Research and development of the hottest high barri

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Research and development of high barrier polyester film

since the British Imperial Chemical Company (i.c.i) and the American DuPont company (DuPont) developed the polyester film in 1948 and realized the industrial production of biaxially stretched polyester film (BOPET) in 1953, biaxially stretched polyester film has been widely used in electronics, electrical appliances, magnetic recording It is widely used in the fields of packaging, decoration, printing plate making and photosensitive materials. With the rapid development of China's plastic packaging products industry, merchants' requirements for the grade of product outer packaging are increasing. BOPET thin film can realize monitoring and operation, which has been widely used in China, and the production capacity and consumption are increasing year by year. From 2002 to 2005, the production capacity of BOPET film in China is shown in Table 1

it can be seen from table 1 that the development speed of China's BOPET film is quite fast. It is estimated that by the end of 2005, the production capacity of China's BOPET film will exceed 560000 tons, exceeding the consumption capacity of the domestic market, which may form a market pattern of supply exceeding demand. In order to occupy a larger share in the limited market space, on the basis of improving the quality of conventional polyester film, film manufacturers have committed to developing some functional polyester films with higher high-tech content and higher added value, such as Matt Film, anti-counterfeiting film, heat sealing film, high barrier film, etc. among them, high barrier polyester film is favored by the majority of food packaging users for its low cost and high performance. Here, the author briefly introduces the application and research and development of high barrier polyester film in China

ways to improve the barrier property of polyester materials

in the field of food packaging, it is required that the outer packaging materials must have high barrier properties to oxygen, carbon dioxide and water, so as to extend the shelf life of food. At present, the barrier property of ordinary polyester film widely used in the field of food packaging to gas is not very ideal. Therefore, many flexible packaging manufacturers use films with excellent barrier properties (nylon, polyvinyl alcohol, polyvinylidene chloride, etc.) to compound with polyester film, such as three-layer, five layer or even seven layer multilayer composite films commonly used in the market at present. Although the purpose of improving the barrier of packaging can be achieved through composite methods, it will virtually increase the packaging cost of food manufacturers, and it does not meet the national requirements for environmental protection packaging. Therefore, food manufacturers urgently need an economic and practical high barrier packaging material that can meet the barrier requirements of food packaging without increasing the packaging cost

BOPET film is a kind of packaging material with strong comprehensive advantages. How to further improve its barrier performance and better meet the needs of users is a common concern of many film manufacturers. At present, the methods to improve the barrier property of polyester film mainly include copolymerization modification, blending modification, surface coating modification and nanocomposite modification

1. Copolymerization modification

in order to improve the barrier property of polyester film, diols, dicarboxylic acids or NDC (dimethyl 2,6-naphthalene dicarboxylate) are usually used as copolymerization carriers to copolymerize and modify polyester. Recently, the copolyester b010 developed by Mitsui Petrochemical Company of Japan is polymerized from terephthalic acid, isophthalic acid, ethylene glycol and a special glycol, which is an amorphous polymer. When it is blended with 20% polyester, the blend can be shaped and processed under the same conditions as polyester, and its gas barrier performance is better than polyester. Amoco company of the United States has introduced a transparent copolyester amosorb3000 containing stable oxygen bonds. Beer bottles made of this copolyester can not only block the oxygen passing through the container wall, but also eliminate the oxygen sealed in the upper part of the container during production

2. Blending modification

add other substances (such as LCP, max6, pen, nano/inorganic particles, etc.) to polyester for blending modification. At present, modified polyester has entered the market. The detailed operation of changing the torque indication of the experimental machine with the blending modified spring is as follows: the film products made of polyester whose lower limit of measurement is after the starting point of verification not only have significantly improved gas barrier performance, but also have improved heat resistance and UV resistance. In addition, foreign countries are studying the blending of polyester, liquid crystal polymer (LCP) and polyethylene naphthalate (pen) to produce thinner and better barrier packaging containers. Liquid crystal polymer has excellent barrier property. In the blend of polyester and liquid crystal polymer, the liquid crystal polymer particles are biaxially stretched to form a molecular structure similar to a sheet, which is staggered in parallel, which can effectively prevent gas penetration. However, using blending method to improve the barrier property of polyester will generally affect the transparency of the resin. Therefore, blending method is not suitable for packaging materials that require high transparency

3. Surface coating modification

surface coating method is an economic and practical method to improve the barrier property of polyester. PPG company successfully developed the gas barrier coating technology for polyester bottles. The coating is composed of two-component epoxy amine, which has excellent toughness and moisture resistance, and can be removed during recycling. The coating thickness of 0.5L polyester bottle is 4 ~ 19 μ m. The barrier performance to oxygen will be improved by 2 ~ 12 times, and will not affect the transparency of the polyester bottle, but also improve the gloss of the bottle. In addition, the hard carbon film coating (DIC) application technology developed by Japan Nissei ASB Machinery Co., Ltd., the amorphous carbon treatment technology on the inner surface of acticl developed by French side company, the glaskin process and sealica process developed by Swiss tetrap AK company, and the new technology of coating 20nm thick SiOx coating on the inner surface of polyester beer bottles developed by Tetra Pak company can be used for the packaging of oxygen sensitive foods, such as ketchup, jam and beer

4. Nanocomposite modification

since the 1990s, nanocomposite modification has become the main way to prepare advanced packaging materials. For example, the nanocomposite packaging material based on polyester, jointly developed by Eastman Chemical Company and nanocor company in the United States in recent years, has greatly improved the barrier and heat resistance of the material, and is more suitable for beverage packaging. The Institute of chemistry of the Chinese Academy of Sciences and Yanshan Petrochemical Company have cooperated to explore and study PET/MMT nanocomposites and their applications. Translucent beer bottles have been made, with barrier properties 3 to 4 times higher than ordinary polyester bottles, and heat resistance has also been improved, with promising application prospects

development example of high barrier polyester film

the penetration of gas in polyester film mainly includes three processes: adsorption, dissolution and diffusion. In order to improve the barrier performance of polyester film, we must also start from these three aspects

Xu Dianli, executive vice president and senior engineer of China Refractory Industry Association in Shandong polyester packaging materials engineering technology, said that Xin successfully added an inorganic powder to polyester resin through in-situ polymerization. In the polymerization process, the inorganic powder forms a layered structure with nano scale, and forms mutually parallel orientations in the stretching process of the film. Because the permeability of this layered structure to the gas is very low, the gas can only "bypass", which virtually increases the "diffusion stroke" of the gas in the film, thereby improving the barrier performance of the film. At the same time, due to the nano-sized dispersion of inorganic powder in polyester resin, the transparency of film products will not be affected within a certain content range

polyester can be synthesized by either transesterification (DMT) or esterification (PTA). The key lies in the organic treatment of inorganic powder and the process control of in-situ polymerization. The following takes the DMT method as an example

due to the weak adhesion between the inorganic powder and the polyester matrix, the film is easy to break during the stretching process, affecting the stability of production. Therefore, it is necessary to treat the inorganic powder organically. The inorganic powder is treated with the corresponding organic treatment agent, the carboxyl group is introduced on its surface, and the inorganic powder is combined with the polyester matrix by chemical bond through polymerization, so as to improve the binding force between them

disperse the organically treated inorganic powder in an appropriate amount of ethylene glycol, stir at room temperature for 12 hours, and wait for use. Dimethyl terephthalate (DMT) and ethylene glycol (eg) are put into the reactor in a metered proportion, and transesterification is carried out at 180 ~ 220 ℃. The end point of the reaction is judged according to the amount of methanol distillation. After the transesterification, the material is introduced into the polycondensation kettle, and the ethylene glycol dispersion of inorganic powder is added at the same time. The polycondensation reaction is carried out under the conditions of 260 ~ 280 ℃ and 60Pa. The motor power is used as the basis for judging the molecular weight of the discharge, and the characteristic viscosity is controlled above 0.65

polyester resins with different powder contents prepared according to the above process are made into polyester film by biaxial stretching. The oxygen transmission is tested as shown in Table 2. It can be seen from table 2 that the addition of inorganic powder plays a certain role in improving the barrier property of polyester film. The larger the axial tension, the pilot test of this high barrier polyester film has been completed. If the product is successfully mass produced, it will fill the gap of such products in China and raise the level of domestic food packaging to a new level

Author: Bai Yongping, Department of Applied Chemistry, Harbin Institute of technology, Zeng Ke

sun Wenxun, Shandong Fuwei Plastic Co., Ltd.

reprinted from: Printing Technology

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