JPH0689095B2 - Method for producing urethane prepolymer for paint - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention is a urethane precoat for paints, which comprises reacting diols and trimethylolpropane (hereinafter abbreviated as TMP) with toluene diisocyanate (hereinafter abbreviated as TDI). The present invention relates to a method for producing a polymer. More specifically, it relates to a method for producing an improved urethane prepolymer for paint, which comprises preparing a prepolymer having a hydroxyl group at the terminal and then adding TMP to react with excess TDI.

[Conventional technology]

Urethane prepolymers for paints are widely used, such as urethane modified with diisocyanate by polyol, burette modified with water and trimer modified with water.

When a long-chain diol is used when urethane modifying a diisocyanate with a polyol, when used as a paint, the coating film has flexibility and rubber elasticity. On the other hand, when a short chain diol or triol is used, the chain is extended or crosslinked (three-dimensional structure) to impart toughness and rigidity to the coating film.

When using a diisocyanate, such as TDI, the problem is that TDI has a small molecular weight, is volatile, and is toxic. TDI due to its volatility and toxicity
Be careful when handling. From this perspective
It can be said that reducing volatility by reacting a diisocyanate such as TDI with a polyol to increase the molecular weight is an effective method. The following references disclose typical compositions and synthetic methods of extended aromatic diisocyanates using these polyols.

U.S. Pat. No. 2,969,386 shows the preparation of urethane polyisocyanates by reacting aromatic diisocyanates such as TDI with short chain diols or triols such as ethylene glycol and TMP.

U.S. Pat. No. 2,969,386 aims to control the free TDI to 1% or less and further suppress the formation of high molecular weight polyisocyanates.

That is, (a) reacting a diisocyanate in a stoichiometric amount or more with a polyol to suppress an undesired polymer compound. (B) contacting the reaction mixture with an aliphatic or acyclic hydrocarbon, and then reacting the mixture unreacted. Extract the diisocyanate (c) Remove by separating the solvent layer containing unreacted diisocyanate and polyol.

By this method, urethane-bonded aromatic diisocyanate containing no unreacted diisocyanate and polymer compound is obtained.

As another synthetic method, after dissolving TDI in an ester-based solvent, a stoichiometric amount of diols such as 1,3-butanediol necessary to form an isocyanate group at the terminal and TMP A urethane prepolymer is obtained by reacting triols.

This method uses TDI and polyol at an NCO / OH functional group molar ratio of approximately 2.0, so the unreacted TDI at the end of the reaction is 1% or less, there is no need to remove unreacted TDI, and long-term storage stability is good. However, this method produces a large amount of polymer compounds, and the compatibility with various solvents such as polyester polyol, acrylic polyol used as a curing agent, toluene, xylene, etc. used as a diluting agent becomes poor, and paint There is a problem in quality and workability when used as a paint, such as a decrease in NCO group content required as an isocyanate for use and an increase in solution viscosity.

[Problems to be Solved by the Invention]

The above-mentioned U.S. Pat.No. 2,969,386 shows a method for producing a urethane prepolymer by reacting an aromatic diisocyanate such as TDI with a short chain diol or triol such as ethylene glycol or TMP. It is possible to obtain a urethane-bonded aromatic diisocyanate containing few polymer compounds.
Further, when the urethane prepolymer obtained by this method is used as a paint, a strong coating film can be obtained because it has a chain extension and a three-dimensional structure that is crosslinked.

This urethane polymer is usually dissolved in an ester solvent such as ethyl acetate or an aromatic hydrocarbon solvent such as xylene before use. There is no problem if this urethane prepolymer is immediately used as a paint, but if it is stored in a solvent for a long period of time, urethane prepolymer, especially trimethylolpropane 3TDI in which 3 molecules of TDI are added to 1 molecule of trimethylolpropane (hereinafter, However, TMP-3TDI is abbreviated as crystallization and precipitates.

TMP-3TDI has a cross-linked three-dimensional structure when used as a paint, which gives strength to the coating film, but TMP-3TDI tends to crystallize, and even if dissolved in a solvent, crystals will precipitate when stored for a long time. Therefore, the long-term storage stability after production is poor, and there are various methods for improving this drawback, but each has its drawbacks. For example, lower the TMP / diol molar ratio
−3 When TDI is reduced, the strength of the coating film when used as a paint deteriorates.In addition, when the isocyanate group excess rate during prepolymer production is decreased and the amount of polymer in the prepolymer is increased, the storage stability is improved, but Urethane prepolymers for coatings having improved long-term storage stability without causing these defects have been desired because they have drawbacks such as a decrease in NCO% of the polymer, an increase in viscosity, and a poor solvent dilutability. .

[Means for solving the problem]

TMP-3TDI is prone to crystallization. Then, it is possible to prevent crystallization by reducing the absolute amount of TMP-3TDI in the urethane prepolymer. However, TMP-3TDI has a three-dimensional crosslinked structure when used in a coating as a trifunctional isocyanate component and imparts strength to the coating film, so the absolute amount of the trifunctional isocyanate component should not be reduced as much as possible.

As a result of diligent studies, the present inventors have found that when it is used as a urethane prepolymer for paints, polyurethane isocyanate in which TDI-3 molecule is added to two diol molecules having a molecular weight closer to TMP-3 TDI than one in which TDI2 molecule is added to one diol molecule. It has been found that the prepolymer containing polyurethane isocyanate in which 3 molecules of TDI are added to 2 molecules of this diol has a good compatibility with various solvents such as xylene and toluene. It was
Therefore, in order to increase the urethane prepolymer component in which 3 molecules of TDI are added to 2 molecules of diol in the urethane prepolymer composition, a small amount of TDI is added to the diol component and reacted.
A part of the diol-TDI-diol is a prepolymer having a hydroxyl group at the terminal, and TMP is added to this prepolymer, or an excess of TDI is added separately to add 3 molecules of TDI to 2 molecules of diol in the urethane prepolymer. A formulation for increasing the amount of urethane prepolymer components was examined. As a result, it was confirmed that the improved urethane prepolymer composition suppressed crystallization of TMP-3TDI and had good compatibility with a solvent, and completed the present invention.

That is, the present invention relates to a method for producing a urethane prepolymer for paint by reacting one or more kinds of diols and TMP with TDI, and reacting with diols in an amount of at least 2 times the molar amount of TDI, Characterized by mixing TMP into the reaction solution after forming a prepolymer having a hydroxyl group, and further reacting it with excess TDI with respect to the hydroxyl group to form a urethane prepolymer having an isocyanate group at the terminal and removing unreacted TDI. And a method for producing a urethane prepolymer for paint.

An object of the present invention is to provide an improved method for producing a urethane prepolymer for a paint, which can be dissolved in an ester solvent such as ethyl acetate or an aromatic hydrocarbon solvent such as toluene and can be stably stored for a long period of time.

The diols used in the method of the present invention are aliphatic diols such as ethylene glycol, diethylene glycol, triethylene glycol propylene glycol, dipropylene glycol, tripropylene glycol, 1,2-butanediol, 1,3-butane. Diol, 1,
4-butanediol and the like can be mentioned. Trimethylolpropane is used as the triol. Further, as the toluene diisocyanate, 2,4-toluene diisocyanate, 2,6-toluene diisocyanate or a mixture thereof is used.

The method of the present invention comprises a two-step operation. In the first step, diols are charged into a reaction vessel, TDI is added dropwise under an inert gas atmosphere, preferably under a nitrogen atmosphere, to react to obtain a diol prepolymer having a hydroxyl group at the terminal. The diol used in the reaction is used alone or as a mixture of two or more. The NCO / OH functional group molar ratio of the diols and TDI is usually in the range of 0.01 to 0.5, preferably in the range of 0.1 to 0.4.

The reaction temperature and the reaction time are 20 to 100 ° C, preferably 40 to 60
The temperature is in the range of 30 minutes to 5 hours, preferably 1 to 2 hours.

The second step operation is to add the diol prepolymer having a hydroxyl group at the terminal and TMP obtained in the first step in a large excess of TDI in an atmosphere of an inert gas, preferably in a nitrogen atmosphere, to obtain a urethane prepolymer. And The diol prepolymer having a hydroxyl group at the terminal and the trimethylolpropane may be added dropwise in the same order or in any order. The reaction temperature and the reaction time are 20 to 100 ° C, preferably 5
The temperature is in the range of 0 to 80 ° C. for 30 minutes to 5 hours, preferably 1 to 2 hours.

The proportion of TDI used in the reaction is such that the NCO / OH functional group molar ratio is usually in the range of 1.5 to 10, preferably in the range of 4 to 6.

Excess unreacted TDI thus obtained is removed from the reaction solution by a general separation method such as pot distillation, thin film distillation, flash distillation, or extraction to obtain a urethane prepolymer composition.

The urethane prepolymer composition is dissolved in various solvents such as esters such as ethyl acetate and butyl acetate or aromatic hydrocarbons such as toluene and xylene, and is used as a coating material in the form of a 40 to 80% urethane prepolymer solution. To be

〔The invention's effect〕

The urethane prepolymer obtained by the method of the present invention can be stably stored in various solvents for a long period of time, and has a high NCO%,
It is a product with low viscosity and good solvent dilutability, and has a great industrial economical advantage.

〔Example〕

 Next, the method of the present invention will be specifically described with reference to examples.

(Storage) Stability test method To a 20 ml sample tube, add 15 g of the sample and 3.75 g of n-hexane, shake well, store at 30 ° C for 2 weeks, and visually observe.

Sample 15g, xylene 2.25g, TMP-3 in a 20ml sample tube
After adding 1 mg of TDI solid and thoroughly shaking and mixing, store at -5 ° C for 2 weeks and visually observe.

Take 15 g of sample in a 20 ml sample tube and add TMP-3 TDI solids of 0.
Add 2-0.3g and mix well, then store at 20 ℃ for 2 weeks,
Observe visually.

Take 15 g of a sample and 3.75 g of n-hexane in a 20 ml sample tube, add 1 mg of TMP-3TDI solid, shake well, store at 30 ° C for 2 weeks, and visually observe.

(Judgment is ◯ when there is no turbidity or precipitate, and x is when turbidity or precipitation occurs.) Solvent dilution test method Add 1 g of sample and 10 g of xylene to a 20 ml sample tube and mix thoroughly. Visually observe the presence or absence of cloudiness.

(The judgment is ◯ when it is cloudy or no precipitate, and x when it is cloudy or precipitate.) Example 1 Propylene glycol 8 g, dipropylene glycol 8 g,
8 g of 1,3-butanediol was placed in a reaction vessel and under a nitrogen atmosphere 5
After heating to 0 ° C., TDI65 / 354.4 g was dropped and reacted at 50 ° C. for 1 hour. This was added dropwise to 433.8 g of TDI65 / 35 under a nitrogen atmosphere, reacted at 60 ° C. for 2 hours, then 21.5 g of TPM was added dropwise and reacted at 60 ° C. for 2 hours.

Excess TDI was removed from this reaction solution by thin film distillation (170 ° C./1 mmHg), and 230.82 g of the colorless solid obtained was dissolved by adding 76.94 g of ethyl acetate to obtain a 75% diluted product. The viscosity of this solution was 1220 cps / 25 ° C.

The NCO group content of dibutylamine was 13.61% and the solubility in toluene was also good. In addition, crystallization of TMP-3TDI was not observed.

Example 2 6 g of propylene glycol, 6 g of dipropylene glycol,
After putting 6g of 1,3-butanediol in a reaction vessel and heating to 80 ° C under nitrogen atmosphere, TDI65 / 35, 8.4g was added dropwise and then at 80 ° C for 1
After reacting for a time, this was TDI65 / 35 under nitrogen atmosphere, 462.5 g
TMP (21.5 g) was added dropwise to the mixture, and the mixture was reacted at 80 ° C for 2 hours.

Excess TDI was removed from this reaction solution by thin film distillation (170 ° C./1 mmHg), and then 200.5 g of the obtained colorless solid was dissolved by adding 69.17 g of ethyl acetate to obtain a 75% diluted product. The viscosity of this solution was 1160 cps / 25 ° C.

The NCO group content of dibutylamine was 13.28% and the solubility in toluene was also good.

Example 3 8 g of propylene glycol, 8 g of dipropylene glycol,
8 g of 1,3-butanediol was placed in a reaction vessel, heated to 50 ° C. under a nitrogen atmosphere, 11.2 g of TDI65 / 35 was added dropwise, and the mixture was reacted at 50 ° C. for 1 hour. TDI65 / 35, 49 under nitrogen atmosphere
Immediately after dropping into 5.9 g, 21.5 g of TMP was dropped and reacted at 50 ° C. for 2 hours.

Excess TDI was removed from this reaction solution by thin film distillation (170 ° C./1 mmHg), and then 228.50 g of the obtained colorless solid was dissolved by adding 76.17 g of ethyl acetate to obtain a 75% diluted product. The viscosity of this solution was 1560 ops / 25 ° C.

The NCO group content of dibutylamine was 13.65% and the solubility in toluene was also good.

Comparative Example 1 350.22 g of TDI65 / 35 was placed in a reaction vessel under a nitrogen atmosphere, and 50
After heating to 0 ° C., 11.42 g of 1,3-butanediol was added dropwise and reacted at 50 ° C. for 2 hours, then 27.76 g of TMP was added dropwise and further reacted at 50 ° C. for 2 hours.

Thin film distillation of excess TDI from this reaction solution (170 ° C / 1mmHg)
After removal by filtration, 50.62 g of ethyl acetate was added and dissolved in 151.85 g of the obtained colorless solid to obtain a 75% diluted product. The viscosity of this solution was 820 cps / 25 ° C.

The NCO group content of dibutylamine was 13.70%, indicating good solubility in toluene.

Comparative Example 2 405.1 g of TDI65 / 35 was placed in a reaction vessel under a nitrogen atmosphere, and the temperature was 50 ° C.
After heating to 50 ℃, 1,3-butanediol 4g, propylene glycol 4g, dipropylene glycol 4g was added dropwise and reacted at 50 ℃ for 2 hours, then TMP21.5g was added dropwise and at 50 ℃ Reacted for 2 hours. Excess TDI was removed from this reaction solution by thin film distillation (170 ° C / 1 mmHg), and then 53.51 g of ethyl acetate was added and dissolved in 160.54 g of the obtained colorless solid to obtain a 75% diluted product. The viscosity of this solution is 1240
It was cps / 25 ° C.

The NCO group content of dibutylamine was 13.68% and the solubility in toluene was also good.

Comparative Example 3 50.92 g of ethyl acetate and TDI6 were placed in a reaction vessel under a nitrogen atmosphere.
After 5/35 and 104.04 g were added and the temperature was raised to 35 ° C, 24.44 g was added dropwise and reacted at 35 ° C for 2 hours.

Next, 6.1 g of 1,3-butanediol was added dropwise, and at 35 ° C another 2
Reacted for hours. The NCO group content of the obtained prepolymer by dibutylamine is 11.20% and the viscosity is 7800 cps / 25 ° C.
Met.

Table 1 shows the results of the storage stability test and the solvent dilution test of Examples 1 to 3 and Comparative Examples 1 to 3.

Claims (1)

[Claims] 1. A method for producing a urethane polymer for paint by reacting one or more kinds of diols and trimethylolpropane with toluene diisocyanate, and reacting with diols in an amount of 2 times or more moles of toluene diisocyanate, After the prepolymer having a hydroxyl group at the terminal is mixed with trimethylolpropane in the reaction solution, or separately, it is reacted with an excess of toluene diisocyanate with respect to the hydroxyl group to form a urethane prepolymer, and unreacted toluene diisocyanate is removed. A method for producing a urethane prepolymer for a paint, which is characterized.