Research on Modern Packaging Mechanics (2)

2.3 Packaging Materials

Packaging material refers to the general name of the materials used to make packaging containers and constitute product packaging. Its types include wood, paper and board, glass, ceramics, metals, plastics, fiber fabrics, composite materials, and adhesives such as coating. Materials and other auxiliary packaging materials, including paper and cardboard, plastics, metal, and glass have become the four major material pillars of the packaging industry.

Packaging materials studies the types, properties, applications, and processing processes of various raw materials used for packaging. In the process of researching, developing and processing packaging materials, there are many complex and profound mechanical problems. For example, during the process of biaxially stretched plastic film, the choice of stretching process, heat setting and temperature, two-way tension, and tension speed have a decisive influence on the mechanical properties, barrier properties, and transparency of the film.

The mechanics problems in the processing technology of various types of packaging materials can be found in the materials science books. Details are not included here.

Buffer packaging materials are the most widely used type of materials in packaging materials, mainly foamed plastic, corrugated cardboard, honeycomb paperboard, molded products, bubble film, fiber, crumb materials, rubber and so on. This kind of material is mainly used for transport packaging. The buffering property is its most important performance. On the one hand, it weakens the response of the product to the external stimulus, and on the other hand it dissipates the energy of the external stimulus. The most classic method of characterizing the cushioning properties of materials is the use of static or dynamic material constitutive relations. In 1952 Jansen proposed the concept of cushioning factor based on deformation energy to characterize the performance of cushioning packaging materials, and later expanded to the concept of dynamic cushioning coefficient. In 1961 Franklin and Hatae proposed the maximum acceleration-static stress curve. Buffering factor has important application in the buffer packaging design, but to test these curves, the test workload is very huge. McDaniel and Oykide, Cost first took a theoretical analysis of the performance of cushioning packaging materials. Hu Qiang et al. proposed a 29-parameter nonlinear viscoelastic model for foamed plastic liners. Gao De consider temperature, multiple shocks, layers, deformations. Factors such as type, put forward the theoretical model of corrugated board buffer, and carried out parameter identification. Liang Yanchun applied the structured neural network method, fuzzy adaptive control technology and evolutionary computation to the problem of three-dimensional nonlinear and hyperbolic tangent nonlinear cushioning material model recognition, and obtained better nonlinear characteristics.

In the past, cushioning materials have been mainly foam plastics. With the development of environmental protection requirements, a number of environmentally friendly cushioning materials have been widely used in product packaging, such as plant fiber materials, honeycomb paperboard, multi-layer corrugated cardboard and pulp molded products, etc. . The research and development of this new type of buffer material and the characterization of buffering characteristics are becoming the focus areas of packaging mechanics research.

2.4 Packaging Container

Packaging containers can be divided into various types of cartons, corrugated boxes, plastic containers, glass containers, metal containers and wooden containers. Because of its outstanding advantages such as light weight, low cost, easy to process printing, easy to fold, and pollution-free, corrugated cartons have become the most important transport packaging containers. They are widely used in food, beverages, fruits, household appliances, daily necessities, glass and Ceramic products and other packaging. Corrugated box compressive performance is an important indicator for evaluating corrugated boxes. Experimental studies have shown that the compressive strength of corrugated boxes has a complex relationship with carton perimeter, aspect ratio, height, base paper crush strength, corrugated type, type of corrugated board, stacking time, temperature and humidity, etc. Hole location, printing area, manufacturing technology, etc. are also relevant. There are many empirical formulas for the compressive strength of corrugated boxes obtained from the test summary, such as Kellicutt's formula, Maltenfort's formula, Wolf's formula, Makee's formula, APM's calculation methods, etc. Among them, Kellicutt's formula is most valued by people. There is still a big gap between the calculation results and the actual measurement based on these formulas. There is no theoretical formula to predict the compressive strength of the carton. Glass jars are another type of widely used packaging containers. The predecessors have conducted extensive experimental studies on the factors affecting the structural strength of glass bottles and cans (tensile strength, internal pressure strength, thermal shock strength, mechanical impact strength, inverted strength, vertical load strength, water impact strength, drop strength, etc.). And theoretical analysis. We know that bottle weight, large, and easy to break are the fate and weakness of glass jars. Reducing the wall thickness, reducing the weight of bottles, and increasing the strength are the most important technological reforms in the current production of glass containers, and they are the main topics for the development and production of modern lightweight bottles. In order to increase the strength of glass jars and prevent glass jars from reducing their strength due to scratches on the surface, on the one hand, glass jars must have the correct design, and on the other hand, the surface of the jars should be reinforced. Although there are many kinds of surface enhancement methods for glass jars at present, the research on such microscopic mechanical mechanics is almost blank.

Plastic bottles are widely used in liquid foods and pharmaceutical packaging due to their excellent performance, and they have a tendency to replace ordinary glass bottles. At present, the types of plastic bottles used in packaging are PE, PP, PVC, PET, PS and PC. By improving the material and bottle forming process to improve its barrier properties, it is the development direction of the plastic bottle to improve the strength and airtightness of the bottle and reduce the weight of the bottle by increasing the stretching ratio.

The finite element simulation technology applied to the bottle forming process has a very important role in improving the design and manufacturing level of plastic bottles, and improving process parameters and processes.

2.5 buffer packaging design method

Buffered packaging design refers to the use of buffer packaging theory to design shock-absorbing buffer structures based on product fragility, transportation environment conditions, and characteristics of cushioning materials. The five-step and six-step buffer packaging designs proposed in the 1980s are still widely used today. A method is a fixed value design category. In fact, the circulation environment conditions, product fragility, cushioning material properties, cushioning structure geometric parameters, etc. all have random features. The ability to describe the buffer packaging to protect products with probability is more scientific and more reasonable. To this end, in 1977, after introducing concepts such as buffer packaging failure probability, reliability index, and state function, Wang Zhiwei proposed a buffer packaging probability design method based on the probability theory, and proposed the concept of optimal buffer packaging for the most economical and most The moderate buffer package design provides a theoretical basis]. Wu Weihan and others discussed the reliability of packaging in the logistics process. Modern computing technology and computer technology have broad prospects for buffer packaging design. Using computers, we can perform numerical analysis and simulation experiments on the buffer packaging system to integrate the buffer packaging design, analysis, and optimization. At present, there is not much work in this area at home and abroad, and a large amount of literature still only stays in the computer-aided design of packaging containers.

In summary, packaging mechanics is an important sub-discipline of packaging engineering disciplines. After decades of development, the scope of its research has continued to expand, and the content of research has continued to deepen. Now it has initially formed its own unique system, which mainly studies The following aspects.

(1) The environmental conditions of the packaging. To investigate, test, evaluate, describe and standardize the environmental conditions (including transportation conditions, climatic conditions, biochemical conditions, etc.) that may be encountered in the basic aspects of the handling, transportation, storage, etc. of the package;

(2) The theoretical basis of packaging dynamics. Establish dynamic models for various packaging systems and develop various numerical methods and related theories;

(3) Brittleness and its evaluation methods. Theoretical and experimental studies on the methods for determining the fragility of various packaging products under different environmental excitations and the theory of boundary damage;

(4) Mechanical properties of packaging materials. Theoretical and experimental studies of static and dynamic characteristics and constitutive relations of various types of packaging materials, development of characterization methods and experimental techniques for buffering properties of buffer materials;

(5) Various types of transport packaging containers. Study the structural strength of transport packaging containers and related mechanical issues in the manufacturing process;

(6) Cushion packaging design. Research on buffer packaging design methods and development of product buffer packaging design, analysis, and optimization integration technologies.

3 Conclusion

The packaging industry is developing from traditional to modern industry. The emergence of new packaging materials, technologies and equipment has enriched the research content of modern packaging mechanics. The development of modern mechanics has also provided the conditions for solving related mechanical problems in packaging engineering. In general, the development of modern packaging mechanics is not long, the research field needs to be further expanded, and the research content needs to be further deepened. The application of modern computing technology, analytical technology, and experimental technology in packaging engineering is still in its infancy. The modernization of China's packaging industry requires the participation of the discipline of mechanics, and it also provides a broader world for the development of the discipline of mechanics. It is hoped that more mechanics workers will be involved in the research of related fields and make due contributions to the rapid development of China's packaging industry.