JP2986109B2 - Multi-layer sheet - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a transparent multilayer structure sheet excellent in heat resistance, transparency and secondary workability.

[Conventional technology]

Conventionally, as a transparent sheet, polyvinyl chloride, polymethyl methacrylate, polycarbonate, polyester, polyarylate and the like are known. However, these sheets have advantages and disadvantages in their properties, and their fields of application have been limited.

That is, the soft polyvinyl chloride sheet is almost satisfactory in terms of transparency, impact strength, and secondary workability, but migration of the plasticizer is regarded as a problem.

On the other hand, a sheet using hard vinyl chloride or polymethyl methacrylate is excellent in transparency, but has low impact strength and poor secondary workability.

Further, a sheet using polycarbonate is excellent in heat resistance, transparency, and impact strength, but has an extremely high glass transition temperature and extremely poor secondary workability. Polyester sheets have good impact strength, secondary workability, and chemical resistance, but have limited heat resistance and are limited in their application fields.

However, the copolymer obtained from polyester and polyarylate improves its heat resistance by blending with polyarylate, so that it can be used in a wide range of applications.On the other hand, with the increase in the blending ratio of polyarylate, There is a problem of reduction in secondary workability.

[Problems to be solved by the invention]

As described above, heat resistance, transparency, and secondary processing properties are both excellent, and it was difficult to obtain a low-cost sheet. By effectively compounding a copolymer consisting of polyarylate and polyester in its main component,
It is an object of the present invention to provide a low-cost sheet that is transparent and has excellent heat resistance and secondary workability.

[Means for solving the problem]

The present inventors have intensively studied for such a purpose, and as a result, using a cheap polyester having good secondary workability at the center of the sheet cross section, a polyester having a glass transition point higher than that on both sides thereof. By using a copolymer of polyarylate, the heat resistance is remarkably improved, and it has been found that the transparency can be maintained even if the container is sterilized in boiling water for a long time, and the present invention has been achieved.

That is, the present invention provides a core layer comprising a thermoplastic polyester having 80% or more ethylene terephthalate units, and a copolymer having a weight ratio of the thermoplastic polyester to the polyarylate in the range of 60:40 to 10:90. And a weight ratio of the core layer and the sheath layer of 60: 4.
0 to 97: 3.

[Action]

The thermoplastic polyester used in the present invention is terephthalic acid, a mixture of terephthalic acid and isophthalic acid, a lower alkyl ester of terephthalic acid, or a mixture of a lower alkyl ester of terephthalic acid and a lower alkyl ester of isophthalic acid and ethylene glycol. It is obtained by a usual esterification reaction or transesterification reaction, or obtained by subjecting it to solid phase polymerization. The thermoplastic polyester having an ethylene terephthalate unit of 80 mol% or more includes the above polyester and a copolymer composed of an ethylene terephthalate unit of 80 mol% or more and another repeating unit, that is, another copolymer component. Various other acid components and polyhydric alcohol components can be used as the other copolymer components.

For example, as the acid component, phthalic acid, isophthalic acid,
Succinic acid, adipic acid, sebacic acid, dodecanedicarboxylic acid, hexahydroterephthalic acid, 2,6-naphthalenedicarboxylic acid, 2,5-dibromoterephthalic acid, diphenyldicarboxylic acid, trimellitic acid, trimesic acid, pyromellitic acid, etc. Examples of the polyhydric alcohol component include propylene glycol, diethylene glycol, tetramethylene glycol, polyethylene glycol, polytetramethylene glycol, 1,6-hexanediol, trimethylene glycol, neopentyl glycol, and p-xylylene glycol. , 1,4-cyclohexanedimethanol, bisphenol A, glycerin, pentaerythritol, trimethanolpropane, trimethanolbenzene, triethanolbenzene and the like.

The molecular weight of the thermoplastic polyester is about 10,000-100,00
A range of 0 is preferable in terms of physical properties and extrudability.

The polyarylate used in the present invention is obtained from an aromatic dicarboxylic acid or a functional derivative thereof and a dihydric phenol or a functional derivative thereof. As the aromatic dicarboxylic acid used in the preparation of the polyarylate, any aromatic dicarboxylic acid may be used as long as it reacts with a dihydric phenol to give a satisfactory polymer, and one kind or a mixture of two or more kinds is used. Preferred aromatic dicarboxylic acids include terephthalic acid and isophthalic acid, and a mixture thereof is particularly preferred in view of melt processability and overall performance. In such a mixture, the mixing ratio is not limited, but terephthalic acid / isophthalic acid = 9/1 to 1/9.
(Molar ratio) is preferred, especially from 7/3 to 3/7 (molar ratio), and more particularly 1/1 (molar ratio) in terms of balance between melt processability and performance.
Is desirable. Specific examples of preferred dihydric phenols include
2,2-bis (4-hydroxyphenyl) propane, 2,2-
Bis- (4-hydroxy-3,5-dibromophenyl) propane, 2,2-bis- (4-hydroxy-3,5-dichlorophenyl) propane, 4,4'-dihydroxydiphenylsulfone, 4,4'-dihydroxy Diphenyl ether,
4,4'-dihydroxydiphenyl sulfide, 4,4'-dihydroxydiphenyl ketone, 4,4'-dihydroxydiphenylmethane, 2,2'-bis (4-hydroxy-3,5-
Dimethylphenyl) propane, 1,1-bis (4-hydroxyphenyl) ethane, 1,1-bis (4-hydroxyphenyl) cyclohexane, 4,4′-dihydroxydiphenyl, hydroquinone and the like. These may be used alone or as a mixture of two or more. Although these dihydric phenols are para-substituted,
Other isomers may be used, and these dihydric phenols may be used in combination with ethylene glycol, propylene glycol or the like.

The most representative of the dihydric phenols is 2,2-bis (4-hydroxyphenyl) propane, which is usually called bisphenol A, and is most preferable in terms of overall physical properties.

Therefore, the most preferred polyarylate in the present invention is a mixture of terephthalic acid and isophthalic acid or a functional derivative thereof (provided that the molar ratio of terephthalic acid groups to isophthalic acid groups is from 9: 1 to 1: 9, especially 7: 3 Or 3:
7) and a dihydric phenol, particularly bisphenol A or a functional derivative thereof. The molecular weight of the polyarylate is preferably in the range of about 7,000 to 100,000 from the viewpoint of physical properties and extrudability.

Regarding a method for producing a copolymer of a thermoplastic polyester and a polyarylate, an insufficient copolymer can be obtained by merely blending the two. As a result, during the heat sterilization in boiling water as described below, there has been a problem that the transparency of the container is reduced. That is, it has been found that when the thermoplastic polyester and the polyarylate are not firmly bound by block copolymerization or random copolymerization, it is difficult to maintain transparency under hot and wet conditions.

For this reason, in order to promote more strongly bonded block copolymerization or random copolymerization, using a thermoplastic polyester and polyarylate, under melting,
It has been found that it is very effective to add a small amount of an alkali such as sodium acetate, sodium hydroxide, potassium hydroxide or the like to form a copolymer by a transesterification reaction, and the above problem has been solved.

The thermoplastic polyester and the polyarylate resin copolymer used as the heat-resistant reinforcing layer in the multilayer structure sheet according to the present invention desirably have a glass transition temperature of 100 ° C. or higher. For that purpose, the blending of the polyarylate in the copolymer is desirable. The ratio must be 40% by weight or more and 90% by weight or less. The reason why the glass transition temperature is desirably 100 ° C or higher is that the hot fill temperature when used for food containers is 100 ° C.
C., and the elasticity of the polyarylate copolymer having a glass transition temperature of 100 ° C. or more hardly decreases from room temperature to around 100 ° C., so that there is no deformation of the container during hot filling.

Since the core layer sandwiched between the heat-resistant reinforcing layers (sheath layers) is made of thermoplastic polyester, the glass transition temperature is about 73 ° C. Therefore, when used at temperatures exceeding 73 ° C., the elastic modulus decreases by about three orders of magnitude, that is, to 10 ⁶ to 10 ⁷ dyne / cm ² , but the elastic modulus of the heat-resistant reinforcing layer decreases the overall elastic modulus. For example, if 10% by weight of the whole is composed of a heat-resistant reinforcing layer, even if it exceeds 73 ° C., a decrease of about one digit, that is, 10 ⁹ dyne / cm
Keep the value of ² .

Further, by arranging the heat-resistant reinforcing layer so as to sandwich the core layer at the center of the sheet cross section, the bending rigidity of the sheet becomes higher than when the heat-resistant reinforcing layer is used instead of the core layer. Since the bending stiffness can be expressed by the product of the elastic modulus and the second moment of area, the reason is proved by the material mechanics as follows. Located core layer having a low modulus of thickness a the center of the sheet cross section, on both sides of the second moment I ₁ when the heat-resistant reinforcing layer of each thickness b / 2 high modulus is located, in the center of the seat section located heat reinforcing layer having a high elastic modulus in the thickness b, and the second moment when the layer of each thickness a / 2 low elastic modulus is positioned and I ₂ on its both sides, low modulus / high modulus = 1 Considering / 10 ³ as the layer that contributes to the bending rigidity, only the heat-resistant reinforcing layer with a high elastic modulus should be compared. Becomes This indicates that the more the heat-resistant reinforcing layer is located as close to the sheet surface as possible, the higher the overall bending rigidity becomes. As the ratio of the heat-resistant reinforcing layer to the whole,
It is desirably 3% by weight or more, and if it is less than 3% by weight, the effect of reinforcing heat resistance is not significant. On the other hand, when the thickness of the heat-resistant reinforcing layer exceeds 40% by weight, workability at the time of thermoforming the sheet is reduced. Therefore, the thickness of the heat-resistant reinforcing layer is preferably 3% by weight or more and 40% by weight or less.

In addition, the heat-resistant reinforcing layer also plays a role of water resistance. That is, the weight ratio of the polyester and polyarylate is
Resin copolymers in the range of 60:40 to 10:90 are hydrophobic and prevent water from entering the core layer.

Therefore, in the case of a food container that contains a food that needs to be heat-sterilized in boiling water, the polyester has a problem that it crystallizes and becomes cloudy during heat sterilization in boiling water. It has been found that when the layer is surrounded by the polyarylate copolymer to form a sheath layer, the polyester is not directly in contact with boiling water, so that the polyester is not subjected to plasticizing action by water and is hardly crystallized.

Further, the polyester of the core layer is isophthalic acid 2-
In the case of a polyester comprising 30 mol%, terephthalic acid 98 to 70 mol% and ethylene glycol 100 mol%,
It turned out that it was hard to become cloudy especially. Further, it was found that when the intrinsic viscosity of the polyester was 0.65 or more, it was particularly difficult to cause cloudiness.

Therefore, the multilayered sheet of the present invention did not become turbid even when sterilized in boiling water, and a transparent food container was obtained. Moreover, since the container is mainly made of the polyester, it is extremely advantageous in terms of cost.

In addition, an ethylene / vinyl alcohol copolymer with high gas barrier properties (EV
By providing a gas barrier layer of OH), polymetaxylylenediamine adipamide, amorphous polyamide resin or the like, a container having heat resistance and gas barrier properties can be manufactured.

In this case, a maleic anhydride graft-modified ethylene-vinyl acetate copolymer, high-density polyethylene, low-density polyethylene, linear low-density polyethylene, or polypropylene or a main component thereof is used as an adhesive layer outside the gas barrier layer. It is preferable to use a composition or the like.

〔Example〕

Next, the present invention will be described in more detail with reference to Examples and Comparative Examples.

Examples 1 to 5 and Comparative Examples 1 to 3 Using polyethylene terephthalate as the core layer and a copolymer of polyethylene terephthalate and polyarylate (Unitika Ltd. polyarylate resin U polymer) as the sheath layer, see Table 1 As shown in Examples 1 to 5 and Comparative Examples 1 to 3, sheets having a thickness of 1.0 mm were prepared by multi-layer extrusion at such respective mixing ratios (indicated by weight%).

The copolymer consisting of polyethylene terephthalate and polyarylate used for the sheath layer was obtained by a twin-screw extruder (PCM-30, manufactured by Ikegi Tekko Co., Ltd.) using polyethylene terephthalate, polyarylate and a small amount of sodium acetate. ~ 30
Transesterification by melt extrusion at 0 ° C,
It is dispensed into strands and pelletized.

In the evaluation of the physical properties of these sheets, the measurement of the temperature at which the flexural modulus was 5 × 10 ⁶ dyne / cm ² and the degree of white turbidity in hot water were checked. As for the secondary workability, a molded product was prepared by performing thermoforming, and the moldability was checked. Table 1 shows the results.

As can be seen from the results in Table 1, those of Examples 1 to 5 according to the present invention have a heat resistance of 95 ° C. or higher in any of the flexural modulus and the degree of cloudiness in hot water, and The secondary workability was also good, but those of Comparative Examples 1 to 3 were not good in at least one of the heat resistance and the secondary workability.

Examples 6 to 8, Comparative Examples 4 to 5 The core layer was composed of 0 to 35 mol% of isophthalic acid, 100 to 65% of terephthalic acid, and 100 mol% of ethylene glycol.
Using a phenol / tetrachloroethane (1: 1) solvent, polyester having an intrinsic viscosity of 1.00 measured at 25 ° C., and a sheath layer comprising the polyethylene terephthalate and polyarylate of Example 3 (Unitika Co., Ltd.) ) Polyarylate resin U polymer), and under the conditions shown in Table 2, the thickness of the core layer was 70% by weight and the thickness of the sheath layer was obtained by multilayer extrusion as shown in Examples 6 to 8 and Comparative Examples 4 to 5. Was set to 30% by weight to prepare a sheet having a thickness of 0.5 mm.

Among the physical properties of these sheets, the heat resistance
The measurement of the temperature at which the flexural modulus was 5 × 10 ⁶ dyne / cm ² and the degree of white turbidity in hot water were checked. As for the secondary workability, thermoforming was performed to form a molded product, and then the moldability was checked. Table 2 shows the results.

As can be seen from the results, Examples 6 to
8 had heat resistance of 95 ° C. or more and good secondary workability despite the sheet thickness being as thin as 0.5 mm, but those of Comparative Examples 4 to 5 Was not good in at least one of heat resistance and secondary workability.

[Effect of the Invention] The multilayer structure sheet according to the present invention can reduce the amount of expensive polyarylate in a very small amount, and has excellent heat resistance and secondary workability. Since it is maintained, it can be widely used for food containers.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-2-162040 (JP, A) JP-A-61-291131 (JP, A) JP-A-58-147449 (JP, A) (58) Investigation Field (Int.Cl. ⁶ , DB name) B32B 1/00-35/00 C08L 67/00-67/08

Claims (3)

(57) [Claims] 1. A core layer composed of a thermoplastic polyester having an ethylene terephthalate unit of 80% or more and a weight ratio of the thermoplastic polyester to the polyarylate of 60: 4.
A multilayer structure sheet comprising a sheath layer made of a copolymer in the range of 0 to 10:90, wherein the weight ratio of the core layer to the sheath layer is 60:40 to 97: 3. 2. The thermoplastic polyester used as the core layer contains 2 to 30 mol% of isophthalic acid and 98 to 70 mol of terephthalic acid.
The multilayer structure sheet according to claim 1, which is a thermoplastic polyester copolymerized by mol%. 3. The multi-layer sheet according to claim 1, wherein the thermoplastic polyester used as the core layer has a limiting viscosity of 0.65 or more.