In September 2021, we received an inquiry from Mr. Abdullah in Saudi Arabia regarding a continuous foaming machine. The client was planning to establish a PU foam factory to produce products for the local and Yemeni markets. He had some basic knowledge about machine usage and selection.

The client had no prior experience in foam production before, so he was particularly concerned about after-sales support and technical assistance.

We began by analyzing the client's target market (specific industry) and understanding the local product requirements (such as foam density, hardness, etc.) to confirm the client's production needs.

Through video conferences, we guided the client through our PU foam production process, providing the client with a concrete understanding of foam production and highlighting the convenience and efficiency advantages of our machines compared to those of other manufacturers.

Drawing upon our more than 20 years of experience in foam foaming, we shared insights with the client about using the machine and common challenges in the foam foaming process, addressing any technical concerns the client may have had.

We also provided the client with factory layout plans to expedite the setup of the entire foam production line while maximizing production efficiency.

Due to the client's high level of trust in our professional service, he ultimately chose us as his supplier for foam machinery and later made repeat purchases for a rebonded foam production line and foam cutting machines.

In December 2021, we received an inquiry from Mr. Hairun in Malaysia. Mr. Hairun is a mattress manufacturer in need of producing rebonded foam. He had limited knowledge about machine usage and selection and had no prior experience with the production process. Therefore, he required guidance from experts who could assist him from the ground up.

We systematically explained the principles of foam production to Mr. Hairun, along with the necessary materials and equipment. We also took him on a tour of our factory to provide a clear understanding of the entire production process.

After understanding Mr. Hairun's preferences for the rebonded foam, including density, softness, and market prices, we offered him the most suitable foam production solution. We also provided him with information on foam production costs and compared raw material prices for his reference.

Based on the client's needs, budget, and existing factory layout, we devised a cost-effective machine configuration and layout plan for his facility, including an assessment of startup costs.

Once the machines were successfully installed, our team of engineers provided Mr. Hairun with one-on-one foam production training. When he successfully produced the foam he desired for the first time, he called us and said, "I am happy with crying, thank you very much!" Afterward, he purchased a batch foam machine from us and continued to reorder foam chemical materials from our company.

The compressive resistance of a foam is related to many factors such as the structure of various chain segments composing the foam, the chemical bonds between molecules, the crystallinity of polymers, the degree of phase separation, the structure of isocyanates, and the proportion of isocyanates used.

1. Slow rebound foam is formed by the reaction of high molecular weight polyols and low molecular weight polyols with isocyanates. The soft segments formed by high molecular weight polyols have large volumes, low crosslink densities, and high activity. They are easy to compress and quickly recover after pressure is removed. The hard segments formed by low molecular weight polyols have small volumes, high crosslink densities, and low activity. They are difficult to compress and also difficult to recover after external forces are removed. This characteristic gives foams their slow rebound feature and is the basis for manufacturing slow rebound foams.

Because the properties of the soft and hard segments in slow rebound foams are different, there is a certain degree of phase separation between them. If there is no phase separation between the segments, the foam body is a tightly bound whole on a macro scale, leading to the phenomenon of "move one hair and the whole body moves," meaning it shrinks as a whole when compressed and expands when pressure is released. However, the microstructure of the foam determines that this situation cannot be achieved completely. Especially in slow rebound foams, various chain segments have different molecular structures, uneven molecular weight distributions, and unavoidable phase separation. Slight phase separation causes some hard segments, due to their low activity, to have difficulty recovering during the recovery process after external forces are removed. These "escapees" more or less restrain the recovery of soft segments, ultimately leading to shrinking.

2. The crystallinity of hard segments, which is stronger than that of soft segments, is also a reason for poor recovery. Materials have similar compatibilities, which also apply in slow rebound foams. Because the hard segments have closer cross-linking points and higher crosslink densities, the small molecules formed are more likely to aggregate together. Due to the presence of hydrogen bonds, these aggregated hydrogen-containing substances enhance the crystallinity of the material, leading to greater cohesive forces. After compression, external forces change the aggregation state of the chain segments, making it easier for polar groups to fuse together. When the external force is released, the new aggregation state, due to strong cohesive forces, is difficult to return to the pre-stressed state, resulting in shrinkage of slow rebound foams.

3. The structure of isocyanates is also a factor affecting the compression resistance of slow rebound foams. TDI is usually used to produce slow rebound foams. Because the two NCO groups in the TDI molecule are at the 2,4- and 2,6- positions, they have a certain angle between them, making them prone to deformation under stress. Especially under hot pressing conditions, significant deformation and heat loss occur, particularly evident in bra cup foams, making recovery from these deformations difficult.

4. The low NCO index of isocyanates used in the preparation of slow rebound foams is also a reason for poor recovery. The NCO index of ordinary foams is usually above 100, while in slow rebound foams , the NCO index is generally between 85-95. This means that 5-15% of the hydroxyl groups do not participate in the reaction. Therefore, although the surface of the foam appears to be a single entity, internally there is a considerable portion of chain segments that are independent of each other.

Solutions for Improving Compression Resistance of Slow Rebound Foams:

1.Use high EO polyether (so-called blowing agent polyether) to replace some slow rebound polyether.

A. High EO polyether has a low hydroxyl value and a large molecular weight. After reacting with isocyanates, the segments formed have molecular weights greater than or close to those formed when ordinary polyether reacts with isocyanates, reducing the degree of phase separation and crystallinity.

B. High EO content polyether has soft and smooth segments, which can provide good slow rebound effects. Additionally, the addition of high EO polyether can effectively improve the low-temperature resistance of slow rebound foams.

2.Add a small amount of polyether-modified polyester to increase the material's cohesive force.

The polyester segments, due to the presence of ester groups, have high internal cohesive forces and good tensile and compressive properties, significantly improving the compressive resistance of slow rebound foams.

3.Use a small amount of high-functionality and high molecular weight polyether as a crosslinking agent, and replace some ordinary polyether with high-activity polyether for slow rebound.

This disrupts the distribution of chain segments, reduces the degree of phase separation, and increases the reaction degree, reducing crystallinity.

4.Use MDI or add MDI to TDI.

MDI has a different structure from TDI and produces foams with better compression resistance and less heat loss. If using MDI, it is best to use modified MDI (with high branching and easy closure of cells); liquid MDI can also be used, as it is intramolecular cyclization and more resistant to compression. Slow rebound foams made with all MDI have much better compression resistance than pure TDI, and many manufacturers are already using this.

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.

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.