FI58786C - FREQUENCY PROCESSING OF POLYAMIDE PRODUCTS WITH INTEGRAL SKUMSTRUKTUR - Google Patents

Description

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C. Patent granted on 10 04 1901 (45)

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Patent · och registrerttyrelten 'Ansektn utiagd och utl. * Kr * ft * n pubHeend 31 * 12.80 (32) (33) (31) Pyydetty Muoiketi * —8 «| lrd priority 10.12.73

Federal Republic of Germany-Förbundsrepubliken Tyskland (DE) P 2361U52.O

(71) Bayer Aktiengesellschaft, Leverkusen, Federal Republic of Germany-Förbundsrepubliken Tyskland (DE) (72) Kurt Schneider, Krefeld, Friedrich Fahnler, Krefeld, Federal Republic of Germany- Förbundsrepubliken Tyskland (DE) (7 ^) Oy Kolster Ab (5 ^) Men Kolster Ab (5 ^) The present invention relates to a process for the preparation of polyamides having a uniform foam structure by polymerizing at least one lactam containing at least 6 ring members in the presence of an activator and a catalyst combination.

It is known to prepare polyamide foams by activated anionic polymerization of lactam, whereby lactam is polymerized with alkali metal compounds of weakly alkaline compounds such as monocarboxylic acids having a P value greater than 3.

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in the presence of salts such as sodium formate or sodium benzoate, using alkali metal carbonates or alkali metal borohydrides as catalysts in concentrations of about 1 mol - $ and polyfunctional isocyanates as blowing agents and activators (German application DE 1 355 = DE 1 3 195 and DE 1,595,655 = US 3,591,533). The average density of these foams is 50-500 kg / m 2. Their mechanical strength is therefore considerably lower than that of the corresponding cellular molded polyamide products. Therefore, they cannot be used in many commercial applications (see Table 1). It is also known from German patent 2,58786 DE 1,067,591 »that cast polyamide products can be prepared by activated anionic polymerization of lactam using strong alkaline catalysts such as alkali metals, alkaline earth metals, their hydrides, oxides, alcoholates or amides and as activators such as acylates. acetylcaprolactam, benzoyl chloride, carbodiimides or cyanamides, but preferably monofunctional or polyfunctional isocyanates. The polymerization reaction can be carried out above or below the melting point of the polymers formed. If temperatures above the melting point are used, the polymerization is preferably carried out in extruders or injection molding machines. If these systems are processed in injection molding machines, the dimensions of the molded polyamide products obtained are accurate, but their monomer and oligomer content is then high according to the monomer-polymer equilibrium condition, which depends on the polymerization temperature.

Polymerization to produce cast products below the melting point of polyamide is generally carried out by die casting without pressure. However, the dimensional inaccuracy due to the shrinkage of the cast articles thus obtained may always be 15% · In addition, cracks appear in the products due to shrinkage.

Known polyamide foams prepared by polymerizing lactams using both weakly basic catalysts, such as sodium borohydride, and also strongly basic catalysts, such as sodium caprolactamate, and using a certain combination of sodium borohydride and isocyanate, for use in multiple applications. Therefore, an attempt was made to produce a polyamide foam which, despite its foam structure, has some advantageous properties and is sufficiently strong. This has been achieved by the process according to the invention, in which the activated anionic polymerization of lactam is carried out by adding a catalyst combination consisting of a strongly alkaline and a weakly alkaline catalyst, which is added in a very defined molar ratio and in certain limited amounts. Namely, if this catalyst combination is added during the polymerization, a polyamide foam having an integral structure is surprisingly obtained, i.e. a foam consisting of a dense, non-foamed outer layer and a foamed core part. In addition to being strong, this foam is characterized by the fact that shrinkage does not occur as usual at a temperature below the melting point of the polyamide formed during polymerization.

The process of this invention is characterized in that the activator is a monofunctional or polyfunctional or protected isocyanate compound, and the catalyst combination contains a strongly alkaline catalyst and a weakly 3,58786 alkaline catalyst in a molar ratio of 3: 1 to 10: 1, preferably molar: the concentration being in the range of 0.01 to 0.5 mol%, preferably in the range of 0.02 to 0.1 mol%, based on lactation, and the molar ratio of strongly alkaline catalyst to said activator being in the range of 1: 1 to 1: 2, preferably in the range 1: 3-3: 1, wherein the strongly alkaline catalyst is an alkali metal, an alkaline earth metal or an alkali metal or alkaline earth metal oxide, hydride or amide or the reaction product of one of these alkaline catalysts with a lactam, and the weakly alkaline catalyst is a carboxylic acid containing 1-20 carbon atom with a P value of <3 and an alkali metal or alkaline earth

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lime metal salt.

Molded polyamide products made by the method of the present invention having a density of 650-1000 kg / m 2 are characterized by a porous outer layer having a selective thickness of 0.1-3 mm and a central portion having a foam structure. Their mechanical properties are excellent. It is particularly advantageous that the cast products do not undergo dimensional shrinkage and thermal expansion, except for their exact dimensions.

This result is all the more surprising given that, as can be seen from Comparative Experiment 2, foaming does not occur in the above-mentioned recommended concentration range if the reaction is carried out without a strongly alkaline catalyst, i.e. only in the presence of a weakly alkaline catalyst. The addition of a certain amount of strongly basic catalyst, apparently solely the addition of the amount of isocyanate required in the known processes, was surprisingly sufficient to form the desired uniform foam.

The process of the invention can be used to polymerize lactams containing at least six ring members, such as caprolactam, heptanoic acid lactam or lauric acid lactam, or mixtures thereof. Suitable strongly alkaline catalysts include alkaline compounds previously disclosed for use in anionic polymerization, for example in German patent DE 1 067 591 = U.S. patent 3 015 652, such as alkali metals and alkaline earth metals and whose oxides, hydrides and amides as well as their reaction products with lactam, such as alkali metal or alkaline earth metal lactams.

The weakly basic catalysts used are alkali metal and alkaline earth metal salts of carboxylic acids containing 1 to 20 carbon atoms and having a P value> 3 (see Table 2), such as sodium formate, potassium benzoate, sodium methyl carbonate or borohydrides of alkali metal and alkaline earth metals. .

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The activators, which are preferably used in concentrations of 0.2 to 1 mol%, based on lactam, can be monofunctional or polyfunctional isocyanates or protected isocyanate compounds, such as isocyanate and lactam auxiliaries, preferably 1,6-hexamethylene diisamecyanate karbamidokaprolaktaami.

Fine solids can be added to the system to form cores, for example, colloidal silica, talc, or asbestos powder, or products that are soluble in monomeric lactams but differ as a fine precipitate in a polyamide, e.g., high melting polyamides or dimeric caprolactam. It has also been found advantageous to add surfactants to promote the foaming reaction, e.g. silicone block polymers disclosed, for example, in German Patent Application 1,702,731 = U.S. Patent 3,702,313. It is further preferred to use suitable mold release agents such as wax-soluble lactam.

In addition, of course, other conventional additives can be used for the ionic polymerization of lactams, for example asbestos, glass fibers, glass spheres, lime or talc as fillers, dyes or pigments, molybdenum disulphide or Teflon.

Melting points are in the range of 90-180 ° C depending on the lactam used and preferably in the range of 100-130 ° C if caprolactam is used. The temperatures of the molds should be 120-200 ° C, preferably 1-10-180 ° C.

The device shown below has been found to be particularly advantageous. In this device, the production of molded polyamide products having a uniform foam structure by means of the present invention can be carried out economically without waste material and casting openings. The device is characterized in that, unlike the devices used in known two-component methods, no separate mixing device is required, since the ingredients are mixed directly in the mold. The mode of operation of the device is shown below by way of example with reference to the method according to the invention. The numbering of the brochure corresponds to Figure 1.

Part of the lactation together with the catalyst combination and, if desired, other additives such as nucleating agents, mold release agents and surfactants is melted in a storage tank 1 at 90-160 ° C and another part of the lactam together with the activator is melted at 110-180 ° C in tank 2. the two components are fed into the mold 6 by means of flexible pumps i * heated by means of feed pumps 3. The mold is heated from 130 ° C to 200 ° C. It is equipped with two injection nozzles 5 mounted in such a way that the two components 58886 are mixed together according to the principle of counter-current injection. The pressure of the nozzles and thus the supply pressure can be adjusted by means of the pumps 3. The amount of melt added to the mold is 65-100% of the mold volume, depending on the desired density of the cast product. The reaction starts after a time interval of about 30 seconds to 3 minutes and the product can be removed from the mold 1-2 minutes after the start of the reaction. The mold is sealed with suitable heat and lactam resistant seals to prevent losses of low viscosity melt, but one or more ventilation ducts may be installed in the separation plane, preferably at the highest point so that air in the mold can escape.

The polyamide foam having a uniform foam structure produced by the method of the invention can be used for the production of various thick-walled molded articles, such as furniture parts, seats, pumps and speaker housings, plastic mattresses and car parts.

The experiments shown in the following examples were performed using the equipment described above. The flexural strength with the given deviation was determined according to DIN 53 ^ 52 and the modulus of elasticity according to DIN 53 ^ 55.

Example 1

Plates measuring 300 x 300 x 10 mm were prepared.

In tank 1, 7.5 kg of caprolactam, 300 g of a solid 18 ~ solution of sodium caprolactamate in caprolactam and 1.5 g of sodium borohydride at 115 ° C were melted under nitrogen. In tank 2, 7.5 kg of caprolactam with 150 g of hexamethylene-1,6-diisocyanate were melted under nitrogen at 125 ° C. The feed pumps and supply lines were heated to the temperature of either vessel 1 or 2, depending on which they were connected to.

The mold was heated to 165 ° C. The pumps fed U50 g of melt from tank 1 and i + 50 g of melt from tank 2 into the mold at a feed pressure of 80 bar and the mold was filled 100 - #. After a polymerization time of U minutes, the polyamide sheet was removed from the mold. Its dimensions are the same as the mold and its surface was uniform and very glossy. After sawing the product, the following structure was revealed! the surface layer was a non-porous polyamide layer about 2.5 mm thick and had a uniform fine-grained cellular foam structure inside, the pores of which were

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0.1-0.5 mm in diameter. The average density was 1.0 g / cm. Other similar molded products were prepared from the stored lactating melts described above using a 5 minute polymerization cycle. The flexural strength at the given deviation was 950 kp / cm and the modulus of elasticity 22,000 kp / cm.

Comparative Example 1

The experimental setup and temperature program were the same as in Example 1.

In Tank 1, 7.5 kg of caprolactam and 300 g of sodium caprolactam (6,58786 mate) 8% solid solution were melted, and in Tank 2, 7.5 kg of caprolactam and 150 g of hexamethylene-1,6-diisocyanate were melted. 10 g of each melt was fed to the mold under the conditions mentioned in Example 1 to such an extent that the mold was completely filled, after a polymerization time of 1 minute, the mold was opened and the cast product was removed.

Unlike the products obtained according to Example 1, the piece did not reproduce the dimensions and contours of the mold. At the top of the plate was about 10 volumes /? depression due to shrinkage and there were large shrinkage openings in different parts of the plate. The density of the material was 1.15 g / cm. The bending strength was) 2 kp / cm and the modulus of elasticity was 30,000 kp / cm. These values did not change as the mold temperature was lowered. Although in the second experiment the shrinkage openings could be reduced by lowering the mold temperature to 150 ° C, the amount of depression at the top of the plate was about 15% by volume.

Comparative Example 2

The procedure was the same as in Example 1. In Tank 1, 7.5 kg of caprolactam and 3 g of sodium borohydride were melted, and in Tank 2, 7.5 kg of caprolactam was melted with 150 g of hexamethylene-1,6-diisocyanate. k50 g of each melt was heated to 120 ° C and fed into a mold heated to 15 ° C. No polymerization and foaming occurred during 30 minutes.

In the next experiment, the sodium borohydride content was increased from 0.02 mol% to 0.1 mol%. Again, no polymerization or foaming occurred during 30 minutes.

Example 2

The experimental setup and temperature program were the same as in Example 1.

In vessel 1, 7.5 kg of caprolactam, 300 g) of an 8% solid sodium caprolactamate solution in caprolactam, 3 g of sodium borohydride and 1.5 kg of silicone stabilizer Aerosil COK 8U® (Degussa) were heated, and in vessel 2, 7.5 kg of caprolactam and 150 g of g of hexamethylene-1,6-diisocyanate. U25 g of each melt was fed to the mold under the conditions mentioned in Example 1 so much that the mold was filled to 95 3?% After the addition of the melts. After 3.5 minutes, a plate having the same dimensions as the mold was removed. Its surface was also uniform and very glossy.

When sawing the board into pieces, the following structure was revealed: The outer surface layer was a non-porous 1.5 mm thick polyamide layer on all sides and evenly inside. . * ·. . . * 3 nen, fine cellular foam structure. The average density was 0.95 kg / cm.

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Example 3

The experimental setup and temperature program were the same as in Example 1.

In vessel 1, 7.5 g of caprolactam, 300 g of sodium caprolactam "8-8% solid solution in caprolactam, 3 g of sodium borohydride, 3 g of talc were melted.

Cr) and 7.5 g of silicone stabilizer L 530w (Union Carbide) and in vessel 2 7.5 kg of caprolactam and 350 g of hexamethylene-bis-urea-caprolactam were melted. 380 g of each melt from tanks 1 and 2 were fed into the mold, which then filled 85. After 3.5 minutes of polymerization, the molded product with a uniform and highly glossy surface was removed from the mold. When the product was sawn into pieces, a flat, very fine cellular structure was revealed. When looking at the thin layer under a microscope, a 0.4-0.5 mm thick, dense outer surface could be seen. The average density of the cast product was 0.85 g / cm 2. Its 2 p bending strength was 850 kp / cnt and its elastic modulus 19500 kp / cm.

Example 4 The mold shown in Example 1 was used. In tank 1, 7.5 kg of lauric acid lactamate was melted together with 225 g of an 18% solid solution of sodium caprolactam in caprolactam and 2 g of sodium borohydride at 165 ° C, and in tank 2, 7.5 kg of lauric acid lactam were melted together with 75 g of hexamethylene, diisocyanate at 165 ° C. The pumps and tubes were heated to 165 ° C and the plate mold to 170 ° C. 400 g of melt was fed into the mold from both tanks. The 12-polyamide sheet was removed from the mold after 2 minutes of polymerization. When sawing the board into pieces, a uniform foam structure could be seen, whereby a 2 mm thick dense polyamide layer completely surrounded the finely divided cellular core. The surface was closed, glossy and non-porous.

Example 5

Pump housings weighing 4 kg were prepared in a polished casting mold made of a zinc-aluminum-magnesium alloy (Zamak). 25 kg of caprolactam, 1000 g of a solid solution of sodium caprolactamate 18-JS in caprolactam, 5 g of sodium borohydride, 25 g of silicone stabilizer L 530 ^ and 25 g of Aerosil C0K 84 w (vessel 1) and 25 kg of caprolactam and 500 g of hexamethylene-1,6- diisocyanate (vessel 2) was melted in separate vessels to 120 ° C. The mold was maintained at 155-160 ° C. The injection nozzles were mounted against each other in the flange portion of the pump housing 6 mm apart (corresponding to the wall thickness of the flange). 2 kg of melt was fed from tank 1 and 2 kg from tank 2 into the mold so that the mold was filled to 100. After 4 minutes, the mold was opened hydraulically 58786 8 and the pump housing was removed, which completely filled the mold and matched the dimensions of the mold. The surface was non-porous and shiny. When sawing, a dense edge area 1.0-1.5 mm thick was revealed, which contained a very fine part with a cellular structure inside. The average density 3 of the cast product was 1.0 g / cm.

table 1

Flexural strength of the elastic modulus to become deviating (kp / cm ^) (kp / cm)

Molded 6-polyamide product made by non-pressure casting, see Comparative Example 1 12l * 0 30,000

Molded β-polyamide product prepared by the process of the invention as shown in Example 2 950 22,000

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6-polyamide foam, density 350 kg / nr according to German application DE 1 570 555 = U.S. Pat. No. 3,591,533 95 1,950

Table 2

Pk values for some carboxylic acids: PKa

Formic acid 3.77

Acetic acid * +, 76

Benzoic acid U, 17

Examples 6-21

The experimental setup was the same as in Example 1 and the method was performed as described in Example 3.

7.5 kg of caprolactam were melted with varying amounts, as shown in Table 3, of a solid solution of sodium caprolactamate 18-JS in caprolactam (Cat.NL) and with varying amounts of sodium borohydride (Cat.B) under nitrogen at 115 ° C in tanks 1 and 7. , 5 kg of caprolactan and 150 g of hexamethylene-1,6-diisocyanate were melted in tank 2. 1 * 50 g of each melt was fed into the mold. The plates were removed from the mold after 3.5 minutes and their structure was determined.

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Claims (8)

10 58786 A process for preparing polyamides having a uniform foam structure by polymerizing a lactam containing at least one ring member of at least 6 ring members in the presence of an Akti catalyst and a catalyst combination, characterized in that the Akti catalyst is a monofunctional or polyfunctional aliphatic alkylate 3: 1 to 10: 1, preferably in a molar ratio of 2: 1 to 20: 1, with a weakly alkaline catalyst concentration in the range of 0.01 to 0.5 molar, preferably in the range of 0.02 to 0.1 molar. calculated, and the molar ratio of strongly alkaline catalyst to said activator is in the range of 1: 1 to 1: 2, preferably in the range of 1: 3 to 3: 1, wherein the strongly alkaline catalyst is an alkali metal, alkaline earth metal or an alkali metal or alkaline earth metal oxide , hydride or amide or the reaction product of one of these alkaline catalysts with lactam, and Heiko The alkaline catalyst is a salt of a carboxylic acid containing 1 to 20 carbon atoms and having a P value of k. 3 and an alkali metal or alkaline earth metal. Process according to Claim 1, characterized in that the lactam is caprolactam, heptanoic acid lactam, lauric acid lactam or a mixture thereof. Process according to Claim 1, characterized in that the weakly alkaline catalyst is sodium formate, potassium benzoate, sodium methyl carbonate or borohydride of an alkali metal or alkaline earth metal. Process according to Claim 1, characterized in that the activator is 1,6-hexamethylene diisocyanate or hexamethylene bis-urea docaprolactam. Process according to Claim 1, characterized in that the polymerization is carried out in a mold which has been heated to a temperature of 120 to 200 ° C. Process according to Claim 5, characterized in that the polymerization is carried out in a mold which has been heated to a temperature of 110 to 180 ° C. Process according to Claim 1, characterized in that part of the lactation mixed with the activator and part of the lactation mixed with the catalyst combination are melted in separate storage vessels at a temperature of 90 to 180 ° C, from which the melts are fed into the mold by means of injection nozzles the two melts are mixed according to the countercurrent principle and polymerized at a temperature of 1 to 0-180 ° C. Device for carrying out the process according to claim 1, characterized in that it comprises two storage tanks equipped with feed pumps, heated flexible tubes and a mold provided with two injection nozzles arranged so that the reactants mix with each other according to the countercurrent principle. u 58786