JPH04298266A - Formation of coated film of pigment dispersion type - Google Patents

Abstract

PURPOSE:To provide the method for circulative formation of coated films to allow the formation of the uniform pigment dispersed films by supplying a uniform pigment dispersed coating liquid which is free from intermixing of impurities and is free from flocculation of pigments. CONSTITUTION:The coating liquid (1) contg. the pigments are circulated in a circulating route (3) and a static type in-pipe mixer (4) is provided in the piping of the circulating route (3). This mixer (4) is constituted to satisfy the product DELTAP.Q>=1.0(kg.cm/sec) of a flow rate Q(cm<3>/sec) and a pressure dropp DELTAP(kg/cm<2>).

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a pigment-dispersed coating film using a pigment-dispersed coating liquid.

0002

[Prior Art] In general, the dip coating method is often used for precision coating, which requires high precision in the thickness of the coating film. Also, from the viewpoint of controlling the liquid level, a circulation method is adopted in which the coating liquid in which the object to be coated is immersed is allowed to overflow from the coating tank and is circulated. In the circulation method, a rotary pump, a diaphragm pump, or the like is used as a means for transferring the coating liquid.

[0003] On the other hand, in recent years in the field of paints and pigments, coated films are required to go beyond mere aesthetics and rust prevention, and to be highly functional. Examples of coloring materials and pigments that aim for such high functionality include recording and display pigments used as electroluminescent materials and electrochromic materials, near-infrared absorbing pigments for optical disks, pigments for color filters, and organic photoconductive materials. Examples include coloring materials for devices such as pressure-sensitive and heat-sensitive materials for printers and copiers, and energy-use coloring materials including organic dyes for solar cells.

[0004] This increased functionality is often achieved in submicron to 20 micron thin films, especially at higher pigment loadings than in conventional paints. Therefore, a pigment-rich, low-viscosity dispersion liquid is used, and it is very difficult to maintain the dispersibility of the pigment, such as precipitation of the pigment or flocculation of the pigment due to a slight shock.

[0005] In order to maintain the dispersibility of pigments, it is possible to add a surfactant as is done in the paint industry, but not only does it take a lot of time to select the surfactant, but the surfactant The agent may become an impurity and have an adverse effect on high functionality, or the circulation of the coating solution may cause foaming in the coating solution, resulting in the formation of coating spots. This coating spot is
Eventually, this will cause variations in device characteristics.

[0006] As a method for preventing such coating unevenness,
Method of applying ultrasonic waves to circulating coating liquid
68081), and a method of adding shear force to the coating liquid immediately before coating, for example, stirring (Japanese Patent Application Laid-open No. 146238/1989,
46239, 146240, 146241 and 1462
42), etc., and a method of collecting and dispersing secondary pigment particles (Japanese Patent Laid-Open No. 60-29752).
and No. 29753) have been proposed. However, the method of redispersing pigments has a problem in processing capacity, and the method of collecting and dispersing secondary pigment particles gradually reduces the concentration of the coating liquid because the P/B (pigment/binder resin) ratio gradually decreases. Management becomes complicated.

[0007] Further, dispersion adjustment of the coating liquid is usually carried out by ball milling or sand milling, but it is inevitable that impurities derived from the grinding agent during kneading will be mixed into the dispersion liquid. As methods for removing these impurities, methods such as a magnetic filter method (Japanese Patent Laid-Open No. 60-208759) and an ultracentrifugation method have been disclosed, but these methods require quite complicated operations.

[0008]

[Problems to be Solved by the Invention] Conventionally, when a pigment-dispersed coating solution is circulated, the pigments aggregate due to the shear force of the pump, resulting in poor dispersibility. The coating film formed using this method lacks gloss and has poor electrostatic properties. Furthermore, when a coating liquid with poor dispersibility is redispersed using a sand mill or a ball mill, there is a problem in that there is contamination with impurities due to the grinding agent.

[0009] Therefore, the present invention provides a method for forming a pigment dispersion coating film with good coating properties and electrostatic properties by using a coating liquid that is free of impurities and has good dispersibility without pigment agglomeration. The purpose is to provide.

0010

[Means for Solving the Problems] In order to solve the above problems, the method of the present invention includes a step of mixing and dispersing a coating liquid containing a pigment using a static in-tube mixer, and coating the mixed and dispersed coating liquid. supplying the coating liquid to a tank and circulating the coating liquid through the static in-tube mixer, and immersing the object to be coated in the coating tank to form a coating film on the surface of the object to be coated. The flow rate Q (cm 3 /sec) of the coating liquid flowing through the static type in-tube mixer, the pressure loss ΔP of the mixer
(kg/cm 2 ), ΔP×Q≧1.0(k
g・cm/sec).

The static in-pipe mixer used in the present invention is one in which right-handed and left-handed twist elements are arranged at a 90 degree angle in a pipe (circulation piping). In the mixer, as the fluid passes through these twisted blades, the fluid itself is split and reversed, and mixed and dispersed.

Any type of pump such as a gear pump, centrifugal pump, or diaphragm pump can be used as a coating liquid transfer device disposed in the circulation path, but in order to perform uniform coating, it is necessary to add a pulsating flow to the liquid flow. It is preferable to use a pump that does not cause Since the coating liquid transfer device causes deterioration in the dispersibility of the pigment, it is desirable to arrange the in-tube mixer downstream of the transfer device.

[0013] The circulation path includes a circulation tank equipped with a stirring device,
By installing equipment to prevent pulsation of the liquid flow, such as a coating liquid replenishment tank, diluent (solvent) replenishment tank, filter, overhead tank, etc., it is possible to automate the coating equipment and improve the quality of the coating film. It is possible.

[0014]

[Function] The coating film forming method of the present invention uses a static in-tube mixer, and the flow rate of the liquid flowing in the in-tube mixer is Q (cm3/sec) and the pressure loss is ΔP (kg/sec).
cm 2 ), then the value of ΔP・Q, which is an index of the mixing energy per unit time of the fluid, is 1.0 (kg・cm/s
ec) or more. As a result, the dispersibility of the pigment dispersion coating liquid can be maintained favorably.

[0015] Furthermore, this in-tube mixer mixes and mixes by passing the fluid itself through twisted blades provided in the mixer.
Dispersion is performed, so there is no contamination with impurities caused by grinding agents that occurs when redispersing with a sand mill or ball mill. Therefore, there is no contamination of impurities, and a coating film can be formed without agglomeration of pigments.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below with reference to the drawings.

FIG. 1 shows a circulating coating apparatus used in the present invention. As shown in Fig. 1, this circulation coating device consists of a coating tank 1, a circulation tank 2, a stirring device 3, a diluent replenishment tank 4, a coating solution replenishment tank 5, a gear pump 6, and a static pipe as a dispersion device. Mixer Hi-Mixer (manufactured by Toray Engineering Co., Ltd.)
7, a filter 8, and an overhead tank 9.

A photoconductive layer was coated on an object to be coated using this circulating coating apparatus. That is, phthalocyanine (Pigment/Bynd
Pigment dispersion coating liquid 10 consisting of er = 1.0) was put into the coating tank, and the object to be coated 12 was attached to the object mounting device 11 equipped with a lifting means, and the circulating flow rate was 6.0 l/min.
Let the coating liquid overflow from the coating tank to a depth of 16 cm/
The object to be coated was coated by dipping in the coating solution at a coating speed of min., and dried to obtain a photoconductive layer.

Binder resins used in the pigment dispersion coating solution include, for example, phenoxy resin, polycarbonate,
There are butyral, saturated polyester, silicone, etc.
One or more of these can be used. These binder resins include dichloromethane, chloroform, 1,
2-dichloroethane, 1,1,2-trichloroethane,
It can be used dissolved in one or more solvents such as nitropropane, toluene, xylene, cyclohexanone, and dioxane. The concentration of binder resin in the solvent is usually 0.1 to 10% by weight, preferably 0.5 to 5% by weight.
It is.

A coating liquid is produced by dispersing a pigment in such a binder resin solution. Pigments used include, for example, phthalocyanine pigments such as copper phthalocyanine, aluminum chlorophthalocyanine, chloro isodium phthalocyanine, titanyl phthalocyanine, and metal-free phthalocyanine, polycyclic quinone pigments, perylene pigments, azo pigments, and squalium salts. , azulenium salts, and the like.

[0021] When the coating liquid described above is applied using the above-mentioned circulation coating device, the coating speed is usually 1 to 50 cm/m.
in, preferably 10 to 20 cm/min. The thickness of the photoconductive layer formed is 0.1 to 0.5 μm, preferably 0.2 to 0.3 μm.

[0022] In the Hi-Mixer (a static type in-tube mixer manufactured by Toray Engineering Co., Ltd.), the dispersion ability is affected by the number of right-handed or left-twisted elements and the flow rate when the fluid passes through the pipe.

In this example, the number of elements is 5 and the nominal diameter is 4c.
m Hi-Mixer and fluid flow rate of 1 l/m.
min, 2 l/min, 4 l/min, 6
Experiments were conducted for the cases of 1/min, 8 1/min, and 13 1/min.

A photoconductive layer was formed by circulating the coating solution at the above-mentioned flow rates and using a dip coating method. Photoconductive layer thickness (φ0) before circulation and static mixer (HiMixer) 500
The photoconductive layer thickness (φ500) after pass circulation was measured and the change in dispersibility was compared. Further, the dispersion/mixing energy added to the coating liquid in the static mixer was estimated by the value of the product ΔP·Q (kgcm/sec) of pressure drop and flow rate. The pressure drop ΔP (kg/cm 2 ) in the static mixer can be determined from the following equation using the Reynolds number (Re).

Re=(21.22・q・ψ)/(μ・D) (1) R
When e<80, ΔP=(0.83・q2・ψ・En)/(Re・D4
) (2) When 80≦Re<800, ΔP=(0.094・q2・ψ・En)/(Re0.
45・D4) (3) When 800≦Re<106, ΔP=(0.0
3・q2・ψ・En)/(Re0.21・D4) However, q: fluid flow rate (l/min), ψ: fluid density (g
/cm3) μ: Fluid viscosity (Poise), En: Hi-Mix
er element number D: Hi-Mixer nominal diameter (cm). Also, the density of the coating liquid at this time is 1.45 l/cm
3, the viscosity is 2.3 x 10-2 poise. Table 1 shows the circulation flow rate, pressure drop ΔP, ΔP·Q, photoconductive layer, film thickness change rate φ500/φ0, and evaluation results for ability to maintain pigment dispersibility.

FIG. 2 shows a graph plotting the relationship between ΔP·Q and φ500/φ0. As is clear from Figure 2, it is possible to maintain good pigment dispersibility in a circulation coating device equipped with a static mixer that allows the value of ΔP・Q to be 1.0 (kg・cm/sec) or more. A good pigment dispersion coating film was obtained.

[0027]

[Effects of the Invention] As explained above, according to the present invention,
Even if a dilute, low-viscosity dispersion containing a large amount of pigment is circulated for a long time, it is possible to obtain a stable pigment dispersion coating solution that does not cause pigment aggregation and contamination. As a result, it is possible to easily obtain a highly functional pigment dispersion coated film with good coating properties and electrostatic properties under highly accurate film thickness control.

[0028]

[Table 1]

[Brief explanation of drawings]

[Figure 1] Diagram showing the configuration of a circulating coating device used in the present invention

[Figure 2] ΔP・Q value and film thickness change rate φ500/φ0
Graph showing the relationship between

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1... Coating tank, 2... Circulation tank, 3... Stirring device, 4... Diluent replenishment tank, 5... Coating liquid replenishment tank, 6... Gear pump, 7... Stationary type in-tube mixer, 8... Filter, 9... overhead tank,
10... Pigment dispersion coating liquid, 11... Coated object attachment device, 1
2...Object to be coated

Claims (1)

[Claims] 1. A step of mixing and dispersing a coating liquid containing a pigment using a static type in-tube mixer, supplying the mixed and dispersed coating liquid to a coating tank, and applying the coating liquid to the static type in-pipe mixer. and a step of immersing the object to be coated in the coating tank to form a coating film on the surface of the object,
The flow rate Q (cm
3/sec), pressure loss ΔP of the mixer (kg/cm2
), ΔP×Q≧1.0 (kg・cm/sec)
A method for forming a pigment dispersion coating film that satisfies the following.