JPH10180967A - Heat-resistant multilayer sheet and container using the sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate the generation of a whitening phenomenon or a deformation at the time of boiling or retort sterilization, and cracks during the dropping and prevent transparency and oxygen barrier properties from deteriorating even after the sterilization by laminating a polyester resin layer at a lower Tg (glass transition temperature) than a high Tg resin layer, on the high Tg resin layer at a specific Tg. SOLUTION: At least, two polyester resin layers or more at a lower Tg than a high Tg resin layer at Tg of 120-180 deg.C containing polyallylate and polyethylenenaphthalate resins are laminated on the resin layer form a heat- resistant multilayer sheet. The examples of the best-suited polyethylenenaphthalate resin used for the high Tg layer and the low Tg layer are of 2,6-naphthalenedicarboxylic acid and ethyleneglycol. The entire thickness of the heat-resistant multilayer sheet after lamination is preferably 0.3-1.1mm, and at least, one of the layers of the sheet is made up of the high Tg layer and is preferably 0.06mm or more and more preferably, 0.1mm or more.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat-resistant multi-layer sheet, and more particularly to a heat-resistant multi-layer sheet having excellent transparency and gas barrier properties and capable of forming a container capable of sterilizing boil and retort, and a container thereof. It is.

[0002]

2. Description of the Related Art Conventionally, as containers for fruit jelly, coffee jelly, pudding, prepared foods, etc., injection-molded containers of polystyrene or two and three layers made of polypropylene (PP) and ethylene / vinyl acetate copolymer (EVOH). Vacuum forming containers for sheets and the like are used.

[0003] However, these have the following disadvantages. That is, a polystyrene injection molded container is good in that it is transparent, but has insufficient heat resistance and is inferior in oxygen barrier properties. Further, since the vacuum-formed container made of PP / EVOH / PP is cloudy, the contents are not very visible. In addition, since EVOH is greatly affected by humidity, PP-EV
In a container made of OH, the oxygen barrier property is significantly reduced during boiling sterilization or retort sterilization. Further, there is a problem that PP smells of olefin or the taste of the contents changes because PP adsorbs a specific component.

[0004]

DISCLOSURE OF THE INVENTION The present invention does not cause whitening or deformation of fruit jelly, coffee jelly, pudding, prepared foods, and the like even when sterilized with hot water, boil, or retort. There is no container to offer. Another object of the present invention is to provide a container which is transparent even after sterilization and does not cause a decrease in oxygen barrier property due to sterilization. Further, the present invention provides a container in which the taste and odor of the contents are not changed by adsorbing a specific chemical substance.

The present invention has been made in view of the above problems, and is transparent even after boil sterilization or retort sterilization.
An object of the present invention is to provide a container made of a polyester resin which has good oxygen barrier properties without change, and has no change in taste or smell of contents.

[0006]

The present invention comprises at least two or more layers of a high Tg resin layer having a glass transition temperature (Tg) of 120 to 180 ° C. and a polyester resin layer having a lower Tg than this layer. A heat resistant multilayer sheet and a container thereof, wherein the high Tg resin layer is a layer containing a polyarylate and a polyethylene naphthalate resin.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail. As the high Tg resin used in the high Tg layer having a Tg of 120 to 180 ° C. of the present invention, a polyarylate resin and a polyethylene naphthalate resin are used in combination. Examples of the polyarylate resin include U polymer (Unitika), APE (Bayer), Dure
l (Hoechst), Ardel (Amoco), NAP
Commercially available products such as (Kanebuchi Chemical Co., Ltd.) are used, but polyarylate having an intrinsic viscosity of 0.4 to 0.65 dl / g and a low melt viscosity synthesized from terephthalic acid, isophthalic acid and bisphenol A is used. The lower the melt viscosity with the resin forming the low Tg polyester-based resin layer, the better the waveform is not generated on the multilayer sheet. High Tg
The Tg of the layer is measured by DSC, and can be measured as one Tg despite including a polyarylate resin and a polyethylene naphthalate resin.

The polyethylene naphthalate resin which can be used for both the high Tg layer and the low Tg layer in the present invention is obtained from 2,6-naphthalenedicarboxylic acid and ethylene glycol. -Dicarboxylic acids that can be contained as copolymerization components other than naphthalenedicarboxylic acid include aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, diphenyl-4,4'-dicarboxylic acid, diphenoxyethane dicarboxylic acid, and derivatives thereof. , Adipic acid, sebacic acid, azelaic acid, succinic acid and other aliphatic dicarboxylic acids and derivatives thereof, cyclohexanedicarboxylic acid, alicyclic dicarboxylic acids and derivatives thereof such as hexahydroterephthalic acid, p-oxybenzoic acid, oxycaproic acid And the like oxyacids and derivatives thereof. The copolymerization amount is preferably 20 mol% or less, more preferably 10 mol% or less, so as not to impair the intrinsic properties of polyethylene naphthalate.

The diol components other than ethylene glycol which can be contained as a copolymer component in the polyethylene naphthalate resin include aliphatic glycols such as diethylene glycol, trimethylene glycol, tetramethylene glycol and neopentyl glycol, and cyclohexane. Alicyclic glycols such as dimethanol; aromatic glycols such as bisphenol A and alkylene oxide adducts of bisphenol A; and the copolymerization amount thereof is 20 mol% within a range not impairing the properties of polyethylene naphthalate. Or less, more preferably 10 mol% or less. The content of the polyethylene naphthalate resin in the high Tg resin layer is preferably 89 to 15% by weight. If the polyethylene naphthalate resin is 90% by weight or more, heat resistance is insufficient, and if it is less than 15% by weight, sheet moldability tends to deteriorate.

The above-mentioned polyethylene naphthalate resin can be produced by a conventionally known production method. That is, 2,6-naphthalenedicarboxylic acid is directly reacted with ethylene glycol and / or the third component to remove water and esterify, followed by polycondensation under reduced pressure, It is produced by a transesterification method in which 2,6-naphthalenedicarboxylate is reacted with ethylene glycol and / or a third component to distill off methyl alcohol and transesterify, followed by polycondensation under reduced pressure.

The intrinsic viscosity of the polyethylene naphthalate resin in the present invention is in the range of 0.50 to 1.10 dl / g, preferably 0.60 to 0.85 dl / g. When the intrinsic viscosity is less than 0.5 dl / g, the strength of the sheet is insufficient,
When the intrinsic viscosity is 1.1 dl / g or more, the melt viscosity is too high at the time of forming an extruded sheet, and the appearance of the sheet is deteriorated.

The polyethylene naphthalate resin used in the high Tg layer of the present invention may be used alone, but may be used by blending it with another resin in advance depending on the purpose. For example, a polyethylene terephthalate resin, a copolymerized polyester resin such as 1,4-cyclohexanedimethanol, a copolymerized polyethylene naphthalate resin such as polyethylene glycol, and the like can be given.

High Tg in the heat-resistant multilayer sheet of the present invention
Polyester resin used for the low Tg polyester resin layer other than the layer, polyethylene terephthalate,
Resin such as third component copolymerized polyethylene naphthalate such as 1,4-cyclohexanedimethanol, polyethylene naphthalate, polyethylene naphthalate, bis (4-β-hydroxyphenyl) sulfonic acid, and the like; Blends can be mentioned.
Of these, polyethylene naphthalate resins are preferred in terms of heat resistance and transparency, and the proportion in the layer is preferably 50% by weight or more. The haze measured on the multilayer sheet and its container is 5% or less, preferably 3% or less. Further, the multilayer sheet is preferably a heat-resistant and transparent sheet capable of maintaining a haze of 5% or less even when subjected to steam treatment at 110 ° C. for 30 minutes.

The heat-resistant multilayer sheet of the present invention has an overall thickness of 0.3 to 1.1 mm, preferably 0.5 to 0.9 mm.
mm. When the thickness of the sheet is smaller than 0.3 mm, heat resistance is not obtained. When the thickness of the sheet is 1.1 mm or more,
It is difficult to obtain a container having a good thickness distribution by vacuum forming, and the material cost increases. The heat-resistant sheet of the present invention comprises at least one high Tg layer and has a thickness of at least 0.0
6 mm or more is preferable, and 0.1 mm or more is more preferable. When the thickness of the high Tg layer is less than 0.06 mm, heat resistance tends to be insufficient. The thickness of the polyester resin layer is
The thickness is obtained by subtracting the thickness of the high Tg layer from the entire sheet thickness. However, if the thickness of the polyester-based resin layer is less than 30% of the total thickness, the oxygen barrier property decreases,
It is preferable that the thickness is 30% or more of the entire sheet thickness.
One example of the thickness configuration of the heat-resistant multilayer sheet of the present invention is high Tg.
Layer / polyester resin layer / high Tg layer = 6/88 / 6-
35/30/35, a preferred configuration example is 10/80/1
0 to 20/60/20.

[0015] In the present invention, the lug portion formed at the time of forming the sheet and the punched remaining sheet formed at the time of vacuum forming of the container are collected, crushed, mixed with the polyester resin, and extruded to form a sheet. It is desirable to select a polyester resin having good compatibility with the resin of the high Tg resin layer and good sheet transparency. Preferred resins for these polyester-based resin layers include polyethylene naphthalate obtained by copolymerizing a third component such as polyethylene naphthalate, 1,4-cyclohexanedimethanol, or bis (4-β-hydroxyphenyl) sulfonic acid with an oxygen barrier. It is preferable in terms of properties.

In the present invention, a heat stabilizer, a thermal oxidation stabilizer, an antistatic agent, a weather resistance stabilizer,
Lubricants and the like can be added as long as the object of the present invention is not impaired. It is also preferable to use a vent-type twin-screw extruder in order to suppress a decrease in the intrinsic viscosity of the polymer during sheet formation and to reduce the acetaldehyde content generated during sheet formation.

Hereinafter, the present invention will be described specifically with reference to examples, but the present invention is not limited to these examples. The method for measuring the main characteristic values will be described below. (1) Intrinsic viscosity (IV) of polyethylene naphthalate (PEN) and polyarylate (PAr) 30 ° C. in a mixed solvent of 1,1,2,2-tetrachloroethane / p-chlorophenol (1: 3 weight ratio) From the solution viscosity at (2) Measurement of Tg by DSC 10 mg of each copolymer was weighed with a DSC type RDC220 manufactured by Seiko Denshi Kogyo KK and measured at a heating rate of 10 ° / min. Analysis of Tg was performed according to JIS K7122. (3) Measurement of haze It was measured with a haze meter manufactured by Toyo Sokki Co., Ltd.

Examples 1 to 4 and Comparative Examples 1 and 2 Two 30 mmφ twin screw extruders manufactured by Ikegai Iron Works Co., Ltd. were used, and a feed block type T table having a lip width of 340 mm for forming two kinds and three layers of sheets was used. Then, a sheet was formed as follows. As a polymer for the skin layer, polyethylene naphthalate of IV = 0.502 and polyarylate U100A (IV = 0.614) manufactured by Unitika Ltd. are blended to form U10.
0A is 20% by weight, 40% by weight, 60% by weight, 8%
It was blended so as to be 0% by weight, supplied to a hopper, and extruded at a barrel temperature of 350 ° C. Polyethylene naphthalate having an IV of 0.682 was extruded as a core layer polymer at a barrel temperature of 300 ° C.

As a comparative example, U100A and polyethylene naphthalate were used as skin layers in the same manner as in the example.
The mixture was extruded by blending so that 00A was 8% by weight and polyethylene naphthalate was 92% by weight. The polymer of the core layer was the same as in the example, and was extruded in the same manner as in the example. Each sheet has a thickness of about 650μ,
The thickness ratio between the skin layer and the core layer was adjusted so as to be 10/80/10 and molded. The obtained sheet is heated at a heater set temperature of 370 ° C. for a predetermined time by a vacuum pressure air molding machine PLAVAC model TVP33 manufactured by Sanwa Kogyo Co., Ltd., and then a mold having a depth of 30 mm and a drawing ratio of 0.33 is heated to 110 ° C. The container was heated to form a container having a capacity of 176 ml.

Next, the molded container was filled with jelly, covered with an easy-peeled lid material, and heat-sealed.
Sterilization is performed for 10 minutes in a constant temperature water bath at less than 100 ° C.
0 ℃ or higher is steam autoclave (TOMY AUTO C
LAVE SS-320) for 30 minutes. The shape and transparency of the container after the treatment were observed and judged as follows. Container shape after processing is the same as before processing ○ 〃 少 し Slight deformation △ 〃 〃 Deformation × Transparency of container after processing is the same as before processing (haze 5% or less) ○ 〃 少 し Slightly white (Haze 6-20%) △ 〃 〃 Whitening (Haze 21% or more) ×

Table 1 shows the shape retention of the container after sterilization and the transparency of the container. As the content of polyarylate in the skin layer increases, the shape retention of the container is improved, and the heat resistance is improved. In the container having a skin layer of polyethylene naphthalate containing 8% by weight of polyarylate of Comparative Example 1, the container slightly deformed at 90 ° C., and the polyethylene naphthalate layer of the core layer became slightly white from 110 ° C., and the container became transparent. Sex is impaired. Further, in the container of Comparative Example 2 having a skin layer made of polyethylene naphthalate containing 92% by weight of polyarylate, the sheet has a large melt viscosity difference between the skin layer and the core layer at the time of sheet molding, so that a wavy pattern is generated on the sheet. Because of the unevenness, wrinkles have occurred on the container surface after the heat resistance test,
Further, it had only heat resistance of 100 ° C. due to poor adhesion to a mold.

[0022]

[Table 1]

Examples 5 to 8 and Comparative Examples 3 to 4 In Examples 1 to 4, the remaining sheets obtained by punching the containers from the sheets were each crushed into pellets. The crushed flakes were blended with polyethylene naphthalate having an IV of 0.682 of the core layer in a weight ratio of 50:50 and put into a hopper for the core layer.
Extruded at ℃. The polymer for the skin layer was prepared in Examples 1 to
Polyethylene naphthalate having an IV = 0.502 and polyarylate U100A manufactured by Unitika Ltd. (IV
= 0.614) to make U100A a total of 20
%, 40%, 60%, and 80% by weight, and supplied to a hopper.
Extruded at 0 ° C.

In Comparative Examples 3 and 4, in the same manner as in Comparative Examples 1 and 2, U100A and polyethylene naphthalate were blended and extruded so that U100A was 8% by weight and 92% by weight, respectively, as a skin layer. The flakes obtained by crushing the remaining sheet after punching the same container as in Examples 5 to 6 were used.
In the same manner as in the above, 50% by weight of polyethylene naphthalate having an IV of 0.682 was blended and extruded. Each sheet was formed so as to have a thickness of about 650 μ and a thickness ratio of the skin layer and the core layer of 15/70/15. When the haze of the formed sheet was measured, Comparative Example 4 was as large as 6.3% due to the corrugation of the sheet, but the haze of each of the other sheets was as good as 3% or less.
In other words, this suggests that the remaining sheet obtained by punching the container was blended with the core layer by 50% by weight, but had good compatibility and was microscopically dispersed. The obtained sheet is heated at a heater set temperature of 370 ° C. for a predetermined time by a vacuum pressure air molding machine PLAVAC model TVP33 manufactured by Sanwa Kogyo Co., Ltd., and then a mold having a depth of 30 mm and a drawing ratio of 0.33 is heated to 110 ° C. To form a container having a capacity of 176 ml.

Next, the molded container was filled with jelly, covered with an easy-peeled lid, and heat-sealed.
Sterilization is performed for 10 minutes in a constant temperature water bath at less than 100 ° C.
0 ℃ or higher is steam autoclave (TOMY AUTO C
(LAVE SS-320) for 30 minutes. The shape and transparency of the container after the treatment were observed and judged as follows. Container shape after treatment is the same as before treatment ○ 前 〃 Slightly deformed △ 〃 〃 Deformation × Transparency of container after treatment is the same as before treatment (haze 5% or less) ○ 〃 少 し Slightly whitened (Haze 6-20%) △ 〃 〃 Whitening (Haze 21% or more) ×

Table 2 shows the shape retention of the container after the sterilization treatment and the transparency of the container. As the content of polyarylate in the skin layer increases, the shape retention of the container is improved, and the heat resistance is improved. In the container having a skin layer made of polyethylene naphthalate containing 8% by weight of polyarylate of Comparative Example 1, the container slightly deformed at 100 ° C., and the polyethylene naphthalate layer of the core layer became slightly white from 110 ° C., and the container became transparent. Sex is impaired. In the case of the container having a skin layer made of polyethylene naphthalate containing 92% by weight of polyarylate of Comparative Example 4, a wave pattern was generated on the sheet due to a large difference in melt viscosity between the skin layer and the core layer at the time of sheet formation. Since the portions were uneven, wrinkles were generated on the container surface after the heat resistance test, and the heat resistance was only 100 ° C. due to poor adhesion to the mold.

[0027]

[Table 2]

Examples 9 to 10 and Comparative Examples 5 to 6 The sheets of Examples 7 and 8 and the PP / EVOH / PP sheet having a thickness of 650 .mu.
The container was vacuum-formed in the same manner as described above. The container was filled with curry, covered with an easy-peeled lid as a lid, and heat-sealed. Next, sterilization treatment was performed at each temperature in the same manner as in Examples 1 to 4, and the shape retention and transparency of the container were evaluated. Further, changes in the taste of the contents after sterilization at 100 ° C. for 20 minutes were evaluated as follows. The taste is not changed. ○ The taste is slightly changed. △ The taste is changed. × The test results are shown in Table 3, but the containers of Examples 9 to 10 have heat resistance, and There was no change in taste. On the other hand, in the container made of PP / EVOH / PP of Comparative Example 5, the haze of the sheet was 65.4%, so that the contents of the container were slightly visible. In this container, a change in taste after sterilization was observed.

[0029]

[Table 3]

[0030]

Since the present invention has a high Tg resin layer of a specific composition, it does not whiten or deform even when sterilized in boiling or retort, does not crack when dropped, is transparent even after sterilization, and has an oxygen barrier. It is possible to provide a container that does not decrease the properties and does not change the taste or odor of the contents due to adsorption of a specific chemical substance.

Claims (3)

[Claims] 1. A glass transition temperature (Tg) of 120 to 18.
A multilayer sheet comprising at least two layers of a high Tg resin layer at 0 ° C. and a polyester resin layer having a lower Tg than the layer, wherein the high Tg resin layer contains a polyarylate and a polyethylene naphthalate resin. A heat-resistant multilayer sheet characterized in that it is a layer to be heated. 2. A container formed from the heat-resistant multilayer sheet according to claim 1. 3. The sheet according to claim 1, wherein the haze after steaming at 110 ° C. for 30 minutes is 5% or less.