Technical Field

The present invention relates to a thermal transfer ink formulation and a thermal transfer medium, such as a ribbon, for use in imaging or encoding characters on paper or like record media documents which enables machine reading of the imaged or magnetic encoded characters.

Background Art

In the printing field, the impact type printer has been the predominant apparatus for providing increased throughput of printed information. The impact printers have included the dot matrix type wherein individual print wires are driven from a home position to a printing position by individual and separate drivers. The impact printers also have included the full character type wherein individual type elements are caused to be driven against a ribbon and paper or like record media adjacent and in contact with a platen.

The typical and well-known arrangement in a printing operation provides for transfer of a portion of the ink from the ribbon to result in a mark or image on the paper. Another arrangement includes the use of carbonless paper wherein the impact from a print wire or a type element causes rupture of encapsulated material for marking the paper. Also known are printing inks which contain magnetic particles wherein certain of the particles are transferred to the record media for encoding characters in manner and fashion so as to be machine readable in a subsequent operation. One of the known encoding systems is MICR (Magnetic Ink Character Recognition) utilizing the manner of operation as just mentioned.

While the impact printing method has dominated the industry, one disadvantage of this type of printing is the noise level which is attained during printing operation. Many efforts have been made to reduce the high noise levels by use of sound absorbing or cushioning materials or by isolating the printing apparatus.

More recently, the advent of thermal printing which effectively and significantly reduces the noise levels has brought about the requirements for heating of extremely precise areas of the record media by use of fast response thin film resistors. The intense heating of the selective resistors causes transfer of ink from a ribbon onto the paper or like receiving substrate. Alternatively, the paper may be of the thermal type which includes materials that are responsive to the generated heat.

Further, it is seen that the use of thermal printing is adaptable for MICR encoding of documents wherein magnetic particles are caused to be transferred onto the documents for machine reading of the characters. The thermal transfer printing approach for use in MICR encoding of documents enables reliability in operation at the lower noise levels.

The use of thermal transfer printing, especially when performing a subsequent sorting operation, can result in smearing or smudging adjacent the printed symbols or digits on the receiving substrate. This smearing can make character recognition, such as OCR (Optical Character Recognition.) or MICR (Magnetic Ink Character Recognition), difficult and sometimes impossible.

Disclosure of Invention

It is an object of the present invention to provide a thermal ink formulation and a thermal transfer medium which eliminates or substantially

reduces smearing or smudging across or adjacent the printed digits or symbols during the sorting operation.

According to the present invention there is provided a thermal transfer ink formulation including a sensible material and a transfer agent contained in a solvent, characterized in that said transfer agent is an alcohol base transfer agent and said formulation also includes a water base latex, a dye and a tetrafluoroethylene.

In another aspect of the present invention there is provided a thermal transfer medium comprising a substrate carrying a thermal sensitive coating including a sensible material and a transfer agent, characterized in that said transfer agent is an alcohol base transfer agent and said thermal sensitive coating also includes a water base latex, a dye and a tetrafluoroethylene.

Brief Description of the Drawing

An embodiment of the invention will now be described, by way of example, with reference to the accompanying drawing, in which:

Fig. 1 illustrates a receiving document and a thermal element operating with a ribbon base having a magnetic thermal functional coating thereon incorporating the ingredients as disclosed in the present invention; and

Fig. 2 shows the receiving document with a part of the coating transferred in the form of a digit, symbol or other mark onto the receiving document.

Best Mode for Carrying Out the Information

The transfer ribbon 20, as illustrated in Figs. 1 and 2, comprises a base or substrate 22 of thin, smooth, tissue-type paper or polyester-type

plastic or like material having a coating or layer 24 on the substrate. The coating 24 is thermally activated and includes magnetic pigment or particles 26 as an ingredient therein for use in imaging or encoding operations to enable machine reading of characters or other marks. Each character or mark that is imaged on a receiving paper document 28 or like record media produces a unique magnetic pattern or image that is recognized and read by the reader. In the case of ribbons relying on the magnetic thermal printing concept, the pigment or particles 26 include magnetic oxides or like sensible materials.

As alluded to above, it is noted that the use of a-thermal printer having a print head element, as 30, substantially reduces noise levels in the printing operation and provides reliability in MICR imaging or encoding of paper or like documents 28. The magnetic thermal transfer ribbon 20 provides the advantages of thermal printing while encoding or imaging the document 28 with a magnetic signal inducible ink. When the heating elements 30 of a thermal print head are actuated, the imaging or encoding operation requires that the pigment or particles of material 26 in the coating 24 on the coated ribbon 20 be transferred from the ribbon to the document 28 in characters 32 for recognition by the reader.

The functional coating or layer 24 exhibits the following characteristics, namely, the coating must be resistant to rubbing and smudging, the coating must not inhibit transfer of the thermal-sensitive material 26 in the coating 24 at normal print head voltage, pulse width and temperature, and the coating 24 must allow a bond of the magnetic thermal-sensitive material 26 in the coating 24 onto the paper 28 upon transfer of such material.

A preferred formulation to satisfy the above characteristics of the magnetic thermal functional coating 24 includes the ingredients in appropriate amounts as set forth in Example I.

EXAMPLE I

100.0 300. 0 800. 0

It is to be noted that Latex EC-1052 is supplied at 40% solids and that Basonyl Black X-22 is supplied at 50% solids. The Latex EC-1052 may be supplied in a range of 38 to 42% solids and the Basonyl Black X-22 may be supplied in a range of 48 to 52% solids dependent upon different suppliers. The amount of N-propanol solvent in the formulation is selected to suit the range of solids of the various ingredients. Other solvents such as Isopropyl Alcohol, Potable Water or a mixture thereof may be used. It is also noted that the percentage of solids in the formulation of Example I is 37.5%.

Example II is another formulation of different ingredients and amounts as follows:

- 6 -

% Dry Range 40.0-55.0 35.0-50.0 5.0-15.0 1.0- 3.0 0.5- 2.0 1.0- 3.0

100.0 250.0 750.0

It is noted that while the ratio of potable water to N-propanol is 15 to 85, the water content can be as much as 50% of the mixture. The amount of the water and N-propanol in the formulation is selected to suit the range of solids of the various ingredients. It is also noted that the percentage of solids in the formulation of Example II is 33.3%.

In the overall practice of the invention, it is desired to provide formulations for the coating 24 of the ribbon 20 which formulations exhibit exceptional resistance to smear in a high speed sorting operation. It has been observed from the use of these formulations that low buildup of the coating or residue occurs on the stainless steel foil which protects .the read and write head in a high speed sorter. A further reduction or lowering of buildup has been observed with the use of the polyvinyl pyrrolidone which has common solubility in water and alcohol. The polyvinyl pyrrolidone is incorporated into the formulation of Example II to improve the coating properties or characters of the thermal transfer ribbon in printing operations without sacrificing, the transferrability of the thermal sensitive material 26 in the coating 24 or the resistance to smear or smudge.

The transfer property of the coating 24 can be improved by use of adhesives such as the Butvar B98 (Example I), polyvinyl alcohol, cellulose acetate butarate or water base emulsions of vinyl acetate.

In the preparation of the magnetic thermal transfer ribbon 20, the formulation layer 24 is coated on the substrate 22. The substrate or base 22, which may be 14 to 35 gauge polyester film, as manufactured by du Pont under the trademark Mylar, or 30 to 40 gauge capacitor tissue, as manufactured by Glatz, should have a high tensile strength to provide for ease in handling and coating of the substrate. Additionally, the substrate should have properties of minimum thickness and low heat resistance to prolong the life of the heating elements 30 of the thermal print head by reason of reduced print head actuating energy.

The coating 24 is applied to the substrate 22 by means of conventional coating techniques such as a Meyer rod or like wire-wound doctor bar set up on a typical coating machine to provide a coating weight of between 5.5 and 8.5 grams per square meter. The coating is made up of approximately 30 to 37.5% nonvolatile material and is maintained at a desired temperature and viscosity throughout the coating process. After the coating is applied to the substrate, the web of ribbon is passed through a dryer at an elevated temperature in the range between 93 and 150 degrees C for approximately 5-10 seconds to ensure good drying and adherence of the coating 24 onto the substrate 22 in making the transfer ribbon 20. The above-mentioned coating weight, as applied by the Meyer rod onto a preferred 9-12 microns thick capacitor grade tissue, translates to an overall total thickness of 10-20 microns. The coating 24 exhibits exceptional transfer characteristics on a variety of paper stocks at print energy level ranges of 0.80 to

1.20 mJ of print energy in the thermal transfer encoder.

The magnetic iron oxide is a reddish or bluish-black amorphous powder in form and magnetic in function, is insoluble in water, alcohol and ether, and is used as a pigment or sensible material. Behenyl alcohol is a long chain, saturated fatty alcohol of high molecular weight (326) which is soluble in a hot alcohol, acetone and ether, and is used as a transfer agent. Latex EC 1052 is a water base latex which is used as an adhesive and which also assists the transfer and binding of the magnetic iron oxide onto the paper 28. The latex is further identified as an aqua vinyl primer having a pH of 8.2 to 8.5 and a viscosity of 25 to 30 inches. Butvar B98 is a polyvinyl acetate resin (further identified as polyvinyl butyral) and is used as an adhesive to adjust the transfer characteristics of the coating 24. The polyvinyl acetate resin imparts improved flexibility, adhesion, cohesion, toughness and rubproofness. The solubility characteristics of Butvar allow compounding with fast drying solvents suitable for high speed printing. Basonyl black X-22 is an azine dye in N-propanol which is used to improve the intensity of the transferred image without sacrificing smear resistance. The Basonyl black X-22 also improves the adhesion of the coating 24 to the substrate 22. PTFE is a polymer, plastic or resin derived from tetrafluoroethylene, is a straight chain unit, has a waxy texture, and is opaque with a milk- white color. PVP (polyvinyl pyrrolidone) is a free flowing white amorphous powder and is soluble in water, chlorinated hydrocarbons, alcohols, amines, nitroparaffins, and lower molecular weight fatty acids.

The availability of the various ingredients used in the present invention is provided by the following list of companies.

Material Supplier

Iron Oxide #0045 BASF

Behenyl Alcohol Fallak Chemical

Latex EC-1052 Environmental Ink Co.

(40% Solids)

Butvar B98 Monsanto

Basonyl Black X-22 BASF

50% Solids)

PTFE SST-3 Diamond Shamrock

PVP GAF

The water or alcohol used as solvents along with the various other ingredients in the present formulations enable the producing of a magnetic thermal transfer ribbon which exhibits resistance to smear and scratch of the transferred image. The N- propanol, the isopropyl alcohol and the potable water are provided by any known supplier. While potable water is acceptable for use in the present invention, deionized water (that which has been purified of salts) is readily available for use in these formulations, or distilled water (that which is void of nonionic impurities) may also be used.

The present invention provides a water base thermal transfer system that does not require the use of a conventional wax. The behenyl alcohol and the water base latex are used as transfer agents. The combination of the water base latex and the behenyl alcohol provides a transfer agent which exhibits exceptional resistance to smear and demonstrates low buildup of residue on the stainless steel foil in a high speed sorter. The basonyl black is used to improve the intensity of the transferred image without sacrificing smear resistance, and is also used to

improve the adhesion and the rheological (flow of matter) properties of the coating 24.

It is thus seen that herein shown and described is a thermal transfer ribbon for use in thermal printing operations which includes a thermal responsive coating on one surface of the ribbon. The coated ribbon enables transfer of coating material onto documents or like record media during the printing operation to form digits or symbols or other marks on the record media in an imaging or in an encoding nature, permitting machine or other reading of the characters. The thermal responsive coating includes a formulation or mixture of ingredients which resist smearing or smudging and scratching of the transferred images or other marks. The mixture or formulation of the various ingredients is dispersed in water, alcohol, or a combined water/alcohol solvent. In the formulation which includes Butvar B98 (Example I), it is preferred to use N-propanol as the solvent.