JP2001138329A - Method and apparatus for recycling resin pellet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for recycling resin pellets by a method in which when a waste material generated in the injection molding of the resin pellets is crushed, the generation of powder causing defective molding is prevented, and when a polyamide resin and a polyester resin, which are deteriorated by heat, or a polyamide resin added with glass fibers are crushed, the lowering of molecular weight by thermal degradation and physical properties by the bending, etc., of the glass fibers is prevented. SOLUTION: In the method for recycling the resin pellets, the waste material generated in the injection molding of the resin pellets is crushed under heating, and the crushed pellets are recycled.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method and an apparatus for recycling waste materials such as runners and sprues generated during injection molding of resin pellets.

[0002]

2. Description of the Related Art When injection molding resin pellets, usually, the pellets are supplied from a hopper to a heating cylinder and melted, and then injected into a closed mold through a nozzle through a sprue and a runner to obtain a desired shape. However, a large amount of waste materials such as sprues and runners are generated. Therefore, if the generated waste material is not effectively recycled, it does not lead to a reduction in the production cost of the molded product.

[0003] As a method of reusing waste material of resin pellets generated during injection molding, conventionally, (1) waste material is crushed into an appropriate size through a pulverizer and then mixed with an appropriate amount of virgin pellets, for example. How to process,
(2) a method in which crushed pellets and virgin pellets are mixed and re-kneaded by an extruder to regenerate pellets having a uniform particle size; (3) a method described in JP-A-9-24515, A method of re-pelletizing the pulverized pellets through a hot screw press to produce pellets having a uniform particle size is known.

However, in the above method (1), the size of the pulverized pellets is sparse, and in particular, due to the presence of powder pellets, for example, when the resin is injected into the hopper of an injection molding machine, A phenomenon (bridge phenomenon) occurs in which the pellets cannot be dropped at the pipe section connecting the plasticizer, which makes continuous processing impossible, or the pellets drop unevenly, resulting in uneven metering. In addition, molding defects such as short shots and overpacks occur during the injection process, resulting in an increase in the molding defect rate or a decrease in product quality.

In the methods (2) and (3), the pellets have a uniform particle diameter, but are applied to polyamide resins and polyester resins which are easily thermally degraded because the pellets are re-melted or re-kneaded. In this case, the molecular weight decreases due to thermal degradation, and when applied to a resin containing glass fiber, the length of the glass fiber becomes short, and a significant decrease in physical properties cannot be avoided.

For example, a polyamide resin reinforced with glass fiber, which is frequently used in the field of precision electronic components such as connectors, is expensive, and recycling of waste materials is strongly desired. Due to the property of deterioration, and the high dependence of physical properties on the glass fiber length, the conventional pulverization method may cause thermal deterioration, or the glass fibers may bend, resulting in deterioration of the physical properties of the molded product, making it impossible to recycle. There are many at present.

In the recycling of waste materials generated during injection molding of super engineering plastics represented by aromatic polyamide resins, polyphenylene sulfide resins, and liquid crystal polymers, it is known that a large amount of powder pellets are generated particularly during pulverization. It is common practice to separately provide a step of removing powder pellets and a step of re-pelletizing by an extruder for recycling.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to grind waste materials generated during injection molding of resin pellets.
Without generating powder pellets that cause molding failure, and when heat-degradable polyamide resin or polyester resin, or when crushing a polyamide resin containing glass fiber, the molecular weight decreases due to heat deterioration, An object of the present invention is to provide a method and an apparatus for recycling resin pellets without physical property deterioration due to bending or the like.

[0009]

According to the present invention, it has been found that the above-mentioned problems can be solved by pulverizing waste materials generated during injection molding of thermoplastic resin pellets under heating conditions. That is, the present invention provides a method for recycling resin pellets, which comprises crushing waste materials generated during injection molding of resin pellets under heating conditions, and reusing the crushed pellets. Further, the present invention provides a pulverizing device for pulverizing waste material generated during injection molding of resin pellets, and a resin pellet recycling device provided with a heating device in a supply portion of the waste material in the pulverizing device. ADVANTAGE OF THE INVENTION According to the recycling method and apparatus of the resin pellet of this invention, generation | occurrence | production of the powder pellet at the time of grinding | pulverizing waste material can be reduced significantly. This enables stable molding even when the recycled pellet material is reused for injection molding, and achieves the acquisition of a molded article maintaining good physical properties. Further, in the method for recycling resin pellets of the present invention, the heating temperature is set at −20 of the deflection temperature under load of the resin (ASTMD648, 1.86 MPa).
When the temperature is kept in the range of from + 20 ° C to + 20 ° C, the effect of suppressing the generation of powder pellets is further improved.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a schematic configuration diagram of a recycling device, FIG. 2 is an explanatory diagram of a heating device, and FIG. 3 is an explanatory diagram of an on-off valve. A virgin material supply hopper 1 is installed above the recycling device shown in FIG. 1, and a virgin material measuring device 2 is installed below the virgin material supply hopper 1. A crusher 4 is installed next to the virgin material supply hopper 1. A heating device 5 is installed in the crusher 4, and waste materials (spools, runners) 3 generated during injection molding are charged by a product take-out robot or the like (not shown). A crushing tube 6 and an overflow port 6a are provided below the crusher 4. A pulverized material measuring device 7 is provided below the pulverizing tube 6.
And the virgin material measuring device 2 are connected by a connecting pipe 8.
A mixed material tank 9 is installed below the crushed material measuring device 7.
The mixing tank 9 is provided with a discharge port 9a.

The heating device shown in FIG.
And a valve 12 that can be opened and closed in conjunction with the molding machine. Heating by a heating device includes hot air heating, heater heating, and radiant heating. In order to make the heating uniform, it is desirable to use hot air heating, and for that purpose, it is preferable to provide a fan 13. The on-off valve shown in FIG. 3 is an on-off valve
a14 and an on-off valve b15. The on-off valve is linked with the molding machine, and the on-off valve a14 opens and closes in each molding cycle.
Next, the on-off valve b15 opens and closes. As a result, the waste material has a resin deflection temperature under load (ASTM D648, 1.86MP).
Heated to a) and crushed by the crusher 4 at the bottom.

In the recycling apparatus having the above configuration, virgin material is first supplied from a virgin material supply hopper 1 and measured by a virgin material measuring device 2. afterwards,
The virgin material reaches the crushed material meter 7 through the connecting pipe 8. On the other hand, the waste material 3 generated at the time of molding is charged into the heating device 5. After the waste material 3 is heated to the deflection temperature under load of the resin by the heating device 5, the on-off valve b 15 opens and closes, is charged into the crusher 4, becomes crushed material, and is discharged into the crushing tube 6.

The pulverized material passes through a pulverizing tube 6 and a pulverized material meter 7.
Weighed by Thereafter, the pulverized material is combined with the virgin material by the pulverizing and measuring device 7, mixed when falling into the mixing tank 9, and stored as a mixed material. The mixed material in the mixing tank 9 is transported from the outlet 9a to an arbitrary place. The electric signal of the recycling device is controlled by the electrical box 10.

The method and apparatus for recycling resin pellets of the present invention are not particularly limited as long as they can be injection molded, and any resin can be applied. Examples of applicable resins include polyamide 6, polyamide 66, polyamide 46, polyamide 6T, polyamide 9T, polyphenylene sulfide, liquid crystal polymer, polymethyl methacrylate, polystyrene, polypropylene, polyethylene terephthalate, polybutylene terephthalate, polyacetal, polycarbonate, and modified. Polyphenylene ether, etc., especially polyamide 6T, polyamide 9T,
It can be suitably applied to resins such as polyphenylene sulfide and liquid crystal polymer.

The method and apparatus for recycling resin pellets according to the present invention are characterized in that an organic or inorganic fibrous filler, a brominated polymer, an antimony oxide, a metal hydroxide or the like, a flame retardant, a colorant, Agent, UV absorber,
The same applies to the case where a light stabilizer, an antistatic agent, a plasticizer, a lubricant, and various polymers are added.

In the method for recycling resin pellets of the present invention, the heating temperature at the time of pulverizing the waste material is kept within a temperature range of −20 ° C. to + 20 ° C. of the deflection temperature under load of the resin (ASTM D648, 1.86 MPa). However, it is important to further suppress the generation of powder pellets. If the heating temperature exceeds the temperature obtained by adding 20 ° C. to the deflection temperature under load, the phenomenon of sticking with the screw of the pulverizer and the pulverized shape tend to be a thin plate, which is not preferred. When the heating temperature is lower than the temperature obtained by subtracting 20 ° C. from the deflection temperature under load, the generation of powder pellets tends to increase, which is not so preferable. A particularly preferred heating temperature in the present invention is a temperature range of -5 ° C to + 5 ° C of the deflection temperature under load.

In the present invention, the deflection temperature under load (ASTM D648, 1.86 MPa) of the resin is defined as a heat transfer rate at a constant speed while applying a standard bending stress through an indenter vertically applied to a sample in a heating bath. This is the temperature when the temperature of the medium is raised and the sample reaches a prescribed deflection (0.26 mm).

[0018]

EXAMPLES The present invention will be described in more detail with reference to the following Examples, which should not be construed as limiting the present invention. . <Example 1 and Comparative Example 1> A recycling apparatus shown in FIG. 1 and an aromatic polyamide resin containing 33 parts by weight of glass fiber (PA9T, manufactured by Kuraray Co., Ltd., Genestar G233)
0), the following experiment was carried out from the injection molding of the resin to the grinding of the waste material. This resin had a melting point of 308 ° C., a glass transition temperature of 125 ° C., and a deflection temperature under load of 285 ° C. (load of 18.6 kg / cm ² ). The deflection temperature under load was measured using a test piece (dimensions 127 mm x 14 mm x 6.4 m) which was injection-molded under standard conditions for each material.
m) using ASTM D648 (load 18.6 kg /
cm ² ).

Injection molding of the above resin under molding conditions of a barrel temperature of 320 ° C. and a mold temperature of 140 ° C. (FANUC α-1)
5) Sprue diameter average 2.5φ, runner diameter 2.0φ
Was molded. The molded product, the sprue, and the runner part were automatically cut, and only the generated waste material of the sprue and the runner was taken out and put into a hopper by a robot. The on-off valve was operated for a molding cycle time of 30 seconds. Waste material was moved from the heating device to the crusher every 30 seconds. The surface temperature of the sprue and runner immediately after molding is 1
60 ° C. When the temperature of the heating device was set to 300 ° C and heating was performed, the surface temperature of the sprue and runner was 28
The temperature rose to 9 ° C. On the other hand, when pulverization was performed without heating, the surface temperature of the sprue and the runner was 119 ° C.

The pulverized material was sieved through a 1.0 mm square sieve to measure the amount of powder pellets. The case where the powder pellet was 1% or less of the whole was evaluated as ○, the case where it was 1 to 3% was evaluated as Δ, and the case where 3% or more was evaluated as ×. 30% crushed material and virgin material 7
The above connector was molded from pellets mixed at 0%,
The standard deviation of the weighing time between 00 shots was measured. Table 1 shows the results of this example and the comparative example.

Examples 2-3 and Comparative Examples 2-3 Instead of the aromatic polyamide resin containing 33 parts by weight of glass fiber in Example 1 and Comparative Example 1, polybutylene terephthalate (PBT, manufactured by Kuraray Co., Ltd.) was used. , Hauser S10
00) and polymethyl methacrylate (PMMA,
An experiment was performed by the same method and operation as in Example 1 and Comparative Example 1 except that Parapet G) (manufactured by Kuraray Co., Ltd.) was used. Table 1 shows the results of this example and the comparative example.

[0022]

[Table 1]

[0023]

According to the method and apparatus for recycling resin pellets of the present invention, the generation of powder pellets at the time of grinding waste material can be greatly reduced. This enables stable molding even when the recycled pellet material is reused for injection molding, and achieves the acquisition of a molded article maintaining good physical properties. Further, according to the method and apparatus for recycling resin pellets of the present invention, it is possible to recycle polyamide resin containing glass fiber, which has been difficult to recycle, without impairing its moldability and physical properties.

[0024]

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a recycling apparatus of the present invention.

FIG. 2 is an explanatory diagram of a heating device.

FIG. 3 is an explanatory diagram of an on-off valve.

[Description of Signs] 1 Virgin material supply hopper 2 Virgin material measuring device 3 Waste material (spool, runner) 4 Crusher 5 Heating device 6 Crushing tube 6a Overflow port 7 Crushed material meter 8 Connecting pipe 9 Mixing material tank 9a outlet 10 Electrical box 11 Heating device 12 On-off control valve 13 Fan 14 On-off valve 15 On-off valve

Claims (4)

[Claims] 1. A method for recycling resin pellets, comprising: crushing waste materials generated during injection molding of resin pellets under heating conditions, and reusing the crushed pellets. 2. The heating temperature is determined by the deflection temperature under load (AS) of the resin.
+2 from -20 ° C of TM D648, 1.86 MPa)
The recycling method according to claim 1, wherein the temperature is in a temperature range of 0 ° C. 3. The recycling method according to claim 1, wherein the resin pellet is a polyamide resin reinforced with glass fiber. 4. A resin pellet recycling apparatus comprising: a pulverizing device for pulverizing waste materials generated during injection molding of resin pellets; and a heating device provided in a waste material supply section of the pulverizing device.