JPS60226567A - Preparation of powder coating compound - Google Patents

Abstract

PURPOSE:To prepare easily and in high accuracy a curable powder coating compound capable of economizing baking time and baking energy which are required after it is applied to various devices and various products, by including a process wherein components are uniformly blended and a process wherein the previously blended components are lagged and aged at a specific temperature. CONSTITUTION:For example, an acrylic resin is blended with a curing agent (e.g., dodecanedicarboxylic acid, etc.), etc. and uniformly blended by melt blending method. The prepared flaky, pelletized, granular or powdery melt blend is lagged and aged at 40-80 deg.C, to give the desired powder coating compound.

Description

[Detailed Description of the Invention] Industrial Field of Application The present invention relates to a method for producing powder coatings for coating various industrial equipment and products, particularly for easily producing thermosetting powder coatings that harden in a short time. The present invention relates to a method for manufacturing with high precision.

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 and then turned into flakes, pellets,
It is made into granules, etc., and then pulverized to a desired particle size using a pulverizer to produce a powder coating. An example of such a manufacturing method is JP-A-52-47031.

Conventionally, accelerating the curing of powder coatings has relied on the type and amount of thermosetting resin and curing agent, as well as the combined use of catalysts, but it has been difficult to produce powder coatings that harden in a short time.

This is because the thermosetting resin and curing agent liquefy when passed through the extruder and become a dispersion medium for the pigment valve, but when the thermal energy applied by heating increases, a curing reaction begins.

For this reason, powder coatings that harden in a short time can be melted and mixed at a temperature of 80 to 140℃, which is the temperature at which the thermosetting resin and curing agent that becomes the dispersion medium melt, 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 of about 80 to 140 degrees Celsius, at which the reaction does not proceed much above the Tg point, and after painting it is mixed at a temperature range of about 160 to 140 degrees Celsius.
Bake hardened at 220°C. In other words, in the conventional manufacturing method using an extruder, only raw materials that do not undergo much reaction even when heated to 80 to 140° C. can be used. 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 these reasons, it has traditionally been difficult to produce powder coatings that harden in a short time.

OBJECTS OF THE INVENTION An object of the present 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 for conveying the object to be coated.

In addition, when an object to be coated with a large heat capacity is preheated, we are investigating the possibility of curing the paint using only the thermal energy possessed by the object.

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, when producing a thermosetting powder coating, is characterized by the step of uniformly mixing each component, and the step of aging the pre-mixed components at a temperature of 40 to 80°C. This is a method for producing powder paint.

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.

Examples of thermosetting resins include acrylic resins, polyester resins, epoxy resins, etc., which are solid at room temperature and have a melting point of 80 to 140°C, which are commonly used for powder coatings. Epoxy resins include epoxy resins with an epoxy equivalent of 400 to 2,000 and a number average molecular weight of 800 to 4,400, which are made from a reaction product of bisphenols such as bisphenol A1 bispheno-/lzF and 1-pyhalogen such as epichlorohydrin, phenol type or cresol type. A reaction product of novolac resin and epichlorohydrin with an epoxy equivalent of 170 to 240
In addition to so-called epoxyphenol novolac resins having a number average molecular weight of 300 to 750, there are triglycidyl isocyanurate-1 to alicyclic epoxy resins.

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, tetrahydrophthalic anhydride, Examples include acid anhydrides such as benzophenonetetracarboxylic anhydride and trimellitic anhydride, acid curing agents such as dodecanedicarboxylic acid, sebacic acid, and adipic acid, and phenolic curing agents such as phenol resins and bisphenol A.

Acrylic resins include various (meth)acrylates, (
There are resins made of at least one species of meth)acrylic acid and its esters, and dicarboxylic acids such as dodecanedicarboxylic acid, sebacic acid, and isophthalic acid are used as the curing agent.

Polyester resins include polybasic acids such as phthalic anhydride, isophthalic acid, terephthalic acid, and maleic anhydride condensed 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 1.
As a curing agent for the resin at 50° C., 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, carlum 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.

The most suitable short-curing powder coating, which is the main target of the method of the present invention, is a system containing a bisphenol-based glycidyl ether type epoxy resin as a main component and a phenol-based curing agent.

The above-mentioned raw materials for powder coatings are stirred in advance using a kneader or the like, if necessary, and then melted and mixed using an extruder to obtain a mixture for powder coatings.

(Hereinafter referred to as a molten mixture.) The molten mixture is extruded from a die of an extruder in the form of flakes, pellets, or granules.

The most important step in the present invention is the step of insulating and aging the molten mixture at 40 to 80°C.

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 at a temperature at which curing does not proceed easily, and then the mixture is heated at 40 to 80°C.
By adopting the heat-retained aging process, we take advantage of the fact that a preliminary reaction is possible, which allows the degree of reaction to be easily adjusted.

In order to pre-react a molten mixture in the form of flakes, pellets or granules, a temperature of 40° C. or higher is required.

If the temperature is less than 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, causing the coating to become 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 about 40°C, a heat retention aging period of about one week is required, and when the temperature is about 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 paint, inventory management, storage space for thermal aging, etc.

For thermal aging, a molten mixture in the form of flakes, pellets, granules, or powder may be placed in a cardboard box or the like. Since flakes, pellets, grains, and powders themselves may fuse together due to heating, the heat retention aging temperature may be selected based on the 70 points of the molten mixture. That is, a molten mixture with a high Tg point (50
~90℃) is ground into powder in advance and then heated to 50~80℃.
It is more efficient and economical to age the grains at a warm temperature because only one crushing is required. However, the molten mixture with a score of 19 below 45-50°C is closer to powder during the heat retention aging process;
50-6 in flake and pellet form as it is easy to fuse.
After aging at 0°C, it is preferable to crush the product when the desired gel time is reached. From the viewpoint of preventing the above-mentioned blocking, the Tg point of the powder coating is preferably 45 to 90°C.

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°C to 30°C, which is the curing condition for powder coatings based on general manufacturing methods, and 200°C for 1 to 3 minutes. .

The most effective coating film formation method using the powder coating produced by the method of the present invention is the melting point of 120-2, which is the general melting point of powder coatings.
This is a method in which the object to be coated is preheated to 60° C. or higher, and then the coating is applied, and the coating is cured using only retained heat without any special baking for curing.

A more specific explanation will be given below with reference to Examples.

Margin table below 1 Paint formulation (1) *1 Epoxy resin manufactured by Yuka Shell L Hoxy Co. *2 Phenolic curing agent manufactured by Yuka Shell Epoxy Co. *3 Phenol novolac type epoxy resin manufactured by Yuka Shell Epoxy Co. *4 Manufactured by Kyoeisha Yushi Co., Ltd. Flow control agent The raw materials were premixed using a kneader and a Henschel mixer for the paint formulations shown in Tables 1 and 2.

This premix was extruded using a Konida manufactured by Busu Co., Ltd. to obtain a uniform melt-mixed paint.

The ease of melt-mixing is evaluated as mixability (*8), and those that are melt-mixed without gelling to obtain a uniform powder coating are marked O, and gelling and impossible to extrude from the co-kneader. Those are shown in Tables 3 and 4 with an X mark.

Then, the molten mixture was crushed with ACM (pulverized ta manufactured by Wire Ironworks Co., Ltd.
The powder was pulverized at 1000 ml and then aged under heat to cause a precursor reaction between the thermosetting resin and the curing agent to obtain a powder coating whose reactivity was adjusted.

Tables 3 and 4 show the conditions for this heat retention aging, etc.

The TQ point and gel time at 200°C of the obtained powder coating were measured and shown in Table 5.6.

This paint was preheated to 240℃ and was 70X 1 with a thickness of 3.2m.
A film thickness of 180 mm was applied to a 50 mm test piece using an electrostatic powder coating machine.
When the test piece was coated to a thickness of ~220μ and allowed 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 test piece of 70 x 150 m 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 ~ A coating film of 80μ was obtained.

Table 7 shows the performance of this coating film.

Table 2 below: Paint formulation (2) *5 Add azobis(2-medylpropionitrile) to a mixture of 15 parts by weight of glycidyl methacrylate, 25 parts by weight of medyl methacrylate, 40 parts by weight of styrene, and 20 parts by weight of isobutyl methacrylate. 2 parts by weight, t- as a chain transfer agent
1 part by weight of dodecyl mercaptan was added and copolymerized according to a conventional method to obtain an acrylic resin having a weighted average molecular weight of 28,000.

*6 Polyester resin manufactured by Bayer *7 ε-caprolactam block isocyanate manufactured by Bayer This paint was preheated to 240°C 3.2. 70X with m thickness
A test piece of 150111#I was coated with an electrostatic powder coating machine to a film thickness of 60 to 100 μm, and a coating film was obtained which was cured by standing to cool.

Table 6 shows the performance of this coating film.

Each manufacturing example is a comparative example in which powder paint A was prepared by only melt-mixing for each paint formulation, and B is an example in which powder paint was prepared by melt-mixing and then heat-retained aging.

*9 The shape is that of a molten mixture.

Table 4 Production Example (2) Each production example is a comparative example in which A powder coating was made 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 The shape is that of a molten mixture.

Table 5 below: Performance of powder coating film (1) *10 Thermal analyzer DT-30 manufactured by Shimadzu *1t 20
Seconds to cure evaluated at 0°C.

Evaluation was made using a ram of 10 mφ using a $120 IN-30671-6,8.

$13 Based on ASTHG-14, the 0 bending angle and impact resistance were evaluated at a temperature of 20° C. and 40° C., respectively. 1 Table 6 Performance of powder coating film (2) *14 Evaluated according to JIS-To 5400 using a 10 mmφ mandrel.

*Is impact resistance distance c just before paint film failure, based on JIS-5400, 172 inches, weight 05 to 9
Margin below m0 $15 JIS = ni-5400 1mm interval test $16 JIS = ni-5400 tsuruto spray test 100 hours.

The evaluation criteria are ASTH [1-610 for rust, 85T for rust]
) l D714.

According to Table 5.6, IA, 6A, and 7A have long gel times and cannot be cured with just the thermal energy of preheating the coated material.
The expected performance has not been reached in minutes.

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, 2B, 3B, 4B and heat aging 1
Comparing 2A, 3A, and 4A that have not done so, 2B, 3
B and 4B have short gel time and high curing properties, so 240℃
The expected coating film performance is fully demonstrated with just the preheating energy of the coated object, and the performance is particularly excellent at -40°C.

Effects of the Invention The present invention makes it possible to produce a powder coating that hardens at 200° C. for 1 to 20 seconds by uniformly mixing raw materials for a powder coating and then aging the mixture under heat.

By adopting a thermal aging process, problems such as gelation during melt mixing in an extruder were resolved.

It is also now possible to adjust the baking time after painting by appropriately selecting the heat aging temperature and time. As a result, useful results such as shortening the baking furnace time and improving conveyor speed were obtained.

applicant Nippon Paint Co., Ltd.

Claims (1)

[Claims] 1. When producing a thermosetting powder coating, there is a step of uniformly mixing each component, and a step of mixing each component in advance for 40 minutes.
A method for producing a powder coating, characterized by comprising a step of thermal aging at ~80°C. 2. The method for producing a powder coating according to claim 1, wherein the step of uniformly mixing the raw materials is by a melt blending method. 3. The method for producing a powder coating material according to claim 1, wherein the molten mixture pre-reacted by keeping it warm is in the form of flakes, pellets, granules, or powder. 4. The method for producing a powder coating according to claim 1, wherein the thermosetting powder coating has a TQ point of 45 to 90°C.