JP2000185380A - Polylactic acid heat-sealable film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To impart low temp. heat-sealability while holding excellent transparency and mechanical strength necessary as a packaging material. SOLUTION: A polylactic acid type heat-sealable film is constituted by forming an acrylic resin coating layer on at least one surface of a polylactic acid type film. In this case, the polylactic acid type film becoming a base material layer is pref. unidirectionally or bidirectionally oriented and the acrylic resin coating layer becoming a heat seal layer has desirably a glass transition point of 0-70 deg.C and a thickness of 0.2-5 μm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a biodegradable composition,
The present invention also relates to a film having a laminated structure, which has transparency and low-temperature heat sealability and is useful as a packaging material.

[0002]

BACKGROUND OF THE INVENTION Various plastic films having biodegradability have been developed due to the recent problem of disposal of plastic films. The biodegradable film is
The film undergoes hydrolysis and biodegradation in soil and water, and the film gradually disintegrates and decomposes, and finally changes into a harmless decomposition product by the action of microorganisms. As such a biodegradable film, a film formed from an aliphatic polyester, polyvinyl alcohol, cellulose acetate, starch or the like is known.

[0003] Among these biodegradable films, polylactic acid-based films have excellent biodegradability. Tokiohira
JP-A-5-508819, JP-A-6-23836, JP-A-7-20527
According to Japanese Patent Publication No. 8, the polylactic acid-based film that has been subjected to the stretching treatment and the heat treatment has excellent tensile strength and elongation, has dimensional stability, and exhibits high light transmittance. It is stated to be further improved.

[0004] On the other hand, when a plastic film is used as a packaging material, the film is required to have heat sealability for the sealing operation of the material to be packaged. In particular, a so-called low-temperature heat-sealing property that enables heat-sealing under a low sealing temperature condition is demanded. However, the polylactic acid-based film has poor heat sealing properties, and thus its use as a packaging material is limited.

Therefore, as a method for improving the heat sealing property of a polylactic acid-based film, Japanese Patent Application Laid-Open Nos. 8-323946 and 10-151715 disclose a polylactic acid-based resin film and another low melting point or non-polylactic acid resin. Laminated films with crystalline biodegradable resin films are described.

However, in order to obtain a laminated film, a method such as a co-extrusion molding method or an extrusion laminating method is employed, so that a large-scale apparatus is required. Difficulty accompanies thinning. As a result, since the other biodegradable resin film layer is laminated on the surface of the polylactic acid-based film at a certain thickness, the heat sealing property is improved, but the original transparency of the polylactic acid-based stretched film, Excellent performance such as mechanical strength is impaired.

[0007] Conventionally, a film in which a vinylidene chloride copolymer resin or an ionomer resin is coated on the surface of a polyolefin-based stretched film such as an OPP film as a heat sealing property-imparting layer is known. Polyolefin resin as material,
Neither heat-sealing imparting resin has biodegradability.

[0008]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a biodegradable film having excellent low-temperature heat sealability while maintaining excellent transparency and mechanical strength required as a packaging material. I do.

[0009]

That is, the present invention relates to a polylactic acid-based heat-sealing film in which an acrylic resin coating layer is formed on at least one surface of a polylactic acid-based film. Are preferably uniaxially or biaxially oriented. The acrylic resin has a glass transition point of 0 to 70 ° C.
Is preferable, and heat sealing can be performed at a low temperature.

[Detailed Description of the Invention] The heat-sealing film according to the present invention is a film in which a polylactic acid-based film base layer and an acrylic resin coating layer are laminated. next,
The configuration of each layer and a method for manufacturing the same will be described.

First, the polylactic acid resin used in the present invention is a homopolymer of lactic acid, a copolymer of lactic acid and another hydroxycarboxylic acid or lactone, or a composition thereof. Lactic acid may be L-lactic acid, D-lactic acid, or a mixture thereof. Other hydroxycarboxylic acids include glycolic acid, 3-hydroxybutyric acid,
Representative examples include 4-hydroxybutyric acid, 3-hydroxyvaleric acid, 4-hydroxyvaleric acid, and 6-hydroxycaproic acid, and derivatives of these hydroxycarboxylic acids such as esterified products may also be used. Examples of the lactone include caprolactone.

The production of the polylactic acid resin can be carried out by co-existing the above-mentioned monomer and, if necessary, a comonomer, and polymerizing by a method such as a condensation polymerization method or a ring-opening polymerization method. For the purpose of obtaining a high molecular weight compound, a small amount of a chain extender such as a diisocyanate, a diepoxy, an acid anhydride, an acid chloride compound or the like may be added at the time of polymerization and may be allowed to coexist. The weight average molecular weight of the produced polymer is preferably in the range of 50,000 to 500,000. Also, the melt flow rate is ASTM
The value measured under a load of 2160 g at 190 ° C. according to D-1238 is preferably 0.1 to 100 (g / 10 minutes). When the molecular weight and the melt flow rate are in the above ranges, a melt viscosity suitable for extrusion molding of a film is exhibited, and sufficient mechanical strength as a laminated film base layer is exhibited.

In forming the film, other polymer materials, plasticizers, lubricants, inorganic fillers, antioxidants, weather stabilizers, antistatic agents, pigments, dyes, etc. are added as long as the object of the present invention is not impaired. can do.

The polylactic acid-based film may be an unoriented cast film or a uniaxially or biaxially oriented film. In order to maintain the high transparency and mechanical strength required for packaging materials, oriented films are more suitable.

The oriented film can be produced by first forming a cast film and then performing a stretching treatment. First, a cast film is prepared by feeding a polylactic acid-based resin to a single-screw or twin-screw extruder, melting it at a temperature higher than its melting point, extruding it through a T-die or the like into a sheet or film, and then rapidly cooling and taking it. can get.

The cast film once formed can be oriented uniaxially or biaxially to orient the film molecules. The stretching method, the cast film, in the temperature range of the glass transition point of the resin or more and below the crystallization temperature, performed by uniaxial stretching method, or sequential biaxial stretching method or simultaneous biaxial stretching method, in the uniaxial direction or biaxial direction An oriented film can be produced.

The stretching conditions vary depending on the composition of the polylactic acid-based resin and the heat history of the unstretched sheet.
The stretching is performed at a stretching temperature of 40 to 100 ° C. and a stretching ratio of 1.5 to 6.0 times.
After the stretching operation, the film is preferably heat-treated again and heat-set to the film. The heat treatment is performed at a temperature in the range from the crystallization temperature of the resin to the melting point.

The film thus produced is oriented in a uniaxial or biaxial direction, and the brittleness of the non-oriented film is improved. And it has excellent physical properties similar to a polypropylene stretched film, a polystyrene stretched film, and a polyethylene terephthalate stretched film. In particular, biaxially oriented exhibits high mechanical strength and is suitable as a packaging material. Further, when the heat setting treatment is performed, the molecular structure of the polymer is stabilized, the crystallinity is increased, and the mechanical strength of the film can be further improved. The thickness of the film is preferably in the range of 5 to 300, preferably 10 to 200 μm in order to obtain a suitable balance between mechanical strength, transparency and biodegradability required for the film base layer.

Since the polylactic acid-based film serves as a base layer of a heat-sealable film having biodegradability, it may be usually a single-layered film of a polylactic acid-based resin. For example, for the purpose of imparting gas barrier properties, it may be used after being laminated with another biodegradable resin film.

In the present invention, an acrylic resin coating layer is formed and laminated on at least one surface of the polylactic acid-based film. It is disclosed that the acrylic resin described in JP-A-7-41739 deteriorates in soil such as compost and has degradability. Similarly, the laminated film according to the present invention also has biodegradability, as shown in Examples described later, and its shape is collapsed only by being left in soil for a long time.

Prior to the step of forming the acrylic resin coating layer, at least one of the coating surfaces of the polylactic acid resin film is subjected to a corona discharge treatment, a frame treatment, an ozone treatment, etc. in order to increase the adhesion and bonding strength between the two layers. A surface activation treatment or an anchor coating treatment using an anchor treatment agent may be performed.

As the acrylic resin used, generally available acrylic resins for heat sealing applications can be used. In particular, a polymer of a monomer selected from the group consisting of acrylic acid, methacrylic acid, and derivatives thereof Which is preferably a homopolymer, a copolymer,
It may be a copolymer of three or more components. If necessary, other unsaturated carboxylic acids and their derivatives may be copolymerized together.

A typical example of the acrylic acid and methacrylic acid derivatives is an alkyl ester. Examples of the alkyl acrylate include methyl acrylate, ethyl acrylate, propyl acrylate, n-butyl acrylate, isobutyl acrylate, tert-butyl acrylate and the like. Is mentioned. Examples of the alkyl methacrylate include methyl methacrylate, ethyl methacrylate, propyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, tert-butyl methacrylate and the like. The derivative may be a hydroxyalkyl ester, for example, 2-
Examples thereof include hydroxyethyl acrylate and 2-hydroxyethyl methacrylate. Examples of the unsaturated carboxylic acid to be copolymerized as required and derivatives thereof include itaconic acid, maleic acid, fumaric acid, and maleic anhydride.

Preferred examples of the polymer include (a) a copolymer of alkyl acrylate and alkyl methacrylate, (b) a copolymer of methacrylic acid or acrylic acid and alkyl acrylate or alkyl methacrylate, or (c) methacrylic acid. Acid or acrylic acid,
A ternary copolymer of an alkyl acrylate and an alkyl methacrylate is exemplified. As a specific example,
Methacrylic acid / methyl acrylate / methyl methacrylate terpolymer, methacrylic acid / isobutyl acrylate / methyl methacrylate terpolymer and the like can be used. These acrylic resins can be usually produced by emulsion polymerization, suspension polymerization, or solution polymerization in the presence of the above-mentioned monomers.

The ratio of each of the above-mentioned components constituting the acrylic resin is not particularly limited, and required physical properties such as sufficient film mechanical strength, low heat sealing temperature, high heat sealing strength, blocking resistance, The ratio of the monomer components may be determined in consideration of the decomposability and the like, and the molecular weight may be adjusted.

On the other hand, when the glass transition temperature of the acrylic resin is in the range of 0 to 70 ° C., preferably 10 to 60 ° C., the heat sealing property is sufficiently exhibited at a low temperature and in a wide temperature range, and the resistance to heat is high. Since the blocking property is also moderately good, the packaging operation can be facilitated, the packaged material can be protected, and the degradation property in soil such as compost is excellent.

In addition, other materials such as a lubricant such as carnauba wax, microcrystalline wax, and polyethylene wax, and inorganic fine particles such as silica, diatomaceous earth, calcium silicate, bentonite, and clay are used as long as the heat sealing property is not impaired. Represented by anti-blocking agents, antistatic agents, ultraviolet absorbers, antioxidants,
A coloring agent or the like can be appropriately added.

Since the purpose of providing the acrylic resin coating layer is to form the heat seal layer, it is sufficient that the necessary heat seal strength can be imparted without impairing the physical properties of the base material layer. Therefore, it is preferable that the layer be as thin as possible. . The thickness of the coating layer for that purpose varies depending on the type of acrylic resin used or the use of the heat-sealing film, but is usually 0.2 to 5 μm (coating amount:
0.2 to 5 g / m ² ), preferably 0.3 to 3 μm (application amount: 0.3 to 3 g / m ² ).
With this thin coating layer, sufficient heat sealing strength can be obtained with such a thickness, the formation of cracks and the like in the coating layer can be avoided, and the transparency and mechanical strength of the polylactic acid-based film may be impaired. Few.

The formation of such a thin coating layer is as follows.
Since the acrylic resin is usually produced in the form of an aqueous solution or an aqueous dispersion, a method of coating with an aqueous solution or an aqueous dispersion is also suitable for forming a coating layer. In particular, a method of directly coating an acrylic resin emulsion is preferable. At that time, an organic solvent such as an alcohol, a softener, or the like can be appropriately added to the coating liquid, if desired.

The concentration of the acrylic resin in the aqueous solution or the aqueous dispersion is preferably from 5 to 40% by weight, and if it is within this range, a thin and uniform film can be easily formed. . As the coating method, any method such as dipping, roll coating, screen printing, and spraying can be adopted. Among them, the roll coating method is suitable for forming a uniform film at a high speed.

After the coating step, the coated acrylic resin aqueous solution or aqueous dispersion is transferred to a drying step. Regarding the drying method and conditions, moisture evaporates and a transparent film layer is formed efficiently. There is no particular limitation as long as the atmosphere is good. Usually, a hot air drier is used, depending on the coating method and other process conditions,
For example, the drying temperature is 60 to 150 ° C., and the drying time is about 5 seconds to 5 minutes.

The desired laminated film can be obtained by giving priority to the step of coating the acrylic resin and the step of stretching the polylactic acid resin film. If the order in which the polylactic acid-based resin film is uniaxially or biaxially stretched and then the acrylic resin is coated is adopted, there is an advantage that the stretching conditions of the polylactic acid-based resin film can be freely set. Conversely, if the order of applying the stretching operation after coating the acrylic resin is adopted, there is an advantage that the coating apparatus can be downsized. In the case of sequential biaxial stretching, a longitudinally stretched film of a polylactic acid-based resin is once formed, then coated with an acrylic resin,
Finally, a method of laterally stretching the film can also be adopted.

At the time of using this heat-sealing film, if necessary, another biodegradable plastic resin layer or a biodegradable natural material layer is anchor-coated on the surface opposite to the acrylic resin coating layer. Or a printed layer may be provided via an adhesive or other adhesive.

[0034]

EXAMPLES Next, the present invention will be described with reference to examples, but the present invention is not limited to these examples. In addition,
The physical properties of the film were evaluated by the following methods. (A) Tensile modulus: JIS K6782 (b) Tensile strength (stress at break, elongation at break): JIS K678
According to 2 (c) Impact strength: Film impact method; 1/2 inch cone, measured from the side opposite to the acrylic resin coated surface

(D) Haze: conforms to JIS K6714, measured from the side opposite to the acrylic resin coated surface. (E) Gloss: conforms to JIS Z8741, measured from the side opposite to the acrylic resin coated surface. (F) heat seal Strength: Using a thermal gradient sealer, at a seal temperature of 90 to 130 ° C (20 ° C intervals), pressure 0.1MPa, time 0.
The acrylic resin-coated surfaces of the films were bonded together under the condition of 5 seconds. After that, the sample width was set to 30 mm,
The T-peel strength was measured at a tensile speed of 300 mm / min, and this was taken as the heat seal strength. (G) Soil degradability: The film was left in the soil for 5 months, and the state of the film was observed.

Example 1 Polylactic acid resin (Mitsui Chemicals)
LACEA H-100E, trade name: density 1.28 (g / cm ³ ), melting point 160 ° C, melt flow rate 10 (g / 10 minutes) (190 ° C / 2
Was predried in an oven, and then fed into an extruder (60 mmφ, cylinder set temperature 200 ° C.) to be melted. Extruded into a film from a T-die provided at the tip of the extruder, quenched to 30 ° C with a cast roll,
m sheets were prepared.

Next, using a sequential biaxial stretching device, the sheet was first stretched 3.0 times at 60 ° C., then stretched 4.5 times at 70 ° C., and then heat-treated at 140 ° C. for 20 seconds (heat set).
Was done. Thereafter, one surface of the film was subjected to a corona discharge treatment to obtain a biaxially oriented film having a thickness of 18 μm.

Next, 50% by weight of methyl methacrylate, 47% by weight of isobutyl acrylate, 3% by weight of methacrylic acid
100 parts by weight of an acrylic copolymer resin having the composition of
An aqueous dispersion (solid content: 20% by weight) composed of 5 parts by weight of carnauba wax was used to coat the polylactic acid-based oriented film on the corona discharge treated side using a Mayer bar. Next, water is evaporated in a hot air drying oven at 90 ° C. for 10 seconds to obtain a thickness of about 1 μm (coating amount: 1 g / m ² ).
Was formed. The physical properties of this laminated film were examined, and the results are shown in Table 1.

(Comparative Example 1) Thickness 18 μm prepared in Example 1
The same physical property measurement as in Example 1 was carried out using the polylactic acid-based biaxially stretched film of m without any coating with an acrylic resin or the like. Table 1 shows the results.

[0040]

[Table 1] (Note) MD indicates the longitudinal stretching direction, and TD indicates the transverse stretching direction.

As is clear from the results in Table 1, Example 1
It shows that the film obtained in (1) can be heat-sealed with sufficient strength for practical use and can be heat-sealed at a low temperature.

[0042]

According to the laminated film of the present invention, an acrylic resin coating layer is formed on the surface of a polylactic acid-based film. It is suitable as a packaging material because of its excellent transparency, mechanical strength, and flexibility, and also has heat sealing properties at a low temperature and a wide temperature range. It is suitable for a wide variety of uses, for example, a packaging film used for manufacturing bags and containers.

More specifically, this film has a low-temperature sealing property, an automatic packaging property, and the like, such as overlap packaging of confectionery boxes of gum, caramel, chocolate, etc., overlap packaging of cassette tape, individual packaging of confectionery and the like. It is suitable for packaging of various foods and non-foods by utilizing its characteristics such as high-speed packaging.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) // B29C 55/02 B29C 55/02 B29K 67:00 B29L 7:00 9:00 (72) Inventor Takeishi 1 road 9th Kitatone, Sowa-cho, Sarushima-gun, Ibaraki Prefecture F-term (reference) in East Sero Co., Ltd. EJ382 GB15 JA05B JA05C JC00 JK01 JL12B JL12C JN01 YY00B YY00C 4F210 AA21 AA25 AG01 AG03 QA02 QC01 QC06 QG01 QG15 4J029 AA02 AB07 AC01 AC02 AD01 AD10 AE03 EA02 EA03 EA05 HEGB H09B

Claims (6)

[Claims] 1. A polylactic acid-based heat-sealing film, wherein an acrylic resin coating layer is formed and laminated on at least one surface of the polylactic acid-based film. 2. The polylactic acid-based heat-sealing film according to claim 1, wherein the polylactic acid-based film is uniaxially or biaxially oriented. 3. The polylactic acid-based heat-sealing film according to claim 1, wherein the acrylic resin has a glass transition point of 0 to 70 ° C. 4. The method according to claim 1, wherein said acrylic resin is a copolymer of a monomer selected from the group consisting of acrylic acid, methacrylic acid, alkyl acrylate, and alkyl methacrylate. The polylactic acid-based heat-sealing film described in Crab. 5. The acrylic resin coating layer according to claim 1,
The polylactic acid-based heat-sealing film according to any one of claims 1 to 4, wherein the thickness is 0.2 to 5 µm. 6. The polylactic acid-based heat-sealing film according to claim 1, wherein the laminated film has biodegradability.