Tear resistant film

#The present invention is directed, generally, to a film that exhibits improved resistance to the undesired growth of a tear, hole, aperture or other discontinuity and a method for making such a film. Specifically, the present invention is directed to an elastomeric film material formed from an elastomeric polymer that exhibits suitable strain crystallization properties, especially at the leading tip of a tear or other discontinuity in the film, to help resist undesired growth of the tear or discontinuity.

#Elastic materials, especially elastic films, are commonly used for a wide variety of applications. For example, disposable absorbent articles typically include one or more components that rely on film materials, especially elastic film materials, to control the movement of liquids and to provide a comfortable, conforming fit when the article is worn by a wearer. However, conventional elastic film materials have been known to at least partially tear when subjected to the normal wear and tear on the article when in use. Such tearing may be related to, for example, material defects, contact with sharp objects, pulling and stretching by a wearer, rigorous activity of a wearer, and/or repetitive mechanical stress experienced during wear and/or manufacture. Additionally, it is not uncommon for film materials to be subjected to vigorous mechanical and/or thermal stress during various manufacturing processes (e.g., incremental stretching processes or bonding processes such as high pressure bonding, thermal bonding, and ultrasonic bonding), which may result in undesirable tears and/or holes in the film. In some instances, it may even be desirable to intentionally include one or more pre-formed discontinuities (e.g., one or more apertures) that extend at least partially through the thickness of the film, for example, to control the breathability, permeability to liquids and/or solids, opacity, and/or extensibility of the article or article component that includes the film.

#Initially, openings in the film, whether desired or undesired, may start out small and be relatively inconsequential with regard to the desired function of the film, article component and/or article. But as the size of the opening grows, it may ultimately lead to partial or complete (catastrophic) failure of the film, article component and/or article. Unintended catastrophic failure of an article or article component is almost always undesirable, but when the article is a disposable absorbent article such as a diaper or training pant, the consequences of catastrophic failure of the article or component may be especially acute due to, for example, the possibility of bodily exudates escaping from the article and/or the article becoming separated from the wearer. To further compound the potential problems associated with conventional films, at least some manufacturers desire to use thinner and/or lower basis weight films to reduce material costs. The aforementioned problems associated with the formation of tears, holes, and apertures in a film may be even more acute in thinner/lower basis weight films.

#FIG. 1 is a plan view of an absorbent article.

#FIG. 2 is a chart of time versus temperature for use with the DSC test.

#FIG. 3 is a side view of grip suitable for use with the Slow Tear Test.

#“Absorbent article” means a device that absorbs and contains body exudates and, more specifically, devices that are placed against or in proximity to the body of the wearer to absorb and contain the various exudates discharged from the body. Exemplary absorbent articles include diapers, training pants, pull-on pant-type diapers (i.e., a diaper having a pre-formed waist opening and leg openings such as illustrated in U.S. Pat. No. 6,120,487), refastenable diapers or pant-type diapers, incontinence briefs and undergarments, diaper holders and liners, feminine hygiene garments such as panty liners, absorbent inserts, and the like.

#“Activation” is the mechanical deformation of a plastically extensible material that results in permanent elongation of the extensible material in the direction of activation in the X-Y plane of the material. For example, activation occurs when a web or portion of a web is subjected to a stress that causes the material to strain beyond the onset of plasticity, which may or may not include complete mechanical failure of the material or portion of the material. Activation of a laminate that includes an elastic material joined to a plastically extensible material typically results in permanent deformation of the plastic material, while the elastic material returns substantially to its original dimension. “Activate,” and variations thereof, means subjecting a material to an activation process.

#“Aperture” means an opening in a film purposefully added during filmmaking or laminate making, which is intended to impart a desired characteristic such as breathability. The growth of an aperture is the increase in the size of the aperture due to mechanical failure of the portion(s) of the film adjacent to the aperture.