Low-hardness silicone rubber fixing rolls

Details Low-hardness silicone rubber fixing rolls Low-hardness silicone rubber fixing rolls

1998-10-06

2001-05-15

Nakarani, D. S. (Department: 1773)

Stock material or miscellaneous articles

Structurally defined web or sheet

Including components having same physical characteristic in...

C428S036900, C428S036910, C428S213000, C428S421000, C428S448000, C428S450000

Reexamination Certificate

active

06231954

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to heat fixing rolls for use in plain paper copiers (PPC), laser beam printers (LBP), and facsimile machines and more particularly, to low-hardness silicone rubber fixing rolls having a silicone rubber layer on a mandrel and an organic resin layer having a low surface energy thereon.
2. Background Art
Fixing rolls having a silicone rubber layer on the outer surface of a metal mandrel and a fluoroplastic resin layer or fluoroplastic latex layer thereon are often used in various business machines such as copiers, laser beam printers, and facsimile machines because the resin layer has superior toner release properties. With the recent speedup of copiers, laser beam printers, and facsimile machines, the fixing device is required to insure a sufficient fixing width or nip width to increase the time taken for fixation. To this end, attempts have been made to reduce the hardness of rubber material to a level unmeasurable with a JIS hardness meter. However, although the rubber material on the fixing roll is made thin, an appropriate nip width is not obtained even under a low nip pressure because of the high resilience of rubber.
Low-hardness rolls at a hardness level unmeasurable with a JIS hardness meter have the problem that the durable adhesion of fluoro-resin covering the outer surface of silicone rubber is adversely affected if silicone rubber experiences substantial hardness variations under different curing conditions (primary vulcanization conditions).
SUMMARY OF THE INVENTION
Therefore, an object of the present invention is to provide a low-hardness fixing roll in which an appropriate nip width is obtained even under a low nip pressure and even when the silicone rubber layer is made thin and which is improved in durable adhesion between the silicone rubber layer and the outer fluoro-resin layer. The term “fixing roll” used herein encompasses both a fixing roll and a pressure roll also known as backup roll.
The present invention is directed at a low-hardness silicone rubber fixing roll comprising a cylindrical solid or hollow metal mandrel, a silicone rubber layer surrounding the outer surface of the mandrel, and an organic resin layer having a low surface energy formed on the outer surface of the silicone rubber layer. The silicone rubber layer is formed by curing to the mandrel an addition reaction curing type liquid silicone rubber composition which cures into silicone rubber having a resilience of up to 30% according to JIS K-6301. The liquid silicone rubber composition is preferably such that when it is cured under primary vulcanization conditions including a temperature of 100 to 200° C. and a time of 10 to 30 minutes, the cured silicone rubber has a maximum hardness and a minimum hardness, the difference between the maximum hardness and the minimum hardness being up to 10 Ascar CSR2 units. Then the fixing roll provides an appropriate nip width even under a low nip pressure and even when the silicone rubber layer is made thin.
Typically, the liquid silicone rubber composition comprises as essential components,
(A) 100 parts by weight of an organopolysiloxane containing per molecule at least two aliphatic unsaturated hydrocarbon groups each attached to a silicon atom only in side chains of the molecule, the content of siloxane units containing the aliphatic unsaturated hydrocarbon groups being 0.05 to 5 mol %,
(B) an organohydrogenpolysiloxane having at least three hydrogen atoms each directly attached to a silicon atom per molecule and represented by the following general formula (1):
wherein R
1
is a substituted or unsubstituted monovalent hydrocarbon group, letters m and n are integers of at least 1, in such an amount that 0.1 to 3.0 mol of the hydrogen atoms directly attached to silicon atoms (i.e., SiH groups) in component (B) are available relative to 1.0 mol of the aliphatic unsaturated hydrocarbon groups attached to silicon atoms in component (A),
(C) a catalytic amount of a platinum catalyst, and
(D) about 5 to 300 parts by weight of a filler.
DETAILED DESCRIPTION OF THE INVENTION
The low-hardness silicone rubber fixing roll of the invention includes a cylindrical metal mandrel. A silicone rubber layer is formed on the outer surface of the mandrel by curing an addition reaction curing type liquid silicone rubber composition thereto, the cured silicone rubber having a resilience of up to 30% according to JIS K-6301. An organic resin layer having a low surface energy is formed on the outer surface of the silicone rubber layer.
The metal mandrel of the fixing roll may be formed of any desired metal material such as iron, aluminum or stainless steel. It may be surface treated with a primer. The mandrel is cylindrical and either solid or hollow.
The silicone rubber layer on the outer surface of the metal mandrel is formed by curing to the mandrel an addition reaction curing type liquid silicone rubber composition which cures into a silicone rubber having a resilience or rubbery rebound of up to 30%, preferably 5 to 25%, more preferably 10 to 20%, according to JIS K-6301. When a liquid silicone rubber composition yielding a resilience of more than 30% is used, an appropriate nip width is not obtained even under a low nip pressure, which is undesirable for roll performance in high-speed fixing devices. A resilience of less than 5% implies that the roll (silicone rubber) once deformed under a nip pressure restores its original shape at a slow rate, which can result in unevenly fixed images in the case of high-speed fixing devices.
In order to manage the hardness of low-hardness rolls at a level unmeasurable with a JIS hardness meter, it is recommended to measure the hardness by an Ascar CSR2 hardness meter which is disclosed in Journal of Japanese Rubber Society, 6, 7 (1996), 516 and manufactured by Kobunshi Keiki K.K. The liquid silicone rubber composition is preferably such that a hardness change under curing conditions (primary vulcanization conditions) is not greater than ±5 Ascar CSR2 units. That is, when it is cured under primary vulcanization conditions including a temperature of 100 to 200° C. and a time of 10 to 30 minutes, the difference between a maximum hardness and a minimum hardness of the cured silicone rubber is not greater than 10 Ascar CSR2 units. If the hardness difference is greater than 10 units, the silicone rubber does not have the desired hardness and does not durably bond with an organic resin layer having a low surface energy such as fluorocarbon resin or fluorocarbon latex.
The liquid silicone rubber composition from which the silicone rubber layer is formed is preferably a composition comprising
(A) 100 parts by weight of an organopolysiloxane, having at least two aliphatic unsaturated hydrocarbon groups attached to silicon atoms in a molecule,
(B) an organohydrogenpolysiloxane having at least two hydrogen atoms each directly attached to a silicon atom per molecule in an amount to give 0.1 to 3.0 mol of the hydrogen atoms directly attached to silicon atoms (i.e., SiH groups) in component (B), relative to 1.0 mol of the aliphatic unsaturated hydrocarbon groups attached to silicon atoms in component (A),
(C) a catalytic amount of a platinum catalyst, and
(D) about 5 to 300 parts by weight of a filler.
Component (A) or aliphatic unsaturated hydrocarbon group-bearing organopolysiloxane is a well-known organo-polysiloxane commonly used as the base of conventional addition reaction curing type liquid silicone rubber compositions. The organopolysiloxane used herein preferably has a viscosity of 100 to 100,000 centipoise (cp) at room temperature (25° C.) and is represented by the following average compositional formula (2):
R
a
SiO
(4−a)/2
  (2)
wherein R is a substituted or unsubstituted monovalent hydrocarbon group and letter is a positive number of 1.9 to 2.4.
In formula (2), R is preferably selected from substituted or unsubstituted monovalent hydrocarbon groups having 1 to 12 carbon atoms, more preferably 1 to 8 carbon atoms. At least two of the

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