JP2605812B2 - Biaxially stretched polyester film - Google Patents

Description

The present invention relates to a biaxially stretched polyester film. More specifically, the present invention relates to a biaxially stretched polyester film which maintains the strength of a practical surface without losing the inherent toughness of the polyester, is easily torn, and has excellent cuttability.

[Conventional technology]

Conventionally, adhesive tapes and packaging bags that use polyethylene terephthalate (hereinafter abbreviated as PET) as a base film have been used because of their superior properties such as high elastic modulus, heat resistance, and water resistance. However, while having these features, there is a major drawback that it is difficult to cut and cannot be easily torn.

Polyester films that can be easily cut by hand include those oriented uniaxially (for example, Japanese Patent Publication No. 55-8551) and those obtained by copolymerizing a diethylene glycol component (Japanese Patent Publication No. 56-50692). Those using a polyester polymer having a molecular weight (for example, JP-B-55-2051)
No. 4 gazette).

[Problems to be solved by the invention]

However, in the above-mentioned prior art, the uniaxially oriented polyester film has a drawback that although it can be easily cut linearly in the orientation direction, it still has no toughness, and has a low draw area ratio, resulting in poor productivity. . In addition, those obtained by copolymerizing a large amount of a diethylene glycol component and the like have the drawback that the inherent properties of PET itself are lost due to the copolymerization and the Tg is reduced, and thickness unevenness due to stretching unevenness is likely to occur due to a decrease in Tg. .

On the other hand, the method of lowering the molecular weight of the polyester is not practical if the molecular weight is reduced until satisfactory cutting properties are obtained, as well as the physical properties of the polyester itself are lost and film breakage during film forming occurs. Not.

[Means for solving the problem]

According to the present invention, there is provided a polyester comprising at least one crosslinkable comonomer component copolymerized at 0.2 to 3.0 mol%, having an intrinsic viscosity of 0.45 to 0.62 and a tear propagation resistance in at least one direction of 280 g / mm or less. The present invention relates to an axially stretched polyester film.

The polyester in the present invention may be any polyester mainly composed of a saturated linear polyester having film forming ability.

Specific examples include, for example, polyethylene terephthalate, polymethylene terephthalate, poly-1,4-cyclohexylene dimethylene terephthalate, polyethylene
Preferred are 2,6-naphthalate and polyethylene-p-oxybenzoate.

Of course, these polyesters may be homopolyesters or copolyesters shown below. That is, in the case of a copolyester, as components to be copolymerized, for example, diethylene glycol, propylene glycol, triethylene glycol, polyethylene glycol, polytetramethylene glycol, neopentyl glycol, p-xylylene glycol, 1,4-cyclohexanedimethanol, 5-sodium Diol components such as sulforesorcin, adipic acid, sebacic acid, phthalic acid,
Isophthalic acid, 2,6-naphthalene dicarboxylic acid, dicarboxylic acid components such as 5-sodium sulfoisophthalic acid,
p-oxyethoxybenzoic acid and the like. The ratio of these copolymerized components is preferably 1 to 14 mol%. More preferably, it is 2 to 10 mol%. However, in the case of polyalkylene glycol, 1 to the obtained polyester
15 wt% is preferred. The copolyester in the present invention includes mixing a homopolyester such as polyethylene terephthalate or polyethylene-2,6-naphthalate within a mixing range in which the properties can be exhibited.

Polyester of the present invention, as long as the effects of the present invention are not impaired, known various additives, for example, a lubricant, an optical brightener,
Pigments, antioxidants, antistatic agents and the like may be added. The lubricant has an average particle diameter of 0.2 to 3 μm from the viewpoint of preventing blocking and transparency of the film, and mechanical strength.
Is preferably added in an amount of 0.005 to 0.8% by weight. More preferably, it is 0.01 to 0.2% by weight.

The crosslinkable comonomer component in the present invention is selected from aromatic polycarboxylic acids and aliphatic trihydric alcohols.
More specifically, the aromatic polycarboxylic acids are selected from benzenetricarboxylic acids such as trimellitic acid and trimesic acid, and benzenetetracarboxylic acids such as melophanic acid and pyromellitic acid. Among them, benzenetricarboxylic acid is preferably used.

The aliphatic trihydric alcohol is selected from glycerin derivatives such as trioxyisobutane, trimethylolpropane, glycerin, and alkyl-substituted glycerin. Among them, trimethylolpropane and glycerin are preferably used.

The biaxially stretched polyester film of the present invention is a biaxially stretched polyester film containing at least one or more of the above-mentioned crosslinkable comonomer components as a copolymer component in an amount of 0.2 to 3.0 mol%, preferably 0.5 to 2.5 mol%. It is a film. The copolymerization amount of the crosslinkable comonomer component is 0.
If the amount is less than 2 mol%, tearing and easy cutting properties are not sufficient, and if it exceeds 3.0 mol%, the polymerization reaction becomes difficult to control, and troubles such as film breakage and stretching difficulty occur during film formation, which is not preferable. .

The intrinsic viscosity of the biaxially oriented polyester film of the present invention is from 0.45 to 0.62, preferably from 0.45 to 0.57. If the intrinsic viscosity of the film is too high, even if the cross-linkable comonomer component is copolymerized, the film will have poor cuttability.If the film is too low, the film-forming and stretching conditions will be narrow, and the film cannot be formed stably. Not practical.

Further, the biaxially stretched polyester film of the present invention has a tear propagation resistance of at least one direction of 280 g / mm or less,
Preferably it is 250 g / mm or less. Further, the breaking elongation in at least one direction is preferably 10 to 150%, more preferably 30 to 100%, and the breaking strength in at least one direction is preferably in the range of 8 to 15 kg / mm ^2. .

The polyester film targeted by the present invention has a thickness of 5
In the case of the present invention, those having a thickness of from 80 to 80 μm, preferably from 10 to 60 μm can achieve both hand-cutting property and toughness.

Next, as an example of the production method of the film of the present invention, a polyester whose repeating unit is mainly composed of ethylene terephthalate will be described.

First, as a method for producing a copolymerized polyester suitable for producing the film of the present invention, an ordinary method for synthesizing a copolymerized polyester can be applied as it is. For example, an acid component is directly esterified with a glycol component, or a dialkyl ester of an acid is transesterified with a glycol component, and this is heated under reduced pressure to remove an excess glycol component, thereby obtaining a copolymerized polyester. be able to.

At the time of performing the polycondensation reaction to produce a polyester, at any point before the start of the polycondensation reaction, 0.005 to 0.8% by weight of inert inorganic particles (average particle size: 0.2 to 3 μm) insoluble in the system are added to the polyester. be able to.

The copolyester thus obtained is sufficiently vacuum-dried according to a conventional method, supplied to an extruder, melt-extruded to form a sheet-like unstretched film, subsequently biaxially stretched, and preferably biaxially stretched. By subjecting the film thus obtained to a further heat treatment, a desired film can be obtained.

Biaxial stretching may be any of longitudinal, horizontal 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 impart anisotropy to the cutting properties, the longitudinal and horizontal stretching ratios may be changed arbitrarily. After the stretching in the longitudinal and transverse directions, the film may be stretched again in any of the longitudinal and transverse directions.

The heat treatment temperature is preferably at least 50 ° C. lower than the softening point of the copolymer, and more preferably at least 30 ° C. lower than the softening point.

(Measurement evaluation method)

The methods for measuring and evaluating the main physical properties used in the present invention are shown below.

Tear Propagation Resistance (Tear Ease) Measured according to JIS-Z1792-1976, with a 12.7 mm cut in a 51 mm long and 64 mm wide test specimen. The unit was g / mm divided by the film thickness. The smaller the tear propagation resistance is, the easier it is to tear and the easier to cut by hand.

Hand-cutting property (easy-cutting property) A film having a thickness of 25 μm was cut from both ends with both hands and classified into the following ranks.

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

Δ: Harder than cellophane, but can be cut.

×: Cutting is difficult and the shape of the cut portion is disturbed.

Tear direction (easy cutability) Take a test piece of 200 mm length and 50 mm width with the main orientation direction as the main axis, make a 10 mm notch in the main axis direction, and tear by hand. The results of the ten tear tests were classified into the following ranks.

○: Linearly torn 8 times or more △: Linearly torn 5 times or more ×: Linearly torn less than 5 times Breaking strength and elongation Specimen width according to JIS-Z1702-1976 10mm, length 10
The strip speed was 0 mm, and the tensile speed was measured at 300 mm / min.

Intrinsic viscosity of polymer The polymer was dissolved in o-chlorophenol and measured at 25 ° C.

〔Example〕

 Examples will be described below in more detail.

Examples 1 to 7, Comparative Examples 1 to 4 Trimellitic acid (hereinafter TM) was used as a crosslinkable comonomer component.
TM), trimethylolpropane (hereinafter abbreviated as TMP), and / or glycerin by adding or changing the amount of addition. Isophthalic acid (hereinafter abbreviated as DMI), polyethylene glycol (hereinafter abbreviated as DMI) PEG) was obtained to obtain copolymerized polyethylene terephthalate having various copolymer compositions.

Extrude and cast this, then 3.
The film was successively stretched 5 times at 90 ° C. and 3.7 times in the transverse direction, and then heat-treated at a temperature 30 ° C. lower than the softening point of the polymer to obtain various 25 μm copolymerized polyethylene terephthalate films.

 Table 1 shows the characteristic values of the obtained film.

As is apparent from Table 1, if the crosslinkable comonomer component is not copolymerized in an appropriate ratio (mol%, based on the total acid component or the total glycol component), the easy-cleavability does not appear. If the ratio is too high, it becomes difficult to control the polymerization reaction. If the intrinsic viscosity of the film is too low, the film cannot be formed stably,
On the other hand, if it is too high, the easy-to-cleave property does not appear.

Example 8 Polyethylene terephthalate obtained by copolymerization with 1.5 mol% of TMTM and 3.0 mol% of DMI was obtained (softening point, 25%).
0 ° C.) was supplied to an extruder, extruded at 280 ° C., and cooled and solidified by a cooling drum having a surface temperature of 40 ° C. to obtain an unstretched sheet. This sheet was heated to 85 ° C., stretched 3.5 times in the longitudinal direction, stretched 4.0 times in the transverse direction at 90 ° C., and heat-treated at 220 ° C. for 15 seconds to obtain a biaxially stretched film having a thickness of 12 μm.

Table 2 shows the characteristic values of this film. The resulting film is easy to tear and has excellent tearing direction,
Moreover, the strength was practical.

Example 9 The copolymerized polyethylene terephthalate (softening point, 252 ° C.) obtained by copolymerizing TMTM in an amount of 1.5 mol% and PEG in an amount of 8% by weight (total polyester, PEG molecular weight of 1000) was the same as in Example 4. To obtain an unstretched sheet. This sheet
Heat to 70 ° C and perform 4.0 times longitudinal stretching, then continue to 80 ° C
And then heat-treated at 220 ° C. for 15 seconds to obtain a biaxially stretched film having a thickness of 25 μm.

The characteristic values of this film are also shown in Table 2 together with the characteristic values of the film of Comparative Example 3. This film could be cut by hand like cellophane and had practical strength.

(Effect of the Invention) The biaxially stretched polyester film of the present invention has a small tear propagation resistance, and has the property of being easily torn and easily cut by hand when it is torn by inserting a notch. Excellent productivity, for example, it can be manufactured under the same film forming conditions as biaxially stretched polyester films. Therefore, it is extremely excellent as a film base material for packaging bags and adhesive tapes.

Claims (3)

(57) [Claims] 1. A polyester comprising at least one crosslinkable comonomer component copolymerized at 0.2 to 3.0 mol%, having an intrinsic viscosity of 0.45 to 0.62 and a tear propagation resistance in at least one direction of 280 g / mm or less. A biaxially stretched polyester film, characterized in that: 2. The biaxially stretched polyester film according to claim 1, wherein the crosslinkable comonomer component is benzenetolucarboxylic acid. 3. The biaxially oriented polyester film according to claim 1, wherein the crosslinkable comonomer component is a trihydric alcohol.