JP2546270B2 - Operating method of extruder - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Object of the Invention

[Industrial applications]

The present invention relates to an improvement in a method of switching a synthetic resin to be processed by an extruder without stopping the operation of the extruder.

[Prior art]

Extrusion of different kinds of synthetic resins is often performed using the same extruder, and for example, extrusion of polyester resin can be performed using an extruder for polyolefin resin. Since it is convenient to switch the processing target without stopping the operation of the extruder, various means have been tried. When the extrusion of the polyester resin is completed and the polyolefin resin is switched to, the polyolefin resin having a melt index of 2 dg / min or less is supplied to the extruder to purge the polyester resin. However, since the polyester resin and the polyolefin resin do not mix with each other, the time required for purging is long and the amount of resin consumed for purging is large, which is uneconomical. For the purpose of rapid purging, it was attempted to wet the pellets of the polyolefin resin with water and supply it to the extruder, and to utilize the steam generated by heating to obtain the purging effect. Is. However, depending on the structure of the screw of the extruder, water often flows back into the hopper and the desired effect is not obtained, and there is also the problem that equipment such as the cylinder, screw, or die will corrode. is there.

[Problems to be Solved by the Invention]

An object of the present invention is to provide an extruder capable of switching a synthetic resin, which is an object to be processed by the extruder during operation, in a short time while avoiding the problem of corrosion of the apparatus and without being influenced by the structure of the apparatus. To provide a method of operation. Structure of the invention

[Means for solving problems]

The operating method of the extruder of the present invention is a method of switching the processing target of the extruder in operation from the first synthetic resin to the second synthetic resin, and the melt index having a compatibility with the second synthetic resin is 4 dg / The purge material is prepared by mixing 1 to 20% by weight of fine moisture-absorbing agent particles containing water in a synthetic resin of min or less, and the second synthetic resin is supplied after the first synthetic resin is purged. Replacing the above-mentioned purging agent. The hygroscopic agent preferably contains 0.05% by weight or more of water. The particles of the hygroscopic agent have a particle size of 0.1 to 150 μ, especially 1
It should be ~ 25μ. Hygroscopic agents include calcium chloride, sodium chloride, magnesium chloride, dibasic sodium phosphate, ammonium chloride, potassium carbonate, potassium alum, magnesium sulfate, sodium nitrate, ammonium sulfate, primary ammonium phosphate, potassium bromide, silica gel, zeolite. , One or more of sucrose, fructose, glucose, sorbinose, multinose and lactose are used. The purging material may have a form in which pellets of a synthetic resin and a hygroscopic agent that have absorbed moisture are mixed, or a form in which a hygroscopic agent is dispersed and contained in a synthetic resin to absorb water. In the latter case, a masterbatch can be mixed and used in ordinary pellets.

[Work]

The purge material supplied to the extruder foams when the moisture becomes water vapor when heated, and the volume significantly expands inside the extruder. As a result, the purge material spreads all over the place and acts to expel the first synthetic resin. When the first synthetic resin is polyester, it is partially hydrolyzed by contact with steam at high temperature,
It is a low molecular weight and therefore low viscosity liquid. This helps the purging action due to foaming as described above. If the water content of the foaming agent is less than 0.05% by weight of the purge material, sufficient foaming cannot be achieved and the effect is small. If water is added as a liquid, backflow to the hopper will occur and foaming will be biased, but by dispersing it in the purge material, such problems disappear. Equipment corrosion is also greatly reduced due to less direct contact with water. The finer the hygroscopic agent, the more uniformly dispersed the water in the purge material, and the higher the effect of foaming. If the amount of the hygroscopic agent added is less than 1% by weight, it is difficult to uniformly disperse it, and it is not possible to retain a sufficient amount of water, so that good foaming cannot be achieved. If you want to add a large amount of water,
It is more advantageous to increase the water retention capacity by using a hygroscopic force and a strong hygroscopic agent than increasing the amount of hygroscopic agent added.
In any case, in order to facilitate the extrusion operation, the amount of the hygroscopic agent added should be kept within the upper limit of 20% by weight. By using a synthetic resin having a high melt viscosity of 4 dg / min or less as the synthetic resin used for the purging material, the purging effect can be obtained with the foaming state smoothly spreading to every corner of the extruder. It has been found that a synthetic resin having a low melt viscosity has a low ability to expel the first synthetic resin when used as a purge material.

Example 1 Zeolite having a particle size of 5 to 20 μ was allowed to stand in air containing normal humidity for several days indoors to reach a moisture absorption equilibrium,
20% by weight of a polyolefin resin "Mirason 16P" (Mitsui Petrochemical Co., Ltd.) was dispersed to prepare a purge material containing 2% by weight of water as a whole. 1 Kg of the above-mentioned purge material was supplied to the extruder that finished the extrusion of the polyester resin "G6763" (Eastman Kodak), and then "Mirason 16P" was supplied. It took about 10 minutes to bite the purge material. During this time, the extruder temperature was consistently set at 300 ° C. After supplying "Mirason 16P" for 1 hour, "Mirason 11P
When P "(the same) was extruded to produce a film, no fish eye was generated.

Example 2 Calcium carbonate having a particle size of 20 to 30 μ was placed in air having a humidity of 90% overnight to absorb moisture, and 10% by weight of this was dispersed in “Mirason 16P” to obtain a total water content of 1.5% by weight. A purge material containing was obtained. In the operation of Example 1, instead of the zeolite-containing purging material, the above-mentioned calcium carbonate-containing purging material was used for purging for 10 minutes, followed by purging with "Mirason 16P" for 1 hour. After that, no fish eyes were observed in the film formed by extrusion molding of "Mirason 11P".

[Comparative example]

After extrusion of the polyester resin "G6763", only "Mirason 16P" was supplied and purged for 1 hour and 10 minutes. In the film obtained by the subsequent extrusion molding of "Mirason 11P",
Fish eyes were occurring. EFFECTS OF THE INVENTION According to the operating method of the present invention, it is possible to shorten the time required for switching the synthetic resin to be processed by the extruder and reduce the amount of purging material used. Therefore, work efficiency is improved and cost reduction is realized by reducing auxiliary material costs.

Claims (6)

(57) [Claims] Claim: What is claimed is: 1. A method for switching a processing target of an extruder during operation from a first synthetic resin to a second synthetic resin, which is compatible with the second synthetic resin and has a melt index of 4 dg / min.
Fine hygroscopic agent particles containing water in the following synthetic resin 1
A method for operating an extruder, comprising supplying a purge material containing 20% by weight to an extruder, purging the first synthetic resin, and then supplying a second synthetic resin to replace the purge material. 2. The method according to claim 1, wherein the fine hygroscopic agent particles contain water in an amount of 0.05% by weight or more.
Operating method of paragraph. 3. The operating method according to claim 1, which is carried out using a hygroscopic agent having a particle size of 0.1 to 150 μm. 4. As a hygroscopic agent, calcium chloride, sodium chloride, magnesium chloride, dibasic sodium phosphate, ammonium chloride, potassium carbonate, potassium alum,
Claims to be carried out using one or more of magnesium sulfate, sodium sulfate, ammonium sulfate, ammonium monophosphate, potassium bromide, silica gel, zeolite, sucrose, fructose, glucose, sorbinose, multinose and lactose Operating method in the first section. 5. A method for supplying a second synthetic resin after supplying a synthetic resin which is compatible with the second synthetic resin and has a melt index of 4 dg / min or less, following the supply of the purge material. Operating method of the first item in the range. 6. The operating method according to claim 1, wherein the first synthetic resin is polyester and the second synthetic resin is polyolefin.