What exactly is the source of film odor?

The odor in the film mainly comes from these parts: various additives of the resin itself and its own low molecular substances; Odor generated during film processing; Odor during soft packaging processing; Odor produced during storage.

1、 Influence of resin itself

1. The film is generally made of high molecular weight resin. The resin is composed of molecules of different sizes. The molecular weight distribution of different resins is different, and the content of low molecules is also different. Low molecular substances are easy to be oxidized and volatilized during extrusion processing, resulting in odor.

2. The resin synthesis process is divided into the solution method and the meteorological method. The two different synthesis methods have different odors: the solution method is better than the meteorological method in theory because many low molecular substances are removed after the solution is removed after synthesis.

3. A lot of additives should be added to the resin to improve its performance. These additives are the biggest source of taste: the smoothing agent is generally an acylamine compound with a sweet taste. Antistatic agents have a very pungent taste, and cannot be used in low odor packaging. The opening agent is generally inorganic, usually calcium carbonate and silicon dioxide.

But as far as the opening effect is concerned, silica is far better than calcium carbonate. But calcium carbonate is better than silica in taste. Antioxidants are usually phenols, which also have a certain taste. In general, the linear molecule must be added with antioxidant because of the problem of catalyst residue.

Color masterbatch: commonly used white masterbatch will generally add some wax and stearate as dispersant and lubricant. These low-molecular-weight substances will precipitate during processing and have a strong taste, so they should be placed in the middle layer as much as possible in multi-layer co extrusion.

2、 Influence of film processing technology

Generally speaking, the higher the processing temperature is, the higher the odor will be. Because the low molecular substances in the resin will volatilize more easily in the high-temperature processing environment. A small amount of carbonic acid, aldehydes and other substances produced by high-temperature oxidation will cause a strong smell. Therefore, in theory, tape casting will have a higher flavor than film blowing. Equipment with internal cooling must be better than equipment without internal cooling. The taste of water cooling will be the lowest.

3、 Influence of Flexible Packaging Processing Process

Without considering the influence of the film taste, the ink, adhesive, solvent and printing compound process control in the flexible packaging process also have a great influence on the film taste.

1. Printing inks can be divided into benzene and benzene free inks. Benzene free inks can also be divided into polyurethane and alcohol soluble inks. Different substrates use different inks. Each series of inks has different flavors due to different resins and pigments. Therefore, it is particularly important to choose the ink with low taste and good solvent release effect in soft packaging processing.

2. In the composite processing, we usually use two-component solvent based polyurethane adhesive, two-component solvent based aliphatic adhesive and two-component solvent-free polyurethane adhesive. In order to ensure the different performance requirements of packaging bags, we have a lot of knowledge in the selection of adhesives. The adhesives of various brands have strong functionality and different performance, Therefore, we should consider both the influence of the adhesive itself on the film taste and whether the composite interlayer strength meets the customer's requirements.

3. In the evaluation of the odor of the film, we found that if the solvent used to dilute the ink and adhesive is not sufficiently volatilized during the printing and laminating process, too much solvent will be left between the composite film layers. These solvents will slowly migrate and gradually contact the contents, which will change the taste of the food. Therefore, it is very important to set reasonable process parameters and carry out effective online control.

In addition, with the rapid development of the industry in recent years, solvent-free coating technology has been widely used, which can effectively avoid the risk of solvent residues, and should be said to be a good choice for composite processing.

4、 Storage conditions

The resin and finished products shall be placed away from the odor source. If placed in an odorous environment for a long time, irritant molecules will adsorb on the surface and cause some special taste. The same is true in transit. The storage temperature should be lower than 35 ℃, otherwise the low molecular substances will migrate out quickly, causing the taste to increase. The ambient temperature in the processing workshop should not be too high, otherwise, low molecular substances will be precipitated in the production process.

In a word, if you want to achieve the goal of low odor, you should first consider the selected resin in the design formula of the film. All kinds of additives in the formula should be as few as possible, and the processing temperature should be as low as possible. It is best to use equipment with internal cooling or downblowing water cooling process for production. Only in this way can the soft package factory obtain the film with low taste and customer satisfaction.