JPH0262122B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to an acrylonitrile polymer fine powder having a specific particle size, and is particularly useful for producing electrostatic recording materials that have excellent fine line image forming properties, excellent writability, and heat resistance. The present invention relates to useful acrylonitrile polymer fine powder particles. [Prior Art] An electrostatic recording medium has a support, a conductive layer, and a dielectric layer as its basic components, and an electrostatic image is formed on the dielectric layer by some method, and this latent image is developed using a colored substance. This is to record images. Conventionally, the electrostatic recording material used is a dielectric layer made of an insulating resin with inorganic fillers such as zinc oxide, titanium oxide, calcium carbonate, silica, alumina, etc. The surface is extremely smooth, and there are disadvantages in that the recorded image may be chipped during storage, and the writing ability is also insufficient. As a method to improve the retention and writability of recorded images, a method has been used to increase the content of inorganic filler contained in the dielectric layer.
The high insulation properties of the dielectric layer decrease in proportion to the increase in the content of the inorganic filler, and the ability to form electrostatic latent images decreases.
This has resulted in disadvantages such as a decrease in recorded image density and an increase in the weight of the recording medium. An electrostatic recording medium that does not have such drawbacks is disclosed in JP-A-55-110254, which contains a dielectric layer containing a powder resin of at least 75% by weight of an acrylonitrile polymer with a particle size of 10μ or less. The acrylonitrile polymer used here has an average particle size of 6 to 8 μm, and by using one that does not contain particles with a particle size of 10 μm or more, electrostatic recording without the above-mentioned problems can be achieved. I'm getting a body. [Problems to be Solved by the Invention] As mentioned above, the acrylonitrile polymer fine particles contained in the electrostatic recording medium disclosed in the above publication have an average particle diameter of 6 to 8 μm. 10μ
However, electrostatic recording media equipped with a dielectric layer containing such acrylonitrile-based fine particles have good line recording density and writability, but fine line image When electrostatic recording is performed by transmission, the ability to form fine lines is inferior to that of conventional electrostatic recording materials containing inorganic fillers, resulting in a lack of practicality. [Means for Solving the Problems] Therefore, the present inventors are currently studying to obtain an electrostatic recording material having a dielectric layer containing an acrylonitrile polymer powder as a filler that does not have the above-mentioned difficulties. Although the acrylonitrile polymer powder used in the invention has an average particle size of 6 to 8μ,
The particle size distribution is extremely wide ranging from 0.1 to 10μ, and those with a dielectric layer containing acrylonitrile polymer powder with a wide particle size distribution have poor fine line image formation, especially those with a particle size distribution of 1μ or less. It was found that those containing powder particles not only had poor writability but also lacked fine line image forming properties, although the reason was unknown. [Means for solving the problem] Therefore, as a result of various studies, the present inventors found that the volume average particle diameter was in the range of 2 to 4μ, and the maximum particle diameter was in the range of 2 to 4μ.
It has been shown that an electrostatic recording medium free from the above-mentioned drawbacks can be obtained by using acrylonitrile polymer fine powder that does not contain 10% by weight or more of fine powder particles of 1 μ or less and does not contain fine powder particles with a minimum particle size of more than 6 μ. The present invention has been completed. The gist of the present invention is that the present invention is made of an acrylonitrile polymer containing at least 90% by weight or more of acrylonitrile polymer units, has a reduced viscosity of 1.5 or more, is substantially free of impurities, and has an average particle size of 2 to 20%.
The present invention relates to a fine acrylonitrile polymer powder having a particle size of 4μ, containing no more than 10% by weight of powder particles with a particle size of 1μ or less, and containing no powder particles with a particle size of more than 6μ. The acrylonitrile polymer used in carrying out the present invention has 90 acrylonitrile polymer units.
It is necessary that it contains at least % by weight. Polymers containing less than 90% by weight of acrylonitrile polymer units have a low glass transition temperature, and the polymer powder particles tend to aggregate and form lumps, and when used as a filler, they have insufficient dispersibility in resins. ,
It has insufficient solvent resistance and is easily soluble in solvents, making it unsuitable as a filler. Furthermore, if the glass transition temperature decreases, the surface of the polymer particles will melt during pulverization, making it impossible to obtain an acrylonitrile polymer powder with a small particle size and narrow particle size distribution. Other copolymerizable monomers that can be copolymerized with acrylonitrile include styrene, vinyl chloride, α-
Methyl styrene, alkyl methacrylate, phenyl methacrylate, cycloalkyl methacrylate, alkyl acrylate, phenyl alkyl ester, cycloalkyl acrylate, acrylamide, acrylic acid, methacrylic acid, itaconic acid, styrene Examples include sulfonic acid, vinylsulfonic acid, and salts thereof. Reduced viscosity of the acrylonitrile polymer used in the present invention (100 ml of 0.5 g of acrylonitrile polymer)
The viscosity (as measured at 25°C when dissolved in dimethylformamide) must be 1.5 or higher. If the reduced viscosity is 1.5 or less, the solvent resistance is poor, the heat resistance is insufficient, and the grindability is insufficient, making it difficult to obtain the acrylonitrile polymer targeted by the present invention. To make an acrylonitrile polymer with a reduced viscosity of 1.5 or more, it is recommended to use an aqueous suspension polymerization method or a radical polymerization method using a polymerization solvent in a ratio of organic agent/water = 4/1 to 1/4. good. It is difficult to increase the degree of polymerization of acrylonitrile polymers made by solution polymerization, as shown in Japanese Patent Publication No. 49-31753, and the resulting acrylonitrile polymer powder has poor solvent resistance and heat resistance. In addition, since about 1% of the solvent remains in the acrylonitrile polymer powder, the powder tends to aggregate, and it is difficult to make it free from fine particles with an average particle size of 2 to 4 μm and 1 μm or less. Furthermore, Japanese Patent Publication No. 57-31732 discloses an invention in which acrylonitrile is polymerized in the presence of a cationic emulsifier to obtain spherical acrylonitrile polymer particles with a particle size of 1 to 2000 μm. The resulting polymer particles also have an extremely wide particle size distribution, including polymer particles of 1μ or less, and the surface of the polymer particles is highly hydrophilic. Because of its high hydrophilicity, it is difficult to use it as a filler in the production of highly insulating materials such as electrostatic recording materials. Therefore, it is desirable that the acrylonitrile polymer of the present invention is substantially free of impurities such as emulsifiers and organic solvents. In order to make the fine powder of the acrylonitrile polymer of the present invention, the acrylonitrile polymer made by the water-based polymerization method as described above is fed to a dry crusher equipped with a classifier, and polymer particles of 6μ or more are separated. While recirculating to the grinding system, polymers with a particle size of 1μ or less are removed.
An acrylonitrile polymer powder having a volume average particle diameter of 2 to 4 μm may be used. The acrylonitrile polymer used in the present invention is
Because it contains virtually no impurities and is made by aqueous suspension polymerization or aqueous radical polymerization,
The density of the polymer particles is high, and the crushability thereof is extremely superior to that of acrylonitrile polymers made by other polymerization methods. The acrylonitrile polymer particles of the present invention are
Contains no more than 10% by weight of fine particles of 1μ or less, and 6μ
It is necessary that the particles do not contain the above fine particles and that the volume average particle diameter is in the range of 2 to 4 microns. When an acrylonitrile polymer powder containing particles with a particle size of 6 or more is used as a filler for forming an electrostatic recording medium, fine line image breakage tends to occur. On the other hand, when acrylonitrile powder containing a large amount of particles with a particle size of 1 μm or less is used as a filler for forming an electrostatic recording material, it not only deteriorates the writing characteristics but also forms fine line images for unknown reasons. Sexuality begins to decline significantly. The acrylonitrile polymer powder of the present invention has the properties described above, and has excellent dispersibility in paints, coated paper resins, and film resins, and has good heat resistance, solvent resistance, and water resistance. It also has excellent weather resistance, particularly excellent insulation properties, and fully exhibits its characteristics when used as a filler for forming a dielectric layer for electrostatic recording materials. The insulating resin that can be used to make the dielectric layer for forming an electrostatic recording medium containing the above-mentioned acrylonitrile polymer fine particles needs to have a volume resistivity of 10 ¹² Ω·cm or more, Examples include acrylic resins, methacrylic resins, vinyl acetate resins, styrene resins, and polyester resins, and these resins can be used alone or in combination of two or more. The method of mixing the insulating resin and the acrylonitrile polymer resin is not particularly limited.
This can be carried out using a conventional mixer such as a ball mill, atrider, or Banbury mixer. To make an electrostatic recording medium using the above insulating resin solution, 1 to 20g/
By coating and drying to a film thickness of m ² , an electrostatic recording material with excellent fine line image formation, high image density, and good writability can be obtained. Note that paper, plastic film, etc. can be used as the substrate. The present invention will be explained in more detail with reference to Examples below. In addition, in the study related to the present invention, a Coulter counter (aperture counter) was used to measure the particle size.
50μ, manufactured by Nikkaki), and the volume average particle diameter was used as the average particle diameter. Example 1 Production of acrylonitrile polymer {A} Water from 1 and 0.15 g of concentrated sulfuric acid were put into the polymerization tank from 2, and after purging with nitrogen gas, it was heated to 50°C and heated to 200°C.
After adding 0.51 g of potassium persulfate and 25 ml of distilled water, 2.43 g of acidic sodium sulfite was dissolved in 25 ml of water and gradually added to the polymerization system by a dropwise method. After polymerizing at 50°C for 4 hours, the polymer was separated, washed, dehydrated, and then dried at 70°C. The resulting polymer had a reduced viscosity of 1.9 and an average particle size of 25μ. This polymer was designated as an acrylonitrile polymer {A}. The powder of the acrylonitrile polymer {A} obtained as described above was subjected to a fine pulverizer, and the classification conditions were changed to obtain acrylonitrile powder having the particle size characteristics shown in Table 1. (Particle size measurement was carried out using a Coulter Counter (aperture size 50 μm) manufactured by Nikikaki.) On the other hand, as an insulating resin, methyl ketone, a resin mainly composed of 80 parts of methyl methacrylate, 5 parts of ethyl acrylate, and 5 parts of glycidyl methacrylate, was used. Acrylonitrile polymer powder was uniformly dispersed in a methyl ethyl ketone solution in advance and added to the solution (solid content concentration 30%) so that the powder concentration was 5% by weight, and uniformly dispersed using a ball mill. The surface of this dispersion was treated so that the surface resistance value was 10 ⁷ Ω, and then it was spread on quality paper (weighing 50 g/m ² ).
An electrostatic recording medium was prepared by coating and drying the coating so that the weight after drying was 6 g/m ² . Table 1 shows the results of forming thin line images on the electrostatic recording paper thus obtained using a fixed multihead having a line density of 8 lines/mm and 16 lines/mm under conditions of 20°C and 65% RH.

[Table] Example 2 Production of acrylonitrile polymers {B} to {F} A four-necked flask with an internal volume of 2 was charged with the charging composition shown in Table 2, and polymerization was started at 55°C until the polymerization system became cloudy. At the start of the polymerization, add the additional solvent shown in Table 2, complete the polymerization in 70 minutes, separate the polymer, wash with water and dry to reduce the average particle size.
20~30μ acrylonitrile polymer {B}~
{F} was obtained.

[Table] The acrylonitrile polymer obtained as described above was fed to a pulverizer equipped with a classifier, and the acrylonitrile polymer with the average particle size shown in Table 3 was A combined powder was obtained. In addition,
Powders with a size of 5μ or more were sent to a further pulverization process, and large particles were removed. An electrostatic recording medium was prepared in the same manner as in Example 1 using the acrylonitrile polymer powder obtained as described above, and the image reproduction ability was measured. The results are shown in Table 3.

【table】

【table】

Claims (1)

[Scope of Claims] 1. An acrylonitrile-based polymer containing at least 90% by weight of acrylonitrile polymer units and having a reduced viscosity of 1.5 or more, containing no particle size exceeding 6μ and 10% by weight of particles having a particle size of 1μ or less. Fine acrylonitrile polymer powder with an average particle diameter of 2μ or more and 4μ or less. 2. The acrylonitrile polymer fine powder according to claim 1, wherein the acrylonitrile polymer fine powder particles are obtained by pulverizing an acrylonitrile polymer produced by an aqueous suspension polymerization method.