JP7443665B2 - Low-temperature dissociation type water-based block polyisocyanate and paint containing it - Google Patents

Description

The present invention relates to a water-based blocked polyisocyanate whose blocking agent dissociates at low temperatures, and a paint containing the same.

Blocked polyisocyanate is a product in which the free isocyanate of the isocyanate group-terminated precursor is blocked by reacting with a blocking agent having an active hydrogen group that can react with the isocyanate group, making the isocyanate activity inactive at room temperature. When heated, the blocking agent dissociates and the isocyanate groups are regenerated.

Block polyisocyanates are widely used in baking paints, such as pre-coated metals used in automobiles, aircraft, building materials, and home appliances. Alcohol-based, phenol-based, lactam-based, oxime-based, and the like are known as general-purpose blocking agents used in blocked polyisocyanates. The dissociation temperature of blocked polyisocyanate varies depending on the type of polyisocyanate, the type of blocking agent, the type of reaction partner, the type and amount of catalyst, etc., but is generally about 130 to 250°C.

In recent years, blocking agents have been developed to dissociate at lower temperatures and harden in a shorter time than before, in order to reduce costs and carbon dioxide emissions during baking coating, and to enable coating on plastic parts. Blocked polyisocyanates are needed. In response to social and industrial demands such as environmental protection and work safety, water-based (aqueous) compositions that do not use organic solvents are required, leading to a shift to block polyisocyanates that can be used in water-based paints. It is being actively carried out.

Active methylene-based blocking agents have been proposed as blocking agents for use in low-temperature-dissociating blocked polyisocyanates (Patent Document 1), but heating to approximately 100°C is required to completely cure the coating film, resulting in plastic members with low heat resistance. cannot be used for In addition, activated methylene-based blocked polyisocyanates are easily hydrolyzed even at room temperature and have poor stability when used as water-based paints.

Imidazole-based agents are known as further low-temperature dissociation blocking agents, some of which provide sufficient coating hardness at 80 to 90°C, and can also be applied to plastic members. However, imidazole-based blocked polyisocyanates are said to have poor stability when used as water-based paints, and it has also been proposed to utilize this property in water-encapsulated gel-forming materials (Patent Document 2).

As a measure to improve the water dispersion stability of imidazole block polyisocyanate, a method of reacting an acid component has been proposed (Patent Document 3). However, the acid component may have adverse effects, such as increasing the dissociation temperature of the blocking agent and reducing the reactivity of isocyanate groups regenerated after dissociation of the blocking agent.

Japanese Patent Application Publication No. 10-231348 Japanese Unexamined Patent Publication No. 56-59832 Japanese Patent Application Laid-open No. 60-40121

The present invention was made based on the above circumstances, and the object thereof is to provide a water-based blocked polyisocyanate whose blocking agent dissociates at low temperatures and which has good storage stability when made into a water-based paint, and a water-based blocked polyisocyanate that has good storage stability when made into a water-based paint. An object of the present invention is to provide a paint containing the following.

The present inventors have conducted extensive research to solve the above problems, and have found that a water-based blocked polyisocyanate obtained using a specific imidazole blocking agent component and a paint containing the same solve the above problems. This discovery led to the completion of the present invention.

That is, the present invention includes the embodiments [1] to [8] below.

[1] A water-based block polyisocyanate obtained from an imidazole-based blocking agent (a), a polyisocyanate (b), and a nonionic hydrophilic group-containing compound (c), wherein the imidazole-based blocking agent (a) is - A low temperature dissociation type water-based block polyisocyanate characterized by being ethyl-4-methylimidazole.

[2] The low temperature dissociation type water-based block polyisocyanate according to [1] above, wherein the polyisocyanate (b) is at least one selected from the group consisting of aliphatic diisocyanates and alicyclic diisocyanates.

[3] The nonionic hydrophilic group-containing compound (c) is at least one selected from the group consisting of polyoxyalkylene alkyl ethers and polyoxyalkylene esters, according to [1] or [2] above. The low temperature dissociation type aqueous block polyisocyanate described above.

[4] The low temperature dissociation type water-based block polyisocyanate according to any one of [1] to [3] above, wherein the polyisocyanate (b) contains an isocyanurate-modified polyisocyanate derived from hexamethylene diisocyanate. Isocyanate.

[5] The low temperature dissociation type water-based block polyisocyanate according to any one of [1] to [4] above, wherein the nonionic hydrophilic group-containing compound (c) is polyethylene glycol monomethyl ether.

[6] A resin composition comprising the low-temperature dissociation type water-based block polyisocyanate according to any one of [1] to [5] above and a main ingredient.

[7] A paint comprising the resin composition according to [6] above.

[8] A coating film obtained from the paint according to [7] above.

According to the present invention, even a blocked polyisocyanate using an imidazole-based blocking agent with a low dissociation temperature can provide a water-based blocked polyisocyanate that has good storage stability when made into a water-based paint, and a paint containing the same.

The present invention will be explained in detail below.

The low-temperature dissociation type water-based blocked polyisocyanate and the coating material containing the same of the present invention are water-based blocked polyisocyanates obtained from an imidazole blocking agent (a), a polyisocyanate (b), and a nonionic hydrophilic group-containing compound (c). The imidazole-based blocking agent (a) is 2-ethyl-4-methylimidazole.

The blocking agent (a) used in the present invention is 2-ethyl-4-methylimidazole, and by using the polyisocyanate sealed with the blocking agent, it has excellent storage stability when made into a water-based paint, and Even if the baking temperature is low, it is possible to obtain a water-based block polyisocyanate whose resulting coating film has good solvent resistance.

The polyisocyanate (b) used in the present invention is preferably an aliphatic polyisocyanate, an alicyclic polyisocyanate, or a combination thereof, including an isocyanurate-modified polyisocyanate derived from hexamethylene diisocyanate. is even more preferable. Furthermore, aromatic polyisocyanates and araliphatic polyisocyanates can be used in combination without departing from the spirit of the present invention.

Examples of aliphatic polyisocyanates include hexamethylene diisocyanate, tetramethylene diisocyanate, 2-methyl-pentane-1,5-diisocyanate, 3-methyl-pentane-1,5-diisocyanate, lysine diisocyanate, trioxyethylene diisocyanate, etc. be able to.

Examples of the alicyclic polyisocyanate include isophorone diisocyanate, cyclohexyl diisocyanate, hydrogenated diphenylmethane diisocyanate, norbornane diisocyanate, hydrogenated tolylene diisocyanate, hydrogenated xylene diisocyanate, and hydrogenated tetramethylxylene diisocyanate.

Examples of aromatic polyisocyanates include 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, 2,4'-diphenylmethane diisocyanate, 2,2'-diphenylmethane diisocyanate, 4, 4'-diphenyl ether diisocyanate, 2-nitrodiphenyl-4,4'-diisocyanate, 2,2'-diphenylpropane-4,4'-diisocyanate, 3,3'-dimethyldiphenylmethane-4,4'-diisocyanate, 4, Examples include 4'-diphenylpropane diisocyanate, m-phenylene diisocyanate, p-phenylene diisocyanate, naphthylene-1,4-diisocyanate, naphthylene-1,5-diisocyanate, 3,3'-dimethoxydiphenyl-4,4'-diisocyanate, etc. be able to.

Examples of the aromatic aliphatic polyisocyanate include 1,3- or 1,4-xylene diisocyanate, 1,3- or 1,4-bis(1-isocyanato-1-methylethyl)benzene, ω,ω'-diisocyanato- Examples include 1,4-diethylbenzene.

Further, allophanate modified products, urea modified products, biuret modified products, uretdione modified products, and isocyanurate modified products of these polyisocyanates may be used in combination.

As the nonionic hydrophilic group-containing compound (c) used in the present invention, polyoxyalkylene alkyl ethers, polyoxyalkylene esters, and nonionic hydrophilic group-containing compounds that are combinations thereof can be preferably used.

Examples of the polyoxyalkylene alkyl ether include polyethylene glycol monomethyl ether, polyethylene glycol monododecyl ether, polyethylene glycol monocetyl ether, polyethylene glycol monooleyl ether, ethylene glycol monododecyl ether, diethylene glycol monododecyl ether, and triethylene glycol monododecyl ether. , tetraethylene glycol monododecyl ether, pentaethylene glycol monododecyl ether, hexaethylene glycol monododecyl ether, octaethylene glycol monododecyl ether, and the like.

Examples of the polyoxyalkylene ester include polyethylene glycol monolaurate, polyethylene glycol monostearate, and the like.

Among these, polyoxyalkylene alkyl ether is preferred, and polyethylene glycol monomethyl ether is most preferred. Further, the number average molecular weight of the polyoxyalkylene alkyl ether and polyoxyalkylene ester is preferably 400 to 4,000, most preferably 400 to 1,000.

The blocked polyisocyanate in the present invention can be produced, for example, by adding the components (a) to (c) described above to an organic solvent and reacting them according to the urethanization reaction/blocking reaction conditions shown below.

As a reaction step, first, urethanization is performed using a polyisocyanate and a nonionic hydrophilic group-containing compound. The amount of the nonionic hydrophilic group-containing compound charged is 1 to 30% by mass, preferably 2 to 20% by mass, based on the polyisocyanate. This urethanization reaction proceeds even without a catalyst, but the reaction can also be accelerated using a known urethanization reaction catalyst. The reaction temperature for the urethanization reaction is usually 20 to 200° C., and the time for the urethanization reaction is usually 1 to 10 hours, although it varies depending on the presence or absence of a catalyst, the amount added, the type of solvent, the solid content concentration, and the temperature.

During the urethanization reaction, it may be diluted to an arbitrary solid content with an organic solvent inert to isocyanate groups.

Examples of organic solvents include aromatic solvents such as toluene and xylene; ketone solvents such as acetone, methyl ethyl ketone, and methyl isobutyl ketone; ester solvents such as ethyl acetate and butyl acetate; ethylene glycol monoethyl ether acetate and propylene glycol monomethyl ether acetate. and glycol ether systems such as diethylene glycol diethyl ether. These solvents can be used alone or in combination of two or more.

Next, a blocking reaction is performed using the isocyanate group-terminated precursor obtained in the above reaction and a blocking agent. The reaction temperature of the blocking reaction is usually 20 to 200°C, and the blocking reaction time is usually 1 to 20 hours. The amount of the blocking agent charged is 1.0 to 2.0 times, preferably 1.0 to 1.5 times, by molar amount based on the free isocyanate group. If a large amount of heat is generated when adding the blocking agent, add it in several portions or add it dropwise to suppress the rapid heat generation.

Furthermore, if necessary, pigments, dispersion stabilizers, viscosity modifiers, leveling agents, antigelation agents, light stabilizers, antioxidants, ultraviolet absorbers, heat resistance improvers, inorganic and organic fillers, plasticizers, A lubricant, an antistatic agent, a reinforcing material, etc. can be added.

The coating material in the present invention contains the above-mentioned water-based block polyisocyanate. The water-based (aqueous) resin used as the main component of the paint preferably has an active hydrogen group, and specifically, for example, polyurethane resin, polyamide resin, saturated or unsaturated polyester resin, saturated fatty acid or unsaturated resin. Examples include alkyd resins modified with saturated fatty acids, acrylic resins, fluororesins, epoxy resins, and cellulose resins. Furthermore, considering coating performance such as gloss, texture, hardness, durability, flexibility, drying properties, and cost, we recommend using saturated or unsaturated polyester resins, alkyd resins modified with saturated or unsaturated fatty acids, and acrylics. Resins are preferred.

The blending ratio of the water-based block polyisocyanate and the main ingredient in the paint of the present invention is effective isocyanate groups in the water-based block polyisocyanate/active hydrogen groups in the main ingredient = 1/9 to 9/1 (molar ratio), preferably 4/ The molar ratio is 6 to 6/4. If it is outside this range, the coating film will be difficult to cure. Note that the effective isocyanate group of the water-based blocked polyisocyanate is an isocyanate group blocked with a blocking agent, and when the blocking agent dissociates, it becomes an effective isocyanate group that can react with an active hydrogen group.

The method for applying the paint obtained in the present invention is not particularly limited, and may be appropriately selected from known methods. Further, the amount of coating, the thickness of the coating film, etc. may be determined as appropriate depending on the material of the surface to be coated. The conditions for curing the coating film depend on the type of blocking agent, main agent, etc., but the water-based blocked polyisocyanate of the present invention can be sufficiently cured at 80° C. for 30 minutes.

Even if the water-based blocked polyisocyanate of the present invention is an imidazole-based blocking agent that is said to have poor storage stability as a water-based paint, if 2-ethyl-4-methylimidazole is used as a specific blocking agent, the dissociation temperature of the blocking agent can be lowered. It has now become possible to obtain a water-based paint with low storage stability and excellent storage stability. Paints using this water-based block polyisocyanate have mild curing conditions and require less energy during heat curing, making them advantageous in terms of the environment and cost. It has also become possible to paint plastic parts with low heat resistance.

Examples and comparative examples of the present invention will be described in detail below, but the present invention is not limited thereto.

<Example 1> [Production 1 of water-based block polyisocyanate]
Coronate HXR (manufactured by Tosoh Corporation, hexamethylene diisocyanate trimer, NCO content 21.8% by mass, trade name) was placed in a four-necked flask equipped with a stirrer, thermometer, heating device, nitrogen seal tube, and cooling tube. 403 g of MPG-081 (manufactured by Nippon Nyukazai Co., Ltd., polyethylene glycol monomethyl ether, trade name), and 300 g of diethyl diglycol (manufactured by Nippon Nyukazai Co., Ltd., diethylene glycol diethyl ether, trade name) were charged, and the inside of the flask was replaced with nitrogen. The mixture was heated to 80° C. with stirring, and reacted at the same temperature for 4 hours to obtain an isocyanate group-terminated precursor. Subsequently, 217 g of 2-ethyl-4-methylimidazole was charged into the obtained isocyanate group-terminated precursor in two portions so that the reaction temperature did not exceed 80°C. After the initial heat generation subsided, the reaction was carried out at 60°C for 10 hours, and when the NCO group peak (around 2270 cm ^-1 ) disappeared in the infrared absorption spectrum (IR measurement), the water-based block polyisocyanate was cooled to room temperature. Obtained BI-1.

<Comparative Example 1> [Production of block polyisocyanate 2]
Into the same manufacturing apparatus as in Example 1, 452 g of Coronate HXR, 89 g of MPG-081, and 300 g of diethyl diglycol were charged, the inside of the flask was purged with nitrogen, and the temperature was heated to 80°C with stirring. The reaction was carried out for a period of time to obtain an isocyanate group-terminated precursor. Subsequently, 159 g of imidazole was charged into the obtained isocyanate group-terminated precursor in two portions so that the reaction temperature did not exceed 80°C. After the initial heat generation subsided, the reaction was carried out at 60°C for 10 hours, and when the NCO group peak (around 2270 cm ^-1 ) disappeared in the infrared absorption spectrum (IR measurement), the water-based block polyisocyanate was cooled to room temperature. Obtained BI-2.

<Comparative Example 2> [Production of block polyisocyanate 3]
Into the same manufacturing apparatus as in Example 1, 432 g of Coronate HXR, 85 g of MPG-081, and 300 g of diethyl diglycol were charged, the inside of the flask was purged with nitrogen, and the temperature was heated to 80°C with stirring. The reaction was carried out for a period of time to obtain an isocyanate group-terminated precursor. Subsequently, 183 g of 2-methylimidazole was charged into the obtained isocyanate group-terminated precursor in two portions so that the reaction temperature did not exceed 80°C. After the initial heat generation subsided, the reaction was carried out at 60°C for 10 hours, and when the NCO group peak (around 2270 cm ^-1 ) disappeared in the infrared absorption spectrum (IR measurement), the water-based block polyisocyanate was cooled to room temperature. Obtained BI-3.

<Comparative Example 3> [Production of block polyisocyanate 4]
Into the same manufacturing apparatus as in Example 1, 419 g of Coronate HXR, 83 g of MPG-081, and 300 g of diethyl diglycol were charged, the inside of the flask was purged with nitrogen, the temperature was heated to 80°C with stirring, and the The reaction was carried out for a period of time to obtain an isocyanate group-terminated precursor. Subsequently, 199 g of 2-ethylimidazole was charged into the obtained isocyanate group-terminated precursor in two portions so that the reaction temperature did not exceed 80°C. After the initial heat generation subsided, the reaction was carried out at 60°C for 10 hours, and when the NCO group peak (around 2270 cm ^-1 ) disappeared in the infrared absorption spectrum (IR measurement), the water-based block polyisocyanate was cooled to room temperature. Obtained BI-4.

<Comparative Example 4> [Production of block polyisocyanate 5]
Into the same manufacturing apparatus as in Example 1, 431 g of Coronate HXR, 85 g of MPG-081, and 300 g of diethyl diglycol were charged, the inside of the flask was purged with nitrogen, and the temperature was heated to 80°C with stirring. The reaction was carried out for a period of time to obtain an isocyanate group-terminated precursor. Subsequently, 184 g of methyl ethyl ketoxime was charged into the obtained isocyanate group-terminated precursor in two portions so that the reaction temperature did not exceed 80°C. After the initial heat generation subsided, the reaction was carried out at 60°C for 10 hours, and when the NCO group peak (around 2270 cm ^-1 ) disappeared in the infrared absorption spectrum (IR measurement), the water-based block polyisocyanate was cooled to room temperature. Obtained BI-5. Table 1 shows the compositions of the water-based block polyisocyanates BI-1 to BI-5.

[Paint formulation storage stability evaluation]
<Paint P-1>
100g of water-based block polyisocyanate BI-1, 457g of Burnock WE-304 (manufactured by DIC, acrylic emulsion, solid content concentration 45% by mass, hydroxyl value 43mgKOH/g, trade name) and 133g of water were mixed, and paint P- I got 1. 150 g of the obtained paint P-1 was placed in a 200 mL sample bottle and stored in a constant temperature bath at 40°C to check the appearance of the paint. It can be said that it is good if it does not gel for 5 days.

<Paint P-2~5>
Paints P-2 to 5 were obtained with the compositions shown in Table 2 using the same preparation method as paint P-1. The storage stability of paint formulations for paints P-2 to P-5 was evaluated using the same evaluation method as paint P-1.

The paint formulations are shown in Table 2, and the storage stability evaluation of the paint formulations is shown in Table 4.

[Coating film solvent resistance evaluation]
<Paint P-6>
100g of water-based block polyisocyanate BI-1, 196g of Burnock WE-306 (manufactured by DIC, acrylic emulsion, solid content concentration 45% by mass, hydroxyl value 100mgKOH/g) and 100g of water were mixed to obtain paint P-6. Ta. The solvent resistance of the coating film of the obtained paint P-6 was evaluated under the following conditions.
・Test conditions Test piece: Paint P-6 was applied to a SPCC-SB steel plate to a thickness of 100 μm (wet).
Curing: After leaving the above coating film at room temperature for 30 minutes, it is baked for 30 minutes in an 80°C constant temperature bath.
Evaluation: The cured coating film was rubbed with absorbent cotton impregnated with methyl ethyl ketone under a load of 500 g, and if there was no damage to the coating film after 50 strokes, it was said to be good.

<Paint P-7~10>
Paints P-7 to 10 were obtained with the compositions shown in Table 3 using the same preparation method as paint P-6. The solvent resistance of paint films P-7 to P-10 was evaluated using the same evaluation method as paint P-6.

The paint formulation is shown in Table 3, and the evaluation of the solvent resistance of the paint film is shown in Table 4.

As shown in Table 4, the paint using the water-based blocked polyisocyanate of the present invention has excellent storage stability due to the effect of 2-ethyl-4-methylimidazole used as a blocking agent, and can be stored at a low temperature of 80°C. However, it can be seen that the dissociation of the blocking agent was good, that is, the reaction with the main agent progressed sufficiently, and a coating film with excellent solvent resistance was obtained.

Claims (7)

A water-based block polyisocyanate obtained from an imidazole-based blocking agent (a), a polyisocyanate (b), and a nonionic hydrophilic group-containing compound (c),
The imidazole-based blocking agent (a) is 2-ethyl-4-methylimidazole,
A low temperature dissociation type water-based block polyisocyanate, characterized in that the nonionic hydrophilic group-containing compound (c) is at least one selected from the group consisting of polyoxyalkylene monoalkyl ethers and polyoxyalkylene monoesters . The low temperature dissociation type water-based block polyisocyanate according to claim 1, wherein the polyisocyanate (b) is at least one selected from the group consisting of aliphatic diisocyanates and alicyclic diisocyanates. The low temperature dissociation type water-based block polyisocyanate according to claim 1 or 2, characterized in that the polyisocyanate (b) contains an isocyanurate-modified polyisocyanate derived from hexamethylene diisocyanate. The low temperature dissociation type water-based block polyisocyanate according to any one of claims 1 to 3, wherein the nonionic hydrophilic group-containing compound (c) is polyethylene glycol monomethyl ether. The low temperature dissociation type water-based block polyisocyanate according to any one of claims 1 to 4,
A resin composition comprising a main agent having an active hydrogen group. A paint comprising the resin composition according to claim 5. A coating film obtained from the coating material according to claim 6.