Many factors affect the foaming process and final product quality when manufacturing polyurethane flexible foam. Among these, natural environmental factors such as temperature, air humidity, and atmospheric pressure play crucial roles. These factors significantly influence foam density, hardness, elongation rate, and mechanical strength.

1. Temperature:

Polyurethane foaming reaction is highly sensitive, with temperature being a key control factor. As material temperature rises, the foaming reaction accelerates. In sensitive formulations, excessively high temperatures can pose risks like core burning and ignition. Generally, it's essential to maintain consistent temperatures for polyol and isocyanate components. Increasing temperature leads to a corresponding decrease in foam density during foaming.

Particularly in summer, elevated temperatures increase reaction speed, resulting in decreased foam density and hardness, increased elongation rate, yet enhanced mechanical strength. To counter hardness reduction, adjusting the TDI index is advisable. Manufacturers must adjust process parameters according to seasonal and regional temperature variations to ensure product quality stability. 

2. Air Humidity:

Air humidity also affects the foaming process of polyurethane flexible foam. Higher humidity causes reactions between isocyanate groups in the foam and airborne moisture, leading to reduced product hardness. Increasing TDI dosage during foaming can compensate for this effect. However, excessive humidity can raise curing temperatures, potentially causing core burning. Manufacturers need to carefully adjust foam process formulations and parameters in humid environments to ensure product quality and stability.

3. Atmospheric Pressure:

Atmospheric pressure is another influencing factor, especially in areas at different altitudes. Using the same formulation at higher altitudes results in relatively lower foam product density. This is due to atmospheric pressure variations affecting gas diffusion and expansion during foaming. Manufacturers operating in high-altitude regions should take note of this and may need to adjust formulations or process parameters to meet quality requirements.

In conclusion, natural environmental factors significantly impact the foaming process and final product quality of polyurethane flexible foam. Manufacturers must adjust process parameters based on seasonal, regional, and environmental conditions to ensure stable foam density, hardness, and mechanical strength, meeting customer demands and standards.

Polyether Polyol: Hydroxyl Value 36, Primary Hydroxyl > 65%, 60%.

Polymeric Polyol: Hydroxyl Value 28, Copolymer 20%, 40%.

Water: 3%.

80TDI and Polymeric MDI (Viscosity 300mpa): 80:20.

T12: 0.025%.

A33: 0.4%.

HR-3 Silicone Oil: 1%.

HA-1 Crosslinker: 6%.

Di(b-dimethylaminoethyl) Ether: 0.15%.

Phase One: Gas Nucleation Process

The raw materials react in the liquid phase or rely on the generation of gas substances and gas volatilization during the reaction. As the reaction progresses and a large amount of heat is generated, the amount of gas substance generated and volatilized continuously increases. When the gas concentration exceeds the saturation concentration, fine gas bubbles begin to form in the solution phase and rise. As the reaction nears its end, a milky phenomenon appears in the liquid polyurethane material, known as the "milky time."

Phase Two: Self-nucleation Process

In this stage, the gas concentration continues to increase and reaches a certain level. After that, the gas concentration gradually decreases, and new bubbles no longer form. The gas in the solution gradually reaches an equilibrium saturation concentration. During this stage, the viscosity of the liquid material gradually increases, and the gas continuously merges and expands in the gradually viscous liquid phase. The volume of the bubbles continues to expand. The viscous liquid phase forming the outer wall of the bubbles gradually thins. Due to the surface tension relationship between the gas and liquid interfaces, the bubble volume increases from small to large, gradually transforming from a spherical shape into a three-dimensional geometric shape composed of polymer thin films, finally forming an open network structure of three-dimensional micropores. In the synthesis process of polyurethane foam, this stage exhibits polymer volume expansion and foam rising.

Phase Three:

After the gas concentration drops to a certain level, bubbles no longer form. With the permeation of the gas, the concentration continues to decrease, reaching the final saturated equilibrium in the process of the polymeric foam wall transitioning from a viscous liquid state to a non-flowing solid state.

In modern industrial production, polyurethane flexible foam play an important role in various fields such as furniture, automotive seats, and shoe insoles. However, the key technical control points for producing high-quality polyurethane flexible foam plastic products cannot be overlooked. Here are several key technical points in the production process:

Control of Toluene Diisocyanate (TDI):

The optimal isomeric ratio of TDI is 80/20. If this ratio is exceeded, it can lead to the formation of large and closed cells in the foam, prolonging the curing time. Particularly in the production of large block low-density foam products, an excessive isomeric ratio can delay heat release, potentially causing the foam center temperature to remain high for a long time, leading to carbonization and even ignition. If the isomeric ratio is too low, the foam product's density and resilience will decrease, and fine cracks may appear on the foam surface, resulting in poor process repeatability.

Addition of External Blowing Agents:

External blowing agents (water) not only reduce the density of the foam but also improve the softness of the product and help remove reaction heat. To prevent center carbonization in the foaming process of large block foam products, a certain amount of water is usually added. However, as the amount of water increases, the amount of catalyst should also increase correspondingly; otherwise, it may prolong the post-curing time of the foam. Generally, for every 5 parts increase in water, 0.2 to 0.5 parts of silicone oil should be added.

Catalyst Ratio:

Organic tin and tertiary amine catalysts are commonly used to control the NCO-OH and NCO-H2O reactions. By adjusting the ratio of different catalysts, the growth of polymer chains and the foaming reaction can be controlled. Under certain product densities, choosing the appropriate catalyst ratio can control the foam's open-cell rate, cell size, and void load value. Increasing the amount of organic tin catalyst can generally produce foams with smaller cell sizes, but excessive use may increase the closed-cell rate. It is necessary to determine the optimal catalyst dosage through experiments to achieve the best performance of foam products.

Foam Stabilizers:

The role of foam stabilizers is to reduce surface tension of the material, making the foam film wall elastic and preventing foam wall rupture until the molecular chain growth and cross-linking reactions lead to material solidification. Therefore, foam stabilizers play a critical role in the production of one-step polyether sponge and must be strictly controlled in usage.

Temperature Control:

The foam generation reaction is highly sensitive to temperature, and changes in material and foaming temperature will affect foaming operations and physical properties. Therefore, temperature control is one of the important conditions to ensure stable foaming processes. The material temperature is generally controlled at 20-25°C.

Stirring Speed and Time:

The stirring speed and time affect the amount of energy input during the foaming process. If stirring is uneven, a large number of bubbles may appear on the foam surface, leading to defects such as cracking. During mixing of Component A, the speed is 1000r/min; after Component B is added to Component A, the high-speed stirring speed is 2800-3500r/min for 5-8 seconds.

In summary, the key technologies for producing polyurethane flexible foam include controlling TDI, adding external blowing agents, adjusting catalyst ratios, using foam stabilizers, temperature control, and controlling stirring speed and time. Proper control of these technical parameters can ensure the production of stable quality and high-performance polyurethane flexible foam plastic products.

Flame-retardant PU flexible foam, also known as fireproof PU flexible foam, is generally a fireproof material synthesized by adding flame retardants to various polyurethane materials.

Function of flame retardants: They can absorb heat and decompose into non-combustible substances at or near the ignition temperature; they can react with the combustion products of the PU flexible foam to produce difficult-to-burn substances, thereby delaying combustion and allowing the ignition point to self-extinguish.

Common flame retardants: Bromine-based flame retardants, chlorine-based flame retardants, phosphorus-based flame retardants, and inorganic flame retardants.

Flame Retardant Grade and Testing for PU flexible foam

Flame retardant grade refers to the obvious property that a substance has or a material exhibits after treatment, which significantly delays the spread of flames.

Flame retardant testing:

HB: The lowest flame retardant grade in the UL94 standard. It requires that for samples 3 to 13 millimeters thick, the burning rate is less than 40 millimeters per minute; for samples less than 3 millimeters thick, the burning rate is less than 70 millimeters per minute; or extinguished before reaching the 100-millimeter mark.

V-2: After two 10-second combustion tests on the sample, the flame is extinguished within 60 seconds. Combustible material may drop.

V-1: After two 10-second combustion tests on the sample, the flame is extinguished within 60 seconds. There should be no combustible material dropping.

V-0: After two 10-second combustion tests on the sample, the flame is extinguished within 30 seconds. There should be no combustible material dropping.