Method Of Recording By Heat Sensitive Multicolor Indication

Abstract

Heat sensitive recording to produce a multicolor indication is effected by bringing a heating element close to or in contact with a heat sensitive recording material for multicolor indication, the recording material has two or more heat sensitive recording layers. The temperature of the heating element is controlled to produce patterns having different colors depending upon the heat sensitive temperature of each heat sensitive layer.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a method of recording by heat sensitive multicolor indication and a heat sensitive recording material used in said method.

2. Description of the Prior Art

Heretofore, it has been well known that the components of a heat sensitive recording system are usually a basic color forming material and an acidic material such as diphenol at a colorless state; and, upon application of a heat pattern the system causes liquefication or vaporization of the acidic material such as diphenol and then the acidic material thus liquefied or vaporized contacts with the basic color forming material to form color. The colorless components of the recording system are usually contained in a single supporting sheet referred to as a "self containing system." Another type of heat sensitive recording system is that composed of two sheets, i.e. one sheet having the first component and the other sheet having the second component. Each component is placed face to face and thereby one component, liquefied or vaporized by application of a heat pattern, transfers to the other component to form a recording. This latter system is known as a "transferring system."

These heat sensitive recording materials have been widely used in the reproduction of documents. A heating element utilizing a miniature semiconductor has been recently developed and arranged into a desk top calculator as a recording head or into a high speed printer as a recording head. As the result, the heat sensitive recording material attracts attention again as a recording material for such recording head.

As the heat sensitive recording material for such a new recording method, there may be used a conventional heat sensitive recording material for usual copying when it is appropriately improved. However, for such recording head different from usual copying field it is particularly preferable to make the important data and numbers distinct from the other ones by using a different color.

It is difficult to form indications of two or more colors on a single sheet by employing conventional heat sensitive materials for prior art copying. In addition, it is not possible to form multicolor indication in view of the reproduction process.

SUMMARY OF THE INVENTION

An object of this invention is to provide a method of multicolor indication of figures such as letters, numbers and the like by using a heating element.

Another object of this invention is to provide a mechanically silent printing method.

A further object of this invention is to provide a multicolor heat sensitive recording material suitable for the above mentioned process.

Still another object of this invention is to provide a recording material for indicating printed letter recording of different color tone on the same recording sheet or tape.

A still further object of this invention is to provide a multicolor recording material capable of producing a permanent print.

The method of recording by heat sensitive multicolor indication according to the present invention can be attained by combining a heating element and a heat sensitive recording material for multicolor indication.

As a heating element in the present invention, there may be used, for example, a heating head as described in U.S. Pat. No. 3,496,333 to E.G. Alexander. Particularly, there is preferred a heat element device having a control circuit containing a current control device capable of switching between a low temperature heating element and a high temperature heating element.

This heating element can control the heat amount and thereby the heating temperature by controlling the current flowing in the heating unit. The heat sensitive material for multicolor indication of the present invention is fundamentally composed of a multilayer heat sensitive recording layer overlying a support, e.g. paper or film, but, if desired, a self-supporting layer may be employed which is produced by admixing a color forming main agent or a color forming auxiliary agent with the support material or making the support layer therefrom.

The heat sensitive recording material for multicolor indication comprises a heat sensitive recording layer of multilayer type overlying a support, and the laminating is effected in an order of heat sensitive temperatures ranging from about 60.degree.C to about 160.degree.C. Different colors are formed depending each specific heat sensitive temperature of the layers in a direction from the outermost layer to the support layer or in the opposite direction.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 shows a cross sectional view of a heat sensitive material according to the present invention;

FIG. 2 is a graph showing temperature characteristic of each heat sensitive layer;

FIG. 3 diagrammatically shows application of a heat element to a heat sensitive material; and

FIG. 4 diagrammatically shows a heat element provided with a current control circuit.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1, a heat sensitive material is composed of a support 1 such as paper and film, a heat sensitive layer II 2 overlying the support and a heat sensitive layer I 3 overlying the heat sensitive layer II.

Referring to FIG. 2, there is illustrated heat color forming characteristics of the above mentioned heat sensitive material. The heat sensitive layer I forms color at a temperature of T.sub.1 (low temperature) while the heat sensitive layer II does not form color at all at T.sub.1 but forms color at T.sub.2 when the temperature is raised from T.sub.1 to T.sub.2. Naturally, in the latter case the heat sensitive layer I has already formed color. For example, assuming that the formed color of heat sensitive layer I is magenta and that of heat sensitive layer II is cyanic, the color of the heat sensitive recording multilayer is magenta at a temperature T.sub.1 and violet at a temperature T.sub.2 since magenta and cyanic colors are mixed.

Referring to FIG. 3, a heat element for low temperature 5 and a heat element for high temperature 6 which are connected with control circuits (not shown) come in contact with or approach the heat sensitive recording multilayer, and the heat element for low temperature 5 causes a magenta color indication and the heat element for high temperature 6 causes a purple color indication.

When at least one layer in the multilayer of the heat sensitive material of FIG. 1 is dyed to yellow, the color at low temperature (T.sub.1) is red as a result of combination of magenta and yellow and the color at high temperature (T.sub.2) is black as a result of combination of magenta, cyanic and yellow. Thus, red and black printings can be effected on a yellow background.

Now referring to FIG. 4, the device is different from that in FIG. 3 and only one heat element 4 is used, and current in each portion of the heat element 4 is controlled by a control circuit 7 to indicate figures, letters and other patterns with two different colors. When two or more heat sensitive layers are used, the performance is similar to the above one and different colors corresponding to the number of layers can be employed for indication.

The heat sensitive material for multicolor indication is composed of heat sensitive recording layers laminated in an order depending upon the heat sensitive temperatures thereof.

The layer of heat sensitive recording material of the present invention essentially comprises a color forming main agent and a color forming auxiliary agent and if desired, additionally contains a softening point adjusting agent, a binder and other additives.

The color forming main agent is a basic material having a color forming group. Representative color forming main agents are: diaryl phthalides such as 3-3 bis (p-dimethyl amino phenol)-6-dimethyl amino phthalide (Crystal Violet Lactone), 3-3 bis (p-dimethyl amino phenol) phthalide (Malachite Green Lactone) and the like; leuco auramines such as N-halophenyl derivatives, N-alkyl halophenyl derivatives, N-(2,5-dichlorophenyl) leuco auramine and the like; acryl auramines such as N-benzoyl auramine, N-acetyl auramine and the like; .alpha.,.beta.-unsaturated arylketones such as dianisylidene acetone, dibenzylidene acetone, anisylidene acetone and the like; basic mono azo dyes such as p-dimethyl amino azo benzene-O-carboxylic acid (Methyl Red), 4-amino azo benzene (Oil yellow-AAB), 4-phenyl azo-1-naphthyl amine and the like; Rhodamine B lactams such as N(p-nitrophenyl) rhodamine B lactam, 3,6'-diamino rhodamine B lactam, 3,6'-diethyl amino rhodamine B lactam, 3,6'-dimethyl amino rhodamine B lactam and the like; polyaryl carbinols such as bis(p-dimethyl amino phenyl) methanol (Michler's hydrol), Crystal Violet carbinol, Malachite Green carbinol and the like; benzoindolino spiropyrans such as 8'-methoxy benzoindolino spiropyran, 4,7,8'-trimethoxybenzoindolino-spiropyran, 6'-chloro-8'-methoxy benzoindolino-spiropyran and the like; phthalans such as 1,1-bis(p-aminophenyl) phthalan, 1,1 -bis(p-benzylaminophenyl) phthalan, 1,1-bis(p-dibenzylaminophenyl) phthalan, 1,1-bis(p-N-methyl anilino phenyl) phthalan and the like; and spiro phthalans such as 6,6'-diamino spiro (phthalan-1,9'-xanthene), 6,6'-diethyl amino spiro (phthalan, 1,9'-xanthene), 6,6'-dimethyl amino spiro (phthalan-1,9'-xanthene) and the like.

The color forming auxiliary agents used in this invention are a material capable of thermally reacting with the color forming main agent to form a conjugated system such as, for example, phenolic compounds, phenol derivatives, phenolic resins and the like.

Representative color forming auxiliary agents suitable for the above mentioned color forming main agents are:

4-tertiary butyl phenol, 4-tertiary amylphenol, 4-phenyl phenol, 4-4'-isopropylidene bis (2-chlorophenol), 4,4'-isopropylidene bis (2-methyl phenol), 4,4-isopropylidene bis (2-tertiary butyl phenol), 4,4'-secondary butylidene bis (2-methyl phenol), 2,2'-dihydroxydiphenyl, 4,4'-seconary butylidene diphenol, 4-tertiary octyl cathechol, bis phenols, 4'-hydroxyacetophenone, methyl-4-hydroxy-benzoate, 4-hydroxy diphenoxide, .alpha.-naphthol, .beta.-naphthol and novolac type phenol formaldehyde condensation products, resol type phenol formaldehyde condensation products and modified phenolic resin and the like. These phenolic materials have melting points ranging from 60.degree. to 150.degree.C. It is preferable to use the material of lower melting point or softening point in a heat sensitive layer close to the heating element and the material of higher melting point or softening point in a heat sensitive layer far from the heating element.

A softening point adjusting agent may be employed for controlling the color forming temperature range. The softening point adjusting agent should be mutually soluble with the color forming main agent and/or color forming auxiliary agent to lower the softening point. They are, for example, low melting point materials, higher fatty acids and crystalline solid plasticizers.

Representative materials of low melting point are:

(a) Amides such as 9,12-octadecane amide, 9-octadecane amide, octadecane amide hexadecane amide, tetradecane amide, dodecane amide, decane amide, octane amide, hexane amide and the like; (b) Paraffines such as chlorinated paraffin; (c) derivatives of fatty acid such as methyl hydroxy stearate, glycerol tri-1,2-hydroxy stearate, partially hydrogenated castor oil.

Representative higher fatty acids are those having 12-20 carbon atoms and 50.degree.-150.degree.C of melting point, such as lauric acid, palmitic acid, stearic acid, myristic acid and the like.

Representative crystalline solid plasticizers are diphenyl phthalate (DPP), dichlorohexyl phthalate (DCHP), ethylene glycol dibenzoate (EGDB), dimethyl isophthalate (DMIP) and the like.

As binders used in the present invention, there may be mentioned methyl cellulose, arabian gum, gelatine, sodium alginate, casein, zinc caseinate, sodium carboxymethyl cellulose, polyvinyl alcohol, pectine, polyvinyl pyrrolidone, starch and its derivatives, copolymer of styrene and maleic anhydride, copolymer of polyethylene and maleic anhydride, copolymer of polyvinyl pyrrolidone and maleinic anhydride, polyacrylate and its copolymer, copolymer of styrene and butadiene, emulsions of polyvinyl chloride, polymethyl methacrylate and polyvinyl acetate and the like. Among them, arabian gum, zinc caseinate, copolymer of styrene and maleic anhydride, and copolymer of styrene and butadiene, are particularly effective.

Color formation caused by combining the representative color forming main agents is as shown in Table 1 below. ##SPC1##

A feature of this invention resides in the fact that recordings of different colors can be formed on one and the same recording sheet or tape by controlling the heating temperature of a heating element. For example, according to the present invention, it is possible in a desk top calculator to indicate the calculating procedure with blue color and the answer and sum with red color, and further in a thermal printer an important sentence can be printed with red color while an unimportant sentence can be printed with blue color. In conventional typewriters there are also employed two color indications, but mechanical typewriters are noisy and only predetermined numbers or letters can be printed. On the contrary, color of a part or a half of each letter or number can be changed according to the present invention.

For example, a heating element is employed which is composed of a linear matrix containing many minor heating portions arranged on one line, and the heating element is moved in a direction perpendicular to the linear matrix and the current supplied to each minor heating portion is controlled corresponding to a pattern. As the result, there can be recorded a multicolor pattern divided into each dot in place of a full letter or number. Such multicolor dot pattern can not be produced by conventional mechanical typewriters.

The following examples are given as being illustrative of the invention, but it will be understood that the invention is not limited thereto. In the examples, parts are by weight unless otherwise specified.

EXAMPLE 1

High temperature color forming layer:

Twenty parts of Crystal Violet Lactone (CVL) and 10 parts of a copolymer of styrene and maleic anhydride were mixed and ground for one hour until CVL particles became 0.5-2 microns in size. 60 parts of phenolic resin and 10 parts of a copolymer of styrene and maleic anhydride in a solution form were mixed and ground for one hour until particles of the phenolic resin became 2-3 microns in size. Then, the above two compositions were mixed and coated on a support (60 microns thick) in 2-5 microns thick (when dried) by a wire bar.

Low temperature color forming layer:

Twenty parts of Rhodamine lactone (RL) and 10 parts of a copolymer of styrene and maleic anhydride were mixed and ground for one hour until particles of RL became 0.5-2 microns in size. A mixture of 55 parts of phenolic resin, 10 parts of a copolymer of styrene and maleic anhydride and 5 parts of myristic acid were ground for one hour until the phenolic resin became 1-2 microns in size. Then, the two compositions obtained above were mixed and coated on the high temperature color forming layer as obtained above in 2-5 microns thick (when dried) by a wire bar to produce a heat sensitive recording material for two color indication.

Printing was effected on the resulting heat sensitive material for two color indication by using a heating element at a relatively low temperature (about 60.degree.-110.degree.C) to produce a red pattern. On the contrary when printing was effected at relatively high temperature (110.degree.-160.degree.C) there was obtained clear violet pattern. Current flow was applied for 5-20 m.sec. in each case.

EXAMPLE 2

High temperature color forming composition:

Twenty parts of CVL and 10 parts of a copolymer of styrene and maleic anhydride were mixed and ground for one hour until the particle size became 0.5-2 microns. On the other hand, 60 parts of bisphenol A and 10 parts of a copolymer of styrene and maleic anhydride were mixed and ground for one hour until particle size of the bisphenol A became 1-3 microns. The resulting two compositions were mixed with stirring and coated on a paper (60 microns in thickness) in 2-5 microns thick (when dried) by a wire bar.

Low temperature color forming composition:

Twenty parts of RL and 10 parts of a copolymer of styrene and maleic anhydride were mixed and ground for one hour until the RL particle became 0.5-2 microns.

55 parts of bisphenol A, 10 parts of a copolymer of styrene and maleic anhydride and 5 parts of myristic acid were mixed and ground until particle size of the bisphenol A became 1-2 microns.

The resulting two compositions were mixed thoroughly and coated on the high temperature color forming layer as obtained above in thickness of 2-5 microns (when dried) by a wire bar. The resulting heat sensitive recording material was subjected to printing test as mentioned in Example 1 above to produce clear bluish violet color.

EXAMPLE 3

High temperature color forming composition:

The high temperature color forming layer as obtained in Example 1 was employed.

Low temperature color forming composition:

Twenty parts of RL and 10 parts of a copolymer of styrene and maleic anhydride were mixed and ground for one hour until particle size of the RL became 0.5 to 2 microns.

55 parts of phenolic resin, 10 parts of a copolymer of styrene and maleic anhydride and 5 parts of ethylene glycol dibenzoate (EGDB) were mixed and ground unti particle size of the phenolic resin became 1-3 microns.

The resulting two components were mixed by stirring and coated on the high temperature color forming layer in 2-5 microns thick (when dried) by a wire bar.

The resulting heat sensitive sheet for multicolor formation which is of low adhesivity was subjected to a printing test as mentioned in Example 1 to produce a clear two color formation.

EXAMPLE 4

High temperature color forming composition:

The high temperature color forming layer as obtained in Example 2 was used.

Low temperature color forming composition:

Twenty parts of RL and 10 parts of a copolymer of styrene and maleic anhydride were mixed and ground for one hour until particle size of RL became 0.5-2 microns.

55 parts of bisphenol A, 10 parts of a copolymer of styrene and maleic anhydride and 5 parts of EGDB were mixed and ground until particle size of the bisphenol A became 1-3 microns.

The resulting two compositions as mentioned above were mixed with stirring and coated on the high temperature color forming layer as obtained above in 2-5 microns thick (when dried) by a wire bar. The resulting heat sensitive sheet had an adhesivity similar to that in Example 3 and was subjected to a printing test in a way similar to Example 1 to produce a clearer and more bluish violet pattern than that obtained in Example 3.

EXAMPLE 5

High temperature color forming layer:

Twenty parts of CVL and 10 parts of a copolymer of styrene and butadiene were mixed and ground for one hour until particle size of the CVL became 0.5-2 microns.

60 parts of phenolic resin and 10 parts of a copolymer of styrene and butadiene were mixed and ground for one hour until particle size of the phenolic resin became 1-3 microns.

The resulting two compositions were mixed by stirring and coated in a way similar to Example 1.

Low temperature color forming composition:

Twenty parts of RL and 10 parts of a copolymer of styrene and butadiene were mixed and ground for one hour until particle size of RL became 0.5-2 microns.

55 parts of phenolic resin, 10 parts of a copolymer of styrene and butadiene and 5 parts of myristic acid were mixed and ground for one hour until particle size of the phenolic resin became 0.1-5 microns.

The resulting two compositions were mixed by stirring and coated on the high temperature color forming layer as obtained above and then subjected to a printing test as in Example 1 to produce a sharp and highly transparent pattern was obtained.

EXAMPLE 6

High temperature color forming layer:

Twenty parts of CVL and ten parts of a copolymer of styrene and butadiene were ground for one hour until CVL particles became 0.5-2 microns in size. 60 parts of bisphenol A and ten parts of copolymer of styrene and butadiene were mixed and ground until bisphenol particles became 1-2 microns in size. Then the above two compositions were mixed and coated in accordance with Example 1.

Low temperature color formation layer:

Twenty parts of RL and ten parts of a copolymer of styrene and butadiene were mixed and ground for one hour until particles of RL became 1-2 microns in size. A mixture of 55 parts of bisphenol A and 10 parts of a copolymer of styrene and butadiene and 5 parts of myristic acid were mixed and ground until bisphenol A particles became 0.5-2 microns. Then the two compositions obtained above were mixed and stirred and coated on the high temperature color forming layer. Printing was held as in Example 1, and then was obtained clear red pattern.

EXAMPLE 7

High temperature color forming layer:

The high temperature color forming layer as obtained in Example 5 was used.

Low temperature color forming layer:

Twenty parts of RL and ten parts of a copolymer of styrene and butadiene were mixed and ground for one hour until RL particles became 0.5-2 microns in size. 55 parts of phenolic resin and 10 parts of a copolymer of styrene and butadiene and 5 parts of EGDB were mixed and ground until phenolic resin particles became 1-2 microns in size. Then the two compositions obtained were mixed and stirred and coated on the high temperature color forming layer and printed in accordance with Example 1. The resulting printing was non-sticky and well.

EXAMPLE 8

The high temperature color forming layer:

The high temperature color forming layer as obtained in Example 6 was used.

The low temperature color forming layer:

20 parts of RL and 10 parts of a copolymer of styrene and butadiene were mixed and ground for one hour until RL particles became 0.5-2 microns in size. 55 parts of bisphenol A and 10 parts of a copolymer of styrene and butadiene and 5 parts of EGDB were mixed and ground until bisphenol A became 1-2 microns in size. Then the two compositions obtained above were mixed and stirred and coated on the high temperature color forming layer in accordance with Example 1.

As the result of printing test by the method of Example 1 a good two color sheet of red and violet was obtained.

EXAMPLE 9

High temperature color forming layer:

20 parts of Malachite Green Lactone (MGL) and 10 parts of a copolymer of styrene and maleic anhydride were ground for one hour until MGL particles became 0.5-2 microns in size. 60 parts of a phenolic resin and 10 parts of a copolymer of styrene and maleic anhydride were mixed and ground for one hour until the phenolic resin particles became 1-2 microns in size. Then the two above obtained were mixed and coated on a film support (60 microns thick) in 2-5 microns thick (when dried) by a wire bar.

Low temperature color forming layer:

The low temperature color forming layer as obtained in Example 1 was used. This was coated in 2-5 microns thick (when dried). As the result of printing test by the method of Example 1, two colors, green and violet, were obtained.

EXAMPLE 10

High temperature color forming layer:

The high temperature color forming layer as obtained in Example 6 was used.

Low temperature color forming layer:

The low temperature color forming composition was prepared by following the procedure of Example 6 except that Malachite Green Lactone was used in place of RL.

A printing sheet was prepared in a way similar to Example 1. The resulting sheet was subjected to a printing test as in Example 1 to produce blue and bluish green patterns.

EXAMPLE 11

20 parts of Leuco Auramine (LA) and 10 parts of a copolymer of styrene and butadiene were ground for one hour until LA particles became 0.5-2 microns in size. 60 parts of phenolic resin and 10 parts of a copolymer of styrene and butadiene were mixed and ground for one hour until phenol resin particles became 1-2 microns in particle. The two above obtained were mixed and coated in a paper of 60 microns thick in 2-5 microns thick (when dried). Then the high temperature color forming layer as obtained in Example 1 was coated on the above color forming layer and further the low temperature color forming layer as obtained in Example 1 was coated thereon. Thickness of each layer was the same as that in Example 1.

The resulting heat sensitive multicolor recording member was subjected to printing test at a low temperature ranging from 60.degree. to 80.degree.C, at a middle temperature ranging from 80.degree. to 110.degree.C, and at a high temperature ranging from 110.degree.C to 160.degree.C to produce clear patterns of red, blue and black, respectively.

EXAMPLE 12

Procedure of Example 1 was repeated except that N-(2,5-dichlorophenyl) leuco auramine was used in place of Crystal Violet Lactone, and printing was effected as in Example 1. As the result, there was obtained printings of black violet and bluish black.

EXAMPLE 13

Following the procedure of Example 6 except that N-benzoyl auramine was used in place of CVL, there were obtained printings of redish orange and yellow.

EXAMPLE 14

Following the procedure of Example 9 except that N(p-nitrophenyl)rhodamine B lactam was used in place of Malachite Green Lactone, there were obtained printings of redish pink and black green.

EXAMPLE 15

Following the procedure of Example 1 except that 8'-methoxybenzoindolinospiropyran was used in place of Crystal Violet Lactone and .beta.-naphthol was used in place of phenolic resin, there were obtained printings of red and brownish black.

Claims

We claim:

1. A method of recording by heat sensitive multicolor indication which comprises the steps of: providing a heat sensitive recording member for multicolor indication having a plurality of heat sensitive recording layers, wherein each said heat sensitive recording layer contains a material which changes color above a predetermined temperature, and wherein the respective resultant colors and predetermined temperatures are different for each said layer; bringing a heating element into contact with or near to said heat sensitive recording member; and developing a desired color on said recording member by controlling the temperature of the heating element in relation to said predetermined temperatures to change the color of a desired one or more of said layers of the recording member.

2. A method of recording by heat sensitive multicolor indication according to claim 1 in which said step of providing said heat sensitive recording member is performed by laminating said layers on a support layer in the order of their respective predetermined temperatures, wherein said predetermined temperatures increase toward said support layer.

3. A method of recording by heat sensitive multicolor indication according to claim 1 in which said color changing material of one of said recording layers comprises at least one phenol compound and a color forming material capable of reacting with the phenol compound to form a conjugated system.

4. A method of recording by heat sensitive multicolor indication according to claim 3 in which the color forming material is a basic material having a color forming group.

5. A method of recording by heat sensitive multicolor indication according to claim 4 in which the basic material is selected from the group consisting of diarylphthalides, leuco auramines, acrylauramines, .alpha., .beta.-unsaturated arylketones, basic monoazo dyes, rhodamine B lactams, polyarylcarbinols, benzoindolinospirophyrans, phthalans and spirophthalans.

6. A method of recording by heat sensitive multicolor indication according to claim 1 in which the predetermined heat sensitive temperatures range from 60.degree.C to 160.degree.C.

7. A method of recording by heat sensitive multicolor indication according to claim 1 in which plural heating elements having different temperatures are used.

8. A recording member for providing a heat sensitive multicolor indication which comprises a laminate having at least two heat sensitive recording layers, wherein each said layer contains a material which changes color above a predetermined temperature; and wherein the respective resultant colors and predetermined temperatures are different for each said layer.

9. A recording member for providing a heat sensitive multicolor indication according to claim 8 in which said heat sensitive recording layers are laminated on a support layer, and the color forming temperatures of the heat sensitive recording layers increase from the surface side to the support layer side.

10. A recording member for providing a heat sensitive multicolor indication according to claim 8 in which the material of at least one said recording layer comprises at least one phenol compound and a color forming material capable of reacting with the phenol compound to form a conjugated system.

11. A recording member for providing a heat sensitive multicolor indication according to claim 10 in which the color forming material capable of reacting with the phenol compound to form a conjugated system is selected from the group consisting of diarylphthalides, leuco auramines, acrylauramines, .alpha., .beta.-unsaturated arylketones, basic monoazo dyes, rhodamine B lactams, polyarylcarbinols, benzoindolinospirophyrans, phthalans and spirophthalans.