ABSORBENT ARTICLE WITH RELEASE LINER FOR PRESSURE-SENSITIVE ADHESIVE

Abstract: Protection system for an absorbent product such as a sanitary pad or the like, comprising a release strip (6) for protecting an adhesive layer on the absorbent product before use. The release strip is releasably adhered by means of a pressure sensitive adhesive (5) to the back sheet (4) of the absorbent product. In order to allow ease of removal of the release strip (6) from the back sheet (4) while still providing a force which feels adequately large to provide secure fixing of the absorbent product inside a user's undergarment, the release force (peel strength) between the release strip (6) and the back sheet (4) is arranged to lie between 0.5 and 1 N.

Description: Tit le : ABSORBENT ARTICLE WITH RELEASE LINER FOR PRESSURE-SENSITIVE ADHESIVE Field of the invention: The present invention concerns a protection system for an absorbent product such as an incontinence pad, sanitary pad, sanitary napkin, diaper, or the like, wherein the protection system comprises a protective strip releasably adhered to a back sheet of the absorbent product by means of an adhesive. Particularly preferred for these products are pressure- sensitive adhesives. The protection system comprises in particular a protective strip, preferably made of a silicone treated material and designed to be adhered to and released from the back sheet of said disposable absorbent product. Background to the invention: Protection systems for adhesion means generally comprise the combination of at least two materials which are temporarily adhered together, i.e. a protective material and one or more adhesion means associated with the surface or a layer of another material. The protective material for absorbent products is generally a release tape component having a low adhesion release surface or layer. Such protection systems may also be systems which allow re-attachment over a plurality of attachment/release cycles. In the field of disposable absorbent products, such protection systems are employed for protecting the adhesives used in several different locations on such products against the adhesive becoming dirty or sticking undesirably to other objects or clothing before use. When the release strip is removed the adhesive is exposed for use. The user then places the absorbent product inside and into contact with their undergarment and generally applies pressure to the absorbent article from above such that the pressure sensitive adhesive of the absorbent product is activated. This activation maintains the absorbent product in contact with the undergarment during use. Thus a fast and convenient way of maintaining the absorbent product in a relatively fixed position with respect to the wearer's undergarment is provided. This relatively fixed position should be maintained while the wearer undergoes a variety of movements, such that the absorbent product is held generally in the correct position with respect to the user' s body so as to allow exudate to be reliably collected and without giving rise to leaks. Known systems commonly comprise a pressure-sensitive adhesive in the form of one or more lines of adhesive applied to the back sheet of the absorbent product, the adhesive being protected by a release strip typically made of paper. Prior art products of the aforementioned type are known for example from US-A-4701178 , US-A-4217901, US-A- 3888255 and US-A-5593750. Such attachment systems should of course be designed in such a way that the user is able to peel the release strip away from the absorbent product without requiring too great a force. When the force is too high, this can lead to tearing of the release strip during removal. When the release strip material tears, the remainder of the release strip on the adhesive often provides no leading edge which can be grasped so as to allow complete removal from the adhesive. Or, in some cases the already exposed adhesive sticks to the user' s fingers or clothing when trying to remove the remaining strip parts which can lead in the product becoming wrinkled and in most cases ruined. This often leads to the product being discarded. Similarly, too great a force can also result in removal of areas of the pressure sensitive adhesive from the back sheet, leaving thus an incomplete adhesive layer on the back sheet, which is clearly undesirable . Similarly however, the release force which the user requires to peel the release strip away from the underlying back sheet should not be too low. If the force is too low, the user is left with the impression that there is insufficient adhesive force in the exposed adhesive to maintain the absorbent product securely in place during movement. The user in such cases often discards the product believing the adhesive to be defective and unable to perform its function. Thus the opposing requirements of the peeling force between the release strip and the back sheet are apparently incompatible. Consequently products are manufactured which have a force level which is generally too high and the release strips are made sufficiently thick and strong to try to avoid tearing. This is however not only uneconomical but the problems of adhesive being torn away from the back sheet when the release strip is removed are not entirely solved. The object of the present invention is to provide a solution to the aforementioned problem. A further object of the present invention is to make the protection system independent of the adhesive type, its pattern on the absorbent product, the back sheet material or the release strip material. The protection system instead should be defined by release force characteristics. One of the advantages of the present invention is therefore that almost any variation of an absorbent product, in terms of its materials or the type of adhesives used, can be adopted since it is possible to adapt the protection system to meet the required release force characteristics in many different ways. For example, if all the material sheets or layers are of a predefined nature, the release force can be altered by changing the width of the adhesion surface, or its thickness. Similarly, if only the materials of the back sheet and release strip are predefined, the type of adhesion means used can be altered in addition to the width and thickness dimensions. Many other modifications of the various available parameters will be understood by the skilled man as allowing a means by which the release force range defined in the claims can be obtained. Once the range is known, the skilled man merely needs to perform simple tests to alter the materials, adhesive, patterns or dimensions of same so as to arrive at a release force within the range. Further problems which can be solved by this invention with respect to known prior art attachment systems for disposable absorbent products will become apparent to the reader of the following description. Summary of the invention: The prevent invention provides a solution to the aforementioned problems during release of a release strip from a back sheet of an absorbent product by means of a protection system as defined in claim 1. As will be apparent, a product in which the release force is more than 1 Newton (N) will often result in one or more of the inconveniences mentioned above. Similarly a product in which the release force is less than 0.5 N will often be judged as defective. Thus, the inventors have arrived at a particularly limited range of values in which the balance of requirements mentioned above is met. Preferred embodiments of the invention are defined in the dependent claims. It should be understood that the term "adhesive" as used herein is intended to imply either a double faced adhesive tape, a tacky surface texture, or coating of, or treatment of, a back sheet, which has the effect of increasing its adherence to a surface or layer, and especially to the user's underwear. Although particular dimensions of the various components or surface weights of adhesives are specified in the following description, it will be clear to the skilled man that the width and length of the various components or the surface weights of adhesives may be changed in order to suit the particular circumstances, as long as the release force range of 0.5 to 1 N is maintained. In particular, the width of the lines of adhesive means and the surface weight of adhesives may depend on the properties of the adhesive used. However, for the same adhesive means, an increase in the width of the lines of adhesive means will generally lead to an increase of the force needed to release the adhered surfaces and, for the same adhesive, an increase of the surface weight of the adhesive on the back sheet will generally lead to an increase in the adhesive force. On the other hand, the length of the lines of adhesive means only depend on the length of the surfaces or layer to be attached together and need not affect the attachment force characteristics . Brief description of the drawings: The invention will now be described in more detail with reference to the accompanying drawings in which: Fig.l illustrates a partly cut-away perspective view of a typical disposable sanitary pad in accordance with the invention, prior to use, the back sheet surface intended for placement against the garment being shown uppermost and on which three lines of pressure-sensitive adhesive are indicated, the adhesive lines being protected by a single peelable, protective strip shown in an almost fully removed position; Fig.2 illustrates a cross-sectional view taken on line II-II of the sanitary pad of Fig.l, where the cutaway portion of Fig. 1 has been reinserted so as to show the side connection of the top sheet and back sheet. Description of preferred embodiments: The protection system of the invention preferably comprises a disposable absorbent product 1 such as an incontinence pad, sanitary pad, sanitary napkin, diaper or other . absorbent product for absorbing body exudate. The absorbent product has an absorbent core 2 enveloped between a top sheet or liner 3 (shown lowermost) and a back sheet 4. The absorbent product 1 is shown as being in the form of a generally planar pad, although the pad may be arched. The absorbent core 2 may be made up of any suitable absorbent material known in the art, such as loosely associated absorbent hydrophilic material like cellulose fibres, e.g. wood pulp, regenerated cellulose or cotton fibres, which may be chemically or physically modified. The absorbent element 2 may also include other natural or synthetic materials, such as foams or polymers. The absorbent product 1 may also comprise layers of materials which are fluid permeable or fluid impermeable. The top sheet 3 is a fluid permeable and may be formed of a variety of materials including cellulose, regenerated cellulose, polyester or other synthetic polymers, together with polymeric fibres or films. This is provided on the body-facing side of the absorbent element 2, the sheet 3 being provided for comfort and comformability and directing the fluid to the underlying absorbent element 2. The back sheet 4 normally comprises a fluid impermeable barrier material, and has the purpose of preventing body fluid from passing through the core onto the undergarment of the wearer is provided on the garment-facing side of the absorbent element 2. This barrier may be any polymeric film such as polyethylene, polypropylene, or cellophane or may be a normally fluid-pervious material that has been treated to be impervious, such as a fluid repellent paper. Other fluid impermeable materials are also known in the art. One suitable material for the back sheet 4 is for example a 22μm thick sheet made by Trioplanex International having product reference ME1148. The top sheet 3 and back sheet 4 may be joined together at their peripheries. An adhesive 5 here shown in the form of three lines of adhesive, overlies a portion of the external, garment-facing back sheet 4 for attaching the absorbent product 1 to an undergarment. The adhesive 5 is preferably a pressure sensitive adhesive and which is preferably laminated to the back sheet 4. Pressure sensitive adhesives are preferred due to their ease of use, which in particular allows the absorbent product to be attached to the user' s undergarment and, if the initial replacement is not correct, to be replaced easily in a new position. The material of the adhesion means 5 can be for example any of a large number of pressure-sensitive adhesives that are commercially available, including the cold, pressure- sensitive adhesives such as the acrylate adhesives, generally combined with tackifiers such as polyterpenes, or the rapid-setting thermoplastic adhesives (or hot melt adhesives) such as styrene and butadiene copolymers. Other ingredients such as fillers, antioxidants and pigments may be included. The adhesive 5 may also comprise a double faced adhesive tape or another type of adhesive. It will also be understood that the adhesion means in accordance with the present invention may have various patterns, such as for example spots, squares, single full or intermittent lines or multiple full or intermittent lines, which may be parallel or not. Other patterns are also possible. The surface weight of adhesive disposed on the external, garment-facing surface or layer of the absorbent product 1 may vary, for example in dependence on the specific adhesive used, but will generally be 60 g/m 2 or lower due to commercial requirements and because larger amounts may provide other problems of too high adhesive forces when attached to the user's undergarment. A surface weight of between about 15 and 60 g/m 2 of adhesive will generally be used and a range between 15 and 40 g/m 2 is preferable. The length of the adhesive pattern can be varied according to the length of the final product and does not affect the release force which is necessary for peeling of the release strip 5 from the back sheet 4 to which it is adhered. The adhesive 5 is protected by a peelable, protective strip 6, provided to protect the adhesive during storage and handling prior to use. Such a protective strip may be made of a paper for example that has been treated so as to be readily releasable from the adhesive element, e.g. a paper strip treated with silicone. Such protective strips are well-known in the art and do not require further explanation here . The particular properties of the release force of the protection system (i.e. the release strip releasably attached to the back sheet) can be determined by the measurement of the release force using an Instron 1122, 4301 or 4464 tensile tester connected to a plotter and an integrator and using a 10 N cell. The test procedure is explained below. To ensure accuracy of results, samples must first be stored for at least 24 hours before the test, and maintained during the test, in a climate chamber at 50±5% relative humidity and 23°± 2°C. The tensile tester is first calibrated and then set up for a pulling speed of 500mm/min and a pulling length of 120 mm. The fixing length is adjusted such that the pulling angle between the strip 6 and the back sheet 4 during the test will be 90°, which is maintained due to the movable lower fixture . The absorbent product is then fixed to the tensile tester by way of two metal paper clamps (minimum 50 mm wide clamps, whereby the minimum width is effectively determined by the total width of the adhesive pattern on the tested sample) , which are used to fix the sanitary towel to a flat fixture or sled. The testing equipment is then set to allow 90° measurement in the lower fixture thereof. The release strip is attached to the upper clamp of the tensile tester. If necessary, tape may be used to extend between the tensile tester upper clamp and the release strip. The angle of 90° (i.e. the pulling angle) is then checked. The test is started and the mean adhesion (release force) over a distance of 100 mm is recorded. To avoid the effects of the starting moment, the measurements after the first 10 mm are used and the test is stopped when 10 mm pulling distance remains. The test is repeated on identical samples so as to obtain the required consistency of results and to obtain a mean adhesion value, i.e. a release force value. For the protection system to meet the criteria set forth in the present invention, a value for the release force of between 0.5 and 1 N has to be obtained. This value is an absolute value, which must be present irrespective of parameters like the pattern or width of the adhesive. With the knowledge of this invention, the skilled man will therefore be able to alter the materials, width or other properties of existing products so as to produce a protection system having the required release force characteristics . One example of an absorbent product in the form of a sanitary napkin fulfilling the requirements of peel force of the invention is described below. The sanitary napkin of the example has the general construction of that illustrated in Figs. 1 and 2. The pressure-sensitive adhesive in the example is a hot melt thermoplastic type and consists of a blend of a block copolymer, synthetic resins and plasticisers . It is sold by Collano, Switzerland, under the trade name ECOMELT H145. The surface weight of adhesive disposed on the external, garment-facing surface of the absorbent product is 29 g/m 2 . The adhesive pattern comprises three lines of adhesive 12 mm wide, separated by a 11 mm gap, the total width being 58 mm. The release strip is a paper strip having a width of 64 mm and a surface weight of 48 gm "2 produced by Lohjan Paperi Oy under product code number ESP 48 and the back sheet material is a 22μm thickness material sold by Trioplanex International under product name ME 1148. The measurement of the release force of this protection system has shown that this product corresponds to the criteria set forth in the present invention. However as explained above, the invention is not limited to any particular materials or types of glue, but may be varied within the scope of the appended claims. Thus, although the present invention has been described with reference to a specific product in a specific arrangement and configurations, such is not to be considered limitative of the invention but merely illustrative thereof.

Claims: CLAIMS 1. Protection system for an absorbent product such as an incontinence pad, sanitary pad, sanitary napkin, diaper, or the like, comprising a protective strip (6) releasably adhered by one surface thereof to a back sheet (4) of said absorbent product by means of an adhesive (5), characterized in that the surface weight of adhesive disposed on the back sheet is between 15 and 40 g/m 2 and the force required to release said protective strip (6) from said back sheet (4) is between 0.5 and 1 Newton when measured using a pulling angle of 90°. 2. Protection system according to claim 1, characterized in that said protective strip (6) is made of paper . 3. Protection system according to claim 1, characterized in that said adhesive (5) is a pressure- sensitive adhesive. 4. Protection system according to any one of claims 1 to 3, characterized in that the protective strip (6) is treated with silicone, at least on the surface thereof which is in contact with the adhesive (5) . 5. Protection system according to any one of the preceding claims, characterized in that the protective strip (6) covers at least the entire area of said adhesive (5) on said back sheet (4). 6. Protection system according to any one of the preceding claims, characterized in that the adhesive (5) on the back sheet is arranged as one or more lines of adhesive of a predetermined width.

Inventors: ELGLUND GUNNEL, ESSLE MARIA, JOHANSSON ANETTE, KOPP KJELL-AAKE, ELGLUND, GUNNEL, ESSLE, MARIA, JOHANSSON, ANETTE, KOPP, KJELL-AAKE
Applicants: ELGLUND GUNNEL, ESSLE MARIA, JOHANSSON ANETTE, KOPP KJELL AAKE, SCA HYGIENE PROD AB, ELGLUND, GUNNEL, ESSLE, MARIA, JOHANSSON, ANETTE, KOPP, KJELL-AAKE, SCA HYGIENE PRODUCTS AB
Application year: 1999
Main classification: A61F13
IPC codes: A61F13