ABSORBENT ARTICLE INCORPORATING ADHESIVE THAT LOSES CONTROLLED AMOUNT OF STRENGTH OVER TIME

Abstract: Absorbent articles, such as diapers, sanitary napkins, incontinence products, and the like that incorporate an adhesive that loses a controlled amount of strength over time are described. The adhesive can be applied as an aid in processing, packaging, or otherwise in the production and use of such articles.

Description: ABSORBENT ARTICLE INCORPORATING ADHESIVE THAT LOSES CONTROLLED AMOUNT OF STRENGTH OVER TIME FIELD OF THE INVENTION The present invention relates to absorbent articles such as diapers, sanitary napkins, and incontinence products. More particularly, the present invention relates to absorbent articles of the foregoing type that incorporate an adhesive that loses a controlled amount of strength over time. The adhesive can be useful as an aid in processing, packaging, or otherwise in the production and use of such articles. BACKGROUND OF THE INVENTION Absorbent articles such as sanitary napkins, pantiliners, disposable diapers, incontinence products, and bandages are designed to absorb and retain liquid and other discharges from the human body and to prevent body and clothing soiling. In the manufacturing of absorbent articles, it is often necessary to fold portions of absorbent articles for further processing, or for packaging. One example of folding portions of an absorbent article is described in U.S. Patent 4,701,178 issued to Glaug, et al. The Glaug, et al. patent discloses a sanitary napkin having flaps with adhesive fasteners thereon. A double-sided release strip covers the pressure sensitive adhesive on the garment facing side of the central absorbent element. The flaps are folded over the release strip and the adhesive fasteners on the flaps are releasably adhered to the release strip. Another such example is described in U.S. Patent 5,201,727 issued to Nakanishi, et al. The Nakanishi, et al. patent discloses a sanitary napkin having a pair of "fixing elements" that extend outward from the lateral edges of an absorbent body. The fixing elements are provided with adhesive portions which are able to be adhered to and separated from other adhesive coated portions on the back side of the sanitary napkin. U.S. Patent 5,472,437 issued to .Akiyama, et al. discloses still another example of folding portions of an absorbent article over other portions thereof. The Akiyama patent discloses a sanitary napkin having side flaps. The flaps each have a flap adhesive fastener and a release portion disposed thereon. The flaps are folded along a folding line so that the release portion covers the adhesive fasteners on the flaps and is separable therefrom. However, in each of these examples, the flaps (or "fixing elements") are provided with pressure sensitive adhesive fasteners thereon that are intended for later use when the absorbent article is worn. A need exists for a method of folding and temporarily retaining portions of an absorbent article that do not have a pressure sensitive adhesive thereon. For instance, U.S. Patent 5,558,663 issued to Weinberger, et al. on September 24, 1996, discloses a sanitary napkin having undergarment covering components that extend laterally outward beyond the side edges of the main body portion of the sanitary napkin. In one embodiment of that sanitary napkin, the undergarment covering components may not have a pressure sensitive adhesive fastener thereon. In the processing and packaging of such an absorbent article, it is desirable to fold the undergarment covering components over the garment-facing side of the main body portion. This will avoid damage to the undergarment covering components during processing and packaging and form a smaller, more conveniently packaged article. The garment-facing side of the main body portion typically has a pressure sensitive adhesive thereon, which is covered with a sheet of release paper to prevent the adhesive from sticking to surfaces other than the wearer's undergarments prior to use. Thus, in folding the undergarment covering components over the garment-facing side of the main body portion, the undergarment covering components will be folded over the release wrapper. In order to fold the undergarment covering components over the sheet of release paper, and have the undergarment covering components stay folded, it is desirable during manufacture to temporarily adhere the undergarment covering components (which in such a case would be devoid of pressure sensitive adhesive fasteners) to the exposed outside surface of the release paper. The adherence of the undergarment covering components to the release paper should satisfy several requirements. First, the adherence should be sufficiently temporary so that the undergarment covering components will unfold or be capable of readily unfolding for use by the consumer. In this regard, it is often only necessary for the adherence to be present for fifteen minutes or less. This is the case if the absorbent article will move to a place in the manufacturing process where the undergarment covering components are maintained in a folded configuration, such as by placing the absorbent article into individual packages or grouped packages which maintain the undergarment covering components in a folded configuration. Second, the adhesive should release so that the undergarment covering components will automatically unfold when the package is opened, or the undergarment covering components should be capable of being readily separated from the release paper when the release paper is removed. Third, when the undergarment covering components are unfolded, the adherence should not damage either the undergarment covering components or the release paper. Pressure sensitive adhesives described in the patents discussed above would not lose a controlled amount of strength over the desired relatively short time periods of interest. It is typically undesirable for adhesives to lose strength. If current pressure sensitive adhesives do lose a portion of their strength, this would typically not be their shear strength. .Any loss of strength would generally take several weeks to several months to occur, and will often occur only when the adhesives are exposed to extreme temperatures (e.g. temperatures in excess of about 60°C). Further, adding a pressure sensitive adhesive patch and complementary release coating to an absorbent article would add unnecessary expense to the absorbent article over and above the cost of a small spot of adhesive that is actually necessary to hold the undergarment covering components in a folded configuration. Temporary adhesives known as "fugitive" adhesives are known. These adhesives have been used most often to create temporary paper-to-paper bonds. When the adhesive bond is broken, such adhesives are no longer tacky and will not adhere to anything. These temporary adhesives have been used primarily for envelopes, labels, and the like. To the applicants' knowledge, "fugitive adhesives are not known in the art for forming a temporary bond on an absorbent article. This is due to the difference in materials used in absorbent articles (which typically include at least some polymeric materials as opposed to only paper), and to the forces which tend to make the folded portions unfold if the folded portions were adequately restrained from doing so. Known fugitive adhesives typically do not form a strong enough initial bond to make them capable of temporarily holding folded portions of absorbent articles in place during a high speed manufacturing process where the folded portions of the absorbent articles could come in contact with other objects in the manufacturing process. Additionally, there are, to applicant's knowledge, no adhesives that can form a relatively strong temporary bond and lose a controlled amount of strength over a selected time period so that the undergarment covering components would be capable of readily unfolding. There are also a number of drawbacks associated with known types of fugitive adhesives. First, adhesives generally have a peel strength component and a shear strength component. Most conventional fugitive adhesives do not lose strength, either in peel or shear. Conventional fugitive adhesives operate by having a low peel strength. In order to securely hold the folded portions of an absorbent article, an adhesive must have a higher initial shear strength. To release the folded portions, both shear and peel strengths, and in particular, shear strength, must be greatly diminished from the initial strengths. In addition, if fugitive adhesives lose strength, they frequently require active heating, radiation, or the like to reduce their strength, all of which are impractical for use with absorbent articles. Others are solvent cross-linked materials that are not suitable for use in absorbent articles. Further, water-based fugitive adhesives used in labeling and envelope applications have relatively low bond strengths when wet (that is, when applied). This may be sufficient for use in bonding paper to paper. It is not, however, sufficient for bonding polymeric to paper materials as is necessary in the applications described herein. Therefore, it is an object of the present invention to provide an absorbent article that has portions, such as undergarment covering components, that can be folded over another portion of the absorbent article, and maintained in a folded configuration for a finite period of time during processing and/or packaging. It is another object of the present invention to provide an absorbent article that has portions, such as undergarment covering components, that are only temporarily adhered to the underlying portion of the absorbent article. It is another object of the present invention to provide an absorbent article that has portions, such as undergarment covering components, that when unfolded, will not damage the underlying portion of the absorbent article, or the undergarment covering component. These and other objects of the present invention will be more readily apparent when considered in reference to the following description and when taken in conjunction with the accompanying drawings. SUMMARY OF THE INVENTION The present invention relates to absorbent articles such as diapers, sanitary napkins, and incontinence products. More particularly, the present invention relates to absorbent articles of the foregoing type that incorporate an adhesive that loses a controlled amount of strength over time (or "temporary strength adhesive"). The adhesive can be useful as an aid in processing, packaging, or otherwise in the production and use of such articles. In one preferred embodiment, the adhesive that loses a controlled amount of strength over time is used on an absorbent article comprising a main body portion and at least one side wrapping element (or "undergarment covering component") extending laterally outward from the main body portion. The main body portion has a body-facing side, a garment-facing side, and an absorbent core positioned between its body-facing side and its garment-facing side. The garment-facing side of the main body portion preferably has an adhesive fastener thereon which is covered by a cover strip. In this embodiment, at least one of the side wrapping elements is temporarily adhered to the cover strip with the temporary strength adhesive. The temporary strength adhesive forms an initially relatively strong bond, and then loses a controlled amount of strength over time so that the side wrapping elements are readily separable from the cover strip on garment-facing side of the main body portion for use. In another embodiment, the temporary strength adhesive can be used to hold the side panels or flaps of a disposable diaper over the chassis assembly (or main body portion) of the diaper for packaging. Numerous other uses of the present invention are also possible. The present invention is also directed to a method of temporarily joining a first component to a second component during a process of making or packaging an absorbent article. In one preferred embodiment, the invention provides a method of folding and retaining a side panel during a process of making or packaging a disposable absorbent article. The term "side panel", as used herein, may include a side wrapping element as described above, a flap, or the portions of a disposable diaper that extend laterally from the end regions of the diaper to form part of a waistband. In this embodiment, the method preferably comprises the steps of: (a) providing an absorbent article comprising a main body portion having a body-facing side, a garment side, an absorbent component between the body-facing side and the garment side, a principal longitudinal centerline, a principal transverse centerline, and two spaced apart longitudinal edges, and a side panel joined to the main body portion of the absorbent article and extending laterally outward beyond at least one of the longitudinal edges; (b) applying an adhesive that loses a controlled amount of strength over time to at least one of the following: the side panel, to a portion of the main body portion of the absorbent article, or to a component joined to the absorbent article that the side panel will come into contact with when folded; (c) folding the side panel about at least one fold line to foπn a folded side panel so that the side panel will contact the portion of the absorbent article or component joined to the absorbent article that it is folded over, and so that the adhesive that loses a controlled amount of strength over time is therebetween; and (d) compressing the folded side panel. BRIEF DESCRIPTION OF THE DRAWINGS While the specification concludes with claims particularly pointing out and distinctly claiming the subject matter which is regarded as forming the present invention, it is believed that the invention will be better understood from the following description which is taken in conjunction with the accompanying drawings in which: Fig. 1 is a top plan view of a preferred embodiment of a sanitary napkin that uses the present invention. Fig. 2 is an end view of the sanitary napkin shown in Fig. 1 with one of the undergarment covering components folded to overlie the garment-facing side of the main body portion, which is temporarily retained thereon by the adhesive described herein. Fig. 3 is a bottom plan view of the sanitary napkin shown in Figs. 1 and 2 with both of the undergarment covering components folded to overlie the garment- facing side of the main body portion. FIG. 4 is a schematic plan view of the garment-facing side of a diaper that can have its side panels temporarily retained using a temporary strength adhesive according to the present invention. DETaAILED DESCRIPTION OF THE INVENTION The present invention relates to absorbent articles such as diapers, sanitary napkins, and incontinence products. More particularly, the present invention relates to absorbent articles of the foregoing type that incorporate an adhesive that loses a controlled amount of strength over time (or "temporary strength adhesive"). The adhesive can be useful as an aid in processing, packaging, or otherwise in the production and use of such articles. FIGS. 1-3 show one preferred embodiment of a disposable absorbent article that uses the present invention, sanitary napkin 20. In the preferred embodiment shown in the drawings, the sanitary napkin has a pair of side wrapping elements. The sanitary napkin can be constructed generally in accordance with, or can comprise any of the features described in U.S. Patent 5,558,663 issued to Weinberger, et al. and U.S. patent application Serial No. 08/493,515 entitled "Absorbent Articles Having Undergarment Covering Components Especially Suited For Folding Around The Edges of an Undergarment" filed on June 22, 1995, in the name of Redwine, et al. (PCT Publication No. WO 97/00655 published on January 9, 1997). The sanitary napkin 20, or other absorbent article, however, can be in any suitable configuration, and is not limited to absorbent articles of the type or having the specific configuration shown in the drawings. The sanitary napkin 20 has two surfaces, a liquid pervious body-contacting surface or "body surface" 20 A and a liquid impervious garment surface 20B. The sanitary napkin 20 is shown in FIG. 1 as viewed from its body surface 20A. The body surface 20A is intended to be worn adjacent to the body of the wearer. The garment surface 20B of the sanitary napkin 20 (shown in FIG. 2) is on the opposite side and is intended to be placed adjacent to the wearer's undergarments when the sanitary napkin 20 is worn. The sanitary napkin 20 has two centerlines, a longitudinal centerline L and a transverse centerline T. The term "longitudinal", as used herein, refers to a line, axis or direction in the plane of the sanitary napkin 20 that is generally aligned with (e.g., approximately parallel to) a vertical plane which bisects a standing wearer into left and right body halves when the sanitary napkin 20 is worn. The terms "transverse" or "lateral" used herein, are interchangeable, and refer to a line, axis or direction which lies within the plane of the sanitary napkin 20 that is generally perpendicular to the longitudinal direction. FIG. 1 shows that the main body portion 21 of the sanitary napkin 20 comprises the portion of the sanitary napkin without the side wrapping elements. The main body portion 21 has two spaced apart longitudinal edges 22, two spaced apart transverse or end edges (or "ends") 24, which together form the periphery 26 of the main body portion. The main body portion also has two end regions, which are designated first end region 28 and second end region 30. A central region 32 is disposed between the end regions 28 and 30. The end regions 28 and 30 extend outwardly from the edges of the central region 32 about 1/8 to about 1/3 of the length of the main body portion. A detailed description of a sanitary napkin having a central region and the two end regions is contained in U.S. Patent 4,690,680 issued to Higgins on September 1, 1987. FIG. 2 shows the individual components of the main body portion 21 of the sanitary napkin 20. The main body portion 21 of the sanitary napkin preferably comprises at least three primary components. These include a liquid pervious topsheet 38, a liquid impervious backsheet 40, and an absorbent core 42 positioned between the topsheet 38 and the backsheet 40. The liquid pervious topsheet, the liquid impervious backsheet, and the absorbent core can comprise any materials described as being suitable for these components in the patents incorporated by reference herein. Typically, the topsheet 38 and backsheet 40 will comprise a polymeric material, which may be a fibrous material, or a film. A particularly preferred apertured film for use as the topsheet is described in U.S. Patent 4,342,314 issued to Radel, et al. on August 3, 1982, and U.S. Patent 4,463,045 issued to Ahr, et al. on July 31, 1984. The backsheet 40 preferably comprises a polyethylene film. The garment surface 20B of the sanitary napkin 20 may include, and preferably does include, fasteners for attaching the sanitary napkin to the wearer's undergarment. Figure 3 shows the central pad fastener 44 which is adapted to secure the portion of the sanitary napkin underlying the main body portion 21 to the crotch region of an undergarment. Any types of fasteners known in the art can be used. Fasteners comprising adhesives have been found to work well for this purpose, with pressure-sensitive adhesives being preferred. Before the sanitary napkin 20 is placed in use, if an adhesive fastener is used, the adhesive is typically covered with a removable cover strip or release liner (or "release paper") 46 in order to keep the adhesive 44 from sticking to a surface other than the crotch portion of the panty prior to use. The term "release paper", as used herein, refers to any material that is suitable for serving as a removable cover for the adhesive fastener. The term "release paper" is, therefore, not limited to strips of paper, but may also comprise films, and the like. The release paper 46 has an inside surface 46A that is placed adjacent to the central pad fastener 44, and an exposed outside surface 46B. Suitable release papers are described in the U.S. Patent 4,917,697. The sanitary napkin 20 comprises a pair of undergarment covering components (or "side wrapping elements") 50 that extend laterally outward beyond the longitudinal side edges 22 of the main body portion 21 from their proximal edges 52 to their distal edges 54. The side wrapping elements 50 extend outward at least from the central region 32 of the main body portion 21. When the sanitary napkin 20 is in use, the side wrapping elements 50 preferably automatically wrap around the side edges of the wearer's undergarments to keep the undergarments free from being soiled with body fluids. In the preferred embodiment shown in the drawings, the side wrapping elements 50 comprise an extension of the topsheet 38 and backsheet 40. In such a case, the body facing surface of the side wrapping elements 50 will comprise an apertured polymeric film, and the undergarment facing side will comprise a polyethylene film. In the preferred embodiment shown in the drawings, the side wrapping elements 50 can, as discussed above, be provided with features described in U.S. Patent 5,558,663 issued to Weinberger, et al. and U.S. patent application Serial No. 08/493,515 filed on June 22, 1995 (PCT Publication No. WO 97/00655 published in the name of Redwine, et al. on January 9, 1997). Preferably, the side wrapping elements 50 comprise a pair of spaced apart zones of extensibility 56 and a stiffened intermediate region 58 between the zones of extensibility. The side wrapping elements 50 are preferably also provided with a hinge 68. The hinge 68 is preferably formed by forming a strainable network region in the desired regions of the side wrapping elements 50. Suitable methods of forming a strainable network region into a material are described in U.S. Patent 5,518,801 issued to Chappell, et al. on May 21, 1996. In the manufacture of the sanitary napkin 20 shown in the drawings, it is desirable to fold the side wrapping elements 50 over the garment-facing side 20B of the main body portion 21. This avoids damage to the side wrapping elements 50 during processing and forms a smaller, more conveniently packaged article. In order to fold the side wrapping elements 50 over the garment-facing side of the main body portion, and have the side wrapping elements 50 stay folded, it is desirable to adhere the side wrapping elements 50 to the exposed outside surface 46B of the release paper 46. However, it may only be necessary for the adherence to be present for a relatively short period of time (e.g., fifteen minutes or less). This is the case if, after applying the adhesive, the absorbent article will move to a place in the manufacturing process where the side wrapping elements 50 are maintained in a folded configuration, such as by placing the absorbent article into individual packages or grouped packages which maintain the side wrapping elements 50 in a folded configuration. To accomplish this, the side wrapping elements 50 are temporarily adhered to the outside surface 46B of the release paper 46 by an adhesive, temporary strength adhesive 70 that loses a controlled amount of strength over time. The adherence of the side wrapping elements 50 to the release paper 46 should satisfy several requirements. First, the adherence should be temporary so that the side wrapping elements 50 will readily unfold or be capable of readily unfolding for use by the consumer. Second, the adhesive should release so that the undergarment covering components automatically unfold when the package is opened, or they should be capable of being readily separated from the release paper when the release paper is removed. Third, when the side wrapping elements 50 are unfolded, the adherence should not be so strong that the unfolding of the side wrapping elements damages the side wrapping elements 50 or the release paper 46. The bond formed by the temporary strength adhesive 70 is measured in terms of shear strength and peel strength in two directions. These are a direction parallel to the fold line where the side wrapping elements 50 are folded, and a direction perpendicular to this fold line. In forming the sanitary napkin 20 shown in the drawings, these directions correspond to the direction that the absorbent article moves through the manufacturing process (the "machine direction" or MD) and the direction perpendicular to the machine direction, the cross-machine direction (or CD), respectively. That is, the machine direction runs in the direction of the longitudinal centerline L of the sanitary napkin, and the cross-machine direction is oriented in the direction of the transverse centerline, T. Of course, in other types of manufacturing operations, these directions may be reversed so the sanitary napkin is running in the direction of the transverse centerline. If this is the case, the MD and CD adhesive strength values specified herein will be reversed. When used to secure the side wrapping elements 50 to the release paper 46 on the garment-facing side 20B of a sanitary napkin 20 as shown in the drawings, the adhesive preferably has an initial machine direction (MD) shear strength of greater than or equal to about 200 grams, more preferably greater than or equal to about 275 grams, and an initial machine direction peel strength of greater than or equal to about 15 grams, more preferably greater than or equal to about 25 grams. The adhesive preferably has an initial cross-machine direction (CD) shear strength of greater than or equal to about 500 grams, more preferably greater than or equal to about 750 grams, and an initial cross-machine direction peel strength of about greater than or equal to about 50 grams, more preferably greater than or equal to about 75 grams. The initial adhesive strength in the cross-machine direction is preferably greater in this embodiment because that is the direction that most of the forces are acting that would tend to unfold the side wrapping elements 50 in the absence of the temporary strength adhesive. The term "initial", as used herein, refers to the point in time at which the temporary strength adhesive is first used to secure the two components or portions of the absorbent article together. These initial bond strengths are needed for up to about 5-10 minutes so that the side wrapping elements 50 can be held in place if the manufacturing line should undergo a temporary shut down. The initial bond strengths needed will, of course, be somewhat dependent on the nature of the materials that are to be temporarily secured, as well as any forces that would tend to unfold the side wrapping elements 50 in the absence of the temporary strength adhesive. The initial bond strength should decay to a second lower bond strength by the time the absorbent article is used by the consumer. The time at which the second lower bond strength occurs may, thus, be referred to as the final bond strength (or the "delivered strength", or as the "consumer bond strength", or simply "consumer strength"). The products will generally take at least 14 days, and more often over 20 days to reach the consumer. For laboratory testing of the strength of the temporary strength adhesive, a shorter period, such as after about five days from the formation of the "initial" bond, can be used. This latter bond strength may, therefore, be referred to as a "five day (or "5 day") bond strength". The five day bond strength should be sufficiently low that the side wrapping elements can be unadhered and deployed without tearing the release paper or the side wrapping elements. The adhesive should meet these needs throughout the typical temperature/humidity conditions encountered during shipment and storage of the sanitary napkin. In the embodiment shown in the drawings, both the consumer bond strength and the five day bond strength preferably comprise a machine direction shear strength of less than or equal to 100 grams, more preferably less than or equal to about 65 grams, and a machine direction peel strength of less than or equal to about 25 grams, more preferably less than or equal to about 15 grams. The machine direction consumer and five day bond strength are of interest because the release paper 46 is removed by peeling it away in the longitudinal direction. Ideally, for the embodiment shown in the drawings, after five days the initial bond strength will preferably decay completely so that the value of all the specified components of the bond strength (in both MD and CD) will be zero. The lower consumer or five day bond strengths specified above are preferably maintained at the elevated temperatures associated with shipping and storage (e.g., about 140°F (about 60°C)). (Bond strengths will often increase when the adhesive becomes hotter due to a wetting (that is spreading and penetrating) of the adhesive.) One suitable adhesive having these strength characteristics is Fuller HL 1629X obtained from H. B. Fuller Company of St. Paul, MN. The Fuller adhesive was developed at the direction of The Procter & Gamble Company for the purposes described herein. Without wishing to be bound by any particular theory, it is believed that the temporary strength adhesive can operate in at least one of the following manners. The temporary strength adhesive may utilize a delayed crystallization which causes the molecules within the adhesive to come together over a relatively short time period. This causes the adhesive to dry out and take a more solid form. This results in the adhesive losing most or all of its bonding capability. .Alternatively or additionally, a "poison" can be added to the adhesive to cause the adhesive to lose most or all of its bonding capability. The poison can be used to disrupt the adhesion properties of the adhesive (that is, the stickiness) over time, such as by interfering with the chemical bonding (hydrogen bonding, covalent bonding, or Van der Waals forces) or physical bonding between the adhesive and the surfaces to which it is temporarily attached. The decay of the adhesive properties of the temporary strength adhesive differs from any decay in adhesive properties that might occur over time in known adhesives. First, the temporary strength adhesive can have relatively high initial bond strengths, such as a machine direction shear strength of about 275 grams, which can be pre-established or designed to decay to less than or equal to about 65 grams (a decay or loss of about 76% of its original strength). Known adhesives do not have such a dramatic reduction in bond strength, particularly shear strength, over the time periods specified herein. In known adhesives, any decay of strength is generally undesirable, and is therefore, not pre-established. The temporary strength adhesive used herein also differs from known types of fugitive adhesives. Most conventional fugitive adhesives do not lose strength, either in peel or shear. Conventional fugitive adhesives operate by having a low peel strength. In order to hold the folded portions of an absorbent article, an adhesive must have a higher initial shear strength. To release the folded portions, both shear and peel strengths, and in particular, shear strength, must be greatly diminished from the initial strengths. In addition, if fugitive adhesives lose strength, they frequently require active heating, radiation, or the like to reduce the strength, all of which are impractical for use with absorbent articles. Others are solvent cross-linked materials that are not suitable for use in absorbent articles. Further, water-based adhesives used in fugitive adhesives in labeling and envelope applications have relatively low bond strengths when wet (that is, when applied). This may be sufficient for use in bonding paper to paper. It is not, however, sufficient for bonding polymeric to paper materials as is necessary in the applications described herein. The temporary strength adhesives described herein may have a decay in any amount that is suitable for the particular purpose. Suitable decays might involve a loss of greater than or equal to about any of the following amounts of its initial strength (or any component of its initial strength, such as shear strength and/or peel strength): 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, or 100% over the time periods described herein. The method of the present invention is carried out as follows. In the preferred embodiment shown in the drawings, during manufacture, a sanitary napkin in the form of FIG. 1 will generally be traveling on a conveyor in the machine direction with its longitudinal centerline, L, oriented in the machine direction. The sanitary napkin 20 will preferably be oriented with its garment-facing side 20B facing upward. The release paper 46 will have already been applied over the central pad fastener 44. The temporary strength adhesive 70 can be applied to the main body portion 21 of the absorbent article 20, to the side wrapping elements 50, or to a component joined to the absorbent article 20 that the side wrapping elements 50 will come into contact with when folded. The temporary strength adhesive 70 is preferably applied to the outwardly facing side 46B of the release paper 46. The temporary strength adhesive 70 can be applied in any shape, and in any amount suitable for temporarily adhering the side wrapping elements 50 to the release paper 46. Typically, the sanitary napkin 20 will be traveling rapidly along on the conveyor, so the application of a circular spot of adhesive may take a tear drop shape (or in the shape of an oval with a "tail" thereon). In this case, the amount of temporary strength adhesive 70 applied to hold each side wrapping element 50 is preferably in the range of between about 0.002 grams to about 0.015 grams, and more preferably is in the range of between about 0.005 grams to about 0.010 grams. This will result in adhesive covering an area about 2-5 mm wide and about 6-12 mm long. The temporary strength adhesive 70 is applied so that one spot of adhesive will lie under each of the side wrapping elements 50 when they are folded over the release paper 46. The side wrapping elements 50 are then folded over the release paper 46. .Any conventional folding means, such as folding plows, can be used for this purpose. Each of the folded side wrapping elements 50 then passes between a compression mechanism, such as a pair of belts, rolls, or other means of compression. The compression mechanism applies enough pressure on the folded side wrapping elements 50 to ensure that the temporary strength adhesive 70 holds the same in a folded configuration, but not enough pressure to undesirably compress the absorbent core 42 of the sanitary napkin 20. Preferably, after the sanitary napkins pass through the compression mechanism, they move to a packaging station where they are packaged into individual packages. In a preferred embodiment of the method described herein, the sanitary napkins are tri-folded about transversely oriented axes so that one end region, such as the first end region 28, of the sanitary napkin is folded over the body-facing side of main body portion, and the other end region 30 is folded over the first end region 28. Suitable ways of folding sanitary napkins and individual packages for the same are described in U.S. Patent 4,556,146 issued to Swanson, et al.; U.S. Patent 5,181,610 issued to Quick; U.S. Patent 5,462,166 issued to Minton, et al.; and U.S. Patent 5,484,636 issued to Berg, et al. If the sanitary napkin 20 is individually packaged in a package like that described in U.S. Patent 4,556,146, Swanson, et al., there are two main ways this can be done. The sanitary napkin 20 can have a separate wrapper (from the release paper 46). In such a case, the wrapper that is used to form the package for the sanitary napkin can be adhesively joined to a portion of the release paper 46. If this type of embodiment is used, the side wrapping elements 50 will be temporarily adhered to the release paper 46 as described above. The wrapper can then be joined to those portions of the release paper 46 that are not covered by the side wrapping elements 50. The sanitary napkin 20, release paper 46, and wrapper can then be tri-folded as a unit. .Alternatively, a single sheet could be used to serve both the functions of the release paper and the wrapper. In the latter case, the panty fastening adhesive 44 will typically be configured so that the side wrapping elements 50 do not contact the panty fastening adhesive 44. The side wrapping elements 50 can then be folded directly over and adhered to the backsheet 40 of the sanitary napkin 20 with the temporary strength adhesive 70. The releasable wrapper 46 can then be applied over the folded side wrapping elements 50 to cover the exposed panty fastening adhesive 44. The sanitary napkin 20 and the release paper 46 can then be tri-folded as a unit to form the package. The sanitary napkin 20 of the present invention is used by opening any individual package and removing the sanitary napkin. Ideally, if the temporary strength adhesive bond strength is low enough, the side wrapping elements 50 will automatically unfold. If the temporary strength adhesive retains some strength, the side wrapping elements 50 can be unfolded by the user by peeling off the release paper 46 to unfold the side wrapping elements 50. The user will then place the sanitary napkin 20 in her panties so that the adhesive (or other fastener) 44 contacts the panty and maintains the sanitary napkin in position within the panty during use. The side wrapping elements 50 automatically wrap around the sides of the wearer's panties by the simple action of the wearer pulling up her panties. The use of the temporary strength adhesive 70 provides a number of advantages. These include, but are not limited to the following. First, the temporary strength adhesive 70 provides a mechanism for holding the side wrapping elements 50 in the desired position for packaging when no separate adhesive fastener is placed on the side wrapping elements 50. Second, the use of a temporary strength adhesive 70 requires fewer steps, and is believed to be less expensive than utilizing a pressure sensitive adhesive fastener on the side wrapping elements in conjunction with a mating release coating for the pressure sensitive adhesive. For example, in the embodiment shown in the drawings, the amount of temporary strength adhesive 70 used need only cover an area of about 20 mm- * - * to about 30 mm-2, whereas typical pressure sensitive adhesives used on conventional sanitary napkin flaps to secure the flaps in place may range in size from patches about 15 mm x 30 mm to about 15 mm x 60 mm (or about 450 mm-2 to about 900 mm-2). Further, the temporary strength adhesive 70 does not require applying a releasably bondable material to the underlying surface or release coating the underlying surface. The use of the temporary strength adhesive 70 differs from prior releasable adhesive systems in a number of respects. These include, but are not limited to, the following. As discussed in the preceding paragraph, there is no need for the underlying surface to be releasable — the release mechanism is contained entirely within the temporary strength adhesive. In addition, after the side wrapping elements 50 unfold, the temporary strength adhesive 70 need not be, and preferably is not tacky as are pressure sensitive adhesives. As a result, there is no potential problem with the temporary strength adhesive 70 undesirably sticking to a wearer's skin. The temporary strength adhesive 70- used in the present invention differs from the fugitive adhesives used in envelopes (and the like) in that it is substantially stronger in initial strength than that used to merely hold two sheets of paper (as opposed to plastic to paper) together. Typically, such sheets of paper bonded with known types of fugitive adhesive are not subject to significant forces acting to separate them during production as are the portions of the absorbent article in the present invention. In alternative embodiments, rather than being provided with side wrapping elements as described above, the sanitary napkin 20 can be provided with side flaps. The flaps can be in any suitable configuration. Suitable flaps are described in U.S. Patent No. Bl 4,589,876 entitled "Sanitary Napkin", issued to Van Tilburg, Certificate of Reexamination issued April 27, 1993; U.S. Patent 4,687,478 entitled "Shaped Sanitary Napkin With Flaps", which issued to Van Tilburg on August 18, 1987; U.S. Patent 5,389,094 entitled "Absorbent Article Having Flaps and Zones of Differential Extensibility" issued to Lavash, et al. on February 14, 1995; and in International Patent Application Serial No. PCT US 96/15957 entitled "Absorbent Article Having Flaps With Step Configuration and Zones of Extensibility" filed on October 3, 1996, in the name of Lash, et al. The use of temporary strength adhesive 70 according to the present invention is not limited to use with sanitary napkins. For example, FIG. 4 shows one preferred embodiment of a diaper that can have its side panels maintained in a folded condition using the temporary strength adhesive described herein. The diaper 520 shown in FIG. 4 has a generally "T-shape". The diaper 520 comprises a chassis assembly 522 that preferably comprises a liquid pervious topsheet 524, a liquid impervious backsheet 526 joined with the topsheet 524, an absorbent core 528 positioned between the topsheet 524 and the backsheet 526. The diaper further comprises extensible leg cuffs 530 each comprising a leg flap panel 531 and one or more elastic members, and elastic strands 554, operatively joined with the leg flap panel 531. In addition, the diaper 520 preferably comprises an extensible back waist feature 532 comprising a central waistband panel 534, a pair of side panels 536, and a hip panel 538. The diaper 520 also comprises a closure system for fastening the diaper on the wearer preferably comprising at least a pair of tape tabs 540 and a landing member preferably comprising a reinforcing strip 541; and an extensible front waist feature 542 comprising a front waist panel 543. The side panels 536 of the back waist feature preferably comprise a structural elastic-like film web. The diaper 520 shown in FIG. 4 is described in greater detail in U.S. Patent 5,569,232 entitled "Absorbent Article With Multiple Zone Structural Elastic-Like Film Web Extensible Waist Feature", issued to Roe, et al. on October 29, 1996. In the case of the diaper 520 shown in FIG. 4, the side panels 536 are preferably folded inward toward the longitudinal centerline L over the topsheet 524 in the direction of the arrows. In addition to sanitary napkins and diapers, other types of absorbent articles could be provided with side panels or flaps that are retained by the method of the present invention. Suitable absorbent articles, at least some of which are in the form of adult incontinence products that could be provided with side panels or flaps that are folded by the method of the present invention, are described in U.S. Patents 5,300,054 issued to Feist, et al. on April 5, 1994, and 5,304,161 issued to Noel, et al. on April 19, 1994. It should be understood, that while the terms "flaps" and "side panels" have been used interchangeably herein, that this is only in the context of the method of the present invention, and it is expressly not admitted that such portions of these different types of absorbent articles are equivalent in terms of structure or function when in use. It should also be understood that the present invention can involve the use of temporary strength adhesives in many different contexts for temporarily securing one portion or element to another portion or element of an absorbent article. These include, but are not limited to, temporarily securing such portions: in an absorbent article, in a method of making an absorbent article, and/or in a package for an absorbent article. The elements of the absorbent article that are temporarily secured may comprise separate components of the absorbent article, or a component of the absorbent article and a component of another article, such as a package for the absorbent article. Alternatively, the elements of the absorbent article that are temporarily secured can be separate portions of a single component of the absorbent article. To include all such possibilities, the present invention may be described in terms of temporarily securing a "first portion" of an absorbent article to a "second portion". In the sanitary napkin illustrated in the drawings, the first portion could be the side wrapping elements, and the second portion could be the release paper. Other examples where this type of adhesion can be used are in situations where an elastic member could be held in an extended condition when the absorbent article is made, but then retracted for use after the strength of the adhesive decays. Absorbent articles that employ mechanisms that could be adapted to utilize a temporary strength adhesive are described in U.S. Patent 5,259,902 entitled "Method for Continuously Attaching Tensioned Elastic Material to an Absorbent Article" issued to Muckenfuhs on November 9, 1993 and U.S. Patent 5,295,988 entitled "Individually Wrapped Disposable Absorbent Article Which Becomes Elasticized When Unwrapped" issued to Muckenfuhs, et al. on March 22, 1994. Another non-limiting example of a use for the temporary strength adhesive is in the interior of an absorbent article for decoupling of various components of the absorbent article. For example, some types of absorbent articles are designed to be expandable. These include the absorbent articles described in U.S. Patent 5,558,656 entitled "Sanitary Napkin Having an Internal Shaping Component" issued to Bergman on September 24, 1996 and U.S. Patent 5,591,148 entitled "Sanitary Napkin Having an Independently Displaceable Central Core Segment" issued to McFall, et al. on January 7, 1997. The temporary strength adhesive could be used to hold the components of the absorbent article relatively flat for packaging, then the temporary strength adhesive could lose strength and allow the absorbent article to expand for use. The disclosures of all patents, patent applications (and any patents which issue thereon, as well as any corresponding published foreign patent applications), and publications mentioned throughout this patent application are hereby incorporated by reference herein. It is expressly not admitted, however, that any of the documents incorporated by reference herein teach or disclose the present invention. It is also expressly not admitted that any of the commercially available materials or products described herein teach or disclose the present invention. TEST METHODS Equipment Scissors Constant Rate of Elongation Tensile Tester, such as the EME 599 tensile testing machine obtained from EME, Inc., P.O. Box 187, Newbury, OH, or an Instron Model 1122 tensile testing machine available from the Instron Engineering Corporation of Canton, Mass. Steps 1. Equipment Preparation • Calibrate the tensile tester according to the manufacturer's instructions. • Set the instrument crosshead to operate at 20 inches/minute (50.8 cm/min.). • Set the gauge length to 1 inch (2.54 cm). The jaws must be a light duty type, at least as wide as the samples. • On the recorder of the electronic tensile tester, set the chart speed to 10 inches/minute (25.4 cm/min.). 2. Sample Preparation Note: .All of the following steps of the sample preparation should be performed without disturbing the adhesive bond in any way. SHEAR ADHESION • cut a rectangular sample out of the absorbent article; the sample must include the two components (or the two portions of the absorbent article) having their surfaces joined by the temporary strength adhesive; in cutting the sample, care should be taken to include all the temporary strength adhesive (at this point, the sample can include absorbent material). • the dimensions of the sample should be great enough that when the trimmed sample is oriented in the tensile testing machine in the direction desired to be tested, it will span the one inch (2.54 cm) gauge length between the jaws of the tensile testing machine. • trim away all material other than the two components (or two portions) of the absorbent article that have their surfaces joined by the temporary strength adhesive (e.g., if the portions of the absorbent article joined by the temporary strength adhesive are the side wrapping element and release paper, trim away absorbent material to leave only the side wrapping element and release paper). • cut the first component at one end of the trimmed sample (e.g., the side wrapping element) so the second component (e.g., the release paper) extends outward beyond the first component (e.g., the side wrapping element) at that end to provide an extending end for gripping in the tensile testing machine. • trim the second component at one end of the trimmed sample (e.g., the release paper) so the first component (e.g., the side wrapping element) extends outward beyond the second component (e.g., the release paper) at that end to provide another extending end for gripping in the tensile testing machine. PEEL ADHESION ("T-PEEL" • cut a sample out of the absorbent article following the first three (3) steps listed above in the sample preparation for the Shear Adhesion test. • the sample should be cut so that it is long enough in the dimension that will be tested to allow an extension of the first component or portion and the second component or portion beyond the ends of the temporary strength adhesive on the same side (when viewing the sample in plan view) of the temporary strength adhesive to be separated, folded back (as described below), and fit between the jaws of the tensile testing machine. • fold the first component (e.g., the side wrapping element) away from the second component (e.g., the release paper) at 180 degrees to enable placement of the free end of the first component between one set of jaws of the tensile testing machine and the free end of the second component between the opposing jaw of the tensile testing machine without inflicting force against the bond. 3. Test Procedure SHEaA l ADHESION • Insert the extending end of the first component or portion of the sample (e.g., the side wrapping element) in the upper, moving jaw of the tensile testing machine and the extending end of the second component or portion (e.g., the release paper) into the stationary jaw of the tensile testing machine (these extending ends of first and second components were on opposite sides of the adhesive when viewing the absorbent article in plan view), with a minimal amount of slack in the sample (but no initial tension). Align the sample so that the adhesive is midway between the upper and lower jaws (vertically and horizontally). • Start the crosshead moving. • Record the maximum force (grams) required to break the adhesive bond. • Return the crosshead to its original starting position and remove the separated strips from the jaws. PEEL ADHESION • Insert the extending end of the first component or portion of the sample (e.g., the side wrapping element) in the upper, moving jaw of the tensile testing machine and the extending end of the second component or portion (e.g., the release paper) into the stationary jaw (the extending ends of first and second components were on the same side of the adhesive when viewing the absorbent article in plan view). Align the sample so that the adhesive is midway between the upper and lower jaws (vertically and horizontally). The sample should be mounted with a small amount of slack, but no initial tension. • Start the crosshead moving. • Record the maximum force (grams) required to break the adhesive bond. • Return the crosshead to its original starting position and remove the separated strips from the jaws. 4. Calculation formula • Report to the nearest whole number (grams). While particular embodiments of the present invention have been illustrated and described, it would be obvious to those skilled in the art that various other changes and modifications can be made without departing from the spirit and scope of the invention. Further, it should be understood that all limits, ranges, and amounts specified herein include all narrower ranges, limits, and amounts that are within the specified limits and ranges. Such narrower ranges, limits, and amounts are incoporated by reference herein, and may be made a part of the appended claims even though for brevity the narrower limits, ranges, and amounts have not specifically been listed. Thus, for example, if the five day shear strength is described as being less than or equal to about 100 grams, then the five day shear strength may also be claimed as being less than or equal to about 90 grams, 80 grams, 70 grams, . . ., etc.

Claims: What is claimed is: 1. .An absorbent article comprising a first portion and a second portion, said absorbent article characterized in that said first portion and said second portion are temporarily held together by an adhesive that loses a controlled amount of strength, preferably a controlled amount of its shear strength, over time so that said first portion and said second portion can be readily separated. 2. The absorbent article of Claim 1 wherein the initial shear strength of said adhesive is greater than or equal to 200 grams. 3. .An absorbent article according to any of the preceding claims wherein said second portion is folded over said first portion, and the folding of said second portion defines a fold line, wherein said adhesive has an initial shear strength in a first direction which is oriented perpendicular to said fold line, and said initial shear strength in said first direction is greater than or equal to 200 grams. 4. An absorbent article according to any of the preceding claims wherein at least one of said first portion and said second portion comprises a polymeric material. 5. An absorbent article according to any of the preceding claims, comprising: a main body portion, said main body portion having a body-facing side, a garment-facing side, and an absorbent core positioned between said body- facing side and said garment-facing side, said garment-facing side having an adhesive fastener thereon which is covered by a cover strip, said cover strip comprising said first portion; and at least one side wrapping element extending from said main body portion, said side wrapping element comprising said second portion, wherein said side wrapping element is folded over said cover strip and temporarily adhered to said cover strip with said adhesive that loses a controlled amount of strength over time. 6. .An absorbent article according to any of the preceding claims wherein said adhesive has: (a) an initial strength when said absorbent article has first been packaged for distribution to a consumer; and (b) a consumer strength when said absorbent article is delivered to a consumer, wherein the time over which said adhesive loses a controlled amount of strength is the period between the time when said absorbent article has been packaged, and the time when said absorbent article is delivered to a consumer. 7. The absorbent article of Claim 6 wherein the adhesive has at least one of the following properties: (a) an initial shear strength that is greater than or equal to 200 grams more than its consumer shear strength; (b) a consumer shear strength of less than or equal to 100 grams; or (c) no consumer shear strength; or (d) a shear strength after five days of less than or equal to 100 grams. 8. The absorbent article of Claims 3, 4, 5, or 6 wherein said adhesive has an initial peel strength in said first direction of greater than or equal to about 15 grams, and an initial shear strength and an initial peel strength in said second direction which is oriented perpendicular to said fold line, wherein said initial shear strength in said second direction is greater than or equal to 500 grams, and said initial peel strength in said second direction is greater than or equal to 50 grams. 9. The absorbent article of Claims 5 or 6 wherein after five days, said adhesive has: a shear strength in said first direction of less than or equal to 100 grams; a peel strength in said first direction of less than or equal to 15 grams; and shear and peel strengths in said second directions that are sufficiently low to allow said side wrapping elements to readily unfold when said cover strip is removed. 10. A method of folding and retaining a folded side panel during a continuous process of making a disposable absorbent article having folded side panels, said method comprising the steps of: (a) providing a main body portion for an absorbent article, said main body portion comprising a body-facing side, a garment side, an absorbent component between said body-facing side and said garment side, a longitudinal centerline, a transverse centerline, and two spaced apart longitudinal edges; (b) providing a side panel for said absorbent article, said side panel being joined to said main body portion and extending laterally outward beyond said longitudinal edges of said main body portion; said method characterized in that it comprises the further steps of: (c) applying an adhesive that loses a controlled amount of strength over time to one of said: (i) side panel; (ii) a portion of said absorbent article that said side panel will come in contact with when folded; (iii) or, an intermediate component placed between said absorbent article and said side panel when said side panel is folded; (d) folding said side panel about at least one fold line to form a folded side panel so that the side panel will contact the portion of the absorbent article or component joined to the absorbent article that it is folded over, and so that the adhesive that loses a controlled amount of strength over time is therebetween; and (e) compressing said folded side panel.

Inventors: COE RICHARD GEORGE, WEINBERGER ERIC PATTON, COE, RICHARD, GEORGE, WEINBERGER, ERIC, PATTON
Applicants: PROCTER & GAMBLE, THE PROCTER & GAMBLE COMPANY
Application year: 1998
Main classification: A61F13
IPC codes: A61F5, A61F13, B65D85