JPS642621B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to polyester sheets for thermoforming. More specifically, the present invention relates to an unstretched polyester sheet for thermoforming that has high transparency, excellent antistatic properties, and provides heat sealability. BACKGROUND ART Unstretched polyester sheets containing terephthalic acid and ethylene glycol as main components are used to be processed into various molded products by plastic processing under heating, a so-called thermoforming method. Polyester sheet molded products are transparent, have good gas barrier properties, and are nontoxic, so they are widely used as packaging materials for foods, medical equipment, etc. However, such polyester and this unstretched sheet are easily charged with static electricity, so they are susceptible to various problems such as spark discharge and adsorption of dirt and dust during processing processes such as film forming, printing, and thermoforming, packaging, and distribution. It has the disadvantage of being prone to failure. Furthermore, polyester sheet molded products are often heat-sealed to take advantage of their excellent gas barrier properties, but polyester is less heat-sealable than other thermoforming materials such as polyvinyl chloride and polystyrene. It also has the disadvantage that the permissible conditions are narrow. That is, sealing cannot be achieved unless the heating plate temperature of the heat sealer approaches the melting temperature of polyester, but if the sealing temperature is too high or the sealing time is too long, there is a problem that the vicinity of the sealing part becomes brittle. Although the purpose is different from the present invention, several methods have been proposed in the past in which polyalkylene glycol and a metal salt of sulfonic acid are simultaneously blended into polyester in order to impart antistatic properties to polyester. For example, in Japanese Patent Publication No. 44-31828, 80% or more of the acid component is terephthalic acid, and at least one polyalkylene glycol or a copolymer thereof that is insoluble in the polyester is added to a polyester that has fiber-forming ability. 0.5 to 2.0% and is represented by the general formula Ar-So ₃ 1/m Me (where Ar is an aromatic residue with or without a substituent, m is an integer from 1 to 3, and Me is a metal atom). Sulfonate derivatives 0.05~
A method of blending 3.0% has been proposed. Also,
JP-A No. 52-47072 proposes a biaxially oriented film in which a polyester-soluble low molecular weight polyalkylene glycol and an alkyl sulfonate derivative are combined, and the low molecular weight polyalkylene glycol is, for example, polyethylene with a molecular weight of 4000 or less. The use of glycols has been shown. However, these methods cannot be directly applied to polyester sheets for thermoforming. That is, one of the major characteristics of polyester sheets for thermoforming is transparency, but unstretched sheets using polyester produced by the above method have impaired transparency and cannot be applied to thermoforming applications. Furthermore, no means for improving heat sealability has been known so far. The inventor of the present invention, as a result of studies aimed at solving these drawbacks and providing a polyester sheet for thermoforming that has both excellent antistatic properties and transparency, and has even better heat sealing properties, developed a polyester sheet with a specific structure. By combining a polyalkylene glycol with a specific molecular weight and a metal salt of sulfonic acid and using specific amounts of each, a thermoformable product that satisfies antistatic properties and transparency at the same time and has improved heat sealability. The inventors have discovered that a polyester sheet for use in plastics can be obtained, and have arrived at the present invention. That is, the present invention provides 75 mol% of dicarboxylic acid
The above is terephthalic acid, and the glycol component is 75
For every 100 parts by weight of a polyester of which mole percent or more is ethylene glycol, (a) 0.1 part to 0.5 part by weight of polyethylene glycol having an average molecular weight of 5,000 to 15,000, and (b) 0.05 part to 0.3 part by weight of an alkali metal salt of an alkylsulfonic acid. This is an unstretched thermoformable polyester sheet made by blending the following parts: The polyester serving as the base of the thermoformable sheet of the present invention is a polyester in which 75 mol% or more of the dicarboxylic acid is terephthalic acid and 75 mol% or more of the glycol component is ethylene glycol. Examples of dicarboxylic acids other than terephthalic acid include aliphatic dicarboxylic acids such as succinic acid, adipic acid, sebacic acid, and dodecanedicarboxylic acid; alicyclic dicarboxylic acids such as hexahydroterephthalic acid and 1,3-adamantanedicarboxylic acid; Aromatic dicarboxylic acids such as isophthalic acid, naphthalene dicarboxylic acid, diphenyl dicarboxylic acid, diphenylsulfone dicarboxylic acid, and benzophenone dicarboxylic acid can be mentioned. The proportion of terephthalic acid in the dicarboxylic acid is 75 mol% or more,
If the amount of terephthalic acid is less than 75 mol%, the softening point of the polyester will decrease, which is undesirable from the standpoint of thermoformability and use of the molded product. Glycol components other than ethylene glycol include 1,
Examples include 3-propanediol, 1,4-butanediol, 1,6-hexanediol, neopentyl glycol, diethylene glycol, 1,4-cyclohexanedimethanol, and p-xylylene glycol. The amount of ethylene glycol in the glycol component is 75 mol% or more, and if the ethylene glycol amount is less than 75 mol%, the softening point of the polyester becomes too low, which is not preferable. The average molecular weight of polyethylene glycol blended into polyester is 5,000 to 15,000. If the average molecular weight is less than 5,000, the antistatic effect will hardly appear, and if the average molecular weight exceeds 15,000, the transparency of the sheet will deteriorate. Even with polyethylene glycol having an average molecular weight exceeding 15,000, if the amount added is small, the transparency of the sheet will be good, but in that case, the antistatic effect will not appear and the heat sealability will not be improved. The blending amount of polyethylene glycol is 0.1 part by weight to 0.5 part by weight per 100 parts by weight of polyester.
parts by weight, preferably from 0.1 parts to 0.45 parts by weight,
Particularly preferred is 0.1 part by weight to 0.3 part by weight. If the blending amount of polyethylene glycol is less than 0.1 part by weight, antistatic properties cannot be provided unless a large amount of metal salt of alkyl sulfonic acid is blended so as to impair the transparency of the sheet, and if the polyethylene glycol exceeds 0.5 part by weight and the transparency of the polyester sheet will be impaired. The alkali metal salt of alkylsulfonic acid used in the present invention is usually a lithium, sodium or potassium salt, and the alkyl group has 8 carbon atoms.
It is preferable that it is above. Usually, a mixture of 8 to 20 carbon atoms, with an average carbon number of about 14, is often used. The amount of the alkali metal salt of alkylsulfonic acid added to the polyester is 0.05 part by weight to 0.3 part by weight, preferably 0.1 part by weight to 0.3 part by weight, per 100 parts by weight of polyester. If the amount of the alkali metal salt of alkyl sulfonic acid is less than 0.05 part by weight, the antistatic properties of the sheet will not be sufficient and the heat sealability will hardly be improved. However, if it exceeds 0.3 parts by weight, the transparency of the sheet will decrease. In the present invention, if the amount of polyethylene glycol blended per 100 parts by weight of polyester is A, and the amount of alkali metal salt of alkyl sulfonic acid is B, the sum of A and B is 0.2 or more. is preferable, more preferably 0.3 or more, particularly preferably 0.4 or more. In the present invention, polyethylene glycol and the alkali metal salt of alkylsulfonic acid can be blended at any stage of producing a polyester sheet for thermoforming, and both can be blended simultaneously or in any order. For example, before starting the polymerization reaction of raw material polyester, during the polymerization reaction,
Polyethylene glycol and alkyl sulfonate can be added in the molten state at the end of the polymerization reaction. It is also possible to mix polyester, polyethylene glycol, and/or an alkali metal salt of an alkyl sulfonic acid in an extruder to form a so-called master chip, which can then be blended with ordinary polyester.
Moreover, when forming a polyester sheet for thermoforming, it may be blended into the raw material polyester. Other polymers may be blended with the polyester of the present invention. Examples of polymers that can be blended include polycarbonate, polybutylene terephthalate, polystyrene, and polymethyl methacrylate. These polymers are preferably blended in an amount of 30% or less. In addition, an antioxidant such as a sterically hindered phenol compound may be added to the polyester of the present invention, and other antistatic agents, colorants, and other additives may also be added as necessary. . The polyester sheet for thermoforming of the present invention can usually be obtained by melt-extruding polyester into a sheet form from an extrusion die, such as a T-die, and rapidly cooling and solidifying the sheet. A casting drum is preferred as the rapid cooling and solidifying means. The polyester sheet for thermoforming of the present invention usually has a surface resistivity of 5×10 ¹² ohms or less, a charging potential half-life time defined later of 60 seconds or less, and a haze value measured on a sheet with a thickness of 250 microns. is 8% or less, and has both desirable transparency and antistatic properties. The polyester sheet for thermoforming of the present invention can be processed by thermoforming, such as vacuum forming, pressure forming, press molding, etc., to form molded products such as containers with excellent transparency, heat sealability, antistatic properties, etc. can. The present invention will be explained in detail with reference to Examples below. Note that "parts" in the text represent parts by weight. Further, in the examples, antistatic properties and transparency were measured by the following methods. The surface resistivity was measured with a vibrating capacitance micropotential ammeter model TR-84M manufactured by Takeda Riken Co., Ltd. The charged potential half-life time is the time it takes for the potential generated on the sample to decay to 1/2 when a voltage of -5 KV is applied for 30 seconds from 2 cm above the sample using an Anato Shokai Static Honest Meter Model S-4104 ( seconds). In addition, the surface resistivity and charging potential half-life time were measured at 20
The test was carried out in an atmosphere of ℃ and 60% RH. Transparency was measured using a digital haze meter NDH-2D model manufactured by Nippon Denshoku Kogyo Co., Ltd. Example 1, Comparative Examples 1 to 3 A mixture of 100 parts of dimethyl terephthalate, 70 parts of ethylene glycol, and 0.025 parts of manganese acetate as a transesterification catalyst was heated with stirring and transesterified for 90 minutes while distilling off the generated methanol. Ta. Next, 1.98 parts of sodium alkyl sulfonate having an average carbon number of 14, and phosphorous acid as a stabilizer.
0.015 parts and antimony trioxide as polymerization catalyst
0.041 part was added, the temperature was raised to 285°C, the system was reduced to a reduced pressure of 60 mmHg for 30 minutes, and then 0.5 mm
The reaction was carried out for 80 minutes under reduced pressure of Hg. The polyethylene terephthalate obtained contains 2 parts of sodium alkylsulfonate per 100 parts of polymer. This is called polyester A. In the same manner as above except that 9.90 parts of polyethylene glycol with a molecular weight of 8000 was added instead of 1.98 parts of sodium alkylsulfonate, 10 parts of polyethylene glycol with a molecular weight of 8000 was added per 100 parts of polymer.
% of polyethylene terephthalate was obtained. This is called polyester B. Polyester A, polyester B and polyethylene terephthalate were mixed in various proportions, and T
It was extruded from a die to form a non-stretched sheet with a thickness of 0.25 mm. Table 1 shows the results of measuring the antistatic properties and transparency of these sheets.

[Table] The sheet of Example 1 has a small surface resistivity, the charged potential attenuates in a short time, and has good antistatic properties. The haze is small and the transparency is good. The sheet of Comparative Example 1 in which the polyethylene glycol of Example 1 was replaced with sodium alkylsulfonate had good antistatic properties, but had high haze and significantly impaired transparency. The sheet of Comparative Example 2 in which the sodium alkyl sulfonate of Example 1 was replaced with polyethylene glycol and the sheet of Comparative Example 3 in which polyethylene glycol was removed from Example 1 both had good transparency, but the surface resistivity value was large, and the charging potential hardly attenuated. Examples 2 to 4, Comparative Examples 4 to 7 Master chips containing 4 parts of various polyethylene glycols having different molecular weights per 100 parts of polyethylene terephthalate were produced using a twin-screw extruder. Using polyester A of Example 1, these polyethylene glycol-containing master chips and polyethylene terephthalate, sodium alkyl sulfonate per 100 parts of polyester
A non-stretched sheet with a thickness of 0.25 mm containing 0.1 part of polyethylene glycol and 0.5 part of polyethylene glycol was formed. Table 2 shows the results of measuring the antistatic properties and transparency of these sheets.

[Table] The sheets of Examples 2, 3, and 4 have good antistatic properties and transparency. On the other hand, the sheets of Comparative Examples 4 and 5 using polyethylene glycol with a low molecular weight had good transparency but insufficient antistatic properties. On the other hand, the sheets of Comparative Examples 6 and 7 using polyethylene glycol with a high molecular weight have good antistatic properties, but have insufficient transparency. Example 5, Comparative Examples 8 and 9 A mixture of 100 parts of dimethyl terephthalate, 70 parts of ethylene glycol and 0.025 parts of manganese acetate was heated with stirring, and transesterification was carried out for 90 minutes while distilling off the generated methanol. Then 1.98 parts of sulfonic acid sodium salt, polyalkylene glycol
5.94 parts of phosphorous acid, 0.015 parts of phosphorous acid, and 0.041 parts of antimony trioxide were added, the temperature was raised to 285°C, the system was reduced to a reduced pressure of 60 mmHg for 30 minutes, and then 0.5 parts of antimony trioxide was added.
The reaction was carried out for 80 minutes under reduced pressure of mmHg. The combinations of polyalkylene glycol and sulfonic acid sodium salt used are as follows, and each is used as a polyester CDE. Polyester C Polyethylene glycol with a molecular weight of 15,000 Sodium alkyl sulfonate polyester with an average carbon number of 14 D Polyester with a molecular weight of 15,000 Sodium alkyl decyl benzene sulfonate Polyester E Ethylene oxide-propylene oxide block copolymer with a molecular weight of 15,000 (However, ethylene oxide and propylene Molar ratio of oxide = 3:1) Sodium alkyl sulfonate having an average carbon number of 14. These three types of polyester are mixed with polyethylene terephthalate at a ratio of 1:19, respectively, and T
An unstretched sheet with a thickness of 0.3 mm was formed by extrusion through a die, and the antistatic properties of the obtained sheet were measured. Table 3 shows the results.

[Table] Example 6 From the mixture below, use a T-die to make a 0.7mm thick
A non-stretched sheet was formed into a film. Polyethylene terephthalate 79.5 parts Polybutylene terephthalate 10 Polyester A of Example 1 7.5 Polyester B of Example 1 3 The surface resistivity of the obtained polyester sheet for thermoforming was 1.8×10 ¹¹ ohms, and the charging potential half-life time was 2.8
Second, the haze was 6.1%. Examples 7, 8, Comparative Examples 10, 11 Polyester A and Polyester B of Example 1 and Polyester D of Comparative Example 8 and polyethylene terephthalate were mixed in various proportions and extruded through a T-die to a thickness of 0.125 mm and a thickness of 0.3 mm. A non-stretched sheet was formed into a film. Using a film heat sealer manufactured by Toyo Tester Sangyo Co., Ltd., the 0.125 mm thick sheet was stacked on the 0.3 mm thick sheet so that it was facing the heating plate, and the sheets were pressed together at a pressure of 2 kg/cm ² for 1 second. The conditions of the seals were divided into two categories: those in which the seal was firmly adhered and the sealed portion would not peel off even if an attempt was made to remove it, and the unsealed portion in the vicinity would be destroyed, and those in which the seal was not sealed. Table 4 shows the heat sealing conditions of these samples. From the results in Table 4, it can be seen that the polyester sheet for thermoforming of the present invention can be
It was found that heat sealing was possible over a wide temperature range.

【table】

[Table] ○: Heat seal in good condition
△: Heat sealed, but adhesive strength is weak
×: Not heat sealed

Claims (1)

[Scope of Claims] 1. For 100 parts by weight of a polyester in which 75 mol% or more of the dicarboxylic acid component is terephthalic acid and 75 mol% or more of the glycol component is ethylene glycol, (a) polyethylene glycol having an average molecular weight of 5,000 to 15,000; A non-stretched polyester sheet for thermoforming, which contains 0.1 part by weight to 0.5 part by weight and (b) 0.05 part to 0.3 part by weight of an alkali metal salt of alkylsulfonic acid.