DE1769604A1 - Foamable thermoplastic materials - Google Patents

Description

1769604 Patent attorney Dipl.-Phys. Gerhard Lledl 8 Munich 22 Steinsdorfstr. 21-22 Tel. 29 84 62

B 3753

MONSANTO COMPANY, 800 North Lindbergh Boulevard, 66 St. Louis, Missouri / USA

Foamable thermoplastic compositions

The invention relates to solid, foamed thermoplastic resins. In particular it relates to foamable mixtures of high pressure and low pressure polyethylenes and objects formed from these masses.

The use of foamed polyethylene as an insulating material for electrical Head is known. In particular, it has found wide use as an insulating material for distribution cables of high frequency television antennas, since it has very favorable electrical properties, namely one

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small dielectric constant and low power factor combined with low density. The polyethylene used for the latter type of insulation should have a cellular structure in which the cells are small in diameter and closed, that is, they are not connected to one another and are evenly distributed in the polymer matrix. The conventional polyethylene foams sometimes suffered from the disadvantage that they had a cellular structure with large voids. These cavities, which in reality is very large cells are produced by the union of numerous smaller cells, which in turn is caused by the fact that the polymer matrix between the small cells break "The conventional foamable Polyäthylenmassen reported continued during extrusion and foaming poor dimensional stability. This lack of dimensional stability of the foamed masses leads to changes in the shape of the foamed, extruded product and is a very undesirable property.

It has now been found that by using a mixture of high pressure and low pressure polyethylenes, the tendency of foamed polyethylenes to form non-uniform cell structures with large voids can be completely overcome.

The aim of this invention were improved foamable compositions made from mixtures of high pressure and low pressure polyethylenes, the foams

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provide higher cell uniformity, d. H. essentially free from Voids than those made with formulations using a single polyethylene resin having the same density like the mix has.

It was also an object of the invention to provide foamable polyethylene compositions to find foams of higher dimensional stability.

Another object of the invention was a foamed thermoplastic Material suitable for electrical insulation. The invention relates to an expandable thermoplastic composition

1. about 30 to about 80 wt. - '', 'of a polyethylene (A) with a

3 3

Density from about 0.910 g cm to about 0.935 g cm;

2. about 10 to about 60 wt -.% Of a second polyethylene (B)

3 with a density greater than 0.945 g / cm;

3. about 0, 1 to about 10 wt -.% Of a propellant and

4. about 0.1 to about 5 wt. - ^ of a metal soap from the group of the metal salts of fatty acids, the metals being bivalent or trivalent and the fatty acid residues containing at least 8 carbon atoms and mixtures thereof.

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The polymers used for the expandable thermoplastic compositions of the invention are high molecular weight polyethylenes

and having a melting point of at least 110. The high pressure *

polyethylene component having a density of 0.910 to about 0.935 g / cm

and preferably from 0.915 to 0.925 g / cm, is used in amounts of about 30 to 80 wt generally -%, and preferably in amounts from 60 to about 80 wt -% used... Polyethylenes of this type can be prepared by polymerizing ethylene at a pressure of approximately 350 to 4,220 atmospheres and at temperatures of approximately 100 to 400 ° C. in the presence of free radical initiators as catalysts. Suitable catalysts are molecular oxygen, compounds of the peroxide type, alkyl hydroperoxides, diperoxydicarbonic acid esters, persulfates, peracids, azo compounds, oximes and the like. If desired, minor amounts of 1 to 15 percent of other monomers can be copolymerized with ethylene. Of these comonomers are mentioned:

α-olefins such as propylene, butene-1, pentene-1, etc., vinyl esters, esters acrylic acid and numerous other compounds that have an ethylenic double bond.

The ethylene polymers used as the low-pressure polyethylene component

of the invention have a density of more than 0.945 g / cm and preferably

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from about 0.950 to about 0.960 g / cm. The amount of the low-pressure polyethylene component is 10 to 60%, preferably 10 to 40% by weight . The low-pressure polyethylenes can be prepared by conventional polymerization processes such as, for example, polymerization in the presence of a Ziegler catalyst or by the so-called Phillips process using a chromium oxide catalyst. The low pressure polyethylenes can also contain a small amount of butene-1 and / or other α-olefinic comonomers as modifiers.

The blowing agents suitable for the formulations of the invention are all known gas-evolving compounds which decompose above the melting temperature of polyethylene, in particular those which decompose at temperatures of about 120 to 180 °. These include the aromatic sulfohydrazides, the aliphatic sulfohydrazides and Aralkylsulfohydrazide such as benzenesulfohydrazide, toluene bis-sulfohydrazid, xylene-bis-sulfohydrazid, biphenyl-bis-sulfohydrazidj / p, ^p} -oxy-bis-benzenesulfohydrazide, ohydrazid methanesulfonic, IsobutanBulfohydrazid, Octansulfohydrazid, α-toluenesulfohydrazide, xylene-bis-sulfohydrazide, and the like; the aromatic sulfosemicarbazides, the aliphatic sulfosemicarbazides, and the aralkylsulfosemicarbazides, such as, for example, benzenesulfosemicarbazides, toluene-bis-sulfosemicarbazide, xylene-bis-sulfosemicarbazide, biphenyl-bis-sulfosemicarbazide, p-bis-p '

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benzenesulfosemicarbazide, methanesulfoseemicarbazide, isobutanesulfoseemicarbazide, octanesulfoseemicarbazide, α-toluenesulfoseemicarbazide, xylene-bisulfoseemicarbazide, and the like; N-nitroso compounds such as N, N '-dimethyl-N, N' -dinitroso-terephthalamide and N, N '-dinitrosopentamethylene tetramine and azo compounds such as azodicarbonamide. Particularly useful propellants are p, p ^J -oxy-bis-benzene sulfohydrazide, azodicarbonamide and mixtures thereof.

In general, the blowing agent in amounts of 0.1 to 10 percent is -.%), Preferably in amounts of 1, 5 to 3 wt -% used The use of mixed blowing agents enables a further Verschäumungstemperaturbereich. Since, for example, azodicarbonamide decomposes at a higher temperature than p, p '-oxy-bis-benzenesulfohydrazide, a mixture of the two enables a larger foaming temperature range than the use of p, p' -oxy-bis-benzenesulfohydrazide alone allows. This greater foaming temperature range allows the blowing agent decomposition temperature to be better matched to the optimum base resin melt viscosity. A useful mixed propellant contains about 1.5 to about 2.5 weight percent p, p 'oxy-bis-benzenesulfohydrazide and about 0.1 to about 1.0 azodicarbonamide.

The density of the foamed products obtained according to the invention varies with the amount of propellant used and the temperature at

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which the mass was foamed or in the case of cable sheathing with the temperature of the extrusion. The density of the foamed products obtained is between 0.1 and 0.9 g / cm. The cheapest density is generally between 0.2 to 0.55 g / cm when used for electrical insulation or for coatings on distribution cables of high-frequency chine antennas be used.

The metallic soaps that can be used are made from metallic salts of fatty acids, the metals being divalent or trivalent and the fatty acid residues having at least 8 carbon atoms. Mixtures too of which are usable. The metal soaps of zinc, lead, calcium, barium, aluminum and magnesium are preferably used. Typical metal soaps are zinc stearate, bljistearate, calcium stearate, Barium stearate, magnesium stearate, aluminum monostearate, aluminum distearate, aluminum hydroxy stearate, aluminum palmitate and aluminum octoate, the preferred metal soap being zinc stearate. The compositions of the invention contain metal soaps in amounts from 0.1 to approximately 5, 0 wt. -T, preferably in amounts of 1.0 to 2.5 wt, - ° ?.

The foamable compositions of the invention can be used in any number of ways can be obtained, provided that they allow a homogeneous mixture of the components. Suitable methods are e.g. B. Mixing in the Banbury mixer, in roller mills, in the extruder or the solution mixture.

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Care must be taken that when the components are mixed, temperatures that are too high are not reached in order to avoid premature decomposition of the propellants. Generally mixing temperatures preferably from 110 * C to 140 C, when a Banbury mixer or the like is used. The polyethylenes of this invention can be mixed prior to the addition of the propellant and metallic soap. However, both polymers can also be mixed together with the other components at the same time.

If the foamable mixture according to the invention is used for insulation electrical conductors or distribution cables for radio frequency television antennas ext erased, the temperature is kept above the decomposition temperature of the propellant, but below the temperature at which the foamed product collapses. Depending on the type of blowing agent and the desired density, the extrusion temperature be between 130 ° and 230 ° c. Preferably a temperature of 150 ° C to 200 ° C is used.

The foamable thermoplastic compositions of the invention can contain other additives, for example fillers such as carbon black, reinforcing agents such as B. contain fibers and plasticizers. The properties of the Mixtures can be maintained or strengthened by adding antioxidants or stabilizers. Pigments or dyes can also be used can be added to obtain colored masses.

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example 1

A mixture of 289 g of a polyethylene with a density of

0.927 g / cm, 6.6 g p, p '-oxy-bis-benzenesulfohydrazide, 4.5 g zinc stearate and 0.15 g of 4,4'-thio-bis-2-tert-butyl-5-methyl-phenol (available under the trade name Santonox R) was in a laboratory roller mill (15, 2 cm 30, 5 cm) at a temperature of Mixed 110 ° C to 120 ° C for five minutes. The resulting mass was then cooled to 27 ° C. Part of this cooled down Mixture was then molded under pressure and foamed by placing 130 g in a press heated to 160 ° C + 0.5 ° C and a stamp pressure of exactly 2270 / was immediately applied. This stamp pressure was maintained for five minutes and then increased to 11,300 kg for 15 seconds. Then the stamp relieved and the foamed sample immediately placed in a water tank for 15 minutes. The resulting foamed sheet had a density of 0.22 g / cm. There were numerous voids in the plate noted, especially in the surface.

Example 2

A mixture (289 g) with a measured density of 0.928 g / cm was prepared by placing 202 g of a polyethylene in a roller mill

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with a density of 0.917 g / cm and 87 g of a polyethylene with a

Density of 0.950 g / cm were mixed . 6.6 g of p, p '-oxy-bis-benzenesulfohydrazide,. 4.5 g of zinc stearate and 0.5 g of 4,4'-thio bis-2-t'ert-butyl-5- methyl- phenol were added. The mixture was then mixed according to Example 1. Following the procedure of Example 1 , a foamed sheet was prepared from the resulting composition. This plate had a density of 0.23 g / cm and had a very fine, uniform cell structure, with no signs of voids being discernible. In particular, the surfaces of the plate were very smooth.

Example 3

In a Banbury mixer 107 kg of polyethylene with a density of

3 3

0.917 g / cm, 45.4 kg polyethylene with a density of 0.950 g / cm , 3.49 kg p, p'-oxy-bis-benzenesulfohydrazide, 338 kg zinc stearate and 0.082 kg 4,4'-thio-bis-2 -tert -butyl-5-methyl-phenol given. The components were mixed thoroughly at a temperature of 135 ° C for two minutes. The mixture was then placed on a differential roll mill where it was rolled, cooled and granulated.

From the granulated mixture were according to the method of

3 Example 1 foamed sheets produced which had a density of 0.24 g / cm and a particularly fine cell structure. The surfaces

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the plates were very smooth and no voids could be found in the test samples to be established.

Example 4

The mass of Example 3 was expanded by passing over a
2 mm (81-mil) aluminum conductor was extruded using a 90 ° crosshead attached to a 6.35 cm diameter ct extruder. The melt temperature was set at 150 ° C. while the screw made 30 revolutions per minute. The linear speed of the wire was set constant at 13.7 meters per minute. The foamed coating had a density of
0.32 g / cm and had an excellent circular cross-sectional geometry with no evidence of dimples or flats. Of the
The coating also had a fine, uniform, closed-cell structure and was without voids.

Example 5

A mixture of 107 kg of polyethylene with a density of 0.917 g / cm,

3
45.4 kg polyethylene with a density of 0.950 g cm, 3.27 kg p, p '-oxy-

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bis-benzenesulfohydrazide, 0.816 kg azodicarbonamide, 4.08 kg zinc stearate and 0.082 kg of 4,4'-thio-bis-2-tert-butyl-5-methyl-phenol was mixed in a Banbury mixer following the procedure of Example 3. Following the procedure of Example 1, however, except that a temperature of 180 was used, foamed panels were made from this material.

The foamed sheets (density = 0.27 g / cm) showed fine uniform cell structure with very smooth surfaces. Voids were not observed.

Example 6

The foamable composition of Example 5 was poured over a 2 mm (81-mil) Aluminum conductor extruded according to the method of Example 4, with the Except that the extrusion temperature was set to 160. The coating (density = 30 g / cm) showed no depressions or flat spots

and had a fine, uniform cell structure without voids.

Example 7

A mixture of 106 kg of polyethylene with a density of 0.917 g / cm,

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45.4 kg polyethylene with a density of 0.950 g / cm, 3.27 kg p, p 'oxy-bis-benzenesulfohydrazide, 0.816 kg of azodicarbonamide, 1.63 kg of zinc stearate and 0.09 kg of 4,4'-thio-bis-2-tert-butyl-5-methyl-phenol mixed in a Banbury mixer following the procedure of Example 3. Following the procedure of Example 1, with the exception that a temperature of 180 was used, foamed sheets were made of this material. The foamed panels

(Density = 0.23 g / cm) showed a fine, uniform cell structure very smooth surfaces. Voids were not observed.

Example 8

The foamable composition of Example 7 was prepared by the method of Example 4 extruded over a 2 mm (81-mil) aluminum conductor, however except that the extrusion temperature was set to 172. The coating (density = 0.31 g / cm) showed no depressions or Flat spots and had a fine uniform cell structure without voids.

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Claims (11)

Claims 1. Expandable thermoplastic material 1. about 30 to about 80 wt -.% Of a polyethylene (A) having a density of about 0.910 g / cm to about 0.935 g / cm ³ ; 2. about 10 to about 60 weight percent of a second polyethylene (B) with a density greater than 0.945 g / cm; 3. about 0.1 to about 10 weight percent of a propellant and 4. from about 0.1 to about 5 wt -.% Of a metal soap selected from the group of the metal salts of fatty acids, wherein the metals are divalent or trivalent and Festtsäurereste at least 8 carbon atoms and mixtures thereof. 2. Composition according to claim 1, wherein the propellant from the group of Sulfohydrazides, sulfosemicarbazides, N-nitroso compounds, azo compounds, and mixtures thereof. 009843/1921 3. A composition according to claim 2, wherein polyethylene (A) in an amount of from about 60 to about 80 wt -% are present -.% And polyethylene (B) in an amount of about 10 to 40 wt.. 4. Composition according to claim 3, wherein the density of the polyethylene (A) 0.915 g / cm and the density of the polyethylene (B) 0.950 to 0.960 g / cm amounts to. 5. A composition according to claim 4, wherein the blowing agent in an amount of from about 1.5 to about 3, 0 wt -.%, And the metallic soap in an amount of from about 1.0 to about 2.5 wt -.% Is present. 6. The composition of claim 5, wherein the metallic soap is zinc stearate. 7. The composition of claim 6, wherein the propellant is p, p '-Qxy-bis-benzenesulfohydrazide. 8. The composition of claim 6, wherein the propellant consists of a mixture from about 1.5 to about 2.5 weight percent p, p * -oxy-bis-benzenesulfohydrazide and about 0.1 to about 1.0 weight percent azodicarbonamide. 009843/1921 9. Composition according to claim 8, wherein the polyethylene (A) has a density of 0.917 g / cm, and in an amount of 67, 5 wt -% is present, the. 3 polyethylene (B) has a density of 0.950 g / cm and in an amount .% is present, the blowing agent consists of a mixture of 2.0 wt - - 29 wt.% p, p '-oxy-bis-benzenesulfohydrazide and 0.5 wt -.% azodicarbonamide and zinc stearate is in an amount of 1, 0 Weight is present. 10. Electrical insulation material made from a rigid thermoplastic polymeric mass with a density of 0.2-0.55 g / cm, which thereby is obtained that at a temperature of 150 ° C to 200 ° C, an expandable, thermoplastic, polymeric mass 1. About 30 to about 80% by weight of a polyethylene (A) with a 3 3 Density from about 0.910 g / cm to about 0.935 g / cm; 2. about 10 to about 60 wt -.% Of a second polyethylene (B) 3 at a density of about 0.945 g / cm; 3. about 0. 5 to about 10.0 wt -.% P of a blowing agent selected from the group p '-oxy-bis-benzenesulfohydrazide and azodicarbonamide and mixtures thereof and 4. from about 0.1 to about 5.0 wt -.% Of a metal soap selected from the group of metal salts of fatty acids, wherein the metals are divalent and trivalent and the fatty acid radicals contain at least 8 carbon atoms and mixtures thereof is expanded. ^ l 11. Wire that is sheathed with an electrical insulating material, which consists of a rigid, thermoplastic, polymeric mass with a 3
Density of from 0.20 to 0.55 g / cm, which is obtained by that over this wire at a temperature of 150 ° C to 200 ° C an expandable, thermoplastic mass 1. about 30 to about 80% by weight of a polyethylene (A) with a 3 3 Density from about 0.910 g / cm to about 0.935 g / cm, 2. about 10 to about 60 wt -.% Of a second polyethylene (B) 3 with a density of approximately 0.945 g / cm, 3. about 0.1 to about 10, 0 wt -.% P of a blowing agent selected from the group p '-oxy-bis-benzenesulfohydrazide and azodicarbonamide and mixtures thereof and 4. about 0.1 to about 5.0% by weight of a metallic soap made from the Group of the metal salts of fatty acids, the metals being bivalent and trivalent and the fatty acid residues having at least 8 carbon atoms and mixtures thereof is extruded and the same is then cooled. 009843/1921