KR100625367B1 - Biaxially oriented polyester film - Google Patents

Abstract

In a film prepared by biaxially stretching a polyester sheet having a glass transition temperature of 60 ° C. or more in the longitudinal direction and the transverse direction and then subjecting it to a tearing treatment, the film has a longitudinal elongation of 100% or more and a longitudinal direction before the tearing treatment. The ^bi- opening property of the present invention, wherein the refractive index is 1.64 or less, the birefringence is 0.03 or more, and the longitudinal strength is 6 kgf / mm ² or more, and the longitudinal elongation of the film after the tearing treatment is 50% or less. Biaxially-stretched polyester film has excellent mechanical and chemical properties, environmental friendliness and food hygiene inherent to polyester, and has excellent tensile properties, so that no breakage occurs during film forming or post-processing, and tear resistance due to tearing treatment It has been greatly improved and useful for openable packaging.

Description

Biaxially oriented polyester film {BIAXIALLY ORIENTED POLYESTER FILM}

The present invention relates to a biaxially stretched polyester film that can be easily cut by hand and easily cutable without notch processing due to its excellent tearing property.

Cellophane films have been widely used as films for easy-open packaging and adhesive tapes. However, cellophane film has a high possibility of causing environmental pollution in the manufacturing process, and there are many restrictions on the production process itself, and the manufacturing cost is high due to equipment investment to prevent environmental pollution. There is a trend.

There are products that are notched on biaxially oriented polypropylene film as a substitute film, but the appearance of the finished product is not beautiful due to the external folding part for notch processing, and it looks bulky, There is a drawback to tearing.

In recent years, interest in polyester films having excellent mechanical and chemical properties and having environmental friendliness and food hygiene stability has increased. In general, polyester biaxially oriented films, like polypropylene films, are poorly cuttable due to their high mechanical properties and can be used as bi-opening packaging films only when they are notched.

Japanese Patent Application Laid-open No. 50-74637 relates to a transverse tearable adhesive tape and proposes a uniaxially stretched film of polyester, but due to the high orientation in the transverse direction, the mechanical strength in the longitudinal direction is insufficient, thus forming a film. There are problems such as breakage of the film in the process or during the post-processing work for packaging.

In addition, Japanese Patent Application Laid-open No. 51-19049 discloses 95 to 30% by weight of a polyester composed of residues of dibasic acids having a melting point of 180 ° C or higher (but more than 85 mol% of dibasic acids are terephthalic acid) and residues of glycols and intrinsic viscosity of 0.35 or less. Discloses a biaxially oriented film for pressure-sensitive adhesive tapes comprising 5 to 70% of low-polymerization polyester, but a film thickness non-uniformity caused by using polyester resins of different polymerization degrees together and a relatively thin thickness packaging film of 25 μm or less In use, there is a problem such as a tearing phenomenon occurs for each part in the post-processing process.

Korean Patent Laid-Open Publication No. 2001-0046253 discloses a biaxially stretched polyester film mixed with modified polybutylene terephthalate, although no breakage occurs during film forming or post-processing, but the tearing direction is longitudinal and thus transverse There is a problem that it is not applicable to a product requiring tearing property.

SUMMARY OF THE INVENTION An object of the present invention is to provide a biaxially stretched polyester film which is useful for two-sealing packaging or adhesive tape because of excellent mechanical and chemical properties in the longitudinal direction and easy cutting without notching.

In order to achieve the above object, in the present invention, a film prepared by biaxially stretching and heat-treating a polyester sheet having a glass transition temperature of 60 ° C. or more in a longitudinal direction and a transverse direction, and then performing a tearing treatment of the film before tearing treatment. The longitudinal elongation is at least 100%, the longitudinal refractive index is at most 1.64, the birefringence is at least 0.03 and the longitudinal strength is at least 6 kgf / mm ² , and the longitudinal elongation of the film after the tearing treatment is 50% or less. To provide a two-sealing biaxially stretched polyester film.

Hereinafter, the present invention will be described in more detail.

The polyester film of the present invention has excellent heat resistance, chemical resistance, solvent resistance, printability, and mechanical properties, and has a biaxially stretched film with improved mechanical direction tensile properties, thereby making it possible to stably produce a film, and to prevent breakage during post-processing. It is a non-tearable film which does not occur and can be used for pressure-sensitive adhesive tapes and packaging because the tearability is greatly improved by the tearing treatment.

The polyester used for the film of this invention can be manufactured by polycondensing the acid component which has aromatic dicarboxylic acid as a main component, and the glycol component which has alkylene glycol as a main component. Specific examples of the aromatic dicarboxylic acid include dimethyl terephthalate, and other aromatic dicarboxylic acid components can be copolymerized within a range that does not significantly change their properties. Specific examples of aromatic dicarboxylic acids other than those that may be used include terephthalic acid, isophthalic acid, naphthalenedicarboxylic acid, dimethylisophthalate and the like. Specific examples of the alkylene glycol include ethylene glycol, and other glycol components may be copolymerized within the range of not significantly changing their properties. Specific examples of glycol components other than those which may be used include diethylene glycol, trimethylene glycol, tetramethylene glycol, 1,4-cyclohexanedimethanol, 2,2-dimethyl (-1,3-propane) diol, and the like. Can be.

In addition, the glass transition temperature of the final polyester resin prepared by copolymerizing the dicarboxylic acid and alkylene glycol must be at least 60 ℃. If the glass transition temperature of the final polyester resin is lower than 60 ℃ it may lose the excellent mechanical and thermal properties inherent to the polyester, in particular polyethylene terephthalate by excessive copolymerization.

In preparing the polyester of the present invention, known additives such as polycondensation catalysts, dispersants, antistatic agents, antistatic agents, sunscreen agents, antiblocking agents and other inorganic lubricants are added within a range that does not impair the effects of the present invention. You may. In addition, a known antistatic or slip treatment for coating may be performed to remove static electricity from the film surface. It is also possible to perform a known corona treatment in order to improve printing characteristics.

The melt-extruded sheet of the polyester resin having a glass transition temperature of 60 ℃ or more described above to obtain a sheet, biaxially stretched in the longitudinal and transverse directions, heat treatment and tearing to prepare a bi-opening polyester film according to the present invention. According to the present invention, the characteristic of the film before the tearing treatment is that the longitudinal elongation is 100% or more, the longitudinal refractive index is 1.64 or less, the birefringence is 0.03 or more, and the longitudinal strength is 6 kgf / mm ² or more. It features.

When the longitudinal elongation of the polyester film is 100% or more, the film is not easily broken, and thus the film can be worked without breaking in the film forming and post-processing process. If the longitudinal elongation is less than 100%, the tensile property is weak, so that breakage occurs in the film forming and post-processing process, and the film cannot be produced.

The refractive index indicates the degree of orientation of the molecular structure of the film, and the mechanical properties such as strength and elongation of the polyester film are determined by the degree of orientation. When the longitudinal refractive index of the polyester film is 1.64 or less, there are fewer molecules oriented in the longitudinal direction, so that the mechanical properties in the longitudinal direction are weakened, thereby making the lateral tear property excellent. If the longitudinal refractive index exceeds 1.64, the molecules are oriented in the longitudinal direction so that the longitudinal strength is large and thus the transverse tearing property is poor.

The birefringence is the transverse refractive index minus the longitudinal refractive index. The birefringence is the orientation of the molecules in the film. If the birefringence is large, the molecules are mainly oriented in the transverse direction. If the birefringence is small, the molecules are mainly oriented in the longitudinal direction. It means to be. If the birefringence of the polyester film is 0.03 or more, the molecules are mainly oriented in the transverse direction and thus have good tearability in the transverse direction. If the birefringence is less than 0.03, the molecules are mainly evenly or longitudinally oriented in all directions, so that the transverse tearing property is poor, such as a tearing in the longitudinal direction when tearing in the transverse direction.

In addition, the longitudinal strength of 6 kgf / mm ² or more can be used well for packaging. If the longitudinal strength is less than 6 kgf / mm ² , the breakage may occur in the film forming process or in the post-processing process such as printing, it may be a defect such as easy tearing in the packaged finished product.

In order to manufacture the polyester film of this invention, it is preferable to make the longitudinal stretch ratio at the time of biaxial stretching to 1.2-2.5 times, and the lateral stretch ratio to 3.0-5.0 times.

If the polyester film has a longitudinal stretching ratio of 1.2 to 2.5 times and a lateral stretching ratio of 3.0 to 5.0 times, the molecules have an appropriate orientation in the transverse direction, and the birefringence becomes 0.03 or more, so that the transverse tearing property is good. If the longitudinal draw ratio is less than 1.2 times, the molecules are not oriented in the longitudinal direction so that the longitudinal strength is less than 6 kgf / mm ² and the film easily breaks. If the longitudinal draw ratio exceeds 2.5 times, the molecules are oriented excessively in the longitudinal direction, so that the longitudinal refractive index is greater than 1.64, and thus the transverse tearability is very low. In addition, if the transverse draw ratio is less than 3.0 times, the film is poor due to insufficient stretching, and the transverse orientation of the molecules is relatively small, so that the birefringence is less than 0.03, so the transverse tearing property is poor. If the lateral stretch ratio exceeds 5.0 times, the polyester film cannot be formed. The polyester film has a stretching limit in which biaxial stretching is possible. If the lateral stretching ratio exceeds 5.0 times after longitudinal stretching, the film cannot sustain the stretching stress and breakage occurs, and thus film formation is impossible.

After the longitudinal stretching and the lateral stretching, heat treatment is performed at a temperature of Tg (glass transition temperature) + 80 占 폚 or lower.

As described above, the polyester film is stretched at 1.2 to 2.5 times the longitudinal stretching ratio and 3.0 to 5.0 times the transverse stretching ratio, and then has a temperature of Tg + 80 ° C. or lower, preferably Tg + 60 ° C. or lower, more preferably Tg + 40. When the heat treatment is carried out at a temperature of less than or equal to ℃ ℃ the longitudinal elongation of the film is 100% or more to have good longitudinal mechanical properties, so that no breakage occurs during the film forming process or post-processing process has a good workability. However, if the heat treatment is performed at a temperature above Tg + 80 ° C., the longitudinal elongation of the film is less than 100% and the longitudinal toughness is less than 5 kgf / mm ² , so that the mechanical strength is poor, resulting in breakage during film forming or post-processing. It often happens.

 The bi-opening polyester film of the present invention is then subjected to a tear treatment of the biaxially stretched film having the above-described characteristics, characterized in that the longitudinal elongation after the tearing treatment is 50% or less.

In order to apply for soft packaging applications requiring tearing properties, the film must have good tearing property, ie easily tearing. The film before the tearing treatment has a longitudinal elongation of 100% or more, so that fracture does not easily occur, thereby providing excellent processability but poor tearability. Therefore, the film is subjected to a tearing treatment in order to impart tearing. The tearing treatment is usually performed by treating the surface of the film fabric with an appropriate mixture of various solvents. In general, contacting the solvent with the film will damage the film from its surface. This is because the solvent in contact with the surface of the film penetrates into the structure of the polymer, causing the molecular structure to swell and severely destroy or bond the molecular structure to dissolve the film. The degree of damage of the film varies according to the type of solvent and the type of film. Polyester film is excellent in chemical resistance and generally is not easily dissolved by a solvent, so only the surface of the film is damaged.

Suitable solvents for the tearing treatment of the polyester film include methanol, ethanol, butanol, iso-propyl alcohol, methyl acetate, ethyl acetate, n-butyl acetate, acetone, methyl ethyl ketone, cyclohexanone, toluene, benzene, xylene and the like. Can be used.

As described above, when the polyester film is subjected to the tear treatment using the solvent, the solvent penetrates into the molecular structure of the film to increase the fluidity of the molecules, so that the molecules move to find a stable state and are more oriented in the transverse direction. In this process, the molecules are not only oriented in the transverse direction but also crystallized to make the molecules more dense. In this teared film, the molecules are oriented in the transverse direction so that the longitudinal elongation is smaller than before the tearing process. Therefore, the film having a longitudinal elongation of 50% or less after the tearing treatment has excellent tearing properties and can be applied as a double-sealing packaging use. If the longitudinal elongation exceeds 50% after the tearing treatment, the film does not easily tear even after the tearing treatment, and thus the film cannot be applied as a double-sealing use.

It is preferable that the polyester film of this invention is 8-25 micrometers in thickness, and longitudinal toughness is 5 kgf / mm <^2> or more.

Typical thicknesses of films used for soft packaging applications range from 8 μm to 25 μm. In this thickness range, when the toughness of the polyester film is 5 kgf / mm ² or more, it has good mechanical properties with respect to the tensile force, so that fracture does not occur during the film forming process or during post-processing such as printing. Toughness is the energy per unit volume applied until the sample breaks. If the toughness is large, the breakage is necessary when a large amount of energy is given, and if the toughness is small, the film is easily broken. If the toughness is less than 5 kgf / mm ^{2, since the} film is easily broken, breakage occurs frequently in the film forming process or in the post-processing process, resulting in a decrease in work efficiency.

As described above, the biaxially stretched polyester film of the present invention has a uniform thickness and excellent printing workability, and easily cuts the finished product without notching without breaking easily in the film forming process or the post-packaging process. It is useful for two open packaging.

Hereinafter, the present invention will be described in more detail with reference to the following examples. However, the following examples are only for illustrating the present invention, and the scope of the present invention is not limited thereto.

Measurement of physical properties and performance evaluation of the biaxially stretched polyester film of the present invention was carried out as follows:

(1) Refractive index and birefringence: The refractive indexes in the longitudinal and transverse directions were measured using an Abbe refractometer, and the birefringence was measured as in Equation 1 below.

Birefringence = transverse refractive index-longitudinal refractive index

(2) Glass transition temperature: differential thermal analyzer (Perkin Elmer, DSC-7), measuring conditions: heating rate 20 ℃ / min

(3) Film strength, elongation and toughness (ASTM D882): measurement of breaking strength and elongation at break using UTM

The toughness (break energy) is the integral (kgf / mm ² ) inside the stress-strain curve in the tensile test.

Measurement condition: sample length 50mm, width 15mm, room temperature (23 ㅁ 2 ℃), tensile speed 200mm / min

(4) Elongation after tearing: longitudinal fracture elongation measurement using UTM after tearing (ASTM D882)

(5) film thickness deviation: using film thickness measurement device

50 points were measured at 5 cm intervals in the longitudinal and transverse directions, respectively, and calculated according to Equation 2.

Thickness deviation (%) of film = (Tmax-Tmin) / (Tave) × 100

Where Tmax = maximum thickness of film, Tmin = minimum thickness of film, Tave = average thickness of film

(6) Tearability: After tearing the specimen which had been teared down by 15 mm in the transverse direction (width) and 300 mm in the longitudinal direction (length), the film was slowly pulled by holding the gap of 10 mm in the middle by hand to observe the tearing state of the film. . If the film is cleanly cut, it is good. If the film is stretched and torn, the cut surface is not clean or cannot be cut by hand.

Example 1

180 mole parts of ethylene glycol were added to an autoglove equipped with a distillation machine with respect to 100 mole parts of dimethyl terephthalate, and manganese acetate was added in an amount of 0.05% by weight relative to dimethyl terephthalate as an ester exchange catalyst at 150 ° C. The reaction was carried out while removing the byproduct methanol while raising the temperature to ℃. After completion of the ester exchange reaction, 0.045% by weight of trimethylphosphate as a stabilizer was added to dimethyl terephthalate and 0.2% by weight of silicon dioxide having an average particle diameter of 2 μm as an antiblocking agent to dimethyl terephthalate. As an antimony trioxide, 0.03% by weight of the polyethylene terephthalate polymer having an ultimate viscosity of 0.57 dl / gr was polymerized for 5 minutes after being transferred to a second reactor equipped with a vacuum facility after 5 minutes. Temperature 78 ° C.). The polyester resin thus prepared was melt extruded at 280 ° C., and then adhered to a cooling roll cooled to 30 ° C. through a conventional T-die to obtain an amorphous sheet having a thickness of 70 μm. The amorphous sheet thus obtained was continuously stretched 1.3 times through a stretching roll in a temperature atmosphere of 80 ° C., transversely stretched 4.5 times in a tenter at 90 ° C., and then heat-set and heat-set at 130 ° C. for 2%. The relaxation process of was performed, and the biaxially stretched film of thickness 12micrometer was obtained.

The tearing treatment was performed by impregnating the film with methyl ethyl ketone (MEK) or toluene for 14 days, and then drying the film at 1 atmosphere and room temperature (23 ± 2 ° C.) for 1 day.

The refractive index, birefringence, elongation, toughness, and tearing elongation and physical properties of the polyester film prepared by the above method after the tearing treatment of the same film were measured by the above-described method. Same as 1. As shown in Table 1, it can be seen that the film subjected to the tearing exhibits good results suitable for easy-opening packaging for easy cutting.

Examples 2 to 3

A stretched film was obtained in the same manner as in Example 1 except that the thickness of the polyester amorphous sheet, the draw ratios of longitudinal stretch and lateral stretch, and the heat treatment temperature were adjusted. The properties of the obtained polyester film are as shown in Table 1, showing good results suitable for use as a double-sealing packaging for easy cutting.

Comparative Examples 1 to 4

A stretched film was obtained in the same manner as in Example 1 except that the thickness of the polyester amorphous sheet, the draw ratios of longitudinal stretch and lateral stretch, and the heat treatment temperature were adjusted. The properties of the obtained polyester film are as shown in Table 1, showing poor results which are not suitable for use as a double-sealing packaging for easy cutting.

The biaxially stretched polyester film of the present invention has excellent mechanical, chemical properties, environmental friendliness, and food hygiene inherent to polyester, and has excellent tensile properties, so that no break occurs during film forming or post-processing, and by tearing treatment. Tear resistance is greatly improved and useful for two open packaging.

Claims (5)

In a film prepared by biaxially stretching a polyester sheet having a glass transition temperature of 60 ° C. or more in the longitudinal direction and the transverse direction and then subjecting it to a tearing treatment, the film has a longitudinal elongation of 100% or more and a longitudinal direction before the tearing treatment. A ^bi- opening biaxially stretched polyester film, having a refractive index of 1.64 or less, a birefringence of 0.03 or more, and a longitudinal strength of 6 kgf / mm ² or more, and a longitudinal elongation of the film after tearing. The method of claim 1, A biaxially stretched polyester film having a thickness of 8 to 25 µm and a longitudinal toughness of at least 5 kgf / mm ² . The method of claim 1, A biaxially stretched polyester film, characterized in that the biaxial stretching is carried out so that the longitudinal stretching ratio is 1.2 to 2.5 times, and the lateral stretching ratio is 3.0 to 5.0 times. The method of claim 1, A biaxially stretched polyester film, characterized in that the heat transfer at the temperature of glass transition temperature (Tg) + 80 ℃ or less. The method of claim 1, Biaxially-stretched polyester film, characterized in that the surface treatment with an organic solvent during the tearing treatment.