METHOD FOR THE PRODUCTION OF INTEGRAL SKIN FOAM

Abstract: A method is disclosed for the production of integral skin foam from a liquid skeleton substance like plastic or inorganic material. The liquid skeleton substance is brought into a chamber and a sonochemical process is brought about, in order to dissolve at least an inert, non-flammable gas as well as a low amount of a hydrocarbon fluid in the liquid skeleton substance. Only said inert, non-flammable gas serves to foam up the skeleton substance by energy supply; the hydrocarbon fluid promotes the formation of the usual dense outer skin of the integral skin foam. The method allows to achieve an optimal density and pore distribution within the integral skin foam.

Description: Description METHOD FOR THE PRODUCTION OF INTEGRAL SKIN FOAM Technical Field This invention relates to a method for the production of integral skin foam according to the preamble of claim 1. Background Art One such type of method is known from DE 32 26 818 Al. Du¬ ring this known method conventional devices are used for the measurement of gas and gas loading. After a measurement of density of a mixture sample which was taken from a ma¬ chine container, or in a bypass the gas loading done at another position is controlled on the basis of this measu¬ rement. The addition of the gas occurs also in a bypass, for example, parallel to a return pipe-line coming from a mixer casing in the vicinity of a machine tank. The gas ad¬ dition in the bypass is done by a capillary tube introduced into the pipe-line and a Venturi-tube. The control of gas loading can be done manually or with the help of a compu¬ ter. The application of the Venturi-principle makes this known method difficult to control because the amount of gas loading is heavily dependent on an interface tension bet¬ ween liquid and gas, wherein high interface tension means small bubbles of the absorbed gas in the liquid and wherein low interface tension means large bubbles of the absorbed gas. In addition to that the known method working according to the Venturi-principle is high energy consuming because the flow in the pipe, in which the Venturi-device is situa¬ ted, must have a high speed, so that the gas loading resul¬ ting according to the type of a water jet blast can func¬ tion at all. Finally it is disadvantageous in the case of the known method, that relatively high quantities of fo¬ aming agent, among others hydrocarbon fluids, are neces¬ sary. Another known method is, for example, mechanical frothing. In this case foaming agent, air and gelling agent are fed to a plastic serving as a skeleton substance and a homoge¬ neous mixture is produced by a mixer (vide A.M. ittfoth, Kunststofftechnisches όrterbuch, Carl Hanser Verlag Mϋn- chen Wien, Part 3, page 146, 1978). The mixture is then poured into a mould. In a subsequent heating operation the mixture expands and solidifies, so that a foamed product is produced. Therein a foaming agent in the form of azo or diazo-compounds is always added, which sets free N 2 or C0 2 , when the foaming agent decomposes under gas formation in the heating operation subsequent to the mixing and thus leads to the foaming up of the skeleton substance and to the formation of foam. In the case of some foaming agents no heating process is necessary, as they decompose even at room temperature. However, even here normally a heating process is conducted afterward in order to cure the foam. Again there are other methods for the production of foam from plastic, e.g. the one-shot process, which is also cal¬ led direct process, or the two-step process. Therein either foaming agents or liquid solvents are admixed to a plastic to be foamed up. The foaming agents decompose at a certain temperature under gas formation and thus foam up the pla¬ stic by forming cavities within the plastic. In the case of production of foams by adding volatile solvents these are admixed to the plastic during the polymerisation, whereby spaces filled with solvent are created, which become cavi¬ ties after the evaporation of the solvent. Foams are produced from polystyrene, polycarbonates or po- lyurethanes, for example, wherein the production of foams from polyurethanes has the greatest technical importance and such foams find use in upholstery, mattresses or wrap¬ pings, for example. Most of the known methods have the disadvantage, that du- ring the use of foaming agents free from chlorofluorocar- bons (CFC), like n-pentane, for example, with air there are easily produced very highly inflammable air-gas mixtures. These air-gas mixtures develop not only in the production phase of the foams, but also during aging of the foams af¬ terward, during which the residual foaming agent is set free from the foam. Production companies for foams which handle such types of foaming agents, therefore require ex¬ tremely high safety precautions. This is also valid for the later aging in rooms, in which the permitted concentration of gas density must be permanently checked and regulated by constant ventilation of the rooms. This requires not only expensive, matured technology within the production com¬ pany, but leads also to a very high emission load of the atmosphere. In the not pre-published DE 41 13 578 Al, which originates from this applicant, a device for the loading of viscous liquids with gases, in particular polyols for the produc¬ tion of polyurethane with preferably carbondioxide is de¬ scribed. If only carbondioxide is applied as gas for the foaming of the plastic during the production of foam, it can result to the formation of urea. This urea then leads to brittleness of the foam. Integral skin foam cannot be produced by this known device, where only C0 2 or any other similar gas is applied for foaming. Disclosure of Invention It is the object of the present invention to improve the type of gas loading of the liquid skeleton substance in a method according to the preamble of claim l, i.e. to make it easier to control and less energy consuming, also regar¬ ding the application of hydrocarbon fluid. This problem is solved according to the present invention by the steps as stated in claim l. In the method according to this invention the gas loading is not done following the Venturi-principle, thus not by a mechanical process, but by a sonochemical process. Under sonochemistry, also called ultrasonic chemistry, a part of chemistry is understood, which deals with the chemical ef¬ fects of ultrasonics. Thereby it has been proved, that the main effects of the sonochemical reactions conductable only in the liquid phase go back to cavitation and the noti¬ ceable products correspond to these of the high temperature chemistry, as the high temperatures lead to molecule disso¬ ciation (εonolyse) in collapsing cavities, among others for the formation of free radicals (Rδmpp-Chemie-Lexikon, Georg Thieme Verlag, Stuttgart, Vol. 6, pages 4802 and 4803). In the case of the sonochemical process, which is utilized in the method according to this invention, vacuum bubbles con¬ tained in a liquid skeleton substance absorb gas. The gas then dispersed in the liquid skeleton substance is dissol¬ ved into the liquid by means of ultrasonics, and indeed even at low pressure, below the solubility pressure. The sonochemical process is energywise less expensive and makes the method according to this invention more simple to con¬ trol than the method known from the DE 32 26 818 Al indica¬ ted earlier. In addition the application of cyclobutane, cyclohexane, cyclopentane or a mixture thereof makes it possible to use less hydrocarbon fluid than in the state of the art technique according to the previously mentioned DE 32 26 818 Al. From the DE-OS 19 17 962 it is actually known indeed, to use an acoustic pressure pump, wherein a medium to be admi¬ xed into a liquid, like air for example, is forced to pass through very fine nozzles, holes or sieve meshes. Thereby fine threads of air or gas flow produced in the liquid are divided or chopped into single, very tiny particles by the subsequent effect of the compression waves. Therein however the operation is a sonic operation, not an ultrasonic ope¬ ration. Furthermore, air or gas bubbles mixed roughly into the liquid can be divided afterward into fine air or gas bubbles with the help of the principles described in the DE-OS 19 17 962. But thereby on the other hand only large air or gas bubbles swimming in the liquid are pumped through together with the liquid through nozzles, holes or sieve meshes by means of pressure impacts and are thus di¬ vided into similar bubbles. As the known acoustic pressure pump is active only in the sonic range, only a purely me¬ chanical effect results on gas and liquid and not anything like the sonochemical effect as in the case of the method according to the present invention. In the case of the lat¬ ter a liquid skeleton substance is brought into a chamber. The skeleton substance is foamed by at least an inert, non¬ flammable gas, which is inserted into the liquid skeleton substance together with hydrocarbon fluid. Thus in the chamber it is already a finished mixture, on which these ultrasonics will act in order to bring about the sonochemi¬ cal process. Contrary to the same according to the DE-OS 19 17 962 it is always effected at first on liquid, air or gas separately, and subsequently fine meshed sieves, nozzles or holes are necessary for the mechanical diminution of air or gas bubbles. By the application of hydrocarbon fluid combined with an inert, non-flammable gas under the action of sonochemical process according to this invention integral skin foam can be produced with optimum density distribution. In the case of the method according to this invention indeed com¬ bustible hydrocarbon is added to the integral skin foam, however, in such a low quantity (preferably below 1% by vo¬ lume of the inert gas and the liquid skeleton substance) , that no combustible evolution of gas can occur. Any em¬ brittling is avoided and the environment is spared. Advantagous formations of this invention form the objects of the sub-claims. The method according to this invention is described herein with the help of the attached drawing. Brief Description of Drawing Fig. 1 shows a partly schematic cross-section of a device, in which the method according to this invention is carried out. Best Mode of Carrying out the Invention The shown device has a resonance chamber 10, which is com¬ posed of four chambers 12 placed opposite to each other in pairs and having the shape of cloverleaves. Each chamber has a concave, arcuate, bowl-shaped back side 12 and is open to the middle point of the resonance chamber 10. In each of the chambers 12 an ultrasonic oscillator 14 is arr- ranged in such a way, that it can be freely flowed-around by a liquid skeleton substance to be treated. The liquid skeleton substance is in the present case polyol, for exam¬ ple. The ultrasonic oscillators 14 consist of membrane pla¬ tes made of barium-lead-titanate as they are used for con¬ ventional water nebulizers. The ultrasonic oscillators 14 are in connection with a process computer controlled fre¬ quency generator through electrodes 18 and 20. Such fre¬ quency generator is used since the geometrical form of the ultrasonic oscillators 14 defines the oscillation frequency thereof, and since a change in frequency actually otherwise would be achieved only by the exchange of the ultrasonic oscillators 14. The resonance chamber 10 has a certain size, which is defi¬ ned by the wave length of the possible oscillation frequen¬ cies of the ultrasonic oscillators 14 and by the desired yield of integral skin foam. The resonance chamber 10 is provided through a pre-chamber 22 with a fine mixture of the liquid skeleton substance, inert non-flammable gas and a hydrocarbon fluid, preferably an azeotropic mixture of several hydrocarbons. The pre- chamber 22 is supplied with the liquid skeleton substance by a supply pipe 24. The azeotropic mixture of hydrocarbons and the inert, non-flammable gas, in the present case car¬ bondioxide, are supplied by another supply pipe 26. In ad¬ dition to that it is also possible to provide one supply line for each of the components, i.e. the azeotropic mix¬ ture of hydrocarbons and the inert, non-flammable gas. In the pre-chamber 22 the fed materials are converted into an extremely uniform mixture of the liquid skeleton sub¬ stance, the azeotropic mixture of hydrocarbons and the in¬ ert, non-flammable gas by a fast rotating cavitation ele¬ ment 28. This mixing is improved still further by the ul¬ trasonic oscillators 14, so that smallest bubbles of the inert, non-flammable gas as well as smallest components of the azeotropic mixture of hydrocarbons are distributed uni¬ formly in the skeleton substance whereby the hydrocarbons and the inert, non-flammable gas are dissolved in the li¬ quid skeleton substance. By an outlet 32 this mixture is poured into a foam mould. In the case of energy supply preferably heating, for exam¬ ple, the inert, non-flammable gas dissolved in the liquid skeleton substance is set free again. This is comparable with dispersing of carbondioxide while opening a mineral water bottle. The inert, non-flammable gas set free foams up thus the liquid skeleton substance, by which the foam is produced. By the additionally added hydrocarbon the dense skin type surface usual for integral skin foam is achieved. Such an integral skin foam has a smooth, dense surface, as it is rated at automobile steering wheels or automobile dashboards. During a subsequent curing process no combustible gas will be set free, so that an aging in specially checked and ven¬ tilated rooms is eliminated. Tests have shown that the hydrocarbon fluid can consist of cyclobutane, cyclohexane or cyclopentane or of a mixture of these substances. Instead of carbondioxide also nitrogen, argon, helium or perhaps even an azeotropic mixture of the same can be used as inert, non-flammable gas in order to foam up the liquid skeleton substance. The skeleton sub¬ stance itself can consist also of inorganic material in¬ stead of plastic. In addition to that it is also possible to convert hard foam, those for insulating of windows for example, into an integral skin foam with solid outer layer by the described method. The values of the reaction temperatures and similar others are the same as those in the case of the production of fo¬ am.

Claims: Claims 1. A method for the production of integral skin foam from a liquid skeleton substance like plastic or inorganic mate¬ rial, which is foamed up by at least one inert, non-flam¬ mable gas, which is set free by energy supply, whereby the inert, non-flammable gas together with a low quantity of hydrocarbon fluid is added to the liquid skeleton substance and whereby only the inert, non-flammable gas serves during the energy supply for the foaming up of the skeleton sub¬ stance and the hydrocarbon fluid promotes the formation of a dense outer skin of the integral skin foam, characterized in that the liquid skeleton substance is brougth into a chamber and a sonochemical process is brought about, in or¬ der to dissolve the gases in the liquid skeleton substance, and the addition of hydrocarbon fluid is less than 1% by vol. of the inert gas and the liquid skeleton substance and consists of cyclobutane, cyclohexane, cyclopentane or a mixture thereof. 2. The method according to claim 1, characterized in that the hydrocabon fluid is an azeotropic mixture of several hydrocarbons. 3. The method according to the claim 1 or 2, characterized in that the inert, non-flammable gas is carbondioxide, ni¬ trogen, argon, helium or an azeotropic mixture thereof. 4. The method for the production of integral skin foam from a liquid skeleton substance substantially as hereinbefore described.

Inventors: POESCHL GUENTER, WAYAND HANS-JUERGEN, POESCHL, GUENTER, WAYAND, HANS-JUERGEN
Applicants: POESCHL GUENTER, PPV VERWALTUNGS AG, WAYAND HANS JUERGEN, PPV-VERWALTUNGS-AG
Application year: 1993
Main classification: B29C67
IPC codes: B01F11, C08J9