JPS6121977B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a powder smoothing agent for powder coatings that improves the smoothness of a coating film by adding a small amount to an epoxy-based, acrylic-based, or polyester-based powder coating composition. Powder coatings are usually epoxy-based, acrylic-based,
It is processed by adding a curing agent, a pigment, a filler, and an appropriate amount of additives to a resin such as polyester. Additives used in powder coatings include smoothing agents, anti-pinhole agents, melt viscosity reducing agents, pigment dispersants, anti-blocking agents, antistatic agents, gloss imparting agents, etc. An essential additive is a smoothing agent. The main substances are acrylic polymers, fluorinated polymers, polysiloxanes, etc., but the majority of these are liquid substances at room temperature, and most of them are incompatible with the resin used. Therefore, when adding it to a powder coating composition, it is necessary to prepare a master batch by melting it at a high concentration and adding it to the resin to be used, and then uniformly dispersing it under vigorous stirring. is the current situation (master batch method). However, even if this masterbatch product is added during kneading of powder coatings, it is difficult to mix uniformly into the entire solid system of pigments, resins, and curing agents, so the effectiveness of the smoothing agent produced by the masterbatch method varies. It's getting easier to come out. Furthermore, such liquid smoothing agents have various disadvantages due to their viscosity at room temperature.
In other words, while low-viscosity types are convenient to handle, such as when taking them out of a container, they tend to impede the powder fluidity of powder coatings using them, making them more likely to cause blocking; The high-priced type is not only inconvenient to handle, as it requires heating to take it out of the container, but excessive heating can cause deterioration of the liquid smoothing agent, and can cause damage to the cured coating of powder coatings using it. Crettering (including repelling, etc.) is likely to occur. Methods for overcoming these drawbacks of the master batch method are disclosed in Japanese Patent Publications No. 51-2485 and No. 53-37094. These techniques have improved the "usability" of liquid smoothing agents, but according to the experimental results of the present inventors, although the smoothness of the cured coating film is at a sufficiently satisfactory level, Even when compared with the cured coating film to which a masterbatch of the agent was added, no superiority could be found. This phenomenon is caused by the fact that the solid carrier used as a carrier for the acrylic polymer and plasticizer in these technologies is essentially incompatible with the resin used to form the coating film, such as silica. Even if the particles are made of inorganic particles such as resin substances, no consideration is given to their compatibility with the resin to form a coating, and the key point is simply to allow them to adsorb (penetrate) onto the surface of the carrier. It's getting old,
Moreover, since the solid carrier itself does not contribute in any way to the smoothing mechanism in forming a cured coating film, this results in the surface property effect of the smoothing agent not being fully utilized. An object of the present invention is to provide a powder smoothing agent for powder coatings that is free from these unreasonable problems and can exhibit excellent effects. The present inventor searched for a powdered smoothing agent and found that 50
Amide wax having a melting point of ℃~145℃,
Average molecular weight is 1000-10000 and glass transition temperature is 20
℃ or less (containing at least 70% by weight of acrylic acid alkyl ester or methacrylic acid alkyl ester in which the alkyl component has 2 to 18 carbon atoms as a monomer component to form the polymer, A single or copolymer containing 30% by weight or less of a monomer that can be copolymerized with a monomer), the weight ratio of the former being 60% and the latter being 40%, and the former being 90% and the latter being 90% by weight. A mixture with a weight ratio of 10% is melted at 210°C or less, cooled, and powdered (hereinafter, the product prepared in this way is referred to as common powder), which is used as a powder coating composition. It has been found that the smoothness of the cured coating film can be significantly improved by adding it. Examples of carboxylic acids for making amide wax include caproic acid, caprylic acid, pelargonic acid, capric acid, undecylic acid, lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid, oleic acid, linoleic acid, and linolenic acid. , diethylhexylic acid, aliphatic carboxylic acids such as hydrogenated castor oil fatty acids, monovalent aromatic carboxylic acids such as benzoic acid, toluic acid, naphthalic acid, succinic acid, glutanic acid, adipic acid, pimelic acid, succinic acid, azelain. acid, sebacic acid,
Examples of amines include polybasic carboxylic acids such as dodecanedicarboxylic acid, phthalic acid, and maleic acid, and mixtures thereof. Alcohol amines, butylamine, hexylamine, octylamine, laurylamine, stearylamine, monoamines such as 2-ethylhexylamine, methylenediamine, ethylenediamine, propylenediamine, trimethylenediamine, hexamethylenediamine, octamethylenediamine, dodecamethylenediamine, diethylenetriamine , polyamines such as triethylenetetramine, xylylene diamine, isophorone diamine, benzylamine, and mixtures thereof. If the melting point of amide wax is lower than 50℃, it is difficult to make the desired common powder, and if the melting point is higher than 145℃, the heat solubility with the acrylic polymer is poor, making it difficult to make a common powder. The effectiveness as a powder leveling agent for body paints is reduced. Acrylic polymers with an average molecular weight of less than 1,000 have difficulty imparting smoothness, and acrylic polymers with an average molecular weight of more than 10,000 are difficult to make into powders that can be used with amide waxes. Acrylic polymers having an average molecular weight of 2,000 to 8,000 are particularly preferred in the present invention. Comparing the combined method of the present invention with the case where each component is used alone, the case where the acrylic polymer is used alone is as described in the masterbatch method above. On the other hand, amide waxes are fairly compatible with epoxy resins, acrylic resins, polyester resins, etc. commonly used in powder coatings (at least about 1% by weight based on the resin used at 150°C). ), and at the baking temperature of the powder coating film,
Compared to resin alone as a binder component, it has the effect of lowering the melt viscosity of the powder coating, which not only further improves the fluidity of the powder coating during the curing process, but also improves the Although it exhibits sufficiently large effects in terms of hole prevention effect, pigment dispersion effect, blocking prevention effect, etc., it does not have the property of actively improving smoothness. In the present invention, the powdered smoothing agent added to the powder coating composition probably melts under heat at 150°C by at least 1% by weight of the resin used. When the amide wax used in the powdered smoothing agent is melted into the resin, it pulls the acrylic polymer and orients it.As a result, it tends to become uniform dispersion stable particles, and the hardening of the cured coating film. This significantly improves smoothness. The common powder of the present invention is a mixture of amide wax and acrylic polymer in a weight ratio of 60 for the former to 40 for the latter to 90 for the former and 10 for the latter. ℃ or less to produce flakes (the film thickness of the flakes is not limited, but about 0.5 to about 5 mm) from the eutectic on a substrate such as a belt flaker, and then , for example, by pulverizing it with a grinder such as a pin mill and adjusting the powder diameter to, for example, about 32 mesh or less. It is well known to those skilled in the art that other means of powdering include spray granulation of the melt, or spray drying from emulsions of certain organic solvents or water. , it can be applied to all of them. The amount of the powder smoothing agent for powder coating of the present invention is:
Required effects (anti-crettering properties, anti-pinhole properties, leveling properties, anti-blocking properties, etc.), properties of the powder coating system, manufacturing conditions of the powder coating,
It depends on several factors such as coating conditions, so it is usually in the range of 0.1 to 10%, preferably 0.25% to 5%, although it is not critical. As for the timing of addition, it may be added during dry mixing or during melt-kneading, and there are no restrictions on the addition method, addition timing, etc. Next, the present invention will be specifically explained using production examples, reference examples, and examples. Production Example 1 (Synthesis of acrylic polymer) As a method for producing the acrylic polymer used in the present invention, ordinary polymerization methods such as emulsion polymerization method, suspension polymerization method, bulk polymerization method, and solution polymerization method can be used. However, a solution polymerization method will be used as a specific example here. While blowing N ₂ gas into a reaction vessel equipped with a stirring device, reflux condenser, dropping funnel, thermometer, and N ₂ gas inlet, toluene was charged in the proportion shown in Table 1 until the temperature reached 110°C. At this time, a solution containing a mixture of monomers, a polymerization initiator (azobisisobutylnitrile, hereinafter abbreviated as AIBN), and toluene in the proportions shown in Table 1 was stirred at 150 RPM for 2 hours.
Drip over time. After dropping the monomer mixture,
Stir for 4 hours to complete the reaction. The temperature during the reaction was always kept constant at 110°C. Next, the pressure of the reaction vessel was reduced to remove toluene, and the mixture was cooled to obtain an acrylic polymer as shown in Table 1.

[Table] Production example 2 (Synthesis of amide wax) In a reaction vessel similar to that used for the synthesis of acrylic polymers, 50 parts of carboxylic acid and its mixture in the proportions shown in Table 2, an equivalent amount of amine, and xylene were charged, and N ₂
By carrying out the reaction in a gas stream at a reaction temperature within the range of 150°C to 210°C for 10 hours while removing the produced water together with xylene, an amide wax having a melting point as shown in Table 2 was obtained. Ta.

[Table] Reference examples Epoxy resin (GT-7004: Nippon Ciba Geigy Co., Ltd. product), acrylic resin (PO-6200: Mitsui Toatsu Chemical Co., Ltd. product) or polyester resin (M-6103, M-6105: Dainippon Ink Chemical Co., Ltd.) Kogyo Co., Ltd. products) and the amide waxes (S-1 to S-16) shown in Table 2 at 1% by weight based on these resins.
The mixture was placed in a large test tube (30 mm in diameter), and the mixture was stirred uniformly in an oil bath kept at 150°C and observed visually under diffuse daylight. As a result, all of the amide wax was transparently dissolved in the powder coating resin. Example 1 (Manufacture of powdered smoothing agent) Mixtures (No. 1 to No. 17) of the acrylic polymer and amide wax obtained in Production Examples 1 and 2 in the proportions shown in Table 3 were heated to a temperature at which they melted into each other. The temperature was raised while stirring until the melt was poured onto a cooled stainless steel plate to form flakes with a film thickness of about 2 mm. After the flakes were sufficiently cooled, they were ground in a pin mill to about 32 mesh or less to obtain a common powder. In addition, a comparative product was obtained by dissolving S-107 in methylene chloride, adding anhydrous colloidal silica in the proportion shown in Table 3, diluting the mixture with methylene chloride to a viscosity that allows spray drying, and spray drying. Prepared by.

[Table] Example 2 The powdered smoothing agent powdered according to the operation shown in Example 1 was added to a standard epoxy powder paint having the formulation shown in Table 4, and after dry mixing, the mixture was heated at 105°C to 115°C. The mixture was melted and kneaded using an extruder kept at ℃. After cooling,
It was ground in a pin mill to obtain a white powder that passed through a 200 mesh sieve. In addition, as a comparative example, a 10% epoxy resin master batch of the acrylic polymer shown in Table 1 alone,
And the amide wax shown in Table 2 alone was pulverized to 32 meshes or less using a pin mill (the acrylic polymer and amide wax added in the following examples of acrylic and polyester powder coatings were adjusted in the same way. ) and then dry mixing to obtain a white powder by the above method.

[Table] Next, apply the obtained powder to a cured film thickness of 50μ or 60μ.
It was sprayed on a zinc phosphate chemical conversion treated board (0.8 x 70 x 150 mm) using electrostatic powder coating method so that the coating film had a smoothness (crettering, pinholes, , leveling). The results are shown in Tables 5 and 6 (Table 5 shows coatings with a film thickness of 50μ, and Table 6 shows coatings with a film thickness of 60μ). The smoothness in the table was evaluated as follows. Crettering: 5-level evaluation from number 0 (value 5) to number 20 or more (value 1). Pinholes: 5-level evaluation from 0 (value 5) to 20 or more (value 1). Leveling: Standard coating plates with 5 levels of leveling ranging from very good leveling (value 5) to uneven coating film (value 1) were prepared and evaluated. The gloss was measured using a gloss meter in accordance with JIS K-54006.7 "60 degree specular gloss measurement method".

【table】

【table】

[Table] As seen in Tables 5 and 6, when the combined method according to the present invention is compared with the use of each component alone and in combination (both components are used separately), the powder of the present invention The effect of the smoothing agent is extremely useful, and when compared with the masterbatch product of acrylic polymer, the effect of the acrylic polymer itself is only at the same level, and the common powder of the present invention is It is clear that the smoothness of the cured coating film is significantly improved. Furthermore, from Table 6, it is clear that the common powder of the present invention exhibits an outstanding effect in preventing pinholes. This is similar to Example 4 shown below.
The same can be said of the acrylic and polyester powder coatings in 6. In addition, the overcoating properties of the coating films obtained in Tables 5 and 6 are shown in Example 3 below. Example 3

[Table] The formulation shown in Table 7 was made into a paint using a three-roll mill, diluted with xylene/n-butanol = 9/1 using a Stormer viscometer to 70KU/25°C, and then toluene/ethyl acetate. /Sorbetso
The viscosity was adjusted to 18 seconds/20°C using a #4 food cup with a mixed solvent of 150/n-butanol = 30/30/30/10. Next, this paint was spray-coated onto the baked coating film obtained in Example 2, and baked and dried at 150° C. for 30 minutes. As a result, the types of combinations shown in Table 4 (A) ~
The coating film of (d) had no problem with overcoatability, but only the comparative coating film of formulation type (e) caused crettering. Example 4 The powdered smoothing agent powdered according to the procedure shown in Example 1 was added to a standard acrylic powder paint having the formulation shown in Table 8, and after dry mixing, the mixture was kept at 115°C to 125°C. The mixture was melted and kneaded using an extruder. The subsequent operations were similar to those in Example 2 to form a paint. The obtained acrylic powder coating was baked at 180°C for 30 minutes. The film thickness after baking is 50μ,
The results are shown in Table 9. Table 8 Parts by weight Acrylic resin (PD-6200) 83.5 Epoxy resin (Epicote #1001) 5.0 Dodecanedicarboxylic acid 11.5 Titanium dioxide 25.0 Note: Epicote #1001 is a product of Ciel Chemical Co., Ltd.

[Table] Example 5 The coating film observed in Table 9 was spray-coated with the paint used in Example 3, and the overcoatability was evaluated. As a result, only the comparative product had poor interlayer adhesion of the coating film. Example 6 The powdered smoothing agent powdered according to the operation shown in Example 1 was added to a standard polyester powder paint having the formulation shown in Table 10, and the subsequent operations were made into a paint according to Example 4. I went to

【table】

[Table] The composition (a) of the obtained polyester powder coating is
The mixture was baked at 190°C for 20 minutes, and the mixture (b) was baked at 180°C for 30 minutes.
The film thickness after baking is 50μ. The results are shown in Tables 11 and 12, respectively.

【table】

[Table] Example 7 Example 3 was applied to the coating film observed in Tables 11 and 12.
The paint used in was spray-coated and the topcoatability was evaluated. As a result, as in the case of epoxy-based powder coatings, cratering occurred only in the comparative product in both formulations (a) and (b).

Claims (1)

[Claims] 1 50 obtained from the reaction of carboxylic acid and amine
Amide wax having a melting point of ℃~145℃,
Average molecular weight is 1000-10000 and glass transition temperature is 20
℃ or less (containing 70% by weight or more of an acrylic acid alkyl ester or a methacrylic acid alkyl ester in which the alkyl component has 2 to 18 carbon atoms as a monomer component to form a polymer, and containing these monomers) a monomer or a copolymer that can contain 30% by weight or less of a monomer that can be copolymerized with a monomer) in a weight ratio of 60 for the former and 40 for the latter to 90 for the former and 10 for the latter. 1. A powder smoothing agent for powder coatings, which is obtained by thermally melting a mixture in a range of proportions at 210° C. or lower, cooling the eutectic, and pulverizing the mixture.