JP5222007B2 - Biodegradable synthetic resin film - Google Patents

Description

  The present invention relates to a biodegradable synthetic resin film. In particular, the present invention relates to a synthetic resin film that is a flexible synthetic resin film and has a characteristic of not deteriorating the global environment.

  As a synthetic resin for film formation, there are many olefin resins, vinyl chloride resins, polyamide resins, polyester resins and the like. Since these are all excellent in weather resistance, they are not easily decomposed even when exposed to wind and rain for a long time. For this reason, films made from these resins will remain indefinitely after being degraded and useless. Therefore, the film that is no longer useful is left unattended and worsens the environment.

  Agricultural and packaging films are consumed in large quantities as films. These films are preferably flexible films. A flexible film must be made of a flexible synthetic resin, but there are few types of flexible synthetic resins. Flexible resin is limited to soft vinyl chloride resin and polyolefin resin. Accordingly, as the synthetic resin film, a soft vinyl chloride resin film and a polyolefin resin film are produced in large quantities and discarded after use.

  The soft vinyl chloride resin film and the polyolefin film are both resins having good weather resistance as described above. Therefore, in order to dispose of these resin films that can no longer be used, there is no suitable method other than incineration. However, when these films are incinerated, they generate a large amount of carbon dioxide at one time and sometimes a carcinogenic poison such as dioxin. The generated carbon dioxide contributes to global warming, deteriorating the habitat of human beings and other living organisms. Therefore, it has been required to provide a new film that does not deteriorate the environment of the earth in place of the conventional film so that the conventional film can be easily decomposed by being devised.

  An attempt to make a conventional film easy to be decomposed includes blending starch powder with a soft vinyl chloride resin or polyolefin resin to impart biodegradability to the resin. This attempt is described in Patent Documents 1 and 2 below. However, in this attempt, the resin remains as it is simply by decomposing the starch, so that the film made of this resin remains perforated, which worsens the arrow tension environment.

  On the other hand, as a new resin film that does not deteriorate the global environment, a synthetic resin film having a property of decomposing spontaneously when buried in soil and being left as it is, a so-called biodegradable synthetic resin film is recommended. The biodegradable synthetic resin film must be made from a biodegradable synthetic resin. Biodegradable resins include fatty acid polyester resins obtained by condensing aliphatic dicarboxylic acids and aliphatic diols, and polyoxyls obtained by polymerizing aliphatic oxycarboxylic acids such as lactic acid. Carboxylic acid resins have been proposed.

  However, polylactic acid obtained by polymerizing the above lactic acid is a hard resin and lacks flexibility, so it is difficult to form a flexible film. Moreover, the above-mentioned fatty acid polyester resin changes greatly depending on what is used for dicarboxylic acid and diol. Therefore, it is not easy to determine the composition of the fatty acid polyester resin suitable for use as an agricultural or packaging film.

  Furthermore, a technique for adding starch powder to a biodegradable resin is also known. For example, Patent Document 3 below describes a biodegradable composition in which starch powder is added to polylactic acid to control the degradation rate. However, this composition is hard and difficult to make into a flexible film. Patent Document 4 below proposes blending starch with a biodegradable fatty acid polyester resin in order to facilitate forming into a film. However, this proposal is not aimed at obtaining a flexible film. In addition, this proposal only requires that a high molecular weight material having a molecular weight of 30,000 to 70,000 and a low molecular weight material having a molecular weight of 300 to 3,000 are blended in a specific ratio as a fatty acid polyester resin. A wide range of fatty acids and alcohols can be used.

Thus, until now, no biodegradable synthetic resin film having flexibility suitable for use in agriculture or packaging has been provided.
Japanese Patent Publication No.52-21536 Japanese Patent Publication No. 52-42187 Japanese Patent Laid-Open No. 5-39381 JP-A-6-313063

  The present invention is intended to provide a biodegradable synthetic resin film having flexibility and rigidity suitable for use in agriculture and packaging.

  This inventor has a number average molecular weight in the range of 10,000 to 200,000 as a resin, and a composition of polyester comprising succinic acid and 1,4-butanediol and lactic acid are copolymerized at a certain ratio. It has been found that the copolymer thus obtained has flexibility equivalent to that of a soft vinyl chloride resin and polyolefin, and is suitable for use as a film. However, this copolymer has the disadvantage that its softening point is somewhat low. The inventor has found that this disadvantage can be solved by blending starch powder into the copolymer. Furthermore, the inventor can add a large amount of starch powder to the copolymer to obtain a uniform composition, and the obtained composition can be easily melted and molded. In addition to the improvement of the softening point, it has been found that various unexpected effects such as improved biodegradability can be obtained. The present invention has been completed based on such knowledge.

  This invention is a film comprising 10 to 90 parts by weight of starch and 90 to 10 parts of synthetic resin, wherein the synthetic resin has a number average molecular weight in the range of 10,000 to 200,000, Is a copolymer comprising 0.02 to 30 mol% lactic acid units, 35 to 49.99 mol% succinic acid units, and mol% 1,4-butanediol units equal to the succinic acid units. The present invention provides a biodegradable synthetic resin film.

  The present invention also provides a biodegradable synthetic resin film obtained by laminating the above-mentioned synthetic resin film not containing starch or a film made of polylactic acid on one or both surfaces of the biodegradable synthetic resin film. is there.

  In the present invention, as a synthetic resin, a lactic acid unit having a composition of 0.02 to 30 mol%, a succinic acid unit of 35 to 49.99 mol%, and a 1,4-butanediol having a mol% equal to the succinic acid unit. Since a copolymer consisting of units was used, this copolymer was originally excellent in biodegradability, and since a starch powder was further added to this copolymer to form a composition, the film made with this was Biodegradability is even better. Moreover, in this invention, since the number average molecular weight of the said copolymer was specified in the range of 10,000-200,000, the composition obtained even if starch powder was added to this was suitable for shape | molding by heating and melting. The film obtained by forming it into a film is still tough and suitable for use in agriculture and packaging.

  Moreover, since the film made only of the copolymer is softened at about 100 ° C., in this invention, 10 to 90 parts by weight of starch powder is added to 90 to 10 parts by weight of the copolymer. The resulting composition has an increased softening point, and the resulting film has a softening point of about 110 ° C. or higher, thus improving heat resistance and can be used in a wide range.

  Furthermore, since the film made of the above copolymer containing starch has a portion of the starch exposed on the film surface, it has a hygroscopic property, and therefore is suitable for packaging a product which is preferable to remove moisture. On the other hand, in applications where this hygroscopicity is a drawback, the hygroscopicity can be weakened by laminating a copolymer film or polylactic acid film not containing starch on its surface.

  Furthermore, if both the synthetic resin and starch used in the present invention are buried in the soil, they will gradually decompose naturally into water and carbon dioxide. The generation of carbon dioxide in this case is gradual and does not pollute the environment because it does not occur in large quantities at the same time as when the resin is incinerated. In addition, both the synthetic resin and starch used herein can be made from plants and are not derived from petroleum. For this reason, the generated carbon dioxide is absorbed by the plant and becomes a synthetic resin and starch again. Therefore, carbon dioxide is circulated and used. For this reason, this invention brings about the effect which prevents global warming and prevents environmental pollution.

  In this invention, the synthetic resin has a composition of 0.02 to 30 mol% lactic acid units, 35 to 49.99 mol% succinic acid units, and a mol% 1,4-butanediol unit equal to the succinic acid units. A copolymer consisting of In the present invention, those having a number average molecular weight of 10,000 to 200,000 are selected from the above copolymers. Such a copolymer is sold as a biodegradable resin by, for example, Mitsubishi Chemical under the trade name GS Pla. In the present invention, such a commercially available resin can be used as it is.

In this invention, starch powder is used. Various types of starch can be used. For example, corn, wheat, rice, potato, sweet potato, tapioca and other starch powders can be used. The starch preferably has a particle size in the range of 2 to 40 μm.
As the starch powder, processed starch or modified starch can be used instead of starch as it is. As the modified starch or modified starch, starch, oxidized starch, hydroxypropyl starch or the like can be used.

  In the present invention, the copolymer and starch powder are mixed in the ratio of the former 10 to 90 parts by weight and the latter 90 to 10 parts by weight, particularly the former 20 to 80 parts by weight and the latter 80 to 20 parts by weight. A mixture of 30 to 70 parts by weight and the latter 70 to 30 parts by weight to make a total of 100 parts by weight is used. When a small amount of about 5 parts by weight of a metal soap such as magnesium stearate or an adhesive resin such as a copolymer of maleic anhydride and olefin is added to the mixture, kneading is facilitated.

  In order to make this mixture into a uniform composition, it is put into, for example, an extruder and heated to 130 to 150 ° C. to melt, the melt is extruded into a string shape, and this is cut into pellets once. Is preferred. At this time, the copolymer is particularly easy to pelletize compared to other resins. If another resin such as polyethylene or polypropylene is used in place of the copolymer, it may not be possible to form pellets due to insufficient bonding by the resin. Because nothing happens.

  In order to make a biodegradable synthetic resin film according to the present invention, the above pellets are again put into an extruder, heated and melted, and the melt is extruded into a film. A calendar roll can be used instead of the extruder. Although there is no special restriction | limiting in the thickness of the film at that time, It is preferable to make the thickness into the range of about 100 micrometers-2000 micrometers.

  In order to laminate the copolymer film or polylactic acid film not containing starch powder on one or both sides of the film thus obtained, a film not containing starch powder is separately prepared in advance, You may affix on the included film. At this time, an adhesive may be used, but it is preferable to bond the surfaces only by melting the surfaces without using the adhesive.

  Also, in order to make a film bonded as described above, rather than pasting the film once taken out as described above, by co-extrusion method, the film is formed at the same time and bonded together into a film. Is preferred. In the co-extrusion method, a resin containing starch powder and a resin not containing starch are melted in separate extruders, and the melts are separately introduced into one same die, on the inlet side of the die. In this method, the films are separately formed into a film shape, and the films are joined and bonded together at the outlet side of the die. Thus, it is preferable to make a laminated film all at once.

In the laminated film, the surface film that does not contain starch powder is made thinner than the film that contains starch powder. The thickness of the film containing no starch is preferably 1/3 to 1/100 of the thickness of the film containing starch.
In the present invention, the object is expressed as a film, but it is not expressed as such in consideration of the thickness of the film. According to a certain book, a film having a thickness of 0.10 mm or less is called a film, and a film having a thickness of more than 0.10 mm is called a sheet. In the present invention, such a distinction is ignored, and a film is called. The seat is included.

  Next, the reason why the film according to the present invention is excellent will be specifically described with reference to Examples and Comparative Examples.

[Example 1]
As the synthetic resin, a copolymer having a number average molecular weight of 70,000 and a composition of 4 mol% lactic acid units, 48 mol% succinic acid units, and 48 mol% 1,4-butanediol units was used. As the starch, tapioca starch having an average particle size of 17 μm was used.

  30 parts by weight of the above starch and 70 parts by weight of the above copolymer and 5 parts by weight of a polyethylene / unsaturated carboxylic acid-modified polypropylene copolymer resin (manufactured by Mitsubishi Chemical Corporation, Modic 912T) as an adhesive resin are added to total 105 parts by weight. Made a mixture of. This mixture was put into a twin screw extruder, the cylinder temperature was kept at 140 to 150 ° C., the die temperature was kept at 160 ° C., extruded into a string shape, cooled and cut into pellets. This pelletization was easy.

The above pellets were again put into an extruder, the cylinder temperature was 130 to 150 ° C., the die temperature was kept at 160 ° C., and the film was extruded into a film to obtain a film having a thickness of 0.3 mm.
This film had moderate flexibility. The softening point was 120 ° C. This film was suitable for use as a packaging film as it was.

The film was vacuum formed into a container. This container was suitable for food such as dry noodles.
The film was cut into a size of 5 cm × 18 cm and buried in soil to evaluate biodegradability. 120 days after burial, the original shape was not retained.

[Example 2]
In this example, the same type of copolymer as used in Example 1, starch and an adhesive resin were used in the same manner. However, the amount of the starch used was reduced while the amount of the copolymer used was reduced. The mixture was further mixed at a ratio of 50 parts by weight of the former and 50 parts by weight of the latter to make a total of 105 parts by weight of the mixture.

This mixture was put into an extruder, and pellets were once obtained in the same manner as in Example 1 and again put into an extruder to form a 0.3 mm thick film. This pelletization and film formation were easy.
The obtained film had moderate flexibility. This film was vacuum formed into a container. This container had a softening point of 125 ° C. and was not deformed even when food at 100 ° C. was added.

Further, the above film was cut into a size of 5 cm × 18 cm, buried in the soil, and allowed to stand for 30 days, 60 days, 90 days and 120 days under natural conditions, and the weight change of the film was measured. The weight reduction rate Y (%) of the film was calculated by the following equation, where X ₀ was the weight of the film before being buried in the soil, and X ₁ was the weight of the film after being left in the soil.
Y (%) = (X ₀ −X ₁ ) ÷ X ₀ × 100

  In addition, for comparison, a composition having only the starch removed from the composition of the film, that is, a similar film composed of 50 parts by weight of the copolymer and 5 parts by weight of the adhesive resin was prepared, and this was the same as the above film. It was buried in the soil and allowed to stand, the change in weight was measured, and the weight reduction rate Y (%) was calculated. The results are shown in Table 1 below.

  Thereby, when starch was added, it was confirmed that a weight reduction rate will increase about 1.5 times.

Example 3
In this example, the same type of copolymer and starch as used in Example 1 were used. However, the amount of copolymer used was further reduced, and the amount of starch used was increased. The adhesive resin was used as it was. That is, in this example, 30 parts by weight of a copolymer, 70 parts by weight of starch, and 5 parts by weight of an adhesive resin were blended to obtain a mixture.

This mixture was put into an extruder, pellets were once made in the same manner as in Example 1, and this was again put into the extruder, and a film having a thickness of 300 μm was made in the same manner as in Example 1. In this case, pelletization and film formation were easy.
The obtained film had moderate flexibility and was suitable as a packaging film. Further, this film had a softening point of 130 ° C.

  This film was vacuum formed to make a rectangular container of 55 mm × 85 mm × 20 mm. The container was placed in an oven maintained at various temperatures for 30 minutes and the deformation of the container was observed. For comparison, a film having a composition not containing only starch was prepared, this film was formed into a rectangular container of the same size, and similarly placed in an oven to observe the deformation of the container. The results are shown in Table 2 below.

  This confirmed that starch increased the softening point of the copolymer and improved heat resistance.

Example 4
In this example, a film made of a starch-containing copolymer is used as an intermediate layer, and a surface film made of a copolymer without starch is bonded to both sides thereof to form a laminated film made of three layers.

  As the intermediate layer, a film having a composition of 70 parts by weight of the starch powder prepared in Example 3 and having a thickness of 240 μm was used, and as the surface layer, the starch used in Example 3 was not included. A film made of only a polymer and having a thickness of 30 μm was used and bonded by a co-extrusion method to obtain a laminated film having a thickness of 0.3 mm consisting of three layers of 30/240/30 μm. The production of this laminated film was easy.

This laminated film had moderate flexibility and a softening point of 130 ° C. This laminated film can be used for packaging as it is. Further, this laminated film was vacuum formed into a container. This container was suitable for containing cooked food.
Further, when this laminated film was buried in the soil and left under natural conditions, the original shape could not be retained in 120 days.

  This laminated film is superior in heat resistance compared to a single-layer film having the same thickness composed of an intermediate layer, and can be easily bonded to another film and sealed, and the starch powder is exposed on the surface. Since there is no, there is an advantage that there is no slime due to moisture. On the other hand, this laminated sheet has the disadvantage that the biodegradability is poor because the starch powder is not exposed on the surface.

Example 5
In this example, a film made of a starch-containing copolymer is used as an intermediate layer, and a film made of polylactic acid without starch is bonded to both sides thereof to form a three-layer laminated film.

  As the intermediate layer, a film having a composition of 30 parts by weight of the starch powder produced in Example 1 and having a thickness of 240 μm was used, and the surface film was made of polylactic acid (manufactured by Toray Industries, Inc., product: name Ecodia). A film having a thickness of 30 μm was used and laminated by a coextrusion method to obtain a laminated film. The production of this laminated film was easy.

This laminated film was flexible and had a softening point of 120 ° C. This laminated film could be used as a packaging bag as it was. Further, this laminated film was vacuum formed into a container. This container was suitable for containing cooked food.
Moreover, when this container was buried in the soil and left under natural conditions, the original shape could not be retained in 120 days.

[Comparative Example 1]
In Example 1, a copolymer film having a thickness of 300 μm was prepared in exactly the same manner as in Example 1 except that only the copolymer was used without using starch.

This film was flexible, and its softening point was 110 ° C. Compared with the film obtained in Example 3, this film was inferior in heat resistance as described in Example 3.
Moreover, when this film was buried in the soil as it was and left under natural conditions, it biodegraded, but the biodegradability was inferior to that obtained in Example 2 as described in Example 2. It was.

[Comparative Example 2]
In Example 1, 70 parts by weight of polyethylene and starch were used in the same manner as in Example 1 except that high-density polyethylene (manufactured by Prime Polymer Co., Ltd., trade name: HDPE, 548B) was used instead of the copolymer. A mixture of 30 parts by weight of powder was made and placed in a twin screw extruder to make pellets.

However, when extruded as a string from a twin-screw extruder, the extrudate foamed and a good pellet could not be obtained.
In addition, the incomplete pellets thus obtained were put into an extruder to be formed into a film, but could not be formed into a film.

Claims (5)

A film comprising 10 to 90 parts by weight of starch powder and 90 to 10 parts of synthetic resin, the synthetic resin having a number average molecular weight in the range of 10,000 to 200,000 and a composition of 0.00. Both sides of a film which is a copolymer comprising 02-30 mol% lactic acid units, 35-49.99 mol% succinic acid units, and mol% 1,4-butanediol units equal to the succinic acid units. The film of the synthetic resin or polylactic acid film not containing the starch powder is bonded to the film, and the thickness of the film or polylactic acid film not containing the starch powder is 1 to 100 of the thickness of the film containing the starch powder. A flexible biodegradable laminated resin film, characterized in that it is reduced to one part . The synthetic resin has a number average molecular weight of 3 to 200,000, a composition of 2 to 20 mol% lactic acid units, 45 to 49.5 mol% succinic acid units, and a number of moles equal to the succinic acid units. The flexible biodegradable laminated resin film according to claim 1, which is a copolymer comprising 1,4-butanediol units. The flexible biodegradable laminated resin film for container molding or agriculture according to claim 1 or 2 , wherein the thickness of the laminated resin film is in the range of 20 to 2000 µm. The laminated resin film according to any one of claims 1 to 3 , wherein the starch powder is a fine powder substantially in the range of 2 to 40 µm. The laminated resin film according to any one of claims 1 to 4 , wherein the starch powder is tapioca starch.