1293319 魏、發明說明 本發明是有關於一種聚烯羥類（polyolefin)發泡顆粒， 且特別是有關於一種具有高密度外殼之聚烯羥類發泡顆粒 及其製造方法。 由聚胺基甲酸酯（polyurethane)、聚苯乙烯（Polystyrene) 或聚烯羥類製成的聚合發泡物，根據其彈性、持久性、輕 的重量以及低熱導性，已廣泛用來作爲一種吸收震動的材 料、熱絕緣材料以及封裝材料。 通吊，聚烯羥類的發泡產物是利用兩步驟來製作，首 先利用汽化的發泡劑注入到樹脂賒例中來製備聚烯羥類發 泡顆粒’然後利用熱將發泡顆粒雕塑成具有預定形狀之最 終發泡產物。 /當—發泡”比例增綱，最_發泡產物會變 ^輕’並龍更少_肖旨，不強賴尺寸的穩定度 白^ = = 改善其強度與尺寸穩定度，發泡顆粒 而會使發泡產物變得較重並且 的膨脹比例應該被降低，商 需要較多的樹脂。BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a polyolefin foamed particle, and more particularly to a polyolefin foamed particle having a high density outer shell and a method of producing the same. Polymeric foams made of polyurethane, polystyrene or polyene hydroxy have been widely used as a basis for their elasticity, durability, light weight and low thermal conductivity. A vibration absorbing material, a thermal insulating material, and an encapsulating material. By hanging, the foaming product of polyene hydroxy is produced by two steps. First, the vaporized foaming agent is injected into the resin sputum to prepare the poly olefinic foaming granules, and then the foamed granules are sculpted by heat. The final foamed product has a predetermined shape. / When - foaming" proportions increase, the most _ foaming products will become lighter and less dragons _ Xiao, not relying on the stability of the size white ^ = = improve its strength and dimensional stability, foaming particles The foaming product becomes heavier and the expansion ratio should be lowered, and the quotient requires more resin.
Mi- 曰的在於提供一種聚烯羥類發相 顆k，可以在較咼的脾· R叶芦—苷々Μ脹比例下得到具有較高強度與較肩 尺寸fe疋度之敢終發泡產牛勿 爲了達到本發明之 聚烯画發泡讎 構，且提供-觀作琴'3層(外殻）之密度高於其內㈣ 羥類發泡顆粒之製作方法，止丨 7128pifl.doc/008 1293319 方法包括利用在熱的環境中在高壓容器中攪拌樹脂顆粒、 發泡劑與水的混合物，藉以將一形成試劑注入到聚烯羥樹 脂顆粒中的一道步驟，接著利用擴散將在表面層（外殼）中 的發泡劑擴散到外部，以降低表面層的發泡劑之濃度，然 後再將樹脂顆粒釋放到一個低壓的環境中，以得到發泡顆 粒。 爲讓本發明之上述目的、特徵、和優點能更明顯易懂， 下文特舉一較佳實施例，並配合所附圖式，作詳細說明如 下： 圖式之簡單說明： 第1A圖爲一張顯示本發明之聚烯羥內發泡顆粒的結 構剖面的掃描式電子顯微鏡照片； 第1B圖爲一張顯示習知之聚烯羥內發泡顆粒的結構 剖面的掃描式電子顯微鏡照片；以及 第2圖繪示爲製作聚烯羥類發泡顆粒之設備裝置簡示 圖。 圖示標記說明： 203 膨脹室 201 注入室 201a 注入室上部的空間 實施例 ，包括注入步驟、擴散步驟 本發明是由三個步驟組成 與發泡步驟。 首先，在注入步驟中，於熱的環境下在一個高壓的注 入室中，利用攪拌樹脂顆粒、水與發泡劑的混合物，將發 7128pifl.doc/008 7 1293319 泡劑注入到樹脂中，此步驟與習知的方法相似。 聚乙燔、聚丙烯、或是各種乙烯與丙烯的共聚物，像 是隨機共聚物、區塊聚合物(block polymer)、或是接合聚 合物都可以用來作爲聚烯羥樹脂。此外，也可以使用包括 乙烯與丙烯的共聚物與其他烯羥類的單體，像是乙烯-丙 烯-1-丁烯的共聚物、乙烯-丙烯-丁二烯的共聚物等，更包 括像是烯羥類的單體與非烯羥類的單體，像是乙烯基醋酸 鹽、苯乙烯等組成之共聚物。 CFC-ll、CFCM2、丙烷、丁烷、戊烷、二氧化碳或其 他可以在樹脂中產生氣泡的物質，都可以用來作爲發泡 劑，因爲蒙特婁協約（Montreal Protocol)對CFC類使用的 限制，而丙烯具有高蒸氣壓，因此較適當的發泡劑爲丁烯 或戊烯。雖然二氧化碳很安全，較無燃燒與***的可能， 但是需要非常高的操作壓力。 注入室的溫度最好是維持在樹脂的融化點與軟化點之 間，藉以使得樹脂的發泡在釋放到低壓的環境中可以順利 的進行，因此注入步驟通常是在溫度約爲攝氏8 0至13 0 度之間進行。 使樹脂顆粒表面層的發泡劑之濃度降低的擴散步驟是 本發明的創新處。 當發泡劑在氣相、液相與固相之間達到熱力動力的濃 度平衡時，即完成發泡劑注入樹脂的步驟’接著利用降低 樹脂周圍的發泡劑濃度，藉以使述之中的發泡劑向外擴 散，因此樹脂中的發泡劑之濃度會由其表面層開始降低’ 7128pifl.doc/008 8 1293319 且當在樹脂相中的擴散速率低時’在一段短時間內表面層 的濃度會比樹脂內部的濃度要低。 可以使用任何適當的方法來降低樹脂顆粒周匿[的發、泡 劑之濃度。 其中有一種方法’可以在注入室中，降低在氣相中的 發泡劑濃度’係利用自注入室中移除氣態的發泡劑來進 行，當氣態的發泡劑被移除時，注入到樹脂中的發泡劑會 擴散到氣相空間中，以達到一個新的平衡。 在此，在移除發泡劑蒸氣期間，利用提供惰性氣體像 是氮氣到注入室中’注入室的壓力應該不會被降低；當注 入室的壓力降低時，因爲在樹脂中的發泡劑汽化便會產生 發泡現象。 另一種降低周圍環中的發泡劑濃度的方法係利用在水 中降低發泡劑之濃度，以水來取代具有較低濃度發泡劑的 水，使其達到另一個平衡。 除了上述的方法以外，對於熟習此技藝者來說，應當 可以利用其他各種方法來降低樹脂顆粒周圍環境中的發泡 劑濃度，而不會改變本發明的擴散步驟界定的範圍。 舉例來§兌’可以將水注入到注入室中，以水來取代在 注入室上端的氣體空間來排出氣體，然後將像是氮氣的惰 性氣體供應到注入室中以移除水，在此之前利用水的取代 步驟與之後提到的利用惰性氣體的置換步驟相同，都是用 以使發泡劑擴散到樹脂外面。 或者，先將水自注入室中移出，然後在輸入惰性氣體 7128pifl.doc/008 9 1293319 取代其中的蒸氣也可以。 在完成擴散步驟以後，在進行發泡步驟時，樹脂顆粒 表層的濃度會比內部要低，其他樹脂顆粒會被放到一個低 壓膨脹室中，在樹脂中的發泡劑會汽化，而產生發泡顆粒， 在此由於表層具有較低的發泡劑濃度，因此會較發泡顆粒 的內部產生較少的泡沫密度，如此即可得到具有高密度外 殼的發泡顆粒，此外殼的密度與厚度可以利用在樹脂顆粒 中發泡劑的濃度梯度來決定，而濃度梯度則受到在樹脂相 中發泡劑的擴散速度，以及在擴散步驟中持續的時間影 響。 上述關於本發明的方法的所有步驟可以在一個容器（注 入室）中進行，也可以在不同的容器中分別進行每一道步 驟，比如在一個高壓的容器中進行注入步驟，以達到有效 率的熱傳遞與混合，然後將內容物移到另一個容器中，接 續進行擴散與發泡步驟。 範例 下面敘述中提到的實例係用以進一步說明本發明，伸 並不用以限制本發明之範圍。 比較範例1 利用第2圖中所示的設備’以傳統的方法製備聚丙稀 發泡顆粒’其中注入室2〇1與膨脹室2〇3的體積分別爲i 公升與40》升，使用直徑胃3mm、溶點爲攝氏16〇度的 聚丙烯樹脂，以丁烷作爲發泡劑，以水作爲一種散佈媒介。 7128pifl.doc/008 10 1293319 將50公克的樹脂與560公克的水加入到注入室201 中，然後利用真空幫浦209將室內的氣體抽掉，之後將50 公克的丁烷加入到注入室201中，以200rmp的轉速攪拌 混合物，並加熱到攝氏125度，並在壓力爲27kg/cm2下將 注入室201維持在攝氏125度下達30分鐘。 在完成注入步驟以後，注入室201中所有的內容誤會 被移到一個低壓的膨脹室203中，而得到具有平均膨脹率 爲40的聚丙烯發泡顆粒。 範例1 利用第2圖中所示的設備，以本發明提供之方法製備 聚丙烯發泡顆粒。 本發明的注入步驟與上述的比較範例1中的注入步驟 之實施方法相同。 在完成注入步驟以後，將注入有發泡劑的樹脂顆粒進 行擴散步驟，在空間201a中的蒸氣混合物排出約30秒， 在排出蒸氣混合物的期間，持續進行攪拌，並利用供應氮 氣到注入室中，以將注入室201的壓力維持在30kg/cm2下。 在完成擴散步驟以後’進行本發明的發泡步驟，此步 驟喜與在上述比較範例1中所述的發泡步驟相同。Mi- 曰 在于 在于 在于 Mi Mi Mi Mi Mi Mi Mi Mi Mi Mi Mi Mi Mi Mi Mi Mi Mi Mi Mi Mi Mi Mi Mi Mi Mi Mi Mi Mi Mi Mi Mi Mi Mi Mi Mi Mi Mi Mi Mi Mi Mi Mi Mi In order to achieve the foaming structure of the polyene painting of the present invention, the production of the three layers (shell) of the viewing machine is higher than that of the inner (four) hydroxy foaming particles, and the method of making the hydroxy foaming particles is stopped. /008 1293319 The method comprises a step of agitating a mixture of resin particles, a blowing agent and water in a high-pressure vessel in a hot environment, thereby injecting a forming agent into the particles of the polyolefin resin, followed by diffusion on the surface The blowing agent in the layer (outer casing) is diffused to the outside to lower the concentration of the foaming agent of the surface layer, and then the resin particles are released into a low pressure environment to obtain foamed particles. The above described objects, features, and advantages of the present invention will become more apparent and understood. A scanning electron micrograph showing a structural cross section of the polyene hydroxy inner foaming granule of the present invention; FIG. 1B is a scanning electron micrograph showing a structural cross section of a conventional polyene hydroxy inner foaming granule; 2 is a schematic view showing an apparatus for manufacturing polyene hydroxy-based foamed granules. Illustrated indicia: 203 Expansion chamber 201 Injection chamber 201a Space in the upper portion of the injection chamber. Embodiments including injection step, diffusion step The present invention is composed of three steps and a foaming step. First, in the injection step, in a high-pressure injection chamber, a mixture of agitating resin particles, water and a blowing agent is used to inject a foam of 7128 pifl.doc/008 7 1293319 into the resin. The steps are similar to the conventional methods. Polyethyl hydrazine, polypropylene, or various copolymers of ethylene and propylene, such as random copolymers, block polymers, or conjugated polymers, can be used as the polyolefin resin. Further, a copolymer comprising a copolymer of ethylene and propylene and another olefinic hydroxyl group such as a copolymer of ethylene-propylene-1-butene, a copolymer of ethylene-propylene-butadiene, and the like may be used. It is a copolymer of a monomer of a olefinic group and a monomer of a non-olefinic hydroxy group, such as a vinyl acetate, styrene or the like. CFC-ll, CFCM2, propane, butane, pentane, carbon dioxide or other substances that can generate bubbles in the resin can be used as a blowing agent because of the limitations of the Montreal Protocol on the use of CFCs. While propylene has a high vapor pressure, a more suitable blowing agent is butene or pentene. Although carbon dioxide is safe and less likely to burn and explode, it requires very high operating pressures. The temperature of the injection chamber is preferably maintained between the melting point and the softening point of the resin, so that the foaming of the resin can be smoothly performed in a low pressure environment, so the injection step is usually at a temperature of about 80 ° C to Between 13 degrees. The diffusion step of lowering the concentration of the foaming agent of the surface layer of the resin particles is an innovation of the present invention. When the blowing agent reaches the concentration balance of the thermodynamic force between the gas phase, the liquid phase and the solid phase, the step of injecting the blowing agent into the resin is followed by reducing the concentration of the blowing agent around the resin, thereby The blowing agent spreads out, so the concentration of the blowing agent in the resin will start to decrease from its surface layer ' 7128 pifl.doc / 008 8 1293319 and when the diffusion rate in the resin phase is low 'the surface layer in a short time The concentration will be lower than the concentration inside the resin. Any suitable method can be used to reduce the concentration of the resin particles. One of the methods 'in the injection chamber, reducing the concentration of the blowing agent in the gas phase' is carried out by removing the gaseous blowing agent from the injection chamber, and when the gaseous blowing agent is removed, the injection is performed. The blowing agent into the resin will diffuse into the gas phase space to achieve a new balance. Here, during the removal of the blowing agent vapor, the pressure of the injection chamber by supplying an inert gas such as nitrogen into the injection chamber should not be lowered; when the pressure in the injection chamber is lowered, because of the blowing agent in the resin Foaming can cause foaming. Another way to reduce the concentration of blowing agent in the surrounding ring is to reduce the concentration of blowing agent in water and replace the water with a lower concentration of blowing agent with water to another equilibrium. In addition to the above methods, those skilled in the art should be able to utilize various other methods to reduce the concentration of the blowing agent in the environment surrounding the resin particles without changing the range defined by the diffusion step of the present invention. For example, §' can inject water into the injection chamber, replace the gas space at the upper end of the injection chamber with water to vent the gas, and then supply an inert gas such as nitrogen to the injection chamber to remove the water. The substitution step using water is the same as the subsequent replacement step using an inert gas, and is used to diffuse the blowing agent to the outside of the resin. Alternatively, the water may be removed from the injection chamber and then replaced with an inert gas 7128pifl.doc/008 9 1293319. After the diffusion step is completed, the concentration of the surface layer of the resin particles is lower than that of the interior during the foaming step, and the other resin particles are placed in a low pressure expansion chamber, and the foaming agent in the resin is vaporized to generate hair. The granules, which have a lower foaming agent concentration, thus produce less foam density than the interior of the foamed granules, thus obtaining foamed granules having a high density outer shell, the density and thickness of the outer shell It can be determined by the concentration gradient of the blowing agent in the resin particles, and the concentration gradient is affected by the diffusion speed of the blowing agent in the resin phase and the duration of the diffusion step. All of the above steps relating to the method of the present invention may be carried out in one vessel (injection chamber), or each step may be carried out separately in a different vessel, such as an injection step in a high pressure vessel to achieve efficient heat. Transfer and mix, then move the contents to another container and continue the diffusion and foaming steps. The following examples are presented to further illustrate the invention and are not intended to limit the scope of the invention. Comparative Example 1 Using the apparatus shown in Fig. 2 to prepare a polypropylene foamed granule in a conventional manner, the volume of the injection chamber 2〇1 and the expansion chamber 2〇3 was i liter and 40 liters, respectively, using a diameter stomach. 3mm polypropylene resin with a melting point of 16 degrees Celsius, using butane as a foaming agent and water as a scattering medium. 7128pifl.doc/008 10 1293319 50 grams of resin and 560 grams of water are added to the injection chamber 201, and then the chamber gas is evacuated by the vacuum pump 209, after which 50 grams of butane is added to the injection chamber 201. The mixture was stirred at 200 rpm and heated to 125 degrees Celsius, and the injection chamber 201 was maintained at 125 degrees Celsius for 30 minutes at a pressure of 27 kg/cm2. After the completion of the implantation step, all contents in the injection chamber 201 were misplaced and moved to a low pressure expansion chamber 203 to obtain polypropylene foamed particles having an average expansion ratio of 40. Example 1 Using the apparatus shown in Fig. 2, polypropylene foamed granules were prepared by the method of the present invention. The implantation step of the present invention is the same as that of the injection step in Comparative Example 1 described above. After the completion of the injection step, the resin particles injected with the blowing agent are subjected to a diffusion step, and the vapor mixture in the space 201a is discharged for about 30 seconds, during which the vapor mixture is discharged, stirring is continued, and nitrogen gas is supplied to the injection chamber. To maintain the pressure of the injection chamber 201 at 30 kg/cm2. The foaming step of the present invention was carried out after the completion of the diffusion step, and this step was the same as the foaming step described in Comparative Example 1 described above.
第1A圖的掃描式電子顯微鏡照片顯示範例1中，以 本發明的方法得到的聚乙烯發泡顆粒的結構剖面圖，如圖 所示，在標示爲A的表層(外殼）中的氣泡會小於標示爲B 的內層中的氣泡，因爲在表層中的小氣泡，所以標示爲C 7128pifl.doc/008 1293319 的表面會較平滑。在比較第1A圖與第圖時就可以發 現新發泡顆粒之特性，第圖也是一張掃描式電子顯微 鏡的照片，顯示一種習知的聚烯羥類發泡顆粒，此習知的 發泡顆粒在整個顆粒中具有均勻的氣泡，因爲在標示爲C 的表層具有大的氣泡而產生粗糙的表面。 新的發泡顆粒在表層較內層具有較高的密度，相較於 習知的發泡顆粒，在同樣的平均膨脹率中，呈現出較高的 強度與較高的尺寸穩定度。 範例2 使用範例1中提到的設備，以及50公克直徑爲2mm、 熔點爲攝氏136度的聚乙烯樹脂、50公克的丙烷（作爲發 泡劑）、560公克的水(作爲散佈媒介）。 將樹脂、丙烷與水加入加入注入室201中並攪拌，加 熱到攝氏95度，並在壓力爲40kg/cm2下維持在此溫度30 分鐘。 然後，在移除含有發泡劑的水與注入室中的發泡劑氣 體期間，利用提供攝氏95度的水到注入室中，藉以將樹 脂表層中的發泡劑擴散出來，提供的水中不含有發泡劑， 此階段注入室的壓力還是維持在40kg/cm2。 在完成擴散步驟以後，將樹脂顆粒移到低壓的膨脹室 203中，可以得到平均膨脹率爲40，且具有高密度外殼之 聚乙烯發泡顆粒。 7128pifl.doc/008 12 1293319 範例3 使用範例1中提到的設備，以及50公克直徑爲2mm、 溶點爲攝氏13 6度的乙稀-丙嫌共聚物、6 0公克的戊院(作 爲發泡劑）、560公克的水(作爲散佈媒介）。 將樹脂、戊烷與水加入加入注入室201中並攪拌，加 熱到攝氏115度’並在壓力爲l〇kg/cm2下維持在此溫度30 分鐘。 然後，利用提供攝氏115度的水到注入室中，將注入 室2〇1上部的空間2〇la中的發泡劑蒸氣取代，藉以將樹 脂表層中的發泡劑擴散出來，然後在供應氮氣以將壓力維 持在10kg/cm2的情況下，將注入室中大部分的水移走。 在完成擴散步驟以後，將樹脂顆粒移到低壓的膨脹室 203中，可以得到平均膨脹率爲28，且具有高密度外殻之 乙烯-丙烯發泡顆粒。 範例4 使用範例1中提到的設備，以及50公克直徑爲2mm、 熔點爲攝氏K5度的乙烯-丙烯-丁二烯的共聚物、50公克 的丁烷（作爲發泡劑）、560公克的水(作爲散佈媒介）。 將樹脂顆粒、丁烷與水加入加入注入室201中並攪拌， 加熱到攝氏1〇〇度，並在壓力爲35kg/cm2下維持在此溫度 30分鐘。 然後，在壓力爲38kg/cm2下提供氮氣來取代注入室201 中的水，並持續供應氮氣以移除發泡劑的蒸氣。 7128pifl.doc/008 13 1293319 在完成擴散步驟以後，將樹脂顆粒移到低壓的膨脹室 203中’可以得到平均膨脹率爲3〇，且具有高密度外殼之 聚乙烯發泡顆粒。 如上範例所述，利用本發明之製作方法可以得到具有 局密度外殼之聚烯羥類發泡顆粒，因爲得到的聚烯羥類發 泡顆粒係利用較少量的樹脂製作，且具有相同強度與尺寸 穩定度，因此本發明的方法提供製作聚烯羥類發泡顆粒一 個可行且經濟的選擇。 雖然本發明已以一較佳實施例揭露如上，然其並非用 以限定本發明，任何熟習此技藝者，在不脫離本發明之精 神和範圍內，當可作各種之更動與潤飾，因此本發明之保 護範圍當視後附之申請專利範圍所界定者爲準。 7128pifl.doc/008 14Scanning Electron Microscope Photograph of Figure 1A shows a cross-sectional view of the structure of the polyethylene foamed granule obtained by the method of the present invention in Example 1, as shown in the figure, the bubble in the surface layer (outer shell) designated A is smaller than The bubbles in the inner layer labeled B, because of the small bubbles in the surface, the surface labeled C 7128pifl.doc/008 1293319 will be smoother. The characteristics of the new foamed granules can be found when comparing Fig. 1A and Fig. 1, and the photograph is also a photograph of a scanning electron microscope showing a conventional olefinic styrene foaming granule, which is known as foaming. The particles have uniform bubbles throughout the particle because the surface layer labeled C has large bubbles creating a rough surface. The new expanded particles have a higher density in the inner layer than in the inner layer, and exhibit higher strength and higher dimensional stability in the same average expansion ratio than the conventional expanded particles. Example 2 The equipment mentioned in Example 1 was used, together with 50 grams of polyethylene resin having a diameter of 2 mm, a melting point of 136 degrees Celsius, 50 grams of propane (as a foaming agent), and 560 grams of water (as a spreading medium). The resin, propane and water were added to the injection chamber 201 and stirred, heated to 95 ° C, and maintained at this temperature for 30 minutes at a pressure of 40 kg/cm 2 . Then, during the removal of the water containing the blowing agent and the blowing agent gas in the injection chamber, water of 95 degrees Celsius is supplied into the injection chamber, thereby diffusing the foaming agent in the surface layer of the resin, and the supplied water is not Containing a blowing agent, the pressure in the injection chamber at this stage is maintained at 40 kg/cm2. After the diffusion step is completed, the resin particles are moved into the low pressure expansion chamber 203 to obtain polyethylene foamed particles having an average expansion ratio of 40 and having a high density outer casing. 7128pifl.doc/008 12 1293319 Example 3 Using the equipment mentioned in Example 1, and 50 grams of ethylene-propylene copolymer with a diameter of 2 mm, a melting point of 13 6 degrees Celsius, and a 60 gram chamber (as a hair Foam), 560 grams of water (as a spreading medium). The resin, pentane and water were added to the injection chamber 201 and stirred, heated to 115 ° C and maintained at this temperature for 30 minutes at a pressure of 10 kg/cm 2 . Then, by supplying water of 115 degrees Celsius into the injection chamber, the blowing agent vapor in the space 2〇1a in the upper portion of the injection chamber 2〇1 is replaced, thereby diffusing the foaming agent in the surface layer of the resin, and then supplying nitrogen gas. With the pressure maintained at 10 kg/cm2, most of the water in the injection chamber was removed. After the completion of the diffusion step, the resin particles are moved into the low pressure expansion chamber 203 to obtain an ethylene-propylene foamed particle having an average expansion ratio of 28 and having a high density outer casing. Example 4 Using the equipment mentioned in Example 1, and 50 grams of a copolymer of ethylene-propylene-butadiene having a diameter of 2 mm, a melting point of K5 degrees Celsius, 50 grams of butane (as a blowing agent), 560 grams Water (as a distribution medium). Resin particles, butane and water were added to the injection chamber 201 and stirred, heated to 1 degree Celsius, and maintained at this temperature for 30 minutes at a pressure of 35 kg/cm2. Then, nitrogen was supplied at a pressure of 38 kg/cm 2 instead of the water in the injection chamber 201, and nitrogen gas was continuously supplied to remove the vapor of the blowing agent. 7128pifl.doc/008 13 1293319 After the diffusion step is completed, the resin particles are moved into the low-pressure expansion chamber 203, and polyethylene foam particles having an average expansion ratio of 3 Å and having a high-density outer shell can be obtained. As described in the above examples, the polyene hydroxy-based foamed granules having a local density of the outer shell can be obtained by the production method of the present invention because the obtained polyene hydroxy-based foamed granules are produced by using a relatively small amount of resin and have the same strength and Dimensional stability, and thus the process of the present invention provides a viable and economical option for making polyalkenyl foamed particles. Although the present invention has been described above in terms of a preferred embodiment, it is not intended to limit the invention, and it is obvious to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the invention. The scope of the invention is defined by the scope of the appended claims. 7128pifl.doc/008 14