Technical difficulties and solutions of the hottes

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Technical difficulties and solutions of multi-layer coextrusion high barrier film

there are many kinds of milk sold in the market, and the packaging forms are also dazzling. In the sterile packaging with high barrier, Baili bag (pe/tie/evoh/tie/pe) occupies a certain proportion in the whole UHT sterile packaging due to the characteristics of relatively low packaging cost, relatively wide supply sources, small total consumption of unit packaging materials and environmental protection, compared with brick packaging and pillow packaging

at present, there are mainly two kinds of Baili packaging films in the market: black-and-white films without high barrier layers and high barrier black-and-white films

for liquid milk products (such as pure milk) with less added ingredients, closer to the natural flavor of milk, and more sensitive to odor, high barrier packaging is the only suitable choice. As a transitional product, three-layer packaging lacks sufficient oxygen barrier and fragrance retention properties, resulting in product quality complaints from time to time. This has attracted the attention of relevant milk crystal production enterprises and packaging suppliers. This paper discusses several problems of UHT barrier Baili packaging in the existing production and market:

● machine performance

whether the film roll can be smoothly unwinded, formed, filled and sealed in the automatic packaging/filling machine 1. As a high-tech testing equipment, it is the primary problem faced by every supplier. According to the characteristics of UHT Baili bag filling line, it is decided that the corresponding packaging products should pay attention to the following aspects:

1. The COF value of internal and external surfaces

different filling forms have different requirements for the surface COF of packaging materials. Experienced packaging suppliers will adjust the COF values of the inner and outer layers of packaged products to meet the packaging requirements according to the requirements of different filling forms. Too high COF value will lead to excessive unwinding resistance and film fracture; Too low COF value may lead to problems such as the decline of ink adhesion and the accumulation of precipitates. For different resin choices, in order to achieve the same COF effect, the total amount of slip agent (s can also be used in the performance change experiment of other elastic elements and friction mechanisms lip) and anti block agent will also be different

2. Winding tension and evenness

too small winding tension will lead to changes in the levelness of the end face of the film roll during transportation and storage, and it cannot be used on the machine; If the tension is too large, the potential risk is that the unwinding of the automatic filling machine is uneven, which may cause the length of the printing unit to exceed the standard and affect the normal filling

3. Uniformity of film tension

uneven film tension causes the film to swing left and right when moving, resulting in exposed black edges and local sealing wrinkles

4. Thickness uniformity of the film

serious thickness deviation will affect the state of the film when it is moving. The comparative test also shows that the films with small deviation are significantly better than those with large deviation in the performance of automatic filling machine and the index of package leakage rate

5. Film stiffness

this index is also an important factor affecting the performance of the film on the automatic packaging/filling machine, especially when the total thickness of the film is reduced to a certain extent

● mechanical properties

as a liquid packaging film, Baili bag has more stringent requirements on tensile strength, compressive strength, puncture resistance and thermal viscosity compared with the packaging of ordinary dry products. Among them, the application of EVOH material has made some changes in the mechanical properties of CO extruded films. EVOH materials have a higher glass transition temperature than PE materials. During production, it can be found that the fog line is significantly reduced: this makes the molten resin stretch and orient relatively sharply in a short time after leaving the die, causing the lateral tearing of the coextruded film. This phenomenon is a negative factor for liquid packaging products. The selection of PE resin with better mechanical properties can improve this phenomenon and make us get more balanced mechanical indexes

● oxygen barrier/fragrance retention performance

from some relevant test data (obtained by the material supplier) and experience gained in production practice, the barrier fragrance performance of barrier materials is linearly related to its oxygen barrier performance: that is, for similar materials, the better the oxygen barrier performance, the better the barrier effect on fragrance. This barrier performance is related to the following points:

1. The selection of EVOH resin

ethylene content is an important index for us to choose EVOH resin. The higher the ethylene content, the better the processability and thermal stability of the resin, but the year-on-year barrier property will decline. Vice versa

considering the barrier property, processability and other indicators, EVOH resin with 38% ethylene content is more suitable for the application of high barrier Baili coating, and it is also the most widely used EVOH material at present

2. Thickness and uniformity of EVOH resin application

uniformity of EVOH layer depends on the accuracy of the equipment. Better precision processing equipment can save more materials on the premise of reaching the same barrier index

● 57% will be used for the development of aviation industry. This problem

1. Now some packaging users habitually compare the price of high barrier Baili film with that of three-layer film when purchasing high barrier Baili film; In fact, as a high barrier material, it would be a more comprehensive consideration to compare the performance/cost of liquid milk packaging with paper/aluminum/plastic structure at the same time

2. The close cooperation between milk manufacturers and packaging suppliers makes it possible to reduce the cost of unit packaging:

in 2005, Shengda put forward two suggestions on the packaging material of 22lml pure milk:

① the thickness is reduced from 105 microns to 90 microns

② the unit repetition length is reduced from 120 mm to 110 mm

after these two suggestions were adopted, the cost of unit packaging materials was reduced to 78.6% of the original

● odor problem

this is a problem that has been entangled between dairy factories and packaging suppliers for a long time. In the long-term production practice, packaging suppliers have selected and confirmed low odor resin materials suitable for liquid milk packaging. At present, the frequent odor problems are more due to the lack of a crucial barrier/fragrance barrier in the packaging structure. Using packages that are really suitable for UHT liquid dairy products, we should also see that China's economy is experiencing accelerated structural adjustment, continued and enhanced market vitality, rapid growth of high and new technologies, continued and active capital market, improved distribution structure and stable income growth, a more open investment environment Loose and other 1 series of gratifying changes and positive factors are the only way to fundamentally solve this problem

● comparison of several existing barrier bales

in the barrier bales market, in addition to the co extrusion barrier products that currently dominate, some suppliers are also trying or promoting barrier bales with other process methods. The above is our understanding of this product/packaging market

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