JP4745135B2 - Stretch-molding resin composition, stretch-molded container, and method for producing stretch-molded container - Google Patents

Description

  The present invention relates to a resin composition suitable for a stretch-molded container having excellent heat resistance and gas barrier properties.

  In recent years, from the viewpoint of environmental protection, biodegradable resins that are converted into harmless degradation products by the action of microorganisms or the like in the natural environment have attracted attention.

  However, biodegradable resins, particularly aliphatic polyesters, are insufficient when used as fluid storage containers such as cosmetic containers and food storage containers, and when used at high temperatures due to insufficient heat resistance. Deform. Furthermore, since the rigidity at high temperature is low, there are practical problems such as low molding processability when the blow container is molded at high temperature, and there is a limit to the use.

  In general, in a crystalline polymer, it is possible to improve gas barrier properties and heat resistance by advancing crystallization. However, in the case of an aliphatic polyester such as polylactic acid, the crystallization rate is low, and even when the mold temperature is set to 90 to 120 ° C., which is optimal for crystallization, it remains in a semi-molten state. By setting the mold temperature close to room temperature, it was finally cooled and solidified, but only a very low degree of crystallinity was obtained (for example, Non-Patent Document 1).

  In polyethylene terephthalate (PET) containers, a method has been proposed in which a crystallizing resin is added to control the crystallization rate of PET to improve molding processability (Patent Documents 1 and 2). However, since the half crystallization time at 180 ° C. is as short as 30 to 100 seconds (0.5 to 1.7 minutes), the crystallization rate is too high when applied to aliphatic polyesters, particularly polylactic acid. There was a problem that a good moldability could not be obtained.

  On the other hand, for the purpose of producing a blow container having excellent heat resistance and molding processability using aliphatic polyester, there are substantially two peaks in the crystallization temperature range of 75 to 160 ° C. measured with a differential scanning calorimeter (DSC). A method using a resin having a peak of (Patent Document 3), a method of mixing an aliphatic polyester resin and a polyacetal resin (Patent Document 4), and the like have been proposed.

  In these methods, the criterion for determining the presence or absence of heat resistance is that in the method of Patent Document 3, “the container is stored in a high-temperature bath at 55 ° C. for 5 days and the dimensional deformation of the side wall of the container is 4% or less”, Patent Document In Method 4, the test piece cut from the container is heated and the temperature at which the test piece hangs is 65 ° C. or higher, and just satisfying this standard cannot be said to have sufficient heat resistance for practical use. It was. Further, the modification by alloy as in Patent Document 4 has a problem that the biodegradability of the aliphatic polyester is lowered.

  In addition, as a method for promoting the crystallization of the aliphatic polyester resin, a technique for improving the crystallization degree by adding an organic compound (Patent Document 5), a resin composition containing a crystal nucleating agent or a crystallization accelerator in the resin. A technique for controlling the crystallization rate of the polymer (Patent Document 6), a technique for improving the crystal orientation and crystallinity by stretching (Patent Document 7), and an alloy with a polymer having a high crystallization speed. A technique to be used (Patent Document 4), a technique to improve crystallinity by dispersing a layered silicate (Patent Document 8), and the like are known.

  However, any of these methods is a method of proceeding with crystallization of a resin originally assumed for injection molding, and thus cannot be applied to stretch molding as it is. Therefore, the crystallization rate of the resin is too high and rapid crystallization occurs during the molding process and molding cannot be performed well. Conversely, the crystallization rate is too low to obtain sufficient heat resistance, or the molding cycle is long. For example, it has been difficult to produce a container excellent in both moldability and heat resistance.

Plastics, Vol. 53, no. 10, 2002, pp. 37-39 JP 2004-010727 A Japanese Patent Laid-Open No. 2004-010742 JP 2002-201293 A JP 2004-091684 A JP 2003-128901 A JP 2003-253209 A JP-A-9-025345 JP 2004-204143 A

  An object of the present invention is to solve the above-mentioned problems of the prior art and to provide a resin composition suitable for molding a stretch-molded container having excellent heat resistance and gas barrier properties.

  As a result of intensive studies to solve the above problems, the inventors of the present invention produced a container having both heat resistance and gas barrier properties by a stretch molding method by controlling the crystallization rate of the aliphatic polyester resin. The present inventors have found that an obtained resin composition can be provided, and arrived at the present invention based on such knowledge.

That is, the gist of the present invention is as follows.
(1) A resin composition containing a layered silicate containing polylactic acid as a main component and intercalating ions between layered silicates with organic ammonium ions, and measured by a differential scanning calorimeter (DSC) A resin composition for stretch molding, characterized in that the time until the calorific value of isothermal crystallization at a crystallization temperature of + 20 ° C. reaches a maximum is 1.5 to 100 minutes.
(2) A stretch-molded container comprising the resin composition according to (1) .
(3) The resin composition according to (1) or (2) is stretch-molded at a temperature within the range of the crystallization temperature of the resin composition ± 20 ° C., and the same as or after the stretch molding. A method for producing a stretch-molded container, characterized by promoting crystallization by heat treatment within a temperature range.

  According to the present invention, an aliphatic polyester resin composition excellent in stretch molding processability is provided, and a stretch-molded container excellent in heat resistance and gas barrier properties is easily produced by stretching the resin composition. be able to. This container can be favorably used as a fluid storage container such as a cosmetic container or a food storage container.

  Hereinafter, the present invention will be described in detail.

  In the resin composition of the present invention, the crystallization speed at the time of crystallization (that is, melt crystallization) that occurs when the molten resin is cooled is an index for judgment.

First, the crystallization temperature (T _c ) of the resin composition is measured using a differential scanning calorimeter (DSC). Next, using DSC, the temperature is raised to the melting point (T _m ) or more of the resin composition, the temperature is lowered to (T _c + 20 ° C.), and the temperature is maintained and the resin is crystallized isothermally. The time (t _max ) from when the temperature reaches (T _c + 20 ° C.) until the calorific value due to crystallization reaches the maximum value can be used as an index representing the crystallization rate. It can be determined that the smaller the value of _tmax , the higher the crystallization rate.

If the isothermal crystallization temperature is too close to T _c , crystallization may be too fast depending on the resin composition and the maximum value may not be clearly detected. _Therefore , t _max is (T _c + 20 ° C.) It is necessary to measure with.

The resin composition of the present invention needs to have a _tmax of 1.5 minutes to 100 minutes. It is preferably 1.7 minutes to 100 minutes, more preferably 5 minutes to 50 minutes, and most preferably 10 minutes to 50 minutes. When t _max is less than 1.5 minutes, rapid crystallization occurs during stretch molding, and thickness unevenness or deformation tends to occur in the molded product. On the other hand, if t _max exceeds 100 minutes, solidification does not proceed in the high-temperature mold during molding, and heat resistance and gas barrier properties tend to be insufficient.

  Examples of the aliphatic polyester in the present invention include (1) glycolic acid, lactic acid, hydroxybutylcarboxylic acid, (2) aliphatic lactones such as glycolide, lactide, butyrolactone, caprolactone, (3) ethylene glycol, propylene glycol, butanediol, etc. (4) oligomers of polyalkylene ethers such as diethylene glycol, triethylene glycol, ethylene / propylene glycol, dihydroxyethylbutane, polyalkylene glycols such as polyethylene glycol, polypropylene glycol, polybutylene ether, (5) Polyalkylene carbonates such as polypropylene carbonate, polybutylene carbonate, polyhexane carbonate, polyoctane carbonate, and polydecane carbonate Main component (70 mass) of at least one raw material selected from sulfonate glycols and oligomers thereof, (6) aliphatic dicarboxylic acids such as succinic acid, adipic acid, suberic acid, azelaic acid, sebacic acid, decanedicarboxylic acid 30% by mass of an aliphatic polyester block and / or random copolymer with other components such as aromatic polyester, polyether, polycarbonate, polyamide, polyurethane, polyorganosiloxane, etc. Those obtained by block copolymerization or random copolymerization in the following range and / or mixtures thereof are also included.

  It is preferable to use a resin containing 50% by mass or more of a resin derived from a plant-derived raw material as the aliphatic polyester resin because the effect of reducing petroleum resources is increased because the plant-derived degree is high. More preferably, the resin composed of plant-derived materials is used in an amount of 60% by mass or more, and more preferably 80% by mass or more. It is particularly preferable to use polylactic acid as a resin made from plant-derived materials because molding processability, transparency, and heat resistance are improved. Moreover, as polylactic acid, although the content ratio of L-lactic acid and D-lactic acid is not specifically limited, As what is marketed, (L-lactic acid / D-lactic acid) = 80 / 20-99.5 / 0. A range of 5 is common.

  The resin composition of the present invention can be produced by adding, for example, additives and other resin components to the aliphatic polyester as the main component.

  When additives are used to prepare the resin composition of the present invention, for example, heat stabilizers, antioxidants, pigments, weathering agents, flame retardants, plasticizers, lubricants, mold release agents, antistatic agents, endblockers , Fillers, dispersants and the like can be used. Examples of heat stabilizers and antioxidants include phosphite organic compounds, hindered phenol compounds, benzotriazole compounds, triazine compounds, hindered amine compounds, sulfur compounds, copper compounds, alkali metal halides, or these. Mixtures can be used. These additives are generally added during melt-kneading or polymerization. Examples of the terminal blocking agent include carbodiimide and oxazoline. Inorganic fillers include talc, layered silicate, calcium carbonate, zinc carbonate, wollastonite, silica, alumina, magnesium oxide, calcium silicate, sodium aluminate, calcium aluminate, sodium aluminosilicate, magnesium silicate, glass balloon , Carbon black, zinc oxide, antimony trioxide, zeolite, hydrotalcite, metal fiber, metal whisker, ceramic whisker, potassium titanate, boron nitride, graphite, glass fiber, carbon fiber and the like. Examples of the organic filler include naturally occurring polymers such as starch, cellulose fine particles, wood flour, okara, fir shell, bran and kenaf, and modified products thereof.

  Moreover, you may add these additives for the reason different from the objective of this invention in the range which does not impair the effect of this invention.

  Since the filler having a high aspect ratio dispersed in the resin has an effect of improving the gas barrier property of the resin composition, it is preferable to use a layered silicate as an additive because the gas barrier property becomes high. For polylactic acid, use of a layered silicate in which the interlayer ions of the layered silicate are substituted with organic ammonium ions improves the dispersibility of the filler and increases the gas barrier property, which is more preferable.

The crystallization rate of the resin composition changes depending on the concentration and type of the additive, and as a result, the value of _tmax changes. For example, when talc is used as an additive, it is preferably added in the range of 0.01 to 10% by weight in order to make t _max within the range of the present invention.

  In order to produce the resin composition of the present invention, a method of mixing different kinds of aliphatic polyester resins or a resin other than aliphatic polyester and an aliphatic polyester resin can also be used. If a resin having a higher crystallization rate than the aliphatic polyester resin as the main component is used, the resin composition of the present invention can be produced by adjusting the mixing ratio in the same manner as the additive.

  In addition, the resin composition of the present invention includes polyamide (nylon), polyethylene, polypropylene, polybutadiene, polystyrene, AS resin, ABS resin, poly (acrylic acid), poly (acrylic acid ester) unless the effects of the present invention are impaired. ), Poly (methacrylic acid), poly (methacrylic acid ester), polyethylene terephthalate, polyethylene naphthalate, polycarbonate, and copolymers thereof may be added. The addition amount is not particularly limited, but in order not to impair the biodegradability of the aliphatic polyester resin, the proportion of the non-aliphatic polyester resin is preferably 20% by mass or less with respect to 100% by mass of the entire resin composition, More preferably, it is 10 mass% or less.

  The resin composition of the present invention may be partially crosslinked. Moreover, it may be modified with an epoxy compound or the like.

  The molecular weight of the aliphatic polyester resin of the present invention is not particularly limited, but is preferably used as long as the melt flow index (MFI) at 190 ° C. and 2.16 kg as an index is in the range of 0.1 to 50 g / 10 min. More preferably, it is the range of 0.2-40 g / 10min.

  The molding method of the container using the resin composition of the present invention is not particularly limited, and a stretch-molded container can be produced by a known blow molding method.

  Examples of the blow molding method include a direct blow method in which a molten parison is formed after the raw material chips are melted and immediately blow-molded, or an injection blow in which a preform (bottomed parison) is first molded by injection molding and then blown. A molding method can be employed. In addition, any of a hot parison method in which blow molding is continuously performed after molding of a preformed body, and a cold parison method in which blow molding is performed by once cooling and taking out the preformed body and then performing blow molding can be employed.

In the present invention, in order to improve the crystallinity of the resin and improve the heat resistance and gas barrier properties of the container, the molded body constituting the container is further stretched and molded at a temperature within the range of _Tc ± 20 ° C. It is preferable to promote crystallization by heat treatment within a temperature range. The heat treatment step may be performed simultaneously with the molding process or after the molding process. In the blow molding described above, when the temperature of the molding die is set within the above range, the heat treatment is performed simultaneously with the molding process, so that the process is simplified, which is more preferable. By using the resin composition of the present invention, it is possible to avoid the problem of molding defects due to rapid crystallization that occurs in the heat treatment step at the same time as the molding process, and it is possible to obtain the desired molded body. When the temperature of the molding die is set lower than the above range, the heat resistance and gas barrier properties of the container that may be difficult to crystallize may be insufficient. Therefore, by performing the heat treatment in the above range after the molding process, the resin crystallinity can be improved and the heat resistance and gas barrier properties of the container can be improved. On the other hand, when the temperature of the molding die is set higher than the above range, there may be a problem of molding processability such as uneven thickness or drawing down due to a decrease in viscosity.

  Examples of the stretch-molded container of the present invention include a fluid container. Although the form is not specifically limited, In order to accommodate a fluid, it is preferable to shape | mold to the depth of 20 mm or more. Although the thickness of a container is not specifically limited, Considering required strength, it is 0.2 mm or more, Preferably it is 0.5-5 mm. Specific examples of containers for fluids include cups for beverages such as dairy products, soft drinks and alcoholic beverages, bottles for beverages, soy sauce, sauces, mayonnaise, ketchup, temporary containers for seasonings such as edible oils, shampoos and rinses Containers, cosmetic containers, agricultural chemical containers, and the like.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further more concretely, this invention is not limited only to an Example.

  In the examples and comparative examples, the measurement methods used for evaluation are as follows.

(1) Melting point _Tm and crystallization temperature _{Tc of the} resin composition:
Using DSC (DSC7 manufactured by Perkin Elmer), the temperature was raised from 25 ° C. to 200 ° C. at 20 ° C./min, and the temperature was maintained for 10 minutes. Thereafter, the temperature was lowered to −55 ° C. at 20 ° C./min, and again raised to 200 ° C. at 20 ° C./min. The top of the exothermic peak obtained during cooling and crystallization temperature T _c of the resin, the top of the endothermic peak obtained during the second heating was taken as the melting point T _m of a the resin composition.

(2) t _max :
About the resin composition before stretch molding, it heated up more than melting | fusing point using DSC, and maintained the temperature for 10 minutes. Thereafter, the temperature was lowered to (T _c + 20 ° C.), and the resin was crystallized isothermally while maintaining the temperature. The time from when the isothermal crystallization temperature (T _c + 20 ° C.) was reached to when the calorific value due to crystallization reaches the maximum value was defined as t _max . It can be determined that the smaller the _tmax , the faster the crystallization resin. In Comparative Example 1, since the crystallization rate was low and the value of _Tc could not be measured, the isothermal crystallization temperature was set to 130 ° C.

(3) Oxygen permeation amount:
The molded bottle was purged with nitrogen gas using a nitrogen gas chamber, sealed with a rubber stopper, and stored for 30 days under conditions of 20 ° C. and 60% relative humidity. The gas in the bottle was collected using a gas tight syringe, and the oxygen concentration change in the bottle was measured with a gas chromatograph (thermal conductivity detector). From the measured values obtained, the amount of oxygen permeation per day (expressed as ml · day ⁻¹ · bottle ⁻¹ ) was determined, and those having a value of 0.1 ml · day ⁻¹ · bottle ⁻¹ or less were good (○) and those exceeding this were regarded as defective (×).

(4) Water vapor transmission rate:
It shows that barrier property is so favorable that this value is small. That is, after filling the molded bottle with pure water and sealing it, and storing it in a dryer at 50 ° C. for 30 days, the one whose content reduction rate is 3% by weight or less is judged as good (◯), and 3% by weight Those exceeding% were regarded as defective (x).

(5) Formability:
The molded bottle was visually evaluated at the time of molding. A bottle having a good appearance after molding and capable of continuous molding was defined as good moldability (◯), and a bottle with uneven thickness or deformation was designated as poor moldability (X).

(6) Heat resistance:
A bottle having a good appearance after heat treatment at 120 ° C. (Examples 13 to 16 and Comparative Examples 1 to 7 and Comparative Examples 9 to 20 ) or 90 ° C. (Comparative Examples 8 and 21 ) for 30 minutes. The heat resistance was good (◯), and the one with uneven thickness or deformation was regarded as poor heat resistance (×).

  Various raw materials used in Examples and Comparative Examples are shown.

(1) Aliphatic polyester resin / polylactic acid (manufactured by NatureWorks, 4031D, weight average molecular weight 190,000, T _m 167 ° C., T _c 110 ° C.)
・ Polybutylene succinate (GS Pla P-10 manufactured by Mitsubishi Chemical Corporation, weight average molecular weight 170,000, T _m 108 ° C., T _c 73 ° C.)

(2) Inorganic additive, fine powder talc (MW HS-T, Hayashi Kasei Co., Ltd., average particle size 2.5 μm)

(3) Organic additive magnesium stearate (manufactured by Wako Kasei Co., Ltd.)
・ Ethylene glycol dimethacrylate (Nippon Yushi Co., Ltd.)
・ Diethylene glycol dimethacrylate (manufactured by NOF Corporation)
・ Glycidyl methacrylate (Nippon Yushi Co., Ltd.)
・ Hexamethylene diisocyanate (Wako Kasei Co., Ltd.)
・ Dibutyl peroxide (Nippon Yushi Co., Ltd.)
・ Erucamide (Wako Kasei Co., Ltd.)
・ Ethylenebisstearylamide (Wako Kasei Co., Ltd.)

(4) Layered silicate somasif MEE (manufactured by Co-op Chemical Co., Ltd., swellable synthetic fluoromica in which interlayer ions are substituted with dihydroxyethylmethyldodecylammonium ions)
・ Somasif MTE (Corp Chemical Co., Ltd., swellable synthetic fluorinated mica in which interlayer ions are replaced with methyltrioctylammonium ions)
・ Esven E (manufactured by Hojun Co., Ltd., montmorillonite with interlayer ions substituted with trimethyloctadecyl ammonium ions)

(Manufacture of resin composition)
Example 13-16, Comparative Examples 1-7, 9-20
To polylactic acid, the additives shown in Table 1 were added in dry blends in respective proportions, and using a PCM-30 type twin screw extruder (screw diameter 30 mmφ, average groove depth 2.5 mm) manufactured by Ikegai Co., Ltd. Melting and kneading were performed at 190 ° C., screw rotation speed 200 rpm (= 3.3 rps), and residence time 1.6 minutes to obtain each resin composition. In addition, the composition of the resin composition was set so that the whole resin composition obtained might be 100 mass%. In all the resin compositions, magnesium stearate as a lubricant at the time of melt kneading was added by dry blending so as to be 0.02% by mass with respect to 100% by mass of the entire resin composition. In Comparative Example 1, only a lubricant was added and melt kneading was performed. Furthermore, about the resin composition of the comparative example 4 and the comparative examples 13-16 , in addition to the additive shown in Table 1, dibutyl peroxide was added to 0.1 mass%, respectively.

Comparative Examples 8 and 21
To polybutylene succinate, the additives shown in Table 1 were added by dry blending at respective ratios, and melt kneading was performed at 130 ° C., screw rotation speed 200 rpm (= 3.3 rps), residence time 1.6 minutes, A resin composition was obtained. In any resin composition, magnesium stearate as a lubricant was added by dry blending so as to be 0.02% by mass with respect to 100% by mass of the entire resin composition during melt kneading.

(Measurement of thermal characteristics)
Subsequently, each obtained resin composition was dried to a moisture content of 300 ppm or less, and the melting point T _m and the crystallization temperatures T _c and t _max were measured using DSC (DSC7 manufactured by PerkinElmer Co., Ltd.). Table 1 shows T _m , T _c , and t _max of each resin composition.

(Stretch molding of resin composition)
Using the injection blow molding machine (ASB-50TH manufactured by Nissei ASB Machine Co., Ltd.), the obtained resin composition was melted at a cylinder set temperature of 200 ° C., which is a temperature higher than the melting point, and filled in a 10 ° C. mold. Cooling for 2 seconds, a 5 mm thick preform (bottom parison) was obtained. This is heated with hot air of 120 ° C., then placed in a low temperature mold or a high temperature mold set at a predetermined temperature, blow molded under conditions of pressure air of 3.5 MPa, an internal volume of 130 ml, a thickness of 1.1 mm A bottle container was prepared. The temperature of the low temperature mold is set to 25 ° C ( Comparative Example 10 ), and the temperature of the high temperature mold is set to 120 ° C (Examples 13 to 16 and Comparative Examples 1 to 7 , 9, 11 to 20 ) or 90 ° C ( Comparative Example 8 and Comparative Example 21 ) were set. The temperature of the high-temperature mold satisfied the condition of the above-mentioned range of T _c ± 20 ° C. for each resin composition.

  In Example 14, the molded container was further heat-treated at 120 ° C. for 30 minutes in a hot air dryer.

  Table 1 shows the evaluation results of the obtained container.

In Examples 13 to 16 , since the _{tmax of the} resin composition is between 1.5 and 100 minutes, the oxygen permeation amount and the water vapor representing gas barrier properties with good moldability in blow molding. The transmittance was also good, and since the heat treatment was performed simultaneously with the molding, the heat resistance of the molded body was also good.

The resin compositions of Examples 13 to 16 had particularly good gas barrier properties because t _max was between 10 and 50 minutes and the layered silicate was included as an additive.

  The resin composition of Example 14 was further improved in gas barrier properties by further heat treatment after molding.

Since the resin compositions of Comparative Examples 1 and 2 have a t _max of more than 100 minutes, there is a problem in molding processing in which solidification does not proceed during molding with a high-temperature mold and draw-down occurs. Because of insufficient crystallization, gas barrier properties and heat resistance were problematic.

Since the resin compositions of Comparative Examples 3 to 8 have a t _max of less than 1.5 minutes, there is a problem in molding processing such that rapid crystallization occurs during molding and thickness unevenness and deformation occur. The gas barrier property could not be evaluated because of the pinholes in the container.

Claims (3)

A resin composition containing a layered silicate containing polylactic acid as a main component and intercalating ions between layered silicates with organic ammonium ions, measured by a differential scanning calorimeter (DSC), crystallization temperature +20 A resin composition for stretch molding, characterized in that the time until the calorific value of isothermal crystallization at 0 ° C. reaches a maximum is 1.5 to 100 minutes. A stretch-molded container comprising the resin composition according to claim 1. The resin composition according to claim 1 or 2 is stretch-molded at a temperature within the range of the crystallization temperature of the resin composition ± 20 ° C, and is heat-treated within the same temperature range simultaneously with or after the stretch molding. And a method for producing a stretch-molded container, which promotes crystallization.