US3496015A - Pressure-sensitive magnetic transfer elements - Google Patents

Description

United States Patent O 3,496,015 PRESSURE-SENSITIVE MAGNETIC TRANSFER ELEMENTS Douglas A. Newman, Glen Cove, and Allan T. Schlotzhauer, Locust Valley, N.Y., assignors to Columbia Ribbon and Carbon Manufacturing Co., Inc., Glen Cove, N.Y., a corporation of New York No Drawing. Filed Nov. 9, 1966, Ser. No. 594,338 Int. Cl. B41c 1/06; B44d 1/02, 1/18 US. Cl. 117-235 6 Claims ABSTRACT OF THE DISCLOSURE Pressure-sensitive transfer elements for the placement of magnetically-sensible images under various conditions of use. The imaging layer has a porous resinous binder containing pressure-exudable liquid ink. The ink comprises a liquid oil vehicle and magnetic pigment having an oil absorption value below 20 and a tap density value above 20.

Magnetic transfer sheets and ribbons are well known to the art. Most of such elements comprise a plastic film foundation carrying a frangible pressure-transferable layer based upon a binder material such as wax or synthetic resin and containing a magnetizable pigment such as black iron oxide.

Magnetic sensing systems and equipment have definite critical tolerances which, if exceeded, result in a failure of the system and a rejection of the data being processed. For MICR work the American Bankers Association has established tolerances with respect to magnetic amplitude signal level, voids and edge tolerances, among others. The signal level of a specific magnetic character must equal from 50% to 200% of a standard level known as the May 27, 1958 Reference measured on a General Electric Magnetic Printing Tester; the voids in the character must be no longer than can be completely confined in a 0.006 by 0.006 square, and the edge irregularities must not extend more than -0.0025" from the nominal edge dimension of the character.

While frangible magnetic transfer elements are generally suitable for direct image work Where the imaging pressure is applied directly to the transfer element as a sharp blow delivered by an impact device such as a typewriter bar, they are not suitable for use in the interior of multi-sheet forms or with pressure-roller imaging devices. Frangible transfer layers have a narrow latitude with respect to transfer pressures. Below a particular level of pressure no transfer occurs; at a particular narrow level a perfect transfer is possible; and above that level excess transfer occurs. The defects resulting from too little or too much pressure are primarily voids, edge irregularities and excess background staining or formation of extraneous particles around the images. When such frangible magnetic transfer elements are used in the interior of multi-sheet forms or are impressed by a roller-pressure device, the level of pressure transmitted to the transfer layer is on the low side so that little or no transfer may occur and the images formed, if any, may contain large voids and edge irregularities which render them incapable of being accurately magnetically sensed or read. Attempts to increase the magnetic amplitude or signal level of such weak images by increasing the amount of magnetic pigment in the frangible transfer composition results in a transfer element which is unsatisfactory for direct impact pressure use due to the high signal level of the background staining produced in this manner and the high signal level of the edge irregularities formed. Thus it is 3,496,015 Patented Feb. 17, 1970 not possible to produce a frangible magnetic transfer element capable of reliable use in the variety of applications encountered for normal business use.

It has been recognized that pressure-sensitive squeezeout type transfer compositions containing ink comprising liquid oil and dispersed pigment produce a uniform exudation of ink under the elfects of various types and degrees of imaging pressure to form smudge-resistant images. While images produced from such compositions are relatively free of voids and edge irregularities, such compositions function in a squeeze-out manner and thus do not transfer a heavy solid mass of composition, as in the case with frangible transfer compositions. While in some cases it is possible to exceed the minimum 50% signal level with conventional squeeze-out transfer sheets, the signal level will drop below the 50% value very often depending upon the conditions of use of the transfer sheets such as the amount of pressure applied, the quality of the copy paper and the position of the transfer sheet relative to the imaging device. For practical purposes it is required that the transfer sheet is capable of producing images having a signal level equal to at least and not exceeding of standard so that the absolute signal level tolerances will be attained under the varying conditions of use.

However it has been discovered that the tolerances established for magnetic sensing cannot be reliably satisfied, particularly in multi-sheet form imaging and roller pressure-imaging, through the use of transfer elements containing frangible or pressure-transferrable magnetic layers. To the contrary, the magnetic layer must be one which does not transfer as a mass under the elfects of imaging pressure but rather which functions by squeezing out or exuding an amount of liquid magnetic ink containing a large amount of magnetic pigment under the effects of even slight imaging pressure of any type. The present invention is concerned with providing improved compositions and transfer sheets of this type.

Pressure-sensitive transfer sheets of the squeeze-out type are known in the carbon paper and ribbon field, such as US. Patents Nos. 2,820,717 and 3,037,879. Attempts to produce magnetic transfer sheets by substituting conventional magnetic pigments for the carbon black and other pigments of such known carbon papers containing liquid oil vehicles have not produced completely satisfactory results since problems accompany the inclusion of conventional magnetic pigments in liquid oily vehicles in such formulations in sufficiently high amounts to produce duplicate images of sufficient magnetic amplitude to be reliably accurately sensed with scanning equipment currently used, particularly when positioned in the interior of a multi-sheet form. Beyond a certain maximum amount the conventional magnetic pigments render the oily vehicle so thick that it cannot be exuded under pressure, and at or below such maximum amount the images produced contain an insuflicient amount of the magnetic pigment to insure the generation of the required magnetic amplitude or signal level particularly in cases where such transfer sheets are used in the interior of multisheet forms or are impressed by means of roller pressure.

With these problems in mind, it is the object of this invention to provide pressure-sensitive transfer elements such as sheets and ribbons which contain large amounts of magnetizable pigment and which are so sensitive to imaging pressure as to produce uniform, sharp dupicate images of high magnetic amplitude even when positioned in the interior of multi-sheet forms and when subjected to roller pressure.

This and other objects and advantages of the inven- 3 tion will be clear to those skilled in the art in the light of the following disclosure.

We have discovered that improved pressure-sensitive transfer elements of the non-frangible squeeze-out type can be formulated so as to produce duplicate magnetic images having the required signal level by formulating the pressure-exudable magnetic ink from a high amount of magnetizable pigment of a particular specific type in association with a liquid oily vehicle which the magnetizable pigment absorbs to a comparatively low extent.

The magnetizable pigments suitable for use according to the present invention are those which have an aver-age particle size of less than 5 microns and preferably less than 1 micron and have a minimum ASTM tap density value above about grams per cubic inch, and have a maximum ASTM oil absorption value below about 20 measured by the spatula method. The tap density of the magnetic pigment is determined by the ASTM method by weighing the maximum amount of the particular magnetic pigment which can be compacted into the space of a cubic inch under the effects of tapping pressure applied against the container. This is a measure of the surface properties and mobility of the pigment since the smoother and more regular the surface the more easily the particles can move about and the more particles which can be compressed into a "given area.

The oil absorption value is a measure of the minimum weight of pure raw linseed oil required to completely wet 100 grams of the particular magnetizable pigment to form a stiff putty-like paste that does not break. Pigments which absorb the oil to a high degree require much more oil to wet 100 grams of the pigment than pigments which absorb the oil to a low degree.

While in the carbon paper field it has been a desirable feature to use high oil-absorbing pigments in squeezeout type carbons in order to produce dark-writing sheets, this consideration does not pertain to the production of magnetically-sensible images since the magnetic amplitude which the images are capable of generating is the essential property. An image which contains black pigment having oil absorbed therein will be much blacker to the eye but will contain less pigment than an image which contains black pigment having a smaller amount of oil absorbed therein and formed from the same type of squeeze-out sheet incorporating the same proportion of oil and pigment. For magnetic sensing it is necessary that the maximum possible amount of magntizable pigment be transferred to the copy sheet in order to generate the greatest possible amplitude, and the intensity or visual readability of such images is of secondary importance.

Conventional magnetic ink character recognition systems (MICR) are sufficiently sensitive to detect and read images which generate a magnetic wave form having an amplitude equal to or above 50% of standard. While it is possible to use magnetic inks having an amplitude of 50% of standard for direct printing Work since the sharpness of the printed characters and the weight of the printed ink is easy to control and to maintain constant, it is not possible to obtain reliably satisfactory results using such inks in the present transfer sheets in view of the important differences in their end use which make it impossible to control the sharpness of the formed image and its content of magnetic to the same extent as is possible in a printing operation. When the transfer sheet is used in the interior of -a multi-sheet form or is impressed by roller pressure, it will liberate less magnetic ink and generate a lower amplitude than when it is used for direct impression Work or is impressed by a type bar. Even when used in identical manner, the magnetic amplitude of the formed images will vary depending on the location of the transfer sheet within the form or the efficiency or degree of wear of the pressure roller impression device.

In actual practice we have found that the present inks must be capable of generating a magnetic amplitude of at least of standard when used under ideal conditions and preferably not in excess of 150% of standard. We have found that if the magnetic ink has this minimum capacity when the images are formed by typing directly against the transfer sheet and transferring the ink to a copy sheet which is well receptive thereto, then the present transfer sheets will be operative under all normal operating conditions such as in the interior of multisheet forms and under the effects of roller pressure. While the amplitude of the images formed by these less efficient methods will be far less than 90% of standard, it will never fall below the 50% value tolerance of conventional MIRC systems.

We have discovered that the magnetizable pigments heretofore used in the transfer sheet field do not provide reliably satisfactory results under all operating condi tions when used as the pigment in liquid oil vehicles in squeeze-out type transfer sheets particularly When positioned in the interior of multi-sheet forms or imaged by means of a pressure roller. The most commonly used magnetic pigment is IRN-lOO which is a ferroso-ferric oxide (Fe O commercially available from C. K. Williams & Co., Easton, Pa. While this material is quite suitable for use in frangible transfer layers, it is not reliably suited to the multi-use transfer elements of the present invention which contain a liquid oil vehicle because of its rough surface characteristics and its high oil absorption. The tap density of this material, having an average particle size of less than 1 micron, is about 12:1 gms./ cu. in. and the oil absorption value is about 50. This is in contrast with the magnetic pigments for use herein which have oil absorption values below about 20 and tap density values above about 20. One such preferred pigment is M07029, a ferroso-ferric oxide commercially available from Pfizer & Co., New York, which has a tap density of about 33 and an oil absorption value of about 12.

The following is a list of other magnetizable iron oxide pigments commercially available from Pfizer & Co. which are suitable for use according to this invention. These suitable materials represent only a fraction of the magnetizable pigments commercially available for a variety of uses, such as in printing inks and magnetic tapes, most of which are unsuitable for use according to the present invention.

Tap Density, Oil Absorption, Trade Designation gms./cu. in. gms./ gms.

MO-8629- 30 14 MO8029 30 14 MO-7029- 33 12 The following example is given by way of illustration and should not be considered limitative.

The magnetic pigment is first dispersed in at least an equal weight of one or more of the oils and is thereafter added to the solution of the resin containing the remainder of the oil. The composition is then coated onto a flexible foundation such as paper or plastic film and dried by evaporation of the volatile solvents to form the solid pressure-sensitive squeeze-out layer.

An attempt to substitute an equal amount of a more conventional magnetic pigment such as IRN-100 for the MO-7029 in the above formulation results in a layer which exudes less magnetic pigment under the effect of imaging pressure to produce images having an inferior signal strength. The oil is absorbed by the IRN-lOO so that the ink phase has little or no fiowability under pressure. The addition of several more parts by weight of oil renders the ink phase fluid and permits the formation of legible black duplicate images under the effects of direct typing pressure. However, the magnetic amplitude of such images is only about 50% of standard compared to a magnetic amplitude of about 120% of standard obtained with images formed from the transfer sheet of the example.

Aside from the critical limitations with respect to the magnetizable pigment and the liquid nature of the oil vehicle, the other components of the present squeeze-out transfer sheets and their proportions are the same as those used heretofore in the carbon paper field, as illustrated for instance by U.S. Patents Nos. 2,820,717 and 3,037,879. While vinyl resin binders are preferred, other materials such as the acrylic resins and polycarbonates, well known in the squeeze-out carbon paper art, may be used. The'oily vehicle must be one which is rapidly flowable at ordinary room temperature and which is substantially unabsorbed by the magnetizable pigment.

The present squeeze-out layers preferably comprise 1 part by weight of resinous binder material, from 1 to 4 parts by weight of liquid oil vehicle and from 2 to 5 parts by weight of the magnetic pigment. The coating solvent may be any suitable volatile organic liquid, and evaporation of the solvent is preferably caused by the application of heat.

In cases where the foundation sheet is paper which tends to absorb the oil from the ink layer, it is preferred to position an oil-impervious resinous intermediate layer between the ink layer and the foundation. However, it is preferred to use a plastic film foundation such as polyethylene terephthalate polyester (Mylar) or similar film and to use a plastic intermediate layer between the film and the ink layer to form a bond between the tWo and to prevent pressure-transfer of the latter in mass, particularly at the higher pressures exerted by some magnetic printing devices.

Variations and modifications may be made and po tions of the improvements may be used without others.

We claim:

1. A pressure-sensitive squeeze-out type magnet transfer element comprising a flexible foundation havir thereon a layer capable of exuding a liquid magnetic it under the effects of varying degrees of imaging pressu. to produce images having a magnetic signal level of fro about to of standard, said layer having a no: transferable porous, spongy structure comprising 1 pa by weight of resinous binder material containing with the pores thereof a pressure-exudable mganetic ink cor prising from about 1 to 4 parts by weight of a liqu oil which is substantially incompatible with said bind material and from about 2 to 5 parts by weight of a ma netic pigment which has an oil absorption value belo about 20 and a tap density value above about 20.

2. A transfer element according to claim 1 in Whit the foundation is plastic film.

3. A-transfer element according to claim 1 in Whit the liquid oil comprises at least one material selectt from the group consisting of butyl stearate, sulfonatc vegetable oil and refined rapeseed oil.

4. A transfer element according to claim 1 in Whit the magnetic pigment comprises iron oxide.

5. A transfer element according to claim 1 in which tl binder material comprises a vinyl resin.

6. A transfer element according to claim 2 in Whit the vinyl resin comprises a copolymer of vinyl ChlOl'i( and vinyl acetate.

References Cited UNITED STATES PATENTS 3,061,454 10/1962 Graf et al. 11736 3,072,577 1/1963 Miller et a1. 25262.54 3,194,676 7/1965 Krumbein et al. 25262.54 3,247,117 4/1966 Shoemaker et a1. 25262.54

OTHER REFERENCES The Chemical Trade Journal and Chemical Enginee Jan. 14, 1927, vol. 80, p. 35. Drugs, Oils and Paints, vc 46, No. 9, p. 330. Reichard-Coulston, Inc.

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