JPS63118377A - Curing of urethane coating film - Google Patents

Abstract

PURPOSE:To quickly obtain a coating film free from foaming, good in appearance, outstanding in impact, heat, water, moisture and chemical resistances, by coating a base material with a specific urethane resin composition followed by treatment with water vapor. CONSTITUTION:An urethane resin composition containing (1) an isocyanate group-terminated urethane prepolymer (e.g., a product made by reaction between an excess amount of polyisocyanate and a compound or polymer having in one molecule two or more OH groups) and (2) a ketimine compound (e.g., a product made by condensation between polyamine and ketone) is coated on a base material for e.g., automobiles followed by treatment with water vapor, thus accomplishing the objective curing of the urethane coating film. The blend ration of the urethane prepolymer to the ketimine compound is pref. such that the ratio of the ketimine to the NCO group falls between 0.5 and 2.0.

Description

[Detailed description of the invention] Official Agency The present invention relates to a method for rapidly curing urethane coatings.

■Ibara■ Urethane resin has toughness, chemical resistance, adhesion to base materials,
Due to its excellent abrasion resistance and gloss, it is widely used in paints, printing inks, adhesives, etc.

For such urethane resins, -C, -liquid type and two-liquid type are known. - The liquid type consists of a so-called urethane prepolymer with a molecular weight of 500 to 10,000, which has two or more isocyanate groups in the molecule, and after being applied to a substrate, the isocyanate groups are usually reacted with moisture in the air. The polymer is cured by polymerization and crosslinking. The two-component type uses a base agent that has two or more active hydrogens in its molecule, for example, two or more hydroxyl groups.
A polyol having two or more inocyanate groups and a curing agent made of a polyisocyanate compound or urethane prepolymer having two or more incyanate groups in the molecule are mixed in a predetermined ratio and applied to a substrate, and the isocyanate groups and active hydrogen are mixed. It is polymerized, crosslinked and cured by the reaction of

In curing the urethane resin as described above, the reaction between the urethane prepolymer or polyisocyanate compound and water or active hydrogen is said to be relatively fast. However, when urethane resin is continuously applied to a base material and cured and dried in a short time, such as in line painting or printing, the curing speed of urethane resin using the above reaction is not practical. Therefore, conventionally, a catalyst is added to the urethane resin and baked at a high temperature of 100° C. or higher, and in some cases, 200° C. or higher, for high-speed curing.

However, in general, when a catalyst is added to a urethane resin, its storage stability decreases, and in particular, in a two-component type, the pot life after mixing the base resin and curing agent is short, and workability is also poor. Furthermore, high temperature baking is not particularly applicable to plastic substrates because drying requires a large amount of energy and also causes deterioration of the substrate.

On the other hand, some urethane resins that can be cured at high speed are already known. For example, a urethane resin composition comprising a polyol having active hydrogen, a polyisocyanate and a diamine is described in British Patent No. 1.109.246. This urethane resin composition cures quickly, but
On the other hand, its pot life is extremely short and its workability is significantly inferior.

To this end, the above-mentioned patent specification also describes that the pot life can be extended by preheating diamines and ketones and adding them to a mixture of polyol and polyisocyanate. As is well known, when a diamine and a ketone are heated, a ketimine compound is produced. In the urethane resin composition containing such a ketimine compound, the ketimine compound reacts with moisture in the air to regenerate diamine, and this diamine polymerizes and crosslinks and cures the polyisocyanate. Therefore, in a urethane resin composition containing a ketimine compound, the reaction between the ketimine compound and water becomes the rate-determining step in the crosslinking reaction of polyisocyanate, so that the pot life of the urethane resin composition can be extended, but on the other hand,
It will take a long time to dry.

Therefore, the present inventors conducted intensive research on a method that can rapidly cure a urethane resin composition containing a ketimine compound, and as a result, the present inventors applied a urethane resin composition to a base material. The inventors discovered that high-speed curing can be achieved by subsequently treating the material with steam, leading to the present invention.

Means for Solving the Problems The method of curing a urethane coating film according to the present invention is to apply a urethane resin composition containing a urethane prepolymer having an isocyanate group at the end and a ketimine compound to a substrate, and then apply the urethane resin composition to a base material, and then apply the urethane resin composition to a base material. It is characterized by processing.

The urethane prepolymer used in the present invention is a relatively low molecular weight polyurethane having a free isocyanate group at the end of the molecule obtained by reacting an excess amount of polyisocyanate with a compound or polymer having two or more hydroxyl groups in the molecule. be.

Examples of the polyisocyanate used to produce such a urethane prepolymer include trimethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, pentamethylene diisocyanate, 1,2-propylene diisocyanate, 1.
2-butylene diisocyanate, 2,3-butylene diisocyanate, 1,3-butylene diisocyanate, 2
, 4.4- or 2.2. Aliphatic diisocyanates such as 4-1-limethylhexamethylene diisocyanate, 2,6-lifecyanatomethylcaproate, e.g.
3-cyclopenkune diisocyanate, 1,4-cyclohexane diisocyanate, 1,3-cyclohexane diisocyanate, 3-isocyanatomethyl-3,5゜5
-trimethylcyclohexyl isocyanate, 4.4'-methylenebis(cyclohexyl isocyanate), methyl-2,4-cyclohexane diisocyanate, methyl-2,6-cyclohexane diisocyanate, 1.4
-bis(isocyanatomethyl)cyclohexane, 1.3
-Cycloalkylene diisocyanates such as bis(isocyanatomethyl)cyclohexane, such as m-phenylene diisocyanate, p-phenylene diisocyanate, 4゜4゛-diphenyl diisocyanate, 1.5-
Naphthalene diisocyanate, 4,4'-diphenylmethane diisocyanate, 2,4- or 2,6-dolylene diisocyanate or mixtures thereof, 4,4'-i-
Aromatic diisocyanates such as luidine diisocyanate, dianisidine diisocyanate, 4.41-diphenyl ether diisocyanate, 1.3- or 1.4-xylylene diisocyanate or mixtures thereof, ω, ω
°-Diisocyanate 1,4-diethylbenzene, 1
．． Aroaliphatic diisocyanates such as 3- or 1,4-bis(α,α-dimethylisocyanatomethyl)benzene,
For example, triisocyanates such as triphenylmethane-4,4',4''-triisocyanate, 1.3.5-triisocyanatebenzene, 2,4.6-1-liisocyanatetoluene, 4.4°-diphenyldimethyl Examples include tetraisocyanates such as methane-2,2', 5,5'-tetraisocyanate, polymerized polyisocyanates such as dimers and dimers of tolylene diisocyanate, and polyphenylpolymethylene polyisocyanate. These may be used alone or as a mixture of two or more.

In addition, 2
Examples of compounds or polyols having 2 or more hydroxyl groups include ethylene glycol, 1.2-propylene glycol, 1.3-propylene glycol, 1.3-butylene glycol, 1.4-butylene glycol, 2I
3-butylene glycol, 1,6-hexanediol,
Neopentyl glycol, 1,4-cyclohexanediol, ■,4-cyclohexane dimetatool, hydrogenated bisphenol A.

Diethylene glycol, triethylene glycol, dipropylene glycol, tripropylene glycol, 1.
Glycols such as 3-xylylene glycol, 1,4-xylylene glycol, 1,5-bentanediol, 2゜4,4-trimethyl-1,3-bentanediol, such as glycerin, trimethylolpropane, trimethylol Low molecular weight polyols such as ethane, 1,2,6-hexanetriol, pentaerythritol, sorbitol, etc., for example, molecular weight 300-10000 and functional group number 2-2
Polyether polyols, polyester polyols, polyether ester polyols, etc. mentioned in No. 4 can be mentioned.

Examples of the polyether polyol include, for example, ethylene glycol, propylene glycol, glycerin, pentaerythritol, etc., as an initiator;
Examples include those obtained by ring-opening addition polymerization of ethylene oxide, propylene oxide, or a mixture thereof, and polytetramethylene ether glycol obtained by ring-opening polymerization of tetrahydrofuran.

Further, as the polyester polyol, for example,
Condensation of di- or tribasic acids such as maleic acid, fumaric acid, succinic acid, adipic acid, sebacic acid, azelaic acid, phthalic acid, isophthalic acid, terephthalic acid, trimellidic acid, etc., and divalent to tetrahydric polyhydric alcohol. Examples include those obtained by reaction. Examples of divalent to tetravalent polyhydric alcohols include ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, 1.3-butylene glycol, 1.4-butylene glycol, 1.
5-bentanediol, 1,6-hexanediol, neopentyl glycol, decamethylene glycol, 2,
4.4-) trimethyl-1,3-bentanediol, cyclohexanediol, cyclohexane dimetatool,
Examples include xylylene glycol, hydroquinone bis(hydroxyethyl ether), hydrogenated hisphenol A, trimethylolpropane, glycerin, 1,2,6-hexanetriol, pentaerythritol, and castor oil. Also used are oil-modified polyester polyols in which higher fatty acids such as coconut oil fatty acids, linseed oil fatty acids, soybean oil fatty acids, cottonseed oil fatty acids, tung oil fatty acids, and castor oil fatty acids are blended into the acid component.

Examples of the polyether ester diol described above include those obtained by reacting the polyether polyol with a polybasic acid to form a polyester, as well as those obtained by a ring-opening copolymerization reaction of an epoxy compound and an acid anhydride. Examples include those having both polyether and polyester segments in the molecule.

Furthermore, as polyols, polybutadiene diol,
Polyisoprene diol and the like can also be used.

The polyols mentioned above can also be used alone or as a mixture of two or more.

The reaction between the polyisocyanate described above and a compound or polyol having two or more hydroxyl groups in the molecule for producing a urethane prepolymer can be carried out without a solvent, but usually, for example, ethyl acetate, acetic acid, etc. The reaction is preferably carried out in an organic solvent containing no active hydrogen, such as butyl, cellosolve acetate, toluene, xylene, methyl ethyl ketone, methyl isobutyl ketone, acetone, tetrahydrofuran, dioxane, or the like. The reaction temperature is about 10
-150°C, preferably about 40-90°C. If the reaction is slow, a conventional urethanization reaction catalyst such as a metal compound, an organometallic compound, an organic amine, etc. may be added as necessary.

The ketimine compound used in the present invention can be obtained by a condensation reaction between a polyamine and ketones. Examples of the polyamine compounds include ethylenediamine, propylene diamine, hexamethylene diamine, xylylene diamine, bis(aminomethyl)cyclohexane, methylenebis(cyclohexylamine), 3-aminomethyl-3,5,5-trimethylcyclohexylamine, 1 -methyl-2,4-diaminocyclohexane and the like. These polyamine compounds may be used alone or as a mixture of two or more.

Furthermore, in the present invention, polyamide amines obtained by reacting excess amounts of these polyamine compounds with polybasic acids such as succinic acid, glutaric acid, adipic acid, azelaic acid, sebacic acid, and dimer acid may also be used as polyamines. Can be done.

In addition, examples of ketones used in the production of ketimine compounds include acetone, methyl ethyl ketone, diethyl ketone, methyl isobutyl ketone, diisobutyl ketone,
Any of aliphatic, aromatic, and alicyclic ketones can be used, such as cyclohexanone, acetophenone, and benzophenone.

The reaction between the above polyamine compound and ketones can be carried out without a solvent, but it is usually carried out in an organic solvent such as ethyl acetate, butyl acetate, cellosolve acetate, toluene, xylene, tetrahydrofuran, dioxane, etc. is suitable. In this reaction, it is usually preferable to use an excess of ketones and to use the remaining ketones as a solvent for the urethane resin composition.

The reaction temperature between the polyamine compound and ketones is about 10-2
50°C, preferably about 50-150°C. In the reaction between a polyamine compound and a ketone, water generated as the reaction progresses is removed from the reaction system, and the reaction is terminated when no free amino groups are present in the reaction mixture.

The urethane resin composition in the method of the present invention is used as a two-component type. That is, in the method of the present invention, the urethane prepolymer obtained as described above and a ketimine compound are mixed to form a urethane resin composition, which is applied onto a substrate. In such a urethane resin composition, the mixing ratio of the urethane prepolymer and the ketimine compound is such that the ratio of ketimine groups to isocyanate groups is 0.2 to 3.0;
Preferably, it is in the range of 0.5 to 2.0.

In the present invention, the urethane resin composition containing the urethane prepolymer and the ketimine compound does not need to contain an organic solvent, but is usually a liquid composition containing an organic solvent that does not have active hydrogen. is preferred. Examples of organic solvents without active hydrogen include esters such as ethyl acetate, butyl acetate, and cellosolve acetate, ketones such as acetone, methyl ethyl ketone, and methyl isobutyl ketone, and aromatic solvents such as toluene and xylene. Hydrocarbons such as cyclic ethers such as tetrahydrofuran and dioxane can be used. Among these organic solvents, acetone, cellosolve acetate, methyl ethyl ketone, tetrahydrofuran, dioxane, etc. not only easily dissolve the urethane prepolymer and ketimine compound, but also promote the penetration and diffusion of water vapor in the coating film of the urethane resin composition. It is a solvent that can be particularly preferably used because of its effectiveness.

In the method of the present invention, when the urethane resin composition is used as a paint or ink, it is preferable to mix pigments, leveling agents, antifoaming agents, stabilizers, etc. into the solution of the urethane prepolymer or ketimine compound in advance. .

According to the method of the present invention, after applying the urethane resin composition obtained as described above to a substrate to form a coating film,
This is treated with steam. Here, the method of steam treatment of the urethane resin coating film is not particularly limited, but it is usually carried out by leaving the base material in a closed chamber filled with steam. The time for steam treatment depends on the composition of the urethane resin composition used and the thickness of the coating film, but usually
This treatment takes about 1 to 10 minutes, and the urethane resin composition provides a dry and cured coating film.

In addition, in the present invention, the base material is not limited at all, and for example,
Examples include wood, paper, glass, ceramics, various metals and alloys, slate, flexible boards, perlite boards, asbestos slates, plastics, and composite materials thereof.

As described above, according to the method of the present invention, the urethane resin composition contains a ketimine compound together with the urethane prepolymer, so such a resin composition is applied to a substrate to form a coating film. Thereafter, it can be dried and hardened by treating it with steam for about 1 to 10 minutes. Moreover, since the urethane resin composition has a long pot life, it has excellent workability. Therefore, the method of the present invention can be advantageously used in fields such as line painting and printing, where a urethane resin composition is continuously applied onto a substrate and dried and cured in a short period of time.

Furthermore, the resulting cured coating film does not have any foaming and not only has an excellent appearance, but also has excellent impact resistance, heat resistance, water resistance, moisture resistance, chemical resistance, etc., so it is suitable for use as paint for automobiles, for example. suitable for

EXAMPLES The present invention will be explained below with reference to Examples, but the present invention is not limited to these Examples in any way. In addition, in the following, parts mean parts by weight.

Example 1 524 parts of 4.4'-methylenebis(cyclohexyl isocyanate) were dissolved in 405 parts of xylene and 1619 parts of methyl ethyl ketone. In this solution there are molecules f 100
750 parts of polybutylene adipate with a molecular weight of 2000
Add 750 parts of polybutylene adipate and dissolve it uniformly, further add 0.2 part of tin octylate,
Heating at a temperature of 75-80℃ for 5 hours, solid content 50%,
Urethane prepolymer solution with amine equivalent weight 2024 404
I got 8 copies.

On the other hand, 169 parts of 3-aminomethyl-3,5,5-)limethylcyclohexylamine were added to 5 parts of methyl isobutyl ketone.
The mixture was dissolved in 33 parts, heated to 110° C., and nitrogen gas was blown into the solution to remove the produced water, and the reaction was allowed to proceed until no water was produced. The azeotropic methyl isobutyl ketone was returned to the reaction solution. Thus, ketimine compound solution 666 with solid content of 50% and having one ketimine bond per 333 parts
I got the department.

785 parts of titanium oxide (Tiebake R-930 manufactured by Ishihara Sangyo Co., Ltd.) was kneaded with 2024 parts of the urethane prepolymer solution, diluted with 785 parts of ethyl acetate, and then 333 parts of the ketimine compound solution was mixed therewith. The pot life of the urethane resin coating composition thus prepared was 2.
It was 0 minutes.

When this coating composition was spray applied to an aluminum plate to a thickness of 50 μm and left in a closed room at 50°C containing saturated steam, a glossy, tough white coating that was completely dry was obtained after 3 minutes. . The physical properties of this coating film were as follows.

Tensile strength 300kg/cd elongation rate
350% tear strength 85 kg/cI (Comparative Example 1) The coating composition of Example 1 was coated on an aluminum plate at a thickness of 50°C.
When the film was left in a closed room at a relative temperature of 50% and a temperature of 50° C. after being coated, it took 20 minutes or more to obtain a dry coating film.

Comparative Example 2 169 parts of 3-aminomethyl-3,5,5-trimethylcyclohexylamine was dissolved in 169 parts of methyl isobutyl ketone to obtain a polyamine solution with a solid content of 50% and an amine value of 332.

Urethane prepolymer solution 202 obtained in Example 1
4 parts and 785 parts of the same titanium oxide as in Example 1 were kneaded and diluted with 785 parts of ethyl acetate.
69 parts were mixed. This coating composition, after mixing,
It gelled after minutes.

Example 2 Saturated linear dibasic acid (0SK-DA 5L- manufactured by Okamura Oil Co., Ltd.)
16) 120 parts of ethylenediamine was gradually added to 286 parts, heated to a temperature of 170 to 180°C, and while removing the water produced with nitrogen gas, the reaction was carried out until no water was produced, resulting in a polyamine with an amine value of 303. A compound was obtained, and 734 parts of methyl isobutyl ketone was added thereto to dissolve it.

A solution of this polyamine and methyl isobutyl ketone is
While heating at 10 to 120° C., nitrogen gas was blown into the reactor to remove produced water, and the reaction was allowed to proceed until no water was produced. The azeotropic methyl isobutyl ketone was returned to the reaction solution.

In this way, 1068 parts of a ketimine compound solution having a solid content of 50% and one ketimine bond per 534 parts was obtained.

On the other hand, 400 parts of 1,3-bis(isocyanatomethyl)cyclohexane and 27 parts of trimethylolpropane were mixed, and this mixture was heated to a temperature of 75 to 80°C for 4 hours to react, and then the unreacted 1,3-bis(isocyanatomethyl)cyclohexane was extracted and removed, and the extraction residue was dissolved in ethyl acetate to obtain a urethane prepolymer solution with a solid content of 50% and an isocyanate group content of 7.3%.

A coating composition was prepared by mixing 1,150 parts of this urethane prepolymer solution with 1,068 parts of the ketimine compound solution. This was applied to a thickness of 50 μm on an iron plate, and then left in a closed room at 50° C. containing saturated steam for 3 minutes to obtain a completely dry, glossy and tough coating film. The physical properties of this coating film were as follows.

Pencil hardness H Adhesion 100/100 Erichsen extrusion test 81℃m Impact resistance (Dupont type) 1/2'x500gx50
cm Bending resistance 2 Dragons Solvent resistance Ethyl acetate Passed Xylene Passed Ethanol Passed Also, when the above coating composition was similarly applied to an iron plate and left in a closed room at a relative humidity of 50% and a temperature of 50'C, It took more than 15 minutes to obtain a dry coating.

Example 3 336 parts of 1.6-hexamethylene diisocyanate were dissolved in 367 parts of xylene and 1469 parts of methyl ethyl ketone, and 1500 parts of polycaprolactone diol having a molecular weight of 1500 was uniformly dissolved in this solution. Furthermore, after adding 0.2 parts of dibutyltin dilaurate, 75 to 8
Heating at a temperature of 0''C for 4 hours yielded 3672 parts of a urethane prepolymer solution with a solids content of 50% and a weight of 11836 parts per amine.

1446 parts of the same titanium oxide as in Example 1 was kneaded into 3672 parts of this urethane prepolymer solution, and 144 parts of ethyl acetate was mixed with 3672 parts of this urethane prepolymer solution.
After diluting with 6 parts, 666 parts of the ketimine compound solution prepared in Example 1 was mixed therewith. The pot life of the coating composition thus prepared was 25 minutes.

The above coating composition was spray applied to an aluminum plate to a thickness of 50 μm, and then left in a closed room at 50° C. containing saturated water vapor. After 4 minutes, a glossy and tough white coating was completely dried. The physical properties of this coating film were as follows.

Tensile strength 250kg/crA elongation rate
400% Tear strength: 60 kg/cot In addition, when the above coating composition is similarly applied to an aluminum plate and left in a closed room at a relative humidity of 50% and a temperature of 50°C, in order to obtain a dry coating film, It took over 17 minutes.

Furthermore, when the polyamine solution prepared in Comparative Example 2 was used in place of the ketimine compound solution in the preparation of the coating composition, the pot life was 4 minutes.

Example 4 444 parts of 3-isocyanatomethyl-3,5,5-trimethylcyclohexyl isocyanate was dissolved in 289 parts of xylene and 1155 parts of methyl ethyl ketone. In this solution, 1000 parts of polyethylene butylene adipate having a molecular weight of 1000 was uniformly dissolved, and then tetra-
n-Butyl-1,3-diacetoxydistanoxane 0.
Add 15 parts and heat at a temperature of 75 to 80°C for 6 hours.
2,888 parts of a urethane prepolymer solution having a solid content of 50% and a weight of 11,444 parts per amine was obtained.

1185 parts of the same titanium oxide as in Example 1 was kneaded with 2888 parts of this urethane prepolymer solution, diluted with 1185 parts of methyl ethyl ketone, and then 666 parts of the ketimine compound solution prepared in Example 1 was mixed therewith. The pot life of the coating composition thus prepared was 25 minutes.

This coating composition was spray applied to an aluminum plate to a thickness of 50 μm, and then left in a closed room at 50° C. containing saturated steam. After 4 minutes, a glossy and tough white coating was completely dried. The physical properties of this coating film were as follows.

Tensile strength 350kg/aa elongation rate
300% Tear strength 80kg/crA Furthermore, when the above coating composition was similarly applied to an aluminum plate and left in a closed room at a relative humidity of 50% and a temperature of 50°C, it was difficult to obtain a dry coating film. It took more than 20 minutes.

Furthermore, when the polyamine solution prepared in Comparative Example 2 was used in place of the ketimine compound in the preparation of the coating composition, the pot life was 4 minutes.

Claims (1)

[Claims] (1) A method for curing a urethane coating film, which comprises applying a urethane resin composition containing a urethane prepolymer having an isocyanate group at the end and a ketimine compound to a base material, and then treating the composition with water vapor.