EP2001939A1

EP2001939A1 - Hydrophobically modified melamine resin foam

Info

Publication number: EP2001939A1
Application number: EP07727203A
Authority: EP
Inventors: Klaus Hahn; Bernhard Vath; Armin Alteheld; Christof MÖCK; Horst Baumgartl
Original assignee: BASF SE
Current assignee: BASF SE
Priority date: 2006-03-28
Filing date: 2007-03-22
Publication date: 2008-12-17
Also published as: JP2009531492A; US20100234480A1; CN101415757A; BRPI0708926A2; KR20090007732A; WO2007110361A1

Abstract

Open-cell foam based on a melamine/formaldehyde condensation product which has been modified hydrophobically with a compound having C6-C20-alkyl groups, especially stearyl groups, such as aluminum stearate or stearyl isocyanate, process for its preparation and use.

Description

Hydrophobically modified melamine resin foam

Description.

The invention relates to a hydrophobically modified, open-cell foam based on a melamine / formaldehyde condensation product, process for its preparation and use.

Open-cell elastic foams based on melamine / formaldehyde resins and processes for their preparation by heating with hot air, steam or microwave irradiation with foaming and crosslinking of a blowing agent-containing solution or dispersion of a melamine / formaldehyde precondensate are known and described for example in EP-A 17672 and EP-A 37470.

They are suitable for various heat and sound insulating applications in buildings and vehicles, as well as insulating and shock-absorbing packaging material. Untreated melamine-formaldehyde foams absorb both hydrophilic and hydrophobic liquids very quickly. The absorption of water can have a negative effect on the properties, for example in an increase in the density or deterioration of the thermal insulation effect.

From EP-A 633 283 it is known to reduce the water absorption of melamine-formaldehyde foams by coating the foam skeleton with a hydrophobing agent, in particular with an aqueous emulsion of a silicone resin. In the examples, a foam with a density of 11 kg / m ^{3 is} used, which is coated in an additional step with a hydrophobing agent and after hydrophobing densities between 72 kg / m ³ and 120 kg / m ³ . Due to the increased density, disadvantages may arise in some fields of application compared to the unmodised melamine-formaldehyde foam, for example for applications in the transport sector, such as aircraft. In addition, the advantageous properties of the melamine-formaldehyde foam with regard to temperature stability and low flammability can be impaired by the high proportion of coating agent. The water uptake of the hydrophobicized materials of more than 20% by volume, listed in the examples, is comparatively high and sufficient to adversely affect the properties of the material. Common water repellents, such as the listed silicones or chloroprenes, are mostly soluble or swell in many organic solvents. Therefore, the contact with organic solvents can lead to a detachment of the hydrophobic layer or a swelling under absorption of the solvent, which can be removed only consuming or time consuming again. DE-A 100 11 388 describes an open-celled melamine resin foam whose cell structure is coated with a fluoroalkyl ester as hydrophobing and oleophobizing agent. In this case, not only the water, but also the oil absorption of the melamine resin foam is reduced.

The object of the present invention was to find an open-celled foam based on a melamine / formaldehyde condensation product which simultaneously has hydrophobic and oleophilic properties and can be prepared in a simple manner. The modified open-cell foam should also be suitable in particular for liquid / liquid separation and as leakage protection for oil tanks.

Accordingly, an open-cell foam based on a melamine / formaldehyde condensation product was found, which is hydrophobically modified with a compound having Ce - C2o-alkyl groups.

Preferably, the open-cell foam is hydrophobically modified with a compound having stearyl groups.

It is advantageous if the hydrophobing effect can be achieved with a small increase in the density of the foam. Particularly suitable are water repellents which are not removed from the foam in contact with organic solvents because they are e.g. are fixed by a covalent chemical attachment or a crosslinking reaction on the surface. Further advantageous hydrophobizing agents are those substances which can be added to the formulation before the foaming of the reaction mixture and have only a slight influence on the foam structure and foam mechanics.

Open cell foam:

The apparent density of the open-cell foam is generally in the range from 3 to 100 g / l, preferably in the range from 5 to 20 g / l. The cell count is usually in the range of 50 to 300 cells / 25 mm. The tensile strength is preferably in the range of 100 to 150 kPa and the elongation at break in the range of 8 to 20%.

For the production of an open-cell foam based on the melamine / formaldehyde (MF) resin preferred as the aminoplast, EP-A 071 672 or EP-A 037 470 discloses a highly concentrated, propellant-containing solution or dispersion of a melamine-formaldehyde precondensate with hot air, steam or water foamed and cured by microwave irradiation.

For the hydrophobic modification according to the invention, the resulting open-cell foam can be obtained by vapor deposition, with a liquid reaction mixture, a solution or aqueous dispersion of a Ce - C2o-alkyl isocyanate, preferably sprayed or impregnated stearyl isocyanate and then hydrophobically modified at temperatures in the range of 40 to 200 ° C. The isocyanate reacts here with remaining methylol groups and amino groups on the surface of the cell stems of the open-cell melamine-formaldehyde foam to form a urethane group or urea group. The reaction is preferably accelerated by the addition of a catalyst.

Alternatively, the hydrophobization of the foam may also be hydrophobically modified by non-reactive compounds having Ce - C 20 -alkyl groups, for example salts of stearyl acid, such as aluminum, sodium, calcium or zinc stearate. In this case, a mixture comprising a melamine / formaldehyde (MF) precondensate, a hardener and a blowing agent, with 0.1 to 10 wt .-%, preferably 1 to 5 wt .-%, based on solids of the mixture, stearate and then heat the mixture with foaming and cross-linking. This process alternative has the advantage that no additional processing steps, such as soaking in a dispersion, expressing the liquid from the foam and drying at elevated temperature are required. The addition of hydrophobic foams can be obtained which have comparable densities as non-hydrophobic foams.

Aluminum stearates, particularly preferably aluminum monostearate, are preferably used as the water repellent, since in this case no significant change in the foam structure or the mechanical properties was observed and the foams obtained are elastic.

In this method, one starts from a melamine / formaldehyde precondensate. Melamine / formaldehyde condensation products may contain, in addition to melamine, up to 50% by weight, preferably up to 20% by weight, of other thermoset formers and, in addition to formaldehyde, up to 50% by weight, preferably up to 20% by weight, of other aldehydes. Particularly preferred is an unmodified melamine / formaldehyde condensation product. Suitable thermoset formers are, for example, alkyl- and aryl-alkyl-substituted melamine, urea, urethanes, carboxamides, dicyandiamide, guanidine, sulfurylamide, sulfonamides, aliphatic amines, glycols, phenol and derivatives thereof. For example, acetaldehyde, trimethylolacetaldehyde, acrolein, benzaldehyde, furfurol, glyoxal, glutaraldehyde, phthalaldehyde and terephthalaldehyde can be used as aldehydes. It is also possible to use etherified precondensates of aldehyde resins. Further details on melamine / formaldehyde condensation products can be found in Houben-Weyl, Methods of Organic Chemistry, Vol. 14/2, 1963, pages 319 to 402. The molar ratio of melamine to formaldehyde is generally less than 1: 1, 0, it is preferably between 1: 1 and 1: 5, in particular between 1: 1, 3 and 1: 1, 8. According to EP-B 37470, the melamine resins advantageously comprise sulfite groups, which can be done, for example, by adding from 1 to 20% by weight of sodium hydrogen sulfite in the condensation of the resin. It has been found that a relatively high sulfite group content with constant melamine to formaldehyde ratio results in a higher formaldehyde emission of the foam. The precondensate used should therefore contain virtually no sulphite groups, ie the sulphite group content should be below 1%, preferably below 0.1% and in particular 0%.

To emulsify the blowing agent and to stabilize the foam, the addition of an emulsifier or an emulsifier mixture is required. As emulsifier anionic, cationic and nonionic surfactants and mixtures thereof can be used.

Suitable anionic surfactants are diphenylene oxide sulfonates, alkane and alkylbenzene sulfonates, alkylnaphthalenesulfonates, olefinsulfonates, alkyl ether sulfonates, fatty alcohol sulfates, ether sulfates, alpha-sulfofatty acid esters, acylaminoalkanesulfonates, acyl isethionates, alkyl ether carboxylates, N-acyl sarcosinates, alkyl and alkyl ether phosphates. As nonionic surfactants, alkylphenol polyglycol ethers, fatty alcohol polyglycol ethers, fatty acid polyglycol ethers, fatty acid alkanolamides, EO / PO block copolymers, amine oxides, glycerol fatty acid esters, sorbitan esters and alkyl polyglucosides can be used. As cationic emulsifiers Alkyltriammoniumsalze, Alkylbenzyldimethy- lammoniumsalze and alkylpyridinium are used. The emulsifiers are preferably added in amounts of from 0.2 to 5% by weight, based on the resin.

To produce a foam from the melamine resin solution, it must contain a propellant, the amount depending on the desired density of the foam. In principle, both physical and chemical blowing agents can be used in the process according to the invention. Suitable physical blowing agents are, for example: hydrocarbons, halogenated, in particular fluorinated hydrocarbons, alcohols, ethers, ketones and esters in liquid form or air and CO 2 as gases. Suitable chemical blowing agents are, for example, isocyanates mixed with water, with the release of CO2 as the effective blowing agent, and also carbonates and bicarbonates mixed with acids which also generate CO2, and azo compounds, such as azodicarbonamide. In a preferred embodiment of the invention, the aqueous solution or dispersion between 1 and 40 wt .-%, based on the resin, of a physical blowing agent having a boiling point between 0 and 8O ⁰ C is added; for pentane, it is preferably 5 to 15 wt .-%.

The hardeners used are acidic compounds which catalyze the further condensation of the melamine resin. The amounts are between 0.01 and 20, preferably between 0.05 and 5 wt .-%, based on the resin. In question are inorganic and organic acids, for example hydrochloric acid, sulfuric acid, phosphoric acid, nitric acid, formic acid, acetic acid, oxalic acid, toluenesulfonic acids, amidosulfonic acids and acid anhydrides.

For some purposes, it may be beneficial, up to 20% by weight, preferably less than 10% by weight, based on the resin, of conventional additives such as dyes, flame retardants, UV stabilizers or fibrous fillers, means of reducing fire gas toxicity or to promote charring.

In addition to the water repellents according to the invention, further water repellents may be added in amounts of from 0.2 to 5% by weight. In question, for example, Silicones, paraffins, silicone and fluorosurfactants, hydrophobic hydrocarbon surfactants, silicone and fluorocarbon emulsions.

The concentration of the melamine / formaldehyde precondensate in the mixture of precondensate and solvent can vary within wide limits between 55 and 85% by weight, preferably between 63 and 80% by weight. The preferred viscosity of the mixture of precondensate and solvent is between I and 300 ° dPas, preferably between 5 and 2000 dPas.

The water repellents and additives according to the invention can be homogeneously mixed with the aqueous solution or dispersion of the melamine resin, it also being possible for the propellant to be pressed in under pressure. However, one can also choose from a fixed, e.g. go out spray-dried melamine resin and then mix this with an aqueous solution of the emulsifier, the curing agent and the blowing agent. The mixing of the components may e.g. be made in an extruder. After mixing, the solution or dispersion is discharged through a nozzle and then immediately heated and foamed.

The heating of the propellant-containing solution or dispersion can in principle - as described in EP-B 17671 - be made by hot gases or high frequency radiation. However, the required heating is preferably carried out by ultra-high frequency irradiation according to EP-B 37470. In principle, microwaves in the frequency range from 0.2 GHz to 100 GHz can be used for this dielectric radiation. For industrial practice frequencies of 0.915, 2.45 and 5.8 GHz are available, with 2.45 GHz being particularly preferred. Radiation source for dielectric radiation is the magnetron, which can be irradiated simultaneously with several magnetrons. Care must be taken that the field distribution is as homogeneous as possible during irradiation. Appropriately, the irradiation is carried out so that the power consumption of the solution or dispersion between 5 and 200, preferably between 9 and 120 KW, based on 1 kg of water in the solution or dispersion. If the power absorbed is lower, then foaming no longer takes place and the mixture only hardens. If you work within the preferred range, the mixture foams faster, the greater the power consumption. Above about 200 KW per kg of water, the foaming speed does not increase significantly.

The irradiation of the mixture to be foamed takes place immediately after it has left the foaming nozzle. In this case, the mixture which foams due to temperature increase and evaporation of the blowing agent is applied to circumferential bands which form a rectangular channel for shaping the foam.

For the production of foams based on a melamine / formaldehyde

Condensation product with low formaldehyde emission can, as described in WO 01/94436, use an MF precondensate with a molar ratio of melamine to formaldehyde of greater than 1: 2. To achieve very low formaldehyde emissions, the foam can be left to dry for 30 minutes at 220 ° C after drying. After tempering, however, the foams are cured and no longer thermoformable.

In order to improve the application properties, the foams can then be tempered and pressed, for example as described in EP-B 37470. The foams can be cut to the desired shape and thickness and laminated on one or both sides with cover layers. For example, a polymer or metal foil can be applied as a cover layer.

The foams can be produced as plates or webs with a height of up to 2 m or as foam foils with a thickness of a few mm. The preferred foam height (in the foaming direction) is between 50 cm and 150 cm when using 2.45 GHz frequency microwaves. From such foam sheets, all desired sheet thicknesses can be cut out. The foams may be topcoated or laminated on one or both sides, e.g. with paper, cardboard, glass fleece, wood, plasterboard, metal sheets or foils, plastic films, which may also be foamed.

One field of application of the foams produced according to the invention is the thermal and acoustic insulation of buildings and parts of buildings, in particular of intermediate walls, but also of roofs, facades, doors and floors; Furthermore, the thermal and acoustic insulation of the engine and interior spaces of vehicles and aircraft witness as well as the low temperature insulation, z. B. of cold stores, oil tanks and tanks of liquefied gas.

Further fields of application are the use as insulating wall cladding as well as insulating and shock-absorbing packaging material. Due to the high hardness of crosslinked melamine resins, the foams can also be used for slightly abrasive cleaning, grinding and polishing sponges.

The open-cell structure of the foams additionally allows the absorption and storage of suitable cleaning, grinding and polishing agents in the interior of the foams.

If one starts from low-formaldehyde precondensates, the foams according to the invention can also be used in the hygiene sector, e.g. in the form of thin nonwovens as a wound dressing or as a component of baby diapers and incontinence products.

Due to the elasticity of the open-cell foam this can be easily inserted for insulation in already prefabricated container parts. Even at low temperatures, for example below -80 ° C, the foam remains elastic. Damage caused by embrittlement does not occur. It is therefore particularly suitable for flexible insulation of moving pipes, for example for filling hoses of liquid nitrogen.

The hydrophobically modified open-cell foam according to the invention is particularly preferably used as a liquid reservoir for a fuel tank, oil tank, tank container for tank vehicles, tank trailers or tankers due to the improved by the hydrophobization leakage protection and leakage protection. The open-cell foam can in this case be introduced into the tank container or attached as leakage protection to the tank container as a sheath. From a liquid tank filled with the hydrophobically modified open-cell foam according to the invention, which is filled with a hydrophobic liquid, the liquid in a hydrophilic environment runs significantly less than from the unmodified foam. For example, significantly less oil would leak into the sea from an oil tanker where leakage occurs than with a tanker filled with unmodified foam.

Another use is the hydrophobically modified open-cell foam according to the invention as a filter cartridge or separation medium for liquid / liquid separation, for example, from the two-phase liquid mixtures of different hydrophilicity selectively a component that corresponds approximately to the hydrophilicity of the foam can be added. For example, a leaked, insoluble in water hazardous substance can be selectively absorbed. By combination of Unmodified and hydrophobized foams can be achieved liquid-liquid separations. It may be beneficial to combine multiple elements of this type to enhance the effect.

Examples

Example 1 Water repellency with stearyl isocyanate

In a glass flask 10 cube-shaped samples (10 ^* 10 ^* 10mm) of an open-celled melamine-formaldehyde foam having a density of 9 kg / m ³ (Basotect®, BASF AG) were added and with a solution of 17.5 g of stearyl isocyanate in 332.5 g of toulol, to which 5 drops of a catalyst (Lupragen N 201, BASF AG, 33% solution of triethylenediamine in dipropylene glycol) were added. The solution with the impregnated foam cubes was heated at 80 ° C for 8 h under reflux. The toluene solution was then decanted off. The foam cubes were freed by pressing the bulk of the liquid absorbed to constant weight. The density of the modified foam samples is 18.5 kg / m ³ . The modified foam floats on a water surface and is not significantly wetted by water, the water absorption is less than 5 vol .-%.

The covalent attachment of stearyl isocyanate to form urethane or urea groups was detected by infrared absorption spectroscopy (IR). No bands typical of isocyanate groups were observed, indicating unreacted stearyl isocyanate. The foam structure observed under the Scanning Electron Microscope (SEM) and the associated mechanical properties were not affected by the modification.

The cube-shaped samples of the modified and unmodified foam were attached to a bar for comparison and soaked in stained toluene. Both foam samples quickly and completely absorbed the toluene. The toluene was stained with a dye (anthraquinone dye, Thermoplastic Blue 684, BASF AG) which is well soluble in toluene but insoluble in water. The impregnated samples were then placed in a vessel filled with water and mechanically stressed by means of the rod by a stirring motion in the water. In the unmodified foam, much of the toluene was contaminated by water while the hydrophobically modified foam held the toluene inside the foam.

Examples 2 and 3: hydrophobing by means of Al stearates

For producing a modified melamine resin foam in which the

Hydrophobing is carried out simultaneously to the foaming, was carried out analogously to the procedure given in the example in WO 0194436. Before foaming the 2 wt .-% aluminum tristearate (Example 2) or 2 wt .-% aluminum monostearate (Dihydroxyalu- miniumstearat) (Example 3) based on the solid, were added in addition blowing agent-containing melamine-formaldehyde precondensate. The foams obtained were first dried at 100.degree. C., and some materials were then tempered for 5 h at 180.degree. C. in order to be able to assess the influence of the temperature control on the hydrophobization.

Examples 4 to 6 and Comparative Experiments V1 and V2:

The procedure was analogous to Example 2, wherein instead of an aluminum stearate no addition (V1) or 2 wt .-% sodium stearate (Example 4), calcium distearate (Example 5), zinc distearate (Example 6) or aluminum diacetate (V2) was added. No influence of the addition of the aluminum stearates on the density of the obtained foams was observed.

The resulting foam samples were partially compressed several times (forged) to destroy any existing cell membranes, which could also lead to a reduction in water absorption.

To determine the hydrophobicity, cube-shaped samples of the foams (3cm ^* 3cm ^* 3cm) were placed on a water surface. The swimming behavior and water absorption were determined gravimetrically after a period of 30 min. The results of the experiments and an evaluation of the elasticity of the materials after manual testing are shown in Table 1.

Table 1

nb: not determined Assessment of elasticity: + elastic, - brittle

The open-cell foams of Examples 1 and 2 have a comparable elasticity as Comparative Experiment V1. The foams produced with the addition of aluminum monostearate or aluminum tristearate, in contrast to melamine-formaldehyde foam, float without additives. The water absorption is lowered again at a Nachemperung of the material.

The water absorption of the material produced using aluminum monostearate is not significantly affected by a milling process, which speaks against the formation of unwanted foam membranes. Foams made using different cation stearates (Examples 4 to 6) also float, but the elasticity of the foam is less than in Examples 2 and 3.

The comparative experiment V2 shows that with the addition of aluminum salts of carboxylic acids with significantly lower compared to the stearyl radical alkyl group, foams can be obtained with good flexibility, but have a lower hydrophobicity.

Example 7: Use for liquid / liquid separation

A drop of stained toluene is added to water. The dye used is readily soluble in toluene (anthraquinone dye, thermoplastic blue 684, BASF AG) but insoluble in water. The hydrophobically modified open-cell melamine-formaldehyde foam according to Example 1 selectively absorbed the stained toluene phase while it is not wetted by the aqueous phase. With the addition of an unmodified Basotect® cube, both the stained toulol and water were taken up in the foam.

Example 8. Use for liquid / liquid separation

The frit insert of a glass filter frit was coated with a hydrophobically modified open-cell melamine-formaldehyde foam blank and a chloroform / water mixture was introduced whose aqueous phase was selectively colored for labeling (Cu-phthalocyanine complex, Basantol Blue 762 liquid, BASF AG). The chloroform (higher density) phase was separated from the aqueous phase and passed through the frit while the aqueous phase remained above the frit.

In the corresponding comparative experiment with an unmodified Basotect® blank, the chloroform / water mixture passed through the frit.

Example 9:

A Y-shaped glass tube with a diameter of about 1 cm was attached such that two orifices faced down and one upwards. The one downside portion of the tube was filled with unmodified MeI-amine / formaldehyde foam. The other part of the tube was filled with a hydrophobically modified foam according to Example 1. Both fabric feeds reached into the part of the Y-shaped pipe where all three pipe sections met. Through the above opening, a little water was first given. This was taken up by the unmodified foam. Subsequently, through the above tube, a little toluene was added to the glass tube, which was taken up by the hydrophobically modified foam.

Into a beaker, selectively stained water (dye: Cu phthalocyanine complex, Basantol Blue 762 liquid, BASF AG) and about the same amount of toluene were added. Chloroform was gradually added to the mixture until the density of the colorless organic phase and the colored aqueous phase had adjusted to such an extent that complete separation of the mixture into two phases did not occur until at least 5 seconds after stirring the mixture. The liquid mixture was stirred again and immediately added to the filled glass tube. It was found that the liquid mixture in the glass tube was separated. The stained aqueous phase drained off over the unmodified foam filled part while the colorless organic phase drained off over the part of the tube with hydrophobically modified foam.

Claims

claims

1. Open cell foam based on a melamine / formaldehyde condensation product, characterized in that it is hydrophobically modified with a compound having Cβ - C20 alkyl groups.

2. open-cell foam according to claim 1, characterized in that it is hydrophobically modified with a stearyl group-containing compound.

3. Open-cell foam according to claim 1 or 2, characterized in that it has a specific apparent density in the range of 3 to 100 g / l.

4. open-cell foam according to one of claims 1 to 3, characterized in that it was prepared from a melamine / formaldehyde condensation product having a molar ratio of melamine / formaldehyde in the range of 1: 1 and 1: 5.

5. A process for producing an open-cell foam according to claims 1 to 4, characterized in that the open-cell foam is sprayed or impregnated with a solution of a Cβ - C20- Alkylisocyanat.es and hydrophobically modified at temperatures in the range of 40 to 200 ° C. ,

6. A process for producing an open-cell foam according to claims 1 to 4, characterized in that a mixture containing a melamine / formaldehyde (MF) precondensate, a curing agent and a blowing agent, with 0.1 to 10 wt .-% , Based on solid of the mixture, aluminum stearates and the mixture then heated with foaming and cross-linking.

7. The method according to claim 6, characterized in that the molar ratio of melamine / formaldehyde of the precondensate in the range of 1: 1 to 1: 5.

8. Use of the open-cell foam according to one of claims 1 to 4 as a liquid reservoir for a fuel tank, oil tank, tank container for tank vehicles, tank trailers or tankers.

9. Use of the open-cell foam according to any one of claims 1 to 4 as a filter cartridge, separation medium for liquid / liquid separation or for receiving spilled organic liquids.