WO2016080503A1 - Powdered coating material - Google Patents

Abstract

[Problem] To provide a powdered coating material for producing a coating that exhibits superior heat resistance and can maintain superior properties over a long period of time in a high-temperature environment of 250°C or higher. [Solution] A powdered coating material containing a naphthalene epoxy resin and an aralkyl resin is prepared. A phenol aralkyl resin is used as the aralkyl resin. The powdered coating material is prepared so that it takes at least 10 hours for the residual weight to become 95% of the initial weight at 250°C as calculated by the Flynn-Wall-Ozawa (FWO) method.

Description

Powder paint

The present invention relates to a powder coating, and more particularly to a powder coating suitable for forming a coating film on a molded product such as an automobile part.

Many resin-based coatings are used for automobiles, including insulation coatings for motors and generators. The methods for producing these coatings include a method using a liquid varnish and a method using a powder coating. From the viewpoint of production efficiency, work environment, reuse of coating, etc., powder coating using a powder coating is used. Is considered advantageous.

Patent Document 1 discloses an epoxy resin having a naphthalene skeleton in 100 parts by weight of an epoxy resin powder containing an epoxy resin having a melting point of 90 ° C. to 140 ° C., an average molecular weight of 1000 to 4000, and an epoxy equivalent of 800 to 4000, and a curing agent. A thermosetting epoxy resin powder coating containing 1 to 10 parts by weight of is disclosed. Here, it is described that the addition of an epoxy resin having a naphthalene skeleton improves the corrosion resistance of the resulting coating film. In Patent Document 1, as a curing agent, an amine curing agent, an acid curing agent, an acid anhydride curing agent, a polyamide curing agent, a phenolic hydroxyl group-containing curing agent, a dicyandiamide curing agent, a cationic polymerization reaction curing agent. In addition, hydrazine-based curing agents and the like are shown.

JP 2003-286436 A

However, with the powder coating of Patent Document 1, it is difficult to obtain a coating film having sufficient heat resistance. In particular, in the automotive field in recent years, it has been required to maintain the coating film performance at a higher temperature for a longer time. For example, in a hybrid electric vehicle (HEV), an electric vehicle (EV), and the like, the drive motor and the vicinity of the generator are exposed to a high-temperature environment of 200 ° C. or higher due to high output. Therefore, a coating film that can maintain performance over a long period of time without being deteriorated even in such an environment is demanded.
Then, an object of this invention is to provide the powder coating material for manufacturing the coating film which is excellent in heat resistance and can maintain the outstanding performance over a long period of time in the high temperature environment of 250 degreeC or more.

As a result of intensive studies in view of the above problems, the present inventors have found that the above problems can be solved by using a powder coating containing an epoxy resin having an naphthalene skeleton and an aralkyl resin, and have arrived at the present invention. That is, the powder coating material of the present invention contains a naphthalene type epoxy resin and an aralkyl resin.
The aralkyl resin is preferably a phenol aralkyl resin.
The time required for the residual weight to reach 95% of the initial weight at 250 ° C. calculated by the Flynn-Wall-Ozawa method of the powder coating of the present invention is preferably 10 hours or more.
The molded article of the present invention is provided with a coating film coated with the above powder coating material.

The powder coating of the present invention can provide a coating film that has excellent heat resistance and can maintain excellent performance over a long period of time in a high temperature environment of 250 ° C. or higher.

Hereinafter, embodiments of the present invention will be described in detail.

The powder coating material of the present invention contains a naphthalene type epoxy resin and an aralkyl resin.
Below, the detail of the powder coating material of this invention is demonstrated.

(1) Epoxy resin In the powder coating of the present invention, a naphthalene type epoxy resin is used as the main epoxy resin. A naphthalene type epoxy resin having a rigid skeleton exhibits a high glass transition temperature (Tg). In addition, a naphthalene type epoxy resin having a naphthalene skeleton having a planar structure has a small steric hindrance, so that the nucleophilic attack of the curing agent is hardly inhibited. For this reason, the curing reaction proceeds in a relatively short time. Since naphthalene type epoxy resin has a condensed ring structure, it has long-term heat resistance. The naphthalene type epoxy resin used for this invention is not specifically limited, The naphthalene type epoxy resin represented by Formula (1), Formula (2), Formula (3), etc., and mixtures thereof can be used. Examples of commercially available products include EPICLON HP-4700, HP-4710, HP-4770, HP-6000 (above, manufactured by DIC Corporation) and the like. In order to improve the brittleness of the resulting coating film, the number of functional groups of the naphthalene type epoxy resin is preferably 2 to 4, and is particularly preferably 2.

The softening point of the naphthalene type epoxy resin used in the present invention is preferably 60 ° C. or higher and 120 ° C. or lower. When the temperature is lower than 60 ° C., the storage stability after the powder coating material may be deteriorated. When the temperature is higher than 120 ° C., it may cause the roughness of the coating surface. In a powder coating using a naphthalene type epoxy resin having a softening point in the above range, a coating film having an excellent appearance is obtained, and productivity is improved. Furthermore, in the above-mentioned powder coating, problems such as powder melting and solidifying during storage hardly occur, and storage stability is improved. Moreover, you may add epoxy resins other than a naphthalene type epoxy resin if desired in the range which does not impair the effect of this invention. It is preferable that the compounding quantity is 40 mass% or less of all the epoxy resins.

(2) Aralkyl resin In the powder coating material of the present invention, an aralkyl resin is used as a curing agent. By using an aralkyl resin as a curing agent for a naphthalene type epoxy resin, the long-term stability of the cured film is improved, and the performance of the film is maintained even after being held for a long time in a high-temperature environment. This is because there are few structures that cause thermal decomposition in the cured product. Since the powder coating material of the present invention has such a high heat-resistant structure and good film formability and adhesiveness, a coating film having high heat resistance can be easily obtained by coating.
The aralkyl resin is represented by the following general formula (4). Among these, a phenol aralkyl resin in which Ar ² is phenol is preferable because it is easily available and has excellent oxygen barrier properties.

(In the formula, Ar ¹ is a phenyl group, a biphenyl group, a fluorenyl group, or a naphthyl group, and Ar ² is a group represented by the following general formula (5-1) or (5-2).)

(In each formula, R represents a hydrogen atom, a hydrocarbon group having 1 to 15 carbon atoms, a trifluoromethyl group, an allyl group or an aryl group, and may be the same or different from each other.
m represents an integer of 0 to 3, and may be the same or different. If they are different, they may be arranged in any order.
n represents an average value of the number of repetitions of 1 to 10. )

In the present invention, it is necessary that the curing agent has the aralkyl skeleton. For example, it was confirmed that even if an epoxy-modified aralkyl resin was added to the main agent, the excellent effect of the present invention could not be obtained when no aralkyl resin was used as a curing agent. Of course, in the configuration in which the above aralkyl resin is used as a curing agent and an epoxy modified product of the aralkyl resin is added to the main component naphthalene type epoxy resin, the same effect as in the present invention can be obtained.
The proportion of the aralkyl resin used is preferably 0.6 to 1.2 equivalents, more preferably 0.7 to 1.0 equivalents, in terms of functional group equivalents per epoxy equivalent of the naphthalene type epoxy resin. preferable. By making the equivalent ratio of naphthalene type epoxy resin and aralkyl resin in the above range, the film formability and adhesiveness of the powder coating are further improved, and the long-term heat resistance of the resulting coating film is further improved.

(3) Additives Various additives can be added to the powder coating material of the present invention as necessary within a range not impairing the effects of the invention. Examples of the additive include a filler, a leveling agent, a colorant, a curing accelerator, an antifoaming agent, an adhesion improver, and an impact modifier.
Examples of the filler that can be used include silica, alumina, aluminum hydroxide, magnesium oxide, calcium carbonate, talc, mica, clay, and cellulose. By adding these fillers, the flow of the powder coating material can be more suitably controlled. In addition, these fillers may be used individually by 1 type, or may mix and use 2 or more types.

(4) Manufacturing method of powder coating material Although the manufacturing method of the powder coating material of this invention is not specifically limited, For example, it can manufacture with the following method. When adding a filler to a powder coating material, first, a naphthalene type epoxy resin and a filler are mixed. Examples of the mixing method include melt mixing using a kneader or an extruder. The mixing temperature and mixing time are not particularly limited, and are set according to the type and composition ratio of the raw materials. Usually, the mixing temperature is preferably 70 ° C. to 150 ° C., more preferably 100 ° C. to 140 ° C. The mixing time depends on the mixing method and the like, but in the case of a kneader, it is preferably 15 minutes to 60 minutes, more preferably 30 minutes to 50 minutes. In the case of an extruder, it is preferably 60 seconds or shorter, and more preferably 30 seconds or shorter.
Thereafter, the obtained mixture is cooled and solidified, and coarsely pulverized. An aralkyl resin and other additives as required are added to the coarsely pulverized product, melt mixed, and then cooled and solidified. Thereafter, the solidified mixture is pulverized and classified to obtain a powder coating material.

(5) Powder coating The powder coating of the present invention contains a naphthalene type epoxy resin and an aralkyl resin. Depending on the mixing conditions, partial polymerization proceeds, and a polymer containing a structural unit derived from a naphthalene type epoxy resin and a structural unit derived from an aralkyl resin is contained.
The particle diameter of the powder coating material of the present invention is not particularly limited, but the volume average particle diameter by laser diffraction / scattering method (JIS 8825-1) is preferably in the range of 30 μm to 70 μm. The volume average particle size can be measured using a laser diffraction particle size distribution analyzer (manufactured by SYMPATEC, HELOS and PODOS analysis software: WINDOX5).
By using a powder coating material having a volume average particle diameter in the above range, better film formability can be obtained.

The horizontal flow rate of the powder coating of the present invention is preferably in the range of 1 to 50%. In general, a powder paint having a large horizontal flow rate has a low viscosity when melted and the paint flows easily, whereas a powder paint having a small horizontal flow rate has a high viscosity and hardly flows when melted. By setting the horizontal flow rate of the powder coating within the above range, coating film defects such as pinholes and sagging are less likely to occur, and a high-quality coating film with a desired film thickness can be easily obtained. The horizontal flow rate of the powder coating is more preferably 5% to 30%.
The horizontal flow rate is calculated by the following method. 1 g of the powder coating material is put into a tablet molding die having an inner diameter of 16 mmφ, and the diameter (a) of the tablet obtained by pressurizing with a load of 90 MPa for 60 seconds is measured with a caliper. The tablet is placed on a slide glass, heated in a hot air dryer at 140 ° C. for 10 minutes, and the tablet diameter (b) is measured in the same manner. The horizontal flow rate (%) is obtained by multiplying the value obtained by dividing the increase in diameter (ba) by heating by the diameter (a) before heating by 100.

The softening temperature of the powder coating material of the present invention is preferably 60 ° C. or higher and 120 ° C. or lower. By making the softening point of the powder coating within the above range, the productivity of the coating film is improved, and a coating film having a more excellent appearance can be obtained. Moreover, in the said powder coating material, problems, such as a powder melt | dissolving and solidifying during storage, do not arise easily and storage stability improves.
In the powder coating material of the present invention, the time required for the residual weight to reach 95% of the initial weight at 250 ° C. is preferably 10 hours or more. As will be described later, this value can be calculated by the Flynn-Wall-Ozawa method using the result of the thermogravimetric change of the powder paint measured using a differential thermothermogravimetric simultaneous analysis (TG / DTA) apparatus. When the above value is 10 hours or longer, sufficient heat resistance can be maintained over a long period of time even when used at 250 ° C. or higher. In addition, the behavior of the thermogravimetric change can be adjusted by the kind and blending amount of the naphthalene type epoxy resin used for the powder coating material of the present invention.

(6) Powder coating method The method of applying the powder coating of the present invention is not particularly limited, and a known coating method can be applied. Specifically, electrostatic coating, triboelectric charging, non-charged coating, fluid immersion, and the like can be given. According to the above method, a coating film can be obtained by applying a powder coating on the surface of the object to be coated and then curing. If necessary, the adhesion of the coating film can be improved by applying a surface treatment to the object to be coated in advance.
Although the film thickness of the coating film obtained from the powder coating material of this invention is not specifically limited, 50 micrometers or more and 500 micrometers or less are preferable.

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples. In the examples, unless otherwise specified, “%” and “part” indicate mass% and mass part.

<Components of powder paint>
(A) Main agent (A1) Naphthalene type epoxy resin: EPICLON HP-4770, manufactured by DIC Corporation (A2) Bisphenol A type epoxy resin: jER1004 Mitsubishi Chemical Corporation (A3) Bisphenol F type epoxy resin: YDF-2004 NS (A4) Cresol novolak type epoxy resin manufactured by Chemical Co., Ltd .: EPICLON N-670 manufactured by DIC Corporation (A5) biphenylaralkylphenol type epoxy resin: NC-3000-H manufactured by Nippon Kayaku Co., Ltd. (B) curing agent (B1- 1) Biphenylaralkylphenol: KAYAHARD GPH-65 Nippon Kayaku Co., Ltd. (softening point: 65 ° C.)
(B1-2) Biphenylaralkylphenol: KAYAHARD GPH-103 manufactured by Nippon Kayaku Co., Ltd. (softening point: 102 ° C.)
(B2) Acid anhydride: 3,3 ′, 4,4′-benzophenonetetracarboxylic dianhydride

(Examples 1-2, Comparative Examples 1-3)
The main component and curing agent were mixed together with a leveling agent and a curing accelerator at a blending ratio (mass) shown in Table 1 with a mixer, and then melt mixed with an extruder. Here, the mixing temperature was 110 ° C., and the mixing time was 30 seconds or less. The mixture was cooled and solidified, and then finely pulverized to obtain powder coating materials of Examples and Comparative Examples. Here, a filler such as an inorganic filler is not added. Moreover, 1 mass part of imidazole was added with respect to 100 mass parts of main agents as a hardening accelerator. Table 1 shows the result of calculating the estimated time until the residual weight of the obtained powder coating material reaches 95% at 250 ° C. by the method described later.

(Example 4, Comparative Examples 4 to 6, Reference Example 1)
The above main agent and filler were melt-mixed with an extruder at the blending ratio (mass) shown in Table 2, then cooled and solidified, and coarsely pulverized. To this coarsely pulverized product, the curing agent shown in Table 2 was added together with a leveling agent and a curing accelerator, mixed with a mixer, and then melt mixed with an extruder. Here, the mixing temperature was 110 ° C., and the mixing time was 30 seconds or less. The mixture was cooled and solidified, and then finely pulverized to obtain powder coating materials of Examples, Comparative Examples, and Reference Examples. Here, silica was used as the filler. Moreover, 1 mass part of imidazole was added with respect to 100 mass parts of main agents as a hardening accelerator. The obtained powder coating was molded into a strip shape to prepare a sample for measuring tensile strength. The tensile strength before heating of each sample and the tensile strength after holding for 200 hours and 1000 hours in an electric furnace at 250 ° C. were measured. The tensile strength was measured based on JIS K 7161. Table 2 shows the results of calculating the ratio of the tensile strength after heating for 200 hours and 1000 hours with respect to the tensile strength before heating (coating film tensile strength maintenance ratio).

(Calculation of the time until the remaining weight reaches 95% at 250 ° C)
The thermogravimetric change of the powder coating sample of an Example, a comparative example, and a reference example was measured using the differential thermal thermogravimetric simultaneous analysis (TG / DTA) apparatus. Here, the temperature increase rate was measured at 5 K / min, 10 K / min, 20 K / min, and 30 K / min, respectively. From each of the results, the temperature when the residual amount reached 95% by weight of the initial weight was read, and the residual amount was 95% of the initial weight at 250 ° C. by the Flynn-Wall-Ozawa method, which is one of the equivariant rate methods. Estimated time to be calculated.

As shown in Table 1, in Comparative Examples 1 and 2 using bisphenol A type epoxy resin and bisphenol F type epoxy resin as the main agent and biphenylaralkylphenol as the curing agent, the residual weight was 95% at 250 ° C. It can be seen that the estimated times to become 2.5 hours and 2.0 hours are extremely short, respectively. Further, even in Comparative Example 3 in which naphthalene type epoxy resin is used as the main agent and acid anhydride is used as the curing agent, the estimated time until the residual weight reaches 95% at 250 ° C. may be as short as 3 hours. confirmed.
On the other hand, in Examples 1 and 2 using naphthalene type epoxy resin as the main agent and different types of biphenylaralkylphenol as the curing agent, the estimated time until the remaining weight reaches 95% at 250 ° C. It was 55 hours and 73 hours, and it was confirmed that the heat resistance was significantly improved as compared with Comparative Examples 1, 2, and 3.
From the above results, the effectiveness of the powder coating of the present invention containing a naphthalene type epoxy resin and an aralkyl resin was confirmed.

From Table 2, it can be seen that in Reference Example 1 obtained from bisphenol A type epoxy resin and acid anhydride, the tensile strength retention after holding at 250 ° C. for 200 hours and 1000 hours is as low as 36% and 18%, respectively. . In Reference Example 1, the ratio of the tensile strength maintenance ratio after holding for 1000 hours to the tensile strength maintenance ratio after holding for 200 hours (tensile strength maintenance ratio after holding for 1000 hours / tensile strength after holding for 200 hours) The maintenance ratio) was 0.5, and it was confirmed that the physical properties of the coating film continued to decline after 200 hours. On the other hand, in Example 4 of the present invention using a naphthalene type epoxy resin and biphenyl aralkyl phenol, the tensile strength maintenance ratios after holding for 200 hours and after holding for 1000 hours were 63% and 59%, respectively. In order to maintain long-term heat resistance, the coating film tensile strength maintenance rate is required to be 50% or more after both 200 hours and 1000 hours. In Example 4, the above requirement may be satisfied. all right. In Example 4, the value of the tensile strength maintenance ratio after holding for 1000 hours / the tensile strength maintenance ratio after holding for 200 hours is as high as 0.94. After holding for 200 hours, the physical properties of the coating film at high temperature It was confirmed that the change was remarkably suppressed. Even when the equivalent ratio is 0.7 or 1 with the same composition as in Example 4, the coating film tensile strength maintenance ratio after holding for 200 hours and after holding for 1000 hours exceeds 50%, and after holding for 1000 hours The value of tensile strength maintenance ratio / tensile strength maintenance ratio after holding for 200 hours exceeded 0.9, and it was confirmed that excellent long-term heat resistance was obtained similarly.
In Comparative Examples 4, 5 and 6 in which the composition of the main agent was changed from that of Reference Example 1, it was confirmed that both the tensile strength maintenance rates after 250 hours and 1000 hours were higher than those of the Reference Example. However, in any of the samples of Comparative Examples 4, 5, and 6, the retention rate after 1000 hours was less than 50%. Moreover, the values of the tensile strength maintenance ratio after holding for 1000 hours / the tensile strength maintenance ratio after holding for 200 hours were 0.83, 0.83, and 0.76, which were not as high as those of Example 4.
In Comparative Examples 4 and 5, biphenylaralkyl type epoxy resin was used as the main agent, but sufficient effects were not obtained. From this, it is considered effective to use a resin having an aralkyl skeleton as the curing agent as in the present invention.

 

Claims (4)

1. Powder coating characterized by containing naphthalene type epoxy resin and aralkyl resin.
2. The powder paint according to claim 1, wherein the aralkyl resin is a phenol aralkyl resin.
3. The time required for the residual weight to reach 95% of the initial weight at 250 ° C. calculated by the Flynn-Wall-Ozawa method of the powder coating material is 10 hours or more. The powder coating described.
4. A molded product comprising a coating film coated with the powder paint according to any one of claims 1 to 3.