Printing Process

1. Field of the Invention

This invention relates to a process for dyeing textile fabric. More particularly, the process relates to forming a dye image of a sublimable dye by magnetic printing, and transferring the dye image to a film of polymeric material through which the dye can sublime and then transferring the dye to a textile fabric by sublimation thereof.

2. Description of the Prior Art

In the conventional printing of textiles, normally the fabric is adhered to a printing blanket that transports it under the printing roll screens. After all colors have been applied, the fabric goes through oven drying, then the dyes are fixed, e.g., by hot air or high pressure and high temperature steam. The textiles are then scoured and dried. In structurally unstable fabrics, such as double knits, waste, due to inadequate registration of the different colors, in some cases may amount to 20 to 30% of the printed textile.

Magnetic printing processes, particularly useful in overcoming the problem in electrostatic copying processes of unsatisfactory copying of large dark areas, are known in the art. Such processes are described, for instance, in U.S. Pat. Nos. 4,099,186 and 4,117,498. The particular processes described in U.S. Pat. Nos. 4,099,186 and 4,117,498 relate to processes wherein a dye and/or other chemical treating agent contained in a ferromagnetic toner is transferred directly to a substrate e.g., such as a textile material, or is transferred to a first substrate such as paper for subsequent transfer to the ultimate substrate.

U.S. Pat. No. 3,860,388 describes a method of dye absorption into the surfaces of plastics by placing a polyethylene film between a dye transfer paper and a sheet of plastic and applying pressure and heat thereto. The dyes sublime through the polyethylene film to the plastic film to be dyed.

U.S. Pat. No. 3,915,628 relates to a continuous dry transfer-printing process for textile webs wherein a continuous inert carrier, advantageously stainless steel, aluminum or paper, is applied to the surface of the web, which is then contacted with the material to which the dye is to be transferred followed by heating and sublimation of the dye.

It has now been found that a process for printing dyes onto substrates such as textile materials using magnetic printing onto a thermally stable, dielectric, non-dye-receptive continuous belt with subsequent transfer of the dye component of the developed image to a polymeric film through which the dye component of the toner will sublime on heating followed by transfer of the dye to the final substrate can be used to virtually eliminate the problem of inadequate registration in multi-color printing of substrates such as textile materials. The process is a dry process and eliminates the need to clean up printing equipment or exhausted dye baths.

More specifically, the process of the invention for printing dyes onto a substrate comprises the steps of: forming a latent magnetic image in a magnetic imaging member comprising a ferromagnetic material imposed on an electrically conductive support; developing the latent magnetic image by applying thereto a ferromagnetic toner comprising a ferromagnetic component, a dye component which is substantially sublimable at from 160.degree. to 215.degree. C., and a resin which substantially encapsulates the ferromagnetic component and the dye component; transferring the developed image to a substrate comprising a continuous belt comprising a thermally stable, non-dye-receptive material which in a preferred aspect of the invention is dielectric; transferring the developed image to film of a thermally stable resin which is permeable to said dye component; laminating another film of a thermally stable resin which is permeable to said dye component to the side of the first film to which the toner was transferred to form a sandwich; bringing the sandwich into contact on both sides with the textile material to be dyed while the sandwich and fabrics are rotated upon a heated drum, to thereby transfer said dye component from the sandwich through the covering layer to both textile materials.

FIG. 1 is a schematic view of the apparatus used to form an image of magnetic toner between two polymeric films.

FIG. 2 is a schematic view of the apparatus used to transfer the dye from the polymeric films to two textile materials.

Referring now to FIG. 1, a plurality of printing stations 11, 12, 13 and 14 are serially disposed along endless belt 15. Each of printing stations comprises a feed hopper 16, a decorator 17, a magnetic imaging member 18 mounted on the surface of a drum and a DC corona or electrically charged roller 21. If desired additional appurtenances such as AC coronas, vacuum knifes and magnetic write heads may be stationed around magnetic imaging member 18 such as disclosed in U.S. Pat. No. 4,117,498 the disclosure of which is hereby incorporated by reference. The endless belt preferably is formed from a dielectric material which is not receptive to dyes and to which toner does not adhere on heating. In the present case there are four printing stations which print magenta, cyan, yellow, and black. There may be a larger or smaller number of printing stations used depending on the design being printed. After toner 22 has been deposited by each of the printing stations 11, 12, 13 and 14 it is passed under infrared heater 23 where the toner is heated. A polymeric film 24 is unwound from roll 25 and fed along with decorated endless belt 15 between oil heated offset roll 26 and nip roll 27 to transfer the toner image from endless belt 15 to polymeric film 24. A polymeric film or paper web 28 is removed from roll 29, fed around oil heated roll 31 and between nip roll 32 and oil heated offset roll 26 to form laminate 33. Laminate 33 is fed around idle roll 34 and taken up on roll 35.

Roll 35 is removed from the system and inserted in the system depicted in FIG. 2. Laminate 33 is fed around idle roll 36 and on to roll 37, where it is fed along with textile material 38 and textile material 39 around drum 41. The sandwich of textile materials 38 and 39 and laminate 33 is urged against drum 41 by endless belt 42 which travels around rollers 43, 44, 45, 46 and 47. Drum 41 is fitted with internal circulating hot oil 48 and external heater 49 the heat from which causes the dye in toner 22 to sublime through polymeric films 24 and 28 to dye fabrics 38 and 39. After sublimation of the dyes laminate 33 and fabrics 38 and 39 are passed around roller 51 and taken up by means not shown. By increasing the dwell time in transfer roll 41, the spent film 33 can be used again, resulting in 4 yards of fabric dyed per yard of film 33. If it is desired to only print onto one fabric film 28 should be such that it is impermeable to the sublimable dye. Paper or aluminized Mylar.RTM. film is suitable for this purpose.

The formation of a latent magnetic image in a ferromagnetic material imposed on an electrically conductive support can be accomplished by techniques known in the art of magnetic recording. Examples of such techniques are described in U.S. Pat. Nos. 4,009,186 and 4,117,498.

In the invention the magnetic image is developed by applying a ferromagnetic toner comprising a ferromagnetic component, a dye component which is substantially sublimable at from about 160.degree. C. to 215.degree. C., and a resin, which substantially encapsulates the ferromagnetic component and the dye component.

The ferromagnetic component of the ferromagnetic toner can consist of hard magnetic particles, soft magnetic particles, or a binary mixture of hard and soft magnetic particles. Such particles are described in U.S. Pat. Nos. 4,099,186 and 4,117,498.

The dye component used in the ferromagnetic toner should be sublimable at a temperature of from about 160.degree. C. to 215.degree. C. Dyes falling into this category include low-energy and medium-energy dyes, with medium-energy dyes being preferred. Examples of such dyes include ##STR1##

The concentration of the dye component in the ferromagnetic toner can vary over a range of from about 1.0% to about 10.0% by weight, based on the total weight of the toner. In a preferred embodiment, the concentration of dye component is about 3.0% and 9.0% by weight, for single and multi passes respectively.

The resin which encapsulates the ferromagnetic component and the dye component of the ferromagnetic toner may be any known, readily fusable, natural, modifed natural, or synthetic resin or polymer. Examples of such resins are described in U.S. Pat. Nos. 4,099,186 and 4,117,498, as well as the specific encapsulation technique therefore.

The relative amounts of resinous material and ferromagnetic component in the toner are determined by the desired adhesive and magnetic properties of the toner particle. Generally, a ratio of resinous material to ferromagnetic material of 0.11:1 to 3.3:1 is useful, with the range of 0.40:1 to 1.0:1 being preferred.

Other components may optionally be added to the ferromagnetic toner, such as those described in U.S. Pat. Nos. 4,099,186 and 4,117,498.

In the invention the developed image is formed on a continuous belt comprising a thermally stable, dielectric, non-dye-receptive material. Examples of such materials include poly(tetrafluoroethylene) on a fiberglass belt material or on a belt of aramide fibers e.g., Kevlar.RTM.. Other useful thermally stable, dielectric, non-dye-receptive materials for use in continuous belts according to the invention include, e.g., commercially available Teflon.RTM. or silicone coated belts.

In the process of the invention the developed image on the continuous belt is transferred by heat and pressure to a film of a thermally stable resin which is permeable to the dye component of the ferromagnetic toner. Examples of resin which can be used to form the covering layer according to the invention include polyester film, e.g., Mylar.RTM., polyamide film (Dartek) polyvinyl chloride films, etc.

Textile materials that may be dyed according to the process of the invention include any polymers that are "disperse dyeable", that is, material capable of forming a solid solution of the dye in the textile material. Such textile materials include polyesters and nylon, with polyesters such as poly(ethylene terephthalate) being particularly preferred.

A yellow toner mix is prepared by mixing 5.0 wt % of ##STR2## 40.0 wt % Carboset XL 11, a terpolymer of methyl methacrylate, ethyl acrylate, and acrylic acid having a glass transition number of 55.degree. C. and an acid No. of 74 mg KOH/g, 1.5 wt % Reax 85 A, a lignosulonate dispersing agent and 53.5 wt % of Magnetic Oxide No. 7029, Fe.sub.3 O.sub.4 type ferroferric oxide.

A red toner mix is prepared by mixing 7.0 wt % of ##STR3## 37.61 wt % carboset XL 11, 1.89 wt % Reax 85 A, and 53.50 wt % Magnetic Oxide No. 7029.

A blue toner mix is prepared by mixing 7.0 wt % ##STR4## 38.1 wt % Carboset, 1.4 wt % Reax 85 A and 53.5 wt % Magnetic Oxide No. 7029.

A black toner mix is prepared by mixing 3.00 wt % of the above yellow dye, 4.50 wt % of the above red dye, 4.00 wt % of the above blue dye, 36.95 wt % of Carboset XL 11, 1.55 wt % Reax 85 A, and 50.00 wt % Magnetic Oxide No. 7029.

The toner mixes are converted into toner by spray drying a dispersion of the components set forth above.

Each of the magnetic imaging members are formed of a 350.mu. inches (8.9.mu. meters) thick layer of acicular chromium dioxide in a binder on an electrically grounded silver-coated rubber roll which is 12 inches (0.3 meter) wide. The magnetic imaging member is magnetically structured to 460 pole reversals/inch (18 pole reversals/mm) or 230 cycles 1 inch (9 cycles/mm) or 55 microns/pole reversal by recording a square wave with a magnetic write head at 35 m Amps and 6 to 8 Volts. A film positive of the individual colors to be printed is placed in contact with the magnetically structured roll and stepwise uniformly illuminated by a Zenon flash at 3.3 KV with a 15.degree. turn per flash, passing through the film positive. The dark areas of the film positive, corresponding to the areas to be printed, absorb the energy of the Xenon flash; whereas the clear areas transmit the light and heat the acicular chromium dioxide beyond is Curie point of about 116.degree. C. thereby demagnetizing the exposed magnetized lines of acicular chromium dioxide. The thusly magnetized rolls are then registered with each other in the apparatus depicted in FIG. 1.

The four toners are individually fed from a slot in the hoppers to decorate the latent magnetic images in each of the magnetic imaging members by a decorator. The decorator comprises a rotating magnetic cylinder inside a non-magnetic sleeve. As the magnetic imaging member rotates after being decorated with toner it first passes an AC corona which serves to neutralize any electrostatic charges which may be adhering toner to the magnetic imaging member. Then, a vacuum knife removes stray toner from the non-image areas. The toner is then negatively charged with a DC corona. The toner is then transferred to a polytetrafluoroethylene coated woven aramide fiber belt. A negatively charged voltage biasing roll on the backside of the belt is used to effect transfer of the toner from the magnetic imaging member to the belt. After toner transfer the imaging member passes in this order, an AC corona, a brush and a vacuum knife to remove any remaining toner, prior to returning to the decorator. This is repeated at each of the remaining printing stations. The toner particles are then coalesced together with a battery of infrared lamps which heat the toner to about 90.degree. C. The belt with the toner image is then fed, along with a 0.5 mil (0.013 m) thick poly(ethylene terephthalate) film, between an offset roll maintained at 110.degree. C. and an unheated nip roll on the backside of the belt to transfer the toner from the belt to the film. The thusly decorated film continues to travel around the heated offset roll for about 90.degree. to a point where it is fed together with another 0.5 mil (0.013 mm) thick poly(ethylene terephthalate) film between the heated offset roll and a nip roll to laminate the two films together, after which the laminate is taken up on a roll.

The laminate is fed, together with a textile fabric on either side, around a drum fitted with internal hot oil heat and external infrared heaters and an endless pressure belt of Teflon.RTM.. The surface of the drum is maintained at 210.degree. C. The first pass around the drum utilizes a residence time of 30 seconds. After passing around the drum the two textile fabrics and the laminate are separately taken up on rolls. The process is repeated using the laminate a second time using a residence time on the drum of 45 seconds and a third time with a residence time on the drum of 60 seconds. The six textile fabrics are all dyed to nearly the same degree and depth of shade. The fabric used is a woven 24 gauge 100% poly(ethylene terephthalate) weighing 5.7 oz/yd.sup.2 (0.19 Kg/m.sup.2).