CS212873B1 - Process for producing a modified melamine-formaldehyde molding compound - Google Patents

Abstract

The invention relates to a method for producing a melamine-formaldehyde molding compound containing a modifier based on lactams and/or aminocarboxylic acids and fillers which are salts of alkaline earth metals. The resin is prepared by condensation of the starting components in the presence of all other additives.

Description

The invention relates to a method of producing a modified melamine-formaldehyde molding compound particularly suitable for injection molding and extrusion processing with improved fluidity and increased strength in weld lines at normal and elevated temperatures.

Melamine modified thermosetting plastics belong to the category of thermosetting materials that can meet the demanding requirements for the production of technical, often demanding and complex moldings, which are mostly produced using progressive processing technologies. Materials of this type must have, in addition to a satisfactory form, easy processing in a relatively wide range of processing parameters and very good flowability. It is required that the moldings have low shrinkage, additional shrinkage, resistance to the formation of cracks at normal and elevated temperatures, especially in places of flow lines, good physical-mechanical and electrical properties. When processing thermosetting plastics, they come into a viscous-liquid state under the influence of heat and pressure and during this process, during injection and extrusion by a flow system, the cavities of the working tool subsequently emerge. At the same time, a chemical reaction gradually begins to take place with the transition to a viscous-liquid state, which is the initial state of the curing process. This process acts against the fluidity of the material at this stage. It is very important that during the visco-liquid state the material has a low viscosity and remains in this state for a sufficiently long time to fill the tool cavity and, conversely, that the subsequent curing process lasts a relatively short time. The entire process of manufacturing molding materials is characterized by a sequence of mechanical-physical operations and the resulting complexity and cost of the process, as well as by the chemical composition itself and its changes, which greatly contributes to the final properties of the molding material. Unmodified materials (e.g., US patent 3,376,239) are completely unsuitable for the above-mentioned use due to low fluidity and insufficient resistance to cracking. Also, the method of dry preparation from solids does not allow for perfect saturation of the filler such as cellulose, which reduces the physical-chemical properties and increases the costs when using solids such as p-formaldehyde. Similarly, in the procedure according to French patent No. 1,512,029, Czechoslovak patent No. 129,445, 126,796, higher economy is achieved by simplifying the process in a special reactor system, but the adverse effect of the unmodified material also does not allow application for injection molding. Also, the procedure with the possibility of using high pressure of 0.5 to 2 MPa according to French patent 1,407,926 shows the same disadvantages. Modification of melamine-formaldehyde material, e.g. guanamine (benzoguanamine, acetoguanamine) improves the flow properties of the material, injection ability, but provides the resulting materials with low plasticity and thus susceptibility to cracking in the sprue and weld lines, in addition, they also show a tendency to additional yellowing due to sunlight. Sulfonamides such as benzene sulfonamide, p- and o-toluene sulfonamide are very good modifiers, but they act as plasticizers and do not eliminate the susceptibility of moldings made from such modified materials to the formation of cracks upon thermal exposure.

often for this purpose modification with phenols, respectively. phenol-formaldehyde resoles and novolaks (USA patent 1,057.400 and British patent 882.140) is used, in which it is possible to significantly increase the resistance to cracking. However, a significant disadvantage remains the complexity of the process with the necessity of using freshly distilled phenol, working under nitrogen, while even this does not prevent additional slight yellowing of the molding compound, respectively. moldings prepared from it. These disadvantages

212 873 partly eliminates the use of lactams, e.g. caprolactam according to French patent 1,576.969, German patent 1,595.368, 1,720.268, 1,576.969. According to these patents, the condensation product of melamine with formaldehyde is first prepared in the presence of two to fifteen percent of caprolactam based on the total weight of the substances mentioned, using soda as a condensation catalyst. It is known that caprolactam, under the mentioned conditions, is converted into -aminocaproic acid, the -NH3 group of which is capable of reacting with formaldehyde and thus enables its incorporation into the macromolecule during the curing of the molding compound. Apart from the use of an uneconomical and laborious method of processing the starting components, i.e. condensate, cellulose and other additives in a malaxer, and the necessity of further drying, it was found that this procedure does not allow for optimal properties even in terms of final properties. It can be analytically proven that under these conditions, part of the caprolactam used remains in a free unreacted form, which is reflected unfavorably, especially in the appearance of the molding by an inhomogeneous shine and, at higher concentrations, by a tendency for the material to stick to the molding mold. The use of higher concentrations above the stated limit, i.e. above 15%, is completely impossible.

The above disadvantages are eliminated by the method of producing modified melamine-formaldehyde molding compound by condensation of starting components, the essence of which is that the condensation is carried out in the simultaneous presence of 10 to 100% by weight of a modifier based on lactam and/or aminocarboxylic acids, based on the weight of melamine, 0.1 to 60% by weight of salts of alkaline earth metals or their mixtures, for example, barium sulfate and sulfide or calcium carbonate, based on the total weight of the reactants, and in the presence of additives such as cellulose, lubricants, condensation catalysts, plasticizers and dyes, or the lactam and/or aminocarboxylic acid are first subjected to pre-condensation with formaldehyde * or a mixture of formaldehyde and melamine.

The modification effect of the lactam or its acid according to the present invention is so significant that the resulting modified mass exhibits a very low viscosity, e.g. according to the shear stress values. The modified mass prepared in this way can be injected and at a low specific pressure of 130 to 150 MPa against the commonly used pressure of 200 to 250 MPa for similar materials. The modified mass according to the present invention ensures a sufficiently long time of staying in the plastic state during processing and excellent safety against hardening of the mass in the plasticizing cylinder during the injection molding process. The proposed production method makes it possible to use a high content of mineral fillers in the range of 0.1 to 60% of the total weight of the modified aminoplast, which act simultaneously as catalysts and condensation stabilizers. At the same time, they significantly improve the visual quality of the final product, especially by suppressing flow lines and in combination with the content of lactam or corresponding -aminocarboxylic acids in an amount of 20 or more percent by weight, high strength and resistance to cracking are ensured even in the case of metal deposits. Given that the proposed method allows the use of significantly higher concentrations of the modifier than has been described so far - exceptionally good rheological properties were achieved, in particular high flowability, low shear stress, long residence time in the viscous-liquid state, low dissipation, at high shear rates, etc. This production method also allows any combination of the proposed modifiers, i.e. combinations of lactams with each other, or their .alpha.-aminocarboxylic acids, or even combinations of .alpha.-aminocarboxylic acids and lactams with each other.

212,873

For a more detailed explanation of the nature of the invention, examples of embodiments are given below.

Example 1

Melamine 50,- kg Caprolactam 12,- kg Formalin 70,- kg Beech cellulose 25,- kg Calcium carbonate 45,- kg Potassium hydroxide 0.1 kg Sodium tetraborate 0.25 tg Lubricant 2,- kg Dye 1,- tg After all the ingredients have been added, condensation takes place in the reactor under intensive stirring at 100 °C for 40 min. , after which the product in the form of granules is dried under a vacuum of 0.05 MPa. Example 2 I have a laminate 50,- kg Lauryllactam 15,- kg Formalin 70,- kg ’ Spruce cellulose 20,- kg Wood flour 15,- kg Mixture of sulfate and sulfide barnate (Litopon) 30,- kg Triethanolamine 1.5 kg Sodium hydroxide 0.1 kg Lubricant 2,- kg Dye i,- kg After entering all components take place in a reactor with intensive mixing condensation at 95 °C for 30 min., where the product in the form of granules is dried under a vacuum of 0.05 MPa. Example 3 Melamine 50,- kg Semi-product of caprolactam - mu 8 formalin 50,- kg Formalin 50,- kg Aspen cellulose 35,- kg Calcium carbonate 30,- kg Triethanolamine 1.5 kg Potassium hydroxide 0.1 kg Lubricant 1,- kg Dye 1,- kg

After all components have been introduced, condensation takes place in the reactor with intensive stirring at 95 °C for 30 min., after which the product in the form of granules is dried under a vacuum of 0.05 MPa.

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Example 4

Melamine 50,- kg Tu-aminocaproic acid 50,- kg Formalin 70,- kg Calcium carbonate 25,- kg Mixture of sulfide and sulfate barnaceous 25,- kg Spruce cellulose 35,- kg Sodium tetraborate 0.1 kg Potassium hydroxide 0.1 kg Lubricant 1,- kg Dye 1,“ kg After entering all components take place in a reactor with intensive mixing condensation at 105°C for 20 min. , after which the product in the form of granules is dried under a vacuum of 0.08 MPa. Example 5 a) Caprolactam 30,- kg Formal 90,- kg Potassium hydroxide 0.2 kg Aspen cellulose 30,- kg b) Melamine 50,- kg Barium sulfate 40,- kg Sodium tetraborate 0.35 kg Sodium hydroxide 0.1 kg Lubricant 1.5 kg Dye 1,“ kg

The components ad a) are introduced into the reactor and heated with intensive stirring at a temperature of 90 to 95 °C for 15 min., whereby the lactam ring opens with the formation of the corresponding carboxylic acid or its salt. Then the components ad b) are introduced into the reactor and

here another 15 minutes. at a temperature of 90 to 95 °C, a modified melaminoform is formed maldehyde mass. Then the product in the form of granules is dried under vacuum of 0.05 MPa. Example 6 a) Melamine 50,- kg Formalin 70,- kg Aspen cellulose 35,- kg Triethanolamine 2,- kg Lubricant 1,- kg b)Caprolactam 20,- kg Calcium carbonate 40,- kg Phthalic anhydride 0.5 kg

The components a) are introduced into the reactor and heated with intensive stirring at a temperature

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90°C for 10 min. Then the components ad b) are introduced and during the next 20 min. at a temperature of 90 to 95°C, a modified melamine formaldehyde mass is formed. The condensation product is then dried under a vacuum of 0.08 MPa.

Example 7

Melanin 40,- kg Caprolactan 15,- kg Formalin 70,- kg Triethanolamine 2,- kg Melanin 10,- kg Aspen cellulose 30,- kg Calcium carbonate 30,- kg A mixture of sulfide and ayran barnaceous 20,- kg Lubricant 2,- kg Formic acid 0.10 kg

The components a) are heated in a reactor with stirring at a temperature of 95 °C for 30 min., during which the lactam ring opens and a precondensate is formed. The precondensate is passed into the reactor with the components a) where, within 10 minutes, condensation occurs at a temperature of up to 100 °C and a modified melamine formaldehyde mass is formed. The product is quickly dried at a temperature of up to 100 °C.

Claims (1)

A process for the production of a modified melamine-formaldehyde molding composition by condensation of melamine and formaldehyde, characterized in that the condensation is carried out in the presence of 10 to 100% by weight of a lactam-modifier and / or N-aminocarboxylic acid based on melamine, 0.1 to 60% by weight of the salts of corrosive earth metals or mixtures thereof, for example barium sulphate and sulphate or calcium carbonate, based on the total weight of the reactants, and in the presence of additives such as cellulose, lubricants, condensation catalysts, plasticizers and coloring agents; the aminocarboxylic acid is first precondensed with formaldehyde or a mixture of formaldehyde and melamine.