Aqueous ink for stamp paper printing and preparation method thereof

Abstract

The present invention discloses a water-based ink for stamp paper printing and a preparation method thereof, and relates to the field of printing. The process comprises the following steps: (1) preparing a water-based ink formula; (2) selecting a suitable grinding process to control fineness; (3) preparing a suitable dilution viscosity; (4) pre-treating the paper before printing; (5) controlling the parameters of the printing machine during the printing process; and (6) drying the printed product. The process can greatly reduce the emission of volatile organic substances, improve the printing working environment, effectively solve the problems of ink drying, blurring on paper, missing dots, etc., and improve the quality and stability of printed products.

Description

Technical Field

[0001] The invention relates to the technical field of water-based ink printing, and in particular to a water-based ink for stamp paper printing and a preparation method thereof. Background Art

[0002] There are many types of printing inks, which are divided into benzene, ketone, ester and alcohol according to the solvent system. These are all volatile organic compounds (VOCs). During the production of inks and the printing process, they evaporate and fill the entire workshop, and are discharged to the outdoor atmosphere through the workshop air windows or exhaust devices, seriously polluting the environment. At present, water-based inks are gradually replacing solvent-based inks in the printing field, but their slow drying speed, easy blurring on paper and surface tension problems limit their application. Therefore, it is necessary to develop a water-based ink process to solve these problems. Summary of the invention

[0003] In order to overcome the problems existing in the prior art, the present invention provides a water-based ink for stamp paper printing and a preparation method thereof, which can achieve a product fineness of ≤7μm with low energy consumption and high efficiency. The process can greatly reduce the emission of volatile organic substances, improve the printing working environment, effectively solve the problems of ink drying, blurring on paper, missing dots, etc., and improve the quality and stability of printed products. The product performance is equivalent to or better than solvent-based inks, and can gradually replace solvent-based inks.

[0004] The invention provides a water-based ink for stamp paper printing, comprising the following components: resins A and B, pigment C, solvent D, water-based dispersant F and defoamer G; wherein the resin A is a polyurethane resin, and the resin B is an acrylic resin.

[0005] Furthermore, a drying aid is also included.

[0006] Furthermore, in terms of mass percentage, the total amount of resin A and resin B is 60%-66%, pigment C is 10%-15%, solvent D is 19%-21%, aqueous dispersant F is 1%-3%, defoamer G is 1%, and drying aid is 1%-2%.

[0007] The formulation of water-based ink includes selecting suitable resins, pigments and drying aids. The key to selecting resins is good alcohol resistance, water resistance and good drying performance. 80% of the drying performance of the finished ink is provided by the drying performance of the water-based resin. The selection of pigments requires good light resistance and weather resistance. The total amount of resin in the formula is 60%-66%, the solvent ratio is 19%-21%, and the pigment ratio is 10%-15%. This ratio of resin and solvent can make the finished ink reach a suitable viscosity and achieve good printing effects. Resins A and B, pigment C, solvent D, dispersant F and defoamer G are necessary components in the formula. Drying aids can be selectively added according to the actual printing speed of the customer. Adding drying aids helps to speed up the drying speed of water-based ink, but it should not exceed 2%.

[0008] The present invention also provides a method for preparing the above-mentioned water-based ink for stamp paper printing, comprising the following steps:

[0009] S1. Weigh the aqueous dispersant, resin A, solvent, and pigment according to the ratio in the formula, add the aqueous dispersant, resin A, solvent, and pigment to the stirred tank in sequence at a speed of 40-45 Hz and a dispersion time of 1 hour for premixing;

[0010] S2. Grind the obtained color paste using a nano-grinding machine and two series-connected sand mills, grind while dispersing, pay attention to the material temperature ≤50°C and the fineness to <7μm during the grinding process, and obtain the pre-material grinding liquid;

[0011] Use nano-level grinding equipment, that is, the equipment grinding accuracy can reach below 1 micron at the lowest. When grinding, use two sand mills in series to improve grinding efficiency and reduce energy consumption. 9% solvent needs to be reserved before grinding. Each grinding cycle needs to clean the walls of the dispersion kettle and turnover kettle with the reserved solvent. Pay special attention to the sedimentation problem at the bottom of the material during the first grinding. It is best to grind while dispersing, otherwise the ink that has not been cleaned will stick to the wall and affect the fineness. During the grinding process, pay attention to the material temperature not being too high, preferably ≤50℃, to prevent the resin from denaturing under high temperature. The reserved solvent can also reduce the material temperature while cleaning the kettle wall to prevent the resin from denaturing. If the production equipment is not fully sealed, care should be taken to avoid the volatilization of the solvent. If the amount of solvent volatilization is large, the solvent loss should be supplemented to prevent affecting the viscosity of the finished ink.

[0012] S3, calculate the resin B required for the rear material in proportion, weigh it and add it to the grinding liquid of the front material, then add the weighed defoamer and drying aid, stir and disperse at a speed of 30 Hz for 30 minutes, and filter with a 10 μm filter bag to obtain the water-based ink product for stamps;

[0013] After the finished product is made, it is necessary to prepare the appropriate dilution viscosity for printing, according to the quality of the paper, water absorption and compatibility with water-based ink. According to different printing requirements, choose the appropriate dilution viscosity and dilution solvent to reduce the occurrence of blurring problems on the paper. If the printing environment is a non-constant temperature environment, the effect of temperature on viscosity needs to be considered. When the temperature is high, the viscosity of water-based ink will be lower, and when the temperature is low, the viscosity will be higher. At a temperature of 25°C, the printing dilution viscosity is preferably around 17s (Zahn 3# viscosity cup). Too high viscosity is not conducive to the transfer of ink, and too low viscosity is easy to penetrate the stamp paper, causing wrinkles on the back.

[0014] S4. Pre-treat the paper before printing. The temperature of the paper is controlled at 25-30℃, and the humidity is controlled at 5%-7%. Too high a temperature will cause the four sides of the paper to rise and fall and warp, while too low a temperature will cause shrinkage and form a "tight edge". During the printing process, control the parameters of the printing press, including speed, pressure, scraper angle, etc. The speed of the printing press is set to 80-100m / min. Too fast may cause the ink to not dry completely and cause anti-sticking. The printing pressure affects the clarity and color saturation of the printed product, and is also related to the durability and long-term preservation of the printed product. Adjust the printing press plate roller pressure to 0.3Mpa and the scraper angle to 80° to ensure that the ink is evenly coated on the paper and fully combined with the paper surface to reduce the occurrence of surface tension problems.

[0015] S5. Dry the printed matter. You can use air-cooled drying ovens, ultraviolet dryers and other equipment to completely remove the moisture in the water-based ink, improve the drying speed and print quality. If you use hot drying equipment, the temperature should not exceed 35°C, otherwise it will cause deformation of the printed matter.

[0016] Beneficial effects: In terms of formula, the present invention uses two water-based resins in combination with water-soluble additives to reduce the VOC content while effectively solving the problems of water-based ink drying, blurring on paper, missing dots, etc. In terms of preparation process, this patent adopts a process of grinding with two sand mills in series, adopts an integrated hot and cold water cooling external internal and external circulation, and automatically adjusts the operation of the refrigeration system according to the set temperature to maintain a stable temperature during the grinding process. The fineness of the product can be reduced to ≤7μm with low energy consumption and high efficiency. The product performance is equivalent to or better than solvent-based inks, and can gradually replace solvent-based inks. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is the water-based ink industry flow chart. DETAILED DESCRIPTION

[0018] Example 1

[0019] (1) Ratio of raw materials for water-based ink for stamps: Based on surface printing water-based ink, a black water-based ink with a specific formula is prepared, including PU water-based resin A: Guangzhou Zhenguan 3655 (30%), PA water-based resin B: Guangzhou Guanzhi 2305 (30%), high-color carbon black pigment C: Cabot 250R (12%), solvent D: 50% ethanol (21%) and amine compound drying aid E: Shijiazhuang Liantai 602N (1%-2%), anionic carboxylate water-based dispersant F: Jiangsu Jintu WF813 (2%-3%), polyether water-based defoamer G: Jiangsu Jintu X635 (1%-2%). Resins A and B, pigment C, solvent D, water-based dispersant F and defoamer G are necessary components. Drying aids can be selectively added according to the actual printing speed of the customer. Adding drying aids helps to speed up the drying speed of water-based ink, but it should not exceed 2%.

[0020] (2) Grinding process control: dispersant F Jiangsu Jintu WF813 (2%), solvent D 50% ethanol (11%), and PU resin A Guangzhou Zhenguan 3655 (30%) are added to the dispersion kettle in sequence for dispersion and mixing. Solvent D 50% ethanol (10%) is reserved to rinse the dispersion kettle and the wall of the turnover kettle during the grinding process. Pigment C Cabot 250R carbon black (12%) is added during the dispersion process for high-speed dispersion at a speed of 40-45 Hz and a dispersion time of 1 hour, so that the pigment is fully wetted by the resin system to form a uniform suspension state. Then the grinding process begins. Two sand mills are used in series during grinding, wherein the zirconium bead particle size of sand mill A is 0.8-1.2 mm, and the zirconium bead particle size of sand mill B is 0.6-0.8 mm. The particles first pass through sand mill A and then through sand mill B. When grinding, it is necessary to control the grinding temperature so that it is not too high. The speed of sand mill A should not be too high. The first grinding can be done at 40-45 Hz, and the speed of sand mill B can be appropriately increased to 45-50 Hz. Sampling should be carried out at the beginning of each grinding to observe and record the decrease in fineness. Control the flow of the sand mill, and reserve 10% of the solvent for cleaning the kettle wall. After washing, the solvent is mixed into the ground material through the grinder. After grinding by sand mill B, start the second grinding according to the fineness, and stop grinding when the fineness meets the requirements. Then mix PA resin B Guangzhou Guanzhi 2305 (30%) and drying aid E Shijiazhuang Liantai 602N (2%) and disperse them. The dispersion speed should not be too fast, about 30 Hz is appropriate, and the duration is controlled within half an hour. After the dispersion is completed, take samples for testing.

[0021] (3) According to the quality of the paper, its water absorption, compatibility with water-based ink and customer needs, the original ink is prepared with appropriate dilution viscosity for printing. It can be diluted with pure water. At a temperature of 25°C, the printing dilution viscosity is preferably about 17s (Zahn 3# viscosity cup) to reduce the occurrence of blurring on the paper. If the printing environment is a non-constant temperature environment, the effect of temperature on viscosity needs to be considered. When the temperature is high, the viscosity of the water-based ink will be lower, and when the temperature is low, the viscosity will be higher.

[0022] (4) Choose 80g / m 2 As the printing substrate, stamp paper is pretreated before printing, such as appropriate wet water treatment, to control the moisture content of the paper at 5%-7%. If the moisture content of the paper is too low, the paper will become brittle, its toughness and elasticity will be reduced, and static electricity will be easily generated during the printing process. If the moisture content is too high, it will make it difficult for the ink to dry, the hardness and stiffness of the paper will decrease, and the surface strength will be affected, which may cause deinking, stratification and other undesirable phenomena in the printed product. This helps the paper maintain a stable size and flatness during the printing process, and avoids static electricity problems. During the paper printing process, static electricity will affect the uniformity and adhesion of the ink. Therefore, electrostatic dust removal can also be used to reduce the impact of static electricity on the paper on the printing quality.

[0023] (5) Control the parameters of the printing machine, the speed of the printing machine is 80-100m / min, the plate pressure is adjusted to 0.3Mpa, and the scraper angle is 80°. Use cold air drying equipment to dry the printed matter, and do not use high-temperature drying equipment to dry it, so as to avoid affecting the printing substrate and printing quality.

[0024] The raw material ratio table of water-based ink for stamps in Examples 2-4 is as follows, and the other steps are the same as in Example 1.

[0025] Table 1: Ratio of raw materials for water-based ink for stamps in Example 2-4

[0026]

[0027] Effect: The water-based ink process and its application of the present invention can greatly improve the environmental problems of solvent-based inks such as large VOC emissions and strong odor, and can effectively solve the drying problem of water-based inks, the blurring problem on paper and the surface tension problem, and improve the quality and stability of printed products. The VOC content in the entire formula is strictly controlled within the standard of ≤15% required by absorbent substrates. Experiments have shown that the products printed by this process dry quickly, have rich colors, high clarity, and good anti-blurring properties.

[0028] Table 2 Performance test of this patented product

[0029] Performance Indicators This product Solvent-based inks Scrape good good Color Density ＞1.9 ＞1.9 Point loss rate ＜2％ ＜2％ VOCs content ＜15％ ＞40％ Drying speed excellent excellent Printing adaptability excellent excellent Adhesion (3M tape tearing) No shedding No shedding

Claims

1. A water-based ink for stamp paper printing, characterized in that: The invention comprises the following components: resins A and B, pigment C, solvent D, aqueous dispersant F and defoamer G; Resin A is polyurethane resin, and resin B is acrylic resin.

2. A water-based ink for stamp paper printing as claimed in claim 1, characterized in that: Also included are drying aids.

3. A water-based ink for stamp paper printing as claimed in claim 2, characterized in that: In terms of mass percentage, the total amount of resin A and resin B is 60%-66%, pigment C is 10%-15%, solvent D is 19%-21%, aqueous dispersant F is 1%-3%, defoamer G is 1%, and drying aid is 1%-2%.

4. The method for preparing a water-based ink for stamp paper printing according to any one of claims 1 to 3, characterized in that: The following steps are involved: S1. Weigh the aqueous dispersant, resin A, solvent, and pigment according to the ratio in the formula, add the aqueous dispersant, resin A, solvent, and pigment to the stirred tank in sequence at a speed of 40-45 Hz and a dispersion time of 1 hour for premixing; S2. Grind the obtained color paste using a nano-grinding machine and two series-connected sand mills, grind while dispersing, pay attention to the material temperature ≤50°C and the fineness to <7μm during the grinding process, and obtain the pre-material grinding liquid; S3, calculate the resin B required for the latter material in proportion, weigh it and add it to the former material grinding liquid, then add the weighed defoamer and drying aid, stir and disperse at a speed of 30 Hz for 30 minutes, and filter with a 10 μm filter bag to obtain the water-based ink product for stamps; S4. Pre-treat the paper before printing, control the paper temperature at 25-30℃, humidity at 5%-7%, open the printing press speed to 80-100m / min, adjust the printing press roller pressure to 0.3Mpa, and the scraper angle to 80°; S5. Dry the printed matter.

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