How to choose the formula of gravure printing ink for high-temperature retort-resistant bags? Specifically, the selection of ink connecting materials, the selection of toners and pigments, the selection of special wax powder for ink, etc.
Selection of retort bag ink binder(RESIN)
There are no more than two types of ink BINDER suitable for gravure on-machine printing: high-temperature-resistant polyurethane resin for gravure ink and ternary chlorine-acetic acid resin with high chlorine content and medium viscosity.
Gravure ink uses high-temperature resistant polyurethane resin, the chemical name is polyurethane plastic resin, and the English abbreviation code is PU. It is a liquid resin obtained by reacting polyurethane monomer resin liquid with polyether polyol or polyester polyol through a catalyst and other additives. According to the composition of these liquid resin raw materials, it is divided into polyether type and polyester type. species, and are divided into soft and hard.
When selecting the POLYURETHANE BINDER for ink, we require that the ink has excellent adhesion to the plastic film, the ink film has good heat resistance and water boiling resistance, good solvent release, low residual content, and moisturizing of the pigment. Good wettability and high gloss.
The main components of polyurethane resin liquids for inks currently on the market are polyurethane compounds, isopropyl alcohol, methyl ethyl ketone, toluene, etc. The appearance is colorless or light yellow transparent viscous liquid, and the solid content is generally 25 -35%, the amount added in the ink formula is usually 35-45%.
The high chlorine content chlorine-vinegar resin used in high-temperature resistant inks is actually a copolymer of vinyl chloride (VC) and vinyl acetate (VAC), which is essentially a dry paint base. When the ink is printed on the surface of the plastic film, after the volatile organic solvent contained in the ink system evaporates quickly, the high chlorine content ternary chlorine-acetic resin can be combined with compatible resins from other systems to form an ultra-thin ink film.
In the formula of gravure composite high-temperature retort-resistant bag ink, we generally choose inks that have high toughness after film formation, long-lasting flexibility, abrasion resistance, low water swelling, low air permeability, high-temperature retort resistance, etc. Chlorine vinegar resin.
Selection of high-temperature composite retort-resistant toners and pigments
The composite high-temperature retort-resistant bag ink for gravure printing has a series of special requirements for its toner and pigment: the color must be bright and the glossiness must be good, and the colorful world must be decorated with dazzling colors; the tinting strength must be high, which is a measure The conditions for the significance and economic value of the pigment; the transparency and hiding power should be good. According to the different uses of the ink, there are different requirements for the transparency and hiding power of the pigment; the amount of oil absorption should be small, so that the ink concentration can be easily increased and the ink properties can be improved. Easy to adjust; good wetting and dispersion. The dispersion ability of the pigment in the ink binder directly affects the success or failure of ink making.
Other physical and chemical properties, such as light resistance, heat resistance, solvent resistance, acid and alkali resistance, migration resistance, etc., are few and far between. Only suitable varieties can be selected according to the special requirements of the application.
The pigments used in the composite high-temperature retort-resistant bag ink for gravure printing must first be resistant to solvents, and secondly, they must be resistant to high-temperature retort and can withstand high temperatures above 120°C without decomposing and discoloring.
According to the standard of retort-resistant bag ink, all black pigments used in the ink should be channel carbon black; most white pigments use silica-modified rutile titanium dioxide, and some use alumina-modified ones, but they are resistant to temperature and turn yellow. The color ink has slightly poorer performance; color inks must be selected for ink testing conditionally, such as phthalocyanine blue and phthalocyanine green that have been resinized on the surface of the pigment particles, benzimidazolone azos, condensed azos, etc., according to the test They can withstand high temperatures above 180°C without discoloration.
Selection of wetting and dispersing agents for gravure ink systems
The wetting and dispersion of high-temperature resistant toners and pigments is an important part of the manufacturing technology of high-temperature retort-resistant gravure plastic composite inks. The ink developer and pigments are crushed into fine particles so that they can be evenly distributed in the mixed binder of the ink. , in order to obtain a stable suspension mixed medium viscosity system.
Wetting and dispersing agents are essentially special surfactants that have both wetting and dispersing functions for pigments. Its wetting and dispersing effect is to reduce the surface tension of the substance, so that the molecules of the surfactant are adsorbed on the surface of the pigment, thereby generating charge repulsion or steric hindrance, preventing harmful flocculation of the pigment, and keeping the dispersed system in a stable suspension state. .
The dispersant used in the composite high-temperature retort-resistant bag ink for gravure printing is generally an anionic surfactant. Its main component is carbonate or special metal aluminum chromium compound. It is a light yellow or yellow-brown liquid and is an oil-soluble dispersion. It is an agent that improves the dispersion of pigments in ink, prevents overflow and discoloration of pigments in ink, improves color concentration and color development, and enhances the adhesion and composite fastness of ink film and plastic film.
Selection of special wax powder for high-temperature retort-resistant bag ink
Some special high-temperature resistant wax powder is usually added to the ink formula of composite high-temperature retort-resistant bags for gravure printing. It can provide excellent anti-wear and scratch resistance for the high-temperature-resistant ink film of the printed product, prevent adhesion and increase the ink loading. Fluidity, improved printability and improved post-processing performance, etc.
When designing the formula of composite high-temperature retort-resistant bag inks for gravure printing, most of them use molecular linear synthetic polyethylene wax with high melting point and strong hardness. There are two methods of pre-adding and post-adding in the ink production process. The general addition amount is: 0.5-1.0% of the total weight of ink. Under normal circumstances, it is added before grinding the ink coarse material, which is beneficial to dispersion and improving fluidity; however, be careful not to make the grinding temperature too high to avoid deformation and agglomeration of these wax powder particles, which will affect its performance.
There are also ink system resins and organic solvents to make a paste - wax slurry, which is added during the viscosity and color matching stage of ink making; however, in doing so, it is necessary to prevent certain organic solvents with strong penetrating power from dissolving the wax powder particles. Recrystallization occurs and the wax becomes coarse, losing the proper performance of the special wax powder.
Selection of antistatic agents for high-speed printing
When gravure plastic ink is printed at high speed, the accumulation of static electricity will cause problems such as offset, blur, spots, whiskers, edge rejection, etc. In severe cases, fires, explosions and other vicious events may even occur. Therefore, the purpose of adding antistatic agents to ink is to reduce the surface resistance of the plastic film during the printing process and eliminate static electricity to solve the above problems that occur during printing.
Anionic antistatic agents are generally used in plastics and inks, including higher fatty acid salts, alkyl phosphate ester salts, alkyl sulfate ester salts, and sulfonate ester salts. This type of compound can be dissolved in water, ketones, alcohols, etc. Organic solvents such as benzene and benzene are sold as organic solvent aqueous solutions containing 30-60% of active substances. The composite high-temperature retort-resistant bag ink for gravure printing mainly uses an isopropyl alcohol solution of ethyl phosphate as an antistatic agent. The added amount accounts for 0.1-0.4% of the total ink, and has no adverse effects on the ink properties.
Selection of Adhesion Promoting Resins and Fumed Silica Powders
In the ink system of polyurethane and chlorine-vinegar resin in the composite high-temperature retort-resistant bag ink for gravure printing, due to the insufficient flexibility of the chlorine-acetyl resin itself, adhesion-promoting resin needs to be used to improve its flexibility; composite for gravure printing Some modified chlorinated polypropylene resin liquid must be added to the formula of high-temperature retort-resistant bag ink. Its solid content is generally about 15-25%, which can improve the adhesion of polyurethane ink on plastic films and enhance the dispersion effect and fluidity.
Fumed silica powder, also called matte powder, generally undergoes organic surface treatment and is easy to disperse. Its role in the composite high-temperature retort-resistant bag ink for gravure printing: A. Prevent pigment settlement and maintain the long-term rheological properties and fineness of the ink; B. Improve the sagging performance of the ink film when printing on the machine, preventing The generation of water marks; C. It can also be used like wax powder to facilitate the even coating of adhesive and improve the composite fastness.
Selection of organic solvents for gravure high temperature resistant retort bag ink system
Plastic gravure ink mainly relies on solvent evaporation to dry and form a film. When the ink is printed on the surface of the substrate, the thickness of the ink film decreases and shrinks due to the solvent evaporation. The film formation of ink solvent volatilization is mainly divided into two stages: the first is the "wet stage", which is controlled by the surface layer; the second is the "dry stage", where the solvent evaporation rate is controlled by the diffusion of the solvent in the overall ink film. When there is a true solvent, it ensures that the resin and other polymers can fully stretch and interact with each other, and the leveling properties are good.
If the true solvent evaporates too quickly and the remaining solvent is only a co-solvent, the polymer molecules tend to form tight curls or even precipitate. What is particularly important is that the volatilization of the solvent causes endothermic cooling and an increase in polymer concentration, which increases the surface tension of the ink film and causes the solution to flow from the low surface tension area to the high surface tension area. This is called peak flow, which easily produces "orange peel" and floating color phenomenon, so maintaining the necessary amount of true solvent is an important condition to ensure the leveling of the ink film.
For polyurethane and chlorine-vinyl resin ink systems, in addition to toluene, xylene, ethyl acetate, methyl ethyl ketone, and isopropyl alcohol, acetone, methyl isobutyl ketone, ethylene glycol monobutyl ether, Special organic solvents such as propylene glycol methyl ether. Among them, benzene and alcohol are only co-solvents for polyurethane and chlorine-vinyl resin. Although ketones and esters are true solvents, they evaporate too quickly.
Therefore, special solvents such as methyl isobutyl ketone, ethylene glycol monobutyl ether, and propylene glycol methyl ether must be used to adjust the volatilization rate and solubility, enhance the dispersion power of the mixed solvent, and improve the dissolution parameters so that the ink always presents a good fluid status to ensure the smooth progress of printing work.
Polyurethane resin is a versatile material that can be used in the preparation of gravure printing ink for film. Gravure printing is a method of printing that uses engraved cylinders to transfer ink onto a substrate, and it is commonly used for high-volume printing applications such as packaging and labeling.
as a binder to provide adhesion and durability to the ink. It can also be used to adjust the viscosity and flow properties of the ink, which is important for ensuring consistent print quality and optimal ink transfer to the substrate.
We could provide solvent based polyurethane resin, polyurethane emulsion, acrylic resin, waterborne polyurethane dispersion to meet diversified requirement.
