A water-based printing coating for transparent bopp and its preparation method and application

Abstract

The application belongs to the technical field of material science, polymer coating and printing, and specifically discloses a water-based printing coating for transparent BOPP, a preparation method and application thereof. The raw materials of the printing coating include pure water, water-based resin, filler, wetting dispersant, crosslinking agent and film-forming aid. The water-based resin includes two water-based acrylic resins with different Tg values and modified acrylic resin, the filler is fumed silica with different particle sizes, and the film-forming aid is an alcohol aid. By optimizing the types, particle sizes and proportions of the components, the printing coating has low haze, high adhesion, anti-blocking property, water resistance and excellent printing performance. The coating is suitable for various printing modes such as flexographic printing and full rotary letterpress printing, and can meet the printing of all basic colors.

Description

Technical Field

[0001] This invention relates to the fields of materials science, polymer coatings, and printing technology, specifically to a water-based printing coating for transparent BOPP, its preparation method, and its application. Background Technology

[0002] Biaxially oriented polypropylene (BOPP) film possesses excellent strength, transparency, and gloss, making it a promising material for the packaging industry, widely used in food packaging, labeling, and electronic components. However, due to its low surface energy, strong chemical inertness, and smooth surface, BOPP film is difficult to wet and absorb inks. Currently, the most common method is pretreatment through film surface modification, including corona treatment, flame treatment, and plasma treatment. However, these methods all exhibit varying degrees of degradation effects (the dyne value of the film surface decreases rapidly over time), leading to decreased coating adhesion and unstable product quality. Alternatively, a polymer coating can be applied to the BOPP film surface to bond the BOPP substrate and printing inks, thereby ensuring its printability.

[0003] Currently, commonly used polymer emulsions include oil-based and water-based emulsions. Because oil-based polymer emulsions generally contain organic solvents such as benzene, which are environmentally unfriendly, water-based polymer emulsions are preferred as coating materials. However, water-based coating materials have several drawbacks. First, they are highly selective in terms of printing inks; generally, coatings cannot simultaneously support the printing of all basic colors (cyan, magenta, yellow, and black), leading to ink smudging after color matching. Second, they are highly dependent on the printing method (letterpress, flexographic, full-rotary, half-rotary, etc.), printing speed, and UV lamp irradiation intensity. Higher printing speeds or lower UV lamp irradiation intensity significantly affect printing performance. Furthermore, general coatings cannot simultaneously achieve optimal haze, printability, and anti-blocking properties: at high temperatures, the dyne value of the coating continuously decreases, resulting in insufficient printability, and the coating is prone to sticking and increased haze at high temperatures. Summary of the Invention

[0004] The purpose of this invention is to provide a water-based printing coating for transparent BOPP, its preparation method and application, to solve the problems of insufficient adhesion, printing performance greatly affected by printing speed and UV lamp irradiation intensity, poor durability, decrease in Derkin value at high temperature, coating adhesion and increased haze of existing water-based coatings for BOPP films.

[0005] To achieve the above objectives, the specific technical solution adopted by the present invention is as follows:

[0006] In a first aspect, the present invention provides a transparent BOPP water-based printing coating, comprising, by weight percentage: 70-85% pure water, 15-30% water-based resin, 0.03-0.12% filler, 0.05-0.15% wetting and dispersing agent, 0.1-0.3% crosslinking agent, and 0.5-3% film-forming aid. Wherein:

[0007] The water-based resin is typically selected from T... g Two different waterborne acrylic resins (Resin A and Resin B) and a modified acrylic resin (Resin C) are used to balance the wide applicability to printing methods, printing conditions, and printing inks. The Tg of Resin A is controlled between 0-15℃, avoiding the endpoint of 0, and preferably 5℃, to ensure basic printability of the coating (both letterpress and flexographic printing). Furthermore, the addition amount of Resin A should be controlled between 10-18%, preferably 12%. The Tg of Resin B is controlled between 75-100℃, preferably 85℃. A Tg below 75℃ can easily cause adhesion of the coating after winding at high temperatures. A Tg above 100℃ will decrease the dyne value of the coating surface, leading to poor printability, and will also increase the haze of the coating. Additionally, the addition amount of Resin B should be controlled between 1-9%, preferably 3%. An addition amount below 1% can easily cause adhesion of the coating after winding at high temperatures, while an addition amount above 9% will affect the printability and water resistance of the coating. The selection of resin C is crucial. The temperature gradient (Tg) needs to be controlled between 20-50℃, preferably 30℃. A Tg below 20℃ will affect the printing speed of rotary letterpress printing and the irradiation intensity of the UV lamp (slow printing speed leads to a sharp drop in efficiency, and high irradiation intensity leads to increased energy consumption). A Tg above 50℃ will affect the universality of rotary letterpress printing inks. Furthermore, the amount of resin C added should be controlled between 3-10%, preferably 6%. An addition amount below 3% will decrease the fastness of rotary letterpress printing, while an addition amount above 10% will decrease the fastness of flexographic printing. This resin is a modified acrylic resin, including at least one of polyurethane-modified acrylic resin, epoxy resin-modified acrylic resin, hydroxyl-modified acrylic resin, and epoxy-polyurethane-modified acrylic resin, preferably epoxy-polyurethane-modified acrylic resin.

[0008] The filler is fumed silica (S1 and S2) with different particle sizes. The particle size of S1 is controlled at 2-6 μm, preferably 3 μm, and the particle size of S2 is controlled at 0.5-0.8 μm, preferably 0.6 μm. The main purpose is to use the difference in particle size to achieve fine control of coating performance. S2 has a smaller particle size (nanoscale), which can effectively fill the gaps in resin molecules, improving the density, wear resistance and adhesion of the coating. S1 has a slightly larger particle size, which mainly improves the anti-blocking performance of the coating. Both are indispensable. If only S1 is added, the water resistance of the coating will decrease, and ink loss will occur in full-rotation letterpress printing and flexographic printing due to insufficient coating density. If only S2 is added, the anti-blocking performance of the coating is poor and the haze of the coating is high. In addition, the addition amount of S1 is 0.05%, and the addition amount of S2 should be controlled between 0.015% and 0.06%, preferably 0.03%. If the addition amount is too high, the coating will have high haze, and if the addition amount is too low, the coating will have poor anti-blocking performance.

[0009] The crosslinking agent is aziridine, and the preferred addition amount is 0.2%, which mainly improves the water resistance of the coating surface.

[0010] The wetting and dispersing agent is a polyether-modified organosilicon compound, specifically Dow DOWSIL 67, TEGOWET 245, BYK-345, HOS 1450, etc., with HOS 1450 being preferred. Its addition amount is preferably 0.09%, and its main function is to improve the wetting properties of the coating surface and the dispersion properties of the coating.

[0011] The film-forming aid is an alcohol-based film-forming aid, whose main function is to promote rapid film formation and improve the haze of the coating surface. Alcohol-based film-forming aids can be selected from propylene glycol methyl ether acetate (PMA), dipropylene glycol methyl ether (DPM), ethylene glycol, propylene glycol, and n-dodecyl alcohol, with PMA being preferred. The amount of film-forming aid added should be controlled between 0.5% and 3%, preferably 1%. Adding less than 0.5% has little effect on improving haze, while adding more than 3% significantly reduces the performance of flexographic printing and full-rotation letterpress printing.

[0012] Secondly, the present invention provides a method for preparing the above-mentioned water-based printing coating. The method is as follows: fillers S1 and S2 and wetting and dispersing agents are added to pure water and stirred and dispersed for 10-20 minutes. Then, resin A, resin B, resin C and film-forming aids are added and stirred and dispersed for 10-20 minutes. Finally, crosslinking agent is added and stirred and dispersed for 10-20 minutes to obtain a water-based emulsion. The water-based emulsion is coated on one side of a transparent BOPP base film and heated and cured to form a water-based printing coating.

[0013] Preferably, the thickness of the transparent BOPP base film is 30-100 μm.

[0014] Thirdly, the present invention provides the application of the above-mentioned water-based printing coating or the water-based printing coating prepared by the above-mentioned preparation method in the printing coating of transparent BOPP film.

[0015] Preferably, the water-based printing coating is suitable for flexographic printing and full rotary letterpress printing, and is suitable for cyan, magenta, yellow, black and white inks.

[0016] This invention achieves the following beneficial effects through formula optimization:

[0017] 1. The water-based printing coating of this invention can effectively improve the adhesion between the coating and the BOPP substrate, as well as between the coating and the printing ink, thereby achieving wide applicability to printing inks (full coverage of the basic color of printing ink YMCK + white).

[0018] 2. The water-based printing coating of this invention can effectively improve the printing speed and the influence of UV lamp irradiation intensity on the coating printing performance, and improve the coating's applicability to printing conditions and printing methods.

[0019] 3. The water-based printing coating of the present invention maintains good water resistance after being immersed in an ice-water mixture for 24 hours, which significantly improves the durability of the coating.

[0020] 4. The water-based printing coating of this invention can maintain low haze, high dyne value, and good anti-blocking properties even at high temperatures. This solves the problems of existing coatings experiencing a continuous decrease in dyne value, easy adhesion, and increased haze at high temperatures. Attached Figure Description

[0021] Figure 1 These are photographs showing the printing effect of the transparent BOPP printing coatings obtained in Example 1, Comparative Example 3, Comparative Example 8, and Comparative Example 10. Detailed Implementation

[0022] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0023] Example 1

[0024] This embodiment is the preferred embodiment, providing a transparent BOPP water-based printing coating, which comprises the following raw materials by weight percentage: resin A: 12%, resin B: 3%, resin C: 6%, fumed silica S1: 0.05%, fumed silica S2: 0.03%, wetting and dispersing agent: 0.09%, crosslinking agent: 0.2%; film-forming aid: 1%, pure water: 77.63%.

[0025] Wherein: Resin A is a water-based acrylic resin, more specifically pure acrylic resin, with a Tg of 5℃; Resin B is a water-based acrylic resin, more specifically styrene-acrylic resin, with a Tg of 85℃; Resin C is an epoxy-polyurethane modified acrylic resin, with a Tg of 30℃. The particle size of fumed silica S1 is approximately 3μm, and the particle size of fumed silica S2 is approximately 0.6μm. The wetting and dispersing agent is a polyether-modified organosilicon compound (HOS 1450). The crosslinking agent is aziridine. The film-forming aid is an alcohol-based film-forming aid PMA.

[0026] Preparation of water-based printing coating: Fillers S1 and S2 and wetting and dispersing agent are added to pure water and stirred and dispersed for 10-20 min. Then resin A, resin B, resin C and film-forming aid are added and stirred and dispersed for 10-20 min. Finally, crosslinking agent is added and stirred and dispersed for 10-20 min to obtain water-based emulsion. Using a transparent BOPP with a thickness of 30-100 μm as a base film, the water-based emulsion is coated on one side of the base film and heated and cured to form water-based printing coating.

[0027] Example 2

[0028] This embodiment provides a water-based printing coating for transparent BOPP, which is basically the same as in Embodiment 1, except that: the Tg of resin B is 95°C and the addition amount is 7%; the Tg of resin C is 45°C and the addition amount is 9%; and the addition amount of pure water is 70.63%.

[0029] Example 3

[0030] This embodiment provides a water-based printing coating for transparent BOPP, which is basically the same as in Embodiment 1, except that: the Tg of resin B is 80°C and the addition amount is 2%; the Tg of resin C is 25°C and the addition amount is 4%; and the amount of pure water added is 80.63%.

[0031] Performance test comparison

[0032] For the comparative examples in the following performance test settings that involve changes in the amount of raw materials (resin, filler, film-forming aid), the amount of pure water should be adjusted accordingly to keep the total amount of the formula at 100%.

[0033] (1) To study the effect of resin glass transition temperature and addition amount on coating, comparative examples 1-11 were set up to compare with the examples. The variables of comparative examples 1-11 compared with the examples are shown in the table below:

[0034]

[0035] ① The basic performance of the coating (haze, dyne value, water resistance, and anti-blocking performance) of the above embodiments and comparative examples were tested. Generally, a haze ≥ 3.5% significantly reduces transparency and affects visual effect; a dyne value < 36 significantly reduces the printing performance of the coating (the higher the dyne value, the higher the surface energy, the easier the ink spreads, and the stronger the adhesion); the anti-blocking performance was tested by placing the finished sample roll in a 70℃ oven for 7 days, taking it out, cooling it to room temperature, and pulling it off forcefully to observe whether the coating sticks off (yes is judged as NG, no is judged as OK); the water resistance performance was tested by soaking the printed finished product in an ice-water mixture for 24 hours, pulling the tape off forcefully, and observing whether the ink comes off (yes is judged as NG, no is judged as OK).

[0036] The results are shown in the table below. The selection of the glass transition temperature of resin A, resin B and resin C, the selection of the amount of resin B and resin C added, and the selection of the resin C modification material are crucial to this invention and have a significant impact on the basic performance of the coating.

[0037]

[0038] ② To study the effect of resin C on the printing performance of the coating (full-rotation letterpress, flexographic printing speed and UV lamp irradiation intensity) (mainly the effect on the basic color ink YMCK + white ink, the printing method can be referenced) Figure 1 The coatings of the comparative examples and embodiments involving changes in resin C were subjected to outsourced printing performance tests. UV lamp curing was performed simultaneously using full-rotation letterpress or flexographic printing. If no ink loss was observed in any of the five inks, the result was considered OK.

[0039] The test results are shown in the table below. When the Tg value of resin C is controlled between 20-50℃, the addition amount is controlled between 3-10%, and the structure is epoxy-polyurethane modified acrylic resin, the printing performance is OK whether flexographic printing or full-rotation letterpress printing is increased from 50m / min to 75m / min or the UV lamp power is reduced from 100% to 70%, as shown in Examples 1, 2, and 3. When the Tg of resin C is below 20℃, the ink loss is heavier in full-rotation letterpress printing when the printing speed is increased or the UV lamp power is reduced, as shown in Comparative Example 3. When the Tg value of resin C is above 50℃... Both rotary letterpress printing and flexographic printing exhibit varying degrees of ink fading, as shown in Comparative Example 4. When the amount of resin C added is less than 3%, rotary letterpress printing shows significant ink fading, as shown in Comparative Example 7. When the amount of resin C added is greater than 10%, the performance of flexographic printing decreases significantly, as shown in Comparative Example 8. When the structure of resin C is epoxy resin modified acrylic, polyurethane resin modified acrylic, or hydroxyl-modified acrylic, increasing the printing speed or reducing the UV lamp power results in significant ink fading in rotary letterpress printing, and flexographic printing also shows varying degrees of ink fading, as shown in Comparative Examples 9, 10, and 11. Therefore, the selection of resin C is crucial (Tg value, addition amount, and structural characteristics of the modified resin).

[0040]

[0041] The following three comparative examples will be provided for detailed explanation: Comparative Example 3 differs from the Example mainly in the glass transition temperature of resin C, which is 12°C; Comparative Example 8 differs from the Example mainly in the amount of resin C added, which is 15%; Comparative Example 10 differs from the Example mainly in the resin structure, with resin C being a polyurethane-modified acrylic resin. All other parameters are consistent with the Examples. From the above results, it can be seen that the Examples are all OK in terms of six dimensions: haze, dyne value, anti-blocking performance, water resistance, full-rotation letterpress printing (the influence of printing speed and UV lamp irradiation intensity), and flexographic printing (the influence of printing speed and UV lamp irradiation intensity). However, Comparative Example 3 has a problem with significant ink shedding in full-rotation letterpress printing (due to high printing speed or low UV lamp irradiation intensity), Comparative Example 8 has a problem with significant ink shedding in flexographic printing, and Comparative Example 10 has a problem with slight ink shedding in full-rotation letterpress printing. See details below. Figure 1 .

[0042] (2) To study the synergistic effect of fillers S1 and S2 and the influence of their addition amount on coating performance, comparative examples 12-15 were set up to compare with the examples. The variables of comparative examples 12-15 compared with the examples are shown in the table below:

[0043]

[0044] The coating haze, anti-blocking properties, water resistance, full-rotation letterpress printing, and flexographic printing were tested on Examples 1 and Comparative Examples 12-15. The testing methods were the same as before. In the full-rotation letterpress and flexographic printing tests, the results were judged as NG and OK, respectively, based on whether ink smudging occurred. The test results are shown in the table below. It can be seen that fillers S1 and S2 play a synergistic role and are both indispensable.

[0045]

[0046] (3) To study the effect of the amount of film-forming aid added on the coating performance, the present invention sets up Comparative Examples 16-17 for comparison with the Examples. The variables of Comparative Examples 16-17 compared with the Examples are shown in the following table:

[0047]

[0048] The coating haze, dyne value, full-rotation letterpress printing, and flexographic printing performance of Example 1 and Comparative Examples 16-17 were tested using the same methods as before. The test results are shown in the table below. When the amount of film-forming aid added is controlled between 0.5% and 3%, the coating haze, dyne value, full-rotation letterpress printing, and flexographic printing performance all meet the requirements. If the amount of film-forming aid added is too low, the coating haze will be high; if the amount added is too high, it will affect the coating dyne value, full-rotation letterpress printing, and flexographic printing performance. Therefore, its addition amount should be strictly controlled.

[0049]

[0050] This specific embodiment is merely an explanation of the present invention and is not intended to limit the present invention. Any changes made by those skilled in the art after reading the specification of the present invention, as long as they are within the scope of the claims of the present invention, will be protected by patent law.

Claims

1. A water-based printing coating for transparent BOPP, characterized in that, The raw materials include: pure water, water-based resin, filler, wetting and dispersing agent, crosslinking agent, and film-forming aid; The aqueous resin includes resin A, resin B, and resin C; resin A and resin B are aqueous acrylic resins, the Tg of resin A is controlled at 0-15℃, and the Tg of resin B is controlled at 75-100℃; the Tg of resin C is controlled at 20-50℃, and resin C is a modified acrylic resin selected from at least one of polyurethane modified acrylic resin, epoxy modified acrylic resin, hydroxyl modified acrylic resin, and epoxy-polyurethane modified acrylic resin. The filler is composed of two types of fumed silica, S1 and S2, with different particle sizes; the particle size of S1 is controlled at 2-6 μm, and the particle size of S2 is controlled at 0.5-0.8 μm. The crosslinking agent is aziridine; the wetting and dispersing agent is an organosilicon; and the film-forming aid is an alcohol-based film-forming aid.

2. The transparent BOPP water-based printing coating according to claim 1, characterized in that, The Tg of resin A is 5℃, the Tg of resin B is 85℃, and resin C is an epoxy-polyurethane modified acrylic resin with a Tg of 30℃.

3. The transparent BOPP water-based printing coating according to claim 1, characterized in that, The particle size of S1 is controlled at 3 μm, and the particle size of S2 is controlled at 0.6 μm.

4. The transparent BOPP water-based printing coating according to claim 1, characterized in that, The raw materials of this water-based emulsion, by mass percentage, include: 70-85% pure water, 0.03-0.12% filler, 15-30% water-based resin, 0.05-0.15% wetting and dispersing agent, 0.1-0.3% crosslinking agent, and 0.5-3% film-forming aid.

5. The transparent BOPP water-based printing coating according to claim 4, characterized in that, The three resins account for the following percentages by mass in the total formulation: Resin A 10-18%, Resin B 1-9%, and Resin C 3-10%.

6. The transparent BOPP water-based printing coating according to claim 5, characterized in that, The mass percentages of the two fillers in the total formulation are as follows: S1 0.05%, S2 0.015%-0.06%.

7. The transparent BOPP water-based printing coating according to claim 6, characterized in that, The raw materials, by mass percentage, include: Resin A 12%, Resin B 3%, Resin C 6%, Filler S1 0.05%, Filler S2 0.03%, Wetting and Dispersing Agent 0.09%, Crosslinking Agent 0.2%, Film-forming Aid 1%, and the balance is water.

8. The method for preparing the water-based printing coating according to any one of claims 1-7, characterized in that, The procedure is as follows: Add fillers S1 and S2 and wetting and dispersing agent to pure water and stir and disperse for 10-20 minutes. Then add resin A, resin B, resin C and film-forming aid and stir and disperse for 10-20 minutes. Finally, add crosslinking agent and stir and disperse for 10-20 minutes to obtain an aqueous emulsion. Coat the aqueous emulsion onto one side of a transparent BOPP base film and heat to cure to form an aqueous printing coating.

9. The application of the water-based printing coating according to any one of claims 1-7 or the water-based printing coating prepared by the preparation method according to claim 8 in the printing coating of transparent BOPP film.

10. The application according to claim 9, characterized in that, The water-based printing coating is suitable for flexographic printing and full rotary letterpress printing, and is suitable for cyan, magenta, yellow, black and white inks.

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