KR101305663B1 - Thermo-shrinkable polyester film - Google Patents

Abstract

The present invention relates to a heat-shrinkable polyester film, shrinkage by providing a heat-shrinkable polyester film having a rate of change in the shrinkage rate in the main shrinkage direction over time within 95 seconds at 95 ℃ 4.0 to 10.0% / sec By ensuring the uniformity of shrinkage in the process, the appearance quality is excellent, there is no occurrence of print distortion, and at the same time, there is an effect to reduce the production cost in the shrinkage process and improve productivity.

Description

Heat-shrinkable polyester film {Thermo-shrinkable polyester film}

The present invention relates to a polyester film having heat shrink properties.

Heat-shrinkable film is used for coating, binding, or exterior of various containers such as bottles and cans and long lengths such as pipes and rods, and is used for various packaging materials or labels, and is mainly heat-shrinkable polyester It is a film.

Heat-shrinkable films are used for the purpose of shrinkage (integral) packaging, shrinkage labels, cap seals, etc. for various containers such as PET containers, polyethylene containers, glass containers, etc., by using properties that shrink by heating.

In order to manufacture a label or the like, the raw polymer is usually melt-extruded continuously to produce an unstretched film. Then, it stretches and obtains a heat shrinkable film roll. The film is unwound from this roll while slit to the desired width and rewound onto the roll. Subsequently, text information or drawings such as various product names are printed. After the end of printing, the tubes are manufactured by overlapping the left and right ends of the film with each other by means of solvent bonding or the like (tubing process). At this time, the slit process and the printing process may be reversed in order. The obtained tube is again wound onto a roll, and then unwound in a later step to cut the tube to an appropriate length, thereby forming a label. If one opening of the label is joined, a bag can be produced.

Put the label or bag obtained in this way on the container, and the inside of the shrink tunnel (steam tunnel) of the type which spouts steam and heat shrinks, or the shrink tunnel (hot wind tunnel) of the type which spouts hot air and heat shrinks, By passing through and heat shrinking a label, a bag, or the like, the final product, that is, a labeling container can be obtained by being in close contact with the container.

After a shrinkage process such as a shrinking tunnel or a hot-air tunnel, the label should shrink evenly and adhere to the container. Otherwise, a twisted or crushed shape may occur.

This phenomenon is a result of not uniform contraction for a certain time under a given temperature, such a difference in the degree of shrinkage, that is, non-uniformity of shrinkage causes a poor appearance of the label and, if the degree is severe, printing distortion and the like.

In addition, as shrinkage nonuniformity occurs, the shrinkage process is delayed, which inevitably leads to a decrease in productivity.

The present invention provides a heat shrinkable polyester film that can provide a uniform shrinkage rate over time under a certain temperature.

The present invention provides a heat-shrinkable polyester film that can ensure the printing uniformity after shrinkage process to ensure the shrinkage uniformity and improve the productivity.

In one embodiment of the present invention, when measured by a heat shrinkage stress tester for measuring the thermal shrinkage and thermal stress (Thermal shrinkage-force) in a certain length direction, in the main shrinkage direction over time within 95 seconds at 95 ℃ It provides a heat shrinkable polyester film having a shrinkage rate of change of 4.0 to 10.0% / sec.

In addition, according to the embodiment of the present invention, the heat-shrinkable polyester film, the shrinkage stress in the main shrinkage direction at 95 ° C may be 0.6 to 1.3 kg / mm 2.

According to an exemplary embodiment of the present invention, the heat-shrinkable polyester film is terephthalic acid, oxalic acid, malonic acid, succinic acid, adipic acid, suberic acid, azelaic acid, sebacic acid, phthalic acid, isophthalic acid, naphthalenedicarboxylic acid And dicarboxylic acid components containing at least one dicarboxylic acid such as diphenyl ether dicarboxylic acid, ethylene glycol, neopentyl glycol, propylene glycol, trimethylene glycol, tetramethylene glycol, hexamethylene glycol, diethylene At least one copolyester selected from copolyesters obtained from a diol component comprising at least one diol such as glycol, polyalkylene glycol, 1,4-cyclohexane dimethanol; Or a mixture of homopolyester and copolyester.

In this case, the copolyester may include 80 mol% or more of terephthalic acid units in the dicarboxylic acid units, and 14 to 24 mol% of units other than ethylene glycol in the diol units.

In this case, the homo polyester may be polybutylene terephthalate or polytriethylene terephthalate.

In addition, the copolyester may be one containing 85 to 93% by weight of the total polyester resin.

According to an embodiment of the present invention, the heat-shrinkable polyester film of the present invention includes a process of extruding a polyester, preheating, stretching in the width direction, and then performing heat treatment, but setting the heat treatment section temperature to be lower than the preheat section temperature. It may be prepared by the manufacturing method.

At this time, the preheating section temperature is 80 to 100 ℃, the heat treatment section temperature may be a room temperature to 95 ℃.

According to a preferred embodiment of the present invention, the heat-shrinkable polyester-based film further includes, after extruding the polyester, additionally stretching in the mechanical direction by a ratio of 0.1 to 5% of the natural draw ratio naturally occurring in the process in the mechanical direction. It may be prepared by.

In another embodiment of the present invention is a method of producing a heat-shrinkable polyester film by extruding and stretching the polyester as the following steps: extruding the polyester at 200 ~ 350 ℃; Preheating the extruded sheet; Stretching; And a heat treatment step, wherein the temperature of the heat treatment section is set to be lower than the temperature of the preheat section, and when measured by a heat shrink stress test apparatus for measuring thermal shrinkage and thermal stress in a predetermined length direction. It provides a method for producing a heat-shrinkable polyester film, characterized in that the rate of change in shrinkage in the main shrinkage direction over time at 95 ° C within 5 seconds is 4.0 to 10.0% / sec.

Preferably, the preheating section temperature is 80 to 100 ℃, the heat treatment section temperature may be a room temperature to 95 ℃.

In the preferred manufacturing method according to the invention, after the step of extruding the polyester, it may further comprise the step of additionally stretching in the mechanical direction by 0.1 to 5% ratio than the natural draw ratio naturally occurring in the process in the mechanical direction.

The present invention can reduce the occurrence of shrinkage unevenness during the shrinking process by causing even shrinkage within a short time due to the rapid shrinkage rate change over time under a certain temperature, lowering the label appearance defect rate, there is no occurrence of print distortion, etc. This has the effect of improving productivity.

1 is a graph (change in shrinkage with time) as a result of analyzing a heat-shrinkable polyester film obtained according to Example 1 by Testrite MKV Shrinkage-Force Tester (Testrite Ltd).
FIG. 2 is an example of a graph of a heat-shrinkable polyester film analyzed by a thermomechanical analyzer.

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

Shrink film achieves maximal uniaxial orientation through low temperature uniaxial stretching, and eliminates the residual stress relief through heat treatment, so that uniaxially oriented molecular chains retain their residual stress. It is manufactured on the principle of contraction by force.

The final shrinkage process is carried out in the shrinking tunnel through the hot air or steam and the shrinking process is performed for a certain time in the shrinking tunnel. At this time, the shrinkage of the label may become nonuniform with time, and such shrinkage nonuniformity may result in poor label appearance and print distortion.

According to one embodiment of the present invention, the heat-shrinkable polyester film of the present invention at 95 ℃ when measured by a heat shrinkage stress tester for measuring thermal shrinkage and thermal stress (Thermal shrinkage-force) in a certain length direction It is a heat-shrinkable polyester film having a rate of change in shrinkage rate in the main shrinkage direction of 4.0 to 10.0% / sec over 5 seconds.

An example of the thermal shrinkage stress tester is the Testrite MKV Shrinkage-Force Tester.

By the way, Testerite MKV Shrinkage-Force Tester is usually for testing thermal stresses of yarns and cords, and shrinkage rate of yarns and cords is insignificant compared to the shrinkage rate required for shrink films. It is not applicable to the test equipment.

In this regard, in order to evaluate the shrinkage rate over time using a heat shrinkage stress tester, the maximum shrinkage measurement range (35.8%) is first determined to obtain a measurable length change range. When the maximum shrinkage measurement range is confirmed, the maximum allowable sample length is set so that the maximum measurable sample length and length change range can be calculated from this. Determine the maximum shrinkable length of the measurement sample and determine the length of the sample arbitrarily within the measurable range on the instrument. In order to keep the selected sample of a certain length flat in the measuring device, give a certain load and measure the shrinkage with time at a certain temperature. In this case, since the measuring device calculates the shrinkage rate based on the sample length set on the device, the measured shrinkage rate is converted into the length strain value again to obtain the length strain value according to time, and the measurement is made by dividing this by the length of the actual measurement sample. The length strain of a sample can be calculated | required. From these, the rate of change of the shrinkage rate over time can be calculated.

* The meaning of the rate of change of shrinkage rate over time under a certain temperature is related to the shrinkage uniformity and production rate with respect to temperature, the heat-shrinkable polyester film according to a preferred embodiment of the present invention Rate of shrinkage in the main shrinkage direction over time at a constant temperature is 4.0 to 10.0% / sec. In particular, considering the residence time in the actual shrinkage process, the rate of change in the shrinkage rate in the main shrinkage direction over time within 5 seconds is 4.0 to 10.0% / sec.

If the rate of shrinkage change with time under a certain temperature is less than 4.0% / sec, a long time heat treatment is required to obtain the required shrinkage characteristics, or a high temperature heat treatment is required, resulting in a decrease in production rate or an increase in process cost. At the same time, the physical property of the label is reduced, and when it is greater than 10.0% / sec, stress may be concentrated in the container due to instant shrinkage, which may cause the container to be distorted.

In addition, the heat-shrinkable polyester film according to the present invention may have a shrinkage stress in the main shrinkage direction of 0.6 to 1.3 kg / mm 2 as measured by the apparatus described above. It is possible to derive the force that the label adheres to the container from the value of the shrinkage stress, and having this range of shrinkage stress values may be advantageous in terms of container adhesion and maintaining a stable form of the label in the container.

According to the present invention, such a test is performed under a temperature of 95 ° C. in consideration of a temperature range in which the shrinkage label is processed and a range in which no melting by heat occurs.

The heat-shrinkable polyester film that satisfies these properties is terephthalic acid, oxalic acid, malonic acid, succinic acid, adipic acid, suveric acid, azelaic acid, sebacic acid, phthalic acid, isophthalic acid, naphthalenedicarboxylic acid, diphenyl ether dica A dicarboxylic acid component containing at least one known dicarboxylic acid such as carboxylic acid, ethylene glycol, neopentyl glycol, propylene glycol, trimethylene glycol, tetramethylene glycol, hexamethylene glycol, diethylene glycol, At least one copolyester selected from copolyesters obtained from a diol component comprising at least one known diol such as polyalkylene glycol, 1,4-cyclohexane dimethanol and the like; Or from mixtures of homopolyesters and copolyesters.

In this case, the copolyester may be a copolyester in which terephthalic acid units constitute 80 mol% or more of dicarboxylic acid units, and 14 to 24 mol% of units other than ethylene glycol units in the diol units. Units other than ethylene glycol units in the copolyesters have a function of inhibiting crystallization to increase the shrinkage rate, and it may be advantageous in terms of film processability and physical properties that the ratio of the units is within the above range.

In this invention, the said copolyester itself can be manufactured by the manufacturing method of polyester generally performed. For example, the direct esterification method which reacts diol directly with dicarboxylic acid, the transesterification method which makes diol act on the dimethyl ester of dicarboxylic acid, etc. are mentioned.

According to an embodiment of the present invention, the glass transition temperature of the copolyester is 67 to 77 ° C, and the intrinsic viscosity is 0.60 to 0.70 dl / g. At this time, the glass transition temperature may be adjusted according to the composition of the monomer used to prepare the polymer, the intrinsic viscosity may vary depending on the degree of polymerization, in the present invention, the glass transition temperature and intrinsic viscosity within the above range through such adjustment Copolyesters can be used.

Copolyester may be used alone, may be used in combination, or may be used as a mixture with a homopolyester resin, in the case of a mixture with the homopolyester resin may be 85 to 93% by weight. .

On the other hand, in the case of a mixture of two or more kinds of polyesters, that is, polyester resins, at least 80 mol% of the total dicarboxylic acid units of the polyester resin mixture is terephthalic acid, and 14 to 24 mol% of the total diol units of the polyester mixture. The thing which is a unit other than an ethylene glycol unit can be used.

As an example, in the present invention, a polybutylene terephthalate resin is included as a homopolyester, and a film can be produced using a mixture of such polybutylene terephthalate resin and copolyester. As the homopolyester, polytriethylene terephthalate may be used in place of or mixed with polybutylene terephthalate.

At this time, the content of the homopolyester including the polybutylene terephthalate may be 7 to 15% by weight of the total polyester resin.

In general, when the shrinkage film is used in commercial use, the adhesive film is adopted by dissolving the shrink film in a solvent. If the content of polybutylene terephthalate is too low, the adhesive strength of the solvent may be low, and thus commercial use may be difficult. On the other hand, if the content is too high, the shrinkage in the main contraction direction (for example, the width direction (TD)) may be lowered, and the mechanical properties of the direction perpendicular to the main contraction direction (for example, the mechanical direction (MD)) A decrease in (strength) may occur. In general, the film undergoes many roll processes in commercial use, and mechanical properties of the mechanical direction are required. If the mechanical properties are bad, breakage or breakage of the film may occur.

In addition, in order to improve the slipperiness in the film production, lubricants such as silicon dioxide, titanium dioxide, silica powder, calcium carbonate may be added, and various additives such as antistatic agent, anti-aging agent, UV-protective agent, and dye may be added if necessary. It can also be added.

The polyester heat-shrink film of the present invention having the above characteristics can be produced by, for example, the following manufacturing process.

The material for producing a polyester film is dried using a conventional dryer and then extruded at 200 to 350 ° C. Any known method such as T-die extrusion or tubular extrusion may be used for the extrusion.

The extruded product is rapidly cooled, for example by a method such as electrostatic contact, to obtain an unstretched film.

The unstretched film is subjected to a roller or the like that is naturally advanced in the mechanical direction, and then preheated, stretched in the width direction, and then heat treated.

In this case, when the temperature of the heat treatment section is lower than the temperature of the preheating section, it may be advantageous in increasing the residual stress on the shrink film to increase the shrinkage rate and shrinkage rate.

As a preferred example, the temperature of the preheating section is 80 to 100 ℃, the temperature of the heat treatment section may be adjusted in the room temperature to 95 ℃ range.

On the other hand, in addition to the draw ratio generated by the natural progression in the mechanical direction prior to preheating in addition to the stretching in the mechanical direction in addition to 0.1 to 5% draw ratio can improve the physical properties of the mechanical direction of the film, which is shrink uniformity It is also advantageous from the side.

The stretching in the width direction may be performed to be 3.0 to 5.0 times the original length.

In addition, when the draw ratio of the shrink film is small, the shrinkage rate may be reduced. On the other hand, when the draw ratio is too high, it is difficult to cause breakage or improvement of physical properties, and thus the draw ratio is about 3.0 times the original length. It can be selected within the range of about 5.0 times.

As the stretching method, a conventional apparatus is used, and known methods such as roll stretching, tenter stretching, tubular stretching, and the like can be applied.

Hereinafter, the embodiments of the present invention will be described in more detail, but the scope of the present invention is not limited to these examples.

The evaluation method used in the present invention is as follows.

(1) Shrinkage rate change rate with a certain time under a certain temperature

Testrite MKV Shrinkage-Force Tester (manufactured by Testrite Ltd., maximum shrinkage measuring range 35.8%, reference sample length 250mm) is used to evaluate shrinkage, but the instrument is intended for the evaluation of shrinkage of yarn or cord. In order to evaluate the heat shrinkage rate of the shrink film, it is necessary to prepare the specimen as described below, and to correct or convert the result.

Specifically, it is as follows.

-Fabrication of specimen: length (main contraction direction) 120mm, width 15mm

-Fixation of specimens: Samples in which the shrinkage caused by heat is produced by binding 10 mm of each end in the longitudinal direction of the specimens to a film which does not generate heat deformation at the corresponding measurement temperature, that is, the lengths of the samples according to Examples and Comparative Examples to be 100mm, and at the end of the coupling to the film deformation is not caused by heat to one flat of the sample gives an initial load 20g / mm ^2, is mounted in the measuring device is positioned in the forward central portion of the measuring device.

At this time, the length of the sample that caused the shrinkage due to heat was selected as 100 mm, and the result of confirming the measurement range of the maximum shrinkage rate of the test equipment was 35.8%, and the measurable length strain value of the corresponding device was 89.5mm. It was because the shrinkage rate could be measured most stably as a result of calculating the maximum length of the sample.

The maximum length of the sample may vary depending on the shrinkage rate. The maximum sample length according to the shrinkage rate is calculated as follows.

For example, in the case of a film having a shrinkage rate of 70% under the above measurement conditions, the maximum sample length is 127.9 mm (89.5 mm / 0.7), and when the shrinkage rate is 80%, 111.9 mm (89.5 mm / 0.8).

Therefore, from the calculation based on the measurable length strain value derived from the above maximum shrinkage at the reference sample length of 250 mm, it is most stably that the length of the sample capable of measuring the shrinkage for high shrinkage of 70% or more is 100 mm. Since the measurement can be performed, the length of the measurement sample was set to 100 mm.

-Method of measurement: Measure shrinkage with time under the condition of 95 ℃ under the condition of measuring device.

-Correction of the result value: Obtain the length deformation value of the measured sample measured on the basis of the sample length (250mm) set in the measuring device, and convert it to the value based on the length of the measured sample.

E.g.) If the length strain of the sample to be measured is 10%,

Actual length deformation of the sample = 250 mm × 0.1 = 25 mm

Length strain of measured sample = 25mm / 100mm × 100 = 25%

The length strain of the measurement sample thus obtained was defined as the shrinkage rate.

-Interpretation of results: The shrinkage of the measurement sample begins in calculating the shrinkage rate with time to prevent confusion in the analysis of shrinkage behavior that may be caused by binding to a film that does not generate heat deformation for the production of the measurement sample. The time immediately before the starting point was "0" seconds, and the shrinkage rate from this point to 5 seconds was converted from the value of the measuring device, and the rate of change of the shrinkage rate was calculated by the following equation.

<Equation 1>

Rate of shrinkage change (% / sec) = value of shrinkage change / elapsed time

(2) shrinkage stress

Using the Testrite MKV Shrinkage-Force Tester (Testrite Ltd), the shrinkage stress in the main shrinkage direction was measured over time at a temperature of 95 ° C., and the shrinkage stress value was obtained by dividing the cross section by the following equation (2).

At this time, the width of the sample was 15mm, and the initial load was 20g / mm ² to fix the sample flat.

<Equation 2>

Shrinkage stress = measured shrinkage stress (Kg) / cross-sectional area of sample (width × thickness; mm ² )

Ex) Shrinkage stress measurement value: 10N (1.02Kg = 10 / 9.8 Kg)

Sample cross section: 0.75 mm ² (for sample width 15 mm and thickness 50 μm)

Shrinkage Stress (Kg / mm2) = 1.02 / 0.75 = 1.36

(3) heat shrinkage

 After cutting the film in a forward direction of 20 cm × 20 cm, heat shrinking for 10 seconds under no load in 95 ° C ± 0.5 ° C of hot water, and then measuring the numerical value in the width direction (TD) of the film, It was.

<Formula 3>

(4) Shrinkage Uniformity Evaluation

The label printed on the shrink film and the label made by gluing the end with the solvent was put on the container and passed through the steam-type shrink tunnel, and the label appearance defect of the final product (labeled container) and the number of defects due to print distortion By evaluating the shrinkage uniformity.

At this time, the length of the steam tunnel was 1.5m, and the steam was installed at the top and bottom of two 1.2m long injection pipes so that the label of the container passed inside could be shrunk. . The steam temperature is equipped with a temperature controller and a heater to control the temperature of the tunnel inlet and the outlet, respectively.The inlet temperature is set to 77 ℃ and the outlet temperature is set to 86 ℃. The shrinkage uniformity was measured by measuring the number of defects in appearance and print distortion in the final product (labeled container) by shrinking the label with a residence time of 5 seconds.

Based on 1000 evaluation samples, the ratio of the normal product was defined as shrink uniformity, and this was calculated by the following Equation 4.

<Equation 4>

(5) intrinsic viscosity

200 mg of the specimen was added to 20 ml of a mixed solvent of phenol and tetrachloroethane 50/50, and the mixture was heated at about 110 ° C. for 1 hour and then measured at 30 ° C.

(6) Glass transition temperature by DMTA-method

Hold the sample at an initial load of 2.5N for a sample with a width of 10mm and a length of 30mm (main contraction direction), and raise the temperature by setting the static force, which is the force holding the sample, to 2.5N to prevent deformation of the sample due to flow. Storage modulus using a dynamic mechanical thermal analyzer (EPLEXOR 500, Gabo) with a measurement frequency of 10 Hz and a dynamic force of 2.5% in the temperature range of 0 to 150 ° C. , E ') and loss modulus (E "), and the loss tangent (Loss tangent, tanδ) according to Equation 5 below, wherein the temperature corresponding to the maximum tanδ value is converted into the dynamic glass transition temperature (Tg). This was obtained.

<Equation 5>

Loss tangent (tanδ) = Loss Modulus (E ") / Storage Modulus (E ')

(7) Shrink start temperature, maximum shrinkage expression temperature, maximum shrinkage stress

Using a thermal stress tester (KE-2, Kanebo Eng.), The film specimen having a width of 4 mm (MD direction) and a length of 50 mm (TD direction) was fixed at an initial load of 0.125 kg / mm2, followed by a temperature increase rate of 2.5 The graph was obtained by measuring the shrinkage stress according to the temperature while raising the temperature to ℃ / sec.

In this graph, the temperature at which the shrinkage stress value equal to the initial load of 0.125kg / mm2 is first shown is the shrinkage start temperature (Ts), and the temperature at the point where the maximum shrinkage stress value is first appeared is the maximum shrinkage expression temperature (T). _(Smax)), and it was defined as a stress value at this time, the maximum shrinkage stress (S _max).

(8) Shrinkage speed, shrinkage strain rate, maximum shrinkage strain temperature

Using a thermomechanical analyzer (model Diamond TMA, manufacturer Perkin Elmer), prepare a film specimen in the dimensions of 4mm in width (MD direction) and 15mm in length (TD direction) to give a load of 2mN / μm to the specimen. , The strain rate in the transverse direction (TD) according to the temperature change in the temperature range 30 to 90 ℃ at a temperature increase rate of 10 ℃ / min, and the main shrinkage according to the temperature in the temperature range 70 to 85 ℃ The rate of change of the length of the transverse direction (TD) was calculated to determine the shrinkage speed.

For example, the length variation in the main contraction direction according to temperature by the thermomechanical analyzer is represented by a graph as shown in FIG. 2, that is, a graph of a probe position according to temperature.

This can be calculated using Equation 6 below to calculate the shrinkage at each temperature.

&Lt; EMI ID =

Shrinkage Ratio = {1-((First Length + Probe Position) / First Length)} × 100

For example, when the probe position is -5.0 mm from the graph of FIG. 2, the shrinkage ratio is calculated to be {1-((15mm + (-5mm)) / 15mm)} × 100 = 33.3%. Here, 15 mm is the length in the main contraction direction of the specimen.

On the other hand, the temperature range was set to 30 to 90 ° C., and the strain in the transverse direction (TD) was measured according to the temperature change, and then the derivative was deduced to derive the shrinkage strain rate, and the maximum value was defined as the shrinkage strain rate. .

* In addition, the maximum shrinkage strain temperature was measured by measuring the temperature of the section in which the maximum shrinkage strain rate appeared in the shrinkage strain rate graph.

(9) Confirmation of shrinkage process characteristics through container manufacturing

The label printed on the shrink film and the label made by gluing the end with the solvent was put on the container and passed through the steam-type shrink tunnel, and the label appearance defect of the final product (labeled container) and the number of defects due to print distortion Was evaluated.

At this time, the length of the steam tunnel was 1.5m, and the steam was installed at the top and bottom of two 1.2m long injection pipes so that the label of the container passed inside could be shrunk. . The steam temperature is equipped with a temperature controller and a heater to control the temperature of the tunnel inlet and the outlet respectively.

The tunnel inlet temperature is set to 80 ℃ and the outlet temperature is set to 90 ℃, and the label is shrunk with the residence time of the labeled container in the tunnel as 5 seconds, resulting in defects in appearance and print distortion in the final product (labeled container). By measuring the high temperature shrinkage uniformity (yield A).

In addition, the tunnel inlet temperature is set at 75 ° C and the outlet temperature is 84 ° C, and the label is shrunk with the residence time of the container with the label inside the tunnel as 4 seconds, resulting in poor appearance and print distortion in the final product (labeled container). The number of occurrence was measured to measure the low temperature shrinkage uniformity (yield B).

The shrinkage uniformity is defined as the shrinkage uniformity of the ratio of the normal product based on 1000 evaluation samples, it was obtained by the following equation 7.

Equation (7)

Relative process efficiency (R) = (Yield B / Yield A) × 100 (%)

&Lt; Example 1 >

Polycondensation was carried out by direct esterification using 100 mol% of terephthalic acid as a dibasic acid component, 100 mol% of ethylene glycol and 24 mol% of neopentyl glycol as glycol components, and 0.05 mol of antimony trioxide (relative to acid components) as a catalyst. Combined. The polymer thus obtained contained 500 ppm of silicon dioxide powder having an average particle diameter of 2.7 µm and dried by a conventional method to prepare a copolyester having an intrinsic viscosity of 0.67 dl / g and a glass transition temperature of 76 ° C.

On the other hand, by using 100 mol% of terephthalic acid and 100 mol% of 1,4-butanediol, 0.015 parts by weight of tetrabutyl titanate was added as a catalyst to obtain a polybutylene terephthalate resin. (Intrinsic viscosity 0.97㎗ / g, glass transition temperature 30 ℃)

91 wt% of copolyester and 9 wt% of polybutylene terephthalate were blended and extruded from an extruder at 280 ° C., followed by rapid cooling and solidification to obtain an unstretched film.

The unstretched film was transferred through a roller which is conveyed in a mechanical direction, passed through a preheating section having a temperature of 87 ° C., stretched at 4.0 times the width at 84 ° C., and then subjected to a heat treatment section having a room temperature to 60 ° C. . The obtained film is a heat shrink film having a thickness of 50 µm, and the physical property values of the film are shown in Table 1.

<Example 2>

An unstretched film obtained in the same manner as in Example 1 was used.

The non-stretched film was further stretched in the mechanical direction by 0.4% magnification in addition to the naturally occurring draw ratio in conveying the roller through the conveying roller in the mechanical direction, thereby obtaining a heat-shrinkable polyester film in the same manner as in Example 1. . The obtained film is a heat shrink film having a thickness of 50 µm, and the physical property values of the film are shown in Table 1.

<Example 3>

An unstretched film obtained in the same manner as in Example 1 was used.

Thereafter, the temperature was set to 95 ° C. in the preheating section, the film was stretched at 4.0 times the width at 87 ° C., and then the temperature of the heat treatment section was set to 85 ° C., in the same manner as in Example 1 above. A heat shrinkable polyester film was obtained. The obtained film is a heat shrink film having a thickness of 50 µm, and the physical property values of the film are shown in Table 1.

<Example 4>

In the same manner as in Example 3, a heat-shrinkable polyester film was prepared, except that the extruded unstretched film was subjected to a stretching roll having a naturally occurring draw ratio of 3% in the mechanical direction (natural draw ratio + 3% ) In the mechanical direction at the draw ratio.

The obtained film is a heat shrink film having a thickness of 50 µm, and the physical property values of the film are shown in Table 1.

Reference Examples 1 and 2

Heat-shrinkable polyester films were obtained in the same manner as in Example 2 and Example 4, except that the draw ratio in the mechanical direction was adjusted to (natural draw ratio + 7%).

<Comparative Examples 1 and 2>

A heat-shrinkable film was prepared in the same manner as in Examples 1 to 2, except that the preheating temperature was 90 ° C and the heat treatment section temperature was 96 ° C.

Intrinsic viscosity
(㎗ / g) Dynamic Tg
(℃) Contraction ratio
(%) Analysis by heat shrink stress tester Shrinkage Process Characteristics Contraction speed
(ΔL / ΔT) Shrinkage
speed
(dL / dT) maximum
Shrink
transform
Temperature
(℃) Shrink
Uniformity
(%) Shrinkage rate
(% / sec) Shrinkage stress
(kg / ㎡) MD TD Ts
(℃) T
(S _max )
(℃) S _max (kg / ㎡) Yield A (%) Yield B (%) Relative Process Efficiency (R%) Example 1 0.609 94.3 2.4 74.5 80.2 93.0 1.29 99.8 99.7 99.9 3.0 7.7 80.8 99.7 9.1 1.21 Example 2 0.688 94.7 2.7 74.0 79.4 92.4 1.26 99.8 99.8 100 3.2 7.9 80.5 99.9 8.7 1.07 Example 3 0.672 93.3 3.2 63.5 86.1 95.6 1.01 99.7 99.5 99.8 1.2 4.7 85.7 98.7 5.9 0.87 Example 4 0.671 95.3 4.8 61.4 86.7 96.1 0.99 99.7 98.5 98.8 1.0 4.5 86.4 98.5 4.7 0.73 Reference
Example 1 0.687 98.5 8.0 69.5 83.3 96.2 0.98 87.5 72.5 82.9 2.0 6.0 82.6 75.3 7.5 1.05 Reference
Example 2 0.673 97.4 7.7 60.2 87.8 98.7 0.89 86.7 71.2 82.1 0.7 4.2 87.4 65.2 4.1 0.61 Comparative Example 1 0.653 89.0 1.8 51.5 92.7 100.7 0.64 99.6 51.4 51.6 0.3 3.4 90.0 53.2 3.8 0.59 Comparative Example 2 0.652 89.7 1.9 50.4 93.3 102.1 0.63 99.7 52.1 52.3 0.2 3.1 90.0 50.8 3.5 0.50

As a result of measuring the physical properties, it can be seen that the shrinkage uniformity of the shrinkage rate in the main shrinkage direction in a predetermined time under a predetermined temperature is 4.0 to 10.0% / sec.

In addition, it can be seen that when the shrinkage stress in the main shrinkage direction is 0.6 to 1.3kg / mm 2, the shrinkage uniformity is excellent.

On the other hand, Figure 1 shows a graph of the change in shrinkage with time of the heat-shrinkable polyester film obtained in Example 1.

Claims (4)

(a) extruding the polyester at 200 to 350 ° C; (b) drawing in the mechanical direction by a ratio of 0.1 to 5% of the natural draw ratio naturally occurring in the process in the mechanical direction; (c) preheating the extruded sheet at 80 to 100 ° C; (d) stretching in the width direction from 3.0 to 5.0 times; And (e) comprising the step of heat treatment at room temperature to 95 ℃, is prepared by the method of manufacturing a heat-shrinkable polyester film, characterized in that the temperature of the heat treatment section is set to be lower than the temperature of the preheating section,
When measured by a heat shrinkage stress tester for measuring thermal shrinkage and thermal stress in a constant length direction, the rate of change in the shrinkage rate in the main shrinkage direction over time within 95 to 5 seconds is 4.0 to 10.0%. / sec, the shrinkage uniformity calculated by the following formula 1 is 95% or more,
At least one dicarboxylic acid such as terephthalic acid, oxalic acid, malonic acid, succinic acid, adipic acid, suberic acid, azelaic acid, sebacic acid, phthalic acid, isophthalic acid, naphthalenedicarboxylic acid, diphenyl ether dicarboxylic acid Dicarboxylic acid component to contain, such as ethylene glycol, neopentyl glycol, propylene glycol, trimethylene glycol, tetramethylene glycol, hexamethylene glycol, diethylene glycol, polyalkylene glycol, 1,4-cyclohexane dimethanol At least one copolyester selected from copolyesters obtained from a diol component comprising at least one diol; Or a mixture of homopolyester and copolyester,
The copolyester is a heat-shrinkable polyester film containing at least 80 mol% of terephthalic acid units in dicarboxylic acid units and 14 to 24 mol% of units other than ethylene glycol in diol units.
[Formula 1]

The heat-shrinkable polyester film according to claim 1, wherein the shrinkage stress in the main shrinkage direction at 95 ° C is 0.6 to 1.3 kg / mm 2. The heat-shrinkable polyester film of claim 1, wherein the homo polyester is polybutylene terephthalate or polytriethylene terephthalate. The heat-shrinkable polyester film of claim 1, wherein the copolyester is contained in an amount of 85 to 93% by weight based on the total polyester resin.

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