JP2003154619A - Polyester film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a heat-shrinkable polyester film suitable for a full label of a bottle, especially, for a full label of a PET bottle, extremely reduced in the generation of wrinkles due to shrinkage, shrinkage irregularity and strain, having appearance like paper and excellent in the visibility of the printed patterns or characters applied to the inner surface of the film. SOLUTION: In the heat-shrinkable polyester film, the concealing degree of the whole of the film is not more than 0.2, a layer containing cavities is provided at least on the single surface of the film and the center line average roughness of the surface of the layer containing the cavities is not less than 0.1 μm.

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, it is a heat-shrinkable polyester resin that has an appearance similar to Japanese paper and has excellent visibility of patterns and letters on the inner surface of the film, and that wrinkles, shrinkage spots, and distortion due to heat shrinkage are extremely low. Regarding film.

[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.

For this reason, a special coating such as coating with cellulose fibers is conceivable, but there are problems that uniform coating is not easy, the durability of the coating film is poor, and the film after coating has poor transparency. is there.

[0005] Further, there is also a film in which an incompatible resin or inorganic particles are blended to contain voids, but merely containing voids keeps the film hiding property high,
When a film is used as a label, there are problems such as poor visibility of patterns and letters when printed on the inner surface side, and the inability to obtain a Japanese paper-like appearance. For example, Japanese Patent Laid-Open No. 2-16
No. 130 discloses crystalline polypropylene of 3 to 40 wt.
%, A microbubble-containing polyester film is disclosed, which is used for a base material such as a whiteboard, has a very high hiding power, and is not transparent. Further, Japanese Patent Application Laid-Open No. 63-193822 discloses a heat-shrinkable polyester film having fine bubbles containing 2 to 30 wt% of a polyolefin polymer, which also has a large hiding property and is of Japanese paper. It doesn't look like that. In addition, JP-A-63-2353
No. 38 publication contains 5 to 30 wt% of white inorganic particles,
A white polyethylene terephthalate film having a void ratio of 5 to 30% is disclosed, but this is also used for a base material such as a telephone card, has an excellent concealing power, and cannot give a transparent feeling. Further, a film formed with a Japanese paper-like pattern in which an incompatible resin and inorganic particles are mixed is disclosed in JP-A-2-180933.
Since it is intended for writing, it is not sufficient as a Japanese paper pattern, and it also has a high hiding property of the film, and the visibility of patterns and characters when printing on the inner surface side when the film is used as a label is poor. Have the challenges of.

[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. It has excellent visibility of patterns and letters on the inner surface when the film is used as a label, and is especially used for labels that have the appearance of Japanese paper with very few wrinkles, shrinkage spots, and distortion due to shrinkage. To provide a heat-shrinkable polyester film.

[0008]

The polyester film of the present invention has a degree of hiding of the whole film of 0.2 or less, and is provided with a layer containing cavities on at least one side,
The center line average roughness (Ra) of the surface of the void-containing layer is 0.1.
It is a polyester film having a thickness of at least μm, which solves the above problems. 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.
In this case, it is preferable that the polyester film is composed of at least two layers.

[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, triethylene glycol and polyethylene 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 preferably less than 4 mol%.

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.

Any 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.

In order to have an appearance like Japanese paper, 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 an estimate, but by blending a specific thermoplastic resin that is incompatible with the above polyester, mixing and extruding under specific conditions, a larger cavity is formed than the conventional void-containing polyester film, and It is considered that the scattering is reduced, and the formed large cavities make the surface uneven, resulting in the appearance of Japanese paper.

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 which is incompatible with the polyester is preferably 10% by weight or more, more preferably 18% by weight or more based on the entire void-containing layer. If the amount of the thermoplastic resin is less than 10% by weight, the voids inside the film are incomplete and the appearance of paper is not obtained, which is not preferable. The thickness of the void-containing layer is preferably in the range of 10 to 50 μm and 10
If it is less than μm, it is difficult to obtain a Japanese paper-like appearance. Again 5
When it exceeds 0 μm, the degree of hiding tends to increase. A layer that does not contain voids or a layer that contains voids may be laminated on the void-containing layer, but it is necessary that the thickness is such that the hiding power of the entire film does not decrease too much.

The hiding power of the entire film is preferably less than 0.2, more preferably 0.15 or less. When the degree of hiding exceeds 0.2, it is not preferable because the printed design, characters, etc. applied to the inner surface side when the film is used as a label becomes difficult to visually recognize.

Centerline average roughness (Ra) of the surface of the void-containing layer
Is preferably 0.1 μm or more, more preferably 0.2
It is at least μm. Centerline average roughness Ra of the surface of the void-containing layer
Is less than 0.1 μm, the appearance of the surface of the void-containing layer does not look like paper and is not preferable. Further, it is preferable that the void-containing layer has an appearance of a texture unique to Japanese paper.

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 10 to 200 μm, and 20
˜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 raw material used in the present invention is dried using a dryer such as a hopper dryer, a paddle dryer, 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 order to achieve the object of the present invention, it is practical to use the lateral direction as the main shrinkage 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.

[0035]

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, and heat-shrinked in warm water at a predetermined temperature of ± 0.5 ° C. for a predetermined time without load, 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.

[0038]   Thermal shrinkage = ((length before shrinkage-length after shrinkage) / length before shrinkage) × 100 (%) (1)

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

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.

[0042] No wrinkles, jumps, or insufficient shrinkage occurred: ○ Wrinkles, jumps, or insufficient shrinkage occurred: ×

(3) Concealment Degree Macbeth PROCESS MEASUREMEN
Using a TS Macbeth densitometer (type: TR927),
The degree of concealment was measured with a transmission measurement and an aperture size of 3 mm.

(4) Center line average roughness (Ra) Three-dimensional fine shape measuring instrument (ET-30H, manufactured by Kosaka Laboratory Ltd.)
K) was used to measure the center line average roughness (Ra) of the surface of the cavity-containing layer under the conditions of a cutoff of 80 μm and a drive speed of 100 μm / s.

(5) 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) 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: ×

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) As a void-containing layer, a polyester system in which 17% by weight of polyester A, 53% by weight of polyester B, 10% by weight of polyester C and 20% by weight of polymethylpentene (“TPX DX845” of Mitsui Chemicals, Inc.) were mixed. As the void-free layer, the resin is a polyester resin obtained by mixing 37% by weight of polyester A, 53% by weight of polyester B, and 10% by weight of polyester C,
Each was melted at 280 ° C., laminated extruded through a T die, and rapidly cooled by a chill roll to obtain a laminated unstretched film.

The laminated unstretched film was preheated to a film temperature of 80 ° C., and then stretched in a transverse direction at 76 ° C. by a factor of 4 to obtain a laminated heat-shrinkable polyester film having a thickness of 50 μm. .

(Example 2) As a void-containing layer, 20% by weight of polyester A, 53% by weight of polyester B, 10% by weight of polyester C, and 17% by weight of polymethylpentene (“TPX DX845” of Mitsui Chemicals, Inc.) were mixed. As the void-free layer, the resin is a polyester resin obtained by mixing 37% by weight of polyester A, 53% by weight of polyester B, and 10% by weight of polyester C,
Each was melted at 280 ° C., laminated extruded through a T die, and rapidly cooled by a chill roll to obtain a laminated unstretched film.

A laminated heat-shrinkable polyester film having a thickness of 50 μm was obtained from the laminated unstretched film in the same manner as in Example 1.

(Example 3) As a void-containing layer, a polyester system in which 24% by weight of polyester A, 53% by weight of polyester B, 10% by weight of polyester C and 13% by weight of polymethylpentene (“TPX DX845” of Mitsui Chemicals, Inc.) were mixed. As the void-free layer, the resin is a polyester resin obtained by mixing 37% by weight of polyester A, 53% by weight of polyester B, and 10% by weight of polyester C,
Each was melted at 280 ° C., laminated extruded through a T die, and rapidly cooled by a chill roll to obtain a laminated unstretched film.

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

Example 4 As a void-containing layer, 17% by weight of polyester A, 53% by weight of polyester B, 10% by weight of polyester C, ionomer (Mitsui DuPont)
Polychemical Co., Ltd. "Himilan 1705") 20% by weight of the polyester-based resin is used as the void-free layer, and polyester A 37% by weight, polyester B 53% by weight, and polyester C 10% by weight are mixed respectively. It was melted at 280 ° C, laminated and extruded from a T die, and rapidly cooled with a chill roll to obtain a laminated unstretched film.

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

(Comparative Example 1) 17% 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 ″) 20% by weight of 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.

(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 processed 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.

[0066]

[Table 1]

As is clear from Table 1, the films obtained in Examples 1 to 4 all have good shrink finish, and the films have the appearance of Japanese paper, and when the films are used as labels. The visibility of printed patterns and letters on the inner surface of the is also good. The laminated heat-shrinkable polyester film of the present invention has high quality and high practicality, and is particularly suitable for a shrink 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 large hiding power of the film, and the visibility of printed patterns and characters applied to the inner surface side when the film is used as a label is poor. . As described above, all the heat-shrinkable polyester films obtained in Comparative Examples were inferior in quality and were not practical.

[0069]

INDUSTRIAL APPLICABILITY According to the present invention, it is used for bottle labels, and particularly for labels that require a visual appearance such as Japanese paper and the visibility of printed patterns and characters applied to the inner surface side when a film is used as a label. A suitable heat-shrinkable polyester film can be obtained.

When the laminated heat-shrinkable polyester film of the present invention is used as a label for a bottle, it is possible to obtain a good finish with very few wrinkles, shrinkage spots, distortion and insufficient shrinkage due to heat shrinkage, and , It is extremely useful as a label application in which the appearance like a Japanese paper and the visibility of a printed design or characters provided on the inner surface side when a film is used as a label are required.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) B29L 7:00 B29L 7:00 9:00 9:00 9:00 F term (reference) 4F100 AK01B AK08 AK41A AK41B BA02 BA07 DJ00B EH20 EJ37 GB15 GB90 JA03 JB16B JK14B JN01 YY00B 4F210 AA12 AA24 AC03 AE01 AF16 AG01 AG03 AG20 AH54 AH81 RA03 RC02 RG02 RG04 RG43

Claims (4)

[Claims] 1. A hiding degree of the whole film is 0.2 or less, and a layer containing a cavity is provided on at least one surface,
The center line average roughness (Ra) of the surface of the void-containing layer is 0.1.
A polyester film characterized by having a thickness of at least μm. 2. The shrinkage rate of hot water of the polyester film according to claim 1 in the main shrinkage direction is a processing temperature of 85 ° C.
A polyester film which has a treatment time of 30% or more in 10 seconds and is 10% or less in 85 ° C. for 10 seconds in the direction orthogonal to the main shrinkage direction. 3. The polyester film according to claim 1 or 2, wherein the polyester resin contains an incompatible thermoplastic resin. 4. The polyester film according to claim 1, comprising at least two layers.