HEAT-SHRINKABLE POLYESTER-BASED FILM

Abstract

The invention provides a heat-shrinkable polyester-based film, where the heat-shrinkage ratio in the width direction is high and the irregularity of thickness is small. The heat-shrinkable polyester-based film of the present invention contains 90 mol % or more of ethylene terephthalate unit based on 100 mol % of whole ester unit, wherein, the heat-shrinkable polyester-based film satisfies the requirements: (1) heat-shrinkage ratio in a width direction measured by shrinking the film for 10 seconds in 90° C. hot water is 50%-75%, (2) heat-shrinkage ratio in a longitudinal direction measured by shrinking the film for 10 seconds in 90° C. hot water is −6% or more and 14% or less, (3) heat-shrinkage ratio in the longitudinal direction measured by shrinking the film for 10 seconds in 70° C. hot water is -6% or more and 6% or less, and (4) irregularity of thickness in the width direction is 1%-20%.

Claims

1. A heat-shrinkable polyester-based film comprising ethylene terephthalate unit by 90 mol % or more out of whole ester unit 100 mol %, wherein, the heat-shrinkable polyester-based film satisfies the following requirements (1) to (4): (1) heat-shrinkage ratio in a width direction measured by shrinking the film for 10 seconds in 90° C. hot water is 50% or more and 75% or less, (2) heat-shrinkage ratio in a longitudinal direction measured by shrinking the film for 10 seconds in 90° C. hot water is −6% or more and 14% or less, (3) heat-shrinkage ratio in the longitudinal direction measured by shrinking the film for 10 seconds in 70° C. hot water is −6% or more and 6% or less, and (4) irregularity of thickness in the width direction is 1% or more and 20% or less.

2. The heat-shrinkable polyester-based film according to claim 1, further satisfying the following requirement (5): (5) maximum heat shrinkage stress in the width direction measured by shrinking the film for 30 seconds in 90° C. hot air is 4 MPa or more and 13 MPa or less.

3. The heat-shrinkable polyester-based film according to claim 2, further satisfying the following requirement (6): (6) degree of crystallinity calculated from density is 1% or more and 15% or less.

4. The heat-shrinkable polyester-based film according to claim 1, further satisfying the following requirement (6): (6) degree of crystallinity calculated from density is 1% or more and 15% or less.

Description

EXAMPLES

[0072] Next, the present invention will be specifically described with reference to Examples and Comparative examples, but the present invention is not limited to the aspects of the Examples at all, and can be appropriately modified within the scope not departing from the gist of the present invention.

[0073] The following properties were evaluated for each polyester film described in Table 2 below.

Heat-Shrinkage Ratio (Heat-Shrinkage Ratio in Hot Water)

[0074] A polyester-based film was cut out into a square of 10 cm×10 cm, and dipped in hot water with a predetermined temperature of [(90° C. or 70° C.)±0.5° C.] in a no-load state for 10 seconds to be heat-shrunk, followed by being dipped in water with a temperature of 25° C.-0.5° C. for 10 seconds, and then pulled out from the water. A dimension in the longitudinal direction and a dimension in the width direction of the film was measured, and a heat-shrinkage ratio was calculated according to the following Equation 1, respectively. The direction having a larger heat-shrinkage ratio was determined as the main shrinkage direction (width direction).

Heat-shrinkage ratio (%)={(length before shrinkage−length after shrinkage)/length before shrinkage)}×100   Equation 1

Irregularity of Thickness in the Width Direction

[0075] From the roll of the film, a wide belt-shaped film sample having a size in the longitudinal direction of the film of 40 mm× and a size in the width direction of the film of 1.2 m was sampled. Using a continuous contact type thickness gauge manufactured by Mikuron Measuring Instrument Co., Ltd., the thickness was continuously measured at a measuring speed of 5 m/min along the width direction of the film sample (measuring length was 1 m). The maximum thickness at a time of measuring was determined as Tmax., the minimum thickness was determined as Tmin., and the average thickness was determined as Tave.. According to the following Equation 2, the irregularity of thickness in the width direction of the film was calculated.

Irregularity of thickness (%)={(Tmax.−Tmin.)/Tave.}×100   Equation 2

Maximum Heat Shrinkage Stress

[0076] A sample having a length of 200 m in a main shrinkage direction (width direction) and a width of 20 mm (longitudinal direction) was cut out from a polyester-based film, and measured using a strength and elongation measuring machine with a heating furnace (TENSILON, registered trademark of ORIENTEC Co., LTD.). The heating furnace was previously heated to 90° C., and the distance between chucks was set to of 100 mm. The ventilation to the heating furnace was temporarily stopped, and the door of the heating furnace was opened. Thereafter, the sample was attached to chucks, and the doors of the heating furnace was quickly closed, followed by resuming the ventilation. The heat shrinkage stress in the width direction was measured by shrinking the film for 30 seconds in 90° C. hot air, and the maximum value thereof was determined as a maximum heat shrinkage stress (MPa).

Haze

[0077] According to JIS K 7136, measurement was performed using a haze meter “500A” (manufactured by Nippon Denshoku Industries Co., Ltd.). The measurement was performed twice, and the average value was calculated.

Degree of Crystallinity

[0078] According to Density gradient tube method in JIS K 7112, using an aqueous solution of calcium nitrate, the density d of the sample of about 3 mm square was measured, and the degree of crystallinity was calculated according to the following Equation 3.

Degree of crystallinity (%)={dc×(d.Math.da)/(d×(dc−da)}×100   Equation 3

dc: 1.455 g/cm.sup.3 (the density of the perfect crystal of polyethylene terephthalate)
da: 1.335 g/cm.sup.3 (the density of the perfect amorphous of polyethylene terephthalate)
d: the density of the sample (g/cm.sup.3)

Tg (Glass Transition Temperature)

[0079] Using a differential, scanning calorimeter manufactured by Seiko Instruments & Electronics Ltd. (Model: DSC220), according to JIS-K7121-1987, Tg was measured. Specifically, the unstretched film (10 mg) was heated from −40° C. to 120° C. at a heating speed of 10° C./min, and endothermic curve was measured. Tangent lines were drawn before and after the inflection point on the measured endothermic curve, and intersection was regarded as a glass transition temperature (Tg: ° C.).

Evaluations of the Shrinkage Finish Property

[0080] One end of the polyester-based film was attached to the other end, and welded by an impulse sealer (manufactured by Fujiimpulse Co., Ltd.) to obtain a cylindrical label with the width direction being in the circumferential direction. This label was put on a commercially available PET bottle (content is present; “Oi, Ocha” manufactured by Ito en, Ltd), and was heat-shrinked through a steam adjusted at 85° C. (tunnel passing time: 30 seconds). The shrinkage finish property of the label was evaluated by visual observation on five ranks according to the following criteria. The defects described below mean a jumping, a wrinkle, an insufficient shrinkage, a label edge fold, a shrinkage whitening and the like.

5: Finish property was best (no defects were observed)
4: Finish property was good (1 defect was observed)
3: 2 defects were observed
2: 3 to 5 defects were observed
1: Many defects (6 defects or more) were observed

Preparation of Polyester Raw Material

Preparation of Polyester Raw Material A

[0081] To a stainless steel autoclave equipped with a stirrer, a thermometer and a partially circulating cooler, dimethyl terephthalate (DMT) 100 mol % as a dicarboxylic acid component, and ethylene glycol (EG) 100 mol % as a polyol component were added in such a manner that the amount of ethylene glycol was 2.2 times the amount of dimethyl terephthalate in terms of a molar ratio. An ester exchange reaction was carried, out using zinc acetate 0.05 mol % (based on the add component) as an ester exchange catalyst and antimony trioxide 0.225 mol % (based on the add component) as polycondensation catalyst while generated methanol was distilled away to outside of the system. Thereafter, a polycondensation reaction was carried out at 280° C. under a reduced pressure of 26.7 Pa to obtain a polyester (A) having an intrinsic viscosity of 0.58 dl/g. This polyester is polyethylene terephthalate. The intrinsic viscosity (dl/g) was measured using Ostwald viscometer at 30° C. by dissolving polyester (0.2 g) in the mixed solvents of phenol/1,1,2,2-tetrachloroethane (60/40, weight ratio; 50 mL). This polyester raw material A is corresponding to polyethylene terephthalate. The composition of the monomer component for polyester raw material A is shown in Table 1. In Table 1, in the “acid component” column, the content of each monomer component in 106 mol % of whole add component is shown, and in the “polyol component” column, the content of each monomer component in 100 mol % of whole polyol component is shown.

Preparation of Polyester Raw Materials B to D

[0082] By the same method as the polyester raw material A, as shown in Table 1, polyester raw materials B to D with different monomer components were obtained. The polyester raw material B was produced by adding SiO.sub.2 (Sylysia 266 manufactured by Fuji Silysia Chemical Ltd.; average particle diameter 1.5 μm) as a lubricant with a ratio of 7,000 ppm to polyester. Each polyester raw material was chipped appropriately. In Table 1, TPA means terephthalic acid, BD means 1,4-butanediol. CHDM means 1,4-cydohexanedimethanol, and DEG means diethylene glycol which is a byproduct. The intrinsic viscosity of each polyester raw material was B: 0.58 dl/g, C: 0.80 dl/g, and D: 1.20 dl/g, respectively.

TABLE-US-00001 TABLE 1 Composition of polyester raw material (mol %) Added Polyester Acid Polyol amount of raw component component lubricant material TPA EG BD CHDM DEG (ppm) A 100 99 — — 1 — B 100 99 — — 1 7000 C 100 68 — 30 2 — D 100 — 100 — — —

[0083] Using the above polyester raw materials A to D, various polyester-based films described in Table 2 were obtained.

Example 1

[0084] Polyester A and Polyester B were mixed in a mass ratio of 95:5, and introduced into an extruder. This mixed resin was melted at 280° C., extruded from T-die, and wound around a rotating metallic roll cooled to a surface temperature of 30° C., so that the mixed resin was rapidly cooled, thereby obtaining an about 150 μm-thick unstretched film. Tg of the unstretched film was 75° C.

[0085] The obtained unstretched film was guided to a transverse stretching machine (tenter), and preheated at 140° C. for 5 seconds. The film after preheating was continuously introduced into the first half zone of the transverse stretching, and the film w as stretched in the transverse direction by 2.1 times at 105° C. Thereafter, in the second half zone of the transverse stretching, the film was stretched in the transverse stretching direction by 1.8 times at 82° C. The total transverse stretch ratio was 3.8 times. Finally, the heat treatment was performed in the heat treatment zone at 50° C. for 3 seconds, thereafter cooled, and both edges were cut and removed, followed by being wound up into a roll with a width of 500 mm. Thereby, a transverse stretched film with a thickness of 40 μm was continuously manufactured over a predetermined length, and the film of Example 1 was obtained.

Examples 2 to 6, Comparative Examples 1 to 3 and 5

[0086] In the same manner as Example 1 except that the condition of transverse stretching in Example 1 was changed as shown in Table 2, the films of Examples 2 to 6, Comparative Examples 1 to 3 and 5 were produced.

Comparative Example 4

[0087] Polyester raw material A, Polyester raw material B, Polyester raw material C, and Polyester raw material D were mixed in a mass ratio of 18:5:67:10, and introduced to the extruder. This mixed resin was melted at 280° C., extruded from T-die, and wound around a rotating metallic roll cooled to a surface temperature of 30° C., thereby obtaining an about 150 μm thick unstretched film. Tg of the unstretched film was 68 ° C.

[0088] Then, in the same manner as Example 1 except that the condition of transverse stretching in Example 1 was changed as shown in Table 2, the film of Comparative Example 4 was produced.

[0089] The characteristics of each film produced in those ways were evaluated by the above methods. These results are also shown in Table 2.

TABLE-US-00002 TABLE 2A Exam- Exam- Exam- Exam- Exam- Exam- ple 1 ple 2 ple 3 ple 4 ple 5 ple 6 Composition Polyester A 95 95 95 95 95 95 of raw Polyester B 5 5 5 5 5 5 material for Polyester C 0 0 0 0 0 0 film (mass %) Polyester D 0 0 0 0 0 0 Amount of ethylene glycol monomer (mol %) 99 99 99 99 99 99 Amount of terephthalic acid monomer (mol %) 100 100 100 100 100 100 Ratio of amorphous component (mol %) 1 1 1 1 1 1 Glass transition temperature Tg (° C.) 75 75 75 75 75 75 Transverse Preheating zone Temperature T1 (° C.) 140 130 130 130 130 130 stretching First stretching Temperature T2 (° C.) 105 110 90 100 100 90 Ratio 2.1 2.2 2.1 2. 2.2 1.9 Second stretching Temperature T3 (° C.) 82 82 82 81 70 82 Ratio 1.8 1.9 1.9 2.0 2.1 1.9 Total stretch ratio 3.8 4.2 4.0 4.0 4.6 3.6 (First stretching * Second stretching) Temperature 50 50 75 50 50 50 Thickness (μm) 40 40 40 40 40 40 Heat-shrinkage ratio in 70° C. hot water (%) Longitudinal direction −4.3 −2.0 5.1 2.4 2.8 5.4 Width direction 24.0 34.0 15.0 27.0 44.1 18.9 Heat-shrinkage ratio in 90° C. hot water (%) Longitudinal direction −4.1 −2.0 7.0 −0.3 −1.8 3.6 Width direction 63.4 64.0 51.0 67.2 72.1 60.9 Irregularity of thickness in the width direction (%) Width direction 17.3 18.9 17.9 19.1 15.9 11.0 Maximum heat shrinkage stress in 90° C. hot Width direction 4.5 6.4 7.8 9.3 11.6 8.4 air (MPa) Haze (%) 4.8 4.5 4.6 5.3 5.8 4.5 Density (g/cm.sup.3) 1.3413 1.3428 1.3484 1.3491 1.3441 1.3427 Degree of crystallinity (%) 5.7 7.0 12.0 12.7 8.2 7.0 Evaluation result of shrinkage finish property 5 5 4 5 5 4 indicates data missing or illegible when filed

TABLE-US-00003 TABLE 2B Compar- Compar- Compar- Compar- Compar- ative ative ative ative ative Example 1 Example 2 Example 3 Example 4 Example 5 Composition Polyester A 95 95 95 18 95 of raw Polyester B 5 5 5 5 5 material for Polyester C 0 0 0 67 0 film (mass %) Polyester D 0 0 0 10 0 Amount of ethylene glycol monomer (mol %) 99 99 99 68.7 99 Amount of terephthalic acid monomer (mol %) 100 100 100 100 100 Ratio of amorphous component (mol %) 1 1 1 21 1 Glass transition temperature Tg (° C.) 75 75 75 68 75 Transverse Preheating zone Temperature T1 (° C.) 90 130 80 80 130 stretching First stretching Temperature T2 (° C.) 85 70 80 80 95 Ratio 1.9 2.0 1.6 2.1 2.1 Second stretching Temperature T3 (° C.) 85 70 80 80 95 Ratio 1.9 1.8 1.5 2.1 1.8 Total stretch ratio 3.6 3.6 2.4 4.4 3.8 (First stretching * Second stretching Heat treatment Temperature 50 50 50 81 50 Thickness (μm) 40 40 40 40 40 Heat-shrinkage ratio in 70° C. hot water (%) Longitudinal direction 5.9 16.0 2.4 −0.3 1.2 Width direction 4.9 20.0 11.0 32.1 4.0 Heat-shrinkage ratio in 90° C. hot water (%) Longitudinal direction 13.5 5.0 3.8 4.5 10.8 Width direction 26.8 65.0 55.3 58.7 23.5 Irregularity of thickness in the width direction (%) Width direction 8.0 9.0 27.7 22.0 19.6 Maximum heat shrinkage stress in 90° C. hot air (MPa) Width direction 17.3 16.0 6.3 5.3 7.1 Haze (%) 5.6 5.2 4.1 6.0 5.9 Density (g/cm.sup.3) 1.3497 1.3486 1.3401 1.2959 1.3463 Degree of crystallinity (%) 13.2 12.2 4.6 — 10.2 Evaluation result of shrinkage finish property 1 2 4 5 1

[0090] Despite using polyethylene terephthalate having a very low ratio of the amorphous component of 1 mol %, in the heat-shrinkable films of Examples 1 to 6 which satisfy the requirements of the present invention, the heat-shrinkage ratio in the width direction was high, the irregularity of thickness in the width direction was reduced, the heat-shrinkage ratio in the longitudinal direction was also kept low, and the shrinkage finish property when covering as a label was also good (Evaluation 4 or 5).

[0091] In contrast, in Comparative Example 1, since the temperature T1 during preheating was low at 90° C., the heat-shrinkage ratio in the width direction at 90° C. was low at 26.8%, the shrinkage finish property of the label was extremely deteriorated (Evaluation 1).

[0092] In Comparative Example 2, while the temperature T1 during preheating was controlled to be high temperature stipulated in the present invention, since the temperature T2 during first transverse stretching was low at 70° C., which was the same temperature as the temperature T3 during second transverse stretching, the heat-shrinkage ratio in the longitudinal direction at 70° C. was high at 16.0%, the shrinkage finish property of the label was deteriorated (Evaluation 2).

[0093] In Comparative Example 3, the temperature T1 during preheating, the temperature T2 during first transverse stretching, and the temperature T3 during second transverse stretching were all 80° C., the total stretch ratio was also low at 2.4 times, therefore the irregularity of thickness in the width direction was high at 27.7%.

[0094] In Comparative Example 4, since the polyester film containing a lot of amorphous component is used, the irregularity of thickness in the width direction was extremely high at 22.0%. In Comparative Example 4, since the amorphous raw material other than polyethylene terephthalate was used, the calculation method of degree of crystallinity determined by the above Equation 3 could not be applied, thus “-” is used in the column in Table 2.

[0095] In Comparative Example 5, the temperature T1 during preheating and the temperature T2 during first transverse stretching were controlled to the range stipulated in the present invention, the temperature T3 during second transverse stretching was high at 95° C., and this is an example of controlling at T2=T3. As a result, the heat-shrinkage ratio in the width direction at 90° C. was low at 23.5%, the shrinkage finish property of the label was extremely deteriorated (Evaluation 1).

INDUSTRIAL APPLICABILITY

[0096] Since the heat-shrinkable polyester-based film of the present invention has the above-mentioned characteristics, it may be suitably used for labels for bottles or banding films used for banding lunch boxes or the like.