WO1992012196A1 - Process for the manufacture of polyurethane foam - Google Patents

Abstract

The invention concerns a new process for the manufacture of polyurethane (PUR) foam by the poly-addition of polyols and polyisocyanates in the presence of water as the foaming agent, the water being bound to a finely particulate solid substrate with a large internal surface area.

Description

 Process for the production of polyurethane foams

The present invention relates to a new process for the production of polyurethane foams (PUR foams) by polyaddition of polyols and polyisocyanates in the presence of water as blowing agent, the water being bound to finely divided silica having a large inner surface.

Up to now, rigid PU foams, in particular integral PUR foams, have been produced practically exclusively by adding a suitable polyol, to which a few percent chlorofluorocarbons (CFCs) are mixed as blowing agents, with a suitable polyisocyanate immediately before processing, eg injection or pouring into a mold, intimately mixed in a mixing head in a stoichiometric ratio. The two components react exothermically with one another, as a result of which temperatures of 100-150 ° C., in particular 120-130 ° C., arise in the reaction mixture. At these temperatures, the CFC gasifies and generates foam bubbles in the mixture which are retained When the mixture has reacted and solidified By tempering the mold to, for example, 30-60 ° C., the evaporation of the CFCs is largely suppressed in the layers adjacent to the mold, so that little or no foam bubbles form in this area As a result, the molded body is practically given a pore-free outer skin which merges more and more into the foam structure on the inside, as a result of which a high strength is achieved with a relatively high weight of the molded body. Since the solid outer skin is integrated with the foam body, such products are referred to as integral foam. However, the use of CFCs is extremely damaging to the environment, whereby it must be taken into account that not only the handling in the production of the moldings poses problems, but above all the CFC residues enclosed in the foam bubbles when using the moldings slowly and are released into the environment in an uncontrolled manner and thus contribute to a continuing risk.

Many attempts have therefore been made to replace CFCs as blowing agents with other easily evaporating and environmentally friendly substances. However, a satisfactory solution has not yet been found for this.

For the production of PUR flexible foam, it is known to use polyalkylene glycol ether as a polyol and to add water to this as a reaction component. By increasing the proportion of polyisocyanate beyond the stoichiometric content, part of the polyisocyanate reacts with the added water to form carbon dioxide and urea, the carbon dioxide serving as a blowing agent. Alternatively, a carboxylic acid can be added instead of water, which reacts with polyisocyanates to form carbon dioxide and the corresponding acid amide.

EP 0 358 282 discloses a process for producing soft, flexible polyurethane foam in which water is added to the polyol component as a blowing agent and a soluble organic polyelectrolyte, for example polyacrylate. However, if one tries to apply this method to the production of rigid foam, in particular integral foam, then the product is unsatisfactory, since the surface layers which give the strength are too thin and appear porous and lunky. This is due to the fact that the formation of carbon dioxide occurs practically uniformly throughout the foam area and is not slowed down in the outer skin, as is the case with CFCs.

It is known from EP 0 319 866 to produce CFC-free, hard polyurethane foams by using water and / or carbon dioxide as blowing agents in the polyol component, which are bound to zeolitic adsorbents which have pore openings of at least 0.7 nm are. This method requires additional loading with air as a propellant and flow aid. The zeolite should be used in a relatively large amount of about 10-25% by weight of polyols, which has a negative effect on the foam.

It was therefore an object of the present invention to find a process by means of which a rigid PU foam, in particular a PUR integral foam, can be produced using water as the blowing agent and which has the known foam in its structure and surface properties ¬ fen is comparable to CFCs as a blowing agent, but its environmental friendliness during production and use is superior.

Surprisingly, this is achieved through the measures described in the main _nκprππh. The measures of the non-claims serve to promote the further development of the invention. It is extremely surprising that a measure as simple as the binding of the water serving as blowing agent to silica gel and the uniform suspension in the polyol component before it is mixed with the polyisocyanate form a perfect PUR foam, in particular one PUR integral foam. What this is based on has not yet been clarified, but it is assumed that the water remains largely bound to the silica gel when mixed with the polyol and does not dissolve in the polyol. It is only when the temperature rises due to the reaction of polyol and polyisocyanate that the water is likely to be desorbed in large quantities and reacted with the polyisocyanate, so that large foam bubbles are formed in the interior of the molded part, where the temperatures are particularly high . In the outer skin, where the temperature remains relatively low, the desorption of the water is greatly slowed down, so that only small bubbles form here before the curing of the polyurethane foam begins. The molded part is therefore delimited by a solid, closed surface which integrates itself in the desired manner with the coarse-pored inner zone via a fine-pored intermediate zone.

As an alternative to the method of mixing the required amount of water with the silica gel and then dispersing it in polyol, water contained in the polyol can also be bound by stirring in anhydrous silica gel, as a powder or in the form of a paste with polyol. In order to establish the balance between free and bound water, however, a long time must elapse. The materials used correspond to what has already been used for the production of the known rigid PU foams, ie the polyols used are predominantly longer polyester and polyether polyols, optionally also branched compounds with terminal hydroxyl groups. The polyols used are usually mixtures with average molecular weights of 500 to 10,000, preferably approximately 1,000 to 2,000. Diamines can also contribute to chain extension. Polyols and chain extenders together have a hydroxyl number of about 300 to 500 for rigid foam and about 80 to 200 for flexible foam.

In the art, 2,4- or 2,6-toluene diisocyanate (TDI), 4,4'-methylene di-phenyl isocyanate (MDI), 1,6-hexamethylene diisocyanate, 1,5-naphthylene diisocyanate are usually used as isocyanate or isophorone diisocyanate (IPDI) is used. MDI is preferred according to the invention because it is relatively non-toxic and little carcinogenic.

For hard integral foams, 100-110 parts by weight, in particular 105-108 parts by weight, polyisocyanate and 0.2-1.0 parts by weight of water are used per 100 parts by weight of polyol. For semi-rigid integral foams, 40-60 parts by weight, in particular 45-50 parts by weight, polyisocyanate and 0.2-1.0 parts by weight of water are used per 100 parts by weight of polyol.

The reaction between polyols and polyisocyanate is usually triggered by catalysts which are added to the polyol component. According to the prior art, the Ka a1yRarnr ^p n_ known in the prior art for the production of PUR foams, in particular tertiary amines or organotin compounds, can be used. Furthermore, as in the prior art, additional auxiliaries such as emulsifiers, foam stabilizers and pigments, and in particular for the production of non-flammable or flame-retardant polyurethane foams, are added.

The silica gel used is, in particular, a pyrogenic silica which, owing to its particularly high specific surface area of up to 200 m 2 / g, is able to adsorb water particularly well.

So that the particles can be suspended well in the polyol and do not separate during processing, particle sizes up to 500 μm, in particular up to about 1-50 μm, are most suitable. Mixtures with fine-particle silica gel (approx. 50 μm) were stored for months without impairing their function. On the other hand, the binding strength of the water to the particles has to be taken into account, which mainly depends on the specific surface. To bind a sufficient amount of water to the particles, the inner surface should be about 1-200 µm / g in order to keep the admixed amount of silica gel low.

Housing, machine covers, vehicle body parts, planters, decorative pots, building claddings, ceiling claddings, even furniture, etc. can be produced from the hard PUR integral foams as produced according to the invention. Like the well-known PUR integral foams, the material has excellent properties: small specific weight with good mechanical values, electrical insulation, temperature. SO1arinn. Great chemical resistance, dense surface, which allows subsequent painting and processing, provided that the foam is not already colored by the added pigments. A specialty of the products according to the invention are foams which are self-extinguishing. They are particularly required for use in rail vehicles, cars, airplanes and products that are particularly endangered by public traffic, such as parts of telephone houses, letter boxes, etc.

Semi-hard PUR integral foams, such as those produced according to the invention, can be used with fire protection equipment for road and rail vehicles, for aircraft and water vehicles and for applications which have special fire protection regulations, for example armrests, headrests, shock protection edges, covers, which have to have a certain elasticity, manufacture side panels, cover strips, seat cushions, office furniture, train luggage rack panels, door handle panels, etc.

example 1

Integral polyurethane foam, hard

0.6 l of water are mixed with 0.15 kg of silica gel (Aerosil 200 from Degussa) to form a stiff paste and then into a mixture of 200 kg of polyol (Elastolit D 08- 002 oF, EPU-BASF, OH- Number 395), which contains 0.2 kg triethylamine and 0.13 kg tin (II) octoate, is added with intensive stirring.

100 parts of this mixture are mixed with 108 parts of 4,4'-methylendi- (phenyl isocyanate) (MDI) in a mixing head and injected into molds preheated to 50'C. The mixture reacts in the course of 3-10 minutes with vigorous foaming, the layers lying against the mold showing very little foaming and the outer skin being closed.

An alternative recipe for hard PUR foams that are self-extinguishing can be prepared as follows:

30.0 kg polyol

1.5 kg halogenated organic phosphoric acid ester

0.5 kg pigment paste

0.150 kg water paste, prepared as described above

9.0 kg aluminum hydroxide

6.0 kg ammonium polyphosphate

Mix everything well.

For foaming, parts by weight of the above are used

Polyol mixture 105 parts by weight of isocyanate (MDI) added. Example 2

PUR integral foam, semi-hard

A paste is produced from 22 kg of halogenated organic phosphoric acid ester, 1.5 kg of pigment powder and 30.0 kg of aluminum hydroxide powder by intimate mixing. A suspension is prepared from 30 kg of polyol (Elaεtofoam I 4101, EPU-BASF, polyether polyol / diamine mixture, OH number 120) and 7.5 kg of aluminum hydroxide powder, and this 22.5 kg of the above-described flame retardant paste and 0. 2 kg of the water / silica gel paste described in Example 1 were added. In addition, 0.035 kg triethylamine and 0.02 kg tin (II) octoate are added and the entire mixture is thoroughly mixed in a mixing kettle for 30 minutes to 2 hours.

Since the mixture prepared above tends to separate due to the added aluminum hydroxide and the mixture loses activity, it can only be stored for about 1 day.

To produce the integral foam, the mixture is mixed with 7.5 kg MDI in a mixing head and immediately injected into the molds preheated to 60'C. The molded pieces are removed from the mold after 3-15 minutes and have a dense outer skin of approximately 0.15-1.0 mm thick, which merges into the large-pore core zone over a region of 3-8 mm of a fine-pored intermediate layer. With a direct flame, these molded parts can be burnt, which however do not continue to burn when the flame is taken on. A non-flame retardant, semi-hard PUR foam can be obtained from the following mixture:

30.0 kg polyol

0.2 kg of water paste, prepared as described above

0.035 kg organic amine compound

0.020 kg organometallic compound

Mix everything together very well.

For foaming with the isocyanate component in the mixing head

Add 12.75 kg MDI.

Claims

P a t e n t a n s r u c h e A process for the production of hard PUR foams by polyaddition of polyols and polyisocyanates in the presence of water as a blowing agent and, if appropriate, conventional auxiliaries and additives, characterized in that the water contains finely divided silica gel suspended in the mixture with a specific - See surface of 1-200 m / g is bound, which has an average grain size of less than 500 microns. Process according to Claim 1, characterized in that for hard integral foams, 100-110 parts by weight, in particular 105-108 parts by weight, polyisocyanate and 0.2-1.0 parts by weight of water per 100 parts by weight of polyol are used, and the silica gel is used in an amount sufficient to bind the water. A method according to claim 1, characterized in that for semi-rigid integral foams per 100 parts by weight of polyol 40-60 parts by weight, in particular 45-50 parts by weight, poly isocyanate and 0.2-1.0 parts by weight. Parts of water are used, and the silica gel is used in an amount sufficient to bind the water. 4th Method according to one of claims 1 to 3, characterized in that the water is first mixed with the silica gel to form a stiff paste, this is thoroughly mixed with the polyol and the other auxiliaries which are compatible with the polyol and then with the polyisocyanate and which is mixed with these compatible auxiliaries and filled and foamed in the form intended for foaming. 5. The method according to claim 4, characterized in that for the production of an integral foam, the mold is tempered to a temperature of 30-60 ^* C and the outer parts of the foam mixture which are in contact with the mold are not or only less foamed than the core area, which is caused by the Heat of reaction at a temperature of 100-150 "C, preferably 120-130'C, is foamed. 6. The method according to at least one of claims 1 to 5, characterized in that the silica gel has an average grain size of about 1 to 50 microns. 7. The method according to claims 1 to 6, characterized gekenn¬ characterized in that the mixture contains a flame retardant ent. 8. The method according to claim 7, characterized in that halogenated phosphoric acid esters, alkali polyphosphates and / or aluminum hydroxide are used as flame retardants.