Metal founding – Process – Shaping a forming surface
Reexamination Certificate
2001-04-06
2002-03-26
Foelak, Morton (Department: 1711)
Metal founding
Process
Shaping a forming surface
C164S246000, C521S056000, C521S059000, C521S060000, C526S201000
Reexamination Certificate
active
06360807
ABSTRACT:
FIELD OF THE INVENTION
The present invention is directed to processes for forming styrenic copolymers. In particular, the present invention is directed to processes for forming copolymers of styrenic and acrylic monomers. The invention is further directed to processes for forming expandable and expanded styrenic-acrylic copolymers.
BACKGROUND OF THE INVENTION
Styrenic polymers have a wide variety of applications, including the formation of expanded polystyrene which can be used to make a variety of products. Processes for forming styrenic polymers include emulsion polymerization, suspension polymerization, and the use of particular suspensions or emulsion aids.
Polymer particles are useful in applications such as the formation of expanded resins, for example, expanded polystyrene. Expanded polystyrene and other expanded resins can be prepared from expandable polymeric particles made by contacting the polymeric particles with a volatile compound known as a “blowing agent” or “expanding agent”. Such agents include aliphatic hydrocarbons such as butane, pentanes, hexanes, and halogenated hydrocarbons such as trichloromethane, trichlorofluoromethane, and methyl chloride. The particles in contact with the expanding agent may be expanded by heating, or by exposure to reduced pressure as in a vacuum. The size and size distribution of the expanded particles will depend upon the size and size distribution of the expandable particles.
Expanded and expandable polymeric resins have applications in packaging, consumer products, and in materials processing. Examples of materials processing applications for expanded polymeric resins include so-called “lost foam casting”, also called “evaporative pattern casting”. In lost foam casting, molten metal is poured into a pattern made of expanded polymeric material, i.e. a foam, coated with a refractory material surrounded and supported by unbounded sand. The foam is decomposed by the heat of the molten metal and replaced by the metal.
However, parts cast of metals such as iron, using expanded polystyrene foams, may have an unacceptable amount of surface defects and/or folds. The use of foams made of styrenic/acrylic copolymers can improve the quality of foam molds and metal parts made using such molds. Expandable resin compositions made of styrene-acrylic copolymers are described in U.S. Pat. No. 5,403,866.
A need remains for new and/or improved processes for forming styrenic copolymers.
SUMMARY OF THE INVENTION
One aspect of the present invention is a method for forming a styrenic copolymer. The method includes providing polymeric seeds in an aqueous medium; combining with the polymeric seeds, in the aqueous medium, a suspending agent and one or more surfactants in a ratio of about 1:175 or less to the weight of suspending agent, to form a seed mixture; providing a monomer mixture comprising from about 50 to about 90 percent by weight of one or more acrylic monomers, from about 10 to about 50 weight percent of one or more styrenic monomers, and one or more initiators; combining the monomer mixture with one or more expanding agents to form a reaction mixture; combining the seed mixture with about 100 to about 2500 weight percent of the reaction mixture, based on the weight of the seeds in the seed mixture, of the seed mixture to form a polymerization mixture; and heating the polymerization mixture to a polymerization temperature to effect formation of the copolymer.
In preferred embodiments, the total amount of one or more acrylic monomers in the monomer mixture is about 85 weight percent or less. In highly preferred embodiments, the total amount of styrenic and acrylic monomers in the monomer mixture includes from about 50 to about 85 percent by weight of one or more acrylic monomers, and from about 15 to about 50 percent by weight of one or more styrenic monomers.
In certain highly preferred embodiments, the styrenic monomers in the monomer mixture include at least one of styrene or alpha-methyl styrene.
In other highly preferred embodiments, the acrylic monomers in the monomer mixture include at least one of methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, 2-ethyl hexyl methacrylate, n-butyl acrylate, n-hexyl acrylate, and 2-ethyl hexyl acrylate.
In some embodiments, the polymeric seeds comprise, as polymerized units, one or more styrenic monomers.
In some embodiments, the polymeric seeds comprise, as polymerized units, one or more non-styrenic monomers, such as, for example, acrylic monomers.
In some embodiments, the polymeric seeds comprise, as polymerized units, styrenic monomers and non-styrenic monomers.
In certain preferred embodiments, the polymeric seeds comprise, as polymerized units, methyl acrylate.
A further aspect of the invention is a process for preparing a pattern for use in making metal castings. The method includes providing styrenic copolymer particles having diameters from about 150 to about 600 microns; pre-expanding the particles by subjecting the particles to atmospheric steam to obtain a density of about 0.5 to about 2.0 pounds per cubic foot; and molding the particles into the desired pattern having a density of about 2.0 pounds per cubic foot or less.
Another aspect of the present invention is a pattern for use in molding molten metal, formed from a styrenic copolymer by molding into a desired pattern styrenic copolymer particles having diameters from about 150 to about 600 microns, the particles having been pre-expanded by subjecting the particles to atmospheric steam to obtain a density of about 0.5 to about 2.0 pounds per cubic foot. In preferred embodiments, the pattern has a density of about 2.0 pounds per cubic foot or less.
These and other aspects of the invention will become apparent to those skilled in the art in view of the following disclosures and the appended claims.
DETAILED DESCRIPTION OF THE INVENTION
The present invention provides methods for forming styrenic copolymers. Monomers to be polymerized are provided in the form of a reaction mixture. The reaction mixture can be combined with small polymer particles referred to as “seeds”.
Seeds for use in the methods described herein may be styrenic or non-styrenic. Also, the seeds may be copolymeric. For example, the seeds may include copolymers of styrenic monomers and acrylic monomers such as methyl methacrylate. The seeds may include acrylic monomers such as methyl methacrylate, and may be, for example, acrylic homopolymers such as polymethylmethacrylate. Moreover, mixtures of two or more types of styrenic and/or non-styrenic seeds may be used.
The use of polymeric seeds in forming the styrenic copolymers can allow the formation of polymeric particles having narrower size distributions than are obtained using some conventional processes. The formation of styrenic polymers by incorporation of polymeric seeds is described in U.S. patent application Ser. No. 09/473,606, the disclosure of which is hereby incorporated herein by reference in its entirety.
Polymeric seeds can be prepared using methods known to those skilled in the art, including conventional emulsion or suspension polymerization methods, such as those disclosed in Odian, Principles of Polymerization, pp. 319-339 and pp. 287-288, John Wiley & Sons, Inc. (1982); or methods disclosed in U.S. Pat. Nos. 4,336,173; 4,459,378; and 2,673,194. The disclosures of each of the patents and publications referred to herein are hereby incorporated herein by reference in their entirety.
The polymer seeds are preferably provided in an aqueous seed suspension, as described hereinbelow. The styrenic monomers in the reaction mixture can be the same as or different from those polymerized in the seeds, and the ratios of monomers in the reaction mixture can be the same as or different from the ratios of polymerized monomers in the seeds. The total amount of styrenic monomers in the reaction mixture when combined with the seeds is preferably at least about 100 weight percent, more preferably at least about 200 weight percent, still more preferably at least about 300 weight percent, and even more preferabl
Schwarz Richard Anton
Sonnenberg Fred
Duane Morris & Heckscher LLP
Foelak Morton
StyroChem Delaware, Inc.
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