In May 2022, we received an inquiry from Mr. Agus, a customer in Indonesia, regarding a semi-automatic foam machine. Mr. Agus operates a small foam production factory mainly produces rebonded foam and virgin foam, and his products are sold locally. Due to issues related to aging equipment and significant material wastage in his factory, Mr. Agus was interested in upgrading his old machinery. Additionally, the foam he was producing had large pinholes and inside-burn, which he wanted to address.

First, our technical engineers provided Mr. Agus with a new foam production solution. Since foam production can be influenced by local temperature and humidity, after several attempts and improvements to the engineer's formula, the client ultimately achieved the low-density foam he desired, resolving the issues of large pinholes and inside-burn in the foam.

Given that the client's factory equipment was old and had low production efficiency, with frequent machine breakdowns, we proposed a comprehensive equipment upgrade plan based on his budget and specific circumstances.

Our production department customized a machinery solution for the client that reduced the use of molds, and the top-flat device on the machine minimized material wastage during the foam production process. As a result, the client was highly satisfied with the solution provided.

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.

Aluminum Hydroxide

Also known as hydrated alumina. The aluminum hydroxide used as a fire retardant is mainly @-tri-hydrated alumina. It appears as a white fine crystalline powder with an average particle size of 1-20 micrometers. Its relative density is 2.42, refractive index is 1.57, and 30% slurry pH is 9.5-10.5. The dehydration initiation temperature is 200 degrees Celsius, with an absorption heat of 2.0 KJ/G.

During combustion, it releases a large amount of chemically combined water, absorbs a considerable amount of heat, slows down the polymer's thermal degradation rate, reduces the material surface temperature, delays and suppresses the combustion of the substrate. It will generate a large amount of steam on the substrate surface, diluting the oxygen in the combustion zone, reducing the concentration of smoke and toxic flammable gases. The aluminum oxide generated during combustion can promote the formation of a carbonized protective layer on the polymer surface.

Melamine

Commonly known as melamine, it is a white monoclinic crystal with low toxicity, non-flammable, and a melting point of 354 degrees Celsius. It undergoes endothermic sublimation and rapid decomposition under high heat. At temperatures between 250-450 degrees Celsius, it can absorb a large amount of heat and release nitrogen during decomposition, slowing down the material's combustion rate. At the same time, it forms a carbonized barrier layer on the substrate surface, acting as a fire retardant. However, there are some dispersion problems, so it needs to be used in combination. When used as a fire retardant, high-temperature decomposition can produce toxic cyanide gas.

Organophosphorus Flame Retardant

Tris(1,3-dichloro-2-propyl)phosphate (TDCPP)

A pale yellow transparent viscous liquid. It contains 7.2% phosphorus and 49.4% chlorine, with a flash point of 251.7 degrees Celsius, ignition point of 282 degrees Celsius, and spontaneous combustion temperature of 514 degrees Celsius. It starts to decompose at 230 degrees Celsius and is soluble in alcohols, benzene, carbon tetrachloride, etc. When used at 5%, it can achieve self-extinguishing properties, and at 10%, it can make the material self-extinguish or non-flammable, while also having water resistance, light resistance, and antistatic properties.

Fire Retardant Polyether Polyol

1. Formula Ingredients:

Polyether polyol 3050: Mn3000;

Flame-retardant polyether polyol: Hydroxyl value 28, flame-retardant solid mass fraction 23%;

Silicone oil: L580

Triethylene diamine solution: Mass fraction 33%;

Tin octoate solution: Mass fraction 33%;

TDI: Industrial grade

How to Solve the Issue of Thread Breakage or Dropping in a Quilting Machine?

First, check if the thread clamp is rusty or has debris. If such issues are found, clean the thread clamp with a cloth. Additionally, push up the optical axis of the quilting machine and check if the distance between the hook tip and the needle is around 2 millimeters. If there is a deviation, adjust the hook left, right, up, or down accordingly. Regular maintenance and cleaning of the equipment are also essential.

How to Maintain a Quilting Machine?

Clean the equipment at the start and end of each work shift to remove debris and dust, ensuring smooth operation of the needle and hook. Regularly lubricate areas with significant wear using machine oil or grease to facilitate smooth high-speed operation. Bearings with oil nozzles should be greased at least once a year to prevent excessive machine wear. Insufficient air pressure or unopened cylinders can cause temporary loss of some functions, so ensure the cylinders are activated before turning on the machine. When shutting down, do not turn off the machine power directly; first, turn off the computer, then the power.

The amount of TDI to be added in the formulation can be calculated using the following procedure and formula. 100 parts by weight of polyol polymer.

A  represents the mass of TDI consumed in completely reacting with the hydroxyl and carboxyl groups of the polyol polymer.

A = 87*100/56*1000*(Acid Value of the polyol polymer}+ Hydroxyl Value)

=0.1554 * (Acid Value of the polyol polymer}+ Hydroxyl Value)

B  represents the mass of TDI consumed in completely reacting with the water in the system (including both the water in the formulation and the water present in the reactive components).

B = 174/84*Water %

=9.667*Water %

C is the total mass of TDI consumed by the hydroxyl groups, carboxyl groups, and water in the polyol polymer, calculated based on the equivalent weight. This represents the theoretically required mass of TDI for chemical equivalence.

C = A + B

The actual amount of TDI to be used is calculated as follows:

Actual TDI Amount = (A+B)*Isocyanate Index

Example Calculation:

For 100 parts by weight of polyethylene adipate, with a hydroxyl value of 56, an acid value of 0.5, and negligible water content, and an additional water content of 3.0 parts by weight in the formulation. Assuming the TDI index is set to 1.05, the required amount of TDI in the formulation is calculated as follows:

1. Calculate A:

A = 0.1554*(56 + 0.5) = 8.749

2. Calculate B:

B = 9.667*3 = 29.001

3. Calculate  C:

C = A + B = 8.749 + 29.001 = 37.750

4. Calculate the actual amount of TDI to be added:

Actual TDI Amount = 37.750 * 1.05 = 39.64