JP2003276080A - Thermoforming material of polyethylene terephthalate resin and method for producing thermoformed molding of polyethylene terephthalate resin - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing a molding of a polyethylene terephthalate (PET) resin which is high in heat resistance, good in transparency, excellent in physical properties such as rigidity and impact resistance, and improved in gas-barrier properties and other characteristics by a relatively simple means, and to provide a thermoforming material applicable to the method. <P>SOLUTION: A thermoforming polyethylene terephthalate resin material of a stretched film or sheet is obtained by stretching a polyethylene terephthalate resin film or sheet at least in one direction, at a temperature between the glass transition point and melting point of the resin in a draw ratio of 1.5-5. In the method for producing the thermoformed molding of the polyethylene terephthalate resin, the thermoforming material is thermoformed. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polyethylene terephthalate resin thermoforming material, a method for producing a polyethylene terephthalate resin thermoformed article, and a polyethylene terephthalate resin thermoformed article.

[0002]

2. Description of the Related Art Polyethylene terephthalate (PET)
Molded products of resin have high strength and are excellent in various characteristics such as transparency, chemical resistance, light resistance, and abrasion resistance, and can be molded into a sheet-shaped or various-shaped container for beverages, liquid foods, etc. It is widely used in various applications such as containers and food trays.

As described above, the PET molded article has excellent characteristics, but depending on its application, the characteristics such as heat resistance, impact resistance and gas barrier property may not be sufficient.
In order to improve these characteristics, various studies have been made on the resin composition, processing conditions and the like. However, among the above-mentioned characteristics, especially regarding heat resistance and impact resistance,
It is considered that they have contradictory properties, and it is difficult to improve both properties at the same time. For example, a method has been studied in which a polyethylene terephthalate resin containing a nucleating agent for promoting crystallization, which is usually called CPET, is molded into a sheet by an extruder and is used to promote crystallization at the same time as thermoforming. (Japanese Patent Laid-Open Nos. 2000-355091 and 2000-2
97162). However, although the molded product obtained by this method has improved heat resistance, it has a problem in that it is whitened and its transparency is lowered, and its impact resistance is low, especially at low temperatures.

Further, in Japanese Patent Laid-Open No. 8-1765, an attempt has been made to obtain a transparent and heat-resistant molded product by increasing the draw ratio when thermoforming a crystalline resin sheet. Therefore, a thermoforming device having a specific structure to be used is disclosed. However, in the method using such a thermoforming apparatus, the resin sheet is simultaneously stretched during thermoforming, and a complicated thermoforming apparatus is required, and it is difficult to obtain a sufficient stretch ratio, It is also difficult to set suitable conditions for stretching, punching loss after molding becomes large, and it is not possible to obtain excellent thermoformed products at the same time for various properties such as heat resistance, impact resistance, gas barrier property. It's extremely difficult.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the problems of the prior art as described above, and its main purpose is to have high heat resistance and good transparency. A method for producing a molded product of polyethylene terephthalate (PET) resin, which is excellent in various physical properties such as rigidity and impact resistance and has improved properties such as gas barrier property, by a relatively simple means, and effectively in the production method. It is to provide a thermoforming material that can be used.

[0006]

The inventor of the present invention has conducted extensive studies in order to achieve the above object. As a result, a stretched film or sheet obtained by stretching a polyethylene terephthalate resin material formed into a film or sheet into a temperature range of not less than the glass transition point and not more than the crystal melting point by at least 1.5 to 5 times in one direction. Found that the molecular orientation and the oriented crystallization proceed appropriately, and that the stretching residual capacity in the thermoforming step is sufficient. And
In the case of producing a thermoformed product using a film or sheet made of a polyethylene terephthalate resin stretched in this manner, oriented crystallization sufficiently progresses during thermoforming,
We have found that various physical properties such as tensile strength, tear strength, impact resistance, etc. can be improved without impairing transparency, and at the same time, molded products excellent in various physical properties such as heat resistance and gas barrier property can be obtained. The present invention has been completed.

That is, the present invention provides the following polyethylene terephthalate resin thermoforming material, a method for producing a polyethylene terephthalate resin thermoformed product, and a polyethylene terephthalate resin thermoformed product. 1. Polyethylene terephthalate resin film or sheet made of a stretched film or sheet obtained by stretching the film or sheet in the temperature range from the glass transition point to the melting point by 1.5 to 5 times in at least one direction. material. 2. The stretched film or sheet has a crystallinity of 10 to 45.
%, The polyethylene terephthalate resin thermoforming material according to the above item 1, wherein the elongation at break in the stretched direction in the atmosphere at 100 ° C. is 50 to 1300%. 3. The polyethylene terephthalate resin thermoforming material according to item 1 or 2, wherein the stretched film or sheet is heat set after stretching. 4. A method for producing a polyethylene terephthalate resin thermoformed product, which comprises thermoforming the polyethylene terephthalate resin thermoforming material according to any one of items 1 to 3 above. 5. The method for producing a polyethylene terephthalate resin thermoformed product according to item 4, wherein heat setting is performed after thermoforming. 6. Polyethylene terephthalate resin thermoforming, which has a crystallinity of 15% or more, a haze value of 15% or less, and an increase in the haze value of 15 points or less after immersion in hot water of 100 ° C. for 5 minutes. Goods.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION PET resin film or sheet In the method of the present invention, a film or sheet made of polyethylene terephthalate (PET) resin is used as a starting material for carrying out the stretching treatment.

There is no particular limitation on the kind of PET resin used for forming the film or sheet, and not only the homo-form of polyethylene terephthalate but also a part of terephthalic acid such as 2,6-naphthalenedicarboxylic acid, Isophthalic acid, hexahydroterephthalic acid, hexahydroterephthalic acid, hydroxybenzoic acid, diphenyldicarboxylic acid, diphenyletherdicarboxylic acid, diphenylsulfonedicarboxylic acid, diphenoxyethanedicarboxylic acid, 3,5-dicarboxybenzenesulfonic acid,
Copolymer resins substituted with one or more of oxalic acid, succinic acid, glutaric acid, sebacic acid and the like, and ester derivatives thereof can also be used.

Further, a part of ethylene glycol is used, for example, in a small amount of cyclohexanedimethanol, 1,2-propylene glycol, trimethylene glycol, tetramethylene glycol, pentamethylene glycol, hexamethylene glycol, neopentyl glycol, 1,4.
Copolymer resins substituted with one or more of bishydroxybenzene, polyalkylene glycol (eg, polyethylene glycol, polytetramethylene glycol, polypropylene glycol) can also be used.

Further, trifunctional or higher functional compounds such as glycerin, pentaerythritol, trimellitic acid, 5-hydroxyisophthalic acid and the like may be used in such a degree that the polymer is substantially linear. For example, a copolymerized PET resin substituted with p-phenylphenol, benzyloxybenzoic acid, naphthalene monocarboxylic acid, polyethylene glycol monomethylene ether, etc. can also be used.

The PET resin used for producing a PET resin film or sheet has an intrinsic viscosity (IV value).
It is preferably about 0.6 to 0.9 dl / g.

The PET resin may be newly polymerized or synthesized, or may be a recycled resin. When a recycled resin having a low intrinsic viscosity is used, the intrinsic viscosity may be improved by solid phase polymerization or other methods.

The PET resin may be used after being sufficiently dried according to a conventional method. Further, if necessary, various known additives such as stabilizers, antibacterial agents, colorants, antistatic agents, slip agents, and other polymers may be mixed in small amounts.

If necessary, a small amount of a crystal nucleating agent may be supplementarily added. The usable range of the nucleating agent varies depending on the type of PET resin used as a raw material, the stretching conditions,
Although it cannot be determined unconditionally, if the amount of the nucleating agent used is too large, large spherulites will be formed and whiteness will decrease transparency, so it may be within the range where such adverse effects do not occur. preferable. As the crystal nucleating agent (accelerator), an inorganic nucleating agent such as talc, silica or kaolin, a polyolefin resin such as high density polyethylene resin, a polybutylene terephthalate oligomer, an organic nucleating agent such as sodium benzoate, sodium stearate, etc. is used. be able to.

The PET resin film or sheet may be any film or sheet obtained by using the above-mentioned PET resin, and its manufacturing method is not particularly limited. For example, a PET resin film or sheet used in the present invention can be obtained by supplying a PET resin as a raw material to an extruder and molding it. in this case,
For example, a film manufactured by cooling the extruded film or sheet melt with a casting roll and cooling it through a flat die connected to an extruder can be preferably used. Further, a product obtained by inflation molding by connecting a circular die to an extruder may be used, or a product obtained by calender molding may be used.

The thickness of the PET resin film or sheet used as a starting material is not particularly limited, but normally, a thickness of about 0.1 to 6 mm can be used. Stretching process In the present invention, the above-mentioned PET resin film or sheet is stretched at least in one direction by 1.5 to 5 times in a temperature range of not less than the glass transition point and not more than the melting point to obtain a stretched film or sheet.

The film or sheet stretched under such conditions is in a state where molecular orientation and oriented crystallization are appropriately advanced, and when the film or sheet is thermoformed, the oriented crystallization is further advanced to obtain tensile strength, Tear strength, impact resistance, gas barrier property,
It is possible to obtain a thermoformed product that is excellent in various properties such as heat resistance. Further, since the above-mentioned stretched film or sheet has an appropriate stretch surplus upon thermoforming, it can be made into a desired molded article by thermoforming.

The method for stretching the PET resin film or sheet is not particularly limited, and any method can be appropriately adopted as long as the film or sheet can be physically stretched. For example, in general, the stretching method is 1
An axial stretching method, a biaxial stretching method and the like are known, but any of these methods may be used. Among these, the uniaxial stretching method is a method of stretching a PET resin film or sheet in only one direction, and usually, a device in which a plurality of rollers are combined is used and stretching is performed at a high take-up roller speed. The method is adopted. In addition, the biaxial stretching method is a method of stretching in two directions in the vertical and horizontal directions, and usually, an apparatus in which a roller used in the uniaxial stretching method is combined with a device called a tenter for widening is used. In the biaxial stretching method,
There are a sequential method of stretching in the longitudinal and lateral directions alternately and a simultaneous method of stretching in the longitudinal and lateral directions at the same time, but either method may be used. Moreover, as a method other than the above-mentioned uniaxial stretching method or biaxial stretching method,
For example, a method of stretching the balloon of the film by inflating it with a high pressure may be used.

In the present invention, the PET to be stretched is the object.
It is necessary to carry out the stretching operation within a temperature range not lower than the glass transition point of the resin and not higher than the melting point. By performing the stretching operation within such a temperature range, a stretched film or sheet in which the molecular orientation and the oriented crystallization have appropriately proceeded can be obtained.

On the other hand, when the stretching operation is performed at a temperature below the glass transition point, neck-in occurs during stretching,
The stretched portion may spread from that portion, and it is difficult to obtain a stretched film or sheet having uniform and good properties. Further, even when the temperature during the stretching operation exceeds the melting point, it is difficult to obtain sufficient molecular orientation and oriented crystals. For example, when a sheet is produced by the extrusion casting method, the resin discharged from the T die has a temperature higher than the melting point, but the resin sheet thus obtained has insufficient molecular orientation and oriented crystallization. Is.

The above stretched film or sheet is required to have a stretch ratio of 1.5 to 5 in at least one direction. That is, when the uniaxial stretching method is adopted, the stretching ratio in the stretching direction must be within the range of 1.5 to 5 times, and when the biaxial stretching method is adopted,
It is necessary that the stretching ratio is within a range of 1.5 to 5 times in each stretching direction. In the present invention, in particular,
It is preferable that biaxial stretching is carried out in two longitudinal and lateral directions, and the stretching ratio in each direction is within a range of 2 to 3 times.

In general, the behavior when a PET resin film or sheet is stretched at a constant rate at a temperature not lower than the glass transition point and not higher than the melting point is a graph showing stress on the vertical axis and elongation or time on the horizontal axis. When it is expressed, it first exhibits rubber elasticity, but elongation without stress increase in a short time, so-called flow stretching, continues for a very long time, stress increases sharply after a bending point and breaks in a short time. The last period is a range called oriented crystallization stretching. By stretching in such a range, oriented crystallization can be sufficiently advanced, but oriented crystallization stretching is a very narrow range. . Ordinary thermoforming is performed in the range of flow drawing, and although the molecular orientation is made to some extent, crystallization hardly progresses and the crystallinity is usually 5%.
The value is less than or equal to the degree and close to 0%.

In the present invention, by stretching the PET resin film or sheet in at least one direction by 1.5 to 5 times, molecular orientation and oriented crystallization are appropriately promoted, and moreover, the stretching residual capacity during thermoforming is moderate. It can be a stretched film or sheet. By performing thermoforming using such a stretched film or sheet, oriented crystallization proceeds efficiently in a short time, and various properties such as tensile strength, tear strength, impact resistance, gas barrier property, heat resistance, etc. It is possible to obtain a thermoformed product which is excellent in transparency and also has good transparency.

The specific draw ratio may be appropriately determined within the range of the draw ratio described above, depending on the type of the thermoformed product of interest. For example, a film or sheet having a relatively small draw ratio has a large draw capacity in the thermoforming step, and is suitable for a molded product called a deep product having a large drawing ratio, and a film or sheet having a high draw ratio. Since it has a small drawing margin, it is suitable for shallow objects with a small drawing ratio.

The thickness of the film or sheet after the stretching treatment is not particularly limited and may be appropriately determined according to the intended thermoformed product, but it is usually in the range of about 0.05 to 1 mm. .

In the present invention, the crystallinity of the stretched film or sheet obtained by the above stretching operation is 10 to 45.
%, And more preferably 25 to 40%. If the crystallinity of the stretched film or sheet is too low, it is difficult to obtain a high crystallinity by thermoforming, and it is difficult to obtain a thermoformed product having sufficient properties. On the other hand, if the crystallinity is too high, the stretching margin is too small, which is unsuitable as a molding material.

In the present invention, for the crystallinity (%), a sample having a size of about 3 to 30 mm square is cut out from a stretched film or sheet at three or more points without being substantially biased in a portion used for thermoforming. , The crystallinity of each sample was 0 based on the density value obtained by the density gradient tube method.
% Is the average value of the values calculated by the following formula, where the density is 1.3330 g / cm ³ and the crystallinity is 50% is 1.3913 g / cm ³ .

Crystallinity (%) = 50 × (density−1.3330) /
(1.3913-1.3330) Furthermore, the stretched film or sheet obtained by the above stretching operation preferably has a breaking elongation percentage in the stretched direction of 50 to 1300% when held in the atmosphere at 100 ° C. , 100 to 1000% is more preferable.

When the elongation at break is within the above range, it is possible to obtain a stretched film or sheet having excellent thermoformability and capable of obtaining a thermoformed product having good characteristics. On the other hand, if the elongation at break is too small, it is unsuitable as a molding material due to lack of the stretch capacity, and if the elongation at break is too large, the stretching effect is insufficient, and Even if molding is performed, the obtained molded product has insufficient molecular orientation and oriented crystallization, and thus cannot obtain sufficient characteristics.

The elongation at break in directions other than the stretched direction is not particularly limited and may be out of the above range, but the elongation at break in all directions is preferably in the above range. .

In the present invention, the elongation at break at 100 ° C. is determined by using a tensile tester equipped with an air oven.
The temperature inside the oven was adjusted to 100 ° C, the sample was set and held for 3 minutes, and then a tensile test was performed at a speed of 100 mm / min. The elongation at break was measured as a percentage of the length of the sample before the test. Is the value obtained as.

In order to satisfy the above-mentioned conditions of crystallinity and elongation at break for the stretched film or sheet,
Stretching conditions may be appropriately set according to the type of resin used, but the stretched material may be heat set, if necessary.

The heat setting is a process of heating the PET resin film or sheet to be processed to a high temperature during the stretching process while maintaining the tensile state. The temperature of the heat setting may be a material temperature that is equal to or higher than the glass transition point of the material used and equal to or lower than the melting point, but is preferably higher than the temperature during the stretching treatment. The heat setting time is not particularly limited, but usually 0.1 to 3
It is preferably about 0 seconds. By performing the heat setting, residual strain or residual stress is released, and it is possible to eliminate or reduce obstacles such as large shrinkage due to preheating of thermoforming and molding which is difficult due to enormous shrinking stress.

The material characteristics after heat setting are 10
When kept in an air oven at 0 ° C for 5 minutes, the heating dimensional shrinkage in any direction is preferably 30% or less, and the shrinkage stress when the material is fixed in an air oven at 100 ° C is 5 kg. / Mm ² or less is preferable.

The stretched film or sheet made of PET resin obtained by the above-mentioned method has a suitable degree of molecular orientation and oriented crystallization and has a stretching capacity in the thermoforming step. Therefore, the obtained stretched film or sheet,
While having good thermoforming performance, molded products formed using this have various properties such as tensile strength, tear strength, impact resistance, etc., in which oriented crystallization sufficiently progresses without impairing transparency. The physical properties are improved and various physical properties such as heat resistance and gas barrier properties are also excellent.

The stretching treatment may be carried out as an independent process or as an in-line process such as extrusion.

After the stretching treatment, thermoforming may be continuously performed in-line. In this case, it is not necessary to return the material to room temperature after the stretching treatment, and the material can be continuously moved to the molding zone for thermoforming. In addition, the stretching process,
It is necessary to carry out the thermoforming as a completely separate step, which makes it possible to obtain a thermoforming material that satisfies all the above conditions at the same time. There is no particular limitation on the thermoforming method using a stretched film or sheet obtained by the method thermoforming process described above, for example, vacuum forming, pressure forming, plug-assist pressure forming, etc. matched die molding, appropriately applying a known thermoforming methods it can. In particular, it is preferable to use a molding machine that can obtain a considerably large molding pressure as compared with the molding of ordinary PET materials. From this point of view, it is preferable to use the matched die molding which can apply a large force and can easily adjust the temperature such as heating and cooling and heat set.

The specific molding pressure may be appropriately determined according to the degree of stretching and thickness of the material used, the dimension of the molded product (molding projected area, drawing ratio, etc.).

The thermoforming temperature may be a temperature not lower than the glass transition point of the main material resin and not higher than the melting point, but usually 10
Thermoforming is often performed in a temperature range of about 0 to 150 ° C.

Generally, before thermoforming, 2
Preheating is performed for 20 to 150 seconds at an oven temperature of 00 to 300 ° C. As the preheating method, various methods such as radiant or convection heating with an electric heater, infrared heating radiant heating, heating with a gas combustion flame, and pinching heating with a heating plate can be adopted. Since the stretched film or sheet may shrink during preheating, in order to avoid this, a method of fixing the peripheral edge of the material, two opposing edges, etc., and preheating by sandwiching with a hot plate Etc. may be appropriately adopted.

By performing heat setting during thermoforming, residual strain or residual stress can be released, crystallization can be promoted, and dimensional stability and heat resistance can be further improved. As a heat setting method at the time of thermoforming, specifically, the high temperature may be maintained for a certain period of time with the mold attached. The heat setting temperature may be a material temperature that is equal to or higher than the glass transition point of the material used and equal to or lower than the crystal melting point, and is preferably higher than the temperature during preheating and extension. The heat setting time is not particularly limited, but usually,
It is preferably about 0.1 to 30 seconds. PET resin thermoformed product The thermoformed product thus obtained has large tensile strength, tear strength, impact resistance and the like, and has improved heat resistance, gas barrier property and the like. In addition, the molded product has high transparency and is free from fogging.

In particular, according to the present invention, the crystallinity is 15%.
Or more, more preferably 25% or more, haze value is 15%
Below, more preferably 10% or less, a molded product having both high crystallinity and transparency, good heat resistance and less likely to whiten, and haze after immersion in hot water at 100 ° C. for 5 minutes. It is possible to obtain a thermoformed product having high strength, transparency, and heat resistance, which has not been obtained by the conventional PET resin thermoformed product, in which the value increase is 15 points or less, more preferably 8 points or less.

The value (point) of increase in haze value after immersion in hot water is determined from the haze value (%) of the molded article measured after immersion in hot water before immersion in hot water. It is a value obtained by subtracting the haze value (%) of the molded product.

Further, according to the present invention, the dimensional shrinkage ratio after immersing in hot water of 100 ° C. for 5 minutes is 15% or less, more preferably 8% or less, which is excellent in dimensional stability upon heating. You can get the goods.

Thermoformed articles satisfying the above characteristics are highly transparent unless they are colored or otherwise added, and are subjected to tension, tearing,
It is excellent in mechanical strength such as impact resistance, does not cause whitening or clouding even when heated with hot water, and has good dimensional stability during heating, making it particularly suitable for applications requiring heat resistance. .

The thermoformed product satisfying each of the above characteristics can be obtained by increasing the oriented crystallinity of the molded product in the above-mentioned manufacturing method. Specifically, the stretching during production of the thermoforming material and the stretching during thermoforming were combined by adjusting the degree of stretching during production of the thermoforming material according to the degree of stretching during the thermoforming step. It suffices that the degree of stretch exceeds the bending point of the flow stretch of the material and is within the limit of extension fracture, that is, within the range of oriented crystallization stretch.

Further, in order to reduce the dimensional shrinkage during heating to a low value, in addition to increasing the oriented crystallinity, heat setting may be sufficiently performed as necessary.

The crystallinity of the PET resin thermoformed product of the present invention is measured by measuring the crystallinity of a stretched film or sheet for 10 or more samples cut from the molded product and having a size of about 3 to 30 mm square. Similarly to the method, the average value of crystallinity calculated based on the density measured by the density gradient tube method is used. In this case, at least one sample for each surface is cut out in accordance with the shape of the molded product so that samples for crystallinity measurement can be taken from each part of the surface of the molded product without bias. The crystallinity of the thermoformed product obtained by such a method is preferably 15% or more, more preferably 25% or more.

The haze value of the thermoformed product is JIS
It is a value measured based on K-7105.

Further, the dimensional shrinkage after being immersed in hot water of 100 ° C. for 5 minutes is 30 to 50 m in advance on the surface of the thermoformed product.
It is a value in which a marked line having an interval of about m is put in, the distance between the marked lines is measured after hot water immersion to obtain a contracted width, and the contracted width is expressed as a percentage with respect to the marked line width before hot water immersion. .
It should be noted that the thermoformed product is provided with five or more sets of marked lines so that the locations and directions are different as much as possible, and the average value of the dimensional shrinkage ratios of these sets of marked lines is taken as the dimensional shrinkage ratio of the thermoformed product. To do. In this case, when the molded product has a complicated shape, the molded product may be appropriately cut open, pressed and marked with a marked line, and the linear distance of the material surface is measured.

In addition, in such a measurement, when a plurality of measurements cannot be freely performed in one molded product,
It may be performed using a plurality of samples molded under the same conditions.

A so-called CP containing a crystallization accelerator is added.
By using a material called ET, it is possible to obtain a PET resin thermoformed product having a high degree of crystallinity, but this molded product is strongly whitened even with a slight crystallization and has a low transparency, The impact strength is also inferior. Especially molded products with high crystallinity have low impact resistance and crystallinity of 35%.
The above is not practical. On the other hand, according to the manufacturing method of the present invention, it is possible to obtain a thermoformed product having high transparency and sufficient thermal shock resistance even if it has a high crystallinity of about 55%. .

The thermoformed article obtained by the method of the present invention is
It has good heat resistance, and has excellent characteristics that it is difficult to be softened and deformed even when hot water is poured, and it is difficult to shrink the dimensions. In addition, since it has good gas barrier properties, it has low gas permeability to oxygen, carbon dioxide, etc., and can maintain a regulated gas composition for maintaining a vacuum state and freshness for a long time, and has good properties as a food packaging material. It is a thing.

[0055]

The thermoformed product obtained by the present invention is excellent in tensile strength, tear hardness, impact resistance and the like, has improved heat resistance and gas barrier property, and has high transparency and almost no cloudiness. It is not a molded product.

Such a thermoformed article can be effectively used for packaging foods and the like and for various miscellaneous goods. In particular, when it is used for food packaging, brittle damage that is likely to occur during refrigeration or the like can be suppressed, and further, the gas barrier property is good, so that the storability of food can be improved. Further, since the heat resistance is improved, hot water or high-temperature food can be stored, and heating in a microwave oven or the like is possible, which greatly expands the range of applications.

[0057]

EXAMPLES The present invention will be described in more detail with reference to examples.

Example 1 Using a polyethylene terephthalate resin having an IV value of 0.61, a thickness of 1.5 m was obtained by a T-die extrusion casting method.
m PET resin sheet was prepared.

This PET resin sheet was stretched 3 times in the machine direction (MD) at 85 ° C. and further transversely (TD) at 160 ° C.
After stretching 3 times, the temperature in the furnace at an air temperature of 220 ° C is increased to 1.2.
Heat setting was carried out by passing the material in seconds to obtain a stretched sheet for thermoforming. The PET resin used as a material had a glass transition point of 79 ° C and a melting point of 252 ° C. The following properties of the obtained stretched sheet were measured. The results are shown in Table 1 below. * Crystallinity: Based on the density value obtained by the density gradient tube method, a total of 3 samples of about 5 x 5 mm were cut out from the center part of the stretched sheet and two parts of 50 mm in the left-right width direction. , Is the average value of the values calculated by the following formula.

Crystallinity (%) = 50 × (density−1.3330) /
(1.3913-1.3330) * Tensile strength: Strength just before fracture when stretched at a speed of 100 mm / min. * Elongation at break: A value obtained by measuring the elongation length at break when the sample was elongated at a speed of 100 mm / min as a percentage of the length of the sample before the test. * Heat elongation at 100 ℃ in the air: 1 in an oven at 100 ℃
The elongation length at break when elongated at a speed of 00 mm / min was calculated as a percentage of the length of the sample before the test. * Heat shrinkage stress at 100 ° C in air: Maximum stress when a test piece is fixed in an oven at 100 ° C. * Boiling water heat shrinkage: A test line is marked with a width of 50 mm, heated in boiling water for 5 minutes, the width of the marked line before and after heating is measured to obtain the contracted width, and this is the marked line before heating. Value obtained as a percentage of the width. Then, after preheating the above-mentioned stretched sheet in an air oven so that the sheet temperature becomes 115 ° C., two transparent lids of a round dish with an outer diameter of 132 mm and a depth of 9 mm are taken by a vacuum pressure method, and a mold is formed. It was thermoformed. The mold temperature during thermoforming was 50 ° C., and the pressing time was 4 seconds.

The obtained molded product had a high haze of 2.4% and high transparency, and was good. The measurement results of various characteristic values of the molded product are shown in Table 2 below. In Table 2, the tensile strength is the strength immediately before breaking when stretched at a speed of 100 mm / min, and the elongation at break is the elongation length at break when stretched at a speed of 100 mm / min. Is a value obtained as a percentage of the length of. In addition, the crystallinity of the thermoformed product is at least one piece from each side of the thermoformed product and has a size of about 5 × 5 mm.
Of the sample, and for a total of 10 samples,
It is the average value of the crystallinity obtained by the above method.

Further, in order to evaluate the practical heat resistance of the obtained thermoformed product, the molded product was immersed in boiling water at about 100 ° C. for 5 hours.
It was kept for a minute, returned to room temperature, dried, and the appearance was observed. As a result, the shape was almost completely retained, no haze or whitening phenomenon was observed, and the haze value was hardly increased, and good heat resistance was exhibited. Further, in this test, five sets of marked lines were preliminarily put on the molded product so that the positions and directions were different as much as possible, and the shrinkage ratio between the marked lines after the test was measured.
This value is also shown in Table 2.

Example 2 Using the stretched sheet obtained in the same manner as in Example 1, one transparent lid of a lunch box pack of 168 mm × 168 mm × 25 mm (depth) was prepared by the following method and heated using a mold. Molded.

A molding machine called a hot plate molding machine was used for thermoforming, sandwiching a hot plate set at 226 ° C. for 1.8 seconds for preheating, and air-pressing with an air pressure of 3 kg / cm ² for 5 seconds for molding. The mold temperature was 230 ° C., that is, the temperature at which heat setting was possible.

The obtained molded product had a high haze of 2.3% and high transparency, and was good. Further, the practical heat resistance was evaluated in the same manner as in Example 1, but the shape was almost completely retained, no clouding or whitening phenomenon was observed, and the haze value hardly increased. The measurement results of various characteristic values measured in the same manner as in Example 1 are also shown in Table 2 below.

Example 3 Using the stretched sheet obtained in the same manner as in Example 1, two transparent trays for delicacies having a size of 180 × 98 × 15 mm (depth) were thermoformed in the following method using a mold. did.

A vacuum pressure air forming machine was used for thermoforming, and after preheating the sheet temperature to 130 ° C. in an air oven,
Molding was performed by air pressure for 10 seconds at a mold temperature of 230 ° C., that is, a temperature at which heat setting proceeds.

The obtained molded product had a haze of 2.3% and high transparency, and was good. Further, the practical heat resistance was evaluated in the same manner as in Example 1, but the shape was almost completely retained, no clouding or whitening phenomenon was observed, and the haze value was hardly increased. The measurement results of various characteristic values measured in the same manner as in Example 1 are also shown in Table 2 below.

Comparative Example 1 Using a polyethylene terephthalate resin having an IV value of 0.65, a thickness of 0.18 m was obtained by a T-die extrusion casting method.
A non-stretched sheet of m was obtained. The properties of the obtained non-stretched sheet are shown in Table 1.

Using this non-stretched sheet, the outer size is 245 ×
A 212 × 40 mm egg pack material was thermoformed. This egg pack material is for folding 10 eggs in the center parallel to the long side.

For thermoforming, a vacuum forming machine was used to preheat the unstretched sheet to 110 to 115 ° C., and then the mold temperature was 40 ° C.
Continuous molding was performed in a cycle of 5.5 seconds.

The obtained molded product had a haze of 3.4%. This molded product was evaluated for practical heat resistance in the same manner as in Example 1. As a result, the shape was greatly destroyed during the heat resistance test, and it became almost opaque due to the strong whitening phenomenon, and it was difficult to accurately measure it due to severe deformation, but the increase in the haze value far exceeded 30 points. It was a thing.
Further, this product was fragile to the touch.

Table 2 below also shows the measurement results of various characteristic values measured in the same manner as in Example 1.

Comparative Example 2 A polyethylene terephthalate resin having an IV value of 0.68 was used and a thickness of 0.4 m was obtained by a T-die extrusion casting method.
A non-stretched sheet of m was obtained. The properties of the obtained non-stretched sheet are shown in Table 1.

Using this unstretched sheet, a diameter of 130 m
A round plum container having a depth of m and a depth of 60 mm was thermoformed. A vacuum forming machine is used for thermoforming, and an unstretched sheet is set to 110 to 115.
After preheating to ℃, 36 shots per shot were taken at a mold temperature of 40 ℃, and continuous molding was performed for 6 seconds per cycle.

The obtained molded product had a haze of 3.8%. This was evaluated for practical heat resistance in the same manner as in Example 1. As a result, the shape collapsed significantly during the heat resistance test,
Furthermore, the strong whitening phenomenon makes it almost opaque, and it is difficult to measure accurately because of deformation, but the increase in haze value far exceeds 30 points. Also, this product was fragile to the touch.

The measurement results of various characteristic values measured in the same manner as in Example 1 are also shown in Table 2 below.

[0078]

[Table 1]

[0079]

[Table 2]

As is clear from the above results, Example 1
The thermoformed products obtained in Nos. 3 to 3 had high crystallinity, high strength, and good physical properties. Further, it showed small heat shrinkage and good heat resistance.

On the other hand, in the thermoformed products obtained in Comparative Examples 1 and 2, the crystallization hardly progressed, the strength was low, the heat shrinkage was large, and the heat resistance was poor. .

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Claims (6)

[Claims] 1. A polyethylene terephthalate comprising a stretched film or sheet obtained by stretching a polyethylene terephthalate resin film or sheet at least in one direction by 1.5 to 5 times in a temperature range from a glass transition point to a melting point. Resin thermoforming material. 2. A stretched film or sheet having a crystallinity of 10
The polyethylene terephthalate resin thermoforming material according to claim 1, which has a breaking elongation of 50 to 1300% in the stretched direction in the atmosphere of about 45% to 100 ° C. 3. The polyethylene terephthalate resin thermoforming material according to claim 1, wherein the stretched film or sheet is heat set after stretching. 4. A method for producing a polyethylene terephthalate resin thermoformed product, which comprises thermoforming the polyethylene terephthalate resin thermoforming material according to any one of claims 1 to 3. 5. The method for producing a polyethylene terephthalate resin thermoformed product according to claim 4, wherein heat setting is performed after thermoforming. 6. A crystallinity of 15% or more and a haze value of 15%.
A polyethylene terephthalate resin thermoformed product characterized by having an increase in haze value of 15 points or less after immersion in hot water of 100 ° C. for 5 minutes.