JP2017202641A - Polyethylene film and packaging materials - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polyethylene film that is easy to tear without laser processing and the like at low cost, and packaging materials containing the same.SOLUTION: A polyethylene film is inflation-molded in a blow ratio of 1.2-3.2 with low-density polyethylene (LDPE) having a density of 0.91-0.93 g/cmbased on JIS K7112. The polyethylene film has excellent tearability and therefore, can be suitably used in, for example, packaging materials that are opened to take out its contents.SELECTED DRAWING: None

Description

  The present invention relates to an easily tearable polyethylene film and packaging material obtained by molding low density polyethylene (LDPE).

  Polyolefins typified by polyethylene and polypropylene are generally used as packaging materials after being formed into a film by inflation molding or cast molding, or bonded to another film by extrusion lamination, dry lamination, or the like. In this packaging material, since the end user takes out the contents, that is, opens the bag, it is one of the important factors that the opening operation is easy. Therefore, easy openability and easy cutability are usually required.

  As the polyolefin film, linear low density polyethylene (LLDPE), polypropylene or the like is often used because of its strength and molding stability. However, these films require not only a large force for tearing, but also it is difficult to cut them in a straight line, which may cause the contents to leak.

  As a film for imparting easy-openability and easy-cutting properties to packaging materials, for example, Patent Document 1 proposes a laminate film obtained by laminating a plurality of films as having characteristics in composition and materials. Has been. Patent Document 2 proposes a film using a cyclic polyolefin (COC, COP) as one of the layers constituting the film in a multilayer film obtained by coextrusion such as T-die molding. Furthermore, in Patent Document 3, a sealant layer, a base material layer made of polyamide, and an adhesive layer made of acid-modified polyolefin are obtained by coextrusion such as inflation molding, and the thicknesses of the adhesive layer and the sealant layer are determined. A film in which the degree of orientation of the film is defined within a certain range has been proposed.

  Moreover, as a film provided with the above-described easy-openability and the like by processing, Patent Document 4 proposes a method of performing a half-cut process with a laser and preliminarily attaching a cut line.

JP 2001-199023 A JP 2007-245612 A JP 2015-223706 A JP-A-11-77872

  However, as proposed in Patent Documents 1 and 2, it is more expensive to stack a plurality of types of films than a single-layer structure. In particular, as in the proposal of Patent Document 2, when a cyclic polyolefin is used, it is extremely expensive compared to general polyolefins such as polyethylene and polypropylene. Further, in the proposal of Patent Document 3, the degree of orientation of the base material layer, which is one layer of the laminated film, is defined. However, since the base material layer is polyamide, it is intended for applications that require strength. This cannot be applied immediately to typical polyolefins such as polyethylene and polypropylene. Therefore, in these proposals, it is extremely difficult to meet various demands related to easy opening from the viewpoint of cost.

  On the other hand, in the proposal of Patent Document 4, since it is necessary to prepare equipment capable of laser processing, there is a problem that equipment costs increase. In addition, there is a possibility that fine dust may be generated at the time of laser processing, and if this adheres to a film, when used as a packaging material, for example, if the content is an electronic component, the quality will be, and if it is an oral preparation Furthermore, depending on the contents, there may be unfavorable factors, such as concerns that the human body may be adversely affected.

  An object of the present invention is to obtain a polyethylene film which can be easily torn without laser processing or the like at low cost, and a packaging material comprising the same.

<1> Low density polyethylene (LDPE) having a density of 0.91 g / cm ^{3 to} 0.93 g / cm ³ , wherein the polyethylene film is blown at a blow ratio of 1.2 to 3.2 It is.

  <2> The polyethylene film according to <1>, wherein the melt flow rate (MFR) (g / 10 minutes, 190 ° C.) is 0.1 or more and 4.0 or less.

  <3> The polyethylene film according to <2>, wherein the MFR is less than 1.0.

  <4> The polyethylene film according to any one of <1> to <3>, wherein an orientation ratio in the MD direction / TD direction is 1.2 to 2.5.

  <5> The polyethylene film according to any one of <1> to <4>, which has a thickness of 40 μm to 200 μm.

  <6> A packaging material comprising the polyethylene film according to any one of <1> to <5>.

  In this specification, the MD direction means Machine Direction, that is, the flow direction or the vertical direction during film formation, and the TD direction means Transverse Direction, that is, the direction perpendicular to the film flow direction or the horizontal direction.

  The polyethylene film of the present invention is made of low-density polyethylene (LDPE) and molded at a blow ratio of 1.2 to 3.2. Therefore, it is accompanied by laser processing or the like at low cost without laminating films or using cyclic polyolefin. It can be easily torn.

  Since the packaging material of the present invention is made of the polyethylene film of the present invention, it can be easily torn at low cost without laser processing or the like.

FIG. 1 is a schematic diagram of inflation molding. FIG. 2 is a diagram showing an example of the packaging material of the present invention. FIG. 3 is a photograph of the tear shape when a film molded at a blow ratio of 1.2 in Example 1 is torn in the TD direction. FIG. 4 is a photograph of the tear shape when a film molded at a blow ratio of 1.8 in Example 1 is torn in the TD direction. FIG. 5 is a photograph of the tear shape when a film molded with a blow ratio of 1.2 in the comparative example 1 is torn in the TD direction.

The polyethylene film of the present invention is blown from low density polyethylene (LDPE) having a density of 0.91 g / cm ^{3 to} 0.93 g / cm ³ .

  If it is not LDPE, the tear strength is high and the desired tearability cannot be obtained, and the material cost also increases. On the other hand, if the density is higher than this range, the impact strength will be low, and it will be easy to tear, while if it is lower than this range, the elastic modulus will be low, and the automatic filling machine will be used when storing the contents as packaging materials. It becomes difficult to do by etc. In other words, when the present invention is used as a packaging material, for example, an application in an agricultural material such as 10 to 30 kg of fertilizer, rice, and soil is assumed, but if the density of LDPE is outside the above-described range, Not suitable for use.

  The melt flow rate (MFR) (g / 10 min, 190 ° C.) of LDPE is preferably 0.1 or more and 4.0 or less, and more preferably 0.1 or more and less than 1.0.

  When MFR exceeds 4.0, the strength of the film tends to be weak. In other words, the tearability of the film easily tears the intended part, but it is not preferable from the quality of the product that the unintended part is torn, but if the MFR is high, the film is unexpectedly torn. There is a risk that. Also, inflation molding tends to be difficult.

  Further, if the MFR is 1.0 or more, the blow ratio is changed flexibly to make molding difficult, and the strength such as tensile strength may be lowered.

  The density of LDPE can be measured using a commercially available specific gravity measuring device based on JIS K7112, and its MFR should be measured at a 2.16 kg load using a commercially available melt indexer based on JIS K7210. Can do.

  LDPE is molded at a blow ratio of 1.2 to 3.2. When the blow ratio is less than 1.2, it becomes difficult to tear, and when the blow ratio exceeds 3.2, molding becomes difficult due to restrictions on the apparatus.

  The blow ratio is not particularly limited as long as it is within this range, but a higher one is preferable considering that the tear strength is lowered.

  The blow ratio is synonymous with the film expansion ratio. For example, as shown in the inflation molding schematic diagram of FIG. 1, the resin (film) 12 extruded on the die 11 of the inflation molding machine 10 is blown with air. It is a value (E / D) obtained by dividing the diameter (E) by the diameter (D) of the die.

  For other conditions such as film take-up speed during inflation molding and LDPE resin temperature, applicable conditions may be selected and adopted while taking into consideration the performance of the molding machine, and there is no particular limitation. .

  The polyethylene film thus obtained has an MD / TD orientation ratio, that is, a value obtained by dividing the MD orientation value by the TD orientation value from 1.2 to 2.5. It is preferable. If this orientation ratio exceeds 2.5, the tear strength may increase. Moreover, it is difficult to produce a film having an orientation ratio of less than 1.2 due to device limitations.

  If LDPE is molded at a blow ratio under the above-described conditions, a film having good tearability can be obtained, but it is difficult to analyze what blow ratio was produced after the film was produced. On the other hand, the film obtained by the blow ratio of the said conditions is settled in the orientation ratio in this range substantially, and shows favorable tearability. That is, in the present invention, the blow ratio is a condition for producing a film having good tearability, whereas the orientation ratio in the MD direction / TD direction shows good tearability in the film after production. Significant as an indicator.

  The degree of orientation can be measured by infrared dichroism from the obtained IR spectrum using, for example, a Fourier transform infrared spectrophotometer (FT-IR). At this time, in the polarization measurement, the measurement was performed with the polarizer installation angle set to 0 °, the film (a) MD adjusted to 0 °, and (b) TD set to 0 °. The absorbance ratio between (a) and (b) is calculated from the obtained spectrum, and the degree of orientation may be obtained. For the spectrum analysis, commercially available analysis software may be used.

  The thickness of the obtained polyethylene film is preferably 40 μm to 200 μm, considering that it is used for packaging materials that require the above-described easy-openability. The thickness can be measured using a commercially available dial gauge based on JIS K7130.

  In the polyethylene film of the present invention, for example, a known layer such as a sealant layer or an adhesive layer, which is made of a commonly used material, may be appropriately laminated depending on the purpose.

  In addition, for example, known components that can be used such as an antistatic agent, a heat stabilizer, an antioxidant, a lubricant, an ultraviolet absorber, and a colorant may be appropriately added depending on the purpose.

  Since the polyethylene film of the present invention has such a property that it can be easily torn, it can be applied in various applications where the property is required, such as packaging materials including packaging bags. It is suitable for applications that require openability and easy cutability.

  The packaging material may be formed in a generally known configuration according to the purpose. For example, a top seal 21 at the top and a bottom seal 22 at the bottom, as in the packaging bag 20 shown in FIG. A corner seal 23 is provided at the corner on the top side, and an opening 24 for opening is formed on the corner seal 23.

  Examples of the present invention will be described below, but the present invention is not limited to the following examples.

Example 1
Based on JIS K7210, the melt flow rate (MFR) (g / 10 minutes, 190 ° C.) measured at a load of 2.16 kg using a melt indexer (F-F01, manufactured by Toyo Seiki Seisakusyo Co., Ltd.) is 0. 35,
Based on JIS K7112, from a low density polyethylene (LDPE) having a density measured using a specific gravity measuring device (SGM-220U-02 EB-32, manufactured by Shimadzu Corporation) of 0.920 g / cm ³ ,
A blown ratio was sequentially increased from 1.2 with an inflation molding machine (manufactured by Plako Co., Ltd.) to produce a polyethylene film.

  The thickness of this film was 80 μm when 30 points were measured at intervals of 50 mm based on JIS K7130 using a dial gauge (manufactured by Ozaki Manufacturing Co., Ltd., FFA-1), and the average value was calculated. It was.

  In addition, including the example described later, if the blow ratio is higher than 3.2, the amount of resin discharged is insufficient, a film cannot be obtained with a predetermined thickness, and the film is difficult to take up or wind up. I could not.

  The obtained film was measured for (1) degree of orientation and (2) general physical properties (tensile strength and elongation, tear strength, tensile modulus) as follows. The results are shown in Table 1. In addition, photographs of tearing shapes when the formed films are torn in the TD direction at blow ratios 1.2 and 1.8 are shown in FIG. 3 for blow ratio 1.2 and for blow ratio 1.8. 4 respectively.

(1) Orientation degree Polarization measurement was performed using FT / IR-6600 manufactured by JASCO Corporation, and the degree of orientation of MD and TD was evaluated by infrared dichroism from the obtained IR spectrum.

  In the polarization measurement, the polarizer was set at an angle of 0 °, and (a) MD was adjusted to 0 ° and (b) TD was adjusted to 0 °. The absorbance ratio of (a) and (b) was calculated from the obtained spectrum, and was defined as the degree of orientation. In the spectrum analysis, Spectra Manager Version 2 spectrum analysis version 2.14.00 manufactured by JASCO Corporation was used.

  Further, the orientation ratio (MD / TD) of both was calculated from two significant digits from the obtained MD and TD orientation values.

(2) General physical properties-Tensile strength and elongation Based on JIS K7127, using a universal testing machine (AG-X500N, manufactured by Shimadzu Corporation), the film test piece was pulled at a tensile speed of 300 mm / min. Is the tensile strength, and the elongation of the film is the tensile elongation.
-Tear strength Based on JIS K7128-1, the average test force when the displacement when pulled at a tensile speed of 200 mm / min using the above-mentioned universal testing machine was 20 mm to 120 mm was taken as the tear strength. In addition, although MD may flow in the TD direction, the obtained numerical value was adopted as a measurement value.
-Tensile elastic modulus Based on JIS K7161-1, it calculated from the inclination of the test force when the strain changes from 0.05% to 0.25% at a tensile speed of 300 mm / min using the universal testing machine described above.

(Example 2)
In Example 1, a film having substantially the same thickness was prepared in the same manner except that LDPE was changed to MFR 0.4 (g / 10 min, 190 ° C.) and density 0.926 / cm ^3. Each general physical property was measured. The results are shown in Table 2.

(Example 3)
In Example 1, a film having substantially the same thickness was prepared in the same manner except that LDPE was changed to MFR 1.0 (g / 10 min, 190 ° C.) and density 0.924 / cm ^3. Each general physical property was measured. The results are shown in Table 3. In this example, each data is not measured at a blow ratio of 1.8.

Example 4
In Example 1, a film having substantially the same thickness was prepared in the same manner except that LDPE was changed to MFR 2.0 (g / 10 min, 190 ° C.) and density 0.924 / cm ^3. Each general physical property was measured. The results are shown in Table 4. In this example, each data is not measured at a blow ratio of 1.8.

(Example 5)
In Example 1, a film having substantially the same thickness was prepared in the same manner except that LDPE was changed to MFR 3.0 (g / 10 min, 190 ° C.) and density 0.924 / cm ^3. Each general physical property was measured. The results are shown in Table 5. In this example, each data is not measured at a blow ratio of 1.8.

(Example 6)
In Example 1, a film having substantially the same thickness was prepared in the same manner except that LDPE was changed to MFR 4.0 (g / 10 min, 190 ° C.) and density 0.924 / cm ^3. Each general physical property was measured. The results are shown in Table 6. In this example, each data is not measured at a blow ratio of 1.8.

(Comparative Example 1)
In Example 1, the same thickness is obtained in the same manner except that LDPE is changed to linear low density polyethylene (LLDPE) having an MFR of 0.8 (g / 10 min, 190 ° C.) and a density of 0.9255 / cm ^3. A film was prepared. In this example, only data at blow ratios 1.8 and 3.2 were measured. The results are shown in Table 7. Moreover, the photograph which image | photographed the tearing shape at the time of tearing the film shape | molded with the blow ratio 1.2 to TD direction is shown in FIG.

[Discussion]
From the results of the examples shown in Tables 1 to 7, the following was found. For convenience of comparison in each example, Table 8 shows a list of each film substrate, MFR, and density.

(1) Regarding the relationship between MFR and blow ratio From Examples 1 to 6, it can be confirmed that the tear strength tends to be lowered by increasing the blow ratio in the range of MFR 0.35 to 4.0. In particular, it was confirmed that the tear strength in the TD direction tends to be consistently low (see Tables 1 to 6). Therefore, regardless of the MFR value, a film is produced by inflation molding with a blow ratio of 1.2 or more from LDPE having a density in a predetermined range, showing good tearability and tearing out the contents. A film suitable for use in packaging materials and the like that are required to be obtained.

  On the other hand, if the blow ratio is increased from 3.2, the upper limit of the blow ratio is 3.2 because the blow ratio cannot be produced due to mechanical constraints.

  Also, from Example 6, MFR4.0 LDPE has good tearability but is weak in consideration of other general physical properties such as tensile strength (see Table 6). MFR is preferably 4.0 or less in order to be suitable for the above-mentioned use.

  Furthermore, from Examples 3 to 6, LDPE with MFR of 1.0 or more could not be molded at a blow ratio of 1.0 (see Tables 3 to 6), so that the blow ratio was changed flexibly to produce a film. More preferably, the MFR is less than 1.0. Moreover, since tensile strength etc. are high, it is more preferable that MFR is less than 1.0 also from a physical property surface.

  Here, with LDPE having a low MFR of less than 1.0, a film excellent in tearability while maintaining good strength can be obtained because the orientation is easily affected by the blow ratio because the molecular chain is long. Guessed.

(2) Relationship between blow ratio and orientation degree In any example, it was confirmed that the orientation degree in the MD direction decreased while the orientation degree in the TD direction increased as the blow ratio increased. That is, the orientation ratio in the MD / TD direction tends to decrease as the blow ratio increases, and a lower tear ratio indicates better tearability. And when showing the favorable tearability, the orientation ratio is in the range of 1.2-2.5 in most cases.

(3) Relationship between LDPE and LLPDE From Comparative Example 1, the LLPDE also shows a tendency for the tear strength to decrease as the blow ratio increases, and the degree of orientation is similar to that of LDPE (Table) 7), the absolute value of strength including tear strength is higher than that of LDPE.

  Moreover, even if the photographs of FIGS. 3 to 5 are compared, when the LDPE film of Example 1 is torn in the TD direction, a substantially linear tear shape can be obtained (see FIGS. 3 and 4), but the comparative example. The LLDPE film 1 has a large uneven shape (see FIG. 5).

  Therefore, LLDPE cannot be said to have good tearability and is not preferable as a resin used for the polyethylene film of the present invention.

  The present invention can be applied to various uses that require easily tearable properties.

10 Inflation molding machine 11 Die 15 Resin (film)
20 Packaging Bag 21 Top Seal 22 Bottom Seal 23 Corner Seal 24 Cut

Claims (6)

A polyethylene film, which is a low density polyethylene (LDPE) having a density of 0.91 g / cm ^{3 to} 0.93 g / cm ³ and is blown at a blow ratio of 1.2 to 3.2.   The polyethylene film according to claim 1, wherein a melt flow rate (MFR) (g / 10 min, 190 ° C) is 0.1 or more and 4.0 or less.   The polyethylene film according to claim 2, wherein MFR (g / 10 minutes, 190 ° C.) is less than 1.0.   The polyethylene film according to any one of claims 1 to 3, wherein an orientation ratio in the MD direction / TD direction is 1.2 to 2.5.   The polyethylene film according to claim 1, which has a thickness of 40 μm to 200 μm.   A packaging material comprising the polyethylene film according to any one of claims 1 to 5.