WO2009012284A1

WO2009012284A1 - Environmentally sensitive diapers manufactured with renewable resources

Info

Publication number: WO2009012284A1
Application number: PCT/US2008/070126
Authority: WO
Inventors: Susan O'connell
Original assignee: Groupo P.I. Mabe, S.A. De C.V.
Priority date: 2007-07-16
Filing date: 2008-07-16
Publication date: 2009-01-22

Abstract

This invention is directed to the production of environmentally sensitive absorbing articles, including diapers. In one exemplary embodiment, a disposable diaper includes a topsheet, a backsheet and an absorbent element interposed between the topsheet and backsheet. The backsheet and topsheet are made from a bicomponent spunbond nonwoven material including a renewable polymer and a nonrenewable thermoplastic polymer. The bicomponent spunbond nonwoven material contains an inner core including the renewable polymer and an outer sheath including the nonrenewable thermoplastic polymer.

Description

ENVIRONMENTALLY SENSITIVE DIAPERS MANUFACTURED WITH

RENEWABLE RESOURCES

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of and priority to U.S. Provisional Application No. 60/959,668, filed on July 16, 2007, the entire disclosure of which is incorporated by reference herein.

FILED OF THE INVENTION [0002] The present invention relates to environmentally sensitive absorbent articles such as diapers, sanitary napkins and training pants, which use bicomponent spunbond nonwoven materials. The absorbent materials have the advantage of being produced from sustainable resources rather than petroleum-based sources and thus have considerable environmental benefits relative to currently available absorbent products.

BACKGROUND OF INVENTION

[0003] The production of environmentally friendly absorbent articles has been a longstanding goal in the hygiene industry. This is particularly true for disposable diapers, which have increasingly been the source of ecological problems. Environmental problems are encountered in both the manufacture of the diapers and the disposal of the diapers in landfills. In terms of manufacture, there are significant environmental issues regarding both the absorbent materials (pulp, Superabsorbent polymer) as well as the nonwoven material used as the topsheet, backsheet and other parts of the diaper. The pulp of a diaper may be produced from chlorinated compounds, hence resulting in the release of chlorine-based derivatives into the environment. The topsheet and backsheet are generally synthesized from polymers produced from nonrenewable petroleum-based materials. Production of such polymers consumes valuable fossil fuel resources. Moreover, the majority of these polymers are not biodegradable and thus contribute to the growing ecological concerns. [0004] In the majority of disposable diapers, the backsheet and topsheet closest to the skin are made of a soft nonwoven fabric. Polypropylene is typically the material used for the topsheet being that it is comfortable and it facilitates the transfer of urine quickly to the layers underneath. Furthermore, spunbond polypropylene can be manufactured and converted at high speeds and generally has low basis weights compared to other types of nonwovens, including carded and airlaid. However, besides being a nonrenewable source, polypropylene is not self- degradable and is readily stable under typical environmental conditions, thus making its disposal highly problematic. [0005] Considerable efforts have been made to produce topsheets and backsheets from sustainable natural fibers such as cellulose or biodegradable polymers, but these have typically been with carded nonwovens which is a slower process and thus more costly than spunbond nonwoven. Moreover, producing nonwoven diaper topsheets and backsheets from microbally produced biodegradable polymers or synthetic aliphatic polyesters has met with limited success owing to difficulties associated with spinning and subsequent bonding of the fibers. Generally, methods of producing such fibers as topsheets and backsheets on diapers has been too costly to be practical. Biodegradable film blends such as a combination of polyethylene and starch have also been employed as nonwovens in the manufacture of diapers. [0006] Despite problems thus far encountered towards the production of more environmentally friendly diapers, producing a nonwoven fabric for diaper manufacture that is biodegradable, inexpensive, comfortable and highly flexible would be an important advance in the diaper industry. To this end, there has recently been interest in producing nonwoven products for diapers from renewable materials, particularly synthetic aliphatic polyesters. In particular poly(lactic acid) (PLA), a linear aliphatic thermoplastic polyester derived from 100% renewable sources, can be used to form nonwoven materials that can be incorporated into diapers. The nonwoven produced from PLA is durable and flexible. Furthermore, producing fibers from the correct grade of PLA might produce nonwovens that are equally comfortable to the currently available polypropylene-based nonwovens while at the same time having significant advantages from an environmental standpoint. Importantly, PLA nonwoven fabrics are compo stable and return naturally to the soul releasing carbon dioxide and water. [0007] Because of their environmental advantages, biopolymer resins like PLA have found increasing use in packaging applications and as a replacement for traditional petroleum-based plastics in a variety of applications. It has been recognized that PLA fibers can be used in the production of nonwoven products. For example, a fiber grade of bio-plastic was available from Natureworks under the brand name Inego Fibers. Inego fiber has been incorporated into different carded nonwoven materials primarily in Europe, and some of these materials are being used on niche diapers / hygiene products.

[0008] However, for various reasons, carded nonwoven materials are not ideal for use in the manufacture of absorbent products, particularly diapers. Firstly, the high cost and significant production time needed in the production of carded nonwovens is not economically practical. Secondly, the carded thermal bond fabrics used in the diaper have fairly high basis weights, particularly in comparison with traditional nonwoven polypropylene material, made through a spunbond process. As a result, more synthetic polypropylene is required to produce a fiber blend with the desired basis weight. In addition, we noticed that when the fiber blend was over -30% PLA by weight, the assembly of the carded PLA nonwoven top sheet and backsheet with the absorbent pad proved to be problematic. In particular, we had problems working with the ultrasonic sealing equipment on our assembly lines. In short, the Natureworks carded PLA could only be incorporated into the diaper at relatively low percentages, which is particularly unfavorable from an environmental standpoint. [0009] Accordingly, it would be desirable to incorporate renewable biopolymer resins such as PLA into absorbent articles like diapers without the problems discussed above. In particular, it would be desirable to produce the nonwoven material used in the diaper from spunbond rather than carded technology. Although we were aware of a grade of PLA for spunbond, the nonwoven material produced from this polymer was extremely stiff, and not suitable for hygiene applications.

[0010] Hence, one of the objects of the present invention is to generate the nonwoven renewable biopolymeric materials used in the diaper from spunbond rather than carded nonwoven technology. Another object of the present invention is to use the spunbond nonwoven fabric in the development of an environmentally sensitive diaper. SUMMARY OF INVENTION

[0011] The present invention overcomes the ecological disadvantages associated with the manufacture of absorbent articles by using biodegradable, renewable polymers in the nonwoven material of the said absorbent articles. This invention relates to absorbent articles, including disposal diapers, which use a novel bicomponent spunbond nonwoven of a particular configuration comprising a renewable polymer and a thermoplastic such as polypropylene. Such absorbent articles have the advantage over currently marketed absorbent products in that they reduce the use of petroleum-based materials being used in the absorbent article while affording the same level of comfort and performance. The bicomponent spunbond nonwovens used in this invention can replace traditional polypropylene spunbond materials without affecting the manufacturing process, product appearance or performance. Moreover, the bicomponent spunbond materials used in this invention are compatible with the ultrasonic sealing equipment used in the production of absorbent processes and they possess a low basis weight. As a result, significantly less petroleum-based materials and significantly more sustainable materials can be used in the inventive absorbent products described in this application.

DETAILED DESCRIPTION OF THE INVENTION

[0012] The invention covers the use of multicomponent spunbond nonwoven fibers comprising renewable polymers in the production of diapers and other absorbent materials. Multicomponent spunbond technology is used in the production of nonwovens made from two or more fibers, combined into a single type of fiber. In general, at least two distinct polymeric components are spun together to form a single fiber. The resultant multicomponent fibers often possess properties which differ from the individual components. The concept of multicomponent fibers is covered in U.S. Patent Nos. 5,425,987 and 6,417,121, which are hereby incorporated by reference. The multicomponent spunbond process can be performed using either pre-coalescent dies, wherein the distinct polymeric components are contracted prior to extrusion from the extrusion orifice, or post-coalescent dies, in which the distinct polymeric components are extruded through separate extrusion orifices and are contracted after existing the capillaries to form the multicomponent fibers. [0013] For the purposes of the present invention, component is defined as a separate part of the fiber that has a spatial relationship to another part of the fiber. The multicomponent fibers used in the present invention generally consist of two components, a polymer derived from a renewable source and a thermoplastic such as polypropylene. A multicomponent fiber with two polymeric components is referred to as a bicomponent fiber. In the present invention, the renewable polymers incorporated into the bicomponent fiber include, but are not limited to, polylactic acid (PLA) polyhydroxyalkanoates (PHA), and poly(hydroxycarboxylic) acids. Thermoplastic polymer resins based on sustainable / renewable resources such as PLA or PHA have been developed as alternatives to traditional plastic polymers such as polypropylene or polyethylene. Such polymers are disclosed in U.S. Patent Nos. 5,142,023, 5,525,706, 5,661,026, and 5,663,063, which are hereby incorporated by reference.

[0014] The individual fiber components comprising the bicomponent fibers can be arranged in various orientations. These distinct orientations are referred to as configurations. Preferred configurations include sheath core, side-by-side, tipped and mixed fibers. A particularly preferred configuration is the sheath core configuration. In a sheath core configuration, a first polymeric component comprises the sheath while a second polymeric component comprises the core. In such a configuration, the core component is positioned in the interior of the fiber and extends substantially the entire length of the fiber and is surrounded by the sheath component on the outer surface of the fiber. Importantly, one or more of the distinct polymeric components used to form the bicomponent fiber can comprise a blend of two or more polymeric materials. Thus, in the sheath core configuration, the sheath, the core or both can be a blend of two polymeric materials. Moreover, the sheath and/or core component can include additives such as pigments, dyes, antioxidants and the like. [0015] In one embodiment of the present invention, the spunbond nonwoven material of the environmentally friendly absorbent articles is generated from bicomponent fibers arranged in the sheath core orientation such that a renewable polymer comprises the core or the sheath of the spunbond fiber. The second component of the bicomponent fiber comprises a thermoplastic polymeric material such as polypropylene or polyethylene. Accordingly, the thermoplastic polymer, preferably polypropylene, can be incorporated as either the core or the sheath component of the bicomponent fiber. [0016] In one preferred embodiment of the present invention, the bicomponent nonwoven material of the absorbent article is comprised of PLA and polypropylene. In this embodiment, the core comprises predominantly PLA while the sheath comprises predominantly polypropylene. It was found that the bicomponent fibers produced from the sheath core design configured with PLA comprising the core and polypropylene comprising the sheath result in bicomponent fibers that when bonded into nonwoven webs, are ideal for use in absorbent products. For example, nonwovens produced from these bicomponent fibers can be used in various components of absorbent products including diapers, sanitary napkins and training pants. Components of the inventive absorbent articles best suited to use the nonwoven materials of the present invention include, but are not limited to, the topsheet, backsheet, cuff, core and wrap.

[0017] In an alternative embodiment, the bicomponent nonwoven material of the diaper is comprised of PHA and polypropylene. In this embodiment, the core comprises predominantly PHA while the sheath comprises predominantly a thermoplastic polymer, preferably polypropylene.

[0018] The percentage of the individual components can vary, dependent on the absorbent product and the spunbond apparatus being used to generate the nonwoven material. Optimization of the percentages of individual components in the bicomponent fiber should take into account various factors, including comfort (e.g. softness and texture), compatibility with the spunbonding apparatus and sealing equipment, and environmental concerns. As discussed in the Background of Invention section, carded nonwovens generated from PLA are not necessarily amenable to work with ultrasonic sealing equipment common in absorbent product processes, unless used in low percentages. Such nonwovens are not advantageous from an environmental perspective. The bicomponent spunbond nonwoven materials of the present invention can comprise a much higher percentage of the renewable polymer (e.g. PLA) and still maintain the ability to work with the ultrasonic sealing equipment. Moreover, unlike the single component spunbond PLA we tested, the bicomponent nonwoven material of the present invention feels exactly like traditional spunbond pure polypropylene fibers, but uses much more sustainable material. [0019] The renewable polymer in the bicomponent nonwoven webs of the present invention should be present in an amount of about 20% to about 99%, preferably from about 30% to about 80%, and more preferably from about 40% to about 60% by weight. The renewable polymer may be incorporated as the sheath component of a sheath core configured multicomponent fiber. More preferably, the renewable polymer is incorporated as the core component of the sheath core configured multiple component fiber while a thermoplastic polymer such as polyethylene comprises the sheath component. In one particularly preferred embodiment, the nonwoven materials of the inventive absorbent articles are comprised of 50% PLA and 50% polypropylene by weight. In another particularly preferred embodiment of the present invention, the nonwoven materials of the inventive absorbent articles are comprised of 50% PHA and 50% polypropylene by weight.

[0020] As discussed above, the individual components of the bicomponent fibers may be comprised of a single polymeric material or may be comprised of a blend of two polymeric materials. For example, in one embodiment of the present invention, the core component of the sheath core configured nonwoven webs used in the inventive absorbent articles is comprised of 100% renewable polymer (e.g. PLA or PHA) while the sheath component is comprised of 100% polypropylene.

[0021] In a particularly preferred embodiment of the present invention, both the sheath and core components of the sheath core configured nonwoven webs used in the inventive absorbent materials are comprised of a renewable polymer and polypropylene. The amount of individual polymer in each separate component will vary depending on the specific polymers used and the spunbonding apparatus being employed. Typically, the core component is present in the amount of about 50% to about 99% of renewable polymer, preferably from about 70% to about 95% renewable polymer, and more preferably from about 80% to about 90% renewable polymer by weight. Likewise, the sheath component is present in the amount of about 50% to about 99% of polypropylene, preferably from about 70% to about 95% polypropylene, and more preferably from about 80% to about 90% renewable polymer by weight. [0022] Being that the goal of the present is to produce environmentally friendly absorbent articles, several factors need be considered in developing nonwovens to incorporate into these absorbent articles. It is important that the nonwoven material provide the same level of comfort as petroleum based nonwovens and have basis weights on the same scale as the spunbond polypropylene nonwoven materials. Furthermore, the nonwoven webs must be produced in a highly cost effective manner. Moreover, the nonwoven webs that are produced must be amenable to working with equipment that is common in the manufacture of absorbent products. [0023] These goals have all been met with the absorbent articles of the present invention. As an example, the topsheet, backsheet, cuff, core and wrap of a diaper can be produced from bicomponent spunbond nonwoven webs comprising a renewable polymer and polypropylene. As discussed above, a particularly preferred configuration of the nonwoven material to be used in the inventive absorbent articles is the sheath core configuration with the renewable polymer as the predominant component of the sheath and polypropylene as the predominant component of the core. Such a configuration of nonwoven material works well with the ultrasonic sealing equipment necessary to be utilized in diaper manufacture. The basis weight of the material is typically less than 20 grams per square meter (gsm ) and more preferably less than 15 gsm. Bicomponent spunbond nonwovens of this and related configurations can replace traditional polypropylene spunbond nonwovens without influencing the manufacturing process. As a result, absorbent articles (e.g. diapers) can be manufactured and converted at high speeds and be highly cost effective, particularly in comparison to the manufacture of diapers comprising nonwoven material generated from carded or airlaid processes. The ease of manufacture and the low basis weights enable the use of a greater amount of renewable polymers and therefore a smaller amount of petroleum based polymers in the diaper. Thus, the diapers and other absorbent articles of this invention possess important environmental advantages over currently available absorbent products.

[0024] Equally important, the inventive absorbent articles provide the same level of comfort as those articles manufactured using polypropylene spunbond material. Hence, diapers manufactured with sheath core configured nonwoven material with a renewable polymer as the core and polypropylene as the sheath, look, feel, perform and process like diapers containing traditional nonwoven material using spunbond polypropylene, but use more sustainable material.

[0025] The inventive absorbent articles also exhibit good bonding, suitable strength, and strikethrough and rewet values comparable to absorbent articles using standard polypropylene topsheets and backsheets. Moreover, liquid distribution properties of the inventive absorbent articles are comparable to absorbent articles using standard polypropylene topsheets and backsheets. For the purposes of the present invention, strikethrough is defined as the time required for a given amount of fluid to pass through a nonwoven product. Rewet is defined as the amount of fluid which will tend to flow from an absorbent core back toward the outer face of a nonwoven product when the core is completely saturated with fluid. [0026] It will be readily apparent to one involved in the production of personal hygiene products, particularly absorbent articles, how to manufacture diapers employing the renewable polymer containing nonwovens described above. For example, disposable diaper manufacture is standard in the art. In general, disposable diapers normally comprise three elements: a liquid permeable topsheet to be placed next to the wearer's skin; a liquid impermeable backsheet which forms the outer surface of the diaper; and an absorbent element interposed between the topsheet and backsheet. Generally, in diaper manufacture, the absorbent pad is vacuum- formed, then attached to the topsheet and backsheet. Sealing of the components together is accomplished using heat or ultrasonic vibrations. Examples regarding the manufacture disposable diapers have been described in U.S. Patent Nos. RE. 26,152, 3,860,003, 4,324,425, 4,337,771, 4,352,355, 4,253,461 and 4,515,595, which are hereby incorporated by reference. [0027] It will be further appreciated that other technological innovations related to the manufacture of environmentally sensitive absorbent products can be combined with those disclosed in the present application. With respect to diapers, the renewable nonwoven materials described in this application can be used in the topsheet, backsheet, cuff, core and wrap. In addition, the absorbent core can be made from more environmentally favorable materials: totally chlorine-free pulp, which eliminates the release of chlorine-based derivatives into the environment, and bio-based absorbent polymers in place of traditional superabsorbent which is derived from petroleum based materials. Such diapers will have significantly less petroleum-based materials and significantly more sustainable materials than leading brands of diapers while at the same time showing comparable performance to the leading brands.

EXAMPLES [0028] As an example of the environmentally friendly diapers of the present invention, a disposable diaper using a backsheet and topsheet comprising a bicomponent sheath core configured nonwoven containing PLA has been manufactured and tested. The nonwoven material of the backsheet and topsheet contains 50% PLA by weight and 50% polypropylene by weight. The core component of the fibers of the nonwoven material consists of 90% PLA by weight and 10% polypropylene by weight. The sheath component consists of 90% polypropylene by weight and 10% PLA by weight. The basis weight of the bicomponent spunbond material is 13.5 gsm, which is almost identical to that of traditional nonwoven materials manufactured from pure polypropylene. Following generation of the spunbond nonwoven web, the components including the topsheet, backsheet and the absorbent pad were joined together and cut into diaper-sized units. Assembly of the diaper components ran smoothly on standard equipment and did not require any modification.

[0029] The resultant diaper looked and felt identical to diapers using pure polypropylene as the backsheet and topsheet. The performance of the inventive diaper was compared to that of the traditional spunbond pure polypropylene diapers. Comparison trials indicated that the inventive diaper products can be formed having distribution, strikethrough and rewet properties comparable to diapers using standard polypropylene backsheets and topsheets. Table 1 shows the performance (strikethrough, rewet and distribution values) of the inventive diapers described in Example 1 for three separate trials. Table 2 shows the performance of diapers formed using standard polypropylene topsheets and backsheets for three separate trials. It is evident that the results show comparable performance between the two different types of diapers. Table 1: Performance data on diaper described in Example 1

Table 2: Performance data on diaper using standard polypropylene topsheet and backsheet

[0030] It will be appreciated that the PLA could be replaced with other suitable renewable polymers including PHA.

Claims

1. A disposable diaper comprising a topsheet, a backsheet and an absorbent element interposed between said topsheet and backsheet, wherein said backsheet and said topsheet are made from a bicomponent spunbond nonwoven material comprising a renewable polymer and a nonrenewable thermoplastic polymer, wherein said bicomponent spunbond nonwoven material contains an inner core substantially consisting of the renewable polymer and an outer sheath substantially consisting of the nonrenewable thermoplastic polymer.

2. The disposable diaper of claim 1 wherein said renewable polymer is selected from the group consisting of poly(lactic) acids (PLA) polyhydroxyalkanoates (PHA), and poly(hydroxycarboxylic) acids and said thermoplastic polymer is polypropylene.

3. The disposable diaper of claim 2 wherein said renewable polymer is PHA and said thermoplastic polymer is polypropylene.

4. The disposable diaper of claim 2 wherein said renewable polymer is PLA and said thermoplastic polymer is polypropylene.

5. The disposable diaper of claim 2 wherein the inner core is composed of 100% of said renewable polymer and the outer sheath is composed of 100% polypropylene.

6. The disposable diaper of claim 2 wherein the inner core is comprised of about 90% to about 99% of the renewable polymer and 1% to about 10% of polypropylene by weight and the sheath is comprised of about 90% to about 99% polypropylene by weight and about 1% to about 10% of the renewable polymer by weight.

7. The disposable diaper of claim 6 wherein the renewable polymer is PLA.

8. The disposable diaper of claim 6 wherein the renewable polymer is PHA.

9. The disposable diaper of claim 6 wherein the bicomponent nonwoven material is comprised of from about 40% to about 60% renewable polymer by weight and from about 40% to about 60% polypropylene by weight.

10. The disposable diaper of claim 6 wherein the bicomponent nonwoven material is comprised of about 50% renewable polymer by weight and about 50% polypropylene by weight.

11. The disposable diaper of claim 1 wherein the absorbent element is comprised of a totally chlorine free pulp.

12. The disposable diaper of claim 1 wherein the absorbent element contains bio-polymer superabsorbent.

13. The disposable diaper of claim 1 further comprising stretchable side panels with grip pads.

14. The disposable diaper of claim 1 further comprising a cuff, a core and a wrap, wherein said cuff, core and wrap are made from a bicomponent spunbond nonwoven material comprising a renewable polymer and a nonrenewable thermoplastic polymer.

15. The disposable diaper of claim 1 wherein the basis weight of the nonwoven material is less than 20 grams per square meter.

16. The disposable diaper of claiml wherein the basis weight of the nonwoven material is between about 13 and about 16 grams per square meter.

17. A absorbent article comprising a topsheet, a backsheet and an absorbent element, wherein said backsheet and said topsheet are made from a bicomponent spunbond nonwoven material comprising a renewable polymer and a nonrenewable thermoplastic polymer, wherein said bicomponent spunbond nonwoven material contains an inner core substantially consisting of the renewable polymer and an outer sheath substantially consisting of the nonrenewable thermoplastic polymer.

18. The absorbent article of claim 16, said article selected from the group consisting of a sanitary napkin and training pants.