DE102004042297A1 - Open-cell and cross-linked polymer foam made of polyolefins and polystyrene - Google Patents

Abstract

The invention relates to open-cell and crosslinked polymer foams of polyolefins and polystyrene. The foams according to the invention have a proportion of open cells of 40 to 99% and a gel content of 40 to 95% and can be used as packaging or insulating material.

Description

Technical area

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

Open-cell polymer foams are often used as packaging material due to their softness and high resilience or insulation material used. In addition, they own one porous structure, their use as filter material or as sound-insulating Material possible power.

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 A1 ) or introducing and igniting a blast gas mixture, however, the open-cell polyolefin foams produced in this way still have a rigid basic structure.

to Improvement of elasticity of polyolefin foams With closed cells, it is known polymer blends of polyolefins and polystyrene. Polyolefins such as polypropylene or polyethylene are however, incompatible with polystyrene, i. Blends of these polymers are difficult to produce because the melts hardly mix and split it back into the components. Accordingly, they are made therefrom moldings often inhomogeneous.

By adding compatibilizers such as long side chain polymers or hydrogenated polystyrene-butadiene block copolymers ( EP 0 313 653 B1 ) mixtures of incompatible polymers can be stabilized. It is also 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 4,694,025 ) to improve.

adversely In addition to the complex process control, these systems have their own low degree of crosslinking. The low degree of crosslinking results probably from the incompatibility of the components and the too without networking already difficult miscibility. Become the components crosslinked before the mixture, so their miscibility still decreases further.

A process for producing lightly crosslinked, open-cell polyethylene and polystyrene polymer foams is disclosed 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 producing crosslinked polymer foams from polystyrene and polyethylene, wherein first a grafting of the polyethylene with azidosilanes to improve the miscibility of the polymeric components is carried out. This slightly cross-linked mixture is then mixed in an Exruder with an alcohol-containing propellant gas mixture, so that the mixture foams after exiting the extruder. The use of alcohol-containing propellant gases 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 excessive crosslinking, the method of US 4,694,025 only slightly crosslinked foams made. The degree of crosslinking of the foams is not specified.

networked polyolefin opposite uncrosslinked foams an increased mechanical stability but usually have a closed cell structure. Especially for Applications for sound insulation or shock absorption would it be desirable, Use materials from open-cell polyolefin foams. It was therefore the object of the present invention, materials of this kind without to provide the disadvantages of the prior art.

Presentation of the invention

object The present invention is therefore open-celled and crosslinked Polymer foams, containing 50 to 95% by weight of polyolefins and 5 to 50% by weight of polystyrene, wherein the polymer foam has an open cell content according to ASTM D2856 from 40 to 99% and a degree of crosslinking according to gel content according to ASTM 2765 of 40 to 95%.

Of the Proportion of open cells of the polymer foam according to the invention is preferred 60 to 99%, in particular 85 to 95% or 90 to 99%.

Of the Proportion of polystyrene in the polymer foam is at most 50 wt.%, But can be set within wide limits. Preference is given to amounts of polyolefin and polystyrene of 60 and 40 wt.%, 70 and 30 wt.%, 80, respectively and 20% by weight, 90% and 10% by weight. The weights are relative on the entire mixture of polymer foam.

When Polyolefins are in particular polyethylene and / or polypropylene, each used as homopolymer, copolymer or polymer blend.

It can also mixtures of several different polystyrenes, polyethylenes and / or polypropylenes, e.g. B. with different molecular weights or Melt flow indices are used.

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

Prefers contain polymer foams according to the invention in addition the polymeric components (polyolefin and polystyrene) no further Polymers, so that the o.g. Weight percentages of polyolefin and Add polystyrene to 100%. Optionally, it is possible to obtain low levels of 1 to 10 wt.% (Based on the polymer content in the foam) of another Polymers such as polyethylene vinyl acetate, polyethylene ethyl acetate, polyethylene vinyl butyral, hydrogenated polystyrene and / or polybutene.

Further additions can Color additives, antioxidants, pigments, carbon black or crosslinking aids such as B. triallyl isocyanurates.

For a good one Mixing result of 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 from 0.5 to 10 g / 10 min., preferably 1.5 to 4.0 g / 10 min (190 ° C, 2.16 kg) and / or polystyrenes having a melt flow index of 0.5 to 8, preferably 1 to 5 g / 10min (200 ° C, 5 kg) is used. The melt flow indices are according to DIN 53735 certainly.

to Determination of the degree of crosslinking of the foam according to the invention its gel content is used. Here, according to ASTM 2765 in an organic solvent (Xylene, benzene or similar) insoluble Residue the polymer foam determined and in relation to the amount used of the foam. The polymer foams according to the invention preferably have gel components from 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 at 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:

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

Optionally, the polymer foams according to the invention have compression set residues according to the following table:

• a) Vermischen zumindest eines Teils der polymeren Komponenten bei einer Temperatur über deren Glastemperaturen,
• b) Zumischen von Vernetzungsmitteln, Verschäumungsmitteln und/oder des Restanteils der polymeren Komponenten,
• c) Vernetzen der polymeren Komponenten,
• d) Aufschäumen der vernetzten Mischung und
• e) Mechanisches Öffnen der Zellen

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 of crosslinking agents, foaming agents and / or the remaining portion of the polymeric components,
• c) crosslinking of the polymeric components,
• d) foaming the crosslinked mixture and
• e) Mechanical opening of the cells

The crosslinking of the polymeric components can be carried out using the customary chemical crosslinking agents, such as peroxides (in particular dicumyl peroxide, benzoyl peroxide or di- (2-tert-butyl-peroxoisopropyl) benzene (DIB)), where proportions of 0.1-5 wt. Pre-crosslinking or grafting of the polyethylene is not required in the process according to the invention EP 0 181 637 A2 mentioned vinyl or azidosilanes, also in combination with an organometallic compound such as dibutyltin laurate are therefore preferably not used.

It is possible, too, the polymer foams according to the invention Electron beams, e.g. B. as γ or β radiation to crosslink with a radiation dose of 0.5 to 6 Mrad.

As a foaming agent in process step d) physically acting blowing agents such as CO ₂ , pentane or fluorocarbons, and mixtures thereof, in each case preferably be used without the addition of alcohol.

alternative is the use of chemical foaming agents, i. Links, the thermally in gaseous Products are split, possible. In particular azo compounds in a proportion of 5 - 20% wt .-% (based on the polymeric components) used. Particularly suitable is azodicarboxylic acid amide (Porofor ADC / Z-C2 of Bayer).

There incompatible for the preparation of the polymer foam according to the invention Polymers are used, the mixing process is more crucial Meaning of the homogeneity of the product obtained. Here is the use of correspondingly high shear for one sufficient mixing quality the incompatible polymer components necessary.

in the inventive method may be the mixture of the polymeric components as well as the admixing the crosslinking and / or foaming agent according to the method steps a) and b) discontinuously in one or more kneaders, extruders, Bussknetern, Stempelknetern and / or calendering done.

to Simplification of the process, it is also possible in the process step a) only a part of the polymeric components, preferably in the mentioned Tools, premix and the remaining portion of the polymeric components in process step b) to mix. It is preferred in the first mixing step a) 10 to 90%, particularly preferably 30 to 70% of the total amount premixed to polymeric components as a masterbatch.

Conveniently, for the preparation of the masterbatch in a) the total amount of polystyrene submitted 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.

optional can already allocate a part or the total to this masterbatch Crosslinking and / or foaming agents added become. In another, optionally continuous, z. In one Extruder, carried out Mixing step are then mixed in the remaining components. In this way it is possible the usually laborious discontinuous process steps to a minimum. It is also possible the additives completely in the mixing of the masterbatch with the other polymeric constituents admit.

step a) can therefore be discontinuous in one of the mentioned tools and process step b) are carried out continuously in an extruder.

In Process step a) and / or b) may additionally contain additives such as dyes, inert fillers, UV stabilizers or soot to improve conductivity be mixed.

The preparation of the foams of the invention can be carried out as the preparation of conventional polyolefin foams. Such methods are the expert from eg EP 188 540 A1 or WO 99/64502 A1.

Prefers the foams of the invention are through Radiation crosslinking with subsequent foaming at 170 to 200 ° C produced in continuous webs with a thickness of 0.5 to 4 cm.

The mechanical opening the polymer foams according to method step e) can z. B. by rolling or kneading of the foam. Preferably the mechanical opening takes place the cells by the polymer foam to 1 to 80%, preferably 1 to 50%, more preferably 2 to 25% and especially 5 to 10 % of the original Thickness is compressed.

Lies the closed-cell polymer foam as sheet goods offers the use of a pair of rollers or calender. The aspired Fraction of open cells determines the required roller pressure; This can easily be determined by orienting experiments become. In practice, has proved to be the roll spacing 2 to 25%, preferably 5 to 10% of the original foam thickness.

The Polymer foams according to the invention can be used for Warmth- or sound insulation z. B. in the construction sector, in particular for isolation of windows and doors, as filter material, as packaging material, in particular for electronic parts or computer, as cushioning material for car or airplane seats, in sleeping bags, clothing, Laptop bags, or in the automotive sector z. B. for sound insulation in the engine compartment be used.

determination the degree of crosslinking

to Determination of the degree of crosslinking is weighed out 0.3 ± 0.01 g of the foam sample (Value 1), in a metallic net (linen weave, w: 0,50 mm, d: 0.20 mm, 36 mesh) and the weight determined (value 2). Per test sample 150 ml of xylene are placed in a round bottom flask, three samples each together in a test flask loaded, this corresponds to a volume of xylene of 450 ml per Test tube. By means of an electric heating bench, the xylene is boiled, the test samples added and refluxed for 6 hours cooked. Subsequently become the test samples for at least Dried for 8 hours in a convection oven at 70 ° C. After drying the weight is determined again (value 3).

The degree of crosslinking in percent is calculated according to the following formula:

Process step a) Starting materials: Porofor ADC / Z-C2 17.36% by weight SABIC LDPE 2102 TX00 57.85Gew. %

polystyrene 158K (BASF) 24.79 % By weight

The Mixing of the components was carried out via a steam-heated die kneader (Vapor pressure 5 bar). For this purpose, the polymers to be mixed Put in the kneader, the stamp closed and until it reaches a melt temperature of 153 ° C mixed for about 8 minutes.

following the punch was raised, the mixture in terms of homogeneity of a visual inspection and optionally the stamp cleaned of adhering granules. Subsequently was the amount of blowing agent added to the polymer blend, the stamp closed and until reaching a melt temperature of 155 ° C for about 3min and mixed for 15s.

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

Process step b)

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

The extruder used is a twin-screw extruder with a melt pump designed for the production of polyolefin foams. The screw diameter is 90 mm, the L / D ratio 25. Both the screw 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 main component with 97.8% by weight of the polymer / blowing agent mixture and as a crosslinking agent, a batch of 20% of 1,3-di- (2-tert-butyl-peroxiisopropyl) benzene in LDPE with 2, 2 wt.% Fed and extruded through a slot die a matrix. Maschienenparameter: Extruder throughput: 255kg / h Screw speed: 70U / min Melt pump speed: 21U / min Screw temperature: 80 ° C

Cylinder temperatures:

Zone 1: 130 ° C, Zone 2: 120 ° C, Zone 3: 90 ° C, Zone 4: 90 ° C, Zone 5: 130 ° C, Zone 6: 135 ° C, Neck: 125 ° C, nozzle temperature: 130 ° C

Process step c) and d)

The extruded matrix was continuously driven into an oven, in which both the crosslinking agents, and the blowing agents for Reaction be brought and thus to a foaming of the massive plastic plate led. The transport of the matrix took place via a metallic net.

Maschienenparameter:

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)

Of the obtained foam had a thickness of 10-12 mm and was then twice by a pair of rollers with a roller distance of about 1 mm mechanically open.

The crosslinked and open-cell polymer foam thus prepared had the following properties:

Claims (10)

Open-celled and crosslinked polymer foam, containing 50 to 95 wt.% Polyolefins 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%. Open-celled 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. 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 discharge is 0.1 - 5%. Open-cell and cross-linked polymer foam after one the claims 3 to 7, characterized in that polyolefins having a melt flow index from 0.5 to 10 g / 10 min (190 ° C, 2.16 kg) and polystyrene with a melt flow index of 0.5 to 8 g / 10 min (200 ° C, 5 kg) can be used. Process for making an open-cell and crosslinked polymer foam according to claim 1 to 4, characterized by the method steps: a) mixing at least a portion of the polymeric components at a temperature above their Glass transition temperatures, b) admixing of crosslinking agents, foaming agents, and / or the remainder of the polymeric components c) crosslinking the polymeric components, d) foaming the crosslinked mixture and e) Mechanical opening the cells Method according to claim 5, characterized in that that the process steps a) and b) discontinuously in one or several kneaders, extruders, Bussknetern, Stempelknetern and / or Calendering performed become. Method according to claim 5, characterized in that that process step a) discontinuously in a kneader or Calender and process step b) continuously in an extruder carried out becomes. Method according to one of claims 5 to 7, characterized that in process step a) a part of the polymeric components premixed and the remaining amount added in step b) becomes. Method according to one of claims 5 to 8, characterized that in process step a) a part of the polymeric components, the total amount of polystyrene and a part of the polyolefin contains, premixed and the remaining amount of the polyolefin in process step b) is added. Use of the open-cell and crosslinked polymer foam according to one of the claims 1 to 4 for heating or sound insulation, as filter material, as packaging material, as cushioning material for Car or airplane seats, in sleeping bags, clothes, laptop bags, or in the automotive sector.