JP2012091396A - Uniaxially oriented laminated film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laminated film which has excellent split properties and interlayer adhesion, and has heat seal properties.SOLUTION: The uniaxially oriented laminated film is a co-extruded laminated film in which at least one of base material layers essentially composed of a polylactic acid polymer is provided with a layer composed of a composition including aliphatic polyester having a lactic acid content of ≤5 wt.% by ≥85 wt.%. A value in one direction in the film face of a storage modulus(E') in dynamic viscoelasticity measurement is ≥1.4 times the value in a direction orthogonal to the one direction.

Description

  The present invention relates to a film having a lactic acid polymer, which is a resin derived from a natural plant, as a base layer, and more particularly to a uniaxially stretched laminated film having heat sealability.

  Plastic films with excellent transparency and heat sealability are required in a wide range of fields including fishery, agricultural, architectural, and medical applications, including general packaging materials such as food preservation bags. Yes.

  The transparency can usually be expressed by the light transmittance, and the higher the transmittance, the better the transparency. A film excellent in transparency can be seen from the outside, and is preferably used as a packaging material.

  Heat sealing refers to a method in which films are stacked using a heating bar, a heating plate, a heating roll, or the like, and the contact portions are bonded with heat and pressure.

  By the way, as a plastic (thermoplastic resin) material widely used in conventional plastic products, polyethylene, polyamide, polystyrene, and the like can be mentioned. These materials use finite resources such as petroleum as raw materials. There is concern about the depletion of those resources. In addition, these petroleum resources are substances that have been created by fixing carbon on the earth over a long period of time, and a large amount of carbon dioxide is discarded when the resin obtained from these is disposed of or disposed of by incineration. There is a concern about the deterioration of the global environment and global warming due to the increase in carbon dioxide.

  On the other hand, biological materials are superior to petroleum-based resources in that carbon dioxide and methane are taken up and fixed in the production process, can be recycled, and are non-depleted resources. A variety of materials have been developed as bio-derived materials. Especially for polylactic acid, a mass production method from corn has been established and mass production is possible, and the material is excellent in transparency. It is also attracting attention as a raw material for packaging films, and research and development of packaging films using lactic acid polymers as raw materials has been conducted.

  Patent Documents 1 and 2 disclose a heat-sealable film having a layer mainly composed of aliphatic polyester as a heat seal layer on at least one surface of a base material layer composed mainly of polylactic acid.

  However, in the production method described in Patent Document 1, since the base material layer mainly composed of polylactic acid is biaxially stretched, the tearability when opening the bag obtained by heat sealing becomes insufficient. There is a problem that it ends up. Moreover, since the base material layer and the heat seal layer containing aliphatic polyester as a main component are bonded together, there is a problem that interlayer adhesion becomes insufficient in addition to an increase in the number of film forming steps.

  The film described in Patent Document 2 is excellent in interlayer adhesion because the heat seal layer is laminated by coextrusion. However, since the film is biaxially stretched, it is also a bag obtained by heat seal. The tearability when opening is insufficient.

JP 2001-122289 A JP 2004-306482 A

  This invention is made | formed in view of the said situation, The solution subject is to provide the heat-sealable uniaxially stretched laminated film excellent in tearability and interlayer adhesion.

  As a result of intensive studies in view of the above problems, the present inventors have found that the above problems can be easily solved by a film having a specific configuration, and have completed the present invention.

  That is, the gist of the present invention is that a layer made of a composition containing 85% by weight or more of an aliphatic polyester having a lactic acid content of 5% by weight or less is formed on at least one of the base material layers mainly composed of a polylactic acid-based polymer. A coextruded laminated film having a storage elastic modulus (E ′) in a dynamic viscoelasticity measurement in which the value in one direction within the film plane is 1.4 times or more the value in the direction perpendicular to the direction. It exists in the uniaxially stretched laminated film.

  According to the present invention, a laminated film excellent in tearability and interlayer adhesion can be easily provided, and the industrial value of the present invention is high.

  The film of the present invention is a coextruded laminate of a base layer mainly composed of a polylactic acid polymer and a heat seal layer mainly composed of a predetermined aliphatic polyester, and is formed by coextrusion. Furthermore, it is obtained by stretching the film in only one direction, usually 1.5 to 5 times, and the storage elastic modulus (E ′) in dynamic viscoelasticity measurement (measured at a frequency of 10 Hz and a temperature of 20 ° C.) It is a uniaxially stretched laminated film whose value in one direction is 1.4 times or more of the value in the direction that embraces the direction.

  The polylactic acid-based polymer used in the present invention is a polymer mainly composed of L-, D- or DL-lactic acid units, and may contain other hydroxycarboxylic acid units as a small amount copolymerization component, It may also contain a small amount of chain extender residues.

  As a polymerization method for the polylactic acid polymer, known methods such as a condensation polymerization method and a ring-opening polymerization method can be employed. For example, in the condensation polymerization method, polylactic acid 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), polylactic acid can be obtained by using lactide, which is a cyclic dimer of lactic acid, using a selected catalyst while using a polymerization regulator or the like as necessary. .

  As monomers copolymerized with polylactic acid, optical isomers of lactic acid (D-lactic acid for L-lactic acid, L-lactic acid for D-lactic acid), glycolic acid, 3-hydroxybutyric acid, Bifunctional aliphatic hydroxy such as 4-hydroxybutyric acid, 2-hydroxy-n-butyric acid, 2-hydroxy-3,3-dimethylbutyric acid, 2-hydroxy-3-methylbutyric acid, 2-methyllactic acid, 2-hydroxycaproic acid Examples thereof include lactones such as carboxylic acid, caprolactone, butyrolactone, and valerolactone.

  The preferred range of the weight average molecular weight of the polylactic acid polymer used in the present invention is 60,000 to 700,000, more preferably 80,000 to 400,000, and particularly preferably 100,000 to 300,000. If the molecular weight is too small, practical physical properties such as mechanical properties and heat resistance may not be exhibited. If the molecular weight is too large, the melt viscosity tends to be too high and the molding processability tends to be inferior.

  The predetermined aliphatic polyester used in the present invention has, for example, a structure represented by the following formula (1), and includes an aliphatic (including an alicyclic group, the same shall apply hereinafter) dicarboxylic acid unit and an aliphatic diol unit. It is a polymer with the main component

In the above formula, R ¹ and R ² are an alkylene group or a cycloalkylene group having 2 to 10 carbon atoms. n is the degree of polymerization necessary for the weight average molecular weight to be 20,000 to 300,000. n pieces of R1 or R ² may each be the same or different.

  Moreover, it replaces with the ester bond residue in the said formula, and can contain a urethane bond residue and / or a carbonate bond residue to 5% of a weight average molecular weight. This urethane bond residue and carbonate bond residue are residues resulting from a chain extender.

  Examples of the aliphatic carboxylic acid component include aliphatic dicarboxylic acids such as succinic acid, adipic acid, suberic acid, sebacic acid, and dodecanedioic acid, and anhydrides and derivatives thereof. On the other hand, examples of the aliphatic alcohol component include aliphatic diols such as ethylene glycol, butanediol, hexanediol, octanediol, cyclopentanediol, cyclohexanediol, and cyclohexanedimethanol, or derivatives thereof. In any case, the main component is a bifunctional compound having an alkylene group or cycloalkylene group having 2 to 10 carbon atoms. Of course, two or more of these carboxylic acid components or alcohol components may be used.

  Further, in order to improve the melt viscosity, a branch may be provided in the polymer. For example, trifunctional or higher functional carboxylic acid, alcohol or hydroxycarboxylic acid may be used. Specifically, a polyfunctional component such as malic acid, tartaric acid, citric acid, trimellitic acid, pyromellitic acid, pentaerythlit or trimethylolpropane can be used. If these components are used in a large amount, the resulting polymer will have a crosslinked structure and will not be thermoplastic, or even if it is thermoplastic, a microgel having a highly crosslinked structure will be formed, and when it is made into a film, There is a risk of becoming. Therefore, the proportion of these polyfunctional components contained in the polymer should be very small and should be limited to such an extent that the chemical and physical properties of the polymer are not greatly affected.

  Further, if necessary, a non-aliphatic dicarboxylic acid such as terephthalic acid and / or a non-aliphatic diol such as an ethylene oxide adduct of bisphenol A, or lactic acid and / or a hydroxycarboxylic acid other than lactic acid, as a small amount copolymerization component. May be used.

  Furthermore, in addition to the above-mentioned aliphatic dicarboxylic acid unit and aliphatic diol unit, and each of the above-mentioned small copolymer components, as other small copolymer monomers, lactic acid and / or hydroxycarboxylic acid units other than lactic acid are used. Also good.

  The weight average molecular weight of the predetermined aliphatic polyester is preferably in the range of 20,000 to 300,000, and preferably 100,000 to 250,000. If the weight average molecular weight is less than 20,000, the properties as a polymer tend to be inferior. In particular, improvement in heat sealability may not be expected, and problems such as bleeding on the film surface over time may occur. Moreover, when a weight average molecular weight is larger than 300,000, melt viscosity will become high too much and it may cause the fall of the extrusion moldability when making it into a film.

  For the purpose of adjusting these molecular weights, a small amount of chain extender can be used after polymerization to the extent of oligomers as described above. Examples of the chain extender include compounds having two or more functional groups that react with a carboxyl group or a hydroxyl group, which is a terminal structure of the aliphatic polyester. Typical examples include diisocyanate compounds such as tolylene-2,4-diisocyanate, tolylene-2,6-diisocyanate, 4,4-diphenylmethane diisocyanate, hexamethylene diisocyanate, and diphenol compounds such as bisphenol A. When these react, they are contained in the polymer structure as urethane bond residues and carbonate bond residues, respectively. The proportion contained in these structures is up to 5% of the weight average molecular weight, and if it exceeds this, the characteristics (crystallinity, melting point, physical properties, biodegradability, etc.) as the aliphatic polyester may be impaired. .

  In addition, it is preferable that the glass transition point (Tg) of aliphatic polyester is 0 degreeC or less from the point of the impact-resistant improvement effect and cold resistance.

  Particularly suitable aliphatic polyesters include, for example, polyethylene suberate, polyethylene sebacate, polyethylene decanedicarboxylate, polybutylene succinate, polybutylene adipate, polybutylene sebacate, polybutylene succinate / adipate, and copolymers thereof. Most preferably, a copolymer having 1,4-butanediol, succinic acid, or adipic acid as a main component is used. A method for mass production of succinic acid from a biological raw material has been established, and a technology for producing 1,4 butanediol from succinic acid has also been established. Therefore, both have come to be able to produce 100% biologically derived polybutylene succinate using biological raw materials. At present, polybutylene succinate, which is a biological raw material only for succinic acid, can be obtained industrially, and in the near future, 100% biological raw material polybutylene succinate (PBS) can be expected. Polybutylene succinate (PBS) in which only succinic acid is derived from plants is commercially available, for example, under the trade name “GSPla” (manufactured by Mitsubishi Chemical Corporation).

  In order to adjust the predetermined aliphatic polyester, a known method such as a direct method or an indirect method can be employed. For example, the direct method is a method in which an aliphatic carboxylic acid component and an aliphatic alcohol component are directly polymerized while removing water contained in these components or generated during the polymerization to obtain a high molecular weight product. . The indirect method is an indirect production method in which the polymer is polymerized to the level of an oligomer and then increased in molecular weight using a small amount of chain extender, as in the case of the polylactic acid polymer.

  As the predetermined aliphatic polyester used in the present invention, in addition to the above-described predetermined aliphatic polyester (hereinafter referred to as “first aliphatic polyester”), the polylactic acid polymer and the first aliphatic polyester are used. Block copolymers (partly transesterified products, including products containing small amounts of chain extender residues).

  This block copolymer can be prepared by any method. For example, either a polylactic acid polymer or a first aliphatic polyester is separately prepared as a polymer, and the other constituent monomer is polymerized in the presence of this polymer. Usually, a block copolymer of polylactic acid and aliphatic polyester is obtained by polymerizing lactide in the presence of an aliphatic polyester prepared in advance. Basically, polymerization can be carried out in the same manner as in the case of preparing a polylactic acid polymer by the lactide method, except that an aliphatic polyester is allowed to coexist. At this time, lactide polymerization proceeds, and at the same time, an appropriate transesterification reaction occurs between the polylactic acid and the aliphatic polyester, and a copolymer having relatively high randomness is obtained. When an aliphatic polyester urethane having a urethane bond is used as a starting material, ester-amide exchange is also generated.

  In the present invention, in order to improve the tearability of the heat-sealable film, it is necessary that the lactic acid content contained in the predetermined aliphatic polyester used is 5% by weight or less. By setting the lactic acid content to 5% by weight or less, the crystallinity of the aliphatic polyester resin is increased, and the tearability when opening a bag obtained by heat sealing is improved. Particularly preferably, it is 2% by weight or less.

  Furthermore, in order to improve the tearability of the film, it is necessary that the composition mainly composed of the aliphatic polyester used contains 85% by weight or more of the aliphatic polyester having a lactic acid content of 5% by weight or less. . When content of the said aliphatic polyester is less than 85 weight%, the fall of the crystallinity of a heat seal layer will be caused and tearability will become inadequate. The content of the aliphatic polyester is preferably 95% by weight or more.

  In the composition containing the aliphatic polyester of the present invention as a main component, various physical properties such as antifogging property, antistatic property, slipperiness and self-adhesive property are further improved within the range not exceeding the gist of the present invention. For the purpose, various additives can be appropriately blended as necessary. As various additives, for example, an aliphatic alcohol fatty acid which is a compound of an aliphatic alcohol having 1 to 12 carbon atoms, preferably 1 to 6 carbon atoms and a fatty acid having 10 to 22 carbon atoms, preferably 12 to 18 carbon atoms. Examples thereof include monoglycerin oleate, diglycerin monooleate, polyglycerin oleate, glycerin triricinoleate, glyceryl acetyl ricinoleate, polyglyceryl stearate, polyglycerin laurate, methyl acetyl ricinoleate, ethyl acetyl. Ricinolate, butylacetylricinoleate, propylene glycol oleate, propylene glycol laurate, pentaerythritol oleate, polyethylene glycol oleate, polypropylene glycol oleate, sorbitan oleate, sorbitan la , Polyethylene glycol sorbitan oleate, and polyethylene glycol sorbitan laurate. Polyalkylene ether polyols can be used, and specific examples include polyethylene glycol and polypropylene glycol. Furthermore, at least one compound selected from paraffinic oil and the like can be added. It is preferable to add these additives in an amount of usually 0.1 to 12 parts by weight and 1 to 8 parts by weight with respect to 100 parts by weight of the resin component constituting each layer.

  For the purpose of adjusting various physical properties, various compounding agents, specifically, heat stabilizers, light stabilizers, light absorbers, plasticizers, inorganic fillers, colorants, pigments, and the like can be added.

  The packaging film of the present invention contains a polylactic acid polymer and a predetermined aliphatic polyester in addition to a layer mainly composed of a polylactic acid polymer and a layer mainly composed of a predetermined aliphatic polyester. It can have a regeneration layer. These can use, for example, trimming loss that occurs when both ends of the formed film are cut and trimmed, so that waste of material can be eliminated and material cost can be reduced. The reproduction layer can be provided between the base material layer mainly composed of a polylactic acid-based polymer and the heat seal layer mainly composed of a predetermined aliphatic polyester. For example, a base layer composed mainly of a polylactic acid polymer or a heat seal layer composed mainly of a predetermined aliphatic polyester is composed of two layers, and one layer has trimming loss at both ends of the film. By returning, a reproduction layer can be provided between the base layer composed mainly of the polylactic acid polymer and the heat seal layer composed mainly of a predetermined aliphatic polyester. In this case, in addition to the thickness ratio and composition ratio of each layer, the layer containing the return is either a base material layer mainly composed of a polylactic acid polymer or a heat seal layer mainly composed of a predetermined aliphatic polyester. The mixing ratio of the two components can be adjusted depending on whether the base is used.

  Next, a film forming method of the polylactic acid polymer and the predetermined aliphatic polyester will be described.

  First, when the constituent material of each layer is a mixed composition, the constituent material of each layer is preferably mixed in advance and pelletized as necessary. As a mixing method at this time, for example, it may be pre-compounded in advance using a same-direction twin-screw extruder, a kneader, a Hayshell mixer or the like. You may make it throw in. 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. For example, in the case of an intermediate layer, the lactic acid-based polymer and additives as necessary are sufficiently dried to remove moisture, and then melt-mixed using a twin screw extruder, and a plasticizer is removed from the vent port. What is necessary is just to produce a pellet by extruding into a strand shape while adding a predetermined amount.

  Next, the constituent materials of each layer may be separately put into an extruder, melt extruded, and coextruded by T-die molding or inflation molding to be laminated. At this time, it is preferable to form a film by practically pulling the melt extruded from the T die as it is while rapidly cooling it with a casting roll or the like.

  When importance is attached to the tearability and heat resistance of the film, the melt-extruded sheet is cooled and solidified by a cooling roll, and then heated below the crystallization temperature of the resin. It is preferable to employ a longitudinal stretching that stretches 1.5 to 5 times, or a flat stretching method that sequentially biaxially stretches and / or simultaneously biaxially stretches 1.5 to 5 times in both the longitudinal and transverse directions of the film. As the stretching temperature, the temperature of the extruded sheet is preferably set in the range of 30 to 90 ° C, and more preferably in the range of 50 to 80 ° C. If the stretching temperature is within this range, it is preferable because both the polylactic acid polymer and the aliphatic polyester can be made close to the elastic modulus suitable for stretching. The draw ratio is preferably in the range of 1.5 to 5 times, and more preferably in the range of 1.5 to 4.0 times. If the draw ratio is within such a range, the tearability can be improved without causing troubles such as breakage and whitening of the extruded sheet.

  The laminated film of the present invention is particularly preferably stretched 1.5 to 5.0 times only in one of the longitudinal direction and the transverse direction of the film in order to emphasize tearability. Thus, in the film having anisotropy in the orientation direction of the molecular chain, specifically, in the storage elastic modulus (E ′) measured at a frequency of 10 Hz and a temperature of 20 ° C. by dynamic viscoelasticity measurement, A uniaxially stretched laminated film having a storage elastic modulus of 1.4 times or more of the storage elastic modulus in the direction perpendicular to the stretching direction in the plane is obtained.

  Further, when importance is placed on productivity and / or economy, it is preferable to melt-extrude a material resin from an annular die and perform inflation molding. Moreover, as a cooling method in that case, any of the method of cooling from the outer surface of a tube and the method of cooling from both the outer side of a tube and an inner surface may be sufficient.

  The film thus obtained is reduced in heat shrinkage rate and natural shrinkage rate, depending on the purpose such as suppression of occurrence of width shrinkage, longitudinal stretching between heating rolls as required, various heat setting, Heat treatment such as aging may be performed. As the heat treatment conditions, the heat treatment temperature is preferably set in the range of 40 to 100 ° C, and more preferably in the range of 60 to 90 ° C. If the heat treatment temperature is 40 ° C. or higher, the effect of the heat treatment can be sufficiently obtained, and if it is 100 ° C. or lower, the problem of formability such as stickiness of the film on the roll does not occur.

  In addition, for the purpose of imparting and promoting antifogging properties, antistatic properties, adhesiveness, and the like, treatments such as corona treatment and aging, and surface treatments and surface treatments such as printing and coating may be performed.

  In order to make the obtained laminated film into a bag shape, the layer containing the polylactic acid polymer as a main component is used as an outer layer, and the layer containing the predetermined aliphatic polyester as a main component is used as an inner layer. It is produced by heat sealing the film edge. Since the film mainly composed of the predetermined aliphatic polyester is used as the inner layer, the heat seal is a heat seal between the films mainly composed of the predetermined aliphatic polyester. For this reason, heat sealing at a low temperature is possible. Specifically, heat sealing becomes possible at 100 to 150 ° C.

  It should be noted that the upper and lower limits of the numerical range in the present invention are those of the present invention as long as they have the same operational effects as those in the numerical range even if they are slightly outside the numerical range specified by the present invention. It is included in the equivalent range.

  Hereinafter, although an Example and a comparative example demonstrate in more detail, this invention does not receive a restriction | limiting at all. In addition, the various measured value and evaluation about the film displayed in this specification were performed as follows.

(1) Storage elastic modulus (E ')
Using the dynamic viscoelasticity measuring method described in JIS K-7198 A method, using a dynamic viscoelasticity measuring device “DVA-200” manufactured by IT Measurement Control Co., Ltd., the direction having the maximum value in the plane of the film And a direction orthogonal to the direction, measured from −100 ° C. to 200 ° C. at a temperature rising rate of 1 ° C./min at a vibration frequency of 10 Hz and a strain of 0.1%, and stored at a temperature of 20 ° C. from the obtained data The elastic modulus (E ′) was determined.

(2) Tearability A film (laminated film in this example) was cut into a width of 150 mm and a length of 150 mm, and folded so that the aliphatic polyester surfaces serving as a heat seal layer were in contact with each other. Three sides other than the folds of the overlapped film were sealed to form a three-side sealed bag. A metal heating bar capable of temperature control was used for the seal. The produced three-sided seal bag was opened in the film longitudinal direction, and the ease of tearing was evaluated according to the following criteria.
◎: Level that can be used comfortably when opened ○: Level that feels some resistance when opened, but no problem in practical use ×: Level at which tear propagation stops halfway when opened, and excessive resistance is felt

Example 1:
Regarding the resin composition forming the heat seal layer, 100 parts by mass of polybutylene succinate “GSPla AZ91T” manufactured by Mitsubishi Chemical Corporation as the aliphatic polyester and diglycerin monooleate “Riquemar” manufactured by Riken Vitamin Co., Ltd. as the antifogging agent 2.0 parts by mass of “O-71-D” was put into a same-direction twin-screw extruder set at an extrusion set temperature of 180 to 200 ° C., melt kneaded and processed into a pellet form. On the other hand, with respect to the resin composition forming the reproduction layer, “NaturalWorks 4032D” (L-form / D-form = 98.6 / 1.4, weight average molecular weight: 200,000) manufactured by NatureWorks as a polylactic acid polymer is Mitsubishi Chemical. Using polybutylene succinate “GSPla AZ91T” manufactured by Co., Ltd., the mass ratio is 80/20, and the mixture is put into the same direction twin screw extruder set at the extrusion set temperature of 180 to 200 ° C. Processed into a shape. The resin composition for forming the heat seal layer, the resin composition for forming the regeneration layer, and the polylactic acid-based polymer for forming the base material “NatureWorks 4032D” manufactured by NatureWorks are joined together from separate extruders to form three layers. Co-extruded at a T-die temperature of 180 to 200 ° C., and a layer mainly composed of a polylactic acid polymer was rapidly cooled and solidified by a cast roll set at a temperature of 50 ° C. to obtain an unstretched laminated film having a total thickness of 84 μm. The laminated film was stretched three times in the longitudinal direction at 50 to 80 ° C. with a roll stretching machine, and the total thickness was 28 μm (heat seal layer / recycled layer / base material layer = 3.3 μm / 9.9 μm / 14.8 μm). A uniaxially stretched laminated film was obtained. The results of evaluating the obtained film are shown in Table 1 below.

Comparative Example 1:
The unstretched laminated film obtained in the same manner as in Example 1 was stretched 1.7 times in the longitudinal direction at 50 to 80 ° C. by the flat stretching method, and then stretched 1.7 times in the transverse direction to obtain a total thickness. A biaxially stretched laminated film of 28 μm (heat seal layer / regeneration layer / base material layer = 3.3 μm / 9.9 μm / 14.8 μm) was obtained.

  For example, the film of the present invention can be suitably used in a wide range of fields such as fishery, agricultural, architectural and medical use, as well as general packaging materials using food storage bags as typical examples.

Claims (1)

It is a coextruded laminated film having a layer made of a composition containing 85% by weight or more of an aliphatic polyester having a lactic acid content of 5% by weight or less on at least one of a base material layer containing a polylactic acid-based polymer as a main component, A uniaxially stretched laminated film characterized in that the value in one direction of the storage elastic modulus (E ′) in the dynamic viscoelasticity measurement in the film plane is 1.4 times or more the value in the direction perpendicular to the direction.