DD243702A1 - METHOD FOR THE EQUIVALENT DISTRIBUTION OF ELECTROPHOBER AUXILIARIES ON POLYOLEFING RANULATES - Google Patents

Abstract

For mixing of small amounts of electrophobic powder to schuppenfoermiger additives with polyolefin granules, the surface is provided as a result of storage and transport processes with a disturbing negative electrostatic charge, with a mixing cost of a total of 0.2 to 2.4 s / kg granules and temperatures of At least 20 K below the Vicatemperatur of the polyolefin is initially a low-melting adjuvant H, which is largely neutral compared with electrostatically charged surfaces, in concentrations of 0.001 to 0.09 wt .-% with the polyolefin granules in the mixer. The mixing process is carried out at temperatures close to the melting point of the excipient H. After a brief interruption of the mixing process, the electrophobic additive, optionally with further polyolefin granules, is mixed in a second mixing stage. The electrophobic additives are completely, uniformly and permanently fixed on the granule surface. Free dust or disturbing deposits in the mixing devices do not occur.

Description

Adjuvants in addition to other low-melting auxiliary components H, which are largely neutral to electrostatically charged surfaces due to their molecular structure, in polyolefin granules at temperatures which are at least 20 K below the Vicattemperatur of the polyolefin, in a drum mixer, in the invention with a total mixing cost of 0.2 to 2.4s / kg of granules, the polyolefin is mixed with an excipient H in a concentration of 0.001 to 0.09 wt .-% at a temperature of the granules in the range de, melting point of component H, the adjuvant H by interrupting the mixing process is fixed on the granule surface and the electrophobic excipient in concentrations of 0.01 to 1.0Gew .-% (based on the granules) at temperatures at least 5 K below the melting point of the component H, optionally with the addition of further granules, is mixed. Essential to the invention is that the excipient H is first fixed on the polyolefin granules without further additives in the above-mentioned manner. Of secondary importance is whether the entire granule surface is wetted completely with the excipient H. Based on the small required amount of this excipient, the uniform wetting of the granules with the excipient H in the drum mixer is not achievable. Sufficient for the process according to the invention is a Teiibenetzung. This is also confirmed by the fact that together with the electrophobic excipient further untreated polyolefin granules can be introduced into the mixture.

The decisive advantages of the method according to the invention are that the adjuvant H must be present only in relatively small amounts and that the mixing effort is so low that the polyolefin granules are kept in a temperature range in which a melting of the polyolefin is excluded even for limited proportions , An advantageous variant of the method is the use of special low-melting heat stabilizers, because at the same time a positive effect on the workability is achieved. Such modified polyolefins can be exposed during processing to higher thermal loads without thermo-oxidative damage. Octadecyl-S-ß.ö-di-tert-butyl ^ -hydroxiphenyO-propionate proved to be particularly suitable. For this substance, there is a favorable linkage of its chemical action during the polyolefin processing process and its melting point in connection with the required mixing temperature according to the invention. The melting point of 325 K for the octadecyi-S-O-di-tert-butyl-hydroxyphenyl-propionate requires granule temperatures of about 320 to 330K during the first part of the mixing. Such temperatures can be achieved, for example, for high-pressure polyethylene granules in a simple manner without additional temperature control when freshly granulated product from a synthesis plant is collected in batches and after a short, determined according to the ambient temperature intermediate storage is fed to the mixer.

A particularly preferred process variant provides for the low-melting adjuvant H to be used in an amount of from 20 to 35% by weight of the total amount of adjuvant.

Furthermore, it is advantageous to discharge the finished granule mixture into a correspondingly dimensioned metering funnel, which allows the continuous loading of a conveyor line.

embodiments

To carry out the experiments shown in the following table, a drum mixer with a volume of 20Oi was available. As a mixing tool was a dreiflüglige, propeller-like device that rotates at the end of a centrally mounted in the mixer drive shaft close to the container bottom

 High-pressure polyethylene granules were used as polyolefin

A mean particle size of 50mm ³ ,

A melt index of 0.21g / 10min,

A density of 0.921 g / cm ³ ,

- a Vicat temperature of 375 K and

- An electrostatic surface charge of -5.2 to -7.1 kV / cm used.

Table 1 lists the auxiliaries used.

Table 1 excipient Melting point K comment Octadecyl-3- (3,5-di-tert-butyl 325 flowable Overview of the used excipients butyl-4-hydroxyphenyl) - powder Ser. No. propionate I oligomeric 2,2,4-trimethyl- 395 dust 1,2-dihydroquinoline oligomeric 2,2,4-trimethyl- 395 shed Il 1,2-dihydroquinoline mitPulver- and dust 111 proportion of Poly (2,2,6,6-tetramethyl) 403 flowable DVDeridin ^ .i dicvO- powder IV

ethylenoxibernstein-Säureester

The mixer worked in batches according to the following scheme (see also Table 2):

1. filling the mixer simultaneously with granules and the excipient H,

2. mixing the components at a wall temperature of the mixer of 323 K,

3. interrupting the mixing process,

4. adding the electrophobic excipient or a further amount of granules together with the electrophobic excipient,

5. Mixing all components without external heat,

6. complete emptying of the mixer through a discharge flap with a rotating mixing tool into a collecting funnel,

7. Continue like 1.

The metering of the individual components was carried out by means of a volumetrically controlled measuring tube for the granules and by means of a metering screw applied to a bulk weigher for each of the excipients. By means of a suitable spatial arrangement of the dosing and mixing elements and an electronic control was guaranteed that the beds of excipients directly

associated Granulatstrom.bzw. completely into the mixer.

The experiments carried out according to the invention were trouble-free during the processing of 30 tons of polyethylene. Comparative Example 5 was stopped after 12t throughput, because the mixture produced due to an extremely high

unbound dust was not manageable.

During the execution of the experiments samples were taken after every 0.5 t, 11.10 t and 30 t polyethylene throughput.

Table 3 lists the electrostatic surface charge measurement results. These measurements were taken with

a Statimeter Il the company VEB Statron Fürstenwalde executed.

Table 2

Overview of the embodiments Lfd. 1st mixing stage

No dosing quantities

PE auxiliary

material

Temperature PE

Speed stirrer

mixing time

37.5 kg

15OgII 15OgIII

320

3 - 15OgIV not comparative examples according to the invention

4 deleted

5 deleted

6 deleted

322 322 323

Break after mixing stage s

1 75 kg 6OgI 75 kg 2nd mixing stage 6OgI dosing electro- 320 196 80 150 mixed 2 37.5 kg 6OgI Ser. 15OgIII PE phober 320 196 60 150 expenditure 3 75 kg 6OgI 75 kg No. 15OgII Auxiliary 320 196 80 150 Comparative examples according to the invention: 75 kg 15OgIII material 4 320 196 90 deleted s / kg 5 320 196 120 deleted 6 320 196 120 deleted Tempe rotary mixed Tempe ra .number Time ture door stirrer mixture PE K min ~ ¹ S K

322 1.07 321 1.07 1.33 323 1.07 1.2 1.6 1.6

Table 3

Surface charge of granule samples

example sampling surface charge kV / cm 1 after 11 + 6 / + 7 after 10 t + 6 / + 8 2 after 11 + 7 / + 6.5 after 10t 8 + / + 6 3 after 11 + 5.5 / + 6 after 10t + 5 / + 5 4 after 11 + 4.5 / + 5 after 10t + 5 / + 4 (Jl after 11 -1 / -1.5 after 10t ± / -1.5 6 nachi t -2 / ± 0 10h -1 / -1.R

To check the uniform distribution of the electrophobic excipient on the granules, the adjuvants No. II, III and IV were mixed with 3 wt .-% of their structure-adequate nitrosyl radical. This mixture was used as a stabilizer component in the experiments, about 2.5 kg each at the beginning and end of the experiment. After carrying out the stabilizer formation according to the above-mentioned procedure with stabilizer compositions according to Table 2 on the granulator surface granules were measured individually by ESR spectroscopy. From the concentration of the detected radicals an exact relative measure for the uniform distribution on the granules can be obtained. The spectra obtained is further characterized by the spin expression of the nitrosyl radicals (high local spin concentration). Thus, the spectrum represents the stabilizer adhering to the surface. For the present case of a uniform granule size can be determined directly by the measured concentration, the amount of stabilizer and thus its distribution. The results are shown in Table 4.

Table 4

Representation of the relative measure for the distribution of the electrophobic excipients No. II, I Example Sampling Number of average values

Ifd. No measured deviation

Grains arbitrary

I or IV on the granule surface smallest largest

Value value

units

1 after 0.5 t 8th 18.27 ± 2.16 13.71 20.81 after 11 8th 17.91 ± 2.31 13,90 20.13 after 30 t 16 18.46 ± 2.47 14.04 21.15 2 after 11 8th 17.57 ± 2.52 13.06 20.76 after 30t 8th 17.39 ± 2.19 13.42 20.81 3 after 0.5t 8th 5.98 ± 0.59 4.81 6.81 after 11 8th 6.43 ± 0.67 5.67 7.12 after 30 t 16 6.64 , ± 0.64 5.73 7.30 4 after 11 8th 13.72 ± 4.92 10.26 24,80 after 30 t 8th 21.16 +7.68 11.52 28.16 5 after 11 4 14.29 - 9.79 27.84 6 after 11 4 12.81 - 9.33 23.18 after 30 t 4 16.22 - 10.12 29.77

The mixtures of Examples 1, 4 and 6 were fed directly to a twin-screw extruder and homogenized at melt temperatures of 513K. Upon the removal of homogenized granule samples, an uneven distribution of the excipient in Comparative Experiments 4 and 6 could already be seen by visual observation based on different discoloration, which is attributable to the content of trimethyldihydroquinoline. The product according to Example 1 was uniformly light yellow in color. Although the products of Examples 4 and 6 had a similar base color, but contained about 10 to 15% granules with intense yellow to brown color and much higher content of 2,2,4-trimethyl-1,2-dihydroquinoline (see Table 5 ). In experiment 6 it was conspicuous that after interruptions of the homogenization regularly dark gray to black discolored products were discharged from the extruder, which were detectable even after hours as punctiform impurities in the product stream.

Table 5

Content of oligomeric 2,2,4-trimethyl-1,2-dihydroquinoline (after melt homogenization)

example

Serial No. Content of excipient No. II or III (% by weight)

Mean of smallest largest

10 measurements value value

0.23

0.41

0.53 0.39 0.61

1 section 0.211 0.18 4 sample 0,149 0.09 intensely discolored ter product share 0,440 0.32 section 6 sample 0,137 0.08 intensely discolored ter product share 0.491 0.28

Claims (4)

Invention claim: 1. A method for uniformly distributing electrophobic excipients on polyolefin granules, wherein in addition to the electrophobic excipients used in small amounts further low-melting auxiliary components H, which are largely neutral to electrostatically charged surfaces due to their molecular structure, are used in a drum mixer at temperatures at least 20 K below the Vicatemperatur of the polyolefin, characterized in that the polyolefin with the excipient H in a concentration of 0.001 to 0.09 wt .-% at a temperature of. With a total mixing cost of 0.2 to 2.4s / kg granules Granulate is mixed in the range of the melting point of the excipient H, the excipient H is fixed by interrupting the mixing process on the granule surface and the electrophobic excipient in concentrations of 0.01 to 1.0Gew .-% (based on the granules) at temperatures of at least 5K below the melting point ktes of component H, optionally with the addition of further granules, is added. 2. The method according to item 1, characterized in that the excipient H is a processing stabilizer for preventing the thermo-oxidative degradation of the polyolefin. 3. The method according to item 2, characterized in that octadecyl-3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate is used as excipient H. 4. The method of item 1, 2 or 3, characterized in that the proportion of the excipient H is 20 to 35Gew .-% of the total amount of excipient in the polyolefin. Field of application of the invention The invention relates to the dry mixing of polyolefin granules with small amounts of several powdery to flaky auxiliaries whose individual molecules have electrophobic properties due to their structure. Characteristic of the known technical solutions For the equipment of polyolefins with a wide variety of excipients for the adjustment of certain application properties, a variety of process engineering solutions are used commercially. It is known, for example, the dry mixture of the components in the form of powder or semolina approximately the same grain size in agitators or pneumatic mixing devices. The disadvantage here is the risk of segregation phenomena during storage and transport operations, because by density differences and possibly also similar electrostatic charge of the individual components no sufficient adhesion of the Hüfsstoffteilchen is given to the Polyolefinteilchen. From our own investigations into the processing of powdered and flaky, electrophobic excipients it is known that dust-like excipient portions settle relatively permanently on the walls of pipelines and containers, preferably on the mixer inner wall. In this way it comes to unwanted concentration fluctuations in the final product. DD 207810 describes a way to neutralize the electrostatic surface charge of, for example, low density polyethylene, wherein the delivery lines and mixing units for the polyethylene are suitably coated. Preferred coating material is polytetrafluoroethylene. A disadvantage of this procedure is the considerable expense for the production of the coated equipment and the need for their regular renewal due to the rapid removal of the coatings at high granulate throughput. Another method for electrical pretreatment, especially of mineral and organic fillers for polyolefins, is given in DE 3017752. Even with this procedure, the disadvantage of additional equipment and energy expense before the actual mixing process of the polyolefin with the fillers. If the mixing of the components takes place in the melt state of the polyolefin, as described in principle in DE 2349756, must be provided in addition to very uniform additive dosage sufficient shear to ensure the uniform distribution of the excipients can safely. However, this simultaneously increases the risk of irreversible damage to the polymer. It is also known to plasticize only a part of the polymer composition for receiving the auxiliaries. Thus, according to DE 2756359 for introducing titanium dioxide and cadmium salts, the surface of the fine-grained plastic particles in the presence of the excipients in the melt state. After a mixing time then micro glass beads are added, which act as a release agent for the plasticized and optionally coagulated plastic particles. Such a procedure is not applicable for many applications of polyolefins because of the additional release agent required. In addition, the exact coordination of mixing time and surface temperature of the plastic particles is complicated and associated with the risk of production disruption due to premature sticking of the particles. Object of the invention The object of the invention is to distribute electrophobic adjuvants uniformly and strongly fixed on the surface of polyolefin granules during a dry mixing process with low mixing effort. Explanation of the essence of the invention The object of the invention was, as a prerequisite for a uniform final concentration of the excipients in the polyolefin during the dry mixing process by appropriate measures to make the adverse negative electrostatic surface charge of the polyolefin ineffective.
The solution of the problem is given by a method for uniformly distributing small amounts of electrophobic