JP5062941B2 - Biodegradable resin injection molding method - Google Patents

Description

  The present invention relates to an injection molding method using a biodegradable resin, and more particularly to an injection molding method of a polylactic acid resin that improves impact strength and heat resistance temperature and facilitates processing of a molded product.

  In recent years, electronic devices such as notebook computers, mobile phones, and PDAs have been increasingly mobile. Along with this, the casing of portable electronic devices is required to be small and light, to withstand the heat generated by built-in electronic components, and to withstand impacts such as collision and dropping. In order to satisfy these conditions, the housing of the electronic device uses a light metal material and a resin together.

  On the other hand, products that are friendly to the global environment, that is, recyclable products and manufacturing methods are being studied. For this reason, biodegradable resins have begun to be used in place of light metals and resins. Polylactic acid is applied as this biodegradable resin. The casing mainly composed of polylactic acid is roughly decomposed into water and carbon dioxide by microorganisms. As a result, a resin based on polylactic acid is a product suitable for recycling.

FIG. 2 is a front view of a housing made of polylactic acid resin.
This resin casing is approximately 265 mm long, approximately 10 mm long, approximately 175 mm wide, and approximately 0.8 mm thick. This housing is generally made by an injection molding method. Specifically, the polylactic acid resin heated and melted is injected into the cavity of the mold of the injection molding machine, the polylactic acid resin is filled into the cavity, and the polylactic acid resin is individualized. Subsequently, the individualized polylactic acid resin is released from the cavity to form a molded product. That is, the mold temperature is manufactured without changing the mold at a constant temperature, for example, 20 degrees C to 40 degrees C, until the molded product is released from the injection of the polylactic acid resin.

  However, the casing made of this polylactic acid resin is lower than the impact resistance strength and heat resistance temperature of the specified conditions. For this reason, it is necessary to improve impact strength and heat resistance temperature.

These impact strength and heat resistance temperature are improved by promoting crystallization of the biodegradable resin. As a specific technique for promoting crystallization, there is a technique described in Patent Document 1 below. In the molding method disclosed in Patent Document 1, a crystal nucleating agent such as talc, silica, and calcium lactate is added to a biodegradable resin in order to promote crystallization.
JP, 08-193165, A There is a technique indicated in the following patent documents 2 as other techniques. In the molding method disclosed in Patent Document 2, in order to promote crystallization, a biodegradable resin is formed into a molded product and then annealed to promote crystallization of the molded product. Japanese Patent Laid-Open No. 08-73628

  However, in the said patent document 1, a molded article becomes weak. Furthermore, sink marks occur on the surface of the molded product. For this reason, it is unsuitable for a housing. Next, in Patent Document 2, it takes a long time for the annealing process and is unsuitable for mass production, and the molded product is deformed during the annealing process. Further, in the injection molding method in which the mold as described above is kept constant at a low temperature of 20 ° C. to 40 ° C., the crystallization of polylactic acid is slow and requires a lot of time. For this reason, if it is performed at a temperature for promoting crystallization, for example, a constant temperature of 90 to 110 ° C., it takes a long time to cool the molded product. When the temperature is higher than the glass transition temperature, the crystallized portion and the noncrystallized portion, especially when the crystal portion is crystallized, the noncrystallized portion is softened and soft. For this reason, the molded product is deformed when released from the mold, and burrs are generated on the end surface of the product, and sink marks are formed on the surface of the product, resulting in a defective product. For this reason, it is necessary to remove the burrs generated in the molded product, and the yield decreases due to sink marks generated in the molded product.

  The object of the present invention is to improve the impact resistance strength and heat resistance temperature of molded products made of polylactic acid, and the molded products are not brittle, the molded products are not deformed, and further processing time is not required and the yield is improved. Thus, a method for producing a biodegradable resin optimal for mass production is provided.

  The present invention relates to an injection molding method in which the biodegradable resin is cooled and solidified after the biodegradable resin is injected into a mold, and the biodegradable resin has a glass transition temperature or higher and the biodegradable resin has a maximum crystallization. A step of injecting into the mold cavity below the temperature of the speed, and then maintaining the temperature within ± 10 degrees C for a predetermined time from the temperature of the maximum speed of crystallization of the biodegradable resin in order to crystallize the biodegradable resin And a step of releasing the biodegradable resin at a temperature lower than or equal to 10 ° C. from the glass transition temperature.

As described above, since the biodegradable resin is injected into the mold having a temperature equal to or higher than the glass transition temperature and lower than the temperature of the maximum crystallization rate of polylactic acid, no flash is generated on the molded product. Furthermore, since the biodegradable resin is maintained at a predetermined crystallization time at ± 10 ° C. from the maximum crystallization temperature of polylactic acid, crystallization of the biodegradable resin can be promoted. In addition, the biodegradable resin is cooled to a temperature lower by 10 ° C. or more from the glass transition temperature. For this reason, there is no shape deformation when the molded product is released from the mold.

  An embodiment of the present invention will be described.

  Next, the present invention will be specifically described based on examples.

First, a biodegradable resin composition that is a molding material is prepared.
<Preparation of biodegradable resin>
Polylactic acid (trade name; Lacia H-100J, manufactured by Mitsui Chemicals, Inc.) and polybrene succinate (trade name, manufactured by Showa Polymer Co., Ltd .; Bionore 1020) were used.

  A biodegradable resin was prepared using a kneader between the polylactic acid 90% wt and the polybrene succinate 10% wt. As the kneading machine, Nippon Steel Works Co., Ltd. trade name; TEX30α was used. The manufacturing conditions are a cylinder temperature of 180 ° C. and a screw rotation speed of 150 rpm. Samples 1 to 8 were prepared from the kneaded resin using an injection molding machine (product name α-300B, manufactured by FANUC Corporation) under the following production conditions. The molding conditions of this injection molding machine are a cylinder temperature of 180 ° C., an injection speed of 25 mm / second, and a holding pressure of 1800 Kg / cm. The mold temperature control of this injection molding machine used a system made up of a temperature rising simple boiler and valve unit made by Cisco. The temperature increase rate is about 2.8 degrees C / second, and the temperature decrease rate is about 1.5 degrees C / second. An Si02 inorganic film is provided on the cavity inner wall of the mold. By providing this inorganic film, the temperature of the inner wall of the cavity of the mold can be made uniform. This inorganic film is formed by spraying Si02 using a spray. In addition to SiO2, at least one of TiAlN, fluorine, PBI (polybenzimidazole) and the like can be used.

Next, the production of each sample will be described.
<Sample manufacturing conditions>
FIG. 1 is a diagram showing a temperature cycle of a mold for producing a sample or a polylactic acid resin. In FIG. 1, T2 is a mold temperature (degree C) when injecting the polylactic acid resin, Tmax is a temperature for crystallization of the polylactic acid resin (degree C), S1 is a temperature holding time (second), and S2 is crystallization. The process time (seconds) and Tmin are temperatures (degrees C) at which the sample is released from the mold. The initial temperature of the mold temperature is about 30 degrees C. This mold is heated at a rate of temperature increase of 2.8 degrees C / sec. When the mold temperature reaches T2 degrees C, the polylactic acid resin is injected from the kneader into the mold, that is, into the cavity. The polylactic acid resin is held at the Tmax temperature degree C for S1 time. After a predetermined time elapses, cooling is performed at a temperature lowering rate of 1.5 degrees C / second. The sample that has been cooled and cooled at the Tmin temperature C during the temperature reduction is released from the mold. Therefore, the resin is crystallized within the period of the crystallization time S2. The molded product is repeatedly made in this temperature cycle.

The specific production conditions for each sample are as described below.
The manufacturing conditions of sample 1 are T2 of 60 degrees C, Tmax of 100 degrees C, S1 of 0 seconds, S2 of 64 seconds, and Tmin of 30 degrees C.
The production conditions of Sample 2 are T2; 60 degrees C, Tmax; 100 degrees C, S1 is 60 seconds, S2: 124 seconds, Tmin: 30 degrees C.
-The manufacturing conditions of the sample 3 are T2; 60 degree C, Tmax; 100 degree C, S1 for 120 seconds, S2; 184 seconds, Tmin;
-The manufacturing conditions of the sample 4 are T2; 40 degree C, Tmax; 100 degree C, S1 for 60 seconds, S2; 131 seconds, Tmin; That is, the manufacturing condition of the sample 4 is that the mold temperature when the polylactic acid resin is injected is 40 ° C., which is lower than the glass transition temperature of the polylactic acid resin of 60 to 100 ° C.
-The manufacturing conditions of the sample 5 are T2; 100 degree C, Tmax; 100 degree C, S1 for 60 seconds, S2; 110 seconds, Tmin; 30 degree C.
-The manufacturing conditions of the sample 6 are T2; 60 degree C, Tmax; 130 degree C, S1 for 60 seconds, S2; 162 seconds, Tmin; 30 degrees C. That is, the manufacturing conditions of the sample 6 are that the temperature Tmax for crystallizing the sample is 130 ° C., and the crystallization speed of polylactic acid exceeds 90 to 110 ° C.
-The manufacturing conditions of the sample 7 are T2; 30 degree C, Tmax; 30 degree C, S1 is 0 second, S2: 68 second, Tmin; 30 degree C. That is, the manufacturing condition of the sample 7 is that the mold temperature T2 when the polylactic acid resin is injected, the temperature mold temperature Tmax for crystallizing the sample, and the temperature Tmin for releasing the sample from the mold are always constant at 30 degrees C. It is kept. In other words, it is the general conventional technique described in the prior art.
-The manufacturing conditions of the sample 8 are T2; 100 degree C, Tmax; 100 degree C, S1 is 0 second, S2: 208 second, Tmin; 100 degree C. In other words, the manufacturing condition of the sample 8 is that the mold temperature T2 when the sample is injected, the temperature mold temperature Tmax for crystallizing the sample, and the temperature Tmin for releasing the sample from the mold are always kept constant at 100 degrees C. ing.
<Evaluation of sample>
Each sample was evaluated for crystallinity (DSC), impact strength, heat resistance temperature, burrs, sink marks and deformation of the molded product.
(1) Crystallinity (DSC) was measured using a differential scanning calorimeter (trade name DSC100, manufactured by Seiko Denshi Co., Ltd.). The differential scanning calorimeter is obtained by the following arithmetic: Crystallinity (DSC)% = (ΔHm−ΔHcc) ÷ ΔHm
(However, ΔHm; Crystal melting peak calorific value ΔHcc: Crystallization peak calorific value at the time of temperature rise.) The larger the numerical value (DSC)%, the more crystallized, the smaller the crystallizing. Indicates that it has not been.
(2) Impact strength was measured by measuring Izod impact strength. Specifically, using an Izod impact tester (trade name: B-121202403, manufactured by Toyo Seiki Co., Ltd.), an Izod impact test was performed in accordance with JIS 7110.
(3) Evaluation of heat-resistant temperature was performed by load deflection temperature ISO75 test. Specifically, a test specimen (length 80 mm × width 10 mm × thickness 4 mm) having a deflection temperature under load is prepared, and both ends are set so that the distance between fulcrums of the specimen is 64 mm in a heat transferable liquid. Fixed. Then, a bending stress of 1.80 MPa is applied to the central portion of the test piece, and the liquid is heated at a heating rate of 120 ° C./hr, and the temperature when the central portion of the test piece has a deflection of 0.32 mm is set. Measure and evaluate.
(4) The evaluation of burrs, sink marks and deformation of the molded product was performed visually. The burr is a resin in which a resin entering the gap between the pressed molds is formed in the molded product. When an unnecessary object of 0.1 mm or more is found on the end surface of the molded product, it is evaluated that there is a burr. Next, sink marks are depressions generated on the surface of the molded product, and a visible depth of, for example, 0.1 mm or more was evaluated as having sink marks. Subsequently, the deformation was evaluated when the outer shape of the molded product was deformed by 0.1 mm or more inward or outward.

  Each said evaluation was performed about the samples 1-8. The results of each evaluation are shown in Table 1.

＜試料の評価結果＞
試料１は温度保持時間Ｓ１が０（秒），結晶化工程時間Ｓ２が６４（秒）であるために結晶化が５８％であり、結晶化度が低い。このためアイゾット衝撃強度が低く７．８(Kgf・cm/ 平方cm) である。耐熱温度は低く６０度Ｃである。そしてバリ、ひけ、変形は無い。
試料２、３、５は結晶化が１００％であり、バリ、ひけ、変形は無い。
試料４は結晶化が１００％である。しかしＴ２がガラス転移温度以下のために、射出時に樹脂の表層面が個化された後、再溶融されながら流入する。この時に金型内圧力が増し、金型相互の隙間に樹脂が入り込みバリが発生した。

<Sample evaluation results>
Since sample 1 has a temperature holding time S1 of 0 (seconds) and a crystallization process time S2 of 64 (seconds), the crystallization is 58% and the crystallinity is low. Therefore, the Izod impact strength is low, 7.8 (Kgf · cm / square cm). The heat-resistant temperature is as low as 60 degrees C. And there are no burr, sink, and deformation.
Samples 2, 3, and 5 are 100% crystallized and have no burrs, sink marks, or deformation.
Sample 4 has 100% crystallization. However, since T2 is equal to or lower than the glass transition temperature, the resin surface layer is individualized at the time of injection, and then flows in while being remelted. At this time, the pressure inside the mold increased, and the resin entered the gap between the molds to generate burrs.

  Sample 6 has 100% crystallization. However, since Tmax is equal to or higher than the temperature of the maximum crystallization speed, the viscosity of the resin is low, and the resin easily flows and enters the gaps between the molds to generate burrs. Further, the surface of the molded product is high temperature, and the surface temperature of the molded product becomes non-uniform due to this high temperature, which seems to have caused sink marks. And since the molded product was released above the glass transition temperature, the molded product was deformed by pressing the extrusion pin.

  In the sample 7, the temperature of T2 is constant at 30 ° C., and the crystallization process time S2 is 68 (seconds), which is a short time. For this reason, crystallization is low and is 38%. Therefore, the Izod impact strength is low, 7.8 (Kgf · cm / square cm). The heat-resistant temperature is as low as 60 degrees C. Further, the surface of the molded product was a low temperature below the glass transition temperature, and a part of the surface of the molded product contracted, and the surface was individualized in a non-uniform state to generate sink marks.

  Sample 8 had a constant temperature of 100 ° C., and the polylactic acid resin was not individualized. For this reason, the molded product was deformed when it was released, and burrs were generated on the entire end surface of the molded product. Therefore, Izod impact strength and heat resistant temperature could not be measured.

  As a result, the method for producing a molded product mainly composed of a biodegradable resin injects polylactic acid resin into a mold having a temperature higher than the glass transition temperature and lower than the maximum crystallization speed of polylactic acid, thereby maximizing crystallization of polylactic acid. After the resin is crystallized by holding at the speed temperature for a predetermined time, the molded product is preferably released from the mold by cooling to a temperature lower than the glass transition temperature by 40 ° C. or more.

  Similar effects can be obtained when the biodegradable resin is composed of at least one of polylactic acid, polyhydroxybutyrate, and polybrene succinate in addition to the mixture of polylactic acid and polycaprolactone.

  Silicone flame retardants, organometallic salt flame retardants, organophosphorous flame retardants, metal oxide flame retardants, metal hydroxide flame retardants, and the like can be further added to the biodegradable resin composition. . Thereby, a flame retardance improves and a fire spread can be suppressed, the fluidity | liquidity of a biodegradable resin composition improves, and a moldability can be made favorable.

  Examples of the silicone-based flame retardant include alkyl siloxane (trade name “X40-9805” manufactured by Shin-Etsu Silicone Co., Ltd.) and alkyl phenyl siloxane (trade name “MB50-315” manufactured by Dow Corning Silicone Co., Ltd.).

  Specific examples of the organic metal salt flame retardant include organic sulfonic acid metal salts such as potassium trichlorobenzene sulfonate, potassium perfluorobutane sulfonate, potassium diphenylsulfone-3-sulfonate, aromatic sulfonic imide metal salts, Alternatively, a polystyrene sulfonate alkali metal salt in which a sulfonic acid metal salt, a sulfate metal salt, a phosphate metal salt, or a borate metal salt is bonded to an aromatic ring of an aromatic group-containing polymer such as a styrene polymer or polyphenylene ether. Can be used. Examples of the organic phosphorus flame retardant include phosphine, phosphine oxide, biphosphine, phosphonium salt, phosphinate, phosphate ester, phosphite ester, and the like. More specifically, triphenyl phosphate, methyl neopentyl phosphite, pentaerythritol diethyl diphosphite, methyl neopentyl phosphate, phenyl neopentyl phosphate, pentaerythritol diphenyl diphosphate, dicyclopentyl high positive phosphate, Dineopentyl hypophosphite, phenyl pyrocatechol phosphite, ethyl pyrocatechol phosphate, dipyrrocatechol high positive phosphate and the like can be used.

  As said metal oxide type flame retardant, magnesium oxide etc. can be used, for example. As the metal hydroxide flame retardant, for example, magnesium hydroxide can be used.

  The biodegradable resin composition may further contain a lactic acid polyester as a modifier. This not only improves impact resistance, but also improves the flame retardant effect. As the lactic acid-based polyester, a polymer obtained by copolymerizing lactic acid, dicarboxylic acid and diol can be used. Examples of the dicarboxylic acid include succinic acid, adipic acid, sebacic acid, decanedicarboxylic acid, cyclohexanedicarboxylic acid, phthalic acid, terephthalic acid, and isophthalic acid. Examples of the diol include ethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, and the like. As the lactic acid-based polyester, for example, trade name: EXP-PD-150 manufactured by Dainippon Ink Co., Ltd. can be used. Further, as other modifiers, 1,3-butanediol sebacate and the like can be used.

  Mica, montmorillonite, kaolin and the like can be further added to the biodegradable resin composition as a filler.

  The biodegradable resin composition may further contain hemp fibers, chitin / chitosan, coconut shell fibers, kenaf, short fibers derived therefrom, powders derived therefrom, and the like as fillers. Thereby, the rigidity and heat resistance of a molded object can be improved. These are natural materials and do not deteriorate the biodegradability of the molded body.

  The biodegradable resin composition further contains, as a filler, glass fiber, carbon fiber, glass flake, glass bead, ceramic bead, asbestos, wollastonite, clay, mica, sericite, zeolite, bentonite, montmorillonite, synthetic mica. , Dolomite, kaolin, fine powdered silicic acid, feldspar powder, potassium titanate, shirasu balloon, calcium carbonate, magnesium carbonate, barium sulfate, calcium oxide, aluminum oxide, titanium oxide, aluminum silicate, silicon oxide, gypsum, Novaclite, dosonite or It is preferable to add clay or the like. Thereby, the rigidity of a molded object can be enlarged. The filler may be subjected to surface treatment such as coating with polylactic acid or fatty acid, or may be surface treated with a silane coupling agent or the like.

  The biodegradable resin composition may contain other additives as necessary. For example, a carbodiimide compound, an isocyanate compound, an oxazoline compound, or the like can be added as a substance capable of suppressing the hydrolysis of the resin. Moreover, plasticizers, such as polyester and polyether other than lactic acid type, can also be added and used as needed. Furthermore, weather resistance improvers, antioxidants, heat stabilizers (hindered phenols, hydroquinones, phosphites and their substitutes), ultraviolet absorbers (resorcinol, salicylate, benzotriazole, benzophenone, etc.), lubricants (graphite) , Fluororesins, etc.), mold release agents (montanic acid and salts thereof, esters thereof, half esters thereof, stearyl alcohol, stearamide and polyethylene wax, etc.), coloring agents (dyes comprising nigrosine and pigments comprising cadmium sulfide and phthalocyanine) An inhibitor (phosphite, hypophosphite, etc.), a compatibilizing agent and the like can be blended. These kneadings improve heat resistance, bending strength, impact strength, flame retardancy, and the like. The biodegradable resin mixed with these materials is optimally applied to a molded body such as a casing for an electronic device typified by a notebook personal computer or a mobile phone by using this manufacturing method.

  The method for producing a molded article mainly composed of the biodegradable resin of the present invention improves the impact strength and heat resistance temperature of a molded article made of polylactic acid, and the molded article is not brittle and the molded article is not deformed. In addition, it is possible to provide a method for producing a biodegradable resin that is optimal for mass production by improving the yield without requiring much processing time.

The figure which shows the temperature cycle of the metal mold | die or polylactic acid resin which produces a sample, It is a schematic diagram of the housing | casing which consists of polylactic acid resin.

Explanation of symbols

T2: temperature at which the sample is injected into the mold (degree C),
Tmax: temperature at which the sample is crystallized (degree C),
S2: crystallization process time (seconds),
Tmin: temperature (degree C) at which the sample is released from the mold.

Claims (3)

In the injection molding method of cooling and solidifying the biodegradable resin after injecting the biodegradable resin into the mold,
The biodegradable resin glass transition temperature or higher, a step of injecting the first of said mold cavity temperature is and crystallization below the maximum speed of the temperature of the biodegradable resin,
To subsequently crystallizing the biodegradable resin, there the temperature of the crystallization the maximum speed of the biodegradable resin to a temperature range of ± 10 ° C, and the second is higher than the first temperature second temperature And holding for a predetermined time in
Then injection molding method of the biodegradable resin, characterized in that and a step of releasing at 10 ° C or more lower temperature below the biodegradable resin from the glass transition temperature. The biodegradable resin is polylactic acid, polyhydroxybutyrate, injection molding process of a biodegradable resin according to claim 1, characterized by comprising at least one of polybutylene Chi succinate.   The biodegradable resin injection molding method according to claim 1 or 2, wherein the biodegradable resin is released from the glass transition temperature at a temperature lower by 40 ° C or more.

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