JP2003321562A - Heat shrinkable polyester-based film and label - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a heat shrinkable polyester-based film used for labels of bottles, especially a label having paper-like appearance on the surface, especially Japanese paper-like appearance having remarkably little wrinkles, shrinking irregularity and formation of strain. <P>SOLUTION: The heat shrinkable polyester-based film has ≥3 μm difference in thickness per 1 cm length between a main shrinking direction and the crossing direction, contains voids inside of the film and has <5 μm void size in at least one side surface layer in the thickness direction and ≥5 μm void size in the central part in the thickness direction. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polyester film, and more particularly to a polyester film having a Japanese paper-like appearance suitable for label applications. More specifically, the present invention relates to a heat-shrinkable polyester film that has the appearance of Japanese paper and has very few wrinkles, shrinkage spots, and distortions due to heat shrinkage.

[0002]

2. Description of the Related Art As a heat-shrinkable film, particularly a heat-shrinkable film for a label on the body of a bottle, a film made of polyvinyl chloride, polystyrene or the like is mainly used. However, regarding polyvinyl chloride, in recent years
Generation of chlorine-based gas when incinerated at the time of disposal poses a problem, and polystyrene has problems such as difficulty in printing due to insufficient solvent resistance. Furthermore, when collecting and recycling PET bottles, labels of resins other than PET, such as polyvinyl chloride and polyethylene, must be separated from PET bottles. For this reason, polyester-based heat-shrinkable films that do not have these problems have been attracting attention.

[0003] In particular, when it is used as a label for PET bottles, it is required to have a new function, and one of them is to have a Japanese paper-like appearance.

Therefore, a special coating such as coating with cellulose fiber is considered, but there are problems that uniform coating is not easy and the durability of the coating film is poor.

[0005] Further, there is also a film in which an incompatible resin or inorganic particles are blended to contain voids. However, merely containing voids increases the hiding property of the film, but the film surface is relatively smooth. However, there is a problem that a Japanese paper-like appearance cannot be obtained. For example, Japanese Patent Laid-Open No. 2-161
No. 30 gazette contains 3 to 40% by weight of crystalline polypropylene.
Although a fine bubble-containing polyester film containing is disclosed, this is used for a base material such as whiteboard, the film surface is relatively excellent in smoothness, and a paper-like appearance cannot be obtained. . In addition, JP-A-6
Japanese Patent Laid-Open No. 3-193822 discloses a heat-shrinkable polyester film having micro bubbles containing 2 to 30 wt% of a polyolefin polymer, which has an appearance like tracing paper and is like Japanese paper. You can't get a nice look. Also, JP-A-63-235338
The publication discloses a white polyethylene terephthalate film containing 5 to 30 wt% of white inorganic particles and having a void ratio of 5 to 30%, which is also used as a base material for telephone cards and the like. The surface is relatively smooth and does not give the appearance of Japanese paper. Further, a film having a Japanese paper-like pattern formed by blending an incompatible resin and inorganic particles is disclosed in Japanese Patent Application Laid-Open No. 2-180933, but for the purpose of writing, it has an appearance like a Japanese paper. There are issues such as not being sufficient.

[0006] As described above, in the case of a label application in which the appearance is finished like Japanese paper, the performance is insufficient with the conventional polyester film or heat shrinkable polyester film.

[0007]

SUMMARY OF THE INVENTION The present invention is intended to solve the above problems, and an object of the present invention is to provide a polyester film for a bottle label, especially a paper-like appearance on the surface. And to provide a heat-shrinkable polyester film used for a label, which has the appearance of Japanese paper, in which wrinkles, shrinkage unevenness, and distortion due to shrinkage are extremely small.

[0008]

The heat-shrinkable polyester film of the present invention contains 0.01 to 0.4% by weight of ethers, and has a length in the main shrinkage direction and a direction perpendicular to the main shrinkage direction. The difference in film thickness per cm is 3μ
m or more, containing a cavity inside the film, having a cavity diameter of at least one surface layer in the film thickness direction of less than 5 μm, and having a cavity diameter of 5 μm or more in the central portion in the film thickness direction. It is a polyester-based film, which solves the above problems. In this case, the apparent specific gravity of the polyester film is preferably less than 1.0. In this case, the hot water shrinkage of the polyester film is 30% or more in the main shrinking direction at a processing temperature of 85 ° C. for a processing time of 10 seconds, and in the direction orthogonal to the main shrinking direction at 85 ° C. for 10 seconds. It is preferably 10% or less. In this case, it is preferable that the polyester film contains an incompatible thermoplastic resin.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be specifically described below.

Examples of the dicarboxylic acid component constituting the polyester used in the present invention include aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, naphthalenedicarboxylic acid and orthophthalic acid, adipic acid, azelaic acid, sebacic acid, decanedicarboxylic acid and the like. And the alicyclic dicarboxylic acid, and the like.

Aliphatic dicarboxylic acids (eg adipic acid,
When sebacic acid, decanedicarboxylic acid, etc.) is contained, the content is preferably less than 3 mol%. A heat-shrinkable polyester film obtained by using a polyester containing these aliphatic dicarboxylic acids in an amount of 3 mol% or more does not have sufficient film rigidity during high-speed mounting.

Further, it is preferable not to contain a polycarboxylic acid having a valence of 3 or more (eg, trimellitic acid, pyromellitic acid, and their anhydrides). With the heat-shrinkable polyester film obtained by using the polyester containing these polyvalent carboxylic acids, it becomes difficult to achieve the required high shrinkage ratio.

As the diol component constituting the polyester used in the present invention, ethylene glycol, propanediol, butanediol, neopentyl glycol,
Aliphatic diols such as hexanediol, alicyclic diols such as 1,4-cyclohexanedimethanol, aromatic diols and the like can be mentioned.

The polyester used in the heat-shrinkable polyester film of the present invention contains at least one of diols having 3 to 6 carbon atoms (for example, propanediol, butanediol, neopentyl glycol, hexanediol, etc.). , Glass transition point (Tg) 60-75 ° C
The polyester adjusted to 1 is preferable.

Further, in order to obtain a heat-shrinkable polyester film having a particularly excellent shrink finish, it is preferable to use neopentyl glycol as one of the diol components.

A diol having 8 or more carbon atoms (such as octane diol) or a polyhydric alcohol having 3 or more valences (such as trimethylolpropane and trimethylolethane,
Glycerin, diglycerin, etc.) are preferably not contained. With the heat-shrinkable polyester film obtained by using the polyester containing these diols or polyhydric alcohols, it becomes difficult to achieve the required high shrinkage ratio.

It is preferable that diethylene glycol and triethylene glycol are not contained as much as possible. Particularly, since diethylene glycol is a by-product component at the time of polyester polymerization, it is likely to exist, but in the polyester used in the present invention, the content of diethylene glycol is 4 mol%.
It is preferably less than.

In the present invention, the polyethylene glycol content is preferably 0.01 to 0.4% by weight, more preferably 0.05 to 0.3% by weight.
By adding polyethylene glycol in the above range, it is possible to improve the adhesiveness without affecting the appearance of a Japanese paper tone. When the content of polyethylene glycol is less than 0.01% by weight, it is not preferable in terms of solvent adhesiveness. On the other hand, if it exceeds 0.4% by weight, the surface of the film becomes almost smooth, and it is difficult to obtain a Japanese paper-like appearance.

The content ratio of the acid component and the diol component of the present invention is the content ratio of the entire polyester to the acid component and the diol component when two or more kinds of polyesters are mixed and used. It does not matter whether transesterification is performed after mixing. Further, in order to improve the slipperiness of the heat-shrinkable film, for example, an inorganic lubricant such as titanium dioxide, particulate silica, kaolin, calcium carbonate, or the like, and an organic lubricant such as a long-chain fatty acid ester may also be contained. preferable. Further, if necessary, additives such as a stabilizer, a colorant, an antioxidant, an antifoaming agent, an antistatic agent and an ultraviolet absorber may be contained.

Each of the above polyesters can be produced by polymerizing by a conventional method. For example, the polyester can be obtained by a direct esterification method in which a dicarboxylic acid and a diol are directly reacted, a transesterification method in which a dimethyl dicarboxylic acid ester is reacted with a diol, and the like. The polymerization may be performed by either a batch method or a continuous method.

To have a paper-like appearance,
For example, it is effective to provide a layer containing a cavity on at least one side. It is preferable to mix at least one specific thermoplastic resin that is incompatible with the above polyester in the void-containing layer. A specific thermoplastic resin that is incompatible with the polyester is blended, mixed, extruded, and stretched to form cavities inside the film, and it is believed that a film having a paper-like appearance is obtained due to the cavities. . The following is estimated, but blended with a specific thermoplastic resin incompatible with the above polyester, mixed under specific conditions,
By extruding, larger cavities than the conventional void-containing polyester film are formed, light scattering is reduced, and differences in the diameter of the formed cavities partially occur, resulting in large irregularities on the surface and a Washi-like appearance. It is supposed to become.

Examples of the specific thermoplastic resin which is incompatible with the above polyester include polymethylpentene resin and ionomer resin.

The blending amount of the thermoplastic resin incompatible with the polyester is preferably 11% by weight or more, more preferably 13% by weight or more based on the whole void-containing layer. If the amount of the thermoplastic resin is less than 11% by weight, voids inside the film are incomplete, and a paper-like appearance is not obtained, which is not preferable. Further, a layer containing no void may be laminated on the void containing layer. In that case, the thickness of the void-containing layer is preferably 40 μm or more. When the thickness of the void-containing layer is less than 40 μm, the hiding property is poor and it is difficult to obtain a Japanese paper-like appearance.

The film thickness difference is 3 per 1 cm of the length of the main shrinkage direction of the film and the direction perpendicular to the main shrinkage direction.
It is preferably at least μm, more preferably at least 5 μm. If the thickness difference between the films is less than 3 μ, it does not have the appearance of Japanese paper and is not preferable.

The thickness of the heat-shrinkable polyester film of the present invention is not particularly limited, but the heat-shrinkable film for labels is preferably 40 to 200 μm, and 50
˜100 μm is more preferable.

The heat-shrinkable polyester film of the present invention is treated in warm water under no load, and the heat-shrinkage ratio = ((length before shrinkage-length after shrinkage) / (Length before shrinkage) x 100 (%) The hot water shrinkage rate of the film calculated by the formula is 85 ° C
It is 30% or more, preferably 35 or more in a treatment time of 10 seconds, and 85 ° C. in the direction orthogonal to the main shrinkage direction.
10% or less in 10 seconds, preferably 6% or less.

When the hot water shrinkage in the main shrinkage direction is less than 30% at 85 ° C. for 10 seconds, insufficient shrinkage is likely to occur when used as a bottle label, which is not preferable.

If the hot water shrinkage ratio in the direction orthogonal to the main shrinkage direction exceeds 10%, the height of the label tends to deviate, which is not preferable.

A specific example of the method for producing the heat-shrinkable polyester film of the present invention will be described below, but the production method is not limited to this example.

The polyester resin used in the present invention is dried using a dryer such as a hopper dryer, paddle dryer or the like, or a vacuum dryer, melted at a temperature of 200 to 300 ° C. and extruded into a film. For extrusion, any existing method such as a T-die method or a tubular method may be adopted. After extrusion, it is rapidly cooled to obtain an unstretched film.

Next, the obtained unstretched film is stretched in the transverse direction by 3.0 times or more, preferably 3.5 times or more.

Next, if necessary, heat treatment is performed at a temperature of 70 to 100 ° C. to obtain a heat-shrinkable polyester film.

Further, if necessary, re-stretching may be performed in the transverse direction. In particular, a film having a Japanese paper-like appearance can be stably obtained by forming the film under the following conditions.

The polyester resin used in the present invention and the thermoplastic resin which is incompatible with the polyester resin are preferably mixed as close to the extruder as possible. By mixing immediately before, segregation with the polyester resin is less likely to occur, and a film having a more stable appearance can be obtained.

The extruded resin temperature is preferably 260 ° C to 300 ° C. If the temperature of the extruded resin is less than 260 ° C., the voids formed by the thermoplastic resin that is incompatible with the polyester resin are relatively small, and it is difficult to obtain the appearance like Japanese paper. Further, when the temperature of the extruded resin is 300 ° C. or higher, the thermoplastic resin is likely to be poorly dispersed in the extruder, and as a result, a film having a stable appearance cannot be obtained or film formation is likely to be unstable.

In order to achieve the object of the present invention, it is practical to use the lateral direction as the main contraction direction.
An example of the film forming method in which the main shrinkage direction is the lateral direction has been shown, but also when the main shrinkage direction is the longitudinal direction, the stretching direction in the above method is changed by 90 degrees, and the same operation as in the above method is performed. Can be formed into a film.

[0037]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples as long as the gist thereof is not exceeded.

The evaluation method of the film of the present invention is as follows.

(1) Heat Shrinkage The film was cut into a square of 10 cm × 10 cm, heat-shrinked in warm water at a predetermined temperature of ± 0.5 ° C. for a predetermined time without heat, and then the length of the film was increased. Then, the dimension in the lateral direction was measured, and the heat shrinkage rate was calculated according to the following equation (1). The direction in which the heat shrinkage rate was large was defined as the main shrinkage direction.

[0040]   Heat shrinkage rate = ((length before shrinkage-length after shrinkage) / length before shrinkage) x 100 (%) ... (1)

(2) Shrinkage-finishing heat-shrinkable film was previously prepared by Toyo Ink Mfg. Co., Ltd.
Three-color printing was performed using the grass, gold, and white inks, and the label with a folded diameter of 10.8 cm and a height of 6.1 cm was produced using a heat seal, with the printed surface facing outward.

Using a steam tunnel (model: SH-1500-L) manufactured by Fuji Astec Inc, a transit time of 2.5 seconds,
500 ml glass bottles (height 2
The test was performed using a 0.6 cm, central portion diameter of 6.5 cm (a bottle manufactured by Yoshino Kogyo Co., Ltd. and used for afternoon tea of Kirin Beverage Co., Ltd.) (measurement number = 20).

The evaluation was conducted visually, and the criteria were as follows.

[0044] No wrinkles, jumps, or insufficient shrinkage occurred: ○ Wrinkles, jumps, or insufficient shrinkage occurred: ×

(3) Thickness difference Contact thickness gauge manufactured by Anritsu Corporation (model: KG60 / A)
Using a. Vertical direction 5 cm, horizontal direction 50 cm, b. The thickness was measured in the longitudinal direction of each of the samples of 5 cm in the longitudinal direction and 50 cm in the lateral direction (measurement number 20), the difference between the maximum thickness and the minimum thickness was read for each 1 cm in length from the obtained chart, and the averaged result was obtained. And

(4) The observation surface of the cavity diameter sample was cut out smoothly with a microtome,
Ion Sputter (E-1030 manufactured by Hitachi, Ltd.)
Was used to deposit platinum for 150 seconds. The vapor deposition sample was subjected to an electrolytic emission scanning electron microscope (Hitachi Ltd.
S-800) was used to take a cross-sectional photograph of the film in the thickness direction, and the diameter of the cavity was determined from the photograph.

(5) The apparent specific gravity film is accurately cut into a square of 5.00 cm × 5.00 cm, the thickness of the film is measured at 50 points, and the average thickness is t.
μm. The weight of this film was measured up to 0.1 mg, this was taken as wg, and the apparent specific gravity was calculated by the following formula (2).

Apparent Specific Gravity = w / 5 × 5 × t × 10000 (2) (6) Intrinsic Viscosity Using an Ostwald viscometer, 200 mg of a sample was mixed with 20 of phenol / tetrachloroethane = 50/50.
The mixture was added to ml, heated at 110 ° C for 1 hour, and then measured at 30 ° C.

(6) Washi-like appearance The appearance of the obtained film was visually observed and judged according to the following criteria. There is a Japanese paper texture: ○ No Japanese paper texture: ×

(7) Solvent Adhesion The obtained film was subjected to an adhesion process using 1.3-dioxolane, and the adhesion was evaluated according to the following criteria. Strong adhesion: ○ Weak adhesion: △ No adhesion: ×

The polyesters used in the examples are as follows.

Polyester A: Polyethylene terephthalate (Intrinsic viscosity (IV) 0.75 dl / g) Polyester B: Polyester consisting of 70 mol% ethylene glycol, 30 mol% neopentyl glycol and terephthalic acid (IV 0.72 dl / g) Polyester C: Polybutylene terephthalate (IV
1.20dl / g)

(Example 1) 18% by weight of polyester A,
A resin obtained by mixing 67% by weight of polyester B and 15% by weight of polymethylpentene (“TPX DX845” manufactured by Mitsui Chemicals, Inc.) with 0.15% by weight of polyethylene glycol (molecular weight 1000) was used as a resin.
It was melted at 80 ° C., extruded from a T-die, and rapidly cooled with a chill roll to obtain a laminated unstretched film.

The unstretched film had a film temperature of 80.
After preheating until the temperature reaches ℃, use a tenter to move it in the horizontal direction.
The film was stretched 4 times at 0 ° C. to obtain a heat-shrinkable polyester film having a thickness of 80 μm.

(Example 2) 17% by weight of polyester A,
Polyester B 58% by weight, polyester C 10% by weight, polymethylpentene (“TPX D” manufactured by Mitsui Chemicals, Inc.)
X845 ”) 17% by weight of a polyester resin and polyethylene glycol (molecular weight 1000) are mixed with 0.1
The resin mixed with wt% was melted at 280 ° C., extruded from a T die, and rapidly cooled with a chill roll to obtain an unstretched film.

The unstretched film was processed in the same manner as in Example 1 to obtain a heat-shrinkable polyester film having a thickness of 80 μm.

Example 3 As both outer layers of the film, 18% by weight of polyester A and 67% by weight of polyester B,
Polymethylpentene (Mitsui Chemicals, Inc. “TPX DX8
45 ") 15% by weight of a polyester-based resin and 0.15% by weight of polyethylene glycol (molecular weight 1000) are used as the center layer of the film, wherein 20% by weight of polyester A, 75% by weight of polyester B and polymethylpentene are used. (The same as above) A polyester resin mixed with 5% by weight was melted at 280 ° C., and the extrusion discharge amount of both outer layers and the central layer was 1: 1, and laminated extrusion was performed from a T die and rapidly cooled with a chill roll. A laminated unstretched film was obtained.

A laminated heat-shrinkable polyester film having a thickness of 80 μm was obtained from the laminated unstretched film in the same manner as in Example 1.

Example 4 As both outer layers of the film, 17% by weight of polyester A and 63% by weight of polyester B,
Polymethylpentene (Mitsui Chemicals, Inc. “TPX DX8
45 "), a polyester resin mixed with 17% by weight and a resin mixed with 0.15% by weight of polyethylene glycol (molecular weight 1000) are used as the center layer of the film, 20% by weight of polyester A, 75% by weight of polyester B, polymethylpentene. (The same as above) A polyester resin mixed with 5% by weight was melted at 280 ° C., and the extrusion discharge amount of both outer layers and the central layer was 1: 1, and laminated extrusion was performed from a T die and rapidly cooled with a chill roll. A laminated unstretched film was obtained.

A laminated heat-shrinkable polyester film having a thickness of 80 μm was obtained from the laminated unstretched film in the same manner as in Example 1.

(Comparative Example 1) 32% by weight of polyester A,
A polyester resin containing 63% by weight of polyester B and 5% by weight of polymethylpentene (“TPX DX845” manufactured by Mitsui Chemicals, Inc.) was melted at 280 ° C., extruded from a T die, and rapidly cooled with a chill roll to obtain an unstretched film. Obtained.

The unstretched film was processed in the same manner as in Example 1 to obtain a heat-shrinkable polyester film having a thickness of 50 μm.

(Comparative Example 2) 17% by weight of polyester A,
53% by weight of polyester B, 10% by weight of polyester C, polystyrene (Japan Polystyrene Co., Ltd. “G797
N ") 20% by weight of a polyester resin mixed with 2%
It was melted at 80 ° C., extruded from a T-die and rapidly cooled with a chill roll to obtain an unstretched film.

The unstretched film was processed in the same manner as in Example 1 to obtain a heat-shrinkable polyester film having a thickness of 50 μm.

(Comparative Example 3) 17% by weight of polyester A,
A polyester resin in which 53% by weight of polyester B, 10% by weight of polyester C, and 20% by weight of polypropylene (Grand Polymer Co., Ltd. “Grand Poly F102WC”) were mixed was melted at 280 ° C., extruded from a T die, and rapidly cooled by a chill roll. An unstretched film was obtained.

The unstretched film was treated in the same manner as in Example 1 to obtain a heat-shrinkable polyester film having a thickness of 50 μm.

(Comparative Example 4) 32% by weight of polyester A,
53% by weight of polyester B, 10% by weight of polyester C, polymethylpentene (“TPX D” manufactured by Mitsui Chemicals, Inc.)
(X845 ″) 5% by weight of a polyester resin was melted at 280 ° C., extruded from a T die, and rapidly cooled by a chill roll to obtain an unstretched film.

The unstretched film was processed in the same manner as in Example 1 to obtain a heat-shrinkable polyester film having a thickness of 50 μm.

Table 1 shows the evaluation results of the films obtained in Examples 1 to 4 and Comparative Examples 1 to 4.

[0070]

[Table 1]

As is clear from Table 1, all of the films obtained in Examples 1 to 4 have good shrink finish, and the films have the appearance of Japanese paper and the heat shrinkability of the present invention. The polyester film is of high quality and has high practicality, and is particularly suitable for a shrinkable label which is required to have an appearance like Japanese paper.

On the other hand, the heat-shrinkable films obtained in Comparative Examples 1 to 4 have a relatively smooth film surface and do not have the appearance of Japanese paper. As described above, all the heat-shrinkable polyester films obtained in Comparative Examples were inferior in quality and were not practical.

[0073]

Industrial Applicability According to the present invention, a heat-shrinkable polyester film suitable for bottle labels, particularly for labels requiring an appearance like Japanese paper, can be obtained.

When the heat-shrinkable polyester film of the present invention is used as a label for a bottle, it is possible to obtain good finish properties with very few wrinkles, shrinkage spots, distortion and insufficient shrinkage due to heat shrinkage, and to make washi paper. It is extremely useful as a label application that requires such an appearance.

Continued front page    F-term (reference) 4F074 AA65 AB02 AC17 AC26 AC32                       AG01 AG11 CA01 DA03 DA12                       DA22 DA23 DA33                 4J002 CF031 CF041 CF051 CF081                       CH022 GG02

Claims (7)

[Claims] 1. A difference in film thickness per 1 cm in the main shrinkage direction of the film and a direction orthogonal to the main shrinkage direction is 5.
The average diameter of the voids in the film is at least 5 μm in the film thickness direction on one side surface layer portion
Is less than 1 and the average cavity diameter in the central portion in the film thickness direction is 1
5 μm or more and 0.01 to 0.4 of ethers
A heat-shrinkable polyester-based film, characterized in that the heat-shrinkable polyester-based film is contained. 2. The heat-shrinkable polyester film according to claim 1, wherein the ether is polyethylene glycol. 3. The heat-shrinkable polyester film according to claim 1 or 2, wherein the polyethylene glycol has an average molecular weight of 1,000. 4. The heat-shrinkable polyester film according to claim 1, wherein the apparent specific gravity is 1.0.
A heat-shrinkable polyester film characterized by being less than. 5. The shrinkage rate of hot water of the heat-shrinkable polyester film according to claim 1, 2, 3 or 4 is 30 at a processing temperature of 85 ° C. for a processing time of 10 seconds in the main shrinking direction.
% Or more and 8 in the direction orthogonal to the main contraction direction.
A polyester film having heat shrinkability, which is 10% or less at 5 ° C. for 10 seconds. 6. The heat-shrinkable polyester film according to claim 1, 2, 3, 4, or 5, wherein the polyester resin contains an incompatible thermoplastic resin. . 7. The method according to claim 1, 2, 3, 4, 5, or 6.
A label prepared by using the heat-shrinkable polyester film described in.