JP7218028B1 - Powder coating compositions, coatings and articles - Google Patents

Abstract

[Problem] To provide a powder coating composition capable of forming a smooth coating film (having good coating film smoothness) and hardly causing unintended "sagging" during coating (having good anti-sagging properties). provide. The powder coating composition contains a resin and a curing agent, and (i) has a melt mass flow rate of 10 to 20 g/10 min measured under conditions of a temperature of 120° C. and a load of 1.20 kg. and (ii) using a rheometer, frequency: 1.0 Hz, mode: vibration mode, measurement temperature range: room temperature to 160 ° C., heating rate: 10.0 ° C./min, measured at 120 ° C. The absolute value |η*| of the complex elastic modulus of is 0.01 to 20 Pa·s. [Selection drawing] Fig. 1

Description

The present invention relates to powder coating compositions, coatings and articles. More specifically, it relates to a powder coating composition, a coating film formed from the powder coating composition, and an article provided with the coating film.

Powder coatings are often used for coating metal members and the like.
Since powder coatings have advantages that solvent-based coatings do not have, they are being actively developed. In addition, since powder coatings do not volatilize organic solvents into the atmosphere during coating, they have recently attracted attention in terms of environmental performance.

Prior art relating to powder coatings includes, for example, Patent Documents 1 to 11 below.

Japanese Patent Publication No. 2020-524734 JP 2020-142477 A Japanese Patent Publication No. 2019-536296 JP 2017-190419 A Japanese Patent Publication No. 2013-526639 Japanese Patent Application Publication No. 2013-502464 Special Table 2013-067800 Japanese Patent Publication No. 2012-517491 JP 2012-041464 A Japanese translation of PCT publication No. 2011-514920 Japanese Patent Publication No. 2010-523780

One of the properties required for powder coating compositions is the ability to form a smooth coating film (coating film smoothness).
In addition, as another performance required for the powder coating composition, unintended "sagging" is unlikely to occur during coating (when the powder coating composition is heated and melted) (sagging prevention).
However, as far as the present inventors know, it has been difficult in conventional powder coating compositions to achieve both high levels of coating film smoothness and anti-sagging properties. In other words, in order to form a smooth coating film, the fluidity of the molten powder coating should be high.

The present invention has been made in view of such circumstances. One of the objects of the present invention is that it is possible to form a smooth coating film (good coating film smoothness), and it is difficult for unintended "sagging" to occur during coating (good anti-sagging property). It is to provide a powder coating composition.

The present inventors completed the invention provided below and solved the above problems.

1.
A powder coating composition comprising a resin and a curing agent and satisfying the following [Characteristic 1] and [Characteristic 2].
[Characteristic 1]
The powder coating composition has a melt mass flow rate of 10 to 20 g/10 min, measured at a temperature of 120° C. and a load of 1.20 kg.
[Characteristic 2]
The absolute value |η ^* | of the complex elastic modulus of the powder coating composition at 120° C. measured using a rheometer under the following measurement conditions is 0.01 to 20 Pa·s.
(Measurement condition)
・Frequency: 1.0Hz
・Mode: Vibration mode ・Measurement temperature range: Room temperature to 160℃
・Temperature increase rate: 10.0°C/min
2.
1. A powder coating composition according to
A powder coating composition, wherein the resin comprises a polyester resin.
3.
1. or 2. A powder coating composition according to
A powder coating composition, wherein the resin has a melt viscosity of 1800 to 9500 mPa·s at 200°C.
4.
1. ~3. A powder coating composition according to any one of
A powder coating composition, wherein the resin has a melt mass flow rate of 1 to 15 g/10 min measured at a temperature of 120° C. and a load of 1.20 kg.
5.
1. ~ 4. A powder coating composition according to any one of
A powder coating composition, wherein the curing agent comprises a β-hydroxyalkylamide.
6.
1. ~ 5. A powder coating composition according to any one of
A powder coating composition, wherein the curing agent comprises a blocked isocyanate.
7.
1. ~6. A powder coating composition according to any one of
A powder coating composition having |η ^* | of 0.1 to 1 Pa·s.
8.
1. ~6. A powder coating composition according to any one of
A powder coating composition having |η ^* | of 5 to 20 Pa·s.
9.
1. ~8. A coating film formed from the powder coating composition according to any one of.
10.
9. Article provided with the coating film according to.

According to the present invention, a powder coating that can form a smooth coating film (good coating film smoothness) and is unlikely to cause unintended "sagging" during coating (good anti-sagging property). A composition is provided.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram (a diagram schematically showing a cross-section of an apparatus) for explaining an apparatus for producing a powder coating composition;

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The drawings are for illustrative purposes only. The shape and dimensional ratio of each member in the drawings do not necessarily correspond to the actual article.

In this specification, the notation "X to Y" in the description of numerical ranges means X or more and Y or less, unless otherwise specified. For example, "1 to 5% by mass" means "1% by mass or more and 5% by mass or less".

In the description of a group (atomic group) in the present specification, a description without indicating whether it is substituted or unsubstituted includes both those having no substituent and those having a substituent. For example, the term “alkyl group” includes not only alkyl groups without substituents (unsubstituted alkyl groups) but also alkyl groups with substituents (substituted alkyl groups).
The notation "(meth)acryl" used herein represents a concept that includes both acryl and methacryl. The same applies to similar notations such as "(meth)acrylate".
The term "organic group" as used herein means an atomic group obtained by removing one or more hydrogen atoms from an organic compound, unless otherwise specified. For example, a "monovalent organic group" represents an atomic group obtained by removing one hydrogen atom from an arbitrary organic compound.

<Powder coating composition>
The powder coating composition of this embodiment contains a resin and a curing agent.
The powder coating composition of the present embodiment satisfies [Characteristic 1] and [Characteristic 2] below.
[Characteristic 1]
The powder coating composition has a melt mass flow rate (MFR) of 10 to 20 g/10 min measured at a temperature of 120° C. and a load of 1.20 kg.
[Characteristic 2]
The absolute value |η ^* | of the complex elastic modulus of the powder coating composition at 120° C. measured using a rheometer under the following measurement conditions is 0.01 to 20 Pa·s.
(Measurement condition)
・Frequency: 1.0Hz
・Mode: Vibration mode
・Measurement temperature range: Room temperature to 160°C
・Temperature increase rate: 10.0°C/min

Since the powder coating composition of the present embodiment satisfies the properties 1 and 2, it has good coating film smoothness and good anti-sagging properties.

Hereinafter, the reason why the performance of the powder coating composition is considered to be improved by satisfying the characteristics 1 and 2 will be explained through the circumstances leading to the production of the powder coating composition as described above by the inventors. Just to be sure, the following description includes speculation. Moreover, the present invention is not limited by the following description.

The present inventors have considered that the performance of powder coating compositions such as coating film smoothness and anti-sagging properties is related to the melting behavior when the powder coating composition is heated. . Based on this idea, powder coating compositions were melted under various conditions, and the relationship between melting behavior and properties such as coating film smoothness and anti-sagging properties was investigated.

As a result of the investigation, the present inventors found that the melting behavior of the powder coating composition at "120°C" seems to be closely related to the performance of the powder coating composition. The temperature of "120° C." is considered to be a special temperature in a certain sense that "melting of the resin has started, but the curing reaction has not yet started sufficiently" in ordinary powder coating compositions. It is therefore reasonable to infer that the melting behavior at this temperature is particularly relevant to the performance of powder coating compositions.

Based on the above studies and inferences, the present inventors proceeded with further studies. Specifically, various indices considered to be related to the melting behavior of the powder coating composition at 120°C were investigated. Then, [1] the value of the melt mass flow rate at 120 ° C., and [2] the absolute value of the complex elastic modulus at 120 ° C. measured using a rheometer |η ^* | It was found that it seems to be related to properties such as smoothness and anti-sagging.

The reason why the above indicators [1] and [2] are related to properties such as coating film smoothness and sagging resistance is presumed as follows. Note that the indexes [1] and [2] are not independent indexes, and it is presumed that both parameters contribute to both the smoothness of the coating film and the anti-sagging property.

[1] Melt mass flow rate value at 120° C.: It is believed that a moderately high melt mass flow rate makes the molten powder coating "easier to spread" and enhances smoothness. In addition, it is believed that the melt mass flow rate is not too high, thereby suppressing "unintended flow" until the molten powder coating is cured, thereby suppressing sagging.

[2] Regarding the absolute value |η ^* | of the complex elastic modulus at 120°C measured using a rheometer: that |η ^* | is not too large means that the melt of the powder coating at 120°C It is thought that it means that it deforms flexibly in response to periodic stimuli from the outside. For this reason, it is thought that when |η ^* | In addition, it is thought that when |η ^* | is not too small, "unintended flow" is suppressed until the molten powder coating is cured, thereby suppressing sagging.

Incidentally, one of the reasons why the index of "complex elastic modulus" as in [2] is related to coating film smoothness and sagging resistance is thought to be the influence of external stimuli during coating film formation. In other words, when painting, it is assumed that various "external stimuli" (such as minute vibrations) may disturb the smoothness of the coating film or induce sagging. is within a certain numerical range, the ^smoothness of the coating film and the anti-sagging property may be enhanced.

Based on the above findings, the present inventors specifically found that [1] the melt mass flow rate measured under the conditions of a temperature of 120° C. and a load of 1.20 kg is 10 to 20 g/10 min, and [2] Using a rheometer, a new powder coating composition having a complex elastic modulus absolute value |η ^* | of 0.01 to 20 Pa s at 120°C measured under the above conditions, prepared. Thus, it was possible to obtain a powder coating composition having good coating film smoothness and good anti-sagging properties.

The powder coating composition of the present embodiment can be produced by employing suitable production conditions in addition to using suitable raw materials. Briefly describing the “appropriate manufacturing conditions”, the powder coating composition of the present embodiment preferably uses a kneader (extrusion kneader, rotating screw to move raw materials) having a structure similar to an injection molding device. (Equipped with a mechanism that heats while heating), appropriately setting the rotation speed of the screw to appropriately control the time during which the raw material is heated, appropriately setting the temperature for heating the raw material, and heating the raw material It is possible to manufacture by devising such as performing in two steps of high temperature and low temperature.
The method for producing the powder coating composition of this embodiment will be described later in detail.

The description of the powder coating composition of the present embodiment will be continued below.

(resin)
The powder coating composition of this embodiment contains a resin. The type of resin is not particularly limited, and resins known in the field of powder coatings can be used. Polyester resins, polyurethane resins, epoxy resins, and the like can be cited as resins that are preferable for application to powder coatings. In this embodiment, it is preferable to use a polyester resin or an epoxy resin, and it is more preferable to use a polyester resin.

As one aspect, the polyester resin preferably has a hydroxy group. More specifically, when the polyester resin has a hydroxyl group, the hydroxyl value is preferably 10-60 mgKOH/g, more preferably 25-50 mgKOH/g.
The hydroxyl value can typically be measured according to JIS K 0070.

Examples of polyester resins containing hydroxyl groups include hydroxyl-terminated polyester resins. In addition, since polyester resins with various hydroxyl values are commercially available from DIC Corporation and the like, it is possible to select a suitable hydroxyl value from commercially available polyester resins.

As another aspect, the polyester resin preferably has an acid group (such as a carboxy group). More specifically, when the polyester resin has acid groups, the acid value is preferably 10 to 60 mgKOH/g, more preferably 20 to 40 mgKOH/g.
Similarly to the hydroxyl value, the acid value can typically be measured according to JIS K 0070.

Examples of polyester resins having acid groups include carboxyl-terminated polyester resins. In addition, since polyester resins with various acid values are commercially available from DIC Corporation and the like, a suitable acid value can be selected from commercially available polyester resins.

The polyester resin may have both hydroxy groups and acid groups.

The weight average molecular weight of the polyester resin is not particularly limited. For example, it is 3,000 to 50,000, preferably 5,000 to 40,000, more preferably 5,000 to 20,000. The degree of dispersion (weight average molecular weight/number average molecular weight) of the polyester resin is not particularly limited, and is, for example, 1-10, preferably 1.4-8.
The weight average molecular weight and degree of dispersion can be measured as values converted to standard polystyrene by gel permeation chromatography (GPC).

The properties of the polyester resin are not particularly limited. However, from the viewpoint of making the composition powdery, it is preferably solid at room temperature (25°C). Also, the softening point of the polyester resin is preferably 80 to 150°C, more preferably 100 to 130°C. It is considered that the smoothness of the obtained coating film can be improved by adjusting the amount within this range.

Usable epoxy resins are not particularly limited. Specific examples of epoxy resins include phenol novolak type epoxy resin, cresol novolak type epoxy resin, cresol naphthol type epoxy resin, biphenyl type epoxy resin, biphenyl aralkyl type epoxy resin, phenoxy resin, naphthalene skeleton type epoxy resin, bisphenol A type epoxy resin. Resins, bisphenol F type epoxy resins, glycidyl ether type epoxy resins, aromatic polyfunctional epoxy resins, aliphatic epoxy resins, aliphatic polyfunctional epoxy resins, alicyclic epoxy resins, polyfunctional alicyclic epoxy resins, etc. can be done.

The epoxy resin may contain a trifunctional or higher polyfunctional epoxy resin. Specifically, 2-[4-(2,3-epoxypropoxy)phenyl]-2-[4-[1,1-bis[4-([2,3-epoxypropoxy]phenyl)ethyl]phenyl] Propane, phenolic novolac epoxy, tetrakis(glycidyloxyphenyl)ethane, α-2,3-epoxypropoxyphenyl-ω-hydropoly(n=1-7){2-(2,3-epoxypropoxy)benzylidene-2, 3-epoxypropoxyphenylene}, 1-chloro-2,3-epoxypropane/formaldehyde/2,7-naphthalenediol polycondensate, dicyclopentadiene type epoxy resin, and the like.

A commercially available product may be used as the epoxy resin. For example, Mitsubishi Chemical Corporation's "jER" (registered trademark) series, Nippon Steel & Sumikin Chemical Co., Ltd.'s "Epotote" series epoxy resins, and the like may be used.

The epoxy equivalent (g/eq) of the epoxy resin is not particularly limited. For example, 200-3000, preferably 500-2000.
The weight average molecular weight of the epoxy resin is not particularly limited. It is preferably 20,000 or less, more preferably 2,000 to 20,000, and more preferably 5,000 to 15,000. A weight average molecular weight can be calculated|required as a standard polystyrene conversion value by a gel permeation chromatography (GPC), for example.

From the viewpoint of making the composition powdery, the epoxy resin is preferably solid (powder) by itself. The physical properties of the epoxy resin are preferably adjusted as appropriate from the viewpoints of kneadability during paint production, meltability of the paint during baking, toughness of the paint film after baking, and the like. For example, the softening point of the epoxy resin is preferably 60-130°C, more preferably 80-120°C.

Physical properties such as the melt viscosity and melt mass flow rate of the "resin itself" can also be mentioned as a viewpoint of selecting the resin. By using a resin with suitable physical properties, it is easy to produce a powder coating composition that can obtain a powder coating composition that satisfies the characteristics 1 and 2, and the coating film smoothness and sagging prevention of the powder coating composition. You may be able to further enhance your sexuality.
Specifically, the melt viscosity of the resin itself at 200° C. is preferably 1,800 to 9,500 mPa·s, more preferably 3,000 to 9,500 mPa·s, and more preferably 3,000 to 6,000 mPa·s. For an example of the method for measuring the melt viscosity, refer to Examples given later.
Further, the melt mass flow rate of the resin itself measured at a temperature of 120° C. and a load of 1.20 kg is preferably 1 to 15 g/10 min, more preferably 1 to 10 g/10 min, and even more preferably 1 to 7 g/10 min. is.

The powder coating composition of the present embodiment may contain only one resin, or may contain two or more resins.
The amount of the resin is, for example, 10 to 80% by mass, preferably 25 to 75% by mass, more preferably 40 to 70% by mass, based on the total non-volatile components in the powder coating composition (100% by mass).

(curing agent)
The powder coating composition of this embodiment contains a curing agent.
The curing agent is not particularly limited as long as it cures the composition by, for example, reacting with the resin when the powder coating composition is heated.

β-Hydroxyalkylamides are preferably used as curing agents. β-Hydroxyalkylamides are sometimes referred to as "primides". This compound has good curing performance, especially when the resin contains acid groups.
The β-hydroxyalkylamide may be any compound as long as it is a compound in which the β-carbon of the amide group is substituted with a hydroxy group. For example, a compound containing two or more structures in which the β-carbon of an amide group is substituted with a hydroxy group in one molecule can be used. Specifically, compounds containing 2 to 6 structures in which the β-carbon of the amide group is substituted with a hydroxy group in one molecule are preferable.

More specifically, the β-hydroxyalkylamide is a compound having two or more (more specifically 2 to 6) structures represented by —CO—NR ^a R ^b in one molecule. preferable.
Here, R ^a and R ^b each independently represent a hydrogen atom or a monovalent organic group. However, at least one (or both) of R ^a and R ^b is a group represented by —CR ³ R ⁴ —CR ⁵ R ⁶ —OH (R ³ , R ⁴ , R ⁵ and R ⁶ are each independently a hydrogen atom or a monovalent organic group).

Examples of monovalent organic groups for R ^a and R ^b include alkyl groups, cycloalkyl groups, alkoxy groups, aryl groups, aralkyl groups, alkylcarbonyl groups, alkoxycarbonyl groups, and alkylcarbonyloxy groups. .
Examples of monovalent organic groups for R ³ , R ⁴ , R ⁵ and R ⁶ include the same monovalent organic groups as those for ^Ra and ^Rb . Preferably, all of R ³ , R ⁴ , R ⁵ and R ⁶ are hydrogen atoms.

Another example of a curing agent can include isocyanate compounds (including blocked isocyanate compounds). The isocyanate compound has good curability especially when the resin has a hydroxyl group. In terms of storage stability, blocked isocyanate compounds are more preferred.
The isocyanate compound is preferably a polyfunctional isocyanate. The polyfunctional isocyanate is preferably di- to hexa-functional (ie, has 2-6 reactive isocyanate groups per molecule), more preferably di- to tetra-functional.

The powder coating composition of the present embodiment may contain only one curing agent, or may contain two or more curing agents.
The amount of the curing agent in the powder coating composition of the present embodiment is preferably 1 to 20% by mass, more preferably 1.5 to 10% by mass, based on the total nonvolatile components of the composition (100% by mass). , more preferably 2 to 5% by mass.
From another point of view, the content of the curing agent in the powder coating composition of the present embodiment is preferably 1 to 50% by mass, more preferably 1 to 50% by mass, based on the total amount of the resin and the curing agent (100% by mass). is 2 to 40% by mass, more preferably 3 to 25% by mass.

(pigment)
The powder coating composition of this embodiment preferably contains a pigment. By using pigments, in addition to the effects that pigments are normally used for, such as ``it is possible to give the desired color to the coating film'' and ``it is possible to adjust the luster of the coating film,'' it is possible to improve the physical properties of the coating film. In some cases. The term “physical properties of the coating film” refers to the properties of the coating film as a whole, such as the flexibility of the coating film.

Pigment particles include known inorganic pigments, organic pigments, and other colored pigments. Specifically, white pigments such as titanium oxide (titanium white), zinc oxide (zinc white), lead white, basic lead sulfate, lead sulfate, lithopone, zinc sulfide, antimony white; carbon black, acetylene black, lamp black , graphite, iron black (black iron oxide), aniline black; yellow pigments such as Naphthol Yellow S, Hansa Yellow, Pigment Yellow L, Benzidine Yellow, Permanent Yellow, yellow iron (yellow iron oxide); chrome orange, chromium Orange pigments such as vermilion and permanent orange; Brown pigments such as iron oxide and amber; Red pigments such as red iron oxide, red lead, permanent red, quinacridone red pigments, and diketopyrrolopyrrole red pigments; cobalt Purple pigments such as purple, fast violet, and methyl violet lake; blue pigments such as ultramarine blue, Prussian blue, cobalt blue, phthalocyanine blue, and indigo; and green pigments such as chrome green, Pigment Green B, and phthalocyanine green. Of course, usable pigment particles are not limited to these.

The pigment particles may include extender pigments. Usable extender pigments are not particularly limited. Examples include barita powder, barium sulfate, barium carbonate, calcium carbonate, gypsum, clay, silica, white carbon, diatomaceous earth, talc, magnesium carbonate, hydrous magnesium silicate, alumina white, gloss white, and mica powder.

The pigment particles preferably contain titanium oxide particles from the viewpoint of high whiteness, compatibility with resin, further improvement of coating film properties, and the like.

The size (particle size, etc.) of the pigment particles is not particularly limited. The size may be appropriately set according to various purposes. The average particle size of the pigment particles is preferably 0.1 to 25 μm, more preferably 0.1 to 10 μm, still more preferably 0.2 to 5 μm.
Regarding the average particle size of the pigment particles, if there is a catalog value, that value can be adopted. Alternatively, an average value from a number distribution obtained by dimensional measurement of images of individual average particle diameters using a transmission electron microscope (TEM), a scanning electron microscope (SEM), or the like may be employed. In principle, the measurement measures the size of primary particles (particles that are not agglomerated). The number of particles to be measured during measurement is preferably at least 100 in terms of accuracy. Software may be utilized to streamline particle size measurements.

When the powder coating composition of the present embodiment contains a pigment, it may contain only one pigment, or may contain two or more pigments.
When the powder coating composition of the present embodiment contains a pigment, the amount thereof is preferably 5 to 80% by mass, more preferably 10 to 60% by mass, more preferably 10 to 60% by mass, based on the total non-volatile components of the powder coating composition. is 20 to 40% by mass.

(Other ingredients)
The powder coating composition of the present embodiment may contain optional components other than those described above, if necessary.

As an example, the powder coating composition of the present embodiment may contain an additive component (surface conditioner) that has the effect of increasing the smoothness of the coating surface. Surface modifiers include plasticizers, silicone compounds, waxes, antifoaming agents, leveling agents, anti-popping agents (components that break air entrained during coating), and the like, which are known in the field of coatings.

Among surface conditioners, examples of leveling agents include BASF's "Acronal" (registered trademark) series (containing (meth)acrylic resin), Kyoeisha Chemical Co.'s "Polyflow" (trade name) series, and ESTRON. The "Regiflow" (trade name) series manufactured by CHEMICAL and the "Modaflow" (trade name) series manufactured by Monsanto can be mentioned. Moreover, benzoin etc. can be mentioned as an example of an antifoaming agent.

As another example, the powder coating composition of the present embodiments may contain some catalyst.
Catalysts include tin octylate, dibutyltin di(2-ethylhexanoate), dioctyltin di(2-ethylhexanoate), dioctyltin diacetate, dibutyltin dilaurate, dibutyltin oxide, dioctyltin oxide, dibutyl Organometallic compounds such as tin fatty acid salts, lead 2-ethylhexanoate, zinc octoate, zinc naphthenate, zinc fatty acids, cobalt naphthenate, calcium octylate, copper naphthenate, tetra(2-ethylhexyl) titanate. . Furthermore, known urethane curing catalysts such as tertiary amines and phosphoric acid compounds can also be used. These catalysts act as curing catalysts, especially when isocyanates or blocked isocyanates are used as curing agents.
In this embodiment, an organotin-based curing catalyst is preferably used.

As still another example, the powder coating composition of the present embodiment may contain one or more of a pigment dispersant, an ultraviolet absorber, a light stabilizer, an antioxidant, a magnetic powder, a charge control agent, and the like. .

The amount of the above-mentioned other components is not particularly limited, and an appropriate amount may be used in consideration of the purpose of use and balance with other performance. The amount of other components is, for example, 0.01 to 10% by mass, specifically 0.01 to 5% by mass, based on the total powder coating composition.

(Supplementary information about characteristics 1 and 2)
As described above, the melt mass flow rate may be 10-20 g/10 min. The melt mass flow rate is preferably 10-16 g/10 min, more preferably 10-14 g/10 min.

As described above, |η ^* | may be 0.01 to 20 Pa·s, and |η ^* | is preferably 0.1 to 1 Pa·s as an example.
As another example, |η ^* | is preferably 5 to 20 Pa·s.

<Coating film, article with coating film>
A coating film can be formed by, for example, baking the powder coating composition of the present embodiment on the surface of a substrate. Specifically, a coating film can be formed by applying the powder coating composition of the present embodiment to the surface of a substrate, heating and baking the composition.

As a method for applying the powder coating composition to the surface of the substrate, a method known in the field of powder coating can be appropriately used. For example, an electrostatic powder spraying method, a fluidization immersion method, an electrostatic fluidization immersion method, or the like can be preferably used. The film thickness at this time may be appropriately adjusted, for example, between 30 and 1000 μm.

The substrate having the powder coating composition applied to its surface is heated, for example, at 120 to 250° C. for 5 to 60 minutes, such as by putting it in a furnace. This melts the paint and forms a coating film on the surface of the substrate. That is, an article provided with a coating film can be obtained.

<Method for producing powder coating composition>
The powder coating composition of this embodiment is preferably produced by the following procedure.
(1) Prepare necessary amounts of each component such as a resin, a curing agent, and a pigment.
(2) Using a Henschel mixer, a blender, etc., each component is uniformly mixed to obtain a mixture.
(3) The mixture obtained in (2) above is introduced into a kneader (extrusion kneader, which can be heated while moving the raw material with a rotating screw) and melt-kneaded. The temperature at this time is, for example, 80 to 140.degree.
(4) Cool the kneaded product obtained in (3) above to 50° C. or lower. Any cooling method can be adopted. For example, it can be left at room temperature, a cooling roll, a cooling conveyor, and the like.
(5) The cooled kneaded product is pulverized using a pulverizer or the like. Examples of the pulverizer include a mechanical type, an airflow type, and the like, and are not particularly limited. Further, the pulverization may be carried out, for example, in two steps of coarse pulverization and fine pulverization.
(6) Classify so as to obtain a desired particle size. A sieve or an air classifier can be used for classification.

In the present embodiment, in particular, by appropriately controlling the melt-kneading conditions in (3) above, the MFR is 10 to 20 g/10 min, and |η ^* | is 0.01 to 20 Pa· s can be produced. Although the details are unknown, it is believed that the resin and the curing agent are appropriately mixed by appropriate condition control. There is also the possibility that part of the resin and part of the curing agent will react. As a result, it is possible to obtain a powder coating composition whose MFR and |η ^* | at a temperature of 120°C, where "the resin has started to melt, but the curing reaction has not yet started sufficiently", are within the numerical ranges described above. it is conceivable that.

Specific melt-kneading conditions will be described with reference to FIG. 1, which schematically shows the structure of a kneader.

FIG. 1 is a schematic cross-sectional view of a kneader (extrusion kneader) applicable to the production of the powder coating composition of this embodiment.
The kneader of FIG. 1 has a cylinder 2 and a screw 8 provided inside the cylinder 2 .
The cylinder 2 has an inlet 4 for charging raw materials of the powder coating composition and an outlet 6 for discharging the kneaded raw materials.
Cylinder 2 also has temperature control means for heating and/or cooling the raw material moving within cylinder 2 by rotation of screw 8 (temperature control means itself not shown in FIG. 1). The cylinder 2 can have a plurality of independently temperature controllable temperature control means. Specifically, the cylinder 2 can set different heating/cooling conditions in the first zone 10, which is the area close to the inlet 4, and the second zone 20, which is the area close to the outlet 6. .

In this embodiment, the heating conditions in the first zone 10 and the second zone 20, and the rotation speed of the screw 8 (correlation with the residence time of the raw material / kneaded material in the cylinder 2) are set appropriately. is preferred. By appropriately setting the heating conditions in each zone and the rotation speed of the screw 8, a powder coating composition that satisfies the properties 1 and 2 described above can be produced.

Specific manufacturing conditions are as described in Examples below. Although it is necessary to finely adjust the manufacturing conditions depending on the raw materials used, rough "guidelines" for the manufacturing conditions are shown in (i) to (iii) below. Incidentally, the guideline shown here is based on the knowledge of the production of powder coating compositions using the kneader (manufactured by Buss AG, trade name: PCS 70) used in the examples below.
[Guidelines]
(i) The set temperatures of the first zone 10 and the second zone 20 are adjusted between 55 and 130.degree. If the raw material is heated at a temperature exceeding 130°C (e.g., 140°C), an unintended curing reaction of the raw material will proceed, resulting in the production of a powder coating composition that does not satisfy Specific 1 and/or Property 2. There is In addition, if the set temperature of at least one of the first zone 10 and the second zone 20 is less than 55° C. (for example, 50° C.), the softening of the raw materials is insufficient, so that the raw materials are not sufficiently uniformly mixed, resulting in As a powder coating composition that does not satisfy the specific 1 and / or characteristic 2 may be produced.
(ii) The set temperature of the first zone 10 and the set temperature of the second zone 20 are different by 35 to 45°C. Although the details are unknown, by rotating the screw while heating in such a “two-stage”, the raw material is kneaded with a relatively small shear force when the raw material passes through the high-temperature zone, and the low-temperature zone It is thought that the raw materials are kneaded with a relatively large shear force when they pass through (because the raw materials become "softer" at high temperatures and "harder" at low temperatures). By kneading the raw materials with such "different magnitudes of shear force", it is speculated that the raw materials are particularly appropriately mixed to produce a powder coating composition that satisfies properties 1 and 2. be done. Incidentally, the set temperature of the first zone 10 may be higher and the set temperature of the second zone 20 may be lower, or vice versa.
(iii) Appropriately adjust the residence time of the raw materials in the kneader. Specifically, by appropriately setting the rotation speed of the screw 8, the time during which the raw material (or its kneaded product) stays in the kneader is controlled. The residence time is preferably 10-300 seconds, more preferably 20-150 seconds. Incidentally, in the kneader used in the examples described later, the rotation speed of the screw is preferably set to 100 to 300 rpm, more preferably 125 to 275 rpm, so that the raw material (or its kneaded product) is in the kneader. Staying time can be properly controlled.

Although the embodiments of the present invention have been described above, these are examples of the present invention, and various configurations other than those described above can be adopted. Moreover, the present invention is not limited to the above-described embodiments, and includes modifications, improvements, etc. within the scope of achieving the object of the present invention.

Embodiments of the present invention will be described in detail based on examples and comparative examples. It should be noted that the invention is not limited to the examples only.

<Synthesis of resin and measurement of various physical properties of resin>
(Polyester resin A)
A stainless steel reaction vessel equipped with an agitator, a heating device, a thermometer, a fractionator and a nitrogen gas filling tube was prepared. In this container, 93.6 g (0.90 mol) of neopentyl glycol, 3.6 g (0.040 mol) of 2-methyl-1,3-propanediol, 1.24 g (0.020 mol) of ethylene glycol, 5.37 g (0.040 mol) of trimethylolpropane (the above is the alcohol component) was charged. Then, the contents were all melted by heating to 160° C. while stirring.

After melting, half of a mixture (carboxylic acid component) of 124.6 g (0.75 mol) of terephthalic acid and 41.5 g (0.25 mol) of isophthalic acid, and 0.12 g of di-n-butyl tin oxide (0.5 mmol) was charged into the container. Then, the temperature was gradually raised to 240° C. while removing the generated condensed water out of the system with a nitrogen gas stream while preventing the top temperature of the fractionator from exceeding 100° C. Thus, an esterification reaction was carried out.
During the reaction, the amount of condensed water produced was measured at appropriate times. After confirming that the amount of condensed water produced exceeded 90% of the theoretical amount assuming complete reaction of the carboxylic acid component, the system was cooled to 180°C.
After cooling, the rest of the acid component was added, and then the temperature was again raised to 240° C. by the same operation to carry out an esterification reaction. After the amount of condensed water produced exceeded 95% of the theoretical amount assuming that the carboxylic acid component had completely reacted, the reaction was continued for an additional 30 minutes. Then, it was cooled to 180°C.
After that, 9.6 g (0.050 mol) of trimellitic anhydride was added and an addition reaction was carried out at 180° C. for 1 hour. After that, it was cooled to room temperature.
A polyester resin A was obtained as described above.

(Synthesis of polyester resins B and C)
Various polyester resins were synthesized in the same manner as polyester resin A, except that the amount of monomer used (relative mol amount) was changed as shown in Table 1.
However, the polyester resin C was synthesized by terminating the reaction in the synthesis of the polyester resin A described above before performing the addition reaction with the acid anhydride (trimellitic anhydride).

(Measurement of acid value)
JIS K 0070 "Testing methods for acid value, saponification value, ester value, iodine value, hydroxyl value and unsaponifiable matter of chemical products", measured according to the method specified in "3.1 Neutralization titration method" bottom. Specifically, it was measured as follows.

A certain amount of polyester resin was dissolved in tetrahydrofuran. Then, titration was performed with a 0.1 mol/L potassium hydroxide solution using phenolphthalein as an indicator. Then, the acid value was calculated by the following formula.
Acid value (mgKOH/g) = V x 56.11 x F/m
V: amount of 0.1 mol/L potassium hydroxide solution used for titration (mL)
F: Potency of 0.1 mol/L sodium hydroxide aqueous solution m: Mass of sample (g)

(Measurement of hydroxyl value)
JIS K 0070 "Testing methods for acid value, saponification value, ester value, iodine value, hydroxyl value and unsaponifiable matter of chemical products", measured according to the method specified in "7.1 Neutralization titration method" bottom. Specifically, it was measured as follows.

5 mL of an acetylation reagent (pyridine acetic anhydride solution prepared by adding pyridine to 25 g of acetic anhydride to make the total volume 100 mL) was added to a given amount of polyester resin and heated. Thereafter, titration was performed using a potassium hydroxide solution and phenolphthalein as an indicator. Then, the hydroxyl value was calculated by the following formula.
Hydroxyl value (mgKOH/g) = [V x 56.1 x C/m] + D
V: titration volume (mL)
C: concentration of titrant (mol/L)
m: Mass of sample (g)
D: acid value of the sample to be measured (mgKOH/g)

(Measurement of glass transition temperature (Tg))
The glass transition temperature (Tg) was measured according to JIS K 7121-1987 using a differential scanning calorimeter ("EXSTAR6000" manufactured by Seiko Instruments Inc.).
Specifically, 10 mg of the polyester resin to be measured was heated from −40° C. to 200° C. at a heating rate of 20° C./min under a nitrogen stream to obtain a DSC curve. The temperature at the intersection of the extended line of the baseline on the low temperature side and the tangent line indicating the maximum slope in the transition portion (ie curve portion) (so-called extrapolated glass transition start temperature) was read as the glass transition temperature Tg. An empty container was used as a reference substance.

(Measurement of molecular weight and dispersity)
The weight average molecular weight Mw, the number average molecular weight Mn and the degree of dispersion Mw/Mn were measured and calculated by gel permeation chromatography (GPC). The apparatus, conditions, etc. used are as follows.
・ Equipment used: HLC8220GPC (manufactured by Tosoh Corporation)
・ Columns used: TSKgel SuperHZM-M, TSKgel GMHXL-H, TSKgel G2500HXL, TSKgel G5000HXL (manufactured by Tosoh Corporation)
・Column temperature: 40°C
・ Standard material: TSKgel standard polystyrene A1000, A2500, A5000, F1, F2, F4, F10 (manufactured by Tosoh Corporation)
・ Detector: RI (differential refraction) detector ・ Eluent: Tetrahydrofuran ・ Flow rate: 1 mL / min

(Measurement of melt viscosity)
The melt viscosity of the resin was measured using CAP2000VISCOMETER (manufactured by Brookfield) under temperature conditions of 200°C.

(Measurement of melt mass flow rate)
The melt mass flow rate of the resin was measured in the same procedure as <Measurement of Melt Mass Flow Rate of Powder Coating Composition> described later.

Information about the resins is summarized in Table 1.

<Production of powder coating composition>
(Example 1)
(1) First, the following materials were prepared.
· Polyester resin A (acid value 34 mgKOH / g, number average molecular weight 11,800, weight average molecular weight 38,700, polydispersity 3.3) 95 parts by mass · Primid XL552 (β-hydroxyalkylamide curing agent: EMS-CHEMIE AG, hydroxyl value 600 to 725 mgKOH/g) 5 parts by mass Titanium dioxide (manufactured by Ishihara Sangyo Co., Ltd., trade name: CR-95, average particle size 0.36 μm, oil absorption 17 ml / 100 g) 55 parts by mass Surface Regulator (manufactured by BASF, fluidity imparting agent, trade name: Acronal 4F) 2 parts by mass Antifoaming agent (benzoin) 2 parts by mass

(2) The above ingredients were thoroughly mixed with a Henschel mixer to prepare a mixture.
(3) The mixture obtained in (2) above is put into a heatable extrusion kneader (manufactured by Buss AG, product name: PCS 70) while moving the raw materials with a rotating screw, and the screw is rotated. The mixture was heated while heating to obtain a kneaded product.
The extruder kneader has a structure as described in FIG. 1, in particular a first zone and a second zone, each adjustable to different temperatures. The temperatures of the first zone and the second zone were set to the temperatures shown in Table 2. Further, the rotation speed of the screw was the rotation speed shown in Table 2 (the residence time of the raw material in the extrusion kneader changes depending on the rotation speed).
(4) The kneaded product obtained in (3) above was cooled to 50°C or lower.
(5) The kneaded material cooled in (4) above was pulverized by a hammer-type impact pulverizer to obtain a pulverized material.
(6) The pulverized material obtained in (5) above was classified with a 150-mesh sieve.
A powder coating composition was prepared as described above.

(Examples 2-9 and Comparative Examples 1-4)
A powder coating composition was prepared in the same manner as in Example 1, except that the composition of the materials and the manufacturing conditions (temperature settings in the first and second zones, and the rotation speed of the screw) were as shown in Table 2. manufactured.

Details of each material in Table 2 are as follows (description of the materials described in Example 1 is omitted).
・ Curing agent VESTAGON (registered trademark) B-1530): Polyisocyanate blocked with ε-caprolactam, manufactured by Evonik Co., Ltd.

・Pigment Escalon special grade #3: manufactured by Sankyo Seifun Co., Ltd., calcium carbonate, average particle size 20 μm, oil absorption 22 mL/100 g
・ Catalyst TN-12: manufactured by Sakai Chemical Industry Co., Ltd., dibutyl tin dilaurate

<Measurement of Melt Mass Flow Rate of Powder Coating Composition>
JIS K 7210-1: 2014 (Plastics-Determination of melt mass flow rate (MFR) and melt volume flow rate (MVR) of thermoplastics-Part 1: standard test method), the following conditions was measured using a melt flow index tester MB-1 manufactured by Imoto Seisakusho Co., Ltd.
・Test temperature: 120°C
・Nominal load: 1.20 kg
・Others: The powder coating composition was used as a sample in powder form. The amount of filled sample and the cut-off time interval were in accordance with "Table 4-Guidelines for test parameters" of the same JIS.

<Measurement of |η ^* |>
The dynamic viscoelasticity of the powder coating composition was measured under the following conditions. From the measurement results, the storage modulus and loss modulus at 120°C were obtained. Then, the absolute value |η ^* | of the complex elastic modulus at 120° C. was obtained from the formula {(storage elastic modulus) ² +(loss elastic modulus) ² } ^1/2 .
・ Apparatus: Dynamic viscoelasticity measuring device AR-G2 (manufactured by TA Instruments)
・Plate: 40mm parallel plate ・Measurement mode: Time sweep ・Gap: 1000μm
・ Variable control: 1% strain ・ Heating rate: 10.0 ° C./min
・Measurement interval: 12/min
・Frequency: 1.0Hz
・Mode: Vibration mode ・Temperature range: Room temperature to 160℃

<Performance evaluation>
(Preparation of test plate)
A cold-rolled steel sheet (standard: SPCC-SD, width 75 mm×length 150 mm×thickness 0.8 mm) was prepared as a substrate for forming a coating film. This was suspended in the vertical direction, and the powder coating was electrostatically coated on the steel plate using a corona charging electrostatic powder coating machine (manufactured by Asahi Sunac Co., Ltd., product name: PG-1 type) (coating voltage : -60 kV). After coating, the plate was baked at 180° C. for 20 minutes and then allowed to cool to room temperature, thereby obtaining a steel plate (hereinafter referred to as a test plate) provided with a coating film (cured film) having a thickness of 60 μm.

(Evaluation of coating film smoothness)
The surface condition of the coating film on the obtained test plate was visually observed and evaluated according to the following criteria.
5: The surface of the coating film is smooth with no irregularities (rounds) or bumps. 4: The surface of the coating film is slightly uneven (rounds), but there is no problem with smoothness. Slightly unevenness (round) is observed on the surface, and the level of smoothness is slightly low, but there is no problem 2: Unevenness (round) is clearly observed on the coating film, and the level of smoothness is low 1: Repelling on the surface of the coating film, There are bumps, etc., and the appearance is clearly poor

(Evaluation of anti-sagging property)
The powder coating composition was placed on the same base material (cold-rolled steel sheet) as that used for preparing the test plate so as to form a cylindrical shape with an inner diameter of 12 mm and a thickness of 2 mm. This steel plate was heated at 180° C. for 2 minutes while being laid flat, and then immediately after that, the steel plate was placed vertically and further heated. Regarding this heating time, based on the type of resin used, etc., Examples 1 to 9 and Comparative Examples 1 to 3 were heated at 160 ° C. for 20 minutes, and Example 9 and Comparative Example 4 were heated at 180 ° C. for 20 minutes. and By the way, since the powder coating composition cures while flowing when heated, a state in which the initially formed cylindrical shape extends downward, that is, a so-called "sagging" cured product is formed on the steel plate. Become.
The steel plate after heating for 20 minutes was observed, and the state of sagging was evaluated according to the following criteria.
5: Sagging is less than 1.8 cm based on the point (bottom end) where the powder coating composition was installed 4: Sagging is 1.8 cm or more and less than 2 cm based on the point (bottom end) where the powder coating composition was installed 3: Sagging is 2 cm or more and less than 4 cm based on the point (bottom end) where the powder coating composition is installed 2: Sagging is 4 cm or more and less than 5 cm based on the point (bottom end) where the powder coating composition is installed 1: Powder coating composition Sagging is 5 cm or more based on the point (bottom end) where the object is installed

Table 2 shows the composition, properties and performance evaluation results of the powder coating composition.

As shown in Table 2, a powder coating composition containing a resin and a curing agent, having an MFR of 10 to 20 g/10 min, and |η ^* | of 0.01 to 20 Pa s, Good coating film smoothness and anti-sagging properties were exhibited (Examples 1-9).
On the other hand, a powder coating composition having an MFR outside the range of 10 to 20 g/10 min and/or |η ^* | It was inferior to Examples 1 to 9 in anti-sagging (Comparative Examples 1 to 4).

2 cylinder 4 inlet 6 outlet 8 screw 10 first zone 20 second zone

Claims (7)

including a resin and a curing agent,
the resin comprises a polyester resin,
the curing agent comprises a β-hydroxyalkylamide or blocked isocyanate;
A powder coating composition that satisfies [Characteristic 1] and [Characteristic 2] below. However, powder coating compositions falling under <powder coating composition X> below are excluded.
[Characteristic 1]
The powder coating composition has a melt mass flow rate of 10 to 20 g/10 min, measured at a temperature of 120° C. and a load of 1.20 kg.
[Characteristic 2]
The absolute value |η ^* | of the complex elastic modulus of the powder coating composition at 120° C. measured using a rheometer under the following measurement conditions is 0.01 to 20 Pa·s.
(Measurement condition)
・Frequency: 1.0Hz
・Mode: Vibration mode ・Measurement temperature range: Room temperature to 160℃
・Temperature increase rate: 10.0°C/min
<Powder coating composition X>
A powder coating composition comprising a resin, a curing agent, and inorganic particles,
The surfaces of the inorganic particles are hydrophobized,
The inorganic particles have an average particle size of 0.01 to 5 μm,
A powder coating composition having a melt mass flow rate of 8 to 30 g/10 min measured at a test temperature of 120° C. and a nominal load of 1.20 kg. A powder coating composition according to claim 1 ,
A powder coating composition, wherein the resin has a melt viscosity of 1800 to 9500 mPa·s at 200°C. The powder coating composition according to claim 1 or 2,
A powder coating composition, wherein the resin has a melt mass flow rate of 1 to 15 g/10 min measured at a temperature of 120° C. and a load of 1.20 kg. The powder coating composition according to claim 1 or 2,
A powder coating composition having |η ^* | of 0.1 to 1 Pa·s. The powder coating composition according to claim 1 or 2,
A powder coating composition having |η ^* | of 5 to 20 Pa·s. A coating film formed from the powder coating composition according to claim 1 or 2. An article comprising the coating of claim 6 .

Images