KR102316951B1 - Powder coating composition - Google Patents

Abstract

The present invention relates to a powder coating composition having excellent weather resistance, gloss and adhesion.

Description

Powder coating composition {Powder coating composition}

The present invention relates to a powder coating composition having excellent weather resistance, gloss and adhesion.

Metals such as aluminum, titanium, and copper are used as main materials for parts such as buildings, automobiles, and aircraft, and the surface of the metal is coated with a paint composition to protect it from a harsh external environment. The coating composition requires various physical properties such as weather resistance, corrosion resistance, acid resistance, alkali resistance, gloss, and adhesion. , it is important to secure gloss, adhesion, etc.

For this reason, research on a coating composition having excellent weather resistance has been conducted. For example, Korean Patent Publication No. 10-2013-0082191 discloses a powder coating composition for a roof rack of an automobile made of aluminum. The powder coating composition includes a polyester resin and an epoxy curing agent, which has a disadvantage in that long-term weather resistance is poor because an epoxy resin is applied. In order to solve this problem, there is a paint composition using a hydroxyalkyl amide-based curing agent instead of an epoxy curing agent. However, when hydroxyalkylamide is applied, pinholes are generated, so weather resistance and adhesion are poor, and gloss adjustment is also difficult. there is

The present invention provides a powder coating composition having excellent weather resistance, gloss and adhesion.

The present invention provides a powder coating composition comprising at least two types of polyester resin and a curing agent.

The present invention provides a powder coating composition having excellent weather resistance, gloss and adhesion. In particular, the powder coating composition according to the present invention has excellent long-term weather resistance and gloss retention properties, and is suitable for coating with metal (eg, aluminum bar for construction) exposed to sunlight for a long period of time.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated. However, it is not limited only by the following content, and each component may be variously modified or selectively mixed as needed. Accordingly, it should be understood to include all modifications, equivalents and substitutes included in the spirit and scope of the present invention.

The "weight average molecular weight" used in the present invention is measured by a conventional method known in the art, and can be measured, for example, by a gel permeation chromatograph (GPC) method. In addition, a functional group such as “acid value” may be measured by a method well known in the art, for example, may represent a value measured by a method of titration.

The powder coating composition according to the present invention includes at least two types of polyester resin and a curing agent. In addition, the powder coating composition of the present invention may further include additives commonly used in the powder coating field, if necessary. Hereinafter, the composition of the powder coating composition of the present invention will be described.

polyester resin

The powder coating composition according to the present invention includes a polyester resin as a main resin. The polyester resin serves to secure weather resistance and mechanical properties when painting is applied.

The polyester resin may be a carboxyl group-containing polyester resin having a carboxyl (-COOH) group at the end of the polymer. The carboxyl group-containing polyester resin has a crosslinked structure introduced therein, and at least one of monomers and polymers having a hydroxyl group as a terminal functional group and at least one of monomers and polymers having a carboxyl group as a terminal functional group are polymerized under a catalyst. it could be

The monomer having the hydroxyl group as a terminal functional group may include a polyfunctional alcohol, and the polyfunctional alcohol may be a difunctional or more, for example, 2 to tetrafunctional alcohol. The type of the polyfunctional alcohol is not particularly limited, and for example, ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, trimethylolpropane (Trimethylol) propane), methyl propanediol, pentaethylene glycol, tripropylene glycol, cyclohexanedimethanol, 1,2-butylene glycol , neopentyl glycol, 1,6-hexanediol (1,6-Hexanediol), one selected from the group consisting of glycerol (Glycerol) or a mixture thereof may be used.

The polymer having the hydroxyl group as a terminal functional group may be prepared by polymerizing a monomer having the hydroxyl group as a terminal functional group. The type of the polymer having the hydroxyl group as a terminal functional group is not particularly limited, and for example, one selected from the group consisting of polyethylene glycol and polypropylene glycol or a mixture thereof may be used.

The monomer having the carboxyl group as a terminal functional group may include a polyfunctional acid, and the polyfunctional acid may be a difunctional or more, for example, 2 to tetrafunctional acid. The type of the polyfunctional acid is not particularly limited, for example, terephthalic acid, isophthalic acid, 1,4-cyclohexanedicarboxylic acid (1,4-Cyclohexane dicarboxylic acid), adipic acid (Adipic acid), sebacic acid, phthalic anhydride, trimellitic anhydride, benzoic acid, one selected from the group consisting of tetrahydrophthalic anhydride, or Mixtures thereof may be used. For example, the polyfunctional acid may include isophthalic acid, and the isophthalic acid may be included in an amount of 90 wt% or more based on the total weight of the polyfunctional acid. When isophthalic acid is included in the above content, excellent weather resistance and matte appearance can be secured.

The polymer having the carboxyl group as a terminal functional group may be prepared by polymerizing a monomer having the carboxyl group as a terminal functional group.

The polyester resin may be a mixture of two types of polyester resins. For example, the polyester resin may be a mixture of the first polyester resin and the second polyester resin having different acid values.

The first polyester resin may have an acid value of 25 to 35 mgKOH/g, for example, 28 to 32 mgKOH/g, and the second polyester resin may have an acid value of 25 to 40 mgKOH/g, for example 30 to 36 mgKOH/g, in another example 31 to 36 mgKOH/g. When the acid values of the first polyester resin and the second polyester resin exceed the above ranges, there may be restrictions on the implementation of matte gloss, or the pinhole phenomenon may become severe due to moisture generation according to the condensation reaction. Mechanical properties may be deteriorated, and there may be problems in that weather resistance and corrosion resistance are deteriorated.

The first polyester resin may have a weight average molecular weight (Mw) of 5,000 to 12,000, for example, 8,500 to 11,000, and the second polyester resin may have a weight average molecular weight (Mw) of 10,000 to 25,000, for example 12,000. to 20,000. When the weight average molecular weight of the first polyester resin and the second polyester resin is out of the above range, the appearance may be poor.

The first polyester resin may have a melt viscosity (200 °C, Brookfield viscometer) of 4,000 to 7,000 mPa.s, for example, 4,000 to 5,000 mPa.s, and the second polyester resin has a melt viscosity (200 °C, Brookfield viscometer) from 2,000 to 5,000 mPa.s, for example from 3,000 to 4,000 mPa.s. When the melt viscosity of the first polyester resin and the second polyester resin is out of the above range, workability may be poor.

By mixing and using two types of polyester resins having physical properties within the above range, it is possible to exert the effect of not only imparting excellent weather resistance to the coating film, but also improving mechanical properties such as impact resistance.

The first polyester resin may be included in an amount of 1 to 20% by weight, for example, 5 to 15% by weight, based on the total weight of the powder coating composition. The second polyester resin may be included in an amount of 40 to 60% by weight, for example, 45 to 60% by weight, based on the total weight of the powder coating composition. For example, the mixing ratio of the first polyester resin and the second polyester resin may be 1:3 to 10, for example, a weight ratio of 1:4 to 7.5. When the two types of polyester resins are mixed in the above-mentioned range, properties such as weather resistance, gloss, and mechanical properties of the coating film can be improved.

hardener

The powder coating composition according to the present invention is not particularly limited as long as it is a curing agent in the art that can undergo a curing reaction with the polyester resin.

The curing agent may be an isocyanurate-based curing agent, a glycidyl ester-based curing agent, or an isocyanate-based curing agent. For example, triglycidyl isocyanurate (TGIC), diglycidyl terephthalate (DGT), triglycidyl trimellitate (TML), ε-caprolactam block isophorone diisocyanate, etc. may be used as the curing agent. have. When triglycidyl isocyanurate (TGIC) is used as the curing agent, the appearance and weather resistance of the coating film can be further improved by suppressing the occurrence of pinholes in the coating film.

The hydrogen equivalent weight (HEW) of the curing agent may be 50 to 200 g/eq, for example, 90 to 210 g/eq.

The curing agent may be included in an amount of 1 to 15% by weight, for example, 1 to 10% by weight, based on the total weight of the powder coating composition. When the content of the curing agent is in the above-described range, long-term weather resistance, adhesion, leveling properties, etc. of the coating film may be improved.

additive

The powder coating composition of the present invention may optionally further include additives commonly used in the powder coating field within a range that does not impair the intrinsic properties of the composition.

Non-limiting examples of additives usable in the present invention include a leveling agent, an anti-pinhole agent, an ultraviolet absorber, a matting agent, and the like, and these may be used alone or in combination of two or more.

The leveling agent is to improve the appearance characteristics of the coating film while enhancing adhesion in the composition by leveling the coating composition so that it is coated evenly and smoothly. The leveling agent may be at least one selected from acrylic, silicone, polyester and amine leveling agents, for example, may be an acrylic leveling agent. Non-limiting examples of the acrylic leveling agent include polyacrylate polymer, polymethacrylate polymer, polyethylacrylate, polybutylacrylate, and poly-2-ethylhexyl acrylate.

The pinhole inhibitor may cause volatile substances to be released from the coating film during the curing process, thereby preventing pinholes in the coating film and improving the appearance characteristics. Non-limiting examples of the pinhole inhibitor include amide-based (eg, ceraflour 960 (BYK)), polypropylene-based, and stearic acid-based pinhole inhibitor. For example, the pinhole inhibitor may be benzoin or a mixture of benzoin and an amide-based pinhole inhibitor.

UV absorbers can improve external durability after painting. Non-limiting examples of the ultraviolet absorber include benzotriazole-based, benzylidenehydant-based, benzophenone-based, benzoguanine-based and the like, and these may be used alone or in combination of two or more.

The matting agent serves to lose or reduce the gloss of the coating film. Non-limiting examples of the matting agent include polyolefin wax, mercaptobenzothiazole, acrylic acid, acrylic acid copolymer resin, and the like, and these may be used alone or in combination of two or more. When two or more types of the matting agent are mixed and used, excellent glossiness may be exhibited. For example, the matting agent may be a mixture of polyethylene wax and acrylic acid or a mixture of mercaptobenzothiazole and acrylic acid. The mercaptobenzothiazole may be a metal salt-containing mercaptobenzothiazole.

The additive may be appropriately added within a content range known in the art, for example, may be 0.1 to 10% by weight based on the total weight of the powder coating composition. When the content of the additive is within the above-described range, physical properties such as the appearance of the coating film may be improved.

pigment

The powder coating composition of the present invention may further include a pigment commonly used in the coating field, such as an extender pigment, a colored pigment, or a mixture thereof, within a range that does not impair the inherent properties of the composition.

The extender pigment fills the pores in the coating film, complements the formation of the coating film, and plays a role in imparting oiliness or mechanical properties to the coating film. Therefore, when an extender pigment is included, a good coating film appearance can be obtained, and hardness, impact resistance, rust resistance, etc. can be improved.

As the extender pigment, those commonly used in powder coating compositions may be used without limitation, and non-limiting examples include calcium carbonate, clay, talc, magnesium silicate, kaolin, mica, silica, aluminum silicate, aluminum hydroxide, sulfuric acid. barium, etc. The above-mentioned components may be used alone or two or more may be used in combination.

Colored pigments can be used to express a desired color (colored) in a paint or to increase the strength or gloss of a paint film. As these colored pigments, organic pigments, inorganic pigments, metallic pigments, aluminum-paste, pearls, etc. commonly used in paints can be used without limitation, and these can be used alone or in combination of two or more. can Non-limiting examples of usable colored pigments include azo-based, phthalocyanine-based, iron oxide-based, cobalt-based, carbonate-based, sulfate-based, silicate-based, chromate-based pigments and the like, for example, titanium dioxide, zinc oxide, bismuth vana date, cyanine green, carbon black, iron oxide, iron sulfur oxide, navy blue, cyanine blue, and mixtures of two or more thereof. Inorganic pigments such as titanium dioxide and zinc oxide may be colored white when used alone. As another example, the inorganic pigment may be mixed with other colored pigments to match a specific color.

The pigment may be in an amount of 0.1 to 40% by weight, for example, 20 to 35% by weight, based on the total weight of the powder coating composition. When the content of the pigment is within the aforementioned range, the color expression of the coating film may be excellent, and mechanical properties, impact resistance, adhesion, and the like of the coating film may be improved.

The powder coating composition according to the present invention may be prepared by a method known in the art, and for example, may be prepared through processes such as raw material basis weight, dry pre-mixing, dispersion and coarse pulverization, pulverization and classification. For example, a raw material mixture containing a polyester resin, a curing agent, a matting agent, a pigment and other additives is put into a container mixer to be uniformly mixed, and the mixed composition is melt-mixed and then pulverized. For example, the raw material mixture is melt-dispersed at 70 to 130° C. by a melt-kneading device such as a kneader or an extruder to produce chips with a predetermined thickness (eg, 1 to 5 mm). Thereafter, the prepared chips are pulverized to a range of 40 to 80 μm using a grinding device such as a high-speed mixer, and then classified to prepare a powder coating composition.

The classification process is not particularly limited, and, for example, may be filtered with 80 to 200 mesh. Accordingly, it is possible to obtain a powder coating having an average particle size in the range of 20 to 80 μm. The average particle diameter of the powder is not particularly limited, but when it satisfies the above-described range, coating workability and appearance characteristics of the coating film may be improved.

In order to improve the fluidity of the powder coating, the surface of the powder coating particles according to the present invention may be coated with a fine powder such as polyethylene wax or fumed silica. As a method of performing such a treatment, a pulverizing mixing method in which fine powder is added while mixing, or a dry mixing method using a Henschel mixer or the like can be used.

The powder coating composition of the present invention exhibits excellent long-term weather resistance and excellent mechanical properties, so it is suitable for application for coating aluminum bars for construction exposed to sunlight for a long period of time. In addition, the powder coating composition according to the present invention can be used as a semi-glossy/matte powder coating because loss or reduction of gloss is appropriately controlled and excellent gloss retention is exhibited.

Hereinafter, the present invention will be described in more detail through examples. However, the following examples are provided to help the understanding of the present invention, and the scope of the present invention is not limited to the examples in any sense.

<Example 1-10>

According to the composition shown in Table 1 below, each component was put into a mixing tank and premixed, and then melt-dispersed at 100° C. in a disperser to prepare chips. The prepared chips were pulverized with a high-speed mixer to prepare the powder coating composition of Examples 1-10 having an average particle size of 25 to 55 μm. The usage unit of each component in Table 1 below is weight %.

<Comparative Example 1-6>

A powder coating composition of Comparative Examples 1-6 was prepared in the same manner as in Examples, except for the composition shown in Table 2 below. The usage unit of each component in Table 2 below is weight %.

Polyester resin 1: carboxyl polyester (acid value: 30 mgKOH/g, weight average molecular weight: 9,700, viscosity (200 °C): 4,400 mPa.s, isophthalic acid content 100%)

Polyester resin 2: carboxyl polyester (acid value: 28 mgKOH/g, weight average molecular weight: 9,500, viscosity (200 °C): 6,500 mPa.s, isophthalic acid content 90%)

Polyester resin 3: carboxyl polyester (acid value: 25 mgKOH/g, weight average molecular weight: 5,000, viscosity (200 °C): 5,000 mPa.s, isophthalic acid content 80%)

Polyester resin 4: carboxyl polyester (acid value: 33 mgKOH/g, weight average molecular weight: 14,900, viscosity (200 °C): 3,500 mPa.s, isophthalic acid content: 100%)

Polyester resin 5: carboxyl polyester (acid value: 36 mgKOH/g, weight average molecular weight: 12,000, viscosity (200 °C): 3,000 mPa.s, isophthalic acid content: 90%)

Polyester resin 6: carboxyl polyester (acid value: 25 mgKOH/g, weight average molecular weight: 10,000, viscosity (200 °C): 2,000 mPa.s, isophthalic acid content: 75%)

Hardener 1: Triglycidyl isocyanurate (HEW: 105)

Curing agent 2: hydroxyl alkyl amide (HEW: 84, EMS company)

Additive 1: Leveling agent (P-67, ESTRON)

Additive 2: Pinhole Prevention Agent (BENZOIN)

Additive 3: UV absorber (TINUVIN 144, BASF)

Additive 4: UV absorber (TINUVIN 405, BASF)

Additive 5: matting agent (mercaptobenzothiazole and acrylic acid mixture, KT 109P)

White pigment: TIO ₂

Yellow pigment: BAYFERROX 420 (LANXESS)

Red Pigment: BAYFERROX 130M (LANXESS)

Black Pigment: Carbon Black

Extender Pigment: Barium Sulfate (BARYTE HB-M)

<Experimental example - evaluation of physical properties>

The physical properties of the powder coating compositions prepared in each Example and Comparative Example were measured as follows, and the results are shown in Table 3-4 below.

Specimen preparation

The powder coating compositions according to Examples and Comparative Examples were respectively coated on an iron plate having a size of 75 mm × 150 mm × 0.7 mm, and then cured according to curing conditions to prepare a 70 μm dry film thickness specimen.

Appearance (leveling)

By visually observing the external state of each specimen, pinholes and cratering were measured.

Polish

The 60 degree gloss of each specimen was measured using a gloss meter.

adherence

According to the ISO 2409 test method, 10 cells were made at intervals of 1 mm in each specimen to perform a tape adhesion test, and then the degree of peeling was observed.

(No peeling: 0, peeling: 1)

impact

After dropping a 500 g weight to each specimen from a height of 50 cm using a Dupont impact tester, it was checked whether cracks occurred in the coating film.

weather resistance

Each specimen was put into the WOM maintained according to the PV3930 standard, and after 1,000 hours, the gloss retention and color difference of the coating film were checked.

As shown in Table 3-4, the coating films formed of the powder coating compositions of Examples according to the present invention were generally superior in physical properties to the coating films formed of the powder coating compositions of Comparative Examples. In particular, it was confirmed that the coating films formed from the powder coating compositions of Examples were excellent in appearance, adhesion, impact properties and weather resistance.

Claims (5)

A polyester resin comprising a first polyester resin and a second polyester resin and a curing agent,
The first polyester resin has an acid value of 28 to 32 mgKOH / g, a weight average molecular weight (Mw) of 8,500 to 11,000, and a melt viscosity (200 ° C., Brookfield viscometer) of 4,000 to 5,000 mPa.s,
The second polyester resin has an acid value of 31 to 36 mgKOH / g, a weight average molecular weight (Mw) of 12,000 to 20,000, and a melt viscosity (200 ° C., Brookfield viscometer) of 3,000 to 4,000 mPa.s,
The mixing ratio of the first polyester resin and the second polyester resin is 1:3 to 10 by weight of the powder coating composition. delete delete The powder coating composition according to claim 1, wherein the curing agent has a hydrogen equivalent weight (HEW) of 50 to 200 g/eq. The powder according to claim 1, wherein the powder comprises 1 to 20% by weight of the first polyester resin, 40 to 60% by weight of the second polyester resin, and 1 to 15% by weight of the curing agent, based on the total weight of the powder coating composition. paint composition.