JP2002060504A - Method for sealing heat-shrinkable film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for sealing a heat-shrinkable film with a solvent, in which the irregular adhesion at the sealed part is prevented and a yield of a tubular product is improved. SOLUTION: This method for sealing the heat-shrinkable film into the tubular product, comprising dissolving a part of the heat-shrinkable film in a solvent to bond the film, characterized by using a chlorine-free solvent and controlling water contents of the solvent to <=5%. The solvent is preferably tetrahydrofuran or a mixture of the tetrahydrofurn with any other solvent such as dioxolane.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for sealing a heat-shrinkable film (including a sheet), and more particularly, to joining a heat-shrinkable film with a solvent when joining the heat-shrinkable film into a tube. The present invention relates to a sealing method for melting and joining.

[0002]

2. Description of the Related Art Heat shrinkable films are widely used for shrink wrapping, shrink labels, cap seals and the like, utilizing the property of shrinking by heating. When the heat-shrinkable film is used for covering containers, bottles (including plastic bottles), cans, rods (pipes, rods, wood, various rod-like objects), etc. (hereinafter abbreviated as containers, etc.), A shrinkable film formed in a tube shape is covered with the container or the like and thermally shrunk.

As a method for forming a heat-shrinkable film, particularly a polyester-based film into a tubular shape, a method using a solvent (including a swelling agent) is disclosed in JP-A-6-345878. In this method, a heat-shrinkable polyester film having a density of 1.3 to 1.35 is bonded with 1,3 dioxolane or a mixture of an organic solvent compatible with 1,3 dioxolane. Examples of compatible organic solvents include aliphatic hydrocarbons, aromatic hydrocarbons, ethers, ketones, esters, and alcohols.

Further, the method of using a solvent for bonding a polyester-based heat-shrinkable film is not limited to a method using 1,3 dioxolane as a main component, but also a method using tetrahydrofuran (TH).
F) A method of using a single solvent or a mixture of THF with another solvent such as 1,3 dioxolane has been widely practiced.

[0005] In these methods using a solvent, a solvent is applied to a portion to be joined at one end of a heat-shrinkable film, and the portion to be joined at the other end is overlapped and joined before the solvent is dried to form a tube. To

[0006]

The bonding strength is determined by the solvent used for bonding and the characteristics of the base film.
When an appropriate solvent is not used for the base film, there is a problem that the base film is peeled off due to insufficient bonding force or the form of the base film is violated by the solvent. However, when the sealing method using the solvent is performed, even if the same heat-shrinkable film is used and the same solvent is used, the bonding state of the sealing portion may vary, and the yield of the tubular body may be reduced. However, there was a problem that was reduced.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to prevent a variation in the joining state of a sealing portion when sealing a heat-shrinkable film using a solvent. It is an object of the present invention to provide a method for sealing a heat-shrinkable film that can improve the yield of a state body.

[0008]

Means for Solving the Problems The inventors of the present application have studied the causes of the above-mentioned variations in the bonding state, and have found that the concentration of water contained in the solvent greatly affects the sealing property. In the conventional sealing method, since the solvent is dried without heating, all the solvents used have relatively low boiling points, for example, THF is 66 ° C., and dioxolan is 78 ° C.
It is. These solvents can be freely mixed with water and easily absorb moisture in the air. Therefore, if the management of the water content of the solvent is neglected, the water concentration in the solvent will increase.

Using THF as a solvent and changing the water concentration in the THF, the amount of solvent penetration and evaporation into the polyester film was measured.
As shown in (b), it was found that the value greatly changed depending on the moisture concentration and the type of the polyester film.
(A) shows the case of 100% THF, and (b) shows the case of a mixed solution of THF10: water1. The measurement was performed by immersing a polyester film having a predetermined area and thickness in a solvent for a predetermined time (30 seconds), and then measuring the weight of the film. In FIGS. 1A and 1B, the solvent evaporates from the point of the peak, and the film weight is reduced.

The polyester films used have the same thickness (55 μm) and different shrinkage rates (horizontal direction / vertical direction) when immersed in warm water (80 ° C. × 10 seconds). The shrinkage of each sample is
Sample A is 72% /-1%, sample B is 52% / 2%, and sample C is 42% / 1%.

In order to achieve the above object, according to the first aspect of the present invention, when a heat-shrinkable film is joined in a tube shape, a part of the heat-shrinkable film is dissolved with a solvent and joined. In the above, a non-chlorine solvent is used as the solvent, and the water concentration in the solvent is controlled to 5% or less. The moisture concentration can be measured at room temperature by the Karl Fischer method.

A non-chlorine-based solvent is used as a solvent for bonding the heat-shrinkable film, and the solvent has good compatibility with water and easily absorbs water. In addition, since the solvent used for bonding is not heated for drying, but is naturally dried, the solvent is easily volatilized, and dew condensation may occur during volatilization. Due to these phenomena, if the bonding is performed in a state where the water concentration in the solvent is higher than 5%, the bonding state tends to vary. However, by controlling the water concentration in the solvent to 5% or less, a bonding state having a necessary adhesive strength can be obtained by working for a predetermined time for bonding. Moisture concentration of 5
% Or less, an appropriate amount of an inorganic salt such as calcium chloride or anhydrous magnesium sulfate may be added to the solvent.

[0013] In the second aspect of the present invention, in the first aspect, the heat-shrinkable film is a polyester film. Therefore, according to the present invention, in the heat-shrinkable polyester film, a bonded state having an adhesive strength required in a sealing method using a solvent can be obtained.

According to a third aspect of the present invention, in the first or second aspect, the solvent has a boiling point of 11
0 ° C. or less. According to the present invention, heating is not required for drying the solvent applied to the heat-shrinkable film for bonding.

According to a fourth aspect of the present invention, in the first aspect of the present invention, the solvent is a simple substance or a mixed solvent of a cyclic ether such as tetrahydrofuran or dioxolane. Therefore, in the present invention, the yield of the tubular body of the heat-shrinkable film manufactured by the sealing is improved in the sealing method using a solvent such as THF which has been widely used in the past.

According to a fifth aspect of the present invention, in the first aspect of the present invention, the solvent is tetrahydrofuran or a mixture of tetrahydrofuran and another solvent. According to the present invention, tetrahydrofuran, which is easy to handle among the cyclic ethers, is the main component of the solvent, so that the operation is simplified.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment in which the present invention is embodied in a polyester heat-shrinkable film will be described below.

As the polyester used as the material of the heat-shrinkable film, an ethylene terephthalate copolymer polyester containing terephthalic acid as a dicarboxylic acid component and ethylene glycol as a diol component as a main component is preferably used. Examples of the copolymerization component include diphthalic acid such as isophthalic acid, adipic acid, and sebacic acid, and diol components such as neopentyl glycol, diethylene glycol,
Copolymerized polyesters using 4-cyclohexanedimethanol, 1,3-butanediol, and the like are easily available industrially, and also have good shrinkage characteristics and are preferable.

In the copolyester used in the present invention, the total amount of the dicarboxylic acid component and the diol component is 200 mol%, and the total amount of the copolymer components is at least 20 mol%, more preferably at least 30 mol%. It is good to do. Copolymerized polyesters having a total copolymerization component of less than 20 mol% are not preferred because the crystallinity when formed into a film is high, the shrinkage finish is poor, and the solvent sealing property is inferior.

The polyester may be a mixture of butylene terephthalate-based or cyclohexane terephthalate-based polyester other than ethylene terephthalate-based polyester, or a polymer other than polyester in an amount of 30% by weight or less. Good.

The heat-shrinkable film is produced, for example, as follows. The copolymerized polyester obtained by the polycondensation reaction is melt-extruded at a temperature of 200 to 320 ° C. At the time of extrusion, any existing method such as a T-die method or a Cubra method may be employed. When using the T-die method, after extrusion,
The film is rapidly cooled on a casting drum having a surface temperature of 15 to 80 ° C. to form an unstretched film having a thickness of 30 to 300 μm. The obtained unstretched film is heated to 1.0 to 2.0 at a roll temperature of 60 to 120 ° C. using a heated longitudinal stretching roll.
, Preferably 1.0 to 1.5 times longitudinal stretching. After longitudinal stretching, using a tenter at a stretching temperature of 60 to 120 ° C.
The film is horizontally stretched 7 to 7.0 times, heat-treated at a temperature of 60 to 100 ° C., and then cooled and wound up.

The heat-shrinkable film is sealed by applying a predetermined amount of a solvent to one end face of the heat-shrinkable film to be joined,
Immediately, the other end faces are overlapped and joined in a tube shape. The work is performed at room temperature (23 ° C),
The solvent is air dried.

As a solvent, tetrahydrofuran (THF)
Using a 1: 1 mixture of THF and 1,3 dioxolane, changing the water content in the solvent and bonding the polyester-based heat-shrinkable film to form a tubular body, and checking the bonding state of the bonding part did.

Evaluation of the bonding state is as follows. In an atmosphere at 23 ° C., one or two drops of a solvent are dropped on the surface of one film, and the other is superposed so that the shrinkage directions are the same, and then the film is rolled. A bond was applied in which the two sheets were adhered to each other and a force for peeling the two sheets apart in the shrinking direction was applied, and after sufficient peeling of the bonding interface, the entire peeled surface was whitened due to ductile fracture or brittle fracture. Conversely, even after bonding, the bonding interface can be confirmed,
After peeling, those having a peeled surface not sufficiently whitened were rejected.
Table 1 shows the results.

[0025]

[Table 1] As is evident from Table 1, when the water concentration is 5% or less, the joint has a sufficient peel strength regardless of whether the solvent is THF alone or a mixture of THF and 1,3 dioxolane. became. However, when the water concentration was 10% or more, the peel strength of the joint became small, and the specimen was rejected.

This embodiment has the following effects. (1) When a part of the heat-shrinkable film is dissolved in a solvent and joined into a tube, a non-chlorine solvent is used as the solvent and the water concentration in the solvent is controlled to 5% or less. did. Therefore, it is not noticed that the water concentration in the solvent is high, and it is possible to prevent the occurrence of defective bonding due to the sealing, thereby improving the yield of the tubular body.

(2) Since the solvent for sealing has a boiling point of 80 ° C. or less, the solvent applied to the heat-shrinkable film can be dried smoothly, and the sealing can be reliably performed in a short time. (3) Since the solvent for the seal is a simple substance or a mixed solvent of a cyclic ether such as tetrahydrofuran or dioxolane, the heat shrinkage produced by the seal in a sealing method using a solvent such as THF which has been widely used conventionally. The yield of the tubular body of the film is improved.

(4) The solvent for sealing is tetrahydrofuran or a mixture of tetrahydrofuran and another solvent. Therefore, even among the cyclic ethers, tetrahydrofuran, which is easy to handle and has low toxicity to the human body, is a main component of the solvent, so that the operation is simplified.

The embodiment is not limited to the above, and may be, for example, as follows. The solvent is not limited to THF or a mixture of THF and dioxolan, and other cyclic ethers such as dioxane may be used alone or mixed. However, dioxane is THF
Boiling point is higher (101.6 ° C) than that of dioxolan
Therefore, THF and dioxolan are more preferable.

The solvent is not limited to the cyclic ether, but the polyester film is dissolved with a non-chlorine solvent and the boiling point is 1
It is sufficient that the temperature is 10 ° C. or less. Also in this case, the solvent applied to the heat-shrinkable film can be dried without heating. Other solvents include acetone, methyl ethyl ketone, cyclohexane and the like.

The heat-shrinkable film is not limited to a polyester film, and may be applied to a method of sealing a polyvinyl chloride film or a polystyrene film. Polyvinyl chloride film and polystyrene film have higher solubility than polyester film,
It is necessary to reduce the amount of application at the time of sealing.

The heat-shrinkable film is not limited to a single-layer structure, but may have a laminated structure. The technical ideas other than those described in the claims, which are grasped from the respective embodiments, will be described below.

(1) In the invention described in claim 1 or 2, the solvent has a boiling point of 80 ° C. or less.

[0034]

As described in detail above, claims 1 to 5 are provided.
According to the invention described in (1), when sealing the heat-shrinkable film using a solvent, it is possible to prevent a variation in the joining state of the sealing portion and improve the yield of the tubular body.

[Brief description of the drawings]

FIGS. 1A and 1B are graphs showing differences in the amount of solvent permeation into a film when the water concentration in the solvent is changed.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) B29K 67:00 B29K 67:00 105: 02 105: 02 C08L 67:00 C08L 67:00 (72) Inventor Kazuhiro Nishiwaki 5-8, Mitsuya-cho, Nagahama-shi, Shiga Prefecture F-term in Nagahama Plant, Mitsubishi Plastics Co., Ltd. 4F211 TA07 TC09 TD11 TN90 TQ01

Claims (5)

[Claims] In a sealing method for joining a heat-shrinkable film by dissolving a part of the heat-shrinkable film with a solvent when joining the heat-shrinkable film into a tube, a non-chlorine-based solvent is used as the solvent, A method for sealing a heat-shrinkable film, wherein the moisture concentration in the film is controlled to 5% or less. 2. The method according to claim 1, wherein the heat-shrinkable film is a polyester film. 3. The method for sealing a heat-shrinkable film according to claim 1, wherein the solvent has a boiling point of 110 ° C. or lower. 4. The method for sealing a heat-shrinkable film according to claim 1, wherein the solvent is a simple substance or a mixed solvent of cyclic ethers such as tetrahydrofuran and dioxolan. 5. The method for sealing a heat-shrinkable film according to claim 1, wherein the solvent is tetrahydrofuran or a mixture of tetrahydrofuran and another solvent.