KR20120115027A - Water dispersable polyurethane resin, method for preparing the same, and coating composition for pcm comprising the same - Google Patents

Abstract

PURPOSE: A manufacturing method of a water-dispersible polyurethane resin is provided to simplify coating process through four steps by using an optimum content of specific reactant, and to satisfy main physical properties required for a thin film. CONSTITUTION: A manufacturing method of a water-dispersible polyurethane resin comprises: a step of manufacturing an isocyanate group-terminated polyurethane prepolymer I in a terminal of an isocyanate group; a step of manufacturing a crosslinked polyurethane prepolymer II by reacting the prepolymer I and a polyfunctional monomer; a step of neutralizing the prepolymer II by adding the amine into the prepolymer II, and manufacturing the polyurethane water-dispersed resin I by adding water to the outcome; and a step of manufacturing a chain extended polyurethane water-dispersed resin II by reacting the water-dispersed resin I and a chain extender.

Description

Polyurethane water-dispersible resin, manufacturing method thereof, and paint composition for PCM including the same {WATER DISPERSABLE POLYURETHANE RESIN, METHOD FOR PREPARING THE SAME, AND COATING COMPOSITION FOR PCM COMPRISING THE SAME}

The present invention relates to a polyurethane water dispersion resin, a method of manufacturing the same and a coating composition for PCM comprising the same, and more particularly, by preparing a polyurethane water dispersion resin in four steps using a specific reactant in an optimum content, The present invention relates to a polyurethane water-dispersion resin, a method of manufacturing the same, and a PCM coating composition including the same, which can simplify the coating process, satisfy the main physical properties required by a thin film, and have excellent environmental friendliness.

Polyurethane resins are generally used for various paints, adhesives, binders and coatings because of excellent wear resistance, adhesiveness, non-tackiness and rubber elasticity. These polyurethane resins are being converted from conventional solvent-type polyurethane resins to polyurethane dispersion (PUD) due to increased awareness of environmental pollution, increased regulations, and a steady increase in solvent prices. Many reports regarding the urethane resin composition have been made.

However, unlike conventional solvent-type polyurethane resins, the polyurethane water dispersion resin inevitably introduces anion centers for water dispersion, which causes drying speed, storage stability, adhesion, mechanical properties, water resistance, and chemical resistance (acid resistance, acid resistance). Alkaline), heat resistance, etc. are somewhat poor, so the use range is quite limited. Specifically, when the polyurethane water dispersion resin composition is used as a coating material for surface-treated steel sheet, there is a problem that the corrosion resistance and chemical resistance (acid resistance, alkali resistance) that are essential requirements are much shorter than the conventional solvent-type resin.

Meanwhile, in order to reduce costs, paint companies are exploring how to paint on galvanized steel sheet production lines rather than color coating lines in pre-coated metal (PCM) paints. This galvanized steel sheet production line uses an induction oven with high efficiency since the line speed is more than twice as fast as a general color coating line and does not require high temperature for drying and curing. In addition, since the coating is generally applied to a degree of temporarily rust-proofing with a thin film using a water-soluble product, there is no facility for applying a solvent type paint. Therefore, in terms of equipment, a paint that can form a coating film in a short time at a low temperature without using a solvent type paint is required.

In addition, the products produced in the color coating line are designed with chrome or chromium-free type pretreatment before the paint application process. However, the galvanized steel sheet production line is not equipped with a separate facility for such treatment, and in general, there is only one or two coaters, so it is necessary to express all the appearance and properties required by only one or two coatings.

In addition, with the recent increase in demand for color steel sheets for home appliances, the appearance of products for home appliances, clean appearance characteristics, high strength in stamp molding methods, and flexibility to withstand the conditions where steel sheets are pushed deeply and excellent corrosion resistance It is required, and it is a reality that it is necessary to show the main physical properties even with a thin coating film within 10㎛.

Accordingly, a situation is required to develop a coating composition for PCM, which can be used to form a coating film quickly even at a low temperature, simplify the coating process, and satisfy the main physical properties required by a thin film, or a polyurethane water-soluble resin used therein. to be.

The present invention is to solve the problems of the prior art as described above, it is possible to quickly form a coating film at a low temperature without curing and chromium-related pretreatment process, and to satisfy the main physical properties such as processability, corrosion resistance, chemical resistance, strength even with a thin film only It is an object of the present invention to provide a polyurethane water dispersion resin and a coating composition for PCM including the same.

In order to achieve the above technical problem, the present invention (a) 100 parts by weight of a diol containing a carboxyl group; 600 to 800 parts by weight of polyol; And reacting 600 to 800 parts by weight of the isocyanate compound to prepare a polyurethane prepolymer I at the end of the isocyanate group; (b) 100 parts by weight of the prepolymer I obtained; And reacting 0.3 to 1.5 parts by weight of the multifunctional monomer to prepare a polyurethane prepolymer II having a crosslinked structure; (c) neutralizing the prepolymer II by adding 1 to 5 parts by weight of the amine to 100 parts by weight of the prepolymer II obtained, and then adding water to prepare a polyurethane water dispersion resin I; And (d) 100 parts by weight of the obtained aqueous dispersion resin I; And it provides a method for producing a polyurethane water-dispersion resin comprising the step of producing a chain-extended polyurethane water dispersion resin II by reacting 1 to 5 parts by weight of a chain extender.

In another aspect, the present invention provides a polyurethane water dispersion resin prepared according to the manufacturing method and a coating composition for PCM comprising the same.

In still another aspect of the present invention, there is provided a steel sheet, which has a coating film formed by drying the coating composition on a surface thereof.

When the polyurethane water dispersion resin prepared according to the present invention is applied to PCM paint, the coating film can be quickly formed at low temperature without curing and chromium-free pretreatment process, so that the coating process is simplified, and processability, corrosion resistance, chemical resistance, It can meet the required major physical properties, such as strength, it is possible to provide a paint with excellent environmental friendliness to use water rather than a solvent.

Hereinafter, the present invention will be described in detail.

[Polyurethane Water dispersion  Manufacturing Method of Resin]

(a) Prepolymer  Manufacture of I

The first step of the polyurethane water dispersion resin manufacturing method according to the invention, 100 parts by weight of a diol containing a carboxyl group; 600 to 800 parts by weight of polyol; And reacting 600 to 800 parts by weight of the isocyanate compound to prepare polyurethane prepolymer I at the end of the isocyanate group.

As the diol containing a carboxyl group, a compound having at least one carboxyl group and two (or optionally three or more) hydroxy groups simultaneously may be used without particular limitation. In one embodiment, free acid glycols containing one or more carboxyl groups can be used. For example, the di-hydroxy C _{1 - 6} alkanoyl acid, such as dimethylol propanoic acid (propionic acid), diethyl propane acid, dibutyl propane acid and dimethylol butanoic acid; 2,6-dihydroxy benzoic acid; Dihydroxy ethylsulfuric acid; And at least one selected from dihydroxy maleic acid, and at least one selected from dimethylol propanoic acid and dimethylol butanoic acid is particularly preferable. The free acid functionality of the compound is essential to undergo the solubilization step as an ionic group.

If the relative content of the diol containing carboxyl groups for the polyol and isocyanate compound is too low outside the above range, the water dispersion stability may be lowered, and if the content is too high, the water resistance may be lowered.

In the present invention, as the ion center used in the reaction, a cation center, an anion center, and an anion center of the non-ion method are used. The anion center includes a sulfonate type and a carboxylate type, and preferably a carboxylate type.

As the polyol, a polyol having two or more functional groups may be one or more selected from polyester polyols, polycarbonate polyols, polyether polyols, and polycaprolactone polyols, but is not necessarily limited thereto.

Preferably, the number average molecular weight is 1,000 to 2,000, and polyester polyol and polycarbonate polyol are used alone, or more preferably, a mixture of both. The polyester polyol may contain an ester group to express adhesiveness, and the polycarbonate polyol may improve water resistance, chemical resistance and solvent resistance. In addition, the number average molecular weight is preferably in the range of 1,000 to 2,000 in terms of water resistance and crack prevention of the paint dry coating, and the hydroxyl value of the polyol is preferably in the range of 30 to 70 mgKOH / g in view of stability and water resistance of the aqueous phase.

The polyol is included in an amount of 600 to 800 parts by weight, more preferably 650 to 750 parts by weight, based on 100 parts by weight of the diol containing a carboxyl group. If the content is less than 600 parts by weight, the molecular weight of the resin is lowered, the physical properties after the coating film is lowered, if the content is more than 800 parts by weight, the melt flow of the resin is weak and the dispersion stability is lowered.

Isocyanate compounds include aliphatic, cycloaliphatic and aromatic isocyanate compounds having two or more functional groups, such as methane diisocyanate, butane-1,1-diisocyanate, ethane-1,2-diisocyanate, butane-1,2-diisocyanate, Transvinyl diisocyanate, heptane-1,7-diisocyanate, 2,2-dimethyl-pentane-1,5-diisocyanate, hexane-1,6-diisocyanate, octane-1,8-diisocyanate-nonane- 1,9-diisocyanate, dimethylsilane diisocyanate, diphenylsilane diisocyanate, cyclohexane-1,4-diisocyanate, dicyclohexylmethane-4,4-diisocyanate and tetramethyl-1,3-xylene di One or more selected from isocyanates may be used, but is not necessarily limited thereto.

Preferably, dicyclohexylmethane-4,4-diisocyanate and tetramethyl-1,3-xylene diisocyanate are used alone or in combination. In addition, when the content of tetramethyl-1,3-xylene diisocyanate is 800 parts by weight or more based on 100 parts by weight of the diol containing a carboxyl group, the viscosity of the resin is lowered, which is advantageous for water dispersion, but also causes side effects in which the flexibility is lowered. It is preferable to adjust the content suitably.

The isocyanate compound contains 600 to 800 parts by weight, more preferably 650 to 750 parts by weight based on 100 parts by weight of the diol containing a carboxyl group. If the content is less than 600 parts by weight, the chain extension reaction proceeds inadequately to reach the molecular weight for securing the required physical properties. If the content is more than 800 parts by weight, the reaction is difficult to control.

(b) Prepolymer II Manufacturing

The second step of the polyurethane water dispersion resin manufacturing method according to the invention, 100 parts by weight of the prepolymer I obtained; And reacting 0.3 to 1.5 parts by weight of the multifunctional monomer to prepare a polyurethane prepolymer II at the end of the isocyanate group containing a crosslinked structure in the main chain.

As the multifunctional monomer added for the crosslinking structure introduction, one or more selected from melamine, trimethylol propane, trimethylamine, glycerin, pentaerythritol, and hexamethylene diisocyanate trimer may be used, but is not necessarily limited thereto. Preferably, melamine which is a trifunctional group is used.

The polyfunctional monomer is contained 0.3 to 1.5 parts by weight, more preferably 0.5 to 1.2 parts by weight based on 100 parts by weight of prepolymer I. If the content is less than 0.3 parts by weight, the crosslinking reaction proceeds insufficiently to reach the molecular weight for securing the required physical properties. If the content is more than 1.5 parts by weight, the molecular weight increases due to the excessive crosslinking reaction, making it difficult to control the reaction. Lose.

(c) polyurethane Water dispersion  Preparation of Resin I

In the third step of the method for preparing a polyurethane water dispersion resin according to the present invention, 1 to 5 parts by weight of an amine is added to 100 parts by weight of the obtained prepolymer II to neutralize the prepolymer II, and then water is added to the polyurethane water dispersion. This step is to prepare Resin I.

As the amine used to neutralize the prepolymer II, tertiary amines are preferred, and tertiary amines which do not contain hydroxyl groups capable of reacting with terminal isocyanates are more preferred.

Alkyl-substituted amines or alkanol amines may be used as the amine neutralizing agent, and preferably methyldiethanolamine, 2-amino-2-methylpropanol, phenyldiethanolamine, trimethylamine, triethylamine, benzyldimethylamine, At least one selected from diisobutylamine and normalmethyl-2-pyrrolidone is used.

The amine neutralizer is added in an amount of 1 to 5 parts by weight, more preferably 2 to 4 parts by weight, based on 100 parts by weight of prepolymer II. If the addition amount is less than 1 part by weight, the stability of the water in the resin powder in the dispersed state is lowered. If the addition amount is more than 5 parts by weight, a problem due to an excessively high pH occurs.

The pH of the polyurethane water dispersion resin is preferably 7.0 to 8.5 in order to have a water dispersion stability, and if necessary, after neutralizing with an amine, alcohol may be added as a diluent to reduce the viscosity, and then water dispersion may be performed.

The amount of water added for water dispersion is preferably 100 to 220 parts by weight, more preferably 120 to 200 parts by weight, based on 100 parts by weight of prepolymer II. If the amount is less than 100 parts by weight, it may not be possible to obtain stable particles after water dispersion, and if the amount is more than 220 parts by weight, the viscosity of the paint may be lowered due to a decrease in solid content, thereby greatly reducing the thickness of the coating film and reducing workability. .

In one embodiment, the water dispersion proceeds over 10-40 minutes and immediately after the water dispersion raises the temperature to 55-65 ° C. for about 60 minutes. This is a process for stabilizing the water dispersion resin, which includes releasing the unpolymerized prepolymer on the flask wall.

(d) polyurethane Water dispersion  Suzy II Manufacturing

The fourth step of the polyurethane water dispersion resin manufacturing method according to the invention, the obtained water dispersion resin I 100 parts by weight; And reacting 1 to 5 parts by weight of a chain extender to prepare a polyurethane water dispersion resin II (final polyurethane water dispersion resin) having a chain extension crosslinked structure.

The chain extender is added to react the unreacted isocyanate present in the water dispersion resin I, and for example, low molecular weight diamines and dialcohols can be used. Preferably, 1 is selected from isophorone diamine (IPDA) exhibiting excellent corrosion resistance among low molecular weight diamines, hexamethylenediamine (HMDA) having good elongation, and adipic acid dihydrazide (ADH) having excellent solvent resistance. Use more than one species.

The chain extender is contained in an amount of 1 to 5 parts by weight, more preferably 2 to 4 parts by weight, based on 100 parts by weight of the water-dispersed resin I. If the content is less than 1 part by weight, it is difficult to increase the molecular weight, and if the content is more than 5 parts by weight, the molecular weight may be rapidly increased to cause a gelation reaction.

In one embodiment, the polyurethane water dispersion resin prepared according to the present invention has a solid content of 25 to 35% (by weight), a viscosity of 20 to 100 cPs, a number average molecular weight of 30,000 to 70,000, an elongation of 100 to 400% It may be a resin having a hardness of B to H, a pH of 7 to 10 and a tensile strength of 20 to 70 MPa.

[ PCM Paint composition]

According to another aspect of the present invention, there is provided a coating composition for PCM (Pre-Coated Metal) comprising a polyurethane water dispersion resin prepared according to the manufacturing method as described above. Specifically, the composition according to the present invention is a coating composition for PCM based on a thermoplastic polyurethane water-dispersion resin of a dry type rather than a curing type, and can provide a coating having excellent environmental friendliness because it is an aqueous coating composition rather than a solvent type. .

In particular, the present invention comprises an inorganic binder to improve the water resistance and dryness in the thermoplastic polyurethane water dispersion resin, apply a metal chelating agent, adhesion promoter and anti-corrosive corrosion inhibitor to improve adhesion and corrosion resistance with galvanized steel sheet The coating composition for water-soluble type PCM undercoat which mixed an appropriate amount of antifoamers for the improvement of workability, appearance, and antifoaming property is provided. There is no particular limitation on the inorganic binder, the metal chelating agent, the adhesion promoter, the anti-corrosive agent and the antifoaming agent which can be used, and those conventionally used in the field of paint for PCM can be used.

In a preferred embodiment, the coating composition for PCM of the present invention is 20 to 150 parts by weight of water based on 100 parts by weight of solids of the polyurethane water dispersion resin prepared according to the production method of the present invention; 10 to 20 parts by weight of the inorganic binder; 2 to 10 parts by weight of the metal chelating agent; 1 to 5 parts by weight of adhesion promoter; 1 to 10 parts by weight of anticorrosive corrosion inhibitor; And 0.1 to 2 parts by weight of the defoaming agent.

If the amount of the polyurethane water dispersion resin is too small beyond the other range than the other components, it is difficult to achieve the effect of simplifying the coating process and satisfying the main physical properties pursued by the present invention, the wettability (wetting) may be reduced, the amount is in the above range Too much more than other components, the thicker the coating film may be difficult to achieve the effect of the thin film coating pursued by the present invention.

If the content of water is less than 20 parts by weight based on 100 parts by weight of the solid dispersion of the polyurethane water-based resin, the storage property of the paint may be lowered. If the content is more than 150 parts by weight, the viscosity of the paint may be lowered, so that the coating may not be properly formed. .

In addition, when the content of the inorganic binder, the metal chelating agent, the adhesion promoter, the anti-corrosive agent and the antifoaming agent is less than the lower limit, it may cause water resistance, dryness, adhesion, corrosion resistance, workability, antifoaming and deterioration of the appearance. When the upper limit is exceeded, it may be difficult to achieve the effect of simplifying the painting process and satisfying the main physical properties by pursuing the relative content of the polyurethane water dispersion resin.

The paint composition for PCM of the present invention may further include other additives generally used in paints for PCM as needed without departing from the object. For example, pigments (eg, white pigments, extender pigments) for coloring, improving hiding power and hardness of the coating film; Thickener; pH adjusters; Antioxidants; Antisettling agents; And an appropriate amount of rheology control agent and the like.

The coating composition for PCM of the present invention is based on a thermoplastic polyurethane water-dispersion resin of a dry type, not a hardening type, and when the composition is dried at a suitable temperature, for example, PMT (Peak Metal Temperature) 90 to 95 ° C, without a curing system A solid coating film can be formed on the surface of the steel sheet.

The coating composition for PCM to which the polyurethane water dispersion resin according to the present invention is applied can be quickly formed at a low temperature without a separate pretreatment in terms of a painting process, using an induction oven in a galvanized steel sheet production line, and in terms of physical properties. It has workability, solvent resistance, adhesiveness and corrosion resistance equivalent to the method of coating under conventional pretreatment. In addition, even if the coating of thin film 1 ~ 2㎛, which is thinner than the existing 4 ~ 5㎛ coating method, it exhibits the same physical properties and reduces the cost of transporting the plated body to the color coating line after painting. You can get it.

Hereinafter, the present invention will be described more specifically by way of examples. However, these examples are provided only for the understanding of the present invention, and the scope of the present invention is not limited to these examples in any sense.

Example  1 to 4 and Comparative example  1: polyurethane Water dispersion  Resin manufacturing

To prepare a polyurethane water dispersion resin as follows using the raw materials of ingredients and contents shown in Table 1.

After nitrogen was injected into a round four-necked flask equipped with a thermometer and a stirrer, N-methylpyrrolidone (NMP) for dissolving carboxyl group-containing diol, polyol, isocyanate compound, and DMPA was added and reacted at 90 ° C. to prepolymer. I was prepared. Subsequently, a polyfunctional monomer was added to the obtained prepolymer I, and then reacted at 95 ° C. for about 4 hours to prepare a prepolymer II.

Subsequently, the temperature was cooled to 30 ° C., and neutralized by adding 2 to 4 parts by weight (based on 100 parts by weight of prepolymer II) of the amine to the obtained prepolymer II, and then water was added to disperse the polyurethane water dispersion resin I. Prepared. A chain extender was added to the obtained polyurethane water dispersion resin I, followed by reaction to prepare a final polyurethane water dispersion resin II.

[Table 1] Polyurethane Water Dispersion Resin Mixture

1) PE-450: hydroxyl value 105 ~ 115mg / g, KCC

2) UH-200: molecular weight 2,000g / mol, UBE

3) PTMEG 2000: molecular weight 2,000 g / mol, BASF

Example  5 to 8 and Comparative example  2 : PCM Paint manufacturing

To 100 parts by weight of solids of the polyurethane water dispersion resin prepared according to the above Examples and Comparative Examples, 135 parts by weight of water, 15 parts by weight of silica sol as an inorganic binder, 8 parts by weight of zirconyl ammonium carbonate as a metal chelating agent , 4 parts by weight of an epoxy resin as an adhesion promoter, 8 parts by weight of thiourea as an anticorrosion agent, and 0.2 parts by weight of a silicone antifoaming agent as an antifoaming agent to prepare a paint for PCM. In addition, the coating material was coated on a galvanized steel sheet with a thickness of 2 μm and dried at 275 ° C. for 3 s to form a coating film.

The physical properties of the prepared coating film were measured and the results are shown in Table 2 below.

 [Table 2] Paint Property Evaluation Results

1) Appearance: visual evaluation

2) Hardness: 100 times MEK rubbing

-Excellent: no peeling over 100 times

-Good and Normal: No 50 ~ 100 peels

Poor: Less than 50 peels

3) Machinability: 0T bending

Excellent: no crack

Good and medium: cracks 0-20%

Poor: Over 20% crack

4) Adhesion: Taping after workability

-Excellent: no peeling more than 10 times

Good and medium: no peeling 1-5 times

-Poor: 1 peel

5) Chemical resistance: 24 hours 10% NaOH, 10% CH ₃ COOH dipping test

24 hours 5% NaOH, 5% CH ₃ COOH spot test

-Excellent: no Blister

-Good and Normal: Blister 1 ~ 5mm or less

-Bad: more than 5mm Blister,

6) Corrosion resistance: 5% NaCl 480 hours cross cut result

-Excellent: X-CUT 3mm or less, cross section 5mm or less

Good and normal: X-CUT 3 ~ 5mm or less, cross section 5 ~ 7mm

-Bad: X-CUT 5mm or more, cross section 7mm or more

* Based on the above evaluation criteria, the properties of each paint are compared and evaluated in the order of excellent, good, normal and poor according to the degree of excellent physical properties.

As shown in Table 2, in the case of the Example, the physical properties such as curing degree, adhesion, chemical resistance, corrosion resistance, etc. were superior to the comparative example. As a result, according to the present invention, it is confirmed that even a thin dry coating film can effectively meet the physical properties required for the PCM coating material and can form a coating film at a low temperature, thereby simplifying the process.

Claims (9)

(a) 100 parts by weight of a diol containing a carboxyl group; 600 to 800 parts by weight of polyol; And reacting 600 to 800 parts by weight of the isocyanate compound to prepare a polyurethane prepolymer I at the end of the isocyanate group;
(b) 100 parts by weight of the prepolymer I obtained; And reacting 0.3 to 1.5 parts by weight of the multifunctional monomer to prepare a polyurethane prepolymer II having a crosslinked structure;
(c) neutralizing the prepolymer II by adding 1 to 5 parts by weight of the amine to 100 parts by weight of the prepolymer II obtained, and then adding water to prepare a polyurethane water dispersion resin I; And
(d) 100 parts by weight of the water-dispersed resin I obtained; And reacting 1 to 5 parts by weight of a chain extender to prepare a chain-extended polyurethane water dispersion resin II.
Method of producing a polyurethane water dispersion resin comprising a. The method according to claim 1, wherein the diol containing a carboxyl group is at least one selected from dimethylol propanoic acid and dimethylol butanoic acid. The method according to claim 1, wherein the polyol is at least one selected from polyester polyols and polycarbonate polyols, and has a number average molecular weight of 1,000 to 2,000. The method according to claim 1, wherein the isocyanate compound is at least one selected from dicyclohexylmethane-4,4-diisocyanate and tetramethyl-1,3-xylene diisocyanate. The method according to claim 1, wherein the multifunctional monomer is at least one selected from melamine, trimethylol propane, trimethylamine, glycerin, pentaerythritol, and hexamethylene diisocyanate trimer. The method according to claim 1, wherein the chain extender is at least one selected from isophorone diamine, hexamethylene diamine, and adipic acid dihydrazide. Polyurethane water dispersion resin prepared according to any one of claims 1 to 6. To 100 parts by weight of solids of the polyurethane water dispersion resin according to claim 7,
20 to 150 parts by weight of water;
10 to 20 parts by weight of the inorganic binder;
2 to 10 parts by weight of the metal chelating agent;
1 to 5 parts by weight of adhesion promoter;
1 to 10 parts by weight of anticorrosive corrosion inhibitor; And
Defoamer 0.1 ~ 2 parts by weight
PCM coating composition comprising a. A steel sheet, having a coating film formed by drying the coating composition according to claim 8 on a surface thereof.