CA1091970A

CA1091970A - Magnetic non-conductive one component toner with a lubricant coating and method of preparation

Info

Publication number: CA1091970A
Application number: CA268,678A
Authority: CA
Inventors: Ludek Svestka
Original assignee: Elfotec AG
Current assignee: Elfotec AG
Priority date: 1975-12-29
Filing date: 1976-12-23
Publication date: 1980-12-23
Also published as: JPS5283232A; FR2337360B1; FR2337360A1; CH623942A5; BE849894A; GB1573414A; DE2559018A1; NL7614467A; DE2559018C2

Abstract

ABSTRACT OF THE DISCLOSURE
A magnetic one- component toner for electrophotographic image generation and method of its preparation. The electrically conductive ingredient particles of the toner are imbedded in an in-sulating binder sothat the surface of each toner particle is not electrically conductive. A toner prepared according to the method described has high resistivity and good flow properties.

Description

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02 The presen-t invention relates to a magnetic 03 one-component toner and to a method of its preparation.
04 In the electrophotographic creation of images, one 05 frequently employs the so-called two-component toners. These are 06 mixtures of particles which are magnetic or can become magnetized 07 with particles of the toner proper, i.e. the material which 08 creates the tint, and the magnetic particles in such toner 09 mixture serve the purpose of bringing about a magne-tic brush. In use of such a magnetic brush, in a manner known as such, one may 11 develop the latent charge-image upon a photoconductor by means of 12 the triboelectrically charged toner particles. As toner 13 particles are released from the magnetic brush, the toner mixture 14 during such operations becomes impoverished with respect to the toner, i.e. the tinting material, and this now jeopardizes the 16 maintenance of a certain image quality. Even though provision is 17 made for replenishing of the toner proper difficulty is 18 experienced in getting the correct amount thereof.
19 In contrast to this, the so-called one-component toner is not a mixture of magnetic particles or particles which can 21 become magnetized with separate toner particles which can become 22 triboelectrically charged. On the contrary, each particle of a 23 one-component toner contains in it both the magnetic or 24 magnetizable material and the dye pigment or a dye, imbedded in an insulating binder.
26 The magnetic one-component toners for 27 electrophotographic image creation, as commonly employed, are 28 relatively of low resistivity, which means that their resistivity 29 or specific resistance i5 of the order of magnitude of 102 to 106 ohm-cm. That the resistivity is so low is due to the fact that 31 - 2 ~

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01 carbon particles, which are good conductors of electricity, 02 become imbedded into the toner particles or become deposited upon 03 the surfaces thereo~.
04 If the developed charge-image itself is used in the 05 direct process upon the photoconductor as copy, this low 06 resistivity of the toner mostly will not adversely affect the 07 quality of the image which may be produced. If, however, an 08 indirect process is used, mostly called transfer process, to 09 transfer the charge-image developed upon the photoconductor upon another photocarrier, then this low resistivity will have an 11 adverse effect as they bring about a lowering of the black-white 12 contrasts and also a lesser resolution, i.e. picture definition.
13 In or~er to render understandable what is occurring 14 here, the steps of the transfer process will be described briefly.
16 After the charge-image has become developed upon the 17 photoconductor of a copying instrument, the low resistivity 18 one-component toner, will acquire an induced charge which, for 19 example, could be positive. By applying a negative potential to a transfer roller the one-component toner is transEerred to a 21 receiving sheet which is located between the toner irnage and the 22 roller and will serve to accept the final image, the sheet 23 consisting of paper. A paper sheet is not a very good 24 insulator. The one-component toner, is low in resistivity, therefore, during the transfer process, this toner may reverse 26 its charge while in contact with the negatively charged paper 27 sheet. The negatively charged toner starts to migrate in the 28 opposition direction, back to the photoconductor. As time goes 29 on this phenomenon is repeated as often as such toner particles are present in the spacial influence region of the transfer .~

7~3 01 field. It should be kept in mind that this change of the sign of 02 the charge will occur the faster the lower the resistivity of 03 monocomponent toner.
04 ~ow this to-and-fro migration of t:he toner, even in a 05 system of electrodes at rest, is not exactly a rectilinear 06 motion. Therefore, at the effective intervals for the transfer 07 image, where the field zone is broad and because the 08 photoconductor moves and the one-component toner has low 09 resistivity, one gets a picture too blurred and too fuzzy to be acceptable. There is a loss of resolution in the transferred 11 image which is not permitted.
12 The use of a magnetic one-component toner at the 13 electrophotographic image generation, in principle, will allow 14 the construction of a copying machine which is much simp1er than the ones known heretofore, which relied upon the use of 16 two-component toners. One may set up a copying machine in which, 17 the same magnetic brush may be employed, both for the development 18 of the latent charge image, as well as for the cleaning which is 19 required after the act of transfer of the photoconductor which may be used repeatedly. However, it is noted that with the use 21 of the one-component toners of the prior art, which show a low 22 resistivity, difficulties ar encountered in actual embodiments.
23 The pictures simply are too blurred, the black-white contrast is 24 not sufficient and there is lack of resolution.
It now has been discovered that the relatively low 26 resistivity of the known magne-tic one-component toners are 27 responsible for such difficul-ties.
28 One also should keep in mind that the known 29 two-component toners with high resistivity achieve the required fluidity only by the addition of the magnetic or magne-tizable 31 _ ~ _ 01 particles. Without suc~ addition lumps would be formed.
02 With respect to the one-component toners, only those 03 with relatively low resistivity, i.e. with a resistivity of 106 04 ohm-cm or even less, will show the right flow properties, which 05 are lacking in the one-component toners with the higher 06 resistivity.
07 This now means that the present invention should solve 08 the problem of creating a magnetic one-component toner which 09 avoids the above noted disadvantages, especially, one which shows a much higher resistivity than the known magnetic one-component 11 toners and which in addition, satisfies the other requirements 12 for an electrophotographic one-component toner, i.e. one which 13 has the correct particle size distribution, where the particles 14 have the right shape, which permits long storage, gives off very little odor and definitely shows the correct flow 16 characteristics.
17 Additionally, the present invention discloses a method 18 for the production of such a magnetic one-component toner.

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L9~a3 01 Thus, the present invention is related to a magnetic 02 one-component toner for electrophotographic image generation, 03 which toner is characterized in that electrically conducting 04 ingredients of the toner, which preferably are pigment particles, 05 magnetic particles or such which may become :magneti~ed, are 06 imbedded essentially in the toner particles so that the surface of 07 each particle is essentially free from material which conducts 08 electricity and essentially is an electrically insulating binder.
09 The present invention also includes a method for the production of such a one-component toner, which method involves 11 mixing a raw crude or first toner consisting of magnetic or 12 magnetizable material with a pigment material and/or a dye and an 13 electrically insulating binder and then subjecting the mixture to 14 an aEtertreatment so as to improve its properties.
In general, the invention is a magnetic one-component 16 toner for electrographic image generation having electrically 17 conductive, attractable to a magnet, ingredients of the toner 18 imbedded within the toner particles which include binder resins so 19 that the surface of each toner particle is not electrically conductive, and having a specific resistance of at least 1013 21 ohm-cm. The toner particles are coated with a lubricant selected 22 from the group consisting of carbon black, silicon dioxide, and 23 mixtures thereof, carbon black comprising not more than 0.7% based 24 on the weight of the particle on the surface of the particle.
According to a further embodiment, the invention is a 26 method of producing a one-component toner for electrophotographic 27 image generation which comprises a series of steps, the first 28 being forming a toner mass by intimately mixing from about 30% to 29 about 70~ by weight of the mass of a resinous binder, from about ~0% to about 60% by weight of the mass of a material which i5 at L97~

01 least magnetizable selected from the group consisting of a 02 composition containing iron, a composition containing nickel and a 03 composition containing chromium, from about 1 to about 12~ of the 04 weight of the mass of pigment material, and from about 0 to about 05 2% of the weight of the mass of a dye. The toner mass is then 06 placed into a liquid state, and is cooled from the liquid state to 07 a solid state. The toner mass is then subjected to stress, and is 0~ separated by particle size to obtain particles from about 3 to 09 about 45 microns in size.
BRIEF DESCRIPTION OF A PREFERRED EMBODIMENT
11 The invention will be described by reference to several 12 typical examples.
13 The obtention of the desired properties of the new 14 magnetic one-component toner depends upon many parameters, like the selection of s~litable raw materials, the ratios in which the 16 individual ingredients become incorporated into the mixture,the 17 procedural technique and the aftertreatment of the raw toner.

19 1. The magnetic material or the material which can be magnetized:
21 iron oxide, magnetite, iron powder or other compounds of iron, 22 nickel or chromium.

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, 2. Pigment and/or dye: Carbon black and/or black iron oxide: Nigrosine Black, Sudan Deep Black and similar dyes.
3. Binders: Polystyrene, polymethacrylate and the copolymers thereof. The softening points of these resins preferably should lie within 5 the range of 70 to 120 C.
The following mixing ratios for these materials are preferred:
1. Magnetic material 40 60%;
Z. Pigment 0-1Z%;
2a. D~re 0-2%;
3. Binder (resin) 30-70%.
PROCEDURAL TECHNIQUE
In order to obtain the desired properties of the one- component toner, as outlined, the electrically conducting pigment particles and the magnetic (or magnetizable) particles must be arranged inside the toner ~5 E?articles so that they are not ~et~ined upon the surface thereof, because under such condition the toner would have an undesirable conductivity.
The methods suitable for achle~ring this result are as follows:
Method 1. Spray-drying of the toner dispersion from an aqueous or a non-aqueous dispersant.
20 Method 2. Production of the toner by melting, cooling and grinding of the toner mass which origina11y is solid.
Method 3. Aftertreatment of the raw toner which was produ~ed, either .
according to Method 1. or according to Method 2. This aftertreatment first brings about the correct particle si~e distribution. A raw toner 25 as it was produced according to Me_od 1. or according to Method Z.
namely, shows a large range of pa~ticle sizes, with the smallest pa~ticles being smaller than 1 micron, and the largest particles 7~) having diameters approximately between 5(? and 60 microns. Such a range of particle sizes would lead to a poor quality of image and also, would adversely affect the useful life of the photoconductor which comes into contact with the toner particles and will be used repeatedly.
Thus, the first aftertreatment step comprises a sorting of the particles according to their sizes, as with the use o a class-if ication machine which is known in the prior art. One tries to collect particles of the size range from 5 to Z0 rnicrons.
The next aftertreatment step consists in an improvement of the flow properties o the tqnerr The raw toner until this moment h~s rather poor flow propertiesr It ~ust is not suited for the creation o a magnetic brush whichshoulcIperformcorrectly. Thisadvantagemay be overcome by one of the ollowing after treatments:
a) The surace of the taner particles may be treated mechanically or thermally, as by an intensive agitation inside a mixer or in a classi-fic~tion machine, for ex~mple, like the MA~AC type machine manufactured by Donaldson,USA.
b) The surfaces of tlle taner particles are coated with a lubricant, like carbon black and/or silicon dioxide. However, i carbon black i9 used as a lu~ricant one must be sure that the concentration thereof will not become greater than Or7% by weLght, because otherwise, the resistivity (specifi~ resistance) of the inished toner would become decreased in an inacceptable manner.
Following are some typical examples for the one-component toners, according to the present invention:
EXAMPLE 1 r

2(~0 grams of 50~o styrerle methacrylate copolymer, 98 grams 01 magnetite, 2 grams carbon black and 100 grams toluene were 02 homogenized in a ball mill for 1 hour. The disperson obtained is 03 diluted with a mixture of toluene and methylene chloride (ratio 04 1:3) so that another dispersion is obtained which con-tains 12.5%
05 solids. This one then is spray-dried in a NIRO-Minor equipment.
06 The dry toner obtained, which essentially is made up of spherical 07 particles, is treated in a high-velocity mixer, like a Waring 08 blender, with the addition of 0.3% carbon black, for 5 minutes.
09 Next the toner is subjected to the classifying of the particles to collect particles which are between 3 and 45 microns in size, 11 although the particles having sizes between 5 and 20 microns are 12 preferred. The resulting toner flows freely, may be poured 13 easily and has a resistivity of 4.1013 ohm-cm. AEter the 1~ development of the charge-image upon the photoconductive layer of ZnO followed by a corona transfer to plain paper, a high-quality 16 copy is obtained.

18 Following the preparation of the toner, according to 19 example 1, but this time using 5% carbon black and employing styrene-methyl methacrylate, a toner was obtained which showed a 21 soft flow without the addition of a lubricant. All what was 22 necessary was the treatment in the mixer, according -to example 23 1. The resistivity was 1013 ohm-cm, and the quality of the copy 24 was good.

26 75 grams styrene me-thacrylate copolymer in suspension, 27 72 grams magnetite and 3 grams carbon black were homogenized at 28 190C under agitation. The mass of toner obtained was cooled and 29 ground to particle sizes of about 1 mm. Next, about 2~ of a wetting agent, such as Bayer Levapon* 4241 was added and the mass 31 was wet ground in a ball mill. After separation by clecantation 32 and filtration, the toner was 33 *Trade Mark 34 _ 9 _ 97~

thoroughly washed then driecl at 30-40 C. After drying, further processing of the toner was effectecl in the same manner as described in E~ample 1. This toner furnished a copy with a very good resolution, where also the large areas were correctly blackenecl.
EXAMPLE 4.
As in Example 3. However, after coarse milling to particle sizes of 1 mm this toner was finely ground, with the use of an air - j et mill.

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Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A magnetic one-component toner for electrographic image generation having electrically conductive, attractable to a magnet, ingredients of the toner imbedded within the toner particles which include binder resins so that the surface of each toner particle is not electrically conductive and having a specific resistance of at least 1013 ohm-cm.; said toner particles being coated with a lubricant selected from the group consisting of carbon black, silicon dioxide, and mixtures thereof, carbon black comprising not more than 0.7% based on the weight of the particle on the surface of the particle.

2. A magnetic one-component toner for electrophotographic image generation having electrically conductive and magnetizable ingredients which are imbedded within the toner particles having electrically insulating surfaces, and having a specific resistance of at least 1013 ohm-cm.; said toner particles being coated with a lubricant selected from the group consisting of carbon black, silicon dioxide, and mixtures thereof, carbon black comprising not more than 0.7% based on the weight of the particle on the surface of the particle.

3. A one-component toner as claimed in claim 1 in which the lubricant comprises carbon black.

4. A one-component toner as claimed in claim 1 in which the particles are coated with silicon dioxide.

5. A one-component toner as claimed in claim 1 in which the particles are essentially spherical in shape.

6. A method of producing a one-component toner for electrophotographic image generation which comprises the steps of:
(a) forming a toner mass by intimately mixing:

(i) from about 30% to about 70% by weight of the mass of a resinous binder;
(ii) from about 40% to about 60% by weight of the mass of a material which is at least magnetizable selected from the group consisting of a composition containing iron, a composition containing nickel and a composition containing chromium;
(iii) from about 0 to about 12% of the weight of the mass of pigment material; and (iv) from about 0 to about 2% of the weight of a dye;
(b) placing said toner mass into a liquid state;
(c) cooling the toner mass from said liquid state to a solid state;
(d) subjecting said toner mass to stress; and (e) separating the toner mass by particle size to obtain particles of from about 3 to about 45 microns in size.

7. The method according to claim 6 wherein the first two steps (a and b) are performed by homogenizing the ingredients of the toner mass in the presence of a liquid dispersant and diluting the dispersion therefrom, the third step (c) is performed by spray drying the diluted dispersion to obtain the solid state, the fourth step (d) is performed by mixing the mass at high velocity, and the fifth step (e) is performed by subjecting the mass to particle classification to obtain particles having a size between 3 and 45 microns.

8. The method according to claim 6 wherein the first two steps (a and b) are performed by homogenizing the ingredients of the toner mass at a temperature such that the ingredients are in liquid state, the fourth step (d) is performed by reducing the mass to particles of approximately 1 mm in size and grinding the reduced mass in the presence of about 2% by weight of a wetting agent, and the fifth step (e) is performed by removing filtering of the solid particles from liquid in the fourth step (d), washing the solid particles and drying the solid particles to obtain particles of from about 3 to about 45 microns in size.

9. The method of producing a one-component toner for electrographic image generation according to claim 6 wherein the steps are performed by:
(a) homogenizing approximately 200 parts by weight of a 50% styrene-methacrylate copolymer, approximately 98 parts by weight of magnetite, approximately 2 parts by weight of carbon black and approximately 100 part by weight of toluene, (b) diluting the homogenized dispersion with a mixture of toluene and methylene chloride in the ratio of 1 to 3 sufficient to obtain a second dispersion having approximately 12.5% solids, (c) spray drying said second dispersion to obtain a dry toner, (d) mixing said dry toner with 0.3% carbon black in a high velocity mixer; and (e) subjecting the mixture to particle size classification to obtain particles in the size range of 3-45 microns.

10. The method of producing a one-component toner for electrographic image generation according to claim 6 wherein the steps are performed by:
(a) and (b) homogenizing a suspension of approximately 75 parts per weight of styrene-methacrylate copolymer, approximately 67.5 parts by weight of magnetite and approximately 7.5 parts by weight of carbon black at a temperature of approximately 190°C, (c) cooling said mass and reducing the particles of approximately 1 mm, (d) adding 2% wetting agent and wet grinding said particles, and (e) filtering the solids from the liquid formed, washing the filtered solids and drying the solids at a temperature of approximately 30-40°C.