DE102005030953A1 - Closed cell polymer foams are formed by subjecting the foam to an inert gas during foaming, removal from the mould, and storage - Google Patents

Abstract

A process for producing closed cell polymer foams comprises subjecting the polymer foam to an inert gas atmosphere during foaming, removal from the mould, and storage. The foam is polyurethane or polystyrol foam, and the inert gas concentration is reduced after foaming. The temperature during foaming and/or removal from the mould and/or storage, is 25-100o>C. The inert gas pressure is above atmospheric pressure and is carbon dioxide.

Description

object The invention relates to a method for the production of closed-cell Polymer foams, which are characterized by a reduced shrinkage.

Polymer foams are in big Quantity produced and used in many ways. Their use takes place mainly for thermal insulation or for energy absorption, for example in vehicle construction.

Examples for plastic foams are Polyester foams, Polyamide foams, polyolefin foams, PVC foams, polystyrene foams and polyurethane foams, the latter two having the greatest technical significance.

The Production of polyurethane foams by reaction of organic Polyisocyanates compounds having at least two reactive hydrogen atoms, is known and has been described many times. A summary of the Production of polyurethane foams is z. In the plastic manual, Volume VII, "Polyurethane", 1st edition 1966, edited by dr. R. Vieweg and dr. A. Höchtlen and 2nd edition, 1983, and 3rd edition, 1993, each edited by dr. G. Oertel (Carl Hanser Verlag, Munich) given.

The Production of polystyrene foams is described for example in Kunststoffhandbuch, Volume 4 "Polystyrene", Carl Hanser Verlag Munich Vienna, chapter 13.2.

One Problem in the production of closed-cell plastic foams, such as expanded polystyrene or closed-cell polyurethane foams is the so-called shrinkage. By this one understands a volume reduction of foams after their production. The cause of the shrinkage is the out-diffusion the propellant from the cells. Because the speed of diffusing out the propellant is larger As the diffusion of air into the cells, e comes to a negative pressure in the foam. This negative pressure leads to said volume reduction.

If the foam is not cured at this time, it may become one Gluing the cell walls of the foam. this leads to to prevent the foam from returning to its original shape can. This can be achieved by mechanical processing of the cured foam, like walking, partly counteracted. the mechanical processing however, has often a destruction of the cell scaffold result.

Also after curing of the foam, the shrinkage can lead to destruction of the foam matrix, if the blowing agent escapes from the foam very quickly and through the sudden negative pressure very big personnel act on the foam.

It It is known that the gas conditions influence the production of the foams on the shrinkage behavior of the foams.

DE 4421340 describes a polyurethane foam, which should be particularly suitable for cryogenic insulation. For this purpose, a vacuum in the cells should be adjusted by pumping out the gases.

In US 5389695 For example, a polyurethane foam is first produced in a mixture of carbon dioxide and an inert gas of low thermal conductivity. Subsequently, the carbon dioxide is then removed by means of adsorbents from the cell interior. The objective here is rigid foams with reduced thermal conductivity.

JP 52080398 describes the production of polyurethane block foams. To minimize the heating of the finished foam this is cut and deposited the parts in a container. This container is evacuated and filled with nitrogen at a temperature of -100 ° C to cool the material.

JP 53132065 describes the production of polyurethane molded foams. By applying a negative pressure in the mold, foams having good properties are obtained.

The concomitant use of an inert gas during foaming with the concomitant use of a combustible propellant is also known in order to ensure explosion protection during processing. Such a method is described, for example, in EP 639441 described.

EP 867265 describes polyurethane foams which are made in the manufacture of a vacuum in the mixing chamber to prevent the formation of large bubbles in the foam. The component tanks are also placed under vacuum.

DE 10005862 describes the use of inert gas as blowing agent for integral foams. For this purpose, encapsulated blowing agents are used.

DE 4421340 describes a technology for foaming under vacuum, wherein different gas mixtures can be used for pressure equalization after the production of the molded part.

Also known is the supply of an additional propellant gas directly into the mixing chamber, such as in EP 196345 described, whereby the bulk density of the foam is to be reduced.

In DE 3920994 describes a method in which the propellant gas is introduced via a static mixer in the component stream.

DE 4312036 describes the addition of an inert gas during the production of polyurethane foams in order to prevent the formation of explosive gas mixtures when using hydrocarbons as propellant. The inert gas is introduced into the component stream.

US 3870441 and GB 1354341 describe equipment for the continuous production of polyurethane block foams. For this purpose, the reaction mixture is first metered into a trough. The rising foam is then passed over a deflector on a moving belt. Optionally, suction devices may be attached to the sidewalls to prevent collapse of the side-going foam.

To guide the foam in a continuous process for the production of slab foams is in US 4692664 the foam is guided until it reaches a stable state of reaction in a channel equipped with foil strips. Thereafter, unhindered air access is possible.

EP 645226 describes the foaming by means of liquid carbon dioxide. In this case, a pressure reduction of the pressurized foam mixture is generated in order to achieve the slowest possible release of carbon dioxide from the foam. During foaming and immediately thereafter, no special gas atmosphere is used.

WHERE 0047384 describes an apparatus and a method for foaming Polyurethane block foams. To achieve block foaming with minimal skin thickness is the rising foam mixture in one saturated Gas atmosphere, preferably consisting of carbon dioxide foamed. This will be the amount of waste minimized when blending the block product.

To In the present state of the art, it is difficult to be sensitive Plastic foams, in particular closed-cell flexible polyurethane foams, a shrinkage by not open cell walls to prevent. In an analogous manner, insufficient structural stability in rigid foams can be achieved by Gas exchange processes lead to shrinkage. Haptics and surface adhesion on cover layers is often insufficient especially in water-driven polyurethane foams.

Therefore it is common desirable, the foaming to perform under such conditions that shrink Foam lead without further post-processing. If it comes to a shrink, this should not be one destruction of the foam.

It was therefore the task in the production of polymer foams, in particular polyurethane foams to lead the foam process so that the described shrinking processes are delayed, minimized or prevented can be the feel and adhesion of such foams being positive can be influenced.

These Task was surprisingly by solved, that, the polymer foam during the Production, hereinafter also referred to as foaming, during demolding and / or processing and / or storing an inert gas or inert gas mixture is surrounded.

object The invention thus provides a process for the production of polymer foams, characterized characterized in that the polymer foam during manufacture, during Demolding and / or processing and / or storing one Inert gas or inert gas mixture is surrounded.

Objects of Invention are also the closed cell so produced Polymer foams, in particular polyurethane foams and their industrial use.

The according to the inventive method produced closed-cell polymer foams are, for example, polystyrene foams, polyolefin foams, polyester foams, polyamide foams, and Polyurethane hard and soft foams.

Especially can the inventive method be used for the production of polystyrene foams and or polyurethane foams.

at the polystyrene foams can the inventive method be used particularly advantageously in such foams, which are produced by extrusion.

The production of such foams is described for example in the Plastics Handbook, Volume 4 "Polystyrene", Carl Hanser Verlag Munich Wi , chapter 13.2. described. The polystyrene is melted in an extruder and pressed together with the blowing agent through a nozzle, whereby it foams. As propellants, hydrocarbons, halogenated hydrocarbons or carbon dioxide can be used. In particular, when using carbon dioxide as a blowing agent, a pronounced shrinkage occurs.

Also in closed-cell polyurethane foams, shrinkage is the foams mostly very pronounced.

It was surprisingly found that during manufacture, during demolding and / or storage of polyurethane foams by the use of inert gas or an inert gas mixture, the shrinkage behavior of the foams, the feel and the surface adhesion can be positively influenced.

When Inert gases can in principle all gases are used, which with the foams and their starting components are not reactive. Preferably come Carbon dioxide and / or nitrogen are used.

Of the Foam can be mixed with the inert gas according to the different methods Be brought in contact.

In an embodiment the method according to the invention the fogging takes place immediately at the beginning of the foaming process the space in which the foam takes place, with an inert gas. Depending on the type of foam it may be the interior of a Shape or around the surroundings of the strip road. The fog takes place preferably at the outlet of the reaction mixture from the nozzle in the case of extruded foams, such as polystyrene foam, or at the mixing head in the case of polyurethane foam. The fogging can also be delayed, in the case of polyurethane foams For example, after the end of climbing, start. The inert gas atmosphere can until demoulding, finishing, for example, trimming at the Bandstraße, or storage. in a preferred embodiment the method according to the invention The concentration of the inert gas in the inert gas or Inertgasgemisch atmosphere after the conclusion of the foaming gradually reduced.

in the a further embodiment the method according to the invention the plastic foam can after the end of the foaming process or stored after removal or packaging of the foam in an inert gas atmosphere become. The proportion of the inert gas can be dependent be reduced by the use case over time. that's what happens to a slow gas exchange in the cells, leaving only a slight or slow shrinkage takes place, reducing the mechanical stress the foam is lower and no damage to the polymer matrix occurs. To any shrinkage that may occur, the foam can be original Regain volume.

at both methods, the proportion of the intergas in the ambient atmosphere of the foam be reduced over time.

The Temperature during foaming, Removal and / or processing and / or storage of the foam is preferably between 25 and 100 ° C. Preferably, work is carried out above the atmospheric pressure.

object The invention furthermore relates to a process for the production of closed-cell polyurethane foams by reacting a) polyisocyanates with b) compounds having at least two Isocyanate-reactive hydrogen atoms in the presence of c) blowing agents, characterized in that the polymer foam while production, foaming, Removal and / or processing and / or storage of an inert gas or inert gas mixture is surrounded.

The Closed cell polyurethane foams are commonly used by reaction of organic and / or modified organic Polyisocyanates (a) with compounds having at least two with isocyanate groups reactive hydrogen atoms (b) and blowing agents (c) produced.

In detail, the following can be stated for the usable further starting components:
Suitable organic polyisocyanates (a) for the preparation of the polyurethanes of the invention are the aliphatic, cycloaliphatic araliphatic and preferably aromatic polyfunctional isocyanates known per se.

Specific examples are: alkylenediisocyanates having 4 to 12 carbon atoms in the alkylene radical, such as 1,12-dodecane diisocyanate, 2-ethyl-tetramethylene-1,4-diisocyanate, 2-methylpentamethylene-1,5-diisocyanate, tetramethylene-1,4-diisocyanate and preferably hexamethylene-diisocyanate-1 , 6; Cycloaliphatic diisocyanates such as cyclohexane-1,3- and -1,4-diisocyanate and any mixtures of these isomers, 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclohexane (IPDI), 2,4- and 2,6 Hexahydrotoluylendiisocyanat and the corresponding isomer mixtures, 4,4'-, 2,2'- and 2,4'-dicyclohexylmethane diisocyanate and the corresponding isomers mixtures, and preferably aro diisocyanates and polyisocyanates, such as 2,4- and 2,6-toluene diisocyanate and the corresponding mixtures of isomers, 4,4'-, 2,4'- and 2,2'-diphenylmethane diisocyanate and the corresponding isomer mixtures, mixtures of 4, 4'- and 2,2'-diphenylmethane diisocyanates, Polyphenylpolymethylenpolyisocyanate, mixtures of 4,4'-, 2,4'- and 2,2'-diphenylmethane diisocyanates and Polyphenylpolymethylenpolyisocyanaten (crude MDI) and mixtures of crude MDI and toluene diisocyanates. The organic di- and polyisocyanates can be used individually or in the form of their mixtures.

When Compounds having at least two isocyanate-reactive Hydrogen atoms are mostly polyhydric alcohols, preferably Polyether alcohols and / or polyester alcohols used.

Especially are as polyether alcohols and / or polyester alcohols such a functionality from 2 to 8, preferably 2 to 3, and an average molecular weight from 300 to 8,000, preferably from 300 to 5,000.

The used polyether alcohols are prepared by known methods, for example by anionic polymerization with alkali metal hydroxides, such as. B. Sodium or potassium hydroxide or alkali metal such as. For example, sodium methylate, Sodium or potassium ethylate or potassium isopropylate as catalysts and with the addition of at least one starter molecule, 2 to 8, preferably 2 to 3, containing bonded reactive hydrogen atoms, or by cationic polymerization with Lewis acids, such as antimony pentachloride, borofluoride etherate and. a., or bleaching earth as catalysts or by Doppelmetallcyanidkatalyse from a or more alkylene oxides having 2 to 4 carbon atoms in the alkylene radical produced. For special Purpose can also monofunctional starters are involved in the polyether structure.

suitable Alkylene oxides are, for example, tetrahydrofuran, 1,3-propylene oxide, 1,2- or 2,3-butylene oxide, Styrene oxide and preferably ethylene oxide and 1,2-propylene oxide. The Alkylene oxides can individually, alternating successively or used as mixtures become.

When starter molecules For example: water, organic dicarboxylic acids, aliphatic and aromatic diamines having 1 to 4 carbon atoms in the alkyl radical, such as optionally mono- and dialkyl-substituted ethylenediamine, Diethylenetriamine, triethylenetetramine, 1,3-propylenediamine, 1,3- 1,4-butylenediamine, 1,2-, 1,3-, 1,4-, 1,5- and 1,6-hexamethylenediamine, Phenylenediamine, 2,3-, 2,4- and 2,6-toluenediamine and 4,4 ', 2,4'- and 2,2'-diaminodiphenylmethane. As starter molecules Also suitable: alkanolamines, and ammonia. Preferably used are polyvalent, especially bivalent and / or trivalent Alcohols, such as ethanediol, 1,2-propanediol and -2,3, diethylene glycol, Dipropylene glycol, 1,4-butanediol, 1,6-hexanediol, glycerol, trimethylolpropane, pentaerythritol.

The Polyether alcohols, preferably polyoxypropylene and polyoxypropylene polyoxyethylene polyols, have a functionality of preferably 2 to 8 and in particular 2 to 3 and molecular weights from 300 to 8000, preferably 300 to 6000.

Other suitable polyether polyols are polymer-modified polyether polyols, preferably graft polyether polyols, in particular those based on styrene and / or acrylonitrile, which are prepared by in situ polymerization of acrylonitrile, styrene, and polyetherpolyol dispersions which are used as the disperse phase, usually in an amount of from 1 to 50% by weight .-%, preferably 2 to 25 wt .-%, contain: z. As polyureas, polyhydrazides, tert-amino groups bound polyurethanes and / or melamine and z. Described in EP-B-011752 ( US 4304708 ), US-A-4374209 and DE-A-3231497.

The Polyether polyols can used singly or in the form of mixtures.

suitable Polyester polyols can for example, from organic dicarboxylic acids having 2 to 12 carbon atoms, preferably aliphatic dicarboxylic acids having 4 to 6 carbon atoms, polyhydric alcohols, preferably diols, having 2 to 12 carbon atoms, preferably 2 to 6 carbon atoms, prepared by conventional methods become. Usually be the organic polycarboxylic acids and / or derivatives and polyhydric alcohols, preferably in the molar ratio of 1: 1 to 1.8, preferably from 1: 1.05 to 1.2, catalyst free or preferably in the presence esterification catalysts, conveniently in an inert gas atmosphere, polycondensed.

The compounds having at least two isocyanate-reactive hydrogen atoms also include chain extenders and / or crosslinking agents which may optionally be used. As chain extenders and / or crosslinking agents are usually used diols and / or triols having molecular weights less than 400, preferably 60 to 300. Suitable examples are aliphatic, cycloaliphatic and / or araliphatic diols having 2 to 14, preferably 4 to 10 carbon atoms, such as z. For example, ethylene glycol, 1,3-propanediol, decane-1,10, o-, m-, p-dihydroxycyclohexane, diethylene glycol, dipropylene glycol and preferably 1,4-butanediol, 1,6-hexanediol and bis (2-hydroxyethyl) hydroquinone, triols, like 1,2,4- and 1,3,5-trihydroxycyclohexane, triethanolamine, diethanolamine, glycerol and trimethylolpropane and low molecular weight hydroxyl-containing polyalkylene oxides based on ethylene and / or 1,2-propylene oxide and the abovementioned diols and / or triols as starter molecules.

Provided for the preparation of polyurethane foams, chain extenders, Crosslinking agents or mixtures thereof are used this expediently in an amount of up to 10% by weight, based on the weight of the polyol compounds, for use.

When Propellant (c) according to the invention is water in proportions of 1 to 10 wt .-%, preferably in an amount of 1 to 5 wt .-% and particularly preferably from 2 to 4 wt .-%, each based on the Total weight of components (b) to (g) used.

Of the Adding water can be done in combination with other common propellants. Therefor For example, those commonly known from polyurethane chemistry Chlorofluorocarbons (CFCs) as well as highly fluorinated and / or perfluorinated ones Hydrocarbons in question. The use of these substances, however, will from ecological establish highly limited or completely adjusted. In addition to HCFC and HFCs are particularly suitable aliphatic and / or cycloaliphatic hydrocarbons, in particular Pentane and cyclopentane or acetals, such as. As methylal, as an alternative blowing agent at. These physical blowing agents usually become the polyol component added to the system. You can however, also in the isocyanate component or as a combination both the polyol component and the isocyanate component added become.

Farther can the reaction in the presence of catalysts, flame retardants as well as usual Auxiliaries and / or additives are carried out.

When Catalysts for the production of polyurethane foams are in particular compounds used which the reaction of the reactive hydrogen atoms, with the organic, optionally modified polyisocyanates speed up hard. Considered organic metal compounds, preferably organic tin compounds. The organic metal compounds be alone or preferably in combination with strongly basic Amines used.

to Production of the polyurethane foams according to the invention become common also flame retardants, preferably halogen-free flame retardants used. Therefor are in particular: ammonium polyphosphate, aluminum hydroxide, Isocyanurate derivatives and carbonates of alkaline earth metals.

Of the Reaction mixture for the preparation of the flexible polyurethane foams according to the invention may optionally still further aids and / or additives are incorporated. Examples include stabilizers, fillers, dyes, pigments and hydrolysis and fungistatic and bacteriostatic agents acting substances.

When Stabilizers are especially surface-active substances, i. H. Used compounds to assist the homogenization of the Serve starting materials and, where appropriate, are also suitable, the Cell structure of plastics regulate. Examples include emulsifiers, such as the sodium salts of castor oil sulfates or fatty acids as well as salts of fatty acids with amines.

More details about the above other usual Auxiliaries and additives are the specialist literature, such as Monograph by J.H. Saunders and K.C. Frisch "High Polymers" Vol. XVI, Polyurethanes, Part 1 and 2, Interscience Publishers 1962 and 1964, or the above cited Plastics Handbook, Polyurethane, Volume VII, Hanser-Verlag Munich, Vienna, 1st to 3rd edition.

polyurethane foams are advantageously after the one-shot process, for example using the high pressure or low pressure technique in open or closed molds, such as metallic molds produced. Common is also the continuous application of the reaction mixture suitable conveyor belts for Generation of foam blocks.

To In their production, the resulting foam blocks are stored and, if necessary, tailored. It can, as described, all Process steps are carried out under an inert gas atmosphere.

When It has proved particularly advantageous to use polyurethane foams produce by the two-component method. In the process, the structural components become for the Process with the exception of the polyisocyanates to a so-called polyol component, often referred to as component A, unite and with the Isocyanate component, often referred to as component B, for the reaction to bring.

The starting components are at a temperature of 15 to 90 ° C, preferably from 20 to 60 ° C and in particular from 20 to 35 ° C, ge mixed and placed in the open or optionally under increased pressure in the closed mold or applied at a continuous workstation on a tape which receives the reaction mass. The mixing can be carried out mechanically by means of a stirrer, by means of a stirring screw or by high-pressure mixing in a nozzle. The mold temperature is expediently 20 to 110 ° C, preferably 30 to 60 ° C and in particular 35 to 55 ° C.

The polyurethane foams treated by the process of the invention generally have a density of from 20 to 800 kg / m ³ , preferably from 35 to 500 kg / m ³ .

In an embodiment the method according to the invention can with the polyurethane foams after the diffusion compensation the cell structure changed become. This can be done for example by walking. Thereby can with half-hard or rigid foams the elasticity the foams clearly elevated become.

The Polystyrene foams, especially those produced during extrusion Plates are usually also stored after their production. Also here we can all operations from the production and storage to the cutting of the plates under an inert gas atmosphere be performed.

The The present invention will be explained with reference to the examples given, without, however, making a corresponding limitation.

Example 1:

One Closed-cell polyurethane semi-rigid foam, which is insufficient stability of the cell scaffold exhibited was foamed freely and no cell opening process, like walking or kneading. Already set a short time a shrinking process. The foam did not return to its original form back and was useless.

The same foam formulation was foamed in a carbon dioxide atmosphere. To foaming the foam remained for 1 h in a carbon dioxide-enriched atmosphere. The foam showed no shrinkage as long as he remained in this atmosphere.

To Storing in ambient air set a clearly visible shrinkage one. After completion of the gas exchange in the cells, the foam returned to its original form back.

Example 2:

at a foamed by carbon dioxide polystyrene foam was immediately after foaming removed the diffusion-inhibiting topcoat. In a short time There was an undesirable when stored in ambient air dimensional change of the foam.

at Treatment of a similar freshly prepared foam by Breaking the diffusion barrier of the cover layer, one with Carbon dioxide-enriched inert gas surrounding the foam could in an inert gas atmosphere without problems a bonding of two such foam boards take place. The composite body thus produced was storable to ambient air without dimensional change.

Example 3

One closed-cell soft polyurethane foam was used in a carbon dioxide atmosphere manufactured and demolded. After a one-hour storage phase in inert gas the molded part reached the ambient air. There immediately started Shrinking process, however, due to the fact that the foam reacted, no longer led to the sticking together of the cell walls. After graduation the diffusion process, it came to the dimension balance of the foam. The soft foam thus produced had a high proportion of closed Cells.

Example 4

• a) A polyurethane semi-rigid foam was the one produced under normal ambient air and on the other under inert gas. Immediately after completion of foaming, the semi-rigid foam began to shrink in the ambient air and returned after completion of the Diffusion process no longer back to its original shape.
• b) Was this rigid foam in the inert gas and foamed cut, no shrinkage occurred. After spilling the foam put a shrinkage, the foam after completion of the diffusion process in his original Form returned.

Out two foam blocks a 2 cm thick plate was cut out and the flat structures thus produced fulled.

From the foam of Example 4b resulted in a foam having the properties of a high density soft foam, while the foam Example 4a was unusable despite walking.

Claims (7)

Process for the preparation of closed-cell polymer foams, characterized in that, during the foaming, demolding and / or processing and / or storage of the foam, the polymer foam is surrounded by an inert gas or inert gas mixture atmosphere. Method according to claim 1, characterized in that the closed-cell polymer foams are closed-cell polyurethane foams. Method according to claim 1, characterized in that that the closed-cell polymer foams are closed-cell polystyrene foams. Method according to claims 1 and 3, characterized that the concentration of the inert gas in the inert gas or Inertgasgemisch atmosphere after the conclusion of the foaming gradually is reduced. Method according to Claims 1 to 4, characterized that the temperature during foaming, demolding and / or processing and / or storing the foam between 25 and 100 ° C is located. Method according to Claims 1 to 4, characterized that the inert gas is pressing above the atmospheric pressure is used. Method according to Claims 1 to 6, characterized that carbon dioxide is used as the inert gas.