WO2006024658A1

WO2006024658A1 - Open-celled cross-linked polymer foam made from polyolefins and polystyrol

Info

Publication number: WO2006024658A1
Application number: PCT/EP2005/054310
Authority: WO
Inventors: Sascha Rauch; Luis FERNÁNDEZ BENITEZ
Original assignee: Trocellen Gmbh
Priority date: 2004-09-01
Filing date: 2005-09-01
Publication date: 2006-03-09
Also published as: DE102004042297A1

Abstract

The invention relates to open-celled and cross-linked polymer foams made from polyolefins and polystyrol. Said foams have a proportion of open cells of from 40 to 99 % and a gel proportion of from 40 to 95 % and can be used as packaging or insulation material.

Description

description

Open-cell and cross-linked polymer foam made of polyolefins and polystyrene

TECHNICAL FIELD The invention relates to crosslinked polymer foams comprising polyolefins and polystyrene which have a high proportion of open cells, to a process for producing the polymer foams and to their use.

Open-cell polymer foams are often used as packaging material or insulation material due to their softness and high resilience. In addition, they have a porous structure, which makes their use as a filter material or as a sound-absorbing material possible.

Background of the Invention Polyolefin foams are generally closed cell and have low recovery. Although the cells of these foams can be opened mechanically, for. B. by rolling (DE 198 40 203 Al) or introducing and igniting a blast gas mixture, however, the open-cell polyolefin foams thus produced still have a rigid basic structure.

To improve the elasticity of closed cell polyolefin foams, it is known to use polymer blends of polyolefin and polystyrene. Polyolefins such as polypropylene or polyethylene, however, are incompatible with polystyrene, ie blends of these polymers are difficult to produce because the melts hardly mix and re-break into the components. Accordingly, molded articles produced therefrom are often inhomogeneous. By adding compatibilizing agents such as polymers having long side chains or hydrogenated polystyrene-butadiene block co-polymers (EP 0 313 653 B1), mixtures of incompatible polymers can be stabilized. It is furthermore possible to improve the compatibility of polyethylene and polystyrene by grafting the polyethylene with styrene monomers or vinylsilanes (EP 0 055 460 B1, EP 0 646 622 A1, US Pat. No. 4,694,025).

A disadvantage of these systems, in addition to the complex process control whose low degree of crosslinking. The low degree of crosslinking presumably results from the incompatibility of the components and the miscibility, which is difficult even without crosslinking. If the components are cross-linked prior to mixing, their miscibility decreases even further.

A process for producing slightly crosslinked, open-celled polymer foams of polyethylene and polystyrene is disclosed in EP 1 816 37 A2. Here polymer foams are produced by extrusion under certain pressure and temperature conditions. To set these process conditions, the degree of crosslinking must not exceed 10%. For many foam applications, this degree of crosslinking is too low.

US 4,694,025 discloses a process for the preparation of crosslinked polymer foams of polystyrene and polyethylene, wherein first a grafting of the polyethylene with azidosilanes to improve the miscibility of the polymeric components is performed. This slightly cross-linked mixture is then mixed in an exuder with an alcohol-containing propellant gas mixture, so that the mixture foams after exiting the extruder. The use of alcoholic propellants makes the process technologically complex. In addition, the control of the degree of crosslinking is difficult, since this depends not only on the kinetics of the crosslinking reaction, but also on the removal of the alcohol from the mixture. To avoid too much networking with the process of US 4,694,025 produced only slightly crosslinked foams. The degree of crosslinking of the foams is not indicated.

Task Crosslinked polyolefin foams have an increased mechanical stability compared to uncrosslinked foams, but as a rule have a closed cell structure. In particular, for applications for sound insulation or shock absorption, it would be desirable to use materials made of open-cell polyolefin foams. It was therefore the object of the present invention to provide materials of this type without the disadvantages of the prior art.

Presentation of the invention

The present invention therefore relates to open-cell and crosslinked polymer foams containing 50 to 95% by weight of polyolefins and 5 to 50% by weight of polystyrene, the polymer foam having a proportion of open cells according to ASTM D2856 of 40 to 99% and a Degree of crosslinking according to gel content according to ASTM 2765 of 40 to 95%.

The proportion of open cells of the polymer foam according to the invention is preferably 60 to 99%, in particular 85 to 95% or 90 to 99%.

The proportion of polystyrene in the polymer foam is at most 50 wt .-%, but can be adjusted within wide limits. Preference is given to proportions of polyolefin and polystyrene of in each case 60 and 40% by weight, 70 and 30% by weight, 80 and 20% by weight, 90 and 10% by weight.

Polyolefins used are in particular polyethylene and / or polypropylene, in each case as homopolymer, copolymer or polymer blend. It is also possible to use mixtures of a plurality of different polystyrenes, polyethylenes and / or polypropylenes, eg. B. be used with different molecular weights or melt flow indices.

The polymeric components are used in particular without any prior functionalization or compatibilization, such as grafting with silanes or monomers, such as styrene or methacrylate, etching, irradiation, flaming or corona treatment.

Polymer foams according to the invention preferably contain, in addition to the polymeric components (polyolefin and polystyrene), no further polymers, so that the o. G. Weight shares of

Add polyolefin and polystyrene to 100%. Optionally, it is possible to use small amounts of from 1 to 10% by weight (based on the

Polymer fraction in the foam) to other polymers such as polyethylene vinyl acetate, polyethylene ethyl acetate, polyethylene vinyl butyral, hydrogenated polystyrene and / or polybutene.

Other additives may color additives, antioxidants, pigments, carbon black or crosslinking aids such. B. triallyl isocyanurates.

For a good mixing result of the incompatible polymers, it is advantageous to use polymers with certain melt flow indices. In a particular variant of the invention are polyolefins having a melt flow index of 0.5 to 10 g / 10 min., Preferably 1.5 to 4.0 g / 10 min (190 ⁰ C, 2.16 kg) and / or polystyrenes with a melt flow index of 0.5 to 8, preferably 1 to 5 g / 10 min (200 ⁰ C, 5 kg) used. The melt flow indices are determined according to DIN 53735.

To determine the degree of crosslinking of the foam according to the invention, its gel fraction is used. Here, according to ASTM 2765, the residue of the polymer foam which is insoluble in an organic solvent (xylene, benzene or the like) is determined and added in relation to the amount of foam used. Before- The polymer foams according to the invention have gel proportions of 60 to 90 or 70 to 85%.

Inventive polymer foams show excellent resilience. Thus, the compressive stress of the foam according to ISO 3386/1 with a 25% deformation can be 2 to 40 kPa, in particular 5 to 20 kPa. Optionally, the polymer foams according to the invention have compressive stresses according to the following table:

Compressive stress according to ISO 3386/1 value [kPa]

10% deformation 1 - 10

25% deformation 2 - 20, especially 2 - 10

50% deformation 3 - 40, in particular 5 - 30

Furthermore, the compression set of the inventive polymer foams according to ISO 1856 at an initial deformation of 25% after 24 hours unloading time is 0.1 to 5%, in particular 0.1 to 3%.

Optionally, the polymer foams according to the invention have compression molding radicals according to the following table:

Furthermore, the invention relates to a process for the preparation of the polymer foam according to the invention by the process steps: a) mixing at least a portion of the polymeric components at a temperature above their glass transition temperatures, b) admixing crosslinking agents, foaming agents and / or the remainder of the polymeric components, c ) Crosslinking of the polymeric components, d) foaming of the crosslinked mixture and e) mechanical opening of the cells, wherein the process steps c + d can also be carried out in overlapping or together.

The crosslinking of the polymeric components can be carried out with the usual chemical crosslinking agents such as peroxides (in particular dicumyl peroxide, benzoyl peroxide or di (2-tert-butyl peroxo-iso-propyl) benzene (DIB)). Shares of 0.1-5% by weight (based on the polymer components) have proven useful here. Pre-crosslinking or grafting of the polyethylene is not required in the process according to the invention. The vinyl or azidosilanes mentioned in EP 0 181 637 A2, also in combination with an organometallic compound such as dibutyltin laurate, are therefore preferably not used.

It is also possible, the polymer foams according to the invention by electron beams, for. B. such as γ or ß radiation with a radiation dose of 0.5 to 6 Mrad to cross-link.

Foaming in particular uses chemical foaming agents, ie compounds which are thermally broken down into gaseous products. In particular azo compounds in a proportion of 5 to 20% by weight (based on the polymeric components) are used for this purpose. Particularly suitable is azodicarboxylic acid amide (Porofor ADC / Z-C2 from Bayer). Since incompatible polymers are used to produce the polymer foam according to the invention, the mixing process is of crucial importance for the homogeneity of the product obtained. Here, the use of correspondingly high shear forces is necessary for a sufficient mixing quality of the incompatible polymer components.

In the process according to the invention, the mixture of the polymeric components and the admixing of the crosslinking and / or foaming agents according to process steps a) and b) can be carried out batchwise in one or more kneaders, extruders, Bussknetern, Stempelknetern and / or calenders.

To simplify the process, it is also possible in process step a) to premix only a portion of the polymeric components, preferably in the tools mentioned, and to mix in the remainder of the polymeric components in process step b). In the first mixing step a), preference is given to premixing 10 to 90%, particularly preferably 30 to 70%, of the total amount of polymeric components as masterbatch.

Conveniently, the entire amount of polystyrene is initially charged for preparation of the masterbatch in a) and mixed with an appropriate amount of polyolefin. At a weight ratio in the polymer foam of polystyrene to polyolefin of 30:70, a corresponding 50:50 ratio for the masterbatch has been proven. Such a masterbatch can then be filled in process step b) with the appropriate amount of polyolefin.

Optionally, this masterbatch may already be added a part or the total amount of crosslinking and / or foaming agents. In another, optionally continuous, z. B. in an extruder, carried out mixing step then the remaining components are mixed. In this way it is possible to limit the usually labor-intensive discontinuous process steps to a minimum. It It is also possible to add the additives completely in the mixing of the masterbatch with the other polymeric constituents.

Process step a) can therefore be carried out batchwise in one of the said tools and process step b) continuously in an extruder.

In process step a) and / or b), it is additionally possible to admix additives such as dyes, inert fillers, UV stabilizers or carbon black to improve the conductivity.

The preparation of the foams of the invention can be carried out as the preparation of conventional polyolefin foams. Such methods are the expert z. B. from EP 188 540 Al or WO 99/64502 Al known.

As an alternative to chemical crosslinking preferred foams of the invention may wetting followed by foaming at 170 to 200 ⁰ C in endless webs with a thickness of 0.5 to 4 cm are produced by radiation chemical Vernet¬.

The mechanical opening of the polymer foams according to process step e) can, for. B. by rolling or kneading of the foam. Preferably, the cells are mechanically opened by compressing the polymer foam to 1 to 80%, preferably 1 to 50%, particularly preferably 2 to 25% and in particular 5 to 10% of the original thickness.

Due to the proportion of polystyrene in the polymer foam approach according to the invention, the foam in the compression behaves completely different than a pure polyethylene or polyolefin foam: while the cells of a conventional polyolefin foam barely open by pressing in the nip, the foam rather in its strength permanently damaged without a larger proportion of the cells actually is opened, the cells burst very easily in the foam according to the invention, so that in the above beschriebe¬ NEN compression in the nip usually more than 90% of the cells is usually opened.

If the closed-cell polymer foam is in the form of sheet goods, the use of a pair of rollers or calenders is the obvious choice. The desired proportion of open cells determines the required roller pressure; This can be easily determined by orienting experiments. In practice, it has proven useful to set the roll spacing to 2 to 25%, preferably 5 to 10%, of the original foam thickness.

The polymer foams of the invention can be used for heat or sound insulation z. As in the construction sector, in particular for the insulation of windows and doors, as a filter material, as packaging material in particular for electronic parts or computer, as cushioning material for car or aircraft seats, in sleeping bags, clothing, laptop bags, or in the automotive sector z. B. for sound insulation in the engine compartment.

Determination of the degree of crosslinking To determine the degree of crosslinking, 0.3 + 0.01 g of the

Foam sample weighed (value 1), into a metallic net

(Linen weave, w: 0.50 mm, d: 0.20 mm, 36 mesh) wrapped and the weight determined (value 2). For each sample 150 ml

Xylene is placed in a round bottom flask, three test specimens are placed together in a test flask, this corresponds to a volume of xylene of 450 ml per test flask. The xylene is brought to a boil by means of an electric heating bench, the test samples are added and refluxed for 6 hours. Subsequently, the test samples are dried for at least 8 hours in a convection oven at 70 ⁰ C. After drying, the weight is determined again (value 3). The degree of crosslinking in percent is calculated according to the following formula:

Degree of crosslinking ιn% = 100 xlOO

Wertλ

Examples

Process step a)

Starting Materials:

Porofor ADC / Z-C2 (azodicarbonamite) 17.36% by weight

SABIC LDPE 2102 TX00 57.85% by weight

Polystyrene 158K (BASF) 24.79% by weight

The mixing of the components was carried out by means of a steam-heated paste kneader (steam pressure 5 bar). For this purpose, the polymers to be mixed were added to the kneader, the punch closed and mixed until reaching a melt temperature of 153 ⁰ C for about 8 minutes.

Subsequently, the stamp was raised, the mixture was visually inspected for homogeneity and, if appropriate, the stamp was cleaned of adhering granules. The amount of blowing agent was then added to the polymer mixture, the punch closed and mixed until reaching a melt temperature of 155 ⁰ C for about 3 min and 15 s.

The mixture thus obtained was then rolled on steam-heated calender rolls (steam pressure 1.5 bar, temperature roller 1: 60 ⁰ C, temperature roller 2: 75 ⁰ C) to plates, which were fed directly after a granulator / mill.

Process step b)

The granulated polymer / blowing agent mixture served as the starting material of the extrusion process.

The extruder used is a twin-screw extruder with a melt pump, which is designed for the production of polyolefin foams. The screw diameter is 90 mm, the L / D ratio 25. Both the Schneckenge¬ housing, and the screws themselves are water-cooled, the vacuum pump for degassing is a water ring pump. The maximum throughput is 400 kg / h. In the further process, the extruder as the main component with 97.8 wt .-%, the polymer / blowing agent mixture as well as crosslinking agent, a batch of 20% 1, 3-di- (2-tert-butyl-peroxiisopropyl) benzene in LDPE with 2 , 2% by weight fed and extruded via a slot die a so-called matrix.

Machine parameters:

Extruder throughput: 255kg / h screw speed: 70U / min melt pump speed: 21U / min screw temperature: 80 ⁰ C cylinder temperatures:

Zone 1: 130 ⁰ C, Zone 2: 120 ⁰ C, Zone 3: 90 ⁰ C, Zone 4: 90 ⁰ C, Zone 5: 130 ⁰ C, Zone 6: 135 ⁰ C, throat: 125 ⁰ C, Düsentempera¬ tur: 130 ⁰ C

Process Step c) and d) The extruded matrix was run continuously in a horizontal oven with 4 temperature zones in which both the crosslinking agents and the blowing agents were reacted and thus led to a foaming of the matrix. The matrix was transported via a metallic network.

Machine parameters:

Zone 1: 190 ^° C, Zone 2: 210 ^° C, Zone 3: 225 ^° C, Zone 4: 215 ^° C

Network speed: 2.4 m / min

Process Step e) The foam obtained had a thickness of 10-12 mm and was then mechanically opened twice through a pair of rolls with a roll spacing of about 1 mm. The crosslinked and open-cell polymer foam thus prepared had the following properties:

Claims

claims

1. Off-line and cross-linked polymer foam containing 50 to 95 wt.% Polyolefine and 5 to 50 wt.% Polystyrene, characterized by a proportion of open cells according to ASTM D2856 of 40 to 99% and a degree of crosslinking according to gel content according to ASTM 2765 from 40 to 95%.

2. open-cell and crosslinked polymer foam according to claim 1, characterized in that the compressive stress of the polymer foam according to ISO 3386 at a 25% deformation is 2 to 40 kPa.

3. Open-celled and crosslinked polymer foam according to claim 1 or 2, characterized in that the compression set of the polymer foam according to ISO 1856 at an original deformation to 25% after 24 hours of relief is 0.1-5%.

4. open-cell and crosslinked polymer foam according to one of claims 3 to 7, characterized in that polyolefins having a melt flow index MFI of 0.5 - 10 g / 10 min

(190 ⁰ C, 2.16 kg) and polystyrene with a Schmelzltlussin- dex of 0.5 to 8 g / 10 min (200 ⁰ C, 5 kg) wer¬ the used.

5. A process for producing an open-cell and crosslinked polymer foam according to claim 1 to 4, characterized by the process steps: a) mixing at least a portion of the polymeric components at a temperature above their glass transition temperatures, b) admixing crosslinking agents, foaming agents , and / or the remainder of the polymeric components c) crosslinking of the polymeric components, d) foaming of the crosslinked mixture and e) mechanical opening of the cells.

6. The method according to claim 5, characterized in that the

Process steps a) and b) are carried out batchwise in one or more kneaders, extruders, Bussknetern, Stempelkne- tern and / or calenders.

7. The method according to claim 5, characterized in that

Process step a) is carried out batchwise in a kneader or calender and process step b) continuously in an extruder.

8. The method according to any one of claims 5 to 7, characterized in that in step a) a part of the polymeric components are premixed and the remaining amount in step b) is added.

9. The method according to any one of claims 5 to 8, characterized in that in step a) a part of the polymeric components containing the total amount of polystyrene and a part of the polyolefin, premixed and the remaining amount of the polyolefin in step b) is added ,

10. Use of the open-cell and crosslinked polymer foam according to one of claims 1 to 4 for heat or Schalliso¬ lation, as a filter material, as a packaging material, as cushioning material for car or aircraft seats, in sleeping bags, clothing, laptop bags, or in motor vehicle Area.