Bron, Samuel (11/1 Achziv Street, Yoqneam, 20692, IL)
Zilberman, Joseph (13/2 Bat Chen Street, Haifa, 32990, IL)
Titelman, Grigory I. (31 Ben-Yehuda Street, Haifa, 33061, IL)
Bron, Samuel (11/1 Achziv Street, Yoqneam, 20692, IL)
Zilberman, Joseph (13/2 Bat Chen Street, Haifa, 32990, IL)
| 1. | A fire retarded polymer composition comprising heat expandable graphite (HEG), at least one phosphorouscontaining fire retardant and at least one coadditive suitable to depress the migration of phosphorouscontaining 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 fireretarded polymer composition according to claim 1, wherein the polymer is selected from the group consisting of homopolymers of styrene, rubber modified highimpact polystyrenes (HIPS), acrylonitrilebutadienestyrene copolymers (ABS) and styrene acrylonitrile copolymers (SAN). |
| 3. | A fireretarded 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 fireretarded polymer composition according to claim 1, wherein the phosphorouscontaining fire retardant is an organic phosphorous containing compound. |
| 5. | A fireretarded polymer composition according to claim 4, wherein the organic phosphorouscontaining 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 O to 5. |
| 6. | A fireretarded polymer composition according to claim 5, wherein the phosphate esters are selected from triarylphosphates, where "n" in Formula (I) is O, 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 fireretarded polymer composition according to claim 5, wherein the aryl group is selected from phenyl, cresyl, 2,6xylenyl. |
| 8. | A fireretarded polymer composition according to claim 5, wherein the arylene group is a group derived from a dihydric compound. |
| 9. | A fireretarded polymer composition according to claim 8, wherein the arylene group is selected from resorcinol, bisphenol A, 4,4'biphenol. |
| 10. | A fireretarded 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 fireretarded polymer composition according to any one of claims 4 to 10, wherein the organic phosphorouscontaining fireretardant consists of a single compound or a mixture of compounds. |
| 12. | A fireretarded 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 phosphorouscontaining fire retardant; (d) 8 to 20 (preferably 12 to 15) per cent by weight of coadditive is able to depress migration of organic phosphorouscontaining fire retardant on the surface of the polymer. 13. A fireretarded polymer composition according to claim 12, wherein the total amount of HEG and organic phosphorouscontaining fire retardant in said composition is from about 16 to about 25 wt%, preferably 18 to 22. |
| 13. | 5 wt%. |
| 14. | A fireretarded 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 fireretarded 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 fireretarded 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 7087%. |
| 17. | A fireretarded 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 7000C has a specific volume expansion of not less than 50 times. |
| 18. | A fireretarded 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 fireretarded polymer composition according to claim 1, wherein the heat expandable graphite particles are surface treated with a coupling agent. |
| 20. | A fireretarded polymer composition according to claim 1, wherein the coadditive is polycarbonate. |
| 21. | A fireretarded 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 antidripping agents. |
| 22. | A fireretarded polymer composition according to claim 21, comprising at least one coupling agent. |
| 23. | A fireretarded polymer composition according to claim 1, substantially as described and exemplified. |
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-O, V-I 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 fixe-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 650C 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, VoIs. 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 exfoliation 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 7000C). 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 7000C, 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 5000C) 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): (I)
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 O to 5. The phosphate esters can be either triarylphosphates, where "n" in the formula given above is O, 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 limiting 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 #09,545-51)
(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: (Ol) 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 2000C, 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-O or V-I) 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 fixe
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 (5000C)
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 5000C and a high expandability on shock
heating at 7000C (Examples 2, 5, 6, 8, and 9, 10). Table 3
NR - no UL-94 rating (V-O, V-I 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-O 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-O, V-I 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-O to V-
1 and LOI from 29.5 to 27.4 O2%, 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 fixe 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 02%), 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). Table 5
Additive: antioxidant (0.3%) or antioxidant (0.3%) and Teflon (0.5%) or antioxidant (0.3%) and carbon black (1.0%). NR - no UL-94 rating (V-O, V-I or V-2) were achieved. 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 1x1 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-O 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.