CN1359988A - Process for preparing conducting light colour flaky pigment - Google Patents

Abstract

A process for preparing conducting flaky light-colour pigment is characterized by that the flaky substrate is firstly coated with the nucleus layer, which is prepared by hot hydrolysis of diluted Sn salt solution in acidic medium to obtain high-activity Sn(OH4), and then with electrically conductive layer. Its advantages are high adhesion between layers and uniform colour.

Description

Process for preparing light-coloured flaky conductive pigment

Technical Field

The invention relates to a light-colored flaky conductive pigment, which is particularly suitable for preparing coatings, plastics, fibers, rubber and the like which are required to have conductive performance, static resistance or electromagnetic wave shielding.

Background

The conductive pigment refers to a pigment having a conductive ability, and the conventional conductive pigment is metal powder such as gold, silver, copper, zinc, cobalt, nickel, etc.; and non-metallic powders such as carbon black, graphite, and the like. The greatest disadvantage of these conductive pigments is the variety of different colors and the darker colors, which cannot be freely adjusted. In addition, most of the particles are granular, and the number of the particles required for achieving a certain conductive capacity is large, otherwise, the particles cannot be in sufficient contact with each other, and an electric path cannot be formed. In recent years, a flake conductive pigment is developed and applied at home and abroad, which is a conductive pigment in which a conductive layer is coated on the surface of a flake material (such as mica, kaolin, glass flake and the like), and the conductive layer is mostly tin oxide doped with antimony. Because the pigment has light color, usually light grey white, and the particles are flaky, when the pigment is mixed with plastics, paint and the like, color can be matched according to the requirements of customers, the contact area between flaky particles is large, and the required conductivity can be achieved by using less particles, so that the conductive pigment is popular with customers. The method currently used for preparing such pigments is: firstly, making the sheet-shaped base material into water slurry, simultaneously making the coating material into water solution, under the condition of a certain temp. and a certain pH value, gradually adding coating material solution to make these coating materials be hydrolyzed, directly depositing the formed precipitate on the surface of the sheet-shaped base material to form coating layer, then filtering, washing, drying and calcining so as to obtain the invented sheet-shaped conductive pigment. Tin compounds doped with appropriate amounts of antimony are most currently used as coatings. The biggest disadvantages of this preparation method are: the hydrolysis precipitate cannot be ensured to be completely coated on the surface of the flaky substrate. In the initial stage of hydrolysis precipitation, part of the hydrolysis precipitate is not adsorbed on the substrate surface but is dissociated in the liquid phase, often due to low surface activity of the substrate. These hydrolysis precipitates free in the liquid phase have extremely small particles and have a large cohesive force, and may be agglomerated during subsequent drying, and further form a dense, hard sintered body during calcination. The sintered body is difficult to disperse in application media, and the color of the sintered body is different from that of the flaky conductive pigment, so that the application performance of the sintered body is influenced. In addition, the coating layer formed by the method has poor adhesion with a base material, and can partially fall off in the pigment production process under the action of shearing force, and the fallen coating layers can also generate a sintered body during calcination; in the application process, the conductive performance of the coating layer can be influenced because the coating layer partially falls off.

Disclosure of Invention

The invention aims to provide a preparation method of a light-color flaky conductive pigment, which is simple and convenient and does not need to increase equipment. The pigment prepared by the method has no sintered body, the conductive layer of the pigment has good adhesive force with the flaky base material, and the pigment does not fall off in the application process, and has good dispersibility and excellent conductivity.

The technical scheme for realizing the purpose of the invention is as follows: a process for preparing the light-colour flaky electrically conductive pigment includes such steps as preparing the flaky substrate in water to become slurry, adding the solution of tin salt and antimony salt while stirring, hydrolyzing, depositing on the surface of flaky substrate to form a coated layer, separating, washing, drying and calcining₄The crystal nucleus layer comprises the following specific steps:

① cladding the crystal nucleus layer

Preparing a sheet-like substrate having a particle size of 1 to 100 μm into a slurry having a pH of 1.3 to 2.5 and a temperature of 30 to 70 ℃ in water, and slowly adding a tin chloride dilute solution in an amount of 0.9 to 3.3% by weight (SnO) based on the weight of the substrate while stirring₂Metering), feeding for at least 30 minutes to form Sn (OH) on the surface of the sheet-like substrate₄A seed layer;

② coating of conductive layer

Uniformly adding a tin salt solution and an antimony salt solution while stirring, keeping the temperature of the slurry at 60-80 ℃ in the process, simultaneously adding alkali liquor to maintain the pH at 1.5-4.0, adjusting the pH value of the slurry to 7.0-8.0 after the addition is finished, and stirring for at least 30 minutes under the condition of heat preservation, wherein the Sn (OH)₄Formation of Sn (OH) on the seed layer₄And Sb (OH)₃The coating layer (b) is 40-75% (by SnO) of the weight of the base material₂And Sb₂O₃Total amount);

③ Generation of conductive layers

Separating solid by a conventional method, washing, drying, calcining at 650-750 ℃ to form tin oxide/antimony (Sn) with the ratio of tin to antimony being (5-10) to 1_xSb_y)O₂And (3) conducting the layer to obtain the light grey-white flaky conductive pigment with the resistivity of 30-150 omega cm.

In the above preparation method, formThe tin chloride dilute solution used for forming the tin oxide crystal nucleus layer is SnCl₄·5H₂O water solution with the concentration of 10-50 g/L (SnO)₂Meter).

In the above preparation method, the tin salt and antimony salt solution used for forming the tin oxide/antimony conductive layer is SnCl₄·5H₂O and Sb₂O₃Mixing to obtain acidic aqueous solution, or SnCl₄·5H₂O and Sb₂O₃Independently preparing an acidic aqueous solution, and adding the acidic aqueous solution when in use.

In the above preparation method, the sheet-like base material may be natural or synthetic mica, talc, kaolin or glass flake.

The invention has the technical effects that: the method for preparing the light-color flaky conductive pigment comprises the steps of coating a tin oxide crystal nucleus layer on the surface of a naked flaky substrate and then coating a conductive layer. When a tin oxide crystal nucleus layer is coated, a low-concentration thermal hydrolysis mode is adopted: the flaky substrate slurry is added under the acidic condition (PH is 1.3-2.5) at the temperature of 30-70 ℃ for at least 30 minutesA solution of 0.9-3.3% by weight of a base material of 15-30 g/L of a dilute stannic chloride solution to obtain SnCl₄Hydrolysis to Sn (OH)₄And (4) a crystal nucleus. The occurrence of crystal nuclei and the concomitant disappearance of supersaturation can be limited to a relatively short period of time by controlling the hydrolysis under the above conditions, i.e., no free crystal nuclei are present in the slurry and the crystal nuclei do not grow, but the crystal nuclei having a small particle radius and a high degree of dispersion are formed, and the formed crystal nuclei are completely deposited on the surface of the substrate with sufficient stirring to form a thin crystal nucleus layer. Thus, the original exposed surface of the substrate, which is smooth and has low activity, becomes a thin layer of active centers formed by crystal nuclei. Since the seed layer is formed immediately before the conductive coating layer is formed, its activity is high, and it is a homogenous compound Sn (OH) with the conductive coating layer to be formed₄. When a high-concentration tin salt solution containing a small amount of antimony salt is added subsequently, neutralization hydrolysis is carried out while maintaining the pH value at 1.5-3.0 with alkali and the temperature at 60-80 ℃, the formed solution contains Sb (OH)₃Sn (OH)₄The precipitate is easily adsorbed by the above homomorphic nucleus layer with high activity to form a conductive coating layer without much dissociation in the liquid phase. And calcining at the high temperature of 650-750 ℃, so that the crystal nucleus layer and the conductive coating layer are simultaneously converted into the conductive tin oxide/antimony conductive layer. Therefore, the adhesion between the flaky substrate and the conductive layer is greatly improved, the conductive layer cannot be peeled off in the pigment production and application processes, no sintered body exists, the pigment is good in dispersibility in a medium, and the formed color is uniform.

In addition, the formation of the crystal nucleus layer and the formation of the conductive coating layer can be carried out in the same equipment, no device is required to be added, the operation process is simple and easy to implement, and the popularization and the application are easy.

Detailed Description

The present invention will be described in further detail with reference to the following examples, but is not limited thereto.

1. Raw materials

① the sheet-like substrate is preferably mica sheet with particle size of 1-100 μm, preferably 5-25 μm

Mu m, when in use, preparing 5-25% of slurry by using water;

② the stannic chloride is commercial pentahydrate of tetravalent tin salt, SnCl₄·5H₂O, true

When the sodium stannate is used, hydrochloric acid aqueous solution is prepared, and when the concentration of the solution is calculated, the sodium stannate is converted into SnO₂

Calculating;

③ antimony oxide Sb₂O₃Is a commercial industrial product, and is prepared by dissolving in hydrochloric acid

Forming aqueous solution with required concentration;

④ base the base used for adjusting and maintaining the pH can be selected from bases used in conventional methods such as

NaOH, ammonia, etc.;

2. chemical reactions involved in the preparation method of the present invention

① nucleation

② preparing antimony salt solution

③ coating of conductive layer

④ Generation of conductive layers

3. The pigment resistivity measurement method is as follows:

0.5 g of pigment is added into an insulating tube with an inner diameter d of 0.8 cm, and 12.5kg/cm is applied to two ends²The resistance R (ohm) between the two electrodes is measured by an ohmmeter, the height L (centimeter) of the pressed material is measured, and the pigment resistivity rho is calculated according to the following formula_v(ohm. cm) ${\mathrm{\ρ}}_v=R\·\frac{{(d/2)}^2}{L}$

4. Method for testing the application properties of conductive pigments: used for preparing conductive floor coating

80 g of conductive pigment, 210 g of epoxy resin color paste and 130 g of mixed solvent are mixed and dispersed for 30 minutes by a high-speed stirrer until the fineness is less than 40 mu m. The conductive paste was mixed with 50 grams of polyamide sealer to make conductive floor coating. The surface resistance of the paint film was measured by Mil-C-83231(A) and the appearance and color of the paint film were visually observed.

The method of the invention is adopted to prepare the light-color flaky conductive pigment

Example 1

① cladding the crystal nucleus layer

100 g of mica with the particle diameter range of 5-25 mu mThe tablets are suspended in 1000 ml of water to form a slurry, the pH of the slurry is adjusted to 1.7, the mixture is heated to 55. + -. 5 ℃ and62 ml of a 15 g/l (SnO) solution are added continuously and homogeneously in 40 minutes while stirring₂Meter) of fourTin chloride solution in an amount of 0.93% by weight of the mica, wherein the pH of the slurry is always 1.3 to 1.7. After the addition, the mixture was stirred and kept warm for 30 minutes.

② coating of conductive layer

106.0 g SnCl is put in advance₄·5H₂O and 7.32 g Sb₂O₃Dissolving in 70 ml of 31% hydrochloric acid solution, and diluting with water to 350 ml to prepare tin salt and antimony salt solution;

the tin salt and antimony salt solution was added to ① uniformly over 4 hours, during which the slurry temperature was maintained at 75 + -5 deg.C while maintaining the pH at 3.0 + -0.5 with an alkaline solution, after the addition the pH was adjusted to 7.0, and the mixture was stirred for 30 minutes at a temperature to form a conductive coating in an amount of 52.9% of the mica weight.

③ Generation of conductive layers

The solid was separated by a conventional method, washed with water until the washing solution was free of chloride ions, then dried at 110 ℃ and calcined at 700 ℃ for 1 hour, and the conductive coating was converted to a tin oxide/antimony conductive layer to give a pale grayish white flake conductive pigment having a composition of 65% mica and 35% tin oxide/antimony, wherein the ratio of tin to antimony was 6: 1 and the resistivity was 56 Ω · cm.

The conductive floor coating prepared from the conductive pigment prepared in the embodiment 1 has the surface resistance of a paint film of 4.6 multiplied by 10⁵Omega. The paint film has smooth and flat surface and uniform color.

Example 2

① cladding the crystal nucleus layer

The temperature of the mica sheet removing slurry is 45 +/-5 ℃, the pH value is 2.5, and the concentration of the stannic chloride solution is 30 g/L (SnO₂Calculated in volume) of 62 ml, which is 1.86% of the mica weight, the slurry was identical to example 1 except that the pH of the slurry was 1.3 to 2.5 during the addition of tin tetrachloride.

② coating of conductive layer

Using 103.6 g SnCl₄·5H₂O and 7.32 g Sb₂O₃Dissolving in 70 ml of 31% hydrochloric acid solution, and diluting with water to 500 ml to prepare tin salt and antimony salt solution;

the remainder was the same as in example 1, with a coating amount of 51.9% by weight of mica.

③ Generation of conductive layers

The conductive coating layer was converted to a tin oxide/antimony conductive layer in the same manner as in example 1, and the pigment was obtained in a pale grayish white appearance having a composition of 65% mica and 35% tin oxide/antimony, wherein the ratio of tin to antimony was 6: 1, and the pigment had a specific resistance of 32. omega. cm.

The surface resistance of the paint film of the conductive floor paint prepared by the pigment is 3.7 multiplied by 10⁵Omega. The paint film has smooth and flat surface and uniform color.

Example 3

① coating the crystal nucleus layer,

100 g of mica plate with the grain diameter range of 3-15 mu m is made into slurry in 1500 ml of waterAnd (5) feeding. The concentration of the tin tetrachloride solution was 30 g/l (as SnO)₂Calculated), the addition amount is 109 ml, which is 3.27 percent of the weight of the mica. The rest of the process was the same as in example 2.

② coating of conductive layer

With 143.9 g SnCl₄·5H₂O and 10.3 g Sb₂O₃Dissolving in 100 ml of 31% hydrochloric acid solution, diluting with water to 500 ml to prepare tin salt and antimony salt solution;

the remainder was the same as in example 1, except that the coating amount was 72.2% by weight based on the weight of mica.

③ Generation of conductive layers

The conductive coating layer was converted to a tin oxide/antimony conductive layer in the same manner as in example 1 except that the calcination temperature was changed to 750 c, wherein the ratio of tin to antimony was 6: 1. The pigment obtained had an appearance of a pale grayish white pigment with a composition of 57% mica, 43% tin oxide/antimony and a pigment resistivity of 87 Ω · cm. The surface resistance of a paint film of the conductive floor paint prepared by the pigment is 7.6 multiplied by 10⁵Omega. The paint film has smooth and flat surface and uniform color.

Comparative example light-colored, flaky, electrically conductive pigment prepared without coating seed layer

A light-colored conductive flake pigment was prepared under the same conditions as ② and ③ in example 1 directly from 100 g of the same mica sheet as in example 1, and the conductive flake pigment had an apparent pale gray-white color and a resistivity of 230. omega. cm., and the conductive floor coating was formulated with the same conductive flake pigment, and had a paint film surface resistance of 4.6X 10⁷Omega. The paint film has poor surface finish, gray color spots and uneven color.

The method can be carried out in the original device without adding or transforming any equipment, and the operation method is easy to master, so the method is easy to accept by original producers.

The light-color flaky conductive pigment prepared by the method is particularly suitable for application occasions needing light-color antistatic coating and electrostatic spraying of the surface pretreatment coating of a non-metallic substrate.

Claims (4)

1. A process for preparing the light-colour flaky electrically conductive pigment includes such steps as preparing the flaky substrate in water to become slurry, adding the solution of tin salt and antimony salt while stirring, hydrolyzing, depositing on the surface of flaky substrate to form a coated layer, separating, washing, drying and calcining₄The crystal nucleus layer comprises the following specific steps:

① cladding the crystal nucleus layer

Preparing a sheet-like substrate having a particle size of 1 to 100 μm into a slurry having a pH of 1.3 to 2.5 and a temperature of 30 to 70 ℃ in water, and slowly adding a tin chloride dilute solution in an amount of 0.9 to 3.3% by weight (SnO) based on the weight of the substrate while stirring₂Metering), feeding for at least 30 minutes to form Sn (OH) on the surface of the sheet-like substrate₄A seed layer;

② coating of conductive layer

Adding the tin salt and antimony salt solution uniformly under stirringKeeping the temperature of the slurry at 60-80 ℃ while adding alkali liquor to maintain the pH at 1.5-4.0, adjusting the pH to 7.0-8.0 after adding the alkali liquor, and stirring for at least 30 minutes under heat preservation, wherein the Sn (OH)₄Formation of Sn (OH) on the seed layer₄And Sb (OH)₃The coating layer (b) is 40-75% (by SnO) of the weight of the base material₂And Sb₂O₃Total amount);

③ Generation of conductive layers

Separating solid by a conventional method, washing, drying, calcining at 650-750 ℃ to form tin oxide/antimony (Sn) with the ratio of tin to antimony being (5-10) to 1_xSb_y)O₂And (3) conducting the layer to obtain the light grey-white flaky conductive pigment with the resistivity of 30-150 omega cm.

2. The method according to claim 1, wherein the tin chloride solution used for forming the tin oxide seed layer is SnCl₄·5H₂O water solution with the concentration of 10-50 g/L (SnO)₂Meter).

3. The method of claim 1, wherein the tin salt and antimony salt solution used to form the tin oxide/antimony conductive layer is SnCl₄·5H₂O and Sb₂O₃Mixing to obtain acidic aqueous solution, or SnCl₄·5H₂O and Sb₂O₃Independently preparing an acidic aqueous solution, and adding the acidic aqueous solution when in use.

4. The method according to claim 1, wherein the flaky substrate is selected from the group consisting of natural or synthetic mica, talc, kaolin, and glass flakes.