JPH07257660A - Packaging film for food - Google Patents

Abstract

PURPOSE:To obtain a packaging film for food which is excellent in preservability of food, resistance against molds and transparency and which does not accumulate in the natural circumferences after disposal thereof. CONSTITUTION:A packaging film for food is chiefly made of a lactic polymer. Steam permeability of the packing film for food is 50-300g/m<2>.24hr (40 deg.C, 90% RH) and the thickness is 10-500mum.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a food packaging film containing a lactic acid polymer as a main component, which is used as a packaging material for vegetables, fruits, flowers and other processed foods.
Specifically, it is a film made of a thermoplastic polymer composition containing a lactic acid-based polymer having hydrolyzability as a main component, has a specific water vapor permeability, is excellent in transparency, and does not cause mold or the like during use. The present invention relates to a food packaging film which has excellent mold resistance and does not accumulate in a natural environment after disposal.

[0002]

2. Description of the Related Art Conventionally, films, nets, baskets and the like obtained from synthetic resins such as polyolefin, polystyrene and polyvinyl chloride have been used for packaging foods. These packaging materials do not take into consideration the physiological effects of fruits and vegetables particularly during transportation and storage. Therefore, for example, the water vapor emitted from fruits and vegetables and the like causes moisture to be generated due to various causes, causing stuffiness and decay.

As a method for solving such a problem, for example, in JP-A-55-38268, the water vapor permeability is 45 to 250 g / m ² , and the specific oxygen permeability and carbon dioxide gas permeability are A method of packaging a collection of fruits and vegetables using a film or sheet having a certain degree for shipping or storage is disclosed. The publication describes that a biaxially stretched polystyrene film is preferably used as the film or sheet having the above characteristics.
However, the biaxially stretched polystyrene film is excellent as a packaging material for fruits and vegetables in that it has appropriate water vapor transmission rate, oxygen transmission rate, carbon dioxide transmission rate, etc., but is it extremely degradable in the natural environment? Or, since it shows almost no degradability, if it is discarded after use, it will be accumulated as waste unless it is incinerated, collected, or reused.

A method of collecting and reusing packaging materials and the like used industrially after use can be considered. However, it is actually extremely difficult to collect and reuse packaging materials and the like, which are often discarded from general households, such as food packaging materials, because the distribution channels are complicated. Therefore, in recent years, attempts have been made to impart degradability to materials mainly used for disposable applications such as food packaging materials.

For example, JP-A-2-14228 discloses a compounded polymer obtained from a melt containing a degraded starch containing water and at least one substantially water-insoluble synthetic thermoplastic polymer. Further, as the synthetic thermoplastic polymer, polyolefin, polyacetal, thermoplastic polyester, polycarbonate, polyalkylene terephthalate, etc. are disclosed. Further, JP-A-3-31333 discloses a polymer composition for producing a biodegradable plastic article, comprising an ethylene / vinyl alcohol copolymer and a modified starch, wherein the ethylene / vinyl alcohol copolymer is ethylene. Content 10
~ 90% by weight and a melt flow index of 20
Polymer compositions that are .about.50 are disclosed.

[0006] However, food packaging materials using the compounded polymers, polymer compositions, etc. disclosed in the above publications are
It is said that the packaging material collapses and loses its original shape due to the decomposition of starch, but the non-degradable polymer itself such as ethylene / vinyl alcohol copolymer remains as it is, and rather promotes environmental pollution. In addition, the problem of decreased transparency due to the addition of starch, and the fact that exposure of starch to an environment with a high amount of moisture will cause mold and the like to cause mold resistance, resulting in lack of mold resistance. It is not suitable for.

On the other hand, polylactic acid has hitherto been widely known as a hydrolyzable polymer. For example, Japanese Patent Publication No.
Japanese Patent No. 2734 discloses a surgical fiber product composed of filaments of polylactic acid having a specific intrinsic viscosity. Furthermore, in recent years, application of lactic acid-based polymers such as polylactic acid and lactic acid-hydroxycarboxylic acid copolymer as a basic raw material of decomposable general-purpose materials for disposable applications other than the above-mentioned pharmaceutical applications has been considered. However, the fact is that no attempt has been made to use the polylactic acid in the film for food packaging by taking advantage of the unique properties of polylactic acid.

[0008]

DISCLOSURE OF THE INVENTION The present invention solves the above-mentioned problems and has good storability, mold resistance and transparency of food, and does not accumulate in a natural environment after disposal. It is intended to provide a packaging film.

[0009]

As a result of intensive studies, the present inventors have found that a lactic acid-based polymer film obtained from polylactic acid or lactic acid-hydroxycarboxylic acid copolymer is
The inventors have found that the film has appropriate water vapor permeability, excellent mold resistance and transparency, and have completed the present invention.

That is, the present invention relates to a food packaging film containing a lactic acid-based polymer as a main component, wherein the water vapor permeability of the food packaging film is 50 to 300 g / m ² · 24.
The film for food packaging is characterized by having an hr of 10 to 500 μm. The water vapor permeability in the present invention is normal pressure, temperature 40 ± 0.5 ° C., relative humidity 90 ± 2% according to the method specified in JIS Z-0208.
It was measured in.

A feature of the food packaging film of the present invention is that the main component is a lactic acid-based polymer and it has a specific water vapor permeability. Therefore, the food packaging film of the present invention does not accumulate as waste even if it is discarded after use. Further, the food packaging such as fruits and vegetables packaged using the food packaging film of the present invention, because it is possible to suppress the moisture generated from the food to be condensed on the inner surface of the package,
It is excellent in that it can prevent spoilage and mold formation due to moisture. Furthermore, since it has the same level of transparency as existing packaging films, the object to be packaged can be easily observed from the outside, and the image of the appearance of the food is not spoiled.

The present invention will be described in detail below. A lactic acid-based polymer is used in the food packaging film of the present invention. The lactic acid-based polymer in the present invention is a polymer having a lactic acid unit as a repeating structural unit in the molecule, specifically, polylactic acid or a copolymer of lactic acid and another hydroxycarboxylic acid (hereinafter, these Collectively referred to as lactic acid-based polymer). L-body and D for lactic acid
-Form exists, but when simply referred to as lactic acid in the present invention, it means both L-form and D-form unless otherwise specified. Further, the molecular weight of a polymer refers to the weight average molecular weight unless otherwise specified.

As the polylactic acid used in the present invention, the constitutional unit is poly (L-lactic acid) consisting only of L-lactic acid, poly (D-lactic acid) consisting only of D-lactic acid, or L-lactic acid unit and D-lactic acid. Lactic acid units and poly (DL-
Any of lactic acid) can be used.

Examples of the hydroxycarboxylic acid of the lactic acid-hydroxycarboxylic acid copolymer include glycolic acid, 3-hydroxybutyric acid, 4-hydroxybutyric acid, 4-hydroxyvaleric acid, 5-hydroxyvaleric acid and 6-hydroxycaproic acid. . Among these, especially glycolic acid,
6-hydroxycaproic acid is preferred. The above polylactic acid and lactic acid-hydroxycarboxylic acid copolymer are L-
It can be obtained by selecting a necessary one from lactic acid, D-lactic acid and hydroxycarboxylic acid as a raw material monomer or comonomer, and directly performing dehydration polycondensation.
It can also be obtained by ring-opening polymerization of lactide, which is a cyclic dimer of lactic acid, and cyclic esters such as glycolide, caprolactone, propiolactone, butyrolactone, and valerolactone, which are cyclic dimers of glycolic acid. it can. However, in the case of industrial production, the lactic acid-based polymer is preferably obtained by dehydration polycondensation in consideration of cost and simplification of the process.

In the case of direct dehydration condensation, lactic acid or lactic acid and other hydroxycarboxylic acid are azeotropically dehydrated and condensed in the presence of an organic solvent, particularly a diphenyl ether type solvent, and particularly preferably a solvent distilled by azeotropic distillation. By removing water from the solution and polymerizing the solvent in a substantially anhydrous state by returning it to the reaction system, a high-molecular-weight lactic acid-based polymer having strength suitable for the present invention can be obtained.

The molecular weight of the lactic acid-based polymer affects the processability of the film, the strength and degradability of the resulting food packaging film. When the molecular weight is low, the strength of the obtained film is lowered and the film may be broken by tension when used.
In addition, the decomposition rate becomes faster. On the contrary, if it is high, the workability is lowered, and it becomes difficult to form a film. Considering this point, the molecular weight of the lactic acid-based polymer used in the present invention is about 1
The range of about 1,000,000 to about 1,000,000 is preferable. A more preferable range is 100,000 or more and 300,000 or less.

When the lactic acid-based polymer is a lactic acid-hydroxycarboxylic acid copolymer, the content of lactic acid units in the copolymer affects the degradability of the film. From this viewpoint, a copolymer containing 40 mol% or more lactic acid units is preferable. More preferable content of the lactic acid unit is
If the lactic acid-hydroxycarboxylic acid copolymer is a lactic acid-glycolic acid copolymer, at least 70 mol%
Of lactic acid units. In addition, lactic acid-
When the hydroxycarboxylic acid copolymer is a lactic acid-6-hydroxycaproic acid copolymer, copolymers containing 40 to 70 mol% lactic acid units are more preferred.

The optimum molecular weight and copolymer composition of the lactic acid-based polymer used in the film for food packaging of the present invention are determined by the hydrolyzable data on existing or known lactic acid-based polymers according to the longest use period in the intended use. It is decided in consideration of.

It is preferable to add a plasticizer to the base resin in order to impart appropriate flexibility to the lactic acid-based polymer serving as the base.

The plasticizer is preferably a plasticizer having two or more carboxylic acid ester groups in the molecule. Examples thereof include hydroxy polycarboxylic acid ester, polyhydric alcohol ester, and polycarboxylic acid ester. Examples of the hydroxy polycarboxylic acid ester include citrate tributyl citrate (ATBC), tributyl citrate and the like, and polyhydric alcohol ester such as glycerin triacetate (triacetin) and glycerin tripropionate, triethylene. Glycol dicaprate, triethylene glycol ester such as triethylene glycol dicaprylate,
Examples of the polycarboxylic acid ester include dioctyl phthalate (DOP), dibutyl phthalate (DBP) and the like, dioctyl adipate (DOA), adipic acid ester such as diisobutyl adipate (DIBA), and dibutyl sebacate. (DBS), sebacate ester such as dioctyl sebacate (DOS), dioctyl azelate (DOZ), azelaate ester such as dihexyl azelate, and the like.

Among these plasticizers, citric acid ester and glycerol ester are more preferable plasticizers in view of transparency (haze), moisture permeability and food storability of the obtained food packaging film. The plasticizer content is 1 to 100 parts by weight of the lactic acid-based polymer.
It is 50 parts by weight, more preferably 5 to 20 parts by weight.

Further, according to the knowledge of the present inventors, when the lactic acid-based polymer is used outdoors or in an environment where ultraviolet rays are radiated under a fluorescent lamp, it is usually indoors where the ultraviolet rays are not radiated, a dark place, or a raw place. It is known that the strength decreases obviously faster than when it is used in the body, and that phenomena such as embrittlement and fracture may occur earlier than expected. In order to suppress or prevent these photodegradation phenomena, an ultraviolet absorber can be added to and mixed with the lactic acid-based polymer as the main component in the film for food packaging of the present invention, if necessary.

In the present invention, 2- (2'-hydroxy-
Benzotriazoles such as 5′-methylphenyl) benzotriazole, benzophenones such as 2-hydroxy-4-methoxybenzophenone, and p-te salicylate.
The use of UV absorbers such as salicylic acid derivatives such as rt-butylphenyl is preferred.

The content of the ultraviolet absorber affects the weather resistance and transparency of the obtained food packaging film. When the content of the ultraviolet absorber is large, the transparency and the like originally possessed by the lactic acid-based polymer may be deteriorated, which is not preferable. On the other hand, if the amount is small, the effect of suppressing the promotion of decomposition cannot be sufficiently observed when used as a film for food packaging, which is not preferable. From this viewpoint, the content of the ultraviolet absorber is
It is preferably 0.001 to 5 parts by weight with respect to 100 parts by weight of the lactic acid polymer. More preferably 0.01-
2 parts by weight.

Further, it has been found that when a large amount of water is generated from food, dew condensation and fogging occur on the inner surface of the package, which makes it difficult to observe the packaged item from the outside. In order to prevent this fogging, an antifogging agent can be added to and mixed with the lactic acid-based polymer as the main component, if necessary, in the food packaging film of the present invention. In the present invention,
Examples thereof include glycerin fatty acid esters such as glycerin monostearate, sorbitan monolaurate, sorbitan fatty acid esters such as sorbitan monooleate, and antifogging agents such as polyglycerin fatty acid esters and propylene glycol fatty acid esters. The content of the antifogging agent is preferably 0.1 to 10 parts by weight with respect to 100 parts by weight of the lactic acid polymer. It is more preferably 0.2 to 5 parts by weight.

In the food packaging film of the present invention, in addition to the lactic acid-based polymer as the main component, a plasticizer, an ultraviolet absorber, an antifogging agent, and an antioxidant within a range not impairing the object of the present invention, Other additives such as a heat stabilizer, a lubricant, a filler, an anti-coloring agent and a pigment may be contained.

Next, a method for producing the food packaging film of the present invention will be described. A known film-forming method after adding a plasticizer, an ultraviolet absorber, an antifogging agent, an antioxidant, a heat stabilizer, a lubricant, a filler, an anti-coloring agent, a pigment, etc. to the lactic acid-based polymer, if necessary. To form a film. As a method of adding and mixing a plasticizer, an ultraviolet absorber, an antifogging agent and the like to the lactic acid-based polymer, a blending machine such as a blender, a method of using a mixer, or dissolving the lactic acid-based polymer in a solvent such as chloroform, Alternatively, a method of adding and mixing a predetermined amount of a plasticizer, an ultraviolet absorber or the like to a place where a lactic acid-based polymer is heated and melted at 100 to 280 ° C is exemplified.

As a method for forming a film of a lactic acid-based polymer composition containing the above various additives, for example, a solution casting method,
Melt extrusion method, calendar method and the like can be mentioned. The solution casting method uses chloroform, methylene chloride, benzene, acetonitrile, toluene, xylene, dimethylformamide, dimethylsulfoxide, dimethylimidazolidinone, etc. as a solvent to form a solution, and then casts it on a smooth surface to remove the solvent. It is done by doing.

In the case of melt extrusion molding, known T-die method, inflation method and the like are applied. The extrusion temperature is
It is preferably in the range of 100 to 280 ° C, more preferably 1
It is in the range of 30 to 250 ° C. In the case of calender molding, generally known reverse L-type calenders and Z-type calenders are used. Roll temperature is preferably 100-280 ° C
Range, more preferably in the range of 130 to 250 ° C. If the molding temperature is low, molding stability is difficult to obtain, and overload tends to occur. On the other hand, if it is too high, the lactic acid-based polymer may be decomposed, resulting in a decrease in molecular weight, a decrease in strength, coloration and the like. Considering these comprehensively, the above temperature range is preferable.

In the food packaging film of the present invention, the film obtained as described above is preferably stretched at least uniaxially by 1.1 to 10 times, preferably 1.1 to 7 times. The stretching may be uniaxial stretching or biaxial stretching. In the case of biaxial stretching, the uniaxial stretching and the biaxial stretching may be performed sequentially or simultaneously. When the stretching ratio is low, it is difficult to obtain a film having a sufficiently satisfactory strength, and when it is high, the film often breaks during stretching, which is not preferable. Considering these phenomena, the draw ratio is preferably within the above range.

In the case of uniaxial stretching, longitudinal stretching by a roll method or transverse stretching by a tenter is exemplified. In the case of biaxial stretching, these may be combined. The stretching temperature is from the glass transition point (Tg) to Tg + 5 of the lactic acid-based polymer used.
The range of 0 ° C is preferred. More preferably Tg to Tg +
It is in the range of 30 ° C. If the stretching temperature is less than Tg, the stretching is difficult, and if it exceeds Tg + 50 ° C, the strength may not be improved by stretching.

The thickness of the film is usually 10 to 500 μm.
The degree is about 10 to 200 μm. The thickness is appropriately selected depending on the application.

The obtained film may be cut into a square having a side of several tens of cm, a quadrangle such as a rectangle and other polygons, or a circle having a diameter of several tens of cm to wrap the object to be packaged or cut. The end of the film may be fixed with heat seal, an adhesive, an adhesive tape, or the like, and the object to be packaged may be wrapped with a bag-shaped package. At this time, in the case of the edge of the film or the shape of a bag, the mouth may be fixed with a heat seal, an adhesive, an adhesive tape, or the films may be tied together.

[0034]

The present invention will be described in more detail with reference to the following examples. The test method used in this example is as follows. (1) Weight average molecular weight (Mw) A sample is dissolved in chloroform, and the molecular weight in terms of polystyrene is measured by gel permeation chromatography (hereinafter referred to as GPC).

(2) Haze (transparency) Measured in accordance with ASTM-D1003.

(3) Mold resistance It is measured according to the method specified in JIS Z-2911. The criteria for determination 4 weeks after mold inoculation are as follows. 3: No hyphal growth was observed in the sample. 2: The area of the developing part of hypha recognized in the sample does not exceed 1/3 of the total area. 1: The area of the hypha developing part recognized in the sample exceeds 1/3 of the total area.

(4) Degradability in compost 5 × 5 cm film was sampled and the temperature was 35 ° C.
After being buried in compost with a humidity of 30% for 2 months, it is taken out and evaluated as follows. ○: The film is damaged when it is squeezed with your hand. X: The film is not damaged even if it is gripped with a hand.

(5) Water vapor permeability (moisture permeability) Measured in accordance with JIS Z-0208. The measurement conditions are as follows: atmospheric pressure, temperature 40 ± 0.5 ° C., relative humidity 90.
± 2%

(6) Preservability of foods 100 g of spinach immediately after harvesting is washed with water, bound and stored in a sample bag of 30 cm in length and 30 cm in width, and the bag mouth is tied to form a package. The package is left in a refrigerator kept at a temperature of 4 ° C. for 10 days, then taken out from the sample bag, and the appearance of spinach is observed. The judgment criteria are as follows. 3: Freshness remains and there is no wilting or decay. 2: Slightly decayed or wilted. 1: Significant rot occurs, or wilting and yellowing.

Preparation Example 1 90 kg of 90% L-lactic acid was added to 150 ° C./50 mmHg.
After distilling water while stirring for 3 hours, 6.2 g of tin powder
Was added, and the mixture was stirred at 150 ° C./30 mmHg for 2 hours for oligomerization. 28.8 g of tin powder in this oligomer
And 21.1 kg of diphenyl ether were added, and 150 ° C /
The azeotropic dehydration reaction was carried out at 35 mmHg, and the distilled water and the solvent were separated by a water separator, and only the solvent was returned to the reactor. After 2 hours, the organic solvent returned to the reactor was passed through a column packed with 4.6 kg of molecular sieve 3A and then returned to the reactor to carry out a reaction at 150 ° C./35 mmHg for 40 hours. After the completion, 44 kg of dehydrated diphenyl ether was added and diluted, then cooled to 40 ° C., the precipitated crystals were filtered, washed with 10 kg of n-hexane three times, and 60 ° C. /
It was dried at 50 mmHg. This powder was added to 0.5N-HCl
Add 12.0 kg and ethanol 12.0 kg, 35 ℃
After stirring for 1 hour at 60 ° C., the mixture was filtered and dried at 60 ° C./50 mmHg to obtain a polymer. This polymer was treated with a pelletizer and pelletized to obtain polylactic acid P-1. The molecular weight was measured by the above method, and the obtained results are shown in [Table 1].

Preparation Examples 2 to 4 Lactic acid polymers P-2 to P-4 were obtained in the same manner as in Preparation Example 1 except that the conditions of Preparation Example 1 were changed to those shown in [Table 1]. The obtained results are shown in [Table 1].

[0042]

[Table 1]

Examples 1 to 13 Lactic acid-based polymers P-1 to P-4 obtained in Preparation Examples 1 to 4
On the other hand, a plasticizer was blended in the weight ratios shown in [Table 2] to [Table 4], and the film was extrusion-molded at an extrusion temperature of 180 ° C using an extruder equipped with a T-die. Then, in Examples 1 to 3, the obtained film was biaxially stretched in the length direction and the width direction of the film by a factor of 2, respectively.
Then, it was uniaxially stretched 3 to 5 times in the length direction of the film to obtain food packaging films A-1 to A-13 having a thickness of 15 μm. The physical properties of the obtained food packaging film were measured by the above methods, and the obtained results are shown in [Table 2] to [Table 4].

Comparative Example 1 Instead of the polymer used in Example 1, a film containing starch and modified polyvinyl alcohol as main components (manufactured by Nippon Synthetic Chemical Industry Co., Ltd., trade name: Matterby) was extruded in the same manner. It was a film. Then, it was stretched 3 times in the length direction at 120 ° C. to obtain a film HF-1 having a thickness of 15 μm. The transparency, mold resistance and degradability in compost of this film were examined in the same manner as in Example 1. The results are shown in [Table 4].

Comparative Example 2 Commercially available biaxially oriented polystyrene film for food packaging (manufactured by Asahi Dow Co., Ltd., trade name: Styrofilm TH, thickness 1)
6 μm) is called HF-2. HF-2 was evaluated in the same manner as in Example 1, and the obtained results are shown in [Table 4].

[0046]

[Table 2]

[0047]

[Table 3]

[0048]

[Table 4]

[0049]

The food packaging film of the present invention is a film whose main component is a lactic acid-based polymer and which has a specific water vapor permeability. Therefore, the food packaging film of the present invention does not accumulate in the natural environment as waste even if it is discarded after use. Further, food packaging such as fruits and vegetables packaged using the film for food packaging of the present invention can prevent moisture generated from food from condensing on the inner surface of the package, and thus prevent spoilage and mold formation due to moisture. It is excellent in what you can do. Furthermore, since it has the same level of transparency as existing packaging films, the object to be packaged can be easily observed from the outside, and the image of the appearance of the food is not spoiled.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Takayuki Kuroki 2-1, Tango-dori, Minami-ku, Nagoya-shi, Aichi Mitsui Toatsu Chemical Co., Ltd.

Claims (6)

[Claims] 1. A food packaging film comprising a lactic acid polymer as a main component, wherein the food packaging film has a water vapor permeability of 50 to 300 g / m ² · 24 hr and a thickness of 10 to 10.
A film for food packaging, which has a thickness of 500 μm. 2. The lactic acid-based polymer is L-lactic acid, D-lactic acid or a mixture thereof in the substantial absence of water.
Alternatively, the weight average molecular weight obtained by dehydration condensation of L-lactic acid, D-lactic acid or a mixture thereof and hydroxycarboxylic acid in a reaction mixture containing an organic solvent is about 100,000.
The food packaging film according to claim 1, which is a lactic acid-based polymer of 0 to 300,000. 3. The food packaging film contains 1 to 50 parts by weight of a plasticizer having two or more carboxylic acid ester groups in the molecule, relative to 100 parts by weight of the lactic acid-based polymer. The film for food packaging described. 4. A plasticizer having two or more carboxylic acid ester groups in the molecule is selected from citric acid ester, glycerol ester, phthalic acid ester, adipic acid ester, sebacic acid ester, azelaic acid ester and triethylene glycol ester. The food packaging film according to claim 2, which is at least one selected ester compound. 5. The plasticizer having two or more carboxylic acid ester groups in the molecule is at least one plasticizer selected from citric acid ester and glycerol ester. Film for food packaging. 6. The food packaging film according to any one of claims 1 to 4, wherein the food packaging film is stretched at least uniaxially by 1.1 to 10 times.