JPH01197781A - Pressure roller for fixing device - Google Patents

Abstract

PURPOSE:To reduce production of wrinkles in a transfer material by a thin PFA resin (copolymer of tetrafluoroethylene resin and perfluoroalkoxyethylene resin) layer on a soft silicone rubber layer formed on a core. CONSTITUTION:The pressure roller 1 which is faced to a fixing roller 2 is formed in such a way that a silicone rubber layer having hardness of 5-15 deg. (JISA) and a thickness of >=2mm is formed on a core, and then a PAF layer is formed within a thickness range of 20mum-1mm on the silicone rubber layer. When such roller provided with the two layers is used, no difference in the forces produced at the upper and lower surfaces of a transfer material 15 and production of wrinkle in the transfer material 15 is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a pressurized rubber roller of a fixing device that passes a transfer material between a pair of rollers to fix a toner image on the transfer material.

[Prior Art] Conventionally, heat roller fixing devices used in copying machines, laser beam printers, etc. have been made of so-called solid rubber O-5-, in which silicone rubber is formed around a core metal, or with silicone rubber formed around a core metal. A so-called sponge roller is known in which a porous silicone rubber layer is formed and a thin layer of silicone rubber is further formed on the porous silicone rubber layer.

[Problems that IA Ming is trying to solve] However, solid rollers have a large heat capacity, so they are difficult to heat, and they do not have good fixing properties in low-temperature environments.They also suffer from wrinkles that occur between a pair of rollers, especially at 110g/
Wrinkling is relatively easy to occur on thin paper and envelopes that are less than m2 in size, especially since envelopes have triple folds and are shaped like two sheets of paper stacked together, so they cannot be sandwiched between two rollers. Between the two sheets of paper, stress can easily accumulate, and wrinkles are inevitable.

On the other hand, sponge rollers have a disadvantage in that they tend to be expensive because of their complicated structure. Furthermore, with conventional sponge rollers, it is difficult to avoid the phenomenon that the toner is offset to the fixing roller, which causes image stains.

In addition, if silicone rubber is formed on the surface layer, the separation claw will often damage the rubber when it gets dirty with toner or the transfer material jams.Furthermore, if a large amount of silicone oil is applied to the surface, the silicone It has the disadvantage that the rubber swells unevenly.

However, sponge rollers have the advantage that they have a low heat capacity and are difficult to conduct heat, so they have good fixing properties at low temperatures and are less likely to wrinkle thin paper or paper cylinders than solid rollers. The reason for this is that the inside of the sponge roller is softer than the surface layer.

This is thought to be because the stress generated in the nip is easily released into the roller.

[Means for Solving the Problems] The present invention provides a pressure roller for a fixing device having an elastic layer on the outer periphery of a core metal and a fluororesin layer on the outer periphery of the elastic layer, in which the elastic layer has a hardness of 5 to 15. (Based on JIS A), the thickness is two or more layers, and the fluororesin layer is made of PFA resin (a copolymer of tetrafluoride/ethylene resin and perfluoroalkoxyethylene resin) with a thickness of 20B to 1mm. This is a fixed Go stone pressure roller characterized by the following.

Although silicone rubber, fluororubber, etc. can be used for the elastic layer of the present invention, silicone rubber is most desirable in terms of hardness and heat resistance.

Below, silicone rubber is used for the elastic layer, and PFA is used for the outer periphery.
The present invention will be specifically explained by showing an example of a pressure roller having a resin layer.

[Example] FIG. 1 shows an example of a fixing device using a rubber roller of the present invention.

In the figure, 2 is a fixing roller, which is heated by a halogen heater 8 that is an internal heat source.

Here, the fixing roller 2 is a cylindrical aluminum or stainless steel metal vibro having a thickness of 0.7 to 260 mm, and a layer 7 of PFA or PTEFE (tetrafluoroethylene resin) of 50 to 300 #L It is formed with a thickness of

A temperature measuring element 12 such as a thermistor is disposed on the surface of the fixing roller so as to slide in contact with the fixing roller in order to detect and control the surface temperature. Fusing roller 2
A release agent such as silicone oil or a surfactant is applied to the surface of the fixing roller in order to offset a certain amount of the toner, and a cleaning pad 9 is pressed against the surface of the fixing roller to clean off the offset toner. The cleaning pad 9 has a heat-resistant felt 10 (made of Teflon resin or the like containing a mold release agent) fixed by a frame 11 made of heat-resistant resin.

The pressure roller facing the fixing roller 2 is made of silicone rubber with a hardness of 5 to 15 degrees (JISA) and a thickness of 21 or more layers on a metal core 3 made of plated iron or stainless steel. Layer 4 is formed, and P is added on top of this layer.
The layer 5 of FA resin is formed to have a thickness ranging from 20 μm to 1 μm.

The toner image 1B formed on the transfer material 15, such as paper, enters between the nip of the pair of rollers and is fixed.

Reference numeral 14 is a guide for allowing the transfer material to enter between a pair of rollers, and 17 is a guide for guiding the transfer material after fixing. Reference numeral 13 denotes a separation claw for removing transfer material when it adheres to the fixing roller.

A pressure of 4 to 10 kg is applied between the two rollers, and the fixing roller is heated to 160 to 190°C. Normally, the core metal of the pressure roller is 1 strength higher and the diameter is 8
~14m1 or more is required.

Here, the PFA resin on the surface layer may be a seamless shrink tube, or may be sprayed and then melted with heat to form a uniform film.

A soft rubber with a hardness of 5 to 15@ inside the rubber roller is achieved by controlling the action of a catalyst when curing liquid silicone rubber.

One characteristic of such soft rubber is shown below.

Ratio Weight 1.07 Hardness (JIS A) 8゜ Tensile strength 23kg/c intestine 2 Permanent elongation 500% Repulsion elasticity rate: 20% An example of a method for manufacturing a roller will be described below.

The core metal is placed in a mold, and liquid silicone rubber is injected into the mold. At this time, a primer may be applied on the core metal to improve the adhesion between the rubber layer and the core metal.
When curing the silicone rubber, it is necessary to control the addition of catalyst.Furthermore, a PFA resin layer is formed on the surface of this soft silicone rubber roller.At this time, the adhesive force between the silicone rubber layer and the PFA resin layer is strengthened. In order to do this, it is recommended to use a primer or polish the surface of the silicone rubber layer. If a PFA resin shrink tube is used as the surface layer, the inner surface of the PFA tube may be roughened by polishing.

When the PFA resin layer on the surface is applied by spraying, the surface roughness is maintained at an appropriate level. In the case of a shrink tube made of PFA resin, if the surface has a roughness of about 1 to 10 μm layer, it is effective for transporting the transfer material and prevents wrinkles, etc. If it is rougher than this, toner stains tend to adhere to the tube.

In order to prevent wrinkles, the shape of this rubber roller should be made into an inverted crown when forming the silicone rubber into the core metal.This method involves forming the inner surface of the mold when forming the silicone rubber layer. The shape may be an inverted crown shape of about 0.1 mm; if the inverted crown shape is larger than this, there is a possibility that the mold cannot be removed.

The relationship between the elastic layer of this rubber roller and the PF^ resin layer on the surface depends on fixability, frequency of wrinkles, durability of the surface layer,
The degree of toner stains on the roller surface, the strength of the roller,
This cannot be achieved without considering the transportability of the transfer material.

The thickness of the surface layer is determined based on conditions such as abrasion of the surface layer due to paper passing, the strength of the roller, and an appropriate nip of about 1.5 to 4 cm.
01 to 1■ is appropriate. If it is thinner than this, there will be problems with strength, etc. If it is thicker than this, it will not be possible to get a sufficient nip, or if the rubber roller is driven, the roller will slip.

The reason why the two-layer structure described above is effective in preventing roller wrinkles is considered to be as follows.

When the transfer material is passed between a pair of rollers, there will be a slight speed difference between the driving roller and the driven roller. A "discrepancy" occurs between the two. By accumulating such "misalignment".

Wrinkles occur. Another cause of wrinkles is on
It also occurs due to the difference in axial force between the two lower rollers. The force pulled in the axial direction by the upper and lower rollers depends on the surface shape of the rollers (for example, the difference in the amount of reverse crown), the thickness of the paper, and the material, and differs between the upper and lower sides of the transfer material. Depending on the material, the difference in force between the top and bottom becomes large, eventually causing wrinkles.

This difference in force generated between the top and bottom of the transfer material is difficult to accumulate when using a two-layer roller. This is because the surface layer is hard, so the transfer material easily slides on the roller surface, and the inside is soft, so it is difficult to accumulate between the top and bottom of the transfer material. This is done by appropriately controlling the difference in force between the rollers.

In the present invention, toner offset can be prevented,
To prevent paper from wrapping around the pressure roller, PF
A conductive powder such as carbon powder or metal powder may be mixed into the resin layer.

That is, in 1 normal paper feeding, if conductive powder is not put into the rollers, the charge will be -3 kV or more, but by mixing the conductive powder, the charge can be reduced to -1 kV or less.

In this case, it is necessary to release the charge on the roller surface by means such as bringing a conductive static elimination brush into contact with the roller surface.

Furthermore, more favorable effects can be expected by making the PFA resin conductive and adding carbon powder, metal powder, or surfactant to the silicone rubber of the internal elastic layer. At this time, by making the bearing that receives the core metal a conductive bearing, the charge on the roller surface can be leaked.

The amount of carbon in the conductive powder mixed in the PFA resin layer is preferably about 0.1 to 5 wt%.

The surfactant to be added to the silicone rubber may be any fluorine-based surfactant having an alkyl group, including fluorinated alkyl esters, perfluoroalkyl polyoxyethylene ethanol, perfluoroalkyl carboxylates, and perfluoroalkylammonium. salt, perfluoroalkyl betaine, perfluoroalkylamine oxide, perfluoroalkylethylene oxide adduct,
Perfluoroalkyl phosphate esters and non-dissociable perfluoroalkyl compounds are preferred.

Below, we will discuss the results of an examination when 10,000 sheets of paper were actually passed through one layer.

The fixing device shown in Fig. 1 is incorporated into a laser beam printer that has a process speed of about 50 mm/sec and uses negatively charged toner. 2. 8° silicone rubber.
It was formed with a thickness of 95+sm, and a layer of PFA resin was further formed with a thickness of 50 μm around the outer periphery.

The cleaning pad is also impregnated with silicone oil and a fluorine-based surfactant.

In such tests, the fixing properties were good, no wrinkles occurred, and there was little toner adhesion.

In addition, there is no swelling of the silicone rubber due to the application of silicone oil, and no wrinkles occur due to cell destruction, which is the case with conventional sponge rollers.

The embodiments of the present invention have been described using a roller having a two-layer structure, with a hard thin layer on the surface and a relatively thick layer on the inside that is soft.
For example, in the internal soft silicone rubber layer, most of it is a soft silicone rubber layer, and the surface of the silicone rubber layer is Only the eight layers may be rollers made of silicone rubber with a slightly higher hardness.

[Effects of the Invention] As explained above, by forming a soft silicone rubber layer on the core bar and then forming a thin PFA layer on this layer, wrinkles are less likely to occur and durability is achieved. The rubber roller can be made into a rubber roller whose outer diameter does not change when impregnated with oil, and its structure is relatively simple, so it can be manufactured at low cost.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of a fixing device using a pressure roller according to the present invention. l...pressure roller, 2...fixing roller. 3...Core metal, 4...Elastic layer, 5...
・PFA resin layer

Claims (1)

[Claims] (1) A pressure roller for a fixing device having an elastic layer on the outer periphery of the core metal and a fluororesin layer on the outer periphery of the elastic layer,
The elastic layer has a hardness of 5 to 15 degrees (based on JISA) and a thickness of 2 mm or more, and the fluororesin layer has a thickness of 20 degrees.
A pressure roller for a fixing device, characterized in that it is made of PFA resin (a copolymer of tetrafluoroethylene resin and perfluoroalkoxyethylene resin) of μm to 1 mm.