The method of applying on a metallic base coating of thermoplastic material

 

The invention relates to the coating of plastic material on a metal base and can be used in industry for the manufacture of cans. The method includes heating the metallic base to 70-150oWith, the application is first installed on one side of the substrate surface by co-extrusion in the presence of ozone sheet substrate and the molten sheet containing polyolefin layer and an adhesive layer of a modified polyolefin, pressing the adhesive layer to the substrate surface, moving the strip in a second installation with such a speed that the temperature of the strip before coating ranged from 70 to 130oWith, drawing on the other side of the substrate surface in the form of a molten sheet by extrusion in the presence of ozone, heat the substrate with a coating to a temperature exceeding the melting point of the polyolefin, and cool. On the second version as the material applied in the first installation, use polyester consisting of one or more layers, and the second installation - sheet containing the upper polyolefin layer and an adhesive layer of a modified polyolefin. The invention improves the adhesion of the coating layer with the base and exp is k-before:always;">

The invention relates to a method of applying a metallic base coating of a thermoplastic material.

In this application under thermoplastic materials include plastic, consisting essentially of thermoplastics and additives that are introduced with the aim of making thermoplastic certain properties.

Drawing on metal base coating in the form of layers of plastic is a known method that is used in practice; this method is used, in particular, when the metal used must be protected from atmospheric influences, generally cause corrosion, or when necessary to protect the environment from adverse effects of the metal, or when it is desirable to obtain both of these effects, for example in the manufacture of packaging. Cans, for example, has long been manufactured from tin-plated steel packaging, also known as tinplate, which, on the one hand, covered with a layer of plastic to prevent the ingress of metal in food products, as well as to prevent the formation of rust under the influence of food products and, on the other hand, to preserve the attractive appearance of the packaging for a sufficiently long need to apply different coatings on the inner and outer side of the cover. The coating material applied inside, must first ensure good protection against corrosion caused by exposure of the product to be preserved and packaged, and the outer coating must retain an attractive appearance, such as gloss and color, and possess mechanical resistance to scratches and shock.

The step of machining in the manufacturing process of packaging, for example, the folding housing and cover in the manufacture of boxes for food or beverage cans, imposes more stringent requirements to the floor. An important role plays the fact that the outer coating must be resistant to scratches and easily undergo deformation so that it could withstand the fold.

To apply organic top coating, in addition to the treatment of semi-finished products packaging, can coat and at an earlier stage of the production process on the rolls of material, for example, by treatment of the material in the roll coating in film form foil (which is also called lamination roll material), when the plastic film is applied to the substrate, the coating can be applied also by extrusion, when they produce a coating in the FAQ to apply coating on the canvas.

Any method of coating has its drawbacks associated with the nature of the coating material or the method of applying this coating. Obviously, when applying varnishes disadvantage is the evaporation of solvents, this method is even more significant disadvantage when solvents contain volatile organic compounds that are used very often.

Film coatings are generally considered to be disadvantageous from an economic point of view. Production of the film, its winding into rolls, transporting and unwinding of the coils leads to the fact that all of these steps, taken together, do not provide the competitiveness of such production in comparison with varnishing.

Coating by extrusion as a method of coating, is attractive because it does not have these disadvantages from the point of view of efficiency of the process, but this method is difficult to implement in the case of certain combinations. This method is used mainly for applying one-sided or two-sided coating of polyolefins. These polyolefins do not have properties that are necessary for good adhesion with the metal base. For this reason, the adhesion. Specified adhesive layer in this case consists of polyolefins with groups of carboxylic acid or anhydrous groups. Suitable adhesive layers on the basis of polyolefins can be produced, for example, by copolymerization of propylene or ethylene, or combinations thereof with alpha-unsaturated carboxylic acids, beta-unsaturated carboxylic acids, the corresponding anhydrides or corresponding esters or polufinale. Examples of such compounds are acrylic acid, methacrylic acid, crotonic acid, cinnamic acid, maleic acid, maleic anhydride, fumaric acid, etc., the Content of such modifying monomers is generally from 1 to 15 wt.%.

Such monomers improving adhesion able to contact the surface of the base, but this occurs only when the adhesive polyolefin layer for some time is at a temperature above the melting point, resulting in the diffusion of monomers improving adhesion, through the polyolefin at the surface of the base, and the monomer improving adhesion, can enter into chemical or physical interaction with the surface of the base. It is impossible to achieve adhesion, sufficient is poliolefine on the metal base, which is applied to the monomers, which improves adhesion when the base is heated to a temperature below the melting temperature of the respective polyolefin. In this case, the film sticks to the metal pinch roller, which inside is cold and which presses the coating layer to the surface, and the film is wound on the pressure roller. Of course, you can pre-heating of the metal strip to a temperature above the melting temperature of the polyolefin. Thanks to achieve adhesion between the coating layer of a modified polyolefin and a metal strip. However, if you want to apply the coating also on the other side of the strip, and this should be done not simultaneously with the coating on the first side, the problem arises of the coating layer on the first side is damaged in the process of coating the second side, since the temperature of the product above the melting temperature of the coating layer of the polyolefin. As a result, the coating layer is in contact with the steel pressure roller in the molten state when it is very susceptible to damage.

With regard to the modification of plastic film, for example, by oxidizing the surface of the processing in the flame, you should specify that such treatments are often not profitable to apply for a modification on the spot melted very thin sheet of plastic. During processing with the use of electron-ion technology occurs electrostatic charge, resulting in a molten sheet is based on the installation to get the crown and all treatment loses its effectiveness. When using extrusion polyolefin at a very high temperature the free surface of the coating layer is oxidized, and this leads to the fact that the packing material has a strong influence on the taste of the Packed product; processing in a flame accompanied by a flow of gas, which pushes the molten plastic sheet and, in addition, produce large quantities of heat around the burner.

It was found that the modification can be successfully carried out using very small amounts of gaseous ozone, which oxidizes the surface of the sheet of molten polyolefin so that the area of contact of the rolls carrying out the lamination, it is possible to achieve a certain adhesion with the base, even if this basis is preheated to a temperature below the melting temperature of the polyolefin. Such adhesion on IU nomu inside that will allow you to move the base with a coating chamber for further heating, where the adhesion is increased because the temperature is brought to above the melting temperature of the polyolefin, resulting begins diffusion groups, improving the adhesion, the surface, and then there are the chemical or physical interaction.

Further, it was found that the copolymerization of propylene with ethylene leads to the fact that the effect of gaseous ozone is enhanced, thereby improving the initial adhesion of the coating layer to the base.

The method according to the present invention includes the following steps: preheating the basics so directly before coating the base was at a temperature of from 70 to 150oC, preferably from 100 to 130oIn the case where the coating contains polypropylene, and from 80 to 110oIn the case where one-sided or two-sided coating contains polyethylene; implementation in the first installation for coating co-extrusion sheet containing layer polyolefin coating and a layer of a modified polyolefin with high adhesion; drawing on the basis of the cover in the form of a molten sheet in presets the second side, the second installation for coating and heating of the strip so that immediately before coating, the band was at a temperature of from 70 to 130oC, preferably from 80 to 120oIf the coating layer applied in the first machine for coating, consists of polypropylene, and from 80 to 110oIf the coating layer is a polyethylene coating in the presence of ozone basics molten sheet obtained by extrusion in the second installation for coating, pressing it to without coating the surface of the substrate; heating the substrate with a coating so that it reaches a temperature above the melting temperature caused polyolefin; cooling the substrate with a coating.

An alternative method according to the present invention includes the following steps: preheating the basics so directly before coating in the first installation for coating the base was at a temperature of from 70 to 150oC, preferably from 100 to 130oWith; the implementation in the first installation for coating extrusion of the molten polyester sheet comprising one or more si, covered on one side with polyester, the second installation for coating and heating of the strip so that before coating it was at a temperature of from 70 to 130oC, preferably from 90 to 120o;
implementation in the second installation for coating co-extrusion sheet containing top layer of polyolefin and adhesive layer of a modified polyolefin;
the coverage of the surface of the molten sheet in the presence of ozone, clutching the sheet so that the adhesive layer is pressed against the surface of the substrate;
heating the substrate with a coating so that it has reached a temperature exceeding the melting point of the deposited polyolefin;
cooling the substrate with a coating.

In the result of the respective cooling, for example (which is preferable) by lowering into the water, the layer of thermoplastic coating remains amorphous, to the extent possible, in the case of use as a coating layer of the polyester, or has a monocrystalline structure, if the coating used polyolefin. The base with the floor, thus obtained, is able to withstand deformation, for example, as a result of folding. Recrystallization happens to some extent e is a disadvantage, but, on the contrary, is an advantage. As a result of recrystallization increases the crystallinity and, consequently, the hardness of the coating layer.

In some cases it is desirable to add to thermoplastic material low density polyethylene in an amount of preferably 5-20 wt.%. This will improve the manufacturability of the molten sheet, to increase the initial adhesion after treatment with ozone.

In accordance with the present invention receive a metal base covered with thermoplastic material, in which the thickness is 0.05 to 0.30 mm, and the thickness of thermoplastic coating is 3-50 μm.

The layer of plastic is applied, for example, by using an extruder, which can also be obtained multilayer coating.

Polyolefins, such as polypropylene and polyethylene, is applied in molten form on the metal base, for example, as shown in the drawing. The distance between the bevels of the nozzle and the area of contact between two rolls is from 4 to 25 cm, preferably from 8 to 20 see, This method of application can be used for plastics with a low enough melt strength, such as polyesters, only at low relative elongation, i.e. low skorostyami ozone, directed to the molten sheet. Due to the fact that it requires only a small amount of gas, the structure of the molten sheet is not disturbed.

Given the method of application and heat treatment, it is desirable that the thickness of the substrate and the coating layer were within the specified bounds.

Preferably, the thickness of the layer of thermoplastic coatings ranged from 3 to 20 μm. The molten sheet is thin, and the correct feed speed in combination with an appropriate rate basis, this layer can become even thinner, reaching a specified range due to stretching along one axis. From the point of view of material consumption, it is desirable that the layer of plastic was as thin as possible. However, from a functional point of view, you can use higher lower bounds than 3 μm, depending on the application. The metal base may be a material containing mainly iron, for example, steel. It is cheap, attractive possibility of re-use (recycling). Further, the base containing mainly iron, easy to heat with induction and temperature used in the method according to the present esthesia, you should use packaging steel type steel, chrome-plated electrolytic method.

Packaging steel, covered with a thermoplastic containing essentially polypropylene, best suited, for example, for the manufacture of caps. The results of the tests cans that were stored in special conditions and are made of the material according to the present invention and filled with food, showed that the best results are to cover, made of steel packaging according to the present invention with a coating of a layer of polypropylene. The material obtained by the method according to the present invention has good resistance to corrosion and scratches, so that one and the same layer can be used inside and outside of the cans, i.e., the source material can be coated on both sides. The coated material can also be subjected to various kinds of processing.

An example implementation of the invention 1
Applying a layer of a polypropylene coating on both sides of the strip can be produced, for example, as follows:
the finished base made of chromed steel, chrome-plated electrolytic method) pre-heated to 130o;
heated basis about what Anna the zone of contact between the molten sheet of polypropylene, which has a width of 10 to 40 mm more than the width of the base, and which consists of an adhesive layer in contact with the base, and the top layer, the top layer is thicker than the adhesive layer, is applied to the substrate using a system of two extruders, and the plastic threads emerging from them, are connected to the extrusion head for co-extrusion;
a certain amount of gaseous ozone is directed to the molten sheet and as low as possible immediately before the contact zone, so that in this place the percentage of the surface is processed by ozone was maximum; an adequate amount of ozone is 8 mg of ozone per m2;
the obtained multilayer material consisting of chrome steel and polypropylene, cooled only by the length of the contact zone with polished cooling roll so that the applied layer of polypropylene acquired the roughness of the cooling roll, but to the temperature of the multilayer material fell slightly;
oxidation of the surface of the polyolefin in contact with the steel surface will provide sufficient adhesion of the coating to the steel substrate so that the coating has been peeled away from the pressure roll, chilled from the inside out;
the Foundation, which already has the aqueous ozone is applied on the second side of the layer of polyolefin plastic;
in the same production installation strip, coated on both sides, then heated by induction to a temperature of from 150 to 280oC, preferably from 180 to 225oC, kept at this temperature for from 0.5 to 20, and then quickly cooled in a tank of water;
after that make drying with the drying rolls or hot air;
after applying a layer of plastic on both sides of the strip and maximizing adhesion excess plastic is removed from both edges of the strip by means of a suitable cutting method, such as laser cutting or hydraulic cutting;
strip coated wound into a roll or cut into plates;
from the packaging steel, which as described above are coated, made in the usual way, for example, cover. These caps are then processed with the proper composition using conventional method. Then applied the compound is dried in a convection oven under such conditions, to cover reached a temperature of 110 to 150oWith, preferably 110-120oC. Cover made in this way have the best performance characteristics, compared with lids, made of chrome Stal invention 2
All operations are carried out as in example 1, but in this case, the layer polypropylene coating consists of a combination of homopolymer adhesive layer and the homopolymer of the top layer, and then put a layer of polyester coatings;
the finished base made of chromed steel, chrome-plated electrolytic method) pre-heated to 130o;
heated base is passed through a zone of contact of the rubber pressure roll and polished cooling roll;
in this zone of contact between the molten sheet of polypropylene, which has a width of 10 to 40 mm more than the width of the base, and which consists of an adhesive layer in contact with the base, and the upper layer, having a thickness greater than the thickness of the adhesive layer applied to the substrate using a system of two extruders, and the threads of the plastic, leaving them together in the extrusion head for co-extrusion;
gaseous ozone in the amount of 8 mg of ozone per m2sent to the molten sheet and as low as possible immediately before the contact zone so that the percentage of the surface is processed with ozone, this place was the maximum;
the obtained multilayer material consisting of chrome steel and polipropilene layer polypropylene acquired the roughness of the cooling roll, but to the temperature of the multilayer material fell slightly;
oxidation of the surface of the polyolefin in contact with the steel surface will provide sufficient adhesion of the coating to the steel substrate so that the coating has been peeled away from the pressure roll, cooled from the inside;
the Foundation, which already has a cover with one hand, bring in the same production installation of up to 120oWith and put on a second side of the layer of polyester;
in the same production installation strip, coated on both sides, then heated by induction to a temperature of from 150 to 280oC, preferably from 210 to 265oC, kept at this temperature for from 0.5 to 20, and then quickly cools in the tank with water;
after that make drying with the drying rolls or hot air;
after applying a layer of plastic on both sides of the strip and maximizing adhesion, excess plastic is removed from both edges of the strip by means of a suitable cutting method, such as laser cutting or hydraulic cutting;
and, finally, the strip is coated wound into a roll or cut into plates.

An example implementation of the invention 3
Instead homopolymer cleansehealth the same conditions, the adhesion was found to be more reliable and fully comply with the requirements of the following production processes immediately after the contact zone 1.

Comparative example 1
All operations were carried out as in example 1, but without the use of ozone.

After application of the molten sheet in the zone of contact between the steel of the pinch roll, cooled from the inside, began to undo the bands of the resulting layer polyolefin coating, regardless of the degree of roughness of the rolls, resulting in between the base and the coating layer was air, even in cases where the initial part of the coating layer was firmly bonded to the base with tape. Due to exposure to air after the treatment in the furnace for further heating has been a very rough product which is unsuitable for further processing.

Comparative example 2
All operations were carried out as in example 1, but the temperature of the preheating band reached 200oAnd the ozone generator was switched off.

Depending on the thickness of the molten sheet, he was stuck more or less well to the base after contact zone 1. When the thickness of the molten sheet is less than 10 μm quickly froze the pinch roll position with internal cooling, resulting in diffusion groups, improving adhesion, quickly disappeared, and the adhesion was achieved only average. More ukrytiem on one side was 150oWith layer polyolefin coating already applied in the contact zone 1, was destroyed. The result has been very uneven floor.

Further, the present invention is explained in more detail with reference to the drawing, which shows a device for implementing the method of the present invention.

As shown in the drawing, the metal base 1 in the form of a strip is passed, for example, through induction furnace 2.

The base 1, which comes out of the oven 2, for example, vertically, runs around the bending of the roll 3 in the first installation for the coating of which consists of extruder 4, the ozone generator 5, the pressure roll 8, for example, steel, and back-up roll 7, preferably having a rubber layer. The outlet of the ozone generator 5, preferably situated as close as possible to the area where the base 1, and emerging from the extruder 4 sheet 6 come together immediately before the contact zone controversial roll 7 with the clamping roller 8.

The output from the first installation for coating the receiving base 9 having a coating on one side, which is passed through a heater 13 and serves in the second set for coating. This installation contains the second extruder 10, the second generate two sides, exit the device through the furnace 13.

The extruder 4 is suitable for extruding sheet 6 of polyolefin, e.g. polypropylene or polyethylene, having an adhesive layer or containing polyester. The extruder 4 may include one extruder for polyolefin and polyester, to be used the right extruder. The extruder 10 is suitable for polyolefins. The extruder 4 and 10 can be interchanged.


Claims

1. The method of applying on a metallic base coating of thermoplastic material, in which pre-heat the base so that immediately before coating it had a temperature of from 70 to 150oTo perform the first installation for coating the joint extrusion of the sheet containing the polyolefin covering layer and an adhesive layer of a modified polyolefin, is applied to the substrate coating in the form of a molten sheet in the presence of ozone, pressing the adhesive layer to the substrate surface, move the strip coated on one side of the second installation for coating and heat the strip to immediately before coating, the temperature of the strip ranged from 70 to coating, pushing him to the uncovered surface of the substrate, using ozone, heat the substrate with a coating so that it has reached a temperature that exceeds the melting point of the deposited polyolefin, cool base with the floor.

2. The method according to p. 1, in which the coating on the basis of the first guide contains polypropylene, the temperature of the preheated basis directly before application of the coating is from 100 to 130oWith the temperature of the heated strip directly before coating the second installation is from 80 to 120oC.

3. The method according to p. 1, in which the coating on the basis of the first guide contains polyethylene, the temperature of the preheated basis directly before application of the coating is from 80 to 110oWith the temperature of the heated strip directly before coating the second installation is from 80 to 110oC.

4. The method of applying on a metallic base coating of thermoplastic material, in which pre-heat the base so that immediately before coating it had a temperature of from 70 to 150oWith predpochtitel the polyester, consisting of one or more layers of polyester, coated on the base, pressing the molten sheet to the surface of the substrate, and moves the strip, coated on one side with polyester, the second installation for coating and heat the strip so that before coating the temperature ranged from 70 to 130oC, preferably from 90 to 120oTo perform a second installation for coating extrusion of the sheet containing the upper polyolefin layer and an adhesive layer of a modified polyolefin, is applied to the substrate coating in the form of a molten sheet in the presence of ozone, clutching the sheet with the adhesive layer to the substrate surface, heat the substrate with a coating so that it has reached a temperature exceeding the melting point of the deposited polyolefin, cool base coated.

 

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