JP2013018959A - Process for enabling secondary expansion of expandable bead - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide lightweight foamed beads capable of secondary expansion and comprising compostable or biobased polyesters, and to provide a method for producing the same.SOLUTION: The method includes: blending a melt processable composition in an extruder to form an extrudate; incorporating a first blowing agent into the composition, wherein the first blowing agent comprises a physical blowing agent; incorporating a second blowing agent into the composition, wherein the second blowing agent comprises a chemical blowing agent; and pelletizing the extrudate to form a bead.

Description

Cross-reference to related application This application is filed by the inventors of the present application on September 10, 2010, at the US Patent and Trademark Office, entitled “Method of Enabling Secondary Foaming of Expandable Beads”. And claims its benefit based on pending and co-assigned US Provisional Application No. 61 / 381,750, which is hereby incorporated by reference in its entirety.

  The present invention relates generally to a novel lightweight foam manufacturing method, and in particular, a foaming agent that combines melt processing technology with physical and chemical foaming agents to enable secondary foaming of the foam. The present invention relates to a method for producing a foam.

  The polymer foam includes a plurality of voids, also called cells, in the polymer matrix. By replacing the solid plastic with voids, the polymer foam uses fewer raw materials than the solid plastic for a given volume. Thus, the use of polymer foam instead of solid plastic can reduce material costs in many applications. In addition, foam is a very good insulator that can protect building structures from ingress of air and moisture, save utility bills, and increase the strength of buildings.

The material used for expandable polystyrene (EPS) is typically an amorphous polymer that exhibits a glass transition temperature of about 95 ° C. The process of converting EPS resin to expanded polystyrene foam requires three main steps: pre-expansion, aging, and molding. Expandable beads are produced from polystyrene and a blowing agent and then foamed with steam in a pre-foaming machine. The purpose of pre-foaming is to produce foam particles of the desired density for a particular application. During pre-foaming, the EPS beads are charged into a pre-foaming tank equipped with a stirrer and a controlled steam and air supply. The introduction of steam into the prefoamer has two effects. The softening of the EPS beads and the heating of the blowing agent dispersed within the EPS beads, typically pentane, to a temperature above the boiling point. These two conditions expand the volume of the EPS beads. The particle diameter increases while the resin density decreases. The density of the pre-foamed granule is about 1000 kg / m ³ and the density of expanded beads is in the range of 20 kg / m ³ to 200 kg / m ³ , depending on the method, 5 to 50 times Density reduction can be achieved.

  Aging has several advantages. By aging, the vacuum created inside the cell of foam particles can reach equilibrium with the ambient pressure during pre-foaming, evaporate the residual moisture on the foam particle surface and remove excess residual foaming agent. Dissipate. The aging time depends on many factors, such as the content of the blowing agent in the underlying resin, the prefoam density, and environmental factors. Pre-expanded beads that are not properly aged are sensitive to physical and temperature shocks. Such shaping of the beads before aging can cause cell rupture within the particles, resulting in the production of undesirable molded foam portions.

  Once the pre-expanded beads are aged, they are transported to a molding machine that includes one or more cavities formed for the desired molded foam. The purpose of molding is to fuse the expanded particles into a single foam part. EPS can be formed in a simple order. First, the cavity is filled with pre-expanded beads, steam is introduced to heat the mold, the molded foam is cooled in the cavity, and the completed part is injected from the cavity. The bead is softened by the steam introduced into the molding machine and further expanded by the release of a residual blowing agent such as pentane. The combination of these two effects in a closed cavity allows the individual particles to be fused into a single solid foam part.

  There is an increasing demand for biodegradability of many plastic products used in packaging, such as cookie trays and candy packaging. Conventionally, starch films have been proposed as an option for biodegradability. A common approach for producing biodegradable products is to combine polylactic acid (PLA) and starch to make a hydrolyzable composition. Problems have arisen in the production of starch-based polymers, particularly by hot melt extrusion. The molecular structure of starch is adversely affected by the shear stress and temperature conditions required to plasticize starch and pass it through an extrusion die.

  The blowing agent is typically introduced into the polymeric material, and the polymer foam is made in one of two ways. According to one technique, a chemical blowing agent is mixed into the polymer. Chemical blowing agents typically chemically react in polymeric materials under conditions that allow the polymer to dissolve and produce a gas. Chemical blowing agents are generally low molecular weight organic compounds that decompose at a specific temperature and release gases such as nitrogen, carbon dioxide, or carbon monoxide. According to another technique, a physical blowing agent, ie, a blowing agent that is fluid under ambient conditions, is injected into the dissolved polymer stream to form a mixture. By dropping the pressure on the mixture, the blowing agent is expanded and bubbles (cells) are formed in the polymer. Several patents and patent publications describe microporous materials and microcellular processes.

US Pat. No. 6,593,384 by Anderson et al. Describes expandable particles made using a wide range of polymeric materials and physical blowing agents. U.S. Pat. No. 7,226,615 by Yuksel et al. Describes an expandable foam based on a broad disclosure regarding the combination of biomaterial and bicarbonate blowing agent. US Patent Application Publication No. 2006/0167122 by Haraguchi et al. Describes expandable particles derived from a combination of PLA, a blowing agent, and a polyolefin wax. Witt et al. U.S. Patent Application Publication No. 2010/0029793 by describes a method of manufacturing PLA forms with be infiltrated carbon dioxide (C0 ₂₎ in the resin beads.

  U.S. Pat. No. 4,473,665 by Martini-Vvedensky et al. Describes a method for producing a foamed polymer having cells less than about 100 microns in diameter. The described technique saturates the material precursor with a blowing agent, puts the material under high pressure, and nucleates the blowing agent by allowing the pressure to drop rapidly, allowing the formation of cells. The material is then rapidly frozen to maintain the desired dispersion of the microcellular.

  US Pat. No. 5,158,986 by Cha et al. Describes the formation of microporous polymeric materials using a supercritical fluid as a blowing agent. Using a batch process, the patent describes various methods for creating nucleation sites.

  US Pat. No. 5,866,053 by Park et al. Describes a continuous process for forming microcellular foams. The material is nucleated by rapidly reducing the pressure on the single phase solution of blowing agent and polymer. The nucleus growth rate is high enough to form a microcell structure in the final product.

  International Patent Publication No. 98/08667 by Burnham et al. Provides a method and system for producing microporous materials and microporous articles. In one method, a single phase of a fluid, a precursor of a foamed polymeric material is obtained by separating the stream into separate parts, nucleating each separate part separately, and then recombining the streams. The solution and blowing agent are continuously nucleated. The recombined stream can be formed into a desired shape, for example, formed by a die.

  In order to create enough nucleation sites to form microcellular foam, enough blowing agent to create nucleation driving force and prevent cell growth from dominating nucleation events It is generally accepted in the art that a sufficiently high pressure drop rate must be used. As the level of blowing agent decreases, the driving force for nucleation also decreases. However, while higher blowing agent levels lead to the formation of smaller cells (generally a favorable result in the field of microcellular foam), according to conventional thinking, higher blowing agent levels are more Connections (which naturally increase cell size and can impair structural and other material properties) and sub-optimal surface properties (impaired surface properties at higher gas levels are Depending on the tendency, the foaming agent may result in diffusion outside the material).

  That is, it is generally accepted that when changing the blowing agent level in a microporous polymer material, a small cell size and optimal material properties are in a reciprocal relationship.

  The object of the present invention is therefore to avoid the drawbacks of the prior art and to provide compostable or bio-based foams.

  Another object of the present invention is to provide a method for producing compostable or bio-based foams using melt processing techniques. A related object of the present invention is to provide a method for producing compostable or bio-based foams using a combination of various foaming agents.

  Another object of the present invention is to provide compostable or bio-based expanded beads that can be processed using conventional molding equipment.

  Another object of the present invention is to provide expanded beads that can be chemically broken down into lower molecular weight materials by a composting process.

  Yet another object of the present invention is to provide compostable or bio-based expanded beads that can be processed into a three-dimensional shape.

  These and other objects of the present invention are to provide compositions and methods for producing expanded beads from compostable or bio-based polymers and also to use such beads in the manufacture of a variety of items. To be achieved. In one embodiment, lightweight beads are manufactured by melt processing a compostable or bio-based polymer and a combination of physical and chemical blowing agents. In another embodiment, the melt processable composition contains additional additives that improve the rheological properties of the compostable or biobased polymer, making it easier to produce lightweight foam beads. In order to provide a lightweight, compostable or bio-based foam, the foam beads of the present invention can also be further processed using conventional molding equipment. The articles of the present invention are useful in applications where conventional expandable polystyrene (EPS) is currently used, including applications related to protective packaging, silencing, and insulation.

  Polymer compositions are widely used in a number of applications including automotive products, residential building products, electrical products, and consumer products. The polymer may be composed of either a bio-based polymer or a petroleum-based polymer. Compostable or bio-based polymers are preferred to address the environmental issues associated with material disposal and minimizing oil use when it is no longer beneficial for the intended purpose. However, in order for a polymer to be suitable for the intended application, the polymer must meet certain physical and chemical properties. In foamable foams, the polymer composition must be lightweight and processable into a three-dimensional shape that provides impact, sound, and temperature resistance or protection. The invention described herein discloses a compostable or bio-based foam having the attributes necessary to form a product with these attributes.

For purposes of the present invention, the following terms used herein are defined as follows:
By “biodegradable polymer” is meant a polymeric material or resin that can be chemically degraded into lower molecular weight materials.
“Compostable” means that the material is not visually distinguishable and is capable of biodegradation, such as decomposition into carbon dioxide, water, inorganic compounds, and biomass.
“Bio-based” means materials that are composed, in whole or in large part, of biologically derived or renewable agricultural materials, including plant, animal, and marine materials.
"Plasticizer" means a material that is compatible with compostable or biobased polymers after material melt processing. Adding a plasticizer to a compostable or biobased polymer has the effect of reducing the modulus of the coating composition.
“Chain extender” means a material that, when melt processed with a polymer, increases molecular weight by reactively bonding molecular chain ends.
“Melt processable composition” means a blend that has been melt processed, typically at elevated temperatures, using conventional polymer processing techniques such as extrusion or injection molding.
“Melt processing technique” means extrusion, injection molding, blow molding, rotational molding, or batch mixing.
An “extruded product” is a semi-solid material that has been extruded into a continuous shape by pushing the material through a die opening.

  The invention summarized and defined above by the enumerated claims will be better understood by reference to the following description. The description of the embodiments set forth below to enable the invention to be constructed and implemented is not intended to limit the invention, but provides a specific example. Those skilled in the art will recognize that the disclosed concepts and specific embodiments can be readily used as a basis for modifying or designing other methods and mechanisms for carrying out the same purposes as those of the present invention. Let's go. Those skilled in the art will also realize that such identical assemblies do not depart from the spirit and scope of the present invention in its broadest sense.

  The present invention is directed to various products made from compostable or bio-based materials. The compostable bio-based material can include either or both externally or internally modified polymer compositions, which terms are described below.

  Biodegradability refers to a compound that is susceptible to enzymatic degradation by, for example, a microorganism, or a portion of a compound that is susceptible to enzymatic degradation by, for example, a microorganism. In one example, a polymer such as polylactic acid can be hydrolyzed, for example, into lactic acid molecules that are susceptible to enzymatic degradation by a wide variety of microorganisms. Microorganisms typically consume oligomers containing carboxylic acids with a molecular weight of 1000 Daltons or less, preferably about 600 Daltons or less, depending on the chemical and physical properties of the oligomers.

  A biobase is a material that is synthesized from a biological source and is a raw material that is not renewable by integrating at least a portion of the product within the product, such as replacement of petroleum as a replacement for petroleum used in making EPS. Refers to ingredients that reduce the use of Biobased ingredients are used in many products without interfering with their performance.

  Composting is a biological process that decomposes organic waste into useful materials by various microorganisms in the presence of oxygen.

  Preferably, the polymer in the material is degraded by composting. The degradation characteristics of the polymer of this material mainly depend on the type of material made by the polymer. As such, the polymer must have suitable degradation characteristics so that when the final material is processed, significant degradation does not occur until the material reaches its useful life.

  The polymer of the material is further characterized in that the product made from the material becomes compostable within a period of degradation after use. Whereas similar mass-produced, non-degradable products usually take decades to centuries to spontaneously degrade, the materials of the present invention typically degrade in a period of 180 days or less.

  The present invention describes compostable or bio-based foam beads useful for making foam. The foam of the present invention is manufactured using a compound comprising a compostable or bio-based thermoplastic polymer and a combination of blowing agents. Such compostable thermoplastic polymer materials are used to replace foamed polystyrene (EPS) with foamed beads made from compostable or bio-based polymer resins when building foam. Can be used. Ideally, polystyrene would be replaced with compostable or bio-based polymers of the same characteristics chemically and physically.

Additives including plasticizers and chain extenders are optionally included in the compostable or biobased polymer compound. Preferably, the polymer has a biobase content of 50% or more, most preferably a biobase content of 80% or more. These foams can be produced using conventional melt processing techniques such as single and paired screw extrusion methods. In one embodiment, the expanded beads are made by cutting the extrudate at the surface of the extrusion die. The expanded beads are then optionally cooled by contact with water, water vapor, oxygen, carbon dioxide or nitrogen gas. After the beads are cut on the surface of the extrusion die, the beads continue to foam, forming a closed cellular foam structure with a continuous skin layer, i.e. no open cell structure on the surface of the beads. is there. In certain embodiments, the resulting compostable or bio-based expanded beads have a specific gravity of 0.15 g / cm ³ . In another embodiment, the specific gravity of compostable or bio-based foam beads preferably 0.075 g / cm ³ or less, and most preferred is 0.05 g / cm ³ or less. In some embodiments, greater than 50% by weight of the foam contains compostable material as measured by ASTM D6400. In a more preferred embodiment, 80% weight or more of the foam contains compostable material. In the most preferred embodiment, 95% weight or more of the foam contains compostable material.

  The compostable or biobased polymer of the present invention includes melt extenders, including chain extenders and plasticizers, additions that modify the rheology of the blowing agent and optionally the compostable or biobased polymer. Manufactured with goods. Compostable or bio-based polymers may include polymers commonly recognized by those skilled in the art to degrade into compounds with lower molecular weights. Non-limiting examples of compostable or biobased polymers suitable for practicing the invention include polysaccharides, peptides, polyesters, polyamino acids, polyvinyl alcohol, polyamides, polyalkylene glycols, and copolymers Is mentioned.

  In one aspect, the compostable or biobased polymer is a polyester. Non-limiting examples of polyesters include polylactic acid (PLLA), poly-D-lactic acid (PDLA), random or stereoregular copolymers of L-lactic acid and D-lactic acid, and derivatives thereof. Non-limiting examples of other polyesters include polycaprolactone, polyhydroxybutyric acid, polyhydroxyvaleric acid, polyethylene succinate, polybutylene succinate, polybutylene adipate, polymalic acid, polyglycolic acid, polysuccinate, polyoxanate, Examples include polybutylene glycolate and polydioxanone.

  Preferred polymer resins of the present invention include known compostable materials derived from biological resources (eg, compostable biopolymer resins), but compostable synthetic polymers can also be used. Biopolymer polylactic acid (PLA) is the most preferred example because of its known composting capacity and bio-based origin from agricultural feedstock (eg corn). The PLA polymer can be used regardless of whether it is amorphous or anticrystalline. Examples of compostable or biobased polymers include Ingeo 2002D and Ingeo 4060D grade plastics from NatureWorks, LLC and Compostable 5001, and Ingeo 8051D grade foam.

  In the present invention, compostable or bio-based polymers are melt processed with a foaming agent to produce lightweight foam beads. A blowing agent is a melt processable composition (eg, additive, polymeric matrix, and / or optional filler) to produce a cell through degassing at an appropriate time during processing. Premix, a material that can be incorporated into a molten or solid form). The amount and type of blowing agent affects the density of the finished product, depending on the cell structure. Any suitable blowing agent can be used to produce the foam.

  There are two main types of blowing agents: physical and chemical. Physical blowing agents tend to be volatile liquids or compressed gases that change state during the melt processing to form the cell structure. In a preferred embodiment, the physical blowing agent is carbon dioxide. In the most preferred embodiment, a physical blowing agent that is carbon dioxide in a supercritical state is mixed with the molten polymer. Chemical blowing agents tend to become solids that decompose (eg, react with heat with other products) to provide a gaseous decomposition product. The gas produced is finely distributed in the melt processable composition to provide the cell structure.

  Chemical blowing agents are mainly classified into two types, organic and inorganic. Organic blowing agents are available in a wide range of different chemistries, physical shapes and modifications, such as azodicarbonamide. Inorganic foaming agents are more likely to be constrained. Preferably, baking soda is used because it is inexpensive and easily forms carbon dioxide gas. Baking soda gradually decomposes when heated to about 120 ° C. or higher, and significantly decomposes between about 150 ° C. and 200 ° C. In general, the higher the temperature, the faster the baking soda decomposes. Acids such as citric acid are also included in the foamable additive and can be added separately to the melt processable composition to promote the degradation of the blowing agent. Chemical blowing agents are usually supplied in powder or pellet form. The specific choice of blowing agent will be related to cost, desired cell generation and gas generation, and the desired properties of the foam material.

  Examples of suitable blowing agents include water, carbonate and / or bicarbonate and other carbon dioxide releasing materials, diazo compounds and other nitrogen producing materials, carbon dioxide, poly (t-butyl methacrylate) and polyacrylic acid Decomposable polymer materials such as alkanes and cycloalkane gases such as pentane and butane, and inert gases such as nitrogen. The foaming agent may be hydrophilic or hydrophobic. In one embodiment, the blowing agent can be a solid blowing agent. In another embodiment, the blowing agent may comprise one or more carbonates or bicarbonates such as sodium carbonate, potassium carbonate, calcium carbonate and / or magnesium carbonate. For example, the blowing agent may include sodium carbonate and sodium bicarbonate, or may include only sodium bicarbonate. In yet another embodiment, the blowing agent can be an inorganic agent.

The present invention discloses improved production of lightweight foam beads. In an improved method, both physical and chemical blowing agents are incorporated during the extrusion process to produce lightweight foam beads. The physical blowing agent is preferably supercritical CO ₂ and is used as the first raw material for the blowing agent in the process of producing lightweight beads by extrusion and hot surface granulation. By adding the chemical blowing agent to the extrusion process so that the chemical blowing agent is not completely degraded during the extrusion process, the light bead produced will retain some chemical blowing agent in its composition.

The second blowing agent can be incorporated in one of three ways. In the first case, the second blowing agent can be incorporated upstream of the first blowing agent. In the second case, the second blowing agent can be incorporated downstream of the first blowing agent. And in the third case, the second blowing agent can be incorporated simultaneously with the first blowing agent. Preferably, for all cases, the first blowing agent is a physical blowing agent, such as supercritical CO _2. This first blowing agent causes most of the expansion during the extrusion process and is used to produce expanded beads. The purpose of the second foaming agent is to remain largely inert during the process of extrusion and foam bead formation, and to activate during subsequent foam bead processing, allowing further expansion of the beads. . The method of the present invention is carefully designed so that the second blowing agent is not completely consumed during the foam extrusion process. The method of the present invention allows the second blowing agent to remain largely inert during the foam extrusion process, thereby allowing the second blowing agent to be incorporated into the foam beads.

  A chemical blowing agent is considered the most suitable for use as the second blowing agent. For the first and second cases, the chemical blowing agent is added to the molten polymer in the extruder before or after the first blowing agent is charged to the melt. Since the melt is hot, the chemical blowing agent will begin to decompose and be able to generate a gas that can foam the polymer. By controlling the temperature of the melt as well as the residence time of the polymer / blowing agent mixture in the extruder, the degree of blowing agent decomposition can be controlled. Some degradation can occur and gas can be released, but as long as any blowing agent remains in the extrudate, the expanded beads will contain the blowing agent.

For the third case, the second blowing agent is mixed with the first blowing agent and charged simultaneously to the molten polymer. Supercritical CO ₂ is the first blowing agent, a chemical blowing agent is contemplated that is used as a second blowing agent. The chemical blowing agent can be liquid or solid. In a preferred embodiment, supercritical CO ₂ can be used as the carrier phase, dissolving the chemical blowing agent to form a mixture. The mixture is then charged into the barrel of the extruder and mixed with the molten polymer.

  The level of foaming agent content in the concentrate can vary widely. In some embodiments, the foamable additive comprises at least about 2.5 wt% blowing agent, at least about 5 wt% blowing agent, suitably at least about 10 wt% blowing agent. In other embodiments, the foamable additive may comprise about 10-60% by weight blowing agent, about 15-50% by weight blowing agent, suitably about 20-45% by weight blowing agent. In still other embodiments, the foamable additive may comprise about 0.05-90% by weight blowing agent, about 0.1-50% by weight blowing agent, or about 1-26% by weight blowing agent. The most preferred embodiment comprises a concentration of the second blowing agent in the expanded beads of 0.5-5%.

  Although the blowing agent composition may include only the blowing agent, in a more typical situation, the blowing agent includes a polymer carrier that is used to carry or hold the blowing agent. Such blowing agent concentrates may be dispersed in a polymer carrier for transportation and / or handling purposes. The polymeric carrier can also be used to hold or carry any other material or additive that is desired to be added to the melt processable composition.

  In another aspect of the invention, the compostable or bio-based melt processable composition may include other additives. Non-limiting examples of additives include plasticizers, chain extenders, antioxidants, light stabilizers, fibers, foaming agents, foaming additives, antiblocking agents, thermal stabilizers, impact modifiers, biocides , Compatibilizers, tackifiers, colorants, binders, conductive fillers and pigments. The additive may be incorporated into the melt processable composition in the form of a powder, pellet, granule, or any other extrudable form. The amount and type of additives in the melt processable composition can vary depending on the desired physical properties of the polymer matrix and the finished composition. Those skilled in the art of melt processing can select the amount and type of additive appropriate to suit a particular polymer matrix in order to achieve the desired physical properties of the finished material.

  The amount of each component in the meltable, compostable or bio-based polymer foam composition can vary depending on the intended end use. The compostable or biobased polymer may comprise about 40 to about 99% by weight of the final composition. The compostable or biobased plasticizer may constitute about 1-20% by weight of the final composition. The chain extender may comprise about 0.1-5% by weight of the final composition.

A physical blowing agent such as supercritical CO ₂ is mixed with the melt early in the extruder mixing process. In one embodiment, the chemical blowing agent is added after the physical blowing agent and in the cooler part of the extruder. In another embodiment, the chemical blowing agent is added before the physical blowing agent and repeatedly but in the relatively cooler part of the extruder. Thereafter, when the mixture exits the extruder and is cut, supercritical CO ₂ expands to form initial beads. These beads have chemical blowing agents already impregnated therein during the extrusion process. The process must be carefully controlled so that the second blowing agent is not completely consumed during the foam extrusion process. Because the temperature used to add the chemical blowing agent during the extrusion process is low, the chemical blowing agent can remain inert during the extrusion process. Subsequent heating of the beads during the secondary foaming process is expected to pyrolyze the chemical foaming agent and release gas, and therefore, when combined with the appropriate temperature to soften the plastic, It can be expanded to a low density. During the molding process, for example, the beads are heated so as to melt simultaneously, and the chemical foaming agent is activated, thereby causing secondary foaming. That is, the thermal collapse of the blowing agent can be caused during the molding process, thereby allowing for the fusion of beads or a conventional pre-foaming process, which can further reduce the density.

  The melt processable, compostable or bio-based foam compositions of the present invention can be prepared by any of a variety of methods. For example, compostable or bio-based polymers, blowing agents, nucleating agents and optional additives can be mixed by any mixing method commonly used in the plastics industry, such as a mixing extruder. In a preferred embodiment, the chemical blowing agent is incorporated into the extrusion process downstream of the physical blowing agent input and mixing. However, as noted above, the second blowing agent can be incorporated into the melt upstream of the physical blowing agent input and mixing. Typically, the extrusion mixture needs to be cooled before exiting the die to maintain sufficient melt strength and allow for a good cellular structure of the foam. By adding the chemical blowing agent to the low temperature portion of the extruder, the thermal energy that decomposes the chemical blowing agent is reduced and the time for the material to stay in the extruder is reduced. The materials (biodegradable polymers, blowing agents, biodegradable plasticizers and optional additives) can be used, for example, in the form of powders, pellets or granular products. The mixing step is most conveniently performed at a temperature above the melting point or softening point of the polymer. The resulting molten mixture is processed into lightweight strands which are then cut into beads using a strand pelletizer. In another embodiment, expanded beads are produced by cutting expanded strands at the surface of an extrusion die. By cutting the extrudate at the surface of the extrusion die, beads are formed before the foam has fully expanded. After granulation, the expanded beads are formed from the expansion of the extrudate with a physical blowing agent. The expanded beads are cooled by releasing the blowing agent, but can then be cooled by contact with water, water vapor, air, carbon dioxide or nitrogen gas. The resulting beads can be molded into a three-dimensional molded product using conventional equipment used for molding expandable polystyrene. The purpose of the second blowing agent is to remain largely inert so that it can be activated during the subsequent processing of the expanded beads to allow further expansion of the beads. Preferably, the expanded beads contain residual chemical blowing agent and can expand during subsequent molding processes.

  The optimum working temperature is selected according to the melting point, melt viscosity and thermal stability of the composition, but typically the melt processing is carried out at a temperature of about 80 ° C to 300 ° C. Various types of melt processing equipment, such as extruders, can be used to process the melt processable compositions of the present invention. Suitable extruders for use in the present invention are described, for example, in Rauwendaal, C., “Polymer Extrusion,” Hansen Publishers, p. 11-33, 2001.

In one embodiment, the resulting compostable or bio-based expanded beads have a specific gravity of less than 0.15 g / cm ³ . In another embodiment, compostable or bio-based foam beads, preferably 0.075 g / cm ³ less than the specific gravity, and most preferably has a specific gravity of less than 0.05 g / cm ^3.

  In one embodiment, greater than 50% by weight of the foam comprises compostable material as determined by ASTM D6400. In a preferred embodiment, greater than 80% by weight of the foam comprises compostable material. In the most preferred embodiment, greater than 95% by weight of the foam comprises compostable material.

The expandable beads of one embodiment of the invention are made using a compostable or biobased polyester and a compound that includes a blowing agent. Additives including plasticizers and chain extenders are optionally included in the compostable or biobased composition. Expandable beads can be made using conventional melt processing techniques such as uniaxial and biaxial extrusion processes. In one embodiment, compostable or bio-based polymers are mixed with hydrophobic additives by a melt process to produce pellets. These pellets are then impregnated with a blowing agent to make expandable beads. The expandable beads are then heated to cause foaming and create expanded beads. The expanded beads are then molded into a product. In another embodiment, melt processing is used to mix compostable or bio-based polymers, hydrophobic additives, and foaming agents to directly create expandable beads from the melt processing operation. In this case, the extrudate from the die must be rapidly cooled to confine the foaming agent so that the foaming agent does not escape and foaming does not occur. Foaming occurs in a controlled time in the operation of the pre-foaming machine by heating the expandable beads and it is desired that the expanded beads are made. Next, the foam beads are molded. Preferably, the specific gravity of the obtained expanded beads is less than 0.15 g / cm ³ . More preferably, the specific gravity of the expanded beads is less than 0.075 g / cm ^3, and most preferably less than 0.05 g / cm ^3. In a preferred embodiment, greater than 50% by weight of the foam is compostable as measured by ASTM D6400. More preferably, more than 80% of the foam is compostable. In the most preferred embodiment, more than 95% of the foam is compostable.

  In some embodiments, the desired plastic formulation may be compounded as needed to provide a homogeneous material for extrusion. If necessary, the plastic may be pelletized, optionally pulverized, and classified into particles of a predetermined size such as 0.25 mm in diameter. Next, the polymer pellets may be added to a pressure tank containing water with stirring to produce a slurry. Solution stabilizers such as surfactants or salts may be added to inhibit pellet agglomeration and promote diffusion of the hydrocarbon blowing agent into the polymer particles. In some embodiments, the hydrocarbon blowing agent is added to the slurry as a liquid. Preferably, the amount of hydrocarbon blowing agent added to the system is predetermined based on the desired degree of hydrocarbon blowing agent in the expandable beads. The temperature of the pressure tank may be controlled by a circulating hot water bath, for example. In some embodiments, the pressure tank is mechanically sealed and pressurized with a compressed gas such as nitrogen.

  In the present invention, it was conceived that the EPS material can be replaced in the existing equipment of the production plant. EPS raw materials will be replaced with raw materials consisting of compostable or bio-based expandable beads. Hydrocarbon blowing agents have already been used in the production of EPS and have been conceived as blowing agents because of the process of capturing and burning volatile hydrocarbons as fuel. It has been desirable to minimize the cost required to convert an existing plant from EPS to a new compostable or bio-based material.

  An important aspect of the present invention is that a sufficient amount of hydrocarbon blowing agent can be incorporated into a matrix of compostable or bio-based polymer such as PLA. For example, PLA does not show the affinity for pentane absorption exhibited by polystyrene during EPS production. At room temperature, pentane is readily absorbed into solid polystyrene, but this does not occur with PLA. Therefore, it is necessary to make compostable or bio-based polymer compositions that can be impregnated with hydrocarbon blowing agents. To do this, not all hydrophobic additives are preferred, but hydrophobic additives are added to the formulation. Hydrophobic additives having a low hydrophilic-lipophilic balance (HLB) number are preferred. Examples of low HLB number hydrophobic additives include Span 60 (sorbitan monostearate, HLB = 4.7), Span 80 (sorbitan oleate, HLB = 4), and Span 85 (sorbitan trioleate, HLB = 1). .8). Block copolymer nonionic emulsifiers may also be used as hydrophobic additives to increase the solubility of the hydrocarbon blowing agent. An example of a suitable nonionic emulsifier is Unitox 420 ethoxylate (HLB = 4) from Baker Petrolite, which is a low molecular weight block copolymer of polyethylene and polyethylene glycol. To aid in the solubility of the hydrocarbon blowing agent, an acetylated monoglyceride derived from biologically derived oils such as soybean oil or hydrogenated castor oil may be used.

  The composition of compostable or biobased polymer formulations can be further modified by using blends with conventional plasticizers, chain extenders, crosslinkers, and other thermoplastic materials to improve the processability of the resin. Other aspects and foaming ability were improved.

  For example, the material compositions listed in Table 1 below were produced using a melting process by a twin screw extruder. NatureWorks 2002D polylactic acid (PLA), a compostable bio-based polymer, was the main component of all formulations. Additional raw materials include citrate esters (Citroflex A-2, Vertellus Performance Materials), copolyester elastomers (Neostar FN007, Eastman Chemical), stearic acid surface treated calcium carbonate (Omycarb FT, Au Omya North America), sorbitan monostearate (Span 60, Sigma-Aldrich), polyethylene glycol (Carbowax 8000, Dow Chemical), hydrogenated castor oil-derived acetylated monoglyceride Grindsted (Soft-N-Safe, Danisco ( Danisco)), dicumyl peroxide (Sigma-Aldrich), ethoxylated nonionic emulsifier (Unithox 450, Baker Peter) Light), and a special order maleic acid-modified PLA. Maleic acid-modified PLA was prepared by melting 3% by weight maleic anhydride, 0.5% by weight dicumyl peroxide, and 96.5% by weight NatureWorks 2002D PLA in an extruder using a constant temperature profile of 180 ° C. By doing so, it was produced as a precursor of the blend.

  The raw material was fed to the feed throat of a 26 mm co-rotating twin screw extruder (Model LTF 26-40 manufactured by LabTech Engineering Company, LTD). A constant temperature profile of 180 ° C. was used. The extrudate was passed through a die to make a strand, water cooled or air cooled and pelletized. In order to impregnate this composition with a pentane blowing agent, a pre-weighed pellet sample was sealed in a pressure vessel in contact with liquid pentane at room temperature. The sample container was immersed in a water bath for 2 hours and heated to 80 ° C. After 2 hours, the sample was removed and allowed to cool. The pellets were taken out, all the liquid pentane covering the surface was sucked off, dried and weighed. The mass of pentane impregnated in the pellet is calculated from the difference between the final mass and the initial mass and is expressed in Table 1 as a percentage of the sample mass. Control samples, NatureWorks 2002D PLA and maleic acid modified PLA are included as references. After impregnation, the measured pentane content of the control sample was less than 2.5% by weight, but the material containing the hydrophobic additive greatly increased the mass of pentane incorporated by the impregnation process. The materials listed in Table 1 were subsequently foamed by heating on a hot plate to release the pentane foaming agent into the gas phase to produce foamed pellets.

  The invention has been described with reference to specific embodiments. Although specific values, relationships, materials and steps have been set forth for the purpose of illustrating the concepts of the present invention, the principles of the present invention as broadly described can be understood without departing from the spirit or scope of the basic concepts. It will be apparent to those skilled in the art that a number of variations and / or modifications can be made to the invention as shown in the disclosed disclosed embodiments. In light of the above teachings, it should be appreciated that details can be changed by one skilled in the art without departing from the invention taught herein. Although specific embodiments and modifications of the underlying concepts of the present invention have been fully described so far, those skilled in the art will be able to see and explain such basic concepts as they become familiar with them. Obviously, various other embodiments described, as well as possible variations and modifications of the embodiments, will come to mind. All such modifications, alternatives and other embodiments are intended to be included within the scope of the present invention. Accordingly, it should be understood that the invention can be practiced otherwise than as specifically described herein. Accordingly, the embodiments of the invention are to be considered in all respects as illustrative and not restrictive.

Claims (63)

Mixing the melt processable composition in an extruder to form an extrudate;
Incorporating a first blowing agent into the composition, wherein the first blowing agent comprises a physical blowing agent;
Incorporating a second blowing agent into the composition, wherein the second blowing agent comprises a chemical blowing agent;
Pelletizing the extrudate to form beads;
Including a method.   The method of claim 1, wherein the second blowing agent is incorporated downstream of the injection and mixing of the first blowing agent.   The method of claim 1, wherein the second blowing agent is incorporated upstream of injection and mixing of the first blowing agent.   The method of claim 1, wherein the second blowing agent is incorporated simultaneously with injection and mixing of the first blowing agent. The method of claim 1, wherein the first blowing agent comprises supercritical CO ₂ .   The method of claim 1, wherein the second blowing agent comprises carbonate or bicarbonate.   The method of claim 1, wherein the second blowing agent is selected from the group consisting of sodium carbonate, sodium bicarbonate, calcium carbonate, potassium carbonate, and magnesium carbonate.   The method of claim 1, wherein the second blowing agent is selected from the group consisting of azo compounds, hydrazine derivatives, semicarbazides, tetrazoles, nitroso compounds, and carbonates.   The method of claim 1, wherein the melt processable composition comprises a compostable or biobased polymer.   The method of claim 1, wherein the melt processable composition comprises a polymer of polylactic acid.   The method of claim 1, wherein the melt processable composition further comprises a nucleating agent.   The method of claim 1, further comprising extruding the extrudate from a die attached to an end of a die extruder.   13. The method of claim 12, wherein the pelletization occurs at the surface of the extruder die.   13. The method of claim 12, further comprising cutting the extrudate with a rotary blade in contact with the front end surface of the die while foaming the extrudate to produce expanded beads. the method of.   The method of claim 14, wherein pelletization of the extrudate on the surface of an extrusion die occurs prior to full expansion of the first blowing agent.   The method of claim 14, wherein foaming of the beads occurs after pelletization of the extrudate.   The method of claim 1, further comprising foaming the foamed beads by heating. Moving the expanded beads into a mold;
Further foaming and fusing the beads in a mold by heating;
The method of claim 1, further comprising:   The method of claim 1, wherein the beads can maintain an internal pressure within the closed cell structure that results in volume expansion of the expanded beads during heating. A method for producing a foam molded article, comprising:
Producing foam beads by the method of claim 14;
Placing the expanded beads under temperature and pressure conditions such that an expanded molding is obtained.   21. The method of claim 20, wherein the method uses a heated gas to promote the fusion of expanded beads.   The method of claim 21, wherein the method uses steam.   The method of claim 21, wherein the method uses air or a mixture of air and steam.   A composition comprising a bio-based or compostable polymer extrudate comprising a chemical foaming agent, wherein the extrudate is suitable for forming beads having a substantially independent cellular structure. And a composition having a density.   25. The composition of claim 24, wherein the biobased or compostable polymer comprises a polymer of polylactic acid.   25. The composition of claim 24, wherein the beads have an average diameter of less than 10 mm.   25. The composition of claim 24, wherein the beads have a spherical or substantially spherical shape.   25. The composition of claim 24, wherein the beads are capable of holding an internal pressure of gas that exceeds ambient conditions within the closed cell structure of the foam.   A composition comprising an at least partially foamed biobased or compostable polymer comprising a latent chemical blowing agent.   30. The composition of claim 29, wherein the compostable polymer comprises a polymer of polylactic acid.   30. The composition of claim 29, wherein the at least partially expanded biobased or compostable polymer is in the form of beads.   32. The composition of claim 31, wherein the beads are capable of holding an internal pressure of gas that exceeds ambient conditions within the closed cell structure of the foam. A process comprising melt processing a biobased or compostable polymer with both a physical blowing agent and a chemical blowing agent to form an at least partially expanded extrudate, comprising:
A method wherein at least a portion of the chemical blowing agent remains latent in the at least partially foamed extrudate.   The method of claim 1, further comprising activating the latent chemical blowing agent.   35. The method of claim 34, wherein the method of activation uses heat.   35. The method of claim 34, wherein the method of activation uses steam, air, or a mixture of steam and air. A composition comprising:
Compostable or bio-based polymers;
A hydrophobic additive; and
Hydrocarbon blowing agent,
Including
Wherein the polymer, additive, and blowing agent are melt processed into a mixture.   38. The composition of claim 37, wherein the hydrophobic additive comprises a maleic acid modified coupling agent in combination with a hydrophobic amine.   40. The composition of claim 38, wherein the maleic acid modified coupling agent comprises maleic acid modified polylactic acid.   40. The composition of claim 38, wherein the hydrophobic amine comprises a hydrocarbon primary amine.   41. The composition of claim 40, wherein the hydrophobic amine is octadecylamine.   40. The composition of claim 38, wherein the hydrophobic amine comprises a plurality of amine functional groups.   38. The composition of claim 37, wherein the hydrophobic additive is a surfactant having a hydrophilic-lipophilic balance (HLB) number of less than 15.   38. The composition of claim 37, wherein the hydrophobic additive is a nonionic emulsifier.   38. The composition of claim 37, wherein the hydrophobic additive is a biological oil.   38. The composition of claim 37, wherein the hydrophobic additive comprises a sorbitan derivative.   38. The composition of claim 37, wherein the hydrophobic additive comprises a hydrophobically treated inorganic material.   38. The composition of claim 37, wherein the hydrophobic additive comprises polyethylene glycol.   38. The composition of claim 37, wherein the hydrophobic additive comprises a citrate ester.   38. The composition of claim 37, wherein the hydrophobic additive is soluble in low molecular weight hydrocarbons. The low molecular weight hydrocarbon is:
propane;
butane;
Pentane;
Hexane;
Heptane; and
Octane,
51. The composition of claim 50, selected from the group consisting of:   38. The composition of claim 37, wherein the hydrocarbon blowing agent comprises a low molecular weight hydrocarbon. The hydrocarbon blowing agent is:
propane;
butane;
Pentane;
Hexane;
Heptane; and
Octane,
53. The composition of claim 52, selected from the group consisting of: A method of forming a composition comprising:
Compostable or bio-based polymers; and
Hydrophobic additives,
Mixing a mix containing
Processing the mix into a plastic melt mixture;
Pelletizing said mixture to produce pellets;
Impregnating the pellet with a hydrocarbon blowing agent;
Including a method.   55. The method of claim 54, wherein the mix further comprises a hydrocarbon blowing agent.   55. The method of claim 54, wherein the step of processing the mix into a plastic melt mixture comprises melt kneading the mix in an extruder. Extruding the melt mixed extrudate through a die nozzle attached to the end of the extruder:
57. The method of claim 56, further comprising:   55. The method of claim 54, wherein the step of impregnating the pellet with a hydrocarbon blowing agent comprises pressurizing the pellet with gas in a sealed container. The gas is:
propane;
butane;
Pentane;
Hexane;
Heptane; and
Octane,
59. The method of claim 58, selected from the group consisting of:   55. The method of claim 54, wherein the step of impregnating the pellet with a hydrocarbon blowing agent further comprises heating the pellet to a temperature between 20C and 100C. Foaming the impregnated pellets by heating to produce expanded beads:
55. The method of claim 54, further comprising: Transferring the beads to a mold; and further foaming and fusing the beads within the mold by applying heat:
62. The method of claim 61, further comprising: A method for making a foam molded article comprising:
62. Making expanded beads according to the method of claim 61;
Placing the expanded beads under temperature and pressure conditions to obtain an expanded molded article;
Including a method.