EP0953964B1 - Foam-molded sound-absorbing articles - Google Patents

Description

The invention relates to a sound-absorbing foam molding with a sound absorption coefficient in the frequency range of 0.5 to 4 kHz from 50 to 95%.

Open-cell foam plastics based on polyurethanes and Melamine / formaldehyde condensation resins are ideal As sound absorbing materials, they are becoming increasingly popular used in many technical applications. Naturally, however these foams also have some disadvantages, in damp rooms, in the hygiene sector and in dust-sensitive areas Attachments. There was therefore a need for another Foamed plastic with sound-absorbing properties.

It has now been found that not completely welded polyolefin and polystyrene particulate foams having a gusset volume between 10 and 40% a degree of sound absorption DIN 52215 in the frequency range from 0.5 to 4 kHz, preferably from 1.25 to 2 kHz from 30 to 95%, preferably from 50 to 95%.

a) Homopolypropylen,

b) Randomcopolymere des Propylens mit 0,1 bis 15, vorzugsweise 0,5 bis 12 Gew.-% Ethylen und/oder einem C₄-C₁₀-α-Olefin, vorzugsweise ein Copolymer von Propylen mit 0,5 bis 6 Gew.-% Ethylen oder mit 0,5 bis 15 Gew.-% Buten-1 oder ein Terpolymer aus Propylen, 0,5 bis 6 Gew.-% Ethylen und 0,5 bis 6 Gew.-% Buten-1, oder

c) Mischungen von a) oder b) mit 0,1 bis 75, vorzugsweise 3 bis 50 Gew.-% eines Polyolefin-Elastomeren, z.B. eines Ethylen/Propylen-Blockcopolymeren mit 30 bis 70 Gew.-% Propylen.

d) Polyethylen (PE-LLD, -LD, -MD, -HD) und

e) Mischungen aus den unter a bis d genannten Polyolefinen (gegebenenfalls nach Zugabe von Phasenvermittlern).

Polyolefins in the context of the present invention are

a) homopolypropylene,

b) Randomcopolymers of propylene with 0.1 to 15, preferably 0.5 to 12 wt .-% of ethylene and / or a C ₄ -C ₁₀ α-olefin, preferably a copolymer of propylene with 0.5 to 6 wt. -% ethylene or with 0.5 to 15 wt .-% butene-1 or a terpolymer of propylene, 0.5 to 6 wt .-% of ethylene and 0.5 to 6 wt .-% butene-1, or

c) mixtures of a) or b) with 0.1 to 75, preferably 3 to 50 wt .-% of a polyolefin elastomer, for example an ethylene / propylene block copolymer having 30 to 70 wt .-% of propylene.

d) polyethylene (PE-LLD, -LD, -MD, -HD) and

e) mixtures of the polyolefins mentioned under a to d (optionally after the addition of phase mediators).

The crystallite melting point (DSC maximum) of a. to e. listed Polyolefins is generally between 90 and 170 ° C. Their heat of fusion, determined by the DSC method, is preferably between 20 and 300 J / g, the melt index MFI (230 ° C, 2.16 kp for propylene polymers and 190 ° C, 2.16 kp for ethylene polymers) according to DIN 53 735 between 0.1 and 100 g / 10 min.

In a preferred method for producing the EPO particles, polyolefin granules are used, which preferably have average diameters of 0.5 to 5 mm. In a stirred reactor, 100 parts by weight of this granules are dispersed in 100 to 500 parts by weight of water with the aid of a suspending aid. Then, a blowing agent in amounts of preferably 2 to 50 parts by weight, based on 100 parts by weight of polymer, pressed and heated the reactor contents. Suitable propellants are hydrocarbons, such as butane, halogenated hydrocarbons, alcohols and CO ₂ , N ₂ and NH ₃ . The propellant added can be done before or during the heating (this includes holding times) of the reactor contents to the expansion temperature. This should be 5 ° C below to 20 ° C above, preferably 2 to 10 ° C above the crystallite melting point of the polyolefin. In the preferred propylene polymers, the reaction is carried out at 110.degree. C. to 180.degree. Depending on the amount and type of blowing agent as well as the height of the temperature, a pressure is established in the reactor, which is generally higher than 2 bar and does not exceed 100 bar. By choosing the impregnation temperature and the blowing agent, the bulk density of the resulting EPO particles can be controlled. After reaching the relaxation temperature of the reactor is expanded, the relaxation is advantageously carried out in an intermediate container in which a pressure of preferably 0.5 to 5 bar prevails. When the reactor is expanded, the polyolefin granules containing propellant are expanded and EPO particles having an average diameter of from 1 to 20 mm are formed.

The bulk density of the EPO particles is within wide limits between 10 and 200 g / l, adjustable. Particularly suitable are EPO particles with relatively low bulk densities between 15 and 40 g / l. The EPO particles are predominantly closed cell and have a cell number of 1 to 5000 cells / mm ² , in particular 10 to 1500 cells / mm ² .

These foam particles are now in conventional molding machines with the help of water vapor in perforated tools with each other welded. It is essential that, in contrast to the usual Molding production no or at most a slight back pressure during the filling process prevails. In this way, the achieved according to the invention incomplete welding. The amount at voids, i.e., the gusset volume is between 10 and 40%, preferably between 20 and 38%. A small, at least However, selective welding is necessary, so that a coherent Shaped body arises.

In another manufacturing method is in an extruder the Melted polyolefin and a volatile blowing agent, preferably a hydrocarbon again, is pressed. After that the propellant-containing melt is squeezed out to the atmosphere, where she foams. The resulting foam strand is then crushed into foam particles, which in the case of Polyethylene expediently an electron beam crosslinking be subjected. Here are relatively low bulk densities reachable in the range of 10 to 20 g / l. In the case of polyethylene foam particles The semi-finished product can also take place on an air-permeable conveyor belt, the one Hot air duct passes.

Polystyrene foam particles are produced by another method which is also conventional and known per se. For this purpose, the monomeric styrene, optionally in admixture with other olefinically unsaturated comonomers, initiators, auxiliaries and additives is suspended in water and polymerized in the presence of suspension stabilizers. The resulting polystyrene beads are separated, washed and dried. The addition of the blowing agent can already take place during the polymerization, but it is also possible to introduce the blowing agent in a subsequent process step in the polystyrene beads. Suitable propellants are C ₄ -C ₈ hydrocarbons, preferably pentane.

The foaming of the blowing agent-containing polystyrene particles usually also takes place according to those known in the art Procedure, by first with steam in open or closed pre-expanders in many stages largely to be foamed. The prefoamed polystyrene particles have generally an average particle size of 1 to 10 mm, in particular from 2 to 8 mm. The preferred bulk density is 10 to 20 g / l. The production of moldings takes place in block ' Press, wherein previously in a mixer on the foam particle surface a primer (e.g., bitumen) is applied. In the block press, the foam particles are under light Counterpressure welded into a loose composite.

A big advantage of the sound-absorbing foam moldings based on polyolefins and polystyrene is that these Thermoplastic plastics meltable and thus recyclable are.

example 1

For the production of acoustic panels measuring 900 ^× 400 ^× 140 mm, PP foam particles having a mean bulk density of 28 g / l (Neopolen P 9230 from BASF AG) were compressed pneumatically from a container under 0.5 bar using a conventional molding machine a perforated mold nest, which stood under atmospheric pressure transported. The foam particles in bulk in the mold cavity were cross-evaporated with 2,8 bar superheated steam from both sides for 3 seconds each, whereby the shut-off valves in the condensate line were opened, while being spot-welded. After cooling in the mold cavity could be removed after opening the molding machine, a cuboid molding with a density of 33 kg / m ³ , which had a relatively high number of gussets (defects between the punctiform welded foam particles). The gusset share was 35%. The sound absorption coefficient according to DIN 52215 in the frequency range 1.25-2 KHz was between 75 and 90%.

Example 2

The procedure was analogous to Example 1, but with the differences that for filling the under atmospheric pressure mold cavity a differential pressure between filling container and mold cavity applied and the transverse evaporation at 3.2 bar and a steaming time 4 sec.

The resulting rectangular shaped part had a gusset portion from 25% up. The sound absorption coefficient in the frequency domain 1.25-2 kHz was between 55 and 70%.

Example 3

From PP foam particles with a mean bulk density of 17 g / l (Neopolen P 9220), acoustic panels measuring 300 ^x 200 ^x 60 mm were produced on a conventional molding machine. The foam particles were transported pneumatically into a perforated mold cavity under atmospheric pressure. The foam particles in bulk in the mold cavity were cross-evaporated with superheated steam of 2.4 bar from both sides for 3 seconds each time (with the shut-off valves in the condensate line of the machine open). The foam particles were spot-welded. After cooling in the mold cavity a cuboid molded part with a density of 24 kg / m ^{3 could be} removed after opening the molding machine. The gusset portion inside the molding was 30%. The sound absorption coefficient was 80% in the frequency range between 1.25 and 2 kHz.

Example 4

PE foam particles (Neopolen E 1710 BASF AG) with a bulk density of 13 g / l, which had previously been physically crosslinked by electron beam irradiation, were piled up on an air-permeable, circulating conveyor belt (belt width 1100 mm) about 200 mm high and through a Hot air duct transport. The transport speed was 1.6 m / min. and the circulation air in the heating channel 160 ° C. After leaving the 6 m long channel, a punctiform welded contiguous foam particle composite was obtained which had approx. 40% voids. The sound absorption coefficient in the frequency range 1.25 to 2 kHz of this molded part (density: 14 kg / m ³ ) was 85 to 90%.

Claims (2)

1. A sound-absorbent foam molding with a sound-absorption level according to DIN 52215 of from 30 to 95% in the frequency range from 0.5 to 4 kHz, wherein the foam is an incompletely fused molded polyolefin or polystyrene foam with from 10 to 40% interstitial volume.
2. A sound-absorbent foam molding, wherein the foam is a molded polyethylene or polypropylene foam.