KR100710503B1 - Thermosetting powder coating composition for high temperature multilayer pipeline coating primer - Google Patents

Abstract

The present invention relates to a thermosetting powder coating composition for three-layer steel pipe coating, and more particularly, to a thermosetting epoxy resin containing a bisphenol A-type epoxy resin and a urethane-substituted noblock-modified epoxy resin. Hydrogen phenol curing agent, dicyandiamide type auxiliary curing agent and other additives are contained in an appropriate composition ratio, so that they exhibit excellent physical strength and stability at high temperatures and are excellent in adhesion to steel pipes, and in particular, polyolefin thermoplastic resin adhesive layer. The present invention relates to a thermosetting powder coating composition for coating under a three-ply steel pipe having excellent adhesion, corrosion resistance, and impact resistance.

3-ply steel pipe, undercoat, thermosetting powder coating composition

Description

Thermosetting powder coating composition for high temperature multilayer pipeline coating primer             

The present invention relates to a thermosetting powder coating composition for three-layer steel pipe coating, and more particularly, to a thermosetting epoxy resin containing a bisphenol A-type epoxy resin and a urethane-substituted noblock-modified epoxy resin. Hydrogen phenol curing agent, dicyandiamide type auxiliary curing agent and other additives are contained in an appropriate composition ratio, so that they exhibit excellent physical strength and stability at high temperatures and are excellent in adhesion to steel pipes, and in particular, polyolefin thermoplastic resin adhesive layer. The present invention relates to a thermosetting powder coating composition for coating under a three-ply steel pipe having excellent adhesion, corrosion resistance, and impact resistance.

Coated steel pipe research has been conducted for decades to improve corrosion resistance and durability of steel pipes or pipelines buried underground or undersea. In particular, the demand for pipeline construction has increased since the global energy crisis to meet consumer demand for stable gas and oil supply. However, in order to transport longer temperature fluids over longer distances, the environment and conditions associated with pipeline construction and operation have gradually become more severe. Ambient temperatures and conditions vary by location, from high temperatures in the equator, Africa and the Middle East, to cold polar regions, such as Northern Canada, Alaska, and Siberia. Moreover, fluid temperatures, such as natural gas or crude oil, tend to be higher due to higher feed pressures of the gas and crude oil transfer conditions that increase the temperature. Construction of pipelines for transporting high temperature fluids has required greater durability and corrosion resistance.

Coating under steel pipes is influenced not only by temperature, but also by the molecular structure of the polymers making up the coating material. Steel pipe coating material can be largely divided into ethylene-based, polypropylene-based, epoxy-based (fusion bonding epoxy). In addition, a general three-ply coating is composed of a three-ply layer of an epoxy undercoat layer, a polyethylene or polypropylene adhesive layer, and a top coat layer in which polypropylene and polyethylene are extruded. The thickness of the epoxy undercoat film constituting the above three-ply steel pipe is about 50 to 600 µm, the thickness of the polyolefin adhesive is about 250 to 500 µm, and the thickness of the top coat layer of the final polyolefin (polyethylene and polypropylene) is about 2000. The thickness of each coating may vary depending on the type and environment of the transport material.

Polyolefins used as the uppermost layer of the coating are mainly polyethylene and polypropylene, and polyethylene can be divided into low density polyethylene, medium density polyethylene, and high density polyethylene. Low density polyethylene has a difficult service temperature of 60 ° C or higher due to secondary crystallization at 60 ° C. However, improved medium density polyethylene (high density polyethylene) with secondary crystallization at 80 ° C has a service temperature of up to 80 ° C. It is known to pass the ESR (Environmental stress cracking resistance) test. Polypropylene resin is divided into single polypropylene, random polypropylene, mixed polypropylene, and block polypropylene according to the modified manufacturing process. Block polypropylene has high temperature stability and durability, and excellent physical properties at low temperature. It is known that is possible from -30 ℃ to 110 ℃.

On the other hand, melt-bonded epoxy coatings are defined by combinations of epoxy resins and hardeners, but dician diamide curing system epoxy coatings tend to have a rapid decrease in contact electrical resistance over several months due to high hygroscopicity at high temperature and humid conditions. Therefore, the epoxy coating of the phenol curing system has a glass transition temperature of about 100 ℃, it is difficult to apply at a temperature above 100 ℃.

In particular, the pipeline coating accounts for about 5%, which is a very small level of the overall financial costs of installing the pipeline system. However, pipeline systems must have corrosion resistance, leakage protection, and mechanical durability to maintain system design life. The design life of three-ply steel pipe coatings varies somewhat in the region, but is generally estimated to be about 40 years. For these environmental issues and safety considerations, not only costs but also performance and value over time should be considered. In particular, when the internal fluid temperature rises above the design temperature, the service life decreases drastically. Therefore, even at a fluid temperature of 120 ° C. or higher, the corrosion resistance and adhesion of the substrate and the adhesion to the polyolefin adhesive layer should be improved.

The present invention is based on the bisphenol A-type epoxy resin, urethane-substituted noblockac modified epoxy resin, in order to solve the above problems, namely the limitation of the application of the multi-layer undercoat at a temperature of 120 ℃ or more, here the high molecular weight polyhydric phenol The present invention was completed by containing a curing agent and a dicyandiamide co-curing agent in an appropriate composition ratio.

The present invention is not only excellent physical strength and stability at high temperature (100 ~ 130 ℃), but also excellent adhesion to the steel pipe, as well as excellent adhesion to the polyolefin thermoplastic resin adhesive layer, corrosion resistance, impact resistance three-layer steel pipe coating It is an object to provide a thermosetting powder coating composition for.

The present invention relates to a powder coating composition for undercoat, which is based on a thermosetting epoxy resin and contains a curing agent, a pigment, a filler, and a conventional additive.

The thermosetting epoxy resin is 30 to 60% by weight of bisphenol A-type epoxy resin, 40 to 70% by weight of urethane-substituted noblock modified epoxy resin having an equivalent weight of 750 to 850 and 10% by weight or less of a noblock modified bisphenol A type epoxy resin having an equivalent weight of 500 to 600. Contains,

5 to 20 parts by weight of a polyhydric phenol curing agent having a hydroxyl equivalent weight of 400 to 750, 0.1 to 10 parts by weight of dicyanamide-based auxiliary curing agent, 5 to 50 parts by weight of organic and inorganic pigments, based on 100 parts by weight of the thermosetting epoxy resin, Other additives (wetting and flowable additives and anti-corrosion agent) It is characterized by the thermosetting powder coating composition for three-layer steel pipe undercoat containing 1 to 5 parts by weight.

The present invention is described in more detail as follows.

The present invention contains a specific thermosetting epoxy resin and other additives including polyhydric phenol curing agent and dicyanamide-based auxiliary curing agent in a predetermined content ratio, so that they exhibit excellent physical strength and stability at high temperature, and are excellent in adhesion even under high temperature. The present invention relates to a thermosetting powder coating composition for three-layer steel pipe undercoating, which has excellent adhesion to the polyolefin thermoplastic resin adhesive layer, corrosion resistance, and impact resistance.

Next will be described in more detail with respect to each component contained in the thermosetting powder coating composition for three-ply steel pipe undercoat according to the present invention.

In the present invention, as the thermosetting epoxy resin, a bisphenol A-type epoxy resin and a urethane-substituted noblock modified epoxy resin having an equivalent weight of 750 to 850 are used together, and a noblock modified bisphenol A-type epoxy resin having an equivalent weight of 500 to 600 with the above-mentioned resin, if necessary. It may also contain.

The bisphenol A type epoxy resin contained as the thermosetting epoxy resin is a bisphenol epoxy resin having an equivalent weight of 800 to 3000 (preferably 900 to 1900), and a nonylphenol-encapsulated bisphenol having an equivalent weight of 1000 to 2500 (preferably 1,500 to 2,100). It is possible to use a release epoxy resin or a mixture thereof. The bisphenol A-type epoxy resin is contained in the total thermosetting epoxy resin of 30 to 60% by weight, if the content is less than 30% by weight, the storage viscosity of the paint is reduced due to the increase in the content of low-viscosity epoxy resin, resulting in agglomeration during storage. On the other hand, if the content exceeds 60% by weight, the flexibility and shelf life of the powder coating composition is increased, but as the equivalent weight and viscosity are increased, the wetting force is lowered, which is not preferable.

On the other hand, when the equivalent weight of the bisphenol epoxy resin contained as bisphenol epoxy resin is less than 800, the viscosity of the powder coating is low, so that the wettability with the base is improved, but the flexibility is poor and the storage property of the coating is deteriorated. In the case of the film's flexibility is improved, but the adhesion to the base is inferior in the wettability. In addition, when the equivalent weight of the nonylphenol and capped bisphenol A-type epoxy resin is less than 1,000, the viscosity of the powder coating is low, and thus the adhesion to the base is improved, but the flexibility of the coating film is not preferable, whereas the equivalent weight is 2,500. When exceeding, the flowability of the coating composition for coating undercoat falls, and it is unpreferable.

In the present invention, the nonylphenol-encapsulated bisphenol A-type epoxy resin contained as another bisphenol A-type epoxy resin is 0.5 to 5% by weight of nonylphenol at the end of the bisphenol A-type epoxy resin, and the three-ply steel pipe under the present invention. Not only does it improve the adhesion between the acid-containing polyolefin resin adhesive layer, which is an important physical property of the coating powder coating composition for coating, and the thermosetting powder coating composition for undercoat, but also lowers the viscosity of the resin itself, thereby improving the wetting property, thereby improving adhesion to the steel pipe surface. Since it is excellently improved, there is no peeling or cracking of the coating film even when bending, and it is possible to improve corrosion resistance, rust resistance, and chemical resistance. However, when the endyl capping of the nonylphenol is less than 0.5% by weight, there is no viscosity decrease of the epoxy resin, so that the wetting force of the paint is lowered, and thus the negative electrode peelability is lowered. On the other hand, when the endcapping is more than 5% by weight, the paint The flexibility and reactivity of is poor, which is not desirable.

In the present invention, a urethane-substituted noblock modified epoxy resin is contained together with the bisphenol A-type epoxy resin described above as the thermosetting epoxy resin. The urethane-substituted noblock modified epoxy resin is contained in the total thermosetting epoxy resin in 40 to 70% by weight. If the content is less than 40% by weight, the flexibility and storage properties of the powder coating composition are increased due to the increase in the content of bisphenol A type epoxy resin. Although it is increased, the heat resistance due to the lowering of Tg is lowered, which is not preferable. On the other hand, when it exceeds 70% by weight, the coating film is too rigid and the flexibility is not preferable.

In the urethane-substituted noblock modified epoxy resin, the terminal portion of the bisphenol A-type epoxy resin is modified by 25 to 35% by weight with a noblock resin, and the side chain portion is modified with urethane to 2 to 5% by weight of polyisocyanate to increase the crosslinking density. It is modified resin which strengthened heat resistance, and the equivalent range is 750-850. If the terminal portion is less than 25% by weight of modification, the corrosion resistance decreases due to a decrease in the degree of crosslinking, which is not preferable. On the other hand, when it is modified in excess of 35% by weight, the curing rate is increased and the wettability is poor. Not. In addition, when the urethane modification for the side chain portion is less than 2% by weight, there is a problem that the heat resistance is poor, and when more than 5% by weight severely modified, there is a problem that the corrosion resistance is degraded or yellowed at high temperatures.

 In addition, in the present invention, in addition to the bisphenol A-type epoxy resin and the urethane-substituted noblock modified epoxy resin described above as the thermosetting epoxy resin, a noblock modified epoxy resin having an equivalent weight of 500 to 600 is further added in the range of 10% by weight or less in the total thermosetting epoxy resin. By virtue of the excellent base material adhesion of the urethane substituted noblock modified epoxy resin and the additionally mixed noblock modified epoxy resin, the durability and corrosion resistance of the coating can be further improved. However, when the content of the additionally contained noblock modified epoxy resin is more than 10% by weight, adhesion to the base may be improved, but the flexibility of the coating may be deteriorated, which is not preferable. The additionally contained noblock modified epoxy resin is denatured to 5-25% of a noblock resin. If the noblock resin is modified to less than 5%, corrosion resistance is lowered due to a decrease in the degree of crosslinking, which is undesirable. On the other hand, in the case of denaturation exceeding 25%, the curing rate is increased and the wettability is not preferable.

As described above, the thermosetting epoxy resin included in the powder coating composition according to the present invention includes a bisphenol epoxy resin selected from a bisphenol epoxy resin having an equivalent weight of 800 to 3000 and a nonylphenol and uncapped bisphenol epoxy resin having an equivalent weight of 1000 to 2500. Together with a urethane substituted noblock modified bisphenol A type epoxy resin, or if necessary a noblock modified epoxy resin may be mixed.

On the other hand, in the present invention, using the above-mentioned thermosetting epoxy resin as the subject may contain a polyhydric phenol curing agent, dicyanamide-based co-curing agent, pigments, fillers and common additives.

The polyhydric phenol curing agent contains a hydroxyl equivalent of 400 to 750 in a range of 5 to 20 parts by weight with respect to 100 parts by weight of the thermosetting epoxy resin to obtain a thermosetting powder coating composition excellent in the negative electrode peelability and adhesion. If a polyhydric phenol curing agent having a hydroxyl equivalent weight of less than 400 is used, it is hardly reacted with the urethane substituted noblock modified epoxy resin used in the present invention to exhibit high heat resistance, but is not preferable due to reduced flexibility. On the other hand, when the hydroxyl equivalent exceeds 750, the coating film is softened due to the addition of excessive curing agent, which is not preferable. In addition, when the phenol curing agent is used in less than 5 parts by weight based on 100 parts by weight of the thermosetting epoxy resin, the strength and heat resistance of the coating film is lowered due to the decrease in the crosslinking density, whereas when used in excess of 20 parts by weight. The crosslink density of a coating film generate | occur | produces rapidly, and the adhesive force with a polyolefin thermoplastic resin adhesive layer falls, and it is unpreferable.

In addition, in the present invention, the dicyandiamide system may be used in the range of 0.1 to 3 parts by weight based on 100 parts by weight of the thermosetting epoxy resin as an auxiliary curing agent for controlling the curability in the thermosetting powder coating composition. If the amount of use is out of the above range, proper gelling time cannot be obtained and workability is lowered, which is not preferable.

In addition, in the composition of the present invention, conventional additives including pigments and fillers may be contained in a predetermined content ratio. Pigments include organic pigments or inorganic pigments, and specifically, titanium dioxide, ultramarine blue, phthalocyanine blue, phthalocyanine green, carbon black, black iron oxide, chromium green oxide, ferrite yellow, quinto red, etc. are used. Lose. Said pigment uses 5-50 weight part with respect to 100 weight part of thermosetting epoxy resins.

As the filler, barium sulfate, calcium carbonate, silica, alumina hydroxide, mica, feldspar, mica, talc and the like can be used. At this time, the filler is neutral or alkaline, the acidity of 7 to 12 is used. In addition, when using a powder having a particle size of 1 to 10 µm, preferably 2 to 5 µm, the wetting force of the thermosetting powder coating is good, and the adhesion to the base is excellent.

Other additives may include pinhole inhibitors, flow regulators, antioxidants, ultraviolet absorbers, and the like. Flow control agents reduce surface tension and eliminate creering, including polylauryl acrylate, polybutyl acrylate, poly 2-ethylhexyl acrylate, polyethyl 2-ethylhexyl acrylate, polylauryl methacrylate, Polyisodecyl methacrylate or the like may be used, and 0.3 to 2 parts by weight, preferably 0.5 to 1.5 parts by weight, based on 100 parts by weight of the thermosetting epoxy resin.

On the other hand, the three-ply steel pipe undercoat thermosetting powder coating composition according to the present invention can be prepared by the following three-step manufacturing process, in detail as follows.

First, uniformly mix the thermosetting epoxy resin, the polyhydric phenol curing agent, the dicyandiamide co-curing agent, the organic and inorganic pigments in a one step process, and then using a Henschel mixer for about 100 to 600 seconds at 2,000 to 5,000 rpm. A premixing process of dry mixing is performed to uniformly mix the raw materials so as to maintain uniform physical properties during melt mixing.

In a two-step process, a melt-mixing process of melt-mixing the raw material pre-dispersed through the step 1 process using a kneader or extruder at a temperature of 120 ~ 130 ℃. The melt-mixed raw material is passed through a roll and a cooling belt to produce chips having a size between 50 and 100 mm and a thickness of 1 to 5 mm.

In the final three-step process, using the pulverizer (hamma mill, ACM mill, turbo mill, etc.) of the melt-dispersed chip through the two-step process to perform the grinding process for producing a powder coating having a mechanically constant powder particle size The three-ply thermosetting powder coating for undercoat of the present invention is prepared. At this time, the particle size of the powder has a very close relationship with the workability of the powder coating, so that the average particle size is 15 ~ 45 ㎛, particles of 250 ㎛ or more within 0.3% within the particle size conditions of US Patent No. 5319001, which is the appropriate powder particles. Adjust the particle size.

Hereinafter, the present invention will be described in detail with reference to Examples and Comparative Examples as follows, but the present invention is not limited by the Examples.

Examples 1-3

The raw materials of the compositions and contents shown in the following Table 1 were dry mixed at 3,000 rpm for 400 seconds using a Henschel mixer and then melt mixed at a temperature of 120 ° C. using a twin extruder. Then, the melt-mixed raw material is passed through a roll and a cooling belt to produce chips having a size of 50 to 100 mm and a thickness of 1 to 5 mm, and then using an ACM mill to adjust particle sizes under US Pat. No. 5,319,001 particle size conditions. Since a powder coating having a mechanically constant powder particle size was prepared, a thermosetting powder coating composition for three-ply steel pipe undercoat was prepared.

(week)

1) N8070: Nonylphenol and coping bisphenol epoxy resin equivalent to 1800 ~ 2100, Koryo Chemicals

2) N8014: Bisphenol epoxy resin with equivalent weight of 1100 ~ 1200, Koryo Chemicals

3) N8039U: Urethane substituted noblock modified epoxy resin with equivalent weight of 750 ~ 850, Korea Chemical Products

4) N8037: Noble Block Modified Epoxy Resin with Equivalent 500 ~ 600, Equivalent 500 ~ 600, Korea Chemicals

5) KK600: Polyhydric Phenolic Curing Agent, Equivalent 550∼650, Koryo Chemicals

6) DEH41: Accessory Dicydian amide, US Dow Chemical

7) TiO ₂ : DuPont

8) Silica: Average particle size 3 ~ 15 ㎛

9) Barium sulfate: average particle size of 1 ~ 10 ㎛

10) Talc: Average particle size 1 ~ 10 ㎛

11) Mica: Average particle size 3 ~ 15 ㎛

12) Wallastone Light: Average particle size 3 ~ 20㎛

Experimental Example 1 Comparison of Physical Properties for Powder Coatings

Comparative results of physical properties of each of the thermosetting powder coating compositions prepared in Examples 1 to 3 and currently available powder coatings are shown in Table 2 below.

Experimental Example 2 Comparison of Properties for Steel Pipes and Three-ply Steel Pipes

For each of the thermosetting powder coating compositions prepared in Examples 1 to 3 and currently available powder coatings, steel pipes and three-ply steel pipes were coated using the following method.

(1) Manufacturing method of steel pipes coated with thermosetting epoxy powder coating:

A pipe steel pipe having an outer diameter of the pipe of 4 to 60 inches was made to have a surface roughness (profile) of 50 to 100 m by using a short ball or a grit ball. At this time, foreign matter (rust, oil, moisture, etc.) was not left on the surface (SSPC-10, SA 2 1/2 / Near white or white metal). The steel pipe subjected to mechanical pretreatment on the surface was preheated to a surface temperature of 180 to 250 ° C. using a direct heating or induction heating device. Then, hardened by preheated heat to prepare a steel pipe coated with a thermosetting powder coating. If necessary, bake after 10 minutes at 232 ° C for complete curing.

(2) Method of manufacturing 3-ply steel pipe:

The steel pipe subjected to the pretreatment on the surface was preheated to the surface temperature of the steel pipe by using a direct heating or induction heating device to 160 ~ 230 ℃, electrostatic deposition of the thermosetting powder coating composition for the steel pipe underlay prepared on the preheated steel pipe The coating was followed by curing with preheated heat. The adhesive film (Dupont / Fusabond MB 158D, MB 206D or Montel / MOPLEN COAT) was melt-extruded to the undercoat thermosetting powder coating composition 80 to 90% of the curing. At this time, the adhesive film is a product of copolymerization of polyethylene, polypropylene, maleic acid or acrylic acid and reacts with epoxy ring or secondary hydroxyl group of epoxy powder coating paint which is undercoat. ) After melt molding, it is bonded by physical force by physical shrinkage during cooling. Then, using the O-die method and the T-die method as the extrusion method, the outermost layer was extruded in the same manner as polyethylene (NOVA company / Canada) or polypropylene (Montel company / Italy) having excellent weather resistance and moisture resistance. To prepare a three-ply steel pipe.

Cathode peeling, bendability and interlayer adhesion test and cathodic peeling test were carried out using the uncoated steel pipe and the three-ply steel pipe prepared above, and the results are shown in Table 3 below.

Measurements are widely used for measuring the physical properties of paints: DIN 30670, DIN 30678 (German standard), CAN / CSA-Z245.20, CAN / CSA-Z245.21 (Canada Steel Pipe Association standard), NFA 49-711 (France Standard), and the interlayer adhesion between the thermosetting powder coating layer and the thermoplastic adhesive layer was measured by the method of DIN 30670 (German standard) Method II, and the negative electrode peeling test was the accelerated peeling test between the surface and the powder coating layer. It was carried out using the G42 method.

The interlayer adhesion test was carried out for each adhesion test at 23 ℃, 80 ℃, 120 ℃ temperature conditions. Cathode peeling test is the temperature of the surface of the body according to the fluid temperature of the actual steel pipe, but the external conditions to maintain the room temperature conditions in the present invention, the surface temperature of the surface is adjusted to 120 ℃ and the temperature of the electrolyte to 95 ℃ cathode peeling test Proceeded. This experiment was carried out on the bottom coated steel pipe and the three pipes coated with polypropylene adhesive and polypropylene resin, respectively. The results are in Table 3 below.

As described above, in the case of the three-ply steel pipe undercoat thermosetting powder coating composition according to the present invention, a thermosetting epoxy resin and a bisphenol A-type epoxy resin and a urethane-substituted noblock-modified epoxy resin are used as thermosetting epoxy resins. In addition, by using a polyhydric phenol curing agent with a large hydroxyl equivalent weight, it has excellent adhesion to the substrate under severe conditions such as transferring fluid at high temperature, and has excellent adhesion between layers as well as between layers. It is effective in corrosion resistance and negative electrode peeling resistance.

Claims (5)

In the powder coating composition for undercoat, which is based on a thermosetting epoxy resin and contains a curing agent, a curing aid, a pigment, a filler, and a conventional additive, As said thermosetting epoxy resin, 30-60 weight% of bisphenol-A epoxy resin and 40-70 weight% of urethane substituted noblock modified epoxy resin whose equivalent is 750-850, are contained, 3 to 20 parts by weight of the thermosetting epoxy resin, containing 5 to 20 parts by weight of a polyhydric phenol curing agent having a hydroxyl equivalent of 400 to 750 and 0.1 to 10 parts by weight of dicyanamide-based auxiliary curing agent Theft thermosetting powder coating composition. The bisphenol A-type epoxy resin contained in the thermosetting epoxy resin is selected from bisphenol epoxy resins having an equivalent weight of 800 to 3000 and nonylphenol-encapsulated bisphenol A-type epoxy resins having an equivalent weight of 1000 to 2500. Thermosetting powder coating composition for double layer pipe coating. The thermosetting powder coating composition of claim 2, wherein the nonylphenol-encapsulated bisphenol A-type epoxy resin is end-capped with 0.5 to 5% by weight of nonylphenol at the end of the bisphenol A-type epoxy resin. According to claim 1, wherein the urethane-substituted noblock modified epoxy resin is characterized in that the terminal portion of the bisphenol A-type epoxy resin is modified by 25 to 35% by weight with a noblock resin, the side chain portion is 2 to 5% by weight urethane modified Thermosetting powder coating composition for three-layer steel pipe undercoat. The thermosetting powder coating for three-ply steel pipe undercoat according to claim 1 or 2, wherein the thermosetting epoxy resin further contains 10 wt% or less of a noblock modified bisphenol A-type epoxy resin having an equivalent weight of 500 to 600. Composition.