GB1581564A - Magnetic printing member - Google Patents

Description

PATENT SPECIFICATION

( 21) Application No 26609/79 ( 22) Filed 31 March 1977 A ( 62) Divided out of No 1 581 561 _ ( 31) Convention Application Nos 672 553 and 672 552 X ( 32) Filed 31 March 1976 e C ( 31) Convention Application Nos 771 062 and 771 061 _ 1 ( 32) Filed 25 Feb 1977 ( 31) Convention Application Nos 777 242 and 777 241 ( 32) Filed 15 March 1977 in ( 33) United States of America (US) ( 44) Complete Specification published 17 Dec 1980 ( 51) INT CL 3 G 03 G 19/00 ( 52) Index at acceptance B 6 C RK ( 54) MAGNETIC PRINTING MEMBER ( 71) We, E I DU PONT DE NEMOURS AND COMPANY, a corporation organised and existing under the laws of the State of Delaware, located at Wilmington, State of Delaware, United States of America, 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:-

This invention relates to magnetic printing members for use in a magnetic printing process.

One form of copying process in wide usage is the electrostatic copying process Operation of such a process may provide difficulties in that large black areas may not be amenable to copying and the document to be copied may have to be reimaged each time a copy is made The overcoming of these difficulties may be economically prohibitive It is well known that audio signals and digital data can be recorded on magnetic materials Magnetic field configurations in the form of alphabetical characters and pictures can also be produced by selective magnetization or demagnetization of the surface of a ferromagnetic chromium dioxide film The resultant fields are strong enough to attract and hold small magnetic particles such as iron powder The development, that is the making visible, of such a latent magnetic image can be effected by contacting the image surface with a magnetic developer, usually referred to as a magnetic toner, consisting of ferromagnetic particles and pigments encapsulated in a thermoplastic resin binder Such a development process is commonly known as decoration of the latent magnetic image The developed image can then be transferred to and fixed on paper, thus providing a black-on-white copy of the latent image Operation of such magnetic processes, however, may not be completely free of difficulties For example, since most magnetic toner particles are attracted ( 11) 1 581564 by both electrostatic and magnetic fields, stray electrostatic charges which are present on the magnetic surface or toner particles may interfere with the interaction of the magnetic image and the magnetic toner particles More specifically, a portion of the magnetic surface other than that containing the magnetic image may attract enough magnetic toner particles to render unsatisfactory the paper print which subsequently is produced.

There is extensive prior art in the fields of magnetic recording tapes and thermomagnetic recording U S 3,476,595 discloses a magnetic recording tape which is coated with a thin layer of a curved complex of silica and a preformed organic polymer containing a plurality of alcoholic hydroxy groups The disclosure includes coated, ferromagnetic, chromium dioxide, magnetic recording tapes Discussions of acicular chromium dioxide and magnetic recording members bearing a layer of such material may also be found in U S 2,956,955 and 3,512,930 U S 3,554,798 discloses a magnetic recording member which is relatively transparent to light (transmits 5 to 95 %) and which includes a plurality of discrete areas of hard magnetic particulate material supported thereon and bound thereto A magnetically hard material is a material which is permanently magnetizable below the Curie point of the material, as opposed to a magnetically soft material which is substantially nonpermanently magnetizable under similar conditions below the Curie point of the material.

Chromium dioxide is disclosed as an example of a hard magnetic material Decoration of the image may be effected by means of a magnetic pigment, for example, a dilute, alkydoil/water emulsion, carbon black-based printing ink U S 3,522,090 is similar in disclosure to U S 3,554,798 in that it also discloses a light-transparent recording member However, it also discloses that the magnetic material which is capable of magnetization to a hard magnetic state (on the recording member) 1,581,564 may have a coating of a reflective material which is so disposed that the magnetic material is shielded from exposing radiation while the adjacent uncoated portion of the recording member transmits 10 to 90 % of the exposing radiation The reflective coating can be a metallic reflector, such as aluminum, or a diffuse reflective pigment, such as titanium dioxide U S 3,555,556 discloses a direct thermomagnetic recording (TMR) process wherein the document to be copied is imaged by light which passes through the document.

U.S 3,555,557 discloses a reflex thermomagnetic recording process wherein the light passes through the recording member and reflects off of the document which is to be copied Thus, in the direct process, the document must be transparent but the recording member need not be transparent, whereas in the reflex process, the recording member must be transparent but the document need not be transparent For the recording member to be transparent, it must have regions which are free of magnetic particles, that is, a noncontinuous magnetic surface must be used.

U.S 3,627,682 discloses ferromagnetic toner particles, for developing magnetic images, that include binary mixtures of a magnetically hard material and a magnetically soft material, an encapsulating resin and, optionally, carbon black or black or colored dyes to provide a blacker or colored copy.

"Nigrosine" SSB is disclosed as an example of a black dye The encapsulating resin aids transfer of the decorated magnetic image to paper and can be heated, pressed or vapor softened to adhere or fix the magnetic particles to the surface fibers of the paper Ferromagnetic toner particles of the type disclosed in U S 3,627,682 are disclosed as being useful in the dry thermomagnetic copying process of U S 3,698,005 The latter patent discloses such a dry thermomagnetic copying process wherein the magnetic recording member is coated with a polysilicic acid The use of the polysilicic acid coating on the recording member is particularly useful when the magnetic material on the recording member comprises a plurality of discrete areas of particulate magnetic material because a greater number of clean copies can be produced The polysilicic acid, which is relatively non-conductive, exhibits good non-stick properties.

Thus, toner particles which are held to the surface of the recording member by nonmagnetic forces can be easily removed without removing the toner particles which are held to the surface of the recording member by magnetic forces U S 2,826,634 discloses the use of iron or iron oxide magnetic particles, either alone or encapsulated in low-melting resins, for developing magnetic images Such toners have been employed to develop magnetic images recorded on magnetic tapes, films, drums and printing plates.

Japanese 70/52044 discloses a method which comprises adhering iron particles bearing a photosensitive diazonium compound onto an electrophotographic material, to form an image, transfering the image onto a support having a coupler which is able to form an azo dye by reaction with the diazonium compound, reacting the diazonium compound and the coupler and thereafter removing the iron particles U S 3,530,794 discloses a magnetic printing arrangement wherein a thin, flexible master sheet having magnetizable, characterrepresenting, mirror-reversed printing portions is employed in combination with a rotary printing cylinder The master sheet, which consists of a thin, flexible non-magnetizable layer, such as paper, is placed on top of and in contact with a layer of iron oxide or ferrite which is adhesively attached to a base sheet.

The combined layer and base sheet are 'imprinted, for example, by the impact of type faces, so that mirror-reversed, character representing portions of the iron oxide layer adhere to the non-magnetizable layer, thus forming magnetizable printing portions on same Thereafter, the printing portions are magnetized and a magnetizable toner powder, such as iron powder, is applied to and adheres to the magnetized printing portions The powder is then transferred from the printing portions to a copy sheet and permanently attached thereto, for example, by heating U S.

3,052,564 discloses a magnetic printing process employing a magnetic ink consisting of granules of iron coated with a colored or uncolored thermoplastic wax composition The magnetic ink is employed in effecting the transfer of a printed record, using magnetic means, to paper U S 3,735,416 discloses a magnetic printing process wherein characters or other data to be printed are formed on a magnetic recording surface by means of a recording head A magnetic toner which is composed of resin-coated magnetic particles is employed to effect transfer of the characters or other data from the recording surface to a receiving sheet U S 3,250,636 discloses a direct imaging process and apparatus wherein a uniform magnetic field is applied to a ferromagnetic imaging layer; the magnetized, ferromagnetic imaging layer is exposed to a pattern of heat conforming to the shape of the image to be reproduced, the heat being sufficient to raise the heated portions of the layer above the Curie point temperature of the ferromagnetic imaging layer so as to form a latent magnetic image on the imaging layer; the latent magnetic image is developed by depositing a finely divided magnetically attractable material on the surface of the ferromagnetic imaging layer; the imaging layer is uniformly heated above its Curie point temperature after the development to uniformly demagnetize it; and, finally, the loosely adhering magnetically attractable material is trans3 1,581,564 3 ferred from the imaging layer to a transfer layer.

German 2 452 530 discloses electrophotographic toners comprising a magnetic material coated with an organic substance containing a dye which vaporizes at 100 to 2200 C, preferably 160 to 200 'C, at atmosphereic pressure The magnetic material is preferably granular iron and/or iron oxide and the coating is a water-insoluble polymer melting at about 150 'C, e g, polyamides, epoxy resins and cellulose ethers and esters Both basic and disperse dyes can be used in the toners The toners are from 1 to 10 microns in diameter and may also contain silicic acid as anti-static agent Colored or black copies are formed by toner development of the latent image on a photo-conducting sheet of Zn O paper, followed by transfer of the dye in the vapor phase to a receiving sheet by application of heat and pressure.

In carrying out prior art thermomagnetic recording processes, generally, only reddishbrown or black images can be obtained on paper because of the dark hard magnetic components, for example, the iron oxides (y-Fe O, or Fe,04), and the dark soft magnetic components, for example, iron, in the ferromagnetic toners employed therein; because the magnetic components are retained in and may be essential to the formation of the visible images; and because the magnetic components are bound to the paper by the encapsulating resins employed in the ferromagnetic toners It is an object of the present invention to provide a printing member for use in a magnetic printing process means of which a sharp print can be obtained, that is, without objectionable background caused by ferromagnetic toner particles undesirably adhering, for example, electrostatically, to certain areas of the ferromagnetic material during formation of the magnetic image thereon.

According to the present invention there is provided a magnetic printing member comprising a ferromagnetic material forming a magnetic layer on a suport which comprises a dielectric material and an electrically conductive material, whereby the member is capable in use of discharging electric charges at all times from substantially the entire surface of the magnetic layer through the thickness of the magnetic layer to the electrically conductive material, said surface being suitable for recording a magnetic image thereon and printing a substrate using a ferromagnetic toner.

The ferromagnetic material is a semiconductive material which is preferably formed as a continuous coating on the support In one embodiment the support may be metalized dielectric material, e g a metal coating such as aluminium in a film base, such as a polyester film In another embodiment, the support may be a metal sleeve coated with a layer of elastomeric material containing conductive particulate material, e g silver or carbon black, uniformly dispersed therein In a further embodiment, the support may be a metalized plastics material, e g a plastics support plated with metal The support may also comprise a grooved base, which may be of metalized dielectric material, wherein the ferromagnetic material is contained within the grooves.

BRIEF DESCRIPTION OF THE

DRAWINGS In the accompanying drawings, Figure 1 represents an enlarged cross-sectional view of a cylindrical, continuously surface-coated, con 80 ductive magnetic printing member Figures 2 A and 2 B represent top and side views, respectively, in rectilinear form, of the printing member of Figure 1 before orientation of the acicular Cr 02 of layer 2; Figures 2 C and 85 2 D represent the same views after orientation of the acicular Cr O, Figure 3 A represents a side view, in rectilinear form, of the acicular Cr O, of layer 2 but before the Cr O O is magnetically structured; Figure 3 B represents the 90 same view after the Cr O, of layer 2 has been magnetically structured Figure 4 represents an enlarged cross-sectional view of a cylindrical, intermittently surface-coated (in grooves) conductive magnetic printing mem 95 ber Figures 5 to 9 represent certain steps of the magnetic printing process as they apply to the use of the magnetically structured printing member represented by Figure 3 B. Figure 5 depicts the formation of a latent 100 magnetic image on the printing member by Xenon flashing an appropriate film positive.

Figure 6 depicts the printing member having the latent magnetic image imposed thereon.

Figure 7 depicts the printing member, after 105 the latent magnetic image has been decorated with ferromagnetic toner particles, as it is about to be brought into contact with the substrate which is to be printed Figure 8 depicts the substrate after the image consisting of 110 ferromagnetic toner particles has been transferred thereto from the magnetic printing member Figure 9 depicts the substrate after the image has been adhered thereto Figure 10, representing a side view, in rectilinear form, 115 of the printing member of Figure 1, depicts the path of the electrostatic charge being dissipated from the acicular Cr O, of layer 2 to ground through conductive layer 4 Figure 11, in schematic form, depicts a single color 120 magnetic printing device which can be used to carry out certain steps of the magnetic printing process Figure 12, in schematic form, depicts a three color magnetic printing device which can be used to carry out certain steps 125 of the magnetic printing process.

The printing member of the present invention may be used with advantage in the magnetic printing process described and 1,581,564 4 1,8,6 4 claimed in our pending patent application No.

13654/77, from which this application is divided It has been found that the provision of an electrically conductive support for the ferromagnetic material assists in the avoidance of electrostatic charge buildup on the printing member by allowing charge dissipating conductance through its thickness This feature, preferably in conjunction with electrostatic charge neutralizing means, leads to the attainment of clear printed images and substantial absence of background discolouration.

As indicated above, the printing member of this invention is primarily intended for use in carrying out the magnetic printing process described in our co-pending patent application No 13654/77 (Serial No 1,581,561) and reference may be made to that specification for details of its manner of use.

The invention is useful for producing multiple color prints (reproductions) of an original design The invention has particular applicability to the formation of colored prints of an original design consisting of multiple colors In such a system a pluralty of toner decorated magnetic images corresponding to a series of color separation film positives of the original multicolored design are successively transferred to a substrate in register and superimposed one on top of the other so as to form a multicolored print composed of the different color images.

Either multicolor or full color separation film positives are prepared from the original design Multicolor film separations (that is, one film separation for each color in a pattern) can be made either manually by tracing the design or by using a color recognition electronic scanner The preparation of full color (that is, process color) separation film positives can be made either with a camera and colored filters or by using a process color electronic scanner With the former technique, the original design is photographed through three filters, each corresponding in color and light transmission to one of the additive blue, green and red primaries Placing a red filter over the camera lens produces a negative recording of all the red light reflected or transmitted from the original This is known as the red separation negative When a film positive is made from this negative, the silver in the film will correspond to areas which did not contain red but contained the other two colors of light, that is, blue and green In effect, the negative has subtracted the red light from the original design The positive is a recording of the blue and green in the original design and is called the cyan film positive Photographing through a green filter produces a negative recording of the green in the original design The positive is a recording of the red and blue additive primaries, and is called the magenta film positive The use of a blue filter produces a negative which records all of the blue in the original design The positive records the red and green which, when combined as additive colors, produce yellow This is called the yellow film positive For some designs, a black film positive is needed This is obtained by photographing the original design through red, blue and green filters in succession A detailed discussion of the preparation of process color film positives can be found in "Principles of Color Reproduction," J A C Yule, Chapters 1 and 3.

John Wiley and Sons, Inc, 1967.

Electronic scanners can be used for both full color (based on the four process colors) or multicolor (indivdual color recognition) film separations In both types of scanners, the original design is mounted on a horizontally rotating drum which is driven by a step motor operating at approximately 2,000 steps per second A horizontally moving scanning head is mounted in front of the drum The design pattern is illuminated and the reflected colored light is intercepted by the scanning head at each step A series of prisms and mirrors splits the reflected light into red, green and blue components which are then converted into three separate electronic signals In full color separation scanners, the red, green and blue components are processed through an optical electronic converter which provides the yellow, magenta, cyan and black film separation positives In multicolor separation scanners, the red, green and blue components are compared to the amounts of red, green and blue components stored in the scanners computer memory The output is a film separation positive corresponding to each color pattern in the original design As many as twelve different colors can be stored in the computer memory of a multicolor separation scanner.

Suitable electronic color scanners are readily available commercially Electronic scanners have obvious advantages over manual separation techniques due to their lower processing cost, higher speeds ( 2 to 3 hours as compared to 100 to 200 hours) and greater resolution capabilities.

The aforesaid color separation film positives are used to form a plurality of latent magnetic images, as described below, one latent magnetic image corresponding to each color film positive Each latent magnetic image is then decorated with dye-containing ferromagnetic toner particles to form a series of tonerdecorated latent magnetic images corresponding to the color separation images In a typical subtractive multiple color processing system in accord with this invention, each latent magnetic image is decorated with toner particles having a dye color complementary to the original color separation filter Thus, the cyan latent magnetic image corresponding to the red color filter is decorated with toner containing a blue dye; the yellow latent magnetic image corresponding to the blue filter 1,581,564 5,8,6 is decorated with a yellow dye toner and the magenta latent magnetic image corresponding to the green color filter is decorated with a red dye toner The dye images from each of the individual toner-decorated images are transferred in register and superimposed, one on top of the other, on the substrate to form the final multicolor print of the original printed design.

The most important force for magnetic printing is, of course, of magnetic origin.

However, stray electrostatic forces can exceed magnetic forces Since ferromagnetic toner particles are attracted by both electrostatic and magnetic fields, any high electrostatic charge density on the magnetic printing surface (that is, the ferromagnetic material) will generate fields equal to or greater than the magnetic field from the magnetic image The background region, that is, that portion of the printing surface other than that containing the magnetic image, will thus attract enough toner particles to render the final print unattractive, if not indiscernible Static charges usually build up at a sufficiently slow rate so that at least one clear print can be made, but unless some means is provided to dissipate the static charges, after a few prints have been made, the buildup of static charge becomes large enough to cause serious background problems.

As already discussed hereinabove, in this invention, the background problem is eliminated by having the semiconductive ferromagnetic CP i i Ws _binder contmiuously coated on the conductive support, for example, as shown in Figure 1, and optionally, using a charge neutralizing means such as an AC corona as described above Preferably, at least two static neutralizing means, such as two AC coronas, as shown in Figures 11 and 12, are employed in conjunction with the continuously Cr O,-coated conductive support to neutralize any residual charges on the toner.

Since the surface resistivity of the Cr O, coating is approximately 108 ohms/square, the time required for complete static charge dissipation must be less than the time elapsed between electrostatic toner transfer and subsequent toner redecoration; otherwise, static charge will build up on the printing surface.

As can be seen from Figure 10, using the conductive Cr O,-coated printing member 1, the electrostatic surface charge on the Cr O,2 travels through the thickness of the Cr O 2, that is, in the Y direction, instead of along the entire length of the Cr O, surface, that is, in the X direction, in order to reach ground through the conductive support 4 Grounding is accomplished by clamping the Cr O,-coated printing member 1 to printing drum 12 depicted in Figure 11 For a 5-inch ( 12 7 cm) wide printing surface, the X/Y ratio is approximately 104 and, thus, rapid charge dissipation occurs and background free prints are obtained Apparatus in which the printing member of the invention may be used is described and claimed in our co-pending patent application No 79/26608 (Serial No.

1,581,563) 70 In one embodiment of the invention, the electrically conductive support providing the path to ground for the electrostatic charge can be either continuously coated with a layer of ferromagnetic Cr O, or can be provided 75 with a series of grooves which are in turn filled with the Cr O, Figure 1 shows an enlarged cross-sectional view of the continuously surface-coated conductive magnetic printing member 1 comprising a conductive support 80 which is continuously coated with a 50 to 1,000 microinch ( 1 27 to 25 4 X 1 O cm), preferably 100 to 500 microinch ( 2 54 to 12.7 X 10 4 cm), layer 2 of ferromagnetic Cr O, in a resin binder Acicular Cr O, is 85 particularly preferred due to its high coercivity, which allows it to be magnetically oriented to give a high remanence A unique aspect of Cr O, is its outstanding magnetic properties together with its easily attainable 90 Curie temperature of 1160 C Acicular Cr O, can be produced by techniques well known in the art The conductive support can be any appropriate material, for example, a polyethylene terephthalate film 3, about 125 95 microns in thickness, coated with a thin conductive layer of aluminum 4 Commercially available aluminized polyester film is particularly useful as a conductive support The conductive support can be a metallized plastic 100 material, for example, a sleeve of a plastic material, such as an acetal resin, coated with aluminum, nickel, copper or other conductive metal, or it can be a metal sleeve coated with a thin layer of elastomeric material, such as 105 polychllorobutadiene (neoprene), polybutadiene, polyisoprene, butadiene-styrene copolymers, acrylonitrile-butadiene copolymers, etc, or with an epoxy resin, containing conductive particulate matter, for example, carbon black, 110 graphite or silver, uniformly dispersed therein.

The coating of the conductive support with acicular Cr O, can be accomplished in a variety of ways, for example, by gravure coating a slurry of Cr O, and resin in tetrahydrofuran 115 cyclohexanone on a web of aluminized polyester or by spray-coating a conductive metal sleeve However, regardless of the coating technique used, it is desirable to orient the Cr O, by passing the wet coated conductive 120 support between the pole pieces of two bar magnets (approximately 1,500 gauss average field strength) aligned with the same poles facing one another The magnetic flux lines orient the acicular Cr O, Figures 2 A and 2 B 125 show top and side views, respectively, of printing member 1 of Figure 1 before orientation; Figures 2 C and 2 D show these respective views after orientation Ratios of magnetic remanence to magnetic saturation 130 1,581,564 6 1,581,564 6 (B, /Bs) of up to 0 80 with an intrinsic coercivity (i H,) of 510 to 550 oersteds have been obtained on such printing members.

If the oriented Cr O, magnetized printing surface is decorated with ferromagnetic toner particles (for example, 10 to 30 micron particles consisting of a dye and a ferromagnetic component encapsulated in a water-soluble resin binder), the particles will be magnetically attracted to only the edges of the surface as depicted in Figure 3 A In order to achieve even toner decoration of the entire magnetic printing surface, the continuous Cr O 2 coating is magnetically structured, as illustrated in Figure 3 B, so as to create magnetic flux gradients that uniformly attract the magnetic toner particles A number of different techniques can be used to magnetically structure the magnetic printing surface An alternating signal, equivalent to 100 to 1,500 magnetic lines per inch ( 39 to 590 lines per cm), can be recorded on the Cr O 2 surface using a magnetic write head A magnetic line consists of two magnetic flux reversals Alternatively.

a Ronchi ruled transparent film can be placed on top of the uniformly magnetized Cr O, surface and the assembly can then be exposed to a Xenon flash passing through the transparent ruled film The Cr O, under the clear areas of the film is thermally demagnetized to provide the requisite magnetic pattern Thetechnique of roll-in magnetization also can be used to structure the Cr O, surface In this method, a high permeability material, such as nickel, which has been surface structured to the desired groove width is placed in contact with the unmagnetized Cr O, surface A permanent magnet or an electromagnet is placed on the backside of the highly permeable material As the structured high permeability material is brought into contact with the Cr O, surface, the magnet concentrates the magnetic flux lines at the points of contact, resulting in the magnetization of the Cr O, coating The Cr O, surface can also be thermoremanently structured by placing the continuously coated Cr O, surface on top of a magnetic master which has the desired magnetic line pattern recorded on it Thermoremanent duplication of the master pattern on the Cr O, surface is effected by heating the surface above the 116 WC Cr O O Curie temperature As the surface cools down below the Curie temperature, it picks up the magnetic signal from the magnetic master and is selectively magnetized In still another method, a scanning laser beam can be used to structure the magnetic Cr O O surface.

Figure 4 shows an enlarged cross-sectional view of the permanently structured conductive magnetic printing member 1 ' of this invention, comprising a grooved conductive support with the Cr O, and resin binder 2 ' in the grooves.

In this embodiment, the conductive support is preferably a plastic support material 3 ' which has been structured to the desired groove width and depth The grooved plastic support 3 ' is plated with a thin layer of a conductive metal 4 ', such as aluminum, copper, nickel or the like, and the grooves are filled with the Cr O, and resin binder 2 ' As in the case of the continuously coated magnetic printing member illustrated in Figure 1, the Cr O 2 must be oriented during the groove filling operation.

Magnetization of the grooved conductive magnetic printing surface can be readily accomplished by passing the surface in front of a magnetic field.

Further aspects of the invention are depicted in Figures 5 to 9 (shown for simplification as comprising flat surfaces) which show the stepwise formation of the latent magnetic image on the structured printing member 1 (Figures 5 and 6), the decoration thereof with toner particles (Figure 7), the transfer of the toner particles to the substrate (Figure 8) and the toner particles adhered to the substrate (Figure 9) The aforesaid sequences of steps can be carried out using the continuously Cr O,-coated magnetic printing member 1 depicted in Figure 1, the Cr O, surface of which has been oriented (depicted in Figure 2) and magnetically structured (depicted in Figure 3), Figures 2 and 3 shown for simplification as comprising flat surfaces A similar sequence of steps can be envisaged for the grooved magnetic printing member depicted in Figure 4.

It is to be understood, and it wills be obvious to one skilled in the art, that the structured printing member can be imaged in such a way that the substrate will be uniformly chemically treated and/or dyed, depending on the type of ferromagnetic toner used, over a wide area In other words, instead of a pattern-type print, the print can provide a total coloration and/or chemical treatment of the substrate.

Referring further to Figure 5, a latent magnetic image is formed on the surface of the magnetic printing member 1 by placing an image-bearing photocolor separation film positive, prepared as described above, in faceto-face contact with the structured printing surface and uniformly heating, from the backside of the film positive, with a short burst of high energy from a Xenon lamp The dark areas of the film positive, that is, the image areas, absorb the energy of the Xenon flash, while the transparent areas of the film transmit the energy, thereby heating the Cr O, to above the 116 CC Curie point As can be seen from Figure 6, the surface of the magnetic printing member is selectively demagnetized to form a latent magnetic image which consists of a reproduction of the dark areas of the film positive.

Instead of using a photocolor separation film positive, an electronic color scanner can also be used to form the latent magnetic 1,581,564 1,581,564 image The output signal from the scanner drives a magnetic write head which is in contact with the surface of continuously Cr O,coated printing member 1 There is no need to prestructure the printing surface since the data recording of the magnetic write head can provide the required magnetic flux lines to attract the toner particles A permanent record ot tne latent magnetic image can be obtained by decorating the latent magnetic image with a black toner and transferring and fusing it into a transparent film The output of the scanner can also consist of digital color separation data recorded on a magnetic tape and this tape can be used to drive the magnetic write head directly on the printing surface.

Ferromagnetic toner particles are applied to the latent magnetic image to form a decorated magnetic image (as shown in Figure 7) and the substrate to be printed is brought into juxtaposition therewith to effect transfer of the image to the substrate (Figure 8).

The latent magnetic image can be developed by convenient methods which are well known in the art Typical methods include cascade, magnetic brush, magnetic roll, powder cloud and dusting by hand In cascade development, finely divided ferromagnetic toner particles are conveyed to and rolled or cascaded across the latent magnetic image-bearing surface, whereupon the ferromagnetic toner particles are magnetically attracted and secured to the magnetized portion of the latent image In magnetic brush or roll development, ferromagnetic toner particles are carried by a magnet The magnetic field of the magnet causes alignment of the magnetic toner particles into a brushlike arrangement The magnetic brush or roll is then engaged with the magnetic image-bearing surface and the ferromagnetic toner particles are drawn from the brush to the latent image by magnetic attraction The transfer of the ferromagnetic toner particles to the substrate can be accomplished either by pressure, magnetic or electrostatic means, or a combination thereof In the preferred electrostatic means, a positive or negative charge is applied to the backside of the substrate which is in contact with the toner-decorated latent magnetic image In connection with the use of pressure transfer means, the use of high force, for example, about 40 pounds per linear inch (about 70 Newtons per linear cm), generally results in shorter printing surface life, poorer transfer efficiency and poorer image definition on the substrate Such problems are avoided by using electrostatic transfer means wherein there is no substantial amount of pressure between the printing surface and the substrate and, therefore, no abrasion occurs.

The transferred image is temporarily adhered to the substrate (as shown in Figure 9) until permanent fixation of the dye and/or chemical treating agent thereon and/or therein is effected Temporary adhering of the transferred image to the substrate conveniently can be effected by application of heat and/or a suitable solvent (water or an organic solvent), the latter either in the form of a spray or as vapors, for example, water or steam Heating at 90 to 1700 C and steam fusing at 100 'C for 1 to 15 seconds at 760 mm (of Hg) pressure are particularly preferred herein The adhesion of the image to the substrate results from the melting and/or the partial dissolution (in the solvent) of the encapsulating resin Final (permanent) fixation of the dye and/or chemical treating agent of the toner can be accomplished in any way which is consistent with the type of substrate and dye and/or agent which are used For example, dry-heat treatment, for example, Thermosol treatment, at 190 to 230 'C, particularly 200 to 210 'C, for up to 100 seconds can be used to fix disperse dyes on polyester and mixed disperse-fiber reactive dyes on polyestercotton The application of pressure, for example, up to about 1 5 psig ( 10,350 Pascal gauge), may be advantageous High pressure steaming at pressures of 10 to 25 psig ( 69,000 to 172,500 Pascal gauge) accelerates the fixation of disperse dyes on polyester and cellulose triacetate Rapid disperse dye fixation can also be obtained by high-temperature steaming at 150 to 205 'C for 4 to 8 minutes.

High-temperature steaming combines the advantages of short treatment times without the need to use pressure seals High molecular weight disperse dyes can be fixed to polyestercotton using aqueous ethylene glycol or polyethylene glycol-type solvents according to well known prior art procedures Cottage-steaming and pressure-steaming can be used to fix cationic dyes to acid-modified acrylic and polyester fibers and to fix acid dyes, including premetalized dyes, to polyamide and wool fibers.

Cottage-steaming uses saturated steam at a pressure of 1 to 7 psig ( 6,900 to 48,300 Pascal gauge) and 100 % relative humidity.

It may be noted that there is no tendency to remove moisture from the fabric when saturated steam is used As the fabric is initially contacted by the steam, a deposit of condensed water quickly forms on its cold surface Such water serves various functions, such as swelling the fiber and activating the chemical treating agent and/or dye, thereby creating the conditions necessary for the diffusion of the dye and/or agent into the fiber Rapid aging at 100 to 1050 C for 15 to minutes at 760 mm (of Hg) pressure can be used to fix disperse dyes to cellulose acetate fibers and cationic dyes to acid-modified acrylic fibers The aforesaid fixation procedures are all known in the art, for example, as described by Clarke in "An Introduction to

Textile Printing," Third Edition, 1971, pages 58 to 66.

Depending on the nature of the toner dye 1,581,564 and/or chemical treating agent, it may be necessary or desirable to treat the fabric with known auxiliary agents, to achieve certain effects, before final (permanent) fixation of toner dye and/or chemical treating agent For example, it may be necessary to impregnate the fabric with an aqueous solution of an acid or an alkali, such as citric acid, ammonium oxalate or sodium bicarbonate, or in some cases, a reducing agent for the dye Alternatively, these auxiliary agents can be incorporated directly into the toner composition.

After permanent fixation of the dye and/or chemical treating agent, the printed fabric is scoured to remove the ferromagnetic component, encapsulating resin and any unfixed dye and/or chemical treating agent Although the severity of the scouring treatment generally depends on the type of resin and solvent employed, with ferromagnetic toners containing water-soluble or water-solubilizable resins, only a few seconds immersion in a conventional aqueous scour, for example, an aqueous surfactant solution or aqueous alkali, at less than 90 'C, is sufficient to dissolve away the resin and release the ferromagnetic material from the fabric surface In the case of dye-containing toners, a well-defined colored print is obtained on the fabric The transfer of the dye and/or chemical treating agent-containing ferromagnetic toner to the substrate and the temporary adhering thereof on the substrate can be carried out in a continuous operation, that is, in an immediately sequential manner The final (permanent) fixation of the dye and/or chemical treating agent and scouring can be carried out separately in a later operation.

As already suggested above, the magnetic printing process involves a delicate balance of forces in that the areas of the magnetic printing surface which are to retain ferromagnetic toner particles, that is, the image areas, must magnetically attract toner particles, whereas the image-free areas of the printing surface must not On the other hand, the force of magnetic attraction must not be so great as to prevent the substantially complete transfer of the toner from the printing surface to the substrate The strength of the magnetic attraction between the toner particles and the printing surface depends on the physical properties of the printing surface, such as the coercivity (i H) and remanence (Br) of the Cr O 2 coating, the degree of orientation of the Cr O, crystals (Br/Bs), the thickness of the Cr O, coating, the number of magnetic lines on the surface and the properties of the ferromagnetic toner particles, for example, their magnetic susceptibility, shape and size It has been found that optimum decoration, transfer and fusion properties are obtained using a Cr O, coating having a thickness range of 50 to 1,000 microinches ( 1 27 to 25 4 X 10-4 cm), preferably 100 to 500 microinches ( 2 54 to 12 7 X 10-4 cm), a coercity of 200 to 600 oersteds, preferably 350 to 580 oersteds, and an orientation (Br/Bs) of 0 4 to 0 9, preferably 0 6 to 0 9 The surface of the printing member can be magnetically structured to 100 to 1,500 magnetic lines per inch ( 39 to 590 per cm), preferably 150 to 400 magnetic lines per inch ( 59 to 157 per cm).

Further to the above discussion, Figure 11 shows a schematic diagram of a single color magnetic printing device which is useful in performing the invention magnetic printing process The substrate 5 to be printed is fed from feed roll 6, around dancer rolls 7, 8 and 9 to the nip between feed rolls 10 and 11, which rolls cooperate to feed the substrate into physical contact with the surface of magnetic printing member 1, shown in crosssectional view in Figure 1 Magnetic printing member 1 can be a continuously Cr O,-coated aluminized polyester film which is secured and grounded to the outer circumferential surface of a rotating aluminum or copper printing drum 12 Prior to mounting printing drum 12 in the apparatus, the Cr O, surface of the aluminized polyester film affixed thereto is magnetically structured, using a magnetic write head as previously described, into a line pattern containing 300 magnetic lines per inch ( 118 magnetic lines per cm) After structuring the printing surface, a latent magnetic image is formed thereon by placing a photocolor-separated film positive of a design in face-to-face contact with the magnetically structured printing surface on drum 12 and then uniformly heating the printing surface with successive short bursts from a high energy Xenon lamp flashed through the film positive.

After exposure, the Cr O, printing surface on drum 12 contains magnetized areas of Cr O, corresponding to the printed areas of the film positive Printing drum 12 is then mounted in the apparatus and is driven in the direction shown by the arrow by a commercially available drive motor (not shown) which is provided with a speed control unit The printing member containing the latent magnetic image is then decorated (developed) with toner using a suitable decorating means 13 In the particular embodiment illustrated, the decorating means 13 is a magnetic brush decorating means comprising a trough 14 containing a supply of the toner particles 15 The toner particles are magnetically attracted to the surface of the magnetic brush 16 and are conveyed to the surface of printing member 1 where they are stripped from the surface of magnetic brush 16 by a stationary doctor blade 17 Toner particles are drawn from the brush to the latent magnetic image by magnetic attraction; surplus toner falls back into trough 14 for recirculation Although this represents a convenient means for depositing toner on the printing member, any of the numerous decorating means known to those The aforesaid apparatus and description form the basis for a commercial single-color magnetic printer, for example, capable of printing speeds of up to 240 feet ( 73 meters) per minute, having the ability to provide multiple prints from a single latent magnetic image.

As mentioned above, the magnetic printing process has particular applicability to the printing of colored prints of an original design composed of multiple colors Figure 12 shows a schematic view of a multicolor (three color) magnetic printing device embodiment.

The substrate 29 to be printed is fed from feed roll 30 into contact with endless belt 31 which is made of a dielectric filmsb such as polyethylene terephthalate Rollers 32 and 33 serve to drive, in the direction shown by the arrows, and guide endless belt 31 The substrate 29 is electrostatically attracted to endless belt 31 by means of DC (direct current) corona device 34 or by other conventional dry fabric bonding techniques Any electrostatic charge buildup on substrate 29 is neutralized by AC (alternating current) neutralizing corona 35.

The charge-free substrate is conveyed by endless belt 31 to the toner-decorated surface of magnetic printing member 1 positioned at printing station A The ferromagnetic toner is electrostatically transferred from the surface of this printing member 1 to substrate 29 by means of DC corona device 36 After transfer, the toner is fused to substrate 29 using fusing means 37 which is an infrared or steam fusing device The process of applying toner to the surface of magnetic printing member 1 is essentially the same as shown in Figure 11 for the single color magnetic printer.

As further shown at station A in Figure 12, a latent magnetic image of one of the colors (yellow, cyan or magenta) making up the design to be printed is formed on the surface of the magnetic printing member 1 mounted on drum 12 The latent magnetic image is decorated with ferromagnetic toner particles 15 using a suitable decorating means 13 In the particular embodiment illustrated, decorating means 13 consists of hopper 38 having a narrow orifice from which toner particles 15 are smoothly and uniformly dispensed onto the surface of magnetized roll 39 The toner particles adhering to magnetic roll 39 are subsequently driven by magnetic attraction from the roll to the latent magnetic image on the surface of printing member 1.

The surface of toner decorated printing member 1 preferably is neutralized with AC neutralizing corona 18 and vacuum cleaned with vacuum knife 19 to remove toner particles which have adventitiously become attracted to the demagnetized background area After transfer of the toner to substrate 29 using DC corona 36, the surface of printing member 1 is vacuum cleaned with vacuum brush 21 and the residual electrostatic charges skilled in the art can be used Preferably, triboelectric charges generated in toner trough 14 are eliminated by neutralization using AC corona 18 Any toner particles adventitiously adhering to the demagnetized areas of the Cr O, surface are removed by vacuum knife 19 The printing member, bearing the clean decorated image, is then contacted with substrate 5 past DC corona device 20, thus causing the toner particles to be transferred to substrate 5 upon its separation from printing member 1 A negative DC corona device potential of 3 to 20 kilovolts, preferably 4 to 8 kilovolts, is used There is only an insignificant amount of pressure between substrate 5 and the surface of printing member 1, which pressure is generated entirely by the electrostatic charge on substrate 5 Alternatively, transfer of the image can take place in the nip between a resilient pressure roll (not shown) and printing member 1, in which case the pressure roll replaces the corona device Applied pressure against the drum can range from 10 to 40 pounds per linear inch ( 17 6 to 69 6 Newtons per linear cm) However, the most efficient transfer, about 90 per cent of the toner particles are transferred, occurs at the upper limit of this range Such high pressures, however, have a destructive effect on the life of the printing member; hence, lower pressures are preferred if printing member life is a concern Following transfer of the image, the substrate 5 containing the toner image particles is conveyed around idler roller 23 to thermal fusing means 24 which temporarily adheres the toner particles to substrate 5 The fusing means can be a bank of infrared heaters, a contact hot roll or a steam fuser The substrate 5 is then conveyed over idler roll 25 to the nip between rolls 26 and 27 which cooperate to feed substrate 5 onto final take-up roll 28 After transfer, toner particles remaining on the surface of magnetic printing member 1 are removed by means of vacuum brush 21 Preferably, residual electrostatic charges are neutralized by AC neutralizing corona 22 If necessary, an AC corona is also used after DC corona device 20 and before vacuum brush 21 to remove the electrostatic charge on the toner particles which do not transfer, thus enhancing the action of vacuum brush 21 Alternatively, a vacuum knife such as 19 is used instead of vacuum brush 21 In this case, an AC corona preferably is also used after DC corona device 20 and before the vacuum knife to remove the electrostatic charge on the toner particles which do not transfer AC neutralizing corona 22 can then be eliminated The clean electrostatic charge-free surface of printing member 1 is then again decorated with toner in trough 14 and the neutralizing, vacuum knife cleaning, electrostatic transferring, fusing, vacuum brush cleaning and neutralizing steps are continued until the printing cycle is completed.

1,581,564 1,581,564 preferably are neutralized using AC corona 22 Preferably, an AC corona can also be used after DC corona 36 and before vacuum brush 21 to remove the electrostatic charge on the toner particles which do not transfer, thus enhancing the action of vacuum brush 21.

The clean, electrostatic charge-free printing surface is then ready for redecoration followed by the steps of neutralization, vacuum knife cleaning, electrostatic transfer, fusion, vacuum brush cleaning and neutralization This sequence of steps is continued until the printing cycle is completed.

Latent magnetic images of the remaining two colors making up the design to be printed in this embodiment are similarly decorated, transferred and fused at printing stations B and C The fused multicolor printed fabric is taken up by take up roll 40 The image alignment of printing stations A, B and C is achieved electronically by placing a magnetic read head 41, commonly available, at the edge of each printing drum 12 The read head 41 senses the signal on the magnetic surface that is in registry with the image at each printing station This signal is sent to a synchronzation control box (not shown) The speed of endless belt 31 is set manually by a belt drive motor (not shown) A belt speed signal is sent to the synchronization control box which controls the speeds of each of the motors driving the drums at printing stations A, B and C Thus, all of the drums are placed in register by means of the feedback signal from the magnetic read head 41 on each of the drums.

It is to be understood that the aforesaid discussions of figures are devoid of descriptions of the permanent fixation (of dye and/or chemical treating agent) and the ferromagnetic component and resin-removal, (for example, by aqueous scouring) steps of the invention magnetic printing process since these steps, and the equipment which can be employed in connection therewith, are familiar to one skilled in the art of dye chemistry.

In addition to direct fabric printing, the invention also affords the capability of indirectly printing fabrics by utilizing the process in combination with heat-transfer printing In magnetic/heat-transfer printing, ferromagnetic toners containing sublimable dyes are first directly printed to a paper substrate, fused thereon as described above and then subsequently heat-transfer printed from the paper substrate to a fabric substrate employing a combination of heat, pressure and dwell time Heat-transfer printing at 160 to 250 'C, preferably 190 to 2200 C, at 1 to 2 psi ( 6,900 to 13,800 Pascal) pressure for up to seconds dwell time provides good results in the invention magnetic/heat-transfer printing process Under such conditions, the dye sublimes and is transferred to and is fixed within the fabric substrate The resin and ferromagnetic components are subsequently removed by scouring the printed fabric substrate as described above for the magnetic printing process.

The use of the printing member of this invention provides numerous advantages over conventional wet printing processes For example, prints can be produced having halftone or large solid areas which exhibit excellent optical density Since the printing surface is reusable, there is no need for conventional printing screens and rollers A dry toner system is used and no print paste makeup is required This provides minimum water pollution (by dye) on cleanup No additional auxiliary chemicals or gums are required since the ferromagnetic toners can be formulated so as to contain all of the necessary materials.

Moreover, lower printing costs are obtainable due to lower engraving costs and shorter changeover times.

EXAMPLES

In the following examples, unless otherwise noted, all parts and percentages are by weight and all materials employed are readily commerically available.

Example 1.

This example illustrates the preparation, by manual mixing of the ingredients followed by spray-drying, of a ferromagnetic toner con 95 taining a blue disperse dye, magnetic components and an aqueous alkali-soluble resin, and the application thereof to both paper and polyester using a printing member in accordance with the invention A magnetic toner 100 was prepared from 32 7 % of carbonyl iron, 32.7 % of Fe,04, 1 8 % of C I Disperse Blue 56, 5 5 % of ligninsulfonate dispersant and 27.3 % of a polyvinyl acetate copolymer resin.

The carbonyl iron, used as the soft magnetic 105 material and commercially available under the trade name "Carbonyl Iron" GS-6, is substantially pure iron powder produced by the pyrolysis of iron carbonyl A suitable Fe,04 is sold under the trade name "Mapico" Black 110 Iron Oxide and the polyvinyl acetate copolymer resin, under the trade name "Gelva" C 5-VIOM "Gelva" ("GELVA" is a Registered Trade Mark) C 5-VIOM is an aqueous alkali-soluble copolymer of vinyl 115 acetate and a monomer containing the requisite number of carboxy groups and has a softening point of 1230 C.

A 20 % aqueous alkaline solution ( 450 parts) of the polyvinyl acetate copolymer resin 120 was manually stirred with 500 parts of water until thorough mixing was effected Carbonyl Iron GS-6 ( 108 parts) and "Mapico" Black Iron Oxide ( 108 parts) were added and the mixture was thoroughly stirred C I Disperse 125 Blue 56 ( 24 parts of a 24 6 % standardized powder) was stirred in 455 parts of water until completely dispersed, then added to the 1,581,564 above resin solution The resultant toner slurrey was stirred for 30 minutes with a high shear mixer and then spray-dried in a Niro electric spray-dryer The toner slurry was atomized by dropping it onto a disc rotating at 20,000 to 50,000 rpm in a chamber through which heated air was swirling at a high velocity Precautions were taken to stir the toner slurry and maintain a uniform feed composition The exact temperature and air velocity depend mainly on the softening point of the resin An air inlet temperature of 2250 C, an outlet temperature of 85 WC and an atomizer air pressure of 85 psig ( 586,500 Pascal gauge) provided satisfactory results.

The resulting discrete toner particles of magnetic resin-encapsulated dye had a particle size within the range of 2 to 100 microns, mostly within the range of 10 to 25 microns.

The particles were collected in a collection chamber Toner adhering to the sides of the drying chamber was removed by brushing into a bottle and combined with the initial fraction.

The toner sample was finally passed through a 200 mesh screen (U S Sieve Series), thus being less than 74 microns in particle size.

The ferromagnetic toner was mechanically mixed with 0 2 % of a fumed silicate, Quso WR-82, to improve powder flow characteristics.

Toner evaluation was made on a 2 mil ( 0.0508 mm) aluminized "Mylar" ("MYLAR" is a Registered Trade Mark) polyester film continuously coated with 170 microinches ( 43,180 A) of acicular Cr O, in a resin binder.

Suitable acicular Cr O, can be prepared by well known prior art techniques The Cr O,film was magnetically structured to 300 lines per inch ( 12 lines per mm) by recording a sine wave with a magnetic write head A film positive of the printed image to be copied was placed in contact with the magnetically structured Cr O,-coated aluminized polyester film and uniformly illuminated by a Xenon flash passing through the film positive The dark areas of the film positive corresponding to the printed message absorbed the energy of the Xenon flash, whereas the clear areas transmitted the light and heated the Cr O, beyond its 116 WC Curie point, thereby demagnetizing the exposed magnetic Cr O, lines.

The latent magnetic image was manually decorated by pouring the fluidized toner powder over the partially demagnetized Cr O, film and then blowing off the excess The magnetic image became visible by virtue of the toner being magnetically attracted to the magnetized areas.

The toner decorated image was separately transferred to paper and to polyester fabric substrates by applying a 20 kv positive potential from the backside of the substrate by means of a DC corona Other transfer means can also be employed, such as by means of a pressure of 10-40 pounds per linear inch ( 17 6-69 6 Newtons per linear cm) However, such means may lead to shorter film life, poorer transfer efficiency and poorer image definition on the substrate After transfer to the paper or fabric substrate, the toner was fused thereon by infrared radiation, backside fusion ( 1400 C) or by steam fusion ( 100 'C for 10-15 seconds at 1 atm pressure) The latter method is the most economical but is only possible with water-soluble resins.

The image which had been transferred to the paper was then heat transfer printed from the paper to polyester fabric by placing the fused image-bearing paper face-down on the polyester and applying 1 5 to 2 0 psi ( 10,350 to 13,800 Pascal) pressure for 30 seconds at 205-2100 C After direct transfer and fusion to polyester fabric, the dye was fixed in the fabric by heating for 30 seconds at 205210 'C and 1 5 to 2 0 psi pressure ( 10,350 to 13,800 Pascal).

Both fabric samples which had been printed as described above, that is, either directly printed or heat transfer printed from paper, following fixation of the dye, were scoured by immersion in cold water and then in hot detergent A detergent consisting of sodium phosphates, sodium carbonates and biodegradable anionic and nonionic surfactants ("Lakeseal") was used The samples were finally rinsed in cold water and dried A deep blue print was obtained on each fabric.

Example 2.

This example illustrates the preparation of a ferromagnetic dye toner containing a yellow disperse dye, magnetic components and a water-soluble polyacrylic acid resin, and the application thereof to both paper and polyester using a printing member in accordance with this invention.

A ferromagnetic toner was prepared by spray-drying a mixture containing 35 % of a polyacrylic acid resin ("Joncryl" 678) ("Joncryl" is a Registered Trade Mark), 4 % of C I Disperse Yellow 54, 1 2 % of a 1 to 1 mixed lignin-sulfonate/sulfonated naphthaleneformaldehyde dispersant, 30 % of "Mapico" Black Iron Oxide and 29 8 % of Carbonyl Iron GS-6 The spray-dried toner was sieved through a 200 mesh screen (U S Sieve Series) and fluidized with Quso WR-82 in a highspeed Waring blender Outstanding toner flow and decoration properties were obtained using from 0 1 to 0 2 % of Quso WR-82 ("Quso" is a Registered Trade Mark) at low blending speeds for 20 to 30 seconds The toner was used to develop the latent magnetic image on the surface of a Cr O,-coated aluminized polyester printing member (such as 1 as shown in Figure 1) using a printing apparatus such as depicted in Figure 11 Any subsequent numbered references in this example refer to said Figure 11 A continuous 0 18 mil ( 4.6 micron) coating of Cr O, dispersed in a 12 1,581,564 12 resin binder was uniformly applied to the surface of an aluminized 2 mil ( 50 8 micron) polyester film base ("Mylar") The Cr O 2 particles dispersed in the resin binder were applied to the aluminized polyester film in the presence of a magnetic field to orient the particles parallel to the length of the film.

The film was then magnetically structured into a 250 to 450 lines per inch ( 98 to 178 lines per cm) magnetic pattern using a 05 inch ( 1 3 cm) wide magnetic write head The structured film was imagewise demagnetized by exposure to a short burst from a Xenon lamp flashed through an image-bearing photographic transparency The resultant partially demagnetized aluminized Cr O 2 film was then mounted on a rotary drum (such as 12 of Figure 11) The magnetic image on the Cr O 2coated aluminized polyester film was developed with toner particles 15 applied by means of magnetic brush 16 Both the brush and the film drum were driven at the same surface speed at 40 ft/min ( 12 2 meters per minute) Excess toner was removed from the background of the decorated printing member by means of neutralizing AC corona 18 and air knife 19 In this example, a preferred embodiment, the AC corona 18 was employed to neutralize the static charge on the toner particles The pressure of the air stream supplied by the air knife was adjusted to the point where only the excess toner and not the toner decorating the magnetic image was removed Air supplied at a pressure of 0 4 inch ( 1 cm) of water from an orifice held 0.25 inch ( 0 6 cm) from the surface of the printing member fulfilled these conditions The toner-decorated image on the printing member was electrostatically transferred to polyethylene terephthalate fabric 5 by charging the back of the fabric with DC corona device 20 which comprised a corona wire spaced about 0.5 inch ( 1 3 cm) from the fabric and maintained at 5,000 volts negative potential.

Following transfer, the toner partides were fused to the fabric by heating at 90 to 120 'C using two banks of 500 watt infrared lamps 24 placed approximately 1 inch ( 2 5 cm) from the fabric and operating at 93 % efficiency.

The printed polyethylene terephthalate fabric was finally removed on take-up roll 28 Toner particles remaining on the surface of printing member 1 were removed by vacuum brush 21 and the surface was neutralized with AC corona 22 prior to redecoration The use of AC corona 22 represents a preferred embodiment wherein the corona neutralizes the static charge on the toner particles remaining on the surface.

A similar run, made in a similar fashion and providing similar results, was made using paper as the substrate.

Further Examples illustrating the use of the printing member of this invention in magnetic printing of various substrates are given in our co-pending patent application No.

13654/77 (Serial No 1,581,561).

The following experiments illustrate the need to use a conductive printing member in order to eliminate static charge buildup on the printing surface when using electrostatic transfer.

Experiment 1 A 180 microinch ( 4 6 X 10 cm) thick coating of Cr O 2 in a resin binder was applied to the surafce of a 5 mil ( 0 013 cm) polyester film ("Mylar") The resultant Cr O 2 film had a coercivity of 567 oersteds and a restivity of approximately 108 ohms/square The film was mounted and electrically connected to a 5-inch ( 12 7 cm) wide, 5-inch ( 12 7 cm) diameter grounded aluminium drum The Cr O 2 surface was revolved past a DC corona at a speed of 0 4 to 1 5 seconds per revolution.

At only 7,000 volts positive corona potential, a surface charge was found to rapidly build up (resulting in a field increase of approximately 1,000 volts per cm revolution of the drum) on the Cr O 2 film Thus, the Cr O 2 film surface was not conductive enough to dissipate the charge from the corona.

Experiment 2 The conductivity experiment described in Experiment 1 was repeated, except that two AC coronas were placed about 0 25 inch ( 0.6 cm) from the film surface in order to neutralize surface charges At 2,000 volts negative DC corona potential, no surface charge buildup was detected on the Cr O 2 film At 8,000 volts negative DC potential, only a 600 volt per cm buildup was measured on the film surface Thus, the AC coronas effectively dissipated the surface charges below 2,000 volts DC potential on the corona device but did not completely remove all the charge from the film surface at higher potentials.

Experiment 3 A 65 microinch ( 1 65 X 10-4 cm) coating of Cr O 2 in a resin binder was applied to the surface of a 2 mil ( 0 005 cm) aluminized polyester film ("Mylar") During the coating operation, the Cr O 2 was magnetically oriented by passing the coated film between identical poles of two bar magnets having an approximate field strength of 1,500 gauss The coated film was calendered by heating in contact with hot rollers at 90 'C under high pressure.

The resultant Cr O 2-coated film had a coercivity of 526 oersteds and an orientation of 0.80 When tested for static buildup properties as described in Experiment 1, the Cr O 2-coated aluminized film was found to be highly resistant to charge buildup when electrically connected to the grounded drum.

1,581,564 13 1,581,564

Claims (18)

WHAT WE CLAIM IS: -

1 A magnetic printing member comprising a ferromagnetic material forming a magnetic layer on a support which comprises a dielectric material and an electrically conductive material, whereby the member is capable in use of discharging electric charges at all times from substantially the entire surface of the magnetic layer through the thickness of the magnetic layer to the electrically conductive material, said surface being suitable for recording a magnetic image thereon and printing a substrate using a ferromagnetic toner.

2 A magnetic printing member which comprises a ferromagnetic material forming a magnetic layer on a dielectric support and having an electrically conductive layer disposed therebetween whereby the member is capable in use of discharging electric charges through the thickness of the magnetic layer to the electrically conductive layer, said printing member having a surface which is suitable for recording a magnetic image thereon and printing a substrate using a ferromagnetic toner.

3 A printing member according to claim 1 or claim 2 wherein the ferromagnetic material is a continuous coating on the support.

4 A printing member according to claim 2 or claim 3 wherein the dielectric support and the electrically conductive layer comprise a metalized dielectric material.

A printing member according to claim 1 or claim 2 wherein the dielectric support and the electrically conductive layer comprise a metalized plastic material.

6 A printing member according to claim wherein the plastic material is in the form of a sleeve having an outer coating of an electrically conductive metal upon which the ferromagnetic material is supported.

7 A printing member according to any one of the preceding claims wherein the conductive material is vopper, nickel or aluminium.

8 A printing member according to claim 1 wherein the support is a layer of elastomeric material containing conductive particulate material uniformly dispersed therein, said layer beng in the form of a coating on a metal sleeve.

9 A printing member according to claim 8 wherein the conductive particulate material is carbon black.

A printing member according to claim 8 wherein the support is a layer of an epoxy resin containing conductive particulate material uniformly dispersed therein.

11 A printing member according to claim wherein the conductive particulate material is silver.

12 A printing member according to claim 2 wherein the support is a metalized dielectric film.

13 A printing member according to claim 12 wherein the dielectric film is a polyester film.

14 A printing member according to claim 1 or claim 2 wherein the support contains grooves and the ferromagnetic material is in the grooves.

A printing member according to claim 14 wherein the support is a grooved plastics support which is plated with a conductive metal.

16 A printing member according to any one of the preceding claims wherein the ferromagnetic material comprises Cr O 2.

17 A printing member according to claim 16 wherein the ferromagnetic material comprises acicular Cr O 2.

18 A printing member according to any one of the preceding claims wherein the surface of the ferromagnetic layer is magnetically structured.

-19 A magnetic printing member according to claim 1 substantially as described with reference to the accompanying drawings.

BROOKES & MARTIN, Chartered Patent Agents, High Holborn House, 52-54 High Holborn, London WC 1 V 65 E, Agents for the Applicants.

Printed for Her Majesty's Stationery Office by the Courier Press, Leamington Spa, 1980.

Published by the Patent Office, 25 Southampton Buildings, London, WC 2 A l AY, from which copies may be obtained.

1,581,564