JPS5839656B2 - Manufacturing method of polyester film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a polyester film having excellent antistatic properties.

As is well known, polyester films have a high degree of crystallinity, excellent transparent gloss, mechanical properties, chemical resistance, heat resistance, etc., and are therefore rapidly being used year by year for a wide range of applications including packaging.

However, since this polyester itself has a high degree of electrical insulation, the film has the disadvantage that it is susceptible to generation and accumulation of static electricity, causing various problems due to static electricity damage.

For example, the generation and accumulation of static electricity in polyester film can cause problems such as winding around rolls, electric shock to the human body, and difficulty in opening bags during the film forming process, printing, bag making, packaging, etc. This causes deterioration of the product value, such as deterioration, generation of printing marks, ink backflow, dust collection and dirt on the film surface, etc.

Methods for preventing such static electricity damage generally include a method of applying an antistatic agent to the surface of the film and a method of kneading the antistatic agent into a resin to form a film.

The method of applying an antistatic agent to the film surface requires an extra processing step, which is economically disadvantageous, and also has the disadvantage that the effectiveness is easily reduced by friction and washing of the film surface, so it is not an industrial method. Generally, a method is used in which an antistatic agent is kneaded into a resin to form a film.

However, for polyester films, this so-called kneading-type antistatic treatment method produces an antistatic effect by causing the antistatic agent to ooze out from inside the film to the surface, whereas polyester resin has a high secondary transition temperature. Therefore, after film formation, the antistatic agent does not ooze out onto the film surface at temperatures around room temperature.On the other hand, the high film formation temperature conditions and the reactivity of the polar groups of the polyester resin itself Therefore, it is difficult to use most antistatic agents because adding an antistatic agent causes deterioration of the polymer, coloring, and deterioration of physical properties.

In particular, in the case of a biaxially stretched polyester film, the antistatic agent on the film surface escapes and disappears during the stretching process, so that it no longer exhibits any antistatic effect.

Furthermore, many antistatic agents reduce the transparency of the film when incorporated into the polyester film.

As described above, the conventional kneading antistatic treatment methods do not show any antistatic effect on polyester films, or have some drawbacks.

The present inventors have arrived at the present invention as a result of intensive research into a method for obtaining a biaxially oriented polyester film having sufficient antistatic properties without having the above-mentioned drawbacks.

That is, the present invention provides a polyester (hereinafter sometimes abbreviated as terephthalic acid polyester) consisting of a dibasic acid (however, 80 mol% or more of the dibasic acid is terephthalic acid) residue and a glycol residue, 0.1 to 10% of low molecular weight polyalkylene glycol soluble in the polyester
0.05 to 5% by weight of the sulfonic acid metal salt derivative represented by the following general formula % (where R is an alkyl group having 8 to 20 carbon atoms, and Me is an alkali metal or alkaline earth metal). %, and after melting and forming a film, it was stretched in two axes at right angles, and then 160
This is done by heat treatment at a temperature that is above .degree. C. and below the melting point of the polyester.

The terephthalic acid polyester in the present invention is 80 mol%
The above is a polyester composed of a dibasic acid residue, which is terephthalic acid, and a glycol residue.

Dibasic acid residues are mainly terephthalic acid residues, but 2
0 mol% or less may be residues of other dibasic acids.

Other dibasic acid residues include isophthalic acid, phthalic acid,
There are residues of adipic acid, sepathic acid, succinic acid, oxalic acid, etc., and residues of oxyacids such as P-hydroxybenzoic acid can also be used.

In addition, the glycol residue is a normal alkylene glycol residue or cycloalkylene glycol residue, and examples thereof include residues such as ethylene glycol, propylene glycol, trimethylene glycol, tetramethylene glycol, and cyclohexane dimetatool. In particular, residues of ethylene glycol or tetramethylene glycol are used practically.

The polyalkylene glycol used in the present invention is essentially a terephthalic acid polyester (needs to be soluble in the polyester, and the lower the molecular weight, the better.

As explained in Japanese Patent Publication No. 39-5214, polyalkylene glycols that are substantially soluble in terephthalic acid-based polyesters can be highly dispersed in polyesters, and they do not aggregate when observed under a microscope. Particles with a diameter of 0.05 microns or less or particles that are so finely dispersed that they cannot be clearly observed with a microscope.

When polyalkylene glycol that is substantially insoluble in terephthalic acid polyester is used, the resulting polyester film has poor transparency and cannot be used for packaging or other purposes.

High molecular weight polyalkylene glycol is polyester (
It becomes substantially insoluble and reduces transparency when blended into a polyester film.

The polyalkylene glycol used in the present invention can be used in the form of one or more mixtures or copolymers, and specific examples thereof include polyethylene glycol with a molecular weight of 4,000 or less, polypropylene glycol with a molecular weight of 1,000 or less, and polypropylene glycol with a molecular weight of 1,000 or less. Polytetramethylene glycol, polytetrahydrofuran with a molecular weight of 1000 or less, copolymer of ethylene glycol and propylene glycol with a molecular weight of 1500 or less, copolymer of ethylene glycol and tetrahydrofuran with a molecular weight of 1500 or less, propylene glycol and tetramethylene glycol with a molecular weight of 1000 or less and mixtures of two or more of these compounds.

These polyalkylene glycols may be terminally modified if necessary.

Another constituent used in the present invention is a sulfonic acid metal salt represented by the following general formula % (where R is an alkyl group having 8 to 20 carbon atoms, and Me is an alkali metal or alkaline earth metal). Examples of derivatives include sodium octylsulfonate, sorta nonylsulfonate, sodium decylsulfonate, sodium dodecylsulfonate, sodium oleylsulfonate, sodium stearylsulfonate, potassium octylsulfonate, potassium dodecylsulfonate, potassium stearylsulfonate. , the number of carbon atoms in the alkyl group is 8 to 20
Examples include sodium alkylsulfonate having an average carbon number of 13 to 16.

These sulfonic acid derivative compounds have extremely high heat resistance and are also highly compatible with the aforementioned low molecular weight polyalkylene glycol, so they are extremely effective when combined with the special film forming method described below. Demonstrates antistatic properties.

Further, such aliphatic alkyl-substituted sulfonate compounds have better compatibility with polyalkylene glycol than sulfonate compounds containing aromatic groups, and improve the transparency of the film after addition.

The amount of polyalkylene glycol used in the present invention is 0.1
-10% by weight, preferably 0.5-5% by weight, but 0.
If it is less than 1% by weight, it will not have the effect of helping the uniform dispersion of the sulfonic acid derivative compound, and if it is more than 10% by weight, no increase in the effect will be observed (this may cause thermal deterioration of the polyester during film formation or physical damage). Causes adverse effects such as deterioration of properties.

On the other hand, the amount of the sulfonic acid derivative compound used is 0.05 to 5% by weight, preferably 0.1 to 3% by weight.

In the method of the present invention, a sufficient effect can be obtained by using a relatively small amount of antistatic agent, but if it is less than 0.05%, the effect is poor, and if it is more than 5%, the effect hardly increases. On the contrary, it is not preferable to add too much of the terephthalic acid-based polyester because it has negative effects such as deteriorating the transparency of the film and accelerating thermal deterioration of the terephthalic acid polyester.

The method for adding polyalkylene glycol and sulfonic acid derivative compounds to terephthalic acid polyester is from room temperature to
A recommended method is to add a sulfonic acid derivative compound to polyalkylene glycol melted at 100°C, mix the two uniformly by stirring, and then mix the mixture with the terephthalic acid polyester in the form of a solution.

If the polyalkylene glycol used is substantially insoluble in the terephthalic acid polyester and remains separated in the polyester film after film formation, the transparency of the film will be significantly deteriorated.

In addition, when the above-mentioned sulfonic acid metal salt derivative is used alone, it may deteriorate the dispersion state in the polyester, worsening transparency, or forming fish eyes due to undispersed matter, which may deteriorate the physical properties of the film. do.

The film according to the present invention is a polyester film blended with a substantially soluble polyalkylene glycol and a sulfonic acid metal salt derivative having a special structure, which is melt-formed and then biaxially stretched at a temperature of 160°C or higher, and terephthalic acid It is obtained by heat treatment at a temperature below the melting point of the polyester, and the film can be formed using a conventional polyester film forming method, such as the T-die method or the inflation-type polyester.
It can be formed into an unstretched film using a compression method or the like.

The effects of the present invention are more effectively exhibited by a film obtained by biaxially stretching this unstretched film.

The stretching temperature can be almost the same as that for the terephthalic acid polyester alone, but the stretching can be carried out at a different temperature if necessary.

The stretching ratio is 1.2 to 6 times in the vertical direction and 1.2 to 6 times in the horizontal direction.
It can be done about twice as much.

Biaxial stretching is an important condition for exerting the effects of the present invention, and if it is not biaxially stretched, it will lack functionality as a packaging material or other industrial product.

The most characteristic condition of the present invention is that the film is biaxially stretched and then heat-treated at a temperature of 160°C or higher and lower than the melting point of polyester.

The heat treatment may be performed at a temperature of 160° C. or higher and lower than the melting point of polyester for 0.1 seconds to 5 minutes, but it is more efficient and desirable to perform the heat treatment at a temperature in a higher temperature range because the treatment time can be shortened.

The heat treatment can be carried out by exposing the film to an atmosphere set to the above-mentioned temperature conditions or by bringing it into contact with a roller heated to this temperature, but methods other than these may also be employed.

Further, the heat treatment may be performed in a constant length state, a contracted state, or a stretched state, but in the case of contraction heat treatment, it is preferable that the relaxation rate is within 50%, and in the case of extension heat treatment, the elongation rate is preferably within 150%. .

The biaxially oriented polyester film obtained by the present invention has extremely excellent antistatic properties and excellent transparency, and other practical properties are also good.

Although the details of the function of developing antistatic properties and providing good transparency by the method of the present invention are unknown, the inorganic metal sulfonic acid salt derivatization, which does not give a clear melting point, cannot be used alone in polyester. While in a cohesive state,
When added in combination with a polyalkylene glycol soluble in polyester, as a result of the good compatibility of the polyalkylene glycol and the sulfonic acid derivative compound, both components are dispersed very evenly in the polyester, resulting in a good It seems that transparency can be achieved.

When a polyalkylene glycol that is substantially insoluble in the terephthalic acid polyester is used, the film becomes cloudy and its transparency becomes extremely poor.

The biaxially oriented polyester film obtained by the present invention does not show any decrease in work efficiency due to electrostatic charge or decrease in commercial value due to suction of dirt and dust, and has extremely good transparency, and is mainly used for packaging. Suitable for many applications.

The present invention will be specifically explained below with reference to several examples, but it goes without saying that the present invention is not limited to these examples.

The method for measuring the characteristic values in this Example II is as follows.

(2) Transparency Measured by JIS-6714 method.

Expressed in haze. 2) Antistatic property Shishido Shokai KK
20°0.65 using a static honest meter made by
% RH.

Apply voltage 10.0OOV from 15w1 above the sample. The charged voltage generated when applied is a voltage After discontinuing supply, the charged voltage is reduced to 1/2. It refers to the time system.

Example 1 Rice
Polyethylene terephthalate with an intrinsic viscosity of 0.62 measured at 30°C using a mixed solution of phenol/tetrachloroethane = 6/4, polyethylene glycol (PEG42ooo) with a molecular weight of 2000 and mixed sodium alkylsulfonate (As) with an average carbon number of 15. ) in a 1:1 mixture of 10
After stirring well at 0°C, various concentrations were added and mixed at 120°C in a blender, then melt-extruded at 280°C using a 20W screw diameter extruder with a T-die and cooled with a cooling roll at 80°C. An unstretched film with a thickness of 250 μm was obtained.

Next, the film was stretched 3.5 times in the machine direction at 90° C., then 3.5 times in the transverse direction at the same temperature, and then heat-treated at 200° C. for 30 seconds at a constant length.

For comparison, a film without heat treatment and a biaxially stretched film made of only polyethylene terephthalate under the same conditions were obtained.

The antistatic properties of these films are shown in Table 1.

Only the films obtained by the method according to the invention had significantly better antistatic properties.

Example 2 In the same manner as in Example 1, various compounds listed in Table 2 were added to polyethylene terephthalate in various proportions to prepare biaxially stretched films and heat-treated.

Table 2 shows the transparency and antistatic properties of each film.

As is clear from Table 2, only the film obtained by the method of the present invention has excellent antistatic properties and transparency.

Claims (1)

[Claims] 1. A polyester consisting of a dibasic acid (80 mol% or more of the dibasic acid is terephthalic acid) residue and a glycol residue, and a low molecular weight polyalkylene soluble in the polyester. 0.1 to 10% by weight of glycol and a sulfonic acid metal salt derivative represented by the following general formula % (where R is an alkyl group having 8 to 20 carbon atoms and Me is an alkali metal or alkaline earth metal). 0.05 to 5% by weight was blended, and after melt film formation, it was stretched in biaxial directions perpendicular to each other, and then 160
1. A method for producing a polyester film, characterized in that heat treatment is carried out at a temperature not less than 0.degree. C. and not more than the melting point of the polyester.