JPH04281468A - Liquid developer for electrostatic photography - Google Patents

Abstract

PURPOSE:To obtain the developer which is excellent in all of dispersibility, redispersibility, electrostatic chargeability, and preservable stability by incorporating a specific monofunctional macromonomer as an essential component into this developer and to obtain the images of high density and high quality with the high and stable electric resistance of the liquid. CONSTITUTION:This developer contains the monofunctional macromonomer formed by bonding the polymerizable double bond groups of formula II to one terminal of the main chain of a polymer consisting of the repeating unit of formula I as the essential polymerization component of a dispersion stabilizer and contains a copolymer which is soluble or swellable in a carrier liquid. In the formula, X denotes -COO-, -OCO-, CH2OCO-, -CH2COO-, -O-, or phenylene group; Y denotes 1 to 22C hydrocarbon group or hydrogen atom; a, b may be the same as or different from each other and respectively denote a hydrogen atom, halogen atom, cyan group or 1 to 8C hydrocarbon. Z is synonymous with X and C and d may be the same as or different from each other and are respectively synonymous with a or b.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a liquid developer used for developing electrostatic latent images, and in particular has excellent dispersibility, redispersibility, chargeability, image reproducibility, and storage stability. This invention relates to a liquid developer.

0002

[Prior Art] Liquid developers for electrostatic photography generally consist of toner particles made of various colorants such as carbon black and phthalocyanine, and natural or synthetic resins such as alkyd resins, acrylic resins, styrene resins, polyolefin resins, and rosin resins. is dispersed in a highly insulating liquid such as a petroleum-based hydrocarbon, and a charge control agent such as a metal soap is added thereto. Upon contact with the electrostatic latent image, development occurs by electrophoretic deposition of charged toner particles in the liquid developer onto the latent image.

Liquid developers are required to have various properties, but the first and most fundamentally required property is the dispersion stability of toner particles.

In conventional liquid developers, the dispersion stability of the particles was insufficient, and the particles tended to aggregate and settle during storage. If the particles are in an agglomerated state, a good quality image cannot be obtained and the resolution will be poor. In addition, particles that have aggregated and accumulated are difficult to re-disperse, resulting in particles adhering to the inside of the developing machine.
This also led to problems with the developing machine, such as smudged images and clogging of the liquid pump. Various means have been proposed in the past to overcome this problem. It is well known that polymers soluble in dispersion media, especially amphiphilic block or graft copolymers, are very effective as dispersion stabilizers;
For application to liquid developers, see British Patent No. 1,186,
Numerous proposals have been made, including No. 562 (1970). In order to further improve the dispersion stabilizing effect, a means for chemically bonding the dispersion stabilizing resin and toner particles has also been devised, as disclosed in U.S. Pat. Nos. 3,900,412 and 3,990.
, No. 980, etc. Furthermore, it has been considered to construct not only the dispersion stabilizing resin but also the binding resin with the above-mentioned amphiphilic copolymers; for example, in JP-A-58-1
No. 22557, Japanese Patent Application Laid-open No. 1-237668, etc. Although the dispersion stability and redispersibility of toner particles have been considerably improved by these various means, they are still not sufficient, and further improvements are desired. Furthermore, many of the resins proposed above are manufactured through complicated and time-consuming manufacturing processes, which poses a problem in terms of economic efficiency.

[0005] Along with dispersion stability, the chargeability of particles is also extremely important. In order to form clear images with high density,
The toner particles must be uniformly and distinctly positively or negatively charged. Particle charge also contributes to dispersion stabilization through electrostatic repulsion.

[0006] A charge control agent is usually added to the developer to impart charge to the particles. Commonly used charge control agents include metal soaps such as cobalt naphthenate and zirconium naphthenate, metal salts of long-chain alkylbenzenesulfonic acids or long-chain alkylsulfosuccinates, and JP-A-56-149053. It is an ionic or polar substance, such as a copolymer containing a polar component such as N-vinylpyrrolidone disclosed in .

Various problems exist with these charge control agents. Many charge control agents have insufficient charge imparting ability, and therefore sufficient density cannot often be obtained unless the latent image is at a high potential. A further important issue is stability. The charge control agent exerts its effect by being adsorbed onto the surface of the toner particles, but generally, the bond between the particles and the charge control agent is insufficient, so the charge control agent is detached from the particles due to long-term storage or repeated use. , the amount of charge decreases or the polarity is uneven,
There was a tendency for it to become unclear. Another important problem is increasing the conductivity of the liquid. Charge control agents are generally ionic or polar substances and therefore have high electrical conductivity. Therefore, if a sufficient amount of charge is added to the toner particles, the conductivity of the developer will significantly increase, resulting in charge leakage during development, resulting in a significant decrease in development performance. . Although many charge control methods have been proposed, none of them is completely satisfactory in solving the above-mentioned problems, and further improvements have been desired.

[0008]

As described above, conventional liquid developers have many deficiencies in particle dispersion, charging, etc., resulting in problems in storage stability and image quality.

[0009] The present inventors have carried out intensive research to solve the above-mentioned problems with liquid developers, and have found that a copolymer having a certain specific structure is extremely effective in dispersing particles. At the same time, it also has an extremely excellent charge control effect,
The inventors have also discovered that the various problems mentioned above are significantly improved, leading to the present invention.

That is, an object of the present invention is to provide a liquid developer having excellent dispersion stability and redispersibility. Another object of the present invention is to provide a liquid developer with excellent charging properties and charging stability. Still another object of the present invention is to provide a liquid developer with low liquid conductivity and excellent developing performance.

[0011]

[Means for Solving the Problems] The purpose of the present invention is to
In an electrostatographic liquid developer in which a toner containing a colorant and a resin as main components is dispersed in a highly insulating carrier liquid, a polymer consisting of a repeating unit represented by the following general formula (I) is used as a dispersion stabilizer. The following general formula (II) is present at one end of the main chain.
An electrostatic agent characterized by containing a monofunctional macromonomer formed by bonding a polymerizable double bond group represented by as an essential polymerization component, and a copolymer that is soluble or swellable in a carrier liquid. Achieved by photographic liquid developer.

0012

[Chemical formula 3]

[0013]

[C4]

(In formula (I), X is -COO-, -OCO
-, CH2 OCO-, -CH2 COO-, -O-,
Or represents a phenylene group (which may have a substituent). Y represents a hydrocarbon group having 1 to 22 carbon atoms or a hydrogen atom. a and b may be the same or different,
Each represents a hydrogen atom, a halogen atom, a cyano group, or a hydrocarbon group having 1 to 8 carbon atoms. Moreover, in formula (II), Z has the same meaning as X in formula (I). c and d may be the same or different, and each has the same meaning as a or b above. ) Hereinafter, the present invention will be explained in detail.

The highly insulating carrier liquid used in the liquid developer of the present invention is preferably a non-polar liquid having an electrical resistance of 109 Ω·cm or more and a dielectric constant of 3 or less, including aliphatic, alicyclic, and aromatic hydrocarbons. , halogenated hydrocarbons, etc. can be used, but linear or branched aliphatic hydrocarbons are particularly preferred. Such solvents include, for example, octane, isooctane, decane, isodecane, dodecane,
Examples include isododecane, Isopar G, Isopar H, Isopar L (Isopar: a trade name of Exxon), Shellsol 71 (Shellsol: a trade name of Shell Oil Company), and the like. It is also possible to mix and use other arbitrary liquids with these liquids within a range that does not deviate from the above-mentioned preferred values of electrical resistance and dielectric constant.

The material constituting the toner particles in the liquid developer of the present invention is not particularly limited, and various conventionally known materials can be used. That is, various organic or inorganic pigments and dyes such as carbon black, phthalocyanine blue, Hansa yellow, and quinacridone red can be used as coloring agents, and styrene resins, styrene-butadiene resins, acrylic resins, and alkyd resins can be used as binder resins. , ethylene (co)polymer, rosin resin, etc. The ratio of colorant to resin is not particularly limited, but 0.5 to 1 part by weight of resin to 1 part by weight of colorant.
It is preferably blended in an amount of 0 parts by weight, more preferably 1 to 5 parts by weight.

In preparing a developer, the above components are usually dispersed at a relatively high concentration in a highly insulating carrier liquid to first prepare a concentrated dispersion, and then further diluted with a highly insulating carrier liquid to form a developer. is prepared. The concentration of toner particles in the developer is 0.1
Approximately 10% by weight is suitable, more preferably 0.3% by weight.
~3.0% by weight.

The component that plays the most important role in the liquid developer of the present invention is a copolymer containing a macromonomer as an essential copolymer component. This substance exhibits an extremely excellent dispersion stabilizing effect, and by adding this substance, a liquid developer with extremely excellent properties can be obtained.

In this copolymer, the monofunctional macromonomer contained as an essential polymerization component is attached to one end of the main chain of the polymer consisting of repeating units represented by the general formula (I). The number average molecular weight is not particularly limited, but it is preferably 103 or more and 104 or less.

[0020]

[C5]

[0021]

[C6]

(In formula (I), X is -COO-, -OCO
-, CH2 OCO-, -CH2 COO-, -O-,
Or represents a phenylene group (which may have a substituent). Y represents a hydrocarbon group having 1 to 22 carbon atoms or a hydrogen atom. a and b may be the same or different,
Each represents a hydrogen atom, a halogen atom, a cyano group, or a hydrocarbon group having 1 to 8 carbon atoms. Moreover, in formula (II), Z has the same meaning as X in formula (I). c and d may be the same or different, and each has the same meaning as a or b above. ) Groups connecting component (I) and component (II) include C-C bonds (single or double bonds), carbon-heteroatom bonds (heteroatoms include O, S, N, Si, etc.), It is composed of any combination of atomic groups of heteroatom-heteroatom bonds.

[0023] This macromonomer can be produced by a conventionally known synthesis method. For example, a method of introducing a polymerizable group by reacting various reagents at the end of a living polymer obtained by anionic polymerization or cationic polymerization, a polymerization initiator containing a reactive group such as COOH, OH, or an amino group in the molecule and/or Alternatively, there is a method in which a radically polymerized polymer having a reactive functional group at the end obtained using a chain transfer agent is reacted with various reagents to introduce a polymerizable group.

The macromonomer can be synthesized as described above, and the main chain is a polymer of methyl methacrylate, butyl acrylate, styrene, styrene-acrylonitrile, or silicone, and the terminal polymerizable group is methacryloyl. The base is sold by Toagosei Kagaku Co., Ltd., and it is convenient and economically advantageous to use it. Among these, those whose main chain is composed of MMA (AA- manufactured by Toagosei Kagaku Co., Ltd.) are particularly preferably used.
6), or one made of styrene (AS-6). Two or more different types of these macromonomers can also be used in combination.

[0025] Other copolymerization components used together with this macromonomer are selected from those which allow the resulting polymer to be soluble or swellable in the hydrocarbon carrier liquid, and particularly preferred are those having at least 6 carbon atoms. Acrylic acid or methacrylic ester having an alkyl group, such as 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, lauryl methacrylate, stearyl methacrylate, etc. In addition to these monomer components, other types of monomer components can also be used in combination as long as the affinity of the produced polymer to the carrier liquid is not significantly reduced. Examples of such monomers include alkyl (meth) having up to 5 carbon atoms;
Acrylate, styrene or its derivatives, acrylic acid, methacrylic acid, 2-hydroxyethyl (meth)acrylate, glycidyl (meth)acrylate, N,N-
Examples include dimethylaminoethyl (meth)acrylate, N-vinylpyrrolidone, and 2-vinylpyridine.

The present copolymer is preferably soluble in the carrier liquid, but even if it is not completely soluble, it can be used without any problem as long as it shows a certain degree of affinity for the carrier liquid. Even if the copolymer is not completely dissolved in the carrier liquid, it can be mixed uniformly into the developer by adding the copolymer as a solution in a solvent that dissolves it.

The suitable content of the macromonomer in the present copolymer varies depending on the type of the macromonomer and other copolymer components, but is generally in the range of 1 to 70% by weight, preferably 5 to 70% by weight.
A range of 50% is used. If it is less than 1%, the desired effects such as charge control effect will not be sufficiently achieved, and 70%
If it exceeds %, the resulting copolymer will have too little affinity with the carrier liquid and will separate from the liquid, so that the effect will not be sufficiently exerted in this case as well. Although the present copolymer can be produced by a conventional radical polymerization method, a particularly suitable method is a solution polymerization method. That is, it can be produced by dissolving the macromonomer and other copolymerization components in a solvent and heating the solution in the presence of a polymerization initiator. The solvent used here is not particularly limited as long as it dissolves the monomer, but it is preferable to use a solvent that does not contain polar groups so that it will have as little influence as possible even if it is mixed into the liquid developer, such as toluene, xylene, etc. Aromatic hydrocarbons such as the following are preferably used. Any commonly used polymerization initiator can be used, such as azobisisobutyronitrile, azobisisovaleronitrile, benzoyl peroxide, lauroyl peroxide, and the like. Polymerization temperature and polymerization time depend on the type of initiator and monomer used, but are generally 60 to 150°C and 5 to 20 hours.
R or so is preferable.

The developer of the present invention is produced by adding the above copolymer to a liquid developer produced by a conventional method. It is convenient to add the copolymer to the developer as a solution, and the solution obtained by solution polymerization may be used as it is. The solvent used to dissolve the copolymer is preferably one with low polarity so as not to affect the electrical properties even if mixed into the developer, and it is most preferable to use the same solvent as the carrier liquid. If the copolymer has low solubility in the carrier liquid solvent, any other solvent can be used, but aromatic hydrocarbons such as toluene and xylene are particularly preferred. Even if these solvents are mixed into the developer in relatively small amounts, they have almost no effect on the developer performance, so there is usually no need to remove them from the developer. If necessary, it may be removed under reduced pressure.

The amount of the copolymer added is about 0.005 to 5 parts by weight, more preferably about 0.01 to 1 part by weight, per 1 part by weight of the nonvolatile components of the developer. However, if the type of resin or pigment used, the particle size, the composition of the macromonomer copolymer, etc. differ, the above-mentioned optimum addition amount will also differ, so it is not limited to this range.

It has been found that the present copolymer has an excellent dispersion stabilizing effect and, at the same time, an extremely excellent charge control effect. Therefore, there is no need to further add a charge control agent. However, it is also possible to add a small amount of a conventionally known charge control agent. For example, metal salts of fatty acids such as naphthenic acid, octenoic acid, and stearic acid, metal salts of salicylic acid or its derivatives, metal salts of sulfosuccinic acid esters,
Examples include oil-soluble sulfonic acid metal salts, phosphate ester metal salts, phosphate ester surfactants, amino acid derivatives, lecithin, and the like.

[0031] In addition to the excellent dispersion stabilization effect, the unique feature of this copolymer is that it has a strong charge control effect, and this makes it possible to obtain a liquid developer with extremely high performance. .

It is surprising that macromonomer copolymers exhibit strong charge control effects even though they do not have distinct ionic or polar components. Although the mechanism has not yet been elucidated, it is presumed that this copolymer is strongly adsorbed to the toner particle surface, and as a result of some charge transfer between the toner particle surface and the particle surface, the particles become electrically charged.

The polarity of the charge imparted to the toner particles by the addition of the macromonomer copolymer may be positive or negative depending on the type of macromonomer and toner resin;
Generally, a macromonomer whose main chain is composed of styrene or butyl acrylate tends to have positive polarity, and a macromonomer of MMA tends to have negative polarity. Further, when the toner resin contains an acidic group such as COOH, it tends to exhibit negative chargeability. The type of macromonomer and/or toner resin may be selected depending on the desired polarity. By selecting the composition, products with positive or negative charge polarity can be manufactured.
Therefore, it is a great advantage of the present invention that it can be adapted to any printing process.

A major advantage of the macromonomer copolymer as a charge control agent is that it has very little effect of lowering the electrical resistance of the carrier liquid because it does not have an ionic or polar group.

In general, in the wet development method, when the electrical resistance of the developer is less than about 1011 Ω cm, charges leak and dissipate during development, causing problems such as a decrease in image density. When a strongly polar charge control agent is added to the developer in an amount necessary to add a sufficient amount of charge to the particles, the resistance of 1014 to 1015 Ω when no additive is added.
The liquid resistance in cm is 1010 to 1011 Ω cm.
It is often lowered. In contrast, the macromonomer copolymer of the present invention has a resistance of 1012 to 1013Ω at most.
cm2, and therefore high density, high quality images can be obtained.

[0036] In addition to excellent dispersibility and chargeability, redispersibility,
Another notable feature of the developer of the present invention is that it has excellent storage stability. Generally speaking, dispersibility and redispersibility are properties that are difficult to coexist with each other.If we try to improve dispersion stability, the sedimentation rate of particles will be improved, but once the particles have settled, they will accumulate more densely, and redispersibility will decrease. It usually gets worse. However, although the developer of the present invention has extremely good dispersibility, it also has good redispersibility, does not cause troubles such as adhesion to the developing device, and has good storage stability. Always give high quality images.

[0037]

[Examples] Next, the present invention will be specifically explained with reference to Examples, but the present invention is not limited thereto.

(Production of copolymer) Production example 1 30 g of macromonomer AS-6 (styrene macromonomer, manufactured by Toagosei Kagaku Co., Ltd., number average molecular weight of about 6000)
, 70 g of lauryl methacrylate, and 2 g of azobisisobutyronitrile were dissolved in 200 g of toluene, and in a 500 ml three-necked flask equipped with a stirrer, a reflux condenser, and a gas inlet tube, the mixture was heated under a nitrogen atmosphere with gentle stirring.
℃ for 8 hours. A slightly cloudy copolymer solution was obtained.

Production Examples 2 to 5 Each copolymer was produced in exactly the same manner as Production Example 1 using the following monomer components.

Production example macromonomer
Other monomer No.
．． (Amount added)
(Amount added) 2
AA-6 (MMA macromonomer) lauryl methacrylate
(20g)
(80g) 3AA
-6 (MMA macromonomer) stearyl methacrylate
(20g)
(80g) 4 AB-6(
Butyl acrylate lauryl methacrylate macromonomer) (
20g)
(80g) 5 AS-6
(27g) Lauryl methacrylate (70g)

Acrylic acid (3g
) Comparative production example 1 lauryl methacrylate 80g, benzoyl peroxide 1
g was dissolved in 160 g of toluene, and a polymerization reaction was carried out in the same manner as in Production Example 1 to obtain a lauryl methacrylate homopolymer solution. 20 g of methyl methacrylate and 2 g of benzoyl peroxide were added to this solution, and the reaction was further carried out at 80° C. for 8 hours to obtain a graft copolymer solution.

Comparative Production Example 2 Using 80 g of lauryl methacrylate and 20 g of methyl methacrylate as monomers, the reaction was carried out in the same manner as in Production Example 1 to obtain a copolymer solution.

Example 1 The components having the following composition were melted at 90°C, and the mixture was heated at 90°C for 2 hours using a small stirrer using 0.8 mm glass beads as a media.
The pigment was dispersed by stirring for an hour.

<Ingredients>
<Quantity (
g)> Ethylene vinyl acetate copolymer (
Allied Signal AC400)
30 Lionogen Magenta R
(manufactured by Toyo Ink Manufacturing Co., Ltd.) 6 Isopar M (manufactured by Exxon)
After 114 mixing, the mixture was cooled to room temperature, and then 30 g of Isopar G (manufactured by Exxon) was added and wet milled for 2 hours in a sand mill (manufactured by Kanpe) to obtain a dispersion with a solid content of 20% by weight. 65 g of this dispersion was diluted with Isopar G to a solid content of 1% by weight, and 5.2g of the 25% by weight toluene solution of the macromonomer copolymer of Production Example 1 was added thereto to prepare liquid developer 1.

The particle size of the obtained developer was measured using a centrifugal sedimentation type particle size analyzer (SA-CP3 manufactured by Shimadzu Corporation).

The amount of charge generated by the developer was evaluated as follows. First, 1.45g of developer 1 was placed on a liquid electrode (LP-05 type manufactured by Kawaguchi Electric), and +500V was applied to
The current flowing through the electrode for seconds was integrated. Let this be QD. At this time, the polarity of the toner was determined based on whether the toner particles adhered to the positive or negative electrode. Next, the developer is centrifuged to separate only the carrier liquid, 1.45 g of the carrier liquid is placed on a liquid electrode (Kawaguchi Electric LP-05 type), +500V is applied, and the current flowing through the electrode for 0.5 seconds is integrated. did. Let this be QC. QD and QC both represent the amount of charge, and when (QD - QC) is large and Q
A smaller C/QD indicates a larger net charge generated on the toner particles and fewer ionic components in the carrier liquid, which is advantageous for the developer.

The charge stability of the obtained developer was determined by measuring (QD -QC)0 immediately after preparation and (QD -QC)48 after standing at 50°C for 48 hours, and calculating the ratio (QD -QC)48.
Evaluation was made using C)0/(QD-QC)48. The closer this ratio is to 1, the smaller the change in charge amount and the less aggregation of particles, which is advantageous as a developer.

Next, when developer 1 was subjected to a printing test using a wet copying machine DT2500 manufactured by Ricoh Co., Ltd., good images were obtained.

Examples 2 to 5 In Example 1, liquid developers 2 to 5 were prepared using the macromonomer copolymers of Production Examples 2 to 5, respectively (Developer No. is Production Example No. (corresponding to the above), were tested in the same manner as in Example 1, and good images were obtained in all cases.

Example 6 Terminal hydroxyl group-modified polystyrene (manufactured by Toagosei Kagaku Co., Ltd.)
Put 180 g of macromonomer HS-6) and 36 g of Lionogen Magenta R (manufactured by Toyo Ink Manufacturing Co., Ltd.) into a stainless steel pot, heat and melt at 100°C, and then (manufactured by Seisakusho) for 2 hours, and the kneaded mixture was cooled and solidified.
-1 (manufactured by Fuji Paudal Co., Ltd.). This crushed material 40
g and 160 g of Isopar G were put into a sand mill using 0.8 mm glass beads as media, and further Production Example 2
25% by weight toluene solution of macromonomer copolymer 1
9.2 g was added and wet-pulverized for 6 hours to prepare a liquid developer 6 having a solid content of 20% by weight. When tested in the same manner as in Example 1, good images were obtained.

Comparative Examples 1 and 2 In Example 1, Comparative Liquid Developers 1 and 2 were prepared by using the copolymers of Comparative Production Examples 1 and 2, respectively (Developer No. was Comparative Production Example No. ), Example 1
When I tested it in the same way as above, I could only get images with low density. Particle size of prepared developer, Q immediately after preparation
D, QC, and charge stability are shown in Table 1.

[0051]

[Table 1]

[0052]

Effects of the Invention As explained above, the liquid developer of the present invention has excellent dispersibility, redispersibility, chargeability, and storage stability, and also has high electrical resistance, so it can be used at high concentrations and high Give quality images.

Claims (1)

[Claims] [Claim 1] An electrostatographic liquid developer comprising a toner containing a colorant and a resin as main components dispersed in a highly insulating carrier liquid, in which a repeating unit represented by the following general formula (I) is used as a dispersion stabilizer. Contains as an essential polymerization component a monofunctional macromonomer formed by bonding a polymerizable double bond group represented by the following general formula (II) to one end of the main chain of the polymer, and is soluble in the carrier liquid. A liquid developer for electrostatic photography, characterized in that it contains a copolymer that is swellable. [Chemical 1] [Chemical 2] (In formula (I), X is -COO-, -OCO-, CH2
Represents OCO-, -CH2 COO-, -O-, or a phenylene group (which may have a substituent). Y represents a hydrocarbon group having 1 to 22 carbon atoms or a hydrogen atom. a and b may be the same or different, and each represents a hydrogen atom, a halogen atom, a cyano group, or a hydrocarbon group having 1 to 8 carbon atoms. Moreover, in formula (II), Z has the same meaning as X in formula (I). c and d may be the same or different, and each has the same meaning as a or b above. )