JP2002088172A - Heat shrinkable polyester film - Google Patents

Abstract

(57) Abstract: A heat-shrinkable polyester film capable of forming a label film in which foreign matter due to printing ink is not mixed into recycled bottles and ink can be easily removed. SOLUTION: This is a polyester resin film having a 5-sulfoisophthalic acid component in 3 to 8 mol% of all acid components, an ethylene terephthalate unit as a main component, and a glass transition temperature of 50 to 90 ° C. A heat-shrinkable polyester film having a shrinkage ratio of 30% or more when treated with hot air of 1 ° C. for 1 minute was used. The printed layer can be removed by hot water treatment, and when used as a label film, there is no inconvenience due to mixing of printing ink during bottle recycling.

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 for a packaging material used for labels and cap seals having a sufficient heat-shrinkability, and more particularly to a heat-shrinkable polyester film used as a bottle label when used as a bottle label. The present invention relates to a heat-shrinkable polyester film which is detached by washing with hot water and has no coloring due to ink in a recycled bottle, and is suitable for recycling.

[0002]

2. Description of the Related Art Plastic shrink films are used for labels and cap seals on containers, and for covering electronic components. Conventionally, polyvinyl chloride has been used as the resin for the shrink film, but the use of polyester having good heat resistance and mechanical strength is increasing. When polyester is used as the shrink film, an appropriate shrinkage ratio is imparted (see JP-A Nos. 1-4326 and 63-222845), or the shrink temperature is optimized (see JP-A No. 2-222).
No. 153941, JP-A-4-3355041,
Various studies have been made in order to achieve this. It is also developed for plastic bottle labels, and there is a bottle with an appropriate shrinkage rate in a temperature region where the bottle does not undergo thermal deformation.

[0003]

One of the advantages of polyester bottles is that they are recyclable among plastic bottles, and are widely used for beverages. When selecting a film for labeling polyester bottles,
A factor other than shrinkage is the suitability of bottle recycling. This is inconvenient when a bottle is recycled and used for fibers or the like, when foreign matters such as other resins and printing inks are mixed in, the spinnability and the like are remarkably reduced or colored. In this regard, since the polyester label is the same polyester, the inconvenience as described above is reduced even if the label is mixed in a recycled product. Therefore, a remaining problem requires a method of removing ink from the label. In this method, there is a method using an ink which is easily detached by alkali washing or the like, but it is difficult to switch all the printing inks.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and a heat-shrinkable polyester capable of forming a label film from which ink can be easily removed because foreign matter due to printing ink does not enter a recycled bottle. For films.

[0005]

As a result of intensive studies on a polyester film from which printing ink can be easily removed, the problem has been solved by using a film which is easily dissolved by hot water. That is, the heat-shrinkable polyester film of the present invention has a 5-sulfoisophthalic acid component in 3 to 8 mol% of all the acid components, an ethylene terephthalate unit as a main component, and a glass transition temperature of 50 to 90 ° C.
A film of a polyester resin which is 100 ° C.
Characterized in that the shrinkage when treated with hot air for 1 minute is 30% or more. In particular, those having a weight reduction rate of 3% or more when immersed in hot water of 80 ° C. for 10 minutes are desirable.

[0006]

DETAILED DESCRIPTION OF THE INVENTION The heat-shrinkable polyester film of the present invention can remove printing ink from a label by using a resin soluble in hot water. The polyester resin used in the polyester film of the present invention contains 5-sulfoisophthalic acid component in an amount of 3 to 8 mo of the total acid component.
It is a polyester containing 1%, preferably 4 to 7 mol% of ethylene terephthalate units as a main component (50 mol% or more). 5 mol of 5-sulfoisophthalic acid component
If it is less than 1%, the effect of ink desorption by the hot water treatment is small, and if it exceeds 8 mol%, a sufficient degree of polymerization cannot be obtained and film formation is difficult.

The polyester used for the film has a glass transition temperature of 50 to 90 ° C., preferably 60 to 80 ° C.
It is. If the glass transition temperature is lower than 50 ° C., the label is fused to the bottle during heat shrinkage, and the label is not peeled off during the regenerating process. On the other hand, if the glass transition temperature exceeds 90 ° C., the shrinkage onset temperature becomes high, which is unsuitable as a label for polyester bottles.

The polyester resin composition may contain 5-sulfoisophthalic acid component in the above range, ethylene terephthalate unit as a main component, and glass transition temperature in the above range. Aromatic dicarboxylic acid, aliphatic dicarboxylic acid, alicyclic An acid component such as a formula dicarboxylic acid, an aliphatic diol, an alicyclic diol, and an aromatic diol are all used. Aliphatic dicarboxylic acids include oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, azelaic acid, sebacic acid, pimelic acid, suberic acid, undecanoic acid, dodecanedicarboxylic acid, brassic acid, tetradecanedicarboxylic acid, tapsic acid , Nonadecanedicarboxylic acid, docosandicarboxylic acid and the like. As aromatic dicarboxylic acids, isophthalic acid, orthophthalic acid,
Benzenedicarboxylic acids such as 5-tert-butylisophthalic acid, naphthalenedicarboxylic acids such as 2,6-naphthalenedicarboxylic acid, 4,4′-dicarboxydiphenyl;
Dicarboxybiphenyls such as 2,2,6,6-tetramethylbiphenyl-4,4'-dicarboxylic acid, 1,1,3-
Trimethyl-3-phenylindene 4,5-dicarboxylic acid and its substituted product, 1,2-diphenoxyethane-4,
4'-dicarboxylic acid and its substituted products are exemplified.
Examples of the alicyclic dicarboxylic acid include 1,4-dicarboxycyclohexane and 1,3-dicarboxycyclohexane. As the aliphatic diol, diethylene glycol, butanediol, propylene glycol,
1,6-hexanediol, 1,10-decanediol,
Neopentyl glycol, 2-methyl-2-ethyl-
1,3-propanediol, 2-diethyl-1,3-propanediol, 2-ethyl-2-n-butyl-1,3propanediol and the like can be mentioned. As the alicyclic diol, 1,3-cyclohexanedimethanol, 1,4-
Cyclohexane dimethanol and the like. Examples of the aromatic diol include ethylene oxide adducts of bisphenol compounds such as 2,2-bis (4′-β-hydroxyethoxydiphenyl) propane and 2,2-bis (4′-β-hydroxyethoxydiphenyl) sulfone, Len glycol and the like. Other examples include polyalkylene glycols such as polyethylene glycol, polytetramethylene glycol and polypropylene glycol.

The polyester resin used in the present invention can be produced by a known direct polymerization method, transesterification method or the like, and may be prepared by either a continuous method or a batch method. Although the polymerization degree of the polyester resin is not particularly limited, the intrinsic viscosity (measured at 25 ° C. using a mixed solution of phenol / tetrachloroethane and the like as a solvent) is 0.50-1.5 dl / g is preferable.

The obtained polyester resin is formed into a heat-shrinkable polyester film by, for example, the following method. First, the polyester resin is dried or a decrease in the degree of polymerization due to hydrolysis is suppressed by a vent type extruder, and the extruder extrudes the polyester resin onto a cooling drum to form a raw film.

Next, the raw film is vertically or horizontally 1.5 ° C. or more at a temperature higher than the glass transition temperature by 3 ° C. or more.
The film is stretched by -5.0 times, preferably 1.0-4.8 times to give a high shrinkage to the film. Further, if necessary, it is 1.0-1.8 times, preferably 1.0-1.
Stretch 5 times. This is effective for increasing the strength in the direction perpendicular to the main shrinkage direction of the film and preventing the shrinkage in the stretching direction from unnecessarily shrinking. Stretching of the film is performed by a method of simultaneous biaxial stretching, sequential biaxial stretching, or uniaxial stretching, and either the transverse stretching or the longitudinal stretching may be performed first. Although the stretched heat-shrinkable film can be used as a product as it is, heat treatment may be performed at a temperature of 50 ° C. to 150 ° C. for several seconds to several tens of seconds from the viewpoint of dimensional stability. By performing such a heat treatment,
Preferred properties such as adjustment of the shrinkage in the shrinkage direction of the polyester film of the present invention, reduction of shrinkage with time during storage of an unshrinkable film, and reduction of shrinkage unevenness can be exhibited. The thickness of the heat-shrinkable polyester film of the present invention is not particularly limited, but a thickness in the range of 1 to 600 μm is practically used.

In the present invention, conventionally known various processings and appropriate additives can be blended in order to further impart specific performance. Examples of processing include UV, α
Irradiation with rays, β rays, γ rays, or electron beams, treatments such as corona treatment, flame treatment, etc., application of a resin such as vinylidene chloride, polyvinyl alcohol, polyamide, and polyolefin, lamination, and metal evaporation are exemplified.
The heat-shrinkable polyester film of the present invention contains various known additives, if necessary, in addition to the polyester having the above composition. Examples thereof include resins such as polyamide, polyolefin, polymethyl methacrylate, and polycarbonate, titanium dioxide, fine particle silica, kaolin, lubricants such as calcium carbonate, pigments such as titanium oxide and carbon black, ultraviolet absorbers, release agents, and flame retardants. And antistatic agents and antioxidants.

The solubility of the thus obtained heat-shrinkable polyester film of the present invention in hot water is such that when treated with hot water at 80 ° C. for 10 minutes, the weight loss rate is 3% or more, preferably 10% or more. is there. More preferably, it is 10 to 20%. If the weight loss rate is less than 3%, the printed layer is not removed in the hot water washing step, which is inconvenient. The shrinkage when the film is treated with hot air at 100 ° C. for 1 minute is 30% or more, preferably 40% or more. More preferably, it is 40 to 70%. If the shrinkage is lower than 30%, the shrinkage temperature must be increased, which is inconvenient due to the heat resistance of the bottle.

The heat-shrinkable polyester film obtained as described above is suitable as a shrinkable film for labels suitable for bottle recycling in which the printed layer can be removed by hot water treatment. The removal of the printed layer by the hot water treatment is usually performed by immersing the bottle with the label attached thereto in warm water of 80 ° C. for 10 minutes and stirring.

[0015]

EXAMPLES [Preparation of resin] The raw materials shown in Table 1 were put into a reaction vessel equipped with a reflux tower and a stirrer.
pm of magnesium acetate dihydrate was added thereto, and the mixture was reacted at a temperature of from 200 ° C. to 240 ° C. while distilling off by-produced methanol until the amount of methanol distilled out reached 90% of the theoretical amount to obtain an esterified product. .

[0016]

[Table 1]

Then, 300 ppm of triethyl phosphate, 500 ppm based on the weight of the raw material,
ppm of antimony trioxide and 700 ppm of silica were added, and the glycol component by-produced at 285 ° C. was reduced to 5 torr.
Melt polymerization was performed while distilling off under the following high vacuum to obtain a polyester resin. The polyester resin thus obtained had the composition shown in Table 2. The composition was determined by chromatography after hydrolysis. DSC for glass transition temperature
(Heating rate 10 ° C./min).

[0018]

[Table 2]

[Production of Film] Each of the obtained resins is dried by vacuum drying until the moisture content becomes 100 ppm or less, and extruded into a sheet on a cooling roll (25 ° C.) by an extruder. 200 μm). The raw film was processed by a batch type stretching machine to a length of 1.0 times and a width of 4.0.
It was stretched twice. Stretching temperature is 15 ° C higher than glass transition temperature
Stretched at high temperature.

The resulting film was evaluated for shrinkage, detachability of the printed layer by hot water treatment when mounted on a bottle, and hot water solubility. The method for measuring each physical property is described below. -Heat shrinkage rate Shrinkage rate was measured by exposing to hot air of 100 ° C for 1 minute. The contraction rate is based on the following equation. In addition, the measurement was performed along the direction stretched four times. Shrinkage (%) = {(L−L ′) / L} × 100 L: Length before hot air treatment L ′: Length after hot air treatment ・ Removability of print layer Usually used on both sides of film The printing ink was applied by a bar coater, covered with a 500 ml PET bottle in the form of a tube, treated in hot air at 100 ° C. for 1 minute, and shrink-fitted. The part with this label attached was cut into about 1 cm x 1 cm together with the bottle.
It was immersed in 00 g of hot water at 80 ° C. and treated with stirring for 10 minutes, and the degree of detachment of the printed layer was evaluated according to the following criteria. ：: The printed layers on both sides of the film were completely detached. Δ: The label did not separate from the bottle (fusion), and the printed layer remained between the film and the bottle. D: Print layers remained on both sides of the film. -Hot water solubility (weight loss rate) 1 g of the stretched film was immersed in 100 ml of hot water at 80 ° C and stirred for 10 minutes. After drying the film, the weight was measured and the weight loss rate was measured. Reduction rate (%) = {(MM ′) / M} × 100 M: mass before hot water treatment M ′: mass after hot water treatment

[0021]

[Table 3]

As is evident from the above results, the film of the present embodiment has an appropriate heat shrinkage and a high releasability of the printed layer. On the other hand, in Comparative Example 1 using a resin having a low modification rate, the shrinkage rate was small, and the resin was unsuitable as a label film. Comparative Example 2 having a small amount of 5-sulfoisophthalic acid component and Comparative Example 3 having a low glass transition temperature are unsuitable due to the low releasability of the printed layer and the fusion of the film to the bottle. In Comparative Example 4, which has a high glass transition temperature, the heat treatment at 100 ° C. has a low shrinkage and is not suitable as a label film. In Comparative Example 5 in which the amount of 5-sulfoisophthalic acid component was large, even a film could not be formed.

[0023]

According to the polyester film of the present invention, the printed layer can be removed by hot water treatment, and when used as a label film, a heat-shrinkable polyester film free from inconvenience due to mixing of printing ink during bottle recycling. It is. Therefore, the present invention can promote recycling of polyester containers and the like, and is environmentally desirable.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) B29L 7:00 B29L 7:00 C08L 67:02 C08L 67:02 (72) Inventor Hideki Kihara Toyohashi, Aichi Prefecture 4F071 AA45 AA86 AF05Y AF61Y AH05 AH06 BB08 BC01 4F210 AA24 AE01 AG01 RA03 RC02 RG01 RG04 4J029 AA03 AB01 AC02 AD03 AD07 AE03 BA03

Claims (2)

[Claims] 1. A polyester resin film having a 5-sulfoisophthalic acid component of 3 to 8 mol% of all acid components, an ethylene terephthalate unit as a main component, and a glass transition temperature of 50 to 90 ° C., A heat-shrinkable polyester film having a shrinkage of 30% or more when treated with hot air at 100 ° C. for 1 minute. 2. The weight reduction rate when immersed in hot water of 80 ° C. for 10 minutes is 3% or more.
The heat-shrinkable polyester film according to the above.