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.

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.

Beginners are concerned that if the settling plate is not adjusted properly, the liquid flowing out of the nozzle may cause front surging or back surging, affecting the foaming process. Within two minutes after starting the machine, the reaction speed gradually increases, sometimes requiring adjustments to the settling plate. Adjustments to the settling plate are more critical in low-density and high-moisture-content (MC) formulas.



TDI (Toluene Diisocyanate) flow rate can be calculated to correspond to the scale value, but it is recommended to actually measure the TDI flow rate during the first foaming. Flow rate is too important; if the flow rate is not accurate, everything else will be a mess. It's best to rely on the simplest and most intuitive method of measuring the flow rate.



When mixing powders, the mixed stone powder should be left overnight and production should start the next day. For ingredients containing melamine and stone powder, it is recommended to first mix melamine with polyether for a period of time before adding the stone powder.



Foam machine formulas with long mixing chamber in the machine head or more teeth on the stirring shaft usually have less amine and lower material temperature. Conversely, foam machine formulas with short mixing chamber in the machine head or fewer teeth on the stirring shaft usually have more amine and higher material temperature.



For the same formula, when switching between dual-spray swivel heads and single-spray swivel heads with similar nozzle cross-sectional areas, the requirements for mesh thickness and layers are similar.



For the calibration of minor material flow, one method is to measure the return flow of the minor material, and the other is to calibrate it by dividing the total amount used by the foaming time. When there is a significant difference between the two calibration methods, rely on the data from the second calibration method.



Formulas for high-quality soft foam are usually within an unstable range, such as a low TDI index, low water-to-MC ratio, low T-9 dosage, and low silicone oil dosage.

Surfactants used for foam stabilization, also known as foam stabilizers, are a crucial additive in the production of polyurethane foam plastics. When selecting surfactants, what factors should be considered?



Surfactants can be divided into two types: soft foam surfactants and hard foam surfactants. Let's examine each:



Soft Foam Surfactants:

During the initial foaming stage, soft foam surfactants can dissolve to form polyurea, and in the later stages, they can assist in cell opening and bursting. Therefore, when selecting soft foam surfactants, the following factors need to be considered:



1. The activity of the surfactant;

2. The relationship between the operating range of the surfactant and the required dosage range;

3. The impact of the various components of the surfactant on the operating range.



Hard Foam Surfactants:

Hard foam surfactants have a higher degree of cross-linking, making bubbles more stable. They are commonly used for molded products or foaming in restricted cavities. When selecting hard foam surfactants, the following factors need to be considered:



1. Strong emulsification capability of the raw material components;

2. Ability to control the size of the foam cells effectively;

3. Ability to improve material flowability and ensure uniform density distribution.



Surfactants not only play a role in foam stabilization but also affect foam density, elasticity, tensile strength, and other properties. Therefore, when choosing surfactants, factors such as the activity of the raw materials, operating conditions, and foaming process need to be considered.

Chemical change is the process of producing new substances after the molecular groups of various reactants interact with each other. Many properties of substances are determined by their molecular structures, and understanding the molecular and group structures in polyurethane reactants is instructive for production.



The main indicators of British standard flame retardancy are generally threefold: thermal weight loss (the mass lost when the specified size of sponge is heated at a specified temperature for a specified time, with smaller values indicating better thermal stability); smoke density (the amount of smoke generated when the foam burns, indicating the ease of light passing through the smoke, with smaller amounts of smoke being better); and ease of combustion (the more difficult it is to ignite, with further subdivisions based on ignition time and burning rate).



TDI (toluene diisocyanate) has one benzene ring, MDI (diphenylmethane diisocyanate) has two benzene rings, and crude MDI has multiple benzene rings. Benzene rings are very stable substances, requiring a large amount of energy (bond dissociation energy) to break. As the number of benzene rings increases, the thermal stability of the foam increases (crude MDI > MDI > TDI), making it less likely to decompose when heated. With more benzene rings, there are more carbon atoms in the molecule, resulting in more smoke when incompletely burned (crude MDI > MDI > TDI). From the above, it can be concluded that when one formula decreases the amount of TDI and increases the amount of MDI, the thermal stability of the foam will be enhanced. The thermal weight loss index is likely to pass the British standard test, but the smoke density, which is not easy to pass, will increase. At this point, it is advisable to appropriately increase the amount of melamine cyanurate to reduce smoke density.



The higher the molecular weight of the polyether, the worse the thermal stability, but the better the fire resistance. In the production of high-rebound flame-retardant foam, the amount of flame retardant added is only two-thirds that of regular-density flame-retardant foam, yet the flame retardancy remains very good and does not ignite. However, high-rebound flame-retardant foam is more difficult to pass the British standard test than regular foam (thermal weight loss is difficult to pass).



Flame retardants are not very stable when heated. Since the British standard test emphasizes thermal weight loss, the amount of flame retardant in the formula is the minimum required to pass the flame retardancy test.



When both TDI and water content in the formula decrease while methane content increases, the foam is less likely to ignite. The decrease in intrinsic properties due to the reduction of hard segments results in decreased thermal stability, thus reducing the ability to pass the thermal weight loss index.



When the foam density decreases, the TDI content increases, and both smoke density and thermal stability increase.



Inorganic materials like calcium carbonate and barium sulfate do not decompose when heated during British standard tests, but their addition does not improve the foam's properties, so they are not used in the British standard formula.



Besides selecting raw materials, achieving a balance is also crucial when meeting British standards. For example, both TDI and flame retardants, if given too much or too little, make it difficult to pass the test. Foaming is a balanced science, adjusting the formula is about seeking balance, and selecting raw materials is also about seeking balance.