Food packaging bag printing coating and preparation method thereof

Abstract

The invention discloses a food packaging bag printing coating and a preparation method thereof, and belongs to the technical field of packaging bag printing coatings, the coating comprises the following components: a core-shell emulsion, an inorganic pigment, a dispersant, a silane coupling agent, nanometer, a leveling agent, a defoaming agent and the balance of deionized water. The preparation method of the coating comprises the following steps: preparing the core emulsion; preparing a polymerized shell layer emulsion; mixing the core emulsion and the shell emulsion, and emulsifying to prepare a core-shell emulsion; and adding an auxiliary agent and a pigment into the core-shell emulsion to prepare the packaging bag printing coating. According to the invention, waterborne polyurethane is used as a core emulsion of a base material, UV acrylic acid is used as a shell emulsion of a base material, and the migration amount of the coating is lower and more stable through the barrier effect of core-shell structure matrix resin and low residual monomers; and the adhesive force of the coating is enhanced through the silane coupling agent. Due to synergistic stability of the core-shell emulsion structure, the color difference is smaller, and the dispersity of the pigment is good.

Description

Technical Field

[0001] The present invention relates to the technical field of packaging bag printing coatings, in particular to a food packaging bag printing coating and a preparation method thereof. Background Art

[0002] The benzene-soluble chlorinated polypropylene inks widely used in food packaging bags suffer from significant drawbacks, including residual toluene toxicity, corrosion of printing equipment, and ozone depletion, posing a threat to human health and the environment. The solvents and chemicals in traditional inks can easily migrate into food, impacting food safety. Consequently, the development of environmentally friendly inks has begun. These include water-based inks and UV-curable inks. Water-based inks are based on water-soluble resins and contain no volatile organic solvents, while UV-curable inks cure rapidly through ultraviolet light.

[0003] Currently, coatings based on water-soluble resins offer advantages such as low toxicity, low pollution, and easy recycling. However, pigments are prone to agglomeration, making color variation difficult to control. Furthermore, insufficient crosslinking of a single water-soluble resin results in unstable migration. UV-curable inks, which are solvent-free and suitable for flexible substrates, exhibit poor adhesion to packaging bags, are easily peeled off, and exhibit low interfacial bonding strength. Summary of the Invention

[0004] The present invention provides a food packaging bag printing coating and preparation method, which aims to address the defects of prior art coatings based on water-soluble resins, such as the tendency of pigments to agglomerate, difficulty in controlling color difference, and unstable migration. Furthermore, UV-curable inks have poor adhesion to packaging bags and are easily peeled off.

[0005] On the one hand, the present invention provides a food packaging bag printing coating, comprising the following components in weight percentage: core-shell emulsion 50-60%, inorganic pigment 15-20%, dispersant 1-2%, silane coupling agent 1-1.5%, nano The core-shell emulsion comprises water-based polyurethane as the core emulsion and UV acrylic acid as the shell emulsion. The core emulsion comprises the following components in weight percentage: polyester polyol 40-45%, isophorone diisocyanate 25-30%, dimethylolpropionic acid 5-6%, triethylamine 3-3.5%, acetone 10-15%, and the balance is deionized water; the shell emulsion comprises the following components in weight percentage: methyl methacrylate 60-70%, ethyl acrylate 20-30%, UV photoinitiator 1-3%, ammonium persulfate 0.5-1%, emulsifier 2-3%, and the balance is deionized water.

[0006] Furthermore, in the core-shell emulsion, the ratio of the shell emulsion to the core emulsion is 1:1.5~1:2, and the emulsifier is a composite emulsion with SDS:OP-10=2:1.

[0007] On the other hand, the present invention provides a preparation method of a food packaging bag printing coating, comprising the following preparation steps: preparation of a core emulsion: dehydrating a polyester polyol, sequentially adding isophorone diisocyanate, dihydroxymethylpropionic acid, triethylamine, acetone and deionized water, emulsifying to form a WPU emulsion, and filtering to obtain a core emulsion; polymerization preparation of a shell emulsion: mixing methyl methacrylate, ethyl acrylate and an emulsifier, and adding deionized water for ultrasonic dispersion to obtain a pre-emulsion; taking a certain amount of the core emulsion and adding it to a prepared four-necked flask, adding part of the pre-emulsion and part of the ammonium persulfate solution for polymerization to obtain a seed emulsion, dripping the remaining pre-emulsion and ammonium persulfate solution into the seed emulsion to obtain a polymer emulsion, aging the polymer emulsion, adjusting the pH value and filtering to obtain a core-shell emulsion; preparation of a food packaging bag printing coating: taking a certain amount of an inorganic pigment and a dispersant, mixing and grinding with water, and sequentially adding the core-shell emulsion, nano- , silane coupling agent and stir, add leveling agent and defoaming agent and stir evenly, filter and obtain food packaging bag printing coating.

[0008] Furthermore, the polyester polyol dehydration method is: dehydrating the polyester polyol in a vacuum environment at 60° C. for 2 hours.

[0009] Furthermore, the method for adding isophorone diisocyanate, dimethylolpropionic acid, triethylamine, acetone and deionized water is as follows: under nitrogen protection, isophorone diisocyanate is added, and the NCO content is detected by titration to prepare a WPU prepolymer. After the WPU prepolymer is cooled, dimethylolpropionic acid is added until the NCO content drops to 4.5-5%. After cooling to 40°C, triethylamine is added to neutralize the carboxylic acid group to pH=8.0. After adding acetone, deionized water is slowly added under high-speed stirring to prepare a WPU emulsion.

[0010] Furthermore, the prepared WPU emulsion was vacuum distilled to remove acetone, and filtered through a 200-mesh filter to obtain a core emulsion with a solid content of 30%, and the ratio of WPU prepolymer to water was 3:10.

[0011] Furthermore, the emulsion polymerization method is as follows: adding the core emulsion into a four-necked flask, heating it to 75°C, adding part of the pre-emulsion and part of the ammonium persulfate solution into the four-necked flask, stirring and reacting for 30 minutes, and slowly adding the remaining pre-emulsion and ammonium persulfate solution dropwise at a uniform speed within 2 hours while maintaining the temperature at 75°C.

[0012] Furthermore, the polymer emulsion aging method is as follows: heating the polymer emulsion to 85°C and keeping it warm for 1 hour to ensure that the monomer conversion rate is not less than 98%; the polymer emulsion adjustment method is as follows: cooling the matured polymer emulsion to 30°C at room temperature, adjusting the pH value to 8.0 by titrating with ammonia water, and filtering through a 200-mesh filter to obtain a core-shell emulsion; adding a UV photoinitiator to the filtered core-shell emulsion, the UV photoinitiator accounting for 2% of the shell solid content, and ultrasonically dispersing for 30 minutes.

[0013] Furthermore, the inorganic pigment and dispersant are mixed with water and sand-ground to a fineness of no more than 5 μm, and then the core-shell emulsion, nano- , silane coupling agent, stirring at a medium speed of 500 rpm for 20 minutes, adding leveling agent and defoaming agent, stirring at a low speed of 200 rpm for 10 minutes, and filtering the obtained food packaging bag printing coating through a 200-mesh filter.

[0014] The food packaging bag printing coating provided by the present invention is prepared into a coating with stronger cross-linking properties by using a core emulsion of water-based polyurethane as a base material and a shell emulsion of UV acrylic acid as a base material in a certain ratio. The barrier effect of the core-shell structure matrix resin and the low residual monomer make the migration amount of the coating lower and more stable. The interfacial bonding force between the core-shell structure coating and the substrate is enhanced by a silane coupling agent, thereby increasing the adhesion of the coating. The synergistic stabilization of the core-shell emulsion structure reduces color difference, improves pigment dispersibility, and enhances color uniformity and weather resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly illustrate the technical solutions in the present invention or the prior art, a brief introduction is given below to the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0016] Figure 1 The present invention is a schematic flow chart of a method for preparing a food packaging bag printing coating. DETAILED DESCRIPTION

[0017] To make the objectives, technical solutions, and advantages of the present invention more clear, the technical solutions of the present invention will be clearly and completely described below in conjunction with the accompanying drawings. Obviously, the embodiments described are only some of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0018] The dispersant used in the following examples and comparative examples is BYK-190, and the defoamer is BYK-024, both manufactured by BYK-Chemie GmbH, Germany.

[0019] The silane coupling agent used in the following examples and comparative examples is model KH-550, and the manufacturer is Qingdao Hengda Chemical New Materials Co., Ltd.

[0020] The leveling agent used in the following examples and comparative examples is TEGO Glide 410, manufactured by Evonik Industries AG of Germany.

[0021] The UV photoinitiator used in the following examples and comparative examples is TOP-L, and the manufacturer is Changzhou Qiangli Electronic New Materials Co., Ltd.

[0022] The emulsifier used in the following examples and comparative examples is a composite emulsion of SDS:OP-10=2:1.

[0023] As mentioned above, pigments in water-soluble resin-based coatings are prone to agglomeration, making color shading difficult to control. Furthermore, insufficient crosslinking of a single water-soluble resin results in unstable migration. UV-curable inks also have poor adhesion to packaging, making the coating easily peelable and resulting in weak interfacial bonding.

[0024] In view of this, the present invention provides a food packaging bag printing coating, which can be prepared into a coating with stronger cross-linking properties by using a core emulsion with water-based polyurethane as the base material and a shell emulsion with UV acrylic as the base material according to a certain ratio. The barrier effect of the core-shell structure matrix resin and the low residual monomer make the migration amount of this coating lower and more stable. The interfacial bonding force between the core-shell structure coating and the substrate is enhanced by a silane coupling agent, thereby increasing the adhesion of the coating. The synergistic stabilization of the core-shell emulsion structure results in smaller color difference, better pigment dispersion, and higher color uniformity and weather resistance. It includes the following components in weight percentage: WPU / UV acrylic core-shell emulsion 50~60%, inorganic pigment (titanium dioxide, iron oxide powder, etc.) 15~20%, BYK-190 dispersant 1~2%, KH-550 silane coupling agent 1~1.5%, nano 3~5%, TEGO Glide 410 type leveling agent 0.3~0.5%, BYK-024 type defoamer 0.1~0.3%, and the balance is deionized water; The core-shell emulsion uses water-based polyurethane as the core emulsion and UV acrylic acid as the shell emulsion. The core emulsion includes the following components in weight percentage: polyester polyol (PBA) 40-45%, isophorone diisocyanate (IPDI) 25-30%, dimethylol propionic acid (DMPA) 5-6%, triethylamine 3-3.5%, acetone 10-15% (optional), and the balance is deionized water. The shell emulsion includes the following components in weight percentage: methyl methacrylate (MMA) 60-70%, ethyl acrylate (HEMA) 20-30%, UV photoinitiator (TOP-L) 1-3%, ammonium persulfate (APS) 0.5-1%, emulsifier (SDS / OP-10 compound) 2-3%, and the balance is deionized water. The ratio of shell emulsion to core emulsion is 1:1.5-1:2.

[0025] Based on the same general inventive concept, the present invention also protects a method for preparing a printing coating for food packaging bags. Figure 1 As shown, it includes the following steps: S100, preparing a nuclear emulsion; S200, preparing a polymerized shell emulsion; S300, mixing and emulsifying the core emulsion and the shell emulsion to prepare a core-shell emulsion; S400, adding an auxiliary agent and a pigment into the core-shell emulsion to prepare the food packaging bag printing coating.

[0026] These steps may include: S100, dehydrate the polyester polyol under vacuum at 60°C for 2 hours, add isophorone diisocyanate under nitrogen protection, heat in a water bath to 75°C, react for 2 hours, detect the NCO content by di-n-butylamine titration until it is close to the theoretical value, cool to 70°C, add dihydroxymethylpropionic acid and react for 1 hour until the NCO content drops to 4.5, cool to 40°C, add triethylamine to neutralize the carboxylic acid group to pH = 8.0, if acetone is added, slowly add deionized water at a high speed of 1000 rpm, emulsify for 30 minutes to form a WPU emulsion, and stir at a temperature of 45°C and a stirring speed of 150 rpm to form a WPU emulsion. The WPU prepolymer solution is heated in a water bath, and the boiling point of acetone is lowered to 35°C at a pressure of -0.09MPa. The solution is distilled for 1.5 hours until no condensate drips out of the condenser tube at a water temperature below 10°C. The acetone is removed by vacuum distillation. After removing the acetone, deionized water is added to a standard solid content of 30%. The residual acetone in the solution after removing the acetone is less than 100ppm. If no acetone is added, deionized water is added directly after adding triethylamine. After filtering through a 200-mesh filter, a core emulsion with a solid content of 30% is obtained. It is necessary to ensure that the particle size of the core emulsion is 80nm under the DLS test, the ratio of WPU prepolymer to water is 3:10, and there is no precipitation during the storage period of more than 6 months; S200, mixing methyl methacrylate, ethyl acrylate and an emulsifier, adding deionized water and performing ultrasonic dispersion for 15 minutes to prepare a pre-emulsion; S300, according to the ratio of shell emulsion to core emulsion of 1:1.5~1:2, take a certain amount of core emulsion and add it into the prepared four-necked flask, heat it to 75℃ in a constant temperature water bath, add 1 / 3 of the pre-emulsion and half of 0.5g of ammonium persulfate solution, stir and react for 30 minutes to prepare a polymerization seed solution, keep the temperature at 75℃ for 2 hours and slowly add the remaining pre-emulsion and ammonium persulfate solution dropwise to the prepared seed solution to carry out dropwise polymerization, increase the temperature of the four-necked flask to 85℃, keep it warm for 1 hour, and monitor the 1630 The C=C double bond peak disappears, and the monomer conversion rate needs to be greater than 98%. Then, the temperature of the four-necked flask is lowered to 30°C, and titrated with ammonia water to adjust the pH value to 8.0. The flask is filtered through a 200-mesh filter to obtain a core-shell emulsion, and the particle size of the core-shell emulsion is ensured to be between 120 and 150 nm. The PDI is 0.15 as measured by DLS. 1 g of UV photoinitiator is added to the filtered core-shell emulsion, and the UV photoinitiator accounts for 2% of the solid content of the shell layer. The flask is ultrasonically dispersed at a power of 300 W for 30 minutes to obtain a core-shell emulsion. S400, take a certain amount of inorganic pigment and BYK-190 dispersant and mix with water and grind, the ratio of pigment to water is 91:100, grind to a fineness of 5μm, add the core-shell emulsion prepared by ultrasonic dispersion in S300, nano and silane coupling agent, stirring at a stirring speed of 500rpm for 20 minutes, then adding leveling agent and defoaming agent to the semi-finished coating in turn, and adding deionized water to ensure that the solid content of the core emulsion is 30%, stirring at a stirring speed of 200rpm for 10 minutes, filter the prepared coating with a 200-mesh filter to ensure its viscosity at 4 cups for 30 to 40 seconds and pH value at 7.5.

[0027] The calculation formula of the theoretical value of NCO is as follows:

[0028] Where 42 is the molar mass of the NCO group in units of ;

[0029] .

[0030] Example 1: (1) Preparation of core emulsion: 45g of polyester polyol was dehydrated and then 25g of isophorone diisocyanate was added under nitrogen protection. The temperature was raised to 75°C and the reaction was continued for 2 hours. The NCO content was detected by dibutylamine titration until it was close to the theoretical value. The temperature was lowered to 70°C and 5g of dihydroxymethylpropionic acid was added. The reaction was continued for 1 hour until the NCO content dropped to 4.5. The temperature was lowered to 40°C and 3g of triethylamine was added to neutralize the carboxylic acid group. After 10g of acetone was added, 12g of deionized water was slowly added under high-speed stirring at 1000rpm and the mixture was emulsified for 30 minutes to form a WPU emulsion. The mixture was stirred at 45°C. The WPU prepolymer solution containing acetone was heated in a water bath at a stirring speed of 150 rpm, and the boiling point of acetone was reduced to 35°C at a pressure of -0.09 MPa. The solution was distilled for 1.5 hours until no condensate dripped out of the condenser tube at a water temperature below 10°C. The acetone was removed by vacuum distillation. After the acetone was removed, deionized water was added to a standard solid content of 30%. The residual acetone in the solution after the acetone was removed was less than 100 ppm. After filtering through a 200-mesh filter, a core emulsion with a solid content of 30% was obtained. The particle size of the core emulsion was 80 nm under DLS testing, and the ratio of WPU prepolymer to water was 3:10. (2) Preparation of shell emulsion by polymerization: 70 g of methyl methacrylate, 20 g of ethyl acrylate and 2 g of emulsifier were mixed, and 6.5 g of deionized water was added. After ultrasonic dispersion for 15 minutes, a pre-emulsion was prepared; (3) According to the ratio of shell emulsion to core emulsion of 1:1.5, the core emulsion with a solid content of 30% was added to a four-necked flask and heated in a constant temperature water bath to 75°C. One-third of the pre-emulsion and half of 0.5g of ammonium persulfate solution were added and stirred for 30 minutes to prepare a polymerization seed solution. The remaining pre-emulsion and ammonium persulfate solution were kept at 75°C for 2 hours and slowly added dropwise to the prepared seed solution at a uniform speed for dropwise polymerization. The temperature of the four-necked flask was raised to 85°C and kept warm for 1 hour. The 1630 The C=C double bond peak at position 11 disappears, and the monomer conversion rate is 98.5%. Then, the temperature of the four-necked flask is lowered to 30°C, and the pH value is adjusted to 8.0 by titration with aqueous ammonia. The flask is filtered through a 200-mesh filter to obtain a core-shell emulsion, and the particle size of the core-shell emulsion is ensured to be 130 nm. The PDI is 0.15 as determined by DLS test. 1 g of UV photoinitiator is added to the filtered core-shell emulsion, and the UV photoinitiator accounts for 2% of the solid content of the shell layer. The flask is ultrasonically dispersed at a power of 300 W for 30 minutes. (4) Preparation of food packaging bag printing coating: 80g of titanium dioxide and 8g of dispersant were mixed with 73ml of water and ground to a fineness of 5μm. The core-shell emulsion prepared by ultrasonic dispersion in step (3), 20g of nano- and 6g of silane coupling agent, stirred at a stirring speed of 500rpm for 20 minutes, then added 2g of leveling agent, 1.2g of defoaming agent and 82.8g of deionized water to the semi-finished coating in sequence, stirred at a stirring speed of 200rpm for 10 minutes, and filtered with a 200-mesh filter to ensure that its viscosity was 4 cups 30 seconds and the pH value was 7.5.

[0031] Example 2: (1) Preparation of core emulsion: Take 43g of polyester polyol and dehydrate it under vacuum at 60℃ for 2 hours. Under nitrogen protection, add 28g of isophorone diisocyanate, heat it to 75℃, react for 2 hours, and then use dibutylamine titration to detect the NCO content until it is close to the theoretical value. After cooling to 70℃, add 5.5g of dihydroxymethylpropionic acid and react for 1 hour until the NCO content drops to 4.5. After cooling to 40℃, add 3.2g of triethylamine to neutralize the carboxylic acid group to pH=8.0. Slowly add 20.3g of deionized water under high-speed stirring at 1000rpm, emulsify for 30 minutes to form WPU emulsion. After filtering through a 200-mesh filter, the core emulsion is obtained. The particle size of the core emulsion is 90nm under DLS test. (2) Preparation of shell emulsion by polymerization: 65 g of methyl methacrylate, 25 g of ethyl acrylate and 2.5 g of emulsifier were mixed, 4.8 g of deionized water was added, and ultrasonic dispersion was performed for 15 minutes to prepare a pre-emulsion; (3) According to the ratio of shell emulsion to core emulsion of 1:1.7, the core emulsion with a solid content of 30% was added to a four-necked flask and heated in a constant temperature water bath to 75°C. One-third of the pre-emulsion and half of 0.7g of ammonium persulfate solution were added and stirred for 30 minutes to prepare a polymerization seed solution. The remaining pre-emulsion and ammonium persulfate solution were kept at 75°C for 2 hours and slowly added dropwise to the prepared seed solution at a constant speed for dropwise polymerization. The temperature of the four-necked flask was raised to 85°C and kept warm for 1 hour. The 1630 The C=C double bond peak at 140 nm disappeared, and the monomer conversion rate was 98.7%. The temperature of the four-necked flask was then lowered to 30°C, and titrated with ammonia water to adjust the pH value to 8.0. The flask was filtered through a 200-mesh filter to obtain a core-shell emulsion. The particle size of the core-shell emulsion was 140 nm, and the PDI was 0.17 as measured by DLS. 2 g of UV photoinitiator was added to the filtered core-shell emulsion, and ultrasonic dispersion was performed for 30 minutes. (4) Preparation of food packaging bag printing coating: 61.8g of iron oxide powder and 5.45g of dispersant were mixed with 56.2ml of water and ground to a fineness of 5μm. The core-shell emulsion prepared by ultrasonic dispersion in step (3), 14.5g of nano- and 4.7g of silane coupling agent, stirred at a stirring speed of 500rpm for 20 minutes, then added 1.45g of leveling agent, 0.72g of defoaming agent and 74.9g of deionized water to the semi-finished coating in sequence, stirred at a stirring speed of 200rpm for 10 minutes, and then filtered with a 200-mesh filter. The coating viscosity was 35 seconds after coating 4 cups.

[0032] Example 3: (1) Preparation of core emulsion: 40 g of polyester polyol was dehydrated under vacuum at 60 ° C for 2 hours. Under nitrogen protection, 30 g of isophorone diisocyanate was added and the temperature was raised to 75 ° C. After reacting for 2 hours, the NCO content was detected by dibutylamine titration until it was close to the theoretical value. After cooling to 70 ° C, 6 g of dihydroxymethylpropionic acid was added and reacted for 1 hour until the NCO content dropped to 4.5. After cooling to 40 ° C, 3.5 g of triethylamine was added to neutralize the carboxylic acid group to pH = 8.0. 20.5 g of deionized water was slowly added under high-speed stirring at 1000 rpm. The mixture was emulsified for 30 minutes to form a WPU emulsion. After filtering through a 200-mesh filter, the core emulsion was obtained. The particle size of the core emulsion was 100 nm under DLS test. (2) Preparation of shell emulsion by polymerization: 60 g of methyl methacrylate, 30 g of ethyl acrylate and 3 g of emulsifier were mixed, and 3 g of deionized water was added. After ultrasonic dispersion for 15 minutes, a pre-emulsion was prepared; (3) According to the ratio of shell emulsion to core emulsion of 1:2, the core emulsion with a solid content of 30% was added to a four-necked flask and heated in a constant temperature water bath to 75°C. One-third of the pre-emulsion and half of 1g of ammonium persulfate solution were added and stirred for 30 minutes to prepare a polymerization seed solution. The remaining pre-emulsion and ammonium persulfate solution were kept at 75°C for 2 hours and slowly added dropwise to the prepared seed solution at a uniform speed for dropwise polymerization. The temperature of the four-necked flask was raised to 85°C and kept warm for 1 hour. The 1630 The C=C double bond peak at position 11 disappears, and the monomer conversion rate is 98.7%. Then, the temperature of the four-necked flask is lowered to 30°C, and titrated with ammonia water to adjust the pH value to 8.0. The flask is filtered through a 200-mesh filter to obtain a core-shell emulsion. The particle size of the core-shell emulsion is 150 nm. The PDI is 0.19 as measured by DLS. 3 g of UV photoinitiator is added to the filtered core-shell emulsion, and ultrasonic dispersion is performed for 30 minutes. (4) Preparation of food packaging bag printing coating: 50g of titanium dioxide and 3.33g of dispersant were mixed with 45.5ml of water and ground to a fineness of 5μm. The core-shell emulsion prepared by ultrasonic dispersion in step (3), 10g of nano- and 3.4g of silane coupling agent, stirred at a stirring speed of 500rpm for 20 minutes, then added 1g of leveling agent, 0.4g of defoaming agent and 64.8g of deionized water to the semi-finished coating in sequence, stirred at a stirring speed of 200rpm for 10 minutes, and filtered with a 200-mesh filter. The coating viscosity was 40 seconds after coating 4 cups.

[0033] Comparative Example 1: In a stirring container, add 200g of aqueous polyurethane emulsion. Turn on the agitator and stir at a speed of 300r / min. Slowly add 4g of defoamer and continue stirring for 15 minutes to ensure that the defoamer is fully dispersed in the emulsion. While stirring, slowly add 1.6g of leveling agent to the above mixture and continue stirring for 20 minutes to ensure that the leveling agent is evenly dispersed. Add 3g of thickener and 60g of deionized water to make the solid content of the coating reach 30%. Stir continuously to ensure that the viscosity of the coating at room temperature reaches 4 cups 35 seconds. Add 80g of titanium dioxide ground to 5μm fineness and deionized water to mix the color of the coating, and then use a 200-mesh filter to filter the prepared coating.

[0034] Comparative Example 2: In a stirring container, add 200g of epoxy acrylate. Turn on the agitator and stir at a speed of 300r / min. Slowly add 10g of UV photoinitiator and continue stirring for 30 minutes to ensure the uniform dispersion of the photoinitiator. While stirring, slowly add 1g of defoamer, 1.5g of leveling agent and 6g of adhesion promoter to the above mixture in sequence. Continue stirring for 20 minutes after adding each additive to ensure that the various additives are evenly dispersed. Add 52g of deionized water and stir continuously to ensure that the viscosity of the coating at room temperature reaches 4 cups and 35 seconds. Add 78g of titanium dioxide ground to 5μm fineness and deionized water to adjust the color of the coating, and then filter the prepared coating with a 200-mesh filter.

[0035] Comparative Example 3: (1) Preparation of core emulsion: Take 44g of polyester polyol, dehydrate it for 2 hours, then add 27g of isophorone diisocyanate under nitrogen protection, heat it to 75℃, react for 2 hours, and then use dibutylamine titration to detect the NCO content until it is close to the theoretical value. After cooling to 70℃, add 5.5g of dihydroxymethylpropionic acid and react for 1 hour until the NCO content drops to 4.5. After cooling to 40℃, add 3g of triethylamine to neutralize the carboxylic acid group to pH=8.0, slowly add 20.5g of deionized water under high-speed stirring at 1000rpm, emulsify for 30 minutes to form WPU emulsion, and filter it through a 200-mesh filter to obtain the core emulsion. The particle size of the core emulsion is 90nm under DLS test. (2) Preparation of shell emulsion by polymerization: 60 g of methyl methacrylate, 30 g of ethyl acrylate and 3 g of emulsifier were mixed, and 3 g of deionized water was added. After ultrasonic dispersion for 15 minutes, a pre-emulsion was prepared; (3) According to the ratio of shell emulsion to core emulsion of 1:1, the core emulsion with a solid content of 30% was added to a four-necked flask and heated in a constant temperature water bath to 75°C. One-third of the pre-emulsion and half of 1.2g of ammonium persulfate solution were added and stirred for 30 minutes to prepare a polymerization seed solution. The remaining pre-emulsion and ammonium persulfate solution were kept at 75°C for 2 hours and slowly added dropwise to the prepared seed solution at a uniform speed for dropwise polymerization. The temperature of the four-necked flask was raised to 85°C and kept warm for 1 hour. The 1630 The C=C double bond peak at 140 nm disappeared, ensuring that the monomer conversion rate was 98.5%. Then, the temperature of the four-necked flask was lowered to 30°C, and titrated with ammonia water to adjust the pH value to 8.0. The flask was filtered through a 200-mesh filter to obtain a core-shell emulsion. The particle size of the core-shell emulsion was 140 nm. The PDI was 0.17 as measured by DLS. 3.2 g of UV photoinitiator was added to the filtered core-shell emulsion, and ultrasonic dispersion was performed for 30 minutes. (4) Preparation of food packaging bag printing coating: 52g of titanium dioxide and 3.4g of dispersant were mixed with 47ml of water and ground to a fineness of 5μm. The core-shell emulsion prepared by ultrasonic dispersion in step (3), 9.8g of nano- and 3.6g of silane coupling agent, stirred at a stirring speed of 500rpm for 20 minutes, then added 1g of leveling agent, 0.5g of defoaming agent and 62g of deionized water to the semi-finished coating in sequence, stirred at a stirring speed of 200rpm for 10 minutes, and filtered with a 200-mesh filter. The coating viscosity was 38 seconds after coating 4 cups.

[0036] Comparative Example 4: (1) Preparation of core emulsion: Take 44g of polyester polyol and dehydrate it under vacuum at 60℃ for 2 hours. Under nitrogen protection, add 27g of isophorone diisocyanate, heat it to 75℃, react for 2 hours, and then use dibutylamine titration method to detect the NCO content until it is close to the theoretical value. After cooling to 70℃, add 5.5g of dihydroxymethylpropionic acid and react for 1 hour until the NCO content drops to 4.5. After cooling to 40℃, add 3g of triethylamine to neutralize the carboxylic acid group to pH=8.0. Slowly add 20.5g of deionized water under high-speed stirring at 1000rpm, emulsify for 30 minutes to form WPU emulsion, and filter it through a 200-mesh filter to obtain the core emulsion. The particle size of the core emulsion is 88nm under DLS test. (2) Preparation of shell emulsion by polymerization: 60 g of methyl methacrylate, 30 g of ethyl acrylate and 3 g of emulsifier were mixed, and 3 g of deionized water was added. After ultrasonic dispersion for 15 minutes, a pre-emulsion was prepared; (3) According to the ratio of shell emulsion to core emulsion of 1:2.5, the core emulsion with a solid content of 30% was added to a four-necked flask and heated in a constant temperature water bath to 75°C. One-third of the pre-emulsion and half of 1g of ammonium persulfate solution were added and stirred for 30 minutes to prepare a polymerization seed solution. The remaining pre-emulsion and ammonium persulfate solution were kept at 75°C for 2 hours and slowly added dropwise to the prepared seed solution at a constant speed for dropwise polymerization. The temperature of the four-necked flask was raised to 85°C and kept warm for 1 hour. The 1630 The C=C double bond peak at 147°C disappeared, and the monomer conversion rate was 97%. The temperature of the four-necked flask was then lowered to 30°C, and titrated with ammonia water to adjust the pH value to 8.0. The flask was filtered through a 200-mesh filter to obtain a core-shell emulsion. The particle size of the core-shell emulsion was 136 nm, and the PDI was 0.18 as measured by DLS. 3.2 g of UV photoinitiator was added to the filtered core-shell emulsion, and ultrasonic dispersion was performed for 30 minutes. (4) Preparation of food packaging bag printing coating: 52g of titanium dioxide and 3.4g of dispersant were mixed with 47ml of water and ground to a fineness of 5μm. The core-shell emulsion prepared by ultrasonic dispersion in step (3), 9.7g of nano- and 3.6g of silane coupling agent, stirred at a stirring speed of 500rpm for 20 minutes, then added 1.1g of leveling agent, 0.5g of defoaming agent and 63g of deionized water to the semi-finished coating in sequence, stirred at a stirring speed of 200rpm for 10 minutes, and then filtered with a 200-mesh filter. The coating viscosity was 34 seconds after coating 4 cups.

[0037] Comparative Example 5: (1) Preparation of core emulsion: Take 35g of polyester polyol and dehydrate it under vacuum at 60℃ for 2 hours. Under nitrogen protection, add 35g of isophorone diisocyanate, heat it to 75℃, react for 2 hours, and then use dibutylamine titration to detect the NCO content until it is close to the theoretical value. After cooling to 70℃, add 7g of dihydroxymethylpropionic acid and react for 1 hour until the NCO content drops to 4.5. After cooling to 40℃, add 5g of triethylamine to neutralize the carboxylic acid group to pH=8.0. Slowly add 18g of deionized water under high-speed stirring at 1000rpm, emulsify for 30 minutes to form WPU emulsion, and filter it through a 200-mesh filter to obtain the core emulsion. The particle size of the core emulsion is 110nm under DLS test. (2) Preparation of shell emulsion by polymerization: 50 g of methyl methacrylate, 35 g of ethyl acrylate and 5 g of emulsifier were mixed, and 5 g of deionized water was added. After ultrasonic dispersion for 15 minutes, a pre-emulsion was prepared; (3) According to the ratio of shell emulsion to core emulsion of 1:1.7, the core emulsion with a solid content of 30% was added to a four-necked flask and heated in a constant temperature water bath to 75°C. One-third of the pre-emulsion and half of the 2g ammonium persulfate solution were added and stirred for 30 minutes to prepare a polymerization seed solution. The remaining pre-emulsion and ammonium persulfate solution were kept at 75°C for 2 hours and slowly added dropwise to the prepared seed solution at a uniform speed for dropwise polymerization. The temperature of the four-necked flask was raised to 85°C and kept warm for 1 hour. The 1630 The C=C double bond peak disappears, and the monomer conversion rate is 94%. Then, the temperature of the four-necked flask is lowered to 30°C, and the pH value is adjusted to 8.0 by titration with ammonia water. The flask is filtered through a 200-mesh filter to obtain a core-shell emulsion. The particle size of the core-shell emulsion is 124 nm. The PDI is 0.15 as measured by DLS. 3 g of UV photoinitiator is added to the filtered core-shell emulsion, and ultrasonic dispersion is performed for 30 minutes. (4) Preparation of food packaging bag printing coating: 50g of titanium dioxide and 4g of dispersant were mixed with 45.5ml of water and ground to a fineness of 5μm. The core-shell emulsion prepared by ultrasonic dispersion in step (3), 9g of nano- and 6g of silane coupling agent, stirred at a stirring speed of 500rpm for 20 minutes, then added 0.5g of leveling agent, 1g of defoaming agent and 80g of deionized water to the semi-finished coating in sequence, stirred at a stirring speed of 200rpm for 10 minutes, and then filtered with a 200-mesh filter. The coating viscosity was 25 seconds after applying 4 cups.

[0038] Test Example 1: Migration test: The 8 coatings of Example 1, Example 2, Example 3, Comparative Example 1, Comparative Example 2, Comparative Example 3, Comparative Example 4 and Comparative Example 5 were coated on the surface of a 30 μm PE film, and 10 cm × 10 cm samples were taken after curing. Water, 3% acetic acid, 10% ethanol and olive oil were used as migration simulants. 8 cured samples were placed in each group of simulants. Detect residual monomers (such as IPDI, MMA) and additives (such as photoinitiators, silane coupling agents) in migrants.

[0039] Table 1 Migration test results of coatings

[0040] From the comparison of the experimental data of Examples 1 to 3 and Comparative Examples 1 to 4 in Table 1, it can be found that the food packaging bag printing coating prepared by the present invention has lower migration and is more stable.

[0041] By comparison, it can be found that the migration of comparative examples 1, 2, 3, 4, and 5 is stronger, and the coating adhesion stability is lower. Among them, comparative example 1 uses a single aqueous polyurethane emulsion as the base resin, and comparative example 2 uses a single UV acrylate as the base resin. The migration amounts of comparative examples 3, 4, and 5 are obviously lower than those of comparative examples 1 and 2, and the migration amounts are more stable, due to the barrier effect of the core-shell structure base resin and the low residual monomer.

[0042] Test Example 2: Adhesion test: According to ASTM D3359, a 10×10 grid with 1mm spacing was drawn on the coating surface. 3M tape was then used to apply a peel rating (0–5, with 0 being the best). The sample was then aged in an 85°C / 85% RH environment for 7 days, and the cross-cut test was repeated to evaluate the bond strength between the coating and the PE film.

[0043] Table 2 Adhesion test results of coatings

[0044] From the comparison of the experimental data of Examples 1 to 3 and Comparative Examples 1 to 4 in Table 2, it can be found that the food packaging bag printing coating prepared by the present invention has a higher adhesion level, the coating is more stable, and adheres to the packaging bag more firmly.

[0045] Comparison revealed that Comparative Examples 1, 2, 3, 4, and 5 exhibited lower adhesion levels and lower wet-heat stability. Comparative Example 1 employed a single aqueous polyurethane emulsion as the base resin, while Comparative Example 2 employed a single UV acrylate. Furthermore, Comparative Examples 3, 4, and 5 exhibited slightly higher adhesion and wet-heat stability. While the silane coupling agent in the core-shell emulsion enhances interfacial bonding and provides higher wet-heat stability, the lower adhesion of Comparative Examples 3, 4, and 5 compared to Examples 1, 2, and 3 is attributed to the fact that the ratio of the core emulsion to the shell emulsion was not within the appropriate range, and the ratio of the silane coupling agent to other components was unreasonable.

[0046] Test Example 3: Color difference test: use The colorimeter measures the L (brightness), a (red-green deviation), and b (yellow-blue deviation) values ​​of the layer and calculates (Total color difference). The samples were then exposed to a xenon lamp aging chamber (50°C, 500 hours) and the color difference before and after aging was measured to evaluate the uniformity and stability of the coating color.

[0047] Table 3 Color difference test results of coatings

[0048] From the comparison of the experimental data of Examples 1 to 3 and Comparative Examples 1 to 4 in Table 3, it can be found that the food packaging bag printing coating prepared by the present invention has smaller color difference, good pigment dispersibility, color uniformity and high weather resistance.

[0049] By comparison, it can be found that the color difference of comparative examples 1, 2, 3, 4, and 5 is greater, and the aging resistance is the worst. Comparative example 1 uses a single aqueous polyurethane emulsion as the base resin, and comparative example 2 uses a single UV acrylate as the base resin. Moreover, the aging resistance of comparative examples 3, 4, and 5 is better. The anti-oxidation effect and the synergistic stability of the core-shell emulsion structure. The aging resistance of comparative examples 3, 4, and 5 is worse than that of examples 1, 2, and 3. This is because the ratio of the core emulsion to the shell emulsion is not within the appropriate range, and the nano The ratio of other components is unreasonable.

[0050] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above and that the present invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the present invention. Therefore, the embodiments should be considered in all respects as illustrative and non-restrictive, and the scope of the present invention is not limited by the foregoing description, and it is intended that all variations that come within the meaning and scope of equivalents thereof be included within the present invention.

Claims

1. A food packaging bag printing coating, characterized in that: The components include the following weight percentages: core-shell emulsion 50-60%, inorganic pigment 15-20%, dispersant 1-2%, silane coupling agent 1-1.5%, nano 3~5%, leveling agent 0.3~0.5%, defoaming agent 0.1~0.3%, and the balance is deionized water; The core-shell emulsion uses water-based polyurethane as the core emulsion and UV acrylic acid as the shell emulsion. The core emulsion includes the following components in weight percentage: polyester polyol 40-45%, isophorone diisocyanate 25-30%, dimethylol propionic acid 5-6%, triethylamine 3-3.5%, acetone 10-15%, and the balance is deionized water. The shell emulsion comprises the following components in weight percentage: 60-70% of methyl methacrylate, 20-30% of ethyl acrylate, 1-3% of UV photoinitiator, 0.5-1% of ammonium persulfate, 2-3% of emulsifier, and the balance is deionized water.

2. The food packaging bag printing coating according to claim 1, characterized in that: In the core-shell emulsion, the ratio of shell emulsion to core emulsion is 1:1.5~1:2, and the emulsifier is a composite emulsion with SDS:OP-10=2:

1.

3. A method for preparing a food packaging bag printing coating according to claim 1 or 2, characterized in that: The method comprises the following preparation steps: (1) Preparation of core emulsion: Dehydrate polyester polyol, add isophorone diisocyanate, dimethylol propionic acid, triethylamine, acetone and deionized water in sequence, emulsify to form WPU emulsion, and filter to obtain core emulsion; (2) Preparation of shell emulsion by polymerization: Methyl methacrylate, ethyl acrylate and emulsifier were mixed, and deionized water was added for ultrasonic dispersion to prepare a pre-emulsion; (3) Preparation of core-shell emulsion: a certain amount of core emulsion is added to a prepared four-necked flask, part of the pre-emulsion and part of the ammonium persulfate solution are added for polymerization to obtain a seed emulsion, the remaining pre-emulsion and ammonium persulfate solution are added dropwise to the seed emulsion to obtain a polymer emulsion, the polymer emulsion is matured, the pH value is adjusted, and it is filtered to obtain a core-shell emulsion; (4) Preparation of food packaging bag printing coating: Take a certain amount of inorganic pigment and dispersant, mix them with water and grind them, then add core-shell emulsion, nano- , silane coupling agent and stir, add leveling agent and defoaming agent and stir evenly, filter and obtain food packaging bag printing coating.

4. The method for preparing a food packaging bag printing coating according to claim 3, characterized in that: The polyester polyol dehydration method described in step (1) is: dehydrating the polyester polyol in a vacuum environment at 60° C. for 2 hours.

5. The method for preparing a food packaging bag printing coating according to claim 3, characterized in that: The method for adding isophorone diisocyanate, dimethylolpropionic acid, triethylamine, acetone and deionized water in step (1) is as follows: under nitrogen protection, isophorone diisocyanate is added, and the NCO content is detected by titration to prepare a WPU prepolymer. After the WPU prepolymer is cooled, dimethylolpropionic acid is added until the NCO content drops to 4.5-5%. After cooling to 40°C, triethylamine is added to neutralize the carboxylic acid group to pH = 8.

0. After adding acetone, deionized water is slowly added under high-speed stirring to prepare a WPU emulsion.

6. The method for preparing a food packaging bag printing coating according to claim 5, characterized in that: The prepared WPU emulsion was vacuum distilled to remove acetone, and filtered through a 200-mesh filter to obtain a core emulsion with a solid content of 30%, and the ratio of WPU prepolymer to water was 3:

10.

7. The method for preparing a food packaging bag printing coating according to claim 3, characterized in that: The emulsion polymerization method described in step (3) is as follows: the core emulsion is added to a four-necked flask, heated to 75°C, and then part of the pre-emulsion and part of the ammonium persulfate solution are added to the four-necked flask, stirred and reacted for 30 minutes, and the remaining pre-emulsion and ammonium persulfate solution are slowly added dropwise at a uniform speed within 2 hours while maintaining the temperature at 75°C.

8. The method for preparing a food packaging bag printing coating according to claim 3, characterized in that: The polymerization emulsion aging method described in step (3) is as follows: heating the polymerization emulsion to 85° C. and keeping the temperature for 1 hour to ensure that the monomer conversion rate is not less than 98%; The polymer emulsion adjustment method in step (3) is as follows: the matured polymer emulsion is cooled to 30° C. at room temperature, the pH value is adjusted to 8.0 by titrating with ammonia water, and the core-shell emulsion is filtered through a 200-mesh filter to obtain the core-shell emulsion; A UV photoinitiator was added to the filtered core-shell emulsion, with the UV photoinitiator accounting for 2% of the solid content of the shell layer, and ultrasonically dispersed for 30 minutes.

9. The method for preparing a food packaging bag printing coating according to claim 3, characterized in that: Step (4) The inorganic pigment and dispersant are mixed with water and then sand-ground to a fineness of no more than 5 μm, and then core-shell emulsion, nano- , silane coupling agent, stirring at a medium speed of 500 rpm for 20 minutes, adding leveling agent and defoaming agent, stirring at a low speed of 200 rpm for 10 minutes, and filtering the obtained food packaging bag printing coating through a 200-mesh filter.

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