JP2000272004A - Method for producing polyolefin-based heat-shrinkable film - Google Patents

Abstract

(57) [Problem] To provide a polyolefin-based heat-shrinkable film which satisfies both low-temperature shrinkability and dimensional stability at room temperature. SOLUTION: The film is stretched by a tubular stretching method,
A polyolefin-based heat-shrinkable film comprising the following (a) or (b) is subjected to MD (machine direction) at 70 to 90 ° C.
Allow 0-15% relaxation. (A) A mixed composition of a polypropylene resin and a propylene-α-olefin copolymer and / or syndiotactic-polypropylene. (B) A composition whose surface layer is mainly composed of a polypropylene resin and whose intermediate layer is mainly composed of a linear low-density polyethylene resin.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a heat-shrinkable film, and more particularly to a method for producing a polyolefin-based heat-shrinkable film having excellent low-temperature shrinkage and dimensional stability at room temperature.

[0002]

2. Description of the Related Art Conventionally, as a heat-shrinkable film, a stretched film of polyvinyl chloride, polypropylene, or polyethylene resin is known. Above all, a polypropylene-based heat-shrinkable film is preferably used because it has excellent suitability for high-speed automatic packaging and does not generate harmful gases during incineration. However, since the polypropylene heat-shrinkable film does not shrink unless the heat-shrinkable tunnel is heated to a relatively high temperature, the shrink-wrapped body tends to wrinkle, and the film at the corners tends to remain in a horn shape. It has the disadvantage of being inferior. In order to solve such disadvantages, Japanese Patent Application Laid-Open No. 8-151454 and
As disclosed in JP-A-269265 and the like, a low melting point resin is mixed with a polypropylene resin or disclosed in JP-A-58-166049 and JP-A-63-1.
No. 73641, Japanese Patent Application Laid-Open No. 63-214446, and the like, which are the same applicant as the present invention.
As described in No. 1255, a heat-shrinkable film that shrinks even at a relatively low temperature by laminating a polypropylene-based resin and a polyethylene-based resin, that is, has a low-temperature shrinkability has been proposed. As described above, in the method of mixing the polypropylene resin with the low melting point resin or laminating the polypropylene resin and the polyethylene resin, the packaging finish can be improved with the improvement of the low temperature shrinkage. However, the shrinkage ratio of MD at room temperature also increases, that is, the dimensional stability at room temperature deteriorates. Therefore, when the film is stored in a roll, the film is tightened, and the films are blocked with each other. There is a problem that packaging trouble is caused due to deterioration of properties.

[0003]

An object of the present invention is to provide a polyolefin-based heat-shrinkable film that satisfies both low-temperature shrinkage and dimensional stability at room temperature.

[0004]

Means for Solving the Problems The present inventors have intensively studied for a heat-shrinkable film which has solved the above-mentioned disadvantages, and as a result, have reached the present invention.

That is, the present invention relates to a method for producing a polyolefin heat-shrinkable film comprising the following (a) or (b) stretched by a tubular stretching method at 70 to 90 ° C.
A method for producing a polyolefin-based heat-shrinkable film, characterized in that the film is relaxed in the machine direction by 10 to 15%. (A) A mixed composition of a polypropylene resin and a propylene-α-olefin copolymer and / or syndiotactic-polypropylene. (B) A composition whose surface layer is mainly composed of a polypropylene resin and whose intermediate layer is mainly composed of a linear low-density polyethylene resin.

Hereinafter, the present invention will be described in detail. First, as a heat treatment condition of a polyolefin heat-shrinkable film stretched by a tubular stretching method, a temperature of 7 is used.
0-90 ° C., MD relaxation rate is 10-15%. If the temperature is lower than 70 ° C., the dimensional stability at room temperature is inferior. On the other hand, if the longitudinal relaxation rate is less than 10%, the dimensional stability at room temperature is inferior, which is not preferable. If it exceeds 15%, the film is loosened in the heat treatment step, and trouble such as winding of the film around the roll is not preferred. .

[0007] Polypropylene resin and propylene-α-
A polypropylene-based heat-shrinkable film comprising an olefin copolymer and / or a syndiotactic-polypropylene mixed composition has the features that the film is strong and excellent in suitability for high-speed automatic packaging.

The polypropylene resin used in the present invention is an ethylene-propylene copolymer or an ethylene-propylene-butene terpolymer, and ethylene or ethylene and butene is added to propylene in an amount of 2 to 10%.
Random copolymerized, melting point 130-145 ° C
Is used. If the melting point exceeds 145 ° C., the low-temperature shrinkage is inferior, which is not preferable. If the melting point is lower than 130 ° C., the blocking resistance is inferior, which is not preferable.

As the propylene-α-olefin copolymer and the syndiotactic polypropylene mixed with the polypropylene resin, those having a melting point of 105 to 130 ° C. are used. Those having a melting point of less than 105 ° C are not preferred because of poor blocking resistance, and those having a melting point of more than 130 ° C are not preferred because of low shrinkage at low temperatures.

As the propylene-α-olefin copolymer used in the present invention, a propylene-butene copolymer obtained by copolymerizing propylene with a relatively large amount of butene is used. Further, as the syndiotactic-polypropylene, a syndiotacticity having a syndiotactic pentad fraction of 0.7 or more measured by ¹³ C-NMR is used.
Good polypropylene is used. Such syndiotactic-polypropylene is disclosed in, for example,
-41303, JP-A-2-41305, JP-A-2-274703, JP-A-2-274704
JP, JP-A-3-179005, JP-A-3-1
It can be obtained by using a catalyst comprising a crosslinked transition metal compound having mutually asymmetric ligands and a cocatalyst as described in JP 79006B.

The propylene-α-olefin copolymer and / or the syndiotactic polypropylene are mixed in a range of 2 to 20% by weight based on the weight of the polypropylene-based resin. You may mix them. If the mixing ratio is less than 2% by weight, the low-temperature shrinkage is inferior because it is inferior, and if it exceeds 20% by weight, the blocking resistance is undesirably reduced.

A polyolefin-based multilayer heat-shrinkable film whose surface layer is composed of a composition mainly composed of a polypropylene-based resin and whose intermediate layer is mainly composed of linear low-density polyethylene has a feature of high tear resistance.

As the polypropylene resin used for the surface layer, the same polypropylene resin as the above-mentioned polypropylene heat-shrinkable film is used.

The linear low-density polyethylene used for the intermediate layer is a copolymer of ethylene and an α-olefin, and has a density in the range of 0.900 to 0.925 g / cm ³ . Those having a density of less than 0.900 g / cm ³ are not preferred because the film strength decreases,
If it exceeds 0.925 g / cm ³ , the low-temperature shrinkability is inferior, so that it is not preferable.

The thickness ratio of the intermediate layer to all layers is as follows:
A range of 30 to 80% is preferred. The thickness ratio of the intermediate layer is 3
If it is less than 0%, the low-temperature shrinkage is inferior, so that it is not preferable.
%, It is not preferable because the stiffness of the film is reduced.

In the intermediate layer, scrap generated in the production process can be recycled. In this case, the intermediate layer is a mixed composition of linear low-density polyethylene and the polypropylene resin used for the surface layer.

Further, the above-mentioned heat-shrinkable polypropylene-based film and multi-layer heat-shrinkable polyolefin-based film may contain other resins, lubricants, anti-blocking agents, antistatic agents, and the like, as long as the object of the present invention is not hindered. Additives such as anti-fogging agents can be used as appropriate.

Next, the method for producing the polyolefin-based heat-shrinkable film of the present invention will be specifically described with reference to an example of a three-layer laminated annular film-forming stretching.

First, the above-mentioned mixed composition comprising linear low-density polyethylene and polypropylene is melt-kneaded by three extruders so as to form an intermediate layer and a polypropylene-based resin as a surface layer. Co-extrusion in a ring,
It is quenched once without being stretched to produce a tubular unstretched film. The obtained tubular unstretched film is supplied to, for example, a tubular stretching apparatus as shown in FIG. At a low temperature, a gas pressure is applied inside the tube to expand and stretch to cause simultaneous biaxial orientation. The stretching ratio is not necessarily the same in the vertical and horizontal directions, but in order to obtain excellent properties such as excellent strength and shrinkage, it is preferable that the film is stretched in the vertical and horizontal directions at least 3 times or more, more preferably at least 3.5 times. . The film taken out of the stretching apparatus is subjected to the heat treatment conditions of the present invention, that is, to a heat treatment at 70 to 90 ° C. in the MD at a relaxation rate of 10 to 15%. The heat treatment method is not particularly limited, but roll heat treatment with a plurality of heat rolls or tenter heat treatment is preferable.

[0020]

Next, the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples. In addition, the following methods were used to evaluate the heat shrinkage at 100 ° C. and the dimensional stability at room temperature shown in this example.

1) Heat shrinkage at 100 ° C. The film is cut with a target of 100 mm in both length and width, and the dimensions are measured. Next, it was immersed in a glycerin bath at 100 ° C. for 10 seconds, the dimensions after immersion were measured, and calculated by the following formula 1. In addition, when this numerical value is 25% or more, it shows that low-temperature shrinkability is excellent. Formula 1 100 ° C. Heat shrinkage (%) = (L ₀ −L ₁ ) × 100 / L ₀ where L ₀ = dimension of sample before shrinkage (mm), L ₁ =
Dimensions of sample after immersion in glycerin (mm) MD, T
Measure each D

2) Room-temperature dimensional stability The film was cut to a target of 200 mm in both length and width, and
Measure the dimensions of Then, after being left in a gear oven at 35 ° C. for 16 hours, the dimensions of the MD were measured and then calculated by the following equation 2. When this value is 2% or less, it indicates that the dimensional stability at normal temperature is excellent. Equation 2 Room temperature dimensional stability (%) = (L ₀ −L ₁ ) × 100 / L ₀ where L ₀ = dimension of sample before shrinkage (mm), L ₁ =
Dimension of sample after leaving in gear oven (mm)

Example 1 A polypropylene resin having a melting point of 136 ° C. (F233D
G: 95% by weight of Grand Polymer Co., Ltd. and 5% by weight of a propylene-α-olefin copolymer having a melting point of 110 ° C. (Tuffmer XR110T; Mitsui Petrochemical Co., Ltd.) at 170 to 240 ° C. by an extruder. Knead, 240 ° C
Extruded from an annular die maintained at a constant pressure. The formed tube was cooled and drawn by passing through a water tank while sliding the outer surface of a cylindrical cooling mandrel in which cooling water circulates, thereby obtaining a tubular unstretched film. This tubular unstretched film was guided to the tubular biaxial stretching apparatus of FIG. 1, heated, stretched four times in each of length and width, and a stretched film was obtained. Thereafter, heat treatment was performed using two heat rolls at a temperature of 75 ° C. and a vertical relaxation rate of 11% to obtain a 15 μm thick polypropylene heat-shrinkable film. As shown in Table 1, the obtained stretched film had good low-temperature shrinkage and dimensional stability at room temperature.

Example 2 A stretched film was prepared under the same conditions as in Example 1, and then heat-treated under the conditions shown in Table 1 to obtain a heat-shrinkable polypropylene film having a thickness of 15 μm. The obtained polypropylene-based heat-shrinkable film was excellent in both low-temperature shrinkage and dimensional stability at room temperature.

Example 3 The propylene-α-olefin copolymer of Example 1 was prepared using a syndiotactic polypropylene (Thiaro SPT-0159; Mitsui Chemicals, Inc.) having a melting point of 125 ° C. and a syndiotactic pentad fraction of 0.79. A stretched film was produced under the same conditions as in Example 1 except that the film was changed to (manufactured by the company).
Thereafter, heat treatment was performed under the conditions shown in Table 1 to obtain a 15-μm-thick polypropylene heat-shrinkable film. The obtained polypropylene-based heat-shrinkable film was excellent in both low-temperature shrinkage and dimensional stability at room temperature.

Example 4 The same polypropylene resin as in Example 1 was used for the surface layer, and a linear low-density polyethylene (Ultzex 1510S; manufactured by Mitsui Chemicals, Inc.) having a density of 0.916 g / cm 3 was used for the intermediate layer. Using a mixed composition of 80% by weight and 20% by weight of the same polypropylene-based resin as the surface layer, using a three-layer annular die so that the thickness ratio of the inner layer, the intermediate layer, and the outer layer becomes 1/5/1. A tubular unstretched film was produced.
Thereafter, in the same manner as in Example 1, a stretched film was prepared at a stretch ratio of 4 times in each of the longitudinal and transverse directions, and heat-treated under the conditions shown in Table 1 to obtain a polyolefin-based multilayer heat-shrinkable film having a thickness of 15 μm. The obtained polyolefin-based multilayer heat-shrinkable film had good low-temperature shrinkage and dimensional stability at room temperature.

Comparative Example 1 A stretched film was prepared under the same conditions as in Example 1, and then heat-treated under the conditions shown in Table 1 to obtain a 15 μm thick heat-shrinkable polypropylene film. The resulting polypropylene-based heat-shrinkable film had good low-temperature shrinkability but poor dimensional stability at room temperature.

Comparative Example 2 A stretched film was prepared under the same conditions as in Example 1, and then heat-treated under the conditions shown in Table 1 to obtain a heat-shrinkable polypropylene-based film having a thickness of 15 μm. The resulting polypropylene-based heat-shrinkable film had good room-temperature dimensional stability but poor low-temperature shrinkage.

Comparative Example 3 A stretched film was prepared under the same conditions as in Example 1, and then heat-treated under the conditions shown in Table 1. However, the film was loosened, and a problem that the film was wound around a roll occurred. .

Comparative Example 4 A stretched film was prepared under the same conditions as in Example 3 and then heat-treated under the conditions shown in Table 1 to obtain a polyolefin-based heat-shrinkable film having a thickness of 15 μm. The resulting polyolefin-based heat-shrinkable film had good low-temperature shrinkability but poor dimensional stability at room temperature.

Comparative Example 5 A stretched film was prepared under the same conditions as in Example 3 and then heat-treated under the conditions shown in Table 1 to obtain a polyolefin-based heat-shrinkable film having a thickness of 15 μm. The resulting polyolefin-based heat-shrinkable film had good room-temperature dimensional stability, but poor low-temperature shrinkability.

Comparative Example 6 A polypropylene resin having a melting point of 142 ° C. (F233D
F; Grand Polymer Co., Ltd.)
After producing a stretched film under the same conditions as in Example 1, heat treatment was performed under the conditions shown in Table 1 to obtain a 15-μm-thick polypropylene heat-shrinkable film. The resulting polypropylene-based heat-shrinkable film had good room-temperature dimensional stability but poor low-temperature shrinkage.

[0033]

[Table 1] * Resin composition A: Polypropylene resin (mp; 136 ° C) / Toughmer XR110T
= 95/5 B: Polypropylene resin (mp; 136 ° C) / Thiaro SPT0159
= 95/5 C: Inner / Outer layer; Polypropylene resin (mp; 136 ° C) Intermediate layer; Linear low density polyethylene / polypropylene resin (mp; 136 ° C) = 80/20 Thickness ratio of each layer; Inner layer / Intermediate layer / Outer layer = 1/5/1 D: Polypropylene resin (mp: 142 ° C)

[0034]

According to the present invention, it is possible to produce a polyolefin-based heat-shrinkable film having excellent low-temperature shrinkability and room-temperature dimensional stability by specifying heat treatment conditions for the polyolefin-based heat-shrinkable film.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a tubular biaxial stretching apparatus used in Examples.

[Description of Signs] 1: Unstretched film 2: Low speed nip roll 3: High speed nip roll 4: Preheater 5: Main heater 6: Cooling air ring 7: Folding roll group

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat ゛ (Reference) B29K 105: 02 B29L 7:00 9:00 F term (Reference) 4F100 AK07A AK07B AK63C AK66A AK66B AL05A AL05B BA02 BA03 BA06 BA10A BA10B BA15 EH171 EJ382 EJ422 JA03 JL04 4F210 AA03 AA08 AA11 AA11A AA11E AE01 AG01 AG03 QA05 QC07 QG01 QG15 QG18 QW12

Claims (1)

[Claims] Claims: 1. A film stretched by a tubular stretching method,
A polyolefin-based heat-shrinkable film comprising the following (a) or (b) is subjected to MD (machine direction) at 70 to 90 ° C.
A method for producing a polyolefin-based heat-shrinkable film, wherein the film is relaxed by 0 to 15%. (A) A mixed composition of a polypropylene resin and a propylene-α-olefin copolymer and / or syndiotactic-polypropylene. (B) A composition whose surface layer is mainly composed of a polypropylene resin and whose intermediate layer is mainly composed of a linear low-density polyethylene resin.