JP2008030494A - Manufacturing process of heat-shrinkable polyester film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To impart lightproof property without printing or processing work. <P>SOLUTION: Present invention relates to a manufacturing process of a film which comprises mainly of a polyester resin and contains a polystyrene resin and a titanium oxide. The film has a laminated structure of layer A/layer B/layer A, wherein the layer B is a cavernous layer. The film is 50% or more in the main contraction direction and 10% or less in the direction orthogonal to the main contraction direction in terms of hot water shrinkage when processed for 10 seconds at 95°C, 40% or less in total light transmittance and 90% or more in haze. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

The present invention relates to a method for producing a heat-shrinkable polyester film, and more particularly to a method for producing a heat-shrinkable polyester film having light-cutting properties.

Recently, an increasing number of cases have used shrink labels for the purpose of protecting the contents of containers from ultraviolet rays. Conventionally, a UV-cut type shrink film made of polyvinyl chloride has been used, but there is an increasing demand for UV-cut type of other materials. Although the specific cut property varies depending on the contents, in the case of foods and beverages, alteration or coloring of the contents occurs at a wavelength of 360 nm to 400 nm, which is ultraviolet light in the long wavelength area, so long wavelength areas, particularly 380 nm and 400 nm. Cutability is important. However, none of the conventional heat-shrinkable polyester films cuts the ultraviolet rays in the long wavelength region described above.

As such a label, a heat-shrinkable film made of polyvinyl chloride, polystyrene, or the like has been mainly used (see Patent Document 1). However, with regard to polyvinyl chloride, a chlorine-based gas when incinerated at the time of disposal in recent years. Occurrence becomes a problem, and polystyrene has problems such as difficulty in printing. Recently, the use of heat-shrinkable polyester film has attracted attention.
JP-A-11-188817

Conventionally, when these heat-shrinkable films are used, white printing is usually performed after pattern printing on the inside of the label. The thickness of the printing ink is usually about 3 μm, which is not sufficient to block light. Furthermore, light blocking is attempted by a method of performing white printing twice, but this is disadvantageous in terms of quality factors (change in shrinkage characteristics due to ink thickness, etc.), delivery time, and cost.

The objective of this invention is providing the manufacturing method of the heat-shrinkable polyester-type film which has light cutting property, without performing printing and a process.

As a result of earnest research to solve the problems of the prior art, the present inventors have found that the object can be achieved by setting the total light transmittance and haze of the heat-shrinkable polyester film to a specific range. Based on this, the present invention has been completed.

That is, the present invention mainly Ri Do a polyester resin, a method of producing a film containing titanium oxide and polystyrene resin, a laminated structure of A layer / B layer / A layer, B layer void-containing The hot water shrinkage rate of the film is 50% or more at a treatment temperature of 95 ° C. and a treatment time of 10 seconds in the main shrinkage direction, and is 10% or less in the direction perpendicular to the main shrinkage direction. The present invention relates to a method for producing a heat-shrinkable polyester film , wherein the rate is 40% or less and the haze is 90% or more.

Alternatively, primarily a method of producing a film made of a polyester resin, a manufacturing method of the heat-shrinkable polyester film, wherein the maximum value of the main shrinkage direction of the shrinkage stress at 90 ° C. of the film is less than 15MPa It is related to.

Or it is a film which consists mainly of polyester resin, Comprising: The solvent adhesive strength by 1 , 3- dioxolane is based on the manufacturing method of the heat-shrinkable polyester-type film characterized by being 4 N / 15mm or more .

In this case, it is preferable that there is at least one layer to which titanium oxide is added. Furthermore, in this case, the titanium oxide content is preferably in the range of 0.1 to 20.0% by weight in terms of film.

In this case, it is preferable that there is at least one layer to which a polystyrene resin is added. Furthermore, in this case, it is preferable that the content of the polystyrene-based resin is in the range of 1.0 to 20.0% by weight in terms of film.

According to the present invention, it is possible to obtain a heat-shrinkable polyester film having a light-cutting property without performing printing or processing, and further having excellent solvent adhesion.

Therefore, it is extremely useful as a heat-shrinkable polyester film for labels, particularly for labels with high commercial value.

The heat-shrinkable polyester film obtained according to the present invention is characterized in that the total light transmittance of the film is 40% or less and the haze is 90% or more, whereby the above-mentioned target is achieved.

The heat-shrinkable polyester film obtained by the present invention is substantially composed of a polyester resin or a polyester resin and titanium oxide and polystyrene resin described later. As a polyester resin, it can use preferably from the polyester composition containing the polyester which has a dicarboxylic acid component and a diol component as a structural component, and a polyester-type elastomer, for example. In the polyester resin composition, the blending ratio of the polyester and the polyester elastomer is usually about 50 to 98% by weight of the former, particularly 70 to 95% by weight, and 2 to 50% by weight of the latter with respect to the total amount of both. It is preferable that it is about 5% by weight, especially about 5 to 30% by weight.

Examples of the dicarboxylic acid component constituting the polyester include aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid and naphthalenedicarboxylic acid, aliphatic dicarboxylic acids such as adipic acid, sebacic acid and decanedicarboxylic acid, and alicyclic rings such as cyclohexanedicarboxylic acid. What is necessary is just to use 1 type, or 2 or more types of well-known dicarboxylic acid, such as a formula dicarboxylic acid. In addition, as the diol component, one kind of known diols such as ethylene glycol, propylene glycol, triethylene glycol, butylene glycol, diethylene glycol, neopentyl glycol, 1,4-cyclohexanedimethanol, tetramethylene glycol ethylene oxide adduct or the like Two or more types may be used.

The polyester elastomer is, for example, a polyester block copolymer comprising a high melting crystalline polyester segment (Tm 200 ° C. or higher) and a low melting point soft polymer segment (Tm 80 ° C. or lower) having a molecular weight of 400 or more, preferably 400 to 800. Polyester elastomers using polylactones such as poly-ε-caprolactone for the low melting point soft polymer segment are particularly preferred.

In order to achieve the total light transmittance and haze specific to the film of the present invention and to give the film a light-cutting property, for example, fine particles such as an inorganic lubricant and an organic lubricant are added to the film in an amount of 0. It is suitable to contain 1 to 20% by weight, preferably 0.5 to 10% by weight. When the content of the fine particles is less than 0.1% by weight, it tends to be difficult to obtain light-cutting properties. On the other hand, when the content exceeds 20% by weight, film strength tends to decrease and film formation tends to be difficult. is there.

The fine particles may be added before polyester polymerization, but are usually added after polyester polymerization. Examples of the inorganic lubricant added as fine particles include known inert particles such as kaolin, clay, calcium carbonate, silicon oxide, calcium tephrate, aluminum oxide, titanium oxide, calcium phosphate, and carbon black, and melt film formation of polyester resin. Insoluble high melting point organic compounds, cross-linked polymers, and metal compound catalysts used in the synthesis of the polyester, such as alkali metal compounds and alkaline earth metal compounds, can be internal particles formed inside the polymer during polyester production.

The average particle diameter of the fine particles contained in the film is usually in the range of 0.001 to 3.5 μm. Here, the average particle diameter of the fine particles is measured by a Coulter counter method. The intrinsic viscosity of the polyester of the present invention is preferably 0.50 or more, more preferably 0.60 or more, and particularly preferably 0.65 or more. If the intrinsic viscosity of the polyester is less than 0.50, the crystallinity becomes high and a sufficient shrinkage cannot be obtained, which is not preferable.

In the present invention, in order to obtain an appropriate light transmittance, for example, it is preferable to contain fine cavities inside. For example, a foam material or the like may be mixed and extruded, but a preferable method is to obtain a cavity by mixing an incompatible thermoplastic resin in polyester and stretching it in at least one axial direction. The thermoplastic resin incompatible with the polyester used in the present invention is arbitrary, and is not particularly limited as long as it is incompatible with the polyester. Specific examples include polystyrene resins, polyolefin resins, polyacrylic resins, polycarbonate resins, polysulfone resins, and cellulose resins. In particular, a polystyrene resin or a polyolefin resin such as polymethylpentene or polypropylene is preferable because of the formation of cavities.

Polystyrene resin refers to a thermoplastic resin containing a polystyrene structure as a basic constituent element. In addition to homopolymers such as atactic polystyrene, syndiotactic polystyrene, and isotactic polystyrene, other components are grafted or block copolymerized. Modified resins, such as impact-resistant polystyrene resins and modified polyphenylene ether resins, and mixtures of thermoplastic resins having compatibility with these polystyrene resins, such as polyphenylene ether, are included.

In preparing the polymer mixture formed by mixing the polyester and the incompatible resin, for example, the chips of each resin may be mixed and melt-kneaded in an extruder and extruded, or both resins may be preliminarily mixed by a kneader. The kneaded product may be further melt extruded from an extruder. Moreover, a polystyrene resin may be added in the polyester polymerization step, and a chip obtained by stirring and dispersing may be melt-extruded.

More film obtained in the present invention is preferably provided with a small layer A of the cavity than at least one surface layer B of the layer B containing a large number of cavities therein. In order to make this configuration, different raw materials are charged into different extruders A and B, melted, bonded in a molten state before the T-die or inside the die, and solidified in close contact with the cooling roll. It is preferable to stretch in the direction. At this time, it is preferable that the incompatible resin of the A layer as a raw material is less than the B layer. By doing so, there are few cavities in the A layer, the surface roughness is reduced, and the film does not impair the aesthetics of printing. In addition, since there are not many cavities, the film does not become weak and the film has excellent wearability.

Furthermore, more film obtained in the present invention is a layer B containing a large number of voids inside the intermediate layer, it is particularly preferable that a small A layer of cavities both surface layers. By adding polystyrene resin, smoke is generated at the time of melt extrusion, fouling the process and causing deterioration in operability. By using the B layer as an intermediate layer, the problem of smoke generation is eliminated, and stable production over a long period of time becomes possible.

Moreover, this invention film may contain additives, such as a stabilizer, a coloring agent, antioxidant, and an antistatic agent, as needed.

The polyester film obtained by the present invention needs to have a total light transmittance of 40% or less as measured according to JIS K 7136. When the transmittance is 40% or more, it is not preferable since the contents can be seen through or the contents cannot be cut and the contents deteriorate. The transmittance is particularly preferably 30% or less.

The polyester film obtained according to the present invention needs to have a haze of 90% or more measured according to JIS K 7136. If the haze is less than 90%, the contents can be seen through, or the contents can deteriorate without being able to cut light rays. The haze is particularly preferably 95% or more.

In the main shrinkage direction of the film obtained by the present invention, the shrinkage rate at 95 ° C. for 10 seconds in hot water is 50% or more, preferably 50 to 80%. If the shrinkage rate is less than 50%, insufficient shrinkage of the label occurs in the narrow part of the bottle. On the other hand, if it exceeds 80%, since the shrinkage rate is large, the label may jump up while passing through the shrink tunnel, which is not preferable. Here, the main shrinkage direction means a direction with a large shrinkage rate.

Moreover, it is preferable that the shrinkage rate in the direction perpendicular to the main shrinkage direction is 0 to 10%. If the shrinkage rate is less than 0%, the horizontal wrinkles of the label that are generated during shrinkage tend to be difficult to disappear. On the other hand, if the shrinkage rate exceeds 10%, the vertical shrinkage of the label increases and the amount of film used increases, making it economical. In this case, neither of them is preferable.

The glass transition temperature Tg of the film obtained by this invention is about 50-90 degreeC, Preferably it is 55-85 degreeC, More preferably, it is the range of 55-80 degreeC. If Tg is within this range, the low temperature shrinkage is sufficient and the natural shrinkage is not too large, and the label finish is good.

The film obtained by the present invention includes aromatic hydrocarbons such as benzene, toluene, xylene, and trimethylbenzene, halogenated hydrocarbons such as methylene chloride and chloroform, phenols such as phenol, furans such as tetrahydrofuran, 1,3- It preferably has solvent adhesion with an organic solvent such as oxolanes such as dioxolane. In particular, from the viewpoint of safety, it is more preferable to have solvent adhesion by 1,3-dioxolane. The solvent adhesive strength is preferably 4 N / 15 mm or more. If it is less than 4N / 15mm, when a label is shrunk into a container, a joint part peels off, which is not preferable.

In order to further improve the solvent adhesiveness of the film obtained by the present invention, for example, it is effective to copolymerize a polyester with a low Tg component.

In order to satisfy the above characteristics, the film of the present invention may be composed of a single layer, but the preferred layer structure is A / B / A. The thickness ratio of the A layer and the B layer is preferably A / B / A = 25/50/25 to 10/80/10. If the thickness ratio of the B layer is less than 50%, the light-cutting property is insufficient, and the contents can be seen through, or the contents cannot be cut and the contents are deteriorated.

Hereafter, the manufacturing method of the film of this invention is demonstrated concretely.

A polyester or copolymer polyester containing an appropriate amount of inorganic particles or the like as a lubricant is dried using a normal hopper dryer, paddle dryer, vacuum dryer or the like, and then extruded at a temperature of 200 to 320 ° C. In extruding, an existing method such as a T-die method or a tubular method may be used.

After extrusion, the film is rapidly cooled to obtain an unstretched film. In the case of the T-die method, a so-called electrostatic application adhesion method is preferably used at the time of rapid cooling because a film with less thickness unevenness can be obtained. The obtained unstretched film is uniaxially stretched or biaxially stretched so that the finally obtained film satisfies the constituent requirements of the present invention.

As a stretching method, in addition to the method of stretching only in the longitudinal axis of the roll or stretching only in the lateral direction with a tenter, the known biaxial stretching is strongly stretched in either the longitudinal or lateral direction, and the other as much as possible. It is also possible to stretch the film small, and re-stretching may be performed as necessary.

In the above stretching, the film is stretched at least 2.0 times, preferably 2.5 times or more in the main shrinkage direction, stretched in a direction perpendicular to the main shrinkage direction as necessary, and then heat-treated.

The heat treatment is usually performed under tension fixation, but it is also possible to perform relaxation or tentering of 20% or less at the same time. As a heat treatment method, an existing method such as a method of contacting a heating roll or a method of gripping a clip in a tenter can be used.

During the stretching step, corona treatment may be applied to one or both sides of the film before or after stretching to improve the adhesion of the film to the printed layer and / or adhesive layer to the adhesive layer.

In addition, during the stretching step, it is possible to apply on one or both sides of the film before or after stretching to improve the adhesion, release properties, antistatic properties, slipperiness, light shielding properties, etc. of the film. .

The film thickness obtained by the present invention is preferably in the range of 15 to 300 μm, more preferably 25 to 200 μm.

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to these examples unless it exceeds the gist.

(1) Total light transmittance and film haze Measured according to JIS K 7136 using NDH-2000T manufactured by Nippon Denka Kogyo Co., Ltd.

(2) Shrinkage stress Tensilon with air oven manufactured by Toyo Seiki Co., Ltd. (model: UTL-4L) is used to set the gap between chucks to 100 mm, the sample shape to 150 mm in the direction of measuring the shrinkage stress, and the direction orthogonal to the measurement direction to 20 mm. When heated in a 90 ° C. air oven for 1 minute, the force developed was recorded on a recorder, the maximum value and the value 30 seconds after the start of measurement were read, and the shrinkage stress was calculated from the following formula to obtain the shrinkage stress. Shrinkage stress = (reading value / sample cross-sectional area before heating) × 9.807 (MPa)

(3) The heat shrinkage rate film was cut into a 10 cm × 10 cm square, and immersed in warm water of 95 ± 0.5 ° C. for 10 seconds under heat-free conditions to cause heat shrinkage. The dimensions were measured, and the thermal shrinkage rate was determined according to the following formula. The direction in which the shrinkage rate was large was taken as the main shrinkage direction.
Thermal shrinkage rate = {(length before shrinkage−length after shrinkage) / length before shrinkage} × 100 (%)

(4) Solvent adhesiveness 1,3-Dioxolane was used to join the film into a tube shape, and the tube-shaped body was cut to a width of 15 mm in the direction orthogonal to the flow direction during processing to obtain a sample. Using Tensilon (model: UTL-4L), the chuck was pulled and peeled at 20 mm, and the peel resistance was measured. When the measured value was 4N or more, it was set as “◯”.

(5) Tg (glass transition point)
Using a DSC (model: DSC220) manufactured by Seiko Denshi Kogyo Co., Ltd., 10 mg of an unstretched film was heated from −40 ° C. to 120 ° C. at a heating rate of 20 ° C./min, and obtained from the endothermic curve obtained. It was. A tangent line was drawn before and after the inflection point of the endothermic curve, and the intersection was defined as Tg (glass transition point).

The polyesters used in Examples and Comparative Examples are as follows.
Polyester A: Polyethylene terephthalate (IV 0.75)
Polyester B: Polyester (IV 0.72) comprising 100 mol% terephthalic acid, 70 mol% ethylene glycol, and 30 mol% neopentyl glycol
Polyester C: Polyester elastomer comprising 70% by weight of polybutylene terephthalate and 30% by weight of ε-caprolactone (reduced viscosity (ηsp / c) 1.30)

(Example 1) As shown in Table 1, as a raw material for layer A, a polyester composition in which 30% by weight of polyester A, 65% by weight of polyester B, and 5% by weight of polyester C are mixed together is a raw material for layer B. 10% by weight of polyester A, 65% by weight of polyester B, 5% by weight of polyester C, 10% by weight of crystalline polystyrene resin (G797N made by Nippon Polystyrene Co., Ltd.) and titanium dioxide (TA-300 made by Fuji Titanium) ) 10% by weight put into separate extruders, mixed and melted, joined by a feed block, and A / B / A thickness ratio after stretching from T die at 280 ° C. is 12.5 μm / 25 μm / 12 The film was melt-extruded while being laminated so as to have a thickness of 5 μm, and quenched with a chill roll to obtain an unstretched film. The unstretched film was stretched 4.0 times in the transverse direction at a film temperature of 70 ° C. with a tenter to obtain a heat-shrinkable polyester film having a thickness of 50 μm.

(Examples 2 to 3 and Comparative Examples 1 to 4) As shown in Table 1, a heat-shrinkable polyester film having a thickness of 50 μm was prepared in the same manner as in Example 1 except that the blending ratio of polystyrene and titanium dioxide was changed. Obtained.

The evaluation results of the films obtained in Examples 1 to 3 and Comparative Examples 1 to 4 are shown in Table 1.

As is clear from Table 1, all of the heat-shrinkable polyester films obtained in Examples 1 to 3 had good light-cutting properties.

The heat-shrinkable polyester film of the present invention is suitable for packaging shrink labels of contents that are high in quality and practical, and are particularly susceptible to deterioration.

On the other hand, although the heat-shrinkable polyester film obtained in Comparative Examples 1 to 3 has light-cutting properties, the solvent adhesive strength is poor, and the heat-shrinkable polyester film obtained in Comparative Example 4 is light-cut. The sex was inferior. Thus, the heat-shrinkable polyester film of the comparative example was inferior in quality and low in practicality.

According to the present invention, it is possible to obtain a heat-shrinkable polyester film having a light-cutting property without performing printing or processing, and further having excellent solvent adhesion.

Therefore, it is extremely useful as a heat-shrinkable polyester film for labels, particularly for labels with high commercial value.

Claims (4)

A method for producing a film mainly comprising a polyester resin and comprising a polystyrene resin and titanium oxide, comprising a layered structure of A layer / B layer / A layer, wherein the B layer is a void-containing layer, The shrinkage rate is 50% or more at a treatment temperature of 95 ° C. and a treatment time of 10 seconds in the main shrinkage direction, 10% or less in the direction orthogonal to the main shrinkage direction, and the total light transmittance of the film is 40% or less. And a method for producing a heat-shrinkable polyester film , wherein the haze is 90% or more. A method of manufacturing a heat-shrinkable polyester film of claim 1, method for producing a heat-shrinkable polyester film, wherein the maximum value of the main shrinkage direction of the shrinkage stress at 90 ° C. is not more than 15 MPa. A method of manufacturing a heat-shrinkable polyester film of claim 1, method for producing a heat-shrinkable polyester film of the solvent adhesion strength by 1,3-dioxolane and wherein the at 4N / 15 mm or more. The heat-shrinkable polyester film according to any one of claims 1, 2, and 3, wherein a polystyrene resin is added to at least the B layer. A method for producing a film.