Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Nitrogen-containing reactant
Reexamination Certificate
2000-11-01
2001-08-14
Foelak, Morton (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Nitrogen-containing reactant
C528S425000
Reexamination Certificate
active
06274701
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to porous materials containing melamine resins that exhibit air permeability and repellency to liquids.
BACKGROUND OF THE INVENTION
Melamine resins first appeared in Europe and later in America, a few years before World War II. Unlike phenolic resins, they have no objectionable odor, yet can be made into flexible to extremely hard lustrous surface coatings that are not easily stained. This is predominately attributed to the remarkable stability of the melamine's triazine ring after being cross-linked into an insoluble matrix. As a cross-linker, melamines have been introduced into molding, laminating, coating, gluing, and textile finishing.
One useful technology for producing microporous materials is thermally induced phase transition (TIPT). The TIPT process is based on the use of a polymer that is soluble in a diluent at an elevated temperature and insoluble in the diluent or forms a gel at a relatively lower temperature. The phase transition can involve a solid-liquid phase separation, a liquid-liquid phase separation or a liquid to gel phase transition. This technology has been employed in the preparation of microporous materials wherein a 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 wherein the thermoplastic polymer on cooling crystallizes out. U.S. Pat. Nos. 4,539,256 (Shipman), 4,726,989 and 5,120,594 (Mrozinski) and 5,260,360 (Mrozinski et al.) describe such films containing a multiplicity of spaced, randomly dispersed, nonuniform shaped, equipped particles of a thermoplastic polymer, optionally coated with a liquid that is immiscible with the polymer at the crystallization temperature of the polymer. Microporous films made by a phase transition from a liquid to a gel have been described in U.S. Pat. No. 4,849,311. Micropores allow permeability to gases, including moisture vapor, but can be relatively impermeable to high surface tension liquids such as water.
SUMMARY OF THE INVENTION
The present invention comprises melamine coated microporous materials, microporous materials containing salts, and related articles. The melamine is a cross-linker that is thermally cured and covalently bonded to various nucleophiles (e.g., hydrocarbon or modified hydrocarbon alcohols, etc.). When the nucleophile is a fluorinated monol or polyol, the resulting coating imparts fluid repellencies to the porous substrate against aqueous or organic solvents, while still maintaining the film's microporous morphology. Melamine saturation of porous substrates renders them essentially nonporous. Nevertheless, such nonporous, cross-linked melamine/ether polyol composites still retain a breathability feature.
The series of melamine coated microporous materials of the present invention may further include polyvalent salts incorporated into an ether/melamine coating. Such a combination enhances the hydrophilicity (water wettability) of the resulting coatings.
Accordingly, the present invention is generally described as a coated porous material (such as a porous film) which comprises a porous material and a coating composition applied to said material derived from the following precursors:
(i) a compound of the formula
wherein R is each independently H, CH
2
OH or CH
2
OR
2
, and R
1
and R
2
are each independently alkyl having 1 to 4 carbon atoms; and
(ii) an alcohol selected from the group consisting of perfluoroalkyl alcohols of the formula
in which R
f
is C
n
F
2n+1
or
where x is 1-12; n is 3-20, and R
3
is H, alkyl of 1-4 carbon atoms or —(CH
2
)
x
—OH, and polyhydric alcohols.
The coated porous material, after the coating composition has been cured, has an air flow Gurley Number equal or less than 2,000 sec/50 cc of air.
The coating composition of the inventive coated porous material may comprise both a perfluoroalkyl alcohol and a polyhdric alcohol (different from the perfluoroalkyl alcohol).
The inventive coated porous materials can be formulated to include polyvalent cations bound within the porous material which cations are not removed by water extraction. For example, coated microporous films can be made hydrophilic as depicted below.
In this case, a multivalent (or polyvalent) salt was incorporated into an ether/melamine coating formulation on the porous material thereby enhancing its hydrophilicity, while immobilizing the salt via secondary bonding forces (eg. polar or ionic) between the cation and the melamine ether chains. Thus, the invention includes a porous material containing polar groups and polyvalent salts bound within the porous material.
The invention also includes within its scope a composite, which is a material made by saturation of a porous substrate with the above described melamine coating composition, which has been cured.
Another aspect of the present invention is a process or method of making a coated porous or nonporous material, i.e. a composite, which includes the following steps:
applying a curable coating composition as above defined in a solvent, on a porous material to cover at least a portion of the material, and
drying the resulting coating sufficiently to remove the solvent and to promote cross-linking or curing, to produce the coated membrane.
Depending on the amount of coating composition applied, the resulting coating membrane may retain its porosity or become nonporous. An effective amount of coating composition to afford a coated membrane having an air-flow Gurley Number of equal or less than 2,000 sec/50 cc of air affords a coated porous material. This coated material is repellent against fluids such as hydrophilic and hydro-/oleophobic solvents while maintaining the microporous morphology of the film.
Saturation of the porous substrate with the above described coating composition renders the morphologies nonporous. This composite of non-porous, cross-linked melamine polyol still retains a breathability feature, i.e. air permeability. Thus, the melamine coated non-porous substrate composites are useful, as breathable high performance barrier films in protective garments. Cured thermally with a catalyst, the above melamine formulations provide a definite processing advantage in that their room temperature pot-life upon mixing is not compromised by any viscosity and/or workable time limitations.
Curable coating compositions containing melamine precursors are also part of the invention. These compositions comprise:
(a) a compound of the formula
wherein R is each, independently, H, CH
2
OH or CH
2
OR
2
, and R
1
and R
2
are each, independently, alkyl having 1 to 4 carbon atoms;
(b) an alcohol, preferably a polyhydric alcohol; and
(c) either
(i) a perfluoroalkyl alcohol of the formula
in which R
f
is C
n
F
2n+1
or
where x is 1-12; n is 3-20, and R
3
is H, alkyl of 1-4 carbon atoms or —(CH
2
)
x
—OH, or (ii) a polyvalent salt;
which coating composition is capable of cross-linking.
The coated porous materials of the present invention, which include non-woven and woven materials and microporous membranes, retain their liquid repellency and moisture vapor permeability properties for extended periods in many types of applications.
DETAILED DESCRIPTION
Coated porous materials, e.g. microporous polyolefin membrane materials, of the present invention exhibit significant air permeability properties and repel aqueous-based as well as a wide variety of non-aqueous based liquids.
Coated porous materials of the present invention exhibit durability of their fluid repellency properties when subjected to rubbing, touching, folding, flexing or abrasive contact. They also display oleophobic properties, resisting penetration by oils and greases and may be heat sealable. The oleophobicity of the membrane materials is most surprising in that the membrane materials contain an oily, oleophilic processing compound which, a priori, one would expect, would promote wetting by other oleophilic materials and which also would inhibit heat
3M Innovative Properties Company
Foelak Morton
Little Douglas B.
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