GB1586511A

GB1586511A - Heat transfers

Info

Publication number: GB1586511A
Application number: GB24962/77A
Authority: GB
Original assignee: Polymark International Ltd
Current assignee: Polymark International Ltd
Priority date: 1977-06-15
Filing date: 1977-06-15
Publication date: 1981-03-18

Description

(54) IMPROVEMENTS IN OR RELATING TO HEAT TRANSFERS (71) We, POLYMARK INTERNATIONAL LIMITED, a British Company of 63 Jeddo Road, Shepherds Bush, London W12 9EE, 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 present invention relates to heat transfers of the kind used for providing an article, especially a textile article, with a decorative and/or informative label, stamp or other marking hereinafter referred to simply as a label.

We have previously disclosed various construction of heat transfer in our British Patents Nos. 928,347; 1,201,713; 1,287,452 and 1,386,392. Briefly, such transfers comprise a temporary support and a label, carried by the support, comprising a resin system which, when placed in contact with an article to be marked and subjected to the action of heat and pressure, is cured into an inert, insoluble and wear-resistant form and thus provides a substantially permanent marking on the article surface.

Markings formed from resin systems as described in the above patents suffer from certain limitations which restrict their usefulness. In particular, they are relatively inextensible after cross-linking and require a high application pressure to secure good adhesion to the fabric being marked. There is also a tendency for the resin to crack if it forms an unsupported bridge between threads of a coarsely woven fabric. Thick fibres, particularly of materials such as wool, which absorb considerable amounts of water during washing, may also cause the transfer to crack during washing.

These considerations limit the use of those resin systems to transfers which are to be applied to fabrics which are of a closely woven constructions such as cotton sheeting; cotton drill; acetate rayon and nylon linings; cotton, cotton/polyester and nylon shirtings, including warp-knit nylon.

The same limitations are further apparent when one considers that application pressures used in the above patents are of the order of 2 to 4 Kg/sq cm., as only fabrics which are not crushed by such pressures can be labelled without damage.

Our co-pending application No 47867/74 (Serial No. 1,523,869) sought to provide heat transfers in which the abovementioned disadvantages were obviated or mitigated and to this end the said application provides a heat transfer in which Ihe label comprises a layer of a polyurethane resin system incorporating a thermoplastic polyurethane elastomer which is the product of the reaction of (A) 1 mole of an essentially linear hydroxyl-terminated polyester having a repeating. unit either of the formula

wherein R is an alkylene radical of 2 to 8 carbon atoms and R' is an alkylene radical of 4 to 10 carbon atoms, or of the formula

where R" is an alkylene radical of 4 to 8 carbon atoms, said linear polyester having an average molecular weight of 600 to 1,200 and an acid number less than 10; (B) from 1.1 to 3.1 moles of a diphenyl diisocyanate having an isocyanate group on each phenyl- nucleus; and (C) from 0.1 to 2.1 moles of at least one free glycol of from 2 to 10 carbon atoms; the combined average hydroxyl number molecular weight of the polyester and the free glycol being from about 450 to 600, and the molar amount of the polyester and glycol combined being essentially equivalent to the molar amount of the diisocyanate compound. The polyurethane resin system further incorporates an acid or acid-yielding catalyst and as a cross-linking agent a compound containing two or more N-alkoxymethyl groups, so that when the layer of the polyurethane resin system is placed in contact with an article to be marked and subjected to heat and pressure the polyurethane is cross-linked into an inert, insoluble and wearresistant form to provide a substantially permanent marking on the article.

Heat transfers produced in accordance with the above application may be used for providing an article such as a textile article with a marking and in particular for providing a stretching fabric, such as knitwear or jersey, with a stretchable label.

However, these applied labels suffer from the disadvantage that they can only be laundered under relatively mild conditions since more severe laundering often causes deterioration and cracking of the label. This is of course particularly disadvantageous if the washing instructions for the applied label are not followed.

It is therefore an object of the present invention to provide a heat transfer in which the above-mentioned disadvantages are obviated or mitigated.

According to the present invention there is provided a heat transfer comprising a temporary support and a label (as herein defined) carried on said support, said label having a layer of polyurethane resin system which layer has been produced from a solution obtained by dissolving in a solvent a thermoplastic polyurethane elastomer which is the product of the reaction of (A) 1 mole of an essentially linear hydroxyl-terminated -polyester having a repeating unit either of the formula

wherein R is an alkylene radical of 2 to 8 carbon atoms and R1 is an alkylene radical of 4 to 10 carbon atoms, or of the formula

where R" is an alkylene radical of 4 to 8 carbon atoms, said linear polyester having an average molecular weight of above 1,200 and up to 3,000 and an acid number less than 10; (B) from 1.1 to 3.1 moles of a diphenyl diisocyanate having an isocyanate group on each phenyl nucleus; and (C) from 0.1 to 2.1 moles of at least one free glycol of from 2 to 10 carbon atoms; the combined average hydroxyl number molecular weight of the polyester and the free glycol being 450 to 1200 and the molar amount of the polyester and glycol combined being essentially equivalent to the molar amount of the diisocyanate compound, said polyurethane resin system incorporating an acid or acid-yielding catalyst and as a cross-linking agent a compound containing two or more Nalkoxymethyl groups, whereby when the layer of the polyurethane resin system is placed in contact with an article to be marked and subjected to heat and pressure the polyurethane is cross-linked into an inert, insoluble and wear-resistant form to provide a substantially permanent marking on the article.

The polyesterurethanes used in the present invention are therefore similar to those used in our co-pending application but have a polyester component of higher molecular weight. Although these two types of polyurethane are of very similar chemical structure it has been found that those used in accordance with present invention possess a number of unexpected and surprising properties which allow improved heat transfers to be obtained.

In particular the labels of the heat transfers in accordance with the invention may be applied to an article under the action of heat and pressure to produce thereon a marking which has good resistance to hot washing and which retains its appearance even after many such washings.

The transfers may be used for applying a stretchable label to a stretchy fabric and such labels have better stretch recovery for thinner labels than is the case with labels produced from the polyesterurethanes described in application no. 47867/74 (Serial No. 1,523,869). This obviously reduces the quantity of polyesterurethane required to produce the label and therefore cuts down on cost and production time.

Furthermore, the polyesterurethane resin system used in the invention may be more rapidly cross-linked than that described in application no. 47867/74 (Serial No. 1.,523,869) thus reducing the time of the transfer operation, and, in addition, there is less resin flow during this operation so that brighter, more opaque colours are obtained.

A further practical advantage associated with the invention is that, during production, solutions or inks of the polyesterurethane dry to non-tacky films thus facilitating manufacture of the transfer.

The polyesterurethanes as used in the present invention do however have the drawback that they are less soluble in commonly used solvents, than the polyesterurethanes described in application no. 47867/74 (Serial No. 1.523,869). However, the presently used polyesterurethanes may be dissolved in cyclohexanone with high speed mixing and heat transfers may be prepared in a normal manner from such solutions provided that precautions are taken to contain the irritating cyclohexanone vapours.

It will be appreciated that under comparatively severe dissolution conditions, there is the possibility that the polyesterurethane is degraded to a slight extent before passing into solution. It is therefore to be understood that references herein to dissolving the polyesterurethane in a solvent are intended to cover passage of the polymer into solution either with or without such degradation.

Referring now more specifically to the components of the resin system for use in preparing the heat transfers of the invention, the polyesters of the repeating formula

may be prepared by the reaction of a saturated aliphatic glycol having 4 to 10 carbon atoms and the hydroxyl groups on its terminal carbon atoms, and a dicarboxylic acid of the formula HOOC--R POOH where R is an alkylene radical of 2 to 8 carbon atoms, or the anhydride thereof.

Preferably, the polyester used for producing the polyurethane has 4 to 8 methylene groups per ester group. Examples of polyesters which may be used for preparing the polyurethanes are designated below under the headings A(i)-(v): A(i) Polyesters prepared from adipic acid and 1,4-butane diol (both R and R' having 4 carbon atoms), and having approximate molecular weights of 1,210, 2,000, 2,500, or 3,000; A(ii) Polyesters prepared from succinic acid (R having 2 carbon atoms) and 1,8octane diol (R' having 8 carbon atoms) and having an approximate molecular weight of 2,000; A(iii) Polyesters prepared from adipic acid and 1,8-octane diol and having an approximate molecular weight of 2,000; A(iv) Polyesters prepared from sebacic acid (R having 8 carbon atoms) and 1,8octane diol and having an approximate molecular weight of 2,000; and A(v) Polyesters prepared from caprolactone having a molecular weight of approximately 2,000.

The term diphenyl diisocyanate compound as used herein is generic to compounds having two phenyl groups which are bonded either directly to each other or through the intermediary of one or more atoms such as carbon or oxygen, each phenyl group having an -NCO substituent.

Diphenyl methane diisocyanate is found to be particularly suitable for producing the polyurethane resin and for this, and other diphenyl diisocyanate compounds the diphenyl-p,p'-diisocyanate isomer is preferred. Suitable diisocyanates for use in preparing the polyurethanes are listed below: B(i) 4,4'-diphenylmethane diisocyanate B(ii) 3,3'-dichloro 4,4'-diphenylmethane diisocyanate B(iii) 3,3'-dimethyl 4,4'-biphenyl diisocyanate B(iv) 4,4'-diphenylether diisocyanate B(v) 3,3'-dimethyl 4,4'-diphenylether diisocyanate B (vi) 4,4'-diphenyldimethylmethane diisocyanate B(vii) 4,4'-dibenzyl diisocyanate.

Preferably also the free glycol which is used to prepare the polyurethane is a linear glycol of the formula HO(CH2)nOH, n being 2 to 10% (preferably 2 to 8).

Examples of suitable glycols are designated C(i)-C(v) below: C(i) ethylene glycol C(ii) 1,4-butane diol C(iii) hexylene glycol C(iv) 1,8-octane diol C(v) 1,10-decane diol.

Suitable polyester polyurethanes for use in the present invention are available from Bayer under the name Impranil (Registered Trade Mark).

The thermoplastic polyurethane incorporates a cross-linking agent and an acid or acid-yielding catalyst so that, under the application conditions, the polyurethane is converted to an inert, insoluble and wear-resistant form.

The cross-linking agent used to cure the polyurethane resin under the application conditions is selected such that the resin will not cure during long periods of storage at ambient temperature or at the temperatures encountered in preparing the transfer but, nevertheless, will be rapidly cured at the temperature of transfer application to provide a substantially permanent marking. The crosslinking agents are compounds containing two or more N-alkoxymethyl groups, more preferably two or more N-methoxymethyl groups, and several specific examples are listed in the following table.

N,N'-bis-(methoxymethyl) uron, tri-methoxymethyl melamine, hexa-methoxymethyl melamine, tetra-methoxymethyl urea, urea-formaldehyde precondensates containing methoxymethyl groups, melamine-formaldehyde precondensates containing methoxymethyl groups, hexa-ethoxymethyl melamine, urea-formaldehyde precondensates containing ethoxymethyl groups, melamine-formaldehyde precondensates containing ethoxy-methyl groups, N,N'-bis-(methoxymethyl)-meta-phenylenediamine, alkylated melamine or urea resin precondensates, butylated melamine or urea resin precondensates.

The cross-linking agent may be used in an amount of up to 30% by weight based on the weight of the dry resin, with a preferred range of 520% by weight.

As catalyst for the cross-linking agent, there is preferably used a non-volatile acid, phosphoric acid, citric acid, o-phthalic acid, iso-phthalic acid, itaconic acid induce a significant degree of cross-linking at ambient temperature thus giving a heat transfer of poor shelf life, and weaker acids do not act sufficiently quickly under the marking conditions.

As examples of suitable acidic curing agents there may be mentioned tartaric acid, phosphoric acid, cirtic acid, o-phthalic acid, iso-phthalic acid, itaconic acid and salicylic acid. Alternatively, a compound which yields the acid under the marking conditions may be used and in this respect the anhydrides and ammonium salts of the acids may be used.

The amount of acid or acid-yielding curing agent required depends on the pKa of the acid, its basicity and its equivalent weight. An amount of curing agent-in the range 0.5 to 10% by weight based on the dry weight of the resin will normally be found satisfactory and the best results are obtained with a range of I to 4% by weight.

Heat transfers in which the polyurethane resin system incorporates a crosslinking agent and acidic catalyst as described above are found to have an excellent shelf life but, under the application conditions, the polyurethane is rapidly crosslinked into an inert, insoluble and wear-resistant form and produces a substantially permanent marking which is resistant to severe conditions of laundering, pressing and dry cleaning to which the article may be subjected. However, in spite of the cross-linked structure, the marking is extensible and may be used on such fabrics as knitwear and jersey.

Transfer labels prepared according to the present invention can also be applied to loosely constructed or bulked fabrics at pressures as low as 0. I Kg/sq. cm., which means that such fabrics can be labelled without an unsightly pressure mark.

The present invention thus allows the following fabric types to be successfully labelled: jersey knitted cotton, wool, and nylon, including sports shirts, and swimwear; bulked polyester nylons and acrylics as used for ladies dresses, and fabrics with an open weave. Some plastics and plastics coated articles may also be labelled.

The reduced pressure of application also means that there is a greatly reduced tendency for the label to strike through a single thickness of fabric and show on the other side. Distortion of the fabric in the label area is also reduced.

Several different forms of heat transfer fall within the scope of the present invention and their structure will now be described in more detail.

In all cases, the transfer incorporates a temporary support on which the label is carried and which is removed after the marking operation. The support may consist of a suitable release agent, for example cellulose triacetate either as an unsupported film or laminated or coated to a suitable grade of paper. Alternatively, the support may consist of polyethylene terephthalate in film form, commonly sold under the Trade Marks MELINEX or MYLAR, either unsupported or laminated to a suitable grade of paper. There are also a number of proprietory release-coated papers which may be used.

In one form of transfer, the label is provided by coating the support with a solution of the polyurethane resin system, containing catalysts and curing agents, which is then dried so as to form a continuous layer of resin. Onto this layer is printed, in mirror image form, the required design with an ink preferably comprising the same resin system as that used for the continuous layer and made up typically as an approximately 25% solution in an organic solvent such as a ketone (e.g. cyclohexanone) or mixtures of ketones, alcohols and aromatic hydrocarbons. The ink is pigmented in the normal manner and printing effected by converitional techniques such as screen printing.

When this transfer is applied to an article the continuous layer is uppermost in the applied label and thus forms a protective layer for the printed characters.

Optionally, a second continuous layer of the same or different polyurethane resin as the first continuous layer may be applied to the top of the transfer so as to sandwich the printed characters and form a background layer when the label is applied to the article. If desired, this background layer may be of contrasting colour to the printed characters.

In the case of a three-layered structure of this type, it is possible to use conventional printing inks since they will be protected by the two resin layers.

In another type of heat transfer, the required marking of a printing ink based on the polyurethane may be applied directly to the support and then covered with a continuous layer of a polyurethane resin system. If a pigmented solution is used for this continuous layer, it provides a coloured background for the applied label.

In a still further form of transfer, a marking of one or more individual printed characters or markings based on a polyurethane resin system is applied to the temporary support and this assembly may itself be used as a heat transfer so that the printed characters constitute the label. It is however, found that a large amount of pigment must be used in the ink so as to obtain the required intensity of colour and that this deleteriously effects the bonding properties of the label. These difficulties can be overcome by applying to each printed character a substantially coterminous or slightly overlapping layer of polyurethane resin system, preferably clear, to act as a bonding layer. If desired, each printed character may be sandwiched between two such layers so as to provide a bonding layer and a protective layer for the label.

The heat transfers according to the invention are generally used for applying labels to flexible articles and in particular textile materials.

In order to apply the label to the article, the heat transfer assembly is placed in contact with the article, support surface uppermost, and the assembly is pressed generally at a pressure of 0.1A Kg-cm2 at a temperature of generally 150-2500C for generally 2-20 seconds so that the polyurethane resin system in contact with the article is cured and becomes bonded to the article. The pressure is relieved and the temporary support peeled off to leave the label firmly bonded to the article surface.

The invention will now be further described, by way of example, with reference to the following examples.

Examples of polyurethanes which may be used for producing heat transfers are those produced in accordance with Table I from the various polyesters, diisocyanates and glycols listed hereinbefore under the headings A-C. Such polyurethanes may be produced by a process similar to that used in Preparations 1 to 3 as described in co-pending application No. 47867/74 (Serial No. 1.523,869).

Each of polyurethanes 1 to 12 was dissolved in cyclohexanone to give twelve stock solutions each containing 20% by weight of the polyurethane and printing lacquers were subsequently prepared by the addition of 2% by weight hexamethoxymethyl melamine and 0.2% by weight citric acid to the stock solutions. Printing inks were then prepared by the addition to the printing lacquers of 10% by weight titanium dioxide, 6% by weight of cadmium red or 3% by weight of carbon black to give white, red or black inks respectively.

Transfers were then produced from the inks and printing lacquers by screen printing onto a laminate of paper and Melinex (Trade Mark for polyester film) which acts as a release coating, the whole laminate acting as a temporary support.

TABLE I

Polyurethane Combined No. Polyester MW Moles Glycol Moles average MW Diisocyanate Moles 1 A(i) 1,210 1 C(ii) 1.7 500 B(ii) 2.7 2 A(i) 2,000 1 C(ii) 1.7 800 B(i) 2.7 3 A(i) 2,500 1 C(ii) 1.6 1,000 B(iii) 2.6 4 A(i) 3,000 1 C(iv) 1.7 1,200 B(iv) 2.7 5 A(i) 1,210 1 C(v) 0.24 1,000 B(vi) 1.24 6 A(i) 2,000 1 C(iv) 1.2 1,000 V(vii) 2.2 7 A(i) 1,210 1 C(i) 1.1 600 B(i) 2.1 8 A(ii) 2,000 1 C(ii) 1.7 800 B(i) 2.7 9 A(iii) 2,000 1 C(ii) 1.7 800 B(i) 2.7 10 A(iv) 2,000 1 C(ii) 1.2 800 B(i) 2.7 11 A(i) 1,210 1 C(ii) 2.1 450 B(i) 3.1 12 A(v) 2,000 1 C(ii) 1.7 800 B(i) 2.7 A single coloured heat transferable emblem was prepared by printing, in reverse, a character onto the temporary support using one of the inks and subsequently overlaying the character with a layer of the printing lacquer made from the same or different polyurethane as the ink so as to give a total thickness of about 50 microns. Multicolour transfers were prepared by printing the colours in sequence and finally overlaying the characters with a layer of printing lacquer to give a total thickness of approximately 50 microns.

The transfers thus produced were applied to a variety of textile fabrics, both woven and knitted, and including stretchable fabrics using a heated press at 2000C for 5 seconds at a pressure of 1 Kg/cm2 and subsequently removing the temporary support.

The applied markings were tested by stretching, washing at various temperatures and ironing. All withstood washing at temperatures up to boiling. The resistance- to ironing and normal stretching, even after repeated washing and wearing was satisfactory.

Claims

WHAT WE CLAIM IS:

1. A heat transfer comprising a temporary support and a label (as herein defined) carried on said support, said label having a layer of polyurethane resin system which layer has been produced from a solution obtained by dissolving in a solvent a thermoplastic polyurethane elastomer which is the product of the reaction of (A) 1 mole of an essentially linear hydroxyl-terminated polyester having a repeating unit either of the formula

where R1' is an alkylene radical of 4 to 8 carbon atoms, said linear polyester having an average molecular weight of above 1,200 and up to 3,000 and an acid number less than 10; (B) from 1.1 to 3.1 moles of a diphenyl diisocyanate having an isocyaflate group on each phenyl nucleus; and (C) from 0.1 to 2.1 moles of at least one free glycol of from 2 to 10 carbon atoms; the combined average hydroxyl number molecular weight of the polyester and the free glycol being 450 to 1200 and the molar amount of the polyester and glycol combined being essentially equivalent to the molar amount of the diisocyanate compound, said polyurethane resin system incorporating an acid or acid-yielding catalyst and as a cross-linking agent a compound containing two or more Nalkoxymethyl groups, whereby when the layer of the polyurethane resin system is placed in contact with an article to be marked and subjected to heat and pressure the polyurethane is cross-linked into an inert, insoluble and wear-resistant form to provide a substantially permanent marking on the article.

2. A heat transfer according to claim 1 wherein the polyester has 4 to 8 methylene groups per ester group.

3. A heat transfer according to claim 1 or 2, wherein said free glycol has the formula HO(CH2)nOH wherein n is from 2 to 8.

4. A heat transfer according to any of claims I to 3 wherein the diphenyl diisocyanate is a diphenyl-p,p'-diisocyanate.

5. A heat transfer according to any one of claims 1 to 4 wherein the diphenyl diisocyanate is a diphenyl methane diisocyanate.

6. A heat transfer according to any one of claims I to 5, wherein the crosslinking agent is present in an amount of up to 30% by weight based on the weight of the dry resin.

7. A heat transfer according to claim 6, wherein the cross-linking agent is used in an-amount of 520% by weight.

8. A heat transfer according to.any one of claims 1 to 7, wherein the Nalkoxymethyl groups are N-methoxymethyl groups.

9. A heat transfer according to claim 8 wherein the cross-linking agent is a methoxymethyl melamine compound.

10. A heat transfer according to claim 9, wherein the cross-linking agent is hexamethoxymethyl melamine.

I I. A heat transfer according to any one of claims 1 to 10 wherein the catalyst is a non-volatile acid having a pKa of from 2 to 5 or a compound yielding such an acid under the marking conditions.

12. A heat transfer according to claim 11, wherein the non-volatile acid has a pKa of from 2.5 to 3.5.

13. A heat transfer according to claim 11 or 12, wherein the acid is present in an amount of 0.5 to 10% by weight based on the dry weight of the resin.

14. A heat transfer according to claim 13 wherein the acid is used in an amount of 1 to 4% by weight based on the dry weight of the resin.

15. A heat transfer according to any one of claims 11 to 14 wherein the acid is citric acid or tartaric acid.

16. A heat transfer according to any one of claims 11 to 14 wherein the acid yielding compound is the ammonium salt or anhydride.

17. A heat transfer according to any one of claims 1 to 16 wherein the label comprises a continuous layer of the polyurethane resin system and a marking based on the same or different polyurethane resin system carried by the continuous layer.

18. A heat transfer according to any one of claims 1 to 16 wherein the label comprises two continuous layers of the same or different polyurethane resin system and a marking sandwiched therebetween.

19. A heat transfer according to claim 18 wherein the marking is based on a polyurethane resin system.

20. A heat transfer according to any one of claims 1 to 19 wherein the label comprises a marking, a background layer and a continuous unpigmented layer, all based on the same or different polyurethane resin system.

21. A heat transfer according to any one of claims 1 to 16 wherein the label comprises a marking based on the polyurethane resin system and a layer of the same or different polyurethane resin system co-extensive with, or slightly overlapping, the boundary edges of the marking for forming a bonding layer when the label is applied to an article.

22. A heat transfer according to claim 21 wherein the marking is sandwiched between two layers of the same or different polyurethane resin system, said layers being co-extensive with, or slightly overlapping, the boundary edges of the marking.

23. An article marked with a heat transfer according to any one of the preceding claims.

24. A method of labelling articles comprising applying a heat transfer according to any one of claims 1 to 22 to the article under the action of heat and pressure to form an inert, insoluble, wear-resistant marking on the article.

25. A heat transfer as claimed in claim 1 substantially as hereinbefore described.