Polyurethane foam plastics
DATE：2022/4/11 8:51:51 / READ： / SOURCE：This station
Polyurethane foam plastics
There are many types of polyurethane foam, but the molding process generally has to pass through the following process.The raw material to the metering system consists of the first mock exam, the foaming system, the first one, the foaming process, the first product, the curing process, the collection, the raw material preparation, the spraying, and the curing and foaming of other materials, although the finished product type is not complete, but the basic process is similar. The following are introduced in the order of technological process.
1、 Raw material preparation hollow board production line www.handern.com com
1. raw material components of polyurethane foam plastics
After vaporization, it is not the source of bubbles, and the reaction heat can be removed to avoid "scorching" ground foam in a center due to high strength
External curing agents (such as CFC, or CIL. C; etc.) to improve the properties of heat, steel aging, heat aging, etc. provide various color foreign antioxidant pigments
() the main material of ammonia is toluene diisocyanate (TDI), which is divided into:
CH; 2,4-TDI CH; - NCO and 2.6-tdi OCN - NCO NCO hollow board production line www.handern.com com
Two isomers with different chemical structures usually use a mixture of 2,4 - and 2.6-isomers. The proportion of these two isomers is called isomer ratio. The expression often writes the proportion of 2.4-body in the front (or above), and the proportion of 2,6-body in the back (or below): for example, 80 / 20 is toluene diisocyanate containing 80% 2,4-body and 20% 2,6-body. In the foaming production process, toluene diisocyanate reacts with the hydroxyl of polyester or polyether resin to form polyurethane; React with water to generate carbon dioxide gas for foaming; And react with the intermediate product formed by hydrolyzed salt to make the polymer cross-linked. In addition, the isomerization ratio is also an important factor in foaming. Below 40 ℃, the reaction speed of 2.4-tdi is 5 ~ 10 times faster than that of 2,6-TDI. When the temperature rises to about 100 ℃, there is no difference between the two activities. At the end of solidification reaction, 2.6-tdi is more conducive to the completion of solidification reaction than 2,4-TDI. The higher the isomerization ratio, the quicker the gas and solidification reaction is, the more the foam tends to the obturator structure. Commonly used isocyanates in foam plastics are: two benzyl methane, diisocyanate, and polymethylpolyphenyl isocyanate (PAP1) and so on, which are qualitative in hard frequency material, while soft foam plastics are commonly used in TDI. We rent MDI, Papi or TD oligomers to obtain higher stiffness and better size hollow plate production line www.handern.com com
(2) polyether resin or resin is the main raw material for foamed plastics production. Polyester is a resin with hydroxyl groups at the molecular end, which is generally polycondensated with binary light acid and polyol. Polyether is made of oxidized olefins and polyols. Light foam plastics contain polyfunctional polyols with low functional groups, low hydroxyl value and high molecular weight, three functional polyether polyesters or polyester polyesters with a molecular weight of 2000 or two functional groups with a molecular weight of 3000. Hard foam and plastic are usually polyether or polyester polyol with hydroxyl functionality of 3 ~ 8 and average molecular weight of 400 ~ 800. In recent years, in order to meet the needs of new varieties and new processes, the "high activity polyether" has been developed in the aspects of propylene oxide polyether polyol, that is, ethylene oxide is connected to the secondary hydroxyl end of propylene oxide polyether polyol to make it become the primary hydroxyl, so as to improve the reaction activity of polyol.
(3) in the production of catalyst polyurethane foam, the catalyst can regulate polymerization rate (chain growth) and gas generation rate (foaming). The former mainly catalyzed by organotin catalyst to accelerate its reaction, so that the foam wall has enough strength to contain gas, which is also controlled the rate of gas production at the same time, while tertiary amine catalyst is mainly conducive to foaming reaction. In addition, when organotin catalyst is used, it can inhibit unnecessary side chain reaction and is beneficial to the final quality of foam plastic products. Therefore, in the industrial one-step foaming system. The catalyst usually selected is the mixed system of organotin and tertiary amine compounds. Adjusting the ratio of the two parts can effectively control the chain growth rate and the foaming rate of the foam plastics. The commonly used tertiary amine catalysts are N-methyl morphorphine, triethylamine, triethylenediamine and 4-methyl 1,3-butanediamine. Common organotin catalysts include tributyltin acetate and dibutyltin diacetate. Hollow board production line www.handern.com com
(4) foaming agents used in polyfoam plastics are commonly used in water and low boiling point fluorine hydrocarbons, and water and isocyanates act as carbon dioxide as foaming gas. However, it should be noted that polymers produced by water and isocyanate have polyurea structure. If they are not mastered properly, they will become brittle. As water foaming, the heat generated is much larger than that of low boiling point solvents. Carbon dioxide passes faster in the foam and facilitates opening. Therefore, water bubbles are often used in soft foam production. Rigid foam has high porosity and low boiling point fluorine hydrocarbon as foaming agent. When the hetero tire reacts with the active hydrogen compound, it will release a large amount of heat to vaporize the fluorine compound and produce a large number of bubbles. They do not chemically change other components. The specific types are trifluoromethane (f point 24) dimethyl (f12298 ℃). (5) the most important foam stabilizer of foam stabilizer is silicone based renting agent. The role of stabilizer is to reduce the surface tension, is conducive to the formation of foam, and can be used as raw material emulsifier, make it become a homogeneous mixture, ensure the entire foam generation reaction uniform. It has been proved by practice that foam stabilizer is one of the key components in the production of foam plastics. Soft foam plastics depend more on stabilizer than rigid foam plastics. The amount of 0.5%~2.5% should be branched and suspended stabilizer. Rigid foam is highly stable because of the high crosslinking degree. The molecular weight of the stabilizer is generally lower than that of the soft foam plastics, and the non hydrolytic foam stabilizer is commonly used.
(6) Effect of acid and alkali on the reaction like many fusible heavy metal compounds, alkali is a strong catalyst for the reaction of isocyanate, while acid usually has a weak catalytic effect on some isocyanate reactions. In practical application, some acids are often used as stabilizers of isocyanate system because they neutralize the trace alkali produced in the process of polyether polymerization or inactivate some metal catalysts, so as to achieve the stable effect. Hollow board production line www.handern.com com
Author：admin