KR101415412B1 - Near-infrared curable pulverulent paints composition - Google Patents

Abstract

TECHNICAL FIELD [0001] The present invention relates to a thermosetting powder coating composition capable of near infrared (NIR) curing, and more particularly, to a powderless coating composition which exhibits a matte gloss and is capable of near infrared curing with excellent appearance and corrosion resistance.

Near infrared rays, Powder coating, Polyester resin

Description

[0001] NEAR-INFRARED CURABLE PULVERULENT PAINTS COMPOSITION [0002]

TECHNICAL FIELD The present invention relates to a thermosetting powder coating composition capable of near infrared (NIR) curing, and more particularly, to a powder coating composition capable of near-infrared ray curing with excellent appearance and corrosion resistance.

In general, powder coatings do not contain volatile components (VOC) and are powdered, which is a major difference from solvent-based coatings. Because of these two differences, powder coatings have many features and advantages. Such powder coatings have no pollution problem due to air pollution and drainage of the coating chamber, there is no risk of poisoning or fire by the solvent, and there is no wrinkling phenomenon or flow phenomenon when forming a film, And it is economical because it can be reused because the paint can be recovered easily and efficiently, and there is an advantage that the cost for incineration or disposal of the waste generated in the painting room is reduced because there is no waste.

However, the powder coating is difficult to form, difficult to form a thin film, and has a relatively high heating temperature. Among them, the most problematic is the high curing temperature. In order to solve this problem, development of curable coatings at 150 ° C has been continuously studied. Among them, a method of using a UV curing machine instead of a conventional hot air oven Recently, near infrared ray curing methods have been continuously studied.

However, the conventional methods for the near infrared ray hardenable powder coatings are extremely limited, and some of them are as follows.

Korean Patent Application No. 2001-7005914 discloses that the content of barium sulfate and / or aluminum oxide in the powder coating is controlled to 1 to 50 wt% and the amount of carbon black is controlled to 0.1 to 5 wt% Curing time which can be obtained by the light ray and a method of controlling the surface temperature of the coated substrate by the powder coating, characterized in that it is possible to change the color by controlling the NIR energy, There is no mention of such as.

In Korean Patent Application No. 2006-7008211, thermal radiation emitted by a coated substrate is scanned by a special infrared optical system, converted into an electrical signal, and constituted of an electrical signal, wherein each pixel Exhibit different hues as a function of detected thermal radiation. From these shades, different curing qualities and incomplete curing of the coating or part of the coating can be sensed. The evaluation of these hues can be made, for example, by EDP (electronic data processing) through a reference isotherm, which makes qualitative and quantitative statements about the cured state possible. However, this method relates to a method and apparatus for determining the curing state by scanning energy, and there is no mention of the composition or other properties of the powder coating material.

U.S. Patent No. 6,406,757 discloses a powder coating composition containing a resin crosslinkable by a functional group capable of forming a hydrogen bond. The powder coating composition is used for powder coating on a metal or non-metal surface . According to this, the functional groups are present at a concentration of 100 mmol / kg or more with respect to the coating powder composition, and the composition for powder coating is melted and cured by NIR irradiation using the substrate. The coating films cured in this way exhibit excellent flow properties, good mechanical properties and good solvent resistance. However, there is no mention of other physical properties or characteristics of the coating film.

On the other hand, in general, the coating film gloss of the powder coating is such that a three-dimensional microstructure formed on the surface of the coating film scatters incident light, reduces the amount of reflection, and extinguishes the coating film. Depending on the amount of reflection, a gloss, a semi- (Flat). Also, since the powder coating material is a solid coating, it is melted by heat to form a coating film. Therefore, the viscosity of the powder coating material is lower than that of a solvent or a water-based coating material.

With respect to the quenching method of the above-mentioned powder coating materials, there is a method of quenching by adding a compound which directly reacts the resin forming the coating film of the coating and the curing agent by a method using a reactive quencher, And is widely used in high temperature curable powder coatings. However, the reaction between the resin, which is the main component of the curing reaction, and the curing agent proceeds slowly at a low temperature, and the quenching does not proceed completely even when the curing reaction is completed.

Korean Patent Laid-Open Publication No. 2006-0077822 discloses a method of using a reaction rate difference, that is, a method of forming fine irregularities by mixing two coating materials having different reaction rates to different shrinkage rates of a polymer due to a curing reaction. By changing the coating ratio, the difference in the curing speed between the two systems is changed, and the gloss is controlled by changing the bending of the irregularities.

As a method for extinguishing powder coating materials, there is a method of using phase separation. This is because a polymer capable of forming two phases during coating film formation is added to a coating material to separate two phases to form different coating films, But the basic components for the phase change are complicated and are not widely used. In addition, European Patent No. 165,207 discloses a method of using extender pigments and wax widely used in a solvent type, but it has a disadvantage in that it is ineffective and deteriorates physical properties and appearance due to excessive use of wax and pigment.

An object of the present invention is to provide a matte powder coating composition which has a matte gloss which is difficult to realize at the time of near-infrared ray curing and at the same time has a beautiful appearance and is capable of near-infrared ray curing excellent in long term physical properties such as corrosion resistance and water resistance.

The powder coating composition of the present invention comprises 10 to 30% by weight of a polyester resin containing terephthalic acid, 30 to 60% by weight of a polyester resin containing an isophthalic acid, 1 to 20% by weight of an acrylic resin having a glycidyl functional group, And 1 to 15 parts by weight of triglycidyl isocyanurate as a curing agent and 100 parts by weight of an acid functional group as a curing agent are added to 100 parts by weight of a base resin comprising 5 to 30% by weight of a polyester resin having two kinds of carboxyl groups having different physical properties 1 to 10 parts by weight of a curing agent and 10 to 40 parts by weight of a filler.

The polyester resin containing terephthalic acid used in the present invention has an acid value of 20 to 45 mgKOH / g, an equivalent of 1300 to 2100, a melting point of 100 to 140 ° C and a viscosity of 25 to 50 poises (200 ° C, ICI viscometer) If the acid value is less than 20 mgKOH / g, the physical properties may deteriorate and the gloss may increase. If the acid value is more than 45 mgKOH / g, the reactivity becomes faster and pinholes may be generated. If the melting point is lower than 100 ° C, the storage stability lowers, and when the melting point exceeds 140 ° C, the appearance becomes poor, and when the melt viscosity is lower than 100 ° C, If it is less than 25 poise, the coating film flow phenomenon becomes severe, which is undesirable. If it exceeds 50 poise, the leveling is lowered.

The polyester resin containing terephthalic acid is preferably used in an amount of 10 to 30% by weight in the base resin. If it is less than 10% by weight, the mechanical properties of the polyester resin are greatly lowered. If the content is more than 30% by weight, Which is undesirable.

The polyester resin containing isophthalic acid used in the present invention has an acid value of 20 to 45 mgKOH / g, an equivalent weight of 1300 to 2200, a melting point of 100 to 140 ° C and a viscosity of 15 to 35 poises (200 ° C, ICI viscometer) If the acid value is less than 20 mgKOH / g, the reactivity tends to be low and the gloss may increase. When the acid value is more than 45 mgKOH / g, the reactivity is accelerated to cause pinholes, When the melting point is less than 100 ° C, the storage stability is lowered. When the melting point is higher than 140 ° C, the appearance becomes poor, which is not preferable. If the melt viscosity is less than 15 poise, the coating film flow phenomenon becomes undesirable, and if it exceeds 35 poise, the leveling becomes poor, which is not preferable.

The polyester resin containing the isophthalic acid is preferably used in an amount of 30 to 60% by weight in the base resin. When the content is less than 30% by weight, the weather resistance of the coating film is low, and if it exceeds 60% by weight, It is not preferable.

The acrylic resin having a glycidyl functional group used in the present invention preferably has an epoxy equivalent of 500 to 900, a melt viscosity of 30 to 50 poise, and a glass transition temperature of 70 to 90 ° C. When the equivalent weight is less than 500, If the melt viscosity is less than 30 poise, the flowability is excessively excessive and a problem occurs in the outer appearance. If the melt viscosity is more than 50 poise, When the glass transition temperature is less than 70 ° C, the hardness of the coating film is low and tacky. When the glass transition temperature is more than 90 ° C, the impact resistance is deteriorated.

The acrylic resin having the glycidyl group functional group is preferably used in an amount of 1 to 20% by weight in the base resin. When the amount is less than 1% by weight, the difference in reactivity is not so significant, If the content is more than 100% by weight, the coating film may be too hard and the flexibility may be deteriorated.

In the present invention, a polyester resin having two kinds of carboxyl groups having different physical properties is used. Among them, the polyester resin 1 having a carboxyl group is used for slightly raising the gloss of the matte in the matte coating system and has a viscosity of 2,500 to 4,500 it is preferable that the viscosity of the coating film is less than 2,500 cps and the appearance of the coating film is poor. If the viscosity is more than 4,500 cps, When the equivalent weight is less than 450 ° C, the storage stability is deteriorated. When the glass transition temperature is less than 55 ° C, the storage stability is lowered, and when the equivalent weight is less than 75 ° C , The viscosity of the resin is increased to cause a problem in leveling, which is not preferable.

Examples of the polyester resin 1 having a carboxyl group include A-229-30A, A-244-A and A-251 of DIC Corporation, which may be used alone or as a mixture of two or more.

The polyester resin 2 having a carboxyl group used in the present invention is used for reducing gloss and has a viscosity of 5,500 to 8,000 cps (Brookfield C & P, 200 ° C), an equivalent of 400 to 700 and a glass transition temperature of 35 to 75 ° C If the viscosity is less than 5,500, the appearance of the coated film is poor. If the viscosity is more than 8,000, there is a problem in leveling. If the viscosity is less than 400, the reactivity becomes poor due to low reactivity, If the glass transition temperature is lower than 35 ° C, the storage stability tends to deteriorate. If the glass transition temperature is higher than 75 ° C, the viscosity of the resin is increased to cause leveling problems, which is not preferable .

Examples of the polyester resin 2 having a carboxyl group include A-266 and A-249-A of DIC Corporation, which may be used alone or as a mixture of two or more thereof.

The mixture of the polyester resins 1 and 2 having a carboxyl group is not particularly limited, and the mixture of the polyester resins 1 and 2 having a carboxyl group is preferably 5 to 30 wt% %. If it is less than 5% by weight, leveling is undesirable. If it is more than 30% by weight, gloss becomes extremely high and a pattern may be formed on the appearance.

There are two types of curing agents to be used in the present invention, and it is preferable to use triglycidylisocyanate and a curing agent having an acid functional group together. The above-mentioned curing agent having an acid functional group is used to lower the light and to complement the mechanical properties. In the course of forming a long film of long chain resin of such a chain, the acrylic resin is first reacted with the acrylic resin to form a long linear chain Thereby giving flexibility of the coating film. However, when a curing agent having an acid functional group is used alone, the appearance may be severely deteriorated and adhesion may also be lowered. Therefore, triglycidyl isocyanurate curing agent is used together.

In the present invention, it is preferable that the triglycidylisocyanurate has an equivalent weight of 100 to 200 and a melting point of 80 to 130 ° C. If the equivalent weight is less than 100, the curing property is deteriorated and the mechanical strength is lowered, If the melting point is less than 80 ° C, blocking may occur. If the melting point exceeds 130 ° C, the dispersion temperature is affected and the dispersibility is lowered It is not preferable.

The triglycidyl isocyanurate curing agent is preferably used in an amount of 1 to 15 parts by weight based on 100 parts by weight of the base resin. If the amount of the triglycidyl isocyanurate curing agent is less than 1 part by weight, It is not preferable because the coating film is easily broken.

In the present invention, the curing agent having an acid functional group is not particularly limited in its kind, but preferably dodecanedioic acid (DDDA) and sebacic acid may be used alone or in combination of two or more, Preferably 200 to 200 and a melting point of 90 to 125 ° C. If the equivalent weight is less than 100, curability is deteriorated and mechanical strength is lowered, which is undesirable. When the equivalent weight is more than 200, the coating film is too hard and flexibility may be deteriorated. If the melting point is less than 90 ° C, the blocking phenomenon may occur. If the melting point exceeds 125 ° C, the dispersion temperature is affected and the dispersibility is not preferable.

The curing agent having an acid functional group is preferably used in an amount of 1 to 10 parts by weight based on 100 parts by weight of the base resin. If the amount is less than 1 part by weight, It is not preferable because the coating film is fragile.

The filler to be used in the present invention is not particularly limited, but barium sulfate, calcium carbonate, silica, aluminum oxide, aluminum hydroxide and wollastonite can be preferably used, and calcium carbonate and wollastonite The filler is preferably used in an amount of 10 to 40 parts by weight based on 100 parts by weight of the base resin. When the amount of the filler is less than 10 parts by weight, storage stability and dispersibility are deteriorated, If the amount is more than 40 parts by weight, the flexibility is undesirably low.

In the coating composition of the present invention, additives other than the above-mentioned components, such as pinhole preventing agents and flow control agents, which are commonly used in coating compositions, can be used without limitation in the usual dosage range.

Typically, the pinhole preventing agent is used for releasing volatile substances from the coating film upon curing, and the kind thereof is not particularly limited, but benzoin can be preferably used.

The amount of the pinhole inhibitor is preferably 0.2 to 2 parts by weight based on 100 parts by weight of the base resin. If the amount of the pinhole inhibitor is less than 0.2 parts by weight, the pinhole and appearance of the coating film become poor, It is not desirable to become tangible.

The flow control agent may be used in an amount of 1 to 5 parts by weight based on 100 parts by weight of the base resin. If the amount of the flow control agent is less than 1 part by weight, crating may occur, If it exceeds 5 parts by weight, the appearance becomes poor, which is not preferable.

The powder coating composition of the present invention is prepared by homogeneously premixing the components in a mixer for 2 to 6 minutes and then applying MP-30PC (APV) or extruder (TSK-20, manufactured by THEYSOHN Maschinenbau GmbH) ), And the melt-mixing process may be repeated at least twice.

The mixture thus obtained is cooled in a cooling roller and then pulverized using Hammer mill or Fritz mill, and then passed through a sheave to obtain a powder paint having an average particle size of 20 to 60 탆. The particle size of the powder coating is also one of the most important factors in forming the appearance of the powder coating. The smaller the particle size, the smoother appearance of the powder coating can be obtained.

However, if the number of particles is low, it is difficult to transport the powder in a fixed amount, and the resultant coating will have a bad influence on the workability of coating due to the formation of lumps. In addition, when the particle size is more than 60 μm, the appearance of the coating film is deteriorated. And the range of distribution should not be wide.

The coating material prepared as described above is coated by an electrostatic method, which is a general powder coating method, and is then subjected to NIR curing. The NIR hardening is performed at a temperature of 10 to 90% within a range of 1 to 60 seconds, preferably 30 seconds, and at a speed of 1.5 to 60 m / min (curing time: 1 to 60 seconds). When the energy is less than 10%, it becomes uncured. When the energy is more than 90%, adherence and appearance are bad, which is not preferable. When the curing speed is less than 1.5 m / min, the paint rubs due to excessive energy, and if it exceeds 60 m / min, bubbles or pinholes are generated, which is not preferable.

 The powder coating composition according to the present invention is curable with near infrared rays, exhibits a matte gloss, has excellent appearance and corrosion resistance.

Hereinafter, the present invention will be described in more detail with reference to examples. However, these examples do not limit the scope of the present invention.

Example  And Comparative Example

The mixture was uniformly mixed for 6 minutes in a mixer according to the composition shown in the following Table 1 and then melt-mixed twice uniformly using Exturder (TSK-20, manufactured by THEYSOHN Maschinenbau GmbH) at a temperature range of 100 to 130 DEG C, Cooled on the cooling roller. Then, the powder coating composition was pulverized using a hammer mill to prepare a powder coating composition having an average particle size of 50 탆. The coating composition was applied to a 0.7 mm cold rolled steel sheet pretreated with zinc phosphate and cured by near infrared rays to obtain a coating film After the specimens were prepared, the physical properties of the specimens were measured. The results of the examples are shown in Table 2, and the results of the comparative examples are shown in Table 3, respectively.

Table 1

                                                        (Unit: parts by weight)

Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Terephthalic acid polyester resin ^{1 )} 23 16 29 20 9 20 40 21 Isophthalic acid polyester resin ^{2 )} 48 45 34 50 40 25 30 24 Acrylic resin having glycidyl functional group ^{3 )} 14 5 8 10 30 15 6 24 Carboxyl group polyester resin 1 ⁴⁾ 7 18 15 10 11 20 11 22 Carboxyl group polyester resin 2 ⁵⁾ 8 16 14 10 10 20 13 9 Triglycidyl isocyanurate ^{6 )} 5 8 10 11 5 8 10 11 Curing agent having an acid functional group ^{7 )} 2 5 6 4 2 5 6 4 Filler ^{8 )} 25 20 30 20 25 20 30 50 Pinhole inhibitor ^{9 )} 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 Flow control agent ^{10 )} One One One One One One One One

Note) 1) CNF00055 (manufactured by KCS)

2) CNF33176 (manufactured by KCS)

3) AC-2102 (manufactured by Alkenes)

4) A-229-30-A (manufactured by DIC Corporation)

5) A-249-A (manufactured by DIC Corporation)

6) Nissan Chemical Co.

7) Sebacic acid

8) OMYACARB 5 (manufactured by OMYA, Korea)

9) Benzoin (manufactured by Mi-won)

10) PLP-100 (manufactured by SK Chemical Co., Ltd.)

Table 2

Example 1 Example 2 Example 3 Example 4 Leveling Good Good Good Good Polish(%) 11 10 12 9 Attachment 100/100 100/100 100/100 100/100 Impact 40cm / 500g 30cm / 500g 40cm / 500g 30cm / 500g Flexibility Good Good Good Good Corrosion resistance 1.5mm 1.0 mm 2.0mm 1.5mm Water resistance 100/100 99/100 100/100 100/100 Baking condition
(Energy (%), Speed) 37%, 7m / min 38%, 9 / min 39%, 8m / min 36%, 7m / min

Table 3

Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Leveling Pinhole generation Haze Burned Good Polish 40 20 Not measurable 20 Attachment 100/100 Bad 100/100 100/100 Impact 20cm / 500g X 30cm / 500g 30cm / 500g Flexibility Good Crack of coat Good Crack Corrosion resistance 2.5 mm 4.0mm 3.0 mm 3.5mm Water resistance 85/100 90/100 Not measurable 80/100 Baking condition
(Energy (%), Speed) 37%, 7m / min 38%, 9 / min 39%, 8m / min 36%, 7m / min

Note) 1) Leveling: Visual determination / Smoothness of film is judged visually

2) Gloss: Non-wax K gloss meter / 60 degree reflectance

3) Adhesiveness: Whether or not 100 sheets of 1mm spacing are attached to the coating film

4) Impact: DuPont Impact Tester (1/2 "φ)

5) Flexibility: 3/16 "MANDREL BAR

6) Corrosion resistance (salt spray): Test method according to KS D9502

7) Water resistance: Appearance and adhesion after 240 hours immersion in water at 40 ℃

8) Baking condition: NIR OVEN evaluation

As shown in Table 2 and Table 3, the powder coating composition according to the present invention exhibits a matte gloss and has excellent appearance and corrosion resistance.

Claims (9)

10 to 30% by weight of a polyester resin containing terephthalic acid, 30 to 60% by weight of a polyester resin containing isophthalic acid, 1 to 20% by weight of an acrylic resin having a glycidyl functional group and a viscosity of 2,500 to 4,500 cps 100 parts by weight of a base resin comprising 5 to 30% by weight of a mixture of a polyester resin 1 having a carboxyl group and a polyester resin 2 having a carboxyl group having a viscosity of 5,500 to 8,000 is mixed with 100 parts by weight of triglycidyl isocyanurate 1 to 15 parts by weight of a curing agent having an acid functional group, 1 to 10 parts by weight of a curing agent having an acid functional group, and 10 to 40 parts by weight of a filler. The powder coating material according to claim 1, wherein the polyester resin containing terephthalic acid has an acid value of 20 to 45 mgKOH / g, an equivalent weight of 1300 to 2100, a melting point of 100 to 140 ° C and a viscosity of 25 to 50 poise Composition. The polyester resin according to claim 1, wherein the isophthalic acid-containing polyester resin has an acid value of 20 to 45 mg KOH / g, an equivalent weight of 1300 to 2200, a melting point of 100 to 140 ° C and a viscosity of 15 to 35 poises Coating composition. The powder coating composition according to claim 1, wherein the glycidyl functional group-containing acrylic resin has an epoxy equivalent of 500 to 900, a melt viscosity of 30 to 50 poise, and a glass transition temperature of 70 to 90 ° C. 2. The polyester resin composition according to claim 1, wherein the polyester resin 1 having a carboxyl group has an equivalent weight of 450 to 650 and a glass transition temperature of 55 to 75 캜, the polyester resin 2 having a carboxyl group has an equivalent weight of 400 to 700 and a glass transition temperature of 35 to < RTI ID = 0.0 > 75 C. < / RTI > The powder coating composition according to claim 1, wherein the triglycidyl isocyanurate has an equivalent weight of 100 to 200 and a melting point of 80 to 130 ° C. The powder coating composition according to claim 1, wherein the curing agent having an acid functional group has an equivalent weight of 100 to 200 and a melting point of 90 to 125 ° C. The powder coating composition according to claim 7, wherein the curing agent having an acid functional group is at least one selected from dodecanedioic acid and sebacic acid. The powder coating composition according to claim 1, further comprising 0.2 to 2 parts by weight of a pinhole inhibitor and 1 to 5 parts by weight of a flow control agent.