MXPA97007979A - Method for curing compositions of recubrimie - Google Patents

Abstract

The present invention relates to: In a method of curing a coating composition, which has been applied to a substrate, such as a road or a cellulosic compound, the coating is exposed to UV radiation and microwaves to cause rapid curing, from where the covered substrate is allowed to be used, handled, stacked and / or stored shortly after

Description

Method for Curing Coating Compositions The invention relates to a method for curing aqueous coating compositions, comprising the use of radiation, and aqueous coating compositions curable by radiation. For some years methods have been known that comprise the use of microwave radiation to cure floating coatings on substrates. For example, WO 90/02613 discloses a method for forming a film of a paint, containing water, on a temperature sensitive substrate, and then irradiating the coated substrate with microwave to cure the coating. The method is described to provide a rapid cure of both zinc silicate paints and emulsion paint systems on temperature sensitive substrates that could be damaged by the baking conditions normally required for curing, and to allow Paint films are cured very fast in the online apparatus. As indicated in WO 90/02613, a great majority of floating coatings contain some volatile plasticizers known in the art as coalescents. These coalescents are needed to ensure that during the drying process the polymer is sufficiently soft to form an appropriate film and then evaporate and leave a strong and resistant coating. Although the microwave treatment of such coatings results in rapid evaporation of water, coalescents that evaporate slower tend to remain behind in the coating, which, until they have evaporated from the coating, leaves it insufficiently strong for covered substrates that they are stacked and stored shortly after treatment, otherwise they stick together and cause considerable damage when they eventually re-separate. Although the problems of blocking and poor stacking capacity are mentioned in WO 90/02613, as a result of the use of emulsion paints containing a coalescing material to reduce the minimum temperature of film formation, and this prior art seems to be directed to the Resolution of said problem, particularly concentrates on providing a curing method for zinc silicate paint systems. We have found that suitable results for emulsion-type coating compositions, which contain coalescents, can not be obtained following the teaching of WO 90/02613; the covered substrates stick together when stacked for a short period of time after the microwave treatment. Ultraviolet curable compositions have been used in the industry for some time, including as compositions for coating substrates. These compositions may be high solids compositions containing low amounts or no volatile components, or low solids, solvent based or diluent based compositions, which contain significant amounts of volatile components such as organic solvents or water. For example, the UV curable component can be an unsaturated pre-polymer. It has been recognized that the use of such UV-curable unsaturated pre-polymers, which are found in aqueous coating compositions, is particularly advantageous for the environment and easy to apply, which is why, with water as the diluent, the Viscosity can be regulated as much as desired without having to add an organic, volatile, contaminating solvent, and the inherent non-contaminating nature of a UV curing coating does not decrease by adjusting its viscosity. UV-curing floating coatings can be applied easily and safely by spraying (automatic or manual), curtain coating, flow coating or roll coating. In addition, due to the evaporation of the water during the drying process (and the resulting shrinkage of the film that this causes), the brilliance of these coatings is easily controlled with the addition of low amounts of standard leveling agents known in the art (eg, amorphous silicas). However, even with these advantages, the UV-curing floating coatings have a major impediment: the water contained in the newly applied film must evaporate almost completely before the coating is cured with UV rays. Otherwise, the water will be permanently trapped in the film and this will compromise the resistance to coating stains and adversely affect the appearance of a clear coating (introduction of steam). This preferred requirement to evaporate the water before exposure to UV rays means that the drying phase of a floating, UV curing coating takes longer than the UV curable, 100% non-volatile coating. As an example, it is common that the time between the application and stacking of a coating, of curing with UV rays, 100% non-volatile, is as short as 1 minute, while for a floating coating, of UV curing, This same time can be 10 minutes or more. Thus, the industrial use of the floating coating, curing with UV rays, suffers from a loss of productivity compared to the UV curable coating, 100% non-volatile. The productivity of a modern industrial process is extremely important and thus, although the floating coatings, of curing with UV rays, offer several advantages in comparison with the coverings of curing with UV, 100% non-volatile, the floating coatings, of curing with UV rays are not able to realize their full potential due to their low productivity. Therefore, the object of the present invention is to provide a curing method for coating compositions that is rapid and that provides a cured coating composition that is strong enough to allow the handling, stacking and storage of the substrates a shortly after coating, while removing or at least significantly reducing the amount of blocking damage to the surface of the covered and cured substrate. The present invention also seeks to provide an efficient and suitable method for curing coating compositions that do not contain a coalescent. Thus, the present invention provides a method for curing a floating coating composition, comprising the following steps: a) applying to the substrate the floating coating composition comprising polymer solids, of which at least 5% by weight of them it is curable with ultraviolet rays. b) irradiate the covered substrate with microwave radiation; and c) irradiating the covered substrate with ultraviolet radiation. The combination of irradiating a coating with microwave and ultraviolet radiation advantageously outweighs the productivity problems associated with the use of conventional UV curable coatings (either a composition that contains in part a UV curable component or a composition formed of a thermostable coating that contains 100% UV rays Microwave drying alone suffers from low productivity (panels can not be stacked after evaporation of water) and floating coatings, UV curing, suffer little productivity (typically require up to 10 minutes or more of drying time after application, before they can be cured with UV rays), but when combined, these two techniques surprisingly offer a highly productive coating process, they also allow that covered substrates are handled and stacked shortly after treatment, without fear that The substrates stick together. The process can allow the coating on the substrate to cure enough for the substrate to be used, handle and stack and / or stack approximately 90 seconds after the coating has been applied: drying the coating by microwave can take so little about 60 seconds from the application, and the UV curing of the dry coating can take as little as 30 seconds. Preferably, the coating composition comprises at least 25% by weight, based on the total weight of the polymer solids in the coating composition, of a UV curable component, and in particular, a composition which is preferred is preferred. comprising polymer solids of which at least 50% by weight is curable with UV rays. The UV curable component can be selected from one or two main categories: 1.) polymerized, free radical polymerized (meth) acrylate functionalized polymers, and 2.) cationically polymerized epoxies, the categories of which are well known and well documented in the literature. technique. The functionalized polymers of (meth) acrylate usually comprise monomers and functional oligomers of (met) acrylate, combined with a photoinitiator to facilitate curing with UV rays. These functional oligomers of (meth) acrylate are typically prepared by a) the reaction of difunctional epoxies with (meth) acrylic acid, b) the reaction product of difunctional isocyanates with hydroxy functional (meth) acrylates, or c) the condensation product of (meth) acid acrylic and hydroxyl groups on a polyester column, or a hydroxy (meth) acrylate with residual acid groups on a polyester column. Cationic systems tend to be based on cycloaliphatic epoxies and a photoinitiator that decompose to provide a "super" acid with UV radiation. The super acid catalyses the cationic polymerization of the epoxy. A general description of these systems can be found in "Radiation Curin in Polymer Science and Technology" (Curing radiation in polymer science and technology). Vol, 1: Fundamentáis in Methods. Edited by J P Fouassier and J E Rabek. published by Elsevier Applied Science (1993).

The coating composition used in the method of the present invention may also contain a thermoplastic component, which is preferably between 0 and 95% by weight, based on the total weight of the polymer solids in the coating composition. Said combination of thermoplastic and UV curable components has hitherto not been used in the same coating composition; UV coatings are considered to be high-development coatings, while thermoplastic coatings are considered as not being able to achieve the same high level of hardness and / or chemical resistance compared to entangled UV coatings. In other words, the two types of coatings are used in mutually exclusive applications, and mixing together the two types of coating is not something that the expert would do since no synergistic effects are observed. Suitable thermoplastic materials are those typically found in conventional latex paints, for example, floating or water-diluted polymers such as poly (meth) acrylates, styrene-acrylics, vinyls, ethylene-vinyl-acrylic terpolymers, alkyds , polyesters, polyurethanes, nitrocellulose, cellulose-acetate-butyrate, polyethers, polyamides, epoxy-esters or vinyl halides. Preferably, the thermoplastic material is a homopolymer or copolymer formed from the polymerization of one or more of the following monomers: ethylene, a vinyl monomer; an aromatic alkenyl monomer, such as styrene, methyl styrene, dimethyl styrene, diethyl styrene, chlorostyrene and isopropyl styrene; an acrylamide monomer, such as ethyl acrylamide and methyl acrylamide; and an alkadiene monomer, such as butadiene and isoprene. Typical vinyl monomers include, but are not limited to, vinyl halides, vinylidene halides, vinyl acetate and acrylonitrile. Chlorine and bromine are exemplary halide parts of the vinyl halide and vinylidene halide monomers. The thermoplastic materials can be processed in a conventional manner. As an alternative for a thermoplastic component, the coating composition may also comprise a two-pack or two-component system, comprising two components that are normally stored in separate containers and when mixed together, immediately prior to application, form a thermosetting polymer. by means of a chemical reaction as opposed to UV irradiation. The method of the present invention has application in said coating composition system, since the UV component of the coating composition can be cured by UV radiation to form a reinforced coating, before the components of two packages have had the opportunity to react together; hence, the productivity of the application of said coating composition is improved. Suitable thermosetting materials may include, for example, floating or diluting polyols-polyisocyanates in water, polyamines-epoxies, carboxy functional acrylic-epoxies, carboxy functional acrylic-carbodiimides.

The stage in which it is irradiated with UV radiation to the covered substrate may be before, subsequent to or concomitant with the microwave radiation step, but it is preferred to irradiate the covered substrate with UV after the microwave irradiation step has been substantially completed. .

The composition may also contain other ingredients conventionally used in latex paints. The equipment and methods for conventional UV curing can be used in the process of the present invention. Similarly, equipment and methods for conventional microwave drying, such as those described in WO 90/02613, can be used in the process of the present invention. In another aspect of the present invention, there is provided an apparatus for curing a floating coating composition, comprising a component curable with UV rays in an amount of at least 5% by weight, based on the total polymer solids in the composition, which has been applied to the substrate, wherein the apparatus comprises a microwave radiation source and a UV radiation source, each of which is located near the coating and each is capable of emitting sufficient radiation in the coating and , together, they are capable of causing the coating to cure in a period of three minutes, preferably 2 minutes, and more preferably 1.5 minutes, of the exposure of the coating to radiation. After the exposure period, the coating may be sufficiently cured for the covered substrate to be used, handled, stacked and / or stored, as required. Substrates that can be covered using the method of the present invention comprise, at least in part, any of the materials selected from the cellulose-containing group, such as wood and paper, and cellulose compounds, such as MDF, hardboard and particulate carton.; plastics; metals; mineral substrates; and construction material, such as tarmac, brick and cement; and any composite material comprising one or more of these materials. Advantageously, either the substrate is a path and the composition is a paint to mark the path, which may additionally comprise reflecting beads, preferably glass beads, which are normally used in said paints, or the substrate is a composite of cellulose, vg for interior furnishing applications, and the floating composition is a sealant. The present invention will now be described with reference to the following examples. EXAMPLE: This example illustrates that the method disclosed in WO / 90/02613, when used to dry a dispersion polymer, acrylic, thermoplastic, (a TP polymer), provides a completely dry coating when tested with the thumb , ASTM D1640-83 part 7.6, and this is advantageous in comparison to a traditionally dried thermoplastic coating, where thermal convection drying is used.

A floating coating containing a TP polymer (TP formulation) is applied by means of conventional spraying to a glass plate (80 g wet coating / m2) and the coating is passed through a commercial microwave dryer. The coating emerges two minutes later, and is completely dried as defined by ASTM D1640-83 part 7.6. Measuring the weight before and after the passage through the microwave dryer, we noticed that the coating lost approximately 48 gr./m2, which is close to the theoretical limit of weight loss of this coating. The same TP polymer coating does not dry completely, when applied in the same way to a glass plate and dried at 50 ° C (a temperature commonly used in the coating industry) in a thermal convection oven; (ASTM D1640-83 part 7.6 did not work) after two minutes of cooking. In the same way, the weight loss was followed and it was found that it was only about 15 gr./m2. This shows that the microwave dryer is more efficient at removing water than the thermal convection oven.

TP formulation Ingredient Parts in Weight Source Primal E-2955 (37%) 85.33 Rohm and Haas Co. , (Acrylic dispersion Philadelphia, PA, thermoplastic) E.U.A.

Water 2.13 city services Zinplex 15 1.70 Ultra-Additives, (Ionic interlacing) Lehmann and Voss, Hamburg, Germany.

Butyl-glycol 5.25 Union Carbide, (coalescent) New Jersey, E.U.A Byk 024 0.29 Bik Chemie Wesel, (defoaming) Germany.

Tego Foamex 800 0.37 Tego Chemie, Essen (defoaming) Germany.

Deuteron MK 0.79 Schoener, Bremen, (agent of Germany mat) Michem 39235 1.39 Michelman, (wax emulsion) Cincinatti, Ohio, E.U.A.

Mobilcer M 2.48 Mobil, Paris, (wax emulsion) France. Acrysol SCT-275 0.48 Rohm and Haas Co (non-ionic rheology modifier) TOTAL 100.00 Approximately 34% by weight of solids. EXAMPLE IB: This example shows that the coating composition of Example IA, when dried according to WO / 90/02613, is surprisingly inefficient in producing a strong coating with stacking capability. The same floating coating (TP formulation) is applied by spraying on two covers (60 grams of wet coating / m2 per cover) to two flat panels veneered in oak (17cm x 23cm), using the following application and veneering procedure : spray application of air followed immediately by the TI minutes in a drying device, followed by sanding with sandpaper with stearate No. 320, followed by application by air spray of the second cover and immediately followed by the minutes T2 in a drying device. After the application and drying of the two covers, the panels are immediately tested for blocking resistance by placing the painted sides together and storing them under a pressure of approximately 255 kg./m2, for a minimum of three hours. After said storage, the panels are separated and the degree of difficulty to separate them together with the degree of damage of the painted surfaces is noted. The results of the blocking tests are shown in Table 1 below.

TABLE 1 Results of the Block Test IT device, T2, Difficulty% of the of drying mins. mins of separation surface damaged Microwave 2 2 difficult 33 break away with hand 2 2 Impossible oven of 100 separation convection thermal 10 oven Does not stick or convection "in the minimum thermal The percentage of the damaged surface is measured by visual inspection of the panels.

EXPERIMENT 2A.

The floating coating, UV curing, described in the UV Formulation, is applied by spraying to a black plastic substrate (60 gr. wet / m2) which is then passed through a device of microwave drying for two minutes. After the microwave drying, the coating is dried according to with the ASTM D1640-83 part 7.6, in addition, the coating is very transparent and does not appear milky or Nebulosity due to trapped water.

UV formulation Ingredient Parts Source in weight Primal E-3120 (40%) 91.04 Rohm and Haas Co.

(Acrylic dispersion Philadelphia, PA, UV curable) E.U.A.

Darocur 1173 0.55 Ciba-Geigy, Basel (photoinitiator) Switzerland. Water 5.30 city services Tego Glide 410 0.23 Tego Chemie, Essen, (antirayas agent) Germany Surfynol 104 H 0.73 Air Products, (non-ionic surfactant) Allentown, PA, USA Acrysol RM-8W 0.69 Rohm and Haas Co. (diluted to 5% in water) (non-ionic rheology modifier) Deuteron MK 0.79 Schoener, Bremer, (matting agent) Germany TOTAL 100.00 Approximately 39% by weight of solids EXPERIMENT 2B. After applying the UV curing coating to the substrate, as described in Experiment 2A, the coating is dried in a thermal convection oven for two minutes. However, after said treatment, the film does not dry and is cloudy (presumably due to the water still trapped in the film).

As observed in the fully thermoplastic coating (Experiment IA), the drying of a floating, UV curing coating with a microwave device is more efficient than with a thermal convection oven.

EXPERIMENT 3: The two floating coatings, previously mentioned, (TP and UV Formulations) are mixed in the weight indices shown to produce three more floating coatings. These five floating coatings are described in Table 2.

Table 2 COMPOSITION Reference of Parts by weight of Parts by weight of the formulation Formulation TP formulation UV TP 100 0 Mixture 1 75 25 Mixture 2 50 50 Mixture 3 25 75 The five floating varnishes listed in Table 2 are applied by spraying on two covers (45 grams of wet coating / m2 for each cover) to two flat panels veneered in oak (17cm x 23cm), using the following application procedure and drying: the spray application of air was followed by two minutes in a microwave drying device, in some cases (see Table 3) followed by 30 seconds in a UV curing device (Full scale model of Superfici Co., Monza, Italy, using two mercury lamps of 11 kilowatts each), followed by sanding with No. 320 stearate paper, followed by the application of air spray of the second cover , followed, immediately, by two minutes in a microwave drying device, in some cases (see Table 3) followed by 30 seconds in a UV curing device (full scale model of Superfici Co., Monza, Italy , using two mercury lamps of 11 kilowatts each). After application and drying of the two covers, the panels are immediately tested for blocking resistance by placing the painted sides together and storing them under a pressure of approximately 255 kg / m2 for a minimum of three hours. After storage, the panels are separated and the degree of difficulty to separate them together with the degree of damage of the painted surfaces is noted. The results of the blocking tests are shown in Table 3 below.

From the results of the blocking resistance, it is clearly shown in Table 3 that a floating coating, which has been dried with microwaves and has not given UV radiation, has no block resistance. In the absence of UV exposure, all five formulations have a very low blocking resistance which makes them essentially not useful in a finishing line, modern, industrial. Although microwave drying is appropriate for rapid water removal, surprisingly it does not produce the block (piling) resistance needed, and therefore, can not be used in practice. The only combination that allows a certain level of block strength (and therefore allows commercial use) is to use a varnish containing at least a minimum part of a polymer or pre-polymer that is capable of curing under UV radiation, and drying by UV radiation and microwaves. As can be seen in Table 3, to reduce the damage caused to the surface in the blocking test described above, the coating composition must contain a component curable with UV rays.

Table 3 Results of the Block Test Reference ¿Exposicic * > n Difficulty% of the of the TJV rays? of surface separation damaged form TP Not Impossible of 100 break away TP Yes Impossible of 100 break away Mixture 1 No Much strength 50 Required Mix 1 Yes Some strength 33 Required Mixture 2 Not Impossible of 100 break away Mixture 2 Yes Very low 0 strength required Mix 3 Not much strength 33 required Mix 3 Yes Not sticky 0 in the least UV Not Much strength 33 required UV Yes Not sticky 0 in the least

Claims (10)

Claims

1. A method for curing a floating coating composition, comprising the following steps: a) applying the coating composition, comprising polymer solids of which at least 5% by weight is UV curable, to the substrate; b) irradiate the covered substrate with microwave radiation; e c) irradiate the substrate with UV radiation.

A method according to claim 1, wherein the polymeric solids part of the coating composition comprises at least 25%, and preferably at least 50% by weight, of a UV curable component.

3. A method according to claim 1 or 2, wherein the coating composition also comprises a thermoplastic component.

A method according to claim 1 or 2, wherein the coating composition also comprises a thermosetting polymer, which is preferably formed from a two component system comprising two components which, when mixed together, undergo a chemical reaction to form the thermostable polymer.

5. A method for curing a floating coating composition, according to any of the preceding claims, wherein the coating composition is applied in layers to the substrate, either as the sole coating composition or in conjunction with a second coating composition.

6. A method according to claim 5, wherein the second coating composition does not contain a UV curable component.

A method according to any one of the preceding claims, wherein the substrate comprises, at least in part, any of the materials selected from the cellulose-containing group, such as paper and wood, and cellulose compounds, such as MDF, hard cardboard and particulate cardboard; plastics, metals; mineral substrates; and construction materials, such as tarmac, brick and concrete; and any combination or compound thereof.

A method according to any one of the preceding claims, wherein the coating is a floating paint for road construction, and the substrate is a road.

9. A floating coating composition, comprising a thermoplastic component and a UV curable component, wherein the UV component comprises at least 5% by weight, preferably 20% by weight, more preferably 25% by weight, weight, and even more preferably at least 50% by weight, of the total solids of the polymer in the composition.

10. Apparatus for curing a floating coating composition, comprising a component curable with UV rays in an amount of at least 5% by weight, based on the total polymeric solids in the composition, which has been applied to the substrate, wherein the apparatus comprises a source of microwave radiation and a source of UV radiation, where each is located near the coating and each is capable of emitting sufficient radiation in the coating, and which, together, are capable of causing the coating dry and cure in a period of three minutes, preferably two minutes and more preferably 1.5 minutes, of exposure to radiation.