The structural design of the packaging material must fully meet the protective requirements of the content without excessive functions, so as to achieve the most economical packaging cost. Different content properties and different post-processing methods require that the packaging materials also have corresponding functional properties. The following is a brief overview.
1. The form and weight of the contents
For bulky objects, the puncture resistance of the packaging material to some bulky hard objects should be considered, such as trotters, chicken feet, peanuts and other packaging.
For powdery objects, due to the electrostatic dust suction effect, the heat sealing part absorbs the powder and affects the reliability of the bag sealing. It should be considered to improve the antistatic property of the film. Generally, add 0.1 to the thermal cover of the three-layer coextrusion heat sealing film ~ 3% antistatic agent masterbatch.
The liquid has a great influence on the sealing integrity when filling and packaging, and the same packaging material has different sealing pollution resistance to different sealing contaminants. For example, the heat sealing strength of K-OPP20 // PE empty bags is 32.5N / 15mm , The sealing strength for inclusions in 10% brine is 12.5 N / 15mm (heat sealing condition: sealed in 30ml, 150 ℃ -0.1MPa-1s, the same below), the sealing strength for vinegar inclusions is 18.0N / 15mm The sealing strength for inclusions in soy sauce was 10.0 N / 15mm, and the sealing strength for inclusions in milk was 4.0 N / 15mm. Generally, a certain proportion of mLLDPE is added to the heat-seal layer of the co-extruded heat-seal film to improve the heat-seal resistance of the film to inclusions.
The shape of the contents is also an important factor that affects the drop resistance of the packaging bag. The better the fluidity of the object with the same weight, the greater the impact force on the seal of the packaging bag when it is dropped, and the more likely it is that the bag will break and fall. It is necessary to choose packaging materials with high heat seal strength and good toughness.
The weight and shape of the content directly affect the drop resistance of the packaging bag during the circulation process. Therefore, the same content and different weights require different packaging materials. For example, for washing powder bags, the BOPP // PE structure is generally used when it is less than 800g, the PET // PE structure is mostly used for about 1kg, and the PA // PE structure is mostly used for more than 1.7kg.
2. The nature of the content
For the packaging of photosensitive articles or articles containing photosensitive components, the shading requirements of the packaging materials need to be considered. For example, some boiled bamboo shoot bags use the KNY // PE structure, which can reduce the ultraviolet response (yellowing) of boiled bamboo shoots.
Grease is easily oxidized and deteriorated, and at the same time, liquid grease may penetrate the front of the packaging material. BOPA material with good oil resistance and oil permeability resistance should be selected as the barrier layer. The oil resistance of PE is not as good as that of CPP, but the pollution resistance of CPP to oil seal is far inferior to that of PE film modified with mLLDPE blend, which needs to be weighed and selected according to the specific packaging requirements.
For contents containing acid and alkali components, focus on the corrosion resistance of packaging materials and adhesives to avoid delamination caused by the migration of these corrosive components to the interface of the adhesive layer and aluminum foil layer of the composite film through the inner layer material. For example, in a PET // AL // RCPP structured marinated beef packaging bag, after opening the packaging bag, it was found that the AL // RCPP layer that directly contacts the beef has delaminated, while the peel strength of other parts is very good ( As shown in Figure 2-1).
Figure 2-1 Partial delamination of marinated beef packaging bags
Solvent components have a strong swelling effect on polymers, especially liquid pesticides containing mixed solvent components. At present, there is no adhesive that can fully meet the packaging requirements in this regard. If necessary, accelerated testing is required to confirm the packaging The adaptability of the bag to the packaging of specific ingredients.
3. Packing method
Vacuum packaging is a common packaging method, which requires that the packaging material has a good gas barrier capacity and a certain edge sealing width (to reduce the influence of side penetration). The three-side sealing bag shape is used instead of the back sealing bag shape. . It should be pointed out that vacuum packaging can effectively inhibit the deterioration caused by aerobic bacteria. For the deterioration caused by anaerobic bacteria, it is necessary to cooperate with an appropriate sterilization process to extend the shelf life.
Inflatable packaging is often used for contents that are not suitable for vacuum packaging, such as biscuits, potato chips and other easily crushable items. Inflatable packaging also requires that the packaging material has a certain gas barrier capacity, and at the same time requires that the packaging bag has good airtightness and sealing strength. For example, the commercially available potato chip inflatable packaging bags are all sealed with teeth to enhance the airtightness of the packaging bag .
Barrier packaging A certain amount of deoxidizer and moisture-proof agent is enclosed in the packaging bag. It is a relatively mature quality-preserving packaging method, which requires the packaging material to have the corresponding barrier capacity. It is worth mentioning that some people think that the use of high-barrier materials on the front of the packaging material is high-barrier packaging, but it is not. For example, the folded back-sealed bag shape enhances the display effect, but ignores the overall tightness of the packaging bag. In this way, it is easy to form small holes connecting the inside and outside at the overlap of the multi-layer composite film, which makes the moisture-proof and deoxidizing packaging have a high quality retention discount.
Some packaging bags only fill more air when they are sealed, but only make the packaging bags bulge to enhance the display. At this time, the packaging bags are also required to have good airtightness.
4. Sterilization method
Heating sterilization using water as a medium is currently divided into boiling, semi-high temperature cooking, and high temperature cooking. The selected packaging materials, inks, and adhesives must meet the corresponding sterilization and cooking conditions. RCPP is generally used for the inner layer of cooking packaging, but RCPP material has the disadvantage of poor drop resistance for liquid packaging. At this time, you can choose cooking grade RPE, but the transparency is slightly reduced.
The sterilization methods of packaging bags include heating sterilization, microwave sterilization, radiation sterilization, ultra-low temperature sterilization, etc. Different sterilization methods have different performance requirements for packaging materials, and the packaging materials must meet the corresponding sterilization Claim.
5. Circulation conditions
The circulation environment of food packaging is generally divided into normal temperature, cold storage, freezing, etc. At low temperatures, attention should be paid to the low temperature resistance of packaging materials. For example, ordinary CPP is not suitable for use below 0 ℃, LDPE film can be further improved by blending modification Low temperature resistance.
Due to the vast territory of China and the large regional environmental differences, the design of packaging materials must fully consider these differences. For example, the same is the inflatable packaging, the inflation volume of the packaging bags sold to the plateau and coastal areas is different.
6. Packaging machinery
Automatic packaging machines are divided into vertical and horizontal types. The vertical packaging machine has higher requirements on the thermal adhesive strength of the packaging materials when filling. The hot tack strength refers to the sealing strength of the packaging material when it is not cooled after being sealed, and its value is much lower than the sealing strength detected at normal temperature.
The friction coefficient of the packaging material affects the performance of the machine during automatic packaging and the accuracy of product positioning. Generally, the vertical packaging machine requires that the coefficient of friction of the packaging material (the coefficient of friction between the hot cover and the steel plate) is smaller, while the coefficient of friction of the horizontal packaging material (the coefficient of friction between the hot cover and the contents) is slightly larger. In addition, automatic packaging also has certain requirements for the friction between the surface of the packaging material and the steel roller. Generally, the requirements are too large, and too small will cause the material to deviate.
For products shipped in packaging bags, the sealing strength, opening and resistance to sealing pollution are generally required.
The above requirements are only the basic information that needs to be considered for the packaging material structure design and process design. The actual application is much more complicated. Different contents, different post-processing methods, different circulation conditions, etc., have different requirements for the performance of packaging materials, and inks. The requirements for adhesives are also different, and the packaging materials need to be designed differently according to different functional requirements.