DE1215363B - Use of formamidinesulfinic acid as a latent hardening agent for aminoplasts - Google Patents

Description

Use of formamidinesulfinic acid as a latent curing agent for Aminoplasts There are already numerous to accelerate the hardening of aminoplasts Hardening agent became known. A number of requirements are imposed on these hardeners which are not always and at the same time fulfilled to the desired extent. A good hardener should meet the following conditions: 1. At room temperature or a moderately increased temperature should be no or only a slight reaction-accelerating Effect must be present so as not to adversely affect the shelf life of the product.

2. The accelerating effect should be at the processing temperature occur quickly and the reaction speed is multiplied as much as possible.

3. The effect should only start at a temperature at which the material is already plastic, so that a perfect flow and closed Surface is guaranteed when pressing.

4. The hardener should also be in aqueous solution at room temperature or not yet be effective at a moderately elevated temperature, so for as long as possible Service life of the resin solution is guaranteed.

5. In addition, the hardener may change the properties of the finished product do not adversely affect, d. i.e., there must be no signs of over-hardening, such as embrittlement and cracking occur.

Most known hardeners generally have the points 1 to 3 fulfilled more or less well. For hardeners that also meet the requirements of the Point 4, the effectiveness is usually too low, or it will be adversely affects the properties of the finished product (point 5).

As hardeners for aminoplasts containing sulfur and nitrogen atoms Cyanthioformamide (Fig. 1), ethylene diamine sulfite (Fig. 2), acetoxime toluene sulfonate (Fig. 3) and propionamide sulfate (Fig. 4). As shown in FIGS. 3 and 4 clearly illustrate, show acetoxime toluenesulfonate and propionamide sulfate in the following Concentration range according to the invention almost no reaction-accelerating effect on melamine resin. Also with ethylenediamine sulfite and cyanthioformamide (Fig. 2 and 1) is the reaction-accelerating effect in the concentration control according to the invention rich much less than in the method according to the invention. Cyanthioformamide is yellow and easily decomposed, which is also disadvantageous.

It has now been found that all of the above are required of a hardener Properties are met in a particularly good way through the use of formamidinesulfinic acid (Aminoiminomethanesulfinic acid) latent containing sulfur and nitrogen atoms Hardeners for aminoplasts in quantities of a few I / 100 / o, based on the solid resin content.

By adding quantities of the order of magnitude of a few 1 / ioo 0 / o leave this product to an aminoplast resin, in particular a melamine resin there are already considerable acceleration effects at the processing temperature achieve (Fig. 5).

The compound mentioned can be added to aqueous melamine resin solutions will. Despite the high reaction rate at elevated temperature, the The useful life of the resin solutions is very long. When heated, however, occurs immediately the desired effect. Of particular importance is that a certain pH value is not fallen below despite the strong acceleration effect and therefore none - there is a risk of over-hardening due to the pH value being too low. Other uses of the hardening agent are: Accelerating the hardening of urea resins and Mixed resins z. B. based on urea and melamine as well as based on melamine and phenolic resins.

Said curing agent is of particular importance, e.g. B. at the production of decorative laminates and surface finishing of hardboard or chipboard, where a good and fast flow on the one hand and, on the other hand, rapid hardening after perfect flow is required must be in order to prevent the resin from sagging into the substrate.

This hardener is just as interesting in production of decorative foils for decorating pressed parts. Since these foils against The end of the pressing cycle must be placed on the three-quarters hardened pressed part particularly fast curing is required. On the other hand, the resin solution must itself be stable long enough to carry out the impregnation without losses can.

Other possible areas of application are: hardening acceleration in molding compounds and resin liquors, z. B. for textile finishing. -As particularly surprising when using formamidinesulfinic acid as a hardening agent, especially in aqueous Solution, is to evaluate the fact that quantities that practically extend the shelf life of the Do not influence the solution, when heating up quickly and have a lasting effect. Obviously, the normal mechanism of action of a common hardener, which is mainly based on a lowering of the pH value, a second autocatalytic one Effect superimposed. The quick effect is obviously due to the fact that the Oxidation of aminoiminomethanesulfonic acid formed by the free formaldehyde present the rate of oxidation dej: formamidinesulfinic acid is additionally accelerated.

To determine the reaction rate of an aqueous melamine resin solution, the z. B. for the impregnation of foils for further processing on decorative Laminates are used, the so-called are generally used Cooking test. Here, a 500% aqueous resin solution is placed in a test tube, the test tube closed with a cotton ball and the sample so long in the boiling Heat water until it becomes cloudy. The time to creation the turbidity is called the resistance to boiling.

A commercially available melamine resin which has a boiling resistance of 150 minutes is prepared by stirring into water to produce a 500% resin solution which has a pH of 9.3. Formamidinesulfinic acid is added to this resin solution. 0fo hardener, pH after dissolving {resistance to boiling | durability Formamidinsulnic acid, the hardener in minutes | Days based on Festnarz 150 7 0.02 1 9.0 1 60 7 0.05 8.8 26 7 0.07 8.75 6 to 7 0.1 8.3 10 after 4 days slight cloudiness EXAMPLE I A commercially available melamine molding compound was mixed with 0.1% formamidinesulfinic acid (based on the molding compound) and then compressed under the usual conditions corresponding to DIN standards.

The improvements can be seen in the following comparative figures: Molding compound + 0.10 / 0 without formamide Addition of insufflic acid Flexural strength, kg / cm2 ..... 873-1006 Impact strength, kgcm / cm2. 5.0 7.0 Overhardening factor *) 1.67 3.0 *) Overhardening reactor = pressing time that can be used as a maximum without overhardening phenomena occurring on the compact, divided by the pressing time that is at least required to produce hardened compacts.

In the example above, there is the desired increase in the overhardening factor due to the fact that the pressing time at which overhardening phenomena occur, not reduced by the addition of formamidinesulfinic acid compared to the molding compound without hardener is, on the other hand, the pressing time until sufficient curing is shortened will.

Example II A commercially available melamine molding compound was 0.1 0 / o Formamidinesulfinic acid (based on molding compound) mixed and then under the usual, pressed in accordance with the DIN standards.

The improvements can be seen in the following comparative figures: Molding compound + 0.1% without porrnamid Formamide Addition of insulfinic acid Flexural strength, kg / cm2 ..... 873 1006 Impact strength, kgcm / cm2. . 5.0 7.0 tZ hardening factor *). . . 1.67 3.0 *) Top hardening factor = maximum pressing time that can be used without overhardening phenomena occurring on the compact, divided by the minimum pressing time required to produce hardened compacts.

In the example above, there is the desired increase in the overhardening factor due to the fact that the pressing time at which overhardening phenomena occur, not reduced by the addition of formamidinesulfinic acid compared to the molding compound without hardener will, on the other hand, however, the pressing time is greatly reduced until sufficient curing.

Claims (1)

Claim: Use of formamidinesulfinic acid (aminoiminomethanesulfinic acid) latent hardening agent containing sulfur and nitrogen atoms agent for aminoplasts in amounts of a few I / 100 / o, based on the solid resin content. Publications considered: "Chemisches Zentralblatt", 1941, U, p. 2622; 1940, II, p. 2549; 1941, I, p. 459; 1951, I, p. 1535.