A powder coating for easily releasing the weld seam of a food can and a preparation method thereof

Abstract

The present invention provides a powder coating for food can welds that is easy to demould, which belongs to the technical field of coatings, and specifically relates to a powder coating for food can welds that is easy to demould, comprising: modified polyester resin, titanium dioxide, barium sulfate, epoxy resin, leveling agent, surface modified silica, charge enhancer, wetting agent and degasser. The powder coating does not contain solvents and volatile toxic substances, and is safe and non-toxic. At the same time, the coating formed by the powder coating is dense, has good adhesion, impact strength and toughness, and can be well combined with different types of primers and powder coatings at joints after film formation, and can ensure the demoulding effect without affecting the overall anti-corrosion effect, which helps to improve the food safety level.

Description

Technical Field

[0001] The invention belongs to the technical field of coatings, and in particular relates to an easy-to-release powder coating for a weld of a food can and a preparation method thereof. Background Art

[0002] Powder coating is a solid coating made of solid resin as the main raw material, with the addition of additives, fillers, pigments, etc. It does not contain solvents and water, and has the advantages of safety, non-toxicity, and high raw material utilization rate. It is widely used in the fields of shipbuilding, pipelines, automobiles, wood, plastics, etc. It is also ideal for coating barrels and cans of various foods, beer, beverages and aerosols. Currently, it is increasingly used in beverage cans, food cans, and aerosol cans.

[0003] At present, most of the food cans on the market are metal cans. Due to the large variety of food in the cans, direct contact between the food and the inner wall of the food can will lead to a decrease in the quality of the food in the can, which will lead to safety and hygiene problems. At present, the more effective treatment method is to apply a layer of coating on the inner wall of the food can to avoid direct contact between the food and the inner wall of the food can. Food safety has now become the focus of people's attention. Metal cans for food are in direct contact with food, and their inner wall coatings have attracted widespread attention from the whole society. The coating formed by the coating inside the metal can for food should adhere well to the inside of the container and have sufficient chemical resistance to avoid reacting with the food contents or leaching into the food contents to cause the food to produce peculiar smell or discoloration, deterioration, and threaten people's health. Suitable powder coatings can also be used on seals, can ends, and on the outside and inside of cans, drums or containers that are in direct contact with food and alcoholic and non-alcoholic beverages; the coating can also be used to protect the seams of the container (for example, in three-piece cans used in the food industry).

[0004] Chinese patent CN112745745A discloses a food-grade coating powder coating, including polyester resin, HAA, TGIC, benzoin, wear resistance agent, anti-yellowing agent, sand grain agent, organic soil, titanium dioxide, carbon black. Chinese patent CN101932665A discloses a powder composition, an amorphous and COOH-functional first polyester obtained from IPA and / or TPA and up to 10 mol% of neopentyl glycol (NPG); (B) a second optional COOH-functional polyester obtained from an aliphatic diacid and an aliphatic diol, and (C) a curing agent containing a functional group capable of reacting with the COOH of the polyester.

[0005] In addition to the above, the coating should also have a good demoulding effect so that the food can be better separated from the food can. However, the demoulding effect of the current food can powder coating is poor. For example, the coating used for the inner wall of the luncheon meat demoulding empty can on the market is epoxy phenolic aluminum powder coating. In order to make it easy to pour out the luncheon meat can after the easy-open lid is opened, it is necessary to add more polyethylene modified micropowder with demoulding effect to the epoxy phenolic aluminum powder coating to make the inner wall coating surface very smooth so that the minced meat in the can can be separated from the empty can under the action of external force. However, the surface of the epoxy phenolic aluminum powder coating is very smooth, which will make the micropowder coating on the empty can weld not covered, and the adhesion between the empty can weld patch coating is not strong, which seriously affects the overall anti-corrosion effect or demoulding effect of the demoulding empty can coating layer.

[0006] The current solutions to the powder coating re-coating effect on the welds of empty cans are not ideal: one is to use the surface coating to leave gaps for the base coating, so that the powder coating only covers the base coating, which makes defective construction difficult and the anti-corrosion effect of the empty can coating layer is not ideal; the second is to reduce the proportion of polyethylene micropowder with demoulding effect in the demoulding coating, that is, to reduce the surface slipperiness of the coating to achieve the purpose of strong bonding with the powder coating. The disadvantage is that the fat content in the luncheon meat must be increased to ensure the demoulding effect.

[0007] In view of this, it is necessary to propose a new easy-to-release powder coating for the weld of food cans. Summary of the invention

[0008] The purpose of the present invention is to solve some or all of the problems existing in the prior art and to provide a powder coating for food can welds that is easy to demould. The powder coating does not contain solvents and volatile toxic substances, is safe and non-toxic, and at the same time, the coating formed by the powder coating is smooth and dense, has good adhesion, impact strength and toughness, and can be well combined with different types of primers and powder re-coating coatings at joints after film formation, and can ensure the demoulding effect without affecting the overall anti-corrosion effect, thereby helping to improve the level of food safety.

[0009] To achieve the above object, the present invention is achieved through the following technical solutions:

[0010] In one aspect, the present invention provides a modified polyester resin, wherein the modified polyester resin is prepared by reacting terephthalic acid and diol as monomers; wherein:

[0011] The glycols include ethylene glycol, dihydrocarveol, and guaifenesin.

[0012] In some specific embodiments, the molar ratio of ethylene glycol, hydroxycitronellol and guaifenesin in the diol is 10:0.5-1:0.5-1.8, preferably 10:0.5-0.8:0.8-1.2.

[0013] In other specific embodiments, the molar ratio of terephthalic acid to glycol is 1:1.0-1.5, preferably 1:1.1-1.3.

[0014] In some other specific embodiments, the modified polyester resin is prepared by the following method:

[0015] Terephthalic acid, ethylene glycol and hydroxycitronellol are mixed, and a catalyst is added to carry out an esterification reaction. After the reaction reaches an acid value of less than 10 mgKOH / g, guaifenesin is added and the reaction is continued until the acid value is less than 70 mgKOH / g. Then, a polycondensation reaction is carried out until the acid value is less than 60 mgKOH / g to obtain the modified polyester resin.

[0016] Furthermore, in the process of preparing the modified polyester resin, the catalyst is at least one of a titanate catalyst and an organotin catalyst, preferably a titanate catalyst and an organotin catalyst mixed and added in any proportion; wherein the organotin catalyst is preferably any one of dibutyltin, stannous octoate, and monobutyl tin oxide, and the titanate catalyst is preferably any one of tetramethyl titanate, tetrabutyl titanate, and tetraisopropyl titanate; and the amount of the catalyst added is 0.1-0.3% of the total weight of the raw materials, preferably 0.2-0.25%.

[0017] Furthermore, in the process of preparing the modified polyester resin, the temperature of the esterification reaction is 210-250° C., preferably 220-230° C.; and the pressure is 0.1-0.5 MPa, preferably 0.2-0.3 MPa.

[0018] Furthermore, during the preparation of the polyester resin, the polycondensation temperature is 250-270° C., preferably 260-270° C.; the pressure is lower than 150 Pa, preferably lower than 130 Pa.

[0019] The invention uses terephthalic acid as a dibasic acid and ethylene glycol, hydroxycitronellol and guaifenesin as dibasic alcohols to prepare a modified polyester. Compared with traditional polyester materials, the polyester molecules prepared by the invention have more flexible long chain segments and more rigid chain segments in side chains, which reduces the brittleness of the resin after curing, and increases its strength and toughness. The corrosion resistance of the obtained polyester is improved by adjusting the input ratio of each monomer. The polyester is used as a main material of a powder coating, which helps to improve the impact strength and toughness of the coating, has a significant benefit effect on the corrosion resistance of the coating, and increases food safety.

[0020] On the other hand, a powder coating for easily demoulding the weld of a food can comprises the modified polyester resin and surface-modified silica mentioned above, wherein the added amount of the surface-modified silica is 0.2-0.3 times the weight of the modified polyester resin.

[0021] In other specific embodiments, the surface-modified silica is prepared by first treating silica with an aminosilane coupling agent to obtain aminosilane coupling agent-modified silica, and then reacting with glycidyl 2-methoxyphenyl ether.

[0022] Furthermore, the preparation method of the surface modified silicon dioxide comprises the following steps:

[0023] 1) dispersing silicon dioxide in a solvent by ultrasonication, adding an aminosilane coupling agent to react, and obtaining aminosilane coupling agent-modified silicon dioxide;

[0024] 2) Adding the aminosilane coupling agent modified silica obtained in step 1) and epoxypropyl 2-methoxyphenyl ether into a solvent, stirring and reacting to obtain surface modified silica.

[0025] Preferably, in the preparation steps 1) and 2) of the surface-modified silica, the solvent is acetone or dichloromethane; the amount of the solvent is 10-50 times the weight of the material, more preferably 10-20 times.

[0026] Preferably, in step 1) of preparing the surface-modified silicon dioxide, the frequency of the ultrasound is 25-40 kHz.

[0027] Preferably, in the surface-modified silica preparation step 1), the aminosilane coupling agent is one of γ-aminopropyltriethoxysilane, γ-aminopropyltrimethoxysilane, N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane, N-(β-aminoethyl)-γ-aminopropyltriethoxysilane, N-(β-aminoethyl)-γ-aminopropylmethyldimethoxysilane, N-β-(aminoethyl)-γ-aminopropylmethyldiethoxysilane, and γ-aminoethylaminopropyltrimethoxysilane, and is further preferably N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane or N-(β-aminoethyl)-γ-aminopropyltriethoxysilane; the added amount is 0.1-0.25 times the weight of the silica.

[0028] Preferably, in the surface-modified silica preparation step 1), the reaction temperature is 50-70° C., more preferably 50-55° C.; the reaction time is 8-20 h, more preferably 8-15 h.

[0029] Preferably, in the surface-modified silica preparation step 2), the weight ratio of the aminosilane coupling agent-modified silica to glycidyl 2-methoxyphenyl ether is 1:0.1-0.2, more preferably 1:0.15-0.18.

[0030] Preferably, in the surface-modified silica preparation step 2), the reaction temperature is 50-70° C., more preferably 50-60° C.; the reaction time is 0.5-5 h, more preferably 2-3 h; and the stirring rate is 150-500 r / min.

[0031] The present invention utilizes the above method, firstly utilizes an aminosilane coupling agent to modify the surface of silicon dioxide, and then utilizes glycidyl 2-methoxyphenyl ether to perform further modification treatment, and successfully grafts glycidyl 2-methoxyphenyl ether onto the surface of silicon dioxide through the aminosilane coupling agent, thereby increasing the binding force and compatibility between silicon dioxide and resin, and adding the glycidyl 2-methoxyphenyl ether into the coating, the remaining high-activity groups on the surface of silicon dioxide enable the coating to form a film on the surface of an object and form certain crosslinks, the formed film layer is dense, the adhesion is improved, and the coating can be better combined with different types of primers and powder coatings for joints, and it is also found that the coating has a certain enhancement effect on the wear resistance of the coating.

[0032] In other specific embodiments, the food can weld easy-to-release powder coating further comprises titanium dioxide, barium sulfate, epoxy resin, leveling agent, silicon dioxide, charge enhancer, wetting agent and degassing agent.

[0033] Furthermore, the epoxy resin is bisphenol A epoxy resin, and the epoxy equivalent is 720-850 g / mol, preferably 780-800 g / mol.

[0034] Furthermore, the leveling agent is one or more polyether leveling agents, preferably Powdermate 486CFL or Powdermate 570FL. The leveling agent can promote the coating to form a flat, smooth and uniform coating film during the drying and film-forming process. The polyether leveling agent is a reactive leveling agent among powder coating leveling agents, has a long molecular chain, is solid at room temperature, and therefore does not need to adsorb any carrier, and has 100% effective ingredients.

[0035] Furthermore, the charge enhancer is one or more of long-chain polar ester compounds, preferably dodecyl acrylate. The molecules of the long-chain polar ester compounds contain polar ester groups and saturated alkyl chains, which are used to enhance the charge of the powder coating during electrostatic spraying, and eliminate or reduce the Faraday cage effect of the powder coating during electrostatic spraying.

[0036] Furthermore, the wetting agent is one or more of alkyl polyoxyethylene ethers, preferably the wetting agent ZX-105.

[0037] Furthermore, the deaerator includes but is not limited to food grade calcium stearate, stearyl stearate, polyester or a mixture of the above, preferably food grade calcium stearate.

[0038] Furthermore, the food can weld seam easy-to-release powder coating comprises the following components in parts by weight:

[0039] 100 parts of modified polyester resin, 20-30 parts of titanium dioxide, 4-6 parts of barium sulfate, 3-8 parts of epoxy resin, 0.1-1.5 parts of leveling agent, 0.2-1 parts of surface modified silica, 0.1-1 parts of charge enhancer, 0.1-0.5 parts of wetting agent and 0.4-1 parts of degassing agent.

[0040] Preferably, the food can weld easy-to-release powder coating comprises the following components in parts by weight:

[0041] 100 parts of modified polyester resin, 20-30 parts of titanium dioxide, 4-6 parts of barium sulfate, 3-8 parts of epoxy resin, 0.5-0.8 parts of leveling agent, 0.4-0.6 parts of surface modified silica, 0.4-0.5 parts of charge enhancer, 0.1-0.2 parts of wetting agent and 0.4-0.5 parts of degassing agent.

[0042] Further preferably, the food can weld easy-to-release powder coating comprises the following components in parts by weight:

[0043] 100 parts of modified polyester resin, 26.6 parts of titanium dioxide, 5.2 parts of barium sulfate, 5.6 parts of epoxy resin, 0.6 parts of leveling agent, 0.45 parts of surface modified silica, 0.42 parts of charge enhancer, 0.14 parts of wetting agent, and 0.42 parts of degassing agent.

[0044] On the other hand, the present invention also provides a method for preparing a powder coating for easily demoulding a weld of a food can, comprising the following steps:

[0045] Step 1, mixing, granulating, crushing and grinding the raw materials to obtain coarse powder;

[0046] Step 2: Recrystallize the coarse powder obtained in step 1, and sieve out powder with a particle size of 40-50 μm after surface treatment to obtain the powder coating for the weld seam of the food can that is easy to release.

[0047] Furthermore, in step 2, the recrystallization temperature is 60-75°C, preferably 70°C.

[0048] Furthermore, in step 2, the surface treatment conditions are: temperature 60-70°C, vacuum degree -0.075 to -0.085MPa, and time 1-5h; preferably, the surface treatment conditions are: temperature 65°C, vacuum degree -0.080MPa, and time 3.5h.

[0049] In another aspect, the present invention further provides the use of the aforementioned modified polyester resin in the preparation of a powder coating for easily demoulding the weld of a food can.

[0050] In another aspect, the present invention further provides the use of the surface modified silicon dioxide described above in the preparation of a powder coating for easily releasing the weld seam of a food can.

[0051] The beneficial effects of the present invention are:

[0052] The present invention uses a special modified polyester resin as the main raw material to prepare a powder coating for food can welds that is easy to demould. Compared with traditional polyester materials, the polyester molecules prepared by the present invention have more flexible long chain segments and rigid chain segments in the side chains, and their strength and toughness are increased. By adjusting the input ratio of each monomer, the corrosion resistance of the obtained polyester is improved. Using it as the main material of the powder coating is helpful to improve the impact strength and toughness of the coating, and has a significant gain effect on the corrosion resistance of the coating, thereby increasing food safety. The present invention also adds surface-modified silica to the coating. By loading aminosilane coupling agent and epoxypropyl 2-methoxyphenyl ether on the surface, the bonding force and compatibility of silica and resin can be increased. When it is added to the coating, the remaining high-activity groups on the surface of silica enable the coating to form a film on the surface of the object and form a certain crosslinking. The formed film layer is dense, the adhesion is improved, and it can be well combined with different types of primers and powder coatings at the joints. In addition, it is found that it has a certain gain effect on the wear resistance of the coating.

[0053] In summary, the present invention provides a powder coating for food can welds that is easy to demould. The powder coating does not contain solvents or volatile toxic substances, and is safe and non-toxic. At the same time, the powder coating has a smooth and dense coating, good adhesion, impact strength and toughness, and can be well combined with different types of primers and powder touch-up coatings at joints after film formation, and can ensure the demoulding effect without affecting the overall anti-corrosion effect, which helps to improve the level of food safety. DETAILED DESCRIPTION

[0054] The following non-limiting examples can enable those skilled in the art to more fully understand the present invention, but do not limit the present invention in any way. The following content is merely an exemplary description of the scope of protection claimed in this application, and those skilled in the art can make various changes and modifications to the invention of this application based on the disclosed content, and they should also fall within the scope of protection claimed in this application.

[0055] In the present invention, unless otherwise specified, the numerical range "ab" represents an abbreviation of any real number combination between a and b, where a and b are real numbers. For example, the numerical range "1-10" means that all real numbers between "1-10" have been listed in this document, and "1-10" is just an abbreviation of these numerical combinations. The "range" disclosed in the present invention can be in the form of lower limit and upper limit, which can be one or more lower limits, and one or more upper limits respectively.

[0056] The method for using the food can weld easy demoulding powder coating provided by the present invention comprises: using a powder spray gun to deposit the powder coating on a substrate, or other known powder deposition methods such as fluidized bed technology can be used. After deposition, the powder can be heated to a temperature of 150-250° C. to cause the particles to flow and fuse together to form a smooth, uniform, continuous, and pit-free coating on the surface of the substrate.

[0057] The present invention is further described below by way of specific examples. Unless otherwise specified, the various chemical reagents used in the examples of the present invention are obtained through conventional commercial channels.

[0058] Example 1

[0059] A powder coating for easily releasing the weld of a food can, comprising the following components in parts by weight:

[0060] 100 parts of modified polyester resin, 26.6 parts of titanium dioxide, 5.2 parts of barium sulfate, 5.6 parts of bisphenol A epoxy resin (epoxy equivalent is 790g / mol), 0.6 parts of Powdermate 486CFL leveling agent, 0.45 parts of surface modified silica, 0.42 parts of dodecyl acrylate, 0.14 parts of wetting agent (ZX-105), and 0.42 parts of food-grade calcium stearate.

[0061] The modified polyester resin is prepared by the following method:

[0062] 166g of terephthalic acid, 62g of ethylene glycol, and 10.44g of hydroxycitronellol are mixed, 0.26g of monobutyltin oxide and 0.26g of tetraisopropyl titanate are added, and esterification is carried out at 230°C and 0.3MPa to react until the acid value is lower than 70mgKOH / g, 19.8g of guaifenesin is added, and the reaction is continued until the acid value is lower than 70mgKOH / g; the temperature is raised to 255°C, and the pressure is controlled to be lower than 130Pa to carry out melt polycondensation until the acid value is lower than 60mgKOH / g to obtain a polyester resin.

[0063] The surface modified silica is prepared by the following method:

[0064] 10 g of silica was placed in 100 g of solvent, and 2 g of N-(β-aminoethyl)-γ-aminopropyltriethoxysilane was added after ultrasonic dispersion. The mixture was stirred at 55° C. (stirring rate: 300 r / min) for reaction for 14 h, and centrifuged for washing to obtain aminosilane coupling agent-modified silica. 10 g of aminosilane coupling agent-modified silica and 1.6 g of glycidyl 2-methoxyphenyl ether were added to 100 g of dichloromethane, stirred at 55° C. for reaction for 2.5 h, and centrifuged for drying to obtain surface-modified silica.

[0065] This embodiment also provides a method for preparing a powder coating for easily demoulding a weld of a food can, comprising:

[0066] Step 1, mixing, granulating, crushing and grinding the raw materials to obtain coarse powder;

[0067] Step 2: recrystallize the coarse powder obtained in step 1 at 70° C., perform surface treatment at 65° C. and vacuum degree -0.080 MPa for 3.5 hours, and sieve out powder with a particle size of 40-50 μm to obtain the powder coating for the food can weld that is easy to release.

[0068] The surface gloss of the coating was measured at 20 degrees gloss using the procedure described in ASTM D523 (Standard Test Method for Specular Gloss). The gloss of the coating obtained in Example 1 after curing and film formation was found to be 76.3%. The surface of the formed paint film was smooth, which could ensure a good demoulding effect.

[0069] Example 2

[0070] A powder coating for easily releasing the weld of a food can, comprising the following components in parts by weight:

[0071] 100 parts of modified polyester resin, 28 parts of titanium dioxide, 5 parts of barium sulfate, 4.5 parts of bisphenol A epoxy resin, 0.6 parts of Powdermate486CFL leveling agent, 0.4 parts of surface modified silica, 0.4 parts of lauryl acrylate, 0.15 parts of wetting agent (ZX-105), and 0.4 parts of food grade calcium stearate.

[0072] Example 3

[0073] A powder coating for easily releasing the weld of a food can, comprising the following components in parts by weight:

[0074] 100 parts of modified polyester resin, 27.8 parts of titanium dioxide, 4.8 parts of barium sulfate, 4 parts of bisphenol A epoxy resin, 0.5 parts of Powdermate 486CFL leveling agent, 0.6 parts of surface modified silica, 0.45 parts of dodecyl acrylate, 0.1 parts of wetting agent (ZX-105), and 0.4 parts of food-grade calcium stearate.

[0075] The coatings obtained in Examples 1-3 were cured on metal plates, and then performance tests were performed. The test results are shown in Table 1.

[0076] Table 1

[0077]

[0078] As shown in Table 1, the powder coating for easily demoulding the weld of a food can provided by the present invention has an adhesion of 0 level, a wear resistance (pencil hardness) of more than 6H, an impact strength of more than 87kg / cm, and will not bubble, crack or fall off after being immersed in 5% HCl and 5% NaOH for 500h.

[0079] Examples 4-7, Comparative Examples 1-2

[0080] Examples 4-7 and Comparative Examples 1 and 2 provide a series of powder coatings for food can welds that are easy to release. The difference from Example 1 is that the amounts of guaifenesin and hydroxycitronellol added in the preparation of the polyester resin are different, that is, the ratios of ethylene glycol, hydroxycitronellol, and guaifenesin in the diol are different, as shown in Table 2 for details.

[0081] Table 2

[0082] Group Ethylene glycol (g) Hydroxycitronellol(g) Guaifenesin(g) Molar ratio of three components Example 1 62 10.44 19.8 10:0.6:1 Example 4 62 10.44 5.94 10:0.6:0.3 Example 5 62 10.44 9.9 10:0.6:0.5 Example 6 62 10.44 35.64 10:0.6:0.8 Example 7 62 10.44 39.6 10:0.6:2 Comparative Example 1 62 0 19.8 10:0:1 Comparative Example 2 62 10.44 0 10:0.6:0

[0083] The powder coatings prepared in Examples 1, 4-7 and Comparative Examples 1-2 were tested for performance. The results are shown in Table 3.

[0084] Table 3

[0085]

[0086]

[0087] As shown in Table 3, the coatings prepared in Examples 1, 5 and 6 have an impact strength higher than 86 kg / cm, and no bubbling, cracking or falling off occurs when immersed in 5% HCl and 5% NaOH solutions, indicating that the coatings prepared according to the components, proportions and methods of the present invention have good impact resistance and acid and alkali corrosion resistance, and are helpful to increase food safety; from the results of Example 1, Comparative Examples 1 and 2, it can be seen that the addition of hydroxycitronellol and guaifenesin to the polyester resin can improve the strength and corrosion resistance of the polyester resin, thereby increasing the performance of the final product coating; by comparing the results of Examples 1, 4-7, it can be obtained that as the content of guaifenesin in the polyester resin increases, it helps to further enhance the performance of the coating, and it can be concluded that the ratio of ethylene glycol, hydroxycitronellol and guaifenesin in the polyester resin is appropriately selected as 10:0.5-1:0.5-1.8.

[0088] Examples 8-11, Comparative Examples 3-4

[0089] Examples 8-11 and Comparative Examples 3-4 provide a powder coating for easily demoulding the weld of a food can. The difference from Example 1 is that different amounts of epoxypropyl 2-methoxyphenyl ether are added during the preparation of the surface-modified silica, as shown in Table 4.

[0090] Table 4

[0091] Group Aminoethylaminoethylaminopropyltrimethoxysilane(g) Glycidyl 2-methoxyphenyl ether(g) Example 1 2 1.6 Example 6 2 0.5 Example 7 2 1 Example 8 2 1.8 Example 9 2 2 Comparative Example 3 2 0 Comparative Example 4 0 0

[0092] The powder coatings prepared in Examples 1, 8-11 and Comparative Examples 3 and 4 were tested for performance. The results are shown in Table 5.

[0093] Table 5

[0094] Group Adhesion Wear resistance Example 1 Level 0 7H Example 6 Level 1 4H Example 7 Level 0 6H Example 8 Level 0 7H Example 9 Level 0 5H Comparative Example 3 Level 1 3H Comparative Example 4 Level 2 3H

[0095] It can be seen from the data in Table 5 that the adhesion and wear resistance of the coatings obtained in Comparative Examples 3 and 4 are significantly lower than those in Example 1, which shows that the modification of silicon dioxide by glycidyl 2-methoxyphenyl ether not only helps to improve the adhesion performance of the coating, but also has the effect of increasing wear resistance; By comparing Examples 1, 8-11, it can be concluded that in the preparation process of surface-modified silicon dioxide, the optimal dosage ratio of glycidyl 2-methoxyphenyl ether and silicon dioxide is 0.15-0.18:1.

[0096] The above description of the embodiments is to facilitate the understanding and use of the invention by those skilled in the art. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative work. Therefore, the present invention is not limited to the above embodiments, and improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the present invention should be within the scope of protection of the present invention.

Claims

1. A modified polyester resin, characterized in that: The modified polyester resin is prepared by reacting terephthalic acid and diol as monomers; wherein, The diol comprises ethylene glycol, hydroxycitronellol and guaifenesin; the molar ratio of ethylene glycol, hydroxycitronellol and guaifenesin in the diol is 10:0.5-1:0.5-1.

8.

2. The modified polyester resin according to claim 1, characterized in that The molar ratio of ethylene glycol, hydroxycitronellol and guaifenesin in the diol is 10:0.5-0.8:0.8-1.

2.

3. The modified polyester resin according to claim 1, characterized in that The molar ratio of terephthalic acid to glycol is 1:1.0-1.

5.

4. The modified polyester resin according to claim 1, characterized in that The preparation method of the modified polyester resin comprises the following steps: Terephthalic acid, ethylene glycol and hydroxycitronellol are mixed, and a catalyst is added to carry out an esterification reaction. After the reaction reaches an acid value of less than 10 mgKOH / g, guaifenesin is added and the reaction is continued until the acid value is less than 70 mgKOH / g. Then, a polycondensation reaction is carried out until the acid value is less than 60 mgKOH / g to obtain the modified polyester resin.

5. A powder coating for easily releasing the weld of a food can, characterized in that: The coating comprises the modified polyester resin according to any one of claims 1 to 4 and surface-modified silica; The surface modified silica is added in an amount of 0.2-1 part relative to 100 parts of the modified polyester resin; The preparation method of the surface modified silicon dioxide comprises the following steps: 1) dispersing silicon dioxide in a solvent by ultrasonication, adding an aminosilane coupling agent to react, and obtaining aminosilane coupling agent-modified silicon dioxide; 2) adding the aminosilane coupling agent modified silica obtained in step 1) and glycidyl 2-methoxyphenyl ether into a solvent to react to obtain the surface modified silica; In step 1), the amount of the aminosilane coupling agent added is 0.1-0.25 times the weight of silicon dioxide; In step 2), the weight ratio of the aminosilane coupling agent modified silica to glycidyl 2-methoxyphenyl ether is 1:0.1-0.

2.

6. The easy-to-release powder coating for welding seams of food cans according to claim 5, characterized in that: In step 1), the aminosilane coupling agent is at least one of γ-aminopropyltriethoxysilane, γ-aminopropyltrimethoxysilane, N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane, N-(β-aminoethyl)-γ-aminopropyltriethoxysilane, N-(β-aminoethyl)-γ-aminopropylmethyldimethoxysilane, N-β-(aminoethyl)-γ-aminopropylmethyldiethoxysilane, and γ-aminoethylaminopropyltrimethoxysilane.

7. The easy-to-release powder coating for welding seams of food cans according to any one of claims 5 to 6, characterized in that: The coating also contains titanium dioxide, barium sulfate, epoxy resin, leveling agent, silicon dioxide, charge enhancer, wetting agent and degassing agent.

8. The powder coating for easily releasing weld seams of food cans according to claim 7, characterized in that: The food can weld seam easy-to-release powder coating comprises the following components in parts by weight: 100 parts of modified polyester resin, 20-30 parts of titanium dioxide, 4-6 parts of barium sulfate, 3-8 parts of epoxy resin, 0.1-1.5 parts of leveling agent, 0.2-1 parts of surface modified silica, 0.1-1 parts of charge enhancer, 0.1-0.5 parts of wetting agent and 0.4-1 parts of degassing agent.

9. The powder coating for easily releasing weld seams of food cans according to claim 7, characterized in that: The food can weld seam easy-to-release powder coating comprises the following components in parts by weight: 100 parts of modified polyester resin, 20-30 parts of titanium dioxide, 4-6 parts of barium sulfate, 3-8 parts of epoxy resin, 0.5-0.8 parts of leveling agent, 0.4-0.6 parts of surface modified silica, 0.4-0.5 parts of charge enhancer, 0.1-0.2 parts of wetting agent and 0.4-0.5 parts of degassing agent.

10. The method for preparing the easily demoulding powder coating for food can welds according to any one of claims 5 to 9, characterized in that: The steps include: Step 1, mixing, granulating, crushing and grinding the raw materials to obtain coarse powder; Step 2: Recrystallize the coarse powder obtained in step 1, and sieve out powder with a particle size of 40-50 μm after surface treatment to obtain the powder coating for the weld seam of the food can that is easy to release.

11. Use of the modified polyester resin according to any one of claims 1 to 4 in preparing a powder coating for easily demoulding the weld of a food can.

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