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Modified MDI -- Study on the application of (coarse MDI) in slow springback of molding

2020-07-14 16:29:30
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Preface

As everyone knows, polyurethane slow rebound foam is also called memory foam viscoelastic foam. Its unique feature is that it can conform to the shape of the load, making the contact area the most, the maximum the stress gradient most small, the stress concentration point can be relieved, there is no local extrusion thorn pain. Therefore, slow springback block foam is widely used as mattress, cushion so on, which is beneficial to the blood circulation of the human body, is a high comfort health care foam. A kind of

Theoretically, the resilience of polyurethane foam is related to the degree of separation the glass transition temperature. The slow springback foam can be obtained by adjusting the glass transition temperature of the foam to the service temperature reducing the phase separation of the foam. The usual technological route is to mix low hydroxyl value soft foamed polyether polyether with higher hydroxyl value to improve crosslinking density of foam, thereby improving the glass transition temperature decreasing the degree of phase separation. For example, cn1606580, cn1572186 cn1229803 are all based on this theory [1-3]. A kind of

Traditional slow rebound polyurethane block foams are prepared by TDI. In recent years, due to the increasing attention to environmental protection, people pay more more attention to MDI, only in the field of molding, but also in the field of block foam to try MDI process [4-10]. In this paper, a modified MDI, wannate 8107, is introduced for the preparation of slow rebound foam. A kind of

The reason for adopting MDI prepolymerization technology is that the foaming density of MDI based foam is higher than that of TDI base. In order to maintain the same foaming density, the MDI system needs a higher amount of water. However, with the increase of water content the increase of urea / carbamate ratio, the urea phase can be separated the Microsoft region of polyether, resulting in instability of foam resulting in a stiff hand feel poor aging properties. MDI based slow springback foam was prepared by prepolymer technology, that is, using high molecular weight polyhydroxyl compound to react with MDI to form prepolymer, which can control the phase separation process in foaming process improve the final performance of foam. Especially when preparing low density foam, MDI prepolymer technology is more important. Secondly, the storage performance of MDI can be improved by prepolymerization of MDI.

Main chemical characteristics of MDI

The TDI for preparing slow rebound foam is usually 2,4,80% (mass fraction, the same below), 20% is 2,6 body. It is colorless yellowish transparent liquid at room temperature, has strong pungent smell crystallizes below 10 ℃. It is a highly toxic dangerous product has strict requirements for transportation. MDI used in this experiment can be stored at 0 ℃ liquid at room temperature. MDI has no irritating smell. The vapor pressure at 25 ℃ is about 1.33 × 10-3 PA, which is 1 / 2700 of TDI. It has low volatility relatively low toxicity to human body. It is a non dangerous goods. It has no special requirements for transportation no pollution in the production foaming process. It is conducive to industrial safety protection is welcomed by production construction personnel. The molecular structure of MDI is similar to that of TDI, which contains - NCO benzene ring. The experimental results show that MDI TDI have the following differences:

Hardness curve of TDI MDI system with index

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