In the process of polyethylene production, a small amount of oligomer, namely low molecular weight polyethylene, is produced. It is widely used because of its excellent cold resistance, heat resistance, chemical resistance and wear resistance. In normal production, this part of wax can be directly added to polyolefin processing as an additive to improve the optical translation and processing performance of the product. Polymer wax is a good desensitizer, and can also be used as dispersion lubricant for plastics and pigments, moisture-proof agent for corrugated paper, hot melt adhesive and floor wax, and automobile beauty wax.

Second, the chemical properties

Polyethylene wax R-(CH2-CH2)n-CH3, with molecular weight of 1000-5000, is a white, tasteless and odorless inert substance, which can be melted at 104- 130℃ or dissolved in solvents and resins at high temperature, but the temperature is reduced. During the film-forming process of powder coating, when the coating is cooled, polyethylene wax is precipitated from the coating solution to form fine particles, which float on the surface of the coating film, playing the roles of texture, matting, smoothness and scratch resistance; Various patterns can be obtained by properly selecting micro-powder wax and coating system.

Third, technological development.

Micro-powder technology is a high-tech developed in recent years. Generally, particles with a particle size less than 0.5μm are called ultrafine particles, those with a particle size less than 20μm are called microparticles, and aggregates of ultrafine particles are called ultrafine powder.

There are three main methods to prepare polymer particles: one is to start with coarse particles and adopt physical methods such as mechanical crushing, evaporation, condensation and melting; Secondly, with the action of chemical reagents, molecules in various dispersed states gradually grow into particles of expected size, which can be divided into two types: dissolution and emulsification. Third, directly adjust the polymerization or degradation preparation. Such as PMMA micropowder, controllable molecular weight PP, dispersion polymerization to prepare PS microparticles, thermal cracking to radiation cracking to prepare PTF micropowder. At first, we prepared PWEax micropowder in China, and it reached the advanced level of similar products abroad through the test in Shanghai powder engineering pilot base. The main technological process is physical method.

(A) the application of polyethylene glycol micropowder

1. Polyethylene wax for coatings can be used to prepare high-gloss solvent-based coatings, such as water-based coatings, powder coatings, canned coatings, ultraviolet curing, metal decorative coatings, etc. , and can also be used as daily moisture-proof coatings such as cardboard.

2, ink, overprinter varnish, printing ink. PEWax can be used to prepare letterpress water-based ink, solvent gravure ink, lithographic/offset printing ink, ink, overprint varnish and so on.

3. Cosmetics and personal care products. Beeswax can be used as raw material for powder cake and antiperspirant/deodorant.

4. Micro-powder wax for coiled material. Wax for coil has two requirements: that is, when improving the surface smoothness and hardness of the coating, the leveling and water sensitivity of the coating should not be affected.

5. Hot melt adhesive. PEWax micropowder can be used to prepare hot melt adhesive for hot stamping.

6. Other applications. PEWax can also be used as an isolation agent for cast-pressed metal parts and foam parts, an additive for rubber-plastic sheets and pipes, a modifier and an electrorheological agent for purple oil, a carrier and a lubricant for masterbatch.

(2) Development of modified polyethylene wax

In the early 1990s, we modified low molecular weight polyethylene wax, and there were many reports about carboxylation and grafting. Abroad, Germany, France, Poland and Japan applied for patents. China also applied for related patents in two stages.

According to literature research and market analysis, polyethylene wax and modified polyethylene wax, especially after micronization, will have greater development. The surface effect and volume effect of polyethylene micro-powder wax provide excellent physical and chemical properties for the development of new products, and more series of ultra-fine powders will be available to meet the requirements of various fields such as ink, coatings and finishing agents.

Four. Application and mechanism in coatings

Wax for coatings is mainly added in the form of additives. Wax additives generally exist in the form of water emulsion, which was originally used to improve the surface anti-swelling performance of coatings. It mainly includes improving the smoothness, scratch resistance and water resistance of the coating film. In addition, it can also affect the rheological properties of coatings, and its addition can make the orientation of solid particles such as aluminum powder in metal flash paint uniform. It can be used as matting agent in matte paint. According to its particle size and particle size distribution, the extinction effect of wax additives is also different. Therefore, wax additives are suitable for glossy paints and matte paint. Microcrystallization modified polyethylene wax can be used to improve the surface properties of waterborne industrial coatings. Such as Ffka-906, the smoothness, anti-adhesion, scratch resistance and extinction effect are enhanced after being added, which can effectively inhibit pigment precipitation. The addition amount is 0.25%-2.0%.

(a) Characteristics provided by wax in coating film

1. Wear resistance, scratch resistance and scratch resistance: wax is distributed in the coating to protect the coating, prevent scratches and scratches, and provide wear resistance; Such as container coatings, wood coatings, decorative coatings, etc. Everyone needs this function.

2. Control of friction coefficient: Usually, its low friction coefficient is used to provide excellent smoothness of the coating, and at the same time, it has the soft touch of special silk due to different types of wax.

3. Chemical resistance: Due to the stability of wax, the coating film can be given better water resistance, salt water spray resistance and other properties.

4. Prevention of adhesion: avoid adhesion and adhesion of coating or printed matter.

5. Control the glossiness: Choose a suitable wax, and different amounts of wax will have different extinction effects.

6. Prevent the deposition of silicon dioxide and other hard knots, and increase the storage stability of the coating.

7. Anti-metal marking: Especially in the coating for printed cans, it can not only provide good processability, but also protect the storage stability of printed cans.

(2) Characteristics and mechanism of wax in coatings

There are many kinds of wax, and the forms of wax in coatings can be roughly divided into the following three types:

1. Frosting effect: For example, when the melting point of the selected wax is lower than the baking temperature, the wax melts into a liquid state during baking, and after cooling, a frosty thin layer is formed on the surface of the coating.

2. Spherical axis effect: This effect is that the wax is exposed through its own particle size close to or even greater than the thickness of the coating film, thus showing the scratch resistance and scratch resistance of the wax.

3. Floating effect: No matter what the particle shape of wax is, in the process of film formation, the wax drifts to the surface of the coating film and spreads evenly, so that the top layer of the coating film is protected by wax, showing the characteristics of wax.

(3) Production method of wax

1. melting method: the solvent is heated and melted in a closed high-pressure container, and then discharged under appropriate cooling conditions to obtain the finished product; Disadvantages are poor quality control, high operating cost and danger, and some waxes are not suitable for this method.

2. Emulsification method: Fine and round particles can be obtained, which is suitable for water-based systems, but the added surfactant will affect the water resistance of the coating film.

3. Dispersion method: add the wax into the tree wax/solution and disperse it with a ball mill, roller or other dispersing equipment; The disadvantage is that it is difficult to obtain high-quality products and the cost is high.

4. Micro-pulverization method: the production process of jet-micro-pulverizer or micro-pulverizer/classifier can be adopted, that is, the crude wax is gradually broken into particles after colliding with each other at high speed, and then blown out under weightlessness and collected by centrifugal force. This is the most widely used manufacturing method at present.

Although there are many ways to use wax, micronized wax is still the most, and there are many kinds of micronized wax in the market, and the production process of each manufacturer is different, which makes the particle size distribution, relative molecular weight, density, melting point, hardness and other properties of micronized wax from different manufacturers somewhat different.

The manufacture of polyethylene wax generally includes high pressure and low pressure polymerization; Among them, the polyethylene wax prepared by high pressure method has branched chain, and its density and melting temperature are low, while the wax with low specific gravity can be prepared by low pressure method. Polyethylene waxes have different densities. For example, nonpolar PE wax prepared by low pressure method is usually hard with low density (low branching and high crystallinity) and has good wear resistance and scratch resistance, but it is slightly poor in smoothness and friction coefficient reduction.