RU2232781C2 - Foamed plastics prepared from mixture of syndiotactic polypropylenes and thermoplastic polymers - Google Patents

Abstract

FIELD: polymer production.

SUBSTANCE: invention, in particular, relates to foamed plastics prepared from syndiotactic polypropylenes and foaming thermoplastic polymer resins. Mixed polymer foamed plastic contains 0.1 to 60 wt % of syndiotactic propylene resin, which may be propylene homopolymer or copolymer, and 40 to 99.9 wt % of foaming thermoplastic polymer resin. The latter is selected from group including (i) flexible polyolefin resin with the exception of isotactic polypropylene, (ii) isotactic polypropylene with tangent delta below 1.5 determined using sample 2.5 mm thick and 25 mm in diameter at 190^оС and oscillation rate 1 radian/sec; and (ii) polystyrene with average molecular mass below 240000. Density of mixed foamed plastic ranges from 9 to 100 kg/m³.

EFFECT: improved quality allowing use of foamed plastics as insulation and shock-absorption materials as well as in the form of packaging and in manufacture of molded articles such as cups and trays.

25 cl, 2 dwg, 6 tbl, 12 ex

Description

The invention relates to foams in general and more particularly to foams obtained from syndiotactic polypropylenes and foaming thermoplastic polymer resins.

Foams have a number of uses, including thermal insulation, packaging, and the manufacture of molded products such as cups and trays. Depending on the final destination of the foam, it is desirable that it has certain properties or a combination of properties. For example, when used as an insulating material or cushioning material for packaging, it is highly desirable to expand the foam to low densities.

In addition, foams having a high deformation temperature are desirable in a number of applications, including insulation at high ambient temperatures. For example, Japanese Patent Laid-open No. 08-231747 describes a foamed sheet with a density in the range of 0.1 to 0.5 g / cm ³ obtained by extrusion and foaming of a propylene resin composition consisting of 5-70 weight percent of a certain syndiotactic polypropylene and 95 -30 weight percent of a certain isotactic polypropylene with a certain amount of endothermic chemical blowing agent, and it was found that this foam sheet has good heat resistance. Depending on the specific purpose of such insulating foams, it is also desirable that such foams, in addition to a high deformation temperature, also have flexibility. The requirements for the degree of flexibility and heat resistance vary depending on the end use of the insulating foam. For example, when used in the automotive industry or for insulating hot water pipes, in some cases a flexible foam is required having a thermal deformation temperature of more than 90 ° or more than 110 ° C-120 ° C. In addition, in order to comply with Underwriters Laboratory Test UL 1191 Appendix A, foams used as fillers in personal flotation devices, in addition to softness and flexibility, must withstand temperatures of 60 ° C for an extended period of time.

However, obtaining in the same foam and the properties of flexibility (i.e. low moduli of elasticity) and high temperature deformation is difficult to achieve.

Typically, both the flexibility of a given resin (i.e., the elastic modulus) and the thermal deformation temperature of the resin are directly related to the melting point of the resin. In other words, if the resin has a low modulus of elasticity (i.e., high flexibility), it is usually required to have a lower melting point, whereas if the resin has a high deformation temperature, it is usually required to have a higher melting point. In addition, even if the properties of flexibility and the high temperature of thermal deformation are found in the same resin or mixture of resins, then the resin or mixture of resins may not be able to foaming or foaming by conventional methods, such as an extrusion method. Branched polyolefin resins obtained using the free-radical high-pressure method are capable of foaming with the formation of a flexible foam by extrusion, but for some applications this foam lacks thermal stability. Examples of branched polyolefin resins include low density polyethylene homopolymer resins having a density ranging 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. Catalytic linear polyolefin homopolymer resins (using, for example, Ziegler Natta or metallocene catalysts), such as high density polyethylene and isotactic polypropylene (iPP) resins, have a relatively high thermal deformation temperature, but there are difficulties with foaming during extrusion. In addition, foams obtained from such rigid homopolymer resins do not have sufficient flexibility. A less rigid linear copolymer resin can be obtained by the catalytic method, but such a resin suffers from the same insufficient foaming ability as homopolymers. The temperature at which the use of polyolefin resin foam is possible can be increased by crosslinking. For example, crosslinked foam of low density polyethylene resin can be used at a higher temperature than uncrosslinked foam, but for some applications, using a temperature below 100 ° C is not enough. In addition, crosslinked resin is more expensive to manufacture and is not used in a re-cycle.

Foams made from a mixture of high melting point polyolefin resins (e.g., high density polyethylene and iPP) and low density polyethylene resin (LDPE) are difficult to extrude to low density foam because expansion depends on the transition during curing of the high melting point resin which has poor foaming ability. When applying the crosslinking approach, such a mixture causes another kind of difficulty. In this method, the foaming composition is extruded into the sheet at a low temperature, in which the blowing agent and the crosslinking agent remain substantially unactivated. Often, the required processing temperature for a linear high melting point polyolefin exceeds the temperature that the blowing agent and the crosslinking agent can withstand and can activate them prematurely.

However, depending on the specific purpose, it is not always desirable that the insulating foam be flexible. Rigid foams having high deformation temperatures are also desirable. Rigid insulating foams are often made from alkyl aromatic polymers such as polystyrene, which, due to the influence of the environment, are substantially expanded by carbon dioxide. However, low density foams, such as polystyrene, which expand with carbon dioxide, have small cell sizes.

However, in order for the rigid foam to easily form in a convenient extrusion process and be easy to manufacture, it is necessary that the foam has an increased mesh size. A foam having a small mesh size is not only difficult to extrude to produce a large cross section, but also difficult to process (for example, split into pieces and cut to final sizes). For ease of preparation, it is desirable that the foam has a mesh size of more than 0.4 mm.

Various attempts have been made to obtain alkyl aromatic foams having an increased cell size by incorporating additives that increase the cell size (see, for example, US Pat. Nos. 4,229,396 and 5,489,407). However, conventional cell enlarging additives are difficult to introduce into the extruder, and they tend to influence the temperature of thermal deformation of the foam product.

In addition to foams for insulation having a high deformation temperature, which are either 1) flexible or 2) rigid with increased mesh size, flexible foams that are made from thermoplastic polymers having a T _g above 0 ° C. When used as a cushioning material for packaging or vibration absorption, flexible foam protects the product by absorbing shock energy and vibration in its cellular structure. Energy is absorbed both in the gaseous and in the polymer phase. A foam having cell walls that irreversibly disperse mechanical energy into heat is desirable. The polymer resin dissipates mechanical energy most efficiently at the glass transition temperature (T _g ) of the resin (see, for example, Properties of Polymers, third edition, Chapter 14, "Acoustic Properties", ed. By DW Van Krevelen, Elsevier, Amsterdam-London, New York-Tokyo, 1990). The most common polymer resins, such as polyethylene and polypropylene, are flexible, but have a relatively low T _g that is below 0 ° C and, therefore, are not suitable for use as cushioning materials for packaging and for absorbing vibration.

Thus, in engineering there remains a need for 1) flexible foams having a high deformation temperature; 2) rigid alkylaromatic foams having a high deformation temperature and increased cell size, which are easy to obtain and in which thermal deformation is stable; 3) elastic thermoplastic foams obtained from a thermoplastic polymer having a T _g above 0 ° C.

These needs are met by the present invention. Thus, the present invention relates to polymer foams obtained from a mixture of syndiotactic polypropylene (sPP) resin and a foaming thermoplastic polymer resin.

Thus, in a first embodiment of the present invention, polymer foams are prepared from a mixture of sPP resin and a flexible thermoplastic polymer resin that is flexible and has a high deformation temperature. The polymer resins in accordance with the first embodiment of the present invention are suitable as insulating foams in high ambient temperature conditions where flexible foam is required, as in a number of applications in the automotive industry and for insulating hot water pipes. In addition, since the sPP resin has a T _g of 4 ° C, the polymeric foams according to the first embodiment of the present invention are also suitable as cushioning materials for packaging or as a material that absorbs noise or vibration.

A typical mixed polymer foam in accordance with the first embodiment is:

a mixed polymer foam containing: a) from 0.1 percent to 60 percent by weight of sPP resin; b) from 40 percent to 99.9 percent by weight of a flexible thermoplastic polymer resin;

a mixed polymer foam containing: a) from 10 percent to 50 percent by weight of sPP resin; b) from 50 percent to 90 percent by weight of a flexible thermoplastic polymer resin;

a mixed polymer foam containing: a) from 30 percent to 50 percent by weight of sPP resin; b) from 50 percent to 70 percent by weight of a flexible thermoplastic polymer resin.

In a second embodiment of the present invention, polymeric foams are prepared from a mixture of sPP resin and a rigid thermoplastic polymer resin, which are rigid, have a high deformation temperature and an increased cell size. The additive in the form of sPP resin, which increases the cell size of the rigid thermoplastic polymer foam, is easily introduced into the extruder and does not adversely affect the temperature of thermal deformation of the foam.

Typical mixed polymer foams in accordance with a second embodiment of the present invention are:

a mixed polymer foam containing: a) from 0.1 percent to 60 percent by weight of sPP resin; b) from 40 percent to 99.9 percent by weight of a rigid thermoplastic polymer resin; and

a mixed polymer foam containing: a) 0.2 percent to 5 percent by weight sPP resin: b) 95 percent to 99.8 percent by weight of a rigid thermoplastic polymer resin.

Figure 1 shows a thermogram of a freshly extruded foam of the present invention obtained by differential scanning calorimetry.

Figure 2 shows the thermogram of the foam of the present invention after incubation at 120 ° C for 5 days, obtained by differential scanning calorimetry.

The present invention provides foams obtained from a mixture of sPP resin and a foaming thermoplastic polymer resin. The blended polymeric foams of the present invention possess a combination of the desired properties, which previously was difficult, if not impossible, to achieve.

For example, the first embodiment of the present invention provides polymer foams obtained from a mixture of sPP resin and a flexible thermoplastic polymer resin, which foams are flexible and have a high deformation temperature. Mixed polymer foams in accordance with the first embodiment of the present invention are suitable as insulating foams in high-temperature environments where flexible foam is desired, such as in a number of automotive applications and for insulating hot water pipes. Elastic insulating foams of the first embodiment of the present invention exhibit higher spatial stability than when producing foams only from a flexible thermoplastic polymer resin. As described above, flexible resins having a high thermal deformation temperature are prepared using a flexible thermoplastic polymer resin as a foaming thermoplastic polymer resin in a mixture. Without associating this with any particular theory, it is believed that the addition of sPP resin provides a mixed foam with a high temperature of thermal deformation with little destruction of the expansion of the foam due to the slow crystallization rate of the resin. The slow sPP crystallization rate, which creates problems associated with lengthening the injection cycle, is successfully used in the production of the foams of the present invention. Due to the slow crystallization rate of sPP, the resin does not crystallize at the foaming temperature of the flexible thermoplastic resin, but crystallizes at ambient temperature or during secondary heating after the foam of the first embodiment of the present invention is obtained from the mixture and stabilized. Once crystallized, the sPP resin component provides a mixed foam with a relatively high deformation temperature due to the high melting point (namely 130 ° C.) of the crystals. This phenomenon is demonstrated by differential scanning calorimetry, as shown in FIG. 1 and FIG. 2. Figure 1 shows a thermogram of a foam of the present invention, obtained from 50/50 by weight of a mixture of LDPE resin and sPP resin, immediately after extrusion, obtained by differential scanning calorimetry, showing the endotherm at approximately 113 ° C and the absence of the endotherm at approximately 130 ° C, melting points of sPP crystals. Figure 2 shows the foam thermogram of Figure 1 after being held at approximately 120 ° C for 5 days, showing an endotherm at approximately 113 ° C and an endotherm at approximately 130 ° C, melting point of sPP crystals. The differential scanning calorimetric thermograms shown in FIGS. 1 and 2 show that the LDPE resin and the sPP resin are immiscible and that the sPP resin phase in the mixture crystallizes during heating at approximately 120 ° C.

In addition, the sPP resin as a component of the mixture does not crystallize completely during aging of the foam at ambient temperature, but further crystallization is subsequently observed upon heating. This secondary crystallization can be favorably used in thermoforming a foamed product so that sPP molecules in an amorphous state allow the foam sheet to deform in the form of a template with further crystallization during thermoforming, whereby the shape of the molded product is well preserved. The addition of sPP resin also increases the spatial stability of the flexible foam. For example, it was found that the foam of the present invention, obtained from a mixture of sPP resin and LDPE resin and expanded with isobutane, has greater spatial stability than the foam of LDPE resin expanded with isobutane. This increased spatial stability is surprising given that at least one sPP resin has low crystallinity (about 30 percent) [see Wheat, W.R., "Rheological Explanations for Syndiotactic Polypropylene Behaviors," ANTEC 95 Preprint] and relatively high permeability to gases and vapors [see Schardl, J. et al., "Syndiotactic Polypropylene Overview Clear Impact Polymer," ANTEC 95 Preprint].

In addition, the flexible insulating polymer foam of the first embodiment of the present invention is also suitable as a cushioning material for packaging or a material that absorbs noise and vibration. sPP resin has a T _{g of the} order of 4 ° C-6 ° C and, thus, can be effective in dissipating mechanical energy into heat. However, the sPP resin alone cannot be easily foamed by extrusion. In contrast, the mixture of sPP resin and the flexible thermoplastic polymer resin of the first embodiment of the present invention is not only foaming, but the resulting foam also carries the properties of a separate resin component. Thus, it is expected that the foams obtained from such an immiscible polymer mixture carry different T _g , and thus it is expected that they will favorably contribute to the absorption of noise and vibration over a wide range of frequencies and temperatures.

A second embodiment of the present invention provides polymer foams made from a mixture of sPP resin and a rigid thermoplastic polymer resin, which foams are rigid, have a high deformation temperature and have an increased mesh size. Thus, the mixed polymer foams of the second embodiment of the present invention are suitable for use as insulating foams in areas where foam molding is required. The additive sPP resin, which increases the cell size of the rigid thermoplastic polymer foam, is easily loaded into the extruder and does not affect the temperature of thermal deformation of the foam. Since until now it was not known that polypropylene resins were compatible with at least one rigid thermoplastic polymer resin, such as polystyrene (see, for example, US patent No. 4386187, examples 18 and 22 and US patent 5460818, example 3) , and that expanding the foam of an incompatible polymer mixture is often difficult in the absence of a compatibilizing additive (see, for example, US Pat. No. 4,020,025), it was rather unexpected that adding ax sPP resin to the polystyrene resin does not destroy, but helps expand the polystyrene resins .

In other embodiments of the present invention, the sPP resin and the foaming thermoplastic polymer resin are usually mixed with each other in a weight ratio of from 0.1: 99.9 to 60:40. In a first embodiment, wherein the foaming thermoplastic polymer resin is a flexible thermoplastic polymer resin, a preferred ratio of sPP resin to flexible thermoplastic polymer resin is from 10:90 to 50:50, with a ratio of from 30:70 to 50:50 being preferred. In a second embodiment, wherein the foaming polymer resin is a rigid thermoplastic polymer resin, a preferred ratio between sPP and rigid thermoplastic polymer resin is from 0.1: 99.9 to 5:95.

Suitable sPP resins for use in any embodiment include all substantially (substantially) syndiotactic propylene homopolymers and propylene copolymers with polymerizable monomers. Typical examples include homopolymers of polypropylene, 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 / min to 50 dg / min, and homopolymers and copolymers having a melt flow rate of from 0.1 dg / min to 10 dg / min. Also preferred are sPP resins having a syndiotacticity of greater than 75 percent. An example of a suitable sPP resin is an sPP resin having a melt index of 2 dg / min (as 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. Examples of such sPP resins are the syndiotactic form of copolymer polypropylene resins of the EOD-96-28 and EOD-96-07 categories, available from Fina Oil and Chemical Company.

Thermoplastic resins suitable for use in the present invention include all kinds of thermoplastic polymers that are capable of foaming during the extrusion process. 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 iPPs, with those resins having a melt index from 0.1 to 20 dg / min, and those having a melt index of 0.2 dg / min to 10 dg / min are particularly preferred. In addition, when the flexible thermoplastic polymer resin is an ethylene / vinyl acetate copolymer, a resin with a vinyl acetate content of 5 percent to 30 percent is preferred, and a resin with a vinyl acetate content of 8 percent to 20 percent is particularly preferred. Furthermore, when the flexible thermoplastic resin is iPP, a resin that has a high melt strength when used in an extrusion process with a tangent delta of less than 1.5 is particularly preferred, and a resin with a tangent delta of less than 1.2 is particularly preferred (tangent delta represents is the ratio of the loss modulus to the accumulation modulus determined using a 2.5 mm thick sample and 25 mm diameter at 190 ° C and 1 radian / s oscillation speed, as shown in US Pat. No. 5,527,573. An example of suitable ethylene is / vinyl acetate copolymer resin is an ELVAX460 category resin available from Du Pont-Dow Inc. An example of a suitable iPP resin is a high melt strength PROP-FAX PF-814 category IPP resin available from Montell Polyolefins Co. NV. Examples of a rigid thermoplastic polymer resin, alkyl aromatic resins such as polystyrene resin are suitable for use in the second embodiment of the present invention An example of a suitable polystyrene for use in the second embodiment of the present invention is polystyrene having medium th molecular weight less than 240,000.

Optionally, a nucleating agent may be added to the foaming mixture. The amount of nucleating agent used to make the foams of the present invention varies depending on the desired mesh size, foaming temperature and nucleating composition. Suitable nucleating agents include calcium carbonate, barium stearate, calcium stearate, talc, clay, titanium dioxide, silicon dioxide, barium stearate, kieselguhr, a mixture of citric acid and sodium bicarbonate. When using them, the amount of nucleating agent used can range from 0.01 to 5 parts by weight per hundred parts by weight of a polymer resin mixture (parts per hundred parts).

Foaming agents suitable for preparing the present foams 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 blowing agents include carbon dioxide, nitrogen, argon, water, air, and helium. Organic blowing agents include aliphatic hydrocarbons having 1-6 carbon atoms, aliphatic alcohols having 1-3 carbon atoms, and fully and partially halogenated aliphatic hydrocarbons having 1 to 4 carbon atoms. Aliphatic hydrocarbons include methane, ethane, propane, n-butane, isobutane, n-pentane and isopentane, neopentane. Aliphatic alcohols include methanol, ethanol, n-propanol and isopropanol. Fully and partially halogenated aliphatic hydrocarbons include chlorocarbons, fluorocarbons and chlorofluorocarbons. Chlorocarbons suitable for use in the present invention include methyl chloride, methylene chloride, ethyl chloride and 1,1,1-trichloroethane. Fluorocarbons suitable for use in the present invention include methyl fluoride, methylene fluoride, ethyl fluoride, 1,1-difluoroethane (HFC-152a), 1,1,1-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 . Partially halogenated chlorofluorocarbons suitable for use in the present 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 may also be used, but they are not preferred for environmental reasons. Chemical blowing agents for use in the present invention include azodicarbonamide, azodiisobutyronitrile, benzenesulfonhydrazide, 4,4-hydroxybenzenesulfonylsemicarbazide, p-toluenesulfonylsemicarbazide, N, N′-dimethyl-N, sodium N′-dinitrosoterephthinamide bicarbonate, and tri-sodium bicarbonate, and . It is also contemplated that mixtures of all of these blowing agents are within the scope of the present invention. The form of the most suitable blowing agents depends on the method used to produce the foam base and on the desired foam density. Preferred blowing agents for the extrusion process and the batch process for producing molding balls are physical blowing agents, with volatile organic blowing agents being preferred. Preferred blowing agents for the process for producing crosslinked foam are degradable blowing agents and nitrogen.

The amount of blowing agent included in the melt of the polymeric material to produce a foaming gel is from 0.1 to 5, preferably from 0.4 to 4, and most preferably from 0.9 to 3 grammoles per kilogram of polymer.

Furthermore, in order to improve the insulating ability, the present foams may optionally contain an infrared absorber (transmission blocker) such as carbon black, graphite and titanium dioxide. When using an infrared absorber, it can be contained in the foam in an amount of 0.1-25 weight percent and, more preferably, 4.0-10.0 weight percent, based on the weight of the polymer mixture. Carbon black can be of any type known in the art, such as furnace black, thermal black, acetylene black and pipe black. A preferred carbon black is thermal black. Preferred thermal carbon black has an average particle size of 150 nanometers or more.

Preferably, the foams of the present invention have spatial stability. Although the sPP resin itself acts as a stability regulating agent, in some cases it is desirable to include an additional stability regulating agent to further increase the spatial stability of the foam of the present invention. For example, an additional stability control agent to the sPP resin may be desirable when the sPP resin is mixed with polyethylene or ethyl / vinyl acetate copolymer resin in an amount of less than 30 percent and the mixture expands with isobutane. A stability regulating agent may be particularly desirable in the preparation of products of a substantially closed cellular structure in the form of a thick (thicker than 4 mm) sheet and strip (thinner than 12 mm) from the above mixture. In contrast, an additional stability regulating agent may not be necessary when foams with substantially open cells are produced.

Spatial stability is measured as a percentage of the volume of the foam during its aging from the initial volume of the foam, measured within 30 seconds after expansion of the foam. Using this definition, a foam that retains 80 percent or more of the initial volume for a month is satisfactory, while a foam that retains 85 percent or more is preferred, and a foam that retains 90 percent or more is particularly preferred. Volume is measured in a suitable way, such as cubic displacement of water.

Preferred stability control agents include C _10-24 fatty acid amides and esters. Such agents are disclosed in US Pat. Nos. 3,644,230 and 4,214,054. Most preferred agents include stearyl stearamide, glycerol monostearate, glycerol monobenate and sorbitan monostearate. Typically, such stability control agents are used in an amount of from 0.1 to 10 parts per hundred parts of polymer.

Various additives can also be included in these foams, such as inorganic fillers, pigments, antioxidants, acid scavengers, ultraviolet absorbers, flame retardants, processing aids that improve processing and extrusion.

The blended polymeric foams of the present invention can also be prepared using techniques well known to those skilled in the art that include an extrusion process as well as a batch process using a degradable blowing agent and crosslinking, with the extrusion process being preferred.

The blended polymer foams of the present invention can be crosslinked or non-crosslinked. For excellent guidance on how to obtain the structure of polymer foam and its processing, see S.R. Park, "Polyolefin Foam", Chapter 9, Handbook of Polymer Foams and Technology, edited by D. Klempner and K.C. Frisch, Hanser Publishers, Vienna, New York, Barcelona, 1991.

Non-crosslinked foams of the present invention can be obtained using a conventional extrusion method for producing foam. A foam structure is usually obtained by heating a pre-mixed mixture of an sPP resin and a thermoplastic polymer resin (i.e. a polymeric material) to form a plasticized or molten polymeric material by incorporating a blowing agent therein to form a foaming gel and extruding the gel through an extruder head to form a foamed product. Prior to mixing with the blowing agent, the polymer material is heated to its temperature T _g or higher, or to its melting point. The blowing agent can be introduced or mixed into the molten polymer material by any methods known in the art, such as using an extruder, mixer or mixer. The blowing agent is mixed with the molten polymer material at an elevated pressure sufficient to prevent significant expansion of the molten polymer material and for general homogeneous dispersion of the blowing agent therein. The nucleating agent may optionally be mixed into the molten polymer or mixed dry with the polymer material prior to plasticization or melting. The foaming gel is usually cooled to a lower temperature in order to optimize the physical characteristics of the foam structure. The gel is then extruded or transported through the die head of the desired shape into a low or low pressure zone to form a foam structure. In the low-pressure zone, the pressure is lower than in the zone where the foaming gel was before extrusion through the die. The reduced pressure may be above atmospheric or below atmospheric (vacuum), but atmospheric pressure is preferred.

The uncrosslinked foams of the present invention can be formed into bonded filaments by extruding a pre-blended mixture of sPP resin and a thermoplastic polymer resin (i.e., polymeric material) through an extruder die with a large number of holes. The holes are arranged so that during the extrusion process contact is made between adjacent flows of the molten extrudate and that the contacting surfaces adhere to each other sufficiently to obtain a uniform foam structure. The molten extrudate streams emerging from the die take the form of filaments or profiles, which are preferably foamed, joined and stick together to form a uniform structure. It is desirable that the individual connected yarns or profiles remain stuck together in a homogeneous structure to prevent delamination of the yarns under the influence of stresses during the production, molding and use of foam. A device and method for producing a foam structure in the form of joined threads are described in US Pat. Nos. 3,573,152 and 4,324,720.

The present foam structure can also be molded into non-cross-linked foam balls suitable for molding into articles. Foamed balls can be obtained by extrusion or batch processes. In the extrusion method, the foam strands leaving the die head with a large number of holes connected to a conventional foam extrusion apparatus are granulated to form foam balls. The foam balls are heated, if necessary, to the melting point of the sPP resin, so that the sPP molecules can crystallize, thereby forming a pseudogrid structure, which gives the foam balls resistance to thermal degradation. In a batch process, individual resin particles, such as granular resin beads, are suspended in a liquid medium in which they are substantially insoluble, such as water; they are impregnated with a blowing agent by introducing a blowing agent into a liquid medium at elevated pressure and temperature in an autoclave or other pressure vessel and are quickly discharged to atmospheric or reduced pressure to expand to produce foamed balls. This method is well described in US patent No. 4379859 and 4464484.

Crosslinked foams of the present invention can be obtained either by crosslinking the foam using a degradable blowing agent, or by a conventional extrusion method.

Using a crosslinking method using a degradable blowing agent, the crosslinked foams of the present invention can be prepared by mixing and heating a pre-mixed mixture of sPP resin and a thermoplastic polymer resin (i.e. a polymeric material) with a degradable chemical blowing agent to produce a foaming plasticized or molten polymer material, extruding the foaming foam molten polymer material through the head, including crosslinking in the molten floor dimensional material and bringing the molten polymeric material to an elevated temperature to form the foam structure. The polymer material and the chemical blowing agent can be melt blended or mixed by any methods known in the art, for example using an extruder, mixer or mixer. The chemical blowing agent is mixed with the polymer material, preferably in dry form, before heating the polymer material to a molten state, but can also be added to the polymer material in the molten phase. Crosslinking may be caused by the addition of a crosslinking agent or by exposure to radiation. The induction of crosslinking and exposure to elevated temperatures for foaming or expansion can occur simultaneously or sequentially. If a crosslinking agent is used, it is introduced into the polymeric material in the same manner as the chemical blowing agent. In addition, if a crosslinking agent is used, the foaming molten polymer material is heated or exposed to a temperature preferably below 150 ° C. to prevent decomposition of the crosslinking agent or blowing agent and to prevent premature crosslinking. When using radiation crosslinking, the foaming molten polymer material is heated or subjected to a temperature, preferably below 160 ° C., to prevent decomposition of the blowing agent. The foaming molten polymer is extruded or transported through an extruder die of a desired shape to form a foam structure. The foam structure is then crosslinked and exposed to elevated or high temperature (typically 150 ° C-250 ° C), for example in a furnace, to form a foam structure. When using radiation crosslinking, the foam structure is irradiated to crosslink the polymer material, which is then exposed to elevated temperature, as described above. Such a structure can be successfully obtained in the form of a sheet or thin strip in accordance with the above method, using either a crosslinking agent or radiation.

In addition to using a crosslinking agent or radiation in the method of crosslinking the foam using a degradable blowing agent, crosslinking can also be carried out using silane crosslinking, as described in C. P. Park, Supra, Chapter 9.

Crosslinked foams of the present invention can also be obtained in the form of a continuous flat structure by extrusion using an elongated (long-land) head of the extruder, as described in GB 2145961A. In this method, the polymer, the degradable blowing agent and the crosslinking agent are mixed in an extruder, heating the mixture to allow the polymer to crosslink and decompose the blowing agent in an elongated head; molded and removed from the foam structure through the head, the foam structure and the head contact being lubricated with a suitable lubricant.

The crosslinked foams of this invention can also be molded into crosslinked foam balls suitable for molding into articles. To obtain foamed balls, discrete resin particles, such as granular resin balls, are suspended in a liquid medium in which they are substantially insoluble, such as water; impregnated with a crosslinking agent and a blowing agent at elevated pressure and temperature in an autoclave or other pressure vessel; quickly transferred to atmospheric or reduced pressure to expand and form foam balls. A feature of this method is that the polymer beads are impregnated with a blowing agent, cooled, discharged from the vessel, and then expand when heated or using steam. In a modification of this method, the suspended beads can be impregnated with a styrene monomer along with a crosslinking agent to form a copolymer grafted onto the polymer material. The blowing agent can impregnate the resin beads in suspension or alternatively in an anhydrous state. The expandable balls are then expanded by steam heating and formed in the usual molding process for expandable polystyrene foam balls.

The foam balls can then be molded by any method known in the art, such as loading the foam balls into a ball compression mold, and heating the balls, for example with steam, to cause the balls to join and weld together to form an article. Optionally, the balls may be preheated with air or other blowing agents prior to loading into the mold. For excellent techniques for the above method and molding methods, see S.R. Park, Supra, pp. 227-233, US Patent Nos. 3886100, 3959189, 4168353 and 4429059. Foamed balls can also be obtained by preparing a mixture of polymer, a crosslinking agent and degradable mixtures in a suitable mixer or extruder, and molding the mixture into balls and heating the balls for crosslinking and expansion.

There is another way to obtain stitched balls suitable for molding into products. The polymer material is melted and mixed with a physical blowing agent in a conventional extrusion apparatus to produce a substantially continuous foamed filament. The foamed yarn is granulated or pelletized to form foamed beads. Then the foamed balls are crosslinked using radiation. The crosslinked foam balls can then be joined and molded to produce various products, as described above for other methods for producing foam balls. For a further description of this method, see US Pat. No. 3,616,365 and C. P. Park, Supra, pp. 224-228.

In addition to the above, a silane crosslinking technique can be used in the extrusion process. For a description of this method, see S.R. Park, Supra, Chapter 9 and U.S. Patent No. 4,714,716. Using the silane crosslinking method together with the conventional extrusion method, a vinyl functional silane or an azidofunctional silane is grafted onto the polymer and extruded to form a foam. The extruded foam is then exposed to warm moist air to effect crosslinking.

Crosslinked foams of the present invention can be obtained in the form of a foam sheet or a foam bundle, or by any method described in C. Park, Supra, Chapter 9, pages 229-235.

Typically, having substantially closed cells in nature, the foams of the present invention may have open cells. In addition, the foams of the present invention have a mesh size (namely, mesh diameter) of from 0.01 mm to 10 mm, with 0.1-5 mm being preferred, and 0.4-3 mm being particularly preferred. In addition, the foams of the present invention have a density of from 9 kg / m ³ to 200 kg / m ³ , with a density of 11 kg / m ³ to 100 kg / m ³ being preferred, and a density of 15 kg / m ³ to 50 kg / m ³ .

The foams of the present invention can take any physical configuration known in the art, such as extruded sheets, rods, planks, profiles / beads and bundles. The foam structure can also be formed by molding expandable balls into any of the above configurations or any other configurations.

Thus, in accordance with the foregoing, the following foams are typical foams of the present invention:

a mixed polymer foam containing: a) from 0.1 percent to 60 percent by weight of sPP resin; b) from 40% to 99.9% by weight of a foaming thermoplastic polymer resin;

a mixed polymer foam containing: a) from 0.1% to 60% by weight of sPP resin; b) from 40% to 99.9% by weight of a foaming thermoplastic polymer resin, the foam having a density of from 9 kg / m ³ to 300 kg / m ³ , preferably from 11 kg / m ³ to 100 kg / m ³ and most preferably from 15 kg / m ³ to 50 kg / m ³ ;

a mixed polymer foam containing: a) from 0.1% to 60% by weight of sPP resin; b) from 40% to 99.9% by weight of a flexible thermoplastic polymer resin;

a mixed polymer foam containing: a) from 0.1% to 60% by weight of sPP resin; b) from 40% to 99.9% by weight of a flexible thermoplastic polymer resin, the foam having a density of from 9 kg / m ³ to 300 kg / m ³ , preferably from 11 kg / m ³ to 100 kg / m ³ and most preferably from 15 kg / m ³ to 50 kg / m ³ ;

a mixed polymer foam containing: a) from 0.1% to 60% by weight of sPP resin; b) from 40% to 99.9% by weight of a rigid thermoplastic polymer resin;

a mixed polymer foam containing: a) from 0.1% to 60% by weight of sPP resin; b) from 40% to 99.9% by weight of a rigid thermoplastic polymer resin, the foam having a density of from 9 kg / m ³ to 300 kg / m ³ , preferably from 11 kg / m ³ to 100 kg / m ³ and most preferably from 15 kg / m ³ to 50 kg / m ³ ;

a mixed polymer foam containing: a) from 0.1% to 60% by weight of sPP resin; b) from 40% to 99.9% by weight of a flexible polyolefin resin;

a mixed polymer foam containing: a) from 0.1% to 60% by weight of sPP resin; b) from 40% to 99.9% by weight of a flexible polyolefin resin, the foam having a density of from 9 kg / m ³ to 300 kg / m ³ , preferably from 11 kg / m ³ to 100 kg / m ³ , most preferably from 15 kg / m ³ to 50 kg / m ³ ;

a mixed polymer foam containing: a) from 0.1% to 60% by weight of sPP resin; b) from 40% to 99.9% by weight of LDPE resin;

a mixed polymer foam containing: a) from 0.1% to 60% by weight of sPP resin; b) from 40% to 99.9% by weight of LDPE resin, the foam having a density of from 9 kg / m ³ to 300 kg / m ³ , preferably from 11 kg / m ³ to 100 kg / m ³ , most preferably from 15 kg / m ³ up to 50 kg / m ³ ;

a mixed polymer foam containing: a) from 0.1% to 60% by weight of sPP resin, which is a propylene homopolymer; b) from 40% to 99.9% by weight of a foaming thermoplastic polymer resin;

a mixed polymer foam containing: a) from 0.1% to 60% by weight of sPP resin, which is a propylene homopolymer; b) from 40% to 99.9% by weight of a foaming thermoplastic polymer resin, the foam having a density of from 9 kg / m ³ to 300 kg / m ³ , preferably from 11 kg / m ³ to 100 kg / m ³ , most preferably from 15 kg / m ³ to 50 kg / m ³ ;

a mixed polymer foam containing: a) from 0.1% to 60% by weight of sPP resin, which is a propylene homopolymer; b) from 40% to 99.9% by weight of a flexible thermoplastic polymer resin;

a mixed polymer foam containing: a) from 0.1% to 60% by weight of sPP resin, which is a propylene homopolymer; and b) from 40% to 99.9% by weight of a flexible thermoplastic polymer resin, the foam having a density of from 9 kg / m ³ to 300 kg / m ³ , preferably from 11 kg / m ³ to 100 kg / m ³ , most preferably from 15 kg / m ³ to 50 kg / m ³ ;

a mixed polymer foam containing: a) from 0.1% to 60% by weight of sPP resin, which is a propylene homopolymer; b) from 40% to 99.9% by weight of a rigid thermoplastic polymer resin;

a mixed polymer foam containing: a) from 0.1% to 60% by weight of sPP resin, which is a propylene homopolymer; b) from 40% to 99.9% by weight of a rigid thermoplastic polymer resin, the foam having a density of from 9 kg / m ³ to 300 kg / m ³ , preferably from 11 kg / m ³ to 100 kg / m ³ , most preferably from 15 kg / m ³ to 50 kg / m ³ ;

a mixed polymer foam containing: a) from 0.1% to 60% by weight of sPP resin, which is a propylene homopolymer; b) from 40% to 99.9% by weight of a flexible polyolefin resin;

a mixed polymer foam containing: a) from 0.1% to 60% by weight of sPP resin, which is a propylene homopolymer; b) from 40% to 99.9% by weight of a flexible polyolefin resin, the foam having a density of from 9 kg / m ³ to 300 kg / m ³ , preferably from 11 kg / m ³ to 100 kg / m ³ , most preferably from 15 kg / m ³ to 50 kg / m ³ ;

a mixed polymer foam containing: a) from 0.1% to 60% by weight of sPP resin, which is a propylene homopolymer; b) from 40% to 99.9% by weight of LDPE resin;

a mixed polymer foam containing: a) from 0.1% to 60% by weight of sPP resin, which is a propylene homopolymer; b) from 40% to 99.9% by weight of LDPE resin, the foam having a density of from 9 kg / m ³ to 300 kg / m ³ , preferably from 11 kg / m ³ to 100 kg / m ³ , most preferably from 15 kg / m ³ up to 50 kg / m ³ ;

a mixed polymer foam containing: a) from 0.1% to 60% by weight of sPP resin, which is a propylene homopolymer having a syndiotacticity of more than 75%; b) from 40% to 99.9% by weight of a foaming thermoplastic polymer resin;

a mixed polymer foam containing: a) from 0.1% to 60% by weight of sPP resin, which is a propylene homopolymer having a syndiotacticity of more than 75%; b) from 40% to 99.9% by weight of a foaming thermoplastic polymer resin, the foam having a density of from 9 kg / m ³ to 300 kg / m ³ , preferably from 11 kg / m ³ to 100 kg / m ³ , most preferably from 15 kg / m ³ to 50 kg / m ³ ;

a mixed polymer foam containing: a) from 0.1% to 60% by weight of sPP resin, which is a propylene homopolymer having a syndiotacticity of more than 75%; b) from 40% to 99.9% by weight of a flexible thermoplastic polymer resin;

a mixed polymer foam containing: a) from 0.1% to 60% by weight of sPP resin, which is a propylene homopolymer having a syndiotacticity of more than 75%; b) from 40% to 99.9% by weight of a flexible thermoplastic polymer resin, the foam having a density of from 9 kg / m ³ to 300 kg / m ³ , preferably from 11 kg / m ³ to 100 kg / m ³ , most preferably from 15 kg / m ³ to 50 kg / m ³ ;

a mixed polymer foam containing: a) from 0.1% to 60% by weight of sPP resin, which is a propylene homopolymer having a syndiotacticity of more than 75%; b) from 40% to 99.9% by weight of a rigid thermoplastic polymer resin;

a mixed polymer foam containing: a) from 0.1% to 60% by weight of sPP resin, which is a propylene homopolymer having a syndiotacticity of more than 75%; b) from 40% to 99.9% by weight of a rigid thermoplastic polymer resin, the foam having a density of from 9 kg / m ³ to 300 kg / m ³ , preferably from 11 kg / m ³ to 100 kg / m ³ , most preferably from 15 kg / m ³ to 50 kg / m ³ ;

a mixed polymer foam containing: a) from 0.1% to 60% by weight of sPP resin; b) from 40% to 99.9% by weight of ethylene / vinyl acetate copolymer resin;

a mixed polymer foam containing: a) from 0.1% to 60% by weight of sPP resin; b) from 40% to 99.9% by weight of ethylene / vinyl acetate copolymer resin, the foam having a density of from 9 kg / m ³ to 300 kg / m ³ , preferably from 11 kg / m ³ to 100 kg / m ³ , most preferably from 15 kg / m ³ to 50 kg / m ³ ;

a mixed polymer foam containing: a) from 0.1% to 60% by weight of sPP resin; b) from 40% to 99.9% by weight of the iPP resin; a mixed polymer foam containing: a) from 0.1% to 60% by weight of sPP resin; b) from 40% to 99.9% by weight of the iPP resin, the foam having a density of from 9 kg / m ³ to 300 kg / m ³ , preferably from 11 kg / m ³ to 100 kg / m ³ , most preferably from 15 kg / m ³ up to 50 kg / m ³ ;

a mixed polymer foam containing: a) from 0.1% to 60% by weight of sPP resin; b) from 40% to 99.9% by weight of an alkyl aromatic polymer resin;

a mixed polymer foam containing: a) from 0.1% to 60% by weight of sPP resin; b) from 40% to 99.9% by weight of an alkyl aromatic polymer resin, the foam having a density of from 9 kg / m ³ to 300 kg / m ³ , preferably from 11 kg / m ³ to 100 kg / m ³ , most preferably from 15 kg / m ³ to 50 kg / m ³ ;

a mixed polymer foam containing: a) from 0.1% to 60% by weight of sPP resin; b) from 40% to 99.9% by weight of a polystyrene polymer resin;

a mixed polymer foam containing: a) from 0.1% to 60% by weight of sPP resin; b) from 40% to 99.9% by weight of a polystyrene polymer resin, the foam having a density of from 9 kg / m ³ to 300 kg / m ³ , preferably from 11 kg / m ³ to 100 kg / m ³ , most preferably from 15 kg / m ³ to 50 kg / m ³ ;

The following are examples of the present invention, which should not be construed as limiting the scope of the invention. Unless otherwise specified, all percentages, parts or proportions are by weight.

The following examples of foams obtained from a mixture of sPP resin and a foaming thermoplastic polymer resin were obtained using a 19 mm screw extruder having additional zones for mixing and cooling at the end of conventional sequential feeding, melting and measuring zones. An opening for introducing a blowing agent is provided on the extruder body between the homogenization and mixing zones. At the end of the cooling zone, the output part of the forming channel of the extruder head is connected, having a rectangular hole. The height of the hole is adjustable, while the width is set to 38 mm.

Example 1

Obtaining foam from sPP resin and LDPE resin

Example 1 demonstrates the production of a foam in accordance with the present invention, which is obtained from 50/50 by weight of a mixture of LDPE resin and sPP resin, which is expanded using isobutane as a blowing agent in the extrusion process. Tests carried out with the resulting foam in accordance with this example show that the polymer mixture is capable of forming foam by extrusion and that the foam is spatially stable and can withstand relatively high temperatures.

Get a 50/50 by weight granular mixture of LDPE resin having a melt index of 0.7 dg / min (determined according to ASTM D-1238 at 190 ° C / 2/16 kg), a density of 0.923 g / cm ³ and a melting point of 115 ° C (determined by differential scanning calorimetry (DSC) at the peak of the endotherm during heating at 10 ° C / min) and the syndiotactic form of a copolymer of polypropylene resin of category EOD 96-28 (available from Fina Oil and Chemical Company) having a melt flow rate of 2 dg / min (determined using ASTM D-1238 at 230 ° C / 1.16 kg), a density of 0.88 g / cm ³ and a melting point of 130 ° C.

A mixture of granular resins and additives consisting of talcum powder (nucleating agent) in an amount of 0.2 parts per hundred parts of resin (hs) and an antioxidant grade Irganox 1010 (available from Ciba-Geigy Corp) in an amount of 0.1 hs is fed to the extruder with a total 3.26 kilograms per hour (kg / h). The following extruder zone temperatures are maintained: 160 ° C in the feed zone, 190 ° C in the melting zone, 200 ° C in the homogenization zone, and 200 ° C in the mixing zone. Isobutane (a blowing agent) is introduced into the mixing zone at the same speed of 414 g / h (12.7 hs). The temperature of the cooling zone gradually decreases, and the hole of the head is set in such a way as to obtain a foam of good quality. For example, at a temperature in the cooling zone of 107 ° C, a temperature in the head of 105 ° C and a hole diameter of 1.0 mm, excellent polystyrene foam is obtained mainly with closed cells (open cell content is approximately 32 percent according to ASTM D-2856 Procedure A). The foam has a density of 24.8 kg / m ³ , a mesh size of 1.2 mm, a thickness of approximately 12 mm and a width of approximately 19 mm.

Test 1

The spatial stability of the foam from example 1

A foam sample of approximately 15 cm length is cut from the foam just obtained in Example 1, and the volume of the foam sample is measured approximately 2 minutes after extrusion and then periodically during aging at ambient temperature. The foam exhibits excellent spatial stability without shrinkage of its volume 30 minutes after extrusion, when shrinkage was about 97 percent of the original volume. Within one day, the foam is fully restored to more than 100 percent of its original volume.

Test 2

Thermal stability of the foam of example 1

On the first day after extrusion from the foam obtained in example 1, cut a sample with a length of 8 cm. The sample is placed in a convection oven, maintaining a temperature of 121 ° C, and periodically measure its volume. The foam volume as a percentage of the initial volume is presented as a function of the exposure time in the furnace, as shown in table 1.

As you can see, the foam shrinks to 70 percent of the original volume and retains this volume after prolonged exposure to high temperature, while polyethylene foam based on the same LDPE resin, which was used in example 1, is completely destroyed at the same temperature. The high temperature resistance of the mixed foam is also confirmed by the DSC thermogram shown in FIG. 1 and FIG. 2 discussed above. Figure 1 and Figure 2 compares the DSC thermograms of the newly extruded foam (Figure 1) and the foam after being in the furnace (Figure 2). Subjected to aging in the oven, the foam is exposed to a temperature of 121 ° C for five days. The foam aged in the oven shows a sharp peak at about 130 ° C, except for a peak at about 113 ° C. In contrast, the freshly extruded foam does not show a strong peak at 130 ° C, which is the melting peak of sPP crystals. The thermogram shows that the LDPE resin and the sPP resin used in Example 1 are immiscible and that the sPP resin phase in the mixture crystallizes during heating at 121 ° C.

Test 3

The thermoforming properties of the foam of example 1

Two 5-centimeter samples are cut from the foam obtained in example 1 and heated in a furnace with a temperature of 121 ° C for 5 minutes. Then, heated foam samples are removed from the oven and immediately placed one on top of the other, applying soft pressure to one another. The foam samples adhere well without noticeable shrinkage, showing that foam balls suitable for molding can be formed from the foam of Example 1 and that the foam of Example 1 can then be thermoformed.

Comparative Example A.

Obtaining foam obtained from sPP resin

The foam of Comparative Example A is prepared for testing the expandability of a foam obtained only from sPP resin.

A copolymer polypropylene resin of category EOD 96-28 (available from Fina Oil and Chemical Company) having a melt flow rate of 2 dg / min (determined according to ASTM D-1238 at 230 ° C / 2.16 kg), density 0.88 g / cm ³ and a melting point of 130 ° C, mixes with 0.4 ppm talcum powder (nucleating agent) and 0.1 ppm Igranox 1010 (available from Ciba-Geigy Corp). The following extruder zone temperatures are maintained: 160 ° C in the feed zone, 190 ° C in the melting zone, 200 ° C in the homogenization zone, and 200 ° C in the mixing zone. Isobutane (blowing agent) is introduced into the mixing zone with a total speed of 414 g / h (12.7 hs). The temperature of the cooling zone is gradually lowered from 160 ° C to 80 ° C, decreasing by approximately 5 ° C and keeping this temperature for 5-10 minutes to see if a good quality foam can be obtained. The temperature of the head is maintained the same as in the cooling zone. The diameter of the head hole is maintained at 0.8 mm when the temperature drops in the cooling zone to 95 ° C. Below 95 ° C, the head opens slightly wider to give increased pressure.

Test 4

Foaming ability of sPP resin from comparative example A

The melt from comparative example A above does not expand at all at temperatures below 95 ° C. At temperatures above 95 ° C, the foam expands slightly, but immediately contracts. At 80 ° C, the extruder pressure rises sharply, indicating that the melt is too viscous and freezes in the cooling zone. A further decrease in the cooling temperature cannot be allowed. Conclusion: sPP resin alone cannot expand into a stable foam by extrusion.

Example 2 and Comparative Example B

Obtaining a mixed foam of sPP resin and LDPE resin

Example 2 shows the production of a foam in accordance with the present invention, which is obtained from a mixture of LDPE resin and sPP resin, and the percentage level of sPP resin varies to check the effect of the level of sPP resin in the mixture on the foaming properties and spatial stability of the foam. Comparative example B is a foam obtained only from LDPE resin.

As shown in table 2, granular mixtures are prepared in the prescribed ratio from LDPE resin having a melt index of 0.7 dg / min (determined according to ASTM D-1238 at 190 ° C / 2.16 kg), density 0.923 g / cm ³ and a melting point of 115 ° C (determined by differential scanning calorimetry (DSC) at the peak of the endotherm during heating at 10 ° C / min), and the syndiotactic form of a copolymer polypropylene resin of category EOD 96-07 (available from Fina Oil and Chemical Company), having a melt flow rate of 2 dg / min (determined according to ASTM D-1238 at 230 ° C / 2.16 kg), a density of 0.88 g / cm ³ and melting point 130 ° C.

A mixture of granular resin and 0.2 ppm talc powder (nucleating agent) is fed into the extruder with a total speed of 3.1 kg / h (due to the difference in feed characteristics between the mixtures, the actual extrusion rate slightly differs by approximately 3 kg / h-3.2 kg / hour, despite the fact that an attempt is made to maintain the same speed by adjusting the speed of rotation of the screw). The following temperatures are maintained in the extruder zones: 160 ° C in the feed zone, 190 ° C in the melting zone, 200 ° C in the homogenization zone, and 220 ° C in the mixing zone. The temperature of the cooling zone is maintained, as shown in table 2. Isobutane (blowing agent) is introduced into the mixing zone at the speed indicated in table 2. The temperature of the cooling zone is gradually reduced, and the diameter of the head opening is adjusted to obtain a good quality foam. The head temperature is maintained at 110 ° C for comparative example B, examples 2.1-2.3 and 105 ° C for example 2.3 and 2.5. Foam samples are taken at the optimum temperature of the cooling zone for each sample, as shown in table 2, and with a hole diameter of the head, which varies from 1.1 mm to 1.2 mm.

Data on the spatial stability of the foam are summarized in table 2 along with the density, size of the cells and data on the openness of the cells.

As shown in Table 2, a good quality foam is obtained from a preparation containing up to 40 percent sPP resin. The mixture in a ratio of 50/50 LDPE / sPP at a selected cooling temperature of 107 ° C looks slightly hot. The foam thickness ranges from 6.1 mm to 8.2 mm, and the foam width ranges from 14.7 mm to 18.4 mm. A sample of approximately 15 cm in length is cut off from each foam foam just obtained, and the volume of the foam sample is measured approximately 2 minutes after extrusion and then periodically during aging at ambient temperature.

Conclusions:

The mixture tends to give larger mesh sizes than pure LDPE resin. Mixtures having 40 and 50 percent sPP tend to produce more open cells. When sPP resin is added, the foam exhibits better spatial stability. A mixture containing 30 percent or more sPP provides a foam having satisfactory spatial stability, with a minimum foam volume of more than 89 percent during aging.

Example 3 and comparative example C

Obtaining a mixed foam of sPP resin and LDPE resin

Example 3 demonstrates the production of a foam in accordance with the present invention, which is obtained from a mixture of LDPE resin and sPP resin, the level of blowing agent being varied in order to determine whether a high level of blowing agent can improve the foaming of a mixture having a high level of sPP resin. The temperature of the cooling zone is also lowered in order to determine its effect on the expansion of the foam.

As shown in table 3, in the prescribed ratio, granular mixtures are prepared from LDPE resin having a melt index of 0.7 dg / min (determined according to ASTM D-1238 at 190 ° C / 2.16 kg), density 0.923 g / cm ³ and a melting point of 115 ° C (determined by differential scanning calorimetry (DSC) at the peak of the endotherm during heating at 10 ° C / min), and the syndiotactic form of a copolymer polypropylene resin of category EOD 96-07 (available from Fina Oil and Chemical Company) having a melt flow rate of 2 dg / minute (determined according to ASTM D-1238 at 230 ° C / 2.16 kg), density 0.88 g / cm ³ Melting point 130 ° C.

A mixture of granular resin and 0.2 ppm talc powder (nucleating agent) is fed into the extruder with a total speed of 3.1 kg / h (due to the difference in feed characteristics between the mixtures, the actual extrusion rate slightly differs by approximately 3 kg / h-3.2 kg / hour, despite the fact that an attempt is made to maintain the same speed by adjusting the speed of rotation of the screw). The following temperatures are maintained in the extruder zones: 160 ° C in the loading zone, 190 ° C in the melting zone, 200 ° C in the homogenization zone, and 220 ° C in the mixing zone. The temperature of the cooling zone is maintained, as shown in table 3, and isobutane (blowing agent) is introduced into the mixing zone in the amounts indicated in table 3. The temperature of the cooling zone is gradually reduced, and the opening of the matrix is adjusted to obtain good quality foam. The head temperature is maintained at 110 ° C for comparative example C, examples 3.1 and 3.2, and 100 ° C for example 3.3. Foam samples are taken at the optimum temperature of the cooling zone for each sample, as shown in table 3, and with a hole diameter of the head, which varies from 1.1 mm to 1.2 mm.

The spatial stability data for the foam is summarized in table 3 along with the density, cell size, and cell openness data.

As shown in table 3, good foams are obtained from mixtures containing up to 50 percent sPP resin. A mixture with a ratio of 40/60 LDPE / sPP is at the boundary of the possibility of obtaining a foam. In order to obtain a foam from the mixture, the temperature of the cooling zone should be reduced to 82 ° C. Polyfoam is extremely satisfactory with a high level of open cells. All foams were relatively low in density, reflecting a high level of blowing agent. It is shown that the apparent content of open polystyrene cells is relatively high, more than 36 percent. The ASTM D-2856-A open cell method tends to overestimate the content of open flexible foam cells. The foams obtained in these examples have a lower density and lower modulus than the same indices in Example 2, which results in a larger number of errors in the measurements of the content of open cells. One explanation for this reevaluation of open cells is seen from the spatial stability data for LDPE foam. Despite the relatively high content of visible open cells (41 percent), the foam shrinks by as much as 50 percent during aging and recovers relatively slowly.

Example 4 and comparative example D

Obtaining foam from a mixture of sPP resin and ethylene / vinyl acetate copolymer resin

Example 4 demonstrates the production of a foam in accordance with the present invention, which is obtained from a mixture of ethylene / vinyl acetate copolymer (EVA) resin and various amounts of sPP resin in order to determine the effect of the level of sPP resin on foam formation and spatial stability of the foam. Comparative Example D is prepared only from EVA resin.

As shown in table 4, in the prescribed ratio, granular mixtures are prepared from Elvax 460 resin (supplied by Du Pont-Dow Inc.) having a melt index of 2.5 dg / min (determined according to ASTM D-1238 at 230 ° C / 2 , 16 kg), a density of 0.941 g / cm ³ and a melting point of 88 ° C, and a syndiotactic form of a copolymer polypropylene resin of category EOD 96-07 (available from Fina Oil and Chemical Company) having a melt flow rate of 2 dg / min, density 0 88 g / cm ³ and a melting point of 130 ° C.

A mixture of granular resin and 0.4 ppm of talc powder (nucleating agent) is fed into the extruder with a total speed of 3 kg / h (due to the difference in loading characteristics between the mixtures, the actual extrusion rate varies slightly, as shown in table 4, decreasing from 3 kg / h to 2.6 kg / h, at a fixed rotational speed of the screw of the extruder). The following temperatures are maintained in the extruder zones: 120 ° C in the loading zone, 150 ° C in the melting zone, 180 ° C in the homogenization zone, and 180 ° C in the mixing zone. The temperature of the cooling zone is maintained, as shown in table 4, and isobutane (blowing agent) is introduced into the mixing zone in the amounts indicated in table 4: 380 g / h for comparative example D and examples 4.1 and 4.2 and 450 g / h for examples No. 4.3 and 4.4 (due to the change in the feed rate of the polymer and the blowing agent, the level of the blowing agent in the resin varies from 12.7 hours to 17.3 hours (see table 4). The head clearance is fixed at 1.75 mm throughout the test and the temperature heads are maintained at 0 ° C-5 ° C lower than the temperature in the cooling zone. TED on foam dimensional stability (see. the methods shown in Example 1) are summarized in Table 4 along with the density, cell size and data on cell opening.

As shown in table 4, good foams are obtained from mixtures containing up to 40 percent sPP resin. In contrast to the data on open cells, the foams obtained in comparative example D and examples 4.1 and 4.2 were mainly with closed cells, which was verified using the finger compression test. The foams obtained in examples 4.3 and 4.4 have open cells. And in this case, data on open cells of soft polyolefin foams are not reliable. The EVA foam obtained in comparative example D suffers from excessive shrinkage (minimum volume is 25 percent), even if ASTM D-2856-A shows that the foam contains 83 percent of the open cells.

Conclusion:

And this time, good foams are obtained from a mixture of sPP resin and a foaming ethylene / vinyl acetate resin, it being shown that sPP resin improves spatial stability and that sPP resin in an amount of 30 percent or more gives a foam having satisfactory spatial stability.

Test 5

Thermal stability of the foam of comparative example D and example 4

After aging for 16 days, the foams obtained in comparative example D and example 4 are exposed to heat, as described in test 2, the Foam samples are placed in an oven in which the temperature is maintained at 90 ° C. After 1 hour and then after 8 days, the samples are removed and measured for a change in volume, as shown in table 5.

As shown in Table 5, all foams shrink, but foams containing sPP resin retain their volume to a greater extent than foams (cf. Example D) that do not contain sPP resin. The foam obtained from a mixture containing 40 percent sPP resin retains 83 percent volume after 8 hours in an oven.

Example 5

Obtaining foam from a mixture of sPP resin and iPP resin

In Example 5, a mixture of high melt strength foaming (HMS) iPP resin and sPP resin are used to make the foam in accordance with the present invention.

A granular mixture of 50/50 by weight is obtained from an iPP resin of the Pro-fax PF-814 category (available from Montell Polyolefins Co. NV) having a melt index of 3 dg / min (determined by ASTM D-1238 at 230 ° C./2, 16 kg), a density of 0.90 g / cm ³ and a melting point of 160 ° C, and a syndiotactic form of a copolymer polypropylene resin of category EOD 96-07 (available from Fina Oil and Chemical Company) having a melt flow rate of 2 dg / min, density 0.88 g / cm ³ and a melting point of 130 ° C.

A mixture of granular resins and additives consisting of talcum powder (nucleating agent) in an amount of 0.2 parts per hundred parts of resin (hs) and an antioxidant grade Irganox 1010 (available from Ciba-Geigy Corp.) in an amount of 0.1 hs are pre-mixed and loaded into the extruder with a total speed of 4.2 kg / hour. Temperatures are maintained in the cooling zone, 160 ° C in the feed zone, 190 ° C in the melting zone, 200 ° C in the homogenization zone and 200 ° C in the mixing zone. Isobutane (blowing agent) is introduced into the mixing zone at a constant speed in the amount of 10.7 hours. The diameter of the head bore is maintained at approximately 0.8 mm. The temperature of the cooling zone and the opening of the head are set so as to obtain foams. At a temperature of the cooling zone from 170 ° C to 160 ° C, good foams are obtained mainly with closed cells. For example, the foam obtained at 160 ° C. has a density of 26.3 kg / m ³ , a mesh size of 1.8 mm, an open cell content of 17 percent, a thickness of approximately 11 mm and a width of approximately 20 mm. The foam is durable and tough.

Comparative Example E

Obtaining foam from a mixture of sPP resin and iPP resin

In comparative example E, the method of example 5 is repeated, but using a 20/80 mixture of the same iPP and sPP resins, rather than a 50/50 mixture.

In the cooling zone, the temperature is determined from 180 ° C to 150 ° C, the foam cannot be obtained.

Example 6 and Comparative Example F

Obtaining foam from a mixture of spP resin and polystyrene resin

In Example 6, a mixture of polystyrene (PS) resin and sPP resin was expanded with CO ₂ using the same apparatus and the same method as used in Example 1. Comparative Example F was prepared only from PS resin.

As shown in table 6, in a predetermined ratio, a granular mixture is prepared from a PS resin having an average molecular weight of 150,000, a density of 1.05 g / cm ³ and T _{g of} 104 ° C, and an sPP resin of category EOD 96-07 (available from Fina Oil and Chemical Company) having a melt flow rate of 2 dg / min (determined according to ASTM D-1238 at 230 ° C / 2.16 kg), a density of 0.88 g / cm ³ and a melting point of 130 ° C.

A mixture of granular resin and 0.1 ppm of barium stearate is pre-mixed and fed to the extruder at a total speed. The following temperatures are maintained in the extruder: 130 ° C in the feed zone, 160 ° C in the melting zone, 200 ° C in the homogenization zone, and 200 ° C in the mixing zone. Carbon dioxide is introduced into the mixing zone at a constant rate of 4.6 hours. The temperature of the cooling zone is brought to 132 ° C-134 ° C to obtain a foam of good quality. The temperature of the head is maintained at 145 ° C throughout the entire production process. The diameter of the head hole is set and maintained equal to 1.5 mm. The thickness, density of the foam, the size of the cells and the content of open cells are shown in table 6.

As shown in table 6, sPP resin increases the size of the cross section and the size of the cells. It is shown that polystyrene containing 2 percent and 5 percent sPP resin does not have open cells. A mixture of 80/20 PS / sPP resins provides a foam having a certain number of open cells.

Claims (25)

1. Mixed polymer foam containing from 0.1 to 60 wt.% Syndiotactic propylene resin, which is a homopolymer or copolymer of propylene, and from 40 to 99.9 wt.% Foaming thermoplastic polymer resin, characterized in that the density of the mixed foam is from 9 to 100 kg / m ³ , while the foaming thermoplastic polymer resin is selected from the group comprising a flexible polyolefin resin, with the exception of isotactic polypropylene, isotactic polypropylene having a tangent delta of less than 1.5, defined Using a sample 2.5 mm thick and 25 mm in diameter at 190 ° C and 1 rad / s oscillation rate, polystyrene having an average molecular weight of less than 240,000. 2. The mixed polymer foam according to claim 1, characterized in that the foam has a density of from 11 to about 100 kg / m ³ . 3. The mixed polymer foam according to claim 1 or 2, characterized in that the foam has a density of from 15 to 50 kg / m ³ . 4. The mixed polymer foam according to claim 1, characterized in that the flexible polyolefin resin is a low density polyethylene resin. 5. The mixed polymer foam according to claim 4, characterized in that the low density polyethylene resin has a melt index of from 0.1 to 20 dg / min. 6. The mixed polymer foam according to any one of claims 1 to 4, characterized in that the syndiotactic polypropylene resin is a copolymer of propylene with ethylene. 7. The mixed polymer foam according to any one of claims 1 to 5, characterized in that the syndiotactic polypropylene resin is a copolymer of propylene with 1-butene. 8. The mixed polymer foam according to any one of the preceding paragraphs, characterized in that the syndiotactic polypropylene resin has a melt flow rate of from 0.05 to 50 dg / min. 9. The mixed polymer foam according to any one of the preceding paragraphs, characterized in that the syndiotactic polypropylene resin has a syndiotacticity of more than 75%. 10. The mixed polymer foam according to claim 1, characterized in that the flexible polyolefin resin is an ethylene / vinyl acetate copolymer resin. 11. The mixed polymer foam of claim 10, wherein the ethylene / vinyl acetate copolymer resin has a vinyl acetate content of from 5 to 30%. 12. The mixed polymer foam of claim 10 or 11, characterized in that the ethylene / vinyl acetate copolymer resin has a melt index of from 0.2 to 10 dg / min. 13. The mixed polymer foam according to claim 1, characterized in that the isotactic polypropylene has a tangent delta of less than 1.2. 14. The mixed polymer foam according to claim 1, characterized in that the mass ratio of syndiotactic polypropylene resin to a flexible thermoplastic polymer resin in the mixed foam is from 10:90 to 50:50. 15. The mixed polymer foam according to 14, characterized in that the mass ratio of syndiotactic polypropylene resin to a flexible thermoplastic polymer resin in the mixed foam is from 30:70 to 50:50. 16. Mixed polymer foam according to any one of the preceding paragraphs, characterized in that the mixed foam is a foam obtained by extrusion. 17. The mixed polymer foam according to claim 16, characterized in that isobutane is used as a blowing agent in the extrusion process. 18. The mixed polymer foam according to claim 16 or 17, characterized in that carbon dioxide is used as a blowing agent in the extrusion process. 19. Mixed polymer foam according to any one of the preceding paragraphs, characterized in that the mixed foam has a mesh size of from 0.01 to 10 mm 20. The mixed polymer foam according to any one of the preceding paragraphs, characterized in that the mixed foam is cross-linked. 21. Mixed polymer foam according to any one of the preceding paragraphs, characterized in that the mixed foam is crosslinked. 22. Mixed polymer foam according to any one of the preceding paragraphs, characterized in that the mixed foam is in the form of a sheet. 23. Mixed polymer foam according to any one of claims 1 to 21, characterized in that the mixed foam has the shape of a strap. 24. The mixed polymer foam according to item 23, wherein the mixed foam has the shape of a foam strip of connected threads. 25. Mixed polymer foam according to any one of claims 1 to 21, characterized in that the mixed foam has the shape of balls.

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