JP2014055236A - Heat-shrinkable polyester film for book packaging - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a heat-shrinkable polyester film suitable for book packaging.SOLUTION: A heat-shrinkable polyester film for book packaging is formed by a polyester resin mainly containing ethylene terephthalate and of which sum total of one or more kind of monomer components which can be an amorphous component in total monomer components is 16 mol% to 27 mol%, and satisfies following requirements (1) to (4). (1) A maximum heat-shrinking stress in a main shrinkage direction measured in hot air at 90°C is 1 MPa to 6 MPa. (2) A heat shrinkage rate in the main shrinkage direction is 15% to 50% when treated in a warm water at 70°C for 10 seconds. (3) Elmendorf tear transmission strengths in the main shrinkage direction and in an orthogonal direction with the main shrinkage direction are both 300 mN or less. (4) One and more kinds of characters, patterns and marks are printed.

Description

  The present invention relates to a heat-shrinkable film suitable for packaging of a book, and is a heat-shrinkable polyester film for book packaging having an information transmission function on which any one or more of letters, designs and symbols are printed. .

  2. Description of the Related Art Conventionally, a book has been packaged with a film in order to prevent reading and to prevent the book from being deteriorated such that a book is soiled or a cover is creased. There is also data indicating that the purchase of a book packaged in film will increase because the purchaser wants a clean book. Such a film packaging of a book, for example, covers a book with a heat shrinkable film, and then heat-shrinks the film into a book by passing it through a table-top shrink wrapping machine in a bookstore as described in Patent Document 1. It is performed by the method of making it adhere. To prevent browsing, it is possible to wrap only about half of a book, but in order to maintain the aesthetics of a book, it is necessary to wrap the entire book with a film. There are many shops that may be referred to as overlap. For the overlap, a colorless and transparent heat-shrinkable film is used so that the cover of the book can be seen. Among various heat-shrinkable films, a polyvinyl chloride heat-shrinkable film is mainly used. .

  However, although the polyvinyl chloride heat-shrinkable film has excellent shrinkage properties, it has low heat resistance, and also has problems such as generation of hydrogen chloride gas when it is discarded and incinerated, and causes dioxins. . In addition, polystyrene film has poor solvent resistance and must use ink with a special composition during printing, and must be incinerated at a high temperature, and a large amount of black smoke is generated with an unpleasant odor during incineration. There is a problem of doing.

Registered Utility Model No. 3067592

  The current overlap is simply a clear and transparent film that wraps the entire book, which is effective in preventing reading and maintaining the beauty of the book's appearance. Has not demonstrated anything.

  For this reason, the present inventors consider using a heat-shrinkable polyester film as an overlap and printing the overlap to provide an information transmission function. I tried to divert it to packaging. However, with a simple desktop shrink machine, the film did not shrink well, or the shrinkage force was too strong, and after the film was shrunk, the book was warped.

  Accordingly, the present invention has been made to provide a heat-shrinkable polyester film suitable for book packaging that does not have the above-mentioned problems.

The present invention that has solved the above problems is a polyester resin comprising ethylene terephthalate as a main component, and the total of one or more monomer components that can be amorphous components in all monomer components is 16 mol% or more and 27 mol% or less. Is a heat-shrinkable polyester film for packaging, which satisfies the following requirements (1) to (4).
(1) The maximum heat shrinkage stress in the main shrinkage direction measured in hot air at 90 ° C. is 1 MPa or more and 6 MPa or less,
(2) The thermal shrinkage rate in the main shrinkage direction when treated with hot water of 70 ° C. for 10 seconds is 15% or more and 50% or less,
(3) The Elmendorf tear propagation strength in the main shrinkage direction and the direction orthogonal to the main shrinkage direction is 300 mN or less,
(4) One or more of characters, symbols and symbols are printed.

  In the heat-shrinkable polyester film for packaging, the thickness is preferably 3 to 20 μm.

  The present invention also includes a method of using the heat-shrinkable polyester film for packaging, wherein the book is covered with a heat-shrinkable polyester film for packaging and heat-shrinked.

  The heat-shrinkable polyester film for packaging of the present invention shrinks neatly at low temperatures, has excellent transparency, and excellent printability. Therefore, when it is heat-shrinked over a book, it has a beautiful appearance. Since printed information can also be transmitted, it is important to contribute to the improvement of book sales.

  The heat-shrinkable polyester film for packaging of the present invention (hereinafter sometimes simply referred to as a heat-shrinkable polyester film) is a film for packaging a book. The book to be packaged in the present invention may be a book (paperback book, book, technical book, etc.) or magazine (weekly magazine, monthly magazine, mook book, comic, etc.). If it is a specialized book or encyclopedia with an outer box, it can be packed from the top of the outer box. The appearance can be kept beautiful including the outer box. Hereinafter, the heat-shrinkable polyester film will be described.

  The polyester used for the heat-shrinkable polyester film of the present invention has an ethylene terephthalate unit as a main constituent component. The ethylene terephthalate unit is preferably 50 mol% or more, more preferably 60 mol% or more, in 100 mol% of the polyester structural unit. Other dicarboxylic acid components constituting the polyester of the present invention include aromatic dicarboxylic acids such as isophthalic acid, naphthalenedicarboxylic acid and orthophthalic acid, aliphatic dicarboxylic acids such as adipic acid, azelaic acid, sebacic acid and decanedicarboxylic acid, And alicyclic dicarboxylic acid.

  Moreover, it is preferable not to make polyester contain trivalent or more polyvalent carboxylic acid (for example, trimellitic acid, pyromellitic acid, and their anhydrides). In a heat-shrinkable polyester film obtained using a polyester containing these polyvalent carboxylic acids, it is difficult to achieve a necessary high shrinkage rate.

  The diol component constituting the polyester includes aliphatic diols such as ethylene glycol, 1,3-propanediol, 1,4-butanediol, neopentyl glycol, hexanediol, and alicyclic compounds such as 1,4-cyclohexanedimethanol. Examples thereof include aromatic diols such as diol and bisphenol A.

  The polyester used in the present invention is a cyclic diol such as 1,4-cyclohexanedimethanol or a diol having 3 to 6 carbon atoms (for example, 1,3-propanediol, 1,4-butanediol, neopentyl glycol, Polyesters containing one or more of hexanediol and the like and having a glass transition point (Tg) adjusted to 60 to 70 ° C. are preferred.

  Further, the polyester has a total of 16 or more monomer components that can be amorphous components in all monomer components (in 100 mol% of the polyhydric alcohol component or 100 mol% of the polyvalent carboxylic acid component in the polyester resin). The mol% or more, preferably 17 mol% or more, more preferably 18 mol% or more, particularly preferably 19 mol% or more. The upper limit of the total amount of monomer components that can be amorphous components is 27 mol%.

  Examples of the monomer that can be an amorphous component include neopentyl glycol, 1,4-cyclohexanedimethanol, isophthalic acid, 1,4-cyclohexanedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, and 2,2-diethyl-1. , 3-propanediol, 2-n-butyl-2-ethyl-1,3-propanediol, 2,2-isopropyl-1,3-propanediol, 2,2-di-n-butyl-1,3- Examples thereof include propanediol and hexanediol. Among these, it is preferable to use neopentyl glycol, 1,4-cyclohexanedimethanol or isophthalic acid.

  The polyester preferably does not contain a diol having 8 or more carbon atoms (for example, octanediol) or a trihydric or higher polyhydric alcohol (for example, trimethylolpropane, trimethylolethane, glycerin, diglycerin, etc.). . In the heat-shrinkable polyester film obtained by using polyesters containing these diols or polyhydric alcohols, it is difficult to achieve a necessary high shrinkage rate. Further, it is also preferable that the polyester does not contain diethylene glycol, triethylene glycol, or polyethylene glycol as much as possible.

  In addition, when a polyester elastomer is used in combination, the degree of amorphousness is increased, and heat shrinkage characteristics, particularly heat shrinkage characteristics in a low temperature region, are improved, which is a preferred embodiment of the present invention. The polyester elastomer that can be used is a polyester block copolymer comprising a high melting crystalline polyester segment (hard segment) and a low melting point soft polymer segment (soft segment) having a molecular weight of 400 or more. The high melting point crystalline polyester segment is a segment having a melting point of 200 ° C. or higher when a polymer is formed only from its constituent components, and the low melting point soft polymer segment is a polymer formed only from its constituent components , Refers to a segment having a melting point or softening point of 80 ° C. or lower.

  The high-melting crystalline polyester segment includes, for example, residues of aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, 1,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, pentamethylene glycol, 2,2- Polyester comprising aliphatic, aromatic or alicyclic diol residues such as dimethyltrimethylene glycol, hexamethylene glycol, decamethylene glycol, p-xylene glycol, cyclohexanedimethanol; p- (β-hydroxyethoxy) Polyester comprising residues of oxyacids such as benzoic acid and p-oxybenzoic acid pivalolactone; aromatics such as 1,2-bis (4,4′-dicarboxymethylphenoxy) ethane and di (4-carboxyphenoxy) ethane Ether dicarboxylic acid residue and the above aliphatic, A polyether ester comprising an aromatic or alicyclic diol residue; a residue of an aromatic amide dicarboxylic acid such as bis (N-paracarboethoxyphenyl) terephthalimide and the above aliphatic, aromatic or fatty acid Polyamide esters composed of residues of cyclic diols can be shown. Copolyesters using two or more of the above dicarboxylic acid residues and / or diol residues can also be used.

  The low melting point soft polymer segment (soft segment) having a molecular weight of 400 or more shows a substantially amorphous state in the polyester block copolymer, and the polymer was formed only from the constituent components of this segment. In this case, the melting point or softening point is 80 ° C. or lower. The molecular weight of the low melting point soft polymer segment is preferably 400 to 8000, more preferably 700 to 5000. Moreover, it is preferable that the ratio of the low melting-point soft polymer segment in a polyester-type elastomer is 1-90 mass%. A particularly desirable ratio is 5 to 80% by mass.

  Typical low melting point soft polymer segments include polyethylene oxide glycol, polypropylene oxide glycol, polytetramethylene oxide glycol, glycol of ethylene oxide / propylene oxide copolymer, glycol of ethylene oxide / tetrahydrofuran copolymer. Polyethers such as polyneopentyl azelate, polyneopentyl adipate, polyneopentyl sebacate, etc., but from the point of compatibility with the polyester constituting the polyester film, poly-ε -Polyester elastomers using polylactones such as caprolactone in the soft segment are particularly preferred.

  In the present invention, the ε-caprolactone-based polyester elastomer comprising a copolymer polyester of terephthalic acid, butanediol, and ε-caprolactone increases the degree of amorphousness and improves the heat shrinkage property, particularly the heat shrinkage property at low temperatures. Since the effect is great, it can be preferably used. Moreover, shrinkage finish property is also improved by using this ε-caprolactone-based polyester elastomer. In order to sufficiently obtain these effects, it is preferable that the ε-caprolactone-based polyester elastomer is 1 to 30 mol% in 100 mol% of the polyester resin constituting the polyester film. 3-25 mol% is more preferable and 5-20 mol% is especially preferable. If the amount of the ε-caprolactone-based polyester elastomer is less than 1 mol%, sufficient heat shrinkability at a low temperature range cannot be obtained, and there is a risk of insufficient shrinkage or poor shrinkage finish. Moreover, when it exceeds 30 mol%, since there exists a possibility that physical strength, such as a tear resistance of a film, intensity | strength, and heat resistance, may not fully be obtained, it is unpreferable.

  In the resin forming the heat-shrinkable polyester film of the present invention, various additives as required, for example, waxes, antioxidants, antistatic agents, crystal nucleating agents, viscosity reducing agents, heat stability An agent, a coloring pigment, an anti-coloring agent, an ultraviolet absorber and the like can be added. Further, it is preferable to add fine particles as a lubricant for improving the workability (slidability) of the film. As the fine particles, any one can be selected. For example, as inorganic fine particles, silica, alumina, titanium dioxide, calcium carbonate, kaolin, barium sulfate, etc. As organic fine particles, for example, acrylic resin Examples thereof include particles, melamine resin particles, silicone resin particles, and crosslinked polystyrene particles. The average particle size of the fine particles can be appropriately selected as necessary within a range of 0.05 to 3.0 μm (when measured with a Coulter counter).

  As a method of blending the above particles into the resin forming the heat-shrinkable polyester film, for example, it can be added at any stage for producing the polyester resin, but it can be added at the esterification stage or transesterification reaction. After completion, it is preferable to add as a slurry dispersed in ethylene glycol or the like at a stage before the start of the polycondensation reaction, and proceed with the polycondensation reaction. Also, a method of blending a slurry of particles dispersed in ethylene glycol or water using a vented kneading extruder and a polyester resin material, or a dried particle and a polyester resin material using a kneading extruder It is also preferable to carry out by a method of blending and the like.

  Furthermore, the heat-shrinkable polyester film of the present invention can be subjected to corona treatment, coating treatment, flame treatment, etc. in order to improve the adhesion of the film surface.

  Next, characteristics required for using the heat-shrinkable polyester film of the present invention for the present packaging will be described.

  First, in the heat-shrinkable polyester film of the present invention, the maximum heat-shrinkage stress in the film main shrinkage direction measured in hot air at 90 ° C. must be 1 MPa or more and 6 MPa or less. When the pressure exceeds 6 MPa, the warp of the book increases after the film is covered with a film and thermally contracted. The maximum heat shrinkage stress in hot air at 90 ° C. is preferably 5 MPa or less, and more preferably 4 MPa or less. The smaller the maximum heat shrinkage stress in the hot air at 90 ° C., the smaller the warp of the book. However, 1 MPa is necessary to develop the heat shrink force at 70 ° C., so the lower limit was set to 1 MPa.

In addition, the heat-shrinkable polyester film of the present invention is a main shrinkage of the film calculated by the following formula (I) from the length before and after shrinkage when treated for 10 seconds in 70 ° C. warm water without load. The direction of heat shrinkage (that is, hot water heat shrinkage of 70 ° C.) must be 15% or more and 50% or less.
Thermal shrinkage rate = {(length before shrinkage−length after shrinkage) / length before shrinkage} × 100 (%) Formula (I)
When the hot water heat shrinkage rate in the main shrinkage direction at 70 ° C. is less than 15%, the shrinkage amount is small, and thus the shrinkage unevenness, wrinkles, and tarmi occur in the package after heat shrinkage. The hot water heat shrinkage in the main shrinkage direction at 70 ° C. is preferably 17% or more, and more preferably 19% or more. On the other hand, if the hot water heat shrinkage rate in the main shrinkage direction at 70 ° C. exceeds 50%, the shrinkage rate increases and the film cannot be gently shrunk, so that the shrinkage is distorted during the heat shrinkage. The hot water heat shrinkage in the main shrinkage direction at 70 ° C. is preferably 48% or less, and more preferably 46% or less.

  Furthermore, the heat-shrinkable polyester film of the present invention must have an Elmendorf tear propagation strength of 300 mN or less in the main shrinkage direction and the direction orthogonal to the main shrinkage direction. The Elmendorf tear propagation strength was determined by the following method.

[Measurement method of Elmendorf tear propagation strength]
According to JIS K 7128-2, a film is cut into a rectangle with a measuring direction of 63 mm and a non-measuring direction of 75 mm, and a test piece is prepared by inserting a 20 mm slit from the edge in the center of the measuring direction. Elmendorf tear propagation strength was measured using a testing machine.

  If the Elmendorf tear propagation strength is greater than 300 mN in any of the main shrinkage direction and the direction perpendicular to the main shrinkage direction, it is not preferable because the film after heat shrinkage is not easily cut off from the book. The Elmendorf tear propagation strength is preferably 280 mN or less, more preferably 260 mN or less in any direction. Since the Elmendorf tear propagation strength decreases as the film thickness decreases, the lower limit is not particularly limited.

  Further, the heat-shrinkable polyester film of the present invention needs to be printed, and one or more of letters, designs, and symbols are printed. Thereby, the information transmission function can be secured. The text may be anything other than a store name, information that has been written in a conventional book band, such as the contents of a book or the words of a recommended person, or a word for shoplifting prevention such as shoplifting prohibition. The designs and symbols are not particularly limited, and if a design with a ribbon is printed, it is useful when presenting a book. A lottery mark may be attached to the front surface, and “winning” or “off” may be printed on the back surface of the film so that only the purchaser can perform the lottery. It leads to sales promotion of book. Further, a book may be used as an advertising medium, and an advertisement unrelated to the book may be printed.

  The thickness of the heat-shrinkable polyester film of the present invention is not particularly limited, but is preferably 3 μm or more and 20 μm or less. If the thickness of the film is less than 3 μm, processing such as printing may be difficult. On the other hand, when the film thickness is thicker than 20 μm, the force (shrinkage stress × thickness) at the time of film shrinkage becomes large, and the warpage of the packaged book after shrinkage becomes unfavorable. The thickness of the film is more preferably 5 μm or more and 18 μm or less, and further preferably 7 μm or more and 16 μm or less.

  The above-described heat-shrinkable polyester film of the present invention is obtained by melting and extruding the above polyester raw material with an extruder to form an unstretched film, and the unstretched film is uniaxially stretched or biaxially stretched by a predetermined method shown below. Can be obtained. The polyester can be obtained by polycondensing the above-described preferred dicarboxylic acid component and diol component by a known method. Usually, two or more kinds of chip-like polyester are mixed and used as a raw material for the film.

  When the raw material resin is melt-extruded, the polyester raw material is preferably dried using a dryer such as a hopper dryer or a paddle dryer, or a vacuum dryer. After the polyester 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. In extruding, 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 from a die onto a rotating drum and rapidly solidifying it can be suitably employed.

  A heat-shrinkable polyester film in which the longitudinal direction or the width direction of the film is the main shrinkage direction can be obtained by appropriately using the obtained unstretched film for transverse stretching and longitudinal stretching. A preferred production method is as follows.

  In order to achieve the object of the present invention, the main shrinkage direction of the film may be either the film longitudinal (longitudinal) direction or the lateral (width) direction. In the following, the transverse stretching-longitudinal stretching method in which the transverse stretching is performed first and then the longitudinal stretching will be described. However, even in the longitudinal stretching-transverse stretching in which the order is reversed, the main shrinkage direction may be changed. .

  First, stretching in the transverse direction is performed. Stretching in the transverse direction is preferably performed at 65 ° C. to 85 ° C. for about 3.5 to 5 times in a state where both ends of the film in the width direction are held by clips in the tenter (first tenter). Prior to stretching in the transverse direction, preheating is preferably performed, and the preheating is preferably performed until the film surface temperature reaches 70 ° C to 100 ° C.

  After transverse stretching, the film is preferably passed through an intermediate zone where no aggressive heating operation is performed. If there is a temperature difference between the transverse stretching zone of the first tenter and the intermediate heat treatment zone, the heat of the intermediate heat treatment zone (hot air itself or radiant heat) flows into the transverse stretching process, and the temperature of the transverse stretching zone is not stable, so the film quality is stable. Therefore, it is preferable to carry out the intermediate heat treatment after passing the film after the transverse stretching and before the intermediate heat treatment through the intermediate zone over a predetermined time. In this intermediate zone, when a strip-shaped paper piece is hung in a state where the film is not passed through, the accompanying flow accompanying the running of the film, the transverse stretching zone and the middle so that the paper piece hangs almost completely in the vertical direction. When hot air from the heat treatment zone is shut off, a stable quality film can be obtained. A transit time of about 1 second to 5 seconds is sufficient for the intermediate zone. If it is shorter than 1 second, the length of the intermediate zone becomes insufficient, and the heat shielding effect is insufficient. In addition, the intermediate zone is preferably long, but if it is too long, the facility becomes large, so about 5 seconds is sufficient.

  After passing through the intermediate zone, intermediate heat treatment before longitudinal stretching is performed. This is because the shrinkage in the lateral direction is adjusted by this intermediate heat treatment. When the temperature of the intermediate heat treatment after the transverse stretching is increased, the molecular orientation that contributes to the shrinkage is relaxed, but the shrinkage rate decreases because crystallization proceeds. From this viewpoint, the intermediate heat treatment is preferably performed at 65 to 140 ° C. When the temperature of the intermediate heat treatment zone is lower than 65 ° C., the thermal shrinkage rate in the transverse direction does not show any change with respect to the thermal shrinkage rate after transverse stretching. On the other hand, if it is higher than 140 ° C., the shrinkage in the transverse direction becomes zero, but it is not preferred because it becomes difficult to stretch in the longitudinal direction after crystallization. Moreover, the passage time of the intermediate heat treatment zone is preferably 2 seconds to 20 seconds. If it is shorter than 2 seconds, the length of the intermediate heat treatment zone is insufficient, and it becomes difficult to adjust the thermal contraction rate in the lateral direction. The intermediate heat treatment zone is preferably longer, but about 20 seconds is sufficient. Thereby, a lateral uniaxially stretched film is obtained.

  In the present invention, it is preferable to subsequently perform longitudinal stretching. Therefore, the laterally uniaxially stretched film may be introduced into a longitudinal stretching machine in which a plurality of roll groups are continuously arranged. In longitudinal stretching, preheating is preferably performed with a preheating roll until the film temperature reaches 65 ° C to 110 ° C. When the film temperature is lower than 65 ° C., it becomes difficult to stretch the film in the longitudinal direction (that is, breakage tends to occur), which is not preferable. On the other hand, when the temperature is higher than 110 ° C., the film tends to adhere to the roll, and the roll is not easily soiled by continuous production.

  When the film temperature falls within the above range, longitudinal stretching is performed. The longitudinal draw ratio differs depending on whether the main shrinkage direction is the longitudinal direction or the transverse direction. When the main shrinkage direction is the longitudinal direction, the longitudinal stretching ratio is preferably 2 to 5 times. On the other hand, when the main shrinkage direction is the transverse direction, the longitudinal draw ratio is preferably 1.2 to 1.8 times.

  After the longitudinal stretching, the film is preferably once cooled, and preferably cooled with a cooling roll having a surface temperature of 20 to 40 ° C. before the final heat treatment. The rapid cooling after the longitudinal stretching is preferable because the molecular orientation of the film is stabilized and the natural shrinkage of the film after becoming a product is reduced.

  Next, when the film after longitudinal stretching and cooling is introduced into a second tenter for heat treatment (relaxation treatment) and subjected to heat treatment or relaxation treatment, the shrinkage rate can be adjusted, which is a preferred embodiment. . The relaxation treatment is a step of loosening the film at 0% to 30% in a state where both ends in the width direction of the film are held by clips. The contraction rate in the lateral direction can be changed by the relaxation rate. When the relaxation rate is increased, there is little change in the contraction rate in the vertical direction, but the contraction rate in the horizontal direction is lowered. The lower limit of the relaxation rate is 0%, and the upper limit is 99%. However, a high relaxation rate is not preferable because there is a demerit that the film product width is shortened. Therefore, the upper limit of the relaxation rate is preferably about 30%.

  The heat treatment (relaxation treatment) temperature is preferably 65 ° C to 140 ° C. When the heat treatment temperature is lower than 65 ° C., the shrinkage rate of the film does not change. On the other hand, if the heat treatment temperature is higher than 140 ° C., the film is crystallized, and the film does not shrink in both the longitudinal and transverse directions, which is not preferable as a heat shrinkable film.

  Then, if it winds up while cutting and removing both ends of the film, a heat-shrinkable polyester film roll is obtained.

  The heat-shrinkable polyester film of the present invention is used for book packaging. When used for book packaging, cut both ends of the film with a solvent such as dioxolane, or heat sealed and cut into a single product so that the circumferential direction of the book is the shrinking direction of the film A bag product in which the bottom of the tube is also bonded to a bag after cutting is useful. In the case of a cut product, a book is put in a tube, and in the case of a bag product, the book is put in a bag and passed through a shrink machine. Whether it is a tube or a bag, it is preferable that the outer peripheral length of the book to be packaged is about 1.03 to 1.1 times longer than the outer peripheral length of the book to be wrapped since the appearance after heat shrinkage becomes beautiful. The heat-shrinkable film may be provided with notches and perforations.

  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.

<Preparation of polyester raw material>
Synthesis example 1
In a stainless steel autoclave equipped with a stirrer, a thermometer and a partial reflux condenser, 100 mol% of dimethyl terephthalate (DMT) as a dicarboxylic acid component and 100 mol% of ethylene glycol (EG) as a polyhydric alcohol component, Charge ethylene glycol to a molar ratio of 2.2 times that of dimethyl terephthalate, and use 0.05 mol% of zinc acetate (based on the acid component) as a transesterification catalyst to distill out the methanol produced. The transesterification reaction was carried out. Thereafter, 0.225 mol% of antimony trioxide (based on the acid component) was added as a polycondensation catalyst, and a polycondensation reaction was performed at 280 ° C. under a reduced pressure of 26.7 Pa. The intrinsic viscosity was 0.75 dl / g. Polyester (A) was obtained. This polyester is polyethylene terephthalate.

Synthesis example 2
In the same manner as in Synthesis Example 1, polyesters (B) to (F) shown in Table 1 were obtained. In the table, BD is 1,4-butanediol, NPG is neopentyl glycol, CHDM is 1,4-cyclohexanedimethanol, DEG is diethylene glycol, and ε-CL is ε-caprolactone. In the production of polyester (F), SiO ₂ (Silicia 266 manufactured by Fuji Silysia) was added as a lubricant at a ratio of 7,000 ppm with respect to the polyester. The intrinsic viscosities of polyesters B, C, D, E, and F were 0.72 dl / g, 0.80 dl / g, 1.20 dl / g, 0.77 dl / g, and 0.75 dl / g, respectively. Each polyester was appropriately formed into a chip shape. The composition of each polyester is shown in Table 1.

  The evaluation method of the heat-shrinkable polyester film and the package after packaging is shown below.

[Heat shrinkage (hot water heat shrinkage)]
The film is cut into a 10 cm × 10 cm square, immersed in hot water at 70 ° C. ± 0.5 ° C. for 10 seconds under no load, and thermally contracted, and then immersed in water at 25 ° C. ± 0.5 ° C. for 10 seconds. Then, the film was drawn out from the water, and the dimensions in the vertical and horizontal directions of the film were measured. The thermal shrinkage rate was determined according to the following formula (I). The direction in which the heat shrinkage rate is large was taken as the main shrinkage direction.
Thermal shrinkage rate = {(length before shrinkage−length after shrinkage) / length before shrinkage} × 100 (%) Formula (I)

[Maximum heat shrinkage stress value]
A sample having a length of 200 mm in the main shrinkage direction and a width of 20 mm was cut out from the heat-shrinkable film, and a toughness measuring instrument with a heating furnace (Tensilon (registered trademark of Orientec)) manufactured by Toyo Baldwin (currently Orientec). STM-50). The heating furnace was previously heated to 90 ° C., and the distance between chucks was 100 mm. Blowing of the heating furnace was temporarily stopped, the heating furnace door was opened, the sample was attached to the chuck, and then the heating furnace door was immediately closed to resume the blowing. The contraction stress was measured for 30 seconds or more, and the contraction stress (MPa) after 30 seconds was defined as the maximum thermal contraction stress value (MPa).

[Measurement method of Elmendorf tear propagation strength]
According to JIS K 7128-2, a film is cut into a rectangle with a measuring direction of 63 mm and a non-measuring direction of 75 mm, and a test piece is prepared by inserting a 20 mm slit from the edge in the center of the measuring direction. Elmendorf tear propagation strength was measured using a testing machine.

[Shrinkage finish and warpage]
Using a printing machine on the heat-shrinkable polyester film, printing was performed in this order with grass-colored, blue, and white inks manufactured by Toyo Ink Co., Ltd. A tube-shaped label was prepared by adhering both ends of the heat-shrinkable film after printing with dioxolane. At this time, the main shrinkage direction of the film was a circumferential direction (a direction perpendicular to the solvent adhesion portion). The outer peripheral length was 10% longer than the outer peripheral length of the book ("ONE PIECE", 50th volume, published by Shueisha). The tubular label was cut into the same dimension as the vertical length (height) of the book to produce a cut product. This book was covered with a tube-shaped label, and was hot shrunk by applying hot air at 100 ° C. (wind speed 12 m / sec) for 10 seconds. This packaging body covered with the film after shrinkage was obtained.

  About the obtained this package, the number of wrinkles was counted, and when the number of wrinkles was 2 or less, it was evaluated as ◯, when the number of wrinkles was 3 to 4, Δ, and the case where there were 5 or more wrinkles as x.

  In addition, after checking the thickness of the book from the horizontal to the entire circumference, the thickness of the highest position (maximum height) and the thickness of the lowest position (minimum height) are measured, The difference between the maximum height and the minimum height was defined as the warpage of the present package, and when the warpage was 2 mm or less, the evaluation was evaluated as ◯, the case of more than 2 mm and 4 mm or less was evaluated as Δ, and the case of over 4 mm.

[Openability]
The obtained package was provided with a notch having a length of 3 mm in the longitudinal direction of the book using scissors. The film after shrinkage was torn by hand from the notch. When the film was torn and peeled off, it was evaluated as good, and when it could not be peeled off without being broken cleanly, it was evaluated as bad.

Example 1
The above-mentioned polyester A, polyester B, polyester D, and polyester F were mixed at a mass ratio of 6: 66: 24: 4 and charged into an extruder. Thereafter, the mixed resin was melted at 280 ° C., extruded from a T die, wound around a rotating metal roll cooled to a surface temperature of 30 ° C., and rapidly cooled to obtain an unstretched film having a thickness of 96 μm. At this time, the take-up speed of the unstretched film (rotational speed of the metal roll) is about 20 m / min. Met. Thereafter, the unstretched film was guided to a tenter (first tenter) in which a transverse stretching zone, an intermediate zone, and an intermediate heat treatment zone were continuously provided. 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 80 ° C., the film is stretched 4 times at 70 ° C. in the transverse direction in the transverse stretching zone, and passed through the intermediate zone (pass Time = about 1.2 seconds), led to an intermediate heat treatment zone, and heat treated at 90 ° C. for 8 seconds to obtain a laterally uniaxially stretched film having a thickness of 24 μm.

  Further, the laterally stretched film was guided to a longitudinal stretching machine in which a plurality of roll groups were continuously arranged, preheated on a preheating roll until the film temperature reached 70 ° C., and then stretched 3 times. Thereafter, the longitudinally stretched film was forcibly cooled by a cooling roll set at a surface temperature of 25 ° C.

  Then, the cooled film is guided to a tenter (second tenter), heat-treated for 10 seconds in an atmosphere at 90 ° C. in the second tenter, and cooled after relaxing in the lateral direction (film width direction) by 15%. By cutting and removing both edges, a biaxially stretched film having a thickness of about 9 μm was continuously formed over a predetermined length to obtain a film roll made of a heat-shrinkable polyester film. And the characteristic of the obtained film was evaluated by the above-mentioned method. The evaluation results are shown in Table 3. This package was excellent in shrink finish, warpage, and openability.

Example 2
A biaxially stretched film roll having a thickness of about 9 μm was obtained in the same manner as in Example 1 except that the polyester B was changed to the polyester C in Example 1. And the characteristic of the obtained film was evaluated by the above-mentioned method. The evaluation results are shown in Table 3. This package was excellent in shrink finish, warpage, and openability.

Example 3
In Example 2, polyester D was changed to polyester E. Further, the intermediate heat treatment temperature of the first tenter was changed from 90 ° C. to 87 ° C., the preheating roll temperature in longitudinal stretching was changed from 70 ° C. to 67 ° C., and the heat treatment temperature of the second tenter was changed from 90 ° C. to 87 ° C. Otherwise in the same manner as in Example 2, a biaxially stretched film roll having a thickness of about 9 μm was obtained. And the characteristic of the obtained film was evaluated by the above-mentioned method. The evaluation results are shown in Table 3. This package was excellent in shrink finish, warpage, and openability.

Example 4
In Example 1, a biaxially stretched film roll having a thickness of about 9 μm was obtained in the same manner as in Example 1 except that the longitudinal stretching ratio was changed to 2. And the characteristic of the obtained film was evaluated by the above-mentioned method. The evaluation results are shown in Table 3. This package was excellent in shrink finish, warpage, and openability.

Example 5
In Example 3, the raw material polyester is the same as in Example 3 except that the polyester B, the polyester E, and the polyester F are changed to a mass ratio of 70: 26: 4, and the longitudinal draw ratio is changed to 3.5 times. A biaxially stretched film roll having a thickness of about 9 μm was obtained. And the characteristic of the obtained film was evaluated by the above-mentioned method. The evaluation results are shown in Table 3. This package was excellent in shrink finish, warpage, and openability.

Example 6
In Example 1, the thickness was about 9 μm in the same manner as in Example 1 except that the transverse stretch ratio in the first tenter was changed from 4 times to 3.5 times and the longitudinal stretch ratio was changed from 3 times to 2 times. A biaxially stretched film roll was obtained. And the characteristic of the obtained film was evaluated by the above-mentioned method. The evaluation results are shown in Table 3. This package was excellent in shrink finish, warpage, and openability.

Example 7
In Example 1, a biaxially stretched film roll having a thickness of about 9 μm was obtained in the same manner as in Example 1 except that the polyester A, the polyester B, the polyester D, and the polyester F were changed to a mass ratio of 26: 55: 15: 4. It was. And the characteristic of the obtained film was evaluated by the above-mentioned method. The evaluation results are shown in Table 3. This package was excellent in shrink finish, warpage, and openability.

Example 8
In Example 1, the transverse stretch ratio in the first tenter was changed from 4 times to 4.5 times, the intermediate heat treatment temperature was changed from 90 ° C to 70 ° C, and the longitudinal stretch ratio was changed from 3 times to 1.5 times. A biaxially stretched film roll having a thickness of about 9 μm was obtained in the same manner as in Example 1 except that the relaxation rate in the second tenter was changed from 15% to 0%. And the characteristic of the obtained film was evaluated by the above-mentioned method. The evaluation results are shown in Table 3. The main shrinkage direction of this film is the transverse direction. This package was excellent in shrink finish, warpage, and openability.

Comparative Example 1
The above-mentioned polyester A, polyester B, polyester D, and polyester F were mixed at a mass ratio of 6: 66: 24: 4 and charged into an extruder. Next, the mixed resin was melted at 280 ° C., extruded from a T-die, wound around a rotating metal roll cooled to a surface temperature of 30 ° C., and rapidly cooled to obtain an unstretched film having a thickness of 40 μm. At this time, the take-up speed of the unstretched film (rotational speed of the metal roll) is about 20 m / min. Met. Subsequently, the unstretched film is led to a longitudinal stretching machine in which a plurality of roll groups are continuously arranged without being led to the first tenter, and after preheating until the film temperature reaches 70 ° C. on the preheating roll. The film was stretched 4 times. Thereafter, the longitudinally stretched film was forcibly cooled by a cooling roll set at a surface temperature of 25 ° C.

  And the film after cooling is led to a tenter (second tenter), heat-treated for 10 seconds in an atmosphere of 90 ° C. in the second tenter, and both edges are cut and removed, whereby the thickness is about 10 μm. A biaxially stretched film was continuously formed over a predetermined length to obtain a film roll made of a heat-shrinkable polyester film. And the characteristic of the obtained film was evaluated by the above-mentioned method. The evaluation results are shown in Table 3. This package was inferior in openability.

Comparative Example 2
In Example 1, a biaxially stretched film roll having a thickness of about 9 μm is obtained in the same manner as in Example 1 except that the polyester A, the polyester B, the polyester D, and the polyester F are changed to a mass ratio of 31: 50: 15: 4. It was. And the characteristic of the obtained film was evaluated by the above-mentioned method. The evaluation results are shown in Table 3. Since the shrinkage stress is high, this package has a large warpage.

The heat-shrinkable polyester film of the present invention can be used for coating and packaging a book. The heat-shrinkable polyester film for packaging of the present invention shrinks neatly at low temperatures, has excellent transparency, and excellent printability. Therefore, when it is heat-shrinked over a book, it has a beautiful appearance. Since printed information can also be transmitted, it is important to contribute to the improvement of book sales.

Claims (3)

The main constituent component is ethylene terephthalate, and the total of one or more kinds of monomer components that can be amorphous components in all monomer components is formed from a polyester resin that is 16 mol% or more and 27 mol% or less. A heat-shrinkable polyester film for packaging according to 1) to (4).
(1) The maximum heat shrinkage stress in the main shrinkage direction measured in hot air at 90 ° C. is 1 MPa or more and 6 MPa or less,
(2) The thermal shrinkage rate in the main shrinkage direction when treated with hot water of 70 ° C. for 10 seconds is 15% or more and 50% or less,
(3) The Elmendorf tear propagation strength in the main shrinkage direction and the direction orthogonal to the main shrinkage direction is 300 mN or less,
(4) One or more of characters, symbols and symbols are printed.   The heat-shrinkable polyester film for main packaging according to claim 1, wherein the thickness is 3 to 20 µm. A method for using a heat-shrinkable polyester film for packaging, comprising: covering the book with the heat-shrinkable polyester film for packaging according to claim 1 or 2;