A pigment anti-migration dyeing master batch for PLA tea bag and a preparation method thereof

Abstract

This invention discloses a pigment anti-migration dyeing masterbatch for PLA tea bags and its preparation method, belonging to the field of polymer materials technology. It comprises the following components: 35-55 parts carrier; 40-70 parts colorant; 8-20 parts compound anti-migration agent; 2-5 parts dispersant; and 1-4 parts compatibilizer. The carrier is a blend of PLA and PBAT, wherein the mass ratio of PLA to PBAT is (5-8):1. The compound anti-migration agent is composed of layered silicate, cross-linked modified porous starch, and nano-silica, with a mass ratio of 1:(0.5-1.5):(0.3-0.8). This invention significantly inhibits the migration behavior of pigments under high-temperature brewing conditions through the compound anti-migration agent, ensuring the safety of tea bag use.

Description

Technical Field

[0001] This invention relates to the field of polymer materials technology, and in particular to a pigment anti-migration dyeing masterbatch for PLA tea bags and its preparation method. Background Technology

[0002] Polylactic acid (PLA) is a bio-based biodegradable material made from renewable plant resources such as corn and cassava through fermentation. It possesses excellent biocompatibility and compostability, and has been widely used in food packaging, disposable tableware, tea filter bags, and other fields. PLA tea bags are highly favored due to their environmentally friendly properties, becoming an important alternative to traditional nylon and paper tea bags.

[0003] However, commercially available PLA tea bags are mostly white or natural-colored, which fails to meet consumers' needs for classifying and identifying different teas. To give PLA tea bags richer colors, color masterbatches are usually added during the PLA spinning process. However, existing PLA color masterbatches have two prominent problems when applied to tea bags: first, the pigments easily migrate from the tea bag fibers to the tea soup under high-temperature brewing conditions, affecting not only the clarity of the tea soup but also potentially posing food safety risks; second, PLA itself has poor heat resistance and is easily degraded during processing, resulting in poor coloring effects from the color masterbatches.

[0004] To address the aforementioned issues, some improvements have been proposed in the existing technology. For example, Chinese patent application CN114456579A discloses a low-water-absorption PLA masterbatch that improves material properties by adding fillers such as hollow glass microspheres and activated calcium carbonate. However, this technology primarily focuses on reducing water absorption and is not sufficiently targeted at addressing pigment migration issues. Furthermore, the filler system is relatively complex, making it difficult to balance anti-migration effects with processing performance. Patent CN110591316A uses montmorillonite as a barrier agent to improve the barrier properties of PLA films, but montmorillonite alone tends to aggregate in PLA and has limited anchoring effect on pigment molecules, resulting in unsatisfactory anti-migration effects.

[0005] Therefore, this invention proposes a pigment anti-migration dyeing masterbatch for PLA tea bags and its preparation method. Summary of the Invention

[0006] The purpose of this invention is to address the shortcomings of existing technologies by proposing a pigment anti-migration dyeing masterbatch for PLA tea bags and its preparation method.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] On one hand, the present invention proposes a pigment anti-migration dyeing masterbatch for PLA tea bags, comprising the following components:

[0009] 35-55 copies of the carrier;

[0010] Colorant 40-70 parts;

[0011] Compound anti-migration agent 8-20 parts;

[0012] 2-5 parts dispersant;

[0013] 1-4 parts compatibilizer;

[0014] The carrier is a blend of PLA and PBAT, wherein the mass ratio of PLA to PBAT is (5-8):1;

[0015] The compound anti-migration agent is composed of layered silicate, cross-linked modified porous starch and nano silica, with a mass ratio of 1:(0.5-1.5):(0.3-0.8).

[0016] Preferably, the colorant is a surface-coated organic pigment, which is selected from at least one of phthalocyanine blue, phthalocyanine green, quinacridone red, and isoindoline yellow, and its average particle size D50 is controlled between 0.5 and 2.0 μm.

[0017] Preferably, the layered silicate is organically modified montmorillonite or palygorskite, with an interlayer spacing d001 of 2.5-4.0 nm; the cross-linked modified porous starch has a specific surface area of ​​50-150 m². 2 / g, with an average pore size of 5-15nm, and a thermal weight loss of 1% at a temperature ≥250℃; the particle size of the nano-silica is 20-80nm.

[0018] Preferably, the dispersant is at least one of polyethylene wax, oxidized polyethylene wax, or ethylene bis-stearamide; the compatibilizer is glycidyl methacrylate-grafted PLA or maleic anhydride-grafted PLA.

[0019] Preferably, it further includes 0.5-3 parts of antioxidant and 0.5-2 parts of lubricant; the antioxidant is a compound of hindered phenolic antioxidant and phosphite antioxidant; the lubricant is calcium stearate or zinc stearate.

[0020] On the other hand, the present invention proposes a method for preparing pigment anti-migration dyeing masterbatch for PLA tea bags, comprising the following steps:

[0021] (1) Pretreatment: Layered silicate, cross-linked modified porous starch and nano silica are mixed in proportion and vacuum dried at 80-100℃ for 2-4h to obtain a compound anti-migration agent;

[0022] (2) High-speed mixing: Add the carrier, colorant, compound anti-migration agent, dispersant, compatibilizer and other additives into a high-speed mixer according to the formula, and mix at a speed of 500-1500 rpm for 5-15 min to obtain the premix;

[0023] (3) Melt extrusion: Add the premix to a twin-screw extruder, control the extrusion temperature to 150-180℃ and the screw speed to 200-400rpm, and carry out melt blending extrusion;

[0024] (4) Granulation and drying: After the extruded strip is cooled by water and granulated, it is vacuum dried at 50-70℃ for 4-8 hours to obtain the pigment anti-migration dyeing masterbatch.

[0025] Preferably, the twin-screw extruder in step (3) has nine temperature control zones, and the temperature of each zone is set as follows: Zone 1 150-155℃, Zone 2 155-160℃, Zone 3 160-165℃, Zone 4 165-170℃, Zone 5 170-175℃, Zone 6 175-180℃, Zone 7 170-175℃, Zone 8 165-170℃, Zone 9 160-165℃, and the die head temperature is 165-170℃.

[0026] Preferably, the pretreatment in step (1) further includes intercalation treatment of the layered silicate before mixing: the layered silicate is dispersed in anhydrous ethanol, an intercalating agent is added, and the mixture is stirred at 60-80°C for 4-8 hours. After filtration, washing, and drying, the organic modified layered silicate is obtained; the intercalating agent is hexadecyltrimethylammonium bromide or dodecyldimethylbenzylammonium chloride.

[0027] The present invention has the following technical effects:

[0028] This invention significantly inhibits the migration behavior of pigments under high-temperature brewing conditions through a compound anti-migration agent, ensuring the safety of tea bags.

[0029] This invention uses PLA and PBAT blend as a carrier and adds compatibilizer to improve the flexibility and processing fluidity of the masterbatch, so that the colorant can be evenly dispersed during spinning and improve the coloring effect.

[0030] This invention uses cross-linked modified porous starch, which solves the problem of easy thermal decomposition of ordinary starch at PLA processing temperature, ensuring the thermal stability and long-term safety of the material. Detailed Implementation

[0031] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0032] Raw material source:

[0033] PLA: NatureWorks, USA, grade 4032D, weight-average molecular weight 2.0 × 10⁻⁶ 5 ;

[0034] PBAT: Lanshan Tunhe, brand name TH801;

[0035] Phthalocyanine Blue Pigment: BASF, Germany, grade K7090, D50=1.2μm, rosin surface coating treatment;

[0036] Quinacridone red pigment: BASF, Germany, brand name F5RK, D50=1.5μm, rosin surface coating treatment;

[0037] Organically modified montmorillonite: Zhejiang Fenghong, grade DK4, interlayer spacing 3.2nm, modified with organic quaternary ammonium salt;

[0038] Ratosite: Zhongxiang, Hubei Province, industrial grade, treated with hexadecyltrimethylammonium bromide intercalation, interlayer spacing 3.5 nm;

[0039] Cross-linked modified porous starch: Shandong Yousuo, brand name KL-100, specific surface area 100m² 2 / g, average pore size 10nm, 1% thermal weight loss at 258℃;

[0040] Nano silica: Evonik, Germany, grade A200, particle size 40nm;

[0041] Polyethylene wax: Samsung Korea, grade PE-520;

[0042] Ethylene bis-stearamide: Shanghai Shanpu, industrial grade;

[0043] Glycidyl methacrylate grafted PLA: prepared in the laboratory, grafting rate 1.2%;

[0044] Maleic anhydride-grafted PLA: prepared in the laboratory, grafting rate 1.0%;

[0045] Antioxidant 1010 / 168 compound: BASF, mass ratio 1:2;

[0046] Calcium stearate: Shijiazhuang Zhongtian, industrial grade.

[0047] Example 1

[0048] A pigment anti-migration dyeing masterbatch for PLA tea bags, by weight, comprises: 35 parts PLA, 5 parts PBAT; 55 parts phthalocyanine blue pigment; 12 parts compound anti-migration agent, composed of organic modified montmorillonite, cross-linked modified porous starch, and nano-silica in a mass ratio of 1:1:0.5; 3 parts polyethylene wax; 2 parts glycidyl methacrylate grafted PLA; 1.5 parts antioxidant 1010 / 168 compound; and 1 part calcium stearate.

[0049] Preparation method:

[0050] (1) Pretreatment: Organic modified montmorillonite, cross-linked modified porous starch and nano silica are mixed in proportion and vacuum dried at 90°C for 3 hours to obtain a compound anti-migration agent;

[0051] (2) High-speed mixing: Add PLA, PBAT, phthalocyanine blue pigment, compound anti-migration agent, polyethylene wax, grafted PLA, antioxidant and calcium stearate to a high-speed mixer and mix at 1000 rpm for 10 min;

[0052] (3) Melt extrusion: Add the premixed material to the twin-screw extruder. The screw length-to-diameter ratio L / D = 40. The temperature of each zone is set as follows: Zone 1 152℃, Zone 2 158℃, Zone 3 163℃, Zone 4 168℃, Zone 5 172℃, Zone 6 178℃, Zone 7 172℃, Zone 8 168℃, Zone 9 162℃, Die head 168℃, and screw speed 300 rpm.

[0053] (4) Granulation and drying: After the extruded strip is cooled by water and granulated, it is vacuum dried at 60°C for 6 hours to obtain pigment anti-migration dyeing masterbatch.

[0054] (5) Spinning application: The obtained dyeing masterbatch is mixed with PLA base material at a mass ratio of 1:20, and then spun at 210℃ using a melt spinning machine at a spinning speed of 1200m / min to obtain PLA tea bag fiber.

[0055] Example 2

[0056] This embodiment is basically the same as Example 1, except that the mass ratio of each component in the compound anti-migration agent is adjusted to 1:1.5:0.8, while the other components and preparation methods are the same.

[0057] Example 3

[0058] This embodiment is basically the same as Embodiment 1, except that the colorant is replaced with 55 parts of quinacridone red pigment, while the other components and preparation methods are the same.

[0059] Example 4

[0060] This embodiment is basically the same as Example 1, except that the mass ratio of PLA to PBAT in the carrier is adjusted to 6:1, with 36 parts of PLA and 6 parts of PBAT. The other components and preparation methods are the same.

[0061] Example 5

[0062] This embodiment is basically the same as Example 1, except that the amount of compound anti-migration agent is adjusted to 18 parts, the ratio of the three components is kept at 1:1:0.5, and the other components and preparation methods are the same.

[0063] Comparative Example 1

[0064] This comparative example is basically the same as Example 1, except that no compound anti-migration agent is added, that is, the formulation does not contain organic modified montmorillonite, cross-linked modified porous starch and nano silica. The amount of carrier and other additives is adjusted accordingly, and the other preparation methods are the same.

[0065] Comparative Example 2

[0066] This comparative example is basically the same as Example 1, except that the compound anti-migration agent is replaced with an equal amount of single-component organic modified montmorillonite, that is, it contains only layered silicate and does not contain porous starch and nano silica. The other preparation methods are the same.

[0067] Comparative Example 3

[0068] This comparative example is basically the same as Example 1, except that the compound anti-migration agent is replaced with an equal amount of hollow glass microspheres, activated calcium carbonate and quartz powder in a mass ratio of 2:11:4. The other preparation methods are the same.

[0069] Comparative Example 4

[0070] This comparative example is basically the same as Example 1, except that the compound anti-migration agent is replaced with an equal amount of cross-linked modified porous starch, that is, it contains only porous starch and does not contain layered silicate and nano silica. The other preparation methods are the same.

[0071] Performance testing methods:

[0072] (1) Total migration test: Referring to GB 31604.8-2021 "National Food Safety Standard for Determination of Total Migration of Food Contact Materials and Articles", the dyeing masterbatch and PLA base material were mixed at a mass ratio of 1:20 and spun into tea bag fibers. 10g of fiber was cut into pieces, soaked in 200mL of 95℃ hot water for 30min, the soaking liquid was evaporated, the residue was weighed, and the total migration was calculated. Each sample was tested 3 times and the average value was taken.

[0073] (2) Specific migration test of colorant: Referring to GB 31604.1-2015 "National Food Safety Standard General Rules for Migration Test of Food Contact Materials and Articles", the content of organic pigments in the 95℃ hot water soaking solution was determined by high performance liquid chromatography-mass spectrometry (HPLC-MS), and the detection limit was 0.01 mg / L.

[0074] (3) Tea turbidity test: After brewing the tea bag fiber according to the above conditions, take the tea soup and measure the turbidity value (NTU) at room temperature using a turbidity meter (Shanghai Xinrui, WGZ-200 type). Each sample is tested 3 times and the average value is taken.

[0075] (4) Tinting strength test: Refer to GB / T 5211.19-2015 "General test methods for pigments and extender pigments - Part 19: Determination of tinting strength", and use a standard white board as a reference to measure the color difference value ΔE of the spun fiber. The larger the ΔE value, the stronger the tinting strength.

[0076] (5) Thermal stability test: Thermogravimetric analyzer (TA Q500) was used in a nitrogen atmosphere with a heating rate of 10℃ / min to determine the mass loss rate of the sample at 200℃.

[0077] Performance test results:

[0078] The dyeing masterbatches obtained in Examples 1-5 and Comparative Examples 1-4 were respectively made into PLA tea bag fibers according to the method of step (5) in Example 1. The performance was evaluated according to the aforementioned test method, and the results are shown in Table 1.

[0079] Table 1 Performance test results of each embodiment and comparative example

[0080]

[0081] As can be seen from the data in Table 1:

[0082] (1) The total migration amount in Examples 1-5 was 4.9-6.7 mg / dm³. 2 All of these values ​​meet the national standard of ≤10mg / dm³. 2 The required concentration is far lower than the 28.7 mg / dm³ of Comparative Example 1. 2 The total migration amount in Comparative Example 4 was 19.8 mg / dm³. 2 The result was still significantly higher than in the example, proving that a single component cannot achieve a synergistic effect.

[0083] (2) The specific migration amount of the colorant in Examples 1-5 was not detected (<0.01 mg / L), while it was detected to varying degrees in Comparative Examples 1, 2 and 4, indicating that the triple mechanism of blocking, adsorption and filling of the present invention can lock the pigment molecules more thoroughly.

[0084] (3) The turbidity of the tea soup in Examples 1-5 was ≤0.9 NTU, which was much lower than that of Comparative Example 1 (3.5 NTU), and the clarity of the tea soup was significantly improved. The turbidity of Comparative Example 3 was 1.6 NTU, which was better than that of Comparative Example 1, but still higher than that of the embodiments of the present invention.

[0085] (4) Regarding thermal stability, the weight loss of Examples 1-5 at 200℃ was less than 1%, while that of Comparative Example 1 was as high as 1.52%, indicating that the addition of the anti-migration agent helps to improve the thermal stability of the material. The cross-linked modified porous starch did not undergo significant decomposition at the processing temperature.

[0086] (5) Compared with Comparative Example 3, Examples 1-5 have significant advantages in terms of total migration, coloring power, and tea turbidity, proving that the anti-migration system of the present invention is superior to the filler combination in the prior art.

[0087] Example 1 of efficacy verification: Effect of different anti-migration agent ratios

[0088] To further investigate the effect of the proportion of each component in the compound anti-migration agent on its performance, based on Example 1, the amount of layered silicate was kept at 1 part, and the amount of cross-linked modified porous starch and nano silica was adjusted to keep the total amount of the three at 3 parts. A series of samples were prepared and tested, and the results are shown in Table 2.

[0089] Table 2 Performance test results for different anti-migration agent ratios

[0090]

[0091] As shown in Table 2, when the mass ratio of layered silicate, cross-linked modified porous starch, and nano-silica is in the range of 1:(0.5-1.5):(0.3-0.8), the total migration is ≤6.8 mg / dm³. 2 The tea infusion turbidity was ≤1.0 NTU, which is at a low level; beyond this range, the anti-migration effect decreased. This indicates that the synergistic effect of the three components has an optimal ratio range, and too much or too little will affect the integrity of the barrier network.

[0092] Example 2: Effect of cross-linking modification on the thermal stability of porous starch

[0093] To verify the necessity of cross-linking modification, masterbatches were prepared using unmodified ordinary corn starch and cross-linked modified porous starch according to the formulation of Example 1, and their thermal stability and final performance during processing were tested. The results are shown in Table 3.

[0094] Table 3. Effect of starch modification method on performance

[0095]

[0096] As shown in Table 3, unmodified ordinary starch underwent significant thermal decomposition during processing, leading to yellowing of the masterbatch, increased thermal weight loss, and higher total migration and turbidity compared to the cross-linked modified sample. This indicates that cross-linked modified porous starch is crucial for ensuring the thermal stability and anti-migration effect of the material.

[0097] Example 3: Effect of spinning process on fiber properties

[0098] Using the masterbatch obtained in Example 1 as the subject, the effect of different spinning temperatures on fiber properties was investigated, and the results are shown in Table 4.

[0099] Table 4 Effect of spinning temperature on fiber properties

[0100]

[0101] As shown in Table 4, good spinnability and fiber properties can be obtained by controlling the spinning temperature in the range of 200-220℃. Excessive temperature will lead to PLA degradation and increase migration.

[0102] Based on the above experimental results, this invention successfully constructs a triple pigment migration inhibition system through the synergistic combination of layered silicate, cross-linked modified porous starch, and nano-silica, which involves blocking, adsorbing, and filling pigments. Layered silicate forms a physical barrier to extend the migration path, porous starch adsorbs and anchors pigment molecules, and nano-silica fills the gaps between molecular chains to densify the structure. All three are indispensable; neither a single component nor a combination of any two cannot achieve the same effect. Compared with existing technologies, this invention has significant advantages in terms of total migration amount and tea infusion turbidity.

[0103] Furthermore, this invention addresses the problem of easy thermal decomposition of ordinary starch at PLA processing temperatures by employing cross-linked modified porous starch. The use of PLA / PBAT blending with the addition of a compatibilizer improves the carrier's flexibility and processability. A gradient temperature-controlled extrusion process ensures thorough mixing of all components. The entire technical solution is logically sound, highly feasible, and the resulting product fully meets the safety requirements for food contact materials.

[0104] In summary, the pigment anti-migration dyeing masterbatch for PLA tea bags provided by this invention and its preparation method achieve excellent pigment locking effect through innovative compound anti-migration agent design. The resulting tea bags are safe and environmentally friendly under high-temperature brewing conditions, and the tea soup is clear, showing good prospects for industrial application.

[0105] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A pigment anti-migration dyeing masterbatch for PLA tea bags, characterized in that, Includes the following components: 35-55 copies of the carrier; Colorant 40-70 parts; Compound anti-migration agent 8-20 parts; 2-5 parts dispersant; 1-4 parts compatibilizer; The carrier is a blend of PLA and PBAT, wherein the mass ratio of PLA to PBAT is (5-8):1; The compound anti-migration agent is composed of layered silicate, cross-linked modified porous starch and nano silica, with a mass ratio of 1:(0.5-1.5):(0.3-0.8).

2. The pigment anti-migration dyeing masterbatch for PLA tea bags according to claim 1, characterized in that, The colorant is an organic pigment that has undergone surface coating treatment. The organic pigment is selected from at least one of phthalocyanine blue, phthalocyanine green, quinacridone red, and isoindoline yellow, and its average particle size D50 is controlled between 0.5 and 2.0 μm.

3. The pigment anti-migration dyeing masterbatch for PLA tea bags according to claim 1, characterized in that, The layered silicate is organically modified montmorillonite or raptosite, with an interlayer spacing d001 of 2.5-4.0 nm; the cross-linked modified porous starch has a specific surface area of ​​50-150 m². 2 / g, with an average pore size of 5-15nm, and a thermal weight loss of 1% at a temperature ≥250℃; the particle size of the nano-silica is 20-80nm.

4. The pigment anti-migration dyeing masterbatch for PLA tea bags according to claim 1, characterized in that, The dispersant is at least one of polyethylene wax, oxidized polyethylene wax, or ethylene bis-stearamide; the compatibilizer is glycidyl methacrylate-grafted PLA or maleic anhydride-grafted PLA.

5. The pigment anti-migration dyeing masterbatch for PLA tea bags according to claim 1, characterized in that, It also includes 0.5-3 parts of antioxidant and 0.5-2 parts of lubricant; the antioxidant is a compound of hindered phenolic antioxidant and phosphite antioxidant; the lubricant is calcium stearate or zinc stearate.

6. A method for preparing a pigment anti-migration dyeing masterbatch for PLA tea bags as described in any one of claims 1-5, characterized in that, Includes the following steps: (1) Pretreatment: Layered silicate, cross-linked modified porous starch and nano silica are mixed in proportion and vacuum dried at 80-100℃ for 2-4h to obtain a compound anti-migration agent; (2) High-speed mixing: Add the carrier, colorant, compound anti-migration agent, dispersant, compatibilizer and other additives into a high-speed mixer according to the formula, and mix at a speed of 500-1500 rpm for 5-15 min to obtain the premix; (3) Melt extrusion: Add the premix to a twin-screw extruder, control the extrusion temperature to 150-180℃ and the screw speed to 200-400rpm, and carry out melt blending extrusion; (4) Granulation and drying: After the extruded strip is cooled by water and granulated, it is vacuum dried at 50-70℃ for 4-8 hours to obtain the pigment anti-migration dyeing masterbatch.

7. The method for preparing pigment anti-migration dyeing masterbatch for PLA tea bags according to claim 6, characterized in that, The twin-screw extruder in step (3) has nine temperature control zones, and the temperature of each zone is set as follows: Zone 1 150-155℃, Zone 2 155-160℃, Zone 3 160-165℃, Zone 4 165-170℃, Zone 5 170-175℃, Zone 6 175-180℃, Zone 7 170-175℃, Zone 8 165-170℃, Zone 9 160-165℃, and the die head temperature is 165-170℃.

8. The method for preparing pigment anti-migration dyeing masterbatch for PLA tea bags according to claim 6, characterized in that, The pretreatment in step (1) further includes intercalation treatment of the layered silicate before mixing: the layered silicate is dispersed in anhydrous ethanol, an intercalating agent is added, and the mixture is stirred at 60-80℃ for 4-8 hours. After filtration, washing and drying, organic modified layered silicate is obtained; the intercalating agent is hexadecyltrimethylammonium bromide or dodecyldimethylbenzylammonium chloride.

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