preface

in the process of polyurethane rigid foam for refrigerators, the one-step method is generally used. for refrigerator and other freezing equipment, foam in the complex structure of the large cavity distribution and uniformity, the degree of fine uniformity of foam pores, foam closed rate and other factors have a great impact on the overall performance of the refrigerator, these factors are related to the foam and the cavity wall bonding firmness, foam size stability, etc.. with the emergence of new varieties of rigid polyurethane foam raw materials, and in response to the refrigerator production plant to improve production efficiency, reduce costs and the urgent need to speed up the production pace of the situation, we have reviewed the relevant information, a variety of amine catalysts for screening and improvement, a series of controlled application tests, and in hcfc a 14b1 for the foam blowing agent in the refrigerator with polyurethane rigid foam application. these are discussed below.

main raw materials and specifications a polyether, oh value 430mgkoh-g a’, moisture appreciation 0.1%: b polyether, oh value 400mgkoh-g a’, moisture egg 0.1%; c polyether, oh value 360mgkoh-g a’, moisture `0.1%: d polyether oh value 480mgkoh-g a’, moisture sense 0.1%; a, b, c, d four polyether are produced by shanghai gaoqiao petrochemical plant iii; levelling agent, acid value `0.1%; moisture appreciation 0.1%; water, distilled water; hcfc a 141b, purity) 99.5%, imported: p201nco31.5%, imported; catalytic system a, b e, d, e, self-matched.

methods we investigated the effect of several catalyst systems in the formulation on the foaming process in our experiments, which were carried out at an ambient temperature of 20 soil 1°c. the stirring speed was 3000 rpm-min’, and each component was weighed in a plastic cup according to the formula except paip, stirred and mixed well, and then the temperature was adjusted to 20°c. the ip was then added to the pre-measured material temperature of 20°c,

then, a cylindrical transparent mold lined with transparent plastic film with elevation scale was set on the plastic cup and timed to record the emulsion time, fiber time, non-stick time and post-curing time of the foaming process as well as the foaming height at certain time intervals. in order to judge the difference of the demoulding characteristics of each catalytic system of foam materials, we mixed different materials as described above and poured them into the test square mould (length x width x height of 2c5m, mould temperature of 45℃, lined with transparent plastic film) for several tests, respectively, 150 seconds, 180 seconds, 210 seconds, 240 seconds, 270 seconds, 300 seconds, 330 seconds, 360 seconds after the start of mixing. the rate of increase in the thickness of the foam formed by each catalyst system was measured for different time periods of demoulding. in the same way, the material was mixed and poured into the l-mold, and the physical properties of the foam in different parts of the l-mold were measured and compared for different catalytic systems.

when the fiber time is the same, the emulsion time of different catalytic systems are not equal, if the length of time interval from emulsion time to fiber time is used to measure the advantages and disadvantages of foam fluidity, the long interval means that there is ample time before the fiber time, the material can be filled with large and complex shape of the mold cavity, the foam distribution is uniform, the density gradient is small, such as the time interval to evaluate the advantages and disadvantages of foam fluidity, from good when the fiber time is the same, the non-stick time and post-curing time of each catalytic system is different, usually the fiber time to non-stick time and non-stick time to the length of the interval after curing time to measure the curing speed, the interval is short means that the curing reaction is fast, the demoulding time can be shortened accordingly. if the time interval to evaluate the relative speed of curing reaction, the order from fast to slow is: when coh, d, e. 3.2 to foam speed curve and rise height and flow index to analyze the foam liquidity from table 3 and the figure can be seen, d catalytic system foam rise speed, especially the initial rise speed, curing height and the final height are better and high, flow index, the average density of foam

in the process of polyurethane rigid foam foaming for refrigerators, foam fluidity and foam curing speed are the main signs of foaming process performance. it can be seen from table 5: good material fluidity, uniform distribution of foam everywhere, small density gradient of foam, bubble pore structure close to uniform fine spherical shape, high closed pore rate, low thermal conductivity, small change rate after foam forming, foam curing speed, can shorten the demoulding time of refrigerator production, improve production efficiency. the selection of suitable amine catalytic system is the key to improve the foam flow and curing speed of refrigerator rigid foam with hcfc 1l4b as blowing agent. the role of different catalytic systems are different.

(l) early-onset catalytic system, the foam nucleation at the time of initiation to promote the role of the thermal conductivity and improve the dimensional stability.

(2) delayed catalytic system, delaying the fiber time, so that the foam is filled with the cavity, good fluidity, small density gradient in each part of the mold, uniform distribution, conducive to the bonding of the foam body and the cavity wall.

(3) promote post-curing catalytic system, which can make the foam from fiber time to post-curing time interval shortened, can be released as soon as possible, thus helping to improve the strength and dimensional stability of the foam system.

(4) the choice of suitable catalytic system can obtain the combination material system with early hair characteristics, superior foam flow and strong post-curing speed.