What Is Foam Mattress Making Machinery?

In annual fire incidents, a significant proportion of ignitions are caused by foam, including sofa fires and various ignitions from soft packaging. These incidents occur far too frequently. How can we fundamentally eliminate or reduce such events?

One effective approach is to start from the source materials, much like treating the root cause of an illness. Adding flame retardants to polyurethane foam can effectively prevent ignition.

Now, let's understand flame-retardant foam:

Flame-retardant foam, also known as fire-resistant foam, has a chemical name of polyurethane foam material, which is divided into soft foam (mainly used for furniture) and rigid foam (mainly used for insulation). Generally, it is a fireproof material synthesized by adding various flame retardants to polyurethane.

The product's fire-retardant effect meets the requirements of ASTM Standard 117 and national standards. The usage method is the same as regular foam.

The combustion of polymers is a very complex and intense oxidation reaction. The process occurs as the polymer is continuously heated by an external heat source, initiating a free radical chain reaction with oxygen in the air. This releases some heat, further intensifying the degradation of the polymer, generating more flammable gases, and making the combustion more severe.

There are two methods for the flame retardancy of fire-resistant foam:

One is to chemically introduce flame-retardant elements or groups containing flame-retardant new elements into the molecular structure of the foam. The other method is to add compounds containing flame-retardant elements to the foam. The former method uses flame-retardant substances called reactive flame retardants, while the latter method uses substances called additive flame retardants.

Currently, the vast majority of flame retardants used in foam are additive flame retardants, while reactive flame retardants are mainly used in thermosetting resins such as epoxy resins and polyurethanes. The primary function of flame retardants is to interfere with the three basic elements required for combustion: oxygen, heat, and fuel. This can generally be achieved through the following means:

Flame retardants can produce heavier non-flammable gases or boiling liquids that cover the surface of the foam, interrupting the connection between oxidation and fuel.

By absorbing heat through decomposition or sublimation, flame retardants reduce the surface temperature of the polymer.

Flame retardants generate a large amount of non-flammable gases, diluting the concentration of flammable gases and oxygen in the combustion area.

Flame retardants capture radical free radicals, interrupting the chain reaction of oxidation.

The internal temperature of foam is as indispensable as vitality is to a person. If the post-cure temperature of the sponge is too low, its physical properties will not be optimal, and there will be significant fluctuations in these properties.

Once the foam is well developed, its internal temperature rapidly rises to over 120 degrees Celsius due to the exothermic reaction occurring under poor heat dissipation conditions, becoming one of the fire hazard risks.

The internal temperature of the foam is crucial for forming its superior properties. Foam matured at specific external temperatures exhibits exceptionally superior physical properties like tensile strength. Some calculate the foam temperature through formulas, while others use software to input formulas and automatically calculate the internal temperature of the foam. So, what factors influence the internal temperature of the foam? Is it significant to know these factors? It's akin to how modern phone cameras are high-resolution, but does that render professional photography useless? Are adjustments like aperture, focal length, and exposure time pointless? To better control things, one must grasp more of the key variables of that thing. Let's start with basic principles to understand the changes in internal foam temperature.

First, let's grasp a few basic rules.

The temperature of a space is directly proportional to the amount of heat energy injected into that space and inversely proportional to its size.

For example, if 10 kilojoules of heat are distributed in an 8-liter space, the temperature of that space is 20 degrees Celsius. If the same 10 kilojoules of heat are distributed in a 4-liter space, the temperature becomes 40 degrees Celsius.

The amount of heat input is directly proportional to the heat input value and the speed of heat input.

For instance, if 100 kilojoules of heat are released at speed "v," the heat input is "A." If the same 100 kilojoules of heat are released at 2v speed, the heat input becomes 2A.

The size of a space is directly proportional to the absolute temperature.

For example, a 1-liter space at 0 degrees Celsius becomes 1.366 liters at 100 degrees Celsius because (273.15 + 100)/(273.15 + 0) = 1.366.

The size of a space is inversely proportional to atmospheric pressure.

The lag in methane vaporization needs to be considered.

Next, let's examine how fine-tuning the formula affects the internal foam temperature.

Since this is fine-tuning, we'll approximate that the surrounding environment remains unchanged before and after the adjustments. Let's consider the effects of adjusting water and methane on the internal foam temperature.

For example, if a formula increases methane by 5%, we can be certain that the internal foam temperature decreases because methane vaporization absorbs heat, reducing the heat input to the foam, and increasing the space to accommodate heat. Similarly, if the water content is increased by 5%, the added water releases heat upon injection into the foam, raising the heat input, and the reaction of the added water generates gas, increasing the space for heat. So, does the internal foam temperature increase or decrease in this case? Experience indicates that the internal foam temperature increases. This suggests that the increased heat input due to this change contributes more to the increase in internal foam temperature than the gas produced by water diluting the temperature.

The changes involving foam index, heat release, and heat dissipation all increasing can make it difficult to intuitively guess whether the internal foam temperature will rise or fall. One might need to insert a probe after foaming to compare internal temperatures or calculate to reach a conclusion.

For calculations, several formulas (algebraic expressions) derived from the earlier basic rules are needed, along with some data: the heat released when water reacts with TDI to form carbon dioxide in kilojoules per mole, the heat absorbed during methane vaporization in kilojoules per mole. To estimate the total foam internal temperature, one must know the heat released when forming amino methyl formate, urea methyl formate, urea, and biuret (polyurea), in kilojoules per mole, and the reaction rate (reaction time).

This also explains why the density calculated from the foam index drastically differs from the theoretical and actual values for foams without fillers at 50 densities. The lower the density, the more closely the theoretical and actual values of foam density match.

The reaction of PU foam is based on two main chemical components: polyether polyols and isocyanates, along with other additives including water, dichlorodifluoromethane, foam stabilizers, and catalysts. These materials are instantly and vigorously mixed, reacting to form foam, a process that generates a considerable amount of heat.

Foam plastic is a porous material with a large surface area. While the heat generated at the edges of the foam can dissipate, the heat in the central part, due to the insulation effect of the foam, is more difficult to remove. In a typical reaction, the heat released raises the temperature of the center of the foam block to achieve curing. It has been observed that within 2 to 6 hours after foaming, temperatures can rise to 140-160°C, and sometimes even higher, around 180°C. If the temperature continues to rise, it can lead to core burning, smoking, and even spontaneous combustion.

Additionally, prolonged exposure of polyurethane foam to sunlight can trigger an auto-oxidation reaction, causing polymer degradation, discoloration, embrittlement, and a decrease in physical properties, rendering it unusable. Since the industrialization of polyurethane, core burning and aging have been hot topics of research and concern in the polyurethane industry.

Antioxidants are crucial additives in polyurethane foam production. Proper antioxidants prevent the decomposition of polyols, reduce the formation of by-products, decrease the risk of core burning, and can delay thermal oxidative aging during product use, thereby extending its lifespan. Commonly used antioxidants for PU foam are typically liquid and fall into three categories: aromatic amines (such as 5057), hindered phenols (such as 1135), and phosphite esters (such as PDP). For applications with low color requirements, a combination of aromatic amines and hindered phenols is generally used, while applications with higher color requirements may use a combination of hindered phenols and phosphite esters.

Furthermore, if products are frequently exposed to sunlight, a certain amount of UV stabilizers should be added to improve lifespan and resistance to yellowing. UV stabilizers mainly consist of UV absorbers and hindered amine light stabilizers (HALS). UV absorbers, such as benzotriazoles, benzophenones, and triazines, absorb harmful UV radiation and convert it into heat through intramolecular hydrogen bond transfer or cis-trans isomerization. HALS refers to amines with two methyl groups on each α-carbon atom, which, after photooxidation, transform into nitroso radicals. These radicals are considered stable components that can capture free radicals, regenerate nitroso radicals by reacting with peroxide radicals. UV blocking agents include carbon black, zinc oxide, titanium dioxide, and other pigments, which are used as colorants. These agents utilize their high dispersibility and covering power to reflect harmful UV radiation, protecting the polymer.