JPH0134528B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a polyester having excellent transparency and heat-sealing properties, which is produced by the tubular method from a copolyester consisting of terephthalic acid as an aromatic dicarboxylic acid component, ethylene glycol and 1,4-cyclohexanedimethanol as a diol component. The present invention relates to a shrink wrapping film and a method for producing the same. Conventionally known heat-shrinkable packaging films include polyvinyl chloride, polypropylene, and polyethylene. Of these, 100 are polyvinyl chloride heat shrinkable films.
It shows good shrinkability even at relatively low temperatures around ℃, but there are problems with hygiene due to the plasticizers, heat stabilizers, etc. that are added, and hydrogen chloride is generated when the film is incinerated after use. The following shortcomings have been pointed out. In addition, polypropylene heat-shrinkable film has been fully biaxially stretched and has good heat-shrinkability. The disadvantage is that the strength is not very high. On the other hand, heat-shrinkable films made of ethylene-based polymers such as polyethylene are widely used for shrink packaging because they are inexpensive and have high strength at the heat-sealed part, but they have low shrinkage stress. , poor heat resistance, and other properties are not necessarily satisfactory. In addition, homopolyester resins such as polyethylene terephthalate have excellent strength, rigidity, transparency, heat resistance, and oil resistance, and the stretched film is used for many purposes such as magnetic tape, but the temperature is usually slightly higher than room temperature. Since it crystallizes at high temperatures, it has poor impact resistance and poor heat sealability, so it is generally not suitable as a film for shrink wrapping. In order to improve these drawbacks, it is effective to copolymerize the polyester with various third components to suppress crystallization of the polyester and thereby improve impact resistance. The present inventors have developed a polyester with heat resistance by biaxially stretching a copolyester consisting of terephthalic acid as an aromatic dicarboxylic acid component and ethylene glycol and 1,4-cyclohexanedimethanol as a diol component under specific conditions. sex,
We have succeeded in providing a shrink packaging film that maintains advantages such as oil resistance, exhibits low-temperature heat shrinkability and large heat shrinkage stress, has excellent transparency, and has good heat sealability. That is, the present invention consists of (1) terephthalic acid as an aromatic dicarboxylic acid component, ethylene glycol and 1,4-cyclohexanedimethanol as a diol component, and 1,4-cyclohexanedimethanol is 10 to 40 mol% in the diol component. A polyester shrink wrapping film with excellent transparency and heat-sealing properties, which is mainly made of a certain copolyester, and the resin composition are melt-extruded from an annular die, and the cooled tubular unstretched film is heated to form the tubular body. 2 due to the pressure of the gas supplied inside and the speed difference of the Nipprol.
When performing axial stretching, the film surface temperature (T _f1 ) in the stretching zone is selected within the range of Tg-15≦T _f1 ≦Tg + 15 (Tg: secondary transition temperature by DTA), and the film is The surface temperature is set to 0.54T _f1 -6 < T _f2 <0.54T _f1 +15 (where T _f2 is the film surface temperature at a point 4.5 d (d is the diameter of the original film) from the end of stretching). Add 2 both vertically and horizontally
This is a method for producing a polyester shrink wrapping film, which is characterized by stretching the film by a factor of 6 to 6 times. The raw material copolyester resin used in the present invention contains a small amount of homopolymer produced as a by-product during the polymerization process, and may have a small amount of branching, but is basically a linear copolymer. be. However, as raw materials for heat-shrinkable packaging films, 1,
4-Cyclohexane dimethanol content is 10 to
It needs to be 40 mol%. If the content of 1,4-cyclohexanedimethanol in the diol component of the copolyester is more than 40 mol %, the viscosity of the resin will increase, causing problems in extrusion moldability, making it impractical. If the amount is less than 10 mol%, the impact resistance and heat sealability will decrease, making the film unsuitable for shrink packaging. If necessary, other resins, such as polyethylene terephthalate, may be mixed into this copolyester to the extent that the properties of the copolyester are not impaired. In addition, many methods have already been proposed as methods for biaxial stretching to give films latent heat shrinkability, but films with good heat shrinkability can be obtained by using the specific resin adopted in the present invention. In order to obtain this, a tubular unstretched film that has been cooled and solidified is sandwiched between two pairs of nip rolls positioned above and below, and while heated, the pressure of the gas supplied into the tubular film and the pressure of the two pairs of nip rolls are adjusted. Most desirable is a tube-like simultaneous biaxial stretching method in which the film is simultaneously biaxially stretched vertically and horizontally by adjusting the circumferential speed. In the so-called inflation method, in which the tube extruded from the die is blown up using gas pressure, an effective high degree of orientation does not occur because the film is blown up while it is still in a molten state. It is difficult to obtain a film that exhibits high shrinkage at extremely low temperatures. In addition, in the tenter type simultaneous biaxial stretching method, the thermal history during stretching is longer than in tubular methods such as the inflation method and the tube type simultaneous biaxial stretching method, so it is difficult to obtain a film with a high heat shrinkage rate. This is difficult, and due to the so-called bowing phenomenon, it is difficult to achieve vertical and horizontal balance. The method of the present invention performs simultaneous biaxial orientation by expansion stretching in a temperature range where an effective high degree of orientation occurs by applying a tube-shaped simultaneous biaxial stretching method, and achieves good low-temperature heat shrinkability, A transparent and heat-sealable film is produced from a specific copolyester. The raw material resin used in the present invention is non-crystalline, and has the property that its transparency and resistance to stretching deformation change relatively rapidly with temperature changes within a small range of temperatures within which it can be stretched. When an unstretched film whose crystallization has been suppressed with a crystalline resin such as linear homopolyester or polypropylene is simultaneously expanded and stretched, rapid crystallization occurs at the same time as molecular orientation in the initial stage of stretching, resulting in a rapid increase in Young's modulus of the film. amorphous materials, such as the resins used in the present invention, are In this case, even though molecular orientation occurs as the stretching progresses, crystallization does not occur, so the resistance to appropriately suppress the speed of stretching deformation is insufficient, and the stretching progresses too rapidly. It becomes difficult. the result,
Not only is the bubble during stretching unstable and easy to pop, but if one part of the bubble begins to expand even slightly more than the other parts and becomes thinner, that part will expand preferentially over other parts. As a result, the bubble shape becomes distorted, and the thickness unevenness of the film increases significantly, resulting in an extremely low commercial value. As a result of various studies to eliminate this drawback, we found that effective orientation and uniform and stable stretching cannot be achieved unless the temperature gradient of the film surface temperature in the stretching zone and the film surface temperature after the end point of stretching is set accurately. It was found that no progress was made. That is, if the surface temperature of the film in the stretching zone is too high, it not only tends to break, but also reduces the bubble internal pressure and therefore the stretching tension, reducing the effectiveness of stretching, and the strength and heat shrinkage rate of the stretched film. On the other hand, when the film surface temperature in the stretching zone is too low, the bubble internal pressure and thus the stretching tension become excessive, increasing the frequency of film breakage, that is, bubble puncture. Further, even if the film does not break, the film may become uneven in thickness, its transparency may deteriorate, and a whitening phenomenon may occur. That is, it has been found that the film surface temperature (T _f1 ) in the stretching zone can be appropriately selected within the range of Tg-15≦T _f1 ≦Tg+15 (Tg: second-order transition temperature by DTA). Similarly, in order to proceed smoothly with the stretching, the film surface temperature after the stretching end point should be set to 0.54T _f1 -6 < T _f2 < 0.54T _f1 +15 (T _f2 : 4.5 d (d) from the stretching end point). It was found that stretching can be carried out by applying a negative temperature gradient as shown by (the film diameter)) (the film surface temperature at the point where the film has advanced). That is, if the slope is insufficiently descended, the entire bubble will shake, increasing the unevenness in the thickness of the stretched film, and in severe cases will lead to punctures. Furthermore, if the temperature gradient is too high, the internal pressure of the bubble will increase, resulting in poor stability in the stretching zone, leading to melting and rupture of the bubble. By accurately adjusting the temperature conditions as described above, stable stretching became possible, and the obtained film had good transparency and thickness unevenness. In addition, the stretching ratio can be selected depending on the heat shrinkage rate required depending on the application, but in order to use it for ordinary heat-shrinkable film applications, it is preferable to stretch it to 2 times or more, and from the viewpoint of stretchability, It is preferable to stretch the film by a factor of 2 times or less because it can be stably stretched. The film biaxially stretched in this manner and taken out from the stretching device can be annealed if necessary. Since the film of the present invention has excellent impact resistance and transparency, it can be used for packaging heavy items, especially items that require aesthetic appearance, such as aerosol cans for pesticides, record jackets, books, cloth items, etc. suitable. Hereinafter, the present invention will be specifically explained based on Examples. The measurement items shown in the examples were determined by the following methods. 1. Heat shrinkage rate A film cut into a square of 10 cm in length and width was immersed in a glycerin bath at a predetermined temperature for 10 seconds, and calculated using the following formula. 10-A/10×100 However, A indicates the length of one side (unit: cm) after immersion. 2 Heat shrinkage stress Conforms to ASTM2838-69. 3 Haze Conforms to ASTM D1003-61T. 4 Melting seal strength Peeling strength of the sealed portion when heat-sealed with a normal melt sealer is shown in g/cm width. Fusing seal conditions: Voltage 110V, current 7A, pressure time 1 second 5 Impact strength According to ASTM D-256. 6 Film surface temperature Using a surface thermometer connected to a chromel-constantan type thermocouple (4.5Ω) with a thickness of approximately 1 mm in diameter and an exposed length of approximately 15 mm, touch the tip of the thermocouple to the film surface and read the indication after 30 seconds. The value was taken as the film surface temperature. If the radiant heat from the heat source is strong, cover the side of the thermocouple that does not touch the film with aluminum foil to avoid its effects. Example 1 Terephthalic acid as aromatic dicarboxylic acid component,
Ethylene glycol and 1, as diol components
Copolyester consisting of 4-cyclohexanedimethanol and containing 30 mol% of 1,4-cyclohexanedimethanol in the diol component (Tg: 81
) were melt-kneaded at 200 to 270°C and extruded downward through an annular die maintained at 255°C. The slit diameter of the annular die is 75mm and the slit gap is 0.8mm.
It is. The extruded tube-shaped film is slid on the outer surface of a cylindrical mandrel with an outer diameter of 66 mm and inside which circulates cooling water at 20°C, and the outside is cooled with water by passing through a water tank and brought to room temperature. A tube-shaped unstretched original fabric having a diameter of about 66 mm and a thickness of 135 μm was obtained. This unstretched original fabric was introduced into a biaxial stretching device and expanded and stretched. The film is heated to the stretching temperature by adjusting the voltage and current using multiple infrared heaters, and the film is cooled to the specified temperature after stretching, T _f2 , by an air flow directed toward the stretching zone from a place closer to the high-speed nip roll than the stretching zone. Then, pressurized air is sent into the tubular film between the low-speed and high-speed nip rolls (Fig. 1, 2 and 3), and by adjusting the air pressure and the circumferential speed ratio of the low-speed and low-speed nip rolls, the tubular biaxial film is tripled in length and three times in width. Stretched. Table 1 shows the results regarding stability, etc. during stretching. For stretching conditions No. 1 and No. 9, T _f1 is outside the scope of the present invention, and for stretching conditions No. 4 and 5, T _f2 is outside the scope of the present invention. The tubular stretched film that showed good stretchability is folded and taken out from the stretching machine, guided into a tube-shaped annealing device, heated with 80°C hot air from a tube-shaped heating cylinder, annealed for about 10 seconds, and then cooled. The tube was cooled to room temperature by cold air, then folded again, taken out, and rolled up. Example 2 Terephthalic acid as aromatic dicarboxylic acid component,
The diol component consists of ethylene glycol and 1,4-cyclohexanedimethanol,
A copolyester (Tg: 78°C) containing 15 mol % of 1,4-cyclohexanedimethanol in the diol component was simultaneously biaxially stretched in the same manner as in Example 1. The results regarding stability during stretching, etc. are also shown in Table 1. Stretching condition No.10 is T _f1 is No.11.
No. 14 has T _f2 outside the scope of the present invention. As the films of Examples 1 and 2 and Comparative Example 1,
Polyethylene terephthalate film simultaneously biaxially stretched into a tube shape by a conventional method, Comparative Example 2
Table 2 shows the physical properties of polypropylene film, which is commonly used as a shrink wrapping film.

【table】

[Table] Yes.
As can be seen from Table 2, it is clear that the heat-shrinkable copolyester of the present invention has superior transparency and impact resistance, as well as strong heat-sealing strength, compared to polyethylene terephthalate shrinkable films.
It can be seen that the physical properties as a shrink wrapping film, such as heat shrinkability and heat shrink stress, are superior to polypropylene shrink films. Example 3 Using the film of Example 1, the film of Example 2, and the films of Comparative Examples 1 and 2 shown in Table 2, a commercially available insecticide aerosol can with a diameter of 6 cm and a height of 18 cm was prepackaged. It was passed through a commercially available shrink tunnel for 8 seconds with hot air blowing at .degree. As shown in Table 3, the copolyester of the present invention adhered tightly despite the irregularities of the packaged shape, resulting in a wrinkle-free package. Due to the excellent transparency of the film, the printing and contents of the packaged product were clearly visible, giving it a beautiful appearance.

【table】 [Brief explanation of drawings]

FIG. 1 is an explanatory diagram of manufacturing conditions for the film of the present invention. The above description, 1... unstretched film, 2... low speed nip roll, 3... high speed nip roll, a...
...Stretching zone, b...Stretching end point, c...T _f2 measurement position, that is, a point 4.5d from b, d...Diameter of unstretched film.

Claims (1)

[Scope of Claims] 1 Consisting of terephthalic acid as an aromatic dicarboxylic acid component, ethylene glycol and 1,4-cyclohexanedimethanol as diol components,
And, the haze obtained by biaxially stretching a film mainly made of a copolyester containing 10 to 40 mol% of 1,4-cyclohexanedimethanol in the diol component, and a fusing seal strength of 400
A polyester heat-shrinkable packaging film having a width of at least g/cm and a heat shrinkage rate of at least 20% in each stretching direction at 100°C. 2 Consisting of terephthalic acid as an aromatic dicarboxylic acid component, ethylene glycol and 1,4-cyclohexanedimethanol as a diol component,
A composition mainly composed of a copolyester containing 10 to 40 mol% of 1,4-cyclohexanedimethanol in the diol component is melt-extruded from an annular die, and the cooled tubular unstretched film is placed inside the tubular body under heating. When biaxial stretching is performed using the pressure of the supplied gas and the speed difference of the Nippro roll, the film surface temperature (Tf1) in the stretching zone is set to
The film surface temperature after the end of stretching is 0.54Tf1-6<Tf2<0.54Tf1+15 (Tf2 is 4.5d from the end of stretching (d is the diameter of the original film).
1. A method for producing a polyester shrink wrapping film, which comprises stretching the film 2 to 6 times in length and width while applying a negative temperature gradient represented by (the film surface temperature at a point where the film has advanced).