JP2009208389A - Polylactic acid-based resin molding and its molding method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polylactic acid-based resin molding with advantages such as easy moldability, excellent suitability to electromagnetic environment and easy sortability for use by recycling. <P>SOLUTION: This polylactic acid-based resin molding 1 is of such a structure that a shield member 20 made of a rolled steel sheet press-molded to the same shape as a molding main body 10, is integrally molded in close contact with the inside of the molding main body 10 of almost rectangular lid shape. The shield member 20 has holes 20a opened side by side at an equal interval in the longitudinal and crosswise directions, and the holes 20a are internally filled with the polylactic acid-based resin in the way that the resin is flush with the shield member 20. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a polylactic acid-based resin molded article excellent in mechanical strength and electromagnetic wave shielding performance, and can be suitably used for a housing material of an electric device such as a personal computer.

  Conventional general-purpose plastics such as polyethylene, polypropylene, and polyethylene terephthalate have been used in a wide range of applications due to their transparency and mechanical strength. However, when these plastics are disposed of and disposed of in landfills, they remain in the soil without being decomposed indefinitely, so that the environmental impact is a problem. Biodegradable plastics are attracting attention as plastics for solving these problems. Biodegradable plastics are decomposed by microorganisms in the soil and finally become carbon dioxide gas and water, so that there is no environmental problem due to such residues in the soil.

  Among the biodegradable plastics, polylactic acid is relatively inexpensive, has high mechanical strength, can be injection-molded, and has excellent transparency. For example, its application to the electric / electronic / OA field has been studied. ing.

  However, polylactic acid has a drawback that it has poor release properties when injection molding is performed. For this reason, in the case of performing injection molding, it is necessary to devise measures such as increasing the draft from the injection direction of the mold, and there is a problem that the degree of freedom in mold design is low. Further, in a large molded product, it may be difficult to release the mold only by such a device design.

  In order to solve such problems, it has also been proposed to prevent crystallization and improve mold release properties by mixing D-form polylactic acid and L-form polylactic acid (Patent Document 1). In addition, a proposal has been made to improve mold release in injection molding by mixing polylactic acid or a copolymer of lactic acid and hydroxycarboxylic acid with a fatty acid amide or a mixture of fatty acid and fatty acid amide (Patent Document 2).

  On the other hand, when a polylactic acid resin is used in a housing of an electronic device such as a personal computer, a mobile phone, or a digital home appliance, it is necessary to prevent malfunction caused by electromagnetic waves from the outside. On the other hand, these digital devices also have a problem of generating electromagnetism that causes malfunction between devices. That is, in every electronic device, electromagnetic interference (EMI) generated from the electronic device and interference resistance (EMS) from the electromagnetic interference are problems.

  Furthermore, when the recycling use of the polylactic acid resin molded product is considered, it is necessary to separate and collect the polylactic acid resin.

JP 2006-001973 A JP-A-8-27363

  However, none of the above-mentioned conventional polylactic acid-based resin moldings have all of the ease of molding, compatibility with electromagnetic environment, and ease of separation during recycling.

  The present invention has been made to solve the above-mentioned conventional problems, and provides a polylactic acid-based resin molded body that is easy to mold, has excellent electromagnetic environment compatibility, and can be easily separated at the time of recycling. The purpose is to do.

  The polylactic acid resin molded body of the present invention is characterized in that a shield member made of a metal thin plate material and a polylactic acid resin covering one surface of the shield member are integrally molded.

In the polylactic acid resin molded body of the present invention, a shield member made of a metal thin plate material is covered with a polylactic acid resin and integrally molded. Here, “the shield member made of a metal thin plate material is covered and integrally molded with a polylactic acid resin” means that one surface side of the shield member made of a metal thin plate material is a polylactic acid resin. The other side of the shield member is molded so as to be exposed without being bonded to the polylactic acid resin. If it is like this, when the polylactic acid-type resin composition form of this invention is used as a housing of an electronic device, there exists an effect which the shielding member which consists of metal thin plate-shaped materials shields electromagnetic waves. For this reason, if the polylactic acid-type resin molding of this invention is used as a housing of an electronic device, it can prevent that an electronic device malfunctions by the EMI noise from the outside. Further, it is possible to prevent the EMI noise generated by the electronic device placed inside the polylactic acid resin composition form of the present invention from leaking to the outside.
The metal thin plate material may be a mesh material. This is because it is possible to shield electromagnetic waves even in this case. Further, the weight can be reduced.

  In addition, the shield member made of a metal thin plate material plays a role as a reinforcing material, and the mechanical strength of the polylactic acid-based resin molded body is increased. For this reason, the deformation | transformation at the time of the die cutting from a shaping | molding die is prevented, and shaping | molding becomes easy. In addition, since the metal sheet material is integrally molded, the natural frequency and vibration mode of the polylactic acid resin molded body can be changed by changing the shape and thickness of the metal sheet material. This makes it possible to easily resonate electronic devices.

  Furthermore, even when recycling the polylactic acid-based resin molded body, the shield member made of a metal thin plate material is integrally bonded to the polylactic acid-based resin on one side, and the shield member Since the other side is molded so as to be exposed without adhering to the polylactic acid resin, the metal and the polylactic acid resin can be removed simply by peeling the shield member from the polylactic acid resin from the other side. Can be collected separately. For this reason, separate collection of metal and polylactic acid resin is extremely easy.

  Therefore, according to the polylactic acid-based resin molded article of the present invention, molding is easy, the electromagnetic wave shielding property is excellent, and recycling is easy.

  In the polylactic acid resin molded article of the present invention, the shield member has a plurality of through holes, and the through holes are filled with the polylactic acid resin so as to be flush with the surface of the shield member. It is preferable. In this case, the amount of the metal thin plate material used is reduced, the weight can be reduced, and the manufacturing cost is reduced. The size and number of the through-holes may be appropriately determined in consideration of the mechanical strength, weight, vibration characteristics required for the polylactic acid-based resin molding, electromagnetic wave shielding ability required for the shield member, and the like.

  The polylactic acid-based resin molded article of the present invention can be produced as follows. That is, the method for molding a polylactic acid resin molded body of the present invention includes a first step of preparing a first mold and a second mold for producing a polylactic acid resin molded body, A second step of closely attaching a shield member to the mold, a third step of aligning a second die to the first die having the shield member closely attached thereto, the first mold and the second And a fourth step of injecting a polylactic acid resin melt from a gate formed by the mold gate, wherein the polylactic acid resin melt comprises Injection is performed so as to press the shield member from the vertical direction toward the first mold side.

In the polylactic acid-based resin molded body of the present invention, a first mold and a second mold for producing a polylactic acid-based resin molded body are prepared as the first step, and the first step is performed as the second step. The shield member is brought into close contact with the mold. This is for reliably covering one side of the shield member with the polylactic acid resin. At this time, in order to ensure that the shield member is in close contact with the first mold, it is also preferable that the shield member and the first mold are in close contact using a double-sided tape or the like.

  Then, as a third step, the first mold with the shield member in close contact is covered with the second mold. And as a 4th process, the melt of a polylactic acid-type resin is injected from the gate formed of the 1st metal mold | die and the 2nd metal mold | die. At this time, since the melt of the polylactic acid resin is injected so as to be pressed against the first mold from the vertical direction with respect to the shield member, the shield member is strongly pressed against the first mold during the injection molding. For this reason, the polylactic acid resin injected from the gate is prevented from entering between the shield member and the first mold, and is surely filled in the gap between the shield member and the second mold. The For this reason, the polylactic acid resin molded body of the present invention in which one side of the shield member facing the second mold is covered with the polylactic acid resin can be reliably produced.

  As the polylactic acid resin used in the polylactic acid resin molded article of the present invention, various additives such as other plastics, softeners, flame retardants, lubricants, extenders, etc., as long as the resin is a main component of polylactic acid. May be added.

  The polylactic acid may be synthesized by the user himself, but it is also possible to use a commercially available product because it is easily available. Specifically, Nature Works (registered trademark) manufactured by Cargill-DOW, U'z (registered trademark) manufactured by Toyota Motor Corporation, Lacti (registered trademark) manufactured by Shimadzu Corporation, Unitika Co., Ltd. Terramac (registered trademark) made by Mitsui Chemicals, Inc. (Registered trademark), Palgreen (registered trademark) manufactured by Tosero Co., Ltd., and the like.

  The lactic acid constituting the polylactic acid may be any of L-lactic acid, D-lactic acid, and a mixture of L-lactic acid and D-lactic acid. Moreover, it is preferable that the weight average molecular weights of polylactic acid are 30,000 or more and 1 million or less. If the weight average molecular weight of polylactic acid is less than 30,000, the strength of the molded product is small, and if it exceeds 1,000,000, the fluidity during heating is insufficient and injection molding becomes difficult.

  The flame retardant polylactic acid-based resin composition of the present invention can be subjected to various modifications by adding secondary additives as necessary within a range that does not impede achievement of the problems of the invention. Examples of secondary additives include antioxidants, ultraviolet absorbers, colorants, pigments, antibacterial agents, stabilizers, electrostatic agents, nucleating materials, various other fillers, and the like.

On the other hand, the shield member integrally formed with the polylactic acid-based resin can be manufactured by press-molding a metal thin plate material. The metal thin plate material may be plated to improve the corrosion resistance. Moreover, you may use the metal thin plate-shaped raw material in which chemical conversion films, such as a phosphate film, are formed so that press molding etc. may be easy. The material of the metal thin plate material is not particularly limited, and iron, aluminum, stainless steel, copper, zinc, brass or the like can be used. Among these, since iron is inexpensive and excellent in mechanical strength, it has a great effect of reinforcing the polylactic acid-based resin layer and is suitable.
The thickness of the metal thin plate material is appropriately selected depending on the material, required mechanical strength, electromagnetic wave shielding performance, and the like, but is generally 0.1 mm to 1.0 mm.

  Hereinafter, the polylactic acid resin molded body of an embodiment embodying the present invention will be described in detail with reference to the drawings.

Example 1
A polylactic acid resin molded body 1 of Example 1 shown in FIG. 1 is used for a front panel of a desktop personal computer main body. In this polylactic acid-based resin molded body 1, a shield member 20 (see FIG. 2) made of a rolled steel plate press-molded in the same shape as the molded body main body 10 is in close contact with the inside of the molded body main body 10 having a substantially rectangular lid shape. Are integrally formed (see FIG. 3). The thickness of the rolled steel sheet is 0.3 mm. As shown in FIG. 1, the polylactic acid-based resin molded body 1 is provided with an inclined surface 1a and further has a rectangular hole 1b for inserting a DVD.

  As shown in FIG. 2, holes 20 a having a diameter of 6 mm are formed in the shield member 20 so as to be arranged at equal intervals in the vertical and horizontal directions. As shown in FIG. 4, a polylactic acid resin is shielded inside the holes 20 a. It is filled so as to be flush with 20.

<Manufacture of polylactic acid resin>
As a raw material for the molded body 1 constituting the polylactic acid resin molded body 1 of Example 1 configured as described above, a polylactic acid resin having the following composition was used.
90 parts by weight of polylactic acid (manufactured by Unitika Ltd., Terramac TE4000)
(Dried at 100 ° C for 4 hours)
Polybutylene succinate (manufactured by Showa Polymer Co., Ltd., Bionore (registered trademark) # 1020) (hereinafter abbreviated as "PBS") ... 10 parts by weight

  And after mixing these, it injected | threw-in to the medium-sized twin-screw extruder (Technovel Co., Ltd. product, KZW15-30TGN), and it heat-melt-kneaded and pelletized.

<Formation>
Using the polylactic acid resin pellets obtained as described above, molding was performed as follows. That is, first, a rolled steel plate is prepared, cut into the shape of the developed view of the shield member 20 shown in FIG. 2, and then pressed to produce the shield member 20. Then, as shown in FIGS. 5 and 6, the shield member 20 is placed on the male mold 30 having the convex portions 30 a that are in close contact with the shield member 20.

  Next, as shown in FIG. 7, the female mold 31 is combined with the male mold 30. Here, the female mold 31 is formed with the male mold 30 so as to have a gap that matches the molding die shape of the polylactic acid-based resin molded body 1, and further for injecting the resin. The gate 32 is formed. As shown in FIG. 8, the gate 32 is formed such that polylactic acid resin is injected from a direction perpendicular to the shield member 20. For this reason, at the time of injection molding, the shield member 20 is pressed against the male mold 30 by introducing the molten polylactic acid resin. For this reason, the polylactic acid resin is prevented from entering between the shield member 20 and the male mold 30. The molten polylactic acid resin is injected into the gate 32 from an injection molding machine (not shown). In addition, it is also preferable that the shield member 20 and the male mold 30 are adhered to each other using a double-sided tape. In this case, it is possible to more reliably prevent the polylactic acid resin from entering between the shield member 20 and the male mold 30.

  Finally, the female mold 31 and the male mold 30 are separated from each other, the polylactic acid resin molded body 1 of Example 1 is removed from the mold, and the molding is completed.

(Example 2)
In Example 2, a polylactic acid resin having the following composition was used. Others are the same as those in the first embodiment, and a description thereof will be omitted.
-Polylactic acid (Unitika Ltd., Terramac TE4000)-90 parts by weight
(Dried at 100 ° C for 4 hours)
・ Polybutylene succinate (manufactured by Showa Polymer Co., Ltd., Bionore (registered trademark))
# 1020) (hereinafter abbreviated as "PBS") ... 10 parts by weight RP agent (Asahi Kasei Duranate TSA) ... 0.5 parts by weight

(Example 3)
In Example 3, a polylactic acid resin having the following composition was used. Others are the same as those in the first embodiment, and a description thereof will be omitted.
-Polylactic acid (Unitika Ltd., Terramac TE4000)-90 parts by weight
(Dried at 100 ° C for 4 hours)
・ Polybutylene succinate (manufactured by Showa Polymer Co., Ltd., Bionore (registered trademark))
# 1020) (hereinafter abbreviated as "PBS") ··· 10 parts by weight · RP agent (Asahi Kasei Duranate TSA (registered trademark)) ··· 0.5 parts by weight · Flame retardant・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ 10 parts by weight (Ammonium polyphosphate (Clariant: Peco Frame)

Example 4
In Example 4, a polylactic acid resin having the following composition was used. Others are the same as those in the first embodiment, and a description thereof will be omitted.
-Polylactic acid (Unitika Ltd., Terramac TE4000)-90 parts by weight
(Dried at 100 ° C for 4 hours)
・ Polybutylene succinate (manufactured by Showa Polymer Co., Ltd., Bionore (registered trademark))
# 1020) (hereinafter abbreviated as “PBS”) ··· 10 parts by weight · RP agent (Asahi Kasei Duranate (registered trademark) TSA) ··· 0.5 parts by weight · Flame retardant・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ 10 parts by weight (Ammonium polyphosphate (Clariant: Peco Frame)
・ Nucleating agent (Toyota Motor: UZ'KX238P) ... 10 parts by weight

(Comparative Example 1)
In Comparative Example 1, molding was performed with polylactic acid resin without using the shield member 20. The polylactic acid resin used is the same as in Example 1.

(Comparative Example 2)
In Comparative Example 2, all the molding was performed with polylactic acid resin without using the shield member 20. The polylactic acid resin used is the same as in Example 2.

(Comparative Example 3)
In Comparative Example 3, molding was performed entirely with polylactic acid resin without using the shield member 20. The polylactic acid resin used is the same as in Example 3.

(Comparative Example 4)
In Comparative Example 4, molding was performed with a polylactic acid resin without using the shield member 20. The polylactic acid resin used is the same as in Example 4.

  About the polylactic acid-type resin molding of Examples 1-4 obtained as mentioned above and Comparative Examples 1-4, it measured about the electromagnetic compatibility (EMC) test and the dimensional accuracy of a molding.

<Electromagnetic compatibility (EMC) test>
In order to measure the electromagnetic interference (EMI) generated from the electronic devices incorporated in the polylactic acid resin molded bodies of Example 3 and Comparative Example 1 and the interference resistance (EMS) from the electromagnetic interference, an EMC test was performed. The test method was performed by using a polylactic acid-based resin molding as a part of the housing of a personal computer and measuring the electromagnetic waves generated at various frequencies in the anechoic chamber. For the measurement, a turntable rotating 360 degrees was placed on a table (height 80 cm) placed in an anechoic chamber, and a personal computer to be measured was placed on the turntable, and the measurement was performed while rotating. The receiving antenna was placed at a position 10 m from the personal computer to be measured, and the measurement was performed at the angle with the strongest electromagnetic wave when the turntable was rotated. The antenna was measured at a height at which the electromagnetic wave intensity became maximum in an operating range of 1 to 4 m in height, and measurement was performed in both the horizontal direction and the vertical direction.

  The measurement results in Example 3 are shown in FIGS. 10 and 11, and the measurement results in Comparative Example 1 are shown in FIG. From these figures, the polylactic acid-based resin molded body of Example 1 satisfies the VCCI class B standard (step-shaped solid line in the figure), whereas the polylactic acid-based resin molded body of Comparative Example 1 As shown in FIG. 12, when the antenna was set to be vertical in the measurement at 507.93 MHz, the VCCI class B standard (step-shaped solid line in the figure) was greatly exceeded (circled in FIG. 12). Peak). From the above results, it was confirmed that in the polylactic acid-based resin molded body of Example 3, the electromagnetic wave shielding effect was remarkably increased because of the shielding member.

<Dimensional accuracy>
As shown in FIG. 9, the dimensional accuracy of the molded body was evaluated by a distance G (see FIG. 9) of deviation from the design value at the center of the linear portion in the longitudinal direction of the polylactic acid-based resin molded body 1. As a result, as shown in Table 1, in Examples 1 to 4 in which the shield member 20 was inserted, the shift distance G was 1 mm, whereas in Comparative Examples 1 to 4 in which the shield member 20 was not inserted, either It became 2.2 mm or more, and it was confirmed that the dimensional accuracy of the molded body is remarkably improved by inserting the shield member 20.

  In the polylactic acid-based resin molded body 1 obtained as described above, since the shield member 20 made of a metal plate is covered and integrally formed with the polylactic acid-based resin 1, electromagnetic waves are generated by the shield member 20 made of the metal plate. Shielded. For this reason, the electromagnetic interference (EMI) which generate | occur | produces from an electronic device is prevented, and it will be excellent also in the disturbance tolerance (EMS) from an electromagnetic interference.

  Moreover, since the mechanical strength of the polylactic acid-based resin molded body 1 is enhanced by the shield member 20 made of a rolled steel plate, deformation at the time of die-cutting from the mold is prevented, and molding becomes easy.

  Furthermore, even when recycling the polylactic acid-based resin molded body 1, the rolled steel sheet and the polylactic acid-based resin are separated and collected simply by peeling off the shield member 20 made of the rolled steel sheet from the molded body body 10. Can be easily reused.

  Therefore, according to the polylactic acid-based resin molded body 1 of the example, the molding is easy, the electromagnetic shielding property is excellent, and the separation at the time of recycling is easy.

  The shield member 20 has a plurality of holes 20a, and the holes 20a are filled with polylactic acid resin so as to be flush with the surface of the shield member 20. Therefore, the weight can be reduced and the manufacturing cost can be reduced.

<Vibration analysis>
With respect to the natural frequency of the polylactic acid resin molded bodies of Example 1 and Comparative Example 1, numerical analysis was performed according to the finite element method. In the numerical analysis, it was assumed that an optical drive with a maximum rotation speed of 10000 rpm (frequency 167 Hz) was installed as a general optical drive in a personal computer.

As a result, in Comparative Example 1 that does not use a shield member, the third-order natural frequency is 171.1 Hz, which may resonate, whereas in Example 1 that uses a shield member, the natural frequency is up to 145 Hz. It was found that the resonance problem with the optical drive can be avoided.
From the above results, it was confirmed that the resonance countermeasure of the polylactic acid-based resin molded body can be easily achieved by integrally molding with the shield member.

  In the above embodiment, an iron thin plate material is used as the metal thin plate material, but a mesh-like wire netting material may be used instead. Even in this case, the electromagnetic wave can be shielded, and the weight can be further reduced.

  The present invention is not limited to the description of the embodiment of the invention. Various modifications may be included in the present invention as long as those skilled in the art can easily conceive without departing from the description of the scope of claims.

1 is a perspective view of a polylactic acid resin molded body of Example 1. FIG. It is a perspective view of a shield member. 1 is a cross-sectional view of a polylactic acid resin molded body of Example 1. FIG. 2 is a partially enlarged cross-sectional view of a polylactic acid resin molded body of Example 1. FIG. It is sectional drawing of a shield member and a male metal mold | die. It is sectional drawing of the state which covered the shield member on the male metal mold | die. It is sectional drawing in the state which covered the shield member on the male metal mold | die, and also covered the female metal mold | die. It is an expanded sectional view of the gate vicinity in the state which covered the shield member on the male metal mold | die, and also covered the female metal mold | die. It is a bottom view of the polylactic acid-type resin molding 1. It is a graph which shows the electromagnetic environment compatibility test (antenna horizontal) result of the polylactic acid-type resin molding of Example 3. It is a graph which shows the electromagnetic environment compatibility test (antenna perpendicular | vertical) result of the polylactic acid-type resin molding of Example 3. 6 is a graph showing electromagnetic environment compatibility test results of a polylactic acid resin molded article of Comparative Example 1.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Molded object main body 20 ... Shield member 24 ... Through-hole 30 ... 1st metal mold | die (male metal mold | die)
31 ... Second mold (female mold)
32 ... Gate

Claims (3)

  A polylactic acid-based resin molded body, wherein a shield member made of a metal thin plate material and a polylactic acid-based resin covering one surface of the shield member are integrally molded.   2. A plurality of through holes are formed in the shield member, and the through holes are filled with the polylactic acid resin so as to be flush with the surface of the shield member. Polylactic acid resin molded body. A first step of preparing a first mold and a second mold for producing a polylactic acid-based resin molded body;
A second step of closely attaching the shield member to the first mold;
A third step of aligning a second mold with the first mold having the shield member adhered thereto;
A fourth step of injecting a melt of polylactic acid resin from a gate formed by the first mold and the second mold, and a method for producing a polylactic acid resin molded body comprising:
A method for molding a polylactic acid-based resin molding, wherein the melt of the polylactic acid-based resin is injected so as to be pressed against the shield member from the vertical direction toward the first mold side.

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