KR20050068345A - Thermosetting epoxy powder coating composition for dual top coating and its coating system - Google Patents

Abstract

The present invention relates to a powder coating composition for multilayer steel pipe top coat and a coating method of a multilayer steel pipe using the same, and more particularly, to a powder coating composition for multilayer steel pipe top coat containing an epoxy resin, a curing agent, an inorganic filler, a curing accelerator, and a conventional additive. To prepare a powder coating composition for top coat using a small amount of a specific foaming agent formed in a microcapsule or micro spare structure, and to coat the multilayer steel pipe through a continuous process of pretreatment and preheating step, coating step and water cooling step using the same. In the top coat process, the top coat layer of the foamed coating film is formed by using the top coat powder containing the specific blowing agent, and the time interval between the top coat and the top coat and between the top coat and the water cooling under specific conditions. By introducing a coating method to adjust, mechanical properties such as impact resistance and bending resistance of the coating film Improved so as to hence improve a property multi-layer steel pipe theft powder coating composition and relates to a coating method of the multi-layer steel pipe using the same.

Description

Thermosetting Epoxy powder coating composition for dual top coating and its coating system}

The present invention relates to a powder coating composition for multilayer steel pipe top coat and a coating method of a multilayer steel pipe using the same, and more particularly, to a powder coating composition for multilayer steel pipe top coat containing an epoxy resin, a curing agent, an inorganic filler, a curing accelerator, and a conventional additive. To prepare a powder coating composition for top coat using a small amount of a specific foaming agent formed in a microcapsule or micro spare structure, and to coat the multilayer steel pipe through a continuous process of pretreatment and preheating step, coating step and water cooling step using the same. In the top coat process, the top coat layer of the foamed coating film is formed by using the top coat powder containing the specific foaming agent, and the time interval between the top coat coat and the top coat coat and the top coat coat and the water cooling process under specific conditions. By introducing a coating method to adjust, mechanical properties such as impact resistance and bending resistance of the coating film The present invention relates to an improved powder coating composition for a multilayer steel pipe top coat and a method of coating a multilayer steel pipe using the same.

In general, as a coating agent for the corrosion protection and protection of various steel pipes, such as water pipes, gas pipes, oil pipes, etc., coating is performed, and three-layer olefin coating and fusion bonded epoxy single coating are widely used.

The three-layer olefin coating method is a method of applying a thermosetting epoxy powder coating, using a polyethylene modified with unsaturated carboxylic acid as an adhesive layer, and applying a medium density polyolefin as an external protective layer. Epoxy type is widely used to prevent corrosion of steel pipes in such a way that it can secure high corrosion resistance and adhesion and excellent mechanical properties of top-level polyolefins. However, polyolefins used as outer protective layers require extrusion system equipment, and there are many limitations in using them as steel pipes such as the complexity of coating work and the vulnerability of UV rays to polyolefins.

In addition, the fusion bonded epoxy single coating method is a method of coating the epoxy powder coating alone at a high coating thickness without using a polyethylene adhesive layer and a medium density polyolefin. Compared with the 3-ply olefin coating method, it has excellent properties such as ease of operation, the need for extrusion system equipment of polyolefin, and paintability, but relatively low mechanical properties such as impact resistance and flex resistance at high temperatures. There are problems such as inherent weathering vulnerability.

Accordingly, a thermosetting powder coating composition and a coating method for multilayer steel pipes that have been developed by complementing the excellent mechanical properties of the 3-ply olefin coating coating method and the unstable properties at high temperature of the fusion bonded epoxy single coating method have been developed.

The coating method of thermosetting powder coating for double-layered steel pipe was first developed by 3M and DuPont, USA. It is superior in impact resistance and flexibility compared to the two existing coating methods, and it is easy to work and saves the equipment. It is widely applied to steel pipe line of industry. However, this coating method includes a process of repainting the epoxy powder coating to the existing fusion bonded epoxy single coating, there is a problem that is not economically efficient.

Therefore, the current research on the coating composition and method for steel pipe having a low cost coating system and high functional properties that can be applied to a high-temperature transfer steel pipe line at the same time, is actively being studied worldwide.

Among them, the fusion bonded epoxy single coating method, which has a good corrosion resistance even at a high temperature of 150 ° C. or higher, is used, but it is expensive and has a higher impact resistance than the coating method of a thermosetting powder coating for a multilayer steel pipe. There is a downside to falling. In addition, by applying the existing three-ply coating method and applying urethane foam to the final coating, there is a four-ply coating method, which was developed to have excellent physical properties even at high temperatures, but due to the investment of additional equipment and high painting price There is a limitation in use.

Accordingly, the present inventors have tried to solve the problems such as mechanical properties and price competitiveness deterioration inherent in the coating method of the conventional double-layered steel pipe, and as a result, a small amount of the powder coating composition for top coat used in the existing double-layered steel pipe When the powder coating composition is formed by using a foaming agent of a specific structure, and used in the top coating during the continuous coating process of steel pipe, the foaming agent forms a fine foamed structure by thermal decomposition, and when the water is cooled immediately, the formed micro-foamed structure is formed. The present invention has been completed by finding that mechanical properties such as impact resistance and flex resistance are improved due to the compact structure.

Accordingly, an object of the present invention is to provide a powder coating composition for multi-layer steel pipe coating by using a powder coating composition containing a small amount of a foaming agent of a specific structure when coating a steel pipe, and improving mechanical properties such as impact resistance and bending resistance.

In addition, the present invention is a coating of a multilayer steel pipe coated with a series of continuous single process of water coating and immediately after coating the powder coating composition for multi-layer steel pipe top coat with improved mechanical properties, and then water cooling. Another object of the present invention is to provide an improved coating method that can easily perform coating of a multilayer steel pipe having improved mechanical properties and price competitiveness.

The present invention is a top coating powder coating composition containing an epoxy resin, a curing agent, an inorganic filler, a curing accelerator and a conventional additive,

The powder coating composition for multilayer steel pipe coating contains 1 to 9 parts by weight of a foaming agent forming a microcapsule or micro spare structure based on 100 parts by weight of the powder coating composition.

In addition, the present invention is a powder coating method consisting of pre-treatment and pre-heating step, coating step and water cooling step of steel pipe coating,

Forming a molten coating layer having a thickness of 300 to 500 μm by coating the undercoat in a prearrangement with a spray gun in the coating step;

1 second to 2 minutes after the molten coating layer is formed, the top coat of the coating film foamed by continuously coating the top coat with a thickness of 100 to 300 μm in a post-array with a powder coating composition comprising a microcapsule or a micro spare structure. Forming a layer;

The coating method of the powder coating for multilayer steel pipe top coat which water-cools the top coat layer of the foamed coating film formed in 5 to 10 minutes is further characterized.

Hereinafter, the present invention will be described in more detail.

The present invention uses a predetermined amount of a foaming agent for forming a microcapsule or a micro spare structure in the powder coating composition for coating, which is used for coating a multilayer steel pipe containing an epoxy resin, a curing agent, an inorganic filler, a curing accelerator and a conventional additive. The foaming agent formed into a specific structure provides thermal coating powder composition for thermal decomposition in the coating process to form a fine foamed structure.

In addition, by forming a top coat layer of the foamed coating film using the powder coating for the top coat, by adjusting the time interval between the top coat and top coat, and the time interval between the top coat and water cooling to form a fine micro-foam layer The present invention provides a coating method of a multilayer steel pipe that significantly improves mechanical properties such as impact resistance and bending resistance of a coated coating film.

The composition of the powder coating composition for multilayer steel pipe coating according to the present invention is 70 to 90 parts by weight of epoxy resin, 1 to 15 parts by weight of a curing agent, 1 to 9 parts by weight of a foaming agent forming a microcapsule or micro spare structure, and inorganic fillers 1 to 1 It is preferable to contain 10 weight part and 1-5 weight part of hardening accelerators and a normal additive.

The epoxy resin which is a resin component of the present invention has a high equivalent weight, and a resin having excellent bendability and impact resistance is used, and a bisphenol-A solid epoxy resin having an epoxy equivalent of 400 to 3000 may be used. 70 to 90 parts by weight of the epoxy resin is used, if the amount is less than 70 parts by weight, the reaction is faster, the foam layer is not formed properly, when the amount exceeds 90 parts by weight, the paint is uncured problem occurs.

In addition, the curing agent may be used alone or in combination of phenolic curing agents or dicyandiamide widely used in conventional epoxy resin curing. The curing agent is used in 1 to 15 parts by weight, the amount is less than 1 part by weight is used hardly occurs hardening, when the amount exceeds 15 parts by weight the reaction is faster to form a foam layer is not properly formed, the effect as added It is not economical because it cannot be obtained.

Powder coating composition for multi-layer steel pipe top coating according to the present invention is to form a microcapsule or micro spare structure instead of adding 45 parts by weight or more of an inorganic filler with respect to the whole composition to improve mechanical properties such as impact and flexural properties. There exists a characteristic in technical structure to containing a fixed amount of foaming agents.

In general, the blowing agent used in the chemical reaction is divided into organic and inorganic, which is added to plastic or rubber to thermally decompose under specific conditions such as reaction temperature, pressure and time to form a fine foam structure. The formed micro-foamed structure gives excellent effects such as high elasticity, high strength, thermal insulation, low specific gravity, sound insulation and shock absorption to the material containing the same, such as vehicle bumpers, interior materials, packaging materials, life jackets, shoes and flooring materials Its use is wide.

In the present invention, such a blowing agent is used by introducing a new concept of blowing agent to form a microcapsule or micro spare structure. Acrylic resin is used as the main component of the foaming agent, and since the capsule of the thermoplastic component is wrapped around the central hydrocarbon structure, when the heat is absorbed from the outside, the hydrocarbon structure inside the foam swells when it is melted. The fine foam structure will be formed. Such foaming agent is foamed up to about five times the original shape by heat absorption, and can be mainly used in industrial fields such as paint, ink, foam wallpaper and injection for shoe soles.

These blowing agents are classified according to temperature or time such as low temperature, medium temperature and high temperature. In order to apply them to conventional powder coatings, the minimum initial foaming temperature of the blowing agent is used to control the temperature and pressure in the extruder generated during dispersion during the paint manufacturing process. In addition to being able to withstand, the average particle size of the blowing agent should be chosen appropriately.

Therefore, the present invention is not characterized by the simple introduction of a new concept foaming agent that forms a known microcapsule or microspare structure, and has specific characteristics applicable to the powder coating for multilayer steel pipe coating while having the above characteristics. It is characterized by selectively introducing and using a blowing agent having.

The foaming agent of the microcapsule or micro spare structure applicable to the present invention has an average particle size of 20 to 40 µm, and foaming starts gradually at a high initial foaming temperature of 120 to 160 ° C., resulting in rapid foaming at a temperature of 190 to 220 ° C. The dispersibility and average particle size of the powder coating thus formed are suitable for the use of the multilayer steel pipe top coat. The foaming agent is used in 1 to 9 parts by weight, the amount is less than 1 part by weight of the foam layer is low, the effect can not be obtained in the wear resistance and impact resistance, etc., if it exceeds 9 parts by weight of the foam layer is high adhesion to the roadway It is inferior in physical properties, such as boiling water resistance and negative electrode peelability.

In addition, the present invention is used in conjunction with the use of the specific blowing agent compared to the conventional use of only a large amount of inorganic filler used for improving the physical properties. Such inorganic fillers are commonly used, for example, feldspar powder, titanium dioxide, carbon black, barite powder and silica powder may be used. The inorganic filler can be selectively added to improve the desired physical properties, in the present invention can be used to select the ones that have an effect on the wear resistance and impact resistance, and the like that has an effect on the flexibility. In general, the steel pipes formed by forming a double layer with the above wear resistance and impact resistance and having a high degree of corrosion resistance and adhesion are very effective in an environment having many elements causing surface damage to the coated steel pipes such as stone and sand. In addition, the excellent flexibility of the steel pipe is very effective in post-processing, such as curves caused when the coating steel pipe line embedded after manufacturing.

The inorganic filler is used in 1 ~ 10 parts by weight, when the amount is less than 1 part by weight sagging (sagging) occurs during coating is difficult to form a coating film, when exceeding 10 parts by weight, physical properties such as bending resistance is lowered Problem occurs.

In addition to the curing accelerator and conventional additives used in the present invention can be used, the curing accelerator is triphenylphosphine, benzyl triphosphonium chloride, butyl triphenyl phosphonium chloride, tetraphenyl phosphonium chloride and MIA5 (SKW company Products) and the like, and conventional additives may include flow enhancers, acrylic additives, olefin waxes, pigments, hydrophilic and hydrophobic silicas for improving the flowability of anti-flow and degassing paints, and the like. As the flow preventing agent, acrylic and silicone may be used. Examples of the acrylic may include Modaflow, PV-5 (manufactured by Monsanto), PL-201 (manufactured by Wally), and Acronal-4F (manufactured by BASF). This can be used.

The curing accelerator and the usual additives are used in an amount of 1 to 5 parts by weight. If the amount is less than 1 part by weight, poor appearance and curability of the paint are lowered. The problem of not forming occurs.

On the other hand, the present invention is a powder coating composition for top coat containing a small amount of the specific blowing agent, and when the coating on a multilayer steel pipe using the same requires special conditions in the process, if the conventional general process when the coating method Since the required property improvement effect cannot be obtained, a new multilayer steel pipe conduit is required.

Therefore, the coating method of the continuous process using the powder coating composition for multilayer steel pipe top coating according to the present invention will be described in detail as follows.

The undercoat powder coating composition used together before applying the top coat powder composition used in the present invention may be well known in the art. For example, the epoxy powder coating composition [US Patent No. 3876606, No. 4251426, No. 568615], which has excellent thermal stability and is widely applied as a powder coating for steel pipe coating, and the silane coupling agent are effectively applied. Epoxy powder coating compositions (Korea Patent No. 2002-55793) and the like which have improved the adhesion of the coating film and the water resistance of the coating to improve the boiling resistance and the negative electrode peeling resistance can be used for the undercoat.

Referring to the painting process according to the invention as follows.

First, the pretreatment and preheating conditions for the substrate to be coated are carried out according to the conventional steel pipe coating pretreatment method, and the surface treatment of the substrate is blasted to Swedish standard SA2.5 or higher using a grit or shotball, and the profile of the body is 40 to It is 100 micrometers. In addition, the surface treatment is carried out with chemicals such as chromate and phosphoric acid, or foreign substances on the surface are removed by washing with air or steam. Preheating conditions of the body preheats the steel pipe to the temperature of 190 ~ 270 ℃ using a gas combustion oven or induction coil.

Next, the preheated substrate is coated with a conventional method, for example, electrostatic spraying or the like, to form a molten coating layer having a thickness of 300 to 500 µm, and then contains a specific blowing agent within at least 1 second to 2 minutes. The coating composition for top coat is continuously coated with a thickness of 100 to 300 µm as in the above-mentioned undercoating method. The continuous coating process of the lower coat and the upper coat powder coating is primarily performed by discharging the powder coating undercoat from the pre-array spray gun arrangement, and almost simultaneously with the steel pipe in the post-array arrangement of the spray gun. In addition, the adjustment of the coating thickness and coating conditions of each layer can be controlled by a relatively simple method of controlling the number and amount of spray guns installed in the front and rear arrays.

The top coat coated with the continuous coating is allowed to settle the foam layer to a minimum of 1 to 2 mm using cooling water within 5 to 10 minutes to form a multilayer powder coating film. Foaming starts after the top coat and the top coat, and the size represents about 3 to 5 mm in height, and when sprayed or touched with a coolant to the steel pipe that has been painted, the thickness is reduced to about 1 to 2 mm. If the foamed part is naturally cooled without a water cooling process, the foaming itself gradually sinks, and thus, a large void layer is formed in the foaming layer, so that impact resistance is lowered. Therefore, 5 to 10 minutes after foaming occurs. It is necessary to cool down the heat with cooling water inside to obtain physical properties such as impact resistance and flex resistance.

The multi-layered steel pipe formed by the above method is suitable for controlling the time when painting the multilayered steel pipe in a continuous process by using a powder coating composition for coating containing a specific foaming agent, thereby improving economic efficiency and mechanical resistance such as impact resistance and bending resistance of the steel pipe. Due to the improved physical properties, it can be used in places where the use environment of sand, stone, etc. was restricted.

Hereinafter, the present invention will be described in more detail with reference to the following examples, which are not intended to limit the present invention.

Examples 1-2 and Comparative Examples 1-2

After blending with the composition shown in the following Table 1 (Examples 1 and 2, Comparative Examples 1 and 2), and then uniformly mixed to be uniformly mixed using a container mixer, extruder and kneader (PLK- 46, PCM-30, ZSK-25) was melt mixed at 1000 ℃ DPTJ through an extruder, to prepare a powder coating composition using a grinder.

Classification (parts by weight) Hado Example 1 Example 2 Comparative Example 1 Comparative Example 2 Epoxy resin Bisphenol A ¹⁾ 32 86 80 54 32 Metamorphic Noblock A ²⁾ 32 32 Hardener Phenol ³⁾ 4 9 8 Dician diamide ⁴⁾ One 3 2 One Blowing agent ⁵⁾ 4 4 Curing accelerator ⁶⁾ One One One One One Additive ⁷⁾ One One One One One Inorganic filler A ⁸⁾ 29 5 42 25 B ⁹⁾ 5 1): epoxy equivalent 1150 (Korea Chemical) 2): epoxy equivalent 800, silane A 2.6 parts by weight of mixed parts (Korea Chemical) 3): hydroxyl equivalent 250 (Korea Chemical) 4): casamide 783, DMPF ( Thomas Swan) 5): Unicel-MS Series (Dongjin Semichem), Explosion DU Series (Akzo Nobel) 6): MIA 5 (SKW) 7): PV 5 (Willy), Benzo Phosphorus (manufactured by Miwon Corporation) 8): 2 to 4 parts by weight of feldspar powder (MS material), 1 to 3 parts by weight of titanium dioxide (manufactured by DuPont, Ishihara), 0.5 to 1 part by weight of carbon black (MA white product) 9): 1 to 3 parts by weight of titanium dioxide (manufactured by DuPont, Ishihara), 1 to 2 parts by weight of silica powder (manufactured by US Silica), 1 to 2 parts by weight of barite powder (Korean semiconductor material), 0.5 to 0.5 parts by weight of carbon black (MA white product) 1 part by weight

Experimental Example

After coating on the specimen produced by using the powder coating composition for multilayer steel pipe top coating obtained in Examples 1 to 2 and Comparative Examples 1 to 2, the physical properties were measured by the following method and are shown in the following Table 2.

Specimen Fabrication

1) Specimen Condition

100 x 100 x 6 T, 220 x 22 x 6.4 mmT or 220 x 22 x steel pipes, cold rolled steel plate, polished with grit or shot, etc., to make the blast anchor profile of the surface of the body 40 ~ 100 ㎛, SA2 1 / Pretreat the surface with the cleaning condition of 2.

2) How to paint

After preheating the specimen to 210 to 230 ° C. in an oven, the powder coating undercoat is applied to a coating thickness of 300 to 400 μm by applying an ordinary electrostatic spraying method or a fluid deposition method, and then for 20 to 30 seconds. Then, the powder coating top coats prepared in Examples 1 and 2 and Comparative Examples 1 and 2 were successively coated at 100 to 300 µm. When the top layer swelled and swelled, the foam layer was allowed to cool down with cooling water at least within 5-7 minutes.

3) Property measurement

The physical properties of the coating film coated using the coating material prepared by the above formulation are shown in the following two tables, and the physical property test was generally used in steel pipe standards and was based on the certified CAN / CSA Z245.20 standard.

division Example 1 Example 2 Comparative Example 1 Comparative Example 2 Flexibility O ◎ △ O Boiling water resistance ◎ ◎ △ O Impact resistance ◎ ◎ O △ Cathodic Peeling Resistance ◎ ◎ O O Wear resistance ◎ O O △ ◎: excellent, O: good, △: insufficient

As shown in Table 2, Examples 1 to 2 coated with a top coat using a powder coating composition containing a specific blowing agent according to the present invention are more flexible and navigable than Comparative Examples 1 to 2 using a conventional powder coating composition. The mechanical properties such as water resistance, impact resistance, negative electrode peel resistance and abrasion resistance have been greatly improved, and the use of a small amount of a specific blowing agent and inorganic filler in combination with the conventional inorganic filler in addition to the improvement of the physical properties can be achieved. It was confirmed that it is efficient. In addition, Example 1 and Example 2 was found to use the inorganic filler in accordance with the required physical properties to control the physical properties by the selective use of each component.

Comparative Example 3

The powder coating composition for top coat prepared in Example 1 was prepared in the same manner, but after the coating process was conventionally applied by the following coating method, the physical properties were measured by the same method as described above. It is shown as follows.

[How to paint]

The sample was preheated to 210 to 230 ° C in an oven, and then coated with powder coating with a film thickness of 300 to 400 µm using a conventional electrostatic spray method or flow deposition method, followed by 3 minutes. The powder coating topcoat prepared in Example 1 was continuously coated at 100 to 300 µm. When the top layer swells and swells, the foam layer cools down with cooling water in at least one minute.

division Example 1 Comparative Example 3 Flexibility O △ Boiling water resistance ◎ △ Impact resistance ◎ O Cathodic Peeling Resistance ◎ O Wear resistance ◎ O ◎: excellent, O: good, △: insufficient

Example 1 and Comparative Example 3 is performed by differently coating the coating composition (Example 1) and the conventional coating method (Comparative Example 3) of the present invention, the same multilayer steel pipe coating powder coating composition, as shown in Table 2 above As can be seen from the example, the results show better results, and thus the physical property difference may occur depending on the coating method.

As described above, the multilayer steel pipe continuously coated with a powder coating for undercoat and a powder coating for coating containing a specific foaming agent with a short time interval has higher boiling resistance, negative electrode resistance, impact resistance, etc. Its mechanical properties are superior to its superiority and its economic utility is excellent, and it can be used in various fields because there is no restriction on steel pipe usage environment.

Claims (4)

In the powder coating composition for top coat containing an epoxy resin, a curing agent, an inorganic filler, a curing accelerator and the usual additives, 1 to 9 parts by weight of the blowing agent to form the microcapsules or micro-spare structure is a powder coating composition for lamination steel pipe top coating. According to claim 1, 70 to 90 parts by weight of epoxy resin, 1 to 15 parts by weight of a curing agent, 1 to 9 parts by weight of a blowing agent forming a microcapsule or micro spare structure, 1 to 10 parts by weight of an inorganic filler and a curing accelerator and usually Powder coating composition for multi-layer steel pipe top coating, characterized in that it contains 1 to 5 parts by weight of the additive. The powder coating composition of claim 1, wherein the foaming agent has an average particle size of 20 to 40 µm, an initial foaming temperature of 120 to 160 ° C, and a maximum foaming temperature of 190 to 220 ° C. In the coating method of powder coating consisting of pre-treatment and pre-heating step, coating step and water cooling step of steel pipe coating, Forming a molten coating layer having a thickness of 300 to 500 μm by coating the undercoat in a prearrangement with a spray gun in the coating step; 1 second to 2 minutes after the molten coating layer is formed, the top coat of the coating film foamed by continuously coating the top coat with a thickness of 100 to 300 μm in a post-array with a powder coating composition comprising a microcapsule or a micro spare structure. Forming a layer; The coating method of the powder coating for multilayer steel pipe top coating, wherein the top coat layer of the foamed coating film formed above is water cooled within 5 to 10 minutes.