Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41M—PRINTING, DUPLICATING, MARKING, OR COPYING PROCESSES; COLOUR PRINTING
  • B41M5/00—Duplicating or marking methods; Sheet materials for use therein
  • B41M5/26—Thermography ; Marking by high energetic means, e.g. laser otherwise than by burning, and characterised by the material used
  • B41M5/382—Contact thermal transfer or sublimation processes
  • B41M5/385—Contact thermal transfer or sublimation processes characterised by the transferable dyes or pigments
  • B41M5/388—Azo dyes

Definitions

• This specification describes an invention relating to thermal transfer printing and more particularly to a thermal transfer printing sheet carrying a dye or a mixture of dyes and to a thermal transfer printing process in which dye is transferred from the transfer sheet to a receiver sheet by the application of heat.
• a heat-transferable dye is applied to a sheet-like substrate, in the form of an ink, usually containing a polymeric or resinous binder to bind the dye to the substrate, to form a transfer sheet.
• This is then placed in contact with the material to be printed, the receiver sheet, and selectively heated in accordance with a pattern information signal whereby dye from the selectively heated regions of the transfer sheet is transferred to the receiver sheet and forms a pattern thereon the shape and density of which is in accordance with the pattern and intensity of heat applied to the transfer sheet.
• a dye for TTP is its thermal properties, brightness of shade, fastness properties, such as light and heat fastness, and facility for application to the substrate in the preparation of the transfer sheet.
• the dye should transfer evenly, in a predetermined relationship to the heat applied to the transfer sheet so that the depth of shade on the receiver sheet is smoothly related to the heat applied and a good density gradation can be achieved on the receiver sheet.
• Brightness of shade is important in order to obtain as wide a range of shades with the three primary dye shades of yellow, cyan and magenta.
• the dye must be sufficiently mobile to migrate from the transfer sheet to the receiver sheet at the temperatures employed, typically 150-400°C, more especially 300-400°C, it is generally free from ionic and water-solubilising groups, and is thus not readily soluble in aqueous or water-miscible media, such as water and alkanols.
• aqueous or water-miscible media such as water and alkanols.
• suitable dyes are also not readily soluble in the solvents which are commonly used in, and thus acceptable to, the printing industry, such as aromatic hydrocarbons, alkanols and alkyl- and cycloalkyl-ketones.
• the dye can be applied as a dispersion in a suitable solvent, it has been found that brighter, glossier and smoother final prints can often be achieved on the receiver sheet if the dye is applied to the substrate from a solution.
• the dye should be readily soluble in the ink medium, particularly if it has a relatively low extinction coefficient. It is also important that a dye which has been applied to a transfer sheet from a solution should be resistant to crystallisation so that it remains as an amorphous layer on the transfer sheet for a considerable time.
• the phenyl group A which is preferably free from groups carrying acidic hydrogen atoms capable of forming inter-molecular hydrogen bonds, such as OH, NH2, SO3H & COOH, preferably carries from one to three, and more preferably at least two, of the defined electron-withdrawing groups and may also carry one or more other groups not having electron-withdrawing characteristics, such as C 1-4 -alkyl and C 1-4 -alkoxy.
• A carries at least one, and more preferably two or three electron-­withdrawing groups selected from NO2, CN, -SO2-C 1-4 -alkyl, especially -SO2CH3 and halogen, especially bromo or chloro, and optionally also C 1-4 -alkyl, especially CH3, or C 1-4 -alkoxy, especially -OCH3. It is further preferred that A carries two or three groups selected from NO2, CN and -SO2CH3. The substituents are preferably in the ortho and/or para positions with respect of the azo link.
• a preferred substituted phenyl group, A, in the dyes of Formula I, giving orange to violet shades, is of the formula: wherein X1 is NO2, CN or -SO2CH3; and X2 is NO2, CN, -SO2CH3 or H. and an especially preferred substituted phenyl group is of the formula: wherein X1 is NO2, CN or -SO2CH3, gives strong magenta dyes of Formula I.
• a preferred substituted phenyl group A in dyes of Formula I, giving blue shades, is of the formula: wherein Y1 & Y2 are independently selected from CN, NO2 and halogen, especially Cl or Br, provided that they are not both NO2 or both halogen.
• Y1 and Y2 are both CN or that Y1 is CN and Y2 is NO2.
• substituted phenyl group, A are: 2,4-dinitrophenyl, 2-cyano-4-nitrophenyl, 2,4-dicyanophenyl, 2-nitro-4-cyanophenyl, 3,4-dicyanophenyl 2,5-dichloro-4-nitrophenyl 2,4-dinitro-6-chlorophenyl, 2,4-dinitro-6-bromophenyl, 2,4-dinitro-6-cyanophenyl, 2,6-dicyano-4-nitrophenyl, 2-chloro-4-nitrophenyl 2-methylsulphonyl-4-nitrophenyl 2-methoxy-4-nitrophenyl 2,6-dicyano-4-methylphenyl 2,5-dichlorophenyl 2-methoxy-5-nitrophenyl 4-nitrophenyl
• the radical, E, of the coupling component is preferably derived from one of the following coupling components:
• Suitable coupling components in accordance with Formulae V, VI and VII are: lilolidine julolidine N-benzylaniline N-ethyl-N-(2-acetoxyethyl)aniline N,N-diethylaniline N-ethyl-N-(2-phthalimidoethyl)aniline N,N-bis(2-acetoxyethyl)aniline N,N-bis(2-ethoxycarbonylethyl)aniline N-ethyl-N-(2-cyanoethyl)aniline N-ethyl-N-(n-butyl)aniline N,N-di(n-propyl)aniline N-ethyl-N-(2-ethoxyethyl)aniline N,N-bis(2-methoxycarbonylethyl)aniline N-ethyl-N-(2-ethoxycarbonylethyl)aniline N,N-bis(2-methoxycarbony
• Preferred dyes of Formula I giving orange to violet shades, are of the formula: wherein X1 is NO2 or CN, X2 is selected from NO2, CN, -SO2CH3 & H; R10 & R11 are each independently selected from C 1-4 -alkyl, -C2H4CN, C 1-4 -alkylene-OCO-C 1-4 -alkyl and C 1-4 -alkylene-COO-C 1-4 -alkyl and R12 is H, CH3 or -NHCOCH3; or of the formula: wherein X1, X2, R9 & R10 are as hereinbefore defined.
• X2 is NO2, CN or -SO2CH3.
• An especially preferred class of dyes in accordance with Formula IX, giving a magenta shade, has the formula: wherein X1 & R12 are as hereinbefore defined; and R14 & R15 are each independently selected from C 2-4 -alkyl, C 1-4 -alkylene-OCO-C 1-4 -alkyl and C2H4CN.
• X1 is CN
• R12 is methyl
• R14 is ethyl, n-propyl, n-butyl or -C2H4OCOCH3
• R15 is -C2H4OCOCH3.
• Preferred dyes of Formula I giving a blue shade, are of the formula: wherein Y1 represents NO2 or CN, Y2 represents CN, Cl or Br and R14 & R15 are each independently selected from C 2-4 -alkyl and C 1-4 -alkylene-OCO-C 1-4 -alkyl; R5 is H, C 1-4 -alkyl or C 1-4 -alkoxy; and R12 is H, CH3 or -NHCOCH3.
• Y1 and Y2 are both CN or that Y1 is CN and Y2 is NO2 and that R5 is H, R12 is -NHCOCH3 and R14 & R15 are C 2-4 -alkyl.
• Thermal transfer printing sheets carrying a compound of Formula I in which the coupling component is a substituted aniline of Formula V, wherein one or both of R3 and R4 is an alkyl group, especially ethyl or propyl, carrying an electron withdrawing group, especially CN, OCO-C 1-4 -alkyl or COO-C 1-4 -alkyl, are especially preferred species of the present invention because of their very good stability.
• Stability of a dye on the transfer sheet is an important property because dyes with poor stability (i) tend to crystallise on the sheet and as a result do not transfer evenly onto the receiver sheet during the TTP process and/or (ii) tend to transfer under pressure alone so that (a) the receiver sheet becomes coloured in areas to which no heat is applied, while it is in contact, under pressure, with the transfer sheet during the TTP process and (b) dye is transfered from the front to the back of the transfer sheet when the transfer sheet is rolled up.
• a dye of Formula I generally has good thermal properties giving rise to even prints on the receiver sheet, whose depth of shade is related to the quantity of applied heat so that a good gradation of colour density can be obtained.
• a dye of Formula I also generally has strong coloristic properties and good solubility in a wide range of solvents, especially those solvents which are widely used and accepted in the printing industry, such as alkanols, e.g. ethanol, isopropanol & butanol, aromatic hydrocarbons, such as toluene and ketones such as MEK, MIBK and cyclohexanone.
• solvents especially those solvents which are widely used and accepted in the printing industry, such as alkanols, e.g. ethanol, isopropanol & butanol, aromatic hydrocarbons, such as toluene and ketones such as MEK, MIBK and cyclohexanone.
• the blue dye of Formula XII in which Y1 & Y2 are both CN, R5 is H, R12 is -NHCOCH3 and R14 & R15 are both C2H5 allows the achievement of a strong bright greenish-blue print on the receiver sheet of moderate lightfastness and high optical density.
• the related dye in which Y2 is NO2 allows the achievement of a strong bright mid-blue shade print of good lightfastness and high optical density.
• the dyes of Formula I give orange to blue shades.
• another important shade in trichromatic printing is black and mixtures of the present dyes, especially of dyes giving orange shades and dyes giving reddish blue shades, can be used to give good strong black shades.
• Preferred orange dyes for use in such mixtures are of the formula: wherein Z is H or -OCOCH3.
• Preferred blue dyes for use in such mixtures are of the formula: wherein R is H or -OCH3; Q is selected from H, -OCOCH3 and -COOC2H4OCH3; and Q1 is selected from H, -C2H5 and -C2H4OCOCH3.
• the relative proportions of the blue dye of Formula XII or XIV and the orange dye of Formula XIII required to produce a mixture giving a black shade depend on the shade of black required and the relative strengths of the component dyes. However the relative proportions generally range from 90:10 to 10:90 and more preferably from 70:30 to 30:70.
• the radical, A1, of the heteroaromatic amine, A1-NH2 may be substituted by non-ionic groups, preferably those which are free from acidic hydrogen atoms, unless these are positioned so that they form intramolecular hydrogen bonds.
• substituents are NO2; CN; CNS; halogen, especially F, Cl & Br; CF3; C 1-4 -alkyl; C 1-4 -alkoxy; C 1-4 -alkoxy-C 1-4 -alkyl; cyano-C 1-4 -alkyl; -SO2NH2; -SO2F; -SO2Cl; -CONH2; -COF; -COCl; C 1-4 -alkylthio; -SO2-C 1-4 -alkyl; -CON-(C 1-4 -alkyl)2; -SO2N(C 1-4 -alkyl)2; -COO-C 1-4 -alkyl and -CO-C
• suitable heteroaromatic residues, A are: 2,3-dicyanoimidazol-5-yl, 1-ethyl-2,3-dicyanoimidazol-5-yl, 5-nitrothiazol-2-yl, 3-methyl-4-cyanoisothiazol-5-yl, 4-cyanoisothiazol-5-yl, 6-fluorosulphonylbenzothiazol-2-yl, 6-thiocyanobenzothiazol-2-yl, 6-methylsulphonylbenzothiazol-2-yl, 6-methoxybenzothiazol-2-yl, 5-nitro-2,1-benzoisothiazol-3-yl, 6-nitrobenzothiazol-2-yl, 1-ethyl-3,4-dicyanopyrazol-5-yl, 3,5-dicyanothiophen-1-yl, 3-cyanomethyl-4-cyanopyrazol-5-yl, 3,5-dinitrothiophen-1-yl, 6-cyanopyrido[
• the radical E present in the dye of Formula XV is preferably derived from a coupling component of Formula V.
• Preferred dyes of Formula XV are the magenta dyes where A1 is 3-methyl-4-cyanoisothiazol-5-yl, 4-cyanoisothiazol-5-yl and 1-cyanomethyl-3,4-dicyanopyrazol-5-yl, and where E is the radical of an aniline of Formula V where R2 is H, Cl or C 1-4 -alkyl, especially CH3; R5 is H; and R3 & R4 are each independently selected from C2-C4-alkyl, optionally substituted by -OCO-C 1-4 -alkyl, and especially from C2H5, n -C4H9, and C2H4OCOCH3.
• the preferred dyes of Formula XV are preferably used in admixture with the preferred dyes of Formula XI to prepare transfer sheets which have good storage stability and which give rise to magenta-shade prints of moderate lightfastness, of brighter shade than those derived from dyes of Formula XI and of significantly higher strength than is achievable with dyes of Formula XI alone.
• the dyes of Formula XV are usually, but not necessarily, the minor components of the mixture.
• the substrate may be any convenient sheet material capable of withstanding the temperatures involved in TTP, up to 400°C over a period of up to 20 milliseconds (msec), yet thin enough to transmit heat applied on one side through to the dye on the other side to effect transfer to a receiver sheet within such short periods, typically from 1 to 10 msec.
• suitable materials are paper, especially high quality paper of even thickness, such as capacitor paper, polyester, polacrylate, polyamide, cellulosic and polyalkylene films, metallised forms thereof, including co-polymer and laminated films, especially laminates incorporating a polyester layer on which the dye is deposited.
• Such laminates preferably comprise, in addition to the polyester, a backcoat of a heat-­resistant material, such as a thermosetting resin, e.g. silicone or polyurethane, to separate the heat source from the polyester so that the latter is not melted.
• a heat-­resistant material such as a thermosetting resin, e.g. silicone or polyurethane
• the thickness of the substrate may vary within wide limits depending upon its thermal characteristics but is preferably less than 50 ⁇ m and more preferably below 10 ⁇ m.
• the coating preferably comprises a binder and one or more dyes of Formula I, optionally with one or more dyes of Formula XV.
• the ratio of binder to dye is preferably at least 1:1 and more preferably from 1.5:1 to 4:1 in order to provide good adhesion between the dye and the substrate and inhibit migration of the dye during storage.
• the binder may be any resinous or polymeric material suitable for binding the dye to the substrate.
• suitable binders are cellulose derivatives, such as ethylhydroxyethylcellulose (EHEC), hydroxypropylcellulose (HPC), ethylcellulose, methyl­cellulose, cellulose acetate and cellulose acetate butyrate; carbohydrate derivatives, such as starch; alginic acid derivatives; alkyd resins; vinyl resins and derivatives, such as polyvinyl alcohol, polyvinyl acetate, polyvinyl butyral and polyvinyl pyrrolidone; polymers and co-polymers derived from acrylates and acrylate derivatives, such as polyacrylic acid, polymethyl methacrylate and styrene-acrylate copolymers, polyester resins, polyamide resins, such as melamines; polyurea and polyurethane resins; organosilicones, such as polysiloxanes, epoxy resins and natural resins
• the coating may also contain other additives, such as curing agents, preservatives, etc., these and other ingredients being described more fully in EP 133011A, EP 133012A and EP 111004A.
• a transfer printing process which comprises contacting a transfer sheet coated with a dye of Formula I with a receiver sheet, so that the dye is adjacent to the receiver sheet, and selectively heating an area of the transfer sheet whereby dye in the heated area of the transfer sheet may be selectively transferred to the receiver sheet.
• the transfer sheet is preferably heated to a temperature from 250°C to 400°C, more preferably 300°C to 400°C, for a period of from 0.5 to 30 msec, more preferably from 1 to 10 msec, while it is maintained in contact with the receiver sheet.
• the depth of shade of print on any area of the receiver sheet will vary with the time period for, and temperature at, which the transfer sheet is heated while in contact with the receiver sheet.
• the receiver sheet conveniently comprises a white polyester sheet material, especially of polyethylene terephthalate (PET).
• PET polyethylene terephthalate
• the dye of Formula I is known for the colouration of textile materials made from PET
• the colouration of textile materials by dyeing or printing, is carried out under such conditions of time and temperature that the dye can penetrate the PET and become fixed therein.
• the time period is so short that penetration of the PET is less effective and the receiver sheet is preferably provided with a receptive layer on the side to which the dye is applied, into which the dye can more readily diffuse to form a stable image on the receiver sheet.
• Such a receptive coating may comprise a thin layer, applied to the receiver sheet by co-extrusion or solution coating techniques, of a modified polyester or a different polymeric material which is more permeable to the dye than PET.
• the nature of the receptive coating will affect to some extent the depth of shade and quality of the print obtained but it has been found that the present dyes give particularly strong and good quality prints compared with other dyes which have been previously proposed for thermal transfer printing on any specific receiver sheet.
• the design of receiver sheets with receptive layers is discussed in EP 133,011A & EP 133,012A.
• a further 25 inks were prepared by the same method as Ink 1 using each of the azo dyes or mixtures of azo dyes indicated in Table 1 below.
• a thermal transfer sheet was prepared by forming a 24 ⁇ m coating of Ink 1 (using a Mayer bar) on the precleaned (with dichloromethane) surface of a sheet of PET film (6 ⁇ m, MELINEX) having a thermally protected back-coat layer (2 ⁇ m). The coating was dried in hot air stream.
• the transfer sheet is hereinafter referred to as TS1.
• a further 25 transfer sheets (TS2 to TS26) were prepared by the method of Example 1 using Inks 2 to 26 in place of Ink 1.
• Transfer sheet TS1 was sandwiched with a composite receiver sheet comprising a white PET substrate and a receptive layer on the side in contact with the printed surface of TS1.
• the sandwich was placed on the cylindrical drum of thermal transfer printing machine.
• the sandwich passed over a matrix of closely spaced pixels which were selectively heated in accordance with a pattern information signal to a temperature of 350°C for periods from 1 to 10 msec, whereby a quantity of the dye, in proportion to the heating period, at the position on the transfer sheet in contact with a pixel while it was hot, was transferred from the transfer sheet to the receiver sheet.
• the pattern information signal was formulated so that the heating period of the pixels was increased at regular intervals as the sandwiched passed over the matrix so that the printed pattern was in the form of a scale composed of bands of colour of increasing depth of shade. After passage over the array of pixels the transfer sheet was separated from the receiver sheet. Superficial dye which had not penetrated the receptor layer on the receiver sheet was removed by the application and removal of a strip of self-adhesive tape.
• the printed receiver sheet is hereinafter referred to as RS1.
• a further 25 receiver sheets (RS 2 to RS 26) were printed by the method of Example 27 using TS2 to TS 26 in place of TS1.
• the reflectance optical density of the print on each receiver sheet was measured by examination of the band having the maximum depth of shade with a Sakura digital densitometer and the results of the measurements are given in Table 1. Magenta dyes were examined through a green filter and blue dyes were examined through a red filter.
• Dye A 3-acetylamino-4-(2,4-dinitro-6-bromophenylazo)-N,N-diethyl­aniline
• Dye B 5-acetylamino-4-(2,4-dinitro-6-bromophenylazo)-2-methoxy-­N,N-diethylaniline
• Dye C 4-(4-nitrophenylazo)-N-(2-cyanoethyl)-N-(2-acetoxyethyl)­aniline
• Dye D 1-ethyl-3-cyano-4-methyl-5-(4-[2-(2-methoxyethoxy)ethoxy]­carbonylphenylazo)-pyrid-2,6-dione
• Dye E 1-ethyl-3-cyano-4-methyl-5-(2-nitrophenylazo)-pyrid-2,6-dione Black 1 0.43g Dye A + 0.16g Dye B + 0.42
• Each of these mixtures was formed into an ink by the method for Ink 1 and the ink used to prepare a transfer sheet by the method of Example 1.
• Each black mixture was transfered by the method of Example 27 to produce a receiver sheet having an even black shade.
• An ink (Ink A) was made according to the procedure of Ink 1 using the same weight of 1-amino-2-phenoxy-4-hydroxyanthraquinone in place of Dye 1.
• a transfer sheet (TSA) was prepared accoring to Example 1 using Ink A in place of Ink 1.
• a printed receiver sheet (RSA) was prepared by the method of Example 27 using TSA in place of TS1.
• the reflectance optical density of RSA was measured by examination of the band having maximum depth of shade with a Sakura digital densitometer under the same conditions as the asessment of receiver sheets RS1 to RS26. The result of the measurement is shown below in comparison with that of RS1 (taken from Example 27 in Table 1)

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• Physics & Mathematics (AREA)
• Optics & Photonics (AREA)
• Thermal Transfer Or Thermal Recording In General (AREA)
• Coloring (AREA)
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• Impression-Transfer Materials And Handling Thereof (AREA)

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• 1987
  • 1987-01-30 DE DE19873788072 patent/DE3788072T3/de not_active Expired - Lifetime
  • 1987-01-30 EP EP19870300841 patent/EP0235939B2/fr not_active Expired - Lifetime
  • 1987-02-25 JP JP62040511A patent/JP2716434B2/ja not_active Expired - Lifetime

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