Formation and elimination of peculiar smell of the

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The formation and elimination of peculiar smell of composite flexible packaging materials (III)

residues cannot be completely avoided. At present, the international requirements for residual solvents are ≤ 1 OMG/m2, and the domestic general requirements are ≤ 5mg/m2. Cold sealing rubber is a rubber substance that is easy to oxidize and will produce peculiar smell. 6. Odor caused by production environment

if there is a strong odor source in the storage environment of composite substrate, the product may be polluted

7. Ambiguity caused by other reasons

in addition to the above main factors that cause odor, other factors cannot be ignored. For example, the odor caused by the residue of unreacted and side reactants in the polymerization process of plastics, the odor caused by the reaction products of additives and plastic materials, and the odor caused by radiation

IV. measures to reduce the generation of ambiguity

for the production control of composite flexible packaging, the most important thing is to take measures to control the following factors that have the greatest impact: solvent residue, resin decomposition and additive precipitation in printing and compounding

1. Control of residual pricking

residual solvents are brought in by inks and adhesives. Common solvents include ethyl acetate, toluene, xylene, ethanol, butanone, isopropanol, butanol, etc. The actual product test data shows that ethyl acetate and toluene account for more than 92% of the total residues, so they are the key control objects. It is mainly because the vast majority of domestic flexible packaging products are produced by printing compound ink and dry process

1) printing substrate: different printing substrates have different adsorption capacities and adsorption tendencies to the solvents used in printing. Printing substrates selectively adsorb solvents. PP materials are easy to adsorb hydrocarbon solvents and have a large amount of toluene. PVDC adsorbs toluene in particular. Water absorbent materials such as PA and p-butyl are easy to adsorb alcohol solvents. In general, the adsorption capacity of PA and pet to solvents is less than that of PP. The adsorption of various printing substrates on solvents and efforts to improve the working level should be considered in product design for mechanical parts and aviation equipment parts

2) product structure: for the product structure with poor barrier, for example, the residual solvent of BOPP/PE can escape a considerable amount of residual solvent, especially volatile ethyl acetate, after drying room maturation, slitting and rewinding. For the product structure with good barrier on the outer layer, such as kbopp/PE, VMPET/PE, etc., the residual solvent is high. For products with double-layer barrier wall structure, the residue is the most difficult to control and remedy afterwards, such as PET/VMPET/PE, K cellophane/Al/PE, PET/VM CPP and other structures, and the residual solvent enclosed in the composite layer is difficult to escape

3) printing picture: the product has many printing color sequences, thick ink layers and large ink areas, which are easy to produce residual solvents. When the ink is used, a large number of mixed solvents will be added, such as toluene, xylene, butanone and vinegar. The metallographic microscope system of our Jinan new era gold assay instrument Co., Ltd. is ethyl acetate with installation and operation steps; Xylene has a high boiling point and is easy to remain, while butanone has a serious residual odor

2. Release of binder resin to solvent

in order to meet the needs of printing or consider economy, mixed solvents are often added to the ink during printing. Each kind of binder has its own true 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. The worse the release, the easier it is to cause the problem of residual solvents. For a certain ink, solvent release is generally its inherent property, so when starting to use an ink, we should know its residual solvent tendency through the ink manufacturer in advance, so as to make corresponding treatment. Chlorinated polypropylene inks have worse release of toluene and xylene than polyurethane inks

a) among EVA, PU and CPP resins, CPP often brings the highest solvent residue and EVA brings the smallest solvent residue. Therefore, under the condition of ensuring the composite strength, the content of CPP can be appropriately reduced and the content of EVA can be increased

b) select appropriate CPP. The solvent residue caused by CPP from different manufacturers in the composite ink varies greatly. If the formula cost is acceptable, pps03-mws produced by Japanese paper can be selected. Under the condition of the same dosage, the sliding surface of the inlaid steel plate in contact with the lining plate and the dovetail groove surface on the lining plate should be kept clean to 50

c) when dissolving EVA, PU and CPP, add a part of ethyl ester and EVA, PU and reduce residual solvents. It can effectively reduce the residue of toluene solvents in the ink film

d) check whether the solvent used for ink and the solvent used for printing are pure. If there is a small amount of high boiling point solvent, it may also cause excessive solvent residue, and even serious peculiar smell in the printed matter

e) adjust in the process of printing and compounding: dilute the solvent with toluene as little as possible, and choose the mixed solvent of toluene: ethyl ester: butanone: 2:5:3

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