SK286996B6 - Expandible polystyrene particles, their mixture , process for their preparation and shaped product prepared from them - Google Patents

Abstract

Expandible polystyrene particles are provided with a marking formed by at least one brightening agent that absorbs UV rays. This brightening agent is incorporated in rod-shaped, extrusion-blown granulate particles with an essentially uniform grain size. A method for producing polystyrene particles of this type provides that polystyrene is extruded and granulated together with at least one expanding agent and at least one brightening agent.

Description

Technical field

The invention relates to expandable polystyrene particles provided with a marking which is formed by UV-absorbing brightening agent incorporated into the particles, to a mixture of such particles and to a process for the production of such particles and polystyrene foam moldings made of such particles, respectively. mixtures.

BACKGROUND OF THE INVENTION

It is known that polystyrene particles which contain foaming agents can be expanded by heating the water vapor (prefoaming process) with a multiple increase in their volume, and can subsequently be processed by welding to arbitrarily shaped articles, such as blocks. Such molded products are used predominantly as insulating materials in the construction sector (for example, for building facades or refrigerated), as well as packaging materials.

Expandable polystyrene particles (EPS) are produced most often by suspension polymerization of styrene followed by impregnation with a blowing agent. This results in pearl particles of different sizes.

However, it is possible to produce expandable polystyrene particles by extrusion, whereby polystyrene with a suitable MFI (Melt Flow Index) is melted, impregnated with a propellant, cooled and passed through a perforated plate. The fibers which are formed are cooled as quickly as possible with a water bath in order to prevent foaming of the polystyrene. Subsequently, the cooled fibers are granulated in known manner into small cylindrical particles having a substantially uniform size. These particles can be processed in an analogous manner to those produced by suspension polymerization.

Polystyrene and copolymers of styrene with other compounds, such as α-methylstyrol, acrylonitrile, maleic anhydride, butadiene, divinylbenzole, can be used as the main constituent.

Suitable foaming agents are, under normal conditions, gaseous or liquid hydrocarbons having a boiling point below the softening point of the polymer. Typical of these compounds are propane, butane, pentane and hexane.

In addition, all conventional excipients such as nucleating agents, flame retardants, UV stabilizers, plasticizers, antioxidants and acid scavengers can be used. Surface treatment with pigments and coating materials is also possible to prevent agglomeration and static charge, as well as to reduce cooling time or to reduce water uptake.

Increasingly, expandable polystyrene granules having special properties, such as EPS with reduced water absorption, are coming to the market. This entails the risk that the individual types of polystyrene granules are interchanged at the place of use, so that an unsuitable product is used for the particular purpose desired. The individual products can be distinguished from each other in terms of their properties and chemical composition, but this can only be done by costly chemical analyzes.

It is known from EP 470 455 A that the antistatic suspension suspension polymerization products produced can be distinguished from those not equipped by coating them with a fluorescent dye which absorbs in the UV region. However, this does not allow for satisfactory type-specific labeling. As mentioned above, suspension polymerization results in different particle sizes, which are further processed into different types of articles, so that type-specific (i.e. particle-specific) labeling is only possible after screening by surface treatment. However, such a surface treatment loses its effect by subsequent surface treatment, in particular by dyeing. A further disadvantage of such surface marking is that in the steam pre-foaming process an undefined large portion of the marking substance is washed off the surface of the particles.

It is known from GB 1 059 777 A that labeling is incorporated into polystyrene particles produced by suspension polymerization. Also for this are disadvantages related to different particle sizes.

SUMMARY OF THE INVENTION

SUMMARY OF THE INVENTION It is an object of the invention to avoid these disadvantages and to improve the expandable polystyrene particles of the aforementioned type in such a way that type-specific marking is achieved which is resistant to the subsequent surface treatment of the particles and / or particles. claims arising from processing into final products. The invention solves this problem by providing the polystyrene particles as rod-shaped, extrusion-gassed granulate particles with a substantially uniform particle size containing at least one such brightener. The polystyrene particle material treated in this way is labeled specifically for each type since the polystyrene particles obtained are at least substantially the same size as a result of the extrusion and granulation process. The coloring of the interior of the individual particles with the marking material has the consequence that the surface of the particles after the granulation process can be processed in any way, even by coloring the material, without affecting the marking. Even the surface coloring of the granulate particles does not alter the marking properties, since the surface coloring does not affect the interior of the particles. The marking inside the particle can be easily visualized by cutting it. While in daylight the optical properties of the polystyrene particles thus formed remain unchanged, when the UV light particles (wavelength 270 to 430 nm) are observed, the marking will be immediately visible, so that a material labeled in some way can easily be distinguished from other materials or materials. other way of marking materials. The screening of the extruded particles on the screen is unnecessary, unlike the particles produced by suspension polymerization.

According to a preferred embodiment of the invention, the brightener is located within the granulate particles uniformly distributed to ensure, on the one hand, the same marking quality for all the granulate particles, on the other hand, so that the degree of marking is independent of random factors.

Suitable marking materials are optical brighteners (fluorescent dyes that absorb in the UV range) such as Uvitex FP (4,4'-bis (2-methoxystyryl) -1,1'-biphenyl) or Uvitex OB (2,5-thiophenediylbis) (5-tert-butyl-1,3-benzoxazole)), both from Ciba Geigy GmbH. For commercial reasons, it is sufficient that the concentration of the brightener in the colored granulate is kept small, typically between 1 and 100 ppm.

If the polystyrene particles obtained by extrusion contain more than one incorporated brightener, then the brighteners may be adapted to emit differently colored light from each other under UV irradiation. This will greatly expand the labeling possibilities, since mixed colors or color combinations can now also be achieved for labeling, for example by using yellow and blue fluorescent brighteners, green marking, using red and yellow fluorescent brighteners, orange staining, etc. Examples of such fluorescent primers in various colors are Luminux Gelb CD 305, Luminux Blau CD 311, Luminux Griin CD 321 from Honeywell.

The size of the granulate particles depends on the number and diameter of the extrusion nozzles and the way the granulate particles are drawn and cut from the fibers that exit the nozzles. The granular particles generally have a diameter of 0.3 to 2 mm, preferably 0.5 to 1.2 mm, and a length of 1 to 4 mm, preferably 1.3 to 2.5 mm.

The pre-dyed granulate material having a substantially uniform particle size can itself be used as a raw material for the production of any molded foamed articles or the like. However, for commercial reasons, in view of the cost of the marking material within the scope of the present invention, it is preferable to make a mixture of EPS particles, with only a certain proportion of the particles incorporating a incorporated brightener that absorbs UV radiation. The type-specific marking does not come out of vain when the size of the labeled particles essentially coincides with the size of the unlabeled particles. The mixing ratio can be arbitrarily chosen from the technical point of view, but it has proven to be advantageous when the labeled EPS material is added in a percentage range between 0.5 and 50 wt. %, preferably 1 to 15 wt. %. This provides sufficient labeling as well as a commercially acceptable solution.

The mixture of EPS particles may comprise extrusion-gassed granulate particles, but it is also possible to mix the EPS-labeled granules of the present invention with the particles obtained by suspension polymerization, provided that the particle size range that is specific to the particle size is maintained. appropriate material type.

As with the polystyrene particles per se, brighteners emitting in different colors can be advantageously used in the mixture, if the mixture comprises at least two portions of particles containing different brighteners emitting different colors. In this way, it is possible to mark the mixture, respectively. produced by the product, which during UV irradiation fluoresces in mixed colors, respectively. color combinations.

The labeled particles of the mixture, as well as the unlabelled particles, may be surface-colored because, as already mentioned, the marking will not suffer under this.

The composition may also contain conventional additives, for example, aliphatic, cycloaliphatic and aromatic bromine compounds, which act as flame retardants, such as hexabromocyclododecane. Furthermore, the effect of fire protection agents can be improved by the addition of synergists. Typical examples of such fire protection synergists are dicumyl and dicumyl peroxide.

The process according to the invention for the production of expandable polystyrene particles of the kind to which the invention relates is characterized in that the polystyrene is extruded and granulated together with at least one propellant and at least one brightener. If appropriate, further propellants and / or additives, for example flame retardants, can be fed and co-extruded during extrusion.

In order to ensure a uniform distribution of the fluorescent substance in the particles, which is present only in very small amounts, it is expedient to extrude the masterbatch with a brightener content of 0.25 to 1 wt. % together with the remaining polystyrene material. An alternative to this is that the brightener is applied to the small polystyrene particles, in particular the polystyrene granulate, by means of a mixing unit before being fed to the extruder.

Such type-specific EPS mixtures can be processed into polystyrene foam moldings of any shape and density, in particular for insulation purposes in the construction sector, for example for building facades, refrigeration, but also as packaging materials.

DETAILED DESCRIPTION OF THE INVENTION

Example 1

Polystyrene with a molecular weight of about 220,000 was melted in an extruder along with 1.3% HBCD, 0.2% dicumyl and 1% 1% masterbatch (1 wt% Uvitex FP, 99 wt% polystyrene), added 6.3% pentane, stirred, cooled to about 120 ° C and passed through an orifice nozzle. The resulting fibers with a diameter of about 0.8 mm were cooled below the freezing point in the water bath and subsequently granulated by means of an extruder granulator (granulate length 1.5 mm).

kg of this granulate was mixed with 475 kg of polymerized EPS having a bead diameter of from 0.6 to 1.1 mm using a drum mixer and coated with coating materials customary for this purpose to avoid sticking during the foaming process.

The resulting mixture was then pre-foamed in a discontinuous prefoamer to a density of 30 g / l. After intermediate storage for 24 h, blocks of 600 x 600 x190 mm were produced.

The formed moldings could not be distinguished in daylight from unlabeled EPS moldings. When irradiated with a UV lamp (wavelength 366 nm), the labeled foam particles could be clearly identified both surfacely and in cross-section by blue fluorescence.

The admixture of the labeled EPS granulate caused no change in the processing or end product properties.

Example 2

The procedure was as in Example 1, but the finished mixture of EPS particles was surface-colored. To this end, 500 kg of EPS mixture was mixed with 0.5 kg of green dye (Hein Farbpulver; Hein-Farben) and subsequently fixed with 3.5 liters of isopropanol.

After the foaming process foam moldings having an evenly green surface were also produced. By cutting the shaped articles, the UV-light marking could be made easily visible.

Claims (17)

PATENT CLAIMS CLAIMS 1. Expandable polystyrene particles which are labeled as UV absorbing brightening agents incorporated into the particles, characterized in that the polystyrene particles are rod-shaped, extrusion-gassed granular particles having a substantially uniform particle size comprising at least one such particle size. incorporated brightener. Polystyrene particles according to claim 1, characterized in that each brightening agent is uniformly distributed within the granular particles. Polystyrene particles according to claim 1 or 2, characterized in that the proportion of brightening agents is 1 to 100 ppm. Polystyrene particles according to any one of claims 1 to 3, characterized in that the granular particles have a diameter of 0.3 to 2 mm, preferably 0.5 to 1.2 mm, and a length of 1 to 4 mm, preferably 1.3 to 2.5 mm. Polystyrene particles according to any one of claims 1 to 4, characterized in that they comprise more than one incorporated brightener, the brighteners emitting differently colored light from each other under UV irradiation. 6. An EPS particle mixture, characterized in that only a certain proportion of the particles comprises at least one brightener which absorbs UV rays. Composition according to claim 6, characterized in that the proportion of labeled particles is 0.5 to 50% by weight. %, preferably 1 to 15 wt. %. A composition according to claim 6 or 7, characterized in that it comprises labeled, extruded-gasified granulate particles and suspension-polymerized non-labeled particles. Composition according to claim 6, 7 or 8, characterized in that it comprises at least two proportions of particles which contain different brighteners which emit different colors. Composition according to any one of claims 6 to 9, characterized in that the particles of the composition are surface-colored. Composition according to any one of claims 6 to 10, characterized in that it contains additives, in particular flame retardants, for example hexabromocyclododecane. A process for producing expandable polystyrene particles according to any one of claims 1 to 5, characterized in that the polystyrene is extruded and granulated together with at least one propellant and at least one brightener. Method according to claim 12, characterized in that further propellants and / or additives, for example flame retardants, are fed and co-extruded during extrusion. Method according to claim 12 or 13, characterized in that the masterbatch is extruded with a brightening agent content of from 0.25 to 1 wt. % together with the remaining polystyrene. Method according to any one of claims 12 to 14, characterized in that each brightener is applied to the polystyrene in particulate form, in particular the granulate, by means of a mixing unit before being fed to the extruder. 16. A polystyrene foam molded article of mutually welded EPS particles, characterized in that a certain proportion of the particles comprises at least one brightener that absorbs UV rays. Use of a polystyrene foam molded article according to claim 16 for insulation purposes in the construction industry.