DE2064070B2 - METHOD FOR MANUFACTURING HEAT-RESISTANT MOLDED PARTS - Google Patents

Description

The invention relates to molding compositions based on thermosetting phenolic resins for the Production of heat-resistant molded parts are particularly suitable.

As is known, moldings made from the curable molding compositions based on phenolic resins, in general, at temperatures up to 150 ⁰ C and a short time up tu 200 ⁰ C are thermally stable. ("Phenolic Resins" AAK W hiteh ο use and EGK P ritche 11 [1967], p. 51). Prolonged heating beyond this temperature range ultimately leads to the destruction of the molded part, which is evident from a change in shape, the appearance of cracks and bubbles and the surface becoming dull.

For some applications, however, moldings with a thermal resistance of above 200 ° C, e.g. B. over 250 ° C required.

Powder of calcined petroleum coke (the term "calcined" means that the coke has ^{been freed from all constituents that can be volatilized up to 1200 0} C at high temperatures) on the one hand has been successfully used to improve the chemical resistance of cold-curing resole-based coke Molding compounds, graphite, charcoal or other carbon-containing substances, on the other hand, have been used as fillers for the production of molding compounds for molded parts which are corrosion-resistant and are therefore primarily used in chemical apparatus engineering. The known molding compositions containing petroleum coke are, however, only cured cold. They are processed into filter plates, diffusion plates or the like. In the case of cold hardening, however, it is not possible to produce moldings of any shape. Rather, the method is limited in terms of shape.

ίο From DT-PS 9 18 834 there is also the hardening of Phenolic molding compounds that contain between 48 and 70 percent by weight of the total molding compound Substances with electrical conductivity such as graphite, soot, coal or the like. Contain under the action of pressure and heat known. The use of coke containing over 99% carbon is included in it, however not described.

Masses are known from DTPS 9 46,847 who are not cured under pressure, but only in the heat and should only be used for linings, the curing under pressure which bans. The large number of fillers also includes the carbonaceous materials graphite and carbon black, which contain far less than 99% elemental carbon.

Furthermore, from DT-OS 15 69 524 friction plates are known, the phenol-formaldehyde salts and carbon powder contain. About the use of coke with a purity of over 99%, about the amounts of There is no information in this publication about carbon powder or about possible hardening under pressure contain. According to the only example, there is no coal, but a highly condensed carbon compound used in an amount of 49%.

Finally, from US-PS 33 91 103 the production of molding compositions is known that under pressure and heat are to be hardened and contain finely divided oxidized petroleum coke as filler. This should have less than 1% total share of minerals and ash and by oxidation of a petroleum coke with an initial hydrocarbon content of more than 3% (according to the practical information between 5.2 and 11.7%) due to oxidation at low temperatures are produced, with the hydrocarbons in oxygenated compounds with the result be transferred that the so oxidized petroleum coke contains at least 7% oxygen.

The invention now relates to a process for the production of heat-resistant molded parts on the Based on thermosetting phenolic resins with a content of elemental carbon, which thereby is characterized in that molding compounds which are used as fillers at least 4 and at most 35, preferably 15 to 35 Percentage by weight, based on the total mass, of elemental carbon in the form of petroleum coke or Coal tar pitch coke each containing over 99% carbon, under pressure and contain Cured by the action of heat.

The molded parts thus obtained withstand several days of thermal stress, for. B. at 280 "C in Air without practically changing the shape, surface and the initial flexural strength. Such a one Increasing the thermal stability by using this filler is surprising. The moldings can have the most varied of shapes.

The coke used in the present invention has a Purity of over 99% and is made from residues in the large-scale oil and coal tar distillery

«On received (petroleum or coal tar pitch coke). Such a carbon black may, for example, have been previously heated with exclusion of air to temperatures of about 2000 ^C C under a packed bed of coke. The coke used according to the invention behaves chemically completely indifferently in the temperature range from 200 to over 300 ^{° C. under consideration.} In addition, _{it has} advantageous surface properties, which are due to the high adsorption capacity of coal. Therefore, when the molding compound is processed or when a molded h ^ r frame body is subjected to thermal stress, gases or liquids arising in the interior are adsorbed on the large inner surface of the carbon. This avoids the undesirable formation of bubbles and cavities. Since the carbon has a relatively low density, it can be easily incorporated into the resin used. Finally, the relatively good thermal conductivity of carbon - if it has a graphite structure - causes a uniform temperature distribution within the said molded part, which prevents the occurrence of local overheating phenomena which can lead to thermal decomposition of the resin.

The carbon is expediently in finely divided form, e.g. B. used as a powder with a grain size of 1 to 1000 μ, preferably from 10 to 200 μ. The specific surface area can be 3 to 5 m ² / g, coefficient of thermal expansion to 12cal / cm sec ⁰ C and the pore volume between 8 and 9 ■ 10- ⁶ / ° C, the thermal conductivity of 6 about 3 to 5%.

As phenolic resins, for. B. in question: Resoles and novolaks, melamine-phenol mixed condensates with a phenol content of more than 20 percent by weight and epoxy resins that are more than 20 percent by weight phenolic resins (Resole and / or Novolak) included.

Suitable phenolic resins are those based on phenols and derivatives, e.g. B. phenol, diphenylol propane or methane, cresol, xylenol, resorcinol on the one hand and aldehydes, e.g. B. formaldehyde, acetaldehyde, furfural, Isobutyraldehyde, unsaturated and / or saturated mono- and dialdehydes, such as acrolein, glyoxal, Crotonaldehyde, the acidic range being used in the case of novolaks, and the molar ratio Phenol to aldehyde at least 1, in the case of resoles in the alkaline range and that Molar ratio phenol: aldehyde at most 1, e.g. B. 1: 1.5 to 1: 2, as is well known.

Suitable melamine-phenolic resins are those that by known processes from melamine, phenols and aldehydes, e.g. B. each of the above, produced and the molar ratio of melamine to phenol is 1: 0.2 to 10, which contain more than 20% phenol.

Suitable epoxy resins are those based on epichlorohydrin and diphenylolpropane and / or methane or higher molecular weight aliphatic compounds in which the oxirane grouping is formed by subsequent oxidation was introduced. These can contain phenolic resins, resols and / or novolaks, ζ. B. contain the above.

If phenol novolak is used as the base, formaldehyde, Paraformaldehyde, polyoxymethylene glycol, trioxane, tetraoxymethylene, Hexamethylenetetramine, acetaldehyde, paraldehyde, furfural, methylal, 1,3-dioxolane. Diethyl formal, as well as triphenolhexamethylenetetramine and glycerin can be used.

Molding compounds based on epoxy resins with more than 20% phenol can mainly be mixed with acid anhydride, such as with the anhydride of phthalic acid and its partial and totally hydrogenated homologues, pyromellitic dianhydride, 3,6-E ndomethylene / d-tetrahydrophthalic acid, Na die- or Methylnadicäureanhydrid der

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(R-H or methyl)

Hexachloroendomethylene tetrahydrophthalic anhydride and maleic anhydride as well as with amines or Amides, e.g. B. ethylenediamine, diethylenetriamine, m-phenylenediamine, 4,4'-diaminediphenylmethane, dicyandiamide, Amides of long-chain fatty acids, BFv amine complexes, 2-mithylimidazole, dimethylbenzylamine or the like. are crosslinked, the proportion of hardeners varying depending on the nature of the epoxy resins can be. These hardeners are generally used in equimolecular amounts, based on the epoxy groups, implemented.

When using phenolic resins, it is also possible to use the curable resin in the form of a mixture of novolak and hexamethylenetetramine, which has been prepared with intensive stirring, and then to add the carbon and optionally other fillers. Resoles and novolaks can also be used as a mixture with one another. The addition of hexamethylenetetramine has proven particularly advantageous. The quantitative ratio of novolak: resole can be any, but is advantageously 80 to 50%: 20 to 50% with 5 to 10% hexamethylenetetramine, based in each case on the total amount of resin by weight. Molding compositions in which the components mentioned are within this quantity range can be ^{exposed directly to thermal stress at 230 °} C. (shock resistance). Moldings made from molding compositions based on pure novolak hexarmithylenetetramine achieve the same _sü thermal resistance at 280 ° C., but this can be increased by bringing them to this temperature within at least about 45 minutes when heated for the first time. Moldings based on novolak and hexamethylenetetramine produced by injection molding are, however, thermally shock-resistant up to 280 ° C. even without this slow heating.

In the production of the molding compounds, for. ti. by kneading, a fairly high friction is observed due to the use of elemental _b0 carbon, which can be varied by using lubricants. This is in many cases, e.g. 13. Advantageous in injection molding.

Suitable lubricants are 1. B. higher fatty acids (, <; such as stearic acid, metal salts, in particular the calcium, aluminum and / or zinc salts of a higher fatty acid, preferably with 16 to 22 carbon atoms and especially stearic acid, fatty acid derivatives in the form

of esters, amides, imides, nitriles and / or sulfonates, e.g. B. also ester waxes of montan acids. Here derivatives of saturated and / or unsaturated fatty acids, the long-chain radical of which has 16 to 24 carbon atoms contains, can be used. Furthermore, as lubricants 5 are high molecular substances with molecular weights of 5000 to 50,000, for example silicones or aliphatic Compounds such as polyethylene, polypropylene and polyisobutylene are suitable. So the friction is through mutual adjustment of the amount of elemental carbon and that of the lubricant controllable. the The amount of lubricant is generally 0.1 to 1 percent by weight, based on the total mass. at Due to the high level of carbon friction, it is advisable to increase the amount of lubricant for higher carbon contents to increase up to 2 percent by weight. Instead of uniform connections, the production of the resins or, of course, mixtures can always be used as additives.

Due to the thermal stability of the molding compounds, the molding time can be shortened because of the improved thermal conductivity of the fillers the possibility of processing the molding compounds higher temperature - but within the curing temperature of the synthetic resins - is given. This This fact causes an improved material flow due to the lower viscosity at higher temperatures is effected. This results in a higher throughput.

You can also use the phenolic resin in water and / or conventional organic without adverse results Dissolve solvents and then add the carbon and optionally asbestos and / or glass fibers or melt the resin first and then mix the carbon and asbestos fibers. Next to Carbon and optionally asbestos and / or glass fibers, the masses can also contain other fillers and / or contain reinforcing substances, such as kaolin, talc, wollastonite, but the proportion of Carbon in these substances at least 20 percent by weight of the total amount of filler and reinforcing material be. Other common additives, such as calcium carbonate, calcium-magnesium carbonate, aluminum oxide, Aluminum hydroxide, magnesium oxide, can be contained in the masses.

The molding compositions according to the invention can be used for the production of moldings that can withstand high thermal loads, z. B. those with a perfectly closed surface, especially for electrical engineering purposes, use, since the electrical properties of the products made from the molding compounds as a result of the Carbon enveloping insulating synthetic resins are good. In particular, the molding compounds are used for production suitable for isolators, switches, regulators and other electrical components. It is also possible to manufacture moldings that come into contact with corrosive liquids, z. B. vessels, pipes, laminated bodies, parts of heatable or heatable devices, eg. B. heating plates, -body or the like f, o

In the following
Parts by weight.

Examples are always parts

example 1

200 parts of a novolak made from phenol and formaldehyde with a molar ratio of 1: 0.6 in the presence of hydrochloric acid as a catalyst, (melting point 65 ° C) and 200 parts of a solid resole, produced by the condensation of phenol and formaldehyde in Molar ratio 1: 2 in the presence of magnesium oxide (melting point 50 ° C), with 40 parts of hexamethylenetetramine, 15 parts of zinc stearate, 20 parts of a montan wax, 300 parts of fine-fiber asbestos and 200 Share calcined petroleum coke with a grain size of up to 450 μ in a mixer at room temperature for 15 minutes homogenized. The mixture is on a heated roller mill within 3 minutes to a homogeneous, processed plasticized fur. The product obtained is allowed to cool at room temperature. It will be ground.

From the obtained molding composition produced by the compression molding method at 180 ⁰ C and under a pressure of 300 kg / cm ² molded at a press time of 3 minutes. These moldings are abruptly subjected to thermal stress over 4 hours at 300 ⁰ C. After this test, the molded parts show neither cracks nor bubbles. They can therefore be used at a working temperature of 260 to 300 ^c C. In addition to the thermal properties mentioned, the molded parts also have good corrosion resistance to acids and dilute alkali at elevated temperatures.

Example 2

55 parts of novolak according to Example 1, 20 parts of glass fibers with a cut length of 3 mm, 20 parts of calcined petroleum coke powder, grain size up to 450 μ, 2 parts of polyethylene wax and 1 part of zinc stearate are mixed at room temperature for 45 minutes and then homogenized on a heated extruder to form a molding compound plasticized. The moldings produced in the compression molding process are, like the moldings according to Example 1, resistant if they are heated ^{the first time from room temperature to 300 ° C. within a minimum period of 45 minutes.} Thereafter, the molded parts can also be subjected to shock loads at this temperature. Molded parts produced by the injection molding process can immediately be ^{subjected to shock loads at 300 °} C. without changing their shape or surface.

Example 3

400 parts of the resol used according to Example 1 are 15 parts of zinc stearate, 20 parts of a Ester wax, 300 parts of fine-fiber asbestos (fiber length 0.1 to 0.5 mm), 25 parts of magnesium oxide and 250 Share calcined coal tar pitch coke with a grain size of up to 450 μ in a mixer at room temperature well mixed together and then on a twin roll mill into one within 2 minutes homogeneous fur plasticized. The molded parts produced from this molding compound as in Example 1 have also has a shock resistance at 300 ° C.

Example 4

870 parts of novolak from Example 1, 80 parts of hexamethylenetetramine and 50 parts of powdered calcined petroleum coke with a grain size of up to 450 μm are homogenized and plasticized in a heated vacuum kneader equipped with Sigma blades. The reactive mixture is allowed to ^{react at an internal temperature of 90 °} C. for 10 minutes until the viscosity of the melt increases noticeably. The condensation water is then removed in vacuo within 20 minutes. After removal from the kneader, the highly viscous mixture is cooled and then ground.

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A 5 mm thick plate produced in the compression molding process is over intact a four-hour storage at 280 ⁰ C, when placed within 45 minutes to this temperature.

Example 5

83 parts of a 60% aqueous melamine-phenol mixed condensate with a molar ratio of melamine: phenol such as 1: 1, which has been prepared in a known manner, are mixed with 1.5 parts of zinc stearate, 1.5 parts of tell-tale montan ester wax, 27 parts of fine-fiber asbestos ( Fiber length <0.1 to 0.5 mm) and 20 parts of calcined petroleum coke powder with a grain size of up to 450 μ are completely homogenized in a kneader. After the mixture has passed a sieve, the water is removed in a belt dryer ^{at 70 ° C. within 20 minutes.} In the compression molding process standard bars are prepared by a four-hour storage intact at 28O ⁰ C when it is brought to this temperature at the first time within a minimum period of 45 minutes.

The moldings produced according to Examples 1 to 5 were tested. The received The results are shown in the table below.

Physical Properties

Examples
1

Flexural Strength, kp / cm ²
Impact strength, kpcm / cm ²
Notched impact strength, kpcm / cm ²
Dimensional stability according to Martens, ⁰ C heat resistance class
Water absorption, mg
Surface resistance, comparative number Specific volume resistance, Ω cm Dielectric loss factor, tg ό

715 1200 805 1200 850 3.8 6 to 8 4.3 5 to 6 4.0 1.8 6 to 8 2.0 1.5 to 2 2.0 > 180 175 > 180 140 160 4th 4th 4th 2 4th 23 20th 15th 80 to 100 20th 10 10 11th 10 " 10 10 " 10 ¹⁰ 1012 ΙΟ ' ² 10 ¹⁰ 0.11 0.23 0.10 0.10 0.08

With the requirement according to the invention that the coke should have a minimum content of 99% carbon, it is not a formal, but an essential characteristic. This follows from the following comparison tests:

Three samples of a petroleum coke with a 10% content of volatile constituents were treated with air ^{at 250, 325 and 350 ° C. for 24 hours in a layer height of 5 mm.} No change in the appearance of the coke could be seen. From these 3 samples and a coke according to the invention, molding compounds were then produced according to the following recipe:

Weight percent Novolak 35.0 Hexamethylenetetramine 5.0 Magnesia 3.0 Coke according to the invention 20th lubricant 1.2 asbestos 25.8

In all cases the individual components were mixed intensively. Then all the masses were ^{precondensed at 125 to 130 0} C within 3 minutes on a laboratory roller mill. The molding compounds were then pressed under the same conditions at 160 ⁰ C and 200 at a 3-minute extruded moldings. After 24 hours of storage at room temperature, they were exposed to the following thermal loads:

1.Heating from room temperature to 200 ° C.

2. lOstündigcs holding at 280 ⁰ C,

In this test, the molded bodies produced with the oxidized petroleum coke were already in the dei Heating phase destroyed by cracking at 260 "C. The Test bodies with the coke according to the invention, on the other hand, were still better after the 10 hour exposure intact.

From these experiments it is clear that dei the subject of the invention a considerable technical seeing progress brings with it

Claims (6)

Patent claims: 1. Method of making heat-resistant Molded parts based on thermosetting phenolic resins with an elemental content Carbon, characterized in that molding compounds, which are at least 4 and as fillers at most 35, preferably 15 to 35 percent by weight, based on the total mass, of elemental Carbon in the form of petroleum coke or coal tar pitch coke, each containing over Contains 99% carbon, can be hardened under the action of pressure and heat. 2. The method according to claim 1, characterized in that the molding compositions contain the phenolic resin Contained in the form of a mixture of resole and novolak. 3. The method according to claim 1 or 2, characterized in that the molding compositions are an ester wax contains montanic acids as a lubricant. 4. Process according to Claims 1 to 3, characterized in that the molding compositions also have other Contain fillers and / or reinforcing materials, the proportion of carbon in the total amount of fillers and / or reinforcing agents but at least 20 percent by weight. 5. The method according to claims 1 to 4, characterized in that the molding compositions asbestos and / or contain glass fibers as reinforcing fillers. 6. A method for the production of molded parts according to claim 1 to 5, characterized in that the phenolic resin compound used first dissolved in a solvent and then the carbon and optionally asbestos and / or glass fibers have been added or that the resin initially melted and then the carbon and asbestos fibers were added.