High-temperature-resistant zinc sulfide, polymer composition and preparation method and application thereof

Abstract

The invention discloses high-temperature-resistant zinc sulfide, a polymer composition and a preparation method and application of the high-temperature-resistant zinc sulfide, the high-temperature-resistant zinc sulfide comprises the following components in parts by weight: a zinc sulfide matrix, the surface of the zinc sulfide matrix is provided with a silicon dioxide-based coating layer, the content of the silicon dioxide-based coating layer is 4.0-8.0 wt%, and the content of the polymer composition is 0.1-0.5 wt%. The average particle size of the zinc sulfide matrix is 20 nm to 1000 nm. The application problem that current zinc sulfide is not resistant to high temperature can be well solved.

Description

Technical Field

[0001] This invention relates to the field of inorganic pigments and fillers and functional inorganic powder materials synthesis, specifically to a high-temperature resistant zinc sulfide, a polymer composition, its preparation method, and its application. Background Technology

[0002] Titanium dioxide (TiO2) has long been used as a mainstream inorganic whitening and masking pigment and filler in plastics due to its extremely high refractive index and excellent hiding power. However, TiO2 also has several limitations: high cost, negative impact on melt flowability during high-temperature melting and processing, and the potential for accelerated hydrolysis in certain polyester or polycarbonate systems, leading to yellowing or performance degradation in the products. Therefore, finding inorganic pigments and fillers that can replace or partially replace TiO2 has become an important direction for optimizing material formulations.

[0003] Zinc sulfide (ZnS) has potential applications in pigments, phosphors, and functional fillers due to its optical properties and relatively low cost. However, unmodified ZnS is prone to oxidation, surface defect diffusion, or color shift (yellowing) during high-temperature processing or long-term thermal aging. Furthermore, in polymer melt processing (especially glass fiber-containing engineering plastics), the mechanical properties, surface hardness, and dispersibility of the particles can lead to problems such as glass fiber cutting / wear, uneven color, and poor thermal stability. While TiO2 is an excellent white pigment / filler, it is costly, may cause glass fiber cutting during processing, and can negatively impact electrical / optical properties in some applications. Therefore, developing a high-temperature resistant zinc sulfide material that is stable during high-temperature processing, color-stable, and well-dispersible in engineering plastics has significant industrial value. Summary of the Invention

[0004] In order to solve the technical problems existing in the background art, one of the objectives of the present invention is to provide a high-temperature resistant zinc sulfide, comprising the following components in parts by weight: a zinc sulfide matrix, a silica-based coating layer disposed on the surface of the zinc sulfide matrix, the silica-based coating layer having a content of 4.0 to 8.0 wt%, and an average particle size of 20 nm to 1000 nm for the zinc sulfide matrix.

[0005] As a preferred embodiment, the zinc sulfide matrix is ​​doped with transition metal ions, the doping metal being cobalt ions or their compounds, with a doping content of 0.001 to 1.0 wt%.

[0006] As a preferred embodiment, the silica-based coating layer is formed on the surface of the zinc sulfide substrate by adding a silicon solution to a zinc sulfide suspension for coating and curing, wherein the silicon solution is one of sodium silicate, silicon tetrachloride, and tetraethyl orthosilicate (TEOS).

[0007] To address the aforementioned technical problems, a second objective of this invention is to provide a polymer composition of high-temperature resistant zinc sulfide comprising the above-mentioned technical solution.

[0008] As a preferred option, polycarbonate and high-temperature resistant zinc sulfide are included, with the amount of high-temperature resistant zinc sulfide added being 0.1–20 wt%.

[0009] To address the aforementioned technical problems, a third objective of this invention is to provide a method for preparing high-temperature resistant zinc sulfide, comprising the following steps: S0, prepare zinc sulfate solution and sulfide solution in deionized water, and add the two solutions to the reaction vessel at a controlled rate to form zinc sulfide suspension; S1, the suspension is hydraulically filtered, washed and re-slurried to obtain slurry; S2, add silicon solution and alkaline regulator to the slurry to maintain the pH of the system at 9.0 to 9.5 and keep it at 60℃ for coating and curing to obtain zinc sulfide coated slurry with silicon dioxide-based coating layer; S3, zinc sulfide coated slurry is hydraulically filtered, washed, and dried under vacuum at 70°C to obtain dry powder; S4 involves calcining dried powder at 800°C to 900°C under a sulfur-containing atmosphere or an equivalent protective atmosphere to obtain high-temperature resistant zinc sulfide with a dense surface coating.

[0010] As a preferred embodiment, in S0, 0.001 to 1.0 wt% of cobalt sulfate in nonahydrate / heptahydrate / other forms is added to the zinc sulfate solution as a dopant beforehand.

[0011] As a preferred embodiment, the silica-based coating layer is formed from one or more of sodium silicate, silicon tetrachloride, and tetraethyl orthosilicate.

[0012] As a preferred embodiment, in S2, before the silica coating, a flexible organosilicon-based interface layer is formed on the surface of the zinc sulfide substrate. The interface layer is prepared by any one or a combination of the following methods: adding a silane coupling agent to the slurry at 0.05 to 2.0 wt% and allowing the silane coupling agent to adsorb / hydrolyze and condense with the zinc sulfide surface at pH 4-9 and temperature 20-80°C; and / or adding a low molecular weight polydimethylsiloxane (PDMS) to the slurry at an amount of 0.1 to 5.0 wt% and holding it at 40-120°C for 0.5 to 4 hours to form a flexible interface layer with a thickness of 5 to 80 nm on the zinc sulfide surface, so that the final product exhibits a multilayer structure of core-flexible interface layer-silica-based coating layer.

[0013] To address the aforementioned technical problems, the fourth objective of this invention is to provide the application of the aforementioned high-temperature resistant zinc sulfide in replacing titanium dioxide as a pigment or filler for whitening, masking, or enhancing scattering, thereby improving yellowing at high temperatures.

[0014] Compared with the prior art, the present invention has the following beneficial effects: (1) High temperature resistance and not easy to yellow: The dense silica layer acts as a diffusion barrier, which inhibits the oxidation / desulfurization reaction of zinc sulfide at high temperature, thus maintaining color stability; after calcination, the coating layer becomes denser, which further improves thermal stability.

[0015] (2) Better thermal processing stability: During the melt processing of engineering plastics (e.g., PA6 / PA66 melt extrusion or injection molding), the coating reduces the wear and cutting of glass fiber by zinc sulfide and improves mechanical compatibility; the coating can also improve the interfacial bonding with the polymer and facilitate dispersion.

[0016] (3) Partial replacement of TiO2: In certain color matching or functional filler applications, ZnS, which has advantages in cost, density or optical / electrical properties, can partially replace TiO2 after being modified by this method.

[0017] (4) The process is controllable and easy to scale up industrially: the coating uses common silicon sources and alkaline adjustment, and the drying and calcination parameters are clear, which is conducive to scale-up production. Attached Figure Description

[0018] Figure 1 These are thermal analysis diagrams of zinc sulfide before and after modification in Example 1 and Comparative Example 1 of this invention; Figure 2 This is an electron microscope image of the high-temperature resistant zinc sulfide prepared in Example 1 of this invention. Detailed Implementation

[0019] The present invention is further illustrated below with reference to specific embodiments. These embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Experimental methods in the following embodiments, unless otherwise specified, are generally performed under conventional conditions in the art or as recommended by the manufacturer; the raw materials and reagents used, unless otherwise specified, are all commercially available from the conventional market. Any non-substantial changes and substitutions made by those skilled in the art based on the present invention are within the scope of protection claimed by the present invention.

[0020] The reagents used in the various embodiments and comparative examples of this invention are described below. Unless otherwise specified, the raw materials used in the embodiments and comparative examples of this application are all conventional raw materials: Zinc sulfate heptahydrate: Jiangxi Shenye, purity 99.8%; Cobalt sulfate nonahydrate: Huayou Cobalt Industry, purity 99.9%; Sodium sulfide: Sichuan Jinchuan, 60%; Sodium silicate: Changsha Jingkang, 99.5%; Silicon tetrachloride: Nanjing Shuguang; TEOS: Nanjing Shuguang; KH550: Nanjing Shuguang; Polydimethylsiloxane (PDMS): Silicon Harbor Chemical; Polyamide: Pingdingshan Shenma Nylon PA66 EPR27; Titanium dioxide: Huiyun Titanium Dioxide R666; Examples 1-8 The preparation method of high-temperature resistant zinc sulfide according to various embodiments of the present invention includes the following steps: S0, prepare zinc sulfate solution and sulfide solution in deionized water, and add the two solutions to the reaction vessel at a controlled rate to form zinc sulfide suspension; S1, the suspension is hydraulically filtered, washed and re-slurried to obtain slurry; S2, add silicon solution and alkaline regulator to the slurry to maintain the pH of the system at 9.0 to 9.5 and keep it at 60-80℃ for coating and curing to obtain zinc sulfide coated slurry with silicon dioxide-based coating layer, wherein the silicon solution is one of sodium silicate, silicon tetrachloride and tetraethyl orthosilicate; S3, zinc sulfide coated slurry is hydraulically filtered, washed, and dried under vacuum at 70°C to obtain dry powder; S4 involves calcining dried powder at 800°C to 900°C under a sulfur-containing atmosphere or an equivalent protective atmosphere to obtain high-temperature resistant zinc sulfide with a dense surface coating.

[0021] In particular, Examples 6 and 7 include the following additional steps: In S2, before silica coating, a flexible organosilicon-based interface layer is formed on the surface of the zinc sulfide substrate. This interface layer is prepared by adding a silane coupling agent to the slurry and allowing it to adsorb / hydrolyze and condense with the zinc sulfide surface at pH 6 and 60°C. Then, low molecular weight polydimethylsiloxane (PDMS) is added to the slurry, and the mixture is kept at 8°C for 2 hours to form a flexible interface layer on the zinc sulfide surface. This results in a multi-layered structure of core-flexible interface layer-silica-based coating layer in the final product. Specifically, the addition ratio in Example 6 was 0.5 wt% APTES / 1.0 wt% PDMS, and in Example 7 it was 0.2 wt% APTES / 3.0 wt% PDMS.

[0022] Comparative Examples 1-3 Comparative Example 1 The difference between this comparative example and Example 1 is that no silica source solution was added.

[0023] Comparative Example 2 The difference between this comparative example and Example 1 is that calcination was performed without a sulfur-containing atmosphere or an equivalent protective atmosphere.

[0024] Comparative Example 3 High-quality titanium dioxide available commercially.

[0025] This embodiment and comparative example provide a series of zinc sulfide formulations, the weight parts of each component and process parameters of which are shown in Table 1.

[0026] Table 1. Formulations and process parameters for examples and comparative examples

[0027]

[0028] Performance testing SEM / TEM morphological observation After dispersing the powder sample with alcohol, drop it onto a carbon film copper mesh (TEM) or aluminum substrate (SEM) and allow it to dry naturally. Use field emission scanning electron microscopy (FE-SEM) to photograph the surface morphology to observe the continuity of the coating; use transmission electron microscopy (TEM) to measure the coating thickness and confirm the core-shell structure. Care should be taken to avoid heating or oxidizing the sample during operation.

[0029] Thermal analysis Thermogravimetric analysis (TGA) was used to heat the material to 700 °C in air at a rate of 10 °C / min, and the weight loss curves were recorded. The weight loss rate was used to evaluate the thermal stability and protective effect of the material under high-temperature conditions.

[0030] Color difference test Injection-molded samples were prepared by incorporating the powder into the PA66 matrix at 5 wt%. The L*a*b values ​​were measured using a spectrophotometer under standard gloss / color difference measurement conditions (D65 light source, 10° viewing angle). After heat aging (200℃×4h), the color was measured again and ΔE was calculated.

[0031] Measurement of glass fiber breaking rate and fiber length distribution PA66 matrix containing 30 wt% glass fiber was melt-mixed with the target powder and injection molded. After sampling, the matrix was dissolved or chemically removed from the composite material, the glass fibers were separated, and the fiber length distribution was measured under optical microscopy or scanning electron microscopy. The breakage rate (defined as the proportion of fibers less than the initial length threshold) was calculated using statistical software. This was used to evaluate the effect of particles on the mechanical damage of the glass fibers.

[0032] Table 2 Performance test results of each embodiment and comparative example

[0033] like Figure 1-2As shown, the modified zinc sulfide prepared by this invention exhibits improved high-temperature resistance and a dense, well-dispersed microstructure with a silica shell coating. Through a systematic comparison between Examples 1–8 and Comparative Examples 1–3, this invention verifies and quantifies the effects of different parameters such as Si precursor, Si content, calcination temperature, particle size, and flexible interface layer on the high-temperature stability (TGA), yellowing resistance (ΔE), and influence on glass fiber damage (breakage rate and average fiber length) of zinc sulfide in glass fiber reinforced polymers.

[0034] 1. Silica coating significantly improves high-temperature stability and resistance to yellowing: Examples 1–4 (all with SiO2 coating) showed significantly lower TGA weight loss rates than Comparative Example 1 (without SiO2 coating) and Comparative Example 2 (calcined without protective atmosphere), with weight loss rates of 5.86–6.04%, corresponding to ΔE of only 1.2–2.4. This demonstrates that a continuous and dense SiO2 shell can effectively block oxygen / moisture intrusion and inhibit the oxidation / desulfurization of ZnS at high temperatures, thereby achieving resistance to yellowing.

[0035] 2. Effect of Si precursor on coating density: Example 1 (sodium silicate) and Example 2 (TEOS) showed similar performance, both forming a continuous and dense shell (shell thickness 15–18 nm); however, Example 3 (using silicon tetrachloride instead of sodium silicate) had a thinner shell and local unevenness, resulting in slightly inferior thermal protection and color difference performance (larger ΔE).

[0036] 3. Trade-off between calcination temperature and Si content: Example 4 demonstrated optimal thermal stability and the lowest ΔE (weight loss 5.86%, ΔE 1.2), but also observed an increased tendency for particle agglomeration, suggesting a trade-off between densification and dispersibility in practical applications. Example 5, while still providing some protection, showed a decrease in thermal stability and ΔE, proving that 800–900℃ is the preferred calcination range.

[0037] 4. The outstanding effect of the flexible interface layer in reducing glass fiber damage: Examples 6 / 7 (constructing an APTES / PDMS flexible interface layer before SiO2 coating) demonstrated processability advantages on the glass fiber system: the lowest glass fiber breakage rate and the largest average fiber length (the breakage rate of Examples 6 / 7 was significantly lower than all examples and comparative examples with only hard shell coating), while thermal stability and ΔE were not significantly weakened. This three-layer structure of "core-flexible interface-dense shell" provides elastic buffering under melt shear / impact, significantly reducing the sharp cutting of glass fibers by hard phase particles, and has significant application prospects for existing glass fiber modification systems.

[0038] 5. Particle size effect: Although Example 8 (large core D50 ≈ 800 nm) maintained a certain resistance to yellowing, it was not as effective as the small / medium particle size samples (Examples 1 / 2 / 6 / 7) in reducing glass fiber damage. This suggests that particle size control (preferred D50 range of 20–1000 nm) plays an important role in achieving optimal overall performance.

[0039] 6. Explanation of Comparative Examples 1 and 2: Comparative Examples 1 (without SiO2 coating) and 2 (calcined without protective atmosphere) respectively illustrate the necessity of coating and protective atmosphere in achieving high temperature resistance and maintaining chemical integrity: no coating will significantly reduce TGA and ΔE performance, while under the wrong calcination atmosphere (Comparative Example 2) it will lead to shell discontinuity / cracks and decreased thermal stability.

[0040] In summary, the modified zinc sulfide material obtained by the technical solution of the present invention is stable in high-temperature processing, has stable color, can be well dispersed in engineering plastics, and is friendly to glass fiber modification systems, thus having significant industrial value.

[0041] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A high-temperature resistant zinc sulfide, characterized in that: It comprises the following components in parts by weight: a zinc sulfide matrix having a silica-based coating layer on its surface, the silica-based coating layer being present in a content of 4.0 to 8.0 wt%, and the zinc sulfide matrix having an average particle size of 20 nm to 1000 nm.

2. The high-temperature resistant zinc sulfide according to claim 1, characterized in that: The zinc sulfide matrix is ​​doped with transition metal ions, wherein the doped metal is cobalt ions or its compounds, and the doping content is 0.001-1.0 wt%.

3. The high-temperature resistant zinc sulfide according to claim 1, characterized in that: The silica-based coating layer is formed on the surface of the zinc sulfide substrate by adding a silicon solution to a zinc sulfide suspension for coating and curing. The silicon solution is one of sodium silicate, silicon tetrachloride, and tetraethyl orthosilicate.

4. A polymer composition comprising high-temperature resistant zinc sulfide as described in any one of claims 1–3.

5. The polymer composition according to claim 1, characterized in that: It includes polyamide and high-temperature resistant zinc sulfide, wherein the amount of high-temperature resistant zinc sulfide added is 0.1–20 wt%.

6. A method for preparing high-temperature resistant zinc sulfide as described in any one of claims 1-5, characterized in that, Includes the following steps: S0, prepare zinc sulfate solution and sulfide solution in deionized water, and add the two solutions to the reaction vessel at a controlled rate to form zinc sulfide suspension; S1, the suspended hydraulic filter is washed and re-slurryed to obtain a slurry; S2, the silicon solution and alkaline regulator are added to the slurry to maintain the pH of the system at 9.0 to 9.5 and the system is kept at 60°C for coating and curing to obtain zinc sulfide coated slurry with a silica-based coating layer; S3, the zinc sulfide coated slurry is hydraulically filtered, washed, and dried at 70°C under vacuum to obtain dried powder; S4, the dried powder is calcined at 800°C to 900°C in a sulfur-containing atmosphere or an equivalent protective atmosphere to obtain a high-temperature resistant zinc sulfide with a dense surface coating.

7. The preparation method according to claim 6, characterized in that: In S0, 0.001 to 1.0 wt% of cobalt sulfate in nonahydrate / heptahydrate / other forms is added as a dopant to the zinc sulfate solution beforehand.

8. The preparation method according to claim 7, characterized in that: The silica-based coating layer is formed from one or more of sodium silicate, silicon tetrachloride, and tetraethyl orthosilicate.

9. The preparation method according to claim 7, characterized in that: In S2, before silica coating, a flexible organosilicon-based interface layer is formed on the surface of the zinc sulfide substrate. The interface layer is prepared by any or a combination of the following methods: adding a silane coupling agent at 0.05 to 2.0 wt% to the slurry and allowing the silane coupling agent to adsorb / hydrolyze and condense with the zinc sulfide surface at pH 4-9 and temperature 20-80°C; and / or adding a low molecular weight polydimethylsiloxane at an amount of 0.1 to 5.0 wt% to the slurry and holding it at 40-120°C for 0.5 to 4 hours to form a flexible interface layer with a thickness of 5 to 80 nm on the zinc sulfide surface, so that the final product exhibits a multilayer structure of core-flexible interface layer-silica-based coating layer.

10. The application of high-temperature resistant zinc sulfide as described in claims 1-3 as a pigment or filler to replace titanium dioxide for whitening, masking, or scattering, and to improve yellowing at high temperatures.

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