The film is mainly made of polyvinyl chloride, polyethylene, polypropylene and other resins. It has softness, ductility, good processing performance and printing performance. It has been widely used in food, medicine, chemical industry and other fields. However, due to the cost of resin production High, the impact on the environment is large, usually need to add fillers to reduce costs.
Due to the performance problems of common fillers, the transparency of the film will be affected. At present, the particle size of the talc filler for transparent masterbatch on the market is micron, the particle is coarse, and the transparency and strength are poor; the sodium sulfate filler is a water-soluble substance, which is easily soluble in water, and has poor water resistance and weather resistance. Not suitable for products with higher requirements.
Because of its high transparency and good gloss, nano-barium sulfate is often used in films that require high transparency. On the other hand, it is prepared by the reaction of sulfuric acid and barium carbonate. With the same weight of masterbatch, the blown film area is small, resulting in high film production cost.
As a new type of filler, nano-calcium carbonate has the advantages of small particle size and large specific surface area, which can increase the strength of plastic films, and has the advantages of small specific gravity and low manufacturing cost. However, due to the small particle size of nano-calcium carbonate, it is easy to cause poor compatibility between agglomeration and plastics, which affects its transparency and dispersion.
Liu Yaxiong used barium sulfate, stearic acid soap, phosphate coupling agent and citric acid ester to conduct inorganic-organic composite modification of nano-calcium carbonate, and investigated the effect of active nano-calcium carbonate on the properties of PE films.
1. Preparation of active nano-calcium carbonate
Preparation process: limestone and anthracite are mixed in a shaft kiln at a ratio of 10:1, and the calcination temperature is 1000±100℃ to obtain lime and kiln gas; the kiln gas is purified to obtain clean kiln gas; quicklime and hot water are placed in a rotary digester Carry out digestion reaction to obtain milk of lime, sieve and age the milk of lime to obtain refined milk of lime, adjust the temperature of milk of lime to be 18～30 ℃, and the concentration is 6%～10%; pump the refined milk of lime into the carbonization reactor, Introduce clean kiln gas (containing 30% to 35% CO2), add crystal form control agent (sorbitol), stir to carry out carbonization reaction, and prepare nano calcium carbonate slurry. When the pH value of slurry is 7 to 8, stop carbonization ; Slowly add an aqueous solution of sodium sulfate and barium chloride prepared in a molar ratio of 1:1, continue stirring for 60 min, until the surface of the nano-calcium carbonate is coated with barium sulfate, and then continue to carbonize the slurry to a pH value of ≤ 7, add the surface modifier. The agent is stirred for 90 minutes for activation; the filter cake is obtained by pressure filtration, and the moisture content of the filter cake is 35% to 40%; it is placed in an electric heating constant temperature drying box to dry to a moisture content of ≤0.5%; the product is packaged after being pulverized by a jet mill.
2. Preparation of PE film
The prepared nano-calcium carbonate was mixed in a high-speed mixer according to the formula in the table below, and the temperature was 110° C., and stirred for 5 minutes to obtain a mixture.
Add the mixture into the twin-screw extruder, and control the temperature of heating, constant temperature, heat preservation, and discharge area respectively: 165, 160, 155, 145 ℃, after extrusion and dicing, add PE in the proportion of 20% Blown film, prepare PE film, and conduct performance test.
3. Analysis of results
(1) Influence of crystal shape control agent dosage on film properties
Sorbitol is a polyol that can improve the solubility of Ca(OH)2, promote the formation of small particles during the reaction, increase the specific surface area of nano-calcium carbonate, and have a positive effect on improving the light transmittance of the film.
As the amount of sorbitol increases, the particles become smaller and the specific surface area increases, which is beneficial to light diffraction and the transparency rate increases; but when the specific surface area reaches a certain level, the oil absorption value increases, the processing resistance increases, and the force between particles is strong. , resulting in a decrease in dispersion. After comprehensive consideration, the dosage of sorbitol was determined to be 0.6% of nano calcium carbonate.
(2) Influence of coating amount of barium sulfate on film properties
The shape of nano-calcium carbonate is cubic. The main purpose of adding barium sulfate to coat nano-calcium carbonate is to form a deposition layer with a sponge structure, generate a certain porosity, improve dispersion, increase light transmittance, and then improve transparency.
With the increase of the amount of barium sulfate, the nano-calcium carbonate is coated with barium sulfate, and the dispersibility and light transmittance become better. When the dosage reaches more than 10%, the light transmittance does not change much. Considering the cost factor, the amount of barium sulfate is determined. It is 10% of the dry basis of nano calcium carbonate.
(3) Influence of surface modification on film properties
Phosphate and tributyl citrate are dissolved by stearic acid soap and coated on the surface of nano-calcium carbonate. Stearic acid soap can improve dispersibility, phosphate coupling agent has a strengthening effect, and tributyl citrate increases compatibility. It can reduce the oil absorption value, improve the dispersibility and improve the light transmittance.
On the whole, when the dosage of sorbitol as the crystal form control agent is 0.6% of the nano calcium carbonate, 10% barium sulfate of the nano calcium carbonate is used as the inorganic surface treatment agent, and 4% stearic acid soap and 1% ester coupling are used. The specific surface area of the prepared nano calcium carbonate is 30.6m2/g, the oil absorption value is 19.2gDOP/100g, the average particle size measured by electron microscope is 40nm, and the D50 measured by laser particle sizer is 0.43 μm, the prepared PE film has good dispersibility, and the light transmittance can reach 88.9%.
Nano calcium carbonate has a smaller specific gravity than nano barium sulfate, and is more than 50% smaller than nano barium sulfate masterbatch, and the masterbatch of the same weight can blow a larger area, which can reduce the production cost of masterbatch.