DE1694651A1 - Process for the production of shaped, porous bodies from expanded polystyrene - Google Patents

Description

The invention relates to a method for producing porous, shaped bodies from expanded polystyrene, ie polystyrene foam, on extruders of a type customary for this purpose, the polystyrene containing one or more nucleating agents ^{11 in} addition to customary blowing agents.

Bs is known for the production of thin sheets of polystyrene foam to use a starting material, which consists of an expandable styrene polymer, which in homogeneous *

Dispersion contains a propellant in amounts between 1 and 15 percent by weight, xrelches usually consists of a polystyrene-insoluble liquid or gaseous hydrocarbon or a polystyrene-soluble or insoluble halogenated hydrocarbon. Such blowing agents generally have a boiling point below the softening point of polystyrene.

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The thin sheets of polystyrene foam obtained in this way are however, not homogeneous because of the stresses involved in the puffing occur during extrusion. During this manufacturing phase, another disadvantage is also noticeable in the conversion of the blowing agent, which is originally dispersed in the polymer, into a gas, relatively large bubbles form, which in Extrusion direction are extended and give the material a high rigidity and a low isotropy.

In order to avoid these disadvantages, it has already been proposed so-called "nucleating agents", these are substances that support the propellant and promote the formation of micro-gas bubbles, fe to use. The microbubbles formed in this way remain in homogeneously incorporated in the polymer and improve its properties, i.e. they cause a lack of tension, an extreme low specific weight, high flexibility and high elasticity.

The best nucleating agents known to date include SiIi zium dioxide and silicates, boric acid and organic acids such as citric acid in combination with substances that have the ability to through Reaction with the first-mentioned substances to release carbon dioxide.

However, these nucleating agents have the disadvantage that they cannot be used to set or regulate the specific weight of the foamed product. The addition of increasing amounts of citric acid W (from 0.5 to 1.5 percent by weight) together with corresponding amounts of NaHCO2 does not, for example, lead to a reduction in the specific gravity of the missed material, as would have to be assumed, but rather - im On the contrary - in some cases to an increase in the same. As a result, it is very difficult to obtain a foamed material with a predetermined specific gravity when foaming. Materials a wedge-forming agent of the type known up to now is added «

The invention makes it an object to address the disadvantages of the previously known Procedure to turn off and porous, molded body made of polystyrene with excellent properties.

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The invention relates to a process for the production of porous, molded bodies made of polystyrene foam, which is characterized is to extrude a foamable polystyrene in the presence of a new class of nucleating agents which are organic Polymers and / or copolymers of unsaturated monomers which have one or more ^ free ^ carboxyl groups (-CGOH ^ groups) or Acid anhyaride groups (-d-0-O groups).

Surprisingly, it has been found that when using the nucleating agents According to the invention, foamed products can be obtained which have specific weights in a predetermined manner Have area, whereby a precise control of the properties of the end product is made possible.

A preferred group of nucleating agents according to the invention comprises polymers of maleic anhydride, acrylic acid, fumaric acid, Itaconic acid, citraconic acid and other substances and mixed polymers of substances with an acidic character of the type mentioned and copolymers of the substances mentioned with aliphatic vinyl esters such as Vinyl acetate, vinyl propionate, alkyl acrylate and methacrylates, etc.

The following products have proven to be particularly suitable for the purposes of the present invention: Copolymers of acrylic and / or methacrylic acid with 2-ethylhexyl acrylate * and / or methacrylate, which 5 to 100 percent by weight of chemically bonded acrylic and / or Contain methacrylic acid; Copolymers of maleic anhydride with vinyl acetate containing 5 to 100 percent by weight maleic anhydride contain, as well as products that result from partial salt formation on the polymers of methacrylic and / or acrylic acid, whereby the degree of salt formation is between 0 and 95 #.

Will the salt formation with a weak base such as ammonia or with weak and / or volatile organic bases carried out so the level of salt formation can even reach $ 100.

The nucleating agents according to the invention can be used alone or as well be used in suitable mixtures with one another, the ΐ. Quantities in individual cases on the type of substances used and; ^ of the acidic properties of the polymeric substances that act as germs

* in the original Italian text: etilesil acrilato 10 98 29/1743

mm Δ. wm

educational resources are used, depend.

Particularly favorable results are obtained if the nucleation with tel in amounts of 0.1 to 10 parts by weight, based on 100 parts by weight of polymer.

Although the nucleating agents according to the invention have their full effect when used alone, it can be beneficial to use them in a mixture with substances that react with them Develop carbon dioxide, i.e. with substances such as alkali carbonates or bicarbonates or ammonium carbonates or bicarbonates; these substances are used in amounts slightly greater than that stoichiometric with respect to the acidic hydrogen atoms of the polymer Substance calculated quantities.

A particularly suitable means of releasing carbon dioxide is according to the invention sodium bicarbonate.

The polymeric compounds used as nucleating agents and the substances from which CO ₂ can be released can be added to the foamable polystyrene either simultaneously or in succession, either before or during the extrusion.

In either case, it is beneficial to premix the polymeric material with the nucleating agent and the substance from which CO _{2 is} released before the mixture is introduced into the extruder.

The porous, molded polystyrene foam body made according to the invention are produced, have a particularly low specific weight and are characterized by a homogeneous distribution of cells, all of which are very small in size, and have a practically constant diameter, from what the overall result is that the foamed material has high flexibility and high elasticity.

In the context of the invention, the expression polystyrene homopolymers des styrenes and copolymers of styrene with other polymerizable monomers, the copolymers at least

1 0 U K / Q / 1 7 I ₁ ι

chemically bound 50 percent by weight styrene or / derivatives thereof contain. Suitable Substances are, for example, copolymers of styrene and / or the ring-substituted and / or vinyl group-substituted derivatives of styrene with various monomers such as esters of acrylic and / or methacrylic acid, acrylonitrile, methacrylonitrile, divinic benzene, vinyl pyridine inter alia as well as graft polymers of styrene or mixtures of monomers containing a high percentage of styrene on synthetic and / or natural. Rubber and finally mixtures of the aforementioned materials.

In the context of the invention, the expression "foamable polystyrene" is understood to mean a polymer material of the type mentioned above which, in homogeneous dispersion, contains one or more blowing agents in amounts μ of 2 to 20 parts by weight, based on 100 parts by weight of polymer material.

The blowing agent incorporated into the polymeric material in any known manner can be introduced (i.e. during or after the polymerization), can consist of a liquid or a gas.

In the case of liquids, it is advantageous to use hydrocarbons or halo-substituted hydrocarbons, alone or in mixture with one another, whose boiling point at Atmosphärendruok between 20 and 100 ⁰ G. These substances are generally non-solvents or only swelling agents for the polymer material.

In the case of gases it is advantageous to use hydrocarbons such as propane or butane or chlorofluorocarbons that differ from methane or To derive ethane, to use; only of these connections have the Ability to dissolve the polymer material or to dissolve itself in the polymer material.

The propellant used is preferably pentane or petroleum ether with a boiling range from 30 to 60OQ.

The expression "extruder of conventional design" is used within the scope of the invention understood any extruder that is usually used for extrusion

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dation of polymer materials made of styrene, vinyl chloride, vinylidene chloride, Ethylene, propylene, acrylonitrile, etc. can be used.

The invention is explained in more detail using the following example.

example

The specific weights (in kg / j & ir at 25 ⁰ G) of foamed polystyrene are compiled in the following table; the foamed Pc lystyrol was prepared from 100 parts of foamable polystyrene em in the form of globules mm with a diameter between 0.5 and 1.5, the $ 5 petroleum ether (b.p. 30-51 ⁰ C) were obtained by extruding at 140 ⁰ C. The polystyrene beads were mixed with the following substances:

Citric acid (tests 1, 2, 3) (comparison tests) Citric acid + NaHGO _{5 (tests 4, 5,} 6) "Potassium met ^ asilicate (tests 7, 8, 9)"

Mixed polymer of 2-ethylhexyl acrylate and A ¹ * (experiments 10, 11, 12)

Mixed polymer of 2-ethyl-

hexyl acrylate and acrylic acid + NaHCO ₅ (experiments 13,14,15)

In experiments 1 to 9, nucleating agents of known type were used; these tests were carried out for comparison; in the Runs 10-15 were nucleating agents according to the invention ™ used.

All experiments were carried out in an NMR-type laboratory extruder (National Rubber Machines - USA), which has a diameter of 2.54 cm, a length to diameter ratio of δ and a cross section of the head nozzle of 2 15 mm.

Versuohe 10 to 15 were carried out with a mixed polymer, which consists of 89 ropes of acrylic acid and 11 ropes of 2-ethylhexyl acrylate in chemical bond - existed.

From each of the polystyrene foams made with the materials mentioned several photographs were taken with the help of a HSCHERT MP

A * = aoryl acid 109829/1743

Microscope made in normal translucent light at 2Ox magnification on cross-sections with a thickness of 0.5mm,

β -

TABEL

Ingredients Yers. Vers. Vers. Vers. Yers. Yers. Yers. Yers. Yers. Vers. No. 1 No. 2 No. 3 No. 4 No. 5 No. 6 No. 7 No. 8 No. 9 No. 10

Polystyrene parts by weight 100 100 100 100 100 100 100 100 100 100 Citric acid ^M 0.5 1 1.5 0.5 1 1.5-Met) iasilicate ^M ------ o. 5 1 1.5 -

Mixed polymer of ⁿ 2-ethylhexyl acrylate and acrylic acid

NaHCO ₅ ^M

₅ specific gravity kg / ^ m ⁵ 78

Polystyrene parts by weight Citric ^{Acid M} Metjiasilikat "mixed polymer from

2-ethylhexyllaery-

lat and acrylic acid "

NaHCO ₅ -

specific weight kg / ^ m ⁵

- - . No. 1.5 - - 0 - O, . 1 - 1, - 1 - - No 1, 0.5 - 5 172 100 95 69 , 6 1.2 O, 84 8th - 1, - - 00 1, 125 65 Yers - 12th 71 78 3 106 76 103 107 - 66 • 1? Yers. No 5 Yers. No • H Yers. 100 55 100 1 I.
* \ - - 10

From the data in the table it can be seen that the known nucleating agents (Trials 4> 5,6,7,8 and 9) with an increase in their amount in one case (trials 4,516) an increase in specific gravity of the foamed product, while in the other case (tests 7,8,9) there is no effect.

In contrast, when using the nucleating agents according to FIG According to the invention, a decrease in specific gravity in increasing amounts (experiments 13, 14, 15). So it could be clearly shown that the known nucleating agents when added in amounts greater than 0.5 parts per 100 parts of polystyrene behave like a normal mineral charge and consequently lead to an increase in the specific gravity, ^ j (They then no longer act actively in the sense that a support u <| n regulation of the blowing agent takes place), while the polymeric nucleating agents show an opposite effect according to the invention, i.e. they act as true nucleating agents even at amounts above 0.5 parts and promote and regulate the blowing effect of the blowing agent in the sense that the use of larger amounts also leads to a decrease the specific weight is achieved.

The invention is illustrated by a series of photographs, from which the internal structure of the materials, which have been produced according to tests 1 to 15, emerges.

From these photographs one can get a clear impression of the " Size and uniformity of the cells that are inside the material formed during extrusion win. The following can be deduced from the photographs:

a) Experiments with citric acid alone

The presence of citric acid brings about an even distribution of the bubbles within the mass; this effect is enough but not enough to achieve a uniform three-dimensional structure (see experiments 1, 2, 3).

b) Experiments with citric acid and bloarbonate:

The distribution of the bubbles within the mass is more limited and more regular than in the previous case (experiments 4,5,6).

" ¹⁰ " 109329 / 174T

c) Experiments with metal silicate alone :

In this case the structure of the bubbles is more regular than in poly etyrene foam, which is made from a foamable product without nucleation medium has been produced; In any case, this is also evident here an inhomogeneity very similar to that found in products that with citric acid alone, was observed (see. Experiments 7,8,9).

d) Experiments with a copolymer of acrylic acid and ethylhexyl aorylate: ~ ~

In this case the structure appears very regular, the individual However, cells are quite large in size. However, in this case, even if it is high, the specific gravity increases M Adding increasing amounts of the nucleating agent (see experiments 10, 11, 12).

e) Experiments with a copolymer of acrylic acid mixed with

HaHQO ₃ :

The structure of the cells is regular as in case b), but the size of the cells as well as the specific weight increase in the present case Fall with the addition of increasing amounts of additives (see experiments 13, 14, 15).

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Claims (2)

Claims Contains 1. A process for producing porous molded bodies of polystyrene foam by extruding verschäumbarem polystyrene, the blowing agent of known type, in the presence of at least one nucleating agent, characterized in that the nucleating agent of organic polymers composed of unsaturated monomers, ₀ at least one acidic group of the formula -COOH or -COC-, and are used in amounts of 0.1 to 10 parts by weight per 100 parts by weight of polystyrene. 2. The method according to claim 1, characterized in that the Nucleating agents are used in a mixture with substances that are able to release carbon dioxide in situ For: Montecatini Edison S.p.A. Lawyer OQZt ⁰ I / 4T - <(i Blank page