JP2006103202A - Method of molding polylactic acid resin composition and its molding - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of molding a polylactic acid resin composition having an excellent heat resistance and its molding. <P>SOLUTION: The method of molding the polylactic acid resin composition including the step of repeating quick heating and quick cooling of the surface of a mold cavity comprises the steps of feeding a polylactic acid resin composition improved in crystallization speed into the cavity with a surface temperature of 90-140°C, holding the state for 5-60 seconds for crystallization, quickly cooling the cavity surface to 40-80°C, holding the state for 5-30 seconds and taking out the molding. The polylactic acid resin composition molding is obtained by this molding method and has a heat resistance temperature of ≥110°C. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for molding a polylactic acid resin composition and a molded body of a polylactic acid resin composition obtained by the molding method.

  In recent years, biodegradable resins such as polylactic acid have attracted attention from the viewpoint of environmental conservation. Among the biodegradable resins, polylactic acid is one of the resins with the highest heat resistance, and can be mass-produced, so the cost is low and the utility is high. Furthermore, polylactic acid is a plant-derived resin that can be produced using plants such as corn and sweet potato as raw materials, and can contribute to saving depleted resources such as petroleum.

  However, polylactic acid has a slow crystallization rate and is generally molded with a low-temperature mold and is taken out in an amorphous state by quenching at the time of molding, so that only a molded product having no heat resistance can be obtained.

  Thus, various polylactic acid resin compositions with improved crystallization speeds have been reported in order to bring out the heat resistance of polylactic acid. For example, a resin composition composed of polylactic acid and layered clay mineral (Patent Document 1), a resin composition composed of polylactic acid and crystalline SiO2 (Patent Document 2), polylactic acid and inorganic particles of talc and boron nitride. Resin composition (Patent Document 3), resin composition composed of polylactic acid and crystal nucleating agent such as talc (Patent Document 4), resin composition composed of polylactic acid and layered silicate (Patent Document 5), poly There is a resin composition (Patent Document 6) composed of lactic acid and a (meth) acrylic acid ester compound. However, the normal molding method still requires a very long molding cycle to obtain the desired heat resistance, resulting in poor production efficiency. In the case of molding at a mold temperature in the crystallization peak temperature region of polylactic acid, there is a problem that the cooling time until it is solidified to a take-out state is very long.

  Further, Patent Documents 7 and 8 disclose molding methods in which the mold temperature is repeatedly rapidly cooled and rapidly heated. Patent Document 9 discloses that this molding method is used as a molding method of a resin having a slow crystallization, such as polylactic acid. However, even if this method is used for polylactic acid, it takes a long time to crystallize to a level where the heat resistance is improved, which is not practical. Furthermore, although there is a description of the mold temperature when the resin is supplied, the specific conditions regarding the holding time, the temperature after cooling, and the holding time are not disclosed. It is difficult to conceive of molding conditions for obtaining a molded article of a polylactic acid resin composition having improved properties.

As described above, the optimum molding conditions for the polylactic acid resin composition having an improved crystallization rate are currently unknown.
JP 2003-73538 A Japanese Patent Laid-Open No. 10-87976 JP-A-8-3432 JP 2003-253209 A Japanese Patent Laid-Open No. 9-169893 JP 2003-128901 A Japanese Patent Laid-Open No. 10-100196 JP 2001-150506 A JP 2001-191378 A

  The present invention is intended to solve the above problems, and according to the present invention, a molded body of a polylactic acid resin composition having excellent heat resistance can be easily obtained.

  As a result of intensive studies to solve the above problems, the present inventors have made polylactic acid resin with improved crystallization speed as a molding method for obtaining a molded product of polylactic acid resin composition having excellent heat resistance. The present inventors have found a method of repeatedly quenching and rapidly heating the surface of a mold cavity with a specific temperature condition, holding time, and heating / cooling rate by using the composition.

  That is, the molding method of the polylactic acid resin composition of the present invention is a molding method in which the surface of the mold cavity is repeatedly rapidly cooled and heated, and the crystallization rate is improved in the cavity having a surface temperature of 90 to 140 ° C. The lactic acid resin composition is supplied, held and crystallized for 5 to 60 seconds, and then the cavity surface is rapidly cooled to 40 to 80 ° C. and held for 5 to 30 seconds, and the molded product is taken out.

  In the method for molding a polylactic acid resin composition of the present invention, the polylactic acid resin composition having an improved crystallization rate has a heat of crystallization of 20 J when differential thermal analysis (DSC) is performed at a temperature drop rate of 2 ° C./min. / G or more of the resin composition.

  In the method for molding a polylactic acid resin composition of the present invention, the mold temperature heating and cooling rates are 60 ° C./min or more.

  Furthermore, the molded body of the polylactic acid resin composition of the present invention is obtained by the molding method and has a heat resistant temperature of 110 ° C. or higher.

  ADVANTAGE OF THE INVENTION According to this invention, the molding method and molded object of the polylactic acid resin composition which have the outstanding heat resistance are provided. Furthermore, according to the present invention, since the plant-derived polylactic acid resin composition is used, the dependence on petroleum-based products is low, and it is possible to contribute to saving depleted resources.

  Hereinafter, the best mode for carrying out the present invention will be described in detail.

  In the present invention, the mold surface temperature when supplying the polylactic acid resin composition with improved crystallization speed to the mold cavity needs to be 90 to 140 ° C. Preferably it is 100-120 degreeC, More preferably, the range of 105-110 degreeC is mentioned. If it is less than 90 ° C., it takes a long time until crystallization proceeds to the extent that heat resistance is expressed, the molding cycle becomes long, and the resin stays in the cylinder and deteriorates. On the other hand, if it exceeds 140 ° C., it is close to the melting point of the polylactic acid resin, so it is difficult to solidify and crystallization does not proceed.

  In the present invention, the holding time after supplying the resin into the cavity needs to be held for 5 to 60 seconds, preferably 5 to 45 seconds, and more preferably 5 to 30 seconds. If it is less than 5 seconds, crystallization does not proceed sufficiently, and the resulting molded product has no heat resistance. If it exceeds 60 seconds, the crystallization has progressed sufficiently, and the heat resistance cannot be improved for a long holding time, and the total molding cycle becomes long.

  Thereafter, the cavity surface is rapidly cooled, and the molded product is taken out. At this time, the cavity surface temperature should be 40 to 80 ° C., preferably 50 to 70 ° C. If it is less than 40 degreeC, the cooling time of a metal mold | die will become long, and also the improvement effect of mold release property has reached the saturation state. Moreover, when it exceeds 80 degreeC, the mold release property of a molded article will worsen and a moldability will be inferior.

  Furthermore, the holding time after cooling needs to be 5 to 30 seconds, preferably 10 to 20 seconds. If it is less than 5 seconds, the cooling is not sufficient, the releasability of the molded product is deteriorated, and the moldability is inferior. If it exceeds 30 seconds, it is sufficiently cooled, the effect of improving the releasability has reached saturation, and the total molding cycle becomes longer.

  The polylactic acid resin composition having an improved crystallization rate in the present invention has a heat of crystallization of 20 J / g or more, preferably 30 J / g or more when differential thermal analysis (DSC) is performed at a temperature drop rate of 2 ° C./min. More preferably, the resin composition is 40 J / g or more. If it is less than 20 J / g, the crystallization rate is not sufficient, and it is difficult to obtain a molded product exhibiting heat resistance even by the molding method of the present invention.

  Examples of polylactic acid resin compositions with improved crystallization speed include polylactic acid and talc, crystalline SiO2, aliphatic carboxylic acid amides, aliphatic carboxylates, aliphatic alcohols and aliphatic carboxylic acid esters. A resin composition comprising polylactic acid and a layered clay mineral, and a layered silicate, and a resin composition comprising polylactic acid and a (meth) acrylic acid ester compound. Examples include, but are not limited to, polylactic acid resin manufactured by Co., Ltd., Terramac TE-6100 series, TE-7000 series, TE-8000 series, and the like.

  Layered clay minerals include smectites such as montmorillonite, beidellite, saponite and hectorite; kaolinites such as kaolinite and halosite; vermiculites such as dioctahedral vermiculite and trioctahedral vermiculite; teniolite and tetralithic Examples include mica, mascobite, illite, sericite, phlogopite and biotite.

  The layered silicate is an ammonium salt having one or more hydroxyl groups in the molecule, such as dihydroxyethylmethyloctadecylammonium, methyldodecylbis (polyethylene glycol) ammonium, methyldiethyl (polypropyleneglycol) ammonium, 2-hydroxyethyltriphenylphosphonium. The treated product is particularly preferred because of its high affinity with polylactic acid resin and improved dispersibility of the layered silicate.

  (Meth) acrylic acid ester compounds include glycidyl methacrylate, glycidyl acrylate, glycerol dimethacrylate, trimethylolpropane trimethacrylate, trimethylolpropane triacrylate, allyloxy polyethylene glycol monoacrylate, allyloxy polyethylene glycol monomethacrylate, polyethylene glycol dimethacrylate, Polyethylene glycol diacrylate, polypropylene glycol dimethacrylate, polypropylene glycol diacrylate, polytetramethylene glycol dimethacrylate, and these alkylene glycol parts may be copolymers of alkylenes of various lengths, butanediol methacrylate, butanediol acrylate Etc. In particular the invention is not limited thereto.

  These polylactic acid resin compositions are preferably made into a polylactic acid resin composition of MFR 1 to 15 by blending with the above compound using a polylactic acid resin having a melt flow rate (MFR) of 10 to 50.

  Furthermore, the mold temperature heating and cooling rate is 60 ° C./min or more, preferably 70 ° C./min or more, more preferably 80 ° C./min or more. When the temperature is less than 60 ° C./min, it takes time to reach a predetermined temperature, and the molding cycle becomes long, which is not preferable.

  As a method of repeatedly quenching and rapidly heating the mold cavity surface at the heating rate and the cooling rate described above, there is a method of circulating the heating medium and the cooling medium through the flow path in the mold. The heating medium is at least one selected from hot water, pressurized water, and steam, and the cooling medium is preferably cooling water. The heating method may use a heater or induction heating.

  Moreover, it is preferable that the metal mold | die used by this invention is a structure which can switch the heating and cooling of the surface of a metal mold cavity in a short time. For example, it is preferable that the mold is provided with a flow path capable of alternately flowing a heating medium and a cooling medium in the vicinity of the cavity surface.

  In addition, as a molded product of the polylactic acid resin composition of the present invention, specifically, dishes such as serving trays, dishes, bowls, bowls, chopsticks, spoons, forks, knives, caps for containers, rulers, writing instruments, CD cases, etc. Office supplies, kitchen triangle corners, trash cans, washbasins, toothbrushes, combs, hangers and other daily necessities, plastic toys, air conditioner panels, refrigerator trays, various resin cases for appliances, bumpers, instrument panels And resin parts for automobiles such as door trims. In addition, the form of a molded object is not specifically limited, What kind of form may be sufficient if it can manufacture with an injection molding machine.

Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the examples. The measuring method used for evaluation of the resin composition of an Example and a comparative example is as follows.
(1) Tensile test:
Tensile strength and tensile elongation were measured in accordance with ISO standards (ISO-527).
(2) Bending test:
The flexural strength and flexural modulus were measured according to the ISO standard (ISO-178).
(3) Impact strength:
The notched Charpy impact strength was measured according to the ISO standard (ISO-179).
(4) Thermal deformation temperature (DTUL):
According to the ISO standard (ISO-75), the heat distortion temperature was measured at a load of 0.45 MPa.
(5) Heat of crystallization:
It calculated | required from the crystallization peak at the time of temperature-falling at 2 degree-C / min after complete melting using a DSC apparatus (Pyrisl DSC by Perkin Elmer).
(6) Melt flow rate (MFR):
In accordance with JIS K7210, measurement was performed under the conditions of Appendix A, Table 1, F.

[Example 1]
Using Unitika Terramac resin TE-7000 (MFR1) as a polylactic acid resin composition with improved crystallization speed, the resin is supplied into a cavity with a surface temperature of 120 ° C., held for 20 seconds, crystallized, and then cooled. The cavity surface was rapidly cooled to 60 ° C. at a rate of 60 ° C./min and held for 10 seconds, and the molded body was taken out. Subsequently, the cavity surface is rapidly heated to 120 ° C. at a heating rate of 60 ° C./min, and the next shot is started. The results are shown in Table 1.

[Example 2]
Using Unitika Terramac resin TE-7000 (MFR1) as a polylactic acid resin composition with improved crystallization speed, the resin is supplied into a cavity having a surface temperature of 135 ° C., held for 5 seconds, crystallized, and then cooled. The cavity surface was rapidly cooled to 80 ° C. at a rate of 60 ° C./min and held for 15 seconds, and the molded body was taken out. Subsequently, the cavity surface is rapidly heated to 135 ° C. at a heating rate of 60 ° C./min, and the next shot is started. The results are shown in Table 1.

Example 3
Using Unitika Terramac resin TE-7000 (MFR1) as a polylactic acid resin composition with improved crystallization speed, the resin is supplied into a cavity having a surface temperature of 105 ° C., held for 45 seconds, crystallized, and then cooled. The cavity surface was rapidly cooled to 45 ° C. at a rate of 60 ° C./min and held for 5 seconds, and the molded body was taken out. Subsequently, the cavity surface is rapidly heated to 105 ° C. at a heating rate of 60 ° C./min, and the next shot is started. The results are shown in Table 1.

Example 4
Using Unitika Terramac resin TE-7307 (MFR1) as a polylactic acid resin composition with improved crystallization speed, the resin is supplied into a cavity having a surface temperature of 120 ° C., held for 20 seconds, crystallized, and then cooled. The cavity surface was rapidly cooled to 60 ° C. at a rate of 60 ° C./min and held for 10 seconds, and the molded body was taken out. Subsequently, the cavity surface is rapidly heated to 120 ° C. at a heating rate of 60 ° C./min, and the next shot is started. The results are shown in Table 1.

Example 5
Using Unitika Terramac resin TE-8210 (MFR1) as a polylactic acid resin composition with improved crystallization speed, the resin is supplied into a cavity having a surface temperature of 120 ° C., held for 20 seconds, crystallized, and then cooled. The cavity surface was rapidly cooled to 60 ° C. at a rate of 60 ° C./min and held for 10 seconds, and the molded body was taken out. Subsequently, the cavity surface is rapidly heated to 120 ° C. at a heating rate of 60 ° C./min, and the next shot is started. The results are shown in Table 1.

[Comparative Example 1]
Using Unitika Terramac resin TE-7000 (MFR1) as a polylactic acid resin composition with improved crystallization speed, the mold temperature is maintained at 105 ° C. for 150 seconds and crystallized by a normal molding method, and the molded product is taken out. It was. The results are shown in Table 2.

[Comparative Example 2]
Using Unitika Terramac resin TE-4000 (MFR20) as a normal polylactic acid resin, the mold temperature was held at 150 ° C. for 150 seconds and crystallized by a normal molding method, and the molded body was taken out. The results are shown in Table 2.

[Comparative Example 3]
Using Unitika Terramac resin TE-4000 (MFR20) as a normal polylactic acid resin, the resin is supplied into a cavity with a surface temperature of 105 ° C., held for 60 seconds, crystallized, and then cooled at a cooling rate of 60 ° C./min. The surface was rapidly cooled to 45 ° C. and held for 5 seconds, and the molded product was taken out. Subsequently, the cavity surface is rapidly heated to 105 ° C. at a heating rate of 60 ° C./min, and the next shot is started. The results are shown in Table 2.

[Comparative Example 4]
Using Unitika Terramac resin TP-4000 (MFR5) as a normal polylactic acid resin, the resin is supplied into a cavity having a surface temperature of 105 ° C., held for 60 seconds, crystallized, and then cooled at a cooling rate of 60 ° C./min. The surface was rapidly cooled to 45 ° C. and held for 5 seconds, and the molded product was taken out. Subsequently, the cavity surface is rapidly heated to 105 ° C. at a heating rate of 60 ° C./min, and the next shot is started. The results are shown in Table 2.

  Examples 1 to 5 are molding methods according to the present invention, and the surface of the mold cavity is repeatedly rapidly and rapidly quenched at a specific temperature condition, holding time, and heating / cooling rate using the polylactic acid resin composition having an improved crystallization rate. Since a heating method was used, a molded article of a polylactic acid resin composition having excellent moldability and particularly heat resistance of 110 ° C. or higher could be obtained.

  Comparative Example 1 uses a polylactic acid resin composition having an improved crystallization speed. However, since it is a normal molding method, a molded product of heat-resistant polylactic acid resin can be obtained, but the molding cycle is There is a problem that the molded body is partially deformed at the time of mold release.

  Since Comparative Example 2 is a normal molding method using ordinary polylactic acid resin, crystallization does not proceed during molding, and the mold temperature remains high, so that it can be taken out from the mold without deforming the molded body. There wasn't.

  Although Comparative Examples 3 to 4 used a method in which the surface of the mold cavity was repeatedly rapidly and rapidly heated at a specific temperature condition, holding time, and heating / cooling rate, a normal polylactic acid resin was used. However, crystallization did not proceed sufficiently, and a molded product of polylactic acid resin having heat resistance could not be obtained.

Claims (4)

  In a molding method in which the surface of a mold cavity is repeatedly rapidly cooled and rapidly heated, a polylactic acid resin composition having an improved crystallization rate is supplied into a cavity having a surface temperature of 90 to 140 ° C. and held for 5 to 60 seconds. Then, the cavity surface is rapidly cooled to 40 to 80 ° C., held for 5 to 30 seconds, and the molded product is taken out.   The polylactic acid resin composition having an improved crystallization rate is a resin composition having a heat of crystallization of 20 J / g or more when differential thermal analysis (DSC) is performed at a temperature drop rate of 2 ° C./min. A method for molding the polylactic acid resin composition according to claim 1.   The method for molding a polylactic acid resin composition according to any one of claims 1 to 2, wherein the mold temperature heating and cooling rates are 60 ° C / min or more.   A molded article of a polylactic acid resin composition obtained by the molding method according to any one of claims 1 to 3 and having a heat resistant temperature of 110 ° C or higher.