When establishing a polyurethane foam factory, careful consideration of the site selection and construction conditions is crucial for its success. Several principles guide the selection of the factory site:

Firstly, the principle of optimizing and reorganizing existing resources of project units is essential. This ensures that the factory can make the best use of available resources without unnecessary duplication.

Secondly, the principle of saving land and reducing investment is vital. By selecting a site that is efficient in its land use, the factory can minimize costs and maximize efficiency.

Thirdly, the principle of facilitating transportation and reducing product production costs is significant. A location that allows for easy transportation of raw materials and finished products helps in lowering overall production costs.

Lastly, the principle of preventing urban pollution and protecting the environment is paramount. Choosing a site away from densely populated areas helps in reducing the impact of factory operations on the city's environment.

In addition to these site selection principles, various factors related to construction conditions must also be considered:

Geographic location and transportation conditions play a crucial role. An ideal location would have good access to transportation networks, such as highways or railways, facilitating the movement of goods.

Resource status and social conditions are important factors. This includes assessing local service supporting facilities, availability of labor resources, and government policies that might affect the factory's operations.

Natural conditions, such as climate, geological factors, and seismic considerations, should not be overlooked. Understanding these factors helps in planning for any potential risks or challenges during construction and operation.

Factory construction conditions such as water supply, drainage, power supply, and heating are essential for the smooth functioning of the facility. Adequate provisions for these utilities must be ensured during the planning stages.

In conclusion, the successful establishment of a polyurethane foam factory hinges on a thoughtful analysis of both site selection principles and construction conditions. By adhering to these considerations, the factory can be set up in an optimal location with the necessary infrastructure for efficient and sustainable operations.

1. Basic Reactions

The formation of polyurethane foam involves two basic reactions: foaming reaction and polymerization reaction (also called gel reaction).

Foaming reaction: Isocyanate reacts with water to produce a reaction of di-substituted urea and carbon dioxide. The reaction equation is as follows:

2R-N=C=O + HOH → R-NH-CO-NH-R + CO2↑

The released carbon dioxide acts as the bubble core, causing the reaction mixture to expand, resulting in foam with an open-cell structure.

Polymerization reaction: The hydroxyl group in the polyether undergoes a stepwise polymerization reaction with isocyanate to form an aminoformate. The reaction equation is as follows:

R=N=C=O + R′-OH → R-NH-COO—R′

2. Polyols

Domestic block foam production uses 3-functionality, molecular weight 3000 (hydroxyl value 56) or 3500 (hydroxyl value 48, less commonly used) soft foam polyethers.

3. Polyisocyanates

The main polyisocyanate used is toluene diisocyanate (TDI). There are three main types of TDI industrial products: pure 2,4-TDI (or TDI100), TDI80/20, and TDI65/35. TDI80/20 has the lowest production cost and is the most widely used variety in industrial applications.

The molecular weight of TDI is 174, with two isocyanate groups (-N=C=O) having a molecular weight of 84. Therefore, the isocyanate content in TDI is 48.28%.

The amount of TDI used has a significant impact on foam properties. In foam formulations, the excess of TDI is expressed as the isocyanate index, which is the ratio of actual usage to theoretical calculated amount. When producing soft foam, the index is generally 105-115 (100 is equal to the theoretical calculated amount). Within this range, as the TDI index increases, the foam hardness increases, tear strength decreases, tensile strength decreases, and elongation at break decreases. If the TDI index is too high, it can lead to large and closed cells, long maturation times, and foam burning; if the TDI index is too low, it may lead to cracking, poor rebound, low strength, and significant compression permanent deformation.

4. Blowing Agents

Water reacting with TDI to produce carbon dioxide is the main blowing agent used in soft foam foaming. Increasing the amount of water in the formulation will increase the urea content, increase foam hardness, decrease foam density, and reduce foam load-bearing capacity. However, TDI reacts with water to produce a large amount of heat. If the water content is too high, it can cause the foam to burn or ignite.

Methylene chloride is a physical blowing agent with a boiling point of 39.8°C. It is a non-flammable gas that can vaporize during foaming, reducing foam density and hardness. The amount of methylene chloride added should prevent the foam from burning while ensuring that too much does not remove too much heat, affecting foam curing. The amount of methylene chloride used is limited.

5. Catalysts

The main role of catalysts is to adjust the speed of foaming and gel reactions to achieve a good balance.

Triethylenediamine (A33, a 33% solution of diisopropyl ether or dipropylene glycol) is the most important tertiary amine catalyst in soft foam production. It is 60% effective in promoting the reaction between isocyanate and water, i.e., foaming reaction, and 40% effective in promoting the reaction between hydroxyl and isocyanate, i.e., gel reaction.

Dibutyltin dilaurate (A-1) is a general-purpose tertiary amine catalyst for soft foam. It is 80% effective in promoting foaming reaction and 20% effective in promoting gel reaction. It is often used in combination with triethylenediamine.

Improper use of amine catalysts can have a significant impact on the product. Too much amine can cause:

(1) Short reaction time, rapid increase in initial viscosity, and excessive smoking during foaming.

(2) Foam cracking. Too little amine will result in slow initiation speed, affecting foam height.

Dibutyltin dilaurate is the most commonly used organic tin catalyst, which is very easy to hydrolyze and oxidize in the presence of water and tertiary amine catalysts in polyether mixtures.

The lower the foam density, the narrower the adjustable range of dibutyltin dilaurate. The effect of tin dosage on foam is as follows:

Too little dosage: Foam cracking.

Too much dosage: Rapid increase in viscosity, foam forming closed cells and shrinking, forming skins on the top and sides.

6. Foam Stabilizers (also called Silicone Oils)

Foam stabilizers reduce the surface tension of the foam system mixture, thereby stabilizing the bubbles, preventing foam collapse, and controlling the size and uniformity of voids.

Increasing the amount of silicone oil from the minimum amount to an appropriate level can produce well-opened foam plastics. When the amount is too high, the closed-cell rate of the foam increases.

7. Other Influencing Factors

In addition to the formulation, process parameters, and environment also have a certain impact on foam properties.

Raw material temperature: Under relatively normal ambient temperatures (20-28°C), the raw material temperature is controlled at 25±3°C, preferably within a range of ±1°C. It can also be controlled within the range of 28-30°C.

The effect of temperature increase or decrease on the speed of foaming and gel reactions varies. An increase in temperature results in a much greater increase in polymerization reaction compared to foaming reaction. Catalysts need to be adjusted for temperature changes.

For the same formulation, using the same amount of blowing agent, foam density is also related to altitude. In high-altitude areas, foam density noticeably decreases.

Calculation of foaming distance for continuous foaming machine

Given: Bubble release time for the formula is 108 seconds, conveyor belt speed during foaming is 4.6 meters per minute. Calculate the swinging and trough foaming distances.

Foaming distance when swinging: (108/60) x 4.6 = 8.28 meters

Foaming distance when troughing: [((108-18)/60)] x 4.6 = 6.9 meters

Explanation: For the same formula, continuous foaming machine has a shorter bubble release time than small bubbles. The calculated foaming distance is shorter than the actual foaming distance. This method only provides approximate confirmation of the foaming distance, supporting the adjustment of the settling plate. Troughing: 18" indicates the time in seconds that the raw material stays in the overflow trough.

Calculation of foaming height for continuous foaming machine

Given: Formula flow rate: 80 kilograms per minute for polyether, 20 for white polyether, 60 for TDI, 20 for stone powder, conveyor belt speed 4.5 meters per minute, mold width 1.65 meters, producing foam with a density of 25 kilograms per cubic meter. What is the foaming height in meters?

Total formula weight: 80 + 20 + 60 + 20 = 180 kilograms

Formula volume: 180/25 = 7.2 cubic meters

Base area of conveyor running per minute:

4.5 x 1.65 = 7.425 cubic meters

Foaming height: 7.2/7.425 = 0.97 meters

Explanation: Silicone oil, amine, and tin are not considered here as they offset the amount of carbon dioxide used during the foaming process. Moisture content (MC) is not considered because MC does not increase foam weight when vaporized.

Foaming Daily Operation

Beginners worry that improper adjustment of the settling plate will cause the liquid sprayed from the nozzle to surge forward or backward, affecting foaming. The reaction rate gradually increases within the first two minutes after starting the machine, sometimes requiring corresponding adjustments to the settling plate. Adjustments to the settling plate are more critical in formulas with low density and high MC.

TDI flow rate can be calculated by determining the corresponding scale value for the flow rate, but it is recommended to measure the TDI flow rate during the first foam production. Flow rate is too important; if the flow rate is incorrect, everything else will be a mess. It's best to rely on the simplest and most intuitive method of measuring flow rate.

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

Formulas for foam machines with longer mixing chamber or more teeth on the mixing shaft typically have less amine and lower material temperature. Conversely, formulas for foam machines with shorter mixing chamber or fewer teeth on the mixing shaft typically have more amine and higher material temperature.

For the same formula, when switching between dual spray swing heads and single spray swing heads, if the cross-sectional area of the two nozzles is similar, the requirements for the fineness and number of layers of the mesh are similar.

Correction of small material flow rate can be done by measuring the return flow rate of the small material, or by dividing the total usage by the foaming time for correction. When the values obtained from the two correction methods differ significantly, the data from the second correction method should be used.

Formulas for soft foam with better properties are usually in an unstable range, such as lower TDI index, lower water to MC ratio, lower T-9 dosage, and lower silicone oil dosage. Just like in our jobs, there must be effort before reward.

Have you ever wondered how polyurethane plastic foam is formed? In the previous article, we revealed the basic reactions behind it: isocyanates, polyether (or polyester) polyols, and water, all work together to create this magical substance. So, does this mean that in actual production, we only need these three raw materials? The answer is far from it. In our actual production process, in order to more precisely control the reaction rate and produce products with excellent performance, we often need to harness the power of various additives. These additives not only have wide-ranging applications but also can play a huge role in making our production process more efficient and stable.

Surfactants / Silicone Oil

Surfactants, also known as silicone oil, are also called foam stabilizers. In the production process of polyurethane foam, its role is crucial. The basic duty of silicone oil is to reduce the surface tension of the foaming system, thus improving the miscibility between components, adjusting the size of bubbles, controlling the bubble structure, and enhancing foam stability. Furthermore, it also bears the responsibility of preventing foam collapse. Therefore, it can be said that silicone oil plays an indispensable role in the production of polyurethane foam.

Catalysts

Catalysts play a crucial role in the synthesis process of polyurethane, mainly by accelerating the reaction between isocyanates, water, and polyols. This reaction is a typical polymerization reaction. Without the presence of catalysts, this reaction may proceed very slowly or even not at all. Currently, catalysts on the market are mainly divided into two types: amine catalysts and organic metal catalysts. Amine catalysts are compounds based on nitrogen atoms, which can effectively promote the polymerization reaction of polyurethane. Organic metal catalysts, on the other hand, are compounds that particularly affect the reaction between polyols and isocyanates in the formation of polyurethane, usually organotin compounds. The characteristic of these catalysts lies in their ability to precisely control the reaction process, resulting in a more uniform and stable final product.

Blowing Agents

Blowing agents are substances that generate gas during the polyurethane reaction and help form foam. Depending on the way gas is generated, blowing agents are usually divided into chemical blowing agents and physical blowing agents. Chemical blowing agents refer to substances that undergo chemical changes during the reaction, generate gas, and promote foam formation. Many common substances in our daily lives are actually chemical blowing agents, such as water. Physical blowing agents, on the other hand, are substances that generate gas through physical means. For example, dichloromethane (MC) is a common physical blowing agent.

Other Additives

Relying solely on basic raw materials is far from enough to make products have outstanding performance. In order to meet various needs, other additives are cleverly incorporated into the production process, and their roles should not be underestimated. For example, flame retardants can add flame resistance to products, crosslinking agents can enhance their stability, colorants and fillers can give products a more colorful appearance and texture, and various other additives with different functions are also playing their roles. It is these carefully selected additives that comprehensively improve the performance of the products and bring users a better user experience.