Note: Descriptions are shown in the official language in which they were submitted.
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19 Background of the Invention
This invention relates generally to size classi~
21 fied small particles, and more specifically to size classi-
22 fication of electrostatographic toner particles, and thei~
23 use adamixed with carrier particles in the electrophoto-
24 graphic copying process.
In electrophotography, a photoconductor is charged
26 and then exposed imagewise to light. In the area o~ the
27 photoconductor exposed to light, the charge dissipates or
28 decays while the dark areas retain the èlectrostatic charge.
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1 The diEference in the charge levels between the
2 areas exposed to light and the dark areas prod-lces electri-
3 cal fields therebetween. Thereafter, the resultant latent
4 electrostatic image on the photoconductor is developed by
5 depositing small colored particles, which are known as toner
6 particles having a charge so as to be directed by the electri-
7 cal fields to the image areas of the photoconductor to
8 develop the electrostatic image.
9 A number of means are known for developing the
10 latent electrostatic image by the application of the toner
11 particles. One of these is known as cascade development and
12 is described in U.S. Patent No. 2,638,552 to Wise. Another
13 means is known as the magnetic brush process. This method
14 is described in U.S. Patent No. 2,874,063 to r7reig~
In each of the cascade and magnetic brush develop-
16 ment processes, a two component developer material is
17 utilized. The developer material comprises a mixture of
18 small toner particles and relatively large carrier particles.
19 The toner particles are held on the surfaces of the rela-
20 tively large carrier particles by electrostatic forces which
21 develop from the contact between the toner and carrier
22 particles producing triboelectric charging of the toner and
23 the carrier to opposite polarities. When the developer
24 material is moved into contact with the latent electrostatic
25 image of the photoconductor, the toner particles are attracted
26 to the latent image.
27 The toner and carrier particles of the developer
28 material are specially made and processed so that the toner
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1 obtains the correct charge polarity and magnitude of charge
2 to insure that the toner particles are preferentially
3 attracted to the desired image areas of the photoconductor.
4 The toner particles are then transferred electrostatically
to the desired copy sheet, after which the transferred image
6 of toner particles is fused by heat and/or pressure to
7 produce the final product of a fused copy of the desired
8 image.
9 One of the problems encountered is to provide the
best possible quality of a final image on the copy sheet.
11 This is generally referred to as copy quality. Copy quality
12 includes such things as image clarity, i.e., clear delineation
13 of lines; uniform darkness of the image areas; background
14 quality, i.e., grayness or lack of it in the background
lS areas; and other somewhat intangible eatures that go toward
16 making a good "quality" copy.
17 Other factors that merit consideration in the
18 developing process vis-a-vis toner is the overall utilization
19 of toner per copy. Of course from an economic point of view
the less toner used per any given image the better. Also in
21 a system in which unused toner is cleaned from the air by
22 use of a filter, it is important to minimize the amount of
23 unused toner to thereby extend the life of the filter.
24 Further, when heat fusing is used it is desirable
to provide an image that will have the best possible heat
26 transfer characteristics to minimize the amount of heat
27 needed to fuse the image. This is important not only from
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1 an energy point of view, but also with more rapid heat
2 transfer by the toner, the fusing time or temperature can be
3 reduced.
4 All of these factors play important roles in
5 developing an optimum toner particle.
6 One of the principal contributing characteristics
7 of the toner particles in achieving optimum results in the
8 above-noted areas is the size and size distribution of the
9 toner particles. This fact in itself is well known, and
10 there have been several prior art proposals for various
lI systems of toner particle classification.
12 U.S. Patent No. 3,674,736 to Sherman et al discloses
13 pigmented polymer particles suitable "for use as toner...
14 and as developers for electrostatic process," and the method
15 of making such toners. This patent claims material having
16 an average particle diameter within the range of from about
17 1 to 30 microns (NMD) and a GSD of less than about 1.5. sy
18 extrapolation and the use of Gaussian distribution this can
19 be related to a particular size distribution.
~.erman Offenlegungsschrift 2,522,771 (unexamined
21 published patent application) filed May 22, 1975 and pub-
22 lished December 11, 1975 assigned to Xerox, discloses toner
23 particles which essentially have the same distribution as
24 those of the Sherman et al patent. This r~erman reference
25 discloses toner with a size distribution by number or pop-
26 ulation wherein less than 30% of the particles are less than
27 5 microns, about 25% are between 8 and 12 microns, and less
28 than 5% are greater than about 20 microns. This ~,erman
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1 reference also discloses a fine index ratio of less than
2 about 2.50 and a coarse index ratio of less than about 1.50.
3 Summary of the Invention
4 According to the present invention, a size classi-
5 fied toner material is provided which has a particle size
6 distribution as follows:
7 less than 15% by weight are greater than 16
8 microns, from 7 to 15% by weight are less than 5 microns,
9 the remainder are from 5 to 16 microns, the median particle
10 size by weight being from 8 to 12 microns.
11 The toner particles are mixed with carrier par-
12 ticles to form a developer for use in an electrostatic
13 copying process. The toner as used in a magnetic brush type
14 developer in the presence of carrier while running against
15 the photoconductor surface, will result in equilibration of
16 the toner particle size distribution and will preferably
17 generate the following size distribution:
18 Median by weight 6.5 - 9.5~
19 % by weight < 5~ 15.0 - 30.0%
~ by weight > 16~ <12.0 %
21 In even more particular aspects the size distribu-
22 tion of the particles of the original toner is as follows:
23 less than 2~ by weight are greater than 16 microns,
24 between 9 and 15% by weight are less than 5 microns, the
25 remainder are from 5 to 16 microns, the average particle
26 size being from 8.5 to 9.5 microns.
27 Description of the Preferred ~mbodiments
28 It has been found that by utilizing toner classi-
29 fied according to this invention, greatly improved results
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1 are realized as compared to conventional toner in the areas
2 of copy quality, filter life, toner utili~ation, and fusing
3 quality. Standard or conventional toner, as exemplified by
- 4 that used in IBM Series III Copier/Duplicator ls classified
5 as follows:
6 0.8~ + 0.4% by weight less than 5 microns, about
7 35% by weight greater than 16 microns, less than 0.5% by
8 weight greater than 32 microns, the median particle size by
g weight being 13.6 + 0.6 microns. In measuring size distri-
10 bution a Coulter counter is utilized in a conventional
11 manner.
12 In order to compare toners, examples of various
13 toners were prepared with size distribution as shown in
14 Table I.
Table I
16 Example IExample IIExample III
17 Median Particle Size 13.5~ 11.0~ 8.5u
by Weight
18
Percent by Weight .8% 7.1~ 11.8%
19 Less Than 5~
20 Percent by Weight 30.0~ 15.0% 1.0%
Greater Than 16
21
22 Each of the toners was formulated of a mixed resin system which
23 is used for toner in the IBM Series III Copier. Example I
24 is representative of conventional prior art toner, and
25 Examples II and III are examples of toner according to this
26 invention.
27 About one part by weight of toner of each of the
28 examples was mixed with about 99 parts by weight of a con-
29 ventional carrier, formed of a coating of PTFE on steel
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1 shot, formed according to the teaching of U.S. Patent No.
2 3,947,271. Each mixture was placed in a conventional copy
3 machine, of a type commercially available, known as IBM
4 Series III Copier/Duplicator, and copies were made. Toner
was added to each mixture to maintain an essentially con-
6 stant toner concentration. The toner/carrier mix was run
7 10,000 copies to bring the toner particle size in the mix to
8 equilibrium. This equilibration of the toner particle size
9 results from the action of the toner, carrier, and photo-
conductor during machine operations and actually alters the
11 particle size until it reaches essentially an "equilibrium"
12 point, at a relatively constant toner concentration, after
13 which the size distribution will remain essentially con-
14 stant. This break-in or equilibration of the toner is
desirable, since it provides more uniform copy quality than
16 a developer which has only the initially sized toner dis-
17 tribution. Furthermore, the copy quality achieved with an
18 equilibrated bin mix is more representative of machine
19 performance than an unequilibrated mix. The equilibrated
values for each example are shown in Table II below.
21 Table II
22 Example I Example II Example III
23 Median Particle Size 11.0~ 9.0~ 7.0
by Weight
24
Percent by Weight 14.0% 17.0% 28.0%
Less Than 5~
26 Percent by Weight 24.0% 11.0% 1.0%
Greater Than 16~
27 Following the break-in period, additional copies
28
29 were run to test the copy quality. The following tests were
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1 performed to determine the copy quality, and performance of
2 the toner.
3 Background Quality
4 The background quality of the copies was measured
5 with an S-4 Brightness Tester and Colorimeter manufactured
6 by Diano Corporation. This unit is used to measure the
7 reflectance of a surface. Results are reported as the
8 percent of change in reflectance of the paper before and
9 after making a copy. Generally a background measurement
10 resulting from a change in the reflectance of the paper of
11 more than about 1.5~ is objectionable, and is unacceptable
12 copy quality due to high background.
13 Recycle Rate
14 The copy machine is equipped with a filter to
15 clean the recycled toner. This is a physical cleaning
16 device, and the life of the device is inversely proportional
17 to the recycle rate. In other words, the lower the recycle
18 rate the better the toner performance. Recycled toner is
19 that which was deposited onto the photoconductor but not
20 transferred to the copy sheet.
21 Toner Yield
22 Toner yield is the number of copies made at a
23 given optical density per pound of toner used.
24 Optical Density
Optical density is the measurement of the "solid~
26 ness" or "fill" of the image lines on the copy sheet after
27 fusing.
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1 Fused Quality of Offset Master
2 Offset master papers are a difficult substrate on
3 which to fuse toner. The fuse quality test for offset
4 master papers consists of making copy on offset master paper
5 and then judging qualitatively the adhesion of the toner
6 image to the substrate.
7 Table III below summarizes the results of the
8 optical density, background quality, recycle rate, toner
9 yield, and fuse quality tests which were performed on copies
10 made while using toner described in the three above examples.
11 Table III
12 Example I Example II Example III
13 Optical Density 00.95 01.15 01.15
14 Background 01.20 00.90 00.90
15 Recycle Rate (mg/copy) 30.00 22.00 14.00
16 Toner Yield (copies/lb) 14.00 17.00 25.00
17 Fuse Quality of Unacceptable Acceptable Superior
Offset Master
18
19 It can be seen from the table above that Example
20 III is by far the best toner, Example II is the next best and
21 Example I is the worst. It will be noted that even Example
22 II which is at the limits of the ranges of the invention is
23 a significant improvement over the prior art toner as exempli-
24 fied in Example I. Indeed the background is significantly
25 less, there is substantially less toner recycled, a higher
26 yield of copies per pound of toner is obtained, and the
27 toner forms an acceptable offset master whereas the toner of
28 Example I does not. These benefits are even more improved
29 with the toner of Example III.
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1 These results show that toner, as initially added
2 or utilized in a developer mix should have a size distribution
3 wherein less than 15~ by weight are greater than 16 microns
4 in size, between 7 and 15% are less than 5 microns in size,
5 the remainder being from 5 to 16 microns in size and wherein
6 the median size by weight is from 8 to 12 microns. More
7 preferably the size distribution should be less than 2% by
8 weight being greater than 16 microns, between 9 and 15% by
g weight being less than 5 microns, the remainder being from 5
10 to 16 microns, with the median size by weight being from 8.5
11 to 9.5 microns. These size distributions relate to the size
12 distribution of fresh and unused toner. The equilibrated
13 size distribution after break-in should be as follows:
14 Median by weight 06.5 - 09.5
~ by weight < 5~` 15.0 - 30.0
16 % by weight > 16~ 12.0
17 The reasons for such improvement are not all
18 completely understood, but it is believed that the following -
19 factors contribute significantly.
Reflection is a measurement which indicates back-
21 ground quality and the unaided eye can see particles on the
22 background. By reducing the number of particles greater
23 than 16~, the number of particles which are observable to
24 the unaided eye is reduced significantly, thus producing a
25 better background appearance.
26 The recycle rate is believed to be reduced in the
27 following manner: Since there are fewer large particles,
28 and the particles are more nearly equal in size, the particles
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1 will receive more nearly equal electrostatic charges. Large
2 particles have lower charge-to-mass ratios and are less
3 responsive to force fields in development and transfer;
4 hence, they tend not to adhere as readily, and thus will
5 more readily be removed and recycled. Further, it is known
6 that large particles have a greater tendency to dust onto
7 the background area because of their low charge-to-mass
8 ratio. Therefore the lower the number of particles greater
9 than 16~ the lower the recycle rate will be.
With respect to more efficient toner utilization,
11 copy is made "black" by the application of a layer of toner
12 particles which is held by electrostatic attraction. The
13 depth of the layer plays no part in the "blackness" of the
14 copy as long as the area of the substrate covered is equiva-
15 lent. Thus, one can use a layer of "thinner" particles,
16 rather than "thicker" particles, and therefore the weight
17 or volume of toner used to produce an image on the substrate
18 will be less per layer of particles. By reducing the number
19 of particles greater than 16 microns in size, the weight of
20 particles per layer will be reduced, and will thus result in
21 increasing the number of copies per pound of toner.
22 With respect to fuse quality of offset printing
23 masters, the quality of the printing is greatly improved
24 with toner of the presént invention. It is believed that
25 this is rélated to better heat transfer characteristics. It
26 is theorized that the thinner layers of the particles of the
27 present invention will provide a shorter heat path than the
28 thicker particles of the prior art. This will improve the
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1 ~use quality characteristics of the toner and wi11 result in
2 better adhesion of the toner to the substrate. This property
3 is also significant with other substrates, allowing more
4 rapid fusin~ than that which is achievable with thicker
layers of toner particles.
6 It has been found that within the narrow limits,
7 outstanding copy quality is obtained, having marked improve-
8 ment over conventional prior art toner and excellent toner
9 utilization is obtained. ~owever, as the broadest limits
are approached, especially as the number of particles larger
11 than 16 microns in size approaches the upper limits, the
12 copy quality improvement over conventional particle size
~3 distributions becomes less significant. Even so, within the
14 broad limits, substantially improved toner is achieved.
Within the narrow limits, and especially with the number of
16 particles of less than 16 microns in size being less than
17 2%, outstanding copy quality is obtained.
1~ While the invention has been particularly shown
19 and described with reference to preferred enbodiments thereof,
it will be understood by those skilled in the art that various
21 changes in form and details may be made therein without
22 departing from the spirit and scope of the invention.
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