Printing is a graphic reproduction technique that transfers the ink on the surface of a printing plate to the material being reproduced by mechanical pressure or other attractive force. Printing can be divided into four categories: letterpress printing, offset printing, gravure printing, and screen printing. No matter which method is used for printing, the ink must be used. After the printing process is completed, the ink adhered to the ink roller of the printing machine must be cleaned to ensure that the subsequent printing works normally. Therefore, the ink contaminated on the cleaning printing machine is a regular job in the printing industry. For this reason, the composition and performance of the printing ink, the type of the printing ink cleaning agent and its preparation method, performance characteristics, emulsive ink cleaning agent and semi-water based cleaning A description of the differences and linkages of the formulation ink cleaners.
1. Composition and properties of printing ink
Printing ink is composed of several components such as binders, fillers, colorants and additives. In the preparation according to the printing requirements according to a certain ratio of mixing and mixing, and after rolling pressure ink process. Printing ink is a colloid with a complicated structure. It is formed by uniformly dispersing solid particles such as pigments with a particle size of about 0.1 μm in a binder. Pigments include inorganic pigments and organic pigments. Inorganic pigments may be inorganic elements, metal oxides, or inorganic salts. Such as carbon black, titanium white, chromium green, inorganic pigments are characterized by stable chemical properties, light resistance and heat resistance, the disadvantage is poor coloring. The organic pigments are synthetic organic compounds, which have many advantages such as bright colors and strong printing adaptability. The disadvantages are poor light and heat resistance. The black pigments used in printing inks are mostly inorganic substances, and the color inks used are mostly Organic pigments.
Commonly used connection materials are vegetable oil type and solvent oil type. Vegetable oil types such as linseed oil, tung oil, and dehydrated castor oil contain dry vegetable oils with an unsaturated double bond structure; solvent oil types such as engine oil kerosene and other non-drying mineral oils; benzene, xylene, methanol, ethanol, isopropanol, etc. evaporate Organic solvents. In addition, natural resins such as rosin and pitch, and synthetic resins such as phenolic resins and polyamide resins are also used as binders.
The additives used in the ink include linseed oil, which adjusts the viscosity of the ink, brighteners that increase the gloss of the ink, and driers that promote drying of the ink. The types of driers include fatty acids, naphthenic acid, cobalt, manganese, and aluminum salts of octylic acid. These salts can be oxidized by oxygen in the air. The valence of the metal ions increases and the oxidative strength increases, which promotes the oxidative polymerization of dry oils. Therefore, these additives catalyze the film formation of dry oil oxidative polymerization crosslinks. effect. In addition, some inks also contain fillers such as colloidal calcium carbonate.
According to the main mechanism of ink drying, the ink is divided into four categories: oxidative polymerization drying type, osmotic drying type, volatile drying type and photosensitive curing type.
The oxidative polymerization drying ink is a linking material made of mineral oil, dry vegetable oil and synthetic resin, which is usually used as offset printing ink. When this kind of ink is transferred to the printing surface, the low-viscosity mineral oil in the ink penetrates into the interior of the paper due to the attraction force of the capillaries in the paper, so that the viscosity of the ink gradually increases, and the high-viscosity dryness is increased during the process. The surface area of ​​the colloidal air and the contact between the vegetable oil and the synthetic resin is gradually increased. The double bonds of the unsaturated fatty acids in the dry vegetable oil are oxidatively crosslinked to form a network structure, so that the viscosity of the ink rises rapidly and is finally fixed on the surface of the paper and dried. .
The penetrating dry ink is a connection material made of dry mineral oil, rosin, asphalt, or synthetic resin, which is commonly used as a relief ink. When the inorganic mineral oil in the ink penetrates into the interior of the paper, rosin, asphalt, and synthetic resins dry to form a film on the surface of the paper.
Volatile drying ink is used to dissolve rosin or synthetic resin compounded with strong volatile benzene and alcohol solvents. Commonly used as gravure ink and aniline ink. Because the boiling point of xylene and other solvents are all around 100oC, they evaporate quickly in the air. When the solvent evaporates, the remaining resin will oxidize and polymerize on paper.
Photosensitive curable inks do not contain solvents in the binder and contain liquid organic polymer monomers. For example, an ultraviolet curable ink contains a linker formed from a high molecular monomer containing an unsaturated double bond, such as methacrylate and pentaerythritol triacrylate, and a photoinitiator such as benzophenone and other components. After being coated on the surface of the paper, the photoinitiator is activated by ultraviolet irradiation to initiate the free radical polymerization of the high-polymer monomer, which is cured and dried on the surface of the paper.
Regardless of the type of printing ink, their common requirement is that they must maintain stable flow properties before they are transferred to the surface of the paper during the printing process, and must lose fluidity and cure and dry as soon as possible after transferring to the surface of the paper; Good adhesion to printing materials; ink should have good transferability; printing ink composition on paper must maintain a long-lasting and correct color.
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1. Composition and properties of printing ink
Printing ink is composed of several components such as binders, fillers, colorants and additives. In the preparation according to the printing requirements according to a certain ratio of mixing and mixing, and after rolling pressure ink process. Printing ink is a colloid with a complicated structure. It is formed by uniformly dispersing solid particles such as pigments with a particle size of about 0.1 μm in a binder. Pigments include inorganic pigments and organic pigments. Inorganic pigments may be inorganic elements, metal oxides, or inorganic salts. Such as carbon black, titanium white, chromium green, inorganic pigments are characterized by stable chemical properties, light resistance and heat resistance, the disadvantage is poor coloring. The organic pigments are synthetic organic compounds, which have many advantages such as bright colors and strong printing adaptability. The disadvantages are poor light and heat resistance. The black pigments used in printing inks are mostly inorganic substances, and the color inks used are mostly Organic pigments.
Commonly used connection materials are vegetable oil type and solvent oil type. Vegetable oil types such as linseed oil, tung oil, and dehydrated castor oil contain dry vegetable oils with an unsaturated double bond structure; solvent oil types such as engine oil kerosene and other non-drying mineral oils; benzene, xylene, methanol, ethanol, isopropanol, etc. evaporate Organic solvents. In addition, natural resins such as rosin and pitch, and synthetic resins such as phenolic resins and polyamide resins are also used as binders.
The additives used in the ink include linseed oil, which adjusts the viscosity of the ink, brighteners that increase the gloss of the ink, and driers that promote drying of the ink. The types of driers include fatty acids, naphthenic acid, cobalt, manganese, and aluminum salts of octylic acid. These salts can be oxidized by oxygen in the air. The valence of the metal ions increases and the oxidative strength increases, which promotes the oxidative polymerization of dry oils. Therefore, these additives catalyze the film formation of dry oil oxidative polymerization crosslinks. effect. In addition, some inks also contain fillers such as colloidal calcium carbonate.
According to the main mechanism of ink drying, the ink is divided into four categories: oxidative polymerization drying type, osmotic drying type, volatile drying type and photosensitive curing type.
The oxidative polymerization drying ink is a linking material made of mineral oil, dry vegetable oil and synthetic resin, which is usually used as offset printing ink. When this kind of ink is transferred to the printing surface, the low-viscosity mineral oil in the ink penetrates into the interior of the paper due to the attraction force of the capillaries in the paper, so that the viscosity of the ink gradually increases, and the high-viscosity dryness is increased during the process. The surface area of ​​the colloidal air and the contact between the vegetable oil and the synthetic resin is gradually increased. The double bonds of the unsaturated fatty acids in the dry vegetable oil are oxidatively crosslinked to form a network structure, so that the viscosity of the ink rises rapidly and is finally fixed on the surface of the paper and dried. .
The penetrating dry ink is a connection material made of dry mineral oil, rosin, asphalt, or synthetic resin, which is commonly used as a relief ink. When the inorganic mineral oil in the ink penetrates into the interior of the paper, rosin, asphalt, and synthetic resins dry to form a film on the surface of the paper.
Volatile drying ink is used to dissolve rosin or synthetic resin compounded with strong volatile benzene and alcohol solvents. Commonly used as gravure ink and aniline ink. Because the boiling point of xylene and other solvents are all around 100oC, they evaporate quickly in the air. When the solvent evaporates, the remaining resin will oxidize and polymerize on paper.
Photosensitive curable inks do not contain solvents in the binder and contain liquid organic polymer monomers. For example, an ultraviolet curable ink contains a linker formed from a high molecular monomer containing an unsaturated double bond, such as methacrylate and pentaerythritol triacrylate, and a photoinitiator such as benzophenone and other components. After being coated on the surface of the paper, the photoinitiator is activated by ultraviolet irradiation to initiate the free radical polymerization of the high-polymer monomer, which is cured and dried on the surface of the paper.
Regardless of the type of printing ink, their common requirement is that they must maintain stable flow properties before they are transferred to the surface of the paper during the printing process, and must lose fluidity and cure and dry as soon as possible after transferring to the surface of the paper; Good adhesion to printing materials; ink should have good transferability; printing ink composition on paper must maintain a long-lasting and correct color.
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