WO2009009252A1

WO2009009252A1 - Blowing agent impregnation enhancement in bead foam

Info

Publication number: WO2009009252A1
Application number: PCT/US2008/066814
Authority: WO
Inventors: Jürgen SCHELLENBERG; John Gordon-Duffy; Barbara Erling; Freidhelm Bunge
Original assignee: Dow Global Technologies Inc.
Priority date: 2007-07-05
Filing date: 2008-06-13
Publication date: 2009-01-15
Also published as: EP2164894A1

Abstract

Impregnate polymeric beads containing 100 parts of an alkenyl aromatic polymer, 0.1 to 8 parts of a blowing agent impregnation enhancer selected from a group consisting of saturate aliphatic hydrocarbons having 20 to 60 carbon atoms and ester products of a saturated mono-carboxylic acid having 14 to 20 carbon atoms with an alkyl alcohol having 3 to 5 carbon atoms with 2 to 9 parts of a blowing agent by softening the polymer beads containing the impregnation enhancer to within 40°C of the beads softening temperature and impregnating the beads with blowing agent to prepare an expandable polymer bead. Expand the expandable polymer bead to prepare an expanded polymer bead foam.

Description

BLOWING AGENT IMPREGNATION ENHANCEMENT IN BEAD FOAM

Cross Reference Statement

This application claims the benefit of U.S. Provisional Application No .60/958, 374, filed July 5, 2007.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to expandable polymeric beads, a process for using the expandable polymeric beads to prepare expanded polymer bead foam and expanded polymer bead foam.

Description of Related Art

Expandable polymeric beads are useful for preparing expanded polymer bead foam. Expandable polymeric beads are thermoplastic polymer beads that are impregnated with a blowing agent. Upon softening the polymer beads the blowing agent expands the beads into a cellular polymer structure.

Expansion of multiple expandable polymeric beads in a constrained mold is useful for preparing polymer foam structures comprising multiple expanded polymer foam beads fused to one another and forming a foam block in the shape of the mold.

One common method for impregnating blowing agent into polymeric beads is by exposing the polymeric beads to blowing agent under pressure and then waiting for the blowing agent to penetrate into (that is, impregnate) the polymeric beads.

United States Patent (USP) 5561170, for example, discloses a method for preparing expandable thermoplastic polymer beads by impregnating the beads with blowing agent in a aqueous suspension. Impregnation of blowing agent in USP 5561170 occurs by exposing 100 weight-parts polystyrene particles to

6.6 weight-parts pentane for nearly eight hours - four hours at a temperature that is increasing from 108⁰C to 125⁰C and another four hours at 125⁰C. It is desirable to shorten the impregnation time required to impregnate alkenyl aromatic polymer beads with blowing agent in order to reduce the processing time and increase productivity.

It is also desirable to minimize the amount of blowing agent necessary in preparing expanded alkenyl aromatic polymer bead foams. Blowing agents used in preparing expanded polymer bead foam typically comprise or consist of organic hydrocarbons, particularly pentane. Such blowing agents qualify as volatile organic compounds (VOCs). VOC emissions are environmentally undesirable. Reducing the amount of blowing agent used in expanded bead processes can reduce VOC emissions from such processes.

BRIEF SUMMARY OF THE INVENTION The present invention is a result of surprisingly discovering that certain additives, when present in alkenyl aromatic polymer beads, facilitate impregnation of the polymer beads with blowing agent. As a result, impregnation time and amount of blowing agent required for impregnation can be unexpectedly reduced over current impregnation processes while still achieving similar or more desirable foam densities and compressive strengths.

In a first aspect, the present invention is an expandable polymer bead comprising the following components: (a) 100 parts by weight of an alkenyl aromatic polymer; (b) 0.1 to 8 parts by weight of one or more blowing agent impregnation enhancer selected from a group consisting of saturate aliphatic hydrocarbons having 20 to 60 carbon atoms and ester products of a saturated mono-carboxylic acid having 14 to 20 carbon atoms with an alkyl alcohol having 3 to 5 carbon atoms; (c) 2 to 9 parts by weight of a blowing agent distributed throughout the polymer bead; (d) 0 to 7 parts by weight of an infrared attenuating agent; and (e) 0 to 10 parts by weight of one or more additional additive.

Particular embodiments of the first aspect include one or any combination of more than one of the following further characteristics: component (a) comprises or is polystyrene; component (b) is one or more component selected from mineral oil and isobutyl stearate; component (c) is one or more isomer of pentane; component (d) is present and is one or more component selected from carbon black and graphite; and the expandable polymer bead has a smallest dimension and a largest dimension and the ratio of smallest dimension to largest dimension is less than 0.8.

In a second aspect, the present invention is a process for preparing expandable polymer beads comprising the steps of: (a) Preparing polymer beads of a polymer composition that has a softening temperature and comprises 100 parts by weight of an alkenyl aromatic polymer, 0.1 to 8 parts by weight of one or more blowing agent impregnation enhancer selected from a group consisting of saturate aliphatic hydrocarbons having 20 to 60 carbon atoms and ester products of a saturated mono- carboxylic acid having 14 to 20 carbon atoms with an alkyl alcohol having 3 to 5 carbon atoms, 0 to 7 parts by weight of an infrared attenuating agent, and 0 to 10 parts by weight of one or more additional additive; (b) Heating the polymer beads to a blowing agent impregnation temperature that is within 40 degrees Celsius of the polymer composition's softening temperature; and (c) Impregnating the polymer bead with 2 to 9 parts by weight blowing agent.

Particular embodiments of the second aspect include one or any combination of more than one of the following further characteristics: the alkenyl aromatic polymer comprises or is polystyrene; the blowing agent impregnation enhancer is one or more component selected from mineral oil and isobutyl stearate; the blowing agent is one or more isomer of pentane; one or more infrared attenuating agents selected from carbon black and graphite are present in the polymer beads; the polymer beads have a smallest dimension and a largest dimension and the ratio of the smallest dimension to the largest dimension is less than 0.8; and impregnation of blowing agent in step (c) occurs while the polymer beads are suspended in an aqueous medium. In a third aspect, the present invention is an expanded polymer bead foam comprising one or more expanded polymer foam bead, wherein the one or more expanded polymer foam bead comprises the following components: (a) 100 parts by weight of an alkenyl aromatic polymer; (b) 0.1 to 8 parts by weight of one or more blowing agent impregnation enhancer selected from a group consisting of saturate aliphatic hydrocarbons having 20 to 60 carbon atoms and ester products of a saturated mono-carboxylic acid having 14 to 20 carbon atoms with an alkyl alcohol having 3 to 5 carbon atoms; (c) 0 to 7 parts by weight of an infrared attenuating agent; and (d) 0 to 10 parts by weight of one or more additional additive.

Particular embodiments of the third aspect include one or any combination of more than one of the following further characteristics: component (a) comprises or is polystyrene; component (b) is one or more component selected from mineral oil and isobutyl stearate; and component (c) is present and is one or more component selected from carbon black and graphite . DETAILED DESCRIPTION OF THE INVENTION

Unless otherwise indicated, ranges herein include end points . Expandable Polymer Beads

One aspect of the present invention is an expandable polymer bead. A "bead" can take on any shape including spherical or cylindrical. One desirable feature of the present invention is that the bead does not need to be spherical. In fact, an expandable polymer bead of the present invention can have a smallest dimension and a largest dimension such that the ratio of the smallest dimension to the largest dimension is less than 0.8, even 0.7 or less and can be 0.6 or less. Herein, a bead "dimension" is a distance connecting two points on a bead's surface and extending through the bead's centroid. The polymer bead comprises one or more alkenyl aromatic polymer. Desirably, more than 50 percent by weight (wt%) , more desirably 70 wt% or more, still more desirably 90 wt% or more and most preferably 100 wt% of the polymer bead based on total polymer weight in the polymer bead is one or more alkenyl aromatic polymer.

Desirable alkenyl aromatic polymers include polymers containing styrene monomer units polymerized therein, preferably polymers that are based on styrene. Polymers "based on styrene" contain more than 50 wt% polymerized styrene monomers based on total polymer weight. Polystyrene homopolymer and styrene-acrylonitrile copolymer are two particularly desirable alkenyl aromatic polymers.

The polymer beads are "expandable", which means they are capable of expanding into a cellular structure (a polymer foam) . In order to be "expandable" the polymer beads contain a blowing agent. Suitable blowing agents include any of those known or yet to be discovered that are suitable for preparing expandable polymer beads. Desirable blowing agents include one or more hydrocarbon having from three to six carbons, preferably one or more isomer of butane (for example, isobutane and/or n-butane) and/or one or more isomer of pentane (for example, isopentane and/or n-pentane and/or cyclopentane) . Blowing agent is present in the expandable polymer bead at a concentration in a range of two weight-parts ("parts") or more, preferably 2.5 parts or more, more preferably three parts or more and nine parts or less, typically eight parts or less and more typically 7.5 parts or less based on 100 parts alkenyl aromatic polymer.

The expandable polymer beads have blowing agent distributed throughout them, meaning blowing agent is present proximate to each bead's surface and extending through each bead's core. Distribution of blowing agent throughout the polymer bead is evident upon expansion of the polymer bead by a cellular structure at the bead's core as well as the bead's surface. When blowing agent is not distributed throughout the polymer bead, due to incomplete penetration, expansion of the polymer bead results in only a cellular structure, generally a fine cellular structure, proximate to the bead surface while the bead core remains free of cellular structure .

The expandable polymer beads further comprise one or more blowing agent impregnation enhancer selected from a group consisting of saturated aliphatic hydrocarbons having 20-60 carbon atoms and ester combinations of a saturated mono-carboxylic acid having 14-20 carbon atoms with an alkyl alcohol having 3-5 carbon atoms. Surprisingly, the group of components act as blowing agent impregnation enhancers for the polymer beads. Blowing agent penetrates into the polymer faster when one or more of the blowing agent impregnation enhancers is present in the polymer bead than when the blowing agent impregnation enhancer is not present. As a result, it takes less time to impregnate polymer beads throughout with blowing agent than it takes in an absence of blowing agent impregnation enhancer. A further surprising benefit of the impregnation enhancer is that less blowing agent can be used to impregnate polymer beads to the same degree and with blowing agent distribution throughout the polymer bead than without the impregnation enhancer. A yet additional surprising benefit is that blowing agent impregnation enhancers allow use of lower impregnation temperatures to achieve a similar extent of blowing agent impregnation into polymer beads as compared to impregnation of beads without blowing agent impregnation enhancers. The blowing agent impregnation enhancer is present at a concentration in a range of 0.1 to eight weight parts based on 100 weight parts alkenyl aromatic polymer. The blowing agent enhancer can be present at a concentration of 0.1 weight parts or more, more preferably 0.2 weight parts or more and preferably seven weight parts or less, more preferably 5.5 weight-parts or less. Suitable examples of aliphatic hydrocarbons having 20-60 carbon atoms include mineral oil (for example, white mineral oil), synthetic oil and paraffin oil.

Suitable examples of ester combinations of a saturated mono-carboxylic acid having 14-20 carbon atoms with an alkyl alcohol having 3-5 carbon atoms include isobutyl stearate, isopropyl palmitate and isopropyl myristate.

The expandable polymer beads can also contain up to seven parts by weight, based on 100 parts alkenyl aromatic polymer, of an infrared attenuating agent. Infrared attenuating agents diminish penetration of infrared radiation through a material. Suitable infrared attenuating agents include any one or combination of carbon black, graphite, titanium dioxide, and metal flake. Additional additives may also be present in the expandable polymer beads at a concentration of all additional additives of up to ten parts by weight, based on 100 parts alkenyl aromatic polymer. Additional additives include nucleating agents, flame retardants, colorants, nanoparticles, and antistatic additives.

The expandable polymer beads of the present invention are useful for preparing expanded polymer bead foam.

Process for Preparing Expandable Polymer Beads In a second aspect, the present invention is a process for preparing the foamable polymer beads of the first aspect. The first step in the process is to prepare polymer beads containing 100 weight parts of one or more alkenyl aromatic polymer, 0.1 to eight weight parts of a blowing agent impregnation enhancer, up to seven weight parts of one or more infrared attenuating agent and up to ten weight parts of one or more additional additives. The alkenyl aromatic polymer, blowing agent impregnation enhancer, infrared attenuating agent and additional additives are as described for the expandable bead aspect of the present invention. Many methods of preparing polymer beads are well known in the art, any of which are suitable for this step of the present process. Suitable methods for preparing polymer beads include suspension polymerization processes, extrusion processes, micropelletization processes, mass polymerization processes and mechanical dispersion processes.

In a suspension polymerization process, disperse monomer in an aqueous phase with the help of suspension stabilizers. Polymerize the dispersed monomers by free-radical initiators to form finely divided polymer beads.

In an extrusion process, melt a polymer composition in an extruder, then extrude the molten polymer composition, typically in small diameter streams, and then pelletize the extruded polymer. The pellets can serve as polymer beads. In a micropelletization process, form small nearly spherical polymer beads by pelletizing molten polymer in an aqueous medium.

In a mass extrusion process, polymerize monomer in an absence of significant amounts of solvents using free-radical initiators and/or thermal initiation. Devolatilize the resulting polymer and cut it into pieces or granules to serves a polymer beads.

Further descriptions of suitable suspension polymerizations, extrusion processes, micropelletization processes and mass polymerization processes are in A. Echte: Handbuch der Technischen Polymerchemie (Handbook of industrial Polymer Chemistry) : VCH Weinheim-New York-Basel- Cambridge-Tokyo 1993.

In a mechanical dispersion process, feed a polymer melt into a liquid (generally, an aqueous liquid) containing surface active additives through, for example, a rotor-stator mixer or a twin screw extruder to form a fine dispersion of polymer particles in the liquid. Further description of a mechanical dispersion process for preparing polymer beads is in United States patent 7,056,496, particularly Example 2 (incorporated herein by reference). One of the desirable features of the present invention is that the polymer beads can be non-spherical and still enjoy a benefit of efficient blowing agent impregnation. As noted above, the polymer beads may have a ratio of smallest dimension to largest dimension that is less than 0.8, even 0.7 or less, even 0.6 or less.

The polymer beads have a softening temperature. A softening temperature for a polymer corresponds to the glass transition temperature (Tg) in the case of amorphous polymers and the melting temperature (Tm) in the case of crystalline and semi-crystalline polymers. Additives and the blowing agent impregnation enhancer can affect the softening temperature of a polymer. Measure the softening temperature of polymer beads by determining the Tg for the polymer bead composition, or Tm if using only crystalline or semi- crystalline polymers in the polymer composition, using a differential scanning calorimetric method as though the sample were a neat polymer.

The second step in the process is to heat the polymer beads to an impregnation temperature within 4O⁰C of the polymer bead's softening temperature. The temperature can be above or below the polymer bead's softening temperature.

The third step is to impregnate the polymer beads with two to nine weight parts of a blowing agent such that the blowing agent penetrates throughout the polymer bead. Upon such impregnation, blowing agent should be present at the core as well as proximate to the surface of the polymer beads. Such impregnation throughout the polymer bead is evident upon expansion of the polymer bead by creation of a cellular structure at the core as well as proximate to the surface of the polymer bead.

Impregnate the polymer beads with blowing agent by exposing the polymer beads to blowing agent at the impregnation temperature and allowing the blowing agent to penetrate into the polymer beads. The blowing agent is as described in regards to the expandable polymer bead aspect of the present invention. In its broadest scope, the present process can employ any means of impregnating the polymer beads with blowing agent. It is common to conduct the third step by exposing the polymer beads to blowing agent under pressure in order to accelerate blowing agent penetration into the polymer beads.

One desirable way of impregnating polymer beads with blowing agent is to disperse the polymer beads into an aqueous medium within a vessel and then pressurize the vessel with blowing agent. See, for example, USP 5,561,170

(incorporated herein by reference) for one description of blowing agent impregnation of polymer beads in an aqueous suspension .

A desirable and surprising feature of the present process is that impregnation of the blowing agent into polymer beads is more efficient when the blowing agent impregnation enhancer is present in the polymer beads than for beads without a blowing agent impregnation enhancer. Blowing agent impregnation is more efficient as evidenced by the fact impregnation occurs throughout a polymer bead (that is, from proximate to the bead's surface to the bead's core) containing blowing agent impregnation enhancer using less blowing agent, less impregnation time and/or lower impregnation temperatures than impregnation of polymer beads without the blowing agent impregnation enhancer. A further benefit of the present invention is that because less blowing agent is necessary to prepare a polymer foam, and because the blowing agent is typically one or more volatile organic compound (VOC) , the present invention realizes less VOC emissions than processes for preparing similar density and compressive strength bead foams.

The process aspect of the present invention is useful for preparing expanded polymer bead foam. Expanded Polymer Bead Foam

A third aspect of the present invention is an expanded polymer bead foam ("bead foam") . Bead foam can comprise a single expanded polymer bead, but typically comprises multiple polymer beads. Expanded polymer beads have a polymer skin surrounding a cellular interior. The expanded polymer beads of the present invention have a cellular structure throughout each bead, meaning a cellular structure exists from proximate to a bead's surface through the bead's core. Bead foams that do not have a cellular structure throughout each bead (that is, that have non-cellular polymer cores) are difficult to cut with a hot wire since the dense core of the beads tend to break the hot wire.

The bead foam of the present invention comprises 100 weight parts of an alkenyl aromatic polymer, 0.1 to eight weight parts of a blowing agent impregnation enhancer, up to seven weight parts of an infrared attenuating agent and up to ten weight parts of one or more additional additive. The alkenyl aromatic polymer, blowing agent impregnation enhancer, infrared attenuating agent and additional additives are as described with regards to the expandable polymer bead aspect of the present invention.

Prepare bead foam using expandable polymer beads and triggering their expansion, typically within a mold to define the final shape of the bead foam. Prepare the bead foam of the present invention using the expandable polymer beads of the first aspect using any means suitable for preparing general bead foam. One method for preparing the bead foam of the present invention is by subjecting the expandable polymer beads of the first aspect to steam for a period of time. The steam softens the polymer in each bead and allows the impregnated blowing agent to expand the softened polymer bead into a cellular structure. The expandable polymer bead may be coated with a material to facilitate bead cohesion upon expansion. Suitable materials include mono-, di- and triglycerides of higher fatty acids with a chain length containing 8 to 22 carbons, as well as any combination of such mono-, di- and tri-glycerides .

Bead foam of the present invention typically has a density of five grams per liter (g/1) or more and 200 g/1 or less. The bead foam can have a density of 7 g/1 or more, even 10 g/1 or more and can have a density of 100 g/1 or less, or 45 g/1 or less. Measure bead foam density according to EN standard method 13163.

The bead foam additionally has a compressive strength depending on the aforementioned densities according to the dependence given in EN standard method 13163. For example, at a density of 17.8 grams per liter the bead foam has a compressive strength of at least 55 kilopascals, preferably 69 kilopascals or more, and more preferably 72 kilopascals or more. Measure compressive strength according to EN standard method 13163.

The bead foams of the present invention are useful for many applications including thermal insulation and package cushioning . Examples

The following examples serve to further illustrate embodiments of the present invention.

Comparative Example A

Prepare polymer beads using an extrusion process. Combine in an extruder 100 weight parts of a styrene homopolymer (204,000 weight-averaged molecular weight (Mw)) and 0.11 weight parts of a polyethylene wax (A-C™ brand polyethylene wax A3, A-C is a trademark of Honeywell international Inc.) . Extrude the polymer composition into a cylindrical shape five millimeters in diameter and cut into granules three millimeters in length. The granules constitute polymer beads.

Impregnate the polymer beads with pentane blowing agent. Disperse 200 grams of the polymer beads into an aqueous solution of 1300 milliliters demineralized water and eight grams of a five-percent by weight polyvinyl alcohol (PVA) in water mixture. Prepare the dispersion in a reaction vessel. Seal the vessel and add 14 grams of pentane (an 80 wt% n- pentane and 20 wt% isopentane mixture) . Heat the vessel to 125⁰C for six hours to form foamable polymer beads impregnated with pentane. Cool the reaction vessel to 25⁰C and recover the foamable polymer beads by filtrations, centrifugation and drying under air for 30 minutes.

Evaluate the extent of blowing agent impregnation by expanding a sample of the foamable polymer beads. Expose the foamable polymer beads to boiling water for three (3) minutes to induce expansion. Cut one set of sample beads in half both immediately after boiling and another set of sample beads in half after storing for 30 minutes.

Both sets of sample beads reveal a fine cellular structure proximate to the bead surface skin and a non- cellular polymer composition at the core of the bead. The analysis reveals that pentane blowing agent impregnation was limited to proximate to the bead surface and failed to extend to the polymer bead core. As a result, blowing agent was not impregnated throughout the polymer bead.

Example 1 - Impregnation Time Comparison Prepare polymer beads in an extruder as in Comparative Example A but by combining 95.5 weight-parts polystyrene homopolymer (205,000 Mw), 0.11 weight-parts polyethylene wax (A-C A3) and 4.5 weight-parts white mineral oil (a saturated aliphatic hydrocarbon having 35 carbon atom on average per chain) .

Impregnate the polymer beads with pentane to form expandable polymer beads in like manner as in Comparative Example A, except expose the beads to pentane for four (4) hours instead of six. Evaluate the extent of blowing agent impregnation as in Comparative Example A. Both sets of sample beads reveal a cellular structure extending throughout the polymer beads, from proximate to the bead surface through the bead core. The expandable polymer beads of Example 1, in comparison to Comparative Example A, illustrate that the white mineral oil blowing agent impregnation enhancer facilitated more extensive blowing agent impregnation into the polymer beads over a shorter impregnation time.

Example 2 - Inclusion of Infrared Attenuator

Repeat Example 1 except further include 3.5 weight-parts of graphite (6 micrometer average particle size) in forming polymer beads. During impregnation, disperse the polymer beads into an 1300 milliliters of demineralized water containing 16 grams of a five-percent by weight mixture of PVA in water.

As in Example 1, both sets of sample beads reveal a cellular structure extending throughout the polymer beads, from proximate to the bead surface through the bead core.

The expandable polymer beads of Example 2, as compared to Comparative Example A, illustrate that the white mineral oil blowing agent impregnation enhancer facilitated more extensive blowing agent impregnation into the polymer beads over a shorter impregnation time even in the presence of infrared attenuator. This is particularly surprising considering that infrared attenuators, particularly those having a particle size as large as six micrometers, typically act as nucleating agents, which could concentrate blowing agent proximate to the surface of the polymer beads and produce an inhomogeneous cellular structure in the bead.

Example 3 - Use of Less Blowing Agent

Prepare polymer beads in like manner as in Example 1 except without the polyethylene wax. Impregnate the polymer beads to form expandable polymer beads using an aqueous suspension similar to that of Example 1 except disperse 400 grams of polymer beads into 1100 milliliters of demineralized water with 16 grams of a 5 weight-percent PVA in water mixture and add 22 grams of pentane. Analyze the expandable polymer beads in like manner as in Example 1. As in Example 1, both sets of sample beads reveal a cellular structure extending throughout the polymer beads, from proximate to the bead surface through the bead core .

Both Examples 1 and 3, as compared to Comparative Example A, illustrate that less blowing agent is necessary to achieve an expandable polymer bead having blowing agent impregnated throughout the polymer bead than a similar polymer bead that does not contain a blowing agent impregnation enhancer. Comparative Example A failed to achieve blowing agent impregnation throughout the polymer beads at a blowing agent concentration of 7 weight-percent blowing agent based on polymer bead weight. Example 1 illustrated blowing agent impregnation throughout similar polymer beads that contain a blowing agent impregnation enhancer using the same blowing agent concentration (7 weight-percent based on polymer bead weight). Example 3 illustrated blowing agent impregnation throughout similar polymer beads that contain a blowing agent impregnation enhancer using a blowing agent concentration of only 5.5 weight-percent based on polymer bead weight. Example 4 - Ester Impregnation Enhancer Prepare polymer beads by suspension polymerization of styrene in an aqueous phase with pickering stabilizers using free-radical initiators but in an absence of blowing agent to prepare essentially spherical polymer beads having a diameter of about 0.8 millimeters and comprising 99.0 weight-parts styrene homopolymer (200,000 Mw) and 1 weight-part iso-butyl stearate .

Impregnate the polymer beads to form expandable polymer beads by dispersing 400 grams of the polymer beads into 1100 milliliters of deionized water containing 16 grams of a 5- percent by weight mixture of PVA in water and then adding 28 grams of pentane. Heat the dispersion to 125⁰C for four (4) hours. Isolate and analyze the expandable polymer beads as in Example 1. As in Example 1, both sets of sample beads reveal a cellular structure extending throughout the polymer beads, from proximate to the bead surface through the bead core .

Example 5 - Molded Expanded Polymer Bead Foam Prepare a molded expanded polymer bead foam using the expandable polymer beads from any of Examples 1-4. Coat the expandable polymer beads with 0.24 weight-percent, based on the weight of the expandable polymer beads, of a mixture of mono-, di- and tri-glycerides of higher fatty acids with a chain length of 8 to 22 carbons. Then, prefoam the expandable polymer beads using steam. Dry the prefoamed bead for 24 hours at 7O⁰C.

Place the beads 556 grams of the pre-foamed beads into a perforated block mold that is 50 centimeters (cm) by 25 cm by 25 cm in dimensions. Expand the prefoamed bead within the mold by subjecting them to low pressure steam until reaching a pressure of 0.7 bar in the block mold to further expand and fuse the beads to one another. Remove the resulting expanded polymer bead foam block from the mold and allow to dry at 7O⁰C for 72 hours. The resulting foam block has a density of approximately 17.8 grams per liter and a compressive strength at 10% deformation of approximately 76.2 kilopascals according to EN 13163.

Claims

CLAIMS :

1. An expandable polymer bead comprising the following components :

(a) 100 parts by weight of an alkenyl aromatic polymer;

(b) 0.1 to 8 parts by weight of one or more blowing agent impregnation enhancer selected from a group consisting of saturate aliphatic hydrocarbons having 20 to 60 carbon atoms and ester products of a saturated mono-carboxylic acid having 14 to 20 carbon atoms with an alkyl alcohol having 3 to 5 carbon atoms;

(c) 2 to 9 parts by weight of a blowing agent distributed throughout the polymer bead; (d) 0 to 7 parts by weight of an infrared attenuating agent; and

(e) 0 to 10 parts by weight of one or more additional additive.

2. The expandable polymer bead of Claim 1, wherein component (a) comprises polystyrene.

3. The expandable polymer bead of Claim 1, wherein component (a) is polystyrene.

4. The expandable polymer bead of Claim 1, wherein component (b) is one or more component selected from mineral oil and isobutyl stearate.

5. The expandable polymer bead of Claim 1, wherein component (c) is one or more isomer of pentane.

6. The expandable polymer bead of Claim 1, wherein component (d) is present and is one or more component selected from carbon black and graphite.

7. The expandable polymer bead of Claim 1, wherein the expandable polymer bead has a smallest dimension and a largest dimension and the ratio of smallest dimension to largest dimension is less than 0.8.

8. A process for preparing expandable polymer beads comprising the steps of: (a) Preparing polymer beads of a polymer composition that has a softening temperature and comprises 100 parts by weight of an alkenyl aromatic polymer, 0.1 to 8 parts by weight of one or more blowing agent impregnation enhancer selected from a group consisting of saturate aliphatic hydrocarbons having 20 to 60 carbon atoms and ester products of a saturated mono-carboxylic acid having 14 to 20 carbon atoms with an alkyl alcohol having 3 to 5 carbon atoms, 0 to 7 parts by weight of an infrared attenuating agent, and 0 to 10 parts by weight of one or more additional additive;

(b) Heating the polymer beads to a blowing agent impregnation temperature that is within 40 degrees Celsius of the polymer composition's softening temperature; and

(c) Impregnating the polymer bead with 2 to 9 parts by weight blowing agent.

9. The process of Claim 8, wherein the alkenyl aromatic polymer comprises polystyrene.

10. The process of Claim 8, wherein the alkenyl aromatic polymer is polystyrene.

11. The process of Claim 8, wherein the blowing agent impregnation enhancer is one or more component selected from mineral oil and isobutyl stearate.

12. The process of Claim 8, wherein the blowing agent is one or more isomer of pentane.

13. The process of Claim 8, wherein one or more infrared attenuating agents selected from carbon black and graphite are present in the polymer beads.

14. The process of Claim 8, wherein the polymer beads have a smallest dimension and a largest dimension and the ratio of the smallest dimension to the largest dimension is less than 0.8.

15. The process of Claim 8, wherein impregnation of blowing agent in step (c) occurs while the polymer beads are suspended in an aqueous medium.

16. An expanded polymer bead foam comprising one or more expanded polymer foam bead, wherein the one or more expanded polymer foam bead comprises the following components : (a) 100 parts by weight of an alkenyl aromatic polymer;

(c) 0 to 7 parts by weight of an infrared attenuating agent; and

(d) 0 to 10 parts by weight of one or more additional additive.

17. The expanded polymer bead foam of Claim 16, wherein component (a) comprises polystyrene.

18. The expanded polymer bead foam of Claim 16, wherein component (a) is polystyrene.

19. The expanded polymer bead foam of Claim 16, wherein component (b) is one or more component selected from mineral oil and isobutyl stearate.

20. The expanded polymer bead foam of Claim 16, wherein component (c) is present and is one or more component selected from carbon black and graphite.