Polyurethane rigid foam formula and calculation method

Polyurethane rigid foam formulaand calculation method

1. The most important thing to calculate in the rigid foam composite material is whether the ratio of black and white materials (weight ratio) is reasonable. Another formal term seems to be whether the “isocyanate index” is reasonable. Translated into dialect, it means “by weight” The white materials and black materials mixed in proportion 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

㈠ 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). The formula number is multiplied by their respective The hydroxyl value is then added to get the number Q, S1 = Q÷56100

Water: 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 together) 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 the most 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 say how much additional -NCO is consumed. Be clear. 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. You 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 first prerequisite for low thermal conductivity. At this time, we first consider adding 403 or certain aromatic amine ethers into the system (their role is to first react with -NCO, and their products react with other components The mutual solubility and emulsification stability are 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 is foamed alone, and its cell structure is better (for example, starting with sorbitol 635SA has much finer and more uniform cells than 1050 starting with sucrose, and 835 containing glycerin as a starting agent is finer than 1050. Even the so-called 4110 grade polyether, the one starting with propylene glycol is better than the one starting with diethylene glycol. Good. Different polymerization catalysts are used in polyether production, 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 ingredients that can improve the fineness of the cells. Density polyester composition. Fourth, appropriately add low-viscosity substances to adjust the overall viscosity (such as 210 polyether)

3. 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, 330N, etc. 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. Refrigerator and freezer continuous production lines 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 is small. Within the rangeChemical agent: A-33 is an essential catalyst in imitation wood. It 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 the best. 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 lose its effectiveness. 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 best 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 to reduce viscosity, colorants, anti-yellowing, etc. You can add something non-reactive to reduce the viscosity of the white material, such as DBP or the like 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.