Multilayer films

Details Multilayer films Multilayer films

2002-01-25

2004-03-09

Chen, Vivian (Department: 1773)

Stock material or miscellaneous articles

Structurally defined web or sheet

Including components having same physical characteristic in...

C428S304400, C428S317900, C428S318400, C428S319300, C428S319900, C428S423100, C428S423700, C428S475200, C428S480000, C428S481000, C428S483000, C428S910000, C528S300000, C528S302000, C528S307000, C528S308000, C528S308600, C528S308700

Reexamination Certificate

active

06703115

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to multilayer films that are characterized by preferably having increased moisture vapor transmission rates (MVTR).
BACKGROUND OF THE INVENTION
Stretching of properly formulated films that are fabricated from polyolefins filled with solid particles (e.g., a mineral such as calcium carbonate), under appropriate conditions, is known to create porous structures that allow for the diffusion of water vapor while providing liquid barrier. This is a desirable property in markets such as hygienics, industrial and medical. Indeed, a major consideration in the comfort of a garment is its ability to maintain a balance between heat production and heat loss. The loss of heat through clothing may occur through direct dry heat loss or by moisture evaporation. In respect to the latter, the moisture vapor transmission rate of the material utilized in forming the garment is generally related to the breathability of the material. Breathability is the ability to diffuse moisture/water vapor through a film or garment. In addition to this property, there are many applications requiring that the material used in preparing the garment be impermeable to a liquid. Such applications include diaper back sheets, sanitary napkins, medical protective garments, surgical incise drapes, transdermal patches, wound care bandages and dressings, intravenous site dressings, ostomy site dressings, breathable construction films such as housewrap, among others. In general, porous films do not provide a sufficient barrier to bacteria and/or virus, or to wind.
Films, which are permeable to water vapor and are porous but yet are intended to be impermeable to a liquid, are described in U.S. Pat. Nos. 4,626,252 and 5,073,316. As disclosed, a porous film is obtained by mixing a polyolefin resin, an inorganic filler and a plasticizer; forming a film from the mixture; and uniaxially or biaxially stretching the film. Films of this type are also disclosed in U.S. Pat. No. 5,998,505 and PCT International Application Publication No. WO 98/05501.
Examples of multilayer breathable films are described in the following U.S. patents.
U.S. Pat. No. 6,114,024 describes a method of making a stretched, multilayer breathable film having at least 5 layers that is a barrier to bacteria. The outer layer is made of a non porous, non filler containing breathable polymer to provide bacteria barrier and to extend the process time by protecting the extruder die from build up of the filler contained in its most inner layer. This method teaches the need for microporous tie layers between the outer non-porous, non-filler containing layers and the inner filler-containing layer.
U.S. Pat. No. 5,164,258 describes a multilayer breathable film consisting of outer layers of a breathable hydrophobic material (microporous), a core hygroscopic barrier layer (monolithic), and adhesive layers disposed between the core layer and the two outer layers. This patent teaches the use of filled, unstretched polyolefins as structural support as outer layers for an inner oxygen barrier layer during steam sterilization. During steam sterilization the inner layer absorbs large amounts of water reducing its barrier to oxygen. The breathable outer layers described allow for the desorption of water from the inner layer, thus recovering the package oxygen barrier.
U.S. Pat. No. 5,143,773 discloses a multilayer film consisting of a water absorbing central layer (monolithic) with a humoctant (water absorbing material) having on one side a water impermeable, non-porous, non-breathable layer and on another side a microporous layer. This multilayer film is useful for packaging water sensitive materials where the relative humidity inside the package must be controlled.
U.S. Pat. No. 4,828,556 discloses multilayer breathable film consisting of a polyvinyl alcohol monolithic layer between two microporous non-woven web layers.
U.S. Pat. No. 4,863,788 discloses a multilayer film consisting of a microporous membrane having on one side a continuous film protective layer and on another side a cellular foam adhesive layer and a fabric substrate.
U.S. Pat. No. 4,758,239 discloses a multilayer breathable film consisting of a water-soluble polymeric layer having on one side a microporous sheet.
SUMMARY OF THE INVENTION
It is accordingly an object of the present invention to provide new and improved multi-layer films.
It is a further object of this invention to provide novel multi-layer films, which preferably are characterized by having improved moisture vapor transmission rates (MVTR).
These and other objects and advantages of the present invention will be apparent to those skilled in the art from the following detailed description and claims.
In accordance with the present invention, it has been found that the above and still further objects are achieved by providing, in a first embodiment, a multilayer film comprising:
(a) a first layer comprising from about 70 to 100 weight percent of at least one or more thermoplastic polymer(s) having a MVTR value of at least 300 g-&mgr;m/m
2
-hour, as determined in accordance with ASTM Test Method E-96D, and from 0 to about 30 weight percent filler, and
(b) a second layer comprising from about 20 to about 80 weight percent of at least one or more thermoplastic polymer(s) and from about 20 to about 80 weight percent filler and the second layer having in stretched form a MVTR value, according to ASTM E-96D, greater than the MVTR value, according to ASTM E-96D, of the at least one or more thermoplastic polymer(s) of the second layer,
wherein the second layer comprises an amount of filler differing from the amount of filler in the first layer when the at least one or more thermoplastic polymer(s) of the first layer and the at least one or more thermoplastic polymer(s) of the second layer are the same, wherein the first layer is adjacent to the second layer, and wherein the multilayer film, in stretched form, has a MVTR value, according to ASTM E-96D, greater than the MVTR value, according to ASTM E-96D, of the at least one or more thermoplastic polymer(s) of the first layer.
In a second embodiment of the present invention, there is provided a multilayer film comprising:
(a) a first layer comprising
(i) from about 70 to 100 weight percent of at least one or more linear or branched or chain extended, random, aliphatic-aromatic copolyester(s) having a MVTR value of at least 300 g-&mgr;m/m
2
-hour or g-mil/m
2
-day, as determined in accordance with ASTM Test Method E-96D, and comprising repeating units of:
wherein
R
1
is selected from one or more of the groups consisting of C
2
-C
8
alkylene or oxylalkylene and the mole percent of R
1
is from about 80 to 100;
R
3
is selected from one or more of the groups consisting of C
2
-C
8
alkylene or oxylalkylene; C
2
-C
8
alkylene or oxylalkylene substituted with one to four substituents independently selected from the group consisting of halo, C
6
-C
10
aryl, and C
1
-C
4
alkoxy; C
5
-C
12
cycloalkylene (for example, 1,4-cyclohexanedimethanol); C
5
-C
12
cycloalkylene substituted with one to four substituents independently selected from the group consisting of halo, C
6
-C
10
aryl, and C
1
-C
4
alkoxy; and the mole percent of R
3
is from 0 to about 20;
R
2
is selected from one or more of the groups consisting of C
2
-C
12
alkylene or oxyalkylene; C
2
-C
12
alkylene or oxylalkylene substituted with one to four substituents independently selected from the group consisting of halo, C
6
-C
10
aryl, and C
1
-C
4
alkoxy; C
5
-C
10
cycloalkylene; C
5
-C
10
cycloalkylene substituted with one to four substituents independently selected from the group consisting of halo, C
6
-C
10
aryl, and C
1
-C
4
alkoxy; and the mole percent of R
2
is from about 35 to about 95;
R
4
is selected from one or more of the groups consisting of C
6
-C
10
aryl; C
6
-C
10
aryl substituted with one to four substituents independently selected from the group consisting of halo, C
6
-C
10
aryl, and C
1
-C
4
alkoxy; C
5
-C
10
cycloalkylene; C
5
-C
10
cycloalkylene substituted with

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