Flexible film for film strips

Abstract

An elastic film having an elastic film layer based on styrene block copolymer, such that the elastic film layer is formed from a first styrene block copolymer and a second styrene block copolymer without the addition of polystyrene. The first styrene block copolymer has a styrene portion of less than 25% by weight and the second styrene block copolymer has a styrene portion of more than 26% by weight. A ratio of the first styrene block copolymer to the second styrene block copolymer is between 6:1 and 2:3.

Claims

1. An elastic film, comprising: an elastic film layer formed from a first styrene block copolymer and a second styrene block copolymer without the addition of polystyrene; wherein the first styrene block copolymer has a styrene portion of less than 25% by weight and the second styrene block copolymer has a styrene portion of more than 26% by weight; and wherein the ratio of the first styrene block copolymer to the second styrene block copolymer is between 6:1 and 2:3.

2. The elastic film according to claim 1, wherein the first styrene block copolymer has a hardness of less than 45 Shore A and the second styrene block copolymer has a hardness of more than 45 Shore A.

3. An elastic film, comprising: an elastic film layer formed from a first styrene block copolymer and a second styrene block copolymer without the addition of polystyrene; wherein the first styrene block copolymer has a styrene portion of less than 25% by weight and the second styrene block copolymer has a styrene portion of more than 26% by weight; and wherein the ratio of the first styrene block copolymer to the second styrene block copolymer is between 5:1 and 1:1.

4. The elastic film according to claim 1, wherein the elastic film layer comprises a three-layered configuration, formed by co-extrusion, that is situated between two non-elastic cover layers.

5. The elastic film according to claim 4, wherein each of the non-elastic cover layers has a thickness between 1.5 μm and 6 μm.

6. The elastic film according to claim 4, wherein the non-elastic cover layers are formed from polyolefin;

7. The elastic film according to claim 6, wherein the polyolefin is polyethylene, polypropylene, or mixtures of polyethylene and polypropylene.

8. The elastic film according to claim 1, wherein the elastic film layer has a thickness between 30 μm and 60 μm.

9. The elastic film according to claim 1, defined by an energy recovery value of more than 0.6.

10. The elastic film according to claim 1, wherein after an initial activation by stretching by 500%, a force necessary for a stretching by 100% is less than 1 N per 19 mm specimen width.

11. The elastic film according to claim 1, wherein after an initial activation by stretching by 500%, a force necessary for a stretching by 200% is less than 1.5 N per 19 mm specimen width.

12. The elastic film according to claim 1, wherein a styrene-isoprene-styrene block copolymer is provided as the first and the second styrene block copolymers.

13. The elastic film according to claim 1, wherein the elastic film layer comprises, in addition to the first styrene block copolymer and the second styrene block copolymer, admixtures, additions and additives having an overall portion of less than 10% by weight.

14. A disposable diaper, comprising: a diaper body comprising a front part, a rear part and a core configured to absorb a liquid, the core positioned between a fluid-tight outer layer and a fluid-permeable inner layer; and first and second elastic laminate sections, each having first and second ends; wherein the first ends of the first and second elastic laminate sections are connected to the diaper body and provided as lateral connections between the front part and the rear part of the diaper body; and wherein first and second closure elements are connected to the respective second ends of the first and second elastic laminate sections.

15. The disposable diaper as set forth in claim 14, wherein the first and the second elastic laminate sections comprise an elastic film; and wherein the elastic film comprises an elastic film layer formed from a first styrene block copolymer and a second styrene block copolymer without the addition of polystyrene; wherein the first styrene block copolymer has a styrene portion of less than 25% by weight and the second styrene block copolymer has a styrene portion of more than 26% by weight; and wherein the ratio of the first styrene block copolymer to the second styrene block copolymer is between 6:1 and 2:3.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Further features and advantages of the invention will become apparent from the description of embodiments that follows, with reference to the attached figures, wherein:

[0051] FIG. 1 shows an elastic laminate for diaper closures, according to the invention, in a relaxed state;

[0052] FIG. 2 shows the elastic laminate shown to FIG. 1 in a fully stretched state at a stretching limit;

[0053] FIG. 3 shows a cross-section of the elastic laminate;

[0054] FIG. 4a shows a displacement-force diagram for a stretching of an elastic film provided for forming the elastic laminate;

[0055] FIG. 4b shows the area under the curve ascertained during the stretching in the displacement-force diagram in FIG. 4a;

[0056] FIG. 4c shows the area according to FIG. 4b for the return of the elastic film; and

[0057] FIG. 5 shows the schematic representation of a disposable diaper.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0058] The following is a detailed description of example embodiments of the invention depicted in the accompanying drawings. The example embodiments are presented in such detail as to clearly communicate the invention and are designed to make such embodiments obvious to a person of ordinary skill in the art. However, the amount of detail offered is not intended to limit the anticipated variations of embodiments; on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present invention, as defined by the appended claims.

[0059] FIG. 1 shows a top view of an elastic laminate for diaper closures. When viewed in combination with the sectional representation according to FIG. 3, it is evident that the elastic laminate comprises two nonwoven-fabric layers 1, which also form the outer sides of the elastic laminate. Strips 2 of an elastic film, which are incorporated between the nonwoven-fabric layers 1 by an adhesive 3, extend along a stretching direction D.

[0060] According to the invention, the strips 2 are incorporated under preload between the nonwoven-fabric layers 1, wherein the nonwoven-fabric layers 1, in a relaxed state, represented in FIG. 1, are pleated along the stretching direction D due to the return force of the strips 2 which were incorporated under preload, i.e., said nonwoven-fabric layers are gathered along the strips 2. A t the point at which the strips 2 extend, the nonwoven-fabric layers 1 remain flat due to a preferably all-over adhesion by the adhesive, while ruffle-shaped gatherings form between the strips 2, which result in a highly non-uniform, soft surface of the elastic laminate. The elastic laminate therefore has a structure in the relaxed state that is very pleasant and is gentle on the skin.

[0061] The nonwoven-fabric layers 1, the strips 2, and the adhesive 3 are not shown to scale in FIG. 3. The thickness of the strips in the relaxed state is between 30 μm and 80 μm, wherein the width b determined perpendicularly to the stretching direction D is between 3 mm and 12 mm. The distance a measured from the edges of adjacent strips 2 also is between 3 mm and 12 mm, although the distance preferably is selected to be slightly greater than the width b in the specific exemplary embodiment, purely by way of example. In principle, the strips 2 of the elastic film in the relaxed state extend over 10% to 80% of the total area of the elastic laminate.

[0062] FIG. 2 shows the elastic laminate according to FIG. 1 in a stretched state. The extent of the stretching of the elastic laminate in this case corresponds to the tension of the strips of the elastic film during production. Correspondingly, the nonwoven-fabric layers 1 also are stretched again so far that the above-described pleating is eliminated again. The elastic laminate stretched along the course of the strips is therefore flat. The elastic laminate can be stretched further only by applying a substantially greater amount of force, because only those pleats that were previously formed via the contraction of the preloaded strips are pulled straight again, although without also changing the structure of the nonwoven-fabric layers, up to the point of the stretching and the flat arrangement of the nonwoven-fabric layers, which is shown.

[0063] A further stretching of the elastic laminate would result in a structural change and stretching of the nonwoven-fabric layers, i.e., a disproportionately greater amount of force must be applied for this purpose. From the perspective of a user, a stretching limit is clearly noticeable, wherein the overall stability of the elastic laminate at the stretching limit is substantially provided by the nonwoven-fabric layers.

[0064] Within the scope of the invention, this also enables the strips 2 of the elastic film to be designed to be particularly easily stretched and to not need to have a high tensile strength. With respect to the tensile strength and tear resistance on the one hand, and with respect to the elastic return on the other hand, a distribution of functions between the nonwoven-fabric layers 1 and the strips 2 of the elastic film is implemented.

[0065] According to FIG. 3, the film from which the strips 2 are formed can have a three-layered configuration comprising an elastic film layer 4 between two thin, non-elastic cover layers 5. The cover layers 5 are designed to be so thin and preferably also weakened by an activation that the elastic properties of the strips 2 and, therefore, of the elastic laminate formed therefrom, are determined by the elastic film layer 4. The elastic film layer 4 is formed based on styrene block copolymer. Specifically, the elastic film layer 4 consists of a first styrene-isoprene-styrene block copolymer and a second styrene-isoprene-styrene block copolymer, wherein the first styrene-isoprene-styrene block copolymer comprises a styrene portion between 10% and 20% by weight and has a hardness of less than 44 Shore A. The second styrene-isoprene-styrene block copolymer comprises a styrene portion between 30% and 40% by weight and has a hardness of more than 46 Shore A. The elastic film layer is formed without the addition of polystyrene and also contains less than 15%, preferably less than 10% additives, and particularly preferably contains approximately 6% additives.

[0066] Within the scope of the invention, the ratio of the first styrene-isoprene-styrene block copolymer to the second styrene-isoprene-styrene block copolymer is between 6:1 and 2:3; in the specific exemplary embodiment, this ratio is 3:1.

[0067] Due specifically to the first, very soft styrene-isoprene-styrene block copolymer and the omission of polystyrene in the formulation of the elastic film layer, a very soft stretching behavior also results in the machine direction, wherein a low tensile strength can be accepted, as described above.

[0068] It is assumed that the thin cover layers 5 also impart a stabilizing effect on the elastic film layer 4, as a core layer, during the co-extrusion.

[0069] The elastic film layer 4 has a thickness between 30 μm and 60 μm, for example 44 μm, while the cover layers formed from a mixture of polyethylene and polypropylene in the exemplary embodiment only have a thickness between 1.5 μm and 6 μm, for example 3μm.

[0070] In order to minimize a negative influence of the cover layers 5 on the elastic properties of the film and of the elastic laminate formed therefrom, the elastic film can be subjected to an activation. The activated film resulting upon discontinuation of the tensile forces is then used for forming the laminate, wherein the length that results after the activation and after the force is discontinued, and that may have a permanent deformation, is used as the starting length for the additional stretches.

[0071] For example, FIG. 4a shows a displacement-force diagram for an elastic film that was initially activated by a stretching by 500%. FIG. 4a therefore shows the elastic behavior of the elastic film that has been activated in this way, starting from the new starting length which may have a permanent deformation. It is evident that the elastic film can be initially stretched by 100% using a low force of less than 1 N per 19 mm specimen width and can then be stretched by 200% using a force of less than 1.5 N per 19 mm specimen width. With the aid of the elastic film, an elastic laminate comprising cover layers made of a nonwoven fabric may therefore be produced, and the elastic laminate can be easily stretched along the strips 2 during the incorporation of strips of the elastic film in the stretched state up to the stretching limit established by this preliminary stretching.

[0072] The strips 2 preferably are formed from the elastic film in such a way that the strips extend in the machine direction, i.e., the production direction, of the elastic film. FIG. 5 shows the preferred application of the elastic laminate according to FIGS. 1 and 2. FIG. 5 shows a disposable diaper comprising a basic diaper body 6. The disposable diaper 6 comprises a core 7 that absorbs a fluid between a fluid-tight outer layer and a fluid-permeable inner layer, wherein two sections 8 of the above-described elastic laminate are connected to the basic diaper body 6 and are provided as lateral connections between a front part and a rear part of the basic diaper body 6. Specifically, each of the sections 8 is connected at a first end to the basic diaper body 6 and, at a second end, support a closure element 9, for example, a hook material. The closure elements are intended to be fastened on a front section of the basic diaper body when the disposable diaper is worn, for which a contact surface, which is also referred to as a “landing zone”, is provided there for this purpose.

[0073] As will be evident to persons skilled in the art, the foregoing detailed description and figures are presented as examples of the invention, and that variations are contemplated that do not depart from the fair scope of the teachings and descriptions set forth in this disclosure. The foregoing is not intended to limit what has been invented, except to the extent that the following claims so limit that.