Calculation method for polyurethane rigid foam formula
1、 The most important thing to calculate in the combination of hard foam materials is whether the weight ratio of black and white materials is reasonable. Another formal statement seems to be called the “isocyanate index”, which translates to “the white and black materials mixed according to weight ratio must fully reflect”. Therefore, all things involved in the reaction with – NCO in the white material should be taken into consideration. The theoretical molar consumption of – NCO for each component is calculated as follows
One main ingredient: polyether, polyester, silicone oil (common hard foam silicone oil has hydroxyl value, because of the dilution of diethylene glycol and the like, some foam stabilizer silicone oil also contains amino), multiply the formula number by their respective hydroxyl value, and then add the number Q, S1=Q ÷ 56100
Two water: formula amount of water W S2=W ÷ 9
Three small molecules involved in the consumption of – NCO: formula weight K, molecular weight M, functional degree N S3=K × N/M (using two or more small molecules needs to be calculated separately and then added) S=S1+S2+S3
Basic formula requires crude MDI dosage [(S × 42) ÷ 0.30] × 1.05 (so-called isocyanate index 1.05)
In fact, the above calculation is only a basic consumption. Due to the complexity of the black and white material reaction process, the actual consumption of – NCO is definitely more than this number. For example, in the case of a trimeric catalyst, no one can explain how much additional – NCO is consumed. In addition, there is moisture in the polyether, and a higher concentration of 0.1% is very serious; The hydroxyl value of polyether is also based on their promotional materials. I have seen a range of polyether hydroxyl values ranging from 90mgKOH/g, and the calculated value can only be used as a reference and cannot be taken seriously!
“Refrigerator and Freezer” Category of Experimental Design
Important requirements and instructions for this composite material system
1. Good liquidity, with a density distribution that is as uniform as possible. Firstly, viscosity should be considered. Only when the viscosity of the system is small can the initial flowability be good (the average viscosity of the main components is below 6000mPa. S, and the combined material is below 350mPa. S). Secondly, the potassium and sodium impurities in the system should be controlled at a low limit (within 20ppm) to avoid premature trimerization reaction, that is, the system viscosity increases too early. If the fluidity is poor, drawing marks will appear when the foaming material travels to the far end of the injection port, causing the foam cell structure to become olivine like. This position must not be able to resist low-temperature shrinkage.
2. The pores are fine and dense, and the thermal conductivity should be low. It is not difficult to understand that fine pore size is the first prerequisite for low thermal conductivity. At this point, the first consideration is to add 403 or some aromatic amine ethers into the system (their function is to first react with – NCO, their products are miscible with other components, emulsifying stability is improved, and the initial nucleation stability of the foaming system is ensured, that is, to avoid bursting bubbles, so that the pores are fine). Secondly, the foam structure of polyether itself is better when foaming alone (for example, 635SA with sorbitol as the starting point is much finer and more uniform than 1050 foam with sucrose as the starting point, and 835 with glycerol as the starting point is finer than 1050 foam, even the so-called 4110 grade polyether contains propylene glycol. The starting catalyst is better than diethylene glycol. Different polymerization catalysts are used to produce polyethers, and the properties of the produced polyethers also vary. The molecular weight distribution of polyethers catalyzed by potassium hydroxide is narrower than that catalyzed by dimethylamine. In addition, the process control during polyether production – temperature control, vacuum pumping, PO – i.e., control of epoxy propane flow rate, PO raw material quality, post-treatment, etc. – all directly affect the pore structure of polyether foaming, Consider adding some polyester components that can improve the density of foam pores. Fourthly, add low viscosity substances appropriately to adjust the overall viscosity (such as 210 polyether)
3. Good resistance to low temperature and shrinkage. This needs no further explanation. One is the level of functionality, with an overall average of 4 or above. Secondly, the distribution of crosslinking points in the foam body is uniform after molding (the intuitive explanation is that the reaction activity of the main polyether should not differ significantly, and the continuous approximate spatial structure should be much more stable.)
4. Good adhesion. The so-called adhesive surface refers to the adhesion between the foam body and the refrigerator, freezer shell and liner. In fact, it refers to the flexibility of the foam body and its shrinkage resistance (the adhesion of foam to the shell can be improved by the amount of water, reducing the overall hydroxyl value, and adding flexible structural components such as 210 and 330N)
5. Low cost. At present, the competition in the refrigerator and freezer industry is intensifying, and no one can afford to use expensive combination materials with excellent performance. Therefore, we must consider the cost (for example, aromatic polyester has a lower price than polyether, so some can be added)
6. Security. This is a special requirement for the cyclopentane system (at least cyclopentane is not added as much as you want like F11, it is not difficult to understand that adding polycyclic pentane is more of a safety hazard)
7. To ensure the continuous stability of the foaming production process, the continuous production line of refrigerators and freezers is generally controlled very stably, but occasional fluctuations in process parameters cannot be ruled out, such as material temperature and environmental temperature being one or two degrees higher, and the proportion of black and white materials fluctuating within a small range. Therefore, it is required that the combination materials have a certain degree of “tolerance”
8. Black material compatibility. Each black material has its own unique characteristics and activity, so adjusting the white material system is sometimes exceptionally necessary. (It’s okay to cooperate with 5005, which does not mean that it can switch freely with 44v20)
Selection direction of main polyether polyester
1. Solubility. The system composed of polyether, polyester/silicone oil/water/catalyst/physical foaming agent should have good solubility and homogeneous stability – it should be stored for at least a period of time without layering.
2. Functional composition and skeletal type. In principle, the higher the functionality, the more “ideal” the physical performance values (size stability, compressive strength, etc.) of the foamed body. However, polyethers with high functionality often have higher viscosity (hanging more PO can also reduce viscosity, and the price cannot be lowered). Therefore, on average, four functionalities can be easily handled; Furthermore, if aromatic structures (benzene rings) are introduced into the polyether system, it will undoubtedly enhance the physical properties of the foam.
3. Reactive activity. Polyethers containing primary hydroxyl groups (and small molecule crosslinking agents such as triethanolamine) have high activity, but they may affect the flowability in the middle and later stages of foaming reactions to some extent. So, its addition amount must be controlled within a certain range.
4. Hydroxyl value combination. Based on the preset water usage and black and white material ratio, the average hydroxyl value range of the main components can be roughly calculated backwards, generally ranging from 380-410mgKOH/g
5. Economy. Not only does it refer to the low purchase prices of polyethers and polyesters, but also to the consideration of the proportion of black and white materials in other aspects, after all, black material prices are currently high.
6. The convenience of commercial procurement. After finally adjusting a formula, it turned out that the raw materials on the market were only useful and not sought after by others. Unless one is wealthy and has a staggering monthly usage, the guarantee of ingredient supply depends on the shallow level of friendship.
Selection of defoamer (silicone oil)
1. Compatibility with other components of the composite material. This is not difficult to understand, otherwise manufacturers of silicone oil would not have compiled so many models – F11, 141B, cyclopentane, all water, polyester, sucrose polyether, and so on. Proper selection of silicone oil models can significantly control the low limit of thermal conductivity.
2. Compatibility and nucleating ability with black materials. There aren’t many people following this. In fact, in most cases, poor foaming is caused by the insufficient emulsifying ability of silicone oil on the entire black and white material system.
3. Liquidity. Silicone oil, which can make the pores of the foaming system finer, can significantly improve the foaming flowability, and another evidence is that the foaming speed is slightly accelerated.
4. Stability and dosage. Some silicone oils will gradually deteriorate when exposed to water, alkaline catalysts, chlorinated foaming agents, or chlorinated flame retardants; Some require an increase in dosage (at least 2.5%) to indicate that it is silicone oil.
5. Price range. If it can be done at 22 yuan/kg, there is no need to use imported 45 yuan/kg. It should be noted that the price difference of 14kg silicone oil per ton of composite material is over 200 yuan.
Determination of water share
1. Adhesion. The amount of water used is high, and the surface of the foam is brittle, resulting in poor adhesion to the shell surface. Generally, the amount of water used in refrigerators and freezers is 1.7-2.3% (specifically referring to the 141B system and cyclopentane system)
2. Selection of physical foaming agent system. Nowadays, environmental protection is being promoted everywhere. 141B has long said that it will be used in limited quantities, but there are actually F11 (or blended F11) composite materials trading on the market. The amount of water can only be negotiated according to the situation: F11 type -0.6/1.6141B type -1.7/2.2, cyclopentane type -2.0/2.4
3. Economy. Water is indeed very cheap, but if it is used too much, the amount of black material needs to be added, so there is still a high chance of not being cost-effective (naturally, customers who use combination materials will pay for it).
Determination of catalytic system
1. Preliminary requirements. Many friends used to think that milky white hair started to grow slower, and they waited for the material to flow thinly to their respective positions before starting straight. In fact, it is not the case. Firstly, liquid materials are prone to leakage from the gaps in the box, causing dirt to stick to the mold; Secondly, it affects the fine density and overall structure of the pores, thereby increasing the thermal conductivity of the foam body; Thirdly, an increase in the starting speed will actually accelerate the movement speed of the foaming material. Generally speaking, 6-8 seconds is the best time to release the milky white from the gun.
2. Mid term liquidity. During the foaming and shaping period, the longer the mid-term flow time (drawing minus milky white time), the better, which can ensure that the foam fills all corners of the box without causing severe deformation of the foam cells. The most ideal state is 3-5 seconds before the start of wire drawing, when the foam has been fully filled and there is obvious material leakage from the farthest exhaust hole.
3. Post curing. This requirement doesn’t need to be too strict, anyway, the mold is not cold in continuous production. If the production line has an insulated bed, there is no fear of not being able to harvest the crops at the end of the term.
4. Suggest pairing. Am-1+cyclohexylamine.
Process confirmation
1. Determination of foaming system: 141B or cyclopentane. The range of water volume/physical foaming dosage is predetermined. Firstly, clarify the process details of the target production line: foaming machine type, infusion flow rate, temperature control value before infusion, insulation temperature control value and insulation time of the kang channel, where the box infusion port is located and the route of foaming material flow, and the process of mold closing and hole sealing after infusion. 3. The current (working) environmental temperature and humidity changes. 4. Inquire with on-site operators and quality inspectors about any defects in the current process and raw materials, and ask them to propose any other specific requirements
Specific experiments
1. Solubility: ① Add a short glass rod to a 100ml small beaker, reset to zero, pour in the main polyether (polyester) in sequence, and stir well to see if it is transparent. ② Add silicone oil, catalyst, and water, stir well, and check if it is transparent Add physical foaming agent and stir well to see if it is transparent (note that the volatile physical foaming agent should be replenished after stirring) The pre prepared composite samples should be stored for at least 3 days without any layering or transparency Store the composite samples at 35 ℃ and 15 ℃ for 24 hours to check if they are transparent. If conditions permit, it is necessary to measure the viscosity of the composite materials in the design (25 ℃ and normal production temperature) to see if there is a significant fluctuation in viscosity with temperature changes.
2. Anti shrinkage: After 1 hour of free foaming, cut the sample into regular square shapes, measure the size of the edges, and place them in a -20 ℃ freezer for 24 hours to observe the size changes. Linear shrinkage within 2% is acceptable
3. Free foaming: execute free foaming according to the designed black and white material ratio and temperature control, paying attention to material speed, core density, and drawing marks.
4. Liquidity: After determining the density and velocity of free bubbles, a liquidity test must be conducted. The simple method is to mix the quantitative foaming material (usually 200g) well and immediately put a slightly larger long plastic bag on the mouth of the foaming cup. Straighten it vertically and let it grow upwards until it forms shape (requires two people to operate). The ratio of the height L from the cup mouth to the top to the weight G of the material will be an important parameter to evaluate the flowability of the composite material. The larger the L/G, the better the flowability. Afterwards, the core density should be measured in sections as an auxiliary reference (the difference in density from low to high should not be too large, otherwise the flowability cannot be considered good, especially in the section at the highest point). In fact, if there are too many experiments, during normal free foam foaming, the shape of the remaining bubbles in the cup can be used to roughly judge the quality of the flowability: the more the bubbles are removed from the cup, the better they look like mushrooms, and the more they look like straight sticks, the worse they are.
5. Tolerance of process conditions: ① Perform foaming with preset temperature control of+3 and -3 ℃ to see if good fluidity and foam cell structure are still maintained (the gap between the foam cells of “fast material” and “slow material” should not be too large). ② Conduct a constant amount of white material and a free foaming test with a black material content of+10% and -10%. If there is no significant shrinkage of the foam body at room temperature for 30 minutes, it is considered acceptable.
“Refrigerator and Freezer” Category in Trial Production
This is simple. The entire barrel of material is put into trial production on the machine, produced according to the predetermined (or actual) process conditions, and the finished product is loaded and cooled on the machine. The shrinkage and insulation of the box are checked. General procedure: The finished foam in the trial production box needs to be sampled and tested for comprehensive data such as thermal conductivity. What needs to be fine tuned on site generally includes: temperature control of foam material, proportion of black and white materials, addition of catalyst, and adjustment of curing temperature
Combination Material/Process Control of Imitation Wood Products (Internal Discussion Version) [White Material System Requirements and Product Requirements]
1. White material viscosity: It involves the initial fluidity (machine foaming type), stirring and mixing effect (including manual foaming type), as well as the flow rate and black and white material ratio after firing, and should not exceed 2000mPa in principle S (25 ℃, the same below), except for high-density (free foam density above 130kg/m3).
2. Compatibility: Unless freshly prepared or white materials are mixed and beaten on the machine in a whole barrel, the white materials should be homogeneous and transparent without layering (if using silicone oil white materials with lower turbidity points, they may also be opaque at low temperatures, but layering is not allowed), especially for handmade materials.
3. Liquidity: Generally, the fluidity requirements for imitation wood are not very high, which depends on the reasonable arrangement of its own production process. For special size closed mold pouring products, it is still required that the material has good fluidity during the foaming process, at least it will affect the density distribution of the product.
4. Adapt to changes in black material variety and black and white material ratio: It is best for the white material system to switch between black material varieties (M20S, 44V20, 5005, etc.) with slight adjustments to process parameters (material temperature, pipe pressure, etc.) or to ensure that the product meets the requirements within a reasonable fluctuation range of black and white material ratio.
5. The thickness and hardness of the skin on the surface of the product: Wooden imitation products must ensure that the surface is “hard enough”, and generally require a certain thickness of the skin to ensure surface hardness. Specific indicators are difficult to quantify due to factors such as product density requirements and changes in operating environment temperature and humidity. Some special products require both the inside and outside to be rigid, and can even use self tapping screws without slipping.
6. Surface smoothness and bubbles of products: The surface of the product should be smooth and free of bubbles, pinholes, or dark bubbles (some products may have lower requirements on the back, such as picture frames or wall hanging)
7. White line: This is the most common defect (irregular white patches or long lines appearing on the surface of the product, which are obviously soft), and should be avoided as much as possible, at least the white spots should be hard enough.
8. Bubble density: The internal bubbles of the product are dense and uniform, and the smaller the number of outstanding large bubble eyes (with a diameter of more than 0.2mm), the better.
9. Painting and pasting gold foil: After painting or pasting gold foil on the product, it will not peel off or bubble.
10. Durable: The product is stable, and the large-sized wool embryo product not only cannot shrink from cold after opening the mold, but the final product cannot deform even after crossing the sea and enduring extreme cold and heat.
11. Impact resistance: Has sufficient toughness (usually able to withstand flat or thrown impacts up to 1 meter high).
12. Corrosion resistance on the surface of the product: Before applying paint or foil, the product often needs to be washed with a solvent to remove the release agent and undergo roughening treatment. If this is not achieved, it will definitely not work
[Description of Raw Material Selection]
1、 Main polyether (polyester):
① Most cases are dominated by 4110 (with a majority share of over 60%). As one of the most widely used hard foam polyether varieties, it has an ideal rigid skeleton and flexible long chains (sucrose and diols are used as initiators to graft epoxy propane), and its price is also reasonable. There are not many products suitable for imitating wood in the market, at least stable quality is required. It is best not to choose those that are doped, have varying hydroxyl values/viscosity with PO prices, and have insufficiently fine pores. In terms of the production formula for 4110, the most suitable starting type for wood imitation is [sucrose+glycerol] (unfortunately, I have only used it twice so far and it seems that it is not available for sale now), followed by [sucrose+propylene glycol] starting type, and the remaining is [sucrose+ethylene glycol or diethylene glycol] starting type. Other blending types are really not useful. The specifications of 4110 also require attention, with viscosity generally ranging from 2500-3500Pa S. It is even lower for use as a full water foaming system. Hydroxyl value: Products made above 430mgKOH/g are only hard but not tough, requiring the addition of other low hydroxyl value polyethers, preferably within the range of 380-420mgKOH/g. Color Appearance: If the color is too dark, it indicates poor control during the production process of polyether. In addition, the resulting product will have a darker appearance and make the white line contrast more dazzling, which most customers are not satisfied with.
② 403. Suggest adding some (3-12%). With it, the pores will be fine and dense, and there will be much less bubbles, pinholes, and dark bubbles on the surface of the product, and the overall hardness of the product will also be improved. The problem is that it is too sticky, which is not conducive to controlling the viscosity of the white material. At present, the quality of 403 in the market is also mixed. The real 403 should be started with ethylenediamine, and the raw materials are indeed a bit expensive (it seems to be over 20 yuan/kg). Some people have misconceptions that adding urea and glycerol to the starting agent or increasing the PO amount to reduce costs. The ammonia smell of adding urea is strong, and the foam pores are coarse. The hardness of adding glycerol is affected, and the viscosity of 403 with more PO is lower and not hard enough.
③ Sorbitol type. Represented by the 635 series (10-20%). Cost considerations may not be included, but after use, the overall hardness and surface effect of the product can also be significantly improved (such as smoothness, pinholes, etc.). Trouble: This type of polyether has a high viscosity and price.
④ Soft foam polyether. 220, 210, 330N, and even grafted polyether (such as 36/28). Ordinary hard imitation wood can be omitted. It is necessary to add high-end products and flower pots. This type of polyether has a low hydroxyl value, good flexibility of the product, and the surface skin thickness of the product will be improved. Disadvantages: Except for 210, others have poor compatibility with the main polyether and tend to be layered and independent.
⑤ Polyester. Aromatic polyester (5-20% depending on the quality and quality of the raw materials). In principle, the use is not encouraged. The biggest purpose of adding is to make the cost “cost-effective”, but it can be troublesome if the small materials are not properly matched. High acidity can cause coarse bubbles, numerous pinholes, and even white mist on the surface of the product
⑥ Other polyols. (Within 8%). There are various natural vegetable oils or their modified derivatives that can be used to improve product flexibility and slightly reduce costs. The risk is the same as ⑤, and if not used properly, the consequences will be borne by oneself.
⑦ Other ideas: If the product belongs to high value-added products, it can be considered to use imported similar polyethers, especially those with full water foaming systems. Domestic polyether raw materials are difficult to reach Dow’s level.
2、 Auxiliary small molecule substances: (0.5-3%) include glycerol and its starting small molecule polyether, N-ethanolamine (N: 1, 2, 3), small molecule diols, and even MOCA (which is carcinogenic, it is best not to touch). Their functions include early reaction, overall hardening, or adding skin thickness and hardness to shorten the production cycle. It is also necessary to choose a suitable model and use a reasonable amount.
3、 Silicone oil: (1.5-2.5%)
This follows the trend of other raw materials (raw material matching). Generally, hard foam silicone oil can be used, but to improve some of the product’s properties (fine pores, white lines, fluidity), it should still take some effort. It is best not to use items priced below 24 yuan/kg. Pay special attention that the silicone oil model may need to be changed after the change of the polyether (ester) body.
4、 Catalysts: ① Pre type: A-1, Am-1, with the function of controlling the initiation time, driving other catalysts to exert their effects, improving cell density, and improving the fluidity of the foaming process. The dosage should be within 0.5%, depending on the amount of “water” used. When the weather conditions are stable, it is best to have a “fixed number”. ② Stable type: cyclohexylamine, dosage 0.3-0.6%, currently the most cost-effective hard foam catalyst, with average catalytic ability in each stage. ③ Main catalyst: An essential catalyst in A-33 imitation wood, which directly affects the peeling effect and product hardness, with a dosage of at least 0.4%. The A-33 here refers to the solution of solid amine (triethylenediamine) and small molecule diol, and is not a commercially available sponge product (there are many counterfeit products) Organic tin: The imported T-12 is the best, and a very small amount (one in ten thousand) can significantly improve the peeling effect and shorten the mold opening time. It should be noted that the storage cycle of the white material should be careful, as ordinary organic tin is not resistant to hydrolysis and will gradually fail. For example, T-12, when used in combination materials for a week, the signs of failure will be obvious. It is recommended to use a hydrolysis resistant T-120/T-6 Triple type: It is best to harden with PC-41 (0.3-0.5%) without affecting the pore structure. For a period of time, the effect was not ideal when DMP-3 reached 0.5%. Someone used dimethylethanolamine, which is said to be quite useful. I tried it and found that the bubbles showed signs of thickening, so I didn’t dare to play with fire (although the 4110 used at that time didn’t look like it was made by humans) Other types: Dimethylbenzylamine (0.5%) improved products do not have good quality, unless used for decorative wire corner plates with lower density, longer dimensions, and closed mold injection, which can improve the fluidity of the material. The data shows that N-methyl and dicyclohexylamine can thicken the crust, but unfortunately, I haven’t even obtained samples after searching for several years! DBU has tried it out and can thicken the crust. If it’s too expensive, it’s better to increase the amount of A-33.
5、 Currently, most foaming agents are used in combination with 141B/water foaming systems. Water content is 0.2-0.7%, and ordinary imitation wood 141B should generally not exceed 10 parts. The usage of 141B will directly affect the thickness and hardness of the crust, and excessive use will also cause dark bubbles on the surface
6、 Other additives such as viscosity reducing agents, colorants, and anti yellowing agents can be added to reduce the viscosity of white materials by 3%, such as DBP. Just add colorants, antioxidants, etc. directly without worrying too much.
7、 The filling here is only for manual foaming. Inert fine powder can be added to enhance rigidity. Attention: Do not add things with high water content. Hehe, you have learned how to design formulas (if you know equivalent, it is easier to understand. Unfortunately, current high school and university textbooks do not teach equivalent, they are all called molar ratios, which can cause dizziness)
Next, I will ask the teacher a few questions:
1. How to mix hard foam polyethers such as 4110403
2. Catalyst selection: How to choose triethanolamine, DMEA, DMCHA, and PMDETA, and what is the approximate proportion
3. Selection of silicone oil and foaming agent
What is the range of NCO index and why is there an index of 2.5
5.42 refers to the molecular weight of – NCO, 0.30 refers to the – NCO% content of crude MDI
Related reading recommendations:
微信扫一扫打赏
