JP5070192B2 - Heat-resistant transparent A-PET container - Google Patents

Description

  The present invention relates to a food container for storing and selling food in a convenience store and the like. More specifically, the food containing oil has heat resistance without deformation even at 150 ° C. when the food containing oil rises by microwave heating, and is excellent. The present invention relates to a heat-resistant transparent A-PET container having transparency.

In food stores such as convenience stores, department stores, and supermarkets, food containers such as trays, cups, and bowls are packed with food such as side dishes, noodles, and salads. Such a food container is composed of a container main body for storing food and a lid for sealing the container main body. Generally, the container main body is made of polypropylene, foamed polypropylene, polypropylene with filler, polyethylene, foamed polyethylene, foamed. It is manufactured by thermoforming a sheet of polystyrene, heat-resistant foamed polystyrene, A-PET (Amorphous PET) or the like with a vacuum, compressed air, or vacuum / pressure forming machine. The lid is formed of a sheet of A-PET, biaxially stretched polystyrene (OPS), polypropylene (PP), or the like (see Patent Document 1).
In recent years, uniaxially stretched PET (polyethylene terephthalate) films have been used as IT-related touch panels and liquid crystal display elements because of their high transparency and heat resistance (see Patent Documents 2, 3, and 4).

JP 2005-329972 A JP 2000-82335 A JP 2000-82336 A Japanese Patent Laid-Open No. 5-165035

By the way, in recent years, foods purchased at convenience stores and the like have been routinely heated in a microwave oven in a state where they are stored in a food container. The food containing the oil increased in temperature to about 150 ° C. Accordingly, food containers are required to have high heat resistance that can withstand up to 150 ° C.
Furthermore, in food containers, high-transparency is required in order to be able to recognize the contents food clearly at a glance and improve the merchantability.

  However, none of the above-described various conventionally used sheets satisfies both of high heat resistance and high transparency at the same time. That is, among these various sheets, those having high transparency include A-PET sheets and OPS (biaxially oriented polystyrene) sheets. These sheets soften at about 70 ° C. and have high heat resistance. It did not have sex. The PP sheet has high heat resistance but is inferior in transparency.

  In addition, although the uniaxially stretched PET film used for a touch panel etc. is highly transparent and heat resistant, as described in Patent Document 2, it is heat-fixed at 220 ° C. after TD (lateral) uniaxial stretching. It does not stretch even when heated and cannot be molded with a thermoforming machine.

  As described above, conventionally, food containers that are directly heated in a microwave oven have been required to have high heat resistance and high transparency. However, food containers that satisfy both of these requirements have not been proposed yet.

  The present invention has been made in view of the above problems, and an object thereof is to provide a food container having high heat resistance and high transparency.

  The present inventors have intensively studied to solve the above-described problems, paying attention to A-PET sheets and OPS sheets having high transparency, and can achieve the problems by improving the heat resistance of these sheets. I thought it was possible. However, OPS sheets have concerns about safety and hygiene due to elution of residual monomers, dimers and trimers, and additives, and have studied to improve the heat resistance of A-PET sheets that are excellent in food safety and hygiene.

  As a result of the above studies, the present inventors have intensively studied to improve the heat resistance of the A-PET sheet, and raise the crystallinity of the A-PET sheet by orientation crystallization by stretching and crystallization by heat fixation. It was found that high heat resistance that can withstand 150 ° C. can be imparted, and that a biaxially stretched OPP film is laminated to prevent easy tearing due to uniaxial stretching, and the present invention has been completed. It came to do.

The heat-resistant transparent A-PET container according to claim 1 is a laminated sheet in which an A-PET sheet is heated and uniaxial primary stretched, and then a stretched A-PET sheet primary-fixed and an OPP film are bonded together. Is heat-molded at 80 to 150 ° C. with a mold of a thermoforming machine and secondarily stretched by molding, and then secondarily fixed at 130 to 155 ° C. in the same mold, and the stretched A-PET sheet is After the A-PET sheet was uniaxially primary stretched 2 to 4 times in the MD direction at a stretching temperature of 90 to 120 ° C. using a roll stretching device, it was primarily heat-set at a temperature 5 to 20 ° C. higher than the stretching temperature. And the degree of crystallinity expressed by the following formula of the stretched A-PET sheet is 22% or more and less than 30%, the OPP film has a stretch ratio of 3 to 6 times in MD and TD directions, and an area ratio of Biaxial to be 9-36 times After being lengthened, was thermally fixed to relax both MD and TD directions, Ri 0.5% to 10% der shrinkage in both MD and TD directions of 120 ° C. glycerin bath, after the secondary stretching, secondary heat The stretched A-PET layer of the container formed by being fixed has a crystallinity represented by the following formula of 30% or more .

In the heat-resistant transparent A-PET container according to claim 1, in the uniaxial primary stretching / primary heat setting step, the crystallinity of the A-PET sheet is increased within a range where thermoforming can be performed, and further, In the next heat setting step, the laminated sheet is molded into the shape of a container, and at the same time, the crystallinity of the stretched A-PET sheet is further increased to improve heat resistance. As a result, the container can withstand 150 ° C. Of heat resistance. In addition, since the biaxially stretched OPP film is laminated, the strength as a container is maintained by making up for the defect that the stretched A-PET sheet easily breaks due to the lateral force. In addition, after biaxial stretching so that the stretching ratio in the MD direction and TD direction is 3 to 6 times (area ratio is 9 to 36 times), both MD and TD directions are relaxed and heat-fixed, and 120 ° C. glycerin. Since the shrinkage ratio of the bath is 0.5 to 10% in both the MD and TD directions, the biaxially stretched OPP film is highly transparent and can be thermoformed. Further, the laminated sheet is thermoformed at 80 to 150 ° C. and secondarily stretched, and then secondarily heat-set at 130 to 155 ° C., which is within the optimum crystallization temperature range of PET, in the same mold. The crystallinity of the stretched A-PET layer (laminated in the heat-resistant transparent A-PET container) can be increased to 30% or more by crystallization by orientation and crystallization by heat setting.

Moreover, after extending | stretching A-PET sheet | seat uniaxial primary-stretching 2 to 4 times in the MD direction at the extending | stretching temperature of 90-120 degreeC, a stretched A-PET sheet is formed by carrying out primary heat setting at the temperature 5-20 degreeC higher than extending | stretching temperature. Therefore, the crystallinity can be controlled to 20% or more and less than 30% while maintaining transparency. Moreover, it can be manufactured inexpensively with simple equipment using a roll.

Furthermore, the crystallinity shown by the following formula of the stretched A-PET sheet is a crystallinity that can be thermoformed by setting it to 22% or more and less than 30%, and the following secondary stretching / secondary heat setting step Thus, the crystallinity can be increased to 30% or more so that high heat resistance can be obtained.

Furthermore, by giving a crystallinity of 30% or more of the stretched A-PET layer after secondary stretching / secondary heat setting to 30% or more, high transparency and high heat resistance of 150 ° C. are imparted. I can do it.

  The heat-resistant transparent A-PET container of the present invention uses an A-PET sheet, and this A-PET is in an amorphous state, and its crystallinity is about 5 to 7%. A commercially available A-PET sheet can be used as the A-PET sheet, and the resin used for the A-PET sheet need not have a high intrinsic viscosity (IV value). A sheet formed from a resin having a viscosity of 0.6 dL / g or less or a resin using flakes of recovered PET bottles may not have good surface properties and requires special pretreatment.

  The A-PET sheet as described above is subjected to uniaxial primary stretching, followed by primary heat setting to form a stretched A-PET sheet. In order to form the stretched A-PET sheet, the A-PET sheet obtained by molding in advance may be stretched, or the A-PET sheet immediately after molding may be sent inline to the stretching means by a T-die molding machine.

  The stretching temperature for uniaxial primary stretching is preferably 90 to 120 ° C, and more preferably 95 to 110 ° C. When the stretching temperature is less than 90 ° C., the tension is excessively applied when the A-PET sheet is stretched to cause uneven stretching, and the uneven thickness of the stretched A-PET sheet easily occurs. The sheet becomes cloudy and surface roughness occurs, and a transparent and good stretched A-PET sheet cannot be obtained.

  The draw ratio is preferably 2 to 4 times, and more preferably 2.6 to 3.7 times. When the draw ratio is less than 2 times, a cold crystallization point is observed from differential scanning calorimetry (DSC) measurement, the crystallinity becomes less than 22%, and the molded body is whitened by thermoforming described later. On the other hand, if it exceeds 4 times, slipping is likely to occur on the stretching roll during stretching, and a slipped portion and a non-slipable portion are generated, so that a transverse wave pattern is generated on the stretched A-PET sheet.

  As the stretching apparatus, for example, a stretching apparatus using a heating roll can be used, but it may be a single-stage stretching in a short section of the heating roll or a multi-stage stretching of two or more stages.

  The temperature for primary heat setting is not particularly limited, but is preferably 5 to 20 ° C. higher than the stretching temperature from the viewpoint of relaxing orientation by annealing. If the heat setting temperature is not higher than 5 ° C. than the stretching temperature, the thermal shrinkage rate of the stretched A-PET sheet is increased, and if it is higher than 20 ° C. than the stretching temperature, the surface becomes rough and whitened.

  In addition, in the said heat setting temperature range, since the shrinkage | contraction rate of a stretched A-PET sheet becomes small and deformation | transformation can be reduced when manufacturing a thermoformed body, it is more preferable to set it as the high heat setting temperature.

  The speed of the heat setting roll is set to be about 0.5 to 10% slower than the stretching roll speed in order to match the orientation relaxation of the sheet.

  The stretched A-PET sheet that has undergone the uniaxial primary stretching and primary heat setting steps as described above preferably has a crystallinity of 22% or more and less than 30% represented by the following formula. If the degree of crystallinity is less than 22%, there is a cold crystallization point, and there is a possibility of whitening when heated in secondary stretching. Further, if it is 30% or more, thermoforming becomes difficult, and it becomes difficult to obtain reproducibility of the mold.

  Subsequently, an OPP film is bonded to the stretched A-PET sheet subjected to the above-described uniaxial primary stretching and primary heat setting to form a laminated sheet.

  The OPP film preferably has a stretch ratio of 3 to 6 times in the MD direction (film flow direction) and TD direction (a direction perpendicular to the film flow direction), and an area ratio of 9 to 36 times. preferable. When the draw ratio is less than 3 times, the gloss of the film is inferior, and the thermal shrinkage due to the orientation becomes small, which is not suitable for preventing drawdown. When the draw ratio exceeds 6 times, it is excellent in gloss and suitable for preventing drawdown, but the thermal shrinkage rate due to orientation increases, and peeling from the stretched A-PET sheet when thermoformed, thermoforming It is inferior in stability and mold reproducibility. Moreover, it is preferable that the draw ratio of MD direction and TD direction is substantially the same magnification. By using substantially the same magnification, it is possible to suitably prevent the drawdown during thermoforming and the mold reproducibility of the molded product. The stretching method may be a simultaneous biaxial method, a sequential biaxial method, or a simultaneous biaxial method using a tubular method.

  Further, the OPP film is heat-treated after being biaxially stretched and relaxed in both the MD direction and the TD direction. This heat treatment is not particularly limited, but a tenter (constant temperature chamber) or a heat roll is used. The relaxation rate is 5 to 25% in both the MD direction and the TD direction. If the relaxation rate is less than 5%, the shrinkage rate when molded into a container increases, and the container is deformed. Less. 7 to 15% is preferable with the same relaxation rate in both the MD direction and the TD direction.

  In the OPP film, the shrinkage ratio of the 120 ° C. glycerin bath is 0.5 to 10% in both the MD direction and the TD direction, and preferably 0.5 to 8%. If the shrinkage rate is less than 0.5%, drawdown cannot be prevented, and if the shrinkage rate exceeds 10%, drawdown during thermoforming can be prevented, but peeling from the sheet and stability of thermoforming, The mold reproducibility is poor.

  The polypropylene resin used for the OPP film is a polypropylene homopolymer resin, ethylene, propylene random copolymer resin or a mixed resin thereof, and the MFR is preferably 1.0 to 10.0 g / 10 min.

As a method of laminating the stretched A-PET sheet and the OPP film to form a laminated sheet, dry lamination or thermal lamination is used. In the dry laminating method, one raw material to be bonded is subjected to corona treatment, an adhesive dissolved in a solvent is applied with a gravure roll, the solvent is evaporated and evaporated in a drying oven, and the other raw material to be bonded is bonded. Is subjected to corona treatment, and the corona-treated surface is superposed on the adhesive-coated surface and bonded by pressing with a nip roll.
In the thermal laminating method, both raw materials to be bonded are subjected to corona treatment, a resin adhering to both raw materials is interposed between the corona-treated surfaces, heat is applied with a hot roll, and pressure bonding is performed with a nip roll. It is a method of pasting. Since the adhesive resin melts and adheres, it is necessary to apply heat to a temperature at which the adhesive resin melts.
The laminated sheet is formed by laminating the stretched A-PET sheet and the OPP film as described above, and the stretched A-PET sheet is mainly responsible for the heat resistance. Since it is axially stretched, it compensates the drawback of being easily split by the lateral force of the stretched A-PET sheet, and maintains the strength as a container.

  A heat-resistant transparent A-PET container is formed by heat-molding the laminated sheet as described above with a mold of a thermoforming machine, and secondary stretching by molding, followed by secondary heat setting in the same mold. The temperature for secondary stretching is preferably from 80 to 150 ° C, more preferably from 90 to 140 ° C. When the stretching temperature is less than 80 ° C., undulation occurs in the molded body. Further, when the temperature exceeds 150 ° C., the draw down of the sheet increases, and wrinkles (bridges) are generated in the molded body when it is molded. The secondary heat setting temperature is preferably 130 to 155 ° C., which is within the range of the optimum crystallization temperature of PET. If it is less than 130 degreeC, it will become out of the range of the optimal crystallization temperature, and an effect will decrease. If it exceeds 155 ° C., it is still within the range of the optimum crystallization temperature, but since it is close to the melting point (160 ° C.) of the polypropylene resin, it becomes soft or melts and tends to cause troubles such as adhesion to the molding machine or deformation.

  The optimum crystallization temperature of the PET is shown in FIG. FIG. 3 is a graph showing the relationship between the crystallization temperature and the half crystallization time, and shows the optimum crystallization temperature with an average molecular weight of 20500, 32000, and 45000.

After the secondary stretching as described above, the stretched A-PET layer of the container formed by secondary heat setting preferably has a crystallinity of 30% or more represented by the following formula. If it is less than 30%, sufficient heat resistance cannot be obtained.

The thermoforming method by the thermoforming machine is not particularly limited, and any of vacuum forming, pressure forming, and vacuum / pressure forming may be used.
The heat-resistant and transparent A-PET container of the present invention can be applied to various containers that require heat resistance and transparency. For example, it is most suitable for food containers, particularly containers heated in a microwave oven.

The process for producing the heat-resistant transparent container according to the present invention will be described with reference to the drawings.
FIG. 1 is a schematic view of an apparatus for producing a longitudinal uniaxially stretched A-PET sheet, and FIG. 2 is a schematic view of a thermoforming machine. FIG. 3 is a graph showing the crystallization speed of PET.

  In FIG. 1, 1 is an A-PET sheet, 2 is a preheating roll, 3 is a nip roll, 4 is a heating roll, 5 is a stretching roll, 6 is a heat setting roll, 7 is a longitudinally uniaxially stretched A-PET sheet, A- The PET sheet 1 is first preheated to 70 to 90 ° C. with the preheating roll 2 and then heated to 90 to 120 ° C. with the heating roll 4. Then, the heated A-PET sheet 1 is stretched 2 to 4 times in the longitudinal direction by the stretching roll 5. Further, the uniaxially stretched A-PET sheet 1 is heated and fixed at a temperature 5 to 20 ° C. higher than the temperature heated by the heating roll 4 by the heat fixing roll 6, and the longitudinal uniaxially stretched A-PET sheet 7 is formed. Complete.

  In FIG. 2, 11 is a thermoformed upper heater plate, and 12 is a thermoformed lower heater plate, for heating the laminated sheet before thermoforming. Reference numeral 13 denotes a thermoforming upper die, 14 denotes a thermoforming lower die, 15 denotes a thermoforming lower die embedded heater, and 16 denotes a thermoforming body. First, the thermoforming upper heater 11 and the thermoforming lower heater The laminated sheet 8 is placed between the laminated sheet 8 and heated so that the surface temperature of the laminated sheet 8 is 80 to 150 ° C. Next, this heated laminated sheet 8 is thermoformed with a thermoforming upper mold 13 and a thermoforming lower mold 14 and taken out.

  The thermoformed lower mold 14 is heated by the thermoformed lower heater plate 12 to 130 to 155 ° C. which is within the range of the optimum crystallization temperature, so that the thermoformed body is heat-set at 130 to 155 ° C.

[Example 1]
A 0.6-mm thick A-PET sheet (crystallinity 6.1%) manufactured by Athena Industry Co., Ltd. was stretched with a T-17 type roll stretching device manufactured by Nippon Steel Works Co., Ltd. Manufactured. That is, a preheating roll temperature of 80 ° C., a heating roll temperature (stretching temperature) of 95 ° C., a stretching roll temperature of 80 ° C., and a heat fixing roll temperature of 100 ° C. are fed out at a rate of 25 m / min. A stretched A-PET sheet having a thickness of 0.21 mm was obtained by stretching 2.8 times between the rolls in one step. This stretched A-PET sheet was transparent without wrinkles, had a crystallinity of 27.5% determined from DSC measurement values, the cold crystal peak disappeared, and was highly crystallized.

<Crystallinity>
The melting behavior of the stretched A-PET sheet was measured with a Seiko Electronic DSC220 differential scanning calorimeter and obtained based on the following formula. The measurement sample was measured by raising the temperature to 20 to 300 ° C. at a rate of temperature increase of 10 ° C./min while flowing 10 mg of nitrogen and 50 ml / min.

Next, a polypropylene homopolymer resin having an MFR of 7.0 g / 10 min was simultaneously biaxially stretched by the tubular method at a MD direction of 4.0 times and a TD direction of 4.0 times, and within the tenter, the MD direction was 10%. , Relaxed 10% in the TD direction and heat fixed at 150 ° C to obtain an OPP film (30 μm thick × 800 mm wide × 1000 m long: 120 ° C glycerin bath shrinkage is 1.5% MD and 3% TD) It was.
Next, this OPP film was subjected to a corona treatment of 50 W · min / m ² , and a gravure roll with 95 screen lines by helio engraving was applied to Nakajima Seiki Engineering Co., Ltd. dry laminating machine LX-3 on this corona treated surface. The urethane adhesive (main agent: TM569, curing agent: CAT37, solvent: ethyl acetate) manufactured by Toyo Morton Co., Ltd. was applied at a processing speed of 28 m / min, and then hot air temperatures of 40 ° C, 65 ° C, 55 Dried in 3 zones at 0 ° C.
Further, one side of the stretched A-PET sheet was subjected to a corona treatment of 50 W · min / m ² , and the corona-treated surface of the stretched A-PET sheet and the adhesive-coated surface of the OPP film were combined to obtain a nip pressure. Bonding was performed at a linear pressure of 18 kg-cm to obtain a laminated sheet. This laminated sheet was aged in a constant temperature room at 46 ° C. for 3 days.

  Next, this laminated sheet was softened by heating with an “FKC type” vacuum / pressure forming machine manufactured by Asano Laboratories Co., Ltd. so that the surface temperature was 130 ° C., and the upper diameter was 175 cm × 120 cm, the flange width was 1 cm, the lower part Using a female aluminum mold with a 150 cm x 95 cm diameter and 2.5 cm deep round bottom and corners, set the aluminum mold temperature to 145 ° C and apply vacuum of 0.5 MPa while applying vacuum and pressure. When it was molded and taken out from the mold, it was solidified to some extent by blowing cold air to obtain a food tray container (heat resistant transparent A-PET container).

  The obtained food tray container was transparent, was not deformed, and was a molded body according to the mold. The crystallinity of the stretched A-PET layer was 37.5%.

<Evaluation of heat resistance>
The food tray container was filled with edible oil, and the presence or absence of deformation was observed while raising the temperature in a microwave oven (National NE-EZ2). Although it observed while measuring temperature from 100 degreeC, there was no deformation | transformation to 150 degreeC, and transparency was also hold | maintained. Therefore, it can be said that it has heat resistance up to 150 ° C.

<Evaluation of drop strength>
After 200 ml of water was filled in the food tray, a lid material composed of a PET film layer (12 μm) / O-NY film layer / easy peel layer (35 μm) was sealed by heat sealing. A drop test was conducted by dropping the sealed sample from a height of 2.0 m onto a hard concrete floor with a horizontal bottom, a vertical major axis, a vertical minor axis, and a vertical corner first.

The results are shown in Table 1.

  There is no breakage in any dropping direction, and the OPP film layer compensates for the weakness of the stretched A-PET layer in the lateral direction. The convenience store shelves are about 1.8m, so if they can withstand a drop height of 2.0m, they can withstand practical use.

Schematic of the manufacturing apparatus of the stretched A-PET sheet used for the heat-resistant transparent A-PET container according to the present invention. Schematic of thermoforming apparatus used for heat-resistant transparent A-PET container according to the present invention Diagram showing the relationship between crystallization temperature and semi-crystallization time

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 A-PET sheet 2 Preheating roll 4 Heating roll 5 Stretching roll 6 Heat setting roll 7 Longitudinal uniaxial stretching A-PET sheet 8 Laminated sheet 11 Thermoforming upper heater plate 12 Thermoforming lower heater plate 13 Thermoforming upper die 14 Thermoformed lower mold 15 Thermoformed lower mold embedded heater 16 Heat resistant transparent A-PET container

Claims (1)

After the A-PET sheet is heated and uniaxial primary stretched, a stretched A-PET sheet that has been primarily heat-fixed and an OPP film are laminated and integrated into a laminated sheet at a temperature of 80 to 150 ° C. using a mold of a thermoforming machine. After the secondary stretching by molding and secondary stretching by molding, the stretched A-PET sheet is stretched at a temperature of 130 to 155 ° C. in the same mold, and the stretched A-PET sheet is stretched using a roll stretching device. After being uniaxially primary stretched 2 to 4 times in the MD direction at a temperature of 90 to 120 ° C., primary heat setting is performed at a temperature 5 to 20 ° C. higher than the stretching temperature, and the stretched A-PET sheet has the following formula: The crystallinity shown is 22% or more and less than 30%, and the OPP film was biaxially stretched so that the stretching ratio in the MD direction and the TD direction was 3-6 times and the area ratio was 9-36 times. Later, both MD and TD directions relax Was subjected to hot fix, Ri 0.5% to 10% der in shrinkage both MD and TD directions of 120 ° C. glycerin bath, after the secondary stretching, secondary heat fixed with formed containers stretching A- A heat-resistant transparent A-PET container, wherein the crystallinity of the PET layer represented by the following formula is 30% or more .

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