CS250997B1 - A method for producing a blend of polypropylene and low density polyethylene - Google Patents

Abstract

Polypropylene and polyethylene blends for extrusion coating with increased melt elasticity are prepared by melting and kneading 65 to 90% by weight of polypropylene granulated with stabilizers and 10 to 35% by weight of granulated low-density polyethylene at a temperature of 150 to 300 °C with 0.001 to 0.2% by weight of organic peroxides dissolved in 0.1 to 2% by weight of aliphatic hydrocarbons characterized by a kinematic viscosity of 30 to 5Gb mm2/s.

Description

The present invention relates to polypropylene and low density polyethylene compositions with increased melt elasticity. In particular, it relates to materials where polypropylene is the predominant component. Their application is, for example, extrusion coating.

jr čs. copyright certificate δ. No. 210738 discloses a process for producing a blend of polypropylene and low density polyethylene for extrusion coating, comprising 80 to 95% by weight of polypropylene having a melt index reduced by radically initiated degradation and 5 to 20% by weight of low density polyethylene having a melt index of 2 to 70 g / 10 min. and stabilizers and processing aids by extruding a blend of powdered polypropylene having a flow index of 0.2 to 10 g / 10 min. (230 ° C, 21.16 N) and low density polyethylene with a flow index of 2 to 70 (190 ° C, 21.16 N). The mixture is melted and kneaded at a temperature of 150 to 300 ° C in the presence of 0.02 to 0.2 parts by weight of organic peroxides and 0.1 to 0.6 parts by weight of a synergistic mixture of phenolic, phosphite and sulfur stabilizers per 100 parts of the polyolefin mixture.

The advantage of this method is that the degradation of polypropylene and its modification by low-density polyethylene is achieved by only one pass through the extruder, which provides significant savings in both energy and labor costs and other costs compared to previously used processes, since a separate polypropylene degradation operation is eliminated. However, the process requires that the production process is based on powdered polypropylene, which, although it permits perfect mixing with organic peroxides and stabilizers, before introducing the mixture into the extruder, but also has some disadvantages. Since polypropylene-air powder mixtures are explosive, the method requires the manufacturer to have equipment to ensure the inerting of part of the mixing and metering of raw materials, for example with nitrogen.

This technical and economic problem is solved by the production of the said mixtures from polypropylene granulate.

SUMMARY OF THE INVENTION The present invention provides a process for the production of a blend of polypropylene and low density polyethylene for extrusion fusion and kneading in the presence of organic peroxides, phenolic stabilizers or mixtures thereof with phospholite or sulphide stabilizers and processing additives. 3 to 30 g / 10 min, granulated with stabilizers and 10 to 35% by weight of granulated low density polyethylene having a flow index of 2 to 70 g / 10 min. melts and kneads at 150 to 30 ° C with 0.001 to 0.2% by weight organic peroxides dissolved in 0.1 to 2% by weight aliphatic hydrocarbons characterized by a kinematic viscosity of 30 to 500 mm ² / s.

The stabilizers used to prepare the polypropylene granules used include phenolic stabilizers such as 1-hydroxy-2,6-di-tert-butyl-4-methylbenzene, 3-methyl-6-tert-butylphenol / pentaerythritol tetra (4-hydroxy-3,5). di-tert-butylphenol) prooionate, etc., sulfur secondary antioxidants such as dilauryl-3,3'-thiodipropionate, distearyl 3,3'-thiodipropionate and phosphite stabilizers such as tris- (1'-phenyl-4-ethylphenyl) phosphite, tris- phenyl-4-nonyl) phosphite.

Calcium stearate is generally used as a processing additive to improve the flow properties of the polymer blend.

The use of synergistic mixtures of the aforementioned stabilizers then makes it possible to effect the initiated degradation of the polypropylene in the presence of low-density polyethylene without crosslinking the polyethylene component.

The organic hydroxides as radical sources are selected so that their half-life is 30 to 200 at 180 ° C. Di-tert-butylperoxide, 1,1-bis (tert-butylperoxy) -3,3,5'-trimethylcyclohexane, dicumylperoxide, tert-butylperbenzoate or 2,5 dimethyl-2,5 di (tert-butylperoxy) hexane may be used.

The medium used for diluting the organic peroxide, which is a hydrocarbon with a climatic viscosity of 30 to 500 mm / a. it is chosen so that this is readily miscible with the polymeric components, has a surface tension such that the polymer granules are well wetted by it, and has a high boiling point so that it does not flow during production or processing. For example, high boiling petroleum distillates or unsaturated polymerization products meet the above requirements. Examples of the first group are so-called white mineral oils, examples of the second polypropylene oil group.

The process for preparing said mixtures starts by mixing the granules of polypropylene and low density polyethylene, to which the appropriate amount of peroxide diluted with a suitable medium is added continuously or impact. Other stabilizers or excipients may also be added. The mixture thus prepared is granulated on a single or multi-screw extruder of suitable geometry, i.e. equipped with mixing zones. The temperature in the individual zones of the extruder is adjustable and is set in the range of 150 to 300 ° C.

Polypropylene / low density polyethylene blends prepared by the process of this invention have modified rheological properties. Of particular importance is the increase in melt elasticity, as measured by the ratio of the diameter of the extruded string to the diameter of the nozzle. The melt elasticity during extrusion deposition is an important parameter that decisively affects the melt taper and, therefore, causes uneven application. This has been known for a long time (E.J. Kaltenzacher, J.K. Kund, R.A. Mendelson, SES Journal, November 1967, p. 55).

Thus, it is desirable that the polypropylene composition have both a high melt-stretching ability and an elasticity. These properties are mutually exclusive in pure PP and surprisingly this problem is eliminated by the process of the invention, which is another great advantage.

The following examples illustrate the invention. The product flow indexes in the examples are measured according to ČSN 660861, condition number 12 (230 ° C, 21.16 N). The elasticity of the melt is a measure of its reversible deformation. Its measure, a relatively easily accessible measurement, is the increase in the diameter of the string extruded from the circular nozzle. ČSN 64301 Ο-Branched polyethylene (basic provision) states in articles 60 to 64 the characteristics of PZ (ratio of diameter change after extrusion) for evaluation of melt elasticity.

However, the above process cannot be used for polypropylene or mixtures thereof because the material has too much melt flow. The measurements were made in the following modification:

The melt was extruded through a circular die mounted on a single screw extruder. The nozzle parameters were 2.0 mm in diameter and length to diameter ratio of 3.5. The melt temperature was 190 ° C and the output was 750 g / hour. The leaking string was photographed along with the scale, and the string diameter was read on a negative magnified tenfold at a distance of (real) mm from the outlet. As in CSN 643010, the result is expressed as the ratio of diameter change after extrusion i (PZ) and calculated as follows:

string diameter in mm

PZ = nozzle diameter in mm

The parts shown in the examples are by weight. Parts of stabilizers and processing additives are given relative to polypropylene (polypropylene = 100 parts), the proportions by weight of low-density polyethylene, peroxide and diluent medium are based on the whole polymer part (polypropylene + polyethylene = 100 parts).

For comparison, the procedure according to MS. Certificate No. 210738 (Example 1).

Example 1

100 parts of polypropylene powder with a flow index = 3.7 g / 10 min were placed in a fluid mixer. After starting the stirrer, 0.15 parts of a phenolic stabilizer (2,6-di-tert-butyl-4-methylphenol), 0.2 parts of a phosphite stabilizer of tris- (1'-phenyl-4-ethylphenyl) -phosphoric acid ester, 1 part of secondary sulfur antioxidant (distearyl thiodipropionate) and 0.12 parts of 2,5-dimethyl-2,6- (di-tert-butylperoxy) hexane peroxide.

The mixture was stirred at 25 ° C for 45 minutes. Then 20 parts of low density polyethylene powder with a flow index = 20 g / 10 min were added. The mixture was stirred at the same temperature for 30 minutes. The resulting powder mixture was fed into a twin-screw extruder with a screw diameter of 53 mm and a ratio of length to screw diameter = 29, a kneading zone at a distance of 14 diameters from the hopper.

In four adjustable bands the following temperatures (from the hopper) were: 215, 230, 215 and 165. The extruder head temperature was 200 ° C. The screw speed was 80 rpm. The resulting polymer blend had a flow index = 33 g / 10 min. and PZ = 1.35 ·

Example 2

30 parts of polypropylene granulate with a flow index = 10 g / 10 min were placed in a cone mixer. (stabilization of 0.15 parts of 2,6-di-tert-butyl-4-methyl phenol and additive with 0.1 part of calcium stearate) and 20 parts of low density polyethylene granulate with a flow index of 20 g / 10 min (stabilization of 0.05 parts of 2.6 diter-butyl) -4-methyl phenol and a density of 0.917 g / cmb The raw materials were mixed for 30 minutes at 22 DEG C. Peroxide (2,5-dimethyl-2,5 (tert-butylperoxy) hexane, diluted 0) was added dropwise to the granulate mixture with stirring. 5 parts of a high boiling petroleum distillate (white light oil) with a peroxide of 0.04 parts The polymer-oil-peroxide system was blended for an additional 30 minutes before being fed into a twin screw extruder as used in Example 1, but of these conditions:

temperature 190, 195, 200, 200 ° C, head 200 ° C, speed 60 rpm.

The resulting polymer blend had a flow index = 23 and a PZ = 1.65.

Example 1 and d 3

The procedure was as in Example 2, except that the spent polypropylene granulate had a flow index of 17 g / 10 minutes and was stabilized with 0.1 part of 2,6 di-tert-butyl-4-methyl phenol, 0.1 part tris Phosphoric acid (1'-phenyl-4-ethyl-phenyl) ester,

0.1 part dlstearyl thiodipropionate and additivated 0.1 part calcium stearate.

The resulting polymer blend had a flow index = 32 and a PZ = 1.51.

Example 4

The procedure was as described in Example 2, but with the difference that the polypropylene granulate used had a flow index = 30 g / 10 minutes and a peroxide concentration of 0.00 parts.

The resulting polymer blend had a flow index = 33 and a PZ = 1.53.

Example 5

The procedure was as described in Example 2 except that the polypropylene granulate used had a flow index = 3.2 g / 10 minutes and a peroxide concentration of 0.04 parts.

The resulting polymer blend had a small Flow Index = 16 g / 10 minutes and a PZ = 1.71.

Example 6

The procedure was as in Example 2, except that the polypropylene granulate had a flow index = 25 g / 10 minutes and a low density polyethylene had a density of 0.920 g / cm 2 and a flow index of 2 g / 10 minutes. The peroxide concentration was 0.03 parts.

The resulting polymer blend had a flow index = 29 g / 10 minutes and a PZ = 1.70.

Example 7

The procedure was as described in Example 2, except that the low density polyethylene granulate used had a flow index = 70 g / 10 minutes and a density of 0.917 g / c. The peroxide concentration was 0.03 parts.

The resulting polymer blend had a flow index = 37 g / 10 minutes and a PZ = 1.56.

Example

The procedure was as described in Example 2, except that 65 parts of polypropylene granulate and 35 parts of low density polyethylene granules were used. The peroxide concentration was 0.03 parts.

The resulting polymer blend had a flow index = 33 g / 10 minutes and a PZ = 1.78.

Example 9

The procedure was as described in Example 8, except that 90 parts of polypropylene granulate and 10 parts of low density polyethylene granules were used.

The resulting polymer blend had a flow index = 3.5 g / 10 minutes and a PZ = 1.38.

Example 10

The procedure was as in Example 8, except that 5 parts of a low density polyethylene granulate with a flow index of 7 g / 10 minutes and a density of 0.919 g / c and 15 parts of a low density polyethylene granulate with a flow index of 20 g / 10 were used. 10 minutes and density 0.917 g / cn \

The resulting polymer blend had a flow index = 32 and a PZ = 1.54.

Example 11

The procedure was as in Example 6, except that the low density polyethylene granulate had a flow index = 20 and a density of 0.917 g / c and the oil concentration was 0.1 parts.

The resulting polymer blend had a tic index = 34 g / 10 minutes and a PZ = 1.52.

Example 12

The procedure was as described in Example 11, except that the oil concentration was 2 parts.

The resulting polymer blend had a flow index = 34 g / 10 minutes and a PZ = 1.50.

Example 13

The procedure was as described in Example 12, but with the difference that the oil concentration was 0.5 parts.

The resulting polymar blend had a low flow index = 34 g / 10 minutes and a PZ = 1.52.

Example 14

The procedure was as in Example 13, but with the difference that the temperatures set in the extruder bands were 150, 200, 260 and 300 ° C, the head temperature 300 ° C.

The resulting polymer blend had a flow index = ^38 g / 10 minutes and a PZ = 1.46,

Example 15 /

The procedure was as in Example 13, except that polypropylene oil (an oligomeric product of propylene polymerization) was used to dilute the peroxide.

The resulting polymer blend had a flow index = 34 g / 10 minutes and a PZ = 1.51.

Claims (1)

Process for producing a blend of polypropylene and low density polyethylene for extrusion application by melting and kneading the blend in the presence of organic peroxides, phenolic stabilizers or mixtures thereof with phosphite or sulfur. stabilizers and processing aids, characterized in that 65 to 90% by weight of polypropylene having a flow index of 3 to 30 g / 10 minutes granulated with stabilizers and 10 to 35% by weight of granulated low density polyethylene and a flow index of 2 to 70 g / 10 minutes are melted; knead at 190 to 300 ° C with 0.001 to 2% by weight of organic peroxides dissolved in 0.1 to 2% by weight of aliphatic hydrocarbons characterized by a kinematic viscosity of 30 to 500 mm ² / s.