Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
2000-04-13
2002-09-17
Niland, Patrick D. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C002S161700, C002S168000, C427S372200, C427S385500, C428S423100, C524S589000, C524S590000, C524S839000, C524S840000, C528S044000, C528S045000, C528S049000, C604S327000, C604S328000, C604S347000
Reexamination Certificate
active
06451908
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention 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 polyalcoholand 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.
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 particularly desirable to prepare such dispersions which have enhanced shear stability.
SUMMARY OF THE INVENTION
In one aspect, the present invention is a process for preparing a polyurethane film comprising the steps of preparing a nonionic prepolymer formulation, the prepolymer formulation comprising a diisocyanate, an active hydrogen containing material, and a monol; and preparing an aqueous dispersion of the prepolymer, in the presence of a surfactant. Both steps occur in the substantial absence of an organic solvent.
In a second aspect, the present invention is a polyurethane film comprising a film prepared with a process which includes preparing a polyurethane dispersion from a formulation including from 0.1 to 2.0 percent by weight of a monol.
In a third aspect, the present invention is an aqueous polyurethane dispersion useful for preparing polyurethane films. The dispersion comprises the product of dispersing in water a nonionic polyurethane prepolymer prepared from a prepolymer formulation including a diisocyanate, one or more diols and a monol. The dispersion is formed in a two or more step process wherein, in a first step the prepolymer is formed and, in a subsequent step, an aqueous dispersion of the prepolymer is formed, in the presence of a surfactant. Both steps occur in the substantial absence of an organic solvent.
The present invention has the advantage of having increased shear stability. The dispersions of the present invention do not settle or coagulate prematurely. Moreover, the films of the present invention do not include the dermal irritants which occur in natural rubber latex. The films and dispersions of the present invention are thus suitable for use in applications such as, for example, medical applications.
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 or coagulated. 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 500P*. (*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. Preferably the prepolymers of the present invention are prepared with MDI or mixtures of MDI and TDI. Even more preferably, the prepolymers of the present invention are prepared with MDI as the only aromatic diisocyanate.
In one embodiment of the presen
Bhattacharjee Debkumar
Koonce William A.
Parks Franklin E.
Niland Patrick D.
The Dow Chemical Company
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