JP5476533B2 - Heat shrinkable film for polyolefin sleeve packaging - Google Patents

Description

  The present invention relates to a heat-shrinkable film for polyolefin sleeve packaging suitable for book or comic sleeve packaging, excellent in transparency, gloss, packaging finish, fusing and sealing properties, easy to dispose of and excellent in cost.

  Traditionally, shrink-wrapping a package with a heat-shrinkable film has been widely used for reasons such as protection of the package, the ability to package irregularly-shaped packages beautifully, and suitability for automatic packaging. ing. The heat-shrinkable film used in these shrink wrappings is selected according to the shape of the package, the shipping form, the packaging speed, the packaging machine, etc., for example, sleeve shrink wrapping, overlap shrink wrapping, stretch shrink wrapping, etc. The required characteristics differ depending on the packaging method.

At present, books and comics sold at bookstores are also often used for packaging of books and comics because of the prevention of stains, the aesthetics of display, and the simplicity of packaging. Mainly transparency, gloss, and low temperature shrinkage A polyvinyl chloride film excellent in the above is used. However, the polyvinyl chloride film has a problem that hydrogen chloride is generated during incineration of the film after use, and the price is higher than that of the polyolefin film.

  In the case of sleeve packaging, in addition to the polyvinyl chloride film, a film manufactured by an inflation method using polyethylene as a main raw material has been widely used. A film produced by the inflation method is stretched at a temperature equal to or higher than the melting point of the raw material, so that it has excellent low-temperature sealing properties, but is inferior in transparency and gloss, and poor in heat resistance and low-temperature shrinkage. For this reason, when books and comics are shrink-wrapped, there are problems such as poor transparency and gloss and poor appearance due to poor shrinkage and many wrinkles.

Furthermore, as a film suitable for sleeve packaging made of polypropylene as a main raw material by a tubular stretching method, JP-A-55-103931 discloses a heat-shrinkable film that has been stretched in the longitudinal direction after tubular stretching. Manufacturing methods have been proposed. However, since the film obtained in the invention has a small stretch ratio of tubular stretching, when a book or comic is shrink-wrapped, the transparency and gloss are not sufficient, and after low temperature shrinkability, the film is shrink-wrapped. There were many wrinkles and bad appearance.

JP-A-55-103931

  The present invention has been made in view of the above circumstances, and is suitable for book and comic sleeve packaging, excellent in transparency, gloss, packaging finish, fusing sealability, easy to dispose of, and excellent in cost. It is an object of the present invention to provide a heat-shrinkable film for a sleeve packaging.

(1) An unstretched film which is a single layer composed mainly of a propylene-based resin or has a layer mainly composed of a propylene-based resin on both surface layers is stretched in both longitudinal and lateral directions by tubular biaxial stretching. was subjected to stretching of from 5 to 6.0 times, obtained by subjecting the stretched 1.05 to 1.5 times in the longitudinal direction at a temperature lower 10 ° C. or higher than the melting point of the material using a hot roll , A heat-shrinkable film for polyolefin sleeve packaging having a thickness of 6 to 12 μm ,
( 2 ) The polyolefin sleeve packaging according to the above (1) , wherein the layer mainly composed of propylene resin is at least three layers having both surface layers and an inner layer mainly composed of ethylene resin. Heat shrinkable film,
( 3 ) Both surface layers of layers mainly composed of propylene-based resin, both intermediate layers mainly composed of propylene-based resin (hereinafter referred to as “metallocene PP”) produced using a metallocene catalyst, and ethylene-based resin The heat-shrinkable film for polyolefin sleeve packaging according to the above (1) or (2) , wherein the heat-shrinkable film is a 5-layer having a core layer mainly composed of
(4) The heat-shrinkable film for polyolefin-based sleeve packaging according to any one of (1) to (3) above, which is used for heat-shrinkable packaging of books,
It is related to.

  The polyolefin heat-shrinkable film of the present invention is suitable for sleeve packaging of books such as books and comics, is excellent in transparency, gloss, packaging finish, fusing sealability, easy to dispose of, and excellent in cost. There is an effect.

Hereinafter, the present invention will be described in detail.
In order to produce the film of the present invention, first, an unstretched polyolefin heat-shrinkable film is subjected to tubular biaxial stretching. The stretching ratio of the tubular stretching is preferably 3.5 to 6.0 times both vertically and horizontally. When the draw ratio is less than 3.5 times, good transparency, glossiness and sufficient shrinkage cannot be obtained, so that the appearance of the book or comic is deteriorated, which is not preferable. If the draw ratio exceeds 6 times, the low-temperature shrinkage, tear resistance, and impact resistance deteriorate, which is not preferable.

The film after tubular stretching is re-stretched. This re-stretching needs to be performed at a temperature lower than the melting point of the raw material by 10 ° C. or more using a hot roll, and by stretching 1.05-1.5 times in the longitudinal direction, A film that is excellent in shrinkability, can suppress lateral shrinkage, is free of wrinkles during packaging, and does not have a sleeve surface turned up. After tubular stretching, if the film is re-stretched at a temperature higher than the melting point of the raw material of −10 ° C., the film breaks or the shrinkage in the vertical direction cannot be sufficiently obtained, and the shrinkage force is reduced, so that sufficient packaging finish is obtained. I can't. In addition, after stretching heat treatment and relaxation treatment at a temperature higher than the melting point of the raw material −10 ° C., even if stretching is performed in the longitudinal direction, the stretching orientation in the longitudinal and transverse directions imparted by tubular stretching is completely relaxed. As a result, the strength such as tear resistance is significantly reduced.

The ratio of redrawing is preferably 1.05 to 1.5 times, and more preferably 1.1 to 1.3 times. When the redrawing ratio is less than 1.05, the shrinkage in the transverse direction is large, so that the sleeve surface is turned up, the shrinkage in the longitudinal direction is insufficient, and there are many wrinkles and the appearance is unfavorable. When the restretch ratio exceeds 1.5 times, the film is liable to break during restretching, which is not preferable.

The resin used for the surface layer in the present invention is particularly preferably a propylene-based resin since the packaging of books and comics is a fusing seal method. Polyethylene-based resin can be used for the surface layer, but the resin is fused to the fusing seal bar, and it tends to be in a state of pulling the thread, so it is not preferable because it looks bad especially in books and comics packaging with a seal line on the back cover Absent.

  The propylene-based resin used in the present invention has a melting peak temperature measured by a differential scanning calorimeter (hereinafter referred to as DSC) of 130 to 165 ° C., a melt flow rate (hereinafter referred to as MFR, a measuring temperature of 230 ° C., A propylene homopolymer or a copolymer of propylene and an α-olefin having a load of 2.16 kgf) in the range of 1.0 to 10.0 g / 10 min. For example, propylene-ethylene, propylene-butene copolymer, and the like, and propylene-ethylene-butene terpolymer are mentioned, which mainly serve to impart heat resistance and high elastic modulus. Among these, a crystalline propylene-α-olefin random copolymer is preferably used in consideration of the balance between heat resistance, high elastic modulus, heat shrinkage characteristics and transparency.

  When the melting peak temperature of the propylene-based resin is less than 130 ° C., the heat resistance is low, which is not preferable. Further, if the MFR is less than 1.0 g / 10 minutes, there is a problem that the motor load at the time of melt extrusion becomes high, and if it exceeds 10.0 g / 10 minutes, the fusing sealability when using an automatic packaging machine is lowered. Therefore, it is not preferable.

In the present invention, there is no problem if one or more layers mainly composed of propylene-based resin are included, but low-temperature shrinkage, tear resistance, and impact resistance can be achieved by configuring three or more layers laminated with ethylene-based resin. Can be improved. Furthermore, by using a structure of five or more layers in which metallocene PP is laminated, the low-temperature shrinkability can be improved and the elastic modulus can be imparted, so that the workability during automatic packaging can be improved.

  The metallocene PP used by laminating with the above-mentioned propylene-based resin and the later-described ethylene-based resin has a melting peak temperature in the range of 110 to 130 ° C., and if it is less than 110 ° C., the heat resistance of the multilayer film as a whole becomes low. It is not preferable, and if it exceeds 130 ° C., the low temperature shrinkage is lowered, which is not preferable. A MFR of 0.5 to 10.0 g / 10 min is preferably used. If it is less than 0.5 g / 10 minutes, there is a problem that the motor load at the time of melt extrusion becomes high, and if it exceeds 10.0 g / 10 minutes, the fusing and sealing properties are lowered, which is not preferable.

The ethylene-based resin used by laminating with the propylene-based resin and metallocene PP described above has a density at 23 ° C. in the range of 0.900 to 0.940 g / cm ³ , a low-density polyethylene having a long chain branch, ethylene, Linear low-density polyethylene, ethylene-, which is a copolymer with an α-olefin having 4 to 20 carbon atoms, including butene-1, pentene-1, hexene-1, 4-methylpentene-1, and octene-1. Consists of at least one selected from vinyl acetate copolymer, ethylene-aliphatic unsaturated carboxylic acid copolymer, ethylene-aliphatic unsaturated carboxylic acid ester copolymer, ionomer resin, low temperature shrinkage, tear resistance It acts to impart impact resistance. Of these, linear low-density polyethylene is preferably used because it can impart excellent low-temperature shrinkage.

If the density of the polyethylene-based resin is less than 0.900 g / cm ³ , the tensile modulus and heat resistance are undesirably lowered, and if it exceeds 0.940 g / cm ³ , the low-temperature shrinkability is undesirably lowered. A melt index (hereinafter referred to as MI, measuring temperature 190 ° C., load 2.16 kgf) of 0.3 to 5.0 g / 10 min is preferably used. If it is less than 0.3 g / 10 minutes, there is a problem that the motor load at the time of extrusion becomes high, and if it exceeds 5.0 g / 10 minutes, the stretching stability is lowered, which is not preferable.

The layer structure of the present invention has no problem as long as at least one layer mainly composed of propylene-based resin is included. In addition, a propylene-based resin, a metallocene PP, and an ethylene-based resin can be mixed and used within a range that does not hinder the object of the present invention. The resin that can be mixed is the same as the propylene-based resin, metallocene PP, and ethylene-based resin used in the present invention, and can also be used for scrap recycling.

In each layer, additives such as a lubricant, an antiblocking agent, an antistatic agent, an antifogging agent, an antioxidant, and a nucleating agent can be appropriately used for the purpose of providing each effective action.

In the present invention, the thickness of the polyolefin-based heat-shrinkable film is preferably 6 to 12 μm, more preferably 8 to 10 μm, in consideration of finish and fusing sealing properties. When the thickness of the film of the present invention exceeds 12 μm, it is difficult to obtain good finish and fusing sealing properties. Moreover, if it is less than 6 micrometers, since tear resistance and impact resistance fall, it is not preferable.

Next, the manufacturing method of the film of this invention is shown. The method for producing the film of the present invention using the above resin can be performed by a known tubular stretching method or roll re-stretching method.
Hereinafter, the case of three-layer laminated annular film-forming stretching will be described as an example.
First, a propylene resin is melted and kneaded by three extruders so that both surface layers and ethylene resin become a core layer, and is coextruded into a tube from a three-layer annular die, and then rapidly cooled and solidified without stretching. An unstretched film is produced. The obtained tube-shaped unstretched film is supplied to a tubular stretching apparatus, and gas is introduced into the tube at a highly orientable temperature range, for example, 10 ° C. or lower, preferably 15 ° C. or lower, below the melting point of the core layer. Pressure is applied to cause simultaneous biaxial orientation by expansion and stretching. In order to obtain physical properties such as excellent transparency, glossiness and shrinkage, the stretching ratio is preferably stretched 3 to 6 times in both length and width.

After the tubular stretching step, the temperature is 10 ° C. or more lower than the melting point of the core layer raw material, for example, stretching 1.05 times or more in the longitudinal direction between a heating roll of 60-100 ° C. and a cooling roll of 20-40 ° C. Then, annealing is performed. The combination of the heating roll and the cooling roll is not limited to one pair, and may be two or more pairs. The product thickness is adjusted by the thickness of the tubular unstretched film in consideration of the stretch ratio of tubular stretching and roll restretching, and the thickness is 6 to 12 μm.

EXAMPLES Hereinafter, although an Example demonstrates this invention concretely, this invention is not limited to these Examples.
In addition, each physical property measurement shown in a present Example was based on the following method.

1. Film thickness: measured according to JIS-Z1709.

2. Thickness ratio: Measured by observing the cross section of the film with a microscope.

3. Haze: Measured according to JIS-K7105.

4). Gloss (60 °): Measured according to JIS-Z7105.

5. 120 ° C. heat shrinkage ratio: A film cut into a square of 100 mm in length and breadth is immersed in a glycerin bath at 120 ° C. for 10 seconds, then rapidly cooled in water, and the length in each length and width is measured. The vertical and horizontal heat shrinkage rates were calculated.

6). Sleeve packaging suitability: Commercial large comics were packaged using Comic Shrinker PAPC LC II manufactured by Daiwatex Co., Ltd., and the following items were evaluated according to the following criteria.
<Wrinkles>
○: No wrinkles after packaging.
X: Wrinkles are noticeable after packaging.
<Turn the sleeve surface>
○: The sleeve surface is not turned over, and the comic is wrapped without any problem.
×: There is a portion where the sleeve surface is turned up and the comic is exposed.
<Fusing sealability>
○: The seal is well cut and the state where the thread is pulled is not observed.
(Triangle | delta): The state where the cutting | disconnection of the seal | sticker was a little bad and the thread | yarn was pulled slightly is observed.
X: The seal was poorly cut and a state where the yarn was pulled was observed.

Example 1
As shown in Table 1, a propylene-ethylene copolymer resin having a melting peak temperature of 140 ° C. and an MFR of 2.3 g / 10 min is used as both surface layers, the melting peak temperature is 125 ° C., and the MFR is 4. Metallocene PP having characteristics of 0 g / 10 min is used as an intermediate layer, and linear low density polyethylene having characteristics of 0.920 g / cm ³ and MI of 1.0 g / 10 min is used as a core layer. Melting and kneading was performed with an extruder, and the extrusion amount of each extruder was set so that the thickness ratio would be 1/1/5/1/1, and coextrusion was performed downward with a five-layer annular die. The formed five-layer tube was cooled by passing through the water tank while the outer surface of the cylindrical cooling mandrel in which the cooling water circulated was slid, and was taken out to obtain an unstretched film.
This tubular unstretched film is guided to a tubular biaxial stretching device, stretched 4.5 × 4.5 times in the longitudinal and lateral directions, this stretched film is guided to a hot roll device, heated at 80 ° C. and heated at 30 ° C. After stretching 1.15 times between the two rolls of the cooling roll, it was further subjected to relaxation heat treatment of about several percent with a heat roll appropriately adjusted to 30 to 90 ° C., cut into two upper and lower sheets, One sheet was wound on one roll to obtain a laminated biaxially stretched film having a film thickness of 9 μm.
The drawability was good, there was no up-and-down movement of the drawing point and the swinging of the drawing tube, non-uniform drawing conditions such as necking were not observed, and the flatness was good. The evaluation results of the obtained film were as shown in Table 1 and were good.

Example 2
As shown in Table 1, a laminated biaxially stretched film was obtained in the same manner as in Example 1 except that the heating roll of the hot roll apparatus was set to 90 ° C.
The drawability was good, there was no up-and-down movement of the drawing point and the swinging of the drawing tube, non-uniform drawing conditions such as necking were not observed, and the flatness was good. The evaluation results of the obtained film were as shown in Table 1 and were good.

Example 3
As shown in Table 1, a laminated biaxially stretched film was obtained in the same manner as in Example 2 except that stretching was performed 1.2 times between two rolls, a heating roll and a cooling roll.
The drawability was good, there was no up-and-down movement of the drawing point and the swinging of the drawing tube, non-uniform drawing conditions such as necking were not observed, and the flatness was good. The evaluation results of the obtained film were as shown in Table 1 and were good.

Example 4
As shown in Table 1, a laminated biaxially stretched film was obtained in the same manner as in Example 2 except that stretching was performed 1.28 times between two rolls, a heating roll and a cooling roll.
The drawability was good, there was no up-and-down movement of the drawing point and the swinging of the drawing tube, non-uniform drawing conditions such as necking were not observed, and the flatness was good. The evaluation results of the obtained film were as shown in Table 1 and were good.

Example 5
As shown in Table 1, a propylene-ethylene copolymer resin having a melting peak temperature of 138 ° C. and an MFR of 2.5 g / 10 min as a single layer is melt-kneaded with a single extruder, A laminated biaxially stretched film was obtained in the same manner as in Example 3 except that the film was coextruded downward and the draw ratio was 4.0 × 4.0.
The drawability was good, there was no up-and-down movement of the drawing point and the swinging of the drawing tube, non-uniform drawing conditions such as necking were not observed, and the flatness was good. The evaluation results of the obtained film were as shown in Table 1 and were good.

Example 6
As shown in Table 1, a propylene-ethylene copolymer resin having a melting peak temperature of 140 ° C. and an MFR of 2.3 g / 10 min is used as both surface layers, the melting peak temperature is 115 ° C., and MI is 2. Using a linear low-density polyethylene having the characteristics of 0 g / 10 min as a core layer, melt-kneading with three extruders, and setting the extrusion amount of each extruder so that the thickness ratio becomes 1/5/1 A laminated biaxially stretched film was obtained in the same manner as in Example 3 except that it was coextruded downward with a three-layer annular die and the stretch ratio was 5.0 × 5.0.
The drawability was good, there was no up-and-down movement of the drawing point and the swinging of the drawing tube, non-uniform drawing conditions such as necking were not observed, and the flatness was good. The evaluation results of the obtained film were as shown in Table 1 and were good.

Example 7
As shown in Table 1, a laminated biaxially stretched film was obtained in the same manner as in Example 3 except that the film thickness was 13.5 μm.
As shown in Table 1, the stretchability was good, there was no vertical movement of the stretching point or swinging of the stretching tube, non-uniform stretching conditions such as necking were not observed, and the planarity was also good. The evaluation results of the obtained film are as shown in Table 1, and since the thickness exceeds 12 μm, the cutting at the time of fusing sealing is somewhat bad, and the appearance after packaging is slightly affected.

Comparative Example 1
As shown in Table 2, after the tubular stretching, a laminated biaxially stretched film was formed in the same manner as in Example 1 except that it was subjected to a relaxation treatment of about several percent with a heat roll adjusted to 30 to 90 ° C. Obtained.
As shown in Table 2, the stretchability was good, there was no vertical movement of the stretching point and the swinging of the stretching tube, non-uniform stretching conditions such as necking were not observed, and the planarity was also good. The evaluation results of the obtained film are as shown in Table 2, and the shrinkage in the horizontal direction is large, the wrinkles and the sleeve surface are turned over, the appearance after packaging is poor, and the book or comic may be stained.

Comparative Example 2
As shown in Table 2, after the tubular stretching, a laminated biaxially stretched film was formed in the same manner as in Example 5 except that it was subjected to a relaxation treatment of about several percent with a heat roll appropriately adjusted to 30 to 90 ° C. Obtained.
As shown in Table 2, the stretchability was good, there was no vertical movement of the stretching point and the swinging of the stretching tube, non-uniform stretching conditions such as necking were not observed, and the planarity was also good. The evaluation results of the obtained film are as shown in Table 2, and the shrinkage in the horizontal direction is large, the wrinkles and the sleeve surface are turned over, the appearance after packaging is poor, and the book or comic may be stained.

Comparative Example 3
As shown in Table 2, a laminated biaxially stretched film having a film thickness of 9 μm was obtained in the same manner as in Example 3 except that the stretching ratio was 2.8 × 2.8.
As shown in Table 2, the stretchability was good, and there was no vertical movement of the stretching point or rocking of the stretching tube, but a non-uniform stretching state such as necking was not observed, and the planarity was slightly inferior. It was. The evaluation results of the obtained film were as shown in Table 1. Since the transparency and gloss were inferior and the shrinkage was also inferior, there were many wrinkles and the appearance after packaging was poor.

The heat-shrinkable packaging material of the present invention is suitable for sleeve packaging of books and comics, and has excellent transparency, gloss, packaging finish, fusing sealability, easy disposal and cost-effective polyolefin-based sleeve packaging It can be suitably used as a heat-shrinkable film.

Claims (4)

An unstretched film that is a single layer composed mainly of a propylene-based resin or has a layer composed mainly of a propylene-based resin on both surface layers is stretched in a longitudinal and lateral direction by a tubular biaxial stretching ratio of 3.5 to 6 After the stretching process of 0.0 times , the thickness obtained by performing the stretching process of 1.05 times to 1.5 times in the longitudinal direction at a temperature lower than the melting point of the raw material by 10 ° C. or more using a hot roll. A heat-shrinkable film for polyolefin sleeve packaging having a thickness of 6 to 12 μm . The heat shrinkability for polyolefin sleeve packaging according to claim 1 , wherein the layer mainly composed of propylene resin is at least three layers having both surface layers and an inner layer mainly composed of ethylene resin. the film. The layers mainly composed of a propylene-based resin are both surface layers, both intermediate layers mainly composed of a propylene-based resin produced using a metallocene catalyst, and five layers having a core layer mainly composed of an ethylene-based resin. The heat-shrinkable film for polyolefin-based sleeve packaging according to claim 1 or 2 . The heat-shrinkable film for polyolefin-based sleeve packaging according to any one of claims 1 to 3 , wherein the heat-shrinkable film is used for heat-shrink packaging of books.