Development of PVDC composite membrane
BY：Industry news
CLICK：563
POST：2021-05-31
We have been studying the PVDC plastic processing technology since 1993. After fully digesting and absorbing PVDC processing technology and understanding the development trend of food packaging at home and abroad, we have been working on the research of PVDC laminated composite film since 1997. In the development process, the biggest difficulty we encountered is that the shrinkage of PVDC is too large to be compounded.
We know that as a composite substrate, it is necessary to ensure its dimensional stability to ensure the appearance flatness of composite film after composite. Because of its own characteristics and processing technology, PVDC has a high shrinkage rate of hot water at 100 ℃ and can not guarantee the normal composite and composite effect. We improve the resin formulation and control the production process, so that the shrinkage rate of resin can be reduced to a certain extent. If the conventional dry composite process is used, PVDC film must pass through 60-80 ℃ long drying path. In this case, it will still shrink greatly (see Fig. 1), but the composite film with stable size and flat surface can not be obtained. Therefore, we adopt solvent-free composite process and composite equipment. In the process of composite, because the contact time between the roller and the film is very short, the heat transmitted from the coating roller to PVDC is limited. The selection of the applicable process temperature can not only guarantee the decrease of adhesive and viscosity, but also avoid the shrinkage caused by heating during PVDC composite.
After that, how to solve the deformation and delamination of PVDC in high temperature cooking is another important topic. We have passed a lot of experiments, on the one hand, we adjust the tension of the first and second winding on the composite process equipment to make it match; On the other hand, through the interlaminar treatment and a series of experiments of adhesion, the adhesive suitable for high temperature cooking (121 ℃, 30min) was screened. The adhesive has high initial adhesion and later bonding strength. It makes PVDC in the middle layer of the composite film suffer more adhesive force than that of PVDC when it is heated and shrinks. It effectively ensures the adhesion fastness and appearance flatness of the composite film during cooking and after cooking.
With the successful adoption of these two technical measures, the technology of directly manufacturing high temperature resistant cooking composite film by PVDC is a key problem. Through several years of practice, we have made a complete technological breakthrough: according to the requirements of sterilization temperature of the compound membrane packaging content, we used CPE (< 100 ℃) and CPP (121 ℃) as the heat seal layer respectively, which effectively guaranteed the heat sealing strength; Through the improvement of PVDC processing technology, the problems of frequent bubble breaking and the yield of finished products are solved when reducing the thickness of PVDC. The thickness is less than 20 μ The cost ratio of PVDC is effectively reduced under the premise of ensuring the performance of M PVDC substrate film, so that the overall cost of PVDC composite film is reduced to the degree close to that of three layer nylon composite film. We have developed three layers of PVDC laminated film which is suitable for bag making and automatic molding machines; BOPP (or BOPET) /pvdc/cpe, three-layer high temperature laminating composite membrane: BOPP (or BOPET) /pvdc/cpp, four layer anti puncture high temperature laminating composite membrane: BOPP (or BOPET) /pvdc/bopa/cpp and other special functional PVDC composite films.
The production technology is the first in China, filling the gap in China, and has applied for the national invention patent. The PVDC laminated composite films produced are sent to the national plastic product quality inspection center and the PVDC technology center of Dow Chemical Company of the United States for comprehensive testing. All the indexes meet the requirements of the national standard GB / t10004-1998 for high temperature cooking composite film and bag (see Table 2). It has the following characteristics:
The transmission of water vapor is 4.2cm3/m2.24h.atm and 1.6g/m2.24h respectively. The shelf life of meat food packed with it can reach 6 months after being digested at high temperature (121 ℃, 30min);
The mechanical strength and barrier of the laminated composite film produced by the trampoling through sizzling yard nucleus are not reduced after sterilization at 121 ℃ and 30min, and the composite film is not deformed, cracked, and layered, and the surface is smooth and smooth, and the dimension stability is good;
The bonding strength between bopp/pvdc layers is very large and cannot be stripped after cooking, and the peel strength between layers of pvdc/cpp reaches about 5N;
4. The transparency is high, which meets the people's desire to see the contents of the package;
5. The mechanical properties and heat sealing properties are good, and can be used in many kinds of packaging machinery;
6. The composite of many kinds of substrate films, such as OPP, BOPET, BOPA, CPE, CPP, PVC, Al pet, etc;
Good stability: no chemical reaction with acid, alkali, salt, etc., and strong solvent and grease resistance.
Eight said lung Lang is good: in line with national health standards, it is non-toxic and harmless to human body.
We know that as a composite substrate, it is necessary to ensure its dimensional stability to ensure the appearance flatness of composite film after composite. Because of its own characteristics and processing technology, PVDC has a high shrinkage rate of hot water at 100 ℃ and can not guarantee the normal composite and composite effect. We improve the resin formulation and control the production process, so that the shrinkage rate of resin can be reduced to a certain extent. If the conventional dry composite process is used, PVDC film must pass through 60-80 ℃ long drying path. In this case, it will still shrink greatly (see Fig. 1), but the composite film with stable size and flat surface can not be obtained. Therefore, we adopt solvent-free composite process and composite equipment. In the process of composite, because the contact time between the roller and the film is very short, the heat transmitted from the coating roller to PVDC is limited. The selection of the applicable process temperature can not only guarantee the decrease of adhesive and viscosity, but also avoid the shrinkage caused by heating during PVDC composite.
After that, how to solve the deformation and delamination of PVDC in high temperature cooking is another important topic. We have passed a lot of experiments, on the one hand, we adjust the tension of the first and second winding on the composite process equipment to make it match; On the other hand, through the interlaminar treatment and a series of experiments of adhesion, the adhesive suitable for high temperature cooking (121 ℃, 30min) was screened. The adhesive has high initial adhesion and later bonding strength. It makes PVDC in the middle layer of the composite film suffer more adhesive force than that of PVDC when it is heated and shrinks. It effectively ensures the adhesion fastness and appearance flatness of the composite film during cooking and after cooking.
With the successful adoption of these two technical measures, the technology of directly manufacturing high temperature resistant cooking composite film by PVDC is a key problem. Through several years of practice, we have made a complete technological breakthrough: according to the requirements of sterilization temperature of the compound membrane packaging content, we used CPE (< 100 ℃) and CPP (121 ℃) as the heat seal layer respectively, which effectively guaranteed the heat sealing strength; Through the improvement of PVDC processing technology, the problems of frequent bubble breaking and the yield of finished products are solved when reducing the thickness of PVDC. The thickness is less than 20 μ The cost ratio of PVDC is effectively reduced under the premise of ensuring the performance of M PVDC substrate film, so that the overall cost of PVDC composite film is reduced to the degree close to that of three layer nylon composite film. We have developed three layers of PVDC laminated film which is suitable for bag making and automatic molding machines; BOPP (or BOPET) /pvdc/cpe, three-layer high temperature laminating composite membrane: BOPP (or BOPET) /pvdc/cpp, four layer anti puncture high temperature laminating composite membrane: BOPP (or BOPET) /pvdc/bopa/cpp and other special functional PVDC composite films.
The production technology is the first in China, filling the gap in China, and has applied for the national invention patent. The PVDC laminated composite films produced are sent to the national plastic product quality inspection center and the PVDC technology center of Dow Chemical Company of the United States for comprehensive testing. All the indexes meet the requirements of the national standard GB / t10004-1998 for high temperature cooking composite film and bag (see Table 2). It has the following characteristics:
The transmission of water vapor is 4.2cm3/m2.24h.atm and 1.6g/m2.24h respectively. The shelf life of meat food packed with it can reach 6 months after being digested at high temperature (121 ℃, 30min);
The mechanical strength and barrier of the laminated composite film produced by the trampoling through sizzling yard nucleus are not reduced after sterilization at 121 ℃ and 30min, and the composite film is not deformed, cracked, and layered, and the surface is smooth and smooth, and the dimension stability is good;
The bonding strength between bopp/pvdc layers is very large and cannot be stripped after cooking, and the peel strength between layers of pvdc/cpp reaches about 5N;
4. The transparency is high, which meets the people's desire to see the contents of the package;
5. The mechanical properties and heat sealing properties are good, and can be used in many kinds of packaging machinery;
6. The composite of many kinds of substrate films, such as OPP, BOPET, BOPA, CPE, CPP, PVC, Al pet, etc;
Good stability: no chemical reaction with acid, alkali, salt, etc., and strong solvent and grease resistance.
Eight said lung Lang is good: in line with national health standards, it is non-toxic and harmless to human body.