Introduction to polyurethane and its raw materials

Classification of polyurethane

1.According to different raw materials and formulation changes, polyurethane foam is divided into flexible, semi-rigid, and rigid foams.

-Flexible: seats, headrests, mattresses

-Semi-rigid: armrests, steering wheels

-Rigid: steering wheel cores, cold storage insulation and waterproofing

2.Classified by polyol type: polyester-based and polyether-based; we mainly use polyether-based.

3.By ISO classification: TDI, TM, MT, MDI.

4.By foaming method: block foam, molded foam, and spray polyurethane foam.

Applications:

-Block foam: composite foam, sponge

-Molded foam: seats, armrests, headrests

-Spray foam: cold storage insulation and waterproofing

Polyurethane foam formation

Mixing: ISO and POL are mixed in the mixing head.

Cream time: Foam does not rise immediately after mixing. It flows for a while, then turns white and begins to rise.

Cream time is the interval from end of mixing to foam rise.

Longer cream time means better flowability, aiding material distribution in molds.

Rise: Related to foam filling ability and curing speed.

Stringing: Indicates degree of foam gelation.

Shrinkage: Key indicator of foam openness and stability.

Polyurethane raw materials

Mainly composed of ISO part (black material or component B) and polyether blend (white material or component A).

ISO component: TDI, TDI&MDI, MDI

Polyether blend component: Polyether polyol and polyester polyol

Additives:

-Catalysts: foaming amine catalysts and gelling amine catalysts

-Foam stabilizer: silicone oil

-Blowing agents: H₂O, F-11, F-12, dichloromethane

-Flame retardants: ammonium phosphate, antimony oxide, halogenated compounds (hydrocarbons, alcohols, esters, ethers), aluminum hydroxide

-Anti-aging agents

-Chain extenders: triethanolamine (used by us)

-Pigments

-Mold release agents

ISO component of polyurethane raw materials

TDI (Toluene diisocyanate): Mainly 2,4- and 2,6-isomers. Three main industrial products: T100, T80/20, T65/35

-Low density foams

-Good tensile strength and rebound

-Poor aging resistance

-High hazard

MDI (Methylene diphenyl diisocyanate): Modified MDI (MMDI) includes MDI + (4,4-MDI, 2,4-MDI)

High reactivity, fast reaction

Less dependent on mold temperature, suitable for low-temp molds

Fast post-curing

Excellent aging resistance

Poor tear strength

Low cost

Ideal for high hardness, high-density products

TDI&MDI:

To reduce cost, MDI is added to TDI.

Common ratios: TM70/30, TM80/20, depending on formulation.

Polyether polyols: Currently using GP-1618, ZS-104

Sponge-related parameter descriptions:

Functionality: Higher functionality improves elasticity and aging resistance

Primary hydroxyl content: Higher content means higher reactivity

Viscosity: Lower viscosity improves material flowability and processing performance; related to solid content—higher solid content increases viscosity

Solid content: Higher content leads to harder foam products

Formulation ratio: Critical to product hardness, physical properties, and cell openness

Future trends of polyether and polyester polyols:

High-functionality polyether polyols

High solid content, low viscosity polymer polyols

Low volatility

High molecular weight with narrow molecular weight distribution

Increased primary hydroxyl content

Polyurethane chemistry

Two main reaction equations:

Note: These are the two main reactions. Over 10 side reactions exist, so controlling balance is key to desired results.

Polyurethane chemistry: Ratio of A and B components

Based on equivalent ratio, calculate how many grams of B are needed per 100 g of A.

Foaming index (INDEX): ISO actual usage / ISO theoretical usage × 100

INDEX typically ranges from 60–110.

Higher INDEX = harder foam

Ideal INDEX:

-TDI systems: 90–105

-MDI systems: 85–95

For seat foams (TDI or TDI&MDI systems), component ratio:

-A component = 100

-B component (soft foam) = 30–50

-B component (rigid foam) = determined by hydroxyl value and water content, usually much higher than soft foam

Polyether blend

A uniform mixture of polyether, water, catalysts, and stabilizers in specific proportions; also known as component A.

Typical formulations for cold-cured flexible foam and performance: