WO2012173224A1

WO2012173224A1 - Injection molding method

Info

Publication number: WO2012173224A1
Application number: PCT/JP2012/065334
Authority: WO
Inventors: 小倉　徹; 河崎　英敏; 盛男藤原
Original assignee: 富士フイルム株式会社
Priority date: 2011-06-16
Filing date: 2012-06-15
Publication date: 2012-12-20
Also published as: JP5781471B2; KR20140027244A; CN103561933A; JP2013018283A

Abstract

A pressure sensor (27) is inserted into a tip of a heating cylinder (13) of an injection molding device (10). During a measurement process, a little amount of grain-shaped biomass resin (45) and a little amount of powder-shaped additive (46) are supplied from constant feeders (52, 54) to a hopper (40) lying at an inlet (28). Right below the inlet (28), a material is supplied through certain periods of time with an opening left in a space in the heating cylinder (13). A controller (25) calculates a backing power (PJ) of a screw (14) based on a pressure value detected with the pressure sensor (27), and controls a driving unit (18) so that the power multiplied by a coefficient (K) (1.2 ~ 2.0) becomes a driving power (PH) added to the screw (14).

Description

Injection molding method

The present invention relates to an injection molding method in which a melt molding material is injected into a mold using a screw having a metering function.

An injection molding method is widely known as a representative plastic molding. In this injection molding method, an injection molding machine in which a screw is disposed in a heating cylinder, and a mold composed of a male mold and a female mold are used. In a general injection molding method, a metering step (also referred to as a plasticizing metering step), a mold clamping step, an injection filling step, a pressure holding and cooling step, and a mold release step are sequentially executed.

In the weighing process, a molding material mainly composed of plastic is supplied into the heating cylinder. The molding material is fed toward the cylinder tip while being melted by the heat from the heating cylinder and the frictional heat generated by the screw rotation. This melt molding material is stored at the tip of the cylinder without flowing out of the nozzle. When the storage amount of the melt molding material is increased, the rotating screw is pressed backward and moved backward in the direction opposite to the nozzle. From the retreated position of the screw, the storage amount of the melt molding material is measured. When the screw returns to the predetermined retracted position, the rotation of the screw is stopped and the metering process ends.

Next, after combining the male and female molds and clamping, the nozzle at the tip of the heating cylinder is connected to the mold gate. The molten molding material is injected and filled into the cavity in the mold with a high pressure by moving toward the tip of the cylinder while the rotation of the screw is stopped. After the injection filling, the nozzle is kept pressed against the gate of the mold so that the melt molding material in the mold is maintained at a predetermined pressure. Thereafter, the mold is cooled to solidify the molded product. Finally, the mold is separated into a male mold and a female mold, and the molded product is taken out.

In the weighing process, the molding material in the hopper is supplied to the heating cylinder. A sufficient amount of molding material exceeding the molding material required for one injection molding is stored in the hopper, and the molding material is sequentially supplied into the heating cylinder by its own weight. A supply method (referred to as a normal supply method) in which the molding material is supplied from the hopper into the heating cylinder by its own weight in accordance with the screw feed amount, and the heating cylinder is always filled with the molding material is generally used.

The molding material supplied into the heating cylinder is melted and stirred, and sent to the liquid reservoir at the tip of the cylinder as a molten molding material. This melt molding material is prevented from leaking from the tip of the nozzle by a shut-off nozzle (nozzle equipped with a needle-like valve) or the like, and therefore accumulates in the liquid reservoir. In response to the storage of the melt molding material, the screw is retracted under the pressure.

When the screw moves backward, the screw moves backward under the pressure of the molding material filled at the tip of the heating cylinder. Here, since the feeding amount of the molding material in the heating cylinder increases as the rotation speed of the screw increases, the time (measuring time) until the screw moves backward from the initial position (advance position) to the specific position is shortened. On the other hand, the lower the number of rotations of the screw, the smaller the feed amount of the molding material, and the longer the measurement time. When the screw rotation speed is constant, the lower the pressure that the screw receives from the rear end side, the faster the screw retracts, and the shorter the metering time, and the higher the screw, the longer the metering time. *

In the metering process, if the melt molding material rotates together with the screw (referred to as “both around”), the melt molding material cannot be conveyed to the liquid reservoir. In order for the melt molding material to be conveyed, the melt molding material rotates slower than the rotation of the screw or does not rotate due to friction between the melt molding material and the cylinder inner wall (both the positional relationship with the screw changes). is required.

However, if the melt molding material has a high density or has a large friction, when the melt molding material is pressed against the inner wall of the cylinder, it sticks to the inner wall of the cylinder and is difficult to move. As a result, when the screw tries to push the melt molding material, the screw itself may be retracted against the resistance of the melt molding material adhered to the inner wall of the cylinder (this is referred to as “screwing phenomenon”). This acts so that the melt molding material adhered to the inner wall of the cylinder functions as a nut and the screw functions as a bolt, and only the screw moves backward.

When the melt molding material is completely adhered to the inner wall of the cylinder, the screw moves backward due to the resistance, and the pressure of the melt molding material in the liquid reservoir cannot be increased. However, in the usual injection molding, the structure and molding of the screw so that the melt molding material is conveyed downstream without sticking to the cylinder inner wall by moderate friction that does not “turn around” with the screw. Conditions are selected.

Japanese Patent Application Laid-Open No. 2003-21508 describes an injection molding machine that can manufacture a high-quality molded product that does not cause internal distortion or the like by controlling the retreating force and the advancing force of a screw. In this injection molding machine, in the metering process, the molding material is supplied to the heating cylinder at a constant rate, and the screw rotates at a constant speed in the heating cylinder, and the molten molding material is stored in the liquid reservoir at the tip of the heating cylinder. Send in towards. A pressure sensor that measures the molten resin pressure is disposed in the liquid reservoir. While monitoring the resin pressure with the pressure sensor, the axial position of the screw is adjusted so that the resin pressure is maintained at a predetermined value, thereby adjusting the volume of the liquid reservoir. At the same time, the resin pressure is sent to the calculation unit, and the backward force acting on the tip of the screw is calculated using the cross-sectional area of the screw. The servo motor generates a forward force having the same magnitude as the backward force and presses the rear end of the screw. This balances the retreating force and the advancing force of the screw in a weighing process or the like.

Japanese Patent Application Laid-Open No. 2006-272867 describes an injection molding machine that prevents a mold and a screw from being damaged due to abnormal resin pressure during an injection / holding process. In this injection molding machine, a resin pressure sensor is disposed in the liquid reservoir. Further, a back pressure sensor (load cell) acting on the rear end of the screw is provided. The controller compares the resin pressure measured by the resin pressure sensor with the back pressure value measured by the back pressure sensor during the injection / holding process, and if the difference between the two measured values is within the allowable range. The injection / holding process is continued, and when it is outside the allowable range, the injection / holding process is forcibly terminated to prevent damage to the mold or the like.

By the way, as a method for reducing the burden on the natural environment, it has been attempted in various fields to use a resin material derived from a living organism such as a plant instead of a petroleum resin material. Such a resin material is also referred to as a biomass resin (bioplastic). Among them, a polylactic acid resin (PLA) or a cellulose resin is carbon neutral, and its practical application has been studied. However, many of the molded products made of biomass resin have poor heat resistance compared to molded products of general resins, and have a drawback that the molded products are easily burnt.

¡The heat resistance and flame retardancy of biomass resin can be improved by mixing additives. In the case of general resins, when various additives according to the purpose are mixed into the base resin as the main component, these materials are put all at once into a kneader and mixed and dispersed thoroughly. Body pellet material. Then, the pellet material thus obtained may be put into an injection molding machine and molded. In this regard, when biomass resin is used as the base resin, powdery additives are indispensable to improve the flame retardancy of molded products, and many of these additives are added to the kneader together with the biomass resin. However, it is difficult to obtain a sufficient mixing / dispersing action. For this reason, it is necessary to first pelletize the biomass resin as the main component, and then add the pellets and additives to a kneader and mix and disperse them sufficiently to re-pelletize.

Therefore, when the injection molding process is included, three times of heat treatment is applied to the biomass resin that originally has poor heat resistance, and this thermal history causes a decrease in molecular weight, coloring, and the like, causing the quality of the molded product to deteriorate significantly. . To reduce the number of heat histories, stop the kneading process of mixing pellets with the pelletized biomass resin and re-pelletizing, and then add various powdered additives together with the biomass resin pellets to the injection molding machine. What is necessary is just to supply to this cylinder. This method is used as a “direct material charging kneading molding method (Direct Mixing: DM molding method)”, and eliminates the need for a pretreatment for blending a plurality of types of molding materials into pellets. Thereby, the thermal history of the molding material can be reduced, the quality of the molded product can be maintained high, and the process cost can be reduced.

As described above, for example, in order to obtain a high-quality molded product with a biomass resin having improved heat resistance, in addition to a granular base resin as a main component, a powdery additive for enhancing heat resistance A DM molding method in which is directly put into an injection molding machine is advantageous. However, additives for increasing the heat resistance generally lower the mechanical strength. Therefore, additives such as powder additives and compatibilizers are also used in combination.

As described above, when DM molding is performed by combining a powdery additive with a granular base resin, different types of materials such as granular and powdery materials are used in a cylinder of an injection molding machine. It becomes difficult to sufficiently knead and disperse. In particular, when the proportion of the powdery material exceeds 30%, unevenness tends to occur in the kneading / dispersing of the granular material and the powder material. Uneven kneading / dispersion of the material becomes a factor that fluctuates the friction between the material and the inner wall of the cylinder, adversely affects the measuring process, and results in variations in the weight and physical properties of the molded product.

In the present invention, even when a powder material and a granular material such as a pellet are directly supplied to an injection molding machine, the molding material is sufficiently mixed in a cylinder and stable weighing is performed. We propose an injection molding method that can obtain molded products with stable quality.

In the injection molding method according to the present invention, a molding material made of a plurality of materials including a granular material as a base resin and a powdery additive is supplied into a heating cylinder from an inlet, and a screw is provided inside the heating cylinder. The molding material is sent to the tip of the cylinder and stored while being kneaded and dispersed in the cylinder. The screw is retracted by the pressing force from the stored molding material, and the metering is completed when the screw is retracted to the weighing setting position.Then, the screw is advanced and the material is pushed into the mold at a high pressure to perform injection molding. Is called. When measuring, the pressure from the molding material stored in the cylinder tip is detected. Weighing is performed with the applied force obtained by multiplying the screw retraction force determined according to the detected pressure value multiplied by a preset coefficient from the range of 1.2 to 2.0 as the forward force. . The molding material is supplied by a limited supply that is sparsely charged from the inlet, and the molding material is supplied directly below the inlet while leaving a gap in the molding material transfer space formed between the inner wall of the heating cylinder and the screw. Is done. With this limited supply, the time required for metering is the standard when filling and supplying granular material while filling the molding material transfer space formed between the inner wall of the heating cylinder and the screw directly under the inlet. Make it longer than the weighing time.

The weighing time of the present invention is preferably 1.5 to 3 times the above-mentioned standard weighing time. If the metering time is shorter than the lower limit of this range, kneading between the granular base resin and the powdered additive tends to be insufficient, and if the metering time is longer than the upper limit, the molding material, especially powdery additive There is concern about thermal degradation of Such conditions are particularly suitable when the ratio of the powdery additive is 30% by weight or more of the granular material.

As a specific example, a polylactic acid resin or a cellulose resin can be used as a base resin, and a flame retardant or a compatibilizing agent can be used as an additive. In performing the limited supply in which the supply of these molding materials is dispersed in time and supplied in small amounts, a method of continuously supplying the granular base resin and the powdered additive in small amounts into the heating cylinder, Further, there are a method of intermittently supplying these materials to the cylinder, a method of alternately supplying a granular base resin and a powdery additive. The molding cycle includes a weighing process, a mold clamping process, an injection filling process, a pressure holding cooling process, and a mold release process, and the molding material is measured between the start of the pressure holding cooling process and the end of the mold release process. Is done.

According to the present invention, there is no great variation in weight even when different materials such as granular and powder are not kneaded sufficiently and are directly fed to the cylinder of the injection molding machine and molded. A molded product with stable quality can be obtained. The method of the present invention is also effective for a pellet material such as an elastomer whose resin resistance on the inner wall of the cylinder varies greatly depending on the shape and supply state of the pellet.

Schematic configuration diagram of an injection molding apparatus for carrying out the injection molding method of the present invention Diagram explaining the zone configuration of the screw Diagram explaining injection molding cycle The figure explaining the position of the screw in the middle of the measurement process The figure explaining the position of the screw at the end of the weighing process The figure explaining the position of the screw in the injection and filling process The figure explaining the position of the screw in a mold opening and a measurement process.

As shown in FIG. 1, an in-line screw type injection molding apparatus 10 suitably used in the method of the present invention includes a heating cylinder 13 having a nozzle 12 at its tip, and a screw 14 is rotatably disposed therein. The At the rear end of the screw 14, a drive device 18 is provided that includes a motor 16 that rotates the screw 14 and a piston 17 that moves the screw 14 in the axial direction (left and right direction in FIG. 1). The piston 17 is provided with a back pressure sensor 21 and a position sensor 22. The back pressure sensor 21 detects a back pressure that generates a resistance force when the screw 14 moves backward in the measuring process. The position sensor 22 detects the retracted position of the screw 14, that is, the measurement completion position. These detection results are input to the controller 25.

The driving device 18 has a function of controlling the back pressure of the piston 17 in cooperation with the controller 25. For this reason, the drive device 18 is provided with a pump 19a, a pressure adjusting device 20, and a servo valve 20a that are on / off controlled in response to a command from the controller 25. The pump 19a supplies air from the tank 19 to the piston 17 according to the back pressure. The pressure adjusting device 20 sets the back pressure of the piston 17 in accordance with a setting instruction from the controller 25. The servo valve 20a is feedback-controlled based on a control signal sent from the controller 25 according to the back pressure value detected by the back pressure sensor 21 so that the back pressure set by the pressure regulator 20 is maintained.

A heater 26 is wound around the outer periphery of the heating cylinder 13 to heat the molding material supplied to the inside of the heating cylinder 13 at a predetermined temperature necessary for plasticization. The molding die 30 includes a fixed mold 32 having a cavity 31 formed therein and a movable mold 33, and the tip of the nozzle 12 is connected to a sprue 34 of the fixed mold 32. Further, the piston 17 presses and moves the screw 14 in the left direction (forward direction) in FIG. 1 to perform an injection operation, and the molten resin is injected into the molding die 30 through the nozzle 12 with a predetermined pressure. .

A charging port 28 is formed on the rear end side in the length direction of the heating cylinder 13, and a hopper 40 is attached above the charging port 28. A material supply device 50 is provided above the hopper 40, and the molding material supplied from the material supply device 50 is supplied into the heating cylinder 13 through the hopper 40 and the inlet 28. The material supply device 50 includes

drums

51 and 53. The drum 51 is charged with a biomass resin 45, which is a granular material, as a base resin that is a main component of the molding material, and the drum 53 is added with a powdery material. The object 46 is thrown in.

Measured feeders

52 and 54 are provided at the outlets of the

drums

51 and 53, and the biomass resin 45 and the additive 46 that have been measured are supplied to the hopper 40 from the respective measured

feeders

52 and 54. When supplying a general molding material in the form of granules called pellets to the heating cylinder 13, it is standard that the molding material is supplied to the hopper 40 without interruption due to its own weight. For this reason, immediately below the inlet 28, the molding material is densely filled so that there is almost no gap in the space formed between the inner wall of the heating cylinder 13 and the screw 14.

On the other hand, in this embodiment, each of the biomass resin 45 and the additive 46 is weighed by the weighing

feeders

52 and 54, and then is supplied to the hopper 40 little by little over time. Specifically, a certain amount of the biomass resin 45 and the additive 46 are temporally from the time when the screw 14 is rotated and the measuring process is started until the screw 14 is stopped and the measuring process is completed. Dispersed and supplied to the hopper 40. For this reason, the biomass resin 45 and the additive 46 are supplied immediately below the charging port 28 while creating a gap in the molding material transfer space formed between the inner wall of the heating cylinder 13 and the screw 14.

In addition, when supplying the biomass resin 45 and the additive 46 from the weighing

feeders

52 and 54 to the hopper 40, each of them is continuously supplied in small quantities during the weighing process period, or each of them is fed during the weighing process period. At the same time, it may be intermittently supplied in small increments, or may be alternately supplied in small amounts. The measuring feeder is not particularly limited as long as it does not interfere with the supply of the molding material, and a screw feeder, a vibratory feeder, a pocket-type constant-capacity feeder, a table feeder, a circle feeder, or the like can be used.

The controller 25 includes a type of molding material (type of resin, type of additive, etc.), shape of the material (powder, granule, liquid, pellet), mixing ratio (ratio of base resin and additive), injection Depending on various factors such as molding conditions (injection amount per shot, cylinder heating temperature, screw rotation speed, back pressure setting value, etc.), the necessary kneading time data required for uniform and sufficient mixing of the molding material Have been entered. The necessary kneading time data obtained in advance by a preliminary test or the like is used. In addition, the supply amount of the molding material per unit time in the weighing

feeders

52 and 54 with respect to the weighing time is input so that the weighing time becomes equal to or longer than the necessary kneading time.

The controller 25 confirms that at the start of the first molding and that the previous molding has entered the holding pressure cooling process based on information from the pressure sensor 27, the back pressure sensor 21 and the position sensor 22 at the tip of the cylinder. Each of the molding materials is started to be supplied from the

feeders

52 and 54 to the hopper 40 according to the selected supply program.

As shown in FIG. 2, the screw 14 in the heating cylinder 13 is divided into three zones, a supply zone 41, a compression zone 42, and a metering zone 43 in order from the inlet 28 side. At the time when the weighing process is started, the weighing zone 43 is located immediately below the inlet 28. The molding material charged into the hopper 40 is supplied from the charging port 28 to the supply zone 41, and is conveyed through the heating cylinder 13 to the screw tip side by the rotation of the screw 14. The molding material conveyed in the heating cylinder 13 is gradually caused by shearing heat generated between the surface of the rotating screw 14 and the inner wall of the heating cylinder 13 and heat from the heater 26 provided on the outer periphery of the heating cylinder 13. To be melted.

In the compression zone 42, melt-kneading of the molding material is started, and the melt-kneaded molding resin is further conveyed to the tip side and reaches the measuring zone 43. A pressure sensor 27 is provided on the inner wall at the tip of the heating cylinder 13 to detect the pressure of the accumulated molten resin. The detected pressure value is transmitted to the controller 25. As the melt-kneaded molding material accumulates at the cylinder tip 15, the screw 14 receives the pressure and moves backward, and when it reaches the measurement setting position (see FIG. 5), the rotation of the motor 16 is stopped and the backward movement is also stopped. To do.

As shown in FIG. 3, the injection molding cycle is a repetition of a metering process, a mold clamping process, an injection filling process, a pressure keeping cooling process, and a mold release process. In the measuring step, the screw 14 is rotated in the heating cylinder 13 by driving the motor 16. Since the molding material is supplied to the heating cylinder 13 through the hopper 40 at the start of the metering process, the molding material is fed to the cylinder tip side while being kneaded and melted (plasticized) by the rotation of the screw 14, and gradually the cylinder tip portion. 15 (see FIG. 4).

As the storage amount of the molding material at the cylinder tip 15 increases, a retracting force based on the pressure of the stored molding material itself is applied to the screw 14. For this reason, when the position sensor 22 detects that the screw 14 has moved backward while rotating and has moved back to a preset measurement setting position, the motor 16 stops, and at the same time, the rotation and backward movement of the screw 14 also stop. The measurement of the time is finished (FIG. 5). The time required for this measuring process is the measuring time.

The mold clamping process is a process of closing the movable mold 33 and the fixed mold 32 in the mold open state to form a molding space in the molding die 30, and the movable mold 33 is moved by a mold clamping cylinder (not shown). It moves in the direction of the fixed mold 32 and makes contact. Thereafter, the nozzle touch for joining the sprue 34 of the fixed mold 32 to the nozzle 12 is performed, but the molding may be repeated in the joined state.

In the injection filling process (also referred to as injection process or filling process), the molding material melted in the heating cylinder 13 and in a fluid state and stored in the cylinder tip 15 is transferred from the nozzle 12 to the molding metal by the advance of the screw 14. Injection into the mold 30. Thereby, the molten molding material is filled in the cavity 31 of the molding die 30.

The holding pressure cooling step performs holding pressure in which pressure is applied to the cavity 31 by the screw 14 even after being injected and filled, and cooling for solidifying the filled resin in that state. Holding pressure continues to apply pressure to the molding material filled in the cavity 31 of the molding die 30 so that small bubbles are removed and the detailed shape formed in the cavity 31 is transferred to the molded product. The holding pressure is completed substantially in the first half of the holding pressure cooling step, but the cooling is continued after that until the molded product is sufficiently rigid when it is released.

In the mold release process, the movable mold 33 is moved away from the fixed mold 32 by the mold clamping cylinder to open the molding die 30 (see FIG. 6), and is molded by the protruding pin 35 just before the end of the mold opening operation. The product is released from the movable mold 33.

In the holding pressure cooling step in each of the above steps, the screw 14 is rotated when the filled resin is solidified to some extent even before the holding pressure is completed, and the next measuring step is started. Moreover, what is necessary is just to complete | finish a measurement process by the time cooling is complete | finished. Of course, the metering start time can be shifted later in time, but the molding cycle can be made more efficient by performing the (n + 1) th cycle metering step during the nth cycle holding pressure cooling step as described above. Can do.

Next, the injection molding method according to the present invention will be described with reference back to FIG.

When various factors such as the type of molding material and molding conditions are input to the controller 25, the controller 25 selects a measurement time required for the molding material from the input necessary kneading time data. In addition, the controller 25 starts measuring the biomass resin 45 and the additive 46 for one cycle stored in the measuring

feeders

52 and 54 from the measuring

feeders

52 and 54 within the measuring time from the start to the end of the measurement. The supply amounts of the biomass resin 45 and the additive 46 per unit time supplied to the hopper 40 are calculated and set in the weighing

feeders

52 and 54. As a result, both a certain amount of biomass resin 45 and additive 46 weighed by the weighing

feeders

52 and 54 are dispersed and supplied to the heating cylinder 13 little by little between the start and end of the weighing process. Will come to be.

Suppose that the necessary kneading time required for kneading the biomass resin 45 and the additive 46 uniformly and sufficiently is 20 seconds, the metering time in the metering process is determined to be at least 20 seconds. Within this measuring time, the material for one cycle stored in the measuring

feeders

52 and 54 is limitedly supplied to the hopper 40. The supply amount of the material per unit time or the supply speed of the material is supplied from the start of supply. It is preferable to be as uniform as possible until the end. Therefore, a small amount continuous supply method (referred to as flipping) in which the molding material is continuously and gradually dropped from the weighing

feeders

52 and 54 to the hopper 40, or an intermittent supply method in which a constant amount is intermittently dropped to the hopper 40 at regular intervals. It is preferable to adopt. In the case of intermittent supply, it may be alternately supplied from the weighing

feeders

52 and 54.

When the weighing process starts, the controller 25 starts to limit supply of the respective molding materials from the weighing

feeders

52 and 54 to the hopper 40 based on the information from the pressure sensor 27, the back pressure sensor 21, and the position sensor 22, and the motor 16 is turned on. Drive to rotate the screw 14.

When the melted molding material is gradually fed forward and collected at the cylinder tip 15, the screw 14 is pushed back and starts moving to the rear of the heating cylinder 13. The pressure sensor 27 provided at the cylinder tip 15 detects the resin pressure S (MPa) of the molten molding material, and the back pressure sensor 21 detects the back pressure T that urges the screw 14 forward. When the resin pressure S is detected, the controller 25 calculates a backward force PJ applied to the screw 14 under the resin pressure S, and calculates a forward force PH obtained by multiplying the calculated backward force PJ by a coefficient K. Then, the back pressure T for obtaining the forward force PH is set in the pressure adjusting device 20.

Incidentally, since the screw 14 moves the molding material to the front of the heating cylinder 13 by its own rotation, the resin resistance at that time becomes a reaction force PT and presses the screw 14 in the backward direction. For this reason, in the backward direction, a reaction force PT due to resin resistance is applied to the screw 14 in the backward direction, and a forward force PH due to the back pressure T is applied in the forward direction (PH = PJ + PT). ). Accordingly, the forward force PH is reduced by the reaction force PT due to the resin resistance, and the reaction force PT easily fluctuates due to the influence of the rotational speed of the screw 14 and the kneading condition of the molding material. The forward force PH to be added to becomes unstable.

In this regard, in this injection molding apparatus, the controller 25 keeps the optimum forward force PH so that the forward force PH is not excessive and the fluctuation of the reaction force PT due to the resin resistance can be ignored. To be able to. For this reason, the controller 25 uses the backward force PJ determined corresponding to the resin pressure S detected by the pressure sensor 27 as a reference, and sets a coefficient K set in the range of 1.2 to 2.0 to the backward force PJ. The back pressure T is controlled so that this force “K · PJ” acts on the screw 14 as the forward force PH.

The value of the coefficient K can be prepared in advance according to various factors such as molding materials and molding conditions by conducting preliminary tests and the like in advance. Use it. As a result, even if the reaction force PT due to the resin resistance may fluctuate, the forward force PH is adjusted in a well-balanced manner so as to follow the backward force PJ based on the resin pressure at that time. Therefore, the measurement time (kneading time) does not fluctuate greatly, and a high-quality molded product is obtained while using a molding material composed of a granular base resin and a powdery additive. It becomes possible.

“PH / PJ = K” is obtained by adjusting the forward force PH using the coefficient K as described above. The value of the coefficient K is arbitrary as long as it is in the range of “1.2 to 2.0”. Specifically, 1.2, 1.3, 1.5, and 1.8 are prepared and molded. It can be switched as appropriate according to the conditions. When the coefficient K is close to 1 or 1, the frictional resistance is almost ignored. For this reason, in reality, the screw 14 is easily retracted due to the frictional resistance of the resin, and the molding material cannot be fed toward the cylinder tip 15, so that the molding material easily rotates together with the screw 14. On the other hand, if the coefficient K exceeds “2.0”, the forward force PH with respect to the screw 14 becomes excessive, making it difficult for the screw 14 to move backward, extending the measurement time and causing the thermal deterioration of the molding material.

Generally, in a state where the molding material is densely packed in the supply zone 41 of the screw 14, the resin resistance when the screw 14 is rotated increases and is likely to fluctuate. For this reason, it is disadvantageous to keep the rotational speed of the screw 14 constant, but if the molding material supplied to the supply zone 41 is made small by the above-mentioned limited supply, the resin resistance is small and the fluctuation is also suppressed. The reaction force PT can also be reduced.

In the molding method of the present invention, since the molding material is dispersed in time and supplied to the heating cylinder 13, it takes time to measure the molding material required for each molded product. When supplying the molding material to the cylinder as a standard, for example, when only the above-described granular biomass resin 45 is poured into the hopper 40 by its own weight without passing through the quantitative feeder 52 and is supplied to the heating cylinder 13 from the inlet 28 as it is. If other conditions are common, the combination of the number of rotations of the screw 14 and the measurement time is as follows in order to ensure that the molding material is in a good state of melting and kneading and does not cause thermal deterioration in the molding material. The combinations shown in [Table 1] are confirmed as appropriate. Since the molding material is only in the form of granules, the coefficient K is set to “2.5”.

If the measuring time shown in [Table 1] is the standard measuring time at each screw speed, in the case of the method of the present invention, the granular material and the powdered material are used by the measuring

feeders

52 and 54. Since the feed is distributed in small amounts over time, the metering time at each screw speed should be extended to about 1.5 to 3 times the standard metering time so that the kneading proceeds sufficiently. Is preferred. In addition, when the molding material to be used is inferior in heat resistance, the upper limit of the measurement time may be preferably less than 3 times in order to avoid staying in the heating cylinder 13 for a long time.

The rotational speed of the screw 14 is preferably set to 30 to 300 rpm in consideration of both improvement in kneading performance and deterioration due to shear heat generation, but more preferably in the range of 50 to 200 rpm, which is suitable for each rotational speed. Weighing should be done under weighing time. In addition, when the rotation speed of the screw 14 is less than 30 rpm, sufficient uniform kneading cannot be performed, and when it exceeds 300 rpm, the molding material may be deteriorated by shearing heat generation. In particular, when the base resin of the molding material is a biomass resin, the risk of deterioration increases when it exceeds 300 rpm.

Although not shown, adding a device for cooling the outside of the heating cylinder of the injection molding machine by means such as air blowing can suppress the temperature rise due to the shear heat generation of the material, and increase the screw rotation speed. Can be set.

The injection molding method of the present invention is a standard material supply, that is, a material supply in which granular molding material is poured into the hopper 40 by its own weight, and the space in the measuring zone 41 of the screw 14 is almost densely filled with the molding material. On the other hand, a material supply method is adopted in which the granular material and the powder material are supplied while being limited to small amounts in time so that a gap is generated in the space in the measurement zone 41. For this reason, the number of rotations of the screw 14 can be appropriately selected from 50 to 200 rpm, for example, but the ratio of the metering time to the standard metering time becomes long. However, the molding material is not clogged at the outlet of the hopper 40 or inside the heating cylinder 13, the resin resistance when the molding material is transferred forward is kept low, and a uniform kneading action is obtained.

A molding test was performed using the injection molding method of the present invention, and samples of Examples 1 to 6 and Comparative Examples 1 to 6 were molded while changing molding conditions. About these samples, the various tests were done on common conditions and the quality was evaluated. Hereinafter, the outline of the molding test and the evaluation result will be described.

[Molding materials]
The following were used as molding materials.
・ Polylactic acid resin (pellet): Nature Works, 4032D 100 parts by weight ・ Flame retardant (powder): ADEKA, Adeka Stab FP2200 35 parts by weight ・ Compatibilizer (powder): Fushimi Pharmaceutical, Ravitor FP110 20 parts by weight Anti-decomposition agent (powder) ... Mitsubishi Rayon, Metabrene W600A 5 parts by weight, PTFE drip inhibitor (powder) ... Daikin Industries, FA500H 0.5 part by weight, hydrolysis inhibitor (powder) ... Rhein Chemie, Starbuxol 1FL 3 parts by weight, filler (fine powder) ... Nihon Talc Industrial, P3 8 parts by weight <total> 171.5 parts by weight

As the polylactic acid resin, one previously dried at 80 ° C. for 5 hours in a hot air dryer was used. Moreover, the difficult agent used what was previously dried under reduced pressure for 5 hours at 80 degreeC in the vacuum dryer. The powder ratio of the molding material is 41% by weight.

[Injection molding equipment]
The SG150U-3 manufactured by Sumitomo Heavy Industries, Ltd. was used as the injection molding equipment for the test, and JIS dumbbell test pieces, Charpy test pieces, and UL test pieces (thickness 1.6 mm) were simultaneously injection molded into this injection molding equipment. A mold that can be used was set. The heater temperature of the injection molding apparatus was set to 195 ° C.-195 ° C.-190 ° C.-180 ° C.-30 ° C. from the nozzle side. In addition, the injection amount per shot was set to 120 g. In the injection molding, the material was sufficiently purged, and after 50 shots were discarded, 50 shots were molded.

As the mold used for the test molding, those having cavities for molding three types of test pieces used in various tests were used, and three types of test pieces were obtained for each molding process. About the sample for 50 shots, the test piece used for the flame retardance test mentioned later diverted all 50 shots for weight measurement. For the Charpy impact test, break elongation test, and flame retardancy test, 5 pieces obtained every 10 shots out of 50 shots were used as test pieces. The test methods and criteria are as follows.

(Weight measurement)
The weight of the test piece was measured using an electronic balance. If the fluctuation range (weight deviation) of each individual weight is 0.8% or less with respect to the average value of the weights of 50 test pieces, it will be accepted, and if even one piece exceeds 0.8%, it will be rejected. did. Table 2 shows the maximum fluctuation width in the sample.

(Charpy impact test)
For the Charpy impact test, a test piece having a length of 80 mm ± 2 mm, a width of 10 mm ± 0.2 mm, and a thickness of 4 mm ± 0.2 mm was formed according to JISK-7111, and the test piece was notched (notch radius 0). .25 mm ± 0.05 mm and notch width 8.0 mm ± 0.2 mm). The mass of the notched test piece was 4.2 g. The test apparatus used was IMPACTTESTER (analog type) manufactured by TOYOSEIKI. Five specimens sampled every 10 shots were subjected to a Charpy impact test according to JISK-7111, and the case where the minimum value was 5 (KJ / m ² ) or more was determined to be acceptable.

(Elongation at break)
The test piece was molded according to JIS (K-7113, No. 1 type test piece). The test piece was gripped using a Shimadzu autograph (AGS-J type), pulled at a pulling speed (50 mm / min) until it broke, and the elongation at break (breaking elongation) was measured. If the elongation at break of the five test pieces was the lowest and it was 6% or more, it was judged acceptable, and if it was less than 6%, it was judged unacceptable.

(Flammability test: UL-94V)
A test piece having a length of 127 mm, a width of 12.7 mm, and a thickness of 1.6 mm was molded. UL94-V is the most basic flammability test for plastic parts and the like. A flame of a gas burner is applied to a test piece of a specified size to examine the degree of combustion of the test piece. The grades are 5VA, 5VB, V-0, V-1, V-2, and HB in descending order of flame retardancy. All five samples are V-1 or higher (5VA to V-1). ) Flame retardancy was accepted.

Examples 1 to 6 and Comparative Examples 1 to 6 were evaluated for each test item, those that passed all of the test items were evaluated as acceptable, and those that failed even at one item were evaluated as failed. . These evaluation results are shown in the following [Table 2] together with the molding conditions and measurement conditions of Examples 1 to 6 and Comparative Examples 1 to 6.

In the above [Table 2], “restricted” means a limited supply in which a fixed amount of molding material measured by the measuring feeder is gradually supplied to the hopper during the measuring period. “Filling” means a feeding method in which the molding material is fed to the hopper by its own weight without using a weighing feeder, and the cylinder is filled almost densely. In the column of the measurement time ratio, the ratio of the measurement time of each example and comparative example to the standard measurement time for each screw revolution described in [Table 1] is shown. .

For Examples 1 to 6, an experiment was performed by setting six combinations of the value of the coefficient K, the number of rotations of the screw, and the measuring time, and all of them passed the evaluation criteria. In these examples, the material supply is limited so that the weighing time is within an appropriate range, and each weighing time is 1.5 times to 3 times the standard weighing time in [Table 1]. It is in the double range. As a result, when performing injection molding using this injection molding apparatus, it is possible to sufficiently knead and disperse the molding material while avoiding excessive shearing heat generation due to high-speed rotation of the screw, and to prevent an adverse effect on the heat history. The molding conditions were confirmed.

In Comparative Examples 1 and 2, the value of the coefficient K is inappropriate, and the measurement time does not fall within the appropriate range with respect to the screw rotation speed. If the measuring time is short, a plurality of types of molding materials cannot be sufficiently kneaded, and if it is too long, thermal deterioration of the material is inevitable. Even if the coefficient K is in an appropriate range, the measurement time is not in an appropriate range depending on the degree of limited supply, and good evaluation results cannot be obtained (Comparative Examples 3 and 4). Comparative Examples 5 and 6 are material supply by a filling method, and it is understood that there is no practicality when injection molding is performed with a molding material containing 30% by weight or more of a powder material in addition to a granular material.

Although the injection molding method of the present invention has been described in detail above, the present invention is not limited to the above-described examples, and various improvements and modifications may be made without departing from the scope of the present invention. Of course. The method of the present invention is also effective when injection molding is performed using a pellet material such as an elastomer whose resin resistance (PT) on the cylinder inner wall varies greatly depending on the shape and supply state of the pellet.

Claims

A molding material obtained by mixing a plurality of materials including a granular material serving as a base resin and a powdery additive is supplied into a heating cylinder from an inlet, and the screw is rotated inside the heating cylinder to form the molding material. Is stored in the cylinder tip while being kneaded and dispersed, and the screw is moved backward by the pressing force from the stored molding material to the measurement setting position, and then the screw is advanced to perform injection molding. A method,
When performing the measurement, the pressure from the molding material stored at the tip of the cylinder is detected, and the retraction force acting in the direction of retreating the screw based on the detected pressure is applied to 1.2-2. Apply a force multiplied by a preset coefficient in the range of 0 as a forward force to the screw,
In addition, a limited supply is performed in which the molding material is loosely charged from the inlet, and molding is performed while leaving a gap in the phase space of the molding material formed between the inner wall of the heating cylinder and the screw immediately below the inlet. Supply materials,
The time required for the metering is a standard metering time when filling and supplying the granular material so as to densely fill the transfer space of the molding material formed between the inner wall of the heating cylinder and the screw immediately below the inlet. Longer than.
The injection molding method according to claim 1,
1.5 times the standard measuring time when filling and supplying the granular material so as to densely fill the transfer space of the molding material formed between the inner wall of the heating cylinder and the screw immediately below the inlet. Weighing is performed in 3 times the weighing time.
In the injection molding method according to claim 2,
In the molding material, the ratio of the powdery additive is 30% by weight or more.
The injection molding method according to claim 3,
The base resin is a polylactic acid resin or a cellulose resin, and the additive is a flame retardant or a compatibilizing agent.
The injection molding method according to claim 3,
The limited supply is performed by continuously supplying a small amount of molding material into the cylinder.
The injection molding method according to claim 3,
The limited supply is performed by intermittently supplying a molding material into the cylinder.
The injection molding method according to claim 3,
In the limited supply, a base resin as a molding material and a plurality of additives are alternately supplied.
The injection molding method according to claim 1, wherein
One cycle of injection molding includes a weighing process, a mold clamping process, an injection filling process, a pressure holding cooling process, and a mold release process, and the measurement is performed from the start of the pressure holding cooling process to the end of the mold release process. A process is performed.