GB1595580A - Transfer printing of fabrics - Google Patents

Description

(54) TRANSFER PRINTING OF FABRICS (71) We, AULT & WIBORG LIMITED, a British Company, of Standen Road, London, SW18 STJ, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- The traditional method of printing fabrics comprises printing the dye (which term is used herein to include organic and inorganic dyestuffs and pigments) onto the fabric while in a liquid carrier. As a result the fabric printer has to be equipped with machinery for producing the desired patterns.More recently sublimable dye transfer printing techniques have been devised and these are advantageous since they make it much easier for the fabric printer to produce a wide range of designs and to change his designs easily with changing fashions. Thus, a sublimable dye is printed in the chosen design onto a transfer web, generally of paper, and the fabric printer then lays the web against the fabric to be printed and heats the web, thereby subliming the dye and causing it to transfer from the web to the fabric, where it condenses bagk into solid form on the fibres of the fabric.

With polyester fibres dyes are available which give a fast pattern, that is to say it is not easily removed by washing, cleaning or wear, and the method had gained great commercial acceptance for printing fabrics based wholly or mainly on polyester fibres. Satisfactory results can also be obtained on acrylic fibres. Some of the sublimable dyes will dye fast onto polyamide fibres, but others are taken up very well by the polyamide fibre (in fact sometimes better than the polyester is taken up), but are released again on washing so that they are not fast. An even greater problem exists with natural and hydrophilic fibres, especially cellulosic fibres such as cotton. They do not take the dye up very well in the first place and the dye is not held fast onto the fibres, so that the colour is not resistant to washing.

Accordingly alhough sublimable dye transfer printing is a very desirable system of printing fabrics it cannot be applied satisfactorily to many commercially available fabrics.

Methods of pretreating fibres in various ways to make them receptive to dyes of various types are of course well-known and indeed there is a wide body of art dealing with the treatment of fibres for various purposes. However none of these methods have solved the problem which exists, and as a result other attempts have been made at preparing fabrics, such as those formed of cotton or cotton polyester mixtures, for sublimable dye transfer printing. For instance in British Specification 1,441,203 cotton fibres in a fabric are partially esterified by reaction with, for example, acetic acid prior to printing. More usual methods involve applying an aqueous resin system onto the cotton fabric, followed by curing of the system and sublimable dye transfer printing, either simultaneously with or subsequent to the curing.Such methods are described in, for example, German Auslegeschrift 2436783 and British Patent Specification 1445201. Typical of the resins used is hexamethyoxymethyl melamine resin. Typically 60 to 90% of the aqueous resin system is water.

The total pickup of aqueous resin system is usually quite large, for example 75% is mentioned in some of the examples in German 2436783. A typical coating amount for the dry resin is 5%.

These methods necessitate equipment for applying an aqueous system to the fabric and for drying the system and curing it, and thus necessarily involve the use of, for instance stenter frames and extensive drying apparatus. Also the resins used tend to age the fabric and to impair its handle, and in particular to make it feel rather coarse and to make it easily tom, especially at the large amounts generally used.

Thus although these known techniques do permit sublimable dye transfer printing techniques to be applied to fabrics that cannot otherwise be printed by these techniques they are unsatisfactory in that they damage the fabric and require the use of expensive machinery, and thus tend to lose the very advantages of economy and versatility that sublimable dye transfer printing is meant to afford.

It has been our object to devise a method that maintains these advantages and which renders cotton and other fabrics suitable for sublimable dye transfer printing.

According to the invention we apply onto a fabric 0.1 to 10 g/m2 of a substantially solvent free polymerisable lacquer that is compatible with the fibre and that on curing forms a polymer compatible with a sublimable dye, and we then polymerise the lacquer and print the compatible sublimable dye onto the fabric by heat transfer printing.

The lacquer may be applied over parts only of the fabric, i.e. parts where sublimable dye is to be printed, or over the entire surface of the fabric. Where parts only of the fabric have the lacquer applied to it the dye is of course applied to these parts, and in calculating the rate of application of the lacquer reference is made only to the areas over which the lacquer is actually applied.

Generally the rate of application will be as low as possible, having regard to the fibre type and the dye that is to be printed, since this is both economically desirable and improves the handle of the fabric. Generally it is below 3 g/m2 but is often more 0.1 g/m2. A pick up of 0.5 to 2 g/m2 is generally preferred.

Any conventinal method of applying the lacquer can be used, but since it is important in the invention that only small amounts of lacquer are applied and since it is essential for uniformity of properties that there should be a uniform application, the method chosen must permit accurate application of small amounts. Accordingly it is -generally preferred to use gravure or flexographic printing methods, although methods such as rotary screen, roller coating or spraying methods can be used if approDriate control over coating rates is exercised.

Because of the low and accurate coating rates that are applied in the invention it is necessary that the lacquer should have very low viscosity. Viscosity can be measured in seconds by the method known as BS B4 Cup at 250C. All viscosities in the specification are measured by this method. The lacquer should have a viscosity of no .more than 90 seconds, most preferably 70 seconds or less. Generally the lacquer has a viscosity of from 15 to 60 seconds, with best results generally being achieved with viscosities of less than 40 seconds. If the lacquer is thixotropic, as is sometimes preferred, it should have such viscosity when it does flow.

A small amount of solvent, that is to say a non-reactive solvent that does not participate in the polymerisation, may be included in the lacquer, for instance to reduce its viscosity. In some instances the amount of solvent may be up to, say 30% but preferably it is less, generally being below 10%. Since the amount of solvent is always so low, and since the pick up of lacquer is low the amount of solvent picked up by the fabric is extremely low and so none of the problems encountered when using large amounts of aqueous system arise in the invention. Thus it is unnecessary to provide tensioning apparatus such as tenter frames or drying apparatus. If a solvent is to be used it may be water or an organic solvent or a mixture thereof.Generally organic or aqueous organic systems are preferred, isopropanol being particularly useful, although n-propanol, ethanol and halogenated hydrocarbons are included amongst other useful solvents. In addition non-reactive additives may be included in the mixture and could include proprietary anti-static agents, flame retardants, optical brighteners or pigment extenders. The total amount is generally less than 10%.

The invention can be applied to fabrics containing a wide range of fibre types, for instance, cotton, rayon, viscose, Vincel (a registered Trade Mark), wool, polyester, polyamide, acrylic acetate and silk and mixtures of any of these. It can be applied to all fabrics, so as to provide a standardised substrate on which the sublimable dye transfer printing step can be conducted, but is of most value when applied to fabrics containing hydrophilic fibres, especially cotton or other cellulosic fibres or polyamide fibres, either alone or as at least 50% of the fibre content, e.g. mixed with polyester.

The particular lacquer will be chosen having regard to the fibres to be treated.

It is necessary that the polymerisable lacquer should be compatible with the fibre and that on curing it should form a polymer that is compatible with the dye to be printed onto it. If the lacquer is not compatible with the fibre then an inadequate film is formed over or in the fibre structure with the result that there will be inadequate pick up of the dye and/or poor wash fastness. Thus on a microscopic scale it will be seen that the dye is not present uniformly over the fabric, but instead has a variable density and presents a speckled appearance. If the cured polymer is not compatible with the sublimable dye, then again there may be low pick up and in particular there will be poor wash fastness.Broadly therefore whether or not the lacquer is compatible with the fibres and the dye with. the cured polymer is easily determined simply by observing the final result, in that if there is good pick up of the dye and it is held fast, then both the lacquer and the polymer are compatible, but if there is low pick up and/or the dye is not held fast, then either the lacquer is incompatible with the fabric or the polymer is incompatible with the dye, or both. By referring to good pick up and the dye being held fast we mean that the pick up and the degree of fastness should to at least similar to that traditionally obtained at present using sublimable dyes on polyester fibres.

In order to ensure that the lacquer is compatible with the fibre it should include at least 30%, and preferably at least 50%, by weight of one or more polymerisable components that are hydrophilic, in the sense that at least 2%, and preferably at least 3% by weight water can be added to the monomer with stirring before the monomer becomes cloudy. In some instances it is preferred that at least 10%, and preferably at least 30%, by weight of the lacquer should be very hydrophilic material, for instance material that will absorb at least 5 and preferably at least 15% water before becoming cloudy. Preferably the hydrophilic components include free hydroxy, epoxy or carboxy groups that will promote the hydrophilic properties.Provided a sufficiently hydrophilic lacquer is obtained, then substantially uniform coating of the fibres is achieved, and in particular a substantially uniform film over the fibres can be achieved and this is desirable for compatibility. The lacquer will also to some extent be absorbed into the fibres due to the hydrophilic nature of some at least of the components of the lacquer.

The film formed on curing should be substantially hydrophobic in order that it is sufficiently receptive to the sublimable dyes, which themselves are normally hydrophobic. Hydrophobicity may be achieved partly as a result of the hydrophilic groups in hydrophilic monomers being eliminated by the polymerisation but primarily by the use of a substantial amount, for example at least 30% of a monomer in the lacquer which is itself hydrophobic, preferably being incapable of absorbing any water before becoming cloudy. It seems probable that in the preferred processes the dye, when it condenses onto the polymer, dissolves into the polymeric structure to some extent at least.

More than 50% by weight, and usually more than 70% and preferably more than 80% by weight of the lacquer consists of polymerisable ingredients. The other ingredients that may be present in the lacquer include minor amounts of solvent, as discussed above, and minor amounts, generally less than 10%, of additives to reduce viscosity, improve flow or improve coating properties. If the lacquer is to be cured by heating, then it may include an appropriate initiator or catalyst, but it is preferred in the invention that the lacquer should be photopolymerisable in which event it will include conventional additives for photopolymerisable lacquers such as photoinitiators and photosensitisers.Preferably photopolymerisation is brought about by irradiation with ultra-violet light although the lacquer can be formulated so as to be polymerised by other photoirradiation provided the irradiation used is of a wavelength or intensity such that substantial polymerisation of the lacquer under ambient lighting conditions before and during coating is avoided.

The lacquer is preferably based on one or more main film formers and one or more cross-linking monomers, at least one of the polymerisable monomeric components in the mixture serving as a reactive solvent for the lacquer. However the main film former tends to be very viscous, e.g. above 200 seconds, and the cross-linking monomers that are optimum for the properties of the final film may not by themselves have sufficiently low viscosity to reduce the viscosity of the lacquer to the desired low values. Accordingly it is desirable to include also a reactive monomer that may contribute to the cross-linking, but in particular will react into the polymer and will reduce the viscosity of the lacquer. Such materials, termed reactive viscosity reducers, may themselves have a viscosity as low as 10 or 20 seconds.

A wide range of polymeric lacquers are now known, for instance for use as bases for printing inks that are to be printed onto paper and for application as gloss finishes to furniture and metal surfaces, and it is easily possible to select from the commercially available materials a lacquer that will be suitable for use on the particular fabric being treated, except that it may be necessary to reduce its viscosity either by adding solvent or by adding reactive viscosity reducer. The main film former may be for instance an epoxy acrylic, an unsaturated polyester or an acrylic urethane. Suitable epoxy acrylics are epoxy maleic anhydride-hydroxy acrylics, and acrylic diesters of liquid epoxy resins.Suitable unsaturated polyesters include esters of unsaturated acids such as maleic acid (or anhydride), fumaric acid, itaconic acid, citraconic acid, mesaccnic and aconitic acids, optionally mixed with ortho, iso or terephthalic acid, with polyhydric alcohcls which may be applied (for instance ethylene glycol) or aromatic Preferably the film former is of high molecular weight so that only a low degree of cross-linking is necessary to achieve a desirable glass transition temperature. The acrylic urethanes are isocyanate modified acrylics. The amount of film former is generally from 15 to 50, preferably 20 to 30%, by weight of the lacquer.

The main cross-linking monomer is preferably an acrylic monomer. Suitable materials are triacrylate or tetra-acrylates such as pentaerithritol monohydroxy triacrylate or tetra-acrylate and trimethylolpropane triacrylate. They are chosen as materials that are traditionally used for cross-linking the chosen film former. The amount is generally from 20 to 50% of the lacquer and is preferably 1 to 1.5 times the weight of the main film former.

The reactive viscosity reducer is preferably also an acrylate, such as triethylene glycol diacrvlate, monoacrylated phenolethyleneoxide adduct and polyethylene glycol diacrylate. The amount is preferably from 20 to 50% by weight of the lacquer and is normally 0.75 to 1.25 times the weight of the main cross-linking monomer.

After the lacquer has been applied to the fabric it is polymerised, normally by passing the fabric under an appropriate source of light.

If desired the lacquer may be applied in two or more coating steps in which event the lacquer may be photo polymerised between each coating step or in a single photo polymerisation step after the final coating step.

The heat transfer printing step is conducted by conventional means. Thus a transfer substrate, usually paper, that has been printed by a conventional technique (such as intaglio, planographic relief or screen printing) with a sublimable dye is pressed against the treated fabric and the dye sublimed by the application of heat while the substrate and the fabric are in contact. Sufficient pressure is applied to maintain contact during transfer. The ambient air pressure may be below atmospheric pressure so as to increase the efficiency of dye sublimation and transfer. The dye may may be carried on the transfer paper in any sublimable solid form, for instance a solid solution of dispersion. The dye may be any sublimable organic or inorganic dyestuff or pigment or mixture thereof. Sublimable dyes providing a wide range of colours are well known and are usable in the invention.

The following are some examples of the invention. In all these, percentages are by weight unless otherwise specified.

Example 1.

A lacquer was formulated comprising 31.7% of an acrylic urethane main film former (e.g. acrylic urethane in AP 565 supplied by Synthese Holland).

38.15% of a triacrylate as a cross-linking monomer (e.g. O.T.A. 480 supplied by UCB Belgium).

14.1% triethylene glycol diacrylate as a reactive viscosity reducer.

0.05% silicone oil as a slip agent.

4.8% epoxidised octyl Tall oil as a non-reactive secondary viscosity reducer.

1.0% cellulose acetate butyrate as a flow agent.

10.2% of equal amounts of benzophenone and methyl diethanolamine as a photo-initiator system.

This formulation had a viscosity of 70 seconds.

Cotton fabric was treated by the application of the lacquer from the printing roller of a Duncan Lynch dry offset proofing tester to give a cured film weight of approximately 3 grams per square metre. The film was cured by passing the coated fabric under a U.V. lamp (medium pressure mercury arc lamp 80 watts/cm at a speed 30 m/minute).

The treated cotton fabric was then printed with heat transfer paper on a flat bed transfer press for 30 seconds at 200cm. The transfer paper had previously been printed by sheetfed offset lithography using three inks. Ink 1 contained dispersed dye Yellow 3. Ink 2 contained dispersed dye Red 60. Ink 3 contained dispersed dye Blue 180.

At the same time untreated cotton fabric of the same type was printed with a similar transfer paper. A dramatic difference was observed on comparison of the untreated and treated printed cotton. With all three colours, colour yield was much greater on the treated fabric. The results are shown in Table 1. It was observed that wash fastness of the printed cotton was considerably improved by the pretreatment.

Moreover, the pretreatment had not significantly affected the handle of the cotton fabric.

Example 2.

The lacquer identified in Example 1 was applied twice to the cotton without intermediate curing. This double coat was then cured and printed as described in Example 1.

A further improvement in colour yield was observed relative to untreated cotton and cotton treated as Example 1, as shown in Table 1.

Example 3.

The treatment described in Example 1 was applied twice to cotton, i.e. sequence was: a. Application of Formulation 1, b. Curing, c. Repeat application of Formulation 1, d. Second curing.

Conditions for both irradiations were the same and as described in Example 1.

Cotton treated in this manner showed the highest colour strength after printing, as shown in Table 1. Prior curing of the first coat, before application and cure of a second coat had sealed the surface, allowing more of the second application to remain on the surface where its effect in increasing the dye substantivity is the greatest.

TABLE 1 Effect of different pre-treatments on the Colour Density of Cotton, Heat Transfer printed with various dyes.

SUBSTRATE YELLOW 3 Optical Density Absorption %

Neutral Blue Neutral Blue Filter Filter Filter Filter Untreated Cotton 0.21 0.37 38 57 Treated Cotton One treatment and cure as 0.23 0.63 41 77 Example 1 Treated Cotton Two treatments and cure as 0.26 0.72 45 81 Example 2 Treated Cotton One treatment and cure repeated 0.27 0.74 46 82 as in Example 3 TABLE 1 continued Effect of different pre-treatments on the Colour Density of Cotton, Heat Transfer printed with various dyes SUBSTRATE RED 60 Optical Density % Absorption

Neutral Blue Neutral Blue Filter Filter Filter Filter Untreated Cotton 0.31 0.41 51 61 Treated Cotton One treatment and cure as 0.39 0.68 59' 79 Example 1 I Treated Cotton Two treatments and cure as 0;;40 0.74' 60 82 Treated Cotton One treatment and cure repeated 0.42 0.77 62 83 as n Example 3 BLUE 180 Optical Density % Absorption

Neutral Blue Neutral Blue Filter Filter Filter Filter Untreated Cotton 0.32 0.34' 52 54" Treated Cotton One treatment and cure as 0.64' 0.73 77 81 Example 1 Treated Cotton Two treatments and cure as 0.72 0.76 81 83 Example 2 Treated Cotton One treatment and cure repeated 0.81 0.84 85 86 as in Example 3 % Absorption - (100 - % reflection) Measurements -were made on a Macbeth RD100Reflectance Densitometer Example 4.

A lacquer was formulated containing 24.9% of an acrylic urethane film former (e.g. AP 565).

30% of a triacrylate cross-linking monomer (e.g. O.T.A. 480), 30.5% of a monoacrylated phenol ethyleneoxide adduct as reactive viscosity reducer (e.g. DPAM 473 supplied by Lankro).

10% of benzophenone and 5% n-methyl diethanolamine as photo initiator.

0.5% methylether of hydroquinone 20% solution in trimethylolpropane triacrylate as a retarder.

This composition had a viscosity of 35 seconds, but desirably 7% isopropanol was added to reduce its viscosity to 20 seconds.

A cotton fabric was coated with this composition by means of a rotogravure engraved cylinder 150 screen to give a cured film weight of about 1.5 grams per square metre. Curing was effected by passing the fabric under a UV lamp (Primarc 80 watts per cm) at 30 metres per minute. The cotton was then transfer printed as in Example 1 to achieve equally good results.

This process could be operated either with the composition free of isopropanol or with the diluted composition described. The advantage of operating with a diluted composition is that greater printing speeds can be achieved, for instance 275 metres per minute, and also microscopic examination showed that a more uniform distribution of the lacquer on the fabric and of the result dye could be achieved.

Good results were also obtained when the lacquer was used instead on nylon fabrics (thereby increasing the range of dyes that can be printed onto them to obtain a fast colour) and onto viscose rayon fabrics.

Example 5.

A lacquer was formed consisting of 24.5 parts of an epoxy acrylate film former (e.g. Evecryl 601 supplied by UCB), 30% triacrylate cross-linking monomer (e.g. O.T.A. 480), 30% monoacrylated phenol ethyleneoxide adduct (e.g. DPAM 473), 10% benzophenone and 5% n-methyl diethanolamine as photoinitiator system, 0.5% methylether of hydroquinone 20% solution in trimethylol propane tri acrylate, as retarder.

This lacquer had a viscosity ot 36 seconds.

It was printed on various fabrics, including cotton, nylon 6 and viscose rayon, by means of an engraved cylinder (150 screen) and was then cured as described in Example 4 to give a cured film weight of approximately 1.5 grams per square metre.

Transfer printing was then conducted as in Example 1 on the cotton and under appro priate conditions onto nylon or viscose rayon. Thus onto nylon the printing was conducted at 1900C for 30 seconds while on the viscous rayon it was conducted at 210 C for 30 seconds. Good pick up and fastness were obtained in all instances.

WHAT WE CLAIM IS: 1. A method of printing a fabric comprising applying onto the fabric 0.1 to 10 g/m2 of a substantially solvent free polymerisable lacquer that is compatible with the fibres of the fabric and that on curing forms a polymer compatible with a sublimable dye, curing the lacquer, and printing the compatible sublimable dye onto the fabric by heat transfer printing.

2. A method according to claim 1 in which the amount of lacquer applied is less than 3 g/m2.

3. A method according to claim 1 in which the amount of lacquer applied is 0.5 to 2 g/m2.

4. A method according to any preceding claim in which the lacquer has a viscosity of 70 seconds or less as measured by BS B4 Cup at 25"C.

5. A method according to claim 4 in which the lacquer has a viscosity of from 15 to 40 seconds.

6. A method according to any preceding claim in which the lacquer comprises

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (13)

**WARNING** start of CLMS field may overlap end of DESC **. Example 4. A lacquer was formulated containing 24.9% of an acrylic urethane film former (e.g. AP 565). 30% of a triacrylate cross-linking monomer (e.g. O.T.A. 480), 30.5% of a monoacrylated phenol ethyleneoxide adduct as reactive viscosity reducer (e.g. DPAM 473 supplied by Lankro). 10% of benzophenone and 5% n-methyl diethanolamine as photo initiator. 0.5% methylether of hydroquinone 20% solution in trimethylolpropane triacrylate as a retarder. This composition had a viscosity of 35 seconds, but desirably 7% isopropanol was added to reduce its viscosity to 20 seconds. A cotton fabric was coated with this composition by means of a rotogravure engraved cylinder 150 screen to give a cured film weight of about 1.5 grams per square metre. Curing was effected by passing the fabric under a UV lamp (Primarc 80 watts per cm) at 30 metres per minute. The cotton was then transfer printed as in Example 1 to achieve equally good results. This process could be operated either with the composition free of isopropanol or with the diluted composition described. The advantage of operating with a diluted composition is that greater printing speeds can be achieved, for instance 275 metres per minute, and also microscopic examination showed that a more uniform distribution of the lacquer on the fabric and of the result dye could be achieved. Good results were also obtained when the lacquer was used instead on nylon fabrics (thereby increasing the range of dyes that can be printed onto them to obtain a fast colour) and onto viscose rayon fabrics. Example 5. A lacquer was formed consisting of 24.5 parts of an epoxy acrylate film former (e.g. Evecryl 601 supplied by UCB), 30% triacrylate cross-linking monomer (e.g. O.T.A. 480), 30% monoacrylated phenol ethyleneoxide adduct (e.g. DPAM 473), 10% benzophenone and 5% n-methyl diethanolamine as photoinitiator system, 0.5% methylether of hydroquinone 20% solution in trimethylol propane tri acrylate, as retarder. This lacquer had a viscosity ot 36 seconds. It was printed on various fabrics, including cotton, nylon 6 and viscose rayon, by means of an engraved cylinder (150 screen) and was then cured as described in Example 4 to give a cured film weight of approximately 1.5 grams per square metre. Transfer printing was then conducted as in Example 1 on the cotton and under appro priate conditions onto nylon or viscose rayon. Thus onto nylon the printing was conducted at 1900C for 30 seconds while on the viscous rayon it was conducted at 210 C for 30 seconds. Good pick up and fastness were obtained in all instances. WHAT WE CLAIM IS:

1. A method of printing a fabric comprising applying onto the fabric 0.1 to 10 g/m2 of a substantially solvent free polymerisable lacquer that is compatible with the fibres of the fabric and that on curing forms a polymer compatible with a sublimable dye, curing the lacquer, and printing the compatible sublimable dye onto the fabric by heat transfer printing.

2. A method according to claim 1 in which the amount of lacquer applied is less than 3 g/m2.

3. A method according to claim 1 in which the amount of lacquer applied is 0.5 to 2 g/m2.

4. A method according to any preceding claim in which the lacquer has a viscosity of 70 seconds or less as measured by BS B4 Cup at 25"C.

5. A method according to claim 4 in which the lacquer has a viscosity of from 15 to 40 seconds.

6. A method according to any preceding claim in which the lacquer comprises

a main film former selected from epoxy acrylics, unsaturated polyesters and isocyanate modified acrylics, anacrylic crcss-linking monomer, and an acrylic reactive viscosity reducer.

7. A method according to any preceding claim in which the lacquer includes at least 30% by weight of a hydrophilic polymerisable monomer and the cured polymer is hydrophobic.

8. A method according to any preceding claim in which the lacquer is a photocurable lacquer, includes a photoinitiator and polymerisation is conducted by irradiation.

9. A method according to claim 8 in which the irradiation is ultra-violet radiation.

10. A method according to any preceding claim in which the fabric comprises cotton fibres.

11. A method according to any preceding claim in which the fabric comprises polyamide fibres.

12. A method according to claim 1 substantially as herein described.

13. Fabric printed by a method according to any preceding claim.