

13. An absorbent article (1) according to claim 12, characterised in that the absorbent article (1) has two transverse fold lines (17, 18), wherein the absorbent article (1) is intended to be folded along the two transverse fold lines (17, 18) in its packaged state, and wherein the absorbent article (1) is divided into a first end portion (19), a second end portion (20) and a centre portion (21) situated between the end portions (19, 20), substantially defined by the two transverse fold lines (17, 18) and that the adhesive capacity of the adhesive (14) in said end portions (19, 20) is higher than the adhesive capacity of the adhesive in said centre portion (21).

14. An absorbent article (1) according to claim 13, characterised in that the adhesive capacity of the adhesive (14) is such that the adhesive strength of the adhesive (14) to an undergarment material lies in the range 2.0 -3.0 N/product for the end portions (19, 20) and in the range 1.5 - 2.5 N/product for the centre portion (21).

15. An absorbent article (1) according to claim 13 or 14, characterised in that the adhesive capacity of the adhesive (14) in said first end portion (19) is higher than the adhesive capacity of the adhesive (14) in said second end portion (20).

16. An absorbent article (1) according to claim 13 or 14, characterised in that the adhesive capacity of the adhesive (14) in said second end portion (20) is higher than the adhesive capacity of the adhesive (14) in said first end portion (19).

17. A method for production of an absorbent article (1) of the type given in claim 1, characterised in that the method comprises the steps of:

- application of an adhesive (14) in the form of a UV-curable adhesive in a non-UV- cured state at least partly to the outer surface (13) and in the outer fibrous material layer (3a), and after application, exposing the adhesive (14) to UV-curing by UV-radiation.

18. A method according to claim 17, characterised in that application of the adhesive (14) occurs directly to the outer surface (13) and in the outer fibrous material layer (3a).

19. A method according to claim 17, characterised in that application of the adhesive (14) occurs by transfer coating, whereby the adhesive (14) is first applied to a protective layer intended to be placed at least partly over the outer surface (13) of the absorbent article (1) and is then transferred to the outer surface (13) and the outer fibrous material layer (3a) through application of the protective layer on the outer surface (13).

20. A method according to any of claims 17-19, characterised in that application of the adhesive (14) occurs to the outer surface (13) and in the outer fibrous material layer (3a) in at least two areas of the absorbent article (1), wherein the outer surface (13) and the outer fibrous material layer (3a) at least partly are provided with the adhesive (14) in said at least two areas, and that at least two of said areas are exposed to different doses of UV-radiation.