Thermal paper with preprinted indicia

Details Thermal paper with preprinted indicia Thermal paper with preprinted indicia

2001-12-21

2004-10-12

Hess, Bruce H. (Department: 1774)

Record receiver having plural interactive leaves or a colorless

Having a colorless color-former, developer therefor, or...

C503S226000

Reexamination Certificate

active

06803344

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to thermosensitive recording materials with high quality images preprinted thereon.
BACKGROUND OF THE INVENTION
Direct thermal paper is a thermosensitive recording material on which print or a design is obtained without an ink ribbon by the application of heat energy thereto. Direct thermal paper comprises a base sheet, a base coating and a thermosensitive coating with color forming chemicals that respond to heat.
The most common type of thermosensitive coating used on direct paper is the dye-developing type system. This typically comprises a colorless dye (color former), a bisphenol or an acidic material (color developer) and sensitizer. These solid materials are reduced to very small particles by grinding and incorporated into a coating formulation along with any optional additives such as pigments, binders and lubricants. The coating formulation is then applied to the surface of a support system, typically a base sheet and base coating. The color is formed by application of heat to the thermosensitive coating to melt and interact the three color producing materials.
Thermal printing on thermosensitive recording materials provides a number of advantages over printing on plain paper using inked ribbons. One advantage is that thermal printers are less noisy than impact printers. With fewer mechanical operations, thermal printers are believed to be more reliable than impact printers. There are some compromises which must be made when switching from bond paper to thermal paper because the color producing components require special handling and conditions.
To replace plain paper receipt rolls, it is often desirable that the thermal paper also provides security features and preprinted information such as store logos, advertisements, rules and regulations, etc. It is also desirable that this preprinted indicia be of high quality.
By adding features to thermal paper, care must be taken not to pre-react the reactive components within the thermosensitive coating of the thermal paper or prevent the formation of an image on the thermal paper when passed through a thermal printer. Certain chemical factors can adversely affect and degrade the performance of the thermosensitive coatings and should be avoided such as some organic solvents, plasticizers, amines and certain oils.
The use of ink with optically variable compounds as a security measure is well known. Optically variable compounds change color or reflect a unique wavelength in response to a change in ambient conditions such as exposure to a light source other than ambient light or a change in ambient temperature. Optically variable compounds as defined herein include fluorescent compounds and photochromic compounds which respond to infrared or ultraviolet light, thermochromic compounds which change color at different temperatures and near infrared fluorescent (NIRF) compounds which reflect radiation in the near-infrared range. Examples of fluorescent compounds include those described in U.S. Pat. Nos. 4,153,593, 4,328,332 and 4,150,997. Examples of thermochromic compounds are described in U.S. Pat. Nos. 4,425,161; 5,427,415; 5,500,040; 5,583,223; 5,595,955; 5,690,857; 5,826,915; 6,048,347; and 6,060,428. Examples of near infra-red compounds (NIRF) include those described in U.S. Pat. Nos. 5,292,855; 5,423,432 and 5,336,714. The use of fluorescent compounds as a security feature for thermosensitive recording materials is described in U.S. Pat. No. 5,883,043. The use of NIRF compounds as a security feature for thermosensitive recording materials is described in U.S. Pat. No. 6,060,426, assigned to the assignee as the present invention.
To protect thermal paper from environment conditions, and premature coloration from handling, a number of developments have been made. One is to produce a barrier or protection on top of the thermal coating as disclosed in U.S. Pat. Nos. 4,370,370; 4,388,362; 4,424,245; 4,44,819; 4,507,669 and 4,551,738. A U.V. cured silicone acrylate/methacrylate protective coating for a thermosensitive layer is described in U.S. Pat. No. 4,604,635.
U.S. Pat. No. 5,595,955 discloses coating a latent image comprising a thermochromic ink on the reverse side of thermal paper with a thin protective layer.
SUMMARY OF THE INVENTION
The present invention provides a thermosensitive recording material such as thermal paper, comprising a base sheet, an optional base coating, a thermosensitive coating on the top surface of the base sheet or the optional base coating, a backcoating on the side of the base sheet opposite the thermosensitive coating and a printed image on the top surface of the backcoating. The backcoating has incorporated therein a fluorescent compound, a thermochromic compound, a photochromic compound, or a near infrared fluorescent compound (NIRF).
When used as a security feature, the amount of NIRF compound within the backcoating must be sufficient to be sensed by a photon detector operating in the near infrared region of 650 nm to 2500 nm. For a photochromic or fluorescent compound to provide a security feature, the amount of these compounds within the backcoating must be sufficient to generate a latent image when exposed to infrared or ultraviolet light. To provide a security feature, the amount of thermochromic compound within the backcoating must be sufficient to generate or eliminate an image when exposed to temperatures greater than ambient temperature.
The backcoating containing the fluorescent compound, photochromic compound, thermochromic compound and/or NIRF compound can be a U.V., infrared or electron beam cured coating or an air dried coating such as a flexographic or lithographic coating. The backcoating is preferably U.V. cured. This will eliminate the exposure of reactive components within the thermosensitive coating to heat which can cause the reactive components to prematurely color. The backcoat provides a medium in which the optically variable compounds will provide their security function while shielding the reactive components of the thermosensitive coatings from these optically variable compounds. This shielding will preserve the activity of the optically variable compounds as well as the activity of any reactive components within the thermosensitive coating of the thermal paper so that the thermosensitive coating will still generate color when exposed to heat.
In certain embodiments, two or more optically variable compounds can be present in the backcoating to provide two modes of security. For example, optically variable compounds responsive to ultraviolet light can be combined with NIRF compounds which are responsive to near-infrared radiation. In alternative embodiments, the backcoating can overcoat a separate image of a security ink. This requires an additional printing step and is not preferred.
The backcoating can be applied by conventional coating processes such as flexography, gravure, wet-offset printing, letter press and relief printing and where necessary cured by air drying or U.V., infrared or electron beam curing techniques. Following the cure of the backcoating, an image is printed over the backcoating by conventional printing techniques such as flexography, gravure, wet-offset printing, letter press and relief printing.
The thermosensitive recording media of the present invention have a base sheet and a thermosensitive coating positioned on one side of the base sheet. Optionally, a base coating is positioned between the thermosensitive coating and the base sheet. Conventional base sheets and base coatings can be used in the thermosensitive recording materials of the present invention. The base sheet can comprise those materials used in conventional thermosensitive recording materials and at least includes those derived from synthetic and natural fibers such as cellulose (natural) and polyester (synthetic) fibers. The base coating is typically comprised of an inert pigments and binders and provides a smooth surface for the thermosensitive coating. The base sheet and base coatings must not contain any reactive elements w

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