MXPA01005630A - Method for producing expandable polystyrene particles - Google Patents

Abstract

The invention relates to a method for producing expandable polystyrene polymers in the form of particles, containing 5-50 wt.%exfoliated graphite and, optionally, 2-20 wt.%phosphorous compound as flame-producing agents. According to the invention, said polystyrene compounds are produced by means of suspension polymerization of styrene in the presence of flame-producing agents.

Description

METHOD TO PRODUCE EXPANDABLE POLYSTYRENE PARTICLES The invention relates to expandable particulate styrene polymers, which have been provided with halogen-free flame retardants. Molded polystyrene foams are widely used to insulate buildings and building components. For this application they must be flame retardants. The flame retardants usually used to classify the flame retardants of polystyrene foams comprise halogens. For environmental reasons, the use of halogens in foams should be reduced. It is an object of the present invention to provide expandable polystyrene particles which can be processed to give foams which achieve fire ratings B 1 and B 2 and which have been produced without the use of halogen-containing flame retardants. It has been found that this object is achieved by a process for preparing particulate expandable styrene polymers by polymerizing styrene, where appropriate together with the comonomers, in aqueous suspension with the use of blowing agents before, during or after polymerization where the polymerization is carried out in the presence of 5 to 50% by weight, based on the monomers, of expanded graphite.

The invention also provides particulate expandable styrene polymers, comprising from 5 to 50% by weight, based on the styrene polymer, of uniformly distributed expanded graphite with an average particle size of 20 to 100 μm, preferably 30 to 80 μm . Expanded graphite is described in the literature in combination with red phosphorus and / or with phosphorus-containing compounds as a flame retardant for compact polystyrene. However, it has been found in previous experiments that halogen-free flame retardants that can be used by compact polystyrene can not be used in the production of foam, since there is either a severe adverse effect on the foaming process or a excessive reduction in the heat resistance of the foam. Surprisingly, however, this is not the case in the present invention. US-A 3,574,644 describes the addition of expanded graphite as flame retardant by combustible materials, inter alia for foams wherein the amounts of expanded graphite present are to be from 20 to 40% by weight. The expanded graphite can either be incorporated in the expandable material above for expansion or coated in this material after the expansion process. The preparation of expandable polystyrene particles by polymerization of styrene in the presence of expanded graphite is not described. JP-A 03-167 236 discloses a polystyrene foam comprising, as a flame retardant, expanded graphite whose surface is completely covered with a film-forming resin. This coating is indicated as being necessary to avoid corrosion of the machinery processed by acids always present in the expanded graphite. However, an additional and complicated operation is required. In addition to expanded graphite, the polystyrene foam may also comprise conventional flame retardants, for example, organic halogenated phosphates. The polystyrene foam is preferably prepared by mixing polystyrene foam particles with an adhesion promoter and with the expanded expanded graphite. The expanded graphite particle size is preferably to be of 30 to 120 mesh, corresponding to a diameter of about 120 to 540 μm. At particle sizes below 150 mesh (104 μm) it is said that the flame retardant action of expanded graphite is markedly reduced. The crosslinked structure of graphite layer allows it to form specific types of intercalation compounds. In these compounds, which are known as interstitial compounds, foreign atoms or foreign molecules have been absorbed in the spaces between the carbon atoms, sometimes in stoichiometric relationships. These graphite compounds, for example, sulfuric acid as the foreign molecule, are also prepared on an industrial scale and are called expanded graphites. The density of this expanded graphite is from 1.5 to 2.1 g / cm3, and its average particle size is generally from 20 to 2000 μm, in the present case preferably from 20 to 100 μm, and in particular from 30 to 80 μm. The phosphorus compounds that can be used are inorganic or organic phosphates, phosphites or phosphonates, and also red phosphors. Examples of preferred phosphorus compounds are diphenyl phosphate, triphenyl phosphate, diphenylcresyl phosphate, ammonium polyphosphate, resorcinol diphenyl phosphate, melamine phosphate, dimethyl phenylphosphonate, and dimethyl methylphosphonate. In the suspension polymerization of the invention, it is preferable to use styrene alone as the monomer. However, up to 20% of the weight of the styrene may have been replaced by other ethylenically unsaturated monomers, such as alkylstyrenes, divinylbenzene, acrylonitrile, diphenylether, or α-methylstyrene. During the suspension polymerization, the use may be made of the usual auxiliaries, for example, peroxide initiators, suspension stabilizers, blowing agents, chain transfer agents, expansion aids, nucleating agents, and plasticizers. The expanded graphite is added during the polymerization in amounts of 5 to 50% by weight, preferably 8 to 30% by weight, and the phosphorous compound in amounts of 2 to 20% by weight, preferably 3 to 10% by weight. The blowing agents are added in amounts of 3 to 10% by weight, based on the monomer. They can be added before, during, or after polymerization of the suspension. Suitable blowing agents are aliphatic hydrocarbons having from 4 to 6 carbon atoms. It is advantageous for the inorganic Pickering dispersants to be used as suspension stabilizers, for example, magnesium pyrophosphate or calcium phosphate. It has been found that when expanded graphite of relatively low particle size is used, that is, expanded graphite with an average diameter of 20 to 100 μm, preferably 30 to 80 μm, the stability of the suspension is better than when they use rougher expanded graphite particles, and the particles produced have a lower internal water content. The polymerization of suspension produced in the form of a bead, essentially round particles with an average diameter in the range of 0.2 to 2 mm. They can be coated with the usual coating agents, for example, metal stearates, glycerol esters, or fine particle silicates. The expandable polystyrene particles can be prepared not only by the suspension polymerization of claim 1, but also, as in claim 7, by mixing the molten styrene polymer and the blowing agent with expanded graphite whose average particle size is 20 to 100 μm, and also, when appropriate, with the phosphorous compound, extruding, cooling and granulating. Subsequent impregnation of the styrene polymer granules comprising expanded graphite is also possible. The expandable polystyrene particles can be processed to give polystyrene foams with densities of 5 to 100 g / 1, preferably 10 to 50 g / 1. For this, the expandable particles are pre-foamed. This usually takes place by heating the particles with steam where it is known as pre-skimmers. The resulting pre-foamed particles are then melted to form molders. For this, the pre-foamed particles are introduced into narrow molds without gas, and the particles are brought into contact with the vapor. The molders can be removed after cooling.

Example 1 61.0 of dicumyl peroxide and 20.2 g of dibenzoyl peroxide are dissolved in 18.0 kg of styrene, and 900 g of dimethyl phenylphosphonate (5% by weight, based on styrene) are added. The organic phase is introduced into 20.2 liters of demineralized water in a 50 liter mixing vessel. The aqueous phase comprises 35.0 g of sodium pyrophosphate and 70.0 g of magnesium sulfate (Epsom salt). The suspension was rapidly heated to 90 ° C and then, for a period of 4 hours at 130 ° C. 1 hour later 90 ° C were reached, 1.8 g of the K 30 emulsifier (Bayer AG) were measured. After an additional hour, 2.7 kg of the expanded graphite (UCAR, Grafuard 160-80, average particle size 100 μm), in 2.0 kg of styrene were suspended, were added to the reaction mixture. After an additional 30 minutes, 1.6 kg of pentane was measured. Finally, the termination of the polymerization takes place at the final temperature of 130 ° C. The resulting polystyrene beads comprising the blowing agent are isolated by decanting, washing, and drying to remove internal water. They are foamed by conventional processes to give foam beads and then sintered to give foam blocks or shapers. The resulting foam blocks or molders meet the requirements of classifications of jurisdiction B 1 and B 2.

Example 2 3.6 kg of polystyrene (VPT, BASFG Aktiengesellschaft), 61. Og of dicumyl peroxide and 20.2 g of tert-butylperoxy 2-ethylhexanoate were dissolved in 14.4 kg of styrene and 900 g of dimethyl phenylphosphonate (5%) were added. by weight, based on styrene and polystyrene). 2.7 kg of an expanded graphite with an average particle size of 45 μm were then suspended with stirring. The organic phase was introduced into 20.2 liters of demineralized water in a 50 liter mixing vessel. The aqueous phase comprises 35.0 g of sodium pyrophosphate and 70.0 g of magnesium sulfate (Epsom salt). The suspension was heated rapidly to 90 ° C and then, for a period of 4 hours at 130 ° C. 60 minutes after having reached 90 ° C, 1.8 g of K 30 emulsifier (Bayer AG) was measured. After an additional 90 minutes, 1.6 kg of pentane was measured. Finally, the polymerization termination takes place at the final temperature of 130 ° C. The resulting polystyrene beads comprising the blowing agent are isolated by decanting, washing and drying to remove internal water. They are foamed by conventional processes to give foam beads and then sintered to give foam blocks or shapers. The resulting foam blocks or molders meet the fire rating requirements B 1 and B 2.

Example 3 A mixture of polystyrene, and also 15% by weight of expanded graphite (average particle size 45 μm) and 5% by weight of red phosphorus are continuously introduced into an extruder with an internal screw diameter of 53 mm and it melts. 6% by weight of pentane is continuously injected into the extruder as a blowing agent, through an inlet port in the extruder, and incorporated into the melt. The melt is granulated to give particles in the form of beads, through an underwater granulator attached to the die plate of the extruder and operating under pressure. Foam beads of volume density of 15 g / 1 were obtained twice by foaming, using steam. These foam beads, and a foam moulder produced from these, meet the requirements of fire ratings B 1 and B 2 to DIN 4102.

Claims (9)

1. A process for preparing particulate expandable styrene polymers by polymerization of styrene, where appropriate together with the comonomers, in aqueous suspension with the use of blowing agents before, during, or after polymerization, which comprises carrying out the polymerization in the presence of 5 to 50% by weight, based on the monomers, of expanded graphite.

2. The process as claimed in claim 1, wherein from 2 to 20% by weight, based on the monomers, of a phosphorous compound are also present during the polymerization.

3. The process as claimed in claim 2, wherein the phosphorous compound is red phosphorus, or an organic or inorganic phosphate, phosphite or phosphonate.

4. The process as claimed in claim 2, wherein the phosphorous compound is triphenyl phosphate, diphenylcresyl phosphate, ammonium polyphosphate, melamine phosphate, dimethyl phenylphosphonate, or diphenyl phosphate. The process as claimed in claim 1, wherein the expanded graphite has a density of 1.5 to 2.1 g / cm and an average particle size (larger diameter) of 20 to 2000 μm). 6. The process as claimed in claim 5, wherein the average particle size is from 20 to 100 μm. 7. The expandable, particulate styrene polymer which comprises from 5 to 50% by weight, based on the styrene polymer, of expanded graphite as a uniformly distributed flame retardant, wherein the expanded graphite has an average particle size of 20. at 100 μm. 8. The particulate, expandable styrene polymer, as claimed in claim 7, which also comprises from 2 to 20% by weight, based on the styrene polymer of a phosphorus compound. 9. The use of the expandable polystyrene particles as claimed in claim 1 or 7 to produce molded polystyrene foams that meet the requirements of fire ratings B 1 and B 2.