JP3049802B2 - Heat-shrinkable polyester film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat-shrinkable polyester film which exhibits heat shrinkage characteristics particularly suitable in the field of packaging materials for coating or bundling, and is lightweight and rich in cushioning properties.

[0002]

2. Description of the Related Art Tubular bodies formed from a heat-shrinkable plastic film include, for example, containers, bottles (including plastic bottles), and can-bars (pipes, rods, wood, various rods) (hereinafter referred to as containers). For covering or bundling, in particular, covering a part or the whole of these caps, shoulders, trunks, etc., and used for the purpose of marking, protection, bundling, improving the commercial value, etc. In addition, it is widely used in the field of packaging, such as boxes, bottles, boards, sticks, notebooks, etc., or in close contact with an object to be packaged, such as a skin pack, and uses shrinkage and shrinkage stress. Application development is expected.

Conventionally, a heat-shrinkable film made of polyvinyl chloride, polystyrene, polyethylene, hydrochloric acid rubber or the like is used for the above-mentioned applications. The heat-shrinkable film is formed into a tube and then covered with the containers or heat-shrinked by being packed and packed. Was.

[0004] However, these films have poor heat resistance, and have the drawback that when they are subjected to a boil treatment or a retort treatment, they melt or rupture and cannot maintain a film-like body.

[0005] Further, in applications requiring printing, printing pinholes due to poor ink transfer (fine irregularities due to fish eyes due to additives or polymer gels in the film)
However, even if printing was successfully performed, the film shrinks (shrink at room temperature) after that, causing a problem that a dimensional change occurs in the printing pitch.

On the other hand, polyester-based heat-shrinkable films have greatly improved the above-mentioned drawbacks and have received much attention recently.

However, the polyester-based heat-shrinkable film has a problem that the heat-shrinkage rate is higher than that of the above-mentioned heat-shrinkable films of polyvinyl chloride, polystyrene, polyethylene or hydrochloric acid rubber. If the heat shrink rate is high, uneven shrinkage of the film occurs, and the commercial value is greatly reduced. For example, when used as a shrink label for bottles, if the shrinkage rate is too high, shrinkage spots will concentrate on the shoulder where the shrinkage rate is highest, and air will not escape smoothly from the inside and air bubbles will form in the seal part. Problems such as biting occur. The occurrence of such shrinkage spots leads to print density unevenness, which significantly reduces the aesthetics of the product, and needs to be solved.

Further, a polyester-based heat-shrinkable film has better heat resistance than a heat-shrinkable film made of air-purified polyvinyl chloride, polystyrene, polyethylene, or hydrochloric acid rubber. Although there is no problem such as melting or rupture, there is a problem that secondary sagging occurs due to boil treatment or retort treatment and lowers the commercial value, so it is necessary to solve this.

Further, since the heat-shrinkable polyester film does not have a cushioning property as in the case of the above-mentioned film, it has an effect of preventing bottle breakage against impact upon transportation or sale when packaging or labeling a glass container. Can not expect. Thus, if cushioning properties can be imparted to the film itself, the commercial value will be further improved.

[0010]

SUMMARY OF THE INVENTION In view of the circumstances of the prior art, the present invention provides (1) a moderate heat shrink speed and less occurrence of shrinkage spots; (2) secondary treatment by boiling treatment or retort treatment. (3) It is an object of the present invention to provide a polyester-based heat-shrinkable film having characteristics such as not causing sagging and (3) imparting an appropriate cushioning property to the film itself and improving the ability to prevent breakage of a glass container. .

[0011]

According to the present invention, there is provided a composition comprising a polyester mainly composed of ethylene terephthalate repeating units and a polystyrene resin having an extractable amount of n-hexane of 5% by weight or less. Film
A heat-shrinkable polyester film characterized in that the heat shrinkage in hot air at 100 ° C. is 30% or more in at least one of the film longitudinal direction and the width direction.

In the present invention, the polyester mainly composed of ethylene terephthalate repeating units is
It is a thermoplastic polyester containing preferably 50 mol% or more of ethylene terephthalate repeating units obtained by a polymerization reaction of terephthalic acid and / or a derivative thereof and ethylene glycol. That is, the polyester is a homopolymer of polyethylene terephthalate or a copolymer of another dicarboxylic acid component and / or a diol component and / or an oxycarboxylic acid, and the copolymer component is not limited. The polyesters may be used alone or as a mixture of two or more. When two or more kinds are used in combination, a combination of polyethylene terephthalate and a copolymerized polyester or a combination of copolymerized polyesters may be used. Further, it may be a combination with a homopolyester such as polybutylene terephthalate, polyethylene 2,6-naphthalate, or polycyclohexylene dimethyl terephthalate. Use of two or more polyesters in combination is a more preferred embodiment because films having various properties can be produced.

The polyester can be produced by melt polymerization in a conventional manner, but is not limited thereto, and may be a polyester obtained by another polymerization method. The degree of polymerization of the polyester is preferably 0.3 to 1.2 in terms of intrinsic viscosity.

The polystyrene resin used in the present invention is:
A random copolymer, a block copolymer and a graft copolymer mainly composed of styrene repeating units obtained by polymerizing a styrene monomer and a polystyrene homopolymer obtained by copolymerizing other monomers. Furthermore, blends and polymer alloys in which other polymers are blended with such polymers are also included. For example, general-purpose amorphous polystyrene, crystalline polystyrene having stereoregularity, impact-resistant polystyrene, acrylonitrile-styrene copolymer, acrylonitrile-butadiene-styrene resin and the like can be mentioned.

Further, the polystyrene resin is preferably a polystyrene resin having an extractable amount of n-hexane of 5% by weight or less. Polystyrene resins that are usually used as raw materials for molded products include improved mold release, improved fluidity in the mold, improved extrudability, improved slidability, thermal degradation, and thermal oxidation degradation. A large amount of a modifying agent or a polymerization aid is added for the purpose of prevention, or emulsification or suspension during polymerization. For example, higher fatty acids, their esters, amides, metal salts, higher fatty alcohols, liquid paraffin, silicone oil and the like can be mentioned. Polystyrene resin is
Contains low molecular weight polystyrene and monomers. They bleed out to the surface of the film at the time of melt-extrusion molding, stretching orientation treatment, or heat setting treatment. Therefore, the wettability of the surface is significantly deteriorated.
Such a void-containing film on the surface may be scratched or uneven when coated with ink or a coating agent. Alternatively, the adhesion of these coating films is poor. Furthermore, when the material that has bleed out to the surface is washed with an organic solvent, etc., the wettability is temporarily improved, but bleed out occurs again from the inside to the surface, and the wettability and adhesion are reduced. I will.

Therefore, it is preferable in the present invention to use a polystyrene resin having an n-hexane extractable content of 5% by weight or less.

The polystyrene having an extractable amount of n-hexane of 5% by weight or less in the present invention can be prepared by, for example, a conventional bulk polymerization,
N-polystyrene obtained by emulsion polymerization, suspension polymerization, etc.
Polystyrene such as hexane or n-heptane is insoluble and is obtained by performing extraction washing with a non-polar organic solvent. It can also be obtained by providing a vent and exhausting when extruding a polystyrene obtained by a conventional method into chips. Of course, when polymerizing or extruding into chips, the n-
It is preferable that an additive that is easily extracted into hexane is not added as much as possible.

The amount of the polystyrene resin to be mixed with the polyester is preferably 1% by weight to 40% by weight based on the entire polymer mixture. If the amount is less than 1% by weight, the effect on the improvement of the heat shrinkage property and the provision of the cushioning property becomes insufficient, so that it is not preferable. Conversely, if the content exceeds 40% by weight, the effects of improving the heat shrinkage properties and providing the cushioning property are saturated, and the heat resistance and strength of the polyester film are undesirably impaired.

In preparing a polymer mixture obtained by mixing the polyester and the polystyrene resin, for example, chips of each resin may be mixed and melt-kneaded in an extruder and then extruded. The kneaded resin may be melt-extruded from an extruder. Also,
Chips obtained by adding a polystyrene-based resin in the polyester polymerization step and stirring and dispersing them may be melt-extruded.

The polymer mixture may contain a lubricant such as titanium dioxide, calcium carbonate, silica or kaolin, a pigment, a colorant, a light stabilizer, a fluorescent agent, an antistatic agent, etc., depending on the application. It is. These additives may be added directly to the polymer mixture, or may be added as a high concentration to the polymer, that is, as a so-called master batch.
Moreover, you may add in the superposition | polymerization process of each polymer.

The film of the present invention has a thickness of 6 to 250 μm.
Is preferable.

The film of the present invention must have a heat shrinkage of at least 30% in at least one of the longitudinal direction and the width direction at 100 ° C. If it is less than 30%, the required shrinkage of each part cannot be achieved when the shrinkage is performed along with the surface of the irregularly shaped package. 90% is appropriate for the upper limit.

A film obtained by using the above-mentioned polymer composition by an arbitrary method such as an extrusion method or a calendering method has a thickness of 2.5 in one direction.
Stretched to 7.0 times, preferably 3.0 times to 6.0 times, and 1.0 to 2.0 times or less in a direction perpendicular to the direction,
Preferably, it is stretched from 1.1 times to 1.8 times. Stretching in the first direction is performed to obtain a high heat shrinkage rate, and stretching in the direction perpendicular to the first direction has poor impact resistance and tear resistance of the film stretched in the first direction. Is extremely effective in solving the problem.

However, when the film is stretched more than 2.0 times, the heat shrinkage in the direction perpendicular to the main shrinkage direction becomes too large,
The finish is wavy. To suppress this undulation,
It is recommended that the heat shrinkage be 15% or less, preferably 8 to 9% or less, more preferably 7% or less. There is no particular limitation on the stretching means, and methods such as roll stretching, long gap stretching, and tenter stretching are applied, and the shape thereof may be flat or tubular.

The stretching is performed sequentially in biaxial stretching, simultaneous biaxial stretching,
It is performed by axial stretching or a combination thereof. The film of the present invention is stretched, for example, uniaxially in the longitudinal direction, uniaxially in the horizontal direction, biaxially in the vertical and horizontal directions. It is valid, and the order can be either. When the simultaneous biaxial stretching method is performed, the stretching order may be any of vertical and horizontal simultaneous, vertical and horizontal advance. The heat setting in these stretchings is carried out according to the purpose, but it is recommended to pass through a heating zone of 30 to 150 ° C. for about 1 to 30 seconds in order to prevent dimensional change under high temperature in summer. In addition, stretching up to 70% may be applied before and / or after such treatment. In particular, it is preferable to stretch in the main direction and relax in the non-contraction direction (direction perpendicular to the main contraction direction), and it is better not to perform the extension in the perpendicular direction.

In order to exhibit the preferred characteristics of the present invention, not only the above-mentioned stretching ratio but also preheating and stretching at a temperature higher than the average glass transition point (Tg) of the polymer composition, for example, at about Tg + 80 ° C. This is also an effective means. In particular, the processing temperature in the main direction stretching (main shrinkage direction) is extremely low in order to suppress the heat shrinkage in the direction perpendicular to the direction and bring the minimum value to the temperature range of 80 ± 25 ° C. as described above. is important. Further, after stretching, the film is cooled while applying stress to the film while being stretched or tensioned, or further cooled, so that the longitudinal shrinkage characteristics are better and more stable.

The thus obtained film preferably has a plane orientation coefficient of 100 × 10 ⁻³ or less. If the plane orientation coefficient exceeds 100 × 10 ⁻³ , the sheet is easily broken by an external impact force, and is easily broken even by a slight damage. On the other hand, the birefringence is preferably 15 × 10 ^{−3 to} 160 × 10 ⁻³ , and if the birefringence is less than 15 × 10 ⁻³ , the heat shrinkage and shrinkage stress in the longitudinal direction are insufficient, and 160 × 10 ⁻³ is insufficient. If it exceeds, the scratch resistance and the impact strength decrease, and even if it becomes a film, its usefulness decreases in practical use.

The film of the present invention may be a single-layer film or a multilayer film. Means such as laminating a function-imparting substance on the film surface in order to impart printability, antistatic property and the like is a useful method from the viewpoint of increasing the value of a product and is recommended. There is no restriction on how to do these.

[0029]

EXAMPLES The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples unless it exceeds the gist. The measuring method used in the present invention is shown below.

1. Heat shrinkage ratio The distance between the sample marks was set to 200 mm, and the film was set to a width of 15 mm.
mm and heated with hot air at 100 ° C for 1 minute,
The length between the marked lines was measured and determined.

2. Heat Shrink Rate The same sample as used for the heat shrink rate measurement was used at 70 to 105 ° C.
The heat shrinkage at each temperature was determined in the same manner as in the measurement of the heat shrinkage at a pitch of 5 ° C. The relationship between each measured temperature and the heat shrinkage was plotted in the figure, and the rate of change of the heat shrinkage in the range of 20 to 50% was obtained by linear approximation and displayed in units of% / 10 ° C. The heat shrink rate thus obtained is 5 to 40% / 10
° C is practical. In particular, those having 10 to 30% / 10 ° C. are particularly preferable.

3. Thermal Shrinkage Residual Stress Retention Time (at 50% Relaxation) A piece of material having a width of 20 mm and a length of 150 mm was sampled using Tensilon, and a 100 mm mark was drawn on the film.
The upper and lower chucks, each of which was set to a thickness of 100 mm, were fitted with a mark of exactly 100 mm, mounted in hot air at 100 ° C., and the time required for the shrinkage stress to become zero was measured.

4. Apparent Specific Gravity of Film The film was accurately cut out into a square of 5.00 cm × 5.00 cm, and its thickness was measured at 50 points to obtain an average thickness tμ.
m, its weight is measured to 0.1 mg and wg,
It was calculated by the following equation. Apparent specific gravity (-) = W / 5 x 5 x t x 10,000

5. Void Content of Film Calculated by the following equation. Cavity content (volume%) = 100 × (1−true specific volume / apparent specific volume) where true specific volume = xi / di + x ₂ / d ₂ + x ₃ / d ₃ + ...
+ Xi / di +... Apparent specific volume = 1 / apparent specific gravity of film In the above formula, xi represents the weight fraction of the i component, and di represents the true specific gravity of the i component. The values of true specific gravity used in the calculations in the examples were polyester resin 1.40, general-purpose polystyrene resin 1.05, and crystalline polypropylene resin 0.91.

6. Cushioning property Using a dial gauge (KK, Ozaki Seisakusho) equipped with a 3 mmφ circular flat-bottom measuring element, a measuring pressure of 10 gf /
The thickness t ₀ was measured in cm ² , then a weight was applied as it was, the measurement pressure was increased to 5 kgf / cm ² , and the thickness t ₁ was measured 10 seconds after the weight was applied. Further remove weight topped 30 seconds after carrying the weight was measured thickness t _2. The compression ratio and the recovery ratio were calculated from the following equations. As the compression rate and the recovery rate are both larger, the cushioning property is better and the effect of preventing bottle breakage can be expected.

EXAMPLE 1 85% by weight of a polyethylene terephthalate resin having an intrinsic viscosity of 0.75 dl / g and a melt flow index of 3.0 g
10% by weight of general polystyrene 10% by weight (preliminarily washed with heptane, the amount of n-hexane extruded is 0.9% by weight
Was melt-extruded from a T-die at 285 ° C. with a twin-screw extruder, and solidified electrostatically on a cooling rotating roll to obtain an unstretched film having a thickness of 180 μm. The film was stretched 1.2 times in the machine direction and then 4.1 times in the transverse direction, and then cooled under stretching in the transverse direction by about 20% to obtain a heat-shrinkable film having a thickness of 40 μm.

The film obtained in this example has a high heat shrinkage and a moderate shrinkage rate, and even in a practicality test for shrink labels for bottles, the shrinkage spots and the print density unevenness were observed. A product with excellent aesthetic feeling was obtained without generation of any. In addition, the film had excellent retention properties of residual stress after shrinkage, and no secondary sagging of labels occurred even when the PET bottle bottle labeled with the film was boiled. Further, the film had excellent cushioning properties and good bottle breaking properties. The contact angle between the film and water was 80 °, and the printability was good.

Example 2 A heat-shrinkable film was obtained in the same manner as in Example 1, except that the mixing ratio between the polyester resin and the polystyrene resin was changed. The film obtained in this example also had excellent characteristics and was of high quality.

Examples 3 to 6 Shrinkable films were obtained in the same manner as in Example 1 using various polyester resins and polystyrene resins as shown in Table 1. The films obtained in these examples are:
All had excellent properties and were of high quality.

Comparative Example 1 A heat-shrinkable film was obtained in the same manner as in Example 1, except that the polyethylene terephthalate resin alone was used without blending the polystyrene resin. Although the film obtained in this comparative example had a high heat shrinkage, it had a high heat shrinkage rate, so that in a practical test for shrink labels for bottles, shrinkage spots and print spots were generated, and the quality was low. Also,
The film was inferior in retention of residual stress after shrinkage, and when a PET bottle bottle labeled with the film was boiled, secondary sagging of the label occurred. Further, the film was inferior in cushioning properties and inferior in bottle breaking characteristics.

Comparative Example 2 A heat-shrinkable film was obtained in the same manner as in Example 1, except that a crystalline polypropylene having a melt flow index of 2.5 g / 10 min was used instead of the polystyrene resin. Was. The film obtained in this comparative example has excellent cushioning properties and good bottle breaking characteristics, but has a large heat shrinkage rate, so that in the practicality test for shrink labels for bottles, shrinkage spots and print spots are observed. It occurred and was of low quality. The film has a contact angle with water of 1
It was as high as 04 ° and poor in printability.

Table 1 shows the compositions of the resins used for forming the films in the above Examples and Comparative Examples, and Table 2 shows the properties of the obtained films.

[0043] (Note) PET: Polyethylene terephthalate copolymer Polyesteres A: Terephthalic acid / isophthalic acid // ethylene glycol (molar ratio 80/20 // 100) Copolymer polyester B: terephthalic acid / sephatic acid // ethylene glycol (molar ratio 53) / 47 // 100) Copolymer polyester C: terephthalic acid // ethylene glycol / neopentyl glycol (molar ratio 100 // 70/30)

[0044]

[0045]

As shown in the above examples, the film of the present invention exhibits a stable heat shrinkage in a specific direction, and can give a beautiful and strong packaging state in a covering package or a binding package. Excellent utilization value can be exhibited.

────────────────────────────────────────────────── ─── Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI // B29K 67:00 105: 02 105: 04 B29L 7:00 (72) Inventor Atsushi Taga 2-chome Katata 2-chome, Otsu City, Shiga Prefecture No. 1 Toyo Spinning Co., Ltd. Research Institute (72) Inventor Shinji Sawazaki 344 Maehata, Kizu, Oji, Inuyama-shi, Aichi Prefecture Toyo Boshoku Co., Ltd. Address Toyobo Co., Ltd. Inuyama Plant (56) References JP-A-62-124928 (JP, A) JP-A-3-292338 (JP, A) JP-A-3-178421 (JP, A) (58) Survey Field (Int.Cl. ⁷ , DB name) C08J 5/18 CFD B29C 61/06-61/10 C08J 9/00 C08L 25/04 C08L 67/03

Claims (1)

(57) [Claims] 1. Extraction of polyester mainly composed of ethylene terephthalate repeating units and n-hexane
Is a film composed of a composition with a polystyrene resin having a content of 5% by weight or less, and a heat shrinkage in hot air at 100 ° C. of 30% or more in at least one of the longitudinal direction and the width direction of the film. A heat-shrinkable polyester film characterized by the above-mentioned.