JP2001030238A - Production of thermoplastic resin pellet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce thermoplastic resin pellets, to which a powdery additive is added, capable of being stably transported by air immediately before a next process without allowing the additive to fall off from the pellets. SOLUTION: In a method for producing thermoplastic resin pellets while adding two or more kinds of powdery additives thereto, when the degree of compaction of at least one powdery additive A is 57-81% and the degree of compaction of the other powdery additive B is lower than 57%, the addition amt. of the powdery additive A is twice or more that of the powdery additive B in a weight ratio.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing thermoplastic resin pellets by blending two or more kinds of powdery additives into thermoplastic resin pellets. More specifically, the powdery additive is composed of at least one kind of highly adherent powder, and the retention rate of the additive is good even when the pellet to which the additive is attached is transported. The present invention relates to a method for producing a thermoplastic resin pellet having a powdery additive attached thereto.

[0002]

2. Description of the Related Art In general, thermoplastic resins have excellent processability, chemical resistance, electrical properties, mechanical properties, etc., and are therefore processed into injection molded articles, hollow molded articles, films, sheets, fibers and the like. It is used for various purposes. However, rigidity, heat resistance, transparency, water resistance, impact resistance, etc. may not be sufficient for some applications.

[0003] Conventionally, various additives have been used to improve these properties for various uses of thermoplastic resins. There are various methods for adding these additives to the thermoplastic resin, such as a method of adding at the time of polymerization of the thermoplastic resin, a method of adding the solution in the form of pellets, a method of adding and kneading at the time of re-melting, and forming a master pellet. Method is adopted.

However, each of these methods has the following disadvantages. That is, the addition method at the time of polymerization has a disadvantage that a part of the additive is deteriorated due to the heat history at the time of polymerization, the polymerization equipment is easily stained, and the cleaning cycle is short. In addition, a large number of polymerization series are required to cope with various kinds. Next, in the method of forming a master pellet, similarly to the method of adding at the time of polymerization, there is a concern about deterioration due to the heat history of the additive.

A method of adding a solution to a pellet is as follows.
If it is used in the next step as it is, the molded article may contain bubbles or cause a decrease in mechanical properties, and usually involves a step for removing the solvent such as drying, which has a drawback that the manufacturing process becomes complicated.

As a method of solving these problems in the prior art, there is a method of adding a powdery additive to thermoplastic resin pellets immediately before the next step. This is a preferred method in which the steps are simplified, and the cost is advantageous.

By the way, there are various methods for transporting thermoplastic resin pellets, such as bucket transportation, conveyor transportation, pump transportation by a snake pump, transportation in a container, and gas transportation. It is widely used because it has advantages such as stable transportation with less trouble and labor saving.

However, when the thermoplastic resin pellets to which the powdery additives are added are transported by gas just before the next step, particularly for the powdery additives having low adhesion, the thermoplastic resin pellets fall off from the pellets and the desired additive is added. Not only can you not secure the amount,
Dropped powder often accumulates at the bottom of the container, causing quality anomalies and process troubles in the next process.

In order to solve this problem, a liquid binder such as a spreading agent is used in combination. However, depending on the type of the spreading agent used, the quality such as the strength of the article in the next step is deteriorated. During the gas transport of the pellets, there is a problem that the frictional force between the pellets and the transport pipe increases and the pellets are clogged.

[0010]

SUMMARY OF THE INVENTION An object of the present invention is to solve the problem that the additives fall off from the pellets when the thermoplastic resin pellets to which the powdery additives have been added are transported by gas just before the next step. Another object of the present invention is to provide a method for producing a thermoplastic resin pellet capable of performing stable gas transport.

[0011]

Means for Solving the Problems In order to solve the above problems, the method for producing thermoplastic resin pellets of the present invention mainly has the following constitution. That is, a method for producing thermoplastic resin pellets in which two or more kinds of powdery additives are added, wherein the degree of compression of at least one kind of powdery additives (A) is 57 to 81%, )), The degree of compression of all other powdery additives (B) is 57
%, The total amount of the powdery additive (A) is (A)
A thermoplastic resin pellet characterized in that the weight ratio is at least twice the total amount of the other powdery additives (B) except for the total amount.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The thermoplastic resin referred to in the present invention is:
Examples thereof include polyolefin, polyester, polyamide, polyacetal, polyether, polysulfone, and polysulfide. Among them, mechanical properties, electrical properties,
A polyamide resin is preferably used because it is excellent in oil resistance, processability, dyeing property and the like.

As the polyamide resin, for example, polycaproamide (nylon 6), polytetramethylene adipamide, polyhexamethylene adipamide, polyhexamethylene sebacamide, polyhexamethylene dodecamide, polyundecamethylene adzide Pamide, polyundecamide, polydodecamide, polytrimethylhexamethylene terephthalamide, polyhexamethylene isophthalamide, polyhexamethylene terephthal / isophthalamide, polybis (4-amicyclohexyl) methane dodecamide, polymethaxylylene adipamide, polyundecamethylene There are homopolymers or copolymers such as terephthalamide, polyundecamethylene hexahydroterephthalamide, and the like, or mixed polyamides thereof. Among them, polycaproamide is particularly preferable because of good balance between physical properties and price.

In the present invention, the pellets are formed by cooling a molten resin extruded in a gut shape from a polymerization reactor, and then cutting the resin into pieces each having a length of 0.1 to 50 mm.
This refers to a granular substance of a degree, regardless of whether it has undergone a step of extracting and removing unreacted substances, a step of drying, a step of solid-phase polymerization, or the like, after passing through.

Examples of the powdery additives used in the present invention include a heat-resistant agent, a weathering agent, a dispersant, a lubricant, a nucleating agent, a flame retardant, a reinforcing material, a surface modifier, a stabilizer, a colorant, and an ultraviolet absorber. , An antistatic agent and an antibacterial agent. These may be added alone or in combination.

[0016] The polyamide resin and articles made thereof which are preferably used in the present invention are relatively easily oxidatively deteriorated, particularly when exposed to oxygen at a high temperature, and are remarkably oxidatively deteriorated, resulting in a decrease in the degree of polymerization and various physical properties. Causes decline. Numerous compounds have been proposed as an antioxidant such as a heat-resistant agent for preventing the oxidative deterioration of the polyamide. For example, N, N'-diphenyl-p-
Amine compounds such as phenylenediamine, diallyl-p-phenylenediamine, di-β-naphthyl-p-phenylenediamine, 2-mercaptobenzimidazole,
Imidazole compounds such as benzimidazole, thiazole compounds such as 2-mercaptothiazole, 4,
4'-dihydroxydiphenylcyclohexane, 2,
Phenolic compounds such as 2′-methylenebis (4-ethyl-6-tert-butylphenol), organic or inorganic phosphorus compounds such as stearyl phosphate, phosphorous acid or a salt thereof, hexaiodobenzene, pentaiodobenzene, etc. Organic halogenated compounds, copper acetate,
Copper compounds such as organic copper salts such as copper stearate, inorganic copper salts such as copper chloride and copper iodide, and inorganic compounds such as sodium iodide, potassium iodide, potassium bromide, ammonium chloride, ammonium bromide, and sodium bromide. A halide or the like is used alone or as a mixture. Among them, it is known that copper compounds exhibit surprisingly excellent effects. Cuprous halide such as cuprous iodide (CuI) is particularly preferably used because of its good solubility in polyamide.

It is essential that the at least one powdery additive (A) used in the present invention has a degree of compression of 57 to 81%. If the degree of compression of the powder is less than 57%, the retention of other powdery additives on the pellets during gas transport of the pellets to which the powdery additives have been added will be poor. Powder compression degree is 81
%, The powder adheres to the wall of the device when added to the pellets because the adhesion of the powder becomes too strong,
There are problems that the powder does not disperse well and is clogged by the transport piping.

All other powdery additives (B) other than the powdery additive (A) used in the present invention are powders having a weaker adhesion than the powdery additive (A). As a guide, it is desirable to use A particles (particle diameter of 40 to 100 μm) and C particles (several tens of μm or less) and B particles (80 to several hundred μm) in the gel dart powder classification diagram.

Originally, the most important and simple index for indicating the adhesion of powder is the particle size. However, it is generally difficult to measure the particle size of submicron-order particles, and errors often occur. Further, if the particle shape is different, it is difficult to relatively express the magnitude of the specific surface area where the particle diameter is directly related to the particle adhesion.

In the present invention, the degree of compression is a characteristic value measured with a powder tester PT-N manufactured by Hosokawa Micron Corporation. An index indicating how much the powder is compressed by applying a vertical force to the powder naturally deposited in a specific cup, and is expressed by the following equation (1). The greater this value, the greater the powder adhesion. Compressibility [%] = [(solid apparent specific gravity-loose apparent specific gravity) / solid apparent specific gravity] x 100 ・ (1) In equation (1), loose apparent specific gravity means that powder is allowed to fall freely and to be deposited. It is the bulk density of the powder when it is exposed. In the case of a powder having high adhesion and cohesion, the powder that falls freely does not fall to adhere to other powders and fill the gaps between the powders, and the volume increases, so that the loose apparent specific gravity decreases. However, since the value of the loose apparent specific gravity changes greatly depending on the shape of the particles, in addition to being affected by the value of the true density, it is necessary to completely express adhesion or adhesion and cohesion only with the value of the loose apparent specific gravity. I can't do that either.

Next, in the formula (1), the solid apparent specific gravity is a bulk density when the powder that has been freely dropped is sufficiently compressed. In this case, since the gap between the powders is filled as much as possible, a large value of the solidified apparent specific gravity means that the adhesion and cohesion of the powder is relatively large.

The degree of compression represented by the formula (1) is suitable for expressing the adhesion between the powder and the pellets, which is the subject of the present invention, and is applied to the pellets by the force of stirring. Because, in this case, the powder is considered to be compressed and adhered to the pellets under the force of stirring, and it is preferable to use an index of how much the powder is compressed. Also,
This characteristic value is a dimensionless unit as can be seen from equation (1),
The effect of true density has been negated.

Note that the compressibility of the same substance is completely different if the particle size is different. Therefore, in order to obtain the powdery additive (A) having a degree of compression of 57 to 81%, the following preferred compounds are selected, and the particle size may be in the range of 0.15 to 4.6 µm.

As a specific example of the powdery additive (A) used in the present invention, when it is added to a polyamide resin, the solubility of the cuprous halide, which is a preferred heat-resistant agent described above, in polyamide is further enhanced. From the viewpoint of having an effect, 2-mercaptobenzimidazole, stearic acid, flake lactam and the like are preferable, and these may be used in combination. Among them, 2-mercaptobenzimidazole having an antioxidant effect is particularly preferable.

Further, the powdery additive used in the present invention
The total amount of (A) is the same as for all other powdery additives except (A).
It is essential that the weight ratio is at least twice the total amount of (B). If the total amount of the powdered additive (A) is less than twice the weight of the total amount of all other powdered additives (B) other than (A), a high The effect of the adhesive powder as a binder becomes insufficient, and the retention of the pellets during pneumatic transportation becomes poor.

The method of adding the additives to the pellets in the present invention is not particularly limited, and examples thereof include a method using a stirrer, a fluidized bed, a low-speed rotating body, a high-speed rotating body, and the like. Further, they may be added in a batch system or in a continuous system, and there is no particular limitation on the order of addition of a plurality of powdery additives.

The method for transporting the thermoplastic resin pellets to which the powdery additive obtained by the production method of the present invention is attached is not particularly limited, and may be bucket transportation, conveyor transportation, pump transportation by a snake pump, or the like, or put in a container. Various methods such as a transportation method and a gas transportation are included. Among these, gas transport is desirable because it has advantages such as stable transport with few troubles and labor saving, and transport is performed under the condition that the moving speed of gas in the transport pipe is 30 m / s or less. Is usually the case.

[0028]

The present invention will now be described more specifically with reference to examples. In order to obtain the degree of compression in the examples, the physical properties of (a) and (b) were evaluated as follows, and the following equation was used.
Determined by (1). Compressibility [%] = [(solid apparent specific gravity-loose apparent specific gravity) / solid apparent specific gravity] × 100 (1) (1) Loose apparent specific gravity Loose apparent specific gravity is the bulk density of powder. Place the specified container (apparent specific gravity cup) directly below the sieve with a chute. The weight of the apparent specific gravity cup is measured in advance. The measured value is stored in the memory by inputting it to the operation panel. Next, 100 to 200 g of the powder for measurement is put into the sieve, and the sieve is vibrated. The powder falls through the chute,
Naturally accumulates in the cup. Measure the weight of the cup full of powder. When the measured value is input to the operation panel, the loose apparent specific gravity is automatically calculated by the following equation (2) by the calculation function of the device, and is displayed on the panel. Loose apparent specific gravity [g / cc] = (weight of cup full of powder-empty cup weight) / cup volume ... (2) (2) Solid apparent specific gravity Solid apparent specific gravity is sufficient for powder. Means the bulk density when compressed to First, the cup weight is measured and the value is input as in (a). The powder is dropped through the vibrating sieve and naturally deposited on the cup, and at the same time, the powder is compressed by tapping the cup (forcibly applying a vertical motion to the cup). The weight of the cup filled with the powder that has been sufficiently compressed is measured, and when the value is input, the apparent specific gravity is automatically calculated according to the following equation (a) and displayed on the panel. Solidified apparent specific gravity [g / cc] = (weight of cup full of powder-empty cup weight) / cup volume ... (3) (c) Powder additive Magnesium oxide, oxidation equivalent to reagent grade Titanium, 2-mercaptobenzimidazole and cuprous iodide were prepared. Further, 2-mercaptobenzimidazole and cuprous iodide were pulverized by SK-Jet O Mill manufactured by Seishin Enterprise Co., Ltd. to produce powders of various particle sizes. The compression degree was measured using a powder tester PT-N manufactured by Hosokawa Micron Corporation.

Example 1, Comparative Example 1 ε-Caprolactam and a small amount of water were charged into an autoclave and heated to carry out polymerization. The molten polymer was extruded from an autoclave into a gut and pelletized. The pellets were cylindrical, the inner diameter at the bottom was 1.4 mm, and the height was 2.3 mm. The pellet
It was immersed in hot water of about 95 ° C., taken out after 24 hours, centrifuged to remove the surface moisture, and subsequently dried in a vacuum drier to obtain nylon 6 pellets. The pellets are weighed, and 0.1% by weight of 2-mercaptobenzimidazole (various particle sizes) and magnesium oxide are prepared based on the pellets, and 0.05% by weight of cuprous iodide (various particle sizes) is prepared for each of them. Diameter) or titanium oxide.
Furthermore, these were made by Tamaki Auto Blender (TACM-70).
Nylon 6 pellets, then 2-mercaptobenzimidazole or magnesium oxide, and finally cuprous iodide or titanium oxide.
Stir for 10 minutes to mix evenly. The pellet mixed with the powder was sucked by a vacuum hose connected to a stainless steel pipe of about 60 m, and transported in the stainless steel pipe. The speed of transport of the pellets was 2.81 m / s. The pellet before transportation and the pellet after transportation are sampled, and the concentration of the powdery additive contained in each ((A) and (B), respectively)
Was measured, and the retention of the powdery additive was calculated by the following equation (4). Retention of powdered additive = (B / A) × 100 (4) The value of the retention was an average of three experiments. As a measure of the retention, the case where the retention was 90% or more was regarded as good. Table 1
As shown in Table 2, when the amount of 2-mercaptobenzimidazole having a degree of compression of 57 to 81% is 0.10% by weight, the retention of cuprous iodide or titanium oxide exceeds 90%, and the powdery additive ( The binder effect by A) was remarkably observed.

[0030]

[Table 1] On the other hand, as shown in Table 2, when the compressibility of 2-mercaptobenzimidazole or magnesium oxide is lower than 57%, the retention of cuprous iodide or titanium oxide is lower than 90% because of poor particle adhesion. Was. If it is higher than 81%, the powder adheres to the wall surface of the blender and does not mix well with the pellets during mixing by the auto blender because the particle adhesion is too strong.
-The amount of mercaptobenzimidazole was about 80% of the input). The dispersion state of the powder was also poor.

[0031]

[Table 2]

(Comparative example 2)
A similar experiment was conducted by preparing 0.09% by weight of 2-mercaptobenzimidazole (various particle diameters) and magnesium oxide, and 0.05% by weight of cuprous iodide (various particle diameters) or titanium oxide. Was performed to determine the powder retention. As shown in Table 3, the amount of the powdery additive (A) was 0.0
At 9% by weight (1.8 times the powdery additive (B)), the binder effect is small even if the degree of compression of the powdery additive (A) is between 57 and 81%, and the powdery additive (B) ) Was greatly reduced as compared with Example 1.

[0033]

[Table 3]

[0034]

According to the production method of the present invention, when the thermoplastic resin pellets to which the powdery additive is added are transferred by gas transportation or the like, the retention of the powdery additive is excellent. This has the effect of obtaining a product of uniform quality and stabilizing operability. Therefore, the pellets obtained by the production method of the present invention are suitable for articles such as resin molded articles, films, and fibers.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4F201 AA29 AB06 AB16 AC04 AR20 BA01 BA02 BC01 BC12 BC15 BC37 BK01 BK15 BQ07 4J002 BB011 CB001 CF001 CH001 CL001 CL011 CL031 CN021 CN031 DD027 EV026 FD070

Claims (5)

[Claims] 1. A method for producing thermoplastic resin pellets, wherein two or more powdery additives are added, wherein at least one powdery additive (A) has a degree of compression of 57 to 81%. When the compressibility of all other powdery additives (B) other than (A) is lower than 57%, the total addition amount of the powdery additives (A) is less than 57%. 2 by weight relative to the total amount of the powdery additive (B)
A method for producing thermoplastic resin pellets, which is at least twice as large. 2. The method for producing thermoplastic resin pellets according to claim 1, wherein the thermoplastic resin is a polyamide resin. 3. The method for producing thermoplastic resin pellets according to claim 2, wherein the polyamide resin is a nylon 6 resin. 4. The method for producing thermoplastic resin pellets according to claim 1, wherein the powdery additive (A) is 2-mercaptobenzimidazole. 5. The method for producing thermoplastic resin pellets according to claim 1, wherein the powdery additive (B) is cuprous halide.