Preparation of foaming agent
DATE：2022/5/9 9:04:10 / READ： / SOURCE：This station
Preparation of foaming agent
Bubble mechanism: when gas is suspended in liquid or solid, it becomes bubble. Many bubbles gather together and are isolated from each other by the film in close contact with each other, which is called "foam". Foam is actually a dispersion system of gas in solid or liquid. In the production process of formaldehyde foam, there are two dispersion systems. During foaming, the gas is dispersed in the liquid, the air is the dispersant, and the aqueous solution such as resin is the dispersant; As the foam hardens, solidifies, dries and dehydrates, it gradually becomes a gas dispersed in the solid, with air as the fractional substance and urea formaldehyde resin as the dispersant.Urea formaldehyde and other aqueous solutions have great surface tension, so air is not easy to disperse in them. Therefore, surfactant must be added to reduce its surface tension and make air easy to disperse and bubble in the solution.
The foaming mechanism of surfactant mainly depends on the infiltration of asymmetric molecules, which changes the attraction between water-soluble molecules and reduces the surface tension. When air enters the aqueous solution, the arrangement of surfactant is shown in figure 7-40. At this time, the lipophilic nonpolar group in the surfactant molecule faces the air, and the hydrophilic polar group faces the water layer, thus forming a foam. However, the stability and service life of foam largely depend on the dispersant, because the dispersant constitutes the wall of foam. Generally speaking, when the dispersant is a substance with gel like structure, it is most beneficial to the stability of foam. Therefore, the viscosity and concentration of resin solution are directly related to the stability of foam. In addition, since gravity and evaporation can also make the foam wall thinner or deformed, the water content of foam, ambient temperature and other conditions that can promote gravity and evaporation will constitute defoaming factors.
Active agents are divided into anion type, cation type and non-ionic type. At present, anionic surfactants are mainly used. With the rapid development of petroleum industry, sulfonated air has the fastest development, the largest output and the most varieties of anionic surfactants
Bubble shape diagram of surfactant molecules part of non-polar groups in surfactant molecules part of intermediate groups in surfactant molecules part of acids. Such as the widely used pulling powder (the commercial name of alkyl naphthyl sulfonic acid), sodium dibutyl benzene sulfonate, etc.
(3) Acid foaming agent (also acting as hardener) and acid free foaming agent shall be used for the preparation of solution. The formula is shown in table 7-28.
Table 7-28 quality ratio name of typical formula of foaming agent quality ratio acid free foaming agent: sodium dibutyl benzene sulfonate actually acid free foaming agent is the key to determine the foaming ability. The pH value of acid foaming agent is the key condition for resin hardening. Generally, the pH value of foaming agent solution is about 1.1 ~ 1.3. The pH value of the resin solution is about 6.8 ~ 7. Phenol is added to the formula to increase the stability of foam. 4. Prepare sulfosulfonate, put it into the preparation pot, start the mixing, and heat it with swallow steam in the jacket. When the reaction temperature is 70-80 ℃, add the dissolved phenol solution and continue stirring for 1 hour. After all the reaction is dissolved, add the reactant into the high-level tank of acid free foaming agent for standby, which is acid free foaming agent. The limited lifting operation method is the same as above.
(5) For the preparation of foaming and foam block, first open the tank door without acid foaming agent, and then foam under the action of air compressor. After the outflow is stable, open the high-level tank steel door with acid foaming agent, and appropriately reduce the flow of acid free foaming agent; After the outflow of the two foaming agents is stable and the foam of the foaming agent is stable and uniform, open the valve of the high-level tank of the resin solution, wait until the generated styrofoam is continuous and uniform, and then make it flow into the wood mold soaked in glycerin and sent to the curing process for curing.
(6) Curing and post-treatment of the foam block at room temperature 122, and demoulding after 24h curing and pre molding. After demoulding, 14% of the water of the foam has been removed from the foam, which needs post-treatment. Let it stand for about 24 hours, drain the acid liquid, wait for it to dry slightly, and then put it into the drying channel heated by steam for drying. The temperature of the first drying channel is 30-40 ℃, that of the second channel is 40 ~ 45 ℃, and that of the third channel is 45 ~ 50 ℃. The foam block shall be sent to the second drying channel after the first drying channel is dried for 24h. Generally, it shall be dried for about 24h. The unit weight shall be sampled and tested. If the unit weight is not greater than 20kg/m, it is qualified. Otherwise, send it to the third drying channel to continue drying.
In the drying process, due to the influence of high temperature, the water escapes rapidly, resulting in the destruction of some foam, and then causing the shrinkage of foam. The higher the drying temperature or the faster the temperature rise, the greater the shrinkage. According to the measurement, when the drying temperature is less than 50 ℃, the shrinkage is very small. In addition, keeping a certain temperature during drying can also reduce the shrinkage. Therefore, the drying conditions can be specified as follows: the temperature is less than
Hel56 ℃, humidity not less than 85%.
(7) The cutting tools for packaging foamed plastics are fine, mechanical or sharp tools; Fine steel wire, etc. The finished products with good drying quality can not be cut. Due to improper drying, the hard skin layer on the surface shall be cut off. When the finished products are to be transported for a long distance, they shall be moisture-proof
Packing after wrapping with paper.
(8) For labor protection, direct contact with materials and absorption of formaldehyde, methanol and other harmful gases, the main protective measures are to seal the equipment as far as possible to prevent the selection of harmful gases or discharge the harmful gases out of the workshop immediately.
(9) foam plastic production
The control factors in the process are listed in table 7-29. Table 7-29 causes and elimination methods of various abnormal phenomena in the control elements of raw materials: the iron content of raw material formaldehyde is too high. When storing and transporting, it is 7 due to unclean containers or neutralizing kaizhoubao with sodium hydroxide solution. After stirring, it is allowed to stand for one night, and the corrosion is taken into the clear solution of rust layer. During the manufacturing condensation of resin, the resin is sticky (1) when the pH value is adjusted,
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