JPH04278330A - Heat-shrinkable polyester based laminated film - Google Patents

Abstract

PURPOSE:To obtain a heat-shrinkable polyester based laminated film shrinkable at low temp, capable of achieving uniform shrinkage generating no shrinkage irregularity and having good heat resistance from a practical aspect. CONSTITUTION:A polyester resin (A) (glass transition point; 55 deg.C) obtained from terephthalic acid, isophthalic acid, ethylene glycol and diethylene glycol and a polyester resin (B) (glass transition point; 81 deg.C) obtained from terephthalic acid, ethylene glycol and 1,4-cyclohexanedimethanol are prepared. These resins are extruded in a three-layer state in a molten state to laminate films (b1), (b2) composed of the resin (B) to both surfaces of the film (a) composed of the resin (A). The thickness of the film (a) is set to 40mum and the thickness of each of the films (b1), (b2) is set to 40mum. This laminated film is stretched by three times in its laterial direction at 85 deg.C to prepare a heat-shrinkable polyester based laminated film. This heat-shrinkable laminated film is suitable as the shrink label of a PET bottle.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to a heat-shrinkable polyester laminated film, and more specifically, a heat-shrinkable polyester film that has good low-temperature shrinkability and uniform shrinkability, and is particularly useful as shrink labels for various containers. Regarding laminated film.

0002

BACKGROUND OF THE INVENTION Heat-shrinkable films are widely used for shrink wrapping, shrink labels, cap seals, etc. by taking advantage of their ability to shrink when heated. In particular, heat-shrinkable vinyl chloride resin film has good low-temperature shrinkability and printability, so polyethylene terephthalate (PET)
Widely used as shrink labels for containers and glass containers.

However, vinyl chloride resins have problems such as not having sufficient heat resistance and generating toxic gases such as hydrogen chloride when incinerated. Furthermore, when a heat-shrinkable vinyl chloride resin film is used as a shrink label for a PET container, there is a problem in that the PET container cannot be collected and reused together with the shrink label.

On the other hand, heat-shrinkable films made of polyethylene terephthalate resin have properties not found in vinyl chloride resins, such as excellent heat resistance and no toxic gases such as hydrogen chloride generated when incinerated. It is expected to be used as a shrink label for containers in place of polyvinyl chloride resin film.

However, since polyethylene terephthalate resin has high crystallinity, its heat-shrinkable film has a high heat-shrinkage start temperature, and the shrinkage rate tends to increase rapidly as the temperature rises. The sealability is also insufficient, and when used as shrinkable labels for various containers, there are problems in terms of workability and productivity in the heat shrinking process, and uniform shrinkability.

[0006]Recently, various improvements have been proposed for polyester heat-shrinkable films. For example, JP-A No. 57-42726 discloses a transparent, heat-sealable product using a copolyester resin consisting of terephthalic acid as a dicarboxylic acid component and ethylene glycol and 1,4-cyclohexanedimethanol as a diol component. Heat-shrink packaging films have been proposed. Furthermore, Japanese Patent Application Laid-Open No. 60-206839 proposes to improve shrinkage unevenness and heat sealability by incorporating isophthalic acid as a copolymerization component.

Furthermore, Japanese Patent Publication No. 10332/1983 discloses that an amorphous copolyester resin derived from 1,4-cyclohexanedimethanol and terephthalic acid or its derivatives and ethylene glycol, and terephthalic acid or its derivatives and ethylene glycol. A highly shrinkable polyester film is disclosed in which a composition comprising a polyester resin comprising a derivative thereof and ethylene glycol is formed and stretched.

Furthermore, in JP-A-60-232948 and JP-A-60-253545, a polyethylene terephthalate layer is made of a copolymerized polyester resin modified with isophthalic acid or a mixture of this resin and polyethylene terephthalate. A polyester laminated film for shrink wrapping is disclosed in which a polyester layer made of a cyclohexanedimethanol-modified copolymerized polyester resin or a polyester layer made of a mixture of this resin and polyethylene terephthalate is laminated and stretched.

[0009] In these conventional techniques, an amorphous copolyester resin is used as a raw material for a heat-shrinkable polyester film, or an amorphous copolyester resin and a crystalline polyester resin are mixed or laminated. By suppressing the crystallization of polyester, the heat shrinkage rate is higher, the shrinkage stress is reduced, the heat seal strength is higher, and the heat seal part is stronger than a heat shrinkable film made only from polyethylene terephthalate. It is said that improvements such as less tearing and uneven shrinkage will be achieved.

0010

However, with these conventional techniques, it is still not possible to obtain a heat-shrinkable polyester film having sufficient shrinkage characteristics. That is, the heat-shrinkable polyester film obtained by the above-mentioned conventional technique still has a higher shrinkage temperature than the heat-shrinkable vinyl chloride resin film, and furthermore, the shrinkage rate increases rapidly at the temperature at which shrinkage starts. have.

[0011] Therefore, problems such as a decrease in workability and productivity and occurrence of uneven shrinkage in the heat shrinking process are unavoidable. In particular, when used as a shrink label for containers such as bottles whose neck and body sizes are different, the rapid increase in shrinkage rate as the temperature rises will cause uneven adhesion and distortion of printing. This poses a serious problem in practice.

[0012] The present invention is intended to solve the above-mentioned problems, and its purpose is to achieve good low-temperature shrinkability, uniform shrinkage without unevenness, and improved heat resistance for practical use. An object of the present invention is to provide a good heat-shrinkable polyester laminated film.

[0013]

[Means for Solving the Problems] The heat-shrinkable polyester laminated film of the present invention has a dicarboxylic acid component consisting of terephthalic acid and isophthalic acid, and a diol component selected from ethylene glycol, diethylene glycol, and neopentyl glycol. The dicarboxylic acid component consists of terephthalic acid and the diol component is applied on both sides of the film (a) made of a copolymerized polyester resin (A) consisting of the above diols and containing 1 to 80 mol% of isophthalic acid in the dicarboxylic acid component. Films (b1) and (b2) made of a copolyester resin (B) consisting of ethylene glycol and 1,4-cyclohexanedimethanol, and 1 to 80 mol% of 1,4-cyclohexanedimethanol in the diol component A polyester laminated film with a three-layer structure in which the glass transition point TgA of the copolymerized polyester resin (A) and the TgB of the copolymerized polyester resin (B) are expressed by the formula 10°C≦T
gB −TgA ≦40°C, and the above film (a
) accounts for 10 to 90% of the total thickness of the polyester laminated film, thereby achieving the above object.

In the present invention, the copolymerized polyester resin (A) has a dicarboxylic acid component consisting of terephthalic acid and isophthalic acid, and a diol component selected from ethylene glycol, diethylene glycol, and neopentyl glycol as copolymerization components. It consists of the above diols, and the isophthalic acid in the dicarboxylic acid component is 1 to 8.
It contains 0 mol%, which lowers the crystallinity than polyethylene terephthalate and lowers the glass transition point TgA.
becomes lower. Note that it is preferable that the dicarboxylic acid component contains 1 to 80 mol% of isophthalic acid.

[0015] Furthermore, the copolymerized polyester resin (B) is
The dicarboxylic acid component consists of terephthalic acid, and the diol component consists of ethylene glycol and 1,4-cyclohexanedimethanol, and the diol component contains 1 to 80 mol% of 1,4-cyclohexanedimethanol. Crystallinity is lower than that of terephthalate, and the glass transition point TgB is higher. In addition, it is preferable that 1 to 40 mol% of 1,4-cyclohexanedimethanol is contained in the diol component.

Furthermore, the glass transition point TgA of the resin (A) and the glass transition point TgB of the resin (B) are selected so as to satisfy the following formula: 10°C≦TgB -TgA≦40°C. When TgB - TgA is below 10°C, the shrinkage rate of the heat-shrinkable laminated film obtained by stretching rapidly increases at the temperature at which shrinkage starts. On the contrary, Tg
When A - TgB exceeds 40°C, proper stretching becomes difficult, making it impossible to obtain a heat-shrinkable laminated film having preferable heat-shrink properties.

In the laminated film of the present invention, films (b1) and (b2) made of the copolymerized polyester resin (B) are laminated on both the front and back surfaces of the film (a) made of the copolymerized polyester resin (A). It has a three-layer structure. When each copolymerized polyester resin is used alone without being laminated, the heat-shrinkable film obtained by stretching the resin does not exhibit sufficiently favorable heat-shrinkage characteristics.

For example, in a single-layer heat-shrinkable film made of copolymerized polyester resin (A), the shrinkage start temperature tends to be too low for practical use, and the shrinkage rate increases rapidly at the shrinkage start temperature. Furthermore, in a single-layer heat-shrinkable film made of copolymerized polyester resin (B), it is difficult to obtain a sufficiently low shrinkage start temperature, and moreover, the shrinkage rate increases rapidly at the shrinkage start temperature.

Furthermore, in the three-layer heat-shrinkable laminated film of the present invention, the ratio of the copolymerized polyester resin (A) to the total thickness of the film (a) is 10 to 9.
0%, preferably 20 to 80%. Film (a
) in the total thickness is less than 10% or more than 90%, which is not preferable because the properties of one of the resins will be strongly manifested and uneven shrinkage will become large. Note that the total thickness of films (b1) and (b2) is 10 to 90% of the total thickness;
The thickness of the films (b2) and (b2) is generally 5 to 45%, and it is particularly preferable that the thicknesses of the films (b1) and (b2) be the same in order to prevent the laminated film from curling.

[0020] The heat-shrinkable laminated film of the present invention first comprises:
It is manufactured by forming an unstretched three-layer laminated film (original film) and stretching it at a temperature that orients the molecules. The raw film is made by melt-extruding each copolymerized polyester resin into a three-layer sheet using a flat die or circular die of a known three-layer extrusion device, or by melt-extruding each copolymerized polyester resin into a single-layer sheet. Molding is carried out by melt extrusion molding and laminating three layers using a known lamination device, or by laminating three layers using an extrusion lamination device.

[0021] Then, this raw film is stretched at least 1.5 to 6 times in one axial direction by a known stretching method such as a roll stretching method, a tenter stretching method, or a tubular stretching method, and if necessary, By heat setting, the heat-shrinkable laminated film of the present invention is manufactured. In this case, the stretching temperature is based on the highest glass transition point (TgB) of the resin used, and is suitably a temperature in the range of TgB -20°C to TgB +40°C, preferably a temperature in the range of TgB to TgB +15°C. It is. Also,
The total thickness of the heat-shrinkable laminated film is generally 10 to 120μ, preferably 30 to 7μ, from the viewpoint of appearance and shrinkage speed.
0μ is suitable as a shrink label.

[0022]

[Function] The copolymerized polyester resin (A) constituting the heat-shrinkable laminated film of the present invention is composed of one or more diols selected from ethylene glycol, diethylene glycol, and neopentyl glycol as a diol component as a copolymerization component. The dicarboxylic acid component contains 1 to 80 mol% of isophthalic acid, which results in lower crystallinity and lower glass transition point TgB than polyethylene terephthalate. In addition, the copolymerized polyester resin (B) contains 1 to 80 mol% of 1,4-cyclohexanedimethanol in the diol component, which has lower crystallinity than polyethylene terephthalate.
The glass transition point TgA increases.

The heat-shrinkable laminated film of the present invention has a glass transition point TgA of the resin (A) and a resin (B
) glass transition point TgB is expressed by the formula 10℃≦TgB
-TgA ≦40°C, and the film (a) made of resin (A) is coated with resin (B
) films (b1) and (b2) are laminated,
Furthermore, the ratio of the total thickness of the film (a) is 10 to
90%, and since the glass transition points of the two resins laminated in this way are different, it becomes difficult to cause gradual shrinkage and uneven shrinkage.

[0024] Furthermore, the heat-shrinkable laminated film of the present invention is
Since the film (a) having a low glass transition point is sandwiched between the films (b1) and (b2) having a high glass transition point from both sides, the heat resistance is improved as a whole.

[0025]

[Examples] Hereinafter, the present invention will be explained in detail by giving examples and comparative examples. Example 1 The dicarboxylic acid component consists of 90 mol% of terephthalic acid and 10 mol% of isophthalic acid, and the diol component consists of 80 mol% of ethylene glycol and 20 mol% of diethylene glycol.
copolymerized polyester resin (A) consisting of mol%, copolymerized polyester resin (B) whose dicarboxylic acid component consists of terephthalic acid, and whose diol components consist of 70 mol% of ethylene glycol and 30 mol% of 1,4-cyclohexanedimethanol. I prepared this. The glass transition point TgA of the resin (A) was 55°C, and the glass transition point TgB of the resin (B) was 81°C. Note that this glass transition point was measured using a differential scanning calorimeter (DSC).

The above resin (A) and resin (B) are melt-extruded into a three-layer sheet form using a flat die of a three-layer extrusion device, and on both the front and back sides of a film (a) made of resin (A), An unstretched laminated film (original film) in which films (b1) and (b2) made of resin (B) were laminated was molded. The thickness of layer (a) of this raw film is 40 μm, and the thickness of layers (b1) and (b2) of this raw film is 40 μm each.
μ. This raw film was stretched 3 times in the transverse direction at a temperature of 85° C. to produce a heat-shrinkable laminated film.

[0027] Regarding this heat-shrinkable laminated film, 60
The shrinkage rate in the transverse direction was measured every 10°C in the temperature range of ~110°C. This shrinkage rate is determined by the length of the heat-shrinkable laminated film in the transverse direction.
00 mm and width 10 mm, heat-shrinked in hot air set to the measurement temperature for 5 minutes, and calculated from the change in length. In addition, a lattice pattern was printed on this heat-shrinkable laminated film, which was laterally rolled and heat-sealed to produce a tubular heat-shrinkable label. Place this heat-shrinkable label over the body of the PET bottle, including the shoulder, and
After passing it through an oven at ℃ and shrinking it by heating,
The appearance of the label was observed for distortion and wrinkles in the printing. The results are summarized in Table 1.

Example 2 In Example 1, the thickness of layer (a) of the raw film was 6
The thickness of the (b1) layer and (b2) layer of the original film was changed to 30 μm. Other than that, the same procedure as in Example 1 was carried out. The results are summarized in Table 1.

Example 3 In Example 1, the thickness of layer (a) of the raw film was 8
The thickness of the (b1) layer and (b2) layer of the original film was changed to 20 μm. Other than that, the same procedure as in Example 1 was carried out. The results are summarized in Table 1.

Example 4 In Example 1, the copolymerized polyester resin (A) was
The dicarboxylic acid component consists of 83 mol% of terephthalic acid and 17 mol% of isophthalic acid, and the diol component consists of 73 mol% of ethylene glycol and 27 mol% of diethylene glycol.
The copolymerized polyester resin (A) consisting of mol% (glass transition point TgA: 64°C) was used. In addition, the thickness of the (a) layer of the raw film was set to 50μ, and the thickness of the (b) layer of the raw film was set to 50μ.
The thicknesses of the 1) layer and the (b2) layer were each changed to 50 μm. Other than that, the same procedure as in Example 1 was carried out. The results are summarized in Table 1.

Example 5 In Example 4, the thickness of layer (a) of the raw film was 7
The thickness of the (b1) layer and (b2) layer of the original film was changed to 40 μm. Other than that, the same procedure as in Example 4 was carried out. The results are summarized in Table 1.

Example 6 In Example 4, the thickness of layer (a) of the raw film was 1
00μ, and the thicknesses of the (b1) layer and (b2) layer of the original film were each changed to 25μ. Other than that, the same procedure as in Example 4 was carried out. The results are summarized in Table 1.

Example 7 In Example 1, the copolymerized polyester resin (A) was
Copolymerized polyester resin (A) (glass The transition point TgA was changed to 57°C). In addition, the thickness of the (a) layer of the raw film was set to 60μ, and the (b1) and (b2) layers of the raw film were set to 60μ.
) The thickness of each layer was changed to 30μ. Other than that, the same procedure as in Example 1 was carried out. The results are summarized in Table 1.

Example 8 In Example 1, the copolymerized polyester resin (A) was
A copolymerized polyester resin (B) in which the dicarboxylic acid component consists of 92 mol% of terephthalic acid and 8 mol% of isophthalic acid, and the diol component consists of 75 mol% of ethylene glycol and 25 mol% of diethylene glycol (glass transition point TgA is 53 ° C.) changed. In addition, the thickness of the (a) layer of the raw film was set to 60μ, and the thickness of the (b1) layer of the raw film was set to 60μ.
) layer thickness was changed to 20μ, and the thickness of the (b2) layer of the original film was changed to 40μ. Other than that, the same procedure as in Example 1 was carried out. The results are summarized in Table 1.

Comparative Example 1 Copolymerized polyester resin (B) used in Example 1
was melt-extruded into a single-layer sheet using a flat die of a single-layer extrusion device to form an unstretched single-layer film (original film) with a thickness of 120 μm. This raw film was stretched 3 times in the transverse direction at a temperature of 85° C. to produce a heat-shrinkable single-layer film. Regarding this heat-shrinkable single-layer film, the heat shrinkage rate and the appearance of the label were measured and evaluated in the same manner as in Example 1. The results are summarized in Table 1.

Comparative Example 2 Copolymerized polyester resin (A) used in Example 1
was used. Other than that, the same procedure as Comparative Example 1 was carried out. The results are summarized in Table 1.

Comparative Example 3 Copolymerized polyester resin (A) used in Example 4
was used. In addition, the thickness of the original film was changed to 150 μm. Other than that, the same procedure as Comparative Example 1 was carried out. The results are summarized in Table 1.

Comparative Example 4 Copolymerized polyester resin (A) used in Example 8
was used. Other than that, the same procedure as Comparative Example 1 was carried out. The results are summarized in Table 1.

[0039]

[Table 1]

[0040]

[Effects of the Invention] As mentioned above, the heat-shrinkable polyester laminated film of the present invention is capable of low-temperature shrinkage, and can undergo low-temperature shrinkage at around 70°C, which is the shrinkage start temperature of a heat-shrinkable vinyl chloride resin film. This improves workability and productivity in the heat shrinking process. Moreover, as the shrinkage temperature rises, the shrinkage rate does not increase rapidly but gradually increases, making it possible to achieve uniform shrinkage without uneven shrinkage.

In particular, when this heat-shrinkable laminated film is used as a cylindrical shrink label for a container such as a bottle that has a narrow neck and a thick body, the shrinkage rate gradually increases, resulting in uneven shrinkage between the neck and body. The adhesion is good and there is no distortion in printing.

In addition, this heat-shrinkable laminated film has a structure in which the film (a) with a low glass transition point is sandwiched from both sides by the film layers (b1) and (b2) with a high glass transition point. As a result, the heat resistance is improved. In particular, when the film (b1) layer and the film (b2) layer are made to have the same thickness, curling becomes difficult, the workability of labeling angular containers, etc. is improved, and the finish is also good.

Furthermore, unlike vinyl chloride resin, it does not generate toxic gases such as hydrogen chloride when incinerated, and since this heat-shrinkable laminated film is made of the same type of resin as PET containers, it can be used without leaving the label attached. It has the advantage that PET containers can be recovered and reused.

Claims (1)

[Claims] Claim 1: The dicarboxylic acid component is composed of terephthalic acid and isophthalic acid, and the diol component is composed of one or more diols selected from ethylene glycol, diethylene glycol, and neopentyl glycol, and the isophthalic acid component in the dicarboxylic acid component is A film (a
), the dicarboxylic acid component consists of terephthalic acid, and the diol component consists of ethylene glycol and 1,
Consisting of 4-cyclohexanedimethanol, 1,4-cyclohexanedimethanol in the diol component ranges from 1 to 80
A polyester laminated film having a three-layer structure in which films (b1) and (b2) made of a copolymerized polyester resin (B) having a mol% of The TgB with the polymerized polyester resin (B) is expressed by the formula 10°C≦TgB −
A heat-shrinkable polyester laminated film obtained by stretching a polyester laminated film that satisfies TgA≦40°C and accounts for 10 to 90% of the total thickness of the film (a).