Maintain a perfect product appearance

Learn how to use UV/EB, water-based coatings and adhesives to achieve the ultimate aesthetic results.
Energy Curing Coatings and Adhesives If the inks are not properly matched, the coatings and adhesives are likely to cause poor print appearance, especially when using energy-curable ink products. Therefore, in determining the root cause of print quality defects, the important influence of additives on the quality of paints/adhesives and ink formulations cannot be ignored.
Dave Steele, SICPA's Eastern Region Technical Manager, listed some of the common undesirable effects caused by incorrect formulation of the paint, which is often either too high or too low humidity or poor adhesion. If the coating is applied to an ink surface containing an excessive amount of silicone resin, the coating may have a honeycomb or needle-like pinholes, resulting in extremely poor coverage and surface effects. Too high an amount of silicone in the ink can also result in reduced coating adhesion efficiency between the coating and the ink.
Mr. Steele said: "In the printing process that includes coating, measuring the amount of silicone in the ink is the most effective method." It means that less silicone should be used in the first color printing, and then in the first Gradually add the silicone content in the two colors, the third color, and the fourth color. The formulation of the UV coating may also include the selection of monomer and oligomer materials, and it may also be possible to select specific additives.
The most common unsightly effects caused by UV coatings may be a few gloss levels. Mr. Jim Wittig, vice president and chief technical officer of Rad-Cure, believes that gloss is determined by the type of material and the weight of the paint. Porous absorbent materials and lower grammage paints tend to have very low gloss. Another less noticeable factor is the anilox roll. The ceramic anilox roll transfers more paint at a given number of meshes, while a fine anilox roll (with a higher number of elements) can deposit the coating. It is smoother and therefore has a correspondingly higher gloss.
Sometimes the anilox roller on the product is transferred to the product, it will also cause the product surface roughness is not smooth. In addition, the rough surface of the roller, high viscosity or poor fluidity of the coating may also cause adverse effects. The maximum distance between the point of application of the coating and the curing device will allow the coating to flow before it solidifies, and the chance of transfer of the textured pattern to the product is greatly reduced, thereby increasing the gloss of the product surface.
Poorly formulated or excessively cured coatings can often cause yellowing of the product surface. Mr. Wittig suggested that you must be careful when selecting paints. Do not choose materials that tend to yellow. Also pay attention to the speed of curing: "If you cure a paint with high speed ingredients at a lower speed, the product is likely to overcure, and yellow appearance will occur at this time." At a lower speed, lower the curing lamp Energy is a good way to reduce yellowing at this time.
For UV/EB coatings and adhesives, fluidity and uniformity are important factors that affect the overall appearance of the finished product. According to Paul Robinson, Product Manager of the UV/EB division of Wikoff Color, the time difference between coating and curing determines how well the coating spreads across the printed surface. If the time before curing is long, the paint will flow and distribute evenly, hiding the incompleteness caused by the cracking of the film. That is, lower viscosity paints have better fluidity and shorter curing time.
According to Kevin Rea, UV/EB product manager at Northwest Coatings, adhesives for film lamination usually do not exhibit "peaks and troughs" because the smoothing effect is achieved through roller compaction. However, short pre-curing times in film-laminating applications may cause the film to peel off, sticky or grainy texture.
Mr. Rea emphasized that the delivery system can be applied to situations where UV/EB requirements are not very strict. Frequently operating suction systems, cassette anilox rollers, and high-speed screen coating devices sometimes produce excessive bubbles or "bubbles," which may cause the smoothness and gloss of the cured film to decrease, resulting in pinholes, voids, and voids. And craters, or unsightly spots or 'silver effect' in some film structures. Although proper adjustment of the suction force or the on-line speed can reduce the occurrence of these stain defects, in some specific cases, it is still necessary to change the composition of the substance.
Mr. Rea also reminded printers to pay attention to the force exerted on the printing surface—it should be slightly higher than the liquid tension of the UV/EB product, to avoid the formation of small droplets or webs on the surface of the substrate. One less obvious cause of the formation of low-energy surfaces is the flowable material in the substrate, ink, or basecoat layer that moves to the surface of the object after heating or pressing. Similarly, material supplier recommendations are also very important to avoid and resolve such challenges.
Waterborne Coatings and Adhesives As Elmer Griese, Market Manager at Cork Industries, puts it, many of the application problems that lie ahead of UV/EB coatings are similar to those that arise when using waterborne coatings. In order to achieve the best level of gloss, he pointed out that: 1) to use wet and heavy enough paint; 2) to use high-capacity smooth materials; 3) to use paint with high-gloss components; 4) Use a coating with a higher solid content; 5) Increase the viscosity of the coating.
Although tackiness is an extremely important factor in the successful application of all liquid coatings, special attention must be paid to the estimation and maintenance of the pH when applying aqueous materials. The technical director of SICPA, Mr. Derrick Ayers, also believes that "the majority of resin materials used in waterborne coatings are not actually dissolved in water, so they require a specific pH to maintain true dissolution."
Incorrect pH can accumulate in non-graphical areas of the flexographic plate, causing ghosting, drying on the anilox roll or cylinder, or excessive wear of the platen by the plate under very extreme conditions.
Mr. Ayers also proposed another potential difficulty leading to unsatisfactory quality: the printing plate expands. “Inappropriate selection of defoamers or excessive use of ethylene glycol or organic solvents may cause the flexo plate to expand, causing a drop in print quality and damage to the plate.”
If the water-based paint dries too fast or becomes brittle, it will easily form 1/64" to 3/4" thin lines on the substrate. According to Dennis Oscar, product manager for waterborne coatings at Northwest Coatings, printing thicker four-color ink layers is more prone to cracking and is often eradicated by adding trace amounts of paint and lowering the temperature of adhesion. He also added, "If these measurement processes do not work, you can add 0.25% to 0.50% propylene glycol to the paint to increase the softness of the paint." These additives slow down the drying speed of the water-based paint, but It also increases the possibility of solidification.
Tom Rolando, Project Technical Manager of Soft Packaging Adhesives and Coatings Group HB Fuller, believes that for water-based adhesives, in order to obtain the best appearance requirements, in addition to ensuring that the film and ink are adhered to the first-class standard, inks In addition to the compatibility of the agents and the choice of suitable adhesive products, corona-treated films are also used. He emphasized that any application of adhesives should pay attention to the control of the weight of the paint. For any production process, it is advisable to define the adhesives, inks and coatings in the laboratory or according to the guidelines before production. The various chemical materials used are well compatible.
Mr. Charles Wasserman, Technical Manager of Waterborne Materials at Northwestern Paints, said that when applied to a metallized or glossy film surface, cold sealing/adhesion can be difficult. The three main appearance problems often encountered in this case are: streaks, surface irregularities, and deinking, pitting, and ink film defects.
Mr. Wasserman pointed out that the streaks were caused by the accumulation of material under the squeegee. A micro-etching of the squeegee blade and roller area that oscillates back and forth can solve this problem. At the same time, printing companies should also choose cold sealing/adhesion materials with slower drying speed and higher stability.
The surface unevenness is caused by many different factors, including the damage of the squeegee blade (as above), the characteristics of blistering and microbubbles, the insufficient flow of material after the drum ink hole is transferred, and the like. Wasserman recommends careful selection of defoamers and the addition of slow drying aids to the material to increase the humidity of the product on the surface of the substrate and address the lack of flow.
In order to get rid of problems such as deinking, pitting, and ink film defects when the printed product is free from cold sealing/adhesion, he recommends corona treatment of the film. If the original coating surface treatment method is not correct, or the surface is contaminated with slip additives such as silicone or wax, these problems are even more serious.