JPH0649351B2 - Heat shrinkable film - Google Patents

Description

TECHNICAL FIELD The present invention relates to a film having excellent heat resistance and good shrinkability. More specifically, it relates to a heat-shrinkable film comprising a foamed layer and a propylene-based copolymer layer on one or both sides of which is unfoamed.

[Conventional technology]

The conventional heat-shrinkable film is characterized in that it usually starts shrinking at 80 to 100 ° C. and exhibits a large shrinkage ratio of 30% or more at about 120 to 130 ° C. However, in this film, the raw materials generally used as the raw material of the film are polyvinyl chloride (PVC), polystyrene (PS), low density polyethylene (LD
Since it is a resin whose melting temperature is less than 120 ° C such as PE), it could not withstand high temperature treatment such as retort sterilization.

On the other hand, a heat-shrinkable film using a polypropylene resin having good heat resistance is also generally used, but this film requires a high temperature of 150 ° C. or higher to obtain a heat shrinkage ratio of 30% or higher. Since the film is a polypropylene resin alone (not a composition), it has poor buffering properties and heat resistance. In particular, as a film that shrinks as a label for bottles, special containers, etc., a film having heat resistance, cushioning properties, and heat insulating properties is demanded.

From these facts, the present inventors partially have not only heat resistance capable of withstanding heat sterilization, but also good buffering properties, and also having a large heat shrinkability of 30% or more at a temperature of 140 ° C. Various searches were conducted to obtain a heat-resistant shrink film. As a result, (A) 50 to 90% by weight of an ethylene-propylene block copolymer having an ethylene content of 3 to 20% by weight and
(B) A heat-resistant shrinkable film comprising a composition of 50 to 10% by weight of an ethylene-propylene random copolymer having an ethylene content of 2 to 15% by weight and having an expansion ratio of 3.0 times or less. (Japanese Patent Application No. 61-208).

However, when photographic printing or printing of a precise pattern is printed on the surface of the film, it is not always satisfactory.

[Problems to be solved by the invention]

From the above, the present invention not only has a heat resistance that can sufficiently withstand a film without these defects (problems), that is, when it is heated and sterilized at a temperature of 120 ° C. for 30 minutes, 140 25 at a temperature of ℃
% Heat shrinkage, and when printed on the surface, the finish is very good, and it is possible to print excellent images such as photo prints and precise designs, especially for bottles and special containers. The purpose is to obtain a film having a buffer property as a label.

[Means and Actions for Solving Problems]

According to the present invention, the problem is a heat-shrinkable film comprising a foam layer and an unfoamed propylene polymer layer laminated on one side or both sides of the foam layer, wherein the foam layer (A) ethylene Ethylene with a copolymerization ratio of 3.0 to 20% by weight
The foam layer comprises a composition in which 50 to 90% by weight of a propylene block copolymer and (B) an ethylene-propylene random copolymer in which the copolymerization ratio of ethylene is 2.0 to 15% by weight is 50 to 10% by weight. The heat-shrinkable film, which has a foaming ratio of 10 times or less, can be solved. Hereinafter, the present invention will be specifically described.

(A) Ethylene-Propylene Block Copolymer The ethylene copolymerization ratio of the ethylene-propylene block copolymer used in the present invention is 3.0 to 20% by weight.
And preferably from 3.0 to 18% by weight, particularly from 3.0 to
15% by weight is preferred. The ethylene copolymerization ratio of this ethylene-propylene block copolymer is 3.0% by weight.
When it is less than 1, the foaming uniformity of the resulting composition is not good.
On the other hand, if it exceeds 20% by weight, the Young's modulus of the film is low, and the waist becomes weak, which is not preferable.

This block copolymer is industrially produced by copolymerizing propylene and ethylene using a stereoregular catalyst (so-called Ziegler-Natta catalyst) or by combining this copolymerization and propylene homopolymerization in two or more stages. It is widely used, and its manufacturing method and physical properties are well known.

(B) Ethylene-Propylene Random Copolymer Further, the ethylene copolymerization ratio of the ethylene-propylene random copolymer used in the present invention is 2.0 to 1
It is 5% by weight, preferably 3.0 to 15% by weight, and particularly preferably 3.0 to 12% by weight. This ethylene
When the ethylene copolymerization ratio of the propylene random copolymer is less than 2.0% by weight, not only the heat sealability is poor, but also the heat shrinkability is poor. On the other hand, if it exceeds 15% by weight, the heat resistance is poor.

Also in the case of the ethylene-propylene block copolymer, even in the case of this ethylene-propylene random copolymer,
The melt flow index (measured according to JIS K7210 under the condition of 14 and hereinafter referred to as "MFR") is usually 0.1 to 20 g / 10 minutes, and 0.5 to 20 g / 10.
Min is preferable, and 1.0 to 15 g / 10 min is particularly preferable. If the MFR is less than 0.1 g / 10 minutes, foam molding becomes difficult. On the other hand, when it exceeds 20 g / 10 minutes, the strength of the obtained film decreases and it becomes difficult to uniformly control the foaming state.

(C) Composition Ratio The composition ratio of the ethylene-propylene block copolymer in the composition of the present invention is 50 to 90% by weight (that is,
The composition ratio of the ethylene-propylene random copolymer is 5
0 to 10% by weight), preferably 50 to 85% by weight, and particularly preferably 55 to 85% by weight. When the composition ratio of the ethylene-propylene block copolymer in the composition is less than 50% by weight, the Young's modulus of the obtained film is small and the stiffness is lowered. On the other hand, if it exceeds 90% by weight, the shrinkability and sealing property of the obtained composition are not improved.

(D) Production of Composition In producing the composition of the present invention, a chemical foaming agent that is well known in the field of propylene-based resins is added. The compounding ratio (composition ratio) of this chemical foaming agent is the above-mentioned ethylene-propylene block copolymer and ethylene-
It is generally 0.1 to 1.5% by weight (preferably 0.1 to 1.2% by weight) based on the total amount of the propylene random copolymer.

The composition of the present invention can be obtained by uniformly blending the ethylene-propylene block copolymer, the ethylene-propylene random copolymer and the chemical foaming agent within the range of the above composition ratio. In this case, additives such as stabilizers for oxygen, heat and ultraviolet rays, lubricants, plasticizers and antistatic agents which are generally used in the field of olefin resins are used within a range that does not essentially change the characteristics of the shrink film of the present invention. You may mix in.

As a mixing method, a method of dry blending using a mixer such as a Henschel mixer and a tumbler that are commonly used in the field of olefin resins can be adopted.

(E) Propylene-based polymer The propylene-based polymer used for producing the unfoamed propylene-based polymer layer constituting the film of the present invention may be a propylene homopolymer, which produces the above composition. Either the ethylene-propylene block copolymer or the ethylene-propylene random copolymer used for the purpose may be used.

In producing the propylene-based polymer layer, only one of these polymers may be used, or two or more of them may be used in combination. Further, an ethylene-propylene copolymer rubber which is generally used or a multi-component copolymer rubber containing ethylene propylene as a main component may be blended with these polymers. Further, the copolymerization ratio of propylene is 55 to 75% by weight.
You may further mix the ethylene-propylene random copolymer which is. When the rubber is compounded, its composition ratio is at most 20% by weight. When the random copolymer is blended, its composition ratio is at most 25% by weight. Further, when the rubber and the random copolymer are blended, the composition ratio of them is 30% by weight at the maximum.

In producing the propylene-based polymer layer of the present invention, the additive used for producing the above-mentioned composition is added to the propylene-based polymer or blend within a range that does not substantially change the properties of the layer. You may let me.

(F) Production of heat-shrinkable film The heat-shrinkable film of the present invention is produced by a molding method such as an inflation method using a coextrusion molding machine generally used in the field of propylene-based resins, a T-die method or the like. A co-extrusion molding of a propylene-based polymer (including a compound) on both sides or one side of the foamed layer consisting of and a film of the laminated film is formed and stretched by using a heating roll or the like. be able to. When only the chemical foaming agent is used in the molding of the foamed film as described above, the expansion ratio is 3.0 or less, and the composition of the present invention performs gas foaming which is generally performed at the time of molding. This allows a foaming ratio of up to 10 times.

As another method for producing the laminated film, a method for preparing a raw material of a foamed film of the composition in advance by the method described above, and laminating a propylene-based polymer on the raw material by an extrusion laminating method, or a propylene-based polymer There is a method of laminating films by a dry laminating method and stretching by the above method, and a method of extrusion laminating a propylene-based polymer on the surface of the foamed film of the composition.

Conventionally, a foamed film made of a propylene-based polymer alone generally has a foaming ratio of 3.0 times or less. Expansion ratio is 3.
When it exceeds 0 times, the surface of the obtained foamed film is rough and the appearance is poor, and printing is inappropriate. Even if the expansion ratio exceeds 3.0, the laminated film of the present invention has an unfoamed propylene polymer layer by coextrusion, so the surface of the laminated film is smooth and has a good appearance. . When the foaming accelerator is added and the expansion ratio is 10 times or less, the appearance of the laminated film is very good.

In the heat-shrinkable film of the present invention thus obtained, the thickness of the unexpanded propylene-based polymer layer is usually 3 to
It is 50 μm, preferably 5 to 50 μm, and particularly preferably 5 to 40 μm. The thickness of the unfoamed propylene-based polymer layer in the film is generally 2 to
It is 40%, and particularly preferably 5 to 25%.

Further, the expansion ratio of the foam layer is 10 times or less, 1.05
It is preferably 10 to 10 times, and particularly preferably 1.2 to 8.5 times.

[Examples and Comparative Examples]

Hereinafter, the present invention will be described in more detail with reference to Examples.

In the examples and comparative examples, the heat shrinkage rate is 130.
The heat shrinkage in the longitudinal direction (M direction) at each temperature of ° C and 140 ° C was measured according to JIS Z1709. The Young's modulus was measured according to ASTM D-882. The evaluation of the foamed state was performed by observing the surface of the obtained foamed layer with the naked eye, and the evaluation criteria are described below.

⊚: Very good ∘: Good Δ: Slightly bad ×: Poor Examples 1 to 8 and Comparative Examples 1 to 3 Ethylene-propylene having an ethylene content of 8.0% by weight shown in Table 1 for each blending amount. Block copolymer [MF
R 10 g / 10 min, hereinafter referred to as "PP (1)"] and ethylene-propylene random copolymer having an ethylene content of 6.9 wt% [MFR 9.0 g / 10 min, hereinafter "PP
(2) ”] and the total amount of these copolymers is 10
0.4-1.0 part by weight of azo-dicarboxylic amide (chemical blowing agent) was preliminarily dry blended for 5 minutes by using a Henschel mixer with respect to 0 part by weight.

An ethylene-propylene random copolymer having an MFR of 10.0 g / 10 minutes and an ethylene copolymerization ratio of 3.0% by weight as a propylene-based polymer of an unfoamed film layer for coextrusion. [Hereinafter referred to as "PP (3)"] was used.

Each mixture thus obtained (foaming agent-containing composition)
And PP (3) were coextruded at a temperature of 210 ° C. using a coextrusion T-die molding machine with screw diameters of 65 mm and 50 mm, and rapidly cooled at 4 cm from the tip of the die to form a thick foam layer and unfoamed layer. A multilayer sheet was produced. For forming the foamed film, only the chemical foaming agent was used when the expansion ratio was 3.0 times or less, but when it exceeded 3.0 times,
In addition to the chemical foaming agent, commonly used gas foaming was used together (Examples 1 to 6). In Comparative Examples 1 to 3, the propylene-based polymer was not used, and a coextrusion molding machine having a screw diameter of 65 mm was used to perform the same extrusion. Further, in Examples 7 and 8, only the single foamed film was preformed by the same composition and formulation as in Example 3. In Example 7, a laminated film was prepared by using a commercially available unstretched propylene polymer film having a thickness of 40 μm with a urethane adhesive interposed on one side of this simplex foam film using a dry laminator. Furthermore, in Example 8, a propylene-based polymer having an MFR of 20.0 g was extrusion-laminated at a molding temperature of 300 ° C. on one side of a single foamed film to prepare a laminated film.

Using each heating sheet obtained in this way,
Stretching was performed at a temperature of about 120 ° C. in the longitudinal direction so that the stretching ratio was 4.0 times, and a film having a thickness of 200 μm (of which the unstretched propylene-based polymer layer had a thickness of 10%) was produced. did. 130 ° C and 140 ° C for each of the obtained films
The thermal shrinkage and Young's modulus in the M direction at each temperature of ° C were measured. Further, the foamed state of the foamed layer was visually observed. The results are shown in Table 1.

Photographic printing was performed on each of these films, and the films obtained in all the examples were extremely clear in photographic printing as in the case of the printing of a normal unstretched propylene-based copolymer film. However, in Comparative Example 1, when the photographic printing was performed, the fine portion was blurred and lacked in sharpness because the surface was slightly rough. Further, in Comparative Examples 2 and 3, the surface was rougher than that of Comparative Example 1, so that not only fine division of photographic printing but also fine print was unclear. Further, the heat insulating properties of the products obtained in Examples 5 and 6 were much better.

〔The invention's effect〕

By containing the ethylene-propylene random copolymer in the above composition ratio in the heat-shrinkable film of the present invention, the heat shrinkage rate at the same temperature can be increased by 15 to 20%. That is, the temperature for obtaining the same shrinkage can be lowered by 15 to 20 ° C. Also, the heat sealing temperature is 10 to 20 ° C.
Not only it becomes possible to bond at a low temperature, but also the appearance of the seal portion is remarkably improved, and excellent sealing suitability can be obtained. Further, in the heat-shrinkable film of the present invention, the unexpanded propylene-based polymer layer has a multi-layered structure on the surface of the foamed layer, so that the expansion ratio is high and therefore the heat insulating effect is large. Moreover, when the propylene-based polymer layer is printed, it exhibits excellent printability and is most suitable for photographic printing.

Further, when this heat-shrinkable film is used as a label for bottles and containers, it has good buffering properties and heat insulating properties, and has excellent heat resistance even at relatively high temperatures of 120 ° C. or higher. Even if the retort sterilization is carried out for 30 minutes at the temperature, there is no change and it can be used well. In addition, since the Young's modulus is high, the suitability for wrapping in containers is excellent,
The heat-shrinkable film of the present invention is most suitable as a shrink label film for beverage bottles and the like that require retort sterilization.

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Claims (1)

[Claims] 1. A heat-shrinkable film comprising a foamed layer and an unfoamed propylene polymer layer laminated on one or both sides of the foamed layer, wherein the foamed layer has a (A) ethylene copolymerization ratio. The ethylene-propylene block copolymer, which is 3.0 to 20% by weight, has a copolymerization ratio of 50 to 90% by weight and (B) ethylene.
A heat-shrinkable film comprising a composition having an ethylene-propylene random copolymer content of 2.0 to 15% by weight and a content of 50 to 10% by weight, and having a foaming ratio of 10 or less.