Oily offset printing ink and preparation method thereof

Abstract

The invention relates to oil-based offset printing ink and a preparation method thereof. The oil-based offset printing ink comprises the following raw material components in percentage by mass: 20-35% of pigment; 27-55% of mixed resin; 15-30% of soybean oil; 5-15% of a diluent; 0.5-10% of an auxiliary agent; the mixed resin comprises rosin modified resin, polyurethane resin and linseed oil modified alkyd resin. The specific mixed resin is mixed with the soybean oil, the diluent, the auxiliary agent and the pigment according to a certain content, so that on one hand, the cross-linking and curing speed of the connecting material of the ink can be effectively increased, and volatilization and permeation of an oil material are avoided; on the other hand, the dispersity of the pigment can be effectively improved, and the ink concentration is improved; the drying speed can be increased, and the ghosting problem can be solved.

Description

Technical Field

[0001] This invention belongs to the field of ink technology, and relates to an oil-based offset printing ink, specifically a black offset printing ink that effectively addresses the "ghosting" problem and its preparation method. Background Technology

[0002] "Ghosting" is a printing industry term referring to faint, unwanted traces of light or shadow on printed materials. This occurs when large amounts of printed material are stacked together (e.g.,...). Figure 1 and Figure 2 As shown, when the image is not dry, different areas of the same pattern are subjected to different pressures due to the different patterns, resulting in different mirror effects and thus lighter shades.

[0003] Chinese invention patent application number 201210574374.5 discloses a method and system for preventing printing ghosting, belonging to the field of printing technology. This application first scans the printing plate to obtain the blank areas; then it statistically analyzes the ink distribution information on the plate and the maximum ink fill information of the blank areas; next, it obtains the ink fill information of the blank areas based on the ink distribution information and the maximum ink fill information; finally, it fills the blank areas with ink according to the ink fill information. This application performs reasonable ink filling based on ink quantity statistics and the blank areas of the printing plate, ultimately achieving a balanced ink usage across the entire plate, avoiding ghosting, and resulting in good printing quality. It is evident that the most common method in the industry to overcome ghosting currently involves starting with the printing process, using reasonable ink filling to prevent ghosting.

[0004] In recent years, the phenomenon of "ghosting" has become increasingly frequent. Simply applying appropriate ink filler cannot completely eliminate it; the root cause needs to be investigated. Investigations have revealed that this problem is more likely to occur when printing companies use highly absorbent, high-whiteness paper. However, the cost of paper in printing is usually far higher than the cost of ink, so printing companies are generally unwilling to change the paper and can only make matching adjustments to the ink. Summary of the Invention

[0005] To solve the aforementioned technical problems, it is necessary to deeply analyze the root causes of the "ghosting" phenomenon in order to confirm whether the problem can be resolved through ink adjustments. Therefore, the purpose of this invention is to provide a black offset printing ink that effectively addresses the "ghosting" problem.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is: an oil-based offset printing ink, comprising the following raw material components in weight percentage: Pigment 20-35%; Mixed resin 27~55%; Soybean oil 15-30%; Diluent 5~15%; Additives 0.5-10%; The mixed resins include rosin-modified resin, polyurethane resin, and linseed oil-modified alkyd resin.

[0007] Ideally, the mass percentages of the rosin-modified resin, polyurethane resin, and linseed oil-modified alkyd resin are 20-30%, 2-10%, and 5-15%, respectively.

[0008] Furthermore, the pigment is carbon black with a particle size of 15-25 micrometers and a pH of 8-10.

[0009] Preferably, the diluent is a mixture of one or more components selected from C25-C30 mineral oil, linseed oil, and tung oil.

[0010] Optimally, the additive is a mixture of preservative, surface enhancer, composite drier, dispersant and surfactant. The preservative is a mixture selected from one or more of tert-butylhydroquinone, butylated hydroxyanisole, butylated hydroxytoluene, tert-butylhydroquinone and propyl gallate. The surface enhancer is a mixture selected from one or more of paraffin oil, polyethylene wax and oxidized polyethylene wax. The composite drier is a mixture selected from one or more of manganese isooctanoate, cobalt isooctanoate, zinc isooctanoate and cerium dioxide. The dispersant is a polyurethane block copolymer type dispersant. The surfactant is an organosilicon compound.

[0011] Furthermore, the mass percentage of each component in the additive is as follows: Preservatives: 0.1-2%; Surface enhancer 0.1~4%; Compound drying agent 0.1~3%; Dispersant 0.1~0.5%; Surfactant 0.1~0.5%.

[0012] Furthermore, it also includes water, the mass of which is 1.2 to 1.5 times the mass of the pigment.

[0013] Furthermore, the pigment is moistened with the water and mixed evenly before use.

[0014] Another object of the present invention is to provide a method for preparing the above-mentioned oil-based offset printing ink, comprising the following steps: (a) The formulated amounts of the mixed resin, soybean oil, and diluent are mixed to prepare a binder; (b) Passing the pigment through rollers to control its fineness within a suitable range; (c) The binder, the pigment and the additive are mixed, and after adjusting the properties, they are filled into cans.

[0015] Ideally, in step (b), the fineness ranges to ≤5 micrometers.

[0016] Ideally, in step (b), the pigment is moistened with water and stirred before use; then it is mixed with the surfactant and heated under negative pressure to remove moisture.

[0017] Due to the application of the above technical solution, the present invention has the following advantages compared with the prior art: This invention relates to an oil-based offset printing ink. By mixing a specific mixed resin with soybean oil, diluent, additives, and pigments in a certain proportion, it can effectively improve the cross-linking and curing speed of the ink's binder, preventing oil evaporation and penetration. On the other hand, it can effectively improve the dispersibility of pigments, thereby increasing the ink concentration. Furthermore, it produces a synergistic effect: the drying speed is improved, and the ghosting problem can be overcome.

[0018] In addition, selecting specific carbon black with a pH of 8-10 and a particle size of 15-25 micrometers is beneficial for improving drying performance (because slow drying means a long time for the diluent to evaporate, which can easily lead to ghosting); furthermore, carbon black with smaller particle size has relatively fewer capillaries and absorbs less diluent, which helps to further suppress ghosting (smaller particle size carbon black has higher blackness and can also effectively reduce ink layer thickness).

[0019] Mixing carbon black with water (preferably followed by soaking for 0.3 to 0.8 hours) allows the water to fully fill the capillaries in the pigment. Since oil and water are immiscible, oil is unlikely to penetrate the pigment capillaries during ink production, thus further overcoming the ghosting problem caused by oil absorption by the capillaries. Furthermore, the surface of basic carbon black typically contains basic functional groups that promote water evaporation. During drying, these basic functional groups accelerate water removal by reducing the surface tension at the liquid-solid interface. Even with water soaking, the effect on ink drying during printing is negligible. Attached Figure Description

[0020] Figure 1 A schematic diagram illustrating the principle behind the "ghosting" problem; Figure 2 A schematic diagram illustrating another principle behind the "ghosting" problem. Detailed Implementation

[0021] Analysis suggests that the "ghosting" problem occurs when printing companies use highly absorbent, high-whiteness paper, and the reasons are roughly as follows: like Figure 1The diagram illustrates the principle of the "ghosting" problem. Phenomenon ① is that in areas where both sides of the paper have patterns, the solvent penetration of the later-printed surface is inhibited, causing its surface gloss to be higher than the surrounding area, forming a latent image (i.e., "ghosting"). Phenomenon ② is that the solvent and volatile gases from the later-printed pattern are absorbed by the pattern on the opposite side of the printed material, causing its gloss to increase, thus forming "ghosting." Figure 2 The diagram illustrates the principle of the "ghosting" problem. Phenomenon ① is that areas with patterns on both sides inhibit solvent penetration from the opposite side. In the blank area on the opposite side, the first-printed side experiences greater penetration and lower gloss. Phenomenon ② is that the blank area on the opposite side absorbs the solvent from the pattern and the gases volatilized from the reaction, resulting in a decrease in the pattern's gloss. Those skilled in the art often fail to correctly understand the root cause of these technical problems.

[0022] Therefore, this invention provides an oil-based offset printing ink, comprising the following raw material components by mass percentage: pigment 20-35%; mixed resin 27-55%; soybean oil 15-30%; diluent 5-15%; and additives 0.5-10%. The mixed resin includes rosin-modified resin, polyurethane resin, and linseed oil-modified alkyd resin. In the oil-based offset printing ink, the preferred mass percentages of the rosin-modified resin, polyurethane resin, and linseed oil-modified alkyd resin are 20-30%, 2-10%, and 5-15%, respectively (based on the total amount of the oil-based offset printing ink). By mixing a specific mixed resin with soybean oil, diluent, additives, and pigment in a certain proportion, the cross-linking and curing speed of the ink's binder can be effectively increased, preventing oil evaporation and penetration. Furthermore, the dispersibility of the pigment can be effectively improved, thereby increasing the ink concentration. A synergistic effect is also achieved: the drying speed is improved, and ghosting problems can be overcome.

[0023] The pigment is carbon black with a particle size of 15-25 micrometers and a pH of 8-10. Further, the oil-based offset printing ink also includes water (the amount of water is not included in the mass of the oil-based offset printing ink because it evaporates during subsequent heating; the water is preferably soft water or deionized water), and the mass of the water is 1.2-1.5 times the mass of the pigment. The pigment is preferably moistened with the water and mixed evenly before use. Selecting a specific type of carbon black is beneficial for improving drying properties (because slow drying results in a long evaporation time for the diluent, easily leading to ghosting); in addition, small-particle-size carbon black has relatively fewer capillaries, absorbing less diluent, which helps to further suppress ghosting (small-particle-size carbon black has higher blackness and can also effectively reduce ink layer thickness). Mixing the carbon black with water (preferably soaking for 0.3-0.8 hours) allows the water to fully fill the capillaries in the pigment; since oil and water are immiscible, it is difficult for oil to penetrate into the pigment capillaries during ink production, thus further overcoming the ghosting problem caused by oil absorption by the capillaries. In addition, the surface of alkaline carbon black usually contains alkaline functional groups, which can promote the evaporation of moisture. During the drying process, these alkaline functional groups accelerate the removal of moisture by reducing the surface tension of the liquid-solid interface. Even if soaked in water, the effect on ink drying is negligible during printing.

[0024] The diluent is a mixture of one or more of C25-C30 mineral oil, linseed oil and tung oil, preferably a mixture of C25-C30 mineral oil, linseed oil and tung oil in a mass ratio of 5~6:2~3:1.

[0025] The additive is a mixture of preservative, surface enhancer, composite drier, dispersant, and surfactant. The preservative is a mixture selected from one or more of tert-butylhydroquinone, butylated hydroxyanisole, butylated hydroxytoluene, tert-butylhydroquinone, and propyl gallate. The surface enhancer is a mixture selected from one or more of paraffin oil, polyethylene wax, and oxidized polyethylene wax. The composite drier is a mixture selected from one or more of manganese isooctanoate, cobalt isooctanoate, zinc isooctanoate, and cerium dioxide. The dispersant is a polyurethane block copolymer dispersant, and the surfactant is an organosilicon compound. The preferred mass percentage of each component in the additive is: preservative 0.1-2%; surface enhancer 0.1-4%; composite drier 0.1-3%; dispersant 0.1-0.5%; surfactant 0.1-0.5% (based on the total amount of oil-based offset printing ink).

[0026] The preparation method of the above-mentioned oil-based offset printing ink includes the following steps: (a) mixing the formulated amounts of the mixed resin, soybean oil, and diluent to obtain a binder; (b) passing the pigment through a roller to control its fineness within a suitable range; (c) mixing the binder, the pigment, and the additives, adjusting the properties, and then filling and packaging into cans. In step (b), the fineness range is ≤5 micrometers. Before use, the pigment is moistened with water and stirred until homogeneous; subsequently, it is mixed with the surfactant and heated under negative pressure to remove moisture.

[0027] The present invention will be further described below with reference to embodiments.

[0028] Examples 1-3 and Comparative Examples 1-5 each provide an oil-based offset printing ink and its preparation method, the raw material composition of which is shown in Table 1.

[0029] Table 1. Composition of each raw material in Examples 1-3 and Comparative Examples 1-5 (unit: kg)

[0030] Note: In Examples 1-3 and Comparative Examples 1-4: the pigment is carbon black, brand name Mitsubishi #2300; the rosin-modified resin can be commercially available, DC2116 in the above examples; the polyurethane resin is commercially available oil-based polyurethane resin, CX-613 in the above examples; the linseed oil-modified alkyd resin can be commercially available, PJ600-100 Runfeng in the above examples; the diluent is a mixture of C25-C30 mineral oil (Yuanye S30005), linseed oil and tung oil in a mass ratio of 6:3:1; the preservative is tert-butylhydroquinone; the surface reinforcing agent is polyethylene wax; the composite drying agent is a mixture of manganese isooctanoate and zinc isooctanoate in a mass ratio of 1:1; the dispersant is TiloSperse 38161; the surfactant is silicone oil (unless otherwise specified, all raw materials are commercially available directly according to their names). In Comparative Example 5: the pigment is carbon black N220, and other raw materials are the same as in Example 1.

[0031] The preparation method of the above-mentioned oil-based offset printing ink includes the following steps: (a) The binder is prepared by mixing the formulated amounts of mixed resin, soybean oil and diluent; (b) Soak the pigment in water for 0.5 hours to allow the water to fully fill the capillaries in the pigment, and stir to mix well; then mix it with surfactant and binder, and remove the water by vacuum heating under negative pressure (90°C); pass the pigment through three rollers to control its fineness ≤5 microns; (c) The product from step (b) is mixed with other additives, and after adjusting its properties, it is filled and packaged.

[0032] The performance of the oil-based offset printing inks in Examples 1-3 and Comparative Examples 1-4 was tested, and the results are shown in Table 2.

[0033] Table 2 Performance table of products in Examples 1-3 and Comparative Examples 1-5

[0034] Note: (1) Test method for sample concentration: X-Rite eXact, D50 / 2°, Status T, WhiteBacking, and test data under the same ink volume.

[0035] The test method for drying time: The data were measured using a Japanese-made rotary drying tester under environmental conditions of 25±2℃ and 50±20% humidity.

[0036] VOCs testing method: Refer to GB / T 23986-2009 and use a GC-2010Plus gas chromatograph for analysis.

[0037] Ghosting effect test method: After proofing by overlaying colors on both sides, place it under constant pressure for 24 hours, and compare the ink difference between the central cutout area and the surrounding area to evaluate the degree of ghosting (1 (poor) - 5 (good)).

[0038] The above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. An oil-based offset printing ink, characterized in that, It includes the following raw material components by mass percentage: Pigment 20-35%; Mixed resin 27~55%; Soybean oil 15-30%; Diluent 5~15%; Additives 0.5-10%; The mixed resins include rosin-modified resin, polyurethane resin, and linseed oil-modified alkyd resin.

2. The oil-based offset printing ink according to claim 1, characterized in that: The mass percentages of the rosin-modified resin, polyurethane resin, and linseed oil-modified alkyd resin are 20-30%, 2-10%, and 5-15%, respectively.

3. The oil-based offset printing ink according to claim 2, characterized in that: The pigment is carbon black with a particle size of 15-25 micrometers and a pH of 8-10.

4. The oil-based offset printing ink according to claim 1, characterized in that: The diluent is a mixture of one or more of the following: C25-C30 mineral oil, linseed oil, and tung oil.

5. The oil-based offset printing ink according to claim 1, characterized in that: The additives are a mixture of preservatives, surface enhancers, composite driers, dispersants, and surfactants. The preservatives are a mixture selected from one or more of tert-butylhydroquinone, butylated hydroxyanisole, butylated hydroxytoluene, tert-butylhydroquinone, and propyl gallate. The surface enhancers are a mixture selected from one or more of paraffin oil, polyethylene wax, and oxidized polyethylene wax. The composite drier is a mixture selected from one or more of manganese isooctanoate, cobalt isooctanoate, zinc isooctanoate, and cerium dioxide. The dispersant is a polyurethane block copolymer dispersant, and the surfactant is an organosilicon compound.

6. The oil-based offset printing ink according to claim 5, characterized in that, The mass percentage of each component in the additive is as follows: Preservatives: 0.1-2%; Surface enhancer 0.1~4%; Compound drying agent 0.1~3%; Dispersant 0.1~0.5%; Surfactant 0.1~0.5%.

7. The oil-based offset printing ink according to claim 3, characterized in that: It also includes water, the mass of which is 1.2 to 1.5 times the mass of the pigment.

8. The oil-based offset printing ink according to claim 7, characterized in that: The pigment is moistened with the water and mixed evenly before use.

9. A method for preparing the oil-based offset printing ink according to any one of claims 1 to 7, characterized in that, Includes the following steps: (a) The formulated amounts of the mixed resin, soybean oil, and diluent are mixed to prepare a binder; (b) Passing the pigment through rollers to control its fineness within a suitable range; (c) The binder, the pigment and the additive are mixed, and after adjusting the properties, they are filled into cans.

10. The oil-based offset printing ink according to claim 8, characterized in that: In step (b), the fineness range is ≤5 micrometers. The pigment is moistened with water and stirred before use; then it is mixed with the surfactant and heated under negative pressure to remove moisture.

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