Packaging application of the hottest PVDC coating

2022-08-02
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Packaging application of PVDC coating film

I. Basic Introduction PVDC is a kind of high molecular material. PVDC used in packaging is vinylidene chloride copolymer. This high molecular material has very good gas (oxygen, nitrogen, carbon dioxide) barrier, moisture/humidity resistance, outstanding fragrance/odor protection and excellent oil resistance. The application of PVDC in food packaging originated in the 1930s. The 70 year application history has proved the superior performance of PVDC as a high barrier packaging material. Although EVOH and other high barrier packaging materials have come out in the 70 rooms, the authority and representativeness of PVDC as a high barrier packaging material have not been shaken due to obvious defects in the comprehensive performance of packaging. According to the statistics of American packaging materials, in 1984, the amount of PVDC used for packaging in the United States reached 74800 tons, of which 21800 tons were PVDC latex, accounting for 90% of the amount used for food and drug packaging. Therefore, it can be estimated that the amount of coating film is about 55000 tons. According to the statistics of the German packaging industry in 2001, the average annual growth of PVDC latex coating film in Europe has been 7% since the 1980s. Thus, by 2002, the output of PVDC latex coating film in Europe was 160000 tons. PCMC Corporation of the United States, the largest manufacturer of PVDC emulsion coating machines in the world, provided 180000 tons of coating machines worldwide from 1980 to 1997. In 1997, the annual consumption of PVDC emulsion coating film in Japan was 23900 tons, of which the BOPP coating film 1 manually controlled 9900 tons of two gauge rods, accounting for 8.23% of the BOPP consumption; 1000 tons of pet coating film, accounting for 2.63% of pet consumption; 3000 tons of nylon coated film, accounting for 9.07% of the output of nylon film. According to this law, the annual consumption of BOPP coating film in China should be 82300 tons. Generally speaking, any packaging material in normal use can be called "a barrier material", but the term "high barrier packaging material" generally accepted by everyone is limited to packaging materials that show high barrier performance to oxygen. The barrier polymer is very limited. Barrier polymers generally contain one of the following groups: hydroxyl (-oh), cyano (-c ≡ n), halogen (-cl or -f), ester group (-co-), amide group (-cnh-) O O in most cases, when the oxygen transmission of a packaging material is ≤ 10 cm3/a (23 ℃), it also has good barrier to nitrogen, carbon dioxide and many organic vapors and odors. At the same time, it also has good surface non absorption of odor and difficult migration of small molecules. Among the three recognized high barrier packaging materials including EVOH and PVA, PVDC is the only high barrier transparent material certified by FDA to be in contact with food. The following table shows the barrier data of the three materials. The relative humidity of the polymer and the oxygen transmittance cm3 μ M/a 23 ℃ oxygen permeability change water resistance (wet and damp) performance PVA 0% 0.039/very poor PVA 95% 97 increase 2487 times very poor EVOH (70%voh) 0% 0.066/very poor EVOH (70%voh) 95% 12 increase 182 times very poor nylon 60% 5.8/poor nylon 695% 19 3.3 times poor PVDC (90%vdc) 0% 0.97/very good PVDC (90%vdc) 95% 0.97 no change is very good. It can be seen from the table that considering the humidity resistance, Only PVDC has the best "comprehensive barrier". It should be mentioned that the development of China's flexible packaging industry is largely affected by Japan. PVDC coating film is called "K coating film" in Japan, so PVDC coating is also called "K coating film" in most parts of China. For example, PVDC coating BOPP, pet and nylon are respectively called Kop, kpet and K nylon

II. Typical packaging demonstration (I). Cake (PIE) packaging 1. Product characteristics: high fat, high moisture, high protein, strong flavor, sugar 2. Packaging purpose A. anti grease oxidation: the grease is easy to be oxidized by oxygen in the air, resulting in the rancidity of the fat. The rancidity of the fat will produce a throat pricking flavor, which seriously affects the quality of the cake. B. Stable water holding capacity: the cake will harden after losing water, which will affect the softness; Cake water absorption will increase the activity of water, which is conducive to the proliferation of mold; When the water content increases, the protein may be hydrolyzed, especially in the presence of oxygen, the protein will be hydrolyzed quickly, and the hydrolysate has a fishy smell. The change of moisture will cause the change of sugar form, which may lead to the change of cake shape; And it will produce wine taste under the action of saccharifying enzyme. C. Flavor: the flavor should be the inherent quality of food and should not be lost with the extension of storage period. It is necessary to keep the flavor. 3. It is recommended to use kop/cpp (PE) composite film and deoxidizer for packaging materials. Bopp/cpp or pet/cpp are not recommended. The analysis is as follows. 1)、 Barrier data base membrane barrier performance table kop22 kpet15 bopp20 pet12 cpp30 water permeability (g/m2.d) 3.559.0354.0 oxygen permeability (ml/m2.d) 1271200 110800 fragrance retention (after 48h) no fragrance leakage is better without obvious fragrance retention function leakage no fragrance retention function composite membrane barrier performance kop22/cpp30 KPE clockwise or counterclockwise adjusting clip t15/cpp20/cpp30 pet12/cpp30 water permeability (g/m2.d) 1.87 2.22 2.77 3.59 oxygen permeability (ml/m2.d) 11.8 6.9 48097 fragrance preservation (after 48h) No fragrance leakage is better than no obvious fragrance retention function leakage 2). Preliminary calculation (random sampling of commercial cakes) package size (two cakes inside); eighteen × six × 7=756 (ML), area: 552 cm2=0.0552 (M2) cake size: diameter: 6cm, height: 5cm, volume: 2*3.14/4*36*5=282 (ML) empty volume in the packaging bag: =474 (ML) there will be residual oxygen during packaging: 474*21%=100 (ML) 8-9 g of deoxidizer will be selected, The oxygen absorption capacity is 200 ml

calculation table of the time to maintain the anaerobic state in the packaging bag kop22/cpp30 kpet15/cpp bopp20/cpp30 pet12/cpp30 oxygen flow (ml/d) 0.0552*11.8 =0.65 0.0552*6.9 =0.38 0.0552*480 =26.5 0.0552*97 =5.35 anaerobic state time (d) ()/0.65 =153 ()/0.38 =263 ()/26.5 =3.7 ()/5.35 =18.73. Basic conclusions a and suggestions kpet15/cpp30 is used to pack the cake, which has a long shelf life (nearly 9 months), Moreover, the fragrance retention is the best, but the moisture resistance is slightly poor, but it is also better than other non PVDC coating films. Compared with kop22/cpp30, it is slightly worse, but it can also maintain an anaerobic state for 5 months, and the fragrance preservation is also good. B. It is also recommended to reduce the size of the packaging bag while keeping the volume of the cake unchanged, which can not only save the cost of packaging materials, but also improve the shelf life. In the above example, if the length, width and height of the packaging bag are all reduced by 1 cm, then the volume of the bag is only 510 ml. under the condition that the amount of deoxidizer remains unchanged, the shelf life of kop22/cpp30 packaging can be increased to 234 days (nearly 8 months shelf life), a net increase of nearly 3 months; The shelf life of kpet15/cpp30 can reach 400 days. (2) Fresh milk/yogurt packaging film 1. Overview: at present, there are three main types of fresh milk and yogurt packaging on the market, namely bottled, boxed (often called Tetra Pak) and bagged. The materials used for bagging mainly include three-layer coextrusion and five layer coextrusion PE film. The outermost layer of three-layer co extrusion is high-density PE with white titanium dioxide, the middle layer is adhesive, and the inner layer is high-density PE with black masterbatch. The outermost layer of the five layer coextrusion is high-density PE of white titanium dioxide. In the middle, some resins with oxygen resistance such as nylon or EVOH are arranged. The sub layers on both sides are adhesives, and the inner layer is high-density PE of white titanium dioxide. Five layer coextrusion has better oxygen resistance than three-layer coextrusion, so the packaged milk has a longer shelf life, but the price is much higher. The high barrier key development introduced here is based on the processing of thermoplastic polyimide (PI) engineering plastic resin, heteronaphthalene biphenyl polyethersulfone ketone copolymer resin (PPESK), high-end fluoroplastics, special fibers, filter materials, high-temperature functional films, high-performance resin based composites, high-temperature insulation materials, high-temperature functional coatings, high-temperature special adhesives. The fresh milk packaging film is not a five layer coextrusion film, It is to coat a layer of high barrier material PVDC high barrier coating film on the surface of the three-layer coextrusion film. The product produced by this process is to make the oxygen resistance of the three-layer coextrusion film reach the level of five layer coextrusion, and the cost of the material is between three and five layers, so it is an economic high barrier fresh milk packaging film. 2. Packaging and material characteristics: the main ingredients of fresh milk include fat (~3.7%), protein (~3.5%), lactose (~4.9%) and water (~87%). Some nutrients such as calcium and cellulose are often added during processing. The main factors affecting the deterioration of fresh milk are light, oxygen, temperature, carbon dioxide, milk volatilization and leakage. Light - in the process of processing and storage, light causes the loss of vitamins in milk, and photochemical reactions will take place in milk, which will also change the quality of milk and cause the decomposition of some nutritional characteristics. The use of black and white film structure may solve the problem of illumination. Oxygen -- oxygen will make the fat in milk sour and go bad, and the sour milk will give off a disgusting smell; Oxygen can also oxidize and deteriorate proteins, resulting in the qualitative change of finished products. Three layer co extrusion can not solve the problem of oxygen isolation. Only five layer co extrusion or three layer co extrusion/coating PVDC can overcome the problem of oxygen penetration. Temperature - temperature is conducive to the reproduction of bacteria. Low temperature storage is conducive to the preservation of fresh milk and yogurt. Carbon dioxide -- carbon dioxide has an important impact on the flavor change of fresh milk, especially yogurt, and the growth of microorganisms. Three layer coextrusion can not block carbon dioxide. Only five layer coextrusion or three layer coextrusion/coating PVDC can overcome the different gas permeability problems of carbon dioxide residual stress in terms of preservation degree, crystallinity, crystal particle size, etc. Volatilization and leakage of milk -- the volatile components in fresh milk and yogurt must be packed with barrier materials

three layer coextrusion, five layer coextrusion, three layer coextrusion/coating PVDC barrier comparison three layer coextrusion, five layer coextrusion, three layer coextrusion/pvdc oxygen transmission (cm3/m2.24h.0.1mpa) ~2000 2~3 2~5 carbon dioxide transmission (cm3/m2.24h.0.1mpa) ~12000~200 ~200

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