Styrene-based heat shrinkable film

Abstract

Provided is a styrene-based heat-shrinkable film that can reduce costs while reducing environmental impact, exhibits excellent molding processability, and can achieve a desired heat shrinkage rate. The styrene-based heat-shrinkable film is derived from a styrene-based resin composition and satisfies the following properties (1) to (3). (1) The styrene-based resin composition contains a styrene-butadiene copolymer resin having a styrene / butadiene blending ratio of 70 / 30 to 95 / 5, and a recycled styrene resin, and the blending ratio expressed as styrene-butadiene copolymer resin / recycled styrene resin is set to a value within the range of 90 / 10 to 70 / 30. (2) The heat shrinkage rate of a styrene-based heat-shrinkable film in the main shrinkage direction when immersed in hot water at 100°C for 10 seconds is 35% or more. (3) The nominal tensile strain at break in the direction perpendicular to the main shrinkage direction of the styrene-based heat-shrinkable film is 150% or more.

Description

[Technical Field]

[0001] The present invention relates to a styrene-based heat-shrinkable film (hereinafter, sometimes simply referred to as a heat-shrinkable film). More specifically, the present invention relates to a styrene-based heat-shrinkable film that does not substantially use expensive biomass SBC as a raw material, has a small environmental impact, exhibits a desired heat shrinkage rate, and further exhibits excellent molding processability. [Background technology]

[0002] Conventionally, heat-shrinkable films made of fossil fuel-derived resins have been widely used. Examples of resin materials used in heat-shrinkable films include fossil fuel-derived resins such as vinyl chloride, polypropylene, polyethylene, polystyrene, polyolefin, and polyethylene terephthalate. Such fossil fuel-derived resins are made from limited resources such as petroleum, and therefore have problems such as future resource shortages and environmental impact.

[0003] Therefore, a heat-shrinkable film (shrink film) containing a biomass styrene-butadiene copolymer and a resin having a predetermined Vicat temperature has been proposed, with the aim of reducing the environmental impact and improving the shrink finish (see, for example, Patent Document 1). More specifically, it is a heat-shrinkable film made by blending 50 to 98 mass% of biomass styrene-butadiene copolymer and 45 mass% or more of a resin (such as polystyrene resin or polyester resin) with a Vicat softening temperature of 75 to 90°C.

[0004] Also, a styrene-based packaging film has been proposed that aims to improve the straight cutting properties when opening or separating thick, sturdy products by hand, and to reduce the environmental impact (see, for example, Patent Document 2). More specifically, it is a styrene-based packaging film derived from biomass SBC, characterized in that the thermal shrinkage at 110°C is 1 to 15% in the length and width directions, and the thickness (t) and tear strength (R) satisfy the relationships shown in the formulas (1) and (2).A preferred embodiment of the styrene-based packaging film is derived from a styrene-based resin containing 40 to 98% by mass of recycled styrene with a melt flow rate of 4 to 7 g / 10 min in the biomass SBC. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] WO2022 / 138039 (Claims, etc.) [Patent Document 2] Patent No. 6851849 (Claims, etc.) Summary of the Invention [Problem to be solved by the invention]

[0006] However, the heat-shrinkable film described in Patent Document 1 not only requires a considerable amount of expensive biomass SBC as the main component, but also has the problem that a considerable amount of a specific resin with a Vicat softening temperature of 75 to 90°C, more preferably 75 to 85°C, must be blended and mixed uniformly. As a result, problems have been observed in that the nominal tensile break strain is significantly reduced, the processing properties are deteriorated, the haze is reduced, and further, the heat shrinkage rate is also likely to be reduced. Furthermore, since a considerable amount of biomass SBC needs to be used to achieve a predetermined biomass content, the manufacturing cost of the shrink film increases, which is economically disadvantageous.

[0007] Furthermore, the packaging film described in Patent Document 2 not only needs to use expensive biomass SBC as the main component, taking into consideration the ease of manual tearing and straight cutting when separating, but also, in a preferred embodiment, contains 40 to 98 mass % of recycled styrene resin with a specified MFR. As a result, the nominal tensile breaking strain of the packaging film is significantly reduced, which leads to problems such as a deterioration in processing characteristics or a tendency for the compounding composition to become non-uniform. Furthermore, if a biomass SBC contains a significant amount of recycled styrene resin with a specified MFR, the heat shrinkage rate tends to decrease, making it difficult to use the heat shrinkable film in a wide range of applications.

[0008] Therefore, an object of the present invention is to provide a styrene-based heat-shrinkable film that reduces the environmental impact without substantially using expensive biomass SBC, exhibits excellent molding processability, and further, can stably obtain a desired heat shrinkage ratio even under specified heat shrinkage conditions (100°C, 10 seconds). [Means for solving the problem]

[0009] The present inventors have found that the above problems can be solved by including a specific styrene-butadiene copolymer resin and a recycled styrene resin in a blending ratio within a predetermined range. That is, the present invention provides a styrene-based heat-shrinkable film derived from a styrene-based resin composition, which is characterized by satisfying the following properties (1) to (3). (1) The styrene-based resin composition contains a styrene-butadiene copolymer resin (hereinafter sometimes referred to as SBC) having a styrene / butadiene blending ratio of 70 / 30 to 95 / 5, and a recycled styrene resin, and the blending ratio expressed as SBC / recycled styrene resin (converted into polymerization amount, the same applies hereinafter) is within the range of 90 / 10 to 70 / 30. (2) The heat shrinkage rate of a styrene-based heat-shrinkable film in the main shrinkage direction when immersed in hot water at 100°C for 10 seconds is 35% or more. (3) The nominal tensile strain at break in the direction perpendicular to the main shrinkage direction (MD direction) of the styrene-based heat-shrinkable film, measured in accordance with JIS K 7161-1:2014 (corresponding to ISO 527-1:2012, the same applies below), is 150% or more. In this way, by satisfying at least the properties (1) to (3), it is possible to provide a styrene-based heat-shrinkable film that can reduce the environmental impact and production costs while substantially not using expensive biomass SBC, can stably obtain the desired heat shrinkage rate, and further exhibits excellent molding processability.

[0010] In addition, when constructing the styrene-based heat shrinkable film of the present invention, it is preferable that the nominal tensile strain at break in the main shrinkage direction (TD direction), measured in accordance with JIS K 7161-1:2014, is 30% or more. In this way, by adjusting the nominal tensile strain at break in the main shrinkage direction (TD), it is possible to exhibit more desirable molding processability not only in the MD direction of the film but also in both the TD direction.

[0011] In forming the styrene-based heat shrinkable film of the present invention, it is preferable that the haze measured in accordance with JIS K 7136:2000 (corresponding to ISO 14782:1999, the same applies hereinafter) is 10% or less. In this way, by adjusting the haze value, which is an index of transparency, the properties (1) to (3) are satisfied and usability and the like are further improved.

[0012] Furthermore, when constructing the styrene-based heat-shrinkable film of the present invention, it is preferable that the maximum point stress of the styrene-based heat-shrinkable film in the direction perpendicular to the main shrinkage direction (MD direction), measured in accordance with JIS K 7161-1:2014, is 30 MPa or more. In this way, by adjusting the maximum point stress in the MD direction, it is possible to improve the mechanical properties such as impact resistance of the heat shrinkable film.

[0013] Furthermore, when constructing the styrene-based heat-shrinkable film of the present invention, it is preferable that the tensile strength of the recycled styrene resin, measured in accordance with JIS K 6932-2:1997 (equivalent to ISO 1622-2:1995), is within the range of 36 to 60 MPa. By adjusting the tensile strength of the recycled styrene resin in this way, it is possible to suppress a decrease in the heat shrinkage rate of the heat shrinkable film even when a predetermined amount of recycled styrene resin is blended.

[0014] Furthermore, when constructing the styrene-based heat-shrinkable film of the present invention, it is preferable that the melt flow rate (200°C, 5 kg load) of the recycled styrene resin, measured in accordance with JIS K 7210-1:2014 (equivalent to ISO 1133-1:2011, the same applies hereinafter), is set to a value within the range of 3 to 10 g / 10 min. By adjusting the melt flow rate (MFR) in this manner, it becomes possible to mix the styrene-butadiene copolymer resin more uniformly, and the heat shrinkable film can exhibit more desirable molding processability and heat shrinkage rate.

[0015] In forming the styrene-based heat-shrinkable film of the present invention, the amount of butadiene in the styrene-based resin composition is preferably 8% by weight or more relative to the total amount of the styrene-based resin composition. By adjusting the amount of butadiene in this manner, the heat shrinkable film can more easily exhibit a desirable heat shrinkage rate.

[0016] In forming the styrene-based heat-shrinkable film of the present invention, it is preferable that the thickness is set to a value within the range of 20 to 80 μm. By setting the thickness of the heat shrinkable film to a value within the specified range in this way, it is possible to achieve better transparency and handling while satisfying at least the properties (1) to (3), and further improve the manufacturing process of the heat shrinkable film itself. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 1(a) is a cross-sectional view of the styrene-based heat-shrinkable film of the present invention, and FIG. 1(b) is a view provided for explaining a method of using the styrene-based heat-shrinkable film of the present invention. [Figure 2] FIG. 2 is a diagram showing the relationship between the blending ratio of recycled styrene resin in a styrene-based heat-shrinkable film and the heat shrinkage rate in the main shrinkage direction (TD). [Figure 3] FIG. 3 is a diagram showing the relationship between the blending ratio of recycled styrene resin in a styrene-based heat-shrinkable film and the nominal tensile strain at break in the direction (MD direction) perpendicular to the main shrinkage direction. [Figure 4] FIG. 4 is a diagram showing the relationship between the blending ratio of recycled styrene resin in a styrene-based heat-shrinkable film and the nominal tensile strain at break in the main shrinkage direction (TD). [Figure 5] FIG. 5 is a diagram showing the relationship between the blending ratio of recycled styrene resin in a styrene-based heat-shrinkable film and the maximum point stress in the direction (MD direction) perpendicular to the main shrinkage direction. [Figure 6] FIG. 6 is a diagram showing the relationship between the blending ratio of recycled styrene resin in a styrene-based heat-shrinkable film and the maximum point stress in the main shrinkage direction (TD direction). [Figure 7] FIG. 7 is a diagram showing the relationship between the blending ratio of recycled styrene resin in a styrene-based heat-shrinkable film and haze. [Figure 8] FIG. 8 is a diagram showing the relationship between the blending ratio of recycled styrene resin in a styrene-based heat-shrinkable film and total light transmittance. DETAILED DESCRIPTION OF THE INVENTION

[0018] [First embodiment] As illustrated in Figs. 1(a) to (b), the present invention relates to a styrene-based heat-shrinkable film 10 derived from a styrene-based resin composition, which is characterized by satisfying the following properties (1) to (3): (1) The styrene-based resin composition contains a styrene-butadiene copolymer resin (SBC) having a styrene / butadiene blending ratio of 70 / 30 to 95 / 5, and a recycled styrene resin, and the blending ratio (by weight) expressed as SBC / recycled styrene resin is set to a value within the range of 90 / 10 to 70 / 30. (2) The heat shrinkage rate of a styrene-based heat-shrinkable film in the main shrinkage direction (TD) when immersed in hot water at 100°C for 10 seconds is 35% or more. (3) The nominal tensile strain at break of the styrene-based heat-shrinkable film in the direction perpendicular to the main shrinkage direction (MD direction), measured in accordance with JIS K 7161-1:2014, is 150% or more. Hereinafter, a styrene-based heat-shrinkable film satisfying at least the properties (1) to (3) and a styrene-based resin composition as a raw material for constituting the same will be specifically described.

[0019] 1. Styrene-based resin composition The styrene-based heat shrinkable film of the present invention is derived from a styrene-based resin composition, and preferably has a layer made of, for example, a styrene-based resin composition. The styrene-based resin composition is characterized by containing SBC and recycled styrene resin, with the SBC / recycled styrene resin blending ratio (blending ratio) being within the range of 90 / 10 to 70 / 30. The reason for this is that recycled styrene resin can reduce the environmental impact while also reducing costs, and furthermore can exhibit excellent moldability and a desired heat shrinkage rate. That is, by containing at least SBC and recycled styrene resin in such a blending ratio, it is possible to achieve a good balance between excellent moldability and excellent impact resistance. Furthermore, by blending recycled styrene resin in a predetermined ratio, it is possible to reduce the haze of the heat-shrinkable film and further prevent an increase in haze. Therefore, it can be said that the styrene-based heat-shrinkable film of the present invention also has excellent optical properties. Therefore, the blending ratio of SBC / recycled styrene resin is more preferably set to a value within the range of 90 / 10 to 75 / 25, and even more preferably to a value within the range of 90 / 10 to 80 / 20.

[0020] FIG. 2 shows the relationship between the blending ratio of recycled styrene resin in the blending ratio of SBC / recycled styrene resin in the styrene-based resin composition and the heat shrinkage rate in the main shrinkage direction (TD) of the heat-shrinkable film. That is, the X-axis represents the blending ratio (parts by weight) of recycled styrene resin, and the Y-axis represents the heat shrinkage rate (%) in the main shrinkage direction (TD direction) of the heat shrinkable film. The plotted data correspond to Examples 1 to 3 (each Example is denoted as EX, and the same applies hereinafter) and Comparative Examples 1 to 3 (each Comparative Example is denoted as CE, and the same applies hereinafter) described below. As shown by the characteristic curve in FIG. 2, it can be seen that there is a linear relationship between the blending ratio of recycled styrene resin and the heat shrinkage rate of the heat shrinkable film in the TD direction. Therefore, it is understood that when the blending ratio of recycled styrene resin is 10 to 30 parts by weight (i.e., when the blending ratio of SBC / recycled styrene resin is 90 / 10 to 70 / 30), a high thermal shrinkage rate in the TD direction of 35% or more can be obtained as a heat-shrinkable film.

[0021] Furthermore, even if the styrene-based heat-shrinkable film of the present invention contains a predetermined amount of recycled styrene resin, it can achieve a high heat shrinkage ratio even at a relatively low temperature of 100°C for 10 seconds. Therefore, it can be said that it is suitable for heat-shrinkable films (including packaging films) that require a high shrinkage ratio at a low heating temperature. Furthermore, the styrene-based heat-shrinkable film of the present invention can exhibit the effects described above in terms of heat shrinkage, moldability, and optical properties by adjusting the blending ratio of these two components. Moreover, these effects can be obtained not only in multilayer heat-shrinkable films but also in single-layer heat-shrinkable films, which also makes the film superior in terms of convenience and ease of production.

[0022] (1) Styrene-butadiene copolymer resin The lower limit of the content of styrene-butadiene copolymer resin (SBC) in such a styrene-based resin composition is usually 65% ​​by weight or more, preferably 70% by weight or more, more preferably 75% by weight or more, and even more preferably 80% by weight or more, based on the total amount. On the other hand, the upper limit of the SBC content is usually preferably 95% by weight or less, and more preferably 90% by weight or less, based on the total amount. In other words, by including SBC in such a content ratio and using recycled general-purpose polystyrene resin in combination in a specified blend ratio, it is possible to reduce the environmental impact and also to achieve a desirable heat shrinkage rate.

[0023] Such a styrene-butadiene copolymer resin is a resin containing at least a styrene-butadiene copolymer, and the blending ratio of styrene / butadiene is usually 70 / 30 to 95 / 5, preferably in the range of 77 / 23 to 93 / 7, and more preferably in the range of 80 / 20 to 90 / 10. By using SBC in such a blending ratio, it is possible to exhibit favorable molding processability, and in particular, it is possible to exhibit excellent impact resistance and molding processability in a well-balanced manner. Furthermore, recycled styrene resin alone may not have sufficient impact resistance and molding processability, but by combining SBC containing styrene and butadiene at such a blending ratio with recycled styrene resin at a predetermined blending ratio, it is possible to exhibit favorable impact resistance and molding processability, and further, favorable heat shrinkage properties.

[0024] The styrene-butadiene copolymer is a copolymer having styrene monomer and butadiene monomer as monomer components. Examples of such styrene monomers include styrene, o-methylstyrene, p-methylstyrene, p-tert-butylstyrene, 1,3-dimethylstyrene, α-methylstyrene, vinylnaphthalene, vinylanthracene, and 1,1-diphenylethylene, either singly or in combination. A particularly preferred styrene monomer is styrene. The butadiene monomer may be 1,3-butadiene or 1,2-butadiene, either singly or in mixture of two or more. The styrene-butadiene copolymer may be prepared by polymerizing monomer components using a predetermined polymerization method, or it is also preferable to use a commercially available product.

[0025] In addition, it is also preferable that the styrene-butadiene copolymer contains, as part of the raw material monomers, a monomer component other than the styrene monomer and the butadiene monomer. Such a monomer component may include at least one of conjugated dienes other than butadiene, vinyl monomers, polymerizable unsaturated carboxylic acid esters, and polymerizable unsaturated carboxylic acid anhydrides.

[0026] The copolymerization form of such a styrene-butadiene copolymer may be, for example, a random copolymer, a block copolymer, or a graft copolymer, and is preferably a block copolymer. That is, the styrene-butadiene copolymer is more preferably a styrene-butadiene block copolymer. The block structure of such a styrene-butadiene block copolymer preferably contains styrene and butadiene in the styrene / butadiene blending ratio as described above. Such a block structure allows the film to exhibit favorable impact resistance and moldability, and in turn, allows the film to exhibit favorable heat shrinkage properties as a heat shrinkable film.

[0027] Such a styrene-butadiene block copolymer may be a copolymer having alternating styrene blocks in which only styrene monomer is polymerized and butadiene blocks in which only butadiene is polymerized, and examples of such a block copolymer include one or a combination of two or more of the following: That is, styrene-butadiene block copolymers having styrene blocks at both ends, such as styrene-butadiene-styrene block copolymers (SBS) and styrene-butadiene-styrene-butadiene-styrene block copolymers (SBSBS). Also included are styrene-butadiene block copolymers having a styrene block and a butadiene block at the terminals, such as styrene-butadiene copolymer (SB) and styrene-butadiene-styrene-butadiene copolymer (SBSB). Further, there are styrene-butadiene block copolymers having butadiene blocks at both ends, such as butadiene-styrene-butadiene copolymer (BSB) and butadiene-styrene-butadiene-styrene-butadiene copolymer (BSBSB). Among these, a styrene-butadiene block copolymer having styrene blocks at both ends is particularly preferred, and SBS is particularly preferred.

[0028] Such a styrene-butadiene copolymer can be obtained by a production method known in the art, or a commercially available styrene-butadiene copolymer may be used. Preferably, such a styrene-butadiene block copolymer is produced by, for example, living polymerization (living radical polymerization, living anionic polymerization, or living cationic polymerization).

[0029] The styrene-butadiene copolymer resin may be a resin containing only a styrene-butadiene copolymer, or it is also preferable that the resin contains additives such as an antioxidant, a colorant, and a heat stabilizer in addition to the styrene-butadiene copolymer. The content of the styrene-butadiene copolymer in the styrene-butadiene copolymer resin is usually preferably 90% by weight or more, more preferably 95% by weight or more, and even more preferably 98% by weight or more, relative to the total amount (100% by weight), or may be 100% by weight.

[0030] Furthermore, the Vicat softening temperature of such styrene-butadiene copolymer resin is not particularly limited, but is generally preferably 100°C or lower, more preferably 95°C or lower, and even more preferably 90°C or lower. The Vicat softening temperature can be measured by a method conforming to the B50 method (corresponding to ISO 306:2013) of JIS K 7206 "Plastics - Thermoplastics - Determination of Vicat softening temperature (VST)".

[0031] Furthermore, it is generally preferable that the MFR (200°C, 5 kg load) of the styrene-butadiene copolymer resin, measured in accordance with JIS K 7210-1:2014, is set to a value within the range of 4 to 8 g / 10 min. The reason for this is that by using a styrene-butadiene copolymer resin having such an MFR, extrusion molding becomes easy and the desired heat shrinkage rate becomes easy to achieve. Therefore, it is more preferable that the MFR is set to a value within the range of 4.5 to 7.5 g / 10 min, and even more preferable that it is set to a value within the range of 5.0 to 7.0 g / 10 min.

[0032] Furthermore, the styrene-butadiene copolymer resin is preferably a virgin (unused) styrene-butadiene copolymer resin. That is, the styrene-butadiene copolymer resin is preferably a virgin styrene-butadiene copolymer resin obtained by recycling molded articles, unlike the recycled styrene resin described below.

[0033] (2) Recycled styrene resin The upper limit of the amount of such recycled styrene resin to be blended is usually 35% by weight or less, preferably 30% by weight or less, more preferably 25% by weight or less, and even more preferably 20% by weight or less, based on the total amount of the styrene-based resin composition. On the other hand, the lower limit of the amount of recycled styrene resin to be blended is usually preferably 5% by weight or more, more preferably 8% by weight or more, and even more preferably 10% by weight or more, relative to the total amount of the styrene-based resin composition. The reason for this is that by setting the amount of recycled styrene resin to a value within a specified range, it becomes easier to achieve desirable molding processability and heat shrinkage while still achieving the effect of reducing the environmental impact of recycled general-purpose polystyrene resin. For example, when 1 kg of styrene-based heat-shrinkable film is burned, the amount of carbon dioxide emitted is approximately 0.179 kg for recycled styrene resin, while it is 2.453 kg for virgin material, which shows that it has a significant effect in reducing environmental impact and is also inexpensive. Furthermore, by including such a recycled styrene resin, the transparency (based on haze or total light transmittance) of the styrene-based heat-shrinkable film can be improved.

[0034] Therefore, such recycled styrene resin may be a styrene resin obtained by recycling used polystyrene resin, or may be a molded article formed from general-purpose polystyrene (GPPS). Such recycling may be either material recycling or chemical recycling. For example, such recycled styrene resin is preferably a resin material obtained by crushing, washing, and regenerating pellets from used GPPS.

[0035] Furthermore, it is generally preferable that the MFR (200°C, 5 kg load) of such recycled styrene resin, measured in accordance with JIS K 7210-1:2014, is set to a value within the range of 3 to 10 g / 10 min. The reason for this is that by adjusting the MFR within the specified range, the copolymer becomes more easily mixed with the styrene-butadiene copolymer, and when actually used as a heat-shrinkable film, it becomes easier to obtain a specified heat shrinkage rate, and further, the processing characteristics in film production can be improved. Therefore, it is more preferable that the MFR of such recycled styrene resin is set to a value within the range of 3.3 to 9 g / 10 min, even more preferably within the range of 3.5 to 8 g / 10 min, and even more preferably within the range of 3.7 to 7 g / 10 min. It is also preferable that the molecular weight distribution (Mw / Mn) of the recycled styrene resin, based on the weight average molecular weight (Mw) and the number average molecular weight (Mn), falls within a range of 2-4. The reason for this is that by adjusting the molecular weight distribution within a predetermined range, a heat-shrinkable film having a good balance between mechanical strength and moldability can be obtained. Therefore, the molecular weight distribution (Mw / Mn) is more preferably set to a value within the range of 2.1 to 3.8, even more preferably set to a value within the range of 2.2 to 3.5, and even more preferably set to a value within the range of 2.4 to 3.0.

[0036] (3) Butadiene content The amount of butadiene in the styrene resin composition is usually preferably 8% by weight or more relative to the total amount of the styrene resin composition. This is because the heat shrinkable film can be made to exhibit desirable heat shrink properties and can also be given desirable elongation properties, for example, elongation properties represented by nominal tensile break strain. On the other hand, if the butadiene content is too high, the heat shrinkable film becomes too flexible, making it difficult to handle and difficult to produce stably, and further, the desired tension may not be obtained during packaging. Therefore, the amount of butadiene in the styrene resin composition is preferably set to a value within a range of 9 to 40% by weight, more preferably a value within a range of 10 to 20% by weight, and even more preferably a value within a range of 12 to 16% by weight, based on the total amount.

[0037] (4) Additives It is also preferable that such a styrene-based resin composition contains predetermined amounts of various additives within the scope of the object of the invention. Such additives may include, for example, at least one of an antiblocking agent, an antistatic agent, an antioxidant, an ultraviolet absorber, a light stabilizer, a plasticizer, a coupling agent, and a processing aid.

[0038] For example, when the styrene-based resin composition contains a known antiblocking agent such as an organic antiblocking agent or an inorganic antiblocking agent, the composition can be easily processed into a roll, and the composition can be more stably produced even in a long shape. More specifically, suitable organic antiblocking agents include HIPS (high impact polystyrene), crosslinked acrylic resins, crosslinked polyester resins, crosslinked polystyrene resins, and silicone resins. On the other hand, suitable inorganic antiblocking agents include inorganic particles (silica, talc, or calcium carbonate), inorganic oxides, and carbonates.

[0039] The content of the antiblocking agent in the styrene-based resin composition is usually preferably in the range of 0.1 to 4 wt %, more preferably in the range of 0.2 to 3 wt %, and even more preferably in the range of 0.3 to 2 wt %, relative to the weight of the styrene-based resin composition. This makes it possible to exert an anti-blocking effect while suppressing the influence on the heat shrinkage properties and molding processability of the heat shrinkable film.

[0040] The styrene-based resin composition also preferably contains an antistatic agent. As the antistatic agent, surfactant-based antistatic agents are preferred, and nonionic surfactants are particularly preferred. The content of the antistatic agent in the styrene-based resin composition is preferably in the range of 0.1 to 4 wt %, more preferably in the range of 0.2 to 3 wt %, and even more preferably in the range of 0.3 to 2 wt %, relative to the weight of the styrene-based resin composition. This makes it possible to exert the effect of the antistatic agent while suppressing the influence on the heat shrinkage properties and molding processability of the heat shrinkable film.

[0041] 2. Styrene-based heat-shrinkable film (1) Heat shrinkage rate A1 As a characteristic (2) of the present invention, the styrene-based heat-shrinkable film is characterized in that the heat shrinkage rate (hereinafter, sometimes simply referred to as heat shrinkage rate A1) in the main shrinkage direction (usually TD direction) when immersed in hot water at 100°C for 10 seconds is 35% or more. The reason for this is that by controlling the heat shrinkage rate to a predetermined value, the range of uses for the styrene-based heat shrinkable film can be expanded, the thickness can be easily controlled within a predetermined range in production, and the film can be made more user-friendly. However, if the heat shrinkage rate is too high, applicable production methods, usable monomer types, yields, etc. may be excessively limited. Therefore, the heat shrinkage rate A1 is more preferably set to a value within the range of 35 to 70%, even more preferably set to a value within the range of 40 to 65%, and even more preferably set to a value within the range of 45 to 60%.

[0042] FIG. 2 shows the relationship between the blending ratio of recycled styrene resin in the blending ratio of styrene-butadiene copolymer resin / recycled styrene resin in the styrene-based resin composition and the thermal shrinkage rate in the main shrinkage direction. The X-axis shows the thermal shrinkage rate (%), and the Y-axis shows the blending ratio (parts by weight) of recycled styrene resin. The lot data corresponds to Examples 1 to 3 and Comparative Examples 1 to 3 described below. As shown in FIG. 2, it can be seen that when the blending ratio of recycled styrene resin is 10 to 30 parts by weight (i.e., when the blending ratio of styrene-butadiene copolymer resin / recycled styrene resin is 90 / 10 to 70 / 30), a desirable heat shrinkage rate of 35% or more in the main shrinkage direction can be obtained.

[0043] (2) Heat shrinkage rate A2 As a characteristic of the present invention, it is preferable that the styrene-based heat-shrinkable film has a heat shrinkage rate (sometimes referred to as heat shrinkage rate A2) of 10% or less in a direction perpendicular to the main shrinkage direction (usually MD direction) when immersed in hot water at 100°C for 10 seconds. The reason for this is that by controlling the heat shrinkage rate to a predetermined value, unnecessary shrinkage in the MD direction during the shrink treatment of the styrene-based heat shrinkable film is suppressed, making it easier to realize a desired design on the film. However, if the heat shrinkage rate A2 is too low, the film may be excessively deformed during heat shrinkage. Therefore, the heat shrinkage rate A2 is more preferably set to a value within the range of -10 to 10%, even more preferably set to a value within the range of -8 to 8%, and even more preferably set to a value within the range of -5 to 5%.

[0044] (3) Nominal tensile strain at break in the direction perpendicular to the principal shrinkage direction As characteristic (3) of the present invention, the styrene-based heat-shrinkable film is characterized in that the nominal tensile strain at break (meaning the strain at break when there is a yield point in the SS curve, or the strain at break when there is no yield point; the same applies hereinafter) in the direction (MD) perpendicular to the main shrinkage direction (TD) measured in accordance with JIS K 7161-1:2014 is 150% or more. The reason for this is that by controlling the nominal tensile strain at break to a predetermined value or more, the molding processability of the styrene-based heat-shrinkable film is improved, and the convenience when using the styrene-based heat-shrinkable film, for example, when packaging containers, is improved. However, if the nominal tensile strain at break becomes too high, the dimensional stability or film strength may be adversely affected, and the appropriate tension may not be maintained during packaging. Therefore, it is more preferable that the nominal tensile strain at break is set to a value within the range of 100 to 500%, even more preferably within the range of 150 to 350%, and even more preferably within the range of 200 to 300%.

[0045] FIG. 3 shows the relationship between the blending ratio of recycled styrene resin in the blending ratio of styrene-butadiene copolymer resin / recycled styrene resin in the styrene-based resin composition and the nominal tensile strain at break in the direction (MD) perpendicular to the main shrinkage direction (TD). The X-axis shows the blending ratio (parts by weight) of recycled styrene resin, and the Y-axis shows the nominal tensile strain at break (%) in the MD direction. The plotted data correspond to Examples 1 to 3 and Comparative Examples 1 to 3. As shown by the characteristic curve in FIG. 3, it can be seen that there is a linear relationship between the blending ratio of recycled styrene resin and the nominal tensile break strain of the heat shrinkable film. Therefore, it is understood that when the blending ratio of recycled styrene resin is 10 to 30 parts by weight (i.e., the blending ratio of styrene-butadiene copolymer resin / recycled styrene resin is 90 / 10 to 70 / 30), a nominal tensile break strain of 150% or more can be obtained, and desirable molding processability can be easily obtained.

[0046] (4) Nominal tensile strain at break in the principal shrinkage direction Furthermore, the styrene-based heat shrinkable film preferably has a nominal tensile strain at break in the main shrinkage direction (TD direction) of 30% or more, as measured in accordance with JIS K 7161-1:2014. The reason for this is that by controlling the nominal tensile strain at break to a predetermined value, it is possible to maintain an appropriate tension in the main shrinkage direction during packaging in a container, while also improving moldability. However, if the nominal tensile strain at break becomes too high, the dimensional stability or film strength may be adversely affected, and the appropriate tension may not be maintained during packaging. Therefore, it is more preferable that the nominal tensile strain at break in the main shrinkage direction is set to a value within the range of 60 to 200%, even more preferably within the range of 80 to 150%, and even more preferably within the range of 100 to 130%.

[0047] FIG. 4 shows the relationship between the blending ratio of recycled styrene resin in the blending ratio of styrene-butadiene copolymer resin / recycled styrene resin in the styrene-based resin composition and the nominal tensile strain at break in the main shrinkage direction. The X-axis shows the blending ratio (parts by weight) of recycled styrene resin, and the Y-axis shows the nominal tensile strain at break (%). The plotted data correspond to Examples 1 to 3 and Comparative Examples 1 to 3. As shown by the characteristic curve in FIG. 4, it can be seen that the blending ratio of recycled styrene resin and the nominal tensile break strain of the heat shrinkable film have a linear relationship with small variation and a high correlation coefficient. Furthermore, when the blending ratio of recycled styrene resin is 10 to 30 parts by weight (i.e., the blending ratio of styrene-butadiene copolymer resin / recycled styrene resin is 90 / 10 to 70 / 30), a nominal tensile break strain of 150% or more is obtained, and it can be said that desirable molding processability is exhibited.

[0048] (5) Maximum stress in the direction perpendicular to the principal shrinkage direction Furthermore, it is generally preferable that the maximum point stress of the styrene-based heat-shrinkable film in the direction (MD direction) perpendicular to the main shrinkage direction (TD direction), measured in accordance with JIS K 7161-1:2014, is a value of 30 MPa or more. The reason for this is that by limiting the maximum point stress in such a film to a value within a predetermined range, the impact resistance of the heat shrinkable film can be improved, and the film strength can be increased. On the other hand, if the maximum point stress of the film before heat shrinkage is excessively large, the handling property may be deteriorated and the flexibility required for packaging may be lacking. Therefore, it is more preferable that the maximum point stress be set to a value within the range of 30 to 60 MPa, even more preferably within the range of 32 to 50 MPa, and even more preferably within the range of 33 to 45 MPa.

[0049] FIG. 5 shows the relationship between the blending ratio of recycled styrene resin in the blending ratio of styrene-butadiene copolymer resin / recycled styrene resin in the styrene-based resin composition and the maximum point stress in the direction (MD) perpendicular to the main shrinkage direction (TD). The X-axis shows the blending ratio (parts by weight) of the recycled styrene resin, and the Y-axis shows the maximum stress (MPa) of the heat-shrinkable film in the MD direction. The plotted data correspond to Examples 1 to 3 and Comparative Examples 1 to 3. As shown by the characteristic curve in FIG. 5, it can be seen that the blending ratio of recycled styrene resin and the maximum stress of the heat shrinkable film have a linear relationship with small variation and a high correlation coefficient. Therefore, when the blending ratio of recycled styrene resin is 10 to 30 parts by weight (i.e., when the blending ratio of SBC / recycled styrene resin is 90 / 10 to 70 / 30), a maximum point stress of 30 MPa or more can be obtained, and desirable mechanical properties and impact resistance can be exhibited. However, if the proportion of recycled styrene resin is too high, the desired nominal tensile break strain cannot be obtained. However, by setting the blending ratio of recycled styrene resin to 10 to 30 parts by weight (i.e., a blending ratio of styrene-butadiene copolymer resin / recycled styrene resin of 90 / 10 to 70 / 30), it is possible to achieve the desired nominal tensile break strain and a more desirable maximum point stress. That is, by using such a compounding ratio, it is possible to obtain desirable values ​​for both the moldability and impact resistance of the heat shrinkable film, and in turn, it is possible to improve the moldability.

[0050] (6) Maximum stress in the direction of principal shrinkage Furthermore, it is preferable that the maximum point stress of the styrene-based heat shrinkable film in the main shrinkage direction (TD direction) measured in accordance with JIS K 7161-1:2014 is 50 MPa or more. The reason for this is that by limiting the maximum point stress in such a film to a value within a predetermined range, the impact resistance of the heat shrinkable film is improved, and undesirable deformation of the film during or after packaging can be prevented, for example. On the other hand, if the maximum point stress of the film before heat shrinkage is excessively large, it may have an adverse effect on the heat shrinkability, which may result in poor handling properties or a lack of flexibility required for packaging. Therefore, it is more preferable that the maximum point stress in the main shrinkage direction of the heat shrinkable film is within the range of 50 to 100 MPa, even more preferably within the range of 60 to 95 MPa, and even more preferably within the range of 65 to 90 MPa.

[0051] FIG. 6 shows the relationship between the blending ratio (parts by weight) of recycled styrene resin in the blending ratio of styrene-butadiene copolymer resin / recycled styrene resin in the styrene-based resin composition and the maximum point stress in the main shrinkage direction (TD direction). The X-axis shows the blending ratio (parts by weight) of the recycled styrene resin, and the Y-axis shows the maximum stress (MPa) of the heat-shrinkable film in the TD direction. The plotted data correspond to Examples 1 to 3 and Comparative Examples 1 to 3. As shown by the characteristic curve in FIG. 6, it can be seen that the maximum point stress in the TD direction increases until the blending ratio of recycled styrene resin reaches about 20 parts by weight, and then gradually decreases. Therefore, it can be seen from FIG. 6 that the styrene-based heat-shrinkable film of the present invention can achieve a maximum point stress of 60 MPa or more, which provides desirable mechanical strength, impact resistance, and the like.

[0052] (7) Hayes It is also preferable that the haze of a styrene-based heat-shrinkable film (usually 40 μm thick) measured in accordance with JIS K 7136:2000 is 10% or less. The reason for this is that by specifically limiting the haze value of such a film to a value within a predetermined range, it becomes easier to quantitatively control the transparency of the heat-shrinkable film, and since the transparency is good, it is possible to further enhance versatility. More specifically, if the haze value of the film before heat shrinkage exceeds 10%, the transparency decreases, which may make it difficult to apply the film to decorative purposes and the like. On the other hand, if the haze value of the film before heat shrinkage is too small, it becomes difficult to control stably, and the production yield may decrease significantly. Therefore, it is more preferable that the haze value of the heat shrinkable film is within the range of 0.1 to 10%, even more preferably within the range of 0.3 to 8.0%, particularly preferably within the range of 0.5 to 6.0%, and even more preferably within the range of 0.5 to 5.0%.

[0053] FIG. 7 shows the relationship between the blending ratio of recycled styrene resin in the blending ratio of styrene-butadiene copolymer resin / recycled styrene resin in the styrene resin composition and the haze of the styrene heat shrinkable film. The X-axis shows the blending ratio (parts by weight) of the recycled styrene resin, and the Y-axis shows the haze (%) of the heat-shrinkable film. The plotted data correspond to Examples 1 to 3 and Comparative Examples 1 to 3. As shown in the characteristic curve in FIG. 7, by blending a predetermined amount of recycled styrene resin, the haze is reduced and the transparency of the heat shrinkable film is improved.

[0054] (8) Total light transmittance It is also preferable that the total light transmittance of the styrene-based heat-shrinkable film measured in accordance with JIS K 7136:2000 is 90% or more. The reason for this is that by specifically limiting the total light transmittance of such a film to a value within a predetermined range, it becomes easier to quantitatively control the transparency of the heat-shrinkable film, and since the transparency is good, it is possible to further enhance versatility. More specifically, if the total light transmittance of the film before heat shrinkage is less than 90%, the transparency decreases, which may make it difficult to apply the film to decorative purposes and the like. On the other hand, if the total light transmittance of the film before heat shrinkage is excessively high, it becomes difficult to stably control it, and the production yield may decrease significantly. Therefore, it is more preferable that the total light transmittance of the heat shrinkable film is set to a value within the range of 92 to 99%, and even more preferably within the range of 93 to 98%.

[0055] FIG. 8 shows the relationship between the blending ratio of recycled styrene resin in the blending ratio of styrene-butadiene copolymer resin / recycled styrene resin in the styrene resin composition and the total light transmittance of the styrene heat-shrinkable film. The X-axis shows the blending ratio (parts by weight) of recycled styrene resin, and the Y-axis shows the total light transmittance (%) of the heat-shrinkable film. The plotted data correspond to Examples 1 and 2 and Comparative Examples 1 and 2, which use recycled general-purpose polystyrene A. From the characteristic curve in FIG. 8, it can be seen that the styrene-based heat-shrinkable film of the present invention exhibits high total light transmittance by blending a predetermined amount of recycled styrene resin.

[0056] (9) Thickness The thickness of the heat shrinkable film is preferably set to a value within the range of 20 to 80 μm. The reason for this is that by controlling the thickness to a value within a predetermined range, not only is the usability improved, but the specific gravity is controlled to a value below a desired value, and excellent heat shrinkability, transparency, etc. can be obtained. More specifically, if the heat shrinkable film has a thickness of less than 20 μm, it may become difficult to adjust the specific gravity or the coefficient of thermal expansion, or the handling properties may be significantly reduced. On the other hand, if the thickness of the heat shrinkable film exceeds 80 μm, the transparency may decrease and it may become difficult to achieve a uniform thickness. Therefore, it is more preferable that the thickness of the heat shrinkable film is set to a value within the range of 30 to 75 μm, and even more preferable that it is set to a value within the range of 40 to 70 μm.

[0057] (10) Layer composition The styrene-based heat-shrinkable film may be a single-layer styrene-based heat-shrinkable film or a multi-layer styrene-based heat-shrinkable film. In the case of a single-layer styrene-based heat-shrinkable film, the styrene-based heat-shrinkable film may have only a layer formed from the above-mentioned styrene-based resin composition. On the other hand, in the case of a multilayer styrene-based heat-shrinkable film, it is preferable that the styrene-based heat-shrinkable film has, in addition to the layer formed from the styrene-based resin composition described above, another layer laminated on one or both sides of the base layer. Therefore, in order to more effectively exert the effects of the present invention, the thickness (μm) of the layer formed from such a styrene-based resin composition may account for 50% or more, preferably 60% or more, and more preferably 70% or more of the total thickness (μm) of the film. The thickness (μm) of the layer formed from such a styrene-based resin composition may be, for example, 99% or less, 95% or less, or 90% or less of the total thickness (μm) of the film, and the remaining thickness may be such other layer. The other layer may be, for example, a resin layer different from the styrene-based resin composition. Therefore, in order to improve the transparency and / or flexibility of the film, the resin layer is preferably, for example, a styrene-based resin layer, particularly a styrene-based resin layer copolymerized with butadiene.

[0058] [Second embodiment] The second embodiment relates to a method for producing the heat shrinkable film of the first embodiment.

[0059] 1. Preparation of raw materials and melting process First, the styrene-butadiene copolymer resin, the recycled styrene resin, and any additives are prepared as raw materials, which may be the materials described above. Next, the raw materials are weighed and charged into the stirring vessel, and are preferably heated and melted in the stirring vessel until they become homogeneous, thereby obtaining a styrene-based resin composition.

[0060] 2. Raw sheet production process Next, the styrene-based resin composition obtained by uniformly mixing the raw materials is dried to an absolute dry state as necessary, and then typically extrusion-molded to prepare a raw sheet of a predetermined thickness. More specifically, it is preferable to carry out extrusion molding using an extruder under conditions of an extrusion temperature of 180 to 260°C, preferably 200 to 240°C, and more preferably 210 to 230°C. With regard to the ratio of the length (L) to the diameter (D) of the extruder, it is usually preferable that L / D is a value within the range of 20 to 40, and more preferably L / D is a value within the range of 25 to 35. The extrusion screw diameter is preferably set to a value within the range of 15 to 35 mm, and more preferably to a value within the range of 20 to 30 mm. In this way, extrusion molding is carried out using a predetermined extruder to obtain a raw sheet having a predetermined thickness, for example, 100 μm to 1000 μm, preferably 150 μm to 500 μm, and more preferably 200 μm to 300 μm. The type of extruder is not particularly limited, but typically a single-screw extruder or a twin-screw extruder can be used.

[0061] 3. Styrene-based heat-shrinkable film production process Next, the obtained raw sheet is preferably stretched by moving it over and between rolls while being heated and pressed using a shrink film manufacturing device. More specifically, the stretching ratio in the TD direction is usually preferably set to a value within the range of 300 to 600%, more preferably to a value within the range of 330 to 500%, and even more preferably to a value within the range of 350 to 450%. On the other hand, the stretching ratio in the MD direction is usually preferably set to a value within the range of 80 to 120%, more preferably to a value within the range of 85 to 115%, and even more preferably to a value within the range of 90 to 110%.

[0062] That is, a styrene-based heat-shrinkable film can be produced by performing the stretching treatment in this manner. Furthermore, in the stretching process, it is preferable to additionally perform a preheating process and a fixing process. Therefore, it is usually preferable to set the preheating temperature to a value within the range of 85 to 110°C, and more preferably to a value within the range of 90 to 105°C.

[0063] The stretching temperature is preferably set to a value within the range of 90 to 130°C, more preferably within the range of 95 to 120°C, and even more preferably within the range of 100 to 110°C. Such a stretching temperature is particularly suitable for stably stretching a raw sheet formed from such a styrene-based resin composition.

[0064] Next, after the stretching, it is also preferable to carry out a relaxation operation. The heat setting temperature in such a relaxation operation is usually preferably set to a value within the range of 65 to 100°C, more preferably a value within the range of 70 to 95°C. By such a relaxation operation, the stretching ratio in the TD direction is preferably set to a value within the range of 250 to 650%, and more preferably to a value within the range of 350 to 550%.

[0065] On the other hand, the stretching ratio in the MD direction is usually preferably set to a value within the range of 80 to 120%, and more preferably to a value within the range of 90 to 110%. Furthermore, in such a relaxation operation, only the stretching ratio in the TD direction may be changed, and the stretching ratio in the MD direction may not be changed.

[0066] 4. Inspection process for styrene-based heat shrinkable film (optional process) It is preferable to provide a predetermined inspection step (optional step) by continuously or intermittently measuring the following characteristics of the produced styrene-based heat-shrinkable film. That is, by measuring the following properties through a predetermined inspection process and confirming that the values ​​fall within the predetermined ranges, a styrene-based heat-shrinkable film can be obtained that has more uniform specific gravity separation properties and heat-shrinkage properties. 1) Visual inspection of the appearance of styrene-based heat shrinkable film 2) Thickness variation measurement 3) Tensile modulus measurement 4) Tear strength measurement 5) Viscoelasticity measurement using SS curves

[0067] [Third embodiment] The third embodiment relates to a method of using the styrene-based heat-shrinkable film of the first embodiment. Therefore, any known method for using shrink films can be suitably applied. For example, when using a styrene-based heat-shrinkable film, first, the styrene-based heat-shrinkable film is cut to an appropriate length and width and formed into a long cylindrical object. Next, the long cylindrical product is fed to an automatic label attachment device (shrink labeler) and further cut to the required length. The container is then fitted onto the contents. Examples of such containers include, but are not limited to, resin containers (e.g., PET resin containers, particularly PET bottles, and polyolefin resin containers, particularly PP bottles) and glass containers (e.g., glass bottles). These containers may be, for example, containers for beverages, food such as seasonings, cosmetics, medicines, or daily necessities.

[0068] Next, the styrene-based heat-shrinkable film fitted around the container is heat-treated by passing it through a hot air tunnel or steam tunnel at a predetermined temperature. These tunnels provide radiant heat such as infrared rays, or heated steam at about 100°C is blown onto the film from the surrounding area, thereby uniformly heating the styrene-based heat-shrinkable film and causing it to shrink. Therefore, by adhering the label to the outer surface of the container, a labeled container can be quickly obtained.

[0069] That is, the styrene-based heat shrinkable film of the present invention can achieve a desired heat shrinkage ratio and improve moldability while reducing the environmental impact and costs by using a styrene-butadiene copolymer resin having the specific composition detailed in the first embodiment and a styrene-based resin composition containing recycled styrene resin. Furthermore, the impact resistance of the heat shrinkable film can be improved. [Example]

[0070] Next, the present invention will be described in more detail by way of examples. However, the present invention is not limited to the following examples, and can be practiced by making appropriate modifications, all of which are included in the technical scope of the present invention.

[0071] [Example 1] 1. Raw material preparation First, the following styrene-butadiene copolymer resin and recycled styrene resin to be used in Example 1 were prepared.

[0072] 1) Styrene-butadiene copolymer resin Styrene-butadiene block copolymer Styrene / butadiene ratio is 85 / 15 The molecular weight of the styrene block is 24,000 and 125,000

[0073] 2) Recycled styrene resin Recycled general-purpose polystyrene A Tensile strength (JIS K 7161-1:2014, 50mm / min): 50MPa Vicat softening temperature (JIS K 7206, 50℃ / hour, 1kg): 90℃ MFR (JIS K 7210-1:2014, 200℃ / 5kg weight): 3.8g / min Glass transition temperature: 99.6℃

[0074] A styrene-based resin composition was prepared by melt-mixing 90 parts by weight of the styrene-butadiene copolymer resin and 10 parts by weight of the recycled styrene resin. The styrene resin composition is preferably extruded using a vacuum vent twin-screw extruder, for example, at an extrusion temperature of 190 to 230°C, preferably 200 to 220°C, with an L / D ratio of 20 to 40, preferably 25 to 35, and an extrusion screw diameter of 15 to 35 mm, preferably 20 to 30 mm. Then, it is preferable to form a raw sheet having a predetermined thickness, for example, 30 μm to 1000 μm, preferably 50 μm to 300 μm, and more preferably 100 μm to 200 μm.

[0075] Next, the raw sheet was stretched 100% in the direction perpendicular to the main shrinkage direction (MD) and 400% in the main shrinkage direction (TD) at 100° C. in a shrink film manufacturing device, thereby obtaining a styrene-based heat-shrinkable film. Since the styrene / butadiene blending ratio of the styrene-butadiene block copolymer is 85 / 15, the butadiene blending amount of the styrene-based heat-shrinkable film is 13.5% by weight.

[0076] 2. Evaluation of styrene-based heat-shrinkable films The obtained styrene-based heat-shrinkable film was evaluated for the heat shrinkage rate etc. Table 1 shows the obtained evaluation results.

[0077] (1) Evaluation 1: Heat shrinkage rate The thermal shrinkage was measured when the sample was immersed in hot water at 100°C for 10 seconds. The styrene-based heat-shrinkable film was sampled in a size of 100 mm in both the main shrinkage direction (TD) and the direction perpendicular to the main shrinkage direction (MD), and immersed in hot water at 100° C. for 10 seconds. After immersion, the film sample was quickly removed from the hot water, and the dimensional changes in both the length and width were measured using a scale with 0.5 mm graduations. According to the following formula, the shrinkage ratio was calculated in each of the main shrinkage direction and the direction perpendicular to the main shrinkage direction. Shrinkage rate (%) = {100 (mm) - length after immersion (mm)} / 100 (mm) x 100

[0078] (2) Evaluation 2: Nominal tensile strain at break The nominal tensile strain at break in the main shrinkage direction (TD) and the direction perpendicular to the main shrinkage direction (MD) was measured using a method in accordance with JIS K 7161-1:2014. The equipment, measurement conditions, and measurement value calculation method used in the measurement are as follows: n=5, and the average value was taken as the measurement value.

[0079] Measuring device: Desktop precision universal testing machine AGS-X (Shimadzu Corporation) Sample size: 10mm wide x 150mm long Distance between chucks: 60mm, distance between marked lines 40mm, speed: 200mm / min Nominal tensile strain at break (elongation, %) = {Elongation (mm) - Distance between gauge lines (mm)} ÷ Distance between gauge lines (mm) x 100

[0080] (3) Evaluation 3: Maximum point stress The maximum point stress in the main shrinkage direction (TD direction) and the direction perpendicular to the main shrinkage direction (MD direction) was measured using a method in accordance with JIS K 7161-1:2014.

[0081] (4) Rating 4: Haze The haze was measured by a method in accordance with JIS K 7136:2000.

[0082] (5) Rating 5: Total light transmittance The total light transmittance was measured by a method in accordance with JIS K 7136:2000.

[0083] [Table 1]

[0084] [Example 2] In Example 2, a styrene-based heat-shrinkable film was produced and evaluated in the same manner as in Example 1, except that the blending amounts of the styrene-butadiene copolymer resin and the recycled styrene resin were changed to 70 parts by weight and 30 parts by weight, respectively. The obtained evaluation results are shown in Table 1. The butadiene content of this styrene-based heat-shrinkable film is 10.5% by weight.

[0085] [Example 3] In Example 3, a styrene-based heat-shrinkable film was produced and evaluated in the same manner as in Example 1, except that the following recycled styrene resin was used as the recycled styrene resin instead of the recycled styrene resin used in Example 1. The obtained evaluation results are shown in Table 1. The butadiene content of this styrene-based heat-shrinkable film is 13.5% by weight. The comparative example 1 shown in the table is the same as that described above.

[0086] <Recycled styrene resin> Recycled general-purpose polystyrene B Tensile strength (JIS K 7161-1:2011): 50.84 MPa MFR(JIS K 7210-1:2014):6.5g / 10min Glass transition temperature: 103℃

[0087] [Comparative Example 1] In Comparative Example 1, a styrene-based heat-shrinkable film was produced and evaluated in the same manner as in Example 1, except that the blending amounts of the styrene-butadiene copolymer resin and the recycled styrene resin were changed to 100 parts by weight and 0 part by weight, respectively (i.e., the recycled styrene resin was not used and the styrene-butadiene copolymer resin was used). The obtained evaluation results are shown in Table 1. The butadiene content of this styrene-based heat-shrinkable film is 15% by weight.

[0088] Comparative Example 2 In Comparative Example 2, a styrene-based heat-shrinkable film was produced and evaluated in the same manner as in Example 1, except that the blending amounts of the styrene-butadiene copolymer resin and the recycled styrene resin were changed to 50 parts by weight and 50 parts by weight, respectively. The obtained evaluation results are shown in Table 1. The butadiene content of this styrene-based heat-shrinkable film is 7.5% by weight. Note that a nominal tensile breaking strain of "0" means that the film breaks.

[0089] Comparative Example 3 In Comparative Example 3, a styrene-based heat-shrinkable film was produced and evaluated in the same manner as in Example 3, except that the blending amounts of the styrene-butadiene copolymer resin and the recycled styrene resin were changed to 50 parts by weight and 50 parts by weight, respectively. The obtained evaluation results are shown in Table 1. The butadiene content of the styrene-based heat-shrinkable film is 7.5% by weight. [Industrial Applicability]

[0090] According to the present invention, a styrene-based heat-shrinkable film that satisfies at least the predetermined properties (1) to (3) is provided. The film contains a specific styrene-butadiene copolymer resin and a recycled styrene resin, and by adjusting the blending ratio of these components in a specific manner, it is possible to reduce the environmental impact while suppressing costs, and further to achieve the desired heat shrinkage rate and mechanical strength.

[0091] Therefore, such a styrene-based heat-shrinkable film can achieve a high heat shrinkage rate even under relatively low temperature shrinkage conditions, such as 100°C for 10 seconds, making it suitable as a packaging film that requires a high shrinkage rate at a low heating temperature. Moreover, such styrene-based heat-shrinkable films are excellent in mechanical strength, particularly in moldability and impact resistance, and are therefore less likely to break, for example, when packaging containers or during use.

[0092] Furthermore, according to the method for producing a styrene-based heat-shrinkable film of the present invention, it has become possible to stably produce the above-mentioned styrene-based heat-shrinkable film. Therefore, the styrene-based heat-shrinkable film of the present invention can be suitably applied to various PET bottles, outer covering materials for lunch boxes, etc., thereby significantly expanding its versatility, and since it can reduce costs and environmental impact, it can be said that its industrial applicability is extremely high. [Explanation of symbols]

[0093] 10: Styrene-based heat shrinkable film 20: PET bottles

Claims

1. A styrene-based heat-shrinkable film derived from a styrene-based resin composition, characterized in that the film satisfies the following properties (1) to (3): (1) The styrene-based resin composition contains a styrene-butadiene copolymer resin (excluding biomass SBC resin) having a styrene / butadiene blending ratio of 70 / 30 to 95 / 5, and a recycled styrene resin, and the blending ratio (in terms of polymerization amount) expressed by the styrene-butadiene copolymer resin / recycled styrene resin is set to a value within the range of 90 / 10 to 70 / 30. (2) The styrene-based heat-shrinkable film has a heat shrinkage rate of 35% or more in the main shrinkage direction when immersed in hot water at 100° C. for 10 seconds. (3) The nominal tensile break strain of the styrene-based heat-shrinkable film in a direction perpendicular to the main shrinkage direction, measured in accordance with JIS K 7161-1:2014, is 150% or more.

2. The styrene-based heat-shrinkable film according to claim 1, characterized in that the nominal tensile strain at break in the main shrinkage direction, measured in accordance with JIS K 7161-1:2014, is 30% or more.

3. 3. The styrene-based heat-shrinkable film according to claim 1, wherein the haze of the styrene-based heat-shrinkable film measured in accordance with JIS K 7136:2000 is 10% or less.

4. The styrene-based heat-shrinkable film according to claim 1 or 2, characterized in that the styrene-based heat-shrinkable film has a maximum point stress in a direction perpendicular to the main shrinkage direction, measured in accordance with JIS K 7161-1:2014, of 30 MPa or more.

5. The styrene-based heat shrinkable film according to claim 1 or 2, characterized in that the recycled styrene resin has a tensile strength measured in accordance with JIS K 6923-2: 1997 of 36 to 60 MPa.

6. The recycled styrene resin has a melt flow rate (200 ° C., 5 kg load) measured in accordance with JIS K 7210-1:2014 of 3 to 10 g / 10 min. The styrene-based heat-shrinkable film according to claim 1 or 2.

7. 3. The styrene-based heat-shrinkable film according to claim 1, wherein the amount of butadiene in the styrene-based resin composition is 8% by weight or more based on the total amount of the styrene-based resin composition.

8. 3. The styrene-based heat-shrinkable film according to claim 1, wherein the thickness of the styrene-based heat-shrinkable film is set to a value within a range of 20 to 80 μm.

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