JPH0259468B2 - - Google Patents

Description

[Detailed description of the invention]

TECHNICAL FIELD The present invention relates to a heat roller fixing device for an electrophotographic copying machine, and specifically, a heat roller comprising a conductive core material and an offset prevention layer laminated thereon, and a conductive core material that is in pressure contact with the heat roller. A heat roller fixing device consisting of a pressure roller having an insulating layer formed thereon, and a copy paper holding a toner image formed by an electrophotographic method being passed between the two rollers to fix the toner image on the copy paper. In particular, the present invention relates to a heat roller fixing device in which no anti-offset agent is applied to the surface of the heat roller. Prior Art This type of heat roller fixing device is characterized by the fact that the copy paper does not get smeared by the offset preventive agent and has a good texture after fixing, compared to a device that uses an offset preventive agent. Since this is not necessary, there are advantages such as simplifying the fixing device and reducing costs. However, on the other hand, it has the disadvantage that offset is very likely to occur. In the past, various methods have been proposed to prevent this offset, such as using a heating roller laminated with a fluororesin having excellent mold releasability and heat resistance as an offset prevention layer to improve the releasability between the heating roller and the toner. Alternatively, in order to improve the releasability of the toner itself, various efforts have been made to select the binder resin or add a release agent such as low molecular weight polypropylene, but offset cannot be prevented unless an offset inhibitor is used. That was difficult. Furthermore, the heating roller, which is laminated with fluororesin as an offset prevention layer, has a surface that can be used for copying paper, separation claws, etc.
There is a problem of wear and damage caused by contact with the temperature control element. In particular, when the offset prevention layer is made thinner for the purpose of improving heat conduction, the heating roller core bar is exposed, leading to an extreme decrease in mold release properties.
This causes an offset. Therefore, the offset prevention layer needs to have a thickness of 30 to 40 microns, but in this case there is a problem that heat conduction is poor and the stability of the heating roller surface temperature is poor. Conventionally, for the purpose of improving wear resistance, there are products in which pigments are mixed into fluororesin, or products in which fluororesin powder is mixed into a binder with good wear resistance.
All of them had the disadvantage that they had poor releasability as a fixing roller and were prone to offset. Purpose The present invention solves the above-mentioned problems in a heating roller in which a fluororesin having excellent mold releasability and heat resistance is laminated as an anti-offset layer. The purpose is to provide a heating roller. In order to achieve the above object, the present inventor has developed a heating roller in which an offset prevention layer made of a fluororesin is formed on a conductive core material directly or through a primer layer (adhesive layer), for example, by blasting or the like. In a fixing device that combines a press roller with an insulating layer formed on a conductive core material, when copy paper holding a positively charged toner image is fixed, an offset phenomenon occurs only in the initial period, and to some extent On the other hand, when copying paper holding a negatively charged toner image is fixed, the offset phenomenon does not occur only in the initial period, but after a certain amount of time it begins to occur, and the causes are as follows:
Both rollers are charged due to friction or frictional contact between the heating roller and the pressure roller and between each roller and the copy paper, and the heating roller starts to be negatively charged at the beginning, but after a certain period of time, it becomes positively charged, contrary to what it was before. It was confirmed through experiments that the charging and offset phenomenon was caused by electrostatic adsorption of toner. Therefore, in a heat roller fixing device of the type that uses a heating roller laminated with a fluororesin as an offset prevention layer and does not apply an offset prevention agent to the surface of the heating roller, in order to prevent offset, at least the heating roller must be It is necessary to either not charge the charged toner to be used until it is electrostatically attracted, or to charge it to the same polarity as the charged toner, preferably to hardly charge it at all. At the same time, in order to improve wear resistance and thermal conductivity, the additive for offset prevention that satisfies the above relationship must have excellent wear resistance and thermal conductivity. thing. Summary of the Invention The present inventor has focused on the above-mentioned points, and as a result of various researches, the present inventor has added 9 to 25% by weight, preferably 12 to 20% by weight, of carbon fiber to the offset prevention layer made of fluororesin.
Furthermore, the above-mentioned wear resistance can be achieved by adding fluorocarbon in a total amount of less than 30% by weight, preferably 28% by weight or less, and preferably less than 28% by weight. They have found that this can be significantly improved, and have completed the present invention. The heat roller fixing device according to the present invention includes a heating roller formed by laminating an offset prevention layer on a conductive core material, and a pressure roller formed by forming an insulating layer on the conductive core material and in pressure contact with the heating roller. In a hot roller fixing device which fixes the toner image onto the copy paper by passing the copy paper holding the toner image between the two rollers, the offset prevention layer preferably contains 9 to 25% by weight of carbon fiber. is 12-20
It is further characterized in that it is made of a fluororesin containing fluorocarbon in a total amount of less than 30% by weight, preferably 28% by weight or less, in addition to carbon fibers. The material for the conductive core material of the heating roller and pressure roller is aluminum, aluminum alloy,
Iron alloys such as stainless steel and other metals are used. The primer layer is formed of a heat-resistant primer containing fluororesin, etc., which is commercially available as an adhesive undercoat for the metal materials such as iron alloys and aluminum alloys. Primer) 459-882, MPG-RD manufactured by Mitsui Fluorochemicals, etc. are used. The offset prevention layer can be made of a material such as tetrafluoroethylene resin (PTFE), tetrafluoroethylene-perfluoroalkoxyethylene copolymer resin (PFA resin), or tetrafluoroethylene-hexafluoropropylene copolymer resin (FEP resin). It is formed mainly from a fluororesin with excellent moldability and heat resistance, and in this fluororesin,
Contains carbon fiber with excellent wear resistance, thermal conductivity, electrical conductivity, and flexibility. Specifically, Kureka M-107T or Kureka M-201S manufactured by Kureha Chemical Industry Co., Ltd.
Mitsubishi Rayon Pyrofil NR7003 or PyroFil EHMS10STA, Toray Trading Card T008A
Or trading card M40, Beshuite made by Toho Rayon Co., Ltd.
1000, Vesphite HM-6000, and Carbon GF-20 or GF-3 manufactured by Nippon Carbon Co., Ltd. can be used. The carbon fiber is added to the fluororesin in an amount of 9 to 25% by weight, preferably 12 to 20% by weight, but if it is less than 9% by weight, the effect of adding it will be weak, and if it exceeds 25% by weight, it will release from the mold. This is because their gender is on the decline. Furthermore, it has better wear resistance than carbon fiber, and
It has better mold release properties than fluorine resins, and is an inorganic polymer compound produced by a chemical reaction between fluorine and carbon or graphite, and contains fluorinated carbon represented by the molecular formula (CF)n. Specifically, carbon fluoride manufactured by Daikin Industries, Ltd., carbon fluoride manufactured by Nippon Carbon, etc. can be used. This fluorinated carbon is added to the fluororesin together with the above-mentioned carbon fibers, and the amount added together with the carbon fibers is less than 30% by weight, preferably less than 28% by weight. This is because if fluorocarbon is added to such an extent that the total amount is 30% by weight or more, the wear resistance effect will not be observed and will actually decrease. The insulating layer of the pressure roller is formed of a commonly used material exhibiting rubber-like elasticity, such as natural rubber or synthetic rubber. Example An example of the present invention will be described below. The heat roller fixing device according to the present invention shown in FIG. 1 consists of a heat roller 1 and a pressure roller 6. The heat roller 1 forms a primer layer 3 on the surface of a metal roller 2 as a conductive core material by a conventional method. Then, the offset prevention layer 4 is coated with a fluororesin containing 9 to 25% by weight of carbon fiber or fluorocarbon in which the sum of carbon fibers and carbon fibers is less than 30% by weight.
While laminating the metal rollers 2, a heater 5 is installed inside the metal roller 2.
It is rotatably driven by a motor (not shown). The pressure roller 6 is constructed by forming an insulating layer 8 on the surface of a metal roller 7 as a core material, and is brought into contact with the heating roller 1 . The heating roller 1 is heated by the heater 5 during operation of the fixing device, and the temperature thereof is appropriately set at 140 to 120° C. depending on the type of toner used. In the figure, 9 is a separation claw, 10 is a guide plate, and 11 is a paper discharge roller. The fixing device configured as described above supplies a copy paper B holding a positively or negatively charged toner image A formed by electrophotography between both rollers 1 and 6, and passes the copy paper B while being pinched to form the toner image A. When it is fixed on copy paper B, copies without offset can be obtained from the initial stage of fixing, and it has excellent abrasion resistance and thermal conductivity. This will be explained in detail in the following experimental example. Experimental Example 1 Using an aluminum roller as a conductive core material, a 6 μm thick primer layer of primer paint (MPG-RD manufactured by Mitsui Fluorochemicals) was formed on the roller surface using a conventional method, and a powder layer was further applied on the roller surface. PFA resin made by Kureha Chemical Industry Co., Ltd. Creca M-
107T (fiber length 50μ, diameter 7-10μ) carbon fiber and Daikin Industries, Ltd. fluorocarbon (CF) n (average particle size
1μ) in the proportions shown in the composition column of Table 1 (Experiments Nos. 1 to 26) was baked and coated, and then layered to a thickness of 30 to 40μ by polishing to form an offset prevention layer and applied to a heating roller. was manufactured. Separately, a pressure roller was manufactured by coating the surface of an aluminum roller with commercially available silicone rubber, and these rollers were used to construct the heat roller fixing device shown in FIG. Using this device, a positively charged toner image (toner: mainly composed of styrene/acrylic resin, average particle size 14μ, charge amount 10-12μc/
g) and copy paper holding a negatively charged toner image (toner: mainly composed of styrene/acrylic resin, average particle size 14μ, charge amount 8 to 10μc/g). 170℃,
Fixing is performed at a rate of 12 sheets per minute, and positively charged toner images are fixed after 5 minutes of continuous paper feeding, and negatively charged toner images are fixed after 20, 30, or 60 minutes of continuous paper feed. The offset properties of either of these were investigated. The results are shown in FIG. In addition, if there is a temperature difference between the objects in contact during contact charging, there is a phenomenon in which the charging polarity is affected by the temperature difference, so the temperature of the heating roller is varied within a range that includes the temperature range normally used. The offset characteristics at each temperature are illustrated. In FIG. 2, the shaded area shows the case where the degree of offset is heavy, the horizontal line part shows the case where the degree is light, and the plain area shows the case where there is no offset. As is clear from FIG. 2, when carbon fiber is added to the PFA resin of the offset prevention layer, the offset property is improved, but the rate of improvement in the offset property differs depending on the amount added. That is, Experiment No. 2, No. 11
As shown in the figure, the offset property is not improved even if 7% by weight of carbon fiber is added, but it is improved by adding 9% by weight from Experiment No. 12, and it improves as the amount added increases. However, as is clear from Experiments No. 5, No. 9, and Nos. 18 to 20, as the amount of carbon fiber added increases, the offset property decreases. This is due to a decrease in the releasability of the anti-offset layer due to an increase in the amount added, and also that the amount of fluorocarbon added for the purpose of improving wear resistance is 13% by weight of carbon fiber even if the amount added is increased. There was almost no change in Experiment No. 4, No. 8, No. 16, and No. 24 for carbon fiber 11% by weight. becomes an inverse relationship, and the experiment
In No. 14, the offset property of negatively charged toner was improved, and the carbon fiber of 20% by weight was also compared to Experiment No. 18.
Although the offset property of No. 26 was slightly improved, there was almost no change in the other experimental Nos. Therefore, it can be said that fluorinated carbon hardly contributes to the improvement of the offset property as a whole. As is clear from Experiment No. 26, it was confirmed that even if the amount of carbon fluoride added was increased, the releasability of the offset prevention layer was not impaired. From this, the offset property can be improved by simply comparing the amount of carbon fiber added (the amount of fluorocarbon added is not considered). Here, it is shown that the wider the uncoated area without offset, that is, the non-offset temperature range, the better the degree of improvement in offset property and the higher the practicality. Now, this relationship is shown in the offset property column of Table 1. From a practical point of view, good results are indicated by ○, very good results are indicated by ◎, and those which are not practical are indicated by ×. Note that ◎ indicates that the non-offset temperature range is 40°C or higher. As is clear from the offset property column of Table 1, the degree of improvement in the toner-to-toner offset property was determined by the amount of carbon fiber added in Experiment Nos. 3 and 3.
6. No.10, No.13, No.20, and No.22 are different. Next, the wear resistance of the heating roller was examined. This was carried out using a JIS standard K7204 Taber type wear tester, and the test conditions were a wear wheel CS-17,
The wear mass was determined under a load of 1 kg and a rotation speed of 1500 times. The results are shown in the abrasion resistance column of Table 1, and
The relationship between the amount of carbon fiber added and the Taber wear mass for the amount of carbon fluoride (CF) n added of 0, 1, 5, and 15% by weight was determined, and this is shown in FIG. As is clear from Table 1 and Figure 3, if the offset prevention layer was made of conventional PFA resin alone, a wear mass of 13 mg would occur, but by adding carbon fiber, the wear resistance was improved, and fluorocarbon When added, the improvement is remarkable. Furthermore, from FIG. 3, it is inferred that when the amount of fluorinated carbon (CF) n added is increased beyond 15% by weight, the curve shifts further to the left. However, if the amount of fluorocarbon added exceeds 30% by weight in total with carbon fiber, Table 1
As is clear from Experiments No. 10, No. 19, No. 20, No. 25, and No. 26, no improvement in wear resistance was observed, and on the contrary, it was confirmed that the wear resistance decreased, which was not desirable. Here, based on the results of both of the above experiments, a comprehensive evaluation of offset property and abrasion resistance was performed, and the results are shown in Table 1 as follows: cases where both are improved; cases where either one is not improved; Based on this comprehensive evaluation, the amount of carbon fiber added is 9 to 25
If the amount of fluorocarbon added is less than 30% by weight in total with carbon fiber, the offset property and abrasion resistance will be superior to the conventional case of only PFA resin. Furthermore, carbon fluoride (CF) n
When the amount of carbon fiber added is 9% by weight,
Although it is possible to add up to 20% by weight, as shown in Figure 3, the carbon fluoride (CF) n = 15% by weight curve is compared to the (CF) n = 5% by weight curve when the amount of carbon fiber added is 9% by weight or more.
The wear resistance is only superior in a narrow range of less than 11% by weight, and that fluorocarbon (CF) n = 5% by weight is better in a wide range of 11 to 20% by weight. Carbon fluoride (CF) n=1
The weight % curve shows a slight improvement in wear resistance over the (CF) n = 0 weight % curve, whereas the (CF) n = 5 weight % curve shows a significant improvement in wear resistance. It can be said that the amount of added carbon dioxide (CF) n is preferably about 5% by weight. Furthermore, the addition of carbon fiber or carbon fluoride significantly improved thermal conductivity, and the surface temperature of the heating roller remained stable. In addition, in the case where 9 to 20% by weight of carbon fiber and 5% by weight of fluorinated carbon are added to PFA resin, that is, the abrasion mass is 5 mg or less, the thickness of the offset prevention layer of the heating roller in the example is approximately 20μ. Even if it is made thinner, the wear resistance is sufficient, and as a result, the thermal conductivity can be further improved. Next, in order to investigate the relationship between the improvement of offset property and the charging characteristics of the heating roller, we investigated the relationship between the heating roller's temperature
The temperature is set to 170℃, and 12 sheets of blank A4 size copy paper are passed per minute at a speed of 11cm/sec between both rollers set to a pressure of 40Kg. and the minimum surface potential were measured using a vibrating surface potentiometer. Now, experiment No. 1, 11, 12, 14,
The results for samples No. 16 and No. 22 are shown in FIGS. 4 to 9. As is clear from this, this charging characteristic is
As shown in FIG. 10, the curves are roughly divided into four curves A to D. That is, curve A shows that there is little or no charge, curve B shows that the paper is positively charged from the beginning, and the surface potential of the paper is below +200V, and curve C shows that the charging polarity changes from negative to positive depending on the paper feeding time. , if its surface potential is in the range of -100V to +200V,
and curve D have the same relationship as curve C, but curve C
This is a case where there is a large change compared to . Charging characteristics based on the above measurement results are shown in the charging characteristics column of Table 1 by curves A, B, C, and D, respectively.
Display in . As is clear from the results of this experiment, adding carbon fiber to the PFA resin suppresses the frictional electrification of the heating roller, which prevents electrostatic adsorption of positively or negatively charged toner and reduces offset properties. It was confirmed that this was improved. In this experimental example, the amount of carbon fiber added was 9% by weight.
If the temperature rises above, the surface potential of the heating roller will be -100V.
~+200V, and the offset property has been improved.However, this surface potential changes depending on the pressure roller used, the material of the copy paper, environmental conditions, especially humidity, etc., and furthermore, the toner used Due to the fact that the amount of charge varies depending on the type of
It is necessary to consider that the range of the offset phenomenon also changes. What should be noted here is Experiment No. 7, No. 15,
As is clear from No. 23, when the amount of carbon fiber added is 12% by weight or more, the charging characteristics show little or no charging as shown in curve A. In this case, regardless of the above conditions, It is possible to prevent offset of both positive and negative toner, therefore,
Setting the amount of carbon fiber added to 12% by weight or more means that
From a practical standpoint, it can be said that this is the most preferable heating roller in a fixing device of a copying machine that uses both positive and negative toner. Note that when the amount of carbon fiber added exceeds 25% by weight, as shown in Experiment No. 10 and No. 20, although the heating roller is not charged, the mold releasability deteriorates as described above, and the offset property decreases. Therefore, when the amount of carbon fiber added is 12 to 25% by weight, offset of both positive and negative toners can be prevented without being influenced by the above conditions. In addition, the addition of carbon fluoride was tested in combination with carbon fiber.
Less than 30% by weight than No. 19, No. 25, preferably Experiment No. 24
It is necessary to keep the content within 28% by weight. From the above, when the amount of carbon fiber added is 12 to 20% by weight, the non-offset temperature range of both positive and negative toners is 40°C or higher, regardless of the above conditions, and fluorocarbon ( When the amount of CF)n added is 5% by weight, the wear resistance is significantly improved, the thickness of the offset prevention layer can be reduced, and the thermal conductivity is improved. Next, in order to investigate the relationship between the improvement of offset properties and the electrical resistance of the heating roller, we measured the volume resistance of the offset prevention layer laminated on a 10 cm square aluminum plate using an electrical resistance measuring device (Ultra High Megohmmeter manufactured by Takeda Riken Co., Ltd.). Measured using The results are shown in the electrical resistance column of Table 1. From this experimental result, we found that the electrical resistance of the heating roller decreases as the amount of carbon fiber added to the PFA resin increases, and that when the electrical resistance is greater than 10 ¹⁵ Ω・cm, the offset phenomenon is likely to ^occur . ~10 ¹⁵
In the Ω・cm range, the offset property is improved,
It was confirmed that the offset property was good below 10 ¹² Ω·cm, especially below 10 ¹¹ Ω·cm and above 10 ⁶ Ω·cm. Experimental Example 2 In Experimental Example 1, Pyrofila manufactured by Mitsubishi Rayon Co., Ltd. was used as the carbon fiber added to the PFA resin.
Experimental Example 1 was used except that NR7003 (fiber length 6mm was crushed to 1mm or less, diameter 7-8μ) was added and mixed at the ratio shown in the composition column of Table 2 (Experiment Nos. 27-30). The experiment was conducted in exactly the same manner. The results of offset properties are shown in FIG. 11, and the results of abrasion resistance, charging properties, and electrical resistance are shown in Table 2. In this experiment, the amount of fluorocarbon added was only 5% by weight, but it was found that the offset property and abrasion resistance were improved almost the same as in Experimental Example 1, and the frictional electrification of the heating roller was improved. It was confirmed that the electrical resistance also showed a similar tendency. Comparative Example In Experimental Example 1, instead of adding carbon fiber and carbon fluoride to the PFA resin, carbon black (Carbon Black MA-8 manufactured by Mitsubishi Chemical Industries, Ltd.) was used.
An experiment was carried out in the same manner as in Experimental Example 1, except that 25% by weight of chlorine was added. Here, the amount of carbon black added was set at 25% by weight because the maximum amount that could be added to the offset prevention layer was selected in order to improve offset properties. The results of offset properties are shown in FIG. 11, and the results of abrasion resistance, charging properties, and electrical resistance are shown in Table 2. From this comparative experiment, offset property and abrasion resistance can be improved by adding carbon black alone, but for this purpose, an addition amount of 25% by weight is required, and from the relationship with mold release property, offset property is improved. There is a drawback that it cannot be improved further. Effects As is clear from the above explanation, according to the present invention, by containing 9 to 25% by weight of carbon fiber in the fluororesin forming the offset prevention layer of the heating roller, positively or negatively charged toner images can be improved. It is possible to prevent the offset of
By containing less than or equal to 100%, the wear resistance can be improved, and by reducing the thickness of the offset prevention layer of the heating roller, it is possible to improve the thermal conductivity and reduce the cost of the heating roller itself. There is an advantage that it can be done. In addition, by containing 12 to 20% by weight of carbon fiber in the fluororesin, it can be used in both positive and negative ways without being affected by various conditions such as the pressure roller used, the material of the copy paper, environmental conditions, and the amount of charge of the toner. This has the advantage that offset of the charged toner image can be prevented. Further, in the present invention, there is no need to use an offset prevention liquid, and excellent effects such as the ability to simplify the fixing device and reduce costs can be obtained.

【table】

【table】

【table】 [Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of a heat roller fixing device according to the present invention, FIG. 2 is a diagram showing offset characteristics in Experimental Example 1 according to the present invention, and FIG. 3 is a diagram showing fluorocarbon (CF)
Figures 4 to 10 show the relationship between the Taber abrasion mass and the amount of added carbon fiber with respect to the amount of n added, and FIGS. FIG. 11 is a graph showing changes in the offset characteristics in Experimental Example 2 and Comparative Example according to the present invention. 1... Heating roller, 2, 7... Metal roller, 3
... Primer layer, 4 ... Offset prevention layer, 6
... Pressure roller, 8 ... Insulating layer.

Claims (1)

[Scope of Claims] 1 Consists of a heating roller formed by laminating an offset prevention layer on a conductive core material, and a pressure roller formed by forming an insulating layer on the conductive core material, which presses against the heating roller. , a hot roller fixing device for fixing a toner image onto a copy paper by passing the copy paper holding a toner image between the two rollers, wherein the offset prevention layer preferably contains carbon fibers in an amount of 9 to 25% by weight, preferably 12 to 25% by weight; A heat roller fixing device characterized by being made of fluororesin containing 20% by weight. 2. The heat treatment according to claim 1, wherein the fluororesin contains fluorinated carbon in addition to carbon fiber, and the sum of the contents is less than 30% by weight, preferably less than 28% by weight. Roller fixing device.