JP2002088187A - Method for producing colored expandable styrene polymer bead - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a homogeneously colored bead- shaped expandable styrene polymer (EPS beads) in a simple method. SOLUTION: Colored expandable styrene polymer beads are obtained by polymerizing styrene in an aqueous suspension in the presence of a coloring pigment or a dye, if needed, with <=20 wt.% of a comonomer (an ethylenically unsaturated comonomer, especially an alkylstyrene, divinylbenzene, acrylonitrile or α-methylstyrene) and adding a foaming agent before, during or after the polymerization.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001] The present invention relates to a method for producing an evenly colored, expandable styrene polymer in the form of beads (EPS beads).

[0002] Polystyrene molded foams have been known for a long time and have been successful in many fields. This type of foam is produced by impregnating a polystyrene bead with a foaming agent to cause foaming, and then welding the obtained foamed beads to obtain a molded product.

[0003] In some applications, colored foams are required, for example, for aesthetic reasons or for marking molded articles. These have hitherto been produced by coloring the surface of EPS or foam beads or by adding a coloring pigment together with a blowing agent to a polystyrene melt in an extruder. Organic dyes are not commonly used in this method because of their poor solubility in molten polystyrene and the unsatisfactory coloring effect achieved.

It is an object of the present invention to produce, in a simple manner, evenly colored EPS beads.

[0005] We have found that this objective is to polymerize styrene in an aqueous suspension in the presence of a color pigment or dye.
It has been found that it is optionally carried out with up to 20% by weight of comonomer and is achieved by adding a blowing agent before, during or after the polymerization.

The invention further relates to beads wherein the styrene-soluble organic dye comprises from 0.1 to 15% by weight, preferably from 0.3 to 5% by weight, of the dye uniformly distributed in the styrene polymer. And a foamable styrene polymer in the form of

[0007] Patent application WO 97/45477 describes EPS beads containing carbon black. Carbon black is added here to reduce the thermal conductivity of the foams made therefrom. Aesthetic effects are not intended. Carbon black is not a coloring pigment for the purposes of the present invention, in particular, carbon black does not dissolve in styrene. When the suspension polymerization of styrene is performed in the presence of a dye that dissolves in styrene, there is a possibility that the surface effect may adversely affect the progress of the polymerization.

In the present invention, the term "expandable styrene polymer" means a styrene polymer containing a blowing agent.

The EPS beads according to the invention can be used as a polymer matrix, in particular up to 20% by weight, based on the weight of homopolymerized polystyrene or polymer, with ethylenically unsaturated comonomers, in particular alkylstyrene, divinylbenzene, acrylonitrile or α. -Including styrene copolymers with methylstyrene.

In the suspension polymerization of the present invention, a conventional auxiliary agent such as a peroxide initiator, a suspension stabilizer, a foaming agent, a chain transfer agent, a flame retardant, a foaming auxiliary agent, a nucleating agent, and a plasticizer is added. Can be. The blowing agent is 3 to 1 based on the styrene polymer.
An amount of 0% by weight is added. These can be added before, during or after the suspension polymerization. Suitable blowing agents are aliphatic hydrocarbons having 4 to 6 carbon atoms. Pentane is preferred. It is advantageous to use magnesium or calcium phosphate as inorganic pickling dispersants, for example suspension stabilizers.

For the solubility of the suspension, especially in the case of polymerization in the presence of color pigments, the polystyrene (or the corresponding styrene copolymer) in styrene (or a mixture of comonomer and styrene) becomes It has been found preferable to be present at the start. The starting material here is a polystyrene solution, preferably in a concentration of 0.5 to 30% by weight, especially 3 to 20% by weight, in styrene. The new polystyrene can now be dissolved in the monomer, but the production of expandable polystyrene uses the so-called surrounding parts, which have been sieved out as too large or too small beads during the separation of the bead distribution It is advantageous to do so. In practice, the surrounding part which is not suitable for this type of use has a diameter of more than 2.0 mm or less than 0.2 mm. Re-crushing of polystyrene and re-crushing of expanded polystyrene can also be performed. The suspension polymerization is carried out at a temperature of from 90 to 140 ° C. by a conventional method.

The dyes or color pigments are preferably added during the polymerization in an amount of 0.1 to 15% by weight, in particular 0.3 to 5% by weight. They are preferably hydrophobic, so that they are mainly present in the organic phase of the water / styrene two-phase system, preferably in the range of more than 95%. Dyes or colored pigments with amphiphilic properties are specially employed. These affect the formation of EPS beads during polymerization. Such surfactant effects should be taken into account in the overall control of the method. In this case, the amphiphilic dyes or color pigments are preferably not metered in during the polymerization, for example when the conversion is between 30 and 90%. Instead of the dyes and pigments mentioned above, it is in principle possible to use all dyes or pigments.

[0013] The styrene-soluble organic dye is advantageously dissolved in styrene or a blowing agent and added in this form to the polymerization batch. They are preferably soluble in styrene to a range above 0.1%, especially above 1%.

Suitable coloring pigments are usually inorganic or organic substances.

As a special feature, it is possible to use colored pigments whose color effect does not absorb light and instead causes interference. Such pigments are significant in having a color effect that depends on the viewing angle.

The color pigment is advantageously suspended in finely divided form in styrene or a blowing agent and added in this form to the polymerization batch.

The EPS beads obtained by polymerization are in the form of round beads having an average diameter of 0.2 to 2 mm. These are from 5 to 35 g / l, preferably from 8 to 25 g / l,
And especially polystyrene foams having a density of 10 to 15 g / l. For this, the foamable beads are foamed beforehand. This is generally done in a so-called prefoaming machine by heating the beads with steam.

The beads prefoamed by such a method are then welded to obtain a molded article. For this, the pre-expanded beads are introduced into a mold that is not hermetically closed and treated with steam. After cooling, the molding can be removed.

[Example] 50 g of thermoplastic blue (made by BASF Actchengezelshaft), 60 g
Of dicumyl peroxide and 20 g of dibenzoyl peroxide are stirred in 20 kg of styrene and dissolved during the process. This mixture is suspended in 20 l of demineralized water in a 50 l stirred reactor. The aqueous phase contains 70 g of sodium pyrophosphate and 13 g
Contains 0 g of magnesium sulfate. At 130 ° C.
Heat with stirring for at least 6 hours. Two hours after reaching 80 ° C., 3.5 g of emulsifier K30 (manufactured by Bayer AG)
Add. After a further 30 minutes, 1.5 kg of pentane are metered in. Finally, the suspension polymerizes and the polymerization is completed at 130 ° C. Cooling and separation of the aqueous phase yields uniformly colored beads with an average diameter of 0.7 mm. The beads can be foamed using steam. The obtained expandable beads are uniformly colored blue, and a foam molded article is obtained therefrom.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Roberto, Gardoni Germany, 67063, Ludwigshalfen, Leuschnerstrasse, 36F term (reference) 4F074 AA32 AG06 BA35 BA39 CA33 CA49 DA02

Claims (8)

[Claims] 1. The polymerization of styrene in an aqueous suspension in the presence of a color pigment or dye, optionally with up to 20% by weight of a comonomer, before, during or after the polymerization,
A method for producing uniformly colored expandable styrene polymer beads (EPS beads), comprising adding a blowing agent. 2. The polymerization is carried out in the presence of 0.1 to 15% by weight of a pigment or dye based on the styrene polymer.
The method described in. 3. The process according to claim 1, wherein the suspension polymerization is carried out in the presence of an organic dye which is soluble in styrene in a range above 0.1% by weight. 4. The method according to claim 1, wherein a solution of polystyrene in styrene is used in the suspension polymerization. 5. A concentration of 0.5 to 30% by weight, preferably 5% by weight.
5. The process according to claim 4, wherein a solution of polystyrene in styrene at a concentration of from about 20% by weight is used. 6. The method according to claim 1, wherein a hydrophobic pigment or dye is used. 7. An expandable styrene polymer in the form of beads, wherein the styrene-soluble organic dye contains 0.1 to 15% by mass of the dye uniformly distributed in the styrene polymer. 8. Use of an expandable styrene polymer in the form of beads according to claim 7 for the production of a foam having a density of from 5 to 35 g / l.