Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Composite having voids in a component
Reexamination Certificate
1999-01-15
2001-01-09
Pezzuto, Helen L. (Department: 1713)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Composite having voids in a component
C428S315900, C428S500000, C442S183000, C442S394000, C442S398000
Reexamination Certificate
active
06171689
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to flame retardant microporous articles (e.g., films, sheets or membranes) formed from a polymer and diluent composition in which the diluent is phase separated from a thermoplastic polymer to make the article.
BACKGROUND OF THE INVENTION
Microporous films, sheets or membranes have a structure that enables fluids to flow through them. The effective pore size is at least several times the mean free path of the flowing molecules, namely, from several micrometers down to about 100 Angstroms. Such sheets are generally opaque, even when made from an originally transparent material, because the surfaces and internal structure scatter visible light.
Microporous membranes or films have been utilized in a wide variety of applications, such as the filtration of solids, the ultrafiltration of colloidal matter, diffusion barriers or separators in electrochemical cells, in the preparation of synthetic leather, and in the preparation of fabric laminates. The latter utilities require the membranes to be permeable to water vapor but not liquid water when preparing such articles as shoes, raincoats, outer wear, camping equipment such as tents, and the like. Moreover, microporous membranes or films are utilized for filtration of antibiotics, beer, oils, bacteriological broths, as well as for the analysis of air, microbiological samples, intravenous fluids, vaccines, and the like. Microporous membranes or films are also utilized in the preparation of surgical dressings, bandages, and in other fluid transmissive medical applications.
Microporous membranes or films may be laminated to other articles to make laminates having particular utility. Such laminates may include a microporous layer and an outer shell layer to provide a particularly useful garment material. Further, the microporous films or membranes may be utilized as a tape backing to provide such products as vapor transmissive wound dressings or hair setting tapes.
The art is replete with various methods of producing microporous materials. One useful technology found is thermally induced phase separation (TIPS). The TIPS process is based on the use of a polymer that is soluble in a diluent at an elevated temperature and insoluble in the diluent at a relatively lower temperature. The “phase separation” can involve a solid-liquid phase separation, or a liquid—liquid phase separation. This technology has been employed in the preparation of microporous materials wherein thermoplastic polymer and a diluent are separated by a liquid—liquid phase separation as described in U.S. Pat. Nos. 4,247,498 and 4,867,881. A solid-liquid phase separation has been described in U.S. Pat. No. 4,539,256 wherein the thermoplastic polymer on cooling crystallizes out. The use of nucleating agents incorporated in the microporous material is also described as an improvement in the solid-liquid phase separation method, U.S. Pat. No. 4,726,989.
SUMMARY OF THE INVENTION
The present invention provides new single and multilayer flame retardant microporous polymeric materials, prepared by a solid-liquid phase separation process, which contain an integral flame retardant. The microporosity is achieved by stretching the film, by diluent removal or by a combination of both techniques.
Accordingly, the present invention in its first aspect is a microporous material containing a crystallizable polymer component and at least 10 parts by weight of a flame retardant additive. More specifically, the present invention is a microporous material including:
(a) about 20 (preferably 30) to 90 parts by weight of a polymer component,
(b) about 0.1 to 70 (preferably greater than 10, most preferably 15 to 70) parts by weight of an diluent component, the diluent component being miscible with the polymer component at a temperature above the liquid-solid phase separation temperature, the diluent component able to phase separate from the polymer component through crystallization separation upon cooling below the liquid-solid phase separation temperature; and
(c) about 10 to 60 (preferably 15 to 40) parts by weight of a flame retardant additive.
A second aspect of the present invention is a method of making a microporous article including the steps of:
(a) melt-blending to form a solution comprising about 10 to 75 parts by weight of a crystallizable thermoplastic polymer component, about 15 (preferably 20) to 80 parts by weight of an diluent component that is miscible with the polymer component at a temperature above the liquid-solid phase separation temperature, and 10 to 60 parts by weight of a flame retardant additive;
(b) forming a shaped article of the melt-blended solution,
(c) cooling said shaped article to a temperature at which phase transition occurs between said diluent and said polymer component through crystallization precipitation of the polymer component to form a network of polymer domains, and
(d) creating porosity by stretching said article at least in one direction to separate adjacent crystallized polymer domains from one another, and/or by removing at least part of the diluent component, to provide a network of polymer spherulites connected by fibrils.
A third aspect of the present invention is a multilayer microporous film containing at least one layer of a microporous material as described above.
The article formed from liquid-solid phase separation, before orientation, is solid and generally transparent comprising an aggregate of a first phase of spherulites of crystallized thermoplastic polymer and a second phase of the diluent component. The flame retardant additive may be dissolved in the polymer component and/or the diluent component or may form a third phase of flame retardant dispersed in the matrix as a solid or liquid. The polymer domains may be described as spherulites and aggregates of spherulites of the polymer. Adjacent domains of polymer are distinct but they have a plurality of zones of continuity. That is, the polymer domains are generally surrounded or coated by the diluent component, but not completely. There are areas of contact between adjacent polymer domains where phase separation has not occurred and there is a continuum of polymer from one domain to the next adjacent domain in such zones of continuity.
On orienting or stretching, the polymer domains are pulled apart, permanently attenuating the polymer in the zones of continuity thereby forming fibrils that interconnect the polymer spherulites, and forming minute voids between coated particles, creating a network of interconnected micropores, thereby rendering the article permanently translucent. On orienting or stretching, the diluent component remains coated on or surrounds, at least partially, the surfaces of the resultant thermoplastic polymer domains. The degree of coating depends upon the affinity of the compound for the surface of the polymer domain, whether the compound is a liquid or solid, whether orientation dislodges or disrupts the coating and on other factors which may be relevant. The domains are usually at least partially coated after orientation. Substantially all of the domains appear to be connected by fibrils. The size of the micropores is controlled by varying the degree of stretching, percent of diluent and flame retardant additive component, melt-quench conditions, diluent component removal and heat-stabilization procedures. The fibrils for the most part do not appear to be broken by stretching but they are permanently stretched beyond their elastic limit so that they do not elastically recover to their original position when the stretching force is released. As used herein, “orienting” means such stretching beyond the elastic limit so as to introduce permanent set or elongation of the article. Stretching below the elastic limit is also effective if the article is annealed or heat-set while under tension.
The microporous article may comprise a single microporous layer, or may comprise a multilayer article having at least one microporous layer as defined above. The article may include additional microporous layers, or add
Kaytor Scott R.
Kollaja Richard A.
3M Innovative Properties Company
Kokko Kent S.
Pezzuto Helen L.
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