JP2000351869A - Recovering method for thermoplastic resin waste - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for stably feeding a resin to be recovered from a separator to an extruder without causing the degradation of the resin to thereby recover the resin by dissolving a thermoplastic resin waste in a solvent, recovering a specified proportion of the solvent in a separator, and feeding a resin composition containing a specified amount of the solvent. SOLUTION: A thermoplastic resin waste is dissolved in a solvent, preferably in an amount of 1-10 times that of the resin, at normal temperature or higher e.g. in a dissolution vessel and then is transferred, preferably through a heating zone, to a separator which preferably is a depressurized chamber. In the separator 92-99 wt.% of the solvent is separated and recovered, and the solvent separation is ended when 0.5-10 wt.% of the solvent is still remaining, and the waste is transferred to an extruder. The remaining solvent can further be removed by installing a vent at a part of the heating zone of the extruder. A polyester, a polyamide, PS, PP, etc., are listed as the thermoplastic resin. Aromatic and aliphatic hydrocarbons, and their halogenated products are listed as the solvent.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for recovering a thermoplastic resin used in the form of a molded article or the like in a recyclable form.

[0002]

2. Description of the Related Art As a means for recovering a used thermoplastic resin, there are known a method of melting and recovering a thermoplastic resin molded product by heat and a method of dissolving and recovering the same in an organic solvent.

However, the method of melting and recovering with heat is problematic in that the resin is degraded by heating and the treatment of odor generated from the resin is problematic. It is difficult to separate the resin continuously and smoothly into the extruder, and in many cases, it is necessary to increase the temperature and reduce the viscosity to operate the resin.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method in which a recovery resin is supplied stably from a separator for separating a solvent and a resin, and the recovery resin is smoothly introduced into an extruder. Another object of the present invention is to provide a method for recovering a resin that does not require any processing.

[0005]

SUMMARY OF THE INVENTION The present invention is directed to a method for dissolving thermoplastic resin waste in a solvent, and then dissolving the waste in a separator.
The present invention relates to a method for recovering thermoplastic resin waste, comprising recovering a solvent in an amount of 0.5% by weight and supplying a resin composition containing the solvent in an amount of 0.5 to 10% by weight to an extruder.

Examples of the thermoplastic resin include thermoplastic polyesters such as polytetrafluoroethylene, polyamides, acrylic resins, polystyrene, polyethylene, polypropylene, and vinyl chloride resins.

The solvent varies depending on the resin, but generally includes aromatic hydrocarbons, aliphatic hydrocarbons, halides thereof, ethers, esters, ketones, and mixtures thereof. Can be.

In order to dissolve the thermoplastic resin waste in a solvent, it can be achieved by bringing the waste into contact with a solvent which is at room temperature or heated in a dissolving tank. Usually, the solvent is used in an amount of 1 to 10 times, preferably 1.5 to 5 times the weight of the resin.

[0009] The dissolved thermoplastic resin solution is transferred to a separator via a heating section, and the solvent is separated in the separator by various known means. The separator is usually a simple decompression chamber. As one specific separation means, after blowing out dissolved oxygen by blowing an inert gas into the resin solution,
The solution can be heated, if necessary, under reduced pressure to evaporate the solvent. Normally, it is not necessary to introduce an inert gas during operation, but an inert gas such as a nitrogen gas is used to release the vacuum when the operation is stopped.

The vaporized solvent can of course be recovered by a recovery device and reused for dissolving the thermoplastic resin waste.

In the separator, 92-99.5 of the solvent
%, Preferably 95-98% by weight,
Separation of the solvent is terminated with 0.5 to 10% by weight, preferably 3 to 6% by weight of the solvent remaining, and the mixture is transferred to an extruder. If the amount of the residual solvent is less than 0.5% by weight, the viscosity of the resin increases, the pressure loss in the heater increases, and there is a risk of clogging. And the resin deteriorates. If the residual solvent is more than 10% by weight, the viscosity of the resin decreases, but the adhesiveness of the resin increases due to the solvent, and the resin adheres to the wall of the apparatus and cannot be smoothly extracted from the inside of the separator. . In addition, since the evaporation load in the extruder increases, a large amount of solvent is extracted from the vent, and at that time, the rate at which the resin is blown out from the vent together or the proportion of the resin mixed into the solvent increases, and neither is preferable. .

The thermoplastic resin containing 1 to 8% by weight of the solvent exiting the separator keeps appropriate fluidity even if the heating temperature is not so high because of the residual solvent. The passage (pipe) is smoothly transferred, there is no fear of blocking the passage, and there is no fear of blockage.
Discoloration can be avoided. The resin discharged from the separator is usually supplied to a portion corresponding to a hopper of an extruder by a pipe.

In the present invention, for example, a vent is provided in a part of the heating section of the extruder to remove the residual solvent. Naturally, the volatile solvent is recovered.

[0014]

FIG. 1 shows an example of an apparatus for carrying out the method of the present invention.
Shown in

In a tank (not shown), a resin solution obtained by dissolving thermoplastic resin waste in a solvent is sent to a heating unit by a high-pressure pump. In the heating section, the resin solution is heated to a predetermined temperature by flowing the resin solution through a flow path provided in the heat medium. As a particularly preferred embodiment of the heating unit, the heating medium flows through the outer pipe of the double pipe,
The heating unit has a structure for heating the resin solution flowing through the inner pipe. In the heated resin solution, a part of the solvent evaporates in the flow path of the heating unit, and the pressure in the flow path increases. Due to this pressure increase, the boiling point of the solvent is increased, and the amount of heat obtained from the heated surface can be maintained mainly as the sensible heat of the resin solution. The resin solution that has reached the predetermined temperature is supplied to the separator.

Since the pressure of the separator is set low,
The pressure drops rapidly from the outlet of the heating section to the vicinity of the separator inlet, and drops to the pressure inside the separator at the separator inlet. Due to the decrease in pressure, the boiling point of the solvent drops significantly, the amount of heat retained as sensible heat shifts to latent heat of evaporation, most of the solvent evaporates in the separator, and the temperature of the resin drops as the resin precipitates. . The separator is set at a considerably lower pressure than the heating section, usually at a sub-atmospheric pressure. The pressure setting is determined with reference to the boiling point of the solvent, but it is preferable that the evaporation temperature of the solvent is within a temperature range where cooling and recovery is possible and the pressure is set as low as possible. Normally, water is used as the refrigerant in the separator.
As described above, the pressure is preferably set as low as possible in a temperature range of 25 ° C. or more.

The precipitated resin falls vertically in the separator, is extruded by an extruder connected to a lower portion, and is applied to a pelletizer as needed. The residual solvent when supplied to the extruder is 0.5 to 10% by weight, and the residual solvent evaporates in the former stage of the extruder, and the evaporated solvent passes through a vent, a pipeline, a condenser, and passes through a solvent. Sent to tank.

The solvent generated from the separator is sent to a condenser through a pipeline, and the solvent recovered here is sent to a solvent tank, and if necessary, reused as a solvent for dissolving resin waste.

[0019]

EXAMPLES The present invention will be described below in detail with reference to examples, but the present invention is not limited thereto.

A resin solution (26 ° C.) obtained by dissolving 33% by weight of polystyrene resin waste in 67% by weight of a solvent for polystyrene (in this case, normal propyl bromide) described in Japanese Patent Application No. 10-112490 is shown. The processing was performed using the apparatus of No. 1. That is, the resin solution is discharged at a discharge pressure of 810.
It was transferred to the heating unit at a rate of 15 kg / hr using a high-pressure pump of kPa. The heating unit has a diameter of 2 in a heat medium at 175 ° C.
A 1.7 mm (15 A) circular tube is installed with a length of 10 m. The separator is maintained at a low pressure of 46.7 kPa, where the steam temperature generated is 10
The temperature is controlled at 52 ° C. by cooling water at 0 ° C. Most of the solvent evaporates in the separator, and a resin containing 3.0% by weight of the solvent with respect to the resin is precipitated. The precipitated resin particles are sent to a portion corresponding to a hopper of an extruder via a pipe provided at a lower portion of the separator. The extruder used was a different direction rotary twin screw type extruder having a shaft diameter (outer diameter) of 46 mm and a shaft length of 900 mm, and two vents at a location relatively closer to the outlet from the receiving frontage. And most of the remaining solvent is discharged from here. This discharged solvent is recovered through a pipeline in the same manner as other solvents. The concentration of the resin contained in all the recovered solvents was 1 ppm or less, and the solvent was a high-purity solvent. The extruded resin is subjected to a pelletizer and reused as molding pellets. The solvent concentration in the pellet is 150 ppm (w
t).

[0021]

According to the present invention, the resin particles for recovery are stably supplied from the discharge port of the separator to the extruder, and the thermal decomposition of the resin can be suppressed to an extremely low level.

[Brief description of the drawings]

FIG. 1 shows a flow sheet according to an embodiment of the present invention.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Akimasa Oda 74-18 Yawata Kaigan-dori, Ichihara-shi, Chiba Japan Refine Co., Ltd. Chiba Plant (72) Inventor Masaya Nakamura 6-23-5 Kugahara, Ota-ku, Tokyo Shares Company Null F term (reference) 4F301 AA12 AA15 AA16 AA18 AA20 AA25 AA27 BA01 BA21 BC02 BC13 BC36 BC40 BD01

Claims (1)

[Claims] 1. After dissolving thermoplastic resin waste in a solvent, 92-99% by weight of the solvent is recovered in a separator,
A method for recovering thermoplastic resin waste, comprising supplying a resin composition containing 0.5 to 10% by weight of a solvent to an extruder.