GB2306167A

GB2306167A - Flame retardant thermosetting resin compositions

Info

Publication number: GB2306167A
Application number: GB9621241A
Authority: GB
Inventors: Martin Davies; Mohammad Naseer Qureshi; Barry Woodfine
Original assignee: Kobe Steel Europe Ltd
Current assignee: Kobe Steel Europe Ltd
Priority date: 1995-10-11
Filing date: 1996-10-11
Publication date: 1997-04-30
Anticipated expiration: 2016-10-11
Also published as: GB9520808D0; GB2306167B; GB9621241D0

Abstract

A flame retardant thermosetting resin composition, comprises a thermosetting polymer selected from an acrylic-type resin, a urethane-acrylic resin, a polyester resin, a polyester-acrylic resin, a polyol-acrylic resin or an epoxy resin, and up to 100 parts by weight, per 100 parts by weight of polymer, of a flame retardant additive comprising from 40 to 90% by weight of an inorganic flame retardant material and from 60 to 10% by weight of a halogenated organic flame retardant material, in which the inorganic flame retardant material is hydrated alumina and one or more compounds of antimony, zinc, magnesium, tin, iron, molybdenum or boron. The composition may be reinforced with fibres e.g. glass fibres.

Description

FLAME RETARDANT THERMOSETTING RESIN COMPOSITIONS WITH ENHANCED PROCESSABILITY This invention relates to a thermosetting polymer, preferably of the acrylic-type (e.g. modified acrylic resins), which possesses excellent (non-) flammability characteristics, specifically including product performance in the British Standard BS476 surface spread of flame test. The invention is characterised in that the level of flame retardancy is achieved with lower levels of predominantly inorganic flame retardant additive than is commonly used for these resin types and that this reduction in the level of additive results in enhanced processability.

Thermosetting resins are attractive materials to use for glass fibre (GF) composite manufacture due to a number of different features, such as their cure characteristics and thermomechanical properties when cured. However, these resins generally possess insufficient flame retardance when used in an unmodified form and it is essential to incorporate flame retardant (FR) additives in order to overcome this deficiency.

In acrylic-type resins, it is common practice to use alumina trihydrate (ATH) as the FR additive. This is exemplified by European Patent Application 50,448 (to Westinghouse Electric Corp) and Japanese Patent Application 6,049,391 (to Nichias Corp) where acrylic or modified acrylic resins are flame retarded with quantities of ATH. The efficiency of ATH in imparting flame retardancy to these resins is such that the use of 100-300 parts of ATH per 100 parts of resin as claimed in EP 50,448 A and JP 6,049,391 A is typical.

It is also known that the minimum level of ATH FR required in (thermosetting) modified acrylic resin (eg Modart)/GF composites is also dependent on the GF loading. This effect has been demonstrated for composite performance in the BS476 surface spread of flame test, as detailed in the paper "Potential Applications of Low Smoke Fire Retardant Methacrylate Based Composites" by D.R. Sayers et al, presented at the "Composites Asia Pacific" conference held in Adelaide, Australia in 1989. In this paper, the ATH loading required to achieve class 1 performance at 56% volume GF is quoted at around 60 parts whilst at 20% volume GF the figure is around 180 parts of ATH.In a real-world application (the Tangara Mass Transit System in Sydney, Australia), the resin formulation developed to satisfy the flammability regulations contained 100 parts ATH per 100 parts of modified acrylic resin when used in a 60% weight (around 45% volume) GF composite, as detailed in paper 3-B by T.

Bryan et al presented at 44th Annual Conference of the Composites Institute held in Dallas, USA in 1989. In general terms, products with GF usage levels of around 30-45 volume% require > 100 parts of ATH to satisfy the requirements of the highest classification (class 1) of the BS476 surface spread of flame test. In the specific case of 40% Vf GF (Vf = volume fraction), it is widely accepted by skilled practitioners that modified acrylic resin requires 120 parts ATH as a minimum quantity to attain class 1 in the BS476 surface spread of flame test.

The combined requirements of high ATH loading (for flammability issues) and GF content (to satisfy the mechanical property requirements) lead to restrictions on the processability of such systems. An example where the high level of ATH can compromise the processability is the liquid moulding technique known as resin transfer moulding (RTM). In order to overcome these problems and maintain high rates of resin impregnation, the development of a specialised RTM moulding technique known as network injection moulding (NIM) has been undertaken, as reported on pages 34-38 of the November 1994 issue of "Reinforced Plastics". NIM allows mouldings to be produced from resins containing high loadings ( > 100 parts) of solid additives.However, for general RTM usage, the processability obstacles remain and the need to develop a flame retardant resin system containing a low loading of solid FR additive (eg 50-70 parts) can be demonstrated.

It has been common practice in the carpet manufacturing industry to use an antimony/organohalogen FR package in acrylic fibres, although this is much less common now. The combination of antimony trioxide + organohalogen (Br or C1) is a well known and widely used FR package for many materials and is effective at lower addition levels than required for ATH. Typically, 40 parts would be used. However, these FR additives appear not to have been used in modified acrylic resin products and comparative examples 4,5 and 7 demonstrate the relative inefficiency of this FR package in providing for resistance to flammability ("time to ignition" in the Tables). Zinc-based compounds are widely reported alternatives to antimony in chlorine-containing FR packages but comparative examples 8 and 9 demonstrate the ineffectiveness of these materials also.

We have suprisingly found that the combination of antimony/organohalogen with a similar level of ATH provides for a dramatic increase in time to ignition, as found in example 10 where flammability could not be sustained. The level of ATH used is too low to account for this behaviour, as demonstrated by comparative Example 2. Our findings also extend generally to combinations of inorganic flame retardants and halogenated organic flame retardants.

The present invention provides a flame retardant thermosetting resin composition, comprising a thermosetting polymer selected from an acrylic-type resin, a urethane-acrylic resin, a polyester resin, a polyester-acrylic resin, a polyol-acrylic resin or an epoxy resin, and up to 100 parts by weight, per 100 parts by weight of polymer, of a flame retardant additive comprising from 40 to 90% by weight of an inorganic flame retardant material and from 60 to 10% by weight of a halogenated organic flame retardant material, in which the inorganic flame retardant material is hydrated alumina and one or more compounds of antimony, zinc, magnesium, tin, iron, molybdenum or boron.

The inorganic flame retardant material is preferably alumina trihydrate and one or more compounds selected from oxides of antimony, zinc, magnesium, iron, tin and molybdenum; zinc borate; zinc stannate and zinc hydroxystannate. Most preferably, the inorganic flame retardant material comprises a combination of alumina trihydrate and antimony trioxide.

The halogenated organic flame retardant material is generally a brominated or chlorinated organic compound. In one embodiment, the halogenated organic flame retardant material includes a benzene or cyclopentadiene ring substituted by at least two and more preferably four bromine or chlorine atoms. The halogenated organic flame retardant material is preferably selected from aliphatic linked bromophenyl derivatives, bromophthalate derivatives, bromoacrylate derivatives, brominated bisphenol-A derivatives, brominated carbonate oligomers, brominated polystyrene and aliphatic brominated or chlorinated compounds. A preferred material is of the general formula BrxPh-R-Ph Brx where x is 1-5, Ph is phenyl and R is C14 alkylene.

Most preferred is bis(pentabromophenyl)ethane.

The thermosetting polymer is generally a free-radicalcurable resin or a condensation/addition-curable resin. Preferably, the thermosetting polymer is an acrylic-type resin, a urethane-acrylic resin, a polyester resin, a polyester-acrylic resin, a polyolacrylic resin or an epoxy resin.

The content of flame retardant additive is preferably up to 75 parts by weight per 100 parts by weight of polymer, more preferably from 30 to 70 parts by weight per 100 parts by weight of polymer. The flame retardant additive preferably comprises at least 50% by weight of inorganic flame retardant material and less than 50% by weight of halogenated organic flame retardant material. In a more preferred aspect, the flame retardant additive comprises from 25 to 80% by weight of alumina trihydrate, up to 60% by weight of an antimony and/or zinc flame retardant compound, and from 10 to 60% by weight of halogenated organic flame retardant material.

The flame retardant thermosetting resin composition may include a fibrous reinforcing filler. The fibrous reinforcing filler may be glass fibre. The content of glass fibre is preferably from 20 to 60% by volume, based on the total of polymer and glass fibre.

The invention extends to the use of a flame retardant thermosetting resin composition, as defined above, in resin transfer moulding. The invention also includes a moulded article formed from a flame retardant thermosetting resin composition as defined above.

Our invention relates to the development of a thermosetting, preferably modified acrylic resin system containing up to 100, preferably < 75 parts of FR additive and which can be used in non-specialised RTM processes. Suprisingly, we have found that the level of solid FR additive can be reduced substantially below 100 parts whilst retaining the required level of flame retardance generally accepted to be provided only by higher loadings. This enables the production of GF composite products to be undertaken by standard RTM processing routes.

We have developed a modified acrylic resin system which contains very low levels of solid FR additive (preferably ca. 30-70 parts) and which also maintains the level of flame retardancy achieved in standard ATH-filled modified acrylic resin formulations.

The level of solid FR additive used in the resin formulation is low, preferably only 75 parts or less.

The majority of the FR additive is preferably an inorganic FR material (eg ATH or other metal compounds) with a smaller level of organic additive also present. The organic additive is a halogenated material. This combination of FR additives provides for a range of excellent non-flammability characteristics from the resin formulation, including class 1 performance in the BS476 surface spread of flame test. The fire performance of the FR combination is superior to that achieved by the individual FR components when used separately in modified acrylic resin formulations and no antagonistic effects are observed between the actions of the different components if selected correctly.

This provides for resin formulations with improved processing attributes compared to FR/modified acrylic resins quoted in the literature. This enhanced processability is obtained without recourse to any processing aids or additives.

The resin systems provide for good flame retarding characteristics combined with excellent processability. This displays advantages over current state-of-the-art modified acrylic resin systems where high loadings of ATH are used in order to acquire the necessary flame retardancy. These high loadings compromise the processability of these resin systems.

This aspect of the invention provides for commercial advantages in product areas where moulding cycle time plays a significant part in the overall cost of the product. In certain moulding techniques, such as RTM, the invention allows the use of standard moulding procedures rather than specialist techniques. This represents an additional advantage.

In addition to reductions in viscosity, the lower solids content will provide for improved filtration characteristics during moulding. The cure of the resin formulation can be achieved by many of the standard free-radical curing agents activated by thermal or photolytic methods. Alternatively, the resin may be curable by condensation/addition. The thermosetting polymer may be an acrylic-type resin, a urethane-acrylic resin, a polyester resin, a polyester-acrylic resin, a polyol-acrylic resin or an epoxy resin.

The invention is illustrated by the following Examples.

EXAMPLES Materials : Modar - modified acrylic resin (Ashland) DMA - dimethylaniline (Aldrich) BPO - 40% benzoyl peroxide by weight in water (Elf) ATH - alumina trihydrate (Alcan) ZB - zinc borate (Borax) ZHS - zinc hydroxystannate (Joseph Storey & BR< Co) Sb203 - antimony trioxide (Aldrich) Saytex 8010 - proprietary brominated organic FR (Ethyl) Saytex BT93 ethylenebistetrabromophthalimide (Ethyl) Saytex 120 - tetradecabromodiphenoxybenzene (Ethyl) Saytex 102E - decabromodiphenyloxide (Ethyl) FR 1025M - pentabromobenzylacrylate (Dead Sea Bromine) Dechlorane+ - 2:1 adduct of hexachlorocyclopentadiene and 1,5-cyclooctadiene (OxyChem) General experimental procedure : The specified amounts of Modar resin and FR additives and synergists were mixed together and de-aerated.The curing agents (typically 0.3phr DMA and 3.75phr BPO) were then added and mixed carefully without introducing any bubbles.

This mixture was then introduced into the mould and cured. [For the curing agents cited above, the cure schedule was 30 minutes at ambient temperature.) Test methods : Cone Calorimeter (ISO 5660). The method detailed in the standard was followed. The sample dimensions used were 10x10x0.6cm and a gap of 2.5cm set between the heater and the upper surface of the sample. The output of the heater measured at the sample surface position was 50kW/m2. Time-toignition, peak heat release rate (PHRR) and the 3 minute average heat release rate (AHRR) results have been quoted in the Tables.

BS476 parts 6 & were carried out in full accordance with the standard.

Comparative Examples 1-9. Sheets of approximately 6mm thickness were produced according to the general method described above. The chemical composition of the fabricated sheets is detailed in Table 1, together with the results of tests carried out on a Cone Calorimeter.

Examples 10-24. The same procedure was adopted as in the comparative examples 1-9. The results of the Cone Calorimeter testing are given in Tables 2 and 3.

Example 25. The formulation used in Example 10 was injected into a flat mould of 2-2.5mm thickness using a Hypaject RTM machine manufactured by Plastech and cured at ambient temperature. Two layers of ELTX 1169 GF mats (produced by Tech Textiles) had been preformed to shape and preplaced in the mould cavity prior to resin injection. The GF composite produced was of ca.

40% volume fraction of GF. The sheet was cut into test pieces of appropriate size and tested in accordance with BS476 parts 6 & . The result of BS476 part 6 test was an overall fire propagation index of 5.84; comprising sub-indices of 0.27 (i1) 4.67 (i2) and 0.9 (i3). The result of BS476 part 7 test was a class 1 performance with a flame spread of only 50mm registered for the GF composite compared to an upper limit of 165mm of flame spread as specified for class 1 performance. The results obtained in BS476 parts 6 & combine to give the so-called class 0 performance as defined in Approved Document B of the UK Building Regulations (1985).

Table 1.

Example Formulation PHRR AHRR Time to no. details (parts) (kW/m2) (kW/m2) ignition (s) Modar 100 548 366 31 2 Modar 100 245 175 35 ATH 50 3 Modar 100 126 91 104 ATH 120 4 Modar 100 166 80 37 Saytex 8010 30 sb2 3 10 5 Modar 100 105 68 33 FR 1025M 30 Sb203 10 6 Modar 100 368 219 34 Dechlorane+ 30 7 Modar 100 236 173 42 Dechlorane+ 30 sb2 3 10 8 Modar 100 198 127 30 Dechlorane+ 30 ZB 10 9 Modar 100 176 97 30 Dechlorane+ 30 ZB 5 ZHS 5 Table 2.

Example Formulation PHRR AHRR Time to no. details (parts) (kW/m2) (kW/m2) ignition (s) 10 Molar 100 48 40 US* ATH 30 Saytex 8010 30 SbzO3 10 11 Modar 100 83 60 60 ATH 20 Saytex 8010 30 Sb203 10 12 Modar 100 125 68 58 ATH 20 Saytex 8010 30 Saytex 8010 20 ZB 10 ZHS 10 14 Nodal 100 106 75 47 ATh 12 5 106 25 Saytex 8010 10 ZB 25 ZHS 25 15 Molar 100 220 111 64 ATh 50 Saytex 8010 10 ZHS 5 16 Modar 100 121 69 29 ATh 20 Saytex BT93 10 ZB 5 ZHS 5 17 Nodar 100 70 40 58 ATH Modar 23 23 Saytex 8010 20 Sb2O3 7 * Note : US indicates that the flame was transient in nature and was not sustained during the test.

Table 3.

Example Formulation PHRR AHRR Time to no. details (parts) (kW/m2) (kW/m2) ignition (s) 18 Nodar 100 103 73 88 ATH 20 Saytex BT93 30 Sbzoa lo 19 Modar 100 102 53 71 ATH 20 Saytex 120 30 Sb2O3 10 20 Hodar 100 132 74 57 ATH 20 Saytex 102E 30 Sb2 3 10 21 Modar 100 75 68 58 ATH 20 FR 1025M 30 Sb2O3 10 22 Madar 100 160 124 63 ATH 30 Dechlorane+ 20 23 Modar 100 158 127 53 ATH 20 Dechlorane+ 30 sb2 3 10 24 Modar 100 245 174 47 ATH 20 Dechlorane+ 30

Claims

CLAIMS: 1. A flame retardant thermosetting resin composition, comprising a thermosetting polymer selected from an acrylic-type resin, a urethane-acrylic resin, a polyester resin, a polyester-acrylic resin, a polyolacrylic resin or an epoxy resin, and up to 100 parts by weight, per 100 parts by weight of polymer, of a flame retardant additive comprising from 40 to 90% by weight of an inorganic flame retardant material and from 60 to 10% by weight of a halogenated organic flame retardant material, in which the inorganic flame retardant material is hydrated alumina and one or more compounds of antimony, zinc, magnesium, tin, iron, molybdenum or boron.
2. A flame retardant thermosetting resin composition according to claim 1, in which the inorganic flame retardant material is alumina trihydrate and one or more compounds selected from oxides of antimony, zinc, magnesium, iron, tin and molybdenum; zinc borate; zinc stannate and zinc hydroxystannate.
3. A flame retardant thermosetting resin composition according to claim 2, in which the inorganic flame retardant material comprises a combination of alumina trihydrate and antimony trioxide.
4. A flame retardant thermosetting resin composition according to any of claims 1 to 3, in which the halogenated organic flame retardant material is a brominated or chlorinated organic compound.
5. A flame retardant thermosetting resin composition according to claim 4, in which the halogenated organic flame retardant material is selected from aliphatic linked bromophenyl derivatives, bromophthalate derivatives, bromoacrylate derivatives, brominated bisphenol-A derivatives, brominated carbonate oligomers, brominated polystyrene and aliphatic brominated or chlorinated compounds.
6. A flame retardant thermosetting resin composition according to any of claims 1 to 5, in which the thermosetting polymer is a free-radical-curable resin or a condensation/addition-curable resin.
7. A flame retardant thermosetting resin composition according to any of claims 1 to 6, in which the thermosetting polymer is an acrylic or modified acrylic resin.
8. A flame retardant thermosetting resin composition according to any of claims 1 to 7, in which the content of flame retardant additive is up to 75 parts by weight per 100 parts by weight of polymer.
9. A flame retardant thermosetting resin composition according to claim 8, in which the content of flame retardant additive is from 30 to 70 parts by weight per 100 parts by weight of polymer.
10. A flame retardant thermosetting resin composition according to any of claims 1 to 9, in which the flame retardant additive comprises at least 50% by weight of inorganic flame retardant material and less than 50% by weight of halogenated organic flame retardant material.
11. A flame retardant thermosetting resin composition according to any of claims 1 to 10, in which the flame retardant additive comprises from 25 to 80% by weight of alumina trihydrate, up to 60% by weight of an antimony and/or zinc flame retardant compound, and from 10 to 60% by weight of halogenated organic flame retardant material.
12. A flame retardant thermosetting resin composition according to any of claims 1 to 11, including a fibrous reinforcing filler.
13. A flame retardant thermosetting resin composition according to claim 12, in which the fibrous reinforcing filler is glass fibre.
14. A flame retardant thermosetting resin composition according to claim 13, in which the content of glass fibre is from 20 to 60% by volume, based on the total of polymer and glass fibre.
15. A flame retardant thermosetting resin composition substantially as hereinbefore described with reference to any of the Examples.
16. Use of a flame retardant thermosetting resin composition according to any of claims 1 to 15 in resin transfer moulding.
17. A moulded article formed from a flame retardant thermosetting resin composition according to any of claims 1 to 15.