CA1116799A - Expandible polystyrene particles and process for preparing same - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

The specification describes expandible polystyrene particles having improved characteristics and the a process for preparing same. In particular the present invention relates to expandible polystyrene particles, useful for producing moulded bodies, especially large blocks, having a uniform cellular structure and requiring a particularly short residence time in the mould.

Description

This invention relates to e~pandible polystyrcne particles haviny improved characteristics and to a process for preparing same. In particular the present invention relates to expandible polystyrene particles, useful for producing moulded bodies, especially large blocks, having a uniform cellular struct-ure and requiring a particularly short residence time in the mould.
As is known, shaped bodies made of expanded styrene polymers may be produced by moulding polymer particles containing gaseous or liquid expanding agents in closed but not gas-tight moulds at a temperature exceeding both the boiling point of the expanding agent and the softening point of the polymer.
According to a conventional method, the polymer particles containing the expanding agent are first heated (pre-expansion) in an open or closed vessel, until a pre-determined apparent density is reached. Then, after a suitable ageing period, the aged particles are further expanded by heating (moulding) in a pressure-resistant but not gas-ti~3ht mould. Such heating causes the particles to sinter to a body having the shape of the mould.
After moulding, the shaped body is allowed to cool in the mould for a time-period sufficient to avoid deformation of the shaped body when removed from the mould.
To reduce the residence time in the mould it has been suggested to incorporate into the styrene polymer small amounts of halogenated organic compounds.
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~ lowever, known compounds suitable for the purpose in practice exhi.bit several drawbacks. In fact they develop bad odours duriny the pre-expansion step or they do not permit the simultaneously attaining of other desirable characteristics, such as:
- shrinkage of the block thickness should not exceed 1%, - moisture content of the expandible particles should not exceed 0.3%, and _ a fine cell homogeneous s~ructure o~ the expanded block.
Thus it is an object of embodiments of this invention ~o prepare expandible polystyrene particles suitable for pro-ducing moulded bodies with a fine-cell homogeneous structure, having the above-cited shrinkage and moisture characteristics ~nd requiring a particularly short residence time in the mould.
The present invention provides expandible polystyrene particles comprising an expanding agent and an amount not exceed-ing 1~ by wei~ht of at least one organic compound oE general formula (I) or (II): -~

- R -A - ~ ~2 ~ A-R4 (I) ~X)m ~(X) f=~ m A-R5 (II) (X)n jr~

~ . . . . .

wherein ~ is -0- or -C00-;
whcn ~ is -0-. _ R2 and R3, which are the same or different from each other, are alkyl and/or phenyl radicals, optionally halogen substituted;
R5 is a non-halogenated alkyl radical having 4 to 18 carbon atoms or a fully 18 or partially halogenated alkyl radical having 9 to 18 carbon atoms; X is halogen or an optionally halogenated alkyl radical having 1 to 8 carbon atoms;
m is an integer from 0-4;
n is an integer from 0 to 5, and Rl and R4, which are the same or different from each other, are alkyl radicals, optionally halogenated, having 1 to 18 carbon atoms, with the exception that when R2 and R3 are alkyl radicals, ~ i5 bromine and m is 2, Rl and R~ are non-halogenated alkyl radicals having 1 to 18 carbon atoms, or fully or partially halogenated alkyl radicals having 9 to 18 carbon atoms;
when A is -C00-:
. .
Rl, R~ and R5, which are the same or difEerent from each o-ther, are optionally halogen-substituted alkyl radicals containing 1 to 18 carbon atoms; R2 and R3, which are the same or different from each other, are alkylor phenyl radicals, optionally halogen-substituted; X is halogen or an alkyl radical having 1 to 8 carbon atoms; _ is an integer fro~. 0 to 4, and _ is an integer from 0 to 5 ~ ' r/

~ ~ ~63 The expandible polystyrene particles can be obtained by polyme~izing styrene in the presence of at least one compound having the above general formula (I) or (II) and of a conventional e~panding agent.
To produce the expanded moulded bodies, the expandible particles are first pre-expanded, then aged and finally moulded in a pressure-resistant but not gas-tight mould.
The expandible polystyrene particles and expanded shaped bodies made therefrom, in particular blocks, simultaneously exhibit the following characteristics:
a) short residence time in the mould, generally less than 50% of the time required to cool blocks prepared from pre-expanded particles not containing the above-cited compounds of general formula (I) or (II);
-b) a shrinkage of the block thickness less than 1%;
c) total moisture content of the expandible particles lower than 0.3~ and pract:ically identical with that of particles prepared in I-he absence of an organic compound oE general formula (I) or (II);
d) fine-cell homogeneous struc-ture of the expanded block;
and e) complete absence of acrid odours during the pre-expansion step.
The compounds to be incorporated into the expandible polystyrene particles may be selected from amongst a wide class of products having the above-indicated formula (I) or (II).

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~ mon~ such compounds, those not containing halogen and wlth ~1~ R~ and R5 having more than 8 carbon atoms have heen particularly interesting from an industrial viewpoint.
The compound or compounds of general formula (I) and/or (II) are usually added to styrene or to a styrene or to a monomeric mixture before or during polymerization, optionally in admixture with the expanding agent.
~ lthough even small amounts of the above-mentioned compounds, such as 0.005% by weight in respect of the monomer, can influence the polymer properties. In practice however best results are found when amounts ranging from 0.05 to 0.2% by weight are used.
In this Specification and in the Claims, by "styrene polymer" or "polystyrene" we mean styrene homopolymers, as well as~copolymers oE styrene with other vinyl and/or vinylidene monomers, the copolymers containing at least 50~ by weight of chemically combined styrene.
~xamples of such co-monomers are alpha-methylstyrene, styrenes halogenated in the nucleus, acrylonitrile, metha-crylonitrile, esters of acrylic and/or methacrylic acids with alcohols containing 1 to 8 carbon atoms, and N-vinyl-compounds such as vinylcarbazole. The class of styrene copolymers include also copolymers containing besides styrene and, optionally the aforesaid vinyl and/or vinylidene monomers, small amounts of monomers containing two doublebonds, such as divinyl-benzene.

Besides the compounds having general formulae ~) and (II), in the polymerlzation process according to this invention, well-known expanding agents are generally added.
Particularly suited as expanding agent are aliphatic hydrocarbons, either alone or in suitable mutual admixtures, containing from 2 to 6 carbon atoms, such as propane, butane, n-pentane, iso-pentane, hexane, cyclohexane and the like, and halogenated derivatives of aliphatic hydrocarbons containing from l to 3 carbon atoms, such as chlorofluoro-derivatives of methane, of ethane and of ethylene.
- Besides the expanding agents, the styrene polymers according to this invention may contain other additives, such as flame-extinguishing agents, organic and inorganic fillers, dyes, antistatic agents, non-agglomerating agents to prevent the formation of crumbs during the pre-expansion, plasticizers and other similar compounds.
The steps of polymerization of styrene, preferably in an aqueous suspension, admixtur~s of the expanding agent, pre-expansion of the expandible par~icles thus obtained, agein~
and transformation of the pre-expanded and aged particles into shaped bodies, by moulding in closed moulds, are preferably carried out according to techniques well-known to those skilled in the Art and widely described, for example, .in "Rigid Plastic Foams" by T.N. Ferrigno, Reinhold Publishing Corp., New York, USA (1963).
The following Examples are given to better illustrate the present invention.

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~X~MPI.IS l to 13 Various pol~merization tests were carried out in aqueous suspensions of mixtures made up of:
- styrene monomer lO0 parts by weight - deionized water lO0 - polymerization initlator (mix-ture of tert. -butylperoxide and tert. -butylperben70ate) 0.2 _ acrylic acid/2-ethyl-hexyl-acrylate copolymer (ratio by weight = 89/ll) as suspending agent 0.
- NaCl 0.10 " " "
- compound having general form-ula (I) or (II) of the type and in the amount indicated in the Table.
Polymerization was carried out at temperatures ranging from 100C to 140C for a total period o 20 hours.
During the polymerization, 8 parts by weight of an expand-ing agent consisting of a mixture of n-pentane and iso-pentane were admixed to the aforesaid suspension.
After cooling to room temperature, filtering, washing with water and drying at 35-40C for 7 hours, the polymer was subjected to screening in order to obtain expandible poly-styrene particles having diameters between 0.9 and 1.6 mm.
Said particle~ contained about 6% by weight of expanding ; agent.
The expandible particles were admixed with a conventional non-agglomerating agent in an amount equal to 0.15% by weight.

r/ - 8 -~dmixillc3 w~s c~rried out in a S~C;~ screw-mixer, at room temperature, ~or about 10 minutes.
The expandible particles so treated were fed to a pre-ex-pander (Erlenbach Mod. K2), with a screw-inlet on the bot-tom and an outlet of the pre-expanded material from the top, in which they were pre-expanded by means of steam at 95-100C for about 5 minutes.
The pre-expanded particles were allowed to age in air, at room temperature, for approximately 24 hours.
The pre-expanded and aged particles were introduced into a Rauscher block-making press to fill a mould having the following dimensions: 100 x 100 x 50 cm. Moulding was effected by means of steam at 1 kg/cm2 gauge. Density, cooling time, thickness shrinkage and sintering degree were determined on the moulded block.
The values of such characteristics are ~iven in the following Table. "Cooling time" of the blocks means the time required to cause the pressure inside the block to fall to zero, at the conclusion oE the treatment with steam. Both shrinkage and sinterin~ degree of the blocks were determined ~ hours after moulding. The sintering degree was evaluated on a thin plate, obtained from the central par~ of the block by hot-slinging, and determined as the percentage of expanded particles which broke when the plate was broken. The cellular structure of the expanded beads, for all the samples, was homogeneous with fine cells.

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Accordin~ to the Ta})le, the following compounds were used:

a~ cH3-coo ~, Cl? r b ) CH 3-C 00 ~ C ~ OOC-CE~ 3 Br [~ Br c) 17 35 COO ~} C ~<~} C-C17H35 17 35C~ CH3 C17 35 [~) .

e) Cl7H33Br2-coo~3 CH3 OOC-C17E133Br2 18 37 COO~) - 12- .

Br CH3 Br ~r Br ~} C ~ -C~l2 I H I 2 h) 18 37 0~} C ~} 18 37 . . CH3 i ) C12H 2 3Br2-O _<~' CH~ 12 2 3 2 " CH
1) 18 37o~l ~ o_C18E137 ~J .
.. CIH3 m) 12 23 2 o ~ C ~} C12 23Br2 n) 18 37 ~

~rom thc Va1UeS recoIded in the Table it is apparerlt tha-~ the presel~ce of the or~anic co~pound havina general ~ormula (I) or (lI) in the ex~andib1e styrene polymers permitted the simultaneously obtaining of a series o~ desirable properties, s1lch as:
- low moisture content of the ex~andible particles,`
in any case of the same value as that of the particles not containing the pxoducts of the present invention;
_ total absence of odours during pre-expansion;
- short cooling -time of the bloc1~s;
- - shrinkage of the bloc~ thicknass lower than 1%;
- high sintering degree, and - fine-call homogeneolls structure.

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Claims (9)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. Expandible polystyrene particles comprising an expanding agent and an amount not exceeding 1% by weight of at least one organic compound of the general formula (I) or (II):

(I) (II) wherein A is -O- or -COO-;
when A is -O-, R2, and R3, which are the same or different from each other, are alkyl and/or phenyl radicals, optionally halogen-substituted;
R5 is a non-halogenated alkyl radical having 4 to 18 carbon atoms or a fully or partially halogenated alkyl radical having 9 to 18 carbon atoms;
X is halogen or an optionally halogenated alkyl radical having 1 to 8 carbon atoms;
m is an integer from 0 to 4;
n is an integer from 0 to 5; and R1 and R4, which are the same or different from each other, are alkyl radicals, optionally halogenated, having 1 to 18 carbon atoms, with the exception that when R2 and R3 are alkyl radicals, X is bromine and m is 2, R1 and R4 are non-halogenated alkyl radicals containing 1 to 18 carbon atoms, or fully or partially halogenated alkyl radicals having 9 to 18 carbon atoms;

when A is -C00-:

R1, R4 and R5, which are the same or different from each other, are optionally halogen-substituted alkyl radicals having l to 18 carbon atoms; R2 and R3, which are the same or different from each other, are alkyl or phenyl radicals, optionally halogen-substituted; X is halogen or an alkyl radical having 1 to 8 carbon atoms; m is an integer from 0 to 4, and n is an integer from 0 to 5.

2. Expandible polystyrene particles according to claim 1 containing from 0.05 to 0.2% by weight of at least one compound having the above general formula (I) or (II).

3. Expandible polystyrene particles according to claim 1, wherein the organic compound is a halogen-free compound of general formula (I) or (II) in which R1, R4 and R5 are alkyl radicals containing more than 8 carbon atoms.

4. Expandible polystyrene particles according to claim 1, 2 or 3, wherein the polystyrene is a copolymer of styrene and at least one other vinyl and/or vinylidene compound copolymerisable with styrene, the copolymer containing at least 50% by weight of copolymerised styrene.

5. A process for preparing expandible polystyrene particles as claimed in claim 1, wherein polymerization of styrene is carried out in the presence of an expanding agent and of an amount not exceeding 1% by weight with respect to the monomer of at least one organic compound of the general formula (I) or (II).

6. A process as claimed in claim 5, wherein the amount of compound having the above general formula (I) or (II) is from 0.05 to 0.2% by weight with respect to the monomer.

7. A process as claimed in claim 5 wherein the organic compound is a halogen-free compound having general formula (I) or (II) and in which R1, R4 and R5 are alkyl radicals containing more than 8 carbon atoms.

8. A process as claimed in claim 5, 6 or 7, wherein styrene is copoly-marized with at least one other vinyl and/or vinylidene compound copoly-merizable with styrene in such amounts, as to obtain a copolymer containing at least 50% by weight of copolymerized styrene.

9. Shaped bodies of expanded polystyrene obtained by moulding pre-expanded expandible particles as claimed in claim 1, 2 or 3 in a non-gas-tight pressure-resistant mould.