GB2028353A - Filled polyurethane foam - Google Patents

Abstract

A filled polyurethane foam, useful in noise-reducing applications by virtue of being both a sound insulator and a sound absorber, contains from 10 to 55% by weight of filler and more than 25% by volume of closed cells, has a density of from 100 to 500 kg/m<3>, a sound energy loss factor of up to 0.4 and a dynamic E-modulus of more than 10<6> N/m<2> at 200 Hz/20 DEG C.

Description

SPECIFICATION Filled polyurethane foam This invention relates to filled polyurethane foam which is suitable for noise-reducing applications.

Noise reducing foams are known for example from German Auslegeschrift No. 1,923,161, which relates to a mat for lining walls of motor vehicle bodies, the mat being adapted in particular to the shape of the bodywork panel to be lined, and being made of polyurethane foam. To obtain considerable noise insulation, this polyurethane foam contains at least 60% of a filler, has a unit weight of from 0.5 to 1.25 kg/l and is used in a weight per unit area of from 5 to 10 kg/m2. Since this foam is merely intended for obtaining a considerable degree of noise insulation, a sound wave striking a wall lined with a mat of filled polyurethane foam such as this is reflected to a greater extent than it would be if the wall were unlined.

The effect of this mat is based on the fact that high sound insulation is always accompanied by high reflection of the sound waves by walls.

In contrast to sound insulation, sound absorption involves a high degree of transmission, i.e. a low degree of reflection, as can be seen in particular from Skudrzyk, "Grundlagen der Akustik", Vienna 1950, pages 121/122. According to this work, the sound energy behaviour of a sound wave which is reflected and transmitted by a separating wall is given by the relationship: EE=ER+ED (1) from which the relationship between the degree of reflection and degree of absorption may be calculated in accordance with the following formula:: 1-(ER/EE)=ED/EE=1 - R2=D2=a (2) In these equations, EE represents the intensity of the impinging sound wave, ER represents the intensity of the reflected sound wave, ED represents the transmitted sound intensity, R represents the degree of reflection, D represents the degree of transmission and cur the degree of absorption.

The Article by H. Oberst "Werkstoffe mit extrem hoher innerer Dampfung" in Acustica, 1955, pages 144 to 151 describes the mode of operation of a closed-cell foam which by virtue of its molecular composition exhibits high internal damping, i.e. has high internal sound losses. The loss factor of the mechanical energy of sound, and the E-modulus of this system were not only determined from measurements on bending strips, but they were also calculated from measurements in an impedance tube.

Afoam such as this is marketed underthe name "Vibrophon" by Messrs. Grunzweig & Hartmann.

This foam consists of foamed polyvinyl chloride (PVC) which is adjusted to high internal damping by the addition of suitable plasticisers in accordance with H. Oberst's recommendations. This foamed PVC, which has closed cells, reaches an absorption level of about 70%, is unfilled and can only be used at a maximum temperature of 60"C (333"K).

The sound-absorbing effect of closed-cell foams such as these is based on the fact that the impinging sound wave sets the foam skeleton vibrating. The relaxation of the plastics, particularly plasticised thermoplasts, converts this vibrational energy into other forms of energy, above all heat. It is known from Oberst's works that the relaxation processes in plastics can be displaced into desired frequency and temperature ranges by control of the plasticiser content. Since so-called rigid foams are not adjusted to high relaxation in the technically interesting frequency and temperature ranges, they do not show a sound absorption in this range which is effective for practical purposes. This applies for example to foamed polystyrene and also to closed-cell rigid foams based on polyurethane.

The often good sound absorption of open-pore polyurethane foams is also generally known. In open-pore foams such as these, conversion of the vibrational energy of the air into other forms of energy is obtained by mechanical friction on the cell walls, i.e. by a different mechanism than in the flexible closed-cell PVC foam prepared in accordance with Oberst's recommendations. Where flexible foams of this type also contain closed cells, the closed cells only participate to a negligible extent in the energy-conversion processes.

In order to save on costs, weight and work, for example, it is therefore desirable to provide a material which in a single lining layer performs several noise reducing functions at the same time.

According to the present invention there is provided a filled polyurethane foam which contains from 10 to 55% by weight offiller and more than 25% by volume of closed cells, and which has a density of from 100 to 500 Kg/m3, a sound energy loss factor of up to 0.4 and a dynamic E-modulus of more than 10g N/m2 at 200 Hz/20 C.

Such foams have been found, through high internal losses, to convert sound energy into other forms of energy by means of relaxation mechanisms and, as a result, have both a sound-insulating and a sound-absorbing effect. With such foams, the relationship (1) given hereinbefore is adapted to: EE = ER+ED+EV (3) where Ev represents the energy loss.

The filled polyurethane foam of the invention is preferably the reaction product of a component A comprising a polyol having an OH number below 150, a filler, a blowing agent and a reaction accelerator, and a component B comprising an isocyanate. For example, the foam may be formed by reacting components A and B in a ratio by weight of from 5:1 to 8:1.

The constituents of component A are discussed below: The polyols which may be used, for example dipropylene glycol and trimethylol propane, preferably have different chain lengths in the molecule and preferably have OH-numbers of from 40 to 120. These various types of polyols may be used either individually or in mixtures of two or more as polyol component for the production of the foams accord ing to the invention.

Blowing agents which may be used to produce the foams include water and halogen alkanes, for example monofluorodichloromethane ortrichloroethylene. Single blowing agents or mixtures thereof may be used.

As reaction accelerators, which function to control the polyaddition velocity for foam formation, there may be used for example the conventional accelerators, such as triethanolamine and/or dimethyl ethanolamine and/ortriethylene diamine and/or dibutyl tin dilaurate.

The fillers which may be used are preferably dense fillers such as ground or powdered minerals, preferably with a specific gravity of more than 2 g/cc. By way of example there may be mentioned heavy spar, ground shale and ground quartz, optionally in admixture with one another or for example with chalk and/ortalcum and/or carbon black.

As examples of component B there may be mentioned tolylene - 2,4 - diisocyanate and naphthylene - 1,5- diisocyanate.

The foam according to the invention may be produced by a process corresponding to that described in German Auslegeschrift No. 1,923,161.

The following table relates to Examples which illustrate the invention. In the Examples the reactants used to produce the foam are not specified.

They were, however, all selected from the constituents of components A and B which are discussed above.

Example I II III Component A Parts by % by Parts by 8 by Parts by by weight weight weight weight weight weight Polyol 15.8 38.6 15.8 38.6 15.8 39.7 Blowing agent 3.6 8.8 3.6 8.8 3.6 9.0 Reaction 0.29 - 0.7 0.29 0.7 0.42 - 1.15 accelerator Fillers 21.3 51.9 21.3 51.9 20.0 50.2 40.99 100.0 - 40,99 100.0 39.82 100.05 Component B Isocyanate 6.83 6.12 - 5.69 Ratio A : B - 6:1 6.7:1 7.1 The foams obtained become softer in the sequence of Example I to Example Ill, which means that when the foam is in the form of a mat of given mass per unit area, the absorption of sound by the mat increases from Example I to Example Ill. Conversely, in the sequence Example Ill to Example I the foam becomes more rigid, which means that the insulation of sound by the mat increases in that sequence due to the greater rigidity.

Foams according to the invention which are not listed in the table have also been obtained using increasing ratios between component A and component B, up to 8:1. In these cases, undercrosslinked polyurethane foams which are softer than the fully crosslinked or overcrosslinked foams were formed by virtue of the non-stoichiometric mixtures used.

For a better understanding of the invention and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings in which: Figure 1 shows open pores and closed cells in a foam according to the invention; Figure 2 is a plot showing the insulation of sound according to DIN. 52 210 which is achieved on metal sheets carrying 3 cm and 6 cm thick layers of a foam according to the invention corresponding to Exam ple II; Figure 3 shows the frequency response of the degree of absorption determined in a resonance chamber in accordance with DIN 52212 using the foam of Figure 2; Figure 4 shows curves of the degree of absorption determined in a Kundttube in accordance with DIN 52212 with vertically impinging sound using foams corresponding to Examples I to III; and Figure 5 shows the frequency response of the degree of absorption of a foam according to the invention produced in accordance with Example II but with a ratio of components Ato B of 8:1.

In Figure 1 is shown a foam having a surface 11 and pores 12 which communicate with the surface through passages 13. In use of such foam for noise reduction, vibrating air is damped by friction on the walls of the micro-passages 13 and the pores 12 and at the changes in cross-section. There are also shown closed cells 14, the walls 15 of which consti tute parts of the foam skeleton. If the foam vibrates under the effect of impinging sound waves, the cells 14 and their walls 15 are deformed at the frequency of the sound vibration. If the foam skeleton comprises a plastics material which has been plasticised for high relaxation, this vibrational energy is converted by relaxation processes into other forms of energy.

Curve 1 of Figure 2, represents the frequency response of the sound insulation of a 1 mm thick metal sheet, curve 2 represents the frequency response of the sound insulation of a dividing wall consisting of an identical 1 mm thick metal sheet to which is bonded a 3 cm thick layer of foam according to the invention (Example II), and curve 3 represents the frequency response of the sound insulation of a similar dividing wall in which the thickness of the foam layer is increased to 6 cm. The conspicious feature of curves 2 and 3 is the good frequency response of the sound insulation.In a comparison study (not shown) a sound-insulating mat according to German Auslegeschrift No. 1,923,161 was bonded to an identical 1 mm thick metal sheet, and it was found that the sound insulation curve was parallel to that of the pure metal, but increased by an amount which corresponded to the increase in weight. By contrast, the foams according to the invention are seen to produce a frequency response of the sound insulation which corresponds to that which is known for double walls, double walls being walls which consist of two heavy wall sections joined together by a resilient material. Thus, the foams according to the invention as used here produce the frequency response which is characteristic of expensive double walls without the need for the second covered heavy wall section.

If the sound absorption is measured in a resonance chamber in accordance with DIN 52 212, a frequency response of the type shown in Figure 3 is obtained for the degree of absorption of the foams according to the invention. This frequency response shows, for the single layer of foam on a metal sheet, the typical trend of a resonance absorber (which normally consists of a flexible, resilient porous substrate covered by a surface layer). Thus with this foam of the invention, the surface layer otherwise necessary for resonance absorbers is not required. The absorption curve of Figure 3 was determined on the same foam bonded sheet from which curve 3 in Figure 2 was determined. Thus it may be concluded that the foam according to the invention both insulates and absorbs, with absorption values of about 90% being possible.

Figure 4 shows the frequency response of the degree of absorption of metal sheets bonded with two samples of the foam according to the invention, curve 1 relating to foam having a density of 160 kg/m3 and curve 2 to a foam having a density of 220 kg/m3. These curves also show a frequency response which is typical of resonance absorbers. It must again be emphasised that the measurements were made on sheets carrying only a single layer of foam with, in this case, a thickness of 30 mm; there was no surface layer or covering layer.

It is possible by suitably adjusting the relaxation processes to obtain a frequency response of the absorption of the type shown in Figure 5. In this case, the relaxation maximum was displaced into the region of lowfrequencies, giving high absorption in the range below 300 Hz. With open-pored absorbers of traditional construction, this would have required layer thicknesses of more than 20 cm, in contrast to the minimal foam thicknesses of only 30 mm used on the metal sheet on which the measurements were made. The high absorption in the range above 1000 Hz emanates from the friction of the vibrating air on the walls of open pores. This Figure shows that, by suitably adjusting the relaxation process, it is possible using foams according to the invention simultaneously to utilise the various absorption mechanisms in separate frequency ranges. Thus there may be energy conversion by relaxation in the low-frequency range and energy conversion by friction in the high-frequency range, so that it is possible using foams of the invention to achieve high absorption with minimal thickness, even in the low-frequency range.

Claims (16)

1. A filled polyurethane foam which contains from 10 to 55% by weight of filler and more than 25% by volume of closed cells, and which has a density of from 100 to 500 Kg/m3, a sound energy loss factor of up to 0.4 and a dynamic E-modulus of more than 106 N/m2 at 200 Hz/20 C.

2. Afoam according to claim 1 which is the reaction product of a component A comprising a polyol having an OH number below 150, a filler, a blowing agent and a reaction accelerator, and a component B comprising an isocyanate.

3. Afoam according to claim 2 when formed by reacting components A and B in a ratio by weight of from 5:1 to 8:1.

4. A foam according to claim 2 or 3, wherein the blowing agent comprises water andlor a halogen substituted alkane.

5. A foam according to claim 2, 3 or 4 wherein the reaction accelerator comprises triethanolamine, and/or dimethyl ethanolamine and/or triethylene diamine and/or dibutyl tin dilaurate.

6. Afoam according to claim 2,3,4 or 5, wherein the isocyanate is tolylene -2, 4 - diisocyanate or naphthylene - 1, 5 - diisocyanate.

7. A foam according to any one of claims 2 to 6 wherein the polyol has an OH number of from 40 to 120.

8. A foam according to any one of claims 2 to 7, wherein the polyol comprises dipropylene glycol and/ortrimethylol propane.

9. Afoam according to any one of the preceding claims wherein the filler has a density which is greaterthan 2 g/cc.

10. A foam according to any one of the preceding claims wherein the filler is heavy spar, ground shale, or ground quartz or mixtures of any two or more thereof, optionally in admixture with chalk and/or talcum and/or carbon black.

11. A foam according to any one of the preceding claims when in the form of a mat.

12. A foam according to claim 1,substantiallyas described in Example I, II, or lil.

13. A foam according to claim 1 substantially as described with reference to any Figure of the accompanying drawings.

14. In combination, a metal sheet and, as sound insulator and sound absorbertherefor, a filled polyurethane foam according to any one of the preceding claims.

15. A combination according to claim 14, substantially as described with reference to any one of Figures 2 to 5 of the accompanying drawings.

16. The use of a filled polyurethane foam according to any one of claims 1 to 13 as a sound insulator and absorber.