JPH0628950B2 - Multilayer structure sheet - Google Patents

Description

TECHNICAL FIELD The present invention relates to a transparent multi-layered sheet for food containers having excellent heat resistance, transparency and secondary processability.

(Prior Art) Conventional transparent sheets include polyvinyl chloride, polymethylmethacrylate, polycarbonate, polyester,
Polyarylate and the like are known. However, these sheets have advantages and disadvantages in their characteristics, and their application fields are limited.

That is, the soft vinyl chloride sheet has transparency, impact strength,
Although it is almost satisfactory from the viewpoint of secondary workability, migration of plasticizer is regarded as a problem.

On the other hand, sheets made of hard vinyl chloride or polymethylmethacrylate have excellent transparency but low impact strength and poor secondary processability.

Further, although the sheet using polycarbonate is excellent in heat resistance, transparency and impact strength, its glass transition temperature is too high and its secondary workability is extremely poor. Polyester sheets are good in impact strength, secondary processability, and chemical resistance, but their heat resistance is limited and their application fields are limited.
However, a resin composition obtained from polyester and polyarylate is disclosed in JP-A-49-61247 and JP-A-50-96652.
As already known in the publication, the heat resistance is improved by blending polyarylate, which makes it possible to develop a wide range of applications, but on the other hand, there is a problem that the secondary workability decreases as the blending ratio of polyarylate increases. is there.

(Problems to be solved by the invention) As described above, heat resistance, transparency, and secondary workability are all excellent,
It was difficult to obtain a low-priced sheet, but a resin composition consisting of polyarylate and polyester in the main component of a low-priced polyester that is inferior only in heat resistance among those properties was effective. It is an object of the present invention to provide a low-priced sheet that is transparent by combining it and is excellent in heat resistance and secondary workability.

(Means for Solving the Problem) As a result of intensive studies conducted by the present inventors for such a purpose, as a result, an inexpensive polyester having good secondary processability was used at the center of the sheet cross section, and higher polyester was used on both sides thereof. It was found that the use of a resin composition comprising a polyester having a glass transition point and polyarylate significantly improves the heat resistance, and that transparency can be obtained even when the container is sterilized in boiling water for a long time, and the present invention has been reached. It was done.

That is, the present invention provides a core layer made of a thermoplastic polyester having at least 80 mol% or more of ethylene terephthalate units, and a resin composition in which the weight ratio of the thermoplastic polyester to the polyarylate is in the range of 60:40 to 0: 100. A sheet having a sheath layer made of (hereinafter referred to as a polyarylate resin composition), wherein the weight ratio of the core layer and the sheath layer is 60:40 to 98: 2, and a multilayer structure sheet for food containers Is the gist.

(Function) The thermoplastic polyester used in the present invention means a low polymer obtained by a usual esterification reaction or a transesterification reaction from terephthalic acid or a lower alkyl ester of terephthalic acid and ethylene glycol by melt polymerization by a usual method. It is obtained by or solid-phase polymerization treatment. The thermoplastic polyester having at least 80 mol% or more ethylene terephthalate units means a copolymer composed of 80 mol% or more ethylene terephthalate units and other repeating units, that is, other copolymerization components. As the other copolymerization component, various acid components and alcohol components can be used.

For example, acid components include 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, pyrolimellitic acid, etc., and the alcohol component includes propylene glycol, diethylene glycol, tetramethylene glycol, polyethylene glycol, polytetramethylene glycol, 1,6-hexanediol, trimethylene glycol. , Neopentyl glycol, p-xylylene diglycol, 1,4-cyclohexanedimethanol, bisphenol A, glycerin, pentaerythritol, trimethanolpropane, trimethanolbenzene, triethanol Or the like can be mentioned benzene.

The molecular weight of the thermoplastic polyester is preferably in the range of about 10,000 to 100,000 in terms of physical properties and extrusion processability.

The polyarylate used in the present invention is obtained from an aromatic dicarboxylic acid or its functional derivative and a dihydric phenol or its functional derivative. The aromatic dicarboxylic acid used for preparing the polyarylate may be any one as long as it reacts with the 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 mixtures thereof are particularly preferable in terms of melt processability and overall performance.
When such a mixture is used, the mixing ratio is not limited, but terephthalic acid / isophthalic acid = 9/1 to 1/9 (molar ratio) is preferable, and particularly in view of melt-melt processability and performance balance. / 3 to 3/7 (molar ratio), more preferably 1/1 (molar ratio). Specific examples of preferred dihydric phenol 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 ' -Dihydroxydiphenyl sulfone, 4,4'-dihydroxydiphenyl 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-hydroxy) Phenyl) ethane, 1,1-bis (4-hydroxyphenyl) cyclohexane, 4,4′-dihydroxydiphenyl, hydroquinone and the like can be mentioned. These may be used alone or in combination of two or more. Although these dihydric phenols are para-substituted, other isomers may be used, and ethylene glycol, propylene glycol or the like may be used in combination with these dihydric phenols.

The most representative dihydric phenol is 2,2-bis (4-hydroxyphenyl) propane, which is usually called bisphenol A, and is most preferable from the viewpoint of comprehensive physical properties.

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

In the present invention, the thermoplastic polyester and the polyarylate resin composition used as the heat resistant reinforcing layer in the multilayer structure sheet preferably have a glass transition temperature of 100 ° C. or higher. Therefore, the compounding ratio of the polyarylate in the resin composition is required. 40% by weight or more is required. Glass transition temperature
The reason why the temperature is preferably 100 ° C or higher is that a hot film can be formed when used in a food container or the like, and the elastic modulus of the polyarylate resin composition hardly decreases up to around 100 ° C. Since the core layer sandwiched between the heat resistant reinforcement layers is made of thermoplastic polyester, the glass transition temperature is about 73.
℃. Therefore, when it is used above 73 ℃, its elastic modulus decreases by about 3 orders of magnitude, that is, it decreases to 10 ⁶ to 10 ⁷ dyne / cm ² , but the elastic modulus of the heat resistant reinforcement layer controls the overall elastic modulus. Therefore, for example, if 10% by weight of the whole is made up of heat resistant reinforcement layer, it will decrease by about one digit even if the temperature exceeds 73 ° C, that is, 10 ⁹ dyne / c
Keep the value of m ² .

Furthermore, since the heat-resistant reinforcing layer is located so as to sandwich the core layer in the center of the sheet cross section, the bending rigidity of the sheet is higher than that when the heat-resistant reinforcing layer is used instead of the core layer. The bending rigidity can be expressed by the product of the elastic modulus and the second moment of area, and the reason for this is proved by the material mechanics as follows. The second moment of area I ₁ in the case where the low-elasticity core layer of thickness a is located in the center of the seat section and the heat-resistant reinforcing layers of high elastic modulus are located on both sides of the core layer in thickness b / 2, the center of the seat section When the high-elasticity heat-resistant reinforcing layer of thickness b is located and the low-elasticity layers of thickness a / 2 are located on both sides thereof, the second moment of area is I ₂ , and the low elastic modulus / high elastic modulus = 1 / 1
0 The layer contributing to the bending stiffness considered as ^3, it is sufficient to compare only resistant reinforcing layer having a high elastic modulus Becomes This shows that the flexural rigidity of the whole becomes higher as the heat-resistant reinforcing layer is located as close to the sheet surface as possible. The ratio of the heat resistant reinforcement layer to the whole is as follows.
It is preferably 3% by weight or more, and if less than 3% by weight, the heat-proof reinforcing effect is not remarkable. Also, the thickness of the heat resistant reinforcement layer is 40% by weight.
If it exceeds, the workability at the time of thermoforming the sheet is deteriorated.
Therefore, the total thickness of the heat resistant reinforcing layer is preferably 3% by weight or more and 40% by weight or less.

At the same time, the heat resistant reinforcement layer also plays a role of water resistance.

That is, the resin composition in which the weight ratio of the polyester to the polyarylate is in the range of 60:40 to 0: 100 is hydrophobic and prevents water from entering the core layer.

Therefore, in the case of a food container containing a food that needs to be heat-sterilized in boiling water, there is a problem that the polyester crystallizes and becomes cloudy during heat-sterilization in boiling water. It has been found that when a layer is surrounded by the polyarylate resin composition to form a sheath layer, the polyester does not come into direct contact with boiling water, so that the polyester does not undergo a plasticizing action by water and is difficult to crystallize.

Therefore, by using the multilayer structure sheet of the present invention, a transparent food container can be obtained which does not become cloudy even when sterilized in boiling water. Moreover, since the container is mainly made of the polyester, it is extremely advantageous in terms of cost.

In addition, by providing a gas barrier layer of ethylene-vinyl alcohol copolymer, polymetaxylylene adipamide, amorphous polyamide resin, etc., which has a high gas barrier property, as a separate layer in the center of the core layer, heat resistance is improved. It is also possible to manufacture a container having a gas barrier property.

In this case, an adhesive layer on the outside of the gas barrier layer
Ethylene-vinyl acetate copolymer modified with maleic anhydride graft, high density polyethylene, low density polyethylene,
It is preferable to use linear low-density polyethylene and polypropylene, or a composition based on these.

Further, resin scraps generated during secondary processing of the multilayer structure sheet can be used as the core layer.

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

Examples 1-5 and Comparative Examples 1-3 Polyethylene terephthalate alone is used as the core layer, and a composition comprising polyethylene terephthalate and polyarylate (Unitika polyarylate resin U polymer) is used as the sheath layer. As shown in Examples 1 to 5 and Comparative Examples 1 to 3, the composition ratio (indicated by weight%) was used to produce a sheet having a thickness of 1.0 mm by a multilayer extrusion molding machine. In the evaluation of the physical properties of these sheets, the heat resistance was measured at a temperature at which the flexural modulus was 5 × 10 ⁶ dyne / cm ² and checked for the degree of turbidity in hot water. As for the secondary workability, thermoforming was performed to make a molded product, and then the moldability was checked.

The results are shown in Table 1.

As can be seen from the results, the example according to the present invention has
It has heat resistance of ℃ or higher and good secondary workability.

(Effects of the Invention) The multilayer structure sheet according to the present invention can reduce the amount of expensive polyarylate to a very small amount, is excellent in heat resistance and secondary processability, and can be widely used for food container applications. .

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kosei Okamoto 23 Koji Sakura Uji, Uji City, Kyoto Prefecture Masami Kobayashi Examiner, Central Research Institute of Unitika Ltd. (56) Reference JP-A-63-237951 (JP, A)

Claims (1)

[Claims] 1. A core layer made of a thermoplastic polyester having at least 80 mol% or more of ethylene terephthalate units, and a resin composition having a weight ratio of the thermoplastic polyester to the polyarylate in the range of 60:40 to 0: 100. A multilayer structure sheet for food containers, characterized in that the weight ratio of the core layer to the sheath layer is 60:40 to 98: 2.