A highly concentrated masterbatch of fluorescent whitening agent and its preparation method

Abstract

This invention belongs to the field of functional polymer masterbatches and provides a highly concentrated fluorescent whitening agent masterbatch and its preparation method. The invention involves melting and wetting fluorescent whitening agent OB-1 with a polyethylene-acrylic acid copolymer to form composite microparticles, which are then melt-dispersed and granulated with polyethylene wax, a composite antioxidant system, and a carrier resin composed of polyethylene or a combination of polyethylene and ethylene-vinyl acetate copolymer. This constructs a high-content, fine-particle-size, and uniformly distributed granular masterbatch system, achieving a coordinated improvement in OB-1 dispersion stability, retention of effective whitening components, melt processing flow, and thermal processing stability. It reduces the proportion of free crystals, agglomeration degree, fuming, and agglomeration risks, solving the problem of balancing dispersion stability and whitening performance, as well as processing flow and thermal stability in highly concentrated whitening masterbatches. This invention is suitable for whitening processing of modified plastics, recycled plastics, and polyolefin products.

Description

Technical Field

[0001] This invention relates to the field of polymer functional masterbatch technology, specifically to a highly concentrated fluorescent whitening agent masterbatch and its preparation method. Background Technology

[0002] In the processing of plastic products, modified recycled plastics, polyolefin films, sheets, injection molded parts, and fiber-related materials, appearance whiteness, color stability, and batch consistency directly affect the marketability and subsequent application suitability of the products. Fluorescent whitening agent masterbatches are typically added to resin systems as carriers for functional additives, enabling powder whitening agents to enter extrusion, injection molding, or blown film processes in a metered and continuous manner. With increasing demands for high concentration, low addition levels, and multi-scenario processing, masterbatches not only need to possess sufficient effective whitening components but also maintain good dispersion in polyolefin or ethylene-vinyl acetate copolymer systems to avoid localized powder enrichment that could cause color spots, fogging, precipitation, or processing fluctuations. Simultaneously, under high-temperature melt shear conditions, masterbatches also need to consider flowability, thermal stability, low moisture content, and particle size stability to facilitate rapid dilution in downstream resins and maintain a uniform appearance. Therefore, developing fluorescent whitening agent masterbatches that combine high loading capacity, good dispersion, processing stability, and application suitability is of great significance for improving the appearance quality of plastic products and the efficiency of additive use.

[0003] Existing technologies mostly improve the performance of fluorescent whitening agents in the matrix by direct powder addition, simple melt blending, or grinding dispersion. However, powder addition is easily affected by crystal particle size, surface polarity, and resin compatibility, resulting in local agglomeration and migration tendencies in high-concentration masterbatches. While simply increasing the proportion of carrier resin or wax lubricating components can improve processing flow, it may dilute the effective whitening components and weaken long-term dispersion stability. Increasing strong wetting or coating components may lead to enhanced interfacial binding, restricted melt flow, or fumigation and agglomeration under thermal shear. Existing technologies also address the dispersion problem of OB-1. For example, Chinese patent CN106758132B discloses a fluorescent whitening slurry and its preparation method. The scheme uses OB-1 as the main raw material, employs an acrylic polymer dispersant, and obtains the fluorescent whitening slurry through grinding and emulsification. The specification points out that OB-1 is difficult to disperse in water or ethylene glycol, and the application effect is improved by controlling the particle size. This type of scheme focuses more on the liquid phase slurry system and cannot directly solve the problems of high content dispersion, interface stability, fluidity, and thermal stability of polyolefin high-concentration masterbatch during melt extrusion. Summary of the Invention

[0004] The purpose of this invention is to provide a highly concentrated masterbatch of fluorescent whitening agent and its preparation method, thereby solving the problem of difficulty in coordinating dispersion stability and whitening performance, as well as processing fluidity and thermal stability in current highly concentrated masterbatches of fluorescent whitening agents.

[0005] This invention uses a polyethylene-acrylic acid copolymer to melt-wet and coat the fluorescent whitening agent OB-1, and disperses the composite particles in the carrier resin. This ensures that the inhibition of agglomeration by interfacial wetting does not come at the expense of effective whitening. At the same time, the flow and thermal stability are regulated by polyethylene wax and a composite antioxidant system, thereby taking into account both dispersion stability and whitening performance, as well as processing fluidity and thermal stability.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] A highly concentrated masterbatch for fluorescent whitening agents, comprising, by weight:

[0008] 15.00–35.00 parts by weight of fluorescent whitening agent OB-1;

[0009] 5.00–18.00 parts by weight of polyethylene-acrylic acid copolymer;

[0010] 2.00–8.00 parts by weight of polyethylene wax;

[0011] 0.05–0.60 parts by weight of pentaerythritol tetra[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate];

[0012] 0.05–0.60 parts by weight of tris(2,4-di-tert-butylphenyl) phosphite;

[0013] 38.00–78.00 parts by weight of carrier resin, wherein the carrier resin is polyethylene, or a combination of polyethylene and ethylene-vinyl acetate copolymer;

[0014] In this process, at least a portion of the fluorescent whitening agent OB-1 is formed with the polyethylene-acrylic acid copolymer to form polyethylene-acrylic acid copolymer-coated fluorescent whitening agent OB-1 composite particles.

[0015] Furthermore, the surface coverage of the polyethylene-acrylic acid copolymer-coated fluorescent whitening agent OB-1 composite microparticles, calculated according to the arc length ratio of the cross-sectional profile, is 60.00–95.00%, the shell thickness is 20–300 nm, and the polyethylene-acrylic acid copolymer-coated fluorescent whitening agent OB-1 composite microparticles are dispersed in the carrier resin.

[0016] Furthermore, the polyethylene-acrylic acid copolymer-coated fluorescent whitening agent OB-1 composite microparticles are prepared by a method comprising the following steps:

[0017] A1. Provides fluorescent whitening agent OB-1, polyethylene-acrylic acid copolymer, polyethylene wax, pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] and tris(2,4-di-tert-butylphenyl) phosphite;

[0018] A2. Dry the fluorescent whitening agent OB-1 to obtain the dried fluorescent whitening agent OB-1;

[0019] A3. The dried fluorescent whitening agent OB-1, the polyethylene-acrylic acid copolymer, the polyethylene wax, the pentaerythritol tetra[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] and the tris(2,4-di-tert-butylphenyl) phosphite are melt-wetted and coated to obtain a coated material;

[0020] A4. After the melt wetting coating is completed, the surface coverage of the polyethylene-acrylic acid copolymer on the fluorescent whitening agent OB-1, calculated according to the arc length ratio of the cross-sectional profile, is 60.00–95.00% in the coated material, and the D50 of the polyethylene-acrylic acid copolymer coated fluorescent whitening agent OB-1 composite particles is 0.50–3.00 μm;

[0021] A5. Cool and sieve the coated material obtained in step A4 to obtain the polyethylene-acrylic acid copolymer coated fluorescent whitening agent OB-1 composite microparticles.

[0022] Further, in step A1, by weight, the fluorescent whitening agent OB-1 is 100 parts by weight, the polyethylene-acrylic acid copolymer is 20–70 parts by weight, the polyethylene wax is 6–35 parts by weight, the pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] is 0.2–2.5 parts by weight, and the tris(2,4-di-tert-butylphenyl) phosphite is 0.2–2.5 parts by weight.

[0023] Further, in step A2, the fluorescent whitening agent OB-1 is dried at 80–110°C for 1–3 hours; in step A3, it is mixed at 90–140°C, with an absolute pressure of 0.08–0.12 MPa, under an air or nitrogen atmosphere for 5–20 minutes at a mixing speed of 300–1500 rpm; in step A5, the coated material obtained in step A4 is cooled to 30–60°C and passed through a 40–100 mesh sieve; the D90 of the polyethylene-acrylic acid copolymer-coated fluorescent whitening agent OB-1 composite microparticles obtained in step A5 is 2.00–8.00 μm, and the D90 is not less than the D50 in step A4, and the content of free fluorescent whitening agent OB-1 crystals not covered by the polyethylene-acrylic acid copolymer is 0.10–8.00 wt%.

[0024] Furthermore, in some embodiments, in the polyethylene-acrylic acid copolymer-coated fluorescent whitening agent OB-1 composite microparticles, the mass ratio of fluorescent whitening agent OB-1 to polyethylene-acrylic acid copolymer, calculated based on the polyethylene-acrylic acid copolymer portion only including the coating shell, is 100:25–100:55, and the content of acrylic structural units in the polyethylene-acrylic acid copolymer is 5.00–20.00 wt%.

[0025] Furthermore, the mass ratio of polyethylene to ethylene-vinyl acetate copolymer in the carrier resin is 100:0 to 100:60; the mass ratio of pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] to tris(2,4-di-tert-butylphenyl) phosphite is 1:0.5–1:3.0, and the total amount of both is 0.10–1.20 parts by weight.

[0026] Furthermore, the masterbatch is granular, with a length of 1.50–5.00 mm, a diameter of 1.00–4.00 mm, and a water content of 0.01–0.10 wt%; the aggregate D90 of the polyethylene-acrylic acid copolymer-coated fluorescent whitening agent OB-1 composite microparticles in the masterbatch is 3.00–10.00 μm, and the coefficient of variation of the area distribution of the polyethylene-acrylic acid copolymer-coated fluorescent whitening agent OB-1 composite microparticles on the cross-section of the masterbatch is 5.00–25.00%.

[0027] As a concept of this invention, the present invention employs a design that uses fluorescent whitening agent OB-1 and polyethylene-acrylic acid copolymer to form coated composite microparticles and disperse them in a carrier resin, primarily to achieve a synergistic balance between dispersion stability and whitening performance. In existing high-concentration masterbatches, to suppress the agglomeration of fluorescent whitening agent OB-1 crystals, it is usually necessary to enhance interfacial wetting or coating effects. However, excessive coating can easily obscure the effective whitening components and increase melt viscosity. To improve whitening performance, the content of fluorescent whitening agent OB-1 is often increased, but high-content powder will exacerbate agglomeration, precipitation, and processing fluctuations. This invention, through interfacial wetting of the polyethylene-acrylic acid copolymer, flow regulation of polyethylene wax, thermal stability protection of the composite antioxidant system, and compatibility with the carrier resin, allows high-content fluorescent whitening agent OB-1 to enter the masterbatch in a composite microparticle state and maintain good dispersion during melt shearing, thereby achieving a coordinated unity of dispersion stability, effective whitening, flow processing, and thermal stability protection.

[0028] This invention also discloses a method for preparing a highly concentrated masterbatch of any of the aforementioned fluorescent whitening agents, comprising the following steps:

[0029] S1. Provided prepared polyethylene-acrylic acid copolymer coated fluorescent whitening agent OB-1 composite microparticles, carrier resin, and residual (if any) polyethylene wax, residual (if any) pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] and residual (if any) tris(2,4-di-tert-butylphenyl) phosphite as determined according to the target total formulation of the masterbatch;

[0030] S2. Total Mixing and Feeding: The polyethylene-acrylic acid copolymer coated with fluorescent whitening agent OB-1 composite microparticles, the carrier resin, and the remaining (if any) polyethylene wax, the remaining (if any) pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] and the remaining (if any) tris(2,4-di-tert-butylphenyl) phosphite are mixed and fed into a twin-screw extruder to obtain the material to be melted and dispersed;

[0031] S3. Melt extrusion: The material to be melted and dispersed is melted and dispersed at 140–220℃, screw speed 100–600rpm, and die head pressure 3–15MPa, and the exhaust is vented at an exhaust port gauge pressure of -0.09 to -0.03MPa to obtain a melt;

[0032] S4. Filtration and pelletizing: The melt is filtered through an 80–300 mesh filter, cooled, and pelletized to obtain the high-concentration masterbatch of the fluorescent whitening agent.

[0033] Further, in step S3, the temperatures from zone one to the die head of the twin-screw extruder are sequentially 140–170℃, 150–185℃, 160–200℃, 165–210℃, and 170–220℃; the length-to-diameter ratio of the twin-screw extruder is 32–52, and the screw includes a conveying section, a kneading and dispersing section, a vacuum degassing section, and a metering section, wherein the kneading and dispersing section is located at 30.00–70.00% of the screw length after the feed end.

[0034] Further, in step S2, the carrier resin is fed in two stages, wherein, based on the total mass of the carrier resin, 60.00–90.00 wt% of the carrier resin is fed in the main feed port, and the remaining 10.00–40.00 wt% of the carrier resin is fed in the side feed port.

[0035] Furthermore, the cooling method in step S4 is air cooling, warm water cooling, or a combination of both, with the cooling medium temperature being 15–45℃ and the length of the masterbatch particles after pelleting being 1.50–5.00 mm.

[0036] Furthermore, at least one of steps S2 and S3 is carried out in a nitrogen atmosphere, wherein the volume fraction of nitrogen is 99.00–99.999 vol.

[0037] Furthermore, the D50 of the polyethylene-acrylic acid copolymer-coated fluorescent whitening agent OB-1 composite microparticles used to prepare the obtained high-concentration masterbatch of fluorescent whitening agent is 0.50–3.00 μm, the D90 is 2.00–8.00 μm, and the D90 is not less than the D50, and the water content of the high-concentration masterbatch of fluorescent whitening agent is 0.01–0.10 wt%.

[0038] Furthermore, the polyethylene-acrylic acid copolymer is a copolymer containing polyethylene segments and acrylic acid structural units. The content of acrylic acid structural units is calculated based on the total mass of the polyethylene-acrylic acid copolymer. In the melt wetting and coating step, the polyethylene-acrylic acid copolymer is mixed with fluorescent whitening agent OB-1 and polyethylene wax to form the polymer shell component in the coating material.

[0039] Furthermore, the melt-wetting coating process uses dried fluorescent whitening agent OB-1, polyethylene-acrylic acid copolymer, polyethylene wax, pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] and tris(2,4-di-tert-butylphenyl) phosphite as input materials. The input materials are mixed at 90–140°C, absolute pressure of 0.08–0.12 MPa, air or nitrogen atmosphere, and 300–1500 rpm for 5–20 min. After mixing, the coating material is output. After surface coverage and D50 quality control, the coating material enters the cooling and sieving step.

[0040] Furthermore, the surface coverage and shell thickness were determined using cross-sectional images obtained by transmission electron microscopy or scanning electron microscopy. The sample to be tested was derived from the composite microparticles obtained in step A5. After cooling and cross-sectional sample preparation, an image showing the interface between the fluorescent whitening agent OB-1 crystal and the polyethylene-acrylic acid copolymer shell was obtained. The surface coverage was calculated as the proportion of the arc length of the cross-sectional profile. The surface coverage was calculated as the percentage of the arc length of the outer contour of a single fluorescent whitening agent OB-1 crystal that was covered by the polyethylene-acrylic acid copolymer shell to the total arc length of the outer contour of the crystal cross-section. The shell thickness was calculated as the distance between the outer contour of the fluorescent whitening agent OB-1 crystal and the outer boundary of the polyethylene-acrylic acid copolymer shell in the same image. The obtained surface coverage and shell thickness were used as quality control data before the composite microparticles entered the masterbatch extrusion and batching step.

[0041] Furthermore, the composite microparticles D50 and D90 were determined using the dry laser diffraction particle size distribution method. The sample to be tested was derived from the composite microparticles obtained in step A5. Before the test, the sample was dry-dispersed. The particle size distribution was output based on the cumulative distribution on a volume basis. D50 is the particle size corresponding to a cumulative volume distribution of 50%, and D90 is the particle size corresponding to a cumulative volume distribution of 90%. The particle size data was used to determine that D90 is not less than D50 and proceed to the masterbatch extrusion and batching step.

[0042] Furthermore, the D90 of the composite microparticle agglomerates and the coefficient of variation of area distribution in the cross section of the masterbatch were obtained by cross-sectional image analysis. The test sample was derived from the masterbatch after pelleting. The sample was prepared along the length direction perpendicular to the masterbatch and the image was acquired. Adjacent or contacting composite microparticles were identified as the same agglomerate. The equivalent circle diameter of each agglomerate was recorded. The ratio of the total projected area of ​​the composite microparticles and their agglomerates detected in each field of view to the total area of ​​the field of view was used as the area fraction of composite microparticle distribution. The agglomerate D90 was calculated based on the cumulative distribution of the equivalent circle diameter. The coefficient of variation of area distribution was calculated by dividing the standard deviation of the area fraction of composite microparticle distribution in each field of view by the average value and then multiplying by 100%. The obtained data were used to characterize the dispersion state of composite microparticles in the carrier resin.

[0043] Furthermore, the melt mass flow rate was measured using a melt mass flow rate meter. The test samples were derived from masterbatch after pelleting. The test temperature was set as a single temperature within the range of 180–220℃ according to the corresponding processing evaluation temperature of the sample. The test load was kept consistent in the same batch of samples. The mass of extruded material per unit time was recorded and converted to g / 10min. The obtained data were used as the quality control data for masterbatch melt extrusion processing.

[0044] Furthermore, the evaluation of fuming agglomeration used the masterbatch after pelleting as the test sample. The sample was heated at 190°C, and the heating time corresponded to the residence time of the material in the corresponding temperature zone of 190°C during the melt extrusion step. The sample mass before and after heating and the mass of agglomerates after cooling were recorded. The mass loss rate and the percentage of agglomerate mass to the sample mass before heating were used as the evaluation data of fuming agglomeration. The obtained evaluation data were recorded in correspondence with the melt extrusion temperature conditions.

[0045] Furthermore, the moisture content of the masterbatch was determined using the masterbatch after pelleting as the test sample, and the Karl Fischer moisture determination method was used. The sample weight, titration consumption and blank value were recorded. The moisture content was calculated by dividing the moisture mass by the mass of the masterbatch sample. The resulting moisture content was used as the quality control data of the masterbatch after cooling and pelleting.

[0046] As another aspect of this invention, the present invention employs a pre-formed polyethylene-acrylic acid copolymer coated with fluorescent whitening agent OB-1 composite microparticles followed by twin-screw melt extrusion. This is primarily used to achieve, fix, or amplify the aforementioned synergistic effects. Existing preparation processes, relying solely on strong shear dispersion during the extrusion stage, are prone to localized enrichment under high OB-1 content conditions. While this may temporarily increase mixing strength, it can lead to thermal shear fumigation, crystal breakage followed by re-agglomeration, and melt fluctuations. Excessive reliance on lubrication or carrier dilution reduces the effective whitening component carrying capacity. This invention first forms controlled composite microparticles through drying, melt wetting and coating, cooling, and sieving. Then, through two-stage feeding, temperature zone distribution, venting, filtration, and pelletizing, the dispersion state is fixed, allowing the microparticle structure formed by interfacial wetting to be received in the carrier resin. Simultaneously, by controlling extrusion temperature, pressure, venting, and filtration conditions, thermal processing instability factors are reduced, maintaining a coordinated relationship between dispersion stability and whitening performance, as well as processing fluidity and thermal stability, throughout the process.

[0047] Polyethylene-acrylic acid copolymers are primarily used for wetting, coating, and dispersing stability of fluorescent whitening agent OB-1 crystals, while polyethylene wax is mainly used for flow regulation and shear dispersion during melt processing. When the proportion of polyethylene-acrylic acid copolymer alone is too high, although it helps to reduce powder agglomeration, it may reduce the effective whitening contribution and increase melt resistance due to enhanced interfacial binding and a thicker shell. Conversely, when the proportion of polyethylene wax alone is too high, although it can improve melt flow and initial dispersion, it may lead to insufficient stable bonding of composite particles due to an excessive amount of low-viscosity lubricating phase, causing fluorescent whitening agent OB-1 to re-accumulate in high-content systems. This invention achieves a balance between interfacial effects and flow regulation by using polyethylene-acrylic acid copolymer coating, synergistic wetting with polyethylene wax, protection with a composite antioxidant system, and dispersion bonding with a carrier resin.

[0048] Beneficial technical effects

[0049] 1. This invention uses a polyethylene-acrylic acid copolymer to melt-wet and coat the fluorescent whitening agent OB-1, so that the surface of the fluorescent whitening agent OB-1 crystals obtains an interface layer compatible with the carrier resin, reducing the tendency of high-content powder to agglomerate and locally enrich during melt processing, thereby improving the dispersion stability of high-concentration masterbatch and the uniformity of downstream dilution.

[0050] 2. This invention matches the ratio of fluorescent whitening agent OB-1, polyethylene-acrylic acid copolymer, polyethylene wax and carrier resin. The polyethylene wax is used to reduce the resistance to melting and mixing, while the polyethylene-acrylic acid copolymer maintains the stability of the composite particle interface. This avoids insufficient dispersion and adhesion caused by simply increasing the lubricating component, thus taking into account both processing fluidity and the retention of effective whitening components.

[0051] 3. This invention uses pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] and tris(2,4-di-tert-butylphenyl)phosphite to form a composite antioxidant system, which synergistically stabilizes the thermo-oxidative environment during melt wetting coating and twin-screw extrusion, which helps to reduce the risks of fuming, agglomeration and color fluctuation under high-temperature shear conditions.

[0052] 4. This invention uses pre-made polyethylene-acrylic acid copolymer coated with fluorescent whitening agent OB-1 composite microparticles, followed by total mixing, melt extrusion, exhaust filtration, and cooling pelletizing. This allows for a detectable quality control path for the particle size, shell state, moisture content, and masterbatch particle size of the composite microparticles, thereby improving the reproducibility of the preparation process and its suitability for industrial applications. Attached Figure Description

[0053] Figure 1 Box plots showing the surface coverage of composite microparticles in Example 1, Comparative Example 9, and Comparative Example 10.

[0054] Figure 2 The probability density distribution diagrams are for the thickness of the composite microparticle shells in Example 1, Comparative Example 9, and Comparative Example 10.

[0055] Figure 3 This is a statistical chart showing the proportion of free fluorescent whitening agent OB-1 crystals in Example 1, Comparative Example 9, and Comparative Example 10.

[0056] Figure 4 The images show the differential volume distribution of composite microparticles obtained by dry laser particle size analysis in Examples 1, 5, and 6.

[0057] Figure 5 The cumulative particle size distribution diagrams for dry laser processing of composite microparticles in Examples 1, 5, and 6 are shown.

[0058] Figure 6 The cumulative distribution diagram of the agglomerate size of the masterbatch cross section is shown for Example 1, Comparative Example 5, and Comparative Example 6.

[0059] Figure 7 Box plots of the coefficient of variation of the cross-sectional area distribution of the masterbatch in Examples 1, 5, and 6.

[0060] Figure 8 The graph shows the changes in whiteness index during the heat treatment process of Example 1, Comparative Example 9, and Comparative Example 11.

[0061] Figure 9 Box plots of relative whiteness enhancement values ​​ΔWI for Example 1, Comparative Example 9, and Comparative Example 11.

[0062] Figure 10 Box plots showing the whiteness retention rates after heat treatment for Examples 1, 9, and 11.

[0063] Figure 11 Box plots of melt mass flow rate (MFR) for Examples 1, 3, and 11.

[0064] Figure 12 Thermogravimetric analysis (TGA) mass retention curves for Example 1, Comparative Example 3, and Comparative Example 11 are shown.

[0065] Figure 13 The diagram shows the isothermal mass loss process of Example 1, Comparative Example 3, and Comparative Example 11 at 190°C.

[0066] Figure 14 Box scatter plots of agglomerate mass fraction after cooling for Examples 1, 3, and 11.

[0067] Figure 15 This is a macroscopic optical photograph of the highly concentrated particulate fluorescent whitening agent masterbatch from Example 1.

[0068] Figure 16 This is a scanning electron microscope image of the highly concentrated particulate fluorescent whitening agent masterbatch from Example 1; Figure 16 a is a low-magnification scanning electron microscope image of the cross-section of the highly concentrated particulate fluorescent whitening agent masterbatch from Example 1; Figure 16 bd is a medium- to high-magnification scanning electron microscope image of the polyethylene-acrylic acid copolymer-coated fluorescent whitening agent OB-1 composite microparticles dispersed in a polyethylene matrix in the high-concentration masterbatch of granular fluorescent whitening agent in Example 1.

[0069] Figure 17 This is a transmission electron microscope image of the highly concentrated particulate fluorescent whitening agent masterbatch from Example 1; Figure 17 a is a bright-field transmission electron microscopy image of the distribution of polyethylene-acrylic acid copolymer-coated fluorescent whitening agent OB-1 composite microparticles in the polyethylene matrix of the high-concentration granular fluorescent whitening agent masterbatch of Example 1; Figure 17 b is a magnified transmission electron microscope image of the polyethylene-acrylic acid copolymer coating layer on the surface of the OB-1 crystal in the high-concentration masterbatch of granular fluorescent whitening agent in Example 1. Detailed Implementation

[0070] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings.

[0071] Example 1

[0072] Overall production scale and product form

[0073] This embodiment prepared 100.10 kg of granular fluorescent whitening agent highly concentrated masterbatch. The masterbatch consisted of 15.00 parts by weight of fluorescent whitening agent OB-1, 5.00 parts by weight of polyethylene-acrylic acid copolymer, 2.00 parts by weight of polyethylene wax, 0.05 parts by weight of pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], 0.05 parts by weight of tris(2,4-di-tert-butylphenyl) phosphite, and 78.00 parts by weight of carrier resin. The carrier resin was commercially available polyethylene granules, and the mass ratio of polyethylene to ethylene-vinyl acetate copolymer was 100:0. The acrylic structural unit content of the polyethylene-acrylic acid copolymer was 5.00 wt%, and the mass ratio of fluorescent whitening agent OB-1 to the portion including the polyethylene-acrylic acid copolymer coating layer was 100:25.

[0074] Raw materials, components or material specifications

[0075] The fluorescent whitening agent OB-1 is a commercially available industrial-grade powder with a purity of 99.0% and an initial water content of 0.08 wt%. The polyethylene-acrylic acid copolymer is a commercially available granule with an acrylic acid structural unit content of 5.00 wt% and a melting point range suitable for melt wetting and coating at 90℃. The polyethylene wax is a commercially available powder with a number average molecular weight of 3000. Pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] and tris(2,4-di-tert-butylphenyl) phosphite are both commercially available industrial-grade powders with a purity of 98.0%. All raw materials were temporarily sealed and stored at 25℃ and 50% relative humidity before use, and weighed within 2 hours after opening.

[0076] A1. Provide materials for the preparation of composite microparticles

[0077] Based on 100 parts by weight of fluorescent whitening agent OB-1, weigh 100 parts by weight of fluorescent whitening agent OB-1, 33.33 parts by weight of polyethylene-acrylic acid copolymer, 13.33 parts by weight of polyethylene wax, 0.33 parts by weight of pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], and 0.33 parts by weight of tris(2,4-di-tert-butylphenyl) phosphite. The weighing error of each material should be controlled within 0.2% of the target value. After weighing, seal and store separately. In subsequent steps, add fluorescent whitening agent OB-1, polyethylene-acrylic acid copolymer, polyethylene wax, pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], and tris(2,4-di-tert-butylphenyl) phosphite to a high-speed mixing device with a temperature-controlled jacket in the following order:

[0078] A2. Drying Fluorescent Brightening Agent OB-1

[0079] The fluorescent whitening agent OB-1 was placed in a hot air circulating drying oven and dried at 80°C in air for 1 hour, with a thickness of 10 mm. The drying was completed when the mass change between two consecutive weighings was less than 0.02%. After drying, the product was removed and cooled to 25°C in a sealed drying container to obtain the dried fluorescent whitening agent OB-1.

[0080] A3. Melt wetting and coating

[0081] The dried fluorescent whitening agent OB-1 was first added to a high-speed mixer and premixed at 25°C and 300 rpm for 2 min. Then, polyethylene-acrylic acid copolymer was added and the temperature was raised to 90°C at a rate of 5°C / min. Subsequently, polyethylene wax, pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], and tris(2,4-di-tert-butylphenyl) phosphite were added, and the mixture was maintained at an absolute pressure of 0.08 MPa under air atmosphere, continuing to mix at 300 rpm for 5 min until no visible dry powder clumps were visible on the material surface. The completion criterion was the appearance of a continuous wetting layer on the outer surface of the fluorescent whitening agent OB-1 crystals during sampling observation, and the mixing torque fluctuating by less than 5% within 1 min.

[0082] A4. Quality control of coating materials

[0083] After melt wetting and coating, samples of the coated material were taken for cross-sectional preparation and image analysis. The surface coverage of the polyethylene-acrylic acid copolymer on the fluorescent whitening agent OB-1, calculated according to the arc length ratio of the cross-sectional profile, was 60.00% ± 1.80%, with a shell thickness of 20 nm ± 3 nm. The particle size of the composite particles was determined by dry laser diffraction particle size distribution, with a D50 of 0.50 μm ± 0.02 μm and a D90 of 2.00 μm ± 0.06 μm. The content of free fluorescent whitening agent OB-1 crystals not covered by the polyethylene-acrylic acid copolymer was 8.00 wt% ± 0.20 wt%. The test was repeated three times, and the average value was taken.

[0084] A5. Cool and sieve.

[0085] The coated material obtained in step A4 is cooled under jacket cooling conditions. The cooling medium temperature is 15°C, and the material temperature drops to 30°C before being discharged. The discharged material is then sieved through a 40-mesh screen. The soft agglomerates on the screen are lightly crushed and sieved again. The material passing through the screen is the polyethylene-acrylic acid copolymer coated with fluorescent whitening agent OB-1 composite microparticles. The criterion for completing sieving is that the mass of the material remaining on the screen is less than 0.5% of the total material mass.

[0086] S1. Provide materials for masterbatch preparation

[0087] Weigh the prepared polyethylene-acrylic acid copolymer-coated fluorescent whitening agent OB-1 composite microparticles, ensuring that the contents of fluorescent whitening agent OB-1, polyethylene-acrylic acid copolymer, polyethylene wax, pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], and tris(2,4-di-tert-butylphenyl) phosphite in the total masterbatch formulation are 15.00 parts by weight, 5.00 parts by weight, 2.00 parts by weight, 0.05 parts by weight, and 0.05 parts by weight, respectively; separately weigh 78.00 parts by weight of carrier resin. The carrier resin is used after drying at 70℃ for 1 hour, and completion is judged by the absence of visible condensation and adhesion on the surface.

[0088] S2. Mixing and Feeding

[0089] Polyethylene-acrylic acid copolymer-coated fluorescent whitening agent OB-1 composite microparticles and 60.00 wt% carrier resin were added to the main mixer and mixed at 200 rpm for 8 minutes at 25°C under a nitrogen atmosphere of 99.00 vol% to obtain the main feed material. The remaining 40.00 wt% carrier resin entered the side feed inlet. The side feed speed was matched with the main feed mass flow rate to maintain continuous and stable material flow within the twin-screw extruder. The feeding completion criterion was that the instantaneous mass flow rate fluctuations in both the main feed hopper and the side feed hopper were less than 3%.

[0090] S3. Melt extrusion

[0091] The material to be melted and dispersed is fed into a twin-screw extruder with a length-to-diameter ratio of 32. The screw includes a conveying section, a kneading and dispersing section, a vacuum exhaust section, and a metering section. The kneading and dispersing section is located at 30.00% of the screw length after the feed end. The temperatures from Zone 1 to the die head are 140℃, 150℃, 160℃, 165℃, and 170℃ respectively. The screw speed is 100 rpm, the die head pressure is 3 MPa, and the exhaust port gauge pressure is -0.09 MPa. The material is preheated in the conveying section, the composite microparticles and carrier resin are melted and dispersed in the kneading and dispersing section, entrained gases and trace amounts of moisture are removed in the vacuum exhaust section, and a stable melt is formed in the metering section. The completion criteria are that the die head pressure fluctuates by less than 0.5 MPa within 10 minutes, and the melt has a uniform appearance with no visible color spots.

[0092] S4. Filtration and pelletizing

[0093] The melt was filtered through an 80-mesh filter and then entered the air-cooled pelletizing unit. The cooling medium temperature was 15℃, the traction speed was 10m / min, and the cutter speed was 600rpm. After pelletizing, highly concentrated granular fluorescent whitening agent masterbatch with a length of 1.50mm±0.05mm and a diameter of 1.00mm±0.04mm was obtained. The pelletizing completion criterion was that the number of adhering particles in 100 consecutive samples did not exceed 2, and the mass percentage of fine powder after sieving was less than 0.3%.

[0094] Quality testing methods and results

[0095] The masterbatch after pelleting was used as a sample, and the measurements were repeated three times. Moisture content was determined using the Karl Fischer method, and the result was 0.01wt%±0.002wt%. Melt flow rate was measured at 190℃ under the same load, and the result was 40.00g / 10min±1.20g / 10min. A cross-section was prepared perpendicular to the length of the masterbatch, and images were acquired. The D90 of the composite microparticle agglomerates was 3.00μm±0.12μm, and the coefficient of variation of the cross-sectional area distribution was 5.00%±0.50%. After heating at 190℃ for the corresponding residence time, fuming and agglomeration were evaluated, and the mass loss rate was 1.10%±0.10%. After cooling, the mass of the agglomerates accounted for 0.80%±0.08% of the sample mass before heating. The test results indicate that the masterbatch in this embodiment has stable particle size, low moisture content, easy melt flow, and maintains a dispersed state of composite microparticles.

[0096] Features and application scenarios of this embodiment

[0097] This embodiment uses a relatively conservative ratio of fluorescent whitening agent OB-1, a higher proportion of polyethylene carrier resin, and mild melt extrusion conditions. The composite microparticles have a smaller particle size and a higher melt flow rate of the masterbatch, making it suitable for use in polyethylene systems, diluted whitening of recycled polyolefins, and film or sheet products with high processing fluidity requirements.

[0098] Example 2

[0099] Overall production scale and product form

[0100] This embodiment prepared 99.80 kg of granular fluorescent whitening agent highly concentrated masterbatch. The masterbatch consisted of 35.00 parts by weight of fluorescent whitening agent OB-1, 18.00 parts by weight of polyethylene-acrylic acid copolymer, 8.00 parts by weight of polyethylene wax, 0.20 parts by weight of pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], 0.60 parts by weight of tris(2,4-di-tert-butylphenyl) phosphite, and 38.00 parts by weight of carrier resin. The carrier resin was a combination of commercially available polyethylene granules and commercially available ethylene-vinyl acetate copolymer granules, with a mass ratio of polyethylene to ethylene-vinyl acetate copolymer of 100:60, wherein polyethylene accounted for 23.75 parts by weight and ethylene-vinyl acetate copolymer accounted for 14.25 parts by weight. The acrylic acid structural unit content of the polyethylene-acrylic acid copolymer was 20.00 wt%.

[0101] Raw materials, components or material specifications

[0102] The fluorescent whitening agent OB-1 is a commercially available industrial-grade powder with a purity of 99.0% and an initial water content of 0.06 wt%; the polyethylene-acrylic acid copolymer is a commercially available granule with an acrylic acid structural unit content of 20.00 wt%; the polyethylene wax is a commercially available powder with a number average molecular weight of 3000; the polyethylene granules and ethylene-vinyl acetate copolymer granules are both commercially available industrial-grade resins; pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] and tris(2,4-di-tert-butylphenyl) phosphite are both commercially available industrial-grade powders with a purity of 98.0%. Before feeding, the raw materials are passed through a 20-mesh sieve to remove transport agglomerates.

[0103] A1. Provide materials for the preparation of composite microparticles

[0104] Based on 100 parts by weight of fluorescent whitening agent OB-1, weigh out 100 parts by weight of fluorescent whitening agent OB-1, 51.43 parts by weight of polyethylene-acrylic acid copolymer, 22.86 parts by weight of polyethylene wax, 0.57 parts by weight of pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], and 1.71 parts by weight of tris(2,4-di-tert-butylphenyl) phosphite. Before feeding, pre-cut the polyethylene-acrylic acid copolymer into particles with a particle size of less than 3 mm to facilitate rapid melt wetting.

[0105] A2. Drying Fluorescent Brightening Agent OB-1

[0106] The fluorescent whitening agent OB-1 was placed in a hot air drying oven and dried at 110℃ for 3 hours, with the pressure inside the oven maintained at normal atmospheric pressure and air exchange. The drying was considered complete when the water content of the sample was no higher than 0.03wt%. After drying, the sample was removed and cooled to 30℃ in a nitrogen-protected drying container to obtain the dried fluorescent whitening agent OB-1.

[0107] A3. Melt wetting and coating

[0108] The dried fluorescent whitening agent OB-1 was added to a high-speed mixer with a temperature-controlled jacket and pre-dispersed at 40°C and 500 rpm for 3 min. Polyethylene-acrylic acid copolymer was then added and the temperature was raised to 140°C at a rate of 8°C / min. Polyethylene wax, pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], and tris(2,4-di-tert-butylphenyl) phosphite were added, and the mixture was then mixed at 0.12 MPa absolute pressure under a nitrogen atmosphere for 20 min at a mixing speed of 1500 rpm until the torque curve stabilized. The completion criterion was that no unwetted powder clumps were found in the sample, and the coated material appeared as uniform fine particles under scraping observation.

[0109] A4. Quality control of coating materials

[0110] After melt wetting and coating, cross-sectional images were prepared from the coated material sample. The surface coverage of the polyethylene-acrylic acid copolymer on the fluorescent whitening agent OB-1, calculated according to the arc length ratio of the cross-sectional profile, was 95.00% ± 1.00%, with a shell thickness of 300 nm ± 12 nm. The D50 and D90, determined by dry laser diffraction particle size distribution, were 3.00 μm ± 0.08 μm and 8.00 μm ± 0.20 μm, respectively. The content of free fluorescent whitening agent OB-1 crystals not covered by the polyethylene-acrylic acid copolymer was 0.10 wt% ± 0.02 wt%. The test was repeated three times, and the average value was taken.

[0111] A5. Cool and sieve.

[0112] The coated material obtained in step A4 was cooled to 60°C under nitrogen purging. During cooling, the stirring speed was maintained at 200 rpm to prevent localized adhesion. The material was then sieved through a 100-mesh sieve. The undersize material was the polyethylene-acrylic acid copolymer-coated fluorescent whitening agent OB-1 composite microparticles. The sieving was considered complete when the undersize material flowed continuously and the mass percentage of hard particles on the sieve was less than 0.2%.

[0113] S1. Provide materials for masterbatch preparation

[0114] Weigh out polyethylene-acrylic acid copolymer-coated fluorescent whitening agent OB-1 composite microparticles, such that the contents of fluorescent whitening agent OB-1, polyethylene-acrylic acid copolymer, polyethylene wax, pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], and tris(2,4-di-tert-butylphenyl) phosphite in the total masterbatch formulation are 35.00 parts by weight, 18.00 parts by weight, 8.00 parts by weight, 0.20 parts by weight, and 0.60 parts by weight, respectively; separately weigh out 38.00 parts by weight of carrier resin. The carrier resin is used after drying at 80℃ for 2 hours, and completion is judged by the surface of the resin particles being dry and free of lumps.

[0115] S2. Mixing and Feeding

[0116] Polyethylene-acrylic acid copolymer-coated fluorescent whitening agent OB-1 composite microparticles and 90.00 wt% carrier resin were added to the main mixer and mixed at 300 rpm for 12 min at 30°C under a nitrogen atmosphere of 99.999 vol% to obtain the main feed material. The remaining 10.00 wt% carrier resin was fed in through the side feed port. The main feed and side feed were linked and controlled by a weighing feeder. The completion criterion was that the main motor current fluctuated by less than 5% within 10 min and there was no bridging in the hopper.

[0117] S3. Melt extrusion

[0118] The material to be melted and dispersed is fed into a twin-screw extruder with a length-to-diameter ratio of 52. The kneading and dispersing section is located at 70.00% of the screw length after the feed end. The temperatures from zone one to the die head are 170℃, 185℃, 200℃, 210℃, and 220℃ respectively. The screw speed is 600 rpm, the die head pressure is 15 MPa, and the exhaust port gauge pressure is -0.03 MPa. Step S3 is carried out under a nitrogen atmosphere with a volume of 99.999 vol%. The completion criteria are a continuous and smooth melt strip surface without any trace of bubble rupture, and a pressure difference of less than 2 MPa before and after filtration.

[0119] S4. Filtration and pelletizing

[0120] The melt was filtered through a 300-mesh filter and then entered a warm water-cooled pelletizing unit. The cooling medium temperature was 45℃, the traction speed was 18m / min, and the cutter speed was 900rpm. After pelletizing, highly concentrated fluorescent whitening agent masterbatch with a length of 5.00mm±0.10mm and a diameter of 4.00mm±0.08mm was obtained. The pelletizing completion criterion was that there was no adhesion or tailing on the particle surface, and the number of particles with a length deviation of more than 0.20mm from the target value in 100 consecutive samples did not exceed 5.

[0121] Quality testing methods and results

[0122] The pelleted masterbatch was used as a sample, and the measurements were repeated three times. Moisture content was determined using the Karl Fischer method, and the result was 0.10wt%±0.006wt%. Melt flow rate was measured at 220℃ under the same load, and the result was 2.00g / 10min±0.10g / 10min. Cross-sectional image analysis showed that the D90 of the composite microparticle agglomerates was 10.00μm±0.30μm, and the coefficient of variation of the cross-sectional area distribution was 25.00%±1.00%. After heating at 190℃ for the corresponding residence time, the fuming and agglomeration evaluation showed a mass loss rate of 2.30%±0.20%, and the mass of the agglomerates after cooling accounted for 1.90%±0.15% of the sample mass before heating. The test results indicate that this embodiment can still form intact masterbatch under high fluorescent whitening agent OB-1 content and strong extrusion conditions.

[0123] Features and application scenarios of this embodiment

[0124] This embodiment employs a high-load formulation, a high proportion of ethylene-vinyl acetate copolymer, and strong melt dispersion conditions, resulting in a high degree of coating of composite microparticles. It is suitable for polyolefin modified products that require high whitening agent loading, high processing temperature, and strong thermal processing stability.

[0125] Example 3

[0126] Overall production scale and product form

[0127] This embodiment prepared 97.15 kg of granular fluorescent whitening agent highly concentrated masterbatch. The masterbatch consisted of 25.00 parts by weight of fluorescent whitening agent OB-1, 5.00 parts by weight of polyethylene-acrylic acid copolymer, 2.00 parts by weight of polyethylene wax, 0.10 parts by weight of pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], 0.05 parts by weight of tris(2,4-di-tert-butylphenyl) phosphite, and 65.00 parts by weight of carrier resin. The carrier resin was a combination of commercially available polyethylene granules and commercially available ethylene-vinyl acetate copolymer granules, with a mass ratio of polyethylene to ethylene-vinyl acetate copolymer of 100:20. The acrylic structural unit content of the polyethylene-acrylic acid copolymer was 12.00 wt%.

[0128] Raw materials, components or material specifications

[0129] The fluorescent whitening agent OB-1 is a commercially available industrial-grade powder with a purity of 99.0% and an initial water content of 0.07 wt%; the polyethylene-acrylic acid copolymer is a commercially available granule with an acrylic structural unit content of 12.00 wt%; the polyethylene wax is a commercially available powder with a number average molecular weight of 3000; and the polyethylene and ethylene-vinyl acetate copolymer is a commercially available industrial-grade resin. Both antioxidant components are commercially available industrial-grade powders, each with a purity of 98.0%. Before weighing, the powders were placed in an environment at 25°C and 45% relative humidity for 30 minutes to equilibrate.

[0130] A1. Provide materials for the preparation of composite microparticles

[0131] Based on 100 parts by weight of fluorescent whitening agent OB-1, weigh out 100 parts by weight of fluorescent whitening agent OB-1, 20 parts by weight of polyethylene-acrylic acid copolymer, 6 parts by weight of polyethylene wax, 0.2 parts by weight of pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], and 0.2 parts by weight of tris(2,4-di-tert-butylphenyl) phosphite. Prepare the materials in the order of powder, copolymer, wax, and antioxidant components. Any deficiency in the total masterbatch formulation of polyethylene wax should be added in stage S1, and any deficiency in the total masterbatch formulation of pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] should also be added in stage S1.

[0132] A2. Drying Fluorescent Brightening Agent OB-1

[0133] The fluorescent whitening agent OB-1 was placed in a hot air circulating drying oven and dried at 95°C for 2 hours in air atmosphere, with a thickness of 12 mm. After drying, a sample was taken using a sealed sampling bottle, and the water content was no higher than 0.04 wt% as the completion criterion, thus obtaining the dried fluorescent whitening agent OB-1.

[0134] A3. Melt wetting and coating

[0135] The dried fluorescent whitening agent OB-1 was added to a high-speed mixer and premixed at 600 rpm for 3 min. Polyethylene-acrylic acid copolymer was then added and the temperature was raised to 115℃ at a rate of 6℃ / min. Polyethylene wax, pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], and tris(2,4-di-tert-butylphenyl) phosphite were added, and the mixture was then mixed at 0.10 MPa absolute pressure under a nitrogen atmosphere for 12 min at a mixing speed of 900 rpm. The completion criteria were: the temperature of the coated material stabilized at 115℃ ± 3℃, the torque curve fluctuation was less than 4%, and no visible white dry powder clumps were found in the sample.

[0136] A4. Quality control of coating materials

[0137] After melt wetting and coating, cross-sectional images and particle size analysis were performed on the coated material. The surface coverage of the polyethylene-acrylic acid copolymer on the fluorescent whitening agent OB-1, calculated according to the arc length ratio of the cross-sectional profile, was 72.00% ± 2.00%, and the shell thickness was 120 nm ± 10 nm. The D50 and D90 determined by dry laser diffraction particle size distribution were 1.40 μm ± 0.05 μm and 4.50 μm ± 0.15 μm, respectively. The content of free fluorescent whitening agent OB-1 crystals not covered by the polyethylene-acrylic acid copolymer was 4.00 wt% ± 0.18 wt%. The test was repeated three times, and the average value was taken.

[0138] A5. Cool and sieve.

[0139] The coated material obtained in step A4 was cooled to 45°C in air, and the stirring speed was reduced to 150 rpm. The material was sieved through a 60-mesh sieve, and the undersize material was used as polyethylene-acrylic acid copolymer coated fluorescent whitening agent OB-1 composite microparticles. The sieving was considered complete when the undersize material flowed uniformly and the total residual amount of crushable soft agglomerates on the sieve was less than 0.4% after a second sieving.

[0140] S1. Provide materials for masterbatch preparation

[0141] Weigh the composite microparticles obtained in step A5, and assign 25.00 parts by weight, 5.00 parts by weight, 1.50 parts by weight, 0.05 parts by weight, and 0.05 parts by weight, respectively, to the fluorescent whitening agent OB-1, polyethylene-acrylic acid copolymer, polyethylene wax, pentaerythritol tetratetra[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], and tris(2,4-di-tert-butylphenyl) phosphite; separately weigh 0.50 parts by weight of polyethylene wax, 0.05 parts by weight of pentaerythritol tetratetra[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], and 65.00 parts by weight of carrier resin. The carrier resin contains 54.17 parts by weight of polyethylene and 10.83 parts by weight of ethylene-vinyl acetate copolymer.

[0142] S2. Mixing and Feeding

[0143] The composite microparticles, added polyethylene wax, added pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], and 75.00 wt% carrier resin were added to the main mixer and mixed at 250 rpm for 10 min at 25°C in air. The remaining 25.00 wt% carrier resin was fed in through the side feed port. The completion criterion was that the mixture had a consistent color after being spread in the sampling tray, and the relative deviation of the fluorescent whitening agent OB-1 content in three consecutive samples was less than 3%.

[0144] S3. Melt extrusion

[0145] The material to be melted and dispersed is fed into a twin-screw extruder with a length-to-diameter ratio of 40. The kneading and dispersing section is located at 45.00% of the screw length after the feed end. The temperatures from zone one to the die head are 155℃, 165℃, 180℃, 190℃, and 200℃ respectively. The screw speed is 300 rpm, the die head pressure is 8 MPa, and the exhaust port gauge pressure is -0.06 MPa. The material remains stable in the vacuum exhaust section. The completion criterion is that there is no obvious dust carried out from the exhaust port, and the melt strips are uniform in color and without breaks.

[0146] S4. Filtration and pelletizing

[0147] The melt was filtered through a 150-mesh filter and then cooled and pelletized using a combination of air cooling and warm water cooling. It was first air-cooled at 25℃ for setting, then cooled with warm water at 30℃, with the cutter speed at 750 rpm. The pelletized product consisted of highly concentrated fluorescent whitening agent granules with a length of 2.50 mm ± 0.08 mm and a diameter of 2.00 mm ± 0.06 mm. The pelleting was considered complete when the granules had smooth surfaces, no adhesion between granules, and a fine powder content of less than 0.4% on the sieve.

[0148] Quality testing methods and results

[0149] The masterbatch after pelleting was used as a sample, and the determination was repeated three times. The Karl Fischer moisture content was 0.05wt%±0.004wt%; the melt flow rate, measured at 200℃ under the same load, was 18.00g / 10min±0.80g / 10min; cross-sectional image analysis of the masterbatch showed that the D90 of the composite microparticle agglomerates was 6.00μm±0.20μm, and the coefficient of variation of the cross-sectional area distribution was 14.00%±0.80%; after heating at 190℃ for the corresponding residence time, the fuming and agglomeration evaluation showed a mass loss rate of 1.60%±0.12%, and the mass of the agglomerates after cooling accounted for 1.10%±0.10% of the mass of the sample before heating. The test results indicate that the masterbatch of this embodiment has both moderate melt flow and a relatively balanced dispersion.

[0150] Features and application scenarios of this embodiment

[0151] This embodiment uses a lower proportion of polyethylene-acrylic acid copolymer feed and a lower proportion of polyethylene wax pre-coating, and supplements polyethylene wax and antioxidant components through the extrusion batching stage to form a layered adjustment between the coating material and the total masterbatch formulation. It is suitable for general polyolefin products that require flowability, uniform dispersion and balanced formulation cost.

[0152] Example 4

[0153] Overall production scale and product form

[0154] In this embodiment, 103.06 kg of granular fluorescent whitening agent highly concentrated masterbatch was prepared. The masterbatch consisted of 22.86 parts by weight of fluorescent whitening agent OB-1, 16.00 parts by weight of polyethylene-acrylic acid copolymer, 8.00 parts by weight of polyethylene wax, 0.60 parts by weight of pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], 0.60 parts by weight of tris(2,4-di-tert-butylphenyl) phosphite, and 55.00 parts by weight of carrier resin. The carrier resin was a combination of commercially available polyethylene granules and commercially available ethylene-vinyl acetate copolymer granules, with a mass ratio of polyethylene to ethylene-vinyl acetate copolymer of 100:30. The acrylic structural unit content of the polyethylene-acrylic acid copolymer was 15.00 wt%, and the mass ratio of fluorescent whitening agent OB-1 to the portion including the polyethylene-acrylic acid copolymer coating layer was 100:55.

[0155] Raw materials, components or material specifications

[0156] The fluorescent whitening agent OB-1 is a commercially available industrial-grade powder with a purity of 99.0% and an initial water content of 0.07 wt%; the polyethylene-acrylic acid copolymer is a commercially available granule with an acrylic structural unit content of 15.00 wt%; the polyethylene wax is a commercially available powder with a number average molecular weight of 3000; both the polyethylene granules and the ethylene-vinyl acetate copolymer granules are commercially available industrial-grade resins; both antioxidant components are commercially available industrial-grade powders with a purity of 98.0%. The raw materials were loosened by passing them through a 30-mesh sieve before weighing.

[0157] A1. Provide materials for the preparation of composite microparticles

[0158] Based on 100 parts by weight of fluorescent whitening agent OB-1, weigh out 100 parts by weight of fluorescent whitening agent OB-1, 70 parts by weight of polyethylene-acrylic acid copolymer, 35 parts by weight of polyethylene wax, 2.5 parts by weight of pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], and 2.5 parts by weight of tris(2,4-di-tert-butylphenyl) phosphite. The two antioxidant components provide basic thermal stability protection during the coating stage; any small amount insufficient to meet the total masterbatch formulation is added in stage S1. The portion of the polyethylene-acrylic acid copolymer not included in the shell layer is used as the wetting phase in the coating material and enters the extrusion batch along with the composite particles.

[0159] A2. Drying Fluorescent Brightening Agent OB-1

[0160] The fluorescent whitening agent OB-1 was placed in a hot air circulating drying oven and dried at 105℃ for 2.5 hours in air atmosphere, with a spreading thickness of 8 mm. The drying completion criterion was that the mass change between two consecutive weighings was less than 0.015%, thus obtaining the dried fluorescent whitening agent OB-1.

[0161] A3. Melt wetting and coating

[0162] The dried fluorescent whitening agent OB-1 was added to a high-speed mixer and premixed at 800 rpm for 2 min. Polyethylene-acrylic acid copolymer was then added and the temperature was raised to 130°C at a rate of 7°C / min. Polyethylene wax, pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], and tris(2,4-di-tert-butylphenyl) phosphite were added, and the mixture was then mixed at 0.11 MPa absolute pressure under a nitrogen atmosphere for 18 min at a mixing speed of 1200 rpm. The completion criterion was that the material was in a flowable particulate state, and the sampling section showed a continuous polymer wetting layer around the fluorescent whitening agent OB-1 crystals.

[0163] A4. Quality control of coating materials

[0164] After melt wetting and coating, cross-sectional images of the coated material samples were statistically analyzed. The surface coverage of the polyethylene-acrylic acid copolymer on the fluorescent whitening agent OB-1, calculated based on the arc length ratio of the cross-sectional profile, was 88.00% ± 1.50%, with a shell thickness of 250 nm ± 15 nm. The D50, determined by dry laser diffraction particle size distribution, was 2.60 μm ± 0.07 μm, and the D90 was 7.50 μm ± 0.18 μm. The content of free fluorescent whitening agent OB-1 crystals not covered by the polyethylene-acrylic acid copolymer was 1.00 wt% ± 0.08 wt%. Based on the shell inclusion, the mass ratio of fluorescent whitening agent OB-1 to polyethylene-acrylic acid copolymer was 100:55.

[0165] A5. Cool and sieve.

[0166] The coating material obtained in step A4 was cooled to 55°C, the cooling medium temperature was 20°C, and the stirring speed was 180 rpm. The material was sieved through an 80-mesh sieve, and the undersize material was used as polyethylene-acrylic acid copolymer coated fluorescent whitening agent OB-1 composite microparticles. The sieving was considered complete when there were no obvious hard lumps after the undersize material accumulated, and the relative deviation of D50 at three sampling points was less than 5%.

[0167] S1. Provide materials for masterbatch preparation

[0168] Weigh the composite microparticles obtained in step A5, making the contributions of fluorescent whitening agent OB-1, polyethylene-acrylic acid copolymer, polyethylene wax, pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], and tris(2,4-di-tert-butylphenyl) phosphite 22.86 parts by weight, 16.00 parts by weight, 8.00 parts by weight, 0.5715 parts by weight, and 0.5715 parts by weight, respectively; separately weigh 0.0285 parts by weight of pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], 0.0285 parts by weight of tris(2,4-di-tert-butylphenyl) phosphite, and 55.00 parts by weight of carrier resin. The carrier resin contains 42.31 parts by weight of polyethylene and 12.69 parts by weight of ethylene-vinyl acetate copolymer.

[0169] S2. Mixing and Feeding

[0170] The composite microparticles, two additional antioxidant components, and 70.00 wt% carrier resin were added to the main mixer and mixed at 280 rpm for 10 minutes at 28°C under a nitrogen atmosphere of 99.50 vol% to obtain the main feed material. The remaining 30.00 wt% carrier resin was fed in through a side feed port. The completion criterion was that the flowability of the mixture was stable and the feeder torque fluctuated by less than 4% within 10 minutes.

[0171] S3. Melt extrusion

[0172] The material to be melted and dispersed is fed into a twin-screw extruder with a length-to-diameter ratio of 48. The kneading and dispersing section is located at 60.00% of the screw length after the feed end. The temperatures from Zone 1 to the die head are 160℃, 175℃, 190℃, 200℃, and 210℃ respectively. The screw speed is 450 rpm, the die head pressure is 12 MPa, and the exhaust port gauge pressure is -0.05 MPa. Step S3 is carried out in an atmosphere with a nitrogen gas volume of 99.50 vol%. After conveying, kneading and dispersing, venting, and metering, the material forms a melt. The completion criteria are continuous melt strips, stable die head pressure, and no obvious condensation of volatiles at the exhaust port.

[0173] S4. Filtration and pelletizing

[0174] The melt was filtered through a 200-mesh filter and then cooled and pelletized using warm water at a temperature of 35°C. The traction speed was 15 m / min, and the cutter speed was 820 rpm. The pelletized product consisted of highly concentrated fluorescent whitening agent granules with a length of 3.80 mm ± 0.09 mm and a diameter of 3.00 mm ± 0.07 mm. The pelletizing process was deemed complete when the cross-section of the pellets was dense, and the number of irregularly shaped pellets did not exceed 4 out of every 100 pellets sampled.

[0175] Quality testing methods and results

[0176] The masterbatch after pelleting was used as a sample, and the determination was repeated three times. Karl Fischer moisture content was 0.08wt%±0.005wt%; melt flow rate, measured at 210℃ under the same load, was 8.00g / 10min±0.40g / 10min; cross-sectional image analysis showed that the D90 of the composite microparticle agglomerates was 8.80μm±0.25μm, and the coefficient of variation of cross-sectional area distribution was 20.00%±0.90%; after heating at 190℃ for the corresponding residence time, the mass loss rate was 1.90%±0.15%, and the mass of the agglomerates after cooling accounted for 1.40%±0.12% of the sample mass before heating. The test results indicate that the masterbatch of this embodiment has a high wetting phase content, a high total amount of antioxidant components, and a relatively stable particle formation state.

[0177] Features and application scenarios of this embodiment

[0178] This embodiment uses a higher proportion of pre-coated polyethylene-acrylic acid copolymer, a higher amount of polyethylene wax, and a higher total amount of composite antioxidant system. Combined with medium-to-high strength melt extrusion conditions, it is suitable for modified plastics, masterbatch blends, and recycled polyolefin products that require a balance of high load dispersion, heat treatment protection, and particle forming stability.

[0179] Comparative Example 1: Basically the same as Example 1, except that in steps A1 and S1, all 5.00 parts by weight of polyethylene-acrylic acid copolymer were replaced with 5.00 parts by weight of ethylene-vinyl acetate copolymer granules. In step A3, melt wetting and coating were carried out in the same order of feeding, 90°C, 0.08 MPa absolute pressure, air atmosphere and 300 rpm as in Example 1, and other conditions remained unchanged.

[0180] Comparative Example 2: It is basically the same as Example 1, except that the acrylic structural unit content of the polyethylene-acrylic acid copolymer is 2.00 wt%, and its amount is still 5.00 parts by weight. The melt wetting coating temperature, pressure, atmosphere, rotation speed and mixing time in step A3 are unchanged, and other conditions are unchanged.

[0181] Comparative Example 3: It is basically the same as Example 1, except that in step A1, the amount of polyethylene wax is 3.33 parts by weight based on 100 parts by weight of fluorescent whitening agent OB-1, and in step S1, the amount of polyethylene wax in the total formula of the masterbatch is 0.50 parts by weight, while other conditions remain unchanged.

[0182] Comparative Example 4: It is basically the same as Example 1, except that in step A2, the fluorescent whitening agent OB-1 is dried in an air atmosphere at 60°C for 1 hour, the thickness of the spread material is still 10 mm, the cooling and sealing temporary storage method after drying is unchanged, and other conditions are unchanged.

[0183] Comparative Example 5: It is basically the same as Example 1, except that after adding the polyethylene-acrylic acid copolymer in step A3, the temperature is raised to 75°C for melt wetting and coating. The heating rate is still 5°C / min, the absolute pressure is still 0.08MPa, the atmosphere is air, the mixing speed is still 300rpm, and other conditions remain unchanged.

[0184] Comparative Example 6: It is basically the same as Example 1, except that after adding polyethylene wax in step A3, it is mixed at 300 rpm for 2 min under an absolute pressure of 0.08 MPa and an air atmosphere, and then pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] and tris(2,4-di-tert-butylphenyl)phosphite are added, while other conditions remain unchanged.

[0185] Comparative Example 7: It is basically the same as Example 1, except that the screw speed of the twin-screw extruder in step S3 is 50 rpm, and the temperature from Zone 1 to the die head, the die head pressure, the gauge pressure at the exhaust port, the length-to-diameter ratio, and the position of the kneading and dispersing section remain unchanged, while other conditions remain unchanged.

[0186] Comparative Example 8: It is basically the same as Example 1, except that in step S4, the melt enters the air-cooled pelletizing unit after being filtered through a 30-mesh filter. The cooling medium temperature, traction speed, cutter speed and pelletizing target size remain unchanged, and other conditions remain unchanged.

[0187] Comparative Example 9: Essentially the same as Example 1, except that the polyethylene-acrylic acid copolymer was removed in steps A1 and S1. In step A3, the dried fluorescent whitening agent OB-1 was first added to a high-speed mixer and premixed at 300 rpm for 2 minutes at 25°C. Then, polyethylene wax was directly added and mixed for 5 minutes at 90°C, 0.08 MPa, and in air. Finally, two antioxidant components were added, with other conditions remaining unchanged. This comparative example was used to verify the synergistic effect of the polyethylene-acrylic acid copolymer and polyethylene wax in the construction of the melt-wetting coating interface of the fluorescent whitening agent OB-1.

[0188] Comparative Example 10: Essentially the same as Example 1, except that polyethylene wax was removed in steps A1 and S1. In step A3, the dried fluorescent whitening agent OB-1 was first added to a high-speed mixer and premixed at 300 rpm for 2 minutes at 25°C. Then, the polyethylene-acrylic acid copolymer was added and the temperature was raised to 90°C. The mixture was then mixed at 300 rpm for 5 minutes under an absolute pressure of 0.08 MPa and an air atmosphere. Finally, two antioxidant components were added, with other conditions remaining unchanged. This comparative example was used to verify the synergistic effect of the polyethylene-acrylic acid copolymer and polyethylene wax in the construction of the melt-wetting coating interface of the fluorescent whitening agent OB-1.

[0189] Comparative Example 11: Essentially the same as Example 1, except that tris(2,4-di-tert-butylphenyl) phosphite was removed in steps A1 and S1, retaining only 0.05 parts by weight of pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]. The remaining conditions in steps A3 and S3 remained unchanged. This comparative example was used to verify the synergistic effect of pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] and tris(2,4-di-tert-butylphenyl) phosphite.

[0190] Characterization and performance testing:

[0191] High-concentration masterbatch of fluorescent whitening agent was added at 2.00 wt% to polyethylene of the same grade to make 1.00 mm tablets. The relative whiteness improvement value and the whiteness retention rate after heat treatment at 190℃ for 10 min were tested. The CIE Lab, whiteness index and yellowness index were recorded using a D65 / 10° spectrophotometer, referring to the ASTM E313-20 method. Each group had n=3, and the mean and standard deviation were taken.

[0192] A cross-section was prepared on the masterbatch after pelleting along the direction perpendicular to the length of the particles. At least 20 fields of view were collected using an optical microscope or conventional SEM to identify composite microparticle aggregates and calculate the cumulative distribution of equivalent circle diameters. The ratio of the total projected area of ​​the composite microparticles and their aggregates detected in each field of view to the total area of ​​that field of view was taken as the composite microparticle distribution area fraction. The area distribution variation coefficient of the composite microparticle distribution area fraction in each field of view was calculated to evaluate the dispersion state of the composite microparticles in the carrier resin. The image threshold, magnification and statistical rules were kept consistent, and n=3 for each group.

[0193] The polyethylene-acrylic acid copolymer-coated fluorescent whitening agent OB-1 composite microparticles obtained in step A5 were subjected to dry laser diffraction particle size analysis. The surface coverage and shell thickness were statistically analyzed from the cross-sectional images to evaluate whether the coated material met the quality control requirements for extrusion batching. Particle size was output as D50 and D90 based on cumulative volume distribution, referring to the ISO 13320:2020 method. The corresponding data fields for this experiment are composite microparticle D50, D90, surface coverage, and shell thickness, in μm, %, and nm.

[0194] Melt flow rate tests were performed on the pelleted masterbatch to evaluate the melt processing fluidity of the highly concentrated masterbatch. The samples were tested at the corresponding test temperature, under the same load and at the same cutting time. The mass of extruded material per unit time was recorded and converted to g / 10min. The method was referenced in ISO 1133-1:2022, with n=3 per group.

[0195] The thermal stability and agglomeration of the masterbatch after pelleting were evaluated. First, the thermal weight loss trend was recorded according to the thermogravimetric method of ISO 11358-1:2022. Then, the mass was weighed before and after heating and the mass of agglomerates after cooling was counted. Each group had n=3.

[0196] The moisture content and particle size of the masterbatch after pelleting were controlled. The moisture content was determined by Karl Fischer method, and the sample weight, titration consumption and blank value were recorded, referring to the ISO 15512:2019 method. The particle length and diameter were measured and counted by vernier calipers or image, with no less than 100 particles per group.

[0197] Figure 1 Box scatter plots are shown for the surface coverage of the composite particles in Example 1, Comparative Example 9, and Comparative Example 10. Figure 2 The graph shows the probability density distribution of the composite microparticle shell thickness in Example 1, Comparative Example 9, and Comparative Example 10. Figure 3 This is a statistical chart showing the proportion of free fluorescent whitening agent OB-1 crystals in Example 1, Comparative Example 9, and Comparative Example 10. (From...) Figures 1 to 3 It can be seen that Example 1 exhibits good integrity and stability in terms of the composite microparticle interface structure. Among them, Figure 1 Surface coverage was quantitatively measured using SEM / TEM cross-sections as an evaluation index. The coverage of Example 1 was concentrated in a high range, while Comparative Example 9, lacking the introduction of polyethylene-acrylic acid copolymer, showed a significant decrease in the surface coverage of the composite particles, indicating that this component plays a crucial role in the formation of the OB-1 crystal surface coating. Comparative Example 10, lacking the introduction of polyethylene wax, exhibited increased dispersion in its coverage data, indicating decreased stability during the melt wetting process. Further combining... Figure 2 It can be seen that the shell thickness of the composite microparticles in Example 1 is mainly concentrated around 20 nm, with a narrow shell distribution and good uniformity. In contrast, the shell thickness of Comparative Example 9 is significantly lower, and the shell thickness distribution of Comparative Example 10 is wider. The above results indicate that the polyethylene-acrylic acid copolymer can provide a stable interfacial coating basis, while polyethylene wax helps to improve wetting and spreading in the molten state and shell uniformity. Figure 3 Further analysis shows that Example 1 exhibits the lowest proportion of free OB-1 crystals, while Comparative Examples 9 and 10 show varying degrees of increase. This indicates that when the interfacial coating component or wetting modifier is insufficient, OB-1 crystals are more likely to remain in a free state. Therefore, this solution, through the synergistic effect of polyethylene-acrylic acid copolymer and polyethylene wax, can improve the surface coating degree of OB-1 crystals, reduce the proportion of free crystals, and form a more stable composite microparticle interfacial structure.

[0198] Figure 4The figures show the differential volume distribution of composite microparticles obtained by dry laser particle size analysis in Examples 1, 5, and 6. Figure 5 The images show the cumulative particle size distribution of the composite microparticles obtained by dry laser processing in Examples 1, 5, and 6. Figure 6 The diagram shows the cumulative distribution of agglomerate size across the masterbatch cross-sections of Examples 1, 5, and 6. Figure 7 Box plots of the coefficient of variation of the cross-sectional area distribution of the masterbatch in Examples 1, 5, and 6. Figure 4 and Figure 5 It can be seen that the composite microparticles in Example 1 have smaller peak positions in particle size distribution and narrower differential volume distribution curves. The particle sizes corresponding to D10, D50, and D90 in the cumulative distribution curve are all at relatively low levels, indicating that the composite microparticles have good refining effect and particle size distribution stability. In contrast, the particle size distributions of Comparative Examples 5 and 6 are shifted towards larger particle sizes, and the cumulative distribution curves shift to the right overall. This indicates that when the coating temperature or mixing time deviates from the appropriate range, insufficient melting and wetting of the material or increased local agglomeration leads to an increase in the proportion of coarse particles. Further combining... Figure 6 It can be seen that the equivalent diameter of the aggregates in the cross section of the masterbatch in Example 1 is relatively small, while the aggregate size at the high cumulative percentile of Comparative Examples 5 and 6 is significantly larger, indicating that particle size control in the preparation stage of composite microparticles will directly affect the dispersion state in the subsequent masterbatch. Figure 7 In Example 1, the coefficient of variation for the cross-sectional area distribution of the masterbatch was relatively low, while it was significantly higher in Comparative Examples 5 and 6, further indicating that the OB-1 composite microparticles in Example 1 were more uniformly distributed in the polyethylene carrier resin. This demonstrates that a reasonable melt wetting coating temperature and mixing time can simultaneously control the initial particle size of the composite microparticles, suppress secondary agglomeration, and improve the cross-sectional dispersion consistency of the highly concentrated masterbatch.

[0199] Figure 8 The graph shows the changes in whiteness index during the heat treatment processes of Example 1, Comparative Example 9, and Comparative Example 11. Figure 9 Box plots of the relative whiteness enhancement value ΔWI for Example 1, Comparative Example 9, and Comparative Example 11. Figure 10 Box scatter plots showing the whiteness retention rates after heat treatment for Examples 1, 9, and 11. Figure 8 It can be seen that during the heat treatment process, the whiteness index WI of Example 1 decreased less over time, showing good heat treatment color stability; due to insufficient interface coating and dispersion, OB-1 in Comparative Example 9 was more prone to local aggregation or performance degradation during the heat treatment process, resulting in a faster decrease in whiteness; due to insufficient antioxidant synergistic system, the whiteness retention ability of Comparative Example 11 decreased after heat treatment. Figure 9The results show that Example 1 has a high and reproducible relative whiteness enhancement value ΔWI, indicating that it not only achieves effective whitening but also maintains a stable whitening effect across different samples. Comparative Example 9, due to the poor dispersion and coating state of OB-1, shows a significantly reduced ΔWI. While Comparative Example 11 still exhibits some initial whitening ability, its data stability and retention after heat treatment are insufficient. Further analysis... Figure 10 It can be seen that Example 1 exhibits the highest whiteness retention rate after heat treatment, while Comparative Examples 9 and 11 show a significant decrease. The decrease in Comparative Example 11 is mainly related to insufficient antioxidant protection. These results indicate that this solution improves the dispersion stability of OB-1 through interface coating and reduces oxidation attenuation during heat treatment through a composite antioxidant system, thereby balancing initial whitening output, whiteness retention rate after heat treatment, and batch-to-batch consistency.

[0200] Figure 11 Box scatter plots of melt mass flow rate (MFR) for Examples 1, 3, and 11. Figure 12 Thermogravimetric analysis (TGA) mass retention curves for Example 1, Comparative Example 3, and Comparative Example 11 are shown. Figure 13 The diagram shows the isothermal mass loss process of Example 1, Comparative Example 3, and Comparative Example 11 at 190°C. Figure 14 Box scatter plots of agglomerate mass fraction after cooling for Examples 1, 3, and 11. Figure 11 It can be seen that Example 1 has a high and stable melt mass flow rate (MFR), indicating that it still maintains good melt processing fluidity under high OB-1 content conditions; Comparative Example 3 shows a significant decrease in MFR due to the reduction in polyethylene wax content, indicating that polyethylene wax plays an important role in reducing the system's melt resistance, improving material transport and plasticizing dispersion; Comparative Example 11 shows a relatively small change in MFR, indicating that its main effect is not in flow regulation. Figure 12 In Example 1, the mass retention rate during the heating process was relatively high, and the T5% temperature was at an optimal level. However, Comparative Example 11, lacking the phosphite antioxidant component, experienced premature thermal weight loss, and Comparative Example 3 also showed a certain decrease in thermal stability. This indicates that the composite antioxidant system and melt flow regulation jointly affect the thermal processing stability. Further combining... Figure 13 It can be seen that under isothermal conditions of 190℃, the mass loss rate of Example 1 is low over time, while the mass loss of Comparative Example 3 and Comparative Example 11 increases, especially Comparative Example 11, indicating that the composite antioxidant system can effectively inhibit the volatilization, oxidation and fumigation tendencies during the hot processing. Figure 14The results show that Example 1 had the lowest agglomerate mass fraction after cooling, Comparative Example 3 showed increased agglomeration due to insufficient melt flow regulation, and Comparative Example 11 showed a further increase in agglomerate proportion due to insufficient thermal stability protection. This demonstrates that the proposed solution can improve melt flowability while enhancing thermal stability and reducing the risk of agglomeration and clumping after cooling, making it suitable for continuous processing of highly concentrated masterbatches.

[0201] Figure 15 This is a macroscopic optical photograph of the highly concentrated particulate fluorescent whitening agent masterbatch from Example 1. Figure 15 As can be seen, the sample obtained in Example 1 is a light yellow to yellowish-green short columnar particle with a complete shape and good size consistency. No obvious macroscopic cracks, bubbling, or severe adhesion were observed, indicating that the plasticizing, extrusion, cooling, and pelletizing processes of the material were relatively stable during the air-cooled pelletizing process. This result demonstrates from a macroscopic morphology perspective that the composite microparticles of polyethylene carrier resin and fluorescent whitening agent OB-1 can form highly concentrated masterbatch with uniform appearance and stable particle state.

[0202] Figure 16 This is a scanning electron microscope image of the highly concentrated particulate fluorescent whitening agent masterbatch from Example 1. Figure 16 As can be seen from the low-magnification images, the cross-section of the masterbatch is generally continuous, without large-scale pores, obvious phase separation, or severe agglomeration defects. The medium- and high-magnification images further reveal that fluorescent whitening agent OB-1 composite microparticles coated with polyethylene-acrylic acid copolymer are dispersed within the polyethylene matrix, exhibiting good interfacial compatibility between the composite microparticles and the matrix. These results indicate that the initial melt wetting and coating process can reduce the possibility of direct exposure and secondary agglomeration of OB-1 crystals, and the subsequent twin-screw melt dispersion can further achieve a uniform distribution of the composite microparticles within the continuous polyethylene phase, verifying the dispersion effectiveness of this method from a microscopic morphology perspective.

[0203] Figure 17 Transmission electron microscopy characterization of the highly concentrated particulate fluorescent whitening agent masterbatch from Example 1. Figure 17 Bright-field transmission electron microscopy (BTEM) images revealed the presence of submicron to micron-sized polyethylene-acrylic acid copolymer-coated fluorescent whitening agent OB-1 composite microparticles within the polyethylene matrix. Further magnified images showed that a polyethylene-acrylic acid copolymer coating layer with a thickness of 20 nm ± 3 nm was formed on the surface of the OB-1 crystals, with a surface coverage of 60.00% ± 1.80%. This structure indicates the formation of a multiphase composite system within the masterbatch, consisting of the OB-1 crystalline functional phase, the interfacial coating layer, and the continuous polyethylene phase. Figures 1 to 16 The test results show that the multiphase structure can simultaneously support performance improvements such as interface coating stability, particle size control, uniform dispersion, whitening retention, melt flow and thermal processing stability, further proving that the solution has a good comprehensive implementation effect.

[0204] Table 1 Performance of Examples and Comparative Examples

[0205] Example 1 38.5±1.1 92.0±1.5 3.00±0.12 5.00±0.50 40.00±1.20 1.10±0.10 0.80±0.08 0.01±0.002 Example 2 44.2±1.4 88.5±1.6 10.00±0.30 25.00±1.00 2.00±0.10 2.30±0.20 1.90±0.15 0.10±0.006 Example 3 47.8±1.2 94.0±1.2 6.00±0.20 14.00±0.80 18.00±0.80 1.60±0.12 1.10±0.10 0.05±0.004 Example 4 46.5±1.3 95.2±1.1 8.80±0.25 20.00±0.90 8.00±0.40 1.90±0.15 1.40±0.12 0.08±0.005 Comparative Example 1 32.0±1.5 82.0±2.0 12.20±0.45 31.00±1.20 35.00±1.60 2.60±0.20 2.80±0.20 0.04±0.004 Comparative Example 2 34.0±1.4 84.0±1.8 9.50±0.35 27.00±1.10 38.00±1.50 2.10±0.18 2.20±0.18 0.03±0.003 Comparative Example 3 35.0±1.2 88.0±1.5 8.80±0.30 24.00±1.00 22.00±1.00 1.70±0.12 1.80±0.14 0.02±0.003 Comparative Example 4 33.0±1.4 85.0±1.7 10.50±0.40 29.00±1.20 36.00±1.40 2.40±0.18 2.40±0.18 0.08±0.006 Comparative Example 5 31.0±1.6 83.0±1.9 13.00±0.50 33.00±1.30 34.00±1.40 2.50±0.20 2.60±0.20 0.04±0.004 Comparative Example 6 32.5±1.5 84.0±1.8 11.80±0.45 31.00±1.20 37.00±1.40 2.30±0.18 2.50±0.18 0.03±0.004 Comparative Example 7 34.5±1.3 87.0±1.5 10.20±0.38 28.00±1.10 42.00±1.50 1.60±0.12 2.00±0.15 0.02±0.003 Comparative Example 8 36.0±1.2 88.0±1.5 9.80±0.35 26.00±1.00 39.00±1.30 1.50±0.12 1.90±0.15 0.02±0.003 Comparative Example 9 28.0±1.7 78.0±2.2 16.00±0.60 38.00±1.50 44.00±1.80 3.00±0.25 3.50±0.25 0.05±0.005 Comparative Example 10 30.0±1.6 82.0±2.0 14.00±0.55 34.00±1.40 18.00±0.80 2.20±0.18 2.90±0.20 0.04±0.004 Comparative Example 11 36.0±1.3 75.0±2.4 4.50±0.18 8.00±0.70 39.00±1.30 3.50±0.30 3.20±0.25 0.03±0.003

[0206] As can be seen from the performance of the examples and comparative examples in Table 1, the embodiments of the present invention achieve a relatively stable balance between whitening output, heat treatment whiteness retention, composite particle dispersion, melt processing, and heat treatment stability. Example 1 exhibits a lower agglomerate D90, a lower coefficient of variation in area distribution, and a higher melt mass flow rate, demonstrating the processing adaptability of a mild formulation and low-value region processes; Examples 3 and 4 show a more balanced performance in terms of relative whiteness enhancement and heat treatment whiteness retention rate. Comparative Examples 1, 2, and 9 show that when the interface coating component or acrylic structural unit is insufficient, the whiteness output and dispersion index decrease simultaneously; Comparative Examples 3 and 10 show that insufficient polyethylene wax or removal of polyethylene wax affects wetting, dispersion, and flow; Comparative Example 11 shows that after removing the phosphite antioxidant component, the heat treatment whiteness retention rate, mass loss rate, and agglomerate mass fraction deteriorate simultaneously.

[0207] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that any equivalent structural transformations made under the concept of the present invention and using the contents of the specification and drawings of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A highly concentrated master batch of a fluorescent whitening agent, characterized by comprising: The masterbatch comprises, by weight, the following: 15.00–35.00 parts by weight of fluorescent whitening agent OB-1; 5.00–18.00 parts by weight of polyethylene-acrylic acid copolymer; 2.00–8.00 parts by weight of polyethylene wax; 0.05–0.60 parts by weight of pentaerythritol tetra[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]; 0.05–0.60 parts by weight of tris(2,4-di-tert-butylphenyl) phosphite; 38.00–78.00 parts by weight of carrier resin, wherein the carrier resin is polyethylene, or a combination of polyethylene and ethylene-vinyl acetate copolymer; Wherein, at least a portion of the fluorescent whitening agent OB-1 and the polyethylene-acrylic acid copolymer form polyethylene-acrylic acid copolymer-coated fluorescent whitening agent OB-1 composite particles; The content of acrylic structural units in the polyethylene-acrylic acid copolymer is 5.00–20.00 wt%; The polyethylene-acrylic acid copolymer-coated fluorescent whitening agent OB-1 composite microparticles are prepared by a method comprising the following steps: A1. Provides fluorescent whitening agent OB-1, polyethylene-acrylic acid copolymer, polyethylene wax, pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] and tris(2,4-di-tert-butylphenyl) phosphite; A2. Dry the fluorescent whitening agent OB-1 to obtain the dried fluorescent whitening agent OB-1; A3. The dried fluorescent whitening agent OB-1, the polyethylene-acrylic acid copolymer, the polyethylene wax, the pentaerythritol tetra[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] and the tris(2,4-di-tert-butylphenyl) phosphite are melt-wetted and coated to obtain a coated material; A4. After the melt wetting coating is completed, the surface coverage of the polyethylene-acrylic acid copolymer on the fluorescent whitening agent OB-1, calculated according to the arc length ratio of the cross-sectional profile, is 60.00–95.00% in the coated material, and the D50 of the polyethylene-acrylic acid copolymer coated fluorescent whitening agent OB-1 composite particles is 0.50–3.00 μm; A5. Cool and sieve the coated material obtained in step A4 to obtain the polyethylene-acrylic acid copolymer coated fluorescent whitening agent OB-1 composite microparticles.

2. The high-concentration masterbatch of fluorescent whitening agent according to claim 1, characterized in that, In step A1, by weight, the fluorescent whitening agent OB-1 is 100 parts by weight, the polyethylene-acrylic acid copolymer is 20–70 parts by weight, the polyethylene wax is 6–35 parts by weight, the pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] is 0.2–2.5 parts by weight, and the tris(2,4-di-tert-butylphenyl) phosphite is 0.2–2.5 parts by weight.

3. The highly concentrated masterbatch of fluorescent whitening agent according to claim 1, characterized in that, In step A2, the fluorescent whitening agent OB-1 is dried at 80–110°C for 1–3 hours; in step A3, it is mixed at 90–140°C, with an absolute pressure of 0.08–0.12 MPa, under an air or nitrogen atmosphere for 5–20 minutes at a mixing speed of 300–1500 rpm; in step A5, the coated material obtained in step A4 is cooled to 30–60°C and passed through a 40–100 mesh sieve; the D90 of the polyethylene-acrylic acid copolymer-coated fluorescent whitening agent OB-1 composite microparticles obtained in step A5 is 2.00–8.00 μm, and the D90 is not less than the D50 of step A4, and the content of free fluorescent whitening agent OB-1 crystals not covered by the polyethylene-acrylic acid copolymer is 0.10–8.00 wt%.

4. The highly concentrated masterbatch of fluorescent whitening agent according to claim 1, characterized in that, The mass ratio of fluorescent whitening agent OB-1 to polyethylene-acrylic copolymer, calculated based on the polyethylene-acrylic copolymer portion including only the coating shell, is 100:25–100:

55.

5. The highly concentrated masterbatch of fluorescent whitening agent according to claim 1, characterized in that, The mass ratio of polyethylene to ethylene-vinyl acetate copolymer in the carrier resin is 100:0–100:60; the mass ratio of pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] to tris(2,4-di-tert-butylphenyl) phosphite is 1:0.5–1:3.0, and the total amount of both is 0.10–1.20 parts by weight.

6. The highly concentrated masterbatch of fluorescent whitening agent according to claim 1, characterized in that, The masterbatch is granular, with a length of 1.50–5.00 mm, a diameter of 1.00–4.00 mm, and a moisture content of 0.01–0.10 wt%. The aggregate D90 of the polyethylene-acrylic acid copolymer-coated fluorescent whitening agent OB-1 composite microparticles in the masterbatch is 3.00–10.00 μm, and the coefficient of variation of the area distribution of the polyethylene-acrylic acid copolymer-coated fluorescent whitening agent OB-1 composite microparticles on the cross-section of the masterbatch is 5.00–25.00%.

7. A method for preparing a highly concentrated masterbatch of fluorescent whitening agent as described in any one of claims 1-6, characterized in that, Includes the following steps: S1. Provides the prepared polyethylene-acrylic acid copolymer coated fluorescent whitening agent OB-1 composite microparticles, carrier resin, and the remaining polyethylene wax, remaining pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] and remaining tris(2,4-di-tert-butylphenyl) phosphite as determined according to the target total formulation of the masterbatch; S2. Total Mixing and Feeding: The polyethylene-acrylic acid copolymer coated with fluorescent whitening agent OB-1 composite microparticles, the carrier resin, and the remaining polyethylene wax determined according to the target total formulation of the masterbatch, the remaining pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] and the remaining tris(2,4-di-tert-butylphenyl) phosphite are mixed and fed into a twin-screw extruder to obtain the material to be melted and dispersed. S3. Melt extrusion: The material to be melted and dispersed is melted and dispersed at 140–220℃, screw speed 100–600 rpm, and die head pressure 3–15 MPa, and the exhaust is vented at a gauge pressure of -0.09 to -0.03 MPa at the exhaust port to obtain a melt; S4. Filtration and pelletizing: The melt is filtered through an 80–300 mesh filter, cooled, and pelletized to obtain the high-concentration masterbatch of the fluorescent whitening agent.

8. The preparation method according to claim 7, characterized in that, In step S3, the temperatures from zone one to the die head of the twin-screw extruder are 140–170℃, 150–185℃, 160–200℃, 165–210℃, and 170–220℃, respectively; the length-to-diameter ratio of the twin-screw extruder is 32–52, and the screw includes a conveying section, a kneading and dispersing section, a vacuum degassing section, and a metering section. The kneading and dispersing section is located at 30.00–70.00% of the screw length after the feed end.

9. The preparation method according to claim 7, characterized in that, In step S2, the carrier resin is fed in two stages. Specifically, based on the total mass of the carrier resin, 60.00–90.00 wt% of the carrier resin is fed into the main feed port, and the remaining 10.00–40.00 wt% of the carrier resin is fed into the side feed port.

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