JPH06114934A - Manufacture of thermally shrinkable polyester series film - Google Patents

Abstract

PURPOSE:To obtain a film having thermal shrinking characteristics of the same degree as that of a polyvinyl chloride series film having no shrinkage irregularity and excellent strength and shrinking characteristics by preheating a film made of polyethylene terephthalate series polymer and polyarylate resin, uniaxially orienting it, and thermally fixing it. CONSTITUTION:A polyester series resin composition having a glass transition temperature of 50-80 deg.C in which 20-60wt.% of polyarylate resin is mixed with polyethylene terephthalate series polymer is extrusion molded in a film state. Then, the film is preheated to a temperature range of the glass transition temperature to (glass transition temperature +20 deg.C). Thereafter, it is uniaxially oriented twice or more in a temperature range of (glass transition temperature +10 deg.C) to (crystallizing temperature -30 deg.C), further thermally fixed in a temperature range of further 45 deg.C or higher to less than the glass transition temperature, and subsequently cooled to the ambient temperature. Thus, a uniaxially oriented thermally shrinkable film having excellent tensile fracture elongation in a direction perpendicular to the elongating direction is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention displays the contents and distributors of food and drink such as cola, juice, beer and cup noodles, pharmaceuticals, miscellaneous goods, industrial materials, stationery, toys, tools and various other products. As a label or cap seal for packaging, to prevent foreign matter from entering, to prevent dry batteries from discharging, to prevent deterioration of products due to oxidation or moisture absorption, as a safety shield to prevent contamination during product display, or as a bundle for bundling The present invention relates to a method for producing a heat-shrinkable polyester film used as a material or the like.

[0002]

2. Description of the Related Art Recently, there has been a decrease in tropical rain forests, global warming due to carbon dioxide gas generated by burning materials, acid rain and forest destruction due to NO _x, etc. As a result of pollution problems such as the occurrence of cancer, the use of "earth-friendly" products has been required. For this reason, good printability and clean packaging are possible.Therefore, even in heat-shrinkable labels where polyvinyl chloride films have been used exclusively so far, there is a demand to switch to materials that do not contain chlorine compounds. As a result, polyester films such as polyethylene terephthalate (hereinafter referred to as PET) film having good transparency have been picked up and developed.

Since polyester films have been required to have high physical strength and very high dimensional stability, as shown in Japanese Examined Patent Publication No. 3039/5639, a stretched film is heated at a temperature higher than the stretching temperature. Had been heat treated in. However, in the packaging material such as the label described above, the heat shrinkability, especially in the label to be attached to the container such as a bottle or can targeted by the present invention, the property of heat shrinking only in one direction, that is, the uniaxial heat shrinkability is required. There is. Moreover, since vinyl chloride resins have been the mainstream for label applications, heat shrinkage characteristics similar to those of vinyl chloride resins are required. For example, various types as disclosed in JP-A-51-88550 are disclosed. Has been examined. However, as seen in Japanese Patent Laid-Open No. 3-135534, it is difficult to obtain heat shrinkability like a vinyl chloride film by using only one type of polyester polymer, and two or more types of polymers having different glass transition temperatures are used. Has been required to be blended.

On the other hand, in the method for producing a uniaxial heat-shrinkable film of polyvinyl chloride, a tenter method of stretching in the transverse direction is generally adopted, and the general condition is that the film first has a glass transition temperature T _g + (20 ~ 30) after preheating in the range of ° C., at the temperature before and after that, stretched in the width direction at the desired ratio,
Next, the film is heat-set at a temperature of glass transition temperature T _g + 10 ° C. or higher in the hope that the strain in the longitudinal direction and the shrinkage unevenness during storage will be relaxed and the gradient of the heat shrinkage curve will be gentle. If these conditions are directly applied to the production of the polyester heat-shrinkable film, the heat-shrinkable film obtained has a value of 5% or less in which the elongation at break in the direction perpendicular to the stretching direction is extremely small, that is, the yield point is reached. It is known to break depending on whether or not. Especially in the manufacture of tubular labels and cap seals,
In various processes such as printing, laminating and cutting, impact tension is applied in addition to mere tensile tension.Therefore, films with low tensile strength and low tensile strength are ruptured in those processes and manufactured each time. It causes the inconvenience of stopping. Therefore, the tensile strength is high and the elongation at break is 100
It has been desired to develop a film that does not break during the production due to the above-mentioned percentage, and the process does not stop.

[0005]

Therefore, the object of the present invention is to have excellent transparency, heat resistance, mechanical strength and chemical resistance, and also to generate toxic gas during combustion and damage the combustion furnace during waste treatment. Polyester film, which has few problems such as the above, has the same heat shrinkage characteristics as the polyvinyl chloride film that has been used most in the market so far, and the occurrence of shrinkage unevenness and pucker wrinkles during heat shrinkage is extremely small. , 100% tensile elongation at break in the direction perpendicular to the stretching direction
As described above, it is an object of the present invention to provide a uniaxial heat-shrinkable film having a shrinkage in the stretching direction at 100 ° C. of 50% or more and a shrinkage in the direction perpendicular to the stretching direction of 10% or less.

[0006]

The present applicant has previously extruded a polyester composition having a glass transition temperature of 50 to 80 ° C., which is obtained by blending a PET polymer with 20 to 60% by weight of polyarylate, and then, A polyester film that is uniaxially stretched in the transverse direction to impart heat shrinkage, has the same heat shrinkability as a vinyl chloride film, and has very little shrinkage unevenness or wrinkle-like wrinkles during heat shrinkage. I found that. We have used this composition to
We examined the stretching conditions to achieve a shrinkage of 50% or more in the drawing direction at 00 ° C, a shrinkage of 10% or less in the direction perpendicular to the drawing direction, and a tensile elongation at break of 100% or more in the same direction. . In the uniaxially stretched film, it is generally considered that the tensile strength in the stretching direction is large but the strength in the orthogonal direction is small because the fibrillation phenomenon occurs. To prevent this phenomenon, there is a method of dealing with biaxial stretching as shown in JP-A-62-91555, but this method requires equipment for longitudinal stretching and increases the number of steps. The only drawback is that the control becomes complicated.

The inventors of the present invention are responsible for the decrease in tensile elongation at break in the direction perpendicular to the stretching direction in the uniaxial stretching method.
It is considered that the orientation and crystallinity of the polyester-based polymer lie in the degree of improvement.To improve it, the crystallization rate in the transverse stretching and the stretching rate, as well as the crystallinity after stretching within a certain range Further studies were conducted, focusing on the fact that it is sufficient to control the temperature and perform cooling for freezing. As a result, the glass transition temperature of polyethylene terephthalate-based polymer blended with 20 to 60% by weight of polyarylate resin is 50 to 50%.
After extrusion-molding a polyester resin composition at 85 ° C into a film, the film is preheated in a temperature range of glass transition temperature or higher and glass transition temperature + 20 ° C, then glass transition temperature + 10 ° C or higher, crystallization temperature- Tensile rupture in the direction perpendicular to the stretching direction when stretched in the uniaxial direction at least 2 times in the temperature range up to 30 ° C, further heat set in the temperature range above 45 ° C and below the glass transition temperature, and then cooled to room temperature. Elongation is 100% or more, thermal shrinkage at 100 ℃ in the stretching direction
The present invention has been completed by finding that the uniaxial heat-shrinkable film of 50% or more and 10% or less in the perpendicular direction has very excellent properties.

The present invention will be described in detail below. Generally, the polyester resin greatly changes in glass transition point and compatibility with a resin to be blended depending on its component composition.
Depending on the ratio of the polymer blend, they are apparently homogeneously compatible, or the compatibility is lowered, and a two-phase morphology of a matrix (sea) part and island-shaped parts dispersed therein appears. When a general polymer is uniformly compatible, the elastic modulus around the glass transition temperature changes rapidly like a single polymer.
However, in the state where there are two phases (or more) that are finely phase-separated, the elastic modulus around the glass transition temperature changes in multiple stages or changes gently. The polyester composition used for producing the heat-shrinkable polyester film of the present invention is composed of a PET polymer and polyarylate.

This PET-based polymer has a glass transition temperature
40 ~ 85 ℃ is good, and if it is lower than 40 ℃, the shrinkage initiation temperature of the film becomes too low and partial shrinkage occurs during storage of the film, and if it is higher than 85 ℃, the film shrinks. Not only the stretching temperature becomes high but also the shrinkage starting temperature becomes too high, which is not preferable in processing. P
The composition of the ET polymer is composed of a dicarboxylic acid component and a diol component, and as the dicarboxylic acid component, terephthalic acid is preferably 70 mol% or more, particularly 85 mol% or more. In combination with 10 to 30 mol% or less of naphthalene dicarboxylic acid, and conversely to lower the glass transition temperature, isophthalic acid, orthophthalic acid, succinic acid, glutaric acid, adipic acid,
One of the known dicarboxylic acids such as sebacic acid, azelaic acid, speric acid, oxalic acid, and malonic acid may be used alone or in combination with two or more in consideration of compatibility.

As the diol component, ethylene glycol of 70 mol% or more, particularly 90 mol% or more is preferable, and propylene glycol, pentanediol, hexanediol, propylene glycol, etc. are taken into consideration while taking into consideration the glass transition temperature and the compatibility with the resin to be blended. Neopentyl glycol,
Diethylene glycol, triethylene glycol, polyethylene glycol, 1,4-butanediol, 1,4
-A known diol component such as cyclohexanedimethanol may be used alone or in combination of two or more. The PET-based polymer can be obtained by combining the above two components and conducting a condensation reaction.

The other component of the polyester composition, polyarylate, is a polyester having an aromatic ring in the molecule, and among these, a polycondensate of terephthalic acid or isophthalic acid and bisphenol A is preferable,
Even polycondensates of other diphenols and basic acids have moderate compatibility with PET and have a glass transition temperature of 15
Any material in the range of 0 to 200 ° C can be used. Here, if the glass transition temperature is lower than 150 ° C,
Not only is it difficult to obtain, but blending with a PET-based polymer reduces the effect of expanding the shrinkage temperature range. On the other hand, if the glass transition temperature is higher than 200 ° C, not only the glass transition temperature of the entire film system becomes high and it becomes difficult to stretch, but also the shrinkage initiation temperature becomes high, which makes it unsuitable for processing in a conventional shrink furnace.

When a PET polymer is blended with a polyarylate resin, the glass transition temperature and the shrinkage onset temperature increase depending on the blending ratio. When the blend ratio is less than 20% by weight, the slope of the heat shrinkage temperature curve becomes steep as in the case of the PET polymer alone.
On the other hand, if it exceeds 60% by weight, the glass transition temperature of the blended product rises and the stretching temperature becomes too high, resulting in 80 to 110 ° C.
Not only becomes difficult to stretch but also the heat shrinkage initiation temperature becomes too high. When the temperature for heat shrinkage becomes high, there is no fear that the stretched film will naturally shrink during storage, but shrinkage in a general shrink tunnel furnace becomes difficult. Considering these points, the blending ratio of the polyarylate resin is 20 to 60% by weight, preferably 20 to 40% by weight. The polyester composition thus obtained has a glass transition temperature of 50 to 85 ° C., preferably 60 to 85 ° C., regardless of its form, such as a homogeneous polymer, block polymer, and polymer blend. If the temperature is less than 50 ° C, the stretched film will spontaneously shrink during storage and become distorted and cannot be put on the product. In addition, it is difficult to shrink a heat-shrinkable film having a glass transition temperature of 85 ° C or higher with a conventional shrink furnace with high productivity. In addition to the above-mentioned polymer components, the polyester-based composition contains, if necessary, a stabilizer, a lubricant, a colorant, an antioxidant, an antistatic agent, an organic or inorganic material for improving the lubricity between films. Lubricants and the like may be added.

The heat-shrinkable polyester film produced by the method of the present invention is obtained by adding the polyester composition to, for example, T
After extrusion molding into a film using a die, this film is preheated in the temperature range of glass transition temperature or higher and glass transition temperature + 20 ° C, and then glass transition temperature + 10 ° C or higher,
Stretched in the temperature range up to -30 ° C in the uniaxial direction in either the longitudinal or transverse directions by a factor of 2 or more, preferably 2.5 or more.
A temperature range of 45 ° C or higher and lower than the glass transition temperature, preferably
It can be obtained by heat-setting in a temperature range of 50 ° C. or higher and a glass transition temperature of −5 ° C. for 0.1 to 0.4 minutes, particularly preferably 0.1 to 0.3 minutes, and then cooling to room temperature.

In the above, when the preheating is carried out at a temperature lower than the glass transition temperature, it becomes difficult to draw it at least twice in the next drawing step, and when it is carried out at a temperature higher than the glass transition temperature + 20 ° C. The thickness uniformity of the resulting heat-shrinkable polyester film is impaired, and the shrinkage ratio in the stretching direction at 100 ° C is less than 50%. When the stretching is carried out at a temperature lower than the glass transition temperature + 10 ° C, the number of defective products in the mounting test increases, and when the stretching is carried out at a temperature higher than -30 ° C, the obtained film looks like ground glass. In addition to being clouded and locally distorted, the tensile cutting elongation in the direction perpendicular to the stretching direction is reduced. When the draw ratio does not reach 2 times, the shrinkage ratio of the obtained film at 100 ° C in the drawing direction is less than 50%.
When heat setting is performed at a temperature lower than 45 ° C, the tensile cutting elongation in the direction perpendicular to the stretching direction can be 100% or more, but the shrinkage ratio in the same direction at 100 ° C is
When the temperature exceeds 10% and the temperature exceeds the glass transition temperature, the tensile cutting elongation in the direction perpendicular to the stretching direction decreases. Further, if the heat setting time is less than 0.1 minutes, the shrinkage ratio in the direction perpendicular to the stretching direction becomes high, and if it exceeds 0.4 minutes, the tensile cutting elongation in the same direction decreases.

[0015]

EXAMPLES Hereinafter, specific embodiments of the present invention will be described with reference to experimental examples, but the present invention is not limited to these descriptions. Experiment Nos. 1 to 5, 10, 11 and 13 (invention), No. 6 to
9, 12, 14 and 15 (comparative example) and No. 16 (reference example): As shown in Tables 1 and 2, the following PET-based polymer and a bisphenol type polyarylate resin having a glass transition temperature of about 180 ° C. (table Medium AR) and mixed with a hot-air tray dryer at 150 ° C. for 6 hours to obtain polyester compositions having glass transition temperatures and crystallization temperatures shown in Tables 1 and 2.・ PET-1 ・ ・ ・ Polymer consisting of PET only, glass transition temperature: 80 ℃.・ PET-2: PET polymer in which a part of terephthalic acid is replaced with 10 mol% of sebacic acid, glass transition temperature: 43
° C. -PET-3: PET polymer in which a part of terephthalic acid is replaced with 5 mol% of sebacic acid and 5 mol% of isophthalic acid, glass transition temperature: 50 ° C. -PET-4: PET polymer in which a part of terephthalic acid is replaced with 10 mol% of isophthalic acid, glass transition temperature:
73 ° C.

From this, pellets were formed using a nylon type screw in an extruder with a hopper in which a dry nitrogen gas of 100 to 110 ° C. was made to flow and a diameter (D) = 40φ, L (extruder length) / D = 25. Build and subsequently 400 width on the same extruder
mm, lip gap 0.5mm, T-die attached, thickness 1
A film of 00 μm was formed. Extruder temperature conditions are C ₁ = 190 ° C., C ₂ = 280 for both pellet and film forming.
℃, C ₃ = 300 ℃, at die temperature = 300 ° C., pellets after extrusion into a film both were quenched to below the glass transition temperature.
This film was stretched using a transverse uniaxial stretching machine with a length of 10 m under the conditions shown in Tables 1 and 2, then heat-set and immediately cooled to room temperature to obtain a heat-shrinkable film. Experiment N
o.16 is a commercially available polyvinyl chloride heat-shrinkable film 40G
The case of using (manufactured by Shin-Etsu Chemical Co., Ltd.) is shown as a reference example. For each of the above films, perform the following measurements,
The results are also shown in Tables 1 and 2.

Measurement of tensile strength: A test piece was punched out from a stretched film with dumbbell No. 1, left in a room at 23 ° C. and 50% high temperature and high humidity for one day and night, and then stretched at a speed of 200 mm / min, and longitudinal (table The yield value and the elongation at break are measured in both directions, which is defined as medium MD) and lateral direction (designated as TD in the table).・ Measurement of shrinkage at 100 ℃: 10cm from stretched film
Cut out a square test piece with a size of × 10 cm, dip it in a 100 ° C hot water bath for 30 seconds, and measure the shrinkage in both the vertical and horizontal directions (the same as above). -Mountability: A PET bottle of 1 liter filled with water at 25 ° C is covered with a tube-shaped label prepared by back-adhering each film, and passed through a steam shrink tunnel furnace maintained at 90 to 95 ° C. The shrinkage state at the shoulder and body of the bottle when heat-shrinked was observed and evaluated according to the following criteria. ◎: Clean appearance without shrinkage unevenness ○: Appearance without shrinkage unevenness △: Appearance with slight shrinkage unevenness ×: Appearance with remarkable shrinkage unevenness

[0020]

The heat-shrinkable polyester film obtained by the method of the present invention has a yield value in any direction.
4.0 kg / cm ² or more, tensile breaking elongation in the direction perpendicular to the stretching direction is 100% or more, and shrinkage at 100 ° C is 50 in the stretching direction.
% Or more and 10% or less in the direction perpendicular to the stretching direction,
Good packaging suitability in mounting test.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Seiji Hashimoto, Inventor, Tohada, Kamisu-cho, Kashima-gun, Ibaraki Prefecture, Towada, Shin-Etsu Chemical Co., Ltd. Towada No. 1 Shin-Etsu Chemical Co., Ltd., Polymer Functional Materials Research Center

Claims (1)

[Claims] 1. A polyethylene terephthalate-based polymer
After extruding a polyester resin composition having a glass transition temperature of 50 to 85 ° C, which is prepared by blending 20 to 60% by weight of a polyarylate resin, into a film, the film is heated to a glass transition temperature or higher, a glass transition temperature + 20 ° C. Temperature range up to, glass transition temperature + 10 ℃ or more, crystallization temperature -30
Stretched more than 2 times in uniaxial direction in the temperature range up to ℃,
Heat set in the temperature range of 45 ° C or higher and lower than the glass transition temperature,
A method for producing a heat-shrinkable polyester film, which comprises subsequently cooling to room temperature.