JPH0479822B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Field of Application) The present invention is directed to a heat-shrinkable polyester film (including sheets; the same applies hereinafter) that exhibits particularly suitable properties in the field of packaging materials such as covering and bundling.
It is related to. (Prior Art) Tube-shaped bodies made of heat-shrinkable plastic film are used, for example, in containers, bottles (including plastic bottles), cans and rod-shaped bodies (pipes, rods, etc.).
For covering or bundling wood, various rod-shaped bodies), etc. (hereinafter abbreviated as containers), especially for covering part or all of their caps, shoulders, bodies, etc., for marking, protecting, and bundling. In addition to being used for the purpose of improving product value, it is also widely used in the field of integrated packaging such as boxes, bottles, boards, sticks, notebooks, etc., or in the field of packaging items in close contact with the packaged items such as skin packs. , it is expected that it will be used in applications that take advantage of its shrinkage properties and shrinkage stress. Conventionally, heat-shrinkable films made of polyvinyl chloride, polystyrene, polyethylene, hydrochloric acid rubber, etc. have been used for the above-mentioned purposes, and the film has been formed into a tube-like body and then covered with the above-mentioned containers or packaged and heat-shrinked. However, these films have a drawback that they have poor heat resistance, and when subjected to boiling or retort processing, they melt or burst, making it impossible to maintain the film-like structure. Furthermore, in applications that require printing, printing pinholes (microscopic irregularities caused by fissures caused by additives or polymer gels in the film) may occur due to poor ink transfer, and even if printing is successful, there may be problems afterward. There was also the problem that the film would shrink (shrink at room temperature), causing dimensional changes in the printing pitch. On the other hand, tubes using polyester heat-shrinkable films have been made on a trial basis in the past, but they have not been able to achieve a sufficiently high heat-shrinkage rate in the desired direction, or There is a problem in that it is not possible to reduce thermal shrinkage in a direction perpendicular to the direction, and it has been difficult to apply the method to the above-mentioned applications. (Problems to be Solved by the Invention) The above-mentioned conventional techniques using general-purpose heat-shrinkable films such as polyvinyl chloride, polystyrene, polyethylene, etc. have the following problems. (a) Absence of near-perfect uniaxial shrinkage The conventional film described above is completely unsuitable for applications where it is ideal to have large shrinkage in one direction but no shrinkage in a direction perpendicular to this. . For example, if we consider attaching a shrink label to the surface of a bottle by shrinking it in the horizontal direction, shrinking the label vertically, that is, in the vertical direction of the bottle, means that the label does not come to the specified position and shrinks up. This results in poor appearance. To prevent this, it is necessary to reduce the shrinkage in the vertical direction, but if we simply orient the film only in the horizontal direction for this purpose, it is immediately understood from common sense regarding the properties of polymeric chemicals. It is easy to tear, and the strength is also weakened because it becomes easy to fibrillate. Considering that strength in the longitudinal direction is important for preventing bottle breakage, particularly when the bottle is dropped, simple unidirectional stretching is not a good method. In addition, there are many cases where it cannot be used for other purposes unless it has impact resistance. For this reason, it is desired to develop a film that has extremely low shrinkage in a certain temperature range, but has sufficiently large shrinkage in the direction perpendicular to the temperature range. (b) Insufficient heat resistance None of the conventional films mentioned above can withstand high-temperature boiling or retort processing, making them unsuitable for sterilization. For example, when retort processing is performed, the conventional film breaks or ruptures during processing, and all functions are lost. Therefore, it is desired to provide a heat-shrinkable film that can withstand boiling and retorting. (c) Poor printability Each of the above conventional films has its own drawbacks in terms of pinhole formation due to halftone printing, adhesion with a wide variety of inks, and the like. For example, with polyvinyl chloride, ink pinholes are likely to occur due to gel-like substances, and in continuous tube processing,
A pinhole will exist in the middle of the long film. If this is fed to an automatic labeling machine, the product will be manufactured with pinholes left behind, so all products must be inspected at the end, and the labor and reprocessing required by sampling will significantly reduce the actual operating rate. do. If this pinhole defect were to be inspected and removed after printing, the film would have to be made into a continuous film again after being cut, and it would be necessary to join it with adhesive tape. As a result, there are seams, and defective products occur due to the effects of the seams in that area and in the front and back, and defective packages must be removed during the process. Furthermore, in high-precision printing, the printing pitch decreases (shrinkage over time) due to shrinkage of the film after printing, and moreover, it is difficult to manage because it constantly changes under distribution temperature conditions. Therefore, for polyvinyl chloride shrink film, etc., refrigerated trucks and low-temperature warehouses are required. For this reason, it is desired to provide a heat-shrinkable film that can be printed without pinhole defects and that does not change over time after printing. (d) Occurrence of craze Polystyrene is prone to craze and has poor chemical resistance. Therefore, during use, it is easily damaged by chemicals and the printed surface becomes dirty. Therefore, a film with excellent chemical resistance and durability is desired. (e) Industrial waste issues The amount of plastic bottles used has increased rapidly in recent years. When considering the recovery of these bottles, there is a problem that they cannot be recovered and reused, especially if a different type of film such as polyvinyl chloride or polystyrene is used to cover a polyester bottle. Furthermore, polyvinyl chloride has the problem of corrosion due to chlorine gas, so a heat-shrinkable film that does not cause waste pollution is desired. (f) Shrinkage spots The heat shrinkability of the conventional film mentioned above tends to lack uniformity, and if heat is applied, areas where sufficient shrinkage and areas where insufficient shrinkage are formed separately.
Next, even if heat is applied once again, no further re-shrinkage occurs, and the surface becomes uneven.
Therefore, it is desired to provide a heat-shrinkable film that does not cause shrinkage spots. The present invention has been made in view of these circumstances and aims to provide a polyester film free from the defects described in (a) to (f) above. (Means for solving the problem) The present invention is a film consisting of a copolyester containing terephthalic acid and ethylene glycol as main components and a compound represented by the following formula (1) as a copolymerization component, which A heat-shrinkable polyester film characterized in that the heat shrinkage rate in hot air at 100° C. is 30% or more in at least one of the longitudinal direction and the width direction of the film. (R ₁ and R ₂ are C ₂ to C ₅ alkyl groups) The heat-shrinkable polyester of the present invention contains terephthalic acid and ethylene glycol as main components and the compound shown in formula (1) above as a copolymerization component. can be,
The content of the compound represented by formula (1) above is preferably in the range of 1 to 60 mol%. Particularly preferably 5 to 50 mol%.
If the compound represented by formula (1) above is less than 1 mol%,
When heat treated in hot water at 100°C, the retention time of residual stress is shortened, and when coated on a bottle, for example, undesirable phenomena such as loosening of the shoulders due to sterilization treatment occur. On the other hand, if it exceeds 60 mol%, the effect of improving the residual stress holding time during heat treatment is saturated, and amorphousness progresses, resulting in loss of heat resistance properties. The polyester copolymer in the present invention can be produced by a conventional polyester production method. For example, even if it is a method using terephthalic acid and ethylene glycol, and a direct ester method of the compound of formula (1),
Alternatively, it may be produced by transesterification of dimethyl terephthalate, ethylene glycol, and the compound of formula (1). Furthermore, the polyester copolymer in the present invention may be produced by blending copolymers within and outside the scope of the present invention with homopolyester or other copolyester, and
As long as the compound of formula (1) is in the range of 1 to 60 mol %, it may be produced by any method. Examples of the compound represented by the formula (1) include 2,3 diethyl-1,3 propanediol, 2-n-butyl-2-ethyl-1,3 propanediol, 2,2
-isopropyl-1,3-propanediol,
2,2-n-butyl-1,3-propanediol, 2-n-butyl-2-isopropyl-1,3
Propanediol, 2,2-pentyl-1,3-
Examples include propanediol. The heat-shrinkable polyester of the present invention has terephthalic acid as its main acid component, but other acid components may be copolymerized as long as their properties are not significantly changed. For example, aliphatic dibasic acids such as adipic acid, sebacic acid, azelaic acid, isophthalic acid, diphenylcarboxylic acid, 5-tertiarybutyl isophthalic acid, 2,2,6,6-tetramethylbiphenyl 4 , 4 dicarboxylic acid and other aromatic dibasic acids, 2,6 naphthaene dicarboxylic acid, 1,1,3
Examples include aromatic dibasic acids such as trimethyl-3 phenyl indene 4,5 dicarboxylic acid. Similarly, the glycol component has ethylene glycol as its main component and the compound represented by formula (1) above as a copolymerization component, but other components may be copolymerized as long as their properties are not significantly changed. For example, aliphatic diols such as diethylene glycol, neopentyl glycol, propylene glycol, butanediol, and hexanediol;
An example is a diol of a (4-oxyphenyl)propane derivative. Furthermore, lubricants such as titanium dioxide, particulate silica, kaolin, calcium carbonate, etc. may be added as necessary, and furthermore, antistatic agents, anti-aging agents, ultraviolet ray inhibitors, dyes, etc. may be added as coloring agents. I can do it. In addition, the preferable intrinsic viscosity as a film base material is 0.50-1.3 dl/g. Films obtained by any method such as extrusion or calendaring using such polymers can be made by 2.5 times or more in one direction.
Stretched 7.0 times, preferably 3.0 to 6.0 times, and 1.0 to 2.0 times or less in the direction perpendicular to the direction, preferably
Stretched 1.1 to 1.8 times. Stretching in the first direction is performed to obtain a high heat shrinkage rate, and stretching in a direction perpendicular to the first direction is performed to improve the impact resistance and tear resistance of the film stretched in the first direction. It is extremely effective in solving problems. However, when stretched more than 2.0 times, the thermal shrinkage in the direction perpendicular to the main shrinkage direction becomes too large, resulting in a wavy finish. To suppress this waving, the heat shrinkage rate should be 15% or less, preferably 8 to 9%.
Hereinafter, it is recommended that the content be more preferably 7% or less. There are no particular restrictions on the stretching method;
Methods such as roll stretching, long-gap stretching, and tenter stretching are applied, and the shape does not matter whether it is flat or tube-shaped. Further, the stretching may be carried out by successive biaxial stretching, simultaneous biaxial stretching, uniaxial stretching, or a combination thereof. Also, for the film of the present invention, for example, one vertical axis, one horizontal axis, two vertical and horizontal axis
Axial stretching is carried out, and particularly in biaxial stretching, successive biaxial stretching in which one of the longitudinal and lateral directions is carried out first is effective, and the order of stretching may be either first. When carrying out the simultaneous biaxial stretching method, the stretching order may be either simultaneous in the longitudinal and lateral directions, first in the longitudinal direction, or first in the lateral direction. Heat setting in these stretching processes is carried out depending on the purpose, but in order to prevent dimensional changes under high temperatures in summer, it is recommended to pass the film through a heating zone at 30 to 150°C for about 1 second to 30 seconds. Further, expansion up to a maximum of 70% may be applied either before or after such processing. In particular, it is preferable to stretch in the main direction and relax in the non-shrinkage direction (direction perpendicular to the main shrinkage direction), and it is better not to stretch in the perpendicular direction. In order to exhibit the preferable characteristics of the present invention, it is necessary not only to maintain the above-mentioned stretching ratio, but also to maintain a temperature higher than the average glass transition temperature (Tg) of the polymer composition, for example, Tg+80.
Preheating and stretching at a temperature of about 0.degree. C. can also be cited as an effective means. Especially main direction stretching (main shrinkage direction)
The above-mentioned processing temperature is extremely important for suppressing the thermal shrinkage rate in the direction perpendicular to the above-mentioned direction and for bringing the minimum value within the temperature range of 80±25° C. as described above. Further, after stretching, by cooling the film while applying stress by keeping it in a stretched or tensioned state, or by cooling the film successively, the front-rear shrinkage characteristics become better and more stable. The plane orientation coefficient of the film obtained in this way is
It is preferably 100×10 ^-3 or less. The plane orientation coefficient is
This is because if it exceeds 100×10 ^-3 , it becomes easy to break due to an impactful external force and becomes easy to break even with the slightest external trauma. On the other hand, the birefringence is 15×10 ^-3 ~160×
10 ^-3 is preferred; if the birefringence is less than 15 x 10 ^-3 , the thermal shrinkage rate and shrinkage stress in the longitudinal direction will be insufficient;
If it exceeds 10 ^-3 , the drag resistance and impact strength will decrease, and even if it is made into a film, its practical usefulness will decrease. The practical thickness of the film of the present invention is in the range of 6 to 250 μm. The film of the present invention has a heat shrinkage rate at 100℃.
Must be at least 30%. If it is less than 30%, it will not adhere to the surface of the irregularly shaped packaged object sufficiently when it is shrunk. As for the upper limit, 90% is reasonable. The film of the present invention must maintain residual stress for 2 minutes or more when it is relaxed by 50% and heat treated in hot air at 100°C. It is more preferable to hold the temperature for 4 minutes or more. If the retention time of the residual stress is short, secondary sagging will occur, and for example, when a bottle is coated, phenomena such as loosening of the shoulders due to sterilization treatment will occur, which is undesirable. The film of the present invention will be explained below in terms of its uses. Boil processing and retort processing are performed in packaging applications, particularly in the packaging of foods and beverages. None of the existing heat-shrinkable films can sufficiently withstand these treatments. The film of the present invention can withstand heat sterilization by boiling and retort processing, has a good original film appearance, and also has a good finish due to heat shrinkage, and has a higher heat shrinkage stress than PVC and can be bound The quality is also excellent. Therefore, it is possible to strongly cover or bind and package heavy items or deformed molded items without causing them to collapse. In addition, at the heat shrinkage rate level of 50 to 70% required for packaging, the heat shrinkage rate in the direction perpendicular to the main shrinkage direction is the lowest. The process up to completion involves heat shrinking in the temperature range (80±25°C) that shows the minimum amount of shrinkage. As a result, a feature was obtained in which the error in finished dimensions was reduced. For packaging that utilizes heat shrinkability, heat shrinkage is complete (a state in which the package is in close contact with the packaged item and cannot be shrunk any further, even if it has the ability to shrink further).
Subsequent heating has become a common practice, and plays an important role in achieving complete shrinkage to account for numerous product variations. At this time, if the shrinkage ability of the film has reached saturation, the film will undergo linear expansion due to the subsequent heating, and even though it has been made to shrink tightly, it will instead expand. There is a problem that loosening occurs. In order to prevent such a situation, the present invention recommends increasing the shrinkage stress and further stretching after stretching as described above. Moreover, in this point, the meaning of orientation as used in the present invention exists. This will be described in more detail below. (a) Unidirectional shrinkability: One of the roles of a shrink film is to prevent the destruction of the packaged items and the collapse of the package, and for this purpose, it must have high impact resistance and be large in the main direction. It is necessary to obtain the shrinkage rate. In this respect, the film of the present invention has a high shrinkage rate and high impact resistance, so that beautiful packaging can be obtained, and moreover, it exhibits excellent durability in terms of protecting the packaged items. This tendency is confirmed by the drop bag test. Furthermore, due to its almost perfect unidirectional shrinkability, the finished dimensional stability after shrink wrapping is good. (b) Heat resistance: All conventional general-purpose films cannot withstand high-temperature boiling or retort processing, making them unsuitable for sterilization. They break during processing and lose their functionality, but The film of the invention exhibits excellent utility as a heat-shrinkable film that can be subjected to boiling or retort processing. (c) Printability: Conventional films have inherent drawbacks such as the generation of pinholes due to halftone printing and adhesion with ink, but this polyester film has chemical resistance and is improved by making it a copolymer. Printability was improved due to improved adhesion. (d) Industrial waste issues: The use of plastic bottles has been rapidly expanding in recent years. When considering the recovery of such bottles, it is preferable that they be made of the same material, and it is advantageous in this respect to apply the film of the present invention to the packaging of polyester bottles. (e) Shrinkage spots: The film of the present invention has a large shrinkage rate and high shrinkage stress, and shows a tendency to shrink if it is heated continuously even in secondary heating, so that shrinkage spots do not occur. (Example) Examples will be described below, and the measurement methods used in the examples are as follows. 1 Heat shrinkage rate The distance between the sample marks is 200 mm, and the width of the film is
It was cut into 15 mm pieces and measured at each temperature. For heating
Each was heated for 1 minute using hot air at 100°C. 2 Heat shrinkage residual stress holding time (at 50% relaxation) Using Tensilon, create a sample piece with a width of 20 mm and a length of 150 mm. Mark a 100 mm mark on the film of the sample piece, and place it on the top and bottom chucks set at 50 mm. accurately
Attach with the 100mm marked lines aligned, process in hot air at 100℃, and measure the time until the shrinkage stress becomes 0 or the residual stress after 10 minutes. If the stress is to be maintained after 10 minutes, calculate it in the same way as the heat shrinkage stress. Example 1 Using a stainless steel autoclave, 100 moles of terephthalic acid as the dibasic acid component and 170 moles of ethylene glycol as the glycol component were prepared.
Polycondensation was carried out by a direct esterification method using 30 mol of 2-diethyl-1,3-propanediol and 0.025 mol (based on the acid component) of antimony trioxide as a catalyst. The composition of this copolyester is as follows: the acid component is 100 mol% terephthalic acid, the glycol component is 70 mol% ethylene glycol, 2,2 diethyl-1,3
Propanediol is 30 mol%, and the intrinsic viscosity is
It was 0.70 dl/g. This polyester is melt extruded at 280℃, and the thickness
An unstretched film of 200 μm was obtained. The film was stretched 1.2 times in the machine direction, then 4.1 times in the cross direction, and then cooled under about 20% stretch in the cross direction to reduce the thickness.
A heat-shrinkable film of 40 μm was obtained. The birefringence and plane orientation coefficient of the obtained film were 72×, respectively.
10 ^-3 and 51×10 ^-3 . The physical properties of this film are shown in Table 1. As shown in Table 1, a high shrinkage rate and a sufficiently long heat shrinkage residual stress retention time were obtained, and good results were obtained in practical tests. Examples 2 to 7 Heat-shrinkable films made of polyester having the compositions shown in Table 1 were obtained in the same manner as in Example 1. Table 1 shows the characteristic values of the heat-shrinkable film obtained. All of the heat-shrinkable films had sufficiently satisfactory results in terms of heat-shrinkage rate and heat-shrinkage residual stress retention time, and good effects were obtained in practical tests. Comparative Examples 1-2 Polyester films having the compositions shown in Table 1 were obtained in the same manner as in Example 1. Comparative Example 1 is ordinary polyethylene terephthalate. Comparative Example 2 is a copolymerized polyester in which 10 mol% of isophthalic acid is copolymerized as a dibasic acid component. Although the heat shrinkage rate of the film obtained in this comparative example is good, the heat shrinkage residual stress retention time is short, and secondary sagging occurs during boiling and retort processing, so it cannot be used for practical use. The heat shrinkage rate was also high and the aesthetic appearance was impaired in practical tests. Examples 8 to 9 In Example 8, polyethylene terephthalate was used as the polyester resin (A), and 2,2 diethyl-1,3 propanediol was used as the polyester resin (B).
Using mol% copolymerized polyethylene terephthalate, each was uniformly blended at a weight ratio of 50:50.
An unstretched film having a thickness of 180μ was obtained by melt extrusion at 300°C. In Example 9, an unstretched film with a thickness of 180 μm was obtained in the same manner as in Example 8 except that the polyester resin (B) in Example 8 was changed to 2-n-butyl-2-ethyl-1,3-propanediol. . The properties of the stretched film obtained by stretching the film in the same manner as in Example 1 are shown in Table 2. All of the obtained films have excellent heat shrinkage properties and are of high quality.

【table】

【table】

[Table] (Effects of the Invention) Since the film of the present invention is constructed as described above, it exhibits stable heat shrinkability in a specific direction, and can provide a beautiful and strong packaging state in covering packaging or bundling packaging. It can demonstrate excellent utility value in a wide range of fields.

Claims (1)

[Scope of Claims] 1. A film made of a copolyester containing terephthalic acid and ethylene glycol as main components and a compound represented by the following formula (1) as a copolymerization component, the polyester film being heated at 100°C. 1. A heat-shrinkable polyester film having a heat shrinkage rate in hot air of 30% or more in at least one of the film's longitudinal direction and width direction. (R ₁ and R ₂ are C ₂ to C ₅ alkyl groups) 2 The heat shrinkability according to claim 1, which is a copolymerized polyester containing 1 to 60 mol% of the compound represented by formula (1). Polyester film.