Polyurethane rigid foam formulation and calculation method

First, the most important thing to calculate in the hard foam combination is the ratio of black and white materials (weight ratio) is reasonable, another formal statement seems to be called “isocyanic acid index” is reasonable, translated into the vernacular is “the proportion of white and black materials mixed by weight to completely react to the end The translation is “the white material and the black material must be completely reacted by weight”. Therefore, everything in the white material that is involved in the reaction with -NCO should be taken into account. Theoretical molar amount of -NCO consumed by each component is calculated as follows

 

(i) the main material: polyether, polyester, silicone oil (ordinary hard foam silicone oil have hydroxyl value, because the addition of diethylene glycol and other dilution, some foam stabilizer type silicone oil also contains amino) formulation number multiplied by the respective hydroxyl value, and then add up the number of Q, S1 = Q ÷ 56100

(ii) water: the amount of water formulation W S2 = W ÷ 9

(iii) involved in the consumption of – NCO small molecules: the formulation amount of K, its molecular weight is M, the functional degree of N S3 = K × N / M (with more than two small molecules need to be calculated separately and then add up) S = S1 + S2 + S3

The amount of crude MDI required for the basic formula [(S × 42) ÷ 0.30 ] × 1.05 (the so-called isocyanic acid index 1.05)

In fact, the above calculation is only a basic consumption, due to the complex reaction process of black and white material, the actual -NCO consumption must be more than this number, such as the case of triple catalyst, how much additional consumption of -NCO, no one can say clearly. In addition, there is water in the polyether, 0.1% higher is very serious; polyether hydroxyl value is also to see people’s leaflet, I have seen polyether hydroxyl value range across 90mgKOH/g, that calculation number out only for reference, can not be serious!

 

This combination material system important requirements and instructions

1, fluidity should be good, density distribution “as far as possible” uniform. First of all, the viscosity should be considered, only the system viscosity is small, the initial liquidity will be good (the average viscosity of the main part of 6000mPa.S below, the combination of material 350mPa.S below), followed by the system in the potassium, sodium miscellaneous ions should be controlled in a low limit (within 20ppm), so that the control to avoid the triple reaction in advance, that is: the system viscosity becomes large prematurely. If the liquidity is not good, foam material marching to the distal end of the injection port will appear draw marks resulting in the olive sphere of the bubble hole structure, this position must not resist low-temperature shrinkage.

2, the bubble hole is fine and dense, the thermal conductivity should be low. It is not difficult to understand the bubble pore is the first premise of low thermal conductivity, at this time, the first consideration is to add 403 or some aromatic amine ether into the system (their role is to first react with -NCO, its products and other components of the mutual solubility, emulsion stability, and to ensure that the initial nucleation of the foaming system is stable, that is, to avoid bursting bubbles, so that the bubble pore fine) followed by the polyether itself alone foaming its bubble pore structure to be good ( For example, 635SA with sorbitol as the starting point is much finer and more uniform than 1050 with sucrose as the starting point, and 835 with glycerol as the starting agent is finer than 1050, even for the so-called 4110 grade polyether, the one with propylene glycol as the starting point is better than diethylene glycol. The polymerization catalysts used for polyether production are different, and the properties of the produced polyethers are also different: the molecular weight distribution of polyethers catalyzed by potassium hydroxide is narrower than that catalyzed by dimethylamine. (In addition: polyether production process control —– temperature control, evacuation, PO – that is, propylene oxide flow control, PO raw material quality, post-treatment, etc. —– will also directly affect the polyether foaming pore structure) Third, you can consider adding some polyester components that can improve the fine density of pores. Fourth, the appropriate addition of low-viscosity material to adjust the overall viscosity (such as 210 polyether)

3, low temperature resistance to shrinkage to be good. This needless to say. First, the degree of functionality, the overall average to 4 or more. Secondly, the foam body molding space crosslinking point distribution is uniform (intuitive explanation is: the main polyether reaction activity as far as possible, the continuous approximate space structure to be much more stable.)

4, good bonding. The so-called bonding superficially refers to the foam body and refrigerator, freezer shell and liner bonding between, in fact, refers to the foam body flexibility, and resistance to shrinkage, (water dosage, reduce the overall hydroxyl value, add flexible structural components, such as 210, 330N and so on can improve the adhesion of foam to the shell)

5, the cost is lower. At present, the refrigerator, freezer industry competition white-hot, excellent performance and expensive combination of materials no one can afford, so we must consider for the cost (such as aromatic polyester price than the polyether low, you can add some.)

6, safety. This is the special requirements of the cyclopentane system (at least cyclopentane is not like F11 as much as you want to add, it is not difficult to understand the addition of more cyclopentane has more security risks)

7, to ensure the continuous stability of the foam production process refrigerators, freezers, continuous production lines are generally very stable control, but does not exclude the occasional fluctuations in process parameters, such as material temperature, ambient temperature a degree or two higher, the proportion of black and white material fluctuations in a small range, etc., so the combination of materials required to have a certain “tolerance”

8、Black material matching. Each black material own traits, activity is different, then, the white material system to adjust sometimes seems to be exceptionally necessary. (With 5005’s okay, in no way means and 44v20 can be arbitrarily switched)

The main polyether polyester selection direction

 

1, phase solubility. Refers to ” polyether, polyester / silicone oil / water / catalyst / physical foaming agent ” composed of the system should be good mutual solubility, homogeneous and stable —– at least stored for a period of time can not be delaminated.

2, functional degree composition and skeleton type. In principle, the higher the degree of functionality, the physical properties of the foaming body values (dimensional stability, compressive strength, etc.) on the more “ideal”, but often the high degree of functionality of the polyether viscosity on the large side (more hanging PO can also reduce viscosity, and the price can not come down), so, on average, 4 degrees of functionality can deal with a sloppy; In addition, if the polyether system Aromatic structure (benzene ring) is introduced, no doubt will also enhance the physical properties of the foam.

3. Reactivity. Polyether containing primary hydroxyl structure (and small molecules such as triethanolamine cross-linking agent) activity is high, but more or less will affect the foam reaction in the late liquidity. Therefore, the amount of its addition must be controlled within a certain ring circumference.

4, hydroxyl value with. According to the amount of water, black and white material ratio preset, you can roughly back-calculate the average hydroxyl value of the main part of the range, generally 380-410mgKOH/g

5、Economy. Not only refers to polyether, polyester procurement price is low, should also be integrated with other aspects to consider the proportion of black and white materials, after all, now the price of black materials is high.

6, the convenience of market procurement. It is difficult to adjust a formula, the results of raw materials on the market just you useful others will not ask, unless the wealth of the monthly amount of amazing, otherwise the ingredients supply can guarantee only depends on the “friendship” shallow.

The choice of levelling agent (silicone oil)

1, and the combination of other ingredients of the compatibility of the material. This is not difficult to understand, otherwise, the production of silicone oil manufacturers will not make up so many models —— what F11 type, 141B type, cyclopentane type, full water type, polyester type, sucrose polyether type and so on. The silicone oil model is properly matched, it can obviously control the low limit of thermal conductivity.

2、Matchability with black material, nucleation ability. Not many people are concerned about this. In fact, in most cases, the “bad bubble hole” is the result of the silicone oil’s emulsification ability of the whole system of black and white materials is not enough.

3, fluidity. Can make the foam system pore fine silicone oil can obviously enhance the foam liquidity, while another supporting evidence is: foam speed slightly accelerated.

4、Stability and dosage. Some silicone oil met with water, alkaline catalyst, chlorine foam or chlorine flame retardant will gradually deteriorate; some must increase the dosage (dosage of 2.5% or more) to show that it is a silicone oil.

5, price. Can use 22 yuan / kg to get the need to use the imported 45 yuan / kg, to know that each ton of combination material in the silicone oil 14kg that the difference is over 200 yuan.

Determination of the share of water

1, bonding. Water dosage, the surface of the bubble body is brittle, and the adhesion of the shell surface is poor, general refrigerator, freezer material water dosage 1.7-2.3% (specifically 141B system and cyclopentane system)

2, the selection of physical foaming agent system. Now everywhere shouting environmental protection, 141B has long been said to be limited use, but under the market there are actually F11 type (or blending type F11) combination material transactions. The amount of water can only follow the line price: F11 type — 0.6/1.6, 141B type — 1.7/2.2, cyclopentane type — 2.0/2.4

3、Economy. Water is indeed very cheap, but it uses more, the amount of black material will have to be added, so it is still not cost-effective chances (naturally, it is the customer who uses the combination of materials to pay for it.

Catalytic system to determine

1. Pre-requirement. In the past, many friends think that the milky white hair is slower to start, and then straighten up after the material flows to the bottom of their respective “posts”. In fact, it is not, one: the liquid material is very easy to leak out from the gap in the box caused by dirt sticky mold; second: the impact of the fine density of the bubble hole and the overall structure, so as to pull up the thermal conductivity of the bubble body; third: the speed of hair will speed up the foam material marching speed. Generally speaking, out of the gun milky white time 6-8 seconds is the best.

2, medium-term flow. During the foam shaping, medium-term flow time period (wire drawing minus whitening time) the longer the better, to ensure that the bubble body fill all corners of the box, and not to the bubble hole deformation serious. The most ideal state is 3-5 seconds before the start of drawing, the foam has been filled in place, the most distal exhaust hole has obvious escape material appears.

3、Later curing. This requirement does not have to be too strict, anyway, continuous production in the mold is not cold, if the production line has insulation kangdao, not afraid of expiration of the crop.

4、Recommended with Am-1 + cyclohexylamine.