On The Problems of Common Occurrence In the Process of Hologram Images Transferring
With the concept of energy-saving and emission-reduction continually popularized in China, the Hologram Images Transferring process is more and more widely applied in cigarette package printing, however, some problems and malfunctions may frequently occur on the production line of cigarette package. In this thesis, the problems of common occurrence in the Hologram Images Transferring process and the corresponding solutions are to be introduced by the Author, whose practical working experiences are integrated in the introduction too, so as to provide some valuable information for sharing with colleagues in the same trade.
On The Problems of Common Occurrence In the Process of Hologram Images Transferring
1. Film Crinkling
Under certain strain strength, with the aid of pressing device, Holographic Transferring Film can transfer hologram patterns onto the surface of presswork sheet. During the whole process, Holographic Transferring Film must go through more than one film-guiding roller, so that it is liable to occur film crinkling. The main causes are:
(1) The rewinding tension of Holographic Transferring Film is too large, making the tension on the two ends of the film roll different from each other and then the film crinkled. For that, it is needed to adjust the uniformities between film outlet-roller, guiding-roller and damping-roller, which is a time-consuming job. Furthermore, when use the Holographic Transferring Film for a next time, the operation directions once with different tensions will reverse, and then the system has to be reset. As to this, the normal solution is to rewinding the Holographic Transferring Film roll once again after its rewinding, which can regulate the tension, and help to heat-dissipate.
(2) There is no quality fault in the Holographic Transferring Film, and without embossing press, film crinkling never occurs, but once the Film gets an embossing press, it crinkles. The problem mainly caused by the different pressures on the two ends of film-press roller. In that case, the pressure in the cylinder at each end of the film-press roller need to be regulate, that is to readjust the limiting screws at the stroke end of the cylinder, which located at inner side of wall plate. Due to its hard-to-touch location point, the adjusting should be carry out with a feeler gauge and don’t forget to timely tighten it to the locking point. However, as for some Hologram images Transferring Equipments, the cylinders’ pressures on film-press rollers’ ends can be separately readjust, so it is very convenient to regulate.
(3) If the tension on Holographic Transferring Film at the guiding-rollers is not the same, the film delivering speed and transferring speed will not be even and then will make film crinkled.
2. Pinholes & white flakes on hologram pattern
At the positions of these pinholes & white flakes, there are only UV varnishing but no hologram pattern appears, or neither UV varnishing nor hologram pattern appears. Specific cases as follows:
(1) Pinhole or white flake with fixed shape and fixed distributing position. Main causes: 1there is one or more pits on the surface of coating plate or anilox roller, so that on the transferred sheets’ surface there is no UV varnishing at the position responsive to the pit, the hologram patter is of course missing. 2If seam-avoid marked Holographic Transferring Film is adopted and the spread coating of UV varnishing is no problem, the occurrence of the above mentioned case may originate form the flaws on the surface of Holographic Transferring Film, for example, there is no hologram pattern at the responsive position of each repeated perimeter of the Holographic Transferring Film, of course Pinhole or white flake will emerge after transferring.
(2) Pinhole or white flake with unfixed shape and unfixed distributing position. Main causes: 1 the quality of the Holographic Transferring Film is not steady and liable to stick off UV varnishing during transferring, for example, OPP Holographic Transferring Film produced with recycled film is more liable to such problem; 2 addition agent for UV varnishing was not properly added, or the amount of added wax, silicon oil, pasty element or other substances was too large, making UV varnishing cannot sufficiently enter into the mesh hole of Holographic Transferring Film; 3 in the transferring of some cigarette packages, UV offset printing in large area is adopted and need to implement multi-color overprinting, due to the high content of UV printing ink and its property of quick solidification, the ink-coat on the surface of transferred sheets is often not smooth. In order to reinforce the hologram transferring effect, many company engaged in cigarette package printing adopt the process of “printing ink surface coated with whole plate base oil coat+ hologram images transferring ”, However, in the base oil coat, the content of silicon oil or flatting agent may be too high then reduce the adhesive power of the base oil coat on the surface of printing oil, resulting that some peeling off base oil coat be entrapped by Holographic Transferring Film (base oil coat flakes can be seen on Holographic Transferring Film), then make the transferring inadequate and white flakes emerge on the transferred sheets; 4 the working time of UV lamp is too long, and the effective power of the lamp is insufficient, which cause the UV varnishing cannot solidify adequately and some peeling off UV varnishing entrapped by Holographic Transferring Film, in such a case, the UV lamp must be replaced as soon as possible. The performance life of ordinary domestic UV lamp is about 100-1500h; 5 film crinkling causes inadequate transferring, resulting that whites flakes emerges in large area.
(3) In the middle of transferred sheets’ tail end and in the direction of paper delivery, large area of white flakes stripes or inadequate transferring emerged. The main cause for that is severe deformation of printing stock. If low-grade white paperboard with grey ground was used, due to the temperature fluctuation in workshop,“ lotus-leaf-edge”would appear on the paperboard because of moisture absorption and disabsorption, which would impede the excluding of the air between paperboard and Holographic Transferring Film during transferring operation. Solution: arrange the manufacture schedule appropriately, pay attention to the protection of printing stock and the controls of temperature and humidity in work shop.
(4) Pinholes or white flakes emerge on part area of the surface of transferred sheets, especially on the transverse area of the article, the transferring effect on one side is good while on the other side is not good. Main causes include: 1 the press rubber roller was aged and degraded, its hardness was reduced and its body was heavily worn. The old roller needs to be reconditioned or replaced with a new one. It is recommended to buy a new roller form the original manufacturer, and more attention should be paid to the roller’ rubber layer, which must be made of UV-resistance rubber. Furthermore, in order to delay the aging of press rubber roller, it is recommended to use ethanol to clean the roller, and never use esters solvent (which is liable to produce residue) as clean agent in the maintenance of the roller; 2 If flexographic plate was adopted in the coating unit, and if the pressure of anilox-roller was not adjusted properly, above mentioned problem might be caused, in such a case, transferring pressure and anilox-roller’ pressure on printing plate should be readjusted; 3 if there are foreign substances (e.g. paper piece) held up in the Leveling Section of the Hologram Images Transferring Equipment, and the strain strengths and speeds on the conveying belt’s left and right sides are not the same with each other, the paper in Leveling Section will deflect and not locate at right place, which can impede the excluding of the air between paper and Holographic Transferring Film during transferring operation, and then cause the above mentioned problem.
(5) When adopting a certain UV varnishing in Hologram Images Transferring, no white flakes emerge in the production in summer, but in the production in winter, even the same UV varnishing is used, white flakes emerge nevertheless. Such a problem mainly takes place in northern China, and the crystallization of some a agent (e.g. photosensitizer, flatting agent ) in UV varnishing due to the low ambient temperature is the main cause. If the crystallization temperature of flatting agent is at 10℃, once below 10℃, the agent will be in semi-solid state instead of liquid state, and then has a negative influence on the regular operation of hologram images transferring. Solution: heating the UV varnishing to the temperature of 40℃ - 50℃ before putting it into service; only adopting low-temperature-resistance UV varnishing; and revising the recipe of varnishing to improve the effect.
(6) At the initial stage of hologram images transferring operation, only a few of Pinholes or white flakes emerge, however, at later stages, more and more Pinholes or white flakes will emerge and the chief cause is dust. Therefore, during equipment maintenance, please carefully check if there is any dust held up on the guiding-roller, and regular and frequent wiping and cleaning is also required. It is highly recommended for printing enterprises with convenient conditions to equip workshop with dustproof installations to keep the workshop no-dust and clean. If no dustproof installation can be equipped in workshop, the door of workshop should be carefully closed, and the guiding roller should be clean four (4) times at least in one working shift, normally do the cleaning at the same time of Holographic Transferring Film replacing.
On the whole, the key points to cope with pinholes and white flakes can be summarized as “four levels” and “four cleans”;, four levels: ensure the forward part and rearward part keep level with each other when setting up the equipment, keep Holographic Transferring Film level and flat during transferring operation, keep printing stock level and flat, and only select UV varnishing with good level-ability; four cleans: keep the plate (flexographic plate or gravure plate) clean, ensure UV varnishing be cleanly filtered, keep guiding-roller clean and neat, and keep workshop clean.
3. Undesirable hologram images transferring effect (e.g. rough hologram pattern surface, bad surface gloss)
Main causes: 1 the amount of UV varnishing is inadequate (causes: the number of anilox-roller lines is too high ,or the depth of mesh hole is not enough); 2 the viscosity of varnishing is too low; 3 too much solvent (e.g. alcohol) was added into the coating for the purpose of cost reducing, or use the solvent improperly; 4 the Holographic Transferring Film had been used for too many times and the mesh holes on it turned fragmentary, so that the laser exposure effect is not very good then has a negative influence on the surface gloss of the hologram pattern; 5 under low ambient temperature, the UV varnishing had turned crystallized.
4. Hologram pattern appearing in changed, yellowish color
Hologram pattern appears in changed, yellowish color after embossing and transferring operation. (commonly referred to as “changing yellow” ) . Such a problem is especially liable to take place on High-speed Hologram Images Transferring Equipment with high power UV lamp. That is mainly because the photosencitizer in the recipe of the UV varnishing was not rightly selected, for example, the low price – low performance Irgacure 651 was selected. Solution: request the supplier of the UV glazing oil to replace the photosencitizer with desirable ones (e.g. Irgacure 184, Darocur 1173); reduce the power of the UV lamp properly.
5. Granular pocks on the surface of hologram pattern
Such an appearance normally cannot be seen by naked eye without the help of 10 × magnifier. In fact, it is dust and print ink particles that cause such a problem.
As for offset printing, the main cause is that the printing ink was not processed up to enough smoothness, the ink’s particles are not fine and the ink-coat is too thick. It is recommended to make the color hue of ink as dark as possible in the preparation of printing ink, or apply a UV varnishing coat on the printed article after operation.
As for gravure printing, such a problem maybe caused by the dust created in cross-cutting of papers. Besides replacing the cross-cutter, more attention should be paid to the direction of patch-up, the gripper edge for transferred sheets should be located ahead along the paper delivery direction of the web, and then the gripper edge will be taken as cutting inlet of paper’s cross-cutting, the gap between upper and lower cross-cutters should be readjusted too. Furthermore, the end tail of single piece of article should get an additional cut (e.g. a cut of 1mm), so that the rough edge be cut off and the amount of dust be reduced.
6. As for transferring after foil stamping, UV vanishing’s adhesive on aluminum surface not very good
A fingernail-scratch, or applying a 3M sealing tape on the surface of foil stamped pattern, can make the UV varnishing scaled off. Main causes: 1 the compatibility between UV varnishing and aluminum is undesirable. 2 the time interval between foil stamping and transferring was too long, the coat of aluminum surface had been oxidized through such a long time.
7. As for transferring after foil stamping, too much “foil-splashing” on foil stamping patterns’ edge
Main causes: 1 the aluminum edge had not been foil stamped sturdily; 2 the aluminum is not compatible with the UV varnishing, and the varnishing has some dissolution effect on the aluminum.
Solution: 1 re-select the aluminum to be used; 2 test the compatibility between aluminum and UV varnishing. A simple test method is to select 2 kinds of UV coatings with similar transferring effect, then put aluminum samples with same length and width into the paper cups filled with 2 kinds of UV varnishing, now, examine and compare the time length for the dissolution of each aluminum sample in one of the 2 paper cups, then, the UV varnishing with longer dissolution time should be taken for further test.
8. The hologram pattern’s surface is unsmooth and not suitable for packaging machine processing
Main causes: the solidification speed of UV varnishing is not compatible with the power of UV lamp and the production speed, leading the Hologram Transferring Film into a poor condition after hologram images transferring operation; addition agents for UV varnishing were not properly added, for example, the amount of flatting agent added was too little, while the amount of antifogging agent added was too much.
In order to determine whether the un-smoothness of hologram pattern’s surface is suitable for packaging machine processing or not, a frictionmeter can be used. Please note: sometimes even the hand feel of the hologram pattern is smooth, it is still not good for packaging machine processing, which depending on the type of resin (e.g. polyurethane) in the recipe of UV varnishing, and the type of flatting agent added in the coating, so the supplier of the UV varnishing are required to collaborate to solute the problem.
9. During packaging machine processing, the hologram pattern on the corners of a cigarette case is easy to be rubbed off
Such a problem is liable to take place especially when there is UV base coating on the surface of cigarette case, therefore, the compatibility between UV base coating and UV varnishing is of great importance. If aqueous base coating is to be used, please don’t use wax or silicon oil as addition agent. As for gravure printing, solvent-borne type base oil is recommendable, and gravure printing thinner, Plastisol printing ink or gold vanish can also be used because of their good compatibility with UV varnishing. As for offset printing, on the contrary, solvent-borne type base coating is not recommendable, therefore, the compatibility between UV base coating and UV varnishing should be carefully tested, and for product (article) with a thinner ink coat, no UV base coating spreading is needed.