Polyurethane rigid foam formula and calculation method

1. What needs to be calculated in the hard foam composite material is whether the ratio of black and white materials (weight ratio) is reasonable. Another formal term seems to be called “isocyanate index”, whether it is reasonable. Translated into dialect, it is “by weight ratio” The mixed white materials and black materials must be completely reacted.” Therefore, everything in the white material that participates in the reaction with -NCO should be taken into consideration. The theoretical molar amount of -NCO consumed by each component is calculated as follows.
(1) Main ingredients: polyether, polyester, silicone oil (ordinary hard foam silicone oils have hydroxyl values, because they are diluted with diethylene glycol, and some foam stabilizer silicone oils also contain amino groups). Multiply the number of formulas by their respective hydroxyl values. Then add the number Q, S1 = Q÷56100
㈡Water: The formula amount of water W S2 = W÷9
(iii) Small molecules that participate in the consumption of -NCO: the formula amount is K, its molecular weight is M, and its functionality is N S3 =K×N/M (if two or more small molecules are used, they need to be calculated separately and then added) S = S1 S2 S3
The amount of crude MDI required for the basic formula [(S×42)÷0.30]×1.05 (so-called isocyanate index 1.05)
In fact, the above calculation is just a basic consumption. Due to the complex reaction process of black and white materials, the actual consumption of -NCO must be more than this number. For example, if there is a trimerization catalyst, no one can tell clearly how much additional -NCO is consumed. In addition, there is moisture in the polyether, and if it is higher than 0.1%, it will be very serious. The hydroxyl value of the polyether can also be determined from other people’s leaflets. I have seen polyether hydroxyl values ​​ranging from 90 mgKOH/g. After calculating the number, you can only refer to it. Can’t be serious!

[Experimental Design] “Refrigerator, Freezer” Category
Important requirements and instructions for this combined material system
1. The fluidity should be good and the density distribution should be as uniform as possible. First, we must consider the viscosity. Only when the viscosity of the system is small will the initial fluidity be good (the average viscosity of the main component is below 6000mPa.S, and the combined material is below 350mPa.S). Secondly, the potassium and sodium ions in the system must be controlled at a low limit. (within 20ppm), which can control and avoid the trimerization reaction in advance, that is, the system viscosity increases prematurely. If the fluidity is poor, drawing marks will appear when the foam material travels to the far end of the injection port, causing the cell structure to become rugby-balled. This location must not be able to withstand low-temperature shrinkage.
2. The cells are fine and the thermal conductivity is low. It is not difficult to understand that fine cells are the prerequisite for low thermal conductivity. At this time, first consider adding 403 or certain aromatic amine ethers into the system (their role is to first react with -NCO, and their products are mutually soluble with other components. The emulsification stability is improved and the nucleation stability of the foaming system is ensured in the early stage, that is, foaming is avoided, thereby making the cells finer.) Secondly, the polyether itself has a better cell structure when foamed alone (for example, 635SA starting with sorbitol is better than The cells of 1050 starting with sucrose are much finer and more uniform, and the 835 starting with glycerin is finer than 1050. Even for the so-called 4110 grade polyether, the one starting with propylene glycol is better than the one starting with diethylene glycol. Polyether production uses different polymerization catalysts, and the properties of the polyether produced are also different: the molecular weight distribution of polyether catalyzed by potassium hydroxide is narrower than that catalyzed by dimethylamine. In addition: process control during polyether production—temperature control, Vacuuming, PO – that is, propylene oxide flow control, PO raw material quality, post-processing, etc. – will also directly affect the cell structure of polyether foaming) Third, you can consider adding some chemicals that can improve the cell density. Polyester composition. Fourth, appropriately add low-viscosity substances to adjust the overall viscosity (such as 210 polyether)
3. It has better low temperature resistance and shrinkage resistance. This goes without saying. One is functionality, the overall average is above 4. Secondly, the spatial cross-linking points are evenly distributed after the foam is formed (the intuitive explanation is: the reactivity of the main polyethers should be as similar as possible, and the continuous approximate spatial structure is much more stable.)
4. Good adhesion. The so-called adhesion on the surface refers to the adhesion between the foam and the outer shell and liner of the refrigerator or freezer. In fact, it refers to the flexibility of the foam and its resistance to shrinkage (moisture content, reducing the overall hydroxyl value, adding a flexible structure Ingredients such as 210 and 330N can improve the adhesion of the foam to the shell)
5. Lower cost. At present, the competition in the refrigerator and freezer industry is fierce, and no one can afford expensive combination materials with excellent performance, so we must consider the cost (for example, aromatic polyester is cheaper than polyether, so you can add some.)
6. Security. This is a special requirement for the cyclopentane system (at least cyclopentane cannot be added as much as you want like F11. It is not difficult to understand that adding more cyclopentane has greater safety risks)
7. Ensure the continuous stability of the foaming production process. The continuous production lines of refrigerators and freezers are generally very stable in control, but occasional fluctuations in process parameters are not ruled out. For example, the material temperature and ambient temperature are one or two degrees higher, and the proportion of black and white materials fluctuates within a small range. Wait, so the combination materials are required to have a certain degree of “tolerance”
8. Black material compatibility. Each type of black material has different properties and activities. Therefore, it is sometimes very necessary to adjust the white material system. (In conjunction with 5005��4110″ is the main component (most share is more than 60%). As a widely used rigid foam polyether variety, it has an ideal rigid skeleton and flexible long chain (sucrose and glycol are used as starter graft rings Oxygen propane), the price is also right. There are not many on the market that are suitable for imitating wood. At least the quality must be stable. It is best not to use those that are doped, have hydroxyl value/viscosity that fluctuates with the price of PO, and have insufficiently fine cells. As far as the production formula of 4110 is concerned, the [sucrose glycerin] starting type suitable for imitation wood (unfortunately, I have only used it twice so far, and it seems that it is no longer available for sale), followed by the [sucrose propylene glycol] starting type. The rest is the starting type [sucrose ethylene glycol or diethylene glycol]. Other blending types are really difficult to use. The specifications of 4110 are also particular, viscosity: generally 2500-3500mPa.S, used for all-water hair. The foam system is even lower. Hydroxyl value: Products higher than 430mgKOH/g will only be hard and not tough, and other polyethers with low hydroxyl values ​​need to be added, preferably within the range of 380-420mgKOH/g. Chroma Appearance: A color that is too dark indicates poor control during the polyether production process. Furthermore, the appearance of the resulting product will be darker and the white line contrast will be more dazzling. Most customers will not be satisfied with this.
②403. It is recommended to add some amount (3-12%). With it, the cells will be fine and dense, there will be far fewer bubbles, pinholes, and dark bubbles on the surface of the product, and the overall hardness of the product will also increase. The problem is that it is too sticky and is not conducive to controlling the viscosity of the white material. The 403 currently on the market is also mixed. The real 403 should be started from ethylenediamine. The raw materials are indeed a bit more expensive (it seems to be more than 20 yuan/kg). Some people have mistaken ideas and add urea and glycerin to the starter. Or increase the PO volume to reduce costs. The ammonia added with urea has a strong smell, the cells are thicker, and the hardness of the glycerin is affected. The 403 with more PO connections has a lower viscosity and is not hard enough.
③Sorbitol type. Represented by 635 series (10-20%). You don’t need to consider the cost, but after use, the overall hardness and surface effect of the product can be significantly improved (smooth, pinholes, etc.). Trouble: This type of polyether has a high viscosity and a high price.
④Soft foam polyether. 220, 210, 330N, and even grafted polyether (36/28 and the like). Ordinary hard imitation wood can be omitted. A must-have for high-end products and flower pots. This type of polyether has a low hydroxyl value, the product has good flexibility, and the surface crust thickness of the product will be improved. Disadvantages: Except for 210, the others have poor mutual solubility with the main polyether and tend to separate into layers.
⑤Polyester. Aromatic polyester (5-20% depending on the quality and properties of the raw materials). In principle, its use is discouraged. The purpose of adding large pieces is to make the cost “effective”, but if the small materials are not properly matched, there will be a lot of trouble. A high acid value will result in thick cells, many pinholes, and even “white fog” appearing on the surface of the product.
⑥Other polyols. (Within 8%). There are a variety of natural vegetable oils or their modified derivatives that can be used, which can improve the flexibility of the product and also slightly reduce the cost. The risk is the same as ⑤, if you use it incorrectly, you will be responsible for the consequences.
⑦Other ideas: If the product is a high value-added product, you can consider using imported similar polyether, especially the all-water foaming system. It is difficult for domestic polyether raw materials to reach the level of Dow.
2. Auxiliary small molecules:
(0.5-3%) There are glycerin and its starting small molecule polyethers, N ethanolamine (N: one, two, three), small molecule glycols, and even MOCA. Its functions are early reaction, overall hardening, or It increases the thickness and hardness of the skin and shortens the production cycle. It is also necessary to choose the appropriate model and use a reasonable amount.
3. Silicone oil:
(1.5-2.5%) This follows other raw materials (raw material matching). General hard foam silicone oil can be used, but if you want to improve some properties of the product (fine cells, white lines, fluidity), you should still spend more. point. It is best not to use those priced below 24 yuan/kg. Pay special attention to the fact that the silicone oil model may need to be changed after the main body of the polyether (ester) changes.
4. Catalyst:
① Preliminary type: ROAOCAT-A1, ROAOCAT-5 catalyst, whose function is to control the starting time, drive other catalysts to work, improve the cell density, and improve the fluidity of the foaming process. The dosage is within 0.5%, depending on the amount of “water” used. It is a “fixed number” when the weather conditions are stable
② Stable type: ROAOCAT-8 Catalysts, dosage 0.3-0.6%, currently the most cost-effective hard foam catalyst, with average catalytic capacity in each period.
③Main catalyst: An essential catalyst in A-33 imitation wood, which directly affects the skinning effect and product hardness. The dosage is at least 0.4%. The A-33 here refers to solid amine (triethylenediamine) dissolved in small molecular glycol, not a commercially available sponge product (there are many counterfeit products).
④Organotin: ROAOCAT-D22 is good. A very small amount (one ten thousandth) can significantly improve the skinning effect and shorten the mold opening time. What needs to be noted is: be careful about the storage period of the white material, because ordinary organic tin is a tin catalyst that is not resistant to hydrolysis and will gradually fail. Like D22, the signs of failure will be obvious after a week of being used in the composite material. It is recommended to use water-resistant catalysts. Solution type.
⑤Three-cluster: It is easy to use ROAOCAT-41 (0.3-0.5%) to harden without affecting the cell structure. I have used DMP-30 at 0.5% for some time, but the effect was not very satisfactory. Dimethylethanolamine can also be used in small amounts. ⑥Other types: Dimethylbenzylamine (0.5%) is not good at improving product quality, unless it is used for decorative gussets with lower density, longer dimensions, and closed-mold infusion, which can improve the fluidity of the material. . ROAOCAT-112 catalyst can thicken the crust and increase foam hardness.
5. Foaming agent combination
Most of them are now 141B/water foaming system. The water content is 0.2-0.7%, and the ordinary imitation wood 141B should generally not exceed 10 parts. The amount of 141B used will directly affect the thickness and hardness of the crust. Using too much will also cause dark bubbles on the surface.
6. Other additives for viscosity reduction, colorants, anti-yellowing, etc.
You can add something non-reactive to reduce the viscosity of the white material, such as DBP to 3%. Just add colorants, antioxidants, etc. directly, no need to worry.
7. Filling
This is only for manual foaming. You can add inert fine powder to enhance rigidity. Note: Do not add anything with too high water content.

Catalysts can thicken the crust and increase foam hardness.
5. Foaming agent combination
Most of them are now 141B/water foaming system. The water content is 0.2-0.7%, and the ordinary imitation wood 141B should generally not exceed 10 parts. The amount of 141B used will directly affect the thickness and hardness of the crust. Using too much will also cause dark bubbles on the surface.
6. Other additives for viscosity reduction, colorants, anti-yellowing, etc.
You can add something non-reactive to reduce the viscosity of the white material, such as DBP to 3%. Just add colorants, antioxidants, etc. directly, no need to worry.
7. Filling
This is only for manual foaming. You can add inert fine powder to enhance rigidity. Note: Do not add anything with too high water content.