JP6934936B2 - Heat shrinkable film - Google Patents

Description

The present invention relates to heat shrinkable films.
The present application claims priority based on Japanese Patent Application No. 2017-064407 filed in Japan on March 29, 2017, the contents of which are incorporated herein by reference.

Heat-shrinkable films are widely used for shrink-packing and shrink-labeling of containers. Generally, the heat-shrinkable film is separated along the perforations provided on the film in advance, discarded separately from the container, and recycled.
Heat-shrinkable films include shrinkage, printability, environmentally friendly materials, strong film stiffness, excellent shrinkage finish (for example, less wrinkles and shrinkage spots), and sewing machines. Excellent eye openability, excellent wearability (for example, label rupture is unlikely to occur during wearing), low natural shrinkage rate, and excellent film stability during storage (for example, during storage) It is required that the film is less likely to wrinkle or change in size).

Examples of the heat-shrinkable film used for shrink-wrapping and shrink-labeling of containers include polyvinyl chloride-based heat-shrinkable films, polyester-based heat-shrinkable films, and polystyrene-based heat-shrinkable films (Patent Documents 1 and 2).
The polyvinyl chloride-based heat-shrinkable film is excellent in shrinkage finish, perforation opening property, and wearability, and has a low natural shrinkage rate, but has problems such as generation of toxic chlorine-containing gas during incineration. Further, the polyester-based heat-shrinkable film is excellent in film stability and waist strength during storage, but has problems such as shrinkage finish, perforation opening property, and poor wearability.
On the other hand, polystyrene-based heat-shrinkable films are superior in shrinkage finish, perforation opening property, and wearability as compared with films using the above other materials, but have a high natural shrinkage rate and are stable during storage. I have a problem with sex.

Japanese Unexamined Patent Publication No. 2006-0442219 Japanese Unexamined Patent Publication No. 2012-031339

The present invention has been made in view of the above circumstances, and has excellent shrinkage finish, perforation opening property, and wearability, and is compared with a conventional polystyrene-based heat-shrinkable film during storage. An object of the present invention is to provide a polystyrene-based heat-shrinkable film having improved film stability.

Embodiments of the present invention have the following aspects.
[1] A heat-shrinkable film containing a polystyrene-based resin, which has a heat-shrinkability of 15% or less in the main shrinkage direction when immersed in water at 70 ° C. for 10 seconds, and is immersed in water at 98 ° C. for 10 seconds. When immersed, the heat shrinkage rate in the main contraction direction is 60% or more, the Elmendorf tear strength in the main contraction direction is in the range of 3 to 10 N / mm, and the Elmendorf tear strength in the direction orthogonal to the main contraction direction is 10. It is in the range of ~ 20 N / mm, the contraction stress in the main contraction direction when left at 85 ° C for 5 minutes is 4.0 N / mm ² or less, and the contraction stress in the main contraction direction when left at 40 ° C for 7 days. A heat-shrinkable film having a shrinkage rate of 1.5% or less.
[2] The heat-shrinkable film is formed by stretching in the main shrinkage direction after extrusion molding, and the stretching has a residual heat temperature of 100 ° C. or higher, a stretching temperature and a heat fixing temperature of 90 ° C. or higher, and a stretching ratio of 4. The heat-shrinkable film according to [1], which is stretched to be .9 or more.

The heat-shrinkable film of the present invention has excellent shrinkage finish, perforation opening property, and wearability, and the stability of the film during storage is improved as compared with the conventional polystyrene-based heat-shrinkable film. There is.

The heat-shrinkable film of the present invention (hereinafter, also referred to as “the present film”) contains a polystyrene-based resin.

(Polystyrene resin)
The polystyrene-based resin may be any known material used for producing heat-shrinkable films, and may be a styrene-butadiene copolymer, a styrene-butadiene-styrene copolymer, a styrene-ethylene-butadiene-styrene copolymer, or the like. Polystyrene-based thermoplastic elastomers such as styrene-vinyl polyisoprene-styrene copolymer; styrene-methacrylic acid copolymer, styrene-methyl methacrylate copolymer, styrene-ethyl methacrylate copolymer, styrene-butyl methacrylate copolymer Impact-resistant styrene-based resins such as copolymers and styrene-phenylmethacrylate copolymers can be mentioned. Of these, one type may be used alone, or two or more types may be used.

(Other resin)
The present film may contain a resin other than the polystyrene-based resin as another resin as long as the effects of the present invention are not impaired. As the other resin, known ones used for the production of heat-shrinkable films may be used. Examples of other resins include olefin resins (propylene resins and the like), polyester resins, acrylic resins and the like. As these other resin components, one kind may be used alone, or two or more kinds may be used.

(Content of resin component)
When the total mass of all the resins constituting the film is 100%, the content of the polystyrene-based resin is preferably 50 to 100% by mass, more preferably 80 to 100% by mass.

(Heat shrinkable film)
When this film is immersed in water at 70 ° C. for 10 seconds, the heat shrinkage rate in the main shrinkage direction (hereinafter, also referred to as "heat shrinkage rate 1") is 15% or less, and is 5 to 15%. Is preferable, and 7 to 12% is more preferable. When the heat shrinkage rate 1 is 15% or less, the shrinkage of the film by a normal steam tunnel is moderated, wrinkles and shrinkage spots are prevented, and the shrinkage finish is good.

When this film is immersed in water at 98 ° C. for 10 seconds, the heat shrinkage rate in the main shrinkage direction (hereinafter, also referred to as "heat shrinkage rate 2") is 60% or more, and is 60 to 80%. Is preferable, and more preferably 65 to 75%. When the heat shrinkage rate 2 is 60% or more, the shrinkage property is excellent, the container can be mounted on various containers, and mounting troubles due to insufficient shrinkage can be prevented.
When this film is immersed in water at 100 ° C. for 10 seconds, the heat shrinkage rate in the main shrinkage direction (hereinafter, also referred to as "heat shrinkage rate 3") is 60% or more, and is 60 to 80%. Is preferable, and more preferably 65 to 75%. When the heat shrinkage rate 3 is 60% or more, the shrinkage property is excellent, the container can be mounted on various containers, and mounting troubles due to insufficient shrinkage can be prevented.
_{Further, the difference (Δ 23} ) between the heat shrinkage rate 2 and the heat shrinkage rate 3 is preferably within ± 1%. If Δ ₂₃ is within ± 1%, it can be mounted on various containers, and mounting troubles due to insufficient shrinkage can be further prevented.

In the present invention, the "heat shrinkage rate" is a value measured at 70 ± 0.5 ° C., 98 ± 0.5 ° C. and 100 ± 0.5 ° C., respectively, according to JIS Z1709.

The Ermendorf tear strength of this film in the main contraction direction (hereinafter, also referred to as “TD direction”) is in the range of 3 to 10 N / mm, preferably in the range of 3 to 8 N / mm, and is preferably in the range of 3 to 6 N. More preferably, it is in the range of / mm. If the Ermendorf tear strength in the MD direction is in the range of 3 to 10 N / mm, the perforation opening property is excellent. Here, "excellent in opening property of perforations" means, for example, when a label using this film is separated by a perforation provided along a direction perpendicular to the main contraction direction of the label, in the main contraction direction. It means that the label can be easily peeled off from the container without tearing the label.

The Ermendorf tear strength of this film in the direction orthogonal to the main contraction direction (hereinafter, also referred to as “MD direction”) is in the range of 10 to 20 N / mm, preferably in the range of 10 to 17 N / mm. , 10-14 N / mm, more preferably. If the Ermendorf tear strength in the TD direction is in the range of 10 to 20 N / mm, the perforation opening property is excellent.

In the present invention, the "Elmendorf tear strength" is a value obtained by dividing the measured value in the MD direction and the TD direction by the film thickness according to JIS K7128-2.

This film, when left at 85 ° C. 5 min, main shrinkage direction of the shrinkage stress is at 4.0 N / mm ² or less, preferably 3.5 N / mm ² or less, 3.0 N / mm It is more preferably ^{2 or less.} When the shrinkage stress in the main shrinkage direction is 4.0 N / mm ² or less, it is possible to prevent the label from breaking from the perforation when the label using this film is attached to a container or the like. Excellent for.

In the present invention, the "shrinkage stress" refers to a sample piece having a length of 80 mm and a width of 25 mm in the main shrinkage direction, which is held in a chuck equipped with a load cell at a distance of 50 mm between chucks in an oven at 85 ° C. It is the maximum stress per unit cross-sectional area measured when it is charged and left for 5 minutes.

When this film is left at 40 ° C. for 7 days, the shrinkage rate in the main shrinkage direction (hereinafter, also referred to as “spontaneous shrinkage rate”) is 1.5% or less, and 1.2% or less. It is preferably 1.0% or less, and more preferably 1.0% or less. When the natural shrinkage rate is 1.5% or less, shrinkage during storage can be reduced, wrinkles and dimensional changes are unlikely to occur in the film during storage, and the stability of the film during storage is excellent.

The natural shrinkage rate is the shrinkage rate in the main shrinkage direction when a sample having a length of 500 mm in the main shrinkage direction is left at 40 ° C. for 7 days, and is a value calculated by the following formula (I).
Natural shrinkage rate [%] = {[(500)-(length after leaving [mm])] / (500)} × 100 ... (I)

This film may be a single-layer film made of a polystyrene-based resin, or may be a multilayer film having an outermost layer made of a polystyrene-based resin and another layer made of a polystyrene-based resin and another resin. Further, the present film may be a transparent film, or may be an opaque film or a colored film such as white from the viewpoint of printability.
The heat-shrinkable film may contain additives such as fillers, stabilizers, antioxidants, UV absorbers, antistatic agents, lubricants and the like.

In the case of a single-layer film, the thickness of this film is preferably 20 to 80 μm, more preferably 40 to 60 μm.

In the case of a multilayer film, the thickness of the outermost layer of this film is preferably 2 to 8 μm, more preferably 4 to 6 μm, and the total thickness of the other layers is preferably 18 to 78 μm, more preferably 16 to 54 μm. ..

(Example of use)
The heat-shrinkable film is not particularly limited, but is mainly used as a label for bottle containers. When used as a label, the heat-shrinkable film may be printed in order to improve the design.
As a method of attaching a label made of a heat-shrinkable film to a bottle container, for example, the heat-shrinkable film is cut to a predetermined length, and the ends of the cut films are joined to form a tubular body. An example is a method in which a bottle container is inserted into a tubular body and then heated to shrink.

(Manufacturing method of heat-shrinkable film)
This film can be obtained by a known method (T-die method, inflation method, or the like, in the case of a multilayer film, a coextrusion method thereof). For example, but not limited to this, the material is extruded into a flat shape or a tube shape from a die heated to 160 to 240 ° C., and the unstretched product obtained is obtained in the main shrinkage direction (TD direction). It is preferable to extend biaxially in the direction orthogonal to each other (MD direction). In this case, sequential biaxial stretching in the MD direction and TD direction may be performed, or simultaneous biaxial stretching may be performed.
The stretching in the TD direction is preferably performed in three steps of a preheating step, a stretching step and a heat fixing step.
The film of the present embodiment is stretched at a residual heat temperature of 100 ° C. or higher, a stretching temperature and a heat fixing temperature of 90 ° C. or higher, and a stretching ratio of 4.9 or higher in the step of performing the stretching step in the TD direction of the production. It is preferable to do so. By performing the stretching step under these conditions, the natural shrinkage rate of the film can be set to an appropriate value.

(Action effect)
As described above, the heat-shrinkable film of the present invention has excellent shrinkage finish, perforation opening property, and wearability in order to satisfy each of the above physical characteristics, and has conventional polystyrene-based heat-shrinkability. Compared to film, the stability of the film during storage is improved.

Hereinafter, the present invention will be specifically described with reference to Examples, but the present invention is not limited to the following description.
The measurement of each physical property value of the heat-shrinkable film in the examples and the evaluation of each evaluation item were carried out according to the following description and criteria.

(Heat shrinkage rate)
According to JIS Z1709, 70 ± 0.5 ° C (measurement temperature of "heat shrinkage rate 1"), 98 ± 0.5 ° C (measurement temperature of "heat shrinkage rate 2") and 100 ± 0.5 ° C. ("heat shrinkage rate 2"). The heat shrinkage rate of the heat shrinkable film at the measurement temperature of "heat shrinkage rate 3") was measured.

(Elmendorf tear strength)
According to JIS K7128-2, the tearing force was measured in the MD direction and the TD direction of the heat-shrinkable film, and each was divided by the thickness of the heat-shrinkable film to calculate.

(Shrink stress)
The maximum value of the stress measured when a sample piece having a length of 80 mm and a width of 25 mm in the main contraction direction was left at 85 ° C. for 5 minutes was defined as the contraction stress.

(Natural shrinkage rate)
A sample having a length of 500 mm in the main shrinkage direction of the heat-shrinkable film was left at 40 ° C. for 7 days, and then the length of the sample was measured and calculated by the following formula (I).
Natural shrinkage rate [%] = {[(500)-(length after leaving [mm])] / (500)} × 100 ... (I)

A tubular body in which a heat-shrinkable film is cut to a predetermined width and length, and the ends of the cut heat-shrinkable film are joined to each other so that the main shrinkage direction of the heat-shrinkable film is the circumferential direction. I made a label for. Then, after inserting the bottle container into the tubular body, the label was attached by heat shrinking. The appearance of the label after heat shrinkage was visually observed, and the shrinkage finish and wearability were evaluated.

(Shrink finish)
The presence or absence of wrinkles and shrinkage spots on the label after heat shrinkage was visually determined and evaluated according to the following criteria.
◯: No wrinkles or contraction spots occurred.
X: Wrinkles or contraction spots have occurred.

(Wearability)
The presence or absence of rupture on the label after heat shrinkage was visually determined and evaluated according to the following criteria.
◯: No rupture has occurred.
X: A rupture has occurred.

(Perforation openability)
The above-mentioned tubular label having perforations in the direction directly opposite to the main contraction direction was attached to the bottle container. However, the perforations were formed by inserting holes having a length of 1 mm at intervals of 4 mm, and two perforations were provided over a width of 20 mm and a length of 200 mm in the direction of the perforations (MD direction). Then, the perforations on the label were torn with the fingertips, and it was determined whether or not the perforations provided in the MD direction were torn.
◯: The label was torn along the perforation.
X: The label was not torn along the perforation, or the label was torn in a direction other than the TD direction.

(Film stability during storage)
After the heat-shrinkable film was stored at 40 ° C. for 7 days, the presence or absence of wrinkles and dimensional changes on the heat-shrinkable film was visually determined, and the stability of the film during storage was evaluated according to the following criteria.
◯: No wrinkles or dimensional changes have occurred compared to the conventional product.
X: Wrinkles or dimensional changes occur in the same manner as the conventional product.

<Example 1>
(Raw material for polystyrene-based heat-shrinkable film)
The polystyrene-based heat-shrinkable film of the examples described below has a three-layer structure composed of the following components.
For the intermediate layer of the polystyrene-based heat-shrinkable film, a mixture of SBC (A) and SBC (B), which is a styrene-butadiene copolymer, was used as a raw material.
For both outer layers of the polystyrene-based heat-shrinkable film, a mixture of a styrene-butadiene copolymer (SBC (A)) and an impact-resistant polystyrene-based resin (referred to as "HiPS" in Table 1) was used as a raw material.
Table 1 shows the bicut softening point and melt mass flow rate of each component (referred to as “MFR” in Table 1), and the component ratios of the components of each layer.

(Manufacture of polystyrene-based heat-shrinkable film)
The raw materials of the polystyrene-based heat-shrinkable film were mixed in the blending amounts shown in Table 1 and co-extruded from a three-layer die kept at 200 ° C. to obtain a polystyrene-based film raw fabric having a three-layer structure. The thickness of both outer layers of the original film was 34 μm, and the thickness of the intermediate layer was 270 μm. Next, this original film was stretched 1.35 times in the MD direction at 85 ° C. to obtain a stretched film made of a polystyrene-based resin having a thickness of 250 μm. Further, the film subjected to the stretching treatment in the MD direction was preheated at 105 ° C. for 10 seconds, then stretched 5.00 times in the TD direction at 98 ° C., and then kept in a stretched state at 97 ° C. for about 15 seconds. A polystyrene-based heat-shrinkable film was obtained.

<Comparative example 1>
A polystyrene-based heat-shrinkable film was obtained in the same manner as in Example 1 except that the stretching conditions were changed as shown in Table 2.

<Comparative example 2>
(Raw material for polyester-based heat-shrinkable film)
The polyester-based heat-shrinkable film of Comparative Example 2 described below has a single-layer structure and is a P-SF polyester-based resin manufactured by SK Chemical Corp. (referred to as “polyester (A)” in Table 1). A mixture of a silica gel master batch (referred to as "silicayl MB" in Table 1), which is EPM7E-325 manufactured by Sumika Color Co., Ltd., was used as a raw material.
Table 1 shows the glass transition point of the polyester A used (denoted as “Tg” in Table 1), the ultimate viscosity (denoted as “IV” in Table 1), and the component ratios of the components constituting the film.

(Manufacturing of polyester-based heat-shrinkable film)
The raw materials of the polyester-based heat-shrinkable film were mixed at the blending amounts shown in Table 1 and extruded from a die kept at 260 ° C. to obtain a polyester-based film raw fabric having a thickness of 200 μm and a single-layer structure. A polyester-based heat-shrinkable film was obtained in the same manner as in Example 1 except that the original film having a single-layer structure was used and the stretching conditions were changed as shown in Table 2.

Table 3 shows the results of measuring each physical property value of the heat-shrinkable film obtained in each example by the above method.
Table 4 shows the results of evaluation of each evaluation item based on the above criteria.

As shown in Tables 3 and 4, the polystyrene-based heat-shrinkable film of Example 1 is more stable during storage than the polystyrene-based heat-shrinkable film of Comparative Example 1 having a natural shrinkage rate of more than 1.5%. The sex was improved.
The polyester-based heat-shrinkable film of Comparative Example 2 using the polyester-based resin was inferior in shrinkage finish, wearability, and perforation opening property as compared with the heat-shrinkable film of Example 1.

Claims (2)

A heat-shrinkable film containing a polystyrene-based resin.
When immersed in water at 70 ° C. for 10 seconds, the heat shrinkage rate in the main shrinkage direction is 15% or less.
When immersed in water at 98 ° C. for 10 seconds, the heat shrinkage rate in the main shrinkage direction is 60% or more.
The Ermendorf tear strength in the main contraction direction is in the range of 3 to 10 N / mm.
The Ermendorf tear strength in the direction orthogonal to the main contraction direction is in the range of 10 to 20 N / mm.
The contraction stress in the main contraction direction when left at 85 ° C. for 5 minutes is 4.0 N / mm ² or less.
A heat-shrinkable film having a shrinkage rate of 1.5% or less in the main shrinkage direction when left at 40 ° C. for 7 days. The method for producing the heat-shrinkable film according to claim 1.
The heat-shrinkable film is formed by stretching in the main shrinkage direction after extrusion molding, and the stretching has a residual heat temperature of 100 ° C. or higher, a stretching temperature and a heat-fixing temperature of 90 ° C. or higher, and a stretching ratio of 4.9 or higher. A method for producing a heat-shrinkable film.