JP2012179734A - Injection molding method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an injection molding method capable of uniformly mixing a polylactate-based resin, a polyphosphate flame retardant, and phosphazene when they are directly supplied to an injection molding device.SOLUTION: The pellet-shaped polylactate-based resin 50, the powder-shaped polyphosphate flame retardant 52, and the powder-shaped phosphazene compound 54 are directly supplied to the injection molding device 10 which includes a cylinder 14, and a screw 16 having a supply section 40, a compression section 42, and a measurement section 44. In the supply section, the pellet-shaped polylactate-based resin, the powder-shaped polyphosphate flame retardant, and the powder-shaped phosphazene compound are ground and mixed, and then fed to the compression section. In the compression section, the pellet-shaped polylactate-based resin, the powder-shaped polyphosphate flame retardant, and the powder-shaped phosphazene compound are melted to form a molten material. In the measurement section, the molten material is measured, and the measured molten material is injected from the injection molding device into a die 30. The screw includes a flight 16B and a step 16C which is adjacent to a side surface at the downstream side of the flight and lower than the flight.

Description

  The present invention relates to an injection molding method, and more particularly, to a method for injection molding by directly supplying a polylactic acid resin, a phosphazene compound and a polyphosphate flame retardant to an injection molding apparatus.

  Conventionally, petroleum resin has been mainly used as a resin molding material used for injection molding. However, problems such as air pollution, global warming, and ozone depletion have become apparent, and attempts have been made to build a recycling-type energy-saving society as a countermeasure. As one of them, conversion from a petroleum resin molding material to a biological plant resin molding material has been attempted.

  Plant-based resin molding materials include so-called biomass resins (also referred to as biomass plastics or bioplastics), and attempts have been made to produce various products using these as molding materials.

  A typical example of the biomass resin is a polylactic acid resin (also referred to as PLA). Polylactic acid-based resins can be expected to eliminate carbon dioxide uptake and generation in the global environment, and this idea is called carbon neutral.

  When a molded product is produced using a polylactic acid resin as a molding material, the molded product is required to have flame retardancy and mechanical strength. Patent Document 1 discloses a thermoplastic resin composition containing a polylactic acid resin, a phosphorus-containing flame retardant, and phosphazene in order to enhance flame retardancy without impairing mechanical strength. In Patent Document 1, a polylactic acid resin, a phosphorus-containing flame retardant, and phosphazene are kneaded with a kneader to obtain a resin mixture, and the resin mixture is injection molded using an injection molding apparatus. If the resin mixture is produced by a kneader before being supplied to the injection molding apparatus, there is a problem that the polylactic acid resin is exposed to high heat for a long time, and the resin is colored or reduced in molecular weight.

  Patent Document 2 discloses that each material is directly supplied to an injection molding machine for injection molding without kneading each material with a kneader. When each material is directly supplied to the injection molding machine and injection molding is performed on the polylactic acid resin, the polyphosphate flame retardant, and the phosphazene, it is required to uniformly mix the materials in the supply unit of the injection molding machine. However, since the polylactic acid-based resin is in the form of pellets, the phosphazene compound and the polyphosphate flame retardant are powders, and the shapes of the materials are different, it is difficult to mix them uniformly. When the materials are not uniformly mixed, there is a problem that the polyphosphate flame retardant decomposes and reacts with the polylactic acid resin to lower the physical properties of the polylactic acid resin.

  Polyphosphate flame retardants have a high phosphorus content and can provide very high flame retardant performance, especially when trying to flame-retardant brittle materials such as polylactic acid resins (also referred to as PLA resins or PLA). Is preferable because a flame retardant effect can be obtained with a small amount of addition, and a decrease in physical properties can be minimized. On the other hand, however, the polyphosphate flame retardant has the problem of degrading the polyester. When it is gradually heated in the screw of an injection molding device, a part of it decomposes, and the decomposition product decomposes PLA, which is a kind of polyester, to reduce the strength of the molded product or to color it. End up.

JP 2006-143484 A Japanese Patent Laid-Open No. 10-316832

  The present invention has been made to solve the above-described problems. In the case where a polylactic acid resin, a phosphazene compound, and a polyphosphate flame retardant are directly supplied to an injection molding apparatus, these materials are treated with PLA. An injection molding method capable of uniformly mixing while suppressing deterioration of the resin is provided.

  The injection molding method of the present invention includes a step of directly supplying a pellet-shaped polylactic acid resin, a powdered phosphazene compound, and a powdered polyphosphate flame retardant to an injection molding apparatus, and the injection molding The apparatus includes a cylinder and a screw having at least a supply unit, a compression unit, and a metering unit. In the supply unit, the pellet-shaped polylactic acid resin, the powdered phosphazene compound, and the powdered polyphosphorus A step of crushing and mixing the acid salt flame retardant and sending it to the compression part; and in the compression part, the pellet-like polylactic acid resin, the powdery phosphazene compound, and the powdery polyphosphate flame retardant Forming a molten mixture with the measuring unit, measuring the molten mixture in the measuring unit, and injecting the measured molten mixture into the mold from the injection molding apparatus Includes a degree, the.

  The measuring unit may include an element having a mixing / dispersing function, or may be configured of an element having a mixing / dispersing function.

  According to the present invention, in the supply unit of the injection molding apparatus, the pellet-shaped polylactic acid resin, the powdered phosphazene compound, and the powdered polyphosphate flame retardant are crushed and mixed and sent to the compression unit. . Before the material is sufficiently heated, the polylactic acid resin, the powdered phosphazene compound, and the powdered polyphosphate flame retardant are sufficiently mixed by applying shear in the supply unit. Thereafter, as the material is heated, the phosphazene compound having a low melting point is first melted and the surface of the compatible PLA particles is widely covered and coated. When the PLA is subsequently melted and stirred, the attack of the polyphosphate flame retardant on the PLA at a high temperature can be suppressed. As a result, a desired member can be molded without deteriorating the physical properties of the molded product.

  In the injection molding method according to another aspect of the present invention, preferably, the screw is adjacent to a side surface on the downstream side of the screw flight in a region of a screw shaft, a screw flight, and a supply portion of the screw shaft. And a step difference lower than the height.

  By providing a step, in the injection molding weighing process, when the screw moves backward while rotating and pushes the molding material to the molten resin reservoir at the screw tip, the material is screw space with a narrow clearance (screw and screw). Can be introduced into the space created by the inner wall of the barrel being inserted. Sufficient shearing force can be applied to the pellet-shaped polylactic acid resin, powdered phosphazene, and polyphosphate flame retardant. As a result, each material can be uniformly dispersed and mixed in the supply section.

  In the injection molding method according to another aspect of the present invention, preferably, the step has a height of 0.5 to 0.9 times the height of the screw flight, and is 1/3 of the pitch of the screw flight. It has a width of ~ 2/3.

  In the injection molding method according to another aspect of the present invention, preferably, the height of the step gradually decreases from upstream to downstream.

  The injection molding method according to another aspect of the present invention preferably further includes an additional step that is lower than the step on the downstream side surface of the step.

  According to the injection molding method of the present invention, when a polylactic acid resin, a phosphorus-containing flame retardant, and a phosphazene are directly supplied to an injection molding apparatus, they are mixed uniformly before melting these materials in the injection molding apparatus. can do.

The schematic block diagram of an injection molding apparatus. The fragmentary sectional view of a screw. Explanatory drawing for demonstrating the injection molding method. (A) (B) The fragmentary sectional view of a screw. (C) The figure which shows the molten state of a mixture. The fragmentary sectional view of a screw.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. The present invention will be described with reference to the following preferred embodiments, but can be modified in many ways without departing from the scope of the present invention, and other embodiments than the present embodiment can be used. be able to. Accordingly, all modifications within the scope of the present invention are included in the claims.

  FIG. 1 is a schematic configuration diagram illustrating an example of an injection molding apparatus. As shown in FIG. 1, the injection molding apparatus 10 includes a cylinder 14 having a nozzle 12 at the tip, and a screw 16 is rotatably disposed in the cylinder 14. At the opposite end of the nozzle 12 and at the rear end of the screw 16, the motor 16 that rotates the screw 16 and the screw 16 are fixed in the axial direction (left and right direction in FIG. 1) based on the set values of pressure and speed. A motor / piston device 22 including a piston device 20 that moves forward and backward by a stroke is provided. The piston device 20 causes the screw 16 to advance leftward in FIG. Further, the piston device 20 is provided with a back pressure sensor 17 for detecting the back pressure at which the screw 16 moves backward in the measuring step.

  A heater 24 is wound around the outer periphery of the cylinder 14. The cylinder 14 is heated to a predetermined temperature by the heater 24 based on the melting temperature (plasticization temperature) of the molding material to be injection molded. The tip of the nozzle 12 is connected to a gate 32 of a mold 30 that forms a cavity 28 therein. The mold 30 includes a fixed mold 30A and a movable mold 30B, and the movable mold 30B opens and closes the fixed mold 30A.

  Regarding the direction of the injection molding apparatus 10, the side on which the mold 30 is disposed is referred to as a downstream side, and the side on which the piston apparatus 20 is disposed is referred to as an upstream side.

  The portion of the screw 16 having a screw groove (from the material supply port to the screw tip) has a length 20 to 30 times the diameter D. A supply unit 40, a compression unit 42, and a measuring unit 44 are provided from the upstream side toward the downstream side. The supply part 40 has a length 4 to 10 times the diameter D, the compression part 42 has a length 4 to 10 times the diameter D, and the measuring part 44 has a length 5 to 15 times the diameter D. Have The screw 16 includes a screw shaft 16A, a flight 16B, and a step 16C. The step 16C has a lower height than the flight 16B, and is provided adjacent to the downstream side surface of the flight 16B. The step 16 </ b> C is provided adjacent to the flight 16 </ b> B in the area of the supply unit 40.

  The role of the supply part 40, the compression part 42, and the measurement part 44 is demonstrated. As shown in FIG. 1, the screw 16 mainly includes a supply unit 40, a compression unit 42, and a measuring unit 44.

  In the supply unit 40, the groove depth of the screw 16 (the height of the flight 16B) is constant. The supplied material is conveyed toward the tip of the screw 16 through the space delimited by the flight 16 </ b> B by the rotation of the screw 16.

  The compression part 42 is a section where the groove depth of the screw 16 (the height of the flight 16B) is temporarily reduced. The material is compressed here and melts under a large shear force and heat. In the present embodiment in which a polylactic acid resin, a phosphazene compound, and a polyphosphate flame retardant are used, the polylactic acid resin melts and the phosphazene compound also melts. On the other hand, the polyphosphate flame retardant is finely dispersed without melting.

  In the measuring unit 44, the molten phosphazene compound and the polyphosphate flame retardant are dispersed in the molten polylactic acid resin. Further, by applying a shearing force, and by a dispersing function, components that are insufficiently dispersed are further dispersed.

  In the longitudinal direction of the cylinder 14, a material charging port 25 is formed at the opposite end of the nozzle 12 in order to supply the molding material into the cylinder 14. A hopper 26 is attached to the material inlet 25.

  FIG. 2 is a partial cross-sectional view of the supply unit 40 of the screw 16. A step 16C is provided adjacent to the downstream side surface of the flight 16B. The step 16C preferably has a height H2 that is 0.5 to 0.9 times the height H1 of the flight 16B. By setting the height H2 of the step 16C to 0.5 to 0.9 times or less the height H1 of the flight 16B, sufficient shear can be given due to the effect of pressing the material against the inner wall of the barrel. In the present embodiment, the step 16C has a linear inclined surface in a cross-sectional view from the flight 16B toward the screw shaft 16A. That is, the height of the step 16C gradually decreases from upstream to downstream.

  The step 16C preferably has a width W of 1/3 or more and 2/3 or less of the pitch P between the flights 16B. By setting the width W of the step 16C to 1 / 3P or more and 2 / 3P or less, the smooth supply of pellets is not hindered, and a sufficient shearing force is applied when the material is pressed against the barrel inner surface along the step. preferable.

  If the width W is set to 2 / 3P or more, the groove depth is uniformly reduced. The pellet does not enter the groove smoothly. In such a case, the ratio between the pellets and other materials may change temporarily, and the physical properties of the injection molded article may change, which is not preferable. If it becomes 1 / 3P or less, it will become difficult to push a material well on a barrel inner wall, and the mixing effect of a material will fall.

  Next, preferable conditions for the molding material used in the present invention will be described.

  Various types of polylactic acid resins can be used, and examples thereof include lactic acid homopolymer resins and lactic acid copolymer resins. Moreover, the lactic acid component which is a raw material of the polylactic acid-based resin is not particularly limited. For example, L-lactic acid, D-lactic acid, DL-lactic acid or a mixture thereof, or L-lactide or D-lactide which is a lactic acid cyclic dimer. , Meso-lactide, or mixtures thereof.

  The production method of the polylactic acid resin is not particularly limited, and various resins synthesized by a conventionally known method can be used. The lactic acid homopolymer resin is, for example, L-lactic acid, D-lactic acid, DL-lactic acid or the like, or a mixture thereof directly dehydrated or condensed, or L-lactide, D-lactide, meso-lactide, or these It can be obtained by ring-opening polymerization of a mixture or the like. The lactic acid copolymer resin can be obtained, for example, by copolymerizing a lactic acid monomer or lactide and another component copolymerizable with the monomer. Examples of other copolymerizable components include dicarboxylic acids, polyhydric alcohols, hydroxycarboxylic acids, lactones, etc. having two or more ester bond-forming functional groups in the molecule, and various constituents thereof. And various polyesters, various polyethers, and various polycarbonates.

  Further, the weight average molecular weight of the polylactic acid-based resin is not particularly limited, but is preferably 50,000 to 500,000, and more preferably 100,000 to 250,000.

  A weight average molecular weight of 50,000 or more is preferable because the strength of the obtained molded product of the present invention is further increased. A weight average molecular weight of 500,000 or less is preferable because the molding material used for injection molding tends to be uniform, and the strength of the resulting molded product tends to increase.

  The polylactic acid resin is supplied to the injection molding apparatus 10 in the form of pellets. The shape and size are preferably 1.2 to 1.5 times the deepest groove depth (height of the flight 16B) of the material supply portion of the screw 16. When the depth is 1.2 times or less of the groove depth, the pellets are difficult to enter the groove, which may hinder material supply. If it is 1.5 times or more, when the pellets are sent to the tip of the screw 16 in the screw groove, it becomes difficult to scrape off other powder components in the screw 16 groove, and the powder to the screw shaft 16A Component deposition may occur, which is not preferable.

  As the flame retardant used in the present embodiment, polyphosphate is preferable.

  As typical salts of polyphosphates, lithium salts, sodium salts, calcium salts, barium salts, iron (II) salts, iron (III) salts, aluminum salts, etc. as metal salts, methylamine salts as aliphatic amine salts, Examples include ethylamine salts, diethylamine salts, triethylamine salts, ethylenediamine salts, piperazine salts, and examples of aromatic amine salts include pyridine salts, triazine salts, melamine salts, and ammonium salts.

  As the phosphazene compound used in the present embodiment, a cyclic aryloxyphosphazene compound is preferable.

  Examples of the cyclic aryloxyphosphazene compound include those represented by the following formula (1).

In the formula (1), n represents an integer of 3 to 8, A represents a group selected from the group consisting of the following A1 group and A2 group, and at least one is an A2 group.
Group A1: An aryloxy group having 6 to 20 carbon atoms in which at least one group selected from an alkyl group having 1 to 6 carbon atoms, an alkenyl group, and an aryl group may be substituted.
A2 group: A substituted aryloxy group represented by the following formula (2).

  In the formula (2), Y represents a group selected from the group consisting of a phenylene group, a biphenylene group, and a naphthalene group, and Q represents a Hammett's substituent constant σp of 3.0 or more and no active hydrogen. Indicates a substituent. Two or more Q may be substituted in Y.

  The above-mentioned cyclic aryloxyphosphazene compounds represented by the formula (1) are preferably those in which n in the formula (1) is 3 or 4.

An example of the cyclic aryloxyphosphazene compound represented by the formula (1) has the following A1 group and A2 group as A in the formula (1).
A1 group: one of a phenoxy group and a methylphenoxy group.
A2 group: Y is a phenylene group, Q is selected from the group consisting of an acyl group, an alkoxycarbonyl group, an aryloxycarbonyl group, an alkylsulfinyl group, an alkylsulfonyl group, an arylsulfonyl group, an acyloxy group, an acylthio group, and a cyano group What is the group

More specific examples of the cyclic aryloxyphosphazene compound of such an example are those having the following A1 group and A2 group as A in the formula (1).
A1 group: Phenoxy group.
A2 group: 4-acetylphenoxy group, 4-propionylphenoxy group, 4-benzoylphenoxy group, 4-methylsulfinylphenoxy group, 4-methylsulfonylphenoxy group, 4-phenylsulfonylphenoxy group, and 4-cyanophenoxy group Group selected from the group.
Other examples of the cyclic aryloxyphosphazene compound represented by formula (1) include all of A in formula (1) being 4-acetylphenoxy group, 4-propionylphenoxy group, 4-benzoylphenoxy group, 4-methylsulfinyl It is selected from the A2 group consisting of a phenoxy group, a 4-methylsulfonylphenoxy group, a 4-phenylsulfonylphenoxy group, and a 4-cyanophenoxy group.

  In the cyclic aryloxyphosphazene compound represented by the formula (1), all halogen atoms of the cyclic phosphonitrile dihalide represented by the following formula (3) are usually substituted with the following A2 group. It is obtained by substituting with a group selected from the group consisting of the following A1 group and A2 group.

In formula (3), n represents an integer of 3 to 8, and X represents a halogen atom.
A1 group: an aryloxy group having 6 to 20 carbon atoms in which at least one group selected from an alkyl group having 1 to 6 carbon atoms, an alkenyl group, and an aryl group may be substituted.
A2 group: A substituted aryloxy group represented by the following formula (2).

  In formula (2), Y represents a group selected from the group consisting of a phenylene group, a biphenylene group, and a naphthalene group, and Q has a Hammett's substituent constant σp of 3.0 or more and has active hydrogen. No substituents. Two or more Q may be substituted in Y.

  Polyphosphate flame retardants have a high phosphorus content and provide very high flame retardant performance, so that flame retardancy can be achieved with a small addition amount, especially when brittle materials such as PLA are to be flame retardant. However, it is preferable because the deterioration of physical properties can be minimized. On the other hand, the polyphosphate flame retardant has a problem of decomposing polyester. When it is gradually heated in the screw, part of it decomposes, and the degradable organism decomposes PLA, which is a kind of polyester, to lower the strength of the molded product or to color it.

  A phosphazene compound that solves this problem and improves physical properties such as impact resistance, has a high affinity with PLA, and also exhibits a compatible function of easily coating PLA, is added. Thereby, the attack of the flame retardant to the PLA can be suppressed, and a high-grade flame retardant can be applied without degrading the PLA.

  Phosphazene is a common name for a group of compounds having double bonds with phosphorus and nitrogen as constituent elements. It may be a cyclophosphazene having a cyclic structure, a chain polymer obtained by ring-opening polymerization thereof, a cyclopolymer obtained by modifying cyclophosphazene with a polyfunctional compound, and the like. The phosphazene is supplied in powder form to an injection molding apparatus.

  The phosphazene compound also has a flame retardant effect. However, the effect is not sufficient, and in the present embodiment, the function of a compatibilizing agent or the like that improves physical properties such as impact resistance is important.

  Next, the injection molding method will be described with reference to FIGS.

  First, as shown in FIG. 3, a pellet-shaped polylactic acid resin 50, a powdered polyphosphate flame retardant 52, and a powdered phosphazene compound 54 are fed from the hopper 26 through the material inlet 25. It is supplied into the cylinder 14. The polylactic acid resin 50, the polyphosphate flame retardant 52 and the phosphazene compound 54 are supplied to the supply unit 40 of the rotating screw 16.

  Immediately after the supply, as shown in FIG. 4 (A), the polylactic acid resin 50, the polyphosphate flame retardant 52, and the phosphazene compound 54 are randomly supplied between the flights 16B in the supply unit.

  However, with the transfer of the screw 16, as shown in FIG. 4B, in the supply unit 40, the polylactic acid resin 50, the polyphosphate flame retardant 52, and the phosphazene compound 54 are in a solid state before melting. , Pressed against the step 16C. Since the gap between the cylinder 14 and the step 16C is narrow, a large shearing force is applied to the mixed material of the polylactic acid resin 50, the polyphosphate flame retardant 52, and the phosphazene compound 54. The mixed material before melting is crushed by the shearing force, and the polylactic acid resin 50, the polyphosphate flame retardant 52, and the phosphazene compound 54 are uniformly mixed. A mixed material containing a large amount of powder (polyphosphate flame retardant 52, phosphazene compound 54) (when the powder material is added 30% or more with respect to the weight of the pellet alone) is effectively melted by the screw 16 (Polylactic acid resin 50) can be mixed and dispersed.

  When the mixed material is sent from the supply unit 40 to the compression unit 42, the step 16C is adjacent to the side surface on the downstream side of the flight 16B so that the mixed material is not clogged between the flights 16B. That is, the step 16C and the flight 16B have a substantially parallel positional relationship.

  Regarding the installation position of the step 16C, it is preferable not to provide the step 16C on the flight 16B of the compression unit 42. When the step 16 </ b> C is arranged in the compression part 42, a greater shearing force is applied to the polylactic acid resin 50 in the compression part 42. This is because excessive shearing heat is applied to the polylactic acid resin 50 and the polylactic acid resin 50 deteriorates.

  On the other hand, when the supply unit 40 does not have the step 16C, the supply unit does not compress the material, so that the material is not sufficiently sheared. In particular, the polyphosphate flame retardant and the phosphazene compound do not become fine and do not mix sufficiently. Therefore, the distribution on the surface of PLA is not uniform, and even if the phosphazene compound starts to dissolve, the surface of PLA cannot be sufficiently covered. In other words, the coating of the phosphazene compound is uneven, and the portion of the polyphosphate flame retardant having a large particle diameter is in direct contact with the PLA, and when PLA dissolves, the influence of the polyphosphate flame retardant (decomposes PLA) Becomes larger.

  FIG. 4C shows the molten state of the mixture in the compression section 42. In the present embodiment, the polyphosphate flame retardant 52 and the phosphazene compound 54 are pulverized and mixed uniformly in the supply unit 40. The refined phosphazene compound 54 dissolves quickly and covers most of the surface of the polylactic acid resin 50. As a result, the coating of the phosphazene compound 54 can prevent the polylactic acid resin 50 from being decomposed by the polyphosphate flame retardant 52.

  Next, the mixed material obtained by uniformly mixing the polylactic acid resin 50, the polyphosphate flame retardant 52 and the phosphazene compound 54 is transferred to the compression unit 42 by the rotation of the screw 16. In the compression section 42, the mixed material is melted and kneaded.

  The mixed material (also referred to as molding material) melted in the compression unit 42 is transferred to the measuring unit 44. The molten mixed material is stored in the cylinder tip 14A. Then, the screw 16 retreats while rotating due to the back pressure of the stored molten mixed material. When reaching a preset measurement value, the screw stops rotating and the measurement ends.

  The molding material that has been melted and fluidized in the cylinder 14 is injected into the mold 30 through the nozzle 12 by the advancement of the screw 16. Thereby, the molten molding material is filled in the cavity 28 of the mold 30.

  Even after the molten molding material is filled in the cavity 28 of the mold 30, pressure is applied to the cavity 28 by the screw 16. Thereby, the molding material in the cavity 28 is formed into a cavity shape.

  The molding material is cooled and solidified so that the molded article has sufficient rigidity when released. The mold 30 is opened by moving the movable mold 30B away from the fixed mold 30A by the mold clamping cylinder. Thereby, the molded product is released from the mold 30.

  FIG. 5 is a partial cross-sectional view of the supply unit 40 of the screw 16. The shape of the step 16C is different from the shape of the step 16C shown in FIG.

  As shown in FIG. 5A, the step 16C includes an arc-shaped inclined surface having a curvature toward the screw shaft 16A in a cross-sectional view. Further, as shown in FIG. 5B, the step 16C includes an inclined surface having a curvature toward the upper side with respect to the screw shaft 16A in a sectional view. As shown in FIG. 5C, the step 16C includes an additional step 16D. Each step 16C, 16D has a flat surface and an inclined surface. The additional step 16D has a lower height than the step 16C.

[Example]
Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples. However, it is not limited to these.

(Molding material)
Polylactic acid resin (pellet) manufactured by Nature Works TE2000 100 parts by weight flame retardant (powder) Clariant AP422 (ammonium polyphosphate) 42 parts by weight compatibilizer (powder) Fushimi Pharmaceutical Rabitol FP110 (phosphazene) 15 parts by weight elastomer (powder) ) Mitsubishi Rayon Metabrene W600A 5 parts by weight anti-drip agent (powder) Daikin Industries, Ltd. FA500H 0.3 parts by weight hydrolysis inhibitor (powder) Rhein Chemie Starbuxol 1FL 2 parts by weight nucleating agent (fine powder) Nippon Talc Kogyo P3 5 Part by weight In addition, the polylactic acid resin was dried in a hot air dryer in advance at 80 ° C. for 5 hours and then cooled to 30 ° C. before use. The flame retardant was dried in advance at 80 ° C. for 5 hours in a vacuum dryer and cooled to 30 ° C. before use.

(Injection molding equipment)
SG150U manufactured by Sumitomo Heavy Industries, Ltd. was used as the injection molding device for the test. Charpy test piece, UL test piece (thickness 1.6mm) and dumbbell (JIS K-7113 compliant No. 1 type test piece) ) Set a mold that can be injection molded at the same time. The heater temperature of the injection molding apparatus was set to 180 ° C-185 ° C-175 ° C-175 ° C-20 ° C from the nozzle side. Also, the shot amount per shot was set to 50g.

(Examples and comparative examples)
As for the screw shape, injection molding was performed with a screw having no protrusion, a protrusion A, a protrusion B, and a protrusion C. The protrusions A to C have the shapes shown in FIG. The performance was compared with the Charpy impact test value and UL flammability test value of the compacts.

(Screw shape)
Screw is effective L / D = 23
Screw flight pitch = 0.84D
Supply section length = 8 pitch Groove depth of supply section (deepest part) = 5 mm
Compressed part length = groove depth after 5 pitch compression = 2 mm
Measuring section length = 14 pitches (Charpy impact test)
Charpy impact test piece according to JISK-7111, length 80mm ± 2mm, width 10mm ± 0.2mm, thickness 4mm ± 0.2mm, notch processing (notch radius 0.25mm ± 0.05mm, 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. Then, the test pieces obtained in the above examples and comparative examples are subjected to a Charpy impact test according to JISK-7111. ).

(Flammability test: UL94-V)
As the test piece, an injection molded test piece having a length of 127 mm, a width of 12.7 mm, and a thickness of 1.6 mm was used. UL94-V is the most basic flammability test for plastic parts and the like, and the degree of combustion of the test piece is examined by applying a flame of a gas burner to a test piece having a specified size. The grades are 5VA, 5VB, V-0, V-1, V-2, NOT V in order from the highest flame retardancy. A flame retardance of 2 or less was regarded as rejected (x).

(Dumbell elongation test)
The test piece was prepared according to JIS (K-7113 type 1 test piece). Using this Shimadzu autograph (AGS-J type), this test piece was gripped at a grip width (100) mm and pulled at a pulling speed (50 mm / min) to measure the elongation (breaking elongation) value. did.
Elongation at break was 6% or more as pass (◯), and less than 6% was rejected (x).

  Table 1 summarizes the screw types and test results.

  DESCRIPTION OF SYMBOLS 10 ... Injection molding apparatus, 12 ... Nozzle, 14 ... Cylinder, 16 ... Screw, 16A ... Screw shaft, 16B ... Flight, 16C ... Step, 16D ... Additional step, 17 ... Back pressure sensor, 18 ... Motor, 20 ... Piston Device, 22 ... Motor / Piston Device, 24 ... Heater, 26 ... Hopper, 28 ... Cavity, 30 ... Mold, 32 ... Gate, 40 ... Feeding Unit, 42 ... Compression Unit, 44 ... Metering Unit

Claims (5)

A step of directly supplying a pellet-shaped polylactic acid resin, a powdered phosphazene compound, and a powdered polyphosphate flame retardant to an injection molding apparatus, wherein the injection molding apparatus supplies at least a cylinder; A screw having a section, a compression section, and a weighing section,
In the supply unit, the step of feeding the pellet-like polylactic acid resin, the powdered phosphazene compound, and the powdered polyphosphate flame retardant to the compression unit while crushing and mixing,
Forming a molten mixture of the pellet-shaped polylactic acid-based resin, the powdered phosphazene compound, and the powdered polyphosphate flame retardant in the compression section;
A step of measuring the molten mixture in the measuring unit;
Injecting the weighed molten mixture from the injection molding device into a mold;
An injection molding method comprising:   2. The injection molding according to claim 1, wherein the screw has a screw shaft, a screw flight, and a step which is adjacent to a side surface on the downstream side of the screw flight in a region of a supply portion of the screw shaft and is lower than the height of the screw flight. Method.   The injection molding according to claim 2, wherein the step has a height of 0.5 to 0.9 times the height of the screw flight and a width of 1/3 to 2/3 of the pitch of the screw flight. Method.   The injection molding method according to claim 2 or 3, wherein the height of the step gradually decreases from upstream to downstream.   The injection molding method according to claim 2 or 3, further comprising an additional step lower than the step on a side surface on the downstream side of the step.

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