Breathable film layer compositions

Details Breathable film layer compositions Breathable film layer compositions

2000-02-14

2002-08-13

Nakarani, D. S. (Department: 1773)

Stock material or miscellaneous articles

Composite

Of polyamide

C428S480000, C428S522000, C524S310000, C524S377000

Reexamination Certificate

active

06432547

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to compositions that are useful for forming a breathable fluid impermeable barrier layer. The breathable film layer finds utility in durable goods such as tents, footwear, rainwear, etc., as well as for absorbent disposable articles such as disposable diapers, feminine napkins, and medical devices and dressings. The compositions are preferably applied as a continuous film with a non-contact coating method.
SUMMARY OF THE INVENTION
The present invention is directed to compositions that are useful for forming breathable film layers and articles constructed therefrom. The composition comprises at least one thermoplastic polymer compounded with at least one diluent or a radiation curable composition. The composition is impermeable to fluids and exhibits a water vapor transmission rate of at least 100 g/m
2
/day.
In one embodiment, the present invention relates to a composition comprising from about 10 wt-% to about 75 wt-% of at least one breathable thermoplastic polymer and from about 25 wt-% to about 90 wt-% of at least one diluent. In a preferred embodiment, the breathable thermoplastic polymer is water sensitive. In another preferred embodiment, the breathable thermoplastic polymer is a methacrylic acid copolymer. In a most preferred embodiment, the breathable thermoplastic polymer is a polyether block amide. The diluent is a plasticizer, wax, tackifying resin or mixture thereof and preferably a plasticizer having ether or alcohol oxygen linkages such as polyethylene glycol.
DETAILED DESCRIPTION OF THE INVENTION
By “breathable” it is meant that the composition allows for the passage of moisture vapor. The preferred water vapor transmission rate (WVTR) depends on the end-use application. However, in the context of the present invention, “breathable” refers to a WVTR of at least 100 g/m
2
/day as measured in accordance with ASTM E96 for a 40 &mgr;m to 50 &mgr;m coating.
By “impermeable” it is meant that the composition does not allow for the passage of fluids at a pressure of 10 psi. This terminology is clarified as needed throughout the description. For example, the Eastman AQ copolyesters are body fluid (saline solution) impermeable, yet water soluble (permeable).
The present invention employs a thermoplastic composition comprising at least one thermoplastic polymer and at least one diluent or a radiation responsive composition.
The thermoplastic compositions are particularly useful for forming a continuous fluid impermeable barrier layer. However, in many embodiments the compositions are also suitable for use as hot melt adhesives. Preferably, the barrier layer is formed in accordance with the method described in U.S. Pat. No. 5,827,252 issued Oct. 27, 1998, incorporated herein by reference.
In accordance with U.S. Pat. No. 5,827,252, the thermoplastic composition is relatively low in viscosity in comparison to typical film grade materials. Accordingly, the thermoplastic composition exhibits certain Theological characteristics, preferably falling within a rheological window. The complex viscosity at high shear rates, for example at about 1,000 radians/second, is less than about 500 poise. The complex viscosity at low shear rates, for example at less than about 1 radian/second, ranges from about 100 poise to about 1,000 poise. Thermoplastic compositions having a wide window of application are those which exhibit the appropriate rheological properties at a variety of application conditions, particularly at low temperatures. The desired Theological properties are preferably obtained at temperatures less than about 180° C., more preferably at temperatures less than about 160° C., even more preferably at temperatures less than 140° C., and most preferably at temperatures less than about 120° C.
The barrier layer may be of a conventional film thickness, for example from about 0.8 to about 2 mils. Alternatively, the barrier layer may advantageously be very thin, employing a coating weight thickness from about 1 g/m
2
to about 10 g/m
2
. For embodiments wherein the barrier layer is very thin or for embodiments that employ a composition which is not radiation curable, the barrier layer is typically of low film strength, obtaining its tear resistance from the substrate it is coated to. However, for embodiments employing a radiation curable system or higher coating thicknesses, the barrier layer alone may exhibit sufficient film strength to be self-supporting, particularly for disposable absorbent article applications.
The resulting barrier layer is impermeable to (body) fluid and is characteristically breathable. Breathability is expressed as a function of water vapor transmission rate (WVTR) measured in accordance with ASTM E-96 for a 40-50 &mgr;m barrier layer coating on porous nonwoven or of a neat barrier film layer in the case of self-supporting film layers. The barrier layer has a water vapor transmission rate of at least about 100 g/m
2
/day, preferably at least 200 g/m
2
/day, more preferably at least 400 g/m
2
/day, even more preferably at least 800 g/m
2
/day and most preferably from about 1000 to 2000 g/m
2
/day or higher.
In the case of compositions that are not intended to be radiation cured, the breathable composition of the present invention comprises at least one thermoplastic polymer and at least one diluent. The thermoplastic polymer, the diluent, or both are sufficiently breathable such that the formulated composition exhibits the desired WVTR rate.
The term “polymer” refers to a component having a Mw greater than about 3000 and preferably greater than about 10,000. In embodiments wherein the thermoplastic polymer employed has a high moisture vapor transmission rate, the diluent is sufficiently compatible with the thermoplastic polymer but need not be breathable. However, for embodiments wherein the thermoplastic polymer is not sufficiently breathable, the diluent preferably contributes to the breathability of the mixture. The thermoplastic polymer is typically polar in nature and may also be described as breathable, water sensitive including water swellable, water soluble or water dispersible, or biodegradable.
Consistent with the definition of breathable thermoplastic compositions, breathable thermoplastic polymers are those having a WVTR water vapor transmission rate of at least about 100 g/m
2
/day, preferably at least 200 g/m
2
/day, more preferably at least 400 g/m
2
/day, even more preferably at least 800 g/m
2
/day and most preferably from about 1000 to 2000 g/m
2
/day or higher. Breathable polymers typically contain low reactivity oxygen linkages. The oxygen linkages are preferably along the polymer backbone, as in the case of polyesters and polyethers. However, terminal low reactivity oxygen linkages may also contribute breathability as in the case of long chain (high molecular weight) polyols, as well as hydroxylated and epoxidized thermoplastic compounds. Additionally, the applicants surmise that certain thermoplastic polymers containing silicone-oxygen linkages such as siloxane may also be suitable. Particularly in the case of employing polymers having terminal oxygen linkages, care should be taken in selecting the additional ingredients in the thermoplastic mixture to insure such ingredients will not react.
Representative examples of breathable polymers include linear saturated polyesters such as Dynapol or Dynacoll polymers from Creanova Inc, (Piscataway, N.J.), polyether block amide and polyester ether block copolymers available from Elf Atochem (Birdsboro, Pa.) as PEBAX or Hoechst Celanese (Dallas, Tex.) as RITE-FLEX respectively. Within each class of polymers, the most preferred polymers are generally those exhibiting the highest degree of gas permeability such as PEBAX 2533 SN01 and PEBAX 3533 SN 01.
The breathable thermoplastic composition of the present invention may comprise one or more water sensitive thermoplastic polymers. However, since these materials are characteristically swellable, dispersible, or soluble in water, these materials typically lack the water impermeability properties re

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