EP1771502A2

EP1771502A2 - Method for the production of flameproof, expandable polystyrol

Info

Publication number: EP1771502A2
Application number: EP05772383A
Authority: EP
Inventors: Klaus Hahn; Gerd Ehrmann; Joachim Ruch; Markus Allmendinger; Bernhard Schmied; Jan Holoch
Original assignee: BASF SE
Current assignee: BASF SE
Priority date: 2004-07-15
Filing date: 2005-07-08
Publication date: 2007-04-11
Also published as: KR20070042180A; DE102004034516A1; MX2007000052A; WO2006007995A2; WO2006007995A3

Abstract

The invention relates to a method for the production of flameproof, expandable styrol polymers (EPS) by extruding a styrol polymer melt containing a propellant and flameproof agents through a nozzle plate with subsequent under water granulation. The residence time of the flameproof agent is less than 30 minutes at a melting temperature in the region of between 140 to 220 °C.

Description

Process for the preparation of flame-retardant, expandable polystyrene

description

The invention relates to a process for the preparation of flame-retardant, expandable styrene polymers (EPS) by extrusion of a blowing agent and flame retardant-containing styrene polymer melt through a die plate with subsequent submerged water granulation.

Processes for the preparation of flame-retardant, expandable styrenic polymers by extrusion of a blowing agent-containing styrenic polymer melt are e.g. from EP-A 0 981 574, WO 97/45477 or WO 03/46016. In this case, the flameproofing agent is optionally melted together with other additives together with polystyrene and subsequently a blowing agent is added.

In order to homogeneously mix in the blowing agent and, if appropriate, further additives, the polystyrene melt generally has to be kept at temperatures well above the glass transition temperature of the polystyrene for a certain time. This can lead to the decomposition of a considerable proportion of the flame retardant added, which leads to discoloration and lesser effectiveness in the expandable polystyrene.

The object of the present invention was therefore to find an economical and gentle process for the preparation of flame-retardant, expandable styrene polymers.

Accordingly, a process for the preparation of flame-retardant, expandable styrene polymers (EPS) by extruding a propellant and Flammschutzmittel- containing styrene polymer melt through a nozzle plate with subsequent Unterwas¬ sergranulation found, the residence time of the flame retardant at a melt temperature in the range of 140 to 220 ° C is less than 30 minutes.

The melt temperature and residence time are selected according to the invention such that a homogeneous incorporation of the flame retardant is ensured and decomposition is minimized. The melt temperature is preferably in the range from 140 to 220 ^° C., preferably in the range from 160 to 210 ^° C., particularly preferably in the range from 170 to 200 ^° C. The residence time of the flame retardant should be less than 30 minutes in the stated temperature ranges, preferably less than 15 minutes, particularly preferably less than 10 minutes.

Preferably, therefore, the blowing agent is first mixed homogeneously into the styrene polymer melt, and then the flame retardant and, if appropriate, a flame-retardant synergist of the thickening-polymer-containing styrene polymer melt are metered in. The flame retardant is preferably premixed in a side extruder with a proportion of polystyrene polymer melt and the styrene polymer melt is metered in the main stream. As a rule, the proportion of styrene polymer which is fed via the side extruder is less than 20% by weight.

It has been found that styrenic polymers having molecular weights M w of less than 170,000 on granulation lead to polymer abrasion. 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 shearing and / or temperature influence, the molecular weight of the expandable polystyrene is generally 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 build-up can be influenced inter alia by the molecular weight distribution of the styrene polymer. The expandable styrene polymer should therefore preferably have a molecular weight distribution with a polydispersity MJM _n of at most 3.5, particularly preferably in the range from 1.5 to 3.0 and very particularly preferably in the range from 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 ester (ASA), methyl acrylate-butadiene-styrene (MBS), methyl methacrylate-acrylonitrile-butadiene-styrene (MABS) - polymers or mixtures thereof or with polyphenylene ether (PPE).

The styrene polymers mentioned can be used to improve the intrinsic 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. -%, preferably in the range of 1 to 10 wt .-%, bezo¬ gen on the polymer melt, blended. 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, for example, maleic anhydride-modified styrene copolymers, polymers or organosilanes containing epoxide groups.

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

The propellant-containing styrene polymer melt generally contains one or more propellants in a homogeneous distribution in a proportion of 2 to 10 wt .-%, preferably 3 to 7 wt .-%, based on the propellant-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 distributed internal water droplets can be introduced into the styrene polymer matrix. This can be done, for example, by the addition of water into 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 μm form foams with sufficient cell number and homogeneous foam structure during foaming.

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. The flame retardants used are organic bromine compounds having a bromine content of at least 70% by weight. Especially suitable are aliphatic, cycloaliphatic and aromatic bromine compounds, such as hexabromocyclododecane, penta bromomochlorocyclohexane, pentabromophenyl allyl ether. The flame retardant is generally used in amounts of 0.2 to 5, preferably from 0.5 to 2.5 wt .-%, based on the styrene polymer.

The styrenic polymer melt dicumyl or dicumyl peroxide is preferably added as a flame-retardant synergist. Other suitable flame retardant synergists are thermal free-radical formers having half-lives of 6 minutes at temperatures ranging from 110 to 300 ⁰ C, preferably 140 to 23O ⁰ C, the fen liquid or in water, or Kohlenwasserstof¬ Weis oil are soluble. Di-tert-butyl peroxide (Trigonox® B), tert-butyl hydroperoxide (Trigonox® A80), a solution of dicumyl peroxide in pentane or an aqueous solution of a peroxide or hydroperoxide are preferably used as the flame retardant synergist. The flame retardant synergist is preferably pure or in the case of solids under normal conditions (1 bar, 23 ⁰ C) is einge¬ nearly saturated solution, so it with classic pumping systems directly to a tempered and pressurized space can be dosed. Due to the presence in the liquid phase, a metering is possible in such a way that even quantities of low-decomposition peroxides have sufficient amounts to withstand the process or extrusion conditions and still achieve homogeneous mixing. As a rule, the flame-retardant synergist is used in amounts ranging from 0.05 to 1% by weight, preferably in the range from 0.1 to 0.5% by weight.

Further, the styrenic polymer melt may contain additives, nucleating agents, fillers, plasticizers, 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 microdisperse distribution of the pigments in the styrene polymer, it may be expedient in particular for polar pigments to use a dispersing assistant, for example organosilanes, polymers containing epoxy groups or maleic anhydride-grafted styrene polymers. Preferred plasticizers are mineral oils, 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 carried out by the apparatuses or apparatus combinations known in plastics processing. For mixing, static or dynamic mixers, for example extruders, are suitable. The polymer melt can be produced directly from be removed from a polymerization or directly produced in the mixing extruder or a separate Aufmmelzextruder by melting polymer granules. The cooling of the melt can take place in the mixing units or in separate coolers. For granulation, for example, pressurized underwater granulation, granulation with rotating knives and cooling by spray-atomization of tempering liquids or sputtering granulation are considered. 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 supported at a temperature in the range of 140 to 300 ⁰ C, preferably in the range of 160 to 240 ⁰ C plate through the nozzle. 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 Polysty¬ rolschmelze. 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 of 0.2 to 1.5 mm, preferably in the range of 0.3 to 1.2 mm, particularly preferably in the range of 0.3 to 0.8 mm. Thus, even after strand expansion, granule sizes of less than 2 mm, in particular in the range of 0.4 to 1.4 mm, can be set in a targeted manner.

The strand expansion can be influenced, in addition to the molecular weight distribution, by the nozzle geometry. The nozzle plate preferably has bores with a ratio L / D of at least 2, the length (L) designating the nozzle region whose diameter corresponds at most to the diameter (D) at the nozzle exit. Preferably, the ratio LJD is in the range of 3 - 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 outlet diameters (D). The various embodiments of the nozzle geometry can also be combined.

A particularly preferred process for the preparation of expandable Styrolpoly¬ mers comprises the steps

a) polymerization of styrene monomer and optionally copolymerizable monomers to give a styrene polymer having an average molecular weight in the range from 160,000 to 400,000 g / mol,

b) degassing of the resulting styrene polymer melt,

c) mixing of the blowing agent and optionally additives in the Styrolpoly¬ merschmelze by means of static or dynamic mixer at a temperature of at least 150 ⁰ C, preferably 180 - 26O 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) introducing the flame retardant via a side extruder,

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 take place directly behind the nozzle plate under water at a pressure in the range of 1 to 25 bar, preferably 5 to 15 bar.

Due to the polymerization in stage a) and degassing in stage b), a polymer melt is directly available for the blowing agent impregnation in stage d) and melting of styrene polymers is not necessary. This is not only more economical but also leads to expandable styrene polymers (EPS) with low styrene monomer contents since the mechanical shear action in the melting region of an extruder, which as a rule leads to a back-breaking of monomers, avoids that will. In order to keep the styrene monomer content low, in particular below 500 ppm with Styrolmonomergehalten, it is also appropriate to keep the mechanical and thermal energy input in all subsequent process steps as low as possible. Shear rates are therefore particularly preferably below 50 / sec, preferably 5 to 30 / sec, and at temperatures below 260 ⁰ C and short residence times in Be¬ range from 1 to 20, preferably 2 to 10 minutes, in stages) d to f) respected. It is especially preferred to use exclusively static mixers and static coolers throughout the process. The polymer melt can be pumped and discharged by pressure pumps, eg gear pumps.

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

When using peroxides as flame retardants, the residual styrene contents of the propellant-containing granules are surprisingly significantly reduced. Due to the peroxide addition, only a slight reduction in the average molecular weight is observed, but no substantial formation of oligomers or monomers is found. On the one hand, this makes it possible to use polystyrene melts having higher residual monomer contents, which in turn involves less expense in the degassing after the polystyrene reactor. On the other hand, starting from already largely degassed polystyrene, the residual monomer contents can be lowered even further. In this way, EPS granules can be achieved with residual monomer contents below 250 ppm.

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

The EPS granules may be blended with glycerol monostearate GMS (typically 0.25%), glyceryl tristearate (typically 0.25%) finely divided silica Aerosil R972 (typically 0.12%) and Zn stearate (typically 0.15%), and antistatic coating.

The expandable styrene polymer granules according to the invention can be prefoamed in a first step by means of hot air or steam to foam particles having a density in the range of 8 to 100 g / l and welded in a second step in a closed mold to particle moldings. Examples:

Example 1 - 6:

To a main stream of a blowing agent-containing polymer melt (polystyrene with a viscosity number VZ of 74 ml / g, average molecular weight M _w of 185,000 g / mol and a polydispersity M _w ZM _n of 2.6 and 6 wt .-% n-pentane) was after Cooling of 26O ⁰ C to 190 ⁰ C via a side extruder in a polystyrene melt at 190 ⁰ C premixed hexabromocyclododecane (HBCD FR 1206 HAT Fa. Eurobrom) and dicumyl according to the information in Table 1 (weight percent, based on polystyrene) added. The additive concentration (HBCD + dicumyl) in the side stream was 33% by weight. The resulting polymer melt was passed through a nozzle plate with 32 bores (0.75 mm diameter) at a throughput of 60 kg / h and granulated by means of pressurized underwater granulation to form compact granules with a narrow size distribution. The total residence time of the HBCD and dicumyl from the point of addition to the granulation was 8 minutes.

Examples 2 and 4 used micronized HBCD with a mean particle size d (50) of 2 μm and micronized dicumyl with a mean particle size d (50) of 7 μm.

Comparative Experiments V1 to V4

Example 1 was repeated except that HBCD and / or dicumyl as a flame retardant synergist were omitted. In Comparative Experiment V2 HBCD was added to the polystyrene melt in the main stream at 22O ⁰ C prior to addition of the blowing agent. The residence time of the HBCD at a temperature above 19O ⁰ C was 40 minutes. The resulting EPS granules were colored very brown.

The expandable polystyrene granules obtained were prefoamed in flowing steam to form foam particles having a density of about 20 g / l and, after storage for 24 hours in gas-tight forms, welded to foam bodies by means of steam.

After storage of the foam body for 72 hours, the fire behavior was determined. For this purpose, the foam bodies were ignited in a horizontal fire test for 2 seconds with a Bunsen burner flame and then removed from the flame. Afterburning times of less than 6 seconds are suitable for passing the B2 test according to DIN 4102. The amount of flame retardant (dosage and measured in the EPS particle foam) and the results of the fire protection test are summarized in Table 1. Table 2 shows the foaming behavior of Examples 2 and 4 and Comparative Experiment V1.

Table 1 :

Table 2: Bulk density as a function of the foaming time

Claims

claims

1. A process for the preparation of flame-retardant, expandable Styrolpolyme- ren (EPS) by extrusion of a propellant and flame retardant-containing Sty- rolpolymerschmelze through a nozzle plate with subsequent underwater granulation tion, characterized in that the residence time of the Flammschutzmit¬ means in a Melting temperature in the range of 140 to 22O ⁰ C less than 30 minutes.

2. The method according to claim 1, characterized in that the residence time of the flame retardant at a melt temperature in the range of 170 to 200 ⁰ C is less than 15 minutes.

3. The method according to claim 1 or 2, characterized in that the flame retardant of the Teibmittel-containing styrene polymer melt is metered.

4. The method according to any one of claims 1 to 3, characterized in that the flame retardant is premixed in a side extruder with a proportion Styrolpolymer¬ melt and the styrene polymer melt is metered in the main stream.

5. The method according to any one of claims 1 to 4, characterized in that the flame retardant is an organic bromine compound having a bromine content of at least 70 wt .-% is used.

6. The method according to claim 5, characterized in that is used as Flammschutzmit¬ tel hexabromocyclododecane.

7. The method according to any one of claims 1 to 6, characterized in that the styrene polymer melt additionally dicumyl or dicumyl peroxide is added as Flamm¬ Schutzsynergist.

8. The method according to claim 7, characterized in that the Flammschutz¬ medium and the Flammschutzsynergist is micronized prior to addition to a mean particle diameter in the range of 0.1 to 50 microns.