WO2006058733A1 - Expandable styrene polymer granulates and particulate expanded plastics with a reduced thermal conductivity - Google Patents

Abstract

The invention relates to expandable styrene polymer granulates, which contain a) between 5 and 50 wt. % of a filler, selected from pulverulent inorganic materials such as talcum, 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. The invention also relates to a method for producing said granulates and to particulate expanded plastics that are obtained from the latter and that have a reduced thermal conductivity.

Description

Expandable styrene polymer granules and particle foams with reduced thermal conductivity

description

The invention relates to expandable styrene polymer granules which

a) 5 to 50 wt .-% of a filler selected from powdery inorganic materials such as talc, chalk, kaolin, aluminum hydroxide, aluminum nitrite, aluminum silicate, barium sulfate, calcium carbonate, titanium dioxide, chalk, calcium sulfate, kaolin, silica, quartz powder, Aerosil , Alumina or wollastonite and

b) 0.1 to 10 wt .-% carbon black or graphite, and to processes for their preparation and obtainable therefrom foam particles with reduced thermal conductivity.

It is known to add athermane materials such as carbon black (EP-A 372 343) or graphite (EP-A 981 574) to reduce the thermal conductivity of polystyrene foams. Here, depending on the type and incorporation high amounts of athermanous materials are needed, which can lead to problems in the homogeneous incorporation due to the nucleating effect. Furthermore, the mechanical properties of the foams produced therefrom and its fire behavior can be adversely affected.

Process for the preparation of flame-retardant, expandable styrene polymers by extrusion of a blowing agent-containing styrene polymer melt are z. B from EP-A 0 981 574 and WO 97/45477. Here, halogenated flame retardants, such as hexabromocyclododecane (HBCD), optionally together with other additives, e.g. Flame retardant synergists, such as dicumyl peroxide or dicumyl, melted with polystyrene and then added a propellant.

The object of the present invention was therefore to remedy the disadvantages mentioned and to provide self-extinguishing styrene polymer particle foams with low thermal conductivity, and to a process for producing expandable styrene polymers which can be processed by prefoaming and sintering with hot air or steam to form self-extinguishing styrene polymer particle foams.

Accordingly, the above-described expandable styrenic polymer granules were found.

Preferably, the carbon black or graphite is used in amounts of 2 to 8 wt .-%. Carbon black with an average primary particle size in the range from 10 to 300 nm, in particular in the range from 30 to 200 nm, is preferably used. The BET surface area is preferably in the range of 10 to 120 m ² / g.

The graphite used is preferably graphite having an average particle size in the range from 1 to 50 μm.

With particular preference the EPS granulate contains hexabromocyclododecane (HBCD) as flame retardant and dicumyl or dicumyl peroxide as flame retardant synergist.

The weight ratio of flame retardant synergist to organic bromine compound is usually in the range of 1 to 20, preferably in the range of 2 to 5.

Furthermore, particle foam moldings obtainable by welding prefoamed foam particles of expandable, filler-containing, thermoplastic polymer granules were found, wherein the particle foam has a density in the range of 8 to 200 g / l, preferably in the range of 10 to 50 g / l.

Surprisingly, despite the presence of fillers, the particle foam moldings according to the invention exhibit a high degree of closed-cell quality, with more than 60%, preferably more than 70, particularly preferably more than 80% of the cells of the individual foam particles being closed-celled as a rule.

Suitable fillers are organic and inorganic powders or fibrous materials, as well as mixtures thereof. As organic fillers z. As wood flour, starch, flax, hemp, ramie, jute, sisal-cotton cellulose or aramid fibers are used. As inorganic fillers z. As carbonates, silicates, barite, glass beads, zeolites or metal oxides are used. Preference is given to pulverulent inorganic substances, such as talc, chalk, kaolin (Al ₂ (Si ₂ O ₅ ) (OH) ₄ ), aluminum hydroxide, magnesium hydroxide, aluminum nitrite, aluminum silicate, barium sulfate, calcium carbonate, calcium sulfate, silica, quartz powder, Aerosil , Alumina or wollastonite or spherical or fibrous inorganic materials such as glass beads, glass fibers or carbon fibers.

The mean particle diameter or, in the case of fibrous fillers, the length should be in the range of the cell size or smaller. Preference is given to an average particle diameter in the range from 1 to 100 μm, preferably in the range from 2 to 50 μm.

Particular preference is given to inorganic fillers having a density in the range from 2.0 to 4.0 g / cm ³ , in particular in the range from 2.5 to 3.0 g / cm ³ . The whiteness / brightness (DIN / ISO) is preferably 50 to 100%, in particular 70 to 98%. The oil number according to ISO 787/5 of the preferred fillers is in the range of 2 to 200 g / 100 g, in particular in the range of 5 to 150 g / 100 g.

The nature and amount of the fillers can influence the properties of the expandable thermoplastic polymers and the particle foam moldings obtainable therefrom. The proportion of the filler is generally in the range of 1 to 50, preferably 5 to 30 wt .-%, based on the thermoplastic polymer. At Füllstoff- held in the range of 5 to 15 wt .-%, no significant deterioration of the mechanical properties of the particle foams, such as flexural strength or compressive strength is observed. The use of adhesion promoters, such as maleic anhydride-modified styrene copolymers, epoxy group-containing polymers, organosilanes or styrene copolymers with isocyanate or acid groups, can significantly improve the binding of the filler to the polymer matrix and thus the mechanical properties of the particle foam moldings.

In general, inorganic fillers reduce flammability. In particular, by the addition of inorganic powders, such as aluminum hydroxide, the fire behavior can be significantly improved.

Surprisingly, the thermoplastic polymer granules according to the invention also show a low propellant loss during storage, even at high filler contents. Due to the nucleating effect, it is also possible to reduce the blowing agent content, based on the polymer.

As thermoplastic polymers, for example, styrene polymers, polyamides

(PA), polyolefins, such as polypropylene (PP), polyethylene (PE) or polyethylene-propylene copolymers, polyacrylates, such as polymethyl methacrylate (PMMA), polycarbonate (PC), polyesters, such as polyethylene terephthalate (PET) or polybutylene terephthalate (PBT), poly - ether sulfone (PES), Polyehterketone or polyether sulfides (PES) or mixtures thereof are used. Particular preference is given to using styrene polymers.

It has been found that styrene polymers with molecular weights M _w of less than 160,000 lead to polymer abrasion during granulation. The expandable styrene polymer preferably has a molecular weight in the range from 190,000 to 400,000 g / mol, more preferably in the range from 220,000 to 300,000 g / mol. Due to the reduction in molecular weight by shear and / or temperature, the molecular weight of the expandable polystyrene is usually about 10,000 g / mol below the molecular weight of the polystyrene used.

In order to obtain the smallest possible granulate particles, the strand expansion after the nozzle exit should be as low as possible. It has been shown that the strand expansion is influenced, inter alia, by the molecular weight distribution of the styrene polymer. can be flown. The expandable styrene polymer should therefore preferably have a molecular weight distribution with a nonuniformity M _w / M _n of at most 3.5, more preferably in the range of 1.5 to 2.8 and most preferably in the range of 1.8 to 2.6.

As styrene polymers, preference is given to glassy polystyrene (GPPS), toughened polystyrene (HIPS), anionically polymerized polystyrene or toughened polystyrene (A-IPS), styrene-a-methstyrene copolymers, acrylonitrile-butadiene-styrene polymers (ABS), styrene-acrylonitrile (SAN ) Acrylonitrile-styrene-acrylic esters (ASA), methyl acrylate-butadiene-styrene (MBS), methyl methacrylate-acrylonitrile-butadiene-styrene (MABS) - polymers or mixtures thereof or with polyphenylene ether (PPE) used.

The styrene polymers mentioned can be used to improve the mechanical properties or the thermal stability, if appropriate by using compatibilizers with thermoplastic polymers, such as polyamides (PA), polyolefins, such as polypropylene (PP) or polyethylene (PE), polyacrylates, such as polymethyl methacrylate (PMMA), Polycarbonate (PC), polyesters, such as polyethylene terephthalate (PET) or polybutylene terephthalate (PBT), polyether sulfones (PES), polyether ketones or polyether sulfides (PES) or mixtures thereof, generally in proportions of not more than 30% by weight in total , preferably in the range of 1 to 10 wt .-%, based on the polymer melt, are mixed. Furthermore, mixtures in the above amounts ranges with z. B hydrophobically modified or functionalized polymers or oligomers, rubbers such as polyacrylates or polydienes, z. As styrene-butadiene block copolymers or biodegradable aliphatic or aliphatic / aromatic copolyesters possible.

Suitable compatibilizers are e.g. Maleic anhydride-modified styrene copolymers, polymers or organosilanes containing epoxide groups.

The styrene polymer melt may also be admixed with polymer recyclates of the above-mentioned thermoplastic polymers, in particular styrene polymers and expandable styrene polymers (EPS) in amounts which do not substantially impair their properties, generally in quantities of not more than 50% by weight, in particular in amounts of from 1 to 20 wt .-%.

The blowing agent-containing styrene polymer melt generally contains one or more blowing agents in a homogeneous distribution in a proportion of 2 to 10 wt .-%, preferably 3 to 7 wt .-%, based on the blowing agent-containing styrene polymer melt. Suitable blowing agents are the physical blowing agents commonly used in EPS, such as aliphatic hydrocarbons having 2 to 7 carbon atoms, alcohols, ketones, ethers or halogenated hydrocarbons. Preference is given to using isobutane, n-butane, isopentane, n-pentane. To improve the foamability, finely divided internal water droplets can be introduced into the styrene polymer matrix. This can be done for example by the addition of water in the molten styrene polymer matrix. The addition of the water can be done locally before, with or after the propellant dosage. A homogeneous distribution of the water can be achieved by means of dynamic or static mixers.

As a rule, from 0 to 2, preferably from 0.05 to 1.5,% by weight of water, based on the styrene polymer, is sufficient.

Expandable styrene polymers (EPS) with at least 90% of the internal water in the form of inner water droplets with a diameter in the range of 0.5 to 15 microns form when foaming foams with sufficient cell count and homogeneous foam structure.

The amount of blowing agent and water added is chosen so that the expandable styrene polymers (EPS) have an expansion capacity α, defined as bulk density before foaming / bulk density after foaming, at most 125, preferably 25 to 100.

The expandable styrene polymer pellets (EPS) according to the invention generally have a bulk density of at most 700 g / l, preferably in the range from 590 to 660 g / l. When using fillers, depending on the type and amount of the filler, bulk densities in the range of 590 to 1200 g / l may occur.

Further, in addition to the fillers, the styrenic polymer melt may contain additives, nucleating agents, plasticizers, flame retardants, soluble and insoluble inorganic and / or organic dyes and pigments, e.g. IR absorbers such as carbon black, graphite or aluminum powder together or spatially separated, e.g. be added via mixer or side extruder. In general, the dyes and pigments are added in amounts ranging from 0.01 to 30, preferably in the range of 1 to 5 wt .-%. For the homogeneous and microdispersed distribution of the pigments in the styrene polymer, it may be expedient in particular for polar pigments to use a dispersing aid, for example organosilanes, polymers containing epoxy groups or maleic anhydride-grafted styrene polymers. Preferred plasticizers are mineral oils, low molecular weight styrene polymers, phthalates, which can be used in amounts of from 0.05 to 10% by weight, based on the styrene polymer.

To prepare the expandable styrene polymers according to the invention, the blowing agent is mixed into the polymer melt. The process comprises the stages a) melt production, b) mixing c) cooling d) conveying and e) granulation. Each of these Stages can be performed by the apparatus or apparatus combinations known in plastics processing. For mixing, static or dynamic mixers are suitable, for example extruders. The polymer melt can be taken directly from a polymerization reactor or produced directly in the mixing extruder or a separate melt extruder by melting polymer granules. The cooling of the melt can be done in the mixing units or in separate coolers. For example, pressurized underwater granulation, granulation with rotating knives and cooling by spray misting of tempering liquids or atomization granulation are suitable for the granulation. Apparatus arrangements suitable for carrying out the method are, for example:

a) Polymerization Reactor - Static Mixer / Cooler Granulator b) Polymerization Reactor - Extruder - Granulator c) Extruder - Static Mixer - Granulator d) Extruder - Granulator

Furthermore, the arrangement may include side extruders for incorporation of additives, e.g. of solids or thermally sensitive additives.

The propellant-containing styrene polymer melt is usually at a temperature in the range of 140 to 300 ⁰ C, preferably in the range of 160 to 24O ⁰ C promoted through the nozzle plate. Cooling down to the range of the glass transition temperature is not necessary.

The nozzle plate is heated at least to the temperature of the blowing agent-containing polystyrene melt. Preferably, the temperature of the nozzle plate is in the range of 20 to 100 ⁰ C above the temperature of the blowing agent-containing polystyrene melt. This prevents polymer deposits in the nozzles and ensures trouble-free granulation.

In order to obtain marketable granule sizes, the diameter (D) of the nozzle bores at the nozzle exit should be in the range from 0.2 to 1.5 mm, preferably in the range from 0.3 to 1.2 mm, particularly preferably in the range from 0.3 to 0 , 8 mm lie. In this way granule sizes below 2 mm, in particular in the range from 0.4 to 1.4 mm, can be set precisely even after strand expansion.

The strand expansion can be influenced by the geometry of the die, apart from the molecular weight distribution. The nozzle plate preferably has bores with a ratio L / D of at least 2, wherein the length (L) designates the nozzle region whose diameter corresponds at most to the diameter (D) at the nozzle exit. Preferably, the ratio L / D is in the range of 3 to 20. In general, the diameter (E) of the holes at the nozzle inlet of the nozzle plate should be at least twice as large as the diameter (D) at the nozzle outlet.

An embodiment of the nozzle plate has bores with conical inlet and an inlet angle α less than 180 °, preferably in the range of 30 to 120 °. In a further embodiment, the nozzle plate has bores with conical outlet and an outlet angle ß smaller than 90 °, preferably in the range of 15 to 45 °. In order to produce targeted granule size distributions of the styrene polymers, the nozzle plate can be equipped with bores of different exit diameters (D). The various embodiments of the nozzle geometry can also be combined.

A particularly preferred process for making expandable styrenic polymers comprises the steps

a) polymerization of styrene monomer and optionally copolymerizable monomers,

b) degassing the resulting styrene polymer melt,

c) mixing of the blowing agent and optionally additives into the styrene polymer melt by means of static or dynamic mixer at a temperature of at least 150 ⁰ C, preferably 180-260 ⁰ C.

d) cooling of the blowing agent-containing styrene polymer melt to a temperature at least 12O ⁰ C, preferably from 150 to 200 ⁰ C,

e) adding the filler,

f) discharge through a nozzle plate with holes whose diameter at the nozzle outlet is at most 1, 5 mm and

g) granulating the blowing agent-containing melt.

In step g), the granulation can be carried out directly behind the nozzle plate under water at a pressure in the range of 1 to 25 bar, preferably 5 to 15 bar.

Owing to the polymerization in stage a) and degassing in stage b), a polymer melt is directly available for the blowing agent impregnation in stage c) and melting of styrene polymers is not necessary. This is not only more economical but also leads to expandable styrenic polymers (EPS) with low styrenic molar monomer, since the mechanical shear in the melting range of an extruder, which usually leads to a back-cleavage of monomers, is avoided. In order to keep the styrene monomer content low, in particular below 500 ppm with Styrolmomomergehalten, it is also appropriate to keep the mechanical and thermal energy input in all subsequent process steps as low as possible. Therefore, shear rates below 50 / sec, preferably 5 to 30 / sec, and temperatures below 26O ⁰ C and short residence times in the range of 1 to 20, preferably 2 to 10 minutes in stages c) to e) are particularly preferred. Particular preference is given to using only static mixers and static coolers in the entire process. The polymer melt can by pressure pumps, z. B. gear pumps funded and discharged.

A further possibility for reducing the styrene monomer content and / or residual solvents such as ethylbenzene is to provide high degassing by means of entrainers, for example water, nitrogen or carbon dioxide, in step b) or to carry out the polymerization step a) anionically. The anionic polymerization of styrene leads not only to styrene polymers with a low styrene monomer content but at the same time to low styrene oligomer contents.

To improve the processability, the finished expandable styrene polymer granules can be coated by glycerol esters, antistatic agents or anticaking agents.

The expandable styrene polymer pellets (EPS) according to the invention generally have higher bulk densities, depending on the filler type and content, which are generally in the range from 590 to 1200 g / l.

The expandable thermoplastic polymer granules according to the invention exhibit a good expansion capacity even at low propellant contents. Even without a coating, the bond is significantly lower than with conventional EPS beads.

Fillers with particle sizes in the range from 0.1 to 100 .mu.m, in particular in the range of 0.5 and 10 .mu.m result in a reduction of the thermal conductivity by 1 to 3 mW in the polystyrene foam at contents of 10 wt .-%. Therefore, comparatively low thermal conductivities can be achieved even with smaller amounts of IR absorbers, such as soot and graphite.

To reduce the thermal conductivity, preference is given to using an IR absorber, such as carbon black or graphite, in amounts of from 0.1 to 10% by weight, in particular in amounts of from 2 to 8% by weight. When using smaller amounts of fillers, eg. B. under 5 wt .-%, it is also possible to use carbon black in amounts of 1 to 25 wt .-%, preferably in the range of 10 to 20 wt .-%. At these high carbon black contents, the carbon black addition is preferably mixed into the styrene polymer melt via the main stream and a side stream extruder. Addition via extruder makes it possible to easily break down the carbon black agglomerates to an average agglomerate size in the range from 0.3 to 10 μm, preferably in the range from 0.5 to 5 μm, and homogeneous dyeing of the expandable styrene polymer granules to form dense-cell foam particles having a density in the range of 5 to 40 kg / m ³ , in particular 10 to 15 kg / m ³ can be foamed. The particle foams obtainable with 10 to 20 wt .-% carbon black by foaming and sintering λ achieve a thermal conductivity determined at 1O ⁰ C according to DIN 52612, in the range of 30 to 33mW / mK.

Carbon black with an average primary particle size in the range from 10 to 300 nm, in particular in the range from 30 to 200 nm, is preferably used. The BET surface area is preferably in the range of 10 to 120 m ² / g.

The graphite used is preferably graphite having an average particle size in the range from 1 to 50 μm.

A preferred process for preparing expandable styrene polymers comprises the steps

a) mixing in (i) an organic blowing agent,

(ii) 5-50% by weight, based on the styrenic polymer, of a filler selected from pulverulent inorganic substances, such as talc, chalk, kaolin, aluminum hydroxide, aluminum nitrite, aluminum silicate, barium sulfate, calcium carbonate, titanium dioxide, calcium sulfate, silicic acid, quartz powder, Areosil, alumina or wollastonite and

(iii) from 0.1 to 10 wt .-%, based on the Styolpolymerisat, carbon black or graphite in the Styrolpolmerisatschmelze by means of static or dynamic mixer at a temperature of at least 150 ⁰ C,

b) cooling the propellant and filler-containing polymer melt to a temperature of at least 12O ⁰ C.

c) discharge through a nozzle plate with holes whose diameter at the nozzle outlet is at most 1.5 mm and

d) granulating the blowing agent-containing melt directly behind the nozzle plate under water at a pressure in the range of 1 to 20 bar. The expandable, styrene polymer granules according to the invention can be prefoamed by means of hot air or steam to foam particles having a density in the range of 8 to 200 kg / m ³ , preferably in the range of 10 to 50 kg / m ³ and then welded in a closed mold into foam moldings.

Examples:

In a polystyrene melt of PS 158 K BASF Aktiengesellschaft with a viscosity number VZ of 98 ml / g (M _w = 280,000 g / mol, nonuniformity M _w / M _n = 2.8) in an extruder 7 wt .-%, based on polystyrene, pentane mixed. After cooling the propellant-containing melt of originally 260 ⁰ C to a temperature of 190 ⁰ C, a mixture of polystyrene melt, filler (chalk, Ulmer white (Omya)), IR absorber (carbon black or graphite, UF298 Kropfmühl) and Flame retardant (HBCD) according to Table 1 was added and mixed into the main stream. In addition, at the level of the side-type extruder via a metering lance, the pentane-added flame retardant synergists dicumyl (DC) or dicumyl peroxide are metered into the cooled main stream by means of a piston pump. The mixture of polystyrene melt, blowing agent, flame retardant and synergist was at 60 kg / h through a nozzle plate with 32 holes (diameter of the nozzle 0.75 mm) promoted. With the help of pressurized underwater granulation, compact granules with a narrow size distribution were produced.

These granules were prefoamed in flowing steam to foam beads (20 g / l), stored for 24 hours and then welded in gas-tight forms with steam to foam bodies.

The thermal conductivity / »was measured at 10 ⁰ C in accordance with DIN 52,612th burning times of below 6 seconds are suitable in order to exist the B2 test according to DIN 4102nd

Table 1:

Claims

claims: 1. Expandable styrene polymer granules containing a) 5 to 50 wt .-% of a filler selected from powdered inorganic substances such as talc, chalk, kaolin, aluminum hydroxide, aluminum nitrite, aluminum silicate, barium sulfate, calcium carbonate, titanium dioxide, calcium sulfate, silica, quartz, Aerosil, alumina or wollastonite and b) 0.1 to 10 wt .-% carbon black or graphite. 2. Expandable styrene polymer granules according to claim 1, characterized in that they contain 0.2 to 5 wt .-% of an organic bromine compound having a bromine content of at least 70 wt .-% as a flame retardant. 3. Expandable styrene polymer granules according to claim 2, characterized in that they contain 0.05 to 1.0 wt .-% dicumyl or dicumyl peroxide as Flammschutzsynergist. 4. Expandable styrene polymer granules according to any one of claims 1 to 3, characterized in that they contain 3 to 7 wt .-% of an organic blowing agent. 5. A process for preparing expandable styrenic polymer granules comprising the steps a) meddle (i) an organic blowing agent, (ii) 5-50% by weight, based on the styrenic polymer, of a filler selected from pulverulent inorganic substances, such as talc, chalk, kaolin, aluminum hydroxide, aluminum nitrite, aluminum silicate, barium sulfate, calcium carbonate, titanium dioxide, calcium sulfate, silica, quartz powder, Areosil, alumina or wollastonite and (iii) 0.1 to 10 wt .-%, based on the styol polymer, carbon black or graphite in the Styrolpolmerschmelze by means of static or dynamic mixer at a temperature of at least 150 ⁰ C, b) cooling the blowing agent and filler-containing polymer melt to a temperature of at least 120 ^° C., c) discharge through a nozzle plate with holes whose diameter at the nozzle outlet is at most 1, 5 mm and d) granulating the blowing agent-containing melt directly behind the nozzle plate under water at a pressure in the range of 1 to 20 bar. 6. A process for producing particle foam moldings, characterized in that one prefoams expandable styrene polymer granules according to claim 1 in a first step by means of hot air or steam to foam particles having a density in the range of 8 to 200 g / I and in a second step in a closed Mold welded.