GB1565596A - Developer for electrostatic image and process for preparation thereof - Google Patents

Description

(54) DEVELOPER FOR ELECTROSTATIC IMAGE AND PROCESS FOR PREPARATION THEREOF (71) We, KONISHIROKU PHOTO INDUSTRY CO. LTD., a Corporation organized and existing under the laws of Japan, of 1--10, 3-Chome, Nihonbashi Muro-machi, Chuo-ku, Tokyo, Japan do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- The present invention relates to a developer for a latent electrostatic image and in more detail, to the improvements of a one-component developer for a latent electrostatic image.

Development of a latent electrostatic image can be by dry developing methods or wet developing methods. In either method, the developer is usually a two-component mixture consisting of a carrier or toner.

During development by said twocomponent developer, the toner is consumed and the carrier is not. In the dry developing methods, when in general a mixture of toner and carrier is mechanically and fully agitated, the toner will produce a charge of polarity opposite to the carrier becoming electrically charged to a specified polarity and toner particles are adhered to a latent electrostatic image to obtain a powder image.

Accordingly as there is an increase in the number of times a given sample of a twocomponent developer is used, the mixing ratio of toner to carrier varies, and there will be a corresponding change in the copy density, and thus it is necessary to replace the toner which is consumed. Further, there is the drawback that as the number of times the mechanical agitation is carried out increases, the frictional charging properties of a carrier vary, and since this change results in fogging and staining of a copied product, a fresh carrier must be substituted.

To eliminate the drawback, a onecomponent developer making a main component of only a toner and containing no carrier component has been proposed.

For example, in British Patent No. 1,282,017 there is disclosed a so-called magnetic toner in which ferromagnetic particles such as ferroferric oxide, a thermoplastic resin such as epoxy resin and an electrically conductive carbon black are combined.

Such a magnetic toner could eliminate the above-mentioned drawback of a twocomponent developer, but on the other hand, there is the drawback that because of the electrical conductivity of said magnetic toner, it is difficult to use a corona discharger in transferring it to the paper.

That is, it is because when said magnetic toner is transferred to the paper, using a corona discharger, a powder image consisting of said magnetic toner is partly or wholly destroyed and no satisfactory transferred image is obtainable.

And in Japanese Laid-open Patent Applications No. 17739/74 and No. 90335/75 there is disclosed and known an insulating toner, which is aimed at transferring a toner image to the ordinary paper. However, both applications disclose an insulating magnetic toner provided with a resinous layer on the surface. To impart charge to these magnetic toners, it is necessary to employ corona discharge, and there is the drawback that when a corona discharger is built into a developing device, the device becomes complicated and expensive, resulting in troublesome procedures and maintenance control.

To overcome this drawback, the invention provides a developer comprising only a toner, whose main components are a resin and a magnetic substance mentioned in Japanese Laid-open Patent Application 26046/76, said magnetic substance being fine particles having negative frictional charging properties and uniformly dispersed in resin, further which is composed of toner particles whose form is such that fine particles of the magnetic substance are substantially exposed on the resin surface of the toner particles which are, as a whole, electrically insulating.Said a developer comprising a toner only, with no carrier particles, does not have the drawbacks of a two-component developer consisting of the conventional toner and carrier, and since it is insulating as a whole, it avoids the drawbacks arising from the difficulty of using a corona discharger, which have previously been encountered with an electrically conductive magnetic toner. For preparing said toner there are spray dry methods using a solvent, and crush granulation methods using no solvent.

When said toner particles are used, positive and negative charges are imparted to toner particles by means of friction between particles, and aggregations of toner particles are made with a magnet to effect good development.

However, said toner has a strong electrostatic cohesiveness, so that separation of toner particles attracted to each other electrostatically is bad and fluidity is poor, as compared with a twocomponent developer, the conventional one-component electrically conductive developer and a one-component developer using an insulating magnetic toner consisting of resin-coated toner particles.

Therefore, transportability with a screw feeder, is a problem. That is, there are problems that much time is required for classification of particles into sampler of different sizes, or a toner is fused and adhered within a screw feeder or particles which have cohered are recovered without being separated to lower classification efficiency and so forth. And there are problems that a toner prepared by the crush granulation methods most widely used for preparing a toner causes remarkable pollution to an electrophotosensitive: material, when it is used in an electronic copying machine forming repeated copies, and that on repeated use, sensitivity is decreased, and ghost images occur, and formation of an image becomes poor. It could not be said that it was satisfactory.

The inventors have found that pollution of the electrophotosensitive material caused by said toner and the formation of ghost images occur when there are fine particles 1 micron or less in particle diameter on the particle surface composed of magnetic fine particles and resinous particles and when this magnetic toner is, for instance, passed through a hot air current at a temperature higher than the softening point (e.g. 100 to 500"C) of the component resin, fine particles 1 micron or less in particle diameter on the surface portion can be substantially eliminated by agglomeration.

What is important in this heat treatment step is that a state in which toner particles are well dispersed so that they do not produce aggregates of particles is preferable.

It is because these aggregates cohere by heat to produce large particles. It has been found that the tendency to agglomerate said magnetic toner can be overcome by adding 0.01 to 1 .0V by weight of hydrophobic silica particles, based on the total weight of the toner, either at the time of preparing the toner or by subsequent mixing with toner particles.

The present invention relates to a one component developer for a latent electrostatic image comprising a particulate magnetic toner whose main components are a resin and a magnetic substance uniformly dispersed in said resin and substantially exposed on said particle surface, and said magnetic toner is electrically insulating, and has a volume resistance of 10'4cm. or above wherein 0.01 to 1.0 ,; by weight, based on that total amount of the magnetic toner, of particulate hydrophobic silica is supported on the particle surface or is distributed among particles of said toner.

It is found that the decay factor of potential of the toner particles is 50 t or less.

The value of the volume resistance is obtained by placing a brass electrode plate 4 to 5 mm thick on a specimen put into a container having a brass bottom, impressing a voltage of 100 V on this electrode plate in a state where a pressure of 1 kg/cm2 is given to the electrode plate, and making the value of the current after the initial absorption current has fully decreased and its value has become substantially constant. The decay factor of potential is measured by development of a given area on the zinc oxide sensitized paper, noting the toner potential immediately after photoirradiation and then 3 minutes after photoirradiation, by a light-transmitting potentiometer, and expressing ratio between both potentials as a percentage. Further, toner adhering to a latent electrostatic image on the sensitized body will generally have a high amount of charge of 1 to 20 microcoulombs/cm3.

It is desirable that a magnetic substance to be used in the present invention be negatively or positively charged by frictional charge, preferably black in color easily dispersible in resin and chemically stable and easily made into fine particles 1 micron or less in particle diameter; and hence, magnetite (ferrosoferric oxide) is most preferable. Alternatively, it is possible to use an alloy or compound containing an element showing ferromagnetism such as iron, cobalt, and nickel, various types of ferrite, or an alloy such as manganesecopper aluminum or chromium dioxide, which does not contain a ferromagnetic element but shows ferromagnetism by appropriate heat treatment. These magnetic substances are preferably 0.1 to 1 micron in average particle diameter and the amount incorporated in the toner is preferably 30 to 60 parts by weight, based on 100 parts by weight of the toner.And resin is selected in consideration of frictional charging properties with a magnetic substance to be used, a preparing process and conditions, covering properties against the magnetic substance, easiness of fixing by heat. There can be used a homopolymeric or copolymeric styrene resin, acrylic resin, vinyl resin, epoxy resin, cellulose or substituted cellulose, polyester or polyurethane.

Further, besides a magnetic substance and resin, pigments or dye-stuffs can be mixed and used as a colorant. However, it is necessary that such conductive material as carbon black be in such small amounts that it does not damage the electrically insulating properties of the toner.

If necessary, a charge controlling agent, e.g., metallic soaps, fatty acids, alcohols and fatty amides having at least 8 carbon atoms, lubricating hydro-carbons on lubricating esters, can be incorporated in the toner.

A developer of the present invention, can be produced by a conventional process for crush granulation. For instance, the resin, any colorant, the magnetic substance and if necessary, a charge-controlling dyestuff can be preliminarily mixed, e.g. with a ball mill, and then heated and kneaded at a temperature lower than the melting point of the resin e.g., normally at 60 to 1200C, e.g. with a two-roll kneader or extruderkneader, cooled and solidified, and pulverized with a pulverizer, such as a hammer mill and a jet mill. Further, fine, powdery toner particles having a diameter of 1.0 micron or less, sticking to larger particles or to each other, and any components of the toner not incorporated into the toner particles. can be eliminated by blowing a toner into a spray drier made by Niro.Inc. together with hot air whose temperature is higher than the melting point of the resin component of said toner, thereby making such fine particles cohere to each other or to larger particles. In this step, hydrophobic silica powder is preferably added to loosen cohesion of toner particles.

Toner having a desired particle diameter can be obtained using a conventional zigzag classifier made by Alpine, Inc. And in this step also, it is desirable that hydrophobic silica powder be preferably added to minimize the cohesion of toner particles.

Further, when the cohesion of the toner after classification into particles in a desired size range is great, hydrophobic silica must be added. The content of said hydrophobic silica is in the range of 0.01 to 1.004 by weight, based on the total weight of said toner.

When the content of hydrophobic silica is less than 0.01 Sn by weight, it is hard to overcome the cohesiveness of the toner particles, and when it exceeds 1.00/, by weight, images are too pale and fogging occurs.

As hydrophobic silicas are exemplified Aerosil R-972 (made by Aerosil, Japan), D 17 (made by Degussa Co.), etc. They are preferably fine powders 100 m,u or below in particle diameter. Hydrophilic silica, which has not been subjected to hydrophobing, e.g., Aerosil 2200 ("Aerosil" is a Registered Trade Mark), has the drawback that absorption of water diminishes the volume resistance at high humidity and an image comprising a toner containing such silica is too pale.

To mix toner with hydrophobic silica, it is sufficient to place the hydrophobic silica in a mixer e.g. a V-type mixer or a tubular mixer and, while mixing operations are being continued, gradually add the toner. In this case it is necessary not to impart an excessive shear force to the mixing line and to conduct mixing operations gently.

However, simple mixing methods will take several hours up to termination of mixing, and What is more, it is difficult to perfectly break down a strongly cohered mass of hydrophobic silica.

Thus, a spherical substance such as glass, porcelain and iron 0.2 to 4 mm in diameter is added to the mixing line so as not to apply excessive shear force to the toner for the efficient mixing of these cohesive particles.

For instance, 100 parts by weight of the toner and 0.3 part by weight of hydrophobic silica are placed in a V-type mixer at the same time with 30 parts by weight of glass beads 1 to 2 mm in diameter, mixing is conducted and the glass beads are removed by passing through a sieve of 100 U.S.

Standard mesh.

According to such methods, the secondary cohered bodies of said silica fine are completely broken down after about 20 minutes and the silica is uniformly dispersed in the toner.

The one component developer for a latent electrostatic image of the present invention obtained as described above has no drawback of the conventional two component toner and carrier simply because it is a one-component developer.

without using a carrier, but has the following excellent characteristics: Because the magnetic toner particles are electrically insulating as a whole, a clear image is obtained even with the use of a corona discharger, which is held to be the drawback of a conventional electrically conductive magnetic toner. Because of the hydrophobic silica, the substantial cohesiveness of said magnetic toner can be improved, efficiency of classification into suitable possible size ranges is good, abrasion resistance of a fixed image is good, pollution of electrophotosensitive material decreases and heat resistance is enhanced.

Example 1 Epon 1004 (epoxy resin made by Shell Chemical) 240 g Styrene (90 mol%)/dimethyl- amino-ethylmethacrylate (10 mol%) copolymer 12 g Ferrosoferric oxide, powders, Mapico black BL-500 (made by Chitan Industrial Co.) 360 g Toluene 280 g Acetone 120 g After the above was dispersed 32 hours in a porcelain bar mill and granulated by spray dry methods of rotary disc type.The conditions of spray drying are as follows: Solvent Toluene 1,680 g Acetone 720 g Non-volatile solid portion 600 g Number of rotation of disc 44,000 rpm Temperature of dry air 1700C By this, ferrosoferric oxide and epoxy resin were uniformly mixed; on the particle surface ferrosoferric oxide was exposed from the surface of epoxy resin, and black spherical toner particles about 10 microns in average particle diameter, in which the whole toner is electrically insulating, were obtained. To 500 g of said magnetic toner were added 1.5 g (0.3% by weight) of hydrophobic silica fine powders (Aerosil R972) (made by Aerosil, Japan); mixed with a V-type mixer; further classified to an average particle diameter of 12 microns using a zigzag classifier. To the classified toner was further added 0.1% by weight of Aerosil R-972 to obtain a developer.

Example 2 Without being preliminarily mixed, with the use of a pressure kneader, 50 parts by weight of Hymer SBM-73 (made by San-yo Chemical), a styrene-acrylic copolymer resin haying a melting point of 1200C, 50 parts by weight of Mapico Black Bl-100 (made by Chitan Industrial Co.), 1.5 parts by weight of Oil Black BS (made by Orient Chemical), 2.0 parts by weight of zinc stearate and 1.0 part by weight of Carbon MA-100 (made by Mitsubishi Chemical) were fused and kneaded directly. Then it was cooled and pulverized, and further blown into a hot air current at 250"C in a spray dryer with the use of air nozzles to conduct heat treatment.To this was added with mixing 0.010/, by weight of Aerosil R972 (made by Aerosil, Japan) and a toner 13 microns in average particle diameter was obtained with a zigzag classifier. Said toner is not cohesive but usable as it is as a developer.

Example 3 parts by weight Copolymer having a melting point of 105"C obtained by copolymerizing diethyl aminoethylmethacrylate and styrene at a copolymerization ratio of 5:95 55 Calcium stearate 2.0 Mapico Black BL-100 (made by Chitan Industrial Co.) 45 Carbon MA-8 (made by Mitsubishi Chemical) 2 were fused and kneaded directly with the use of a pressure kneader, without being preliminarily mixed. This was cooled and pulverized and 0.5% by weight of Aerosil R972 (made by Aerosil, Japan) was added for mixing and blown into a hot air current at 240"C in a spray dryer with the use of air nozzles to conduct heat treatment. To this was added with mixing 0.2% by weight of Aerosil R-972 and the mixture was classified with zigzag classifier to obtain a toner 10 microns in average particle diameter.

On conducting development tests between said toner as obtained and the one in which further 0.1 to l.Q% by weight of Aerosil R-972 was added with mixing to said toner, it was found that the one in which the total usage of Aerosil R-972 exceeded 1.0?, by weight brought extremely poor image quality. With a developing device portion detached from a commercial copying machine of U-Bix (Registered Trade Mark) 800 type (made by Konishiroku Photo Industrial), a latent image was formed on zinc oxide sensitized paper and development was conducted with the toner obtained by the steps of said Examples 1 to 3 with the use of an electromagnetic brush developing device. After the development, charge was given and an electric source of an exposure device was switched off.Then images were transferred to ordinary paper, resulting in a good image.

Example 4 parts by weight Hymer-SBM-73 (styrene acrylic copolymer made by San-yo Chemical) 50 Mapico Black BL-100 (ferro soferric oxide made by Chitan Industrial Co.) 50 Oil Black BS (made by Orient Chemical) 1.5 Carbon Black MA-100 (made by Mitsubishi Chemical) 1.0 were mixed and kneaded directly with a pressure kneader without preliminary mixing of any of the components. The product was cooled and crushed into fine powders to obtain a developer intermediate.

To 100 parts by weight of this intermediate were added 0.1 part by weight of Aerosil R972 (Aerosil, Japan) and further 100 parts by weight of iron balls about 0.5 mm in diameter; the mixture was introduced directly in a V-type mixer, mixed for 30 minutes and then the iron balls were removed with a sieve of 100 mesh. This intermediate containing fine powders was blown into an hot air current of 230"C to conduct heat treatment. To 100 parts by weight of the thus obtained intermediate were added 0.2 part by weight of Aerosil R972 and 30 parts by weight of glass beads about 3 mm in diameter. The mixture was introduced directly in a V-type mixer and mixed for 45 minutes and the glass beads were separated with a sieve of 100 mesh.

Then, the mixture was subjected to classification with a zigzag classifier, and a powder having a particle diameter between 5,um and 25,um was separated to produce a developer for a latent electrostatic image as specimen 1.

Separately a comparative specimen (specimen 2) was obtained in the same way as above except that no Aerosil R-972 was added.

Further, separately, a comparative specimen (specimen 3) was obtained as in specimen 1, except that the amount of said carbon black MA-100 to be added was increased to 10 parts by weight and electrical resistance was thereby lowered to 1 01 Qcm .

And a further comparative specimen (specimen 4) was obtained in the same way as in specimen 3 except that no Aerosil R972 was added.

There were measured the yield, expressed as a percentage ratio by weight of the developer, which was the final product obtained by classifying specimen 1 and comparative specimens (specimens 2-4) to the intermediate after crushing, and the maximal classified amount, i.e. the ratio by volume of the amount of intermediate that was 25 ,um or above in particle diameter (which was removed by screening) to the total amount of developer; and the weight average particle diameter in ,am. The results are given in Table 1.

TABLE 1 Maximal Weight average classified particle dia.pm Characteristics Yield % amount n Specimen No. 1 75 15 13 Comparative specimen 2 45 50 13 3 71 19 15 4 70 18 15 It is found in Table 1 that specimen 1 of the present invention is high in yield and has a low maximal classified amount, but specimen 2 (containing no hydrophobic silica) has a lower yield, while the maximal classified amount, which is not useful product, greatly increases. And in a known electrically conductive magnetic toner with an increased amount of carbon as in specimens 3 and 4, there is no change in yield irrespective of the presence or absence of hydrophobic silica.

WHAT WE CLAIM IS: 1. A one component developer for a latent electrostatic image comprising A particulate magnetic toner whose main components are a resin and a magnetic substance, uniformly dispersed in said resin and substantially exposed on said particle surface, and said magnetic toner is electrically insulating, and has a volume resistance of 10'4cm. or above wherein 0.01 to 1.0% by weight, based on the total amount of the magnetic toner, of particulate hydrophobic silica is supported on the particle surface or is distributed among particles of said toner.

2. A developer as claimed in Claim 1 wherein said resin is a homopolymeric or copolymeric styrene resin, acrylic resin, vinyl resin, epoxy resin, cellulose or substituted cellulose, polyester or polyurethane.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (12)

1. **WARNING** start of CLMS field may overlap end of DESC **.

   Example 4 parts by weight Hymer-SBM-73 (styrene acrylic copolymer made by San-yo Chemical) 50 Mapico Black BL-100 (ferro soferric oxide made by Chitan Industrial Co.) 50 Oil Black BS (made by Orient Chemical) 1.5 Carbon Black MA-100 (made by Mitsubishi Chemical) 1.0 were mixed and kneaded directly with a pressure kneader without preliminary mixing of any of the components. The product was cooled and crushed into fine powders to obtain a developer intermediate.

   To 100 parts by weight of this intermediate were added 0.1 part by weight of Aerosil R972 (Aerosil, Japan) and further 100 parts by weight of iron balls about 0.5 mm in diameter; the mixture was introduced directly in a V-type mixer, mixed for 30 minutes and then the iron balls were removed with a sieve of 100 mesh. This intermediate containing fine powders was blown into an hot air current of 230"C to conduct heat treatment. To 100 parts by weight of the thus obtained intermediate were added 0.2 part by weight of Aerosil R972 and 30 parts by weight of glass beads about 3 mm in diameter. The mixture was introduced directly in a V-type mixer and mixed for 45 minutes and the glass beads were separated with a sieve of 100 mesh.

   Then, the mixture was subjected to classification with a zigzag classifier, and a powder having a particle diameter between 5,um and 25,um was separated to produce a developer for a latent electrostatic image as specimen 1.

   Separately a comparative specimen (specimen 2) was obtained in the same way as above except that no Aerosil R-972 was added.

   Further, separately, a comparative specimen (specimen 3) was obtained as in specimen 1, except that the amount of said carbon black MA-100 to be added was increased to 10 parts by weight and electrical resistance was thereby lowered to 1 01 Qcm .

   And a further comparative specimen (specimen 4) was obtained in the same way as in specimen 3 except that no Aerosil R972 was added.

   There were measured the yield, expressed as a percentage ratio by weight of the developer, which was the final product obtained by classifying specimen 1 and comparative specimens (specimens 2-4) to the intermediate after crushing, and the maximal classified amount, i.e. the ratio by volume of the amount of intermediate that was 25 ,um or above in particle diameter (which was removed by screening) to the total amount of developer; and the weight average particle diameter in ,am. The results are given in Table 1.

   TABLE 1 Maximal Weight average classified particle dia.pm Characteristics Yield % amount n Specimen No. 1 75 15 13 Comparative specimen 2 45 50 13

   3 71 19 15

   4 70 18 15 It is found in Table 1 that specimen 1 of the present invention is high in yield and has a low maximal classified amount, but specimen 2 (containing no hydrophobic silica) has a lower yield, while the maximal classified amount, which is not useful product, greatly increases. And in a known electrically conductive magnetic toner with an increased amount of carbon as in specimens 3 and 4, there is no change in yield irrespective of the presence or absence of hydrophobic silica.

   WHAT WE CLAIM IS: 1. A one component developer for a latent electrostatic image comprising A particulate magnetic toner whose main components are a resin and a magnetic substance, uniformly dispersed in said resin and substantially exposed on said particle surface, and said magnetic toner is electrically insulating, and has a volume resistance of 10'4cm. or above wherein 0.01 to 1.0% by weight, based on the total amount of the magnetic toner, of particulate hydrophobic silica is supported on the particle surface or is distributed among particles of said toner.
2. 2. A developer as claimed in Claim 1 wherein said resin is a homopolymeric or copolymeric styrene resin, acrylic resin, vinyl resin, epoxy resin, cellulose or substituted cellulose, polyester or polyurethane.
3. 3. A developer as claimed in Claim 1 or 2

   wherein said magnetic toner also contains at least one additive selected from metallic soaps, fatty acids, alcohols and fatty amides having at least 8 carbon atoms, lubricating hydrocarbons and lubricating esters.
4. 4. A developer as claimed in any preceding Claim wherein said magnetic substance is cobalt, iron, nickel, an alloy thereof, an oxide thereof, ferrite or a mixture thereof.
5. 5. A developer as claimed in Claim 4 wherein the particle diameter of said magnetic substance is 0.1 to 1 micron and said magnetic substances comprises 30 to 60 parts by weight based on 100 parts by weight of the toner.
6. 6. A developer as claimed in any preceding claim wherein said magnetic toner does not contain fine particles 1 micron or less in particle diameter.
7. 7. A developer as claimed in any preceding Claim wherein said magnetic toner contains one or more types of electric charge inhibitors, pigments and dyestuffs.
8. 8. A process for the preparation of a developer according to any of the preceding Claims which comprises uniformly mixing a powder of the magnetic substance with the powdered resin, kneading cooling, crushing and heat treating the resulting mixture, and adding the hydrophobic silica.
9. 9. A process as claimed in Claim 8 wherein said heat treating comprises placing said resulting mixture and said hydrophobic silica in an atmosphere having a temperature higher than the softening point of said resin, and the heat treated product is classified giving a product having a specified range of particle diameters.
10. 10. A process as claimed in Claim 9 wherein said temperature is 100 to 5000 C.
11. 11. A developer as claimed in Claim 1 and substantially as hereinbefore described with reference to any of the Examples.
12. 12. A process as claimed in Claim 8 substantially as hereinbefore described and with reference to any of Examples 1 to 3.