Red playing card sheet based on PVC and preparation method thereof

Abstract

The invention relates to the field of polymer composite materials, in particular to a red playing card sheet based on PVC and a preparation method of the red playing card sheet. The red playing card sheet based on PVC is prepared from the following components: PVC resin, modified porous chitin elastic particles, a compound heat stabilizer, phthalocyanine red, an antibacterial agent and polyethylene wax. Butyl acrylate is subjected to a prepolymerization reaction, then a chitin solution is added to adjust the pH value, the heat preservation reaction is continued, butyl acrylate is firstly prepolymerized to form a poly (butyl acrylate) seed body, and then in the pH value adjusting process, the poly (butyl acrylate) seed body is polymerized to form a poly (butyl acrylate) seed body; chitin wraps a poly (butyl acrylate) seed body under the action of an emulsifier lauryl sodium sulfate to form a porous shell layer, porous chitin elastic particles with mutually interwoven chitin and poly (butyl acrylate) are formed, and the toughness and tensile strength of PVC can be greatly improved by blending, melting and extruding the porous chitin elastic particles and subsequent PVC.

Description

Technical Field

[0001] The invention relates to the field of polymer composite materials, in particular to a PVC-based red playing card sheet and a preparation method thereof. Background Art

[0002] Playing cards are a widely used entertainment tool, and the performance of their sheet material directly affects the user experience and service life. Traditional playing cards are mostly made of paper or plastic substrates. Due to the characteristics of paper fiber structure, it is easy to absorb moisture and deform, and the edges are easily worn and delaminated. After long-term use, the surface coating is easy to peel off, resulting in blurred patterns, and it is easy to breed mold in a humid environment. Although plastic sheets have certain waterproof properties, they are hard and have poor flexibility. Repeated bending can easily cause permanent creases or even breakage.

[0003] In recent years, polyvinyl chloride (PVC) has gradually been used in the manufacture of playing cards due to its excellent plasticity, weather resistance, waterproof and stain-resistant properties, and good feel. However, it also has the problem of high hardness and poor flexibility of the plastic substrate, which is prone to permanent creases after bending. In addition, the surface adhesion of PVC material is poor, and it is easy to migrate when using pigments to color it, and the coloring stability is poor. Summary of the Invention

[0004] In order to solve the above technical defects, the present invention has developed a method for preparing red playing card sheets based on PVC. By preparing modified porous chitosan elastic particles and compounding heat stabilizers, and blending them with PVC, the sheet obtained has excellent toughness and tensile strength, and good pigment coloring stability.

[0005] A PVC-based red playing card sheet, characterized by comprising the following components: 50-70 parts by weight of PVC resin, 6-10 parts by weight of modified porous chitosan elastic particles, 2-3 parts by weight of a composite heat stabilizer, 1-3 parts by weight of phthalocyanine red, 0.5-2 parts by weight of an antibacterial agent, and 0.5-1 part by weight of polyethylene wax; The composite heat stabilizer is prepared by slowly adding a lanthanum nitrate solution to an L-glutathione solution, adjusting the pH, heating and stirring, centrifuging, filtering, drying, and mixing with pentaerythritol.

[0006] A method for preparing a red playing card sheet based on PVC, comprising the following steps: S1: Preparation of porous chitosan elastic microparticles Chitosan powder is sequentially subjected to alkaline soaking and stirring treatment, acid soaking treatment, and hydrogen peroxide soaking treatment to obtain purified chitosan powder, which is then dispersed in an alkaline composite aqueous solution and repeatedly subjected to multiple freeze-thaw operations to obtain a chitosan solution. Butyl acrylate and dicyclopentadiene acrylate are added to a mixed solution of sodium lauryl sulfate, potassium carbonate, and deionized water in a nitrogen atmosphere. After heating in a water bath, azobisisobutyronitrile is added to maintain the temperature, and then the chitosan solution is added. The temperature is slowly increased to adjust the pH to neutral, the temperature is continued to be maintained, and the mixture is filtered, washed, and dried to obtain porous chitosan elastic microparticles. S2: Preparation of compound heat stabilizer Lanthanum nitrate hexahydrate is dissolved in deionized water to prepare a lanthanum nitrate solution, L-glutathione is dissolved in deionized water to prepare an L-glutathione solution, the lanthanum nitrate solution is added to the L-glutathione solution under a nitrogen atmosphere with stirring, the pH is adjusted, the temperature is increased with stirring, the mixture is centrifuged, filtered, dried, and then mixed with pentaerythritol to obtain a composite thermal stabilizer; S3: Modification of porous chitosan elastic particles and co-extrusion of PVC composites Methyl N,N-dihydroxyethyl-3-aminopropionate, porous chitosan elastic particles and p-toluenesulfonic acid are reacted at high temperature in a nitrogen atmosphere to obtain modified porous chitosan elastic particles. PVC resin, modified porous chitosan elastic particles and a compounded heat stabilizer are heated and mixed, then placed in a vacuum for treatment. The mixture is then mixed with phthalocyanine red, an antibacterial agent and polyethylene wax, melt-blended and extruded into granules, and then placed in a calender for calendering to obtain red playing card sheets.

[0007] Furthermore, step S1 of preparing porous chitosan elastic particles comprises the following steps: S1.1: 8-10 parts by weight of chitosan powder are dispersed in 60-80 parts by weight of a 5 wt% NaOH aqueous solution and stirred vigorously for 20-24 hours. The precipitate is filtered and rinsed with distilled water until neutral. The precipitate is then dispersed in 60-80 parts by weight of an 8 wt% HCl aqueous solution and soaked for 15-20 hours. The precipitate is filtered and rinsed with distilled water until neutral. The precipitate is then dispersed in 4-6 wt% hydrogen peroxide and heated to 75-80°C and soaked for 6-8 hours. The precipitate is filtered and washed with distilled water until neutral and then dried to obtain purified chitosan powder. S1.2: Disperse the purified chitosan powder in an alkaline composite aqueous solution at a mass ratio of 1:(8-10), freeze the mixture at -50°C to -45°C for 4-5 hours, and then thaw the mixture at room temperature. Repeat the freeze-thaw operation 3-4 times under the same conditions to obtain a chitosan solution. S1.3: Take 100-120 parts by weight of deionized water, add 3-5 parts by weight of sodium lauryl sulfate and 2-4 parts by weight of potassium carbonate, and stir until completely dissolved. Then, introduce nitrogen to exhaust the air in the container, then add 15-20 parts by weight of butyl acrylate and 0.3-0.5 parts by weight of dicyclopentadiene acrylate and stir evenly. Then, heat in a water bath to 60-65°C, add 0.1-0.2wt% of azobisisobutyronitrile and stir for 4-5 minutes, keep warm for 15-20 minutes, then add 40-50 parts by weight of chitosan solution and stir at a stirring speed of 1800-2000 rpm for 3-4 minutes. After heating to 80-85°C, add 12wt% hydrogen chloride solution within 25-30 minutes to neutralize the solution. Continue to keep warm for 1-1.5 hours, then filter out the solid matter, rinse with distilled water until neutral, and obtain porous chitosan elastic particles after drying.

[0008] Furthermore, the preparation of the composite heat stabilizer in step S2 comprises the following steps: S2.1: Add 4-8 parts by weight of lanthanum nitrate hexahydrate to 50-75 parts by weight of deionized water and stir magnetically until the solution becomes transparent to obtain a lanthanum nitrate solution. Under a nitrogen atmosphere, add 3-6 parts by weight of L-glutathione to 60-80 parts by weight of deionized water and stir until the L-glutathione is completely dissolved to obtain an L-glutathione solution. S2.2: Under the conditions of 35-40°C, 250-300 rpm, and nitrogen atmosphere, slowly add the lanthanum nitrate solution prepared in step S2.1 to the L-glutathione solution prepared in step S2.1 over 30-40 minutes, then add ammonia water to adjust the pH to 8-8.5, raise the temperature to 60-65°C, and stir at this constant temperature for 3-5 hours. Then, place the mixture in a centrifuge and centrifuge at 4000-4500 rpm for 10-15 minutes. Filter the solid matter, rinse it with deionized water 2-3 times, and then place it at 60-65°C under vacuum and dry it to constant weight. Grind it into powder to obtain a glutathione lanthanum complex. Mix the glutathione lanthanum complex and pentaerythritol in a mass ratio of 1:(2-3) to obtain a composite thermal stabilizer.

[0009] Furthermore, step S3 of modifying the porous chitosan elastic particles and co-extruding the PVC composite material comprises the following steps: S3.1: Place N,N-dihydroxyethyl-3-aminopropionic acid methyl ester and porous chitin elastic microparticles in a container at a mass ratio of 1:(4-6), continuously introduce nitrogen to expel air from the container, add 0.5-0.6 wt% p-toluenesulfonic acid, and stir evenly. Then, heat to 115-120°C and maintain for 6-8 hours. Collect the solid reactant by filtration, wash with methanol 2-3 times, and then dry at 65-70°C for 2-3 hours to obtain modified porous chitin elastic microparticles. S3.2: 50-70 parts by weight of PVC resin, 6-10 parts by weight of modified porous chitin elastic particles, and 2-3 parts by weight of a compounded heat stabilizer are mixed at a high speed at 100-120°C and 600-800 rpm for 10-15 minutes, then transferred to a vacuum filtration bottle and evacuated to a pressure of 10-15 kPa for 10-15 minutes. The mixture is then mixed with 1-3 parts by weight of phthalocyanine red, 0.5-2 parts by weight of an antibacterial agent, and 0.5-1 parts by weight of polyethylene wax, added to a twin-screw extruder for melt blending, cooled, granulated, and dried to obtain a PVC composite masterbatch; S3.3: Add the PVC composite masterbatch into the mold and place it on a four-roll calender. Adjust the roller temperature to 160-180°C and calender it to a thickness of 0.3-0.5 mm to obtain red playing card sheets.

[0010] Furthermore, the alkaline composite aqueous solution of step S1.2 is prepared by mixing NaOH, urea and deionized water in a mass ratio of 1: (0.4-0.5): (8-10).

[0011] Furthermore, the antibacterial agent in step S3.2 is nano-ZnO.

[0012] Furthermore, in step S3.2, the melt blending temperature of the twin-screw extruder is 160-180° C., the screw aspect ratio of the twin-screw extruder is 35-45, and the rotation speed is 150-200 rpm.

[0013] The beneficial effects are as follows: 1. The present invention adds butyl acrylate and dicyclopentadiene acrylate to a mixed solution of sodium lauryl sulfate, potassium carbonate and deionized water for a prepolymerization reaction, then adds a chitosan solution for high-speed stirring, slowly raises the temperature to adjust the pH to neutral, and continues to keep the temperature for reaction. During this process, butyl acrylate is first prepolymerized to form a polybutyl acrylate seed body. Then, during the pH adjustment process, chitosan wraps the polybutyl acrylate seed body under the action of an emulsifier, sodium lauryl sulfate, to form a porous shell layer. After continuing to keep the temperature, polybutyl acrylate continues to grow under the induction of the polybutyl acrylate seed body in the porous shell structure layer, forming porous chitosan elastic particles in which chitosan and polybutyl acrylate are intertwined. The porous chitosan elastic particles can be blended with PVC and melt-extruded subsequently to significantly improve the toughness and tensile strength of the PVC.

[0014] The invention prepares a glutathione-lanthanum complex by combining lanthanum nitrate hexahydrate and L-glutathione, and then compounding the glutathione-lanthanum complex with pentaerythritol to obtain a compound heat stabilizer. The L-glutathione contains thiol, amino and carboxyl groups, wherein the carboxyl and thiol groups can be complexed with lanthanum to form a stable glutathione-lanthanum complex. When the glutathione-lanthanum complex is blended and melted with PVC, the rich group structure of the glutathione-lanthanum complex and the lanthanum can synergistically absorb generated HCl, thereby ensuring that the complex will not decompose during the processing and molding process. The combination with pentaerythritol can improve the rheological properties during blending, prevent uneven dispersion of the compound heat stabilizer, and further enhance the heat stability of the PVC.

[0015] The present invention modifies the surface of the porous chitin elastic particles by using methyl N,N-dihydroxyethyl-3-aminopropionate, which can greatly improve the surface polarity of the porous chitin elastic particles and the dispersion performance in the PVC matrix, so that the porous chitin elastic particles can better play a role in the PVC. In addition, the combination with chitin can better enable subsequent phthalocyanine red to be colored, prevent color difference, and improve coloring stability.

[0016] The present invention heats and mixes PVC resin, porous chitosan elastic particles and a compounded heat stabilizer, and then places the mixture in a vacuum for treatment, so that the softened PVC resin penetrates into the pores of the porous chitosan elastic particles through vacuum impregnation, thereby strengthening the bonding force of the matrix and further improving the toughness and tensile strength of the finished PVC. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 The present invention is a flow chart of a method for preparing a PVC-based red playing card sheet material used in an embodiment of the present invention. DETAILED DESCRIPTION

[0018] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0019] Example 1: A red playing card sheet based on PVC and its preparation method, such as Figure 1 As shown, the following steps are included: S1: Preparation of porous chitosan elastic microparticles S1.1: 8 parts by weight of chitosan powder were dispersed in 60 parts by weight of a 5 wt% aqueous solution of NaOH and stirred vigorously for 20 hours. The precipitate was filtered and rinsed with distilled water until neutral. The precipitate was then dispersed in 60 parts by weight of an 8 wt% aqueous solution of HCl and soaked for 15 hours. The precipitate was filtered and rinsed with distilled water until neutral. The precipitate was then dispersed in 4 wt% hydrogen peroxide and heated to 75°C and soaked for 6 hours. The precipitate was filtered and washed with distilled water until neutral and then dried to obtain purified chitosan powder. S1.2: Dispersing the purified chitosan powder in an alkaline composite aqueous solution at a mass ratio of 1:8, wherein the alkaline composite aqueous solution is prepared by mixing NaOH, urea, and deionized water at a mass ratio of 1:0.4:8, followed by freezing at -50°C for 4 hours and thawing at room temperature. The freeze-thaw operation is repeated three times under the same conditions to obtain a chitosan solution; S1.3: Take 100 parts by weight of deionized water, add 3 parts by weight of sodium lauryl sulfate and 2 parts by weight of potassium carbonate and stir until completely dissolved, introduce nitrogen to exhaust the air in the container, then add 15 parts by weight of butyl acrylate and 0.3 parts by weight of dicyclopentadiene acrylate and stir evenly, then heat in a water bath to 60°C, add 0.1wt% of azobisisobutyronitrile and stir for 4 minutes, keep warm for 15 minutes, then add 40 parts by weight of chitosan solution and stir at a stirring speed of 1800 rpm for 3 minutes, heat to 80°C, add 12wt% hydrogen chloride solution within 25 minutes to make the solution neutral, continue to keep warm for 1 hour, then filter out the solid matter, rinse with distilled water until neutral, and obtain porous chitosan elastic particles after drying.

[0020] S2: Preparation of compound heat stabilizer S2.1: 4 parts by weight of lanthanum nitrate hexahydrate were added to 50 parts by weight of deionized water and magnetically stirred until the solution became transparent to obtain a lanthanum nitrate solution. Under a nitrogen atmosphere, 3 parts by weight of L-glutathione were added to 60 parts by weight of deionized water and stirred until the L-glutathione was completely dissolved to obtain an L-glutathione solution. S2.2: Under the conditions of 35°C, 250rpm and nitrogen atmosphere, slowly add the lanthanum nitrate solution prepared in step S2.1 to the L-glutathione solution prepared in step S2.1, and complete the addition within 30 minutes. Then, add ammonia water to adjust the pH to 8. After heating to 60°C and stirring at constant temperature for 3 hours, place it in a centrifuge and centrifuge at a speed of 4000rpm for 10 minutes. Filter the solid matter and rinse it with deionized water twice. Then place it at 60°C and vacuum dry it to constant weight. Grind it into powder to obtain glutathione lanthanum complex. Mix the glutathione lanthanum complex and pentaerythritol in a mass ratio of 1:2 to obtain a composite thermal stabilizer.

[0021] S3: Modification of porous chitosan elastic particles and co-extrusion of PVC composites S3.1: Methyl N,N-dihydroxyethyl-3-aminopropionate and porous chitosan elastic microparticles were placed in a container at a mass ratio of 1:4. Nitrogen was continuously introduced to expel air from the container. 0.5 wt% of p-toluenesulfonic acid was added and stirred evenly. The mixture was then heated to 115°C and maintained for 6 hours. The solid reactant was collected by filtration, washed twice with methanol, and then dried at 65°C for 2 hours to obtain modified porous chitosan elastic microparticles. S3.2: 50 parts by weight of PVC resin, 6 parts by weight of modified porous chitosan elastic particles, and 2 parts by weight of a compounded thermal stabilizer were mixed at high speed at 100°C and 600 rpm for 10 minutes, then transferred to a vacuum filtration bottle and evacuated to a pressure of 10 kPa for 10 minutes. The mixture was then mixed with 1 part by weight of phthalocyanine red, 0.5 part by weight of nano-ZnO, and 0.5 part by weight of polyethylene wax and added to a twin-screw extruder for melt blending. The melt blending temperature of the twin-screw extruder was 160°C, the screw aspect ratio of the twin-screw extruder was 35, and the rotation speed was 150 rpm. After cooling, granulation, and drying, PVC composite masterbatch was obtained; S3.3: Add the PVC composite masterbatch into the mold and place it on a four-roll calender. Adjust the roller temperature to 160°C and calender it to a thickness of 0.3 mm to obtain red playing card sheets.

[0022] Example 2: A red playing card sheet based on PVC and its preparation method, such as Figure 1 As shown, the following steps are included: S1: Preparation of porous chitosan elastic microparticles S1.1: 10 parts by weight of chitosan powder was dispersed in 80 parts by weight of a 5 wt% aqueous solution of NaOH and stirred vigorously for 20 hours. The precipitate was filtered and rinsed with distilled water until neutral. The precipitate was then dispersed in 80 parts by weight of an 8 wt% aqueous solution of HCl and soaked for 15 hours. The precipitate was filtered and rinsed with distilled water until neutral. The precipitate was then dispersed in 4 wt% hydrogen peroxide and heated to 75°C and soaked for 6 hours. The precipitate was filtered and washed with distilled water until neutral and then dried to obtain purified chitosan powder. S1.2: Dispersing the purified chitosan powder in an alkaline composite aqueous solution at a mass ratio of 1:10, wherein the alkaline composite aqueous solution is prepared by mixing NaOH, urea, and deionized water in a mass ratio of 1:0.5:10, followed by freezing at -50°C for 4 hours and then thawing at room temperature. The freeze-thaw operation is repeated three times under the same conditions to obtain a chitosan solution; S1.3: Take 120 parts by weight of deionized water, add 5 parts by weight of sodium lauryl sulfate and 4 parts by weight of potassium carbonate and stir until completely dissolved, introduce nitrogen to exhaust the air in the container, then add 20 parts by weight of butyl acrylate and 0.5 parts by weight of dicyclopentadiene acrylate and stir evenly, then heat in a water bath to 60°C, add 0.1wt% of azobisisobutyronitrile and stir for 4 minutes, keep warm for 15 minutes, then add 50 parts by weight of chitosan solution and stir at a stirring speed of 1800 rpm for 3 minutes, heat to 80°C, add 12wt% hydrogen chloride solution within 25 minutes to make the solution neutral, continue to keep warm for 1 hour, then filter out the solid matter, rinse with distilled water until neutral, and obtain porous chitosan elastic particles after drying.

[0023] S2: Preparation of compound heat stabilizer S2.1: 8 parts by weight of lanthanum nitrate hexahydrate were added to 75 parts by weight of deionized water and magnetically stirred until the solution was transparent to obtain a lanthanum nitrate solution. Under a nitrogen atmosphere, 6 parts by weight of L-glutathione were added to 80 parts by weight of deionized water and stirred until the L-glutathione was completely dissolved to obtain an L-glutathione solution; S2.2: Under the conditions of 35°C, 250rpm and nitrogen atmosphere, slowly add the lanthanum nitrate solution prepared in step S2.1 to the L-glutathione solution prepared in step S2.1, and complete the addition within 30 minutes. Then, add ammonia water to adjust the pH to 8. After heating to 60°C and stirring at constant temperature for 3 hours, place it in a centrifuge and centrifuge at a speed of 4000rpm for 10 minutes. Filter the solid matter and rinse it with deionized water twice. Then place it at 60°C and vacuum dry it to constant weight. Grind it into powder to obtain glutathione lanthanum complex. Mix the glutathione lanthanum complex and pentaerythritol in a mass ratio of 1:2 to obtain a composite thermal stabilizer.

[0024] S3: Modification of porous chitosan elastic particles and co-extrusion of PVC composites S3.1: Methyl N,N-dihydroxyethyl-3-aminopropionate and porous chitosan elastic microparticles were placed in a container at a mass ratio of 1:6. Nitrogen was continuously introduced to expel air from the container. 0.6 wt% of p-toluenesulfonic acid was added and stirred evenly. The mixture was then heated to 115°C and maintained for 6 hours. The solid reactant was collected by filtration, washed twice with methanol, and then dried at 65°C for 2 hours to obtain modified porous chitosan elastic microparticles. S3.2: 70 parts by weight of PVC resin, 10 parts by weight of modified porous chitosan elastic particles, and 3 parts by weight of a compounded thermal stabilizer were mixed at 100°C and 600 rpm for 10 minutes, then transferred to a vacuum filtration bottle and evacuated to a pressure of 10 kPa for 10 minutes. The mixture was then mixed with 3 parts by weight of phthalocyanine red, 2 parts by weight of nano-ZnO, and 1 part of polyethylene wax and melt-blended in a twin-screw extruder at a melt-blending temperature of 160°C, a screw aspect ratio of 35, and a rotation speed of 150 rpm. The mixture was cooled, granulated, and dried to obtain a PVC composite masterbatch. S3.3: Add the PVC composite masterbatch into the mold and place it on a four-roll calender. Adjust the roller temperature to 160°C and calender it to a thickness of 0.3 mm to obtain red playing card sheets.

[0025] Example 3: A red playing card sheet based on PVC and its preparation method, such as Figure 1 As shown, the following steps are included: S1: Preparation of porous chitosan elastic microparticles S1.1: 8 parts by weight of chitosan powder were dispersed in 60 parts by weight of a 5 wt% aqueous solution of NaOH and stirred vigorously for 24 hours. The precipitate was filtered and rinsed with distilled water until neutral. The precipitate was then dispersed in 60 parts by weight of an 8 wt% aqueous solution of HCl and soaked for 20 hours. The precipitate was filtered and rinsed with distilled water until neutral. The precipitate was then dispersed in 6 wt% hydrogen peroxide and heated to 80°C and soaked for 8 hours. The precipitate was filtered and washed with distilled water until neutral and then dried to obtain purified chitosan powder. S1.2: Dispersing the purified chitosan powder in an alkaline composite aqueous solution at a mass ratio of 1:8, wherein the alkaline composite aqueous solution is prepared by mixing NaOH, urea, and deionized water in a mass ratio of 1:0.4:8, followed by freezing at -45°C for 5 hours and then thawing at room temperature. The freeze-thaw operation is repeated four times under the same conditions to obtain a chitosan solution; S1.3: Take 100 parts by weight of deionized water, add 3 parts by weight of sodium lauryl sulfate and 2 parts by weight of potassium carbonate and stir until completely dissolved, introduce nitrogen to exhaust the air in the container, then add 15 parts by weight of butyl acrylate and 0.3 parts by weight of dicyclopentadiene acrylate and stir evenly, then heat in a water bath to 65°C, add 0.2wt% of azobisisobutyronitrile and stir for 5 minutes, keep warm for 20 minutes, then add 40 parts by weight of chitosan solution and stir at a stirring speed of 2000 rpm for 4 minutes, heat to 85°C, add 12wt% hydrogen chloride solution within 30 minutes to make the solution neutral, continue to keep warm for 1.5 hours, then filter out the solid matter, rinse with distilled water until neutral, and obtain porous chitosan elastic particles after drying.

[0026] S2: Preparation of compound heat stabilizer S2.1: 4 parts by weight of lanthanum nitrate hexahydrate were added to 50 parts by weight of deionized water and magnetically stirred until the solution became transparent to obtain a lanthanum nitrate solution. Under a nitrogen atmosphere, 3 parts by weight of L-glutathione were added to 60 parts by weight of deionized water and stirred until the L-glutathione was completely dissolved to obtain an L-glutathione solution. S2.2: Under the conditions of 40°C, 300 rpm and nitrogen atmosphere, slowly add the lanthanum nitrate solution prepared in step S2.1 to the L-glutathione solution prepared in step S2.1, and complete the addition within 40 minutes. Then, add ammonia water to adjust the pH to 8.5. After heating to 65°C and stirring at constant temperature for 5 hours, place it in a centrifuge and centrifuge at 4500 rpm for 15 minutes. Filter the solid matter and rinse it with deionized water 3 times. Then place it at 65°C and vacuum dry it to constant weight. Grind it into powder to obtain glutathione lanthanum complex. Mix the glutathione lanthanum complex and pentaerythritol in a mass ratio of 1:2 to obtain a composite thermal stabilizer.

[0027] S3: Modification of porous chitosan elastic particles and co-extrusion of PVC composites S3.1: Methyl N,N-dihydroxyethyl-3-aminopropionate and porous chitosan elastic microparticles were placed in a container at a mass ratio of 1:4. Nitrogen was continuously introduced to expel air from the container. 0.5 wt% of p-toluenesulfonic acid was added and stirred evenly. The mixture was then heated to 120°C and maintained for 8 hours. The solid reactant was collected by filtration, washed three times with methanol, and then dried at 70°C for 3 hours to obtain modified porous chitosan elastic microparticles. S3.2: 50 parts by weight of PVC resin, 6 parts by weight of modified porous chitosan elastic particles, and 2 parts by weight of a compounded thermal stabilizer were mixed at high speed at 120°C and 800 rpm for 15 minutes, then transferred to a vacuum filtration bottle and evacuated to a pressure of 15 kPa for 15 minutes. The mixture was then mixed with 1 part by weight of phthalocyanine red, 0.5 part by weight of nano-ZnO, and 0.5 part by weight of polyethylene wax and melt-blended in a twin-screw extruder at a melt-blending temperature of 180°C, a screw aspect ratio of 45, and a rotation speed of 200 rpm. The mixture was cooled, granulated, and dried to obtain a PVC composite masterbatch. S3.3: Add the PVC composite masterbatch into the mold and place it on a four-roll calender. Adjust the roller temperature to 180°C and calender it to a thickness of 0.5 mm to obtain red playing card sheets.

[0028] Comparative Example 1: The difference from Example 1 is that in Comparative Example 1, the modified porous chitosan elastic particles in step S3.2 are replaced with an equal mass of UN488 plasticizer, and the remaining steps are the same as those in Example 1 to prepare a red playing card sheet, which is recorded as Comparative Example 1.

[0029] Comparative Example 2: The difference from Example 1 is that Comparative Example 2 removes step S2 and replaces the compound heat stabilizer in step S3.2 with an equal mass of calcium-zinc composite stabilizer. The remaining steps are the same as those in Example 1 to prepare red playing card sheets, which are recorded as Comparative Example 2.

[0030] Comparative Example 3: The difference from Example 1 is that Comparative Example 3 removes step S3.1 and replaces the modified porous chitosan elastic particles in step S3.2 with porous chitosan elastic particles. The remaining steps are the same as Example 1 to prepare red playing card sheets, which are recorded as Comparative Example 3.

[0031] Comparative Example 4: The difference from Example 1 is that Comparative Example 4 does not perform vacuum treatment after high-speed mixing of the PVC resin, modified porous chitosan elastic particles and compounded thermal stabilizer. The remaining steps are the same as those in Example 1, and a red playing card sheet is prepared, which is recorded as Comparative Example 4.

[0032] Mechanical properties testing The red playing card sheets prepared in Examples 1-3 and Comparative Examples 1, 2 and 4 were tested for tensile strength, flexural strength and elongation at break, respectively. Each set of data was tested three times and the average value was taken. The test results are shown in Table 1.

[0033] Table 1: Mechanical properties of red playing card sheets Tensile strength / MPa Bending strength / MPa Elongation at break / % Example 1 71.2 90.1 291 Example 2 73.5 91.4 298 Example 3 72.4 90.8 295 Comparative Example 1 50.3 63.3 215 Comparative Example 3 65.7 82.2 273 Comparative Example 4 58.4 72.5 244 As can be seen from the data in Table 1, the tensile strength, flexural strength, and elongation at break of the red playing card sheets prepared in Examples 1-3 are all higher than those in Comparative Example 1, Comparative Example 2, and Comparative Example 4, demonstrating that the red playing card sheets prepared in the examples of the present application have high toughness and mechanical properties; From the data of Comparative Example 1, it can be seen that when the modified porous chitosan elastic particles are replaced with the same mass of UN488 plasticizer, the tensile strength, flexural strength and elongation at break of the sheet are all reduced, which proves that the preparation of modified porous chitosan elastic particles can improve the toughness and tensile strength of PVC materials; From the data of Comparative Examples 3-4, it can be seen that the failure to modify the porous chitosan elastic particles with methyl N,N-dihydroxyethyl-3-aminopropionate and the failure to perform vacuum treatment after high-speed mixing of the PVC resin, modified porous chitosan elastic particles and compounded heat stabilizer will lead to a decrease in the mechanical properties of the sheet. This proves that both the preparation of modified porous chitosan elastic particles and vacuum treatment can improve the mechanical properties of the sheet.

[0034] Thermal stability test The red playing card sheets prepared in Examples 1-3 and Comparative Example 2 were tested for thermal stability using TGA. The test temperature was raised from room temperature to 500°C at a heating rate of 25°C / min. The mass retention rates of the sheets were recorded at 100°C, 200°C, 300°C, and 400°C. Three parallel experiments were performed, and the mass retention rates at each temperature were averaged. The test results are shown in Table 2.

[0035] Table 2: Mass retention at different temperatures Quality retention rate / % 100℃ 200℃ 300℃ 400℃ Example 1 99.85 99.52 98.91 42.5 Example 2 99.83 99.49 98.89 41.3 Example 3 99.87 99.53 98.94 44.6 Comparative Example 2 99.71 99.34 94.35 65.8 It can be seen from Table 2 that the mass retention rates of Examples 1-3 are all higher than those of Comparative Example 2 at temperatures below 300°C, which proves that the compound heat stabilizer prepared in the present application can provide excellent thermal stability for PVC materials. However, the thermal stability decreases significantly after 300°C. Analysis suggests that this may be caused by the decomposition of L-glutathione under high temperature conditions. However, the temperature before 300°C is sufficient to ensure that the PVC is fully blended and melted.

[0036] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the present invention. Anyone skilled in the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by one of ordinary skill in the art without departing from the spirit and technical principles disclosed herein are intended to be covered by the claims of the present invention.

Claims

1. A red playing card sheet based on PVC, characterized in that: The invention comprises the following components: 50-70 parts by weight of PVC resin, 6-10 parts by weight of modified porous chitin elastic particles, 2-3 parts by weight of compound heat stabilizer, 1-3 parts by weight of phthalocyanine red, 0.5-2 parts by weight of antibacterial agent and 0.5-1 parts by weight of polyethylene wax; The composite heat stabilizer is prepared by slowly adding L-glutathione solution into lanthanum nitrate solution, adjusting pH, heating and stirring, centrifuging, filtering, drying and mixing with pentaerythritol.

2. A method for preparing the PVC-based red playing card sheet according to claim 1, characterized in that: The following steps are involved: S1: Preparation of porous chitosan elastic microparticles Chitosan powder is sequentially subjected to alkaline soaking and stirring treatment, acid soaking treatment, and hydrogen peroxide soaking treatment to obtain purified chitosan powder, which is then dispersed in an alkaline composite aqueous solution and repeatedly subjected to multiple freeze-thaw operations to obtain a chitosan solution. Butyl acrylate and dicyclopentadiene acrylate are added to a mixed solution of sodium lauryl sulfate, potassium carbonate, and deionized water in a nitrogen atmosphere. After heating in a water bath, azobisisobutyronitrile is added to maintain the temperature, and then the chitosan solution is added. The temperature is slowly increased to adjust the pH to neutral, the temperature is continued to be maintained, and the mixture is filtered, washed, and dried to obtain porous chitosan elastic microparticles. S2: Preparation of compound heat stabilizer Lanthanum nitrate hexahydrate is dissolved in deionized water to prepare a lanthanum nitrate solution, L-glutathione is dissolved in deionized water to prepare an L-glutathione solution, the lanthanum nitrate solution is added to the L-glutathione solution under a nitrogen atmosphere with stirring, the pH is adjusted, the temperature is increased with stirring, the mixture is centrifuged, filtered, dried, and then mixed with pentaerythritol to obtain a composite thermal stabilizer; S3: Modification of porous chitosan elastic particles and co-extrusion of PVC composites Methyl N,N-dihydroxyethyl-3-aminopropionate, porous chitosan elastic particles and p-toluenesulfonic acid are reacted at high temperature in a nitrogen atmosphere to obtain modified porous chitosan elastic particles. PVC resin, modified porous chitosan elastic particles and a compounded heat stabilizer are heated and mixed, then placed in a vacuum for treatment. The mixture is then mixed with phthalocyanine red, an antibacterial agent and polyethylene wax, melt-blended and extruded into granules, and then placed in a calender for calendering to obtain red playing card sheets.

3. The method for preparing a red playing card sheet based on PVC according to claim 2, characterized in that: Step S1: Preparation of porous chitosan elastic particles, specifically comprising the following steps: S1.1: 8-10 parts by weight of chitosan powder are dispersed in 60-80 parts by weight of a 5 wt% NaOH aqueous solution and stirred vigorously for 20-24 hours. The precipitate is filtered and rinsed with distilled water until neutral. The precipitate is then dispersed in 60-80 parts by weight of an 8 wt% HCl aqueous solution and soaked for 15-20 hours. The precipitate is filtered and rinsed with distilled water until neutral. The precipitate is then dispersed in 4-6 wt% hydrogen peroxide and heated to 75-80°C and soaked for 6-8 hours. The precipitate is filtered and washed with distilled water until neutral and then dried to obtain purified chitosan powder. S1.2: Disperse the purified chitosan powder in an alkaline composite aqueous solution at a mass ratio of 1:(8-10), freeze the mixture at -50°C to -45°C for 4-5 hours, and then thaw the mixture at room temperature. Repeat the freeze-thaw operation 3-4 times under the same conditions to obtain a chitosan solution. S1.3: Take 100-120 parts by weight of deionized water, add 3-5 parts by weight of sodium lauryl sulfate and 2-4 parts by weight of potassium carbonate, and stir until completely dissolved. Then, introduce nitrogen to exhaust the air in the container, then add 15-20 parts by weight of butyl acrylate and 0.3-0.5 parts by weight of dicyclopentadiene acrylate and stir evenly. Then, heat in a water bath to 60-65°C, add 0.1-0.2wt% of azobisisobutyronitrile and stir for 4-5 minutes, keep warm for 15-20 minutes, then add 40-50 parts by weight of chitosan solution and stir at a stirring speed of 1800-2000 rpm for 3-4 minutes. After heating to 80-85°C, add 12wt% hydrogen chloride solution within 25-30 minutes to neutralize the solution. Continue to keep warm for 1-1.5 hours, then filter out the solid matter, rinse with distilled water until neutral, and obtain porous chitosan elastic particles after drying.

4. The method for preparing a red playing card sheet based on PVC according to claim 3, characterized in that: Step S2 is the preparation of a composite heat stabilizer, specifically comprising the following steps: S2.1: Add 4-8 parts by weight of lanthanum nitrate hexahydrate to 50-75 parts by weight of deionized water and stir magnetically until the solution becomes transparent to obtain a lanthanum nitrate solution. Under a nitrogen atmosphere, add 3-6 parts by weight of L-glutathione to 60-80 parts by weight of deionized water and stir until the L-glutathione is completely dissolved to obtain an L-glutathione solution. S2.2: Under the conditions of 35-40°C, 250-300 rpm, and nitrogen atmosphere, slowly add the lanthanum nitrate solution prepared in step S2.1 to the L-glutathione solution prepared in step S2.1 over 30-40 minutes, then add ammonia water to adjust the pH to 8-8.5, raise the temperature to 60-65°C, and stir at this constant temperature for 3-5 hours. Then, place the mixture in a centrifuge and centrifuge at 4000-4500 rpm for 10-15 minutes. Filter the solid matter, rinse it with deionized water 2-3 times, and then place it at 60-65°C under vacuum and dry it to constant weight. Grind it into powder to obtain a glutathione lanthanum complex. Mix the glutathione lanthanum complex and pentaerythritol in a mass ratio of 1:(2-3) to obtain a composite thermal stabilizer.

5. The method for preparing a red playing card sheet based on PVC according to claim 4, characterized in that: Step S3, modification of the porous chitosan elastic particles and co-extrusion of the PVC composite material, specifically comprises the following steps: S3.1: Place N,N-dihydroxyethyl-3-aminopropionic acid methyl ester and porous chitin elastic microparticles in a container at a mass ratio of 1:(4-6), continuously introduce nitrogen to expel air from the container, add 0.5-0.6 wt% p-toluenesulfonic acid, and stir evenly. Then, heat to 115-120°C and maintain for 6-8 hours. Collect the solid reactant by filtration, wash with methanol 2-3 times, and then dry at 65-70°C for 2-3 hours to obtain modified porous chitin elastic microparticles. S3.2: 50-70 parts by weight of PVC resin, 6-10 parts by weight of modified porous chitin elastic particles, and 2-3 parts by weight of a compounded heat stabilizer are mixed at a high speed at 100-120°C and 600-800 rpm for 10-15 minutes, then transferred to a vacuum filtration bottle and evacuated to a pressure of 10-15 kPa for 10-15 minutes. The mixture is then mixed with 1-3 parts by weight of phthalocyanine red, 0.5-2 parts by weight of an antibacterial agent, and 0.5-1 parts by weight of polyethylene wax, added to a twin-screw extruder for melt blending, cooled, granulated, and dried to obtain a PVC composite masterbatch; S3.3: Add the PVC composite masterbatch into the mold and place it on a four-roll calender. Adjust the roller temperature to 160-180°C and calender it to a thickness of 0.3-0.5 mm to obtain red playing card sheets.

6. The method for preparing a red playing card sheet based on PVC according to claim 3, characterized in that: The alkaline composite aqueous solution of step S1.2 is prepared by mixing NaOH, urea and deionized water in a mass ratio of 1:(0.4-0.5):(8-10).

7. The method for preparing a red playing card sheet based on PVC according to claim 5, characterized in that: The antibacterial agent in step S3.2 is nano-ZnO.

8. The method for preparing a red playing card sheet based on PVC according to claim 5, characterized in that: In step S3.2, the melt blending temperature of the twin-screw extruder is 160-180° C., the screw aspect ratio of the twin-screw extruder is 35-45, and the rotation speed is 150-200 rpm.

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