US20130174357A1

US20130174357A1 - Method of dyeing high performance fabrics

Info

Publication number: US20130174357A1
Application number: US13/783,444
Authority: US
Inventors: Carolus Albertus VELDHUIS; Andreas Hubertus Wegdam
Original assignee: Ten Cate Protect BV
Current assignee: Ten Cate Protect BV
Priority date: 2008-02-06
Filing date: 2013-03-04
Publication date: 2013-07-11
Also published as: GB0802170D0; WO2009098316A2; EP2286020A2; US20100319140A1; WO2009098316A3; RU2010136839A

Abstract

There is provided a process of dyeing yarn or cloth comprising fibres, comprising dyeing at least part of the fibres with at least two types of dyestuff that dye the same fibres substantially the same colour. One of the types of dyestuff chemically bonds with or is at least partially incorporated into the fibre structure and the other type of dyestuff does not chemically bond with or become at least partially incorporated into the fibre structure.

Description

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation U.S. non-provisional application Ser. No. 12/851,725, filed on 6 Aug. 2010, which is a continuation of international application no. PCT/EP2009/051416 filed on 6 Feb. 2009, which was published under PCT Article 21(2) in English, and which claims priority from GB application no. 0802170.1 filed on 6 Feb. 2008, the contents of which applications are hereby incorporated by reference in their entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention
The invention relates generally to procedures for dyeing yarn, cloth or fibres (particularly for dyeing cloth) and in particular to procedures for providing greater colour durability. The invention also relates to textiles treated according to the inventive procedures, and to garments comprising such textiles.
The present invention finds particular application in dyeing yarn, cloth or fibre that is inherently difficult to dye with dyes that offer adequate light fastness, and can only be well dyed with dyes that are subject to poor light fastness, for example aramid fibres.
The present invention also finds particular application in dyeing yarn, cloth or fibre with dyes of particular colours, the dyes exhibiting such desired colours exhibiting poor light fastness, for example high visibility dyes.
2. Description of the Related Art
An example of fibres, yarns and cloth that are difficult to dye with dyes showing adequate light fastness are aramid based fibres, yarns and cloths. Aramid fibres are highly resistant to heat decomposition, have inherent flame resistance, and are frequently used in work wear for special environments where flame resistance is required. Fabrics made of these fibres are extremely strong and durable, and have been widely adopted for use in clothing for e.g. protective wear for fire-fighters; military personnel, such as aircraft pilots, tank crews and the like; automobile race crews; and industrial workers such as petrochemical workers, who have the potential to be exposed to fire and extensive heat.
The high resistance of aramid fibres to heat decomposition is associated at least partly with a very highly crystalline structure of the fibres. Para-aramid fibres in general and in particular, poly(paraphenylene terephthalamide) (PPTA) fibres, have molecular features of high crystallinity, a stiff molecular chain and high interchain bonding forces resulting in high tensile strength and high modulus. However, the very highly crystalline structure of the aramid fibres, which gives such desirable physical properties, lowers the accessibility of the fibre to dyeing polymer molecules. This means that the fibres are difficult to dye and can only be dyed with a very limited number of dyestuff types using special procedures. For example fibre suppliers typically recommend complicated exhaust dyeing procedures. Exhaust dyeing generally involves the use of a dye bath of moderately large liquor to goods ratio, in which the fibre is immersed for a period of time to adsorb or absorb the dyestuff. This is a typical process for most commercial fabric dyeing. A number of examples of dyeing processes are described in the following patent (application)s.
Cates and others describe in U.S. Pat. No. 4,759,770 a process for the continuously or semi-continuously dyeing and simultaneous improvement of the flame-resistant properties of aramid fibres. U.S. Pat. No. 4,898,596 of Southern Mills describes a process for exhaust dyeing, flame-retardant treating or both dyeing and flame retardant treating aramid fabrics.
An alternative dyeing method involves the use of polar organic solvents to swell the fibres and create voids in the fibre structure to enhance dyeability. These procedures involve solvent exhaust treatments at elevated temperatures with subsequent dyeing.
Although the dyestuffs used in the above procedures are able to bond well to the aramid fibres they suffer from a poor light fastness. That is they lose their colour rapidly on exposure to daylight.
Light fastness is rated on a Grey scale in a range of 1 to 8, with 8 being the most resistant to fading. The applicable ISO standard is 105-B2:1998 and describes the official method for determining the resistance of the colour of textiles of all kinds and in all forms to the action of an artificial light source, representative to daylight. A specimen of textile (the sample) is exposed to artificial light under prescribed conditions, along with a Blue Wool reference. The light fastness is assessed by comparing the change in colour of the specimen with that of the references used. The light fastness ratio necessary for a certain product depends upon the application and the specific colour itself. For e.g. a dark coloured aramid fabric a higher light fastness ratio (4-5) is more easily achieved than for a lighter coloured aramid fabric (4). The light fastness of dyed aramids can be in some cases as low as 1-2, meaning that a garment made of such fabric will maintain an acceptable colour for only a few weeks when used outdoors.
An alternative method of applying colour to aramid fibres is to solution dye the fibres. Solution dyed fibres are prepared by a solution dyeing method in which a quantity of dye or pigment is mixed with the polymer prior to extrusion of the polymer into fine fibres. The dye or pigment thus becomes part of the fibre structure. Solution dyed fibres are more costly than the undyed fibres due, in part, to the additional costs of manufacture, and must be used in the colour provided by the supplier, leaving the weaver with only a limited choice of colours.
None of the above-mentioned processes provides sufficient light fastness properties for aramids.
The current aramid colouring technology hence suffers from the problem that aramid fabrics tend to lose their colour rapidly due to a poor light fastness of the commonly used dyestuffs in exhaust dye systems. Such fading is a serious problem because it typically leads to unacceptably rapid decolouration of the fabric giving a poor appearance. In extreme cases the lack of light fastness can lead to appreciable colour loss even prior to sale of a garment.
At present, efforts to overcome the problem have focussed on three different means for creating a dyed aramid with better light fastness properties: 1) by the selection of the most appropriate dyestuff for use in exhaust dyeing procedures—the most commonly used dyes are presently cationic dyes; 2) by selecting UV-stabilisers to be added to the dyestuff (although useable UV stabilisers for combination with aramid cloths have not yet been developed); and 3) by improving the dyestuff itself.
An alternative method of dyeing aramid fabrics is to use pigment dyestuffs, however these dyestuffs are not used commonly. Predominantly because they do not bond well to the fibres, yarn or cloth and are easily removed by abrasion. Hence, they lack wash fastness in general. The result is that too great a colour loss results through washing of a pigment dyed aramid garment.
It is believed that currently only non-pigment (most usually cationic) dyestuffs are commonly used for dyeing aramids.
An example of another field in which colour durability is a particular problem is the field of high visibility dyeing. High visibility dyes differ from typical plain colour dyes in that they dye textiles various colours that are particularly conspicuous. Fluorescent dyes are examples of high visibility dyes. Yarn, cloth or fibres that is dyed with high visibility dye suffers from the problem of poor colour retention because the high visibility dyes lack adequate light fastness, and hence fade within in an unacceptably fast period of time.
High visibility dyed yarn, cloth and fibre is often used for making clothing. The clothing may take many forms including coats, jackets, overalls, vests, waistcoats, body warmers, shirts, trousers, footwear, hats and gloves. In particular high visibility clothing is used and adapted for protective and industrial wear, especially outdoor clothing.
High visibility clothing is typically worn by persons and animals, such as military horses and dogs, in order to increase their conspicuousness, and is particularly useful in dangerous environments when it is important to easily distinguish the wearer from the background. A poor colour durability is thus of a particular concern in high visibility applications (in particular high visibility clothing) because the product can only be used while it retains suitably strong colouring to be conspicuous. A loss of high visibility colour either leads to dangerous situations in which the clothing is no longer easily visible, or the clothing has to be replaced at significant cost. Additionally, since high visibility clothing is often worn outside, a poor light fastness is of particular concern, since the clothing may be exposed to sunlight for extended periods.
The high visibility dyed yarn, cloth or fibre of the present invention may also advantageously be used for making bags, such as rucksacks and panniers; and tents.
In particular the high visibility dyed yarn, cloth or fibre may be useful in applications requiring lightweight fabrics, especially outdoor fabrics.
Thus there exists a problem in the field of high visibility dyeing that dyed yarn, cloth and fibre shows a poor light fastness. This is a particular problem for high visibility clothing applications.

BRIEF SUMMARY OF THE INVENTION

It is an object of the present invention to provide a process for dyeing fibres, yarn or cloth. The process is in particular applicable to fibres, yarn or cloth having a poor affinity to dye, such as, for example, aramid fibres, yarn or cloth (such as Nomex™); and to the dyeing of fibres, yarn or cloth with high visibility dyestuffs.
There is provided a process of dyeing yarn or cloth comprising fibres, comprising dyeing the fibres with at least two types of dyestuff; characterized in that the two types of dyestuff dye the same fibres substantially the same colour; and that one of the dyestuffs chemically bonds with or is at least partially incorporated into the fibre structure and the other dyestuff does not chemically bond with or become at least partially incorporated into the fibre structure.
The two types of dyestuffs differ from one another at least to the extent by which they become bound to the fibres. One type of binding can be via a chemical bond whereby the dyestuff is directly attached to the fibre by a chemical bond or is attached by a chemical bond to a linking compound itself bound to the fibre, for example as is the case in U.S. Pat. No. 4,525,168. Another type of binding can be a physical binding, e.g. physical incorporation of the dyestuff into the fibre as can be achieved by swelling, incorporation of a dyestuff into the fibre and then shrinking of the fibre to trap the dyestuff. Such a method is discussed in U.S. Pat. No. 4,759,770.
Another form of physical binding may be a simple physical binding whereby, for example, a pigment dyestuff is bound to the fibre through Van Der Waals forces or through the aid of an adhesive which forms an intermediary between the fibre and the pigment dyestuff.
The first type of dyestuff, which will be either indirectly or directly chemically bonded to the fibre or incorporated into the fibre, is selected because it is expected to have a good abrasion and wash resistance, and is preferably a dye. The second type of dyestuff is selected to show good light fastness such that the fabric maintains its colour on exposure to sunlight, and is preferably a pigment.
Those dyestuffs that bond well to aramid fibres and exhibit good wash resistance typically have poor light fastness and are susceptible to fading on exposure to light. The lightfast dyestuffs that are usable with aramids typically show poor wash/abrasion resistance because they are unable to bond well to the fibres.
Those high visibility dyestuffs that bond well to yarn, cloth, and fibre, and exhibit good wash resistance typically have poor light fastness and are susceptible to fading on exposure to light. The lightfast dyestuffs that are usable with aramids typically show poor wash/abrasion resistance because they are unable to bond well to the fibres.
None of the prior art indicates a dyeing process whereby fibres are dyed using a combination of two dyestuff types of substantially the same colour, whereby one of the dyestuffs chemically bonds with or is at least partially incorporated into the fibre structure (e.g. a dye process such as an exhaust dye process) and the other dyestuff does not chemically bond with or become at least partially incorporated into the fibre structure (e.g. a pigment dye process). The prior art merely discusses dyeing processes that use only one of either an exhaust dye process, a continuous dye process or a pigment dye process for each colour.
The poor dyeability of para-aramid fibres is generally discussed in U.S. Pat. No. 4,144,023 to Provost, U.S. Pat. No. 4,985,046 to Hartzler, and U.S. Pat. No. 5,232,461 to Ghorashi, wherein various dyeing processes are disclosed. U.S. Pat. No. 4,144,023 discloses an improved dyeing process wherein wetted aromatic polyamide fibres are crimped and kept moist before dyeing. U.S. Pat. No. 4,985,046 discusses the disadvantages of “spun-in” and “structure prop” methods of dyeing poly(paraphenylene terephthalamide) fibres and discloses a process wherein specially prepared fibres (acid treated or never dried) are contacted with an aqueous solution of a dye promoting species. U.S. Pat. No. 5,232,461 discloses dyeing poly(paraphenylene terephthalamide) fibres by heating them under high pressure. None of these processes makes use of the advantages of combining two types of dyestuff to make use of their specific characteristics to improve the colour fastness of the dyed aramid.
U.S. Pat. No. 5,275,627 discloses the preparation of a camouflage patterned aramid garment wherein an aqueous print paste is applied to an aramid fabric which has been treated with N-cyclohexyl-2-pyrrolidone to promote printability and good colouration. There is no discussion of a method of dyeing using different types of dyestuff having substantially the same colour.
A yarn or cloth comprising fibres dyed with only one of the dyestuffs suffers from either poor light fastness or poor wash/abrasion resistance. In contrast, a yarn or cloth dyed in accordance with the present invention shows improved light fastness and wash resistance. This is believed to result from the culmination of the complementary properties of the two dyestuffs.
There is currently a general prejudice in the art to use only one type of dyestuff when colouring fabrics. Against this prejudice the present inventors have developed fibres, yarns and cloths that have improved colour retention during use. This is achieved by using at least two types of dyestuff, one performing well for light fastness but poorly for wash fastness (for example a pigment), and the other performing well for wash fastness but poorly for light fastness (for example a dye).
Where one of the types of dyestuff is faded through exposure to light or through washing, the other type of dyestuff, which is less affected by the attacking process, maintains the colour of the garment. In this manner a too rapid overall colour loss in the yarn, cloth or fibre may be reduced and the required appearance of a garment incorporating the yarn, cloth or fibre is maintained for longer. This advantageously means that garments requiring certain levels of colouring, determined by various industry standards and statutory provisions, can be used for a longer period of time before they fail the required standards and must be replaced.
The invention can be used to improve colour retention for difficult to dye fibres, yarns or cloths, although the colouring of aramid fibres, yarn and cloth is a particularly preferred embodiment.
The invention is also usable to improve colour retention for yarn, cloth or fibre dyed with specifically coloured dyes, the specifically coloured dyes showing poor light fastness. In particular the invention is useful for dyeing yarn, cloth or fibre with high visibility dyes. With the high visibility dyes the similar problem of light fastness and wash fastness of dyestuffs (as discussed above for aramid fibres) is present. This is not only for high visibility dyes applied to aramid fibres but also for high visibility dyestuffs applied to a broad variety of other fibres, yarns and cloths. The provision of two different types of dyestuff, similarly as discussed above, helps to overcome premature colour loss in high visibility fibres, yarns and cloths as well. This is important because high visibility cloth, for example for garments such as jackets, must meet strict government standards.
A preferred embodiment of the invention is a process for dyeing a fibre, yarn or cloth, comprising the steps of 1. dyeing the fibre with a non-pigment dye (e.g. a cationic dyestuff), and then 2. dyeing the fibre with a pigment dyestuff.
The first type of dyestuff may be selected from a range of dyestuffs; but is preferably a dye, specific examples of which include direct dyestuffs, acids or basic (alkaline) dyes, reactive dyes, aniline dyes, anthraquinone dyes, azo dyes, disperse dyes, macromolecular dyes and sulphur dye or vat dyes. A example of a vat dye pigment is indigo, which during the vat dye process is finely incorporated into cloth by oxidation of its leuco form. However, indigo typically does not bond well to fabric as a dye, so that the present invention preferably does not use indigo. Useful high visibility dyes include those available from novacron (Huntsman), levafix+Remazol (Dystar), sumifix (Farbchemie Braun), and intracron (Yorkshire), particularly the fluor dyes available therefrom.
Particularly preferred high visibility dyes include: Bezaprint (Bezema) commercial name Bezafluor “Orange R”, “Rot R”, “Gelb BA”; Ultraprint (Colorserve) “Ultraprint orange R”, “pink IL”, “yellow G”; and Doramid (M. Dohmen) “fluor orange”, “fluor pink”, “fluor yellow”.
The second type of dyestuff is preferably a pigment; specific examples being Bezaprint (from the company Bezema), Imperon (Dystar), Helizarin (BASF), Unisperse (Ciba), Ultraprint (Colorserve) or Caledon (Dystar). Useful high visibility pigments include those available from novacron, levafix, sumacron, and intracron. A particularly preferred high visibility pigment is Bezafluor from BEZEMA.
The above are non-exhaustible lists of possible dyestuffs. As will be clear to the skilled person other dyestuffs might be used depending on the specific requirements.
Various techniques may be used for applying the dyestuffs including immersion or bath techniques such as foularding, coating techniques such as the so-called “knife-over-roller”, the “dip” and the “reverse roller” screen coaters, screen printing techniques etc.
The fibre, yarn or cloth may preferably be dyed with the first dyestuff by submersion in a dyebath. Alternatively, the fibre, yarn or cloth is preferably dyed with the first type of dyestuff by exhaust dyeing. Exhaust dyeing is typically carried out under high temperature and pressure in a jigger or a jet by exhausting a dye or dye mix into the fibre using cationic dyestuff. Exhaust dyeing is of particular use in dyeing aramid fibres, but is also useful for other applications with hard to dye yarn, cloth and fibre. Other methods of exhaust dying aramids, especially combinations of meta-aramids with para-aramids or other para-aramid rich blends, is by beam dyeing or yarn dyeing. Beam dyeing is performed using a beam onto which the fabric is affixed whereby the dye is forced through the cloth from the inner and or outer side of the beam. This dyes the cloth with minimal friction and generally improves the appearance of the cloth, since it decreases an amount of fibrillation. Yarn dyeing is similar to the beam dye technique but is performed on yarn instead of cloth.
The second type of dyestuff will typically be a pigment and is preferably applied by means of a synthetic resin. Any technique available may be used to affix a resin and pigment blend (e.g. pigment dispersed in a resin or resin emulsion) to the substrate. For example the blend may be painted, printed or padded onto the yarn or cloth.
Preferred resins for attaching the pigment to the substrate are acrylic resins. Acrylic resins offer good wash resistance, since acrylics are resistant to water attack. Examples of preferred acrylic binders include: acrylicstyrolpolymers such as Printofix (Clariant), Acramin (Bayer), Comaprintbinder (BASF), Padicoll (CHT); acrylicbutadiencopolymer such as Tubifast (CHT), Tephabind (Cognis), Printofixbinder (Clariant), and Lyoprint (Huntsman); and acryliccopolymers as Tubipert and Tubiscreen (CHT), Helizarin (BASF), Acramin (Bayer).
A preferred method of applying an acrylic based resin and pigment mixture to a substrate is by use of a dyebath. A dyebath is filled with a mixture of acrylic resin and pigment. The mixture is thinned, preferably with water, to a low viscosity so that it coats and preferably penetrates into a substrate. The substrate is dipped into the dyebath and then removed. To ensure the correct loading of the substrate with the resin mixture. This method is useful for dyeing both aramids and separately for dyeing a range of substrates with high visibility pigments, although it is most useful for dyeing aramids with non-high visibility pigments.
A particular advantage of the dyebath method for applying pigments is that the substrate gains only a minimal weight as a result of the addition of the pigment and resin. This usefully maintains a low weight of the fabric, along with good drape and handle. It also typically results in full penetration of a cloth substrate so that pigment is added on both sides and through the inside of the cloth. This gives a solid colour to the cloth.
Other preferred resins for attaching the pigment to the substrate are polyurethane resins. Examples of preferred urethane binders include polyurethanes such as Luxcolor (CHT), Tubilux (CHT), Tubifix (CHT), Perappret (BASF)
Although polyurethanes are less resistant to water attack than acrylic resins, they can be easier to apply and can be less expensive than acrylics.
Polyurethane based resin and pigment mixtures are preferably applied to substrates as pastes.
A particularly preferred method of applying a polyurethane based resin and pigment mixture is to foam the mixture, and then apply the foamed mixture with a blade or roller. Foaming of the polyurethane prior to application advantageously provides a good handle (cloth like feel) and drape (flexibility) to the resulting dyed yarn or cloth. Foaming can be effected by incorporating a foaming agent into the resin and pigment mixture, and either mechanically or chemically foaming. Suitable foaming agents include surfactants such as non-ionic surfactants, for example alky amine oxide, and anionic surfactants, for example ammonium stearate.
The application of polyurethane resins to textile substrates is known in the field of manufacturing synthetic suede leathers, in particular for making synthetic suede leather for upholstering furniture. In the manufacture of synthetic suede leather a textile having micro-fine denier fibres is impregnated with a polyurethane solution (optionally foamed), and is then subjected to a raising step or sueding step. The function of the polyurethane in such methods is to provide a coating that is sueded or raised to produce the suede effect. Although polyurethane application in the field of synthetic suede production is used for a different purpose, similar resin compositions may be used for application in the present invention.
However, the present invention differs from the field of synthetic suede leathers in that it concerns improvement of the colour durability of hard to dye yarns, cloths and fibres, and of yarns, cloths and fibres dyed with poor durability dyestuffs. The process of the present invention preferably is absent any sueding or raising steps, and is more preferably applied to yarns, cloths or fibres that are not suited to making synthetic suede leather. The products of the present invention preferably do not comprise synthetic suede leather, and more preferably do not comprise surface components that give a suede effect.
More preferably, the present invention is concerned with dyed cloths and yarn offering a substantially plain surface (i.e. not embellished with a raised surface texturing), as may be exemplified by the non-fashion dictated textiles typically used for mechanic's overalls; office clothing; high visibility clothing, protective clothing (e.g. aramid materials).
In the case that the yarn or cloth of the present invention is dyed by application of a resin and pigment mixture, the amount of resin added to the substrate is limited so that the dyed substrate remains flexible with a good drape, and good handle, so that it is similar to typical cloths used in clothing materials. This is particularly important in the case that the dyed cloth or yarn is for making garments, such garments needing to be comfortable to wear, and flexible for ease of movement.
Preferably the weight percent of resin (resin wt %) provided on a dyed yarn or cloth is less than 20% wt of the dyed yarn or cloth (including resin). The weight percent of resin is calculated as:
wt resin/total weight×100
wherein wt resin=weight of the yarn or cloth at completion of the resin dyeing—the weight of the yarn or cloth prior to resin dyeing. Completion of the resin dyeing is at the point at which following curing of the resin, no further significant weight change occurs, e.g. due to solvent evaporation or resin curing processes.
More preferably the resin wt % is up to 19 wt %, preferably up to 17 wt %, preferably up to 15 wt %, preferably up to 12 wt %, more preferably up to 7.5 wt %, and is most preferably 5 wt % or less.
It is also preferable to ensure a minimum resin wt % to provided adequate coverage of the yarn or cloth. Preferably the resin wt % is at least 0.1 wt %, preferably 0.3 wt %, more preferably 0.5 wt %, more preferably 1.0 wt %, more preferably 1.5 wt %, and most preferably is at least 2 wt %.
The cloth according to the present invention preferably comprises at least 2 g/m²of resin (wt resin as calculated above). More preferably at least 4 g/m², more preferably at least 5 g/m², and most preferably at least 6 g/m².
The cloth according to the present invention preferably comprises less than 30 g/m²of resin. More preferably up to 25 g/m², more preferably up to 20 g/m², more preferably up to 15 g/m², and most preferably less than 12 g/m².
Preferably the resin mixture comprises between 2 to 40 grams of pigment per litre; more preferably between 5 to 35 g/l, more preferably 9 to 30 g/l, and most preferably 12 to 20 g/l.
In a preferred method of the present invention the substrate may be provided with a water-repellent finish (e.g. paraffin, silicone or fluorocarbon), a fire-retardant finish, a wicking (softening) finish, an antistatic finish and/or a chemical-attack-resistant finish. The finishing step may be carried out, subsequent to application of the first dyestuff, and prior to addition of the second dyestuff; or subsequent to addition of the second dyestuff.
An alternative and particularly interesting procedure, to those discussed above, that may be used to apply one or both of the dyes is a digital application technique. Such techniques are described in detail in PCT application Nos PCT/EP2004/010732 and PCT/EP2004/010731 both filed on 22 Sep. 2004 the contents of which are hereby incorporated by reference in their entirety. A further apparatus and procedure is disclosed in PCTEP2008/064838 filed 31 Oct. 2008, also incorporated herein by reference. An advantage of these techniques is the accuracy of drop placement that can be achieved, whereby precise quantities of each dyestuff may be deposited at a given point on a substrate from two different deposition arrangements. Deposition may also take place onto both sides of a substrate. Furthermore, since the deposition can be precisely controlled, different colours may be deposited at different locations on the substrate allowing printing of designs and patterns according to the invention whereby each area of the substrate is effectively dyed twice with the same colour according to the two different mechanisms. The dyeing step may also be integrated with one or more digital finishing steps e.g. as described above.
A particularly preferred method of the invention comprises the steps of:

- i) providing a yarn or cloth comprising aramid fibres;
- ii) dyeing the yarn or cloth with a dye, preferably by exhaust dyeing; and
- iii) dyeing the yarn or cloth with a pigment, preferably in a resin dyebath, the resin dyebath preferably comprising acrylic resin;

wherein the dye and the pigment dye the same fibres substantially the same colour.
A particularly preferred method of the invention comprises the steps of:

- i) providing a yarn or cloth comprising fibres, preferably aramid fibres;
- ii) dyeing the yarn or cloth with a high visibility dye; and
- ii) dyeing the yarn or cloth with a high visibility pigment, preferably by applying a resin-pigment paste to the yarn or cloth, preferably the resin comprising polyurethane resin; and most preferably being foamed polyurethane resin;

wherein the dye and the pigment dye the same fibres substantially the same colour.
Another aspect of the invention relates to a yarn or cloth comprising fibres, the fibres being dyed with two types of dyestuff, characterized in that the two types of dyestuff dye the fibres substantially the same colour; and that one of the dyestuff types chemically bonds with or is at least partially incorporated into the fibre structure and the other dyestuff type does not chemically bond with or become at least partially incorporated into the fibre structure.
Preferably the invention provides a yarn or cloth comprising fibres dyed with dye and pigment, the dye and pigment dyeing the same fibres substantially the same colour.
In one embodiment, the fibre, yarn or cloth comprises aramids, the preferred aramid being poly(m-phenyleneisophthalamide). The yarn or cloth may preferably be a blend of aramid fibres and other materials, preferably the yarn or cloth comprises, by weight of the yarn or cloth, greater than 5% wt of aramid fibres, more preferably greater than 20% wt. An example of a commercially available aramid fibre is Nomex™ made by DuPont.
Preferably the cloth comprises greater than 5% (by weight of all fibres in the cloth) of either poly(m-phenyleneisophthalamide) fibres or poly(p-phenyleneterephthalamide) fibres, more preferably greater than 10% and most preferably greater than 20%.
In another embodiment at least one of the dyestuffs is a high visibility dyestuff. The high visibility dyestuffs can be used to dye aramid fibres as described or can be used to dye non-aramid fibres. More preferably the at least two types of dyestuff are high visibility dyestuffs.
Thus in a preferred embodiment the invention provides a yarn or cloth comprising fibres dyed with high visibility dye and high visibility pigment, the dye and pigment dyeing the same fibres substantially the same colour.
A further aspect of the invention relates to a garment (e.g. coats, jackets, overalls, vests, waistcoats, bodywarmers, shirts, trousers, footwear, hats and gloves) comprising the above-described dyed fibre, yarn or cloth; and/or to bags or tents comprising the dyed fibre, yarn or cloth. Preferably the garment is a high visibility garment.
According to another aspect of the invention, there is provided a process of dyeing a yarn or cloth comprising fibres, comprising dyeing at least part of the fibres with at least two types of dyestuff; characterized in that one of the types of dyestuff chemically bonds with or is at least partially incorporated into the fibre structure and the other type of dyestuff does not chemically bond with or become at least partially incorporated into the fibre structure; and the two types of dyestuff are provided coextensively on at least one side of the yarn or cloth.
As used herein the term “yarn” means a continuous length of interlocked fibers.
As used herein the term “cloth” is synonymous with textile and fabric.
A used herein the term “dyestuff” means a substance which imparts colour to a fibre, fabric or cloth.
As used herein the term “dye” means substances that add colour to textiles and which are incorporated into the fibre by a chemical or physical reaction e.g. absorption, or dispersion. Dyes generally show an affinity (chemical attraction) to the substrate that they are used to colour. Preferred dyes include acid dyes; basic dyes; direct dyes; reactive dyes; disperse dyes; vat dyes and sulphur dyes.
As used herein the term “pigment” means a coloured, insoluble, finely divided substance, such as titanium dioxide, used to deluster or colour fibres, yarns or fabrics. Pigments, in contrast to dyes, generally show little or no affinity to the substrate that they are used to colour, and predominantly require an additional binder to fix them to a substrate.
A “high-visibility dyestuff” is a dyestuff suitable for dyeing textiles intended to provide conspicuity so as to gain compliance with European standard EN 471 (2003).
The term “substantially the same colour” as used herein means as appreciated by the human eye when two colour samples are viewed separately from one another under D65 illumination as defined by the CIE (International Commission on Illumination).
In particular two dyestuff types are substantially the same colour when a yarn or cloth coloured with one of the dyestuff types does not significantly change colour once it is subsequently coloured with the second type of dyestuff. Examples of significant changes of colour include changes from red to yellow, red to green, red to blue, yellow to blue, yellow to violet, blue to green, blue to orange, orange to green, orange to violet, green to violet, or vice versa. The effect to be achieved by having two dyestuffs of substantially the same colour is that on loss of colouration in one of the types of dyestuff that colour the yarn or cloth, the yarn or cloth stays substantially the same colour as it was prior to the colour loss, taking into account the fading aspect.
It is possible to achieve substantially the same colour for two different types of dyestuff in different ways. In general, a colour on a substrate can be created by use of a single dyestuff or a mixture of dyestuffs. According to the invention a colour may be achieved with two single dyestuffs, each one selected from each of the groups of different types of dyestuffs. Alternatively the same substantial colour is achievable by using blends of differently coloured dyestuffs selected from within the same dyestuff type. For example, a particular basic dye or dye blend may be selected as the desired colour of the yarn or fabric, then a mixture of pigments is blended to give the same substantial colour as the dye. In this way a blend of pigments is used as one of the types of dyestuff to colour the yarn or fabric. Equally, a pigment or blend of pigments may be selected as the desired colour with a mixture of basic dyes being blended to match therewith.
“Coextensively” provided types of dyestuffs means dyestuff types that are only provided on the yarn or cloth when in combination. That is, wherever one dyestuff type is present on the yarn or cloth, the other dyestuff type is also present so that neither type of dyestuff is independently present on the yarn or cloth. Preferably every square mm of at least one surface of the yarn or cloth, more preferably every 0.25 mm², more preferably every 0.05 mm²of yarn or cloth which comprises one dyestuff type also comprises the other dyestuff type.

DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The following is a description of certain embodiments of the invention, given by way of example only.

Example 1

Dyeing Aramids

A sample of fabric composed of 99 weight % of Aramid and 1% stainless steel was partially dyed with a basic dye, and partially with a pigment.
Production Run of 500 Metres.
Dyeing procedure for 500 meters of cloth with two types of dyestuff.
A basic dyestuff comprising a carrier suitable for aramids and a dye mixture of basic blue CI41 and basic red CI46. In the process 50% of the amount of basic dye recipe was used compared to the amount normally used in a process of fully dyeing a fabric with basic dyestuff. The liquor ratio was 1 kg of undyed cloth (also known as ‘grey cloth’ or ‘base cloth’) to 3 litres of liquid.
The second dyestuff was pigment based and comprised an acrylic copolymer emulsion.
and a pigment mixture of pigment blue CI 15.3 and pigment violet CI 23.
In the example the component percentages of the dye mixture and pigment mixture were chosen so that the dye mix and the pigment mix produced substantially the same colour as each other following application to the sample. The exact component proportions in the mixtures were determined by routine testing of pigment mixtures to obtain a colour matching that of the dye mixture.
The sample was dyed according to the process steps:

- Basic dyeing using a discontinuous dyeing process
- Drying
- Pigment dyeing using a continuous dyeing process
- Washing
- Finishing (water repellent finish)
- Curing

Sample A, dyed by the above described process, was compared to two comparative samples B and C. Sample B was a full basic dyed sample and sample C was a full pigment dyed sample using the same dye recipes.
The light fastness and abrasion/wash fastness of the three samples (A, B, C) were tested using ISO 105-B02: 1998 (light fastness) and ISO105-X12: 1987 (fastness to rubbing). The results are shown in table 1.

TABLE 1

	Light	Fastness to rubbing

Samples	fastness	Dry	Wet

A (basic/pigment)	3-4	3-4	3-4
B (basic)	2	4-5	3-4
C (pigment)	4	2	2-3

Example 2

Dyeing High-Visible Fabrics (Cotton/Modacrylic)

To dye a textile or fabric for high visibility a process comprising the following three steps is used.
1. Dye the fabric with a high visibility reactive dye
2. Dye PPAN (modacrylic) with a high visibility basic dye
3. Dye the cloth with a high visibility pigment dye, whereby the binder is chosen such that it is suitable for both fibres of the blend.
All of steps 1 through 3 are carried out for modacrylic textiles. Only steps 1 and 3 need to be used with cotton, although step can optionally be included.
In between these dyeing steps the sample is subjected to a drying process and after the third dyeing step the sample is finished (e.g. with water repellent) and cured.
Thus, the invention has been described by reference to certain embodiments discussed above. It will be recognized that these embodiments are susceptible to various modifications and alternative forms well known to those of skill in the art.
Many modifications in addition to those described above may be made to the structures and techniques described herein without departing from the spirit and scope of the invention. Accordingly, although specific embodiments have been described, these are examples only and are not limiting upon the scope of the invention.

Claims

What is claimed is:

1. A process of dyeing yarn or cloth comprising fibres, comprising dyeing at least part of the fibres with at least two types of dyestuff; wherein the two types of dyestuff dye the same fibres substantially the same colour; and that one of the types of dyestuff chemically bonds with or is at least partially incorporated into the fibre structure and the other type of dyestuff does not chemically bond with or become at least partially incorporated into the fibre structure.

2. The process according to claim 1, wherein part of the fibres are first dyed with one of the dyestuff types and then subsequently dyed with the other type of dyestuff.

3. The process according to claim 1, wherein the chemically or at least partially incorporated dyestuff type has a lower light fastness and a greater wash fastness than the other dyestuff type.

4. The process according to claim 3, wherein part of the fibres are first dyed with one of the dyestuff types and then subsequently dyed with the other type of dyestuff.

5. The process according to claim 1, wherein the fibres are either poly(m-phenyleneisophthalamide) fibres or poly(p-phenyleneterephthalamide).

6. The process according to claim 1, wherein at least one of the types of dyestuff is a high visibility dyestuff.

7. The process according to claim 1, wherein at least one of the types of dyestuff is a fluorescent dyestuff.

8. A process of dyeing cloth, comprising the steps of:

providing cloth comprising poly(m-phenyleneisophthalamide) or poly(p-phenyleneterephthalamide) fibres; and

dyeing the poly(m-phenyleneisophthalamide) fibres or poly(p-phenyleneterephthalamide) with two types of dyestuff of substantially the same colour.

9. The process according to claim 1, wherein one of the types of dyestuff is pigment and the other type of dyestuff is dye.

10. The process according to claim 9 comprising the steps of:

i) dyeing the yarn or cloth with a dye; and subsequently

ii) dyeing the yarn or cloth with a pigment by applying a blend of resin and pigment to the yarn or cloth and curing the resin.

11. The process according to claim 8, wherein one of the types of dyestuff is pigment and the other type of dyestuff is dye.

12. The process according to claim 11 comprising the steps of:

i) dyeing the yarn or cloth with a dye; and subsequently

13. The process according to claim 9, wherein after curing the yarn or cloth comprises less than 20 wt % resin (based on total weight of dyed cloth).

14. A yarn or cloth comprising fibres, at least part of the fibres dyed with two types of dyestuff, wherein the two types of dyestuff dye the fibres substantially the same colour; and wherein one of the types of dyestuff is chemically bonded with or is at least partially incorporated into the fibre structure and the other type of dyestuff is not chemically bonded with or incorporated into the fibre structure.

15. The yarn or cloth according to claim 14, wherein the fibres are aramid fibres.

16. The yarn or cloth according to claim 14, wherein the fibres are at least one of poly(m-phenyleneisophthalamide) fibres or poly(p-phenyleneterephthalamide) fibres.

17. The yarn or cloth according to claim 14, wherein at least one of the types of dyestuff is a high visibility dyestuff.

18. The yarn or cloth according to claim 14, wherein at least one of the types of dyestuff is a fluorescent dyestuff.

19. The yarn or cloth according to claim 14, wherein one of the types of dyestuff is pigment and the other type of dyestuff is dye.

20. The yarn or cloth according to claim 19, wherein the pigment is fixed to the yarn or cloth with resin, and the yarn or cloth comprises less than 20 wt % resin, based on the total weight of the dyed yarn or cloth.

21. The garment comprising yarn or cloth according to claim 14.