Electrophotography – Image formation – Transfer
Reexamination Certificate
2000-09-21
2002-05-07
Chen, Sophia S. (Department: 2852)
Electrophotography
Image formation
Transfer
C399S237000, C399S324000, C430S126200
Reexamination Certificate
active
06385424
ABSTRACT:
CLAIM OF PRIORITY
This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C. § 119 from an application entitled ELECTROPHOTOGRAPHIC IMAGING SYSTEM AND METHOD TRANSFERRING IMAGE THEREOF earlier filed in the Korean Industrial Property Office on the Sep. 21, 1999, and there duly assigned Serial No. 99-40669.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electrophotographic printing apparatus for printing an image developed on a photosensitive medium, and an image transferring method thereof, and more particularly, to an electrophotographic printing apparatus having a structure so that differences in peeling forces of components contributing to image transfer can be maintained within predetermined ranges, and an image transferring method thereof.
2. Description of the Related Art
In general, an electrophotographic printing apparatus such as a laser printer scans a laser beam on a photosensitive medium to form a latent electrostatic image, develops the latent electrostatic image using developing units, and transfers the developed image to a paper by means of a transfer unit. Electrophotographic printing apparatuses can be classified as wet type or dry type according to the developer usable in the apparatus.
Referring to
FIG. 1
, a general wet type electrophotographic printing apparatus includes a photosensitive medium
10
traveling along a predetermined track, laser scanning units
21
for scanning laser beams on the photosensitive medium
10
to form a latent electrostatic image, developing units
20
for developing the latent electrostatic image on the photosensitive medium
10
, for toners such as black (K), cyan (C), magenta (M) and yellow (Y), a drying unit
30
for drying a carrier covered on the photosensitive medium
10
, a transfer unit
40
for transferring an image (I) from the photosensitive medium
10
, after having been dried by the drying unit
30
, to a paper (P).
The photosensitive medium
10
includes a photosensitive belt
11
as shown in
FIG. 1
, or a photosensitive drum (not shown), or the like. The photosensitive belt
11
travels along a predetermined track while looped around a driving roller
13
, a transfer backup roller
15
, and a steering roller
17
. In the vicinity of the photosensitive belt
11
, an eraser
3
for irradiating the photosensitive belt
11
with light to lower electric potentials distributed on the photosensitive belt
11
to a predetermined level, and a charger
5
for charging the photosensitive belt
11
to raise the potential of the photosensitive belt
11
lowered by the eraser
3
to a predetermined potential are installed.
The drying unit
30
includes a drying roller
31
for contacting the surface of the photosensitive belt
11
on which an image (I) is formed, and absorbing carrier thereon, and a regeneration roller
33
for heating the drying roller
31
so as to evaporate a carrier absorbed by the drying roller
31
. Here, if the drying roller
31
peels off even a portion of an image (I) developed on the photosensitive belt
11
, the quality of the image deteriorates.
The transfer unit
40
includes a transfer roller
41
which is disposed to face the transfer backup roller
15
with the photosensitive belt
11
interposed therebetween and to which an image (I) developed on the photosensitive belt
11
is transferred, and a fuser roller
43
disposed to face the transfer roller
41
while allowing a paper (P) to pass therebetween for fixing an image transferred to the paper (P). Here, an image transferred to the transfer roller
41
is transferred to the paper (P) fed between the transfer roller
41
and the fuser roller
43
.
In the wet type electrophotographic printing apparatus configured as described above, whether or not a developed image is sequentially transferred from the photosensitive belt
11
to a paper (P) is determined by differences in the surface energies of the photosensitive belt
11
, the drying roller
31
, the transfer roller
41
, and the paper (P). That is, since toner forming an image is transferred from one member to another having a larger surface energy than the former, materials of respective members are chosen in consideration of their surface energies.
Here, the surface energy of a member functions as a factor deciding a surface adhering force F
surf
of a toner particle, the surface adhering force F
surf
being defined by the following Formulas 1 and 2.
The surface adhering force F
surf
of a toner particle is expressed as Formula 1 based on Lifshitz-van der Waals equation, as follows:
F
surf
=
ℏ
ω
R
8
π
z
2
,
(
1
)
where R is the radius of a toner particle, z is the distance between particles, and &Hslashed;&ohgr; is the surface energy of a particle.
When the value of the distance between particles z is a constant, a proportional expression shown in Formula 2 is satisfied, as follows:
F
surf
R
∝
ℏ
ω
.
(
2
)
Taking the above relation into consideration, the surface energy can be converted into a value in dyne/cm. Therefore, in the following description, a value of F
surf
/R (dyne/cm) is defined and used as a surface energy.
In addition, the surface energy defined as above is an absolute value of a selected material, and the value can be used in a useful manner if it can be measured directly, but it is very difficult to directly measure the surface energy.
On the other hand, as a method of indirectly measuring the surface energy, there is a method in which after a liquid of known surface tension is dropped on an object, the contact angle of the liquid is measured. This method was proposed by Thomas Young in 1805, and the method is well-known and referred to as Young's equation.
However, when the surface energy is measured indirectly according to such a method, there can be the following problems. First, a point for measuring a contact angle must be determined, but there can be a difference of about 1° to 2° in the contact angle due to variations in the position of the measuring point. As a result, the typical deviation in a value of a surface energy is plus or minus (±) 2 dyne/cm which is generally too large a deviation. Second, since the indirect measuring method is performed on discontinuous points, measurements can be accomplished on sampled points and cannot be performed actually on the entire surface of a roller. Therefore, it is very difficult to apply this method to mass production. Third, at least two standard liquid samples for such indirect measurement are required, and it is often difficult to manage the standard samples. That is, the standard samples are kept in a controlled atmosphere at a predetermined temperature and humidity, in a unopened state.
Also, the surface energy can be determined by measuring and comparing the peeling forces (in gram force per inch (gf/inch)) of at least two components of different materials. In this regard, the peeling force is the force required to peel an adhesive tape attached to a component such as a transfer roller or a photosensitive belt, and is a relative value depending on the type of adhesive tape used for measurement, the pressing force applied during the attachment of the tape, the operation speed of the measuring apparatus, the ambient temperature, and the like.
Referring now to
FIG. 2
is a perspective view of a peeling force measuring apparatus for describing a peeling force measuring method using the such apparatus. As shown in
FIG. 2
, the measuring apparatus
50
, for example, an IMASS SP-2000 manufactured by Instrumentor Inc. includes a stage
51
, and a load cell
53
for measuring a load.
After an object whose peeling force is to be measured, for example, a transfer roller
41
′ is installed on the measuring apparatus, an adhesive tape
55
, for example, 202 Masking Tape of 3M Corp., is taped on the surface of the transfer roller
41
′. Then, after the load cell
5
Ahn Hyung-jin
Lee Won-hyung
Shin Kyu-cheol
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