A method of obtaining a weather-resistant powder coatings

 

The invention relates to a method for producing a weather-resistant powder coatings on metallic or non-metallic surfaces by applying powder cladding composition with subsequent melting and solidification, which apply powder cladding composition comprising hydroxyl and/or carboxyl containing polyester resin with acid structural units exclusively or primarily on the basis of aromatic dicarboxylic acids, their anhydrides and/or esters and low molecular weight polyfunctional epoxides as cross-linking agents, and melting and curing carried out under the influence of NIR radiation in the near infrared region of the spectrum 800-1200 nm within 1-200 C. 7 C.p. f-crystals, 2 tab.

The present invention relates to a method of creating an outdoor weather-resistant powder coatings on metallic and non-metallic substrates.

Decorative or functional cladding surfaces using powder coatings are widely used for coating of metals due to the high economic efficiency of this method and favorable prognosis from the point of view of the protection application. For coatings that are affected by UV radiation, such as those that are exposed to external conditions (construction paints, window profiles, doors, garage doors, metal doors, garden equipment, items, vehicles, etc.,) have been developed resistant powder cladding compositions, for example, on the basis of polyester resins with terminal carboxyl groups. Such polyester resins are usually subjected to curing with low molecular weight, highly functional cross-linking agents, as a polyfunctional epoxides or hydroxyalkylated.

For some time used a known external weather resistant polyester powder coating on the basis of such aromatic carboxylic acids as terephthalic acid or isophthalic acid. Powder coatings based on polyester resins have good mechanical properties and resistance to environmental effects, due to which they are suitable for a range of applications, especially in areas with a temperate climate. These coatings can be obtained cost-effective ways. Powder coating compositions of this type are subjected to hardening at nnyh compounds were unsuccessful. For example, attempts have been made to improve the weather resistance of powder coatings resulting from the use of polyester resins consisting solely or mainly of aliphatic and/or cycloaliphatic components. Such polyester resins are described, for example, in US-PS 5486988 and in EP 0561102. Although the powder coating obtained from the resins have superior weather resistance, they have lower mechanical properties and are characterized by higher raw material cost than formulations based on the above-mentioned aromatic carboxylic acids.

In connection with the foregoing, the present invention is to create a cost-effective from an economic point of view powder coating coatings, which are devoid of the above disadvantages. Mainly, these powder coatings shall meet the requirements of high weather resistance, so that they can be used without failure, for example, in areas with extreme climatic conditions.

This problem can be solved by using a method in which powder cladding coatings based on polyester resins, which contain aromatic dicarboxylic acids, their aredridel epoxy resins, subjected to curing with the use of radiation in the near infrared spectrum (NIR).

Consider powder cladding compositions may contain, for example, 40-95 wt.% polyester and 1-20 wt.% low molecular weight, polyfunctional epoxy resins, and compositions can be other components traditionally used in conventional amounts such that the total number of all components was 100 mass%.

Consider the polyesters have srednecenovogo molecular weight MP, for example, in the range of 500-10000 and the glass transition temperature, for example, 30-80oC.

Consider the polyesters may contain hydroxyl and/or carboxyl group, with the presence of such functional groups HE-the number may be, for example, 10-200, and acid number - 10-200.

NIR radiation used in accordance with the present invention, is a short-wave infrared radiation with a maximum intensity in the wavelength 760-1500 nanometers, preferably 780-1200 nanometers. The use of NIR radiation for drying varnish is a widely known method (, JOT 2/98). In accordance with this way of poroshkovoi without substantial heating of the substrate.

Unexpectedly, it was found that coatings based on polyester resins which contain such dicarboxylic acids as terephthalic or isophthalic acid, their anhydride and/or esters as main structural units, together with low molecular weight polyfunctional epoxides as cross-linking agents solidification under the influence of NIR radiation to acquire a significantly higher resistance than the resistance, usually achieved in the present resin, which is subjected to curing in a traditional way, for example, in an oven with circulating air flow. Mechanical properties, such as, for example, the flexibility of the coating, at least not inferior to the corresponding properties obtained with conventional curing. In addition, hardening under the influence of NIR can significantly reduce the freezing time compared with traditional curing in the oven.

Powder cladding compositions intended for use in the method according to the present invention contain as connecting the basics of hydroxyl - or carboxyl-containing polyesters, which contain as the sole or primary component is example, such as terephthalic acid or isophthalic acid, which react with such traditional aliphatic dialami, as, for example, neopentylglycol, ethylene glycol, butyleneglycol, hexanediol or diethylene glycol or cyclohexanedimethanol. Examples of other aromatic dicarboxylic acids can serve as naphthalene-2,6-dicarboxylic acid, naphthalene-1,5-dicarboxylic acid and phthalic acid. Preferred for use are carboxyl-containing polyesters based on terephthalic acid and isophthalic acid or their anhydrides.

The acid component containing more than 50% of aromatic dicarboxylic acid, based on the fraction of dicarboxylic acid in the polyester is preferred, with particular preference is given to acid component containing more than 50 wt. terephthalic acid and/or isophthalic acid, or their anhydrides and/or esters.

Such aliphatic and/or cycloaliphatic dicarboxylic acids as adipic acid or cyclohexanecarbonyl acid, can serve as an optional secondary components, and the number of aliphatic and/or cycloaliphatic dicarboxylic acids is not more than 50% of the fraction of the number of such polyfunctional branching agents, as, for example, glycerin or trimethylolpropane, as well as additives such as, for example, vulcanization accelerators. It is also possible to use mixtures of different polyesters. Polyesters intended for use in the present invention, can be obtained in the traditional way by the reaction of dicarboxylic acids, their anhydrides and/or esters with dialami (see, for example, D. A. Bates, "The science of powder coatings", so 1 and 2, Gardiner House, London, 1990").

Powder cladding compositions suitable for use in the method according to the present invention, contain a certain amount of low molecular weight polyfunctional epoxides as cross-linking agents that are required for curing. This amount is typically about 1-20 wt.% per system polyester/epoxide. As cross-linking agents can be used, for example, tripyridyltriazine (TGIC), polyglycidyl esters based on terephthalic acid/trimellitic acid (obtained, for example, from CibaChemie under the trade name AralditePT 910), polyfunctional aliphatic oxirane derivatives supplied, for example, by the company DSM Resins under the trade name Uranox

Powder cladding compositions containing the polyester and the epoxy crosslinking agent may optionally contain other conventional components, for example pigments and/or fillers, and such optional additives as flow regulators, degassing agents and/or curing accelerators. These substances are added in quantities which are known to the person skilled in the art. For example, you can use 0-50 wt.% pigments and/or fillers and 0.02-3 wt.% conventional additives.

Powder coating in accordance with the present invention receive by known methods extrusion/grinding, which are known to the person skilled in the art. Can be used in other ways, such as cooking powder spray supercritical solutions or methods with the use of non-aqueous dispersions.

According to the method of the present invention, the above-described powder coating applied on the substrate to be facing the known methods of applying powder materials, for example by the method of electrostatic spraying, after which it is melted and subjected to hardening after exposure to NIR radiation with the maximum of the distribution of intensity of halogen with exceptiona is haunted items suitable for the method of coating according to the present invention, are commercially available devices which can be obtained, for example, from Industrie Service Co. ; for example, for this purpose can be used a halogen lamp with a temperature radiative element K. Can also be used in combination with conventional sources of heat (infrared heaters, convection ovens) and optional additional systems reflector/lens.

Preferably the curing is realized under the influence of NIR radiation without additional combinations.

The coatings produced by the method according to the present invention have exceptional rheological characteristics, good mechanical properties and substantially improved weather resistance compared to powder finish coatings on the basis of the same resins obtained by traditional methods of curing.

The required degree of glossing powder coating can be adjusted by changing the composition of the powder cladding composition. Can be obtained coatings with high gloss and metallic or matte coating.

The powder coating obtained by the method coz what should be followed. The substrate can be used metals such as aluminum, steel, and such materials based on wood, as fiberboard medium density (MDF) or a mixture of different materials. Because the obtained coatings have good mechanical properties, in particular good flexibility, this method is particularly applicable for facing the coils or pre-coated metal (PCM).

The method according to the present invention enables highly efficient obtaining external weather-resistant powder coatings with unique properties resulting from the use of cost-effective raw materials while significantly reducing the time from hardening.

The following examples illustrate the present invention.

Manufacturer of powder coatings Powder cladding compositions listed in the table.1, turned in facing powders using methods traditionally used for the preparation of powder coatings based on intensive mixing, extrusion and grinding.

The obtained powders were applied to the subjects aluminum sheets with electrostatic method of application pokrytogo method of the present invention implemented in a tape device with 500W NIR emissive element from Industrie Service Co. when the value of power per unit area of 120 kW/m2. The freezing time was 5 seconds in example 1, 12; 5 seconds in example 2; 15 seconds in example 3, and 8 seconds in example 4. The operation of drying is carried out when the distance between the emissive element and the substrate in 50 mm

In the comparative examples, the samples were subjected to curing for 10 minutes at 200oWith in an oven with circulating air flow.

All compositions contained 4.2% of the commercially available flow regulator and 0.3% auxiliary degasifying agent (benzoin).

All values are given in mass percent.

The test for resistance to weathering Test of mechanical properties before and after the test on the weather gave the following results for all samples.

Dynamic testing using a falling ball (ASTM D 2794) 20 inch-pounds.

Test for plasticity (DIN EN ISO 1519) 4 mm Test Erichsen (DIN EN ISO 1520) 7 mm Hatch pattern (DIN EN ISO 2094) GtOA All samples tested on the active atmospheric effects, had residual QUV () 313 nm. In table. 2 presents the values of time after which the residual gloss (measured at 60oC) decreased to 50% of the original snub obtain a weather-resistant powder coatings on metallic or non-metallic surfaces by applying a powder cladding composition with subsequent melting and solidification, which apply powder cladding composition comprising 40-95 wt.% the hydroxyl and/or carboxyl-containing polyester resin with acid structural units exclusively, or mainly, on the basis of aromatic dicarboxylic acids, their anhydrides and/or esters, 1-20 wt.% polyfunctional low molecular weight epoxides as cross-linking agents, 0-50 wt.% pigments and/or fillers and 0.02 to 4.5 wt.% traditional additives, and melting and curing carried out under the influence of radiation in the near infrared region of the spectrum with the maximum of the intensity distribution in the area of 800-1200 nm over time 1-200 C.

2. The method according to p. 1, in which the number of aromatic dicarboxylic acids, their anhydrides and/or esters is more than 50 wt.% the number of the acid fraction of the polyester.

3. The method according to p. 1 or 2, in which use powder cladding composition, which contains 40-95 wt.% polyester resin.

4. The method according to p. 3, in which the polyester contains a carboxyl group.

5. The method according to any of the preceding paragraphs, in which use polyester resin on the basis of terephthalic acid and/or isophthalic acid, their anhydrides and/or esters.eftalou acid, and/or isophthalic acid, or their anhydrides and/or esters.

7. The method according to any of paragraphs.1-6, in which the curing is carried out in the course of time in the range of 1-30 C.

8. The method according to any of paragraphs.1-7, in which use elements that emit in the near infrared region of the spectrum with the maximum of the intensity distribution in the range of 0.8-1.2 μm.

 

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