A wide variety of absorbent articles designed to be efficient for the absorption of body fluids such as blood, urine, menses, and the like, are known. Disposable products of this type generally comprise some sort of fluid-permeable topsheet material, an absorbent core, and a fluid-impermeable backsheet material. Heretofore, such absorbent structures have been prepared using, for example, topsheet materials prepared from woven, non-woven, or porous formed-film polyethylene or polypropylene materials. Backsheet materials typically comprise flexible polyethylene sheets. Absorbent core materials typically comprise wood pulp fibers or wood pulp fibers in combination with absorbent gelling materials. One aspect of such absorbent articles that has recently been considered is their disposability. Although such products largely comprise materials which would be expected ultimately to degrade, and although products of this type contribute only a very small percentage of the total solid waste materials generated by consumers each year, nevertheless, there is currently a perceived need to devise such disposable products from materials which are compostable.
A conventional disposable absorbent product is already to a large extent compostable. A typical disposable diaper, for example, consists of about 80% of compostable materials, e.g., wood pulp fibers, and the like. In the composting process soiled disposable absorbent articles are shredded and commingled with organic waste prior to the composting per se. After composting is complete, the non-compostable particles are screened out. In this manner even today's absorbent articles can successfully be processed in commercial composting plants.
Nevertheless, there is a need for reducing the amount of non-compostable materials in disposable absorbent articles. There is a particular need to replace polyethylene backsheets in absorbent articles with liquid impervious films of biodegradable material, because the backsheet is typically one of the largest non-compostable components of a conventional disposable absorbent article.
In addition to being biodegradable, the films employed as backsheets for absorbent articles must satisfy many other performance requirements. For example, the resins should be thermoplastic such that conventional film processing methods can be employed. These methods include cast film and blown film extrusion of single layer structures and cast or blown film coextrusion of multilayer structures. Other methods include extrusion coating of one material on one or both sides of a compostable substrate such as another film, a non-woven fabric, or a paper web.
Still other properties are essential in product converting operations where the films are used to fabricate absorbent articles. Properties such as tensile strength, tensile modulus, tear strength, and thermal softening point determine, to a large extent, how well a film will run on converting lines.
In addition to the aforementioned properties, still other properties are needed to meet the end user requirements of the absorbent article. Film properties such as impact strength, puncture strength, and moisture transmission are important since they influence the absorbent articles durability and containment while being worn.
Once the absorbent article is disposed of and enters a composting process, other properties become important. Regardless of whether incoming waste is preshredded or not, it is important that the film or large film fragments undergo an initial breakup to much smaller particles during the initial stages of composting. Otherwise, the films or large fragments may be screened out of the compost stream and may never become part of the final compost.
During the initial stages of composting, for example where a Daneco drum is employed, the film is exposed to mechanical action, elevated temperatures, and moisture, in addition to microorganisms. Any one or two or all three of these elements can be used to promote the initial breakup of the film or large film fragments to much smaller fragments.
Many biodegradable polymers exist which are sensitive to mechanical action or elevated temperatures, or moisture. Many would individually meet the requirements for composting. However, few if any, can meet all processing, converting, end user, and disposal requirements of films suitable for backsheets of absorbent articles. To meet all these requirements simultaneously in a single film, various biodegradable polymers must be combined in ways which overcome their individual deficiencies and do not compromise the beneficial properties associated with the individual biodegradable polymers.
It is, therefore, an object of the present invention to provide liquid impervious films comprising biodegradable polymers and suitable for use in absorbent articles such as disposable diapers, catamenials, and the like. It is a particular object of the present invention to provide such films wherein the properties of the films meet the requirements outlined below:
a) a machine direction (MD) tensile modulus from about 10,000 to about 100,000 lbs./sq. in. (6.895.times.10.sup.8 dynes/sq. cm. to 6.895.times.10.sup.9 dynes/sq. cm.); PA1 b) a MD tear strength of at least 70 grams per 25.4 microns of thickness; PA1 c) a cross machine direction (CD) tear strength of at least 70 grams per 25.4 microns of thickness; PA1 d) an impact strength of at least 12 cm. as measured by falling ball drop; PA1 e) a moisture transport rate less than about 0.0012 grams per square centimeter per 16 hours; PA1 f) a modulus at 60.degree. C. of at least 5.52.times.10.sup.7 dynes/sq. cm. (800 lbs./sq. in.); and PA1 g) a thickness from about 12 microns to about 75 microns. PA1 a) a machine direction (MD) tensile modulus from about 10,000 to about 100,000 lbs./sq. in. (6.895.times.10.sup.8 dynes/sq. cm. to 6.895.times.10.sup.9 dynes/sq. cm.); PA1 b) a MD tear strength of at least 70 grams per 25.4 microns of thickness; PA1 c) a cross machine direction (CD) tear strength of at least 70 grams per 25.4 microns of thickness; PA1 d) an impact strength of at least 12 cm. as measured by falling ball drop; PA1 e) a moisture transport rate less than about 0.0012 grams per square centimeter per 16 hours; PA1 f) a modulus at 60.degree. C. of at least 5.52.times.10.sup.7 dynes/sq. cm. (800 lbs./sq. in. ); and PA1 g) a thickness from about 12 microns to about 75 microns.