JP5125959B2 - Wet developer and fixing method - Google Patents

Description

  The present invention relates to a wet developer in which toner is dispersed in a carrier liquid, and a fixing method for transferring and fixing a toner image developed using the wet developer to a recording material.

  2. Description of the Related Art An electrophotographic image forming apparatus that forms an electrostatic latent image on a photoconductor (photosensitive drum), adheres toner to the image, and transfers and fixes the image on paper or the like is widely used. In particular, in an image forming apparatus that requires higher image quality and higher resolution, such as an office printer for large-scale printing and an on-demand printing apparatus, a wet developer that uses a wet developer that has a small toner particle diameter and that does not easily disturb the toner image. Development methods are being used.

  In recent years, a high-viscosity, high-concentration wet developer composed of high-concentration toner dispersed as a solid component consisting of a resin and a pigment in an insulating solvent (carrier liquid) such as liquid paraffin or silicone oil. An image forming apparatus using this has been proposed.

  When developing using this wet developer, a thin layer of developer is formed on a developer carrier such as a developing roller, and the thinned developer is brought into contact with the photoreceptor. It is common to develop.

  The latent image on the surface of the photoreceptor is developed with a thin layer of a wet developer, and a toner image is formed on the surface of the photoreceptor. This toner image is transferred to a recording material. Alternatively, the toner image is first temporarily transferred to an intermediate transfer member or the like and then secondarily transferred to a recording material.

  The toner image transferred to the recording material is fixed on the recording material, which is usually paper, by being pressurized and heated by a fixing device. However, the toner image is originally developed using a wet developer in which the toner is dispersed in the carrier liquid, and the carrier liquid is contained not only between the toner but also between the toners and between the toner papers. Moreover, it has a fairly high viscosity.

  It is known that the presence of a high-viscosity carrier liquid hinders fixability during toner image fixing. For example, since the toner image and the recording material are wet with the carrier liquid, the fixability of the toner image is lowered, and the image may be crushed or disturbed during pressure fixing.

  On the other hand, a technique for removing a solvent (carrier liquid) from an unfixed toner image before fixing has been developed.

  For example, a heat source is prepared in front of the fixing device, and the solvent on the recording material is removed by volatilization. Alternatively, the solvent in the toner image is deposited on the surface by heating and removed by a removing means such as squeeze. Further, the adhesion between the toner and the recording material is increased by applying an electric field. Etc. have been proposed.

  However, there are problems such as the safety of volatilized solvent and the increased energy to supply heat of vaporization, the risk of damaging the recording material in the squeeze process, and the occurrence of image distortion and roughness. Was difficult.

  The factor that the high-viscosity solvent hinders the fixability is related to the fact that high dispersibility is required from the viewpoint of storage stability as a wet developer. If the wet developer itself maintains high dispersibility, contact and coalescence of the toner particles do not proceed at the time of fixing, and the toner layer cannot form a condensed state of toner particles and cannot be fixed. become weak.

  On the other hand, if the dispersibility is lowered, there is a risk that toner aggregation occurs during storage of the wet developer and storage stability cannot be maintained.

  Therefore, it is desirable if the solvent can be removed from the toner layer at the time of fixing. However, considering the above-mentioned difficulties, as a wet developer containing a solvent, the storage stability is maintained and the fixing property is not hindered. It is also necessary to examine the thermophysical properties. The present inventor has found that the dynamic viscoelastic temperature characteristic of the wet developer is effective in evaluating the storage stability and fixability.

  Japanese Patent Application Laid-Open No. H10-260260 proposes a technique for measuring dynamic viscoelasticity of a toner image before thermal transfer and controlling the toner image so that the viscoelasticity is within a predetermined range. In the control method, for example, the temperature is raised by a heater to change the viscoelasticity. Thus, by keeping the toner layer in a predetermined softened state in advance, the transfer with the toner melted can be smoothly advanced.

However, in the case of Patent Document 1, softening of toner particles is a problem, and what is controlled is mostly dynamic viscoelasticity as a toner. As a wet developer in which toner particles are dispersed in a solvent, the thermal properties of the toner particles are not directly reflected.
JP 2004-333633 A

  As described above, in the wet development, the toner image before fixing transferred to the recording material contains a carrier liquid (solvent) having a considerably high viscosity between the toner and the toner recording material as well as the toner. Therefore, the fixing property at the time of fixing the toner image is inhibited. However, there are many problems in removing the carrier liquid.

  Even in the presence of a carrier liquid between toners and between toner recording materials, it is effective to reduce dispersibility as a wet developer in order to promote contact and coalescence of toner particles and improve fixability. It is. However, on the other hand, there is a problem in that the storage stability of the wet developer is impaired due to a decrease in dispersibility.

  An object of the present invention is to solve these problems, maintain a storage stability as a wet developer, and have a wet developer having characteristics that are difficult to inhibit fixability, and the wet developer. It is to provide a fixing method used.

The purpose is to provide a carrier liquid,
Toner particles dispersed in the carrier liquid;
A wet developer containing a dispersant for dispersing the toner particles in the carrier liquid,
This is achieved by giving the wet developer a temperature characteristic in which a change in the loss elastic modulus G ″ accompanying a temperature rise of the wet developer forms a peak.

  Provided is a wet developer having specific temperature characteristics, particularly dynamic viscoelasticity, in particular, loss viscoelastic temperature characteristics. As a result, it is possible to provide a wet developer having a characteristic that the storage stability as a wet developer is maintained, and the fixability is hardly inhibited, and a fixing method using the wet developer.

Embodiments according to the present invention will be described with reference to the drawings.

  Wet development using a wet developer is used in image forming apparatuses such as copiers, simple printers, and printers. In general, an electrophotographic image forming process is commonly used for these. First, the electrophotographic wet image forming unit will be described with reference to FIG. 1, and further, the fixability of the toner image developed using the wet developer and transferred to the recording material, and the dynamic of the wet developer. The relationship of the temperature characteristics of viscoelasticity (substituting for loss elastic modulus) will be described.

(Configuration of image forming unit and functional operation)
A configuration example of an image forming unit in an image forming apparatus using a wet developer according to the present embodiment will be described with reference to FIG. FIG. 1 is a diagram illustrating a schematic configuration example of an image forming unit in a wet image forming apparatus.

  In FIG. 1, reference numeral 1 denotes a photosensitive drum, which functions as an image carrier. The image forming unit 10 is centered on the photosensitive drum 1 and has a charging device 2 for uniformly charging the surface of the photosensitive drum 1, and an LED or laser beam on the charged photosensitive drum 1. , An exposure device 3 for forming an electrostatic latent image, a wet developing device 4 for developing the electrostatic latent image using a wet developer, a transfer device 5 for transferring the developed toner image to a transfer material 7, A cleaning device 6 for removing the wet developer remaining on the surface of the photosensitive drum after transfer is provided.

  In some cases, before and after the wet developing device 4, a device for applying or collecting a part of the wet developer in advance is provided. Here, a squeeze device 91 for removing excess wet developer from the developed toner image is provided after the wet developing device 4.

  The transfer material 7 may be a recording material such as recording paper as it is, or may be configured such that the transfer material 7 is transferred again to the recording material using an intermediate transfer belt or the like. In the present embodiment, the transfer material 7 is described as a recording material, that is, a recording paper (hereinafter referred to as recording material 7).

In general, the wet developing device 4 bears a thin layer of a wet developer on the surface and abuts against a developing roller 41 and a developing roller 41 that develop a latent image on the photosensitive drum 1 as an image carrier. A transport roller 42 for transferring the wet developer whose liquid amount has been adjusted to the surface thereof, and a supply roller 43 that contacts the transport roller 42 and supplies the wet developer 8 in the developer tank 44 to the surface. . The supply roller 43 is an anilox roller, and the amount of wet developer supplied is limited by bringing the regulating blade 45 into contact with the peripheral surface of the supply roller 43. Reference numeral 46 denotes a cleaning blade for cleaning the peripheral surface of the developing roller 41 after passing through the developing nip.

  In FIG. 1, only one wet developing device 4 is disposed, but a plurality of wet developing devices 4 may be disposed for color image formation. The color development method, the presence / absence of intermediate transfer, and the like may be set arbitrarily, and an arbitrary arrangement according to it can be taken.

  The photosensitive drum 1 rotates in the direction of arrow A shown in FIG. 1, and the charging device 2 charges the surface of the rotating photosensitive drum 1 to about several hundred volts by corona discharge or the like. On the downstream side of the charging device 2 in the rotation direction of the photosensitive drum, an electrostatic latent image whose surface potential is lowered to about 100 V or less is formed by the laser beam emitted from the exposure device 3.

  A wet developing device 4 is disposed further downstream of the exposure device 3, and the electrostatic latent image formed on the photosensitive drum 1 is developed using the wet developer 8.

  In the wet developing device 4, a wet developer 8 in which toner is dispersed in an insulating solvent (hereinafter also referred to as a carrier liquid) is accommodated in a developer tank 44, and the surface of the conveying roller 42 is supplied by a supply roller 43. A wet developer 8 is supplied.

  The conveying roller 42 conveys a thin layer of the wet developer 8 and transfers it to the developing roller 41. A thin layer of the wet developer 8 is carried on the developing roller 41. Further, due to the potential difference between the developing roller 41 and the electrostatic latent image on the photosensitive drum 1, the toner particles in the thin layer of the wet developer 8 carried on the developing roller 41 become an electrostatic latent image on the photosensitive drum 1. Moving, the electrostatic latent image is developed.

  The developed toner image on the photosensitive drum 1 contains toner and carrier liquid. The squeeze device 91 is, for example, a squeeze roller, and removes excess carrier liquid from the developed toner image. The carrier liquid on the squeeze roller is removed by the blade 92.

  In the transfer device 5 (for example, a transfer roller), the recording material 7 conveyed at the same speed as the peripheral speed of the photosensitive drum 1 is charged, or a voltage is applied to develop the development on the photosensitive drum 1. The toner image is transferred onto the recording material 7.

  A cleaning device 6 (for example, a cleaner blade) that removes the wet developer 8 remaining on the surface of the photosensitive drum 1 is disposed on the downstream side of the transfer device 5. The cleaning device 6 removes the wet developer 8 remaining on the photosensitive drum 1.

  The recording material 7 onto which the toner image has been transferred by the transfer device 5 is conveyed to a fixing device including a pair of fixing rollers 9a and 9b, and is discharged after being heated and fixed.

(Developer composition)
The wet developer 8 used for development will be described. The wet developer 8 disperses colored toner particles at a high concentration in a carrier liquid as a solvent. In addition, additives such as a dispersant and a charge control agent may be appropriately selected and added to the wet developer 8.

  As the carrier liquid, an insulating, non-volatile solvent at room temperature is used. As the non-volatile solvent, it is possible to use insulating oil, for example, general liquid paraffin such as Moresco White and Isopar, silicon oil, and the like.

  The toner particles are mainly composed of a resin and a pigment or dye for coloring. The resin has a function of uniformly dispersing pigments and dyes in the resin and a function as a binder when being fixed to the recording material.

  Examples of the resin that can be used include thermoplastic resins such as polystyrene resin, styrene-acrylic resin, acrylic resin, polyester resin, epoxy resin, polyamide resin, polyimide resin, and polyurethane resin. A plurality of these resins may be mixed and used.

  Commonly commercially available pigments and dyes used for coloring the toner can also be used. For example, carbon black, bengara, titanium oxide, silica, phthalocyanine blue, phthalocyanine green, sky blue, benzidine yellow, lake red D, etc. can be used as the pigment. Solvent red 27, acid blue 9, or the like can be used as the dye.

  As the dispersant, a general oil-soluble dispersant can be used, and more details will be described later.

  The wet developer can be prepared based on a commonly used technique. For example, the resin and the pigment are melt kneaded using a pressure kneader, a roll mill or the like at a predetermined blending ratio and uniformly dispersed, and the obtained dispersion is finely pulverized by, for example, a jet mill. Further, by classifying the obtained fine powder with, for example, an air classifier, a colored toner having a predetermined particle diameter can be obtained.

  Subsequently, the obtained toner is mixed with an insulating oil as a carrier liquid at a predetermined blending ratio. This mixture can be uniformly dispersed by a dispersing means such as a ball mill to obtain a wet developer.

  The volume average particle diameter of the toner is suitably in the range of 0.1 μm or more and 5 μm or less. When the average particle diameter of the toner is less than 0.1 μm, the developability is greatly lowered. On the other hand, when the average particle diameter exceeds 5 μm, the quality of the image is deteriorated.

  The ratio of the toner particle mass to the wet developer mass is suitably about 10 to 50%. If it is less than 10%, toner particles are liable to settle, and there is a problem with the stability over time during long-term storage. Further, in order to obtain a required image density, it is necessary to supply a large amount of developer, the carrier liquid adhering to the paper increases, and it must be dried at the time of fixing, and steam is generated, resulting in environmental problems. If it exceeds 50%, the viscosity of the wet developer becomes too high, making it difficult to manufacture and handle.

  The viscosity of the wet developer is preferably from 0.1 mPa · s to 10,000 mPa · s at 25 ° C. When it is 10,000 mPa · s or more, it becomes difficult to stir the carrier liquid and the toner, and the burden on the apparatus surface for obtaining a uniform wet developer is large.

(Dynamic viscoelasticity of wet developer and its temperature characteristics)
According to the present invention, both the fixability and the storage stability can be controlled by controlling the temperature characteristics of the dynamic viscoelasticity of the wet developer.

  Regarding the dynamic viscoelasticity of the wet developer, there is an aspect in which accurate measurement is difficult depending on the viscosity range. In this embodiment, the loss elastic modulus G ″ that can be measured with higher accuracy is used as a substitute characteristic. Hereinafter, the description will be continued based on the loss elastic modulus, but of course, an index representing the storage elastic modulus and other dynamic viscoelasticity. Can be used.

  The loss elastic modulus G ″ was measured using a rheological property evaluation apparatus (rotary rheometer) ARES-RFS manufactured by TA Instruments, Inc. The plate used was a 50 mm parallel plate, the measurement conditions were a gap of 1 mm, a frequency of 10 Hz, and a strain of 5. %, The heating rate is 10 ° C./min.

<Normal temperature characteristics>
2 shows a temperature characteristic of the loss elastic modulus G ″ in the conventional non-volatile wet developer. The loss elastic modulus smoothly and monotonously decreases as the temperature of the wet developer increases. The higher the viscosity, the lower the viscoelasticity and the softness, which is a characteristic of the carrier liquid to a certain extent and can be said to represent the dispersibility of the toner particles in the carrier.

  That is, the smooth monotonic decrease in the loss elastic modulus in FIG. 2 reflects the loss elastic modulus of the carrier liquid, and it can be said that the wet developer maintains high dispersibility. Therefore, this wet developer is less likely to cause toner aggregation and has good storage stability.

  Next, let us consider a case where a toner image developed using such a wet developer is fixed. The toner image before fixing contains a highly viscous carrier liquid between the toner particles forming the toner image and between the toner and the recording material.

  The wet developer is given a certain degree of dispersibility by a dispersant or the like in consideration of storage stability so that toner particles do not aggregate during storage. In the case of a wet developer having good fixability, dispersibility decreases as the temperature rises for the fixing operation, and toner particles contact and agglomerate. That is, the fixing property is ensured smoothly. However, in the case of a wet developer having poor fixability as shown in FIG. 2, the dispersibility is hardly lowered due to the temperature rise, and reaches the melting temperature of the toner before contact and aggregation of the toner particles occur.

  Thus, the change in dispersibility generally corresponds to the change in loss elastic modulus, that is, the temperature characteristic. The specific relationship will be described later from the viewpoint of the peak of the temperature characteristic.

  The problem here is that the securing of the fixing property and the storage stability are in a trade-off relationship as described above. If good fixability is to be ensured, dispersibility must be sacrificed, and sufficient storage stability cannot be ensured. On the other hand, if the storage stability is to be ensured, a high dispersibility must be maintained, and the fixability tends to be hindered.

  Wet developer retains high dispersibility (high loss modulus) that is unlikely to cause toner aggregation at storage temperature, and low dispersibility (carrier liquid and toner layer) that facilitates toner aggregation and integration at the fixing temperature. It is desirable to have a temperature characteristic that can secure a low loss elastic modulus associated with separation of

<Temperature characteristics with peaks>
FIG. 3 shows an example of the temperature characteristic of the loss elastic modulus G ″ for the wet developer in which the storage stability and the fixing property are easily compatible as described above. This is also the loss elastic modulus G ″ in this embodiment. However, originally, it is dynamic viscoelasticity as described above. A storage elastic modulus or other index indicating dynamic viscoelasticity may be used.

  The present inventor pays attention to the temperature characteristic of the loss elastic modulus of the wet developer, and the degree of trade-off between storage stability and fixability changes depending on whether the temperature characteristic of the loss elastic modulus has a peak. I found it. With reference to FIG. 3, the characteristics of the temperature characteristics in which storage stability and fixability are easily compatible will be described.

  In FIG. 3, the loss elastic modulus monotonously decreases as the temperature of the wet developer initially increases. However, at a temperature lower than the fixing temperature, the loss elastic modulus decreases slowly, and at temperature T1, the loss elastic modulus starts increasing again. Thereafter, the loss elastic modulus stops increasing at a temperature T2 near the fixing temperature, and thereafter the loss elastic modulus continues to decrease monotonously. That is, a peak is formed at the temperature T2.

  What is meant by the change in loss modulus at this peak will be described.

  The temperature T1 is a temperature at which the dispersibility is lowered, that is, a temperature at which toner particles come into contact with each other and aggregation starts. Therefore, when considering the storage stability of the wet developer, it is required to store it at a temperature sufficiently lower than T1. That is, storage stability is better when T1 is sufficiently high.

  As the temperature rises above T1, the lost loss modulus begins to rise. This is considered to be due to the progress of toner aggregation. The loss elastic modulus does not depend only on the carrier liquid, but the entanglement with the agglomerated toner acts and the loss elastic modulus continues to increase.

  When the temperature reaches T2, the loss elastic modulus stops increasing and begins to decrease. This is because the toner is almost aggregated and integrated, and is almost separated from the carrier liquid. Accordingly, the loss elastic modulus changes again so as to depend only on the carrier liquid. That is, it continues to decrease monotonously as the temperature rises.

  From the above, it can be seen that the temperature T2 corresponds to a state where toner aggregation is sufficiently advanced. It is possible to increase the fixing strength by utilizing the aggregation of the toner. Therefore, if the fixing strength of the toner is taken into consideration, it is required to fix at the fixing temperature T2 or higher. That is, when T2 is sufficiently low, the fixing strength can be obtained at a lower fixing temperature.

<Fixability, storage stability and temperature characteristics T1, T2>
From the viewpoint of trade-off between fixability and storage stability,
Storage stability is better when the rising temperature T1 is higher.
And
Fixation is better when the peak temperature T2 is lower.
And furthermore,
T1 ≦ T2
Therefore, as the temperature T1 is closer to the temperature T2 and the temperature T2 is closer to the temperature T1, both storage stability and fixing property can be achieved.

  In the present embodiment, the loss elastic modulus G ″ is employed as a substitute characteristic of dynamic viscoelasticity. Specific examples of the temperature T1 and the temperature T2 that contribute to fixability and storage stability in this case are shown (wet development). (For the composition of the agent, the process conditions for toner image formation and fixing, and the evaluation method for fixing property and storage stability, see Examples described later.)

The storage stability is better when the temperature T1 exceeds 40 ° C, preferably exceeds 55 ° C.
The fixing property is good when the temperature T2 does not exceed 130 ° C., preferably below 100 ° C.
That is, the wet developer from the viewpoint of both storage stability and fixability is
40 ° C <T1 ≦ T2 <130 ° C
It is preferable to satisfy the relationship of
55 ° C <T1 ≦ T2 <100 ° C
It satisfies the relationship.

<T1 = T2 temperature characteristics>
In the description of the temperature characteristics having a peak in FIG. 3, it is stated that the storage stability and the fixing property can be improved as T1 is closer to T2 and T2 is also closer to T1. That is, as long as T1 ≦ T2, it is ideally desirable that T1 = T2.

  However, when T1 = T2, it is not appropriate to say that the loss elastic modulus starts to rise at the temperature T1 and to form a peak at the temperature T2. Therefore, considering the extreme state where T1 and T2 approach each other, the temperature characteristic as shown in FIG. 4 is referred to as the temperature characteristic of T1 = T2.

  FIG. 4 shows an example of the temperature characteristic of the loss elastic modulus G ″ where T1 = T2. The loss elastic modulus keeps trying to rise while approaching T1. During this time, toner aggregation continues within a range that does not affect the loss elastic modulus. When the point indicated by T1 and T2 is reached, the aggregated toner immediately changes to a state separated from the carrier liquid (fixed state) and no longer reaches a peak. As a result, the loss elastic modulus that has been held begins to decrease rapidly. The behavior of the loss elastic modulus G "accompanying such a temperature rise is surely the loss elastic modulus G" accompanying the normal temperature rise of FIG. Therefore, in the present invention, the behavior of the temperature characteristic of the loss elastic modulus G ″ with T1 = T2 shown in FIG. Form It is intended to include the concept of time characteristics ".

  This can be interpreted as that the temperature T1 at which the toners start to aggregate in the wet developer and the temperature T2 at which the integration and melting by the toner aggregation are finished are very close. If so, it is the most desirable state from the viewpoint of both storage stability (T1 should be high temperature) and fixability (T2 should be low temperature).

<Temperature characteristics control method>
In the present invention, the temperature characteristic of the loss modulus in the wet developer is intentionally controlled to give the wet developer a specific temperature characteristic, thereby obtaining a correspondingly good storage stability and fixability. Is.

  The loss elastic modulus may be controlled through dispersibility control using a dispersant. That is, the type and amount of the dispersant added to the wet developer are appropriately selected to control the dispersibility of the wet developer. Control is made so as to be highly dispersible in consideration of storage stability at low temperatures and low dispersibility in consideration of fixing properties at high temperatures. When selecting a dispersant, attention is paid mainly to adsorption groups, compatible groups, and molecular weight. Each of them affects the adsorptivity to the particles, the solubility in the carrier liquid, and the diffusibility of the dispersant. The adsorptive group is preferably selected in consideration of acid / base, hydrogen bond, etc. according to the polarity of the toner surface. For example, when the toner contains a polyester resin, -COOH is present at the terminal and is acidic, so that the dispersant preferably has a basic adsorbing group. The compatible group needs to be appropriately selected according to the carrier liquid molecule. The molecular weight is preferably selected from solubility in a carrier liquid and diffusibility. As the molecular weight increases, the solubility and diffusibility in the carrier liquid decrease and it becomes difficult to uniformly adhere to the toner surface, but after adhering, stable adsorbability is exhibited. When the molecular weight is low, it is easy to dissolve and manufacture, but the diffusibility tends to increase and the dispersibility tends to decrease. Accordingly, it is preferable that the dispersibility exhibits stable dispersibility at a low temperature, and the dispersibility decreases at a high temperature, and exhibits a strong adsorptivity to the toner at a low temperature and dissociates from the toner at a high temperature. From this point of view, the weight is to select the type / number of adsorbing groups, the type / length of compatible groups, and the molecular weight. However, since a phenomenon that does not meet the general rules also occurs, it is important to select a dispersant experimentally.

  Since the temperature characteristics also depend on the temperature characteristics of the dispersant, the type and amount of the dispersant are important.

  As a dispersing agent, as an adsorbing group, an amino group (1 to 3), an aromatic amine such as a pyridinium group, pyrrolidone, imine, polyimine, —COOH, —SO 3 H, —OH, a carbonyl group, an ether group, an epoxy group, Examples thereof include a polymer dispersant containing an ester group, an amide group, or a salt thereof. As the compatible group, those having mainly a hydrocarbon chain, a hydroxy hydrocarbon chain, a polyester chain, a polyamide chain and the like are preferable. It is preferable to have a plurality of these adsorbing groups and compatible groups in the molecule. Examples of the bonding mode include a comb type, a pendant type, a single type, and a star type. Among these, a comb type and a pendant type are particularly preferable. By selecting these adsorbing groups and compatible groups from a plurality of combinations, wider characteristics can be obtained. The molecular weight is preferably about 2000 to 10000, although it depends on the adsorptive group and the compatible group. Examples of preferable dispersing agents include Solsperse S11200, S13940, S19000, S36000 manufactured by Lubrizol, V216, V220, WP550 manufactured by ISP, and BYK-116 manufactured by BYK Chemie. Particularly preferred is Solpers S13940, V216, V220.

  The added amount of the dispersant is 0.5 to 2.0 parts by weight, preferably 0.5 to 1.5 parts by weight, with respect to 100 parts by weight of the toner. When the addition amount is large, the dispersibility becomes too high even at a high temperature, and the fixability tends to decrease. Moreover, when there is little addition amount, the viscosity of a wet developing agent will become high too much, and there exists a tendency for handling to become difficult. However, due to the influence of the molecular weight, molecular weight distribution, dispersibility, adsorptivity, amount of impurities, etc. of the dispersant, it is not necessarily limited to the above range, and it is important to determine an appropriate addition amount according to the dispersant. It is.

  In order to obtain appropriate temperature characteristics, it is also desirable to use a mixture of a plurality of types of dispersants. When each of them is used alone, it is possible to easily obtain more desirable temperature characteristics by using a dispersant in which two types of dispersants having different temperature characteristics are appropriately mixed.

(Temperature characteristics control by mixing two types of dispersants)
Control of temperature characteristics by mixing a plurality of types (two types here) of dispersants having different temperature characteristics will be described.

  By using two types of dispersants, a wet developer that satisfies both fixability and storage stability by appropriately controlling the temperature characteristics of the loss modulus characterized by the rising temperature T1 and the peak temperature T2. Can be obtained.

Even when two kinds of dispersants are used, the purpose of the temperature characteristic in the loss modulus G ″ is as follows:
40 ° C <T1 ≦ T2 <130 ° C
It is preferable to satisfy the relationship of
55 ° C <T1 ≦ T2 <100 ° C
It satisfies the relationship.

  By using two kinds of dispersants, T1 and T2 can be brought closer to each other, and the state of T1 = T2 already described can be brought closer. Thus, storage stability and fixability are satisfied by simultaneously satisfying the conditions that the storage stability is better when T1 is higher and the fixability is better when T2 is lower. The range of choices that can achieve both is increased.

  A plurality of appropriate dispersants are selected for the purpose of the temperature characteristics, and appropriate addition amounts are set. Here, two types of dispersants are selected and mixed. One dispersant is selected from dispersants that can maintain stable dispersibility even at high temperatures, and the other dispersant is selected by selecting a dispersant that is slightly less dispersible at high temperatures and setting an appropriate addition amount. The temperature characteristics can be controlled. More specifically, when selecting from a plurality of similar dispersants, the former is a polymer with a larger number of adsorbing groups and a stronger adsorbing group, and the latter is a lower molecule with an adsorbing group. A dispersant having a small number of weakly adsorbing groups may be selected.

  As the dispersant, it can be appropriately selected from the above-mentioned dispersants, but when two types of dispersants are used, a dispersant that cannot be used when only one type of dispersant is used, That is, it is possible to use a dispersant that does not exhibit a peak as the temperature of the loss elastic modulus G ″ specified in the present invention increases, or a dispersant that has a peak but is difficult to use due to the relationship with the fixing temperature. For example, Solsperse S19000 manufactured by Lubrizol can be used.

  The amount of the two types of dispersants used should be such that the total amount falls within the usage range when one type of dispersant as described above is used.

  Preferred combinations of the two types of dispersants are, for example, a combination of Solsperse S11200 and S13940, a combination of Solsperse S11200 and S19000, and a combination of Solsperse S13940 and S19000.

<Selecting dispersants with different temperature characteristics>
It is preferable to use a dispersant having different temperature characteristics as the two types of dispersants to be mixed. This is because even when two types of dispersants having the same temperature characteristics are mixed, the same temperature characteristics are usually obtained, and the same effect as when one of the dispersants is used is obtained. is there. Of course, the use of two types of dispersants is not limited at all.

  When two kinds of dispersants are mixed and used, there is a great technical significance in realizing a third temperature characteristic that is different from either of the temperature characteristics. That is, when the temperature characteristics are represented by the rising temperature T1 and the peak temperature T2, the following first dispersant and second dispersant are used as the two types of dispersants to be mixed.

The rising temperature for the wet developer using only the first dispersant as a dispersant at a predetermined concentration is T1 (1), the peak temperature is T2 (1),
The rising temperature for a wet developer using only the second dispersant as a dispersant at a predetermined concentration is T1 (2), the peak temperature is T2 (2),
The first dispersant and the second dispersant are selected so that the temperature T1 (1) and the temperature T1 (2) are different and the temperature T2 (1) and the temperature T2 (2) are also different.

<Selecting combination of temperature characteristics for the purpose>
It has been stated that the first dispersant and the second dispersant to be mixed need to have different temperature characteristics (here, temperature T1 and temperature T2). It is necessary to investigate each temperature characteristic (T1 and T2) of the wet developer when the dispersant is used alone.

  At that time, the first dispersant and the second dispersant are only the first dispersant (here, “only” means only one of the first dispersant and the second dispersant). The rising temperature T1 (1) and the peak temperature T2 (1) of the loss elastic modulus G ″ of the wet developer containing 1 part by weight with respect to 100 parts by weight of the toner, and only the second dispersant (here, Of “only” means the same as the above), the rising temperature T1 (2) and the peak temperature T2 (2) of the loss elastic modulus G ″ of the wet developer containing 1 part by weight with respect to 100 parts by weight of the toner, It is preferable to use those having temperature characteristics in which the difference between T1 (1) and temperature T1 (2) and the difference between T2 (1) and temperature T2 (2) are different by 5 ° C. or more. If the temperature is lower than 5 ° C, the technical feature of facilitating temperature control cannot be fully enjoyed. Become. Also, the when the temperature difference is too large, too appeared strong influence of one of the dispersing agent, the upper limit of the difference in the amount problem susceptible of errors of results. Temperature is about 25 ° C..

  What is necessary is just to determine the combination of the temperature characteristic of the 1st dispersing agent and the 2nd dispersing agent for obtaining the target temperature characteristic in the state by which the temperature characteristic only by each dispersing agent was acquired. This can be done according to the following concept.

  First, it is assumed that the target temperature characteristics include a target temperature T1 (0) and a temperature T2 (0). On the other hand, the temperature T1 and the temperature T2 realized by the dispersant obtained by mixing the first dispersant and the second dispersant are set within the range of the temperature T1 (0) and the temperature T2 (0). .

That is,
T1 (0) ≦ T1 ≦ T2 ≦ T2 (0)
Is to satisfy.

  This relationship is divided into T1 (0) ≦ T1 and T2 ≦ T2 (0).

  In order to satisfy T1 (0) ≦ T1, what kind of relationship should T1 (1) and T1 (2) have? The inventor of the present invention has the characteristic of T1 because the dispersant obtained by mixing the first dispersant having the characteristic of T1 (1) and the second dispersant having the characteristic of T1 (2) exhibits the characteristic of T1 ( At least one of 1) and T1 (2) must be at a temperature equal to or higher than T1 (0). If both are lower than T1 (0), the characteristic T1 of the mixed dispersant cannot be higher than T1 (0).

  Therefore, at least one of T1 (1) and T1 (2) must be at a temperature higher than T1 (0).

  The same can be said for T2 ≦ T2 (0) if the high temperature and the low temperature are reversed.

  That is, at least the lower one of T2 (1) and T2 (2) must be a temperature equal to or lower than T2 (0).

FIG. 5 shows a schematic example of the above temperature relationship. The portions of T1 (0) ≦ T1 (2) and T2 (1) ≦ T2 (0) indicated by arrows are examples. Of course, the relationship between the first dispersant and the second dispersant may be reversed. In that case, T1 (0) ≦ T1 (1) and T2 (2) ≦ T2 (0
)

  It should be noted that satisfying these conditions is a necessary condition, and the mixed dispersant does not necessarily satisfy the target range, that is, does not satisfy T1 (0) ≦ T1 ≦ T2 ≦ T2 (0). . After that, it is necessary to adjust the specific temperature characteristic values of the first dispersant and the second dispersant and the ratio of the respective added amounts.

  However, by adopting such a control method, it becomes easy to obtain the desired characteristics. This is because T1 and T2 in the dispersant after mixing can be controlled independently.

  If a single dispersant is used, or if a plurality of dispersants with similar temperature characteristics are used, even if the temperature characteristics can be changed by devising the amount added, T1 and T2 are independent. It is difficult to control. Further, increasing the addition amount too much adversely affects the chargeability of the toner.

  In the method of mixing a plurality of dispersants having different temperature characteristics, it is easy to independently control T1 and T2 as temperature characteristics, and it is not necessary to greatly change the addition amount of the dispersant. It's okay.

<Conformity to multistage fixing>
The wet developer having the temperature characteristics as described above can be said to be a developer suitable for a multistage fixing process. The multi-stage fixing process is a fixing method in which a fixing process that is normally performed is performed a plurality of times in order to improve the fixing property.

  FIG. 6 shows an example of a two-stage fixing device that performs fixing twice. Reference numerals 91a and 91b denote first-stage fixing roller pairs. The recording material 7 on which the toner image before fixing is placed is conveyed in the direction of arrow E, passes between the rollers, the toner image is heated, and the first-stage fixing roller is heated. Fixing is performed.

  In the case of fixing a toner image using the wet developer of the present embodiment, the toner particles are aggregated and integrated by passing through the first stage fixing roller, and separated from the carrier liquid.

  Next, the toner images that have passed through the second-stage fixing roller pairs 92a and 92b and have been aggregated and integrated are further heated to perform second-stage fixing.

  Here, the toner integration further proceeds and the fixing to the recording material 7 is completed. Further, here, the carrier liquid released in the first stage acts as a peeling liquid, and prevents the integrated toner layer from being offset.

  In the case of a toner image using not a wet developer of this embodiment but a wet developer having normal temperature characteristics as shown in FIG. 2, the toner layer is not sufficiently integrated even in the two-stage fixing. Thus, sufficient fixing strength cannot be obtained. Further, separation from the carrier liquid in the first stage fixing is insufficient, and offset is likely to occur in the second stage fixing.

An example in which the above-described wet developer was prepared and the fixability and storage stability were actually evaluated by an image forming process is shown below.
In the following examples, “part” means “part by weight”.

<Creation of wet developer>
Each wet developer used in each Example and Comparative Example described later was prepared as follows.

  15 parts of carbon black (Mobot L manufactured by Cabot) was kneaded with 100 parts of polyester resin (Taoton (Tg65 ° C., Tm 135 ° C.) manufactured by Kao) with a kneader, dispersed, dry pulverized, and a coarsely pulverized toner was prepared. .

  As the carrier liquid, liquid paraffin (Moresco White P40 (manufactured by Matsumura Oil Research Co., Ltd.)) was used.

  80 parts of the carrier liquid, 20 parts of the coarsely pulverized product, and a predetermined amount of the dispersant were wet pulverized in a sand mill to prepare a wet developer. The volume average particle diameter of the toner is 2 to 3 μm.

  The used dispersants and addition amounts (in parts by weight with respect to 100 parts of toner) are shown in Tables 1 and 2 to be described later for each Example or Comparative Example.

  As the dispersing agents shown in Tables 1 and 2, S11200, S19000, S13940, V220, dispersing agent a, and dispersing agent b were used.

Dispersant S11200: Basic polymer dispersant (manufactured by Lubrizol)
Dispersant S19000: Basic polymer dispersant (manufactured by Lubrizol)
Dispersant S13940: Basic polymer dispersant (manufactured by Lubrizol)
Dispersant V220: Basic polymer dispersant (manufactured by ISP)
About the dispersing agent a and the dispersing agent b, it manufactured as follows.

Production of Dispersant a (Basic Dispersing Resin a) 100 parts Moresco White P40 (manufactured by Matsumura Oil Research Co., Ltd.), 30 parts lauryl methacrylate represented by chemical formula (1), N- A basic nitrogen-containing heterocyclic group is prepared by reacting 5 parts of vinyl-2-pyrrolidone and 0.2 part of azobisisobutyronitrile as a polymerization initiator under a nitrogen atmosphere at a reaction temperature of 60 to 70 ° C. for about 12 hours. A basic dispersion resin a comprising the compound was obtained.

Manufacture of Dispersant b (Basic Dispersion Resin b) In the manufacture of Dispersion Resin a, a base similar to Dispersing Resin a was used except that 30 parts of stearyl methacrylate shown in Chemical Formula (3) was used instead of lauryl methacrylate. Dispersible resin b was obtained.

<Temperature characteristics measurement of loss modulus>
The temperature characteristics of the loss elastic modulus G ″ of the wet developer were measured for each example and comparative example.

  The loss elastic modulus G ″ was measured using a rheological property evaluation apparatus (rotary rheometer) ARES-RFS manufactured by TA Instruments, Inc. The plate used was a 50 mm parallel plate, the measurement conditions were a gap of 1 mm, a frequency of 10 Hz, and a strain of 5. %, The rate of temperature increase is 10 ° C./min, and the measurement temperature range is 20 to 140 ° C. or 50 to 170 ° C.

  From the measured temperature characteristics, the aforementioned rise temperature T1 and peak temperature T2 were obtained. The results for each example and comparative example are shown in Tables 1-2.

<Image forming process conditions>
A toner image for each wet developer was formed and fixed using the image forming apparatus having the configuration shown in FIG. The process conditions for image formation are as follows.

  The system speed was 400 mm / s, and negatively charged OPC was used as the photoreceptor. The charging potential of the photosensitive member was −700 v, the developing voltage was −450 v, and the transfer voltage was +600 v.

<Fixability evaluation method>
A fixability test was performed on a fixed sample on which a toner image was formed and fixed by the above process.

Samples were prepared by preparing a solid pattern (10 cm × 10 cm, adhesion amount 2 mg / m ² ) on high-quality paper / coated paper for each Example and Comparative Example, and heat roller fixing (180 ° C. × nip time 80 ms). .

In addition to the usual heat roller fixing, multi-stage fixing (two-stage fixing) as shown in FIG. 6 was also performed.

  For each sample, select a part without offset, rub an eraser (made by Lion Corporation, sand eraser “LION 26111”) twice with a pressing load of 9.8 N, and set the residual ratio of image density to “X” manufactured by X-Rite. -Rite model 404 "and the following four ranks were evaluated. More than Δ is the allowable range.

A: Image density residual ratio is 90% or more,
○: Image density remaining rate is 80% or more and less than 90%,
Δ: Image density residual ratio is 70% or more and less than 80%,
X: Image density residual ratio is less than 70%.

  The results of the fixability test for each example and comparative example are shown in Tables 1-2.

<Storage stability evaluation method>
A storage stability test was performed on the wet developer for each example and comparative example.

  Put each developer up to about half in a sample bottle and store at room temperature (20-26 ° C.) for 6 months. Then, the presence or absence of sedimentation is confirmed by visual evaluation.

It was confirmed whether to re-disperse by shaking, or to re-disperse by stirring with a spatula. Evaluation is in the following four stages. More than Δ is the allowable range.

A: No sedimentation,
○: Shake and re-disperse
Δ: Redispersed by stirring with a spatula
X: Not redispersed.

  The results of the storage stability test for each Example and Comparative Example are also shown in Tables 1-2.

Reference Example 1 is an example where the temperature characteristic of the loss elastic modulus of the wet developer has a peak. T1 = 30 ° C., T2 = 59 ° C., and the fixability was 定 着. Storage stability is also within the allowable range, Δ.

  Comparative Example 1 is an example where the temperature characteristic of the loss elastic modulus of the wet developer has no peak. There is no temperature corresponding to T1 and T2. Fixability was x.

The temperature characteristics of the loss elastic modulus G ″ of Reference Example 1 are shown in FIG. 3. As can be seen from FIG. 3, the wet developer of Reference Example 1 has a clear peak in temperature characteristics, fixing properties and storage stability. Of both.

  On the other hand, the temperature characteristic of the loss elastic modulus G ″ of Comparative Example 1 is shown in FIG. 2. As can be seen from FIG. 2, the wet developer of Comparative Example 1 does not have a clear peak in the temperature characteristic and has good fixing. In addition, although multi-stage fixing was performed, good fixing property was not obtained there, and offset was generated.

Thus, since the temperature characteristic of the loss elastic modulus has a peak, good fixability and storage stability can be obtained.

Reference Examples 2 to 7 are examples in which the temperature characteristic of the loss modulus has a peak, but the rising temperature T1 and the peak temperature T2 are different depending on the type and amount of the dispersant.

Focusing on the temperature T1, as shown in Reference Example 2, if T1 exceeds 40 ° C., the storage stability is improved, and Δ becomes ◯. Further, when T1 exceeds 55 ° C. as in Reference Example 3, the storage stability is further improved (（).

Focusing on the temperature T2, until the reference example 3, but have been obtained good fixation (◎), turned ○ from T2 is then lowered and the fixing property becomes higher 100 ° C. ◎ as in Reference Example 4 Yes. Further, when T2 is 130 ° C. or higher as in Reference Example 5, the fixability is further deteriorated (Δ).

  Thus, although it is within the allowable range, a change in fixing property is observed depending on the temperatures T1 and T2. That is, as described above, the higher the T1, the better the storage stability, and the lower the T2, the better the fixing property.

For reference, each line of which .S1 from S5, shows the temperature characteristics of the loss modulus G "of each wet type developer of Example 1-5 in FIG. 7, each of the respective Reference Example 1 Reference Example 5 Corresponds to temperature characteristics.
FIG. 8 shows the temperature characteristics of the loss modulus G ″ for each of the wet developers of Reference Example 1 and Reference Example 7. R3 and R4 show the temperature characteristics of Reference Example 7 and Reference Example 1, respectively. In this case, the developer using 1 part of the dispersant 13940 in Reference Example 1 and the dispersion in Reference Example 7 show substantially the same temperature characteristics including rising and peaks, and the temperatures T1 and T2 are almost unchanged. The characteristics (fixability and complementary stability) of the developer using 0.5 part of Agent 13940 and 0.5 part of Dispersant S19000 show the same tendency.

  <Selection of dispersant combination>

First, 55 ° C. <T1 ≦ T2 <100 ° C. was set as the aim, and as each of the candidate dispersants, a combination of dispersant b and S13940 was selected, and the combination of the addition amounts was slightly changed, Example 1.
And Reference Example 8 . The two types of dispersants have different temperature characteristics, and at least any T1 is higher than 55 ° C and at least any T2 is lower than 100 ° C.

  The dispersant b shows good fixability and storage stability even when used alone (see Table 1). Therefore, it seems that there is no point in mixing with other dispersants, but includes the aim of bringing T1 and T2 closer by mixing, that is, closer to the state of T1 = T2.

Next, the target was set to 40 ° C. <T1 ≦ T2 <130 ° C., and combinations of S11200 and S13940 and S11200 and S19000 were selected as candidate dispersants, and Example 2 and Example 3 were obtained. The two types of dispersants have different temperature characteristics, and at least any T1 is higher than 40 ° C and at least any T2 is lower than 130 ° C.

The results of Example 1, Reference Example 8, and Examples 2 to 3 are shown in Table 2. These attempts were made to mix two types of dispersants so that T1 and T2 are within the target range, and T1 and T2 are brought closer to each other to optimize both.

FIG. 9 shows the temperature characteristics of the loss modulus G ″ for each of the wet developers of Example 1 and Reference Example 8. The lines S8 and S9 show the temperature characteristics of Example 1 and Reference Example 8 , respectively. Show.

In both Example 1 and Reference Example 8 , T1 and T2 are closer than in the case of using the original dispersant mixed alone. In Example 1 , toner aggregation progresses, and the loss elastic modulus G ″ rises from T1 at a substantially constant state and then decreases rapidly at T2. In Reference Example 8 , T1 = T2, and the loss elastic modulus G ″ reaches T2. Although it gradually decreases, it decreases rapidly at T2. This is the case where T1 = T2 already described, and it can be said that both the fixing property and the storage stability can be achieved at a high level.

The dispersant b used in Example 1 and Reference Example 8 was evaluated as ◎ for both fixability and storage stability even when used alone, but the difference between T1 and T2 was 30 ° C. (see Table 1). ). Even if Example 1 and Reference Example 8 have the same evaluation ◎, the difference between T1 and T2 can be controlled within a very narrow range of 8 ° C and 0 ° C. This makes it possible to achieve both storage stability at a higher temperature by increasing T1 and fixability at a lower temperature by decreasing T2.

In Examples 2 and 3 , T1 is slightly lower at 50 ° C. and 51 ° C. than Example 1 and Reference Example 8 . Therefore, the storage stability is not ◎ but ◯. However, it is within the allowable range, and the fixing property is also good (◎).

  As described above, according to the wet developer of the present embodiment, the toner particles are thermally formed at the fixing temperature by giving the temperature characteristic that the change in the loss elastic modulus with the temperature rise of the wet developer forms a peak. Aggregation between them can be made dominant, and high toner layer strength can be obtained.

  Thereby, it is possible to provide a wet developer having the characteristics that the storage stability as the wet developer is maintained and the fixing property is hardly inhibited. The wet developer is also suitable for a multistage fixing process, and a fixing method appropriately matched with the wet developer can be provided.

  In addition, the above-mentioned embodiment is an illustration and restrictive at no points. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

It is a figure explaining the example of schematic structure of the image formation part in a wet image forming apparatus. It is a graph which shows the example of the temperature characteristic of the loss elastic modulus G "in a common wet developing agent. It is a graph which shows the example of the temperature characteristic of the loss elastic modulus G "about the wet developing agent which concerns on this invention. It is a graph which shows the example of the temperature characteristic of the loss elastic modulus G "which is T1 = T2. It is a figure which shows the relationship between the aim range of a temperature characteristic, and the temperature characteristic of each dispersing agent selected. FIG. 3 is a diagram illustrating a configuration example of a two-stage fixing device that performs fixing twice. It is a graph which shows the temperature characteristic of the loss elastic modulus G "about each wet developer of the reference examples 1-5. It is a graph which shows the temperature characteristic of the loss elastic modulus G "about each wet developer which used the reference examples 1 and 7 independently. 10 is a graph showing temperature characteristics of loss elastic modulus G ″ for each wet developer of Example 1 and Reference Example 8 .

Explanation of symbols

1 Photosensitive drum (image carrier)
2 Charging device 3 Exposure device 4 Wet development device 5 Transfer device (transfer roller)
6 Cleaning device (cleaner blade)
7 Transfer material (recording material)
8 Wet developer 9a, 9b Fixing device (fixing roller)
10 Image Forming Unit 41 Developing Roller (Developer Carrier)
42 Conveying roller 43 Supply roller 44 Developer tank 91 Squeeze device (roller)
92 Blade 91a, 91b, 92a, 92b Two-stage fixing device (fixing roller)

Claims (6)

Carrier liquid,
Toner particles dispersed in the carrier liquid;
A wet developer containing a dispersant for dispersing the toner particles in the carrier liquid,
The dispersant includes a plurality of types of dispersants of at least a first dispersant and a second dispersant,
The first dispersant and the second dispersant have different temperature characteristics,
Loss modulus G of the wet developing agent ", at a temperature T1 following areas decreases with increasing temperature, increases with increasing temperature in the region of from the temperature T1 to a temperature T1 greater than the temperature T2, the temperature T2 A wet developer characterized by having a temperature characteristic that shows a change that decreases as the temperature rises in the above temperature range and that forms a peak at temperature T2 . Before Symbol The first dispersant and the second dispersant, wherein the first rising temperature of the loss elastic modulus G "wet developer containing 1 part by weight of only the dispersion agent to 100 parts by weight of the toner T1 ( 1) and a peak temperature T2 (1), and a rising temperature T1 (2) and a peak temperature T2 of a loss elastic modulus G ″ of a wet developer containing 1 part by weight of the second dispersant alone with respect to 100 parts by weight of toner. The wet developer according to claim 1, wherein (2) has a temperature characteristic different from each other by 5 ° C. or more. The first dispersant and the second dispersant are:
Temperature of the temperature T1 (1) and the temperature T1 higher of (2) is, and the pre-Symbol temperature T1 or higher,
Wet developing agent according to claim 2 in which the temperature of the temperature T2 (1) and the lower temperature T2 (2) is not more than before Symbol temperature T2 is being selected. Before SL temperature T1 and the temperature T2, 40 ° C. <wet developer according to claim 1, characterized in that it satisfies the relationship of T1 ≦ T2 <130 ° C.. Before SL temperature T1 and the temperature T2, wet developing agent according to claim 4, characterized in that satisfies the 55 ℃ <T1 ≦ T2 <100 ℃ relationship. Claim 1 is developed using a wet developer according to any one of 5, fixing method, wherein a toner image transferred to the recording material multistage fixing.

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