JP4721714B2 - Styrene heat shrinkable multilayer film - Google Patents

Description

  The present invention relates to a styrenic heat-shrinkable film having high waist strength, a small natural shrinkage rate, and excellent perforation tearability.

Various containers are generally equipped with printed heat-shrinkable films (labels) to convey information such as product names and precautions for use, or to impart design properties. . As for this heat-shrinkable film, the replacement of polyvinyl chloride, which is a harmful substance during combustion from the viewpoint of environmental issues, has been replaced by other materials. In recent years, the finish after heat shrinkage is good, and from the viewpoint of recycling containers and films. Styrene-butadiene block copolymers with good perforation for separating the slag are often used.
However, this styrene-butadiene block copolymer film has problems such as softness and lack of elasticity, and inferior so-called natural shrinkage in which dimensions change during storage.
In order to remedy these drawbacks, a heat-shrinkable film made of a styrene resin modified with rubber-like polymer particles, so-called impact-resistant polystyrene, is disclosed in Patent Document 1, and a heat-resistant polystyrene film laminated with heat. A shrink film is disclosed in Patent Document 2 and has improved waist strength and natural shrinkage, but the perforation cut, which was an advantage of a styrene-butadiene block copolymer, is inferior. The problem was that separation was difficult.

Japanese Patent Application Laid-Open No. 07-032477 JP 09-114380 A

  The present invention has been made in view of such conventional problems, and provides a styrenic heat-shrinkable film excellent in waist strength and natural shrinkage and excellent in perforation tearing.

As a result of intensive studies to solve the above problems, the present inventor has, as a main component, a styrene monomer and, if necessary, a (meth) acrylate monomer in the presence of a rubbery polymer. A rubber-modified styrenic resin obtained by copolymerizing the monomer mixture, wherein the rubbery polymer forms a particulate dispersed phase in the continuous phase of the copolymer, and has a specific particle size range. When the rubber particles have a specific number of particles, the present inventors have found that the rubber particles meet the purpose and have completed the present invention.
That is, the present invention is a surface layer and the back of the styrene-based heat-shrinkable film comprising a layer of rubber-like polymer in a continuous phase of the scan styrene-based polymer composed mainly of a rubber-modified styrene resin was dispersed to form a crosslinked particles A styrenic heat-shrinkable multilayer film obtained by laminating a layer containing a styrene-conjugated diene block copolymer as a main component on a layer , and the particle size of the rubber particles dispersed in the rubber-modified styrene resin is 0. A styrenic heat shrinkage obtained by stretching a rubber-modified styrenic resin composition in which 500 to 2,000,000 dispersed particles (A) of 005 to 0.2 μm exist in an ultrathin section of 80 nm per 100 μm ² area. Relates to a conductive multilayer film.

  The heat-shrinkable film of the present invention is excellent in natural shrinkage, so that defects due to dimensional changes during storage can be reduced, the film has high rigidity and can be thinned, and can be cut along perforations. Therefore, it has the advantage that separation from the container is easy and the recycling load can be reduced.

The present invention is described in detail below.
The styrenic heat-shrinkable film of the present invention has at least one layer composed mainly of a rubber-modified styrenic resin in which a rubber-like polymer forms dispersed particles and a styrenic (co) polymer is a continuous phase. It is.
The rubber-modified styrenic resin used in the present invention comprises, in the presence of rubber, a styrenic monomer alone or a styrenic monomer and another vinyl monomer copolymerizable with the styrenic monomer ( Co) polymerized.
Examples of the styrene monomer include styrene derivative monomers such as paramethyl styrene, α-methyl styrene, para-t-butyl styrene, and nuclear halogenated styrene in addition to the styrene monomer. These styrenic monomers may be used singly or as a mixture of two or more. Of these, styrene monomer is preferably used.
Examples of the other vinyl monomer copolymerizable with the styrene monomer include (meth) acrylic acid ester, acrylic acid, methacrylic acid, maleic acid, fumaric acid, maleic anhydride, divinylbenzene and the like. These other vinyl monomers may be used alone or in combination of two or more.

Specific examples of (meth) acrylic acid esters include methacrylic acid esters such as methyl methacrylate, ethyl methacrylate, stearyl methacrylate, and methyl acrylate, ethyl acrylate, n-butyl acrylate, 2-methylhexyl acrylate, 2-ethylhexyl acrylate, octyl. Examples thereof include acrylic esters such as acrylates, and these may be used alone or in combination of two or more. Methyl methacrylate, n-butyl acrylate or a mixture thereof is preferable. In this case, since transparency can be provided by setting it as 70-20 weight% of styrene and 30-80 weight% of (meth) acrylic acid ester, it is preferable.
On the other hand, as the rubber polymer, for example, polybutadiene, polyisoprene, styrene-butadiene random copolymer, styrene-butadiene block copolymer, styrene-isoprene random copolymer, styrene-isoprene block copolymer, and these A hydrogenated product obtained by hydrogenating a butadiene or isoprene moiety can be used, and a polybutadiene rubber or a styrene-butadiene rubber is preferable. These may be used alone or in combination of two or more.

The rubber concentration of the rubber-modified styrene resin used in the present invention is 4 to 30% by weight, preferably 8 to 20% by weight. If it is less than 4% by weight, the tearability of the film is poor, and if it is 30% by weight or more, the rigidity of the film is poor. The rubber-modified styrene resin within the above range may be used alone, or a rubber-modified styrene resin having a high rubber concentration may be diluted with a non-rubber-modified styrene resin.
The dispersed particles (A) in the rubber-modified styrene resin used in the present invention are dispersed particles having a particle size of 0.005 to 0.2 μm.
The number of dispersed particles (A) was determined based on the fact that the ultrathin section of 80 nm cut out after the film was fully shrunk sufficiently at an appropriate temperature and time (for example, 130 ° C., 30 minutes) and embedded in epoxy was osmium. After dyeing with an acid, the number per 100 μm ² of the dispersed particles having a particle diameter of 0.005 to 0.2 μm is determined from a photograph taken with a transmission electron microscope (FIG. 1). The dispersed particles (A) in the film of the present invention are in a highly anisotropic form oriented by stretching in the film, and the particles appear to overlap each other due to the small particle diameter (FIG. 2). ), Image analysis is difficult and inaccurate, for example, the particle diameters that are different depending on the cutting angle, and it is necessary to completely contract when performing transmission electron microscope observation.

In this transmission electron micrograph, the number of dispersed particles (A) having a particle size of 0.005 to 0.2 μm needs to be 500 to 2,000,000 per 100 μm ² . The number is preferably 1,000 to 1,000,000. If it is 500 or less per 100 μm ² , the perforation tearability is inferior, and if it is 2000000 or more, the rigidity of the film, ie, the waist strength is inferior.
The particle form of the dispersed particles (A) is not particularly limited, but preferably the crosslinked particles containing two or more occlusions inside the particles are less than 50% of the total number of dispersed particles (A). More preferably, it is less than 30%. If the number of cross-linked particles containing two or more occlusions in the particles is less than 50% of the total number of dispersed particles (A), the balance between the improvement of tearability and rigidity is excellent. The rubber-modified styrenic resin used in the present invention may contain dispersed particles (A) having a particle size of 0.005 to 0.2 μm in the above-mentioned number of particles. It may contain dispersed particles.

The production method of the rubber-modified styrenic resin used in the present invention is not particularly limited, and it is produced by a known method such as emulsion polymerization, bulk polymerization, solution polymerization, bulk continuous polymerization.
An SB block copolymer having at least one styrene block and at least one butadiene block can be added to the rubber-modified styrenic resin used in the present invention in an amount of 15 parts by weight or less, if necessary. When added in an amount exceeding 15 parts by weight, the waist strength of the film is lowered and fish eyes are generated, which is not preferable.
The rubber-modified styrenic resin used in the present invention includes organic polysiloxane compounds, organic stabilizers such as phosphite, inorganic stabilizers such as calcium and tin, antioxidants such as phenols and sulfides, benzophenones, Ultraviolet absorbers such as phenyl salicylate, fatty acids, fatty acid amides, esters, lubricants such as metal soaps, and other fiber reinforcing materials, inorganic fillers, pigments, plasticizers, antistatic agents, release agents, A coloring agent, a flame retardant, etc. can also be mix | blended suitably. In addition, a modifier used in a styrene resin can be applied to modify the properties of the product surface of the film.

Furthermore, by adding a terpene-based resin or a terpene-based hydrogenated resin, the moldability, heat resistance, impact resistance, rigidity balance and appearance characteristics can be improved, and these can be used at 10% by weight or less. .
However, it is necessary that the VICAT softening temperature of the rubber-modified styrene resin composition does not fall below 50 ° C. When the VICAT softening temperature is lower than 50 ° C., the natural shrinkage is inferior.
These additives may be added to the polymerization system, or a method of mixing with a rubber-modified styrene resin and an extruder may be used.

For the front and back layers of the heat-shrinkable film of the present invention, a layer selected from a rubber-modified styrene resin different from the present invention, a styrene-conjugated diene block copolymer, and a mixture of these with a styrene (co) polymer. May be laminated. In particular, laminating a styrene-conjugated diene block copolymer is preferable in that printability and shrinkage speed can be adjusted. At this time, the thickness of the rubber-modified styrenic resin layer used in the present invention is 50% or more of the film thickness, in the sense of satisfying the natural shrinkage, waist strength, and tearability, which are the objects of the present invention. It is essential.
The method for producing the heat-shrinkable film of the present invention is not particularly limited, and after being formed into a sheet by a T-die sheet extruder, a method of stretching uniaxially or biaxially by a uniaxial stretching apparatus or a biaxial stretching apparatus, extrusion It is manufactured by a known method such as a method of stretching the formed tubular film in the circumferential direction, an inflation processing apparatus, or the like.
In addition, there is no restriction | limiting in particular about extending | stretching temperature, a draw ratio, film thickness, etc., It selects according to the use used and a required characteristic. For example, the film is stretched about 2 to 6 times in the direction where shrinkage is necessary, and formed into a film thickness of 10 to 100 μm.

Next, the present invention will be described more specifically with reference to examples.
(1) Component to be used (A) Rubber-modified styrene resin (Rubber-modified styrene resin A-1)
A styrenic resin is produced using a polymerization apparatus in which three 5l-7l-7l polymerizers equipped with a stirrer are connected in series and then a twin screw extruder with a two-stage vent is arranged.
86 parts by weight of styrene, B-S type rubbery polymer (B: butadiene block, S: styrene block, styrene content is 38% by weight, 5% by weight styrene solution viscosity at 25 ° C. is 30 cps, rubbery Polymerization is carried out by supplying a raw material solution consisting of 9 parts by weight of elastic body, 5 parts by weight of ethylbenzene, and 0.04 part by weight of 1,1 bis (t-butylperoxy) cyclohexane to the polymerization machine. Rotate the stirrer at 100 rpm at 120 ° C. in the first stage polymerization machine and polymerize for 2 hours to precipitate rubber particles, then continue the polymerization at 135 ° C. for 3 hours in the second stage polymerization machine to stabilize the rubber particles. Thereafter, the polymerization is further carried out at 145 ° C. for 3 hours in a third-stage polymerization machine to a final polymerization solid content of 69%, and this polymerization solution is removed by a twin-screw extruder equipped with a two-stage vent at 220 ° C. and a vent pressure of 20 mmHg. After volatilization, a rubber-modified styrene resin was obtained. Table 1 shows the physical properties of the resulting rubber-modified styrenic resin A-1.

(Rubber-modified styrene resin A-2 to 3)
As shown in Table 1, rubber-modified styrene resins A-2 to A-3 were obtained in the same manner as A-1, except that the number of stirring was changed.
(Rubber-modified styrene resin A-4)
Using the same polymerization apparatus, 49.9 parts by weight of styrene, 15.5 parts by weight of butyl acrylate, 20.6 parts of methyl methacrylate, B-S type as a rubbery polymer (B: butadiene block, S: styrene block, styrene A rubber-like elastic body having a content of 38% by weight, a 5% by weight styrene solution at 25 ° C. and a viscosity of 30 cps) 9 parts by weight, ethylbenzene 5 parts by weight, 1,1 bis (t-butylperoxy) cyclohexane 0.05 The raw material solution consisting of parts by weight is supplied to the polymerization machine to carry out the polymerization. In the first stage polymerization machine, the agitator is rotated at 100 to 120 ° C. at 80 rpm for polymerization to precipitate rubber particles, and then the polymerization is continued at 120 to 135 ° C. in the second stage polymerization machine to stabilize the rubber particles. Then, the polymerization is further carried out at 135 ° C. to 145 ° C. in a third stage polymerization machine to a final polymerization solid content of 68%, and this polymerization solution is a twin screw extruder with a two stage vent at 220 ° C. and a vent pressure of 20 mmHg. After devolatilization, rubber-modified styrene resin A-4 was obtained.

(Rubber-modified styrenic resins A-5 and A-6)
As shown in Table 1, rubber-modified styrene resins A-5 and A-6 were obtained in the same manner as A-4 except that the solvent composition to be polymerized, the amount of organic oxide, and the number of stirrings were changed.
(Non-rubber modified styrene resin A-7)
The monomer component is 55.1 parts by weight of styrene, 17.1 parts by weight of butyl acrylate, 22.8 parts by weight of methyl methacrylate, and is not rubber-modified in the same manner as A-1 to 6 except that no rubber-like polymer is added. Styrene resin A-7 was obtained.

(Rubber-modified styrene resin A-8)
200 parts of distilled water, 1 part of disproportionated potassium rosinate, 0.03 part of potassium hydroxide in a reactor equipped with a stirrer, reflux condenser, nitrogen inlet, monomer inlet and thermometer, then styrene-butadiene random 50 parts by weight of copolymer latex (weight average particle size 0.08 μm, styrene content 38% by weight) as a solid content was charged, and the temperature was raised to 60 ° C. after substitution with nitrogen. 2 parts of 0.2% ferrous sulfate solution and 0.1 part of sodium pyrophosphate were added, and after 5 minutes, 29 parts by weight of styrene, 12 parts by weight of methyl methacrylate and 9 parts by weight of butyl acrylate, t-dodecyl mercaptan 0.07 part and 0.3 part of cumene hydroperoxide were continuously added dropwise over 2 hours. After completion of the addition, stirring was continued for 1 hour at 60 ° C., then the temperature was raised to 70 ° C. and reacted for 1 hour. . An antioxidant was added to the cooled graft polymerization latex, salted out using magnesium sulfate, followed by washing and drying to obtain a rubber-modified styrene resin A-8.
Table 1 summarizes the properties of the rubber-modified styrene resins A-1 to 6, 8 and the non-rubber-modified styrene resin A-7.

(B) Styrene-conjugated diene block copolymer Asaflex 825 (Asahi Kasei Chemicals SBS, styrene content 77%)
(C) Styrene-conjugated diene block copolymer rubber Toughprene 126 (SB block rubber manufactured by Asahi Kasei Chemicals Corporation, styrene content 40%)

(2) Test method Number of dispersed particles (A): After embedding a heat-shrinkable film that has been completely shrunk at 130 ° C. for 30 minutes with epoxy, and then staining the cut out ultrathin section of 80 nm with osmic acid The sample was taken with a transmission electron microscope to obtain a photograph with a magnification of 10,000 times (see FIG. 1). In the photograph, particles dyed black are dispersed particles of a rubbery polymer. From the photograph shown in FIG. 1, the number of particles was determined for an area of 100 μm ² for the dispersed particles (A) having a particle size of 0.005 to 0.2 μm.
Here, the particle diameter is the particle diameter when the equivalent circle diameter is determined from the particle area in the photograph. In this measurement, a photograph was taken into a scanner at a resolution of 1000 dpi and measured using particle analysis software of an image analysis apparatus IP-1000 (manufactured by Asahi Kasei).
Tearability: Perforation of the film placed on a desk by applying perforations with a hole diameter of 0.5 mm at intervals of 3.85 mm to the obtained film on a straight line in a direction perpendicular to the TD direction (the direction in which the shrinkage is large). The state when one side of the sheet was held by hand and the other side was torn by hand was evaluated as follows.
○: It cuts cleanly along the perforation.
Δ: Cut along the perforation, but cut off from the perforation on the way.
X: Not cut along perforations.
Natural shrinkage ratio: The distance between reference points (original dimension: 300 mm) when the film was allowed to stand at 40 ° C. for 7 days was measured in units of 0.1 mm to obtain the shrinkage ratio.
Tensile modulus: A strip of 150 mm in the MD direction (length) and 15 mm in the TD direction (width) is cut out from the film with a razor, and in accordance with ISO-527-3, the temperature is 23 ° C., the relative humidity is 50%, the chuck is 100 mm, Measurement was performed at a test speed of 1 mm / min. The slope between the stress 2N and 4N was obtained as the apparent elastic modulus.

[ Reference Examples 1 to 9, Comparative Examples 1 to 3]
According to the formulation shown in Tables 2 and 3, first, a sheet having a thickness of 0.3 mm was extruded at an extrusion temperature of 210 ° C., and then, using a biaxial stretching apparatus manufactured by Toyo Seiki Seisakusho, Tables 2 and The film was stretched 1.15 times in the sheet width direction and 5 times in the sheet length direction at the stretching temperature shown in FIG.
The evaluation results of the films obtained are shown in Tables 2 and 3 below.

[Examples 10 , 11, 13, Reference Example 12, Comparative Examples 4, 5]
A 0.3 mm multilayer sheet was extruded with the formulation and multilayer configuration described in Table 4, and then in the width direction of the sheet at the stretching temperature shown in Table 4 using a biaxial stretching apparatus manufactured by Toyo Seiki Seisakusho. The film was stretched 1.15 times and 5 times in the length direction of the sheet to prepare a stretched film.
The evaluation results of the films obtained are shown in the lower part of Table 4.
As is clear from Tables 2, 3 and 4, the heat-shrinkable films of the present invention of Reference Examples 1 to 9 and Examples 10 , 11, 13, and Reference Example 12 are styrene-conjugated diene block copolymer. Compared to a film made of coalescence (Comparative Example 3), it is excellent in rigidity and natural shrinkage and has improved perforation tearability. Films using non-rubber-modified styrenic resins (Comparative Examples 2 and 5) have high rigidity and small natural shrinkage, but are poor in perforation tearability. When the rubber-modified styrene resin having a small number of dispersed particles (A) is used (Comparative Examples 1 and 4), the rigidity is high and the natural shrinkage is small, but the perforation tearability is poor.

  The styrenic heat-shrinkable film of the present invention is excellent in natural shrinkage, can reduce defective products due to dimensional changes during storage, and has high rigidity, so it can achieve thinning of the film, that is, resource saving, and perforation. It is a heat-shrinkable film suitable for various uses because it can be separated from the container and the heat-shrinkable film because of its excellent properties and can reduce the burden during recycling.

A transmission electron micrograph after the film of Reference Example 1 was completely shrunk by heating. A transmission electron micrograph of a cross section parallel to the surface of the film of Reference Example 1.

Claims (4)

Scan styrene rubbery polymer in the polymer continuous phase of styrene in the surface layer and the backing layer of the styrene-based heat-shrinkable film comprising a layer composed mainly of rubber-modified styrene resin was dispersed to form a crosslinked particles - conjugated A styrenic heat-shrinkable multilayer film obtained by laminating layers mainly composed of a diene block copolymer , and the particle size of the rubber particles dispersed in the rubber-modified styrene resin is 0.005 to 0.2 μm. A styrenic heat-shrinkable multilayer film obtained by stretching a rubber-modified styrenic resin composition in which 500 to 2,000,000 dispersed particles (A) are present in an ultrathin section of 80 nm per 100 μm ² area. The polystyrene heat-shrinkable multilayer film according to claim 1, wherein the rubber concentration in the rubber-modified styrene resin is 4 to 30% by weight. The polystyrene-based heat-shrinkable multilayer according to claim 1 or 2, wherein the rubber-modified styrene resin is a copolymer of styrene and an alkyl (meth) acrylate in the presence of a butadiene rubber. the film. 4. The dispersed particles (A), wherein the crosslinked particles containing two or more occlusions in the particles are less than 50% of the total number of the dispersed particles (A). Styrene heat shrinkable multilayer film.

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