WO2013062760A1

WO2013062760A1 - Process to form a shaped foam article with reduced bow

Info

Publication number: WO2013062760A1
Application number: PCT/US2012/059476
Authority: WO
Inventors: Myron J. Maurer; Piyush Soni; Alain Sagnard; Matthew D. Mittag
Original assignee: Dow Global Technologies Llc
Priority date: 2011-10-28
Filing date: 2012-10-10
Publication date: 2013-05-02

Abstract

The invention relates to an improved method of cold forming a shaped foam article (10) with reduced bow (36) wherein the improvement comprising using a mold (65) comprising a B-side comprises a means to reduce bow (36), preferably the B-side comprises a concave surface.

Description

PROCESS TO FORM A SHAPED FOAM ARTICLE WITH REDUCED BOW

FIELD OF THE INVENTION The invention relates to an improved method for cold forming a shaped foam article having reduced bow. The improvement comprises the use of a mold having a surface comprising a means to reduce bow, preferably a concave surface.

BACKGROUND OF THE INVENTION

Various methods and techniques are currently known and employed in the industry for shaping articles from a thermoplastic foam material, such as extruded polystyrene (XPS) foams. For example, shapes such as toys and puzzles can be die-cut from foams that are formed by extruding a thermoplastic resin containing a blowing agent. There are also examples of foam sheet being shaped into articles such as dishes, cups, egg cartons, trays, and various types of food containers, such as fast food clam shells, take out/take home containers, and the like. More complex shaped foam articles can be made by

thermoforming thermoplastic foam sheet. These methods lend themselves to the manufacture of relatively simple shaped articles from typically thin foams which are easily extracted from the molds used to produce them.

Recently, there have been significant advances in shaping more complex, and in particular, thicker (i.e., foams greater than 1mm thick) thermoplastic foam shaped articles, for example see USP Publication 2009-0062410 and WO2011/005658. The process disclosed therein is referred to as a cold forming process. Said process may produce thicker shaped foam articles by pressing unique foam compositions and/or foam structures at ambient temperatures. For example, cold forming polystyrene foam has found success in applications such as doors, wash basins, shower and bath surrounds, refrigerator and freezer panes, surfboards, pallets, doors, transformer mounting pads, automotive articles, and the like. However, some shaped formed articles made by such a cold forming process may exhibit bowing or cupping.

Attempts to reduce bow resulting in thinner shaped foam articles made by traditional forming techniques, such as thermoforming, have been developed. For example, see USP 4,053,549 wherein reinforcing grooves are molded into the shaped foam article to reduce bow. Alternatively, USP 4,058,247 discloses a thin foam packaging tray wherein the geometry of the molded tray is changed (from the desired end-product design) so that when the article to be packaged is inserted into the tray, the weight of the object deforms the tray into the desired end-product shape.

It would be desirable to have a method to reduce bow in thicker more complex shaped foam articles wherein the shaped foam article as produced is the desired end-product shape without any additional reinforcing structures, such as grooves and/or ribs.

SUMMARY OF THE INVENTION The present invention is such an improved method to manufacture a shaped foam article with reduced bow comprising the steps of: (i) extruding a thermoplastic polymer with a blowing agent to form a thermoplastic polymer foam plank, the plank having a thickness, a top surface, and a bottom surface in which said surfaces lie in the plane defined by the direction of extrusion and the width of the plank, wherein the foam plank has a vertical compressive balance equal to or greater than 0.4; (ii) cutting the foam plank to form a foam blank with a pressing surface and a non-pressing surface, (iii) shaping the foam blank into a shaped foam article by (iii)(a) contacting the foam blank with a mold, said mold comprising an A-side having a cavity which contacts the pressing surface of the foam blank and a B-side which contacts the non-pressing surface of the foam blank and (iii)(b)

pressing the pressing surface of the foam blank with the A-side of the mold whereby forming a shaped foam article, wherein the improvement comprises the B-side of the mold comprises a means to reduce bow in the shaped foam article, preferably said means is adjustable.

A preferred embodiment of the present invention is the method described herein above wherein the means to reduce bow is providing a concave surface in the B-side of the mold.

In another embodiment of the present invention, for the method described herein above when the foam blank is bowed in a concave manner the means to reduce bow is providing a concave surface to the B-side of the mold.

In another embodiment of the present invention, for the method described herein above when the foam blank is bowed in a convex manner the means to reduce bow is providing a convex surface to the B-side of the mold.

Preferably in the invention described herein above, the mold, both the A-sided and B-side, is not heated or cooled and the shaped foam article is formed at ambient temperature. Preferably in the invention described herein above, the foam blank has a cell gas pressure equal to or less than 1 atmosphere.

Preferably in the invention described herein above, the thermoplastic polymer is polyethylene, polypropylene, copolymer of polyethylene and polypropylene; polystyrene, high impact polystyrene; styrene and acrylonitrile copolymer, acrylonitrile, butadiene, and styrene terpolymer, polycarbonate; polyvinyl chloride; polyphenylene oxide and polystyrene blend.

Preferably in the invention described herein above, the blowing agent is a chemical blowing agent, an inorganic gas, an organic blowing agent, carbon dioxide, or combinations thereof.

Another embodiment of the present invention is a shaped foam article made by the method described herein above.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustration of the step change in the shaped foam article of this invention.

FIG. 2 is a cross-sectional view of a foam plank.

FIG. 3 is a cross-sectional view of foam blanks cut from the foam plank of FIG. 2. FIG. 4 is a cross-sectional view of a stationary platen comprising a concave portion. FIG. 5 is a cross-sectional view of a foam blank in a forming tool having a stationary platen comprising a concave portion in the open position prior to shaping.

FIG. 6 is a cross-sectional view of a shaped foam article in a forming tool having a stationary platen comprising a concave portion in the closed position.

FIG. 7 is a cross-sectional view of a shaped foam article in a forming tool having a stationary platen comprising a concave portion in the open position after shaping.

FIG. 8 shows the forming tool with a shaped A-side and flat B-side, platens, and stop blocks used in the Comparative Examples. DETAILED DESCRIPTION OF THE INVENTION

The present invention is an improvement in the method of forming shaped foam articles wherein the improvement is a means to reduce bow in the shaped article after forming. The shaped foam article of the present invention can be made from any foam composition. A foam composition comprises a continuous matrix material with cells defined therein. Cellular (foam) has the meaning commonly understood in the art in which a polymer has a substantially lowered apparent density comprised of cells that are closed or open. Closed cell means that the gas within that cell is isolated from another cell by the polymer walls forming the cell. Open cell means that the gas in that cell is not so restricted and is able to flow without passing through any polymer cell walls to the atmosphere. The foam article of the present invention can be open or closed celled. A closed cell foam has less than 30 percent, preferably 20 percent or less, more preferably 10 percent or less and still more preferably 5 percent or less and most preferably one percent or less open cell content. A closed cell foam can have zero percent open cell content. Conversely, an open cell foam has 30 percent or more, preferably 50 percent or more, still more preferably 70 percent or more, yet more preferably 90 percent or more open cell content. An open cell foam can have 95 percent or more and even 100 percent open cell content. Unless otherwise noted, open cell content is determined according to American Society for Testing and Materials ( ASTM) method D6226-05.

Desirably the foam article comprises polymeric foam, which is a foam composition with a polymeric continuous matrix material (polymer matrix material). Any polymeric foam is suitable including extruded polymeric foam, expanded polymeric foam and molded polymeric foam. The polymeric foam can comprise, and desirably comprises as a continuous phase, a thermoplastic or a thermoset polymer matrix material. Desirably, the polymer matrix material has a thermoplastic polymer continuous phase.

A polymeric foam article for use in the present invention can comprise or consist of one or more thermoset polymer, thermoplastic polymer, or combinations or blends thereof. Suitable thermoset polymers include thermoset epoxy foams, phenolic foams, urea- formaldehyde foams, polyurethane foams, and the like.

Suitable thermoplastic polymers include any one or any combination of more than one thermoplastic polymer. Olefinic polymers, alkenyl-aromatic homopolymers and copolymers comprising both olefinic and alkenyl aromatic components are suitable.

Examples of suitable olefinic polymers include homopolymers and copolymers of ethylene and propylene (e.g., polyethylene, polypropylene, and copolymers of polyethylene and polypropylene). Alkenyl-aromatic polymers such as polystyrene and polypheny lene oxide/polystyrene blends are particularly suitable polymers for the foam article of the present invention. Desirably, the foam article comprises a polymeric foam having a polymer matrix comprising or consisting of one or more than one alkenyl-aromatic polymer. An alkenyl- aromatic polymer is a polymer containing alkenyl aromatic monomers polymerized into the polymer structure. Alkenyl-aromatic polymer can be homopolymers, copolymers or blends of homopolymers and copolymers. Alkenyl-aromatic copolymers can be random copolymers, alternating copolymers, block copolymers, rubber modified, or any combination thereof and my be linear, branched or a mixture thereof.

Styrenic polymers are particularly desirably alkenyl-aromatic polymers. Styrenic polymers have styrene and/or substituted styrene monomer (e.g., alpha methyl styrene) polymerized in the polymer backbone and include both styrene homopolymer, copolymer and blends thereof. Polystyrene and high impact modified polystyrene are two preferred styrenic polymers.

Examples of styrenic copolymers suitable for the present invention include copolymers of styrene with one or more of the following: 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.

Polystyrene (PS) is a preferred styrenic polymer for use in the foam articles of the present invention because of their good balance between cost property performance.

Styrene-acrylonitrile copolymer (SAN) is a particularly desirable alkenyl-aromatic polymer for use in the foam articles of the present invention because of its ease of manufacture and monomer availability. SAN copolymer can be a block copolymer or a random copolymer, and can be linear or branched. SAN provides a higher water solubility than polystyrene homopolymer, thereby facilitating use of an aqueous blowing agent. SAN also has higher heat distortion temperature than polystyrene homopolymer, which provides for a foam having a higher use temperature than a polystyrene homopolymer foam.

Desirable embodiments of the present process employ polymer compositions that comprise, even consist of SAN. The one or more alkenyl-aromatic polymer, even the polymer composition itself may comprise or consist of a polymer blend of SAN with another polymer such as polystyrene homopolymer.

Whether the polymer composition contains only SAN, or SAN with other polymers, the acrylonitrile (AN) component of the SAN is desirably present at a concentration of 1 weight percent or more, preferably 5 weight percent or more, more preferably 10 weight percent or more based on the weight of all polymers in the polymer composition. The AN component of the SAN is desirably present at a concentration of 50 weight percent or less, typically 30 weight percent or less based on the weight of all polymers in the polymer composition. When AN is present at a concentration of less than 1 weight percent, the water solubility improvement is minimal over polystyrene unless another hydrophilic component is present. When AN is present at a concentration greater than 50 weight percent, the polymer composition tends to suffer from thermal instability while in a melt phase in an extruder.

The styrenic polymer may be of any useful weight average molecular weight (MW). Illustratively, the molecular weight of a styrenic polymer or styrenic copolymer may be from 10,000 to 1,000,000. The molecular weight of a styrenic polymer is desirably less than about 200,000, which surprisingly aids in forming a shaped foam part retaining excellent surface finish and dimensional control. In ascending further preference, the molecular weight of a styrenic polymer or styrenic copolymer is less than about 190,000, 180,000, 175,000, 170,000, 165,000, 160,000, 155,000, 150,000, 145,000, 140,000, 135,000, 130,000, 125,000, 120,000, 115,000, 110,000, 105,000, 100,000, 95,000, and 90,000. For clarity, molecular weight herein is reported as weight average molecular weight unless explicitly stated otherwise. The molecular weight may be determined by any suitable method such as those known in the art.

Rubber modified homopolymers and copolymers of styrenic polymers are preferred styrenic polymers for use in the foam articles of the present invention, particularly when improved impact is desired. Such polymers include the rubber modified homopolymers and copolymers of styrene or alpha-methylstyrene with a copolymerizable comonomer.

Preferred comonomers include acrylonitrile which may be employed alone or in

combination with other comonomers particularly methylmethacrylate, methacrylonitrile, fumaronitrile and/or an N-arylmaleimide such as N-phenylmaleimide. Highly preferred copolymers contain from about 70 to about 80 percent styrene monomer and 30 to 20 percent acrylonitrile monomer.

Suitable rubbers include the well known homopolymers and copolymers of conjugated dienes, particularly butadiene, as well as other rubbery polymers such as olefin polymers, particularly copolymers of ethylene, propylene and optionally a nonconjugated diene, or acrylate rubbers, particularly homopolymers and copolymers of alkyl acrylates having from 4 to 6 carbons in the alkyl group. In addition, mixtures of the foregoing rubbery polymers may be employed if desired. Preferred rubbers are homopolymers of butadiene and copolymers thereof in an amount equal to or greater than about 5 weight percent, preferably equal to or greater than about 7 weight percent, more preferably equal to or greater than about 10 weight percent and even more preferably equal to or greater than 12 weight percent based on the total weight or the rubber modified styrenic polymer.

Preferred rubbers present in an amount equal to or less than about 30 weight percent, preferably equal to or less than about 25 weight percent, more preferably equal to or less than about 20 weight percent and even more preferably equal to or less than 15 weight percent based on the total weight or the rubber modified styrenic polymer. Such rubber copolymers may be random or block copolymers and in addition may be hydrogenated to remove residual unsaturation.

The rubber modified homopolymers or copolymers are preferably prepared by a graft generating process such as by a bulk or solution polymerization or an emulsion polymerization of the copolymer in the presence of the rubbery polymer. Depending on the desired properties of the foam article, the rubbers' particle size may be large (for example greater than 2 micron) or small (for example less than 2 micron) and may be a monomodal average size or multimodal, i.e., mixtures of different size rubber particle sizes, for instance a mixture of large and small rubber particles. In the rubber grafting process various amounts of an ungrafted matrix of the homopolymer or copolymer are also formed. In the solution or bulk polymerization of a rubber modified (co)polymer of a vinyl aromatic monomer, a matrix (co)polymer is formed. The matrix further contains rubber particles having (co)polymer grafted thereto and occluded therein.

High impact polystyrene (HIPS) is a particularly desirable rubber-modified alkenyl- aromatic homopolymer for use in the foam articles of the present invention because of its good blend of cost and performance properties, requiring improved impact strength.

Butadiene, acrylonitrile, and styrene (ABS) terpolymer is a particularly desirable rubber-modified alkenyl- aromatic copolymer for use in the foam articles of the present invention because of its good blend of cost and performance properties, requiring improved impact strength and improved thermal properties.

Foam articles for use in the present invention may be prepared by an extrusion process. An extrusion process prepares a foamable polymer composition of a thermoplastic polymer with a blowing agent in an extruder by heating a thermoplastic polymer composition to soften it, mixing a blowing agent composition together with the softened thermoplastic polymer composition at a mixing temperature and mixing pressure that precludes expansion of the blowing agent to any meaningful extent (preferably, that precludes any blowing agent expansion) and then extruding (expelling) the foamable polymer composition through a die into an environment having a temperature and pressure below the mixing temperature and pressure. Upon expelling the foamable polymer composition into the lower pressure the blowing agent expands the thermoplastic polymer into a thermoplastic polymer foam. Desirably, the foamable polymer composition is cooled after mixing and prior to expelling it through the die. In a continuous process, the foamable polymer composition is expelled at an essentially constant rate into the lower pressure to enable essentially continuous foaming. An extruded foam can be a continuous, seamless structure, such as a sheet or profile, as opposed to a bead foam structure or other composition comprising multiple individual foams that are assembled together in order to maximize structural integrity and thermal insulating capability.

Accumulative extrusion is a semi-continuous extrusion process that comprises: 1) mixing a thermoplastic material and a blowing agent composition to form a foamable polymer composition; 2) extruding the foamable polymer composition into a holding zone maintained at a temperature and pressure which does not allow the foamable polymer composition to foam; the holding zone having a die defining an orifice opening into a zone of lower pressure at which the foamable polymer composition foams and an openable gate closing the die orifice; 3) periodically opening the gate while substantially concurrently applying mechanical pressure by means of a movable ram on the foamable polymer composition to eject it from the holding zone through the die orifice into the zone of lower pressure, and 4) allowing the ejected foamable polymer composition to expand to form the foam. USP 4,323,528, hereby incorporated by reference, discloses such a process in a context of making polyolefin foams, yet which is readily adaptable to aromatic polymer foam. USP 3,268,636 discloses the process when it takes place in an injection molding machine and the thermoplastic with blowing agent is injected into a mold and allowed to foam, this process is sometimes called structural foam molding.

Suitable blowing agents include one or any combination of more than one of the following: inorganic gases such as carbon dioxide, argon, nitrogen, and air; organic blowing agents such as water, aliphatic and cyclic hydrocarbons having from one to nine carbons including methane, ethane, propane, n-butane, isobutane, n-pentane, isopentane, neopentane, cyclobutane, and cyclopentane; fully and partially halogenated alkanes and alkenes having from one to five carbons, preferably that are chlorine-free (e.g., difluoromethane (HFC-32), perfluoromethane, ethyl fluoride (HFC-161), 1,1,- difluoroethane (HFC-152a), 1,1,1-trifluoroethane (HFC-143a), 1,1,2,2-tetrafluoroethane (HFC-134), 1,1,1,2 tetrafluoroethane (HFC-134a), pentafluoroethane (HFC-125), perfluoroethane, 2,2-difluoropropane (HFC-272fb), 1,1,1-trifluoropropane (HFC-263fb), 1,1,1,2,3,3,3-heptafluoropropane (HFC-227ea), 1,1,1,3,3-pentafluoropropane (HFC-245fa), and 1,1,1,3,3-pentafluorobutane (HFC-365mfc)); fully and partially halogenated polymers and copolymers, desirably fluorinated polymers and copolymers, even more preferably chlorine-free fluorintated polymers and copolymers; aliphatic alcohols having from one to five carbons such as methanol, ethanol, n-propanol, and isopropanol; carbonyl containing compounds such as acetone, 2-butanone, and acetaldehyde; ether containing compounds such as dimethyl ether, diethyl ether, methyl ethyl ether; carboxylate compounds such as methyl formate, methyl acetate, ethyl acetate; carboxylic acid and chemical blowing agents such as azodicarbonamide, azodiisobutyronitrile, benzenesulfo-hydrazide, 4,4-oxybenzene sulfonyl semi-carbazide, p-toluene sulfonyl semi-carbazide, barium azodicarboxylate, Ν,Ν'- dimethyl-N,N'-dinitrosoterephthalamide, trihydrazino triazine and sodium bicarbonate.

The amount of blowing agent can be determined by one of ordinary skill in the art without undue experimentation for a given thermoplastic to be foamed based on the type thermoplastic polymer, the type of blowing agent, the shape/configuration of the foam article, and the desired foam density. Generally, the foam article may have a density of from about 16 kilograms per cubic meter (kg/m³) to about 200 kg/m³ or more. The foam density, typically, is selected depending on the particular application. Preferably the foam density is equal to or less than about 160 kg/m³, more preferably equal to or less than about 120 kg/m³, and most preferably equal to or less than about 100 kg/m³.

The cells of the foam article may have an average size (largest dimension) of from about 0.05 to about 5.0 millimeter (mm), especially from about 0.1 to about 3.0 mm, as measured by ASTM D-3576-98. Foam articles having larger average cell sizes, of especially about 1.0 to about 3.0 mm or about 1.0 to about 2.0 mm in the largest dimension, are of particular use when the foam fails to have a compressive ratio of at least 0.4 as described in the following few paragraphs.

In one embodiment of the present invention, to facilitate the shape retention and appearance in the shaped foam article after pressing the shaped foam blank, particularly foams comprising closed cells, it is desirable that the average cell gas pressure is equal to or less than 1.4 atmospheres. In one embodiment, it is desirable that the cell gas pressure is equal to or less than atmospheric pressure to minimize the potential for spring back of the foam after pressing causing less than desirable shape retention. Preferably, the average pressure of the closed cells (i.e., average closed cell gas pressure) is equal to or less than 1 atmosphere, preferably equal to or less than 0.95 atmosphere, more preferably equal to or less than 0.90 atmosphere, even more preferably equal to or less than 0.85 atmosphere, and most preferably equal to or less than 0.80 atmosphere.

Cell gas pressures may be determined from standard cell pressure versus aging curves. Alternatively, cell gas pressure can be determined according to ASTM D7132-05 if the initial time the foam is made is known. If the initial time the foam is made is unknown, then the following alternative empirical method can used: The average internal gas pressure of the closed cells from three samples is determined on cubes of foam measuring approximately 50mm. One cube is placed in a furnace set to 85°C under vacuum of at least 1 Torr or less, a second cube is placed in a furnace set to 85°C at 0.5 atm, and the third cube is placed in the furnace at 85 °C at atmospheric pressure. After 12 hours, each sample is allowed to cool to room temperature in the furnace without changing the pressure in the furnace. After the cube is cool, it is removed from the furnace and the maximum dimensional change in each orthogonal direction is determined. The maximum linear dimensional change is then determined from the measurements and plotted against the pressure and curve fit with a straight line using linear regression analysis with average internal cell pressure being the pressure where the fitted line has zero dimensional change.

The compressive strength of the foam is determined in accordance with industry standard test methods such as ASTM D1621 or modifications thereof. The compressive strength of the foam article is established when the compressive strength of the foam is evaluated in three orthogonal directions, E, V and H, where E is the direction of extrusion, V is the direction of vertical expansion after it exits the extrusion die and H is the direction of horizontal expansion of the foam after it exits the extrusion die. These measured compressive strengths, C_E, C_V and C_H, respectively, are related to the sum of these compressive strengths, C_T, such that at least one of C_E/C_T, C_V C_T and C_H/C_T, has a value of at least 0.40, preferably a value of at least 0.45 and most preferably a value of at least 0.50. When using such a foam, the pressing direction is desirably parallel to the maximum value in the foam.

The polymer used to make the foam article of the present invention may contain additives, typically dispersed within the continuous matrix material. Common additives include any one or combination of more than one of the following: infrared attenuating agents (for example, carbon black, graphite, metal flake, titanium dioxide); clays such as natural absorbent clays (for example, kaolinite and montmorillonite) and synthetic clays; nucleating agents (for example, talc and magnesium silicate); fillers such as glass or polymeric fibers or glass or polymeric beads; flame retardants (for example, brominated flame retardants such as brominated polymers, hexabromocyclododecane, phosphorous flame retardants such as triphenylphosphate, and flame retardant packages that may including synergists such as, or example, dicumyl and polycumyl); lubricants (for example, calcium stearate and barium stearate); acid scavengers (for example, magnesium oxide and tetrasodium pyrophosphate); UV light stabilizers; thermal stabilizers; and colorants such as dyes and/or pigments.

A most preferred foam article is a shaped foam article which may be prepared from a foamed polymer as described hereinabove and further shaped to give a shaped foam article 10. As defined herein, shaped means the foamed article typically has one or more contour that create a step change (impression) in height 32 of at least 1 millimeter or more in the shaped foam article 10 having thickness 17 as shown in FIG. 1. A shaped article has at least one surface that is not planar.

As per convention, but not limited by, the extrusion of the plank is taken to be horizontally extruded (the direction of extrusion is orthogonal to the direction of gravity). Using such convention, the plank's top surface is that farthest from the ground and the plank's bottom surface is that closest to the ground, with the height of the foam (thickness) being orthogonal to the ground when being extruded.

The forming of the shaped foam articles is surprisingly enhanced by using foam planks that have at least one direction where at least one of CE/CT, CV CT and CH CT is at least 0.4 said one of CE/CT, CV CT and CH/CT (compressive ratio or compressive balance), CE, CV and CH being the compressive strength of the cellular polymer in each of three orthogonal directions E, V and H where one of these directions is the direction of maximum compressive strength in the foam and CT equals the sum of CE, CV and CH-

After the foam plank is formed, a pressing surface is created, for example by removing a layer from the top or bottom surface or cutting the foam plank between the top and bottom surface to create two pressing surfaces opposite the top and bottom surface. A 'pressing surface' is defined as the resulting surface on a foam plank after a layer of foam has been removed. Suitable methods that may be useful to remove a layer of foam are cutting using equipment such as band saws, computer numeric controlled (CNC) abrasive wire cutting machines, CNC hot wire cutting equipment and the like. When removing a layer, the same cutting methods just described may be used and other methods such as planing, grinding or sanding may be used.

When a layer is removed from the top and/or bottom surface of a foam plank 20 and/or the foam plank is cut 25, the resulting foam structure is referred to as a 'foam blank' 28 and 29 each having a thickness 26 and 27 that is less than the original thickness of the foam plank 23, if a foam plank is cut into two foam blanks as in FIG. 2 and FIG. 3, each foam blank will have a non-cut surface (sometimes referred to a skinned surface) 21 and 22, and a new cut surface 34 and 35. If the foam plank is cut in half, i.e., 26 equals 27, then foam blanks 28 and 29 are identical. What differentiates a foam blank form a foam plank is that the foam blank has at least one pressing surface. The foam blank is removed from and/or separated from the foam plank prior to shaping. One or more additional cuts may be necessary to prepare the foam blank to the proper dimensions prior to shaping.

For foam blank 28 the cut surface 34 (e.g., the surface resulting from the cut 25) becomes a first pressing surface, FIG. 3. This terminology applies whether the foam plank is cut in half (providing two foam blanks, each with a pressing surface) or only a few millimeters is cut or removed from the surface of the foam plank (providing a single foam blank with a single pressing surface). Multiple (e.g., 2, 3, 4, 5, or more) foam blanks may be cut from a single foam plank (multiple blanks require multiple cuts). The conventional foam blank is rectangular and results from a cut through, and parallel to, the top and bottom surfaces of the foam plank.

Another embodiment is the "near net-shaped foam blank". A near net-shaped foam blank is formed when the shape of the foam blank is similar to the final shape of the shaped foamed article. In a near net-shaped foam blank sometimes one or more cuts are made in a plane other than parallel to the top and bottom surfaces of the foam plank.

Typically, after the removing or cutting, the plank is at least about several millimeters thick to at most about 60 centimeters thick. Generally, when removing a layer, the amount of material is at least about a millimeter and may be any amount useful to perform the method such as 1.2, 1.4, 1.6, 1.8, 2, 2.5, 3, 3.5, 4, 5 millimeters or any subsequent amount determined to be useful such as an amount to remove any skin that is formed as a result of extruding the thermoplastic foam, but is typically no more than 10 millimeters. In another embodiment, the foam is cut and a layer is removed from the top or bottom surface opposite the cut surface to form two pressing surfaces.

In a particular embodiment, the foam plank having a pressing surface, has a density gradient from the pressing surface to the opposite surface of the foam plank. Generally, it is desirable to have a density gradient of at least 5 percent, 10 percent, 15 percent, 25 percent, 30 percent or even 35 percent from the pressing surface to the opposing surface of the foam plank. To illustrate the density gradient, if the density of the foam at the surface (i.e., within a millimeter or two of the surface) is 3.0 pounds per cubic foot (pcf), the density would be for a 10 percent gradient either 2.7 or 3.3 pcf at the center of the foam. Even though the density of the foam at the pressing surface may be less or greater than the density at the center of the foam, the density of the foam at the pressing surface is preferably less than the density at the center of said foam plank. Likewise, if the foam plank has two pressing surfaces, both desirably have the aforementioned density gradient.

Typically, a thermoplastic foam will have a higher concentration of open cells at an extruded surface of the foam than the concentration of open cells within the core, this is referred to as open cell gradient. The concentration of open cells can be determined microscopically and is the number of open cells per total cells at the surface. Generally, the amount of open cells in this aspect of the invention at the surface is at least 5 percent to completely open cell. Desirably, the open cells at the surface is at least in ascending order of 6 percent, 7 percent, 8 percent, 10 percent, 20 percent, 30 percent, 40 percent, 50 percent, 60 percent, 70 percent, 80 percent, 90 percent and completely open cell at the surface.

The foam may have the open cells formed at the surface by mechanical means such as those described above (e.g., planing, machining, cutting, etc.) or may be induced chemically, for example, by use of suitable surfactants to burst closed cells at the surface.

The foam surface with the higher concentration of open cells is contacted with a die face and pressed as described above. In a preferred embodiment for such foams, the die faces are heated, but the foam is not (ambient 15-30°C) and the foam is pressed.

Surprisingly, the heated die faces being heated results in superior surface contour and appearance, whereas when doing the same with a foam without such open cells at the surface, the appearance of the foam is degraded.

In some instances, when a foam plank is cut to form two foam blanks, especially when cut at the mid-plane to form symmetrical foam blanks, the foam blanks will exhibit a concave bow with a depth 36 such that the cut surface is in compression and the skin (non- pressing) surface is in tension, FIG. 3. Typically, the cut foam will bow in a concave fashion from the cut 25, as pictured in FIG. 3. However, under some conditions, the foam blanks may bow in the opposite, or convex, direction from the cut 25 (not pictured in the drawings).

Bowing is a result of one or more factors including, but not limited to, the polymeric composition of the foam plank, conditions under which the foam plank is extruded and foamed, the dimensions of the foam plank and resulting foam blank(s), the location from which the foam blank is cut from the foam plank, the blowing agent used, the cell gas pressure gradient of the foam, the density gradient of the foam plank, the open cell gradient of the foam, the vertical compressive balance, and the plastic stress/strain captured in the foam as it is formed.

Not to be held to any particular theory, we feel one contributor to the bow in the foam blanks cut from the foam plank is the release of residual stress built up inside the foam plank as a result of manufacturing processes. Residual stresses arise in the foam plank, for example, as a result of thermal gradients generated during manufacturing as well as by cellular orientation resulting from the extrusion process. When this foam plank is cut forming foam blanks, the residual stresses in the foam plank are relieved resulting in a bow in the foam blanks.

Another contributor to the bowing behavior results from the difference in the gas pressure inside the cells of foam plank after cutting on the two opposing surfaces. The process of forming the foam results in entrapped gas inside the cells. The pressure inside the cells of a foam board or plank varies with age of the foam. Until equilibrium with the outer atmosphere is reached, these gases are in dynamic equilibrium with the center or core being at a lower cell gas pressure than the outer surface of the foam plank. Cutting a foam plank prior to reaching equilibrium, creates unequal cell gas pressures on the resulting outer surfaces of the foam blank (e.g., 21 and 34 and 22 and 35) as the cut surface has cells with lower internal cell gas pressure than the cells located near or at the non-pressing surface. This uneven gas cell pressure develops new stresses on the opposing foam blank surfaces which also contribute to bowing.

The blank prior to contacting with a forming tool may be cut to fit into a tool, or may be cut simultaneously, such as in die cutting where the die cutting apparatus is set up such that during the cutting, the shape is simultaneously pressed into the pressing surface, in other words, the foam is compressed into the desired shape. Lastly, the final shape may be cut from the pressed part, for example, the foam blank may be roll pressed to form the shape into the pressing surface and subsequently cut. When cutting the foam, any suitable method may be used, such as those known in the art and those described previously for cutting the foam to form a shaped foam article and/or the pressing surfaces. In addition, methods that involve heat may also be used to cut the foam since the pressed shape has already been formed in the pressing surface.

In one embodiment of the present invention, the foam plank, foam blank, or shaped foam article may be perforated. The foam plank, foam blank, or shaped foam article may have a plurality of perforations. Perforation is defined herein to mean one or more hole which passes partially into and/or entirely through the foam, in other words from a first surface towards and/or through the foam to an opposing second surface. Perforation may occur at any time, in other words, it may be done to the foam plank and/or foam blank prior to shaping, to the shaped foam article, or a combination of the two. The perforations may extend partially into, but not through one or both sides of the foam plank, foam blank, foam core, or shaped foam article. Alternatively, the perforations may extend through the foam plank, foam blank, or shaped foam article, for instance, for a shaped foam article made from a foam plank, the perforations may extend through the depth of the foam plank such that there is an opening through the foam from the upper surface to the lower surface. The foam may be perforated by any acceptable means. Perforating the foam article may comprise puncturing the foam article with a one or more of pointed, sharp objects in the nature of a needle, pin, spike, nail, or the like. However, perforating may be accomplished by other means than sharp, pointed objects such as drilling, laser cutting, high-pressure fluid cutting, air guns, projectiles, or the like. The perforations may be made in like manner as disclosed in USP 5,424,016, which is hereby incorporated by reference.

The pressing surface(s) of the blank is contacted with a forming tool such as a die face. Herein die face means any tool having an impressed shape that when pressed into the foam plank will cause the foam to take the shape of the die face. That is, the material making up the die face is such that it does not deform when pressed against the foam plank, but the foam plank deforms to form and retain the desired shape of the die face.

Typically when pressing, at least a portion of the foam is pressed such that the foam is compressed to a thickness of 95 percent or less of the to be pressed foam thickness (original foam blank thickness) as shown in FIG. 1, which for some foams corresponds to just exceeding the yield stress of the foam. Likewise, when pressing the part, the maximum deformation of the foam (elastically deforming the foam) is typically no more than about 20 percent of the original thickness of the foam ready to be pressed.

The forming tool such as a die face, because a shape is most often desired, typically has contours that create an impression (step change) in height 32 of at least a millimeter in the shaped foam article 10 having thickness 17 as shown in FIG 1. The height/depth 32 of an impression may be measured using any suitable technique such as contact measurement techniques (e.g., coordinate measuring machines, dial gauges, contour templates) and non- contact techniques such as optical methods including laser methods. The height of the step change 32 may be greater than 1 millimeter such as 1.5, 2, 2.5, 3, 3.5, 4, 5, 6, 7, 8, 9 and 10 millimeters to a height that is to a point where there are no more foam cells to collapse such that pressing further starts to elastically deform the plastic (polymer) of the foam. The step change, surprisingly, may be formed where the foam undergoes shear. For example, the foam may have a shear angle 33 of about 45° to about 90° from the press surface 34 of the shaped foam article 10 in a step change 32. It is understood that the shear angle may not be linear, but may have some curvature, with the angle in these cases being an average over the curvature. The angle surprisingly may be greater than 60°, 75° or even by 90° while still maintaining an excellent finish and appearance.

Typically when pressing, at least a portion of the foam is pressed such that the foam is compressed to a thickness of 95 percent or less of the to-be -pressed foam thickness (i.e., the original foam blank thickness), which for some foams corresponds to just exceeding the yield stress of the foam. Likewise, when pressing the part, the maximum deformation of the foam (elastically deforming the foam) is typically no more than about 20 percent of the original thickness of the foam ready to be pressed.

When using a press with a forming tool, such as a mold, the mold commonly comprises two halves. One mold half 50 is affixed to the moveable platen 70 (sometimes referred to as the cavity side or movable forming surface or A-side) and moving with it.

The other mold half 60 is affixed or mounted to the stationary platen 80 (sometimes referred to as the core side or stationary forming surface or B-side). The pressing surface of the foam (i.e., the cut surface) is the surface pressed with the mold half comprising the cavity (i.e., the mold half on the A-side 50). In another embodiment, the surface of the stationary platen acts as the B-side pressing surface. The shape of the article will dictate the design and complexity of the forming tool.

The pressing process to form a shaped foam article from a foam blank may also induce residual stresses into the shaped foam article resulting in an upward bow, or cupping, after forming has taken place. For example, when the shaped foam article is formed it develops unequal residual stresses on the top (pressing surface) and bottom side (non- pressing surface) due to varying amount of compression that is imparted to it in the process of forming by virtue of its shape and geometry. This imbalance of residual stresses causes the foam article to show preferential final state, resulting in an undesired bow, when the residual stresses are relieved. Moreover, for closed cell foams in which the cells collapse in a ductile manner, the internal cell gas pressure increases as the cell volume decreases as a result of compression. For ductile cell walls, this will result in an increased cell gas pressure for the affected region of cells involved in compression and creates a new pressure gradient through the thickness of the shaped foam article. The improvement in the process of the present invention is a step wherein there is a means provided to compensate for bow in the foam blank such that the shaped foam article formed from a bowed foam blank is flat after shaping. For example, one such means is providing slits on the non-pressing surface of the foam blank to decrease the bending stiffness of the shaped foam article. A preferred means to compensate or reduce bow in the final shaped foam article is to provide a surface in the B-side of the mold, or in the stationary platen in the embodiment where it is the B-side pressing surface (not shown in the accompanying drawings), which counteracts, reduces, and/or minimizes the factors contributing to the bow in the foam blank.

Surprisingly, we found for a foam blank bowed in a concave manner, the bow is dramatically reduced if the B-side has a corresponding concave surface, FIG. 4. Herein the direction of bow (concave or convex) is defined in relation to the cut, or pressing, surface of the foam blank. For example, the bowed foam blanks of FIG. 3 are defined to be concave. If the bow were to be the opposite direction (not shown in the drawings) the bow of the foam blank would be defined as convex. The amount of bow 36 can be quantified numerically as the distance measured by laying the foam on a flat surface and measuring the distance from a flat surface to the peak of the bowed surface 34.

In a preferred embodiment of the present invention, the mold half with the cavity 50 (or A-side) is affixed to the movable platen 70 and the mold half without the cavity 60 (or B-side) is affixed to the stationary platen 80. In this embodiment, the mold half without the cavity comprises the means to reduce bow and may or may not further impart shape to the foam blank. Preferably the means to reduce bow is a concave surface. We believe bow is reduced because as the mold closes and the foam blank is compressed, the non-pressing surface of the foam blank is first flexed and subsequently plastically deformed once the non-pressing surface contacts the surface of the lower mold half, due to tensile strains in excess of the yield stress of the foam FIG. 6. When the non-pressing surface is thus plastically deformed, the unequal residual stresses lead to a part with lesser bow and when the mold opens, bowing and/or cupping in the shaped foam article are reduced, if not completely eliminated FIG. 7.

In another embodiment of the present invention, the mold half with the cavity 50 is affixed to the movable platen 70 and the stationary forming surface, effectively the B-side of the mold, is the surface of the stationary platen 80. In this embodiment, the stationary forming surface comprises the means to reduce bow, preferably a concave portion, and may or may not impart further shape to the foam blank. The movable forming surface, or cavity, has a defined shape which is imparted into the foam blank pressing surface 34 when impressed upon the foam blank FIG. 5 to FIG. 7. In another embodiment of the present invention (not illustrated in the accompanying drawings), both the stationary and movable forming surfaces of the forming tool impart shape to the foam blank, the shape imparted to each side may be the same or different.

In a preferred embodiment of the present invention, the pressing surface of the B- side mold is constructed to complement the bowed surface of a foam blank. As defined herein, complementing construction means that if the non-pressing surface of the foam blank 21 is concave, the surface of the mold 65 is concave, FIG. 3 and FIG. 4, alternatively if the non-pressing surface of the foam blank 21 is convex (not shown in the drawings), the B-side surface of the mold 65 will also be convex (not shown in the drawings). Generally, the depth of the concave (or height if convex) bow modification 66 in the surface of the B- side mold 60 is equal to or greater than 50 percent of the amount of bow in a foam blank 36, preferably equal to or greater than 70 percent, more preferably equal to or greater than 80 percent of the amount of bow in the foam blank 36. Generally, the depth of the concave (or height if convex) bow modification 66 in the surface of the B-side mold 60 is equal to or less than 150 percent of the amount of bow in a foam blank 36, preferably equal to or greater than 130 percent, more preferably equal to or greater than 120 percent of the amount of bow in the foam blank 36. In a preferred embodiment, the value for the depth of the concave (or height if convex) bow modification 66 is 120 percent or less than the bow 36 in the foam blank, more preferably, the bow modification 66 is the same as the bow 36 in the foam blank.

In one embodiment of the present invention, the B-side of the mold (or platen) comprises an adjustable means to reduce bow. For example, if the means is a concave surface, the B-side of the mold is constructed so the amount of concavity 66 can be adjusted to increase or decrease as desired. Likewise, if the means is a convex surface, the B-side is constructed so the amount of convexity can be adjusted to increase or decrease as desired. Preferably the adjustment is such that it may be performed easily and/or quickly without the removal of the B-side from the press.

The surface 65 of the bow reducing means in the B-side of the mold, or platen when it is the non-pressing surface, may be fully textured, a combination of textured and smooth, or preferably fully smooth. Preferably the B-side surface of the mold is coated with a non- slip coating, such as a TEFLON™ coating and/or sprayed with a mold release agent.

Alternatively, or in conjunction with a textured and/or smooth mold surface, the non- pressing surface of the foam blank may have applied to it a slip agent, either in the form of a spray of a low friction film.

FIG. 5 to FIG. 7 show the process of forming a shaped foam article 10. The amount of compression each layer of the shaped article 10 experiences varies from the pressing surface 34 to the non pressing surface 21. By modifying the design of the B-side of the mold 60 the region of non pressing surface 21 undergoes plastic deformation in tension which results in a part with reduced bow. During the pressing step, as the foam article 10 is being shaped, it initially flexes until the non pressing surface 21 conforms to the shape of the B-side of the mold 60. We believe, this action stretches the foam beyond its yield strain allowing for plastic deformation of the bottom region of the shaped foam article which resists the bow due to release of internal stresses subsequently after the forming operation is completed in FIG. 7.

Another factor that may contribute to bowing is the resulting cell gas pressure gradient in the shaped foam article 10. The initial cell gas pressure gradient in the foam blank is altered significantly once the compression of the foam begins up until when the forming operation is completed. The process of pressing the foam causes ductile buckling of cells which leads to an increase in gaseous pressure in those regions (i.e., the cell walls remain intact retaining the internal gas, but the cell size is reduced). The gas pressure increase is described by the Ideal gas law, as the volume of the cell decrease, the pressure of the gas increases:

PV = nRT

wherein

P = gas pressure

V = gas volume

N = quantity of gas, number of moles

R = Ideal gas constant

T = absolute temperature of gas

The resulting cell gas pressure gradient in the shaped foam article after forming is thus altered from the original cell gas pressure gradient wherein the cell gas pressure of the cells near and at the pressing surface has increased substantially.

In one embodiment of the present invention the shaping/trimming step of the present invention, the surface of the foam blank 21 opposite the pressing surface(s) 34 of the foam blank is placed on a stationary forming surface, such as the B-side mold 60 or a stationary platen 80. A movable platen 70 which can move toward or away from the stationary platen on which the plank is placed comprises a movable forming surface of the forming tool 50 for example, a single cavity mold or optionally a multiple cavity mold and trimming ribs 51. To shape the foam, the movable platen moves towards the stationary platen such that the pressing surface(s) of the blank 34 is contacted and pressed with the movable forming surface of the forming tool 50. As the mold moves towards and shapes the foam, the trimming rib 51 trims the shaped foam article 10 from the unshaped foam 30 of the foam blank adjacent to and/or surrounding the shaped article 10. In one embodiment, the stationary pressing surface, B-side, comprises one or more groove 61, having a width 62 and depth 63, which align with the trimming rib 51 so that when the movable platen moves to its furthest (closed) position, the tip of the trimming rib 58 extends into the corresponding grove 61, FIG. 6.

For a multi-cavity mold, each cavity may be identical in shape or there may be as many different shapes as cavities or there may be a combination of multiple cavities with the same first shape in combination with multiple cavities with one or more shapes different than the first shape. The layout of cavities in a multi-cavity mold may be side by side, in tandem, or any other desirable configuration. A multi-cavity mold produces more than one shaped article in a plank per molding cycle.

In one embodiment, the die face of the forming tool is heated. In this embodiment, the contact time with the foam is typically from about 0.1 second to about 60 seconds.

Preferably, the dwell time is at least about 1 second to at most about 45 seconds.

When pressing with a heated forming tool such as a die face, the temperature of the die face is not so hot or held for too long a time such that the foam is degraded. Depending on the thermoplastic employed, the temperature of the die face is about 50°C to about 200°C. Preferably, the temperature is at least about 60°, more preferably at least about 70°C, even more preferably at least about 80°C and most preferably at least about 90°C to preferably at most about 190°, more preferably at most about 180°, even more preferably at most about 170°C and most preferably at most about 160°C.

In the most preferred embodiment of this invention, the mold, die face, and/or platen(s) are not heated and the foam blank is shaped at ambient temperature. Ambient temperature herein is referred to as the temperature in which the shaping process is occurring. While ambient temperature is typically defined to be about 23 °C it may be higher or lower depending on the shaping process environment. The method of the present invention may use a molding machine, sometimes referred to as a press, to shape the foam blank into a shaped foam article for the present invention. This process is often referred to as discontinuous as it consists of a cycle where a foam blank is placed in an open mold, the mold closes to form a shaped foam article, then after the shaped article is formed the mold opens. The shaped foam article is removed from the mold, a new foam blank is inserted into the mold and the process repeated. This process is demonstrated for a foam blank in FIG. 5 to FIG. 7.

The shape of the foam article is only limited by the ability to shape foam, a foam article, specifically a shaped foam article may have one or more surfaces, for example if the shaped foam article is a sphere it would have a single surface. More complex shaped foam articles will have more than one surface, for example if the shaped foam article is a bowling ball pin would have two surfaces, the continuous surface and the bottom of the pin. A rod would have three surfaces, a three sided pyramid or an extruded plank, four surfaces, a four sided pyramid, five surface, etc. Depending on the shape of the shaped foam article, it may have 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 or more surfaces.

Transitions from one surface to another may be well defined, such as the six surfaces of a cube, or they may not be well defined, such as the surfaces of a complex shape such as the foam article shaped in the form of roofing shake shingles. TEST METHODS

The density profile through the thickness of each foam blank was tested using a QMS Density Profiler, model QDP-01X, from Quintek Measurement Systems, Inc.

Knoxville, TN. The High Voltage kV Control was set to 90 percent, the High Voltage Current Control was set to 23 percent and the Detector Voltage was approximately 8v. Data points were collected every 0.06 mm throughout the thickness of the foam. Approximate thickness of the foam samples in the plane of the x-ray path was 2 inches. Mass absorption coefficients were calculated for each sample individually, based on the measured linear density of the foam part being tested. The skin density, p_Mn , was reported as a maximum value whereas the core density, p_core , was averaged within an approximate 5 mm range.

The density gradient, in units of percentage, was then computed in accordance with the following equation:

Density Gradient ( percent) = 100 · ^^{Pcore ~ Pstin} ^

P skin The compressive response of each material was measured using a Materials Test System equipped with a 5.0 displacement card and a 4,000 lbf load card. Cubical samples measuring the approximate thickness of each plank were compressed at a compressive strain rate of 0.065 s^"1. Thus, the crosshead velocity of the MTS, in units of inches per minute, was programmed in accordance with the following equation:

Crosshead Velocity = Strain Rate _* Thickness _* 60 where the thickness of the foam specimen is measured in units of inches. The compressive strength of each foam specimen is calculated in accordance with ASTM D1621 while the total compressive strength, CT, is computed as follows:

where Cy, CE and CH correspond to the compressive strength in the vertical, extrusion and horizontal direction respectively. Thus, the compressive balance, R, in each direction (vertical compressive balance, R_v; extrusion direction compressive balance, R_E; and horizontal compressive balance, RH), can be computed as shown below: Rv = CV/CT

RH = CH CT

Open cell content was measured by using an Archimedes method on 25mm x 25mm x 50mm samples.

While certain embodiments of the present invention are described in the following example, it will be apparent that considerable variations and modifications of these specific embodiments can be made without departing from the scope of the present invention as defined by a proper interpretation of the following claims.

Percent crack reduction C_r can be determined from the ratio of the rough crack value

R_cv to the smooth crack value S_cv by the following formula:

C_r = (1 - R_cv/S_cv) _* 100 Wherein crack values are manually calculated for a shaped foam article pressed by a mold with a smooth cavity surface S_cv by first measuring the length of each crack in the shaped foam article (or a specified portion thereof) made from a mold with a smooth cavity surface and then adding each of the individual crack lengths together to get an overall smooth crack value S_cv in units of length. Crack values are manually calculated for a shaped foam article pressed by a mold with a reduced-slip cavity surface R_cv by first measuring the length of each crack, if any, in the shaped foam article (or the same specified portion as used in the shaped foam article pressed from the mold with a smooth cavity surface) made from a mold with a reduced-slip cavity surface and then adding each of the individual crack lengths together to get an overall reduced-slip crack value R_cv in units of length.

EXAMPLES

In the following examples, a STYROFOAM™ IBFWE-BF-A foam plank available from The Dow Chemical Company having a density gradient of -7.89 percent, an average cell gas pressure about 0.7 atmosphere (atm), and a vertical compressive balance (Ry) of 0.53 is cut to provide foam blanks measuring approximately 457mm by 152mm by 40mm, in the length, width and thickness directions respectively. The plank is cut with a Croma 848 hot wire cutter providing a blank with a thickness of 40mm having a cut (or core) surface which is the pressing surface and a planed extruded (or skin) surface (the non- pressing surface). The 40mm blank is then cut the desired dimensions using a JET WBS- 28-3 bad saw. Samples are cut with the band saw from the foam plank parallel to the direction of extrusion and perpendicular to the direction of extrusion and are denoted as "parallel" when the 457mm dimension (length) is in the direction of extrusion or

"perpendicular" when the 152mm dimension (width) is perpendicular to the direction of extrusion. For each Example/Comparative Example a total of 15 samples are prepared and shaped for blanks prepared in the parallel direction. For each Example/Comparative Example a total of 20 samples are prepared and shaped in the perpendicular direction for each example.

The cut (or core) surface of the foam blank is compressed against the A-side 100 of a mold to form a shaped foam article 10, FIG. 8. For Examples 1 to 4, a B-side tool 101 having a concave surface with a maximum depth of 8mm 110 is used and is referred to as the "8mm" B-side. For Comparative Examples A to C, a B-side tool having a flat surface referred to as the'Omm" B-side is used (not shown in FIG. 8). Pressing is done in a PHI Hydraulic Compression Press 120. The B-side of the tool is mounted to the lower movable platen 103. The A-side of the tool is mounted to the stationary platen 104. Stop blocks 105 measuring 88.9mm are placed on the movable platen. The A-side of the mold is not heated or cooled. The B-side of the mold is not heated or cooled. The foam blanks are compressed at ambient temperature of the lab, which is about 23°C. Neither mold half is heated or cooled. A molding cycle consist of 1) opening the mold, 2) placing a foam blank on the B-side surface of the tool, 3) closing the mold until the stop blocks are engaged, 4) opening the mold, and 5) removing the shaped foam article. During the pressing, the foam is subjected to a maximum applied strain of about 50 percent.

For all of the Examples and Comparative Examples, the B-sides of the mold (i.e., flat B-side and concave B-side) are always masked with waxed paper to provide a smooth low coefficient of friction surface. For Examples 1 and 3 and Comparative Examples A and C, the A-side of the mold is masked with 150 grit sandpaper. For Examples 2 and 4 and Comparative Example B, the A-side of the mold is masked with waxed paper.

24 hours after forming, a Keyence LB-301 Laser displacement sensor gauge is used to determine how much bow, if any, exists in the shaped foam article. The results for each of Examples 1 and 2 and Comparative Examples A and B comprise measurements on 15 shaped foam articles. The results for each of Examples 3 and 4 and Comparative Example C comprise measurements on 20 shaped foam articles. The results for each

Example/Comparative Example are evaluated with JMP™, a statistical software package and the results are reported in Table 1.

As can be seen by the results in Table 1 , the shaped foam articles made by the process of the present invention show significantly reduced bow as compared to foams produced according to the prior art.

Table 1

Claims

CLAIMS:

1. An improved method to manufacture a shaped foam article with reduced bow comprising the steps of:

(i) extruding a thermoplastic polymer with a blowing agent to form a thermoplastic polymer foam plank, the plank having a thickness, a top surface, and a bottom surface in which said surfaces lie in the plane defined by the direction of extrusion and the width of the plank, wherein the foam plank has a vertical compressive balance equal to or greater than 0.4;

(ii) cutting the foam plank to form a foam blank with a pressing surface and a non-pressing surface,

(iii) shaping the foam blank into a shaped foam article by

(iii)(a) contacting the foam blank with a mold, said mold comprising an A- side having a cavity which contacts the pressing surface of the foam blank and a B-side which contacts the non-pressing surface of the foam blank and

(iii)(b) pressing the pressing surface of the foam blank with the A-side of the mold whereby forming a shaped foam article,

wherein the improvement comprises the B-side of the mold comprises a means to reduce bow in the shaped foam article.

2. The method of Claim 1 wherein the means to reduce bow is providing a concave surface in the B-side of the mold.

3. The method of Claim 1 wherein the foam blank is bowed in a concave manner and means to reduce bow is providing a concave surface to the B-side of the mold.

4. The method of Claim 1 wherein the foam blank is bowed in a convex manner and means to reduce bow is providing a convex surface to the B-side of the mold.

5. The method of Claim 1 wherein the means to reduce bow in the B-side of the mold is adjustable.

6. The method of Claim 1 wherein the mold, both the A-sided and B-side, is not heated or cooled and the shaped foam article is formed at ambient temperature.

7. The method of Claim 1 wherein the foam blank has a cell gas pressure equal to or less than 1 atmosphere.

8. The method of Claim 1 wherein the thermoplastic polymer is polyethylene, polypropylene, copolymer of polyethylene and polypropylene; polystyrene, high impact polystyrene; styrene and acrylonitrile copolymer, acrylonitrile, butadiene, and styrene terpolymer, polycarbonate; polyvinyl chloride; polyphenylene oxide and polystyrene blend.

9. The method of Claim 1 wherein the blowing agent is a chemical blowing agent, an inorganic gas, an organic blowing agent, carbon dioxide, or combinations thereof.

10. A shaped foam article made by the method of Claim 1.