Coating processes – Direct application of electrical – magnetic – wave – or... – Electrostatic charge – field – or force utilized
Reexamination Certificate
2000-04-13
2003-02-04
Niland, Patrick D. (Department: 1714)
Coating processes
Direct application of electrical, magnetic, wave, or...
Electrostatic charge, field, or force utilized
C427S372200, C427S385500
Reexamination Certificate
active
06514572
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to polyurethane films and more particularly relates to polyurethane films prepared from aqueous dispersions.
While ostensibly reactive with water, it has long been known that polyisocyanate polymers can be used to prepare aqueous polyurethane dispersions. Polyurethane dispersions are generally prepared by chain extending the reaction product of an organic diisocyanate or polyisocyanate and an organic compound having two or more active hydrogen atoms such as polyalkylene ether glycols, poly(alkylene ether-alkylene thioether) glycols, alkyd resins, polyesters and polyester amides, often using an organic solvent. The diisocyanate is used in stoichiometric excess so that the reaction product, also referred to as a polyurethane/urea/thiourea prepolymer, is isocyanate terminated. Examples of polyurethane prepolymer preparations are described in U.S. Pat. Nos. 3,178,310, 3,919,173, 4,442,259, 4,444,976, and 4,742,095, among others.
Polyurethane dispersions are reported as being useful for preparing such diverse materials as: coatings and bonds in U.S. Pat. No. 4,292,226; flexible solvent barriers in U.S. Pat. No. 4,431,763; adhesives in U.S. Pat. No. 4,433,095; and films in U.S. Pat. No. 4,501,852. Films, or rather the process of dipping to make a film, can be a part of the processes for making many articles. Examples of film applications include exam gloves, organ bags, condoms, ostomy bags, and the like. While it is known that such applications can be made with polyurethane dispersions, conventional polyurethane dispersions have sometimes been found to have insufficient physical or handling properties to make them a preferred material for such applications. Also, the use of a solvent can have adverse effects for some applications.
Polyurethanes are the reaction product of a polyalcohol and a polyisocyanate. Typically, the polyisocyanates used to prepare polyurethane dispersions have been aliphatic isocyanates such are disclosed in U.S. Pat. No. 5,494,960. Aromatic polyisocyanates such as toluene diisocyanate (TDI) and methylene diphenyldiisocyanate (MDI) as well as polymethylene polyphenylisocyanate are also known to be useful.
It is known to prepare polyurethane films by methods such as coagulation and casting. While these are commonly used, they are not without problems. For example, in coagulation processes, there is often a requirement for a step to remove coagulants from the films formed by means of washing or leaching. These steps often result in undesirable additional dewatering steps, undesirable waste streams and increased costs due to additional handling.
Accordingly, it would be desirable in the art of preparing polyurethane films from aqueous dispersions, to prepare such films which have physical and handling properties sufficient for their use in conventional film applications. It would be further desirable if such films could be prepared with dispersions which are, in turn, prepared in the absence of organic solvents. It would be even further desirable if such films could be prepared without undesirable extra steps.
SUMMARY OF THE INVENTION
In one aspect, the present invention is a process for preparing polyurethane films comprising electrodepositing the film onto a substrate from a polyurethane dispersion.
In another aspect, the present invention is a polyurethane film prepared with process which includes electrodepositing the film onto a substrate from a polyurethane dispersion.
One advantage of the electrodeposition process of the present invention is that there is no need for an additional step to remove coagulants from the films, as with conventional coagulation processes. Another advantage is that in using electrodeposition, the amount of water that must be removed during a dewatering step is minimized. A third advantage is that the resulting film demonstrates much greater uniformity in thickness as compare to films prepared by conventional coagulation techniques.
The present invention has applicability in, for example, gloves, condoms, medical bags, angioplasty balloons, medical bellows, face masks, blood pressure cuffs and the like. The present invention also has applicability in parts associated with drug delivery mechanisms, including catheters, medical tubing, gaskets and o-rings. Moreover, the present invention has applicability in many non-medical items, such as, for example, non-medical gloves, swim caps, tool handle grips, industrial caps and plugs, windshield wiper boots, toy balloons, toys, electrical parts, covers and gaskets.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The films of the present invention can be prepared from any polyurethane prepolymer dispersion which is sufficiently stable to be stored but not so stable that it cannot be electrodeposited. The dispersion can be prepared in any way which results in a dispersion which can be used to prepare a film having acceptable physical properties for the anticipated use of the film. The dispersions can be done by a batch process or by a continuous process. If done by a batch process, preferably, the dispersion in done by an inverse phase process wherein a small amount of water, including a small amount of anionic surfactant, is first added to a continuous prepolymer phase and mixed and then more water is added with mixing until the phase inverts.
When dispersions of the present invention are prepared by means of a continuous process, preferably they are prepared by means of a high internal phase ratio (HIPR) process. Such processes are known and are disclosed in, for Example, U.S. Pat. No. 5,539,021 to Pate, et al., and WO 98/41552 A1 to Jakubowski, et al. When prepared by either method, the resulting dispersion should have a particle size sufficient to make the dispersion stable. The dispersions of the present invention will have a particle size of from 0.9 to about 0.05, preferably from about 0.5 to about 0.07 and even more preferably, from about 0.4 to about 0.10 microns. Most preferably, the particle size of the dispersions of the present invention is about 0.15 microns.
The polyurethane dispersions of the present invention are prepared from a nonionic polyurethane prepolymer. The nonionic prepolymers of the present invention are prepared with an aliphatic or aromatic diisocyanate. Preferably, the diisocyanate is an aromatic diisocyanate selected from the group consisting of MDI, TDI and mixtures thereof. TDI can be generally used with any commonly available isomer distribution. The most commonly available TDI has an isomer distribution of 80 percent of the 2,4 isomer and 20 percent of the 2,6 isomer. For the purposes of the present invention, TDI with other isomer distributions can also be used, but often at significantly higher cost.
When MDI is used with the formulations of the present invention, it preferably has a P,P′ isomer content of from about 99 percent to about 90 percent. Even more preferably, when MDI is used with the formulations of the present invention, it preferably has a P,P′ isomer content of from about 98 to about 92 percent. Most preferably, when MDI is used with the formulations of the present invention, it preferably has a P,P′ isomer content of about 94 percent. While MDI with such isomer distributions can be prepared by distillation during the MDI process, it can also be prepared by admixing commonly available products such as ISONATE 125M* and ISONATE 50OP*. (*ISONATE 125M and ISONATE 50OP are trade designations of The Dow Chemical Company.)
When mixtures of TDI and MDI are used to prepare the prepolymers of the present invention, they are admixed in a ratio of MDI to TDI of from about 99 percent MDI to about 80 percent MDI. More preferably, when mixtures of TDI and MDI are used to prepare the prepolymers of the present invention, they are admixed in a ratio of MDI to TDI of from about 98 percent MDI to about 90 percent MDI. Most preferably, when mixtures of TDI and MDI are used to prepare the prepolymers of the present invention, they are admixed in a ratio of MDI to TDI of about 96 percent MDI. Pref
Bhattacharjee Debkumar
Gribble Michael Y.
Koonce William A.
McIntyre James A.
Dow Global Technologies Inc.
Niland Patrick D.
LandOfFree
Polyurethane films prepared by electrodeposition from... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Polyurethane films prepared by electrodeposition from..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Polyurethane films prepared by electrodeposition from... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3166230