Note: Descriptions are shown in the official language in which they were submitted.
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T~ TMF!NT OF FABRIC8
This invention relates to a fabric treatment process, in
particular one for rendering fabrics flame retardant with organo
phosphorus compounds.
The flame retardant treatment of cotton fabric with tetrakis
(hydroxymethyl) phosphonium compounds (hereafter called THP
compounds) or precondensates thereof with urea has been described in
USP2983623, 4068026, 4078101, 4145463 and 4494951. The treatment
processes involved impregnation of the fabric with an aqueous solution
of the chemicals, followed by drying, treatment with ammonia to cure
the phosphorus compounds in order to insolubilize the phosphorus onto
the fabric, finally with oxidation and washing to leave a treated
fabric whose flame resistance is retained even after many washes in
use.
However the cure efficiency, (which is a measure of the
effectiveness of the cure in insolubilizing the phosphorus on the
fabric), is not always ideal and a percentage of the expensive
phosphorus chemicals applied in the impregnation step is not cured.
Thus it is washed off the fabric after the cure and wasted,
particularly for cotton polyester fabrics and especially polyester
cotton fabrics. In some cases, adequate flame retardant properties
cannot be provided to the latter with THP compounds Furthermore,
while some techniques enable the necessary flame retardant properties
to be provided to the fabric when first cured, those properties often
diminish significantly on repeated washing.
We have discovered a process which can increase the amount of P
compound fixed onto the substrate especially one comprising non
cellulosic fibres and can enable adequate flame retardant properties
to be provided for fabrics comprising non cellulosic fibres such as
cotton polyester blends.
The present invention provides a process for the flame-retardant
treatment of an organic fibrous substrate containing reactive groups,
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which process comprises impregnating said substrate with an aqueous
solution of an organophosphorus compound, to provide an impregnated
substrate which is dried and cured, by heating at a temperature of at
least 100C.
The organic fibrous substrate is especially one comprising or
consisting essentially of cellulosic fibres. The cellulosic fibres
are preferably natural cotton, but may be ramie, flax, paper or
cardboard or regenerated fibres (e.g. viscose or cuprammonium fibres)
or partly etherified or esterified cellulose (e.g. cellulose acetate
or propionate). The substrate may be substantially completely
cellulosic eg 100% cotton or may contain both cellulosic and non
cellulosic organic fibres, or just contain non cellulosic organic
fibres eg 100% polyester fibres. Inorganic fibres such as glass
fibres are usually absent.
The non cellulosic fibres are preferably polyester or polyamide
fibres but may also be acrylic. The polyamide may be an aliphatic
one, such as copolymers of a polyamine (such as a diamine) preferably
an alkylene diamine, eg of 4-12 carbon atoms and a poly carboxylic
acid eg a dicarboxylic acid, of 4-14 carbon atoms such as an alkylene
dicarboxylic acid (e.g. Nylon 66), or polylactams such as Nylon 6.
Alternatively the polyamide may be an aromatic one, such as aramids
based on aromatic dicarboxylic acids and phenylene diamines. The
acrylic polymer may be polyacrylonitrile homopolymer or copolymer with
vinyl chloride, as in modacrylic fibres. The substrate can contain at
least 20% of cellulosic fibres and up to 80% of coblendable fibres
e.g. 10-80% especially 25-80% of coblendable fibres such as
polyamides. However preferably the substrate comprises cellulosic
fibres and polyester fibres. The substrate usually contains up to 80%
(e.g up to 70%) polyester fibres and from 20% (e.g. from 30%) upwards
of cellulosic fibres, e.g. 1-80% or 1-70%, such as 15-70% particularly
22-38% or 45-75% polyester fibres and 20-99% or 30-99% (such as
30-85%), particularly 62-78% or 25-55% cellulosic fibres.
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Substrates comprising at least 45% non cellulosic fibres, eg
polyester fibres such as 45-100% polyester, are preferred as are ones
comprising 30-78% cellulosic fibres and 22-70% polyester fibres, or
30-62% cellulosic fibres and 38-70% polyester fibres. The polyester
is usually a condensation product containing structural units from an
aliphatic alcohol, e.g. dihydric alcohol, especially ethylene glycol
or butane diol (or mixtures thereof) and an aromatic dicarboxylic
acid, e.g. terephthalic acid, or a mixture thereof with other
dicarboxylic acids, such as isophthalic acid, or sebacic acid.
The substrate fibres may be in the form of thread or non woven
fabric, but are preferably as woven fabric. Mixtures of fibres e.g.
of cellulosic and other fibres may be an intimate or non intimate
mixture but the fibres are preferably in the form of blend of
cellulosic fibres and the other fibres e.g. polyester fibres, as in
cospun blends such as cotton/polyester or polyester/cotton staple
fibre, but may be in the form of core spun yarn with a core of the
other fibre e.g. polyester sheathed in cotton fibres. In a fabric,
the warp and weft fibres are preferably the same, but may be different
e.g. one may be from cotton fibres and the other from e.g. polyester/
cotton fibres. Thus in this specification the term "blend" also
includes unions and union/blends as well as core sheath fibres. The
substrate is preferably a fabric with a weight of 0.05-1.0kg/m2, e.g.
0.150-0.40kg/m2, or 0.05-0.20kg/m2. Examples are polyester/cotton
shirting or sheeting or curtain fabric.
The substrate is treated with the organophosphorus compound. In
the tetrakis (hydroxyorgano) phosphonium compound, each hydroxyorgano
group is preferably an alpha-hydroxyorgano group of 1-9 carbons.
Especially said alpha-(hydroxyorgano) group is one of formula HOC-
(R1R2), wherein each of R1 and R2 (these being the same or different)
represents hydrogen or an alkyl group of 1 to 4 carbons, e.g. methyl,
or ethyl. Preferably R1 is hydrogen, and R2 is methyl or especially
hydrogen, as in tetrakis (hydroxymethyl) phosphonium (THP) compounds.
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The use of tetrakis hydroxyorgano phosphonium compounds in
general will hereafter be exemplified with respect to THP compounds ~
with corresponding molar amounts of the other compounds used instead
of the THP compound.
The substrate is treated with an impregnation solution which is
an aqueous solution of a THP salt mixed with a nitrogen compound
condensahle therewith to form a water soluble precondensate, or a
solution of a precondensate of said salt and nitrogen compound, or a
solution of THP salt, or water soluble self-condensate thereof, or at
least partly neutralised THP salt, (e.g. THP hydroxide), with or
without the nitrogen compound. The impregnation solution may
alternatively comprise a solution of said precondensate and further
nitrogen compound (eg urea), as in a solution with a molar ratio of
total nitrogen compound (free and combined) to THP group (free and
combined) of 0.8-2:1, eg 0.8-1.5:1. The nitrogen compound is
preferably one with at least two NH groups (such as 2-4), but
advantageously contains two NH or especially two NH2 groups. The
nitrogen compound is usually bifunctional and may be an amine but is
especially an amide. Examples of suitable nitrogen compounds are
biuret, guanidine, melamine and methylolated melamines, but urea is
the preferred species for the purposes of this invention, especially
in the absence of melamine or a methylolated melamine. The nitrogen
compound is preferably urea whenever it is present in the
precondensate.
In a preferred embodiment of this invention, the solution
contains a precondensate of THP salt, e.g. chloride or sulphate, and
the nitrogen compound in a molar ratio of nitrogen compound to THP of
0.05-0.8:1, e.g. 0.05-0.6:1, or 0.22-0.8:1, such as 0.25-0.6:1,
especially 0.4-0.6:1. The pH of said solution is usually 2-7.5, such
as 4-6.5, e.g. 4-5. The atom ratio of total N atoms in the nitrogen
compound or condensate to the total P atoms from THP salt or
condensate in the impregnation solution is usually not greater than
4:1, eg 1-3:1.
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In a preferred embodiment of the invention, a fabric compr;sing
non cellulosic fibres, optionally with cellulosic ones, is treated
with an impregnation solution comprising a water soluble condensate of
the organophosphorus compound and a bifunctional nitrogen compound
such as urea. Preferably, these compounds are present in a molar
ratio of 1:0.25-0.6. Subsequent curing of said fabric is by means of
heat, and preferably also ammonia. In another embodiment, when curing
is with heat and ammonia, the impregnation solution contains the
organophosphorus compound and the nitrogen compound, unreacted or
reacted completely or in part.
The concentration of organophosphorus compound in the aqueous
solution may be 5-70% eg 5-35% or 35-70% (expressed by weight as THP+
ion), but is preferably 20-35%.
If desired the solution may contain a wetting agent such as a
nonionic one~eg in amount of 0.05-0.5% by weight of the impregnation
solution, a fabric softener such as a polyethylene one and in
preferred amount of 0.1-2% by weight, and a salt of a strong acid and
weak base(such as an ammonium or alkaline earth metal chloride or
nitrate or ammonium acid phosphate)as catalyst for the heat cure, and
in amount of 0.1-5% by weight.
The treated substrate is impregnated to give an organo phosphorus
pick up of less than 40% e.g. 10-40%~uch as 10-30/O)~especially 20-30%
(as THP ion based on the original weight of the substrate). The
substrate can be impregnated with solution and the wet substrate~e.g.
fabric~usually squeezed to a wet pick up of 50-130%, e.g. 60-100%
(based on the original weight of the substrate). Alternatively~ the
treated substrate may be impreynated with a concentrated impregnation
solution via a minimum add-on, eg foam, technique and a 10-50% wet
pick up.
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The organophosphorus impregnated substrate is then dried and heat
cured either in two separate operations or one continuous operation.
Drying may be in a stenter oven or over heated cans, e.g. steam cans
and may involve heating at 80-160C for 10 min to 10 secs eg at 100C
to 120C for 3 min to 30 secs. Heat curing may be in a stenter or
baking oven at a temperature of at least 100C e.g. at 100-200C or
100-180C (such as 130-170C) for 10-0.5 minutes e.g. 7-1 minutes.
Higher temperature with long curing times should be avoided with
substrates containing at least a majority of cellulosic fibres
especially 100% cotton.
In a preferred embodiment of this invention, the substrate is
further cured by treatment with ammonia, usually gaseous ammonia,
which diffuses through the substrate and/or is forced through the
substrate e.g. by passage of the fabric over a perforated tube through
which ammonia has is emitted. Examples of apparatus and techniques
suitable for the ammonia cure are given in USP 4145463, 4068026 and
4494951, the disclosure of which is hereby incorporated by reference.
If desired the ammonia cure may precede the heat cure, or the curing
may be by heat alone, but preferably the ammonia cure takes place
after the heat cure.
The cured substrate usually has solids add-on of 10-50% or 10-40%
e.g. 10-30% e.g. 10-25% or 15-30% especially 20-30%, (by weight of the
original substrate), hased on a total organophosphorus compound pick
up of 16-36%, e.g. 20-28% (expressed as THP ion on the same basis).
The cured substrate is then usually subjected to at least one of
the following operations: further insolubilization of the cured resin
in the treated substrate, oxidation (in order to convert at least some
trivalent phosphorus to pentavalent phosphorus in the cured resin), or
washing with aqueous base and washing with water.
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Alternatively the oxidation may be performed with a gas
containing molecular oxygen, preferably air, and particularly with the
gas being drawn or blown through the substrate; thus the substrate in
the form of fabric can be passed over a vacuum slot or perforated tube
though which the gas is blown or sucked.
.
After the oxidation, or instead thereof, the cured substrate may
be washed with an aqueous medium, preferably an aqueous solution
of a base, e.g. sodium carbonate, and/or rinsed with water. The
oxidation preferably reduces the residual content of formaldehyde on
the cured substrate. Alternatively the cured substrate may simply be
rinsed with water or submitted to other operations to reduce its
content of watQr soluble materials. Finally the cured fabric is
dried, to give a final substrate.
The final substrate, e.g. fabric, can be used for making workwear
such as overalls, boiler suits and protective clothing including
uniforms, particularly from 30-70% (e.g. 55-70%) cotton and 70-30%,
(e.g. 45-30%) polyester, and household fabrics such as sheets and
curtains particularly from 30-70% (e.g. 30-60%) cotton and 40-70%
polyester.
Processes of the invention with heat and ammonia cure usually
give better flammability results, with fabrics comprising non
cellulosic fibres, than are obtained with just ammonia cure thereby
enabling fabrics to pass more severe flammability tests eg BS6249
(1989) than otherwise. The cured substrates obtained by the process
of the invention may also have less reduction in strength.
In this specification unless otherwise noted parts and
percentages are by weight.
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The invention is illustrated in the following Examples:-
In the Examples were used 4 fabrics A-D details of which were as
follows. All had been previously submitted to a desizing treatment.
Fabr~c Nature ~e~ght kg/m2
A Polyester 0.140
B 67/33 Polyester cotton 0.095
C 100% Cotton 0.280
D 67/33 Polyester cotton 0.285
The polyester cotton fabrics were cospun intimate blends.
ExamPles 1-8
Fabrics A, B and C were impregnated to about 55-95% wet pick up
with an aqueous solution at pH 4.5 of a precondensate of THP chloride
and urea in a molar ratio of 1:0.5, the solution containing an amount
of precondensate corresponding to 25.2% by weight THP+ ion. The
impregnated fabric was then dried for 1.5 minutes in an oven at 100C,
and then heat cured under conditions specified below. In Ex 8 after
the heat cure, the water content of the fabric was returned to normal
by equilibration in a humidity controlled room overnight. The heat
cured fabric of Ex 8 was then cured further with ammonia gas, which
was passed through the fabric in a chamber and in a manner as
described in USP 4145463; the cure time was 4 sec. After the heat
cure step of Ex 1-7 and ammonia cure step of Ex 8 the fabric was
oxidized for 5 min in 5% aqueous hydrogen peroxide solution, washed
for 5 min at 60C in 2g/l sodium carbonate solution and rinsed for 5
mins with cold water. The rinsed fabric was then dried to give a
final fabric. The final fabric was then analysed for P and N and
tested for flame retardancy according to BS 5438 (1989) test 2A; in
the case of Ex 1 and 4-6 the fabric was also tested after washing 50
times at 93C, the washing being as in the manner described in DIN
53920 procedure l with soft water. The results were as follows:
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xample Fabric Heat Cure X Solid Cure Char Fabric % P Cure
min Temp C pick up Efficiency Length Final %P Efficiency
mm
1 A 4 150 l9.7 62.0 109* 1.34* 53.2
2 B 4 150 12.1 69.5 99 1.93 85.2
3 C 2 150 26.0 36.9 92 1.82 57.6
4 C 3 140 26.0 34.3 63
C 4 140 26.2 35.9 52
6 C 6 140 26.2 44.7 72
7 B 2 180 17.0 72.3 110
8 B 2 180 19.0 74.0 140
Denotes figures after 50 washes.
The corresponding char lengths for the final fabrics of Ex 4-6 after
50 washes were 85, 48 and 65 mm respectively.
The cure efficiency was the percentage of final cured solids to the
applied solids pick up. The P efficiency was the percentage of P in
the final fabric to the P applied to the fabric.
Examples 9 and 10
Fabric D was impregnated with an aqueous solution of 1:2 molar
condensate of urea and tetrakis (hydroxymethyl) phosphonium chloride
as described in Ex 1-8 and the excess of liquid squeezed from the
fabric.
In Ex 9 and 10 the fabric was then dried and heat cured in a
single step at 150C for 4 minutes. In Ex 10 the heat cured fabric
was allowed to stand overnight in a humidity controlled room to
equilibrate its moisture content and was then cured further with
ammonia gas which was passed through the fabric in a chamber and in a
manner as described in USP 4145463.
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- After the heat cure step of Ex 9 and ammonia cure step of Ex 10,
the fabrics were oxidized with 10% hydrogen peroxide solution, rinsed
with water, washed with aqueous sodium carbonate and then rerinsed and
dried, to give final fabrics.
The final fabrics were then analysed for P and N and tested for
flame retardancy. For Ex 10 the testing was done before and after
washing 40 times at 93C, the washing being as in the manner described
in DIN 53920 procedure procedure 1 with soft water. The test method
used was according to BS 5438 1989 test 2A and the char length was
determined. The analysis results were as follows:
EXAMPLE FABRIC %P %NChar length
mm
9 Final 1.93 1.36106
10 Final 2.33 1.9764
After 40 washes 2.01 1.87
Examples 11-13
In these Examples fabrics were impregnated with THP precondensate
as in Ex 1 but the concentration of precondensate in the aqueous
impregnation solution was equivalent to 32.76% THP+ ion by weight, and
' the impregnated fabric was not dried at 100C before the heat cure.
Otherwise for Ex 11-13 the processes of Ex 1-8 were repeated with heat
cure and for Ex 12 and 13, the heat cure was followed by cure with
ammonia, which was passed through the fabric in a chamber and in a
manner as described in USP 4145463; the cure time was 4 sec. The heat
cured fabric of Ex 11 and the ammonia cured fabrics of Ex 12 and 13
were then oxidized, washed, rinsed and dried in Ex 1-8. The final
fabrics were then analysed for %P and tested for flame retardancy as
described in Ex 1. The results were as follows.
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Example Fabr~c Heat Cure % Sol~d Cure Char Fabr~c X P
m~n Temp C p~ck up Efflciency Length Final %P Efficiency
mm
11 A 2 150 27.0 63.0 130 2.53 77.7
12 A 2 150 26.1 71.7 110 2.69 84.8
13 B 2 150 22.5 77.8 108 2.68 95.3
Examplesl4 and 15
The process of Ex 9 and 10 was repeated with another 100%
polyester fabric (E) of 0.140 kg/m2 and an intimate blend 60:40 cotton
polyester fabric (F) of 0.268 kg/m2. All the final fabrics and those
after 20 washes passed the flammability tests.
