MX2008002135A - Method for producing foam plates - Google Patents

Abstract

The invention relates to a method for producing moulded foam elements from pre-foamed foam particles in a mould under pressure, said moulded foam elements having a polymer coating that comprises an athermane compound. The invention also relates to moulded foam elements produced therefrom and their use.

Description

METHOD FOR THE PRODUCTION OF FOAM PLATES The invention relates to a process for the production of molded foam elements from pre-foamed foam particles having a polymeric coating and also to molded foam elements produced from thereon. its use. Expanded foams are usually obtained by sintering foam particles, for example pre-foamed expanded polystyrene (EPS) particles or expanded polypropylene (EPP) particles, in molds closed by means of steam. In order for the foam particles to be post-expanded and fused together to form the foam molded element, they must generally comprise small residual amounts of blowing agent. The foam particles should therefore not be stored for a too long time after pre-foaming. In addition, due to the lack of post-spread of crushed recycled foam materials from expanded foams that are no longer usable, only small amounts of these can be mixed for the production of new foam molded elements. WO 00/050500 discloses flame resistant foams produced from pre-foamed polystyrene particles which are mixed with an aqueous solution of sodium silicate and a latex of a high molecular weight vinyl acetate copolymer, cast in mold and dried in air with agitation. This provides only a loose bed of polystyrene particles adhesively bonded together at only a few points and therefore have only unsatisfactory mechanical strengths. WO 2005/105404 discloses an energy saving process for the production of molded foam elements, wherein the prefoamed foam particles are covered with a resin solution having a softening temperature lower than the softening temperature of the expandable polymer. The coated foam particles are subsequently fused together in a mold under external pressure or by post-expansion of the foam particles in a customary manner using hot steam. Here, the water-soluble constituents of the coating can be washed. Due to the relatively high temperatures at the entry points and the cooling of the vapor when condensed, the melting of the foam particles and the density can fluctuate considerably throughout the foam body. In addition, the condensation vapor may be enclosed in the interstices between the foam particles. The reduction of thermal conductivity by the integration of athermanos materials such as carbon black, graphite, aluminum or metal oxides in foams, is known, for example, from WO 98/51734. The introduction of the athermanous materials in expansive polystyrene, however, can influence the foaming behavior. EP-A 620246 discloses expanded polystyrene foams in which particulate inert materials such as carbon black can be obtained on the surface of pre-foamed polystyrene foam particles. This however generally results in high dust contamination during processing and a deterioration of the melt capacity by means of hot steam to form the molded foam elements. Accordingly, it is an object of the present invention to remedy the aforementioned advantages and to discover a simple and energy-saving process for the production of molded foam elements having low thermal conductivity and good mechanical properties. We have therefore found a process for the production of foam molded elements by sintering pre-foamed foam particles having a polymeric coating, wherein the polymeric coating comprises an athermanous compound. As foam particles it is possible to use expanded polyolefins such as expanded polyethylene (EPE) or expanded polypropylene (EPP) or pre-foamed particles of expandable styrene polymers, in particular expandable polystyrene (EPS). The foam particles generally have a mean particle diameter within a range of 2 to 10 mm. The bulk density of the foam particles is generally from 5 to 50 kg / m3, preferably from 5 to 40 kg / m3 and in particular from 8 to 16 kg / m3, in accordance with what is determined according to DIN EN ISO 60. The particles Foam based polymers of styrene can be obtained by pre-foaming EPS to the desired density through hot air or steam in a pre-skimmer. Final apparent densities less than 10 g / l can be obtained here by single or multiple pre-foaming in a continuous pre-foamer or pre-foamer. A preferred process comprises the following steps: a) pre-foaming expandable styrene polymers to form foam particles, b) coating the foam particles with a polymeric solution or aqueous polymer dispersion, c) introducing the coated foam particles into a mold and sinter under pressure in the absence of steam. Due to its high thermal insulation capacity, particular preference is given to the use of pre-foamed expandable styrene polymers comprising heat solids such as carbon black, aluminum or graphite, in particular graphite having an average particle diameter within in a range of 1 to 50 μm, in amounts of 0.1 to 10% by weight, in particular 2 to 8% by weight, based on EPS, and are known, for example, from EP-B 981 574 and EP-B 981 575. The polymeric foam particles can be provided with pyro-retarding agents. For this purpose they may comprise, for example, from 1 to 6% by weight of an organic bromine compound such as for example hexabromocyclodecane (HBCD) and, if appropriate, additionally from 0.1 to 0.5% by weight of bicumyl or a peroxide. The process of the invention can also be carried out using crushed foam particles from recycled foam molded elements. To produce the molded foam elements of the invention, it is possible to use 100% recycled, shredded or proportioned foam materials from 2 to 90% by weight, in particular from 5 to 25% by weight, together with fresh material without significantly affecting the resistance and the mechanical properties. In general, the coating comprises a polymeric film having one or more glass transition temperatures within a range of -60 ° C to + 100 ° C and where fillers can be integrated, if appropriate. The glass transition temperatures of the polymer film are preferably within the range of -30 ° C to + 80 ° C, particularly preferably within a range of -10 ° C to + 60 ° C. The transition temperature Glass can be determined through differential scanning calorimetry (DSC). The molecular weight of the polymer film, according to that determined by gel permeation chromatography (GPC), is preferably below 400.00 g / mol. To cover the foam particles, it is possible to use conventional methods such as spraying, immersing or moistening the foam particles with a polymer solution or a polymer dispersion or drum coating with solid polymers or polymers absorbed in solids in customary mixers, apparatus for spray, submerging apparatus or drum apparatus. Suitable polymers for the coating are, for example, polymers based on monomers such as vinylaromatic monomers such as a-methylstyrene, p-methylstyrene, ethylstyrene, tert-butylstyrene, vinylstyrene, vinyltoluene, 1,2-diphenylethylene, 1,1-diphenylethylene. , alkenes such as ethylene or propylene, dienes such as 1,3-butadiene, 1,3-pentadiene, 1,3-hexadiene, 2,3-dimethylbutadiene, isoprene, piperylene or isoprene, α, β-unsaturated carboxylic acids such as acrylic acid and methacrylic acid, their esters, in particular alkyl esters, such as, for example, C1-io alkyl esters of acrylic acid, in particular butyl esters, preferably n-butyl acrylate, and C1-io alkyl esters of methacrylic acid, in particular methyl methacrylate (MMA), or carboxamides, for example acrylamide and methacrylamide. The polymers may comprise, if appropriate, from 1 to 5% by weight of comonomers such as (meth) acrylonitrile, (meth) acrylamide, ureido (meth) acrylate, 2-hydroxyethyl (meth) acrylate, (meth) acrylate 3 -hydroxypropyl, acrylamidopropanesulfonic acid, methylolacrylamide and the sodium salt of vinylsulfonic acid. The coating polymers can preferably be produced from one or more of the monomers styrene, butadiene, acrylic acid, methacrylic acid, C? -4 alquilo alkyl acrylate, C? _ Alkyl methacrylates, acrylamide, methacrylamide or methylolacrylamide. Suitable binders for the polymeric coating are, in particular, acrylate resins which are preferably applied in the form of aqueous polymer dispersions on the foam particles, if appropriate together with hydraulic binders based on cement, lime cement, or gypsum. Suitable polymer dispersions can be obtained, for example, by emulsion polymerization of free radicals of ethylenically unsaturated monomers such as styrene, acrylates or methacrylates, in accordance with that described in WO 00/50480. Particular preference is given to pure acrylates or styrene-acrylates which are formed of monomers styrene, n-butyl acrylate, methyl methacrylate (MMA), methacrylic acid, acrylamide or methylolacrylamide. The polymer dispersion is prepared in a manner known per se, for example by emulsion, suspension or dispersion polymerization, preferably in an aqueous phase. It is also possible to produce the polymer by solution or bulk polymerization, grind it as appropriate and subsequently disperse the polymer particles in water in the usual manner. In the polymerization, the initiators, emulsifiers or suspension aids, regulators or other auxiliaries customary for the respective polymerization process are used concomitantly, and the polymerization is carried out continuously or in batches at the temperatures and pressures customary for the respective process in suitable reactors. Fillers having particle sizes within a range of 0.1 to 100 μm, particularly within the range of 0.5 to 10 μm, provide a reduction in thermal conductivity by 1-2 mW when present in proportions of 10% by weight in the polystyrene foam. Comparatively low thermal conductivities can therefore be achieved even with relatively small amounts of IR absorbers such as carbon black and graphite. Preference is given to the use of an IR absorber, such as, for example, carbon black, coke, aluminum or graphite in amounts of 0.1 to 10% by weight, in particular in amounts of 2% by weight, based on the solid of coating, for the reduction of thermal conductivity. Preference is given to the use of carbon black having an average primary particle size within a range of 10 to 300 nm, in particular within the range of 30 to 200 nm. The BET surface area is preferably within the range of 10 to 10 m2 / g. As graphite, preference is given to the use of graphite having an average particle size within a range of 1 to 50 μm. The polymeric coating may also comprise additional additives such as inorganic fillers such as pigments or pyro-retardant agents. The proportion of additives depends on their type and the desired effect and in the case of inorganic fillers it is generally from 10 to 99% by weight, preferably from 20 to 98% by weight, based on the polymeric coating comprising additives. The coating mixture preferably comprises intumescent water-binding compositions such as, for example, liquid crystal. This causes a better and faster film formation from the polymer dispersion and consequently a faster curing of the foam molded element. The polymeric coating preferably comprises pyro-retardant agents such as expandable graphite, borates, in particular zinc borates, melamine compounds or phosphorus compounds or intumescent compositions which expand, swell or foam under the action of elevated temperatures, generally above 80-100 ° C, and in the process form an insulating and thermo-resistant foam that protects the thermally insulating foam particles underlying against fire and heat. The amount of pyro-retarding agents or intumescent compositions is generally between 2 and 99% by weight, preferably between 5 and 98% by weight, based on the polymer coating. When pyro-retarding agents are used in the polymeric coating, it is also possible to achieve satisfactory fire protection when using foam particles that do not comprise any pyro-retarding agent, in particular they do not comprise any halogenated pyro-retardant agent, or else to use small amounts of pyro-retarding agent, since the pyro-retarding agent in the polymeric coating is concentrated on the surface of the foam particles and under the action of heat or fire forms a solid structure. The polymeric coating particularly preferably comprises substances which contain chemically bound water or remove water at temperatures above 40 ° C, for example, alkali metal silicates, metal hydroxides, metal salt hydrates and metal oxide hydrates, such as additives Foam particles provided with this coating can be processed to provide molded foam elements that have a higher fire resistance and have a combustion behavior that complies with Class B in accordance with DIN 4102. Suitable metal hydroxides are, in particular , the metal hydroxides of groups 2 (alkaline toric metals) and 13 (boron group) of the Periodic Table. Preference is given to magnesium hydroxide and aluminum hydroxide. The latter is particularly preferred. Suitable metal salts hydrates are all metal salts in whose crystalline structure crystallization water is incorporated. Analogously, suitable metal oxide hydrates are all metal oxides comprising water of crystallization incorporated in the crystal structure. The number of water molecules of crystallization per unit of formula may be as high as possible or may be below this, for example, pentahydrate, trihydrate, or copper sulfate monohydrate. In addition to the water of crystallization, the hydrates of metal salts and hydrates of metal oxides may also comprise water of constitution. Preferred metal salts hydrates are metal halide hydrates (in particular chlorides), sulfates, carbonates, phosphates, nitrates or borates. Suitable metal salt hydrates are, for example, magnesium sulfate decahydrate, sodium sulphate decahydrate, copper sulfate pentahydrate, nickel sulfate heptahydrate, cobalt chloride (II) hexahydrate, chromium chloride hexahydrate ( III), sodium carbonate decahydrate, magnesium chloride hexahydrate and tin borate hydrates. Magnesium sulfate dehydrohydrate and tin borate hydrates are particularly preferred. Additional possible metal salts hydrates are double salts such as alum, for example those of the general formula: M'M '"(S0) 2 • 12 H20 M' can be, for example, a potassium, sodium, rubidium ion , cesium, ammonium, thallium or aluminum, M '"may be, for example, aluminum, gallium, indium, scandium, titanium, vanadium, chromium, manganese and iron, cobalt, rhodium or iridium. Metal oxide oxides suitable with, for example, aluminum oxide hydrate and preferably zinc oxide hydrate or boron trioxide hydrate.

A preferred polymer coating can be obtained by mixing 40 to 80 parts by weight, preferably 50 to 70 parts by weight, of a liquid crystal solution having a water content of 40 to 90% by weight, preferably of 50 to 70% by weight, from 2 to 60 parts by weight, preferably from 30 to 50 parts by weight, of a liquid crystal powder having a water content of 0 to 30% by weight, preferably 1 to 25% by weight and from 5 to 40 parts by weight, preferably from 10 to 30 parts by weight, of a polymer dispersion having a solids content of 10 to 60% by weight, preferably 20 to 50% by weight, or by mixing 20 to 95 parts by weight, preferably 40 to 90 parts by weight, of a suspension of aluminum hydroxide having an aluminum hydroxide content of 10 to 90% by weight, preferably 20 to 70% by weight, from 5 to 40 parts by weight, preferably from 10 to 30 parts by weight, of a polymeric emulsion having a solids content of 10 to 60% by weight, preferably 20 to 50% by weight. In the process of the present invention, the pressure can be produced, for example, by decreasing the volume of the mold through a mobile punch. In general, a pressure is established within a range of 0.5 to 30 kg / cm2. The mixture of coated foam particles is introduced for this purpose into the open mold. After closure of the mold, the foam particles are pressed through the punch, with the air between the foam particles escaping and the volume of the interstices decreasing. The foam particles are bonded through the polymeric coating to provide the molded foam element. The mold is structured in accordance with the desired geometry of the foam body. The degree of filling depends, among other things, on the desired thickness of the future molded element. In the case of foam boards, it is possible to use a mold in the form of a simple box. In the case of more complicated geometries, in particular, it may be necessary to compact the bed of particles introduced into the mold and thereby eliminate undesirable voids. Compaction may be achieved, for example, by stirring the mold, tumbling movements or other suitable measures. To accelerate the setting, hot air can be injected into the mold or the mold can be heated. According to the present invention, no foam is introduced into the mold in such a way that no water-soluble constituent of the polymeric coating of the foam particles is washed and condensed water can not form in the interstices. However, any heat transfer medium such as oil or steam can be used to heat the mold. The hot air or mold is advantageously heated for this purpose at a temperature within a range of 20 to 120 ° C, preferably 30 to 90 ° C. As an alternative or additionally, sintering can be carried out by injecting energy of microwave. In general, microwaves have a frequency within a range of 0.85 to 100 GHz, preferably 0.9 to 10 GHz, and irradiation times of 0.1 to 15 minutes are used here. When hot air having a temperature within a range of 80 to 150 ° C is used or when microwave energy is injected, a pressure gauge of 0.1 to 1.5 bar is usually established in such a way that the process can be effected without external pressure and without reducing the mold volume. The internal pressure generated by the microwaves or elevated temperatures allows the foam particles to undergo a slight additional expansion, and these can fuse together as a result of the softening of the foam particles themselves in addition to the adhesive bond through the polymeric coating . The interstices between the foam particles disappear as a result. To accelerate the setting, the mold in this case can also be further heated through a heat transfer medium in accordance with what is described above. Dual-band plants as used for the production of polyurethane foams are also suitable for the continuous production of the molded foam elements of the invention. For example, pre-foamed and coated foam particles can be applied continuously in the lower band of two metal bands that can, if appropriate, have perforations and be processed with or without compression by the metal bands that move together to produce continuous foam boards. In one embodiment of the process, the volume between the two bands is gradually reduced as a result of which the product between the bands is compressed and the interstices between the foam particles disappear. After a curing zone, a continuous table is obtained. In another embodiment, the volume between the bands can be kept constant and the foam can pass through an area heated by hot air or microwave irradiation where the foam particles are subjected to post-foaming. Here too, the interstices disappear and a continuous table is obtained. It is also possible to combine the two modes of continuous process.

The thickness, length and width of the foam boards can vary within wide limits and these values are limited by the size and closing force of the tool. The thickness of the foam boards is usually from 1 to 500 mm, preferably from 10 to 300 mm. The density of the foam molded elements according to DIN 53420 is generally from 10 to 120 kg / m3, preferably from 20 to 70 kg / m3. The process of the present invention makes it possible to obtain molded foam elements having a uniform density over the entire cross section. The density of the surface layers corresponds approximately to the wave density internal regions of the foam molded element. The process of the invention is suitable for the production of simple or complex foam molded elements such as tables, blocks, tubes, rods, profiles, etc. Preference is given to tables or blocks that can be subsequently cut or sawed to produce boards. They can be used, for example, in building and construction for the insulation of exterior walls. They are used particularly preferably as a central layer for the production of entangled type elements, for example structural insulation panels (SIPs) which is used for the construction of warehouses or cold stores. Additional possible applications are foam pallets such as replacement of wooden pallets, front roof panels, insulated containers, trailers. With a pyro-retardant agent content, they are also suitable for air transport. Examples Preparation of coating mix Bl: 40 parts of liquid crystal powder (Portil N) are added little by little with stirring to 60 parts of liquid crystal solution (Woellner sodium silicate 38/40, solids content 36%, density : 1.37, molar ratio Si02: Na20 = 3.4) and the mixture was homogenized for about 3-5 minutes. Subsequently, 20 parts of an acrylate dispersion (Acronal S790, solids content: approximately 50%) and 5 parts of UF 298 graphite powder from Kropfmühl were subsequently added with stirring. Preparation of coating mixture B2: 40 parts of liquid crystal powder (Portil N) were added gradually with stirring to 60 parts of liquid crystal solution (Woellner sodium silicate 38/40, solids content 36%, density : 1.37, molar ratio Si02: Na20 = 3.4), and the mixture was homogenized for about 3-5 minutes. Subsequently, 5 parts of an acrylate dispersion (Acronal S790, solids content: approximately 50%) and 2 parts of UF 298 graphite powder from Kropfmühl were subsequently introduced with stirring. Preparation of coating mixture B3: 40 parts of liquid crystal powder (Portil N) were added gradually with stirring to 60 parts of liquid crystal solution (Woellner sodium silicate 38/40, solids content 36%, density : 1.37, molar ratio Si02: Na20 = 3.4) and the mixture was homogenized for about 3-5 minutes. 5 parts of an acrylate dispersion (Acronal S790, solids content: approximately 50%) were subsequently introduced with stirring. Polystyrene foam particles I (density: 10 g / l) Expandable polystyrene (Styropor® F 315 from BASF Aktiengesellschaft) is pre-expanded to a density of approximately 10 g / l in a continuous pre-skimmer. Particles of polystyrene foam II (density: 12 g / l) Expandable polystyrene (Neropor® 2200 of BASF Aktiengesellschaft, pearl size of the raw material: 1.4 - 2.3 mm) was pre-foamed at a density of approximately 18 g / l in a continuous pre-skimmer. After a temporary storage time of approximately 4 hours, the particles were subjected to a post-foaming process until achieving the desired density in the same prefoamer. The pre-foamed polystyrene foam particles had a particle size within a range of 6 to 10 mm. Example 1 The polystyrene foam particles were coated with the coating mixture Bl in a weight ratio of 1: 2 in a mixer. The coated polystyrene foam particles were introduced into a mold coated with Teflon which had been heated to 70 ° C and pressed by means of a punch at 50% of the original volume. After curing at 70 ° C for 30 minutes, the molded foam element was removed from the mold. The molded element was further conditioned by storage at room temperature for a number of days. The density of the molded element stored was 44 g / l. Example 2 Example 1 was repeated using polystyrene foam particles comprising graphite, pre-foamed II having a density of about 12 g / l which had been covered with coating mixture B2 in a weight ratio of 1: 2 in a mixer. The density of the molded element stored was 51 g / l. The foam boards of Examples 1 and 2 have a considerably re-accumented thermal conductivity (Table 1). In addition, they no longer leak in the combustion test and do not present retro-softening under the action of heat. They self-extinguish and meet requirements B2 and E. Comparative Experiment 1.

The polystyrene foam particles I were coated with the coating mixture B3 in a weight ratio of 1: 2 in a mixer. The coated polystyrene foam particles were introduced into a mold coated with Teflon which had been heated to 70 ° C and were pressed by means of a punch at 40% of the original volume. After curing at 70 ° C for 30 minutes, the molded foam element was removed from the mold. The molded element was further conditioned by storage at room temperature for a number of days. The density of the molded element stored was 42 g / l.

Claims (10)

1. CLAIMS 1. A process for the production of foam molded elements from pre-foamed foam particles having a polymeric coating having a glass transition temperature within a range of -60 to + 60 ° C in a mold under pressure, wherein the polymeric coating comprises carbon black, coke, aluminum powder or graphite as an inert compound.
2. 2. The process according to claim 1, wherein the polymeric coating comprises carbon black, coke, aluminum powder or graphite as an athermanous compound in amounts of 0.1 to 10% by weight, based on the coating.
3. 3. The process according to claim 1 or 2, wherein the pre-foamed foam particles are sintered in the absence of steam.
4. 4. The process according to any of claims 1 to 3, wherein expanded polyolefin or pre-foamed expandable styrene polymer particles are used as foam particles.
5. 5. The process according to any of claims 1 to 4, wherein the ground particles from recycled foam molded elements are used as foam particles.
6. The process according to any of claims 1 to 5, comprising the steps of: a) pre-foaming expandable styrene polymers to form foam particles, b) coating the foam particles with a polymer solution or polymer dispersion watery and carbon black, coke, aluminum powder or graphite as an athermanous compound, c) introduce the coated foam particles in a mold and sinter under pressure in the absence of steam.
7. The process according to claim 6, wherein a dispersion of acrylate and carbon black, coke, aluminum powder or graphite is used as the coating composition in step b).
8. 8. The process according to claim 6, wherein the expandable styrene polymer used in step a) comprises carbon black, coke, aluminum powder or graphite as the athermanous compound. The process according to any of claims 1 to 8, wherein the polymeric coating comprises alkali metal silicates, metal hydroxides, metal salt hydrates or metal oxide hydrates. The process according to claim 9, wherein the polymeric coating is obtained by mixing: from 40 to 80 parts by weight of a liquid crystal solution having a water content of 40 to 90% by weight , from 20 to 60 parts by weight of a liquid crystal powder having a water content of from 0 to 30% by weight, and from 5 to 40 parts by weight of a polymer dispersion having a solids content of from 10 to 60. % by weight or by mixing 20 to 95 parts by weight of a suspension of aluminum hydroxide having an aluminum hydroxide content of 10 to 90% by weight, of 5 to 40 parts by weight of a dispersion polymer having a solids content of 10 to 60% by weight.