WO2005103136A2

WO2005103136A2 - Fire retarded styrene polymer compositions

Info

Publication number: WO2005103136A2
Application number: PCT/IL2005/000423
Authority: WO
Inventors: Grigory I. Titelman; Samuel Bron; Joseph Zilberman
Original assignee: Bromine Compounds Ltd.
Priority date: 2004-04-22
Filing date: 2005-04-21
Publication date: 2005-11-03
Also published as: IL161592A0; WO2005103136A3

Abstract

A fire-retarded polymer composition comprises heat expandable graphite (HEG), at least one phosphorous-containing fire retardant and at least one co-additive suitable to depress the migration of phosphorous-containing fire retardant on polymer surface, wherein the polymer component of said composition is selected from the group consisting of polystyrene polymer and/or copolymer.

Description

Fire Retarded Styrene Polymer Compositions

Field of the Invention

The present invention relates to a composition consisting of fire-retarded

polystyrene polymers and copolymers, having excellent fire retardancy,

significantly reduced smoke and corrosive gas emission on burning and

significantly suppressed migration of the fire retardant on the surface of

the polymer. In particular, the present invention relates to a halogen-free

and antimony-free, phosphorous-containing fire-retarded composition

comprising polystyrene polymers and copolymers. Polystyrene polymers

and copolymers include: polystyrene (PS), "high impact polystyrenes"

(HIPS), acrylonitrile butadiene/styrene (ABS) copolymers and

styrene/acrylonitrile (SAN) copolymers. .

Background of the Invention

It is desirable that polystyrene polymers and copolymers be flame-

retarded to prevent fire accident or fire spreading when used in various

applications, such as enclosures and internal parts of electric, electronic

and office automation apparatus, interior materials of vehicles, building

materials, etc. Many polystyrene polymer and copolymer materials for

such uses are even required to be fire-retarded by legislation. Known fire

retardant additives used in polystyrene polymer and copolymer materials

include halogen-containing fire retardants, phosphorous- or phosphorous/nitrogen-containing compounds. These additives, however,

have disadvantages.

The halogen-containing fire retardants, which impart a higher level of fire

retardancy (for example, UL-94 V-0, V-1 or V-2) at relatively small

amounts of additive, generate a large amount of soot or smoke upon

burning. Usually, polymer materials comprising halogen-containing fire

retardants require synergistic additives such as antimony oxide, which is

a toxic material. Furthermore, the halogen-containing fire retardants

may emit more or less acidic substances and antimony derivatives at the

time of fire, which may produce adverse effects on human health or

apparatus in the vicinity of a fire site.

The phosphorous- or phosphorous/nitrogen-containing fire retardants,

such as red phosphorous, ammonium polyphosphate [APP], melamine

phosphate or pyrophosphate are effective in rather high amounts, and

only in combinations with other additives such as carbonization agents,

blowing agents, etc. Furthermore, these fire retardants generate soot or

smoke on burning, which produce adverse effects on human health or

apparatus in the vicinity of a fire site.

Other phosphorous-containing fire retardants, such as aromatic phosphate

esters, are effective in relatively small amounts, but only in a few types of

styrene polymers, such as alloys of PC/ABS or PPO HIPS when contain relatively low content of the styrene-containing polymers. For general-

purpose polystyrene polymers and copolymers, such as PS, ABS, HIPS,

SAN they produce practically no fire retardancy effect when applied alone.

Consequently, there is a demand for halogen-free and antimony-free fire

retarded polystyrene polymer and copolymer compositions, possessing a

highly effective fire retardancy, emit less smoke and less corrosive gas, all

these while using a relatively small amount of fire retardant additive. A

promising way to satisfy these requirements is the use of an organic

phosphorous-containing fire retardant. Consequently, techniques have

been developed and disclosed, in which both heat expandable graphite

(HEG) and organic phosphorous type fire retardant are used to yield flame

retardancy in PS and ABS.

Patent of Tosoh Corporation (Japan) discloses fire-retarded polyolefin

polymer compositions [US 6,124,394]. These fire-retarded polymer

compositions contain previously prepared tablets of a phosphorous-

containing fire retardant (APP alone or mixture of organic phosphorous-

containing fire retardant and APP) and HEG. The paper of Fumio Okisaki

published in Meetings of FRCA, March, 1997, San Francisco, California,

describes the use of a combination of an organic phosphorous-containing

fire retardant and HEG in HIPS. The organic phosphorous-based fire

retardants are known for their tendency to strongly migrate to the

polymer surface during the service life of the product containing them [S.V. Levchik, D.A. Bright, G.R. Alessio and S. Dashevsky, Polymer

Degradation and Stability, 77 (2002), 267-272].

The present invention provides a highly effective fire-retardant

polystyrene polymer and copolymer, which emit less corrosive gases and

less smoke on burning, no or reduced migration of fire retardant to

polymer surface (plate out, blooming) compared to halogen-containing

flame -retardants and or organic phosphorous-based flame-retardants.

Additionally, the high fire retardant efficiency is achieved at lower fire

retardant combination content. The fire retardancy of said styrene-

containing polymer and copolymer is based solely on the presence and

activity of HEG and organic phosphorous-containing fire-retardant and co-

additive whose role is to suppress the migration of the phosphorous-

containing compounds from polymer.

It is the object of the present invention to provide a fire-retarded

polystyrene polymer and copolymer, which possesses excellent fire

retardancy properties (emits less corrosive gas and less smoke on burning)

and no or reduced migration of fire retardant on polymer surface, applying

halogen-free and antimony-free fire-retarded additive(s).

It is a further object of the present invention to provide a fire-retarded

polystyrene polymer and copolymer, which possesses excellent fire

retardancy properties and no or reduced migration of fire retardant on polymer surface, applying an organic phosphorous-containing fire-

retarded additive (s).

It is yet a further object of present invention to provide a fire-retarded

polystyrene polymer and copolymer, which possesses excellent fire

retardancy properties and no or reduced migration of fire retardant on

polymer surface, applying HEG and an organic phosphorous-containing

fire-retardant additives.

It is yet a further object of present invention to provide a fire-retarded

polystyrene polymer and copolymer, which possesses excellent fire

retardancy properties and no or reduced migration of fire retardant on

polymer surface, applying HEG and an organic phosphorous-containing

fire-retardant and co-additive(s), depressed migration of said organic

phosphorous-containing fire-retardant on polymer surface, as additives.

It is yet a further object of present invention to provide a fire-retarded

styrene-containing polymer composition, wherein the styrene-containing

polymer is selected from the group consisting of polystyrene polymers and

copolymers.

Other purposes and advantages of the present invention will appear as the

description proceeds. Summary of Invention

The present invention provides a fire-retarded polymer composition

comprising HEG, at least one organic phosphorous-containing fire

retardant and at least one co-additive whose role is to depress the

migration of organic phosphorous-containing fire-retardant on polymer

surface, wherein the polymer component of said composition is selected

from the group consisting of polystyrene polymer(s) and/or

copolymer (s).

Description of the Figures

In all the Scanning Electron Microscope (SEM) micrographs shown in

Figs. 1-6, the samples surfaces were inspected after exposure for one

month at 65°C in an air circulating oven.

Fig. 1 is a SEM micrograph of sample surface referred to as Comparative

Example Ref. 6.

Fig. 2 is a SEM micrograph of sample surface referred to as Example 21.

Fig. 3 is a SEM micrograph of sample surface referred to as Comparative

Example Ref. 7.

Fig. 4 is a SEM micrograph of sample surface referred to as Example 22.

Fig. 5 is a SEM micrograph of sample surface referred to as Comparative

Example Ref. 8.

Fig. 6 is a SEM micrograph of sample surface referred to as Example 24. Description of the Invention

The applicant has surprisingly found that a combination of HEG and

organic phosphorous-containing fire-retardant(s) in the presence of co-

additive imparts highly effective fire retardancy and significant

suppression of the phosphorous-containing fire-retardant migration to a

composition of polystyrene polymer(s) and copolymer(s).

The invention, therefore, provides a fire-retarded composition comprising:

(a) one or more polymers selected from the group consisting of polystyrene polymer and copolymer;

(b) organic phosphorous-containing fire retardant(s);

(c) heat expandable graphite (HEG);

(d) co-additive able to depress migration of phosphorous-containing fire- retardant to the surface of the polymer.

The phosphorous-containing fire-retardant may be single component or

mixtures of components of the same category. The heat expandable

graphite should preferably be able to change its specific volume by

expanding 50 times or more, on shock heating from room temperature to

700°C.

The invention therefore provides a fire-retarded styrene-containing

polymer(s) composition, which comprises: Component A: a polystyrene polymer and/or copolymer, preferably PS,

HIPS, ABS and SAN, at a percent weight which balances to 100% by

weight the following fire retarded combination:

Component B: 4 to 15% (preferably 8 to 10%) by weight of heat expandable

graphite;

Component C: 6 to 12.5% (preferably 8 to 12.5%) by weight of organic

phosphorous-containing fire retardant, preferably triphenyl phosphate,

resorcinol bis(diphenyl phosphate), bisphenol A bis(diphenyl phosphate) or

4,4'-biphenol bis(diphenyl phosphate).

Component D: 8 to 20% (preferably 12 to 15%) by weight of co-additive,

preferably polycarbonate.

The component A may consist of a single polystyrene polymer, a copolymer

or being a mixture of polystyrene polymer(s) and/or copolymer(s).

The styrene-containing polymers and copolymers used in the present

invention are produced from a styrene-type monomer, including styrene

and methylstyrene. The styrene-containing polymers and copolymers

include, inter alia, homopolymers of styrene, rubber modified high-impact

polystyrenes (hereinafter referred to as "HIPS"), aery lonitrile -butadiene -

styrene copolymers (hereinafter referred to as "ABS"), styrene/acrylonitrile

copolymers (hereinafter referred to as "SAN").

The component B of the fire retarded styrene-containing polymer and

copolymer composition of present invention is heat expandable graphite which is well-known in the art, and it is further described by Titelman,

G.I., Gelman, V.N., Isaev, Yu.V and Novikov, Yu.N.,in Material Science

Forum, Vols. 91-93, 213-218, (1992) and in US Patent 6,017,987.

The HEG under fire decomposes thermally into a char of expanded

graphite, providing a thermally insulating or otherwise protective barrier,

which resists further oxidation.

The heat expandable graphite is derived from natural graphite or artificial

graphite, and upon rapid heating from room temperature to high

temperature like to temperature in flame it expands in the c-axis direction

of the crystal (by a process so-called exfoliation or expansion). In addition

to expanding in the c-axis direction of the crystal, the heat expandable

graphite expands a little in the a-axis and the b-axis directions, as well.

The exfohation degree, or the expandability of HEG depends on the rate of

removing the volatile compounds during rapid heating. The expandability

value in the present invention relates to the ratio of the specific volume

obtained following rapid heating to a high temperature (700°C), to the

specific volume at room temperature. A specific volume change of HEG in

the present invention is preferably not less than 50 times for that range of

temperature change (room temperature to 700°C). Such an expandability

is preferred because a HEG having a specific volume increase by at least

50 times, during rapid heating from room temperature to 700°C, has been

found to produce a much higher degree of fire retardancy compared to a graphite that is heat expandable but has a specific volume increase of less

than 50 times in the aforesaid heating conditions.

The carbon content of heat expandable graphite that exhibits under

aforesaid heating conditions a volume expandability of 50 times or higher,

should be 70% to 87% (preferably 77% to 84%) by weight for serving as a

good carbonaceous barrier and for providing a high level of fire retardancy

in combination with organic P-containing flame retardants.

The HEG having a carbon content of more than 87%, provides during

rapid heating a specific volume increase of less than 50 times. Decreasing

the carbon content in HEG to less than 77% under the aforesaid heating

conditions, provides a too-high specific volume at a too-low temperature

(already at 500°C) and the fire retardancy of polymer composition may be

only achieved at higher loading of HEG.

The heat expandable graphite used in the present invention can be produced

in different processes and the choice of the process is not critical. It can be

obtained, for example, by an oxidation treatment of natural graphite or

artificial graphite. The oxidation is conducted, for example, by treatment

with an oxidizing agent such as hydrogen peroxide, nitric acid or another

oxidizing agent in sulfuric acid. Common conventional methods are

described in US Patent 3,404,061, or in SU Patents 1,657,473 and 1,657,474. Also, the graphite can be anodically oxidized in an aqueous acidic

or aqueous salt electrolyte as described in US Patent 4,350,576.

In practice, most commercial grades of the heat expandable graphite are

usually manufactured via an acidic technology.

The heat expandable graphite, which is produced by oxidation in sulfuric

acid or a similar process as described above, can be slightly acidic

depending on the process conditions. When the heat expandable graphite

is acidic, a corrosion of the apparatus for production of the polymeric

composition may occur. For preventing such corrosion heat expandable

graphite should be neutralized with a basic material (alkaline substance,

ammonium hydroxide, etc.).

The particle size of the heat expandable graphite used in the present

invention affects the expandability degree of the HEG and, in turn, the

fire retardancy of the resulting polymer composition.

The heat expandable graphite of a preferred particle size distribution

contains up to 25%, more preferably from 1% to 25%, by weight particles

passing through a 75-mesh sieve. The HEG containing more than 25% by

weight particles passing through a 75-mesh sieve, will not provide the

required increase in specific volume and consequently, will not provide the

sufficient fire retardancy. The heat expandable graphite containing the above particles at a content lower than 1% by weight may slightly impair

the mechanical properties of the resulting polymer composition. The

dimensions of the largest particles of HEG, beyond 75 mesh, should be as

known in the art, in order to avoid the deterioration of the properties of

the polymer composition. In a preferred embodiment, the surface of the

heat expandable graphite particles may be surface-treated with a coupling

agent such as a silane-coupling agent, or a titanate-coupling agent in

order to prevent the adverse effects of larger particles on the properties of

the fire retarded polymer composition. A coupling agent can be separately

added to the composition, as well.

Component C in the present invention is the phosphorous-containing

flame retardant which can be any organophosphorous compound. Organic

phosphorous-containing fire retardants suitable for use as Component C

according to the present invention include phosphates, phosphonates,

phosphinates, phosphites and phosphine oxides. The phosphorous-

containing flame retardant additive may include monomeric, dimeric

and/or oligomeric phosphorous compound.

Organic phosphorous-containing fire retardant additives particularly

suitable for use as Component C include aromatic phosphate esters of

formula (I):

in which Ri, R2, R3 and 4 are the same or different, an aryl group, and

wherein A is a arylene group; and n is an integer from 0 to 5. The

phosphate esters can be either triarylphosphates, where "n" in the formula

given above is 0, or monomeric bisphosphates, where "n" in the formula is

1, or mixtures of said triaryl phosphates and monomeric bisphosphates

with higher oligomers, where "n" for each oligomer is an integer from 2 to

5 (said mixtures hereinafter indicated also as oligomeric phosphates).

The aryl group may be phenyl, cresyl, 2,6-xylenyl, and the like.

The arylene group may be a group derived from a dihydric compound, for

example, resorcinol, bisphenol A, 4,4'-biphenol, and the like.

Especially preferred arylphosphate esters for use herein include triphenyl

phosphate, oligomeric resorcinol bis(diphenyl phosphate), oligomeric

bisphenol A bis(diphenyl phosphate) and oligomeric 4,4'-biphenol

bis(diphenyl phosphate).

According to the present invention said Component C may consist of a

single phosphorous-containing fire retardant material or it may consist of a mixture of two or more different organic phosphorous-containing fire

retardants as herein before mentioned that may be suitable for obtaining

the desired properties of the polystyrene polymer and/or copolymer. Furthermore, said component C may be a mixture comprising at least one

phosphorous fire retardant and halogen-free fire retardant of other types.

Component D could be any polycarbonate, based on bisphenol A which is

commercially available on the market.

According to the present invention, Component B and Component C are

used together in the amount from 16 to 25% (preferably 18% to 22.5%) by

weight in a composition containing Component D in the amount from 8 to

20% (preferably 12-15%) by weight and one or more polystyrene

polymer(s) and/or copolymer(s) thereof (Component A) in an amount

balancing the composition to 100 wt%.

However, it should be emphasized that high fire retardancy effect can be

achieved at different contents or ratios of Components B and C when they

are used together, preferably at 16-25 wt% load, more preferably, at 18-

22.5 wt% load. It should be emphasized that among with high fire

retardancy the effect of significant reducing or total prevention of

migration of the Component C on the surface of polymer can be achieved

at addition of Component D (co-additive), preferably at 8-20 wt% load,

more preferably, at 12-15 wt% load. With a total amount of Components B and C, together, of less than 16

wt%, the polymer composition exhibits still flame retardancy (a relatively

high LOI value) although it has not been classified any more in UL-94

terms. When an amount of Component D of less than 8 wt%. has been

added, the suppression of migration of Component C to the polymer

surface has not been sufficient enough.

On the other hand, an increase of total amount of Components B and C to

more than 25 wt% in composition does not lead practically to a further

increase in fire retardancy, while an increase of amount of Component D

to more than 20 wt% has no further effect in terms of suppression of

Component C migration, but may deteriorate the properties of the polymer

composition.

The polymer composition may contain other kinds of additives known in

the art, such as colorants, antioxidants, light stabilizers, light absorbing

agents, processing additives, coupling agents and lubricants, blowing

agents, anti-dripping agents and fillers.

The above-described fire retardation technique of the present invention

produces a polymer material having excellent fire retardancy, reduced

emission of corrosive gases and less smoke on burning, no or reduced

migration of fire retardant on the polymer surface. Detailed Description of Preferred Embodiments

The present invention is described below more specifically by reference to

examples without hmiting the invention in any way.

Non-limitative examples of Components A, B, C and D are set forth below:

Component A:

(Al) PS (Lacqrene, Elf Atochem ATO)

(A2) HIPS (Styron 472, Dow)

(A3) ABS (Magnum 9010, Magnum 3404, Dow)

(A4) SAN (Luran VLRQ 53, BASF)

Component B:

Commercially available grades used in the following examples are:

(Bl) Heat expandable graphite (GREP-EG, Tosoh Corporation)

(B2) Heat expandable graphite (8099180, Sino-Union Materials)

(B3) Heat expandable graphite (GRAFGuard 220-80N, UCAR Carbon)

The properties of components Bl to B3 are shown in Table 1.

Table 1: Properties of HEG Bl - B3

Component C:

(Cl) Tri-phenyl phosphate (Aldrich catalog #C9, 545-51)

(C2) Oligomeric resorcinol bis(diphenyl phosphate), Fyrolflex RDP,

(Akzo)

(C3) Oligomeric bisphenol A bis (diphenyl phosphate), CR-741, (Daihachi).

(C4) Oligomeric 4,4'-biphenol bis(diphenyl phosphate) with a monomeric

bisphosphate content of more than 75% (developed and synthesized by

applicant).

The organic phosphorous-containing FR (Component C) can be used either

as a viscous liquid (C2, C3), or solid flakes (Cl) or free flowing powder

(C4), or as a preliminarily melt mixed in polystyrene polymer and/or

copolymer (master batching). Component D:

£D1) Polycarbonate PC (such as but not limited to Lexan 141, GE)

Examples 1-20 and Comparative Examples Ref. 1-5

Either PS, HIPS, ABS, SAN and PC in different ratios were used as

Component A. Various amounts of (B), (C) and (D) as shown in Tables 2-4,

were admixed with the Component A in a granulated form. Mixing was

done in a Brabender mixer of 55 cm³ volume capacity at 50 rotations per

minute for a desired time and at a desired temperature, specific for each

polymer and the corresponding series of experiments. Specimens of 3.2

mm thickness were prepared by compression molding in a hot press at

200°C, cooling to room temperature and cutting to standard test pieces.

The flammability was tested by the limiting oxygen index (hereinafter

referred to as "LOI") method, according to ASTM D-2863 and by UL-94

test (Underwriters Laboratories) with bottom ignition by a standard

burner flame for two successive 10-second intervals. Five test-pieces of

each composition were tested and the burning time, given in each

example, are averages of all five tested pieces.

Table 2 demonstrates fire retarded HIPS-based compositions, which

provide a high level of fire retardancy of the polymer material (V-0 or V-1)

for different aryl phosphate esters either at Components B and C presence only in Comparative Examples Ref. 1-4 or at Components B, C and D

presence in Examples 1-4. The samples obtained in Comparative

Examples have a greasy feel, leaves marks on paper after several days. An

addition of Component D to polymer composition allows the reducing of a

total amount of fire retardant combination, increasing LOI values (Table

2). Although a loading of phosphorous-containing FR in polymer

compositions of Examples 1-4 was the same as in Comparative Examples,

the samples of polymer compositions of Examples 1-4 have no greasy feel.

Examples 1-4 demonstrate that the level of fire retardancy and the

suppression of phosphorous-containing FR migration on polymer surface

are independent on the molecular structure of the used phosphorous-

containing fire retardant (Component C).

Table 2

Examples 2, 5-11 (Table 3) demonstrate that phosphorous-containing fire

retardant (Component C) may be used successfully to impart flame

retardancy to any of the tested polystyrene polymers and copolymers

(Component Al — A4) at any of the used types of heat expandable graphite

(Component Bl - B3). Examples 9 - 11 demonstrate that the HEG with a

high expandability on shock heating at relatively low temperature (500°C)

starts to form a barrier too fast and may provide the required fire

retardancy of the polymer composition only at a higher loading of HEG (15

wt%) as compared to other HEG with a relatively low expandability on

shock heating at temperature 500°C and a high expandability on shock

heating at 700°C (Examples 2, 5, 6, 8, and 9, 10).

NR - no UL-94 rating (V-0, V-1 or V-2) were achieved.

The samples of polymer compositions of Examples 5-11 similarly to

polymer composition of Example 2 have no greasy feel.

A total amount of fire retardant combination (containing Components B and C) in a loading range from 12% to 22.5 wt% is used for polystyrene

polymer and copolymer compositions (Tables 2 and 4). Examples 6, 12 and 13 (Table 4) demonstrate that when the content of Component B and Component C in the composition is 10 wt% (total amount of fire retardants 20%), a decrease of the content of Component Dl from 20% to 8 wt% is

possible since it still provides a high level of fire retardancy (both UL-94

rating V-0 and high LOI). However, the samples of polymer compositions

of Example 13 (8% Component Dl) have still slightly greasy feel. Table 4

NR - no UL-94 rating (V-0, V-1 or V-2) were achieved.

Component Dl shows not only a suppression of aryl phosphate esters

migration but also some synergistic effect on the fire retardancy of

polymer compositions: an increased value of LOI was recorded for all

tested polymer compositions at a lower content of fire retardants

combination as compared with the Comparative polymer compositions.

Examples 14-16 clearly show that when the content of Component B and

Component C in the composition is 8 wt% (total amount of fire retardants

16%), a decrease of the content of Component Dl from 20% to 12 wt% still

provides an efficient suppression of aryl phosphate esters migration but

the level of fire retardancy slightly decreased (UL-94 rating from V-0 to V-

1 and LOI from 29.5 to 27.4 O %, Examples 14 and 16). Examples 17-19

show that Heat Expandable Graphite is an essential component of fire retardant combination required to achieve flame retardancy. At the same

total amount of fire retardant (16%) and the same loading of Component

Dl (12%), reducing the HEG content in the fire retardant combination

from 10% to 4% leads to a gradual loss of fire retardancy. Example 20

shows that tested fire retardant combination of present invention has fire

retardant efficiency even at a total amount of fire retardant 12% (LOI

value 26 O₂%), but without providing the required UL-94 rating.

The highest level of fire retardancy is achieved when the amount of fire

retardant combination (Components A+B) in the polymer composition is

16-20 wt%, wherein the content of Component B is 10 wt% and the content

of Component C is 6-10 wt%, and polymer composition contains 12% of

Component D. These fire retardant polymer compositions have no greasy

feel.

Examples 21-26 and Comparative Examples Ref. 6-9 (Table 5)

The Examples 21-26 are further tested for determining UL-94 values for

1.6 mm pieces (Table 5).

HIPS (A2) was used as Component A. Components A, B and C or A, B, C

and D were blended in a co-rotating twin-screw compounding machine

using the formulations as shown in Table 5. Regular amounts of

antioxidant and pigment were added to the mixture on the expense of the

polymer, as far as wt% is concerned. The test specimens were prepared by

injection molding. Fire retardancy was evaluated by vertical flame test

accordingly to UL-94 as described above. The toughness of specimens was

measured as Izod notched impact strength according to ASTM D 256. The

tensile properties were measured according to ASTM D 638:95. The flow

ability was measured as melt flow index (MFI) according to ASTM D 1238-

82.

The migration (blooming) test of aryl phosphate esters on polymer surface

was conducted as follows:

Following a visual inspection of the injection molded specimens, clean

places without any visual defects were chosen and square samples about

lxl cm were cut, coated with gold and investigated in a scanning electron

microscope (SEM) as zero time specimens. Similar samples were

introduced in an oven at 65°C for one month. When taken out of the oven,

the specimens were gold plated and investigated in the SEM.

The fire retardant combination of the present invention imparts a high

level of fire retardancy (V-0 rating for specimens with a thickness of 1.6

mm) of fire retarded polystyrene polymer and copolymer compositions prepared via compounding and injection molding at a total amount of fire

retardants of 18 - 21.5 wt% at various ratios between HEG and organic

phosphorous-containing fire-retardant in accordance with Examples 21-26

and Component Dl content of 15% providing total suppression of aryl

phosphate esters (Figures 1-6), as compared with Comparative Examples

ref. 6-9, which contain both a higher total amount of fire retardant

combination, not always providing high level of fire retardancy for

specimens with a thickness of 1.6 mm (NR for Cl, Ref. 6 and V-2 for C4 in

composition containing carbon black, Ref. 9), and showing heavy migration

of aryl phosphate esters on samples surface.

The SEM micrographs of these Examples are shown in the Figures, as

follows:

Fig. 1 - Comparative Example 6.

Fig. 2 - Example 21.

Fig. 3 — Comparative Example 7.

Fig. 4 - Example 22.

Fig. 5 - Comparative Example 8.

Fig. 6 - Example 24.

The high level of fire retardancy of polystyrene polymers and copolymers,

containing the fire-retardant combination of the present invention, is

accompanied by additional attractive properties. Halogen-free, antimony-

free fire-retarded styrene polymer compositions of the present invention, containing heat expandable graphite and organic phosphorous-containing

FR, exhibit less corrosive gas and demonstrate significantly reduced

smoke emission on burning, with no migration of the fire retardants onto

the surface of the polymer due to special co-additive for migration

suppression. Furthermore, the polystyrene polymer and copolymers

composition demonstrates high melting flow rate (good processability).

Component B (heat expandable graphite) has practically no effect on such

properties of polymer materials as electrical insulation.

Claims

1. A fire-retarded polymer composition comprising heat expandable graphite (HEG), at least one phosphorous-containing fire retardant and at least one co-additive suitable to depress the migration of phosphorous-containing fire retardant on polymer surface, wherein the polymer component of said composition is selected from the group consisting of polystyrene polymer and/or copolymer.

2. A fire-retarded polymer composition according to claim 1, wherein the polymer is selected from the group consisting of homopolymers of styrene, rubber modified high-impact polystyrenes (HIPS), acrylonitrile-butadiene-styrene copolymers (ABS) and st rene- acrylonitrile copolymers (SAN).

3. A fire-retarded polymer composition according to claim 1, wherein the polymer consists of a mixture comprising at least one polystyrene polymer and/or at least one polystyrene copolymer.

4. A fire-retarded polymer composition according to claim 1, wherein the phosphorous-containing fire retardant is an organic phosphorous- containing compound.

5. A fire-retarded polymer composition according to claim 4, wherein the organic phosphorous-containing compound is the aromatic phosphate ester of formula (I):

CD

in which Ri, R₂, R3 and R4 are the same or different, an aryl group, and wherein A is a arylene group; and n is an integer from 0 to 5.

6. A fire-retarded polymer composition according to claim 5, wherein the phosphate esters are selected from triarylphosphates, where "n" in Formula (I) is 0, or monomeric bisphosphates, where "n" in Formula (I) is 1, or mixtures of said triaryl phosphates and monomeric bisphosphates with higher oligomers, where "n" for each oligomer is an integer from 2 to 5.

7. A fire-retarded polymer composition according to claim 5, wherein the aryl group is selected from phenyl, cresyl, 2,6-xylenyl.

8. A fire-retarded polymer composition according to claim 5, wherein the arylene group is a group derived from a dihydric compound.

9. A fire-retarded polymer composition according to claim 8, wherein the arylene group is selected from resorcinol, bisphenol A, 4,4'-biphenol.

10. A fire-retarded polymer composition according to claim 5, wherein the phosphate ester is selected from the group consisting of triphenyl phosphate, resorcinol bis(diphenyl phosphate), bisphenol A bis(diphenyl phosphate), 4,4'-biphenol bis(diphenyl phosphate).

11. A fire-retarded polymer composition according to any one of claims 4 to 10, wherein the organic phosphorous-containing fire-retardant consists of a single compound or a mixture of compounds.

12. A fire-retarded polymer composition according to claim 1, which comprises:

( a) at least one polymer selected from the group consisting of polystyrene polymer and/or copolymer at a percent weight which balances to 100% by weight the composition;

(b) 4 to 15 (preferably 8 to 10) per cent by weight of heat expandable graphite;

(c) 6 to 12.5 (preferably 8 to 12.5) per cent by weight of organic phosphorous-containing fire retardant;

(d) 8 to 20 (preferably 12 to 15) per cent by weight of co-additive is able to depress migration of organic phosphorous-containing fire retardant on the surface of the polymer.

13. A fire-retarded polymer composition according to claim 12, wherein the total amount of HEG and organic phosphorous-containing fire retardant in said composition is from about 16 to about 25 wt%, preferably 18 to 22.5 wt%.

14. A fire-retarded polymer composition according to claim 1, wherein the heat expandable graphite is obtainable by any conventional route from a natural graphite or artificial graphite.

15. A fire-retarded polymer composition according to claim 14, wherein the heat expandable graphite, produced by oxidation of a natural graphite or artificial graphite in sulfuric acid or in nitric acid, can be additionally allowed to neutralize with a basic material.

16. A fire-retarded polymer composition according to claim 1, wherein the heat expandable graphite is obtained by any conventional route from a natural graphite or artificial graphite, and has a carbon content in the range of 70-87%.

17. A fire-retarded polymer composition according to claim 1, wherein the heat expandable graphite is obtained by any conventional route from a natural graphite or artificial graphite, and which upon rapid heating from room temperature to 700°C has a specific volume expansion of not less than 50 times.

18. A fire-retarded polymer composition according to claim 1, wherein the heat expandable graphite has a particle size distribution such that no more than 25% by weight of graphite particles pass through a 75 mesh sieve.

19. A fire-retarded polymer composition according to claim 1, wherein the heat expandable graphite particles are surface treated with a coupling agent.

20. A fire-retarded polymer composition according to claim 1, wherein the co-additive is polycarbonate.

21. A fire-retarded polymer composition according to claim 1, further comprising additives selected from the group consisting of colorants, antioxidants, light stabilizers, light absorbing agents, process oils, coupling agents, lubricants, blowing agents, fillers and anti-dripping agents.

22. A fire-retarded polymer composition according to claim 21, comprising at least one coupling agent.

23. A fire-retarded polymer composition according to claim 1, substantially as described and exemplified.