Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2000-12-06
2003-03-18
Cain, Edward J. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C523S105000
Reexamination Certificate
active
06534561
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to thermoplastic compositions for making a moisture vapour permeable, liquid impermeable layer by coating the composition onto a substrate. The compositions of the present invention can find a variety of applications, wherein moisture vapour permeability is desirable for example within absorbent articles such as diapers, sanitary napkins, panty liners and incontinence products, protective bedding covers, protective clothing and the like.
BACKGROUND OF THE INVENTION
Thermoplastic films which provide a liquid barrier in addition to providing moisture vapour permeability are known in the art. Particularly preferred are hydrophilic continuous films that do not allow the flow of moisture vapour through open pores or apertures in the material, but do transfer substantial amounts of moisture vapour through the film by absorbing water on one side of the film where the moisture vapour concentration is higher, and desorbing or evaporating it on the opposite side of the film where the moisture vapour concentration is lower.
For example WO 95/16746 discloses films prepared from mixtures of a) block copolyether ester, block copolyether amides (e.g. Pebax™) and or polyurethane and b) thermoplastic polymer which is incompatible with a, and c) a compatibiliser. The films are liquid impermeable and have moisture vapour permeability of about 700 g/m
2
·day. Also, U.S. Pat. No. 5,447,783 discloses a vapour permeable water resistant multi component film structure having at least three layers. The outer layers are hydrophobic copolyetherester elastomers having a thickness of 1.3-7.6 micrometers and a WVTR of 400-2500 g/m
2
·24h and the inner layer is a hydrophilic copolyetherester elastomer having a thickness of 7.6-152 micrometers and a WVTR of at least 3500 g/m
2
·24h.
U.S. Pat. No. 5,445,875 discloses a waterproof, bloodproof and virusproof breathable laminate. The laminate comprises a woven
onwoven fabric and an extruded film such as Hytrel™ having a thickness of about 1 mil (25.4 micrometers).
Other composite laminates are described for example in U.S. Pat. No. 5,599,610 which discloses tri-laminated fabric for surgical gowns comprising outer layers of woven fabric and an inner layer of a microporous polyurethane membrane. The microporous film has a thickness of 12-55 micrometers and a MVTR of 1100 g/m
2
·24h upright and 5500 g/m
2
·24h inverted (ASTM E96-B). Polyether-polyurethane adhesive is used to join the layers.
Similarly, U.S. Pat. No. 5,532,053 discloses a high moisture transmission medical film which can be laminated onto a nonwoven material. The laminate film comprises a first layer of polyetherester copolymer and second and third layers selected from a specified group of polymers. The film has a MVTR of greater than 750 g/m
2
·24h (ASTM F1249) and a thickness of less than 1 mil (25.4micrometer) preferably 0.6 mil to 0.75 mil (15-19 micrometers).
U.S. Pat. No. 4,938,752 discloses absorbent articles comprising films of copolyether esters which have reduced water permeability, a water vapour permeability of 500 g/m
2
·24h (as measured in a specified described test) and a thickness of 5-35 micrometers. There is no disclosure of a supportive substrate.
U.S. Pat. No. 4,493,870 discloses a flexible layered waterproof product comprising a textile material covered with a film of a copolyetherester having an MVTR of at least 1000 g/m
2
·24h (ASTM E96-66) having a thickness of 5 to 35 micrometers.
GB 2024100 discloses a flexible layered water resistant article comprising a microporous hydrophobic outer layer which is moisture vapour permeable but resist liquids and a hydrophilic inner layer of polyetherpolyurethane having a MVTR of above 1000 g/m
2
·24h.
Compositions known for providing hydrophilic continuous moisture vapour permeable, liquid impermeable films or layers include thermoplastic polymers such as polyurethanes, poly-ether-amides block copolymers, polyethylene-acrylic acid copolymers, polyethylene oxide and its copolymers, poly lactide and copolymers, polyamides, polyester block copolymers, sulfonated polyesters, poly-ether-ester block copolymers, poly-ether-ester-amide block copolymers, polyacrylates, polyacrylic acids and derivatives, ionomers, polyethylene-vinyl acetate with a vinyl acetate content of more than 28% by weight, polyvinyl alcohol and its copolymers, polyvinyl ethers and their copolymers, poly-2-ethyl-oxazoline and derivatives, polyvinyl pyrrolidone and its copolymers, thermoplastic cellulose derivatives, or mixtures thereof. Such compositions can be used for making layers and films featuring high values of moisture vapour permeability while being liquid impermeable, which therefore are particularly preferred for incorporation in disposable absorbent articles.
However, a problem associated with films and layers made from the above mentioned thermoplastic compositions is that such compositions are typically highly viscous in the plastic state at the process conditions, and are processable only by means of extrusion techniques. Extrusion processes for making films and layers from thermoplastic polymers are well known, but have the disadvantage of being rather complex; they in fact require expensive equipment, typically comprising a high power screw extruder to force the material in the plastic state through a slit die to form the film or layer. Extrusion process conditions also typically involve rather high temperatures and pressures. Moreover an extrusion apparatus for the formation of a film or layer cannot be easily incorporated into a production line, e.g. of disposable absorbent products. Extrusion processes moreover are not suitable for the production of films having a particularly low thickness, e.g. in the range of 5-10 &mgr;m.
Furthermore, in case of laminated composite structures, in which i.e. a layer of the preferred moisture vapour permeable, liquid impermeable composition is laminated to a substrate, e.g. a fibrous layer, the addition of an adhesive in order to ensure permanent fixation of the film onto the substrate is often required. However, this in turn detrimentally affects the overall moisture vapour permeability of the resulting composite, and adds complexity to the production process.
Hence, there is a need to provide compositions for making a hydrophilic continuous moisture vapour permeable, liquid impermeable layer having preferred characteristics of moisture vapour permeability and liquid imperviousness which are also readily processable so as to provide a preferably thin film coating onto a substrate, so avoiding the need of complex traditional extrusion apparatuses.
SUMMARY OF THE INVENTION
The present invention relates to a thermoplastic composition comprising:
a thermoplastic polymer or mixture of polymers having a viscosity higher than 5000 poise at a temperature of 20° C. above the DSC melting point of the polymer or mixture of polymers, evaluated as described in the text, and at a frequency of 1 rad/sec, the thermoplastic polymers being selected from the group consisting of polyurethanes, poly-ether-amides block copolymers, polyethylene-acrylic acid copolymers, polyethylene oxide and its copolymers, poly lactide and copolymers, polyamides, polyester block copolymers, sulfonated polyesters, poly-ether-ester block copolymers, poly-ether-ester-amide block copolymers, polyacrylates, polyacrylic acids and derivatives, ionomers, polyethylene-vinyl acetate with a vinyl acetate content of more than 28% by weight, polyvinyl alcohol and its copolymers, polyvinyl ethers and their copolymers, poly-2-ethyl-oxazoline and derivatives, polyvinyl pyrrolidone and its copolymers, thermoplastic cellulose derivatives, or mixtures thereof,
a suitable compatible plasticiser or blend of plasticisers for adjusting said viscosity,
wherein said thermoplastic composition has a viscosity of from 50 poise to 4000 poise at a frequency of 1 rad/s at a temperature of 210° C. or less and a viscosity of less than 2000 poise at a frequency of 1000 rad/s at a temperature of 210° C. or less.
DETAILED DESCRIPTION OF THE
Corzani Italo
Palumbo Gianfranco
Cain Edward J.
The Procter & Gamble & Company
Wyrozebski-Lee Katarzyna
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