JP2000289159A - Heat-shrinkable film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a heat-shrinkable film which has rapid heat sealing properties and reliable heat shrinkability/impact resistance and further, is excellent in finish quality with pliability and almost free from remaining sharp corners. SOLUTION: This heat-shrinkable film comprises an intermediate layer of a specified straight-chain low density polyethylene resin and a surface layer of a specified polypropylene resin which is integrally laminated on both faces of the intermediate layer. Using this heat-shrinkable film, it is possible to obtain a packaging material which shows a high quality such as outstanding heat shrinkability, impact resistance, pliability or being almost free from remaining sharp edges. In addition, the film has satisfactory rapid heat sealing properties, so that a perfect and certain heat sealing process can be performed with the film, even when an automatic rapid packaging machine is used.

Description

DETAILED DESCRIPTION OF THE INVENTION

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat-shrinkable film having excellent impact resistance, flexibility, heat-shrinkability and high-speed heat sealability.

[0001]

2. Description of the Related Art Conventionally, polyvinyl chloride resin, polypropylene resin, polyethylene resin and the like have been used as a resin constituting a heat shrinkable film. And
Polyvinyl chloride-based heat-shrinkable films have very good shrinkage and mechanical properties, but have many problems in terms of their effect on the environment. Polypropylene-based heat-shrinkable films are suitable for high-speed packaging because of their excellent transparency and heat-sealing properties and the stiffness of the film, but are inferior in impact resistance. There has been a problem that the film often breaks during line or transportation.

Therefore, in order to improve the impact resistance, a polyethylene resin film is laminated and integrated on both sides of a polyethylene resin film to form a multilayer structure, thereby improving the impact resistance and improving flexibility and finish quality. Various good heat-shrinkable films have been proposed (JP-A-58-166049, JP-A-63-2144).
No. 46, JP-A-64-1535, JP-A-2-
No. 1257334).

However, when the above-mentioned multilayer heat shrinkable film is used in a high-speed automatic packaging machine, the high-speed automatic packaging machine is applied with high tension by a seal bar heated to a high temperature, so that the film is pulled before it is solidified. As a result, there has been a problem that a strong heat seal cannot be performed, or that a melt break occurs.

[0004]

DISCLOSURE OF THE INVENTION The present invention provides a heat shrinkable material which is excellent in high-speed heat sealability, heat shrinkage, impact resistance and flexibility, and has excellent finish quality with little corner residue. Provide a film.

[0005]

The heat-shrinkable film of the present invention has a resin temperature of 220 on both surfaces of an intermediate layer made of a linear low-density polyethylene resin having a density of 0.880 to 0.935 g / cm ^3. The surface layer made of a polypropylene resin having a melt tension of 0.8 to 3 g and a melting peak temperature of 120 to 145 ° C. by differential scanning calorimetry at a temperature of 10 ° C. and an extension ratio of 10 times is laminated and integrated. It is characterized by comprising.

The linear low-density polyethylene resin constituting the intermediate layer is not particularly limited as long as it has been conventionally used for a heat-shrinkable film. And these may be used alone or in combination.

[0007] Examples of the copolymer with the other monomer containing ethylene as a main component include a copolymer of ethylene and an α-olefin. Examples of the α-olefin include propylene, 1-butene, and 1-butene. -Pentene, 1-hexene, 4-methyl-1-pentene, 1-octene and the like.

If the linear low-density polyethylene resin has a high density, the transparency decreases, and if the density is low, the resulting heat-shrinkable film becomes weak and cannot be used for high-speed packaging. , 0.880-0.935 g / cm
Limited to ³ . The density of the linear low-density polyethylene resin was measured according to JIS K6760.

If the linear low-density polyethylene resin has a high melt index, the resulting heat-shrinkable film may have low heat-shrinkability. Is preferably 0.3 to 10 g / 10 min.
5 g / 10 minutes is more preferred. The melt index of the linear low-density polyethylene resin is JIS 72
10 based on a condition of 190 ° C. and a load of 2.16 kgf.

The polypropylene resin constituting the surface layer is not particularly limited as long as it has been conventionally used for a heat-shrinkable film. For example, homopolypropylene, propylene-ethylene-butene ternary random copolymer may be used. And a copolymer with an α-olefin containing propylene as a main component. These may be used alone or in combination.

The copolymer with an α-olefin containing propylene as a main component may be any of random, block and random block copolymers.
-As the olefin, ethylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1
-Octene and the like, and an ethylene-propylene random copolymer is preferable.

If the melt tension of the polypropylene resin is high, stable stretching cannot be performed.
On the other hand, if it is low, the heat sealing property is reduced,
Limited to 3g.

The melt tension of the polypropylene-based resin was determined by using a capillary rheometer at a resin temperature of 220 ° C., an L / D of 10 for the capillary, an extrusion speed of 1 m / min, and a take-off speed of 10 m / min. Is 1
It is a take-off load when taken-up under the condition of 0 times.

If the melting peak temperature of the above polypropylene resin by differential scanning calorimetry is high, the low-temperature shrinkability of the resulting heat-shrinkable film is impaired, and if the melting peak temperature is low, the heat-shrinkable film obtained by stickiness occurs. Since lubricity is reduced, the temperature is limited to 120 to 145 ° C.

The melting peak temperature of the polypropylene resin by differential scanning calorimetry is as follows: once the temperature is raised to 220 ° C. using a differential scanning calorimeter, then the temperature is lowered to room temperature or lower at 10 ° C./min. The endothermic peak curve was measured by raising the temperature at 10 ° C./min, and the endothermic peak temperature was obtained by reading the endothermic peak temperature from this endothermic peak curve.

The higher the melt index of the polypropylene resin is, the lower the melt tension may be. Therefore, the lower the melt index, the better. The melt index of the polypropylene-based resin refers to a value measured under the conditions of a temperature of 230 ° C. and a load of 2.16 kgf based on JIS 7210.

The linear low-density polyethylene resin constituting the intermediate layer and the polypropylene resin constituting the surface layer include a lubricant, an antiblocking agent, an antistatic agent, an antifogging agent, an antioxidant, and an ultraviolet absorbing agent. An additive such as a nucleating agent or a crystal nucleating agent may be added within a range that does not impair the physical properties of the intermediate layer and the surface layer.

The lubricant is not particularly limited as long as it has been conventionally used for a heat-shrinkable film, and examples thereof include lauric amide, myristic amide, palmitic amide, stearic amide, and behenic amide. And higher unsaturated fatty acid amides such as saturated fatty acid amides, oleic acid amides and erucic acid amides, and alkylene bisstearic acid amides such as ethylene bisstearic acid amide.

The anti-blocking agent may have any of spherical or amorphous shapes.
Inorganic fine particles such as silica, zeolite, talc, kaolin, etc., cross-linked polymethyl methacrylate resin, cross-linked polystyrene resin, non-melting silicone resin, non-melting silicone rubber, silicone copolymer, amide resin, triazine ring-containing condensation resin, etc. Organic fine particles.

If the particle size of the anti-blocking agent is large, the transparency of the resulting heat-shrinkable film may be reduced. If the particle size is small, the added effect may not be exhibited. ８8 μm is preferred.

As the antistatic agent and the antifogging agent, nonionic surfactants having high heat resistance are preferable.
Examples include fatty acid glycerin esters such as monoglycerin stearate and diglycerin stearate, fatty acid alkylamides such as diethanolamide, fatty acid alkylamines such as diethanolamine, and sorbitan fatty acid esters such as sorbitan monostearate.

Next, a method for producing the heat shrinkable film will be described. As the method for producing the heat-shrinkable film, a method for producing a multi-layer film which is widely used is used. For example, three extruders are prepared, and a linear low-density polyethylene constituting an intermediate layer in each of these extruders. The polypropylene resin constituting the surface resin and the surface layer is supplied and melt-kneaded, and the polypropylene resin sheet is laminated on both sides of the linear low-density polyethylene resin sheet by a multilayer T die or a multilayer annular die. Produce an unstretched multilayer sheet. After the unstretched multilayer sheet is cooled and solidified, the temperature is raised again to a temperature at which the sheet can be stretched, and then a predetermined stretching ratio is obtained by a known stretching method, for example, a tenter stretching method or a tubular stretching method. To produce a heat-shrinkable film.

Among the above-mentioned methods for stretching the multilayer sheet, the tubular stretching method is preferred because the degree of stretching in the longitudinal and transverse directions of the multilayer film can be made uniform. However, when the tubular stretching method is used, it is necessary that the multilayer sheet is obtained by co-extrusion with a multilayer annular die.

The thickness of the multilayer sheet is 200 to 500 μm.
m, the stretching ratio in the machine direction and the transverse direction is preferably 2 to 10 times, the stretching speed is preferably 10 to 100 m / min, and the stretching temperature is preferably adjusted to 50 to 120 ° C. at the sheet temperature before stretching. The thickness ratio of the surface layer / intermediate layer / surface layer of the heat-shrinkable film produced as described above is 1/2 /
1 to 1/10/1 is preferred.

[0025]

The heat-shrinkable film of the present invention has a density in the intermediate layer.
0.880-0.935 g / cm ^ThreeLinear low density poly
Heat shrinkage due to the use of ethylene resin
Package with excellent resistance, impact resistance and flexibility
Can be obtained.

Further, the heat-shrinkable film of the present invention has a resin temperature of 220 ° C. and a spread ratio of 10
The melt tension is 0.8 to 3 g at the same time, and the melting peak temperature by differential scanning calorimetry is 120 to 1
Since it is made of polypropylene resin at 45 ° C, even if it is used in a high-speed automatic packaging machine, it will not be accidentally broken at the heat seal part,
Therefore, heat sealing can be made sufficient.

[0027]

EXAMPLES (Example 1) As a resin constituting the surface layer,
Polypropylene resin (melt tension = 1.03
g, melting peak temperature = 140 ° C., melt index =
2.7 g / 10 min, ethylene content = 4.1% by weight) 1
In addition to preparing a resin composition consisting of 00 parts by weight and 0.05 part by weight of erucamide, as a resin constituting the intermediate layer, a linear low-density polyethylene resin (density = 0.
896 g / cm ³ , melt index = 2.0 g / 1
0 minute, 1-octene content = 14.5% by weight) and 0.05 part by weight of erucamide, and these were supplied to three extruders, respectively, and melt-kneaded.
A multilayer sheet having a thickness of 350 μm was obtained by a three-layer annular die. The multilayer sheet had a surface layer laminated and integrated on both surfaces of the intermediate layer, and the thickness ratio of the surface layer / intermediate layer / surface layer was 1/3/1.

After the multilayer sheet was quenched once, it was supplied to a heating oven and heated to 110 ° C. Subsequently, it was simultaneously biaxially stretched 5 times vertically and 5 times horizontally by a tubular method to obtain a heat-shrinkable film having a thickness of 15 μm.

Example 2 As the resin constituting the intermediate layer, a linear low-density polyethylene resin (density = 0.92)
0 g / cm ³ , melt index = 1.0 g / 10
A 1-octene content of 13.1% by weight) and 0.05 part by weight of erucamide were used to obtain a heat-shrinkable film in the same manner as in Example 1.

Example 3 As a resin constituting the surface layer, a polypropylene resin (melt tension = 1.5)
2 g, melting peak temperature = 136 ° C., melt index = 1.2 g / 10 min, ethylene content = 5% by weight) 10
A resin composition consisting of 0 parts by weight and 0.05 parts by weight of erucamide was used, and a linear low-density polyethylene resin (density = 0.92) was used as a resin constituting the intermediate layer.
0 g / cm ³ , melt index = 1.0 g / 10
A 1-octene content = 13.1% by weight) and 0.05 part by weight of erucamide were used to obtain a heat-shrinkable film in the same manner as in Example 1.

Comparative Example 1 A polypropylene resin (melt tension = 0.6) was used as the resin constituting the surface layer.
4 g, melting peak temperature = 136 ° C., melt index = 5.5 g / 10 min, ethylene content = 3.2% by weight,
A heat-shrinkable film was obtained in the same manner as in Example 1 except that a resin composition consisting of 100 parts by weight of butene (= 8.7% by weight) and 0.05 part by weight of erucamide was used.

Comparative Example 2 As a resin constituting the surface layer, a polypropylene resin (melt tension = 0.7)
(4 g, melting peak temperature = 143 ° C., melt index = 3.5 g / 10 min, ethylene content = 3.7% by weight)
A resin composition consisting of 100 parts by weight and 0.05 part by weight of erucamide was used, and a linear low-density polyethylene resin (density = 0.
920 g / cm ³ , melt index = 1.0 g / 1
A heat-shrinkable film was obtained in the same manner as in Example 1 except that a resin composition comprising 0 minute, 1-octene content = 13.1% by weight) and 0.05 part by weight of erucamide was used.

Comparative Example 3 Polypropylene resin (melt tension = 0.74 g, melting peak temperature = 143)
C., melt index = 3.5 g / 10 min, ethylene content = 3.7% by weight) A resin composition consisting of 100 parts by weight and 0.05 part by weight of erucamide was supplied to an extruder and melt-kneaded. A single-layer sheet having a thickness of 350 μm was obtained by using an annular die.

After the single-layer sheet was once cooled rapidly, it was supplied to a heating oven and heated to 120 ° C. Subsequently, it was simultaneously biaxially stretched 5 times vertically and 5 times horizontally by a tubular method to obtain a heat-shrinkable film having a thickness of 15 μm.

The transparency of the heat-shrinkable film obtained above,
The lubricity, heat shrinkability, flexibility, high-speed wrapping property and finished quality were measured by the following methods, and the results are shown in Table 1.

(Transparency) The haze of the heat-shrinkable film was determined by JI
It was measured according to SK6718.

(Lubricity) The dynamic friction coefficient of the heat-shrinkable film is represented by A
It was measured according to STM D 1894.

(Heat Shrinkability) The heat shrinkage of the heat shrinkable film was measured according to JIS K1709.

(Flexibility) The elastic modulus of the heat-shrinkable film is determined by AS
It measured according to TMD822.

(High-speed wrapping property) 8 cm × 8
A rectangular parallelepiped box having a size of cm × 25 cm and a weight of 1.6 kg was used. The high-speed automatic packaging machine used is sold by Tokiwa Industries under the product name "NEO618S", and the shrink tunnel is manufactured by Hanagata under the product name "P300".
The ones sold by the company were used.

The tunnel furnace length was 2 m and the tunnel passage time was 5 seconds. Then, the article to be packaged was packed using the high-speed automatic packaging machine in the following manner. First, a heat-shrinkable film in a flat state was sent out from a raw material, and holes were made at regular intervals in the width direction by a needle incorporated in a roll.
Then, the flat heat-shrinkable film was formed into a tubular shape by a former to wrap the object to be packaged.

Then, the central overlapping portion of the heat-shrinkable film is melt-sealed (center-sealed) at a temperature shown in Table 1 with a pair of heated rolls. The package is wrapped in a rough state by fusing and sealing (end sealing) the parts at the temperatures shown in Table 1, and the package wrapped by the heat-shrinkable film is supplied to the shrink tunnel for display. The heat-shrinkable film was shrunk by heating to the temperature shown in 1 and the object to be packaged was wrapped tightly with the film to obtain a package. The packaging conditions were a bag length of 380 mm, a packaging speed of 100 pieces / min, and six rows of needle holes.

500 packages were packaged in the manner described above, and the sealing failure rate of the obtained package was defined as high-speed packaging.

(Finish Quality) The finish of the package obtained by the above-mentioned high-speed packaging was visually observed and judged according to the following criteria. 1: The corner is small and there is no wrinkle. It is a very beautiful finish. 2: The corner is small but wrinkles remain slightly. There is no problem finish. 3: There is no wrinkle, but the corners are large and insufficient. 4: Defective product with large corners and many wrinkles.

[0045]

[Table 1]

[0046]

As described above, the heat-shrinkable film of the present invention has the above-mentioned structure, and therefore, it is possible to obtain a package having excellent heat-shrinkability, impact resistance and flexibility, and excellent quality with little residual corner. As well as having excellent high-speed heat sealing properties, complete and reliable heat sealing can be performed even when used in a high-speed automatic packaging machine.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) B29L 9:00 F term (Reference) 3E086 AD16 BA04 BA15 BB51 BB67 BB85 4F100 AK07B AK07C AK63A BA03 BA06 BA10B BA10C GB90 JA03 JA04B JA04C JA06B JA06C JA13A JK10 JK13 JK17 JL12 YY00A YY00B YY00C 4F210 AA08 AA11 AE01 AG01 AG03 RC02 RG02 RG04 RG44

Claims (1)

[Claims] (1) a density of 0.880 to 0.935 g / cm;
On both sides of the intermediate layer of ³ of linear low density polyethylene resin, melt by differential scanning calorimetry with and spreading ratio at 220 ° C. resin temperature is the melt tension at the time of 10-fold is 0.8~3g Peak temperature 120-145 ° C
A heat-shrinkable film characterized in that a surface layer made of a polypropylene resin is laminated and integrated.