JPH01229042A - Readily cuttable polyester film - Google Patents

Abstract

PURPOSE:To obtain the title film useful as a base material for packaging film, etc., having specific tear propagation resistance, excellent toughness, heat resistance, etc., by copolymerizing plural dicarboxylic acids such as metallic sulfonate group-containing aromatic carboxylic acid, etc. CONSTITUTION:(A) Terephthalic acid is copolymerized with (B) 3-12mol% (based on the component A) of metallic sulfonate group-containing aromatic dicarboxylic acid (e.g., 5-sodiumsulfoisophthalic acid), (C) 3-18 mol% (based on the component A) aromatic dicarboxylic acid except the component A (e.g., isophthalic acid) and/or 4-20C aliphatic dicarboxylic acid (e.g., succinic acid) and (D) ethylene glycol, made into a sheet by an extruder and biaxially drawn to give the aimed film having preferably 5-80mum thickness and <=300g/mm tear propagation resistance of uniaxial direction.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention relates to a polyester film with excellent easy-cutting properties.More specifically, it maintains practical strength without losing the toughness inherent in polyester. This invention relates to a biaxially stretched polyester film that can be easily cut by hand.

(Prior art) Adhesive tapes and packaging bags that use polyethylene terephthalate (hereinafter abbreviated as PET) as a base film have traditionally been manufactured using PET film's excellent properties such as high elastic modulus, heat resistance, and water resistance. Although it has these characteristics, it has the major drawback that it is difficult to cut and cannot be easily torn.

Polyester films that can be easily cut by hand include those using low molecular weight polyester polymers (for example, Japanese Patent Publication No. 55-20514), those oriented in the -axial direction (for example, Japanese Patent Publication No. 55-8551), and There are those obtained by copolymerizing a diethylene glycol component or the like (Japanese Patent Publication No. 56-50692, JP-A-59-11320).

[Problem to be solved by the invention]

However, in the conventional technique described above, when the molecular weight is lowered to the point where satisfactory cutting properties are obtained, the physical properties of the polyester itself are lost, and problems such as membrane tearing occur during film forming. occurs and is not practical. Furthermore, although polyester films oriented in the -axial direction can be easily cut linearly in the orientation direction, they still lack toughness and have the disadvantage of poor productivity due to the low stretching area ratio.

On the other hand, in the case of copolymerized diethylene glycol components, when the copolymerization ratio is as high as 15 to 40 mol% (Japanese Patent Publication No. 56-50692), the melting point of the polymer itself decreases significantly, and the elastic modulus decreases. The disadvantage is that the PET film itself loses its original properties. Also, a copolymer of a comonomer containing a metal sulfonate group and an oxyalkylene glycol comonomer (JP-A-59-11
320), although it has been slightly improved, PE is still produced by copolymerization of oxyalkylene glycol components.
It has the drawback that the original characteristics of T itself are lost, and because of the decrease in Tg, thickness unevenness is likely to occur due to uneven stretching.

The purpose of the present invention is to improve such problems and provide an excellent biaxially oriented polyester film that maintains practical strength without losing the original properties of PET and can be easily cut by hand. .

[Means to solve the problem]

In the present invention, as an acid component, (a) terephthalic acid is the main component, (b) 13 to 12 mol% of aromatic dicarbonate containing a metal sulfonate group (based on terephthalic acid), and (c)
Formed from a copolymerized polyester containing an aromatic dicarboxylic acid other than terephthalic acid and/or an aliphatic dicarboxylic acid having 4 to 20 carbon atoms (based on terephthalic acid) in an amount of 3 to 18 mol%, and using ethylene glycol as a diol component. The present invention relates to an easily cutable polyester film having a tear propagation resistance of 3000/mm or less in at least one direction.

The copolymerized polyester in the present invention is obtained by copolymerizing the above-mentioned three or more specific components as acid components in a specific ratio when producing a polyester whose repeating units are mainly composed of ethylene terephthalate.

In other words, the metal sulfonate group-containing comonomer and the oxyalkylene glycol comonomer are copolymerized by using only the acid component as the copolymerization component and using an aromatic dicarboxylic acid containing at least one metal sulfonate group. This is preferable because Tcx decreases less than that of the copolymerized polyester obtained when

In general, a low Tg leads to a decrease in the physical properties of the film, and
Since stretching unevenness is likely to occur during film formation, it is important that the TCI decrease is small in order to maintain the original physical properties of PET itself.

Aromatic dicarboxylic acids containing a metal sulfonate group, which is one of the acid components used in the present invention, include 5-sodium sulfoisophthalic acid, 2-sodium sulfoterephthalic acid, 4-sodium sulfophthalic acid, and 4-sodium sulfophthalic acid. Examples include 2,6-naphthalene dicarboxylic acid and compounds in which sodium is replaced with other metals, such as potassium. Among them, 5-sodium sulfoisophthalic acid is particularly preferable, and aromatic dicarboxylic acids other than terephthalic acid include isophthalic acid, 2,6-naphthalene dicarboxylic acid, diphenyl dicarboxylic acid, and the like, among which inphthalic acid is particularly preferable.

In addition, as the aliphatic dicarboxylic acid having carbon vi4 to 20,
Examples include succinic acid, adipic acid, sebacic acid, dodecanniic acid, and eicosanniic acid, among which succinic acid and adipic acid are preferred, and adipic acid is particularly preferred.

Moreover, as the glycol component in the present invention, polyethylene glycol is preferable.

The amount of these acid components in the copolymerized polyester is 3 to 12 mol%, more preferably 5 to 10 mol%, based on terephthalic acid as an aromatic dicarboxylic acid containing a metal sulfonate group.

It depends on the amount of other acid components, but if the copolymerization amount is less than this, it will be difficult to impart easy cutting properties, and if it is too large, the water resistance and solvent resistance will deteriorate, and the initial elastic modulus and other properties will be significantly reduced. The original properties of polyester are lost, such as deterioration.

In addition, for aromatic dicarboxylic acids other than terephthalic acid and/or aliphatic dicarboxylic acids having 4 to 20 carbon atoms,
It is 18 mol%, more preferably 5 to 15 mol%. Although it depends on the amount of aromatic dicarboxylic acid containing a metal sulfonate group, if the amount of copolymerization is less than this, it will be difficult to impart easy cutting properties, and if it is too much, the original toughness of the PET film will be lost.

The copolymerized polyester of the present invention may contain copolymerized components other than those mentioned above, as long as the effects of the present invention are not impaired. Furthermore, various known additives such as lubricants, optical brighteners,
Pigments, antioxidants, antistatic agents, etc. may be added. The lubricant should have an average particle size of 0.2 to 3 μm from the viewpoint of blocking prevention, transparency, and mechanical strength of the film.
0.005 to 0.8 fiffi% of inert inorganic particles of m
It is preferable to add More preferably, it is 0.01 to 0.2% by weight.

The tear propagation resistance of the film of the present invention in at least one direction is 300 g/mm or less, preferably 150 to 300 g/mm.
g/mm. Also, the elongation at break in at least one direction is 1
It is preferably 0 to 150%, more preferably 3
0 to 100%, and the breaking strength in at least one direction is 8
It is preferably in the range of ~15 kg/mm. If the mechanical properties of the film are outside this range, if the film is too high, it will not be easy to cut, and if it is too low, the film will be weak and brittle and will easily break during molding, and will lack practicality as a film.

The polyester film targeted by the present invention has a thickness of 5 to
A thickness of 80 μm, preferably 10 to 60 μm is preferred in the present invention because it can achieve both manual tearability and toughness.

Next, an example of a method for producing the film of the present invention will be explained.

First, as a method for producing a copolyester suitable for producing the film of the present invention, a conventional method for synthesizing a copolyester can be directly applied. For example, by directly esterifying an acid component with a glycol component, or transesterifying a dialkyl ester of an acid with a glycol component, and heating this under reduced pressure to remove excess glycol component,
1 copolymerized polyester can be provided.

When producing polyester by performing a polycondensation reaction,
At any time before the start of the polycondensation reaction, 0.005 to 0.8 ffiff1% of insoluble inorganic particles (average particle size 0.2 to 3 μm) to the polyester can be added to the polyester.

The copolymerized polyester thus jqed is thoroughly dried in vacuum according to a conventional method, fed to an extruder and melt-extruded to form a sheet-like unstretched film, and then biaxially stretched, preferably biaxially stretched. The desired film can be obtained by further heat-treating the film.

The biaxial stretching may be longitudinal or transverse sequential stretching or biaxial simultaneous stretching, and the stretching ratio is not particularly limited, but is usually 2.
0 to 6.0 times is appropriate. In order to provide anisotropy in cuttability, the longitudinal and transverse stretching ratios can be changed arbitrarily. Also vertical,
After the transverse stretching, the film may be re-stretched in either the longitudinal or transverse direction.

The heat treatment temperature is preferably at least 50°C lower than the melting point of the copolymer, preferably at least 30'C lower than the melting point. Since the melting point of the copolyester used in the present invention is 200°C or higher, the heat treatment temperature is 150'C or higher, more preferably 170°C or higher.

[Measurement evaluation method]

The main physical property measurement and evaluation methods used in the present invention are shown below.

(1) Tear propagation resistance according to J l5-21792-1976, length 51 mm
, a 12.7 mm cut was made in a test piece having a width of 64 mm. The unit was g/mm divided by the film thickness. The lower the tear propagation resistance, the easier it is to cut by hand.

(2) Easy cutting A film with a thickness of 22 μm was cut from the edge using both hands and classified into the following ranks.

○: Can be cut as easily as cellophane or more easily than cellophane.

Δ: It is more difficult to cut than cellophane, but it can be cut.

X: Cutting is difficult and the shape of the cut portion is disordered.

(3) Strength at break, elongation, initial elastic modulus According to J15-21702-1976, the test piece was a rectangular shape with a width of 10 mm and a length of 100 mm, and the tensile speed was 300 mm/min for the elongation at break, and the initial elastic modulus was 20mm/
Measured at min.

The initial elastic modulus was classified into the following ranks.

○: 300kCJ/mm2 or more X: Less than 300kQ/mm2 (4) Heat resistance The melting points of the polymers were measured and classified into the following ranks.

02210℃ or higher
Δ for those in the range of 5 to 50%, X for those exceeding 50%
It was shown in

Thickness unevenness (%) = maximum thickness 8-@small thickness ax+o.

Average Thickness of Film (6) Intrinsic Viscosity of Polymer The polymer was dissolved in 0-chlorophenol and measured at 25°C.

(Example) The present invention will be explained in more detail by showing examples below.

Examples 1 to 3, Comparative Examples 1 to 12 Dimethyl-5-sodium sulfoisophthalic acid (hereinafter abbreviated as 5SIA), isophthalic acid (hereinafter abbreviated as DMI), and adipic acid (hereinafter abbreviated as DMA) were used as copolymerization acid components. Copolymerized polyethylene terephthalate (intrinsic viscosity 0.5
7> is 1q.

This was extruded and cast, and then 3
．． After sequentially stretching 3 times and 3.7 times in the transverse direction at 95°C, it was further heat-treated at a temperature 40°C lower than the melting point of the polymer to a thickness of 22 μm.
15 types of copolymerized polyethylene terephthalate films were obtained.

Table 1 shows the characteristic values of the obtained film.

As is clear from Table 1, easy cleavability is not achieved unless two types of acid components including the 5SIA component are copolymerized in an appropriate ratio (mol %, relative to terephthalic acid).

Moreover, if the ratio is too high, the initial elastic modulus and heat resistance will decrease, which is not preferable.

Example 4 Copolymerized polyethylene terephthalate (
(intrinsic viscosity 0.56, melting point 218°C) was supplied to an extruder, melted and extruded at 280°C, and cooled and solidified in a cooling drum with a surface temperature of 30°C to obtain an unstretched sheet. This sheet was heated to 90°C and stretched 3.0 times in the longitudinal direction, then stretched 3.6 times in the width direction at 95°C, and heat treated at 190°C for 15 seconds to form a biaxially stretched film with a thickness of 12 μm. 1q
Ta.

Table 2 shows the characteristic values of this film. The obtained film could be easily cut by hand like cellophane, and had a practical strength.

Example 5 A copolymerized polyethylene terephthalate having an intrinsic viscosity of 0.61 and a melting point of 213° C. was obtained by copolymerizing with an added amount of SSIA of 6 mol % and an added amount of DMA of 12 mol %.

A two-wheel stretched film was obtained in the same manner as in Example 3, except that the heat treatment temperature was changed to 185°C. The characteristic values of this film are also shown in Table 2 along with the characteristic values of the film of Comparative Example 1.
Shown in conjunction with

〔Effect of the invention〕

The biaxially stretched polyester film of the present invention can be easily cut by hand, and has excellent productivity, toughness, and heat resistance.
Extremely excellent as a film base material for packaging bags and adhesive tapes.

Claims (1)

[Claims] As an acid component, (a) an aromatic dicarboxylic acid 3 containing terephthalic acid as a main component and (b) a metal sulfonate group;
~12 mol% (based on terephthalic acid) and (c) aromatic dicarboxylic acid other than terephthalic acid and/or carbon number 4-20
A film formed from a copolyester containing 3 to 18 mol% of aliphatic dicarboxylic acid (based on terephthalic acid) and using ethylene glycol as a diol component, the film having a tear propagation resistance of 300% in at least one direction.
An easily cuttable polyester film having a cuttability of g/mm or less.