UV Printing Troubleshooting: Questions and Answers
4.Printing Defect
| No. | Item | Printing System |
Phenomenon/ Situation |
Explanation | Cause | Counter-measure |
| 401 | Printing Defect (Ink Skin) | All System | The ink in the duct or on the roller dried, resulting in increased viscosity and generate ink skin. Consequently, foreign particles adhered to the printed material, and in flexographic printing, this led to the development of doctor blade marks. | UV inks can be cured when exposed to both sunlight and fluorescent light. Especially UV inks formulated for energy-saving type are more susceptible to be required careful handling. | Printing circumstance |
A) Use of UV cut fluorescent lights or adjusting their position. B) Prevent the sunlight exposure. C) Cover the ink container with a lid or cover. |
| 402 | Printing Defect (Ink hardening) | Offset Letterpress | The phenomenon which UV ink dry on the roller during the installation of a new machine or the replacement of rubber rollers. This issue particularly occurred depending on the material of the rubber rollers. It can lead to printing defects, such as edge picking, paper delamination, poor ink transfer, and curing failure. | The cause of this phenomenon is the absorption of low molecular weight components in the UV ink into the rubber rollers. | Roller selection and incorrect ink selection |
The fundamental approach is to thoroughly condition the rubber rollers with UV ink prior to use. A) It is recommended to use polyurethane resin-based rubber rollers. B) As a preparatory measure, apply a reducer to the rollers and allow them to properly condition. C) During printing, add additional reducer and context to the ink, and increase the ink volume as necessary. |
| 403 | Printing Defect (Ink Transfer Defect) | Offset | In combi machines, doing UV printing after oil-based ink printing, the UV ink may not transfer properly on the rollers. | If the switch-over cleaning is not thoroughly performed, the residual oil-based ink components that have penetrated the rollers can hinder the transfer of UV ink. | Lack of cleaning | Thoroughly clean the oil-based ink. In some cases, clean by using UV reducer or UV trans white. |
| 404 | Printing Defect (Paper alignment issue) | Offset | Specifically, during the film printing process, paper misalignment and paper feeder jam was observed in the delivery stage, after the two- pass printing when performing multiple prints. | The issue arises due to the generation of static electricity. Particularly in UV printing, it is essential to exercise caution, as static charges are prone to accumulate within the UV lamp housing." | Printing circumstance or Substrate properties |
A) Control of humidity in the printing room B) Consideration of static eliminator devices C) Consulting with the substrate manufacturer. D) Paper laminating is recommended to enhance substrate performance. |
| 405 | Printing Defect (Edge-picking, Paper picking) | Offset, Letterpress | Edge-picking or paper picking occurred during printing on paper. |
This was caused using high-tack ink on printing paper with weak surface tension. UV inks are often designed to have a higher tack than oil-based inks. Furthermore, these problems are more likely to occur in winter season, when temperatures are cooler, because the apparent viscosity increase of the ink is greater. The same problem occurs with the “ink tightness” phenomenon. |
Incorrect paper selection or Characteristics of ink or Printing environment or Ink tightness |
A) Change to paper with higher paper tension. B) Change the ink to a low-tack type or reduce tack by adding Reducer or Contex. C) Increase the water temperature setting of the printing press and increase the room temperature in the printing room. D) Refer to section on No.402 on “Printing defects” (ink tightness). |
| 406 | Printing Defect (Edge-picking,Poor ink transfer) | Waterless Offset | Edge-picking or poor ink transfer occurred during waterless offset printing on film materials. |
Although it happens on the standard UV offset printing, it is much more likely to occur in UV waterless offset printing. Substances such as antistatic agents floating on the surface of the substrate prone to cause this issue. |
Substrate defect or Ink defect |
A) Make ink take-off bars. B) Add UV Contex or UV Reducer in ink. C) Pre-print UV primer on substrate. D) Use different type of ink. |
| 407 | Printing Defect (Reverse trapping) | Offset | A phenomenon in which the yellow tones become muddy during printing due to the yellow ink cylinder, which is mainly used for post-printing, pulling the black or cyan of the pre- printing. |
Basically, it is caused by the difference of tack between pre-printing ink and post-printing ink, and effect of ink volume. Pre-printed inks are not expected to increase the tack in case of UV inks due to less likely set drying, leading to more prone to reverse trapping than oil-based inks. |
Characteristics of ink or Excessive emulsification |
A) Add Contex to yellow to increase ink volume while lowering tack. B) Reduce the ink volume of pre-printed ink by using concentrated type. C) Reduce fountain solution supply during printing. D) Evaluate another blanket. E) Adjust printing pressure among blanket and substrate. |
| 408 | Printing Defect (Gloss) | Offset | Lack of gloss compared to oil-based ink prints. | UV inks cure instantly before leveling, and surface is not as much flat as oil-based inks, leading to less gloss effect. The difference is especially large in areas with two or more color layers. | Characteristics of UV ink |
A) Use softer ink type. B) Use gloss type ink. C) Add OP varnish, UV Reducer or UV Contex. |
| 409 | Printing Defect (Gloss) | OP Varnish | Lack of gloss when applied OP Varnish over the undried ink. |
Depending on OP Varnish, well gloss cannot be achieved when OP Varnish applied over the undried ink. This is affected by character of trapping, wetting, cure shrinkage. Also, the smaller the varnish volume, the more susceptible it is. |
Incorrect OP Varnish selection or Excessive amount of varnish |
A) Choose good trapping OP Varnish over the undried ink. B) Increase amount of OP Varnish. C) Adjust the press temperatures. |
| 410 | Printing Defect (Gloss) | Coating Varnish | In coater varnish printing, the gloss on the ink decreased by passage of time after printing compared to that on white paper. The gloss decreasing was particularly large in areas with heavy patterns. |
This problem prone to occur because the ink surface condition fluctuates due to the penetration of insufficiently cured ink into the paper after the varnish coating dries, this resulting in a decrease in the smoothness of the varnish. This is most likely to occur when there is no interdeck UV, but it can also occur on heavy ink patterns even when there is interdeck UV. |
Curing failure | Change the underlying ink to a concentrate type or a type with good curability. |
| 411 | Printing Defect (Gloss) | Flexo, Coating Varnish | In UV flexo printing and UV coating, the surface is not smooth, resulting in a wavy pattern and lack of gloss. |
If the problem is not caused by ink or varnish, it occurs when the time between printing and UV irradiation is short, this leading to insufficient leveling. Furthermore, it prone to occur when temperature is low as the condition increase ink tackiness itself. |
Machine setup or Printing condition. |
A) Reduce amount of Varnish. B) Reduce/Increase the viscosity of Varnish. C) Increase atmosphere temperature. D) Change plate to smooth type. E) Change Varnish to smooth type. |
| 412 | Printing Defect (Emulsification) | Offset | Emulsification problems occurred, in case such as ink density dropping during printing, ink density not increasing even after turning up the ink dial, unstable ink density such as density change after restarting the machine, fountain solution rising in the ink duct. |
Compared to oil-based inks, UV inks are more polar and therefore emulsify more easily. Due to emulsification progresses, problems due to emulsification phenomena such as reduced density, water sticking, ink pooling on blankets outside the paper width, and flying occur. This is particularly likely to occur with non-absorbent paper such as film, which does not absorb fountain solution. It is also more likely to occur with inks that have good adhesion. |
Excessive amount of dampening water or Excessive amount of ink. Incorrect ink selection. |
A) Basically, reduce the amount of fountain solution. Reduce the amount of fountain solution not only on the printing cylinder corresponded, but also on the prior cylinder. In some cases, after cleaning the rollers, replace the ink with new one and start again with the fountain solution amount reduced. B) Adjust the amount of fountain solution and alcohol. C) Use UV ink for paper if adhesion permits. D) Use concentrate type ink. E) Make ink take-off bars. |
| 413 | Printing Defect(Plate entanglement) | Offset | Halftone printing area become like solid printing area. | This phenomenon is the same as oil-based printing and is less likely to occur than oil-based printing due to the emulsification characteristics of UV inks, but it may occur in dark-color printing, especially in reddish color. | Excessive amount of ink or Machine setup |
A) Lower the ink volume. If possible, increase the density. B) Adjust the amount of fountain solution. C) Lower the temperature of the press's fountain solution and water supply system D) Change the ink concentrate type. |
| 414 | Printing Defect(Plate remove) | Offset | In long-run or jobs with few patterns, the image part of the plate is removed. | Due to its composition, UV ink tends to be more prone to plate removal. Also, same as with oil-based inks, this is more likely to occur when the concentration of fountain solution is high or when the supply of fountain solution is large. |
Characteristics of UV ink or Incorrect plate selection or Excessive emulsification |
A) Use UV-compatible PS plate. B) Confirm the amount of fountain solution. C) Reduce the amount of fountain solution supply. |
| 415 | Printing Defect(Misting) | All Systems | Phenomenon in which ink flies misty on the printing press, splashing onto printed materials and contaminating the area around the press. |
UV inks have almost no gel characteristic and are more prone to occur than oil-based inks. There is a difference in the amount of misting even with UV ink type and amount of ink. Temperature and humidity (static electricity) also have a significant effect and are more likely to occur in winter when humidity is low. |
Characteristics of UV inks Machine setup Printing environment |
A) Use hard or concentrate type inks. B) Adjust the temperature and humidity of the printing press and printing room. C) Control excessive emulsification. |
| 416 | Printing Defect(Flying) | Offset | Phenomenon in which ink splashes occur from the edge of the roller. The cause of this phenomenon is different from misting, and more large particles of ink fly off, contaminating the printing press and printed materials. |
Excessive emulsified ink accumulates too much on the rollers, resulting in the eventual flinging phenomenon. Refer to emulsification section. |
Excessive emulsification | Refer to emulsification section (No.411). |
| 417 | Printing Defect(Blanket swelling) | Offset | The pattern of the previous job appears on the print of the next job, and the blanket swells in the shape of the pattern of the previous job. |
This occurs because the low-viscosity component in the UV ink causes the blanket swelling. Prone to occur in UV inks such as less-energy UV inks and LED-UV inks that contain a large number of photo-initiator components. In addition, in the case of using UV fluorescent P series containing oil-based solvents and use of UV-specific blankets (EPDM type) may cause swelling. |
Characteristics of UV inks Incorrect blanket selection |
A) Change the blanket. (Swelling resistance and resilience should be considered depending on the printing pattern.) B) Change the ink type. |
| 418 | Printing Defect(Roller mark,Gear mark) | Offset | Streaks appear in the horizontal direction against printing direction. |
Basically, caused by machine adjustment failure. Darker colors tend to be more noticeable. It is also more likely to appear the more the ink is over-emulsified and printed with deteriorated flowability. |
Machine adjustment failure Roller deterioration Excessive emulsification |
A) Machine adjustment. B) Rubber roller replacement. C) Refer to section No.411 on emulsification. D) Replace the blanket with a cushioned type. |
| 419 | Printing Defect(Gloss, Chalking) | Flexo | When printed on paper, the bronze floats and not glossy. When the printed surface is scraped with a fingernail, the ink drops off in powder form. | Particularly, when paper with good set-drying properties such as cast-coated paper is used for flexo printing, the low-viscosity UV vehicle content penetrates the paper, resulting in reduced gloss and chalking. This in turn causes both curing and adhesion failure. |
Characteristics of substrates Incorrect ink selection |
A) Change to a paper that is difficult to penetrate. B) Perform a blind stop for pre-printing. C) Increase the printing speed. D) Add Trans White to the ink to increase the ink volume. E) Change to ink with high viscosity or other inks that are difficult to penetrate. |
| 420 | Printing Defect(Pinhole) | Flexo | Pinholes and other defective areas occurred in the printed patterns. |
Insufficient wettability between the raw material and ink prone to result in pinholes. If it is repelled on the plate, it is due to wettability between the ink and the plate. It also occurs when machine oil is mixed in the ink. If ink is the cause, poor ink wetting and low viscosity are more likely to occur. |
Incorrect ink selection Incorrect substrate selection Paper and plate processing errors Contamination |
A) Use of high-viscosity type or type with good wetting. B) Change substrate and plate material. C) Check and clean the plate surface. D) Increase the strength of the corona treatment E) Replace with fresh ink. |
| 421 | Printing Defect(Plate entanglement) | Flexo | Ink fills in the gaps between the dot gain defects on the plate (especially in the highlight area), causing the dots error. | It tends to occur when there is a large amount of ink and strong printing pressure. It also occurs in letterpress printing but is more likely to occur in flexo printing due to its low viscosity character. |
Machine adjustment failure Excessive ink volume |
A) Adjust printing pressure and anilox pressure. B) Reduce the amount of ink. C) Replace the doctor blade and adjust the pressure. |
| 422 | Printing Defect(Swelling of printing plate) | Flexo | Resin plates swell during printing, resulting in dot gain defects and density changes. | This is caused by low molecular weight components in the ink penetrating the plate and causing it to swell. Check the compatibility of the printing plate and ink before use. This is more likely to occur with good adhesion ink type. |
Incorrect plate selection Incorrect ink selection |
A) Change of plate. B) Change of ink type. |
| 423 | Printing Defect(Gear mark) | Flexo, Coating Varnish | Streaks appear in the horizontal direction against printing direction. | Basically, by machine adjustment failure. Dark color is easily noticeable. | Machine adjustment failure | Machine adjustment |
| 424 | Printing Defect(Bubbling, ink loss) | Flexo, Coater | Ink and varnish may bubble in the chamber, varnish tank, and ink pan, resulting in lost image of printed material. | It prone to occur UV varnishes and UV inks, which are solventless and more viscous than water-based varnishes and water-based flexo inks. |
Machine adjustment failure Insufficient supply Incorrect varnish selection |
A) Increase the supply volume to the chamber and adjust the supply with preventing the air mixed in. B) Increase the capacity of the circulation tank. C) Change to ink and varnish with less foaming. |
| 425 | Printing Defect Ink volume | Flexo, Coating Varnish | Volume of ink and varnish cannot be adjusted in flexo and coater varnish, causing less or too much ink and varnish. | In the case of using anilox, the cell capacity may differ even if the number of lines is the same. Basically, the cell capacity is better for control, and the larger the cell capacity, the more ink is produced. Other factors, such as printing pressure and ink temperature, also affect the ink density. This is not only for flexo printing, but also for offset presses with anilox equipment. | Machine adjustment failure | A) Consideration of Anilox. B) Adjustment of printing pressure. C) Temperature adjustment. D) Doctor blade replacement. |
| 426 | Printing Defect (Scraping Unevenness, Doctor Lines) | Flexo, Coating Varnish | UV flexo or coating varnish printed materials occurred raindrop-like stains and lines in the same direction. | In the doctor blade system, scraping defects cause the following occurrences: → A) Ink or varnish wraps around behind the doctor blade, accumulates to a certain extent, and subsequently transfers to the anilox roll, which then transfers to the printed surface, creating a raindrop pattern. → B) Scratches on the doctor blade or anilox roll result in linear streaks. → C) Debris or other foreign objects adhere to the doctor blade, preventing proper scraping of ink or varnish from the cells of the anilox roll, leading to doctor lines. |
Machine settings Doctor blade defects, Insufficient cleaning Contamination |
A-① Increase the pressure of the doctor blade. A-② Change to a stronger doctor blade. A-③ Switch to low-viscosity types of ink or varnish or increase the temperature settings. B-① Replace with a doctor blade or anilox roll to new one. B-②Remove foreign particles by filter the ink or varnish, replace, or change the type. |
| 427 | Printing Defect (Inking) | Flexo | In flexo printing, the solid areas are not sufficiently dense, resulting in printing that lacks balance between solid and dot areas. | Prone to occur in flexo printing. Issue can be caused by factors such as ink viscosity, the smoothness of the substrate, the hardness of the printing plate, and improper machine adjustments. Additionally, since these problems often result from a combination of factors, adjustments from various aspects are necessary. Also, this occurs due to the swelling of the printing plate. | Press adjustments Incorrect ink selection Paper characteristics Incorrect plate selection. |
A) Increase the printing pressure. B) Use low-viscosity ink or change the ink type. C) Use softer plate materials. D) Use a harder cushion tape. E) Change the substrate. F) Separate the dot area and solid area into different plates. |
| 428 | Printing Defect (Scumming) | Waterless Offset | During UV waterless printing, scumming occurred in non-image areas. | UV waterless ink is a solvent-free type of ink and therefore does not provide the solvent-based prevention same as oil-based waterless ink, making it more prone to scumming. Other factors that can influence this issue include mechanical factors such as the temperature of the printing press and printing conditions such as overloading the ink. Ensuring the ink's repellency to the plate surface can help improve the problem. | Characteristics of ink, Improper Machine settings, Temperature conditions, Excessive ink. | A) Lower the water temperature. B) Reduce the amount of ink applied as much as possible. C) Set the nip of the rollers (especially the finishing roller) on the plate surface to be lighter by about 1–2 mm. D) Check the blanket. E) Switch to a harder ink. |
| 429 | Printing Defect (Blanket piling) | All Systems (matte OP Varnish) | During printing, ink or pigment accumulates on the plate and blanket, affecting the image and causing poor ink transfer. This can occur not only with matte OP varnish but also with inks that have poor wetting properties with pigments, additives, and UV vehicles. | Due to the characteristics of matting agents (particle size and wettability) and the influence of ink emulsification, pigments can easily separate from the vehicle, leading to plate and blanket piling. Additionally, this separation tends to occur on the non-printed areas of highly absorbent paper. |
Pigment characteristics, Excessive emulsification. |
A) Add Trans white. B) For non-printed areas, pre-print a trans white as a sealer. C) Reduce the amount of dampening solution supplied during printing. |
| 430 | Printing Defect ( | All Systems (matte OP Varnish) | A donut-shaped ink transfer defect (hickey) appeared on the printed image. | UV ink does not cure unless exposed to ultraviolet light, so hickeys caused by ink skin rarely occur. Therefore, mostly caused by the mixing of foreign particles such as paper dust. Static electricity makes it easier for debris to be attracted. |
Contamination, Printing environment |
A) Remove foreign particles. B) Cleaning press. C) Check and change the substrate. D) Eliminate static electricity. E) In ink case, dilute the ink with trans white or contex and increasing the ink volume can improve the issue. |