JP7594888B2 - Biodegradable heat-sealing resin composition and biodegradable packaging film using the same - Google Patents

Description

The present invention relates to a biodegradable heat-sealable resin composition that has excellent heat-sealing properties. More specifically, the present invention relates to a resin composition that is decomposed by the action of microorganisms, etc., and that, when formed into a film and heat-sealed, exhibits high sealing strength and also has good impact resistance at the sealed portion. The present invention also relates to a biodegradable packaging film that uses the resin composition.

In recent years, there has been concern that plastic products, when discarded in the natural environment, can have a negative impact on ecosystems. As a result, attention has been focused on biodegradable resins that can be decomposed by microorganisms into low molecular weight compounds and natural by-products (carbon dioxide, methane, water, biomass, etc.) that do not have a negative impact on the natural environment. In particular, there has been a shift to biodegradable resins for packaging films that are intended to be disposable.

Patent Document 1 is an invention relating to a packaging sheet, characterized by comprising a biodegradable resin film and a silicon oxide layer formed on one side of the biodegradable resin film. In the invention, it is disclosed that the biodegradable resin film is made of a resin selected from the group consisting of fatty acid polyester, polyhydroxybutyrate, polyesteramide, polycaprolactone, polylactic acid, polyvinyl alcohol, polyhydroxybutyrate-valerate copolymer, polybutylene succinate, polybutylene succinate-adipate copolymer, acetyl cellulose, cellulose acetate, modified aromatic polyester, and acetyl cellulose, or a resin composition in which the resins are mixed together. However, in the examples, only polylactic acid resin film, modified aromatic polyester film, polybutylene succinate resin film, and polybutylene succinate-adipate copolymer are specifically disclosed, and no detailed description is given of the blend of biodegradable resins.

Patent Document 2 is an invention that aims to provide a molded body that has a high biodegradation rate at room temperature, excellent mechanical properties such as moldability and impact resistance, and excellent heat resistance, as well as water vapor/oxygen barrier properties when made into a sheet or container. Patent Document 2 discloses an aliphatic polyester resin composition containing an aliphatic polyester resin (A) containing, as main structural units, a repeating unit derived from an aliphatic diol and a repeating unit derived from an aliphatic dicarboxylic acid, a polyhydroxyalkanoate (B), and an inorganic filler (C), in which the polyhydroxyalkanoate (B) is a copolymer containing, as main structural units, 3-hydroxybutyrate units and 3-hydroxyhexanoate units, the mass ratio of the aliphatic polyester resin (A) to the polyhydroxyalkanoate (B) is 40/60 to 10/90, and the proportion of the inorganic filler (C) relative to the total amount of the aliphatic polyester resin (A), the polyhydroxyalkanoate (B), and the inorganic filler (C) is 15 to 50 mass%.

JP 2002-36422 A JP 2019-178206 A

Many packaging films are heat-sealed during packaging, but many biodegradable resins have a problem of poor heat-sealing suitability. For example, the sheet disclosed in Patent Document 2 is mainly composed of a copolymer containing 3-hydroxybutyrate units and 3-hydroxyhexanoate units as main structural units, and the rigidity of a sheet made of this resin composition increases with time. Therefore, when stacking and heat-sealing films that have been stored for a long time after film formation, it is necessary to shift the heat-sealing temperature to a higher temperature than when heat-sealing a film immediately after film formation. In addition, when a film that has been stored for a long time is heat-sealed, there are problems such as a decrease in heat-sealing strength and a heat-sealed portion that becomes hard and difficult to stretch. If the heat-sealed portion is hard and difficult to stretch, the sealed portion is likely to tear or open when an impact is applied.
The present invention aims to provide a biodegradable heat-sealable resin composition having excellent heat-sealing properties. Specifically, the present invention aims to provide a resin composition that exhibits little change over time even in a high-temperature environment, that is unlikely to change suitable sealing conditions, and that exhibits high sealing strength and excellent sealing elongation even when sealed at a relatively low temperature. Another objective of the present invention is to provide a biodegradable packaging film using the resin composition.

As a result of intensive research into solving the above problems, the inventors have discovered that the above problems can be solved by using a relatively flexible biodegradable resin (aliphatic-aromatic polyester resin) as the main component and blending a specific amount of polylactic acid as a secondary component.

That is, according to the present invention, the following [1] to [4] are provided as means for solving the above problems.
[1] A biodegradable heat-sealing resin composition comprising polylactic acid (A), an aliphatic-aromatic polyester resin (B), and optionally titanium oxide (C), characterized in that the polylactic acid (A) and the aliphatic-aromatic polyester resin (B) are blended in the resin composition in a ratio of polylactic acid (A):aliphatic-aromatic polyester resin (B)=1.0-20.0% by weight:99.0-80.0% by weight.
[2] The biodegradable heat-sealable resin composition according to [1], wherein the titanium oxide (C) is blended in an amount of 30.0 parts by weight or less per 100.0 parts by weight of the total of the polylactic acid (A) and the aliphatic-aromatic polyester resin (B).

[3] A biodegradable packaging film comprising the resin composition according to [1] or [2].
[4] A biodegradable packaging film, characterized in that at least the innermost layer is made of the resin composition according to [1] or [2].

The biodegradable heat-sealing resin composition of the present invention has excellent heat-sealing properties even though it is made of a biodegradable resin. That is, even in a high-temperature environment, there is little change over time, and the suitable sealing conditions do not change significantly even immediately after film formation or after long-term storage. Therefore, there is no need to review the sealing conditions according to the storage conditions of the film at the site where the product is packaged. In addition, even when a film after long-term storage is heat-sealed at a relatively low temperature, it exhibits high sealing strength and excellent sealing elongation, and the impact resistance of the sealed portion is unlikely to decrease. In particular, when titanium oxide is blended, the resin composition can be colored without decreasing the heat-sealing properties.
The biodegradable packaging film made of the resin composition of the present invention has both excellent heat sealability and biodegradability. Furthermore, by making the packaging film multi-layered and using the resin composition of the present invention in at least the innermost layer, new functions can be added to the packaging film.

1 is a graph showing the seal strength of the film of Reference Example 1. 1 is a graph showing the seal elongation of the film of Reference Example 1. 1 is a graph showing the seal strength of the film of Comparative Example 1. 1 is a graph showing the seal elongation of the film of Comparative Example 1. 1 is a graph showing the seal strength of the film of Comparative Example 2. 1 is a graph showing the seal elongation of the film of Comparative Example 2. 1 is a graph showing the seal strength of the film of Reference Example 2. 1 is a graph showing the seal elongation of the film of Reference Example 2. 1 is a graph showing the seal strength of the film of Reference Example 3. 1 is a graph showing the seal elongation of the film of Reference Example 3. 1 is a graph showing the seal strength of the film of Reference Example 4. 1 is a graph showing the seal elongation of the film of Reference Example 4. 1 is a graph showing the seal strength of the film of Example 5. 1 is a graph showing the seal elongation of the film of Example 5.

The present invention will be described in detail below, but the present invention is not limited to the following and various embodiments can be adopted within the scope of the same effects.
The biodegradable heat-sealable resin composition of the present invention (hereinafter, abbreviated as "resin composition" as necessary) comprises polylactic acid (A), an aliphatic-aromatic polyester resin (B), and titanium oxide (C) blended as necessary.

[Polylactic acid (A)]
Polylactic acid (hereinafter, abbreviated as "PLA" as necessary) is a resin in which lactic acid is polymerized through ester bonds, which is hydrolyzed by moisture in the environment to become lower molecular weight compounds, and is eventually decomposed into carbon dioxide and water by microorganisms. PLA can be obtained by producing lactic acid through fermentation of starch contained in corn, potatoes, etc., and then polymerizing this lactic acid. PLA resins made from 100% biomass raw materials are already on the market, and by using these resins, a resin composition with a high biomass content can be obtained.

The PLA used in the present invention may be copolymerized with other hydroxycarboxylic acids, and may contain a small amount of chain extender residues, as long as the properties of the resin are not impaired. Examples of other hydroxycarboxylic acid units include optical isomers of lactic acid (D-lactic acid for L-lactic acid, L-lactic acid for D-lactic acid), glycolic acid, bifunctional aliphatic hydroxycarboxylic acids such as 3-hydroxybutyric acid, 4-hydroxybutyric acid, 2-hydroxy-n-butyric acid, 2-hydroxy-3,3-dimethylbutyric acid, 2-hydroxy-3-methylbutyric acid, 2-methyllactic acid, and 2-hydroxycaproic acid, and lactones such as caprolactone, butyrolactone, and valerolactone. It is preferable to use less than 15 mol% of such other hydroxycarboxylic acid units in the PLA.

[Aliphatic-aromatic polyester resin (B)]
Aliphatic-aromatic polyester resin (hereinafter abbreviated as "PBAT" as necessary) is a polyester obtained by condensation polymerization of an aliphatic dicarboxylic acid, an aromatic dicarboxylic acid, and a diol. It is eventually decomposed into water and carbon dioxide by the action of microorganisms and enzymes.

Examples of the aliphatic dicarboxylic acid include succinic acid, adipic acid, suberic acid, sebacic acid, and dodecanedioic acid. Among them, succinic acid or adipic acid is preferred in consideration of biodegradability. Examples of the aromatic dicarboxylic acid include terephthalic acid, isophthalic acid, and naphthalenedicarboxylic acid. Among them, terephthalic acid and isophthalic acid are preferred in terms of polymerizability, and terephthalic acid is particularly preferred. Examples of the aromatic dicarboxylic acid include aromatic dicarboxylic acids in which a part of the aromatic ring is substituted with a sulfonate salt. As the diol component, an aliphatic diol is preferably used, and particularly ethylene glycol, 1,3-propanediol, 1,4-butanediol, and 1,4-cyclohexanedimethanol are particularly preferred. Among them, in consideration of biodegradability, a diol having 2 to 4 carbon atoms is preferred, and ethylene glycol and 1,4-butanediol are more preferred, and 1,4-butanediol is particularly preferred. It is possible to use two or more kinds of each of the aliphatic dicarboxylic acid component, the aliphatic diol component, and the aromatic dicarboxylic acid component.
As the PBAT, "Ecoflex" (registered trademark) manufactured by BASF Corporation, which contains as its main component a condensation polymer of adipic acid, terephthalic acid, and 1,4-butanediol, can be used.

The blending ratio of PLA (A) and PBAT (B) in the resin composition of the present invention is preferably PLA (A):PBAT (B) = 1.0 to 20.0 wt%: 99.0 to 80.0 wt%, and particularly preferably 2.5 to 17.5 wt%: 97.5 to 82.5 wt%. If the blending ratio of PLA in the resin composition is less than 1.0 wt%, there is a problem that the film is not rigid and stretches too much. In addition, during sheet sealing, the resin becomes difficult to peel off from the sealing blade, and the number of shots (the number of seals per unit time) does not increase. In addition, if it exceeds 20.0 wt%, the sealed portion becomes hard and the impact resistance of the sealed portion decreases.
In addition, since "Ecobio" (registered trademark) manufactured by BASF contains PLA and PBAT, it is also possible to use this resin and further add PLA and/or PBAT so that the blending ratio of PLA and PBAT falls within the above-mentioned range.

[Titanium oxide (C)]
When the resin composition of the present invention is to be colored, it is preferable to use titanium oxide (C). Titanium oxide (C) can color the resin composition of the present invention without deteriorating the heat sealability of the resin composition.
The amount of titanium oxide (C) is desirably 30.0 parts by weight or less, particularly desirably 0.1 parts by weight or more and 30.0 parts by weight or less, and more preferably 2 parts by weight or more and 25 parts by weight or less, per 100.0 parts by weight of the total of polylactic acid (A) and aliphatic-aromatic polyester resin (B). If the amount of titanium oxide (C) is less than 0.1 parts by weight, the coloring effect is poor, whereas if it exceeds 30.0 parts by weight, problems arise such as the film becoming difficult to stretch, the sealed portion easily breaking, and increased costs.

[Additives]
The resin composition of the present invention may contain, for example, lubricants, antioxidants, ultraviolet absorbers, light stabilizers, antistatic agents, pigments, dyes, surfactants, antiblocking agents, modifying resins, etc., within the scope of the invention. Furthermore, biodegradable resins such as polycaprolactone-based resins and polyhydroxybutyrate, and non-biodegradable resins in an amount of 5% by weight or less may be added within the scope of the invention.

It is also desirable to add a compatibilizer to improve the compatibility between PLA and PBAT. Compatibilizers include carboxylic acid anhydrides, such as maleic anhydride, and in particular epoxy-containing copolymers based on styrene, acrylic esters and/or methacrylic esters. The epoxy-containing units are preferably glycidyl (meth)acrylate. Epoxy-containing copolymers of the above type are sold, for example, by BASF Resins B.V. under the trade name Joncryl® ADR. A particularly suitable compatibilizer is, for example, Joncryl® ADR 4368. The amount of the compatibilizer to be added is not particularly limited, but may be, for example, 0.01 to 2.00 parts by weight per 100 parts by weight of the total of PLA and PBAT.

[Biodegradable packaging film]
The biodegradable packaging film of the present invention (hereinafter, abbreviated as "packaging film" as necessary) can be produced by forming the above-mentioned resin composition into a film shape using, for example, an inflation film forming method or a T-die film forming method. In addition, a multi-layer film can be formed using an inflation co-extrusion film forming method or a T-die co-extrusion film forming method. In this case, in order to ensure the heat sealability of the film, at least the innermost layer of the film needs to be formed from the resin composition of the present invention. Preferably, all layers are made of the resin composition of the present invention. The blending ratio of PBAT and PLA may vary slightly depending on the layer, and the type and amount of additives such as coloring pigments that are appropriately blended may vary slightly depending on the layer, but it is desirable that the blending ratio of PLA and PBAT is within the range of the resin composition of the present invention in all layers.

By blending a small amount of carbon black into the packaging film of the present invention, the light-shielding and concealing properties of the packaging film can be improved. The blending amount of carbon black is preferably 0.1 part by weight or more and 1.0 part by weight or less per 100.0 parts by weight of the total of polylactic acid (A) and aliphatic-aromatic polyester resin (B). If the blending amount of carbon black is less than 0.1 part by weight, the light-shielding and concealing effects are poor, and if it exceeds 1.0 part by weight, problems such as increased costs arise.
When carbon black is added to the packaging film of the present invention, it is preferable to add carbon black to a layer other than the outermost layer of the multi-layered film, since the film will have a gray or black appearance if printed on, making it difficult to achieve the desired color tone.

The performance of the packaging film made of the resin composition of the present invention will be confirmed below based on the examples and comparative examples. The performance of the packaging films obtained in the examples and comparative examples will be evaluated by the following method.

<Seal strength>
Two sheets of packaging film are prepared, overlapped, and aluminum seal bars are applied from above and below to heat seal the two sheets of packaging film. The temperature of the upper seal bar is heated to 110°C, and the lower seal bar is not heated. The sealing pressure is 98 KPa, the sealing time is 0.7 seconds, and the seal bar width is 10 mm. Next, the sealed film is cut so that the length of the sealed portion is 15 mm to prepare a test piece. Using the test piece, a T-peel test is performed in accordance with JIS Z1711-1994 to measure the seal strength. The T-peel test is performed on a tensile tester with a chuck distance of 40 mm and a crosshead speed of 500 mm/min.
Next, the seal strength is measured by a T-peel test while changing the sealing temperature to 120° C., 130° C., 140° C., 150° C., and 160° C. In addition, after storing the film in a 60° C. environment (hereinafter, accelerated heating conditions) for 14 days, heat sealing is performed under the above-mentioned conditions, and the seal strength is measured.
The seal strength is preferably more than 8 N/15 mm, and particularly preferably more than 10 N/15 mm, even after 14 days of storage. Seal strengths exceeding 8 N/15 mm are evaluated as ◯, those exceeding 10 N/15 mm as ◎, and those less than 8 N/15 mm as ×.

<Seal stretch>
When measuring the seal strength as described above, the chuck distance at the start of measurement is defined as A, and the chuck distance when the sealed portion peels off is defined as B. The seal elongation is calculated using the following formula 1.
Formula 1: (B−A)/A×100
From the viewpoint of impact resistance of the sealed portion, it is desirable that the seal elongation exceeds 100% even after 14 days of storage. A seal elongation exceeding 100% is evaluated as ◯, and a seal elongation less than 100% is evaluated as ×.

Graphs of seal strength and seal elongation are shown in Figures 1 to 14. In each data point, the dashed line is the value for the film immediately after film formation, and the solid line is the value for the film after 14 days of storage.

<Low temperature sealing properties>
For packaging films with a seal strength exceeding 8N/15mm and a seal elongation exceeding 100%, the sealing temperature is checked, and the lowest sealing temperature is taken as the low-temperature sealability value. Even when sealed at low temperatures, packaging films with a seal strength exceeding 8N/15mm and a seal elongation exceeding 100% have excellent low-temperature sealability. Therefore, the packaging speed can be increased and the power consumption required for packaging can be reduced. In addition, for those whose low-temperature sealability does not change significantly immediately after film formation and after 14 days of storage, the sealing conditions are unlikely to change over time, so the process of adjusting the sealing conditions on-site can be simplified.

[ Reference Example 1]
87.5% by weight of PBAT and 12.5% by weight of PLA were blended to obtain the resin composition of the present invention. This was subjected to an inflation extrusion film forming method to obtain a single-layer packaging film having a thickness of 65 μm. The seal strength of the film is shown in FIG. 1, and the seal elongation in FIG. 2. The maximum seal strength, maximum seal elongation, and low-temperature sealability of the packaging film are also shown in Table 1.
[Comparative Examples 1 and 2]
Comparative resin compositions were prepared in the same manner as in Reference Example 1, except that the blending ratios of PBAT and PLA were changed as shown in Table 1, and single-layer films were produced using the resin compositions. The maximum seal strength, maximum seal elongation, and low-temperature sealability of each film are shown in Table 1. The seal strength of the film of Comparative Example 1 is shown in Figure 3, and the seal elongation is shown in Figure 4. The seal strength of the film of Comparative Example 2 is shown in Figure 5, and the seal elongation is shown in Figure 6.

The packaging film of Reference Example 1, immediately after film formation and after storage for 14 days under accelerated heating conditions, had a seal strength exceeding 10.0 N/15 mm (see FIG. 1) and a seal elongation exceeding 100% (see FIG. 2) in the portion sealed at 130° C. On the other hand, the film of Comparative Example 1 had good seal strength and seal elongation even at a sealing temperature of 130° C. immediately after film formation, but the film changed significantly over time, and the film after 14 days did not have a satisfactory seal strength unless the sealing temperature was raised to 140° C. (see FIG. 3). Furthermore, the seal elongation did not exceed 100% regardless of the sealing temperature (see FIG. 4). The film of Comparative Example 2, when stored for 14 days under accelerated heating conditions, did not have a seal strength exceeding 8 N/15 mm even when the sealing temperature was raised to 160° C. (see FIG. 5). Furthermore, the seal elongation did not exceed 100% regardless of the sealing temperature, immediately after film formation and after storage for 14 days under accelerated heating conditions (see FIG. 6).

[ Reference Examples 2 to 4]
Resin compositions were prepared in the same manner as in Reference Example 1, except that the blending ratios of PBAT and PLA were changed as shown in Table 2, and titanium oxide or calcium carbonate was added to impart white coloring, and single-layer films were produced using the resin compositions. The blending amount (parts by weight) of the white pigment in Table 2 is the ratio relative to 100 parts by weight of the total amount of PBAT and PLA.
The maximum seal strength, maximum seal elongation, and low-temperature sealability of each packaging film are also shown in Table 2. The seal strength of the film of Reference Example 2 is shown in Figure 7, and the seal elongation in Figure 8. The seal strength of the packaging film of Reference Example 3 is shown in Figure 9, and the seal elongation in Figure 10, and the seal strength of the packaging film of Reference Example 4 is shown in Figure 11, and the seal elongation in Figure 12.

※実施例５は、( )が内層の値を表す

*In Example 5, ( ) indicates the value of the inner layer.

The films of Reference Examples 2 and 3, which used titanium oxide as the white pigment, were excellent in low-temperature sealing properties. In particular, the film of Reference Example 2, which contained 25.0 parts by weight of titanium oxide, had very good low-temperature sealing properties. On the other hand, the film of Reference Example 4, which used calcium carbonate, changed its suitable sealing condition from 130° C. to 150° C. after storage for 14 days under accelerated conditions. Therefore, if the storage period of the film becomes long, it becomes necessary to reconsider the sealing conditions when packaging.

[Example 5]
A two-layer packaging film was obtained using an inflation co-extrusion method, with an inner layer and an outer layer. The resin composition of each layer was as follows. The thickness of the obtained film was 65 μm, and the thickness ratio of the outer layer to the inner layer was 8:2.
(Outer layer) A resin composition containing 82.7% by weight of PBAT, 17.3% by weight of PLA, and 5.76 parts by weight of titanium oxide (ratio relative to 100 parts by weight of PBAT + PLA).
(Inner layer) A resin composition containing 82.8% by weight of PBAT and 17.7% by weight of PLA, to which 5.74 parts by weight of titanium oxide and 0.34 parts by weight of carbon black (all parts by weight are relative to 100 parts by weight of PBAT+PLA).
The maximum seal strength, maximum seal elongation and low temperature sealability of the packaging film are also shown in Table 2. The seal strength of the film is shown in Figure 13, and the seal elongation in Figure 14.

It was confirmed that the resin composition of the present invention, when used as the innermost layer of a packaging film, exhibits good sealing properties even in the case of a multi-layer film. In addition, the film of Example 5 contains carbon black in the inner layer, and has a white appearance, but has excellent light-shielding and concealing properties.

Claims (3)

A multi-layer packaging film, at least an innermost layer of which is made of a biodegradable heat-sealable resin composition,
The biodegradable heat-sealing resin composition comprises polylactic acid (A), an aliphatic-aromatic polyester resin (B) , and titanium oxide (C) ;
In the resin composition, polylactic acid (A) and an aliphatic-aromatic polyester resin (B) are
A multi-layer film for packaging , comprising: polylactic acid (A): aliphatic-aromatic polyester resin (B) in the ratio of 1.0-20.0% by weight:99.0-80.0% by weight. 2. The multilayer film for packaging according to claim 1, wherein the biodegradable heat-sealable resin composition contains 30.0 parts by weight or less of the titanium oxide (C) per 100.0 parts by weight of the total of the polylactic acid (A) and the aliphatic -aromatic polyester resin (B). The multilayer film for packaging according to claim 1, further comprising 0.1 part by weight or more of carbon black per 100.0 parts by weight of the total of the polylactic acid (A) and the aliphatic-aromatic polyester resin (B) in the biodegradable heat-sealable resin composition.

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