JP2002019053A - Shrink sheet-like material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a shrink sheet-like material capable of being formed by a tubular film method having excellent productivity and obtaining a high shrinkage factor even by processing at a relatively low temperature. SOLUTION: The shrink sheet-like material comprises a layer containing a polyolefin resin as a main component and a layer containing a polylactic acid as a main component.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat-shrinkable sheet (film or sheet), and more particularly to a shrinkable sheet used for shrink-wrapping containers.

[0002]

2. Description of the Related Art Conventionally, polyvinyl chloride (PVC) film has been the mainstream material used for shrink wrapping and shrink wrapping wrapping. However, various materials other than PVC have been studied from the viewpoint of environmental problems. I have. Therefore, a shrinkable film made of a somewhat soft polyolefin resin has come to be used for shrink wrapping of lunches and prepared foods sold at convenience stores and the like. Polyolefin resin shrink film is a desirable material because it has relatively few problems with endocrine disrupting chemicals, which are combustion products and so-called environmental hormones, and has a low specific gravity, which leads to a reduction in garbage weight. It is difficult to increase the shrinkage. That is, in order to increase the shrinkage of the shrink film of the polyolefin resin, it is necessary to use, for example, a crosslinked resin or an elastomer having strong rubber elasticity, which increases the material cost. The use of the inflation method is excellent in mass productivity, but requires a high stretching temperature. Therefore, in order to obtain a predetermined shrinkage ratio, the shrinking temperature must be increased. On the other hand, in the case of shrink-wrapping or shrink-wrapping an object to be packaged that is vulnerable to high temperatures,
It is necessary to perform low-temperature shrinkage processing at ℃. Therefore, in order to achieve a high shrinkage at a relatively low temperature, at present, tenter stretching or the like, which requires high equipment costs, or tubular stretching or the like, which is inferior in productivity, is used. Therefore, there is a demand for a shrinkable film or sheet that has high productivity and low equipment cost and that can obtain a high shrinkage rate even at a low temperature by using an inflation method.

[0003]

That is, the present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide an inflation method having excellent productivity and obtaining a high shrinkage at a relatively low temperature. To provide a shrinkable sheet material that can be used.

[0004]

The shrinkable sheet of the present invention is characterized in that it has a layer mainly composed of polyolefin resin and a layer mainly composed of polylactic acid. Here, the outermost layer is a layer mainly composed of a polyolefin-based resin, and at least one layer mainly composed of polylactic acid can be provided between the layers mainly composed of the polyolefin-based resin. Further, an adhesive layer can be provided between the layer containing polyolefin-based resin as a main component and the layer containing polylactic acid as a main component. Here, the adhesive layer may be a layer containing an acrylic-modified polyethylene-based resin as a main component. Further, the adhesive layer may be a layer containing an ethylene / epoxy / alkyl acrylate copolymer as a main component. Further, the polyolefin resin may be a linear low density polyethylene resin or an ethylene copolymer.

According to the present invention, there is no idea to combine a layer mainly composed of a polyolefin resin and a layer mainly composed of polylactic acid, that is, to combine them. By combining the materials, a high shrinkage rate was obtained at a relatively low temperature while using an inflation method with excellent productivity, and a flexible shrinkable sheet having improved breaking strength and the like was obtained. . Polylactic acid is a material that is biodegradable and does not cause environmental problems, and its stretched film or sheet has properties similar to stretched PET, and has been studied for various uses. However, polylactic acid is emphasized only for its biodegradability characteristics, and since attention is paid to this biodegradability, its combination with general resins has not been studied at all. However, thanks to mass production, polylactic acid, which was conventionally expensive, has become available at a price close to general-purpose resins. Therefore, the present inventor paid attention to characteristics other than the biodegradability of polylactic acid, and continued research on whether a resin or a laminated body utilizing both such characteristics and characteristics of a general resin could be developed, and completed the present invention. It led to.
With the completion of the present invention, the range of material selection has been significantly expanded,
This has contributed to the expansion of the field of material design.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail. The shrinkable sheet of the present invention has at least one or more layers mainly composed of a polyolefin resin and a layer mainly composed of polylactic acid. Suitable for sheet-like packaging machine,
In consideration of water resistance and the like, it is preferable that the outermost layers on the front and back surfaces have a layer mainly composed of a polyolefin resin. Here, the suitability of the sheet-like material for the packaging machine means that when the sheet-like material is passed through the packaging machine, good sliding properties between parts such as a belt of the packaging machine and the surface of the sheet-like material, and to shrink the stretched film. It means that it has excellent heat resistance when it passes through a shrinking tunnel used for the above. As for polyolefin resins, know-how has been established, such as what kind of mixed material should be selected to satisfy not only such properties but also various properties, and how to use additives. In addition, it is possible to easily select a material and a prescription suitable for a packaging machine. Therefore, it is convenient to form a layer containing a polyolefin-based resin as a main component as both outer layers, since required packaging machine suitability can be easily satisfied.

[0007] In the present invention, the sheet material means a sheet or a film. According to the definition in JIS, a sheet is a thin product that is thin and generally has a small thickness instead of length and width. A film is extremely small in thickness compared to length and width, and the maximum thickness is An optionally defined thin flat product, usually supplied in the form of a roll (JIS K 6900). Therefore, it can be said that a sheet having a particularly small thickness among the sheets is a film. However, the boundary between the sheet and the film is not clear,
Because it ’s difficult to make a clear distinction,
The term "sheet" is used as a concept that includes both sheets and films.

The polylactic acid used in the present invention is, for example, a polymer containing L-lactic acid, D-lactic acid or DL-lactic acid as a main component, or a mixture of these polymers. An isomer (D-lactic acid for L-lactic acid and L-lactic acid for D-lactic acid) can be copolymerized. The polylactic acid may contain a small amount of another hydroxycarboxylic acid or the like as a copolymer component, or may contain a small amount of a chain extender residue. Monomers such as copolymerized components copolymerized with polylactic acid include glycolic acid, 3-hydroxybutyric acid, 4-hydroxybutyric acid, 2-hydroxy-n-butyric acid, 2-hydroxy-3,3-dimethylbutyric acid, Bifunctional aliphatic hydroxycarboxylic acids such as hydroxy-3-methylbutyric acid, 2-methyllactic acid and 2-hydroxycaproic acid; caprolactone; butyrolactone;
Lactones such as valerolactone.

In the present invention, known methods such as a condensation polymerization method and a ring-opening polymerization method can be employed as the polymerization method. For example, in the condensation polymerization method, L-lactic acid, D-lactic acid, D-lactic acid,
Polylactic acid having an arbitrary composition can be obtained by directly dehydrating and condensing L-lactic acid or the like. In the ring-opening polymerization method (lactide method), lactide, which is a cyclic dimer of lactic acid,
A polylactic acid-based polymer can be obtained by appropriately selecting and using a polymerization regulator, a catalyst and the like as needed.

The weight average molecular weight (Mw) of the polylactic acid used in the present invention is preferably in the range of 60,000 to 700,000, more preferably 80,000 to 400,000, particularly preferably 100,000 to 300,000. is there. When the weight average molecular weight of the polylactic acid-based polymer is 60,000 or more, practically usable mechanical properties and heat resistance can be exhibited, and the weight average molecular weight is 7
If it is not more than 0,000, the melt viscosity does not become too high and the moldability does not deteriorate.

A heat stabilizer, a light stabilizer, a light absorber, a lubricant, a plasticizer, an inorganic filler, a colorant, a pigment, etc. are added to the layer mainly composed of polylactic acid for the purpose of adjusting various physical properties. You can also. Furthermore, by applying a corona treatment to the surface of the sheet-like material, it is possible to improve the adhesiveness and the like. For the layer mainly composed of polylactic acid, various additives such as a slip agent, an antioxidant, a plasticizer, and an impact modifier are added, and a blend of a polymer that improves strength and elongation is selected. be able to.

As the polylactic acid used in the present invention, for example, "EcoPLA" (trade name, manufactured by Cargill, USA) can be commercially obtained. The thickness of the layer mainly composed of polylactic acid is not particularly limited, but is preferably in the range of 2 to 50 μm in the present invention.

The polyolefin resin used in the present invention includes low-density polyethylene, linear low-density polyethylene, high-density polyethylene, polypropylene, ethylene /
Examples include vinyl acetate copolymers, ethylene / ethyl acrylate copolymers, ethylene / methyl acrylate copolymers, and their copolymers, blends and cross-linked products, but the present invention is not limited thereto. is not. The type of the polyolefin-based resin can be appropriately selected according to the characteristics required for the shrinkable sheet-like material, and, for example, when the strength of the sheet-like material is important, a linear low-density polyethylene resin is used. When importance is attached to the adhesiveness and heat-fusibility of the sheet material, it is preferable to select an ethylene-based copolymer such as an ethylene / vinyl acetate copolymer or an acrylic-modified polyethylene. In the present invention, an appropriate amount of various additives such as an antioxidant, a slip agent, and an anti-fogging agent can be added to the polyolefin resin, if necessary. The thickness of the layer containing a polyolefin resin as a main component is not particularly limited.
It is preferably in the range of μm.

In the present invention, an adhesive layer, an intermediate layer, a reproduction layer, and the like can be provided as required in addition to the above-mentioned layers, if necessary. For example, when the adhesive strength between the layers is insufficient, an adhesive layer can be formed, and the adhesive layer is formed between a layer mainly containing polyolefin resin and a layer mainly containing polylactic acid. Can be formed. In the present invention, the outermost layer has a layer mainly composed of polyolefin resin, and a layer mainly composed of polylactic acid (intermediate layer) between the layers,
In addition, a configuration having an adhesive layer between the outermost layer and the middle layer, that is, a layer configuration of at least five layers of outermost layer / adhesive layer / middle layer / adhesive layer / outermost layer is preferable. Of course, it may have five or more layers.

As the adhesive used for the adhesive layer, an adhesive of vinyl type, acrylic type, polyamide type, polyester type, rubber type, polyurethane type or the like can be generally used, but a biodegradable adhesive, for example, And polysaccharides such as starch, amylose and amylopectin; proteins and polypeptides such as glue, gelatin, casein, zein and collagen; unvulcanized natural rubber; and aliphatic polyesters. In the present invention, an adhesive made of an acrylic-modified polyethylene resin is preferable, for example, an ethylene / ethyl acrylate copolymer,
Examples thereof include a methyl methacrylate copolymer, an ethylene / acrylic acid copolymer, and an ethylene / methacrylic acid copolymer. The higher the acrylic modification ratio, the more preferable. In the present invention, the use of an ethylene / epoxy / alkyl acrylate copolymer as the adhesive is particularly desirable because sufficient interlayer adhesion can be obtained. The thickness of the adhesive layer is not particularly limited, but is preferably in the range of about 1 to 3 μm.

In the present invention, the thickness ratio of each layer constituting the shrinkable sheet material is not particularly limited, but the thickness of the layer mainly composed of polylactic acid occupying in the total thickness of the shrinkable sheet material. Preferably, the depth ranges from about 25% to 60%. If it is 25% or more, a sufficient shrinkage ratio can be obtained, and
% Or less, the film will not be broken in the normal use range.

The shrinkable sheet material of the present invention can be manufactured based on a manufacturing method by a general inflation method, but the final valve diameter to the die diameter is 5 times or more, that is, the blow-up ratio is 5 times or more. It is desirable. If the blow-up ratio is less than 5 times, a sufficient lateral shrinkage may not be obtained.

[0018]

EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples. Example 1 As a polyolefin resin, an ethylene / methacrylic acid copolymer (EMAA) manufactured by DuPont-Mitsui Polychemicals Co., Ltd.
(Using the product name "Nucrel N1108C", L
-Lactic acid: D-lactic acid = 96: 4 (weight ratio), using polylactic acid having a weight average molecular weight of about 200,000, the thickness of the layer (A) containing a polyolefin resin as a main component is 6 μm, A layer (C) having a thickness of 6 μm as a main component, and a layer configuration of a layer (A) having a polyolefin resin as a main component / a layer (C) having a polylactic acid as a main component having a total thickness of 12 μm. A shrinkable sheet was produced by an inflation method. However, the extrusion temperature is 190 ° C and the blow-up ratio is 6
It was prepared as a double.

Example 2 Example 1 was repeated except that the thickness of the layer mainly composed of polyolefin resin, the thickness of the layer mainly composed of polylactic acid, and the layer constitution were changed as shown in Table 1. A shrinkable sheet having a total thickness of 12 μm was prepared in the same manner as in Example 1.

Example 3 In Example 1, the type of the polyolefin resin, the thickness of the layer mainly containing the polyolefin resin, and the thickness of the layer mainly containing polylactic acid were changed as shown in Table 1, Further, as shown in the layer structure of Table 1, a shrinkable sheet was formed in the same manner as in Example 1 except that a layer formed of EMAA was further formed to have a thickness of 1.5 μm as an adhesive layer or an intermediate layer (B). A product was made.

Example 4 In Example 1, the type of the polyolefin resin, the thickness of the layer mainly containing the polyolefin resin, and the thickness of the layer mainly containing polylactic acid were changed as shown in Table 1. ,
Further, as shown in the layer structure of Table 1, a polyethylene / glycidyl methacrylate / methyl acrylate copolymer (PE / GMA / M) was further used as an adhesive layer or an intermediate layer (B).
A shrinkable sheet was produced in the same manner as in Example 1 except that the layer formed from A) (trade name: Bond First 7N) (manufactured by Sumitomo Chemical Co., Ltd.) was formed to have a thickness of 1.5 μm.

Comparative Example 1 In Example 1, as shown in Table 1, the type of the polyolefin resin and the thickness of the layer mainly composed of the polyolefin resin were changed, and the layer constitution was changed as shown in Table 1. A layer made of PE / GMA / MA is used as an adhesive layer or an intermediate layer with a thickness of 6 μm without providing a layer mainly composed of polylactic acid.
A shrinkable sheet having a total thickness of 12 μm was prepared in the same manner as in Example 1 except that the sheet was provided so that

REFERENCE EXAMPLE As shown in Table 1, a commercially available shrinkable sheet of a polyolefin resin by tubular stretching was prepared for reference.

The shrinkage rates of the obtained shrinkable sheets of Examples 1 to 4, Comparative Example 1, and Reference Example were measured. That is, the shrinkable sheet was immersed in an oil bath maintained at a constant temperature of 120 ° C. for 10 minutes, and the shrinkage in the machine direction (MD) and the transverse direction (TD) were measured. In addition,
If the shrinkage of MD is 30% or more and the shrinkage of TD is 40% or more, there is no practical problem. Table 1 shows the obtained results.

[0025]

[Table 1]

As is clear from Table 1, Examples 1 to 4 can be produced by the inflation method, and
It was found that even at a temperature of 20 ° C., the shrinkage ratio in the MD direction and the shrinkage ratio in the TD direction were almost the same as those of the commercial products listed as reference examples. On the other hand, the shrinkable sheet of Comparative Example 1 could not be put to practical use, and could not be a sheet having a sufficient shrinkage. Further, Examples 1 to
Evaluation of various physical properties such as slipperiness, heat resistance, and strength was performed on the shrinkable sheet material of No. 4, and the shrinkable sheet materials of Examples 1, 2 and 3 were evaluated for tackiness and heat adhesion. The shrinkable sheet of Example 4 is excellent, and the sheet is excellent in strength. It can be seen that desired properties can be easily added by appropriately selecting the type of the polyolefin resin. Was. In addition, when a shrinkable sheet having only a layer made of polylactic acid was formed by an inflation method, it was not practical because the breaking strength was weak.

[0027]

As described above in detail, according to the present invention, it is possible to obtain a sheet-like material having the same shrinkage property as a conventional shrinkable sheet or film by using an inflation method excellent in mass productivity. Thus, an extremely industrially useful technique could be provided.

Claims (6)

[Claims] 1. A shrinkable sheet comprising a layer mainly composed of a polyolefin resin and a layer mainly composed of polylactic acid. 2. The method according to claim 1, wherein the outermost layer is a layer mainly composed of a polyolefin resin, and at least one layer mainly composed of polylactic acid is provided between the layers mainly composed of the polyolefin resin. The shrinkable sheet according to claim 1. 3. The shrinkage according to claim 1, wherein an adhesive layer is provided between the layer mainly composed of polyolefin resin and the layer mainly composed of polylactic acid. Sheets. 4. The shrinkable sheet according to claim 3, wherein the adhesive layer is a layer containing an acrylic-modified polyethylene resin as a main component. 5. The shrinkable sheet according to claim 3, wherein the adhesive layer is a layer containing an ethylene / epoxy / alkyl acrylate copolymer as a main component. 6. The shrinkable sheet according to claim 1, wherein the polyolefin-based resin is a linear low-density polyethylene resin or an ethylene-based copolymer.