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. 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, lowering the overall hydroxyl value,��may be opaque, but cannot be layered), especially with handmade materials.
3. Fluidity: Generally, the fluidity requirements of imitation wood are not very high, which depends on the reasonable arrangement of its own production process. For closed-mold casting products with special sizes, it is still required that the material has good fluidity during the foaming process, at least it will affect the product density distribution
4. Adapt to changes in black material varieties and black and white material ratios: It is best for the white material system to switch black material varieties (M20S, 44V20, 5005, etc.) with slight adjustment of process parameters (material temperature, tube pressure, etc.) Or to ensure that the product meets the requirements within the reasonable fluctuation range of the proportion of black and white materials.
5. The thickness and hardness of the skin on the surface of the product: Imitation wood products must at least ensure that the surface is “hard enough”. Generally, the skin is required to have a certain thickness to ensure the surface hardness. Specific indicators are difficult to quantify because they involve factors such as product density requirements and changes in operating environment temperature and humidity. Some special products require rigidity both inside and outside, and can even be used with self-tapping screws without slipping.
6. Product surface finish and bubbles: The surface of the product should be smooth and clean, without bubbles, pinholes, or dark bubbles (the requirements can be reduced on the back of some products, such as picture frames and wall hangings).
7. White line: This is the most common defect (irregular white spots and long line spots appear on the surface of the product, and the area is obviously soft). It should be avoided as much as possible, at least the white spot should be hard enough.
8. Cell density: The cells inside the product are dense and well-proportioned, and the fewer large cells (above 0.2mm in diameter) that stand out from the crowd, the better.
9. Painting and pasting gold foil: The product will not peel or bubble after being painted or pasted with gold foil.
10. Resistance to deformation: The product is stable. Long-size rough products not only cannot “shrink when exposed to cold” after mold opening, but the final product cannot deform even after traveling across the ocean and experiencing severe cold and heat.
11. Impact resistance: Sufficient toughness (usually able to withstand flat falls and throws from a height of 1 meter).
12. The surface of the product is corrosion-resistant: before painting and foiling, the product often needs to be washed with a solvent to remove the release agent and roughened. If it cannot pass this level, it will definitely not work.
