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
  • G03G9/0819—Developers with toner particles characterised by the dimensions of the particles

Definitions

• the invention relates to a classified electrostatographic toner material, an electrostatographic developer mixture and a development method using this mixture.
• a photoconductor is charged in electrophotography and then exposed imagewise. In the areas in which the photoconductor has been exposed, the charge is discharged or a charge recombination occurs, while the dark areas retain their electrostatic charge.
• the resulting latent electrostatic image is then developed on the photoconductor by depositing small colored particles called toner, which have a charge so that the electric fields direct them to the image areas of the photoconductor, on the photoconductor.
• a number of methods for developing latent electrostatic images using toner particles are known.
• One of these methods is called cascade development and is described, for example, in US Pat. No. 2,618,552.
• Another method is known as a magnetic brush method and is described in U.S. Patent 2,874,063.
• a two-component developer material is used in both cascade and magnetic brush development.
• the developer material consists of a mixture of small toner particles and relatively large carrier particles.
• the toner particles are held on the surface of the relatively large carrier particles by electrostatic forces which arise from the contact between the toner and carrier particles with the formation of triboelectric charges with opposite polarities on the toner and carrier.
• the developer material is contacted with the electrostatic latent image on the photoconductor, the toner particles are attracted to the latent image.
• the toner and carrier particles of the developer material are prepared and treated such that the toner particles are charged with the desired polarity and size to ensure that the toner particles are substantially attracted to the desired image areas of the photoconductor.
• the toner particles are then electrostatically transferred to a desired copy sheet, and thereafter the transferred image of the toner particles is fixed by heat and / or pressure to obtain the fixed copy of the desired image as a final product.
• the copy quality includes properties like a clear picture, i.e. a clear record of lines; uniform darkness of the image areas; Background quality, i.e. gray values or the absence of these values in the background areas and other inaccurate properties, all of which are essential for maintaining good copy quality.
• US Patent 3674736 relates to pigmented polymer particles suitable for use as toners and as developers for electrostatic processes and a method of making such toners.
• NMD average particle diameter of the order of 1 to 30 ⁇ m
• GSD geometric mean deviation of the particle size distribution
• a specific particle size distribution can be derived from these values by extrapolation and the application of a Gaussian distribution.
• German Offenlegungsschrift 2522771 describes toner particles which have essentially the same size distribution as stated in the US patent.
• a toner with a size distribution according to the number or population which contains less than 30% particles with a size below 5 ⁇ m, about 25% particles with a size between 8 and 12 ⁇ m and less than 5% particles a size over 20! Jm.
• a fine index ratio of less than 2.50 and a coarse index ratio of less than 1.50 is also specified in the published patent application.
• German patent application 2101156 discloses a toner material which has 80%, preferably 90% or more, of particles which are in a size range of approximately 5 to 25 ⁇ m. The size of the remaining particles is not characterized. In particular, this published specification contains no information about the ratio of the particles with a diameter below 5 ⁇ m to those with a diameter above 16 ⁇ m.
• the object of the present invention is to provide a classified electrostatographic toner material with which a significantly improved copy quality can be obtained compared to the toner materials according to the prior art.
• the invention also relates to an electrostatographic developer mixture and a development process using this mixture.
• the toner particles are mixed with carrier particles to form a developer mixture for use in an electrostatic copying process.
• a balance in the size distribution of the toner particles is obtained while it hits the photoconductor surface.
• toner materials according to the invention in which the ratio of particles with a diameter below 5 ⁇ m to those with a diameter above 16 ⁇ m deviates from the normal distribution, excellent copying qualities are obtained.
• a common toner used in the copier of the applicant is classified as follows: 0.8 ⁇ 0.4% by weight have a particle size of less than 5 ⁇ m, about 35% by weight have a particle size of more than 16 ⁇ m and less than 0.5% by weight % have a particle size larger than 32 ⁇ m, the median value of the particle size according to the weight distribution being 13.6 + 0.6 ⁇ m.
• a Coulter counter is used in a manner known per se to measure the size distribution.
• Example I relates to known, conventional toners; and Example 11 relates to a toner according to the present invention.
• toner About one part by weight of the toner of each example was mixed with about 99 parts by weight of a known carrier material consisting of steel balls provided with a polytetrafluoroethylene coating. Carrier materials of this type are described in US Pat. No. 3,947,271. Each mixture was tested in Applicant's commercially available 111 series copier and copies were made. Toner was added to each mixture to maintain a substantially constant toner concentration. 10,000 copies were made with the toner / carrier mixture to balance the toner particle size in the mixture. This balance of toner particle size results from the interaction of the toner, the carrier particles and the photoconductor during copying, and in fact the particle size changes until an equilibrium point is reached at a relatively constant toner concentration and the size distribution thereafter remains essentially constant.
• the copier is equipped with a filter, which should clean the returned toner. It is a physical cleaning device and the life of the device is inversely proportional to the return speed. In other words, the lower the return speed, the better the toner behavior.
• a recycled toner is the one that was deposited on the photoconductor but was not transferred to the copy sheet.
• Toner yield is the number of copies that can be made at a given optical density per pound (453.6 g) of toner used.
• the optical density is the measure for the density or the filling of the image lines on a copy after fixing.
• Fixing quality on an offset printing plate Papers for the production of an offset printing plate represent a base on which it is difficult to fix a toner image.
• the fixing quality test for offset papers of this type consists in making a copy on paper for an offset printing plate and then qualitatively assessing the adhesion of the toner image on the base.
• the toner of the example has excellent copy quality and that the toner of example I gives very poor results.
• the toner according to Example II represents a significant improvement over the toner according to Example I. In fact, background formation is much less, much less toner is recycled, a higher number of copies per pound of toner can be made, and useful offset printing plates can be made with the toner, which is not the case with the toner of Example I.
• the toner added to or used in a developer mixture should have a particle size distribution in which particles larger than 16 ⁇ m in an amount below 2% by weight, particles smaller than 5 (Lm in an amount between 9 and 15% by weight and the rest should have a particle size between 5 and 16 ⁇ m, and in which the median value of the particle size should be between 8.5 and 9.5 ⁇ m according to the weight distribution.
• the reflectance is a measure of the background quality, and particles on the background can be seen with the naked eye. By reducing the number of particles larger than 16 ⁇ m, the number of particles that can be observed with the naked eye is considerably reduced, which produces a better background quality.
• the amount returned can be reduced as indicated below. Since there are fewer large particles and the majority of the particles are of the same size, the particles will absorb electrostatic charges of approximately the same size to an increased extent. Large particles have a lower charge-to-mass ratio and are less responsive to the force fields during development and transfer; therefore, they are less prone to adhesion and are therefore easier to remove and return. It is also known that large particles have a greater tendency to form dust on the image background due to their low charge-to-mass ratio. Therefore, the lower the proportion of particles larger than 16 ⁇ m, the lower the amount returned.
• a copy is made black by the application of a layer of toner particles which are held in place by electrostatic attraction.
• the thickness of the layer is irrelevant to the blackness of the copy, as long as the area of the base that is covered is the same size. Therefore, a layer with thinner particles can be used instead of thicker particles, and the weight or volume of the toner used to image the substrate will be lower per layer of particles. By reducing the proportion of particles larger than 16 ⁇ m, the weight of the particles per layer will be reduced, resulting in a greater number of copies per pound of toner.
• the thinner particle layers of the present invention have a shorter path for heat transfer than the thicker particle layers of previously used toners. This improves the fixing quality of the toner and improves the adhesion of the toner to the base. This property is also essential when using other substrates, because it enables faster fixing than when using thicker layers of toner particles.

Landscapes

• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Developing Agents For Electrophotography (AREA)

Applications Claiming Priority (2)

Publications (2)

Family

ID=25302556

Family Applications (1)

Country Status (7)

Families Citing this family (25)

Family Cites Families (2)

• 1978
  • 1978-07-13 CA CA307,348A patent/CA1132827A/en not_active Expired
  • 1978-10-19 DE DE7878101178T patent/DE2861483D1/de not_active Expired
  • 1978-10-19 EP EP78101178A patent/EP0001785B1/de not_active Expired
  • 1978-10-25 AR AR274216A patent/AR223330A1/es active
  • 1978-10-30 JP JP53132741A patent/JPS598822B2/ja not_active Expired
  • 1978-10-31 IT IT29273/78A patent/IT1160021B/it active
  • 1978-11-01 BR BR7807248A patent/BR7807248A/pt unknown

Also Published As

Similar Documents

Legal Events