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Selective Translucency in Breathable Films

IP.com Disclosure Number: IPCOM000021099D
Publication Date: 2003-Dec-22
Document File: 3 page(s) / 38K

Publishing Venue

The IP.com Prior Art Database

Abstract

A method of obtaining translucency in selectable areas of breathable polymer films. Such films possess micropores, which cause the films to appear opaque or cloudy due to differences in refractive index between the polymer and the air within the micropores. The refractive effects of the micropores can be reduced by application of a component with a refractive index similar to that of the film polymer. The component can be applied alone or as a blend with other components, such as inks, to provide selective zones of visibility through a breathable film.

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Selective Translucency in Breathable Films

Breathable films are commonly produced by blending polymers such as polyolefins with calcium carbonate (CaCO3) powders. The compounds are formed into a flat web using an extrusion casting method. The cast film is then machine oriented, where the polymer substrate is stretched while the CaCO3 particle stays in place, thus forming a void around the particle small enough to prevent water penetration, but large enough to allow water vapor to pass through the film.

                  The void serves the primary purpose of making the film breathable, and serves a secondary purpose of providing opacity to the material by creating an interface responsible for the scattering of light. Light scatters when passing through multiple phases with different refractive indices. An object that lacks pigmentation can thus appear white when light is scattered off its surface and back to the observer’s eye. For example, water droplets are usually clear, but clouds appear white due to light scattering off the droplets. The difference of refractive indices between water and air is responsible for the scattering.

                  Thus, breathable films without pigmentation in their formulation also have the ability to appear white/opaque as a result of their porous structure. Calcium carbonate particles appear white in nature and account for about half of a breathable film’s composition, but do not contribute to the opacity of the film per se since their refractive index is very similar to that of the polymer (~1.5). Upon stretching, however, air gaps are introduced into the film, resulting in the transition from a translucent to an opaque white material. This is due to refractive index differences between air (n=1.0) and the polymer (n=1.5), which promote the random scattering of light off the film.

                  It may at times be desirable to provide a breathable film that is nevertheless also translucent, at least in certain areas. One instance where selective translucency of a breathable film would be desired is in the field of disposable diapers. The use of an opaque material for the outer cover of a diaper is generally desirable, since the opacity will help to mask the view of any bodily wastes that the diaper may have imbibed. A diaper may also include a wetness indicator, such as a water-fugitive dye, on the inner surface of the outer cover of the diaper, to inform the caregiver whether the product has received a liquid insult. However, where a breathable film is used as the outer cover, the dye mark may be obscured or blurred by the opacity of the film. In this situation, it may be desirable to make at least the portion of the film that bears the dye mark into a more translucent material, permitting clearer visualization of the dye mark. Breathable film packaging material may also benefit from having selective opaque and light transmissive portions in order to show the product within the packaging.

                  If the air gaps of a breathable film, such as a calcium carbo...