Flame-retardant treatment of fabrics

Abstract: In the flame-retardant treatment of fabrics, there is provided a means for increased "loading" of phosphorus compounds (up to 25% moisture is retained after impregnation and drying of the fabric). This in turn enables a phosphonium compound "add-on" of 50% to 73% (relative to the weight of the fabric) and gives a correspondingly higher degree of flame-retardant properties.

Description: This invention relates to an improved method of treating fabrics to impart flame-retardant properties thereto. A known process for the flame-retardant treatment of fabrics including cellulosic (e.g. cotton) fibres consists of impregnation of the fabric with an aqueous solution of a poly(hydroxyorgano) phosphonium compound, for example, a tetrakis (hydroxyorgano) phosphonium salt. Alternatively, the poly (hydroxyorgano) phosphonium compound may comprise a condensate with a nitrogen - containing compound such as urea. Following impregnation, the fabric is dried and then cured with ammonia to produce a cured, water-insoluble polymer which is mechanically fixed within the fibres of the fabric. After curing, the polymer is oxidised to convert trivalent phosphorus to pentavalent phosphorus and the fabric is washed and dried. Fabrics treated according to the aforesaid process and garments made from such treated fabrics are sold under the Registered Trade Mark PROBAN of Albright & Wilson Limited. Modifications of the said process are disclosed in EP-A-0 451 663 and EP-A-0 451 664. Hitherto, the drying of the impregnated fabric prior to curing must be such that the dried impregnated fabric has a moisture content no greater than 18%, corresponding to an "add-on" of phosphonium compound of 40-44%. Where the moisture content exceeded 18%, migration of the cured phosphonium compound was found to occur, causing permanent staining of the fabric. Limiting the moisture content to a maximum of 18% resulted in turn in a limit to the "add-on" of phosphonium compound and consequently imposed an upper limit on the flame-retardant properties of the treated fabric. For example, our published UK application GB-A-2271787 describes a method of imparting flame-retardant properties to fabric in which 18% moisture content is not exceeded. It has now been found, unexpectedly, that it is possible to dry the impregnated fabric to a moisture content of up to 25% without detrimental effect (especially without staining), thus enabling a higher "add-on" of phosphonium compound and hence a higher level of flame-retardant properties. The "add-on" of phosphonium compound in accordance with the present invention is in the range 50 to 73% relative to the weight of the fabric. Accordingly, the present invention provides a method of treating fabrics including cellulosic fibres to impart flame-retardant properties thereto, characterised by: (a) impregnating the fabric with an aqueous solution of a poly (hydroxyorgano) phosphonium compound, said solution comprising a condensate of tetrakis (hydroxymethyl) phosphonium chloride and urea, to give a phosphonium compound "add-on" in the range 50% to 73% relative to the weight of the fabric, said solution moreover containing one or more primary, secondary or tertiary aliphatic amines which have been protonated and neutralised prior to being added to said solution; (b) drying the impregnated fabric to a residual moisture content in the range 17 to 25% relative to the weight of the fabric; (c) curing the dried impregnated fabric with ammonia to produce a cured, water-insoluble polymer which is mechanically fixed within the fibres of the fabric; (d) batching the fabric for at least one hour prior to oxidation; (e) oxidising the cured polymer with hydrogen peroxide to convert trivalent phosphorus to pentavalent phosphorus; (f) washing and drying the fabric. Preferably, the drying of the impregnated fabric, in stage (b), may be to a residual moisture content in the range 19 to 21% relative to the weight of the fabric. Oxidation, in stage (e), may suitably be carried out in the presence of a wetting agent. The amount of the hydrogen peroxide used for the oxidation may be up to 25% relative to the weight of the fabric. Suitably, the wetting agent is used in an amount of about 2g/litre of oxidation bath. The fabric to be treated according to the present invention may consist essentially of cellulosic (e.g. cotton) fibres. Alternatively, the fabric may comprise both cellulosic and non-cellulosic fibres. Examples of non-cellulosic fibres which may be used include polyamide fibres, acrylic fibres, aramid fibres, polyester fibres and polybenzimidazole fibres. A suitable fabric for treatment according to the present invention is one comprising 60% by weight cotton fibres and 40% by weight polyester fibres. In accordance with the present invention, one or more protonated and neutralised primary, secondary or tertiary aliphatic amines are added to the impregnating solution, as disclosed in GB-A-2271787. The present invention will be illustrated, merely by way of example, as follows: EXAMPLE 1 A black, 100% cotton fabric of weight 280g/m 2 was treated by impregnation with an aqueous solution containing a precondensate of tetrakis (hydroxymethyl) phosphonium chloride and urea, together with protonated and neutralised amines according to GB-A-2271787. (In some comparative treatments, the protonated and neutralised amines were omitted; the presence or absence of these is indicated in the data as "ITC 628/yes/no"). The processing conditions were as follows: dry temperature set 120°C ammonia cure conditions (x2) flow rate 53 litres/min pressure 23 PSI (3.336 kPa) dwell time 21.7sec. 1.1 Simulated Continuous Oxidation Oxidation conditions H 2 O 2 conc. X% (W/W) (see tables) fabric dip one end fabric airing one end Neutralization conditions Na 2 CO 3 conc. 20 g/litre fabric dip 4 ends Detergent washing was conducted in the Jig using a bath containing 3 g/litre of Na 2 CO 3 and 2 g/litre of WA 100* at 60°C for 4 ends. Sodium metabisulphite washing was again carried out in the Jig. The bath contained 5 g/litre soda ash, 2 g/litre WA 100 and 10 g/litre sodium metabisulphite; at 60 C for 3 ends. Hot rinsing was carried out at 60°C for 4 ends and cold rinsing was carried out in the Jig. The processing conditions for individual fabric samples are given in TABLE I (below) and the phosphorus and nitrogen content of the fabric, both after finishing and after durability testing, together with the results of flame-retardancy testing, are given in TABLE II (below). FABRIC SAMPLE CODE ADD-ON OF PHOSPHONIUM CPD (%) ITC 628 YES/ NO H 2 O 2 CONCN. (V/V) H 2 O 2 CONCN. (W/W) RESIDUAL MOISTURE CONTENT (%) DRY ADD-ON (%) 941A 50.0 YES 43% 29% 19-21% 21.8% 942A 50.0 YES 43% 29% 19-21% 23.0% 943A 50.0 NO 43% 29% 21-23% 22.3% 944A 50.0 NO 43% 29% 21-23% 22.9% 941B 55.2 YES 36% 29% 19-21% 26.9% 942B 55.2 YES 36% 29% 19-21% 27.0% 941C 54.3 YES 35% 35% 18-22% 25.7% 942C 54.3 YES 35% 35% 18-22% 25.7% 945 70.5 NO 60% 35% 15-16% 35% All the above processing gave "clear" fabrics, i.e. without surface staining by migration of the cured phosphonium compound. FABRIC SAMPLE CODE as finished after durability FR results P% N% P% N% DIN NFG 942A 3.20 3.06 3.14 3.09 pass pass 944A 3.28 3.15 3.07 2.98 pass pass 942B 3.52 3.51 3.27 3.24 pass pass 945 4.39 4.26 4.09 4.06 pass pass 1.2 Jig oxidation The processing conditions were the same as in 1.1. (above) except for the oxidation conditions: H 2 O 2 conc; x% (w/w) (see tables) Ends 3 batch time 3 min The results are given in Tables III and IV (below). FABRIC SAMPLE CODE ADD-ON OF PHOSPHONIUM CPD (%) ITC 628 YES/ NO H 2 O 2 CONCN. (V/V) H 2 O 2 CONCN. (w/w) RESIDUAL MOISTURE CONTENT (%) DRY ADD-ON (%) 941D 43.8 NO 10% 29% 13-14 23.1 942D 43.8 NO 10% 29% 13-14 23.0 941E 44.3 YES 10% 29% 13-14 21.0 942E 44.3 YES 10% 29% 13-14 20.8 943C 54.8 YES 15% 29% 19-21 27.6 944C 54.8 YES 15% 29% 19-21 27.7 941F 51.7 YES 15% 35% 18-19 26.6 942F 51.3 7 YES 15% 35% 18-19 26.7% All the above processing gave "clear" fabrics, as in 1.1. (above) FABRIC SAMPLE CODE as finished after durability FR results P% N% P% N% DIN NFG 942D 2.99 2.93 2.85 2.84 pass pass 942E 3.08 2.99 2.98 2.95 pass pass 943C 3.58 3.58 3.41 3.38 pass pass 942B 3.52 3.51 3.27 3.24 pass pass 941F 3.69 3.59 3.11 3.07 pass pass 942F 3.75 3.74 3.45 3.34 pass pass EXAMPLE 2 The process of Example 1 (above) was carried out on a sateen weave fabric comprising 60% by weight cotton fibres and 40% by weight polyester fibres, without the addition of the protonated and neutralised amines, i.e. "ITC 628:no". 2.1 Effect of peroxide concentration on surface staining Hydrogen peroxide of 35% w/w strength was used and the results are given in TABLE V (below): FABRIC SAMPLE CODE H 2 O 2 CONC (W/W) ADD-ON OF PHOSPHONIUM CPD (%) RESIDUAL MOISTURE CONTENT (%) SURFACE STAINING 943D 3.5 48.6 18-20 YES 944D 3.5 48.6 18-20 YES 941G 10.0 48.9 17-19 a little 942G 10.0 48.9 17-19 a little 943D 18.0 48.8 18-20 none 944D 18.0 48.8 18-20 none 2.2 Effect of batching on surface staining Hydrogen peroxide of 35% w/w strength was again used, but the fabric was batched for 3 hours prior to oxidation. The results are given in TABLE VI (below): FABRIC SAMPLE CODE H 2 O 2 CONC (W/W) BATCH TIME (HRS) ADD-ON OF PHOSPHONIUM CPD (%) RESIDUAL MOISTURE CONTENT (%) SURFACE STAINING 943D 3.5 - 48.6 18-20 HEAVY 944D 3.5 - 48.6 18-20 HEAVY 942H 3.5 3 48.6 18-20 NONE 942J 3.5 3 48.1 18-20 NONE EXAMPLE 3 In a further example, a 1000m length of a twill fabric comprising 60% by weight cotton fibres and 40% by weight polyester fibres and having a weight of 315 g/m 2 was treated in accordance with the present invention. The processing conditions are shown in TABLE VII (below): FABRIC SAMPLE CODE ADD-ON OF PHOSPHONIUM (%) ITC 628 CPD Yes/No H 2 O 2 CONC. (V/V) H 2 O 2 CONC. (W/W) RESIDUAL MOISTURE CONTENT (%) %P %N 694A 53 NO 46 50 25 3.33 3.54 694B 53 YES 46 50 25 3.51 3.66 All the above processing gave "clear" fabrics, i.e. without surface staining by migration of the cured phosphonium compound.

Claims: A method of treating fabrics including cellulosic fibres to impart flame-retardant properties thereto, characterised by: (a) impregnating the fabric with an aqueous solution of a poly (hydroxyorgano) phosphonium compound, said solution comprising a condensate of tetrakis (hydroxymethyl) phosphonium chloride and urea, to give a phosphonium compound "add-on" in the range 50% to 73% relative to the weight of the fabric, said solution moreover containing one or more primary, secondary or tertiary aliphatic amines which have been protonated and neutralised prior to being added to said solution; (b) drying the impregnated fabric to a residual moisture content in the range 17 to 25% relative to the weight of the fabric; (c) curing the dried impregnated fabric with ammonia to produce a cured, water-insoluble polymer which is mechanically fixed within the fibres of the fabric; (d) batching the fabric for at least one hour prior to oxidation; (e) oxidising the cured polymer with hydrogen peroxide to convert trivalent phosphorus to pentavalent phosphorus; (f) washing and drying the fabric. A method according to Claim 1, characterised in that the impregnated fabric is dried, in stage (b), to a residual moisture content in the range 19 to 21% relative to the weight of the fabric. A method according to Claim 1 or 2, characterised in that the oxidising, in stage (e), is carried out in the presence of a wetting agent. A method according to any one of the preceding claims, characterised in that the amount of the hydrogen peroxide used in stage (e) is up to 25% relative to the weight of the fabric. A method according to any one of the preceding claims, characterised in that the fabric to be treated consists essentially of cellulosic fibres, for example cotton fibres. A method according to any one of claims 1 to 4, characterised in that the fabric to be treated comprises both cellulosic and non-cellulosic fibres. A method according to claim 6, characterised in that the non-cellulosic fibres are polyamide fibres, acrylic fibres, aramid fibres, polyester fibres or polybenzimidazole fibres. A method according to claim 6 or 7, characterised in that the fabric comprises 60% by weight cotton fibres and 40% by weight polyester fibres.

Inventors: LEI XIAO PING, ZAKIKHANI MOHSEN, LEI, XIAO PING, ZAKIKHANI, MOHSEN
Applicants: ALBRIGHT & WILSON UK LTD, ALBRIGHT & WILSON UK LIMITED
Application year: 1995
Main classification: D06M15
IPC codes: D06M101, D06M15, C09K21, D06M13