JPS6262846A - Polypropylene film for shrinkable label - Google Patents

Abstract

PURPOSE:A polypropylene film suitable for shrinkable labels, having a specific thermal shrinkage ratio and a specific birefringence of inner face of film, shrink able greatly in one direction, having balanced physical properties, comprising a propylene resin. CONSTITUTION:A film comprising polypropylene resin consisting of (A) 95-40wt% polypropylene polymer and (B) 5-60wt% petroleum resin and/or terpene resin, having 7-15cal/g crystallization amount of heat is biaxially oriented, to give a film having >=40% heat shrinkage ratio in one direction and <=15% heat shrinkage ratio in a direction rectangular to it when immersed in 100 deg.C hot water for 5min and <=0.01 birefringence in a film face.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a shrinkable label film made of a polypropylene resin.

(Prior art) Conventionally, biaxially oriented polypropylene films, which are evenly stretched in two axial directions and have approximately the same heat shrinkage x2 in both the vertical and horizontal directions, have been widely used as heat-shrinkable polypropylene films. This film is suitable for shrink-wrapping entire packaged items such as instant cup noodle containers, but when used as a shrink label for cylindrical bottles, it is necessary to shrink a lot in one direction. It was unsuitable for some uses.

For this reason, for example, JP-A-57-')7! As shown in Japanese Unexamined Patent Publication No. R33 and JP-A No. 60-5 Guza No. 93, a polypropylene film that is stretched largely in one direction during stretching has been proposed.

(Problems to be Solved by the Invention) The unevenly stretched polypropylene film described above shows significant shrinkage in the stretching direction when heated, but its physical properties such as tensile strength are weak in the direction perpendicular to the stretching direction, and its physical properties are weak in the vertical and horizontal directions. Because of the unbalanced nature of the label, there were drawbacks such as, for example, even if it was placed on a glass bottle as a shrink label, the effect of preventing fragments from scattering when the bottle was broken was small.

Therefore, it is an object of the present invention to provide a polypropylene film suitable for use in shrinkable labels that shrinks significantly in one direction and has well-balanced physical properties.

(Means for Solving the Problems) The present invention is a biaxially stretched film made of polypropylene resin, which has a heat shrinkage rate of ``IO''A or more in one direction when immersed in hot water at 700°C for 5 minutes. , perpendicular to it/
j% or less, and the in-plane birefringence of the film (Δn
) is 0.0/or less, a polypropylene film for shrinkable labels.

As the polypropylene resin in the present invention, in addition to a propylene homopolymer, copolymers of propylene and other olefins such as ethylene and butene/and mixtures thereof can be used. Of course, various additives may be added to these.

70 of the polypropylene film for shrinkable labels of the present invention
The thermal shrinkage rate when immersed in hot water at 0° C. for 5 minutes is required to be 0% or more in one direction and 13% or less in the direction perpendicular to it. When formed into a cylindrical shape and used as a shrinkable label for bottles, etc., if the heat shrinkage rate in the circumferential direction is less than 'i' OX, pock-like irregularities are likely to occur, and it will not adhere well to narrow parts such as the neck of the bottle. As a result, the appearance of the seedlings becomes extremely poor. Here, from the viewpoint of manufacturing, it is practically preferable that aO to about 70%. Further, it is practically preferable for the axial direction of the label to be approximately 15 to 15% in terms of manufacturing. Furthermore, if the heat shrinkage rate at 100℃ is within the above range, it can be shrunk at high speed under conventional label shrinkage conditions, and even when heated at a relatively low temperature of 100℃, a high shrinkage rate can be obtained. This is advantageous if heating is further applied to the container for shrinkage.

It is necessary that the in-plane birefringence (Δn) of the polypropylene film for shrinkable labels of the present invention is 0.01 or less. If this Δn becomes Q-Q/, the strength balance deteriorates, and when the label is shrunk as a label on a glass bottle filled with carbonated drinks, etc., there will be disadvantages such as poor scattering prevention effect when the bottle is broken. It is. This is because the refractive index n in a certain direction of the film strongly depends on the degree of orientation in that direction. This is because the difference in the degree of orientation between the vertical and horizontal directions is small and well-balanced, and when Δn increases, the difference in strength between the vertical and horizontal films increases and the film is torn in the weak direction.

In this way, the polypropylene film for shrinkable labels of this book is characterized by a new structure in which it mainly shrinks in one direction and is relatively well-balanced and largely oriented. It is particularly suitable for label use.

In order to obtain the polypropylene film for shrinkable labels of the present invention, a raw film made of polypropylene resin is first stretched in one direction at, for example, (Tm-50)°C to (Tm-λO)°C, and then, for example, (Tm -ko0)℃～T
Heat treatment in the range of m'C, and further in the direction perpendicular to the initial stretching direction at 70 to 110°C, preferably go°C-/00
How to stretch with 'C, or the first stretch for example (
It is carried out under a high temperature condition of Tm - - θ℃) to Tm, and then in a direction perpendicular thereto to preferably go
It can be obtained by stretching at a temperature of 100°C to 100°C. Note that Tm here is the melting point of the polypropylene resin.

By stretching and orienting the material in one direction in seven stages as described above, sufficient physical strength can be imparted in the stretching direction. By heat treatment at a high temperature after the first stretching or by performing the first stretching itself at a high temperature, it is possible to crystallize the polypropylene resin and completely suppress the thermal shrinkage caused by the first stretching. . Furthermore, the entire stretching step is then carried out at a relatively low temperature in a direction perpendicular to the initial stretching direction to obtain sufficient heat shrinkability in that direction.

Polypropylene-based resins are relatively easy to crystallize, and crystallization may progress too much during high-temperature stretching or heat treatment in the first stage, making it impossible to stretch at a relatively low temperature in the second stage. In order to suppress this crystallinity and make it easier to adjust the heat treatment conditions, it is preferable to set the crystallization heat (Δ) Ic) of the polypropylene resin in the range of 7 to /z (Hal / g). /sca1/ Inuai is more crystalline than i, making it difficult to adjust the heat treatment conditions to obtain a suitable degree of crystallinity, and if it is less than 7 cal/ji, it becomes sticky and has poor workability. The above range is preferable because the physical strength of the film is also reduced.Bo Polypropylene resins having a heat of crystallization within the above range are made by random copolymerization of propylene and other olefins, which have a relatively irregular molecular structure and are difficult to crystallize. Select from propylene-based polymers such as polymers or "C / s cal / j
It can be cleaved by mixing a propylene polymer larger than i with a propylene polymer smaller than 1Jl (2).

Furthermore, by adding preferably 70 to 59% by weight of petroleum resin and/or terpene resin, especially hydrogenated resins, to the propylene polymer, the crystallinity t- of the polypropylene resin can be lowered. da f 7~
/! ; It can also be adjusted to cab/i. If the amount of petroleum resin added is less than 10% by weight, the addition has no effect, and if it is more than 30% by weight, the resin becomes sticky and processability deteriorates, and the physical strength of the resulting film decreases. . Furthermore, the addition of petroleum resin has the effect of producing a film with less natural shrinkage. The melting point Tm of the polypropylene resin obtained in this case is approximately 130°C to ls5°C.

In this way, when using a polypropylene resin with a relatively small amount of crystallization heat, it is easy to obtain a film that shows a high shrinkage rate when heated at a relatively low temperature of 100°C, for example, and it is suitable for containers that do not tolerate high temperature heating. It is particularly advantageous when coated as a shrink label.

In addition, in order to improve the heat sealability, it may be laminated with a resin layer having excellent sealability such as an ionomer ethylene-vinyl acetate copolymer.

(Effect of the invention) The polypropylene film for shrinkable labels of the present invention is io
When immersed in hot water at 0°C for 3 minutes, the heat-shrinkable straw will move in one direction.
Due to its shrinkage characteristics of y-o% or more and 13% or less in the direction perpendicular to it, it is not only suitable as a shrinkable label that requires a large shrinkage rate only in the circumferential direction, but also has an i-refraction z (△n) in the film plane Since it is less than 0.0 /, it has well-balanced physical strength in both the vertical and horizontal directions, and can be suitably used as a shrinkable label to prevent glass bottles from scattering.

In the present invention, the in-plane birefringence of heat-shrinkable straw and film was measured as follows.

Heat shrinkage N: 10cm square film in hot water at 10oC
After soaking for a minute, the vertical and horizontal dimensions a and b'jt were measured and the heat shrinkage rate (X) was determined.

Birefringence Δn in the film plane: n: refraction in the longitudinal direction (progressing direction during manufacturing) of the film KA nB and refraction in the lateral direction inv' using an Atsube refractometer using the disodium D line
i was measured and calculated as △n =/np mv/.

Crystallization heat amount-C: Calculated from the area of the crystallization peak in a chart measured with a differential scanning calorimeter (manufactured by PerkinElmer) at a cooling rate of 1° C./min.

Melting point: Temperature (° C.) of melting peak when measured using a differential scanning calorimeter at a heating rate of 10° C./min (Example) Further explanation will be given below with reference to Examples. Prepare the following three types of resins A, B, O gold, A = & (1) parts by weight, B = 'I
Melt and mix in the ratio of O weight part and C = 20 weight part, crystallization heat ΔHC==9.7 cal/g, melting point Tm==
/ J g °C.

1t[WA7" Robylene-ethylene-random copolymer (melting point: tys"C1△Hc: /6.j cal
/y) Resin B Propylene-α olefin random copolymer (
Melting point: /F&'C1ΔHa: 7.5 cal/l) Resin C hydrogenated petroleum resin (Arakawa Chemical Co., Ltd. trade name Alcon p12!r) The above mixed pellet was melt-extruded from a T-die at about 200°C to form a stretched film. ! The thickness of the original film was adjusted so that the film thickness was 0μ.

Next, as shown in Table 1, this film material was prepared using Comparative Example J.
, & and Example 1 - iiO ℃ or / 3
! The film was heated to r°C and stretched in the take-off direction between λ stretching rolls having different circumferential speeds by a factor of S to 6 times.

Next, while maintaining these dimensions, as shown in Table 1, Comparative Example 3 and Example 1-da were heat-treated by contacting them with a heat-treating roll whose temperature was controlled to 130° C. for 60 seconds.

Further, the temperature was adjusted to 100° C., and the film was stretched 6 times in the transverse direction in a nine tenter.

The resulting film has a heat value when immersed in hot water at ioo°C for S minutes! ! (ratio) is Comparative Example 1-G #i vertical direction is O-
10%, the horizontal direction is Koj~u3'A, and Example 1-da has a vertical direction of 3~j%, and the horizontal direction is II j -! It was SX. Also, the in-plane birefringence Δn of the film is compared to ft
l/-da is o, o o s~0.0ノ! , Example 1-g was 0.00 ll-0,007.

The stretched film thus obtained was measured for the following measurement items, and the results are shown in Table 1.

Tensile strength: Ii! in the vertical and horizontal directions according to yis-xbyy- II was determined. CkQlC layer) Shrink finish: Heat seal the ends so that the larger side of the film shrinks in the circumferential direction, and cut the folded diameter ///, jw, length saw 5
Let it be a cylindrical label of N. Add this label to body diameter 1. g, jm
, total height/jKmm, B A one-way glass bottle with an inner diameter of 26 m is placed over a bottle preheated to 90°C, and the hot air temperature is 210°C.
The shrink tunnel width fl is 0 seconds.

Visually inspect the film condition of the obtained coated bottles. Those with noticeable defects such as waving or shrinkage on the top and bottom edges, or pockmarks on the film surface are marked as ×, and those with the above defects partially produced are marked as Δ and defects. Those with good adhesion to the entire surface were rated as ○.

Shatter prevention effect: The coated bottle has an internal pressure of ~r kg
/crl (gauge pressure) and sealed with carbonated water and tested three each in accordance with J.Eng. S-32301.

Q: Items with a scattering weight of 93% or more within a radius/m The scattering weight within the radius/m is 5~de! % of Δ Items with a scattering weight of 5% or less within a 1m radius And so.

Table 1 As is clear from Table 1, the lateral shrinkage rate is 'I 09
In Comparative Example 11, which had less than Fr, the surface after shrinkage was pockmarked, and in Comparative Example G, which had a longitudinal shrinkage rate of 0 or more than 15%, ripples appeared on the film end surface and the shrinkage appearance was poor. . Moreover, in Comparative Examples 1 to 3, in which the in-plane birefringence Δn of the film is larger than O8θl, the difference in longitudinal and lateral tensile strengths is large, and the scattering prevention effect is inferior or is somewhat omitted.

On the other hand, if the vertical shrinkage is 3 to 5 and 15% or less, and the horizontal shrinkage is 4 to 5 or more, υfurther,
Examples/%9 in which △n is 0.00q to 0.007 and 0.0 or less have excellent shrinkage finish when made into labels, have a well-balanced longitudinal and lateral tensile strength, and have a scattering prevention effect. It's also expensive.

Example 5. A Comparison fl15 Resins A and B used in Example 1-G and Comparative Example 1-G
, Of the process shown in Table 2, either Example 5 and B are melt-mixed in the proportions shown in Table 2 to form pellets, or as in Comparative Example S, resin A is used as it is and melt-extruded through a T-die at 200°C and stretched. The thickness was adjusted so that the final film thickness was 30μ, and an original film was formed. The melting point of these raw fabrics ('C
) and crystallization heat IJlc (cal/dθg) are as shown in Table 2.

Next, these film originals were heated to f/10°C and stretched 1 times in the take-off direction between stretching rolls of different jurisdictions,
Next, while maintaining these dimensions, the film was brought into contact with a heat treatment roll whose temperature was controlled to 130°C for 60 seconds, and further stretched in the transverse direction by Hirozo in a tenter whose temperature was controlled to 100°C.

The shrinkage percentage (%) and Δnl''i of the obtained film are shown in Table 1.

This film was evaluated for tensile strength, shrinkage finish, and anti-scattering effect, and the results are shown in the table below.

As is clear from Table 1, the amount of heat of crystallization (cal
/g) is /2.0%/0.9 and Examples S and 6 are smaller than 73, have a small crystallization tendency, obtain a sufficient transverse shrinkage rate, and have a good shrinkage finish. On the other hand, the heat of crystallization IAc (c
al/g) is/l,,! ;, and 13) Large O-Comparative example! Even when stretched under the same conditions as Examples R and &, the lateral shrinkage due to the progress of crystallization was 36%, which was smaller than Hiroshi 03, and the shrinkage finish was somewhat inferior.

Claims (3)

[Claims] (1) A biaxially stretched film made of a polypropylene resin, which has a heat shrinkage rate of 40% or more in one direction and 15% or less in a direction perpendicular to the same when immersed in hot water at 100°C for 5 minutes, and the in-plane birefringence (Δn) of the film is 0.
A polypropylene thread film for shrinkable labels having a molecular weight of 01 or less. (2) The crystallization heat of polypropylene resin is 7 to 15 c
The polypropylene film for shrinkable labels according to claim 1, which has an al/g. (3) Polypropylene resin is propylene polymer 95
~40% by weight and petroleum resin and/or terpene resin 5~
The polypropylene film for shrinkable labels according to claim 1, characterized in that it is a mixed resin consisting of 60% by weight.