JPS63113059A - Shrink packaging film - Google Patents

Abstract

PURPOSE:To obtain the titled film outstanding in low-temperature shrinkability, transparency, gloss, etc., by incorporating specified quantities of a hydrocarbon resin in a propylene copolymer containing specified amounts of a specific propylene-alpha-olefin copolymer followed by film-forming and drawing. CONSTITUTION:The objective film can be obtained by incorporating (A) 100pts. wt. of a propylene copolymer containing >=30wt% of a propylene-alpha-olefin copolymer which is made from either propylene and >=4C alpha-olefin (e.g., butene-1) or propylene, >=4C alpha-olefin and ethylene, and has the >=4C alpha-olefin content 8-35(pref. 10-30)mol%, ethylene content <=5(pref. <=3)mol% and cold xylene slubles 15-70(pref. 16-50)wt% with (B) 2-10pts.wt. of a hydrocarbon resin with a softening point >=110 deg.C (e.g., petroleum resin), followed by film-forming and drawing.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a shrink packaging film that has excellent low-temperature shrinkage properties, as well as excellent transparency, gloss, and anti-blocking properties.

<Prior art> Polyvinyl chloride, polyethylene, polypropylene, etc. are currently known as materials for shrink wrapping films, but each has advantages and disadvantages, and it is difficult to find one that satisfies all aspects. It has not been done.

Polyvinyl chloride has excellent transparency and low-temperature shrinkability, but it has poor low-temperature resistance and resistance to fused seals.
There are also food hygiene and disposal problems associated with plasticizers.

As for polyethylene, films made from linear low-density polyethylene and subjected to biaxial stretching are available.
It has poor transparency and low-temperature shrinkability that does not reach a satisfactory level.

On the other hand, examples of materials made from polypropylene include propylene-ethylene random copolymers in which ethylene is copolymerized to the extent of 3 to 5 wtχ, and propylene-ethylene-butene-ethylene copolymers in which ethylene is copolymerized to the extent of 3 to 3 wtχ and butene-1 is copolymerized to the extent of 3 to 10 wtχ. 1 ternary random copolymer (Japanese Patent Application Laid-open No. 1983-
A biaxially stretched film is known, but its low-temperature shrinkability is unsatisfactory.

If a propylene-ethylene random copolymer with a further increased ethylene content was used to improve this low-temperature shrinkability, the stretched film would lose its transparency and bleed and whiten over time. , undesirable because of poor blocking resistance. Japanese Patent Publication No. 49-996
No. 45 discloses that a film obtained by stretching a resin composition in which a propylene-ethylene random copolymer is blended with a petroleum resin has excellent low-temperature shrinkability. However, what is disclosed therein is a propylene-ethylene copolymer containing 5% ethylene and 2% petroleum resin.
According to the findings of the present inventor, the anti-blocking performance of the film is extremely poor. In an attempt to improve this blocking performance,
When the blending ratio of petroleum resin is reduced, the above 20w
In order to exhibit the same low-temperature shrinkage as the tχ mixture,
It becomes necessary to use a propylene-ethylene random copolymer with an ethylene content significantly increased from 5wtχ. However, as mentioned above, propylene-ethylene random copolymers containing considerably more ethylene than 5wtχ lose transparency when stretched, bleed white over time, and have poor blocking resistance. Yes, but the blending ratio of petroleum resin is small (but there are similar problems).

Next, among the same propylene copolymers, JP-A-53-
No. 113692 and JP-A-60-127133 each disclose a film obtained by stretching a specific propylene-α-olefin copolymer, and JP-A No. 57-24375.
The publication discloses a film obtained by stretching a composition of a propylene-butene-1 random copolymer and isotactic polypropylene. However, these also have the problem that if they try to achieve satisfactory low-temperature shrinkability, the film becomes extremely soft, resulting in insufficient cohesive strength after shrink wrapping, and some have poor blocking resistance.

<Problems to be Solved by the Invention> In view of the above-mentioned circumstances, the present inventors have developed a material that has significantly superior low-temperature shrinkability, excellent transparency, gloss, and anti-blocking properties.
In addition, we conducted extensive research in an effort to develop a shrink packaging film that was not excessively soft.

As a result, after forming a film, at least The present invention was completed based on the discovery that a shrink wrapping film having all of the above properties can be obtained by uniaxially stretching the film.

That is, the present invention provides a copolymer of propylene and an α-olefin having 4 or more carbon atoms, or a copolymer of propylene, an α-olefin having 4 or more carbon atoms, and ethylene, comprising: (1) an α-olefin having 4 or more carbon atoms in the copolymer; Content is 8
~35 mol% ■ Propylene containing 30% by weight or more of a propylene-α-olefin copolymer in which the ethylene content of the copolymer is 5 mol% or less ■ The cold xylene soluble portion of the copolymer is 15 to 70 wtχ This is a film for shrink packaging, characterized in that it is formed by stretching a resin composition in which 2 to 10 parts by weight of a hydrocarbon resin is disposed in a copolymer in at least one axis after film formation.

The first feature of the film obtained according to the present invention is that it has excellent low-temperature shrinkability, as well as excellent transparency, gloss, and blocking resistance. The second feature is that it is not excessively soft and has excellent binding strength after shrink wrapping.

The third feature is that compared to a film obtained from a single propylene copolymer, wrinkles at some corners are less likely to occur during shrink wrapping and the finish is more beautiful.

The present invention will be explained in detail below.

The propylene-α-olefin copolymer used in the present invention uses a so-called Ziegler-Natsuta catalyst, which is a known catalyst for stereoregular polymerization of α-olefins, as a catalyst system.
That is, transition metal compounds of Groups ■ to ■ of the periodic table and Groups 1 of the periodic table.
A compound consisting of an organic compound of a typical group metal and a third component such as an electron-donating compound is used, and the polymerization method is a solvent polymerization method in which polymerization is performed in a solvent or a gas phase polymerization method in which polymerization is performed in a gas phase. For example, it can be obtained by the method of polymerizing the copolymer (B) described in Japanese Patent Application No. 164505/1982.
Any propylene-α-olefin copolymer that satisfies the conditions specified below may be used.

The propylene-α-olefin copolymer used in the present invention uses a small amount of α-olefin having 4 or more carbon atoms or ethylene as a comonomer. As α-olefins having 4 or more carbon atoms, butene-1, pentene-1
, hexene-1,4-methyl-pentene-1, etc. alone or in combination. For example, when gas phase polymerization is carried out, butene-1 is preferred because it is difficult to liquefy and can maintain a high partial pressure.

The content of α-olefin having 4 or more carbon atoms in the propylene-α-olefin copolymer used in the present invention is 8 to 35 mol%, preferably 10 to 30 mol%. If the content of α-olefin having 4 or more carbon atoms falls below the lower limit, the resin composition obtained by blending the present propylene-α-olefin copolymer may become impossible to stretch at low temperatures, or even This is undesirable because low-temperature shrinkability deteriorates and the transparency of the film after stretching deteriorates. α with carbon number 4 or more
- If the olefin content exceeds the upper limit, the blocking resistance of the stretched film may deteriorate or the film may become excessively soft, which is not preferable.

The ethylene content of the propylene-α-olefin copolymer used in the present invention is 5 mol% or less, preferably 3 mol% or less. When the ethylene content exceeds the upper limit, the transparency of the film deteriorates over time and the blocking resistance deteriorates, which is not preferable.

The cold xylene soluble part (CXS) of the propylene-α-olefin copolymer used in the present invention is 15 to 70wtX1?
Ali, 16-50wtX is preferable. If cxs is below the lower limit of 8, the resin composition obtained by blending the present propylene-α-olefin copolymer may become impossible to stretch at low temperatures, and may have poor low-temperature shrinkage or poor stretching properties. This is not preferable because the transparency of the film deteriorates. CXS
If it exceeds the upper limit, the blocking resistance of the stretched film may deteriorate or the film may become excessively soft, which is not preferable.

The propylene copolymer used in the present invention can be obtained by blending the propylene-α-olefin copolymer described above and the propylene-random copolymer described below.

The propylene random copolymer mentioned here is a well-known crystalline ethylene-propylene random copolymer,
Alternatively, it is an ethylene-butene-1-propylene random terpolymer, etc., with a comonomer content of 1 to 15w.
It is from tz. Moreover, CXS is 15-t% or less. The blending ratio of the propylene-α-olefin copolymer is 30% by weight or more, preferably 40% by weight or more, and more preferably 50% by weight or more. The propylene
If the blending ratio of the α-olefin copolymer falls below the lower limit, the transparency of the stretched film will deteriorate unless the blending ratio of the hydrocarbon resin is increased. Even if the blending ratio of the hydrocarbon resin is increased, Even if the transparency of the film after stretching is improved, the blocking resistance of the film is undesirable.

The hydrocarbon resins used in the present invention include petroleum resins, terpene resins, cyclopentadiene resins, coumaron indene resins, and the like. Among these resins, those having no polar group or those having hydrogen added thereto to have a hydrogenation rate of 95% or more are preferred.

The softening point (ring and ball method) of the hydrocarbon resin used in the present invention is 1
Preferably, the temperature is 10°C or higher. If a material with a softening point of less than 110° C. is used, the resulting film will have poor blocking resistance, which is not preferred.

The resin composition used for film formation of the present invention is obtained by adding 2 to 10 parts by weight of the above hydrocarbon resin to the above propylene copolymer. If the blending ratio of the hydrocarbon resin is below the lower limit, the film may become too soft or the blocking resistance may deteriorate in order to achieve low-temperature shrinkability sufficient to meet the purpose of the present invention, which is not preferable. If the blending ratio of the hydrocarbon resin exceeds the upper limit, the blocking resistance of the film will deteriorate, which is not preferable.

The melt index (g/10 minutes) of the resin composition used for film formation of the present invention is preferably 0.5 to 50 g/10 minutes. If the melt index is below the lower limit, the processability will deteriorate, which is not preferable; if it exceeds the upper limit, the film's stretchability will deteriorate, which is not preferable.

In the present invention, the method for obtaining the resin composition includes:
0, which can be obtained by uniformly dispersing it by any known method.
Examples include extrusion melt blending method and Banbury blending method.

In the present invention, additives such as antistatic agents, antiblocking agents, lubricants, antifogging agents, stability agents, and nucleating agents can be added to the resin composition.

In the present invention, known processing methods such as the T-die casting method and the water-cooled inflation method can be employed as a method for forming the film. In addition, as a method for performing the stretching treatment, known uniaxial stretching methods such as roll stretching, roll rolling, and tenter horizontal uniaxial stretching, as well as known biaxial stretching methods such as tenter biaxial stretching and tubular biaxial stretching, are employed. can.

The stretching temperature ranges from room temperature to below the melting point of the copolymer, but in order to improve the low-temperature shrinkability of the obtained film, it is preferably as low as possible within a range that allows uniform stretching.
The stretching ratio is preferably 2 to 10 times. In this case, M
The stretching ratios of D (longitudinal direction) and TD (horizontal direction) do not necessarily need to be balanced, and can be arbitrarily selected depending on each application. Heat setting may also be performed. In addition, the data and evaluation in Examples and Comparative Examples were performed according to the following method.

(1) α-olefin content in copolymer It was determined from the mass balance during polymerization. Furthermore, the content of butene-1 was further determined using an infrared spectrophotometer using a conventional method based on characteristic absorption at 770 cm −1 . In addition, measurements using an infrared spectrophotometer are performed on propylene-butene-1 copolymer with "C-
A calibration curve was created and quantified based on quantitative values determined by NMR.

(2) Ethylene content in the copolymer measured using an infrared spectrophotometer at 732 cm” and 720 cm.
−' was determined by a conventional method from the characteristic absorption. In addition, in the measurement using an infrared spectrophotometer, a calibration curve was prepared using quantitative values determined by radiation measurement of an ethylene copolymer labeled with I4C, and the amount was determined.

(3) Cold xylene soluble portion (CX S) 5 g of polymer is dissolved in 500 ml of xylene, and then slowly cooled to room temperature. Then, the mixture was left in a bath at 20° C. for 4 hours, filtered, and the filtrate was concentrated, dried, and weighed.

(4) Melt index (Ml) Based on ASTM-D 1238 and t$ (5) Haze value (Haze) Based on ASTM-D1003 (6) Young's modulus of film Based on ASTM-D882 However, test piece shape: 20 x 120 strip chuck opening M: 50 mm Pulling speed: 5 mm/min (7) Heat shrinkage rate A 5 cm square film specimen is placed in a glycerin bath at a predetermined temperature.
Measure the shrinkage rate of MD and TD when immersed for 0 seconds.

(8) Blocking 2 pieces of film 5 cm x 10 cm square
Shift them by cm and stack them, and add 10 kg to the overlapped 5 cm square part.
Conditioning was carried out at 40°C for 24 hours with the load applied.

After removing the load and fully adjusting the temperature to 23℃,
The shear peel strength (g) is determined at a tensile rate of mm/min and is expressed as the value.

Hereinafter, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited to the Examples unless it exceeds the gist thereof.

<Example> Example 1 Propylene copolymer consisting of propylene-α-olefin copolymer (butene-1 content 20.1 mol%, CXS 23.0g/tχ, melt index 3.0g/10 min) Hydrogenated petroleum resin (Arayo Kagaku Alcon P-125, softening point (ring and ball method) 125°C) per 100 parts by weight of the combined
5 parts by weight of was added, and 1 part of BH70 as a stabilizer, 0.4 part of finely powdered aluminosilicate as an anti-blocking agent, and 0.2 part of erucic acid amide as a lubricant were melt-blended using a 65Φ extractor. A resin composition was obtained. About this resin composition, 4
A 00 μm sheet was obtained, and a 90 square sheet was taken from it to obtain a biaxially stretched film under the following conditions.

Stretching machine: Tabletop biaxial stretching machine manufactured by Toyo Seiki Temperature = 70°C Preheating time: 3 minutes Stretching ratio: Mn 2 times, TD5 = times Stretching speed: 15 m/min The physical properties of the approximately 15μ thick film obtained above were Shown in the table. The physical properties of the film are shown as average values of MD and TD.

This biaxially stretched film has excellent low-temperature shrinkability, good transparency, and pro-knocking properties within the allowable range, and is not an excessively soft film, making it an excellent film for shrink packaging. Met.

Example 2 Propylene-α-olefin copolymer (butene-1 content 12.5 mol%, ethylene content 2.5 mol%, C
X526.5gatχ, melt index 3.8g71
A resin composition was obtained in the same manner as in Example 1 except that 4 parts by weight of a hydrogenated petroleum resin (Alcon P-125) was added to 100 parts by weight of a propylene copolymer consisting of a single propylene copolymer. This resin composition was treated under the same conditions as Example 1.
An axially stretched film was obtained.

The physical properties of the film are shown in Table 1. Like the film of Example 1, this biaxially stretched film was excellent as a film for shrink wrapping.

Example 3 100 parts by weight of propylene copolymer consisting solely of propylene-α-olefin copolymer (butene-1 content 15.6 mol%, CX S 19.1g/tχ, melt index 3.5 g/10 min) A resin composition was obtained in the same manner as in Example 1, except that 6 parts by weight of hydrogenated petroleum resin (Alcon P-125) was added thereto. A biaxially stretched film was obtained from this resin composition under the same conditions as in Example 1. The physical properties of the film are shown in Table 1. Like the film of Example 1, this biaxially stretched film was excellent as a film for shrink wrapping.

Example 4 As a propylene-α-olefin copolymer, Example 1
70% by weight of the same material and 30% by weight of propylene-random copolymer (Sumitomo Chemical Co., Ltd. Noblen@RW160, ethylene content 5.OwtX, CX S4.3g/10min, melt index 8.2g/10min) A resin composition was obtained in the same manner as in Example 1 except that 5 parts by weight of a hydrogenated petroleum resin (Alcon P-125) was added to 100 parts by weight of a propylene copolymer consisting of: A biaxially stretched film was obtained from this resin composition under the same conditions as in Example 1. The physical properties of the film are shown in Table 1. Like the film of Example 1, this biaxially stretched film was excellent as a film for shrink wrapping.

Example 5 40% by weight of propylene-α-olefin copolymer (butene-1 content 25.1 mol%, CX S35.1g/tχ, melt index 2.8 g/10 min) and propylene-random copolymer 8 parts by weight of hydrogenated petroleum resin (Alcon P=125) were added to 100 parts by weight of a propylene copolymer consisting of 60% by weight (Noblen'I RW160 manufactured by Sumitomo Chemical ■), and the rest was as in Example 1. A resin composition was obtained in the same manner as above. Regarding this resin composition,
A biaxially stretched film was obtained under the same conditions as in Example 1. The physical properties of the film are shown in Table 1. Like the film of Example 1, this biaxially stretched film was excellent as a film for shrink wrapping.

Example 6 As a propylene-α-olefin copolymer, Example 2
and propylene-random copolymer (Base powder for Sumitomo Chemical Special Noblen@WF893R, ethylene content 2.0 inLχ, butene-1 content 5.1kgtχ, CX53.8kg) 5 parts by weight of a hydrogenated petroleum resin (Alcon P-125) was added to 100 parts by weight of a propylene copolymer consisting of 20% by weight (tχ, melt index 5.8 g/10 min), and the rest was as described in Example A biaxially stretched film was obtained under the same conditions as in Example 1.

The physical properties of the film are shown in Table 1. Like the film of Example 1, this biaxially stretched film was excellent as a film for shrink wrapping.

Example 7 In Example 1, a biaxial test was carried out under the same conditions except that hydrogenated terpene resin (manufactured by Cheap Oil Co., Ltd., Clearon P-125 softening point (ring and ball method) 125°C) was used instead of hydrogenated petroleum resin. A stretched film was obtained. The physical properties of the film are shown in Table 1. Like the film of Example 1, this biaxially stretched film was excellent as a film for shrink wrapping.

Comparative Example 1 A biaxially stretched film was obtained under the same conditions as in Example 1 using only the propylene-α-olefin copolymer used in Example 1. However, during biaxial stretching, the stretching temperature is 7
At 0°C, uniform stretching is difficult, and 80°C is the lowest possible stretching temperature, and the stretching was carried out at 80°C. The physical properties of the film are shown in Table 1, and this biaxially stretched film has the following properties:
Although it was soft, its low-temperature shrinkability was not very good.

Comparative Example 2 A biaxially stretched film was obtained under the same conditions as in Example 1 using only the propylene-α-olefin copolymer used in Example 2. However, during biaxial stretching, the stretching temperature is 7
At 0°C, it is difficult to stretch uniformly, and 80°C is the minimum stretching temperature that can be stretched.Table 1 shows the physical properties of the film that was stretched at 80°C. The shrinkability was not that good.

Comparative Example 3 Based on 100 parts by weight of a propylene copolymer consisting solely of propylene-α-olefin copolymer (butene-1 content 15.1 mol%, CX59.4g/tχ, melt index 4.5g/10 min) Hydrogenated petroleum resin (Alcon P
A resin composition was obtained in the same manner as in Example 1 except that 6 parts by weight of -125) were added. A biaxially stretched film was obtained from this resin composition under the same conditions as in Example 1 except that the stretching temperature was 90°C. In addition, if the stretching temperature is less than 90°C,
Uniform stretching was not possible. The physical properties of the film are shown in Table 1, but this biaxially stretched film had poor low-temperature shrinkability.

Comparative Example 4 A biaxially stretched film was obtained in the same manner as in Example 4 except that the hydrogenated petroleum resin was not added. However, during biaxial stretching, it is difficult to achieve uniform stretching at a stretching temperature of 70°C, and 80°C is the lowest possible stretching temperature, and the stretching temperature was 80°C. The physical properties of the film are shown in Table 1. Although this biaxially stretched film was soft, its low-temperature shrinkability was not so good.

Comparative Example 5 A biaxially stretched film was obtained under the same conditions as in Example 1 using only the propylene-α-olefin copolymer used in Example 5. The physical properties of the film are shown in Table 1. Although this biaxially stretched film had good low-temperature shrinkability, it was excessively soft and had somewhat poor blocking.

Comparative Example 6 Hydrogenated petroleum resin (Alcon P-115, softening point (ring and ball method): 11
A resin composition was obtained in the same manner as in Example 1 except that 20 parts by weight of 5°C) were added. A biaxially stretched film was obtained from this resin composition under the same conditions as in Example 1. The physical properties of the film are shown in Table 1, and this biaxially stretched film has the following properties:
The blocking resistance was extremely poor.

Comparative Example 7 5 parts by weight of hydrogenated petroleum resin (Alcon P-125) was added to 100 parts by weight of propylene-random copolymer (Noblen@RW160 manufactured by Sumitomo Chemical ■), and the rest was the same as in Example 1. A resin composition was obtained. A biaxially stretched film was obtained from this resin composition under the same conditions as in Example 1, except that the stretching temperature was 100°C. Note that uniform stretching was not possible at a stretching temperature of less than 90°C. The physical properties of the film are shown in Table 1, and this biaxially stretched film had poor low-temperature shrinkability and somewhat poor transparency.

Comparative Example 8 As a propylene-α-olefin copolymer, Example 1
Propylene copolymer 100 consisting solely of the same as
8 parts by weight of hydrogenated petroleum resin (Alcon P-70, softening point (ring and ball method) 70°C) were added to the parts by weight, and the rest were as follows:
A resin composition was obtained in the same manner as in Example 1. A biaxially stretched film was obtained from this resin composition under the same conditions as in Example 1. The physical properties of the film are shown in Table 1, and this biaxially stretched film had poor blocking resistance.

<Effects of the Invention> The shrink packaging film produced by the method of the present invention has not only excellent low-temperature shrinkability but also excellent transparency, gloss, and blocking resistance.

In addition, there were few wrinkles in the corners during shrink wrapping, the finish was clean, and the binding strength after wrapping was good. Furthermore, unlike polyvinyl chloride, it does not have the disposal problems and can be manufactured at low cost, so it has extremely great practical value.

Claims (2)

[Claims] (1) A copolymer of propylene and an α-olefin having 4 or more carbon atoms, or a copolymer of propylene, an α-olefin having 4 or more carbon atoms, and ethylene, [1] The copolymer contains an α-olefin having 4 or more carbon atoms. The amount is 8 to 35 mol% [2] The ethylene content of the copolymer is 5 mol% or less [3]
A propylene copolymer containing 30% by weight or more of a propylene-α-olefin copolymer in which the cold xylene soluble portion of the copolymer is 15 to 70% by weight, and a hydrocarbon resin of 2 to 10% by weight.
A film for shrink packaging, characterized in that a resin composition containing parts by weight is subjected to a stretching treatment in at least one axis after film formation. (2) The shrink wrapping film according to claim 1, wherein the α-olefin having 4 or more carbon atoms is butene-1.