JP2012002964A - Fixing device and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fixing device capable of securing sufficient fixability while reducing an unnecessary fixing liquid.SOLUTION: A polar group generating part 2 generates a polar group on a surface of a recording medium to which a unfixed toner is not yet transferred. The polar group is generated on the surface of the recording medium by corona discharge which is an example of the polar group generating part 2, and the bonding with the polar group becomes easy so that the hydrophilicity of the recording medium is improved. The improvement of the hydrophilicity of the recording medium makes a foam-like fixing liquid easy to infiltrate the recording medium, and adhesiveness with a softened toner is improved. With this, resin fine particles are sufficiently softened without occurrence of an offset so as to secure sufficient fixability to the recording medium by coating the resin fine particles with only the necessary and sufficient amount of the foam-like fixing liquid.

Description

  The present invention relates to a fixing device and an image forming apparatus.

  An image forming apparatus such as a printer, a facsimile, and a copying apparatus is an apparatus that forms an image including characters and symbols on a recording medium such as paper, cloth, and an OHP sheet based on image information. In particular, electrophotographic image forming apparatuses are widely used in offices because they can form high-definition images on plain paper at high speed. In such an electrophotographic image forming apparatus, a heat fixing method is widely used in which toner on a recording medium is heated and melted, and the molten toner is pressurized to fix the toner on the recording medium. Yes. This thermal fixing method is preferably used because it can provide a high fixing speed and high fixed image quality.

  In such an electrophotographic image forming apparatus, about half or more of the power consumption is consumed for the heat treatment in the fixing unit. Therefore, suppressing power consumption in the fixing unit is effective as an energy saving measure for the entire image forming apparatus. Conventionally, various fixing methods that do not employ the thermal fixing method have been proposed. Among them, there is known a wet fixing method in which a fixing process is performed using a fixing solution that dissolves or swells toner. This wet fixing method is a very excellent fixing method as an energy saving measure because the heat treatment with a large amount of power consumption as in the heat fixing method is not required. As this wet fixing method, the one described in Patent Document 1 is known. In the wet fixing method disclosed in Patent Document 1, a fixing agent capable of dissolving or swelling unfixed toner is sprayed or dropped on the surface of an object to be fixed on which unfixed toner is disposed at a predetermined position. After swelling, the material to be fixed is dried.

  However, in the wet fixing method of Patent Document 1, an oil-in-water fixing agent in which an organic compound insoluble or hardly soluble in water is dispersed and mixed in water is used. For this reason, when a large amount of the fixing agent is applied to the unfixed toner, the recording medium such as transfer paper absorbs moisture of the fixing agent, and the recording medium is wrinkled and curled. As a result, the stable and high-speed conveyance of the recording medium required for the image forming apparatus is significantly impaired. In order to solve this problem, a large amount of water contained in the fixing agent may be evaporated using a drying device to remove moisture from the fixing agent applied to the recording medium. However, this requires power comparable to the power consumption of the image forming apparatus using the thermal fixing method, and does not reduce power consumption.

  In addition, several oil-based fixing solutions in which a material that dissolves or swells toner is dissolved in an oil-based solvent have been proposed as fixing solutions that do not repel water-repellent unfixed toner. As one example, for example, Patent Document 2 discloses a liquid fixing solution obtained by diluting an aliphatic dibasic acid ester or the like as a component with a material that dissolves or swells a resin component constituting a toner with a non-volatile dimethyl silicone. Has been proposed. Patent Document 3 proposes a compatible liquid fixing solution in which 8 to 120 parts by volume of silicone oil is mixed with 100 volumes of solvent that dissolves toner and is compatible with silicone oil. Yes. Since these liquid fixing solutions contain an oily solvent having a high affinity with the non-fixed toner subjected to the water-repellent treatment, the toner is dissolved or swollen without repelling the non-fixed toner subjected to the water-repellent treatment. It can be fixed on a recording medium.

  As an example of a configuration in which the liquid fixing solution of Patent Documents 2 and 3 is applied to an unfixed toner layer, an application roller 201 is used as shown in FIGS. The liquid fixing solution described in Patent Documents 2 and 3 is applied to the application roller 201, and the liquid fixing solution on the application roller 201 is applied to the unfixed toner layer 203 on the recording medium 202. If the thickness of the fixing liquid layer 204 on the application roller 201 is thinner than the unfixed toner layer 203 in order to apply a small amount of the liquid fixing liquid to the recording medium 202, the position where the application roller 201 is separated from the recording medium 202. Thus, the fixing liquid cannot reach the unfixed toner that contacts the recording medium 202 through the unfixed toner layer. For this reason, all unfixed toner cannot be dissolved or swollen and cannot be completely fixed. As a result, the surface tension generated by the liquid film of the liquid fixing solution on the surface of the application roller 201 is increased, and unfixed toner particles are pulled by this surface tension, and the toner particles are offset on the surface of the application roller 201. As a result, the image on the recording medium 202 is greatly disturbed.

  Conversely, as shown in FIG. 13, when the thickness of the fixing liquid layer 204 on the application roller 201 is sufficiently thicker than the unfixed toner layer 203, the amount of liquid is large at a position where the application roller 201 is separated from the recording medium 202. Therefore, the surface tension due to the liquid film on the surface of the application roller 201 is less likely to act directly on the toner particles. As a result, the toner is not offset to the application roller side. However, since a large amount of liquid fixing liquid is applied to the surface of the recording medium 202, toner particles are flowed on the recording medium 202 by an excessive fixing liquid, resulting in image quality deterioration or a long drying time. Will occur. In addition, a remarkable residual liquid feeling (a wet feeling when touching paper) is generated on the recording medium. Furthermore, when the liquid fixing solution contains water, when the amount of application to a medium containing cellulose such as paper is large, the medium such as paper is significantly curled, and the medium such as paper in the apparatus in an image forming apparatus is conveyed. Sometimes paper jams may occur. As described above, when the fixing is performed with the liquid fixing solutions of Patent Documents 2 and 3, it is necessary to apply a fixing solution thicker than the toner layer thickness in order to prevent toner offset. On the other hand, in order to improve the fixing response, reduce the residual liquid feeling, and prevent curling, it is necessary to apply a small amount of the fixing liquid to the toner layer. As described above, it is extremely difficult to solve the problems associated with the application of the liquid fixing solution in a balanced manner.

  In order to solve the above-described problems in the case of using such a liquid fixing solution, a fixing method has been conventionally proposed in which fixing is performed using a foam-like fixing solution in which the liquid fixing solution is foamed. As a fixing method using this foamy fixing solution, one described in Patent Document 4 is known. This patent document 4 is a fixing method in which a foam-like fixing solution containing a large amount of bubbles is applied to an unfixed toner layer via an application roller which is a foam-like fixing solution application unit. According to the wet fixing method using this foam-like fixing solution, it is possible to prevent offset adhesion of resin fine particles to the foam-like fixing solution applying means, without disturbing the resin fine particles, and to the medium on which the resin fine particles are attached. After coating, the resin fine particles can be quickly fixed on the medium. However, even in the wet fixing method using the foamy fixing solution described in Patent Document 4, when the amount of foamed fixing solution applied is small, offset adhesion of resin fine particles occurs on the application roller serving as the foaming fixing solution applying means. Conversely, if the amount of the foam-like fixing solution applied is large, not only the foam-like fixing solution is simply wasted, but also a flow occurs in the resin fine particles, causing image disturbance. In order to solve such problems, in Patent Document 4, the film thickness of the foamy fixing solution is adjusted to a film thickness that does not cause an offset.

  However, as in the above-described wet fixing method of Patent Document 4, even if an attempt is made to adjust the film thickness of the foam-like fixing solution to a film thickness that does not cause an offset to reduce an unnecessary application amount without causing an offset, If the hydrophilicity indicating the affinity with the resin is poor, the foamy fixing solution cannot sufficiently penetrate into the resin fine particles on the medium. As a result, all resin fine particles are not dissolved or swollen. In this case, the resin fine particles cannot be sufficiently adhered to the medium, and the resin fine particles that could not adhere are transferred to the application roller side, and an offset occurs. For this reason, the resin fine particles transferred by the offset are included in the foamy fixing solution remaining on the application roller, and the fixing solution cannot be reused and must be discarded. It was.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a fixing device and an image forming apparatus capable of ensuring sufficient fixing performance while reducing useless foamy fixing solution.

In order to achieve the above object, the invention of claim 1 is characterized in that a gas is mixed with a liquid fixing solution containing at least a softening agent that softens fine particles containing a resin by dissolving or swelling at least a part of the resin. A polar group is generated on the surface of the medium in a fixing device that applies the generated foamy fixer to the resin fine particle layer on the medium via the foamy fixer coating unit and fixes the resin fine particle layer to the medium. It has polar group generation means, and the foam-like fixing solution is applied to the resin fine particle layer formed on the medium on which the polar group is generated on the surface of the medium by the polar group generation means. It is a fixing device.
According to a second aspect of the present invention, in the fixing device according to the first aspect, the polar group generating means includes at least a corona discharge electrode for performing corona discharge on the medium, and a counter electrode facing the corona discharge electrode. It is characterized by that.
Further, the invention of claim 3 is the fixing device according to claim 2, wherein when the polar group generating means executes corona discharge to generate a polar group on the surface of the medium, the medium is the corona discharge electrode. And the counter electrode.
According to a fourth aspect of the present invention, in the fixing device according to the second or third aspect, the corona discharge electrode and the counter electrode are disposed at a location where the medium is curved toward the medium conveyance direction. It is characterized by.
Further, the invention of claim 5 is the fixing device according to claim 4, wherein the counter electrode is a conductive guide member that guides the medium to be transported along a transport path and is grounded. To do.
According to a sixth aspect of the present invention, there is provided the fixing device according to any one of the second to fifth aspects, further comprising corona discharge set value storage means for storing a corona discharge set value for each type of the medium. The corona discharge set value corresponding to the type of medium is read from the corona discharge set value storage means, and corona discharge is performed on the medium with the read corona discharge set value.
Further, the invention of claim 7 is characterized in that, in the fixing device of claim 1, the polar group generation means includes an ultraviolet irradiation means for irradiating the surface of the medium with ultraviolet rays.
According to an eighth aspect of the present invention, there is provided an image forming means for forming an unfixed toner image on a medium by performing an electrostatic recording process with a toner in which resin-containing fine particles contain a colorant, and any one of the first to seventh aspects. An image forming apparatus comprising: a fixing unit configured to fix the unfixed toner image on a medium by the fixing device according to the item.

  In the present invention, polar groups are generated on the surface of the medium by the polar group generating means before applying the foam fixing solution onto the medium, and the generated polar groups and the water in the foam fixing solution are chemically treated. Make it easier to join. That is, the hydrophilicity of the medium can be improved. Then, resin fine particles are formed on a medium having improved hydrophilicity, and a foamy fixing solution is applied to the formed resin fine particles. For this reason, the moisture of the foam-like fixing solution easily binds to the polar group generated in the medium, and all the foam-like fixing solution penetrates into the medium. As a result, if only a necessary amount of the foam-like fixing solution is applied to the resin fine particles, the resin fine particles can be sufficiently softened without causing an offset, and sufficient fixability can be secured.

  As described above, according to the present invention, there is an excellent effect that sufficient fixability can be secured while reducing useless fixer.

1 is a schematic configuration diagram illustrating a configuration of an image forming apparatus according to an exemplary embodiment. It is the schematic which shows the mechanism of fixing using a foamy fixing liquid. It is the schematic which shows the layer structural example of the foamy fixing solution at the time of application | coating. It is a schematic block diagram which shows the structure of a foamy fixing liquid production | generation means. 1 is a schematic diagram illustrating a configuration of a fixing device mounted on an image forming apparatus according to an exemplary embodiment. It is a figure which shows the structure of a polar group production | generation part. FIG. 6 is a schematic cross-sectional view showing a state when a foam-like fixing solution is applied when the thickness of the foam-like fixing solution is thinner than the toner layer thickness. It is a schematic sectional drawing which shows the mode at the time of application | coating of a foamy fixing solution when the hydrophilicity of a recording medium is bad. FIG. 3 is a schematic cross-sectional view showing a state when a foamy fixing solution is applied when the recording medium has good hydrophilicity. It is a characteristic view which shows the relationship between the corona discharge voltage classified by medium, and a surface contact angle. It is a flowchart which shows a corona discharge process. FIG. 3 is a schematic cross-sectional view showing a state when a liquid fixing solution is applied. FIG. 3 is a schematic cross-sectional view showing a state when a liquid fixing solution is applied.

Hereinafter, embodiments of an image forming apparatus to which the present invention is applied will be described.
FIG. 1 is a schematic configuration diagram illustrating a configuration of an image forming apparatus according to the present exemplary embodiment. The image forming apparatus shown in the figure may be a copying machine, a printer, or a multifunction machine having these functions. 1A is a schematic configuration diagram of the entire tandem image forming apparatus for color electrophotography, and FIG. 1B is an image of the image forming apparatus of the present embodiment of FIG. 1A. It is a schematic block diagram which shows the structure of a formation unit. An image forming apparatus 100 according to this embodiment shown in FIGS. 1A and 1B includes an intermediate transfer belt 101 as a toner image carrier. The intermediate transfer belt 101 is stretched around three support rollers 102 to 104 and rotates in the direction of arrow A in the figure. On the intermediate transfer belt 101, black, yellow, magenta and cyan image forming units 105 to 108 are arranged. Above these image forming units, an exposure device (not shown) is arranged. For example, when the image forming apparatus is a copying machine, each exposure L1 to L4 for reading image information of an original with a scanner and writing an electrostatic latent image on each photosensitive drum according to the image information is performed. Irradiated by an exposure apparatus. A secondary transfer device 109 is provided at a position facing the support roller 104 of the intermediate transfer belt 101 with the intermediate transfer belt 101 interposed therebetween. The secondary transfer device 109 includes a secondary transfer belt 112 that is stretched between two support rollers 110 and 111. As the secondary transfer device 109, a transfer roller may be used in addition to the transfer belt. A belt cleaning device 113 is disposed at a position facing the support roller 102 of the intermediate transfer belt 101 with the intermediate transfer belt 101 interposed therebetween. The belt cleaning device 113 is arranged to remove toner remaining on the intermediate transfer belt 101.

  Further, the image forming unit shown in FIG. 1B will be described. In the image forming units 105 to 108, images irradiated from a charging device 117 and an exposure device (not shown) around the photosensitive drum 116 are provided. A laser beam L corresponding to the signal, a developing device 118, a cleaning device 119, and a charge removal device 120 are arranged. A primary transfer device 121 is provided at a position facing the photosensitive drum 116 with the intermediate transfer belt 101 interposed therebetween. The charging device 117 is a contact charging type charging device employing a charging roller. The charging device 117 uniformly charges the surface of the photosensitive drum 116 by bringing a charging roller into contact with the photosensitive drum 116 and applying a voltage to the photosensitive drum 116. As the charging device 117, a non-contact charging type charging device using a non-contact scorotron or the like may be employed. Further, the developing device 118 causes the toner in the developer to adhere to the electrostatic latent image on the photosensitive drum 116 to visualize the electrostatic latent image. Here, the toners corresponding to the respective colors are made of resin materials colored in the respective colors, and these resin materials are materials that are dissolved or swollen by the foam-like fixing liquid in the present embodiment.

  Further, the developing device 118 has a stirring unit and a developing unit (not shown), and the developer that has not been used for development is returned to the stirring unit and reused. The toner concentration in the agitation unit is detected by a toner concentration sensor, and is controlled so that the toner concentration is constant. Further, the primary transfer device 121 transfers the toner visualized on the photosensitive drum 116 to the intermediate transfer belt 101. Here, a transfer roller is employed as the primary transfer device 121, and the transfer roller is pressed against the photosensitive drum 116 with the intermediate transfer belt 101 interposed therebetween. As the primary transfer device 121, a conductive brush, a non-contact corona charger, or the like can be adopted. The cleaning device 119 removes unnecessary toner on the photosensitive drum 116. As the cleaning device 119, a blade having a tip pressed against the photosensitive drum 116 can be used. Here, the toner collected by the cleaning device 119 is collected by the developing device 118 by a collecting screw and a toner recycling device (not shown) and reused. Further, the static elimination device 120 is constituted by a lamp, and initializes the surface potential of the photosensitive drum 116 by irradiating light.

  The recording sheet 114 as a recording medium is subjected to corona discharge processing by the polar group generation unit 2 and then guided to the secondary transfer unit by the pair of sheet feeding rollers 115, and the toner image is transferred to the recording sheet 114. . At that time, the toner image is transferred by pressing the secondary transfer belt 112 against the intermediate transfer belt 101. The recording paper 114 to which the toner image is transferred is conveyed to the fixing device 1 in the present embodiment by the secondary transfer belt 112. In the fixing device 1 of the present embodiment, the unfixed toner image transferred to the recording paper 114 is a bubble generated from a liquid fixing solution containing a softening agent that dissolves or swells at least a part of the resin contained in the toner. It is fixed on the recording paper 104 that has been surface-activated by the fixing solution.

Next, the fixing device mounted on the image forming apparatus of the present embodiment will be described in detail.
First, the principle of a fixing method using a foam fixing solution will be briefly described. A foam fixing solution containing a softening agent that softens fine particles containing a resin by dissolving or swelling at least a part of the resin on a medium. In this fixing method, the resin fine particles on the medium are softened by being applied to the resin fine particles, and the resin fine particles are fixed on the medium. Needless to say, the resin fine particles described here are not particularly limited as to what they are, but they refer to toners when applied to an image forming apparatus.

  An outline of the fixing mechanism using the foam-like fixing solution is as follows. As shown in FIG. 2, a foam-like fixing solution composed of foam is used as the fixing solution by the foam-like fixing solution generating means described later. As a result, the density of the fixing liquid can be lowered and the fixing liquid layer on the application roller 11 can be thickened. Furthermore, since the influence of the surface tension of the fixing liquid is suppressed, it has been found that the offset of the resin fine particles to the coating roller 11 can be prevented. Further, in the case where the size of the resin fine particles is about 5 [μm] to 10 [μm], in order to apply the foamy fixing solution 14 to the resin fine particle layer 13 without disturbing the fine particle layer, It was found that a range of about 5 [μm] to 50 [μm] is necessary. As shown in FIG. 3, the foam-like fixing solution 20 composed of bubbles 22 is composed of a liquid film boundary (hereinafter referred to as a plateau boundary) 21 that separates each of the bubbles 22.

  The fixing solution contains a softening agent, and this softening agent generally has a strong antifoaming action. Therefore, when the liquid fixing solution is used as the foamy fixing solution as in the fixing device 1 of the present embodiment, the higher the concentration of the softening agent in the fixing solution, the more the foaming property and foam stability of the fixing solution. There is a risk that foaming will be difficult and foaming will be difficult, or the foam-like fixing solution will be liable to break. If it is difficult to foam, it is impossible to obtain a foam fixing solution having a low bulk density. Even if a foam fixing solution having a desired bulk density is obtained, if the foam fixing solution easily breaks, it is This causes the same problem as the configuration in which the liquid fixer is applied. Moreover, as a foaming agent, the anionic surfactant can implement | achieve the foaming property and foam stability which were excellent, and is excellent as a foaming agent. Among anionic surfactants, fatty acid salts are most excellent in foam stability and are most suitable as a foaming agent for fixing solutions. Here, foam stability refers to the property that the fixing solution in the form of foam is difficult to become liquid. As the foam-type fixing solution to be applied to the unfixed toner by the fixing device of the present embodiment, it is desirable that the foam does not disappear even if left in a foam state for 1 minute, and has foam stability enough to maintain the foam state. .

  In order to solve the problem of deterioration of foamability and foam stability when the softener concentration in the fixing solution is increased, the present inventors have made various prototypes based on the type and concentration of the anionic surfactant. It was. Further, a prototype was made by paying attention to a technique called “super fat” described in Non-Patent Document 1, that is, a free fatty acid contained in a solid detergent (soap). Here, to outline the technology called super fat, it is a method of adding a small amount of free fatty acids that are difficult to oxidize to increase the excess fat and oil, leaving a small amount of fat and oil that is not saponified, for example, to enhance the moisturizing action, etc. It is said to be effective. In Non-Patent Document 1, it is known that when a very small amount of fatty acid is added to a soap water-based system, the foaming performance is improved and the foam quality becomes more creamy, which is called super fat soap. It is described. Similar to this super fat, an attempt was made to foam by adding a very small amount of fatty acid to a fixing solution having a softening agent, but both foamability and foam stability were poor.

  On the other hand, the present inventors use a fatty acid salt having 12 to 18 carbon atoms as a foaming agent, and further contain a fatty acid having 12 to 18 carbon atoms in the fixing solution, thereby increasing the concentration of the softening agent. The present inventors have found that it is possible to provide a foamy fixing solution that does not deteriorate the foamability of the fixing solution. In the fixing solution containing the softening agent, the number of carbon atoms of the fatty acid salt is excellent in foaming property as compared with the case where water is simply foamed. Specifically, laurate (12 carbon atoms), myristate (14 carbon atoms), palmitate (16 carbon atoms), and stearate (18 carbon atoms) are suitable. Further, pentadecylic acid (carbon number 15), margaric acid (carbon number 17), and the like are also suitable.

  Here, the action of the fatty acid and the softening agent will be described. The softening agent has an ester group in the chemical structure, and the fatty acid has a carbonyl group in the chemical structure. From this point, the ester group of the softener and the carbonyl group of the fatty acid show an electrical action in the fixing solution system, and this causes a binding action between molecules, and the fixing solution is characterized by foaming properties and Improves foam stability.

  Even in the range of 12 to 18 carbon atoms, the smaller the number of carbons, the better the foaming property, but the foam stability is poor, and the larger the number of carbons, the less foaming properties, but the foam stability is extremely excellent. ing. For this reason, a single fatty acid salt may be contained in the fixing solution, but it is more excellent to mix and contain a fatty acid salt having 12 to 18 carbon atoms. As a mixing ratio, it is desirable to contain the most myristic acid salt (14 carbon atoms) and to lower the ratio of lauric acid salt (12 carbon atoms) and stearic acid salt. More specific fatty acid salt ratios are 0: 6: 3: 1, 1: 5: 3: 1, 1: 4 by weight ratio of laurate: myristate: palmitate: stearate. : 4: 1 is suitable.

  By the way, by containing the fatty acid having the same carbon number as the fatty acid salt as the foaming agent in the fixing solution, the foaming property and foam stability can be maintained even when the concentration of the softening agent is increased. If the concentration of the softening agent is less than 10 [wt%], there is no problem in foaming properties even if no fatty acid is contained. However, when the concentration of the softening agent is 10 [wt%] or more, particularly when the concentration of the softening agent is 30 [wt%] or more, only the fatty acid salt is hardly foamed and the foamability is deteriorated. In the fixing solution in which the concentration of the softening agent is 30 [wt%], when the fatty acid having the same carbon number as the fatty acid salt is contained, the foaming property can be maintained.

  However, if the fatty acid content is too high, the ratio of the fatty acid salt, which is a foaming agent, decreases, and the foamability deteriorates again. Therefore, it is better to make the number of moles of fatty acid salt the same as or larger than the number of moles of fatty acid. Or when the ratio of a fatty acid and a fatty acid salt is in the range of 5: 5 to 1: 9, the foamability is excellent.

  In addition to the combination of fatty acid and fatty acid salt having the same carbon number, for example, the fatty acid salt is amine myristate, the fatty acid is stearic acid, the fatty acid salt is potassium palmitate, and the fatty acid is stearic acid. Different combinations in the range of 12 to 18 may be used. In short, by containing a fatty acid having a carbon number of 12 to 18 in the fixing solution, even if a high-concentration softening agent is contained, the foamability is not deteriorated, the foam stability is excellent, and the density is extremely low. Allows foaming.

  In addition, even if the fixing solution contains a fatty acid having 12 to 18 carbon atoms using other anionic surfactants such as alkyl ether sulfate (AES) as a foaming agent, the foaming property due to an increase in the concentration of the softener It turns out that it is effective in preventing it from getting worse. However, the best combination is a combination with a fatty acid salt.

  Furthermore, fatty acid sodium, fatty acid potassium, and fatty acid amine are suitable as the fatty acid salt. Furthermore, the most suitable fatty acid amine is specifically prepared by heating water, adding a fatty acid, and then adding triethanolamine, followed by heating and stirring for a certain period of time for a saponification reaction. be able to. At this time, by increasing the molar ratio of fatty acid to triethanolamine in the range of 1: 0.5 to 1: 0.9 and the fatty acid ratio, unreacted fatty acid remains after saponification, and the fixing solution Fatty acid and fatty acid amine can be mixed therein. The same is possible with sodium and potassium salts.

  By the way, when the concentration of the softening agent in the fixing solution increases, the softening agent becomes difficult to dissolve in water as a dilution solvent. Therefore, as a result of investigation, by adding polyhydric alcohols, specifically ethylene glycol, diethylene glycol, propylene glycol, 1,3 butylene glycol, glycerin, etc., in the fixing solution, the softener can be dissolved even at a high concentration. And it was found that the foaming property by the fatty acid salt was not deteriorated, but rather the foaming property was improved. The content of the polyhydric alcohol is suitably in the range of 1 [wt%] to 30 [wt%]. If the content is more than 30 [wt%], the foamability is rather deteriorated, which is not suitable.

  On the other hand, generally, in the case of a large bubble of about 0.5 [mm] to 1 [mm], the bubble can be generated relatively easily by simple stirring or the like. (It takes less than 1 second). Thus, attention was paid to the fact that bubbles larger than the desired bubble diameter and having a size that can be visually observed can be easily and quickly obtained. And as a result of earnestly examining a method of quickly generating a fine bubble of about 5 [μm] to 50 [μm] from a large bubble, when a large bubble is separated by applying a shearing force to the large bubble, It was found that microbubbles having a desired size can be generated very quickly compared to the method of generating microbubbles from the liquid state.

  And as shown in FIG. 4, as a big foam production | generation part in the foam-like fixing liquid production | generation means 30 which separates a big foam and produces | generates the foam of a fine prescription after producing | generating a big foam, as shown in FIG. The liquid fixing liquid 32 is supplied to the gas-liquid mixing unit 35 using liquid transporting means such as a transport pump 33 and a liquid transport pipe 34. In the gas / liquid mixing unit 35, a negative pressure is generated in the air port 36 along with the flow of the liquid, and the gas is introduced from the air port 36 into the gas / liquid mixing unit 35 to mix the liquid and the gas. Furthermore, by passing through the microporous sheet 37, a large bubble having a uniform bubble diameter can be generated. The pore diameter is preferably about 30 [μm] to 100 [μm]. The porous member is not limited to the microporous sheet 37 of FIG. 4, and may be a porous member having a continuous foam structure, and may be a sintered ceramic plate, a nonwoven fabric, or a foamed resin sheet having a pore diameter of about 30 [μm] to 100 [μm]. Good. As another method for generating large bubbles, the liquid fixer supplied from the above-described transport pump and the air from the air port are stirred with a blade-like stirrer, and large bubbles are generated while bubbles are involved in the liquid. It is also desirable to have a configuration or a configuration in which a large bubble is generated by bubbling the liquid fixer supplied from the above-described transport pump with an air supply pump or the like.

  Next, in order to divide a large bubble into two or more bubbles, a fine bubble generation 38 in the foam-like fixer generating means 30 as shown in FIG. 4 is used to apply a shearing force to the large bubble. The inner cylinder 38-1 is rotatable with a closed double cylinder. Then, a large foam-like fixing solution is supplied from a part of the outer cylinder from the gas-liquid mixing unit 35, and passes through a gap between the rotating inner cylinder 38-1 and the outer cylinder 38-2 (this is a flow path). However, the rotating cylinder receives a shearing force. Due to this shearing force, the large bubbles are changed into minute bubbles, and a foam-like fixing solution having a desired minute bubble diameter can be obtained from the bubble outlet provided in the outer cylinder 38-2.

Further, the liquid transport speed is determined by the rotational speed of the rotating inner cylinder 38-1 and the length of the inner cylinder 38-1 in the longitudinal direction. Assuming that the inner diameter of the outer cylinder 38-2 is d1 [mm], the cylinder length is L [mm], the outer diameter of the inner cylinder 38-1 is d2 [mm], and the rotation speed is R [rpm], The liquid transport speed V [mm ³ / sec] for generating bubbles is
V = L × π × (d1 ² −d2 ² ) / 4 / (1000 / R)
It was found that it was decided by the formula.

For example, when d1 is 10 [mm], d2 is 8 [mm], L is 50 [mm], and the rotation speed is 1000 [rpm], the liquid conveyance speed is about 1400 [mm ³ / sec] (1.4 [ cc / sec]). Assuming that the foam fixer required to fix A4 paper is 3 [cc], the rise time required to generate the required amount of foam fixer from the liquid fixer is about 2 seconds. It becomes possible to quickly generate a foam-like fixing solution having a desired bubble diameter. A spiral groove may be provided in the inner cylinder to improve liquid transportability in the cylinder.

  In this way, liquid fixing is achieved by combining a large bubble generating unit that changes the liquid fixing liquid into a liquid having a large bubble diameter and a fine bubble generating unit that generates a small bubble by applying shear force to the large bubble. It is possible to produce a foam-like fixing solution having a fine bubble diameter of about 5 [μm] to 50 [μm] in a very short time.

Next, as a means for transporting the liquid fixer from the fixer container to the foaming mechanism, a transport pump is used in FIG. As the transport pump, there are a gear pump, a bellows pump, and the like, and a tube pump is desirable. If there is a vibration mechanism or a rotation mechanism in the fixing liquid, such as a gear pump, the liquid foams in the pump, and the liquid may be compressible, resulting in a decrease in conveying ability. In addition, the above-mentioned mechanical parts or the like may contaminate the fixer or conversely deteriorate the mechanical parts. On the other hand, since the tube pump is a mechanism that pushes out the liquid in the tube while deforming the tube, the only member in contact with the fixing liquid is the tube. By using a member that has liquid resistance to the fixing liquid, No contamination or deterioration of pump system parts. In addition, since the tube is only deformed, the liquid does not foam, and the conveyance capacity can be prevented from being lowered. The bulk density of the foam-like fixing solution is preferably in the range of about 0.01 [g / cm ³ ] to 0.1 [g / cm ³ ]. Further, the fixer only needs to be foamed when applied to a layer of resin-containing fine particles such as toner on a recording medium such as paper, and need not be foamed in the storage container. In the storage container, it is a liquid that does not contain bubbles, and it is desirable to provide a means for forming bubbles in the liquid conveyance path until the liquid is supplied from the container or applied to the resin-containing fine particle layer. This is because the storage container is liquid, and the foamed configuration after the liquid is taken out from the container has a great advantage that the container can be downsized.

  Next, the configuration of the fixing device installed in the image forming apparatus of the present embodiment will be described. FIG. 5 is a schematic diagram illustrating an example of the configuration of the image forming apparatus according to the present exemplary embodiment. In the figure, the same reference numerals as those in FIGS. 1 and 4 denote the same components. As described above, the foam-like fixer generating means 30 generates a foam-like fixer by generating large bubbles from the liquid fixer and then separating the large bubbles to produce fine bubbles. ing. This foamy fixing solution is supplied on the application roller 39 to the upstream side of the portion where the blade 40 of the film thickness adjusting means acts, and is uniformly thinned on the application roller 39. The blade 40 has an optimum film thickness by thinning the foamy fixing solution. The film thickness required here is a film thickness that becomes an optimum value upon fixing on the coating roller. The foamy fixer uniformly thinned on the coating roller 39 is applied to the toner particle layer on the medium to fix the toner particles on the medium.

  In the image forming apparatus of this embodiment, a polar group generation unit 2 as a pre-processing device is provided on the upstream side of the secondary transfer unit. Specifically, the polar group generation unit 2 includes a corona discharge electrode 51 that performs corona discharge, a high-frequency power source 52 that supplies a high-frequency current to the corona discharge electrode 51, and a corona discharge control unit 53 that controls the high-frequency power source 52. And a counter electrode 54 connected to the ground. The corona discharge electrode 51 and the counter electrode 54 are provided so as to face each other, and the medium 114 passes between them. The counter electrode 54 connected to the ground is made of a metal member, and is provided outside the curved portion of the conveyance path of the medium 114. That is, the corona discharge electrode 51 is provided inside the curve. Thus, when the medium 114 is conveyed, the medium 114 is always conveyed so as to be pressed outside the curve of the conveyance path, and as a result, the medium 114 is always conveyed while being pressed against the portion of the counter electrode 54. Become. At this time, since the medium 114 is conveyed while curving in the conveyance direction, the width direction of the medium is in a state of being straightened. The corona discharge electrode 51 has a rod-like or linear shape extending straight along the width direction of the medium 114. And it is provided substantially parallel to the counter electrode 54 over the whole extending direction. That is, as shown in FIG. 6, the gap (W) with the counter electrode 54 is provided to be constant over the entire width direction. This is because if this gap varies, unevenness of corona discharge occurs. The gap (W) is preferably about 1 to 10 mm from the discharge characteristics. As long as the corona discharge electrode 51 has a length corresponding to the width direction of the medium, it is sufficient. That is, if the maximum allowable standard size of the medium in the apparatus is A3, the length of the corona discharge electrode 51 may be about 297 mm.

  The medium 114 is sandwiched and conveyed by the application roller 39 and the pressure roller 41, and a thin foam-like fixing liquid is applied to the medium by the applied pressure. In addition, a cleaning unit 42 is provided on the application roller 39 at a downstream position of a portion where the foamy fixing solution is applied to the medium 114. The cleaning means 42 is provided to remove the foam-like fixing liquid and the offset toner remaining on the application roller 39 after the foam-like fixing liquid application operation. This is because if these are not removed normally, the formation of a stable thin film of the foam-like fixer at the portion of the blade 40 will be hindered.

  The unfixed toner image is transferred from the transfer belt to the medium by the secondary transfer unit. A fixing operation is performed by applying a foamy fixing solution to the unfixed toner image by the application roller 39.

Next, corona discharge and hydrophilicity will be described.
Corona treatment has come to be used as a surface modification means in industrial equipment that performs adhesion and coating treatment. This is because it has been found that the surface hydrophilicity is improved by the corona treatment. The mechanism will be briefly explained. In general, a substance having a low surface energy has poor hydrophilicity and adhesiveness, and as a result, has poor wettability with ink or the like. Therefore, when printing or bonding other materials on a material having a low surface energy, a pretreatment is required to activate the surface to increase the surface energy and assist the operation. In the atmosphere of high-frequency and high-voltage due to corona discharge, which is one of the surface activation treatments, each collision between atoms, molecules, electron ions, excitation of electron energy (moving vigorously), etc. occurs in the electrolysis, In addition, photon emission occurs. When this corona discharge energy is applied to a substance, the surface receives energy, the surface energy is increased, and an activated state (radical state) is obtained. At this time, polar groups such as OH groups and carbonyl groups are generated on the surface of the substance, and the polar groups are easily bonded to moisture contained in the fixing solution, that is, hydrophilicity is improved.

  In fact, when paper is taken up as the most common example of the medium, it has been confirmed in experiments that the contact angle, which is a hydrophilic index, is reduced by applying corona discharge treatment. It has also been confirmed that the contact angle decreases when a fixing solution is used. This indicates that polar groups such as OH groups and carbonyl groups generated by corona discharge treatment have an effect of improving hydrophilicity even for the components of the foam-like fixing solution used in this embodiment. ing. Actually, when the foamy fixing solution was applied to the medium, the coating amount was improved by 20% or more by applying the corona discharge treatment.

  From these facts, it can be seen that the corona discharge treatment can improve the hydrophilicity of the medium by a very simple means. Corona discharge is most efficiently performed at high voltage and high frequency. Specifically, sufficient corona discharge is possible even in the vicinity of 10 kVpp and 20 kHz.

Here, an outline will be given of a mechanism indicating that the treatment for improving the hydrophilicity of the medium by corona discharge contributes to the reduction of the necessary amount of the foam-like fixing liquid necessary for fixing.
The image of the unfixed toner on the medium is merely a powder of fine particles, and the image is disturbed when touched with a finger even a little. Here, when the foam-like fixing solution is applied only when the foam-like fixing solution penetrates partway through the toner layer, the toner particles are foam-fixed in the portion of the toner layer into which the foam-like fixing solution has permeated. A binding force is generated by the liquid. However, since the toner layer in contact with the medium is in a powder form and the binding force is inferior to that of the part into which the foam-like fixing liquid has permeated, the application roller 39 and the medium 114 are separated as shown in FIG. It can be easily understood that the toner is peeled off at the portion where the foam-like fixing liquid has not penetrated and the toner is offset to the application roller 39. From this, it is understood that at least the foamy fixing solution needs to penetrate the entire toner layer. On the other hand, since the toner layer is a powder layer, unless the toner surface is subjected to water repellent treatment or the like, the foam-like fixer is likely to penetrate into the toner particle layer relatively easily by capillary action. If the medium has the same permeability as that of the toner layer, the foam fixer smoothly penetrates into the medium. If the medium has low permeability, the penetration of the foam fixer does not occur between the toner layer and the medium. Blocked between.

  In order to prevent the toner from being offset to the application roller 39, the toner softened by the foam-like fixing liquid needs to be securely adhered to the medium. If the medium is paper, it must be entangled with the paper fibers. However, as shown in FIG. 8B, if the medium has low permeability and the foam-like fixing solution does not penetrate into the medium, the adhesive force of the softened toner to the medium becomes weak, that is, paper fibers. The entanglement with is weakened. As a result, as shown in FIG. 8A, an offset to the application roller 39 is likely to occur. On the other hand, as shown in FIG. 9B, if the permeability of the medium is high, the foam-like fixing solution penetrates into the paper fiber of the medium, and the toner is softened also from the fiber side of the medium. It also works to drag the toner softened by increasing the adhesive force into the fiber. For this reason, as shown in FIG. 9A, the offset to the application roller 39 hardly occurs, and as a result, the fixability can be improved.

  Further, the adhesive force with the medium is also improved for the toner itself softened by the penetration of the foamy fixing solution. As described above, by performing the corona discharge treatment, polar groups such as OH groups and carbonyl groups are generated on the surface of the medium. These not only contribute to the improvement of hydrophilicity with the liquid, but also the adhesive. It has been found that this also contributes to the improvement of the adhesion effect. It can be understood that the softened toner is tacky and behaves in the same way as an adhesive, so that the adhesion with a medium subjected to corona discharge treatment is improved. From this, it can be seen that the fixability is improved when the corona discharge treatment is performed even in the behavior of the toner itself.

  From the above explanation, it was found that if the foam fixing solution has the same conditions and the nip has the same conditions, the higher the permeability of the medium, the better the fixing quality. In order to increase the permeability of the medium, the higher the hydrophilicity of the medium surface, the better. In order to obtain reliable fixing quality even if the permeability of the medium is low, it is necessary to take measures such as increasing the nip time, increasing the nip pressure, or increasing the supply amount of foamy fixer. Don't be. Increasing the nip time or increasing the nip pressure can be a design constraint. Increasing the amount of foam fixer supplied not only saves resources but also increases the supply. The problem that it leads to the load of the service person occurs.

  For these reasons, the polar group generation unit 2 in FIG. 5 performs corona discharge treatment on the medium in the medium transport process, and polar groups are generated on the surface of the medium. As a result, the hydrophilicity of the medium is improved. By improving the hydrophilicity of the medium, the medium absorbs more foamy fixer when the medium is applied with the foamy fixer at the nip portion of the application roller. Accordingly, the residual foamy fixing liquid is reduced on the coating roller after passing through the medium. Since the remaining foam fixing solution may be mixed with the offset toner and must be discarded, it is possible to reduce the amount of the foam fixing solution to be discarded. As a result, waste is reduced and maintenance is improved.

  Of course, it goes without saying that the corona discharge by the polar group generation unit 2 need not always be performed, and it is only necessary to perform the corona discharge only when the recording medium passes through the polar group generation unit 2. By doing so, energy-saving corona discharge is possible. Furthermore, if the corona discharge treatment is performed only on the portion on the medium to which the foamy fixing solution is applied, the efficiency is further improved and the energy is saved.

  Further, in the electrostatic transfer process, toner is transferred by applying an electric field, so that the toner is sensitive to the electric field. Corona discharge treatment generates strong electric fields and electric field fluctuations at high voltage and high frequency. Therefore, when the toner image is transferred and the medium on which the unfixed toner image is formed is subjected to corona discharge treatment, a problem such as scattering of the unfixed toner image occurs, which causes image disturbance. On the other hand, in the medium after being subjected to the corona discharge treatment, charges are not injected into the medium itself, but only OH groups and carbonyl groups are generated and the hydrophilicity is improved. Therefore, it is desirable that the corona discharge treatment to the medium by the polar group generation unit is performed before the toner image is transferred to the medium by the secondary transfer unit. Further, since it is known that the hydrophilicity of the medium after the corona discharge treatment is lowered with time, as shown in FIG. 5, the polar group generation unit 2 is located upstream of the secondary transfer unit. The image of the unfixed toner is transferred to the medium in the secondary transfer unit immediately after the corona discharge treatment to the medium by the polar group generation unit 2 online.

  There are various media. There are thickness, basis weight, size, brand, category, etc. even if limited to paper. Some of them have a continuous characteristic change according to basis weight, for example, and some have specific characteristics depending on brands and categories (inkjet paper, coated paper, etc.).

  Here, as shown in FIG. 10, the hydrophilicity of the medium surface is changed by the corona discharge treatment. In FIG. 10, the surface contact angle indicates hydrophilicity, and the surface contact angle is a contact angle between a substrate and a water droplet when a water droplet is dropped on the substrate. The smaller the surface contact angle, the higher the hydrophilicity. Furthermore, as shown in the figure, the hydrophilicity varies depending on the medium. If the hydrophilicity varies in this way, the characteristics relating to fixing in the present embodiment also vary, which affects the reliability of the product. Therefore, in order to obtain the same hydrophilicity for every medium, it is necessary to set a unique corona treatment for each medium. That is, as shown in FIG. 10, in order to obtain desired hydrophilicity, it is necessary to set the corona discharge voltage values a to c of the media A to C. For this purpose, the corona discharge control unit 53 of FIG. 5 is provided with information holding means (not shown) for holding information on the type of medium, and information on various media stored in a memory table as this information holding means. Accordingly, appropriate corona discharge conditions are given by the corona discharge controller 53. In addition, although it is a specific example, it is shown in the case of manual input, because detecting the thickness, basis weight, brand, etc. with a sensor, regardless of the size of the medium, requires a corresponding cost. . Of course, it may be automatically acquired. Of course, the main premise is that only one type of medium is contained in one paper feed tray, but the user manually inputs which type of medium is set in which tray. As a manual input method, any method may be used, for example, input on the control screen of the apparatus or setting with the dial of the paper feed tray. On the other hand, the information holding means corresponded to various media types, incidental information corresponding to them, and finally corona discharge conditions (voltage, frequency, power, current, duty, etc.) corresponding to the media type. An information table is provided.

  Next, when the input medium type information is acquired in the corona discharge processing flow shown in FIG. 11 (step S101), the information holding means in the corona discharge control unit 53 of FIG. 5 is based on the acquired medium type information. The information in the memory table is collated (step S102). If there is the type information of the input medium, the corona discharge condition corresponding to the type information of the medium is determined (step S103; YES, step S104). The conditions of the corona discharge are transmitted to the corona discharge control unit 53 in FIG. The corona discharge controller 53 controls the corona discharge so that proper corona discharge is performed under these conditions (step S105).

  In this embodiment, corona discharge is used as means for generating a polar group on the surface of the medium in order to improve the hydrophilicity of the medium. However, the present invention is not limited to corona discharge, and can improve the hydrophilicity of the medium. Other means may be used. For example, when UV treatment is performed, the molecular bond of the organic compound (CH-) constituting the recording medium is broken by high-energy ultraviolet rays to form polar groups, and hydrogen atoms are very light, so that oxygen atoms are easily extracted. There is an example in which the hydrophilicity of the medium is improved by reaction, and such means may be used.

  Next, the liquid formulation of the fixing solution will be described. As described above, the foam-like fixing liquid has a configuration in which bubbles are contained in a liquid containing a softening agent. The liquid containing the softening agent preferably contains a foaming agent and a foam-increasing agent in order to stably contain bubbles and to form a foam layer constituting a bubble layer having a uniform bubble size as much as possible. Moreover, it is desirable to contain a thickener since the bubbles are more stably dispersed in the liquid when the viscosity is higher to some extent.

  As the foaming agent, an anionic surfactant, particularly a fatty acid salt is desirable. Since the fatty acid salt has surface activity, the surface tension of the fixer containing water is lowered to make the fixer easier to foam, and the fatty acid salt has a layered lamellar structure on the surface of the foam, so the foam wall (plateau boundary) is another It is stronger than the surfactants and the foam stability is extremely high. Further, in order to make the foaming property of the fatty acid salt effective, it is desirable that the fixing solution contains water. As the fatty acid, a saturated fatty acid resistant to oxidation is desirable from the viewpoint of long-term stability in the air. However, the presence of some unsaturated fatty acid salt in the fixing solution containing saturated fatty acid salt helps to dissolve and disperse the fatty acid salt in water, and has excellent foaming properties at low temperatures from 5 ° C to 15 ° C. It is possible to stabilize the fixing in a wide environmental temperature range, and it is possible to prevent separation of the fatty acid salt in the fixing solution during the long-term standing of the fixing solution.

  Further, as the fatty acid used in the saturated fatty acid salt, saturated fatty acids having 12, 14, 16, and 18 carbon atoms, specifically lauric acid, myristic acid, palmitic acid, and stearic acid are suitable. A saturated fatty acid salt having 11 or less carbon atoms has a large odor and is not suitable for an image forming apparatus used in offices and homes using the fixing solution. In addition, saturated fatty acid salts having 19 or more carbon atoms are less soluble in water and significantly lower the stability of the fixing solution. Saturated fatty acid salts with these saturated fatty acids are used alone or in combination as a foaming agent.

  An unsaturated fatty acid salt may be used, and an unsaturated fatty acid having 18 carbon atoms and 1 to 3 double bonds is desirable. Specifically, oleic acid, linoleic acid, and linolenic acid are suitable. Since the reactivity is strong when the double bond is 4 or more, the stability of the fixing solution is poor. These unsaturated fatty acid salts with unsaturated saturated fatty acids are used alone or in combination as a foaming agent. Moreover, you may mix and use the said saturated fatty acid salt and unsaturated fatty acid salt as a foaming agent.

  Further, in the saturated fatty acid salt or unsaturated fatty acid salt, when used as a foaming agent for the fixing solution, a sodium salt, potassium salt or amine salt is desirable. It is an important factor as a commercial value of the fixing device that the fixing device can be quickly fixed after the power is turned on. In order to be able to fix in the fixing device, it is essential that the fixing solution is in the form of an appropriate foam, but the above fatty acid salt is quickly foamed so that it can be fixed after turning on the power. Can be made in a short time. In particular, when an amine salt is used, foaming occurs in the shortest time when a shearing force is applied to the fixing solution, and it is possible to easily produce a foamy fixing solution. It is possible to create a fixable state in the shortest time.

  The softening agent that is softened by dissolving or swelling the resin contains an aliphatic ester. This aliphatic ester is excellent in solubility or swelling property that dissolves or swells at least a part of the resin contained in the toner or the like.

  The softening agent has an acute oral toxicity LD50 of more than 3 [g / kg], more preferably 5 [g / kg], from the viewpoint of safety to the human body. As aliphatic esters are frequently used as cosmetic raw materials, they are highly safe for the human body.

  Further, the toner is fixed to the recording medium in a device that is frequently used in a sealed environment, and the softener remains in the toner even after the toner is fixed to the recording medium. Preferably does not involve the generation of volatile organic compounds (VOC) and unpleasant odors. That is, the softener preferably does not contain volatile organic compounds (VOC) and substances that cause unpleasant odors. Aliphatic esters have a high boiling point and low volatility and have no irritating odor as compared to generally used organic solvents (toluene, xylene, methyl ethyl ketone, ethyl acetate, etc.). In addition, as a practical odor measurement scale that can measure odors in office environments with high accuracy, the odor index (10 × log) by the three-point comparison odor bag method that is sensory measurement The dilution factor of the substance until it disappears)) can be used as an indicator of odor. The odor index of the aliphatic ester contained in the softener is preferably 10 or less. In this case, an unpleasant odor is not felt in a normal office environment. Furthermore, it is preferable that not only the softening agent but also other liquid agents contained in the fixing solution have no unpleasant odor and irritating odor.

  In the fixing solution according to the exemplary embodiment, preferably, the aliphatic ester includes a saturated aliphatic ester. When the above aliphatic ester contains a saturated aliphatic ester, the storage stability (resistance to oxidation, hydrolysis, etc.) of the softener can be improved. Further, saturated aliphatic esters are highly safe for the human body, and many saturated aliphatic esters can dissolve or swell the resin contained in the toner within 1 second. Furthermore, saturated aliphatic esters can reduce the tackiness of the toner provided on the recording medium. This is considered to be because the saturated aliphatic ester forms an oil film on the surface of the dissolved or swollen toner.

  Therefore, in the fixing solution in the exemplary embodiment, preferably, the general formula of the saturated aliphatic ester includes a compound represented by R1COOR2, wherein R1 is an alkyl group having 11 to 14 carbon atoms, and R2 Is a linear or branched alkyl group having 1 to 6 carbon atoms. If the number of carbon atoms in R1 and R2 is less than the desired range, an odor is generated. That is, the saturated aliphatic ester includes a compound represented by the general formula R1COOR2, R1 is an alkyl group having 11 to 14 carbon atoms, and R2 is a straight chain having 1 to 6 carbon atoms. In the case of a type or branched type alkyl group, the solubility or swelling property with respect to the resin contained in the toner can be improved. Moreover, the odor index of said compound is 10 or less, and said compound does not have an unpleasant odor and an irritating odor.

  Examples of the aliphatic monocarboxylic acid ester that is the above compound include ethyl laurate, hexyl laurate, ethyl tridecylate, isopropyl tridecylate, ethyl myristate, isopropyl myristate, and the like. Many of these aliphatic monocarboxylic acid esters, which are the above compounds, are soluble in oily solvents, but not in water. Therefore, for many of the aliphatic monocarboxylic acid esters which are the above-mentioned compounds, in an aqueous solvent, glycols are contained in the fixing solution as a solubilizing agent and are in the form of a solution or a microemulsion.

  In the fixing solution of the present embodiment, preferably, the aliphatic ester includes an aliphatic dicarboxylic acid ester. When the aliphatic ester includes an aliphatic dicarboxylic acid ester, the resin contained in the toner can be dissolved or swollen in a shorter time. For example, in high-speed printing of about 60 [ppm], it is desirable that the time until the fixing liquid is applied to the unfixed toner on the recording medium and the toner is fixed on the recording medium is within 1 second. When the aliphatic ester includes an aliphatic dicarboxylic acid ester, the time required for fixing the toner on the recording medium by applying a fixing solution to the unfixed toner or the like on the recording medium is 0.1 second. It is possible to be within. Furthermore, since the resin contained in the toner can be dissolved or swollen by adding a smaller amount of the softening agent, the content of the softening agent contained in the fixing liquid can be reduced.

Therefore, in the fixing solution of the present invention, preferably, the general formula of the aliphatic dicarboxylic acid ester includes a compound represented by R3 (COOR4) ₂ , and R3 is an alkylene group having 3 to 8 carbon atoms. And R4 is a linear or branched alkyl group having 3 to 5 carbon atoms. If the number of carbon atoms in R3 and R4 is less than the desired range, odor is generated, and if it is greater than the desired range, the resin softening ability decreases. That is, the aliphatic dicarboxylic acid ester includes a compound represented by the general formula R3 (COOR4) ₂ , R3 is an alkylene group having 3 to 8 carbon atoms, and R4 has 3 or more carbon atoms. In the case of a linear or branched alkyl group of 5 or less, the solubility or swelling property with respect to the resin contained in the toner can be improved. Moreover, the odor index of said compound is 10 or less, and said compound does not have an unpleasant odor and an irritating odor.

  Examples of the aliphatic dicarboxylic acid ester that is the above compound include diethylhexyl succinate, dibutyl adipate, diisobutyl adipate, diisopropyl adipate, diisodecyl adipate, diethyl sebacate, and dibutyl sebacate. Many of these aliphatic dicarboxylic acid esters, which are the above compounds, are soluble in oily solvents, but not in water. Therefore, in an aqueous solvent, glycols are contained in the fixing solution as a dissolution aid and are in the form of a solution or microemulsion.

  Further, in the fixing solution in the present embodiment, the aliphatic ester preferably contains a dialkoxyalkyl aliphatic dicarboxylate. When the above aliphatic ester contains an aliphatic dicarboxylic acid dialkoxyalkyl, the fixing property of the toner to the recording medium can be improved.

In the fixing solution in the present embodiment, preferably, the general formula of the aliphatic dicarboxylic acid dialkoxyalkyl includes a compound represented by R5 (COOR6-O-R7) ₂ , and R5 has 2 or more carbon atoms. An alkylene group having 8 or less, R6 is an alkylene group having 2 to 4 carbon atoms, and R7 is an alkyl group having 1 to 4 carbon atoms. If the number of carbon atoms in R5, R6, and R7 is less than the desired range, odor is generated, and if it is greater than the desired range, the resin softening ability decreases. That is, the above-mentioned aliphatic dicarboxylate dialkoxyalkyl includes a compound represented by the general formula R5 (COOR6-O-R7) ₂ , wherein R5 is an alkylene group having 2 to 8 carbon atoms, and R6 is In the case where it is an alkylene group having 2 to 4 carbon atoms and R7 is an alkyl group having 1 to 4 carbon atoms, it is possible to improve the solubility or swelling property with respect to the resin contained in the toner. . Moreover, the odor index of said compound is 10 or less, and said compound does not have an unpleasant odor and an irritating odor.

  Examples of the aliphatic dicarboxylate dialkoxyalkyl which is the above compound include diethoxyethyl succinate, dibutoxyethyl succinate, diethoxyethyl adipate, dibutoxyethyl adipate, diethoxyethyl sebacate and the like. . In an aqueous solvent, these aliphatic dicarboxylic acid dialkoxyalkyls are contained in the fixing solution as a solubilizing agent, and dissolved or microemulsified. Although not fatty acid esters, citrate esters, ethylene carbonate, and propylene carbonate are also suitable as softening or swelling agents.

  The fine particles containing the resin to be fixed are not limited to toner, and any fine particles containing resin may be used. For example, resin-containing fine particles containing a conductive member may be used. Further, the recording medium is not limited to recording paper, and any of metal, resin, ceramics and the like may be used. However, it is desirable that the medium has permeability to the fixing solution. When the medium substrate does not have liquid permeability, a medium having a liquid-permeable layer on the substrate is desirable. The form of the recording medium is not limited to a sheet shape, and may be a three-dimensional object having a flat surface and a curved surface. For example, the present embodiment can also be applied to applications in which transparent resin fine particles are uniformly fixed on a medium such as paper to protect the paper surface (so-called varnish coating).

  Among the fine particles containing the resin, the toner used in the electrophotographic process has the highest fixing effect in combination with the fixing liquid of the present embodiment. The toner contains a colorant, a charge control agent, and a resin such as a binder resin and a release agent. The resin contained in the toner is not particularly limited. Examples of suitable binder resins include polystyrene resins, styrene-acrylic copolymer resins, polyester resins, and the like, and examples of the release agent include carbanau wax and polyethylene. And wax components. The toner may contain a known colorant, charge control agent, fluidity-imparting agent, external additive and the like in addition to the binder resin. Further, the toner is preferably subjected to a water repellency treatment by fixing hydrophobic fine particles such as hydrophobic silica having a methyl group and hydrophobic titanium oxide to the surface of the toner particles. Among the media, the recording medium is not particularly limited, and examples thereof include paper, cloth, and a plastic film such as an OHP sheet having a liquid permeable layer. The oiliness in the present invention means a property that the solubility in water at room temperature (20 ° C.) is 0.1% by weight or less.

  Further, it is preferable that the foamed fixing solution has sufficient affinity for the water-repellent treated toner particles. Here, affinity means the degree of extended wetting of the liquid with respect to the surface of the solid when the liquid comes into contact with the solid. That is, it is preferable that the foamed fixing solution exhibits sufficient wettability with respect to the water-repellent treated toner. The surface of the toner subjected to water repellency treatment with hydrophobic fine particles such as hydrophobic silica and hydrophobic titanium oxide is covered with methyl groups present on the surface of hydrophobic silica and hydrophobic titanium oxide, and is approximately 20 [mN / M] surface energy. Actually, since the entire surface of the water-repellent treated toner is not completely covered with hydrophobic fine particles, the surface energy of the water-repellent treated toner is approximately 20 to 30 [mN / m]. It is guessed. Therefore, in order to have an affinity for the water-repellent toner (having sufficient wettability), the surface tension of the foamed fixing solution is preferably 20 to 30 [mN / m].

  When using an aqueous solvent, it is preferable to add a surfactant to make the surface tension 20-30 [mN / m]. In the case of an aqueous solvent, it is desirable to contain a unit price or a polyhydric alcohol. These materials have the advantage of increasing the stability of bubbles in the foam-like fixing solution and making it difficult to break the bubbles. For example, monohydric alcohols such as cetanol, and polyhydric alcohols such as glycerin, propylene glycol, and 1,3 butylene glycol are desirable. Further, containing these unit price or polyhydric alcohols has an effect of preventing curling of a medium such as paper.

  In addition, it is also desirable to form an O / W emulsion or a W / O emulsion containing an oil component in order to improve permeability and prevent curling of a medium such as paper, in which case, as a specific dispersant Are preferably sorbitan fatty acid esters such as sorbitan monooleate, sorbitan monosterate and sorbitan sesquioleate, and sucrose esters such as sucrose laurate and sucrose stearate. In addition, as a method for dissolving the softening agent or fixing the microemulsion during fixing, for example, a mechanical stirring means such as a homomixer or a homogenizer using a rotary blade, and a means for applying vibration such as an ultrasonic homogenizer Is mentioned. In any case, a strong shear stress is added to the softener in the fixing solution to dissolve or disperse the microemulsion.

  Further, the toner fixing device pressurizes the dissolved or swollen toner with a component (softener) that dissolves or swells at least a part of the resin contained in the toner after supplying the fixing liquid in the present embodiment to the toner. A pair of smoothing rollers (hard rollers) may be provided. By pressurizing the dissolved or swollen toner with a pair of smoothing rollers (hard rollers), the surface of the layer of the dissolved or swollen toner can be smoothed to give gloss to the toner. Furthermore, by fixing the dissolved or swollen toner into the recording medium, the fixability of the toner to the recording medium can be improved.

Next, examples of specific prescriptions of the fixing solution are shown below.
Diluting solvent: 53% by weight of ion exchange water
Softener: Diethoxyethyl succinate (Croda Croda DES)
10 wt%
Propylene carbonate 20wt%
Thickener: Propylene glycol 10wt%
Foam enhancer: Palm fatty acid diethanolamide (1: 1) type (Matsumoto Yushi, Marpon MM)
0.5wt%
Foaming agent: amine palmitate 2.5 wt%
Amristyl myristate 1.5wt%
Amine stearate 0.5wt%
Dispersant: POE (20) lauryl sorbitan (Kao Leodol TW-S120V)
1wt%
Polyethylene glycol monostearate (Kao Emanon 3199)
1wt%

  As described above, according to the present embodiment, as shown in FIG. 5, the recording medium 114 before the unfixed toner is transferred to the recording medium is subjected to the corona discharge treatment by the corona discharge electrode 51. Polar groups are generated on the surface of the recording medium 114. Further, the hydrophilicity of the recording medium 114 is improved because the polar group and the water of the fixing solution are easily bonded chemically. As a result, the foam-like fixing liquid easily penetrates into the recording medium 114 and the toner can be sufficiently softened, and the toner can easily adhere to the recording medium. Then, a sufficient softening process can be performed by simply applying an amount of the fixing liquid necessary for the fixing process to the unfixed toner. For this reason, it is no longer necessary to apply an excessive amount of the foam-like fixing solution, the waste of the foam-like fixing solution can be reduced, and sufficient fixability can be ensured.

  Further, according to the present embodiment, corona discharge is performed on the recording medium 114 existing between the corona discharge electrode 51 and the counter electrode 53 constituting the polar group generation unit 2. As described above, the corona discharge is performed by the polar group generation unit 2 only when the recording medium 114 exists between the corona discharge electrode 51 and the counter electrode 53. Thereby, when the recording medium 114 does not exist between the corona discharge electrode 51 and the counter electrode 53, corona discharge is not performed, so that power consumption associated with corona discharge is suppressed, and low power consumption is achieved in view of the entire apparatus. be able to.

  Furthermore, according to the present embodiment, as shown in FIG. 5, by performing corona discharge at a curved portion in the conveyance path of the recording medium 114, a uniform corona discharge treatment can be performed on the recording medium. The polar group can be evenly formed on the surface of the substrate. Thereby, the hydrophilicity of the recording medium can be improved uniformly.

  In addition, according to the present embodiment, the counter electrode 53 is a conductive guide, for example, a metal guide member that guides the medium to be transported along the transport path, and thus corona discharge is applied to the medium along the guide member. By performing this, a uniform corona discharge treatment is possible and the hydrophilicity of the medium can be improved uniformly.

  Further, according to the present embodiment, the corona discharge set value storage means stores the corona discharge set value for each medium type. Then, the corona discharge set value corresponding to the type of the recording medium is read from the corona discharge set value storage means. Corona discharge is performed on the recording medium with the read corona discharge setting value. Corona discharge can be performed with an appropriate corona discharge setting value according to various recording media to give the recording medium stable hydrophilicity without variation.

  In addition, according to the present embodiment, polar groups are generated on the surface of the recording medium 114 by irradiating the surface of the medium with ultraviolet rays. The hydrophilicity of the recording medium 114 is improved. As a result, the foam-like fixing liquid easily penetrates into the recording medium 114 and the toner can be sufficiently softened, and the toner can easily adhere to the recording medium.

  Further, in the image forming apparatus including the fixing device of the present embodiment, before transferring the unfixed toner to the recording medium, the recording medium is subjected to corona discharge treatment to improve the hydrophilicity of the recording medium. A foamy fixing solution is applied to the unfixed toner formed on the recording medium. For this reason, when the hydrophilicity of the recording medium is improved, the fixing solution can easily penetrate and the adhesiveness with the softened toner is also improved. Sufficient fixability can be secured while reducing useless foamy fixer.

DESCRIPTION OF SYMBOLS 1 Fixing device 2 Polar group production | generation part 51 Corona discharge electrode 52 Corona discharge control part 53 High frequency power supply 54 Counter electrode 100 Image forming apparatus 114 Recording medium

Japanese Patent No. 3290513 Japanese Patent No. 4185742 JP 59-119364 A JP 2009-008967 A

Ishii Ikuo, “Engineering of Bubbles”, first edition, Techno System Co., Ltd., published on March 25, 2005, p. 489

Claims (8)

Apply a foamy fixer produced by mixing a gas to a liquid fixer containing at least a softening agent that softens resin-containing fine particles by dissolving or swelling at least part of the resin. In the fixing device for fixing the resin fine particle layer to the medium,
The resin fine particle layer formed on the medium has polar group generating means for generating a polar group on the surface of the medium, and the polar group generating means generates the polar group on the surface of the medium. A fixing device that applies a fixing solution. The fixing device according to claim 1.
The fixing device according to claim 1, wherein the polar group generation unit includes a corona discharge electrode for performing corona discharge on the medium, and a counter electrode facing the corona discharge electrode. The fixing device according to claim 2.
The polar group generating means performs corona discharge to generate a polar group on the surface of the medium, only when the medium exists between the corona discharge electrode and the counter electrode. Fixing device to do. The fixing device according to claim 2 or 3,
The fixing device according to claim 1, wherein the corona discharge electrode and the counter electrode are installed at a location where the medium is curved toward the conveyance direction of the medium. The fixing device according to claim 4.
The fixing device, wherein the counter electrode is a conductive guide member that guides the medium to be conveyed along a conveyance path and is grounded. In the fixing device according to any one of claims 2 to 5,
Corona discharge setting value storage means for storing corona discharge setting values for each type of medium, and reading the corona discharge setting values corresponding to the medium type from the corona discharge setting value storage means. A fixing device that performs corona discharge on the medium with a discharge setting value. The fixing device according to claim 1.
The fixing device according to claim 1, wherein the polar group generation unit includes an ultraviolet irradiation unit that irradiates the surface of the medium with ultraviolet rays.   8. An image forming unit that forms an unfixed toner image on a medium by performing an electrostatic recording process with toner in which resin-containing fine particles contain a colorant, and the undetermined state by the fixing device according to claim 1. An image forming apparatus comprising: a fixing unit that fixes a toner image onto a medium.

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