What Is a Purlin?

Polyurethane (PUR) is a polymer with repeating structural unit of urethane segment, which is made by reacting isocyanate and polyol. PUR products are divided into two categories: foamed products and non-foamed products. Foamed products include soft, rigid, and semi-rigid PUR foam; non-foamed products include coatings, adhesives, synthetic leather, elastomers, and Elastic fibers and so on. PUR materials have excellent properties, are widely used, and have a wide variety of products, among which PUR foam is the most widely used.

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Right!

Polyurethane (PUR) is a kind of urethane segment repeater made by the reaction of isocyanate and polyol

The production of PUR foam in China began in the 1950s. The main product is flexible foam. The PUR foam industry has been developed for more than 40 years. In the mid-1960s, China began to produce rigid PUR foam, which is mainly used for the insulation of ships, cold storage, and petrochemical pipelines. By the mid-1970s, there were only more than 10 manufacturers with a production capacity of about 15,000 t / a, and the actual annual output was about 3kt. The 1980s was a period of rapid growth of China's PUR foam plastics, and the output of products continued to increase, with an annual growth rate of 25%. In the 1990s, China s PUR basic materials, additives and products have developed rapidly. 180 to 200 sets of advanced foaming equipment have been introduced, which greatly increased the production capacity and annual output of foam plastic products, and increased the production capacity to 200,000 Above t / a, the average annual growth rate of PUR foam is 20% to 30%. The actual output in 1994 was about 100,000 tons, of which about 60,000 tons were flexible foam.

PUR foam is the most important PUR product. It has a wide range of uses and excellent performance: soft PuR foam and semi-rigid PUR foam are mainly used for furniture padding and decoration materials, car mats, carpet backing, and clothing lining. , Building sound-absorbing materials, sports mats, and mattresses and instrument packaging materials. Among them, the main uses of molded flexible PUR foam are automotive seat cushions and motorcycle and bicycle seat cushions; while rigid PUR foam is mainly used in refrigerators and cold storage industries as heat insulation materials, accounting for rigid foam 57.5% of total consumption. China is the world's largest refrigerator producing country. In 1998, it consumed 80,000 to 100,000 tons of rigid foam plastics, and used 15% of insulation materials for petroleum pipelines, chemical storage tanks and industrial equipment. The building materials were rigid PUR foam. Another large application area of plastics, in 2000, the construction industry consumed more than 70,000 tons of rigid PUR foam. Due to the rapid development of China's construction industry, foam plastics used for building insulation, sound absorption, decorative materials and mobile homes account for 10%; thermal insulation materials used for transportation account for 10%; others account for 7.5%, of which furniture, clothing, The consumption of bicycles is large. In addition, the development of China's automobile industry and motorcycle industry also provides a broad market for molded flexible PUR foam. According to experts' predictions, due to the excellent plasticity of PUR and the strong practicality of material properties, its application in automobiles is increasingly expanding. It is estimated that the demand for PUR in China's automobile industry (excluding Taiwan Province) will reach 44,100 tons in 2005, of which 30,400 tons will be consumed by cars and Jeep cars, 33,000 tons will be consumed by heavy-duty cars, 70,200 tons will be consumed by light vehicles, and 0.05 will be consumed by mini vehicles 10,000 tons, the average consumption of each vehicle reached 14.71kg.

The difference between China and developed countries in this regard is that foreign rigid PUR foam plastics are mainly consumed in the construction industry, accounting for more than 50% of the consumption of rigid foam plastics, and most of our country is used in refrigerators, cold storage, and construction industry. Insulation materials are still in their initial stages. The rapid development of the automotive and motorcycle industries provides opportunities for the development of the PUR foam industry, and its potential market is also very broad. According to forecasts, the current demand for PUR foam in China has reached 800,000 to 1 million t / a.

The development of new technologies focuses on environmental protection. As an industry with an average annual growth rate that is higher than the global economic growth rate, the rapid development of the PUR industry depends on the rapid development of its technology and the continuous expansion of its application fields. In the development of many new products, the research work of PUR blowing agent is particularly interesting. According to the requirements of the Montreal Agreement and the revised National Plan for the Phase-out of ODS in China, the foam industry should completely stop using chlorofluorocarbons as blowing agents by 2010, and completed by large PUR foam companies before 2005 CFC-11 replacement work.

The alternative technologies used are roughly:

(1) Continuous ring flexible foam plastic uses dichloromethane as a foaming agent, which must be combined with rapid curing and liquid carbon dioxide foaming methods;

(2) The box-type flexible foam is foamed with dichloromethane and reduced pressure;

(3) Semi-rigid foam is foamed with HFC-141b, pentane or carbon dioxide. Therefore, the development of new CFC blowing agent alternatives has become the focus of research in various scientific institutions.

Liu Xianming conducted intensive research on the low foaming process. Qiu Yanchen and others discussed the properties of chlorofluorocarbon (CFC-11) substitute cyclopentane and the research results of the application of rigid PUR foam plastics in all-fluorine-free green refrigerators, which solved the flammability of cyclopentane foaming agents. , Explosive and poor solubility in polyether polyols.

Guan Zhiqiang et al. Studied the new generation of alternative technologies for hydrocarbon foaming. According to the application of PUR rigid foam technology in cyclopentane-isopentane foaming in refrigerators, the foaming process and performance were compared with the cyclopentane foaming system.

The results show that compared with the cyclopentane foaming system, the cyclopentane-isopentane foaming system has good processing technology, the amount of foaming infusion in the refrigerator is reduced by 7%, the density of the foam plastic is reduced by 10%, and the size Good stability, density distribution is more uniform than cyclopentane foaming system.

Su Li discussed the technical route of replacing low-density soft PUR foam with full-water foam in chlorofluorocarbons. The results show that the new full-water foam formula can reduce the density of soft slab foam to 15-20kg / m, the density of the molded foam is reduced to 25 kg / m3, while its mechanical properties remain in good condition.

Wang Hongwei compared the foaming characteristics of 4 types of zero ozone depletion potential (ODP) blowing agents [water, hydrocarbons, perchloroalkanes, hydrofluorocarbons (HFCs)] for rigid PUR foams, and focused on them. Taking HFC-134a and HFC-356 as examples, the application of hydrofluorocarbon blowing agent in rigid PUR foam is introduced.

From the results of these studies, it is not difficult to see that most of the CFC replacement in the production of flexible foams uses the dichloromethane route as a transition. Among the zero ODP replacement routes, the technology of foaming with carbon dioxide has made the fastest progress. Of course, HFCs can also be used as a zero ODP replacement, but the priority target of this class of materials has not yet been officially industrialized, and further technical and economic needs to be evaluated. Cyclopentane and dichloromethane foaming can be used to produce self-skinned foam plastic products with good skin layers, but the strict measures and costs required for this method in terms of safety production make it difficult for enterprises to generally accept, a new generation of zero ODP For example, 1,1,1,3,3-pentafluoropropane (HCFC-245fa) and 1,1,1,3,3-pentafluorobutane (HFC-365fmc) are expected to become ideal final substitutes. In terms of rigid PUR foam, for applications where thermal conductivity is not particularly stringent, the use of all-water foam is a simpler option, and for more demanding applications (such as building boards) the replacement problem is more complicated. While studying the foaming agent, in-depth research should also be conducted on the selection of raw materials, optimization of the process route, and improvement of toughness.

Some people have also researched the additives for rigid PUR foam, and have achieved good results. Among them, ammonia-based catalysts have developed rapidly, and bis (dimethylaminoethyl) ether has been successfully developed and commercialized by Jiangsu Chemical Industry Research Institute. Liming Chemical Research Institute has also successfully developed this catalyst and has put it into production. Jintan Auxiliary Factory and other companies produced IV, IV. Dimethylcyclohexylamine has a wide range of uses in rigid PUR foam. A number of new catalysts (including delayed catalysts) for molding foam have also been commercialized. The total content of stannous octoate in the Dong'an Chemical Plant in Shanxi, Cangzhou Fine Chemical Test Plant, Zhuji Fine Chemical Industry Company in Zhejiang Province, and the Chemical Research and Design Institute in Hubei Province is greater than 28%. %. Beijing Elf Ato Integrated Stabilizer Co., Ltd. is the largest manufacturer of dibutyltin dilaurate in China. Silicone stabilizers for rigid PUR foams and silicon-oxycarbon-type foam stabilizers for flexible foams have also long been industrialized. New products have been put on the market in the Jiangsu Chemical Industry Research Institute, Shanghai Gaoqiao Petrochemical Company's No. 3 Chemical Plant, and Zhejiang University Fine Chemical Plant. Sinopec Tianjin Branch Research Institute has also developed and produced foam stabilizers (foam stabilizers) for flexible PUR foams. This product is a (silicone resin / polyoxyalkylene) copolymer and an important aid for flexible PUR foams Agent. It is planned to invest 20 million yuan to construct a 1kt / a soft foam homogenizer. The soft foam stabilizer has a high added value. It is said that its raw material cost is about 20,000 yuan / t. In addition to other costs, the total production cost does not exceed 22,000 yuan / t. Currently, imported soft PUR soft foam stabilizer The price of the agent is 50,000 yuan / t.

In terms of flame retardancy, nitrogen-containing flame retardants, intumescent flame retardants, inorganic flame retardants, and expandable graphite flame retardants can all play an important role in the flame retardance of PUR foam. The mainstream of polymer material flame retardant development has been booming, and many new products have emerged; however, the flame retardant properties and manufacturing processes of various new flame retardants are not perfect, and further research and development and improvement should be made to Obtain a new and efficient halogen-free flame retardant that meets the requirements.