Preparation and use method of ultraviolet curing primer for tinplate

Abstract

The invention belongs to the field of ultraviolet curing materials, and relates to a preparation method and a use method of an ultraviolet curing primer for tinplate, the primer is composed of oligomers containing specific molecules, functional monomers, a photoinitiator and an additive, and by introducing different types of oligomers containing specific molecules, the photoinitiator is added into the ultraviolet curing primer, so that the ultraviolet curing primer is prepared. According to the ultraviolet light curing primer, the adhesive force, the impact resistance and the steaming and boiling resistance of the ultraviolet light curing primer are effectively improved, and the ultraviolet light curing primer is simple in preparation and use method, stable in performance and low in cost and has good market popularization value.

Description

Technical Field

[0001] The present invention belongs to the field of ultraviolet light-curing materials and relates to a preparation method of an ultraviolet light-curing primer for tinplate and a method for using the same. The primer is composed of oligomers with a specific molecular structure, functional monomers, a photoinitiator, and additives. By introducing different oligomers with specific molecular structures, the adhesion, impact resistance, and boiling resistance of the ultraviolet light-curing primer are effectively improved. Background Art

[0002] Tinplate is widely used in the production of food packaging cans or boxes due to its corrosion resistance, non-toxicity, high strength, and good ductility. Before tinplate is used, it must be coated with a primer. The primer protects and extends the tinplate's service life, while also improving the adsorption capacity between the tinplate and printing ink, making it suitable for printing. It also increases the brightness of the packaging pattern and improves the tinplate's post-processing performance. The primer prevents chemical or biological contamination of the contents in the food can or box, reduces the possibility of leakage, preserves the original flavor of the food, and prolongs its shelf life, thereby improving the quality of food packaging.

[0003] Food packaging has very high requirements for primer curing. The commonly used curing method for primers is heat curing. The disadvantages of this method are long curing time, high energy consumption, poor environmental protection, and great harm to the human body. UV curing can improve the above disadvantages, but it often encounters poor curing degree of primer, easy shrinkage during curing, and reduced adhesion, which reduces the adhesion between the paint film and the substrate, and the impact resistance and high-temperature cooking resistance of the paint film do not meet industrial requirements.

[0004] To address the above issues, researchers have adopted a variety of methods to improve them. Polyurethane acrylates in primers can provide good flexibility and a certain degree of adhesion to the cured film, while epoxy acrylates provide hardness, rapid curing, and good adhesion, but their brittleness after curing limits their usage (CN101280154A). Some researchers have introduced thermoplastic polyurethane resins into UV-curing paints to increase the adhesion between glass and plastic, and between metal and plastic (CN104744980A). Alternatively, water-based polyurethane resins have been combined with UV-curable polyurethane acrylates to improve the flexibility of the coating (CN113817394A). The above methods have solved the problems of primer adhesion and flexibility to a certain extent, but obtaining a primer with good adhesion, impact resistance, and excellent high-temperature cooking resistance remains a challenging task. Summary of the Invention

[0005] A method for preparing and using a UV-curing primer for tinplate is disclosed. The UV-curing primer is prepared by mixing and stirring an oligomer, a functional monomer, a photoinitiator, and an additive to fully dissolve the mixture, followed by filtration. The primer is then applied to the tinplate surface after plasma treatment, followed by both light-curing and heat-curing.

[0006] The specific composition of the UV-curable primer is: a total content of two polyurethane acrylate oligomers with different molecular weights and specific molecular structures of 10-20wt%, an epoxy acrylate oligomer content of 3-10wt%, a functional monomer content of 60-80wt%, a photoinitiator content of 4-10wt% and the remainder of additives.

[0007] The two polyurethane acrylate oligomers are polyurethane acrylate oligomers with number average molecular weights of 200-1000 (PU1) and 500-2000 (PU2), and average functionality of 2 or more, and the addition ratio of the two is: PU1:PU2=1:2-1:10.

[0008] The epoxy acrylate oligomer (PEA) has a number average molecular weight of 500-2000, and its addition ratio range is: PEA:PU2=1:2-1:10.

[0009] The polyurethane acrylate oligomer and epoxy acrylate oligomer have specific molecular constituent units, as shown in structural formula 1-4: Structural formula 1 Structural Formula 2 Structural formula 3 Structural formula 4.

[0010] The additive is an adhesion promoter selected from solid acrylic acid or methacrylic acid resin and sulfur-containing acrylate.

[0011] The functional monomers in the primer are selected from monofunctional monomers and difunctional monomers. Specifically, the monofunctional monomer is selected from one or more of acryloylmorpholine, butyl acrylate, octyl acrylate, isobornyl acrylate, benzyl acrylate, tetrahydrofuran acrylate, ethoxyethoxyethyl acrylate, lauryl acrylate, and lauryl methacrylate; and the difunctional monomer is selected from one or more of diethylene glycol diacrylate, triethylene glycol diacrylate, dipropylene glycol diacrylate, tripropylene glycol diacrylate, 1,4-butanediol diacrylate, 1,6-hexanediol diacrylate, neopentyl glycol diacrylate, 2-(propoxy)neopentyl glycol diacrylate, tricyclodecane dimethanol diacrylate, hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, and hydroxypropyl methacrylate.

[0012] The photoinitiator in the primer is selected from phenyl bis (2,4,6-trimethylbenzoyl) phosphine oxide or 2,4,6-trimethylbenzoyl diphenyl phosphine oxide.

[0013] The primer is used by thoroughly stirring and dissolving the oligomer, functional monomer, photoinitiator, and additives, followed by filtration. The primer is then applied to the plasma-treated tinplate surface using a knife coating method, with the film thickness reaching 2-15 μm after drying. The primer is specifically composed of 10-20% by weight of two polyurethane acrylates with different molecular weights and specific molecular structures, 3-10% by weight of epoxy acrylate, 60-80% by weight of functional monomer, 4-10% by weight of photoinitiator, and the remainder of additives. DETAILED DESCRIPTION

[0014] The present invention is described below by way of specific embodiments, but is not limited to the specific embodiments given below.

[0015] The invention provides a UV-curing primer for tinplate. The UV-curing primer specifically comprises: a total content of 10-20 wt% of two polyurethane acrylate oligomers with different molecular weights and specific molecular structures, a content of 3-10 wt% of epoxy acrylate oligomers, a content of 60-80 wt% of functional monomers, a content of 4-10 wt% of a photoinitiator, and the remainder of additives.

[0016] In a preferred embodiment, the primer of the present invention comprises, by weight percentage, PU1: 3wt%, PU2: 9wt%, PEA: 5wt%, adhesion promoter: 2wt%, bifunctional monomer: 45wt%, monofunctional monomer: 30wt%, and photoinitiator: 6wt%.

[0017] Polyurethane acrylate oligomer The polyurethane acrylate oligomer of the present invention is prepared by copolymerization of aliphatic polyurethane and acrylic monomer under certain conditions. It can be prepared in-house or purchased. Examples of available products include CN8010 (fluid viscosity at 25°C is 2000-3000 cps, average functionality is 2) and CN8007 (fluid viscosity at 25°C is 800-1000 cps, average functionality is 4) from Sartomer (Guangzhou) Chemical Co., Ltd.; 6115 (fluid viscosity at 25°C is 2000-3000 cps, average functionality is 2) from Changxing Materials Industry Co., Ltd. J-80 (fluid viscosity at 25°C is 2600-4200cps, average functionality is 2), DR-U299 (fluid viscosity at 25°C is 25000-35000cps, average functionality is 2); Guangdong Lankelu New Materials Co., Ltd.'s 6390 (fluid viscosity at 60°C is 5000-12000cps, average functionality is 4), 6126 (fluid viscosity at 25°C is 400-700cps, average functionality is 4).

[0018] Average functionality refers to the ratio of the number of functional groups that can actually participate in the reaction to the total amount of monomers in the reaction system during the linear polycondensation stage before reaching the gel point in a mixed polycondensation or co-polycondensation reaction involving two or more monomers.

[0019] In one embodiment, the mixed polyurethane acrylate oligomer of the present invention has a fluid viscosity of 2500-3000 cps at 25° C. and an average functionality of 2-4.

[0020] Epoxy acrylate oligomer Epoxy acrylate oligomers are prepared by esterification of epoxy resin and acrylic acid or methacrylic acid and are one of the most widely used oligomers. Their light curing speed is the fastest among all types of oligomers, and the cured film has high hardness, good gloss, corrosion resistance, heat resistance and excellent electrochemical properties. Epoxy acrylate oligomers have a wide range of raw material sources, are inexpensive, and have a simple synthesis process, so they are used in large quantities in light-curing coatings. The film layer after curing of epoxy acrylate oligomers has good adhesion, chemical resistance and strength, but there are also disadvantages, such as insufficient flexibility and high brittleness of the cured film. Therefore, in order to meet the needs of different fields, the combination of polyurethane acrylate with excellent flexibility and epoxy acrylate has become one of the solutions.

[0021] In one embodiment, the epoxy acrylate oligomers described herein can be prepared or purchased. Available options include, but are not limited to, CR91192 from Guangdong Haohui New Materials Co., Ltd. (fluid viscosity of 10,000-20,000 cps at 25°C, average functionality of 2), DSM resin 3020 from Shanghai Kaiyin Chemical Co., Ltd. (fluid viscosity of 32-48 s at 60°C, average functionality of 2), and DSM resin 3051 from Shanghai Kaiyin Chemical Co., Ltd. (fluid viscosity of 1-5 s at 60°C, average functionality of 2).

[0022] Preferably, the epoxy acrylate oligomer of the present invention has a fluid viscosity of 32-48s at 25°C.

[0023] Adhesion promoter Adhesion promoters contain functional groups with active properties, such as phosphates, thiols, and furan rings, which significantly enhance the adhesion of primers to metal surfaces. These resins exhibit good miscibility with other film-forming resins and form chemical bonds with the substrate, effectively creating a chemical bond between the paint film and the substrate. Furthermore, the adhesion promoter and the coating film bond to the substrate through mutual dissolution and entanglement, thereby enhancing adhesion.

[0024] In one embodiment, the adhesion promoter of the present invention has a number average molecular weight of 200-1000 and can be prepared or purchased, including but not limited to 1735 from Guangzhou Haoyi New Materials Technology Co., Ltd. and 5206 from Jining Tangyi Chemical Co., Ltd.

[0025] Functional monomers In one embodiment, the functional monomers described in the present invention are selected from monofunctional monomers and bifunctional monomers. Specifically, the monofunctional monomer is selected from one or more of acryloylmorpholine, butyl acrylate, octyl acrylate, isobornyl acrylate, benzyl acrylate, tetrahydrofuran acrylate, ethoxyethoxyethyl acrylate, lauryl acrylate, and lauryl methacrylate; and the bifunctional monomer is selected from one or more of diethylene glycol diacrylate, triethylene glycol diacrylate, dipropylene glycol diacrylate, tripropylene glycol diacrylate, 1,4-butanediol diacrylate, 1,6-hexanediol diacrylate, neopentyl glycol diacrylate, 2-(propoxy)neopentyl glycol diacrylate, tricyclodecane dimethanol diacrylate, hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, and hydroxypropyl methacrylate.

[0026] The functional monomer of the present invention is a combination of a monofunctional monomer and a difunctional monomer in a certain ratio. Preferably, the monofunctional monomer of the present invention is acryloylmorpholine or butyl acrylate, and the difunctional monomer is 1,4-butanediol diacrylate.

[0027] In a preferred embodiment, the weight ratio of the functional monomers of the present invention is: monofunctional monomer: difunctional monomer = 1: (1-5).

[0028] Photoinitiator Photoinitiators are compounds that absorb energy of a certain wavelength in the ultraviolet (250-420 nm) or visible (400-800 nm) region, generating free radicals, cations, and the like, thereby initiating polymerization, crosslinking, and curing of monomers and oligomers. Examples of photoinitiators used in the present invention include phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide or 2,4,6-trimethylbenzoyldiphenylphosphine oxide.

[0029] In one embodiment, the photoinitiator of the present invention is used in an amount of 4-10 wt %.

[0030] The present invention provides a method for preparing the above-mentioned UV-curing primer for tinplate, comprising the following steps: The initiator was added to a certain amount of monomer and magnetically stirred for 30 minutes to fully dissolve.

[0031] The oligomer was added to the mixture and stirred magnetically for 3-5 h.

[0032] Use medium-speed filter paper to vacuum filter and remove undissolved matter.

[0033] The present invention provides a method for using the above-mentioned UV-curing primer for tinplate, comprising the following steps: After spraying ethanol on the surface of the dust-free cloth, wipe the tinplate surface.

[0034] After the surface is dry, place it in a plasma treatment device with the treatment conditions: 150W, 150S.

[0035] After the treatment is completed, the primer is applied to the tinplate surface with a wire rod.

[0036] Use a 495nm LED lamp to cure for 5-10s, and then place it in a 100℃ oven for 10min.

[0037] Adhesion was tested using a paint film cross-hatch tester; impact resistance was tested using a 1000g, 50cm hammer; and boiling resistance was observed by heating in a 105°C water bath for 30 minutes.

[0038] Example The present invention is described in detail below by way of examples. The following examples are only intended to further illustrate the present invention and are not to be construed as limiting the scope of protection of the present invention. Any non-essential improvements and adjustments made by professionals in this field based on the above-mentioned contents of the present invention still fall within the scope of protection of the present invention.

[0039] PU1: polyurethane acrylate oligomer The polyurethane acrylate oligomer is an aliphatic polyurethane acrylate oligomer, purchased from Guangdong Lankelu New Materials Co., Ltd. as 6126.

[0040] PU2: polyurethane acrylate oligomer The polyurethane acrylate oligomer is an aliphatic polyurethane acrylate oligomer, purchased from Sartomer (Guangzhou) Chemical Co., Ltd. as CN8010.

[0041] PEA: Epoxy Acrylate Oligomer The epoxy acrylate oligomer is DSM resin 3020 purchased from Shanghai Kaiyin Chemical Co., Ltd.

[0042] AR: Adhesion Promoter The adhesion promoter is 5206 purchased from Jining Tangyi Chemical Co., Ltd.

[0043] S1: Monofunctional monomer The monofunctional monomer is n-octyl acrylate.

[0044] S2: Monofunctional monomer The monofunctional monomer is lauryl acrylate.

[0045] S3: Monofunctional monomer The monofunctional monomer is isobornyl acrylate.

[0046] S4: Bifunctional monomer The monofunctional monomer is hydroxypropyl methacrylate.

[0047] S5: Bifunctional monomer The bifunctional monomer is hydroxyethyl acrylate.

[0048] S6: Bifunctional monomer The bifunctional monomer is tricyclodecane dimethanol diacrylate.

[0049] S7: Bifunctional monomer The bifunctional monomer is diethylene glycol diacrylate.

[0050] I: Photoinitiator The photoinitiator is TPO, 2,4,6-trimethylbenzoyldiphenylphosphine oxide.

[0051] Table 1 (Contents are in weight percentage: wt%) Example 1 2 3 4 5 6 7 8 9 10 PU1 3 10 2 1 5 4 2.5 3 3 2.5 PU2 9 10 8 10 10 16 7.5 8 7 8.5 PEA 5 2 2 2 3 10 5 3 4 2.5 AR 2 1 3 4 2 5 3 4 3.5 2.5 S1 15 - 15 15 - 10 10 - 11.5 20 S2 15 15 - 11 13 - 20 25 - 13 S3 - 15 12 - - 20 - 10 25 - S4 15 - - - 20 - 15 - 20 25 S5 30 10 - 20 - 30 20 - - - S6 - 20 20 - 20 - - 20 20 - S7 - 10 30 30 20 - 12 20 - 20 I 6 7 8 7 7 5 5 7 6 6

[0052] The tinplate with primer was subjected to light curing and heat curing treatment to obtain the finished product as a sample for performance testing.

[0053] Adhesion: The sample provided in the example was scratched with a paint crosshatch to create 10 equal-sized squares on the coating, serving as the test area. 3M-600 tape was applied to the test area and then removed rapidly and continuously. The cutting edge of the tape was maintained at a 35-45 degree angle to the coating surface and penetrated the coating. The cutting was continuous and constant, and the coating was evaluated based on the area of ​​coating removal. Grade 1 indicates no coating removal, Grade 2 indicates a coating removal area of ​​1% or greater but less than 5%, Grade 3 indicates a coating removal area of ​​5% or greater but less than 20%, Grade 4 indicates a coating removal area of ​​20% or greater but less than 50%, and Grade 5 indicates a coating removal area of ​​50% or greater. The results are shown in Table 2.

[0054] Impact resistance: The sample provided in the embodiment is placed on one end of the impact table. After releasing the heavy hammer from the top (50 cm), the impacted sample is immersed in a copper sulfate solution for 20 minutes, taken out, washed with clean water, and then wiped dry. The paint film on the sample is observed to see if it is broken, wherein the broken area of ​​the folded or bent paint film appears as a black or red line or continuous dot. The mass of the heavy hammer is 1000 g. The percentage of the area of ​​the broken paint film of the sample to the total area is calculated as the paint explosion rate, and a rating is performed, wherein level 1 is a paint explosion rate of less than 0.1%, level 2 is a paint explosion rate of less than 0.2% and greater than or equal to 0.1%, level 3 is a paint explosion rate of less than 0.5% and greater than or equal to 0.2%, and level 4 is a paint explosion rate of greater than or equal to 0.5%. The results are shown in Table 2.

[0055] Boiling resistance: Hang the sample in a 105℃ water bath and heat for 30 minutes. After the test, the printed surface should not fade, blur, fall off, wrinkle, bubble, or particle, and there should be no whitening or obvious reduction in gloss.

[0056] Table 2 Evaluation results Example Adhesion Impact resistance Retort resistance 1 2 2 good 2 1 1 excellent 3 1 1 excellent 4 1 1 excellent 5 1 1 excellent 6 2 2 good 7 2 2 good 8 1 1 excellent 9 2 2 good 10 1 1 excellent It can be seen from the test results in Table 2 that the UV-curing primer for tinplate provided by the present invention has excellent adhesion, impact resistance and boiling resistance.

[0057] The foregoing embodiments are merely illustrative and serve to illustrate some features of the method of the present invention. The appended claims are intended to claim the widest possible scope that can be envisioned, and the embodiments presented herein are merely illustrative of the selection of combinations of all possible embodiments. Therefore, it is the applicant's intention that the appended claims are not limited by the selection of examples illustrating the features of the present invention. Some numerical ranges used in the claims also include subranges therein, and variations in these ranges should also be interpreted as being covered by the appended claims where possible.

Claims

1. A preparation method of a UV-curing primer for tinplate and a method for using the same, characterized in that: The preparation method of the ultraviolet light curing primer is to mix and stir oligomers, functional monomers, photoinitiators and additives to fully dissolve them and filter them. The use method of the primer is to treat tinplate with plasma, then scrape the primer on the tinplate surface and perform dual treatment of light curing and heat curing.

2. The preparation and use method of the UV-curable primer according to claim 1, wherein the specific composition of the UV-curable primer is: a total content of two polyurethane acrylate oligomers with different molecular weights and specific molecular structures of 10-20wt%, an epoxy acrylate oligomer content of 3-10wt%, a functional monomer content of 60-80wt%, a photoinitiator content of 4-10wt%, and the balance of additives.

3. The preparation and use methods of the UV-curable primer according to claims 1 and 2, wherein the two polyurethane acrylate oligomers are polyurethane acrylate oligomers with number average molecular weights of 200-1000 (PU1) and 500-2000 (PU2), respectively, and an average functionality of 2 or more, and the addition ratio of the two is in the range of PU1:PU2=1:2-1:

10.

4. The preparation and use method of the UV-curable primer according to claims 1 and 2, wherein the epoxy acrylate oligomer (PEA) has a number average molecular weight of 500-2000 and is added in a ratio of PEA:PU2=1:2-1:

10.

5. The preparation and use method of the UV-curable primer according to claims 1 and 2, wherein the polyurethane acrylate oligomer and epoxy acrylate oligomer have specific molecular constituent units, as shown in structural formula 1-4: Structural formula 1 Structural Formula 2 Structural formula 3 Structural formula 4.

6. The preparation and use method of the UV-curable primer according to claims 1 and 2, wherein the additive is an adhesion promoter selected from solid acrylic acid or methacrylic acid resin, and sulfur-containing acrylate.

7. The preparation and use method of the UV-curable primer according to claims 1 and 2, wherein the functional monomer in the primer is selected from monofunctional monomers and difunctional monomers. Specifically, the monofunctional monomer is selected from one or more of acryloylmorpholine, butyl acrylate, octyl acrylate, isobornyl acrylate, benzyl acrylate, tetrahydrofuran acrylate, ethoxyethoxyethyl acrylate, lauryl acrylate, and lauryl methacrylate; and the difunctional monomer is selected from one or more of diethylene glycol diacrylate, triethylene glycol diacrylate, dipropylene glycol diacrylate, tripropylene glycol diacrylate, 1,4-butanediol diacrylate, 1,6-hexanediol diacrylate, neopentyl glycol diacrylate, 2(propoxylated)neopentyl glycol diacrylate, tricyclodecane dimethanol diacrylate, hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, and hydroxypropyl methacrylate.

8. The preparation and use method of the UV-curable primer according to claims 1 and 2, wherein the photoinitiator in the primer is selected from phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide or 2,4,6-trimethylbenzoyldiphenylphosphine oxide.

9. The preparation and use methods of the UV-curable primer according to claims 1 and 2, wherein the primer is used by thoroughly stirring and dissolving the oligomer, functional monomer, photoinitiator, and additives, followed by filtering, and then applying the primer to the plasma-treated tinplate surface by knife coating, with the film thickness after drying being 2-15 μm.

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