Chemical apparatus and process disinfecting – deodorizing – preser – Chemical reactor – Organic polymerization
Reexamination Certificate
1999-02-03
2001-08-28
Tran, Hien (Department: 1764)
Chemical apparatus and process disinfecting, deodorizing, preser
Chemical reactor
Organic polymerization
C422S133000, C422S110000, C422S112000, C422S111000
Reexamination Certificate
active
06280692
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to the production of polyurethane foams, and more particularly, to an apparatus for mixing certain polyurethane precursor materials in an open-loop, single pass, processing system, which eliminates the need for a mixing tank (e.g. a mixer with storage capicity).
BACKGROUND OF THE INVENTION
Historically, the manufacture of rigid foamed polyurethanes has typically included the use of various combinations of a polyol, isocyanate, water, and trichlorofluoromethane (CFC-11) as a foaming or blowing agent. Traditionally, the materials were mixed together in a step-wise process. The polyol provided the polymer component which, when reacted with isocyanate, would polymerize and harden. Both polyol and isocyanate are liquid materials. The blowing agents traditionally used, such as CFC-11, are also liquid at room temperature but upon heating or undergoing rapid pressure reduction will volatilize. The addition of a blowing agent during the mixture process will create gaseous expansion upon either temperature elevation or pressure reduction within the polymerizing polyol matrix thereby causing the polyol to foam. Foamed polyurethanes have good mechanical and thermal insulating properties and show excellent dimensional stability, and chemical resistance. The foaming process allows the polyurethane to expand to fill a void defined by a formed structure such as a refrigerator door or body panel. Polyurethane foams are widely used as thermal insulating materials for home appliances, truck trailers and railroad cars, insulated storage vessels, building materials, and certain parts for automobiles.
It is well known in the art of foam production that use of liquid blowing agents is highly desirable. The reason is that foaming of the polyol is desired to occur as a final step in the process as the reactants are added to their mold. Generally, the blowing agent is added to polyol and mixed, then the blended mixture is subsequently added to isocyanate just prior to injection into a mold. Concerning the mixture of polyol to blowing agent, it has been common practice in those industries making polyurethane foams to use batch mixing process techniques to mix large volumes because of the relative insolubility of some common blowing agents with polyol. In batch mixing, the blowing agent is added to the foam polymer (preferably polyol) and continuously mixed by recirculating the mixture through a mixing reservoir over a lengthy period of time resulting, eventually, in a batch of mixed or, “blended,” polyol and blowing agent. The time of mixing is directly related to the volume being mixed and the degree of difficulty of solubilizing the blowing agent into the polyol. Once the desired ratio of blowing agent and polyol was obtained and the materials thoroughly mixed, the process could be allowed to proceed to the polymerization and foaming steps by the addition of isocyanate and reduction of pressure or elevation of temperature. One aspect of realizing the solubility of some blowing agents with polyol was the necessity of keeping the blowing agent/polyol mix under constant high partial pressure of either an inert gas, such as nitrogen, or causing supersaturated conditions by pumping excess blowing agent into the mixing tank, the tank being kept in a closed loop isolated from and elevated relative to atmospheric pressure. For economic reasons, practitioners typically desired to make large quantity batches mixed well in advance of their needed use. The advance mixing and subsequent storage over a relatively long period of time allowed the use of common quality control techniques, such as sampling and weighing, to test the blended material and ensure compliance with specifications. Much of the mixing techniques were carried out on a trial and error basis. One significant problem of such mixing processes has been the retention of some blowing agents dispersed in the polyol. If, prior to use, the batches were found to be out of specification, the mixtures were reprocessed by adding the amounts of the various components to bring the blend within desired specifications. This process required remixing of the reagents with materials being routed back to mixing chambers. Such processes are inefficient, cumbersome and require additional and expensive equipment.
The prior art offers numerous examples of attempts at advancing the art of making polyurethane foam. Critical to the formation of foam is the amount and homogeneity of dissolved blowing agent. Properties of the quality of the foam will vary greatly depending on the amount, dispersion, and type of the blowing agent used. The present invention provides for an apparatus in which polyol and blowing agent may be mixed under highly controlled pressure levels and flow rates. A significant advantage of the present invention over prior art is the elimination of a need for batch mixing and the ability to monitor and control precisely both the amounts of reagents added together and the mixing thereof. The present invention allows for predetermination of all essential parameters of the materials used in the process of creating blended polyol giving reproducibility, predictability, and consistency in the foam formed from the blended polyol prepared by the present invention.
The present invention is patentably distinguishable from previous improvements in numerous respects. For example, U.S. Pat. No. 4,132,838 entitled, Process and Apparatus for the Preparation of a Reaction Mixture for the Production of Plastic Foams, by K. D. Kreuer et al., discloses an apparatus designed to obtain better control of mixing blowing gases with one of the reagents in order to achieve predictable homogeneity in the polyol/gas mixture. Kreuer's apparatus essentially controlled the velocity of flow rates of one of the reaction reagents into which a gas blowing agent was aspirated. Unlike the present invention which maintains the blowing agent in the liquid phase, Kreuer's device contemplated use of a vapor phase blowing agent, the addition of which to polyol was not under strict user control. Moreover, one embodiment of the Kreur system required return flow to a batch mixing chamber. Likewise, U.S. Pat. No. 4,157,427 entitled, Method for Entraining Gas in a Liquid Chemical Precursor for Reaction Injection Molding, by G. Ferber, disclosed an improvement in sampling the amount of vapor phase blowing agent infused into one of the reaction components. However, like other examples of the prior art, the apparatus contemplated recirculation of the reactant/gas mixture to a batch mixing chamber.
Various other improvements are found in the prior art which concern the mixing of a gas blowing agent. U.S. Pat. No. 4,288,230 entitled Method and a Device for the Production of a Solid-Forming or Foam-Forming Flowable Reaction Mixture, by W. Ebeling and V. Tennemann disclosed determining gas infusion by measuring quantitative flow rates of gas by taking density readings against volumetric flow. This device merely added gas and recirculated the gas/polyol mixture until the desired mix was obtained as determined by taking density and volumetric flow readings. In U.S. Pat. No. 4,376,172 entitled Closed Loop Control of Compressible Fluid Addition to a Mixture of such Fluid and a Liquid, by G. Belangee et al., a recirculation type system is disclosed that uses a plunger to measure the amount of gas blowing agent to be infused.
In U.S. Pat. No. 4,526,907 entitled Process and Device for the Preparation of a Reaction Mixture of at Least Two Components for the Production of Foams, by H. Thiele et al., another method of infusing gas blowing agent is disclosed for use in a closed loop system. Other patents such as, U.S. Pat. No. 4,933,115 entitled Process for the Production of a Flowable Mixture which Reacts to Form Foam from Flowable Components Stored in Storage Containers, by K. Krippl, and U.S. Pat. No. 5,000,882 entitled Apparatus for the Preparation of a Free-Flowing Mixture of Free-Flowing Components which Reacts to Form Foam, by F. Proksa, et al., disclose va
Blentek Systems, Inc.
Bradley Arant Rose & White LLP
Tran Hien
LandOfFree
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