JPH0368634A - Heat-shrinkable polyester film - Google Patents

Abstract

PURPOSE:To prepare a heat-shrinkable polyester film having an excellent heat shrinkability in a specific direction at a low temp. by forming a polyester copolymer comprising a dicarboxylic acid component mainly comprising a terephthalic acid and a specific diol component into a film and orienting the film at about the glass transition temp. CONSTITUTION:A film is formed from a polyester copolymer comprising: a dicarboxylic acid component comprising terephthalic acid (deriv.); and a diol component comprising 50-90mol% ethylene glycol, 5-50mol% neopentyl glycol, and 3-20mol% glycol selected from the group consisting of diethylene glycol, triethylene glycol, and a polyethylene glycol. The resulting film is oriented at about the glass transition temp. to give a heat-shrinkable polyester film, which has a shrinkage in one direction after heated in a glycerin bath for 30sec at 70 deg.C, 80 deg.C, and 90 deg.C of 20% or higher, 30% or higher, and 40% or higher, respectively, has a shrinkage in the direction transverse to above-mentioned direction at 0-100 deg.C of lower than 10%, and is suitable for a shrinkable label, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a heat-shrinkable polyester film that shrinks uniformly at relatively low temperatures and has good finish, heat resistance, strength, etc. after shrinkage.

[Prior art and problems to be solved by the invention] Heat-shrinkable films are used for marking, protecting, bundling, adding value to products, etc. for containers, fishing rods, condensers, fluorescent rods, etc., and are also used for books, notebooks, etc. It has been used for integrated packaging or close-contact packaging. Currently, applications utilizing the shrinkability and shrinkage stress of this heat-shrinkable film are expected in many other fields.

Conventionally, resins such as polyvinyl chloride, polystyrene, and polyolefin have been used as materials for heat-shrinkable films. However, such materials have drawbacks in terms of heat resistance, weather resistance, chemical resistance, etc. For example, although polyvinyl chloride film can be made into a heat-shrinkable film with various shrinkage characteristics, fish eyes occur frequently, and as a result, products using printed films as packaging materials lose their aesthetic appearance and significantly reduce their commercial value. It is easy to become something like that.

Further, in order to obtain a heat-shrinkable film without fish eyes, excessive quality control is required, resulting in problems such as a significant increase in film manufacturing costs. Furthermore, when disposing of polyvinyl chloride, it cannot be incinerated because doing so will cause pollution problems, and additives such as plasticizers in polyvinyl chloride resin bleed out over time, causing dirt and other problems due to the adhesion of dust, making it safer. It also had the problem of being undesirable in terms of sex.

On the other hand, heat-shrinkable films made from polystyrene have a good finish after shrinking, but they have low solvent resistance, so special ink must be used when printing, and natural shrinkage occurs even at room temperature. It had to be stored in a cold place, and its disposal was also a big problem.

Polyester holds great promise as a material that can solve these problems. However, conventionally developed heat-shrinkable polyester films have problems such as not being able to sufficiently increase the heat shrinkage rate in the desired direction, or being unable to reduce the heat shrinkage in the direction perpendicular to the above-mentioned direction. has appeared. Furthermore, the most promising application field for heat-shrinkable films made from polyester is labels for PET bottles, but conventional heat-shrinkable polyester films have a low shrinkage rate at low temperatures, so they must be heated above 80°C. I needed it. However, when conventional heat-shrinkable polyester films are used in PET bottles at such temperatures, problems such as deformation and whitening of the PET bottles occur.

[Means for Solving the Problems] In view of the current situation, the present inventors have conducted intensive research and found that a heat-shrinkable film obtained from a specific polyester copolymer has excellent shrinkage characteristics, This has led to the present invention.

That is, in the present invention, the polyester film contains a dicarboxylic acid component (A) consisting of terephthalic acid or its derivative component (a), ethylene glycol (c>a content 50 to 90 mol%), and neopentyl glycol (d) 53E content 5 to 50%.
mol% and at least one selected from diethylene glycol, triethylene glycol, and polyethylene glycol
Diol component (B) consisting of 3 to 20 mol% of species (e) component
), and the shrinkage rate when heated for 30 seconds in a glycerin bath is 20% or more in one direction at a bath temperature of 70°C and 3 at 80°C.
0% or more, 40% or more at 90°C, and less than 10% in the range of 0 to 100°C in the direction perpendicular to the direction of shrinkage.

The heat shrinkage rate of the heat-shrinkable polyester film of the present invention is:
When heated for 30 seconds in a glycerin bath, it is 20% or more at 70°C in one direction, 30% or more at 80°C, and 40% or more at 90°C. The shrinkage rate of a heat-shrinkable film in one direction is often required to be at least 20%, although it depends on the application. For example, when a heat-shrinkable polyester film is used as a label for a PET bottle, a unidirectional heat shrinkage rate of about 40% is normally required in order to shrink the label tightly to the shoulder of the bottle. In this case, the shrinkage temperature of the film must be set low in view of the heat resistance of the PET bottle.

On the other hand, the shrinkage percentage in the direction perpendicular to the shrinkage direction is preferably smaller from the viewpoint of dimensional stability and yield, but is less than 10%, preferably less than 5% in the range of 0 to 100°C. That is, there should be no abnormal shrinkage of more than 10% in the temperature range.

In addition, it is preferable that the change in shrinkage rate of the heat-shrinkable polyester film with respect to temperature change is small from the viewpoint of shrinkage spots.

Therefore, it is preferably 5%/degree or less at a temperature of 90°C or lower, and more preferably 5%/degree at a temperature of 85°C or lower.

The dicarboxylic acid component (A) of the polyester copolymer used in the present invention consists of terephthalic acid or a derivative thereof. Examples of derivatives of terephthalic acid include dialkyl esters and diaryl esters of terephthalic acid.

Other dicarboxylic acids that can be used as a dicarboxylic acid component in a range of 10 mol% or less include adipic acid,
Sebacic acid, phthalic acid, inphthalic acid, naphthalene-1
, 4- or -2,6 dicarboxylic acid, diphenyl ether-4,4-dicarboxylic acid, and the like.

The diol component (B) of the polyester copolymer used in the present invention contains 50 to 90 mol% of ethylene glycol (c) component and neopentyl glycol (d) lff1 min 5 to 5 mol%.
0 mol% and 5 to 50 mol% of at least one component (e) selected from diethylene glycol, triethylene glycol, and polyethylene glycol color. Glycols that can be used as a diol component in an amount of 10 mol% or less include propylene glycol, butylene glycol, cyclohexanedimethanol, 2.
Examples include 2-bis(4-hydroxyphenyl)propane.

Neopentyl glycol is contained in the diol component in an amount of 5 to 50 mol%. A film obtained from a polyester copolymer containing less than 5 mol % of neopentyl glycol in the diol component does not exhibit sufficient heat shrinkability. In addition, polyester copolymers containing more than 50 mol% of neopentyl glycol in the diol component have a significantly lower melting point or softening point, resulting in poor formability when producing a heat-shrinkable film from the copolymer. The resulting film also has poor heat resistance and mechanical strength, which is not preferable.

Component (e) is contained in the diol component in an amount of 3 to 20 mol%. A film obtained from a polyester copolymer containing less than 3 mol % of the component (e) in the diol component is not preferred because it has a low shrinkage rate at low temperatures, tends to cause shrinkage spots, and has low impact resistance. Component (e) is 20% of the diol components
If the polyester copolymer exceeds mol%, the glass transition temperature and melting point or softening point will be significantly lowered, resulting in poor formability when obtaining a heat-shrinkable film from the copolymer, and the resulting film will also have poor heat resistance. This is not preferable because it deteriorates the properties and mechanical strength.

The degree of polymerization of the polyester copolymer used in the present invention is not particularly limited; ) is 0.40 to 1.2
0 is preferred.

Such a polyester resin is dried and melted by a conventionally known method, melt-extruded from a goo, and then made into a raw fabric by a casting method, a calendering method, or the like. Furthermore, in order to efficiently produce the heat-shrinkable polyester film of the present invention, this raw fabric must be heated near the glass transition temperature, and in order to stably obtain a film that exhibits particularly high shrinkage, it must be heated to a temperature of Tg + 10°C or higher and Tg + 20°C or lower. 2 to 5 times in one direction, preferably 3 times
Stretch it 2 to 4 times. From the perspective of uniaxial shrinkability (dimensional stability in other axes) of the heat-shrinkable film, it is preferable to stretch only the − axis, but there may be insufficient strength in the direction perpendicular to the stretching axis or a decrease in tear strength in the stretching direction. For the purpose of solving the above problems, stretching can be performed by less than twice in the direction perpendicular to the stretching direction.

Furthermore, although the stretched heat-shrinkable film can be used as a product as it is, it can also be used after being heat-treated from the viewpoint of dimensional stability. The heat treatment is at 50℃
It is carried out for several seconds to several tens of seconds at a temperature of ~150°C. By performing such a heat treatment, desirable properties such as adjustment of the shrinkage rate in the shrinkage direction of the polyester film of the present invention, reduction of shrinkage over time during storage of an unshrinked film, and reduction of shrinkage spots can be exhibited.

Although the thickness of the heat-shrinkable film of the present invention is not particularly limited, a thickness in the range of 1 to 600 μm is practically used. For packaging purposes, particularly for packaging foods, beverages, pharmaceuticals, etc., those in the range of 6 to 380 μm are used. Moreover, when used for labels of PET bottles, glass bottles, etc., those having a diameter in the range of 20 to 70 μm are used.

In order to further impart specific performance to the present invention, conventionally known processing and appropriate additives can be incorporated. Examples of processing include irradiation with ultraviolet rays, α rays, β rays, γ rays, or electron beams, treatments such as corona treatment, plasma irradiation treatment, flame treatment, and coating of resins such as vinylidene chloride, polyvinyl alcohol, polyamide, and polyolefin. , lamination, or metal vapor deposition. Examples of additives include resins such as polyamide, polyolefin, polymethyl methacrylate, and polycarbonate, inorganic particles such as silica, talc, kaolin, and calcium carbonate, pigments such as titanium oxide and carbon black, ultraviolet absorbers, mold release agents, Examples include flame retardants.

[Example code] Hereinafter, the present invention will be specifically explained with reference to Examples.

The heat shrinkage rate is determined by cutting out a sample film in a width of 10 mm parallel to the shrinkage rate measurement direction, and cutting out a sample film with a width of 10 mm perpendicular to the direction.
A marked line was drawn at 00 mm, and the sample was immersed in a glycerin bath kept at a constant temperature for 30 seconds, and then the distance between the marked lines was determined.

In addition, the mechanical strength is the breaking stress when a piece of 10m width is cut out parallel to the shrinking direction and stretched to a sample length of 10m using a tensilon manufactured by Orientic Co., Ltd. (J
r SC-2318 compliant).

Examples 1 to 3 and Comparative Examples 1 to 5 A polyester copolymer containing methyl terephthalate, ethylene glycol, neopentylglyfur, and diethyleglycol in the proportions shown in Table 1 was heated to 60°C under vacuum and stirred. Drying was performed for 40 hours.

Thereafter, it was put into a 40 m/mφ extruder together with 300 p p m of calcium stearate and melted.
Extrusion through a T-die set at ~285°C, then 40°C
It was cooled with a casting roller kept at ℃ to obtain an unstretched original fabric. This original fabric was heated at 75°C (85°C only in Comparative Example 1).
horizontally (perpendicular to the machine axis,
The film was stretched 3.5 times in the TD direction (hereinafter abbreviated as TD direction). Table 1 shows the measurement results of the thermal shrinkage rate in the TD direction and the mechanical axis direction (hereinafter referred to as MD direction) and the mechanical strength in the TD direction.

The films of Examples 1 to 3 of the present invention exhibit practically sufficient heat shrinkability. In contrast, the polyethylene terephthalate film (Comparative Example 1) did not exhibit sufficient heat shrinkage. Furthermore, in Comparative Example 2, in which the content of diethylene glycol was outside the range of the present invention, the shrinkability at low temperatures was poor, and in Comparative Example 3, it became impossible to mold.

In Comparative Example 4, in which the content of neopentyl glycol was outside the range of the present invention, the shrinkage rate was small, and in Comparative Example 5, molding was impossible.

[Effects of the Invention] The heat-shrinkable film of the present invention maintains the mechanical properties, transparency, chemical resistance, and heat resistance inherent to polyethylene terephthalate, and has heat-shrinkability in a specific direction at low temperatures. Can be used in a wide range of fields such as shrink wrapping and bundling. It is particularly useful when used as a label for PET bottles because it can be incinerated together with the PET bottles.

Claims (1)

[Claims] The polyester film contains a dicarboxylic acid component (A) consisting of terephthalic acid or its derivative (a) component, 50 to 90 mol% of ethylene glycol (c) component, 5 to 50 mol% of neopentyl glycol (d) component, diethylene glycol, triethylene A film formed from a polyester copolymer consisting of a diol component (B) consisting of 3 to 20 mol% of at least one component (e) selected from glycol and polyethylene glycol, and when heated for 30 seconds in a glycerin bath. The shrinkage rate in one direction is at bath temperature 7
20% or more at 0℃, 30% or more at 80℃, 40% at 90℃
% or more, and 0 in the direction perpendicular to the direction of contraction.
1. A heat-shrinkable polyester film characterized in that it is less than 10% in the range of ~100°C.