JP2006027113A - Lactic acid shrinkable packaging film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a biodegradable packaging film whose raw material is a lactic acid resin and which excels in a low-temperature shrinkage property and has an elongation profile. <P>SOLUTION: A lactic acid shrinkable packaging film which can be utilized as an object for stretch-shrink use also as an object for overlap-shrink use is obtained by using a mixed resin composition which is made by adding a plasticizer (B) to a lactic acid resin (A) comprising: either a composition (A1) of a homopolymer which make L-lactic acid or D-lactic acid as a structural unit; and a composition (A2) consisting of a copolymer which makes both L-lactic acid and D-lactic acid as structural units, and by heat-treating the mixed resin composition at 40-120°C after extending it 2-5 times in lengthwise and transverse directions at 20-100°C, respectively. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a lactic acid-based shrink wrapping film using a lactic acid-based resin as a raw material, and particularly relates to a lactic acid-based shrink wrapping film that can be suitably used for stretch shrink and overlap shrink.

  Shrink packaging has the advantage that it can be packaged neatly and efficiently, and can be packaged efficiently using an automatic packaging machine. Therefore, containers with lids such as lunch boxes and side dishes containers, lids for meat and fresh vegetables, etc. It is used for packaging of various shapes in various fields, such as packaging of empty trays.

  The shrink wrapping method includes, for example, folding the film covering the package back and forth, left and right into the bottom of the package, sealing it with a margin, allowing it to shrink by passing through a hot air tunnel, and feeling tight. Push-up type overlap shrink wrapping, to make the film cylindrical, adhere the overlapping part of the film, insert the package into it, then fold the opening of the cylindrical film into the bottom of the package Pillow-type overlap shrink wrapping that heat seals the entire bottom and passes through the hot air tunnel, three-way seal pillow shrink that passes through the hot air tunnel after fusing or sealing and cutting without folding the opening of the tubular film Packaging, three methods of opening a film after folding a film in half and inserting a package between the films Three-way seal packaging that seals and passes through the hot-air tunnel, L-shaped seal packaging that performs this continuously, two-film seal that covers the item to be packaged, seals the openings on the four sides, and passes through the hot-air tunnel There are various methods such as packaging.

  When packaging foods such as bento, side dishes, meat, and fresh vegetables, stretch shrink packaging that stretches the film using stretch shrink packaging films with plasticized polyvinyl chloride stretch properties is generally used. Recently, from the viewpoint of the characteristics of shrink wrapping and safety and health, a hot air tunnel is attached to a conventional stretch wrapping machine, and the film is stretched and sealed over the package, and then heated through the hot air tunnel. The shrinking packaging method has been adopted, and for this reason, the packaging film used for this type of application includes the stretch and low temperature shrinkage properties required for stretch shrink packaging films, and the heat shrinkage required for overlap shrink packaging films. Both characteristics are being sought.

  By the way, most of the conventional shrink wrapping films were made of vinyl chloride resin, but the development of shrink wrapping films using polyolefin-based raw materials has recently been carried out, and recently, for example, crosslinked polyethylene having specific physical properties. And a stretch film having a layer made of a polyolefin resin and a layer made of a polypropylene resin (see Patent Document 2) are disclosed. ing.

  In recent years, the effective use of depletable resources has become important due to the growing environmental problems, and biodegradable resins that do not adversely affect the natural environment, that is, disintegration / decomposition by hydrolysis in soil or water. The biodegradable resin that will be harmlessly decomposed by the action of microorganisms has been attracting attention, and in the field of shrink wrapping film, shrink using a polylactic acid resin, which is a biodegradable resin A packaging film is disclosed (for example, see Patent Document 3).

Japanese Patent Laid-Open No. 9-216956 JP-A-9-254338 JP 2004-58586 A

However, none of the conventionally proposed shrink wrapping films having biodegradability has been disclosed which has both the characteristics required for stretch shrink and the characteristics required for overlap shrink.
Therefore, the present invention is to provide a lactic acid-based shrink wrapping film using a polylactic acid-based resin as a raw material, and has a low-temperature shrinkage property, a heat shrinkage property, and an elongation property.

The present invention is a mixed resin composition comprising a lactic acid resin (A) and a plasticizer (B) having a molecular weight of 2,000 or less, and the component (B) is added in an amount of 5 to 100 parts by mass. A lactic acid-based resin composition containing 30 parts by mass,
The lactic acid resin (A) includes at least one component (A1) of a homopolymer having L-lactic acid or D-lactic acid as a structural unit, and a co-polymer having both L-lactic acid and D-lactic acid as structural units. A polymer blend containing a component (A2) comprising a coalescence,
In each of the longitudinal direction and the transverse direction, after stretching 2 to 5 times at 20 to 100 ° C., which is 10 ° C. higher than the glass transition point of the lactic acid resin composition, 40 to 120 higher by 20 ° C. or more than the stretching temperature. It is a film obtained by heat treatment at ℃,
A lactic acid-based shrink wrapping film having the following characteristics (α), (β), (γ) and (λ) is proposed.

(Α): The thermal shrinkage rate at 40 ° C. measured by ASTM D1204 is 5% or less in both the vertical direction and the horizontal direction, and the hot air shrinkage rate at 90 ° C. is 20% or more in both the vertical direction and the horizontal direction.
(Β): The tensile fracture elongation at 23 ° C. measured in accordance with JIS K 6732 is 30% to 300%, and the inclination of the tensile strength with respect to the tensile fracture elongation in the region where the tensile elongation is 10% or more is 4 to 15. is there.
(Γ): According to dynamic viscoelasticity measurement of JIS K7198 A method, frequency 10 Hz, strain 0. The peak value of loss tangent (tan δ) at 20 ° C. measured at 1% is in the range of 0.1 to 0.8.
(Λ): Heat of fusion ΔHm required to melt all crystals when the film was heated at a heating rate of 10 ° C./min using a differential thermal scanning calorimeter according to JIS K-7121, and the temperature The difference (ΔHm−ΔHc) from the crystallization heat amount ΔHc generated along with crystallization in the medium is 5 to 25 J / g or more.

In the present invention, the “longitudinal direction” of the film refers to the flow direction when the article to be packaged flows through the packaging machine, and the “lateral direction” of the film refers to the vertical direction and the vertical direction. .
Further, the upper and lower limits of the numerical range in the present invention are within the scope of the present invention as long as they have the same operational effects as those within the numerical range even if they are slightly outside the numerical range specified by the present invention. Is included.

  The lactic acid-based shrink wrap film of the present invention is excellent in biodegradability, low-temperature shrinkage properties, heat shrinkage properties and elongation properties, and therefore various shrink wrappings, particularly shrink wrapping and shrink shrinkage that require both properties of shrink wrapping. It can be suitably used as a film for use.

  Hereinafter, although embodiment of this invention is described in detail, the scope of the present invention is not limited to embodiment described below.

The lactic acid type shrink packaging film of this embodiment is manufactured by using a mixed resin composition comprising the following component (A) and the above component (B) as a main component.
(A) Lactic acid resin (B) Plasticizer with a molecular weight of 2,000 or less

  In addition, when it is described as “main component” in the present specification, it is intended to include the intention to allow other components to be contained within a range that does not hinder the function of the main component. Although the content ratio of the main component is not particularly specified, it generally means a component that occupies 50% by mass or more, particularly 70% by mass or more in the composition.

[Component (A)]
The component (A) lactic acid resin has at least one component (A1) of a homopolymer having L-lactic acid or D-lactic acid as a structural unit, and both L-lactic acid and D-lactic acid as structural units. It is important to use a polymer blend containing the component (A2) made of a copolymer. That is, in order to obtain a low temperature shrinkage characteristic and a heat shrinkage characteristic, it is important that both the structural unit of L-lactic acid and the structural unit of D-lactic acid are included.

Since the component (A1) is at least L-lactic acid or a homopolymer having D-lactic acid as a structural unit, poly (L-lactic acid) in which the structural unit is L-lactic acid, and the structural unit is D-lactic acid. Some poly (D-lactic acid) or a mixture thereof can be used.
However, poly (L-lactic acid) or poly (D-lactic acid) referred to here is ideally a polymer composed of 100% L-lactic acid or D-lactic acid, but inevitably different lactic acid is included in the polymerization. Since there is a possibility, the thing containing 98% or more of L-lactic acid or D-lactic acid is included.
Moreover, as a mixture of the above poly (L-lactic acid) and poly (D-lactic acid), the composition ratio of D lactic acid (D isomer) and L lactic acid (L isomer) is L isomer: D isomer = 94. : 6-80: 20 or L-form: D-form = 6: 94-20: 80, L-form: D-form = 90: 10-85: 15, or L-form: D-form = It is more preferable that it is 10: 90-15: 85. If the composition ratio of the D body and the L body is within this range, the heat shrinkage characteristics of the resulting packaging film are more easily developed.

The copolymer as the component (A2) is composed of L-lactic acid, D-lactic acid and other hydroxycarboxylic acids as structural units in addition to poly (DL-lactic acid) whose structural units are composed of L-lactic acid and D-lactic acid. It may be a copolymer or a copolymer comprising L-lactic acid, D-lactic acid, an aliphatic diol, or an aliphatic dicarboxylic acid.
Moreover, you may blend the polylactic acid-type resin from which the copolymerization ratio of L body and D body differs as a component (A2).

  As the polymerization method of the polylactic acid-based resin, known methods such as a condensation polymerization method and a ring-opening polymerization method can be employed. For example, in the condensation polymerization method, a polylactic acid resin having an arbitrary composition can be obtained by directly dehydrating condensation polymerization of L-lactic acid, D-lactic acid, or a mixture thereof. In the ring-opening polymerization method (lactide method), lactide, which is a cyclic dimer of lactic acid, has an arbitrary composition and crystallinity using an appropriate catalyst while using a polymerization regulator or the like as necessary. A polylactic acid resin can be obtained. For lactide, L-lactide, which is a dimer of L-lactic acid, D-lactide, which is a dimer of D-lactic acid, and DL-lactide composed of L-lactic acid and D-lactic acid can be used. By mixing and polymerizing as necessary, a lactic acid-based resin having any composition and any crystallinity can be obtained.

  The polylactic acid resin used in the present invention preferably has a weight average molecular weight in the range of 50,000 to 400,000, more preferably in the range of 100,000 to 250,000. If it is 50,000 or more, practical physical properties such as mechanical properties and heat resistance can be secured, and if it is 400,000 or less, the melt viscosity is too high and the molding processability is not deteriorated.

The ratio of the component (A1) to the component (A2) is preferably 10:90 to 40:60, particularly 10:90 to 30:70, and particularly preferably 15:85 to 25:75 in terms of mass ratio.
The molar ratio of L-lactic acid and D-lactic acid in the component (A2) comprising the copolymer is preferably L-form: D-form = 98: 2 to 50:50 or 50:50 to 2:98. In particular, 97: 3 to 70:30 or 30:70 to 3:97, particularly 95: 5 to 85:15 or 15:85 to 5:95 is preferable.

In addition to the component (A1) and the component (A2), the component (A) contains an aliphatic polyester resin and / or an aliphatic aromatic polyester resin having a glass transition temperature (Tg) of 0 ° C. or less as a mixed component. May be.
By further mixing these resins, it can be expected to improve the impact resistance and cold resistance in addition to the improvement of the molding processability of the polylactic acid resin, which is the gist of the present invention.

Here, as the aliphatic polyester resin, aliphatic polyester obtained by condensing aliphatic diol and aliphatic dicarboxylic acid, aliphatic polyester obtained by ring-opening polymerization of cyclic lactones, and ring-opening polymerization of cyclic lactones. Examples include aliphatic polyesters and synthetic aliphatic polyesters.
Aliphatic polyesters obtained by condensing the above aliphatic diols and aliphatic dicarboxylic acids are aliphatic glycols such as ethylene glycol, 1,4-butanediol and 1,4-cyclohexanedimethanol, and aliphatic dicarboxylic acids. It can be obtained by condensation polymerization by selecting one or more of succinic acid, adipic acid, suberic acid, sebacic acid and dodecanoic acid. Moreover, a desired resin can be obtained by a chain extension reaction with an isocyanate compound or the like as required.
Specifically, the trade name “Bionore” manufactured by Showa Polymer Co., Ltd. is commercially available.
Typical examples of the aliphatic polyester obtained by ring-opening polymerization of the above cyclic lactones include cyclic monomers such as ε-caprolactone, δ-valerolactone, β-methyl-δ-valerolactone, and the like. Selected and polymerized. Examples of the synthetic aliphatic polyester include cyclic acid anhydrides and oxiranes, such as copolymers of succinic anhydride with ethylene oxide, propylene oxide, and the like.
The preferred range of the weight average molecular weight of the aliphatic polyester is 50,000 to 400,000, more preferably 100,000 to 250,000.

Moreover, as said aliphatic aromatic polyester, in order to improve heat resistance and mechanical strength, the thing which aromatic monomer components, such as 50 mol% or less terephthalic acid, were copolymerized as a dicarboxylic acid component is illustrated preferably. be able to.
The preferred range of the weight average molecular weight of the aliphatic aromatic polyester is 50,000 to 400,000, more preferably 100,000 to 250,000.
Specifically, the product name “Easter Bio” manufactured by Eastman Chemical Co., Ltd., the product name “Eco-Flex” manufactured by BASF, and the like are commercially available.

[Component (B)]
Next, the plasticizer as a component (B) is demonstrated.

  The plasticizer generally has a function of lowering the glass transition temperature (Tg) of the lactic acid-based resin and softening it. However, the plasticizer used in this embodiment is compatible or biodegradable. From the compounds shown in the following (1) to (9), those consisting of one or a combination of two or more having a molecular weight of 2,000 or less are preferred, and in particular, the following (6) and (7) Is preferred.

_{(1) H 5 C 3 (} OH) 3 -n (OOCCH 3) m ( where, 0 <n ≦ 3)
This is glycerol mono-, gee, or triacetate, and a mixture thereof may be used, but n is preferably close to 3.
(2) Glycerin alkylate (the alkyl group may have 2 to 20 carbon atoms and a hydroxyl group residue). Examples thereof include glycerin tripropionate and glycerin tributyrate.
(3) Ethylene glycol alkylate (an alkyl group having 1 to 20 carbon atoms and a hydroxyl group residue may be present). For example, ethylene glycol acetate etc. are mentioned.
(4) Polyethylene glycol alkylate having 5 or less ethylene repeating units (the alkyl group may have 1 to 12 carbon atoms and a hydroxyl group residue). Examples thereof include diethylene glycol monoacetate and diethylene glycol diacetate.
(5) Aliphatic monocarboxylic acid alkyl ester (the alkyl group has 1 to 20 carbon atoms). Examples thereof include butyl stearate. Among them, those having a number average molecular weight of 100 to 2000 are preferable.
(6) Aliphatic dicarboxylic acid alkyl ester (the alkyl group may be a residue having 1 to 20 carbon atoms and a carbosiyl group). Examples thereof include di (2-ethylhexyl) adipate and di (2-ethylhexyl) azelate. Among them, those having a number average molecular weight of 100 to 2000 are preferable.
(7) Aliphatic tricarboxylic acid alkyl ester (the alkyl group may have 1 to 20 carbon atoms and a carboxyl group residue). For example, citric acid trimethyl ester and the like can be mentioned.
(8) Natural fats and oils and their derivatives. For example, soybean oil, epoxidized soybean oil, castor oil, tung oil, rapeseed oil and the like can be mentioned. Among them, those having a number average molecular weight of 100 to 2000 are preferable.

  It is important to mix the component (A) and the component (B) so that the component (B) is 5 to 30 parts by mass with respect to 100 parts by mass of the component (A). More preferably, it is part. If the amount of the plasticizer is in the range of 5 to 30 parts by mass, suitable characteristics as a stretch shrink package can be imparted. On the other hand, if the amount is too small, the softening itself may not proceed. If the amount is too large, there may be a problem that the viscosity is too low during melt extrusion, or problems such as bleeding may occur over time. is there.

  As long as the effect of the present invention is not impaired, a lubricant, heat stabilizer, antioxidant, UV absorber, anti-fogging agent, adhesive, anti-blocking agent, light stabilizer for the purpose of improving slipperiness and preventing blocking. Additives such as nucleating agents, hydrolysis inhibitors and deodorants can be formulated.

(Use)
The lactic acid-based shrink wrapping film of the present invention is a shrink wrapping film, particularly a stretch shrink wrapping film, and in particular, a stretch shrink wrapping film that requires the following characteristics (α), (β), (γ) and (λ): Can be suitably used.
The lactic acid-based shrink wrapping film of the present invention has the following properties (α), (β), (γ) and (λ), but the following (α), (β), (γ) and (λ Each numerical range in ()) specifies the use of the lactic acid-based shrink wrapping film of the present invention.

Characteristic (α) is that the thermal shrinkage rate at 40 ° C. measured by ASTM D1204 is 5% or less in both the longitudinal direction and the transverse direction, preferably 0 to 3%, and the hot air shrinkage rate at 90 ° C. is longitudinal and The characteristic is that it is 20% or more in the lateral direction, preferably 25 to 60%.
When covering the package with a film, it is sealed with a margin of 0 to 20% for the circumferential length in the vertical and horizontal directions of the package, and the package has a tight feeling by passing through a hot air tunnel. It becomes. At this time, if the hot air shrinkage rate at 90 ° C. measured by ASTM D1204 is 20% or more in both the vertical direction and the horizontal direction, a tight feeling can be easily imparted to the packaging film.
Further, when the thermal shrinkage rate at 40 ° C. under the same conditions is 5% or less in both the vertical direction and the horizontal direction, for example, even when stored in a warehouse or the like in summer, the packaging film contracts naturally. Problems such as changes in film dimensions are unlikely to occur.

The characteristic (β) is that the tensile fracture elongation at 23 ° C. measured in accordance with JIS K 6732 is 30% to 300%, preferably 50 to 200%, and the tensile elongation is 10% or more. The tensile strength has a slope of 4 to 15, preferably 7 to 12%.
Stretch shrink wrapping is done in a variety of ways. For example, in the push-up method overlap shrink method, the film is wrapped while being stretched. Therefore, if the tensile breaking elongation of the packaging film near room temperature is 30% or more, it is less likely to break when the film is stretched. Moreover, if the inclination of the tensile breaking strength with respect to the tensile breaking elongation is 4 or more, it is preferable that the film is not stretched locally. Further, when the inclination is 15 or less, the stress when being stretched does not become excessively large, and the container is not deformed by the stress even when a soft container or the like is packaged.

The characteristic (γ) has a peak value of loss tangent (tan δ) at 20 ° C. measured at a frequency of 10 Hz and a strain of 0.1% by dynamic viscoelasticity measurement according to JIS K 7198 A method. , Preferably in the range of 0.2 to 0.7.
The peak value of loss tangent (tan δ) is a physical property indicating a delay in deformation when a force is applied, and is one of parameters indicating a stress relaxation behavior. That is, if the value of loss tangent (tan δ) is small, the stress relaxation is fast, and the restoring behavior for film deformation occurs instantaneously. Conversely, if the value of loss tangent is large, the stress relaxation is slow, and the restoring behavior for film deformation is Become slow.
If the peak value of loss tangent (tan δ) is 0.1 or more, the restoring behavior against deformation of the film does not occur instantaneously. For example, at the moment when the stretching force is removed when packaging while stretching the packaging film. It does not return to its original shape and can be packaged neatly without any defects. On the other hand, if it is 0.8 or less, the restoring behavior will not be too slow.
From such a viewpoint, this value is more preferably 0.2 or more, and further preferably 0.6 or less.

The characteristic (λ) is an index of the crystallinity of the lactic acid resin component in the film, that is, when the film is heated at a heating rate of 10 ° C./min using a differential thermal scanning calorimeter according to JIS K-7121. The difference (ΔHm−ΔHc) between the heat of fusion ΔHm necessary to melt all the crystals and the heat of crystallization ΔHc generated during crystallization during the temperature rise is 5 to 25 J / g, preferably 10 to 20 J / g. It is a characteristic of being.
When ΔHm−ΔHc is 10 J / g or more, the packaging film has preferable heat resistance, and when it is 20 J / g or less, the packaging film has preferable heat shrinkage characteristics.
ΔHm is the amount of heat of crystal melting required to melt all the crystals when the film is heated at a predetermined temperature increase rate, and ΔHc is the temperature increase when the film is temporarily heated at a predetermined temperature increase rate. This is the amount of heat generated during crystallization that occurs in the process. ΔHm−ΔHc indicates the crystallinity of the lactic acid resin in the film, and the larger the ΔHm−ΔHc, the higher the crystallinity of the lactic acid resin in the film.

  The thermal shrinkage at 40 ° C. and 90 ° C., the tensile elongation at break at 23 ° C., the tensile strength, the peak value of loss tangent (tan δ) at 20 ° C., the difference between the heat of fusion ΔHm and the heat of crystallization ΔHc (ΔHm The means for adjusting -ΔHc) is not particularly limited. For example, the composition of the lactic acid resin composition (for example, LD ratio), the type of plasticizer, the blending ratio of components (A) and (B), molding It can be adjusted by appropriately adjusting the processing conditions (particularly the heating conditions after film formation).

(Production method)
Next, although an example of the manufacturing method of the lactic acid-type shrink packaging film of this invention is demonstrated, it is not limited to the following manufacturing method.

First, as a method of obtaining a mixed composition by mixing a lactic acid-based resin and a plasticizer and further other additives as required, for example, a same-direction twin-screw extruder, a kneader, a Hayshell mixer, etc. are used in advance. It may be pre-compounded, or each raw material may be dry blended and directly fed into the film extruder. In any mixing method, it is necessary to consider a decrease in molecular weight due to decomposition of the raw material, but pre-compounding is preferable for uniform mixing. A liquid component such as a plasticizer can be injected from a vent port using a pump or the like separately from the solid component.
Specifically, for example, the lactic acid-based resin and other additives as necessary are sufficiently dried to remove moisture, and then melt-mixed using a twin screw extruder, and the plasticizer is removed from the vent port. While adding a predetermined amount, it is extruded into a strand shape to produce pellets. At this time, the lactic acid resin is melt-extruded in consideration of the melting point of the mixed resin changing depending on the composition ratio of the L-lactic acid structure and the D-lactic acid structure or the mixing ratio of the lactic acid resin and the plasticizer. It is preferable to select the temperature appropriately. In practice, a temperature in the melting temperature range of 160 to 230 ° C. is usually selected. A melt extrusion temperature of 230 ° C. or lower is preferred because there is almost no possibility of a decrease in molecular weight due to decomposition of the raw material.

After the pellets prepared by the above method are sufficiently dried to remove moisture, film forming is performed by the following method.
As a specific example of the film forming method, a tenter stretching method, an inflation method, a tubular method, or the like that stretches by extending a row of clip rows using a tenter can be employed.

  In order to obtain the lactic acid-based shrink wrapping film of the present invention, after forming into a film as described above, 20 to 100 ° C., which is 10 ° C. or more higher than the glass transition point of the lactic acid-based resin composition in each of the vertical and horizontal directions. It is necessary to heat-treat at 40 to 120 ° C., which is 20 ° C. or more higher than the stretching temperature.

  At this time, it is important that the stretching temperature, that is, the temperature of the sheet at the time of stretching is 20 to 100 ° C., preferably 40 to 60 ° C. higher than the glass transition point of the lactic acid-based resin composition. is there. If the temperature of the sheet-like material at the time of stretching is 100 ° C. or less, the elastic modulus of the sheet-like material will not be too low, and troubles such as a drawdown in which the sheet-like material hangs down due to its own weight will not occur. . Further, the heat treatment may be a tension heat fixation or a heat treatment in a relaxed state, and may be selected according to the adjustment of the shrinkage characteristics described above.

  Moreover, it is preferable to heat-process, after extending | stretching a sheet-like material, and processing by a fixed width state, and as heat processing temperature, it is 40-120 degreeC higher than extending | stretching temperature 20 degreeC, Preferably it is set as 60 degreeC-100 degreeC. is important. If the heat treatment temperature is 40 ° C. or higher, a heat treatment effect can be easily obtained, and if it is 120 ° C. or lower, drawdown hardly occurs. Further, if the heat treatment time is 5 seconds or more, the heat treatment effect is easily obtained, and if it is 5 minutes or less, the heat treatment equipment does not become long, so that the economy can be maintained.

As a method of stretch shrink packaging suitable for using the lactic acid-based shrink packaging film of the present invention, push-up type overlap shrink packaging, pillow type overlap shrink packaging, pillow type overlap shrink packaging, three-side seal type pillow shrink packaging, L Examples include mold seal packaging and four-side seal packaging.
Among them, stretch shrink packaging that requires the characteristics (α), (β), (γ), and (λ) described above, for example, a film is stretched and sealed over a package, and then heated through a hot air tunnel. Suitable for shrink wrapping.

In an actual shrink wrapping operation, it is preferable to provide a margin of 20% or less with respect to the circumferential length in the vertical and horizontal directions of the package when covering the package with a film. The vertical direction here refers to the flow direction when the article to be packaged flows through the packaging machine, and the horizontal direction refers to the vertical direction and the vertical direction.
The margin rate of 20% means that the length is increased by 20% with respect to the circumferential length in the vertical and horizontal directions of the package. By providing a margin, it is possible to cope with a conical shape, a truncated cone shape, an irregular shape with protrusions, etc. in addition to a rectangular parallelepiped shape or a cubic shape. When the margin ratio is reduced, wrinkles are likely to remain on a part of the package (partially a part with a small margin ratio or a portion inferior in sliding with the film). On the other hand, if the margin ratio is larger than 20%, there is a tendency that it becomes difficult to obtain a tensioned shrink wrapping body that is in close contact with an object to be packaged, and a beautiful shrink wrapping body is not obtained.
When the margin rate is 0%, it is preferable that the film to be wrapped is covered with the same length as the circumference by extending a film shorter than the circumference by about 5 to 20%.
In addition, when the margin rate is large, or when there is a lot of air in the bag-making due to the bulky and irregularly shaped package, the air sealed in the sealed bag-making cannot be released when shrinking, and the package Since it is difficult to obtain a shrink package that is in close contact with the object, use a roller with a needle, a laser, etc. to open a small hole for air venting, or suppress the external pressure with a roller, etc. It is better to reduce the amount of pre-sealed air. What is necessary is just to select suitably the magnitude | size and number of small holes in that case with the kind and margin rate of a to-be-packaged item.
What is necessary is just to select as a sealing method according to the packaging form which uses normal sealing methods, such as a heat seal, a fusion | melting seal | sticker, and an impulse seal, and you may combine these sealing methods.
For heat shrinkage, hot air, steam, or the like can be used, but a method using hot air that does not require post-treatment is preferred.

  In addition, there is a wrap film (called a house hold wrap in the United States) that is used at home as something similar to a shrink wrap film, but a shrink wrap film has stretch properties and self-adhesiveness. On the other hand, the wrap film does not have elongation characteristics like a shrink wrap film. If the wrap film stretches like a stretch film, it cannot be cut with a saw blade.

Examples are shown below, but the present invention is not limited to the following examples.
The MD of the film indicates the take-up direction (flow direction), and TD indicates the vertical direction (width direction) of the MD.
In addition, the measured value shown in an Example is a value calculated by measuring on the following conditions.

<Measurement of hot air shrinkage>
Measured according to ASTM D1204.

<Tensile fracture strength measurement>
Measurement was performed at 23 ° C. in accordance with JIS K 6732. Moreover, the inclination of the tensile strength with respect to the tensile fracture elongation was calculated by the least square method after the yield stress of the stress-strain curve.

<Dynamic viscoelasticity measurement>
Packaging using a spectro rheometer “VES-F3” manufactured by Iwamoto Seisakusho Co., Ltd., with a vibration frequency of 10 Hz, a strain of 0.1%, and a temperature of 20 ° C. according to the dynamic viscoelasticity measurement method described in JIS K-7198 A method. The loss tangent of the film was measured.

<Packing suitability>
Packaging when using a stretch film packaging machine [FP-40] manufactured by Fujikikai Co., Ltd. and packaging styrene foam trays of length x width x height = 200 x 100 x 20 mm at a speed of 5 pieces / min. The subsequent finish was visually observed and evaluated according to the following criteria.
○: Adhering to the package and no wrinkles, etc. Δ: Adhering to the package, but wrinkles are observed ×: Not adhering to the package

<Confirmation test for shrinkage finish>
The package packaged by the Hanakata L-type automatic packaging machine [HP-10Z] was shrunk and wrapped in a hot tunnel of 100 ° C. for 5-7 seconds in the same Hanakata shrink tunnel [HT-03310]. . The finish after shrinkage was visually observed and judged according to the following criteria.
(Tight feeling)
○: Adhering to the package ×: There is a part not adhering to the package (corner state)
○: Soft ×: Hard or stiff.

<Biodegradability test: Simple compost test>
5 kg of commercially available dog food was mixed with 10 kg of humus for gardening in a commercially available household conposter, and 500 ml of water was further added to form 200 mm thick buried soil. The sample was cut into 40 mm × 100 mm from the film and sandwiched between sample holders composed of two 60 mm × 150 mm wire mesh (3 mm mesh), and the sample was bound through a fine wire. Embedded with the sample holder so that it is perpendicular to the soil of the poster, the bottom of each holder is 25mm above the bottom of the soil and the top is 25mm deep from the surface of the soil. Arranged to be. Two months after embedding, each holder was taken out, the state of the sample surface was observed, and the presence or absence of collapse was visually judged according to the following criteria.
○: The shape of the packaging film is not retained and is almost disassembled. ×: The shape of the packaging film is retained, and even if the film is deformed, it is not destroyed.

Example 1
As component (A), sufficiently dried homopolylactic acid (trade name: NatureWorks 4032D (manufactured by Cargill Dow), L-lactic acid: D-lactic acid = 98.6: 1.4, molecular weight 200,000) (hereinafter “ 20% by mass (abbreviated as “PLA1”), copolymer polylactic acid (trade name: NatureWorks 4060 (manufactured by Cargill Dow), L-lactic acid: D-lactic acid = 87: 13, molecular weight 190,000) (hereinafter “PLA2”) A blend of 80% by mass (hereinafter abbreviated as A1), the component (A) is charged into a hopper, and melted at 230 ° C. and 200 rpm using a φ25 mm twin screw extruder (L / D = 40). Kneading and adding adipic acid ester (PX-884 manufactured by Asahi Denka Co., Ltd., molecular weight 650) (hereinafter abbreviated as B1) as component (B) to 30 ° C. while adding 17 parts by mass from the vent port. A 90 μm sheet was formed by cooling with a temperature-controlled cast. Subsequently, this film was simultaneously biaxially stretched at a temperature of 60 ° C. using a biaxial stretching apparatus (manufactured by TM Long Co., Ltd.) so that the stretching ratio was 4 times in length and 4 times in width, and a lactic acid-based soft film having a thickness of 10 μm. A film was prepared, and then heat treatment was performed at a temperature of 90 ° C. for 2 minutes in a state where the vertical and horizontal directions were constrained.

(Example 2)
A 10 μm film was obtained in the same manner as in Example 1 except that the component (A) in Example 1 was a PLA1 / PLA2 = 10/90 mass% blend (hereinafter abbreviated as A2). The results are shown in Table 1.

(Comparative Example 1)
In Example 1, the component (A) is only PLA1 (hereinafter abbreviated as A3), the ratio of the component (A) and the component (B) is (A) :( B) = 100: 0, and the stretching temperature A 10 μm film was obtained in the same manner as in Example 1 except that the temperature was 65 ° C. The results are shown in Table 1.

Claims (2)

A mixed resin composition comprising a lactic acid resin (A) and a plasticizer (B) having a molecular weight of 2,000 or less, containing 5 to 30 parts by mass of the component (B) with respect to 100 parts by mass of the component (A). A lactic acid resin composition comprising:
The lactic acid resin (A) includes at least one component (A1) of a homopolymer having L-lactic acid or D-lactic acid as a structural unit, and a co-polymer having both L-lactic acid and D-lactic acid as structural units. A polymer blend containing a component (A2) comprising a coalescence,
In each of the longitudinal direction and the transverse direction, after stretching 2 to 5 times at 20 to 100 ° C., which is 10 ° C. higher than the glass transition point of the lactic acid resin composition, 40 to 120 higher by 20 ° C. or more than the stretching temperature. It is a film obtained by heat treatment at ℃,
A lactic acid-based shrink packaging film having the following characteristics (α), (β), (γ) and (λ).
(Α): The thermal shrinkage rate at 40 ° C. measured by ASTM D1204 is 5% or less in both the vertical direction and the horizontal direction, and the hot air shrinkage rate at 90 ° C. is 20% or more in both the vertical direction and the horizontal direction.
(Β): The tensile fracture elongation at 23 ° C. measured in accordance with JIS K 6732 is 30% to 300%, and the inclination of the tensile strength with respect to the tensile fracture elongation in the region where the tensile elongation is 10% or more is 4 to 15. is there.
(Γ): According to dynamic viscoelasticity measurement of JIS K7198 A method, frequency 10 Hz, strain 0. The peak value of loss tangent (tan δ) at 20 ° C. measured at 1% is in the range of 0.1 to 0.8.
(Λ): Heat of fusion ΔHm required to melt all crystals when the film was heated at a heating rate of 10 ° C./min using a differential thermal scanning calorimeter according to JIS K-7121, and the temperature The difference (ΔHm−ΔHc) from the crystallization heat amount ΔHc generated along with crystallization in the medium is 5 to 25 J / g or more. The mass ratio of the component (A1) to the component (A2) in the lactic acid resin (A) is A1 / A2 = 10/90 to 40/60, and L-lactic acid and D-lactic acid in the component (A2) The lactic acid-based shrink packaging film according to claim 1, wherein the molar ratio is L-form: D-form = 98: 2 to 50:50 or 50:50 to 2:98.