Classifications

• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
  • G03G9/00—Developers
  • G03G9/08—Developers with toner particles
  • G03G9/087—Binders for toner particles
  • G03G9/08742—Binders for toner particles comprising macromolecular compounds obtained otherwise than by reactions only involving carbon-to-carbon unsaturated bonds
  • G03G9/08755—Polyesters

Definitions

• This invention relates to a process for forming fixed images on image receiving material, in which by means of toner powder comprising thermoplastic resin, an image is applied to a medium whose surface consists of material having a lower affinity for the softened toner powder than the image receiving material, and the toner powder is transferred by pressure to the image receiving material,the toner powder being softened by heat before and/or during passage through the pressure zone.
• a process of this kind is described inter alia in UK Patent Specification 1 245 426 and US Patent Specifications 3 554 836 and 3 893 761.
• a powder image formed, for example, on a photoconductive or magnetisable image recording material is transferred by pressure to a medium, the surface of which consists of a material having a low affinity for the softened powder, e.g. silicone rubber.
• the powder image is then transferred to image receiving material, again by application of pressure, the powder being softened by heat before and/or during passage through the pressure zone, so that it acquires viscous properties such that, as a result of the pressure exerted on it,it forms a cohesive layer which, preferably at least partially, penetrates into the image receiving material.
• the image is permanently bonded to the image receiving material.
• the powder is heated by heating the medium on which the powder image is situated before transfer to the image receiving material, and possibly by heating the image receiving material itself. In doing so the temperature is so controlled that the powder softens sufficiently to be capable of deforming and being pressed into the image receiving material at a relatively low pressure, but does not soften to such an extent that the cohesion in the powder is so reduced that powder splitting occurs upon separation of the medium and the image receiving material and some of the powder image remains on the medium.
• the toner powders hitherto proposed for use in the process according to the preamble comprise epoxy resin or polystyrene as thermoplastic resin. With such toner powders it is possible to obtain working systems but it has been found that these systems have shortcomings in practice.
• a high medium temperature of at least 130°C is required to heat the toner powder in a relatively short time to a temperature within its working range.
• the working range is the temperature range within which the temperature of the toner powder must lie to enable this powder to be transferred completely and with good adhesion from the medium to the image receiving material. This working range is limited at the bottom by the temperature at which complete transfer and good adhesion of the powder melt are still just obtained, while it is limited at the top by the temperature at which splitting of the powder melt still just does not take place.
• the disadvantage of the high medium temperature required is that the image recording material (e.g. the photoconductive element) with which the hot medium is repeatedly brought into pressure contact, is subjected to a high thermal load, which has an adverse effect on the life of the image recording material.
• the image recording material e.g. the photoconductive element
• Image receiving material comprising thermoplastic substance e.g.highly sized paper and paper pre-printed with ink comprising thermoplastic resin;
• thermoplastic substance e.g.highly sized paper and paper pre-printed with ink comprising thermoplastic resin
• the working range gradually decreases although the speed at which this takes place is lower than in the system in which only the medium is heated in order to soften the powder image.
• the invention provides a process as described in the preamble characterised in that the image is applied by means of toner powder comprising as thermoplastic resin crystalline polyester having a melting point between 50 and 100°C.
• the process according to the invention gives an adequately wide working range at much lower temperatures than hitherto established for such processes using the previously proposed toner powders.
• the result is a much lower energy consumption and a longer life for that medium.
• the medium on which the toner powder is applied imagewise is heated in order to soften the toner powder.
• the working range is then 20°C to 30°C, while its bottom limit will usually be at a medium temperature which is little higher than the melting point of the crystalline polyester being present in the toner powder.
• the process according to the invention can also be performed by applying the heat required to soften the toner powder exclusively or substantially to the image receiving material.
• the heat required to soften the toner powder exclusively or substantially to the image receiving material.
• the exact position and size of the working range are determined, not only by the properties of the toner powder itself, but also by the geometry of the device in which the process according to the invention is performed, the speed at which the device operates, the composition and hardness of the medium to which the toner powder is applied imagewise, the way in which the powder image is softened and the pressure with which the softened toner powder is transferred to the image receiving material.
• the contact time, in particular, between the medium bearing the powder image and the image receiving material is a factor which considerably governs the working range.
• the working range can readily be determined for a specific device by measuring the temperature range within which complete transfer and good adhesion of the powder image to the image receiving material are obtained.
• a reasonable indication of the position and size of the working range of a specific toner powder can be obtained by measuring the visco-elastic properties of the toner powder.
• the working range of the toner powder corresponds to the temperature range within which the loss compliance (J") of the toner powder, measured at a frequency equal to 0.5 times the reciprocal of the contact time in the device used for performing the process according to the invention, is between 10 - 4 and 10 - 6 m 2 /N.
• the visco-elastic properties of the toner powder are measured in a rheometer, the moduli G' and G" being determined as a function of the frequency at a number of different temperatures. The curves found are then reduced to one temperature, the reference temperature.
• the loss compliance (J") is calculated as a function of the frequency.
• the bottom and top limit temperatures of the working range can then be calculated by means of the WLF equation compiled from the displacement factors found during the measurements at different temperatures.
• the toner powder used in the proces according to the invention comprises crystalline polyester having a melting point between 50 and 100°C and preferably between 60 and 85 0 C.
• the melting point of the crystalline polyester is determined by melting the polyester, then cooling the melt to 20 0 C at a cooling rate of 10°C per minute and immediately thereafter re-heating the solid mass at a heating rate of 10°C per minute. During the second heating step the melting point is recorded as being the temperature at which the maximum endothermic heat effect is observed.
• the number-average molecular weight of the crystalline polyester amounts preferably at least 5,000 and most preferably is between 8,000 and 45,000.
• the powder image preferably is formed by means of toner powder comprising crystalline polyester having a number-average molecular weight between 8,000 and 25,000.
• the medium for example, consists of a roller having a diameter of from 20 to 40 mm, which roller has been provided with a silicone rubber covering some tenths of a millimetre thick, and the transfer of the powder image from the medium to the image receiving material is carried out in the nip between this roller and a similar roller which presses against the medium at a force of about 80-100 N/cm.
• the number-average molecular weight of the polyester is determined by GPC measurement with a low angular laser-light scattering detector.
• Suitable crystalline polyesters are:
• the toner powder used in the process according to the invention also comprises colouring material, which may consist of carbon black or of inorganic or organic pigment or dye.
• the toner powder may also comprise other additives, the nature of which depends on the way in which the image is appplied by means of the toner powder.
• toner powder for developing latent magnetic images, or toner powder fed, by magnetic conveying means, to an electrostatic image to be developed will also have to comprise magnetically attractable material, usually in a quantity of between 40 and 70% by weight.
• Toner powders used for developing electrostatic images may also be made electrically conductive in manner known per se by finely distributing electrically conductive material in a suitable quantity into the powder particles, or depositing it on the surface of the powder particles.
• the toner powder is used in a so-called two- component developer
• the powder particles may also comprise a charge control agent that causes the powder particles, upon tribo-electric charging, to accept a charge of polarity opposite to that of the electrostatic image to be developed.
• the known materials can be used as magnetically attractable material, electrically conductive material or charge control agent.
• the result of including fillers, such as magnetically attractable pigment or carbon black, in the toner resin is that the loss compliance of the toner powder is reduced in comparison with that of corresponding toner resin without fillers.
• the toner powder for use in the proces according to the invention comprises crystalline polyester having a relatively low number-average molecular weight of, for example, 5000 - 15000, it may be necessary to include fillers in the toner powder in order to bring the loss compliance of the toner powder to the required level.
• inert fillers such as talc, silica, clay, titanium dioxide and zinc oxide may also be included in the toner powder instead of magnetically attractable and/or electri- cally conductive fillers.
• An electrically conductive filler which has a clear influence on the loss compliance and the electrical conductivity of the toner powder even when relatively small quantities are used from 5 to 15% by weight, is carbon black having a specific area of at least 750 m 2 /g and an oil absorption between 250 and 400 ml/100 g.
• the toner powder can be prepared in known manner by melting the crystalline polyester, finely distributing the colouring material and any other additives in the melt, cooling the melt to a solid mass, and grinding the solid mass into particles of the required particle size, which is generally 8 - 30 micrometers.
• the top limit of the working range may possibly be limited not by the temperature at which splitting of the powder melt occurs, but by the temperature at which the toner powder is already softened during the pressure transfer from the image recording material to the medium and partly adheres to the image recording material. It has been found that in this case the top limit of the working range can frequently be raised by storing the toner powder for some time, e.g. 2 - 7 days, at elevated temperature, but below the softening temperature of the toner powder, e.g, at about 50 o C. During storage at elevated temperature the percentage of crystalline polyester resin in the toner powder increases but it is not clear whether the increase of the percentage of crystallisation is responsible for raising the top limit of the working range.
• the process according to the invention can be performed in the devices known for this purpose, as described, for example in UK Patent 1 245 426, US Patents 3 554 836, 3 893 761 and 4 068 937 and European Patent Application 0045102. It is preferred to heat only the medium on which the powder image is formed before transfer to the image receiving material.
• the working range is wide and is on a much lower level than the working range of the known toner powders based on polystyrene or epoxy resins.
• the medium to which the powder image formed on the photo- conductive image recording material was applied by pressure transfer consisted of a metal roller having a diameter of 25 mm, which roller had been provided with a first covering of pigmented RTV silicone rubber (RTV 200/201 made by Messrs. Possehl, West
• the working range was at a medium temperature of 65 to 85 0 C. If the toner powder was stored for 5 days at 50°C before use the working range was 70 - 100°C.
• the process according to the invention was also carried out by softening the powder image by heating both the medium and the image receiving material.
• the working range was now at a medium temperature of between 40 and 45°C and a temperature of the image receiving material between 70 and 100o C.
• a toner powder of the following composition was produced in the manner described in Example 1:
• the dispersion was heated to approximately 65°C with continuous stirring and held at this temperature for about 10 minutes. It was then cooled to room temperature and the toner particles now covered with carbon were separated from the liquid. The resulting toner powder had a resistivity of 7.10 4 ohm.m.
• the toner powder was used in the electrophotographic copying machine referred to in Example 1.
• the working range was at a medium temperature of about 70 - 125°C.
• a toner powder was prepared in the manner described in Example 1 containing:
• the toner powder was used for the magnetic brush development of electrostatic images formed on a photoconductive image recording material the photoconductive layers of which were made up as described in Example 5 of Netherlands Patent Application No. 7808418 and the support of which consisted of a plastic film covered with a layer of aluminium screened as described in European Patent Application No. 0037193.
• the electrostatic images were formed by electrostatically charging the image recording material, projecting the image of an original onto the photosensitive side of the material, and also exposing the material via its support.
• the powder images formed on the image recording material were transferred to unheated 0cE plain paper in a transfer-fixing device as used in an Océ 1900 copier.
• the working range was at a medium temperature of 70 - 95 0 C.
• Example 2 The proces of Example 1, in which only the medium was heated to soften the powder image, was repeated using a toner powder of the following composition:
• thermoplastic resin polycaprolactone having a number-average molecular weight of 5,200.
• toner powders A up to F inclusive of the composition following hereafter were prepared in the manner described in Example 1:
• the powder images formed with these toner powders on a photo- conductive image recording material were transferred to unheated Océ plain paper in a transfer-fixing device as used in an Océ 1900 copier.
• the working range for the different toner powders was appointed to be at the following medium temperatures:

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• Physics & Mathematics (AREA)
• Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Spectroscopy & Molecular Physics (AREA)
• General Physics & Mathematics (AREA)
• Developing Agents For Electrophotography (AREA)
• Fixing For Electrophotography (AREA)
• Dry Development In Electrophotography (AREA)

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Citations (4)

• 1983
  • 1983-11-30 NL NL8304098A patent/NL8304098A/nl not_active Application Discontinuation
• 1984
  • 1984-11-19 DE DE8484201666T patent/DE3470236D1/de not_active Expired
  • 1984-11-19 EP EP19840201666 patent/EP0146980B1/de not_active Expired
  • 1984-11-21 JP JP59246954A patent/JPS60134250A/ja active Granted

Patent Citations (4)

Non-Patent Citations (2)

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