JPH0477235A - Heat-shrinkable polypropylene film - Google Patents

Abstract

PURPOSE:To produce highly heat-shrinkable film having longitudinal and lateral heat shrinkage factors, which are well balanced with each other, by a method wherein film, which is produced by extruding mixed resin prepared by adding specified petroleum resin to polypropylene resin, is stretched by successive biaxial stretching. CONSTITUTION:Stock film, which is produced by extruding and forming melt extrusion composition, the resin component of which consists of 100 pts. wt. of polypropylene resin and 5 - 30 pts. wt. of petroleum resin is stretched by successive biaxial stretching so as to obtain film having longitudinal and lateral heat shrinkage factors of 35% or more respectively. As the petroleum resin- based hydrocarbon, petroleum resin, hydrogenated petroleum resin, terpene resin, hydrogenated terpene resin or the like is exampled. The normal order of the successive biaxial stretching of the stock film obtained by extrution molding or of processes for stretching longitudinally and laterally is from longitudinal stretching to lateral one. The preferable longitudinal stretching is performed at about 70 - 110 deg.C. The preferable lateral stretching is performed at about 90 - 130 deg.C or is set at stretching temperature, which is higher than the longitudinal stretching temperature by about 15 - 20 deg.C.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention provides a well-balanced polypropylene film having a heat shrinkage rate of 35% or more in each of the longitudinal and transverse directions, which is obtained by a sequential biaxial stretching method. Regarding the film that was released.

[Prior Art] Heat-shrinkable polypropylene films can be used, for example, in cup foods such as cup ramen, food and beverages such as lactic acid bacteria drinks, etc.
It is widely used for shrink-wrapping relatively low-weight items such as notebooks and miscellaneous goods in small rolls, and is also beginning to be used for wrapping objects in the field of conventional vinyl chloride film packaging. .

The heat shrinkage rate required for polypropylene film used as a packaging film for shrink packaging varies depending on the thickness of the film and the item to be shrink-wrapped, but in most cases it is 30 each
% or more is required.

[Problems to be Solved by the Invention] By the way, a heat-shrinkable polypropylene film produced by a sequential biaxial stretching method using the Tenku method has, for example, There is no risk of breakage during the stretching process even when obtaining thin objects with a thickness of 10μ or less, and there is no significant reduction in drawing speed when obtaining thick objects with a thickness of 30μ or more. , has methulide that can be produced extremely efficiently.

However, heat-shrinkable polypropylene films produced by sequential biaxial stretching using the conventional tenter method have a heat shrinkage rate of 20 to 20% at most.
30%, and it is not possible to obtain a polypropylene film that is well-balanced both vertically and horizontally.

For this reason, highly heat-shrinkable polypropylene films have generally been obtained using a simultaneous biaxial stretching method consisting of an inflation method, which has various disadvantages.

In contrast, the present invention is a heat-shrinkable polypropylene film produced by a sequential biaxial stretching method using a tenter method, and which has a high pAII3 well-balanced in each of the vertical and horizontal directions.
A bicondensing polypropylene film, i.e., e.g.
There is no risk of breakage even when producing thin products with a thickness of 10μ or less (also, there is no significant reduction in drawing speed when producing thick products with a thickness of 30μ or more, resulting in extremely high productivity). A polypropylene film created by sequential biaxial stretching using a tenter method that maintains efficiency.
Provides a well-balanced high heat shrinkable film on each side.

[Means for Solving the Problems] The thermo-1132 shrinkable polypropylene film of the invention of Wooden Tablet 1 has a composition for melt extrusion containing 100 parts by weight of a polypropylene resin and 5 to 30 parts by weight of a petroleum resin hydrocarbon as resin components. A film obtained by sequentially stretching an extruded material using a biaxial stretching method, and furthermore,
It is made of a film that has a heat shrinkage rate of 35% or more in both the vertical and horizontal directions.

In addition, the heat-shrinkable polypropylene film of the invention of Wooden Tablet 2 is obtained by sequentially extruding a raw film obtained by extruding a composition for melt extrusion containing 100 parts by weight of polypropylene resin and 5 to 30 parts by weight of petroleum resin. This is a film obtained by stretching by an axial stretching method, and has a heat shrinkage rate of 35% or more in each of the vertical and horizontal directions.

The heat shrinkage rate of the polypropylene film in the present invention is the shrinkage rate (%) when immersed in glycerin at 120°C for 30 seconds.

In the heat-shrinkable polypropylene film of the present invention having the above structure, the polypropylene resin used is a polypropylene homopolymer, a copolymer of vopropylene and ethylene or other copolymer components, or a mixed resin thereof.

The petroleum resin hydrocarbons added and mixed into the polypropylene resin include, for example, hydrogenated petroleum resin, terpene resin, hydrogenated terpene resin, etc. In particular, when petroleum resin is used, Since a resin with a molecular weight of around 1000 and a softening point of 100 to 140°C can be used, the miscibility between the polypropylene resin and the petroleum resin used as an additive resin is good, so it has poor stretching suitability. In particular, the mixed resin has excellent properties in terms of breakage resistance during the stretching process.

In the heat-shrinkable polypropylene film of the present invention, if the amount of petroleum resin hydrocarbon added is less than 5 parts by weight with respect to 100 parts by weight of polypropylene resin in the mixed resin when obtaining the original film, the addition of petroleum resin hydrocarbon The effect of
It becomes difficult to obtain a polypropylene film having a heat shrinkage of 35% or more on each side.

Furthermore, if the amount of petroleum resin hydrocarbon added exceeds 30 parts by weight with respect to 100 parts by weight of the polypropylene resin, the physical properties of the resulting polypropylene film will become insufficient.

In the patient extrusion composition used to obtain the raw fabric,
Furthermore, as in the case of obtaining a normal biaxially oriented polypropylene film, additives such as antioxidants, slip agents, anti-blocking agents, antistatic agents, and Of course, agents, ultraviolet absorbers, etc. can be added as appropriate.

It is desirable to perform extrusion molding of the mixed resin at as low a temperature as possible to prevent deterioration of the resin when obtaining the original fabric to be subjected to uniaxial stretching. Extrusion molding without rinsing at 160"C is not preferred because kneading with the hydrocarbon system tends to be insufficient and the load during extrusion molding becomes high.

The original fabric obtained by extrusion molding is longitudinally stretched using a sequential axial stretching method.
The transverse stretching step is usually carried out in the order of longitudinal and transverse stretching.

In the longitudinal stretching step, if the stretching temperature is too low, stretching unevenness will occur, and if the stretching temperature is too high, the sheet will stick to the rolls, leading to roll stains and melt breakage. For this reason, it is preferable to carry out stretching in the longitudinal direction at a temperature of 70 to 110°C.

It is desirable that the stretching ratio in the longitudinal direction is as high as possible,
If the stretching ratio exceeds 7 times, horizontal stripes are likely to occur and there is a risk of breakage during subsequent stretching in the lateral direction, so it is preferable to use a stretching ratio of 4 to 6 times.

If the heating temperature in the transverse stretching process is low, the heat shrinkage rate of the resulting film will be high, but the risk of breakage during stretching will increase, and if the stretching temperature is too high, the desired high heat Contractibility cannot be obtained.

For this reason, it is usually preferable to carry out the stretching in the transverse direction at a temperature of 90 to 130°C, which is 15 to 20°C higher than the stretching temperature in the longitudinal direction.
It is preferable to set the stretching temperature to a temperature as high as .degree.C.

The optimum heating temperature in the lateral stretching process is determined depending on the content of petroleum resin hydrocarbons in the extruded resin, and if the content of petroleum resin hydrocarbons is small,
It is necessary to set the Kano temperature high.

Furthermore, the stretching ratio in the horizontal direction is preferably set higher than the stretching ratio in the longitudinal direction, and is usually preferably set to about 11 to 15 times the stretching ratio in the longitudinal direction.

[Function] The heat-shrinkable polypropylene film of the present invention is made by using an extruded film of a mixed resin in which 5 to 30 parts by weight of petroleum resin hydrocarbon is added to 100 parts by weight of polypropylene resin for original binding. , which is obtained by subjecting this to stretching by a sequential biaxial stretching method, and has a heat shrinkage rate of 35% or more in each of the longitudinal and transverse directions.

The heat-shrinkable polypropylene film of the present invention having the above structure is a mixture of 100 parts by weight of a polypropylene resin having a melting point of approximately 168°C and a petroleum resin hydrocarbon having a low melting point added at a ratio of 5 to 30 parts by weight. Since the original fabric obtained by extrusion molding the resin is used, biaxial stretching can be performed at a much lower temperature than when stretching an original fabric made of polypropylene resin.

For this reason, when stretching the original fabric, there is no risk of breakage even when obtaining a thin object with a thickness of 10L1 or less, and there is no risk of breakage even when obtaining a thick object with a thickness of 30μ or more. It can be stretched by a sequential biaxial stretching method without any deterioration, and it becomes a well-balanced, highly heat-shrinkable polypropylene film that has heat-shrinkability of 35% or more in each of the vertical and horizontal directions. .

[Example 6] Hereinafter, the specific structure of the heat-shrinkable polypropylene film of the present invention will be explained using manufacturing examples.6 Example 1 A mixed resin of 100 parts by weight of polypropylene resin and 5 parts by weight of petroleum resin was melted and kneaded. After that, extrusion molding was performed using a T-guidry at 200° C. to obtain a raw material (①) consisting of an extruded film with a thickness of 1500 μm.

Next, the above-mentioned original film (2) was stretched in the longitudinal direction at a stretching temperature of 80°C and a stretching ratio of 6 times, and then laterally stretched at a stretching temperature of 130°C and a stretching ratio of 8 times. ,
A heat-shrinkable polypropylene film (A), which is an example product of the present invention, was obtained.

Example 2 A mixed resin of 100 parts by weight of polypropylene resin and 10 parts by weight of petroleum resin was melted and kneaded, and then extruded using a T-guid at 200°C to form a raw film made of extruded film with a thickness of 1500 μm. I got it.

Next, the above-mentioned original fabric (■) was stretched at a stretching temperature of 80'C,
After stretching in the longitudinal direction at a stretching ratio of 6 times, subsequent stretching in the transverse direction at a stretching temperature of 120° C. and a stretching ratio of 8 times was performed to obtain a heat-shrinkable polypropylene film (B), which is an example product of the present invention. ) was obtained.

Example 3 The original fabric ■ obtained in Example 2 above was stretched at a stretching temperature of 8
After stretching in the longitudinal direction at 0° C. and a stretching ratio of 6 times, subsequent stretching in the transverse direction at a stretching temperature of 130° C. and a stretching ratio of 8 times was performed to obtain heat-shrinkable polypropylene, which is an example product of the present invention. A film (C) was obtained.

Example 4 After melting and kneading a mixed resin of 100 parts by weight of polypropylene resin and 15 parts by weight of petroleum resin, extrusion molding was performed using a T-die at 200°C to obtain a raw film consisting of an extruded film with a thickness of 1500 μm. I got it.

Next, the above-mentioned original film (2) was stretched in the longitudinal direction at a stretching temperature of 80° C1 at a stretch ratio of 6 times, and subsequently stretched in the transverse direction at a stretching temperature of 120° C. and a stretch ratio of 8 times. A heat-shrinkable polypropylene film (D), which is an example product of the present invention, was obtained.

Example 5 The original fabric ■ obtained in Example 4 above was stretched at a stretching temperature of 8.
After stretching in the longitudinal direction at 0°C1 at a stretching ratio of 6 times, subsequent stretching in the transverse direction at a stretching temperature of 130°C5 at a stretching ratio of 8 times was performed to obtain heat-shrinkable polypropylene, which is an example product of the present invention. A film (E) was obtained.

Table 1 shows the heat shrinkage percentages (%) of the heat-shrinkable polypropylene films (A) to (E) in Examples 1 to 5 above.

Note that the heat shrinkage rate (%) is a value obtained when immersed in a glycerin bath at 120°C for 30 seconds.

Comparative Example 1 in Table 1 For the original fabric ■ obtained in Example 1 above, the stretching temperature was 8
After stretching in the longitudinal direction at 0°C and a stretch ratio of 6 times, subsequent stretching in the transverse direction was performed at a stretching temperature of 120'C and a stretch ratio of 8 times, breakage occurred during the transverse stretching process. ,
The desired heat-shrinkable polypropylene film could not be obtained.

Comparative Example 2 The original fabric ■ obtained in Example 1 above was stretched at a stretching temperature of 8.
After stretching in the longitudinal direction at 0°C and a stretching ratio of 6 times, subsequent stretching in the transverse direction was carried out at a stretching temperature of 140°C and a stretching ratio of 8 times to obtain a heat-shrinkable polypropylene film (a) for comparison. Obtained.

Comparative Example 3 The original fabric ■ obtained in Example 2 was stretched at a stretching temperature of 8.
After stretching in the longitudinal direction at 0° C.9 at a stretching ratio of 6 times, subsequent stretching in the transverse direction at a stretching temperature of 140° C. and a stretching ratio of 8 times was performed to obtain a heat-shrinkable polypropylene film (b) for comparison. Obtained.

Comparative Example 4 The original fabric ■ obtained in Example 4 above was stretched at a stretching temperature of 8.
After stretching in the longitudinal direction at 0°C and a stretching ratio of 6 times, subsequent stretching was carried out in the transverse direction at a stretching temperature of 140°C and a stretching ratio of 8 times to obtain a heat-shrinkable polypropylene film (c) for comparison. Obtained.

Comparative Example 5 After melting and kneading polypropylene resin, T
Extrusion molding was carried out using a gouer to obtain an original fabric (2) consisting of an extruded film with a thickness of 1500 μm.

Next, the above-mentioned original fabric (2) was stretched in the longitudinal direction at a stretching temperature of 80°C and a stretching ratio of 6 times, and then stretched in the transverse direction at a stretching temperature of 120°C and a stretching ratio of 8 times. However, breakage occurred during the transverse stretching step, and the desired heat-shrinkable polypropylene film could not be obtained.

Comparative Example 6 The original fabric ■ obtained in Comparative Example 5 above was stretched at a stretching temperature of 8.
After stretching in the longitudinal direction at a stretching ratio of 6 times at 0°C, subsequent stretching was performed in the horizontal direction at a stretching temperature of 130°C and a stretching ratio of 8 times, breakage occurred during the stretching process in the horizontal direction.
The desired heat-shrinkable polypropylene film could not be obtained.

Comparative Example 7 The original fabric ■ obtained in Comparative Example 5 above was stretched at a stretching temperature of 8.
After stretching in the longitudinal direction at 0° C.9 with a stretching ratio of 6 times, the film was subsequently stretched in the transverse direction at a stretching temperature of 140° C. and a stretching ratio of 8 times to obtain a heat-shrinkable polypropylene film (d) for comparison. Ta.

The heat shrinkage rates (%) of the heat-shrinkable polypropylene films (a) to (d) in Comparative Examples 2 to 4 and 7 above were determined by the second
Shown in the table.

Note that the heat shrinkage rate (%) is a value obtained when immersed in glycerin solution at 120°C for 30 seconds.

Table Example 6 After melting and kneading a mixed resin of 100 parts by weight of polypropylene resin and 10 parts by weight of terpene resin,
Extrusion molded using a die to create a 1500μ thick raw fabric■
I got it.

Next, the above-mentioned original film (2) was stretched in the longitudinal direction at a stretching temperature of 80° C. and at a stretching ratio of 6 times, and then stretched in the transverse direction at a stretching temperature of 130° C. and a stretching ratio of 8 times.
A heat-shrinkable polypropylene film (F), which is an example product of the present invention, was obtained.

The heat shrinkage rate of the obtained heat-shrinkable polypropylene film (F), that is, the heat shrinkage rate when the film (F) was immersed in glycerin at 120°C for 30 seconds was 40% in the longitudinal direction.
, horizontally 43%.

[Effect] The heat-shrinkable polypropylene film of the present invention is a film obtained by stretching by a sequential biaxial stretching method, and has a heat shrinkage rate of 35% or more in each of the vertical and horizontal directions. , which has high heat shrinkability in a well-balanced manner both vertically and horizontally.

Therefore, it can be directly applied to the packaging field of shrink packages that utilize heat-shrinkable films obtained by the conventional inflation method, and moreover, it can be applied to the packaging field of shrink packages that utilize heat-shrinkable films obtained by the conventional inflation method. Therefore, for example, there is no risk of breakage during the stretching process even when obtaining a thin product with a thickness of 10 μm or less, and there is a significant decrease in the drawing speed when obtaining a thick product with a thickness of 30 μm or more. Since this does not occur, production is extremely efficient.

Claims (1)

[Claims] 1. 5 to 30 parts by weight per 100 parts by weight of polypropylene resin
A film obtained by sequentially stretching an extruded film of a mixed resin to which parts by weight of petroleum resin hydrocarbons have been added using a biaxial stretching method, and which has a heat shrinkage of 35% or more in each of the vertical and horizontal directions. A heat-shrinkable polypropylene film characterized by having a 2. 5 to 30 parts by weight per 100 parts by weight of polypropylene resin
A film obtained by sequentially stretching an extruded film of a mixed resin to which part by weight of petroleum resin is added using a biaxial stretching method, and which has a heat shrinkage rate of 35% or more in each of the vertical and horizontal directions. A heat-shrinkable polypropylene film characterized by: