JPS61112627A - Low-temperature heat-shrink film - Google Patents

Abstract

PURPOSE:To increase thermal contraction coefficient and contraction stress of a low-temperature heat-shrink film as well as improve its transparency by forming a low-density ehtylene-alpha-olefin copolymer having two kinds of side chains with 1-10C alkyls. CONSTITUTION:An ethylene-alpha-olefin copolymer (A) having a density of 0.915-0.935g/cm<4> and side chains with 1-10C 3-30 alkyl group per 1,000 carbon atoms in the main chain is mixed with an ethylene-alpha-olefin copolymer (B) having a density of 0.890-0.910g/cm<3> and side chains with 10-60 alkyl group per 1,000 carbon atoms in the main chain. The proportion of the copolymer (B) is 10-60wt% on the basis of sum total of the copolymers (A) and (B). The mixture is melted and molded to obtain a film having improved transparency of a haze value of 5% or less, a thermal contraction coefficient (in m direction at 90 deg.C) of 30% or more, and a contraction stress of 300g/mm<2> or more, showing high thermal contraction coefficientry and high contraction stress.

Description

DETAILED DESCRIPTION OF THE INVENTION [1] Purpose of the invention (industrial application field) The present invention has high heat shrinkability and shrinkage stress at low temperatures, excellent transparency, and good low-temperature heat sealability. Concerning low temperature thermoshrinkable film. More specifically, it relates to a low-temperature shrinkable film formed by forming a composition containing 21 kinds of side chains, which has large heat-shrinkability and shrinkage stress, excellent transparency, and is also suitable for low-temperature heat sealing. The object of the present invention is to provide a low-temperature heat-shrinkable film with good properties.

CI+) Background of the invention (prior art) Conventional heat-shrinkable films, such as polyvinyl chloride and polypropylene, start shrinking at around 100"C, and shrink by 50-70% at about 130"C. However, in general, high-pressure low-density polyethylene (
LDPE) resin, and the melting point of this resin is 100°C to θ°C. Therefore, it is impossible to create a large shrinkage stress fq at the above-mentioned shrinkage temperature of around 130°C, and even if shrink-wrapped, it lacks tension. There was a drawback.

In addition, as a low-temperature heat-shrinkable film, the above-mentioned high-pressure method LD
Attempts have also been made to slightly stretch PE to a low magnification of 41 to give it low-temperature shrinkability. However, general high pressure LDPE
Since it has many long chain branches, its stretchability is extremely poor, and as a result, stretch breakage occurs immediately, making it difficult to uniformly stretch the film at a high magnification. Therefore, since high-pressure LDPE is stretched non-uniformly at a low magnification (2 to 2.5 times), transparency, which is a very necessary element for packaging films, is also affected by the haze value (cloudiness). It was around 10%, which was not favorable.

(m) Structure of the Invention Based on the above, the present inventors have conducted various searches to obtain a low-temperature heat-shrinkable film in which these drawbacks are improved (Result (A))! degree is 0.915 to 0.935g/c
There is rn'te.

and a copolymer (A) of ethylene and α-olefin in which the number of alkyl groups in the side chain having substantially 1 to 10 carbon atoms is 3 to 30 per 101) 0 carbon atoms in the main chain.

(B) Density is 0.890 to 0.910g/c
It is m'.

and a composition consisting of a copolymer (B) of ethyl μ/ and α-olefin, in which the number of alkyl groups in the side chain having 1 to 10 carbon atoms is 10 to 60 per 1000 carbon atoms in the main chain. It is a heat-shrinkable film formed by molding a product, and the composition ratio of the copolymer (B) of ethylene and α-olefin in the composition is IO to 60% by weight, and the haze value of this film is 5% or less and 90″
A low-temperature heat-shrinkable film having a heat yield* in the M direction at a temperature of C of 30% or more and a shrinkage stress of 300/g mm'' or more.

It has better ripening properties and shrinkage properties than the olefin-based Φ2-combined film, has better transparency, and has better low-temperature heat-sealability than the olefin-based Φ2-combined film. The present invention was achieved by discovering that

(rV) Detailed description of the invention (A) Co-ffi combination of ethylene and α-olefin (A
) The density of the copolymer (A) of ethylene and α-olefin used in the present invention is 0.915 to 935 g/c.
m"'r, especially 0.915~0.930g/c
If a copolymer (A) of ethylene and α-olefin in which rn' is preferably used has a T: degree of less than 0.915 g/C, the shrinkage of the resulting heat-shrinkable film Stress becomes weaker. On the other hand, 0.9351/c
If a copolymer with more than 100 carbon atoms in the main chain of this copolymer is used, the transparency of the film will deteriorate.
The alkyl group in the side chain having 1 to θ carbon atoms per 0 is 3 to θ.
30, preferably 3 to 15, especially 5 to 1
5 bonds are preferred. If a copolymer of ethylene and α-olefin having 1000 carbon atoms in the main chain and less than 3 alkyl groups in the side chain having 1 to 10 carbon atoms is used, the low-temperature shrinkability of the film will deteriorate. On the other hand, when a copolymer of ethylene and α-olefin containing more than 30 molecules is used, it is difficult to form and process a film.

The melt index of the copolymer that is difficult to mold and process (measured according to JIS K-7280 at a temperature of 190°C and a load of 2.18, hereinafter rN, 1.J) Normally 0.05-50g/10
It's a minute.

0, 1-20g/10 minutes is preferable*L<, 0.1-10
g/10 minutes is preferred. M, 1. is 0. '05g/
If a copolymer of ethylene and α-olefin is used for less than 10 minutes, the wire crosstalk and film formability described later will be improved.

On the other hand, if an ethylene copolymer exceeding 50 g/10 minutes is used, the resulting film will have low mechanical strength.

(Japanese) Copolymer of ethylene and α-olefin (B) Furthermore, the density of the copolymer of ethylene and α-olefin (B) used in the present invention is 0.8!10 to 0.
．． ! ]lOg/crn', especially 0.89
5 L O, 910 g/cm' is suitable and 6.1 degrees is 0.8908/cm''.Using a copolymer of unskinned ethylene and α-olefin reduces the shrinkage stress of the resulting film. On the other hand, if an ethylene copolymer with a copolymer density exceeding 0.9101/am'' is used, the low-temperature sealing properties of the obtained film will deteriorate. Further, the number of alkyl groups in the side chain is 10 to 60 per 1000 carbon atoms in the main chain of this copolymer, and 15 to 50 (preferably those of III, particularly 2
A number of 5 to 50 is suitable. 100 carbon atoms in the main chain
If an ethylene copolymer with less than 10 alkyl groups in the side chain is used, the resulting film will have poor low-temperature sealing properties, while if an ethylene copolymer with more than 60 alkyl groups is used, the resulting film will shrink. Insufficient stress. Furthermore, in the copolymer (B) of ethylene and α-olefin, (1) is generally 0.05 to 50
g/10 minutes, preferably 0.1 to 20 g/10 minutes, most preferably 0.1 to IO g/10 minutes.

These copolymers of ethylene and α-olefin (A)
and copolymers of ethylene and α-olefins (CB) are copolymers of ethylene and charcoal, K h of at most 12 α-olefins (e.g., propylene/buteno-1, hexene-14-methylepeno-1, octene-1). 1) and can be produced by copolymerizing using the catalyst system described below.

In these copolymers, “°substantially the number of carbon atoms is 1
~10 (1! The side chain alkyl group ゛° of i means that the alkyl group in the side chain mainly has i\ prime number of 1 to 10, and there is a very slight side chain having 11 or more carbon atoms. It may have an alkyl group of

The catalyst systems used to produce these copolymers of ethylene and α-olefins are so-called Ziegler-Natsuta catalysts, which contain transition metal compounds (e.g. titanium-containing compounds) or supports (e.g. magnenium compounds) as the main catalyst. It is obtained by using an organometallic compound (for example, an organoaluminum compound) as a cocatalyst on a carrier-supported catalyst obtained by supporting a transition metal compound on a carrier-supported catalyst (eg, a treated product thereof). Both of these copolymers are produced by slurry polymerization or solution polymerization.

It can be manufactured by any process such as gas phase polymerization method. 11! The method of construction is well known. Furthermore, these copolymers are widely produced industrially and used in a wide variety of fields.

(C) Composition ratio In the composition for producing the low temperature heat shrinkable film of the present invention, ethylene, α-olefin and copolymer (A)
The composition ratio of the copolymer (B) of ethylene and α-olefin in the total amount of copolymer (B) of ethylene and α-olefin is 10 to 60% by weight, and 15 to 60% by weight.
It is preferably 60% by weight, particularly preferably 15 to 50% by weight. If the composition ratio of the copolymer (B) of ethylene and α-olefin in this composition is less than 10% by weight,
When producing a film from the composition, the moldability becomes poor. On the other hand, if it exceeds 60% by weight, the resulting film will have insufficient shrinkage stress.

(D) Production of composition To produce the composition of the present invention, the above-mentioned ethylene and α-
In this composition, the copolymer with olefin (A) and the copolymer with ethylene and α-olefin (8) may be uniformly blended within the above composition ratio (blending ratio). In manufacturing, all the components may be mixed at the same time. A part of one component may be mixed in advance to produce a so-called masterbatch, and this masterbatch and the remaining components are mixed to achieve the above-mentioned mixing ratio. The composition may be manufactured in such a manner that each of the AII components may be used alone, or two or more types may be used in combination.

The composition of the present invention may be composed of the copolymer of ethylene and α-olefin (A) and the copolymer of ethylene and α-olefin (B). Stabilizer against oxygen, heat and ultraviolet rays, and metal deterioration inhibitor commonly used in the field of polymers.

Additives such as flame retardants, colorants, property improvers, antistatic agents, lubricants, processability improvers, and tack improvers do not impair the properties of the composition obtained according to the present invention. It may be blended as long as it is within the range.

To produce this composition, triblending may be performed using a 3R mixer such as the Henschel mixer, which is commonly used in the olefin polymer industry (Banbury mixer, Nigoo).

It can also be produced by melt-kneading using a mixer such as a roll mill and a single-screw extruder. At this time, a more uniform composition can be obtained by triblending in advance and further melt-kneading the resulting mixture.

(E) Production of film To produce the film of the present invention using the composition produced as described above, air is blown around the circumference of an extruded tube, and then a tubular film is formed while cooling naturally. Although it is possible to use the conventional air-cooled inflation method, it is better to use a method that can provide sufficient cooling.
Films with further improved transparency can be obtained by employing known quenching methods such as the water-cooled inflation method in which the tube is cooled by direct contact with water, and the chill roll method using a cooling roll (chill roll). be able to.

The stretching temperature in producing the low-temperature heat shrinkable film of the present invention is not particularly limited, but is around 90°C, preferably 80 to 1
Exhibits excellent low temperature heat shrinkage properties at 00°C.

(V) Effects of the invention The low-temperature heat-shrinkable film obtained without the invention exhibits the following effects, including the composition used.

By using the composition produced as described above,
It is possible to increase the stretching ratio of the film to 3.0 to 6.0 times, and by uniform stretching, a uniform film with an even thickness can be obtained, and the stretching ratio can be increased to 3 times or more. Since this is possible, the haze value (A5
A film was obtained in which the transparency of the film was sharply improved, with TII D-1003) being 5% or less. Also, M at 90°C
The directional heat loss M rate (JIS Z-1709) is 30% or more, and the shrinkage stress is 300 g/mm' or more, so it has large heat shrinkability and shrinkage stress. In this case, if the stretching ratio is less than 3.0 times, there will be problems such as large stretching unevenness and uneven thickness, and the transparency will also be poor, and if the stretching ratio exceeds 8.0 times, stretching breakage will easily occur, resulting in stable production. Therefore, it is difficult to obtain a film having the desired film properties of the present invention.

Conventionally, films with excellent transparency and low-temperature shrinkability have been made of polyvinyl chloride (PVC), stretched polypropylene (PP), etc., instead of polyethylene resins.

However, the film of the present invention retains the excellent properties of polyethylene (low-temperature heat sealability, flexibility, food safety, etc.), has excellent transparency comparable to PvC or stretched PP film, and has excellent thermal properties. It is a film with shrinkage properties.

(l Examples and Comparative Examples) The present invention will be explained in more detail with reference to Examples below.

In addition, in the examples and comparative examples, haze (Haze)
) was measured according to ASTM D-1003. The heat shrinkage rate is 90% according to JIS Z-1709.
℃ and 100℃. In addition, the heat sealability was measured using tanzak-shaped test pieces (width: 15 layers).
When a test piece was cut out and sealed under conditions of a sealing pressure of 2 kg/crn' and a sealing time of 1 second, it was peeled in a 180 degree direction at a rate of 300 seconds/minute using a tensile test piece. When the heat sealing strength exceeds 1.5kx, the shrinkage stress will be reduced to 3 per minute using Tensilon (temperature rise/fall stacking).
The shrinkage stress in the M direction was measured at 30° C. while raising the humidity.

In addition, the copolymer (A) of ethylene and α-olefin and the copolymer of ethylene and α-olefin used in the Examples and Comparative Examples
- The physical properties of the copolymer with olefin (B) and other olefin polymers are shown below.

[(A) jtir<　coalescence of ethylene and α-olefin (A)]

As a copolymer (A) of ethylene and α-olefin,
A copolymer of ethylene and butene-1 (M, r,
0.8g/10min, hereinafter rPE(+) J Toyun 6
) was used.

[(B) Copolymer CB of ethylene and α-olefin)]

As a copolymer (B) of ethylene and α-olefin,
The density is 0.890 g/cm'', and the average number of ethyl groups is 4 g!4 chains per 1000 carbon atoms in the main chain.
A copolymer of ethylene and butene-1 having 5 (M,
l 1. 0g/10 minutes, hereinafter referred to as rPE(2)] was used.

[(C) Other resin polymers]

As other olefin polymers, by the so-called high pressure method! 11! Low-density ethylene homopolymer (N, 1
．． 3.1 g/10 minutes, under H rpi (3) J): 亲) was used.

Examples 1-3. Comparative Examples 1 to 4 Table 1 shows PE (1) 8 and P in which blend j- is 1ζ
E(2) was preliminarily prepared and tri-plated for 5 minutes using a shell mixer. Each of the obtained mixtures was mixed while melting using a twin-screw extruder (diameter 50Ii11, resin temperature 160°C) to produce pellets (compositions) (Examples 1 to 3 Comparative Examples 3 and 4)
).

Films were produced from each of the compositions and PE (3) obtained as described above by an air-cooling inflation method while sufficiently cooling each composition or PK (3). Each obtained film was pulled out at a film withdrawal speed of 1
A stretched film (thickness: 30 microns, @
6QQmm) was manufactured. Table 2 shows the physical properties of each film obtained.

(The following is a blank space) From the results of the Examples and Comparative Examples shown in Table 1 and above, it is clear that the film obtained by the present invention not only has excellent heat shrinkability at relatively low temperatures, but also has good transparency properties. Furthermore, it is clear that the heat/heat resistance at low temperatures is also excellent.

Patent issued immediately by Showa Denko Co., Ltd. Representative Patent Attorney Sei Kikuchi

Claims (1)

[Claims] (A) Density is 0.915 to 0.935 g/cm^3
and a copolymer (A) of ethylene and α-olefin in which the number of alkyl groups in the side chain having 1 to 10 carbon atoms is 3 to 30 per 1000 carbon atoms in the main chain, and (B) Density is 0.890 to 0.910g/cm^3
and a copolymer (B) of ethylene and α-olefin in which the number of alkyl groups in the side chain having 1 to 10 carbon atoms is 10 to 60 per 1000 carbon atoms in the main chain, It is a heat-shrinkable film formed by molding a composition, the composition ratio of the copolymer (B) of ethylene and α-olefin in the composition is 10 to 50% by weight, and the haze of this film is The value is less than 5% and at 90℃
The thermal contraction rate in the M direction at a temperature of is 30% or more,
A low-temperature shrinkable film with a shrinkage stress of 300 g/mm^2 or more.