JP5106550B2 - Foam extrusion molding equipment - Google Patents

Description

  The present invention relates to a foam extrusion molding apparatus, and more particularly to a foam extrusion molding apparatus for foam extrusion molding of a microcellular foam.

  In recent years, in a method of foaming and extruding a thermoplastic resin using a foaming extrusion molding apparatus, an inert fluid such as clean carbon dioxide gas or nitrogen gas, which is environmentally friendly, is used as a foaming agent to make microcells composed of fine cells. Various methods for forming cellular foam have been studied (for example, see Patent Document 1).

Japanese translation of PCT publication No. 2002-501443

  However, in the foam extrusion molding apparatus used for such molding, usually, the inner peripheral surface of the barrel is polished and honed, and the surface of the screw is hard chrome plated to reduce the surface roughness, thereby reducing the molding material. It is easy to slip.

  On the other hand, the extrusion efficiency (transport efficiency) of the molding material is determined by the difference between the frictional force between the molding material and the barrel and the frictional force between the molding material and the screw. If the value is small, the molding material which is viscous or slippery may have a significantly reduced extrusion efficiency or may not be completely extruded.

  That is, the transportation efficiency of the screw and the frictional force have a relationship represented by the following formula.

R = (fsAs / fbAb)
R: transport efficiency, fs: coefficient of friction between the surface of the screw and the molding material, As: surface area of the screw, fb: coefficient of friction between the surface of the barrel and the molding material, Ab: surface area of the barrel The smaller R is than 1, the higher the transport efficiency. In particular, a single-screw extruder does not have a self-cleaning function like a twin-screw extruder. Therefore, if fb is not larger than fs, a viscous or slippery molding material adheres to the screw and cannot be transported. Is produced.

  An object of the present invention is to provide a foam extrusion molding apparatus that can improve transport efficiency and achieve efficient foam extrusion molding even if the molding material is viscous or slippery. It is in.

  In order to achieve the above object, an invention according to claim 1 is a foam extrusion molding apparatus including a barrel and a screw provided in the barrel, and an inert fluid is provided in the middle of the barrel in the extrusion direction of the screw. Is introduced into the barrel, and the screw has a supply unit, a first compression unit, a first metering unit, and a second compression unit across the position where the introduction unit is provided. And a second quantification unit, and the surfaces of only the supply unit, the first compression unit, and the first quantification unit are covered with a coating layer containing fluorine.

  According to such a structure, since the surface of the supply part of a screw is coat | covered with the coating layer containing a fluorine, the friction coefficient between the surface of a screw and a molding material can be made small. Therefore, the screw transportation efficiency can be increased, and efficient foam extrusion molding can be achieved even if the molding material is viscous or slippery.

  In addition, according to such a configuration, after introducing the inert fluid into the barrel from the introduction portion and supplying it to the molding material being transported, the molding material and the inert fluid are supplied to the second compression portion and the second compression fluid. In the quantification part, it can mix sufficiently.

  The invention described in claim 2 is characterized in that, in the invention described in claim 1, the coating layer is made of polytetrafluoroethylene.

  According to such a structure, since a coating layer consists of polytetrafluoroethylene, the friction coefficient between the surface of a screw and a molding material can be made small easily and reliably.

  The invention described in claim 3 is the invention described in claim 1, characterized in that the coating layer is made of electroless nickel / fluorine composite plating.

  According to such a configuration, since the coating layer is made of electroless nickel / fluorine composite plating, the coefficient of friction between the surface of the screw and the molding material can be easily and reliably reduced.

  According to a fourth aspect of the present invention, in the first aspect of the present invention, the coating layer is made of hard chromium / fluorine composite plating.

  According to such a configuration, since the coating layer is made of hard chromium / fluorine composite plating, the coefficient of friction between the surface of the screw and the molding material can be easily and reliably reduced.

  According to the first aspect of the present invention, the screw transportation efficiency can be increased, and efficient foam extrusion molding can be achieved even if the molding material is viscous or slippery.

  In addition, the molding material and the inert fluid can be sufficiently mixed in the second compression unit and the second metering unit.

  According to the invention described in claim 2, since the coating layer is made of polytetrafluoroethylene, the coefficient of friction between the surface of the screw and the molding material can be easily and reliably reduced.

  According to the invention described in claim 3, since the coating layer is made of electroless nickel / fluorine composite plating, the friction coefficient between the surface of the screw and the molding material can be reduced easily and reliably.

  According to the fourth aspect of the present invention, since the coating layer is made of hard chromium / fluorine composite plating, the coefficient of friction between the surface of the screw and the molding material can be easily and reliably reduced.

It is a schematic whole block diagram which shows one Embodiment of the foam extrusion molding apparatus of this invention. It is a side view which shows the screw of the foam extrusion molding apparatus shown in FIG.

  FIG. 1 is a schematic overall configuration diagram showing an embodiment of a foam extrusion molding apparatus according to the present invention, and FIG. 2 is a side view showing a screw of the foam extrusion molding apparatus shown in FIG.

  In FIG. 1, the foam extrusion molding apparatus 1 includes a barrel 2, a screw 3, a gear box 4, a motor 5, a gas supply unit 6 and a hopper 7, and the screw 3 is configured as a single screw extruder. ing.

  The barrel 2 is formed of a cylindrical member, and a material supply unit 8 to which the hopper 7 is connected is provided at one end (on the upstream side in the extrusion direction (transport direction of the molding material)). Further, a head 9 for discharging the material is provided at the other side end (downstream side in the extrusion direction (transport direction of the molding material)).

  The material supply unit 8 includes a hopper connection unit 10 to which the hopper 7 is connected, and a material supply path 11 for supplying the molding material charged from the hopper 7 into the barrel 2.

  The head 9 is formed with a cylindrical discharge port 12 in which the inner diameter of the barrel 2 is reduced to a small diameter, and a temperature sensor 13 and a pressure sensor 14 are provided at the tip of the discharge port 12.

  Further, a portion between the material supply unit 8 and the head 9 in the barrel 2 is a melt extrusion unit 15 that is extruded (transported) while the molding material is melted and kneaded.

  The melt extrusion unit 15 is provided with a plurality of heaters 16 for each block at predetermined intervals along the extrusion direction. Each heater 16 is provided with a temperature sensor 13. Each heater 16 and each temperature sensor 13 are connected to a CPU (not shown), and each heater 16 is temperature-controlled in units of blocks based on the detected temperature detected by each temperature sensor 13.

  In the middle of the extrusion direction of the melt extrusion unit 15, an introduction unit 30 for introducing an inert gas as an inert fluid from the gas supply unit 6 is provided. The introduction portion 30 is provided with a gas nozzle 31 that is embedded through the barrel 2 from the outer peripheral surface to the inner peripheral surface.

  A sleeve 17 is detachably attached to a portion of the barrel 2 that faces a supply portion 23 of the screw 3 described later. The sleeve 17 is mounted in a mounting groove 18 formed so that the inner peripheral surface of the barrel 2 facing the supply portion 23 is recessed radially outward. In the mounted state, the sleeve 17 faces the screw 3 of the sleeve 17. The inner peripheral surface 19 is provided so as to be flush with the inner peripheral surface 20 of the barrel 2 upstream of the sleeve 17 in the extrusion direction in the extrusion direction. The sleeve 17 can be attached and detached from one end portion of the barrel 2 exposed by removing a connecting portion 33 described later from the material supply portion 8.

  Further, the inner peripheral surface of the sleeve 17 facing the screw 3 described later is roughened so that the center line average roughness Ra of the inner peripheral surface becomes 0.46 to 2.48 by an electric discharge machining method or the like. It has become.

  As shown in FIG. 2, the screw 3 is basically a full flight screw, and integrally includes a screw shaft 21 and a spiral screw strip 22 protruding around the screw shaft 21. . The screw 3 includes a connecting portion 28, a supply portion 23, a first compression portion 24, a first metering portion 25, a mixing portion 29, a second compression portion 26, and a second portion from the downstream side in the extrusion direction to the upstream side in the extrusion direction. The quantification unit 27 is sequentially formed.

  The connecting portion 28 is provided at one end portion of the screw 3 and is connected to a drive shaft 36 described later so as not to be relatively rotatable. The connecting portion 28 is formed in a columnar shape, and the screw strip 22 is not formed.

  The supply unit 23 faces the material supply unit 8 and the sleeve 17, and the screw shaft 21 is formed to have a smaller diameter than the connection unit 28. This ensures a sufficient gap between the inner peripheral surface 19 of the sleeve 17 and the screw shaft 21 to ensure an efficient supply of the molding material.

  The 1st compression part 24 is formed so that the screw shaft 21 may become a large diameter gradually toward the extrusion direction upstream. As a result, the first compression unit 24 has one end of the screw shaft 21 having the same diameter as the supply unit 23 and the other end of the screw shaft 21 having the same diameter as the first metering unit 25 described below. And the other side end is formed in a tapered shape having a larger diameter than the one side end, and the gap between the inner peripheral surface 20 of the barrel 2 and the screw shaft 21 is gradually narrowed, The supplied molding material is compressed.

  The first fixed amount portion 25 has a screw shaft 21 that has the same diameter as the other end portion of the first compression portion 24 and is larger in diameter than the supply portion 28. As a result, the gap between the inner peripheral surface 19 of the sleeve 17 and the screw shaft 21 is made small to ensure quantitative extrusion of the molding material.

  The mixing portion 29 faces the introduction portion 30 of the barrel 2, and the screw shaft 21 is formed to have substantially the same diameter as the other end portion of the first fixed amount portion 25. Moreover, the screw strip 22 is formed in a spline shape. This ensures efficient mixing of the inert gas introduced from the gas nozzle 31 of the introduction part 30 and the molding material.

  The 2nd compression part 26 is formed so that the screw shaft 21 may become a large diameter gradually toward the extrusion direction upstream. As a result, the second compression section 26 has one end of the screw shaft 21 having a smaller diameter than the mixing section 29, and the other end of the screw shaft 21 having the same diameter as the second metering section 27 described below. And the other side end is formed in a taper shape having a larger diameter than the one side end, and the gap between the inner peripheral surface 20 of the barrel 2 and the screw shaft 21 is gradually narrowed. The mixture of the inert gas and the molding material mixed in the part 29 is compressed.

  The second fixed amount portion 27 has a screw shaft 21 that has the same diameter as the other end portion of the second compressing portion 26 and is substantially the same diameter as the mixing portion 29. As a result, the gap between the inner peripheral surface 19 of the sleeve 17 and the screw shaft 21 is made small to ensure quantitative extrusion of the mixture of the inert gas and the molding material.

  The surfaces of the supply unit 23, the first compression unit 24, and the first determination unit 25 of the screw 3 (the surface of the screw shaft 21 and the surface of the screw strip 22) are covered with a fluororesin made of polytetrafluoroethylene or the like. The layer is coated. This coating layer has a thickness of 5 to 30 μm and is formed as 1 to 3 layers.

  When the surface of the screw 3 is required to have hardness, this coating layer is replaced with the surface of the supply unit 23, the first compression unit 24, and the first determination unit 25 of the screw 3 instead of the fluororesin coating layer. Further, it is preferable to form by applying electroless nickel / fluorine composite plating or hard chromium / fluorine composite plating. In this plating, it is preferable that the fluorine content is 5 to 30% by volume and the thickness is 3 to 30 μm.

  As shown in FIG. 1, the screw 3 is rotatably supported by a bearing (not shown) in the barrel 2. In addition, D / L of this screw 3 is set to 25-60. Moreover, the compression ratio in the 1st compression part 24 is set to 1.5-4.0, and the compression ratio in the 2nd compression part 26 is set to 1.5-4.0.

  The gear box 4 is connected to one end portion of the barrel 2 and includes a speed reduction mechanism portion 32 and a connection portion 33. The speed reduction mechanism portion 32 includes a driven pulley 34, a transmission shaft 35 that supports the driven pulley 34, and a speed reduction mechanism (gear mechanism) (not shown). The connecting portion 33 includes a drive shaft 36 that is disposed between the speed reduction mechanism portion 32 and the material supply portion 8 and that transmits power decelerated in the speed reduction mechanism portion 32. The drive shaft 36 is connected to the connecting portion 28 of the screw 3 so as not to be relatively rotatable.

  The motor 5 is disposed on the side of the gear box 4 and includes a pinion shaft 37 and a transmission pulley 38 supported by the pinion shaft 37.

  An endless belt 39 is stretched between the transmission pulley 38 and the driven pulley 34.

  When the motor 5 is driven, the power of the gear box 4 is transmitted through the pinion shaft 37, the transmission pulley 38, the endless belt 39, the driven pulley 34, and the transmission shaft 35, and a predetermined rotation is performed by the reduction mechanism in the gear box 4. After being decelerated to the ratio, it is output from the drive shaft 36 and its power is transmitted to the connecting portion 28 of the screw 3. As a result, the screw 3 is rotated at a predetermined rotational speed.

  The gas supply unit 6 includes a gas tank 40, a supply pump 41, and a gas supply line 42.

  In the gas tank 40, for example, an inert gas such as carbon dioxide (carbon dioxide gas) or nitrogen gas is stored as an inert fluid. The gas tank 40 is connected to a supply pump 41 via a gas supply line 42.

  The supply pump 41 is connected to the gas nozzle 31 via a gas supply line 42. The supply pump 41 is constituted by a fixed supply pump capable of supplying an inert gas stored in the gas tank 40 into the barrel 2 through the gas nozzle 31 at a constant amount per unit time.

  Further, in the gas supply unit 6, the gas supply line 42 is configured to be adjustable in temperature and pressure as a whole, and the supply pump 41 allows the inert gas to flow from the gas nozzle 31 into the barrel 2 in a supercritical state. It is comprised so that it can supply to.

  The hopper 7 is connected to the hopper connection portion 10 of the barrel 2. The hopper 7 is made of a thermoplastic resin such as polyethylene, polypropylene, ethylene-propylene copolymer, polyacrylonitrile, polyamide, polyethylene terephthalate, polylactic acid, polyphenylene sulfide, polycarbonate or the like as a molding material. And pellets of non-crystalline thermoplastic resin such as polystyrene, polyvinyl chloride, polyurethane, polymethyl methacrylate, and the like. Two or more kinds of these thermoplastic resins may be added. The resin to be added may be a raw material resin such as a thermosetting resin encapsulant, toner, and powder coating. In particular, the extrusion foam molding apparatus 1 is suitably used for foam extrusion molding of a resin containing slippery components such as wax, for example, a raw material resin such as toner.

  In this extrusion foam molding apparatus 1, various parts such as a motor 5, a heater 16, a supply pump 41, a temperature sensor 13 and a pressure sensor 14 are connected to a CPU (not shown), and the CPU controls these parts. .

  Next, a method of foaming and extrusion molding a molding material with the foam extrusion molding apparatus 1 will be described.

  In the foam extrusion molding by the foam extrusion molding apparatus 1, first, the CPU 5 drives and controls the motor 5 so that the screw 3 rotates at a predetermined rotational speed (for example, 10 to 110 rotations / minute). For example, each heater 16 facing the supply unit 23, the first compression unit 24, the first determination unit 25, the second compression unit 26, and the second determination unit 27 is set to 60 to 200 ° C., 100 to 250 ° C., 100, respectively. The temperature is controlled to be ˜250 ° C., 100 to 250 ° C., and 100 to 200 ° C.

  Then, a predetermined amount of molding material is continuously charged into the hopper 7. Then, the molding material is continuously charged into the barrel 2 through the material supply path 11, and continuously toward the downstream side in the extrusion direction while being melted in the barrel 2 by the heating of the heater 16 and the rotation of the screw 3. Fluidly.

  At the same time, the supply pump 41 is driven and controlled by the CPU, and a predetermined amount of supercritical gas is sent from the gas tank 40 to the gas nozzle 31 via the gas supply line 42. A critical inert gas is continuously supplied from the gas nozzle 31 into the barrel 2.

  The supply amount of the supercritical inert gas supplied by the drive control of the supply pump 41 by the CPU may be appropriately determined according to the type of molding material and the properties of the target microcellular foam. 5% by weight or less, preferably 3% by weight or less, more preferably, for example, in the case where the inert gas is carbon dioxide, the total of the molding material and the inert gas mixed in the barrel 2 is 0%. 0.05 to 2% by weight, for example, when the inert gas is nitrogen gas, the content is set to 0.05 to 0.5% by weight.

  Then, the molding material that flows while being melted in the barrel 2 sequentially passes through the supply unit 23, the first compression unit 24, and the first metering unit 25 of the screw 3 and reaches the mixing unit 29. The supercritical inert gas supplied from the gas nozzle 31 is continuously mixed.

  Next, the molding material mixed with the supercritical inert gas sequentially passes through the second compression unit 26 and the second metering unit 27 of the screw 3, and the supercritical inert gas is then molded into the molding material. Are mixed and dissolved almost uniformly and discharged from the discharge port 12 to a die (not shown).

  The molding material discharged to the die is uniformly formed with a large number of microbubble nuclei due to temperature drop and pressure release, and then the bubble nuclei grow to uniformly generate a large number of fine cells. As a result, a microcellular foam having fine cells is formed.

  And in such a foam extrusion molding apparatus 1, the transport efficiency and frictional force of the screw 3 have the relationship shown in the following formula.

R = (fsAs / fbAb)
R: transport efficiency, fs: coefficient of friction between the surface of the screw 3 and the molding material, As: surface area of the screw 3, fb: coefficient of friction between the surface of the barrel 2 and the molding material, Ab: surface area of the barrel 2 In the above formula, the smaller R is than 1, the higher the transport efficiency. In particular, a single-screw extruder does not have a self-cleaning function like a twin-screw extruder, so if fb is not larger than fs, a viscous or slippery molding material adheres to the screw 3 and cannot be transported. A case arises.

  However, in this foam extrusion molding apparatus 1, is the surface of the supply unit 23, the first compression unit 24, and the first metering unit 25 of the screw 3 coated with a fluororesin coating layer made of polytetrafluoroethylene or the like? Alternatively, when hardness is required on the surface of the screw 3, since the electroless nickel / fluorine composite plating or the hard chromium / fluorine composite plating is applied as the coating layer, the molding material introduced from the hopper 7 is used. Until the mixing part 29 is reached, the friction coefficient between the surface of the screw 3 and the molding material can be reduced. Therefore, since fs of the said formula in the meantime becomes small, R can be made small and the transport efficiency of the screw 3 can be improved. As a result, since the molding material can be sufficiently supplied to the mixing portion 29, even if the molding material is viscous or slippery, the supercritical state inertness introduced from the molding material and the introduction portion 30 can be obtained. The gas is mixed in the mixing unit 29 and mixed and dissolved sufficiently uniformly in the second compression unit 26 and the second metering unit 27, thereby achieving efficient foam extrusion.

  Further, if the coating layer formed on the screw 3 is made of a fluororesin made of polytetrafluoroethylene or the like, the friction coefficient between the surface of the screw 3 and the molding material can be easily and reliably reduced. .

  Even if the coating layer formed on the screw 3 is made of electroless nickel / fluorine composite plating or hard chromium / fluorine composite plating, the friction coefficient between the surface of the screw 3 and the molding material can be easily and reliably obtained. Can be made smaller.

  Moreover, in this foam extrusion molding apparatus 1, a sleeve 17 is detachably attached to a portion of the barrel 2 facing the supply portion 23 of the screw 3, and an inner peripheral surface 19 of the sleeve 17 is formed by an electric discharge machining method. The center line average roughness Ra of the inner peripheral surface 19 is roughened so as to be 0.46 to 2.48. Therefore, the surface of the barrel 2 (sleeve 17 in the supply portion 23 of the screw 3). The friction coefficient between the inner peripheral surface 19) and the molding material can be increased. Therefore, since fb of the said formula in the supply part 23 becomes large, R can be made smaller and the transport efficiency of the screw 3 can be improved further. As a result, the molding material can be more sufficiently supplied to the mixing portion 29, so that even if the molding material is viscous or slippery, the molding material and the supercritical state introduced from the introduction portion 30 Inert gas is sufficiently mixed in the mixing unit 29 and uniformly mixed and dissolved in the second compression unit 26 and the second metering unit 27 to achieve more efficient foam extrusion molding. Can do.

  Further, in this way, if the inner peripheral surface 19 of the sleeve 17 is roughened by an electric discharge machining method, the friction coefficient between the inner peripheral surface 19 of the sleeve 17 and the molding material in the supply portion 23 of the screw 3 is It can be enlarged easily and reliably. Therefore, the transport efficiency of the screw 3 can be further increased.

  Moreover, since the sleeve 17 is detachable with respect to the barrel 2, it can be appropriately replaced according to its purpose and application. That is, the sleeve 17 having a different surface roughness can be exchanged depending on the purpose and application. Therefore, it is not necessary to directly perform surface treatment on the barrel 2 itself, and the cost can be reduced, and the sleeve 17 is appropriately replaced according to the slipperiness of the molding material, etc. Foam extrusion molding can be carried out with transport efficiency.

Note that the microcellular foam obtained by such foam extrusion molding has, for example, an average cell diameter of 150 μm or less, further 30 μm or less, a cell density of 10 ⁵ to 10 ¹⁰ pieces / cm ³ , and 10 The foaming ratio is ⁶ to 10 ⁹ pieces / cm ³ , the expansion ratio is 2 times or more, and further 3 to 10 times, and it can be obtained as a foam having a desired shape.

  The average cell diameter can be obtained, for example, by averaging the cell diameter in the unit area of the SEM photograph and dividing the average diameter by the number of cells.

  The cell density can be obtained from the following equation using an SEM photograph.

Cell density = N ( ^3/2 ) / (10 ⁻⁴ × √S) ³ (pieces / cm ³ )
N: Number of cells S: Measurement area (μm ² )

  Further, in the above description, the sleeve 17 whose inner peripheral surface is roughened is provided at the portion of the barrel 2 facing the supply unit 23, but the inner peripheral surface is roughened in the entire extrusion direction of the barrel 2. The sleeve 17 may be provided, or the inner peripheral surface 20 of the barrel 2 may be directly roughened without providing the sleeve 17. Further, depending on the purpose and application, the inner peripheral surface 19 of the sleeve 17 and the inner peripheral surface 20 of the barrel 2 may not be roughened.

  In the above description, the foam extrusion molding apparatus 1 is configured as a single-screw extruder. However, the present invention is not limited thereto, and may be configured as a twin-screw extruder. Further, two extruders are connected. You may comprise as a tandem-type extruder.

DESCRIPTION OF SYMBOLS 1 Foam extrusion molding apparatus 2 Barrel 3 Screw 23 Supply part 24 1st compression part 25 1st fixed quantity part 26 2nd compression part 27 2nd fixed quantity part 30 Introduction part

Claims (4)

In a foam extrusion molding apparatus comprising a barrel and a screw provided in the barrel,
In the middle of the extrusion direction of the screw in the barrel, an introduction part for introducing an inert fluid into the barrel is provided,
The screw includes a supply unit, a first compression unit and a first quantitative unit, a second compression unit and a second quantitative unit across a position where the introduction unit is provided,
The foam extrusion molding apparatus characterized in that the surfaces of only the supply unit, the first compression unit, and the first metering unit are covered with a coating layer containing fluorine.   The foam extrusion molding apparatus according to claim 1, wherein the coating layer is made of polytetrafluoroethylene.   2. The foam extrusion molding apparatus according to claim 1, wherein the coating layer is made of electroless nickel / fluorine composite plating.   2. The foam extrusion molding apparatus according to claim 1, wherein the coating layer is made of hard chromium / fluorine composite plating.

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