LEWIS, David Malcolm (13 St. Richards Road, Otley, West Yorkshire LS21 2AL, GB)
WEBB, Paul (50 Church Avenue, HorsforthLeeds, West Yorkshire LS18 5LD, GB)
LU, Yong (37 Miles Hill View, Leeds, West Yorkshire LS7 2EH, GB)
HAWKES, Jamie Anthony (23 Athens, Silver Cross WayGuiseley,Leeds, West Yorkshire LS20 8FH, GB)
LEWIS, David Malcolm (13 St. Richards Road, Otley, West Yorkshire LS21 2AL, GB)
WEBB, Paul (50 Church Avenue, HorsforthLeeds, West Yorkshire LS18 5LD, GB)
LU, Yong (37 Miles Hill View, Leeds, West Yorkshire LS7 2EH, GB)
| Claims : 1. A method of treating a material to improve its flame retardancy, the method comprising applying to the material a composition having a pH of less than 4 and which comprises urea and an acid selected from phosphorous acid, phosphoric acid, sulfamic acid and mixtures thereof. 2. A method according to claim 1 wherein the composition is applied to the material using an exhaustion technique . 3. A method according to claim 1 or claim 2 wherein the composition comprises phosphorous acid. 4. A method according to claim 3 wherein at least 70 wt% of the acid component present in the composition is phosphorous acid. 5. A method according to any preceding claim wherein the weight ratio of urea to acid used in the present invention is from 0.2:1 to 10:1. 6. A method according to any preceding claim wherein the material comprises wool. 7. A method according to any preceding claim which comprises the steps of: (a) preparing a composition comprising urea and an acid selected from phosphorous acid, phosphoric acid, sulfamic acid and mixtures thereof; (b) contacting the material with said composition; and (c) removing the material from contact with the composition . 8. A method according to claim 7 wherein the material is contacted with a heated composition. 9. The use of a composition comprising urea and an acid selected from phosphorous acid, phosphoric acid, sulfamic acid and mixtures thereof to impart flame retardant properties to a material, preferably a material comprising wool. 10. A material treated by a method as claimed in any of claims 1 to 8. 11. A material according to claim 10 having wash-durable flame retardant properties. |
The present invention relates to a method of treating a material. In particular, the invention relates to a method of treating a material to impart flame retardant properties thereto. Suitably, a material thus treated is durable to laundering and/or dry cleaning.
Many materials including, for example, wool and cotton materials require chemical treatment in order to render them flame retardant. Wool is inherently flame retardant although not enough to be used in certain applications, for example mass transit seating.
It is desirable that flame retardant materials are low cost, durable, do not impact on the mechanical properties of the fabric, meet health and safety requirements, are environmentally acceptable, and are able to tolerate traditional dyeing and printing processes for all colour ranges when used on dyed materials.
Flame retardant (FR) compositions for wool based materials originally focused on the use of chromium, which unfortunately coloured the wool material. However in the 1970s the International Wool Secretariat (IWS) developed the λ Zirpro' treatments. The generic title of λ Zirpro' covered a range of treatments which were based on po tas s ium hexafluorozirconate an d potassium hexafluorotitanate salts.
T he λ Z irpro ' treatment s are b a s e d on th e exhau s t i on o f the se negative ly charged s al t s , under acidi c conditi ons , onto pos itively charged s ites in wool . Other flame retardants for wool are based upon halogen donors, which tend to interfere with free radical processes that maintain a flame, although these are environmentally unacceptable. Alternative treatments available are based on phosphate / polyphosphate salts, but these have achieved only limited commercial success, and are not usually durable.
The present invention relates in particular to a method of providing wash-durable flame retardant compositions. Each of the known existing wash-durable flame retardant compositions has one or more disadvantages.
One existing durable FR composition is the λ Zirpro' system mentioned above, in which a solution containing the relevant salt is applied to wool via an exhaustion method. An λ exhaustion' method refers to a process where the material is soaked in the FR solution for a period of time until the active chemical has been absorbed (or Exhausted') onto the material. This is usually done in a winch machine or other batch machine.
Not all dyed wool materials can be treated with the λ Zirpro' system since the hexafluorozirconate system discolours some dyes. The zirconium and titanium hexafluorozirconate salts also have environmental problems associated with them. Zirpro also has another disadvantage in that it can make a fibre more brittle. It is possible to treat wool with Zirpro in top or yarn form, but the brittleness will lead to loss of fibre when it is then spun and weaved. For this reason it is usually desirable to treat materials with a Zirpro process in fabric form. Another durable FR composition is Noflan (RTM) supplied by Firestop (UK) , which is a phosphorous based chemical that is normally applied using a pad bake system, as is described in US6863846 and US 625947. This product however contains a large amount (~30%) of ammonium chloride which has the potential to form hydrochloric acid under humid conditions .
It is an object of the present invention to provide a durable FR composition which overcomes at least one disadvantage of the prior art, whether specifically mentioned herein or otherwise.
According to a first aspect of the present invention, there is provided a method of treating a material to improve its flame retardancy, the method comprising applying to the material a composition having a pH of less than 4 and which comprises urea and an acid selected from phosphorous acid, phosphoric acid, sulfamic acid and mixtures thereof.
By phosphorous acid, we mean to refer to the material having a molecular formula H 3 PO 3 which upon reaction with a base produces phosphite salts.
By phosphoric acid, we mean to refer to the material having a molecular formula H3PO4 which upon reaction with a base produces phosphate salts.
By sulfamic acid we mean to refer to the material having the formula H 2 N-SO 3 H which upon reaction with a base forms sulfamate salts. Preferably the composition is an aqueous composition. It may further comprise other water-mi s cible solvents. Preferably however water is the only solvent present.
In some preferred embodiments the composition consists essentially of water, urea and an acid selected from phosphorous acid, phosphoric acid, sulfamic acid and mixtures thereof. In such embodiments the composition preferably comprises less than 10 wt% further ingredients, preferably less than 5 wt%, more preferably less than 1 wt% .
Preferably the composition has a pH of less than 3.5, more preferably it has a pH of less than 3. Suitably the composition applied to the material has a pH of at least 0.5, for example at least 1 or at least 1.5.
In some preferred embodiments the pH of the composition may have a pH of from 1.5 to 2.5, for example about pH 2.
Preferably the composition applied to the material in the method of the present invention does not comprise a base. In particular, it is preferred that the composition is substantially free of a base comprising a monovalent metallic cation.
In the method of the present invention the composition may be applied to the material by any suitable means. Typically different methods are used depending on the physical form of the material. For example, wool top may typically be treated in a bump machine; fabric may suitably treated in a jet machine or winch machine; garments or other finished articles may typically be treated using a paddle machine; and for yarn a package machine is preferred.
The composition may be applied to the material by any suitable means, for example by a padding or foaming technique. However in especially preferred embodiments the composition is applied to the material using an exhaustion technique. This technique involves immersing the material in the composition for a period sufficient to allow uptake ( λ exhaustion' ) by the material of the active components. Exhaustion may be described as the transfer of a component from a liquor bath to the fibre. The extent of exhaustion is sometimes given as a percentage. For example, a process involving 60% exhaustion of a component would mean that 60% of the total amount of the component in the composition has attached to the fibre, and the remaining 40% remains in solution.
Exhaustion techniques are commonl y used in dyeing processes. In some cases reactive dyes and acid dyes may exhaust to the point that the dye liquor becomes nearly colourless. It should be noted that a component which has exhausted on t o a material ha s no t necessarily "permanently" bonded to the material. In some instances a component may form a permanent covalent bond with a material but in other instances a more transient electrostatic interaction may exist.
It is desirable to achieve very high levels of exhaustion both for economical reasons and environmental reasons . Any chemical not exhausted would end up being discharged in effluent . The liquor ratio used in the method of the present invention, that is the weight ratio of composition to material treated depends on the application method employed. However selection of an appropriate application method and a suitable liquor ratio for use in such an application method is well within the capabilities of the person skilled in the art.
The concentration of each component present in the composition may vary according to the liquor ratio used. Suitably the concentrations of the components are selected to provide a specific treatment level defined as % omf (% on mass of fibre) . This is the percentage by mass of a component which has been fixed onto the material during the treatment process and is calculated by measuring the dry mass of the material at the start and the end of the process. For example, if lOOg of dry material is treated and after processing has dry weight of 103g, then a treatment level of 3% omf has been achieved.
In a preferred embodiment the treatment level of the acid is at least 0.1% omf, more preferably at least 1% omf, more preferably at least 3% omf, and most preferably at least 5% omf.
Preferably the treatment level of the acid is up to 50% omf acid, for example up to 40% omf, preferably up to 30% omf, more preferably up to 20% omf, and most preferably up to 10% omf.
The treatment levels of acid stated above refer to the total amount of acid when a mixture of acids is used. Preferably the composition comprises phosphorous acid. Preferably at least 50 wt% of the acid component present in the composition is phosphorous acid, preferably at least 75 wt%, more preferably at least 90 wt%, for example at least 95 wt%.
In a preferred embodiment the treatment level of urea is at least 0.1% omf, more preferably at least 1% omf, more preferably at least 3% omf, and most preferably at least 5% omf.
Preferably the treatment level of urea is up to 50% omf, for example up to 40% omf, preferably up to 30% omf, more preferably up to 20% omf, and most preferably up to 10% omf .
The weight ratio of urea to acid in the composition used in the present invention is preferably at least 0.2:1, more preferably at least 0.5:1, and most preferably at least 0.8:1.
The weight ratio of urea to acid is preferably up to 10:1, for example up to 5:1, preferably up to 3:1, and most preferably up to 2:1.
The composition used in the method of the present invention may comprise one or more further ingredients.
In some embodiments the composition may further comprise a smoke-reducing compound. Such compounds are well known to those skilled in the art and when present are suitably contained in an amount sufficient to provide a treatment level of from 1 to 25% omf, preferably 15 to 20% omf, more preferably from 7 to 15% omf, for example about 10% omf. Suitable smoke-reducing compounds include halogen- containing materials, fo r example tetrabromophthalic anhydride which is available from Dixon-Chew in West Yorkshire under the trade mark Flameban; along with smoke- reducing materials sold under the trade mark Cetaflam by Avocet Dye & Chemical Co. Ltd.
In some embodiments the composition applied in the method of the present invention may further comprise a water soluble or water dispersable cationic polymeric resin. Preferred ar e cationic cross-linking resins, most preferred are cationic resins which are capable of self cross-linking or cross-linking under a baking or curing regime. Specific selection of the optimum resin can be made according to specific circumstances relating to the end-use by someone skilled in the art. Examples of such components include polyaminoamide-epichlorohydrin resins such as Hercosett 125 (Hercules) or Beetle Resin PT765 (BIP) , polyquaternary ammonium compounds such as Tinofix FRD (Ciba) or Levogen FL (Bayer) or cyclanon E (BASF) , or polyamine aliphatic quaternary amines such as Optifix F (Clariant) .
The use of a cationic polymeric resin may be advantageous as material which has been treated with an acid may have a high concentration of covalently bonded and also unbound phosphite, phosphate or sulfamate residues on the surface. This leads to an anionic surface which is hydrophilic and thus likely to absorb water. The material therefore often becomes damp and may also be prone to shrinkage. The inclusion of a cationic polymeric resin may help to reduce the anionic nature of an acid treated material and thus helps to prevent dampness and shrinkage. Careful choice of an appropriate cationic polymeric resin by those skilled in the art, can improve the physical handle of the fabric and may also impart hydrophobic properties. This method could thus be used to provide waterproof fabrics.
In some embodiments the composition used in the method of the present invention may include a dispersed phase material, for example a pigment, filler or mixtures thereof. For example the composition may include a flame retardant pigment, for example magnesium hydroxide, calcium carbonate, aluminium phosphate, aluminium phosphite, aluminium silicate, magnesium phosphite or magnesium phosphate. Other pigments may be used to impart other properties such as colour, opacity, hydrophobicity, easy iron properties and a soft handle. The range of suitable dispersed phase materials is large. Appropriate selections could however be readily made by the person skilled in the art, according to the precise properties required.
In some embodiments the compositions used in the method of the present invention may include a dye, thereby introducing fabric colouration at the same time as other properties. The dye may for example be a reactive dye, an acid dye, a premetallised dye, or a mordant dye. If such compounds are present in the compositions used in the present invention the material produced may be dyed a deep colour and the dyed material may be fast to multiple washing .
In some embodiments the composition used in the method of the present invention may further comprise a wetting agent. Suitable wetting agents are known to the person skilled in the art.
As mentioned above, the method of the present invention preferably comprises applying to a material an aqueous composition comprising an acid and urea. The composition may suitably be prepared by the addition of urea to an aqueous solution of the acid.
The composition may be provided in concentrated form, to be diluted by the user.
Preferably the material treated in the method of the present invention comprises polyamide fibres, for example natural polyamide fibres for example wool, silk, alpaca, angora, leather etc; or synthetic polyamide fibres, for example Nylon 6, Nylon 6, 6 etc.
Blends or mixtures including polyamide fibres and non- polyamide fibres are within the scope of the present invention .
Preferably the material treated by the present invention comprises wool. It may be pure wool or it may be a mixture or blend comprising wool and one or more other materials. In embodiments in which the material is a mixture or blend, it preferably comprises at least 20wt% wool, preferably at least 30wt%, for example at least 40wt%, more preferably at least 50wt% . Such blends or mixtures may suitably comprise one or more further materials selected from nylon, viscose, lycra, acrylics and polyester. The wool material may comprise wool in any suitable form, for example wool yarn, wool top, wool fabric, wool carpet, or loose wool; and may include cashmere or non-sheep origin animal fibres. Alternatively, the wool material may be in the form of a garment or other finished article containing wool or a woven fabric containing wool or non- sheep origin fibres.
In some embodiments the material may be a fabric including a knitted or woven fabric or a non-woven material.
Suitably the method the present invention may comprise the steps of:
(a) preparing a composition comprising urea and an acid selected from phosphorous acid, phosphoric acid, sulfamic acid and mixtures thereof;
(b) contacting the material with said composition; and
(c) removing the material from contact with the composition.
Suitably step (a) comprises preparing a composition comprising an acid and urea in an appropriate ratio to provide the preferred treatment levels of each as detailed above.
It is well within the capability of the skilled person to select appropriate concentrations based on the amount of material and liquor ratio used to arrive at an appropriate treatment level (as %omf) .
In some preferred embodiments the material is contacted with a heated composition. The composition may be heated prior to contact with the material or during contact with the material.
It may suitably be heated to a temperature of at least 30 0 C, more preferably at least 40 0 C, for example at least 50 0 C, or at least 55°C. It may be heated to a temperature of up to 100 0 C, for example up to 90 0 C, preferably up to 80 0 C, more preferably up to 75°C. In a preferred embodiment a temperature of 60 to 70 0 C is used.
In a preferred embodiment in which step (b ) comprises immersing the material in the composition, the composition is suitably heated after immersion of the material.
Suitably, in step (b) the material is contacted with the composition for a period of at least one minute, preferably at least five minutes, for example at least 10 minutes, suitably at least 15 minutes, at least 30 minutes or at least 45 minutes. In step (c) the material may be contacted with the composition for a period of up to two hours, for example up to 240 minutes, preferably up to 180 minutes, for example up to 150 minutes, preferably up to 120 minutes, for example up to 100 minutes.
Step (c) may in some embodiments comprise physical removal of the material from contact with the composition. For example if the material is immersed in the composition, the material may simply be lifted from the composition or the composition drained from the container comprising the material. In some embodiments step (c) may also include rinsing the composition from the material. Such a rinsing step may suitably comprise applying water to the material. In some embodiments step (c) may comprise applying an aqueous alkali solution to the material in order to raise the final pH of the material. Preferably the water or aqueous alkali will be at ambient temperature.
After rinsing, the material may suitably be dried. It may optionally be sp i n dried. Alternatively and/or additionally it may be dried at an elevated temperature by passing through or into an oven.
Preferably the material is first spin dried to remove excess liquor and then dried in an oven.
In preferred embodiments the material is dried at a temperature of from 30 to 180 0 C, for example 40 to 140 0 C, preferably 60 to 100 0 C. It is suitably dried for a period of at least one minute, preferably at least five minutes, for example at least ten minutes, suitably at least fifteen minutes. It may be dried for a period of up to 6 hours, preferably up to two hours, more preferably up to one hour, suitably up to 45 minutes, for example up to 30 minutes .
In some embodiments the method may comprise of one or more additional further rinsing and/or drying steps.
A material treated by the method of the present invention is suitably provided with wash-durable flame retardant properties. Preferably the material is flame retardant after multiple cleaning treatments. In some embodiments it is desirable that the treated material be durable to dry cleaning. In other embodiments it is desirable that the material be durable to aqueous laundering. Materials treated with a flame retardant composition for use in transportation fabrics (for example aircraft, railway and shipping) must meet various international standards for flame testing / type of wash testing / smoke production / toxicity of smoke evaluation and the like. The standard (s) required depends on the intended use of the material.
In addition, individual aircraft manufacturers (i.e. Boeing & Airbus etc.) have their own requirements and standards that suppliers must meet.
Thus there are many flame tests which could be described. However a suitable test for use in the laboratory is the method set out in BS5438 (Methods of test for flammability of textile fabrics when subjected to a small igniting flame applied to the face or bottom edge of vertically orientated specimens) , where the fabric is supported in a vertical frame with a butane flame of specified length applied perpendicular to the fabric for 15 seconds.
The British standard requires that the length of the observed char must not exceed the size of the test frame (approximately 15cm) . Afterglow supporting a flame front and a hole in the charred region of the fabric are also observations which result in a test fail.
Suitably materials treated by the method of the present invention pass the flame test described in BS5438.
In an alternative test a small Bunsen burner or a kitchen butane torch may be used to assess the flammability characteristics of a material. The flame can be applied at a 45° angle on the bottom edge of the fabric for 15 seconds. For a test pass, after removal of the flame there must be no more than 5 seconds of afterflame on the fabric .
Suitably materials treated according to the present invention pass this simple test.
Without being bound by theory, it is believed that the flame retardant properties of materials treated by the present invention may be explained as follows, with reference by way of example only to the treatment of a wool material with a composition comprising urea and phosphorous acid:
Under acidic conditions protein fibres (for example wool) behave as though they are positively charged, as shown for wool in Scheme 1 :
NH 3 + COOH NH 3 + COO NH 2 COO
WOOL FIBRE WOOL FIBRE WOOL FIBRE
+ve charge zero charge -ve charge pH <4 pH 4-8 pH>8
Scheme 1. Wool surface charge vs pH
Under acidic conditions phosphorous acid exists mainly as the mono-anion and can thus interact electrostatically with the protein substrate (for H 3 PO 3 at 2O 0 C pK al is 2.6 and pK a2 is 6.5) , as shown in scheme 2: OH H-P=O
O + H 3 N-WOOL
Scheme 2. Interaction of phosphorous acid anion with wool under acidic conditions
It is known that phosphorous acids readily oligomerise, especially in concentrated solution or on drying, as shown in scheme 3:
OH H-P=O ■ *
Scheme 3. Oligomerisation of phosphorous acid
Thus it is believed that in this manner a large anion of significant substantivity and exhibiting good wet-fastness on the finished item is obtained.
As well as the above self-esterification, phosphorous acid can esterify serine residues under acidic conditions, especially on drying, to form covalent bonds with the material as shown in Scheme 4:
OH H-P=O + WOOL - CH 2 -CH 2 -OH ■ * { H-P(=O) - 0-CH 2 -CH 2 -WOOL)
I I o o- Scheme 4. Esterification of serine in wool to covalently bond phosphorous acid.
It is believed that the urea present in the system may help improve accessibility through swelling of the wool fibres .
The method of the present invention may be carried out as a batch process or a continuous process. A batch process is preferred.
The method of the present invention suitably provides a wash-durable flame retardant finish for wool containing materials .
According to a second aspect of the present invention there is provided the use of a composition comprising urea and an acid selected from phosphorous acid, phosphoric acid, sulfamic acid and mixtures thereof to impart flame retardant properties to a material, preferably a material comprising wool.
According to a third aspect of the present invention there is provided a material treated by the method of the first aspect.
Preferred aspects of the second and third aspects are as defined in relation to the first aspect, where appropriate .
The invention will now further described in relation to the following non-limited examples. Example 1
A fabric comprising 80% wool & 20% Nylon in a flat woven state, was treated according to the present invention using a wool top dyeing vessel.
A liquor ratio of 15:1 was used (150 Litres: 10Kg fabric)
The method was carried out according to the following instructions:
• Place fabric into dyeing vessel.
• Add Phosphorous Acid 70% Solution (32kg) to vessel already containing water (-70 litres) .
• Dissolve urea (22.5Kg) into water and add to vessel. • Continue filling machine to 150L mark.
• Circulate for 5 minutes.
• Whilst circulating, raise temperature of vessel to 6O 0 C.
• Leave vessel circulating at 6O 0 C for 30 minutes. • Drop liquor from vessel.
• Refill vessel with cold water and rinse for 10 minutes .
• Drop liquor from vessel.
• Remove fabric from the vessel and spin dry. • Place fabric into oven at 90 0 C for 20 minutes or until dry.
• Flame test fabric using two methods: o The method set out in BS5438, where the fabric is supported in a vertical frame with a butane flame of specified length applied perpendicular to the fabric for 15 seconds. o Using a kitchen butane burner, with the flame applied at a 45° angle on the bottom edge of the fabric for 15 seconds.
• The resultant treated fabric passes these two flame tests, by not continuing to burn after the applied flame is removed.
Example 2
A fabric comprising 80% wool & 20% Nylon in a flat woven state, was treated according to the present invention using a wool top dyeing vessel.
A liquor ratio of 15:1 was used (150 Litres: 10Kg fabric)
The method was carried out according to the following instructions :
• Place fabric into dyeing vessel.
• Add Phosphorous Acid 70% Solution (32kg) to vessel already containing water (-70 litres) .
• Dissolve urea (22.5Kg) into water and add to vessel.
• Continue filling machine to 150L mark.
• Circulate for 5 minutes.
• Whilst circulating, raise temperature of vessel to 6O 0 C.
• Leave vessel circulating at 65 0 C for 80 minutes.
• Drop liquor from vessel.
• Refill vessel with cold water and rinse for 10 minutes . • Drop liquor from vessel.
• Refill vessel with cold water and rinse for 10 minutes . • Drop liquor from vessel.
• Refill vessel with cold water and rinse for 10 minutes .
• Drop liquor from vessel. • Remove fabric from the vessel and spin dry.
• Place fabric into oven at 90 0 C for 20 minutes or until dry.
• Flame test fabric using two methods: o The method set out in BS5438, where the fabric is supported in a vertical frame with a butane flame of specified length applied perpendicular to the fabric for 15 seconds. o Using a kitchen butane burner, with the flame applied at a 45° angle on the bottom edge of the fabric for 15 seconds.
• The resultant treated fabric passes these two flame tests, by not continuing to burn after the applied flame is removed.
Example 3
A fabric comprising 100% wool in a flat woven state, was treated according to the present invention using a wool top dyeing vessel.
A liquor ratio of 15:1 was used (150 Litres: 10Kg fabric)
The method was carried out according to the following instructions : • Place fabric into dyeing vessel.
• Add Phosphorous Acid 70% Solution (32kg) to vessel already containing water (-70 litres) . • Dissolve urea (22.5Kg) into water and add to vessel.
• Continue filling machine to 150L mark.
• Circulate for 5 minutes.
• Whilst circulating, raise temperature of vessel to 6O 0 C.
• Leave vessel circulating at 65 0 C for 80 minutes.
• Drop liquor from vessel.
• Refill vessel with cold water and rinse for 10 minutes . • Drop liquor from vessel.
• Refill vessel with cold water and rinse for 10 minutes .
• Drop liquor from vessel.
• Refill vessel with cold water and rinse for 10 minutes.
• Drop liquor from vessel.
• Remove fabric from the vessel and spin dry.
• Place fabric into oven at 90 0 C for 20 minutes or until dry. • Flame test fabric using two methods: o The method set out in BS5438, where the fabric is supported in a vertical frame with a butane flame of specified length applied perpendicular to the fabric for 15 seconds. o Using a kitchen butane burner, with the flame applied at a 45° angle on the bottom edge of the fabric for 15 seconds.
• The resultant treated fabric passes these two flame tests, by not continuing to burn after the applied flame is removed.