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The evaluation of the printing effect of pearlescent ink is generally based on the visual effect of pearlescent. The actual reflection of the brightness and color effect is determined.
Pearlescent pigments have excellent dispersibility. Generally, a slight agitation is required to mix the printing ink with low viscosity. Because the pearlescent ink has a layered structure, the pearlescent pigment and the ink can only be stirred slightly to avoid damage to the pearlescent pigment. Avoid rude mechanical agitation and dispersion. For example: using a three-roller, high-speed agitator, or ball / bead mill will damage the pigment and lose its gloss. In general, the pearlescent pigment is added to the printing ink evenly in the last process of ink production. When using the disperser and high-speed mixer, the mixing time of each batch must be kept constant and shortest, so that the color difference of each batch of products can be avoided. When manufacturing high-viscosity printing inks, such as when offset printing has to use a three-roller, the gap between the rollers must be as large as possible, and the stirring should be completed in the shortest possible time to avoid gloss loss due to pigment damage.
Note: You must use transparent linking materials as much as possible, and avoid using opaque and light-scattering additives.
Due to the transparent light refraction properties and light scattering properties, pearlescent pigments can help create a rich and colorful visual experience. For some special requirements, the colors can be copied as long as they are formulated in strict accordance with the formula parameters.
The pearlescent pigments currently popular on the market are generally composed of mica-titanium dioxide and / or iron oxide. It is non-toxic, chemically stable and harmless to the environment. It can be used in food packaging and meets national standards. Note: Just emphasize the removal of excess ink, the cleaning of printing plate or ink delivery system, the recovery of printed matter and the removal of accumulated printing waste.
The application and function of pearlescent pigment in various printing fields:
Pearlescent pigment used in screen printing
According to my understanding of screen printing, pearlescent pigments are still the most suitable for screen printing. It can be used for the pearlescent pigments of different sizes with screen mesh plates with a suitable mesh size. The mesh should be 1.5 to 1.5 2.5 times. According to the different printing work, it is necessary to choose silk screen pearlescent pigments, substrates and ink connecting materials for matching.
1. How to use pearlescent pigment in printing ink
Pearlescent pigments can be used in all screen ink systems, but it is best to use only with transparent ink binder. The well-dispersed transparent colorant can improve the coloring effect when the dosage is not more than 3% of the finished ink.
For better mixing of pigment and ink, it is best to pre-wet the powdered pigment with the ink solvent. For example thinner. Then mixed into the ink can improve the dispersion ability of the pigment. Avoid ink floating dust and ink viscosity changes.
2. During the printing process of pearlescent pigments
Before printing with pearlescent pigment screen ink, the most suitable screen material should be selected. Basically, various particles of pearlescent pigment can be used for screen printing. When the pearlescent pigment particles are less than 15, 400 mesh / inch, 180 No .; when the particle is between 5-25, the screen number can be up to 355 mesh / inch, that is, 140; when the particle is between 10 and 60, the screen number can be up to 156 mesh / inch, that is, No. 61; the particle is 200 The screen number can be up to 54 mesh / inch, which is No. 21.
In screen printing, due to the relatively thick layer on the substrate, the ink drying parameters need to be strictly controlled. Due to the special morphology of pearlescent pigments, the solvent attached to its surface has a large viscosity, so the drying conditions need to be adjusted to extend the drying time; or the drying (curing) temperature is slightly increased to achieve the particularly required curing strength. For example, when using pearlescent pigments in color wet + wet printing, it should be dried in the overprinting room to avoid the printed colors being transferred to the subsequent printing plates. So far, pearlescent pigments are usually used as spot colors after color printing. Or used in some other industries.
Pearlescent pigments and substrates
In screen printing, pearlescent pigments are available in many directions, but they are most often used in textiles.
Screen printing on textiles today mostly uses water-based inks. Pearlescent pigments have excellent waterproof, alcohol-proof, heat-curable, solvent-resistant, wash-resistant, sweat-resistant, and chemical dry-cleaning characteristics, and are particularly suitable for this application. Secondly, pearlescent pigments can be used in paper, cardboard, plastic film, etc. to obtain satisfactory results.
Pearlescent Pigments and Post-press Processing
Post-press processing of screen printing products using pearlescent pigments will not adversely affect the pearlescent effect.
Post-press processing procedures such as: cold, heat seal, compound, can be processed according to conventional.
Generally, the pearlescent pigment has good scratch resistance, insulation and acid and alkali resistance. The effect of pearlescent pigment printing can be significantly increased by calendering, just as the effect of polishing printed cloth obtained in textile printing. Due to the excellent chemical resistance of pearlescent pigments, other methods can be used, such as: water washing, stone washing, or alkaline crease for denim. Another interesting method is called burnt-out in the textile industry. Due to the chemical resistance of pearlescent pigments, the patterns printed on its fabrics are preserved through acid reaction to form a unique printing effect.
Selection of pearlescent pigments
The use of iridescent interference color can play a beautiful and anti-counterfeiting effect
Pearlescent pigments with different particle sizes; if you choose to use large-particle pearlescent pigments, it is best to use small-particle pigments at the same time, so that you can get a shimmering gloss and will not penetrate the bottom; when used in combination, the ratio is about large-particle pigments; small Granular pigment = 1: 3 or 1: 4.
Note: When using different particles of iridescent interference color pearlescent pigments to mix, you can only use a series of gloss varieties to match, such as Ir. 249 with Ir. 201, etc., otherwise it will lose the interference color pearlescent effect.
Pearlescent pigments can express a richer color when mixed with different color inks.
Selection of wire mesh
Single-fiber silk screen is more suitable for pearlescent printing because it is not easy to block the screen; choose a screen with a thickness of T; choose a suitable mesh size to avoid the screen; usually the mesh size should be 1.5 ~ of the largest pigment size used 2.5 times. Below we give the corresponding screen selection according to the Iriodin pearlescent pigment of Merck Germany.
Requirements for the selection of connecting materials
Colorless and transparent as much as possible, otherwise it will lose the pearl luster; good wetting and bonding with the substrate; good bonding with the pearlescent pigment; good abrasion resistance.
Ink preparation
According to different printing materials and gloss requirements, the concentration of pearlescent pigment is between 8 ~ 15%:
1. Pre-wetting: It is very critical. It is related to the dispersion and test printing performance of pearlescent powder, and it must be carried out in strict accordance with the following procedures:
1. Prepare a suitable solvent
2. Measure about 30% of the weight of the pearlescent powder, add it to the well-known pearlescent powder, and slowly stir. The process is as follows: it seems to have no effect when looking at the market, the stirring resistance gradually increases, and the pearlescent powder forms a small ball , The color becomes dark; continue to stir, the ball breaks into smaller particles, at the same time, the resistance to mixing is significantly reduced, and the mixing becomes easier; finally, the pearl powder becomes a granular mixture of uniform size, and the dark color will stir the pearl powder Let stand for 20 ~ 30 minutes; mix and mix the above mixture with the connecting material. Note: Avoid using high-shear dispersing equipment such as three-roll mill. For drying adjustment, it is necessary to select a suitable drying temperature according to different ink layer thickness and printing speed.
Pearlescent pigments are used in flexographic printing
Flexographic printing inks are classified as low-viscosity liquids. There are three types of solvent, water and light curing (UV). All three inks can use pearlescent pigments. However, the linker with higher transparency should be selected to configure the ink to avoid the loss of pearlescent effect.
When configuring color inks, only dispersible and transparent pigments can be mixed with pearlescent pigments, generally not exceeding 20% ​​of the weight of pearlescent pigments. Too heavy tones will affect the pearlescent effect. Because, pearlescent pigments only have a unique optical interference function in the ink layer with plenty of light, and too many colored pigments cause a large amount of light scattering and loss.
Pre-wetting: In order to achieve the best state of the pearlescent pigment in the ink, it is recommended to pre-wet the pigment with an ink solvent (such as water, alcohol, thinner) equivalent to 30% of its weight, and then mix it with the ink. This procedure avoids the occurrence of floating dust and the viscosity change of the finished ink during the manufacture of the ink, and makes the pearlescent pigment and the ink achieve the optimal mixing state.
The content (weight ratio) of pearlescent pigment is about 15 ~ 25% of the finished ink.
The ink needs to be thoroughly and carefully stirred before printing to make the pigment evenly dispersed in the ink without flocculation or precipitation. In long-run printing, use a circulating ink supply device as much as possible to avoid settling.
Generally, suitable ink additives are used to avoid foaming and prevent pigment precipitation.
If you need to add color to adjust the color, it should be based on visual observation.
Before printing, the ink viscosity needs to be adjusted according to the substrate, printing speed and drying conditions. Usually in water-based inks, for smooth paper or plastic film, the appropriate viscosity is 40 to 60 seconds (DIN4 viscosity cup 23 degrees), for coarser kraft cardboard, corrugated cardboard or gray cardboard, use low Viscosity ink, such as 25 to 35 seconds (DIN4 viscosity cup 23 degrees).
Choosing the right photosensitive resin sheet is very important. For pearlescent printing, I recommend the following varieties: HOF, PLB, PLS, POF and UVB of Seri, FA, FAH and FAR of BASF's "Nyloflex".
There are many types of anilox rollers used in flexographic printing, from traditional steel anilox rollers to laser-engraved ceramic anilox rollers. The choice of anilox roller is determined by the substrate and the required ink layer thickness. Tests have shown that the laser-engraved porcelain roller has the best effect in pearlescent pigment flexographic printing, especially for the transfer of water-based ink. The technical parameters of flexographic printing must be coordinated with the particle size of the pearlescent pigment.
The particle size matching relationship between the anilox roller and the pigment.
The printing effect depends on how much ink is transferred to the substrate. The thick ink layer results in a noticeable gloss effect. Therefore, it is recommended that solvent-based inks use anilox rollers with inking holes as deep as 50. The best printing effect can be obtained by adjusting the printing speed. The ink is preferably able to maintain a short cast after being transferred to the substrate, so that the pigment and the surface of the substrate are kept optimally aligned.
About substrates
There are many kinds of substrates that can be used, including corrugated cardboard, white cardboard, label paper, light and heavy paper, paper towels, kraft paper and plastic film. The choice of substrate has a great influence on the printing effect. A substrate with a smooth and flat surface has the best pearlescent effect.
Post-press processing
Pearlescent pigments have no adverse effects on the post-press processing of flexographic printing products.
The post-press process can be processed as usual. Cold, heat sealing, embossing, calendering, and laminating can be carried out without special adjustment. Calendering and embossing may increase the pearlescent effect because their pigment arrangement is better.
There are also pearlescent pigments with good scratch resistance, insulation, and acid and alkali resistance.
Pearlescent ink used in gravure printing
Low viscosity liquid ink is mainly used in gravure printing. Both solvent-based or water-based inks can use pearlescent pigments, but should choose a linker with higher transparency to avoid loss of pearlescent effect.
When formulating color inks, only good dispersion and transparent pigments can be mixed with pearlescent pigments, generally no more than 20% of the weight of pearlescent pigments. Too heavy tones will affect the pearlescent effect. . Because pearlescent pigment can only have a special optical interference function in the ink layer with abundant light. And excessive amounts of other colored pigments cause a large amount of light scattering and loss.
Pre-wetting: We do nano-scale microscopic observation on the surface of pearlescent pigment, and we can find that there are many extremely fine capillary structures distributed. This results in a relatively large surface energy. In order to achieve the best state of pearlescent pigment in the ink, it is recommended to pre-wet the pigment with an ink solvent (such as water, alcohol, thinner) equivalent to 30% of its weight before mixing into the ink. This procedure avoids the occurrence of floating dust and the viscosity change of the finished ink during the manufacture of the ink, and makes the pearlescent pigment and the ink achieve the optimal mixing state.
The content (weight) of pearlescent pigment is about 15 ~ 30% of the finished ink
The ink needs to be thoroughly and carefully stirred before printing to make the pigment evenly dispersed in the ink without flocculation or precipitation. In the long printing process, try to use the circulating ink supply device to avoid precipitation.
It is recommended to use suitable ink additives to avoid foaming and prevent pigment precipitation.
If you need to add color to adjust the color, it should be based on visual observation.
Before printing, the ink viscosity needs to be adjusted according to the substrate, printing speed and drying conditions. Usually the appropriate viscosity for solvent inks is 14 to 25 seconds (DIN4 viscosity cup 23 degrees), for water-based inks (such as decorative paper ink) need to be higher, until 40 seconds (DIN4 viscosity cup 23 degrees Formula)
Pearlescent pigments in gravure printing
Pearlescent pigments can be used on corroded and engraved plates. Tests have shown that the best effect is achieved by using a cylinder plate with an inking hole opening angle of approximately 120 degrees. When the particle size of the pigment is large (average particle size greater than 25), it is recommended to use a corrosive cylinder, because its special pore shape allows a large amount of ink to pass through, and actively supports the pearlescent effect of pearlescent pigment printing.
The parameters of the plate cylinder and the particle size of the pigment must match each other. It is recommended to prepare the plate cylinder by referring to the data in the table.
In addition, ordinary solvent ink is suitable for plate rollers with an opening angle of 120 degrees, and water type ink is suitable for plate rollers with an opening angle of 140 degrees.
For corroded printing plates, the wall-to-wall ratio is preferably 10: 1 or higher, but not lower than 6: 1.
The printing effect depends on how much ink is transferred to the substrate. The thickness of the ink layer leads to a more pronounced pearlescent effect. Therefore, it is recommended that solvent-based inks use inking holes with a depth of about 50.
The best printing effect can be obtained by adjusting the printing speed. It is best to allow the ink to have a short casting process after it is transferred to the paper, so that the pearlescent pigment and the surface of the substrate are maintained in an optimal parallel arrangement.
Pearlescent pigments and substrates and post-press processing
There are many kinds of substrates that can be used, from PVC in the wallpaper industry to coated paper, cardboard or heavy paper in the packaging and labeling industry, kraft cardboard, paper towels, plastic films, and fabrics.
The choice of substrate has a great influence on the printing effect. Substrates with smooth, flat surfaces obtain the best pearlescent effect.
Pearlescent pigment used in offset printing
Pearlescent pigments in printing inks
Ordinary offset printing ink is a kind of high viscosity ink, which makes it difficult to disperse coarse-grained pearlescent pigments. Therefore, it is best to use specially developed pearlescent offset printing ink. Compared with traditional offset printing ink, the viscosity of pearlescent ink should be slightly lower.
For pearlescent offset printing, it is necessary to adjust the viscosity of the ink according to the printing conditions and the substrate using a debonding agent or thickener. To obtain the best printing effect, special printing rubber must be used. Due to the structure of pearlescent pigment offset printing ink. It is necessary to increase the ink supply. Screen printing can also be used to print continuously adjusted pearlescent effect, but it is important that the number of pigment particles and screen lines match each other. Tests have shown that pearlescent pigments with particles in the range of 5 to 25 can be used for screening on the ground and 60 threads / cm. The denser number of threads may reduce pearlescent effect.
Before the official printing starts, the ink supply system of the printing machine must be fully supplied with ink, and the initial printed sheet should be over-inked. The initial ink supply of pearlescent ink should be 3 to 4 times that of ordinary four-color inks. It must be ensured that before the official printing, the initial ink supply should meet the above requirements. (You can take more printing paper).
Once the ideal pearlescent effect is achieved, the operator should gradually reduce the thickness of the ink to achieve a perfect pearlescent printing effect.
All packaging materials and labels can be printed with pearlescent pigment offset printing ink. The surface of the substrate should be as smooth and flat as possible to make the pigment orientation better. This is extremely important to obtain the ideal pearlescent effect, because the ink layer in offset printing is relatively thin.
Pearlescent pigment offset printing ink has no adverse effect on post-press processing. Multi-color overprinting or glazing, cold and heat sealing, laminating, embossing can be processed as usual.
Pearlescent pigments have good resistance to rubbing, insulation and acid and alkali resistance.
Glazing process
Pearlescent pigments for glazing process
Pearlescent pigments can be dispersed in water-type or UV-type varnishes and used in the glazing process. This process is usually implemented on offset printing glazing units and separate offline glazing machines. The advantages are:
It can express creativity on different printing materials. It has rich light color effects. The expressiveness is both decorative and scratch-resistant. The safety of pearlescent pigments makes it suitable for food packaging. It can be recycled. It is more environmentally friendly. Pearlescent pigments are translucent, so they can be overlaid on a variety of background colors, making it possible for more innovative color ideas.
The hiding power of pearlescent pigments with different particle sizes is different, and users should choose different substrate design forms. Pigments with finer particles can express a soft and delicate luster like silk satin, but their hiding power is also strong, and it is easy to change the color of the first printed text and text.
Pearlescent pigment in varnish
Basic formula: <= 30% pearlescent pigment> = 70% ordinary high-transparency water-based or UV-type varnish
Pre-wetting: In order to achieve the best effect in the use of pearlescent pigments, it is recommended to pre-wet the pigment with a thinner equivalent to 30% of its weight (such as water, alcohol, etc.), and then mix it with varnish. This procedure avoids the occurrence of floating dust and the viscosity change of the finished varnish during operation, so that the pearlescent pigment and the varnish can reach the optimal mixing state. Another way is to pre-wet the pigment with varnish.
Please pay attention to the acidity and alkalinity in the system when using water-based varnish. If the surface of the pigment is slightly acidic, please adjust it with a suitable alkaline additive.
When mixing the pigment with the varnish, pay attention to the uniform and thorough stirring. It is best to add the pigment in batches so that the dispersion is more uniform. Avoid dispersing equipment with high shear forces, otherwise the pigments will be damaged. A suitable defoamer can be added to remove bubbles generated by stirring.
appendix:
The following data are the types and data of some pearlescent pigments of the famous Merck Group.
IriodinÃ’ Pearlets pearl balls are pigment preparations recently developed by Merck for liquid inks (flexo printing, gravure printing and glazing), which are processed from traditional powdered Iriodin pearlescent pigments.
Compared with traditional dry powder pearlescent pigments, IriodinÃ’ Pearlets pearl balls have the following advantages:
§ Convenient operation, no dust § Accurate metering control, reduce waste § Excellent dispersion in ink, no need for wetting § Shortest ink dispense time § Reduce precipitation, facilitate ink reuse § Better pearl gloss effect
The following abbreviations in the pigment model indicate the applicable ink system for this Pearlets:
W water-based ink system S solvent-based ink system UV UV curing ink system
Iriodin® 100 silver white pearlescent series --- pearl light
Provides flawless bright white pearl luster. It can be used alone or in combination with traditional pigments. Depending on the pearlescent particle size, you can simulate the luster that feels the flickering effect from silk.
Iriodin® 200 Symphony Pearl Series --- Light Color
Symphony pearlescent pigments created a new world of design. Through the combination with traditional pigments, the psychedelic effect of Symphony can be obtained from different viewing angles.
Iriodin® 300 golden pearl series --- exquisite golden
Iriodin® golden pearlescent series has a metallic luster effect, but it is not a metallic pigment. It is coated with titanium dioxide and iron oxide on the mica substrate to produce a natural golden color.
Iriodin® 500 --- the metallic luster of the future
Iriodin® Metal Pearlescent Series is not a metallic pigment. However, the effect of this series can simulate the gloss of metallic pigments. This is achieved by coating iron oxide on the mica.
The Pearlprint Litho series is a pigment pre-formulation specially developed for offset printing. It is based on conventional Iriodin pigments and has been specially treated on the surface of the pigment particles to obtain the following performance optimization:
Easy to disperse in ink;
Good transferability in printing operations;
No dust, easy for ink preparation. Pearlescent offset printing inks using Pearlprint Litho series pigments have good printability and better gloss effect.
The series includes silver white, five iridescent interference colors, two kinds of pearl gold and pearl bronze.
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