JPH0356267B2 - - Google Patents

Description

[Detailed description of the invention]

Industrial Application Fields The present invention provides a method for manufacturing powder coatings for coating various industrial equipment and products, particularly for easily and accurately producing thermosetting powder coatings that harden in a short time. Regarding the method. PRIOR ART Powder coatings are composed of thermosetting resins, curing agents, pigments, or various additives. These raw materials are usually melted and mixed using an extruder, etc., then turned into flakes, pellets, granules, etc., and then ground to the desired particle size using a grinder to produce powder coatings. There is 52-47031. Conventionally, accelerating the curing of powder coatings relied on the type and amount of thermosetting resin and curing agent, as well as the combination of catalysts, but powder coatings that cured in a short time were more difficult to manufacture. This is because when passed through the extruder, the thermosetting resin and curing agent liquefy and become a dispersion medium for the pigment, but when the thermal energy applied by heating increases, the curing reaction starts. For this reason, powder coatings that harden in a short time can be melted and mixed at a temperature that is normally 80 to 140℃, which is the temperature at which the thermosetting resin and curing agent that becomes the dispersion medium are melted, and mixed with an extruder. A reaction takes place which must later be cured. Even if the powder coating produced as a result is baked, melt flow does not occur, so the coating film is not uniform, pinholes occur, and the powder coating film does not adhere well to the object to be coated. Defects such as inability to perform properly occur. Therefore, it is usually mixed at a temperature range above the Tg point at which the reaction does not proceed much, approximately 80 to 140℃, and after painting it is mixed at a temperature of 160 to 220℃.
Baked and hardened. In other words, conventional production methods using extruders can only use raw materials that do not undergo much reaction even when heated to 80 to 140°C. Furthermore, even if a powder coating could be produced by this method, it would lack stability as a commercial product because it is difficult to adjust the gel time that governs the curing reaction of the powder coating. For example, first, the pigment and resin are premixed at a relatively high temperature of 100 to 240℃, which is within the range where the resin does not deteriorate, to create a homogeneous mixture, and then, after adding the curing agent, the mixture is heated to 130℃ or lower, where gelation is unlikely to occur. An example of mixed production has been proposed in JP-A-54-137030, but it is a method for producing a powder coating that does not cause gelation, and the production of a short-curing coating has been a difficult problem. Object of the invention The object of the invention is to save energy and shorten the baking time of paints. This saving in baking energy is directly linked to effects such as shortening the length of the furnace for baking the powder coating, or increasing the speed of the conveyor that conveys the object to be coated. In addition, when an object to be coated with a large heat capacity is preheated, the possibility of curing the paint using only the thermal energy possessed by the object is to be investigated. The object of the present invention is to provide a method for easily producing a thermosetting powder coating that cures in a short time as described above. Structure of the Invention The present invention involves uniformly mixing each constituent component of a thermosetting powder coating to produce a first mixture, and then producing the first mixture.
This is a method for producing a powder coating, which is characterized by a two-step process of aging the mixture at 40 to 80°C. The powder coating material to which the method of the present invention can be applied comprises a conventionally known thermosetting resin, curing agent, pigment, or various additives. Thermosetting resins are usually used for powder coatings, are solid at room temperature, and have a melting point of 80 to 140.
℃ acrylic resin, polyester resin, epoxy resin, etc. Epoxy resin is a reaction product of bisphenols such as bisphenol A and bisphenol F and epihalohydrin such as epichlorohydrin, and has an epoxy equivalent of 400 to 2000 and a number average molecular weight of 800.
In addition to the so-called epoxyphenol novolak resin, which is a reaction product of phenol type or cresol type novolak resin and epichlorohydrin, which has an epoxy equivalent weight of 170 to 240 and a number average molecular weight of 300 to 750, triglycidyl isocyanurate, There are alicyclic epoxy resins, etc. Curing agents for these epoxy resins include aromatic diamines such as diaminodiphenylmethane, polyamidoamines which are condensates of aliphatic amines and aliphatic dicarboxylic acids, amine-based curing agents such as dicyandiamide, imidazoles, and anhydrous tetrahydrophthal. Acids, acid anhydrides such as benzophenonetetracarboxylic anhydride and trimellitic anhydride, acid curing agents such as dodecanedicarboxylic acid, sebacic acid and adipic acid, phenolic curing agents such as phenolic resins and bisphenol A, etc. can give. Acrylic resins include resins made of one or more of various (meth)acrylates, (meth)acrylic acids, and their esters, and dicarboxylic acids such as dodecanedicarboxylic acid, sebacic acid, and isophthalic acid are used as curing agents. . Polyester resins are made by condensing polybasic acids such as phthalic anhydride, isophthalic acid, terephthalic acid, and maleic anhydride with polyhydric alcohols such as ethylene glycol and trimethylolpropane, with an average degree of polymerization of 3 to 50 and a softening point of 60 to 150°C. As the curing agent for the resin, isophorone diisocyanate, solid melamine resin, triglycidyl isocyanurate, etc. can be used. It is also possible to use a small amount of thermoplastic resin, such as petroleum resin, in combination with the above thermosetting resin. Pigments that can be added as necessary include inorganic pigments or fillers such as titanium oxide, yellow iron oxide, red iron oxide, silicon oxide, clay, talc, barium sulfate, potassium carbonate, and mica, and organic pigments such as azo and anthraquinone. Pigments etc. are used. In addition, various additives such as fillers, flow control agents, and reinforcing agents are used. As the short-curing powder coating mainly targeted by the method of the present invention, a system containing a bisphenol-based glycidyl ether type epoxy resin as a main component and a phenol-based curing agent is most suitable. Each of the powdered and granular raw materials for the powder coating described above is stirred in advance using a kneader or the like as necessary, and then melted and mixed using an extruder to obtain a first mixture for the powder coating. (Hereinafter referred to as molten mixture.) The molten mixture is extruded from a die of an extruder in the form of flakes, pellets, or granules. The method for producing the first mixture according to the present invention includes not only the above-mentioned molten mixture but also resin, pigment,
The desired powder coating can also be obtained using a powdered first mixture in which each component such as various additives or a mixture thereof is mixed in a finely pulverized state (hereinafter referred to as a powder mixture). The most important thing in this invention is to heat the first mixture at 40 to 80°C.
This is the process of aging at a warm temperature. In the present invention, thermosetting resins, curing agents, pigments, and various additives, which are raw materials for powder coatings that harden in a short time, are made into a uniform molten mixture, powder, or mixture at a temperature that makes it difficult for hardening to proceed, and then By employing a two-stage heat-retaining aging process at 0.degree. C., it takes advantage of the possibility of a preliminary reaction that allows the degree of reaction to be easily adjusted. Temperatures above 40°C are required for pre-reaction of molten mixtures in the form of flakes, pellets and granules. If the temperature is below 40℃, the preliminary reaction will not proceed and it will take too many days, and if it exceeds 80℃, the reaction will proceed too much and it will gel to the extent that it cannot be painted or the fluidity of the coating will decrease, making the coating uneven. This can easily lead to poor finish on the skin or poor adhesion. A preferable thermal aging temperature is 50 to 60°C. When the temperature is around 40°C, a heat retention aging period of about one week is required, and when the temperature is around 80°C, the desired preliminary reaction can be obtained in about 8 hours. Therefore, the temperature may be appropriately selected from the viewpoints of the reaction rate of the coating material, inventory management, storage space for thermal aging, etc. For thermal aging, flakes, pellets, granules,
The powdered molten mixture may be placed in a cardboard box or the like. Since flakes, pellets, grains, and powders themselves may fuse together due to heating, the temperature for thermal aging may be selected depending on the Tg point of the molten mixture. That is, it is more efficient and economical to crush a molten mixture with a high Tg point (50 to 90°C) into a powder in advance and then heat-retain it at 50 to 80°C, since only one crushing is required. However, a molten mixture with a Tg point of less than 45-50°C is more likely to fuse during the thermal aging process as it is closer to powder, so it can be heated to 50-60°C in the form of flakes or pellets.
After aging at a warm temperature, it is best to crush it when the desired gel time is reached. From the viewpoint of preventing blocking mentioned above, the Tg point as a powder coating is 45~45.
90°C is preferred. The powder coating material produced by the method of the present invention can also be electrostatically powder coated and thermally cured to form a coating film in the usual manner. In this case, the curing properties have been improved by heat retention aging, so the thermal energy for curing is 180 to 200, which is the curing condition for powder coatings based on the first manufacturing method.
It should be shorter than 20 minutes at 200℃ and 1 to 3 minutes at 200℃. The most effective method for forming a coating film using the powder coating produced by the method of the present invention is to preheat the object to be coated above 120 to 260°C, which is the general melting point of powder coatings, and then apply the coating. This is a method in which the material is hardened using only retained heat without special baking for hardening. A more specific explanation will be given below with reference to Examples.

[Table] The raw materials for the paint formulations shown in Tables 1 and 2 were premixed using a kneader and a Henschel mixer. This premix was extruded using a Konida manufactured by Busu Co., Ltd. to obtain a uniform melt-mixed paint. Mixability (*8) refers to the ease of melt mixing.
In Tables 3 and 4, those that were melted and mixed without gelling to obtain a uniform powder coating were marked with an ○, and those that gelled and could not be extruded from the co-kneader were marked with an x. Next, the molten mixture was pulverized with an ACM (pulverizer manufactured by Hosokawa Iron Works), and then aged under heat to cause a precursor reaction between the thermosetting resin and the curing agent to obtain a powder coating with an adjusted degree of reactivity. Tables 3 and 4 show the conditions for this heat retention aging, etc.
Shown below. The Tg point and gel time at 200°C of the obtained powder coating were measured and shown in Tables 5 and 6. 70 x 150 with a thickness of 3.2 mm preheated to 240℃ with this paint.
Film thickness 180~ with electrostatic powder coating machine on mm test piece
When it was painted to a thickness of 220μ and left to cool, a coating film was obtained that was cured by the heat of the test piece. The performance of this coating film is shown in Table 5. Next, using production examples 1A and 1B, 3A and 3B, and 6A and 6B, a 70 x 150 mm test piece with a thickness of 0.8 mm was coated with an electrostatic powder coating machine, and then baked at 200°C for 3 minutes to obtain a film thickness of 60 to 80 μm. A coating film was obtained. Table 7 shows the performance of this coating film.

【table】

[Table] 70 x 150 with a thickness of 3.2 mm preheated to 240℃.
Film thickness: 60~ on electrostatic powder coating machine on mm test piece
A coating film of 100μ was coated and cured by cooling. Table 6 shows the performance of this coating film.

[Table] Each production example is a comparative example in which A was made into a powder coating only by melt-mixing for each paint formulation, and B is an example in which powder coating was made by melt-mixing and then heat-retained aging. *9 Shape is that of a molten mixture.

[Table] Each production example is a comparative example in which A was made into a powder coating only by melt-mixing for each paint formulation, and B is an example in which powder coating was made by melt-mixing and then heat-retained aging. *9 Shape is that of a molten mixture.

【table】

【table】

[Table] According to Tables 5 and 6, 1A, 6A, and 7A had long gel times, and curing was insufficient with just the thermal energy used to preheat the coated object, so they did not reach the expected performance. In addition, in both Production Examples 5 and 8, a catalyst was used for the purpose of shortening the gel time, but the mixture gelled in the extruder during melt mixing and could not be made into a powder coating. On the other hand, when comparing 2B, 3B, and 4B that have been aged with heat retention and 2A, 3A, and 4A that have not been aged with heat retention, 2B,
3B and 4B have short gel time and high curing properties, so
The expected coating film performance is fully demonstrated with just the energy required to preheat the object to be coated at 240°C, and the performance is particularly excellent at -40°C. Effects of the Invention The present invention employs a two-step process of uniformly mixing each constituent component for a powder coating to produce a first mixture, and then aging the first mixture under heat.
It has become possible to produce powder coatings that harden in 1 to 20 seconds at 200°C. Heating in an extruder had the risk of gelation during melt mixing, but by adopting a heat retention aging process, it became possible to accelerate curing under mild conditions. It has also become possible to adjust the baking time after painting by appropriately selecting the temperature and time of thermal aging. As a result, useful results such as shortening the baking furnace time and improving conveyor speed were obtained.

Claims (1)

[Claims] 1. A first mixture is produced by uniformly mixing each component of a thermosetting powder coating, and then the first mixture is
A method for producing a powder coating, which is characterized by a two-stage process of heat-retaining aging at 40 to 80°C. 2. The method for producing a powder coating material according to claim 1, wherein the step of uniformly mixing each component is by a melt blending method. 3. The method for producing a powder coating material according to claim 1, wherein the first mixture is in the form of flakes, pellets, granules, or powder. 4 Tg point as thermosetting powder coating is 45-90℃
A method for producing a powder coating according to claim 1, which is a composition of: