JPH08103963A - Manufacture for biodegradable bag - Google Patents

Abstract

PURPOSE: To manufacture a bag-shaped object of excellent content holding capability and biodegradation by attaining high thermal fusion strength from a biodegradable aliphatic polyester film whose main component is poly-(2- oxetanone) by means of thermal fusion treatment under particular conditions. CONSTITUTION: In manufacturing a biodegradable bag, a repetitive unit expressed by a formula is taken as a main repetitive unit, and at least a part of the film consisting of biodegradable aliphatic polyester whose weight-average molecular weight is 20-2000 thousand is compressed for thermal fusion for 0.1-10 seconds within a temperature range between a temperature lower than its melting point by 10 deg.C and the melting point, and is formed into a bag shape. It is thus possible to manufacture a bag-shaped object of excellent content holding capability and biodegradation from a biodegradable aliphatic polyester film whose main component is poly-(2-oxetanone) and whose temperature range is restricted, which can attain high thermal fusion strength because it has high crystallinity.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a biodegradable bag composed of a biodegradable aliphatic polyester film which is decomposed by the action of microorganisms in the environment.

[0002]

2. Description of the Related Art As the problem of waste treatment becomes a social problem, the study of recycling garbage is being considered in various fields. For example, composting of raw garbage discharged from homes is being considered as one means of recycling this garbage resource. In fact, raw garbage is separated and collected in various places and is being processed in composting plants.

Paper bags are currently used for the separate collection of raw garbage for composting. Since paper is a natural material, it can be composted. But it also has many problems. For example, it is easy to be broken by water in raw garbage, its contents are not identifiable because it is opaque and it cannot prevent the mixture of composting incompatible substances, it requires a string of natural material to close its mouth, it needs a place to store because it is bulky. In addition, there are problems in use such as slow biodegradation of paper and global environmental problems such as consumption of wood resources. Such problems are also a factor to suppress the recycling of garbage.

[0004] It is plastic waste that causes the greatest problems in the separate collection. In particular, plastic films are easy to scatter in the environment, do not rot and disappear, the incinerator is easily damaged due to the large amount of combustion heat, and the appearance is large, which shortens the life of landfill sites. Is causing serious problems. Biodegradable plastic materials are attracting attention as one of the solutions to these plastic waste problems.

[0005] For example, it is desired to use it as a garbage bag suitable for composting garbage. In particular,
It is water resistant and does not break due to water in garbage, it is transparent or translucent and its contents can be confirmed, it is thin enough and not bulky, and it can tie the bag's entrance and does not require any string. Further, there is an urgent need to develop a material having a strength capable of withstanding the weight of the contents.

[0006] In addition to garbage bags for garbage, fertilizer bags, bags for agricultural and horticultural wastes, etc. are bags that can be used or recycled as they are without processing the bags after removing the contents. Development is desired.

In recent years, various biodegradable plastic materials have been developed. However, a material satisfying biodegradability, film moldability, processed physical properties, etc. and being used to such an extent as to actually reduce the waste problem has not yet been developed.

For example, since poly (3-hydroxybutyric acid) biosynthesized by microorganisms has a melting point and a decomposition temperature close to each other,
There is a problem with moldability. In addition, the compound with starch has a problem of water resistance, and the chemical compound is concerned about biodegradability.

Poly (2-oxetanone), which is a polyester synthesized from 2-oxetanone, is known to be well decomposed by the action of enzymes secreted by microorganisms, and is a material that can cope with the problem of plastic waste. Is expected to be developed (Mukai et al., Polymers, 50
Volume 10, 715-722 (1993)).

The polymerization reaction formula from 2-oxetanone to poly (2-oxetanone) is as follows.

[0011]

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The fact that poly (2-oxetanone) is a material having good biodegradability is reported by Fields et al. In 1975 (RD Fields and F. Rodriguez, Proc. Int. Biodeg.
radation Symp. 3rd, 775 (1975)), it is well known, but physical properties other than biodegradability have not been reported in detail. Kagaya et al. Have a film-forming ability when the absolute viscosity [η] of the solution is 0.5 or more.
The above-mentioned materials are reported to be capable of fiber-forming ability and cold stretching of the film (Taku Kaguya, Musashi Saina, Kenichi Fukui, Journal of Industrial Chemistry, Vol. 67, No. 6, 951 (1964)). Kazuo et al. Made a film made from chloroform by solvent casting method at room temperature and hot water at 65 ° C at 500-700%.
Stretching and conducting spectroscopic research on film structure (Takeshi Wazai, Takeo Saegusa, Junji Furukawa, Journal of Industrial Chemistry,
67, No. 4, 601 (1964)). Matissen et al. Reported a good value of 103 MPa, in which poly (2-oxetanone) was sandwiched between mylar films, which was heated and compressed to form a 0.5 mm-thick sheet, which was stretched. (T. Mathisen, M. Monica, and A.-C. Albe
rtsson, Journal of Applied Polymer Science, Vol.4
2, 2365 (1991)).

As described above, poly (2-oxetanone)
The development of is limited to the experimental scale stage, and there is no clear report that a film satisfying the various physical properties to be industrially practically used has been formed. Regarding the physical properties of the film, only the tensile strength and melting point have been reported. The reason is that it is not easy to synthesize high molecular weight poly (2-oxetanone) that can be formed into a film, and even if relatively high molecular weight poly (2-oxetanone) can be synthesized, the film forming process is difficult. It seems that it was difficult to synthesize as much as possible, and the conditions of the molding process were not clear.

However, since the results suggesting good biodegradability and tensile strength were obtained, poly (2
-Oxetanone) is expected to grow, and urgent development of practical biodegradable bag-like products such as garbage bags is desired.

[0015]

SUMMARY OF THE INVENTION The object of the present invention is to
Biodegradability of oxetanone as the main structural component of the ring-opening structure,
It is to provide a manufacturing method for obtaining a practical bag-like product from a film having excellent mechanical properties and moldability.

[0016]

Means for Solving the Problems As a result of intensive studies to solve the above-mentioned problems, the present inventors have found that the heat-bonding strength and the practical use can be improved by controlling the pressure-bonding temperature and time of the film. It was found that a biodegradable bag having other good physical properties was obtained, and the present invention was completed.

That is, the present invention provides the following formula (1):

[0018]

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At least a part of a film made of a biodegradable aliphatic polyester having a repeating unit represented by the following as a main repeating unit and having a weight average molecular weight of 2 to 2,000,000 is in a temperature range of 10 ° C. lower than the melting point and lower than the melting point. The method for producing a biodegradable bag is characterized by pressing for 0.1 to 10 seconds and heat-sealing to form a bag.

The biodegradable bioaliphatic polyester film in the present invention basically comprises a biodegradable bioaliphatic polyester having a repeating unit represented by the above formula (1) as a main repeating unit.

The polyester composed of only the main repeating unit is poly (2-oxetanone),
By ring-opening polymerization of oxetanone, or
It can also be obtained by dehydration polycondensation of hydroxypropionic acid.

The biodegradable bioaliphatic polyester in the present invention comprises, in addition to the repeating unit represented by the formula (1), a ring-opening structural unit of a cyclic ester compound other than 2-oxetanone and a cyclic ether compound as a monomer unit. 0.1 to
Including the case of 20% by weight copolymerization. Examples of the cyclic ester include β-butyrolactone, pivalolactone, δ-valerolactone, and ε-caprolactone. Examples of the cyclic ether compound include ethylene oxide and propylene oxide.

The biodegradable bioaliphatic polyester in the present invention is preferably a polymer having a weight average molecular weight of 20,000 or more. If the weight average molecular weight is less than 20,000, mechanical properties such as strength and elongation may be insufficient depending on the purpose of use and method of the film, and it is difficult to put it into practical use. On the other hand, when the weight average molecular weight is extremely high, processing may be difficult due to high viscosity during melt molding. Therefore, it is suitable that the molecular weight is preferably 2,000,000 or less.

The biodegradable bioaliphatic polyester film in the present invention can be obtained by a generally known melt extrusion molding method. Suitable processing methods are, for example, T-die extrusion molding and inflation molding. The biodegradable bioaliphatic polyester film film to be used is usually used for molding in the form of an aliphatic polyester obtained by polymerization, that is, in the form of powder or granules, but it is also a preferred embodiment to pelletize it prior to molding. .

In the melt molding of the film, the processing conditions preferably carried out are barrel and die temperature 8
The temperature is preferably 0 to 180 ° C, more preferably 100 to 150 ° C. At temperatures below 80 ° C, the biodegradable bioaliphatic polyester of the present invention is insufficiently melted, and at temperatures above 180 ° C, thermal decomposition of the biodegradable bioaliphatic polyester of the present invention becomes remarkable, which is not preferable. . However, the barrel temperature just below the hopper can be carried out even at a temperature lower than 80 ° C.

The mechanical properties of the biodegradable bioaliphatic polyester film of the present invention can be further improved by stretching the unstretched film after melt extrusion. As a stretching method, a generally known stretching method such as roll stretching or stretching by a tenter method can be used without any limitation. The stretching conditions may be a temperature range of room temperature to 80 ° C. and a stretching ratio of 2 to 15 times. In order to increase the processing speed and improve the efficiency, it is more preferably carried out in the temperature range of 70 to 80 ° C. Stretching can be carried out in any manner such as uniaxial stretching for forming a uniaxially oriented film, sequential biaxial stretching for biaxial orientation, and simultaneous biaxial stretching for plane orientation. When stretched, the tensile breaking strength in the stretching direction is usually 500 to 5000 kgf.
/ Cm ² .

In the present invention, the thickness of the film is preferably in the range of 1 to 300 μm. Since the biodegradable bioaliphatic polyester in the present invention usually has crystallinity, the crystals formed in the film affect the transparency. The transparency of a film changes depending on the thickness of the film, and the transparency decreases as the thickness of the film increases. For example, in order to develop a semitransparent to transparent mode in which the contents of the bag-shaped product formed from the film of the present invention can be identified, the thickness of the film is preferably 300 μm or less. In order to maintain the flexibility and sufficient mechanical strength, the range of 1 to 100 μm is more preferable.

The biodegradable bag in the present invention is usually formed by heat-sealing at least a part of the melt-extruded film and the stretched film thereof. For example,
In the case of an inflation film, a bag is formed by heat-sealing one end of a tubular film.

In order to retain the contents of the molded bag, the mechanical strength and the fusion strength of the heat-sealed portion are important. For the function of holding the contents, the fusion strength of the heat fusion portion is an important requirement. The heat-sealing strength of commonly used films such as polyethylene is 500 to 10
It is about 00 gf / 15 mm. Therefore, 500gf /
A heat fusion strength of 15 mm or more can be considered as an effective heat fusion strength.

The method for producing a biodegradable bag of the present invention provides a method for causing the biodegradable bioaliphatic polyester film to be heat-sealed so as to exhibit high heat-sealing strength.

The heat fusion phenomenon is a phenomenon in which molecules are diffused and integrated with each other due to partial melting of the film surface portions in contact with each other. The degree of diffusion of the molecules and the intermolecular cohesive force, Further, the re-formation of crystals in the diffused portions has a great influence on the heat fusion strength.

Poly (2-oxetanone) in the present invention
The biodegradable bioaliphatic polyester having as a main structural component has an ester structure in the main chain, has a relatively high intermolecular cohesive force due to its high polarity, and is high because it is a crystalline polymer. Heat fusion strength is expected. However, the biodegradable bioaliphatic polyester film in the present invention, in particular,
The stretched film has a high crystallinity of up to 80% or more. A polymer having such high crystallinity has a sharp melting behavior, and the temperature range from the start of melting to the melt flow is very narrow. When it is extremely close to the melt flow state, the heat fusion portion is constricted due to partial melting, or the relaxation of stretching in a wider range causes a remarkable decrease in heat fusion strength. Therefore, the heat fusion strength is determined by the trade-off between the strength improvement due to diffusion crystallization of molecules due to partial melting and the reduction in mechanical strength of the melted portion.

We have found that the biodegradable bioaliphatic polyester film of the present invention has a region which exhibits a remarkably high heat fusion strength in a very narrow temperature range. If it deviates from that temperature range, an effective fused state cannot be obtained.

The conditions for exhibiting effective heat-sealing strength are that the film is in a temperature range of 10 ° C. lower than its melting point and lower than its melting point, more preferably 5 ° C. lower than its melting point and lower than its melting point, and The conditions are such that the pressure is applied for 0.1 to 10 seconds, preferably 0.5 to 5 seconds, and more preferably 0.5 to 1 second. It is preferable that the closer the temperature is to the melting point, the shorter the pressure bonding time. Only when these conditions are satisfied, an effective and high heat fusion strength of 500 gf / 15 mm or more is developed. 10 ℃ from the melting point of each film
At temperatures below the lower temperature, no thermal fusion occurs or the fusion strength is insufficient. On the contrary, when the temperature exceeds the melting point of each film, the film melts rapidly and the fusion strength becomes unmeasurable. If the pressure bonding time is less than 0.1 seconds, effective heat fusion strength cannot be obtained. In particular, it is remarkable when the temperature is lower than the temperature range of the present invention. On the other hand, if it exceeds 10 seconds, film thinning or fusion cutting occurs, and effective heat fusion strength cannot be obtained. In particular, it is remarkable when the temperature is higher than the temperature range of the present invention.

The heat fusion temperature range is defined as a temperature range lower than the melting point by 10 ° C. or more and not more than the melting point, and the most preferable fusion strength is exhibited depending on the shape of the film, additives, stretching conditions and the like. The heat fusion conditions (heat fusion temperature and pressure bonding time) to be applied are slightly different. The reason for this is based on the difference in the thermal physical properties of the films, for example, the melting point changes depending on the draw ratio.

The melting point of the film of the present invention is generally measured using a differential scanning calorimeter or the like, and the temperature changes depending on various factors such as the type and amount of copolymerization components, stretching conditions, crystal structure and crystallinity. However, it usually exists in the range of 70 to 90 ° C.
For example, in the case of a poly (2-oxetanone) film that does not contain a filler and is uniaxially stretched 4.5 times at 75 ° C., its melting point is 86.5 ° C. and contains 5% by weight of talc.
Poly (2-oxetanone) uniaxially stretched 4.6 times at ℃
In the case of a film, its melting point is 81.3.

As a heat fusion method, generally, a device such as a seal bar type or roller type heat sealer is preferably used. Thermal fusion is performed by sandwiching and pressing the biodegradable bioaliphatic polyester film of the present invention between a pair of seal bars heated to a predetermined temperature. At this time, the biodegradable bioaliphatic polyester of the present invention,
Since the main chain has an ester structure and has high polarity, the surface material of the seal bar is more preferably a surface-treated fluorine resin rather than metal itself, or a resin with low polarity. The heat fusion is performed by sandwiching between a pair of seal bars and applying an appropriate load. The load applied to the seal bar is preferably 0.5 to ⁵ Kgf / cm ² . In general, it is preferable to apply a larger load when the heat fusion temperature is high or when the film is thick.

A filler can be added to the biodegradable bioaliphatic polyester film in the present invention within a range not particularly deteriorating the physical properties. As the filler that can be added, generally known fillers can be used without any limitation, and alkaline earth metal salts are particularly preferable because they contribute to the stabilization of the biodegradable bioaliphatic polyester.

Here, the alkaline earth metal includes calcium, magnesium, barium and the like, but calcium and magnesium are particularly preferable in view of the influence on the environment. Further, the alkaline earth metal salts are hydrochlorides, sulfates, carbonates and silicates of alkaline earth metals,
Specifically, hydrochlorides such as calcium chloride and magnesium chloride; sulfates such as magnesium sulfate and barium sulfate; carbonates such as magnesium carbonate and calcium carbonate; calcium orthosilicate, calcium metasilicate,
It is a hydrated magnesium silicate such as dicalcium silicate, tricalcium silicate, sodium calcium silicate, calcium aluminum silicate, magnesium orthosilicate, magnesium metasilicate, talc, and magnesium silicate. Among these alkaline earth metal salts, silicates, which have low hygroscopicity and are easy to handle, and particularly alkaline earth anhydride salt, which has a particularly remarkable stabilizing effect on the biodegradable bioaliphatic polyester, are most preferably used. . Each of the above alkaline earth metal salts may be used alone or in combination.

The above-mentioned alkaline earth metal salt is preferably used in the film of the present invention in an amount of 20% by weight or less based on the biodegradable bioaliphatic polyester.

The biodegradable bioaliphatic polyester film in the present invention is an antioxidant, depending on its purpose and application.
Auxiliary components such as release agents, weathering agents, antistatic agents, colorants, reinforcing materials, surfactants and inorganic fillers can also be added.

[0042]

INDUSTRIAL APPLICABILITY The method for producing a biodegradable bag of the present invention uses poly (2-oxetanone) having a limited temperature range capable of exhibiting effective heat fusion strength because it has high crystallinity. From the biodegradable bioaliphatic polyester film as the main structural component, a bag having excellent heat retention strength and biodegradability by expressing high heat fusion strength by fusion treatment under specific heat fusion conditions. Provided is a method of molding a shaped article.

The biodegradable bag produced according to the present invention can be put to practical use for various products, for example, bags such as garbage bags and shopping bags. Moreover, the bag is decomposed by microorganisms even when left in the natural environment, and
Converted to compost by compost plant.

[0044]

The present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.

Production Example 1 (1) Preparation of T-die Extruded Film Poly (2-oxetanone) particles (weight average molecular weight 412
000, number average molecular weight 183,000) is supplied to an extruder having a barrel with a diameter of 40 mm and equipped with a T-die, and is fed by a screw into the extruder barrel having a barrel set temperature of 90 to 110 ° C and a T die set temperature of 106 to 110 ° C. The molten film was extruded from the T-die slit. The extruded molten poly (2-oxetanone) is cooled and solidified by a chilled roll in which water having a water temperature of about 23 to 26 ° C circulates, and wound on a winder to have a thickness of about 250 to 2
An 80 μm unstretched film was prepared.

(2) Preparation of Uniaxial Roll Stretched Film The unstretched film was vertically stretched on a roll heated at 75 ° C. between the slow (front) drive roll and the fast (rear) drive roll by 4.5. The film was stretched twice to produce a uniaxial roll stretched film. The melting point of this film is the differential scanning calorimeter (DS
As a result of measurement using C), it was 86.5 ° C.

Production Example 2 (1) Preparation of T-die Extruded Film Poly (2-oxetanone) particles (weight average molecular weight 407
000, number average molecular weight 158,000) was mixed with 5% by weight of talc, and this mixture was fitted with a T-die to a diameter of 40
It is supplied to an extruder having a barrel of mmφ, barrel setting temperature is 90 to 110 ° C, T die setting temperature is 106 to 110 ° C.
The melted film was extruded from the T-die slit by a screw into the extruder barrel. The extruded molten poly (2-oxetanone) / talc mixture is cooled and solidified by a chilled roll having a water temperature of about 23 to 26 ° C. in which water circulates, and wound on a winder to have a thickness of about 250 to 28.
An unstretched film of 0 μm (Sample No. 13) was prepared.

(2) Preparation of Uniaxial Roll Stretched Film The unstretched film was stretched longitudinally on a roll heated to 75 ° C. arranged between a slow (front) drive roll and a fast (rear) drive roll. The film was stretched twice to produce a uniaxial roll stretched film. The melting point of this film is the differential scanning calorimeter (DS
The result of measurement using C) was 81.3 ° C.

Production Example 3 (1) Preparation of pellets Poly (2-oxetanone) particles (weight average molecular weight 392)
000, number average molecular weight 110000) and 5% by weight of talc were mixed, and this mixture was fed to a twin-screw extruder having a barrel temperature of 50 to 100 ° C. The strand extruded from the die was cooled in a water tank and then cut into pellets. The pellets were dried in an oven at 50 ° C overnight.

(2) Preparation of blown film The above pellets were fed to an extruder having a barrel having a diameter of 40 mm and equipped with a blow molding die, and the barrel set temperature was 100 to 110 ° C and the die set temperature was 95 to 100 ° C. The molten tubular film was extruded from the die slit by feeding it into the extruder barrel with a screw. The extruded molten poly (2-oxetanone) / talc mixture was cooled and solidified while being blown up by cold air blown from the center of the die. The tubular film that was blown up was taken up by a winder, and the width was 330 mm and the thickness was about 2
An inflation film having a thickness of 0 to 25 μm was prepared.
The melting point of this film was 77.9 ° C. as measured by a differential scanning calorimeter (DSC).

Examples 1 to 4, Comparative Examples 1 to 2 From the uniaxial roll stretched film prepared in Production Example 1, 15
A test sample of x150 mm was cut out, two test samples were superposed, and a heat fusion test was performed using a heat sealer. In the heat fusion, the temperature of the lower seal bar was fixed at 80 ° C, the temperature of the upper seal bar was set to the temperature shown in Table 1, the sealing time was 1 second or 5 seconds, and the load was 1 Kgf / cm.
Went in ² . The fusion strength was measured by a peeling test method for two films at 23 ° C. and a pulling speed of 10 mm / min. Ten samples were measured, the maximum value and the minimum value were removed, and the rest were averaged to obtain the heat fusion strength (gf / 15 mm). The obtained fusion strength is also shown in Table 1. It was confirmed that the heat sealing strength was equal to or higher than the heat sealing strength of a commonly used polyethylene bag, and that the heat sealing strength was sufficiently higher than that of the comparative example.

[0052]

[Table 1]

Examples 5-8, Comparative Examples 3-4 From the uniaxial roll stretched film prepared in Production Example 2, 15
A test sample of x150 mm was cut out, two test samples were superposed, and a heat fusion test was performed using a heat sealer. For heat fusion, the temperature of the lower seal bar was fixed at 80 ° C, the temperature of the upper seal bar was set to the temperature shown in Table 2, and the sealing time was 1 second or 5 seconds and the load was 1 Kgf / cm.
Went in ² . The fusion strength was measured by a peeling test method for two films at 23 ° C. and a pulling speed of 10 mm / min. Ten samples were measured, the maximum value and the minimum value were removed, and the rest were averaged to obtain the heat fusion strength (gf / 15 mm). The obtained fusion bonding strength is also shown in Table 2. It was confirmed that the heat sealing strength was equal to or higher than the heat sealing strength of a commonly used polyethylene bag, and that the heat sealing strength was sufficiently higher than that of the comparative example.

[0054]

[Table 2]

Example 9 The blown film prepared in Production Example 3 was cut to a width of 6
It was cut into 00 mm, and one of the cut portions was heat-sealed with a heat sealer. The heat fusion was performed by fixing the temperature of the upper and lower seal bars at 75 ° C., the sealing time of 5 seconds, the load of 1 Kgf / cm ² , and the sealing width of 10 mm. About 60% water in this bag
As a result of putting 10 kg of raw garbage such as vegetables containing the same in the room for 3 days, no rupture of the film or leakage of the contents due to opening was observed at all. The bag containing the garbage was directly buried in the weeds at a depth of about 10 to 20 cm below the ground. When it was dug out after 3 months, the film collapsed, and most of the film disappeared with the composting of raw garbage.

Comparative Example 5 A test sample similar to that of Example 1 was cut out from a biodegradable plastic film composed of starch and modified polyvinyl alcohol, and a heat fusion test was performed using a heat sealer. The heat fusion was performed with the temperature of the upper and lower seal bars set to 150 ° C., the sealing time of 1 second, and the load of 1 Kgf / cm ² . The fusion strength was measured by a peeling test method for two films at 23 ° C. and a pulling speed of 10 mm / min. Measure 10 samples, average the rest except the maximum and minimum values,
The heat fusion strength (gf / 15 mm) was used. The fusion strength obtained was 421 gf / 15 mm.

Claims (1)

[Claims] 1. The following formula (1): At least a part of a film made of a biodegradable aliphatic polyester having a weight average molecular weight of 2 to 2 million with a repeating unit represented by
0.1 to 10 in the temperature range of 0 ° C lower than the melting point and lower than the melting point.
A method for producing a biodegradable bag, which comprises press-bonding for 2 seconds and heat-sealing to form a bag.