WO2012137665A1

WO2012137665A1 - Process for producing pellets of glass-fiber-reinforced thermoplastic resin composition

Info

Publication number: WO2012137665A1
Application number: PCT/JP2012/058397
Authority: WO
Inventors: 元一平郡; 一成高田; 邦紘平田
Original assignee: ポリプラスチックス株式会社
Priority date: 2011-04-01
Filing date: 2012-03-29
Publication date: 2012-10-11
Also published as: CN103492141A; CN103492141B; TWI496675B; JP5536704B2; TW201247392A; JP2012213996A; MY162770A

Abstract

A process for producing pellets of a glass-fiber-reinforced thermoplastic resin composition is provided with which the productivity of pellets of a glass-fiber-reinforced thermoplastic resin composition can be rendered higher than in conventional processes and it is possible to minimize the probability that monofilament masses (unfibrillated glass-fiber bundles) remain in the produced pellets. In the process, a thermoplastic resin and glass fibers are kneaded with a screw which comprises a screw element having a specific shape. The specific screw element is a single-thread progressive screw element which has a flight part having circular-arc-shaped notches that satisfy specific requirements.

Description

Method for producing glass fiber reinforced thermoplastic resin composition pellets

The present invention relates to a method for producing glass fiber reinforced thermoplastic resin composition pellets.

As a method for producing glass fiber reinforced thermoplastic resin composition pellets by mixing and kneading glass fibers with a thermoplastic resin, first, a thermoplastic resin is supplied to an extruder and the thermoplastic resin is melted. Next, glass fibers are supplied to the molten thermoplastic resin, and the thermoplastic resin and glass fibers are mixed and kneaded in an extruder. Finally, a method of cooling and granulating the mixture is common. As the extruder, generally, a single-screw extruder and a fully meshed twin-screw extruder in the same direction (hereinafter sometimes referred to as a twin-screw extruder) are used. Compared with a single screw extruder, a twin screw extruder has higher productivity and freedom of operation, and therefore, a twin screw extruder is more preferably used for producing glass fiber reinforced thermoplastic resin pellets. .

The glass fiber used in the production of the glass fiber reinforced thermoplastic resin composition pellets is a monofilament having a diameter of 6 μm to 20 μm, which is bundled into about 300 to 3000 pieces and wound on a roving, or the roving has a length of 1 Cut to 4 mm (hereinafter sometimes referred to as chopped strands). Since chopped glass can be used more easily, in the case of producing glass fiber reinforced thermoplastic resin composition pellets industrially, the thermoplastic resin is supplied to a twin screw extruder, and after the thermoplastic resin is melted, The most common method is to supply chopped glass from the middle of a shaft extruder, mix and knead a molten thermoplastic resin and glass fiber, extrude the mixture, and cool and solidify.

The productivity of the glass fiber reinforced thermoplastic resin composition pellets using the above twin screw extruder is determined by the plasticizing and mixing and kneading ability of the twin screw extruder. The plasticizing ability of the twin screw extruder depends on the screw design, the torque generated by the screw, the groove depth of the screw (the difference between the outer diameter and the valley diameter of the screw), the rotational speed of the screw, and the like. Patent Document 1 discloses a twin-screw extruder having a high plasticizing ability and excellent productivity, in which a value obtained by dividing the distance between the centers of two screws by the third power is defined as torque density.

Also, the mixing and kneading ability of the twin screw extruder depends on the screw design. The residence time decreased with the improvement of the plasticizing ability of the twin screw extruder. For this reason, development of a screw design having an efficient mixing and kneading ability in a short time is required. As described above, studies on techniques for increasing the plasticizing ability and kneading ability of a twin-screw extruder have been conducted.

By the way, as the glass fiber, a monofilament bundle is used as described above. This is because, in the method of supplying glass fibers to a twin-screw extruder without forming a bundle of monofilaments, the monofilament becomes cottony, loses fluidity, and is difficult to handle. The chopped strand is mixed and kneaded in a twin-screw extruder until it is fibrillated and becomes a monofilament. At the same time, the chopped strand is broken by a screw or the like until the monofilament length reaches an average of 200 μm to 800 μm.

If mixing and kneading in the twin-screw extruder is insufficient, the monofilament will not be defibrated, and a part or all of the chopped strand that is in the state of a monofilament aggregate (undefibrated glass fiber bundle) will be resin composition It remains in the product pellet. If some or all of the chopped strands remain in the glass fiber reinforced thermoplastic resin composition pellets, in injection molding, some or all of the chopped strands may be clogged in the gate, making injection molding impossible, or injection molding. Even if it is possible, some or all of the chopped strands are present in the molded product, resulting in poor appearance or reduced function.

Particularly in recent years, with the advancement of electronics-related technology, glass fiber reinforced thermoplastic resin compositions used as parts are required to be thin and molded into complex shapes. The gate nozzle of a molding machine that performs such precision molding is often 1 mm or less. In precision molded products, the presence of undefined glass fiber bundles becomes a very serious defect.

Japanese National Patent Publication No. 11-512666

The use of the twin-screw extruder of Patent Document 1 is said to improve productivity. Particularly in the precision molded product as described above, the residence time is shortened under the condition of a high discharge amount, and the chopped strand is completely removed. It is even more difficult to defibrate monofilaments and shorten the fiber length.

The present invention has been made in order to solve the above-mentioned problems. The object of the present invention is to increase the productivity of glass fiber reinforced thermoplastic resin composition pellets as compared with the prior art, and to collect the monofilaments in the manufactured pellets. It is providing the manufacturing method of the glass fiber reinforced thermoplastic resin composition pellet which can make very low the probability that (un-defibrated glass fiber bundle) remains.

The inventors of the present invention have made extensive studies to solve the above problems.
As a result, the physical quantities obtained by numerical analysis, such as average shear stress history, average shear strain history, specific energy, shortest particle outflow time, etc. are all the number N of pellets containing undefined glass fiber bundles (per unit weight). It is found that there is no clear correlation with the number of pellets containing undefined glass fiber bundles) and the smallest value among the time integral values of shear stress applied to each glass fiber bundle, which is derived by the particle tracking method. It was found that the minimum shear stress history value T _min is correlated with the number N of pellets including undefined glass fiber bundles.
Further, the shear stress generated in the twin screw extruder is analyzed, and when the ratio (Q / Ns) between the discharge amount Q and the screw rotation speed Ns is constant, the minimum shear stress history value T _min is controlled. The present inventors have found that the number N of pellets per unit amount including undefined glass fibers can be controlled.
Further, even if the ratio (Q / Ns) is not constant, the number N of pellets per unit amount including undefined glass fibers can be expressed by a specific formula using the T _min and (Q / Ns). I found out.
Furthermore, the present inventors have found that the above-mentioned problems can be solved by having a screw element having a specific shape for a screw for kneading a thermoplastic resin and glass fiber, thereby completing the present invention. More specifically, the present invention provides the following.

(1) A method for producing glass fiber reinforced thermoplastic resin pellets using a twin screw extruder provided with screws that rotate and mesh with each other, wherein the thermoplastic resin is supplied to the extruder and heated. A plasticizing step of kneading and plasticizing, and after the plasticizing step, supplying one or more bundles of glass fibers to the extruder, defibrating the glass fibers while disentangling the glass fiber bundles, A kneading step of kneading the plasticized thermoplastic resin with a screw, an extrusion step of extruding the glass fiber reinforced thermoplastic resin composition after the kneading step, and the extruded glass fiber reinforced thermoplastic resin composition. A pelletizing step of pelletizing, wherein the thermoplastic resin is at least one selected from polybutylene terephthalate resin, liquid crystalline resin, and polyarylene sulfide resin In the kneading step, the screw includes a single forward feed screw element having a flight part in which an arc-shaped notch satisfying the following inequalities (I) to (III) is formed on the outer periphery. The manufacturing method of the glass fiber reinforced thermoplastic resin composition pellet which has the above.

0.05D ≦ r ≦ 0.15D (I)
7 ≦ n ≦ 20 (II)
Le ≦ 0.3D (III)

(R in the inequality (I) is the radius of the circle forming the arc or the major axis / 2 or the minor axis / 2 of the ellipse forming the arc, and n in the inequality (II) is , The number of notches per lead length of the one-step progressive screw element, and Le in the inequality (III) is the lead length of the one-step progressive screw element, and the inequality (I), (II) D in the inside is a screw diameter.)

(2) A method of producing glass fiber reinforced thermoplastic resin composition pellets using a biaxial extruder equipped with screws that rotate and mesh with each other,
A plasticizing step of supplying a thermoplastic resin to the extruder and heating, kneading and plasticizing;
After the plasticizing step, one or more glass fiber bundles are supplied to the extruder, and the defibrated glass fibers and the plasticized thermoplastic resin are screwed together while defibrating the glass fiber bundles. A kneading step for kneading;
After the kneading step, an extrusion step of extruding the glass fiber reinforced thermoplastic resin composition,
Pelletizing step of pelletizing the extruded glass fiber reinforced thermoplastic resin composition,
The viscosity of the thermoplastic resin is 100 Pa · s or less under the condition of a shear rate of 1000 sec ⁻¹ ;
In the kneading step, the screw has a glass fiber reinforced heat having one or more progressive screw elements each having a flight portion in which an arc-shaped notch satisfying the following inequalities (I) to (III) is formed on the outer periphery. A method for producing a plastic resin composition pellet.

0.05D ≦ r ≦ 0.15D (I)
7 ≦ n ≦ 20 (II)
Le ≦ 0.3D (III)

(R in the inequality (I) is the radius of the circle forming the arc or the major axis / 2 or the minor axis / 2 of the ellipse forming the arc, and n in the inequality (II) is , The number of notches per lead length of the one-step progressive screw element, and Le in the inequality (III) is the lead length of the one-step progressive screw element, and the inequality (I), (II) D in the inside is a screw diameter.)

(3) In the kneading step, the screw has at least one reverse feed screw element having a flight portion having an arc-shaped notch formed on the outer periphery thereof. (1) or (2) A method for producing a thermoplastic resin composition pellet.

According to the present invention, the productivity of the glass fiber reinforced thermoplastic resin composition pellets is increased more than before, and the probability that monofilament aggregates (undefined glass fiber bundles) remain in the manufactured pellets is very high. The fiber length distribution of the glass fiber can be controlled.

FIG. 1 is a schematic diagram illustrating an example of a screw configuration of an extruder. FIG. 2 is a diagram schematically showing a forward feed single screw element having a flight portion in which an arcuate cutout is formed. FIG. 3 is a schematic diagram showing the screw configuration of the extruder used in the examples. FIG. 4 is a diagram showing a specific screw pattern used in the example. FIG. 5 is a diagram showing a specific screw shape used in the example. FIG. 6 shows the minimum shear stress history value (Pa · sec) and the number of pellets in which part or all of the glass fiber bundle is undefined (Q / Ns = 1.0 of the extruder used in the examples). It is a figure which shows the relationship with a piece / pellet 10kg). FIG. 7 shows the minimum shear stress history value (Pa · sec) under the conditions of Q / Ns = 1.0, Q / Ns = 0.8 and Q / Ns = 0.5 of the extruder used in the examples. It is a figure which shows the relationship (correlation line) with the number of pellets (one piece / pellet 10kg) in which some or all of the glass fiber bundles are not defibrated. FIG. 8 shows the minimum shear stress history value (Pa · sec) independent of the Q / Ns of the extruder used in the examples, and the number of pellets in which part or all of the glass fiber bundle is not defibrated (pieces / pellet 10 kg). It is a figure which shows the relationship (correlation line). FIG. 9 is a diagram showing the relationship between the number of notches n and the minimum shear stress history value _Tmin . FIG. 10 is a diagram showing the distribution of shear stress history values for each type of screw element. FIG. 11 is a schematic diagram showing a screw configuration of a screw disposed in the extruder used in the examples and comparative examples.

Hereinafter, embodiments of the present invention will be described. In addition, this invention is not limited to the following embodiment.
<Method for Producing Glass Fiber Reinforced Thermoplastic Resin Composition Pellet>
The manufacturing method of the glass fiber reinforced thermoplastic resin composition pellet of the present invention includes the following steps.
A plasticizing process in which a thermoplastic resin is supplied to an extruder and heated, kneaded and plasticized.
After the plasticization step, one or more glass fiber bundles are supplied to the extruder, and the glass fiber bundles and the plasticized thermoplastic resin are screwed together while the glass fiber bundles are defibrated. A kneading step for kneading.
An extrusion step of extruding the glass fiber reinforced thermoplastic resin composition after the kneading step.
A pelletizing step of pelletizing the extruded glass fiber reinforced thermoplastic resin composition.

The production method of the present invention uses a screw having a specific screw element in the kneading step.

Hereinafter, the manufacturing method of the glass fiber reinforced thermoplastic resin composition pellets of the present invention will be described taking the case of using the twin screw extruder shown in FIG. 1 as an example. FIG. 1 shows a twin-screw extruder including a cylinder 1, a screw 2 disposed in the cylinder, and a die 3 provided at a downstream end portion of the cylinder 1. FIG. 1 also shows the screw configuration of the screw 2. Specifically, the screw 2 includes a supply unit 20, a plasticizing unit 21, a transport unit 22, and a kneading unit 23 in this order from the upstream side. A plasticizing process is performed in the supply unit 20 and the plasticizing unit 21. A kneading step is performed in the conveying unit 22 and the kneading unit 23. The extrusion process is performed after the kneading section 23. And a pelletization process is performed after the glass fiber reinforced thermoplastic resin composition is extruded from the die | dye 3 of an extruder.

The cylinder 1 in which the screw 2 is disposed includes a hopper 10 for supplying a raw material such as a thermoplastic resin to the supply unit 20 and a feed port for supplying auxiliary materials such as a glass fiber bundle to the conveyance unit 22. 11 and a vacuum vent 12 having vacuuming means such as a vacuum pump for performing vacuum deaeration at a predetermined degree of vacuum.

[Plasticization process]
In the plasticizing step, the thermoplastic resin supplied from the hopper 10 is transferred and melted to make a homogeneous melt. First, the thermoplastic resin will be described, and then the details of the plasticizing process until the thermoplastic resin supplied from the hopper becomes a homogeneous melt will be described.

(Thermoplastic resin)
The thermoplastic resin refers to a polybutylene terephthalate resin, a liquid crystalline resin, or a polyarylene sulfide resin. Even a resin having a low viscosity tends to exhibit the effects of the present invention. The above-mentioned resin having low viscosity tends to cause a problem of undefining the glass fiber bundle. This is because if the viscosity is low, shear stress hardly occurs in the molten state, and the glass fiber bundle in which the monofilaments are converged is difficult to be defibrated. The low viscosity resin means that the viscosity of the thermoplastic resin is 100 Pa · s or less under the condition of a shear rate of 1000 sec ⁻¹ .

Generally, the thermoplastic tree used as a raw material is shaped into a pellet. In addition, you may use what made the thermoplastic resin composition containing other components into the pellet form.

(Details of plasticization process)
The plasticizing process is performed in the supply unit 20 and the plasticizing unit 21 of the screw 2. Examples of the screw element used in the supply unit 20 include a transport element made of a flight. Examples of the screw element used for the plasticizing portion 21 generally include a combination of screw elements such as reverse flight, seal ring, forward kneading disk, and reverse kneading disk.

Supplied part 20 transfers resin pellets. The supply unit 20 functions to transfer the resin pellets from the hopper 10 side to the die 3 direction side. In general, preheating by an external heater is performed as a melting preparation stage. Further, since the resin pellet is sandwiched between the rotating screw 2 and the cylinder 1, a frictional force is applied to the resin pellet to generate frictional heat. The resin pellets may start to melt due to the preheating or frictional heat. In some cases, the supply unit 20 needs to adjust the groove depth of the screw 2 and adjust the preheating temperature by a conventionally known method so that the transfer of the resin pellets proceeds smoothly.

The plasticizing unit 21 applies pressure to the resin pellets transferred from the supply unit 20 to melt the resin pellets. In the plasticizing part 21, as a result of applying shear stress to the resin pellets, the resin pellets are further transferred forward (in the direction from the hopper 10 to the die 3) while melting.

[Kneading process]
In the kneading step, after the plasticizing step, one or more glass fiber bundles are supplied to an extruder and the glass fiber bundle is defibrated and melted in the plasticizing step with the defibrated glass fibers. And knead. The kneading step is performed by the conveying unit 22 and the kneading unit 23 of the screw 2. As a screw element used by the conveyance part 22, the element for conveyance which consists of a forward flight, for example is mentioned. Moreover, as a screw element used in the kneading part 23, the combination of screw elements, such as a reverse flight, a seal ring, a forward kneading disk, a reverse kneading disk, is common.

In the manufacturing method of the present invention, a continuous feed having a flight part in which at least a part of the kneading part 22 of the screw 2 has an arc-shaped notch satisfying the inequalities (I) to (III) formed on the outer periphery. A screw element is provided. By providing the screw element in at least a part of the kneading part 22, almost no undefined glass fiber bundle remains in the manufactured pellet.

In the present embodiment, the kneading part 22 includes the screw element and a single reverse feed screw element having a flight part having a notch formed on the outer periphery.

First, the glass fiber bundle will be briefly described. The glass fiber bundle is a chopped strand in which 300 to 3000 monofilaments are bundled. In particular, chopped strands in which 1100 pieces or 2200 pieces are bundled are preferably used. The diameter of the monofilament is not particularly limited, but is preferably in the range of 6 μm to 20 μm, and those having a diameter of 6 μm, 10 μm, and 13 μm are widely distributed in the market. A bundle of monofilaments can be continuously fed to the twin screw extruder while roving. However, the chopped strand from which roving is cut is easy to handle in transportation and supply to a twin screw extruder.

In the conveyance unit 22, the glass fiber bundle and the molten resin introduced from the feed port 11 are conveyed to the kneading unit 23. In this conveyance part 22, it is an area | region where a glass fiber bundle and molten resin are not completely filled into the groove | channel of a screw, but a shearing force is not applied to a glass fiber bundle.

In the kneading part 23, shear stress is applied to the glass fiber bundle and the molten resin. When the shear stress is applied, the glass fiber bundle is defibrated and the monofilament and the molten resin are kneaded.

[Extrusion process, pelletizing process]
There are no particular limitations on how the glass fiber reinforced thermoplastic resin composition is extruded and how it is pelletized. For example, the glass fiber reinforced thermoplastic resin composition extruded into a rod shape from the die 3 can be cut and pelletized. The cutting method is not particularly limited, and a conventionally known method can be used. The discharge amount in the extrusion process corresponds to the discharge amount Q, and the rotation speed of the screw corresponds to the rotation speed Ns.

<Screw element>
As a conventional kneading part of a screw, a combination of screw elements such as a reverse flight, a seal ring, a forward kneading disk, and a reverse kneading disk is generally used. However, in the case of high discharge under conditions where Q / Ns is large, some glass fiber bundles are not defibrated and remain undefibrated.

The present invention is a manufacturing method determined by using, as an index, a shear stress history value received by each glass fiber bundle in an extruder. Specifically, as an index the minimum shear stress history value T _min is the minimum value of the shear stress history value each glass fiber bundle is subjected in a twin-screw extruder. By using the minimum shear stress history value T _min as an index, it is possible to distinguish between a production method in which an undisentangled glass fiber bundle remains and a production method in which an undefined glass fiber bundle hardly remains. This invention is a manufacturing method of the glass fiber reinforced thermoplastic resin composition pellet which hardly produces the pellet with which the undisentangled glass fiber bundle remained.

First, using the minimum shear stress history value T _min as an index will be described. The discharge amount Q of the glass fiber reinforced thermoplastic resin composition, the screw diameter D of the screw element in the kneading unit 23, the screw rotation speed Ns, the minimum shear stress history value T _min , the number N of undefined pellets per unit amount (undissolved The following formula (IV) is derived based on the number of pellets including fiber glass fiber bundles. The following formula (IV) is also useful in that the amount of pellets containing undefined glass fiber bundles can be studied with one formula even if the Q / Ns condition changes. Moreover, even if the kind of screw element which a kneading part has differs, the quantity of the pellet containing an undefined glass fiber bundle can be examined with one numerical formula (IV). However, when the size of the twin-screw extruder is changed, it is necessary to derive the formula (IV) again. Even under the same discharge amount Q and the same screw rotation speed Ns, a small twin screw extruder and a large twin screw extruder have different heat transfer amounts from the cylinders and heat energy applied to the molten resin. It is.

When the twin screw extruder to be used is determined, the screw diameter D is uniquely determined. Based on the screw diameter D, the arbitrarily determined length L of the kneading portion 23, the discharge amount Q as the arbitrarily determined molding condition, and the screw rotation speed Ns, the minimum shear stress history value _Tmin is derived.

The minimum shear stress history value T _min can be derived using conventionally known three-dimensional flow analysis software in a twin-screw extruder. For example, it can be derived by particle tracking analysis as described in the examples. The minimum shear stress history value T _min is a time integral value obtained by performing time integration of the shear stress. The integration section is a section where the shear stress is applied to the molten resin and the glass fiber bundle, and the extrusion shown in FIG. In the case of a machine, it is a section of the kneading unit 23.

The method for deriving the minimum shear stress history value _Tmin is not particularly limited. A method of deriving using commercially available software, a method of deriving by experiment, and the like can be mentioned.

The number N of undefibrated pellets may be derived experimentally or using an analysis method or the like.

And based on these derivation results, the horizontal axis is the minimum shear stress history value T _min , and the vertical axis is the number N of undefined pellets. To derive.

From this graph, it is possible to derive the minimum shear stress history value T _min necessary for setting the number N of undefined pellets to a desired value or less.

Next, the case of changing the size of the twin screw extruder will be described. In this case, the above relational expression needs to be derived again. However, when the above formula (IV) in the case of a predetermined twin-screw extruder has already been derived, different sizes can be easily obtained by the following method. Formulas applicable when using a twin screw extruder can be derived.

Screw diameter D of the screw element, vary from d1 to d2, the following equation (V) is established between the discharge amount Q _M in the discharge amount Q _m and a large extruder in a small extruder and, following equation (VI) is established between the screw rotation speed Ns _M at a screw rotation speed Ns _m and a large extruder a small extruder.

Δ and ε in the above formulas (V) and (VI) are determined so that the specific energy applied to the molten resin is equal. As a method for determining δ and ε, either a theoretical determination method or an experimental determination method may be used. As a theoretical determination method, in general, assuming the adiabatic state, the parameter δ is set so that the specific function, the total shearing amount, the residence time, etc. of the objective function are the same between the small machine and the large machine. And ε are derived. Assuming the difference in heat transfer between the small machine and the large machine, the parameters δ and ε can be derived so that the specific energy as the objective function matches between the small machine and the large machine. As a method for experimental determination, the objective function is a specific energy, or a parameter indicating physical properties is adopted, and the parameter δ is statistically set so that the objective function matches between a small machine and a large machine. And a method of calculating ε.

By deriving the above formulas (V) and (VI) that are established between the small extruder and the large extruder, the number N of unfiltrated pellets per unit amount and the minimum shearing that is established in the large extruder The following mathematical formula (VII) between the stress history value T _min can be easily derived.

Thus, the larger the value of the minimum shear stress history value T _min, there is a tendency that the value of the non-fibrillation pellets number N is reduced. Accordingly, it is necessary to produce glass fiber reinforced thermoplastic resin composition pellets under conditions that increase the minimum shear stress history value _Tmin .

When the viscosity of the thermoplastic resin used as a raw material is high, the value of the minimum shear stress history value _Tmin increases, which is advantageous for defibration of the glass fiber bundle, and glass undefibration is unlikely to occur even by a normal method. The present invention provides a method that is particularly effective when the viscosity of a thermoplastic resin is low and it is difficult to disentangle a glass fiber bundle by a normal method. When the discharge rate is increased by a twin screw extruder, the glass undefibrated bundle is obtained when the viscosity of the thermoplastic resin is 100 Pa · s or less at a shear rate of 1000 sec ⁻¹ at the processing temperature in the extruder. Is likely to occur. Hereinafter, the viscosity is expressed as a value at 1000 sec ⁻¹ ). In particular, fluidity is required in precision molding, and a resin having a viscosity of 30 to 70 Pa · s is used. When glass fiber is added to this and kneaded, the resin composition has a viscosity of 50 to 200 Pa · s. The screw element for defibrating the glass fiber bundle in such a low viscosity region will be described.

A single screw element having a flight part with a notch formed on the outer periphery is preferable because the minimum shear stress history value T _min tends to increase. A single screw element itself having a flight part with a notch formed on the outer periphery is known, and is described, for example, in Patent Document (DE4134026A1).

In particular, the number N of undefined pellets can be suppressed to a small value by using a single progressive screw element described below. In particular, among the screw elements having the above-mentioned notches, it is possible to use the forward-feeding one because the value of the minimum shear stress history value _Tmin is increased, and the glass fiber is used in a shorter time than when other screw elements are used. This is preferable because the bundle can be defibrated.

The single feed progressive screw element used in the kneading section 23 will be described. This one-step progressive screw element has a flight part in which an arc-shaped notch satisfying the following inequalities (I) to (III) is formed on the outer periphery.

0.05D ≦ r ≦ 0.15D (I)
7 ≦ n ≦ 20 (II)
Le ≦ 0.3D (III)

(The r in the inequality (I) is the radius of the circle forming the arc or the major axis / 2 or the minor axis / 2 of the ellipse forming the arc, and n in the inequality (II) is , The number of notches per lead length of the one-step progressive screw element, and Le in the inequality (III) is the lead length of the one-step progressive screw element, and the inequality (I), (II) D in the inside is a screw diameter.)

The one-step progressive screw element will be described with reference to FIG. FIG. 2 is a schematic view of the above-mentioned one-step progressive screw element, where (a) is a sectional view in the axial direction, and (b) is a side view.

As shown in FIG. 2, the single progressive screw element 4 has a flight part 40 and an arc-shaped notch 41 formed on the outer periphery of the flight part 40. The notch 41 is formed in a direction from the outer periphery of the flight part toward the axis of the screw element. 2 shows a case where the ellipse forms an arc shape, but the ellipse or the center of the circle forming the arc shape exists on the outer periphery of the flight part 40 (in FIG. 2A, the center of the ellipse is present). Indicated by O). The notch has an arc shape, and the arc shape is formed by the circle or ellipse, so that there are advantages in manufacturing and an effect of minimizing a decrease in strength of the flight portion due to the notch. In addition, the said circular arc shape should just be formed by said circle | round | yen or ellipse. Further, the present invention is not limited to one in which the entire cutout is formed by the one circle or ellipse described above. However, it is preferable that substantially the entire arc shape is formed by one circle or ellipse.

The arc shape is most preferably a circle. When the arc shape is formed as an ellipse, it is preferable that the direction in which the cutout extends and the direction in which the major axis of the ellipse extend substantially coincide.

The range of the radius r is preferably 0.05D ≦ r ≦ 0.15D. If r is within the above range, the minimum shear stress history value _Tmin tends to increase, which is preferable. A more preferable range of r is 0.06D ≦ r ≦ 0.12D.

Also, the minimum shear stress history value T _min tends to increase as the number of notches n increases. However, since the mechanical strength of the screw element is lowered when the number of notches n is excessively increased, the number of notches n is adjusted within the range of inequality (II). A particularly preferable range of the number of notches n is 10 ≦ n ≦ 12, and the most preferable number of notches is 11.

The lead length Le of the screw element is not more than 0.3 times the screw diameter D of the screw element (Le is not more than 0.3D). If the lead length Le is 0.3D or less, even if the discharge rate Q is very high, undisrupted glass fibers tend not to be contained in the manufactured pellets. It should be noted that the discharge amount Q is very high, for example, when the screw element is provided with an axial length of 2D and a screw diameter D is 47 mm, the screw diameter is 47 mm. This is a twin screw extruder having a diameter D of 69 mm and is 800 kg / h or more. Even in such a high discharge area, problems due to the above-described undefined glass fibers can be suppressed.

As described above, the upper limit of the lead length Le of the screw element used in the present invention is preferably 0.3D or less, but the lower limit is preferably 0.1D or more. Setting it above this lower limit is preferable because the thickness of the flight part is maintained and the strength is maintained.

In the manufacturing method of the present invention, the length of a single screw element having a flight part with a notch formed in the outer peripheral surface used for the kneading part 23 is expressed as L / D (L is a screw in the kneading part 23). When expressed in terms of the axial length of D, D is the screw diameter), it is preferably 1D or more and 20D or less and used continuously. This is because the minimum shear stress history value T _min tends to become larger when used continuously. More preferably, it is 2D or more and 8D or less. In addition, said preferable length changes with kinds of resin. In the case of polybutylene terephthalate resin, it is preferably 2D or more and 3.5D or less.

Furthermore, in the present invention, it is more effective to combine a reverse screw element of a single screw element having a flight part with a notch formed in the outer peripheral surface and the forward screw element. The most effective combination is a combination in which each is alternately arranged. The length of each screw element can be adjusted as appropriate.

From the results of the three-dimensional flow analysis, most of the glass fiber reinforced thermoplastic resin composition passing through a single screw element having a flight part with a notch formed on the outer peripheral surface passes through the notch on the outer peripheral surface. I know I will go forward. However, only a small part flows along the flight. In the portion that flows along the flight, the shear stress applied to the glass fiber bundle is low, so that the glass fiber bundle is difficult to be defibrated. As described above, by increasing the length of the single screw element having the flight portion in which the notch is formed on the outer peripheral surface, the existence probability of the portion that flows along the flight can be lowered. By combining the reverse feed screw element and the forward feed screw element, the existence probability of the portion that flows along the flight can be further lowered.

As described above, in the present invention, in the kneading step, a single feed forward screw element having a flight part with a notch formed on the outer periphery, or a combination of a reverse feed screw element and a forward feed screw element includes almost no glass undefibration. It is possible to efficiently produce a glass reinforced resin composition with high productivity.

Hereinafter, although an example and a comparative example are shown and the present invention is explained concretely, the present invention is not limited to these examples.

<Evaluation 1>
In Evaluation 1, the following materials were used.
Thermoplastic resin: polybutylene terephthalate resin (PBT) (melt index (MI) = 70 g / 10 min, viscosity 60 Pa · s at 1000 sec− ¹ )
Carbon masterbatch glass fiber bundle: 3 mm long chopped strand obtained by bundling 2200 monofilaments having a diameter of 13 μm The composition is as follows.
PBT is 67.5 mass%, carbon masterbatch is 2.5 mass%, glass fiber bundle is 30 mass%
Extrusion conditions are as follows.
Extruder: Same direction full meshing type twin screw extruder TEX44αII (manufactured by Nippon Steel) Screw diameter D of screw element is 0.047m
Extrusion conditions;

Barrel temperature; 220 ° C
Screw design;
(1) Outline The screw of the extruder can be represented as shown in FIG. 3, and the outline of the screw pattern shown in FIG. 3 is as follows.
C1: Hoppers C2 to C5: Supply section C5 to C6: Plasticizing section C6 to C8: Transport section C9: Feed port C10: Kneading section A
C11: Kneading part B (consisting of kneading part b1 and kneading part b2)
(2) The specific screw pattern used in Evaluation 1 is as shown in FIG. A kneading disk having a 45 ° phase shift in the feeding direction is defined as FK, and an element having a notch in one reverse flight is defined as BMS. Moreover, 1.0D etc. represents the length of the kneading part b1.
The screw pattern shown in FIG. 4A is FK1.0D (L / D = 1),
The screw pattern shown in FIG. 4B is FK2.0D (L / D = 2),
The screw pattern shown in FIG. 4 (c) is BMS1.0D (L / D = 1),
The screw pattern shown in FIG. 4 (d) is BMS2.0D (L / D = 2),
The screw pattern shown in FIG. 4 (e) is BMS2.5D (L / D = 2.5),
And L / D is the ratio (L / D) between the lead length (L) of the kneading part b1 and the screw diameter (D) of the screw element. Note that the length L of the kneading part 23 in the description of the embodiment corresponds to the length of the kneading part b1.
(3) Screw shape The screw patterns shown in FIG. 4 differ only in the kneading part B of C11. The shape of the screw of the kneading part B of C11 is shown in FIG. The screw shape of the pattern of FIG. 4 (a) is shown in FIG. 5 (a), the screw shape of the pattern of FIG. 4 (b) is shown in FIG. 5 (b), and the screw shape of the pattern of FIG. 5 (c), the screw shape of the pattern of FIG. 4 (d) is shown in FIG. 5 (d), and the screw shape of the pattern of FIG. 4 (e) is shown in FIG. 5 (e).
The screw shown in FIG. 5 (a) has a kneading part b1 with a forward feed kneading disk having a length of 1.0D, and the kneading part b2 has a reverse feed flight with a length of 0.5D. The screw shown in FIG. A forward kneading disc with a length of 2.0D, a reverse feed flight with a kneading part b2 having a length of 0.5D. The screw shown in FIG. 5 (c) has a single knot containing a knotting part b1 with a length of 1.0D. Reverse feed kneading disk, reverse feed flight with kneading part b2 of 0.5D length The screw shown in FIG. 5 (d) is a single reverse feed kneading disk with kneading part b1 containing notches with a length of 2.0D. The kneading part b2 has a reverse feed flight with a length of 0.5D. The screw shown in FIG. 5 (e) has a kneading part b1 with a notch containing a notch with a length of 2.5D. 0.5D length reverse feed Light

Under the condition of Q / Ns = 1.0, the minimum shear stress history value (Pa · sec) as shown in FIG. 6 and the number of pellets in which part or all of the glass fiber bundle is not defibrated (pieces / pellet 10 kg) Sought the relationship. Specifically, it was derived by the following method.

First, necessary for derivation of the relationship, L / D, the discharge amount Q, screw rotation speed Ns, non fibrillation pellets number N, a plurality determine a set of minimum shear stress history value T _min. L / D, discharge amount Q, screw rotation speed Ns were arbitrarily determined, the minimum shear stress history value _Tmin was derived by the following method, and the number N of undefined pellets was determined by experiment. Specifically, it was determined as follows.

First, the derivation of the minimum shear stress history value (Pa · sec) by simulation will be described.
Resin behavior in the same direction complete meshing type twin screw extruder was analyzed using a three-dimensional flow analysis software in the twin screw extruder (Screw Flow-Multi, manufactured by Earl Flow).
The governing equations used in the analysis are the continuous equation (A), the Navier-Stokes equation (B), and the temperature balance equation (C).

As an analysis assumption, the incompressible fluid was completely melted and completely filled. Moreover, Arrhenius approximation and WLF approximation were used for the viscosity approximation formula. The analysis method is a finite volume method, a SOR method, or a SIMPLE algorithm. As a calculation, a steady analysis is first performed, and an unsteady analysis is performed using this as an initial value. After unsteady analysis, tracer particles were arranged (about 5000 particles), and local information concerning the tracer particles was collected (particle tracking analysis). Minimum value T _min of the time integral value of the shear stress, by integrating the shear stress of the local information relating to the tracer particles time, in which determining the minimum value of the total particle.

Next, derivation of the number of undefined pellets by experiment will be described.
After supplying PBT to a twin screw extruder, glass chopped strands are supplied under the above extrusion conditions, kneaded and mixed, then the resin composition is extruded from the die, and the molten resin composition is taken up from the die to form a strand. The strand was cooled and solidified in a water tank, and the strand was cut into a length of 3 mm with a cutter to produce a pellet. 10 kg of the pellets were collected, glass undefibrated (silver-colored agglomerates) in the black pellets were visually found, and the number of pellets containing glass undefibrated was counted.

An approximate curve (correlation line) representing the relationship between the number of undefined pellets and the minimum shear stress history value was determined by the method of least squares. When Q / Ns = 1.0, the different elements shown in FIGS. 4 (a) to 4 (e) were added to the kneading part B as described above, and the experiment and simulation were performed with different Q values. An approximate curve was obtained. The approximate curve is shown in FIG.

In the above formula (IV), α was 11.5042, and β was −2.200.

Even under the conditions of Q / Ns = 0.8 and Q / Ns = 0.5, as shown in FIG. 7, the minimum shear stress history value (Pa · sec) and a part of the glass fiber bundle or The relationship (correlation line) with the number of undefibrated pellets (pieces / pellet 10 kg) was obtained. FIG. 7 also shows the correlation line when Q / Ns = 1.0.

As shown in FIG. 7, the correlation line is different for each Q / Ns. Therefore, the function of the formula (IV) is approximated by the method of least squares. The approximate curve is shown in FIG. As shown in FIG. 8, it was possible to approximate with one correlation line independent of Q / Ns. Note that γ was 3.0.

As shown in FIG. 8, it was confirmed that the number of undefibrated pellets per unit amount was less than a predetermined value if it was equal to or greater than a predetermined minimum shear stress history value.

As described above, even if the Q / Ns condition changes, Formula (IV) can be used to study the amount of undefined glass fiber bundles contained in the pellet, and the screw element that the kneading unit has It was confirmed that the amount of undefined glass fiber bundles contained in the pellets can be examined with a single mathematical formula (IV) even if the types of are different.

<Evaluation 2>
FIG. 3 shows a raw material having the same composition of PBT resin 70% by mass and glass fiber 30% by mass as used in Evaluation 1 in a twin screw extruder (screw diameter D is 47 mm), and an arc-shaped notch. the screw elements of Article having formed flight portion and a length of 2.0D, to simulate a case of using a twin-screw extruder kneading section 23 shown in FIG. 1, the minimum shear stress history value T _min, cut The relationship of the number of notches (number of grooves) n was derived. The center of the ellipse forming the arc shape is the outer periphery, and the minor axis / 2 of the ellipse is 3 mm and the major axis / 2 is 4.15 mm. Further, the direction in which the major axis extends coincides with the direction in which the cutout extends. The lead length of the screw element was L / D = 0.25, and a comparison was made between a single reverse flight (BMS) and a forward reverse flight (FMS) having a flight part with a notch.

By deriving the minimum shear stress history value T _min in the same manner as Evaluation 1, to derive the relationship between the notch number n and the minimum shear stress history value T _min. The results are shown in FIG.

According to FIG. 9, it was confirmed that the effects of BMS and FMS were almost equivalent. That the change of the minimum shear stress history value T _min due to the notch change in the number of people of FMS is small it has been confirmed. Therefore, it is more stable to use FMS than to use BMS, and the number of undefined glass fibers in the pellet can be suppressed.

<Evaluation 3>
A kneading disc (FIG. 5 (a) and (FIG. 5A) and ( b) Evaluation of each simulation using the symbol FK) and a single reverse feed screw element (Fig. 5 (c) (d) (e) symbol BMS) having a flight part in which a notch is formed. FIG. 10 shows the distribution of shear stress history values obtained by performing time integration of the shear stress of the local information applied to the tracer particles by the same method as described in 1. The center of the notch is the outer peripheral part, the lead length Le of the reverse feed flight (symbol BMS in the figure) is L / D = 0.25, and the radius of the circle forming the arc shape of the notch is r = 3 mm. .

In the kneading disc (FK), the distribution spreads over a wide range from where the shear stress history value is small. Having a small shear stress history value means that there is a high probability that glass undefibration remains. On the other hand, in a single reverse feed screw element having a flight part in which a notch is formed, since the distribution of shear stress history values is narrow, the minimum shear stress history value is large. For this reason, if the screw element which has the said notch is used, it will become difficult to remain | survive an undisentangled glass fiber bundle in a pellet.

<Evaluation 4>
Next, using the minimum shear stress history value as an index, the shape required for the notch element will be described by flow analysis. In the twin-screw extruder shown in FIG. 1 (screw diameter 47 mm), a kneading part is composed of a single screw element having a flight part in which an arc-shaped notch is formed with a composition of 70% by mass of PBT resin and 30% by mass of glass fiber. The simulation when used in the No. 23 was performed. Specifically, the relationship between the minimum shear stress history value T _min obtained by the same method as in Evaluation 1 and the number of notches (groove number) n was obtained. For a single reverse feed screw element (BMS) having an arc-shaped notch as the outer peripheral portion and a flight portion in which the arc-shaped notch is formed, the lead length Le is L / D = 0.2, 0 Evaluation was performed under three conditions of .25 and 0.3. The arc shape is formed from an ellipse, and the minor axis / 2 of this ellipse is 3 mm and the major axis / 2 (the direction in which the notch extends) is 4.1 mm. The results of Evaluation 4 are shown in Table 2.

According to Table 2, the minimum shear stress history value T _min shows a high value when the number n of notches per lead length Le is 13 to 15. The minimum shear stress history value _Tmin is higher when the number of notches n is larger. However, since the mechanical strength of the screw element decreases as the number of notches n increases, it can be said that 13 to 15 is preferable.

<Evaluation 5>
In the twin-screw extruder (diameter 47 mm) shown in FIG. 1, a single screw element having a flight part in which an arc-shaped notch is formed with a composition of 70% by mass of PBT resin and 30% by mass of glass fiber is added to the kneading part 23. A simulation was performed when used. Specifically, the relationship between the minimum shear stress history value T _min obtained by the same method as described in Evaluation 1 and the major axis in the depth direction of the notch is shown. The center of the notch is on the outer periphery of the flight part, the shape of the notch is an ellipse, the short diameter / 2 of the notch on the outer periphery is 3 mm, and the long diameter / 2 (the direction in which the notch extends) is 3 mm, 4 mm, 5 mm. A simulation was performed in some cases. Further, the number of notches n was 11, and the lead length Le of the screw element having the notches was L / D = 0.25. The results of Evaluation 5 are shown in Table 3.

According to Table 3, the minimum shear stress history value T _min has a maximum value when the major axis of the notch groove depth / 2 is 4 to 5 mm. With respect to the diameter D, the radius range of the notch on the outer periphery is 0.064D, and the major axis length / 2 in the groove depth direction is 0.085D to 0.11D.

<Evaluation 6>
Except for changing the size of the minor axis to that shown in Table 3, the minimum shear stress history value _Tmin and the major axis extending in the direction perpendicular to the direction in which the notch is formed are the same as those in Evaluation 4. The relationship was shown. The results of Evaluation 6 are shown in Table 4.

According to the evaluation 6, even if the major axis of the ellipse forming the arc shape extends in the direction perpendicular to the direction in which the notch extends, the larger value of the major axis increases the minimum shear stress history value. It was confirmed that Moreover, from the comparison between Evaluation 5 and Evaluation 6, it is more effective that the major axis of the ellipse extends in the direction in which the notch extends.

<Evaluation 7>
The relationship between the minimum shear stress history value _Tmin and the radius of the circle was shown by the same method as in Evaluation 5, except that the arc-shaped shape was a circle. The results of Evaluation 7 are shown in Table 5.

It was confirmed that the minimum shear stress history value increases as the radius increases even when the arc forms a circle. In addition, from the comparison of evaluations 4 to 6, it was confirmed that the minimum shear stress history value is larger when the circular arc is formed than the ellipse is formed.

<Example>
In the examples, the following materials were used.
Thermoplastic resin: Polybutylene terephthalate resin (PBT) (melt index (MI) = 70 g / 10 min)
Carbon masterbatch glass fiber bundle: 3 mm long chopped strand obtained by bundling 2200 monofilaments having a diameter of 13 μm The composition is as follows.
PBT is 67.5 mass%, carbon masterbatch is 2.5 mass%, glass fiber bundle is 30 mass%
Extruder: Same direction full meshing type twin screw extruder TEX44αII (manufactured by Nippon Steel) Screw diameter D of screw element is 0.047m
The cylinder temperature (° C.) in the molding of the examples is shown in the table below.

The specific screw pattern used in the examples is as shown in FIG. The kneading disc is 90 ° out of phase with each disc, CK, the screw element with a notch in one reverse flight, BMS, and the screw with a notch in one forward flight. Let the element be FMS. The short diameter / 2 of the notch on the outer periphery is 3 mm, and the long diameter / 2 (the direction in which the notch extends) is 4.15 mm.
Comparative Example 1: The screw shown in FIG. 11 (a) is a kneading part (C8) with a 90 ° phase orthogonal kneading disk having a length of 2.5D. Example 1: The screw shown in FIG. 11 (b) is a kneading part (C8). ) Is a single feed progressive screw element FMS having a flight part with a notch formed in the outer periphery of length 2.5D
Example 2: The screw shown in FIG. 11 (c) is a single feed forward screw element FMS in which the kneading part (C8) has a flight part with a notch formed on the outer periphery having a length of 3.0D.
Example 3 The screw shown in FIG. 11 (d) has a kneading part (C8) with a length of 3.0D, a single reverse feed screw element BMS and a forward feed screw having a flight part with a notch formed on the outer periphery. In combination with element FMS, FMS1D is followed by BMS1D, then FMS

Next, derivation of the number of undefined pellets by experiment will be described. After feeding PBT to the twin screw extruder, glass chopped strands were fed to the twin screw extruder. After kneading and mixing under the extrusion conditions shown in Table 7 below, the glass fiber reinforced thermoplastic resin composition is extruded from the die, the melted resin composition is taken from the die, and the strand is cooled and solidified in a water tank, and then the cutter Then, the strand was cut into a length of 3 mm to prepare a pellet. 10 kg of the pellets were collected, and glass undefibrated (silver-colored agglomerates) in the black pellets were searched visually, and the number of pellets containing undefined glass fibers was counted. The number of the pellets is shown in Table 7 below.

In this example, a twin-screw extruder with a screw diameter of Φ = 47 mm is used. With this size, the discharge of Q = 650 kg / h is very high compared to the conventional case. For this reason, in the screw of FIG. 11A that has been generally used conventionally, a large number of pellets including undefined glass fiber bundles are generated. In contrast, in Examples 1 to 3, almost no pellets containing undefined glass fiber bundles were generated.

In the screw of FIG. 11 (a), a 90 ° phase orthogonal kneading disk CK was used, but this was changed to a single progressive screw element FMS having a flight part with a notch formed on the outer periphery. When the length is 3.0D, pellets containing undefined glass fiber bundles are not generated. However, if the discharge rate is further increased, pellets containing undefined glass fiber bundles are generated. In the screw pattern shown in FIG. 11D, the kneading part is a combination of FMS1D, BMS1D, and FMS1D. By combining reverse feed and forward cut-out elements in the kneading section, the generation of pellets containing undefined glass fiber bundles can be further reduced.

DESCRIPTION OF SYMBOLS 1 Cylinder 10 Hopper 11 Feed port 12 Vacuum vent 2 Screw 20 Supply part 21 Plasticizing part 22 Conveying part 23 Kneading part 3 Die 4 Single feed forward screw element 40 Flight part 41 Notch

Claims

A method for producing glass fiber reinforced thermoplastic resin pellets using a twin-screw extruder equipped with screws that rotate and mesh with each other,
A plasticizing step of supplying a thermoplastic resin to the extruder and heating, kneading and plasticizing;
After the plasticizing step, one or more glass fiber bundles are supplied to the extruder, and the defibrated glass fibers and the plasticized thermoplastic resin are screwed together while defibrating the glass fiber bundles. A kneading step for kneading;
After the kneading step, an extrusion step of extruding the glass fiber reinforced thermoplastic resin composition,
Pelletizing step of pelletizing the extruded glass fiber reinforced thermoplastic resin composition,
The thermoplastic resin is composed of at least one resin selected from polybutylene terephthalate resin, liquid crystal resin, and polyarylene sulfide resin,
In the kneading step, the screw has a glass fiber reinforced heat having one or more progressive screw elements each having a flight portion in which an arc-shaped notch satisfying the following inequalities (I) to (III) is formed on the outer periphery. A method for producing a plastic resin composition pellet.

0.05D ≦ r ≦ 0.15D (I)
7 ≦ n ≦ 20 (II)
Le ≦ 0.3D (III)

(R in the inequality (I) is the radius of the circle forming the arc or the major axis / 2 or the minor axis / 2 of the ellipse forming the arc, and n in the inequality (II) is , The number of notches per lead length of the one-step progressive screw element, and Le in the inequality (III) is the lead length of the one-step progressive screw element, and the inequality (I), (II) D in the inside is a screw diameter.)
A method for producing glass fiber reinforced thermoplastic resin pellets using a twin-screw extruder equipped with screws that rotate and mesh with each other,
A plasticizing step of supplying a thermoplastic resin to the extruder and heating, kneading and plasticizing;
After the plasticizing step, one or more glass fiber bundles are supplied to the extruder, and the defibrated glass fibers and the plasticized thermoplastic resin are screwed together while defibrating the glass fiber bundles. A kneading step for kneading;
After the kneading step, an extrusion step of extruding the glass fiber reinforced thermoplastic resin composition,
Pelletizing step of pelletizing the extruded glass fiber reinforced thermoplastic resin composition,
The viscosity of the thermoplastic resin is 100 Pa · s or less under the condition of a shear rate of 1000 sec −1 ;
In the kneading step, the screw has a glass fiber reinforced heat having one or more progressive screw elements each having a flight portion in which an arc-shaped notch satisfying the following inequalities (I) to (III) is formed on the outer periphery. A method for producing a plastic resin composition pellet.

0.05D ≦ r ≦ 0.15D (I)
7 ≦ n ≦ 20 (II)
Le ≦ 0.3D (III)

(R in the inequality (I) is the radius of the circle forming the arc or the major axis / 2 or the minor axis / 2 of the ellipse forming the arc, and n in the inequality (II) is , The number of notches per lead length of the one-step progressive screw element, and Le in the inequality (III) is the lead length of the one-step progressive screw element, and the inequality (I), (II) D in the inside is a screw diameter.)
3. The glass fiber reinforced thermoplastic resin composition according to claim 1, wherein, in the kneading step, the screw has at least one reverse feed screw element having a flight portion having an arc-shaped notch formed on an outer periphery. Pellet manufacturing method.