JPH0733063B2 - Shrink film - Google Patents

Description

TECHNICAL FIELD The present invention relates to a shrinkable film which is lightweight and rich in cushioning properties, and has excellent shrinkage characteristics, weather resistance, strength and the like.

[Problems to be solved by conventional technology and invention]

Conventionally, shrink films made of polyvinyl chloride, polystyrene and the like have been widely used as shrink films for packaging or labels. By using these films, the packaging or labeling by shrinkage can be performed very easily and quickly. However, since these conventional films are usually as thin as 20 to 300 μm, even if a glass container such as a glass bottle is packaged or labeled using the film, the effect that the film has a role of cushion cannot be expected so much. Therefore, unless a cushion material is separately provided around the container, it has a drawback that the glass is broken relatively easily due to the impact during transportation and sale.

In recent years, in order to avoid such complicated packaging, attempts have been made to provide the shrink film itself with a cushioning property, and a film in which air bubbles are mixed with polystyrene or the like has been put into practical use. However, since these films have poor weather resistance and are inferior in strength, they have a drawback that the films are likely to be torn during storage or transportation after packaging or labeling of the container.

Under such circumstances, there has been a demand for a shrinkable film for packaging or label which has cushioning property and excellent shrinkage property, weather resistance and strength.

[Means for solving problems]

In view of the above problems, the present inventors have made earnest studies, and as a result, have found that a shrink film having a specific gravity value and a degree of concealment is a film that can meet the above demands, and have arrived at the present invention.

That is, the gist of the present invention is that the apparent specific gravity of the film is 0.40 or more and 1.30 or less, the degree of hiding of the film is 020 or more, and the shrinkage rate of the film in 5 minutes in a 100 ° C. air oven is Alternatively, the shrinkable film is characterized in that it is 40% or more in one of the lateral directions.

Hereinafter, the present invention will be described in detail.

In the present invention, any method may be used as a method for imparting crushability to the film, but a method in which a large number of fine bubbles are present in the film is industrially easy and inexpensive, and is preferable. As a method of causing bubbles in the film, any of a method of generating bubbles in the film during melt extrusion, a method of generating bubbles in the film during stretching or a subsequent step may be used. From the viewpoint of productivity and thickness unevenness, the method of generating fine bubbles in the film during stretching is most preferable.

The composition of the film of the present invention is preferably composed of two or more kinds of polymers, and is preferably composed mainly of a polyester and a polyolefin-based polymer.

The polyester used in the present invention, as a dicarboxylic acid component, terephthalic acid, oxalic acid, malonic acid, succinic acid, adipic acid, azelaic acid, sebacic acid, phthalic acid, isophthalic acid, naphthalenedicarboxylic acid, diphenyl ether dicarboxylic acid, etc. , One or more known dicarboxylic acids, and as a diol component, ethylene glycol, propylene glycol, trimethylene glycol, tetramethylene glycol, hexameretin glycol, diethylene glycol, polyalkylene glycol, 1,4-cyclohexanediene. It may be any polyester composed of one or more known diol components such as methanol or a copolyester thereof, but mainly polyethylene terephthalate, polybutylene terephthalate, polyethylene Ethylene-2,6-naphthalate, polyesters and copolymers composed of terephthalic acid and 1,4-cyclohexanedimethanol are preferred. Above all, a copolymer of polyethylene terephthalate is particularly preferable because it is inexpensive.

The copolymerized polyester includes a dicarboxylic acid component and /
Alternatively, those obtained by substituting a part of the glycol component with another dicarboxylic acid or glycol component can be used, but it goes without saying that other components such as p-oxybenzoic acid and p-oxy can be used. Oxycarboxylic acids such as ethoxybenzoic acid, benzoic acid, benzoylbenzoic acid, monofunctional compounds such as methoxypolyalkylene glycol, polyfunctional compounds such as glycerin, pentaerythritol, trimethylol and trimethylenepropane are also products. It can be used within a range capable of holding a substantially linear polymer.

As the polyester of the present invention, a copolymer obtained by copolymerizing polyethylene terephthalate as a main component, isophthalic acid as a dicarboxylic acid component, and optionally diethylene glycol, polyalkylene glycol, or 1,4-cyclohexanedimethanol as a diol component. Polyester is particularly preferable because it can be obtained industrially at low cost and has good shrinkage characteristics.

The proportion of the polyethylene terephthalate component in the copolyester is preferably 70 mol%, more preferably 75 mol% or more. If the polyethylene terephthalate component is less than 70 mol%, the strength and solvent resistance of the film are poor, which is not preferable.

Further, in order to improve the slipperiness of the film, an organic lubricant,
It is also preferable to contain fine particles such as an inorganic lubricant.
Further, it may contain additives such as a stabilizer, a coloring agent, an antioxidant and an antifoaming agent, if necessary. As the fine particles imparting slipperiness, known inert external particles such as kaolin, clay, calcium carbonate, silicon oxide, calcium terephthalate, aluminum oxide, titanium oxide, calcium phosphate, lithium fluoride, and the like, in melt film formation of polyester resin Insoluble high-melting point organic compound, cross-linked polymer and metal compound catalyst used in polyester synthesis, for example, internal particles formed inside the polymer during polyester production by an alkali metal compound, alkaline earth metal compound, etc. . The fine particles contained in the film are 0.005 to 0.9% by weight, and the average particle diameter is 0.
001 to 3.5 μm.

The intrinsic viscosity of the polyester of the present invention is preferably 0.50 or more, more preferably 0.60 or more, and particularly preferably 0.65 or more. When the intrinsic viscosity of the polyester is less than 0.50, the crystallinity becomes high and a sufficient shrinkage ratio cannot be obtained, which is not preferable.

Next, the polyolefin polymer used in the present invention, the type is not particularly limited, the polyester used in the present invention has a higher elastic modulus than the polyester in the temperature range of the amorphous state glass transition temperature or higher. It is preferable that the polyolefin polymer has a large number of fine bubbles in the film after the film is stretched and formed into a film.

The reason is not clear, but when the polyolefin polymer is mixed in the polyester and the polyester is stretched at a glass transition temperature or higher and a melting point or lower, the elastic modulus of the polyolefin polymer is the elastic modulus of the polyester. When it is higher, the amount of strain of the polyolefin polymer is smaller than that of the polyester during stretching, and it is considered that minute bubbles are generated between the two. Therefore, when the elastic modulus of the polyolefin polymer is in the temperature range of the glass transition temperature of the amorphous state of the polyester or higher, when the elastic modulus of the polyester is the same as or smaller than the elastic modulus of the polyester, a difference in strain amount does not occur and bubbles are generated. It is not preferable because it hardly occurs.

As the polyolefin-based polymer as described above, polyethylene polypropylene and the like are preferable because they satisfy the above-mentioned physical properties and can be obtained industrially at low cost.

In the present invention, the melt flow index of the polyolefin polymer is preferably 0.2 to 120, more preferably 0.
5 to 50. When the melt flow index is less than 0.2, the bubbles generated become too large, and the shrinkage rate of the obtained film decreases, which is not preferable. On the other hand, if the melt flow index exceeds 120, the crystallinity of the polyolefin polymer becomes very high and the stretchability of the film deteriorates, which is not preferable.

In the present invention, the composition ratio of the film composition,
It is preferable to contain 70 to 98% by weight of polyester and 2 to 30% by weight of polyolefin polymer. When the content of the polyester is less than 70% by weight, the shrinkage rate of the obtained film is not sufficient, which is not preferable. Further, when the content of the polyolefin polymer is less than 2% by weight, the amount of bubbles generated is not sufficient, which is not preferable. On the other hand, if the content of the polyolefin polymer exceeds 30% by weight, the number of bubbles generated is too large and the stretching property is deteriorated such as breakage during stretching, which is not preferable.

In addition, a polymer other than the above polyester and the above polyolefin polymer may be used within a range not changing the gist of the present invention.
It may be added or mixed in an amount of not more than wt%.

The apparent specific gravity of the film of the present invention is required to be 0.40 or more and 1.30 or less, preferably 0.60 or more and 1.30 or less, and more preferably 0.80 or more and 1.25 or less. If the apparent specific gravity of the film exceeds 1.30, the amount of bubbles generated in the film, that is, the volume occupied by the bubbles in the film becomes insufficient, so that the cushioning property of the film deteriorates, which is not preferable. If the apparent specific gravity is less than 0.40, the amount of bubbles generated in the film is too large, and the strength and shrinkage of the film are reduced, which is not preferable.

The hiding power of the film of the present invention needs to be 0.20 or more, preferably 0.30 or more. Apparent specific gravity is 1.
A film having a hiding degree of less than 0.20 even with a film of 30 or less is not preferable because the number of bubbles generated is not sufficient and the cushioning property is also poor.

The shrinkage rate of the film of the present invention in a 100 ° C. air oven for 5 minutes needs to be 40% or more, preferably 50% or more, in either one of the vertical and horizontal directions. When the shrinkage ratio in at least one direction is less than 40%, the film does not adhere to the outer surface of the container after shrinking, which is not preferable for shrink wrapping.

When the film is used for a label, the shrinkage ratio in the direction orthogonal to the shrinking direction is 20% in the vertical or horizontal direction.
The following is preferable. When the shrinkage ratio in the direction exceeds 20%, when used for a label, the printed pattern is misaligned, which is not preferable.

The shrinkage stress of the film of the present invention in the maximum shrinkage direction in 100 ° C. air is preferably 100 g / mm ² or more, further preferably 300 g / mm ² or more, and more preferably 500 g / mm ² or more. If the shrinkage stress of the film is less than 100 g / mm ^2, it is not preferable because the film does not have sufficient adhesion to the bottle when it is mounted on the bottle.

The tensile strength of the film of the present invention in the direction of large shrinkage in the longitudinal or transverse direction is preferably 3 kg / mm ² or more, more preferably 5
kg / mm ² or more, particularly preferably 8 kg / mm ² or more. A film having a tensile strength of less than 3 kg / mm ² is not preferable because the film is easily torn when it is attached to a container or when it is transported after attachment.

According to the method described in JIS A 1415, the film of the present invention preferably has a tensile elongation of 5% or more in a longitudinal direction or a lateral direction of the film, which has a smaller shrinkage, when exposed to a weather meter, preferably 100%. Over time, more preferably 2
00 hours or more.

If the film has a time of less than 100 hours, the weather resistance is not sufficient, and after being stored for a long time, the film is split in the longitudinal or transverse direction of the film in parallel with the direction in which the shrinkage ratio is large, that is, in the main stretching direction of the film. It becomes easy and not preferable.

The thickness of the film obtained as described above is not particularly limited, but the preferred thickness for the shrink film for packaging or label is 5 to 500 μm, more preferably 10 to 500 μm.

Next, the method for producing the film of the present invention will be specifically described.
The present invention is not limited to this example as long as the required characteristics are satisfied.

After drying the polyester, it is blended with a polyolefin polymer and then extrusion-molded to obtain an unstretched film.

As a method for obtaining the unstretched film, any existing method such as a T-die method or a tubular method may be adopted.

The unstretched film is uniaxially or biaxially stretched in the machine or transverse direction. The surface temperature of the film is Tg-10 ° C during the stretching process.
More than Tg + 40 ℃ or less, preferably Tg -10 ℃ or more Tg + 30 ℃ or less uniformly heated to at least one direction 1.6
Double or more, 5.0 or less, preferably 1.6 or more, 4.5 or less, more preferably 2.0 or more, 4.5 times or less, a method including a step of stretching in one stage or two stages or more reduces the thickness unevenness of the film. Therefore, it is preferable. As the stretching method of uniaxial stretching, not only longitudinal uniaxial stretching with a roll or transverse uniaxial stretching with a tenter, but also known biaxial stretching, strongly stretching in either longitudinal or transverse direction and minimizing the other It is also possible to stretch. As a stretching method for biaxial stretching, a known sequential stretching method or simultaneous stretching method can be used, and re-stretching can also be performed.

The film thus obtained can be heat-fixed at 100 ° C. or lower, if necessary, and then used as a wound product.

As described above, according to the present invention, it is possible to obtain a shrinkable film for packaging or a label, which has cushioning properties and excellent shrinkage properties, weather resistance, strength and the like.

〔Example〕

Hereinafter, the present invention will be described in more detail with reference to Examples.
The present invention is not limited to these examples unless it exceeds the gist.

The evaluation method of the film is shown below.

(1) Shrinkage The heat shrinkage was carried out for 5 minutes in a geared oven at a temperature of 100 ° C. ± 2 ° C. under no load, and the shrinkage was calculated according to the following formula.

(2) Apparent specific gravity (g / cm ³ ) Cut out 10cm × 10cm from any part of the obtained film, measure the average thickness at 9 arbitrary points with a micrometer, and then weigh the weight per unit volume. Was calculated. The number of measurements was n = 5, and the average value was used as the measured value.

(3) Concealment Degree The density of transmitted light under a G filter was measured using a Macbeth densitometer TD-904 type. The larger this value is, the higher the hiding power is.

(4) Intrinsic viscosity ([η]) 200 mg of sample was added to 20 ml of a mixed solvent of phenol / tetrachlororetane = 50/50, heated and dissolved at 110 ° C for 1 hour, and then 30 ° C.
It was measured at.

(5) Evaluation as Shrink Film The film was made into a cylindrical shape with an adhesive, covered with a glass bottle, and then passed through a shrink tunnel to bring the film into close contact with the bottle. After shrinkage, the film has almost no wrinkles and there is no looseness between the bottle and the film, ○, the appearance is slightly inferior but practically no problem, and the others are ×. .

(6) Evaluation of cushioning The glass bottle with the film attached in the same manner as in the above determination method (5) is dropped 100 times horizontally from a position of 50 cm in height onto a rubber plate having a thickness of 1 cm, during which time. The case where the glass bottle was cracked or cracked was marked with X, and the case where the bottle was not damaged at all was marked with ◯.

Comparative Example 1 and Example 1 After drying a copolyester having an intrinsic viscosity of 0.70 in which the dicarboxylic acid component was 80 mol% terephthalic acid and 20% isophthalic acid, and the diol component was ethylene glycol,
Powder polypropylene was mixed with a weight ratio of 90:10 and melt-extruded to obtain an unstretched film. The unstretched film is 70
A film having an average thickness of 150 μm was obtained by drawing 1.5 times or 3.5 times between a drawing roll at a temperature of 0 ° C. and a cooling roll. Each was designated as Comparative Example 1 and Example 1.

Comparative Example 2 Only the polyester of Example 1 was dried and melt-extruded to obtain an unstretched film. The unstretched film was stretched and formed into a film in the same manner as in Example 1 to obtain a film having an average thickness of 150 μm, which was referred to as Comparative Example 2.

Comparative Example 3 Except that 10 mol% of ethylene random copolymer polypropylene was used in place of polypropylene in Example 1, mixing and film formation were carried out in the same manner as in Example 1 to obtain a stretched film having an average thickness of 150 μm. It was set to 2.

Example 2 After drying a polyester having an intrinsic viscosity of 0.72 consisting of 85 mol% of terephthalic acid and 15 mol% of isophthalic acid as a dicarboxylic acid component and 85 mol% of diol component as ethylene glycol, 2 mol% of diethylene glycol and 3 mol% of polyethylene glycol The powdery high-density polyethylene was mixed at a weight ratio of 92: 8 and melt-extruded to obtain an unstretched film. The unstretched film was introduced directly into a tenter, stretched 3.0 times at 80 ° C., cooled with cold air, and then wound up to an average thickness of 200 μm.
I got a film. This is Example 2.

Example 3 The polyester and polypropylene of Example 1 were melted in the same composition as in Example 1 and extruded and stretched to form a film by the inflation method. At that time, the surface temperature of the film at the stretching start point was 75 ° C., and the stretching ratio was 2.0 times both in the longitudinal and transverse directions. The average thickness of the obtained film was 100 μm.

This is Example 3.

Table 1 shows the physical properties and characteristics of the films obtained in the above Examples and Comparative Examples.

The film of Comparative Example 1 has a low shrinkage ratio and is not preferable as a shrinkable film, and the film of Comparative Example 2 has a large apparent specific gravity and insufficient cushioning property. The film of Comparative Example 3 has a small apparent specific gravity, but also has a poor masking property because of its small degree of hiding. It can be seen that the films of Examples 1 to 3 are superior in shrinkage property and crushing property to the films of the above Comparative Examples.

〔The invention's effect〕

As described above, it can be seen that a film satisfying the conditions of the present invention has excellent cushioning properties and excellent shrinkage characteristics, and is extremely suitable as a shrinkable film for packaging or labels.

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Claims (2)

[Claims] 1. An apparent specific gravity of a film is 0.40 or more and 1.30 or less, a hiding degree of the film is 0.20 or more, and a shrinkage rate of the film in a 100 ° C. air oven for 5 minutes is either vertical or horizontal. A shrink film which is 40% or more in any one direction. 2. A composition comprising a film comprising 70-98% by weight of polyester and 2% of a polyolefin polymer having a higher elastic modulus than that of the polyester in a temperature range above the glass transition temperature of the amorphous state. ~
Claim 1 characterized by containing 30% by weight
The shrinkable film according to the item.