Compositions of expandable vinyl aromatic polymers with an improved thermal insulation capacity, process for their production and expanded articles obtained therefrom

Abstract

Expandable vinyl aromatic polymers comprising: a matrix obtained by polymerizing 50-100% by weight of one or more vinyl aromatic monomers and 0-50% by weight of at least one co-polymerizable monomer; 1-10% by weight, calculated with respect to polymer (a), of an expanding agent embedded in the polymeric matrix; 0-25% by weight, calculated with respect to polymer (a), of a filler comprising carbon coke having an average diameter of between 0.5 and 100 m, with a surface area, measured according to ASTM D-3037/89, ranging from 5 to 200 m.sup.2/g; 0.05-10% by weight, calculated with respect to polymer (a), of expanded graphite in particle form, with a particle average diameter (size) ranging from 1 to 30 m, a surface area, measured according to ASTM D-3037/89, ranging from 5 to 500 m.sup.2/g and a density ranging from 1.5 to 5 g/cm.sup.3.

Claims

1. An expandable vinyl aromatic polymer composition comprising: a) a polymeric matrix (a) prepared by polymerizing a base comprising 50-100% by weight of a vinyl aromatic monomer and 0-50% by weight of a copolymerisable monomer; b) 1-10% by weight, calculated on polymer matrix (a), of an expanding agent embedded in the polymeric matrix; and an athermanous filler comprising: c) 0.5-25% by weight, calculated on polymer matrix (a), of particulate carbon coke with a mean particle diameter (d.sub.50) (size) of from 0.5 to 100 m, and a surface area, measured according to ASTM D-3037-89 (BET), of from 5 to 200 m.sup.2/g, said particulate carbon coke being selected from calcined coke and needle coke; and d) 0.5-10% by weight, calculated on polymer matrix (a), of particulate expanded graphite with a mean particle diameter (d.sub.50) (size) of from 1 to 30 gm and a surface area, measured according to ASTM D-3037-89 (BET) of from 5 to 500 m.sup.2/g, wherein the athermanous filler is embedded in the polymeric matrix.

2. The composition according to claim 1, wherein the athermanous filler comprises up to 5% by weight, calculated on polymer matrix (a), of carbon black.

3. The composition according to claim 2, wherein the carbon black has a mean particle size (d.sub.50) of from 10 to 500 nm and a surface area of from 5 to 40 m.sup.2/g.

4. The composition according to claim 1, further comprising from 0.1 to 8% by weight, with respect to polymer matrix (a), of a brominated self-extinguishing additive and from 0.05 to 2% by weight, based on polymer matrix (a), of a synergist comprising a labile CC or OO bond.

5. An expanded article obtained with the expandable vinyl aromatic polymer composition according to claim 1 having a density of from 5 to 50 g/1 and a thermal conductivity of from 25 to 50 mW/mK.

6. An extruded expanded sheet of a vinyl aromatic polymer comprising a cellular matrix of a vinyl aromatic polymer (a) having a density of from 10 to 200 g/1, a mean cell size of from 0.01 to 1.00 mm and comprising an athermanous filler comprising: a) 0.5-25% by weight, calculated on cellular matrix (a), of particulate carbon coke with a mean particle diameter (d.sub.50) (size) of from 0.5 to 100 m, and a surface area, measured according to ASTM D-3037-89 (BET), of from 5 to 200 m.sup.2/g, said particulate carbon coke being selected from calcined coke and needle coke; and b) 0.5-10% by weight, calculated on cellular matrix (a), of particulate expanded graphite with a mean particle diameter (d.sub.50) (size) of from 1 to 30 m and a surface area, measured according to ASTM D-3037-89 (BET) of from 5 to 500 m2/g.

7. The extruded sheet according to claim 6, wherein the athermanous filler comprises up to 5% by weight, calculated on the polymer, of the carbon black.

8. A process for preparing the expandable vinyl aromatic polymer composition, in the form of beads or granules, according to claim 1, the process comprising polymerizing in an aqueous suspension a vinyl aromatic monomer, optionally together with a polymerisable comonomer in an amount up to 50% by weight, in the presence of the athermanous filler comprising the particulate coke with a mean particle diameter (size) of from 0.5 to 100 m and a surface area, measured according to ASTM D-3037-89 (BET), of from 5 to 200 m.sup.2/g and the expanded particulate-form graphite with a mean particle diameter (d.sub.50) (size) of from 1 to 30 m, and a surface area, measured according to ASTM D-3037-89 (BET), of from 5 to 500 m.sup.2/g and at least in the presence of a peroxide radical initiator and an expanding agent added before, during or at the end of the polymerizing.

9. The process according to claim 8, wherein the athermanous filler further comprises up to 5% by weight, calculated on the polymer, of the carbon black.

10. The process according to claim 8, wherein a viscosity of a reacting solution of vinyl aromatic monomers, to be suspended in water, is increased by prepolymerizing the monomer, or monomer mixture in bulk, until a polymer concentration of from 1 to 30% by weight is obtained.

11. The process according to claim 8, wherein at the end of the polymerizing, expandable polymer beads or granules having a mean diameter of from 0.2 to 3 mm are obtained, and the athermanous filler is homogenously dispersed therein.

12. A process for preparing through continuous bulk polymerization the expandable vinyl aromatic polymer composition, as beads or granules, according to claim 1, the process comprising: mixing a vinyl aromatic polymer in granules or in powder form or already in a molten state, with a mean molecular weight MW of from 50.000 to 250.000, with the athermanous filler comprising the particulate coke, with a mean particle diameter (d.sub.50) of from 0.5 to 100 m and a surface area, measured according to ASTM D-3037-89 (BET), of from 5 to 200 m.sup.2/g and the expanded particulate-form graphite with a mean particle diameter (d.sub.50) (size) of from 1 to 30 m, and a surface area, measured according to ASTM D-3037-89 (BET), of from 5 to 500 m.sup.2/g and with possible further additives; ii. optionally, if it is not already in the molten state, bringing the polymer mixture to a temperature higher than a melting point of the vinyl aromatic polymer; iii. incorporating the expanding agent and optionally other additives, in the molten polymer; iv. mixing the polymer composition thus obtained by means of static or dynamic mixing elements; and v. granulating the composition thus obtained in a device comprising a die, a cutting chamber and a cutting system.

13. The process according to claim 12, wherein at the end of the granulating, expandable polymer beads or granules with a mean diameter of from 0.2 to 3 mm are obtained, and the athermanous filler is homogenously dispersed therein.

14. The process according to claim 8, comprising incorporating at least the athermanous additive in a master-batch, based on a vinyl aromatic polymer of average molecular weight of from 50.000 to 250.000.

15. A process for producing the extruded expanded vinyl aromatic polymer sheet according to claim 6, the process comprising: a1. mixing a vinyl aromatic polymer in pellet form and an athermanous filler comprising of from 0.5 to 25% by weight, calculated on the polymer, of the particulate coke with a mean particle diameter (d.sub.50) (size) of from 0.5 to 100 m and a surface area, measured according to ASTM D-3037-89 (BET), of from 5 to 200 m.sup.2/g and of from 0.5 to 10% by weight, calculated on the polymer, of the expanded particulate-form graphite with a mean particle diameter (d.sub.50) (size) of from 1 to 30 m, and a surface area, measured according to ASTM D-3037-89 (BET), of from 5 to 500 m.sup.2/g; b1. heating mixture (a1) to a temperature of from 180 to 250 C. so as to obtain a polymeric melt, which is subjected to homogenization; c1. adding at least an expanding agent and optionally the additives, to the polymeric melt; d1. homogenizing the polymeric melt by incorporating the expanding agent; el. homogenously cooling down the polymeric melt (d1) to a temperature not exceeding 200 C. and not below Tg of a resulting polymer composition; and f1. extruding the polymeric melt through a die to obtain a polymer expanded sheet.

16. The process according to claim 15, wherein the athermanous filler added to the vinyl aromatic polymer comprises up to 5% by weight, calculated on the polymer, of the carbon black.

17. The process according to claim 15, wherein the pellet vinyl aromatic polymer is substituted, totally or partially, by the vinyl aromatic polymer compositions, in the form of beads or granules.

18. The process according to claim 15, wherein the pellets of vinyl aromatic polymer are substituted, totally or partially, by vinyl aromatic polymers in which the athermanous filler has been dispersed as either master or as derivatives from post-consumption products.

Description

EXAMPLE 1 (COMPARATIVE)

(1) A mixture is charged into a closed and stirred container, consisting of 150 parts by weight of water, 0.2 parts of sodium pyrophosphate, 100 parts of styrene, 0.25 parts of tert-butylperoxy-2-ethylhexanoate, 0.25 parts of tert-butyl perbenzoate and 2 parts of Calcinated Coke 4023 sold by the company Asbury Graphite Mills Inc. (USA), having a size (d.sub.50) of about 5 m, a BET of about 20 m.sup.2/g. The mixture is heated under stirring to 90 C.

(2) After about 2 hours at 90 C., 4 parts of a solution of polyvinylpyrrolidone at 10% are added. The mixture is heated to 100 C., still under stirring, for a further 2 hours, 7 parts of a 70/30 mixture of n-pentane and i-pentane are added, the whole mixture is heated for a further 4 hours to 125 C., it is then cooled and the batch is discharged.

(3) The granules of expandable polymer thus produced are subsequently collected and washed with water. The granules are then dried in a warm air flow, 0.02% of a non-ionic surface-active agent is added, consisting of a condensate of ethylene oxide and propylene oxide on a glycerine base, sold by Dow (Voranol CP4755) and they are subsequently screened separating the fraction with a diameter ranging from 1 to 1.5 mm.

(4) This fraction proved to represent 40%, 30% being the fraction between 0.5 and 1 mm, 15% the fraction between 0.2 and 0.5 mm, and 15% the gross fraction, between 1.5 and 3 mm.

(5) 0.2% of glyceryl monostearate and 0.1% of zinc stearate are then added to the fraction of 1 to 1.5 mm.

(6) The product is pre-expanded to 17 g/l with vapour at a temperature of 100 C., left to age for 1 day and used for the moulding of blocks (having dimensions of 10401030550 mm).

(7) The blocks were then cut to prepare flat sheets on which the thermal conductivity is measured. The thermal conductivity, measured after 5 days of residence in an oven at 70 C., was 34.5 mW/mK. The thermal conductivity measured on a specimen without an athermanous filler was equal to 40 mW/mK at 17 g/l.

EXAMPLE 2

(8) The same procedure is adopted as in Example 1 with the exception that the coke is substituted with 1 part of expanded graphite of the type ABG1005 produced by the company Superior Graphite. This expanded graphite has a particle size (d.sub.50) of about 6.5 m, a surface area (BET) of about 16.5 m.sup.2/g and a density of 2.15 g/cm.sup.3.

(9) The sheet obtained has a thermal conductivity of 34 mW/mK.

EXAMPLE 3

(10) A mixture is charged into a closed and stirred container, consisting of 150 parts by weight of water, 0.2 parts of sodium tricalcium phosphate, 100 parts of styrene, 0.25 parts of tert-butylperoxy-2-ethylhexanoate, 0.25 parts of tert-butylperbenzoate, 0.01 parts of sodium metabisulphite, 2 parts of the coke used in comparative example 1 and 1 part of expanded graphite used in Example 2. The mixture is heated under stirring to 90 C.

(11) After about 2 hours at 90 C., the mixture is heated for a further 2 hours to 100 C., 7 parts of a 70/30 mixture of n-pentane and i-pentane are added, the mixture is heated for a further 4 hours to 125 C., it is then cooled and discharged.

(12) The granules of expandable polymer thus produced are processed as in comparative example 1, separating the fraction with a diameter ranging from 1 to 1.5 mm.

(13) This fraction proved to represent 60%, 25% being the fraction from 0.5 to 1 mm, 5% the fraction from 0.2 to 0.5 mm, and 10% the gross fraction, from 1.5 to 3 mm. 0.2% of glyceryl monostearate and 0.1% of zinc stearate are added to the fraction of 1 to 1.5 mm.

(14) The expansion and moulding were effected as described in example 1. The thermal conductivity proved to be 32 mW/mK at 17 g/l.

EXAMPLE 4 (COMPARATIVE)

(15) A mixture is charged into a closed and stirred container, consisting of 150 parts by weight of water, 0.2 parts of sodium tricalcium phosphate, 100 parts of styrene, 0.30 parts of tert-butylperoxy-2-ethylhexanoate, 0.25 parts of tert-butylperbenzoate, 0.01 parts of sodium metabisulphite and 4 parts of the coke used in example 1. The mixture is heated under stirring to 90 C.

(16) After about 2 hours at 90 C., the mixture is heated for a further 2 hours to 100 C., 7 parts of a 70/30 mixture of n-pentane and i-pentane are added, the mixture is heated for a further 4 hours to 125 C., it is then cooled and discharged.

(17) The granules of expandable polymer thus produced are processed as in example 1, separating the fraction with a diameter ranging from 1 to 1.5 mm.

(18) This fraction proved to represent 60%, 25% being the fraction from 0.5 to 1 mm, 5% the fraction from 0.2 to 0.5 mm, and 10% the gross fraction, from 1.5 to 3 mm. 0.2% of glyceryl monostearate and 0.1% of zinc stearate are added to the fraction of 1 to 1.5 mm.

(19) The expansion and moulding were effected as described in example 1. The thermal conductivity proved to be 33 mW/mK at 17 g/l.

EXAMPLE 5 (COMPARATIVE)

(20) Comparative example 4 was repeated substituting the Calcinated Coke 4023 with the type Needle Coke 4727 sold by the company Asbury Graphite Mills Inc. (USA) having a size MT50% of about 6 microns, a BET of about 11 m.sup.2/g. The thermal conductivity proved to be 32.5 mW/mK at 17 g/l.

EXAMPLE 6

(21) Comparative example 5 was repeated adding 3% of Needle Coke 4727 and 1% of Graphite ABG1005. The thermal conductivity proved to be 31.2 mW/mK at 17 g/l.

EXAMPLE 7

(22) Example 6 was repeated adding 1.5% of hexabromocyclododecane, Saytex HP900 sold by Albmarle and 0.3% of dicumyl peroxide to make the product fireproof. The fraction of 1 to 1.5 mm is then processed as in Example 1. The sheets are put in an oven at 70 C. for 2 days to remove the residual pentane. Test samples are then collected (9 cm19 cm2 cm) for the fire behaviour test according to the regulation DIN 4102. The test samples pass the test. The thermal conductivity remains unvaried.

EXAMPLE 8 (COMPARATIVE)

(23) 78 parts of polystyrene N1782 produced by Polimeri Europa; 2 parts of ethylene-bis-stereamide; 20 parts of Calcinated Coke 4023 used in Example 1, are mixed in a twin-screw extruder. The extruded product is used as master-batch, in the production of the expandable compositions of the present invention illustrated hereunder.

(24) 89.8 parts of ethylbenzene, 730.0 parts of styrene, 56.2 parts of -methylstyrene and 0.2 parts of divinylbenzene are fed to a stirred reactor.

(25) 123.8 parts of the master-batch prepared as indicated above are fed into the reactor and dissolved (total: 1,000 parts). The reaction is then carried out at 125 C. with an average residence time of 2 hours. The fluid composition at the outlet is then fed to a second reactor where the reaction is completed at 135 C. with an average residence time of 2 hours.

(26) The resulting composition, which is hereafter referred to as Composition (A), having a conversion of 72%, is heated to 240 C. and subsequently fed to the devolatilizer to remove the solvent and residual monomer. It is characterized by a glass transition temperature of 104 C., a melt flow index (MFI 200 C., 5 kg) of 8 g/10, a molecular weight Mw of 200,000 g/mol and a Mw/Mn ratio of 2.8, wherein Mw is the weight average molecular weight and Mn is the number average molecular weight.

(27) Composition (A) is fed, from the devolatilizer, to a heat exchanger to lower its temperature to 170 C.

(28) 120.7 parts of polystyrene N2982 produced by Polimeri Europa, 24.2 parts of BR-E 5300 (stabilized hexabromocyclododecane, sold by Chemtura) and 5.1 parts of Perkadox 30 (2,3-dimethyl-2,3-diphenylbutane, sold by Akzo Nobel) for a total of 150 parts, are fed to a second twin-screw extruder. A gear pump increases the feeding pressure of this molten additive to 260 barg. 47 parts of a mixture of n-pentane (75%) and iso-pentane (25%) are then pressurized and injected into the feeding of the additive. The mixing is completed with the use of static mixers, at a temperature of about 190 C. The composition thus obtained is described hereunder as Composition (B).

(29) Composition (B) is added to 850 parts of Composition (A) coming from the heat exchanger. The ingredients are then mixed by means of static mixing elements for a calculated average residence time of 7 minutes. The composition is then distributed to the die, where it is extruded through a number of holes having a diameter of 0.5 mm, immediately cooled with a jet of water and cut with a series of rotating knives (according to the method described in U.S. Pat. No. 7,320,585).

(30) The pressure in the granulation chamber is 5 bar and the shear rate is selected so as to obtain granules having an average diameter of 1.2 mm. The water is used as a cooling spray liquid and nitrogen is used as carrier gas.

(31) The resulting granules are dried with a centrifugal drier and then covered with a coating. The coating is prepared by adding to the granules 3 parts of glyceryl monostearate, 1 part of zinc stearate and 0.2 parts of glycerine per 1,000 parts of dried granules. The additives of the coating are mixed with the granulate by means of a continuous screw mixer.

(32) The expansion of the granules and moulding were effected as described in Example 1. The thermal conductivity proved to be 32.0 mW/mK.

(33) Some of the sheets, obtained as described in Example 1, are put in an oven at 70 C. for 2 days. Test samples are then collected (9 cm19 cm2 cm) for the fire behaviour test according to the regulation DIN 4102. The test samples pass the test.

EXAMPLE 9

(34) 88 parts of polystyrene N1782; 2 parts of ethylene-bis-stereamide and 10 parts of expanded Graphite ABG1005 are mixed in a twin-screw extruder. The extruded product, hereafter referred to as Composition C, is used as master-batch, in the production of the expandable compositions of the present invention.

(35) 89.8 parts of ethylbenzene, 853.8 parts of styrene, 56.4 parts of -methylstyrene (total: 1,000 parts) are fed to a stirred reactor.

(36) The reaction is carried out at 125 C. with an average residence time of 2 hours. The outgoing fluid composition is then fed to a second reactor where the reaction is completed at 135 C. with an average residence time of 2 hours.

(37) The resulting composition, hereafter referred to as Composition D, having a conversion of 72%, is heated to 240 C. and subsequently fed to the devolatilizer to remove the solvent and residual monomer. The composition is fed, from the devolatilizer, to a heat exchanger to lower its temperature to 170 C.

(38) 154.0 parts of polystyrene N2982, 24.2 parts of BR-E 5300 (stabilized hexabromocyclododecane, sold by Chemtura), 5.1 parts of Perkadox 30 (2,3-dimethyl-2,3-diphenylbutane, sold by Akzo Nobel) and 100 parts of composition C indicated above, for a total of 283.3 parts, are fed to a second twin-screw extruder. A gear pump increases the feeding pressure of this molten additive to 260 barg. 47 parts of a mixture of n-pentane (75%) and iso-pentane (25%) are then pressurized and injected into the feeding of the additive. The mixing is completed with static mixers, at a temperature of about 190 C.

(39) The composition thus mixed is added to 716.7 parts of Composition (D) coming from the heat exchanger. The ingredients are then mixed by means of static mixing elements for a calculated average residence time of 7 minutes. The composition is then distributed to the die, where it is extruded through a number of holes having a diameter of 0.7 mm, immediately cooled with a jet of water and cut with a series of rotating knives as in Comparative Example 8, so as, however, to obtain granules having an average diameter of 1.4 mm.

(40) The resulting granules are dried with a centrifugal drier and then covered with a coating, as described in Comparative Example 8.

(41) The expansion of the granules and moulding were effected as described in Example 1. The thermal conductivity proved to be 32.2 mW/mK.

(42) Some of the sheets, obtained as described in Example 1, are put in an oven at 70 C. for 2 days. Test samples are then collected (9 cm19 cm2 cm) for the fire behaviour test according to the regulation DIN 4102. The test samples pass the test.

EXAMPLE 10

(43) 71.33 parts of polystyrene N1782 produced by Polimeri Europa; 2 parts of ethylene-bis-stereamide; 20 parts of Calcinated Coke 4023; 6.67 parts of graphite ABG1005 were mixed in a twin-screw extruder using the same operating procedures of comparative Example 8 in both the preparation of this masterbatch and in all the other phases as far as the final granule which, expanded and moulded at 17 g/l, showed a thermal conductivity of 31.2 mW/mK.

EXAMPLE 11

(44) A mixture (A) consisting of 97 parts by weight of polystyrene N1782 and 2 parts of Calcinated Coke 4023 and 1 part of expanded graphite of Example 1 is fed in continuous to a system of two extruders in series.

(45) The temperature inside the first extruder is 220 C. to allow the polystyrene to melt and mix it with the additives. 2 parts of ethyl alcohol and 4 parts of carbon dioxide as expanding agent, with respect to 100 parts of the mixture (A) are fed to the mixture thus obtained.

(46) The polymeric melt comprising the expansion system is homogenized and cooled to 120 C. and extruded through a die having a rectangular transversal section and dimensions of 300 mm1.5 mm.

(47) A continuous sheet having a thickness of 120 mm is obtained. The density of the sheet is 35 g/l, the average size of the cells (substantially spherical) inside the sheet is about 500 m. The thermal conductivity proved to be 33 mW/mK.

EXAMPLE 11 (COMPARATIVE)

(48) The same procedure is repeated as in Example 11 with the exception that no athermanous agent is incorporated.

(49) The sheet obtained has a density of 35 g/l and an average size of the cells inside the sheet again of about 500 m. The thermal conductivity proved to be 38 mW/mK.