EP3052557A1

EP3052557A1 - Method of producing polystyrene particles comprising carbon particles having a conical shape

Info

Publication number: EP3052557A1
Application number: EP13785894.0A
Authority: EP
Inventors: Ville Nurminen; Martin Cadek; Sami LIPPONEN; Elina PESONEN; Asko RONKAINEN
Original assignee: Bewi Styrochem Oy
Current assignee: Bewi Styrochem Oy
Priority date: 2013-10-04
Filing date: 2013-10-04
Publication date: 2016-08-10
Also published as: WO2015049413A1

Abstract

Method of producing polystyrene particles, polystyrene particles obtained by such a method, and expandable polystyrene particles containing athermanous particles. In the method, styrene monomers are subjected to a polymerization reaction in the presence of athermanous particles to produce polystyrene particles. According to the invention, the athermanous particles comprise carbon particles having a conical shape, in particular at least 95 % of the carbon particles have the shape of cones, such as open cones, along with some disc-shaped particles. The particles are formed by overlapping carbon layers, with a largest dimension of less than micrometers. Excellent thermal insulation properties are exhibited for expanded products produced from the particles.

Description

METHOD OF PRODUCING POLYSTYRENE PARTICLES COMPRISING CARBON PARTICLES HAVING A CONICAL SHAFIE

Field of the Invention The present invention relates to polystyrene beads. In particular, the invention relates to the production of expandable polystyrene beads with insulating properties. Thus, the invention relates to a method according to the preamble portion of claim 1 as well as expandable polystyrene beads according to the preamble of claim 16 and uses thereof. Background Art

Polystyrene beads are traditionally produced by the suspension polymerisation of styrene, which involves the mechanical dispersion of styrene in water and polymerisation of the resultant monomer droplets by use of a monomer-soluble initiator. Styrene is kept in suspension by continuous agitation and the use of stabilisers. Polystyrene is obtained in the form of beads.

Expanded articles have been used for some time, for example to improve the thermal insulation of buildings. Generally, these articles are prepared by either extrusion or moulding through the swelling of polymer beads. Additives can be used to improve the desired properties of the articles. For example, hexabromocyclododecane is used in typically polystyrene building insulation, both extruded and expanded as a flame-retarding agent. Expanded polystyrene (EPS) is becoming increasingly common for use in such articles. EPS is a rigid and tough, closed-cell foam, generally made of pre-expanded polystyrene beads. Common uses of these EPS beads include moulded sheets for building insulation and packing material for cushioning fragile items. The latest advances in the technology related to these EPS beads concern improving the thermal insulation of the articles prepared from the beads.

In order to improve the thermal insulating properties of polystyrene beads, athermanous particles, such as graphite and carbon black, are incorporated into the polystyrene to produce what is known as grey EPS. The production of grey EPS moulded articles is disclosed in EP 0 620 246. Athermanous material can be added directly to the

polymerisation process, on the surface of the unexpanded EPS beads or to pre-foamed EPS beads before they are moulded. Further processes for the production of such materials are described in EP 0 981 574 and EP 0 981 575, as well as EP 1 608 698.

Generally, the best thermal insulation properties are obtained with graphite particles.

However such particles are expensive to produce. In addition, it is difficult to obtain a uniform particle size distribution. Summary of the Invention

It is an aim of the present invention to provide expanded polystyrene products, containing alternative athermanous particles having good thermally-insulating properties. Thus, the present invention relates to methods of producing polystyrene beads, wherein styrene monomers, and optionally co-monomers are subjected to a polymerisation reaction in the presence of athermanous material and a polymerisation initiator to produce polystyrene beads. It has been found in connection with the present invention that particularly good thermal insulation properties are obtained by incorporating into expandable polystyrene beads of athermanous carbon materials consisting predominantly of particles having an average particle size in the range of about 0.1 to 2.0 um, in particular about 0.5 to 1.9 um, advantageously 0.7 to 1.5 um.

Athermanous particles of the indicated kind are, according to the present invention, carbon particles having a non-spherical form, preferably particles in the shape of cones, such as open or hollow cones. The preferred particles are formed by overlapping carbon layers. Thus, according to the invention, the athermanous material used in expandable polystyrene beads comprises carbon particles having a conical shape, in particular at least 1 %, suitably 10 %, for example at least 25 %, by weight of the carbon particles have the shape of cones, such as open cones. Disc-shaped particles are present to an extent of 99 % or less. The particles are formed by overlapping carbon layers. The particles have a largest dimension of less than 5 micrometers.

Particles of the indicated kind can be produced by plasma torch processes, wherein a hydrocarbon composition is combusted using a plasma flow to form carbon particles.

Excellent thermal insulation properties are exhibited for polymers and articles produced from the expanded beads. More specifically, the method according to the present invention is characterised by what is stated in claim 1.

The expandable polystyrene particles or beads are characterised by what is stated in the characterising part of claim 15.

Expanded polystyrene polymers are characterized by what is stated in claim 22.

Particularly preferred expanded polystyrene polymers are characterized as being obtained by expanding polymer beads produced by a method according to any of claims 1 to 14, polystyrene particles according to claim 15 or expandable polystyrene particles according to any of claims 16 to 21.

Articles, such as heat insulation boards, formed by polystyrene are characterized 28. Considerable benefits are reached with the aid of the present invention. The present invention provides expandable polymer beads that can be used to prepare foamed articles of low thermal conductivity. The present athermanous particles are producible by inexpensive methods, e.g. the plasma torch process mentioned above. Such methods give rise to particles of a narrow particle size distribution which will reduce the extent to which the particles need to be subjected to process steps such as classification.

The particles give properties of thermal insulation equal to over even better than those of graphite. As evidenced by the appended examples, a material according to the present invention, will achieve the same thermal conductivity as a conventional material at a significantly lower density (i.e. with a smaller consumption of material).

Other features and advantages will become apparent from the following description. Detailed Description of Embodiments

The present technology comprises a method of producing expandable polystyrene beads or particles containing athermanous particles. In the present context, the terms "beads" and "particles" will be used interchangeably to designate polystyrene particles obtained by the herein described method.

As mentioned above, the method according to the present technology is based on polymerisation of styrene monomers which are subjected to polymerization in the presence of athermanous particles. The athermanous particles comprise carbon particles which exhibit a conical shape and formed by overlapping carbon layers, with a largest dimension of less than 5 micrometers. Preferably conical carbon particles comprise particles having the shape of hollow open cones. In addition to conical carbon particles the athermanous particles comprise particles which have a generally disc-shaped form. In a preferred embodiment, the carbon particles are formed by overlapping carbon layers.

The individual overlapping carbon layers have a thickness of up to 200 nm, in particular 100 nm or less. Preferably the thickness is 10 nm to 100 nm.

In another embodiment the thicknesses of the layer is 100 to 200 nm. A typical thickness for this embodiment is about 150 nm, i.e. 150 ± 25 nm. It would appear that overlapping carbon layers will assist in efficiently absorbing energy (photons).

The athermanous particles can be produced by a plasma torch process, wherein a hydrocarbon composition is combusted using a plasma flow to form carbon black particles. One suitable process is described in W09842621 which discloses a high-yield method of producing carbon particles which comprise overlapping carbon layers. In the process hydrocarbons are decomposed into carbon and hydrogen by plasma. A plasma arc is formed in a plasma generator which consists of tubular electrodes. The hydrocarbons are introduced into the decomposition reactor in the vicinity of the plasma arc zone by use of a nozzle which aligns the hydrocarbon spray in the axial direction of the reactor, and is designed in such a way that coarse drops are formed. A delay in the hydrocarbon evaporation enhances formation of particles. The process yields open carbon micro-cones with total disclination degrees 60 and/or 1200, corresponding to cone angles of respectively 112.9 and/or 83.6. The cones are closed in the apex. In this material, the conical domains represent at least 10% of the material. In addition disc- or ring-shaped particles are formed.

In view of the advantageous properties of the particles described herein, it is preferred to use athermanous additives primarily consisting of such particles.

According to a preferred embodiment of the present invention, carbon particles having the shape of cones and discs form at least 10 %, in particular at least 50 %, preferably at least 75 %, advantageously at least 90 %, suitably 100 %, of the total weight of athermanous particles present in the polymerization suspension.

In a further preferred embodiment, the athermanous material used in the present expandable beads comprises carbon particles with a conical shape, the content of which is at least 1 %, suitably at least 10 %, for example at least 25 %, by weight of the total weight of carbon particles having overlapping carbon layers. Disc-shaped particles are present to an extent of up to 99 %, for example 25 to 90 % by the weight of the total weight of carbon particles having overlapping carbon layers.

In one embodiment the carbon particles have a narrow particle size distribution. Preferably the particles exhibit a greatest dimension in the range of 0.5 to 2.0 micrometers, in particular 0.7 to 1.0 micrometers.

A narrow distribution will enhance distribution of the particles within the polystyrene bead and assist in obtaining uniform properties. It would appear that absorption of incoming photons will be enhanced when the particles have a narrow particles size in the above indicated range of 0.5 to 2.0 micrometers, in particular 0.7 to 1.0 micrometers.

The polymerisation is typically carried out in the presence of a radical initiator or initiators, typically 1 to 4 initiators being used.

The athermanous particles are incorporated into the polystyrene beads during the polymerization of monomers optionally together with comonomers. Examples of comonomers include acrylonitrile and polybutadiene and potentially other vinyl- comonomers.

The addition of the athermanous particles to the polymerisation mixture results in the production of a grey material (in the following also called expandable polystyrene, EPS). The grey EPS has a considerably lower conductivity than the corresponding white EPS.

Polystyrene beads containing athermanous particles can be produced, for example, by bulk or suspension polymerization. In one embodiment polymerisation is carried out in a static mixer. In another embodiment the polymerisation is carried out in a liquid phase into which the styrene monomers are suspended. In a preferred embodiment the liquid phase is an aqueous phase.

The athermanous particles can be introduced in one or several dosages.

In one advantageous embodiment, a first portion of the styrene monomers to be

polymerised is subjected to polymerisation in the presence of a polymerisation initiator.

The athermanous particles are then introduced into the polymerization mixture by means of a premix which contains a second portion of the monomers which are to be polymerised and the athermanous particles and any further additives. The remaining portion of the monomers to be polymerised is suspended in a liquid phase to form a suspension and is subjected to a polymerisation reaction in the presence of a polymerisation initiator to produce expandable polystyrene beads.

The premix is added when the polymerisation reaction has reached a preselected conversion rate and the polymerisation is continued in order to produce EPS beads. In one embodiment the athermanous particles for example in the form of a premix are added at a conversion rate of 0.1 to 70.0 %, in particular about 1 to 50.0 %, especially about 10.0 to 30.0 %, calculated from the total mass of the styrene monomer.

In another embodiment the athermanous particles for example in the form of a premix are added over a time period smaller than that needed for increasing the conversion rate of the polymerisation by at least 10 % units, preferably over a time period corresponding to the time needed for increasing the conversion rate by 10 to 30 % units.

The content of athermanous particles in the expandable polystyrene beads is typically 0.1 to 15 parts by weight, for example 1 to 10, or 2 to 5, parts by weight, based on 100 parts by weight of styrene. In addition to athermanous particles, the polymerization mixture can be supplemented with other additives or auxiliary agents, such as a (polymeric) fire-retarding agent. In a preferred embodiment, the flame retarding agent is selected from the group of organo- chlorines, organobromines, and brominated polymeric compounds. In a preferred embodiment the auxiliary agents are added in an amount of 0.01 to 5.0 %, in particular 0.05 to 4.0 %, preferably about 0.1 to 3.0 %, advantageously 0.2 to 2.0 % by total mass, of the styrene monomer.

Based on the above, in one specific embodiment a method is provided for producing expandable polystyrene beads in which styrene monomers are polymerised in a suspension at a first temperature in the range of about 75 to 110 °C until a preselected degree of conversion has been reached. A premix of monomer and athermanous particles is added to the suspension. The suspension is heated to a second, higher temperature during the addition of the blowing agent. The temperature of the suspension is then optionally raised to a third temperature higher than the second temperature. Polymerisation is continued until a preselected final conversion degree has been reached. In one example the polymerisation is continued to a conversion rate of at least 95 %, calculated from the styrene monomer and in a preferred embodiment the EPS beads are recovered from the liquid phase. A blowing agents is added during the implementation of the process or afterwards. The blowing agent typically comprises a hydrocarbon, such as an aliphatic hydrocarbon having 3 to 10 carbon atoms. Typical examples of such hydrocarbons comprise C₃ to C₆ aliphatics and isomers thereof. Specific examples are propane, butane, pentane and hexane and isomers thereof, such as isobutane, isopentane and isohexane. The blowing agent is added in amounts of about 0.1 to about 15 parts by weight, typically 1 to 10 parts by weight, per 100 parts by weight of styrene.

Polymerisation can be carried out also in the presence of additives selected from the group of emulsifiers, preferably stabilizers, more preferably fillers e.g. talc, as well as combinations thereof, each additive providing its own additional property to the produced EPS beads e.g. making the beads more stable.

The addition of co monomers varies depending on the quality of the resultant polystyrene beads. For example, polymerization can be carried out in the presence of up to 40 % by weight of ethylenically unsaturated monomer.

In addition to the present athermanous particles other athermanous particles can also be added. Such particles are typically selected from the group of carbon black particles, graphite, graphene and other carbon-based materials.

By the above processing, expanded polystyrene beads are provided. The concentration of the athermanous particles in the beads is typically 0.01 to 20 %, in particular 0.1 to 15 %, preferably about 1 to 7.5 %, advantageously 3 to 5 %, by weight of the polystyrene polymer.

Foamed polystyrene articles can be made from the beads. The foamed articles exhibit excellent thermal insulation properties. In one embodiment the foamed articles comprise insulating boards and panels composed of expanded polystyrene beads. The production of expanded product from polystyrene beads is well-known in the art.

Thus, in one alternative, for producing expanded products, the exapandable beads are heated, for example by using a heat transfer medium such as steam, to a temperature high enough to soften the beads, preferably to a temperature above the glass transition point of polystyrene. Typically, the temperature is in excess of 95 °C, in particular 100 °C or higher. The heating will cause the blowing agent to boil and while the blowing agent is evaporated off the beads, swelling of the beads is achieved and porous particles created, which can molded together to form articles, such as panels, sheets and boards, by using traditional shape or block mo lding methods .

Generally, in expanded styrene polymers the concentration of the athermanous particles is 0.01 to 20 % calculated from the total mass of the polymerized styrene. In one embodiment the insulating board composed of expanded polystyrene beads comprises athermanous particles in a concentration of 0.1 to 15.0 %, preferably 1.0 to 10.0 %, advantageously 3.0 to 6.0 % by total mass of the polymerized styrene.

In addition the board comprises 0.01 to 5.0 %, preferably 0.05 to 4.0 % more preferably 0.1 to 3.0 %, advantageously 0.2 to 2.0 %, calculated from the total mass of the styrene, other auxiliary components, such as emulsifiers, stabilizers, fillers, such as talc, carbon black, graphite particles, fire retardants, for example hexabromocyclododecane or brominated polymeric fire retardants, as well as combinations thereof. Generally, the thermal conductivity of an insulating board according to the present invention, composed of expanded polystyrene beads is, measured at a density of about 15 kg/m³, i.e. roughly 15 ± 2 kg/m³, 0.027 to 0.035 W/(m K).

In the present context, the expression "about 15 kg/m³ is used include a 10 to 20 % variation of the exact value, thus about 15 kg/m³ can be interpreted as being typically 15 ± 2 kg/m³.

The present expanded styrene polymers typically have a thermal conductivity which is 0.031 W/(m K) or lower. The following non-limiting examples illustrate the invention Example 1

2.3 1 of ion-exchanged water, 1.9 g of sodium acetate, and 2.85 g of sodium bentonite were added in stirred 6 1 autoclave. The mixture was heated to 90 °C within lh, while 1.9 kg styrene, 1.9 g polyethylene, 7.6 g tert-butyl peroxy-2-ethylhexanoate, 5.7 g tert- butylperoxy 2-ethylhexyl carbonate, and 2.85 g pig skin gelatine were added in the autoclave. The mixture was kept for 30 min at 90°C. Then 38 g of the new athermanous material, XPB-550 from Orion Engineering Carbons, was added. The mixture was kept for 315 min at 90°C and then 2.85 g of pig skin gelatine was added. Altogether the mixture was kept at 90°C for 320 min whereafter it was heated to 120°C within 2h. While heating to 120°C 152 g of pentane was added. The mixture was kept at 120°C for 2h where after it was cooled down to 37°C within 90 min.

The reaction mixture was removed from the autoclave and the polystyrene beads were washed thoroughly with water. The beads were sieved and the sizes from 0.8 mm to 1.4 mm were pre-expanded to 15 kg/m³ from which 50 mm thick sample plate was moulded. The thermal conductivity was determined from this sample plate.

Results (density 15 kg/m³): Thermal conductivity 31 mW/mK

Example 2

As Example 1 but the used athermanous material was Graphite, SFG6 from TimCal.

Results (density 15 kg/m³): Thermal conductivity 32 mW/mK

As will appear, with a material according to the present invention, a thermal conductivity of 31 mW/ m K can be obtained at a density as low as 15 kg/m³. By contrast, for a conventional material, the same heat insulation properties require that the density is increased to about 18 kg/m³. Example 3

As Example 1 but no athermanous material was used Results (density 15 kg/m³): Thermal conductivity 40 mW/mK. Example 4

As Example 1 but 95 g of XPB-550 was used. In addition, the sample plate was molded using beads that were pre-expanded to 19 kg/m3.

Results (density 19 kg/m³): Thermal conductivity 29 mW/mK.

Claims

1. Method of producing polystyrene particles, comprising

- subjecting styrene monomers to a polymerization reaction in the presence of athermanous particles to produce polystyrene particles;

wherein

- said athermanous particles comprise carbon particles having a conical shape and formed by overlapping carbon layers, with a largest dimension of less than 5 micrometers.

2. The method according to claim 1, wherein the carbon particles comprise conical and optionally disc-shaped particles formed by overlapping conical and flat carbon layers.

3. The method according to claim 1 or 2, wherein at least 50 % by weight, preferably 75 % by weight, in particular at least 90 % by weight of the carbon particles comprises conical and optionally disc-shaped particles of stacked, overlapping carbon layers.

4. The method according to any of claims 1 to 3, wherein the individual overlapping carbon layers have a thickness of up to 200 nm, in particular 100 to 200 nm, in particular about 150 nm.

5. The method according to any of claims 1 to 4, wherein the conical carbon particles comprise particles having the shape of hollow open cones.

6. The method according to any of the preceding claims, wherein said carbon particles are produced by a plasma torch process, wherein a hydrocarbon composition is combusted using a plasma flow to form carbon black particles.

7. The method according to any of the preceding claims, wherein the carbon particles particles have a narrow particle size distribution.

8. The method according to any of the preceding claims, wherein 95 % of carbon particles having the shape of cones, in particularly open cones, and disc-shaped particles, exhibit a greatest dimension in the range of 0.5 to 2.0 micrometers, in particular 0.7 to 1.0 micrometers.

9. The method according to any of the preceding claims, wherein carbon particles having the shape of cones and discs form at least 10 %, in particular at least 50 %, preferably at least 75 %, advantageously at least 90 %, suitably 100 %, of the total weight of athermanous particles present in the polymerization suspension.

10. The method according to any of the preceding claims, wherein the concentration of the athermanous particles is 0.01 to 20 %, in particular 0.1 to 15 %, preferably about 1 to 5 % by weight of the polystyrene polymer.

11. The method according to any of the preceding claims, wherein the polymerization is carried out in a suspension in the presence of a radical initiator.

12. The method according to any of the preceding claims, wherein the polymerization is carried out in the presence of additives selected from the group of emulsifiers, stabilizers, fillers, such as talc, carbon black, graphite particles, fire retardants, for example hexabromocyclododecane or brominated polymeric fire retardants, as well as combinations thereof.

13. The method according to any of the preceding claims, wherein the styrene monomers are polymerized in the presence of comonomers.

14. The method according to any of the preceding claims, wherein the polymerization is carried out in the presence of up to 40 % by weight of ethylenically unsaturated monomer.

15. Polystyrene particles obtained by a method according to any of the preceding claims.

16. Expandable polystyrene particles containing athermanous particles, said athermanous particles comprising carbon particles in the shape of cones formed by stacked, overlapping carbon layers having a largest dimension of less than 5 micrometers.

17. Expandable polystyrene particles according to claim 16, wherein the athermanous particles comprise carbon particles which are shaped as cones, in particular hollow cones, and discs.

18. Expandable polystyrene particles according to claim 16 or 17, wherein 95 % of the carbon particles have the shape of cones, in particularly open cones, and disc-shaped particles, said particles exhibiting a greatest dimension in the range of 0.5 to 2.0 micrometers, in particular 0.7 to 1.0 micrometers.

19. Expandable polystyrene particles according to any of claims 16 to 18, wherein at least 10 %, in particular at least 50 %, preferably at least 75 %, advantageously at least 90 %, suitably 100 %, of the total weight of athermanous particles present in the expandable particles have the shape of cones, in particular hollow cones, and discs.

20. Expandable polystyrene particles according to any of claims 16 to 19, wherein the concentration of the athermanous particles is 0.01 to 20 %, in particular 0.1 to 15 %, preferably about 1 to 5 % by weight of the polystyrene polymer.

21. Expandable polystyrene particles according to any of claims 16 to 20, further containing a blowing agent, in particular selected from the group of propane, pentane, methylene chloride and a chlorofluorocarbon or combinations thereof.

22. Expanded styrene polymer containing athermanous particles, said athermanous particles comprising carbon particles in the shape of cones formed by stacked, overlapping carbon layers having a largest dimension of less than 5 micrometers.

23. Expanded styrene polymer according to claim 22, wherein the athermanous particles comprise carbon particles which are shaped as cones, in particular hollow cones, and discs.

24. Expanded styrene polymer according to claim 22 or 23, wherein 95 % of the carbon particles have the shape of cones, in particularly open cones, and disc-shaped particles, said particles exhibiting a greatest dimension in the range of 0.5 to 2.0 micrometers, in particular 0.7 to 1.0 micrometers.

25. Expanded styrene polymer according to any of claims 22 to 24, wherein the concentration of the athermanous particles is 0.01 to 20 %, in particular 0.1 to 15 %, preferably about 1 to 5 % by weight of the polystyrene polymer.

26. Expanded styrene polymer according to any of claims 22 to 25, having a thermal conductivity which is 0.030 W/(m K) or lower.

27. Expanded styrene polymer according to any of claims 22 to 26, wherein the styrene polymer comprises styrene homopolymer or styrene copolymer, optionally exhibiting up to 40 % by weight of ethylenically unsaturated monomers.

28. Articles, such as heat insulation boards, consisting essentially of a styrene polymer according to any of claims 22 to 27.