JPH0423913B2 - - Google Patents

Description

[Detailed description of the invention]

(Field of Industrial Application) The present invention relates to a polyester film that maintains the excellent mechanical properties and transparency inherent to polyethylene terephthalate film, and has antistatic properties with little humidity dependence. (Prior art) Generally, polyethylene terephthalate film has excellent transparency, mechanical properties, chemical resistance, and heat resistance, so it is used in a wide range of applications such as magnetic tape, photography, metallization, and packaging. . While polyethylene terephthalate film has the above-mentioned excellent properties, polyethylene terephthalate resin itself has high electrical insulation properties, so it is extremely susceptible to static electricity, and the generation and accumulation of static electricity can cause various problems. It's causing it. Particularly in a low humidity atmosphere, static electricity is generated significantly, which is a major drawback in terms of workability, safety, etc. In order to improve the above-mentioned drawbacks, a method of adding a sulfonic acid metal salt derivative, which is an antistatic agent with excellent heat resistance, to polyethylene terephthalate film has been studied. (Problems to be Solved by the Invention) However, in the above method, when a sulfonic acid metal salt derivative is simply added to polyethylene terephthalate, the transparency of the film is not practically impaired, such as 3% or less. With the addition of
There was a problem in that the antistatic property suddenly decreased in a low humidity atmosphere such as a relative humidity of 40% or less. (Means to solve the problem) As a result of repeated studies to improve these shortcomings, we found that polyethylene terephthalate (heat of crystal fusion)
8.5 cal/g) and a third component such that the heat of crystal fusion is 7.5 cal/g or less, and the biaxially stretched film of the copolyester is heated at 160°C or higher.
We have also discovered that by heat-treating the copolyester at a temperature below the melting point, it is possible to obtain a polyester film that maintains the transparency required for practical use and has excellent antistatic properties even in a low-humidity atmosphere. Ta. However, it has been found that such a copolymerized polyester film has a significant decrease in mechanical strength and cannot be put to practical use. Therefore, as a result of further studies to improve this point, we found that by laminating the above copolymerized polyester film to a polyethylene terephthalate film at a specific thickness, the mechanical properties could be practically completely improved without reducing the antistatic properties. We have found that it can be improved to a point where there is no problem, and that transparency can also be significantly improved. That is, in the present invention, at least one side of polyethylene terephthalate is a sulfonic acid metal salt derivative.
Contains 0.05 to 3% by weight, and its heat of crystal fusion is
Obtained by laminating copolyester mainly composed of polyethylene terephthalate with a weight of 7.5 cal/g or less, stretching in the biaxial direction, and then heat-treating at a temperature of 160 ° C. or higher and below the melting point of the copolyester, Tensile strength is 20
The gist of this product is a laminated polyester film that has a weight of Kg/mm ² or more and a half-life of electrostatic voltage of 180 seconds or less at 20°C and 40%RH. Next, the present invention will be explained in detail. In the present invention, polyethylene terephthalate refers to a polyethylene terephthalate homopolymer obtained from ethylene glycol and terephthalic acid or dimethyl terephthalate, as well as a copolymerized polyester consisting essentially of ethylene terephthalate units containing a small amount of other copolymerizable components. Also includes. In addition, the sulfonic acid metal salt derivatives used in the present invention include R-SO ₃ Me,

Compounds having the structure shown in [Formula] can be mentioned. Here R is carbon number 8
~20 alkyl groups, including octyl, nonyl, decyl, undecyl, dodecyl, tridecyl. Further, Me is an alkali metal or an alkaline earth metal, and examples thereof include lithium, sodium, potassium, calcium, barium, and magnesium. Although such sulfonic acid metal salt derivatives may be used alone, a mixture of a plurality of sulfonic acid metal salt derivatives having alkyl groups having different numbers of carbon atoms is usually used.
Further, the amount of the sulfonic acid metal salt derivative added is 0.05 to 3% by weight in the copolymerized polyester, especially
It is preferably 0.1 to 2% by weight. When the amount added is less than 0.05% by weight, sufficient antistatic properties cannot be obtained, and when it is more than 3% by weight, transparency and mechanical properties are impaired. Next, the copolyester of the present invention will be explained. First of all, in the present invention, "mainly polyethylene terephthalate" means 50% of the polymer component.
This means that ethylene terephthalate units account for mol% or more, and 60% or more is particularly preferred. If the ethylene terephthalate unit content is less than 50 mol %, even if it is laminated with a polyethylene terephthalate film as in the present invention, the strength will be greatly reduced and the present invention will not be achieved. Therefore, the copolymerized polyester of the present invention satisfies the above conditions and has a heat of crystal fusion of
It can be obtained by copolymerizing a diol, dicarboxylic acid, or oxycarboxylic acid that can be copolymerized with an ethylene terephthalate unit to an extent of 7.5 cal/g or less, preferably 7.0 cal/g or less. These diols, dicarboxylic acids, and oxycarboxylic acids are not particularly limited, but include the following compounds. That is, the diols include propylene glycol, trimethylene glycol, tetramethylene glycol,
Examples include diethylene glycol, triethylene glycol, tetraethylene glycol, neopentyl glycol, 1,6 hexanediol, and cyclohexanedimethanol. Examples of dicarboxylic acids include isophthalic acid, adipic acid, sebacic acid, malonic acid, succinic acid, oxalic acid, and ester-forming derivatives thereof. Furthermore, examples of the oxycarboxylic acids include parahydroxybenzoic acid and ε-caprolactone, which is an esterified product of oxycarboxylic acid. One of these diols, dicarboxylic acids, and oxycarboxylic acids may be used alone as a copolymerization component, or two or more of these diols, dicarboxylic acids, and oxycarboxylic acids may be used simultaneously as a copolymerization component. To give a more specific example of a copolyester suitable for the present invention, diethylene glycol is
Polyethylene terephthalate copolymer copolymerized with mol% or more, polyethylene terephthalate copolymer copolymerized with triethylene glycol 2.5 mol% or more, polyethylene terephthalate copolymer copolymerized with neopentyl glycol 2.5 mol% or more, cyclohexanedimethanol. Polyethylene terephthalate copolymer copolymerized with 3 mol% or more of adipic acid, polyethylene terephthalate copolymer copolymerized with 3 mol% or more of adipic acid, isophthalic acid.
Examples include a polyethylene terephthalate copolymer copolymerized with 2.5 mol% or more and a polyethylene terephthalate copolymer copolymerized with 3 mol% or more of sebacic acid. Further, methods for adding the sulfonic acid metal salt derivative to the copolymerized polyester include adding and dispersing the sulfonic acid metal salt derivative during polymerization of the copolymerized polyester, and blending and melt-mixing the copolymerized polyester chips and the sulfonic acid metal salt derivative. There are methods such as adding a sulfonic acid metal salt derivative immediately before film formation of the copolyester, but it is also possible to combine these methods. The copolyester containing the sulfonic acid metal salt derivative thus obtained can be formed into a film by a conventional polyester film forming method, such as a T-die method or an inflation method. Therefore, the method of laminating this on a polyethylene terephthalate film includes a method of laminating polyethylene terephthalate and the copolymerized polyester by a coextrusion method;
A method such as extruding them separately from independent dies and immediately laminating them can be used. The laminated unstretched film thus obtained is then biaxially stretched. The stretching can be carried out at almost the same temperature as in the case of polyethylene terephthalate film, but may be carried out at a different temperature if necessary. In addition, the stretching ratio is 1.2 to 6 times in the vertical direction and 1.2 to 6 times in the horizontal direction as necessary.
It can be done within twice the range. This biaxial stretching is an important condition for achieving the present invention, and without biaxial stretching, the properties aimed at by the present invention cannot be obtained. A preferred laminated thickness of the copolymerized polyester in the present invention is from 0.1 μm to 50% of the total thickness of the laminated film, preferably from 0.3 μm to 40% of the total thickness of the laminated film after stretching. If the laminated thickness is less than 0.1μ, the antistatic effect will not be sufficient, and if it is thicker than 50% of the total thickness of the laminated film, the mechanical properties of the film will be significantly reduced.
(The lamination method may be one-sided or double-sided, and the same effect will be obtained as long as the sum of the thicknesses of the laminated parts is equal.) Next, the heat treatment conditions for the biaxially stretched film of the present invention are as follows: first, the temperature is 160°C or higher, preferably
The temperature must be 180°C or higher and the melting point of the copolyester or lower. If the heat treatment temperature is less than 160°C, the antistatic effect aimed at by the present invention cannot be obtained. Further, if the heat treatment temperature is higher than the melting point of the copolyester, the copolyester film, which is the laminated portion, melts and becomes white, resulting in a significant decrease in transparency and mechanical properties. Next, regarding the heat treatment time, it is preferable to carry out the heat treatment within a range of 0.1 to 3 minutes. As the heat treatment method, the above-mentioned film may be exposed to an atmosphere set to the above-mentioned temperature conditions, or the above-mentioned film may be brought into contact with a roller heated to the above-mentioned temperature conditions. Next, a method for measuring characteristic values in the present invention will be explained. (1) Heat of crystal fusion Using a Shimadzu DSC (differential scanning calorimeter) device, polymer pellets were heated at 20°C in a nitrogen stream.
It was determined by dividing the endothermic energy associated with crystal melting obtained when the temperature was increased at a rate of min by the weight of the sample. (2) Antistatic properties (electrostatic voltage half-life) Using a static honest meter manufactured by Shishido Shokai, it was expressed as the half-life value of electrostatic voltage at 20°C, 65% RH, 40% RH, and 30% RH. The applied voltage was 10 KV, and the test was performed from a distance of 15 mm above the sample. (3) Mechanical properties Tensile strength and tensile elongation were measured using an Autograph IM-100 device manufactured by Shimadzu Corporation, and the average values in the longitudinal and transverse directions were taken as the characteristic values. (4) Transparency (Haze) Measured by JIS-K-6714 method. (Function) In the present invention, the effect of the added antistatic agent is significantly improved by copolymerizing polyethylene terephthalate and reducing its crystallinity so that the heat of crystal fusion is 7.5 cal/g or less. Although the details of this principle are not known, it is believed that by lowering the crystallinity, the added antistatic agent can more easily migrate to the film surface during heat treatment at 160°C or higher after biaxial stretching. Conceivable. Therefore, if the heat of crystal fusion exceeds 7.5 cal/g, the antistatic effect of the present invention cannot be obtained. Moreover, the biaxially stretched film of the copolymerized polyester of the present invention has poor mechanical properties and cannot be put to practical use when used alone. By laminating polyethylene terephthalate film at a specific thickness as described in the present invention,
For the first time, it has become possible to provide a film with well-balanced antistatic properties and mechanical properties, as well as significantly improved transparency. (Example) In order to make the present invention easier to understand, the present invention will be specifically explained using comparative examples and examples, but the present invention is not limited to these examples. Comparative Example 1 Using a mixed solution of phenol/tetrachloroethane = 6/4, polyethylene terephthalate with an intrinsic viscosity of 0.63 measured at 30°C was melt-extruded from a T-die at 280°C, cooled on a drum at 80°C, and the thickness was
An unstretched film of 150μ was obtained. Subsequently, this film was stretched 3.5 times in the machine direction at 90°C and then 3.5 times in the transverse direction at 110°C, and then heat set at 210°C for 5 seconds to obtain a biaxially stretched film with a thickness of 12.2μ. . Comparative Example 2 The polyethylene terephthalate of Comparative Example 1 was
A 12.2μ biaxially stretched film was obtained by blending 1 wt % of the sulfonic acid metal salt derivatives shown in the table and using the same method as in Comparative Example 1.

[Table] Comparative Example 3 Using a mixed solution of phenol/tetrachloroethane = 6/4, the intrinsic viscosity measured at 30°C is 0.62~
After blending 1% by weight of the sulfonic acid metal salt derivatives shown in Table 1 with the copolymerized polyester shown in Table 2 of 0.64, a biaxially stretched film of 12.2μ was obtained in the same manner as in Comparative Example 1.

[Table] Comparative Example 4 Polyethylene terephthalate of Comparative Example 1 and Polyethylene terephthalate of Comparative Example 3
A 1% by weight blend of the copolymerized polyester shown in the table and the sulfonic acid metal salt derivative shown in Table 1 was made into a feedblock type two-layer T using separate extruders.
Extrude from the die and use the same method as Comparative Example 1 to 12.2μ
A laminated biaxially stretched film was obtained. The thickness of the copolymerized polyester laminated portion was 4 μm.

【table】

[Table] Example 1 Polyethylene terephthalate of Comparative Example 1 and Polyethylene terephthalate of Comparative Example 1
A 1% by weight blend of the copolymerized polyester shown in the table and the sulfonic acid metal salt derivative shown in Table 1 was extruded from a feedblock type two-layer T die using separate extruders, and the same method as in Comparative Example 1 was carried out for 12.2 hours. A laminated biaxially stretched film of μ was obtained. The thickness of the copolymerized polyester laminated portion was 4 μm. Example 2 Polyethylene terephthalate of Comparative Example 1 and the second
Feedblock type 3 is produced by blending the copolymerized polyester shown in the table with 1% by weight of the sulfonic acid metal salt derivative shown in Table 1 using separate extruders so that the surface layer part is composed of the same polymer.
Extruded from a layer T die in the same manner as Comparative Example 1.
A laminated biaxially stretched film of 12.2μ was obtained. The thickness of the copolymerized polyester laminated portion was 2 μm on one side and 4 μm on both sides. The properties of the films of the above comparative examples and examples were determined by the fourth
Shown in the table. As is clear from this table, only the film of the present invention is excellent in antistatic properties, mechanical properties, and transparency.

【table】

[Table] (Effects of the invention) The laminated polyester film of the present invention is superior to biaxially oriented polyester films due to the appropriate combination of a polyethylene terephthalate layer as a strength material and a copolymerized polyester layer with a remarkable effect of adding an antistatic agent. The antistatic effect in the low humidity range, which is most important in practice, is improved without impairing the mechanical and optical properties. Further, the film of the present invention does not require post-processing such as coating and can be manufactured at low cost, which has a large economic effect.

Claims (1)

[Claims] 1 At least one side of a polyethylene terephthalate film is laminated with a copolyester mainly composed of polyethylene terephthalate, which contains 0.05 to 3% by weight of a sulfonic acid metal salt derivative and whose heat of crystal fusion is 7.5 cal/g or less, and is laminated in a biaxial direction. It is obtained by stretching at 160°C or higher and below the melting point of the copolymerized polyester, and has a tensile strength of 20 kg/mm ² or higher and a half-life of charging voltage at 20°C and 40% RH. A laminated polyester film that lasts 180 seconds or less.