CS240705B1 - Polystyrene based siren - Google Patents

Abstract

A polystyrene-based mixture with improved processing properties, harmless to health, consisting of 100 parts by weight of tough polystyrene prepared by block polymerization and 50 to 130 parts by weight of standard polystyrene. Block polystyrene is plasticized with a very high viscosity oil with a viscosity of 50 to 110 mPa. s in an amount of 0.5 to 5% by weight. Standard polystyrene is plasticized with a mineral oil with a viscosity of 5 to 30 mPa. s. The total amount of oil in the mixture is at most 5% by weight.

Description

The invention relates to a polystyrene-based mixture with improved processing properties, harmless to health and suitable for the production of moldings coming into contact with food. The mixture is a modification of the basic component of resilient polystyrene.

High-density polystyrenes are divided into extrusion and injection types according to processing technology. According to properties and processability, they are further divided into:

medium tough — very workable, high tough — well workable and super tough — with special properties.

[Characteristics and technical parameters are given in ČSN 64 3062. The mixture in question belongs to the category of medium-toughness polystyrenes. It is known that medium-toughness polystyrenes can be prepared directly by suspension graft polymerization or block prepolymerization of styrene in the presence of dissolved rubber with subsequent completion of polymerization by the suspension process.

A method of mixing high-impact polystyrene beads with standard polystyrene beads is also known.

In new block technologies, direct polymerization processes have also been developed for the production of medium-tough types, where tough polystyrene granules emerge at the end of the line.

These technologies use continuous block graft polymerization. This polymerization is only carried out to about 75% conversion and the remaining monomer is removed by degassing under high vacuum.

If a block process is mentioned further on, it is a continuously carried out block graft polymerization to incomplete conversion.

To compare polymerization processes, a proportional index was chosen, which indicates the ratio of the price costs of the compared technology to the technology of producing high-strength polystyrene by block polymerization with suspension finishing, for which an index of 100 was chosen as the basis.

If we compare, on the one hand, the process using suspension technology or block suspension with block processes, and on the other hand, the comparison is as follows:

Process

Raw materials suspensory block styrene ilOO 95 rubber Γ00 111 plasticizer ,100 145 chemicals ilOO 72 total 100 98 Energy electricity 1O0 80 steam 100 10 cooling water 100 60 fuel — 100 total 100 82

The comparison shows that block processes are advantageous primarily due to their low energy consumption, and the better utilization of raw materials is not negligible. However, the comparison table also shows that the continuous method of conducting block polymerization also brings about a worse utilization of rubber and plasticizer, which is given by the statistical distribution of rubber particles during continuous polymerization.

High demands are placed on the plasticizer in block polymerization, especially in terms of stability, viscosity and the presence of volatile components. Plasticizers used in suspension or block suspension polymerization are not suitable, as they would cause the vacuum pumps to become clogged in the degassing section of the block technology.

To achieve good workability of the medium-tough type, it is necessary to dose 5 to 6.5% by weight of mineral oil in block production, which is not economical and such a type does not comply with the health safety directive.

Also, processes working with mixing beads of tough standard polystyrene have numerous disadvantages, in addition to the already mentioned low polymerization performance, there are also demands on complex separation equipment for dust particles of the beads, relatively low performance of extrusion lines and higher energy requirements.

The above disadvantages are eliminated by using a mixture according to the invention characterized in that it consists of 100 parts by weight of tough polystyrene prepared by block polymerization containing from 0.5 to 5 percent by weight of paraffin oil with a viscosity of from 50 to 110 mPa. s at 40 ° C and 50 to 130 parts by weight of standard polystyrene containing 4 to 7% by weight of mineral oil with a viscosity of from 5 to 30 mPa. s at 40 ° C, the total amount of oil in the mixture being at most 5% by weight.

The mineral oil content is usually in the range of 0.5 to 5% by weight. Pellets prepared by the block method completely without plasticizer have deteriorated properties, which is related to the dispersion and shape of the rubber particles, their size and the method of anchoring in the homogeneous phase.

However, when preparing the modifying additive for standard polystyrene, it is not necessary to use such a viscous oil as for the block process, which makes it possible to comply with the hygiene guideline on the maximum permissible content of plasticizers of no more than 5% by weight while improving processability. The mixture may also contain dyes, pigments, antioxidants, internal and surface lubricants as is possible and common for polystyrene plastics.

100 parts by weight of tough polystyrene produced by block polymerization with a molecular weight of 22ΟΌΟΟ and a plasticizer content of 5% by weight were added to the mixer. The plasticizer was paraffin oil with a viscosity of 85 mPa. s at 40 °C. Standard polystyrene beads were added to the pallets in an amount of 82 parts by weight with the following properties:

.Molecular weight 150,000, melt index 35 with a plasticizer content of 4.5% by weight. The plasticizer was a white oil with a viscosity of 13 mPa. s at 40 ³ C. The mixture was mixed and granulated on a laboratory extruder with a screw diameter of 45 mm and a screw length of 28 D.

The flow properties of the material were evaluated on a high-pressure capillary rheometer. Viscosities at shear rates of 100 to 1000 ^-1 s, which are typical for the extrusion and injection molding process, were selected for evaluation. The rate of change of viscosity with increasing gradient is illustrated by the value of the flow exponent N.

Example

The procedure was carried out according to the invention. Do páT a b u 1 k a 1

Medium-toughness Medium-toughness polystyrene produced in block form according to the invention by suspension technology

Í60 °C 100 (Pa.sj 1000 (Pa.s)

N

180 °C 100 (Pa.s) 1000 (Pa.s)

N

200 °C 100 (Pa.s) 1000 (Pa.s)

N

1820

450

2.5

1020

210

3.2

610

140

2.8

620 360

2.9

930

180

3.5

570

120

3.1

220 °C 100 (Pa.s) 1000 (Pa.s)

N

410

110

2.3

360

2.7

Example 2

The procedure was carried out according to the invention. In a belt mixer, 100 parts by weight of rigid polystyrene block were mixed with 54 parts by weight of standard polystyrene according to example 1. The mixture was granulated on a laboratory _extruder . After granulation, the mixture was evaluated. The results are shown in Table 2.

Example 3

The procedure was as in Example 2 and the same raw materials were used as in Example 1, with the difference that 100 parts by weight of block polystyrene pellets were mixed with 122 parts by weight of standard polystyrene beads. The mixture was granulated and evaluated. The results are shown in Table 2.

Example 4

The procedure was carried out according to the invention. In a belt mixer, 100 parts by weight of pellets of block-type high-density polystyrene with a molecular weight of 260,000 containing 2% by weight of mineral oil with a viscosity of 85 mPa.s were mixed at 40°C with 100 parts by weight of standard polystyrene beads according to the previous examples. The mixture was granulated on a laboratory extruder. After granulation, the mixture was evaluated. The results are shown in Table 2.

Example 5

The procedure was as in Example 1, with the only difference that the oil used in the preparation of block polystyrene had a viscosity of 55 mPa.s at 40°C. The properties of the granulate produced are in Table 2.

Table 2- Example Melt flow index Impact resistance Vicat Heat Resistance number ČSN 64 0861 200 °C load 49 N g/lQ min ČSN 64 0612 J/cm ² ČSN 64 0521 method A °C il 14 8.5 65 2 11 8.5 85 3 16 4.5 83 '4 6 8.0 86 5 13 6.0 84

All samples meet the conditions of the General Hygiene Directive No. 49/1978 for classification, i.e. symbol N — for use.

Claims (1)

Polystyrene-based blend with improved processing properties, harmless, characterized in that it consists of 100 parts by weight of tough polystyrene prepared by block polymerization containing from 0.5 to 5% by weight of paraffin oil having a viscosity of from 50 to 50 VYNALEZU 110 mPa. at 40 and 50 to 130 parts by weight of standard polystyrene containing from 4 to 7% by weight of polystyrene; mineral oil having a viscosity of from 5 to 30 mPa. at 40 ° C, the total amount of oil in the mixture being at most 5% by weight.