The best way to eliminate the odor caused by plast

2022-08-07
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Eliminate the peculiar smell produced by plastic gravure printing

the peculiar smell produced by plastic gravure printing can directly cause the cross smell of the contents of food. In serious cases, it will also affect the taste of food and even the health of consumers. At the same time, it will degrade the operating environment and cause unhappiness to operators. In recent years, the problem of peculiar smell produced by plastic gravure printing has been paid more and more attention by relevant enterprises and made a lot of progress. For example, alcohol soluble inks and adhesives have been used for the precautions of Kellogg hardness tester, and the relevant national standards are more stringent

the main factors causing the odor of plastic gravure printing are residual solvents and the odor of raw and auxiliary materials used for plastic gravure printing. The odor and environmental pollution produced during processing are briefly analyzed below

I. residual solvent

after the printing ink is transferred to the film, the solvent on the surface of the printing ink film evaporates first, while the solvent inside the printing ink film must diffuse and penetrate to the surface of the ink film before retrograde evaporation and drying. When the drying enters the final stage, the surface of the printing ink film has solidified, which limits the diffusion of the internal solvent, resulting in the problem of residual solvent

the residual solvent contained in the printed matter is the main cause of the odor of plastic gravure flexible packaging. Its residue can be easily measured by chromatograph to realize qualitative or quantitative management. In case of abnormal value, collect the problematic printed matter and use the senses to sniff it out

most of the organic solvents in the printing ink layer dry instantaneously in the drying oven on the windows working platform, and the residual trace solvents solidify and seal in the ink film, resulting in a residual state

1. Solvent release of binder resin

we know that in order to meet the needs of printing or consider the economy, mixed solvents are often added to the ink during printing. Each kind of binder has its own real solvent, secondary solvent and non solvent. The better the solubility, the greater the affinity between binder resin and solvent molecules. The better the solubility of the solvent to the resin, the worse the release of the resin to the solvent, and the worse the release of the resin to the solvent, the easier it is to cause the problem of residual solvent. For a certain ink, the release of the solvent is generally its inherent property, Therefore, when starting to use an ink, it is necessary to understand its residual solvent tendency through the ink manufacturer in advance, so as to make corresponding treatment

the solvents contained in the printing ink layer belong to mixed solvents, and the volatilization rate of each solvent is different: in this case, the volatilization of the solvent changes, the solvent with strong volatility first escapes, and the components with weak volatility stay behind. The components of the solvent change. It is impossible to obtain a single volatilization rate at a constant rate like a single solvent, and the volatilization of the solvent gradually slows down. If the purity of the solvent is unsatisfactory (e.g. too many high boiling point components) or too many slow drying solvents are used, serious residual solvent problems will occur under normal conditions

2. Drying conditions

drying conditions include drying temperature, air volume (wind speed) and drying device structure, which determine the drying efficiency. If the drying is poor, the amount of residual solvent will increase, so the best possible drying conditions should be created. Increasing the temperature and air volume (wind speed) can undoubtedly strengthen the drying conditions. However, 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 quickly form a film and the internal solvent will not escape. On the contrary, it will increase the residual solvent and produce a peculiar smell

3. Printing speed

the speed of printing determines the length of drying time. Therefore, the vehicle speed should be gradually increased under the condition that the printing ink layer is fully dry. However, if the speed is too fast, the drying of the film after printing cannot be fully guaranteed. Especially, the distance between the last color printing and the winding unit is short (and mostly large ink ground), which is easy to cause the residual solvent to exceed the standard

4. The humidity of the drying medium (air) and the concentration of organic solvents

the humidity of the drying medium (air) has a great impact on the residue. First, the moisture in the air enters the ink, causing the comprehensive volatility of the solvent to deteriorate. Second, the large amount of water in the drying medium (air) also inhibits the volatilization of the solvent. When the humidity increases, the drying speed of the ink will be nearly twice as fast. Therefore, under high humidity conditions, the printing speed should be slowed down as much as possible and the contact between the ink and the air should be reduced to ensure the full drying of the ink. At the same time, the formula of the solvent should be adjusted immediately to prepare a special formula suitable for this climate. Generally, the air humidity in the printing workshop should not exceed 70%. Of course, it should not be too dry, otherwise it is easy to cause electrostatic problems

5. Printing film

films of different materials have different selective absorption tendencies to solvents. For example, aluminum foil, polyester and other films are non absorbent films, and the residual solvent is generally less; Polypropylene films are prone to residual hydrocarbon solvents, while water absorbent films (such as nylon and cellophane) are prone to residual alcohol solvents. In addition, the addition of additives to some plastic films affects the volatilization of solvents, thus increasing the amount of residual solvents

6. Other

(1) aging treatment. The next process can be started only after the residual solvent is fully volatilized and the molecular structure is fully finalized by aging treatment

(2) for multi-color printing, do not overlap too many colors during pattern design. Special color can be used to prevent local ink layer from being too thick

(3) use paper packaging to package products. If high sealing plastic film is used for packaging, it is equivalent to storing all the odor emitted by the product during storage. Once the packaging is opened, the odor will come out (the odor will be significantly reduced after being opened and placed for a period of time). Therefore, the use of breathable paper packaging can fully volatilize the foreign residues and also play a certain role in reducing the odor

(4) in case of bad printing, it can be remedied by ventilation and re drying

II. The odor brought by the raw and auxiliary materials used in plastic gravure flexible packaging

1. Solvent selection

the purity of the solvent in the ink and the solvent used for inking and the excessive content of non-volatile substances (high boiling point solvents, etc.) are important factors leading to ambiguity

when using solvent, the amount of organic solvent toluene or xylene shall be reduced as much as possible and petroleum toluene shall be selected. Coking toluene is extracted from coal tar or crude toluene. It is easy to produce a tar odor when using dry plastic gravure soft packaging, so coking toluene cannot be used. In addition, foreign matters, impurities or rainwater may be mixed into barrels of armored benzene and other solvents that have rusted in a large area or are sometimes used up after a long time of use. When reloading the solvent, due to the deterioration of the solvent quality and other reasons, the solvent in the whole barrel is easy to produce peculiar smell after a long time

2. Printing ink

the peculiar smell of the printed matter is not only caused by the residual solvent, but sometimes caused by the binder resin in the ink, low molecular weight substances of additives and pigment activators; This is the inherent nature of this kind of ink. If necessary, you can ask the ink supplier or reselect the ink

some enterprises use surface printing inks (the influence of compounding on residual solvents is not considered in the formulation design, and some resins have peculiar smell) to replace composite internal printing inks. In addition to affecting the compounding strength, it is also easy to produce peculiar smell

3. Composite base materials

some composite base materials have certain peculiar smell due to excessive corona treatment and improper selection of additives, "The development of new material industry in Shandong Province is still in its infancy, so it should be carefully checked before use.

III. peculiar smell generated during composite processing (resin peculiar smell)

low impurity in resin processing is an important index to evaluate the thermal stability of resin. During extrusion and compounding, polyethylene, polypropylene and other resins extruded from the T-shaped die and the added White Masterbatch will give off resin odor due to oxidation at a high temperature of about 300 ℃. It is difficult to completely remove the resin impurities, but it is possible to reduce their production

(1) in order to reduce the odor, it is effective to reduce the processing temperature of the resin or shorten the distance from the T mold to the composite pressing roller if possible

(2) different types of resins have different odor. Polypropylene has a small odor, while polyethylene has a relatively large odor, while EVA is more likely to produce odor due to its poor thermal stability

(2. the load exceeds the maximum power (for example, the transmission mechanism of the hydraulic universal testing machine is faulty) 3) the odor of the same resin of different brands is also different. Careful comparison shall be made before use

IV. environmental pollution

plastic color printing composite substrates and products may be contaminated if the concentration of environmental organic solvents is high or there are strong odor stimuli such as pesticides nearby during processing, use and storage. When selecting the storage place, pay special attention to the concentration of organic solvents and keep away from strong odor stimulus sources

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