BACKGROUND OF THE INVENTION

1. Field of the Invention: The present invention relates to injection molding of foamed plastic products. In particular, the present invention relates to blowing agents used in injection molding.

2. Discussion of Background:

The use of blowing agents in the foaming of plastic and rubber objects is well known. Blowing agents are chemicals added to plastics and rubber that generate gases at preselected temperatures and pressures, causing expandable materials such as resins to develop a cellular or foam¬ like physical structure.

Currently, foaming processes are accomplished using solid compounds that can be decomposed to generate a gas, liquids that vaporize upon heating, and gases. Foaming agents can additionally be classified into exothermic foaming agents (i.e., azo compounds, hydride, to produce H2 and N2 gases), endothermic foaming agents (i.e., citric acid, sodium bicarbonate, to produce CO2 gas), and combinations of endothermic and exothermic blowing agents. Examples of using blowing agents to produce foamed compositions can be found in Chang, U.S. Patent No. 4,097,421 ; Gebauer, et al., U.S. Patent No. 4,278,769; and White, et al., U.S. Patent No. 4,737,523.

Until the present time, the satisfactory foaming of products has been difficult due to endothermic and exothermic blowing agents lacking chemical and physical stabihty at high temperatures. In addition to being unstable at high temperatures, endothermic and exomermic blowing agent concentrates combined with waxy or other types of carriers are often incompatible with desired resins. As a result, non-uniform, inconsistent foamed products are often produced.

For example, when endothermic blowing agents are used with high melting point thermoplastic resins, the temperatures in the extruder exceed the reaction temperature of endothermic blowing agents, causing premature foaming. Carriers, such as waxy compositions, have been employed to help alleviate this problem, however, the melting temperature differentials between the waxy material, the blowing agent and high melting thermoplastic resins are such that uniform mixing of the constituents is difficult.

Furthermore, exomermic blowing agents are difficult to control in many standard processes. For example, endothermic blowing agents in very low melting materials may be chemically and/or physically incompatible with desired thermoplastic resins and, thus, flow rates will tend to produce inconsistent products.

In addition, using present technology, certain polymers and resins, such as nylon, polycarbonate and polyethylene, are difficult if not impossible to foam. In fact, polymers such as polycarbonate are degraded by blowing agents currently used in foaming processes, causing them to lose their strength and durability in short periods of time.

Despite current efforts, there is a need to provide a simple convenient method for adjusting the rheology of a blowing agent-resin mixture; alleviate the expense and inflexibility of a gas injection means; and provide an improved cellular structure for the foamed product.

The foaming of resins by extrusion and molding methods is well known in the prior art and may be accomplished by a variety of techniques. Generally, blowing agents are injected into a molten resin in the extrusion process, blended, and extruded through a die to a low- pressure zone to produce a foam. Due to difficulties in blending gas foaming materials into molten resins, the foamed product often contains non-uniform foaming characteristics, such as bubbles concentrated in certain areas of the product, and non-uniform bubble dimensions.

Furthermore, the injection system necessary for introducing certain gas foaming materials into the resin, results in a system that economically inhibits the addition of more than one type of blowing agent into the resin. Therefore, it is virtually impossible to optimize the characteristics of the foamed product.

Various attempts have been made to improve the level of foaming uniformity, such as the addition of waxy carriers and the surface treatment of the blowing agents with various chemicals such as mono- glycerides, steric acid, silane coupling agents, fatty acid titanates and mixture of these. However, there is currently a need to provide an economical means to introduce blowing agents into a resin. In addition, there exists a need to improve bubble forming characteristics and, thus, improve the foamed product.

Garcia, et al., in U.S. Patent No. 5,234,963, teach a process and apparatus for compounding and pelletizing chemical foaming or blowing agents in a high melt resin carrier to produce pelletized chemical foaming concentrates that can be used in thermoplastic resins. Although Garcia, et al. disclose an encapsulated foaming gas more compatible with thermoplastic resins, Garcia, et al. do not disclose the use of a molecular sieve to carry and regulate foaming gases in foaming processes.

Molecular sieves are microporous structures composed of either crystalline aluminosilicates, chemically similar to clays and belonging to a class of materials known as zeolites, or crystalline aluminophosphates. A useful characteristic of molecular sieves is their ability to undergo dehydration with httle or no change in crystalline structure, producing "activated" molecular sieves. Dehydration of the molecular sieves can be performed by any method in which water can be removed from the pores of the crystalline structure resulting in empty cavities. Dehydrated molecular sieves are referred to as activated molecular sieves because once the water is removed from the sieve pores, the sieves have a strong tendency to fill the cavity once again with water. The desire of the sieve to recapture the water is so strong, that the sieve will accept any material that is capable of entering the cavity. If more than one material is present that is capable of entering the cavity, the sieve will select which one occupies the cavity based on chemical characteristics such as electrostatic attractions. Molecular sieves are used in many fields of technology: to dry gases and liquids, for selective molecular separations based on size and polar properties, as ion exchangers, as catalysts, as chemical carriers, in gas chromatography, and in the petroleum industry to remove normal paraffin's from distillates. However, heretofore, molecular sieves have not been used in the foaming of resins.

Therefore, it is an object of the present invention to provide a means of introducing the foaming material into an extruder without the use of an injector, provide an economical means of varying foaming gases introduced into the resin, and provide a blowing agent that will produce a foamed structure having bubbles of uniform size and distribution.

SUMMARY OF THE INVENTION

According to its major aspects and broadly stated, the present invention is a blowing agent composition, a method for making a blowing agent and a method for using a blowing agent. More specifically, the present invention is a blowing agent composition comprising molecular traps, such as molecular sieves, and a foaming material. The blowing agent is mixed with a resin and added directly to an extruding or injection molding device to form a foamed plastic product. The foaming material carried by the molecular trap will evolve from the molecular trap at a preselected temperature and pressure to form a foamed product.

The foaming material carried by the molecular trap will evolve from the molecular trap at a preselected temperature and pressure, such as those used in common injection molding and extrusion processes. The foaming material used can be any suitable material that will generate a gas when subjected to heating and pressure changes in a confined space. When the molecular trap is a molecular sieve, the foaming material is a gas, a solid or a liquid and is present in the molecular sieves in amounts up to approximately 26%, preferably 23% by weight of the blowing agent composition. (The blowing agent composition used for these calculations includes the molecular trap and the foaming material. Therefore, if approximately 0.3 grams of the foaming material are used and approximately 1.0 grams of the molecular trap are used, for a total weight of 1.3 grams, the foaming material (0.3g) comprises approximately 23% of the blowing agent composition (1.3g).) More preferably, the foaming material is a gas or a liquid that will vaporize upon heating. The foaming material adsorbed is "trapped" by the molecular sieve crystal and remains trapped until the conditions, such as temperature and pressure, are altered. When the blowing agent

composition is added to a material to be foamed, (i.e., resins, plastics, rubber or other material susceptible to foaming) the gas is released by altering the temperature and pressure to those within a preselected range.

Materials may be desorbed from molecular sieves in the form of a gas in a variety of ways. For example, materials may be desorbed by raising the temperature or lowering the pressure. When present in a resin material, the desorbing gas forms bubbles that cause the resin material to develop a foamed cellular structure. Accordingly, when the temperature is reduced the foamed composition solidifies, leaving bubbles of uniform distribution and size, and the foaming material is readsorbed by the sieve.

In an alternative embodiment, a molecular trap, without the foaming material, can be mixed with a suitable resin and introduced into an extruder or other suitable environment so that the molecular trap are blended into the resin. The resin/molecular trap product is preferably in the form of pellets. The resin/molecular trap pellets can then be exposed to a suitable foaming material, which will diffuse into the resin to the molecular traps to be adsorbed by the molecular traps. Once the molecular traps, located in the resin, have adsorbed the foaming material it is equivalent to the blowing agent composition disclosed above and furthermore, behaves the same as the blowing agent composition above. Therefore, this is simply an alternative method of incorporating a blowing agent into a resin allowing for increased flexibility in the storage of the blowing agent/resin mixture as well as the increased flexibility in the foaming process. The blowing agent composition can be prepared using any suitable molecular traps, or combination of molecular traps, and any suitable additives. Molecular sieves are preferably used as the molecular trap; however, any suitable trapping molecule or substrates can be used. Molecular sieves are naturally occurring or synthetic zeolites

characterized by their ability to undergo dehydration with very httle or no change in crystal structure, thereby providing a high surface area for adsorption or trapping of other molecules. In addition, additives can be adsorbed by the molecular sieve or added to the molecular sieve-foaming material mixture (blowing agent) to give a final product specific physical qualities, such as special surface characteristics; to optimize the rheology of the resins; or to make the blowing agent easier to handle, less explosive and fire resistant.

In addition to molecular sieves, any suitable molecular trap can be used in the blowing agent composition. Suitable molecular traps include, but are not limited to, zeolites, cellulose compounds, silica gels, alumina gels, and carbon compounds, such as carbon cage compounds buckminsterfullerenes (bucky balls) and activated carbon.

The present invention is additionally directed to a method for preparing a composition for use as a blowing agent, comprising exposing a molecular trap to a foaming material, so that the foaming material is carried by the molecular trap in an amount sufficient to foam a resin. The appropriate foaming material can be added to the molecular trap by any suitable means in which the molecular traps are exposed to the foaming material so that the foaming material becomes "trapped" within the molecular traps. Trapped means to bind a molecule by adsorption, absorption, or electrostatic attraction.

Exposure of the foaming material can be performed by introducing the foaming material into a vessel, wherein the vessel contains the molecular traps. The method further comprises agitating, preferably by rotating the vessel, to maximize the exposure of the molecular traps to the foaming material, thus aiding the adsorption of the foaming material by the traps. Alternatively, the vessel containing the molecular traps can be fitted with a gas lance to introduce the foaming

material in gaseous form into the vessel in a first direction and an auger to cause the molecular traps to move in a second direction opposite the direction of the gas flow. The opposite directional movement of the sieves in relation to the gas increases the exposure of the sieves to the gas, thus aiding the adsorption of the gas by the sieves.

The present invention is further a foamable mixture comprising a molecular sieve and a foaming material, wherein the foaming material is carried by the molecular sieve. In addition, the present invention is a method for preparing a foamed composition comprising mixing a blowing agent and a resin to form a first mixture; changing the temperature and pressure of the first mixture to a preselected temperature and pressure so that the blowing agent evolves a gas into the resin forming a foamed composition. Once foaming has occurred, the foamed composition is solidified. Furthermore, the present invention is a foamed composition prepared by this method and comprising a resin, a molecular sieve mixed with the resin, and a foaming material mixed with the resin and the molecular sieve.

A primary feature of the present invention is the use of molecular sieves as carrier/regulators that selectively "trap" specific foaming materials and desorb or release these foaming material at certain temperature and pressure conditions to produce consistently foamed product. Molecular sieves physically trap molecules such as gases, based on the properties of molecular size and electronic attraction.

An advantage of the molecular sieves is that they act as carrier- regulators for foaming materials. The blowing agent composition comprising the foaming material carried by the molecular sieves is mixed with a resin to form a material suitable to be added directly to an extruder. Because the blowing agent can be added directly to the

extruder with the resin, the need for a gas injection system is eliminated, thereby simplifying manufacture and decreasing manufacturing costs.

Another advantage of the foaming material being contained in the molecular sieves is the ease in which the blowing agent composition may be handled. Due to this ease in handling, the foaming characteristics of the resin may be adjusted or tailored to form a foamed product with specific physical characteristics. Mixtures of blowing agents in differing proportions can be added to the resin mixture (the resin may be in solid or liquid form) to optimize the foaming characteristics and the rheology of the resin. Heretofore, the mixing of differing physical blowing agents to optimize foaming characteristics has been economically impractical, because of the necessity of a gas injection system for each physical foaming material added to the resin. A physical blowing agent is a material that is normally a gas at room temperature (such as nitrogen and carbon dioxide). In addition, the ability to adjust the blowing agent composition allows the rheology of the resin to be modified to meet the requirements of the extrusion process. This is important for many reasons, such as when subtle changes are experienced in the feed resin stock. Moreover, this flexibility results in less down time, a more consistent product and less wasted material.

In addition, a feature of the present invention is the use of the desoφtive quahties of the molecular sieves to influence the physical characteristics of a resinous body. It is well known in other applications to use the adsoφtive qualities of molecular sieves; however, the desoφtive qualities of molecular sieves have heretofore not been used as an advantage in foaming processes, such as injection molding or extrusion processes. The use of both the adsoφtion and the desoφtion qualities of the molecular sieves in foaming processes allows for the regulation of foaming materials or additives trapped by the molecular

sieves. For example, a foaming material will remain trapped within the molecular sieves until conditions, such as heating or low pressure, induce the release of the gas from the molecular sieves. Upon subsequent cooling the gas will be readsorbed back into the molecular sieve structure.

An advantage of using molecular sieves to both transport and regulate the foaming gas is that the molecular sieve provides a natural nucleating site of uniform proportion, so that controllable, consistent bubbles are formed within the foamed product in a predictable controlled manner. To provide consistent foaming, prior to the present time it has been necessary to provide nucleating sites by the addition of substances such as talc within the resin.

In addition, an advantage of the present invention is that the blowing agent composition has no adverse effects on the final foamed product.

Still a further advantage of the present invention is that the blowing agent composition is easily mixed with the resin to form a uniform mixture and consequently a uniform product.

Other features and advantages of the present invention will be apparent to those skilled in the art from a careful reading of the Detailed Description of a Preferred Embodiment presented below.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

The present invention relates to a blowing agent that employs a molecular sieve carrier to regulate the foaming materials and provide a nucleating site for the formation of improved foamed products. The adsoφtive quality of molecular sieves has been explored in depth for separation, purification and catalytic techniques; however, the desoφtive

quality of molecular sieves has heretofore been overlooked. It is the puφose of the present invention to use molecular sieves as carriers, regulators and nucleating sites in the foaming of resinous materials.

According to the present invention, the blowing agent composition comprises a molecular sieve and a foaming material, wherein the foaming material is carried in the molecular sieve in an amount up to approximately 26%, and preferably between approximately 23% and 26%, and most preferably approximately 23% by weight of the blowing agent composition. (These percentages are based on the total weight of the blowing agent composition.) The molecular sieves used to adsorb the foaming material are preferably synthetically produced crystalline metal alumino-silicates characterized by their ability to undergo dehydration with very httle or no change in structure, thereby offering a very high surface area for the adsoφtion or trapping of molecules. Unlike other adsorbants, the pores of molecular sieves are precisely uniform in size and dimension. This precision of structure allows specific types of molecules to be readily adsorbed. The molecular sieve selectively excludes molecules larger than the sieve pores and, once in the pores, the molecules are trapped electrostatically. As a result of the electrostatic attraction, molecular sieves display a selective preference based on polarity or polarizable molecules. Selectivity on both molecular size and polarity provides molecular sieves with a high level of adsoφtive efficiency, which has made molecular sieves especially useful in drying and purifying gases and liquids as well as other separation techniques. Molecular sieves have the basic formula M2 nO- AtøOs- xSiθ2- yH2θ where M is a cation of n valence. The crystal structure of molecular sieves is a honeycomb type structure with relatively large cavities, each cavity combined with six adjacent cavities through apertures or pores. The water of hydration is contained within these cavities. The pore size

of the molecular sieves depends on the grade of the sieve. The commonly used Type A molecular sieves contain roughly spherical cavities, approximately 11 angstroms in diameter and about 925 cubic angstroms in volume, that account for almost half the total crystalline volume available for absoφtion. The molecular sieves described in the present invention are classified based on a system used by UNION CARBIDE (for example 3A, 4A, 5 A and 13X). However, any suitable sieve is within the scope of the present invention. In general, the elasticity and kinetic energy of incoming molecules allows passage of molecules up to 0.5 angstroms larger than the diameter of the aperture. For example, the aperture size in the sodium-bearing Type 4A is 3.5 angstroms in diameter. Therefore, molecules with a diameter as large as 4 angstroms are capable of passing into these molecular sieves.

The size and position of the exchangeable cation (Na, Ca, etc.) may affect the aperture size in any particular type of molecular sieve. For example, the replacement of sodium ions in Type 4A with calcium ions produces type 5A, with a free aperture size of 4.2 angstroms. Not wishing to be bound by theory, the cations are also probably responsible for the very strong and selective electronic forces which are unique to these adsorbants. In the case of molecular sieves, selectivity is influenced by the electronic effects of the cations in the cavity as well as the size of the apertures in the alumino- silica frame work. Therefore, molecular sieves can be tailored to adsorb specific molecules by varying the size of the pores and the attractive forces. In the present invention, any suitable molecular sieve can be used to trap the desired foaming agent. The appropriate molecular sieve is dependent on the size, electronegativity and polarizability of the foaming material desired to be trapped. Appropriate sieves for the present invention include, but are not limited to Type 3 A, 4A, 5 A, 13X and

combinations thereof (the A represents angstroms, and 13X has a pore size greater than 5A).

The Type A molecular sieve has a framework composed of truncated octahedral joined in a cubic array. This framework produces a central truncated cube octahedron with an internal cavity of 11 angstroms in diameter. Each central cavity, termed the alpha cage, is entered through six circular apertures formed by a nearly regular ring of eight oxygen atoms with a diameter of 4.2 angstroms. The cavities are thus arranged in a continuous three-dimensional pattern forming a system of unduloid-Uke channels with a maximum diameter of 11 angstroms and a minimum of 4.2 angstroms. The truncated octahedral themselves enclose a second set of smaller cavities 6.6 angstroms in internal diameter (beta cages) and connected to the larger cavities by means of a distorted ring of six oxygen atoms of 2.2 angstrom diameter. Type 4A and Type 13X have the following unit cell formulas:

Type 4A: Naι ₂ [(A10 ₂ ) i2(Si0 ₂ ) 12]- 27H ₂ 0 Type 13X: Na ₈ 6[(Alθ2)86(Siθ2)i()6]- 276H ₂ 0. In both cases the sodium cation can be exchanged with other cations to form other useful products. The product is usually supplied in a pellet or bead form which contains about 20 percent inert clay binder.

A wide variety of molecular sieves are available, each with its own specific and uniform pore size. This variety allows for the sieve to be chosen on the basis of the material to be adsorbed. Characteristics of type 3 A, 4A, 5A and 13X molecular sieves are as follows: Type 3A, is used to adsorb molecules with an effective diameter of less than 3 angstroms, including water and ammonia, and excludes molecules with a diameter of more than 3 angstroms, such as ethane; Type 4A, is used to adsorb molecules with an effective diameter of less than 4 angstroms, including ethanol, hydrogen sulfide, carbon dioxide, sulfur dioxide,

ethylene, ethane, and propene, and excludes molecules with an effective diameter greater than 4 angstroms, such as propene; Type 5A, is used to adsorb molecules having an effective diameter of less than 5 angstroms, including n-butanol, n-butane, saturated hydrocarbons from methane to molecules containing twenty-two carbons. R-12, and excludes molecules having an effective diameter of greater than 5 angstroms, including iso- compounds and all four carbon ring compounds; 13X, is used to adsorb molecules having an effective diameter less than 10 angstroms, and excludes molecules having an effective diameter greater than 10 angstroms (i.e., (C4F9)3N). Each Type molecular sieve adsorbs molecules of the lower type, i.e., Type 5A will adsorb molecules adsorbed by Type 4A and so forth.

Adsorbants, such as solids, liquids or gases (preferably liquids and gases), are held by molecular sieves via strong physical and chemical forces, such as ionic forces, covalent forces and electrostatic attractions. Adsorbants can be desorbed by the application of heat, change in pressure or by displacement with another material, leaving the crystal structure of the molecular sieve in the same chemical state as when it entered. Adsoφtion and desoφtion are completely reversible with the respective isotherm curves coinciding completely. Isotherm curves can be used to regulate the adsoφtion and desoφtion of the foaming materials.

Molecular sieves possess a very high surface area, for example, the external surface area only comprises approximately one percent (1%) of the total surface area. The entire surface area of the molecular sieves are capable and available for adsorbing molecules. Therefore, the external surface area of the molecular sieves is available for adsorbing molecules of all sizes, whereas the internal surface area is available only to molecules small enough to enter the pores. However, because the external surface, comprises approximately one (1%) percent of the total

surface area, materials too large to be adsorbed within the pores will usually only be adsorbed by the external surface to the extent of 0.2 to 1 weight percent.

As mentioned, molecular sieves will not only separate molecules based on size and configuration, but they will also adsorb preferentially based on polarity or degree of chemical unsaturation. Therefore, molecules are held more tightly in the crystal structure if they are less volatile, more polar, or less chemically saturated. The strongest adsoφtive forces are due primarily to cations acting as sites of strong, locahzed, positive charge that electrostatically attract the negative end of polar molecules. Polar molecules are molecules containing heteroatoms such as O, S, Cl, F, or N and are asymmetrical. Dipole moments can also be induced by cations present in the molecular sieves, resulting in the attraction of sites of unsaturation over saturated bonds. In view of these means of attraction, the molecular sieves adsorb not only on the basis of molecular size, but additionally on the basis of electronic forces. For example, molecular sieves will adsorb carbon monoxide (CO) in preference to argon (Ar) and, olefins (C=C) in preference of saturated hydrocarbons (C-C). Although molecular sieves possess the ability to adsorb and desorb, they have predominately been employed simply for their adsoφtive ability, while their desoφtive ability has been used simply to reactivate the molecular sieves for reuse. The ability of molecular sieves to adsorb a single molecule and even a single type of molecule has been obtained for many adsorbants. Therefore, a correlation is easily made between the desired foaming material to be used in the foaming process and the corresponding molecular sieve capable of carrying the foaming material.

Any suitable foaming material that can be adsorbed by molecular traps can be used to foam the desired resin. Suitable foaming materials

include but are not hmited to inert gases, saturated aliphatic hydrocarbons, saturated alicyclic hydrocarbons, aromatic hydrocarbons, halogenated hydrocarbons, and ethers, ketones, and alcohols from one to eight carbons in length. Examples of these foaming materials include carbon dioxide, nitrogen, methane, ethane, propane, butane, pentane, hexane, methylpentane, dimethylbutane. methylcyclopropane, cyclopentane, cyclohexane, methylcyclopentane, ethylcyclobutane, isopropyl alcohol, propyl alcohol, ethanol, butanol, isobutanol, sec- butanol, heptanol, pentanol, isopentanol, hexanol, 1,1,2- trimethylcyclopropane, dichlorodifluoromethane, monochlorodifluoromethane, trichlorotrifuoroethane, dichlorotetrafluoroethane, dichlorotrifluoroethane, monochlorodifluoroethane, tetrafluoroethane, dimethyl ether, 2-ethoxy- acetone, methyl ethyl ketone, acetyl acetone, dichlorotetrafluorethane, monochlorotetrafluoroethane, dichloromonofluoroethane and difluoroethane. Although not all of the above mentioned foaming materials can be adsorbed by the molecular sieves in the preferred embodiment of the present invention, these materials can be adsorbed and subsequently desorbed by other molecular traps within the scope of the present invention. Generally, straight chain and branched hydrocarbons, alcohols, ketones, ethers, esters, carboxylic acids, organohalides and aldehydes comprising from one to eight carbons can be used as appropriate foaming materials for molecular sieves.

In addition to foaming materials, other materials may be adsorbed within the molecular sieves to affect other properties in the foaming process. For example, isopropyl alcohol can be adsorbed within a molecular sieve and introduced into a resin to catalyze crosslinking of the polymers in the foaming process, thereby strengthening the final product. Also, fire retardent compositions such as butyl bromine can be adsorbed

within the molecular sieves to make the foamed product fire retardent.

When the foamed material is solidified, the fire retardent composition will be adsorbed within the molecular sieves. The fire retardent compound will remain in the sieve until its temperature is raised to a predetermined temperature, such as during a fire, causing the evolving of the gas and the extinguishing of the fire. Fire retardent compositions commonly used in foaming processes can be used with the present blowing agent composition. When desired, other additives can be combined with the blowing agent to customize or tailor the properties of the foamed product. Examples of useful additives include but are not limited to plasticizers, lubricants, fillers, extends, pigments, stabilizers and antioxidants.

In addition, additives such as gelatin, powders and viscous liquids can be added to the blowing agent composition. For example, oil may be added to the blowing agent composition to form a suspension, minimizing dusting, combustion and explosive characteristics, and to provide easier handling. The blowing agent can be mixed with the oil by any means of mixing commonly employed in the art, including but not limited to mechanical mixing or mixing using an ultrasonic means. The blowing agent may additionally be formed into pellets, pastes, waxes, or gels to ease introduction into the extruding device.

The blowing agent composition comprising a foaming material adsorbed within a molecular sieve is a solid structure which is easily handled. Although it is preferred that the blowing agent composition be stored in a sealed container to prevent unwanted molecules from replacing the foaming material, the sieve can nevertheless be handled easily when combined with resins and formed into pellets, pastes, waxes, or gels. In other words, the blowing agent can be added to the extruder in the same manner as the resin, and if desired, with the resin.

Furthermore, molecular sieves containing different foaming materials can be added together with a resin to provide the addition of these different foaming materials into a single foaming process. This feature allows for a high degree of flexibility in optimizing the characteristics desired in the foamed product. Heretofore, it has not been economically possible to add a wide variety of foaming materials to the resin in the foaming process. However, using the blowing agent composition in the present invention, the foaming agents added can be adapted to optimize the rheology, resulting in an increase in the temperature decomposition range.

In addition, the foaming material can be added to the molecular trap at any time. For example, molecular traps alone (not containing a foaming material) can be blended with a desired resin in a standard extrusion process. However, because no foaming material is present in the molecular trap, the resin is not foamed. The resultant material is resin having molecular traps dispersed therein, preferably in pellet form. The resin/molecular trap blend is subsequently exposed to a foaming material so that the foaming material can be adsorbed by the molecular traps. The resin/molecular trap mixture is preferably solidified prior to exposing the mixture to the foaming material. Once the foaming material is adsorbed by the traps forming a resin having a blowing agent composition (foaming material adsorbed by molecular traps), the resin/blowing agent composition can be foamed or extruder in the same manner as disclosed for other embodiments of the present invention. Accordingly, a further embodiment of the present invention, is a method for preparing a composition for use as a blowing agent, comprising exposing a molecular sieve to a foaming material so that the molecular sieve will "trap" the foaming material. The foaming material to be trapped must be added to the molecular sieves at a rate sufficient to

allow adsoφtion, but slow enough so the pressure within the vessel containing the sieves remains relatively constant. The rate at which the gas is added to the molecular sieves in the method for preparing the blowing agent is dependent primarily on four variables: (a) the rate at which the material being adsorbed can diffuse to the activated crystals within the pellets. This process is facilitated by maximizing exposure of the molecular sieves to the foaming material.

The exposure of the molecular sieves to the foaming material is accomplished by agitating the vessel in which the sieves are contained. Alternatively, when the foaming material is a gas, the exposure of the sieves to the gas can be optimized by causing the sieves to travel in a direction counter to the direction of the gas. The gas is preferably introduced into the vessel containing the molecular sieves using a gas lance, while an auger is used to facilitate the movement of the molecular sieves in a direction opposite the gas to maximize the exposure of the sieves to the gas.

(b) the relative size of molecules and the molecular sieve pores.

(c) the strength of the adsoφtive forces between the molecular sieves and the adsorbate or the gas to be adsorbed. (d) the temperature.

The blowing agent is produced when the desired foaming gas is adsorbed within the appropriate molecular sieve. Once produced, the blowing agent is preferably stored in a sealed container, so that unwanted materials are not adsorbed by the molecular sieves. The foamed product formed using the blowing agent of the present invention may be rendered flame retardent by adding suitable flame retardent agents, such as brominated compounds or phosphate compounds known in the art. These flame may be adsorbed by the molecular sieves or added to the blowing-agent resin mixture.

A further embodiment of the present invention is a foamable blowing agent-resin mixture comprising a blowing agent and a resin to be foamed. Here again, the blowing agent is composed of a molecular sieve and a foaming material in an amount up to approximately 26% by weight of the blowing agent composition. The blowing agent is mixed with a resin to form the foamable blowing agent-resin mixture. Mixing the blowing agent with the resin so that the blowing agent is uniformly mixed within the resin aids in the consistency of the foamed product. The blowing agent-resin mixture may be mixed by any suitable method, including mechanical or ultrasonic means. The blowing agent-resin mixture is subsequently added to an extruder, cavity mold or similar device for foaming.

When the foaming material is not present in the molecular trap, the same procedure is followed with the molecular trap being mixed with the resin and added to an extruder. However, because no foaming material is present in the trap, foaming does not occur, the product is a resinous material containing the molecular trap dispersed therein. A foaming material, such as a foaming gas (CO2) can then be added to the resin/molecular trap blend to provide a foaming material to the molecular trap. The resin containing the molecular trap/foaming material (equivalent to the blowing agent composition) can then be foamed exactly like the other embodiments of the present invention, such as by extrusion, to form a foamed product.

The mixture of the blowing agent and the resin may vary widely, depending on the characteristics of the foamed product desired.

However, the blowing composition is generally used in an amount of about 0.05% to about 50% by weight, preferably about 0.25% to about 21% by weight, and most preferably in an amount 0.5% to about 7% by weight, based on the weight of the total resin employed. The blowing

agent, resin mixture used is dependent upon the bubble properties desired in the resin product. For example, the blowing agent is preferably used in an amount between about .5% to about 3% for high density foamed products; between about 3% to about 15% for low to medium density foamed products; and between about 5% to about 50% for ultra low density foamed products. The temperature at which foaming occurs is dependent upon the blowing agent and the resin used, as well as the product desired.

Different blowing agents may also be added to the resin to obtain desired foamed product characteristics. In addition, differing proportions of blowing agents can be combined to optimize the foam characteristics, such as flexibility, rigidity, strength and durability of the foamed product. Furthermore, by varying the rheology of the resin mixture, the temperature window for foaming certain resins can be broadened, resulting in the foaming of certain resins that have heretofore been difficult if not impossible to foam. In addition, varying the blowing agent can affect such properties as the melt strength of the polymer to form sturdier products. Until the present time, variance of blowing agent compositions has been economically impractical due to the necessity of gas injection systems to introduce the foaming gases into the resin. Resins employed in the present invention with the blowing agent include but are not hmited to natural and synthetic resins, acrylonitrile- butadiene rubbers, viscous setable ceramic materials and blends thereof, polyolefins (for example, low and high density polyethylene and polypropylene), olefin copolymers (for example, copolymers of ethylene and ethylvinylacetate), polyaromatic olefins, styrenic compounds and polymerized halo-diolefins (for example, neoprene, ethylene-propylene copolymers, polyvinyl chloride, polycarbonate, polyesters, poly-alpha methylstyrene and polystyrene).

Still a further embodiment of the present invention is the use of the blowing agent in the foaming process. As mentioned earlier, an advantage of the blowing agent comprising a molecular sieve and a foaming material is that the foaming material (usually a gas) is introduced into the resin prior to extrusion, thus eliminating the need for a gas injector. In addition, the molecular sieve being uniform in size functions as a nucleation site, thus eliminating the need to add a nucleating agent such as talc. Furthermore, gas bubbles combining in the foaming process to form non-uniform pockets of bubbles is decreased when molecular sieves are used to carry the foaming material, because the foaming gas is produced at the site of nucleation, the molecular sieve. The sieves being both uniform in size and the site of gas formation results in uniform bubbles being formed in the foamed product. Foamed products are prepared with the blowing agent of the present invention by any of the known methods in the art. For example, the blowing agent is mixed with a suitable resin, and extruded or molded by a suitable method, such as pressure molding, die molding, paste molding, calendar molding, extrusion molding or injection molding. Molding means forming an article by deforming the blowing agent-resin mixture in the heated molten state. The foamable blowing agent-resin mixture is added to the extruder through a hopper where the mixture is thoroughly blended, and exposed to heat to expand the resin and form a foamed resin product. Here again, the characteristics of the foamed product can be varied depending on the foaming conditions and the specific compositions used in the process.

The blowing agent-resin mixture can be used to create foam in single screw extrusion, multi-screw extrusion or tandem screw extrusion processes. Because of the nature of the molecular sieve structure, the blowing agent mixes more thoroughly with the resin to form a

homogenous mixture than other gaseous foaming agents added via a gas injection system. Uniform mixing results in a consistent product with a uniform cellular structure.

During the foaming process, the blowing agent-resin is preferably exposed to temperatures and pressures that have been preselected for the specific resin and blowing agent employed, and product characteristics desired. Preferably, the foamable blowing agent-resin composition is exposed to high temperatures and pressures characterized as supercritical conditions. Supercritical conditions are conditions at which the gas is in a "fourth" state of matter, being neither a gas, liquid or a solid, but a fourth state which exhibits unique qualities. Once the gas is exposed to supercritical conditions, gas passes to a low pressure zone in the extruder so that the foaming material adsorbed within the molecular sieves is released, resulting in the foaming of the resin. Upon cooling, the desired foamed resin product is sohdified producing a uniform cellular structure. Any suitable method of foaming, injection molding or extruding known in the art may be used with the present blowing agent to form foamed resins.

The foamed composition produced by the above mentioned process comprises a blowing agent, containing a molecular sieve and a foaming material, and a foamed resin, which has undergone foaming to form a solid cellular structure. In addition, the molecular sieves, foaming materials, resins and additives in the foamed composition are analogous to those mentioned above. The above procedure and composition may be varied, however, it is essential that the molecular sieves and the foaming gas are present in the blowing agent.

It will be clear to those skilled in the art of blowing agents or extrusion of foamable materials that many modifications and substitutions can be made to the blowing agent and its various methods of use described above without departing from the spirit and scope of the invention, which is defined by the appended claims.