Note: Descriptions are shown in the official language in which they were submitted.
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01 BACKGROUND OF THE INVENTION
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
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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
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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
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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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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
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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.
18 MATERIALS
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
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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
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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.
17 EXAMPLE 2
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.
EXAMPLE 3
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
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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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