JP4480600B2 - Manufacturing method of polylactic acid resin foam sheet - Google Patents

Description

  The present invention relates to a method for producing a polylactic acid resin foam sheet.

  Polylactic acid resin is a resin obtained by polymerizing lactic acid resin that exists in nature. It is a biodegradable resin that can be decomposed by microorganisms that exist in nature and has excellent mechanical properties at room temperature. It attracts attention from being.

  Lactic acid, which is a raw material for polylactic acid-based resins, exhibits optical activity because it has an asymmetric carbon atom in the molecule, and racemates in which D-form, L-form, and D-form and L-form are mixed in equal amounts There are three types.

  Therefore, the polylactic acid resin obtained by polymerizing lactic acid can have various properties by adjusting the mixing ratio of the above three kinds of lactic acid and the polymerization method. There are a wide variety of resins ranging from crystalline to non-crystalline, and the melting point or softening point varies.

  On the other hand, as a method for obtaining a foam from a synthetic resin, there is a method in which a synthetic resin and a physical foaming agent are supplied to an extruder and melt-kneaded and then extruded and foamed from the extruder. It is necessary to have enough tension.

  However, when the polylactic acid-based resin is heated from a solidified state, the polylactic acid-based resin is greatly softened or melted at a certain temperature to become a low-viscosity state. The temperature range for expressing the tension that can be maintained is extremely narrow, and the resin is difficult to foam.

  Therefore, various methods such as modifying the polylactic acid-based resin to improve foaming properties have been attempted. Patent Document 1 discloses that D-form and L-form are 2 to 13% by weight, respectively. And a crystalline polylactic acid-based resin obtained by copolymerization at a ratio of 98 to 87% is heated in an extruder, and dimethyl ether and hydrocarbon are used as a blowing agent in the molten resin in a weight ratio of 95/5 to 5 /. A method for producing a crystalline polylactic acid resin foam is disclosed in which a mixture obtained by mixing at a ratio of 95 is press-fitted, and the resulting molten resin is extruded from an extruder and foamed.

  However, the crystalline polylactic acid-based resin foam obtained by the above production method has an open cell ratio higher than 20%, and if the mold temperature is lowered in order to reduce the open cell ratio, it circulates in the mold. As a result, there is a problem that the flow of the molten resin is lowered, and as a result, the appearance of the obtained crystalline polylactic acid resin foam is lowered.

  Patent Document 2 discloses a foaming resin obtained by a cross-linking reaction between a thermoplastic resin mainly composed of a polylactic acid-based resin, (meth) acrylic acid ester and glycidyl ether in the presence of an organic peroxide. A foam formed by foam-molding the composition has been proposed.

  However, since the foam uses (meth) acrylic acid ester and glycidyl ether, the production process becomes complicated, and the biodegradability of the resulting polylactic acid resin foam is reduced. there were.

Japanese Patent Laid-Open No. 2004-307661 JP 2004-51803 A

  The present invention provides a method for producing a polylactic acid resin foam sheet having a low open cell ratio, maintaining the inherent biodegradability of a polylactic acid resin and having an excellent appearance.

The method for producing a polylactic acid resin foamed sheet of the present invention is to supply a polylactic acid resin and a foaming agent to an extruder, melt and knead, and then extrude and foam into a cylindrical shape from a circular mold attached to the tip of the extruder. A method for producing a polylactic acid-based resin foamed sheet by producing a cylindrical foam and developing the cylindrical foam to produce a polylactic acid-based resin foamed sheet, comprising an outlet portion of the circular mold. An annular resin flow path formed between the opposed surfaces of the inner die and the outer die is in communication with the first resin flow path portion having a constant diameter on the extruder side and the first resin flow path portion. A second resin flow path portion that expands in diameter while gradually reducing the resin flow cross-sectional area in the extrusion direction, and the resin flow path surface on the outer die side in the second resin flow path portion is the first resin flow path. Opening angle with respect to the flow direction of the molten resin flowing in the section Is an opening angle β formed by the resin flow surface on the inner die side in the second resin flow channel portion with respect to the flow direction of the molten resin flowing in the first resin flow channel portion. The opening angle α of the resin flow path surface on the die side is larger by 1 to 15 °, and at least the first and second resin flow path portions among the surfaces of the first and second resin flow path portions The surface of the continuous part and the surface of the second resin flow path part are entirely covered with a coating layer made of titanium carbonitride , and a shear rate of 300 to from the second resin flow path part at the outlet part of the circular mold. It is characterized by extruding at 8000 sec- ¹ .

  The polylactic acid-based resin is represented by the following formula 1. This polylactic acid resin polymerizes L-lactic acid and / or D-lactic acid, or opens one or two or more lactides selected from the group consisting of L-lactide, D-lactide and DL-lactide. Any polylactic acid resin can be used.

  When producing a polylactic acid-based resin, only L-form or D-form is used as a monomer, or when L-form and D-form are used in combination as a monomer, either L-form or D-form is larger than the other. When used, the resulting polylactic acid-based resin becomes crystalline. On the other hand, when the L-form and D-form are used as monomers in substantially the same amount, the resulting polylactic acid-based resin becomes amorphous. And when producing a polylactic acid resin foam sheet having excellent heat resistance, a crystalline polylactic acid resin is preferred, and when producing a polylactic acid resin foam sheet having excellent buffering and toughness. An amorphous polylactic acid resin is preferred.

  If the melt flow rate of the polylactic acid-based resin is low, the flowability of the polylactic acid-based resin in the circular mold is reduced and the melt appearance of the polylactic acid-based resin foam sheet is reduced. On the other hand, if it is high, the polylactic acid-based resin may break, and a good polylactic acid-based resin foam sheet may not be produced, so 0.1 to 20 g / 10 min is preferable. In addition, the melt flow rate of a polylactic acid-type resin means what was measured on 190 degreeC and the conditions of the nominal load 2.16kg based on JISK7210.

  The foaming agent is not particularly limited, and is a pyrolytic foaming agent such as azodicarbonamide, dinitrosopentamethylenetetramine, hydrazoyl dicarbonamide, sodium bicarbonate; propane, n-butane, i-butane, n -Saturated aliphatic hydrocarbons such as pentane, i-pentane, hexane, aromatic hydrocarbons such as benzene, xylene, toluene, methyl chloride, 1,1,1,2-tetrafluoroethane, 1,1-difluoroethane, monochloro Examples include halogenated hydrocarbons such as difluoromethane, physical foaming agents such as dimethyl ether, carbon dioxide, and nitrogen. Dimethyl ether, propane, n-butane, and i-butane are preferable, and dimethyl ether, n-butane, and i-butane are more preferable. preferable. In addition, a foaming agent may be used independently or 2 or more types may be used together.

  Also, if the amount of the foaming agent is small, the foaming ratio of the resulting polylactic acid-based resin foam sheet may be reduced, whereas if it is large, the polylactic acid-based resin may be broken. 0.1-10 weight part is preferable with respect to 100 weight part of polylactic acid-type resin, 0.2-8 weight part is more preferable, 0.3-6 weight part is especially preferable.

  In addition, you may add additives, such as a bubble regulator, a crystal nucleating agent, an antistatic agent, a flame retardant, and a coloring agent, to a polylactic acid-type resin. Examples of the bubble regulator include polytetrafluoroethylene, polytetrafluoroethylene modified with acrylic resin, talc, calcium carbonate, borax, zinc borate, aluminum hydroxide, silica, sodium carbonate, sodium bicarbonate, lithium carbonate, carbonate Potassium and the like can be mentioned, and polytetrafluoroethylene modified with polytetrafluoroethylene or acrylic resin is preferable in that it exhibits an excellent bubble refining effect without decomposing the molten polylactic acid resin, Talc is preferred because it promotes crystallization of the crystalline polylactic acid resin.

  If the added amount of the above-mentioned air conditioner is small, the effect of adding the air conditioner may not be exhibited. On the other hand, if it is large, there is a possibility that foam breakage may occur during extrusion foaming of the polylactic acid resin. The amount is preferably 0.01 to 5 parts by weight, more preferably 0.05 to 4 parts by weight, and particularly preferably 0.1 to 3 parts by weight with respect to 100 parts by weight of the system resin.

  The polylactic acid-based resin and the foaming agent are supplied to the extruder together with the additives as necessary, melt-kneaded, and extruded and foamed into a cylindrical shape from a circular mold attached to the tip of the extruder. A foam is produced.

  The extruder is not particularly limited as long as it has been conventionally used for extrusion foaming. A single-screw extruder, a twin-screw extruder, and a plurality of extruders are connected in series. Examples include tandem extruders.

  Here, in order to suppress the open cell ratio of the polylactic acid resin foamed sheet, it is one of effective methods to lower the resin temperature when the molten polylactic acid resin is extruded and foamed from a circular mold. .

  However, as described above, since the melt viscosity of polylactic acid resin greatly changes with temperature, it is difficult to adjust the melt viscosity of polylactic acid resin only by adjusting the resin temperature. If the temperature of the polylactic acid resin during extrusion foaming is lowered too much, the melt viscosity of the polylactic acid resin becomes excessively high and the flow of the polylactic acid resin in the circular mold becomes worse. Only a polylactic acid resin foam sheet having a reduced appearance can be obtained, and extrusion foaming may be unstable.

  In particular, in the case of a crystalline polylactic acid resin, the polylactic acid resin staying in the resin flow path of the circular mold is excessively crystallized as the flow of the polylactic acid resin in the circular mold deteriorates. If this is the case, the appearance of the resulting polylactic acid resin foamed sheet may be deteriorated, or extrusion foaming may become unstable.

Therefore, in the present invention, the surface of the annular resin flow path at the outlet of the circular mold is covered with a coating layer made of titanium carbonitride , and the resin flow path at the outlet of the circular mold and the resin flow path By reducing the frictional resistance between the molten polylactic acid resin flowing through the polylactic acid resin, the polylactic acid resin can smoothly flow through the resin flow path in the circular mold, and the polylactic acid system during extrusion foaming Even if the temperature of the resin is lowered to increase the melt viscosity of the polylactic acid-based resin, it can be accommodated, and the polylactic acid-based resin can be smoothly extruded and foamed from a circular mold.

  More specifically, as shown in FIG. 1, the circular mold 1 used in the present invention includes an inflow portion 2 that is detachably attached to the end of the extruder, and a bolt and a nut at the end of the inflow portion 2. It comprises an outlet portion 3 that is detachably attached by means (not shown).

  An annular resin flow path 23 is formed between the opposing surfaces of the outer die 21 and the inner die 22 in the inflow portion 2, and between the opposing surfaces of the outer die 4 and the inner die 5 of the outlet portion 3. In addition, an annular resin flow path 6 is formed.

  And the annular resin flow path 6 of the said outlet part 3 has a fixed diameter by the side of an extruder (inflow part 2 side), and is a circle connected to the front end side opening end of the resin flow path 23 of the said inflow part 2. An annular first resin flow channel portion 61 and an annular second resin flow channel portion communicating with the first resin flow channel portion 61 and gradually expanding in diameter while gradually reducing the resin flow channel cross-sectional area in the extrusion direction. 62.

Further, as shown in FIG. 1, the surfaces 611 a, 611 b, 621 a, and 621 b of the first and second resin flow path portions 61 and 62 of the outlet portion 3 are entirely covered with the coating layer 7. And this coating layer 7 is excellent in abrasion resistance and corrosion resistance, has low frictional resistance with a molten polylactic acid resin containing a foaming agent, and slipperiness and durability with a molten polylactic acid resin. From this point, it is formed from titanium carbonitride. In the state where the inflow part 2 and the outlet part 3 are connected, the coating layer 7 formed on the surface of the resin flow path 6 of the outlet part 3 and the resin flow of the resin flow path 23 of the inflow part 2 The road surface 23a is adjusted so as to be in a state where the road surface 23a is smoothly and continuously connected over the entire circumference.

  Static electricity may be generated due to friction between the polylactic acid resin flowing through the resin flow path 6 in the outlet 3 of the circular mold 1 and the resin flow path 6. Even when a flammable foaming agent is used among the exemplified foaming agents, the coating layer 7 formed from titanium nitride, titanium carbide, or titanium carbonitride is excellent in electrical conductivity, and thus occurs. The static electricity can be smoothly dissipated to the outside through the ground provided in the extruder through the coating layer 7, and the polylactic acid resin extruded from the circular mold and containing the flammable foaming agent ignites. Can be substantially prevented.

  As a method for forming the coating layer 7 on the surfaces 611a, 611b, 621a, 621b of the first and second resin flow passage portions 61, 62 of the outlet portion 3, a gas phase method, a melt method, a molten salt method, a solution Although a dense and high-purity coating layer can be obtained and a coating layer having a uniform film thickness can be obtained even in a complicated shape, a gas phase method is preferable.

  Further, the vapor phase method includes a diffusion method and a vapor deposition method, and the vapor deposition method is divided into a PVD method (physical vapor deposition method) and a CDV method (chemical vapor deposition method). Of the PVD methods, the PVD method based on ion plating, which is less likely to cause distortion in the die because of processing at a low temperature, is preferable. For the same reason, the plasma CVD method is preferable among the CVD methods.

  In addition, if the thickness of the coating layer 7 is thin, the durability may be lowered. On the other hand, if it is thick, the heat dissipation may be lowered. Therefore, the thickness is preferably 0.05 to 5 μm, preferably 0.1 to 4 μm. Is more preferable, and 0.2 to 3 μm is particularly preferable.

And if the surface of the said coating layer 7 is rough, the frictional resistance between the molten polylactic acid-type resin which passes a resin flow path will become large, and the external appearance of the polylactic acid-type resin foam sheet obtained may fall. Or, the stability of extrusion foaming may be reduced, so the finish symbol is preferably ▽▽▽ (roughness category 1.6S), and the finish symbol is ▽▽▽▽ (roughness category 0.8S) The above is more preferable. Here, the roughness section means the maximum height (R _max ) with respect to the reference length, and specifically, the roughness section 1.6S is the maximum with respect to the reference length of 0.8 mm. The height represents a roughness of 1.6 μm, and the roughness classification 0.8S represents a roughness having a maximum height of 0.8 μm with respect to a reference length of 0.25 mm. The classification of finish symbols and roughness is described in Chapter 17 (17-12) of “Handbook of Mechanical Design and Drawing based on JIS Eighth Edition” issued by Rigaku Corporation.

  Further, as shown in FIG. 2, the resin flow path surface 620b on the outer die 4 side in the second resin flow path portion 62 of the outlet portion 3 of the circular mold 1 is a molten resin flowing through the first resin flow path portion 61. If the opening angle α with respect to the flow direction of the resin is small, there is a possibility that the cylindrical foam extruded and foamed from the circular mold 1 may be wavy. On the other hand, if the opening angle α is large, the second resin in the circular mold 1 is present. Residue of polylactic acid resin accumulates at the opening end of the flow path portion 62, and the appearance of the resulting polylactic acid resin foam sheet is obtained by adhering to or contacting the cylindrical foam. Since it may fall, it is limited to 10-70 degrees and 20-60 degrees is preferable.

  Further, the opening formed by the resin flow passage surface 620a on the inner die 5 side in the second resin flow passage portion 62 of the outlet portion 3 of the circular mold 1 with respect to the flow direction of the molten resin flowing in the first resin flow passage portion 61. The angle β is larger by 1 to 15 ° than the opening angle α of the resin flow path surface 620b of the outer die 4, and is preferably larger by 2 to 10 °, and only 2.5 to 8 °. More preferably, it is larger.

  This is because if the difference between the opening angle β and the opening angle α is too small, it may be difficult to maintain the foaming power of the molten polylactic acid resin, while if too large, melt fracture will occur. This is because the appearance of the resulting polylactic acid-based resin foam sheet may deteriorate.

  The molten polylactic acid resin supplied to the extruder and melt-kneaded flows through the resin flow path 6 of the circular mold 1 and has an annular tip in the second resin flow path 62 of the outlet 3. Although it is extruded and foamed in a cylindrical shape from the opening, the surfaces 611a, 611b, 621a, and 621b of the first and second resin flow channel portions 61 and 62 of the circular mold 1 are entirely covered by the coating layer 7 as described above. Thus, the frictional resistance between the molten polylactic acid resin and the coating layer 7 of the circular mold 1 is reduced.

  On the other hand, when the molten polylactic acid resin is extruded and foamed from the second resin flow path portion 62 of the circular mold 1, foam breakage occurs when the tension of the cell membrane of the polylactic acid resin loses the foaming force. The resulting polylactic acid-based resin foam sheet has a high open cell ratio.

  In order to prevent such bubble breakage during extrusion foaming, the circular mold is usually set to a temperature lower than the temperature of the polylactic acid resin extruded from the extruder. The melt viscosity of the polylactic acid-based resin is adjusted by cooling the polylactic acid-based resin.

  However, if the temperature of the circular mold is set too low, the melt viscosity of the polylactic acid resin becomes too high, and the retention of the polylactic acid resin occurs in the circular mold. The flow path is narrowed and the resin pressure in the circular mold rises beyond the allowable range, or in the case of a crystalline polylactic acid resin, the crystallization of the polylactic acid resin proceeds and the polylactic acid resin The production of the resin foam sheet becomes unstable.

  In particular, in the case of a crystalline polylactic acid-based resin, the temperature range suitable for extrusion foaming is narrow, and adjusting the temperature of the polylactic acid-based resin in an extruder excessively lowers the resin temperature of the polylactic acid-based resin. For safety reasons, the temperature adjustment of the polylactic acid resin by the extruder is set slightly higher for safety reasons, and the resin temperature at the time of extrusion foaming of the polylactic acid resin is set accordingly by the circular mold. Need to fine tune.

  However, in the present invention, as described above, since the frictional resistance between the molten polylactic acid resin and the coating layer 7 of the circular mold 1 is reduced, the temperature of the polylactic acid resin is lowered. Even if the melt viscosity of the polylactic acid resin is slightly increased, the polylactic acid resin does not stay in the resin flow path 6 of the circular mold 1 due to frictional resistance, and the resin flow of the circular mold 1 does not occur. Smoothly circulates in the road 6.

  Therefore, the temperature range of the circular mold 1 for cooling the polylactic acid resin to a temperature suitable for foaming can be widened, and the melt viscosity of the polylactic acid resin can be easily set to a temperature suitable for extrusion foaming. Can be adjusted.

  Moreover, the resin temperature at the time of extrusion foaming of the polylactic acid-based resin can be lowered to lower the melt viscosity, thereby strengthening the tension of the cell membrane, preventing foam breakage at the time of extrusion foaming, and the resulting polylactic acid The continuous cell ratio of the resin-based resin foamed sheet can be kept low, and a greater foaming force is imparted to the polylactic acid-based resin to produce a polylactic acid-based resin foamed sheet having a high expansion ratio of 3 times or more. be able to.

In addition, when the shear rate of the molten polylactic acid resin in the tip opening of the second resin flow path portion 62 of the circular mold 1 is small, the foam is extruded from the tip opening of the second resin flow path portion 62. In this case, sufficient foaming pressure cannot be applied to the polylactic acid resin, and the appearance of the resulting polylactic acid resin foam sheet deteriorates. When melted, melt fracture occurs and the appearance and quality of the resulting polylactic acid-based resin foamed sheet are lowered, so that it is limited to 300 to 8000 sec ⁻¹ .

In addition, the shear rate of the molten polylactic acid resin in the distal end opening portion of the second resin flow path portion 62 of the circular mold 1 is calculated based on the following double pipe calculation formula.
Shear rate (sec ⁻¹ ) = 6Q / [π (L ₂ ² −L ₁ ² ) (L ₂ −L ₁ )]
However, Q is the volume extrusion rate (cm ³ / sec) of the polylactic acid resin (when Q is calculated from the mass extrusion rate (g / sec), the density of the polylactic acid resin is 1.0 g / cm ^3. a L ₁ (cm) is _{(r 0 -t 0/2)} , L 2 (cm) is _{(r 0 + t 0/2} ).

R ₀ and t ₀ are determined as follows. First, a point on the surface of the inner die 5 at the closest distance from an arbitrary point A on the ring-shaped tip edge 4a of the outer die 4 at the outlet portion 3 of the circular mold 1 is defined as a point B, and the ring shape described above. A point B is continuously specified on the surface of the inner die 5 while continuously moving the point A on the leading edge 4a in the circumferential direction, and a circle formed on the inner die 5 by the continuous point B is obtained. The virtual circle 5a is assumed.

The distance between an arbitrary point A on the ring-shaped tip edge 4a and a point B on the virtual circle 5a of the inner die 5 corresponding to the point A is t _0, and the point A and the point B The distance between the intermediate point C and the axis D of the inner die 5 is r ₀ .

Further, when the distance between the ring-shaped tip circle 4a of the outer die 4 and the virtual circle 5a of the inner die 5 is not constant, as shown in FIG. 3, the point A ₁ is arbitrarily set on the ring-shaped tip circle 4a. ~A set ₈ in the circumferential direction for each phase difference of 45 °, a point B ₁ .about.B ₈ corresponding to the points a ₁ ~A ₈ identifies each point corresponding thereto and the point a ₁ ~A ₈ B the arithmetic mean value of the distance t ₁ ~t ₈ with ₁ .about.B ₈ with a t _0, the midpoint C ₁ -C between points B ₁ .about.B ₈ corresponding thereto with each point a ₁ to a _{8 8} is defined, and an arithmetic average value of distances r ₁ to r ₈ between the intermediate points C _{1 to} C ₈ and the axis D of the inner die 5 is defined as r ₀ .

  Thus, a cylindrical foam is manufactured by extruding and foaming a molten polylactic acid resin into a cylindrical shape from the tip opening of the second resin flow path portion 61 of the circular mold 1. After gradually expanding the diameter, it is supplied to a cylindrical mandrel and cooled, and then this cylindrical foam is developed by continuously cutting the inner and outer surfaces in the extrusion direction at an arbitrary position. A lactic acid resin foam sheet can be produced.

  Further, the ratio of the diameter of the virtual circle 5a on the second resin flow path portion 62 of the circular mold 1 to the outer diameter of the mandrel extruder side edge (outer diameter of the mandrel extruder side edge / virtual circle) The diameter of 5a is preferably 2 to 5, and more preferably 2.5 to 4.5.

  Furthermore, a skin layer is formed on the surface of the cylindrical foam by blowing cooling air onto the surface of the cylindrical foam immediately after being extruded and foamed from the circular mold 1, and the appearance of the resulting polylactic acid resin foam sheet Can be improved.

  When the temperature of the cooling air is low, the cylindrical foam is solidified and the elongation of the foam is reduced, and there is a possibility that the surface of the cylindrical foam is cracked. Since a skin layer may not be formed on the surface of the body, 0 to 60 ° C. is preferable.

  Although the case where the surfaces 611a, 611b, 621a, and 621b of the first and second resin flow channel portions 61 and 62 in the circular mold 1 are entirely covered with the coating layer 7 has been described above, the circular mold 1 The load that is most applied to the polylactic acid-based resin that flows through the inside is such as a bent portion such as a connection portion with the first and second resin flow passage portions 61 and 62, and the second resin flow passage portion 62. This is when the resin cross-sectional area gradually passes through the narrowed area.

  Therefore, as shown in FIG. 4, among the surfaces of the first and second resin flow channel portions 61 and 62, the connecting portion of the first and second resin flow channel portions 61 and 62 and the second resin flow channel. Only the surfaces 6a, 6b, 621a, 621b of the part 62 may be entirely covered with the covering part 7. Note that the covering portion 7 and the resin flow passage surface 610 of the first resin flow passage portion 61 not covered with the covering portion 7 are formed in a smooth flat surface having no step over the entire circumference at the boundary between them. Yes.

As described above, the method for producing a polylactic acid resin foam sheet of the present invention is formed between the opposed surfaces of the inner die and the outer die constituting the outlet portion of the circular mold attached to the tip of the extruder. The annular resin flow path communicated with the first resin flow path portion having a constant diameter on the extruder side and the first flow path portion while gradually narrowing the resin flow cross-sectional area in the extrusion direction A second resin flow path portion that expands the diameter, and at least of the surfaces of the first and second resin flow path portions, the continuous portion of the first and second resin flow path portions and the second resin flow path The surface of the surface is entirely covered with a coating layer made of titanium carbonitride , and the friction between the resin flow path at the outlet of the circular mold and the molten polylactic acid resin flowing through the resin flow path The resistance is reduced.

  Accordingly, even a polylactic acid resin having a high melt viscosity by lowering the resin temperature of the polylactic acid resin can be smoothly circulated in the circular mold, and thus the polylactic acid resin having a high melt viscosity. Is not easily broken due to the strong tension of the cell membrane during foaming, and the resulting polylactic acid resin has a low open cell ratio of 20% or less.

  In addition, as described above, since the cell membrane tension of the polylactic acid resin during foaming is strong, a large foaming force can be imparted to the polylactic acid resin, and a polylactic acid resin foam sheet having a high expansion ratio can be obtained. Obtainable.

  As described above, the polylactic acid resin foam sheet produced by the method for producing a polylactic acid resin foam sheet of the present invention has a low open cell ratio, and therefore has excellent secondary foamability at the time of molding. It can be suitably used as a material, cushioning material, industrial member, building material, civil engineering material, agricultural material, and the like.

And in the manufacturing method of the polylactic acid-type resin foam sheet of this invention, since it extrudes from the 2nd resin flow-path part of the exit part of a circular mold | die at the shear rate of 300-8000 sec- ¹ , more polylactic acid-type resin is used. It can be extruded and foamed in a stable state, and a polylactic acid-based resin foam sheet having a low open cell ratio and a high expansion ratio can be reliably produced.

In addition, the polylactic acid-based resin foam sheet manufacturing method includes an opening angle formed by a resin flow path surface on the outer die side in the second resin flow path section with respect to a flow direction of the molten resin flowing in the first resin flow path section. α is 10 to 70 °, and an opening angle β formed by the resin flow path surface on the inner die side in the second resin flow path section with respect to the flow direction of the molten resin flowing in the first resin flow path section is Since the opening angle α of the resin flow path surface on the die side is larger by 1 to 15 °, an appropriate foaming force is given to the polylactic acid resin without retaining the polylactic acid resin in the circular mold. In addition, a polylactic acid resin foam sheet having a low open cell ratio and a high foaming ratio can be produced without causing a wavy phenomenon or melt fracture in the cylindrical foam.

Moreover, the production method of the polylactic acid-based resin foam sheet, since the coating layer is formed from titanium carbonitride, it is possible to further reduce the frictional resistance between the polylactic acid resin in a molten state coating layer The durability of the coating layer is excellent, and a polylactic acid resin foamed sheet can be produced stably over a long period of time.

Example 1
Crystalline polylactic acid resin (trade name “ HV- 6100 ” manufactured by Unitika Ltd., melting point: 167.8 ° C., melt flow rate: 1.2 g / 10 minutes) 100 parts by weight and 2 parts by weight of talc as a foam regulator Is supplied to a first stage extruder of a tandem type extruder in which a single-screw extruder having a diameter of 50 mm as a first stage and a single-screw extruder having a diameter of 65 mm as a second stage are connected via a connecting pipe. did.

  The polylactic acid resin is first heated to 190 ° C. in the first stage extruder, melted and kneaded while gradually heating to 220 ° C., and butane (isobutane: normal butane) from the middle of the first stage extruder. (Weight ratio) = 35: 65) was press-fitted at a ratio of 1.7 parts by weight with respect to 100 parts by weight of the polylactic acid resin, and butane was uniformly dispersed in the polylactic acid resin.

Thereafter, the molten polylactic acid-based resin was continuously supplied from the first-stage extruder to the second-stage extruder via a connecting pipe. After the molten polylactic acid resin is cooled to 163 ° C. in the second stage extruder, the shear rate is 713 sec ⁻¹ and the extrusion speed is 20 kg / hour from the circular mold attached to the tip of the second stage extruder. And extruded and foamed into a cylindrical shape. The resin temperature was measured by inserting a breaker plate between the second stage extruder and the circular mold, and inserting a thermocouple in the center of the breaker plate.

Here, as shown in FIG. 1 , in the circular mold 1, the surfaces 611a, 611b, 621a, and 621b of the first and second resin flow channel portions 61 and 62 are formed by the PVD method using ion plating. The coating layer 7 made of titanium carbonitride having a thickness of 1 μm was entirely covered. In addition, the surface of titanium carbide was ▽▽▽▽ (roughness classification 0.8S) with a finish symbol.

  The opening angle α of the resin flow path surface 620b on the outer die 4 side in the second resin flow path portion 62 is 30 °, and the opening angle β of the resin flow path surface 620a on the inner die 5 side in the second resin flow path portion 62 is It was 35 °.

Further, the circular mold 1 has r ₀ of 2.980 cm, t ₀ of 0.05 cm, and the volume extrusion amount Q of the polylactic acid resin is 5.56 cm ³ / sec. The shear rate of the molten polylactic acid resin in the part was 713 sec ⁻¹ . The diameter of the virtual circle 5a on the second resin flow path portion 62 of the circular mold 1 was 60 mm.

  Then, after gradually expanding the diameter of the cylindrical foam, a cylindrical cooling mandrel (outer diameter: 205 mm, length: cooled by cooling water and having a constant outer diameter over the entire length in the length direction). 400mm) is continuously supplied and cooled, and then a long foamed polylactic acid resin foam is continuously produced by continuously cutting and developing the cylindrical foam in the extrusion direction at any part of the cylindrical foam. And wound into a roll with a winder. In addition, 35 degreeC cold air was sprayed on the inner peripheral surface of the cylindrical foam immediately after extrusion foaming from the circular metal mold | die.

The polylactic acid resin foam sheet has a density of 0.18 g / cm ³ , a thickness of 2.0 mm, an open cell ratio of 16 %, uniform and fine bubbles, and an excellent appearance. It was homogeneous.

(Example 2 )
Crystalline polylactic acid resin (trade name “LACTY 9031” manufactured by Shimadzu Corporation, melting point: 138.8 ° C., melt flow rate: 2.6 g / 10 minutes) 100 parts by weight and 2 parts by weight of talc as a foam regulator The first-stage extruder of a tandem type extruder in which a single-screw extruder with a diameter of 50 mm as the first stage and a single-screw extruder with a diameter of 65 mm as a second stage are connected via a connecting pipe is supplied. .

  The polylactic acid resin is first heated to 150 ° C. in the first stage extruder, melted and kneaded while gradually heating to 180 ° C., and dimethyl ether is added from the middle of the first stage extruder to the polylactic acid resin. By press-fitting at a ratio of 6.2 parts by weight with respect to 100 parts by weight, dimethyl ether was uniformly dispersed in the polylactic acid resin.

Thereafter, the molten polylactic acid-based resin was continuously supplied from the first-stage extruder to the second-stage extruder via a connecting pipe. After the molten polylactic acid resin is cooled to 111 ° C. in the second stage extruder, the shear rate is 455 sec ⁻¹ and the extrusion speed is 25 kg / hour from the circular mold attached to the tip of the second stage extruder. And extruded and foamed into a cylindrical shape. The resin temperature was measured by inserting a breaker plate between the second stage extruder and the circular mold, and inserting a thermocouple in the center of the breaker plate.

  Here, in the circular mold 1, as shown in FIG. 1, the surfaces 611 a, 611 b, 612 a, and 612 b of the first and second resin flow path portions 61 and 62 are formed by the PVD method using ion plating. The coating layer 7 made of titanium carbonitride having a thickness of 1 μm was entirely covered. In addition, the surface of the titanium carbonitride was ▽▽▽▽ (roughness classification 0.8S) with a finish symbol.

  The opening angle α of the resin flow path surface 620b on the outer die 4 side in the second resin flow path portion 62 is 30 °, and the opening angle β of the resin flow path surface 620a on the inner die 5 side in the second resin flow path portion 62 is It was 35 °.

Further, the circular mold 1 has r ₀ of 2.971 cm, t ₀ of 0.07 cm, and the volume extrusion amount Q of the polylactic acid resin is 6.94 cm ³ / sec. The shear rate of the molten polylactic acid resin in the part was 455 sec ⁻¹ . The diameter of the virtual circle 5a on the second resin flow path portion 62 of the circular mold 1 was 60 mm.

  Then, after gradually expanding the diameter of the cylindrical foam, a cylindrical cooling mandrel (outer diameter: 205 mm, length: cooled by cooling water and having a constant outer diameter over the entire length in the length direction). 400mm) is continuously supplied and cooled, and then a long foamed polylactic acid resin foam is continuously produced by continuously cutting and developing the cylindrical foam in the extrusion direction at any part of the cylindrical foam. And wound into a roll with a winder. In addition, 15 degreeC cold air was sprayed on the inner peripheral surface of the cylindrical foam immediately after extrusion foaming from the circular metal mold | die.

The polylactic acid-based resin foam sheet has a density of 0.047 g / cm ³ , a thickness of 2.0 mm, an open cell ratio of 17%, uniform and fine bubbles, excellent appearance, and homogeneity. It was something.

(Comparative Example 1)
The use of a polylactic acid resin (melting point: 167.4 ° C., melt flow rate 1.5 g / 10 min) sold by Unitika under the trade name “TE-6200” as the polylactic acid resin, It was cooled to 161 ° C. instead of 163 ° C. in the extruder, and as the circular mold 1, the surfaces 611a, 611b, 621a, 621b of the first and second resin flow channel portions 61, 62 had a thickness of 30 μm. A polylactic acid resin foam sheet was produced in the same manner as in Example 1 except that a circular mold having the same structure as in Example 1 was used, except that it was entirely covered with a chromium plating layer. As a result, the appearance unevenness occurred on the surface of the polylactic acid resin foam sheet.

Therefore, a polylactic acid-based resin foam sheet was produced in the same manner as described above except that the second extruder was cooled to 164 ° C. instead of 161 ° C. The polylactic acid-based resin foamed sheet had a density of 0.18 g / cm ³ , a thickness of 2.0 mm, and an open cell ratio of 22%.

(Comparative Example 2)
As a polylactic acid resin, a polylactic acid resin (melting point: 167.4 ° C., melt flow rate 1.5 g / 10 minutes) sold by Unitika under the trade name “TE-6200” was used. 1 part by weight instead of 2 parts by weight, 1.5 parts by weight of butane instead of 1.7 parts by weight, and cooled to 162 ° C. instead of 163 ° C. in the second extruder, resin flow path part The shear rate of the polylactic acid resin in the molten state at the tip opening of 62 is set to 2221 sec ^-1 instead of 713 sec ^-1, and the surface of the first and second resin flow passages 61 and 62 is used as the circular mold 1. Example 1 except that 611a, 611b, 621a, 621b are entirely covered with a 30 μm thick chromium plating layer, r ₀ is 2.984 cm and t ₀ is 0.04 cm. Has the same structure as the circular mold used A polylactic acid resin foam sheet was produced in the same manner as in Example 1 except that a circular mold was used and the extrusion rate was 40 kg / hour instead of 20 kg / hour. Appearance unevenness occurred on the surface of the sheet.

Therefore, a polylactic acid-based resin foam sheet was produced in the same manner as described above except that the second extruder was cooled to 166 ° C. instead of 162 ° C. The polylactic acid-based resin foam sheet had a density of 0.18 g / cm ³ , a thickness of 2.0 mm, and an open cell ratio of 21%.

(Comparative Example 3)
The use of a polylactic acid resin (melting point: 167.4 ° C., melt flow rate 1.5 g / 10 min) sold by Unitika under the trade name “TE-6200” as the polylactic acid resin, it was cooled to 161 ° C. instead of 163 ° C. in an extruder, as a circular die 1, using the following circular die, the shear rate of the polylactic acid-based resin in the molten state at the distal end opening portion of the resin flow path 62 A polylactic acid-based resin foam sheet was obtained in the same manner as in Example 1 except for adjusting to 279 sec ⁻¹ . The resulting polylactic acid-based resin foam sheet had a density of 0.20 g / cm ³ , a thickness of 2.0 mm, and an open cell ratio of 30%.

Here, as shown in FIG. 1, in the circular mold, the surfaces 611a and 621a on the inner die 5 side in the first and second resin flow channel portions 61 and 62 are formed by the PVD method using ion plating. , The resin flow channel surfaces 611b and 621b on the outer die 4 side in the first and second resin flow channel portions 61 and 62 are covered entirely with the coating layer 7 made of titanium carbonitride having a thickness of 1 μm. The entire surface was covered with a chromium plating layer having a thickness of 30 μm. In addition, the surface of the titanium carbonitride was ▽▽▽▽ (roughness classification 0.8S) with a finish symbol.

The opening angle α of the resin flow path surface 620b on the outer die 4 side in the second resin flow path portion 62 is 30 °, and the opening angle β of the resin flow path surface 620a on the inner die 5 side in the second resin flow path portion 62 is It was 35 °.

Furthermore, the circular mold 1 has its r ₀ Is 2.973 cm, t ₀ Was 0.08 cm. The diameter of the virtual circle 5a on the second resin flow path portion 62 of the circular mold 1 was 60 mm.

(Comparative Example 4)
As a polylactic acid resin, a polylactic acid resin (melting point: 167.4 ° C., melt flow rate 1.5 g / 10 minutes) sold by Unitika under the trade name “TE-6200” was used. 1 part by weight instead of 2 parts by weight, 1.5 parts by weight of butane instead of 1.7 parts by weight, and cooled to 162 ° C. instead of 163 ° C. by the second extruder, circular mold 1 The following circular mold is used , the volume extrusion rate Q of the polylactic acid resin is 11.1 cm ³ / sec, and the shear rate of the polylactic acid resin in the molten state at the tip opening of the resin flow path portion 62 is 8861 sec ^−1. A polylactic acid-based resin foam sheet was obtained in the same manner as in Example 1 except that it was adjusted to. The obtained polylactic acid-based resin foam sheet had a density of 0.20 g / cm ³ , a thickness of 2.0 mm, and an open cell ratio of 32%.

As shown in FIG. 1, the circular mold 1 has a thickness in which the surfaces 611a, 611b, 621a, 621b of the first and second resin flow channel portions 61, 62 are formed by a PVD method using ion plating. Was covered with a coating layer 7 made of titanium nitride having a thickness of 1 μm. In addition, the surface of the titanium nitride was ▽▽▽▽ (roughness classification 0.8S) by a finishing symbol.

The opening angle α of the resin flow path surface 620b on the outer die 4 side in the second resin flow path portion 62 is 30 °, and the opening angle β of the resin flow path surface 620a on the inner die 5 side in the second resin flow path portion 62 is It was 35 °.

Furthermore, the circular mold 1 has its r ₀ Is 2.992 cm, t ₀ Was 0.02 cm. The diameter of the virtual circle 5a on the second resin flow path portion 62 of the circular mold 1 was 60 mm.

It is the model longitudinal cross-sectional view which showed the circular metal mold | die used by this invention. It is the model longitudinal cross-sectional view which showed the exit part of the circular mold. It is the schematic diagram which showed the front-end | tip opening part of the 2nd resin flow-path part in the exit part of a circular mold. It is the model longitudinal cross-sectional view which showed another example of the circular metal mold | die used by this invention.

1 Circular mold 2 Inflow part
21 outer die
22 Inside die
23 resin flow path 3 outlet 4 outer die 5 inner die 6 resin flow path
61 First resin flow path
610 Resin channel surface
611a, 611b First resin flow path surface
62 Second resin flow path
621a, 621b Second resin flow path surface
620a, 620b Resin channel surface

Claims (1)

A polylactic acid-based resin and a foaming agent are supplied to an extruder and melt-kneaded, and a cylindrical foam is produced by extrusion foaming from a circular mold attached to the tip of the extruder into a cylindrical shape. A method for producing a polylactic acid resin foam sheet, which is expanded to produce a polylactic acid resin foam sheet, which is formed between opposing surfaces of an inner die and an outer die constituting the outlet portion of the circular mold. The annular resin flow path has a first resin flow path portion having a constant diameter on the extruder side, and communicates with the first resin flow path portion to gradually narrow the resin flow cross-sectional area in the extrusion direction. The second resin flow path portion that expands in diameter while the resin flow path surface on the outer die side in the second resin flow path portion opens with respect to the flow direction of the molten resin flowing in the first resin flow path portion. The angle α is 10 to 70 °, and the second resin flow path portion The opening angle β formed by the resin flow path surface on the inner die side with respect to the flow direction of the molten resin flowing in the first resin flow path portion is 1 to 15 than the opening angle α of the resin flow path surface on the outer die side. ° with is larger only, the first, at least of the surface of the second resin flow passage portion, the first, the connecting portion and the surface of the second resin flow passage portion of the second resin flow passage portion, coal Polylactic acid-based resin foam, which is entirely covered with a coating layer made of titanium nitride and is extruded at a shear rate of 300 to 8000 sec ⁻¹ from the second resin flow passage at the outlet of the circular mold. Sheet manufacturing method.