What are the advantages of overhead versus underground


The invention relates to a method and an arrangement for producing markings on transparencies for overhead projection by means of thermal copy.

Several methods are used for marking, in particular lettering, overhead transparencies with light colored lines on a dark colored background.

For example, in DE-OS 27 51 122 an arrangement is described in which a film provided with dye is labeled with a colorless compound present in the writing implement with a change in color. For this purpose, indicator dyes are used that change from blue to yellow in the pH range between the values ​​3 and 5, and writing implements that are filled with a solution of the appropriate pH value.

Furthermore, from DE-OS 29 11 798 an overhead slide is known which achieves a yellow image on a blue background in two other ways. According to the first variant,

a) a reducible blue dye that contains a non-reducible yellow dye, decolorized with a sulfite pencil or

b) the film is colored yellow before the blue dye is applied and then labeled with the sulfite pen or

c) a yellow dye was added to the sulfite stick.



According to the second variant, a color former is developed with a developer substance to give a blue color and applied to a film. The yellow writing, as in the first variant, is achieved by adding a permanent yellow dye to the color reaction system or by coloring the film or by adding a yellow dye to the extinguishing liquid.

Such films are labeled with pens that contain a polar or basic substance. It is known that the color reaction of color precursors with developers is extinguished by polar or basic substances.

In many cases, it is necessary, in addition to the overhead transparencies to be marked, for example, in the course of a lecture, to also present copies. This requires other overhead transparencies, onto which an original template can be transferred directly using a copying process and thus made accessible for projection.

Several methods are used for this purpose. For example, an electrostatic copying process can be used to create a black toner image of an original on a transparent film. Furthermore, by means of a thermal copying process, a colored copy of an original can be obtained on a film which contains a color former in the colorless state, with the aid of an acid sheet.

These methods have in common that you can only produce a dark marking on a light background. Investigations have shown, however, that the best legibility is achieved with overhead projection when light text is on a dark background, ideally yellow writing on a blue background.

Up to now, such films could only be obtained by manually marking the blue-colored overhead films mentioned at the beginning.

The object of the invention is to overcome the disadvantages mentioned and to provide a new method and an arrangement for producing markings on transparencies for overhead projection.

According to the invention this object is achieved in that an acid or base is transferred by means of heat to a film colored dark with a dye that can be lightened by acids or bases at the points provided by an original sheet, thereby causing a color change to a contrasting light color becomes.

When developing the image according to known thermal copying processes, the original and the copy receiving sheet lie close to one another. Infrared radiation falls from an incandescent body onto the original. The radiation is only absorbed in the areas of the original that are darkened, for example by letters, and causes disproportionate heating in these areas. The thermal image is transferred to the tightly fitting copy receiver sheet.

The resulting thermal image on the original is used according to the invention to generate light markings on dark-colored overhead transparencies in two ways:

1. An additional developer sheet, which contains a transferable acid or base, is arranged between the original and an overhead transparency layer side against the layer side, which is colored with a dye that changes when the pH value changes. The color change is then brought about by transferring the acid or base to the heated areas on the colored film.

2. The transferable acid or base is contained in the colored layer of the film itself. The color change is caused by their disappearance in the heated areas. In this case, no additional developer sheet is necessary.



Indicator dyes, but also alkali-sensitive dyes and the color formers, can be used as dyes which can be bleached or which react to changes in pH with a color change. From the series of indicator dyes, for example, bromochlorophenol blue, bromocresol green, bromocresol purple, bromophenol blue, bromothymol blue, bromxylenol blue, methylthymol blue, thymol blue and p-xylenol blue are suitable.

From the series of alkali-sensitive dyes, for example, the compounds listed below are suitable:

Triarylmethane dyes: Ink Blue, C.I. Acid Blue 93; Astrarhodulin Blue, C.I. Basic Blue 1

Xanthene dyes: Rhodamine scarlet G, C.I. 45015 methylene red, C.I. 45006

Methine dyes: Astrazone Red 6B, C.I. Basic Violet7; Astrazon Blue 5RL, C.I. Basic blue 62

Polymethine dyes: Astrazon Violet FRR, C.I. Basic Violet 20



From the series of color formers (color precursors), for example, the following compounds can be used: crystal violet lactone, malachite green lactone, indolinospirane, phenothiazine, thiophenchromene, phthalane and fluorane.

The dyes that are inert or permanent to pH-A change and which serve to produce a colored contrast in bleachable dyes are preferably selected from the series of azo, phthalein and anthraquinone dyes.

The inert dye can be added to the color layer or arranged in a preliminary layer under the color layer. When using a yellow or green base film, there is no need to use inert dyes.

Transferable acids or bases are to be understood as meaning those which can be sublimed, evaporated or melted at the temperatures customary in the thermal copying process. These include, for example, d, 1-mandelic acid, benzilic acid, 2,6-dihydroxybenzoic acid and 2,5-dihydroxybenzoic acid- acid, salicylic acid, methylsalicylic acid, benzoic acid, higher amines such as hexadecylamine and ammonium carbonate.

The acidic or alkaline-coated sheet used as the developer sheet consists of a carrier which is coated with an alkaline or acidic medium which is optionally embedded in a binder.

Known water- or solvent-soluble binders, such as polyvinyl alcohol, polyvinylpyrrolidone, polyvinyl acetate, latices, gelatin, gum arabic, starch ethers, starch esters and acrylates, for example, are used as binders.

The following examples explain the invention.

example 1


1a) paint layer



100 g of photogelatine are soaked in 1 liter of water and dissolved by heating to about 50 ° C. 10 g of bromocresol green and 5 g of anhydrous soda are added to this solution. Then the solution is cast in a thin layer on a sheet of cellulose triacetate (such as is used for the production of photographic films) using a casting machine, allowed to solidify and dried. An intensely blue colored film is produced.

Developer sheet



3 g of nitrocellulose are dissolved in 85 g of acetone and 12 g of 2,6-dihydroxybenzoic acid are added. A polyester film is coated with this solution.

When this acid sheet together with the blue colored film and an original through a thermal copier, a yellow copy is obtained on a blue background.

1b) In a further experiment, the 2-6-dihydroxybenzoic acid in the coating of the developer sheet is replaced by salicylic acid at the same weight ratios. In this example, too, a yellow copy on a blue background is obtained during the thermal copying process.

Example 2



The procedure is as in Example 1 with the proviso that ammonium carbonate is now used instead of anhydrous soda.

When such a film with an original without acid sheet passes through a thermal copier, a yellow copy on a blue background is obtained.

Example 3


Paint layer



10 g of a polyvinyl alcohol with a low degree of saponification are dissolved in 44.5 g of water and 44.5 g of ethyl alcohol. Then 1 g of ink blue C.I.Acid blue 93 is added. This solution is applied in a thin layer to a yellow polyester film and dried. An intensely blue colored film is produced.

Developer sheet



3 g of nitrocellulose are dissolved in 85 g of acetone and 12 g of hexadecylamine are added. A polyester film is coated with this solution.

When. Passing this basic developer sheet together with the blue-colored film and an original through a thermal copier, a yellow copy on a blue background is obtained.

Example 4



The procedure is as in Example 3 with the proviso that 3 g of salicylic acid are now added instead of 0.1 g of hydrochloric acid.

When such a film with an original without an alkali sheet passes through a thermal copier, a yellow copy on a blue background is obtained.

Example 5


Paint layer



In a solution of 10 g of cellulose acetobutyrate in 87 g of ethyl acetate, 1 g of crystal violet lactone, 2 g of bisphenol A and 0.1 g of neozapon yellow (C.I. 18690) are dissolved and this solution is applied to a polyester film. After drying, a blue colored film is obtained.

Developer sheet



3 g of nitrocellulose are dissolved in 85 g of acetone and 12 g of hexadecylamine are added. A polyester film is coated with this solution.

On passage of this alkali sheet together with the blue colored film and an original through a thermal copier, a yellow copy is obtained on a blue background.

Example 6


Paint layer



In 44.2 g of water and 45.0 g of ethyl alcohol, 10.0 g of polyvinyl alcohol with a low degree of saponification, 0.2 g of Echtgründ R C.I. Acid green 14 and 0.6 g astrazon violet F3RL C.I. Basic violet 21 solved. A polyester film is coated with this solution. After drying, a violet film is obtained.

When this film with a developer sheet according to Example 3 and an original passes through a thermal copier, a green copy is obtained on the purple background.

Example 7


Adhesive layer



In a solution of 5.0 g of polyvinyl acetate in 44.9 g of ethyl acetate and 50.0 g of ethyl alcohol, 0.1 g of neozapon yellow C.I. 18690 dissolved and this solution applied to a polyester film. After drying, a yellow colored film is obtained.

Paint layer



10 g of a polyvinyl alcohol with a low degree of saponification are dissolved in 44.5 g of water and 44.5 g of ethyl alcohol. Then 1 g of ink blue C.I. Acid blue 93 added. This solution is applied in a thin layer to the yellow-colored polyester film obtained above and dried. An intensely blue colored film is produced.

Developer sheet



3 g of nitrocellulose are dissolved in 85 g of acetone and 12 g of hexadecylamine are added. A polyester film is coated with this solution.

When this basic developer sheet, together with the blue-colored film and an original, passes through a thermal copier, a yellow copy is obtained on a blue background.


1. A method for producing markings on transparencies for overhead projection by means of thermal copying, characterized in that an acid or base is transferred by means of heat to a film colored dark with a dye that can be lightened by acids or bases at the points specified by an original sheet and thereby a color change to a contrasting light color is effected.
 
2. An arrangement for producing markings on transparencies for overhead projection by means of thermal copying, characterized in that it consists of a transparency which is coated with a dye that changes when the pH changes, and a basic or acidic developer sheet lying thereon .
 
3. Arrangement for producing markings on transparencies for overhead projection by means of thermal copying, characterized in that it consists of a transparency which is coated with a dye that changes when the pH value changes and a transferable acid or base.
 
4. Arrangement according to at least one of claims 2 and 3, characterized in that the transparent film is coated with an indicator dye and a color change of the indicator causing agent is contained in the developer sheet or in the coating of the transparent film in meltable, sublimable or vaporizable form .
 
5. Arrangement according to at least one of Claims 2 and 4, characterized in that the developer sheet is provided with a binder layer which contains a basic or acidic agent.
 
6. Arrangement according to at least one of claims 3 to 5, characterized in that the agent causing the color change is an amine.