Research and Application Prospects of PE Wax Ultrafine Powder

By Qi Shujing, the Research Institute of PetroChina Jilin Petrochemical Co., Ltd.Polyethylene (PE) wax is a kind of polyolefin synthetic wax with a relative molecular weight of 1 000-5 000 g/mol. PE wax with typical molecular weight is a white powder with non-toxicity, narrow molecular weight distribution, high softening point and low melt viscosity, and its applications in plastic sector are very extensive. According to the different manufacturing methods, PE wax can be divided into polymerization type and cracking type. Polymerization type PE wax is generally as a by-product during the polymerization of ethylene, and cracking type PE wax can be obtained through the cracking of pure PE resin or waste plastics. PE wax has excellent mechanical properties and electrical properties, good dispersion and fluidity, good mold-stripping performance, lightfastness, and stability against light and chemical erosion. It is a processing auxiliary for PVC pipes, profiles, films, cables as well as other plastics and rubbers, and it can improve the production efficiency of plastic processing as well as the appearance of products.

Breakthroughs in the production technologies have been achieved

The PE wax ultrafine powder is a high and new technology that has developed in recent ten years. At present, the production and application technologies of ultrafine powder have been industrialized, and have acquired application in more and more sectors. At present, the domestic output of PE wax ultrafine powder cannot meet the market demand, and a large amount needed to be imported every year. The price of PE wax ultrafine powder has been high in recent years, being RMB6 000-13 000/t, and it has a sound profit margin. However, up to know, its production technology in China is not mature. Domestic producers are used to directly sell PE wax powder after spraying without further processing, and thus usually not all of their product properties, such as appearance, particle size, melting point, softening point and acidity, cannot meet the technical requirements at the same time, leading a limited application scope of their products. In order to improve product quality and expand application fields, their production technology and equipment still need to be improved to reach an international level.
Two production processes of PE wax ultrafine powder can be divided into two categories: traditional methods and non-traditional methods. Traditional methods use mechanical forces including wind power and waterpower to crush, smash and grind the materials. Non-traditional methods include chemical coprecipitation method, sol-gel method, spray pyrolysis method and gas-phase method. Currently, domestic players which have relatively advanced production technologies of PE wax ultrafine powder include Beijing University of Chemical Technology and the No.2 Fine Chemical Plant of Nanjing Yangzi Petrochemical Industry Co., Ltd. In addition, Fushun Tongyuan Science and Technology Development Research Institute imported the airflow dispersion nanometer micronization technology from the United States which features simple production process, low cost and controllable particle size. The production technology developed by Beijing University of Chemical Technology also has advantages including simple production process, low cost and controllable particle size. The PE wax micro-powder produced is a white powder with an average diameter of 4-40 micrometers, and mainly used in coatings and printing ink sectors.
In recent years, a new technology for the PE wax ultrafine powder - rapid expansion of supercritical solutions (RESS) has stood out from competing technologies. The new process features low pollute emission, simple manufacturing process, low operating temperature and being suitable for a wide range of materials. Its product has advantages of high purity, homogeneous geometry, and narrowed size distribution. As a green technology for making fine particles, RESS will have broader prospects in the future.

Market prospects are bright

By adding PE wax ultrafine powder, the performance of ink and coatings in the following aspects can be greatly improved:
(1) Due to the small particle size and the ability to migrate to the surface of coated film, the coated film has good matting performance, especially added with silica powder.
(2) It can improve scratch resistance and notch resistance of coatings by reducing the friction coefficient of coatings.
(3) When the proportion of PE wax ultrafine powder reaches 1.5%-2% in coatings, the abrasion resistance of coated film increases by 1-5 times.
(4) It can prevent the products from blocking that is caused by the accumulated overlap of products during the production of coatings and inks.
With the enhancement of people's awareness of environmental protection, waterborne coatings and printing ink will have a great development, promoting the consumption of PE wax ultrafine powder significantly.
At present, the consumption market of PE wax in China is mainly concentrated in Shanghai, Jiangsu province, Zhejiang province, Fujian province, Northeast China, Guangxi region, Guangdong province and Shandong province, etc. The domestic potential market is mainly in the central and western regions like Henan, Hubei and Sichuan provinces. There is often less variety and insufficient supply in the domestic market and China can only rely on the imports or substitutes to satisfy the demands. Major import sources include South Korea, Thailand and Malaysia.
In China, PE wax has been listed as one of the key products to be developed in the country. Sinopec Group has also listed it as one of the products with high added value through product portfolio adjustment. All of these offer a broad market space for the development of PE wax.

Applications in coatings

After adding emulsifiers into PE wax ultrafine powder to make emulsion, adding the emulsion into acrylic resin can greatly improve the hydrophilicity of acrylic resin and improve its performance in anti-skid, anti-adhesion and resistance to stains.
At present, the Asia has become the world’s largest production area and consumption market of coatings with the output in the region accounted for about 45% of the world total. While the consumption of coatings in China accounted for over 50% of the total output in Asia. In recent years, driven by factors such as the tightening policy on energy saving and emission reduction and the enhancement of consumers’ awareness of environmental protection, waterborne coatings has become the strategic development focus of domestic coatings enterprises. China’s coatings sector will increase the investments on the research and development of waterborne coatings.

Applications in road paint

PE wax micro-powder can appropriately control the film gloss and achieve the matting effect, which is important for road painting. However, due to its shortcomings like incompatibility with nitro cellulose, high hardness and high melting point, PE wax ultrafine powder should be dispersed in to toluene before adding into road paints. PE wax with different sizes and varieties has a different matting effect. From fully maintaining luster to deep matting, consumers can allocate the amount of PE wax according to the needs to achieve an ideal effect.

Applications in plastic dyeing

PE wax ultrafine powder can be used as pigment dispersant for plastic dyeing. In the plastic dyeing, dispersion degree of pigment has a great impact on the quality of dyeing products. Therefore, pigment should be mixed in a mixer, uniformly distributed in the dispersing agent in advance to be as a colorant for plastic dyeing. As a dispersant, PE wax ultrafine powder has advantages such as good compatibility with plastics and good heat resistance, good mixing property with pigments, little change on the color of pigment and that of final products. In addition, PE wax ultrafine powder can improve the wetting and dispersing properties of pigment agglomerates, and thus improves the coloring intensity of pigments.

Applications in printing inks

PE wax can be added in PE film, PP film as well as moisture-proof cellophane paper to be used as packaging materials for fruit sugar, milk, fruit juice, skin care products, drug bottles, detergent and food. It is also an excellent wear-resisting agent for inks.
According to the latest research report from SRI of the United States, in the next 5 years, the average annual growth of printing ink market in the world is expected to be 0.7%. Of which, the consumption of printing ink in North America, Western Europe, Asia (excluding China), China, Central and Eastern Europe, South and Central America, and the Middle East and Africa will account for 32%, 25%, 21%, 10%, 6%, 5% and 1% of the world total, respectively.
According to SRIC, despite the decline in the cost of raw materials, the competition is still very fierce. The printing ink producers in Europe will face the pressure from more stringent environmental regulations including the control of solvent emissions and the treatment of wastes. In the next 5 years, China will become a country with the fastest demand growth of printing ink in the world with an average annual growth of 6%.

Conclusion

PE wax ultrafine powder is a kind of polyolefin synthetic wax with high softening point, very low melting viscosity and good dispersion property. It has good compatibility with other wax and polyolefin resins, and also has characteristics such as wet resistance at room temperature, chemical resistance as well as excellent electric properties. It is expected that in the next few years, the applications of PE wax ultrafine powder in coatings, inks and wax products like floor wax, car wax and polishing wax will also have a great development space. At present, the micronization technology has become a research focus. Through the preparation, application and further development of polymer micro-powder, its more new properties and applications will be exploited, and the new fields of functional polymer as well as intelligent materials will be expanded.