Packaging film coating process types, you know how many?

Common coating processes mainly include the following.

(1) Heat seal coating

Heat seal coating can be used on paper, packaging film or aluminum foil, mainly used in the cup and lid market, and can provide tearable seals for rigid containers such as PET, PS, HDPE, and PP.

Heat seal coating uses concave roll coating, roll coating or wire bar coating. The common coating weight of heat seal coating is 907 ~ 1361 g / ream. In order to achieve the best performance, the coating roller and glue tank are usually heated to 48 ~ 52 ℃.

 

(2) Cold seal coating

Cold seal coating can be used on paper, packaging film or aluminum foil, mainly used in confectionery, bread, medicine and other markets. It can provide packaging that can be sealed without heating. The coating adheres to itself under the pressure of the packaging machine.

 

Water-based paint is a mixture of EVA and latex, a mixture of acrylic and latex, or a certain synthetic material. It uses engraved gravure cylinder to coat the back of the printing tape. Normally, it is applied to the sealing position on the package corresponding to the position of the front pattern. The common coating amount of cold seal coating is 907 ~ 1814g / ream.

 

(3) Adhesive coating

Adhesive coating is commonly used in dry lamination. The adhesive tape is removed from the drying channel to remove all solvent or moisture, and then bonded to another tape. The adhesive can be solvent-based, water-based or solvent-free. The coating depends on the type of tape to be compounded, the final packaging application, and the coating method that can be used. In general, the same compound equipment can be used for solvent-based and water-based adhesives, but it is recommended to use a smoothing roller device for water-based adhesives.

 

For solvent-based and water-based adhesives, the best coating method is gravure coating. When the amount of coating required is small, the mesh of the concave roller is fine, and the paint with low viscosity is used at the same time. When a larger coating amount is required, the mesh of the concave roller is thicker, and a coating with higher viscosity is used at the same time. Only in this way can satisfactory results be achieved. The coating amount of solvent-based and water-based adhesives is generally 680 ~ 1134 g / ream.

 

For solvent-free compounding, special compounding equipment is required. The adhesive is applied by a set of rollers rotating at different speeds, the adhesive is metered and then applied to the substrate. The shear force generated by the speed difference allows the adhesive to reach the appropriate amount before being applied to the substrate. The coating amount of solvent-free compound is usually smaller than that of solvent-based and water-based adhesives.

 

(4) Primer coating and surface coating

Primer coating (often called primer), whether water-based or solvent-based, is to improve the adhesion between the packaging film surface and the ink or coating. The primer does not contain colorants or waxes, and is only used when necessary.

 

The surface layer coating is used on the dried ink, which can increase the gloss, heat resistance and wear resistance, so that the surface does not slide. This type of paint contains wax and other additives, but no color.

 

(5) Plastic coating

According to different coating materials, plastic coating mainly has the following types.

 

â‘  PVDC coating. PVDC dairy can be coated in several ways, depending on the characteristics of the substrate and equipment conditions. When accurate measurement is not required, reverse roll coating is often used. When more precise coating amount is required, air knife coating or wire rod coating should be used. The former has no physical contact with the substrate during the coating process and can be used at high speeds. The latter is easy to operate, but only suitable for lower speeds.

The coating amount of PVDC is generally in the range of 1.5 ~ 3.0g / ㎡ . A coating amount lower than the above-mentioned recommended value may reduce barrier properties, while a coating amount higher than the above-mentioned recommended value may not necessarily improve barrier properties. It can be coated on one side or both sides. The base material can use biaxially oriented polypropylene film, biaxially oriented polyester film, aluminum foil, paper, etc .; according to the application, it can be made into various barrier films.

PVDC emulsion can be used for coating on paper, cellophane, PP, PET, PE and nylon, and is used in packaging including fast food, cheese, meat and medicine.

 

PVDC coating has excellent barrier properties, and very low oxygen, odor and moisture permeability. PVDC coating also has good heat sealability, oil resistance, solvent resistance, abrasion resistance, flexibility, gloss and flame retardancy. However, PVDC coatings also have shortcomings. The composite materials are not stable at low temperatures, and the substrates and finished products should be stored in a room temperature environment with a relative humidity of about 50%.

 

â‘¡ PVOH coating. PVOH is a kind of polyvinyl alcohol coated on packaging film, which can provide special oxygen barrier properties for packaging. It has a low haze, does not yellow, and has excellent optical properties. It adopts the reverse concave roll coating method. Before PVOH coating, primer coating is required to optimize the coating fixation.

The PVOH coating should be included in the middle of the composite layer to prevent the coating from getting wet, because once it gets wet, the oxygen barrier of PVOH will be reduced.

 

â‘¢ Silicon oxide coating. Coating silicon oxide / silica on the packaging material can obtain the barrier property similar to aluminum foil. It is often referred to as a "glass" coating, because silicon is the main component for making glass containers. The silicon-coated film has excellent barrier properties and good brightness. These coatings are intended to replace aluminum foil composite materials, especially in packaging where transparency is required. Silicon oxide coatings still have excellent folding resistance and constant barrier properties at high temperatures and temperatures. The evaporation coating method is generally used, and the coating is mechanically combined with the substrate surface.

 

â‘£ Acrylic coating. Acrylic coating is used in plastic films to achieve better heat sealability, packaging mechanical properties, odor barrier, aesthetics and stability. This coating film has low haze, high gloss, and has a glittering effect.

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