CN114854254B - Water-based finishing paint for three-piece food cans and preparation method thereof - Google Patents

Abstract

The invention discloses a water-based finishing paint for a three-piece food can and a preparation method thereof, wherein the water-based finishing paint comprises the following raw materials in percentage by weight: 20 to 65 percent of acrylic resin water dispersion, 1 to 15 percent of acrylic resin water solution, 5 to 15 percent of water-soluble amino resin, 0 to 8 percent of blocked isocyanate, 0 to 5 percent of film forming solvent, 1 to 3 percent of neutralizer, 3 to 8 percent of wax emulsion, 0.1 to 0.5 percent of defoamer, 0.1 to 1.0 percent of wetting leveling agent, 0.1 to 0.5 percent of catalyst and 20 to 30 percent of deionized water. The water-based finishing coating has low VOC content and is environment-friendly, the problem of whitening caused by vapor permeation during high-temperature sterilization can be solved, and the performances of adhesion, processing impact resistance, scratch resistance, wear resistance and the like of the product can meet the requirements of the external coating performance of three cans for food and beverage.

Description

Water-based finishing paint for three-piece food cans and preparation method thereof

Technical Field

The invention relates to the technical field of coatings, in particular to a water-based finishing coating for three-piece food cans and a preparation method thereof.

Background

The three-piece type metal can has been used for about 200 years, and is a packaging container formed by using a coated and printed metal sheet as a material and performing compression joint, adhesion or resistance welding processing, and comprises a can body, a can bottom and a can cover. Is often used as a canning container for food, beverage, dry powder, chemical products and spray products.

The outer wall paint of the canned container for food and beverage products consists of a primer, ink and a finishing paint, wherein the primer comprises a white magnetic paint and a transparent primer, and has the functions of covering a substrate and a printing substrate; the ink provides information and decoration functions, and the finishing coating provides protection functions of corrosion resistance, scratch resistance and the like. The outer wall paint has excellent adhesion, excellent impact resistance, excellent glossiness, excellent high temperature steaming resistance, excellent whitening resistance, excellent wear resistance, excellent scratch resistance and other physical and chemical performance.

Currently, the coating for the outer wall of three-piece cans of food and beverage used in the market is mostly an oil coating. The paint uses a large amount of organic solvents such as dimethylbenzene, trimethylbenzene, tetramethylbenzene and the like in the production and coating processes, has larger pungent smell and a large amount of toxic organic volatile matters, and has VOC content of up to 500-600g/L, thereby causing harm to the health of production workers and causing pollution to the environment. In addition, the oily finishing paint belongs to dangerous chemicals, and is not beneficial to transportation, storage and production safety; the manufacturer needs to pay 4% of consumption tax according to the requirement of environmental protection regulations, and needs to transport by dangerous chemical special vehicles according to the regulations of dangerous chemical transportation management, thereby increasing the production cost.

With the gradual tightening of environmental regulations, development and application of pollution-free and pollution-free environmental protection paint to replace the traditional oily paint for three-piece cans are imperative. The alternative scheme is water-based paint, high-solid-content paint and radiation curing paint, wherein the water-based paint has the advantages of being capable of following the coating production equipment of the prior oil paint and needing no equipment transformation or new equipment compared with the other two alternative schemes. The advantage is a preferable transformation scheme for the three-piece can production industry of foods and beverages with high price competition pressure, which can save the environmental protection transformation cost.

The compactness of the paint film of the water-based paint in the related technology is poor, and the whitening problem is easy to occur during the high-temperature sterilization of three cans of food and beverage.

Disclosure of Invention

In order to solve the problems, the invention provides an aqueous finishing coating for a three-piece food can and a preparation method thereof. The water-based finishing coating has low VOC content and is environment-friendly, the problem of whitening caused by vapor permeation during high-temperature sterilization can be solved, and the performances of adhesion, processing impact resistance, scratch resistance, wear resistance and the like of the product can meet the requirements of the external coating performance of three cans for food and beverage.

In order to achieve the above purpose, an embodiment of one aspect of the present invention provides an aqueous finishing coating for a three-piece food can, comprising the following raw materials in weight percent: 20 to 65 percent of acrylic resin water dispersion, 1 to 15 percent of acrylic resin water solution, 5 to 15 percent of water-soluble amino resin, 0 to 8 percent of blocked isocyanate, 0 to 5 percent of film forming solvent, 1 to 3 percent of neutralizer, 3 to 8 percent of wax emulsion, 0.1 to 0.5 percent of defoamer, 0.1 to 1.0 percent of wetting leveling agent, 0.1 to 0.5 percent of catalyst and 20 to 30 percent of deionized water.

According to the aqueous finishing coating for the three-piece food can, two aqueous acrylic resins are matched in a synergistic manner, and the small-particle-size acrylic resin aqueous solution fills gaps among acrylic resin aqueous dispersions with larger particle sizes, so that the problem of whitening caused by water vapor permeation during high-temperature sterilization is solved. The water-soluble amino resin and the closed isocyanate resin cross-linking agent are matched, so that the performances of the product, such as adhesive force, processing impact resistance, scratch resistance, wear resistance and the like, can meet the performance requirements of the outer coating of the three-piece can for food and beverage. The water-based finishing coating takes water as a dispersion solvent, only a small amount of propylene glycol monobutyl ether solvent and water volatilize in the coating production and coating process, has low VOC content of 50-100 g/L, is environment-friendly, and is a green and safe product without benzene solvents such as 100# and 150# and xylene. The solid content of the water-based finishing coating is 40% -47%, the viscosity (T-4, 25 ℃) is 80-90s, the similar solid content and viscosity range of the conventional oil-based finishing coating for three cans of food and beverage are achieved, the conventional oil-based coating is replaced, the construction is not required to change coating equipment and process parameters, and the labor is saved. The water-based finishing coating has high flash point, the flash point of a closed cup is higher than 93 ℃, the water-based finishing coating is nonflammable, is a non-dangerous chemical, is safe to use, transport and store, can be transported according to common goods, does not need to be transported by a special vehicle for dangerous chemicals, and can save logistics cost.

Optionally, the glass transition temperature of the acrylic resin water dispersion is 20-80 ℃, the acid value is 40-100 mg KOH/g, the hydroxyl value is 30-70 mg KOH/g, the solid content is 40-50%, and the particle size is 150-260 nm.

Further, the acrylic resin aqueous dispersion is polymerized by an emulsion polymerization method from the following raw materials: 1 to 2 percent of N, N-dimethylethanolamine, 0.1 to 1.0 percent of initiator, 10 to 25 percent of styrene, 0.1 to 8 percent of methacrylic acid and 3 to 15 percent of isooctyl methacrylate; 3% -15% of butyl methacrylate; 0.1 to 5 percent of hydroxyethyl acrylate; 0.1 to 5 percent of glycidyl methacrylate; 0.1 to 1.0 percent of emulsifying agent; 50-60% of deionized water.

Optionally, the glass transition temperature of the acrylic resin aqueous solution is-30-0 ℃, the acid value is 60-120 mg KOH/g, the hydroxyl value is 30-70 mg KOH/g, and the solid content is 50-60%.

Further, the acrylic resin aqueous solution is polymerized by a solution polymerization method from the following raw materials: 2 to 5 percent of N, N-dimethylethanolamine, 0.1 to 1.5 percent of initiator, 5 to 20 percent of styrene, 5 to 20 percent of methyl methacrylate, 1 to 7 percent of acrylic acid, 10 to 30 percent of butyl acrylate, 10 to 30 percent of isooctyl acrylate, 0 to 5 percent of hydroxypropyl acrylate, 15 to 30 percent of propylene glycol monobutyl ether and 15 to 30 percent of deionized water.

Optionally, the water-soluble amino resin is a benzoguanamine formaldehyde resin.

Further, the water-soluble amino resin is one or more of n-butanol etherified benzoguanamine formaldehyde resin, isobutanol etherified benzoguanamine formaldehyde resin, high methyl etherified benzoguanamine formaldehyde resin, partial methyl etherified benzoguanamine formaldehyde resin and mixed etherified benzoguanamine formaldehyde resin.

Optionally, the blocked isocyanate is one or more of toluene diisocyanate, hexamethylene diisocyanate and isophorone diisocyanate (IPDI) which are used as a blocking agent of phenol, caprolactam, 3, 5-dimethylpyrazole or butanone oxime; the neutralizing agent is one or more of N, N-dimethylethanolamine, triethylamine, 2-dimethylamino-2-methyl-1-propanol, tourmaline, triethanolamine and sodium hydroxide; the film forming solvent is one or more of ethylene glycol monobutyl ether, ethylene glycol ethyl ether, alkyl ether of n-butyl alcohol and alkyl ether of propylene glycol; the wax emulsion is one or more of palm wax, polytetrafluoroethylene wax, polyethylene wax and polytetrafluoroethylene modified micro powder wax; the wetting and leveling agent is polyether siloxane copolymer; the catalyst is one or more of closed-type p-toluenesulfonic acid, dinonylnaphthalene sulfonic acid, dinonylnaphthalene disulfonic acid and dodecylbenzene sulfonic acid; the defoaming agent is one or more of mineral oil, silicon dioxide, polyether siloxane and polyester.

According to an embodiment of the present invention, the second aspect of the present invention further provides a method for preparing an aqueous finishing coating, including the steps of:

(1) Adding the acrylic resin aqueous dispersion and the acrylic resin aqueous solution into a dispersing cylinder, and dispersing for 5min at a rotating speed of 500 r/min;

(2) Adding a neutralizing agent and a film forming solvent into the solution dispersed in the step (1), and dispersing for 15-20 min at a rotating speed of 700 r/min;

(3) Adding water-soluble amino resin and blocked isocyanate into the solution dispersed in the step (2), and dispersing for 10-15 min at the rotating speed of 600 r/min;

(4) Adjusting the rotating speed of the dispersion cylinder in the step (3) to 500r/min, sequentially adding the wax emulsion, the wetting and leveling agent, the defoaming agent and the catalyst while rotating, and re-dispersing for 15min;

(5) Adding part of deionized water into the solution dispersed in the step (4), dispersing for 10min at the rotating speed of 300r/min, sampling and inspecting, adding the rest of deionized water according to the pH value, viscosity and solid content detected by the sample, and stirring and dispersing uniformly to obtain the water-based finishing coating.

According to the preparation method of the water-based finishing material, two water-based acrylic resins are matched in a synergistic way, and the acrylic resin aqueous solution with small particle size fills gaps among acrylic resin aqueous dispersions with larger particle size, so that the problem of whitening caused by water vapor permeation during high-temperature sterilization is solved, and the performances of the product, such as adhesive force, processing impact resistance, scratch resistance, wear resistance and the like, can meet the requirements of the external coating performance of three cans for food and beverage by matching with the water-soluble amino resin and the closed isocyanate resin cross-linking agent; the prepared water-based finishing coating takes water as a dispersion solvent, only a small amount of propylene glycol monobutyl ether solvent and water volatilize in the coating production and coating process, the VOC content is 50-100 g/L, and the water-based finishing coating is environment-friendly and is a green safety product which does not contain benzene solvents such as 100# and 150# and xylene; the prepared water-based finishing coating has the solid content of 40-47% and the viscosity (T-4, 25 ℃) of 80-90s, achieves the similar solid content and viscosity range of the conventional oil-based finishing coating for three cans of food and beverage, replaces the conventional oil-based coating, does not need to change coating equipment and process parameters in construction, and saves manpower; the prepared water-based finishing coating has high flash point, the flash point of a closed cup is more than 93 ℃, the water-based finishing coating is nonflammable, is a non-dangerous chemical, is safe to use, transport and store, can be transported according to common goods, does not need to be transported by a special vehicle for dangerous chemicals, and can save the logistics cost

Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention.

Detailed Description

The technical scheme of the invention is described below through specific examples. It is to be understood that the mention of one or more method steps of the present invention does not exclude the presence of other method steps before and after the combination step or that other method steps may be interposed between these explicitly mentioned steps; it should also be understood that these examples are illustrative of the present invention and are not intended to limit the scope of the present invention. Moreover, unless otherwise indicated, the numbering of the method steps is merely a convenient tool for identifying the method steps and is not intended to limit the order of arrangement of the method steps or to limit the scope of the invention in which the invention may be practiced, as such changes or modifications in their relative relationships may be regarded as within the scope of the invention without substantial modification to the technical matter.

In order to better understand the above technical solution, exemplary embodiments of the present invention are described in more detail below. While exemplary embodiments of the invention are shown, it should be understood that the invention may be embodied in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

The test materials adopted by the invention are all common commercial products and can be purchased in the market.

The blocked isocyanate according to the embodiment of the invention is used as a crosslinking agent, and is selected from at least one of phenol, caprolactam, 3, 5-dimethylpyrazole, toluene diisocyanate (MDI) of butanone oxime, hexamethylene Diisocyanate (HDI) and isophorone diisocyanate (IPDI), preferably 3, 5-dimethylpyrazole blocked hexamethylene diisocyanate and isophorone diisocyanate curing agent, and commercially available Bayhydur BL XP 2706 of the kestosis company.

Wherein, the water-soluble amino resin of the embodiment of the invention is benzoguanamine formaldehyde resin; the crosslinking agent is at least one selected from n-butanol etherified benzoguanamine formaldehyde resin, isobutanol etherified benzoguanamine formaldehyde resin, high methyl etherified benzoguanamine formaldehyde resin, partial methyl etherified benzoguanamine formaldehyde resin and mixed etherified benzoguanamine formaldehyde resin, preferably mixed etherified benzoguanamine formaldehyde resin, and is selected from Resimene CE8824 of commercially available Inboard or CYMEL 1123 of allnex.

The neutralizer of the embodiment of the invention is at least one selected from N, N-dimethylethanolamine, triethylamine, 2-dimethylamino-2-methyl-1-propanol, tourmaline, triethanolamine and sodium hydroxide. Specifically, the neutralizing agent is present in an amount of about 20 to 100% mol based on the acid in the compound to be neutralized, preferably N, N-dimethylethanolamine.

The film forming solvent in the embodiment of the invention is at least one selected from ethylene glycol monobutyl ether, ethylene glycol ethyl ether, n-butanol and alkyl ether of propylene glycol, and is preferably propylene glycol monobutyl ether.

The wax emulsion of the embodiment of the invention is at least one selected from palm wax, polytetrafluoroethylene wax, polyethylene wax and polytetrafluoroethylene modified micro powder wax, preferably polytetrafluoroethylene modified micro powder wax, and commercially available Lanco of Lubo is selected ^TM A wax emulsion formulated with TF 1780 EFC.

The wetting and leveling agent provided by the embodiment of the invention is a silicon copolymer and a fluorine copolymer with strong surface tension reduction and strong penetrating and diffusing capacity, preferably a polyether siloxane copolymer, and commercially available TEGO Wet270, TEGO Wet280 and TEGO Tain 4100 of Digao company are selected.

Among them, the defoamer of the present embodiment is at least one of mineral oil, silica, polyether siloxane, polyester, preferably polyether siloxane copolymer, and is selected from TEGO Foamex 825 or BYK011 of commercial Digao company.

The catalyst of the embodiment of the invention is a closed sulfonate baking varnish curing catalyst, and is at least one selected from closed p-toluenesulfonic acid, dinonylnaphthalene sulfonic acid, dinonylnaphthalene disulfonic acid and dodecylbenzene sulfonic acid, preferably closed dinonylnaphthalene sulfonic acid. NACURE1419 was selected from the commercially available King company.

The invention will now be described with reference to specific examples, which are intended to be illustrative only and not limiting in any way.

Example 1

An aqueous finishing paint for three-piece food cans comprises the following raw material components:

wherein the glass transition temperature of the aqueous acrylic resin dispersion is 42 ℃ (calculated by fox formula), the acid value (calculated by resin solid amount) is 46.7mg KOH/g, the hydroxyl value (calculated by resin solid amount) is 34.68mg KOH/g, the solid content is 42%, the particle size is 150 nm-260 nm, and the VOC content is 12.5g/L.

Specifically, the preparation of the acrylic resin aqueous dispersion a includes:

to prepare a 1Kg batch, nitrogen was introduced into a four-necked flask having a capacity of 2L, 452g of deionized water and 6.0g of reactive emulsifier were added thereto, heated to 80℃and stirred for at least 10 minutes to displace air in the system, and the reaction vessel was allowed to react all the way under nitrogen. Preparation of acrylic monomer mixture C in a separate premix vessel: 200g of styrene, 30g of methacrylic acid, 50g of isooctyl methacrylate, 60g of butyl methacrylate, 30g of hydroxyethyl acrylate and 48g of glycidyl methacrylate; 30% of the above mixed monomer C was taken and added to a four-necked flask, and stirred and mixed for 30 minutes while maintaining the temperature at 80 ℃. Thereafter, separately, 2g of ammonium persulfate and 10.0g of deionized water were mixed and added to a four-necked flask, and mixed for 30 minutes while maintaining the temperature at 80℃at which point the reaction product was a milky white liquid with slight bluish light. 1.4g of t-butylhydroperoxide was added to the remaining monomer mixture C, and the premix was pumped into a four-necked flask over 120min while maintaining the temperature at 80 ℃. After the premix was pumped, the premix vessel and pumping lines were rinsed with 15g deionized water into a four-necked flask, followed by incubation at 80℃for 30min. Then, 0.7g of t-butylhydroperoxide was added, and the vessel was again rinsed with 5.0g of deionized water and maintained at 80℃for 60 minutes.

0.1g of N, N-dimethylethanolamine, 30.0g of deionized water and 0.008g of ferrous sulfate heptahydrate were mixed and charged into a four-necked flask, and the mixture was kept at 70℃for 30 minutes. 10g of N, N-dimethylethanolamine and 49.8g of deionized water were further mixed and added to a four-necked flask, and the mixture was kept for 30 minutes. The reaction product was filtered off with cooling and had a solids content of 42% NV.

Wherein, the glass transition temperature of the acrylic resin aqueous solution is-18 ℃ (calculated by a fox formula), the acid value (calculated by the resin solid amount) is 91.6mg KOH/g, the hydroxyl value (calculated by the resin solid amount) is 33.82mg KOH/g, the solid content is 50-53%, and the VOC content is 200-230 g/L.

Specifically, preparation of an acrylic resin aqueous solution a:

to prepare a 1Kg batch, 150g propylene glycol monobutyl ether was added to a 2L capacity four-necked flask and heated to 110 ℃. A premix of 70g styrene, 80g methyl methacrylate, 120g butyl acrylate, 140g isooctyl acrylate, 40g hydroxypropyl acrylate, 60g acrylic acid, 13.25g Benzoyl Peroxide (BPO) was prepared in a separate premix vessel. The premix was pumped into the four-necked flask over 150 minutes while maintaining the temperature at 105-110 ℃. After the premix pumping was completed, the premix vessel and pumping lines were flushed with 15g propylene glycol monobutyl ether, followed by incubation at 110℃for 30min. 0.7g of BPO was added, followed by 3.0g of propylene glycol monobutyl ether and incubation at 110℃for 60min. The addition of 0.7g of BPO and 3.0g of propylene glycol monobutyl ether was repeated until the conversion of the reaction was greater than 99%. The batch was cooled to 80℃and 45.0g of N, N-dimethylethanolamine were added and held for 15min. 259.35g of deionized water is added dropwise, the time is 30min, after the deionized water is added, the mixture is stirred and dispersed for 30min, and a reaction product is filtered, wherein the solid content NV (nanometer) is 51.5%, and the VOC (volatile organic compound) content is 224g/L.

Preparation of the water-based finishing paint:

1) Adding the acrylic resin aqueous dispersion A and the acrylic resin aqueous solution A into a clean dispersing cylinder according to the formula amount, adjusting the rotating speed to 500r/min, and dispersing for 5min;

2) After the components in the step 1) are uniformly dispersed, adding N, N-dimethylethanolamine and propylene glycol monobutyl ether in the formula dosage, adjusting the rotating speed to 700r/min, and dispersing for 20min;

3) After the components in the step 2) are uniformly dispersed, adding water-soluble amino resin and blocked isocyanate in the formula dosage, adjusting the rotating speed to 600r/min, and dispersing for 13min;

4) Rotating speed to 500r/min, sequentially adding the wax emulsion, wetting and leveling agent, defoamer and catalyst with the formula dosage while rotating, and dispersing for 15min after the addition is finished;

5) After the dispersion in the step 4), adding 90% deionized water with the formula dosage, dispersing for 10min at the rotating speed of 300r/min, sampling and inspecting, adding deionized water and a neutralizing agent, stirring and dispersing uniformly according to the detected PH value, viscosity and solid content, adjusting the viscosity to 87s (T-4, 25 ℃), the solid content to 44.53%, and the PH value to 8.0-8.5.

6) And (3) filtering and packaging, namely filtering and packaging the qualified product by a 200-mesh filter screen to obtain the finished product of the water-based finishing coating.

Example 2

An aqueous finishing paint for three-piece food cans comprises the following raw material components:

wherein the aqueous acrylic resin dispersion has a glass transition temperature of 26 ℃ (calculated by fox formula), an acid value (calculated by resin solids) of 46.7mg KOH/g, a hydroxyl value (calculated by resin solids) of 57.5mg KOH/g, a solid content of 42%, a particle diameter of 150nm to 260nm, and a VOC content of 12.5g/L.

Specifically, the preparation of the acrylic resin aqueous dispersion B includes:

to prepare a 1Kg batch, nitrogen was introduced into a four-necked flask having a capacity of 2L, 452g of deionized water and 6.0g of reactive emulsifier were added thereto, heated to 80℃and stirred for at least 10 minutes to displace air in the system, and the reaction vessel was allowed to react all the way under nitrogen. Preparation of acrylic monomer mixture C in a separate premix vessel: 180g of styrene, 30g of methacrylic acid, 70g of isooctyl methacrylate, 60g of butyl methacrylate, 50g of hydroxyethyl acrylate and 30g of glycidyl methacrylate; 30% of the above mixed monomer C was taken and added to a four-necked flask, and stirred and mixed for 30 minutes while maintaining the temperature at 80 ℃. Thereafter, separately, 2g of ammonium persulfate and 10.0g of deionized water were mixed and added to a four-necked flask, and mixed for 30 minutes while maintaining the temperature at 80℃at which point the reaction product was a milky white liquid with slight bluish light. 1.4g of t-butylhydroperoxide was added to the remaining monomer mixture C, and the premix was pumped into a four-necked flask over 120min while maintaining the temperature at 80 ℃. After the premix was pumped, the premix vessel and pumping lines were rinsed with 15g deionized water into a four-necked flask, followed by incubation at 80℃for 30min. Then, 0.7g of t-butylhydroperoxide was added, and the vessel was again rinsed with 5.0g of deionized water and maintained at 80℃for 60 minutes.

0.1g of N, N-dimethylethanolamine, 30.0g of deionized water and 0.008g of ferrous sulfate heptahydrate were mixed and charged into a four-necked flask, and the mixture was kept at 70℃for 30 minutes. 10g of N, N-dimethylethanolamine and 49.8g of deionized water were further mixed and added to a four-necked flask, and the mixture was kept for 30 minutes. The reaction product was filtered off with cooling and had a solids content of 42% NV.

In this example, the acrylic resin aqueous solution a was the same as that of example 1, and the production method was the same.

Preparation of the water-based finishing paint:

1) Adding the acrylic resin aqueous dispersion B and the acrylic resin aqueous solution A into a clean dispersing cylinder according to the formula amount, adjusting the rotating speed to 500r/min, and dispersing for 5min;

2) After the components in the step 1) are uniformly dispersed, adding N, N-dimethylethanolamine and propylene glycol monobutyl ether in the formula dosage, adjusting the rotating speed to 700r/min, and dispersing for 16min;

3) After the components in the step 2) are uniformly dispersed, adding water-soluble amino resin and blocked isocyanate in the formula dosage, adjusting the rotating speed to 600r/min, and dispersing for 15min;

4) Rotating speed to 500r/min, sequentially adding the wax emulsion, wetting and leveling agent, defoamer and catalyst with the formula dosage while rotating, and dispersing for 15min after the addition is finished;

5) After the dispersion in the step 4), adding 90% deionized water with the formula dosage, dispersing for 10min at the rotating speed of 300r/min, sampling and inspecting, and then adding deionized water and a neutralizing agent, stirring and dispersing uniformly according to the detected pH value, viscosity and solid content, adjusting the viscosity to 92s (T-4, 25 ℃), wherein the solid content is 44.38%, and the pH value is 8.0-8.5.

6) And (3) filtering and packaging, namely filtering and packaging the qualified product by a 200-mesh filter screen to obtain the finished product of the water-based finishing coating.

Example 3

An aqueous finishing paint for three-piece food cans comprises the following raw material components:

wherein the aqueous acrylic resin dispersion has a glass transition temperature of 26 ℃ (calculated by fox formula), an acid value (calculated by resin solids) of 46.7mg KOH/g, a hydroxyl value (calculated by resin solids) of 57.5mg KOH/g, a solid content of 42%, a particle diameter of 150nm to 260nm, and a VOC content of 12.5g/L.

In this example, the aqueous acrylic resin dispersion A was the same as that of example 2, and the production method was the same.

Preparation of the water-based finishing paint:

1) Adding the acrylic resin aqueous dispersion B, N, N-dimethylethanolamine and propylene glycol butyl ether into a clean dispersing cylinder according to the formula amount, adjusting the rotating speed to 700r/min, and dispersing for 20min;

2) After the components in the step 1) are uniformly dispersed, adding water-soluble amino resin and blocked isocyanate in the formula dosage, adjusting the rotating speed to 600r/min, and dispersing for 10min;

3) Rotating speed to 500r/min, sequentially adding the wax emulsion, wetting and leveling agent, defoamer and catalyst with the formula dosage while rotating, and dispersing for 15min after the addition is finished;

4) After the dispersion in the step 3), adding 90% deionized water with the formula dosage, dispersing for 10min at the rotating speed of 300r/min, sampling and inspecting, and then adding deionized water and a neutralizing agent, stirring and dispersing uniformly according to the detected pH value, viscosity and solid content, adjusting the viscosity to 80s (T-4, 25 ℃), wherein the solid content is 44.61%, and the pH value is 8.0-8.5.

5) And (3) filtering and packaging, namely filtering and packaging the qualified product by a 200-mesh filter screen to obtain the finished product of the water-based finishing coating.

Comparative example 1

An aqueous finishing paint for three-piece food cans comprises the following raw material components:

wherein the glass transition temperature of the aqueous acrylic resin dispersion is 18.8 ℃ (calculated by fox formula), the acid value (calculated by resin solid amount) is 109mg KOH/g, the hydroxyl value (calculated by resin solid amount) is 23.12mg KOH/g, the solid content is 42%, the particle size is 150 nm-260 nm, and the VOC content is 22.5g/L.

Specifically, the preparation of the acrylic resin aqueous dispersion C includes:

to prepare a 1Kg batch, nitrogen was introduced into a four-necked flask having a capacity of 2L, 452g of deionized water and 6.0g of reactive emulsifier were added thereto, heated to 80℃and stirred for at least 10 minutes to displace air in the system, and the reaction vessel was allowed to react all the way under nitrogen. Preparation of acrylic monomer mixture C in a separate premix vessel: 170g of styrene, 70g of methacrylic acid, 78g of isooctyl methacrylate, 60g of butyl methacrylate, 20g of hydroxyethyl acrylate and 20g of glycidyl methacrylate; 30% of the above mixed monomer C was taken and added to a four-necked flask, and stirred and mixed for 30 minutes while maintaining the temperature at 80 ℃. Thereafter, separately, 2g of ammonium persulfate and 10.0g of deionized water were mixed and added to a four-necked flask, and mixed for 30 minutes while maintaining the temperature at 80℃at which point the reaction product was a milky white liquid with slight bluish light. 1.4g of t-butylhydroperoxide was added to the remaining monomer mixture C, and the premix was pumped into a four-necked flask over 120min while maintaining the temperature at 80 ℃. After the premix was pumped, the premix vessel and pumping lines were rinsed with 15g deionized water into a four-necked flask, followed by incubation at 80℃for 30min. Then, 0.7g of t-butylhydroperoxide was added, and the vessel was again rinsed with 5.0g of deionized water and maintained at 80℃for 60 minutes.

0.1g of N, N-dimethylethanolamine, 30.0g of deionized water and 0.008g of ferrous sulfate heptahydrate were mixed and charged into a four-necked flask, and the mixture was kept at 70℃for 30 minutes. 20g of N, N-dimethylethanolamine and 39.8g of deionized water were further mixed and added to a four-necked flask, and the mixture was kept for 30 minutes. The reaction product was filtered off with cooling and had a solids content of 42% NV.

Wherein, the glass transition temperature of the acrylic resin aqueous solution is-18 ℃ (calculated by a fox formula), the acid value (calculated by the resin solid amount) is 91.6mg KOH/g, the hydroxyl value (calculated by the resin solid amount) is 33.82mg KOH/g, the solid content is 50-53%, and the VOC content is 200-230 g/L.

The acrylic resin aqueous solution a of this comparative example was the same as the acrylic resin aqueous solution of example 1, and the production method was the same.

Preparation of the water-based finishing paint:

1) Adding the acrylic resin aqueous dispersion C and the acrylic resin aqueous solution A into a clean dispersing cylinder according to the formula amount, adjusting the rotating speed to 500r/min, and dispersing for 5min;

2) After the components in the step 1) are uniformly dispersed, adding N, N-dimethylethanolamine and propylene glycol monobutyl ether in the formula dosage, adjusting the rotating speed to 700r/min, and dispersing for 20min;

3) After the components in the step 2) are uniformly dispersed, adding water-soluble amino resin and blocked isocyanate in the formula dosage, adjusting the rotating speed to 600r/min, and dispersing for 13min;

4) Rotating speed to 500r/min, sequentially adding the wax emulsion, wetting and leveling agent, defoamer and catalyst with the formula dosage while rotating, and dispersing for 15min after the addition is finished;

5) After the dispersion in the step 4), adding 90% deionized water with the formula dosage, dispersing for 10min at the rotating speed of 300r/min, sampling and inspecting, and then adding deionized water and a neutralizing agent, stirring and dispersing uniformly according to the detected pH value, viscosity and solid content, adjusting the viscosity to 95s (T-4, 25 ℃), wherein the solid content is 44.40%, and the pH value is 8.0-8.5.

6) And (3) filtering and packaging, namely filtering and packaging the qualified product by a 200-mesh filter screen to obtain the finished product of the water-based finishing coating.

Comparative example 2

An aqueous finishing paint for three-piece food cans comprises the following raw material components:

wherein the glass transition temperature of the aqueous acrylic resin dispersion is 18.8 ℃ (calculated by fox formula), the acid value (calculated by resin solid amount) is 109mg KOH/g, the hydroxyl value (calculated by resin solid amount) is 23.12mg KOH/g, the solid content is 42%, the particle size is 150 nm-260 nm, and the VOC content is 13g/L.

The acrylic resin aqueous dispersion C of this comparative example was the same as that of comparative example 1, and the production method was the same.

Wherein the glass transition temperature of the aqueous acrylic resin solution was 9.6 ℃ (fox formula calculation), the acid value (based on resin solids) was 91.6mg KOH/g, the hydroxyl value (based on resin solids) was 33.82mg KOH/g, the solid content was 51.5%, and the VOC content was 224g/L.

Specifically, preparation of an acrylic resin aqueous solution B:

to prepare a 1Kg batch, 150g propylene glycol monobutyl ether was added to a 2L capacity four-necked flask and heated to 110 ℃. A premix of 150g of styrene, 80g of methyl methacrylate, 100g of butyl acrylate, 80g of isooctyl acrylate, 40g of hydroxypropyl acrylate, 60g of acrylic acid, 13.25g of Benzoyl Peroxide (BPO) was prepared in a separate premix vessel. The premix was pumped into the four-necked flask over 150 minutes while maintaining the temperature at 105-110 ℃. After the premix pumping was completed, the premix vessel and pumping lines were flushed with 15g propylene glycol monobutyl ether, followed by incubation at 110℃for 30min. 0.7g of BPO was added, followed by 3.0g of propylene glycol monobutyl ether and incubation at 110℃for 60min. The addition of 0.7g of BPO and 3.0g of propylene glycol monobutyl ether was repeated until the conversion of the reaction was greater than 99%. The batch was cooled to 80℃and 45.0g of N, N-dimethylethanolamine was added and kept for 15min, 259.35g of deionized water was added dropwise over 30min, and after addition of deionized water, the reaction product was filtered off with a solids content of 51.5% NV by stirring for a further 30min.

Preparation of the water-based finishing paint:

1) Adding the acrylic resin aqueous dispersion C and the acrylic resin aqueous solution B into a clean dispersing cylinder according to the formula amount, adjusting the rotating speed to 500r/min, and dispersing for 5min;

2) After the components in the step 1) are uniformly dispersed, adding N, N-dimethylethanolamine and propylene glycol monobutyl ether in the formula dosage, adjusting the rotating speed to 700r/min, and dispersing for 20min;

3) After the components in the step 2) are uniformly dispersed, adding water-soluble amino resin and blocked isocyanate in the formula dosage, adjusting the rotating speed to 600r/min, and dispersing for 13min;

4) Rotating speed to 500r/min, sequentially adding the wax emulsion, wetting and leveling agent, defoamer and catalyst with the formula dosage while rotating, and dispersing for 15min after the addition is finished;

5) After the dispersion in the step 4), adding 90% deionized water with the formula dosage, dispersing for 10min at the rotating speed of 300r/min, sampling and inspecting, and then adding deionized water and a neutralizing agent, stirring and dispersing uniformly according to the detected pH value, viscosity and solid content, adjusting the viscosity to 103s (T-4, 25 ℃), wherein the solid content is 44.40%, and the pH value is 8.0-8.5.

6) And (3) filtering and packaging, namely filtering and packaging the qualified product by a 200-mesh filter screen to obtain the finished product of the water-based finishing coating.

Example 4 preparation of three-piece can outer composite coating:

(1) A three-piece tin plate was coated with a commercially available conventional oil-based white magnetic primer (HyCan 1905) and baked to cure into a film: 12# bar blade coating, baking conditions: the thickness of the dry film of the primer is 12-14 g/square meter at 180 ℃ for 12 min.

(2) Printing ink on the base coat obtained in the step (1), wherein the ink can be ink materials well known in the art, such as baking curable ink, UV or UV-LED photo-curable ink.

(3) Coating the aqueous finishing paint of the example 1, the example 2, the example 3, the comparative example 1 or the comparative example 2 on the printing coating obtained in the step (2), baking and curing to form a film, doctor blade coating an 8# wire rod, and baking under the conditions: the thickness of the dry film of the finishing coating is 6-7 g/square meter after 12min at 180 ℃.

Comparative example 3 preparation of three can outer composite coating

(1) A three-piece tin plate was coated with a commercially available conventional oil-based white magnetic primer (HyCan 1905) and baked to cure into a film: 12# bar blade coating, baking conditions: the thickness of the dry film of the primer is 12-14 g/square meter at 180 ℃ for 12 min.

(2) Printing ink on the base coat obtained in the step (1), wherein the ink can be ink materials well known in the art, such as baking curable ink, UV or UV-LED photo-curable ink.

(3) Coating a commercially available oily finishing coating (HyCan 2705) on the printing coating obtained in the step (2), baking and curing to form a film, doctor-blading an 8# wire rod, and baking under the conditions: the thickness of the dry film of the finishing coating is 6-7 g/square meter after 12min at 180 ℃.

Test examples

1. And (3) solid content testing: according to GB1725, 1-1.1 g of sample to be tested is weighed by an aluminum foil disc with the diameter of 70-75mm, baked for 15min at 180 ℃, and then weighed, and the nonvolatile content is calculated.

2. Viscosity test: according to GB/T1723, the time-consuming flow out of a coating material at 25℃is measured using a T-4 viscosity test cup.

3. Flash point test: according to GB/T5208-2008, the method is carried out by a closed cup method.

4. VOC content testing: according to GB 23985-2009, the specific gravity and the solid content of the paint sample to be detected are measured, and the VOC content (unit g/L) of the paint sample to be detected is calculated.

5. Melamine migration test: according to GB/T31604.15-2016, 4% acetic acid is used as a simulation liquid, a coating film to be detected is soaked in the simulation liquid at 70 ℃ for 1h and 60 ℃ for 10 days, and then the melamine content in the simulation liquid is detected by a liquid chromatograph.

6. Pencil hardness test: according to GB/T6739, the maximum pencil hardness without breaking the coating by plowing is measured with a Chinese pencil.

7. Film gloss test: according to GB/T9754, the 60℃angular gloss of the coating is measured with a gloss meter.

8. Impact resistance test: according to GB/T1732, a 1Kg weight of an impact tester is used to drop and hammer the coating to be tested at a height of 50cm, and whether the coating has cracks after impact is observed.

9. Scratch resistance value test: according to GB/T9279, a scratch resistance tester is used for measuring the minimum load value of the scratch-through coating, namely the scratch resistance value of the coating.

10. Adhesion test: according to GB/T1720, 6 crisscross lattices with 1mm intervals are marked on the coating by using a hundred lattice knife, and then the positions of the marked lattices are torn by using an adhesive tape, so that the falling-off condition of the coating is visually observed.

11. Test of retort resistance: according to GB/T1733, after coating sample preparation, a high-pressure vertical sterilizer is used, and the coating is subjected to high-temperature digestion of a water phase and a steam phase at 127 ℃ for 65min, so as to observe whether the coating has the abnormality of water vapor permeation, whitening and the like.

Table 1 results of performance test of composite coating layer prepared from examples and comparative examples of finishing coating materials

As is clear from Table 1, the difference between the retort resistance (127 ℃ C./65 min) of example 1 and example 3 is that the aqueous solution of acrylic resin is not added in example 3, and it is verified that the aqueous solution of acrylic resin with smaller particle size is added to produce synergistic effect with the aqueous dispersion of acrylic resin with larger particle size, so that gaps among particles of the aqueous dispersion of acrylic resin are filled, and the problems of poor compactness of paint film caused by larger particle size of the aqueous dispersion of acrylic resin and coating whitening caused by water vapor permeation during high-temperature sterilization are solved.

As is clear from table 1, example 1 and example 2 are superior to comparative example 1 and comparative example 2 in scratch resistance and retort resistance, and are distinguished in that the aqueous acrylic resin dispersions used in comparative example 1 and comparative example 2 have lower glass transition temperatures and higher acid numbers than the aqueous acrylic resin dispersions used in example 1 and example 2. The lower the glass transition temperature of the resin, the less scratch resistant the coating film, while the higher the acid value of the resin, the more hydrophilic the coating film is, the less resistant to retort. In order to balance scratch resistance with retort resistance, the glass transition temperature of the aqueous acrylic resin dispersion should be greater than 20℃and the acid value should be less than 100mg KOH/g.

The performances of the examples 1 and 2 are equivalent to those of the comparative example 3, the VOC content is greatly reduced and the flash point is greatly increased compared with the comparative example 3, so that the finishing coating has excellent performances, completely meets the performance requirements of the finishing coating for three cans of food and beverage, can replace the traditional oily finishing coating for three cans, and is safer and more environment-friendly.

In summary, according to the aqueous finishing coating provided by the embodiment of the invention, two aqueous acrylic resins are matched in a synergistic way, and the small-particle-size acrylic resin aqueous solution fills gaps among acrylic resin aqueous dispersions with larger particle sizes, so that the problem of whitening caused by water vapor permeation during high-temperature sterilization is solved, and the performances of the product, such as adhesive force, processing impact resistance, scratch resistance, wear resistance and the like, can meet the requirements of the outer coating of a three-piece can for food and beverage by matching with the water-soluble amino resin and the closed isocyanate resin cross-linking agent; the water-based finishing coating takes water as a dispersion solvent, only a small amount of propylene glycol monobutyl ether solvent and water volatilize in the coating production and coating process, the VOC content is 50-100 g/L, and the water-based finishing coating is environment-friendly and is a green and safe product which does not contain benzene solvents such as 100# and 150# and xylene; the solid content of the water-based finishing coating is 40% -47%, the viscosity (T-4, 25 ℃) is 80-90s, the similar solid content and viscosity range of the conventional oil-based finishing coating for three cans of food and beverage are achieved, the conventional oil-based coating is replaced, the construction is not required to change coating equipment and process parameters, and the labor is saved; the water-based finishing coating has high flash point, the flash point of a closed cup is higher than 93 ℃, the water-based finishing coating is nonflammable, is a non-dangerous chemical, is safe to use, transport and store, can be transported according to common goods, does not need to be transported by a special vehicle for dangerous chemicals, and can save logistics cost.

In the description of the present specification, a description referring to terms "one embodiment," "some embodiments," "examples," "specific examples," or "some examples," etc., means that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the present invention. In this specification, schematic representations of the above terms should not be understood as necessarily being directed to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples. Further, one skilled in the art can engage and combine the different embodiments or examples described in this specification.

While embodiments of the present invention have been shown and described above, it will be understood that the above embodiments are illustrative and not to be construed as limiting the invention, and that variations, modifications, alternatives and variations may be made to the above embodiments by one of ordinary skill in the art within the scope of the invention.

Claims (7)

1. The water-based finishing paint for the three-piece food can is characterized by comprising the following raw materials in percentage by weight: 20 to 65 percent of acrylic resin water dispersion, 1 to 15 percent of acrylic resin water solution, 5 to 15 percent of water-soluble amino resin, 0 to 8 percent of blocked isocyanate, 0 to 5 percent of film forming solvent, 1 to 3 percent of neutralizer, 3 to 8 percent of wax emulsion, 0.1 to 0.5 percent of defoamer, 0.1 to 1.0 percent of wetting leveling agent, 0.1 to 0.5 percent of catalyst and 20 to 30 percent of deionized water;

the glass transition temperature of the acrylic resin water dispersion is 20-80 ℃, the acid value is 40-100 mg KOH/g, the hydroxyl value is 30-70 mg KOH/g, the solid content is 40-50%, and the particle size is 150-260 nm;

the glass transition temperature of the acrylic resin aqueous solution is-30-0 ℃, the acid value is 60-120 mg KOH/g, the hydroxyl value is 30-70 mg KOH/g, and the solid content is 50-60%.

2. The aqueous overprint varnish of claim 1, wherein the aqueous acrylic resin dispersion is polymerized by emulsion polymerization from the following materials: 1 to 2 percent of N, N-dimethylethanolamine, 0.1 to 1.0 percent of initiator, 10 to 25 percent of styrene, 0.1 to 8 percent of methacrylic acid and 3 to 15 percent of isooctyl methacrylate; 3% -15% of butyl methacrylate; 0.1 to 5 percent of hydroxyethyl acrylate; 0.1 to 5 percent of glycidyl methacrylate; 0.1 to 1.0 percent of emulsifying agent; 50-60% of deionized water.

3. The aqueous overprint varnish of claim 1, wherein the aqueous acrylic resin solution is polymerized by solution polymerization from the following materials: 2 to 5 percent of N, N-dimethylethanolamine, 0.1 to 1.5 percent of initiator, 5 to 20 percent of styrene, 5 to 20 percent of methyl methacrylate, 1 to 7 percent of acrylic acid, 10 to 30 percent of butyl acrylate, 10 to 30 percent of isooctyl acrylate, 0 to 5 percent of hydroxypropyl acrylate, 15 to 30 percent of propylene glycol monobutyl ether and 15 to 30 percent of deionized water.

4. The aqueous overprint varnish of claim 1, wherein the water soluble amino resin is a benzoguanamine formaldehyde resin.

5. The aqueous finishing coating according to claim 4, wherein the water-soluble amino resin is one or more of n-butanol etherified benzoguanamine formaldehyde resin, isobutanol etherified benzoguanamine formaldehyde resin, high methyl etherified benzoguanamine formaldehyde resin, partial methyl etherified benzoguanamine formaldehyde resin and mixed etherified benzoguanamine formaldehyde resin.

6. The aqueous finishing coating according to claim 1, wherein the blocked isocyanate is one or more of toluene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate (IPDI) as a blocking agent, phenol, caprolactam, 3, 5-dimethylpyrazole or butanone oxime; the neutralizing agent is one or more of N, N-dimethylethanolamine, triethylamine, 2-dimethylamino-2-methyl-1-propanol, tourmaline, triethanolamine and sodium hydroxide; the film forming solvent is one or more of ethylene glycol monobutyl ether, ethylene glycol ethyl ether, alkyl ether of n-butyl alcohol and alkyl ether of propylene glycol; the wax emulsion is one or more of palm wax, polytetrafluoroethylene wax, polyethylene wax and polytetrafluoroethylene modified micro powder wax; the wetting and leveling agent is polyether siloxane copolymer; the catalyst is one or more of closed-type p-toluenesulfonic acid, dinonylnaphthalene sulfonic acid, dinonylnaphthalene disulfonic acid and dodecylbenzene sulfonic acid; the defoaming agent is one or more of mineral oil, silicon dioxide, polyether siloxane and polyester.

7. The method for preparing the aqueous finishing paint as claimed in claim 1, comprising the steps of:

(1) Adding the acrylic resin aqueous dispersion and the acrylic resin aqueous solution into a dispersing cylinder, and dispersing for 5min at a rotating speed of 500 r/min;

(2) Adding a neutralizing agent and a film forming solvent into the solution dispersed in the step (1), and dispersing for 15-20 min at a rotating speed of 700 r/min;

(3) Adding water-soluble amino resin and blocked isocyanate into the solution dispersed in the step (2), and dispersing for 10-15 min at the rotating speed of 600 r/min;

(4) Adjusting the rotating speed of the dispersion cylinder in the step (3) to 500r/min, sequentially adding the wax emulsion, the wetting and leveling agent, the defoaming agent and the catalyst while rotating, and re-dispersing for 15min;

(5) Adding part of deionized water into the solution dispersed in the step (4), dispersing for 10min at the rotating speed of 300r/min, sampling and inspecting, adding the rest of deionized water according to the pH value, viscosity and solid content detected by the sample, and stirring and dispersing uniformly to obtain the water-based finishing coating.