JPH03290441A - Thermo-shrinkable polyester film - Google Patents

Abstract

PURPOSE:To obtain a thermo-shrinkable polyester film having excellent shrinkage in heating, finish after shrinking, heat resistance and strength, etc., by forming a specific polyester copolymer to a film. CONSTITUTION:A polyester copolymer composed of (A) a dicarboxylic acid component mainly composed of terephthalic acid (derivative) and (B) diol components composed of B1: 60-95mol% ethylene glycol, B2: 2-20mol% diol expressed by the formula (n and m are integer more than 0, with a proviso that n+m>=1) and B3: 3-20mol% at least a species selected from diethylene glycol, triethylene glycol, polyethylene glycol and >=3C saturated aliphatic diol is subjected to film formation to afford the aimed thermo-shrinkable polyester film. Said film has a shrinkage by heating in a glycerin bath for 30sec in at least a direction: >=20% at 70 deg.C bath temperature, >=30% at 80 deg.C and >=40% at 90 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a heat-shrinkable polyester film that has good shrinkability during heating, good finish after shrinkage, heat resistance, strength, etc.

[Prior art and problems to be solved by the invention] Heat-shrinkable films are used for marking, protecting, bundling, and increasing the added value of products such as containers, fishing rods, condensers, and bar-shaped fluorescent lamps, as well as for books, notebooks, etc. It has been used for integrated packaging or close-contact packaging. Currently, there are expectations for applications that utilize the shrinkability and shrinkage stress of this heat-shrinkable film 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.

In addition, excessive quality control is required to obtain a heat-shrinkable film free of fission, 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.

-4 Although the heat-shrinkable film obtained from polystyrene has a good finish after shrinkage, it has low solvent resistance, so special ink must be used when printing, and spontaneous shrinkage occurs even at room temperature. There were problems such as the need to store it in a cool place.

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.

Therefore, in order to solve the above problems, isophtha)Lt acid, 1. A method of producing a film using a polyethylene terephthalate copolymer obtained by using 4-cyclohexane dimetatool, neopentyl glycol, 2,6-naphthalene dicarboxylic acid, etc. as a copolymerization component has been proposed.

However, although the film obtained from the above copolymer has more free heat shrinkage characteristics than the film obtained from polyethylene terephthalate, it has higher shrinkage stress and shrinkage speed, so it may suffer from shrinkage unevenness such as wrinkles during shrinkage. There were problems in that defects occurred and the product value significantly decreased.

[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, the present invention provides that the polyester film contains a dicarboxylic acid component (A) consisting of terephthalic acid or its derivative (a) component, 60 to 95 mol% of an ethylene glycol (b) component, and a diol (C) component represented by the formula <r>. 2-20
mol% and a diol component (B) consisting of 3 to 20 mol% of at least one component (d) selected from diethylene glycol, triethylene glycol, polyethylene glycol, and saturated aliphatic diols having 3 or more carbon atoms. A film is formed from the coalescence, and the shrinkage rate when heated for 30 seconds in a glycerin bath is 20% or more at a bath temperature of 70'C, 30% or more at 80°C, and 40% or more at 90°C in at least one direction. This is a heat-shrinkable polyester film characterized by the following.

(CH2)ncH3 ■ HOCH2CCH2OH --- (I) Dicarboxylic acid component (A) consisting of phthalic acid or its derivative, 60 to 95 mol% of ethylene glycol (b) component, and diol (C) represented by the formula (I) 692 to 20 mol %, and at least one component selected from diethylene glycol, triethylene glycol, and polyethylene glycol (component (I)) and a diol component (B) consisting of 3 to 20 mol %.

(CH2)nCH3 HOCH2CCH2OH---(I) Dialkyl esters, diaryl esters, and the like.

Other dicarboxylic acids that can be used as a dicarboxylic acid component in a range of 10 mol% or less include glutaric acid,
Adipic acid, sebacic acid, oxalic acid, succinic acid, phthalic acid, isophthalic acid, naphthalene-1,4- or -2
, 6-dicarboxylic acid, diphenyl ether-4,4-dicarboxylic acid, and the like.

The diol (C) component represented by the above formula (I) is 2
-Methyl-2-ethyl-1,3-furopanediol, 2
-Methyl-2-propyl-1,3-propanediol and the like.

Examples of the saturated aliphatic diol having 3 or more carbon atoms used in the present invention include those having a linear structure such as 1,4-butanediol and 1゜6-benzenediol, but those having a branched structure may be mentioned. Anything is fine.

Examples of glycols that can be used as the diol component in an amount of 10 mol % or less include cyclohexane dimetatool, 2,2-bis(4-hydroxyphenyl)propane, and the like.

Component (C) is contained in the diol component in an amount of 2 to 20 mol%.゛ A film obtained from a polyester copolymer in which the (C) component is less than 2 mol % in the diol component does not exhibit sufficient shrinkage.Also, a polyester copolymer in which the (C) component is more than 20 mol % in the diol component Since the melting point or softening point of the copolymer is significantly lowered, the moldability of a heat-shrinkable film obtained from the copolymer becomes poor, and the resulting film also has poor heat resistance and mechanical strength, which is not preferred.

(Component (I) is contained in the dicarboxylic acid component in an amount of 3 to 20 mol%.A film obtained from a polyester copolymer containing component (d) in a proportion of less than 3 mol% in the dicarboxylic acid component has a small shrinkage rate at low temperatures; It is not preferred because it tends to cause shrinkage spots and has low impact resistance.

A polyester copolymer in which the component (d) exceeds 20 mol % in the dicarboxylic acid component has a significantly lower glass transition temperature and melting point or softening point, so the moldability when obtaining a heat-shrinkable film from the copolymer is poor. This is not preferable because the heat resistance and mechanical strength of the resulting film deteriorate.

The degree of polymerization of the polyester resin used for the polyester film in the present invention is not particularly limited, but the inherent viscosity (phenol/
Measured at 25° C. in a mixed solvent of equivalent weight of tetrachloroethane> is preferably 0.40 to 1.20.

Such a polyester resin is dried and melted by a conventionally known method, melt-extruded through a T-shaped or circular slit die, and then cooled on a roller, in cooling air, or in a coolant such as water to form a raw fabric. Furthermore, in order to efficiently produce the heat-shrinkable polyester film of the present invention, this raw fabric must be heated to around the glass transition temperature, and in order to stably obtain a film that exhibits especially high shrinkage, it must be heated to a temperature of Tg + 5°C or higher and Tg + 20°C or lower. It is stretched 2 to 5 times, preferably 3 to 4 times in one direction or in two axial directions.

Any conventionally known stretching method and apparatus can be selected. That is, uniaxial stretching such as roll stretching and tenter stretching, simultaneous biaxial stretching such as the so-called pantograph type tenter or inflation method can be used, and sequential multiaxial stretching can be performed by combining these as necessary. You can also do it. When it is desired to set the shrinkage rate of each axis individually, sequential stretching is preferable because it allows stretching conditions to be determined for each axis.

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.

The heat-shrinkable polyester film of the present invention can exhibit desired shrinkage characteristics in the same manner as conventional vinyl chloride resins by appropriately selecting the stretching method and stretching conditions as described above. For example, by stretching the film in two axial directions to form a so-called balance stretched film, it is possible to obtain a film that shrinks evenly in the length and width. Such a film can be used, for example, for simple packaging of products with complex shapes such as foods and molded objects, so-called shrink packaging.

On the other hand, uniaxially shrinkable films can be used for labels on glass bottles, PET bottles, etc. by taking advantage of their uniaxially shrinkable properties. - An axis-stretchable film can be obtained by stretching only pongee. Stretching of less than 2 times in the direction perpendicular to the direction can be carried out.

The heat shrinkage rate of the heat-shrinkable polyester film of the present invention is:
When heated for 30 seconds in a glycerin solution, at least one direction is 20% or more at 70°C, 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 blue part of the bottle. In that case, PET
In view of the heat resistance of the bottle, the shrinkage temperature of the film must be set low.

In addition, in the case of an axially shrinkable film, the shrinkage rate in the direction perpendicular to the shrinkage direction is preferably small from the viewpoint of dimensional stability and yield, but is less than 10% in the range of 0 to 100 ° C. Preferably it is less than 5%. That is, there should be no abnormal shrinkage of more than 10% in the temperature range.

Furthermore, it is preferable that the change in shrinkage rate of the heat-shrinkable polyester film of the present invention with respect to temperature change is small from the viewpoint of shrinkage spots. Therefore, at temperatures below 90°C, 5%/deg
raa or less, and more preferably 5%/degree at a temperature of 85° C. or less.

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

The heat shrinkage rate is determined by cutting a sample film parallel to the shrinkage rate measurement direction to a width of 1 m, and cutting the sample film at intervals of 1 m perpendicular to the direction.
A marked line was drawn using oom m, 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 10 mm wide piece is cut parallel to the shrinking direction and stretched to a sample length of 100 mm using Tensilon manufactured by Orientic Co., Ltd. (J
(based on ISC-2318).

Furthermore, in order to examine the finish of the film after shrinkage, such as wrinkles and uneven shrinkage, we cut out the film with marked lines parallel and perpendicular to the shrinkage direction with a width of 10 mm, and made it into a cylinder using special adhesive. Paste this into a PE
The finished product was attached to a T-bottle (I, 51) and heated for 15 seconds in an air oven at 90° C. to shrink, and the finish was visually evaluated as follows.

0 - Very good - No practical problems △ - Practical problems × - Totally bad Examples 1 to 4 and Comparative Examples 1 to 5 Methyl terephthalate 1, ethylene glycol (EG),
2-ethyl-2-butyl-1,3-propanediol (
A polyester copolymer containing EBPG), 1,4-butanediol (BG), and diethylene glycol (DEC) in the proportions shown in Table 1 was heated to 60°C under vacuum, stirred, and dried for 40 hours. Thereafter, it was put into a 40 m/mφ extruder together with aooppm of calcium stearate, melted, and extruded through a T-shaped die set at 220 to 285°C, and then cooled with a casting roller kept at 40°C to form an unstretched original fabric. And so. This original fabric was heated at 75℃ (
In a tenter heated to 85°C (only Comparative Example 1.2), it was
．． It was stretched 5 times to make a film. Table 1 shows the measurement results of the thermal shrinkage rate in the TD direction and the mechanical axis direction (hereinafter abbreviated 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, and have a good finish without unevenness caused by shrinkage. On the other hand, the polyethylene terephthalate film (Comparative Example 1) did not exhibit sufficient heat shrinkage and had a poor finish. Further, in Comparative Example 2, in which the content of component (c) was outside the range of the present invention, the shrinkage rate was small and the finish was poor, and Comparative Example 3 was unable to be molded.

(d) Comparative example 4 in which the content of the component is outside the range of the present invention
In Comparative Example 5, the shrinkability at low temperatures was poor, and in Comparative Example 5, molding was impossible.

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

Procedural amendment August 10, 1990 1. Indication of the case Japanese Patent Application No. 2-93671 2. Name of the invention Heat-shrinkable polyester film 3. Person making the amendment Relationship to the case Patent applicant Kyobashi, Chuo-ku, Tokyo 2-3-19 No. 5, Detailed Description of the Invention column 6 of the specification to be amended, content of the amendment (I) Second line from the bottom of page 6 of the middle part of the specification: "As other dicarboxylic acids," The statement should be corrected to read, ``As for other dicarboxylic acids or derivatives thereof.''

(2) In the middle part of the specification, page 7, line 3, the phrase "includes dicarboxylic acids, etc." is corrected to "includes dicarboxylic acids, etc. and their lower alkyl esters."

(3) In lines 4 and 5 of page 12 of the Middle East specification, r
Correct the text ``1O%'' to ``20%.''

(4) In the middle part of the specification, page 14, line 18, "methyl terephthalate" is corrected to "dimethyl terephthalate."

Claims (1)

[Scope of Claims] The polyester film comprises a dicarboxylic acid component (A) consisting of terephthalic acid or its derivative component (a), 60 to 95 mol% of an ethylene glycol (b) component, and a diol (c) represented by the formula (I). Component 2 to 20 mol% and at least one kind selected from diethylene glycol, triethylene glycol, polyethylene glycol, and saturated aliphatic diols having 3 or more carbon atoms (d) Component 3 to 20 mol%
A film is formed from a polyester copolymer consisting of a diol component (B) consisting of
The shrinkage rate when heated for seconds is at least 20% in at least one direction at a bath temperature of 70°C, 30% or more at 80°C, and 90°C
A heat-shrinkable polyester film characterized by having a polyester film of 40% or more. (CH2)nCH3 HOCH2CCH2OH---(I) (CH2)mCH3 (n, m are integers greater than or equal to 0, n+m≧1)