Tin cans are rising with the development of canning industry. Although the whole process from raw material production to canning operation is not only complicated but also costly; it has many advantages over other forms of packaging, such as light and high strength than glass containers. The chemical stability is good, because the non-combustible, not broken, very suitable for packaging circulation cycle and long transport lines of goods; In addition, than the paper container stiffness and strength are high, moisture, temperature. At the same time, the recycling of metal containers is also good, is conducive to environmental protection.
DRD two-pieces tin cans advantage
As one of the main types of two cans, DRAWN AND REDRANN CAN (DRD cans) are increasingly widely used. Relative to the three-pieces cans, DRD tank the following advantages can not match, the application prospects are quite broad.
Good safty. The body of tin can is directly drawn and formed, the inner wall of the tank is completely seamless, and the tightness of the can body and the can lid is high, which ensures the safety of the contents.
Nice and generous. There is no seams in the body, the outer surface can be fully printed, the outside smooth and uniform, the whole body appearance lines soft, smooth, with good artistic effect.
Saving, high efficiency. The overall shape of the tank body, do not need the bottom of the seams, not only save the material, but also to simplify the process, improve production capacity is very good, the cost is lower than the three cans.
DRD coating of the three types
Of course, the quality of DRD cans is inseparable from the appropriate tin (chrome) substrate, organic coatings (film), production equipment and process management, the following simple discussion DRD tank coating technology features.
DRD tank coating and ordinary three-tank coating coating is the same, the application conditions are basically the same. The special requirements for the coating are derived from its production mode - due to the canning of the can body and the bottom of the tank several times, the coating on the substrate must be able to withstand multiple tensile deformations to maintain good protective properties, so DRD tank coating Compared to the ordinary three-tank paint is characterized by good impact resistance processing.
Suitable for DRD tank coating requirements are epoxy coatings, polyester coatings, polyvinyl chloride organic sol coatings. These three types of coatings have good impact resistance, from weak to strong in order to epoxy paint <polyester coating
<Organic sol. Chemical resistance is polyester coating <organic sol <epoxy coating. In the actual use of the process, according to the contents and filling conditions to choose the above polyester coating, epoxy coating two coated two baking, or polyester coating (epoxy paint) primer organic sol coating process, the total film thickness in general Control in 16 grams / square meters or more.
Epoxy coating Epoxy coating resin is mainly used bisphenol A and BADGE (bisphenol A glycidyl ether) chain extension, epoxy equivalent of 2500 ~ 4000g / mol 9 type resin. Some R & D personnel will also use epoxy equivalent of 2000 ~ 2400g / mol 7-type resin and 9-type resin mixed with the use to adjust the viscosity, curing and other properties.
Phenolic resin is the preferred curing resin for epoxy coatings, and there are many types of phenolic resins (type of phenol, synthetic catalyst, process route, etc.). In the design of DRD tank coating, it should start from the good impact processing, due to the more reactive groups of epoxy resin, so the preferred bisphenol-containing phenol synthesis of phenolic resin, such phenolic and epoxy resin after curing Of the coating cross-linking density can be moderate, the coating in order to maintain good chemical resistance and impact resistance processing performance. Specific subtle properties can be adjusted according to the ratio of epoxy resin and phenolic resin, and a part of the amino resin can be added to adjust the curing and leveling properties of the coating.
Polyester coating Polyester coating of the main resin is generally selected in the high molecular weight saturated polyester, molecular weight (Mn) is generally selected in the 1,0000 ~ 2,500 Daltons, preferably more than 1,5000 Daltons, this level of polyester Flexibility is very good, resistant to deep red. Polyester Tg (glass transition temperature) point is also an indicator of concern, too low value is likely to cause the coating is softer, resulting in coating after the coating surface sticky sticky, cut edge and other defects; Resulting in more brittle coating, the impact will often appear after a small crack, so according to the actual processing of the coating when the overall conditions carefully select the appropriate polyester resin. In order to improve the chemical resistance of the whole coating, must be with the phenolic resin (the use of phenolic resin curing cross-linking). The above-mentioned molecular weight polyester resin has a small number of crosslinkable groups, and therefore, when the phenolic resin is selected, it is preferable to use a phenolic resin having a bifunctional group or more to form a phenolic resin to be crosslinked, and under certain conditions, Resin and other curing resin appropriate regulation performance. In addition, if the choice of non-bisphenol A type of phenolic resin, through the deployment of polyester coatings can meet the latest national food safety regulations without bisphenol A requirements.
Polyvinyl chloride organic sol coating The coating is the use of polyvinyl chloride particle size characteristics, its high-speed uniform dispersion into the organic solvent, with a certain amount of polyester resin or acrylic resin, and then with phenolic, amino and other curing resin deployment Come into being. The coating is baked and cured to form a slightly solidified semi-plastic coating that retains the high chemical resistance of the polyvinyl chloride material and retains its high tensile workability as a thermoplastic material, with the appropriate Thermosetting resin crosslinking, so that the thermal instability of plastic materials has been significantly improved. By adjusting the proportion of PVC in the coating, the final can be perfectly adapted to the manufacture of DRD cans and subsequent filling sterilization conditions. Similarly, in the paint does not use bisphenol A-containing raw material resin can be made to meet a no bisphenol A regulations of the coating.
Application Solution
The above three coatings are currently applicable to the mainstream varieties of DRD cans, can also be used in accordance with the actual requirements to achieve the complementary between the performance. Of course, in the above-mentioned coatings in the actual production, must also add lubricating wax and additives and other auxiliary materials.
In addition, according to the needs of filling the contents of the paint on the basis of the addition of aluminum paste, titanium dioxide and other filler to adjust the performance of the coating, the general high protein foods need to add aluminum paste to play in the coating to cover the black stain The role of titanium dioxide and other filler can be added to further reduce the coating pores, increase the chemical resistance.
Comparison of coating and coating
Paint and film have their own advantages. Coating wins in the high flexibility, low cost, variety, technology mature; coated iron advantage lies in the high protection, no environmental pollution. These two methods as DRD tank wall protection means have their own advantages and disadvantages, can companies according to the actual situation to choose.