MXPA01002165A - Foams prepared from blends of syndiotactic polypropylenes and thermoplastic polymers - Google Patents

Abstract

Foams prepared from a blend of a syndiotactic polypropylene (sPP) resin and a foamable thermoplastic polymer resin are provided which exhibit a combination of desirable properties which have heretofore been difficult, if not impossible, to achieve. The foams of the present invention are useful in applications such as thermal insulation, packaging, and the formation of molded articles such as cups, and trays.

Description

MORE DEPRIVATED SPUTS BETWEEN MIXING THE D E POLYGROUP P I LEN S I N DIOTÁCTI COS AND POLÍMEROS THERMOPLASTICS FIELD OF THE INVENTION This invention relates to foams in general, and more particularly, to foams prepared from a mixture of syndiotactic polypropylenes and foamable thermoplastic polymer resins.

BACKGROUND OF THE INVENTION Foams are used in a number of applications, including thermal insulation, packaging, and the formation of molded articles such as cups, trays and the like. Depending on the final use of the foam, it is desirable for the foam to exhibit particular properties or combinations of properties. For example, when used as an insulation material or cushion packing material, expansion of the foam to low densities is very desirable. In addition, foams having a high distortion temperature are desirable for a number of applications, including insulation in high temperature environments. Japanese Patent Application No. 08-231747 for example describes a foamed sheet having a density in the range of 0.1 to 0.5 g / cm 3 formed by extrusion-foaming a propylene resin composition consisting of 5-70% by weight of a specific syndiotactic polypropylene and 95-30% of a specific isotactic polypropylene with a specific amount of endothermic chemical blowing agent, it is established that said foamed sheet has good resistance to hot. Depending on the particular use of such insulating foams, it is also desirable that such foams be flexible in addition to having a high distortion temperature. The degree of flexibility and the heat distortion requirements vary depending on the final use of the insulating foam. For example, in some automotive applications or for insulation of hot water pipes, a flexible foam having a heat distortion temperature greater than about 90 ° C, or greater than 10-120 ° C in some cases is required. In addition, in order to comply with Underwriters Laboratory Test U L 1 191 Appendix A, foams used as fillers in personal flotation devices need to withstand temperatures of 60 ° C for a prolonged period of time in addition to being very soft and flexible. However, it is difficult to achieve the properties of flexibility (ie under modulus of elasticity) and high heat distortion temperature in the same foam. Typically, the flexibility of a given resin (i.e., modulus of elasticity) typically requires that the resin have a lower melting point while a resin having a high distortion temperature typically requires that the resin have a low melting point. major merger. Furthermore, even if the properties of flexibility and high heat distortion temperature are found in the same resin or resin mixture, the resin or resin mixture may not be recommended for foaming, or for foaming by a convenient process such as the process of extrusion. Branched polyolefin resins prepared by the high pressure free radical process are foamable in a flexible foam by extrusion, but the foam lacks the temperature resistance for certain applications. Examples of branched polyolefin resins include low density polyethylene homopolymer resins having densities in the range from 0.915 g / cm 3 to 0.932 g / cm 3 and copolymers of ethylene with a vinyl ester such as vinyl acetate and methyl acrylate. Linear polyolefin homopolymer resins prepared by a catalytic process (using for example Ziegler Natta or metallocene catalysts), such as high density polyethylene resins and isotactic polypropylene (yPP), have a relatively high heat distortion temperature. , but they are difficult to foam through the extrusion process. In addition, foams made from such rigid homopolymer resins lack flexibility. A less rigid linear copolymer resin can be made by the catalytic process, but the resin suffers from the same lack of ability to be foamed as is the homopolymers. The use temperature of a polyolefin resin foam can be increased by entanglement. By For example, an interlaced foam prepared from a low density polyethylene resin can be used at a higher temperature than a non-interlaced foam, but the use temperature, which is less than 100 ° C, is not high enough to some applications. In addition, an interlaced foam is expensive to manufacture and is not recyclable. Foams prepared from a mixture of high-melting polyolefin resins (eg, high-density polyethylene and iPP) and low-density polyethylene (LDPE) resin are difficult to expand to a low density foam by process of extrusion, since the expansion of the foam depends on the freezing transition of the high melting point resin which has a poor foaming capacity. When applied to the entanglement approach, such mixing causes another type of difficulty. In that process, a foamable composition is extruded into a sheet at a low temperature where the blowing agent and the interlacing agent remain substantially deactivated. Frequently, the processing temperature required for a linear polyolefin of high melting point exceeds the temperature tolerable by the blowing agent and the entanglement agent and can activate them prematurely. However, depending on the particular end use, it is not always desirable for an insulating foam to be flexible. Rigid foams having high distortion temperatures are also desirable. Rigid foams for insulation they are often prepared from alkyl aromatic polymers, such as polystyrene, which, due to environmental considerations, expand in an increasing manner with carbon dioxide. However, low density foams, such as polystyrene, which are expanded with carbon dioxide exhibit a small cell size. However, in order for a rigid foam to be formed quickly from the convenient extrusion process and be easily manufactured, it is necessary that the foam has an enlarged cell size. A foam having a small cell size is not only difficult to extrude to a large cross section, but is also difficult to manufacture (eg, slicing and cutting to the final forms). For the purpose of rapid fabrication, it is desirable that the foam have a cell size greater than 0.4 mm. There have been several attempts to prepare aromatic alkyl foams having an enlarged cell size by incorporating various additives that enlarge the cell size (see for example, U.S. Patent Nos. 4,229,396 and 5,489,407). However, typical additives for enlarging cells are difficult to feed the extruder and have to affect the heat distortion temperature of the foamed product. In addition to insulation foams that have high distortion temperatures, which are either 1) flexible or 2) rigid with enlarged cell size, the flexible foams that are made from thermoplastic polymers having a Tg above 0 ° C are desirable for end uses that require noise and vibration damping as well as cushioned packing. When used for cushion packing or vibration damping, a flexible foam protects the article by absorbing the impact energy and vibration in its cell structure. The energy is absorbed both in the gas phase and in the polymer phase. A foam having cell walls that irreversibly dissipate mechanical energy into heat is desirable. A polymer resin dissipates mechanical energy more effectively at the glass transition temperature (Tg) of the resin (see, for example, Properties of Polymers, third edition, chapter 14, "Acoustic Properties", edited by DW Van Krevelen , Elsevier, Amserdam-London, New York-Tokyo, 1990). Most conventional polyolefin resins such as polyethylene and polypropylene are flexible, but have a relatively low Tg, that is, below 0 ° C and are, therefore, not useful for final uses of cushion packing or cushioning. vibration. Therefore, a need remains in the art for 1) flexible foams having a high distortion temperature; 2) rigid alkyl aromatic foams having a high distortion heat and enlarged cell size which are conveniently manufactured and wherein the heat of distortion is stable; and 3) flexible thermoplastic foams made from a thermoplastic polymer having a Tg above 0 ° C. needs are met by the present invention. Thus, the present invention provides polymer foams prepared from a mixture of a syndiotactic polypropylene resin (sPP) and a foamable thermoplastic polymer resin. Thus, in a first embodiment of the present invention, polymer foams prepared from a mixture of a sPP resin and a flexible thermoplastic polymer resin which are flexible and have a high distortion temperature are provided. Polymer foams according to the first embodiment of the present invention are useful as insulating foams in high temperature environments where a flexible foam is desired, such as some automotive uses and insulation of hot water pipes. Furthermore, since the sPP resin has a Tg of 4 ° C, the polymer foams according to the first embodiment of the present invention are also suitable as cushioned packaging or in products for noise or vibration damping. The typical mixed polymer foams according to the first embodiment are as follows: a mixed polymer foam, comprising: a) from 0.1% to 60% by weight of a sPP resin; and b) from 40% to 99.9% by weight of a flexible thermoplastic polymer resin. a mixed polymer foam, comprising: a) from 10% to 50% by weight of a sPP resin; and b) from 50% to 90% by weight of a flexible thermoplastic polymer resin; Y a mixed polymer foam, comprising: a) from 30% to 50% by weight of a sPP resin; and b) from 50% to 70% by weight of a flexible thermoplastic polymer resin. In a second embodiment of the present invention, foams of polymers prepared from a mixture of a sPP resin and a rigid thermoplastic polymer resin which are rigid, have high distortion temperatures, and have enlarged cell size are provided. The sPP resin additive, which enlarges the cell size of the rigid thermoplastic polymer foams, is easily fed to the extruder, and does not affect the heat distortion temperature of the foam. Typical blended polymer foams according to the second embodiment of the present invention are as follows: a mixed polymer foam, comprising: a) from 0.1% to 60% by weight of a sPP resin; and b) from 40% to 99.9% by weight of a rigid thermoplastic polymer resin; and a mixed polymer foam, comprising: a) from 0.2% to 5% by weight of a sPP resin; and b) from 95% to 99.8% by weight of a rigid thermoplastic polymer resin. Figure 1 represents the differential scanning calorimetry thermogram of a foam according to the present invention as extruded. Figure 2 represents the differential scanning calorimetry thermogram of a foam according to the present invention as after aging at 120 ° C for 5 days.

The present invention provides foams prepared from a mixture of a sPP resin and a foamable thermoplastic polymer resin. The blended polymer foams of the present invention exhibit a combination of desirable properties that have hitherto been difficult to achieve, if not impossible. For example, a first embodiment of the present invention provides polymer foams prepared from a blend of a sP P resin and a flexible thermoplastic polymer resin said foams are flexible and have a high distortion temperature. Polymer foams blended according to the first embodiment of the present invention are useful as insulating foams in high temperature environments where a flexible foam is desired, such as some automotive uses and insulation of hot water pipes. The flexible, insulating foams of the first embodiment of the present invention exhibit increased dimensional stability on foams prepared from flexible thermoplastic polymer resin alone. As stated above, flexible foams having a high heat distortion temperature are prepared using a flexible thermoplastic polymer resin such as the foamable thermoplastic polymer resin in the blend. Although not wishing to be limited by any particular theory, it is believed that the addition of the sPP resin provides the mixing foam with a high heat distortion temperature while causing few disorders of foam expansion due to the slow crystallization rate of the resin. The slow crystallization rate of a sPP, which has a long cycle time problem in injection molding, is advantageously exploited in the preparation of the foams of the present invention. Due to the slow rate of crystallization, a sPP resin does not crystallize at the foaming temperature of a flexible thermoplastic polymer resin, but crystallizes at room temperature or during secondary heating after a foam of the first embodiment of the present invention is prepared from the mixture and stabilizes. Once crystallized, the resin component of sPP provides the mixed foam with a relatively high heat of distortion due to the high melting point, ie 130 ° C) of the crystals. This phenomenon is demonstrated by differential scanning calorimetry as shown in Figure 1 and Figure 2. Figure 1 represents the differential scanning calorimetry thermogram of a foam according to the present invention prepared from a 50/50 mixture. by weight of a LDPE resin and an extruded sPP resin, which shows an endotherm at about 13 ° C and shows no endothermy at about 130 ° C, the melting point of sPP crystals. Figure 2 represents the differential scanning calorimetry thermogram of the foam of Figure 1 after it has been aged at about 120 ° C. for 5 days, showing an endotherm at approximately 1 13 ° C and does not show endotherm at approximately 130 ° C, the melting point of sPP crystals. The differential scanning calorimetry thermograms shown in Figure 1 and Figure 2 demonstrate that the LDP E resin and the sPP resin are not miscible and that the resin phase of sPP in the mixture undergoes crystallization during heating at about 120 °. C. In addition, the sPP resin component of the mixture does not fully crystallize during the aging of the foam at room temperature, but additional subsequent crystallization is observed by heating. This secondary crystallization can be used beneficially by thermoforming the foam product because the sPP molecules in the amorphous state allow the deformation of the foam sheet to conform to the shape, but they crystallize further during the thermoforming thereby helping fix the thermoformed article. The addition of the sPP resin also increases the dimensional stability of the flexible foam. For example, a foam of the present invention prepared from a mixture of a sPP resin and an LDPE resin expanded with isobutane was found to be more dimensionally stable than an LD PE resin foam with isobutane. This increased dimensional stability is surprising that it gives at least one reported sPP resin having a low crystallinity (about 30%) [see, Wheat, W.R., "Rheological Explanations for Syndiotactic Polypropylene Behaviors", ANTEC 95 Preprint] and a relatively high permeability high to gases and vapors [see, Schardi, J. and cotaboraaores, "Syndiotactic Polypropylene Overview Clear Impact Poplymer", ANTEC 95 Preprint]. In addition, the flexible polymer insulating foams according to the first embodiment of the present invention are also suitable as cushioned packaging or in products for noise and vibration damping. The sPP resins have a Tg of 4-6 ° C and would therefore be effective for dissipating mechanical energy in heat. However, a sPP resin alone is not easily foamable through the extrusion process. In contrast, the mixtures of a sPP resin and a flexible thermoplastic polymer resin according to the first embodiment of the present invention are not foamable only, but the resulting foams also have the properties of the individual component resins. Thus, foams prepared from such a mixture of immiscible polymers are anticipated to have different Tgs and thus, are anticipated to contribute beneficially to dampen noise and vibration over a wide range of frequencies and temperatures. The second embodiment of the present invention provides polymer foams prepared from a mixture of a sPP resin and a rigid thermoplastic polymer resin said foams are rigid, have high distortion temperatures, and have enlarged cell size. Thus, the mixed polymer foams of the second embodiment of the present invention are Suitable for use as insulating foams in applications that require foam to be manufactured. The sPP resin additive, which enlarges the cell size of the foams of rigid thermoplastic polymers, is easily fed to the extruder, and does not affect the heat distortion temperature of the foam. Since it is not known that polypropylene resins are compatible with at least one rigid thermoplastic polymer resin, such as polystyrene (see, for example, US Patent No. 4, 386, 1 87, Examples 18 and 22 and U.S. Patent No. 5,460, 818, example 3) and that the foam expansion of a mixture of incompatible polymers is often difficult in the absence of an additive to compatibilize (see, for example, US Pat. 4,020, 025), the fact that the addition of sPP resin cut to a polystyrene resin does not upset, but aids in the expansion of the polystyrene resin, is somewhat unexpected. In any embodiment of the present invention, the sPP resin and the foamable thermoplastic polymer resin are typically blended in weight ratios from 0.1: 99.9 to 60:40. In the first embodiment, where the foamable thermoplastic polymer resin is a flexible thermoplastic polymer resin, the preferred proportions of sPP resin to flexible thermoplastic polymer resin are from 10:90 to 50:50, with proportions being especially preferred from 30 to 50:50. : 70 to 50:50. In the second embodiment, where the foamable thermoplastic polymer resin is a rigid thermoplastic polymer resin, the Preferred proportions of sPP resin to rigid thermoplastic polymer resin are from 0. 1: 99.9 to 5: 95. SPP resins suitable for use in any embodiment include all propylene homopolymers and substantially syndiotactic propylene copolymers with polymerizable monomers. Typical examples include polypropylene homopolymers, copolymers of propylene with ethylene, and copolymers of propylene with 1-butene, with those homopolymers and copolymers having a melt flow rate of from 0.05 dg / minute to 50 dg / minute being preferred, and those homopolymers and copolymers having a melt flow rate from 0.1 dg / minute to 10dg / minute are preferred. SPP resins having a syndiotacticity greater than 75% are also preferred. An example of a suitable sPP resin is a sPP resin having a melt index of 2 dg / minute (as determined by ASTM D-1238 at 230 ° C / 2.16 kg), density of 0.88 g / cm3, and of 130 ° C. Examples of such sPP resins are polypropylene copolymer resins of syndiotactic form grades EOD-96-28 and EOD-96-07, available from Fina Oil and Chemical Company. Suitable thermoplastic resins for use in the present invention include all types of thermoplastic polymers that are foamable by extrusion processes. Examples of flexible thermoplastic polymer resins suitable for the first embodiment of the present invention include, but are not limited to flexible polyolefin resins, such as LDPE resins, ethylene / vinyl acetate copolymer resins, and iPP, with those resins having a melt index from 0.1 dg / minute to 20 dg / minute being preferred; preferred especially those having a melt index from 0.2 dg / minute to 10 dg / minute. Further, when the flexible thermoplastic polymer resin is an ethylene / vinyl acetate copolymer, those resins having a vinyl acetate content of from 5% to 30% are preferred and those resins having a content of vinyl acetate from 8% up to 20%. In addition, when the flexible thermoplastic polymer resin is an iPP, those resins that have a high melt strength when applied to the extrusion process where tan delta is less than 1.5 are preferred., and those having a tan delta of less than 1.2 are particularly preferred (tan delta is the ratio of modulus lost to storage modulus determined using a specimen of 2.5 mm in thickness and 25 mm in diameter at 190 ° C and a oscillation speed of one radian / second as shown in U.S. Patent No. 5,527,573). An example of a suitable ethylene / vinyl acetate copolymer resin is the ELVAX 460 brand resin, available from Du Pont-Dow Inc. An example of a suitable iPP resin is the iPP resin of high melt strength PRO- FAX PF-grade 814, available from Montell Polyolefins Co. NV. Examples of rigid thermoplastic polymer resins suitable for use in the second embodiment of the present invention are alkyl aromatic resins, such as polystyrene resins. An example of a polystyrene suitable for use in the second embodiment of the invention is a polystyrene having an average molecular weight of less than 240,000. Optionally, a nucleating agent can be added to the foamable mixture. The amount of nucleating agent employed to prepare the foams of the present invention will vary according to the desired cell size, the foaming temperature, and the composition of the nucleating agent. Useful nucleating agents include calcium carbonate, barium stearate, calcium stearate, talc, clay, titanium dioxide, silica, barium stearate, diatomaceous earth, mixtures of citric acid and sodium bicarbonate. When used, the amount of nucleating agent employed may vary from 0.01 to 5 parts by weight per 100 parts by weight of the polymer resin mixture (pph). Blowing agents useful in making the foams present include all types of blowing agents known in the art; physical and chemical blowing agents and mixtures thereof, including inorganic blowing agents, organic blowing agents, and chemical blowing agents. Suitable inorganic spraying agents include carbon dioxide, nitrogen, water, air and helium. Organic blowing agents include aliphatic hydrocarbons having from 1 to 6 carbon atoms, aliphatic alcohols having from 1 to 3 carbon atoms, and aliphatic hydrocarbons totally or partially halogenated having 1 to 4 carbon atoms. The aliphatic hydrocarbons include methane, ethane, propane, n-butane, isobutane, n-pentane, e-sopentane, neopentane. The aliphatic alcohols include methanol, ethanol, n-propanol and isopropanol. The total and partially halogenated aliphatic hydrocarbons include chlorocarbons, fluorocarbons and chlorofluorocarbons. Chlorocarbons for use in this invention include methyl chloride, methylene chloride, ethyl chloride and 1,1,1-trichlorethane. Fluorocarbons for use in this invention include methyl fluoride, methylene fluoride, ethyl fluoride, 1,1-difluoroethane (HFC-152a), 1,1-trifluoroethane (HGC-143a), 1,1,1, 2-tetrafluoroethane (HFC-134a), 1,1, 2,2-tetrafluoroethane (HFC-134), pentafluoroethane, perfluoroethane, 2,2-difluoropropane, 1,1,1-trifluoropropane, and 1, 1, 1, 3 , 3-pentafluoropropane. The partially hydrogenated chlorofluorocarbons for use in this invention include chlorodifluoromethane (HCFC-22), 1,1-dichloro-1-fluoroethane (HCFC-141b), 1-chloro-1,1-difluoroethane (HCFC-142b), 1.1 -dichloro-2,2,2-trifluoroethane (HCFC-123), and 1-chloro-1,2,2,2-tetrafluoroethane (HCFC-124). Fully halogenated chlorofluorocarbons can also be used, but are not preferred for environmental reasons. Chemical blowing agents for use in this invention include azodicarbonamide, azodiizobutyronitrile, benzenesulfohydrazide, 4,4-oxybenzenesulfonyl-semicarbazide, p-toluene sulfonyl semi-carbazide, N, N'-dimethyl-N, N'- dimtrosotereftalamida, and triazine trihydrazine, sodium bicarbonate, and mixtures of sodium bicarbonate and citric acid. Mixtures of all of these blowing agents are also contemplated within the scope of this invention. The most suitable type of blowing agent depends on the process used to make the foam body and the desired density of the foam. Preferred blowing agents for the process of extrusion and batch process for making molding pearls are physical blowing agents, with volatile organic blowing agents being preferred. Preferred blowing agents for interlaced foam processes are decomposable blowing agents and nitrogen. The amount of blowing agent incorporated into the molten material of the polymer to make a foaming gel is from 0.1 to 5, preferably from 0.4 to 4, and most preferably from 0.9 to 3 grams mol per kilogram of polymer. The present foams, optionally, further comprise an infrared absorber (transmission blocker) such as carbon black, graphite, and titanium dioxide, to increase the insulating capacity. When the infrared absorbent is used it may comprise between 1.0 and 25% by weight and preferably between 4.0 and 10.0% by weight based on the weight of the polymer mixture in the foam. The carbon black can be of any type known in the art such as furnace black, thermal black, acetylene black, and channel black. A preferred carbon black It is thermal black. A preferred thermal black has an average particle size of 150 nanometers or more. It is preferred that the foams of the present invention exhibit dimensional stability. Although the sPP resin itself acts as a stability control agent, in some cases, it is desirable to include an additional stability control agent to further increase the dimensional stability of the foams of the present invention. For example, stability control agents in addition to the sPP resin may be desirable when the sPP resin is used at a level of less than 30% in a mixture with a polyethylene resin or ethylene / vinyl acetate copolymer and the The mixture is expanded with isobutane. A stability control agent may be especially desirable in producing thick (i.e., greater than 4 mm) sheets and board products (thicker than 12 mm) of substantially closed cell structure from the preceding mixture. In contrast, an additional stability control agent is probably not necessary or desirable when forming foams with substantially open cells. Dimensional stability is measured by taking the volume of foam during aging as a percentage of the initial volume of the foam, measured at 30 seconds after the expansion of the foam. Using this definition, a foam that recovers 80% or more of the initial volume in a month is tolerable, while a foam that recovers 85% or more, a foam that recovers 90% or more is especially preferred. The volume is measured by a suitable method such as cubic water displacement. Preferred stability control agents include C-α or -24- fatty acid esters and esters. Such agents are seen in U.S. Patent Nos. 3,644,230 and 4,214,054. The most preferred agents include stearyl esteramide, glycerol monostearate, glycerol monobenenate and sorbitol monostearate. Typically, such stability control agents are employed in an amount ranging from 0.1 to 10 parts per 1000 parts of the polymer. Various additives may also be incorporated into the present foam such as inorganic fillers, pigments, antioxidants, acid scavengers, ultraviolet absorbers, flame retardants, process aids and extrusion aids. The blended polymer foams of the present invention can be prepared by techniques and procedures well known to anyone of ordinary skill in the art and include extrusion processes as well as batch processes using a blowing agent that can be decomposed and entangled, being Preferred extrusion processes. The blended polymer foams of the present invention can be interlaced or non-interlaced. Excellent teachings of processes for making polymer foam structures and processing them are seen in C. P. Park, "Polyolefin Foam," Chapter 9, Manual of Foams and Polymer Technology, edited by D. Klempner and K. C. Frisch, Hanser Publishers, Munich, Vienna, New York, Barcelona (1991). The non-interlaced foams of the present invention can be made by a conventional extrusion foaming process. The foam structure is generally prepared by heating a pre-mixed mixture of the sPP resin and the thermoplastic polymer resin (i.e., polymeric material) to form a plasticized or melted polymer material, which incorporates a blowing agent therein. to form a foamable gel, and to extrude the gel through a matrix to form the foam product. Before mixing with the blowing agent, the polymeric material is heated to a temperature at or above its Tg or melting point. The blowing agent can be incorporated or mixed into the molten polymeric material by any means known in the art, such as with an extruder or mixer. The blowing agent is mixed with the molten polymeric material at a high enough pressure to prevent substantial expansion of the molten polymeric material and to generally disperse the blowing agent homogeneously therein. Optionally, a nucleator can be mixed in the polymer melt or mixed dry with the polymeric material before plasticizing or melting. The foamable gel is typically cooled to a lower temperature to optimize the physical characteristics of the foam structure. The gel is extruded or transported after through a matrix of desired shape to a zone of reduced or reduced pressure to form the foam structure. The lower pressure zone is at a lower pressure than that in which the foamable gel is maintained prior to extrusion through the matrix. The lower pressure may be super-atmospheric or sub-atmospheric (vacuum), but preferably at an atmospheric level. The non-interlaced foams of the present invention can be formed into a molten stream form by extruding the premixed mixture of the sPP resin and the thermoplastic polymer resin (i.e., polymeric material) through a multi-orifice array. . The holes are arranged so that contact occurs between adjacent streams of the molten extrudate during the foaming process and the contacting surfaces adhere to each other with sufficient adhesion to result in a unitary foam structure. The molten extrudate streams leaving the matrix take the form of strands or profiles, which foamed, melt and adhere desirably to each other to form a unitary structure. Desirably, the individual melted strands or profiles will remain adhered in a unitary structure to prevent delamination of strands under the efforts encountered in preparing, shaping and using the foam. Apparatus and methods for producing foam structures in the form of melt streams are seen in U.S. Patent Nos. 3,573, 152 and 4,324,720. The current foam structure can also be formed in non-interlaced foam beads suitable for molding into articles. Foam beads can be prepared by an extrusion process or a batch process. In the extrusion process, the foam streams emerging from a multi-hole array attached to a conventional foam extrusion apparatus are granulated to form the foam beads. The foam beads, if necessary, are heated below the melting point of the sPP resin so that the sPP molecules can crystallize, thereby forming a pseudo-network structure that provides resistance to thermal collapse at foam beads. In a batch process, discrete particles of resin such as pellets of granulated resin are suspended in a liquid medium in which they are substantially insoluble such as water; they are impregnated with a blowing agent by introducing the blowing agent into the liquid medium at a high pressure and temperature in an autoclave or other pressure vessel; and is quickly discharged to the atmosphere or a region of reduced pressure to expand to form the foam beads. This process is well taught in the Patents of E. U. Nos. 4,379,859 and 4,464,484. The entangled foams of the present invention can be prepared either by the interlaced foam process employing a blowing agent that is decomposed or by conventional extrusion processes. When the interlaced foam process is used by employing a decomposable blowing agent, the interlaced foams of the present invention can be prepared by mixing and heating a premixed mixture of the sPP resin and the thermoplastic polymer resin (i.e. polymer material) with a chemical agent. blowing agent which can be decomposed to form a plasticized foamable or molten polymeric material, extruding the molten foamable polymer material through a matrix, inducing entanglement in the molten polymeric material and exposing the molten polymeric material at an elevated temperature to release the agent of blowing to form the foam structure. The polymeric material and the chemical blowing agent can be mixed and the melt mixed by any means known in the art such as with an extruder, or mixer. The chemical blowing agent is preferably dry mixed with the polymeric material before heating the polymeric material to a molten form., but can also be added when the polymeric material is in the molten phase. The entanglement can be induced by the addition of an entanglement agent or by radiation. The induction of entanglement and exposure to a high temperature to effect foaming or expansion can occur simultaneously or sequentially. If an entanglement agent is used, it is incorporated into the polymeric material in the same manner as the chemical blowing agent. In addition, if an entanglement agent is used, the foamable molten polymeric material is hot or exposed to a temperature of preferably less than 150 ° C to prevent decomposition of the entanglement agent or blowing agent and prevent premature entanglement. If radiation entanglement is used, the foamable molten polymer material is heated or exposed to a temperature of preferably less than 160 ° C to avoid decomposition of the spreading agent. The foamable molten polymer is extruded or transported through a matrix of desired shape to form a foamable structure. The foamable structure is then entangled and expanded at a high or high temperature (typically, 150 ° C to 250 ° C) such as in an oven to form a foam structure. When the radiation entanglement is used, the foamable structure is irradiated to interlock the polymeric material, which is then expanded to the elevated temperature as described above. The structure can advantageously be made in the form of a thin sheet or board according to the process antepor using either entanglement or radiation agents. In addition to using an entanglement or radiation agent in the interlaced foam process employing a decomposable blowing agent, the entanglement can also be carried out by means of silane interlacing as described in C.P. Park, Supra, Chapter 9. The interlaced foams of the present invention can also be made in a continuous board structure by a extrusion process using a long stroke die as described in GB 2, 145, 961 A. In that process, the polymer the decomposable blowing agent and the interlacing agent are mixed in an extruder, the mixture is heated to allow the polymer to interlock and the blowing agent to decompose in a long matrix; and shaping and driving away from the foam structure through the matrix with the contact of the foam structure and the lubricated matrix by an appropriate lubrication material. The interlaced foams of the present invention can also be formed into interlaced foam beads suitable for molding into articles. To make the foam beads, discrete resin particles such as granulated resin pellets are: suspended in a liquid medium in which they are substantially insoluble such as water; impregnate with an interlacing agent and a blowing agent at a high pressure and temperature in an autoclave or other pressure vessel; and rapidly discharging to the atmosphere or a region of reduced pressure to expand to form the foam beads. One version is that the polymer beads are impregnated with blowing agents, cooled, discharged from the container and then expanded by heating or steam. In a derivative of the above process, the styrene monomer may be impregnated into the suspended lentils together with the entanglement agent to form a graft interpolymer with the polymeric material.

The blowing agent may be impregnated in the resin lentils while in suspension, or alternatively, in a non-hydrated state. The expandable beads are then expanded by steam heating and molded by the conventional molding method for the expandable polystyrene foam beads. The foam beads can then be molded by any means known in the art, such as loading the foam beads into the mold, compressing the mold to compress the beads, and heating the beads such as with steam to effect melting and soldering. the pearls to form the article. Optionally, the beads can be pre-heated with air or other blowing agents before being loaded into the mold. In C. P. Park, Supra, pp. 227-233, U.S. Patent Nos. 3,886, 100, 3, 959, 189, 4, 168, 533, and 4,429, 059, excellent teachings of the above molding processes and methods can be seen. Foam beads can also be prepared by preparing a polymer blend, interlacing agent, and mixtures that can be decomposed in a suitable mixing device or extruder and forming the mixture into lentils (pellets), and heating the lentils to interlock and expand. There is another process for making interlaced foam beads suitable for molding into articles. The polymeric material is melted and mixed with a physical blowing agent in a conventional foam extrusion apparatus to form a strand of essentially continuous foam. The foam strand is granulated to form foam beads. The foam beads are then interlaced by radiation. The interlaced foam beads can then be cast and molded to form various articles as described above for the other foam bead process. In the Patent of E. U. No. 3,616, 365 and C. P. Park, Supra, pp. 224-228 additional teachings of this process are seen. In addition, it is possible to employ SiO interlacing technology in the extrusion process. Teachings of this process are seen in C. P. Park, Supra, chapter 9 and in the Patent of E. U. No. 4, 714,716. When using SiO interlacing processes with conventional extrusion processes, a polymer is grafted with a functional vinyl silane or a functional azido silane and extruded for foams. The extruded foam is then exposed to hot moist air so that entanglement is developed. The entangled foams of the present invention can be prepared by the foam sheet process or foam stock process or any process described in C. P. Park, Supra, Chapter 9, pp. 625-634. 229 to 235. Although, typically, substantially with closed cells by nature, the foams of the present invention may be of open cells or closed cells. In addition, the foams of the present invention have a cell size (ie, diameter of cell) from 0.01 mm to 10 mm, with 0.1 mm to 5 mm being preferred, and 0.4 mm to 3 mm being particularly preferred. In addition, the foams of the present invention have a density from 9 kg / m3 to 200 kg / m3, densities of 11 kg / m3 to 100 kg / m3 being preferred, and 15 kg / m3 to 50 kg being most preferred. / m3. The foams of the present invention can take any physical configuration known in the art, such as extruded sheet, bars, boards, profiles, beads, and masses. The foam structure can also be formed by molding expandable beads in any of the foregoing configurations or any other configuration. Thus, in accordance with the foregoing, the following foams represent typical foams of the present invention: a mixed polymer foam comprising: a) from 0.1% to 60% by weight of a sPP resin; and b) from 40% to 99.9% by weight of a foamable thermoplastic polymer resin; a mixed polymer foam comprising: a) from 0.1% to 60% by weight of a sPP resin; and b) from 40% to 99.9% by weight of a foamable thermoplastic polymer resin, the foam having a density of 9 kg / m 3 to 300 kg / m 3, preferably 1 1 kg / m 3 to 100 kg / m 3, and more preferred from 15 kg / m3 to 50 kg / m3; a mixed polymer foam comprising: a) from 0.1% to 60% by weight of a sPP resin; and b) from 40% to 99.9% by weight of a flexible thermoplastic polymer resin; a mixed polymer foam comprising: a) from 0.1% to 60% by weight of a sPP resin; and b) from 40% to 99.9% by weight of a flexible thermoplastic polymer resin, the foam having a density of 9 kg / m3 to 300 kg / m3, preferably 11 kg / m3 to 100 kg / m3, and more preferred from 15 kg / m3 to 50 kg / m3; a mixed polymer foam comprising: a) from 0.1% to 60% by weight of a sPP resin; and b) from 40% to 99.9% by weight of a rigid thermoplastic polymer resin; a mixed polymer foam comprising: a) from 0.1% to 60% by weight of a sPP resin; and b) from 40% to 99.9% by weight of a rigid thermoplastic polymer resin, the foam having a density of 9 kg / m3 to 300 kg / m3, preferably 11 kg / m3 to 100 kg / m3, and more preferred from 15 kg / m3 to 50 kg / m3; a mixed polymer foam comprising: a) from 0.1% to 60% by weight of a sPP resin; and b) from 40% to 99.9% by weight of a flexible polyolefin resin; a mixed polymer foam comprising: a) from 0.1% to 60% by weight of a sPP resin; and b) from 40% to 99.9% by weight of a flexible polyolefin resin, the foam having a density of 9 kg / m3 to 300 kg / m3, preferably 11 kg / m3 to 100 kg / m3, and more preferred of 15 kg / m3 at 50 kg / m3; a mixed polymer foam comprising: a) from 0.1% to 60% by weight of a sPP resin; and b) from 40% to 99.9% by weight of a LDPE resin; a mixed polymer foam comprising: a) 0.1% to 60% by weight of a resin of s PP, and b) from 40% to 99 9% by weight of an LDPE the foam having a density of 9 kg / m3 to 300 kg / m3, preferably 1 1 kg / m3 at 100 kg / m3 and more preferably from 15 kg / m3 to 50 kg / m3, a mixed polymer foam comprising a) from 0 1% to 60% by weight of a sP P resin which is a homopol propylene grouper, and b) from 40% to 99 9% by weight of a foamable thermoplastic polymer resin, a mixed polymer foam comprising a) from 0 1% to 60% by weight of a ream of sPP which is a propylene propylene homopoly, and b) from 40% to 99 9% by weight of a foamable thermoplastic polymer resin, the foam having a density of 9 kg / m 3 to 300 kg / m 3, preferably 1 1 kg / m 3 a 100 kg / m3, and more preferred from 15 kg / m to 50 kg / m 'a mixed polymer foam comprising a) from 0 1% to 60% by weight of a sP P resin which is a homopoxide of propylene, and b) from 40% to 99 9% by weight of a thermoplastic polymer resin or flexible, a mixed polymer foam comprising a) from 0 1% to 60% by weight of a ream of sPP which is a homopolymer of propylene, and b) from 40% to 99 9% by weight of a resin of flexible thermoplastic polymer, the foam having a density of 9 kg / m3 to 300 kg / m3, preferably 1 1 kg / m3 to 100 kg / m3, and more preferred of 15 kg / m3 to 50 kg / m3, a mixed polymer foam comprising a) of 0 1% at 60% by weight of a sPP resin which is a homopolymer of propylene; and b) from 40% to 99.9% by weight of a rigid thermoplastic polymer resin; a mixed polymer foam comprising: a) from 0.1% to 60% by weight of a sPP resin which is a homopolymer of propylene; and b) from 40% to 99.9% by weight of a rigid thermoplastic polymer resin, the foam having a density of 9 kg / m 3 to 300 kg / m 3, preferably 1 1 kg / m 3 to 100 kg / m 3, and most preferred from 15 kg / m3 to 50 kg / m3; a mixed polymer foam comprising: a) from 0.1% to 60% by weight of a sPP resin which is a homopolymer of propylene; and b) from 40% to 99.9% by weight of a flexible polyolefin resin; a mixed polymer foam comprising: a) from 0.1% to 60% by weight of a sPP resin which is a propylene homopolymer; and b) from 40% to 99.9% by weight of a flexible polyolefin resin, the foam having a density of 9 kg / m 3 to 300 kg / m 3, preferably 1 1 kg / m 3 to 100 kg / m 3, and more preferred from 15 kg / m3 to 50 kg / m3; a mixed polymer foam comprising: a) from 0.1% to 60% by weight of a sPP resin which is a propylene homopolymer; and b) from 40% to 99.9% by weight of a LDPE resin; a mixed polymer foam comprising: a) from 0.1% to 60% by weight of a sPP resin which is a propylene homopolymer; and b) from 40% to 99.9% by weight of a LDPE resin, the foam having a density of 9 kg / m3 to 300 kg / m3, preferably 1 1 kg / m3 to 1 00 kg / m3, and more preferably 15 kg / m3 to 50 kg / m3; a mixed polymer foam comprising: a) from 0.1% to 60% by weight of a sPP resin which is a propylene homopolymer having a syndiotacticity of more than 75%; and b) of 40% to 99.9% by weight of a foamable thermoplastic polymer resin; a mixed polymer foam comprising: a) from 0.1% to 60% by weight of a sPP resin which is a propylene homopolymer having a syndiotacticity of more than 75%; and b) from 40% to 99.9% by weight of a foamable thermoplastic polymer resin, the foam having a density of 9 kg / m 3 to 300 kg / m 3, preferably 1 1 kg / m 3 to 100 kg / m 3, and more preferred from 15 kg / m3 to 50 kg / m3; a mixed polymer foam comprising: a) from 0.1% to 60% by weight of a sPP resin which is a propylene homopolymer having a syndiotacticity of more than 75%; and b) of 40% to 99.9% by weight of a flexible thermoplastic polymer resin; a mixed polymer foam comprising: a) from 0.1% to 60% by weight of a sPP resin which is a propylene homopolymer having a syndiotacticity of more than 75%; and b) of 40% to 99.9% by weight of a flexible thermoplastic polymer resin, the foam having a density of 9 kg / m3 up to 300 kg / m3, preferably 1 1 kg / m3 to 100 kg / m3, and more preferably from 1 5 kg / m3 to 50 kg / m3; a mixed polymer foam comprising: a) from 0.1% to 60% by weight of a sPP resin which is a propylene homopolymer having a syndiotacticity of more than 75%; and b) of 40% to 99.9% by weight of a rigid thermoplastic polymer resin; a mixed polymer foam comprising: a) from 0.1% to 60% by weight of a sPP resin which is a propylene homopolymer having a syndiotacticity of more than 75%; and b) of 40% to 99.9% by weight of a rigid thermoplastic polymer resin, the foam having a density of 9 kg / m 3 to 300 kg / m 3, preferably 1 1 kg / m 3 to 100 kg / m 3, and more preferred 15 kg / m3 at 50 kg / m3; a mixed polymer foam comprising: a) from 0.1% to 60% by weight of a sPP resin; and b) from 40% to 99.9% by weight of an ethylene / vinyl acetate copolymer resin; a mixed polymer foam comprising: a) from 0.1% to 60% by weight of a sPP resin; and b) from 40% to 99.9% by weight of an ethylene / vinyl acetate copolymer resin, the foam having a density of 9 kg / m3 to 300 kg / m3, preferably 1 1 kg / m3 to 100 kg / m3, and more preferred from 15 kg / m3 to 50 kg / m3; a mixed polymer foam comprising: a) from 0.1% to 60% by weight of a sPP resin; and b) from 40% to 99.9% by weight of an iPP resin; a mixed polymer foam comprising: a) from 0.1% to 60% by weight of a s PP resin; and b) from 40% to 99.9% by weight of an iP P resin, the foam having a density of 9 kg / m3 to 300 kg / m3, preferably 1 1 kg / m3 to 100 kg / m3, and more preferred from 15 kg / m3 to 50 kg / m3; a mixed polymer foam comprising: a) from 0.1% to 60% by weight of a sPP resin; and b) from 40% to 99.9% by weight of an alkyl aromatic polymer resin; a mixed polymer foam comprising: a) from 0.1% to 60% by weight of a sPP resin; and b) from 40% to 99.9% by weight of an alkyl aromatic polymer resin, the foam having a density of 9 kg / m 3 to 300 kg / m 3, preferably 1 1 kg / m 3 a 1 00 kg / m3, and more preferred from 15 kg / m3 to 50 kg / m3; a mixed polymer foam comprising: a) from 0.1% to 60% by weight of a sPP resin; and b) from 40% to 99.9% by weight of a polystyrene polymer resin; a mixed polymer foam comprising: a) from 0.1% to 60% by weight of a s PP resin; and b) from 40% to 99.9% by weight of a polystyrene polymer resin, the foam having a density of 9 kg / m 3 to 300 kg / m 3, preferably 1 1 kg / m 3 to 100 kg / m 3, and most preferred from 15 kg / m3 to 50 kg / m3; The following are examples of the present invention, and are not constructed as limiting the scope of the invention. Unless otherwise indicated, all percentages, parts, or proportions are by weight.

The following examples of foams prepared from resin mixtures of PP and foamable thermoplastic polymer resin were prepared using a 19 mm diameter screw-type extruder having additional zones for mixing and cooling at the end of the zones of usual sequence of feeding, fusion and measurement. An opening for injection of blowing agent into the barrel of the extruder is provided between the measuring and mixing zones. At the end of the cooling zone, a die hole having an opening of rectangular shape is attached. The height of the opening is adjustable while its width is fixed at 38 mm.

Example 1 Preparation of a foam mixture of sPP resin and LDPE resin. Example 1 demonstrates the preparation of a foam according to the present invention which was prepared from a 50/50 weight mixture of LDPE resin and an sPP resin which had been expanded using isobutane as the agent of blown by an extrusion process. The tests carried out on foam prepared according to this example show that the polymer mixture is foamable by extrusion, and the foam is dimensionally stable and resists a relatively high temperature. A 50/50 by weight granular blend of LDPE resin having a melt index of 0.7 dg / minute was prepared (determined by ASTM D-1 238 at 1 90 ° C / 2.16 kg), a density of 0.923 g / cm3, and a melting point of 1 15 ° C (determined by differential scanning calorimetry (DSC) at the peak of an endothermic during heating at 10 ° C / minute) and syndiotactic grade EOD 96-28 polypropylene copolymer resin (available from Fina Oil and Chemical Company) having a melt flow rate of 2 dg / minute (determined by ASTM D -1238 at 230 ° C / 2.16 kg), a density of 0.88 g / cm3, and a melting point of 130 ° C. The mixture of granular resins and an additive package consisting of talcum powder (nucleating agent) in 0.2 parts per 100 parts of resins (pph) and antioxidant brand Irganox 101 0 (available from Ciba-Geigy Corp.) at 0.1 pph were fed to the extruder at a uniform rate of 3.26 kilograms per hour (kg / h). The temperatures in the extruder zones were maintained at 160 ° C in the feed zone, 190 ° C in the melting zone, 200 ° C in the measuring zone and 200 ° C in the mixing zone. Isobutane (blowing agent) was injected into the mixing zone at a uniform rate of 414 g / h (12.7 pph). The temperature of the cooling zone was gradually reduced and the opening of the die was adjusted to make a good foam. For example, at a temperature of 107 ° C in the cooling zone, matrix temperature of 105 ° C, and matrix aperture of 1.0 mm, excellent foam of substantially closed cell structure was obtained (open cell content). approximately 32% according to procedure A of ASTM D-2856). The foam had a density of 24.8 kg / m3, cell size of 12 mm, thickness of approximately 12 mm and width of approximately 19 mm.

Test 1 Dimensional Stability of the Foam of Example 1 A foam specimen of approximately 15 cm in length was cut from the freshly prepared foam prepared in Example 1, and the foam specimen volume was measured approximately 2 minutes after extrusion and then, periodically later during aging at an ambient temperature. The foam exhibited excellent dimensional stability with shrinkage no later than 30 minutes after extrusion when its shrinkage dropped to approximately 97% of the original volume. The foam recovered completely to more than 100% of its original volume in one day.

Test 2 Heat Stability of the Foam of Example 1 One day after extrusion, the foam prepared in the Example 1 was cut into a 8 cm long specimen. The specimen was placed in a convection oven maintained at 121 ° C and its volume monitored periodically. The volume of the foam, as a percentage of the original volume, is presented as a function of the exposure time in the oven as shown in Table I TABLE I As shown, the foam shrinks up to 70% of the original volume and remains in that volume during a prolonged exposure to high temperature while a polyethylene foam based on the same LDPE resin used in Example 1 was observed to collapse totally at that temperature. The foam resistance of the mixture at high temperatures is further supported by the DSC thermograms shown in Figure 1 and Figure 2, discussed previously. In Figure 1 and Figure 2, the DSC thermograms of an extruded foam as such (Figure 1) and an oven-aged foam are compared (Figure 2). The oven-aged foam was exposed to a temperature of 121 ° C for five days. Furnace-aged foam shows a sharp peak at about 130 ° C plus one at about 13 ° C. In contrast, the extruded foam as such does not show a sharp peak at 130 ° C which is the peak of melting crystals of sPP. Thermograms indicate that the LDPE resin and the sPP resin used in the Example 1 are not miscible and that the phase of the sPP resin in the mixture undergoes crystallization during heating at 121 ° C.

Test 3 Thermoforming Properties of the Foam of Example 1 Two 5 cm long specimens were cut from the foam prepared in Example 1 and heated at 121 ° C in the oven for 5 minutes. Then, the heated foam specimens were removed from the furnace and sharpened immediately on top of each other with application of gentle pressure against each other. Foam specimens developed satisfactory adhesion without experiencing noticeable shrinkage, indicating that moireable foam beads can be prepared from the foam of Example 1 and that the foam of Example 1 can be thermoformed.

Comparative Example A Preparation of Foam Prepared from SPP Resin The foam of Comparative Example A was prepared in order to test the expansion properties of the foam of a foam made from sPP resin only. Polypropylene copolymer resin copolymer was blended syndiotactic grade EOD 96-28 (available from Fina Oil and Chemical Company) having a melt flow rate of 2 dg / minute (determined by ASTM D-1238 at 230 ° C / 2.16 kg), density of 0.88 g / cm3, and melting point of 1 30 ° C, with 0.4 pph of talc (nucleating agent) and 0.1 pph of Irganox 1010 (available from Ciba Geígy Corp.). The mixture was fed to the extruder at a uniform rate of 3.10 kg / h. Temperatures in the extruder zones were maintained at 160 ° C in the feed zone, 190 ° C in the melting zone, 200 ° C in the measuring zone, and 200 ° C in the mixing zone. Isobutane (blowing agent) was injected into the mixing zone at a uniform rate of 414 g / h (12.7 pph). The temperature of the cooling zone was gradually reduced from 160 ° C to 80 ° C with a decrease of about 5 ° C at each time and kept for 5 to 10 minutes at a temperature in order to see if a good spit The temperature of the matrix was maintained at the same temperature as the cooling zone. The die opening was maintained at 0.8 mm at a temperature of the cooling zone below 95 ° C. Below 95 ° C, the die opened slightly wider to relieve the pressure increase.

Test 4 Foaming Capacity of the sPP Resin of Example Comparative A The melt prepared in Comparative Example A above did not expand at all temperatures below 95 ° C. At temperatures below 95 ° C, the foam expanded slightly, but collapsed immediately. At 80 ° C, the extruder pressure is it rose abruptly, indicating that the melt was very viscous and freezing in the cooling zone. No further reduction in cooling temperature could be tolerated. Conclusion: the sPP resin alone can not be expanded to a stable foam by the extrusion process.

Example 2 and Comparative Example B Preparation of a Resin Mixing Foam of sPP v LDPE Resin Example 2 demonstrates the preparation of foams according to the present invention which were prepared from a mixture of LDPE resin and resin sPP, wherein the percentage level of the sPP resin is varied in order to examine the effect of the sPP resin level, on the mixture, on the foaming capacity properties and the dimensional stability of the foam. Comparative Example B is a foam prepared from LDPE resin only. Granular LDPE resin mixtures having a melt index of 0.7 dg / minute (determined by ASTM D-1238 at 190 ° C / 2.16 kg), a density of 0.923 g / cm3, and a melting point of 1 were prepared. 15 ° C (determined by differential scanning calorimetry (DSC) at the peak of an endotherm during heating at 10 ° C / minute) and syndiotactic copolymer copolymer of EOD grade 96-07 (available from Fina Oil and Chemical Company), which has a flow regime of cast 2 dg / minute (determined by ASTM D-1238 at 230 ° C / 2.16 kg), a density of 0.88 g / cm3, and a melting point of 1 30 ° C at predetermined ratios, as shown in the Table The mixture of granular resins and 0.2 pph of talcum powder (nucleating agent) was fed to the extruder at a uniform rate of 3.1 kg / h (due to a difference in feed characteristics between the mixes, the actual extrusion rate varies slightly in the range from about 3 kg / h to 3.2 kg / h, even when an effort is made to maintain the same regime by adjusting the rotation speed of the spindle). Temperatures in the extruder zones were maintained at 160 ° C in the feed zone, 1 90 ° C in the melting zone, 200 ° C in the measuring zone, and 220 ° C in the mixing zone. The temperature of the cooling zone was maintained as indicated in Table I I. Isobutane (blowing agent) was injected into the mixing zone at the rate indicated in Table 1. The temperature of the cooling zone was gradually reduced and the opening of the die was adjusted to make a good foam. The temperature of the matrix was maintained at 1 10 ° C for Comparative Example B, Examples Nos. 2.1 to 2.3, and at 105 ° C for Examples Nos. 2.4 and 2.5. Foam samples were taken at the optimum temperature of the cooling zone for each formulation as shown in Table II and to a die opening ranging from 1.1 mm to 1.2 mm.

The dimensional data for the foams are summarized in Table I I together with the density data, cell size and open cell. TABLE I I or as: ^ percentage of sPP resin in the mixture 2 parts of isobutane mixed in 100 parts of polymer resin fixed temperature of the cooling zone where the foam was made 4density of the aged foam body for two months determined by displacement of water in kg / m3 5 cell size in millimeters determined by ASTM D-3576 6 open cell content in percentage determined by ASTM D-2856-A 7 Minimum volume of the foam body during aging at a room temperature as a percentage of the initial volume. The minimum volume occurred within one day for all foams 8voumen of the foam body to specific aging at a room temperature as a percentage of the initial volume. N D = not determined As shown in Table I I, formulations containing up to 40% sP P resin produced good quality foams. The 50/50 LDPE / sPP blend foam at the selected cooling temperature of 107 ° C appeared slightly hot. The thickness of the foams ranged from 6.1 mm to 8.2 mm and the width of the foam ranged from 14.7 mm to 1 8.4 mm. A specimen of approximately 15 cm in length was cut from each freshly prepared foam and the volume of the foam specimen was measured after approximately two minutes of the extrusion and then periodically thereafter during aging at room temperature.

Conclusions: Mixtures tend to give a larger cell size than pure LDPE resin. Mixtures that have 40 and 50% sPP tend to develop more open cells. The addition of the sPP resin shows that it improves the dimensional stability of the foam. A mixture containing a sPP level of 30% or more provided a foam having satisfactory dimensional stability with a minimum foam volume during aging greater than 89%.

Example 3 and Comparative Example C Preparation of a Resin Mixing Resin of sPP and Resin LDPE Example 3 demonstrates the preparation of foams according to the present invention which were prepared from a mixture of LDPE resin and sPP resin where the level of blowing agent was varied in order to determine if the capacity Foaming of mixtures having a high level of sPP resin could be improved by a high level of blowing agent. The temperature of the cooling zone was also lowered in order to determine its effect on the expansion of the foam. Granular LDPE resin mixtures having a melt index of 0.7 dg / minute were prepared, (determined by ASTM D-1238 at 190 ° C / 2.16 kg), a density of 0.923 g / cm3, and a melting point of 1 15 ° C (determined by differential scanning calorimetry (DSC) at the peak of a endotherm during heating at 10 ° C / minute) and syndiotactic grade EOD 96-07 polypropylene copolymer resin (available from Fina Oil and Chemical Company) having a melt flow rate of 2 dg / minute, (determined by ASTM D-1238 at 230 ° C / 2.16 kg), a density of 0.88 g / cm 3, and a melting point of 130 ° C in a predetermined ratio, as shown in Table III. The mixture of granular resins and 0.2 pph of talcum powder (nucleating agent) was fed to the extruder at a uniform rate of 3.1 kg / h (due to a difference in feed characteristics between the mixes, the actual extrusion rate varies slightly in the range of about 3 kg / h to 3.2 kg / h even when an effort was made to maintain the same regime by adjusting the rotation speed of the spindle). The temperatures in the extruder zones were maintained at 160 ° C in the feed zone, 1 90 ° C in the melting zone, 200 ° C in the measuring zone, and 220 ° C in the mixing zone. The temperature of the cooling zone was maintained as indicated in Table 11, and isobutane (blowing agent) was injected into the mixing zone at the levels indicated in Table 11. The temperature of the cooling zone was gradually reduced and the opening of the die was adjusted to make a good foam. The temperature of the matrix was maintained at 1 10 ° C for Comparative Example C and Examples Nos. 3.1 and 3.2, and at 100 ° C for Example No. 3.3. Foam samples were taken at the optimum temperature of the cooling zone for each formulation as shown in Table 11 and at a die opening ranging from 1.1 mm to 1.2 mm. The dimensional data for the foams are summarized in Table 11 together with density data, cell size and open cell.

TABLE ll l Notes: 1percent of sPP resin in the mixture parts of isobutane mixed in 100 parts of polymer resin fixed temperature of the cooling zone where the foam was made 4density of the aged foam body during two months determined by displacement of water in kg / m3 5 cell size in millimeters determined by ASTM D-3576 6Content of open cell in percentage determined by ASTM D-2856-A 7 Minimum volume of the foam body during aging at a room temperature as a percentage of the initial volume.

The minimum volume occurred within one day for all foams 8volume of the foam body at specific aging at room temperature as a percentage of the initial volume. ND = not determined As shown in Table ll l there were good foams from mixtures containing up to 50% sPP resin. The 40/60 mixture of LDPE / sP P was marginal in foam processing capacity. In order to make a foam from the mixture, the temperature of the cooling zone had to be decreased as low as 82 ° C. The foam was marginally satisfactory with a high level of open cells. All foams were of relatively low density reflecting a high level of blowing agent. The apparent open cell content of the foams shows to be relatively high, greater than 36%. The open cell method of ASTM D-2856-A tends to overestimate the contents of open cells for a flexible foam. The foams made in these examples are of lower density and lower modulus than those made in Example 2 resulting in a greater measurement error in the content of open cells. An explanation for the overestimation of open cells is observed from the dimensional stability information for the LDPE foam. Despite the apparent relatively high open cell content (41%), the foam shrunk as much as 50% during aging and recovered relatively slowly.

Example 4 v Comparative Example D Preparation of Foam Prepared from SPP Resin Mixture and Ethylene Copolymer Resin / Vinyl Acetate Example 4 demonstrates the preparation of foams in accordance with the present invention which were prepared from a blend of ethylene / vinyl acetate copolymer resin (EVA) and varying amounts of sPP resin in order to determine the effect of the level of the sPP resin on the foaming capacity of the mixture and the dimensional stability of the foam. Comparative Example D was prepared from EVA resin only. Elvax 460 granular resin mixtures were prepared (supplied by Du Pont-Dow Inc.), which have a melt index of 2.5 dg / minute, (determined by ASTM D-1238 at 230 ° C / 2.16 kg), a density of 0.941 g / cm3, and a melting point of 88 ° C and copolymer resin of syndiotactic grade EOD 96-07 polypropylene (available from Fina Oil and Chemical Company) having a melt flow rate of 2 dg / minute, a density of 0.88 g / cm3, and a melting point of 130 ° C in a predetermined relationship, as shown in Table IV.

TABLE IV 2 parts of isobutane mixed in 1 00 parts of polymer resin fixed temperature of the cooling zone where the foam was made 4density of the aged foam body during two months determined by displacement of water in kg / m3 5 cell size in millimeters determined by ASTM D-3576 6 open cell content in percentage determined by ASTM D-2856-A 7 minimum volume of the foam body during aging at a room temperature as a percentage of the initial volume. The minimum volume occurred within one day for all foams 8volume of the foam body at specific aging at room temperature as a percentage of the initial volume. ND = not determined The mixture of granular resins and 0.4 pph of talcum powder (nucleating agent) was fed to the extruder at a uniform rate of 3 kg / h (due to a difference in the feed characteristics between the mixtures, the Actual extrusion varies slightly as shown in Table IV, dropping downwards from 3 kg / h to 2.6 kg / h at a fixed spindle rotation speed). The temperatures in the zones of the extruder were maintained at 120 ° C in the feeding zone, 150 ° C in the meg zone, 180 ° C in the measuring zone, and 180 ° C in the mixing zone. The temperature of the cooling zone was maintained as indicated in Table IV and isobutane (blowing agent) was injected into the mixing zone at the levels indicated in Table IV: 380 g / h for examples Nos. 4.3 and 4.4 (due to the change in the feed rate of polymer and blowing agent, the level of blowing agent in the resin varied from 2.7 pph to 7.3 pph (see Table IV) The space of the die was fixed at 1.75 mm in all the tests and the temperature of the matrix was maintained from 0 ° C to 5 ° C lower than the temperature of the cooling zone The dimensional stability data (see methods given in Example 1) for the foams are summarized in Table IV together with data from density, cell size and open cell As shown in Table IV, good foams were produced from mixtures containing up to 40% sPP resin Contrary to the open cell information, the foams made in the Comparative Example D and Examples Nos. 4.1 and 4.2 were substantially closed cell when they were examined by finger tightness test. The foams made in Examples 4.3 and 4.4 felt like an open cell. Again, the open cell information for soft polyolefin foams was not reliable. The EVA foam made in Comparative Example D suffered from excessive shrinkage (minimum volume = 25%) even though ASTM D-2856-A indicated that the foam contained 83% open cells.

Conclusion: Again, sPP resin blends and a foamable ethylene / vinyl acetate resin made good foams and the sPP resin proved to improve dimensional stability and a level of 30% or more of sPP resin gives a foam that has stability satisfactory dimensional Test 5 Heat Stability of the Foam of Comparative Example D and Example 4 After aging for 16 days, the foams produced in Comparative Example D and Example 4 were subjected to the heat exposure test as described in test 2.

The foam specimens were placed in an oven that had been maintained at 90 ° C. After 1 hour and then after 8 hours, the samples were removed and measured for volume changes as shown in Table V. TABLE V Percentage of -sPP resin in the mixture 2 Retention of foam body volume during aging at 90 ° C As shown in Table V, all foams were shrunk, but foams containing sPP resin retained their volume to a greater degree than foam (Comparative Example D) that did not contain s P P resin. Foam made from a mixture containing 40% sPP resin retained 83% volume after 8 hours in the oven.

Example 5 Preparation of Foam Prepared from SPP Resin Mixture and iPP Resin In Example 5, a mixture of a high melt strength iPP foamable resin and a sPP resin was used to prepare foams in accordance with the present invention. A 50/50 by weight granular blend of an iPP resin of high resistance to Pro-fax fusion grade PF-814 (available from Montell Polyolefins Co. NV) having a melt index of 3 dg / minute was prepared, (determined by ASTM D-1238 at 230 ° C / 2.16 kg), a density of 0.90 g / cm3, and a melting point of 160 ° C and syndiotactic grade EOD 96-28 polypropylene copolymer copolymer resin (available from Fina Oil and Chemical Company) which has a melt flow rate of 2 dg / minute, a density of 0.88 g / cm3, and a melting point of 130 ° C. Granular mixing resins and a package of additives that consisting of talcum powder (nucleating agent) at 0.2 parts per hundred parts of resins (pph) and antioxidant brand Iriganox 1010 (available from Ciba-Geigy Corp.) at 0.1 pph, premixed and fed to the extruder at a uniform rate of 4.2 kg / h. The temperatures in the cooling zone, at 160 ° C in the feed zone, 190 ° C in the melting zone, 200 ° C in the measuring zone, and 200 ° C in the mixing zone. Isobutane (blowing agent) was injected into the mixing zone at a uniform regimen of 10.7 pph. The die opening was maintained at approximately 0.8 mm. The temperature of the cooling zone was adjusted and the die opening was adjusted to produce foams. At temperatures of the cooling zone in the range from 170 ° C to 160 ° C, good foams of substantially closed cell structure were obtained. For example, a foam made at 160 ° C had a density of 26.3 kg / m3, cell size of 1.8 mm, open cell content of 17%, thickness of about 1 1 mm and width of about 20 mm. The foam was strong and resistant.

Comparative Example E Preparation of Foam Prepared from Resin Mixture of sPP v PP Resin In Comparative Example E, the process of Example 5, but using a 20/80 mixture of the same iPP and sPP resins instead of a 50/50 mixture. At a temperature of To the cooling zone explored from 180 ° C down to 1 50 ° C, no foam could be produced.

Example 6 and Comparative Example F Preparation of Foam Prepared from SPP Resin Mixture and Polystyrene Resin In Example 6, mixtures of a polystyrene resin (PS) and a sPP resin, using the same apparatus, were expanded with CO 2. and essentially the same procedure as used in Example 1. Comparative Example F was prepared from PS resin only. Granular PS resin mixtures having an average molecular weight of 150,000, a density of 1.05 g / cm 3, and a Tg of 104 ° C and sPP grade EOD 96-07 resin (available from Fina Oil and Chemical) were prepared. Company) having a melt flow rate of 2 dg / minute (determined by ASTM D-1238 at 230 ° C / 2.16 kg), a density of 0.88 g / cm3, and a melting point of 130 ° C in a default ratio, as shown in Table VI. The mixture of granular resins and 0.1 pph of barium stearate were premixed and fed to the extruder at a uniform rate. The temperatures in the extruder were maintained as follows: 130 ° C in the feeding zone; 160 ° C in the fusion zone; 200 ° C in the measurement area; and 200 ° C in the mixing zone. Carbon dioxide was injected into the mixing zone a uniform regime of 4.6 pph. The temperature of the cooling zone was adjusted in the range from 132 ° C to 134 ° C to produce good foams. The temperature of the matrix was kept uniform at 145 ° C during all the processes. The opening of the matrix was maintained in a fixed opening of 1.5 mm. The thickness, foam density, cell size, and open cell content are shown in Table VI.

TABLE VI 2 Extrusion regime of the polymeric resin in kg / h 3 Thickness of the foam body in millimeters 4Width of the foam body in millimeters 5Density of the aged foam body during a week in kg / m3 determined by water displacement. 6Chamber size in millimeters determined by ASTM D-3576 7Content of open cell in percentage determined by ASTM D-2856-A As shown in Table VI, the sPP resin makes the cross-sectional size and cell size larger. The foams containing 2% and 5% resin of sPP show that they do not have open cells. The PS / sPP 80/20 resin blend provides a foam that has some open cells.

Claims (37)

1. REVIVAL DIVACTIONS 1. A mixed polymer foam comprising: a) from about 0. 1% to about 60% by weight of a syndiotactic polypropylene resin; and b) from about 40% to about 99.9% by weight of a foamable thermoplastic polymer resin, the foam having a density of about 15 kg / m3 to about 50 kg / m3 when the foamable thermoplastic polymer resin is isotactic polypropylene.
2. 2. The mixed polymer foam according to claim 1 wherein the foam has a density of about 9 kg / m3 to about 300 kg / m3.
3. 3. The mixed polymer foam according to claim 2 wherein the foam has a density of about 1 1 kg / m3 to about 100 kg / m3.
4. 4. The mixed polymer foam according to claim 3 wherein the foam has a density of about 15 kg / m3 to about 50 kg / m3.
5. 5. The mixed polymer foam according to claim 1 wherein the foamable thermoplastic polymer resin is a flexible thermoplastic polymer resin.
6. 6. The mixed polymer foam according to claim 1 wherein the foamable thermoplastic polymer resin is a rigid thermoplastic polymer resin.
7. 7. Polymer foam blended according to the

   Claim 5 wherein the foamable thermoplastic polymer resin is a flexible polyolefin resin.
8. 8. The mixed polymer foam according to claim 7 wherein the flexible polyolefin resin is a low density polyethylene resin.
9. 9. The mixed polymer foam according to claim 8 wherein the low density polyethylene resin has a melt index of about 0.1 dg / minute to about 20 dg / minute. 1 0.
10. The mixed polymer foam according to claim 1 wherein the sPP resin is a homopolymer of propylene. eleven .
11. The mixed polymer foam according to claim 10 wherein the sP P resin has a melt flow rate from 0.05 dg / minute to 50 dg / minute.
12. 12. The mixed polymer foam according to claim 1 wherein the sPP resin has a syndiotacticity of more than 75%. 3.
13. The mixed polymer foam according to claim 1 wherein the sPP resin is a copolymer of propylene with ethylene.
14. 14. The mixed polymer foam according to claim 13 wherein the sPP resin has a melt flow rate from 0.05 dg / minute to 50 dg / minute.
15. 15. The foam of mixed polymers according to the

    claim 13 wherein the ream of sPP has a syndiotacticity greater than 75%.
16. 16. The mixed polymer foam according to claim 1 wherein the sPP resin is a copolymer of propylene with 1-butene.
17. 17. The mixed polymer foam according to claim 16 wherein the sP P resin has a melt flow rate from 0.05 dg / minute to 50 dg / minute.
18. 18. The mixed polymer foam according to claim 16 wherein the sPP resin has a syndiotacticity greater than 75%.
19. 19. The mixed polymer foam according to claim 5 wherein the flexible polyolefin resin is an ethylene / vinyl acetate copolymer resin.
20. 20. The mixed polymer foam according to claim 1 wherein the ethylene / vinyl acetate copolymer resin has a content of vinyl acetate from 5% to 30%. twenty-one .
21. The mixed polymer foam according to claim 19 wherein the ethylene / vinyl acetate copolymer resin has a melt flow rate from 0.1 dg / minute to 20 dg / minute.
22. 22. The mixed polymer foam according to claim 5 wherein the flexible polyolefin resin is a foamable iPP resin.
23. 23. The mixed polymer foam according to claim 22 wherein the foamable iPP resin is a resin of high melt strength when applied to the extrusion process where tan delta is less than 1.5.
24. 24. The mixed polymer foam according to claim 6 wherein the rigid thermoplastic polymer resin is a PS resin.
25. 25. The mixed polymer foam according to claim 24 wherein the PS resin has an average molecular weight of less than 240,000.
26. 26. The mixed polymer foam according to claim 5 wherein the sPP resin in the mixed foam is in the range of 10% to 50%.
27. 27. The mixed polymer foam according to claim 26 wherein the sPP resin in the mixed foam is in the range of 30% to 50%.
28. 28. The mixed polymer foam according to claim 1 wherein the mixed foam is prepared by an extrusion process.
29. 29. The mixed polymer foam according to claim 28 wherein the extrusion process uses sobutane as a blowing agent.
30. 30. The mixed polymer foam according to claim 29 wherein the extrusion process utilizes carbon dioxide as a blowing agent.
31. 31 The mixed polymer foam according to claim 1 wherein the mixed foam has a cell size from 0.01 mm to 10 mm.
32. 32. The mixed polymer foam according to claim 1 wherein the mixed foam is not interlaced.
33. 33. The mixed polymer foam according to claim 1 wherein the mixed foam is interlaced.
34. 34. The mixed polymer foam according to claim 1 wherein, the mixed foam is in the form of a sheet.
35. 35. The mixed polymer foam according to claim 1 wherein the mixed foam is in the form of a board.
36. 36. The mixed polymer foam according to claim 1 wherein the mixed foam is in the form of a board of molten strand foam.
37. 37. The mixed polymer foam according to claim 1 wherein the mixed foam is in the form of beads.