Views: 0 Author: Site Editor Publish Time: 2023-07-04 Origin: Site
Nanjing Sumino Seiko co-extruded barrier composite films are usually made from a combination of barrier plastics, polyolefin plastics (moisture-proof plastics, generally also used as heat sealing layers) and adhesive resins, which are described below.
Barrier resins
The former is used to produce general barrier and puncture resistance barrier films, while the latter is used to produce high barrier films. www.susumino.com南京住野精工专业淋膜复合机研发生产
1. Nylon (PA)
Nylon used in the manufacture of barrier co-extruded composite films is mainly nylon 6, in addition to aromatic nylon MXD6, but because the latter is expensive, the actual application is not yet common.
(1) The main characteristics of nylon 6
Has a good barrier oxygen, carbon dioxide and other gases through the performance, belongs to the so-called barrier materials, see Table 2-1; puncture resistance is outstanding; oil resistance, good resistance to organic solvents; high and low temperature performance, can be resistant to 135 ℃ above the high temperature cooking; good health performance, can be used for food, pharmaceutical packaging; nylon has good molding and processing performance, no special processing equipment, the production process is also relatively easy to master.
(2) Coextruded barrier nylon 6 representative products
Coextruded nylon 6 for barrier layer is different from ordinary nylon 6 resin for chemical fibres and engineering plastics, mainly in terms of relatively high molecular weight, high melt strength and good film formation. At present, some famous nylon resin manufacturers have special grades of nylon for co-extruded composite films, such as Mitsubishi Chemical Corporation of Japan, Honeywell of the United States, BASF of Germany, etc.
(3) Nylon co-extruded composite film molding processing points
Nylon plastic is a strong hydrophilic plastic, exposed to the air, it is easy to absorb the moisture in the atmosphere and lead to moisture, and when the moisture content of nylon is greater than 0.1%, that may make the product bubbles, so the molding process before, generally need to be pre-drying treatment (moisture-proof original packaging opened immediately after use, without pre-drying treatment that is added to the extruder application); at high temperatures, nylon is more In order to prevent oxidation and degradation when drying nylon, vacuum oven can be used for drying (in addition to oven heating and drying, industrial production also uses boiling heating, microwave heating and other methods to dry nylon, boiling heating, microwave heating has the advantages of high heating efficiency and short heating time, but the one-time investment is larger), if the ordinary blast box is used for drying The drying temperature should be lower than 100℃.
The affinity between nylon 6 and polyolefin plastics is poor. When using nylon and polyolefin to match the production of co-extruded composite films, adhesive resins must be used to improve the bonding between the nylon and polyolefin layers, otherwise there may be problems with inter-layer delamination, making the produced composite films lose their value.
www.susumino.com南京住野精工专业淋膜复合机研发生产
2. Ethylene vinyl alcohol copolymer (EVOH)
EVOH can be regarded as a copolymer of ethylene and vinyl alcohol according to its molecular structure, which is +CH2-CH2fCH-CH2)m. In EVOH, the content of the ethylene component OH is usually in the range of 30% to 50% (molar fraction). As EVOH is a copolymer structure, the properties vary accordingly with the ethylene and vinyl alcohol content. As the ethylene content increases, the barrier to non-polar gases (oxygen, carbon dioxide, ammonia, etc.) decreases while the moulding and processing properties and moisture resistance improve accordingly.
The characteristics of EVOH are as follows.
www.susumino.com南京住野精工专业淋膜复合机研发生产
(1) Main advantages
Excellent performance of oxygen barrier and other non-polar gases; outstanding fragrance retention; excellent hygiene performance, can be used for food and pharmaceutical packaging; excellent oil and organic solvent resistance; good transparency and gloss; excellent printing performance; good adaptability to environmental protection, waste can be melt regeneration treatment, burning treatment to recover heat does not produce toxic and harmful substances that harm the environment; molding and processing Excellent performance, can be applied to general plastic molding equipment for processing.
(2) Main disadvantages
The price of EVOH is not only much higher than that of ordinary polyolefin plastics, but also more expensive than that of nylon 6; the heat resistance is limited, even for EVOH, which is resistant to cooking, the co-extruded composite film made of it can only withstand a maximum of 121°C.
(3) Key points of EVOH moulding process
EVOH has a certain degree of hygroscopicity, so the moisture content of the pellets should be controlled to less than 0.3% when making the film, and if the material is damp, it must be pre-dried before use, otherwise the product will have bubbles and other defects. When the temperature exceeds 230°C, the structural part of the vinyl alcohol in EVOH rapidly undergoes thermal decomposition, so the extrusion temperature must be kept below 220°C. EVOH remains in the extruder for a long period of time and causes operational problems due to the gelation of the resin by the heat, so when there is a short stoppage in the production process, a small amount of lubricant is added to the EVOH and a high viscosity polyolefin resin is supplied to remove the EVOH resin from the extruder. This is why a small amount of lubricant is added to the EVOH and a high viscosity polyolefin resin is supplied to remove the EVOH resin from the extruder. For long shutdowns during production, the equipment should be cleaned up immediately after stopping operation.
3. Polyvinylidene chloride (PVDC)
Polyvinylidene chloride resin is also a co-extruded barrier multi-layer composite film barrier material, polyvinylidene chloride is a homopolymer of ethylene oxide, it is non-toxic, tasteless, good transparency, high mechanical strength, good toughness, resistance to oil and organic solvents; heat shrinkage and self-adhesive; also has self-extinguishing, odour preservation and excellent moisture, mould and other properties, while having excellent printing and heat sealing properties, and as far as In terms of barrier properties, it is a very desirable barrier material, but there are not yet many applications. Polyvinylidene chloride not only has a high barrier to oxygen and other non-polar gas properties (oxygen barrier and EVOH resin equivalent), but also has a high water and moisture resistance, its water and moisture resistance even more than HDPE resin, ranking first in the commonly used plastics. However, PVDC resin has two major defects: one is the poor thermal stability, into the film conditions are very harsh, even after plasticization, stabilization of the formulation of PVDC plastic, but also must be applied with a special alloy screw, barrel and die of special co-extrusion equipment, under strict control of the process conditions, in order to successfully produce a multi-layer co-extruded film containing PVDV barrier layer, so the development of PVDC class co-extrusion film is very restricted; the second is that the film containing PVDC barrier layer is poorly adapted to environmental protection, due to the lack of thermal stability of PVDC, containing PVDC barrier layer of film trimmings and recycled material, can not yet be recycled through hot melt granulation, while PVDC incineration treatment will produce harmful substances such as vinyl chloride, and even strong carcinogenic substances such as dipyrimidine, and is therefore highly criticized by environmentalists This is also a reason why not many PVDC co-extruded barrier laminated films have been used so far.
Nanjing Sumino Precision Machinery Co., Ltd. is a high-tech enterprise that integrates scientific research, production and sales, and has always adhered to the business philosophy of honesty, equality and customer interest first. We have set up independent research and development technology centres and production departments for seven major types of equipment, including plastic sheet and plate, cast, bi-directional stretch, non-woven non-woven meltblown fabric, laminated film, recycled pelletizing and environmental recycling systems and coating machine manufacturing systems. We offer a full range of technical solutions to meet the specific needs of each customer. The following lines are available for customisation: PE double/three layer co-extrusion lamination line, LDPE (3 in 1) lamination line, PP, PE, PLA double sided lamination line, aluminium foil high speed lamination line, PP spunbond lamination line, textile lining lamination line, hot melt spray lamination line, multi-layer extrusion laminating line, graphene coating laminating line, carbon fibre laminating line.
