Patent Application
20070299152
The advantages of this invention will be apparent upon consideration of the following detailed disclosure of the invention, especially when taken in conjunction with the accompanying drawings wherein:
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the invention belongs. Although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, the preferred methods and materials are described herein. All references cited herein, including published or corresponding U.S. or foreign patent applications, issued U.S. or foreign patents, or any other references, are each incorporated by reference in their entireties, including all data, tables, figures, and text presented in the cited references. In the drawings, the thickness of the lines, layers, and regions may be exaggerated for clarity. It is to be noted that like numbers found throughout the figures denote like elements. The terms “composition” and “formulation” may be used interchangeably herein. In addition, the terms “increased average cell size” and “enlarged average cell size” may be used interchangeably herein. Further, the terms “composition” and “inventive composition” may be used interchangeably herein.
The present invention relates to polymer extruded or expanded foams that contain a cell size enlarging agent that increases the average cell size of the foamed product. The foams may be formed into an insulation product such as building insulation or underground insulation (e.g., highway, airport runway, railway, and underground utility insulation). The cell size enlarging agent increases the average cell size of the foamed product without detrimentally affecting the physical or thermal properties of the product formed. The composition used to form the expanded foams having an increased cell size includes a foamable polymer material, at least one blowing agent, and one or more cell size enlarging agents. The inventive composition is capable of forming a closed-cell foam material with an increased or enlarged average cell size compared to foams with no cell enlargers.
The foamable polymer material is the backbone of the formulation and provides strength, flexibility, toughness, and durability to the final product. The foamable polymer material is not particularly limited, and generally, any polymer capable of being foamed may be used as the foamable polymer in the resin mixture. The foamable polymer material may be thermoplastic or thermoset. The particular polymer material may be selected to provide sufficient mechanical strength and/or the process utilized to form final foamed polymer products. In addition, the foamable polymer material is preferably chemically stable, i.e., generally non-reactive, within the expected temperature range during formation and subsequent use in a polymeric foam. Non-limiting examples of suitable foamable polymer materials include alkenyl aromatic polymers, polyvinyl chloride (PVC), chlorinated polyvinyl chloride (CPVC), polyethylene, polypropylene, polycarbonates, polyisocyanurates, polyetherimides, polyamides, polyesters, polycarbonates, polymethylmethacrylate, polyurethanes, phenolics, polyolefins, styreneacrylonitrile, acrylonitrile butadiene styrene, acrylic/styrene/acrylonitrile block terpolymer (ASA), polysulfone, polyurethane, polyphenylenesulfide, acetal resins, polyamides, polyaramides, polyimides, polyacrylic acid esters, copolymers of ethylene and propylene, copolymers of styrene and butadiene, copolymers of vinylacetate and ethylene, rubber modified polymers, thermoplastic polymer blends, and combinations thereof.
Preferably, the foamable polymer material is an alkenyl aromatic polymer material. Suitable alkenyl aromatic polymer materials include alkenyl aromatic homopolymers and copolymers of alkenyl aromatic compounds and copolymerizable ethylenically unsaturated comonomers. In addition, the alkenyl aromatic polymer material may include minor proportions of non-alkenyl aromatic polymers. The alkenyl aromatic polymer material may be formed of one or more alkenyl aromatic homopolymers, one or more alkenyl aromatic copolymers, a blend of one or more of each of alkenyl aromatic homopolymers and copolymers, or blends thereof with a non-alkenyl aromatic polymer. Notwithstanding the components of the composition, the alkenyl aromatic polymer material may include greater than about 50 and preferably greater than about 70 weight percent alkenyl aromatic monomeric units. In a preferred embodiment of the invention, the alkenyl aromatic polymer material is formed entirely of alkenyl aromatic monomeric units.
Examples of alkenyl aromatic polymers include, but are not limited to, those alkenyl aromatic polymers derived from alkenyl aromatic compounds such as styrene, α-methylstyrene, ethylstyrene, vinyl benzene, vinyl toluene, chlorostyrene, and bromostyrene. A preferred alkenyl aromatic polymer is polystyrene. Minor amounts of monoethylenically unsaturated compounds such as C2 to C6 alkyl acids and esters, ionomeric derivatives, and C2 to C6 dienes may be copolymerized with alkenyl aromatic compounds. Non-limiting examples of copolymerizable compounds include acrylic acid, methacrylic acid, ethacrylic acid, maleic acid, itaconic acid, acrylonitrile, maleic anhydride, methyl acrylate, ethyl acrylate, isobutyl acrylate, n-butyl acrylate, methyl methacrylate, vinyl acetate and butadiene. The foamed products may be formed substantially of (e.g., greater than 95 percent), and most preferably, formed entirely of polystyrene. The foamable polymer material may be present in the composition in an amount from about 60% to about 95% by weight, preferably in an amount from about 80% to about 90% by weight, and more preferably in an amount of about 85% to about 90% by weight. As used herein, the term “% by weight” is meant to indicate a percentage based on 100% total weight of the composition.
The properties of the extruded foam or foam product may be modified by the selection of the molecular weight of the polymer. For example, the preparation of lower density extruded foam products is facilitated by using lower molecular weight polymers. On the other hand, the preparation of higher density extruded foam products is facilitated by the use of higher molecular weight or higher viscosity resins.
The composition also includes at least one blowing agent. Blowing agents useful in the practice of this invention include inorganic blowing agents, organic blowing agents, and chemical blowing agents. Any suitable blowing agent may be used in the practice on this invention. However, due to increased environmental concern over global warming and ozone depletion, it is desirable to utilize inorganic blowing agents. Examples of halo-carbon free inorganic blowing agents (e.g., environmentally friendly, non-ozone depleting blowing agents) include carbon dioxide, argon, water, air, nitrogen, and helium.
Organic blowing agents suitable for use in the present invention include, but are not limited to, C1 to C9 aliphatic hydrocarbons (e.g., methane, ethane, propane, n-butane, isobutane, n-pentane, isopentane, and neopentane), C1 to C3 aliphatic alcohols (e.g., methanol, ethanol, n-propanol, and isopropanol), and fully and partially halogenated aliphatic hydrocarbons having 1 to 4 carbon atoms (e.g., fluorocarbons, chlorocarbons, and chlorofluorocarbons). Examples of suitable fluorocarbons for use in the invention include methyl fluoride, perfluoromethane, ethyl fluoride, 1,1-difluoroethane (HFC-152a), 1,1,1-trifluoroethane (HFC-143a), 1,1,1,2-tetrafluoroethane (HFC-134a), pentafluoroethane, difluoromethane, perfluoroethane, 2,2-difluoropropane, 1,1,1-trifluoropropane, perfluoropropane, dichloropropane, difluoropropane, perfluorobutane, and perfluorocyclobutane. Partially halogenated chlorocarbons and chlorofluorocarbons for use in this invention may include methyl chloride, methylene chloride, ethyl chloride, 1,1,1-trichloroethane, 1,1-dichloro-1-fluoroethane (HCFC-141 b), 1-chloro-1,1-difluoroethane (HCFC-142b), chlorodifluoromethane (HCFC-22), 1,1-dichloro-2,2,2-trifluoroethane (HCFC-123), and 1-chloro-1,2,2,2-tetrafluoroethane (HCFC-124). Examples of fully halogenated chlorofluorocarbons include trichloromonofluoromethane (CFC-11), dichlorodifluoromethane (CFC-12), trichlorotrifluoroethane (CFC-113), 1,1,1-trifluoroethane, pentafluoroethane, dichlorotetrafluoroethane (CFC-114), chloroheptafluoropropane, and dichlorohexafluoropropane. Suitable chemical blowing agents include azodicarbonamide, azodiisobutyro-nitrile, benzenesulfonhydrazide, 4,4-oxybenzene sulfonyl-semicarbazide, p-toluene sulfonyl semi-carbazide, barium azodicarboxylate, and N,N′-dimethyl-N,N′-dinitrosoterephthalamide, and trihydrazino triazine.
The blowing agent may be present in the composition in an amount from about 2.0% to about 18.0% by weight. Preferably, the blowing agent is present in an amount from about 3.0% to about 10% by weight. The blowing agent utilized in the inventive composition is preferably selected such that the composition has a zero ozone depletion and low global warming potential, such as, for example, any inorganic blowing agent and/or non-hydrogenated chlorofluorocarbons (non-HCFCs).
As discussed above, the composition also contains one or more cell size enlarging agents. Desirably, the cell size enlarging agent dissolves or substantially dissolves in the foamable gel formed by the foamable polymer material and blowing agent discussed in detail below. Suitable examples of cell size enlarging agents for use in the inventive composition include ethylene vinyl acetate (EVA), ethylene methyl acrylate (EMA), polyethylene ethoxylate copolymer, polyethylene glycol (PEG), and combinations thereof. Structurally and chemically, these materials are based on polyethylene with added polarity. Preferably, the cell size enlarging agent is ethylene vinyl acetate and/or ethylene methyl acrylate. In addition, the cell size enlarging agent permits the formation of a foam with large cell sizes that are desirable in order to achieve a high insulation value (R-value) and to optimize the physical properties of the foamed product such as compressive strength and dimensional stability.
The use of ethylene vinyl acetate (EVA) and/or ethylene methyl acrylate (EMA) as a blowing agent in polymer foams is contradictory to the current thought of those ordinarily skilled in the art, and as such, one of skill in the art would not readily choose to utilize either of these ethylene compounds as a cell size enlarging agent. Conventionally, much of the testing with polystyrene resin foams has been conducted with a polyethylene additive. It was determined that these polyethylene additives separated from the polymer resin (e.g., polystyrene) and bloomed to the surface. As a result, those of skill in the art generally went looking for other additives for use in conventional blowing agents used in polystyrene foams. However, it was surprisingly and unexpectedly discovered in the present invention that ethylene vinyl acetate and ethylene methyl acrylate mix well or at least sufficiently well at low concentrations in the foamable polymer material and causes an increase in the cell size of the produced foam. Not wishing to be bound by theory, it is believed that the ester groups present on the EVA and the EMA provide a source of energy, and that it is this source of increased energy that increases the cell size within the foam.
In a similar manner of thinking, polyethylene glycol (PEG) is believed to provide better cell size enlarging properties to the foam and increased interaction with the blowing agent due to its increased energy source (i.e., the hydroxyl end group of the glycol) compared to polyethylene oxide (PEO). The fundamental difference between polyethylene oxide and polyethylene glycol is the terminal hydroxyl group of the glycol in the polyethylene glycol. Again, not wishing to be bound by theory, it is believed that it is this energy difference that allows the polyethylene glycol (PEG) to increase the cell size of the foam.
One advantage of the cell size enlarging agent is that it provides an increased cell size to the foamed product without detracting from the physical and thermal properties of a conventional foamed product formed without a cell size enlarging agent. The cell size enlarging agent also provides a smoother surface and minimal or no surface defects to the extruded, foamed product, especially when compared to conventional foamed products. In addition, the improved smoothness of the surface area of the foamed product permits the inventive foam to be used in a wider variety of applications. The average cell size of the inventive foam and foamed products is about 50 microns to about 500 microns and preferably about 150 microns to about 250 microns. The cell size enlarging agent may be present in the inventive formulation in an amount from about 0.1% to about 10% by weight, and preferably in an amount from about 0.25% to about 2.0% by weight.
Additionally, the inventive composition may optionally contain a nucleating agent. Examples of nucleating agents useful in the invention include calcium silicate, calcium carbonate, calcium stearate, clay, silica, titanium dioxide, barium sulfate, diatomaceous earth, and indigo. Adding a nucleating agent to the inventive composition permits the addition of cheap filler materials into the foamed product. Therefore, it is desirable to add as much nucleating agent as possible to introduce a large amount of fillers into the foamed product. However, nucleating agents tend to decrease the cell size of the cells in the foam, which results in undesirable R-values of the final foamed products. As a result, a nucleating agent is not present in large amounts in the present composition (if it is present at all) and the decrease in cell size caused by the nucleating agent may be offset or regulated by the cell size enlarging agent. It is to be appreciated that the addition of talc as a nucleating agent substantially reduces the cell size, and therefore is not a preferred nucleating agent for the present invention. The nucleating agent may be added to the composition in an amount up to about 1.0% by weight, preferably from about 0.1% to about 0.9% by weight, and more preferably from about 0.2% to about 0.4% by weight.
Further, the inventive composition may contain a fire retarding agent in an amount up to about 1.0% by weight. For example, fire retardant chemicals may be added in the extruded foam manufacturing process to impart fire retardant characteristics to the extruded foam products. Preferably, the fire retarding agent is added to the foamable gel, which is described below with respect to the formation of the inventive foam. Non-limiting examples of suitable fire retardant chemicals for use in the inventive composition include brominated aliphatic compounds such as hexabromocyclododecane and pentabromocyclohexane, brominated phenyl ethers, esters of tetrabromophthalic acid, and combinations thereof.
Optional additives such as infrared attenuating agents, plasticizing agents, pigments, elastomers, extrusion aids, antioxidants, fillers, antistatic agents, and/or UV absorbers may be incorporated into the inventive composition. These optional additives may be included in amounts necessary to obtain desired characteristics of the foamable gel or resultant extruded foam products. Although it is preferred that the additives are added to the polymer mixture, they may be incorporated in the polymer mixture before, during, or after the polymerization process used to make the polymer.
To form an alkenyl aromatic polymer foam having an enlarged cell size according to the principles of the instant invention, the foamable polymer material (e.g., an alkenyl aromatic polymer material) and the cell size enlarging agent may be heated to a temperature at or above the polymer's glass transition temperature or melting point to form a plasticized or a melt polymer material. One or more blowing agents may then be incorporated or mixed into the melt polymer material by any conventional method known to those of skill in the art such as, for example, with an extruder, a mixer, or a blender. As the blowing agent is added to the polymer melt, the blowing agent becomes soluble, i.e. dissolves, in the polymer melt and forms a foamable gel. Additionally, the blowing agent may be mixed with the melt polymer material at an elevated pressure sufficient to prevent substantial expansion of the melt polymer material and to generally disperse the blowing agent homogeneously in the melt polymer material. A nucleating agent may be blended in the polymer melt or dry blended with the polymer material prior to plasticizing or melting the foamable polymer material. In an alternate embodiment where polyethylene ethoxylate copolymer and/or polyethylene glycol (PEG) is utilized in a liquid form, it may be added directly to the extruder.
The foamable gel may then be cooled to a die melt temperature. The die melt temperature is typically cooler than the melt mix temperature to optimize physical characteristics of the foamed product. In addition, it is desirable that the die pressure be sufficient to prevent, or at least minimize, pre-foaming of the foamable gel. Pre-foaming is the undesirable premature foaming of the foamable gel before extrusion of the gel into a region of reduced pressure. Thus, the die pressure varies depending upon the identity and amount of blowing agent present in the foamable gel. The foamable gel may then be extruded through a die having a desired shape to a zone of lower or reduced pressure to form the desired foamed structure or foamed product. The zone of lower pressure is at a pressure lower than that in which the foamable gel is maintained prior to extrusion through the die. The lower pressure may be superatmospheric or subatmospheric (i.e., a vacuum), but is preferably at atmospheric level.
Extruded foams have a cellular structure with cells defined by cell membranes and struts. Struts are formed at the intersection of the cell membranes, with the cell membranes covering interconnecting cellular windows between the struts. In the present invention, the inventive composition preferably produces a substantially closed cellular foam with an average density of about 1.0 lbs/ft3 to about 5.0 lbs/ft3, preferably from about 1.5 lbs/ft3-3.0 lbs/ft3 and a cell size of from about 50 microns to about 500 microns which makes the foam especially useful for thermal insulation. It is to be appreciated that the phrase “substantially closed cell” is meant to indicate that the foam contains all closed cells or nearly all of the cells in the cellular structure are closed. It is desirable that not more than about 5.0% of the cells are open cells or otherwise “non-closed” cells. The closed cell structure helps to increase the R-value of a formed, foamed insulation product. R-value is defined as the thermal resistance to heat flow across a sample material of a unit area and known thickness caused by a temperature difference across it (m2*K/W). The R-value per inch may be about 4.0 to about 8.0. In a most preferred embodiment, the R-value per inch is about 5.0. It is to be appreciated that it is within the purview of the present invention to produce an open cell structure, although such an open cell structure is not a preferred embodiment.
Another aspect of the extruded inventive foams is that they possess a high level of dimensional stability. For example, the change in dimension in any direction is about 5% or less. In addition, the foam formed by the inventive composition is desirably monomodal and the cells have a relatively uniform average cell size. As used herein, the average cell size is an average of the cell sizes as determined in the X, Y and Z directions. In particular, the “X” direction is the direction of extrusion, the “Y” direction is the cross machine direction, and the “Z” direction is the thickness. In the present invention, the highest impact in cell enlargement is in the X and Y directions, which is desirable from an orientation and R-value perspective. The extruded inventive foam can be used to make insulation products such as rigid insulation boards, insulation foam, and packaging products.
There are numerous advantages of utilizing the composition of the present invention to form foam products. For example, the blowing agent utilized in the inventive formulation does not have a high global warming potential and has a low or zero ozone depleting potential. In addition, the cell size enlarging agents may be added to the melt polymer in a conventional fashion. Therefore, there is no need to modify existing equipment or change the manufacturing lines to accommodate the cell size enlarging agent. In addition, the cell size enlarging agent is environmentally friendly and does not create any negative environmental concerns. Further, the cell size enlarging agent increases the average cell size of the foamed product without detrimentally affecting the physical or thermal properties of the product.
Having generally described this invention, a further understanding can be obtained by reference to certain specific examples illustrated below which are provided for purposes of illustration only and are not intended to be all inclusive or limiting unless otherwise specified.
Compositions containing polystyrene, a non-ozone depleting blowing agent, and the cell size enlarging agents depicted in
As shown in
In this Example, a glycerol monostearate/ethylene vinyl acetate mixture (GMS/EVA), a glycerol monostearate and polystyrene mixture, and ethylene vinyl acetate (EVA) were utilized as cell size enlarging agents in a foamable composition according to the present invention. The foamable composition containing the desired cell size enlarging agent were run at two different concentrations, namely, 0.5% and 1.0% by weight cell size enlarging agent. In addition, the foamable compositions were run under two atmospheric conditions, specifically, at no vacuum and at 12 mm Hg. The results of the testing are illustrated in
Of the various cell size enlargers shown in
It can be seen from Tables 1-4 that when the components of the cell size were evaluated in the X, Y, and Z directions, the highest impact from the cell size enlarging agents is on the increase in the X and Y directions. Such an increase in the X and Y directions is desirable from an orientation perspective and thus, an R-value perspective (e.g., decreasing diffusion and increasing cell wall density). It can also be seen from Tables 1-4 that the cell size enlargers impact the cell morphology.
The invention of this application has been described above both generically and with regard to specific embodiments. Although the invention has been set forth in what is believed to be the preferred embodiments, a wide variety of alternatives known to those of skill in the art can be selected within the generic disclosure. The invention is not otherwise limited, except for the recitation of the claims set forth below.
This invention was made with Government support under Advanced Technology Program (ATP) Grant No. 70NANB2H3023 awarded by the National Institute of Standards and Technology (NIST). The Government may have certain rights to this invention.
