Rutile type titanium dioxide pigment special for polycarbonate (PC)

Abstract

The invention relates to the technical field of inorganic pigments, and particularly discloses a rutile type titanium dioxide pigment special for polycarbonate (PC). The rutile type TiO2 photocatalyst comprises a rutile type TiO2 core; the inner coating layer is a composite oxide of Al2O3 and ZrO2, and the molar ratio of Al to Zr is 1: (0.3-0.5); the middle coating layer is prepared from MgO nano particles; the outer coating layer is organic silicon resin containing epoxy groups; and the middle coating layer and the outer coating layer are coupled by adopting triisostearoyl titanate. The problems that in the prior art, a rutile titanium dioxide surface modification auxiliary (such as aluminum oxide) is extremely hydrophilic and easily adsorbs water molecules to initiate a hydrolysis reaction, a polysiloxane layer needs to be additionally arranged outside an aluminum oxide layer to prevent water, but the dense aluminum oxide layer prevents polysiloxane from permeating to the titanium dioxide surface, and the service life of the titanium dioxide surface is affected are solved. The anchoring efficiency of the modifier is reduced, a polysiloxane layer is easy to fall off, and the weather resistance is poor.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of inorganic pigments, and particularly discloses a rutile titanium dioxide pigment specially used for polycarbonate (PC). BACKGROUND

[0002] Titanium dioxide is a white pigment with excellent performance, and is widely used in the fields of coatings, plastics, papermaking, inks, electronics and the like, and is known as "industrial monosodium glutamate". The titanium dioxide treated in a special manner can absorb ultraviolet light and shield active electrons generated thereby.

[0003] Polycarbonate (PC) is widely used in the fields of electronic device housings, automobile lamps, optical lenses and the like due to its high light transmittance, impact resistance and heat resistance. However, PC is prone to yellowing and degradation under high-temperature processing and ultraviolet irradiation. In response to this, titanium dioxide is applied in the PC resin system in the industry. The titanium dioxide (TiO2) can not only improve the whiteness of PC by covering the base color, but also reduce the degradation of PC resin by ultraviolet light, improve the performance of PC products and prolong the service life thereof.

[0004] However, the ordinary rutile TiO2 has serious defects in the PC system. Like most polymers, PC is prone to degradation reaction at high temperatures, and the titanium dioxide itself has photocatalytic properties, which may accelerate the PC molecular chain rupture and aggravate the degradation of PC under ultraviolet light or high-temperature environment. Although the rutile type is less active than the anatase type, there is still a risk. This catalytic effect is manifested in the production that the rutile titanium dioxide catalyzes the degradation reaction of polycarbonate during the PC processing (high-temperature melting), resulting in obvious yellowing, viscosity reduction and mechanical property degradation of the material. In order to avoid the yellowing, viscosity reduction and mechanical property degradation of the material caused by the addition of titanium dioxide during the PC processing, the prior art strictly controls the processing temperature (so that the processing temperature is lower than the temperature at which the degradation reaction occurs) and modifies the surface of the rutile titanium dioxide (reduces the catalytic effect), thereby avoiding the degradation reaction of PC. For example, Chinese Patent CN107805321A discloses a preparation method of a polycarbonate special inorganic pigment. Rutile titanium dioxide is used as the raw material, wet beating is carried out, then 1-2% of silicon oxide and 1-3% of aluminum oxide are coated by wet method, washing, drying and steam powdering are carried out to obtain a semi-finished product, the semi-finished product is beaten, 0.5-2% of an organic surface modifier, i.e., amino-modified polysiloxane, is added by wet method for organic treatment, and the treated slurry is dried and crushed again to obtain a polycarbonate special inorganic pigment. That is, the surface of the rutile titanium dioxide is modified again to reduce its catalytic effect.

[0005] The above-mentioned modification of rutile titanium dioxide pigment can reduce the catalytic effect of titanium dioxide within a certain range, but the surface modified substance (such as alumina) itself is extremely hydrophilic. For example, the alumina surface will react with water molecules in the air to form hydroxyl (-OH) groups, thereby exhibiting hydrophilicity. The carbonate groups (-O-CO-O-) in the polycarbonate backbone are easily hydrolyzed and broken down in a humid and hot environment, generating bisphenol A (BPA) and CO2, and significantly accelerating hydrolysis in a humid and hot environment. Therefore, in order to reduce the contact of alumina with air, an organic modification of amino-modified polysiloxane is performed on the outermost layer of titanium dioxide, and the methyl groups of the organically modified and wrapped amino-modified polysiloxane are arranged outward, forming a low-surface-energy hydrophobic layer to reduce the adsorption of water molecules in the air. However, the dense alumina layer hinders the penetration of polysiloxane into the titanium dioxide surface, reducing the anchoring efficiency of the modifier. The connection between alumina and the amino-modified polysiloxane layer is not strong enough, and the polycarbonate product containing this titanium dioxide pigment is easily affected by the external climate during use. The polysiloxane layer is prone to fall off, and the alumina layer exposed after the fall-off adsorbs water molecules in the air, causing the polycarbonate to degrade and rapidly age after the polysiloxane layer on the surface falls off. The weather resistance is poor. SUMMARY

[0006] The purpose of the present application is to provide a rutile titanium dioxide pigment specifically for polycarbonate (PC), to solve the technical problems mentioned above that the surface modifier (such as alumina) of rutile titanium dioxide pigment itself is extremely hydrophilic, easily adsorbs water molecules to cause hydrolysis reaction, and a polysiloxane layer needs to be additionally provided outside the alumina layer for waterproofing, but the dense alumina layer hinders the penetration of polysiloxane into the titanium dioxide surface, reducing the anchoring efficiency of the modifier, and the polysiloxane layer is prone to fall off, which has poor weather resistance.

[0007] To solve the above problems, the technical scheme adopted by the present application is as follows: a rutile titanium dioxide pigment specifically for polycarbonate, comprising a rutile TiO2 core; an inner coating layer: a composite oxide layer of Al2O3 and ZrO2 with micro-cracks, the Al / Zr molar ratio being 1:0.3-0.5; an outer coating layer: an organosilicon resin containing epoxy groups.

[0008] The beneficial effects of the present embodiment are as follows:

[0009] The surface modification substance alumina of the prior art heavy titanium white powder is extremely hydrophilic. The alumina surface will react with water molecules in the air to form hydroxyl (-OH) groups, thereby exhibiting hydrophilicity. The carbonate groups (-O-CO-O-) in the polycarbonate backbone are prone to hydrolysis and breakage in a humid and hot environment, generating bisphenol A (BPA) and CO2, and significantly accelerating hydrolysis in a humid and hot environment. Therefore, in order to reduce the contact of alumina with air, the prior art performs one organic modification of amino-modified polysiloxane on the outermost layer of titanium white powder, utilizes the wrapping effect of the organic modification and the arrangement of the methyl groups of the amino-modified polysiloxane towards the outside to form a low-surface-energy hydrophobic layer, and reduces the adsorption of water molecules in the air to reduce the hydrolysis of polycarbonate. However, the dense alumina layer hinders the penetration of polysiloxane to the surface of titanium dioxide, reducing the anchoring efficiency of the modifier. The connection between the alumina and the amino-modified polysiloxane layer is not firm enough, and the polycarbonate product added with the titanium white powder is prone to polysiloxane layer peeling due to the influence of external climate during use. After peeling, the alumina layer exposed by the polysiloxane layer adsorbs water molecules in the air, and the polycarbonate undergoes degradation reaction, leading to rapid aging after the polysiloxane layer peels off. The problem of poor weather resistance. The rutile titanium dioxide of the present application has a three-layer structure, and the inner coating layer is a composite oxide layer of Al2O3 and ZrO2. When the tetragonal phase (t-ZrO2) of ZrO2 transforms into the monoclinic phase (m-ZrO2), it is accompanied by 9% volume expansion, forming a microcrack network in the Al2O3 matrix. The outer coating layer of silicone resin has more anchoring voids and penetrates more easily to the surface of titanium dioxide, forming a firm connection. Therefore, compared with the prior art, the outer coating layer of the present application is more stable and reliable.

[0010] Further, when connecting the middle coating layer and the outer coating layer, triisostearyl titanate is added for coupling.

[0011] Further, the coating amount of the Al2O3-ZrO2 composite layer is 0.3-0.5% of the mass of the titanium white powder.

[0012] Further, the organosilicon resin containing epoxy groups is γ-(2,3-epoxypropoxy) propyl trimethoxysilane.

[0013] Further, the addition amount of the organosilicon resin is 0.5-0.8% of the mass of the titanium white powder.

[0014] Further, the epoxy value of the organosilicon resin containing epoxy groups is 0.12-0.18 mol / 100g.

[0015] Further, step 1, the sintered crude titanium dioxide produced in the calcination section of the sulfuric acid method for producing titanium dioxide is mechanically pulverized; step 2, water is added to the mechanically pulverized titanium dioxide to adjust the slurry to a solid content of 10%, and a mixed solution of aluminum salt and zirconium salt is slowly added to perform an inner coating layer reaction; step 3, after the inner coating layer reaction is completed, superheated steam is used as a drying medium instead of hot air to perform flash drying; step 4, the dried titanium dioxide is subjected to air flow pulverization, and an organic silicon resin containing an epoxy group is added during the air flow pulverization to complete an outer coating layer; step 5: after the air flow pulverization is completed, the titanium dioxide is separated from the steam to obtain qualified rutile titanium dioxide pigment.

[0016] Further, the organic silicon resin in step 4 needs to be configured as a 5% organic silicon resin ethanol solution, and then introduced into the pulverization cavity from the superheated steam pipeline before the pulverization chamber of the air flow pulverizer.

[0017] BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 The preparation process flowchart of embodiment 1 of the application is shown in the following.

[0019] DETAILED DESCRIPTION

[0020] The following will be further described in detail through specific embodiments.

[0021] The embodiments are shown in the accompanying drawings. Figure 1

[0022] A rutile titanium dioxide pigment specially used for polycarbonate (PC), comprising a rutile TiO2 inner core; an inner coating layer: a composite oxide layer of Al2O3 and ZrO2 with micro-cracks, the Al / Zr molar ratio being 1:0.3-0.5; and an outer coating layer: an epoxy group-containing organic silicon resin.

[0023] Embodiment 1 Raw materials and proportions: rutile TiO2 inner core (average particle size 0.2 μm, purity ≥99%); inner coating layer precursor: aluminum sulfate (Al2(SO4)3) and zirconium oxychloride (ZrOCl2), Al / Zr molar ratio = 1:0.3; outer coating layer: γ-(2,3-epoxypropoxy) propyl trimethoxysilane (epoxy organic silicon resin, epoxy value 0.12 mol / 100g).

[0024] Preparation process ​The titanium dioxide of the present application is titanium dioxide produced by the sulfuric acid method, which needs to be converted into anatase or rutile TiO2 by calcination and dehydration and desulfurization, and the calcined titanium dioxide needs to be mechanically pulverized and air-pulverized to finally obtain the titanium dioxide product. The coating preparation process of the present application is interlaced in this process. The production of the titanium dioxide of the present application before calcination is consistent with the production of the titanium dioxide by the sulfuric acid method in the prior art, and therefore, is omitted here, and only the preparation of the titanium dioxide of the present application after calcination is described.

[0025] The sintered coarse titanium dioxide produced in the calcination section of the production of titanium dioxide by the sulfuric acid method is mechanically pulverized, and a three-stage pulverization system of “jaw crusher + roller mill + sand mill” is used for mechanical pulverization. Specifically, the three-stage pulverization system of “jaw crusher + roller mill + sand mill” is used: the sintered coarse titanium dioxide is fed into the jaw crusher for crushing, and the particle size of the discharge of the jaw crusher is controlled to be ≤10 mm; primary mechanical crushing is completed. The roller mill uses a high-pressure roller mill, and the coarse titanium dioxide after primary mechanical crushing is fed into the roller mill, and the particle size of the discharge of the controller is controlled to be between 40–60 μm; secondary mechanical crushing is completed, and the coarse titanium dioxide after secondary mechanical crushing is already coarse titanium dioxide, and tertiary mechanical pulverization is performed using a sand mill to pulverize the coarse titanium dioxide, and the coarse titanium dioxide is configured into a suspension of 40–50 wt% and fed into the sand mill for mechanical crushing. When configuring, soft water (conductivity ≤10 μs / cm) needs to be used; the zirconium beads of the sand mill are 1.8 mm, the filling rate is 85%, and the rotation speed is 3000 r / min; and the coarse titanium dioxide is directly crushed to below 0.5 μm.

[0026] Inner coating layer formation: the sand-milled thickness TiO2 slurry is dispersed in deionized water (the solid content is adjusted to 10%), heated to 60°C, and a mixed solution of aluminum salt and zirconium salt (concentration 0.5 mol / L) is slowly added, the pH is controlled to 8.5 (adjusted by ammonia water), and the reaction is carried out for 2 hours to form a composite oxide layer of Al2O3 and ZrO2.

[0027] Pressure filtration: after the reaction of the inner coating layer is completed, the slurry is subjected to pressure filtration to obtain a titanium dioxide wet filter cake.

[0028] Heat treatment: the titanium dioxide wet filter cake is subjected to flash drying, and superheated steam is used instead of hot air as the drying medium.

[0029] Specifically: the titanium dioxide wet filter cake is fed into the drying chamber through a screw feeder, and superheated steam (200-400°C) is introduced into the drying chamber. The steam enters tangentially to form a high-speed rotating gas flow, which is in contact with the titanium dioxide wet material through forced convection. The titanium dioxide is instantaneously dispersed and lifted by the high-speed steam flow, forming a gas-solid two-phase flow contact. In this process, the titanium dioxide particles are fully mixed with hot air, the surface area increases sharply, and the moisture evaporates in 0.5-5 seconds. At the same time, the composite oxide layer of Al2O3 and ZrO2 on the surface of the titanium dioxide expands and generates and expands microcracks at 200-400°C and in a water vapor environment. The t-ZrO2 surface is penetrated by the hydroxyl group of water vapor, inducing local phase change (low-temperature aging), and forming a microcrack network in the Al2O3 matrix. An Al2O3-ZrO2 composite layer (coating amount of 5wt% of the mass of titanium dioxide) with microcracks is formed, and the crack width is 50-200nm.

[0030] Outer coating: After flash drying, the titanium dioxide powder is subjected to jet milling. During jet milling, the addition amount of silicone resin in the 5% silicone resin ethanol solution is 5-8% of the mass of the titanium dioxide. A special metering pump + atomizing nozzle is installed on the superheated steam pipeline about 1 meter before the milling chamber of the flat jet mill. The 5% silicone resin ethanol solution is added to the superheated steam using the metering pump + atomizing nozzle. The titanium dioxide is coated with the superheated steam during the milling process in the milling chamber, forming a continuous silicone resin film layer (thickness about 50nm).

[0031] After jet milling, the particle size of the titanium dioxide is 0.2μm. The titanium dioxide is separated from the steam to obtain the titanium dioxide product of the present application.

[0032] Performance test (application of the titanium dioxide of the present embodiment to polycarbonate) Dispersion: The titanium dioxide pigment of the present embodiment is added to the polycarbonate (PC) melt at 1wt%, and injection molded at 290°C into a sheet product (15cm x 15cm x 0.5cm). Microscopic observation shows no agglomeration (refer to GB / T 21868.1). Weather resistance: after xenon lamp aging for 500 hours, the color difference ΔE is <1.5 (compared to ΔE>5.0 of uncoated TiO2).

[0033] Example 2 Example 2 differs from Example 1 in that the Al / Zr molar ratio is adjusted to 1:0.5 (coating amount of 3wt% of the mass of titanium dioxide), and the rest is the same as Example 1.

[0034] After detection, the microcrack density increases, improving the penetration and anchoring effect of the outer coating layer of silicone resin. After complete coating, the adhesion detection (crosshatch method) is improved to ISO 0 level (no peeling).

[0035] Acid resistance test (5% HCl immersion for 24h): no peeling of the coating layer, but local corrosion occurred on the sample with Al / Zr=1:0.3.

[0036] Example 3: Example 3 differs from Example 1 in that the outer coating layer is replaced with a silicone resin with an epoxy value of 0.18 mol / 100 g (increasing the reactive groups), the outer coating amount is 5% of the mass of titanium white powder, and triisostearyl titanate coupling agent is added, the amount of triisostearyl titanate added is 0.5% to 2.0% of the mass of the silicone resin.

[0037] The carboxyl groups on the PC side react to form a chemical bond, and the torque of melt blending is reduced by 15% (indicating that the processing fluidity is improved).

[0038] Wet heat resistance (85°C / 85% RH, 168h): no pigment migration, PC light transmittance retention rate >95%.

[0039] Example 4: Gradient design of composite coating layer thickness Example 4 differs from Example 1 in that the inner coating layer is deposited in two steps; the mixed solution of aluminum and zirconium salts to be added dropwise is divided into two times, 75% of the mass of the mixed solution of aluminum and zirconium salts is added first, and the reaction is carried out for 1 hour, then 25% of the mass of the mixed solution of aluminum and zirconium salts is added for the second coating, and the cracks are distributed in a gradient.

[0040] The impact strength of the PC product is improved to 65kJ / m 2 (50kJ / m 2 for a single coating layer sample), because the crack structure buffers stress.

[0041] Example 5 Example 5 differs from Example 1 in that the preparation process is different, it is directly first airflow pulverized to the required particle size of titanium white powder, then surface film treatment (suitable for laboratory), the specific preparation process is as follows: Inner coating layer formation: disperse the titanium white powder that has been airflow pulverized to the qualified particle size in deionized water (solid content 10%), heat to 60°C, slowly add the mixed solution of aluminum and zirconium salts (concentration 0.5 mol / L), control pH=8.5 (adjust with ammonia water), react for 2 hours to form a composite oxide layer of Al2O3 and ZrO2.

[0042] After the inner coating reaction, the titanium dioxide slurry is filtered into a titanium dioxide filter cake, and heat treated: the titanium dioxide wet filter cake is dried at 300℃ hot air for 1 hour, the water vapor evaporated from the titanium dioxide and the hot air form a humid heat environment, so that the composite oxide layer of Al2O3 and ZrO2 becomes an Al2O-ZrO2 composite layer with micro-cracks (coating amount 8wt%), crack width 50-200nm.

[0043] Outer coating layer coating: the above powder is immersed in a 5% silicone resin ethanol solution, ultrasonic dispersion for 30 minutes, 120℃ curing for 30 minutes, forming a continuous film layer (thickness about 50nm) The above is only an embodiment of the present application, and the specific structure and characteristics of the scheme are not described in detail. It should be noted that for those skilled in the art, without departing from the structure of the present application, a number of modifications and improvements can be made, which should also be considered as the protection scope of the present application, which will not affect the effect and practicality of the patent. The protection scope claimed in this application should be subject to the content of its claims, and the specific implementation mode and the like recorded in the specification can be used to explain the content of the claims.

Claims

1. A rutile titanium dioxide pigment specific to polycarbonate, characterized in that: The rutile TiO2 core; inner coating layer: Al2O3 and ZrO2 composite oxide layer with micro-cracks, Al / Zr molar ratio 1:0.3~0.5; outer coating layer: epoxy group-containing silicone resin.

2. The rutile titanium dioxide pigment dedicated to polycarbonates according to claim 1, characterized in that: When connecting the middle coating layer and the outer coating layer, triisostearyl titanate is added for coupling.

3. The rutile titanium dioxide pigment dedicated to polycarbonates according to claim 1, characterized in that: The coating amount of the Al2O3-ZrO2 composite layer is 0.3-0.5% of the mass of titanium dioxide.

4. The rutile titanium dioxide pigment dedicated to polycarbonates according to claim 1, characterized in that: The epoxy group-containing silicone resin is γ-(2,3-epoxypropoxy) propyl trimethoxysilane.

5. The rutile titanium dioxide pigment dedicated to polycarbonates according to claim 1, characterized in that: The addition amount of the silicone resin is 0.5-0.8% of the mass of titanium dioxide.

6. The rutile titanium dioxide pigment dedicated to polycarbonates according to claim 1, characterized in that: The epoxy group-containing silicone resin has an epoxy value of 0.12-0.18 mol / 100g.

7. A process for the production of a rutile titanium dioxide pigment specific for polycarbonates according to any one of claims 1 to 6, characterized in that: The method comprises the following steps: Step 1: mechanically crushing the coarse titanium dioxide sinter produced in the calcination section of sulfuric acid method titanium dioxide production; Step 2: adding water to the mechanically crushed titanium dioxide to adjust the slurry to a solid content of 10%, and slowly adding a mixed solution of aluminum salt and zirconium salt to perform inner coating layer reaction; Step 3: after completing the inner coating layer reaction, using superheated steam as a substitute for hot air as a drying medium for flash drying; Step 4: performing air flow crushing on the dried titanium dioxide, and adding epoxy group-containing silicone resin during the air flow crushing process to complete the outer coating layer; Step 5: after completing the air flow crushing, separating the titanium dioxide from the steam to obtain qualified rutile titanium dioxide pigment.

8. The rutile titanium dioxide pigment dedicated to polycarbonates according to claim 7, characterized in that: The silicone resin in step 4 needs to be configured as a 5% silicone resin ethanol solution first, and then introduced into the crushing cavity from the superheated steam pipeline before the crushing chamber of the air flow crusher.

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