Handmade mesh sponge foam tutorial
Mesh sponge is a special product of sponge, started late, appeared in the Chinese market in about 1995. The industry generally refers to it as: net sponge, burst sponge, coarse hole sponge. It can be specifically described as: a permeable sponge with a certain aperture size and a pentahedral structure of the main hole connected by a vein wire. Because it is “hollow” and has the strength and ductility of a sponge, it can be widely used in
① Air filtration
② Water-based filtration
③Sound dampening
④ Shock wave cushioning
⑤ Foam metal substrates
⑥ Metallurgical filtration substrate
Various fields such as
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The production of a true mesh sponge is done in two steps: foaming and hole breaking. The size of the mesh pore is controlled when foaming, so we now focus on the “foaming” link.
Before 08 I have been doing hard foam products, soft foam class only contacted the molding class, block of large foam only stay in the theoretical level. Through these years of experiments and production verification, summed up some different from the conventional process and adjustment ideas. Fortunately, I have been doing hard foam for more than ten years.
Thanks to all the brothers and sisters who have helped me in this field: He Shenxiang, Xu Dongming (fifth element), Zou Hanjiang, He Qibin, Qiu Minghua, Wang Jianrong, Yang Zhicheng, Mr. Wei Haidong, Mr. Liu Shouping, Mr. Xiu Yuying, He Xulin, Zheng Fashan, Gong Zhilin, Chen Yinhuai, Liu Yunzhen ……
【The principle of foaming reaction 】
As with ordinary sponges, our main reactions here are still two:
① The reaction between the hydroxyl group of the macromolecular polyol and the TDI isocyanate (the following can be abbreviated as -OH, -NCO):
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② The reaction of water with TDI:
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Here, we simply do not see how the change in sponge pore size is related to the main reaction, it is normal, are born of one parent, the acquired growth environment is the key.
Many brothers have done ordinary sponge, know: sponge raw materials in a component called “silicone oil” component, in fact, it is an intermediate “mediator” role, namely:
1、Responsible for the polyether polyol, water, catalyst, TDI blend well with each other.
2, after the CO2 generation can stabilize the foam airbag wall so that it is elastic, not to be weak to wind a touch to break (otherwise it is collapse bubble no discussion).
3, but also can not be too stable, in the process of foam growth, when the pressure in the air bag reaches a certain point, the wall diaphragm will be wrapped with gas penetration (the overall foam is still a viscous fluid is “burst hole”, the late stage of foam forming is “deflated”) to maintain the stability of the system.
The first step in the production of handmade net cotton, is to issue a certain pore size of cotton, its production characteristics are characterized by: each section of raw materials uniformly (but not necessarily “fully” uniform) mixed, with an obvious “start”, “burst hole “, “rise long”, “gel”, “deflate”, “set” of Foaming process. The key control is “burst hole”, all the factors that can affect the degree of “burst hole”: the nature of raw materials, mixing method, temperature control, air pressure difference, the use of additives, etc. are the target of our research.
(The phenomenon of “burst hole” here is the bursting flash phenomenon when the micro bubbles visible on the liquid surface against the light are broken after the polyether, additives and TDI are formally mixed and poured into the foam box. (Generally, it will occur within 30~40 seconds after the stirring time starts, and the duration will be maintained for 8~15 seconds)
Factors of TDI
You can safely use 80/20 type TDI, i.e., the kind where 2.4 a toluene diisocyanate accounts for about 80% and 2.6 a toluene diisocyanate accounts for 20%. 2.4 -NCO activity is not the same, the reaction between the two and -OH and the reaction with water in the reverse order is not the same, do not underestimate such an activity difference, issued from the CO2 gel (fast chain growth) activity “phase” difference, will directly lead to the sheep body easy to open the hole or not.
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Influence of polyether polyol and polymer polyether polyol
1、Molecular weight distribution
We basically use the three house energy, 3000 molecular weight, fully connected to the propylene oxide made of polyether as the “polyol” main part of the use, we know: the so-called molecular weight is certainly the average. If the head of the polyether macromolecule is 3000, then everyone involved in the reaction of the competitive nature of the same, there is no preferential reaction priority phenomenon. Unfortunately, even the international brands of large companies are not able to make molecular weight “uniform” large molecule polyether to.
The next best thing is that the average molecular weight is 3000, and the actual distribution of 2700-3300 range is already very good.
It is not difficult to understand the following fact: a small molecular weight of a single polyether, because ① it is small and flexible; ② the outer hydroxyl group is closer to the central region and more active, and therefore can compete in the -NCO more preferential reaction. If “nucleation”, “vaporization”, “bursting hole”, “rise and fall”, “longevity”, “deflation”, and “gasification” are used, If “nucleation”, “vaporization”, “burst hole”, “growth”, “outgassing”, “shaping” are distinct stages, it is undoubtedly a perfect foaming process when they are coherent. But in reality, the molecular weight of the polyether is “small”, the reaction activity is “large”, making the reaction of -OH and -NCO ahead of time, and making the initial “nucleation” after the air sac wall Viscosity (strength) becomes larger, so that the difficulty of “burst hole” increases, which eventually leads to the “partnership reorganization” of the starting vesicle cannot be achieved, and the “coarse hole” of the sponge becomes more difficult to achieve the goal.
2、Auxiliary polyether (auxiliary polyol)
Sometimes to improve the performance of the net sponge, we will use such as 210, ED28, 1.4 butylene glycol (to improve the tearing force) and white oil POP (to improve the bearing strength), the idea is good, but because of their own structure makes the “coarse hole” this basic goal is very difficult to achieve.
“210” is a conventional polyether starting from diol and linked to propylene oxide, with a molecular weight of 1000 and a molecular weight of 500 evenly spread to one -OH, which is more active.
The molecular weight of “1.4-butanediol” is even smaller, and the worst thing is that its two -OHs are “primary hydroxyl groups”, so its activity can be imagined.
“ED28” and “POP” have highly active polyethylene oxide (raw material called ethylene oxide, EO) chain segments, which is also very active.
Therefore, after adding them, they will invariably lead to “gel reaction” (-OH and -NCO reaction) in advance, and it is more difficult to achieve the goal of “coarse pore” of sponge.
3、Other polyols
① Castor oil is a natural product, its addition will obviously thicken the pore.
② Oilfield emulsion breaker type because of its block structure, some varieties will thicken the pore.
But in general, we do not encourage the use of these two types, the reason “messy pore” (foaming performance as “burst hole” will last much longer than 15 seconds), and the bubble body of the “film removal” is not ideal. .
③ polyester polyol type of activity will generally be strong, the purpose of coarse pore is more difficult to achieve.
Foaming agent]
Do sponge will be used in the low density formula MC and so on, but MC is a strong solvent, it will lead to foaming other components more fully dissolved and dispersed, so that the starting nucleation number increased, the bubble pore size starting is a small, “congenital deficiency” under the want to coarse pore is certainly not easy, so we better use water as a foaming agent, production also good control.
Water in the foam slurry inside the dispersion state is directly related to the size of the body pore size and the uniformity of the bubble pore. If you have to use phrases to describe the advantages and disadvantages of this dispersion, can cause the water beads “bead diameter itself large”, “bead size uniform” process to meet the principle of being able to send a large pore size, uniform pore mesh.
Catalyst]
Organic tin is not a good choice, stannous octanoate it. It is worth noting that: expired, moisture absorption, partial failure of the T9 will cause the bubble sponge mess hole.
Amines are a big problem: ① A-1
① A-1
Although it can completely catalyze the reaction of H2O and -NCO in the early stage, but because the catalyst is too violent, resulting in a rapid increase in the “nucleation of gas production”, the increase in the number of nucleation will certainly cause the pore size is small. In addition, the catalytic “onset” of A-1 is early, which is not conducive to the manual foaming operation at atmospheric pressure. A-1, A-33
② A-33
Because it is a delayed triethylenediamine solution, its catalytic H2O / -NCO reaction will be delayed a bit, and the temperature is slightly lower, its catalytic -OH / -NCO ability is weak, so it can effectively pull the “nucleation”, “initiation”, “burst hole”, “burst hole” and “burst hole”, The time difference between “nucleation”, “bursting” and “gelation” can be ensured by manual operation and bursting time, so it is the first choice as amine catalyst, and the pore size can be easily enlarged. And the larger the amount, the coarser the pore size, note: its dissolution medium is best a condensed propylene glycol (secondary hydroxyl content is higher), as far as possible, do not use diethylene glycol, ethylene glycol as solvent, the same reason as before. If necessary, the preliminary activity of A-33 can be delayed by itself.
③ Cyclohexylamine
Although it is only used in hard foam, N,N-dimethylcyclohexylamine (cyclohexylamine for short) is a very appealing species in the comparison tests I have done, and it makes a larger pore size than that of A-33 and has a significantly better uniformity of pore size distribution. I executed mass production for a while.
