JP2744443B2 - Resin composition for powder coating - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a resin composition for powder coating.
More particularly, the present invention relates to a polyamide resin composition for powder coating capable of coating a corner portion of an object to be coated with a film thickness not too thin.

(Prior Art) Polyamide powder is widely used in fluid immersion coating and stationary coating as a powder coating because of its excellent properties such as friction and wear properties, strength and heat resistance.

Since polyamide is a thermoplastic resin, the physical properties of the powder before coating and the physical properties of the coated film are basically constant regardless of the coating conditions, and it is easy to handle, but at the time of powder coating, it melts and flows. Even after a smooth surface is obtained, the flow continues because thickening due to crosslinking etc. does not occur, and the coating becomes too thin at the corners of the object to be coated, and in some cases the corners of the object There is a drawback to be exposed. This is a phenomenon called edge break,
Rust is generated on this part during use of the coated product, or the polyamide coating is peeled off from this part.

In order to improve this disadvantage, the following has been performed. The polyamide is polymerized without adding a polymerization degree regulator, and a polyamide having a giant amino acid structure in which one end of the polyamide molecule is a carboxy group and the other end is an amino group is obtained, and a polymerization catalyst is added thereto to powder. In the case of powder coating, polymerization proceeds further in a molten state at the time of coating and the viscosity increases, so that it is possible to prevent the corners of the object to be coated from becoming thinner. Although this method is a good method, it is difficult to stably obtain a relatively low-viscosity polyamide used for powder coating without adding the polymerization degree regulator. The carboxyl group and the amino group condense into amide bonds and water,
This equilibrium is much closer to the amide side, so that polyamide can be easily condensed only by heating, but it is difficult to control the condensation. In other words, unless both ends are polymerized to a certain extent in addition to a polymerization degree regulator such as mono- or dicarboxylic acid, mono- or diamine, polymerization proceeds forever according to heating, and finally insoluble and infusible ultra-high polymer Polyamide is formed.

Therefore, when the polymerization degree controlling agent is not added, it is necessary to adjust the degree of polymerization by keeping the heating time constant, but actually the residence time of the polymerization apparatus has a distribution. Also, when the polymer is taken out of the system, there is a large difference in the residence time between the beginning and the end of the taking out. Further, there is a drawback that an ultra-polymerized polyamide is generated due to stagnation on a vessel wall or the like of the polymerization apparatus, which causes irregularities on the coating film surface.

(Problems to be Solved by the Invention) It is an object of the present invention to easily and stably provide a polyamide powder in which condensation progresses in a molten state during powder coating and hardly causes edge breakage.

(Means for Solving the Problems) That is, the present invention comprises mixing a polyamide (A) in which 70% or more of the terminal groups are carboxyl groups and a polyamide (B) in which 70% or more of the terminal groups are amino groups. The present invention provides a polyamide resin composition for powder coating comprising:

The polyamide described in the present invention can be powder-coated with a polymer or oligomer having an amide bond in the main chain, and examples thereof include nylon 12, nylon 11, nylon 612, and copolymers of these with other polyamide monomers.

A polyamide (A) in which 70% or more of the terminal groups are a carboxyl group (hereinafter sometimes referred to as a terminal carboxylic acid polyamide) and a polyamide (B) in which 70% or more of the terminal groups are an amino group (hereinafter referred to as an amine polyamide) ) May be a dicarboxylic acid,
By adding a diamine in a calculated amount and polymerizing, it can be obtained very easily and stably. This is because, as the polymerization reaction proceeds, the amount of the amine or carboxylic acid that forms the amide decreases, respectively.
This is because it becomes impossible to generate a superpolymer compound.

When diamine or dicarboxylic acid is used as a polymerization degree regulator, a polyamide having both amino groups or carboxyl groups at both terminal groups is produced. In this case, the terminal group
A polyamide in which less than 70% is an amino group or a carboxyl group, in other words, a polyamide in which 30% or more of the terminal groups are a carboxyl group or an amino group has an equivalent ratio of amino group to carboxyl group of 70:30 to 30:70. Since the polymerization is within the range and the polymerization proceeds by itself, as described above, stable polymerization is not performed. If such a polyamide can be obtained stably, it is a polyamide that does not easily cause edge breakage, and there is no need to use a technique of mixing two kinds of inactive polyamides as in the present invention. Since it is difficult to obtain it easily and stably, it does not meet the purpose of the present invention.

On the other hand, in the case of a polyamide using a monoamine or a monocarboxylic acid as a polymerization degree regulator, a part of the terminal group becomes an unreactable group, so that less than 70% of the terminal group is an amino group and a polyamide having an amino group. Even if a polyamide containing less than 70% of carboxyl groups is mixed, the increase in the degree of polymerization is small and does not meet the purpose of the present invention.

Examples of the dicarboxylic acid used in the present invention include adipic acid, dodecane diacid, and terephthalic acid, and examples of the diamine include hexamethylene diamine and isophorone diamine.

Carboxyl groups account for at least 90% of the terminal groups in the terminal carboxylic acid polyamides, and 90% of the terminal groups in the terminal amine polyamides.
It is further desirable that at least% is an amino group. Although the terminal carboxylic acid polyamide and the terminal amine polyamide are each independently stable polyamides, they can be converted into polymerizable polyamides by mixing to exhibit the effects of the present invention. The mixing ratio of the terminal carboxylic acid polyamide and the terminal amine polyamidano is such that, in the mixed polyamide, the ratio of the total amount of carboxylic acid equivalents to the total amount of amine equivalents is 40: 6.
When mixed so that the ratio becomes 0 to 60:40, polymerization proceeds most advantageously during coating.

The terminal carboxylic acid polyamide and the terminal amine polyamide can be melted or mixed in a molten state. The melt mixing is performed in a short time in which polymerization hardly proceeds. If the polymerization catalyst is added after mixing and powdering without adding the polymerization catalyst at the time of this mixing, the polyamide resin composition for powder coating intended for the present invention can be obtained more stably.

The polyamide resin composition for powder coating, which is the object of the present invention, can also be obtained by mixing the fine powders of the terminal carboxylic acid polyamide and the terminal amine polyamide.

Additives such as pigments and stabilizers can be added to the terminal carboxylic acid polyamide and the terminal amine polyamide alone or at the time of mixing.

According to a further preferred embodiment of the invention, the relative viscosity of a 0.5% solution of polyamide in meta-cresol is from 1.10 to 1.30.
By adjusting the amount of dicarboxylic acid and diamine, which are polymerization degree regulators, to polymerize the terminal carboxylic acid polyamide and the terminal amine polyamide, if necessary, they are melted or mixed with a pigment, a stabilizer, etc., or mixed with a solution to be brittle. A polymerizable polyamide oligomer is obtained. This can be easily pulverized, and a polymerization catalyst can be added to the powder, if necessary, and subjected to solid-phase polymerization to obtain a powder having a desired molecular weight. In general, high molecular weight polyamide used for powder coating is tough, so that it is not easy to pulverize and it is necessary to perform freezing and pulverization with liquid nitrogen. However, according to the above method, the pulverization step becomes extremely easy.

(Effect of the Invention) The powder of the polyamide resin composition according to the present invention is prepared by polymerizing a stable terminal carboxylic acid polyamide and a terminal amine polyamide in advance and mixing them to form an active polymerizable polyamide. It can be manufactured stably and can well cover the corners of the article to be coated during powder coating.

Furthermore, as one embodiment of the present invention, if a low-polymerization degree terminal carboxylic acid polyamide and a terminal amine polyamide are mixed and pulverized and then subjected to solid-phase polymerization, the target powder can be easily obtained without using liquid nitrogen for pulverization. .

(Example) Next, the present invention will be described in more detail with reference to examples.

Example 1 A 10 autoclave was charged with 5 kg of lauryl lactam, 290 g of dodecane diacid, and 200 g of water, and after purging with nitrogen, heated to 280 ° C., and the pressure in the can reached 25 kg / cm ² . After maintaining the temperature at 280 ° C. for 7 hours, the temperature was lowered to 250 ° C. while gradually releasing the water vapor pressure in the can to atmospheric pressure over 1 hour. Stirring was continued for 3 hours at 250 ° C in a can with long nitrogen, and the polymer was discharged from the bottom of the can under nitrogen pressure over 1 hour, assuming a large-scale facility, and a white lump of carboxyl was added. An acid polyamide was obtained.

This mass was brittle and easily crushed, the infrared absorption spectrum was consistent with that of nylon 12, and the melting point was 177 ° C. A 0.5% m-cresol solution of the polymer starting to emerge from the bottom of the can has a relative viscosity of 1.17. According to titration with a benzyl alcohol solution, the terminal groups are carboxylic acid equivalent 493 meq / kg, amine equivalent 1
It was 2meq / kg. The relative viscosity of the 0.5% m-cresol solution of the polymer at the end of one hour after the start of the release was also 1.17, indicating that the polymer was obtained stably.

On the other hand, 147 g of hexamethylenediamine was charged in a 10 autoclave instead of 290 g of dodecanediacid, and a slightly yellowish white lump of terminal amine polyamide was obtained in the same manner.

This mass was brittle and easily crushed, the infrared absorption spectrum was consistent with nylon 12, the melting point was 177 ° C, and the relative viscosity of the 0.5% m-cresol solution was 1.19. The terminal group had a carboxylic acid equivalent of 14 meq / kg and an amine equivalent of 453 meq / kg.

50 parts by weight of the terminal carboxylic acid polyamide and 50 parts by weight of the terminal amine polyamide thus obtained, and titanium oxide 5
Parts by weight and stabilizer (Irganox 101 manufactured by Ciba-Geigy)
0) Mix 1.0 part by weight, 200 ℃ with 30mm% φ twin screw extruder
And cooled with water to give a white mass. 0.5% of this lump
The relative viscosity of the cresol solution was 1.20;

This is a small crusher (Hosokawa Micron sample mill)
At room temperature to easily obtain a powder.
When this powder was sieved with 60 mesh, about 90% passed through 60 mesh. To 100 parts by weight of the powder passing through the 60 mesh, 20 parts by weight of a 1% methanol solution of phosphoric acid as a polymerization catalyst was added and mixed, and the mixture was allowed to stand at 60 ° C. for 5 hours.
Solid-state polymerization was performed at 20 ° C for 20 hours.

The relative viscosity of a 0.5% m-cresol solution of the powder thus obtained was 1.61. With this powder, a 3 mm-thick iron plate having a right angle was subjected to fluid immersion coating. The pre-heating treatment of the iron plate was performed at a temperature of 350 ° C. for 7 minutes, immersion for 5 seconds, 1 minute, and then water-cooled. There was no exposure of the iron plate at the corner. 0.5% of this coating
The relative viscosity of the m-cresol solution was 1.95.

On the other hand, 100 parts by weight of nylon 12 having a relative viscosity of 1.62 obtained by using dodecane diacid as a polymerization degree regulator, 5 parts by weight of titanium oxide and 1 part by weight of a stabilizer were similarly extruded, and the same grinder was used together with liquid nitrogen. Crushed. The viscosity of the obtained powder is
It was 1.61. When this powder is sieved with 60 mesh, about 10%
Passed through the mesh. 3m similarly with this mesh passing powder
When an iron plate having a thickness of m was subjected to fluid immersion painting, the iron plate was partially exposed at the corners. The relative viscosity of this coating film was 1.61.

Example 2 Dodecanedioic acid and hexamethylenediamine were used as polymerization degree regulators, respectively, and 0.2% of phosphoric acid was added to carry out polymerization according to a conventional method. Relative viscosity of 0.5% m-cresol solution 1.6
1. Nylon 12 pellets having a carboxylic acid equivalent of 98meq / kg and an amine equivalent of 20meq / kg, and a carboxylic acid equivalent of 21meq / kg and an amine equivalent of 115meq having a relative viscosity of 1.59 of a 0.5% m-cresol solution.
/ kg of nylon 12 pellets were mixed in an equivalent amount and pulverized with liquid nitrogen to obtain a powder passing through 200 mesh.

A 1 mm thick iron plate was electrostatically coated with this powder, heated at 240 ° C. for 6 minutes, and then cooled with water. The relative viscosity of a 0.5% m-cresol solution of the coating film was 1.75.

Example 3 500 g of 11-aminoundecanoic acid, 4 g of adipic acid, 1 g of phosphoric acid
Was heated in a vessel under nitrogen at 210 ° C. for 1 hour, and then heated, and then heated at 250 ° C. for 3 hours to obtain a carboxylic acid terminal polyamide. The infrared absorption spectrum was consistent with that of nylon 11, the melting point was 185 ° C, and the relative viscosity of the 0.5% m-cresol solution was 1.50.
Met. Carboxylic acid equivalent is 115 meq / kg, amine equivalent is 1
It was 8meq / kg.

Similarly, terminal amine polyamide was obtained from 500 g of 11-aminoundecanoic acid, 3.5 g of hexamethylenediamine, and 1 g of phosphoric acid. The infrared absorption spectrum was the same as that of nylon 11, the melting point was 185 ° C, and the relative viscosity of the 0.5% m-cresol solution was 1.48. Carboxylic acid equivalent is 21meq / kg, amine equivalent is 135m
eq / kg.

The terminal carboxylic acid polyamide and the terminal amine polyamide were mixed by an equal weight and kneaded and extruded into a pellet with a 20 mmφ extruder. The relative viscosity of the 0.5% m-cresol solution of the pellet was 1.59.

This pellet is crushed with a small crusher together with liquid nitrogen,
The 60 mesh non-passed product was further pulverized to obtain about 300 g of powder passed through the 60 mesh. A 3 mm-thick iron plate was subjected to fluid immersion coating with this natural powder. Preheating of iron plate is temperature 35
After cooling at 0 ° C. for 7 minutes, immersion for 5 seconds, and standing for 1 minute, water cooling was performed. There was no exposure of the iron plate at the corner. The relative viscosity of a 0.5% m-cresol solution of this coating film was 1.99.

Comparative Example 1 Lauryl lactam 5 kg, water 200 g in 10 autoclaves
And after heating to 280 ° C after purging with nitrogen, the internal pressure of the can is 25k
g / cm ² . After maintaining the temperature at 280 ° C. for 7 hours, the temperature was lowered to 250 ° C. while gradually removing the water vapor pressure in the can until it reached atmospheric pressure over 1 hour. From this state, assuming large-scale equipment, the polymer was gradually discharged from the bottom of the can under nitrogen pressure over 1 hour. The 0.5% m-cresol solution of the polymer starting from the bottom of the can has a relative viscosity of 1.58 and a terminal group having a carboxylic acid equivalent of 61.
The meq / kg and the amine equivalent were 64 meq / kg. Further, the relative viscosity of the 0.5% m-cresol solution of the polymer at the end of one hour after the start of the discharge was 1.75, indicating that the polymerization was proceeding during the discharge and it was difficult to obtain a polymer having the required viscosity.

Comparative Example 2 Lauryl lactam 5 kg, acetic acid 20 in 10 autoclaves
g and 200 g of water, and a polyamide (a) was obtained in the same manner as in Example 1.

The infrared absorption spectrum of this polymer was consistent with that of nylon 12, with a melting point of 177 ° C and a relative viscosity of a 0.5% m-cresol solution of 1.56. The terminal group has a carboxylic acid equivalent of 59meq /
kg, amine equivalent was 9 meq / kg. Since the amount of the terminal methyl group is 67 meq / kg based on the charged amount of acetic acid, the carboxyl group accounts for 44% of the terminal group.

On the other hand, in the same manner, from 5 g of ralyl lactam, 24 g of n-butylamine and 200 g of water, the relative viscosity of a 0.5% m-cresol solution was 1.57, the carboxylic acid equivalent was 7 meq / kg, and the amine equivalent was 58 m.
eq / kg of polyamide (b) was obtained. Since the amount of the terminal alkyl group is 65 meq / kg based on the amount of n-butylamine added, the amino group accounts for 45% of the terminal group.

60 parts by weight of the polyamide (a) thus obtained, 50 parts by weight of the polyamide (b) and 0.2 parts by weight of phosphoric acid were kneaded with an extruder at 200 ° C. to form pellets. The relative viscosity of the 0.5% m-cresol solution of the pellet was 1.59. The pellet was freeze-pulverized together with liquid nitrogen to obtain a 60-mesh powder.

3 mm in the same manner as in Example 1 due to the powder thus obtained.
When a thick iron plate was subjected to fluid immersion coating, the iron plate was partially exposed at the corners. The relative viscosity of this coating film was 1.65, and a sufficient increase in viscosity did not occur.

Claims (7)

(57) [Claims] 1. A polyamide resin composition for powder coating obtained by mixing a polyamide (A) in which at least 70% of terminal groups are carboxyl groups and a polyamide (B) in which at least 70% of terminal groups are amino groups. . 2. A powder coating material comprising a mixture of a polyamide (A) in which 70% or more of the terminal groups are carboxyl groups and a polyamide (B) in which 70% or more of the terminal groups are amino groups. powder. 3. A powder obtained by mixing a powder of a polyamide (A) in which at least 70% of terminal groups are carboxyl groups and a powder of a polyamide (B) in which at least 70% of terminal groups are amino groups. Powder for painting. 4. A powder for powder coating, wherein the powder for powder coating according to claim 2 is blended with a polymerization catalyst. 5. The polyamide (A) and the polyamide (B) having a ratio of the total amount of carboxylic acid equivalents to the total amount of amine equivalents which are different from each other.
The polyamide resin composition for powder coating according to claim 1, which is mixed so as to be 40:60 to 60:40. 6. The polyamide (A) and the polyamide (B) having a ratio of the total amount of carboxylic acid equivalents to the total amount of amine equivalents which are different from each other.
The powder for powder coating according to any one of claims 2 to 4, wherein the powder is mixed so as to have a ratio of 40:60 to 60:40. 7. Polyamide (A) and polyamide (B)
The 0.5% meta-cresol solution of (1) has a relative viscosity of 1.10 to 1.30, and the powder for powder coating according to any one of claims 2 to 6 is subjected to solid-phase polymerization to react polyamides (A) and (B). The powder for powder coating was further polymerized.