JP2010271583A - Electrophotographic toner - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrophotographic toner that obtains good density stability, pulverization properties, and fixability without fogging even using a polylactic acid-based resin which is a biodegradable resin, as a binder resin. <P>SOLUTION: The electrophotographic toner is obtained by melting, kneading, pulverizing, and classifying a raw material which contains at least a polylactic acid-based resin with a number average molecular weight of 5,000-50,000 as a binder resin and a colorant. The crystallinity of the polylactic acid-based resin is 10% or less, more preferably 5% or less. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an electrophotographic toner, and more particularly to an electrophotographic toner using a biodegradable resin as a binder resin.

  Image formation by electrophotography is performed by developing and visualizing an electrostatic image with toner, transferring the obtained toner image onto a sheet, and then fixing it with heat and pressure. As the toner used for such image formation, a toner prepared by kneading a mixture of a binder resin and a colorant or a charge control agent, and adjusting the particle size distribution by pulverization is used.

  Conventionally, petroleum-derived resins such as styrene / acrylic resins and polyester resins have been used as binder resins for toners. However, in recent years, in consideration of the environment, a method has been proposed in which a biodegradable resin that has a low environmental impact during disposal is used as a binder resin for toner.

  One of the most promising resins as a biodegradable resin is polylactic acid. However, general-purpose polylactic acid is a crystalline polyester having a melting point of about 170 ° C., a glass transition point of about 60 ° C., and a molecular weight of about 1 to 150,000. When general-purpose polylactic acid is used as it is as a resin for toner, it is hard. There are problems that the grindability is poor and that the softening temperature is high and it is not suitable for low-temperature fixing.

  In order to solve such a problem, proposals have been made to add a large amount of plant wax to polylactic acid (see, for example, Patent Document 1). However, in this proposal, it is possible to lower the softening temperature of the toner by adding a large amount of wax, but the toner easily aggregates due to the wax component, so that the productivity due to the lowering of the classification efficiency deteriorates. As the toner fluidity deteriorates, problems such as inferior toner transportability in the developing machine occur.

  There is also a proposal of blending a terpene phenol copolymer and a specific wax into a polylactic acid-based biodegradable resin (see, for example, Patent Document 2). This proposal blends the toughness of polylactic acid and the terpene phenol copolymer, which has low resin strength but is effective for low-temperature fixability, to achieve good low-temperature fixability and grindability without sacrificing durability. Both can be achieved.

  However, the blending amount of the polylactic acid-based biodegradable resin is limited to about 30% by weight. If the blending amount is further increased, the grindability is deteriorated and it becomes difficult to prepare a toner. Also, the melt viscosity becomes high, and the low-temperature fixability deteriorates.

  In addition, there is a proposal of blending two types of resins having different softening points into a biodegradable resin for low temperature fixability and fixing stability (for example, see Patent Document 3). In this proposal, the low softening point resin serves as a bridge between the high softening point resin and the biodegradable resin, and the biodegradable resin is uniformly dispersed in the binder resin. However, the blending ratio of the biodegradable resin in the binder resin is about 13% by mass, and at most 33% by mass is the limit. Although there is no clear description, it is considered that one of the causes is that if the blending ratio of the biodegradable resin is further increased, the biodegradable resin is poorly dispersed and the durability and grindability are deteriorated.

  As described above, there are many problems in using a biodegradable resin as a main component of the binder resin of the toner, and even when a part of the biodegradable resin is replaced, the blending amount is limited, while maintaining good characteristics. Therefore, it is desired that more biodegradable resin can be blended as a binder resin for toner.

Japanese Patent No. 2597452 Japanese Patent No. 3779221 JP 2006-91278 A JP 2007-197602 A

  The present invention has been made under the circumstances as described above, and an object of the present invention is to provide an electrophotographic toner that contains a biodegradable resin as a binder resin and that can obtain good pulverizability and fixability. To do.

  As a result of intensive studies in order to solve the above problems, the present inventors have found that an electrophotography containing at least a polylactic acid resin having a number average molecular weight of 5,000 to 50,000 as a binder resin and a colorant. As a toner, it has been found that by controlling the crystallinity of the polylactic acid-based resin within a specific range, a toner having no fogging, excellent density stability, and good crushability and fixability can be obtained.

  That is, one embodiment of the present invention is obtained by melting, kneading, pulverizing, and classifying a raw material containing at least a polylactic acid resin having a number average molecular weight of 5,000 to 50,000 as a binder resin and a colorant. An electrophotographic toner is provided, wherein the polylactic acid resin has a crystallinity of 10% or less.

  More preferably, the crystallinity of the polylactic acid resin can be 5% or less.

  According to the present invention, there is provided an electrophotographic toner that is free from fogging and has good density stability, grindability and fixability despite containing a biodegradable resin as a binder resin.

Hereinafter, various embodiments of the present invention will be described.
An electrophotographic toner according to an embodiment of the present invention is prepared by melting, kneading, pulverizing, and classifying a raw material containing at least a polylactic acid resin having a number average molecular weight of 5,000 to 50,000 as a binder resin and a colorant. An electrophotographic toner obtained as described above, wherein the polylactic acid resin has a crystallinity of 10% or less. The crystallinity means a value calculated using an X-ray diffraction method.

The polylactic acid resin used in the present invention is a resin having the following structural formula.

  So-called polylactic acid is a polymer in which lactic acid is bonded by an ester bond, and has recently attracted attention. In other words, in nature, enzymes that cleave ester bonds (esterases) are widely distributed, so polylactic acid is gradually decomposed by such enzymes in the environment and converted into lactic acid, which is a monomer. And eventually carbon dioxide and water.

  The method for producing polylactic acid used in the present invention is not particularly limited, and a conventionally known method can be used. Fermenting starch such as corn as a raw material to obtain lactic acid, followed by dehydration condensation directly from lactic acid monomer, and synthesis by ring-opening polymerization in the presence of a catalyst via cyclic dimer lactide from lactic acid is there.

  The specific low molecular weight polylactic acid used in the present invention can be arbitrarily adjusted by varying the reaction conditions during polymerization. Also, the molecular weight can be reduced by utilizing the hydrolysis characteristics of polylactic acid, for example, by leaving polylactic acid at high temperature and high humidity.

  Here, the polylactic acid used as a general-purpose resin requires a high molecular weight of about 100,000 as the number average molecular weight, but the polylactic acid used in the present invention is about 5,000 to 50,000. It is necessary that the polylactic acid has a relatively low molecular weight.

  Thus, by reducing the molecular weight, polylactic acid, which has been difficult to pulverize conventionally, can be pulverized relatively easily, and polylactic acid can be added at a high concentration.

  By the way, polylactic acid is a crystalline resin but generally has a low crystallization rate. Usually, in toner production of a pulverization method in which toner materials are mixed, melted and kneaded, and then pulverized and classified to obtain toner, the crystalline state is considered to be an amorphous state because it is rapidly cooled from the molten state.

  However, among the toner materials, some pigments exhibit an effect as a polylactic acid crystal nucleating agent. For example, a copper phthalocyanine pigment generally used for cyan toner has an excellent function as a crystal nucleating agent.

  Through various studies, we have obtained the knowledge that even if a toner is produced under the same conditions, the degree of crystallization varies depending on the pigment, that is, the crystallization speed varies depending on the blending conditions of the materials.

  Here, those having a high crystallization rate have high crystallinity as a result, and those having a low crystallization rate have low crystallinity. Further, in pursuit, it has been found that if the degree of crystallinity is too high, the toner fixability deteriorates. This is considered to be because when the degree of crystallinity is high, the softening start temperature of the resin increases, and in particular, the low-temperature side fixability deteriorates.

  Normally, full-color toners use at least four colors of toner, cyan, magenta, yellow, and black. However, a stable image cannot be output if the fixability differs for each color. Therefore, it is necessary to appropriately control the crystallinity of each toner.

  Examples of the method for controlling the crystallinity include adjustment of the cooling speed in the kneading step. That is, it is possible to adjust the degree of crystallization as a toner by rapidly cooling those having a high crystallization rate and gradually cooling those having a low crystallization rate.

  Here, the degree of crystallinity of the polylactic acid resin used in the present invention is preferably from 0% in an amorphous state to 10%, more preferably from 0 to 5%.

  As a specific method for adjusting the cooling speed of the kneading step, it can be easily adjusted by the circulating water temperature of the rolling roll, the speed of the belt conveyor, the cooling fan air volume, and the like.

  However, in the case of a kneading machine such as an open roll type kneader or a batch kneader, it is kneaded at a relatively low temperature, and in the case of a toner using polylactic acid, it is kneaded at a temperature below the melting point. In some cases, crystallization progresses during kneading and it is difficult to adjust the crystallinity. Therefore, the kneading machine is preferably kneaded at a temperature exceeding the melting point, and a twin-screw extruder is particularly preferred. In any case, the kneaded product having the crystallinity adjusted in this way is pulverized and classified in the same manner as in the conventional manufacturing method to produce a toner.

The electrophotographic toner described above can be produced by a conventionally known method.
For example, a raw material containing a binder resin, a colorant, and other additives as necessary is mixed, and then kneaded by a kneader such as a biaxial kneader, a pressure kneader, or an open roll to obtain a kneaded product. After cooling the kneaded product, the toner can be obtained by pulverizing with a pulverizer such as a jet mill and classifying with an air classifier.

  Here, the particle size of the toner is not particularly limited, but is usually adjusted to be 5 to 10 μm. An external additive can be added to the toner thus obtained in order to improve fluidity, adjust chargeability, and improve durability.

  As the external additive, inorganic fine particles are generally used, and examples thereof include silica, titania, alumina, etc. Among them, silica subjected to hydrophobic treatment (commercially available from Nippon Aerosil Co., Ltd., CABOT Co., Ltd.) is preferable. The particle diameter of the inorganic fine particles is preferably 7 to 40 nm as the primary particle diameter, and two or more kinds may be mixed for improving the function.

  Conventionally known colorants can be used as the colorant used in the electrophotographic toner of this embodiment. For example, as a black colorant, carbon black and as a blue colorant, C.I. I. Pigment 15: 3, and red colorants include C.I. I. Pigment 57: 1, 122, 269, and yellow colorants include C.I. I. Pigment 74, 180, 185 and the like. In consideration of the influence on the environment which is one of the objects of the present invention, a single colorant having high safety is preferable.

  The content of these colorants is preferably 1 to 10% by mass with respect to the whole toner. The colorant may be used in the form of a masterbatch in which a resin and a colorant are dispersed in high concentration in advance.

  A conventionally known release agent can be added to the toner according to the exemplary embodiment as necessary. Examples of such release agents include olefinic waxes such as polypropylene wax, polyethylene wax, and Fischer-Tropsch wax, natural waxes such as carnauba wax, rice wax, and scale insect wax, and synthetic ester waxes.

  In order to improve low-temperature fixability and high-speed printing performance, a release agent having a relatively low melting point of about 60 to 100 ° C. is preferable, and specifically, carnauba wax and synthetic ester wax are preferable. In consideration of environmental impact, natural product carnauba wax is more preferable.

The compounding amount of the release agent is preferably 1 to 10% by mass with respect to the whole toner.
A conventionally known charge control agent of positive charge or negative charge can be added to the toner according to the exemplary embodiment as necessary. Examples of the positive charge control agent include a quaternary ammonium salt, a resin containing an amino group, and the negative charge control agent includes a metal complex salt of salicylic acid, a metal complex salt of benzyl acid, a calixarene type phenolic compound. Examples include condensates and resins containing carboxyl groups.

The blending amount of the charge control agent is preferably 0.1 to 5% by mass with respect to the whole toner.
In addition to polylactic acid, conventionally known toner resins can be added to the toner according to the exemplary embodiment, if necessary. Examples of such resins include styrene / acrylic resins and polyester resins. From the viewpoint of pigment dispersibility and low-temperature fixability, polyester resins developed for toners are preferred. Resin may be individual or may mix 2 or more types.

Examples of the present invention and comparative examples are shown below, and the present invention will be described more specifically.
1. Method for measuring physical properties of components used in Examples and Comparative Examples (Measurement of toner particle diameter)
Equipment: Multisizer II (manufactured by Coulter, Inc.)
Sample: A small amount of sample, purified water, and a surfactant were placed in a beaker and dispersed with an ultrasonic cleaner.
Measurement: The aperture was 100 μm, the count was 50,000, and the volume average particle size was obtained.

(Measurement of glass transition point (Tg))
Apparatus: Differential scanning calorimeter (manufactured by Shimadzu Corporation: DSC-60)
Sample: 8mg
Temperature raising conditions: The temperature is raised to 160 ° C. at 10 ° C./min, cooled to 35 ° C. at a temperature lowering rate of 10 ° C./min, and then raised again to 160 ° C. at 10 ° C./min.
At the time of the second temperature increase, the intersection of two tangents of the curve portion obtained by the transition was taken as the glass transition point.

(Measurement of molecular weight)
Equipment: GPC (manufactured by Shimadzu Corporation), detector RI
The molecular weight Mn is a number average molecular weight measured by GPC (gel permeation chromatography) using a calibration curve prepared with a polystyrene sample having a known molecular weight as a standard.

(Measurement of crystallinity)
Using an X-ray diffraction measurement device (manufactured by Rigaku Corporation, light source CuKα, tube voltage 40 kV, tube current 120 mA), the amorphous and crystalline peak areas of polylactic acid were analyzed, and the degree of crystallinity was determined by the following equation.
Crystallinity (%) = (Crystal peak area) / (Crystal peak area + Amorphous peak area) × 100

2. Production of polylactic acid used in Examples and Comparative Examples (Production process of low molecular weight polylactic acid)
Polylactic acid (manufactured by Kaisho Biochemical Co., Ltd .: REVODE101B, molecular weight (Mn = 120,000) was hydrolyzed in a constant temperature and humidity chamber set at a temperature of 80 ° C. and a humidity of 80% RH. And dried for 1 hour with a hot air dryer (60 ° C. setting).

  The hydrolysis treatment time was varied as shown in Table 1 below to prepare polylactic acids having different molecular weights.

Example 1
Next, each component of the following blending amount was put into a Henschel mixer (standard feather mounted, Mitsui Mining Co., Ltd.) and mixed.

Binder resin: Low molecular weight polylactic acid (molecular weight 14,000) 90 parts by weight Colorant: Carbon black (MOGUL L manufactured by CABOT Co., Ltd.) 4 parts by weight Release agent: Carnauba wax No. 1 powder (Nippon Wax Co., Ltd.) 6 parts by mass After the obtained mixed powder was melt-kneaded with a twin-screw extruder (screw diameter 43 mm, L / D = 34), the melt-kneaded product was set at 10 ° C. for circulating water of the rolling roll. Stretched and cooled to obtain a kneaded product having a crystallinity shown in Table 2 below. Subsequently, the kneaded product after cooling was roughly crushed with a rotoplex (manufactured by Hosokawa Micron Corporation, 2 mm screen). After that, the particles are pulverized and classified with a collision type pulverizer (Nippon Pneumatic Industry IDS-2) and a wind classifier (Nippon Pneumatic Industry DSX-2) so that the average particle diameter of the toner becomes 9.0 μm. Got.

  As an external additive, 2 parts by mass of “RY200” (manufactured by Nippon Aerosil Co., Ltd .: hydrophobic silica, primary particle size of 12 nm) is added to 100 parts by mass of the obtained fine particles, and a Henschel mixer (with stirring reinforcing wings, Mitsui) is added. (Mine Co., Ltd.) for 3 minutes with stirring to obtain a toner.

(Examples 2-8, Comparative Examples 1-7)
Except that the crystallinity based on the molecular weight of polylactic acid, the type of colorant, and the cooling rate of the melt-kneaded product (temperature of circulating water in the rolling roll) was set to various values shown in Table 2 below. A toner was obtained in the same manner as in Example 1.

Example 9
Next, each component of the following blending amount was put into a Henschel mixer (standard feather mounted, Mitsui Mining Co., Ltd.) and mixed.

Binder resin: Low molecular weight polylactic acid (molecular weight 14,000) 90 parts by weight Colorant: Carbon black (MOGUL L manufactured by CABOT Co., Ltd.) 4 parts by weight Release agent: Carnauba wax No. 1 powder (Nippon Wax Co., Ltd.) 6 parts by mass After the obtained mixed powder was melt-kneaded with an open roll kneader (Mitsui Mining Co., Ltd., Needex), this melt-kneaded product (melt kneaded product cut into a string) was cooled with a cooling fan. Was used to obtain a kneaded product having the crystallinity shown in Table 2 below. Subsequently, the cooled kneaded product was crushed, pulverized and classified in the same manner as in Example 1 to obtain fine particles, and an external additive was added to the obtained fine particles to obtain a toner.

(Examples 10 to 13, Comparative Example 8)
The same as in Example 9 except that the crystallinity based on the molecular weight of polylactic acid, the type of colorant, and the cooling rate (cooling fan) of the melt-kneaded product was set to various values shown in Table 2 below. The toner was obtained.
The fogging, density stability, grindability, and fixability of the toners of Examples 1 to 13 and Comparative Examples 1 to 8 obtained as described above were tested and evaluated by the following test methods.

(Test 1-Cover)
The toner is mounted on a non-magnetic one-component developing device “Casio Page Prest N-5” (manufactured by Casio Computer Co., Ltd .: color printer 29 sheets per minute (A4 horizontal), process speed 129 mm / sec) in a normal environment (25 After printing 10,000 sheets of 5% print images continuously using plain paper (XEROX-P paper A4 size) at 50 ° C and 50% RH), blank paper is printed, and the front door is opened during printing. Thus, the printing was forcibly terminated, and the fog toner on the OPC drum at that time was copied onto a mending tape and affixed to a white paper, and compared with a tape from which the fog toner was not collected. The measurement was carried out by obtaining the maximum value of the difference before and after the fog from the XYZ value obtained using a spectroscopic color difference meter “SE-2000” manufactured by Nippon Denshoku Co., Ltd., and evaluated according to the following criteria.

A: The fogging value is less than 2 and good.
○: The fogging value is 2 or more and less than 5, which is good.
Δ: Fog value is 5 or more and less than 10. There is no problem in practical use.
X: A fogging value of 10 or more is bad.

(Test 2-concentration stability)
Using the same apparatus as in Test 1, 14,000 sheets of 5% printed images were continuously printed in a normal environment (25 ° C., 50% RH). In the middle, an A4 solid image is printed every 2,000 sheets, and the image density is measured at the four corners and the center five points to obtain the average density. (At that time, the image defect portion due to white streaks or the like is not measured.) Among the average densities obtained at each sampling point, the density stability is obtained from the maximum value and the minimum value according to the following formula and evaluated according to the following criteria.

Concentration stability (%) = Minimum average density / Maximum average density × 100
A: Concentration stability is 95% or better.
Good: Concentration stability is good at 85% or more.
Δ: Concentration stability is 75% or more and there is no practical problem.
X: The density stability is poor at less than 75%.

(Test 3-grindability)
When pulverizing and classifying the kneaded coarsely pulverized product in the pulverization / classification step, the determination is made based on the yield (mass%) of the particles serving as the toner base. In reality, there is no problem if the yield is 70% or more. At this time, the pulverization conditions are adjusted so that the volume average particle diameter of the toner is 9 μm, the number ratio of 3 μm or less as fine powder is 5% or less, and the volume ratio of 16 μm or more as coarse powder is 3% or less.

○: Yield 65% or more.
X: Yield less than 65%.

(Test 4-Fixability)
The fixing unit is modified so that the temperature of the fixing unit of the same apparatus as in Test 1 can be varied, and a fixing tester is obtained. After obtaining an unfixed image with this apparatus, the fixing temperature of the upper roll was varied in a range of 100 to 200 ° C. every 10 ° C., and the unfixed image was passed through a fixing device. At that time, the lower roll was set at a temperature 10 ° C. lower than the set temperature of the upper roll. The cold offset, hot offset, and peeled nail trace of the image sample were visually evaluated, and a non-offset area was obtained and evaluated. The process speed was 129.3 mm / sec, and the paper was XEROX P paper A4 size (weight 64 g / m ² ). The oil supply roll of the fixing device was removed.

A: The non-offset region is 30 ° C. or higher.
○: The non-offset region is 20 ° C. or higher.
(Triangle | delta): A non-offset area | region is 20 degrees C or less.
X: A non-offset area | region is 10 degrees C or less.
The results of the above tests 1 to 4 are shown in Table 2 below.

From Table 2 above, the following is clear.
First, in Comparative Examples 1 and 2 in which the molecular weight was adjusted only to a value exceeding 50,000 by commercially available polylactic acid and hydrolysis, the grindability was poor and could not be used. On the other hand, in Comparative Example 3 in which the molecular weight was adjusted to less than 5,000 by hydrolysis, the molecular weight of polylactic acid was too low, so that fusion occurred in the pulverizer during toner pulverization, and continuous pulverization could not be performed. .

  On the other hand, using the polylactic acid whose molecular weight was adjusted to the range of 5,000 to 50,000 by hydrolysis, the melt kneaded product was cooled to adjust the crystallinity to 0 to 10%. The toner according to No. 13 showed excellent results in all the characteristics of fogging, density stability, grindability, and fixability.

  However, even in the case of polylactic acid having a molecular weight adjusted to the range of 5,000 to 50,000, in Comparative Examples 4 to 7 in which the cooling rate of the melt-kneaded product is slow and the crystallinity exceeds 10%, the fog and concentration Although stability and grindability were evaluated temporarily, the fixability was poor.

  Further, in Comparative Example 8 in which PigmentBlue-15: 3 was blended as a colorant using an open roll type kneader, crystallization progressed during kneading and the degree of crystallinity exceeded 10%, and satisfactory fixing performance was obtained. No results.

  The present invention can be used for an electrophotographic toner containing a polylactic acid resin as a biodegradable resin as a binder resin.

Claims (2)

An electrophotographic toner obtained by melting, kneading, pulverizing and classifying a raw material containing at least a polylactic acid resin having a number average molecular weight of 5,000 to 50,000 as a binder resin and a colorant,
An electrophotographic toner, wherein the polylactic acid resin has a crystallinity of 10% or less.   The electrophotographic toner according to claim 1, wherein the crystallinity is 5% or less.