Polyurethane paint catalyst

Catalyst for two-component polyurethane paint

In the case of two-component polyurethane paint, which is made by mixing polyol and polyisocyanate, which have been combined with fillers, pigments, catalysts, etc., and then painting and curing, the curing speed is faster when a metal catalyst such as a tin-based catalyst is used, but the usable time is shorter, and the mixed paint may cure before it has been used up. This kind of problem can be avoided by using a thermosensitive catalyst.
The “U-CAT SA Series” is a salt of DBU [Figure 1], and is a thermosensitive catalyst that has low catalytic activity at room temperature, but rapidly demonstrates its activity as a urethane catalyst at high temperatures. When these thermosensitive catalysts are used in two-component polyurethane coatings, the pot life at room temperature is extended, solving the problems mentioned above. Furthermore, the special amine-based thermosensitive catalyst U-CAT 1102 has a pot life that is 2 to 3 times longer than that of the DBU salt U-CAT SA® 102 [Table 1].

(Formula 1) Main chemical reactions during polyurethane foam production
〈Resinification reaction〉
OCN-R-NCO + HO-R'-OH → ~CONH-R-NHCOO-R'-O~
Polyisocyanate Polyol Polyurethane
〈Foaming reaction〉
OCN-R-NCO + H2O → ~R-NHCONH~ + CO2↑
Polyisocyanate + Water + Polyurea + Carbon dioxide

Table 1: Curing time and usable time of two-component polyurethane

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Catalyst	Amount used(parts)	Curing time(min)	Pot life(min)
None	ー	24.0	355
U-CAT 1102	0.2 0.4	10.2 5.0	158 110
U-CAT SA102	0.2 0.4	10.3 5.2	64 40
Dibutyltin Dilaurate	0.2 0.6	10.8 5.0	33 17

●Usable time
The time it takes for the viscosity to double at 25℃
●Curing time
The time it takes for the oscillation cycle to begin to decrease in a pendulum-type viscoelasticity
●Temperature increase rate
Room temperature → 80℃ 25℃／min, 80℃ or above 5℃／min
●Polyol 　Polyester polyol 18.2parts ／Solvent 48.0parts
●isocyanates
　Modified TOI 28.8 parts ／ Toluene 5.0 parts

Table 2: Curing time of aliphatic isocyanates (120°C)

Catalyst	Curing time (min)
DBU	5.5
U-CAT SA1	21
U-CAT SA102	50
Triethylenediamine	>180
Dibutyltin dilaurate	3.0
Lead octanoate	26

●Curing time
The time it takes for the gel to harden and be removed from the hot plate of the gelation tester
●PCL 200 88.1 parts ／ 1,4-BG 11.9 parts ／ IPDI 39.1 parts ／ Catalyst 0.5 parts

As shown in Figure 2, the temperature at which the salt in DBU exhibits catalytic activity differs depending on the strength of the acid, so it is possible to select a catalyst that is suitable for the curing temperature of the polyurethane paint.

〈Catalyst for non-yellowing polyurethane paints〉

The above is based on the use of highly reactive aromatic polyisocyanates, but non-yellowing aliphatic polyisocyanates are sometimes used in polyurethane paints. In this case, amine catalysts are said to be less active than metal catalysts and are not normally used. However, DBU and DBU salts (U-CAT SA series) show relatively high catalytic activity even with aliphatic polyisocyanates [Table 2], and are also used in type 2 polyurethane paints.

〈Catalyst for liquid heat-curing polyurethane paints of the block isocyanate type〉

Block isocyanates are isocyanate groups to which volatile active hydrogen compounds (blocking agents, e.g. phenol, MEK oxime, e-caprolactam, etc.) have been added to render them inactive at room temperature. When these block isocyanates are heated, they dissociate and the original isocyanate groups are regenerated [Formula 2]. Using this principle, it is possible to make one-component heat-curing polyurethane paints that are stable at room temperature and cure when heated by mixing blocked isocyanate and polyol in advance [Formula 2], and these are put to practical use in fields such as paints for electrical wires and cationic electrodeposition coatings.

〈Catalyst for liquid moisture-curing polyurethane paints〉

Liquid moisture-curing polyurethane paints are a type of paint that hardens when exposed to moisture in the air, using NCO-terminated urethane prepolymers made by reacting polyol with an excess of poly。
Liquid moisture-curing polyurethane coatings take a long time to cure without a catalyst, but curing is accelerated when a catalyst is used. However, metal catalysts have the problem of poor paint storage stability. In contrast, U-CAT 660M is a special amine catalyst developed for two-component moisture-curing polyurethane, and shows excellent storage stability even when blended with urethane prepolymers. They also have excellent low-temperature curing properties and are used in two-component moisture curing adhesives and sealants (Table 4).

Table 3: Curing temperature (°C) of block isocyanate

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Catalyst	Amount used (parts)	Tack-free time	Viscosity ratio
U-CAT 660M	0.4	22	1.8
Dibutyltin dilaurate	1.2	24	Gelation (2 weeks)

●NCO-terminated polyurethane prepolymer (NCO% 12.4%)
●Tack-free time min (25°C, 50% R.H.)
●Viscosity ratio Viscosity after 20 months at room temperature / initial viscosity

Formula 3) Main chemical reactions of one-component moisture-curing polyurethane paint
〈Synthesis of NCO-terminated polyurethane prepolymer〉
HO-R1 -OH + OCN-R2-NCO → OCN~~~NCO

Polyol Polyisocyanate NCO-terminated polyurethane prepolymer


OCN~~~NCO + H2O → H2N~~~NH2 + CO2↑
NCO-terminated urethane prepolymer
H2N~~~NH2 + OCN~~~NCO → NHCONH~~~

Catalyst for polyurethane foam

〈Catalyst for water foaming〉

There are two types of foaming agents used to make polyurethane foam: (1) water foaming, which uses carbon dioxide produced when water reacts with NCO groups to create uniform bubbles in the polyurethane, and (2) CFC foaming and pentane foaming, which use low-temperature volatile CFC compounds or pentane to create bubbles using the heat generated by the urethane reaction. However, HCFC-141b (CH3-CFCI2), which is currently the main CFC used as a foaming agent, contains chlorine atoms and destroys the ozone layer in the atmosphere, so it was decided to phase it out completely by the end of 2003. HFC-245fa, HFC-365mfc and pentane are being actively considered as alternatives to HCFC-141b. However, there are problems with these next-generation CFCs, such as the fact that they have a non-zero global warming potential, and the fact that pentane is a fire hazard.
In this respect, water has none of these problems and is also inexpensive, so the use of water alone (total water foaming) or a combination of water and other foaming agents is also being widely investigated.
In the case of water-based rigid mold foam that does not use CFCs, the reaction between the water added as a foaming agent and the isocyanate group forms urea bonds, and as the number of urea bonds increases, the polyurethane becomes brittle, which can easily lead to problems such as the peeling of the foam surface skin layer.
In order to solve the above problem of total water foaming, our company has developed a new catalyst, “U-CAT 420A”, as a result of our investigations. The characteristic of this catalyst is that it has very good skin-forming properties, and the surface of rigid polyurethane foam foamed using “U-CAT 420A” is much smoother than that of conventional catalysts. U-CAT 420A has also attracted attention as a catalyst that can improve the surface of foam even when using a combination of next-generation CFC foaming agents and water. Please note that U-CAT 420A is no longer being introduced.

〈Trimerization catalyst〉

Polyurethane foam is also widely used as thermal insulation in houses and buildings. There are two main methods of manufacturing polyurethane thermal insulation: a factory production method, in which the foam is injected between paper or other surface materials or panels to form boards or panels, and a construction site foaming method, in which the polyol and polyisocyanate components are mixed and sprayed on site. In both cases, flame retardancy is required for polyurethane for fire prevention reasons. However, in June 2000, the Building Standards Law was revised to tighten the fire retardancy standards (enforced in June 2002), and measures were taken to improve the fire retardancy of building materials that use polyurethane foam. One such measure is to increase the proportion of isocyanurate rings in the polyurethane foam [Formula 4]. This method makes use of the fact that isocyanurate rings, which are trimers of isocyanate, are extremely stable in relation to heat. With normal amine catalysts, trimerization (isocyanurate formation) does not progress, and potassium octanoate and potassium acetate, etc., were used as catalysts. However, when using these metal catalysts, the tri-addition reaction is difficult to progress at the edges of the foam where the reaction temperature is difficult to raise, so the flame retardancy of the foam is likely to be insufficient. In this respect, when our special amine-based catalyst “U-CAT 18X” is used, the tri-addition rate is high even at the edges of the foam where the reaction temperature is difficult to raise, and foam with excellent flame retardancy can be obtained [Table 5]. U-CAT 18X is used in thermal insulation boards and panels for houses and buildings, as well as for on-site foaming, and is popular for its ability to produce highly flame-resistant foam even in winter.

〈Reactive polyurethane catalyst〉

Ordinary amine-based catalysts remain in the polyurethane foam even after it has been manufactured, and they gradually diffuse out of the foam, causing problems such as vinyl staining (catalysts that have migrated to the polyvinyl chloride sheet promote dehydrochlorination reactions, causing the polyvinyl chloride sheet to discolor) and fogging (catalysts gradually evaporate from the interior materials of a car and adhere to the window glass, causing it to become foggy). In this respect, the urethane catalyst 'U-CAT 2024', which has a reactive group within its molecule, reacts with the isocyanate group during foam production and is incorporated into the polyurethane framework, so it does not remain in a free state within the polyurethane product. For this reason, U-CAT 2024 is mainly used in the automotive industry as a reactive catalyst for manufacturing non-vinyl stain-resistant or anti-fogging polyurethane foam.

Table 5: Isocyanurate Conversion Rate of Flame-Retardant Foam

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Catalyst/th>		Isocyanurate Conversion Rate
Type	Quantity used (parts)	Lower edge of foam	Center of foam	Upper edge of foam
U-CAT 18X	4 8	69 94	95 104	76 94
Potassium octanoate	4 8	57 69	97 105	75 71
Potassium acetate	4 8	54 73	95 100	65 67

●Amount of catalyst used: Parts per 100 parts of polyol
●Isocyanurate ratio: Calculated using the following formula based on the IR chart of the foamed flame-retardant foam
(height of the isocyanurate peak / height of the urethane peak) X 100

Table 6: Our company's polyurethane resin catalysts

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Product name	Composition	Main features and uses
U-CAT SA1	Phenol salt of DBU	A typical grade of thermosensitive catalyst that has low catalytic activity at low temperatures and rapidly increases its catalytic activity at high temperatures. The stronger the acid, the higher the temperature at which catalytic activity is expressed. For two-component polyurethane coatings, elastomers and adhesives, it has a long pot life and rapidly hardens when heated. It is used as a catalyst to promote demolding in polyurethane foam.
U-CAT SA102	2-Ethylhexanoate salt of DBU
U-CAT SA810	o-Phthalic acid salt of DBU
U-CAT SA506	p-Toluenesulfonic acid salt of DBU
U-CAT SA603	DBU formate	A thermosensitive catalyst. There is a large difference in activity between low and high temperatures. It also has excellent performance in dissociating blocked isocyanates, and is particularly suitable for use in electrical wire coatings.
U-CAT 1102	2-Ethylhexanoic acid	A thermosensitive catalyst. It has a long pot life in two-component polyurethane paints. It is used as a catalyst to promote demolding in polyurethane foam.
U-CAT 660M	Bis(2-morpholinoethyl) ether	Catalyst for moisture curing. Even when added to urethane prepolymers, it shows excellent storage stability. It also shows excellent moisture curing properties even at low temperatures of around 5°C.
U-CAT 18X	Triethylmethylammonium 2-ethylhexane salt	Triethylmethylammonium 2-ethylhexane salt A trimerization catalyst. It excels in polyurethane foam with high flame retardance, and is excellent in the dissociation performance of block isocyanate.
U-CAT 2024	1,1’-｛｛3-(Dimethylamino)propyl｝imino｝ bis(2-propanol) (80% content)	A catalyst with a reactive group in the molecule. Used as a non-pinyl stain or anti-fogging reactive urethane catalyst.

The above is an overview of urethane catalysts, focusing on our catalysts.