Classifications

• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J9/00—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof
  • C08J9/22—After-treatment of expandable particles; Forming foamed products
  • C08J9/224—Surface treatment
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J2201/00—Foams characterised by the foaming process
  • C08J2201/02—Foams characterised by the foaming process characterised by mechanical pre- or post-treatments
  • C08J2201/036—Use of an organic, non-polymeric compound to impregnate, bind or coat a foam, e.g. fatty acid ester
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J2201/00—Foams characterised by the foaming process
  • C08J2201/02—Foams characterised by the foaming process characterised by mechanical pre- or post-treatments
  • C08J2201/038—Use of an inorganic compound to impregnate, bind or coat a foam, e.g. waterglass
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J2325/00—Characterised by the use of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by an aromatic carbocyclic ring; Derivatives of such polymers
  • C08J2325/02—Homopolymers or copolymers of hydrocarbons
  • C08J2325/04—Homopolymers or copolymers of styrene

Definitions

• the present invention relates to beads of expandable vinylaromatic polymers and a .process for their preparation.
• the present invention relates to an expandable polystyrene in the form of beads with a reduced formation of lumps and the process for its preparation.
• Vinylaromatic polymers and among these, polystyrene in particular, are known products which have been adopted for a long time for preparing compact and/or expanded articles which can be used in various applicative sectors, among which the most important are household appliances, the transport and building industries, office machines, etc.
• a particularly interesting sector is the field of thermal insulation, where vinylaromatic polymers are essentially used in expanded form.
• the swelling, or pre-expansion, of the particles is generally effected with vapour, or another gas, maintained at a temperature slightly higher than the glass transition temperature (Tg) of the polymer.
• Tg glass transition temperature
• the particles tend to stick to each other and to avoid this drawback, they are treated with additives generally known as anti-lumping additives.
• additives generally known as anti-lumping additives.
• metallic stearates such as magnesium stearate
• This additive is extremely effective in preventing the beads from sticking during the pre-expansion phase but results in poor adhesion in the moulding phase during the preparation of the end-products .
• U.S. patent 3,520,833 describes the use of lecithin, added with the expanding agent during the impregnation of the particles, as anti-lumping additive.
• U.S. patent 3,444,104 describes the use of calcium and silicon aluminates . The lumps, in this case, are eliminated and the adhesion remains acceptable. The density of the beads in expansion, however, is poor.
• U.S. patent 3,462,293 describes the use of a polymeric latex, for example polyethylene or SAN copolymer, deposited on the particles .
• the subsequent drying treatment of the latex with air requires long times which make the preparation process quite unsuitable for industrial development .
• European patent 449,065 describes the use of oxides such as silica, alumina and titanium oxide. Although these products have a good capacity against the formation of lumps, they have the disadvantage, as specified above, of reducing the adhesion of the expanded beads during the moulding phase.
• the Applicant has now found a simple system for eliminating the formation of agglomerates of swollen vinylaromatic polymer beads without jeopardizing the subsequent ad- hesion and/or expandability.
• An object of the present invention therefore relates to beads of expandable vinylaromatic polymers which comprise: a) a matrix obtained by polymerizing 50-100% by weight of one or more vinylaromatic monomers and 0-50% by weight of at least one copolymerizable monomer; b) 1-10% by weight, calculated with respect to the polymer (a) , of an expanding agent englobed in the polymeric matrix; c) 2 ppm-2% by weight, calculated with respect to the polymer (a) , of an anti-lumping additive, distributed on the surface of the beads, selected from oxides of metals of groups IB and VIIIB or from mixtures consisting of oxides of metals of groups IB, IIB and VIIIB and esters of C 8 -C 25 fatty acids with the same metals.
• a further object of the present invention relates to a process for the preparation of expandable vinylaromatic polymer beads which comprises : polymerizing 50-100% by weight of one or more vinylaro- matic monomers and 0-50% by weight of at least one copolymerizable monomer; englobing an expanding agent in the polymeric matrix; and distributing on the surface of the beads obtained 2 ppm- 2% by weight, calculated with respect to the polymer, of an anti-lumping additive selected from oxides of metals of groups IB and VIIIB or from mixtures consisting of oxides of metals of groups IB, IIB and VIIIB and esters of C 8 -C 25 fatty acids with the same metals.
• the vinylaromatic polymers can be obtained with a polymerization process in aqueous suspension or continuous mass.
• the polymerization in suspension of the vinylaromatic monomer is carried out under conditions and in the presence of ad- ditives well known in the art.
• the suspending agent selected from insoluble inorganic salts, for example calcium or magnesium such as tricalcium phosphate or magnesium phosphate, or from organic suspending agents such as polyvinylpyrrolidone
• the polymerization is carried out in the presence of an initiating system or an expanding system.
• the initiating system generally comprises two peroxides, one with a halving time of an hour at 85-95°C and the other with a halving time of an hour at 110-120°C.
• these initiators are benzoylperoxide and terbutylperben- zoate.
• Any expanding agent capable of being englobed in the polymeric matrix can be used in a combination with the vinylaromatic polymers object of the present invention.
• liquid substances are used, with a boiling point ranging from 10 to 100°C, preferably from 20 to 80°C.
• Typical examples are aliphatic hydrocarbons, freon, carbon dioxide, water, etc.
• the expanding agent can be added to the polymer during the polymerization phase in suspension, or, alternatively, by impregnation of the beads produced at the end of the polymerization or by injection into the molten polymer according to the continuous mass preparation process.
• a polymer is obtained in the form of beads, which can be transformed to produce expanded articles with a density ranging from 5 to 50 g/1, preferably from 8 to 25 g/1, with an excellent thermal insulation capacity.
• additives capable of forming bonds both of the weak type (for example hydrogen bridges) or strong type (for example acid-base adducts) , can be used with the expanding agent.
• additives examples include methyl alcohol, isopropyl alcohol, dioctylphthalate, dimethylcarbonate, compounds containing an amine group, etc. These additives are generally added during the polymerization and/or englobed in the polymer together with the expanding agent .
• the expanding agents are preferably added during the polymerization phase and are selected from aliphatic or cycloaliphatic hydrocarbons containing from 3 to 6 carbon atoms, such as n-pentane, iso-pentane, cyclopentane or their mixtures; halogenated derivatives of aliphatic hydrocarbons containing from 1 to 3 carbon atoms such as, for example, dichlorodifluoromethane, 1, 2 , 2-trifluoroethane, 1, 1, 2-trifluoroethane; carbon dioxide and water.
• the term "vinylaromatic monomer”, as used in the present description and claims, essentially refers to a product which corresponds to the following general formula:
• n is zero or an integer ranging from 1 to 5
• R is a hydrogen atom or a methyl
• Y is a halogen, such as chlo- rine or bromine, or an alkyl or alkoxyl radical having from 1 to 4 carbon atoms .
• styrene ⁇ -methylstyrene, me- thylstyrene, ethylstyrene, butylstyrene, dimethylstyrene, mono-, di-, tri-, tetra- and penta-chlorostyrene, bromo- styrene, methoxy-styrene, acetoxy-styrene, etc.
• ⁇ -methylstyrene are the preferred vinylaromatic monomers.
• the vinylaromatic monomers having general formula (I) can be used alone or in a mixture of up to 50% by weight with other copolymerizable monomers.
• examples of these monomers are (meth) acrylic acid, C ⁇ -C 4 alkyl esters of
• (meth) acrylic acid such as methyl acrylate, methyl- methacrylate, ethyl acrylate, ethylmethacrylate, isopropyl acrylate, butyl acrylate, amides and nitriles of (meth) acrylic acid such as acrylamide, methacrylamide, acrylonitrile, methacrylonitrile, butadiene, ethylene, di- vinylbenzene, maleic anhydride, etc.
• Preferred copolymerizable monomers are acrylonitrile and methylmethacrylate .
• the vinylaromatic polymer or copolymer which is ob- tained has a molecular weight Mw ranging from 50, 000 to 250,000, preferably from 70,000 to 200,000.
• Mw molecular weight
• greater details on a process for the preparation of expandable vinylaromatic polymers in aqueous solution or, more generally, on polymerization in suspension, can be found in Journal of Macromolecular Science, Review in Macromolecular Chemistry and Physics c31 (263) 215-299 (1991) or in international patent application WO 98/51734.
• additives generally used with commercial materials, such as pigments, stabilizers, flame-retardant agents, antistatic agents, detaching agents, shock- resistant agents, etc.
• mineral fillers of athermanous materials during the po- lymerization such as graphite or refracting agents such as titanium dioxide, in a quantity ranging from 0.05 to 25% by weight, calculated with respect to the resulting polymer.
• substantially spherical polymer beads are obtained, with an average di- ameter ranging from 0.2 to 2 mm, inside which the expanding agent is homogeneously dispersed.
• the viscosity of the reagent solution by dissolving the vinylaromatic polymer therein, in a concen- tration ranging from 1 to 30% by weight, preferably from 5 to 20%, calculated with respect to the monomer alone.
• the solution can be obtained either by dissolving a preformed polymer (for example fresh polymer or the waste products of previous polymerizations and/or expansions) in the reagent mixture or by pre-polymerizing the monomer, or mixture of monomers, in mass, in order to obtain the above concentrations, and then continuing the polymerization in aqueous suspension in the presence of the remaining additives .
• the beads are dis- charged from the polymerization reactor, washed and dried.
• the beads produced are subjected to pre-treatment generally applied to traditional materials and which essentially consists in:
• a liquid antistatic agent such as amines, tertiary alkylamines, ethylene oxide-propylene oxide copolymers, etc.
• This agent is to facilitate both the adhesion of the coating and also the screening of the beads prepared in suspension;
• the coating essentially consisting of a mixture of mono-, di- and tri-esters of glycerin (or other alcohols) with fatty acids; and 3. distributing on the surface of the beads, the anti- lumping additive preferably selected from powders of ox- ides of iron (Fe 2 0 3 ) , copper (CuO) and zinc (ZnO) , optionally mixed with the corresponding ester of fatty acids such as stearic acid, palmitic acid, myristic acid, etc.
• the anti-lumping additive is generally used in the form of powders with an average particle-size ranging
• COMPARATIVE EXAMPLE 1 100 parts of styrene monomer, 0.30 parts of benzoyl peroxide, 0.15 parts of terbutylperbenzoate, 100 parts of demineralized water, 0.2 parts of tricalcium phosphate and 20 ppm of sodium dodecylbenzenesulfonate, were charged into a 2 litre reactor equipped with a stirrer. The mixture was then heated to 90°C for 4 hours and to 125°C for a further 6 hours.
• the expanding agent (7 parts of n-pentane) was added during the rise from 90 to 125°C.
• the beads were cen- trifuged, washed with water and dried with air at room tem- perature .
• the product is pre-expanded the following day with vapour at a temperature of 100°C at a density of 20 g/1, evaluating the quantity of clots, which proved to be practically zero.
• the expanded beads are then aged for a day and used the following day for the moulding of boxes (thickness 20 mm) at a pressure of 0.5 bars.
• the adhesion of the beads proved to be 5%.
• the beads polymerized according to Comparative example 1 were lubricated with 0.02% of diethanol alkyl amine and sieved, separating the fraction with a diameter ranging from 0.4 to 0.6 mm.
• the product is pre-expanded the following day with vapour at a temperature of 100°C at a density of 20 g/1, evaluating the quantity of lumps, which proved to be equal to 3 % .
• the expanded beads are then aged for a day and used the following day for the moulding of boxes (thickness 20 mm) at a pressure of 0.5 bars.
• the adhesion of the beads proved to be 40%.
• the beads polymerized according to Comparative example 1 were lubricated with 0.02% of diethanol alkyl amine and sieved, separating the fraction with a diameter ranging from 0.4 to 0.6 mm.
• the product is pre-expanded the following day with va- pour at a temperature of 100°C at a density of 20 g/1, evaluating the quantity of lumps, which proved to be absent.
• Comparative example 2 is repeated, reducing the zinc stearate to 0.05% and adding 0.05% of zinc oxide. There were no lumps and the adhesion was excellent, equal to 70%.
• Comparative example 1 is repeated, substituting the magnesium stearate with 5 ppm of ferric oxide in powder form, produced by Aldrich, with an average particle diame ⁇
• Comparative example 1 is repeated, substituting the magnesium stearate with 5 ppm of copper oxide (CuO) in pow- der form, produced by Aldrich, with an average particle di ⁇

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Health & Medical Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Medicinal Chemistry (AREA)
• Polymers & Plastics (AREA)
• Organic Chemistry (AREA)
• Manufacture Of Porous Articles, And Recovery And Treatment Of Waste Products (AREA)
• Graft Or Block Polymers (AREA)
• Compositions Of Macromolecular Compounds (AREA)

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• 2002
  • 2002-07-31 IT IT001711A patent/ITMI20021711A1/it unknown
• 2003
  • 2003-07-03 AT AT03766128T patent/ATE446982T1/de not_active IP Right Cessation
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