JP2008174728A - Heat shrinkable polyolefinic film and process for producing it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a heat shrinkable polyolefine film that is high in the shrinkability in the longitudinal direction being its main shrinkage direction, excelling in shrink finish performance, perforated line openability and thermal blocking resistance. <P>SOLUTION: In the heat shrinkable polyolefine film, the main shrinkage direction of the film agrees with the longitudinal direction. A hot water thermal shrinkage ratio in the longitudinal direction measured after the treatment in 90°C hot water for 10 sec, a hot water thermal shrinkage ratio in the width direction measured after the treatment in 90°C hot water for 10 sec, a rectangular tear strength in the width direction measured after making 10% shrunk in the longitudinal direction in 80°C hot water. which are respectively adjusted so that they may be fallen in a predetermined range. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a heat-shrinkable polyolefin film and a method for producing the same, and more particularly to a heat-shrinkable polyolefin film suitable for labeling and a method for producing the film.

  In recent years, it has been made of various resins for applications such as exterior packaging for improving the appearance of packages, packaging for avoiding direct collision of contents, and label packaging that also serves to protect glass bottles or plastic bottles and display products. Heat shrink plastic films are widely used. Among these heat-shrinkable plastic films, stretched films made of polyvinyl chloride resin, polystyrene resin, polyester resin, polyolefin resin, etc. are various containers such as polyethylene terephthalate (PET) containers, polyethylene containers, glass containers and the like. In, it is used for the purpose of label, cap seal or integrated packaging.

  However, although the polyvinyl chloride film has excellent shrinkage properties, it has low heat resistance and also has problems such as generation of hydrogen chloride gas during incineration and causing dioxins. Further, when a polyvinyl chloride resin film is used as a shrink label for a PET container or the like, there is a problem that the label and the container must be separated when the container is recycled. On the other hand, polystyrene-based films have a good finished appearance after shrinkage, but have poor solvent resistance, so that there is a problem that an ink having a special composition must be used for printing. In addition, the polystyrene film needs to be incinerated at a high temperature and has a problem that a large amount of black smoke is generated with a strange odor during incineration.

  Therefore, polyester films and polyolefin films having high heat resistance, easy incineration, and excellent solvent resistance have been widely used as shrink labels, and the amount of PET containers in circulation has been increased. The usage tends to increase with the increase. Moreover, as a normal heat-shrinkable polyester film or heat-shrinkable polyolefin film, a film that is stretched at a high magnification in the width direction and greatly shrinks in the width direction (that is, the main shrinkage direction is the width direction). Is widely used (Patent Document 1).

JP 2004-74426 A

  However, the heat-shrinkable polyester film and heat-shrinkable polyolefin film stretched in the width direction described above have poor tearability (so-called perforation opening) when tearing along a perforation perpendicular to the main shrinkage direction. There was a bug. In addition, the heat-shrinkable polyolefin film stretched in the width direction described above has insufficient heat resistance, and when used as a label, storing the installed bottle in an incubator causes so-called blocking. There is a risk of fusing with the bottle label.

  In addition, the heat-shrinkable film that heat-shrinks in the width direction is formed as a cylindrical body so that the width direction becomes the circumferential direction of the bottle when the bottle is attached as a bottle label. Since it has to be cut and heat-shrinked into a bottle after every predetermined length, it is difficult to attach it to the bottle at high speed. Furthermore, in recent years, a novel wrapping method has been developed in which a container is closed in a closed state by covering the periphery (opening) of a synthetic resin single-open container such as a lunch box with a belt-like film. The film shrinking in the width direction is not easy to use for such applications.

  The object of the present invention is to solve the problems of the above-mentioned conventional heat-shrinkable polyester film and heat-shrinkable polyolefin film, and has good shrinkability in the longitudinal direction, which is the main shrinkage direction. Can be installed around the bottle directly from the film roll so that the main shrinkage direction is the circumferential direction of the bottle, and it is practical and easy to use for the above-mentioned new wrapping applications The object is to provide a heat-shrinkable polyolefin film.

Among the present inventions, the invention described in claim 1 is formed in a long shape having a constant width by a polyolefin resin mainly composed of a propylene-α-olefin copolymer, and a main shrinkage direction is a longitudinal direction. The heat-shrinkable polyolefin film, which satisfies the following requirements (1) to (4):
(1) The hot water heat shrinkage in the longitudinal direction is 15% or more and 40% or less when treated in 90 ° C. warm water for 10 seconds. (2) Treated in 90 ° C. warm water for 10 seconds. The hot-water heat shrinkage rate in the width direction perpendicular to the longitudinal direction is -5% to 10%. (3) Width per unit thickness after shrinking 10% in the longitudinal direction in hot water at 80 ° C The perpendicular tear strength in the direction is 50 N / mm or more and 200 N / mm or less. (4) The peel strength when a pressure of 0.4 MPa is applied for 90 seconds while the surfaces of the films are combined and heated to 90 ° C. 1N / 15mm or less

  In addition,-(minus) hot-water heat shrinkage rate means the expansion | extension of a film.

  The invention described in claim 2 is the invention described in claim 1, wherein the polyolefin resin is mainly composed of a copolymer of propylene and ethylene, and the amount of ethylene in the constituent resin is 2.0 mass% or more and 10.0 mass% or less.

  The invention described in claim 3 is the invention described in claim 1, wherein the polyolefin-based resin is mainly composed of a copolymer of propylene, ethylene, and butene. The amount of butene is 3.0% by mass or more and 10.0% by mass or less.

  The invention described in claim 4 is the invention described in claim 1, wherein the polyolefin resin is mainly composed of a copolymer of propylene and butene, and the amount of butene in the constituent resin is 15.0 mass% or more and 35.0 mass% or less.

  The invention described in claim 5 has the laminated structure in which the skin layer is laminated on at least one surface of the core layer in the invention described in any one of claims 1 to 4, and the skin layer includes: An antiblocking agent and / or an antistatic agent is added.

  Invention of Claim 6 is a manufacturing method for manufacturing the heat-shrinkable polyolefin-type film in any one of Claims 1-5, Comprising: An unstretched film is made into the both ends of the width direction within a tenter. After being stretched by a clip at a temperature of 70 ° C. or higher and 140 ° C. or lower at a magnification of 2.5 times or more and 8.0 times or less, the film is stretched at a temperature of 100 ° C. or higher and 155 ° C. or lower for 1.0 second. After heat treatment for a time of 50.0 seconds or less and then cutting and removing the clip gripping portions at both edges in the width direction of the film, the film is 2.0 times longer in the longitudinal direction at a temperature of 70 ° C. or more and 140 ° C. or less. The film is drawn at a magnification of 8.0 times or less.

  The heat-shrinkable polyolefin film of the present invention has high shrinkability in the longitudinal direction, which is the main shrinkage direction, and also has good perforation openability in the direction perpendicular to the main shrinkage direction. Therefore, it can be suitably used as a label for containers such as bottles, and can be attached to containers very efficiently within a short period of time. In addition to exhibiting a very good finish with a very low perforation, it exhibits a very good perforation opening. Furthermore, when used as a label for a container such as a bottle, the heat blocking property is good. In addition, the usability for the above-described novel lapping application is also good.

  In addition, according to the method for producing a heat-shrinkable polyolefin film of the present invention, the heat-shrinkable polyolefin film has high shrinkability in the longitudinal direction as described above, and has good shrink finish, perforation opening, and heat-resistant blocking properties. The film can be manufactured inexpensively and easily.

  The α-olefin copolymerization component of the copolymer of propylene and other α-olefin used in the present invention is preferably an α-olefin having 2 to 8 carbon atoms, such as ethylene, butene-1, and the like. 1, hexene-1,4-methyl-1-pentene and the like can also be used. The copolymer is preferably a random or block copolymer obtained by polymerizing one or more of the α-olefins exemplified above with propylene. Further, among these copolymers, propylene and ethylene are copolymerized and the amount of ethylene is 2.0% by mass or more and 10.0% by mass or less, and propylene and butene are copolymerized. In which the amount of butene is 15.0% by mass or more and 35.0% by mass or less, copolymerized propylene, ethylene and butene, and the amount of ethylene and butene is 3.0. It is particularly preferable to use a material having a mass percentage of 15.0 mass% because good shrinkage characteristics can be obtained.

  Further, the melt flow rate (MFR) of the copolymer is 0.1 to 100 g / 10 min. Is preferably in the range of 0.5 to 20 g / 10 min. More preferably, it is in the range of 1.0 to 10 g / 10 min. It is especially preferable that it is within the range. The melting point of the resin used in the present invention is preferably 70 ° C. or higher and 150 ° C. or lower, more preferably 80 ° C. or higher and 145 ° C. or lower, and particularly preferably 90 ° C. or higher and 140 ° C. or lower. If the melting point exceeds 150 ° C, the crystallinity becomes high and sufficient shrinkage characteristics cannot be obtained. This is not preferable. On the other hand, if the melting point is below 70 ° C, the resin becomes sticky or blocked, making handling difficult. Is not preferable.

  In the present invention, if necessary, the resin used may be various additives and fillers, for example, a heat stabilizer, an antioxidant, a light stabilizer, an antistatic agent, a lubricant, a nucleating agent, as long as the properties are not impaired. Adds flame retardants, pigments, dyes, calcium carbonate, barium sulfate, magnesium hydroxide, mica, talc, clay, zinc oxide, magnesium oxide, aluminum oxide, antibacterial agents, antifogging agents, additives that impart natural degradability, etc. can do. In particular, organic lubricants such as fatty acid amides, fatty acid alkylamines, fatty acid alkylamine esters, and fatty acid monoglycerin esters are representative of handling properties and the meaning of imparting slipperiness, antistatic properties, and heat blocking properties. It is preferable to add an antiblocking agent typified by a surfactant, silica, and PMMA. Furthermore, other thermoplastic resins, thermoplastic elastomers, rubbers, hydrocarbon resins, petroleum resins, and the like may be blended within a range that does not impair the characteristics of the film of the present invention.

  Furthermore, the film of the present invention has the same type of polypropylene resin layer and other resin layers on the surface thereof, for example, a saponified ethylene-vinyl acetate copolymer, a gas barrier resin layer such as polyvinyl alcohol, etc., as long as the properties are not impaired. May be laminated.

  The film of the present invention can be subjected to surface treatment within a range that does not impair the characteristics of the present invention, if necessary. Examples of the surface treatment method include corona discharge treatment, plasma treatment, flame treatment, and acid treatment, and are not particularly limited. It is preferable to perform corona discharge treatment, plasma treatment, and flame treatment that can be carried out continuously and can be easily performed before the winding process of the film production process. Is particularly preferably a corona discharge treatment.

In addition, the heat-shrinkable polyolefin film of the present invention is the longitudinal direction of the film calculated by the following formula 1 from the length before and after shrinkage when treated for 10 seconds in 90 ° C. warm water without load. The heat shrinkage ratio (that is, hot water heat shrinkage ratio at 90 ° C.) of 15% or more and 40% or less is required.
Thermal shrinkage rate = {(length before shrinkage−length after shrinkage) / length before shrinkage} × 100 (%)

  When the hot-water heat shrinkage rate in the longitudinal direction at 90 ° C. is less than 15%, the shrinkage amount is small, and thus wrinkles and tarmi are generated on the label after heat shrinkage, which is not preferable. In addition, the lower limit of the hot water heat shrinkage in the longitudinal direction at 90 ° C. is preferably 18% or more, more preferably 21% or more, and particularly preferably 24% or more. In addition, considering the essential characteristics of the polyolefin-based resin mainly composed of the raw material propylene-α-olefin copolymer, the upper limit value of the hot water heat shrinkage in the longitudinal direction at 90 ° C. is considered to be about 40%. ing.

  The heat-shrinkable polyolefin film of the present invention is a film width direction calculated by the above formula 1 from the length before and after shrinkage when treated for 10 seconds in 90 ° C. warm water under no load. It is necessary that the hot-water heat shrinkage rate is -5% or more and 10% or less.

  If the hot-water heat shrinkage in the width direction at 90 ° C. exceeds 10%, it is not preferable because vertical sink marks are likely to occur during heat shrinkage when used as a label. In addition, the lower limit of the hot water heat shrinkage in the width direction at 90 ° C. is preferably −3% or more, and more preferably −1% or more. Moreover, the upper limit of the hot water heat shrinkage in the width direction at 90 ° C. is preferably 9% or less, more preferably 8% or less, and particularly preferably 7% or less. In addition, considering the essential characteristics of the polyolefin-based resin whose main component is a propylene-α-olefin copolymer, the lower limit value of the hot water heat shrinkage in the width direction at 90 ° C. is about −5%. thinking.

  Further, the heat-shrinkable polyolefin film of the present invention was subjected to 10% shrinkage in the longitudinal direction in warm water at 80 ° C., and then the right-angled tear strength per unit thickness was determined by the following method. The right-angled tear strength in the width direction is required to be 50 N / mm or more and 200 N / mm or less.

[Measurement method of right-angle tear strength]
The film is contracted 10% in the longitudinal direction in hot water adjusted to 80 ° C., and then sampled as a test piece of a predetermined size according to JIS-K-7128. Thereafter, both ends of the test piece are grasped with a universal tensile tester, and the strength at the time of tensile fracture in the width direction of the film is measured under the condition of a tensile speed of 200 mm / min. In addition, about the film which does not shrink 10% at 80 degreeC, the intensity | strength at the time of the tensile fracture in the width direction of the film shrunk by the part which can be shrunk by immersing in warm water of 80 degreeC over about 5 second is measured. . Then, the right angle tear strength per unit thickness is calculated using the following equation 2.
Right angle tear strength = Strength at tensile fracture ÷ thickness ・ ・ Equation 2

  When the right-angled tear strength after shrinking 10% in the longitudinal direction in warm water at 80 ° C is less than 50 N / mm, when used as a label, it may be easily broken by impact such as dropping during transportation. On the contrary, if the right-angled tear strength exceeds 200 N / mm, the cutting property (easy to tear) at the initial stage of tearing the label becomes unfavorable. The lower limit of the right-angled tear strength is preferably 70 N / mm or more, more preferably 90 N / mm or more, and particularly preferably 110 N / mm or more. Moreover, the upper limit value of the right-angled tear strength is preferably 180 N / mm or less, more preferably 160 N / mm or less, and particularly preferably 140 N / mm or less.

  Regarding the cutability when tearing the label at the perforated part, the ease of tearing (the ease of notching) of the first part of the perforated line (the upper or lower part of the label) as described above And easy to tear along the perforation without breaking diagonally or cutting the tab in the middle and tearing in the direction of the perforation to the end with a light force (balance of ease of tearing between the perforation direction and the perpendicular direction) Both of them contribute to the ease of work when actually peeling the label by hand, but the latter can be improved somewhat by improving the pitch of the perforation, etc. The ease of tearing of the first part of the perforation corresponds to the sensory evaluation when actually tearing the label by hand, and is considered to be a more important characteristic. Therefore, the heat-shrinkable polyolefin film of the present invention needs to have a right angle tear strength in the above range. However, it is preferable to set the balance of the ease of tearing in the latter perforation direction and the perpendicular direction within a certain range because the perforation opening property of the heat-shrinkable polyolefin film of the present invention can be further improved. Specifically, when the heat-shrinkable polyolefin film of the present invention was subjected to 10% shrinkage in the longitudinal direction in warm water at 80 ° C., the Elmendorf tear load in the longitudinal direction and the width direction was determined by the following method. The Elmendorf ratio, which is the ratio of these Elmendorf tear loads, is preferably 0.15 or more and 1.5 or less.

[Measurement method of Elmendorf ratio]
The film is attached to a rectangular frame having a predetermined length in a state of being loosened in advance (that is, both ends of the film are gripped by the frame). Then, the film is contracted by 10% in the longitudinal direction by immersing in warm water at 80 ° C. for about 5 seconds until the slack film is in a tension state in the frame (until the slack disappears). Thereafter, the Elmendorf tear load in the longitudinal direction and the width direction of the film is measured according to JIS-K-7128, and the Elmendorf ratio is calculated using the following equation 3. For films that do not shrink 10% at 80 ° C., measure the Elmendorf tear load in the longitudinal and width directions of the film that has been shrunk by the amount that can be shrunk by immersion in warm water at 80 ° C. for about 5 seconds. Do.
Elmendorf ratio = Elmendorf tear load in the longitudinal direction ÷ Elmendorf tear load in the width direction.

  If the Elmendorf ratio is less than 0.15, it is not preferable because it is difficult to tear straight along the perforation when used as a label. On the other hand, if the Elmendorf ratio exceeds 1.5, it is not preferable because it is easy to tear at a position shifted from the perforation. The lower limit value of the Elmendorf ratio is preferably 0.20 or more, more preferably 0.25 or more, and particularly preferably 0.3 or more. The upper limit value of the Elmendorf ratio is preferably 1.4 or less, more preferably 1.3 or less, and particularly preferably 1.2 or less.

  Furthermore, the heat-shrinkable polyolefin film of the present invention has a peel strength (hereinafter referred to as heat-resistant peel strength) of 0 when a pressure of 0.4 MPa is applied for 90 seconds while the surfaces of the films are combined and heated to 90 ° C. .1 N / 15 mm or less is required. Such heat-resistant peel strength is obtained by grasping both ends of each of the two overlapped films with a universal tensile tester and measuring the strength when the two films are peeled off under a tensile speed of 200 mm / min. be able to. When the heat-resistant peel strength exceeds 0.1 N / mm, when a heat-shrinkable polyolefin film is used as a label, blocking is caused by heating (for example, by storing a PET bottle coated with the label in an incubator). Since there is a fear, it is not preferable. The heat-resistant peel strength is preferably 0.05 N / mm or less, and most preferably 0 N / mm.

  The heat shrinkage rate, right-angle tear strength, Elmendorf ratio, and heat-resistant peel strength of the heat shrinkable film can be achieved by using the preferred film composition described above and combining with the preferred production method described later.

  Although the thickness of the heat-shrinkable polyolefin film of the present invention is not particularly limited, the heat-shrinkable film for labels is preferably 10 to 200 μm, and more preferably 20 to 100 μm.

  Further, the heat-shrinkable polyolefin film of the present invention is obtained by melting and extruding the above-mentioned polyolefin resin raw material with an extruder to form an unstretched film, and biaxially stretching the unstretched film by the method shown below. It can be obtained by heat treatment.

  When the raw material resin is melt-extruded, the polyolefin resin raw material is preferably dried using a dryer such as a hopper dryer or a paddle dryer, or a vacuum dryer. After the polyolefin-based resin raw material is dried in such a manner, it is melted at a temperature of 200 to 300 ° C. and extruded into a film using an extruder. For this extrusion, any existing method such as a T-die method or a tubular method can be employed.

  And an unstretched film can be obtained by rapidly cooling the sheet-like molten resin after extrusion. In addition, as a method of rapidly cooling the molten resin, a method of obtaining a substantially unoriented resin sheet by casting the molten resin on a rotating drum from a die and rapidly solidifying it can be suitably employed.

  Further, as will be described later, the obtained unstretched film was stretched in the width direction under predetermined conditions, and then heat-treated once, and then stretched in the longitudinal direction under predetermined conditions. By rapidly cooling, the heat-shrinkable polyolefin film of the present invention can be obtained. In addition, when stretching in the longitudinal direction, the gap ratio (distance from the contact point between the low-speed roll and the film to the contact point between the high-speed roll and the film when stretching in the longitudinal direction) and the film width are appropriately adjusted, so that the gap ratio ( (Stretch gap / film width) can be adjusted in the range of 0.01 to 0.10.

  Hereinafter, a preferred biaxial stretching / heat treatment method for obtaining the heat-shrinkable polyolefin film of the present invention will be described in detail in consideration of the difference from the conventional biaxial stretching / heat treatment method of a heat-shrinkable polyolefin film. .

[Preferred method for forming heat-shrinkable polyolefin film]
As described above, the heat-shrinkable film simply stretched in the width direction has a problem that the perforation opening property in the direction orthogonal to the main shrinkage direction is poor. On the other hand, although there is a high demand for a heat-shrinkable film that shrinks in the longitudinal direction, a wide film cannot be produced by simply stretching an unstretched film in the longitudinal direction. A good film cannot be produced. Moreover, if the method of extending | stretching to a longitudinal direction after extending | stretching previously to the width direction is employ | adopted, the shrinkage | contraction amount to a longitudinal direction will become inadequate, or it will shrink | contract unnecessarily in the width direction.

In the method of stretching in the longitudinal direction after stretching in the width direction (hereinafter referred to as the transverse-longitudinal stretching method), the inventors have performed hot water shrinkage in the longitudinal direction of the film, perforation openability, and heat resistance depending on the conditions in each stretching step. The inventors studied diligently how the blocking property changes. As a result, when the film is manufactured by the horizontal-longitudinal stretching method, the following measures are taken to stably stabilize the film having a high amount of shrinkage in the longitudinal direction and good perforation opening and heat blocking properties in the orthogonal direction. We have determined that it will be possible to manufacture. And the present inventors came to devise this invention based on those knowledge.
(1) Intermediate thermal relaxation treatment after stretching in the width direction (2) Trimming of film edge before stretching in the longitudinal direction Hereinafter, each of the above-described means will be described in order.

(1) Intermediate heat relaxation treatment after stretching in the width direction In the production of the film by the transverse-longitudinal stretching method of the present invention, the unstretched film is stretched in the width direction, and then at a temperature of 100 ° C to 155 ° C. It is necessary to perform heat treatment (hereinafter referred to as intermediate heat relaxation treatment) over a period of from 0.0 seconds to 50.0 seconds. By performing such an intermediate heat relaxation treatment, it is possible to obtain a film having good perforation cutability and no shrinkage spots when used as a label. The reason why it becomes possible to obtain a film having good perforation cutability and no shrinkage spots by performing a specific intermediate heat relaxation treatment after transverse stretching is not clear, but a specific intermediate heat relaxation treatment is not performed. It is thought that this can reduce the shrinkage stress in the width direction while leaving some molecular orientation in the width direction. In addition, the minimum of the temperature of a heat relaxation process is preferable in it being 110 degreeC or more, and it is more preferable in it being 115 degreeC or more. Moreover, the upper limit of the temperature of the heat relaxation treatment is preferably 150 ° C. or less, and more preferably 145 ° C. or less. On the other hand, the time for the thermal relaxation treatment needs to be appropriately adjusted in accordance with the raw material composition within a range of 1.0 second to 50.0 seconds.

  The stretching of the unstretched film in the width direction is a ratio of 2.5 times or more and 8.0 times or less at a temperature of 70 ° C. or more and 140 ° C. or less in a state where both ends of the width direction are held by clips in the tenter. It is necessary to do so. If the stretching temperature is less than 70 ° C., it is not preferable because breakage is likely to occur during stretching. On the other hand, if it exceeds 140 ° C., uneven thickness in the width direction is deteriorated, which is not preferable. The lower limit of the transverse stretching temperature is preferably 75 ° C. or higher, and more preferably 80 ° C. or higher. The upper limit of the transverse stretching temperature is preferably 135 ° C. or less, and more preferably 130 ° C. or less. On the other hand, if the draw ratio in the width direction is less than 2.5 times, not only the productivity is deteriorated but also the thickness unevenness in the width direction becomes worse. On the other hand, if it exceeds 8.0 times, breakage occurs at the time of drawing. In addition, it is not preferable because a large amount of energy and a large apparatus are required for heat relaxation, and productivity is deteriorated. In addition, the lower limit of the transverse stretching ratio is preferably 3.0 times or more, and more preferably 3.5 times or more. In addition, the upper limit of the transverse stretching ratio is preferably 7.5 times or less, and more preferably 7.0 times or less.

(2) Trimming of film edge before being stretched in the longitudinal direction In the production of the film by the transverse-longitudinal stretching method of the present invention, before the film subjected to the intermediate heat relaxation treatment is stretched in the longitudinal direction, the film edge It is necessary to trim a thick portion (mainly a clip gripping portion at the time of transverse stretching) that is not sufficiently transversely stretched. More specifically, a thick portion at the edge of the film using a tool such as a cutter in a portion having a thickness of about 1.1 to 1.3 times the thickness of the central portion located at the right and left edges of the film. It is necessary to stretch only the remaining part in the longitudinal direction while cutting the wall and removing the thick part. In addition, when trimming the film edge as described above, it is preferable to cool the film so that the surface temperature of the film before trimming is 50 ° C. or less. By cooling the film in this way, trimming can be performed without disturbing the cut surface. In addition, trimming of the film edge can be performed using a normal cutter or the like, but if a round blade having a circumferential cutting edge is used, a situation in which the cutting edge is locally dulled does not occur, and the film edge is This is preferable because it can continue to be cut sharply over a long period of time and does not cause a breakage during stretching in the longitudinal direction.

  As described above, by trimming the end of the film before stretching in the longitudinal direction, it becomes possible to stretch the film once subjected to heat relaxation treatment uniformly in the longitudinal direction. It becomes possible. In addition, it is possible to obtain a film having a large shrinkage in the longitudinal direction (main shrinkage direction). Furthermore, since the film can be uniformly stretched in the longitudinal direction, a film having a small thickness unevenness in the longitudinal direction can be obtained. In addition, by trimming the end of the film, bowing during stretching in the longitudinal direction is avoided, and a film having a small difference in physical properties between the left and right can be obtained.

  It should be noted that only one of the above-mentioned means (1) and (2) contributes effectively to the heat shrinkability in the longitudinal direction of the film, the perforation opening property, the heat blocking property, and the stable film forming property. Rather than using the combination of the means (1) and (2), the heat shrinkage in the longitudinal direction, the perforation opening, the heat blocking property, and the stable film-forming property are expressed very efficiently. It is thought that it will be possible.

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to the embodiments of the examples, and can be appropriately changed without departing from the spirit of the present invention. is there. Tables 1 and 2 show properties of the raw materials used in Examples and Comparative Examples, compositions, production conditions of the films in Examples and Comparative Examples (stretching / thermal relaxation treatment conditions, etc.), respectively. In addition, resin raw material AE in Table 1 is as follows.
Resin raw material A: Polypropylene-ethylene random copolymer (Sumitomo Chemical Co., Ltd. S131 ethylene = 5.5% by mass, MFR = 1.2 g / 10 min, melting point 135 ° C.)
Resin raw material B: Polypropylene-ethylene random copolymer (FS2011DG3 ethylene = 0.6% by mass, MFR = 2.5 g / 10 min, melting point 158 ° C., manufactured by Sumitomo Chemical Co., Ltd.) 94% by mass of stearic acid monoglycerin ester (Antistatic agent) 6% by mass added; resin raw material C: polypropylene-ethylene random copolymer (FS2011DG3 ethylene = 0.6% by mass, MFR = 2.5 g / 10 min, melting point 158, manufactured by Sumitomo Chemical Co., Ltd.) ℃) Organic polymer fine particles (CS30 average particle size 3.5 μm, manufactured by Sumitomo Chemical Co., Ltd., 20% by mass) added in 80% by mass / resin raw material D: polypropylene-ethylene random copolymer (FS2011DG3 manufactured by Sumitomo Chemical Co., Ltd.) (Ethylene = 0.6 mass%, MFR = 2.5 g / 10 min, melting point 158 ° C.)
-Resin raw material E: polypropylene-ethylene, butene random copolymer (Sumitomo Chemical Co., Ltd. FSX66E8 ethylene = 2.5 mass%, butene = 6.9 mass%, MFR = 3.0 g / 10 min, melting point 134 ° C.)

  Moreover, the evaluation method of a film is as follows.

[Tm (melting point)]
Using a differential scanning calorimeter (model: DSC220) manufactured by Seiko Denshi Kogyo Co., Ltd., 5 mg of an unstretched film was sampled, and from the peak temperature of the endothermic curve when the temperature was raised from room temperature at a heating rate of 10 ° C./min. Asked.

[Ethylene and butene content]
The content of ethylene or butene in the propylene-ethylene copolymer, propylene-butene copolymer, and propylene-ethylene-butene copolymer is determined according to Polymer Analysis Handbook (1995, published by Kinokuniya Shoten). Determined by 13 C-NMR spectroscopy according to the method described on page. In addition, it can also be determined by the IR spectrum method according to the method described in the section “(i) Random copolymer” on page 256 of the same document.

[Heat shrinkage (hot water heat shrinkage)]
The film is cut into a 10 cm × 10 cm square, heat-shrinked in warm water at a predetermined temperature (90 ° C.) ± 0.5 ° C. under no load for 10 seconds, and then the vertical and horizontal dimensions of the film. Was measured, and the thermal shrinkage rate was determined according to the above formula 1. The direction (longitudinal direction) in which the heat shrinkage rate is large was defined as the main shrinkage direction.

[Heat-resistant peel strength]
Two obtained film samples were prepared, their surfaces were combined, and a pressure of 0.4 MPa was applied for 90 seconds while heating to 90 ° C. with a test sealer (manufactured by Seibu Kikai Co., Ltd .; seal bar width 10 mm). Thereafter, the two overlapping films were cut into strips having a width of 15 mm. Thereafter, the two films were combined at 200 mm / min. Using a universal tensile tester (manufactured by Shimadzu Corporation Autograph). The peel strength when peeled off was measured. In addition, the measurement was performed 5 times and the average value was calculated | required.

[Right-angle tear strength]
The film was shrunk 10% in the main shrinking direction in warm water adjusted to 80 ° C. Moreover, about the film which does not shrink | contract 10% at 80 degreeC, it was made to shrink | contract only by the part which can be shrunk by being immersed in 80 degreeC warm water for about 5 seconds. Thereafter, according to JIS-K-7128, a test piece was prepared by sampling into the shape shown in FIG. 1 (in the sampling, the longitudinal direction of the test piece was set as the main shrinkage direction of the film). After that, grasp both ends of the test piece with a universal tensile tester (Autograph made by Shimadzu Corporation), and measure the strength at the time of tensile fracture in the width direction of the film under the condition of a tensile speed of 200 mm / min. The right angle tear strength per unit thickness was calculated using Equation 2 above.

[Elmendorf ratio]
The obtained film is attached to a rectangular frame in a state of being loosened in advance (with both ends of the film being gripped by the frame), and until the loose film is in a tension state within the frame (until loosening), about 5 The film was shrunk by 10% in the main shrinking direction (hereinafter referred to as pre-shrinking) by immersing in warm water at 80 ° C. for 2 seconds. Moreover, about the film which does not shrink | contract 10% at 80 degreeC, it was made to shrink | contract only by the part which can be shrunk by being immersed in 80 degreeC warm water for about 5 seconds. After that, in accordance with JIS-K-7128, the main shrinkage direction × orthogonal direction = 63 mm × 75 mm is cut out and perpendicular to the edge from the center of the long edge (edge along the orthogonal direction). Thus, the test piece was produced by putting a 20 mm slit (cut). And the Elmendorf tear load of the main contraction direction was measured using the produced test piece. Further, after preliminarily shrinking the film in the main shrinkage direction by the same method as described above, a test piece was prepared by replacing the main shrinkage direction and the orthogonal direction of the film, and the Elmendorf tear load in the orthogonal direction was measured. . Then, the Elmendorf ratio was calculated from the obtained main contraction direction and the Elmendorf tear load in the direction orthogonal to the main contraction direction using the above equation 3.

[Shrink finish]
For a film roll whose main shrinkage direction is the longitudinal direction, the obtained film roll is slit into a width of about 120 mm, and then a small slit roll is created by winding it into a predetermined length, Label printing (three-color printing) was repeatedly applied to the slit roll in advance using grass-colored, gold-colored, and white inks from Toyo Ink Manufacturing Co., Ltd. For each label printing, perforations over the entire width of the film (perforations in which circles of about 1 mm in diameter are continuous at intervals of about 1 mm) in a direction perpendicular to the longitudinal direction of the film roll are provided at intervals of about 22 mm. These were formed in parallel. Then, one end of the roll-shaped film on which the label printing is applied is overlaid on the adhesive applied to a part of the outer periphery of a 350 ml square hot PET bottle (filled with the contents). In this state, the roll-shaped film was drawn out by a predetermined length and wound around the outer periphery of the PET bottle. Thereafter, while the heat-shrinkable films overlapped on the outer periphery of the PET bottle were bonded to each other with the above-mentioned adhesive, the outer film was cut in the vertical direction with a cutter to coat the outer periphery of the PET bottle.

  On the other hand, for the film roll whose main shrinkage direction is the width direction, the heat-shrinkable film was preliminarily printed with three colors with grass-colored, gold-colored, and white inks from Toyo Ink Manufacturing Co., Ltd. And the cylindrical label was created by heat-sealing the both ends of the printed film with a white light sealer (model: No. 310-1) by Hakuko Co., Ltd. Thereafter, the produced label was attached around the PET bottle.

And, using a steam tunnel (model: SH-1500-L) manufactured by Fuji Astec Inc, a PET bottle coated with a label (a PET bottle coated with a label made of a film whose longitudinal direction is the main shrinkage direction, and width) The PET bottle coated with a label made of a film whose direction is the main shrinkage direction) is passed under conditions of a passage time of 10 seconds and a zone temperature of 80 ° C., and the label is thermally shrunk on the outer periphery of the PET bottle. Completed installation. At the time of mounting, the neck portion was adjusted so that a portion with a diameter of 40 mm was one end of the label. The finish after shrinkage was evaluated visually, and the criteria were as follows.
◎: No wrinkles, jumping up, insufficient shrinkage, and no color spots are observed ○: Wrinkles, jumping up, or insufficient shrinkage cannot be confirmed, but some color spots are seen △: Jumping Neither ascending nor insufficient shrinkage has occurred, but spots on the neck are observed. ×: Wrinkles, jumping up, insufficient shrinkage occurred

[Perforation opening]
A label having perforations in a direction perpendicular to the main shrinkage direction was attached to the PET bottle under the same conditions as the measurement conditions for shrinkage finish described above. However, the perforations were formed by putting holes having a length of 1 mm at intervals of 1 mm, and two perforations were provided in the longitudinal direction (height direction) of the label over a width of 22 mm and a length of 120 mm. The bottle was then refrigerated at 5 ° C and the bottle label perforated immediately after removal from the refrigerator was torn off with the fingertips, and the bottles were torn cleanly along the perforation to remove the label from the bottle. And the ratio (%) with respect to all 50 samples was calculated.

[Heat-resistant blocking property]
A heat-shrinkable film was heat-shrinked and mounted on the outer periphery of a 350 ml square hot PET bottle beverage (filled with contents) in the same manner as in the evaluation of the shrink finish. And after five PET bottle drinks which attached the same heat-shrinkable film were piled up vertically and left to stand on 70 degreeC conditions for 5 days, whether there is blocking between the films of the outer surface of PET bottle drinks? These were subjected to sensory evaluation in the following two stages (note that even a slight blocking was indicated as x).
○ ・ ・ No blocking × ・ ・ With blocking

[Example 1]
Using a co-extrusion method, a polyolefin resin is melt-extruded (laminated in a die and extruded) from two extruders (first and second extruders) into a rotating metal roll cooled to 30 ° C. By winding and quenching, an unstretched film (polyolefin-based resin laminated sheet) having a thickness of 400 μm and a two-layer / three-layer structure was obtained. At this time, the take-up speed of the unstretched film (rotational speed of the metal roll) is about 6.8 m / min. Met. The method for forming each layer of the unstretched film (steps until melt extrusion) is as follows. In the following description, the first layer, the second layer, and the third layer are referred to in order from the surface layer of the polyolefin-based resin laminate sheet (that is, the surface of the third layer is a metal roll contact surface). In addition, the discharge amount of the 1st, 2nd extruder in formation of an unstretched film was adjusted so that the thickness ratio of 1st layer / 2nd layer / 3rd layer might become 1/4/1.

Formation of the first layer and the third layer (skin layer) The dried raw material resins A, B, and C were continuously and separately supplied to the hopper of the extruder (first extruder) with a quantitative screw feeder. . The supply amount of the raw material resin A was 90% by mass, the supply amount of the raw material resin B was 8% by mass, and the supply amount of the raw material resin C was 2% by mass. Then, the supplied raw material resins A, B, and C were mixed in a hopper and melt-extruded from a T die at 250 ° C. by a single-screw first extruder.

-Formation of 2nd layer (core layer) The dried said raw material resin A was continuously supplied separately to the hopper of the extruder (2nd extruder) with the fixed amount screw feeder. The supplied raw material resin A was melt-extruded from a T die at 250 ° C. by a single-screw second extruder.

  Thereafter, the obtained unstretched film was guided to a tenter in which a transverse stretching zone, an intermediate zone, and an intermediate heat relaxation treatment zone were continuously provided. In the tenter, the length of the intermediate zone located between the transverse stretching zone and the intermediate thermal relaxation treatment zone is set to about 40 cm. In addition, in the intermediate zone, when the strip-shaped paper piece is hung in a state where the film is not passed through, the hot air from the stretching zone and the hot air from the heat treatment zone are blown so that the paper piece hangs almost completely in the vertical direction. Blocked.

  And after preheating the unstretched film led to the tenter until the film temperature reaches 89 ° C., it is stretched 4.5 times at 89 ° C. in the transverse direction in the transverse stretching zone, and after passing through the intermediate zone Then, the film was led to an intermediate heat relaxation treatment zone and heat treated at a temperature of 145 ° C. for 43 seconds to obtain a transversely uniaxially stretched film having a thickness of 90 μm. Thereafter, using a pair of left and right trimming devices (configured by a round blade having a circumferential cutting edge) provided behind the tenter, the edge of the laterally uniaxially stretched film (about the thickness of the film at the center) A portion having a thickness of 1.2 times) was cut, and the end portion of the film located outside the cut site was continuously removed.

  Furthermore, the film (film width = 500 mm) with the end trimmed as described above was led to a longitudinal stretching machine in which a plurality of roll groups were continuously arranged, and preheated until the film temperature reached 90 ° C. on the preheating roll. Later, the film was stretched 2.0 times between a low-speed stretching roll whose surface temperature was set to 100 ° C. and a high-speed stretching roll whose internal circulating water temperature was set to 30 ° C. The speed of the low-speed roll (the speed of the film moving with the low-speed roll) is 3.0 m / min. The speed of the high-speed roll (the speed of the film that moves with the high-speed roll) is 6.0 m / min. Adjusted. The stretching gap between the low-speed stretching roll and the high-speed stretching roll was adjusted to 30 mm (stretching gap ratio = 0.06).

  And the film roll which wound the biaxially stretched film (heat-shrinkable polyolefin film) of about 50 micrometers by predetermined length by winding up the film after extending | stretching longitudinally as mentioned above to a paper tube was obtained. And the characteristic of the obtained film was evaluated by the above-mentioned method. The evaluation results are shown in Table 3.

[Example 2]
A film roll wound with a heat-shrinkable film was obtained in the same manner as in Example 1 except that the surface temperature of the low-speed stretching roll during longitudinal stretching was set to 110 ° C. And the characteristic of the obtained film was evaluated by the same method as Example 1. The evaluation results are shown in Table 3.

[Example 3]
The speed of the high-speed roll during longitudinal stretching is 15.0 m / min. A film roll obtained by winding a heat-shrinkable film having a thickness of about 20 μm was obtained in the same manner as in Example 2 except that the film was adjusted to (longitudinal stretch ratio = 5.0 times). And the characteristic of the obtained film was evaluated by the same method as Example 1. The evaluation results are shown in Table 3.

[Example 4]
The surface temperature of the low-speed stretching roll during longitudinal stretching is set to 110 ° C., and the speed of the high-speed roll is set to 10.5 m / min. A film roll obtained by winding a heat-shrinkable film having a thickness of about 30 μm was obtained in the same manner as in Example 1 except that the film was adjusted to (longitudinal stretch ratio = 3.5 times). And the characteristic of the obtained film was evaluated by the same method as Example 1. The evaluation results are shown in Table 3.

[Example 5]
A film roll wound with a heat-shrinkable film was obtained in the same manner as in Example 4 except that the resin raw material for forming the core layer was changed to the resin raw material E. And the characteristic of the obtained film was evaluated by the same method as Example 1. The evaluation results are shown in Table 3.

[Example 6]
The speed of the high-speed roll during longitudinal stretching is 9.0 m / min. A film roll obtained by winding a heat-shrinkable film having a thickness of about 36 μm was obtained in the same manner as in Example 4 except that the film was adjusted to (longitudinal stretch ratio = 3.0 times). And the characteristic of the obtained film was evaluated by the same method as Example 1. The evaluation results are shown in Table 3.

[Example 7]
When forming an unstretched resin sheet, the resin raw material supplied to the second extruder is changed as shown in Table 1, and a single-layer structure of only the second layer without forming the first layer and the third layer. The film roll which wound the heat-shrinkable film about 30 micrometers thick was obtained by the method similar to Example 4 except having performed. And the characteristic of the obtained film was evaluated by the same method as Example 1. The evaluation results are shown in Table 3.

[Comparative Example 1]
A heat of about 24 μm in thickness is obtained in the same manner as in Example 1 except that the thickness of the unstretched film of the two-layer / three-layer configuration is 110 μm, the temperature of the intermediate heat relaxation treatment is changed to 70 ° C., and no longitudinal stretching is performed. A film roll wound with a shrinkable film was obtained. And the characteristic of the obtained film was evaluated by the same method as Example 1. The evaluation results are shown in Table 3.

[Comparative Example 2]
The unstretched film having a two-layer / three-layer structure has a thickness of 110 μm, and the unstretched film is guided to the longitudinal stretching machine without undergoing transverse stretching and intermediate heat relaxation treatment, and the speed of the low-speed roll in the longitudinal stretching is 1.0 m / min. And the speed of the high speed roll was changed to 6.0 m / min. A film roll obtained by winding a heat-shrinkable film having a thickness of about 20 μm was obtained by longitudinal stretching in the same manner as in Example 1 except that the ratio was changed to (longitudinal stretching ratio = 6.0 times). And the characteristic of the obtained film was evaluated by the same method as Example 1. The evaluation results are shown in Table 3.

[Comparative Example 3]
A film roll in which a heat-shrinkable film was wound by the same method as in Example 1 except that the resin raw material for forming the skin layer and the core layer and the composition thereof were changed as shown in Table 1, and longitudinal stretching was not performed. Although it tried to obtain, since the breakage occurred frequently in the step of transverse stretching, a film that could be evaluated could not be obtained.

[Comparative Example 4]
The resin raw material for forming the skin layer and the core layer and the composition thereof were changed as shown in Table 1, the temperature of the intermediate heat relaxation treatment was changed to 160 ° C., and the temperature of the low-speed roll during longitudinal stretching was changed to 140 ° C. The film roll which wound the heat-shrinkable film about 30 micrometers thick by the method similar to Example 4 was obtained. And the characteristic of the obtained film was evaluated by the same method as Example 1. The evaluation results are shown in Table 3.

  As is clear from Table 3, the films obtained in Examples 1 to 7 all have high shrinkability in the longitudinal direction, which is the main shrinkage direction, and the shrinkage in the width direction orthogonal to the main shrinkage direction is It was very low. Moreover, all of the films obtained in Examples 1 to 7 had low heat-resistant peel strength, no shrinkage spots, and good shrinkage finish, perforation openability, and heat-resistant blocking properties. That is, the heat-shrinkable polyolefin films obtained in the examples were all high in label quality and extremely practical.

  On the other hand, the heat-shrinkable films obtained in Comparative Examples 1 and 2 had poor perforation openability. Moreover, the film which can be evaluated was not able to be obtained on the conditions of the comparative example 3. Further, the film obtained in Comparative Example 4 has a very low heat shrinkage rate in the longitudinal direction, and when mounted as a label, it cannot be mounted well due to insufficient shrinkage, and was evaluated for perforation opening and heat blocking resistance. Could not get a labeled bottle to get. That is, the heat-shrinkable polyolefin film obtained in the comparative example was inferior in quality as a label and low in practicality.

  Since the heat-shrinkable polyolefin film of the present invention has excellent processing characteristics as described above, it can be suitably used for labeling bottles.

It is explanatory drawing which shows the shape of the test piece in the measurement of a right-angled tear strength (In addition, the unit of the length of each part of the test piece in a figure is mm).

Explanation of symbols

  F ・ ・ Film.

Claims (6)

It is a heat-shrinkable polyolefin-based film that is formed into a long shape with a constant width by a polyolefin-based resin mainly composed of a propylene-α-olefin copolymer, and the main shrinkage direction is the longitudinal direction. A heat-shrinkable polyolefin film characterized by satisfying 1) to (4).
(1) The hot water heat shrinkage in the longitudinal direction is 15% or more and 40% or less when treated in 90 ° C. warm water for 10 seconds. (2) Treated in 90 ° C. warm water for 10 seconds. The hot-water heat shrinkage rate in the width direction perpendicular to the longitudinal direction is -5% to 10%. (3) Width per unit thickness after shrinking 10% in the longitudinal direction in hot water at 80 ° C The perpendicular tear strength in the direction is 50 N / mm or more and 200 N / mm or less. (4) The peel strength when a pressure of 0.4 MPa is applied for 90 seconds while the surfaces of the films are combined and heated to 90 ° C. is 0. 1N / 15mm or less   The polyolefin resin is mainly composed of a copolymer of propylene and ethylene, and the amount of ethylene in the constituent resin is 2.0% by mass or more and 10.0% by mass or less. The heat-shrinkable polyolefin film according to claim 1.   The polyolefin-based resin is mainly composed of a copolymer of propylene, ethylene and butene, and the amount of ethylene and butene in the constituent resin is 3.0% by mass or more and 10.0% by mass or less. The heat-shrinkable polyolefin film according to claim 1.   The polyolefin-based resin is mainly composed of a copolymer of propylene and butene, and the amount of butene in the constituent resin is 15.0% by mass or more and 35.0% by mass or less. The heat-shrinkable polyolefin film according to claim 1.   The core layer has a laminated structure in which a skin layer is laminated on at least one surface, and an antiblocking agent and / or an antistatic agent is added to the skin layer. The heat-shrinkable polyolefin film according to any one of the above. A production method for producing the heat-shrinkable polyolefin film according to claim 1,
The unstretched film is stretched at a magnification of 2.5 to 8.0 times in the width direction at a temperature of 70 ° C. or more and 140 ° C. or less with the clip held at both ends in the width direction in the tenter, and then 100 Heat relaxation treatment at a temperature not lower than 155 ° C. and lower than 155 ° C. for a time not shorter than 1.0 second and not longer than 50.0 seconds, and then cuts and removes clip holding portions at both edges in the width direction of the film, and then 70 ° C. A method for producing a heat-shrinkable polyolefin film, wherein the film is stretched at a temperature of 140 ° C. or less at a magnification of 2.0 times or more and 8.0 times or less in the longitudinal direction.

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