A BOPP pre-coated film for enhancing the adhesion of UV ink and its preparation method

Abstract

The present invention relates to the technical field of ink printing coatings, and particularly to a BOPP pre-coated film for enhancing the adhesion of UV ink and a preparation method thereof. The preparation method of the BOPP pre-coated film includes step a: placing a polypropylene film on a unwind rack for unwinding; step b: placing the unwound polypropylene film into a corona machine to perform corona treatment on the surface of the polypropylene film to obtain a corona-treated polypropylene film; step c: coating the solvent-based coating liquid of the coating layer on the corona surface of the corona-treated polypropylene film through a coater, and baking it in an oven with a set temperature gradient to obtain a BOPP pre-coated film for enhancing the adhesion of UV ink. The purpose is to greatly improve the fastness between the ink and the coating layer, greatly improve the fastness between the coating layer and the polypropylene film layer, and reduce the risk of reverse sticking during winding.

Description

Technical Field

[0001] The present invention relates to the technical field of ink printing coatings, and particularly relates to a BOPP pre-coated film for enhancing the adhesion of UV ink and a preparation method thereof. Background Art

[0002] The ultraviolet radiation curing technology is a brand-new green technology developed since the 1970s of the last century. The ultraviolet curable ink produced by this technology, abbreviated as UV ink, has the advantages of not containing volatile organic compounds (VOC), being less polluting to the environment, having a fast curing speed, saving energy, and being suitable for high-speed automated production. Traditional inks are volatile and have a slow curing speed, which is not conducive to environmental protection. Therefore, UV ink can be said to be a substitute for traditional inks. However, since UV ink uses ultraviolet light as the energy source, after the photoinitiator in the ink is irradiated by ultraviolet light, free radicals or cations are generated to initiate the curing of the polymer, and the curing time is short. Sometimes, this will cause the problem of low adhesion of UV ink on the surface of the substrate film.

[0003] The printing industry has two important detection indexes for evaluating UV ink printed products: 1. After printing with the ink, the color saturation is high, the dot pattern is clear, and the ink spreading property is good. At the same time, there should be no ink bleeding and no defective sawtooth shape. 2. The ink has good adhesion on the printing material, does not delaminate, does not drop ink, and has good abrasion resistance.

[0004] In order to achieve the above performances, the currently common solutions are as follows:

[0005] First, corona treatment is carried out on the substrate film to improve the surface tension of the substrate film itself, so as to increase the wettability of the UV ink. However, the surface tension of the corona-treated material is not stable, and the corona effect will gradually weaken over time. Especially in an environment with high humidity, the corona effect weakens faster. This method can ensure good ink spreading property, but still cannot meet the detection standard of no ink dropping.

[0006] Second, a pre-coating treatment is carried out on the surface of the printing material to improve the adhesion between the printing material and the ink.

[0007] The Chinese patent with the application number CN201910900271.5 discloses a BOPA pre-coated film for enhancing the adhesion of UV ink and its preparation method. However, the substrate disclosed in this patent is a biaxially oriented nylon film (BOPA). The BOPA film belongs to a polar high polymer with a large surface free energy. When untreated, the surface wetting tension can reach 38 - 40 dynes. When using a biaxially oriented polypropylene film (BOPP) and performing a coating pretreatment on the surface of this film, the BOPP film is non-polar, has a high degree of crystallinity, and a very low surface free energy. When untreated, the surface wetting tension is about 30 dynes. The low surface energy of the BOPP film will cause very difficult adhesion between the coating and the BOPP film. To ensure the fastness of the printed ink, it is necessary to first ensure a very high bonding force A between the BOPP film and the coating, bonding force B between the coating and the ink layer, and bonding force C between the tape and the ink layer during testing. If the ink is to pass the adhesion test, it is necessary to ensure that both the adhesion of A and B are greater than C.

[0008] The Chinese patent with the application number CN201610869585.X discloses a method for improving the adhesion of ink in plastic printed products. The method disclosed in this patent is to first perform pretreatment on plastic products. The plastic products are immersed in a hydrochloric acid solution for 2 - 4 h, then washed with deionized water, immersed in an ethanol solution for 5 - 10 min, dried with nitrogen, and quickly placed in a magnetron sputtering device. After evacuating, a mixed gas is filled. Under the conditions of a radio frequency of 10 - 20 MHz and a sputtering voltage of 0.1 - 2 kV, the mixed gas ions are sputtered for 15 - 30 min to obtain a plastic rough product. This method is mainly used for plastic parts. For a whole roll of film, the processing method is complex and cumbersome, and the cost is too high.

[0009] In view of the above problems, the present invention provides a coating for improving the printing performance of BOPP film and its preparation method. Summary of the Invention

[0010] (I) Technical problems to be solved

[0011] The present invention mainly aims at the above problems and proposes a BOPP pre-coated film for enhancing the adhesion of UV ink and its preparation method. The purpose is to solve the problems of poor ink printing fastness, low transparency, easy reverse sticking during winding, and short shelf life of printable coatings.

[0012] (II) Technical solutions

[0013] To achieve the above object, the present invention provides a BOPP pre-coated film for enhancing the adhesion of UV ink, comprising a polypropylene film layer and a coating layer;

[0014] The coating layer is formed by coating a solvent-based coating solution on the corona surface of a polypropylene film layer. The components of the solvent-based coating solution of the coating layer include a copolymerized acrylic resin, a curing agent, and an organic solvent A;

[0015] Among them, the copolymerized acrylic resin is obtained by polymerizing inorganic nano-powders, a surfactant, organic solvent A, acrylate hard monomers, acrylate soft monomers, special monomers, an initiator, and organic solvent B;

[0016] The curing agent is composed of carbon tetrachloride-coated isocyanate;

[0017] The special monomers are one or more of divinylbenzene, tetramethylcyclotetrasiloxane, and diallyl maleate;

[0018] The organic solvent A is one or more of ethyl acetate, propyl acetate, and butyl acetate; the organic solvent B is one or more of toluene, propylene glycol monomethyl ether, or dipropylene glycol methyl ether.

[0019] Furthermore, the mass percentages of the copolymerized acrylic resin, the curing agent, and the organic solvent A in the solvent-based coating solution are (22-28 wt%): (0.05-0.1 wt%): (72-78 wt%); among them, by weight, the curing agent is a 1:2 mixture of isocyanate and carbon tetrachloride for coating; by weight, the copolymerized acrylic resin contains 5-10 parts of inorganic nano-powders, 0.5-2 parts of surfactant, 5-10 parts of organic solvent A, 15-40 parts of acrylate hard monomers, 10-30 parts of acrylate soft monomers, 1-5 parts of special monomers, 0.2-1 part of initiator, and 5-10 parts of organic solvent B.

[0020] Furthermore, the polypropylene film layer is a transparent biaxially stretched polypropylene film layer with a thickness of 30-100 μm, and the thickness of the coating layer is 1-3 μm.

[0021] Furthermore, the inorganic nano-powder materials are one or more of nano-silica, nano-titanium dioxide, and nano-aluminum oxide; the surfactant used for surface modification of the inorganic nano-powders is: silane coupling agent or dispersant or a mixture thereof.

[0022] Furthermore, the acrylate hard monomers are one or more of methyl methacrylate, isobornyl acrylate, and isobornyl methacrylate.

[0023] Furthermore, the acrylate soft monomers are one or more of methyl acrylate, ethyl acrylate, butyl acrylate, and isooctyl acrylate.

[0024] Furthermore, the initiator is benzoyl peroxide or azobisisobutyronitrile.

[0025] To achieve the above object, the present invention provides a method for preparing a BOPP pre-coated film with enhanced UV ink adhesion, and the steps of the preparation method are as follows:

[0026] Step a: Place the polypropylene film on the unwinding rack for unwinding.

[0027] Step b: Place the unwound polypropylene film into a corona machine to perform corona treatment on the surface of the polypropylene film to obtain a corona-treated polypropylene film.

[0028] Step c: After the corona treatment, the corona-treated polypropylene film is passed through a coater, and the solvent-based coating liquid of the coating layer is coated on the corona surface of the corona-treated polypropylene film, and then baked in an oven with a set temperature gradient to obtain a BOPP pre-coated film with enhanced UV ink adhesion.

[0029] Furthermore, the preparation method of the solvent-based coating liquid of the coating layer is as follows: Add the copolymerized acrylic resin and organic solvent A into a reaction vessel and stir, then add the blend of isocyanate and carbon tetrachloride, and continue stirring to finally obtain the solvent-based coating liquid of the coating layer.

[0030] Furthermore, the preparation method of the copolymerized acrylic resin is as follows:

[0031] Surface-treat the inorganic nano powder with a surfactant.

[0032] Disperse and mix the surface-treated inorganic nano powder and organic solvent A in a reaction vessel.

[0033] Add part of the monomers, part of the initiator, and part of the organic solvent B into the above reaction vessel, stir and heat up to the first reaction temperature, and keep warm.

[0034] Then, after mixing the remaining organic solvent B, part of the initiator, and all the remaining monomers evenly, drop them into the above reaction vessel, heat up to the second reaction temperature, and keep warm.

[0035] Mix the remaining organic solvent B and the remaining initiator, drop them into the above reaction vessel, heat up to the third reaction temperature, keep warm for a period of time, and then cool down and discharge to obtain the copolymerized acrylic resin.

[0036] (III) Beneficial Effects

[0037] The above technical solution of the present invention provides a BOPP pre-coated film with enhanced UV ink adhesion. Through specific coating layer configuration and preparation process, the adhesion of the UV ink is strong.

[0038] On the one hand, the solvent-based coating solution of the coating layer contains isocyanate coated with carbon tetrachloride. Due to its high density, the isocyanate wrapped by carbon tetrachloride will settle downward during the coating process and then accumulate on the corona surface of the polypropylene film layer. As the baking temperature rises, carbon tetrachloride evaporates into gas, and the isocyanate curing agent releases -NCO groups at high temperature, which just form chemical bonds with polar groups such as carbonyl, hydroxyl and peroxide generated by corona, greatly improving the fastness between the coating layer and the corona-treated polypropylene film layer;

[0039] On the other hand, due to the certain porous structure of the inorganic nano-powder in the coating layer, the UV ink can penetrate into the depressions and gaps of the coating. After the UV ink is cured, it has anchoring, hooking, wedging and other effects with the nano-powder, having good adhesion and greatly improving the fastness between the ink and the coating layer. Brief Description of the Drawings

[0040] Figure 1 It is a schematic structural diagram of the combination process of a coating layer and a polypropylene film layer disclosed in this application.

[0041] The reference numerals shown in the figure: 1, coating layer; 2, curing agent; 3, hydroxyl; 4, polypropylene film layer. Detailed Embodiments

[0042] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be described clearly and completely below. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the described embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0043] Unless otherwise defined, the technical terms or scientific terms used in this disclosure shall have the ordinary meanings understood by those of ordinary skill in the art to which the present invention belongs.

[0044] The present invention provides a BOPP pre-coated film for enhancing the adhesion of UV ink, including a polypropylene film layer 4 and a coating layer 1 formed by coating a solvent-based coating solution on the surface of the corona-treated polypropylene film layer 4. The components of the solvent-based coating solution of the coating layer 1 include copolyacrylic resin, curing agent and organic solvent A;

[0045] In specific implementation, the preparation method of the solvent-based coating solution of the coating layer 1 includes: adding 22-28 wt% of copolyacrylic resin, 0.05-0.1 wt% of curing agent, and 72-78 wt% of organic solvent A into a reaction vessel for mixing and stirring to finally obtain the solvent-based coating solution. The curing agent is a mixture of isocyanate and carbon tetrachloride in a weight fraction of 1:2, and the mixing and coating are completed by stirring at 5000-6000 r / min in a high-speed mixer for 35-45 minutes.

[0046] Since the curing agent is a blend of isocyanate and carbon tetrachloride, carbon tetrachloride fully wraps the isocyanate. The cured agent 2 wrapped by carbon tetrachloride will sink downward in the solvent-based coating solution of the coating layer 1 due to its high density. Then, the isocyanate accumulates on the corona surface of the corona-treated polypropylene film layer 4. The -NCO group is released by the cured agent 2 and forms chemical bonds with the strongly polar groups 3 such as carbonyl, hydroxyl, and peroxide generated by corona treatment during coating, which can greatly improve the fastness between the coating layer 1 and the corona-treated polypropylene film layer 4.

[0047] By weight, the copolyacrylic resin contains 5-10 parts of inorganic nano powder, 0.5-2 parts of surfactant, 5-10 parts of organic solvent A, 15-40 parts of acrylate hard monomer, 10-30 parts of acrylate soft monomer, 1-5 parts of special monomer, 0.2-1 part of initiator, and 5-10 parts of organic solvent B.

[0048] The isocyanate provided by the present invention has an -NCO content ≥ 13%, a non-volatile component (solid content) of 75.0 ± 2.0%, and a free TDI monomer content ≤ 0.5%, ensuring a sufficient and effective isocyanate group content.

[0049] In the copolyacrylic resin provided by the present invention, the inorganic nano powder material is one or more of nano-silica, nano-titanium dioxide, and nano-aluminum oxide. The nano powder is 50-200 nm, and the wavelength in the visible light band ranges from 390 nm to 750 nm. Light can penetrate the coating, ensuring the transparency of the coating, so that the coating can be used on transparent BOPP films.

[0050] In the copolyacrylic resin provided by the present invention, the surfactant refers to any substance that can improve the compatibility and wettability of the film-forming substance and enhance the adhesion between the film layer formed by the coating solution and the coated surface, such as silane coupling agents, especially A-151 (vinyltriethoxysilane), A171 (vinyltrimethoxysilane), A172 (vinyltri(β-methoxyethoxy)silane), etc.

[0051] In the copolymerized polyacrylic resin provided by the present invention, the organic solvent A is one or more of ethyl acetate, propyl acetate, and butyl acetate; the organic solvent B is one or more of toluene, propylene glycol monomethyl ether, or dipropylene glycol methyl ether. Adding the organic solvent A can reduce the boiling point of the system and improve the drying efficiency; adding the organic solvent B can improve the dispersibility of the resin and ensure the uniformity of each component in the system.

[0052] In the copolymerized polyacrylic resin provided by the present invention, the acrylate hard monomer is one or more of methyl methacrylate, isobornyl acrylate, and isobornyl methacrylate.

[0053] In the copolymerized polyacrylic resin provided by the present invention, the acrylate soft monomer is one or more of methyl acrylate, ethyl acrylate, butyl acrylate, and isooctyl acrylate.

[0054] In the copolymerized polyacrylic resin provided by the present invention, the initiator is benzoyl peroxide or azobisisobutyronitrile.

[0055] Specifically, when implemented, the copolymerized polyacrylic resin can be prepared by the following preparation method:

[0056] A. Preparation of copolymerized polyacrylic resin:

[0057] Step 1: Mix 5 - 10 parts of nano-silica with 0.5 - 2 parts of the surfactant vinyltriethoxysilane and stir with a glass rod for 10 - 20 minutes, then let it stand for 12 - 15 hours to improve its dispersibility;

[0058] Step 2: Add the nano-silica treated with the surfactant and all of the ethyl acetate into the reaction vessel, disperse at 1200 revolutions per minute for 30 - 60 min to form a prepolymerization solution;

[0059] Step 3: Add 30% methyl methacrylate, 30% methyl acrylate, 30% divinylbenzene, 30% azobisisobutyronitrile, and 30% toluene into the reaction vessel, stir and heat up to the first reaction temperature of 80 °C, and keep it at 80 °C for 3.5 h to carry out a free radical polymerization reaction to form an oligomer;

[0060] Step 4: Then mix 60% toluene, 30% azobisisobutyronitrile and the remaining all methyl methacrylate, methyl acrylate, and divinylbenzene evenly, put them into a beaker, and drip them into the reaction vessel with a peristaltic pump. The dripping time is 3 h, heat up to 85 °C, continue the reaction, and keep it warm for 0.5 h;

[0061] Step 5: Mix 10% toluene and 30% azobisisobutyronitrile, drip them into the reaction vessel, heat up to 92 °C, and keep it warm for 2 h; cool down and discharge to obtain the required copolymerized polyacrylic resin.

[0062] Total polyacrylic resin mass fraction summary table:

[0063]

[0064] During specific implementation, the coating liquid can be prepared by the following preparation method:

[0065] B. Preparation of coating liquid:

[0066] Mix 22-28 wt% of the above-mentioned total polyacrylic resin, 0.05-0.1 wt% of the curing agent, and 72-78 wt% of ethyl acetate to obtain the coating liquid, where the curing agent is isocyanate and carbon tetrachloride mixed in a weight fraction of 1:2 and stirred at 5000-6000 r / min in a high-speed mixer for 35-45 minutes to complete the mixing and coating.

[0067] During specific implementation, the BOPP pre-coated film can be prepared by the following preparation method:

[0068] C. Preparation of BOPP pre-coated film:

[0069] The present invention also provides a preparation method of the BOPP pre-coated film for enhancing the adhesion of UV ink, including the following steps:

[0070] Step a: Place the polypropylene film on the unwind rack for unwinding;

[0071] Step b: Place the unwound polypropylene film in a corona machine to perform corona treatment on the surface of the polypropylene film;

[0072] Step c: Pass the corona-treated polypropylene film through a coater, coat the solvent-based coating liquid of the coating layer on the corona surface of the corona-treated polypropylene film, and bake it in an oven with a set temperature gradient to obtain a BOPP pre-coated film for enhancing the adhesion of UV ink with a polypropylene film layer thickness of 30-100 um and a coating layer thickness of 1-3 um.

[0073] During the above corona treatment process, this embodiment provides a set of corona parameters. Corona machine parameters: The treatment voltage range is 15000-18000 V, the gap between the electrode and the film is controlled at 1-2 mm, the output power range is 40-60 kW, and the frequency adjustment range is 15-18 kHz. Environmental requirements for corona treatment: Humidity is 50-65%, temperature is 25-40 °C. The corona machine operates in an environment with an oxygen content of 45-55%.

[0074] Under the action of the optimized corona machine parameters, when the corona machine works in an environment with an oxygen content of 45 - 55%, it can excite strongly polar groups such as hydroxyl, carbonyl, and peroxides with full coverage and high density. At this time, the surface dyne value of the film can reach 50 dyn / cm, and the reaction area can penetrate up to 200 nm below the material surface layer. The strongly polar groups generated by corona react with the -NCO groups released by the curing agent to form chemical bond connections, greatly improving the coating fastness.

[0075] Due to the certain porous structure of the inorganic nano - powder, the UV ink can penetrate into the depressions and gaps of the coating. After the UV ink is cured, it has effects such as anchoring, hooking, and wedging with the nano - powder, having good adhesion and greatly improving the fastness between the ink and the coating layer 1. On the other hand, the added nano - powder improves the coating hardness, and at the same time, the surface has a micro - concave - convex structure, introducing air and greatly reducing the risk of reverse sticking during winding.

[0076] For the BOPP pre - coated film as described above, the thickness of the coating is 1 - 3 μm, the light transmittance is 93 - 97%, and the haze is 0.5 - 1.5%. At room temperature, the coating adhesion is 4 - 5 levels, and the ink adhesion is 4 - 5 levels; after thermal shock cycling, the coating adhesion is 4 - 5 levels, and the ink adhesion is 4 - 5 levels; after high temperature and high humidity, the coating adhesion is 4 - 5 levels, and the ink adhesion is 4 - 5 levels.

[0077] To further reveal the nature of the present invention, the following test methods and examples have described the present invention in detail. It should be understood that, except for these limiting conditions specifically specified in the appended claims, the present invention is not limited by the specific conditions or details stated in these examples.

[0078] The test methods involved in the specific implementation are as follows:

[0079] I. Coating fastness detection method:

[0080] Refer to the standard GB / T 9286 - 1998 for coating fastness detection; according to the test results, it can be divided into the grades shown in the following table (the detection grade ≥ 4 is excellent):

[0081]

[0082] II. Ink fastness detection method:

[0083] At room temperature, print the sample with UV flexographic ink, the ink amount is 10 g / square, the vehicle speed is 50 m / min, the UV lamp wavelength: 340 - 375 nm; the minimum radiation energy is 3000 mJ / cm 2 , and the energy density is greater than 10 mW / cm 2 .

[0084] The ink fastness test is carried out with reference to the standard GB / T 9286-1998; according to the test results, it can be divided into the grades shown in the following table: (the detection grade ≥ 4 is excellent):

[0085]

[0086] III. Thermal shock: Place the sample in an environment of -40°C for 30 minutes, then place the sample in an environment of 50°C for 30 minutes, cycle 100 times, take out the sample and place it at room temperature for 24h and then proceed to the next test.

[0087] IV. High temperature and high humidity: Place the sample in an environment of high temperature and high humidity of 60°C / 90 for 72h, take out the sample and place it at room temperature for 24h and then proceed to the next test.

[0088] V. Haze test: Determination of light transmittance and haze of transparent plastics (GB / T 2410-2008).

[0089] The manufacturers and grades of some raw materials involved in the specific implementation are as follows:

[0090]

[0091] Example 1:

[0092] A. Preparation of copolyacrylic resin:

[0093] Mix 7 parts of nano-silica with 1 part of vinyltriethoxysilane and stir with a glass rod for 10 minutes, then let it stand for 13 hours; add the surface-treated nano-silica and 5 parts of ethyl acetate into the reaction vessel and disperse at 1200 revolutions per minute for 30 min; add 9 parts of methyl methacrylate, 6 parts of methyl acrylate, 0.9 part of divinylbenzene, 0.3 part of azobisisobutyronitrile, and 2.4 parts of toluene into the reaction vessel, stir and heat up to the first reaction temperature of 80°C and keep it warm for 3.5 h; then mix 4.8 parts of toluene, 0.3 part of azobisisobutyronitrile with the remaining all methyl methacrylate, methyl acrylate, and divinylbenzene evenly and put them into a beaker, and drip them into the reaction vessel with a peristaltic pump, the dripping time is 3 h, heat up to 85°C and keep it warm for 0.5 h; mix 0.8 part of toluene and 0.3 part of azobisisobutyronitrile, drip them into the reaction vessel, heat up to 92°C and keep it warm for 2 h; cool down and discharge to obtain the required copolyacrylic resin.

[0094] B. Preparation of coating solution:

[0095] Mix 25 wt% of the above-mentioned copolyacrylic resin, 0.08 wt% of a curing agent, and 74.92 wt% of ethyl acetate to obtain a coating solution. The curing agent is prepared by mixing isocyanate and carbon tetrachloride at a weight ratio of 1:2 and stirring for 40 minutes at 5500 r / min in a high-speed mixer to complete the mixing and coating.

[0096] C. Preparation of BOPP pre-coated film:

[0097] Place a 50-μm BOPP film on a unwind rack for unwinding.

[0098] The unwound BOPP film is subjected to corona treatment on the surface by a corona machine. In the step of surface corona treatment, it includes: treating the film on a corona machine equipped with 6 electrodes. The voltage range is 17000 V, the gap between the electrode and the film is controlled at 1.5 mm, the output power range is 50 kW, and the frequency adjustment range is 16 kHz. The environment during corona treatment: humidity 60%, temperature 34 °C. The oxygen content at the location of the corona machine is 52%.

[0099] Coat the above-mentioned coating solution prepared in step B on the corona-treated surface of the BOPP film using a 120-mesh gravure roll (coating wet weight 8 g / m 2 ), dry it in an oven with a set temperature gradient, baking temperature 130 °C, baking time 20 s, and then wind it up. Hang the large roll of BOPP pre-coated film in a curing oven at 40 °C for 72 h to obtain a BOPP pre-coated film with a polypropylene film layer thickness of 50 μm and a coating layer thickness of 2 μm, which enhances the adhesion of UV ink.

[0100] Comparative Example 1

[0101] The difference between this comparative example and Example 1 is that carbon tetrachloride is not used, and the coating solution is obtained by mixing 25 wt% of copolyacrylic resin, 0.02 wt% of isocyanate, and 74.98 wt% of ethyl acetate.

[0102] Comparative Example 2

[0103] The difference between this comparative example and Example 1 is that nano-silica is not added in the preparation of the copolyacrylic resin. Specifically, the preparation of the copolyacrylic resin includes:

[0104] Add 1 part of vinyltriethoxysilane and 5 parts of ethyl acetate into a reaction vessel, and disperse at 1200 revolutions per minute for 30 - 60 min; add 9 parts of methyl methacrylate, 6 parts of methyl acrylate, 0.9 part of divinylbenzene, 0.3 part of azobisisobutyronitrile, and 2.4 parts of toluene into the reaction vessel, stir and heat up to the first reaction temperature of 80 °C, and keep the temperature for 3.5 h; then mix 4.8 parts of toluene, 0.3 part of azobisisobutyronitrile and all the remaining methyl methacrylate, methyl acrylate, and divinylbenzene evenly, put them into a beaker, and drip them into the reaction vessel with a peristaltic pump. The dripping time is 3 h, heat up to 85 °C, and keep the temperature for 0.5 h; mix 0.8 part of toluene and 0.3 part of azobisisobutyronitrile, drip them into the reaction vessel, heat up to 92 °C, and keep the temperature for 2 h; cool down and discharge to obtain the required copolyacrylic resin.

[0105] The test results are shown in Table 1:

[0106] Table 1 Performance test table of examples and comparative examples

[0107]

[0108] Compared with Example 1, in Comparative Example 1, the fastness of the coating and ink after the ring test is significantly worse. This is mainly because carbon tetrachloride-coated isocyanate curing agent is not used, and the curing agent is not enriched in the interfacial layer but evenly dispersed in the coating liquid. When baking in the drying oven, there are not enough connection points between the curing agent and the active groups generated by corona, resulting in poor coating fastness, especially manifested in the coating fastness after thermal shock and high temperature and high humidity. And as the "foundation" of the ink, the poor coating fastness causes the ink and the coating to fall off together when testing the ink fastness.

[0109] Compared with Example 1, in Comparative Example 2, the ink fastness becomes worse after the ring test. This is mainly because although the coating has good fastness with the BOPP film, there is no inorganic nano powder to provide a porous structure, and the UV ink cannot penetrate into the depressions and gaps of the coating. After the UV ink is cured, it cannot produce anchoring, hooking, wedging and other effects with the coating. The coating fastness is qualified after the ring test, while the ink fastness is unqualified.

[0110] Example 2:

[0111] The difference between the BOPP pre-coated film of this example and that of Example 1 is that: mix 25 wt% of the above copolyacrylic resin, 0.05 wt% of the curing agent, and 74.95 wt% of ethyl acetate to obtain a coating liquid, where the curing agent is a mixture of isocyanate and carbon tetrachloride in a weight ratio of 1:2 and stirred at 5500 r / min in a high-speed mixer for 40 minutes to complete the mixing and coating.

[0112] Example 3:

[0113] The difference between the BOPP pre-coated film of this embodiment and that of the first embodiment is as follows: Mix 25 wt% of the above-mentioned copolyacrylic resin, 0.1 wt% of the curing agent, and 74.9 wt% of ethyl acetate to obtain a coating solution, wherein the curing agent is a mixture of isocyanate and carbon tetrachloride in a weight ratio of 1:2, and the mixing and coating are completed by stirring at 5500 r / min in a high-speed mixer for 40 minutes.

[0114] Example 4:

[0115] The difference between the BOPP pre-coated film of this embodiment and that of the first embodiment is as follows: The unwound BOPP film is subjected to corona treatment on the surface by a corona machine; in the step of surface corona treatment, it includes: treating the film on a corona machine equipped with 6 electrodes. The voltage range is 15000 V, the gap between the electrode and the film is controlled at 1.5 mm, the output power range is 50 kW, and the frequency adjustment range is: 16 kHz. The environment during corona treatment: humidity 65%, temperature 34 °C. The oxygen content at the location of the corona machine is 45%.

[0116] Example 5:

[0117] The difference between the BOPP pre-coated film of this embodiment and that of the first embodiment is as follows: The unwound BOPP film is subjected to corona treatment on the surface by a corona machine; in the step of surface corona treatment, it includes: treating the film on a corona machine equipped with 6 electrodes. The voltage range is 18000 V, the gap between the electrode and the film is controlled at 1.5 mm, the output power range is 50 kW, and the frequency adjustment range is: 16 kHz. The environment during corona treatment: humidity 50%, temperature 34 °C. The oxygen content at the location of the corona machine is 55%.

[0118] Example 6:

[0119] The difference between the BOPP pre-coated film of this embodiment and that of the first embodiment is as follows: The copolyacrylic resin is prepared from the following components in parts by weight:

[0120] 5 parts of nano-silica, 1 part of vinyltriethoxysilane, 5 parts of ethyl acetate, 30 parts of methyl methacrylate, 20 parts of methyl acrylate, 3 parts of divinylbenzene, 1 part of azobisisobutyronitrile, 8 parts of toluene.

[0121] Example 7:

[0122] The difference between the BOPP pre-coated film of this embodiment and that of the first embodiment is as follows: The copolyacrylic resin is prepared from the following components in parts by weight:

[0123] 10 parts of nano-silica, 0.5 part of vinyltriethoxysilane, 5 parts of ethyl acetate, 15 parts of methyl methacrylate, 10 parts of methyl acrylate, 1 part of divinylbenzene, 0.2 part of azobisisobutyronitrile, 5 parts of toluene.

[0124] Example 8:

[0125] The difference between the BOPP pre-coated film of this example and that of Example 1 is that: the polypropylene film layer is a transparent biaxially stretched polypropylene film layer with a thickness of 30 μm, and the thickness of the coating layer is 3 μm.

[0126] Example 9:

[0127] The difference between the BOPP pre-coated film of this example and that of Example 1 is that: the polypropylene film layer is a transparent biaxially stretched polypropylene film layer with a thickness of 100 μm, and the thickness of the coating layer is 1 μm.

[0128] Table 2 Performance test table of Examples 2 - 9

[0129]

[0130] As can be known to those skilled in the art, when the technical parameters of the present invention vary within a certain range, technical effects similar to or the same as those of the above examples can be expected.

[0131] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the technical principle of the present invention, several improvements and modifications can be made, and these improvements and modifications should also be regarded as the protection scope of the present invention.

Claims

1. A BOPP pre-coated film for enhancing the adhesion of UV ink, characterized in that, It includes a polypropylene film layer and a coating layer; The coating layer is formed by coating a solvent-based coating solution on the corona surface of the polypropylene film layer. The components of the solvent-based coating solution of the coating layer include copolymerized acrylic resin, curing agent, and organic solvent A; Among them, the copolymerized acrylic resin is obtained by polymerizing inorganic nano powder, surfactant, organic solvent A, acrylate hard monomer, acrylate soft monomer, special monomer, initiator, and organic solvent B; The curing agent is composed of carbon tetrachloride-coated isocyanate; The special monomer is one or more of divinylbenzene, tetramethylcyclotetrasiloxane, and diallyl maleate; The organic solvent A is one or more of ethyl acetate, propyl acetate, and butyl acetate; the organic solvent B is one or more of toluene, propylene glycol monomethyl ether, or dipropylene glycol methyl ether.

2. The BOPP pre-coated film for enhancing the adhesion of UV ink according to claim 1, characterized in that, In the solvent-based coating solution, the mass percentages of the copolymerized acrylic resin, curing agent, and organic solvent A are (22 - 28 wt%): (0.05 - 0.1 wt%): (72 - 78 wt%); among them, by weight, the curing agent is a mixture of isocyanate and carbon tetrachloride coated in a ratio of 1:2; by weight, the copolymerized acrylic resin contains 5 - 10 parts of inorganic nano powder, 0.5 - 2 parts of surfactant, 5 - 10 parts of organic solvent A, 15 - 40 parts of acrylate hard monomer, 10 - 30 parts of acrylate soft monomer, 1 - 5 parts of special monomer, 0.2 - 1 part of initiator, and 5 - 10 parts of organic solvent B.

3. The BOPP pre-coated film for enhancing the adhesion of UV ink according to claim 1, characterized in that The polypropylene film layer is a transparent biaxially stretched polypropylene film layer with a thickness of 30 - 100 μm, and the thickness of the coating layer is 1 - 3 μm.

4. The BOPP pre-coated film for enhancing the adhesion of UV ink according to claim 1, characterized in that, The inorganic nano powder is one or more of nano silica, nano titanium dioxide, and nano alumina.

5. The BOPP pre-coated film for enhancing the adhesion of UV ink according to claim 1, wherein The acrylate hard monomer is one or more of methyl methacrylate, isobornyl acrylate, and isobornyl methacrylate.

6. The BOPP pre-coated film for enhancing the adhesion of UV ink according to claim 1, characterized in that, The acrylate soft monomer is one or more of methyl acrylate, ethyl acrylate, butyl acrylate, and isooctyl acrylate.

7. The BOPP pre-coated film for enhancing the adhesion of UV ink according to claim 1, characterized in that, The initiator is benzoyl peroxide or azobisisobutyronitrile.

8. A method for preparing an enhanced UV ink adhesion BOPP pre-coated film according to any one of claims 1-7, characterized in that, It includes the following steps: Step a: Place the polypropylene film on the unwind rack for unwinding; Step b: Place the unwound polypropylene film into a corona machine to perform corona treatment on the surface of the polypropylene film to obtain a corona-treated polypropylene film; Step c: After corona treatment, the corona-treated polypropylene film is coated with the solvent-based coating solution of the coating layer on the corona surface through a coater, and then baked in an oven with a set temperature gradient to obtain a BOPP pre-coated film with enhanced UV ink adhesion.

9. The preparation method of the BOPP pre-coated film for enhancing the adhesion of UV ink according to claim 8, wherein, The preparation method of the solvent-based coating solution of the coating layer is: Add the copolymerized acrylic resin and organic solvent A into a reaction vessel and stir, then add the blend of isocyanate and carbon tetrachloride, and continue to stir to finally obtain the solvent-based coating solution of the coating layer.

10. The preparation method of the BOPP pre-coated film for enhancing the adhesion of UV ink according to claim 9, wherein, The preparation method of the copolymerized acrylic resin is: Surface-treat the inorganic nano powder with a surfactant; Disperse and mix the surface-treated inorganic nano powder and organic solvent A in a reaction vessel; Add part of the monomers, part of the initiator, and part of the organic solvent B to the above reaction vessel, stir and heat up to the first reaction temperature, and keep the temperature constant; Then, mix part of the organic solvent B, part of the initiator, and all the remaining monomers evenly, and drop them into the above reaction vessel, heat up to the second reaction temperature, and keep the temperature constant; Mix the remaining organic solvent B and the remaining initiator, drop them into the above reaction vessel, heat up to the third reaction temperature, keep the temperature constant for a period of time, then cool down and discharge to obtain the copolyacrylic acid resin.

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