WO2001094436A2

WO2001094436A2 - Method for producing foamed materials from melamine /formaldehyde condensates

Info

Publication number: WO2001094436A2
Application number: PCT/EP2001/006399
Authority: WO
Inventors: Horst Baumgartl; Bernd Gross; Isidor De Grave; Wulf Trauzettel
Original assignee: Basf Aktiengesellschaft
Priority date: 2000-06-07
Filing date: 2001-06-06
Publication date: 2001-12-13
Also published as: DE10027770A1; AU2001285731A1; WO2001094436A3

Abstract

The invention relates to a method for producing elastic foamed materials which are based on a melamine/formaldehyde condensation product. According to the inventive method, a pre-condensate, having a mol ratio of melamine to formaldehyde which is greater than 1: 2, is foamed. Practically no emission of formaldehyde emanates from the foamed materials. No signal or only a very low signal ranging from 65ppm to 85 ppm occurs in the NMR 13 C/MAS spectrum.

Description

Process for the production of foams from melamine / pormaldehyde condensates

description

The invention relates to a process for producing open-cell elastic foams based on a melamine / formaldehyde condensation product, in which an aqueous solution or dispersion which contains a melamine / formaldehyde precondensate, an emulsifier, a blowing agent and a hardener and possibly contains conventional additives, foamed by heating and the foam cures by crosslinking the precondensate.

European patents 17 621 and 17 672 describe open-cell elastic foams based on melamine / formaldehyde condensation products and processes for their production. A highly concentrated blowing agent-containing solution or dispersion of a melamine / formaldehyde precondensate is foamed and the foam is cured, the foaming being carried out by heating to a temperature above the boiling point of the blowing agent in such a way that a steep increase in viscosity essentially does not start until the foaming process is finished. The heating is preferably carried out with hot air, it can also be done by steam, high-frequency radiation or by utilizing the heat of reaction.

According to EP-B 37470, relatively thick foam molded articles can be produced by heating the blowing agent-containing solution or dispersion by microwave radiation.

According to the patents mentioned, the mol of melamine to formaldehyde obtained can vary within wide limits between 1: 1.5 and 1: 5, preferably between 1: 2 and 1: 3.5. The molar ratio in the examples also lies in this range.

A corresponding, industrially produced, elastic foam is BASOTECT ^® from BASF Aktiengesellschaft. It is being used to an increasing extent for sound and thermal insulation of buildings and parts of buildings. Like all materials made from aminoplast resins, BASOTECT ^® emits very small amounts of formaldehyde. However, formaldehyde emissions increase with increasing temperature and humidity.

BESTATIGUNGSKOPIE The invention was therefore based on the object of providing open-cell, elastic melamine / formaldehyde foams with such low formaldehyde emission, even under warm / humid conditions, that they measured according to the EU standard EN ISO 14 184-1 5 (water storage at 40 ° C, 1 hour) emit less than 40 mg, preferably less than 30 mg, of formaldehyde per kg of foam and thus meet the ÖKOTEX Standard 100 (quality seal of the textile industry for particularly low-pollution textiles).

10

This object is achieved according to claim 1 in that a melamine / formaldehyde precondensate is used in the production of the foam, in which the molar ratio of melamine to formaldehyde is greater than 1: 2, but the molar ratio is 1: 1.5

15 is excluded.

Foams produced in this way with a density of 5 to 50 g-1 " ¹ are characterized in that no or only a very weak signal occurs in the 13 C / MAS spectrum in the range from 65 to 85 ppm, based on the signal intensity of the Melamine rings at 166 ppm.

As a rule, the ratio of the areas in the 13 C / MAS spectrum under the signals between 65 to 85 ppm and 155 and 25 175 ppm should be <0.2, preferably <0.1, particularly preferably <0.05.

The process according to the invention is based on a melamine / formaldehyde precondensate. Melamine / formaldehyde condensation products can, in addition to melamine, up to 50, preferably

30 to 20% by weight of other thermoset formers and, in addition to formaldehyde, contain up to 50, preferably up to 20% by weight of other aldehydes in condensed form. An unmodified melamine / formaldehyde condensation product is particularly preferred. Examples of possible thermoset formers are: alkyl- and aryl-substituted

35 tuned melamine, urea, urethanes, carboxamides, dicyandiamide, guanidine, sulfurylamide, sulfonic acid amides, aliphatic amines, glycols, phenol and their derivatives. As aldehydes e.g. Acetaldehyde, trimethylolacetaldehyde, acrolein, benzaldehyde, furfural, glyoxal, glutaraldehyde, phthalaldehyde and terephthalate

40 aldehyde can be used. More details about melamine /

Formaldehyde condensation products can be found in Houben-Weyl, Methods of Organic Chemistry, Volume 14/2, 1963, pages 319 to 402.

45 The molar ratio. According to the invention, melamine to formaldehyde is greater than 1: 2.0, it is preferably between 1: 1.0 and 1: 1.9, in particular between 1: 1.3 and 1: 1.8. To EP-B 37470 the melamine resins advantageously contain condensed sulfite groups, which can be done, for example, by adding 1 to 20% by weight of sodium bisulfite during the condensation of the resin. It has now been shown that a relatively high sulfite group content with a constant melamine: = formaldehyde ratio results in a higher formaldehyde emission from the foam. The precondensate used should therefore contain practically no sulfite groups, ie the sulfite group content should be below 1%, preferably below 0.1% and in particular zero.

The addition of an emulsifier or an emulsifier mixture is required to emulsify the blowing agent and to stabilize the foam. Anionic, cationic and nonionic surfactants and mixtures thereof can be used as emulsifiers.

Suitable anionic surfactants are diphenylene oxide sulfonates, alkane and alkylbenzenesulfonates, alkylnaphthalenesulfonates, olefin sulfonates, alkyl ether sulfonates, fatty alcohol sulfates, ether sulfates, alpha sulfo fatty acid esters, acylamino alkane sulfonates, acyl thisates, alkyl ether alkyl sulfates and n-acyl phosphates, N-acyl phosphates. Alkyl-phenol 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 nonionic surfactants. Alkyl triammonium salts, alkylbenzyldimethylammonium salts and alkylpyridinium salts are used as cationic emulsifiers. The emulsifiers are preferably added in amounts of 0.2 to 5% by weight, based on the resin.

In order to produce a foam from the melamine resin solution, it must contain a blowing agent, the amount depending on the desired density of the foam. In principle, both physical and chemical blowing agents can be used in the method according to the invention. Examples of suitable physical blowing agents are: hydrocarbons, halogenated, in particular fluorinated, hydrocarbons, alcohols, ethers, ketones and esters in liquid form or air and CO as gases. Possible chemical blowing agents are, for example, isocyanates in a mixture with water, C0 being released as an effective blowing agent, carbonates and bicarbonates in a mixture with acids which also produce C0, and azo compounds such as azodicarbonamide. In a preferred embodiment of the invention, the aqueous solution or dispersion is between 1 and 40 wt .-%, based on the resin, of a physical blowing agent with a Boiling point between 0 and 80 ° C added; pentane is preferably 5 to 15% by weight.

Acidic compounds are used as hardeners, which catalyze the further condensation of the melamine resin. The amounts are between 0.01 and 20, preferably between 0.05 and 5% by weight, based on the resin. Inorganic and organic acids, e.g. Hydrochloric acid, sulfuric acid, phosphoric acid, nitric acid, formic acid, acetic acid; Oxalic acid, toluenesulfonic acids, amidosulfonic acids and acid anhydrides.

The aqueous solution or dispersion is preferably free of further additives. For some purposes, however, it can be advantageous to use up to 20% by weight, preferably less than 10% by weight, based on the resin, of conventional additives, such as dyes.

Add flame retardants, UV stabilizers, agents to reduce fire gas toxicity or to promote charring. Since the foams are generally open-pore and can absorb water, it may be necessary for some applications to add water repellents in amounts of 0.2 to 5% by weight. For example, Silicones, paraffins, silicone and fluorine surfactants.

The concentration of the melamine / formaldehyde precondensate in the mixture of precondensate and solvent can vary within wide limits between 55 and 85, preferably between 63 and 80,% by weight. The preferred viscosity of the mixture of precondensate and solvent is between 1 and 300 ° dPas, preferably between 5 and 2000 dPas.

The additives are homogeneously mixed with the aqueous solution or dispersion of the melamine resin, and the blowing agent can also be injected under pressure, if necessary. However, one can also use a fixed, e.g. spray dried melamine resin and then mix it with an aqueous solution of the emulsifier, hardener and blowing agent. Mixing the components can e.g. be made in an extruder. After mixing, the solution or dispersion is discharged through a nozzle and immediately heated and foamed.

The heating of the blowing agent-containing solution or dispersion can in principle - as described in EP-B 17671 - be carried out 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. With this dielectric radiation it is possible to work with microwaves in the frequency range from 0.2 GHz to 100 GHz. For In industrial practice, frequencies of 0.915, 2.45 and 5.8 GHz are available, with 2.45 GHz being particularly preferred. The radiation source for dielectric radiation is the magnetron, it also being possible to irradiate with several magnetrons at the same time. It must be ensured that the field distribution is as homogeneous as possible during the irradiation.

The irradiation is expediently carried out in such a way that the power consumption of the solution or dispersion is between 5 and 200, preferably between 9 and 120 KW, based on 1 kg of water in the solution or dispersion. If the power consumed is lower, there is no more foaming and the mixture only cures. If you work within the preferred range, the greater the power consumption, the faster the mixture foams. Above about 200 KW per kg of water, the foaming speed no longer increases significantly.

The mixture to be foamed is irradiated immediately after it has emerged from the foaming nozzle. The mixture foaming as a result of the temperature increase and evaporation of the blowing agent is applied to circulating belts which form a rectangular channel for shaping the foam.

After its production, the foams according to the invention are expediently subjected to a temperature treatment. They are heated for 1 to 180 minutes, preferably 5 to 60 minutes, to temperatures between 120 and 300 ° C., in particular between 150 and 250 ° C., water, blowing agent and formaldehyde being largely removed. In practice, annealing at 220 ° C. for 30 minutes is sufficient for the foams according to the invention. The formaldehyde content measured according to the EU standard EN ISO 14184-1 is then less than 40 mg, preferably less than 30 and in particular less than 20 mg per kg of foam. In the test method mentioned, a foam sample is extracted for 1 hour in 40 ° C warm water and the extracted formaldehyde is determined analytically.

The elastic foams produced according to the invention, which preferably contain practically no sulfite groups, have a density of 5 to 50 g-1 " ¹ .

As described in EP-B 37470, the foams can be tempered and pressed in order to improve their performance properties. The foams can be produced as sheets or sheets with a height of up to 2 m or as foam sheets with a thickness of a few mm. The preferred foam height (in the direction of foaming) is between 50 cm and 150 cm when using microwaves of the frequency 5 2.45 GHz. All desired plate or film thicknesses can be cut out from such foam sheets. The foams can be provided on one or both sides with cover layers or laminated, for example with paper, cardboard, glass fleece, wood, plasterboard, metal sheets or 10 foils, plastic foils, which can also be foamed if necessary.

The main area of application of the foams produced according to the invention is the thermal and acoustic insulation of buildings and

15 parts of the building, in particular partitions, but also roofs, facades, doors and floors; furthermore the thermal and acoustic insulation of the interiors of vehicles and aircraft as well as the low-temperature insulation, e.g. of cold stores, oil tanks and containers of liquid gas. Other areas of application are

20 Use as insulating wall cladding and as insulating and shock-absorbing packaging material. Due to the high hardness of cross-linked melamine resins, the foams can also be used for slightly abrasive cleaning, grinding and PoH sponges. The open cell structure of the foams

25 also allows suitable cleaning, abrasive and polishing agents to be taken up and stored inside the foam. The sponges can also be made hydrophobic and oleophobic for special cleaning tasks. Because of the extremely low FA emissions compared to those previously on the

30 M / F foams on the market, the foams according to the invention can also be used in the hygiene sector, e.g. Use in the form of thin nonwovens as a wound dressing or as part of baby diapers and incontinence products.

35 The parts and percentages given in the examples relate to the weight.

Comparative Example 1

40 70 parts of a spray-dried melamine / formaldehyde precondensate (molar ratio 1: 3) are dissolved in water. This resin solution are 3% formic acid, 2% one

-Alkanesulfonate and 10% pentane, each based on resin, added. It is stirred vigorously and then in a foam form

45 made of polypropylene foamed by radiation of microwave energy at 2.54 GHz. After drying the foam at 100 ° C, the 13 C / MAS spectrum shows a broadband, intensive signal between 65 and 85 ppm. The formaldehyde emission is well over 1000 mg per kg of foam. After annealing at 220 ° C for 30 minutes, the signal between 65 and 85 ppm is still clearly pronounced in the 13 C / MAS spectrum (ratio of the signals between 65 to 85 ppm and 155 to 175 ppm approx. 0.4) (see Figure 1) ; the formaldehyde emission is still 150 mg per kg of foam. Even tempering for several hours fails to keep the formaldehyde emission below 50 ppm.

Comparative Example 2

Example 2 of EP-B 37470 was reworked. The melamine resin had a molar ratio of 1: 2 and contained 6% sulfite groups. After 30 minutes of tempering at 220 ° C, the formaldehyde emission was 85 mg per kg of foam, the NMR spectrum showed a clear signal between 65 and 85 ppm.

Example according to the invention

70 parts of a spray-dried melamine resin (molar ratio 1: 1.6) are dissolved in 30 parts of water. 3% of an emulsifier from an ethoxylated fatty alcohol (more than 20 ethylene oxide units) as well as 3% formic acid and 10% pentane, each based on resin, are added to this resin solution.

The mixture is then foamed as described in Comparative Example 1 and dried at 100.degree. The NMR spectrum of the untempered foam shows a signal at 65 to 85 ppm, but it is significantly lower than in comparison example 1, and the formaldehyde emission is also lower at 480 mg. After 30 minutes of tempering at 220 ° C, the formaldehyde is virtually completely eliminated, less than 20 mg per kg of foam (limit of quantification of the analytical method) are measured. No signal between 65 and 85 ppm can be seen in the NMR spectrum (see Figure 2).

Claims

claims

1. Process for the production of elastic foams based on a melamine / formaldehyde condensation product by foaming an aqueous solution or dispersion which contains a melamine / formaldehyde precondensate, an emulsifier, a blowing agent and a hardener, and, if appropriate, customary additives, and subsequent crosslinking the pre-condensate, the solution or dispersion being expanded to the foam by heating, characterized in that a pre-condensate is used in which the molar ratio of melamine: formaldehyde is greater than 1: 2.0, the molar ratio being 1: 1.5 is excluded.

2. The method according to claim 1, characterized in that the molar ratio is between 1: 1.0 and 1: 1.9, in particular between 1: 1.3 and 1: 1.8.

3. The method according to claim 1, characterized in that a precondensate is used which contains practically no sulfite groups.

4. The method according to claim 1, characterized in that the heating is done by microwave radiation.

5. The method according to claim 1, characterized in that the foams are annealed for 1 to 180 min, preferably 5 to 60 min at temperatures between 120 and 300 ° C, preferably between 150 and 250 ° C.

6. Elastic foams based on a melamine / formaldehyde condensation product with a density of 5 to 50 g-1 " ¹ , characterized in that in the 13 C / MAS spectrum in the range from 65 to 85 ppm no or only a very weak signal occurs, based on the signal intensity of the melamine ring at 166 ppm.

7. Elastic foams according to claim 6, characterized in that the ratio of the areas in the 13 C / MAS spectrum among the signals is between 65 to 85 ppm and 155 to 175 ppm <0.2.

Sign. Elastic foams according to claim 6, characterized in that the melamine / formaldehyde condensation product contains practically no sulfite groups.