JPH0450238A - Thermally shrinkable film - Google Patents

Abstract

PURPOSE:To prepare the subject film comprising a polyester resin having a specific glass transition temperature and another resin in a specified ratio, excellent in mechanical strength, heat resistance and transparence and useful for shrinkable labels, etc. CONSTITUTION:The objective film comprises (A) 100 pts.wt. of a polyester resin having a glass transition temperature (Tg1) of >=40 deg.C (e.g. polyethylene terephthalate copolymer) and (B) l-50 pts.wt., preferably 10-30 pts.wt., of a resin having a glass transition temperature (Tg2) satisfied with an equation I or II (e.g. polycarbonate, polybutylene terephthalate elastomer).

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Fields of Application] The present invention is designed to improve the shrinkage properties during heating and the finish after shrinkage without impairing the mechanical strength, heat resistance, transparency, and other properties unique to polyester films. This invention relates to a good heat-shrinkable film.

[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, it is expected that the shrinkability and shrinkage stress of this heat-shrinkable film will be used in many other fields.

Conventionally, resins such as polyvinyl chloride, polystyrene, and polyolefin have been used as materials for heat-shrinkable films. However, such resins 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, it is prone to frequent fish eyes, and products using printed films as packaging materials lose their aesthetic appearance and significantly reduce their commercial value. It's easy to become something like that. Also,
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 cost. Furthermore, if polyvinyl chloride is incinerated during disposal, it will cause pollution problems, and additives such as plasticizers in polyvinyl chloride resin will bleed out over time, attracting dust, etc., resulting in dirt and safety issues. This is also not desirable.

On the other hand, heat-shrinkable films obtained from polystyrene are
Although the finish after shrinkage is good, it has low solvent resistance, so special ink must be used when printing, and natural shrinkage occurs even at room temperature, so it must be stored in a cool place. There was a problem.

Polyester holds great promise as a material that can solve these problems. However, with conventional heat-shrinkable polyester films, it is not possible to sufficiently increase the heat shrinkage rate in the desired direction, or to reduce the heat shrinkage in the direction perpendicular to the above-mentioned direction, resulting in wrinkles in the film. However, there have been problems such as distortion of printing, uneven coloring, etc.

Therefore, an attempt was made to solve these problems by using a resin made by copolymerizing polyester with isophthalic acid, 1,6-cyclohexane dimetatool, neopentyl glycol, 2,6-naphthalene dicarboxylic acid, etc. It is being Although it has become possible to arbitrarily set the heat shrinkage rate of films made of such resins,
Due to the rapid increase in shrinkage rate and high shrinkage rate in an extremely narrow temperature range, it has the disadvantage of causing uneven shrinkage such as wrinkles, and can only be used in limited fields.

[Means for Solving the Problems] That is, the heat-shrinkable film of the present invention is made of polyester resin (A) 1 having a glass transition temperature (Tg1) of 40°C or higher.
00 parts by weight and 1 to 50 parts of resin (B) having a glass transition temperature (Tg*) satisfying formula (I) or formula (II).
It is characterized by consisting of parts by weight.

T g x≦'rgl 20 (I)T g
z≧T g 1+ 20 (II) In the present invention, the glass transition temperature is determined by differential scanning calorimetry using a sample obtained by heating a resin at a temperature higher than the glass transition temperature by 10°C or more for 5 minutes or more, then rapidly cooling it with dry ice, etc. The polyester resin (A) of the present invention preferably has a glass transition temperature (Tg1) of 40° C. or higher, as determined by measurement. This is because when the glass transition temperature is less than 40''C, mechanical strength and chemical resistance are low, and natural shrinkage during storage and whitening during stretching or processing are likely to occur.

In the present invention, at least one selected from terephthalic acid or its derivatives, isophthalic acid or its derivatives
A dicarboxylic acid component consisting of 80 to 100 mol% of a component consisting of seeds and 0 to 20 mol% of a component consisting of a saturated aliphatic dicarboxylic acid or its derivative, and an ethylene glycol component of 60 to 100 mol% and diethylene glycol, triethylene glycol, polyethylene. 0 to 20 mol% of a component consisting of at least one selected from glycol and saturated aliphatic diol and 0 to 20 mol% of a component represented by the following formula (III)
A polyester resin comprising a diol component of 20 mol% is preferred.

(CHI), CHl HOCH, OCH, OH (III) (CH,), CH.

(However, n and to are integers of 0 or more) As derivatives of terephthalic acid or isophthalic acid,
Examples include dialkyl esters and diaryl esters. Further, examples of the saturated aliphatic dicarboxylic acid include glutaric acid, adipic acid, sebacic acid, oxalic acid, and succinic acid.

Other dicarboxylic acids that can be used as a dicarboxylic acid component in a range of 10 mol% or less include naphthalene-1,4-
Alternatively, -2,6-dicarboxylic acid, diphenyl ether-4,4-dicarboxylic acid, etc. can be mentioned.

Saturated aliphatic diols include propylene glycol,
Examples include butylene glycol. Further, examples of the glycol component represented by the (In formula) include neopentyl glycol and the like.

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

In the present invention, the degree of polymerization of the polyester resin is not particularly limited, but from the moldability of the original film, the intrinsic viscosity (measured at 25°C in a mixed solution of equal weights of phenol/tetrachloroethane) is 0. 40 to 1.20 is preferred.

Moreover, as the resin (B) of the present invention, formula (I) or (
Those having a glass transition temperature (Tg2) that satisfies the formula II) are preferred. By mixing such a resin (B) and a polyester resin (A), a portion with a glass transition temperature T g + and a portion with a glass transition temperature Tg are mixed in the film,
It has become possible to give the film unique heat shrinkage properties. That is, the glass transition temperature (
When a resin (B) having a Tgz) is used, as the film is heated, the resin (B) first shrinks, but the film as a whole remains unchanged. When heated further, the polyester resin (A) starts to shrink and the entire film starts to shrink. At this time, since the resin (B) portion has already finished shrinking, it acts as a buffer material that alleviates the shrinkage behavior of the entire film. On the other hand, when using a resin (B) having a glass transition temperature (Tgs) that satisfies formula (II), as the film is heated, the polyester resin (A) first shrinks and the entire film shrinks; The portion of resin (B) present in the resin (B) is not easily deformed by heat, so the shrinkage behavior is gradual. In this way, in order for the resin (B) to act as a relaxation material that alleviates the shrinkage behavior during thermal contraction of the film, the Tsukaras transition temperature ("r g x
) is the glass transition temperature (Tg1) of the polyester resin (A)
) is required to have a difference of at least 20°C or more. Further, a resin that is uniformly dispersed in the film and forms a sea-island structure is preferable, and an amorphous resin that does not undergo thermal change at a temperature higher than the glass transition temperature is more preferable. Examples of such resin (B) include polycarbonate, polybutylene terephthalate elastomer nylon-12, and the like.

The resin (B) is preferably added in an amount of 1 to 50 parts by weight based on too many parts by weight of the polyester resin (A). More preferably, it is 10 to 30 parts by weight. If it is less than 1 part by weight, it will not be effective as a cushioning material, and if it exceeds 50 parts by weight, the excellent properties peculiar to polyester resin will be lost, and it will shrink below a certain temperature, or conversely, it will shrink at a certain temperature. This is because they don't do it.

Next, the method for producing a heat-shrinkable film of the present invention will be briefly described. First, the resin is dried and melted by a conventionally known method, melt-extruded through a T-shaped or circular slit die, and then placed on a roller 1. It is cooled in cooled air or in a refrigerant such as water to form the original fabric.

The obtained raw fabric is heated to a temperature near the glass transition temperature, which is 5 to 20 degrees Celsius higher than the glass transition temperature in order to stably obtain a film that exhibits particularly high shrinkage, and then heated to a temperature of 2 to 5 degrees Celsius in one or two axial directions. It is stretched by 3 times, preferably 3 to 4 times.

As the stretching method, uniaxial stretching such as roll stretching or tenter stretching, or simultaneous biaxial stretching such as pantograph tenter inflation method can be used. Further, if necessary, sequential multiaxial stretching can be performed by combining these. When setting the shrinkage rate for each axis, sequential stretching is preferable because the stretching conditions can be set for each axis. From the perspective of uniaxial shrinkability (dimensional stability in other axes) of the heat-shrinkable film, stretching only in the − axis is preferable, but it may result in insufficient strength in the direction perpendicular to the stretching direction or a decrease in tear strength in the stretching direction. For the purpose of solving the problem, it is also possible to carry out stretching less than twice in the direction perpendicular to the stretching direction.

The stretched heat-shrinkable film can be used as a product as is, but from the viewpoint of dimensional stability etc.
Heat treatment may be performed at a temperature of ~150°C for several seconds to several tens of seconds. By performing such heat treatment, desirable properties such as adjustment of the shrinkage rate during shrinkage of the 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 shrinkage rate of the heat-shrinkable film of the present invention is 2 when heated in glycerin for 30 seconds at 70°C in one direction.
0% or more, 30% or more at 80°C, and 40% or more at 90°C. The shrinkage rate of the heat-shrinkable film in one direction is often required to be at least 20%, although it depends on the intended use. For example, when a heat-shrinkable film is used as a label for a PET (polyethylene terephthalate) 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 rate in the direction perpendicular to the shrinkage direction is preferably smaller from the viewpoint of dimensional stability and yield, but in the range of 0 to 100°C
It is less than 0%, preferably less than 5%.

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 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, alpha rays, beta rays, gamma 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 inorganic particles such as silica, talc, kaolin, and calcium carbonate, pigments such as titanium oxide and carbon black, ultraviolet absorbers, mold release agents, and flame retardants.

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

The heat shrinkage rate can be determined by cutting a sample film to a width of 10 mm parallel to the shrinkage rate measuring direction, and cutting the sample film to a width of 10 mm perpendicular to the direction.
Marked lines were drawn at intervals, and the sample was immersed in a glycerin bath kept at a constant temperature for 30 seconds, and then the intervals between the marked lines were determined.

In addition, the mechanical strength is the breaking stress when a 10 mm wide piece is cut out parallel to the shrinking direction, and the sample is stretched to a length of 100+ inches using Tensilon manufactured by Orientic Co., Ltd. (
(based on JIS C-2318).

Furthermore, marked lines were drawn at 10 mm intervals in parallel and perpendicular directions to the shrinking direction of the film, and the film was pasted together in a cylindrical shape with the shrinking direction as the circumferential direction, and the film was attached to a 1.5 liter PET bottle. It was heated for 15 seconds in an air oven at 0.degree. C., and the finish after shrinkage was visually judged.

A polyester copolymer prepared by polymerizing 80 mol% of terephthalic acid, 13 mol% of isophthalic acid, 7 mol% of adipic acid and 100 mol% of ethylene glyfur was heated to 60°C under vacuum and stirred for 40 hours. Dry. On the other hand, polycarbonate resin (Valex 7025 manufactured by Mitsubishi Chemical Industries @
A) was heated to 120° C. under vacuum and dried with stirring for 3 hours. 100 parts by weight of the obtained polyester resin (glass transition temperature S 8.0°C) and 11 parts by weight of polycarbonate resin (glass transition temperature 148.5°C) were blended,
Calcium stearate 40Il with 3QOppm
/IIlφ extruder and melted, 220-285
It was extruded through a T-shaped die set at 40°C, and then cooled with a casting roller kept at 40°C to obtain an unstretched original fabric. This original fabric was moved in the transverse direction (direction perpendicular to the machine axis, hereinafter abbreviated as TD force direction) using a tenter heated to 75°C.
It was stretched 5 times to make a film. TD of the obtained film
The heat shrinkage rate in the force direction, the mechanical strength in the TD force direction, and the finished state after shrinkage were as shown in Table 1.

Actual m%+2 Contains 100 parts by weight of a polyester copolymer (glass transition temperature 73.3°C) obtained by polymerizing 90 mol% of terephthalic acid, 10 mol% of isophthalic acid and 100 mol% of ethylene glycol and 30 parts by weight of polyoxytetramethylene glycol. A film was prepared in the same manner as in Example 1 except that 25 parts by weight of polybutylene terephthalate elastomer (glass transition temperature 33.7°C) was blended and calcium stearate was not added.

Large 1 eye 11 Polyester copolymer made by polymerizing 100 mol% of terephthalic acid, 70 mol% of ethylene glycol, and 30 mol% of cyclohexane dimetatool (glass transition temperature 825°C)
100 parts by weight and nylon-12 (glass transition temperature 40.
A film was prepared in the same manner as in Example 1, except that 25 parts by weight (3°C) was added and calcium stearate was not added.

Comparative Example 1 A polyester resin obtained in the same manner as in Example was put into a 40 m/mφ extruder together with 300 ppm of calcium stearate and melted, extruded through a T-shaped die set at 220 to 285°C, and then kept at 40'C. The mixture was cooled using a casting roller to obtain an unstretched original fabric.

This original fabric was stretched 3.5 times in the transverse direction (direction perpendicular to the machine axis, hereinafter abbreviated as TD direction) using a tenter heated to 75°C to form a film.

TD of films obtained in Examples 1 to 3 and Comparative Example 1
The heat shrinkage rate in the force direction, the mechanical strength in the TD force direction, and the finished state after shrinkage were as shown in Table 1.

The films of Examples 1 to 3, which are the present invention, can be heated at temperatures of 70 to 80°C without impairing the mechanical properties specific to polyester resin.
It has a low heat shrinkage rate at a temperature of , and exhibits good heat shrinkage characteristics without rapid changes in shrinkage rate. Furthermore, the finish after shrinkage is also very good with no uneven shrinkage. On the other hand, the film shown in the comparative example has a high heat shrinkage rate at a temperature of 70 to 80°C, and a rapid change in shrinkage rate occurs, and the finished product after shrinkage also shows uneven shrinkage such as wrinkles. Ta.

[Effects of the Invention] In addition to the mechanical properties, transparency, chemical resistance, heat resistance, dimensional stability, etc. inherent to polyester, the heat-shrinkable film of the present invention alleviates shrinkage behavior and prevents sudden changes in shrinkage rate. It has excellent heat shrinkage properties and does not cause wrinkles or other uneven shrinkage in the film after shrinkage. Therefore, it can be used in a wide range of fields such as shrink labels, shrink wrapping, and bundling. In particular, when used as a label for a PET bottle, it is useful because it can be incinerated together with the PET bottle.

Claims (1)

[Claims] 100 parts by weight of a polyester resin (A) having a glass transition temperature (Tg_1) of 40°C or higher, and a compound of formula (I) or (
A heat-shrinkable film comprising 1 to 50 parts by weight of a resin (B) having a glass transition temperature (Tg_2) satisfying formula II). Tg_2≦Tg_1-20 (I) Tg_2≧Tg_1+20 (II)