JP4666073B2 - Toner for electrophotography and method for producing the same - Google Patents

Description

  The present invention relates to an electrophotographic toner and a method for producing the same, and more particularly to an electrophotographic toner containing polylactic acid in a binder resin and a method for producing the same.

  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, due to environmental considerations, biodegradable resins that have a low environmental impact during disposal, especially polylactic acid, which is a biodegradable resin derived from biomass made from renewable resources, are used as binder resins for toners. A method has been proposed.

  However, since polylactic acid has a high softening point of 170 ° C. and the fixing temperature must be set high, it cannot be used as it is as a binder resin for toner.

  In order to improve this problem, it has been proposed to lower the softening point by blending other types of resins with polylactic acid (for example, Patent Documents 1, 2, and 3). However, these proposals attempt to solve the problem by lowering the amount of polylactic acid added, and do not meet the objective of reducing environmental burden.

In addition, when a low softening point substance is mixed with polylactic acid, a difference in viscosity between the polylactic acid and the low softening point substance is large in melt-kneading, and uniform dispersion becomes difficult.
JP 2006-91278 A JP 2006-208455 A JP 2007-285150 A

  The present invention has been made in view of the circumstances as described above, and an object of the present invention is to provide an electrophotographic toner having a low environmental load and excellent fixability and a method for producing the electrophotographic toner.

In order to solve the above problems, a first aspect of the present invention is a trimellitic acid, acetic acid, which is a compound having one or more carboxyl groups in a raw material containing polylactic acid having a predetermined softening point and molecular weight as a binder resin. Kneading step of mixing 0.5 to 5 parts by mass of at least one depolymerizing agent selected from phthalic acid with respect to 100 parts by mass of polylactic acid, and kneading the resulting kneaded product And a toner obtained through a classification step, wherein the polylactic acid is depolymerized by the depolymerizing agent in the kneading step, and at least a softening point is reduced. provide.

In the second aspect of the present invention, a raw material containing polylactic acid having a predetermined softening point and molecular weight as a binder resin is selected from trimellitic acid, acetic acid, and phthalic acid, which are compounds having one or more carboxyl groups. A kneading step of mixing 0.5 to 5 parts by mass of the obtained at least one depolymerizer with respect to 100 parts by mass of the polylactic acid and kneading the mixture , and a step of pulverizing and classifying the obtained kneaded product. the said polylactic acid by the depolymerization agent in the kneading process by depolymerization, to provide a method of manufacturing electrophotographic toner characterized in that reduced the least softening point.

  According to the present invention, an electrophotographic toner having a low environmental load and excellent fixability and a method for producing the same are provided.

  Hereinafter, embodiments of the present invention will be described.

An electrophotographic toner according to an embodiment of the present invention includes trimellitic acid, acetic acid, phthalate, which are compounds having one or more carboxyl groups in a raw material containing polylactic acid having a predetermined softening point and molecular weight as a binder resin. A kneading step in which 0.5 to 5 parts by mass of at least one depolymerizing agent selected from acids is mixed with 100 parts by mass of the polylactic acid to knead the mixture, and the resulting kneaded product is pulverized and classified And the polylactic acid is depolymerized by the depolymerizing agent in the kneading step so that at least the softening point is reduced.

  The polylactic acid used as the binder resin in the present embodiment is a resin having the following structural formula.

(OCH (CH ₃ ) CO) _n
Polylactic acid is a polymer in which lactic acid is bonded by an ester bond, and has recently attracted attention as an environmentally friendly biodegradable plastic. 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 manufacturing method of polylactic acid is not specifically limited, A conventionally well-known method can be used. For example, fermenting starch such as corn as a raw material to obtain lactic acid, then dehydrating and condensing directly from lactic acid monomer, or synthesizing from lactic acid via cyclic dimer lactide by ring-opening polymerization in the presence of a catalyst There is a way. There are optical isomers in lactic acid, and there are L-lactic acid and D-lactic acid, and either lactic acid alone or in a mixture may be used.

  In addition, commercially available polylactic acid is synthesized by a ring-opening polymerization method capable of obtaining a higher molecular weight in order to improve heat resistance, and the number-average molecular weight is mainly 100,000 or more. . Such a high molecular weight polylactic acid has a too high softening point and poor fixability, and also has poor grindability. Therefore, it is necessary to depolymerize polylactic acid and reduce the molecular weight.

  Polylactic acid is depolymerized by a depolymerizing agent composed of a compound having one or more carboxyl groups at the time of kneading. That is, a compound having one or more carboxyl groups acts as a depolymerization agent for polylactic acid, reduces the molecular weight of polylactic acid, and lowers the softening point.

  As the compound having one or more carboxyl groups used as the depolymerizing agent, one or more selected from the group consisting of monovalent carboxylic acids, polyvalent carboxylic acids, and reactive derivatives thereof can be used. Specific examples thereof include, for example, acetic acid, propionic acid, lactic acid, trimethylacetic acid, t-butylacetic acid, benzoic acid, terephthalic acid, isophthalic acid, phthalic acid, naphthalenedicarboxylic acid, adipic acid, azelaic acid, sebacic acid, cyclohexane Examples thereof include carboxylic acids such as dicarboxylic acid, trimellitic acid and pyromellitic acid, and lower alkyl esters thereof, and acid anhydrides such as phthalic anhydride, trimellitic anhydride and pyromellitic anhydride. Of these, trimellitic acid, trimellitic anhydride, pyromellitic acid and the like are particularly preferably used.

  Although the usage-amount of a depolymerizing agent is suitably determined by the molecular weight of the polylactic acid after depolymerization, it is 0.5-5 mass parts normally per 100 mass parts of polylactic acid.

  When the amount of the depolymerizing agent used is less than 0.5 parts by mass, the degree of depolymerization is weak and it is difficult to lower the softening point to a desired value. On the other hand, when the amount exceeds 5 parts by mass, the glass transition point of the toner is lowered and the durability is affected, which is not desirable.

  Thus, during kneading, polylactic acid is depolymerized by the action of the depolymerizing agent, the molecular weight is reduced, and the softening point is lowered. The polylactic acid having a softening point of 170 ° C. is desirably lowered to a softening point of, for example, 140 ° C. or less. As a result, a toner containing polylactic acid depolymerized as a binder resin is excellent in all of durability, offset property, and fixing property, and can be suitably used as a toner for low temperature fixing.

  Hereinafter, the method for producing an electrophotographic toner according to an embodiment of the present invention will be described more specifically.

  First, a toner raw material containing polylactic acid, a colorant, and a depolymerizer is mixed with a mixer. As a mixing machine, arbitrary things, such as a Henschel mixer, a super mixer, a V-type blender, and a Nauta mixer, can be used.

  The raw material mixture is then fed to a kneader where it is melt kneaded. The kneading machine is not limited to an open roll type kneader such as a continuous two roll mill, a continuous three roll mill, and a batch type roll mill, but an extrusion kneader such as a twin screw extrusion kneader or a single screw extrusion kneader is used. I can do it.

  FIG. 1 is a front view showing an open type continuous two-roll mill. The open-type continuous two-roll mill includes two open-type rolls 12 and 13 arranged in parallel and a discharge unit 14 through which the kneaded material is discharged. Helical grooves for transporting the kneaded material are formed on the surfaces of the rolls 12 and 13.

  The raw material mixture supplied between the rolls 12 and 13 is repeatedly compressed and kneaded by the rotation of the rolls 12 and 13 while being wound around the surfaces of the rolls 12 and 13, and is discharged by the grooves on the surfaces of the rolls 12 and 13. It moves to the part 14 side, and a kneaded material is discharged | emitted from there.

  FIG. 2 is a side view showing an example of a twin screw extrusion kneader. This twin-screw extrusion kneader includes a hopper 21 to which a raw material mixture is supplied, a cylinder 22 divided into a plurality of zones C1 to C8, and a die nozzle 23 from which a molten mixture is discharged. Each of the zones C1 to C8 of the cylinder 22 is heated to a predetermined temperature by a heater (not shown), and two cylinders are arranged in the cylinder 22 so that their axes are parallel or have a predetermined angle. A cylindrical screw (not shown) is arranged. The screw rotates in the same direction or in the opposite direction.

  The raw material mixture supplied from the hopper 21 is introduced into the cylinder 22 and is melted by the heat from the heated cylinder 22 in the gap between the screws, and is mixed by the compression force and shear force due to the rotation of the screw. Then, it moves to the die nozzle 23 side along the spiral blade of the screw and is discharged from the die nozzle 23.

  As described above, in kneading with these kneaders, polylactic acid is depolymerized by the action of the kneading agent, and as a result, the molecular weight is reduced and the softening point is lowered.

  The melt-kneaded product from the kneader is usually cooled, pulverized, and classified to a predetermined particle size according to the method used for producing the toner to obtain an electrophotographic toner. The cooling means, the pulverizing means, and the classification means are not particularly limited, and those usually used for toner production can be employed. For example, a cooling means by rolling or air flow spraying can be used for cooling, an airflow pulverizer such as a collision plate pulverizer can be used for pulverization, and various airflow classifiers can be used for classification. it can.

  As described above, an electrophotographic toner having a lowered softening point is produced.

  As the colorant that can be used in the electrophotographic toner manufacturing method according to the embodiment of the present invention described above, the following can be used.

  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 in the form of a masterbatch in which a resin and a colorant are dispersed in high concentration in advance.

  The particle size of the toner is not particularly limited, but is usually adjusted to 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 and the like. Of these, hydrophobized silica is preferable, and is commercially available from Nippon Aerosil Co., Ltd., CABOT Co., etc. The primary particle diameter is preferably 7 to 40 nm, and two or more kinds may be mixed for improving the function.

  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, the release agent has a relatively low melting point of about 60 to 100 ° C., and specifically, carnauba wax and synthetic ester wax are preferred. In consideration of environmental impact, natural product carnauba wax is more preferable. The addition amount of the release agent is preferably 1 to 10% by mass with respect to the whole toner.

  A conventionally known charge control agent can be added to the toner according to the exemplary embodiment as necessary. For example, a quaternary ammonium salt, a resin containing an amino group, etc. as a positive charge control agent, a metal complex salt of salicylic acid, a metal complex salt of benzyl acid, a calixarene type phenolic condensate, a carboxyl as a negative charge control agent There are resins containing groups. The blending amount of the charge control agent is preferably 0.1 to 5% by mass with respect to the whole toner.

  Examples of the present invention and comparative examples are shown below to describe the present invention more specifically.

Example 1
100 parts by mass of polylactic acid resin (manufactured by Mitsui Chemicals, Inc .: Tg: 61 ° C., Tm: 170 ° C., Mn: 160000), 1 part by mass of charge control agent “LR-147” (manufactured by Nippon Carlit Co., Ltd.), coloring PR-57.1 “ECR-101” (manufactured by Dainichi Seika Co., Ltd.) 5 parts by weight, mold release agent “Carnauba wax” 3 parts by weight, and trimellitic acid 1 part by weight as a depolymerization agent using a Henschel mixer Premixed.

  The obtained raw material mixture was supplied to an open roll type continuous kneader (manufactured by Mitsui Mining Co., Ltd., trade name: Kneedex) and continuously kneaded to obtain a kneaded product. This kneaded product is pulverized by a feather mill (manufactured by Hosokawa Micron Corporation, FM-1), and further pulverized by a collision plate type pulverizer “IDS-2” (manufactured by Nippon Pneumatic Co., Ltd.), and then an air flow type. Classification was performed with a classifier “DSX-2” (manufactured by Nippon Pneumatic Co., Ltd.) to obtain colored fine particles having a weight average particle diameter of about 9 μm.

  As an external additive, 2 parts by mass of “R972” (manufactured by Nippon Aerosil Co., Ltd .: hydrophobic silica) was added to 100 parts by mass of the obtained colored fine particles and mixed with a Henschel mixer to obtain a toner. The open roll type continuous kneader used at this time has a roll outer diameter of 0.16 [m] and an effective roll length of 0.7 [m].

Example 2
A toner was obtained in the same manner as in Example 1 except that the amount of trimellitic acid was 5 parts by mass.

Example 3
The amount of trimellitic acid is 0.5 parts by mass, and the kneading is performed using a continuous extrusion kneader (Ikegai Co., Ltd., product) instead of an open-roll type continuous kneader (Mitsui Mining Co., Ltd., trade name: Kneedex). Name: PCM-43) A toner was obtained in the same manner as in Example 1 except that

Example 4
The amount of trimellitic acid is 5 parts by mass, and the kneading is performed by a continuous extrusion kneader (Ikegai Co., Ltd., product name) instead of an open-roll type continuous kneader (Mitsui Mining Co., Ltd., product name: Kneedex). A toner was obtained in the same manner as in Example 1 except that it was performed according to PCM-43).

Comparative Example 1
A toner was obtained in the same manner as in Example 1 except that the amount of trimellitic acid was 0 parts by mass.

Comparative Example 2
A toner was obtained in the same manner as in Example 1 except that the amount of trimellitic acid was 0.2 parts by mass.

Comparative Example 3
A toner was obtained in the same manner as in Example 1 except that the amount of trimellitic acid was 5.5 parts by mass.

  For the toners obtained in the above examples and comparative examples, the softening point and the molecular weight were measured, and a printing test was conducted with a color printer “Speedia: V2” (manufactured by Casio Computer Co., Ltd.) to determine the durability. The offset and the fixability were evaluated.

1. Measurement of softening point With respect to 1 g of sample, a flow tester (CFT-500D, manufactured by Shimadzu Corporation) was used as an apparatus, and the temperature at which half of the sample flowed out by the 1/2 method was defined as the softening point. The measurement conditions are as follows.

Temperature increase rate: 6 ° C / min Load: 20kg
Nozzle: 1mm diameter, 1mm length
2. Molecular weight measurement 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.

3. Durability The toner is mounted on the above color printer, and in a normal environment (25 ° C, 50% RH), 5% coverage image is continuously printed. After 10,000 sheets are printed, the toner when the solid image is printed is the doctor blade. The occurrence of white streaks due to fusing was visually evaluated. The process speed was 34.1 mm / sec, and the fixing temperature was 150 ° C.

(Evaluation criteria)
○: No white streak occurred.

  Δ: Several lines can be confirmed.

  X: White streaks can be confirmed instantly.

4). Offset (dispersibility of wax)
The color printer is modified so that the temperature of the fixing part can be varied, and a fixing tester is obtained. After obtaining an unfixed image with the apparatus used in Test 1, the fixing temperature of the upper roll was varied in the range of 100 to 200 ° C. every 10 ° C. with the fixing tester, and the unfixed image was passed through the fixing device. . At that time, the temperature of the lower roll was set to 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 observed to obtain a non-offset region and evaluated as follows.

The process speed was 129.3 mm / sec, and the paper was XEROX P paper A4 size (mass 64 g / m ² ). The oil supply roll of the fixing device was removed.

(Evaluation criteria)
○: The non-offset region is 20 ° C. or higher.

  (Triangle | delta): A non-offset area | region is 10 degreeC or more and less than 20 degreeC.

  X: A non-offset area | region is less than 10 degreeC.

5. Fixing property (softening point)
Based on the measured softening point, the following criteria were used for evaluation.

(Evaluation criteria)
○: Softening point 140 ° C. or lower ×: Softening point 140 ° C. or higher

The above measurement and evaluation results are shown in Tables 1 and 2 below.

  As shown in Tables 1 and 2 above, the toners according to Examples 1 to 6 obtained by kneading polylactic acid together with a depolymerizing agent made of a compound having a carboxyl group such as trimellitic acid, acetic acid, and phthalic acid, It can be seen that the softening point is as low as 140 ° C. or less, and the durability, offset and fixability are all excellent.

  On the other hand, Comparative Examples 1 to 3 in which the amount of the depolymerizing agent is not in the predetermined range are inferior in durability, offset, or fixing property.

It is a figure which shows an open roll type continuous kneading machine. It is a figure which shows a continuous extrusion kneading machine.

Explanation of symbols

  11, 21 ... Hopper, 12, 13 ... Roll, 14 ... Discharge part, 22 ... Cylinder, 23 ... Die nozzle.

Claims (2)

At least one depolymerizing agent selected from trimellitic acid, acetic acid and phthalic acid, which is a compound having one or more carboxyl groups , as a raw material containing polylactic acid having a predetermined softening point and molecular weight as a binder resin A toner obtained through a kneading step of mixing 0.5 to 5 parts by mass with respect to 100 parts by mass of the polylactic acid and kneading the mixture, and a step of pulverizing and classifying the obtained kneaded product,
An electrophotographic toner, wherein the polylactic acid is depolymerized by the depolymerizing agent in the kneading step to reduce at least a softening point. At least one depolymerizing agent selected from trimellitic acid, acetic acid and phthalic acid, which is a compound having one or more carboxyl groups , as a raw material containing polylactic acid having a predetermined softening point and molecular weight as a binder resin A kneading step of mixing 0.5 to 5 parts by mass of 100 parts by mass of the polylactic acid and kneading the mixture , and a step of pulverizing and classifying the obtained kneaded product,
Said the polylactic acid by the depolymerization agent in the kneading step depolymerized method of electrophotographic toner characterized in that the Ru reduce at least the softening point.

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