JP2010234656A - Polypropylene and polyolefin multilayer shrink film with light shielding property - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polypropylene shrink film or a polyolefin shrink film, which has high heat-shrinkability, meltdown sealing properties suitable for a high speed automatic pillow packaging machine of an overlap type and an L-folded automatic packaging machine, and also has a light-shielding rate of 50% or more. <P>SOLUTION: (1) The polypropylene shrink film is prepared by stretching a film vertically and horizontally by three times or more, the film being formed by melting a mixture of a polypropylene resin with 0.5 to 30 wt.% of a light-shielding material of titanium oxide or carbon black and processing it into a sheet shape by coextrusion. (2) The polyolefin multilayer shrink film including at least two or more layers is prepared by laminating a surface layer made of a polypropylene or polyolefin resin and an inner layer containing titanium oxide or a mixture of titanium oxide and carbon black so as to have a thickness of at least 1 μm or more, and stretching the layers vertically and horizontally by three times or more. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a film for heat shrink packaging (hereinafter referred to as shrink) having a light shielding rate of 30% or more. More specifically, a biaxially stretched film based on polypropylene containing 1.0% by weight or more of titanium oxide or 1.0% by weight or more of titanium oxide and 1.0% by weight or less of carbon black to 1.0% by weight of titanium oxide. A multi-layer polyolefin biaxially stretched film of at least two or more layers having a light shielding layer of 1 μm or more mainly composed of polypropylene containing at least 1.0% by weight of titanium oxide and 1.0% by weight or less of carbon black.

  Conventionally, a packaging material having a light-shielding property is required in order to prevent food deterioration and the like. Polyvinyl chloride film, polypropylene film, polyethylene film, crosslinked polyolefin film, etc. are known as heat-shrinkable packaging materials having a thickness of about 10 to 30 μm, but there is no light-shielding property and packaging In particular, the product has disadvantages such as maintaining the freshness of fermented products and the like, and poor discoloration due to ultraviolet rays. In order to solve such a problem, printing is performed on a polypropylene-based or multilayer polyolefin-based shrink film or the like to maintain light shielding properties (Patent Documents 1 and 2). In addition, there are a method for imparting light shielding properties by laminating thin film films such as aluminum, and a report for imparting light shielding properties with aluminum powder (Patent Document 3). However, when an aluminum thin film or the like is used, recycling becomes difficult, and front printing or the like may not be suitable for food packaging due to problems such as odor.

  Polyolefin-based shrink films are excellent in shrinkage and heat resistance, and thus have a beautiful shrink-wrapped finish, and are characterized by relatively high impact resistance and tear resistance. However, when an additive such as a light-shielding pigment or carbon black is mixed to form a film, there is a problem that the stretchability is unstable and it is difficult to obtain a film. Therefore, for example, there was no light-shielding film in which titanium oxide, titanium oxide and carbon black were added to a stretched film as described in (Patent Document 4).

  The present applicant has previously proposed a polypropylene-based shrink film that does not have such drawbacks, is easy to form a film, has a stable stretchability, and has a light shielding property. This is a polypropylene shrink film that has the characteristics of conventional heat-shrinkable packaging materials, such as shrinkage, heat resistance, beautiful shrink-wrapping finish, impact resistance, tear resistance, and light shielding properties. On the other hand, in the shrink film, sufficient cohesive force cannot be obtained in the high-speed packaging machine suitability in the high-speed automatic pillow packaging machine, pinholes and seal opening occur in the seal portion, and the appearance of the package is deteriorated. Therefore, the problem was solved by using multiple layers.

Japanese Patent Laid-Open No. 11-091042 Japanese Patent Laid-Open No. 2003-200966 Japanese Unexamined Patent Publication No. 07-241953 Japanese Unexamined Patent Publication No. 08-059855

The present invention has been made in view of the above situation, and is a light-shielding shrink film having a light shielding rate of 30% or more, which is excellent in both shrinkability and heat resistance, while maintaining the shrink-wrapping finish and shielding light. Provided is a polypropylene film having properties. Another object of the present invention is to provide a polyolefin-based multilayer shrink film that does not impair the packaging aesthetics due to the occurrence of a fusing seal portion pinhole and the opening of a seal in an overlap type high-speed automatic pillow packaging.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors have used a polypropylene-based resin mixed with a masterbatch having a light shielding property containing titanium oxide, and titanium oxide and titanium oxide + The inventors have found that the problem can be solved by laminating a carbon black-added polypropylene layer, and have reached the present invention. (1) A film obtained by melting and mixing a titanium-based (A) or carbon black (B) light-shielding material into polypropylene resin having an MFR of 1.0 to 30.0 g / 10 min and processing it into a sheet by coextrusion. A polypropylene-based shrink film stretched three times or more in length and width, (2) both surface layers (X) made of a polypropylene-based and polyolefin-based resin having an MFR of 1.0 to 30.0 g / 10 min, and an MFR of 1.0 Laminate at least 1 μm or more of inner layer (Y) containing titanium oxide (A) and titanium oxide + carbon black (B) (about 30 g / 10 min. A polyolefin-based multilayer shrink film composed of at least two layers stretched as described above, (3) In the stretching, the difference between the values of the longitudinal and lateral stretch ratios is 0.5. The polyolefin multilayer shrink film according to any one of the above (1) to (3), wherein the longitudinal and lateral stretch ratio is 3.5 times or more is provided below.

That is, the present invention
(1) Polypropylene shrink having a layer containing 1.0% by weight or more of titanium oxide, or a layer in which 1.0% by weight or more of titanium oxide and 1.0% by weight or less of carbon black are mixed and having a light shielding rate of 50% or more. the film,
(2) A polyolefin-based multilayer having a light shielding ratio of 50% or more, including a layer containing 1.0% by weight or more of titanium oxide, or a layer in which 1.0% by weight or more of titanium oxide and 1.0% by weight or less of carbon black are mixed. Shrink film,
(3) A film formed by coextrusion of a polypropylene resin having a melt flow rate (hereinafter referred to as MFR, measurement temperature 230 ° C., load 2.16 kgf) of 1.0 to 30.0 g / 10 min is at least longitudinally. The shrink film according to (1) or (2), obtained by stretching at least 3 times each of the width,
(4) In the stretching, the difference between the longitudinal and lateral stretching ratios is 0.5 or less, and the longitudinal and lateral stretching ratios are 3.5 or more. (1) to (3) Shrink film,
(5) The shrink film according to (1) or (2), which is colored white or grayish white by containing carbon black in titanium oxide or titanium oxide.

The present invention will be specifically described below.
In the present invention, the polypropylene resin (D) used for the inner layer (Y) of the base resin not including the light-blocking masterbatch of the polypropylene shrink film and the polyolefin multilayer shrink film is a differential scanning calorimeter (hereinafter referred to as DSC). ) Measured at a melting peak temperature of 135 to 165 ° C. and an MFR of 1.0 to 10.0 g / 10 min, a polypropylene homopolymer, a copolymer of propylene and an α-olefin, such as propylene- It consists of at least one selected from ethylene, propylene-butene copolymer and the like, and propylene-ethylene-butene terpolymer, and mainly serves to impart heat resistance and waist strength. Among these, a crystalline propylene-α-olefin random copolymer is preferably used in consideration of the balance of heat resistance, waist strength and heat shrinkage characteristics.
When the melting peak temperature of the polypropylene resin (D) is less than 135 ° C., the heat resistance is low, which is not preferable. When the melting temperature exceeds 165 ° C., the low temperature shrinkage decreases, which is not preferable. Further, if the MFR is less than 1.0 g / 10 min, there is a problem that the motor load at the time of melt extrusion becomes high, and if it exceeds 10.0 g / 10 min, the fusing sealability is lowered, which is not preferable.

The thickness of the polypropylene-based shrink film is preferably 10 μm or more, and if it is less than 10 μm, the fusing sealability, heat resistance, and waist strength may be reduced. In the polyolefin-based multilayer polyolefin-based shrink film, the thickness of the inner layer (Y) is preferably 1 μm or more, and if it is less than 1 μm, a light blocking rate of 50% or more cannot be obtained.

In the present invention, in the polyolefin-based multi-layer polyolefin-based shrink film, the inner layer does not necessarily have to be one layer, and can be made into two or more layers as necessary, and a layer configuration of five or more layers as a whole is adopted. Can do. For example, X / X / Y / X / X, X / Y / Y / Y / X, X / X / X / Y / X, X / Y / X / X / X, etc. From the viewpoint of preventing film curling, a symmetric configuration is preferable.

Additives such as lubricants, antiblocking agents, antistatic agents, antifogging agents, and antioxidants to both surface layers (X) and inner layers (Y) of polypropylene shrink films and polyolefin multilayer shrink films, if desired. Can be appropriately used for the purpose of providing each effective action.

In addition to the polypropylene resin of the polypropylene shrink film, metallocene polypropylene can be used. In addition to polypropylene resin, metallocene polypropylene and polyethylene resin can be used for both surface layers (X) of the polyolefin multilayer shrink film, and polypropylene layer resin can be used for the inner layer (Y). In addition, metallocene-based polypropylene can be used, and can also be used for scrap recycling.

Titanium oxide, carbon black, titanium oxide + carbon black, titanium oxide + calcium carbonate can be used as the light-shielding additive, but it is possible to use titanium oxide alone or a combination of titanium oxide and carbon black. preferable. Carbon black alone is not preferable because the stretchability is not stable. Titanium oxide + calcium carbonate is not preferable because stretchability, waist strength, impact resistance, and tear resistance are reduced. Further, in the case of titanium oxide alone, the addition amount is preferably 1.0% by weight or more. More preferably, 1.0 to 80% by weight is contained. If it is 1.0% by weight or less, the desired light shielding ratio of 50% or more cannot be obtained, which is not preferable. In the case of using titanium oxide and carbon black in combination, if 1.0% by weight or more of carbon black is added to 1.0% by weight or more of titanium oxide, the stretchability is deteriorated. In the case of multiple layers, the light-shielding additive can be added to both the surface layer and the inner layer, but it is preferable to add the light-shielding additive to the inner layer.

In general, a polypropylene-based shrink film is manufactured by longitudinally and laterally stretching a sheet formed by coextrusion such as a T die or a cylindrical ring die by a known method such as a tubular method or a tenter method. be able to. The stretching method includes simultaneous biaxial stretching by the tenter method or sequential biaxial stretching and simultaneous biaxial stretching by the tubular method. The present invention will be specifically described with reference to an example of simultaneous biaxial stretching using a single-layer or three-layer laminated annular film forming machine and tubular.

  Next, the manufacturing method of the film of this invention is shown. The method for producing the stretched film of the present invention using the above resin can be performed by a known method. Hereinafter, the case of single-layer or three-layer laminated annular film formation and the simultaneous biaxial stretching of the tubular method will be described as examples and will be specifically described.

(1) In the case of a single layer First, a resin composition obtained by dry blending a master batch of titanium oxide containing a polypropylene resin and a titanium oxide containing carbon black into a polypropylene resin at a ratio of 1.0 to 30% by weight. Is melt-kneaded by a single-layer extruder, extruded into a ring shape, and then rapidly cooled and solidified without stretching to produce a tubular unstretched film. The obtained tube-shaped unstretched film is supplied to a tubular stretching apparatus, and is in a highly orientable temperature range, for example, at a temperature lower than 10 ° C. below the melting point of the inner layer resin, preferably lower than 15 ° C. below the melting point. A gas pressure is applied inside the tube at a temperature to cause simultaneous biaxial orientation by expansion and stretching. In order to obtain excellent physical properties such as strength and shrinkage, the stretching ratio is preferably stretched by 3 times or more in both the longitudinal and lateral directions. The film taken out from the stretching apparatus can be annealed as desired, and the natural shrinkage during storage can be suppressed by this annealing.

(2) In the case of multi-layer First, a resin composition obtained by dry blending a master batch of titanium oxide containing a polypropylene resin with a polypropylene resin as a base resin or a titanium oxide containing carbon black in a proportion of 1.0 to 30% by weight. A resin composition mainly composed of an inner layer, polypropylene resin or polyethylene is charged in both surface layers, melt-kneaded by three extruders, co-extruded in a ring form from a three-layer annular die, and rapidly cooled without stretching. Solidify to produce a tubular unstretched film. The obtained tube-shaped unstretched film is supplied to a tubular stretching apparatus, and is in a highly orientable temperature range, for example, at a temperature lower than 10 ° C. below the melting point of the inner layer resin, preferably lower than 15 ° C. below the melting point. A gas pressure is applied inside the tube at a temperature to cause simultaneous biaxial orientation by expansion and stretching. In order to obtain excellent physical properties such as strength and shrinkage, the stretching ratio is preferably stretched by 3 times or more in both the longitudinal and lateral directions. The film taken out from the stretching apparatus can be annealed as desired, and the natural shrinkage during storage can be suppressed by this annealing.

EXAMPLES Hereinafter, although an Example demonstrates this invention concretely, this invention is not limited to these Examples.
The melt flow rate (MFR) is measured according to JIS.
The conditions of the A method operation (manual cutting method) of K 7210-1976 (test temperature 230 ° C., test load 2.16 kgf, for polypropylene) were followed. The measurement sample was managed at room temperature. The melting point was determined by measuring the peak temperature using a differential scanning calorimeter (DSC) device (manufactured by SII) in a sample of about 10 mg, a heating rate of 10 ° C./min in nitrogen.

Evaluation methods used in Examples and Comparative Examples are as follows.
(1) Raw fabric formability Evaluation was made according to the following criteria.
○: No generation of eyes, good mandrel hugging and stable moldability.
Δ: No formation of eyes, but moldability is unstable due to poor mandrel hugging.
X: Discoloration occurs and moldability is poor.
(2) Evaluability was evaluated according to the following criteria.
○: Stretch stable without bubble shaking.
Δ: Bubble shaking is large and stretching is unstable.
X: Bubble is punctured and cannot be stretched.

The physical properties shown in the examples were measured by the following methods.
(3) Thickness: Measured according to JIS Z 1709.
(4) Light blocking rate: Haze (cloudiness) was measured according to JIS K 7105, and the light blocking rate of (Equation 1) calculated as follows from the transmittance obtained from the haze meter was defined as the light blocking rate.
(5) Tear strength: JIS using a light load tear tester
It measured according to Z1707.
(6) Impact strength: Measured according to JIS P 8134 using a film impact tester.
(7) Heat shrinkage ratio: A film cut into a square of 100 mm in length and breadth is immersed in a glycerin bath adjusted to 100 ° C. for 10 seconds, then rapidly cooled in water, and the lengths in both length and breadth are measured (the original size is A , The post-shrinkage dimension was B), and the thermal shrinkage rate of MD and TD was calculated by the following (Equation 2).

(Equation 1)
Light blocking rate (%) = light blocking rate (%) = 100−transmittance (%)
(Equation 2)
Thermal contraction rate (%) = (A−B) / A × 100 (%)
(However, A is the exact dimension A and B is the vertical or horizontal length (mm) after quenching.)

(8) High-speed automatic packaging machine: Applicable to Tokiwa Kogyo Co., Ltd. automatic packaging machine (model: NEO type, pillow packaging machine), packaging a commercial 900ml liquor pack at a speed of 121 pieces / min (35m / min) The percentage of non-defective products (%) when 20 pieces were passed through the hot air shrink tunnel (Kyowa Denki model: L type) at a rate of 150 ° C. × 3.5 seconds was evaluated according to the following criteria. .
<Evaluation criteria>
○: 90% or more Δ: 50 to less than 90%
×: Less than 50%

(9) Shrink packaging finish and heat resistance: at an automatic packaging machine (model: NEO type, pillow packaging machine) manufactured by Tokiwa Industry Co., Ltd., at a speed of 121 pieces / minute (35 m / minute) of 900 ml sake packs on the market. Wrap and stay in the shrink tunnel set at 2-20 ° C before film burn for 3 seconds, select 5 randomly from the packaging samples after passing through the tunnel, and the shrink packaging finish quality is as follows evaluated.
<Evaluation criteria>
○: The tunnel temperature range in which the average angular height of the packaging sample is 10 mm or less exceeds 10 ° C.
(Triangle | delta): The tunnel temperature range from which the average angle height of a packaging sample will be 7 mm or less is 4-10 degreeC.
X: The tunnel temperature range in which the average angular height of the packaging sample is 7 mm or less is less than 4 ° C.
(Note: Angular height means the height of the projections on the side of the package after heat shrinking the packaging preparatory body with a moderate margin with a shrinking tunnel.)

Example 1
As shown in Table 1, both surfaces of a propylene-ethylene random copolymer (manufactured by Prime Polymer Co., Ltd.) having the characteristics of DSC melting peak temperature of 145 ° C., MFR of 2.3 g / 10 min, and ethylene content of 4.0% As a layer (X), a light-shielding masterbatch (manufactured by DIC) having a MFR of 4.0 g / 10 min and having a characteristic of 4.0 g / 10 min is used as an inner layer (Y), and each of three extruders is 170 to A three-layered ring which is melt-kneaded at 230 ° C. and the extrusion amount of each extruder is set so that the thickness ratio is X / Y / X = 5.5 / 4.0 / 5.5, and maintained at 230 ° C. Co-extruded downward with a die. The formed three-layer tube is cooled by passing through the water tank while the outer surface of the cylindrical cooling mandrel in which the cooling water circulates is slid, and the outer tube is cooled, and the diameter is 117 mm and the thickness is 240 μm. An unstretched film was obtained.

  This tubular unstretched film was guided to a tubular biaxial stretching apparatus, and stretched four times in length and width at 90 to 110 ° C. to obtain a laminated biaxially stretched film. Then, it cooled to room temperature, trimmed the film both ends, and wound up two sheets separately. The final film thickness was 15 μm. The stretchability was good, there was no up-and-down movement of the stretching point, the swinging of the stretching tube, and a non-uniform stretching state such as necking was not observed. As shown in Table 1, the obtained stretched film had a light shielding rate of 65% or more, no reduction in tear strength and impact strength was observed, and the heat shrinkage rate at 120 ° C. was also excellent. In packaging evaluation with a high-speed automatic pillow packaging machine, the rate of non-defective products after shrink wrapping is excellent at 95% or higher during high-speed wrapping, and the heat shrink characteristics are also excellent for shrink wrap finishing, resulting in a beautiful finish. It was good.

Example 2
In Example 1, the inner layer (Y) was replaced with a light-shielding masterbatch (manufactured by DIC) having a titanium oxide concentration of 70 wt% with a MFR of 10.0 g / 10 min, and the thickness ratio was X / Y / X. The extrusion amount of each extruder was set so that = 6.0 / 3.0 / 6.0, and a three-layer biaxially stretched film was obtained in the same manner as in Example 1. The final film thickness was 15 μm.
The stretchability was good, there was no up-and-down movement of the stretching point, the swinging of the stretching tube, and a non-uniform stretching state such as necking was not observed.
As in Example 1, the obtained stretched film had a light shielding ratio of 60% or more, no reduction in tear strength and impact strength was observed, and the heat shrinkage rate at 120 ° C. was excellent. In packaging evaluation with a high-speed automatic pillow packaging machine, the rate of non-defective products after shrink wrapping is excellent at 95% or higher during high-speed wrapping. It was good.

Example 3
In Example 1, a light-shielding masterbatch (manufactured by Toyo Ink Co., Ltd.) in which 0.04 wt% of carbon black was blended with a titanium oxide concentration of 70 wt% having an MFR of 11.0 g / 10 min for the inner layer (Y). Instead, the extrusion amount of each extruder was set so that the thickness ratio was X / Y / X = 6.5 / 2.0 / 6.5, and a three-layer biaxially stretched film was obtained in the same manner as in Example 1. The final film thickness was 15 μm.
The stretchability was unstable as compared with Example 1, and necking was observed. Neither vertical movement of the stretching point nor swinging of the stretching tube was observed. Moreover, the sustainability at the time of trimming was poor, and the continuous acquisition amount was inferior to that of Example 1 and Example 2.
The obtained stretched film had higher light shielding properties (light shielding ratio 75%) than those of Examples 1 and 2, and other physical properties were the same. The packaging suitability in high-speed packaging was equivalent to that of Examples 1 and 2, and was good.

Example 4
As shown in Table 1, a propylene-ethylene random copolymer (Prime Polymer Co., Ltd.) having a DSC melting peak of 145 ° C., an MFR of 2.3 g / 10 min, and an ethylene content of 4.0% is 10 A light-shielding masterbatch (manufactured by DIC) having a titanium oxide concentration of 70 wt% having a characteristic of 0.0 g / 10 min was dry blended to obtain a resin containing 5% titanium oxide. The resin was melt-kneaded at 170-230 ° C. with a single-layer extruder, the extrusion amount of the extruder was set, and co-extruded downward with an annular die maintained at 230 ° C. The formed tube is cooled by passing through the water tank while the outer surface of the cylindrical cooling mandrel in which cooling water circulates is slid, and the outer tube is cooled and taken out. The unstretched film has a diameter of 117 mm and a thickness of 240 μm. Got. This tubular unstretched film was guided to a tubular biaxial stretching apparatus, and stretched at 90 to 110 ° C. four times in length and breadth to obtain a single-layer biaxially stretched film. Then, it cooled to room temperature, trimmed the film both ends, and wound up two sheets separately. The final film thickness was 15 μm.
The stretchability was good, there was no up-and-down movement of the stretching point, the swinging of the stretching tube, and a non-uniform stretching state such as necking was not observed.
The obtained stretched film has a light shielding rate of 31%, tear strength, and impact strength slightly decreased. The degree of thermal shrinkage at 120 ° C is not much different. In the packaging evaluation with a high-speed automatic pillow packaging machine, the packaging suitability in high-speed packaging was inferior to a practical level with a yield rate of 70% or less after shrink-wrapping. With respect to the shrink packaging finish, a beautiful finish was obtained and it was good.

Example 5
In Example 4, a resin obtained by kneading titanium oxide with a propylene-ethylene random copolymer (manufactured by Prime Polymer Co., Ltd.) having an MFR of 2.3 g / 10 min and an ethylene content of 4.0% A monolayer biaxially stretched film was obtained in the same manner as in Example 4 using Tokyo Ink Co., Ltd. The content of titanium oxide was 24%. The final film thickness was 20 μm. The stretchability was slightly unstable with some vertical movement of the stretching point and swinging of the stretching tube, but a non-uniform stretching state such as necking was not observed. The obtained stretched film had a light shielding rate as high as 75% as compared with Example 4, had no reduction in tear strength and impact strength, and was excellent in heat shrinkage at 120 ° C. In the packaging evaluation with a high-speed automatic pillow packaging machine, the non-defective product rate after shrink wrapping was 50% or less at the time of high-speed packaging, which was not practical and was inferior to Example 4. With respect to the shrink packaging finish, a beautiful finish was obtained and it was good.

Comparative Example 1
As shown in Table 2, in Example 1, the inner layer (Y) was replaced with a light-shielding masterbatch (manufactured by Dainichi Seika Co., Ltd.) having a titanium oxide concentration of 60% by weight with a MFR of 40.0 g / 10 min. The extrusion rate of each extruder was set so that the thickness ratio was X / Y / X = 6.0 / 3.0 / 6.0, and a three-layer biaxially stretched film was obtained in the same manner as in Example 1. Next, it cooled to room temperature, trimmed the film both ends, and wound up two sheets separately. The final film thickness was 15 μm.
As for stretchability, the vertical movement of the stretching point and the swinging of the stretching tube were large and unstable. Further, a nonuniform stretching state such as necking was not observed.
The obtained stretched film has a light shielding rate of 75% or more, no reduction in tear strength and impact strength, and the same 120 ° C. heat shrinkage rate. In packaging evaluation with a high-speed automatic pillow packaging machine, the rate of non-defective products after shrink wrapping was 50% or less at the time of high-speed packaging, which was not practical. The shrink-wrapping finish was excellent because of its excellent heat shrinkage characteristics and a beautiful finish.

Comparative Example 2
As shown in Table 2, in Example 4, a resin (manufactured by Dainichi Seika Co., Ltd.) obtained by kneading titanium oxide having a characteristic of MFR of 40.0 g / 10 min was used. A monolayer biaxially stretched film was obtained by the method described above. The final film thickness was 15 μm.
Stretchability was unstable due to vertical movement of the stretching point and swinging of the stretching tube. Further, a nonuniform stretching state such as necking was not observed.
The obtained stretched film had a light shielding rate of 70% or more with respect to Comparative Example 1 and Examples 1 to 5, but the tear strength and impact strength were slightly lowered. No decrease in heat shrinkage at 120 ° C. In packaging evaluation with a high-speed automatic pillow packaging machine, the rate of non-defective products after shrink wrapping is 50% or less and not at a practical level during high-speed packaging. With respect to the shrink packaging finish, a beautiful finish was obtained and it was good.

Comparative Example 3
As shown in Table 2, a propylene-ethylene random copolymer (manufactured by Prime Polymer Co., Ltd.) having a DSC peak of 145 ° C., an MFR of 2.3 g / 10 min, and an ethylene content of 4.0% is a single layer extruder. The mixture was melt-kneaded at 170 to 230 ° C., the extrusion amount of the extruder was set, and co-extruded downward with an annular die maintained at 230 ° C. The formed tube is cooled by passing through the water tank while the outer surface of the cylindrical cooling mandrel in which the cooling water circulates is slid and passed through the water tank. The unstretched film has a diameter of 117 mm and a thickness of 240 μm. Got. This tubular unstretched film was guided to a tubular biaxial stretching apparatus, and stretched four times in length and width at 90 to 110 ° C. to obtain a laminated biaxially stretched film. Then, it cooled to room temperature, trimmed the film both ends, and wound up two sheets separately. The final film thickness was 15 μm.
The stretchability was good, there was no up-and-down movement of the stretching point, the swinging of the stretching tube, and a non-uniform stretching state such as necking was not observed.
The obtained stretched film cannot be obtained with a light shielding rate of 9% because titanium oxide having a light shielding property and titanium oxide and carbon black are not added. Other performances are the reference values of Examples 1 to 5 and Comparative Examples 1 and 2. In packaging evaluation with a high-speed automatic pillow packaging machine, the rate of non-defective products after shrink-wrapping is 95% or more during high-speed packaging. The shrink packaging packaging finish was based on Examples 1-5 and Comparative Examples 1-2.

The polypropylene-based and polyolefin-based multilayer shrink film of the present invention is a film for heat shrink wrapping (shrink) having a light shielding rate of 50% or more, maintaining the conventional shrinkage characteristics, and having no reduction in impact strength and tear strength. Yes, suitable for various shrink wrapping because it has a fusing sealability suitable for overlap type high-speed automatic pillow wrapping machines and L-shaped half-fold automatic wrapping machines, and is excellent in high-speed wrapping machine suitability and shrink wrapping finish. Can be used.

Claims (5)

  A polypropylene-based shrink film having a light shielding rate of 50% or more, including a layer containing 1.0% by weight or more of titanium oxide, or a layer in which 1.0% by weight or more of titanium oxide and 1.0% by weight or less of carbon black are mixed.   A polyolefin-based multilayer shrink film having a light shielding ratio of 50% or more, comprising a layer containing 1.0% by weight or more of titanium oxide, or a layer in which 1.0% by weight or more of titanium oxide and 1.0% by weight or less of carbon black are mixed.   A film formed by coextrusion of a polypropylene resin having a melt flow rate (hereinafter referred to as MFR, measuring temperature 230 ° C., load 2.16 kgf) of 1.0 to 30.0 g / 10 min is at least longitudinally and laterally respectively. The shrink film of Claim 1 or Claim 2 obtained by extending | stretching 3 times or more.   The shrink film according to any one of claims 1 to 3, wherein, in the stretching, the difference between the longitudinal and lateral stretching ratios is 0.5 or less, and the longitudinal and lateral stretching ratios are 3.5 or more. The shrink film according to claim 1 or 2, which is colored white or grayish white by containing carbon black in titanium oxide or titanium oxide.