JP2009280218A - Heat-resistant transparent a-pet container - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a container having high heat resistance and high transparency, and suitable for a food container which is directly heated in a microwave oven. <P>SOLUTION: A laminate sheet in which an oriented A-PET (amorphous PET) sheet 7 subjected to the primary heat fixation after the primary orientation by heating an A-PET sheet is integrated with an unoriented A-PET film or an unoriented A-PET sheet through dry laminate is thermo-formed in molds 13 and 14 of a thermoformer to enhance the crystallization by the secondary oriented crystal by the forming. The oriented A-PET sheet is subjected to the uniaxial primary orientation to 2-5 times in MD (machine direction, longitudinal direction) at the orientation temperature of 90-120°C by using an orientation apparatus by rolls, and further subjected to the primary thermo-formation at the temperature higher than the orientation temperature by 5-20°C. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a food container for storing and selling food in a convenience store and the like. More specifically, the present invention has heat resistance without deformation even at 100 ° C. when the food rises in a microwave oven, and has excellent transparency. The present invention relates to a heat-resistant transparent A-PET container.

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 temperature rises to 100 ° C. Accordingly, food containers are required to have high heat resistance that can withstand up to 100 ° 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 stretched polystyrene) sheets. These sheets soften at about 80 ° 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 even 100 ° C. can be imparted, and that an unstretched A-PET layer is laminated in order to prevent 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 stretched A-PET sheet obtained by heating the A-PET sheet and performing primary stretching after primary stretching, and an unstretched A-PET film or unstretched A-PET sheet. The laminated sheet integrated by dry lamination is heat-molded with a mold of a thermoforming machine, and is characterized in that crystallization is enhanced by secondary stretched orientation crystal by molding.

  The heat-resistant transparent A-PET container according to claim 2 is a thermoforming machine comprising a laminated sheet obtained by extruding a PET resin into a stretched A-PET sheet that has been heat-heated and primary-fixed after the A-PET sheet is primary stretched and integrated by lamination. This is characterized in that the crystallization is enhanced by the secondary stretched orientation crystal formed by heat molding with the mold.

  The heat-resistant and transparent A-PET container according to claim 3 is the heat-resistant and transparent A-PET container according to claim 1 or 2, wherein the stretched A-PET sheet uses a stretching device with a roll, and the A-PET sheet is stretched at a stretching temperature of 90. After uniaxial primary stretching 2 to 5 times in MD (longitudinal direction) at ˜120 ° C., primary heat setting was performed at a temperature 5 to 20 ° C. higher than the stretching temperature.

  The heat-resistant transparent A-PET container according to claim 4 is the heat-resistant transparent A-PET container according to claim 1, 2, or 3, wherein the stretched A-PET sheet after primary stretching and primary heat fixation is represented by the following formula: The degree of crystallinity is 22% or more and less than 30%.

  The heat-resistant transparent A-PET container according to claim 5 is the heat-resistant transparent A-PET container according to claim 1, 3 or 4, wherein the laminated sheet is thermoformed at 80 to 150 ° C. and secondarily stretched. The crystallization is enhanced by oriented crystals.

  The heat-resistant transparent A-PET container according to claim 6 is the heat-resistant transparent A-PET container according to claim 1, 2, 3, 4 or 5, wherein the stretched A-PET layer after secondary stretching is represented by the following formula: The crystallinity is 30% or more.

  In the heat-resistant transparent A-PET container according to claim 1, in the primary stretching / primary heat setting step, the crystallinity of the A-PET sheet is increased within a range that can be thermoformed, and in the secondary stretching step, a 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 the heat resistance, and the heat resistance as a container is also imparted. Moreover, since the unstretched A-PET film or the unstretched A-PET sheet 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 the heat-resistant transparent A-PET container according to claim 2, as in claim 1, in the primary stretching / primary heat setting step, the crystallinity of the A-PET sheet is increased within a range where thermoforming can be performed. In the next stretching step, the laminated sheet is formed into a container shape, and at the same time, the crystallinity of the stretched A-PET sheet is further increased to improve the heat resistance, and the heat resistance as a container is also imparted. Moreover, since the extrusion PET resin layer is laminated | stacked, the defect which is easy to tear to the force of the horizontal direction of an extending | stretching A-PET sheet is compensated, and the intensity | strength as a container is hold | maintained.

  In the heat-resistant transparent A-PET container according to claim 3, the A-PET sheet is uniaxially primary stretched 2 to 5 times in the MD (longitudinal direction) at a stretching temperature of 90 to 120 ° C and then 5 to 20 ° C from the stretching temperature. Since it is a stretched A-PET sheet by primary heat setting at a high temperature, the crystallinity can be controlled to 22% or more and less than 30% while maintaining transparency, and can be manufactured inexpensively with simple equipment using a roll. .

  In the heat-resistant transparent A-PET container according to claim 4, by setting the crystallinity represented by the following formula of the stretched A-PET sheet after primary stretching and primary heat setting to 22% or more and less than 30%, The crystallinity can be thermoformed, and can be close to 30% or higher, which provides high heat resistance in the next secondary stretching step.

  In the heat-resistant transparent A-PET container according to claim 5, the laminated sheet is thermoformed at 80 to 150 ° C. and secondarily stretched, and the degree of crystallinity is increased while maintaining transparency by enhancing crystallization by oriented crystals. It can be 30% or more.

  In the heat-resistant transparent A-PET container according to claim 6, the crystallinity represented by the following formula of the stretched A-PET layer after the secondary stretching is set to 30% or more, thereby being highly transparent and 100 ° C. High heat resistance can be imparted.

  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.

  In the primary stretching / primary heat setting step, first, the A-PET sheet is heated to be primarily stretched. The A-PET sheet may be obtained by molding in advance, or the A-PET sheet immediately after being molded by a T-die molding machine may be sent inline to the stretching means.

  90-120 degreeC is preferable and the extending | stretching temperature of primary extending | stretching has more preferable 95-110 degreeC. When the stretching temperature is less than 90 ° C., 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, and exceeds 120 ° C. Then, 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 5 times, and more preferably 2.2 to 3.7 times. When the draw ratio is less than 2, a cold crystallization point is observed from the differential scanning calorimeter (DSC) measurement, and the crystallinity becomes less than 22%. On the other hand, if it exceeds 5 times, slipping is likely to occur with the stretching roll during stretching, and there is a slip portion and a non-slip portion, so a transverse wave pattern is generated on the sheet, and a good uniaxial primary stretch A-PET sheet is obtained. I can't.

  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 of 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, and if the heat fixing temperature is not higher than 5 ° C. than the stretching temperature, the heat of the sheet Shrinkage rate increases. Moreover, when higher than 20 degreeC than extending | stretching temperature, rough skin will arise and it will become whitening.

  In addition, in the range of the said heat setting temperature, since the heat shrinkage rate of a stretched A-PET sheet becomes small and a deformation | transformation can be decreased 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 primary stretching / primary heat setting step as described above preferably has a crystallinity of 22% or more and less than 30% represented by the following formula. If the crystallinity is less than 22%, it becomes difficult to make the crystallinity 30% or more even after the secondary stretching step. Further, if it is 30% or more, thermoforming becomes difficult, and it becomes difficult to obtain reproducibility of the mold.

  Next, an unstretched A-PET film or an unstretched A-PET sheet is bonded to the stretched A-PET sheet subjected to primary stretching and primary heat setting as described above by a dry laminating method to form a laminated sheet. Alternatively, a laminated sheet is formed by extruding and laminating a PET resin to a stretched A-PET sheet subjected to primary stretching and primary heat setting. That is, as an aspect of a laminated sheet, it is a stretched A-PET sheet / unstretched A-PET sheet, a stretched A-PET sheet / unstretched A-PET film, and a stretched A-PET sheet / PET resin layer.

  The PET resin used for extrusion lamination may be a normal PET resin polymerized from terephthalic acid and ethylene glycol, or a polyester copolymerized with other components.

  In such a laminated sheet, the stretched A-PET sheet mainly has a role of heat resistance, and the disadvantage that it is easily broken by the lateral force of the stretched A-PET sheet is the unstretched A-PET sheet, unstretched A- A PET film or an unstretched PET resin layer supplements and maintains the strength as a container.

  A container is formed by heat-molding the laminated sheet as described above with a mold of a thermoforming machine and performing secondary stretching by molding.

  The stretching temperature for secondary stretching is preferably 80 to 150 ° C, more preferably 90 to 140 ° C. When the stretching temperature is less than 80 ° C., undulation is generated in the molded body. When the stretching temperature is higher than 150 ° C., drawdown of the sheet is increased, and wrinkles are generated in the molded body when it is molded.

  The stretched A-PET layer (the state thermoformed into the container) that has undergone the secondary stretching process as described above needs to have 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 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 food containers heated in a microwave oven.

A process for producing a heat-resistant transparent A-PET 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 stretched A-PET sheet, and FIG. 2 is a schematic view of an apparatus for producing a heat-resistant transparent A-PET container.

  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. The heated A-PET sheet 1 is stretched 2 to 5 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 is a thermoforming upper mold, 14 is a thermoforming lower mold, 15 is a thermoforming lower mold embedded heater, and 16 is a heat-resistant transparent A-PET container. The laminated sheet 7 is installed between the lower heater 12 and heated so that the surface temperature of the laminated sheet 7 is 80 to 150 ° C. Next, the heated laminated sheet 7 is thermoformed by the thermoforming upper mold 13 and the thermoforming lower mold 14 and is held as it is for about 5 seconds and then taken out.

[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 0.26 mm was obtained by stretching in a single step 2.3 times between the rolls. 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, Towa Chemical Co., Ltd. A-PET film (50 μm thick × 1000 mm wide × 1000 m long) was subjected to a corona treatment of 50 w · min / m ² , and the A-PET film subjected to the corona treatment was subjected to Nakajima Seiki Engineering. A gravure roll with 95 screen lines by Helio engraving is set on a dry laminator LX-3 manufactured by Toyo Morton Co., Ltd. (main agent: TM569, curing agent: CAT37, solvent: ethyl acetate) ) Was applied at a processing speed of 28 m / min and dried in three zones of hot air temperatures of 40 ° C., 65 ° C., and 55 ° C. Next, the A-PET film was bonded to a stretched A-PET sheet subjected to a corona treatment of 50 w · min / m ² at a linear pressure of nip pressure of 18 kg-cm to prepare a laminated sheet.

  This laminated sheet was aged in a constant temperature room at 46 ° C. for 3 days. And this laminated sheet was softened by heating to a surface temperature of 120 ° C. with an “FKC type” vacuum / pressure forming machine manufactured by Asano Laboratories Co., Ltd., upper diameter 175 cm × 120 cm, flange width 1 cm, lower part Using a female mold and aluminum mold with a rounded bottom and corner with a diameter of 150 cm x 95 cm and a depth of 2.5 cm, vacuum and pressure molding is performed while applying 0.5 MPa of air pressure to produce 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 degree of crystallinity was 36.3% for the stretched A-PET layer and 9.5% for the unstretched A-PET layer.

<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). There was no deformation at 100 ° C., and a wavy deformation occurred at the bottom of the food tray container at 115 ° C. At 115 ° C., a wavy deformation occurred at the bottom of the food tray container, but there were no other abnormalities, so it is considered that it has a heat resistance of 115 ° 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 falling direction, and the unstretched A-PET layer compensates for the weakness of the stretched A-PET layer in the lateral force. The convenience store shelves are about 1.8m, so if they can withstand a drop height of 2.0m, they can withstand practical use.

[Example 2]
After subjecting the 0.26 mm thick stretched A-PET sheet obtained in Example 1 and the Osaka Resin Co., Ltd. 0.18 mm unstretched A-PET sheet to corona treatment in the same manner as in Example 1. Then, dry lamination was performed in the same manner as in Example 1 to produce a laminated sheet, which was used as a container forming sheet. The container forming sheet was used in the same manner as in Example 1 to obtain a food tray container. The obtained food tray container was transparent and was not deformed, and was a molded body according to the mold. The degree of crystallinity was 35.1% for the stretched A-PET layer and 9.0% for the unstretched A-PET layer.

<Evaluation of heat resistance>
The food tray was filled with edible oil, and the heat resistance was evaluated in the same manner as in Example 1. At 110 ° C., wavy deformation occurred at the bottom of the tray, but no other abnormalities occurred. Therefore, the heat resistance is considered to be 110 ° C.

<Evaluation of drop strength>
The drop strength was evaluated in exactly the same manner as in Example 1.
The horizontal bottom, vertical major axis, vertical minor axis, and vertical corner were all 2.0m drop height, and no damage occurred.

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

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 11 Thermoforming upper heater plate 12 Thermoforming lower heater plate 13 Thermoforming upper die 14 Under thermoforming Mold 15 Heat-molded under-mold embedded heater 16 Heat-resistant transparent A-PET container

Claims (6)

A laminated sheet obtained by integrating a stretched A-PET sheet, which is obtained by heating the A-PET sheet and performing primary stretching after primary stretching, and an unstretched A-PET film or unstretched A-PET sheet, by dry lamination, A heat-resistant and transparent A-PET container characterized in that crystallization is enhanced by secondary stretch oriented crystals formed by heating with a metal mold. A laminated sheet in which PET resin is extruded and integrated with a stretched A-PET sheet that is primary heat-fixed after primary stretching by heating the A-PET sheet, and then formed into a secondary stretch orientation by thermoforming with a mold of a thermoforming machine. A heat-resistant transparent A-PET container characterized by enhancing crystallization with crystals. The stretched A-PET sheet is uniaxially primary stretched 2 to 5 times in the MD (longitudinal direction) at a stretching temperature of 90 to 120 ° C. using a stretching device using a roll, and then 5 to 20 from the stretching temperature. The heat-resistant transparent A-PET container according to claim 1 or 2, wherein the heat-resistant transparent A-PET container is subjected to primary heat setting at a high temperature. The heat-resistant transparent film according to claim 1, 2 or 3, wherein the stretched A-PET sheet after the primary stretching and primary heat setting has a crystallinity of 22% or more and less than 30% represented by the following formula. A-PET container.

The heat-resistant transparent A-PET container according to claim 1, 3 or 4, wherein the laminated sheet is heat-molded at 80 to 150 ° C and secondarily stretched to enhance crystallization by orientation crystallization by stretching. . The heat-resistant transparent A-PET container according to claim 1, wherein the A-PET layer after the secondary stretching has a crystallinity of 30% or more represented by the following formula: .

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