FR2733605A1 - Developer powder for magnetographic printing - Google Patents

Abstract

Developer powder comprising fine dry particles each having a magnetic core coated with a substance having a defined m.pt. in a first range of around 120 deg C, a powdered fluidising agent and a luminescent pigment which luminesces in a desired colour upon exposure to UV. The pigment has a m.pt. in a second range of around 120 deg C. Pref. the final material contains 5-80 wt. % magnetic particles and 40-60 wt. % thermoplastic resin. Pref. the fluidising agent is silica used in an amt. of 0.01-10 wt. %; the lubricant is pref. PTFE used in an amt. of 0.01-10 wt. %; and the conductive and contrasting agent is eg carbon black or SnO2 used in an amt. of 0.01-10 wt. %.

Description

POWDER FOR THE DEVELOPMENT OF LATENT IMAGES, METHOD FOR
MANUFACTURE AND METHOD OF USE
The present invention relates to a powder (dried ink called toner) intended for the development of latent images, as well as for its method of manufacture and use. This powder finds more particularly, although not exclusively, its application in magnetic printing machines in which the printing of characters is carried out without resorting to the impact of preformed characters or needles, on a sheet of receiving paper.

 Printing machines of this type include a recording element consisting, for example, either of a rotary drum, the most widely used solution, or of an endless belt. Magnetically sensitized areas can be formed on the surface of this element. These areas, also called magnetic latent images, correspond to the characters to be printed. These latent images are then developed, that is to say made visible, using a powder developer which, deposited on the recording element, is only attracted by the sensitized zones of the latter. this. The application of this powder developer is carried out by an applicator device, the principle of which is known, in front of which the recording element passes, after which the developer particles which have thus been deposited on the latent images are transferred to a support sheet, such as a sheet of paper for example, on which they are permanently fixed.

 Powder developers that are used in magnetic printing machines must meet many conditions. These developers must in fact be able not only to adhere to the magnetized zones of the recording element, but also to be transferred easily and entirely on the sheet of receiving paper with which they are then brought into contact. These developers must also be able to melt frankly at a relatively low temperature, so that the temperature of their fixing device on the paper can be adjusted to a value such that the risks of ignition or carbonization of the paper are eliminated. must not have a melting point that is too low, otherwise they will soften, which, by making them sticky, will make them adhere more to the recording element and thus prevent them from being transferred entirely to the paper.

In addition, it is necessary that these developers do not generate an unpleasant odor or dangerous vapors at the time when they undergo a fusion. In addition, they must be able to mix with a dye that is often forced to add to increase the contrast between the background color of the paper and that of the images on this paper.

 Furthermore, it is essential that these powder developers consist of relatively fine solid particles, in order to produce good quality images on paper. In addition, these developers, when they are melted, must neither spread on the paper, nor diffuse widely inside it, otherwise the images formed on this paper appear blurred. In addition, it is highly desirable that the particles of this developer do not clump together and charge static electricity so as not to adhere to the parts of the recording element which have not been magnetized. These powdery developers must also not be influenced by humidity. Finally, their properties should practically not undergo changes over time.

 The developing powder comprises very fine dry particles each consisting of a magnetic core coated with a coating substance, this coating substance itself being formed from at least one organic thermoplastic resin associated with a bridging agent. , for example of the silane or titanate type. The organic thermoplastic resin used has a softening point of approximately 60 C and a melting point of the order of 100 to 120 C. It is chosen from the group comprising polyamides, polystyrenes, vinyl resins, vinyl copolymers , ketone resins, acrylic resins, acrylic copolymers and cellulose esters.

 Magnetic or magnetizable particles, for example magnetic iron oxide, whose dimensions are generally less than five microns, are also incorporated into the thermoplastic resin. It should be noted, however, that other ferromagnetic minerals, such as alloys and oxides of nickel, iron or cobalt, or even ferrites, can also be used.

However, although it is preferable to have particles of magnetized material permanently, it is not excluded to use particles of soft magnetic material, such as particles of soft iron for example.

 The quantity of magnetic particles which must be added to the thermoplastic resin in order to obtain a powder of satisfactory development represents from 5 to 80% of the total weight of the final powder. The mixing of all these ingredients is carried out by heating the thermoplastic resin and the bridging agent, so as to obtain a molten mixture to which the magnetic powder is then added and dispersed in the mixture. The molten mixture is then allowed to cool until it solidifies in the mass. After which, it is ground into particles which are classified according to their average dimensions of approximately 5 to 40 microns. A small amount of polytetrafluoroethylene resin is then added to the powder particles thus obtained, this amount representing approximately from 0.001 to 10% of the total weight of the final developing powder.

 Powdered fluidifying agents can also be added to the dry powder particles to improve their flowability. A suitable thinning agent can be, for example, divided colloidal silica. This incorporation is carried out in a proportion of the order of 0.01 to 10% of the total weight of the final developing powder.

 Finally, carbon black particles can be added in a proportion of between 0.01 and 10% of the total weight of the final developing powder. These carbon black particles can be of any of the known types. It should be noted here that this addition of carbon black can be carried out indifferently, either during the operation of melting the organic thermoplastic resin, or after the operations of grinding the solid mixture resulting from the incorporation into this resin of the bridging agent and magnetic particles.

 Preferably, the magnetic particles which are incorporated into the organic thermoplastic resin are either particles permanently magnetized, or particles of a material capable of being permanently magnetized. In the latter case, the magnetization of these particles can be carried out, either during the incorporation of these particles into the organic thermoplastic resin, or after the grinding operations mentioned above. It should be noted here that this magnetization operation is carried out using a constant magnetic induction whose value is between 10 2 and 2 Teslas. Preferably, this magnetic induction has a value of the order of 0.2 Tesla.

 A first object of the invention relates to a powder for the development of latent images which makes it possible to increase the degree of security of the documents printed using this powder.

 This object is achieved by the fact that the developing powder comprising fine dry particles each consisting of a magnetic core coated with a coating substance with a melting point defined in a first range situated around 120 "C., agents powdery fluidization, a pigment incorporated to make the impression, obtained with this powder, luminescent under the action of ultra violet (UV) radiation in any shade of color is characterized in that the luminescent pigment also has a temperature of fusion in a second range located around 120 ".

 According to another characteristic, characterized in that said first and second ranges are between 80 and 200 C.

 According to another particular feature, the first range is between 100 and 120 "C.

 According to another characteristic, characterized in that the second range is between 120 and 200 "C.

 Another object of the invention is to propose a method of using this powder improving its visibility to U.V.

 This object is achieved by the fact that the developing powder comprising fine dry particles each consisting of a magnetic core coated with a coating substance with a melting point defined in a first temperature range is around 120 "C. , pulverulent fluidifying agents, a luminescent pigment incorporated into the powder to make the impression obtained from this luminescent powder under the action of ultraviolet (UV) radiation in any shade of color, is characterized in that said pigment having a temperature in a second range around 120 ° C., heating means make it possible, during the powder fixing process, to obtain a temperature ensuring the concomitance of fusion between the synthetic resins constituting the coating substance and the pigment luminescent, the latter thus forming during this fusion a film adhering strongly to the rest of the powder and making it much richer s visible to U.V.

 Another object of the invention relates to a process for manufacturing the above-mentioned developing powder.

 This process is characterized in that, after having prepared a magnetic or magnetizable toner powder from an organic thermoplastic resin of a bridging agent and magnetic particles incorporated in the resin, making a dry powder mixture from 0.01 to 30% by weight of the aforementioned luminescent pigments with a fluidizing agent, a lubricating agent and a conductive and contrasting agent, which are usually incorporated at this stage.

 According to another feature of the invention, the fluidizing agent is a silica in the proportion of 0.01 to 10% by weight of the mixture.

 According to another feature of the invention, the lubricating agent is a polytetrafluoroethylene in the proportion of 0.01 to 10% by weight of the mixture.

 According to another feature of the invention, the conductive and contrasting agent is a carbon black in the proportion of 0.01 to 10% by weight of the mixture.

 According to another particular feature, the conductive agent is tin dioxide (Sn O2) in the proportion of 0.01 to 10% by weight of the mixture.

 According to another feature of the invention, the proportion of magnetic particles is of the order of 5 to 80% and the proportion of resin is of the order of 40 to 60% by weight of the mixture.

 It is usual, in printers, to permanently fix the developing powder on paper, to use a process of melting this powder. The fusion fixing methods that can be used are fixing by oven or oven, fixing infrared radiation with halogen tubes, fixing by flash, fixing by microwave, etc. However, the synthetic resin or resins contained in the powder are the essential elements in this process of melting this powder.

Another object of the invention therefore relates to the concomitance of the fusion of the luminescent pigment and of the synthetic resins during the fusion fixing, thus the luminescent pigment during the fusion of the powder will come to form a film adhering strongly to the rest of the powder and make it much more visible to
UV

 The following examples are given to illustrate the preferred embodiments of developing powders according to the invention. In these examples, which have no limiting character, the proportions are understood by weight of the overall composition of the developing powder.

EXAMPLE 1
A developing powder is prepared with the following products
WITCO 40% EURELON 913 polyamide resin
HULS SK Aldehyde Ketone Resin 20%
Magnetite MAGNOX B 350 30%
Silane A 187 from UNION CARBIDE 2%
CABOT CORPORATION 1% CAB-O-SIL M 5 Silica
ALGOFLON L 206 polytetrafluoroethylene from MONTEDISON 2%
Carbon black VULCAN XC 72 R from CABOT CORPORATION 1%
Luminous pigment LUMILUX CD 431 by RIEDEL by HAEN 1%
After placing the polyamide resin, the ketone-aldehyde resin, the silane, the magnetic oxide and the fluorescent agent in a slow mixer and thus obtaining a fairly homogeneous mixture, this mixture is heated, for example in a twin screw extruder, so as to melt the two resins and, after melting, obtain a homogeneous molten mixture. The mixture thus formed is then crushed, then crushed and reduced into fine pulverulent particles using a very fine grinding apparatus such as a air jet mill. The powder is then sorted, for example by means of an air selector, so as to separate the powder particles whose dimensions are between 5 and 40 microns.

 The particles thus separated are then dry mixed in a fast mixer with 2% by weight of polytetrafluoroethylene, 1% by weight of colloidal silica, 1% of carbon black and the luminescent pigment Lumilux CD 431.

 The luminescent pigment has a melting point of approximately 154 "C; during a fixation by flash or by infrared radiation with halogen tubes of the impressions obtained with the developing powder described in example 1, the luminescent pigment is subjected at a temperature above 154 "C and therefore melts at the same time as the rest of the powder, forming a film which adheres strongly thereto.

 One thus obtains, after printing and fusion on a paper without optical brightener, a very accentuated red color under the action of UV radiation.

EXAMPLE 2
A developing powder is prepared with the following products
PLIOTONE PTR 6953 styrene-acrylic resin from GOODYEAR 60%
Magnetite MAGNOX B 350 30%
Silane A174 from UNION CARBIDE 2%
CABOT CORPORATION 1% CAB-O-SIL M 5 Silica
ALGOFLON 81 G Polytetrafluoroethylene from MONTEDISON 2%
Carbon black VOLCAN XC 72 R from CABOT CORPORATION 2%
Luminous pigment LUMILUX CD 431 by RIEDEL by HAEN 1%
The luminescent pigment is, as in Example 1, added in a rapid mixer.

 This luminescent pigment has a melting point of approximately 154 ° C., during fixing by hot rollers of the prints obtained with the developing powder described in example 2, the luminescent pigment is subjected to a temperature above 154 "C and therefore enters fusion at the same time as the rest of the powder, forming a film which adheres strongly thereto.

 One thus obtains, after printing and fusion on a paper without optical brightener, a very accentuated red color under the action of UV radiation.

EXAMPLE 3
A developing powder is prepared with the following products
Polyamide resin EURELON 913 from WITCO 30%
HULS SK Aldehyde Ketone Resin 20%
Magnetite MAGNOX B 350 40%
DU PONT TYZOR TPT Titanate 2%
CABOT CORPORATION 1% CAB-O-SIL M 5 Silica
ALGOFLON L 206 polytetrafluoroethylene from MONTEDISON 2%
Carbon black VOLCAN XC 72 R from CABOT CORPORATION 1%
Luminescent pigment NFS LUNAR YELLOW by FIESTA 5%
The luminescent pigment is as in Example 1 added in the rapid mixer.

This luminescent pigment has a melting point of approximately 185 "C; during a flash fixation of the prints obtained with the developing powder described in Example 3, the luminescent pigment is subjected to a temperature above 185" C and therefore melts at the same time as the rest of the powder, forming a film which adheres strongly thereto
One thus obtains, after printing and fusion on a paper without optical brightener, a very accentuated yellow color under the action of UV radiation

EXAMPLE 4
A developing powder is prepared with the following products
Polyamide resin E 93004 from CRAY-VALLEY 30%
HULS SK Aldehyde Ketone Resin 30%
Magnetite MAGNOX B 350 24
Silane A 187 from UNION CARBIDE 2%
CABOT CORPORATION 1% CAB-O-SIL M5 Silica
MONTEDISON ALGOFLON L 206 polyetrafluoroethylene 2%
Carbon black VOLCAN XC 72 R from CABOT CORPORATION 1%
Luminescent pigment E LUNAR YELLOW BY FIESTA 10%
The luminescent pigment is, as in the previous examples, added to the rapid mixer.

This luminescent pigment has a melting point of approximately 134 "C; during a flash fixation of the prints obtained with the developing powder described in Example 4, the luminescent pigment is subjected to a temperature above 134oC and therefore melts at the same time as the rest of the powder, forming a film which adheres strongly thereto
One thus obtains, after printing and fusion on a paper without optical brightener, a very accentuated yellow color under the action of UV radiation

EXAMPLE 5
Polyamide resin EURELON 913 from WITCO 30%
HULS SK Aldehyde Ketone Resin 27%
Magnetite MAGNOX B 350 30%
Silane A 187 from UNION CARBIDE 2%
DEGUSSA AEROSIL 200 silica 1%
ALGOFLON L 206 polytetrafluoroethylene from MONTEDISON 2%
Carbon black VOLCAN XC 72 R from CABOT CORPORATION 1%
LUMINOLAC ORANGE RADIANA luminescent pigment 6%
The luminescent pigment is, as in the previous examples, added to the rapid mixer.

This luminescent pigment has a melting point of approximately 132 "C; during a flash fixation of the prints obtained with the developing powder described in Example 5, the luminescent pigment is subjected to a temperature above 132" C and therefore melts at the same time as the rest of the powder, forming a film which adheres strongly thereto
One thus obtains, after printing and fusion on a paper without optical brightener, a very accentuated orange color under the action of UV radiation.

EXAMPLE 6
KAO polyester resin Z2 50%
BAYER MAG 1730 magnetite 40%
Silane A 174 from UNION CARBIDE 2%
CABOT CORPORATION 1% CAB-O-SIL M5 Silica
Polytetrafluoroethylene MP 1000 from DU PONT 1%
Carbon black CORAX L from DEGUSSA 1%
INVISIBLE FLUO BLUE PETREL 6% luminescent pigment
The luminescent pigment is, as in the previous examples, added to the rapid mixer.

This luminescent pigment has a melting point of approximately 198 "C; during a flash fixation of the prints obtained with the developing powder described in Example 6, the luminescent pigment is subjected to a temperature above 198" C and therefore melts at the same time as the rest of the powder, forming a film which adheres strongly thereto
One thus obtains, after printing and fusion on a paper without optical brightener, a very accentuated blue color under the action of UV radiation

 In the various examples above, the carbon black added as a conducting element can advantageously be replaced in the same proportions by another conducting agent such as, for example, a tin dioxide (Sn O2) which is white in color, thus avoiding the absorption of ultra violet light. This Sn 2 conductive element thus improves the luminescence of the powder thus obtained.

Claims (11)

 1 Development powder comprising fine dry particles each consisting of a magnetic core coated with a coating substance with a melting point defined in a first range situated around 120 "C, powdery fluidizing agents, a pigment incorporated for make the impression, obtained with this powder, luminescent under the action of ultraviolet (UV) radiation in any shade of color, characterized in that the luminescent pigment also has a melting temperature in a second range located around 120 ".  2. Powder according to claim 1, characterized in that said first and second ranges are between 80 and 200 C.  3. Powder according to claim 1 or 2, characterized in that the first range is between 100 and 120 "C.  4. Powder according to claim 1 to 3, characterized in that the second range is between 120 and 200 "C.  5. Method for using the developing powder according to one of claims 1 to 4 comprising fine dry particles each consisting of a magnetic core coated with a coating substance with a melting point defined in a first range of temperature is around 120 "C, powdery fluidizing agents, a luminescent pigment incorporated into the powder to make the impression obtained from this luminescent powder under the action of ultraviolet (UV) radiation in any shade of color, characterized in that, said pigment having a melting temperature in a second range situated around 120 ° C., heating means make it possible, during the powder fixing process, to obtain a temperature ensuring the concomitance of melting between the synthetic resins constituting the coating substance and the luminescent pigment, the latter thus forming during this fusion a film adhering strongly to the rest of the louse dre and making it much more visible to U.V.  6. Method for preparing the developing powder according to one of claims 1 to 4, characterized in that it consists, after having prepared a magnetic or magnetizable toner powder from thermoplastic organic resin of a bridging agent and magnetic particles incorporated into the resin, to make a dry powder mixture of 0.01 to 30% by weight of the aforementioned luminescent pigments with a fluidizing agent, a lubricating agent and a conductive and contrasting agent, which are usually incorporated at this stage.  7. Method according to claim 6, characterized in that the fluidizing agent is a silica in the proportion of 0.01 to 10% by weight of the mixture.  8. Method according to one of claims 6 or 7, characterized in that the lubricating agent is a polytetrafluoroethylene in the proportion of 0.01 to 10% by weight of the mixture.  9. Method according to one of claims 6 to 8, characterized in that the conductive and contrasting agent is a carbon black in the proportion of 0.01 to 10% by weight of the mixture.  10. Method according to one of claims 6 to 8, characterized in that the conductive agent is tin dioxide (Sn O2) in the proportion of 0.01 to 10% by weight of the mixture.  11. Method according to one of claims 6 to 10, characterized in that the proportion of magnetic particles is of the order of 5 to 80% and the proportion of resin is of the order of 40 to 60% by weight of the mixture.