JP2006299270A - Polylactic acid based shrink sheet-like article and packaging material or shrink label material using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a biodegradable polylactic acid based shrink sheet-like article having a sufficient shrink rate; and to further provide a biodegradable polylactic acid based shrink sheet-like article, when used as a label for a beverage bottle, not fusing together with other labels upon sterilization by heating. <P>SOLUTION: The sheet-like article formed from a biodegradable polymer having a polylactic acid based polymer as a main ingredient has a crystal melting calorie (▵Hm) of the polylactic acid based polymer of 5-45 J/g. When the sheet-like article is heated up, a difference between the above ▵Hm and a calorie of crystallization (▵Hc) generated by the crystallization of the polylactic acid based polymer, which is an ingredient of the biodegradable polymer forming this sheet-like article, that is, ▵Hm-▵Hc is 5-32 J/g. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a sheet-like material having a shrinkage property mainly composed of a polylactic acid polymer.

  Sheets and films of polyvinyl chloride, styrene-butadiene copolymer, polyethylene terephthalate, etc. are known as heat shrinkable sheets or films used for shrink wrapping, shrink tying wrapping, shrink labels, etc. Widely used and consumed. However, when these sheets and films are discarded in the natural environment, they remain without being decomposed due to their stability, causing problems such as damage to the landscape and contamination of the living environment such as fish and wild birds.

  Therefore, a material made of a degradable polymer that does not cause these problems is required, and many researches and developments are actually conducted. One example is polylactic acid. It is known that polylactic acid is naturally hydrolyzed in the soil, remains in its original form in the soil, and then becomes a harmless degradation product by microorganisms.

  However, since polylactic acid is inherently brittle, even if it is made into a sheet or film, sufficient strength cannot be obtained and it is difficult to put it to practical use.

  On the other hand, JP-A-5-212790 discloses a heat shrink film for labels made of polylactic acid. This heat shrink film has a high shrink temperature of 140 to 150 ° C., and is used for labels such as glass bottles. It can be used as a high-temperature shrinkable film. In contrast, in general shrink-wrapping and shrink-bound packaging, the packaged body is fresh food, paper boxes, or various containers containing foods and chemicals. Shrinkage processing is performed at a low temperature of about 70 to 120 ° C. In the above publication, it is not shown that the heat shrinkable film for labels has sufficient shrinkage in the low temperature range. Further, even a high-temperature shrinkable label has a poor shrinkage finish, and a portion that floats without being in contact with the object to be shrunk is formed, so that sufficient performance may not be exhibited.

  Japanese Patent Application Laid-Open No. 7-256653 discloses a heat shrink film made of a polylactic acid polymer that satisfies predetermined requirements. This heat-shrinkable film has a low-temperature shrinkage property, but unless it shrinks in a short time, it is heat-set and does not shrink sufficiently. Furthermore, the shrink finish is poor, and there may be a portion that floats without contacting the object to be shrunk.

  Furthermore, when the heat shrinkable film is used as shrinkage packaging or shrinkage wrapping for various containers containing fresh food products, paper boxes, or foods and medicines, the shrinkage rate is usually 10% or more. However, a sufficient shrinkage rate cannot be obtained with the heat shrink film.

  Furthermore, when using the said heat-shrink film for labels, such as a bottle for drinks, after wrapping a label around a bottle, a drink is filled and it heat-sterilizes with a production line. At this time, the labels of adjacent bottles may be fused by heat.

  Therefore, the present invention provides a polylactic acid-based shrinkable sheet material having a sufficient shrinkage rate and biodegradable. Furthermore, when used for a label such as a bottle for beverages, the labels are separated at the time of heat sterilization. An object of the present invention is to provide a biodegradable polylactic acid-based shrinkable sheet that is not fused.

  The present invention provides a sheet-like product formed from a biodegradable polymer containing a polylactic acid-based polymer as a main component, wherein the polylactic acid-based polymer has a heat of crystal melting (ΔHm) of 5-45 J / g, When the temperature of the sheet-like material is raised, the difference between the amount of heat of crystallization (ΔHc) generated by crystallization of the polylactic acid polymer that is a constituent of the biodegradable polymer that forms the sheet-like material and the ΔHm, That is, the above-mentioned problem was solved by setting ΔHm−ΔHc to 5 to 32 J / g.

  By using a polylactic acid-based shrinkable sheet having predetermined ΔHm and ΔHc, it is possible to provide a biodegradable polylactic acid-based shrinkable sheet having a sufficient shrinkage rate. Moreover, when it uses for labels, such as a bottle for drinks, the biodegradable polylactic acid type shrinkable sheet-like material which does not melt | fuse between labels at the time of heat sterilization can be provided.

  According to the present invention, it is possible to provide a polylactic acid-based shrinkable sheet having a sufficient shrinkage ratio and biodegradable.

  Moreover, when it uses for labels, such as a bottle for drinks, the biodegradable polylactic acid type shrinkable sheet-like material which does not melt | fuse between labels at the time of heat sterilization can be provided.

  Embodiments of the present invention will be described below.

  The polylactic acid-based shrinkable sheet material according to the present invention is a sheet-like material molded from a biodegradable polymer whose main component is a polylactic acid-based polymer.

  The biodegradable polymer is a polymer having biodegradability, that is, a property of being degraded by microorganisms. The polylactic acid polymer which is the main component of this biodegradable polymer refers to lactic acid, specifically, a homopolymer of D-lactic acid or L-lactic acid, or a copolymer thereof.

  The polylactic acid polymer can be produced by a known method such as a condensation polymerization method or a ring-opening polymerization method. For example, in the condensation polymerization method, a polylactic acid polymer having an arbitrary composition can be obtained by directly dehydrating condensation polymerization of D-lactic acid, L-lactic acid or a mixture thereof. In the ring-opening polymerization method, polylactic acid having an arbitrary composition is obtained by ring-opening polymerization of lactide, which is a cyclic dimer of lactic acid, in the presence of a predetermined catalyst, using a polymerization preparation agent as necessary. A polymer is obtained. The lactide includes L-lactide, which is a dimer of L-lactic acid, D-lactide, which is a dimer of D-lactic acid, and DL-lactide, which is a dimer of D-lactic acid and L-lactic acid.

  The biodegradable polymer may be composed of only the polylactic acid polymer as the main component, and a biodegradable aliphatic polyester other than the polylactic acid polymer is added to the polylactic acid polymer. May be mixed. The biodegradable aliphatic polyester other than the polylactic acid polymer preferably has a glass transition point Tg of 0 ° C. or lower. By adding a biodegradable aliphatic polyester other than the polylactic acid-based polymer having a glass transition point Tg of 0 ° C. or lower, the resulting polylactic acid-based shrinkable sheet is prevented from breaking when stretched, In addition, the shrink finish can be improved.

  The addition amount of the biodegradable aliphatic polyester other than the polylactic acid polymer is preferably 10 to 100 parts by weight with respect to 100 parts by weight of the polylactic acid polymer. If it is less than 10 parts by weight, it may break, and the shrinkage finish tends to deteriorate due to wrinkles or avatars. On the other hand, when the amount exceeds 100 parts by weight, thickness unevenness is likely to occur without stretching at a uniform magnification during stretching. When such a film is shrunk, the shrinkage finish tends to deteriorate.

  Specifically, biodegradable aliphatic polyesters other than polylactic acid-based polymers include homopolymers or copolymers of hydroxycarboxylic acids other than lactic acid, copolymers of lactic acid and hydroxycarboxylic acids other than lactic acid, An aliphatic polyester obtained from an aliphatic dicarboxylic acid and an aliphatic diol, an aliphatic polyester obtained by ring-opening polymerization of cyclic lactones, a mixture of these polymers, and the like.

  Examples of the hydroxycarboxylic acid other than lactic acid include glycolic acid, 3-hydroxybutyric acid, 4-hydroxybutyric acid, 4-hydroxyvaleric acid, 5-hydroxyvaleric acid, 6-hydroxyvaleric acid and the like. These homopolymers or copolymers, or copolymers of these and lactic acid can be produced by using the polymerization method of the above-mentioned polylactic acid polymer. It can also be produced in the fungus body. In this case, it is biosynthesized by acetyl coenzyme A (acetyl CoA) in the microbial cells including Alkaligenes eutrophas. An example of the so obtained is poly-β-hydroxybutyric acid. Since this poly-β-hydroxybutyric acid itself is insufficient in strength, it is used as a copolymer with poly-β-hydroxyvaleric acid.

  Further, examples of the aliphatic dicarboxylic acid include succinic acid, adipic acid, suberic acid, sebacic acid, dodecanedioic acid and the like, and examples of the aliphatic diol include ethylene glycol and 1,4-butanediol. 1,4-cyclohexanedimethanol and the like. The aliphatic polyester is produced by esterifying any of these aliphatic dicarboxylic acids and aliphatic diols.

  Furthermore, examples of cyclic lactones include ε-caprolactone, δ-valerolactone, β-methyl-δ-valerolactone, and the like, and the aliphatic polyester is produced by ring-opening polymerization thereof.

  In each of the above polymerization steps, a small amount of a chain extender such as a diisocyanate compound, an epoxy compound, an acid anhydride or the like can be used for the purpose of increasing the molecular weight of the polymer obtained.

  The sheet-like material refers to a sheet or a film. By JIS definition, a sheet is a flat product that is thin and generally has a thickness that is small relative to the length and width. A film is a thickness that is extremely small compared to the length and width, and has a maximum thickness. Is a thin flat product that is optionally limited and is typically supplied in the form of a roll (JIS K 6900). Therefore, it can be said that a particularly thin sheet is a film. However, since the boundary between the sheet and the film is not clear and cannot be clearly distinguished, in the present application, as described above, the term “sheet-like material” is used as a concept including both the sheet and the film.

  The biodegradable polymer is formed into a flat or cylindrical unstretched sheet-like material or a melt of a sheet-like material by a general melt-molding method such as an extrusion method, a calendar method, or a press method, A sheet-like material can be obtained by stretching this uniaxially or biaxially by a roll method, a tenter method, a tubular method, an inflation method or the like.

  The heat of crystal melting (abbreviated as “ΔHm”) of the polylactic acid polymer, which is a constituent component of the biodegradable polymer, is preferably 5 to 45 J / g, and preferably 20 to 40 J / g. Further, when the temperature of the sheet-like material is raised, the heat of crystallization (abbreviated as “ΔHc”) generated by the crystallization of the polylactic acid polymer that is a constituent component of the biodegradable polymer that forms the sheet-like material. ) And the above ΔHm, that is, ΔHm−ΔHc is preferably 5 to 32 J / g, and preferably 10 to 30 J / g. When the ΔHm is less than 5 J / g, the obtained sheet-like material is easily fused. When it exceeds 45 J / g, the obtained sheet may not easily shrink. Further, when ΔHm−ΔHc is less than 5 J / g, the obtained sheet-like material is easily fused. When it exceeds 32 J / g, the obtained sheet may not easily shrink.

  The ΔHm is heat-treated at a temperature 30 ° C. lower than the melting point of the polylactic acid polymer that is a constituent of the biodegradable polymer, and the temperature rising rate is 10 ° C./min according to the method described in JIS K7122. The amount of heat required to melt the crystals produced in the polylactic acid polymer when the temperature of the sheet-like material is raised. This is determined from the area of the endothermic peak due to crystal melting that appears near the crystal melting point of the polylactic acid polymer in the differential scanning calorimetry (hereinafter abbreviated as “DSC”) of the sheet-like material. The heat treatment is performed at a temperature lower by 30 ° C. than the melting point of the polylactic acid polymer. This heat treatment allows the polylactic acid polymer to be crystallized. In this crystallized state, ΔHm is measured by increasing the temperature at a predetermined temperature increase rate, so that even a biodegradable polymer having the same composition, for example, D, L-polylactic acid having the same composition, The difference of ΔHm that may be caused by the lot difference can be eliminated.

  ΔHc is the amount of heat of crystallization of the sheet-like material, and is the amount of heat generated during crystallization that occurs in the temperature rising process when the temperature is firstly increased according to the method described in JIS K 7122. It is obtained from the area of the exothermic peak in the DSC of the product.

  The above ΔHm mainly depends on the crystallinity of the polylactic acid polymer itself, and takes a large value for a polylactic acid polymer having high crystallinity. Incidentally, homo poly-L-lactic acid, which is considered to have the highest crystallinity, is about 50 J / g. ΔHc is an index related to the degree of crystallization of the sheet at that time, and when ΔHc is large, crystallization of the sheet progresses during the temperature raising process, that is, the sheet before temperature raising. This indicates that the crystallinity of was relatively low. Conversely, when ΔHc is small, it indicates that the degree of crystallinity of the sheet-like material before the temperature rise is relatively high.

  Therefore, ΔHm−ΔHc is the degree of crystallinity of the sheet-like material based on the crystallinity of the polylactic acid polymer that is a constituent of the biodegradable polymer forming the sheet-like material. Show. Therefore, the smaller ΔHm−ΔHc, the lower the crystallinity of the sheet-like material.

  Therefore, methods for reducing ΔHm−ΔHc include using a polylactic acid polymer having low crystallinity and making a sheet-like material having a relatively low crystallinity. In particular, if a sheet-like material having a relatively low degree of crystallinity is produced from a polylactic acid polymer having low crystallinity, ΔHm-ΔHc can be further reduced. The degree of crystallinity of the sheet-like material depends not a little on the composition of the biodegradable polymer, but is greatly influenced by the film forming conditions.

  Also, in order to lower the crystallinity of the film in the molding process, especially in the tenter method biaxial stretching, an appropriate stretching temperature and stretching ratio can be selected to suppress orientational crystallization or to cool immediately below the crystallization temperature after stretching. Thus, ΔHm−ΔHc can also be reduced by a method such as suppressing crystallization.

  As an example of a preferable biodegradable polymer satisfying the above conditions of ΔHm and ΔHm−ΔHc, a polylactic acid polymer which is a main component of the biodegradable polymer is a copolymer of L-lactic acid and D-lactic acid. The composition ratio of L-lactic acid and D-lactic acid, which are constituent components, is 98: 2 to 94: 6 or 6:94 to 2:98. By using this composition ratio, it is possible to obtain a polylactic acid-based shrinkable sheet having a ΔHm of 5 to 45 J / g and a ΔHm−ΔHc of 5 to 32 J / g. As a result, the crystallinity of the biodegradable polymer becomes appropriate, and when it is made into a sheet-like material, sufficient shrinkage can be obtained. Can be prevented. By the way, even if the composition ratio of L-lactic acid and D-lactic acid is outside the above range, a polylactic acid-based shrinkable sheet material having ΔHm of 5-45 J / g and ΔHm-ΔHc of 5-32 J / g is obtained. Although it is possible to obtain it, it is necessary to pay particular attention to the selection of the stretching temperature and the stretching ratio in order to make ΔHm-ΔHc 5 J / g or more.

  In addition, when using the polylactic acid-type shrinkable sheet containing the said biodegradable aliphatic polyester, the said biodegradable aliphatic polyester may also have crystallinity. In this case, when ΔHm and ΔHc are measured using this polylactic acid-based shrinkable sheet, the measurement value is affected by the crystal of the biodegradable aliphatic polyester. In this case, ΔHm can be obtained by measuring the polylactic acid polymer itself, which is a constituent component of the biodegradable polymer that forms the polylactic acid-based shrinkable sheet. ΔHc is measured using the polylactic acid-based shrinkable sheet, and can be obtained by deriving an amount corresponding to the polylactic acid-based polymer in terms of the value.

  The shrinkage of the resulting polylactic acid-based shrinkable sheet is preferably 10% or more, preferably 20 to 100%, under the conditions of 80 ° C. and 10 seconds. This is because if the shrinkage rate is too low, the shrinkage rate tends to be insufficient for use in shrink wrapping or shrink tying wrapping. In general, the shrinkage rate of the above-mentioned polylactic acid-based shrinkable sheet material may be about 10% for shrink wrapping or shrink-bound packaging, and in the case of a label such as a PET bottle, the shrinkage rate is 30% or more. Good.

  In order to make this shrinkage rate 30% or more, it is preferable that ΔHm−ΔHc is 5 to 20 J / g, which is narrower than the above range. This is because the degree of shrinkage of the polylactic acid-based shrinkable sheet-like material can be further increased.

  The polylactic acid-based shrinkable sheet obtained by this invention can be used as a packaging material or a shrinkable label material. Examples of packages to be packaged and shrinkable label materials include containers, foods such as fresh food, and the like. Examples of the container include a container having a high hardness such as a glass bottle, a glass container, and a hard plastic container, or a container formed from paper, a plastic having a low hardness such as polystyrene, polyethylene, and polyethylene terephthalate. These containers are used for arbitrary uses such as foods, beverages, and medicines.

  The article to be packaged is shrink-wrapped or shrink-bound with the packaging material. At this time, since the polylactic acid-based shrinkable sheet material has a sufficient shrinkage ratio and there is no thickness unevenness at the time of stretching, the shrinkage finish is good when shrink-wrapped, and it looks good in the packaged state. Furthermore, even if heat treatment is performed after packaging, the packaging materials are not fused to each other, so that handling becomes easy. Also, since the polylactic acid-based shrinkable sheet material has good printing performance and can be printed beautifully, when used as a shrinkable label material, first, after printing on the polylactic acid-based shrinkable sheet material, It can be effectively used as a label by shrinking and adhering to the packaging material.

  Examples are shown below, but the present invention is not limited by these. In Tables 1 and 2, “L / D ratio” indicates the composition ratio of L-lactic acid and D-lactic acid constituting the polylactic acid polymer. “Mw” represents the weight average molecular weight of the polylactic acid polymer. Moreover, the measurement and evaluation shown in an Example were performed on the conditions as shown below.

(1) Measurement of heat of crystal melting (ΔHm) Measurement was performed using a polylactic acid polymer itself having a predetermined L / D ratio, which is a constituent component of a biodegradable polymer forming a sheet-like material.

  First, the polylactic acid polymer was heat-treated at a temperature 30 ° C. lower than the melting point of the polylactic acid polymer for 2 hours to crystallize the polylactic acid polymer. Next, using DSC-7 manufactured by Perkin Elmer, from the area of the endothermic peak when 10 mg of the crystallized polylactic acid polymer was heated at a heating rate of 10 ° C./min based on JIS-K7122. ΔHm was determined.

(2) Measurement of heat of crystallization (ΔHc) Using DSC-7 manufactured by Perkin Elmer, the exothermic peak when a 10 mg sample of a sheet was heated at a heating rate of 10 ° C./min based on JIS-K7122. ΔHc was determined from the area.

(3) Heat shrinkage rate A sample of the sheet-like material was cut into 140 mm × 10 mm with the test direction as the longitudinal direction (hereinafter abbreviated as “MD”), and a score between 100 mm was put in the MD, and hot water at 80 ° C. After being immersed in the bath for 10 seconds, the dimension between the evaluation lines was measured, and the heat shrinkage rate was calculated according to the following formula.

Thermal shrinkage rate (%) = {(dimension before shrinkage) − (dimension after shrinkage)} / (dimension before shrinkage) × 100
In Tables 1 and 2, TD indicates the width direction of the sample.

(4) Fusion test Film sheet was cut into a size of 60 mm in length and 30 mm in width and overlapped, and the film was fused for 10 seconds at 80 ° C. under a pressure of 1.5 kgf / cm ² with a heat sealer. I saw. In addition, the case where it was easily peeled by hand was indicated by ○, the case which was slightly fused was indicated by Δ, and the case which was difficult to be peeled off was indicated by ×.

(5) Measurement of Tg Using a Perkin Elmer DSC-7, a 10 mg sheet sample was measured from the thermogram when the temperature was raised at a heating rate of 10 ° C./min based on JIS-K7122 (Tg )

(6) Comprehensive evaluation About the obtained polylactic acid-type shrinkable sheet-like material, comprehensive evaluation was performed from each physical property and a fusion test. The symbols in Tables 1 and 2 mean the following contents.
A: Overall good performance B: Overall better performance B: Overall performance is not sufficient.

Example 1
A polylactic acid polymer having a structural unit of L-lactic acid: D-lactic acid = 90: 10 and a weight average molecular weight of 180,000 was extruded from a T die at 210 ° C. with a 30 mmφ uniaxial extruder to form a castin grinder. And rapidly cooled to obtain an unstretched sheet having a thickness of 220 μm. The obtained unstretched sheet was stretched 4.4 times in the width direction at 77 ° C. to obtain a polylactic acid-based contracted sheet.
ΔHm, ΔHc and heat shrinkage rate of the obtained polylactic acid-based shrinkable sheet were measured, and a fusion test was performed. The results are shown in Table 1.

(Examples 2-5, Comparative Examples 1-4)
A polylactic acid-based shrink film was obtained in the same manner as in Example 1 except that a polylactic acid-based polymer having a structural unit having a ratio of L-lactic acid and D-lactic acid shown in Table 1 or Table 2 was used. ΔHm, ΔHc and heat shrinkage rate of the obtained polylactic acid-based shrinkable sheet were measured, and a fusion test was performed. The results are shown in Table 1 or Table 2.

(Example 6)
As a biodegradable aliphatic polyester, 100 parts by weight of a polylactic acid polymer having a structural unit of L-lactic acid: D-lactic acid = 90: 10 and a weight average molecular weight of 180,000, Showa Polymer Co., Ltd. Bionore # 3003 (trade name) (Tg = −45 ° C.) 25 parts by weight was mixed, and the mixture was extruded from a T die at 200 ° C. with a 30 mmφ single-screw extruder, quenched with a castin gluer, and a thickness of 220 μm. An unstretched sheet was obtained. The obtained unstretched sheet was stretched 4.4 times in the width direction at 77 ° C. to obtain a polylactic acid-based shrink film.
ΔHm, ΔHc and heat shrinkage rate of the obtained polylactic acid-based shrinkable sheet were measured, and a fusion test was performed. The results are shown in Table 1.

Claims (6)

In a sheet-like material molded from a biodegradable polymer mainly composed of a polylactic acid polymer,
The polylactic acid polymer has a heat of crystal fusion (ΔHm) of 5 to 45 J / g,
When the temperature of the sheet-like material is raised, the difference between the crystallization heat amount (ΔHc) generated by crystallization of the polylactic acid polymer that is a constituent of the biodegradable polymer forming the sheet-like material and the ΔHm, That is, ΔHm−ΔHc is 5 to 32 J / g,
A polylactic acid-based shrinkable sheet material having a shrinkage rate of 10% or more at 80 ° C. for 10 seconds.   ΔHm is 20 to 40 J / g, the polylactic acid-based shrinkable sheet-like product according to claim 1.   (DELTA) Hm- (DELTA) Hc is 10-30 J / g, The polylactic acid type shrinkable sheet-like material of Claim 1 or 2 characterized by the above-mentioned.   The composition ratio of L-lactic acid and D-lactic acid, which are constituents of the polylactic acid polymer, is 98: 2-94: 6 or 6: 94-2: 98. The polylactic acid-based shrinkable sheet-like material according to any one of the above.   A packaging material using the polylactic acid-based shrinkable sheet-like material according to any one of claims 1 to 4.   The shrinkable label material which uses the polylactic acid-type shrinkable sheet-like material in any one of Claims 1 thru | or 4.