Coated porous materials

Details Coated porous materials Coated porous materials

2000-11-30

2002-11-26

Niland, Patrick D. (Department: 1714)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

From reactant having at least one -n=c=x group as well as...

C427S372200, C427S385500, C524S589000, C524S590000, C524S591000, C524S839000, C524S840000, C528S070000

Reexamination Certificate

active

06486291

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to coated porous materials that exhibit air permeability and repellency to liquids having a surface tension at least equal to or greater than 20 dynes/cm.
BACKGROUND OF THE INVENTION
Films, fabrics, and fibrous substrates including textiles have been treated with fluorochemical uncrosslinked urethanes to impart water and soil repellency.
Microporous films prepared by thermally-induced phase separation (TIPS) methods are known. U.S. Pat. No. 4,539,256 (Shipman), U.S. Pat. Nos. 4,726,989 and 5,120,594 (Mrozinski) and U.S. Pat. No. 5,260,360 (Mrozinski et al.) describe such films containing a multiplicity of spaced, randomly dispersed, equiaxed, nonuniform shaped particles of a thermoplastic polymer, optionally coated with a liquid that is immiscible with the polymer at the crystallization temperature of the polymer. Micropores allow permeability to gases, including moisture vapor, but can be impermeable to high surface tension liquids such as water.
Microporous membranes have been coated with a urethane such that the pores are filled and the membrane is impervious to passage of gases. On the other hand, U.S. Pat. No. 5,286,279 describes a gas permeable membrane coated with a fluorochemical urethane wherein the urethane is prepared from either 1,4-cyclohexane diisocyanate or methane 4,4,′-diphenyl diisocyanate.
SUMMARY OF THE INVENTION
The present invention fills a need by employing a precursor fluorocarbon urethane composition or curable coating composition to coat a porous material, e.g. a microporous polyolefin membrane. The urethane precursors are crosslinked in situ, upon drying, in such a way that the pathways through the membrane are not blocked or plugged with a coating. As a result, resistance to airflow and bubble point pore size values are retained after coating. Because the coated membrane is highly breathable, durable, and has a low surface energy, it is useful for making ileostomy vent filters, transdermal drug substrates, agricultural and medical apparel, as well as paint and chemical protective garments.
Accordingly, the present invention in its first aspect is a curable coating composition for a porous material containing fluorocarbon urethane precursors including:
(a) a polyisocyanate;
(b) a polyhydric alcohol; wherein at least one member of (a) or (b) has a functionality of greater than 2, and
(c) a perfluoroalkyl alcohol of the formula
R—(CH
2
)
x
—OH,  (I)
in which R is C
n
F
2n+1
or
where x is 1-12; n is 3-20, and R
1
is H, alkyl of 1-4 carbon atoms or —(CH
2
)
x
—OH, wherein said composition is capable of crosslinking.
A second aspect of the present invention is a coated porous material which includes a porous material and a curable coating composition applied to said material which includes the following fluorocarbon urethane precursors:
(i) a polyisocyanate;
(ii) a polyhydric alcohol; wherein at least one member of (i) or (ii) has a functionality of greater than 2, and
(iii) a perfluoroalkyl alcohol of the formula
R—(CH
2
)
x
—OH,  (I)
in which R is C
n
F
2n+1
or
where x is 1-12; n is 3-20, and R
1
is H, alkyl of 1-4 carbon atoms or —(CH
2
)
x
—OH.
Another aspect of the present invention is a process or method of making a coated porous material which includes the following steps:
applying a curable coating composition which includes the above defined fluorocarbon urethane precursor on an organic solvent, on a porous material to cover the material, and
drying the resulting coating sufficiently to remove the solvent and promote cross-linking or curing, to produce the coated membrane which exhibits air permeability and repellency to liquid having a surface tension at least equal to or greater than 20 dynes/cm.
The inventive porous materials having a cured coating, which include non-woven, woven materials, perforated films and microporous membranes retain their liquid repellency and moisture vapor permeability properties for extended periods in all types of applications.
The microporous polyolefin materials may contain a compatible liquid or diluent such as mineral oil along with the fluorocarbon urethane coated material and are referred to as (oil-in) materials. Such a fluorocarbon urethane coating on an oil-in polyolefin membrane provides the membrane the ability to resist wetting by fluids like alcohols, toluene, mineral oil, water-surfactant solutions and ethylene glycol even though the membrane's pore walls are coated with approximately 35-40 wt-% mineral oil or another diluent. The same coating on a polyolefin membrane having no diluent (oil-out) or on other membranes or materials not prepared by thermally induced phase separation (TIPS) provides materials displaying even more repellency such that the coated materials resist wetting by all of the above-mentioned fluids as well as chlorohydrocarbons such as trichloroethane, and hydrocarbons such as decane, octane, heptane and hexane.
The present coated porous materials having a cured coating are repellent to a wide variety of fluids including the above organic fluids and are much more repellent than membranes containing prior fluorocarbon coatings such as the fluorocarbon oxazolidinone coatings on polyolefin membranes described in U.S. Pat. No. 5,260,360.
DETAILED DESCRIPTION
Coated and cured porous materials, e.g. microporous polyolefin membrane materials, of the present invention, exhibit significant air permeability properties and repel aqueous-based as well as non-aqueous based liquids including a wide variety of non-aqueous liquids having a surface tension at least equal to or greater than 20 dynes/cm.
Porous materials of the present invention having a cured coating 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 some (eg. those made from polyethylene (PE), polypropylene (PP) or PE/PP blends) may be heat sealable. For the oil-in version of the invention, the oleophobicity and heat sealing properties of the membrane materials are most surprising since the membrane materials contain an oily, oleophoic processing compound which is a priori, one would expect, would promote wetting by other oleophilic materials and which also would inhibit heat sealing.
Transport of a liquid challenge through most porous materials or fabrics occurs because the liquid is able to wet the material. A possible route through the material is for the liquid to initially wet the surface of the material and to subsequently enter pore openings at the surface of the material followed by a progressive wetting of and travel through interconnected pores until finally reaching the opposite surface of the material. If the liquid has difficulty wetting the material, liquid penetration into and through the material will, for the most part, be reduced. A similar phenomenon occurs in the pores, where reduced wetability, in turn, reduces pore invasion. Generally the greater the numerical difference between the liquid surface tension of the liquid and the surface energy of the porous material (the latter being lower), the less likely it is that the liquid will wet the porous material.
In the case of aqueous solutions containing surface active agents (eg. surfactants) the wetting of the porous materials is usually time-dependent, controlled by the slow diffusion and absorption of surfactants onto the surface of the porous materials.
In the present invention, the extent of barrier protection may be described by four levels, of which the first two describe existing levels and the last two describe levels of protection as a result of the coatings presented by this invention.
Level 1 TIPS membranes without diluents (polypropylene (PP), or high density polyethylene (HDPE)) TIPS membranes with diluents, particle-filled membranes, and polytetrafluoroethylene (PTFE) membranes. In terms of repellency beyond water, these materials immediately wet through with a 0.1 wt. % surfactant, Triton X-10

Affiliated with

Also associated with

Rating

Coated porous materials does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Coated porous materials, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Coated porous materials will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2981206