Application Of PU Foaming Catalyst In Rigid Foam Insulation Materials For Refrigerators And Freezers

What is a pu foaming catalyst? What role does it play in rigid foam insulation materials for refrigerators and ?

Polyurethane foaming catalyst is a key chemical auxiliary agent used to promote the reaction of polyurethane foam molding. In refrigerators, freezers and other refrigeration equipment, polyurethane rigid foam is widely used as a thermal insulation material, and its performance is directly related to the energy saving, service life and overall structural strength of the product.

In the polyurethane foaming process, the main functions of the catalyst are:

Accelerate the reaction between polyols and polyisocyanates (i.e., gel reaction);
Promoting the foaming gas generation reaction (i.e., foaming reaction);
Control the reaction rate and foaming time to obtain the ideal cell structure;
Improves the dimensional stability and mechanical properties of foam.

In short, the catalyst acts like a “switch”, regulating the rhythm and quality of the entire foaming process.

Why do refrigerators and freezers use polyurethane rigid foam as insulation material?

The reason why polyurethane rigid foam is the best choice for refrigerators and freezers is mainly based on the following advantages:

Characteristic	Describe
Very low thermal conductivity	λ ≤ 0.022 W/(m·K), better than traditional materials such as EPS and XPS
High closed porosity	≥90%, strong waterproof and moisture-proof ability
Excellent mechanical properties	High compression strength and good structural stability
Strong self-adhesiveness	Can form an integrated structure with metal inner and outer shells
Green and Environmentally Friendly	Use water or HFCs as blowing agents to reduce ODP impact

In addition, polyurethane rigid foam can fill complex structural cavities and adapt to various special-shaped spaces, providing refrigerator manufacturers with great design flexibility. Therefore, it is one of the current mainstream and efficient insulation materials.

What types of PU foaming catalysts are there? What are their respective characteristics?

According to the different types of catalytic reactions, polyurethane foaming catalysts can be divided into the following categories:

Gelling Catalysts

type	Chemical name	Representative Products	Features
Amine catalysts	Triethylenediamine (TEDA), N-methylmorpholine	Polycat 46, Dabco 33-LV	Accelerate gel reaction and shorten demoulding time
Tin catalyst	Dibutyltin dilaurate (DBTDL)	T-12, T-9	Sensitive to ester groups, suitable for polyester formulations

Blowing Catalysts

type	Chemical name	Representative Products	Features
Weakly basic amines	N,N-Dimethylcyclohexylamine (DMCHA)	Dabco DC2, PC-5	Delay gelation reaction and promote CO₂ release
Strong alkaline amines	Triethylenediamine (TEDA)	Polycat 41	Fast foaming, suitable for low temperature environment

Delayed Action Catalysts

type	Chemical name	Representative Products	Features
Blocked amine catalyst	Bis(N,N-dimethylaminopropyl)urea end-capped	Polycat SA-1, DC 5088	Control reaction delay and extend operation time

Tips: In actual production, multiple catalysts are usually used in combination to achieve the best foaming effect.

How to choose a suitable PU foaming catalyst?

The following factors need to be considered when selecting a catalyst:

Considerations	illustrate
Foam density	The lower the density, the greater the proportion of foaming catalyst should be.
Material temperature and mold temperature	When the temperature is low, the reaction speed needs to be accelerated, otherwise it needs to be slowed down.
Raw material system	Polyether/polyester systems have different sensitivities to catalysts
Environmental requirements	Whether to use tin-free catalyst (such as organic bismuth, zinc)
Production line speed	Continuous production lines require fast demoulding, while intermittent production lines can be slightly slower

For example, in a continuous spraying production line, a combination of fast gel and medium foaming catalyst is recommended; while in intermittent box pouring, a delayed catalyst is preferred to ensure fluidity.

Typical formula parameter reference for PU foaming catalyst

The following is a typical reference for the polyurethane rigid foam formula for refrigerators (based on 100 parts of polyol):

Components	Recommended dosage (phr)	Function
Polyols	100	Main resin
Polyisocyanate (MDI)	130~160	Crosslinking agent
Water (foaming agent)	3.5~5.0	Sources of CO₂
HCFC/HFO physical foaming agent	10~20	Auxiliary foaming
Surfactants	1.5~3.0	Stabilize foam and adjust cell structure
Gel type catalyst	0.3~1.0	TEDA, DBTDL, etc.
Foaming catalyst	0.2~0.8	DMCHA, PC-5, etc.
Delayed Catalyst	0.1~0.5	SA-1, DC 5088, etc.

Experimental suggestions: It is recommended to start with a low dose for preliminary testing, gradually adjust the catalyst ratio, and observe changes in pore uniformity, skin thickness, and demolding time.

Analysis of the influence of catalyst on foam performance

Impact Dimension	Excessive Catalyst Performance	Catalyst too little performance
Cell structure	Large and uneven pore size	Fine pores but easy to collapse
Skin thickness	Thin skin, easily damaged	Thick, dense epidermis
Demolding time	Shortened, prone to premature cracking	Prolongation affects efficiency
Thermal conductivity	Increase, thermal insulation performance decreases	Declining, but rising costs
Mechanical strength	Easy to crack, low compression strength	High strength, but poor elasticity

Therefore, a reasonable combination of catalysts is the key to achieving high-performance foams.

Development trend of environmentally friendly catalysts

As global awareness of environmental protection increases, the use of traditional tin catalysts is gradually being restricted due to potential toxicity issues. In recent years, environmentally friendly catalysts have gradually become a research hotspot:

type	Features	Application Status
Organic bismuth catalyst	Non-toxic, high catalytic activity	Already used in some high-end products
Organozinc Catalyst	Low cost and good stability	Suitable as a replacement for DBTDL
Bifunctional amine catalyst	Possesses both gel and foaming functions	Emerging direction, still in the promotion stage

Policy promotion:

EU REACH regulations have restricted the use of tin-containing catalysts;
China’s “Guidelines for Industrial Structure Adjustment” encourages the use of green catalysts.

In the future, developing new catalysts that are highly efficient, less toxic, and less expensive will become the mainstream direction of the industry.

FAQ

Q1: Is polyurethane foaming catalyst toxic?

A: Most commercial catalysts are low-toxic chemicals, but they may decompose into harmful substances at high temperatures. It is recommended to wear protective equipment and comply with safety regulations when operating.

Q2: Can the catalyst be completely omitted?

A: No. Without a catalyst, polyurethane reacts very slowly and cannot form qualified foam.

Q3: Will the catalyst affect the flame retardant properties of the foam?

A: Some amine catalysts may reduce flame retardancy and need to be used in conjunction with the addition of flame retardants.

Q4: How to determine whether the catalyst is ineffective?

A: The symptoms include longer foaming time, coarse foam cells, and difficulty in demoulding. A preliminary judgment can be made by changing the batch or testing the pH value.

Summarize

Polyurethane foaming catalyst plays an indispensable role in the rigid foam insulation materials of refrigerators and freezers. It not only determines the molding quality of the foam, but also directly affects the energy-saving performance and service life of the product.
At present, with the tightening of environmental regulations and technological progress, catalysts are developing in the direction of non-toxic, high-efficiency, multi-functional and low-cost. Enterprises should actively pay attention to the development of new materials and new processes, and reasonably select and optimize catalyst formulas to enhance product competitiveness.