JP2014133332A - Polybutylene terephthalate-based film for twist packaging - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a film for twist packaging excellent in transparency and glossiness, good in appearance, and having dead holding property and twist holding property.SOLUTION: Either an unstretched raw film made from a polybutylene terephthalate resin or a polyester-based resin composition obtained by blending a polyethylene terephthalate resin of 30 wt.% or less with respect to a polybutylene terephthalate resin, the unstretched raw film being formed at a high cooling rate of 200°C/sec or more, or a film obtained by biaxial drawing of the unstretched raw film under specified conditions, is used as a film for twist packaging.

Description

The present invention relates to an unstretched or biaxially stretched polybutylene terephthalate (hereinafter referred to as PBT) film for twist packaging. More specifically, the present invention relates to a polybutylene terephthalate film for twist packaging which has sufficient dead holding properties and twist retention properties, which are important characteristics in twist packaging, and is excellent in transparency and gloss.

Twist packaging is often used for individual packaging of confectionery and the like, and refers to a method of packaging contents by twisting one or both ends of a film. Conventionally, cellophane has been used for such twist packaging. Since cellophane is excellent in transparency, easy cutting property and twisting property, but has poor moisture resistance, there has been a problem in that physical property values vary with changes in humidity. Therefore, in recent years, a polyester film excellent in moisture resistance has been used. However, a stretched polyester film excellent in heat resistance, water resistance and transparency is too strong, so that it has a low dead holding property and a twist holding property and is difficult to use for the same purpose.

As a method for solving these drawbacks, it has been proposed to use polybutylene terephthalate as the polyester. In Patent Document 1, on at least one surface of the polyester resin layer (A), 30 to 75% by weight of polyethylene terephthalate, 5 to 30% by weight of polybutylene terephthalate, a glass transition temperature of 35 ° C. or higher, and an amorphous polyester, Or the laminated polyester film of the polyester resin layer (B) which consists of 20-40 weight% of copolyester is proposed. Patent Document 2 proposes a polyester film in which a mixing ratio of a polyester mainly composed of a polyethylene terephthalate component and a polyester mainly composed of a polybutylene terephthalate component is 100: 0 to 50:50. In either case, the film is formed by a method of casting onto a cooling drum after extrusion from the die. In this method, when the blending ratio of polybutylene terephthalate in the polyester is increased, it is difficult to perform stable film formation and stretching, such as cracking after cooling. Therefore, it is necessary to keep the blending ratio of polybutylene terephthalate low. However, a polyester film having a polybutylene terephthalate blending ratio of 40% or less in the polyester resin has insufficient dead holding property and twist holding property, and further improvement of these properties has been demanded.

In Patent Document 3 and Patent Document 4, polybutylene terephthalate is used as a main raw material of a polyester film excellent in dead holding property and twist holding property. In Patent Document 3, polybutylene terephthalate is extruded by itself, cooled by a cast method, and unstretched or stretched by 1.7 times to produce a film. The film thus obtained has a dead holding property and a twist. Although it has excellent retainability, the transparency is extremely low. In Patent Document 4, the film is formed by an inflation method, but when the blending ratio of polybutylene terephthalate exceeds 65%, the haze value increases and the transparency is also lowered. That is, in the production of a twist packaging film, it has been difficult to satisfy all of the film forming stability, dead holding property, twist holding property, transparency and glossiness in both the casting method and the inflation method.

JP 2004-181653 A JP 2007-69524 A JP 2004-18023 A JP 2006-187886 A

As described above, cellophane, polyethylene terephthalate film, and the like are generally used for the twist packaging film. However, cellophane has excellent weakness such as transparency, twisting property, and dead holding property, but poor moisture resistance. On the other hand, the polyethylene terephthalate film is excellent in moisture resistance, heat resistance, water resistance and transparency, but has a drawback of poor dead holding property and twist retention. In addition, the film mainly composed of polybutylene terephthalate is excellent in twisting property, dead holding property, moisture resistance and water resistance, but it is difficult to form and stretch stably, and the obtained film is transparent and glossy. There was a problem of appearance and insufficient appearance.
In view of the above, an object of the present invention is to obtain a polybutylene terephthalate film for twist packaging that has excellent transparency and glossiness, good appearance, and has dead holding properties and twist retention properties.

The inventors of the present invention are stable by forming a polybutylene terephthalate resin or a polyester resin composition in which polyethylene terephthalate resin is blended in a range of 30% by weight or less with respect to polybutylene terephthalate resin under predetermined conditions. Unstretched or biaxially stretched polybutylene terephthalate film, and the film is found to be excellent in dead holding property, twist holding property, transparency and glossiness required for a twist packaging film, The invention has been completed.

That is, the present invention provides the following items and means.
[1] At least a polybutylene terephthalate resin or a polyester resin composition in which a polyethylene terephthalate resin is blended in an amount of 30% by weight or less with respect to a polybutylene terephthalate resin, and the haze measured according to JIS-K7105 An unstretched or biaxially stretched polybutylene terephthalate film for twist packaging, characterized by having a value of 5.0% or less and a gloss value of 120% or more.
[2] Immediately after melt extrusion of the resin, the film is formed as an unstretched raw film obtained by quenching at a cooling rate of 200 ° C./second or more, or the original film is longitudinally and laterally 2.0-4. The unstretched or stretched polybutylene terephthalate film for twist packaging according to claim 1, wherein the film is obtained by simultaneous biaxial stretching of 0 times.
[3] The film according to claim 1 or 2, wherein a deposited layer made of an inorganic oxide and / or a coating layer made of a barrier resin is provided on at least one surface of the film. Unstretched or twisted polybutylene terephthalate film for twist packaging.
[4] The unstretched or stretched polybutylene terephthalate film for twist packaging according to any one of claims 1 to 3, wherein a printed layer is provided on at least one surface of the film.

The polybutylene terephthalate film of the present invention is excellent in dead holding property, twist retention, moisture resistance, water resistance, transparency and gloss, and is suitable for twist packaging films. In addition, such a polybutylene terephthalate film for twist packaging can be obtained by stable film formation.

The best mode for carrying out the present invention will be described below.
(Raw material of PBT film) The main raw material used for the PBT film is not particularly limited as long as it is a polyester having butylene terephthalate as a main repeating unit, but specifically, 1,4- as a glycol component. A homotype mainly composed of butanediol and terephthalic acid as a dibasic acid component is preferred. In order to impart optimum mechanical strength characteristics, among polybutylene terephthalate resins, those having a melting point of 200 to 250 ° C. and an IV value of 1.10 to 1.35 dl / g are preferable. Those having a range of 215 to 225 ° C. and an IV value of 1.15 to 1.30 dl / g are particularly preferable.

Further, in the polybutylene terephthalate resin of the present invention, a polyethylene terephthalate resin can be appropriately blended within a range of 30% by weight or less with respect to the polybutylene terephthalate. By blending the polyethylene terephthalate resin, the polybutylene terephthalate resin can be blended. It is possible to moderately suppress the crystallization of the film, and the stretch workability is remarkably improved. The polyethylene terephthalate resin to be blended is not particularly limited as long as it is a polyester having ethylene terephthalate as a main repeating unit, but specifically, ethylene glycol as a glycol component and terephthalic acid as a dibasic acid component as main components. The homotype is particularly preferred. In order to impart optimum mechanical strength characteristics, among the polyethylene terephthalate resins, those having a melting point of 240 to 265 ° C. and an IV value of 0.55 to 0.90 dl / g are preferable, and a melting point of 245 to 260 is preferable. Particularly preferred are those having a IV value of 0.60 to 0.80 dl / g. When blending more than 30% by weight of polyethylene terephthalate resin, the rigidity of the stretched film or unstretched original fabric becomes too high, and as a result, the stretch failure due to the decrease in pressure strength, impact strength, piercing strength and the original fabric cracking occurs. It is not preferable because it occurs. If necessary, additives such as lubricants, anti-blocking agents, inorganic extenders, antioxidants, UV absorbers, antistatic agents, flame retardants, plasticizers, colorants, crystallization inhibitors, crystallization accelerators, etc. Can be added. In addition, the polyester resin pellets used are preliminarily dried so that the moisture content is 0.05 wt% or less, preferably 0.01 wt% or less before heating and melting in order to avoid a decrease in viscosity due to hydrolysis during heating and melting. Furthermore, it is preferable to use it.

(Method for producing polybutylene terephthalate-based unstretched original fabric) In order to stably produce a stretched PBT (hereinafter, OPBT) -based film, it is necessary to suppress crystallization of the unstretched unstretched raw fabric before stretching as much as possible. When the polybutylene terephthalate melt is cooled to form a film, the crystallization temperature region of the polymer is cooled at a certain rate or more, that is, the raw fabric cooling rate is an important factor. The raw fabric cooling rate is 200 ° C./second or more, preferably 250 ° C./second or more, particularly preferably 350 ° C./second or more, and the unstretched raw film formed at a high cooling rate maintains an extremely low crystalline state. Therefore, it is excellent in transparency and gloss, and the stability of the bubble at the time of stretching is dramatically improved. Furthermore, since the film can be formed at a high speed, productivity is also improved. When the cooling rate is less than 200 ° C./second, the crystallinity of the obtained unstretched raw material becomes high, and not only the transparency and gloss are remarkably lowered, but in an extreme case, the stretched bubble bursts and stretches. May not continue.

The raw film forming method is not particularly limited as long as it satisfies the original film cooling rate, but the internal / external direct water cooling method is most suitable in terms of rapid cooling film forming. The outline of the raw film forming method by the internal / external direct water cooling method will be described below. First, polybutylene terephthalate resin is melt-kneaded by an extruder set at a temperature of 210 to 280 ° C. In the case of T-die film formation, the sheet-like molten resin is immersed in a water tank to be directly water-cooled both inside and outside. . On the other hand, in the case of annular film formation, the molten tubular thin film is formed by being extruded downward from an annular die attached downward to the extruder.

Next, it is led to a cooling mandrel connected to the annular die, and the cooling water introduced from each nozzle of the cooling mandrel is brought into direct contact with the inside of the molten tubular thin film to be cooled. At the same time, cooling water flows from the external cooling tank used in combination with the cooling mandrel, and the cooling water directly contacts the outside of the molten tubular thin film to be cooled. The temperature of the internal water and the external water is preferably 30 ° C. or less, and particularly preferably 20 ° C. or less from the viewpoint of rapid cooling film formation. When the temperature is higher than 30 ° C., whitening of the raw material or poor appearance of the original material due to boiling of cooling water is caused, and stretching becomes gradually difficult. The obtained unstretched polybutylene terephthalate film has a thickness of 30 to 200 μm and can be used as it is after the heat treatment. However, it is preferably biaxially stretched from the viewpoints of thinning, strength properties, and thermal stability.

(Manufacturing method of OPBT-based film) The polybutylene terephthalate-based unstretched raw fabric needs to be transported to a stretching zone while maintaining an atmospheric temperature of 25 ° C. or lower, preferably 20 ° C. or lower. Regardless, the crystallinity of the unstretched original fabric immediately after film formation can be maintained. Control of crystallization up to the starting point of stretching can be said to be an important point for stably performing biaxial stretching of the polybutylene terephthalate resin together with the film forming technique of the unstretched raw fabric.

The biaxial stretching method includes a sequential biaxial stretching method and a simultaneous biaxial stretching method, and examples of the simultaneous biaxial stretching method include a tubular method and a tenter method. Is particularly preferred. FIG. 1 is a schematic view of a tubular method simultaneous biaxial stretching apparatus. The unstretched original fabric 1 guided to the stretching zone is inserted between a pair of low-speed nip rolls 2 and then heated with a stretching heater 3 while air is being pressed into it. By blowing air more, MD by the tubular method and TD simultaneous biaxially stretched film 7 were obtained. The stretching ratio is preferably in the range of 2.0 to 4.0 times for each of MD and TD in consideration of stretching stability and strength physical properties, transparency, and thickness uniformity of the obtained OPBT film. When the draw ratio is less than 2.0 times, the drawing is not preferable because the drawing is not stabilized. On the other hand, if it is more than 4.0 times, the twist characteristic is remarkably lowered. The stretching temperature is preferably in the range of 40 to 80 ° C, particularly preferably 45 to 65 ° C. Since the unstretched original fabric manufactured at the high cooling rate has low crystallinity, it can be stably stretched at a relatively low stretching temperature. In high-temperature stretching exceeding 80 ° C., stretching bubbles are vigorously shaken and large stretching unevenness occurs, and a film having good thickness accuracy cannot be obtained. On the other hand, when the stretching temperature is less than 40 ° C., excessive stretch-oriented crystallization occurs due to low-temperature stretching, leading to whitening of the film and the like. By performing biaxial stretching in this manner, it is possible to obtain an OPBT-based film with particularly improved strength properties and low anisotropy.

The obtained OPBT film is put into a heat roll system or a tenter system, or a heat treatment facility combining them for an arbitrary time, and heat treatment is performed at 180 to 220 ° C., particularly preferably 190 to 210 ° C. An OPBT film excellent in properties can be obtained. When the heat treatment temperature is higher than 220 ° C., the bowing phenomenon becomes too large and the anisotropy in the width direction increases, or the crystallinity becomes too high, resulting in a decrease in strength properties. On the other hand, when the heat treatment temperature is lower than 180 ° C., the thermal dimensional stability of the film is greatly reduced, which causes a practical problem.

The thickness of the OPBT film is not particularly limited, but is 10 to 80 μm, preferably 15 to 25 μm when used as a twist packaging material.

The OPBT film produced by the above method has a high haze value of 5.0 or less measured according to JIS-K7105, a gloss value of 120% or more, and an excellent design.

A vapor deposition film made of an inorganic oxide can be provided on one surface of the unstretched or biaxially stretched polybutylene terephthalate film of the present invention. The inorganic oxide is formed by a method of providing a vapor deposition film made of any one of inorganic oxides such as aluminum oxide, silicon oxide, titanium oxide, tin oxide, zinc oxide, magnesium oxide, and calcium oxide, aluminum, or a mixture thereof. I can do it. Note that aluminum oxide or silicon oxide is preferably used as the deposited film. The deposition film can be formed by physical vapor deposition such as vacuum deposition, sputtering or ion plating, or chemical such as plasma chemical vapor deposition, thermal chemical vapor deposition, or photochemical vapor deposition. Although vapor phase epitaxy can be used, vacuum vapor deposition is particularly preferably used in terms of productivity and cost. A method of providing a barrier property by providing a coating layer made of a barrier resin such as polyvinylidene chloride (hereinafter referred to as K coat) on at least one surface of an unstretched or biaxially stretched polybutylene terephthalate film is also preferable.

The twist wrapping material including the unstretched and biaxially stretched polybutylene terephthalate film of the present invention can be used after printing on the film surface by a known printing method such as gravure printing, flexographic printing, or offset printing.

The present invention will be specifically described below with reference to examples and comparative examples.
<Example 1> (Production of OPBT film)
Polybutylene terephthalate resin pellets (homotype, melting point = 224 ° C., IV value = 1.26 dl / g) dried in a hot air dryer at 140 ° C. for 5 hours in an extruder, cylinder and die temperatures of 210 to 275 ° C. The molten tubular thin film was extruded downward from the annular die. Subsequently, after folding through the outer diameter of the cooling mandrel with a calapsa roll, the film was drawn with a take-up nip roll at a speed of 1.2 m / min. The temperature of the cooling water in direct contact with the molten tubular thin film was 20 ° C. on both the inner side and the outer side, and the raw fabric cooling rate was 416 ° C./second. The folding diameter of the unstretched raw fabric was 143 mm, and 1000 ppm of magnesium stearate was previously added as a lubricant to the polybutylene terephthalate resin. The unstretched original fabric 1 formed into a film on the above conditions was conveyed to the low-speed nip roll 2 in 20 degreeC atmosphere, and the vertical and horizontal simultaneous biaxial stretching was performed with the tubular simultaneous biaxial stretching apparatus of the structure shown in FIG. The draw ratio was 2.0 times MD and 2.0 times TD, and the draw temperature was 60 ° C. Next, this biaxially stretched film 7 was put into a heat roll type and tenter type heat treatment facility, respectively, and heat treated at 210 ° C. to obtain a biaxially stretched polybutylene terephthalate film. The biaxially stretched polybutylene terephthalate film had a thickness of 15 μm.

(Measuring method of raw fabric cooling rate) The raw fabric cooling rate was calculated by the following formula. The molten thin film and the raw fabric temperature were measured with a contact-type radiation thermometer. The cooling start point is the part where the molten thin film comes into contact with the cooling water or the cooling device, and the cooling end point is the part where the temperature of the unstretched original fabric reaches 30 ° C.
Raw fabric cooling rate (° C./sec)=(molten film temperature immediately before the cooling start point−raw temperature of cooling end point) (° C.) / (Distance between cooling start point to cooling end point) (m) × cooling start point ~ Raw material passage speed between cooling end points (m / sec)

(Evaluation method of haze value and gloss value of OPBT film) The haze value and gloss value of the OPBT film were measured according to JISK7105. The data is shown in Table 1.

(Evaluation method of dead holding property) The OPBT film was cut into a 16 cm × 16 cm square film, bent in half so that the crease was clear around the diagonal line, and allowed to stand in an environment of 23 ° C. and 50% RH for 24 hours. . The dead-holding property is evaluated by the opening angle of the bent portion, the average value of six tests is calculated, and evaluated according to the following criteria. The results are shown in Table 1.
◎: Dead holding property (opening angle) less than 16 degrees ○: Dead holding property 16 degrees or more and less than 20 degrees ×: Dead holding property 20 degrees or more

(Evaluation method of twist retention)
Cut the OPBT film into a 16cm x 16cm square film, place an iron ball with a diameter of 2cm in the center, wrap it and twist both sides of the iron ball in the opposite direction 1.5 times (540 degrees), 23 ° C, 50 It was left for 24 hours in an environment of% RH. Then, the angle (twist retention) held in a state where the iron ball was twisted on both sides was measured. The average value of five tests was calculated and evaluated according to the following criteria, and the results are shown in Table 1.
◎: Twist retention (holding angle) 450 degrees or more ○: Twist retainability 300 degrees or more, less than 450 degrees ×: Twist retainability less than 300 degrees

<Examples 2-5, Example 7, Comparative Examples 2-3> In Example 1, except that the amount of polyethylene terephthalate resin added to the polybutylene terephthalate resin and / or the draw ratio were changed to the conditions described in Table 1. The same operation as in Example 1 was performed.

<Example 6, comparative example 1> In Example 1, it carried out like Example 1 except having changed the original fabric cooling rate into the conditions described in Table 1.

<Example 8> In Example 1, it carried out like Example 1 except being an unstretched film.
<Example 9> In Example 1, it carried out similarly to Example 1 except having provided the vapor deposition layer in the obtained film.

As shown in Table 1, a film mainly composed of polybutylene terephthalate is suitably used for a twist packaging material having a high level of transparency and gloss that have not been conventionally used, and having a dead holding property and a twist retaining property. I understood that I could do it.

The twist wrapping material including the unstretched or biaxially stretched polybutylene terephthalate film of the present invention has high transparency and gloss, and is excellent in moisture resistance, water resistance, dead holding property, and twist retention. Therefore, it can be suitably used for twist packaging applications such as snacks and sake snacks.

It is the schematic of a tubular simultaneous biaxial stretching apparatus.

DESCRIPTION OF SYMBOLS 1 Unstretched raw fabric 2 Low speed nip roll 3 Stretching heater 4 Cooling shoulder air ring 5 Carapsa roll 6 High speed nip roll 7 Biaxially stretched film

Claims (4)

It consists of at least either a polybutylene terephthalate resin or a polyester-based resin composition in which a polyethylene terephthalate resin is blended in an amount of 30% by weight or less with respect to a polybutylene terephthalate resin, and a haze value measured according to JIS-K7105 is 5 An unstretched or biaxially stretched polybutylene terephthalate film for twist packaging, characterized by having a gloss value of 0.0% or less and a gloss value of 120% or more. Immediately after melt extrusion of the resin, the film is rapidly stretched at a cooling rate of 200 ° C./second or more to obtain an unstretched original fabric, or the original fabric is longitudinally and laterally 2.0 to 4.0 times simultaneously. 2. The unstretched or stretched polybutylene terephthalate film for twist packaging according to claim 1, wherein the film is obtained by biaxial stretching. The twist packaging according to claim 1 or 2, wherein a deposited layer made of an inorganic oxide and / or a coating layer made of a barrier resin is provided on at least one surface of the film. Unstretched or stretched polybutylene terephthalate film. The unstretched or stretched polybutylene terephthalate film for twist packaging according to claim 1, wherein a printed layer is provided on at least one surface of the film.

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