EP1246866A1

EP1246866A1 - Extruded polystyrene foam with vicat temperature over 100 c

Info

Publication number: EP1246866A1
Application number: EP00980360A
Authority: EP
Inventors: Larry M. Miller; Raymond M. Breindel; Mitchell Z. Weekley; Thomas E. Cisar
Original assignee: Owens Corning; Owens Corning Fiberglas Corp
Current assignee: Owens Corning
Priority date: 1999-11-30
Filing date: 2000-11-14
Publication date: 2002-10-09
Also published as: AU1763301A; WO2001040363A1

Abstract

This invention relates to a process for preparing a foam product comprising the steps of (A) forming a foamable mixture of (1) at least one linear styrenic polymer having a vicat softening temperature of greater than least 100°C (212°F), and (2) a blowing agent comprising a major amount of inorganic blowing agent under a pressure sufficient to prevent prefoaming of the mixture and (B) foaming the mixture into a region of reduced pressure to form the foam product. In another embodiment, the invention relates to a process for preparing a foam product comprising the steps of (A) forming a foamable mixture of (1) at least one linear polystyrene having a vicat softening temperature of greater than 100°C (212°F), and (2) a blowing agent comprising a major amount of inorganic blowing agent under a pressure sufficient to prevent prefoaming of the mixture, and (B) foaming the mixture through a die into a region of reduced pressure to form the foam product, wherein the pressure of the forming step (A) is at least twice the pressure at the die. The invention also includes foam boards made from the processes. The invention also relates to foam boards which are halogen free. The foams produced have improved compression strength. These foams have dimensional stable.

Description

EXTRUDED POLYSTYRENE FOAM WITH VICAT TEMPERATURE OVER 100 ° C

TECHNICAL FIELD AND INDUSTRIAL APPLICABILITY OF THE INVENTION The present invention generally relates to processes for preparing extruded foam products and products produced therefrom. More particularly the invention relates to processes for producing such products from styrenic polymers having a vicat softening temperature of greater than 100°C (212°F).

BACKGROUND OF THE INVENTION

Extruded synthetic resinous foams are useful materials for many applications including thermal insulation, decorative purposes, packaging and the like. Thermal insulation is one particularly important application for styrene polymer foams. In this application, it is desirable to maintain the insulating value of the foam for as long as possible. It is also desirable for the foam to have dimensional stability. The desirable characteristics can be achieved, in part, by providing foams having uniform cell size. For a considerable period of time, styrene polymer foams were extruded using various halo-carbons, such as methyl chloride, ethyl chloride, chlorocarbons, fluorocarbons (including HFCs) and chlorofluorocarbons (CFCs) including dichlorodifluoromethane, fluorohydrocarbons or chlorofluorohydrocarbons (which, as the name implies, contain at least one hydrogen atom and have been referred to as "soft CFCs", "HCFCs" and "HFCs"), as blowing agents.

Recently, the use of halo-carbons for applications including aerosols, refrigerants, foam-blowing agents and specialty solvents within the electronics and aerospace industries has been terminated by government regulation or is highly undesirable. This is because halo-carbons are believed to contribute to the destruction of the ozone layer in the stratosphere. Attempts have therefore been made to replace halo-carbons with hydrocarbons such as butane or inert gases such as carbon dioxide. However, there are a number of problems associated with using non-halo-carbon blowing agents including low solubility of the blowing agents in styrene polymers, low quality foam production and so on.

When foams are prepared with inorganic blowing agent as a key ingredient, then the foam may suffer from dimensional stability problems. Because the inorganic blowing agent leaves the foamed product at a faster rate than air enters. The rate of inorganic blowing agent leaving is greater than the rate of air entering, which creates a vacuum in the cell. This vacuum within the cells of the foam may lead to collapse of the foam. This vacuum must be tolerated by the polymers of the foams in order to avoid collapse of the foam. More flexible polymers are better at handling this pressure. One problem with high vicat polymer is their in-elastic or stiffer nature. High vicat polymers are less tolerant of the vacuum in the cells created by the rapid diffusion of the inorganic blowing agent.

It is desirable to have polymer and process which provides extruded foam which is halogen free and which is dimensionally stable.

SUMMARY OF THE INVENTION

This invention relates to a process for preparing a foam product comprising the steps of (A) forming a foamable mixture of (1) at least one linear styrenic polymer having a vicat softening temperature of greater than least 100°C (212°F), and (2) at least one blowing agent comprising a major amount of inorganic blowing agent under a pressure sufficient to prevent prefoaming of the mixture and (B) foaming the mixture into a region of reduced pressure to form the foam product. In another embodiment, the invention relates to a process for preparing a foam product comprising the steps of (A) forming a foamable mixture of (1) at least one linear polystyrene having a vicat softening temperature of greater than 100°C (212°F), and (2) a blowing agent comprising a major amount of inorganic blowing agent under a pressure sufficient to prevent prefoaming of the mixture, and (B) foaming the mixture through a die into a region of reduced pressure to form the foam product, wherein the pressure of the forming step (A) is at least twice the pressure at the die. The invention also includes foam boards made from the processes. The invention also relates to foam boards which are halogen free. The foams produced have improved compression strength. These foams have dimensional stable.

DETAILED DESCRIPTION AND PREFERRED EMBODIMENTS OF THE INVENTION

The foamable mixtures which are extruded and foamed into foam products, such as foam board, foam sheet and other foam structures, in accordance with the inventive process, contain at least one styrenic polymer and a blowing agent. The foamable mixtures may contain other optional additives. The styrenic polymers may be copolymers such as copolymers with other monomers.

The styrenic polymer has a vicat softening temperature of greater than 100 °C

(212°F). In another embodiment, the vicat softening temperature is great that about 102°C (215°F), or greater that 103°C (217°F), or greater than 104°C (219°F), or greater than 105°C (221 °F). The vicat softening temperature is determined by ASTM D-1525.

The vicat softening temperature may be the temperature of a single polymer or a blend of polymers. It has been discovered that polymers or blends thereof with the vicat softening temperatures of greater than 100°C (212°F) are able to produced foams, using one or more inorganic blowing agent as the blowing agent and the foam has small cells and dimensional stability.

The styrenic polymers are linear polymers. The term linear refers to polymer with a single polymeric backbone. It is understood that radial, and Y branched polymers are not linear polymers. The styrenic polymers are derived from styrene monomers. A styrene monomer is an aromatic compound characterized by the general formula

Ar-CH=CH₂ (I)

wherein Ar represents an aromatic hydrocarbon group of the benzene series, for example benzene, naphthalene, anthracene.

The styrenic polymers may be copolymers containing one or more styrene monomers and at least one copolymerizable monomer. A copolymerizable monomer is any monomer that can be polymerized with styrene monomers to form a styrene copolymer. Generally speaking, the copolymerizable monomer is a monomer containing an ethylenically unsaturated group. In one embodiment, the amount of copolymerizable monomer in the styrene copolymers is from about 0.1% to about 10%, and preferably from about 1% to about 5% by weight.

In a preferred embodiment, the copolymerizable monomer containing an ethylenically unsaturated group is an aromatic compound of Formula II and may be represented by the following formula

wherein R,, R₃, R₄, R₅ and R₆ are each independently hydrogen, chlorine, bromine, or alkyl groups containing from 1 to about 8 carbon atoms, and R₂ is hydrogen or methyl, with the proviso that a total number of carbon atoms in the monomer does not exceed 20. In a preferred embodiment, at least one of R₄, R₅ and R₆ are independently chlorine, bromine, or alkyl groups containing from 1 to about 8 carbon atoms. In another preferred embodiment, at least one of R₄, R₅ and R₆ is an alkyl group containing from 1 to about 4 carbon atoms, such as a methyl group, ethyl group, propyl group, isopropyl group or butyl group. In a more preferred embodiment, one of R₄, R₅ and R₆ is an alkyl group containing from 1 to about 4 carbon atoms and two of R₄, R₅ and R₆ are hydrogen. Examples of copolymerizable monomers according to Formula (II) include 3- methyl styrene, 4-methyl styrene, 2,4-dimethyl styrene, 2,5-dimethyl styrene, 4- chlorostyrene, 4-t-butyl styrene, 3-chlorostyrene, 4-chloromethyl styrene, 3-chloromethyl styrene, 4-bromostyrene, 3-bromostyrene, alpha-methyl styrene, alpha-2-dimethyl styrene. In another embodiment, the copolymerizable monomer containing an ethylenically unsaturated group is one or more monomers of acrylonitrile, phenylene ethers, vinyl chloride, vinylidene chloride, olefins such as ethylene, propylene and copolymers thereof, butadiene, maleic anhydride, citraconic anhydride, itaconic anhydride, vinyl acetate, vinyl toluene, and acrylates such as methacrylate, methyl methacrylate, ethyl acrylate.

The flow rate of the melted polymer or blend through an orifice is the melt flow index (MFI) or simply melt index. Determining MFI is a low cost, easily performed technique. Details may be found in a number of publications, such as Principles of Polymer Chemistry, by PJ.Flory, Cornell University Press, Ithaca, New York, 1953. In one embodiment, styrenic polymers or their blends have a melt index from about 1 to about 10, or from about 1.1 to about 8. When blends of styrenic polymers are used, then the melt index is the melt index of the blend. For example, a blend may contain 20% by weight of a 20 MI styrenic polymer and 80% by weight of a 2 MI styrenic polymer. For this blend, the melt index is the composite melt index of the components, namely 3.2. MFI can be determined, for example, in accordance with ISO 1133: 1997(E) (3^rd Edition). It is understood that for blends of polymers, polymers which have vicat softening temperatures below 100°C (212°F) may be used as long as the vicat softening temperature of the blend is greater than 100°C (212°F). In one embodiment, the blends are free of styrenic polymers with a vicat softening temperature of 100°C (212°F) or below.

Useful styrene resins (also referred to herein as polystyrenes) and copolymerizable monomer resins are available commercially from a variety of sources and the resins are available with different properties such as melt flow index, molecular weight and so on. For example, polystyrenes are available from ARCO Chemical Company under the general designation "DYLENE", for example DYLENE D-8; from Polysar Ltd., Sarnia, Ontario; Huntsman h202 (Vicat 105°C (221°F) and melt index of 3 melt index) and h209 (Vicat 98°C (208°F) and melt index of 18) and from Chevron Chemical Co., for example EB-3100.

The blowing agent utilized in the foamable mixtures contains a major amount of inorganic blowing agent. The inorganic blowing agent may be any of those known to the art, such as argon, nitrogen, air, water, carbon dioxide and the like, with carbon dioxide being preferred. In one embodiment, the inorganic blowing agents are those which are gases at atmospheric pressure and temperature. In one embodiment, the amount of the blowing agent added to the foamable mixture is from about 1% to about 16% by weight based on the weight of the styrenic polymer. In another embodiment, the amount of the blowing agent added to the foamable mixture is from about 2% to about 15% by weight based on the weight of the styrenic polymer. In yet another embodiment, the amount of the blowing agent added to the foamable mixture is from about 3% to about 10% by weight based on the weight of the styrenic polymer. In still yet another embodiment, the amount of the blowing agent added to the foamable mixture is from about 4% to about 8% by weight based on the weight of the styrenic polymer. Variations in the amount of blowing agent incorporated into the foamable mixture may be utilized, depending in part on the components of the blowing agent mixtures, to prepare extruded foamed bodies having different desirable characteristics. A major amount of inorganic blowing agent means that the blowing agent contains more than 50% by weight inorganic blowing agent. In one embodiment, the blowing agent contains more than about 60% inorganic blowing agent, and particularly from about 65% to about 100%) of inorganic blowing agent. In another embodiment, the blowing agent contains from about 70% to about 90% of inorganic blowing agent. In yet another embodiment, the blowing agent may be about 100% of inorganic blowing agent.

The blowing agent may be a mixture of an inorganic blowing agent and at least one supplemental blowing agent, such as lower alcohols or hydrocarbons. Lower alcohols or hydrocarbons are those having from 1 to about 6, or from 1 to about 4 carbon atoms. Lower alcohols include methanol, ethanol, propanol, isopropanol and butanol. The lower hydrocarbons include propane, butane, pentane, hexane.

Particularly useful mixtures of blowing agents include mixtures comprising: 51- 90% of carbon dioxide and 10-49% of ethanol; 60-80% of carbon dioxide and 20-40% of ethanol; 60-90%> of carbon dioxide and 10-40% of butane; 51-90% of carbon dioxide and 10-49% of methanol; 60-80% of carbon dioxide and 20-40% of methanol; 51-90% of carbon dioxide and 10-49% of water; and 60-80% of carbon dioxide and 20-40% of water. The optional use of a lower alcohol in combination with carbon dioxide provides extruded foam products or bodies having larger cell sizes (from about 1% to about 25% larger in size) when compared to similar density bodies produced with carbon dioxide without a lower alcohol. Additionally, the blowing agent blends including carbon dioxide may contribute to extruded foam bodies having improved compressive strengths at comparable densities. Extruded polystyrene bodies of acceptable characteristics are obtained utilizing the above blowing agent and blowing agent mixtures, and there is no necessity to use halo-carbon blowing agents.

In a preferred embodiment, the blowing agent is free of halogen blowing agents. Halogen blowing agents include chlorofluorocarbons, fluorocarbons, soft chlorofiuorocarbons, fluorohydrocarbons, and chlorofluorohydrocarbons (typically of methane and ethane). Specific examples of halogen blowing agents include methylchloride, ethylchloride, chlorotrifluoromethane, dichlorodifluoromethane, 1,2,2- trifluoro- 1 , 1 ,2-tri-chloroethane, chlorodifluoromethane, 1 , 1 -dichloro-2,2,2- trifluoroethane, l-chloro-l,l-difluoroethane, 1,1,1,2-tetrafluoroethane and 1,1-di-chloro- 1-fluoro ethane among others. Since halogen blowing agents can be harmful to the environment, their use is not desirable. The blowing agent including blowing agent mixtures utilized in the process may be added to the foamable mixtures in any conventional manner. The blowing agent can be incorporated into the foamable mixture (combined with the two styrenic polymers) before, during or after polymerization. In one embodiment, the blowing agent may be directly injected into the foamable mixture in a heat plastifying and mixing apparatus such as an extruder. When more than one blowing agent is to be utilized, each of the blowing agents may be separately injected into the heat plastifying and mixing apparatus.

In addition to the copolymer and blowing agent, the foamable mixtures may contain, and generally do contain other additives which are included to modify certain characteristics and or properties of the foamable mixtures or the resultant foam bodies. For example, nucleating agents may be included to further reduce the primary cell size. Suitable nucleating agents include talc, calcium silicate, calcium carbonate, clay, silica, titanium oxide, barium sulfate, diatomaceous earth, indigo. In one embodiment, from about 0.01 to about 1 part of nucleating agent per 100 parts of the styrenic polymer is incorporated into the foamable mixture. In a preferred embodiment, from about 0.05 to about 0.5 parts of nucleating agent per 100 parts of the styrenic polymer are incorporated into the foamable mixture.

Plasticizers may also be added to the foamable mixture to facilitate processing of the foamable mixture in an extruder. In one embodiment, the plasticizer is a low molecular weight resin (weight average molecular weight below about 20,000). In another embodiment, the plasticizer is a low molecular weight resin having a weight average molecular weight below about 15,000. In a preferred embodiment, the plasticizer is a low molecular weight resin having a weight average molecular weight below about 10,000. Examples of plasticizers include liquid paraffin or white oil, hydrogenated coconut oil, esters of C₄-C₂₀ monoalcohols, diols glycerine with higher fatty acids, styrene resin, vinyl toluene resin, alpha-methylstyrene resin, lower alcohols (containing 1 to about 4 carbon atoms). In one embodiment, from about 0.1 to about 20 parts of plasticizer per 100 parts of the styrenic polymer is incorporated into the foamable mixture. In a preferred embodiment, from about 1 to about 15 parts of plasticizer per 100 parts of the styrenic polymer are incorporated into the foamable mixture.

Elastomeric rubbers may also be added to the foamable mixture to facilitate processing of the foamable mixture in an extruder and to enhance relaxation of the resultant foam bodies. In a preferred embodiment, the elastomeric rubber is a soluble in a styrenic polymer. Examples of elastomeric rubbers include styrenic rubber, Kraton® (styrene-ethylene/butylene-styrene block copolymer), styrene-butadiene copolymer rubbers, acrylonitrile-butadiene-styrene copolymer rubbers. In one embodiment, from about 0.1 to about 10 parts of elastomeric rubber per 100 parts of the styrenic polymer is incorporated into the foamable mixture. In a preferred embodiment, from about 0.5 to about 5 parts of elastomeric rubber per 100 parts of the styrenic polymer are incorporated into the foamable mixture.

Flame-retardant chemicals may also be added to the foamable mixture to impart flame retardant characteristics to the resulting foamed bodies. Flame-retardant chemicals include brominated aliphatic compounds such as hexabromocyclododecane and pentabromocyclohexane, brominated phenyl ethers, esters of tetrabromophthalic acid, and combinations thereof. In one embodiment, from about 0.1 to about 5 parts of flame- retardant chemicals per 100 parts of the styrenic polymer is incorporated into the foamable mixture. In another embodiment, from about 0.5 to about 3 parts of flame- retardant chemicals per 100 parts of the styrenic polymer are incorporated into the foamable mixture.

Other useful additives include stabilizers, pigments, extrusion aids, antioxidants, fillers, antistatic agents, UV absorbers. These other additives can be included at any amount to obtain the desired characteristics in the foamable mixtures or resultant foamed bodies. The optional additives can be incorporated into the foamable mixture (combined with the two styrenic polymers and blowing agent) before, during or after polymerization.

Generally speaking, the components of the foamable mixture are combined and mixed, followed and/or accompanied by heating to a first temperature under a first pressure to form a plastified foamable mixture. From the extruder, the plastified foamable mixture is cooled to a second temperature (generally referred to as die melt temperature) and extruded into a region of reduced pressure to form a foam product. The second temperature is lower than the first temperature. However, any process for making foams from the foamable mixtures according to the invention may be employed. The first temperature must be sufficient to plastify or melt the mixture. In one embodiment, the first temperature is from about 135°C (275°F) to about 240°C (464°F) (below about 240°C (464°F)). In another embodiment, the first temperature is from about 145°C (293°F) to about 210°C (410°F) (below about 210°C (410°F)). In a preferred embodiment, the first temperature is from about 150°C (302°F) to about 165°C (329°F) (below about 165°C (329°F)). In one embodiment, the second temperature or die melt temperature is from about 140°C (284°F) to about 105°C (221°F) (below about 140°C (284°F)). In another embodiment, the second temperature or die melt temperature is from about 130°C (266°F) to about 110°C (230°F) (below about 130°C (266°F)). In a preferred embodiment, the second temperature or die melt temperature is from about 125°C (257°F) to about 115°C (239°F) (below about 125°C(257°F)).

The first pressure must be sufficient to prevent the foamable mixture containing the blowing agent from prefoaming. Prefoaming involves the undesirable premature foaming of the foamable mixture before it reaches the region of reduced pressure

(foaming of the foamable mixture before foaming is not desired). Accordingly, the first pressure varies depending upon the identity and amount of blowing agent in the foamable mixture. In one embodiment, the first pressure is from about 48 bar ( to about 345 bar. In another embodiment, the first pressure is from about 58 bar to about 325 bar. In a preferred embodiment, the first pressure is from about 80 bar to about 310 bar. The first pressure relates to the extruder discharge pressure, that is the pressure of the extrudate in the die before discharge to the region of lower pressure, for example atmospheric pressure or vacuum, such as a pressure from about 5 to about 25, or from about 10 to about 20 mm Hg absolute. The second pressure is sufficient to induce conversion of the foamable mixture into a foam body. In one embodiment, the second pressure is from about 0 psia (0 kPa) to about 28 psia (193kPa). In another embodiment, the second pressure is from about 1.4 psia (9.65 kPa) to about 21 psia (144 kPa). In a preferred embodiment, the second pressure is from about 2.8 psia (19.30 kPa) to about 15 psia (103 kPa).

The foam bodies (foam products including foam boards, foam sheets, foam insulation and other foam structures) prepared are characterized generally as having a relatively low density, typically less than about 3.75 lbs/ft³ (60.0 kg/m³). Density can be determined, for example, in accordance with ASTM Dl 622-88. In one embodiment, the extruded foam products have a density from 0.100 - 3.75 lbs/ft³ (1.60 - 60.0 kg/m³) In another embodiment, the extruded foam products have a density from 0.5 - 3.68 lbs/ft³ (8.00 - 59.0 kg/m³) In a preferred embodiment, the extruded foam products have a density from 1 - 3.62 lbs/ft³ (16.0 - 58.0 kg/m³). In a more preferred embodiment, the extruded foam products have a density from 1.5 - 3.56 lbs/ft³ (24.0 - 57.0 kg/m³).

The resultant foam bodies generally have a relatively small average cell size, typically less than about 0.4 mm. Average cell size can be determined, for example, according to ASTM D3576-77. In one embodiment, the foam bodies have an average cell size from about 0.01 to about 0.4 mm. In another embodiment, the foam bodies have an average cell size from about 0.05 to about 0.35 mm. In a preferred embodiment, the foam bodies have an average cell size from about 0.1 to about 0.325 mm. In a more preferred embodiment, the foam bodies have an average cell size from about 0.15 to about 0.25 mm.

The resultant foam bodies generally have a relatively uniform average cell size, typically more than about 50% of the cells have a size within about 0.06 mm of the average cell size. In one embodiment, more than about 60% of the cells have a size within about 0.06 mm of the average cell size. In another embodiment, more than about 50% of the cells have a size within about 0.05 mm of the average cell size. In yet another embodiment, more than about 50% of the cells have a size within about 0.045 mm of the average cell size. In one embodiment, the resultant foam has a cross sectional area of at least about

1,200, or at least about 10,000, or at least about 50,000 or at least about 60,000 mm². The resultant foam may have a cross sectional area up to about 600,000, or up to about 500,000 mm².

The resultant foam bodies generally contain a major amount of closed cells and a minor amount of open cells. The relative amount of closed cells can be determined, for example, according to ASTM D2856-A. In one embodiment, more than about 70% of the cells of the resultant foam bodies are closed cells. In another embodiment, more than about 80% of the cells of the resultant foam bodies are closed cells. In a preferred embodiment, more than about 90% of the cells of the resultant foam bodies are closed cells. In a more preferred embodiment, more than about 95% of the cells of the resultant foam bodies are closed cells.

In one embodiment, the resultant foam bodies made in accordance with the present invention have dimensional stability in any direction of about 5% or less. In another embodiment, the resultant foam bodies made in accordance with the present invention have dimensional stability in any direction of about 4% or less. In a preferred embodiment, the resultant foam bodies made in accordance with the present invention have dimensional stability in any direction of about 3% or less. In a more preferred embodiment, the resultant foam bodies made in accordance with the present invention have dimensional stability in any direction of about 2% or less. It has been discovered that it is difficult to prepare foams of greater thickness which have dimensional stability. One advantage of the present invention is the ability to make thick foams with inorganic blowing agents such as carbon dioxide with styrenic polymers having relatively high vicat softening temperatures. In one embodiment the foam products had a thickness of at least about 20 mm. It has been discovered that it is difficult to prepare foams of greater thickness which have dimensional stability. In one embodiment, the foams have a thickness of at least about 30, 40, 50 or 60 mm.

The following examples relate to the method and foam products made by the present invention. Unless otherwise indicated in the examples and throughout the specification and claims, the temperature are in degrees Celsius and the ratio and amounts are by weight.

EXAMPLE 1 A polymer with a vicat temperature of 105°C was fed to a corotating twin screw extruder at a rate of 165 kgs/hr, along with 5 kgs/hr of a flame retardant. Talc was added as a nucleating agent along with a colorant. The mixture was melted in the extruder and mixed with carbon dioxide at 95 grams/minute and ethanol at 25 grams minute. The resulting gel was thoroughly mixed, cooled and foamed to a region of lower pressure, resulting in a 60 mm thick product. The foam board product had a density of 46.2 kgs/cubic meter and an average cell diameter of 0.25mm.

EXAMPLE 2

A blend of styrenic polymer is prepared by feeding 80 Kgs/hr of a first polystyrene having a vicat softening temperature of 105°C and 3 melt index and 20 Kgs/hr of a second polystyrene having a Vicat softening temperature of 95°C and a 18 melt index into the extruder (using an extruder speed of 18 rpm) of example 1. Talc (2 kgs/hr) and colorant

(0.08 Kgs/hr) are also fed into the extruder. The mixture is melted at a temperature of about 220°C in the extruder and mixed with carbon dioxide (110 gms/min) and ethanol (28 gms/min) thoroughly. The resulting gel is cooled to about 110°C and extruded into a region of lower pressure (atmospheric) resulting in a foam product of 39.8 Kgs/cubic meter and an average cell size of 0.25 mm.

While the invention has been explained in relation to its preferred embodiments, it is to be understood that various modifications thereof will become apparent to those skilled in the art upon reading the specification. Therefore, it is to be understood that the invention disclosed herein is intended to cover such modifications as fall within the scope of the appended claims.

Claims

WHAT IS CLAIMED IS:

1. A process for preparing a foam product comprising the steps of (A) forming a foamable mixture of (1) at least one linear styrenic polymer or blend having a vicat softening temperature of greater than least 100°C (212°F), and (2) a non-halogenated blowing agent comprising a major amount of non-halogenated inorganic blowing agent under a pressure sufficient to prevent prefoaming of the mixture and (B) foaming the mixture into a region of reduced pressure to form the foam product.

2. The process of claim 1 wherein the polymer or blend has a vicat softening temperature of greater than 102°C (215°F).

3. The process of claim 1 wherein styrenic polymer or blend has a melt index of about 1.1 to about 10.

4. The process of claim 1 wherein the styrenic polymer is polystyrene.

5. The process of claim 1 wherein the inorganic blowing agent is carbon dioxide.

6. The method of claim 1 wherein the blowing agent is present in an amount from about 2% up to about 15% by weight of the styrenic polymer.

7. The process of claim 1 wherein the blowing agent further comprises a lower alcohol.

8. The process of claim 1 wherein the blowing agent mixture further comprises ethanol.

9. A process for preparing a foam product comprising the steps of (A) forming a foamable mixture of (1) at least one linear polystyrene or blend having a vicat softening temperature of greater than 100°C (212°F), and (2) a blowing agent comprising a major amount of carbon dioxide under a pressure sufficient to prevent prefoaming of the mixture, and (B) foaming the mixture through a die into a region of reduced pressure to form the foam product.

10. The process of claim 9 wherein the pressure of the forming step (A) is at least twice the pressure at the die.

11. The process of claim 9 wherein the polymer or blend has a vicat softening temperature of greater than 102°C (215°F).

12. The process of claim 9 wherein the inorganic blowing agent is carbon dioxide.

13. The method of claim 9 wherein the blowing agent is present in an amount from about 2% up to about 15% by weight of the polystyrene.

14. The process of claim 9 wherein the blowing agent further comprises a lower alcohol.

15. The process of claim 9 wherein the blowing agent mixture further comprises ethanol.

16. The process of claim 9 wherein the pressure of forming step is from about 200 to about 400 bar.

17. The process of claim 9 wherein the pressure in step (B) is from about 70 to about 200 bar.

18. The process of claim 9 wherein the forming step further comprises a homogenizing step which occurs at a pressure which is intermediate to the pressure at the die and the pressure of forming the mixture.

19. An extruded foam board comprising a board formed from a linear styrenic polymer having a vicat softening temperature of greater than 100°C (212°F) and wherein the cell gas of the foam board is halogen free.

20. The foam product of claim 19 wherein the foam has a density less than 3 pounds per cubic foot.

21. The foam product of claim 19 wherein the density is less than 2.5 pounds per cubic foot.

22. The foam product of claim 19 wherein the average size is less than 0.4 millimeters.

23. The foam product of claim 19 wherein the average cell size is less that about 0.2 mm.

24. The foam of claim 19 wherein the foam has a cross sectional area of 600 mm².

25. The foam of claim 19 wherein the foam has a cross sectional area of at least about 50,000 mm².