discussion on the application of catalyst in polyurethane foam for refrigerators
preface
in the foaming process of polyurethane foam for refrigerators, a one-step method is generally adopted. for refrigeration equipment such as refrigerators, factors such as uniform distribution of foam in large cavities with complex structures, the degree of bubble fineness, and the foam closure rate have a great impact on the overall performance of the refrigerator, which are related to the firmness of the bonding between the foam and the cavity wall, the dimensional stability of the foam, etc. with the continuous emergence of new varieties of rigid polyurethane foam raw materials, and in view of the urgent desire of refrigerator manufacturers to speed up the production pace in order to improve production efficiency and reduce costs, we consulted relevant information, screened and improved a variety of amine catalysts, conducted a series of controlled application tests, and applied them to polyurethane rigid foam for refrigerators with hcfc-14b1 as the foaming agent. these situations are discussed below.
main raw materials and specifications a polyether, oh value 430mgkoh·g1′, moisture detection 0.1%: b polyether, oh value 400mgkoh·g1′, moisture egg 0.1%; c polyether, oh value 360mgkoh·g1′, moisture ‘0.1%:d polyether, oh value 480mgkoh·g1’, moisture sensitivity 0.1%; a, b, c, d tetrapolyether are all produced by shanghai gaoqiao petrochemical no. 3 plant; homogenizer, acid value ‘0.1%; moisture detection 0.1%; water, distilled water; hcfc 141b, purity) 99.5%, import: p 21nco 31.5%, imported; catalytic system a, b, e, d, e, self-combined.
methods in the experiment, we investigated the influence of several catalyst systems in the formula on the foaming process, and the experiment was carried out at an ambient temperature of 20 soil and 1 °c. the stirring speed is 3000 rpm, according to the recipe, take all components except paip in a plastic cup, stir and mix evenly, adjust the temperature to 20 °c, and then add the ip of the material temperature measured in advance to 20 °c.
stir for a few seconds, then put a cylindrical transparent mold with elevation scale lined with transparent plastic film on the plastic cup, time, and record the milky time, fiber time, non-stick time and post-curing time of the foaming process, as well as the foaming height at certain intervals. in order to judge the difference in the release characteristics of the foam material composed of each catalytic system, we mix different materials according to the above method and start foaming, pour the human test in the square mold (length x width x height is 2c5m, mold temperature 45°c, lined with transparent plastic film), carry out multiple tests, respectively 150 seconds, 180 seconds, 210 seconds, 240 seconds, 270 seconds, 300 seconds, 330 seconds, 360 seconds after the start of stirring, the release test is done, respectively after the start of stirring. the thickness increase rate of each catalyst system formed by demolding at different times was measured. similarly, using the above method, the material is mixed and poured into the l mold, the physical properties of the foam in different parts of the l mode are determined, and the different catalytic systems are compared and tested
when the fiber time is the same, the milky time of different catalytic systems is unequal, if the time interval from the milky time to the fiber time is used to measure the quality of the foaming fluidity, the long interval time means that there is more time before the fiber time, the material can calmly fill the large and complex shape mold cavity, the foam distribution is uniform, the density gradient is small, if the quality of the foam fluidity is evaluated according to the time interval, then the order from good to bad is d one time boc and one e. when the fiber time is the same, the non-stick time and post-curing time of each catalytic system are different, usually the interval from fiber time to non-stick time and non-stick time to post-curing time is used to measure the speed of curing. if the relative speed of the curing reaction is evaluated according to this time interval, the order from fast to slow is: time coh, d, e. 3.2 foam fluidity analysis by foaming velocity curve, rising height and flow index from table 3 and figure, it can be seen from table 3 and figure that the foam rises rapidly in the catalytic system, especially the initial rise rate, the curing height and final height are good and high, the flow index is large, and the average foam density is high
in the foaming process of polyurethane rigid foam for refrigerators, foam fluidity and foam curing speed are the main indicators of foaming process performance. from table 5, it can be seen that the material has good fluidity, uniform foam distribution everywhere, small foam density gradient, close to uniform fine spherical shape, high closure rate, low thermal conductivity, small change rate after foam forming, fast foam curing speed, which can shorten the demolding time of refrigerators and improve production efficiency. the selection of a suitable amine catalytic system is the key to improving the foam fluidity and curing speed with hard foam in the refrigerator with hcfc-11l4b as the blowing agent. different catalytic systems play different roles.
(l) early-onset catalytic system, which promotes nucleation during foam initiation, which is conducive to improving thermal conductivity and dimensional stability.
(2) delayed catalytic system, delay the fiber time, so that the foam calmly fills the cavity, good fluidity, the density gradient of the product in each part of the mold is small, and the distribution is even, which is conducive to the bonding between the foam body and the cavity wall.
(3) promote the post-curing catalytic system, which can shorten the interval between fiber time and post-curing time, and can be demolded as soon as possible, which is conducive to improving the strength and dimensional stability of the foam system.
(4) by selecting a suitable catalytic system, a composite material system with early occurrence characteristics, superior foam fluidity and strong post-curing speed can be obtained.