DE2014239A1 - Light-weight sandwich structures - Google Patents

Abstract

Articles comprising stable outer layers and a cellular core of a (crosslinked) thermoplastic material pref. an ethylene (co)polymer are prepd. by foaming the plastic material, which contains a solid foaming agent and opt. also a crosslinking agent, between the stable outer layers at temps. above the decomposition temps of the foaming and crosslinking agents, whereby good adhesion is achieved between the layers without use of an additional binder. An org. peroxide cpd. is used as adhesion improver; and the foaming is effected against the weight of at least one of the stable outer layers. A dense marginal zone is obtd. during the foaming step which has a density at least three that of the foam core. Process is suitable for manufacture e.g. of aluminium/plastic foam core/aluminium sandwich elements.

Description

Process for the production of lightweight composite bodies, consisting of stable outer layers and a foam core.

The invention relates to a method for producing lightweight composite bodies , consisting of stable outer layers and a foam core made of a thermoplastic or crosslinked thermoplastic material, preferably based on homo- or Copolymers of ethylene, produced by foaming a, a solid blowing agent, optionally also a crosslinking agent-containing plastic between the stable outer layers at temperatures above the decomposition temperatures of the Propellants and crosslinking agents lie, without the use of an additional adhesive a firmly adhering bond is created.

In such composite bodies is required that the foamed Plastic core is very firmly connected to the stable layer, with the stable Layer or cover layer are supported over a large area by this plastic core target.

It is known to meet these requirements to the nominal size to connect prefabricated confessional cores with the stable cover layers with glue.

if the top layers are made of metal, there is an additional one beforehand Sandblasting and degreasing the metal surfaces are advantageous because they improve the adhesive strength of the binder on the top layer is increased.

I = as DBP 964 716 suggests on degreased and roughened metallic Top layers first a primer made of a mixture of polyesters and isocyanates and then apply a foamable polyester-isocyanate mixture.

After foaming, the foam core adheres well on the top layer.

According to DAS 1 183 675, polystyrene foam is made with any Documents firmly bonded by applying a highly viscous liquid, those by dissolving polystyrene in low-boiling halogenated hydrocarbons and addition of ammonia has been obtained, is applied and predried. The foaming process is then carried out, for example by treatment with steam carried out.

It is also known composite body made of polystyrene foam and to produce a sheet metal support, with the sheet metal support as anchoring means Projections is provided which protrude into the foam body. The sheet metal support of the composite body is for the supply of the hot necessary for Aufachauming Perforated gas (DBP 1 137 199).

The use of adhesives has a number of disadvantages.

The best adhesives are reaction adhesives, i.e. two-component adhesives. However, these only have a limited pot life and are not cheap. Also hionomer adhesives are good adhesives, but also have a limited processing time and are also quite expensive. The most common adhesives are solution-medium or dispersion adhesives and need in processing a flash off time to dry the Solvent or water.

In the case of solvent adhesives, solvents evaporate that are sucked off or have to be adsorbed, as they are not harmless to health. Remaining Solvent residues in the adhesive layer can cause plastic foams and dissolve or even destroy plastic sheets to be glued.

When using adhesives must continue to depend on A selection must be made regarding the materials to be bonded, as most adhesives do have no universal applicability.

When using adhesives it is necessary to have good adhesion to achieve pretreatment of the surface to be bonded, e.g. 3. Degreasing, blasting, Pickling and oxidizing. For surfaces that have thin metal coatings, e.g. Galvanized and cm inert surfaces, is a mechanical or chemical pretreatment not possible.

There are also Iaetalle such as stainless steels, which also after a pretreatment cannot be glued properly.

Most adhesives are thermoplastic, which means that with their intrinsic strength decreases with increasing temperature.

Studies on thermoset adhesives have shown that these too Above 1QOOC, their resistance to EX will be significantly reduced.

Since most adhesives the foaming conditions are mostly at high temperatures lie, not withstand, the gluing has to be part of the foaming process be connected downstream.

But that means an additional work step.

Through special training of the stable layer, z.3. through protrusions, which protrude into the foam core creates an intimate bond between the foam and reached tecksohicht. However, the top layers must have a separate operation be subjected. This method is apparently limited to sheet metal.

The invention is based on the object of lightweight composite bodies made of sturdy outer layers and a foam core that stand out through characterized by high adhesive strength between the foamed inner part and the outer layers. The products should have high strength and be dimensionally stable.

This object is achieved according to the invention by the fact that the to be foamed thermoplastic plastic, preferably based on homopolymers or copolymers of ethylene as an adhesion-improving agent, an organic peroxide compound is added and foaming against the weight of at least one of the stable outer layers performs and that the foaming process is carried out so that a compacted edge zone arises, which has at least three times the density of the foam core.

The invention is described in greater detail on the basis of the following exemplary embodiments described.

Example 1 On a 100 x 100 x 0.1 cm thick aluminum plate was a plate of the same thickness produced by means of an extruder and slot die as follows Composition 100 parts by weight high-pressure polyethylene (d = 0.92 g / cm3) 0.6 "II zinc oxide 1.8 "Perketal (Oxydo; Emmerich / Rh.) 5" II azodicarbonamide placed and on this Plastic plate again an aluminum plate as described above is placed on top. These The combination was foamed in a side-limited porm at 2000C in 18 min -2. The foaming pressure was less than 1.001 kgf. The density in the foam core was 0.06 g cm 3 and an average of 0.39 g cm 3 in the edge zone. The adhesive strength between the stable outer surfaces and the foam was higher than the inherent strength of the foam.

Example 2 A plasterboard measuring 100 x 100 x 3 cm was applied Plastic powder of the following composition evenly in a thickness of 2 cm applied: 100 parts by weight of low-pressure polyethylene (d = 0.94 g / cm³) 1.5 "" perketal (Oxydo; Emmerich / Rh.) 3.5 "" Azodicarbonamide 10 "II Calcium carbonate 0.5" Zinc oxide A steel plate measuring 100 × 100 × 0.2 cm was then placed on top. In a side-limited form, the combination was in 20 min at 180 ° C against the pressure of the metal plate to a size of less than 1.002 kpcm-2. The density in the foam core was 0.14 g cm and an average of 0.5 g cm in the edge zone. Adhesion to the stable The outer layers were higher than the inherent strength of the foam.

Example 3 Was placed on an aluminum plate measuring 100 x 100 x 0.1 cm a 200 / u strong blown film given the following composition: 100 parts by weight high pressure Polyethylene (d = 0.92 g / cm3 2 "'Azodicarbonamide 2.2" "Perketal (Oxydo; Emmerich / Rh) A 5 mm thick plastic plate made of 100 parts by weight was then placed on this sheet Ethylene-vinyl acetate copolymer (85:15) 2 parts by weight of azodicarbonamide 0.5 "" Zinc oxide placed.

Then there was another layer of the above-mentioned film and finally one Aluminum plate measuring 100 x 100 x 0.3 cm. The combination was Foamed in 25 min at i800C.

The foaming pressure to be applied was below 1.001 kgf cm 2.

All layers have firmly bonded when foaming, so that the adhesion was above the inherent strength of the foam. The foam density was 0.15 g cm 9 in the core and 0.48 g cm 3 on the outer surfaces.

Example 4 On an aluminum plate measuring 100 x 100 x 0.03 cm a 500 / u thick plastic film of the following composition was placed: 100 parts by weight of low-pressure polyethylene (d = 0.94 g / cm3) 2 "" Perketal (Oxydo; Smmerich / Rh.) A 2 mm thick plastic sheet of the composition 100 parts by weight was then placed thereon High pressure polyethylene (d = 0.92 g / cm3) 5.5 1l lt azodicarbonamide 0.7 8 zinc oxide.

After another layer of the first-mentioned film, a 100 x 100 x 0.1 cm thick aluminum plate. The combination then came into one delimited form. In addition, there was a delimitation plate, which was held by springs pressed on the latter aluminum plate, on it. The springs were adjusted so that the foaming pressure 1.8 kp step. The mold did not come into an oven at 180 ° C The combination was foamed in 25 minutes. The density in the core was 0.06 g cm 3 and about 0.6 g cm 3 on the metal surface.

Here, too, the adhesion was higher than the inherent strength of the foam.

The advantages achieved with the invention are in particular: that an improved lightweight composite body can be achieved in a simple manner can. The process is particularly useful for thin outer layers made of light metals suitable, as these cannot be sandblasted, otherwise deformations result the heat development can occur. There is also the risk of perforation here of thin layers. But also for other thin layers, e.g. layers of plaster, The method according to the invention is suitable for asbestos, plastic and wood. In all Cases, a bond is obtained between the cover layers and the foam core, which is characterized by its extraordinarily high adhesive force. The lightweight composite body are very strong and dimensionally stable, even if the outer layers are curved or arched are prefabricated. Since no adhesion-improving intermediate layers or glue are used the process is very economical. It is also suitable for manufacturing large-area bodies, e.g. in the construction industry, as heat-insulating or sound-absorbing Elements or can also be used in packaging.

The deposits previously required for the strength of the composite body made of nonwovens can be dispensed with because, according to the process according to the invention, a high compacted edge zone of the foamed part. arises.

Claim

Claims (1)

Claim method for the production of composite confessional bodies, consisting of stable outer layers and a foam core made of a thermoplastic or crosslinked thermoplastic, preferably based on homo- or Copolymers of ethylene, produced by foaming a, a solid blowing agent, optionally also a crosslinking agent-containing plastic between the stable outer layers at temperatures above the decomposition temperatures of the Propellants and crosslinking agents lie, without the use of an additional adhesive a firmly adhering composite is formed, characterized in that a. as an adhesion enhancer Agent uses an organic peroxide compound, b. foaming against that Carries out the weight of at least one of the stable outer layers and c. during foaming a compacted edge zone receives, which is at least three times the density compared to owns the foam core.