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WO2013000679A1 - Expandable graphite - containing vinyl aromatic polymers - Google Patents

Expandable graphite - containing vinyl aromatic polymers Download PDF

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Publication number
WO2013000679A1
WO2013000679A1 PCT/EP2012/060821 EP2012060821W WO2013000679A1 WO 2013000679 A1 WO2013000679 A1 WO 2013000679A1 EP 2012060821 W EP2012060821 W EP 2012060821W WO 2013000679 A1 WO2013000679 A1 WO 2013000679A1
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WO
WIPO (PCT)
Prior art keywords
vinyl aromatic
graphite
aromatic polymers
carbon black
expandable
Prior art date
Application number
PCT/EP2012/060821
Other languages
French (fr)
Inventor
Stéphane Nowe
Philippe Lodefier
Laetitia Urbanczyk
Original Assignee
Total Research & Technology Feluy
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Total Research & Technology Feluy filed Critical Total Research & Technology Feluy
Priority to EP20120727640 priority Critical patent/EP2683763A1/en
Publication of WO2013000679A1 publication Critical patent/WO2013000679A1/en

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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
    • C08J9/0066—Use of inorganic compounding ingredients
    • 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
    • C08J2325/06—Polystyrene

Definitions

  • the present invention relates to expandable vinyl aromatic polymers, in particular, expandable polystyrene granulates (EPS) containing specific carbon black powders.
  • EPS expandable polystyrene granulates
  • the invention also relates to the foams obtained by the sintering of expanded particles that are obtained from those expandable vinyl aromatic polymers and in particular to insulation planks with enhanced heat insulation capacity.
  • Expandable vinyl aromatic polymers are known for a long time for preparing heat insulation planks in the building industry. These planks are obtained by expanding impregnated beads of expandable polymer and moulding the expanded beads by means of pressure and temperature. The expansion of the EPS particles is generally performed with steam, at a temperature slightly higher than the glass transition temperature of the polymer.
  • Thermoplastic vinyl aromatic polymers such as polystyrene can be made expandable by incorporating a blowing agent in the polymeric matrix.
  • Typical blowing agents for vinyl aromatic polymers include at least one liquid hydrocarbon at room temperature containing from 3 to 7 carbon atoms, a halogenated hydrocarbon, carbon dioxide or water.
  • the quantity of blowing agent is conditioned by its molecular weight and by the foam density to be obtained. It usually ranges from 2 to 1 5% by weight, preferably from 3 to 9 %.
  • Expandable polymers are produced in general as beads or granules which, under the action of heat, supplied typically by steam, are first expanded to a desired density and, after a certain aging period, are sintered in moulds to any suitable shape.
  • EPS expansion technology is well known in the art and notably described in EP 126459, US 2006 21 1 780, US 2005 1 56344, US 6 783 710 and WO 2008 141766.
  • Talcum is the most common cell regulator for EPS and various types have been disclosed for this purpose in the prior art.
  • Carbon black is known as an infra red absorber having a positive effect on the thermal conductivity of expanded beads later sintered to insulation planks.
  • EP 372343 A1 describes EPS comprising carbon black and talcum and mentions that the use of 10% carbon black reduces the thermal conductivity by 15%. An abundant patent literature testifies the use of carbon black in this purpose.
  • WO 97 45477 A1 describes an EPS comprising 2-8% carbon black having a BET Nitrogen Surface Area ranging from 10 to 500 m2/g. Some expanded and sintered EPS compositions achieve a thermal conductivity ⁇ between 30-33 mW/mK.
  • EP 620 246 B1 describes expanded polystyrene foam with a density of less than 20 kg/m 3 comprising athermanous particles absorbing infrared radiation.
  • WO 2006-058733 A1 relates to expandable styrene polymer granulates, containing
  • a filler selected from pulverulent inorganic materials such as talc, chalk, kaolin, aluminium hydroxide, aluminium nitrite, aluminium silicate, barium sulphate, calcium carbonate, titanium dioxide, calcium sulphate, silicic acid, quartz powder, aerosil, alumina or wollastonite and
  • thermal conductivity ⁇ is 32 mW/m° K.
  • WO2010/031537 describes the use of isotropic or anisotropic petrole coke with an aspect ratio between 1 and 500.
  • the description mentions a preference for platelet or needle shapes for better IR reflection.
  • the particle aspect ratio on the rate of foam expansion.
  • US6139990 describes modified graphite particles made from scaly graphite.
  • the modified graphite cited has a degree of sphericity > 0.86 and the graphite slices take various directions.
  • this document is hereby incorporated by reference.
  • the present invention aims to provide expandable vinyl aromatic polymers granulates in particular, expandable polystyrene granulates (EPS) containing graphite with a high degree of circularity, optionally associated to flat Graphite and/or various types of Carbon Black . It aims in particular to provide expandable vinyl aromatic polymers with significantly shorter pre-expansion cycles while keeping similar insulation property of the final insulation board.
  • EPS expandable polystyrene granulates
  • the present invention discloses expandable vinyl aromatic polymers comprising graphite having a degree of circularity higher than 0.86.
  • the expandable vinyl aromatic polymers of the invention comprise further one or more types of carbon black.
  • the expandable vinyl aromatic polymers of the invention comprise further one or more types of graphite.
  • the carbon black has a BET specific surface area measured according to ASTM D-6556 is of between 9 and 65 m 2 /g.
  • the graphite having a degree of circularity higher than 0.86 has a particle size D50, measured by laser mastersizer according to
  • the present invention also discloses a vinyl aromatic polymer foam comprising expanded vinyl aromatic polymer particles according to any of the previous claims. Detailed description of the invention
  • polystyrene elastomer- modified polystyrene
  • copolymers of styrene and acrylonitrile SAN
  • SAN acrylonitrile
  • ABS elastomer-modified SAN
  • ABS which is obtained, for example, by grafting (graft polymerization) of styrene and acrylonitrile on a backbone of polybutadiene or of butadiene- acrylonitrile copolymer
  • copolymers with styrene blocks and blocks made of butadiene or isoprene or of a mixture butadiene /isoprene these block copolymers can be linear blocks copolymers or star blocks copolymers, they can be hydrogenated and/orpositionnalized.
  • These copolymers are described in ULLMANN'S ENCYCLOPEDIA OF INDUSTRIAL CHEMISTRY, fith edition (1995) Vol A26, pages 655-659, They are sold by Total Petrochemicals under the trade mark Finaclear®, by BASF under the trade mark Styrolux®, under the trade mark K-Resin® by Chevron Phillips Chemical,
  • SBR Styrene butadiene rubber
  • the vinyl aromatic polymer is polystyrene
  • it could be crystal polystyrene or rubber modified polystyrene.
  • the rubber modified polystyrene is called HIPS (High Impact Polystyrene) .
  • HIPS High Impact Polystyrene
  • the process for making HIPS is well known to those skilled in the art.
  • the rubber is "dissolved” in the styrene monomer (actually the rubber is infinitely swollen with the monomer). This results in two co- continuous phases.
  • the resulting "solution” is fed to a reactor and polymerized typically under shear. When the degree of polymerization is about equal to the weight % of rubber in the system it inverts (e.g.
  • the styrene/styrene polymer phase becomes continuous and the rubber phase becomes discontinuous.
  • the polymer is finished in a manner essentially similar to that for finishing polystyrene.
  • the polymer is prepared using conventional bulk, solution, or suspension polymerization techniques.
  • talc having a mean diameter above about 8 ⁇ , said mean diameter being measured by Laser Mastersizer according to standard ISO 13320:2009, one can cite the 20M00S supplied by the company Rio Tinto Minerals (Talcs de Luzenac).
  • the talc has a mean diameter above about 1 ⁇ and under 100 ⁇ , more advantageously in the range 2-50 ⁇ , preferably in the range 3-20 ⁇ , more preferably in the range 4-12 ⁇ .
  • the D(95) is around 100 ⁇ or below, more advantageously around 50 ⁇ , much more advantageously around 40 ⁇ , preferably around 35 ⁇ . D(95) means that 95% of particles are smaller than this value.
  • the BET of the talc is in the range 1 -20 m2/g and preferably in the range 3-10 m2/g.
  • the proportion of talc is advantageously from 0.5 to 2w% and preferably around 1 %.
  • the proportion can be determined easily by the man skilled in the art.
  • the thermal conductivity of the foam decreases with the increasing proportion of carbon black.
  • the range can be from about 1 to about 6 w%. It is easy with a reduced number of experiments to find the proportion to get a thermal conductivity ⁇ of about 32 mW/m° K or lower of the foam at 20 g/l density.
  • the carbon black has advantageously a surface area (preferably the BET nitrogen surface area), measured according to ASTM D-6556/09, ranging from 5 to 1000 m2/g, more advantageously from 5 to 800 m2/g . Preferably said surface area ranges from 5 to 100m2/g and more preferably from 9 to 75 m2/g.
  • fillers non limitative examples of material able to reduce the thermal conductivity and/or to enhance the properties of the expanded vinyl aromatic polymer.
  • material able to reduce the thermal conductivity and/or to enhance the properties of the expanded vinyl aromatic polymer.
  • it may comprise at least one flame retardant selected in particular from halogenated hydrocarbons, preferably brominated hydrocarbons, in particular C6 to C12 hydrocarbons, such as hexabromocyclohexane, penta- bromomonochlorocyclohexane or hexabromocyclododecane, in an amount which can range from 0.05 to 4 parts, preferably from 0.1 to 1 .5 parts, by weight, per 100 parts by weight of the styrene polymer.
  • the composition may further comprise at least one nucleating agent selected in particular from synthetic waxes, in particular Fischer- Tropsch waxes and polyolefin waxes such as polyethylene waxes or polypropylene waxes, in an amount which can range from 0.05 to 1 part, preferably from 0.1 to 0.5 part, by weight per 100 parts by weight of the vinyl aromatic polymer.
  • the composition may likewise comprise at least one plasticizer, selected in particular from mineral oils and petroleum waxes such as paraffin waxes, in an amount which can range from 0.1 to 1 part, preferably from 0.1 to 0.8 part, by weight per 100 parts by weight of the vinyl aromatic polymer.
  • the composition may additionally comprise at least one agent which facilitates the demoulding of the moulded and expanded articles, selected in particular from inorganic salts and esters of stearic acid, such as glycerol mono-, di or tristearates and zinc stearate, calcium stearate or magnesium stearate, in an amount which can range from 0.05 to 1 part, preferably from 0.1 to 0.6 part, by weight per 100 parts by weight of the vinyl aromatic polymer.
  • inorganic salts and esters of stearic acid such as glycerol mono-, di or tristearates and zinc stearate, calcium stearate or magnesium stearate
  • the mixing is carried out in a chamber equipped with at least one stirring means and under temperature and pressure conditions which are capable of preventing expansion of the composition, preferably in an extruder, in particular a single-screw or twin-screw extruder, or in one or more static mixers at a temperature greater than the glass transition temperature of the polymer, in particular a temperature ranging from 120 to 250° C and under an absolute pressure ranging from 0.1 to 10 MPa.
  • compositions are tested in view of their pre-expansion speed.
  • the pre-expansion operation is conducted at a vapour pressure of 0.1 5 MPa (1 .5 Bar) in a Erlenbach pre-expander EDVD-1 50, always under the same conditions to make the pre-expansion times comparable.
  • the reached final density is 19+/-1 g/l.
  • the recovered beads whose diameter is in the range 0.9-1 .6 mm, are then treated with zinc stearate as coating agent.
  • the treated beads are pre-expanded with steam at 1 .5 bar in a preexpander (EDVD -150 Erlenbach), left to age for 1 day and finally used to mould a board of 8 cm thickness. After 1 day, the density of the board, determined by weighing the board and measuring its dimensions, is 19.3 g/l.
  • the thermal conductivity of the board measured according to the norm ISO 8301 , is 31 mW/mK.
  • the following table shows the physical properties of the carbon black and graphite fillers used in the present invention.
  • Tim rex KS6 Timcal 20 3.4 6.5
  • Comparative examples 1 to 10 contain various carbon black or graphite combinations and have an average pre-expansion time of 15 +/- 2 seconds.
  • Examples 1 1 to 21 according to the invention contain optionally various carbon black or graphite combinations but includes various amounts of graphite having a degree of circularity higher than 0.86 and have an average pre-expansion 10 time of 9 +/- 2 seconds which represents a significant improvement and thus energy saving.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Inorganic Chemistry (AREA)
  • Health & Medical Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Medicinal Chemistry (AREA)
  • Polymers & Plastics (AREA)
  • Organic Chemistry (AREA)
  • Compositions Of Macromolecular Compounds (AREA)
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Abstract

The present invention discloses expandable vinyl aromatic polymers comprising graphite having a degree of circularity higher than 0.86.

Description

EXPANDABLE GRAPHITE - CONTAINING VINYL AROMATIC POLYMERS
Field of the Invention
[0001 ] The present invention relates to expandable vinyl aromatic polymers, in particular, expandable polystyrene granulates (EPS) containing specific carbon black powders. The invention also relates to the foams obtained by the sintering of expanded particles that are obtained from those expandable vinyl aromatic polymers and in particular to insulation planks with enhanced heat insulation capacity. State of the Art
[0002] Expandable vinyl aromatic polymers are known for a long time for preparing heat insulation planks in the building industry. These planks are obtained by expanding impregnated beads of expandable polymer and moulding the expanded beads by means of pressure and temperature. The expansion of the EPS particles is generally performed with steam, at a temperature slightly higher than the glass transition temperature of the polymer.
[0003] Thermoplastic vinyl aromatic polymers such as polystyrene can be made expandable by incorporating a blowing agent in the polymeric matrix. Typical blowing agents for vinyl aromatic polymers include at least one liquid hydrocarbon at room temperature containing from 3 to 7 carbon atoms, a halogenated hydrocarbon, carbon dioxide or water. The quantity of blowing agent is conditioned by its molecular weight and by the foam density to be obtained. It usually ranges from 2 to 1 5% by weight, preferably from 3 to 9 %.
[0004] Expandable polymers are produced in general as beads or granules which, under the action of heat, supplied typically by steam, are first expanded to a desired density and, after a certain aging period, are sintered in moulds to any suitable shape.
[0005] EPS expansion technology is well known in the art and notably described in EP 126459, US 2006 21 1 780, US 2005 1 56344, US 6 783 710 and WO 2008 141766. [0006] Talcum is the most common cell regulator for EPS and various types have been disclosed for this purpose in the prior art.
[0007] Carbon black is known as an infra red absorber having a positive effect on the thermal conductivity of expanded beads later sintered to insulation planks.
[0008] EP 372343 A1 describes EPS comprising carbon black and talcum and mentions that the use of 10% carbon black reduces the thermal conductivity by 15%. An abundant patent literature testifies the use of carbon black in this purpose.
[0009] WO 97 45477 A1 describes an EPS comprising 2-8% carbon black having a BET Nitrogen Surface Area ranging from 10 to 500 m2/g. Some expanded and sintered EPS compositions achieve a thermal conductivity λ between 30-33 mW/mK.
[0010] EP 620 246 B1 describes expanded polystyrene foam with a density of less than 20 kg/m3 comprising athermanous particles absorbing infrared radiation.
[001 1 ] WO 2006-058733 A1 relates to expandable styrene polymer granulates, containing
a) between 5 and 50 wt. % of a filler, selected from pulverulent inorganic materials such as talc, chalk, kaolin, aluminium hydroxide, aluminium nitrite, aluminium silicate, barium sulphate, calcium carbonate, titanium dioxide, calcium sulphate, silicic acid, quartz powder, aerosil, alumina or wollastonite and
b) between 0.1 and 10 wt. % carbon black or graphite.
In example 2 there are 1 wt% carbon black and 10w% chalk, the thermal conductivity λ is 32 mW/m° K.
[0012] Other disclosures discussing similar effects of cell regulators and infrared absorbers such as carbon black are US 2007 01 12082 A1 ; WO 2006 108672 A2; WO 2007 045454 A1 ; WO 2008 141766 A1 and WO 2008 061678 A2.
[0013] WO2010/031537 describes the use of isotropic or anisotropic petrole coke with an aspect ratio between 1 and 500. The description mentions a preference for platelet or needle shapes for better IR reflection. However, there is no comment about the influence of the particle aspect ratio on the rate of foam expansion.
[0014] US6139990 describes modified graphite particles made from scaly graphite. The modified graphite cited has a degree of sphericity > 0.86 and the graphite slices take various directions. As several features of the herein disclosed Graphite type are present in the description of the present invention, this document is hereby incorporated by reference.
[0015] Graphite exists under different forms, as described in the paper Kwiecinska, B. International Journal of Coal Geology, 2004, 57, 99- 116. [0016] In the present invention, it has been discovered that substituting usual flat graphite particles or carbon black by graphite particles with a high degree of circularity (>0.86) leads to significantly shorter pre-expansion cycles while giving good insulation property of the final insulation board. In the present invention the circularity is defined as the ratio of the circumferential length of equivalent circle/circumferential length of projected image of the particle. This definition is given on Figure 4 of the document US, 139,990 incorporated by reference.
[0017] The shorter pre-expansion cycles are explained by the fact that spherical particles have a lower impact on melt viscosity than flat graphite or carbon black. The material thus expands more easily.
Aims of the Invention
[0018] The present invention aims to provide expandable vinyl aromatic polymers granulates in particular, expandable polystyrene granulates (EPS) containing graphite with a high degree of circularity, optionally associated to flat Graphite and/or various types of Carbon Black . It aims in particular to provide expandable vinyl aromatic polymers with significantly shorter pre-expansion cycles while keeping similar insulation property of the final insulation board. Summary of the Invention
[0019] The present invention discloses expandable vinyl aromatic polymers comprising graphite having a degree of circularity higher than 0.86.
[0020] Preferably, the expandable vinyl aromatic polymers of the invention comprise further one or more types of carbon black.
[0021 ] Preferably, the expandable vinyl aromatic polymers of the invention comprise further one or more types of graphite.
[0022] Advantageously the carbon black has a BET specific surface area measured according to ASTM D-6556 is of between 9 and 65 m2/g.
[0023] Preferably, the graphite having a degree of circularity higher than 0.86 has a particle size D50, measured by laser mastersizer according to
IS013320:2009 of between 1 and 30μιη
[0024] The present invention also discloses a vinyl aromatic polymer foam comprising expanded vinyl aromatic polymer particles according to any of the previous claims. Detailed description of the invention
[0025] As regards the vinyl aromatic polymer, mention may be made of:
polystyrene, elastomer- modified polystyrene,
copolymers of styrene and acrylonitrile (SAN), elastomer-modified SAN, in particular ABS, which is obtained, for example, by grafting (graft polymerization) of styrene and acrylonitrile on a backbone of polybutadiene or of butadiene- acrylonitrile copolymer,
mixtures of SAN and ABS,
copolymers with styrene blocks and blocks made of butadiene or isoprene or of a mixture butadiene /isoprene, these block copolymers can be linear blocks copolymers or star blocks copolymers, they can be hydrogenated and/or fonctionnalized. These copolymers are described in ULLMANN'S ENCYCLOPEDIA OF INDUSTRIAL CHEMISTRY, fith edition (1995) Vol A26, pages 655-659, They are sold by Total Petrochemicals under the trade mark Finaclear®, by BASF under the trade mark Styrolux®, under the trade mark K-Resin® by Chevron Phillips Chemical,
SBR (Styrene butadiene rubber).
[0026] In the specific embodiment in which the vinyl aromatic polymer is polystyrene, it could be crystal polystyrene or rubber modified polystyrene. The rubber modified polystyrene is called HIPS (High Impact Polystyrene) .The process for making HIPS is well known to those skilled in the art. The rubber is "dissolved" in the styrene monomer (actually the rubber is infinitely swollen with the monomer). This results in two co- continuous phases. The resulting "solution" is fed to a reactor and polymerized typically under shear. When the degree of polymerization is about equal to the weight % of rubber in the system it inverts (e.g. the styrene/styrene polymer phase becomes continuous and the rubber phase becomes discontinuous. After phase inversion the polymer is finished in a manner essentially similar to that for finishing polystyrene. The polymer is prepared using conventional bulk, solution, or suspension polymerization techniques.
[0027] As regards talc having a mean diameter above about 8 μιη, said mean diameter being measured by Laser Mastersizer according to standard ISO 13320:2009, one can cite the 20M00S supplied by the company Rio Tinto Minerals (Talcs de Luzenac). Advantageously the talc has a mean diameter above about 1 μιη and under 100 μιη, more advantageously in the range 2-50 μιη, preferably in the range 3-20 μιη, more preferably in the range 4-12 μιη. Advantageously the D(95) is around 100 μιη or below, more advantageously around 50 μιη, much more advantageously around 40 μιη, preferably around 35 μιη. D(95) means that 95% of particles are smaller than this value. Advantageously the BET of the talc is in the range 1 -20 m2/g and preferably in the range 3-10 m2/g. The proportion of talc is advantageously from 0.5 to 2w% and preferably around 1 %.
[0028] As regards the carbon black, the proportion can be determined easily by the man skilled in the art. The thermal conductivity of the foam decreases with the increasing proportion of carbon black. The range can be from about 1 to about 6 w%. It is easy with a reduced number of experiments to find the proportion to get a thermal conductivity λ of about 32 mW/m° K or lower of the foam at 20 g/l density. The carbon black has advantageously a surface area (preferably the BET nitrogen surface area), measured according to ASTM D-6556/09, ranging from 5 to 1000 m2/g, more advantageously from 5 to 800 m2/g . Preferably said surface area ranges from 5 to 100m2/g and more preferably from 9 to 75 m2/g. One can cite the Ensaco® 150, Ensaco® 350 supplied by the company Timcal; Lamp Black® 101 , Printex® 30 supplied by Evonik; Black Pearl® 120, Black Pearl® 4040 supplied by Cabot Corp.
[0029] As regards the fillers, non limitative examples of material able to reduce the thermal conductivity and/or to enhance the properties of the expanded vinyl aromatic polymer. One can cite graphite, mica, silica, aluminium flakes, coke, titanium dioxide and barium sulfate.
[0030] One can cite also flame retardants, nucleating agents, plasticizers and agents which facilitate the demoulding of the moulded and expanded articles. In particular it may comprise at least one flame retardant selected in particular from halogenated hydrocarbons, preferably brominated hydrocarbons, in particular C6 to C12 hydrocarbons, such as hexabromocyclohexane, penta- bromomonochlorocyclohexane or hexabromocyclododecane, in an amount which can range from 0.05 to 4 parts, preferably from 0.1 to 1 .5 parts, by weight, per 100 parts by weight of the styrene polymer. The composition may further comprise at least one nucleating agent selected in particular from synthetic waxes, in particular Fischer- Tropsch waxes and polyolefin waxes such as polyethylene waxes or polypropylene waxes, in an amount which can range from 0.05 to 1 part, preferably from 0.1 to 0.5 part, by weight per 100 parts by weight of the vinyl aromatic polymer. The composition may likewise comprise at least one plasticizer, selected in particular from mineral oils and petroleum waxes such as paraffin waxes, in an amount which can range from 0.1 to 1 part, preferably from 0.1 to 0.8 part, by weight per 100 parts by weight of the vinyl aromatic polymer.
[0031 ] The composition may additionally comprise at least one agent which facilitates the demoulding of the moulded and expanded articles, selected in particular from inorganic salts and esters of stearic acid, such as glycerol mono-, di or tristearates and zinc stearate, calcium stearate or magnesium stearate, in an amount which can range from 0.05 to 1 part, preferably from 0.1 to 0.6 part, by weight per 100 parts by weight of the vinyl aromatic polymer.
[0032] As regards the process to make said expandable polymer, it is carried out by mixing the vinyl aromatic polymer in the melted state with the blowing agent or agents, talc carbon black and the fillers.
[0033] In an advantageous embodiment the mixing is carried out in a chamber equipped with at least one stirring means and under temperature and pressure conditions which are capable of preventing expansion of the composition, preferably in an extruder, in particular a single-screw or twin-screw extruder, or in one or more static mixers at a temperature greater than the glass transition temperature of the polymer, in particular a temperature ranging from 120 to 250° C and under an absolute pressure ranging from 0.1 to 10 MPa.
[0034] The production method of such expandable beads has already been described in EP 126459, US 2006 21 1 780, US 2005 1 56344, US 6 783 710 and WO 2008 141766, the content of which is incorporated in the present.
[0035] The expanded beads are then moulded by the use of steam into blocs which are later cut into insulation boards. This process is well known by those skilled in the art.
[0036] Shortening the pre-expansion time saves considerable amounts of steam, thus energy. A few seconds more or less in the pre-expansion phase leads to a considerable difference in energy consumption of the global process of EPS expansion and moulding.
[0037] Examples
In the following examples, high performance compositions are tested in view of their pre-expansion speed. The pre-expansion operation is conducted at a vapour pressure of 0.1 5 MPa (1 .5 Bar) in a Erlenbach pre-expander EDVD-1 50, always under the same conditions to make the pre-expansion times comparable.
The reached final density is 19+/-1 g/l.
[0038] Reference Example 1
A mixture containing 94.7 parts of polystyrene (PS 1450 N of Total Petrochemicals), 1 part of talc from Rio Tinto® (mean particle size measured with laser mastersizer: 10 μιη), 0.3 part of polyethylene wax (HDPE Mn = 2000 g/mol) from Baker Petrolite Polymers Divison and 4 parts of carbon black from Timcal (BET: 65m2 /g) are fed in an extruder. 6w% of pentane (80/20 n-/iso pentane) is injected in the extruder. The sample is finally granulated at die exit by an underwater pelletizer with a face cutting system. The output of the double screw extruder is 50 Kg/h. The recovered beads, whose diameter is in the range 0.9-1 .6 mm, are then treated with zinc stearate as coating agent. The treated beads are pre-expanded with steam at 1 .5 bar in a preexpander (EDVD -150 Erlenbach), left to age for 1 day and finally used to mould a board of 8 cm thickness. After 1 day, the density of the board, determined by weighing the board and measuring its dimensions, is 19.3 g/l. The thermal conductivity of the board, measured according to the norm ISO 8301 , is 31 mW/mK.
[0039] Example 1 is taken as reference for all the following examples which are identical except the variable of carbon black and graphite. All examples contains 6wt% pentane, 1 part Talcum and 0.3 parts of polyethylene wax (HDPE Mn = 2000 g/mol).
All examples exhibit a thermal conductivity between 31 and 33 mW/mK.
The following table shows the physical properties of the carbon black and graphite fillers used in the present invention.
Specification of the various carbon black and graphite types
Specific surf. Area
Carbon black Provider
(BET, mVg)1
CSX 691 Cabot Corp. 16
Black Pearls 120 Cabot Corp. 31
Ensaco 250G Timcal 65
Ensaco 150G Timcal 50
Arosperse 15 Evonik 9
Lampblack 101 Evonik 29 Specific surf. Area D50 D90
Graphite Provider
(BET, mVg)1 μητι μιτι
Tim rex KS6 Timcal 20 3.4 6.5
Mechano-Cap <20 <20
HC Carbon* 5 1 P1 5
(invention)
S12 Kaiyu Industrial <20 <20
3.5-8
(Invention) *(HK) Limited The graphite with high circularity have been sieved to use the particle size fraction of less than 20 μιη
1 : measured according to mastersizer IS013320:2009
Table of comparative examples and examples according to the invention
Figure imgf000010_0001
[0040] Discussion
Graphite with high circularity has a benefic influence on the pre-expansion time. 5 [0041 ] Comparative examples 1 to 10 contain various carbon black or graphite combinations and have an average pre-expansion time of 15 +/- 2 seconds.
[0042] Examples 1 1 to 21 according to the invention contain optionally various carbon black or graphite combinations but includes various amounts of graphite having a degree of circularity higher than 0.86 and have an average pre-expansion 10 time of 9 +/- 2 seconds which represents a significant improvement and thus energy saving.

Claims

1 . Expandable vinyl aromatic polymers comprising graphite having a degree of circularity higher than 0.86.
2 . Expandable vinyl aromatic polymers according to claim 1 comprising further one or more types of carbon black.
3 . Expandable vinyl aromatic polymers according to claim 1 or 2 comprising further one or more types of graphite.
4 . Expandable vinyl aromatic polymers according to claim 2 wherein the carbon black has a BET specific surface area, measured according to ASTM D-6556, of between 9 and 65 m2/g.
5 . Expandable vinyl aromatic polymers according to any of the preceding claims wherein the graphite having a degree of circularity higher than 0.86 has a particle size D50, measured by laser mastersizer according to IS013320:2009 of between 1 and 30μιη
6 . Vinyl aromatic polymer foam comprising expanded vinyl aromatic polymer particles according to any of the previous claims.
PCT/EP2012/060821 2011-06-27 2012-06-07 Expandable graphite - containing vinyl aromatic polymers WO2013000679A1 (en)

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JP2019001999A (en) * 2017-06-13 2019-01-10 株式会社イノアック技術研究所 Conductive foam body
EP2938662B1 (en) 2012-12-28 2019-08-21 Total Research & Technology Feluy Expandable vinyl aromatic polymers containing graphite particles having a polymodal particle size distribution

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EP2938662B1 (en) 2012-12-28 2019-08-21 Total Research & Technology Feluy Expandable vinyl aromatic polymers containing graphite particles having a polymodal particle size distribution
CN103554620A (en) * 2013-10-31 2014-02-05 合肥得润电子器件有限公司 Dampproof polyethylene insulating material for wire harness of communication equipment
JP2019001999A (en) * 2017-06-13 2019-01-10 株式会社イノアック技術研究所 Conductive foam body
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