JP3285623B2 - Dispersant for carbon black - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dispersant and toner for carbon black used in electrophotography and the like.

[0002]

2. Description of the Related Art In an image forming apparatus such as an electrophotographic copying machine, as a developer for visualizing an electrostatic latent image formed on a photoreceptor by a dry developing method, generally, a triboelectric charging unit such as a fine toner and a magnetic carrier is used. And a two-component developer containing a developer. As a typical method for producing fine-grained toner used in the two-component developer, a styrene resin, a styrene- (meth) acrylic resin, a polyester resin or an epoxy resin is used as a binder resin, and a colorant and an offset prevention are used. After melting and kneading the raw materials such as the agent and the charge control agent,
There is a method in which a toner having a desired particle size is obtained by pulverizing with a fine pulverizer and classifying with a classifier. Generally, carbon black is often added as a colorant to a black toner.
In many cases, carbon black is exposed on the fracture surface of the particles, and since carbon black is a conductor, the resistance of the toner is partially reduced. Variations in density, image fogging or toner scattering occur. Conventionally, several methods have been proposed to solve such a problem of poor dispersion. For example, there is a method in which a melt-kneaded material is passed through a kneading device a plurality of times to improve dispersibility. In this method, dispersibility higher than the dispersion equilibrium characteristic of the kneading apparatus cannot be obtained, and even if blindly passing through the kneading apparatus many times, the expected effect cannot be obtained. Further, as another means, there is a method using, as a pre-mixing device, a device which can easily achieve uniform dispersion, such as a flow mixer, a Henschel mixer, a micro speed mixer, a flash mixer, or the like. However, in this method, since the stirring blade in the container is rotated at a high speed, the temperature in the container rises during mixing, and the binder resin adheres to the blades or the container, or is fused to the main shaft portion. Inconvenience is likely to occur. Also, as another means,
There is a master batch method in which a desired kneaded product is obtained by preparing a resin composition containing a high concentration of a coloring agent in advance and then diluting the resin composition with the same fusion resin. However, this method requires a plurality of pulverization steps until a desired toner is obtained, requiring a great deal of energy and cost.

[0003]

An object of the present invention is to provide a carbon black dispersant capable of uniformly dispersing carbon black. It is another object of the present invention to provide a toner that has a small change in charging characteristics and can provide a high-density image without causing toner scattering or image fogging.

[0004]

As a result of intensive studies to solve the above-mentioned problems, a block copolymer comprising a styrene polymer (A component) and a (meth) acrylate polymer (B component) has been obtained. , Carbon black and
Contains carbonized resin, based on 100 parts by weight of carbon black
The dispersant comprising the block copolymer is 3 to 60% by weight.
1 to 30 weight of carbon black with respect to parts and binder resin
% Styrene-based polymer (component A) and
(Meth) acrylic acid ester polymer (component B)
Graft copolymer, carbon black and binder tree
Fat and 100 parts by weight of carbon black
3-60 parts by weight of the dispersant comprising the graft copolymer,
1-30% by weight of carbon black to binder resin
A certain toner was found and the present invention was completed. Examples of the block copolymer in the present invention include an AB diblock copolymer, an ABA triblock copolymer, and a BAB triblock copolymer. Examples of the graft copolymer in the present invention include a graft copolymer having the A component as a trunk and the B component as a branch, and a graft copolymer having the B component as a trunk and having the A component as a branch.
Among the block copolymer and the graft copolymer in the present invention, an AB diblock copolymer or a graft copolymer is more preferred. The component A in the block copolymer or the graft copolymer used in the present invention is a styrene-based polymer, and the component A also includes a styrene- (meth) acrylate-based copolymer.

The styrene monomer unit constituting the component A includes, for example, styrene, o-methylstyrene, m
-Methylstyrene, p-methylstyrene, p-phenylstyrene, p-ethylstyrene, 2,4-dimethylstyrene, pn-butylstyrene, p-tert-butylstyrene, pn-hexylstyrene, pn -Octylstyrene, pn-nonylstyrene, pn-dodecylstyrene, p-methoxystyrene, p-chlorostyrene, 3,4-dichlorostyrene, o-nitrostyrene,
Examples include units derived from styrene derivatives such as m-nitrostyrene and p-nitrostyrene. When the A component is a styrene- (meth) acrylate-based polymer, the (meth) acrylate-based monomer unit includes:
Methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, n-butyl (meth) acrylate, sec-butyl (meth) acrylate, tert-butyl (meth) acrylate, (meth) ) (Meth) acrylates such as pentyl acrylate, hexyl (meth) acrylate, cyclohexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, lauryl (meth) acrylate, and phenyl (meth) acrylate Derived units. The composition ratio of the monomer units in the component A is as follows: styrene-based monomer units / (meth) acrylate-based monomer units = 100/0 to 50/5.
0 is preferable, and 100/0 to 60/40 is more preferable. The number average molecular weight (hereinafter sometimes abbreviated as Mn) of the component A is not particularly limited, but is usually 1000 to 3
It is selected from the range of 100,000, preferably from the range of 2000 to 100,000.

[0006] The (meth) acrylate monomer units constituting the component B include methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, n-butyl (meth) acrylate, and the like. Sec-butyl (meth) acrylate, tert- (meth) acrylate
Butyl, pentyl (meth) acrylate, hexyl (meth) acrylate, cyclohexyl (meth) acrylate,
(Meth) acrylates such as 2-ethylhexyl (meth) acrylate, lauryl (meth) acrylate, phenyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, 2-N- (meth) acrylate, Examples include units derived from (meth) acrylates having a functional group such as N-dimethylaminoethyl and 3-N, N-dimethylaminopropyl (meth) acrylate. B
The number average molecular weight (Mn) of the component is not particularly limited, but is usually selected from the range of 1,000 to 300,000, preferably from 2,000 to 100,000. The composition of the component A and the component B is usually selected from the range of 10/90 to 90/10, but is more preferably 20/80 to 80/20.
Is selected from the range.

[0007] The block copolymer or the graft copolymer used in the present invention may contain any other component as long as it does not affect the present invention. Specific examples of these components include (meth) acrylic acid and its ammonium or metal salt, (meth) acrylamide, N, N-dimethyl (meth) acrylamide, N, N-dimethylaminoethyl (meth) acrylamide, (Meth) acrylamidopropyl-
(Meth) acrylamides such as N, N, N-trimethylammonium chloride, (meth) acrylamido-2-methylpropylsulfonic acid and its ammonium or metal salt, (meth) acrylonitriles, maleic acid, itaconic acid, crotonic acid and Units derived from their esters or salts thereof, maleic anhydride and the like are included. The above monomer unit may be copolymerized in an amount of 1 to 30% by weight, preferably 2 to 20% by weight, based on the block copolymer or the graft copolymer. In this case, it may be copolymerized with either the A component or the B component, or may be copolymerized with both the A component and the B component.

There are various methods for producing the AB type diblock copolymer, and there is no particular limitation. For example, one of the monomers of component A or component B (for example, component A) Is radically polymerized in the presence of a compound containing a thioester and a thiol group in a molecule such as thiolcarboxylic acid, 2-acetylthioethylthiol or 10-acetylthiodecanethiol. The obtained polymer is treated with an alkali such as sodium hydroxide or ammonia to give a polymer having a thiol group at one end, and in the presence of this polymer, a monomer of the other component (for example, The method of obtaining the target block copolymer by radical polymerization of the monomer) is simple and highly efficient, and is most preferable. In this case, a block copolymer in which the component A and the component B are bonded via sulfur is obtained.

There are various methods for producing the graft copolymer, and there is no particular limitation, but a method using a macromonomer is simple. For example, a compound containing a thiol group and a carboxyl group in the molecule, such as thioglycolic acid or thiolactic acid, when radically polymerizing one of the monomers of the component A or the component B (for example, the monomer of the component A). By converting a carboxyl group of a polymer obtained by polymerization in the presence of a functional group into a functional group, it can be converted into a macromonomer having a polymerizable functional group at a terminal. In the presence of the macromonomer, the monomers of the other component (e.g. monomer component B) by La deer Le polymerization, it is possible to obtain a graft copolymer of interest. As a method for obtaining a macromonomer, in addition to the above method, a method utilizing living anionic polymerization, a method utilizing living cationic polymerization, and the like can be mentioned.

[0010] The amount of the dispersant comprising the block copolymer or the graft copolymer to be added to carbon black is 3 to 60 parts by weight, preferably 5 to 50 parts by weight, based on 100 parts by weight of carbon black. .

Next, the toner of the present invention will be described. Examples of the binder resin constituting the toner include styrene such as polystyrene, poly-p-chlorostyrene, and polyvinyl toluene, and a homopolymer of a substituted product thereof;
p-chlorostyrene copolymer, styrene-vinyltoluene copolymer, styrene-vinylnaphthalene copolymer, styrene-acrylate copolymer, styrene-methacrylate copolymer, styrene-α-chloromethyl methacrylate Copolymer, styrene-acrylonitrile copolymer, styrene-vinyl methyl ether copolymer,
Styrene-vinyl ethyl ether copolymer, styrene
Styrene copolymers such as vinyl methyl ketone copolymer, styrene-butadiene copolymer, styrene-isoprene copolymer and styrene-acrylonitrile-indene copolymer; polyvinyl chloride, polyvinyl acetate, polyethylene, polypropylene, polyester , Polyurethane, polyamide, epoxy resin, polyvinyl butyral, polyacrylic resin, polymethacrylic resin, terpene resin, phenolic resin and the like. These binder resins are used alone or as a mixture. Among the above binder resins, a styrene-acrylate copolymer, a styrene-methacrylate copolymer, and a polyester are preferable. The amount of carbon black containing a block copolymer or a graft copolymer as a dispersant used in the toner of the present invention is 1 to 30% by weight, preferably 3 to 20% by weight, based on the binder resin.

In order to control the charge of the toner, a charge control agent may be added. Examples of the charge control agent include oil-soluble dyes such as nigrosine dye, oil black, and spiron black; naphthenic acid, salicylic acid, octylic acid,
Fatty acids, resin acids manganese, iron, cobalt, nickel,
Metal soaps which are metal salts of lead, zinc, cerium, calcium and the like; metal-containing azo dyes, pyrimidine compounds, metal alkylsalicylate chelates and the like. These charge control agents are used in an amount of 0.1 to 5 parts by weight based on 100 parts by weight of the binder resin.
It is preferred to use% by weight. Further, an offset preventing agent may be added to the toner of the present invention in order to prevent the toner from adhering to the fixing roller. Examples of the offset preventing agent include various waxes such as low molecular weight polypropylene, low molecular weight polyethylene, and paraffin wax; low molecular weight olefin polymers of olefin monomers having 4 or more carbon atoms; fatty acid amides, silicone oils, and the like. These anti-offset agents are binder resin 1
It is preferable to use 0.5 to 15 parts by weight with respect to 00 parts by weight.

According to the present invention, the conductivity is 5 × 10 ^{-9 to} 5
× 10 ⁻¹¹ S / cm toner is obtained. A toner having a conductivity within this range has excellent charging characteristics. A toner having a conductivity of 5 × 10 ⁻⁹ to 4 × 10 ⁻¹⁰ S / cm has more excellent charging characteristics. Conductivity of toner is 5
If it is larger than × 10 ⁻⁹ S / cm, the amount of charge of the toner becomes insufficient, so that toner scattering and image fogging occur. If the conductivity of the toner is smaller than 5 × 10 ⁻¹¹ , the charge amount of the toner is excessively increased, and the image density is reduced.

The toner of the present invention can be used in combination with a carrier.
It may be used as a component-based phenomena agent, or it may be used as a one-component phenomena agent containing a carrier.
Examples of the carrier include conventionally known carriers such as iron powder, ferrite, and glass beads. These carriers may be coated with a resin, and the resins used in this case include polyfluorocarbon, polyvinyl chloride, polyvinylidene chloride, phenol resin, polyvinyl acetal, silicone resin, and acrylic resin. These coating resins may be used alone or in combination of two or more.
An appropriate mixing ratio of the toner and the carrier is about 0.5 to 6.0 parts by weight of the toner with respect to 100 parts by weight of the carrier.

[0015]

EXAMPLES The present invention will be described in more detail with reference to the following Examples, but it should not be construed that the invention is limited thereto. In the following examples, “parts” and “%” are based on weight unless otherwise specified.

Synthesis Example 1 In a 1 liter reaction vessel equipped with a stirrer, a condenser, a thermometer, and a nitrogen inlet tube, 50 g of methanol, 150 g of toluene, and a styrene-n-butyl methacrylate copolymer having a thiol group at one end. (Weight ratio: styrene / n-butyl methacrylate = 70/30, Mn = 5000)
50 g, 50 g of methyl methacrylate and 1 g of 2,2′-azobisisobutyronitrile (hereinafter abbreviated as AIBN) were charged, and solution polymerization was carried out at 70 ° C. for 5 hours while introducing nitrogen while stirring. A block copolymer (Mn = 10000) was obtained. Let the obtained block copolymer be resin A. Synthesis Examples 2 to 7 Hereinafter, as shown in Table 1, resins BG were synthesized by changing the types and molecular weights of the monomers.

Synthesis Example 8 400 g of toluene and a styrene-terminated polystyrene macromonomer (Mn = 500) were placed in the same reaction vessel as in Synthesis Example 1.
0) 100 g, methyl methacrylate 100 g and AI
1 g of BN was charged, and solution polymerization was performed at 70 ° C. for 5 hours under nitrogen introduction with stirring to obtain a graft copolymer (Mn = 28000). Let the obtained graft copolymer be resin H.

Synthesis Example 9 In the same reaction vessel as in Synthesis Example 1, 400 g of toluene, 100 g of a polymethyl methacrylate macromonomer (Mn = 5000) with terminal methacrylate ester, and 70 g of styrene
g, 30 g of n-butyl methacrylate and 1 g of AIBN
, And a solution polymerization is carried out at 70 ° C. while introducing nitrogen while stirring to obtain a graft copolymer (Mn = 3200).
0) was obtained. The obtained graft copolymer is designated as resin I.

Example 1 A toner having an average particle size of 10 μm was obtained by melting, kneading, pulverizing and classifying the following composition. The measured conductivity of the toner was 6 × 10 ⁻¹⁰ S / cm. This toner and a ferrite carrier were mixed and adjusted so that the toner concentration became 3%, to prepare a two-component developer. Using this developer, an electrophotographic copying machine (FT)
6550 (manufactured by Ricoh Co., Ltd.), a clear image with high density was stably obtained without toner scattering or image fogging. Table 1 shows the results. (Composition) Styrene-n-butyl methacrylate copolymer (copolymerization ratio: styrene / n-butyl methacrylate = 70/30)
100 parts Carbon black 5 parts Low molecular weight polypropylene 3 parts Chromium-containing azo dye 2 parts Synthetic resin A 2 parts

Examples 2 to 9 Tests were conducted in the same manner as in Example 1 except that the block copolymer used in Example 1 was replaced with the block copolymer or the graft copolymer shown in Table 1. did. Table 1 also shows the results.

Comparative Example 1 A toner was synthesized in the same manner as in Example 1 except that the block copolymer was not added, and aggregation of carbon black in the toner was observed. When the conductivity of the toner was measured, it was 6 × 10
^-10 S / cm, but an image output test was performed because of a large number of poorly charged toner particles. As a result, fogging was observed.

Comparative Example 2 In place of the block copolymer used in Example 1, a random copolymer of styrene-n-butyl methacrylate-methyl methacrylate (copolymer weight ratio = 35/15/5)
0, Mn = 10000), except that toner was synthesized in the same manner as in Example 1. The measured conductivity of the toner was 8 × 10 ⁻⁹ S / cm. An image forming test was performed using this toner in the same manner as in Example 1, and fog was recognized.

Comparative Example 3 A toner was synthesized in the same manner as in Example 1 except that the amount of carbon black was changed to 2 parts.
When the conductivity of this toner was measured, it was 4 × 10 ⁻¹¹ S
/ Cm. Using this toner, an image output test was performed in the same manner as in Example 1. As a result, scattering and fogging were small, but only a low-density image was obtained.

[0024]

[Table 1]

1) n-butyl methacrylate content 30% by weight 2) n-butyl acrylate content 20% by weight 3) 2-ethylhexyl acrylate content 20% by weight 4) acrylic acid content 5% by weight 5) acrylic acid 2- Ethylhexyl content 5% by weight 6) n-butyl methacrylate content 30% by weight

[0026]

According to the toner prepared by adding the carbon black dispersant of the present invention, since the carbon black is uniformly dispersed, the charging characteristics are stabilized, and a high-quality image free from scattering and fog is obtained. Can be

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-60-254157 (JP, A) JP-A-3-200976 (JP, A) JP-A-4-277755 (JP, A) JP-A-3-27775 59569 (JP, A) JP-A-56-116044 (JP, A) JP-A-3-170951 (JP, A) JP-A-1-284564 (JP, A) JP-A-2-103561 (JP, A) JP-A-2-311852 (JP, A) JP-A-4-156554 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G03G 9/08

Claims (2)

(57) [Claims] 1. A block copolymer comprising a styrene polymer (A component) and a (meth) acrylate polymer (B component) , carbon black and a binder resin.
And 100 parts by weight of carbon black.
3 to 60 parts by weight of a dispersant comprising a lock copolymer, binding
1 to 30% by weight of carbon black based on resin
Toner . 2. A graft copolymer comprising a styrene polymer (component A) and a (meth) acrylate polymer (component B) , carbon black and a binder resin.
And 100% by weight of carbon black.
3 to 60 parts by weight of dispersant composed of raft copolymer, binding
1 to 30% by weight of carbon black based on resin
Toner .