MX2008007907A

MX2008007907A - Powder coating composition suitable for thermo-sensitive substrates

Info

Publication number: MX2008007907A
Application number: MXMX/A/2008/007907A
Authority: MX
Inventors: Qui Nguyen Phu; Schneider Mike; Niggemann Frank
Original assignee: E I Du Pont De Nemours And Company; Qui Nguyen Phu; Niggemann Frank; Schneider Mike
Priority date: 2005-12-20
Filing date: 2008-06-18
Publication date: 2008-09-02

Abstract

The present invention provides a powder coating composition obtainable by homogeneous mixing of at least two separately produced powder coating compositions as powder coating bases comprising (A) at least one powder coating base prepared from one or more glycidyl-functionalised (meth)acrylic resin, one or more di- carboxylic acid or the anhydrides thereof having an acid value in the range of higher 400 as hardener (cross-linker), together with at least one coating additive, and optionally pigment and/or filler, and (B) at least one powder coating base prepared from one or more glycidyl-functionalised (meth)acrylic resins, one or more hardeners (cross-linkers) having an acid value in the range of 100 to 400, together with at least one coating additive, and optionally pigment and/or filler, in a mixing ratio of component A) to component B) of 1:3 to 3:1 , relative to the weight;the powder coating composition provides coatings with a desired gloss level and is curable at a temperature under 1800C.

Description

COMPOSITION OF ADEQUATE POWDER COATING FOR THERMOSENSIBLE SUBSTRATES FIELD OF THE INVENTION The present invention is directed to a powder coating composition that provides a controlled gloss coating which is especially suitable for coating substrates and curing at lower temperatures.

BACKGROUND OF THE INVENTION Controlling the gloss and especially the matting of powder coatings and maintaining these superior technology properties of the coating are currently still difficult tasks. The use of matting agents to adjust the brightness to the desired level is well known, see WO 03/102048, U.S. 2003/013978, EP-A-1129788 and EP-A-0947254. Examples of these agents are waxes, silica, glass beads and crystalline resins. These agents commonly do not react at curing temperatures below 180 ° C, and the compositions commonly lead to coatings with a loss in technological properties. Other techniques to form a matting effect are the use of dry mixtures of chemically incompatible powders. REF .: 193077 or the use of different process conditions, such as different curing conditions, as described in EP-A-0706834. For example, WO20044289 discloses a powder coating composition that provides a gloss value below 55% which is prepared by dry blending a composition based on an acrylate resin containing glycidyl groups and a carboxylic acid hardener and a composition based on a material containing carboxyl groups having an acid value in the range of 10 to 300. DE-A 2247779 claims matt powder coatings prepared by dry blending two powder coating compositions based on compositions comprising hardeners which have different gel formation times. However, processes that use these formulations are commonly difficult to control or inefficient, and do not provide coatings that can be cured at a lower temperature range. Therefore, there is a need to provide coating compositions suitable for powder coating applications on substrates that can be cured at a lower temperature range, also for temperature sensitive substrates and which result in controlled gloss coatings.

BRIEF DESCRIPTION OF THE INVENTION The present invention provides a powder coating composition obtainable by the homogeneous mixing of at least two powder coating compositions produced separately as powder coating bases, comprising (A) at least one powder coating base prepared from one or more (meth) acrylic resins functionalized with glycidyl, one or more di-carboxylic acids or the anhydrides thereof having an acid value in the range of more than 400 as a hardener (crosslinker) ), together with at least one coating additive, and optionally, pigment and / or filler, and (B) at least one powder coating base prepared from one or more (meth) acrylic functionalized glycidyl resins, one or more more hardeners (crosslinkers) having an acid value in the range of 100 to 400, together with at least one coating additive, and optionally pigment and / or filling, in a mixing ratio of component A) to component B) from 1: 3 to 3: 1, in relation to the weight. The powder coating composition of this invention provides coatings with a desired level of gloss as well as coating properties, such as high durability and smoothness. The composition of the invention it can be cured at a temperature below 180 SC, and is therefore especially suitable for coating applications on thermosensitive substrates.

DETAILED DESCRIPTION OF THE INVENTION The features and advantages of the present invention will be more readily understood by those of ordinary skill in the art from reading the following detailed description. It should be appreciated that certain characteristics of the invention, which are, for clarity, described above and below in the context of separate modalities, can also be provided in combination in a single modality. Conversely, various features of the invention that are, for brevity, described in the context of a single embodiment may also be provided separately or in any sub-combination. In addition, singular references may also include the plural (for example, "a", "an" and "an" may refer to one or more than one) unless the context specifically indicates otherwise. Slight variations above and below the indicated intervals can be used to achieve substantially the same results as the values within the ranges. Also, the description of these intervals tries to be a continuous interval including each value between the minimum and maximum values. All patents, patent applications and publications referred to herein are incorporated by reference in their entirety. In component A) and B) resins are used (meth) acrylics functionalized with glycidyl as the main binding resins. Glycidyl functionalized (meth) acrylic resins can be produced in a conventional manner from glycidyl (meth) acrylic monomers, as described, for example, in D.A. Bates, The Science of Po der Coatings, volumes 1 and 2, Gardiner House, London, 1990, pages 62-70, and as is known to the person skilled in the art. Examples of glycidyl functionalized (meth) acrylic resins are acrylic resins functionalized with glycidyl or copolymers thereof, for example, Almatex® PD 7610, Almatex® PD-1700 (Siber Hegner GmbH), WorléeCryl® CP 550 (Worlee Chemie GmbH), FINE-CLAD® WYR-903 (Reichold). Almatex® PD 7610 and Almatex® PD-1700 are preferred for use in component A), and WorléeCryl® CP 550 and FINE-CLAD® WYR-902 for use in component B). Glycidyl-functionalized (meth) acrylic resins have an epoxide equivalent weight (EEW) in a range of 300 to 2,000, an epoxy equivalent weight determined by means of ADSAM142, a method code of the EEW test using a self-titrator (Brinkman Metrhohm 751 GPD Titrino) and known to a person skilled in the art, and a glass transition temperature Tg in a range of, for example , 30 to 802C, preferably 40 to 70 Tg determined by means of differential scanning calorimetry (DSC). Glycidyl-functionalized (meth) acrylic resins can be partially replaced by additional resins, such as, for example, diglycidyl ethers of bisphenol, epoxy novolac and other resins containing epoxy groups, in amounts in the range of less than 10% by weight , based on component A). As the hardener in component A), one or more di-carboxylic acids or the anhydrides thereof are used. The di-carboxylic acid or the anhydrides thereof have an acid value in the range of 400, preferably in the range of 410 to 600. Examples are di-carboxylic acids with a number of carbon atoms C in the range of 4. to 20, preferably 10 to 18. As hardener in component B) one or more hardeners are used having an acid value in the range of 100 to 400, preferably in the range of 250 to 350. These hardeners are conventional that they contain carboxyl groups, such as polycarboxylic acids or the anhydrides thereof, which are different from that of component A), polyesters containing carboxyl groups, (meth) acrylates containing carboxyl groups, polyols. Examples are C 12 dodecanedioic acid and Additol® P 791. For this invention, C 12 -dodecanedioic acid in component A) and Additol® P 791 in component B) are preferred. The acid value is defined as the number of mg of potassium hydroxide (KOH) required to neutralize the carboxylic groups of 1 g of the resin. The hardeners of components A) and B) can be partially replaced by additional hardeners useful for the curing of epoxy resins, such as, for example, hardeners containing amide or amino groups, for example dicyandiamide and the derivatives thereof, in amounts in the range of less than 10% by weight, based on each of component A) and B). The powder coating base of A) and B) may contain as additional components the conventional constituents in powder coating technology, such as additives, pigments and / or fillers as known to a person skilled in the art. The additives are, for example, auxiliaries of degassing, flow control agents, leveling agents, texturizing agents, fillers (extenders), photo-initiators, catalysts, dyes. Examples are flow control agents incorporated in the composition according to the invention by means of an inorganic carrier or by means of mixing techniques known to a person skilled in the art. Compounds having antimicrobial activity can also be added to the powder coating compositions. The entanglement reaction can be further accelerated by the presence in the powder coating composition according to the invention of known catalysts by thermal entanglement. These catalysts are, for example, tin salts, phosphides, amines and amides. They can be used, for example, in amounts of 0.02 to 3% by weight, based on the total weight of the powder coating composition. The powder coating base A) and B) may contain transparent, color-imparting and / or special-effect imparting pigments, and / or fillers (extenders). Suitable color imparting pigments are any conventional coating pigment of an organic or inorganic nature. Examples of inorganic or organic color imparting pigments are titanium dioxide, titanium dioxide micronized, carbon black, azo pigments and phthalocyanine pigments. Examples of special effect imparting pigments are metallic pigments, for example, made of aluminum, copper or other metals, interference pigments such as metallic pigments coated with metal oxide and coated mica. Examples of suitable extenders are silicon dioxide, aluminum silicate, barium sulfate and calcium carbonate. The above constituents (additives, pigments and / or fillers) are used in conventional amounts known to the person skilled in the art, for example 0.01 to 30% by weight, based on the total weight of each powder coating base, preference 0.01 to 20% by weight. Component A) contains, for example, 30 to 90% by weight of one or more (meth) acrylic resin functionalized with glycidyl, 1 to 30% by weight of one or more di-carboxylic acids or the anhydrides thereof having an acid value in the range of more than 400 as a hardener (crosslinker), 0.1 to 10% by weight of at least one coating additive and 0 to 30% by weight of pigment and / or filler. Component B) contains, for example, 30 to 90% by weight of one or more (meth) acrylic functionalized glycidyl resins, 1 to 30% by weight of one or more hardeners (crosslinkers) having an acid value in the range of 100 to 400, 0.1 to 10% by weight of at least one additive of coating and 0 to 30% by weight of pigment and / or filler. The powder coating bases of A) and B) are prepared separately by conventional manufacturing techniques used in the powder coating industry, such as extrusion and / or milling processes, known to a person skilled in the art. For example, the ingredients of each powder coating base can be mixed together by dry mixing methods and then milled to a fine powder, which can be graded to the desired grain size, for example, up to an average particle size from 20 to 200 μm. The mixed ingredients can be further heated to a temperature that melts the mixture, and then the mixture is extruded. The extruded material is then cooled on cooling rollers, broken and then ground to a fine powder, which can be classified up to the desired grain size. Each powder coating base can also be prepared by spraying from supercritical solutions, NAD "non-aqueous dispersion" processes or an ultrasonic rest wave atomization process. Moreover, the specific components of the powder coating base according to the invention, for example, additives, pigment, fillers, can be processed with the powder coating particles finished after of the extrusion and grinding by a process of "agglutination" using an impact fusion. For this purpose, the specific components can be mixed with the powder coating particles. During mixing, the individual powder coating particles are treated to soften their surface in such a way that the components adhere to them and agglutinate homogeneously with the surface of the powder coating particles. The softening of the surface of the powder particles can be done by heat treating the particles to a temperature, for example, the glass transition temperature Tg of the composition, in a range of, for example, 50 to 60SC. After cooling the mixture the desired particle size of the resulting particles can be achieved with a sieving process. The powder coating base of component A) and the powder coating base of component B) can be mixed together in a mixing ratio of component A) to component B) from 1: 3 to 3: 1, preferably 1 : 2 to 2: 1. This preferred powder coating composition can provide powder coatings with low or medium gloss. The gloss of the finishes according to this invention is measured at an angle of 60a in accordance with DIN 67 530 and can be adjusted in the range of 1 to 95 gloss units using the composition according to the invention. Typically, a low gloss (matte finish) has a gloss in the range of 1 to 30 gloss units and a medium gloss finish in the range of 30 to 60 gloss units. The present invention also provides a process, in which a powder coating composition comprising A) at least one powder coating base prepared from one or more (meth) acrylic functionalized glycidyl resins, one or more acids di-carboxylics or the anhydrides thereof having an acid value in the range of more than 400 as a hardener (crosslinker), together with at least one coating additive, and optionally pigment and / or filler, and B) at least a powder coating base prepared from one or more (meth) acrylic functionalized glycidyl resins, one or more hardeners (crosslinkers) having an acid value in the range of 100 to 400, together with at least one coating additive, and optionally, pigment and / or filler, in a mixing ratio of component A) to component B) of 1 : 3 to 3: 1, in relation to the weight, is produced in such a way that component A) and component B) are initially produced separately using conventional powder coating production processes, and the two components A) and B) in the indicated mixing ratio are then subjected to an additional operation, for example, a dry mixing or an extrusion operation, to ensure homogeneous mixing of the two components. The powder coating composition of this invention can be applied by, for example, electrostatic spraying, thermal or flame spraying, or fluidized bed coating methods, also, coil coating techniques, all of which are known to those skilled in the art. The technique. The coating compositions can be applied, for example, to metal substrates, non-metallic substrates such as paper, wood, plastic, glass and ceramics, as a coating system or as a coating layer in a multi-layer film construction. In certain applications, the substrate to be coated may be preheated before the application of the powder composition, and then either heated after the application of the powder or not. For example, gas is commonly used for several heating steps, but other methods are also known, for example, microwave, IR or NIR. The powder coating compositions according to the invention can be applied directly onto the surface of the substrate or on a layer of a primer that can be a liquid or powder based primer. The powder coating compositions according to the invention can also be applied as a coating layer of a multi-layer coating system based on liquid or powder coatings, for example, based on a transparent powder coating layer or liquid applied on a base coat layer for imparting color and / or imparting special effects or a powder or liquid top coating, pigmented and a layer applied on a previous coating. v "The applied and melted powder coating layer can be cured by thermal energy.The coating layer can, for example, be exposed to convective, gas and / or radiant heating, for example, infrared (IR) irradiation and / or Near infrared (NIR), as is known in the art, up to temperatures of, for example, 1002C to 200aC, preferably from 1202C to 1802C (target temperature in each case) .The powder coating composition can also be cured by radiation high energy known for a trained person UV (ultraviolet) radiation or electron beam radiation can be used as high energy radiation. UV radiation is preferred. The irradiation can proceed continuously or discontinuously. Double curing can also be used. Double curing means a method of curing the powder coating composition according to the invention wherein the applied composition can be cured, for example, both by UV irradiation and by thermal curing methods known to a skilled person. The present invention is further defined in the following examples. It should be understood that these examples are given by way of illustration only. From the above description and these examples, one skilled in the art can determine the essential characteristics of this invention, and without departing from the spirit and scope thereof, can make several changes and modifications to the invention to adapt it to various uses and terms . As a result, the present invention is not limited by the illustrative examples shown below, but rather is defined by the claims contained herein below. The following examples illustrate the invention.

EXAMPLES Example 1 Manufacture and application of a powder coating composition A powder coating composition according to the invention (formulation 1) is prepared according to the following ingredients: Formulation 1 The ingredients of each component A) and of each component B) are mixed separately and together and extruded separately in a PR 46 extruder (signature: Buss AG) at 1202C.

The mixed and melted formulation is cooled and the resulting material is milled to a D50 value of 40 μm particle size distribution. The final powder composition is the result of mixing 50% by weight of component A) and 50% by weight of component B) by dry mixing to ensure homogeneous mixing. The final powder composition is applied to a metal sheet by electrostatic spraying to a film thickness of 80 μm. Finally the coating is cured in a 170SC convection oven for 10 minutes.

Example 2 Coating test Table 1 The results show a very high durability of the coating as well as superior adhesion on metal substrates after curing at a lower temperature at 170aC. No pitting is observed, and a low gloss value of the coating is obtained. It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention.

Claims

CLAIMS Having described the invention as above, the content of the following claims is claimed as property:

1. A powder coating composition characterized in that it can be obtained by the homogeneous mixing of at least two powder coating compositions produced separately as powder coating bases, comprising (A) at least one powder coating base prepared from of one or more glycidyl functionalized (meth) acrylic resins, one or more di-carboxylic acids or the anhydrides thereof having an acid value in the range of more than 400 as a hardener (interleaver), together with at least one coating additive, and optionally, pigment and / or filler, and (B) at least one powder coating base prepared from one or more (meth) acrylic functionalized glycidyl resins, one or more hardeners (crosslinkers) having an acid value in the range of 100 to 400, together with at least one coating additive, and optionally pigment and / or filler, in a mixing ratio from component A) to component B) from 1: 3 to 3: 1, in relation to the weight.

2. The composition according to claim 1, characterized in that the (meth) acrylic resin functionalized with glycidyl in the components (A) and (B) has a vitreous transition temperature in a range of 30 to 80 ° C.

3. The composition according to claims 1 and 2, characterized in that the hardener in the component (A) has an acid value in the range of 410 and 600, and a number of carbon atoms C in the range of 4 to 20. The composition according to claims 1 to 3, characterized in that the hardener in component (B) has an acid value in the range of 250 and 350. 5. The composition according to claims 1 to

4. , characterized in that the component (A) comprises 30 to 90% by weight of one or more (meth) acrylic resins functionalized with glycidyl, 1 to 30% by weight of one or more di-carboxylic acids or the anhydrides thereof having an acid value in the range of more than 400 as a hardener (crosslinker), 0.1 to 10% by weight of at least one coating additive and 0 to 30% by weight of pigment and / or filler, the weight percentage based on in component (A). 6. Composition in accordance with 1 to 5, characterized in that the component (B) comprises 30 to 90% by weight of one or more resins (meth) acrylics functionalized with glycidyl, 1 to 30% by weight of one or more hardeners (crosslinkers) having an acid value in the range of 100 to 400, 0.1 to 10% by weight of at least one coating additive and 0 to 30% by weight of pigment and / or filler, the percentage by weight based on component (B). 7. Preparation of the composition according to claims 1 to 6, characterized in that it comprises the steps of preparing the powder coating base (A) and the powder coating base (B) separately and then mixing them together. 8. Preparation of the composition according to claim 7, characterized in that the component (A) and (B) are mixed at a mixing ratio of 1: 2 to 2: 1, based on weight. 9. A coated substrate, characterized in that it is coated with the composition according to claims 1 to 6 and cured.