Faculty: Ecology and chemical technology
Speciality "Chemical technology of high molecular connections"
Research of the influence of primer on the quality of adhesion to metallized film
Scientific adviser: Prazdnikova Tatiana

      Over the past decade in the package are widely used various kinds of film materials coated with these thin layer of aluminum — simply put metallized films.
      Main applications of metallized films (both single-layer, or in combination with other films) — the packaging of flowers, ice cream, candy, chips, nuts, etc. — The list is long enough.
      As you know, before applying the paint on the metal film, the latest prayming, its surface is treated with a primer to improve adhesion of paint to the film.
      The purpose of the work — to study the influence of environmental temperature on adhesion of primers based on a variety of organic resins to two kinds of metallized film — metallized polypropylene and polifan.
      The object of study — primers on the basis of different organic resins.
      Relevance of the work. In recent years, enterprises flexography were reported many cases of unsatisfactory performance of the primer on the metallized film in the summer. There is a full or partial peeling layer of primer on the metallized film. In addition, the film is used for food packaging, and it is very important to the primer, which it covered, was safe for both humans and the environment. In recent years, have found wide application biodegradable film, so you need to use a primer that will not interfere with its natural degradation.
      Practical value — the optimization of the primer, reducing the influence of environmental temperature on the quality of the adhesion primer.
      Methods of investigation — standard procedure to determine the quality of adhesion.

      To improve the adhesion of paint to metallic surfaces, as mentioned above, are used Priming paints or primers.
      The most common and effectively improve the adhesion of primers (primers) is still paints based on organic solvents. Because solvents are moistened even non-activated polymer films, and the organic resin contained in the soil have a high affinity for them, in some cases such coatings — the only way to achieve sufficient adhesion.
      The main reason for problems with the adhesion of paints and varnishes — shrinkage of the paint layer in the process of consolidation. In the formation of new chemical bonds decreases the distance between the molecules and, hence, a 10—20% reduced volume, which takes the paint, causing mechanical stress in the varnish or ink film.
      Another difficulty in creating primers linked with water spray sealed surface. Polymer films have low surface activity, they need to handle the corona discharge or flame, but to achieve activation rapidly disappears. In the case of soil to solvent-based printing problems in the films is not as solvent moistened even non-activated surface.
      For wetting of the substrate in the soil should contain a large amount of impurities. The most effective contain silicone, but its presence in the primer creates a problem with drawing on it further paints, so you have to use a non-silicone additives ineffective at high concentrations.
      To date, widely used three main types of primers:
      — water-based;
      — alcohol-based (single-component);
      — on the basis of ethyl acetate (two-component).
      Water-based primers are the main drawback is that they require much more intensive drying than other types of primers that work on flexographic printing machines with a central drum makes it necessary to skip one or even several printing units after the primer and reduce speed print. In addition, these primers are usually most sensitive to the age of the film and not all of them have sufficient water resistance that is not possible to use them for packing ice cream and other products stored at subzero temperatures. Their primary use — gift wrapping and packaging of dry foods, but some water-resistant grade may be used to print packaging for ice cream, etc.
      Primers for alcohol-based dry much faster than water and slightly less sensitive to the age of the film. But not all of them provide the necessary water resistance, which greatly limits their application. In addition, we must remember that this is usually a system based on polyvinyl butyral, and they are incompatible with nitrocellulose based paint if you use them on a single printing unit.
      The third group of primers — two on the basis of ethyl acetate — the least sensitive to the aging of the film, quickly dry, so no restrictions on the printing speed is not, provide the best adhesion and water resistance. However, they are more difficult to use in flexographic printing: according to their chemical nature, they do not admit the slightest presence of alcohols (or rather, any low molecular weight solvents containing an alcohol functional group), and they use 100% ethyl acetate.

      The samples were selected following primers: primer based on nitrocellulose (sample number 1), a primer based on polyurethane resins (sample number 2), a primer based on polyurethane-polyacrylate (sample number 3) and a primer based on epoxy (sample number 4) . The study used metallized polypropylene Novoteks and polyphone brand TWIST PAN.

      Four beakers shown with 10 ml of each sample primer. Then the samples in a glass set in an incubator, where they are kept at a given temperature for 1 hour. Temperature range: 20° C to 50° C. After heating in an incubator with 5 ml sample applied to the metallized polypropylene polyphane. On the surfaces of the film drops rubbed with a hand anilox, to obtain a homogeneous sample layer thickness. After that film samples with primer conditioned for 20 minutes at room temperature to evaporate the remaining solvent, which is located in the primer. Evaporation of the solvent is an excess of dry adhesion primer to the surface of metallized films. After this testing is conducted on the stability of the primer to the wet curl.

      The results are shown in Table 1.

Primer	Temperature, С
	23		25		28		30		33		36		40		45		50
	РР	PF	РР	PF	РР	PF	РР	PF	РР	PF	РР	PF	РР	PF	РР	PF	РР	PF
Sample№1	5	5	5	5	5	5	5	5	5	4	4	4	4	3	3	2	2	2
Sample№2	5	5	5	4	4	4	4	3	3	3	2	2	2	2	1	1	1	1
Sample№3	5	5	5	5	5	4	5	4	5	3	4	3	4	2	3	1	1	1
Sample№4	5	5	5	5	5	5	5	5	4	5	4	4	4	4	3	3	3	3

      Table 1. - Research results

      
      Critical temperature using a 38°C for polypropylene, and 33°C for polyphane.

      
      Critical temperature using a 29°C for polypropylene, and 26°C for poliphane.

      
      Critical temperature using a 39°C for polypropylene and 30°C for poliphane.

      
      Critical temperature using a 37°C for polypropylene, and 39°C for poliphane.
      

      The results showed that the optimum storage temperature is the temperature of the primers 20 — 25° C. With these parameters, all samples of primers showed excellent results in both types of films. At 28 — 33° C, a decrease of adhesion of polyurethane primers (samples number 2 and number 3) to poliphane, with good results of adhesion to the metallized polypropylene, samples number 1 and number 2 have excellent results in both types of films. With increasing temperature to 36° C decreases adhesion to poliphane 1 point for all samples of primers, and a decrease in adhesion to the polypropylene and 1 point for samples №1, №2, №3. Sample №4 shows a stable result on metallized polypropylene. At 40° C, a decrease of adhesion to the samples poliphane №1, №2, №3. Adhesion to the polypropylene is not reduced. With increasing temperature to 45° C decreases adhesion to the metallized polypropylene and poliphane 1 point for all samples. At 50° C adhesion of polyurethane primers (samples number 2 and number 3) for both types of films is missing, the sample number 1 is the adhesion at 2 points in both films. The best result at this temperature showed the sample number 4 — by 3 points in both metallized films.

      Decrease in adhesion with increasing temperature can be explained by the fact that with increasing temperature begins to actively vaporize the solvent, which is part of the primer. The best results were obtained on the adhesion of sample number 4 — on the basis of epoxy primer. But the use of this primer for printing on food packaging is limited. Primer based on epoxy contains a substance (eg, maleic anhydride), forbidden by the legislation of Ukraine for use in food packaging.
      Further work will be aimed at creating a new composition of the primer, with the base — an epoxy resin, as for the food, and for normal packaging of the film.

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