JPS59421B2 - packaging bag - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is a packaging bag made of a biaxially stretched film (hereinafter abbreviated as polyester film) mainly composed of polyethylene terephthalate, and is particularly suitable for frozen foods, retort foods, liquid foods, or heavy items. This relates to packaging bags.

Due to its excellent quality, polyester film has recently been used in various fields, and the demand for it has been increasing year by year.

Demand for packaging applications is gradually increasing due to its non-hazardous properties, excellent mechanical properties, workability, dimensional stability, transparency, resistance to water vapor and oxygen permeability, etc. Films of mostly 11 to 13μ have been used. Generally, when using film as a packaging material, the problem is the size of the area rather than the weight, so the thinner the film used, the more economically advantageous it is, but the quality and processability will deteriorate. Therefore, it is decided based on that balance. By the way, among the demand for packaging materials mentioned above, if polyester film is to be used in the airtight packaging field, it is difficult to thermally fuse and seal it (hereinafter referred to as heat sealing), so polyester film or ethylene-propylene copolymer is used. After packaging, we laminate a heat-adhesive layer such as
It is common to heat-seal at 150° C. for sterilization, and then perform high-pressure steam treatment (retort treatment) at 120 to 140° C. for about 30 minutes. In these processes, the stiffer the film, the easier it is to handle, leading to improved work efficiency and yield, and the better the dimensional stability, the better it will withstand shrinkage during thermal history such as heat sealing and retort processing. In addition, it is possible to prevent a significant decrease in product value due to deterioration of shape retention due to shrinkage or distortion of pictures and letters printed on the film surface, so it is possible to prevent the product value from decreasing significantly due to the deterioration of shape retention due to shrinkage or the distortion of pictures and letters printed on the film surface. The stable polyester film has one aspect that is essentially superior to other packaging materials, such as nylon biaxially stretched film (hereinafter abbreviated as nylon film). However, despite having much better stiffness and dimensional stability, polyester film has poor pinhole resistance in the hermetic packaging field, especially in applications such as frozen foods, retort foods, water products, and heavy goods packaging. Due to its poor elasticity and poor durability against impact near the sealing part, it has hardly been used to date, and its field of use has been limited.

In other words, in these applications, the package is usually subjected to various external impacts during transportation or handling after being sealed and used until it is opened. In extreme cases, a protrusion such as the tail of a frozen shrimp may hit the film, creating a small hole (called a pinhole) in the film, which prevents gas from passing through. In the field where airtight packaging is used with a focus on oxygen resistance and prevention of permeation, preservation becomes completely meaningless, and of course internal contents such as water can leak through pinholes, causing damage to the packaging. This leads to a fatal flaw. Therefore, such excellent pinhole resistance is essential for packaging materials for frozen foods, retort foods, water products, heavy items, and the like. Next, in the case of water packaging, etc.
When a strong impact is applied to a package, the part to which the force was applied is pressed against it, and the other parts tend to bulge due to the reaction. If this impact force exceeds the limit value, the area around the seal will break and the contents will leak. Sometimes I end up doing it. Since such destruction leads to a complete loss of functionality as a packaging material, durability in the vicinity of the sealing area is also an indispensable characteristic for sealing packaging materials, as is pinhole resistance. This fracture near the sealing part is caused by peeling phenomenon at the interface between heat-sealed polyethylene, the laminate interface between polyester film and polyethylene, or parallel to the film surface in the middle of the film thickness, which is seen when the arms of thick films are opened. Unlike the so-called delamination phenomenon, in which the film peels off from the heat-sealed part due to weak adhesive strength, this phenomenon causes the entire film, including the base polyester film and laminate layer, to be torn. However, the location where the seal is torn may be in the seal itself or near the seal, resulting in various complicated situations. The fact that ordinary polyester films have considerably poor practical durability has been the main reason why they have not been able to be used in applications that require such durability. Therefore, even though it lacks rigidity, stiffness, and dimensional stability as mentioned above, nylon film has excellent pinhole resistance and sealing impact resistance, making it suitable for packaging in such applications. It has occupied a major position as a material.

The thickness of most of the nylon films used is 13
The thickness is between 15μ and 15μ. The present inventors continued research to improve this drawback in polyester films while taking advantage of their good rigidity, stiffness, and dimensional stability, and as a result, they arrived at the present invention.

First of all, this is the cause of the difference in properties between polyester and nylon, but considering that for both, for example, the same polyethylene is laminated with the same thickness and heat sealed under the same conditions, there is a significant difference. The boundary surface is the same between polyethylenes, and the adhesive strength at the boundary surface between the film layer and the polyethylene layer is also
The anchor coat creates an adhesion condition equivalent to that of nylon, and furthermore, as mentioned above, pinholes or failure of the seal are a phenomenon in which both the film layer and the polyethylene layer are destroyed at the same time, and are caused by peeling between the film layer and the polyethylene layer. Since this is not a real thing, most of this significant difference is not due to polyethylene, but rather to the difference in durability between the polyester and nylon film base materials. However, when considering these durability as a general mechanical phenomenon, the fact that polyester film is significantly inferior to nylon film is a phenomenon that is difficult to understand. For example, if we assume that the phenomenon of pinholes caused by local rupture in a film is modeled by the rupture of a normal stress-strain curve (hereinafter abbreviated as S-S curve) as shown in Figure 1, then in general, When comparing polyester films and nylon films of similar thickness, the durability of normal fracture phenomena such as energy required to break, initial elastic modulus, force required to break, elongation to break, etc. Generally speaking, polyester films are considerably better in all mechanical parameters that are considered to be effective. Therefore, it is expected that polyester film would be superior in terms of pinhole resistance and impact durability of the sealed portion, but this is not actually the case as described above. On the other hand, the fact that polyester film has higher crystallinity and is harder may have an adverse effect, and in order to improve this, for example, soft raw materials with increased copolymerization rate may be used, as shown in the comparative examples of the present invention. Alternatively, in terms of film forming conditions, even if attempts are made to provide mulberry softness by preventing stretch crystallization by lowering the stretching ratio or by lowering the heat treatment temperature, the pinhole resistance will not only hardly be improved, but will actually worsen. In some cases, the strength and dimensional stability, which are the strengths of polyester film, are seriously impaired. In this way, pinhole resistance, particularly the pinhole resistance of polyester films, seems to be a different matter that cannot be explained or solved by the general concepts and methods regarding durability. The same applies to the destruction of the seal.
This state of destruction is determined by JISP8ll6-60 as mentioned above.
This appears to be similar to the fracture phenomenon observed when measuring the tear propagation resistance (Elmendorff) of films by Generally speaking, polyester film is superior. Furthermore, if economic issues or transparency are ignored, increasing the thickness of the film used is a common means of improving durability. What is strange is that the pinhole resistance improves as the seal gets thicker, but the impact resistance of the seal increases even though the energy required to break or the tear propagation resistance increases. Regardless, the results were abnormal and worsened, making it completely impossible for a polyester film to satisfy both durability requirements at the same time. In this way, the durability of both packaging materials, which is the issue of the present invention, is a phenomenon that cannot be discussed within the normal range of durability, but rather the essential differences related to the structure of polyester and nylon.
For example, nylon film has strong intermolecular forces due to hydrogen bonds between amide groups, and perhaps because of this, it has more than twice the elasticity (elasticity and elastoplasticity) recovery properties of polyester film.I will give you one example. Then 20°C, 300%
After stretching the film by about 20% at a speed of 1/min, when the force is removed and the film is left to stand, polyester film only shows a strain recovery of about 5 to 7%, while nylon film shows a strain recovery of only 1%.
In reality, it was considered that polyester film could never achieve this, as recovery properties of the order of 2 to 1501) were normally exhibited. This recovery property should be related to the fatigue resistance of the film against pinholes caused by vibration of the package or repeated impacts up to rupture, and a correlation with durability is predicted. As a result of intensive study of these problems, the inventors of the present invention have achieved both pinhole resistance and impact resistance (referred to as tear resistance) of the seal portion, which are equivalent to those of nylon film, which were previously unattainable with polyester film. , film thickness 7μ
16μ or less, and is shown by the S-S curve (
By using a polyester film in which the product of (the energy required to break) and (the ratio of the strength at break and the strength at yield point) is kept above a certain value specified in the present invention, the elastic recovery property is better than that of a nylon film. The present invention was achieved by discovering the surprising fact that it is possible to achieve the same characteristics as a nylon film even under conditions where the film is still significantly inferior to the nylon film.

The invention will now be described in further detail.

The present invention relates to a packaging bag with excellent pinhole resistance and tear resistance, which is made of a polyester film having a film thickness of 7 μm or more and 16 μm or less, and the following parameters defined in the present invention satisfy formula (1). be. 'As shown in Figure 1, F A, B, and C are the energy required for rupture (K9%), which is determined from the area up to rupture of the S-S curve, and the strength at the rupture point (H), respectively. and the strength in kg at the yield point.

The film thickness is 7μ or more and 16μ or less, and 9μ or more and 14μ or less.
The following degree is preferable. This is because if the thickness exceeds 16μ, even if this regulation is satisfied and the pinhole resistance is improved, a problem will arise in the tear resistance.

In addition, the thicker the layer, the more disadvantageous it is in terms of economy and transparency, and from this point of view, the thinner the layer is, the more preferable it is.

In addition, AX-c is 500 (K9・%) or more 800 (K9
・%) or less is required, more preferably 560 (K9
・%) or more and 800 (K9・%) or less. (1) Although A, B, and C in the formula are generally parameters related to durability, polyester films with larger values for pinhole resistance and tear resistance have lower values for the same thickness. As is clear from the fact that it has a lower value than nylon film, it is not uniquely associated with pinhole resistance or tear resistance.

However, only by satisfying formula (1) can they improve pinhole resistance and tear resistance to the same level as nylon films, and can also satisfy other required properties such as stiffness and dimensional stability. is a surprising fact. What Equation (1) shows is that in order to improve pinhole resistance and tear resistance, ordinary measures such as simply increasing A or increasing B are insufficient; It is necessary to have a polyester film in which the correlation of the three elements C is well balanced. For example, it is a general mechanical behavior that when the strength B at the breaking point increases, the strength C at the yield point also increases. Therefore, it is generally considered that the larger both B and C, the better the pinhole resistance, etc. However, in this case, a film in which C increases at a rate equal to or greater than B does not have improved pinhole resistance or tear resistance, but rather has deteriorated. Similarly, it is a general mechanical behavior that B (or A) decreases when C decreases, but a film in which B (or A) decreases by an amount equal to or greater than C is also meaningless. Become. Furthermore, for example, a decrease in A or B is in the opposite direction from the normally thought of improvement in durability. However, even in the opposite direction, if the reduction rate of C is greater than that of A or B, the pinhole resistance and tear resistance will improve even without the strong elastic recovery properties of a nine film. Equation (1) also shows the content that is difficult to understand as a general mechanical phenomenon. In this way, and as is clear from the comparison between nylon film and polyester film, improving pinhole resistance and tear resistance of polyester film is simply a means of improving durability, such as simply increasing strength or increasing tear propagation resistance. However, this is not a problem that can be solved at all, and the thickness of the present invention is 1.
It is an essential condition that it is 6μ or less and that formula (1) is satisfied.

Although it is not clear why pinhole resistance can be improved without the strong elastic recovery properties of nylon film if the thickness is 16μ or less and formula (1) is satisfied, (1)
It is assumed that the formula is closely related to the resistance to special impacts that may cause small pinholes or ruptures in actual packages. In addition, in the case of polyester film, by satisfying formula (1), other necessary properties such as dimensional stability and stiffness can be achieved at good values without showing a noticeable decrease unlike nylon film. It is a surprising phenomenon that this is possible, and it is possible to provide an optimal packaging material that requires pinhole resistance and tear resistance. The film characteristic evaluation using the S-S curve specified in this specification is performed in two directions, the machine direction (MD) and the vertical direction (TD), of the biaxially stretched film according to JISC-2318-66, and A, B, and C are averages of the two directions. expressed as a value.
This is measured at ten or more arbitrary locations, and the average value is taken as the characteristic value of the present invention. Note that the film width serving as the standard for A is 10 mm. It is more preferable that the characteristics of MD and TD be similar, but this is not necessarily limiting.
The definition of yield point in the present invention is the point at which plastic deformation occurs, and is the limit at which elastic (elastic and elastoplastic) recovery can be shown when the film is stretched and the stress is removed under the conditions of JISC-2318-66. It is a point. The polyester referred to in the present invention is a polyester whose main component is polyethylene terephthalate, but other copolymerization components may be copolymerized, or additives such as stabilizers, antistatic agents, pigments, etc. may be added to the extent that the transparency is not significantly deteriorated. , or other thermoplastic resins may be mixed.

Further, the molecular weight is not particularly limited as long as it satisfies the present invention as long as it is within a range that can be formed into a film, although the higher the molecular weight, the more preferable it is. The polyester film of the present invention can be obtained by using the above-mentioned raw materials, by appropriately combining stretching and relaxing as shown in the examples, and by heat treatment under conditions that can provide sufficient dimensional stability. , but is not necessarily limited to this. As a means of obtaining a packaging bag, the method shown in the present invention is to perform an anchor coating, then laminate with polyethylene or ethylene-propylene copolymer, and then heat seal the interior after the anchor coating.
There are various possibilities such as coating agent, type of laminate material, laminate thickness, lamination method (including composite methods), heat sealing method, bag shape, etc., but there are no particular restrictions as long as the original purpose can be achieved. Not done. The present invention will be explained in more detail with reference to examples, but is not limited thereto.

Examples 1 to 5, Comparative Examples 1 to 12 Polyethylene terephthalate chips polymerized by a conventional method were extruded to form a film.

The film thickness was standardized to 13μ. The chip properties were that the intrinsic viscosity was 0.60 (measured with the solvent 0-chlorophenol) and the diethylene glycol (DEC) copolymerization rate was 0.5% by weight. The film forming conditions were first 3x MD stretching at 90°C, then 95°C.
The film was relaxed 50% in the MD at C, then stretched 3 times in the TD at 95°C, and then relaxed 50% in the TD at 1000C. 1 more
Simultaneous biaxial stretching in MD and TD was performed at 00°C, and heat treatment was performed at 2300°C. At this time, TD was relaxed to 1001). Example 1 had a simultaneous biaxial stretching ratio of 2.8 times, 2 had a magnification of 2.9 times, and 3
4 is 3.0 times larger, 5 is 3.2 times larger, and 5 is 3.4 times larger, and the film is made into a packaging bag using the method described below. Comparative example 1
is a case where the simultaneous biaxial stretching ratio is 2.6 times under the same conditions, and Comparative Example 2 is a case where the simultaneous biaxial stretching conditions are 110° C. and 2.8 times. In Comparative Examples 3 to 7, stretched crystals were improved by changing the stretching ratio, for example. This is a case where the state of structure generation is changed. Comparative Examples 3 to 5 are cases where sequential biaxial stretching was carried out at a temperature of 95°C at a magnification of 2.5, 3.5, and 4.5 times in MD and TD, and Comparative Example 6 was a case where simultaneous biaxial stretching was performed at a temperature of 95°C and a magnification of 4.5 times. In the case of stretching, Comparative Example 7 is a case in which the film was sequentially biaxially stretched 3.0×3.5 times at 95° C. and then re-MD stretched 1.6 times at 150° C. All heat treatments resulted in 10% relaxation in TD at 230°C. Comparative Example 8 is a case where the heat treatment temperature of Comparative Example 4 was lowered to 190° C. to prevent thermal crystallization. Comparative Examples 9 to 11 are cases where films with thicknesses of 15, 17, and 21 μm were used under the conditions of Comparative Example 4, respectively, and Comparative Example 12 was obtained under the conditions of Comparative Example 4 with a stretching ratio of 3.3 times and the thickness This is a case where a film with a thickness of 17μ is used. Comparative Example 11 is an example in which only equation (1) can be satisfied when the film becomes considerably thicker because the energy A required for breaking gradually increases as the film thickness increases. Table 1 shows the packaging bag quality evaluation results. For pinhole resistance and tear resistance, a packaging bag using a 15μ nylon film is rated as ○, and a 12μ polyester film is evaluated as ×. For stiffness and dimensional stability, ○ indicates the same as using a 12μ polyester film, and △ indicates the same as using a 15μ nylon film. ◎ means better than ○. As is clear from the Examples and Comparative Examples, a preferred packaging bag with excellent pinhole resistance, tear resistance, stiffness, and dimensional stability can be obtained only when the polyester film used satisfies the provisions of the present invention. can be submitted.

It is also clear that in a thickness range of 16 μm or less, it is difficult to achieve a good balance of the three elements A, B, and C specified in this specification simply by changing the stretching and heat treatment conditions. As shown in Comparative Examples 3 and 8, the quality is insufficient even if stretching crystallization and thermal crystallization are significantly prevented, and as shown in Comparative Examples 9 to 12, the durability is not improved by making the film thicker. Although an improvement in pinhole resistance is observed, this is a contradictory phenomenon in which tear resistance deteriorates.As stated in the text, the durability that the present invention aims to improve is due to stretching crystallization, This is a problem that cannot be solved simply by changing the thermal crystallization state or by simply increasing the thickness of the film.
It is an essential condition that the present invention is satisfied. Comparative example 13 Intrinsic viscosity 0.60. Table 1 shows the case of a 13μ film formed under the conditions of Comparative Example 4 using polyethylene terephthalate chips made softer than usual and having a DEG copolymerization rate of 5% by weight.

This regulation is not met, and the quality of the packaging bag is also insufficient. In the case of a polyester film, it has been shown that unless it satisfies the provisions of the present invention, the goal cannot be achieved by ordinary means for improving durability, such as simply making it softer. Practical Examples 6 to 11 and Comparative Examples 14 to 16 Examples 6 to 11 and Comparative Examples 14 to 16 were made into packaging bags using the same chips as in Example 3 and a film formed to a thickness of 7 to 21 μm under the same conditions. This is the case.

B However, in order to approximate the value of A×-, the simultaneous biaxial stretching C stretching ratio was changed as appropriate within the range of 2.65 to 3.5.

The evaluation results are shown in Table 2. If the thickness of the film used exceeds 16μ, including Comparative Example 11, deterioration in tear resistance is unavoidable even if formula (1) is satisfied. This is a necessary condition. A more preferable film thickness is in the range of about 9 to 14 microns. In addition.

The manufacturing method of the packaging bags of this example and comparative example and the evaluation method of pinhole resistance, tear resistance, stiffness, and dimensional stability are described below. First, a urethane-based anchor coating agent was applied to a polyester film at a rate of 0.05g/7rI.
Dry at ℃ for 30 seconds. Next, polyethylene (
Sumikasen L7O5) was laminated to a thickness of 50 μm and left at room temperature overnight. Pinhole resistance evaluation is 16Cr
After packaging 250 g of macaroni in an interior diameter of IL x 13 crrL and sealing it at 150°C with a foot-operated heat sealing device manufactured by Yamamoto with a seal width of 8 mm, it was subjected to a 1400 rotation drop test (15 times/min). The state of pinhole formation was compared with that when a nylon film was used instead of a polyester film. Tear resistance evaluation is for interior diameter 10
Pack 130cc of water in cm x 10C7L and seal it in the same way as above, then package it with a diameter of 15mm. This was done by dropping a disc weighing 500 g onto the package from a certain height and comparing the height at the time of destruction near the sealing part. The strength of the stiffness is determined by workability and handling during these processes, and the dimensional stability is 120℃,
The dimensional changes before and after 30 minutes of retort treatment were compared.

[Brief explanation of drawings]

Figure 1 is a schematic diagram of the force stress-strain curve (SS curve) according to JISC-2318-66, where the stress axis is the stress (strong, K
g), the horizontal axis is strain (elongation, %).

Claims (1)

[Claims] 1 Thickness: 7μ or more and 16μ or less, and 800≧A×B/C≧500, where A: Energy required for rupture (kg/%) B: Strength at breakage point (kg) C: Yield A packaging bag made of biaxially oriented polyethylene terephthalate film that satisfies the value of point strength (kg).