Eliminating odor from plastic gravure printing

The difference in plastic gravure can directly cause the tangency of the food in the contents, and it can also affect the taste of food and even affect the health of the consumers. At the same time it will deteriorate the operating environment, causing the operator to be unhappy. In recent years, the problem of odor generated by plastic gravure printing has received increasing attention from related companies and many advances have been made. For example, alcohol-soluble inks and adhesives have begun to be applied, and the country's relevant standards have become more stringent.

The main factors that form the gravure odor produced by plastic gravure are residual solvents, the odor of raw and auxiliary materials used in plastic gravure printing, the odor produced during processing, and environmental pollution. Here is a brief analysis of the above factors. .

First, residual solvent

After the printing ink is transferred to the film, the solvent on the surface of the printing ink film first evaporates, and the solvent in the printing ink film must diffuse into the surface of the ink film before it can be evaporated and dried retrograde. When drying enters the final stage, the surface of the printing ink film has solidified, which limits the diffusion of the internal solvent and thus causes the problem of residual solvents.

The residual solvent contained in the print is the main cause of the odor of the plastic gravure package. Its residual content can be easily measured using a chromatograph to achieve qualitative or quantitative management. When there is an abnormal value, the printed matter in question is collected and can be judged by the sensory sense.

The organic solvent of the printing ink layer is dried most of the time in the drying oven, and the residual micro-solvent is solidified and sealed in the ink film to cause a residual state.

1, the release agent of the binder resin to the solvent

We know that in order to meet the needs of printing or consider the economy, the ink is often added to the mixed solvent. Each binder has its own true solvent, secondary solvent, and non-solvent. The better the solubility, the greater the affinity between the binder resin and the solvent molecules; the better the solubility of the solvent to the resin snake, the resin to the solvent The worse the release is, the worse the release is, the easier it is to cause residual solvent problems.
For an ink, solvent releasability is generally an inherent property, so when starting to use an ink, it is necessary for the ink manufacturer to know its residual solvent tendency in advance in order to make a corresponding treatment.

The solvent contained in the printing ink layer is a mixed solvent. The volatilization rate of each solvent is different: in this case, the volatilization of the solvent changes, the volatile solvent first escapes, and the weakly volatile component is retained. The composition of the solvent changes, and it is not possible to obtain a single-volume rate at a constant rate as a single solvent, and the volatilization of the solvent gradually slows down. If the purity of the solvent is unsatisfactory (but if there are too many high-boiling components) or if slow-drying solvents are used excessively, severe residual solvent problems can occur under normal conditions.

2, drying conditions

Drying conditions include drying air temperature, air flow rate (wind speed), and drying device structure, which determine the drying efficiency. Poor drying will increase the amount of residual solvent. Therefore, the best dry conditions should be created. Increasing the air temperature and air volume (wind speed) can undoubtedly intensify the drying conditions, but it should be noted that if the printing ink layer is thick, if the drying is too fast, the surface of the ink layer will be rapidly conjunctiva and the internal solvent will not be able to escape. This can lead to increased residual solvents and odors.

3, printing speed

The speed of printing determines the length of drying time. Therefore, the speed of the vehicle should be gradually increased while ensuring that the printing ink layer is sufficiently dry. If the speed is too fast, the film cannot be sufficiently dried after printing. In particular, the distance from the winding unit after the last color printing is short (and the ink is often large), which can easily cause excessive residual solvent.

4. Drying medium (air) humidity and organic solvent concentration

The humidity of the drying medium (air) has a great influence on the residual quantity. One is that the moisture in the air enters the ink, causing the overall volatility of the solvent to deteriorate. The second is the large amount of moisture in the drying medium (air), which also inhibits the volatilization of the solvent. Double the humidity, the drying speed of the ink will be almost twice as slow. Therefore, under high humidity conditions, the printing speed should be reduced as much as possible and the contact between ink and air should be reduced to ensure that the ink is fully dried. At the same time, the formulation of the solvent should be adjusted immediately to formulate a special recipe suitable for this climate. The humidity of the printing shop air should not exceed 70%, of course, it can not be too dry, otherwise it will easily cause static electricity problems.

5, printing film

Films of different materials have different selectivity for solvent absorption. For example, films such as aluminum foil and polyester are non-absorbent films, and there are generally less residual solvents; polypropylene-based films tend to leave hydrocarbon-based solvents, and water-absorbent films (eg, nylon, cellophane) tend to retain alcohol-based solvents. There are also some additives added to the plastic film that affect the volatilization of the solvent, thereby increasing the amount of residual solvent.

6, other

(1) Aging treatment. The residual solvent can be fully volatilized through the aging treatment and the ten structures can be fully set before entering the next process.

(2) For multi-color printing, do not stack too much in the pattern design. If possible, special colors can be used to prevent the local ink layer from being too thick.

(3) Use paper packaging to package the product. If a high tightness plastic film is used for packaging, it is equivalent to storing all the odors that are released during the storage process. Once the package is opened, odors will be released (the odor will be significantly reduced after a certain period of time). Therefore, the use of breathable paper packaging can make the odor residue fully volatilized, and also have a certain effect on reducing odor.

(4) In the event of a bad print, remedial action can be achieved by venting and then drying.

2. The odor of raw and auxiliary materials used in plastic gravure soft packaging

1, solvent selection

The purity of the solvent used in the ink, the purity of the solvent used in the ink transfer, and the presence of non-volatiles (high-boiling solvents, etc.) exceeding the standard are important factors in causing discorders.

When using solvents, the amount of organic solvent toluene or xylene should be minimized and petroleum toluene should be used. Coking plant A is extracted from coal tar or crude toluene, and it is easy to produce a tar odor when used for plastic gravure printing. Therefore, coking toluene cannot be used. In addition, the drums containing toluene and other solvents may not be covered by granules that have been rusted on a large area or may be used up after a long period of use, and foreign matter or rain may be mixed in. When the solvent is reloaded, the quality of the solvent is affected and the quality deteriorates. For example, the solvent in the entire barrel is prone to odor.

2, printing ink

The odor of the printed matter is not caused solely by the residual solvent, but is sometimes caused by the binder resin in the hand ink, the low molecular weight of the auxiliaries, the pigment active agent, etc.; this is an inherent property of the ink, if necessary, Ask the ink supplier or reselect ink.
Some companies use surface printing inks (which do not consider the effect of compounding on residual solvents in formula design, and some resins themselves have odors) instead of composite inks, which can easily cause odor problems in addition to the composite strength.

3, composite substrate

Some composite substrates have a certain odor due to excessive corona treatment, improper selection of additive additives, etc. Therefore, they should be carefully examined before use.

Third, the odor produced during the composite processing (resin odor)

Low odor during resin processing is an important indicator for evaluating the thermal stability of a resin. In extrusion compounding, resins such as polyethylene and polypropylene extruded from a T-die, and added white masterbatch, etc., give rise to resin odor due to oxidation at a high temperature of about 300 degrees Celsius. It is more difficult to completely remove the resin odor, and it is possible to reduce its generation.

(1) In order to reduce odors, it is effective to reduce the processing temperature of the resin or shorten the distance from the T die to the composite press roller, if possible.

(2) The smell of the resin differs depending on the type of resin. Polypropylene has a small odor and polyethylene is relatively large. EVA, due to its poor thermal stability, is more prone to odor problems.

(3) The odor of the same resin of different brands is also different. Should be carefully compared before use.

Fourth, environmental pollution

Plastic color printing composite materials and products in the process of processing, use, and in the process of storage if the concentration of organic solvents in the environment is higher or there is a strong odor stimuli such as pesticides, plastic color composite products may be contaminated. When selecting a storage location, pay special attention to the concentration of organic solvents and sources of strong odor stimuli.