GB2300420A - Flame retardant polyamide composition - Google Patents

Abstract

A shaped product having a thickness of 1.6mm or less and formed from a flame retardant polyamide composition, comprises (a) a semi-aromatic polyamide, or a polymer blend comprising at least 50% by weight of semi-aromatic polyamide, and (b) red phosphorus. The composition optionally further comprises (c) a phenolic resin.

Description

FLAME RETARDANT POLYAMIDE COMPOSITION This invention relates to shaped products of a semiaromatic polyamide (nylon), preferably of the MXD-6 type, which possess superior flame retardancy. The invention specifically relates to the use of compositions which provide for non-dripping flame retardance without the use of halogenated flame retardants. The invention is further characterised in that the flame retardants are used at low levels of addition and that the flame retardancy is maintained in very thin sections.

Polyamides are widely used in a number of different application areas such as mechanical and electrical parts due to a combination of good mechanical, chemical and durability properties. Semi-aromatic polyamides have further advantages over aliphatic polyamides including increased temperature capability. However, these resins suffer from insufficient flame retardance to obtain the UL94 V-O flame class.

In order to improve the fire performance of these resins, it is common practice to use halogenated flame retardants. This has also been the case for MXD-6 nylon, as detailed in Japanese Patent Applications 50-97765, 5864938 and 61-294757 (all to Mitsubishi), where brominated additives have been used to obtain the V-O rating at 1/16 inch (-1.6mm). The use of non-halogenated flame retardants for MXD-6 nylon has been restricted to the use of phthalocyanine green/antimony trioxide combinations (Japanese Patent Application 49-136039 to Mitsubishi) or phosphinates at addition levels of 20 wt% or more to achieve V-O flame class at 1/16 inch (Japanese Patent Application 51-88549 to Toray Inds. KK and Nissan Chem.

Ind. KK). Japanese Patent Application 5-294334 (to Japan Synthetic Rubber) claims the use of flame retardants in GF(glass fibre)/MXD-6 composites but does not demonstrate any flame retardant behaviour, nor does it specify any flame retardants. European Patent Application 93-116210.1 (to Kishimoto Sangyo) claims flame retardant compositions containing blends of semiaromatic and aliphatic nylons but the semi-aromatic nylon content is restricted to less than 30% of the total nylon content. UL94 V-o rating is also restricted to mouldings of 1.6mm minimum thickness.

Certain end-use applications of MXD-6 resin require the use of non-halogenated flame retardants. The presence of heavy metals such as antimony should also be avoided.

Therefore, the need for a MXD-6 resin containing an alternative flame retardant which is efficient at low addition levels can be established. Our invention provides for such resin compositions containing flame retardants hitherto unused in MXD-6 nylon.

The present invention provides a shaped product having a thickness of 1.6mm or less and formed from a flame retardant polyamide composition, comprising (a) a semi-aromatic polyamide, or a polymer blend comprising at least 50% by weight of semi-aromatic polyamide, and (b) red phosphorus.

The composition may further comprise (c) a phenolic resin and/or (d) a fibrous reinforcement. The shaped product preferably has a thickness of 1.2mm or less, more preferably 1.0mum or less.

The compositions of the invention meet UL94 V-0 flame class rating at thicknesses less than 1.6mm, and as low as 0.7mm. Additionally, the composition does not contain halogenated flame retardants or heavy metal oxides.

The semi-aromatic polyamide used according to the invention has alternating aromatic (optionally including aliphatic portions) and aliphatic groups between amide groups along the polymer chain. It preferably comprises multiple units of the following structure: - A - CONH - B - HNCO where one of A and B represents a diva lent aromatic or araliphatic group, and the other of A and B represents a divalent aliphatic group. The divalent aromatic or araliphatic group is preferably (CH2)m-Ph-(CH2)n- or -Ph (where m and n is each independently 1 to 4, and Ph is phenylene, optionally substituted by one or more Cl C4 alkyl groups), in particular xylylene (preferably metaxylylene) or phenylene.The divalent aliphatic group is preferably alkylene, in particular straight-chain alkylene, having 3 to 12 C-atoms, preferably 4 to 8 Catoms. Semi-aromatic polyamides can be made by conventional methods, such as polycondensation of the appropriate diamine and dicarboxylic acid or reactive derivatives thereof. A particularly preferred semiaromatic polyamide is known as MXD-6, the polycondensation product of metaxylene diamine and adipic acid.

The invention may also use blends of a semi-aromatic polyamide with at least one other polyamide or other compatible polymer. The proportion of semi-aromatic polyamide in such blends is at least 50% by weight, preferably at least 70% by weight, and most preferably at least 90% by weight.

The use of red phosphorus flame retardant (preferably in masterbatch form) when present either singly or in combination with phenolic resin in semi-aromatic polyamide formulations provides for the required flame retardancy. The addition level of these flame retardants is low, frequently below 10 wt%. The compositions are effective in both fibre reinforced semi-aromatic polyamide composites or in unreinforced semi-aromatic polyamide mouldings. The presence of other additives such as pigments or flow enhancers does not affect the fire performance of the compositions.

The red phosphorus may be used as such or in the form of a masterbatch. The masterbatch contains the red phosphorus mixed with a carrier polymer, which may be polyamide, such as MXD-6, nylon-6 or nylon-6,6, or other polymers such as polypropylene or EVA (ethylene/vinyl acetate). The proportion of red phosphorus in the masterbatch can vary but is generally about 50% by weight.

The phenolic resin is a resin of the resole or novolac type. The preferred resin is a novolac type. It is generally formed by reaction of a phenol or substituted phenol and formaldehyde. Examples are phenolformaldehyde, cresol-formaldehyde and resorcinolformaldehyde resins. The monomer ratio of formaldehyde to phenol is generally 0.7:1 to 0.9:1 (molar). The density of the resin is generally 1.20 to 1.30 g/cm3.

The melting range of the resin is generally 30 to 2000C, preferably 60 to 1200C. The resin preferably should not contain any curing agents, such as "hexa" (hexamethylenetetramine).

The phenolic resin enhances the flame retardant activity of the red phosphorus. It is particularly desirable for the phenolic resin to be present when the proportion of red phosphorus in the composition according to the invention is relatively low. The proportion of red phosphorus is generally from 2% to 20%, preferably from 2% to 10%, more preferably 2% to 6% by weight based on the total weight of the composition. The proportion of phenolic resin, when present, is generally from 2% to 10%, preferably from 2% to 7%, more preferably 2% to 5% by weight based on the total weight of the composition.

The compositions used according to the invention may include further components, such as those which are conventional in polymer compositions. Such further components include extending and!or reinforcing fillers.

The reinforcing fillers are preferably fibres such as carbon fibre or glass fibre, and may be present in proportions of generally up to 40% by weight, based on the total weight of the composition. Pigments, e.g.

carbon black, may be present, for example in proportions of up to 15% by weight, based on the total weight of the composition. The composition may also include flow enhancers, e.g. calcium stearate, in proportions of generally up to 3% by weight, based on the total weight of the composition.

The composition used according to the invention is formed by mixing together the appropriate components. Such mixing is generally carried out under heating sufficient to melt the polyamide. Suitable apparatus for carrying out the mixing is an extruder. The extruded product can be directly used, or it can be optionally remelted and subsequently processed, for example to form shaped products such as mouldings, filaments, fibres, films and coatings. A particular feature of the invention is that the fire retardant properties are maintained at a high level even when the composition is processed into a shaped product having a thickness of 1.6mm or less, preferably 0.7mm to 1.6mm.

The invention provides for the use of flame retardants in semi-aromatic polyamide which do not contribute halogenated materials or heavy metals to the resin composition. This is an advantage in areas such as electrical parts where it is known that such chemicals can compromise the long-term stability of the electronic circuitry. The low level of flame retardant additive present in these compositions is also advantageous. It would not be expected to compromise the mechanical and other properties of the semi-aromatic polyamide to the same extent as occurs when similar or higher levels of other flame retardant additives are used. There may also be cost benefits from using lower levels of additive.

It is also advantageous that the flame retardant compositions are effective in both fibre reinforced or unreinforced mouldings. This is not always the case with flame retardants used in other polyamides, e.g. aliphatic nylons. We have also established the efficacy of the compositions when other additives such as pigments or flow enhancers are introduced into the mouldings.

The invention is illustrated by the following Examples.

EXAMPLE 1 The appropriate quantities of nylon, red phosphorus, phenolic resin, fibre reinforcement and other additives (all specified below) were mixed together as detailed in Tables 1, 2, 3 and 4 using a 16mm co-rotating twin screw extruder manufactured by Prism. The compositions are shown in wt%. Typically, a melt temperature of 2750C and a screw speed of 200rpm were employed. The extrudate was either cooled in a water bath before being pelletised or allowed to cool on a metal plate.

Test pieces for fire testing were prepared by compression moulding of the extrudate in a 20 tonne press manufactured by George Moore Ltd. The moulding temperature was set at 2750C. Fire performance was assessed in accordance with ASTM D 3801, the UL94 vertical burn test. The results are summarised in Tables 1-4. A V-O result means optimum flame retardancy in this test. A V-l result is less than optimum, but may be adequate for some purposes. Table 4 shows comparative data using nylon 66 instead of MXD-6.

Materials Semi-aromatic (MXD-6) nylon : Reny, a product of Mitsubishi.

Red phosphorus : Amgard CPC405, masterbatch form available from Albright & Wilson (50% by weight red phosphorus mixed with nylon-6 carrier polymer).

Phenolic resin : 9323 LP available from Bakelite.

Carbon fibre : T700S available from Toray.

Glass fibre : P388 available from Vetrotex.

Carbon black : Vulcan XC-72 available from Cabot.

Calcium stearate : Harochem CPR-5 available from Akros.

Tables 1-3 Fire Performance of Reny-based Blends (composition shown in wt%) Table 1

Reny 100.0 70.0 83.3 58.0 60.3 62.5 Amgard CPC405 ---- ---- 16.7 12.0 9.7 7.5 T700S ---- 30.0 ---- 30.0 30.0 30.0 UL94 result NR** NR V-0 V-o V-0 V-1 (0.65mm) * * Thickness of test pieces ** NR = non-rated, i.e. fails test Table 2

Reny | 64.8 54.6 57.4 59.4 60.4 60.4 Amgard CPC405 | ---- 11.0 8.0 5.9 4.8 6.0 9323 LP 5.2 4.4 4.6 4.7 4.8 3.6 T700S 30.0 30.0 30.0 30.0 30.0 30.0 UL94 result NR V-0 V-0 V-0 V-0 V-0 (0.65mm) Table 3

Reny 78.1 58.0 54.0 54.0 Amgard CPC405 15.6 12.0 12.0 5.0 9323 LP 6.3 ---- ---- 5.0 T700S ---- ---- 30.0 30.0 P38 8 ---- 30.0 Harochem CPR-5 ---- ---- 1.0 1.0 Vulcan XC-72 ---- ---- 5.0 5.0 UL94 result V-O V-0 V-o V-o (0.65mm) Table 4

Nylon 66 54.0 54.0 50.0 Amgard 5.0 10.0 9.0 CPC405 9323LP 5.0 - 5.0 T700S 30.0 30.0 30.0 Harochem 1.0 1.0 1.0 CPR-5 Vulcan 5.0 5.0 5.0 XC-72 UL 94 NR NR NR result (0.65mm) EXAMPLE 2 Mouldings of composition as detailed in Table 5 were produced by the method of Example 1 and tested according to the 5V procedure described in the UL94 testing specification. The results are also recorded in Table 5. This is a more severe test than the procedure of Example 1. The maximum rating is 5V-A. The rating achieved, 5V-B, is still good, and superior to the V-O rating of Example 1.

Table 5

Reny 58.0 53.6 Amgard CPC40S 12.0 12.0 9323 LP ---- 4.4 T700S 30.0 30.0 UL94 result 5V-B 5V-B UL94 test piece 0.65 0.65 thickness (mm)

Claims (11)

1. CLAIMS: 1. A shaped product having a thickness of 1.6mm or less and formed from a flame retardant polyamide composition, comprising (a) a semi-aromatic polyamide, or a polymer blend comprising at least 50% by weight of semi-aromatic polyamide, and (b) red phosphorus.
2. 2. A shaped product according to Claim 1, in which the composition further comprises (c) a phenolic resin.
3. 3. A shaped product according to Claim 1 or 2, in which the composition further comprises (d) a fibrous reinforcement.
4. 4. A shaped product according to any of Claims 1 to 3, in which the composition contains from 2% to 20% by weight of red phosphorus, based on the total weight of the composition.
5. 5. A shaped product according to Claim 4, in which the composition contains from 2% to 10% by weight of red phosphorus, based on the total weight of the composition.
6. 6. A shaped product according to any of Claims 2 to 5, in which the composition contains from 2% to 10% by weight of the phenolic resin, based on the total weight of the composition.
7. 7. A shaped product according to Claim 6, in which the composition contains from 2% to 7% by weight of the phenol resin, based on the total weight of the composition.
8. 8. A shaped product according to any of Claims 1 to 7, in which the semi-aromatic polyamide is a polycondensation product of an aromatic or araliphatic diamine and an alkylene dicarboxylic acid.
9. 9. A shaped product according to any of Claims 1 to 8, having a thickness of 1.2mm or less.
10. 10. A shaped product according to Claim 1, substantially as hereinbefore described with reference to any of the Examples.
11. 11. Use of a flame retardant polyamide composition, comprising (a) a semi-aromatic polyamide, or a polymer blend comprising at least 50% by weight of semi-aromatic polyamide, and (b) red phosphorus, for making a shaped product having a thickness of 1.6mm or less.