JPH04356533A - Heat-shrinking polyester film - Google Patents

Abstract

PURPOSE:To obtain a heat-shrinking polyester film which has good low- temperature shrinking properties and can accomplish uniform shrinkage free from uneven shrinkage by forming a film from a composition comprising two specified polyester resins and stretching this film. CONSTITUTION:A heat-shrinking polyester film obtained by forming a film from a resin composition comprising 95-5wt.% polyester resin containing a dicarboxylic acid component comprising terephthalic acid and a diol component consisting of ethylene glycol and 1,4-cyclohexanedimethanol and 5-95wt.% polyester containing a dicarboxylic acid component comprising at least two members selected from among terephthalic acid, isophthalic acid, phthalic acid, phenylenediacetic acid and an aliphatic dicarboxylic acid and a diol component comprising at least one member selected from among ethylene glycol, propylene glycol, butanediol, neopentyl glycol, diethylene glycol and polyalkylene glycol, and then stretching this formed film.

Description

[Detailed description of the invention]

0001

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

0002

2. Description of the Related Art Heat-shrinkable films are widely used for shrink wrapping, shrink labels, cap seals, etc. by taking advantage of their ability to shrink when reheated.

By the way, polyethylene terephthalate (
Uniaxially oriented films such as vinyl chloride resin and expanded polystyrene are mainly used for shrink labels used for various containers such as PET (PET) containers and glass containers. Among them, heat-shrinkable vinyl chloride resin films are widely used because of their good low-temperature shrinkability and printability.

However, vinyl chloride resins have problems such as low heat resistance and generation of hydrogen chloride when incinerated. In addition, there is a problem that a PET container using a heat-shrinkable vinyl chloride resin film as a shrink label cannot be collected and reused together with the shrink label.

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

However, since polyester resins have high crystallinity, their heat-shrinkable films have a relatively high heat-shrinkage start temperature, and the shrinkage rate tends to increase rapidly as the temperature rises. However, when used as shrink labels for various containers, there were problems in terms of productivity and uniform shrinkability.

[0007]Recently, therefore, various improvements have been proposed for heat-shrinkable films made of polyester resins. For example, JP-A No. 57-42726 discloses a transparent, heat-sealable heat-sealable polyester using a copolyester consisting of terephthalic acid as the dicarboxylic acid component and ethylene glycol and 1,4-cyclohexanedimethanol as the diol component. Shrink wrapping films have been proposed.

[0008] Japanese Patent Publication No. 63-7573 proposes to contain isophthalic acid as a copolymerization component to alleviate high crystallinity and improve shrinkage unevenness and heat sealability.

Furthermore, Japanese Patent Publication No. 64-10332 discloses that terephthalic acid or its derivatives, an amorphous copolyester derived from ethylene glycol and 1,4-cyclohexanedimethanol, and terephthalic acid or its derivatives. A highly shrinkable polyester film is disclosed in which a composition comprising a derivative and a polyester polymer comprising ethylene glycol is formed and stretched.

[0010] In the above-mentioned prior literature, as a raw material for a heat-shrinkable polyester film, an amorphous copolyester or an amorphous copolyester and a crystalline polyester are mixed to suppress the crystallization of the polyester. I am using the one that I made. Compared to heat-shrinkable films made from crystalline polyethylene terephthalate, these
It is said that the shrinkage rate is high, the heat-sealing strength is high, the shrinkage force stress is reduced, and uneven shrinkage and ease of tearing of the heat-sealed part are improved.

[0011]

[Problems to be Solved by the Invention] However, these conventional techniques have not yet produced a heat-shrinkable polyester film having sufficient shrinkage characteristics.

That is, the above-mentioned known heat-shrinkable polyester film still has a drawback that the shrinkage temperature is higher than that of the heat-shrinkable vinyl chloride resin film, and furthermore, the shrinkage rate increases rapidly at the temperature at which shrinkage starts. have.

[0013] Therefore, problems such as decreased productivity and occurrence of uneven shrinkage in the shrinking process are unavoidable. In particular, when used as a shrink label for containers such as bottles, whose neck and body are different in size, the rapid increase in shrinkage rate as the temperature rises will cause uneven adhesion and distortion of printing, making it impractical. This is a serious problem.

[0014] This invention has good low-temperature shrinkability, and
An object of the present invention is to provide a heat-shrinkable polyester film that can achieve uniform shrinkage without uneven shrinkage.

[0015]

[Means for Solving the Problems] Invention 1 provides 95 to 5% by weight of a polyester resin (a) whose dicarboxylic acid component is terephthalic acid and whose diol component is ethylene glycol and 1,4-cyclohexanedimethanol;
The dicarboxylic acid component consists of two or more dicarboxylic acids selected from terephthalic acid, isophthalic acid, phthalic acid, phenylene diacetic acid, and aliphatic dicarboxylic acids, and the diol component consists of ethylene glycol, propylene glycol,
It is formed by film-forming and stretching a resin composition consisting of 5 to 95% by weight of a polyester resin (b) consisting of one or more diols selected from butanediol, neopentyl glycol, diethylene glycol, and polyalkylene glycol. This is a heat-shrinkable polyester film.

[0016] Invention 2 also provides a diol containing terephthalic acid and ethylene glycol as main components and selected from naphthalene dicarboxylic acid, diphenylene dicarboxylic acid, diphenyl ether dicarboxylic acid, a diol containing an aromatic nucleus, and a hydroxycarboxylic acid containing an aromatic nucleus. It is characterized by being formed by film-stretching a resin composition consisting of 95 to 5% by weight of a polyester resin (c) containing one or more of the above components and 5 to 95% by weight of the above polyester resin (b). It is a heat-shrinkable polyester film.

[0017] Furthermore, invention 3 is the invention 1 or invention 2 described above.
This heat-shrinkable polyester film is formed by forming and stretching a resin composition comprising 95 to 70% by weight of the resin composition described above and 5 to 30% by weight of polyethylene terephthalate.

The polyester resin (a) used in the above invention 1 contains 1,4 in the diol component as described above.
- Due to the inclusion of cyclohexanedimethanol, the crystallinity is lower than that of polyethylene terephthalate and the glass transition point (Tg) is higher.
4-Cyclohexane dimethanol is 1 in the diol component
It is preferably contained in the range of ~80 mol%,
More preferably, the content is in the range of 5 to 40 mol%.

The polyester resin (b) used in the inventions 1 and 2 has lower crystallinity than polyethylene terephthalate because it is composed of two or more dicarboxylic acids and the diol component as described above. However, it has a low glass transition point (Tg).

[0020] The polyester resin (c) used in the above invention 2 contains terephthalic acid and ethylene glycol as main components, and also contains dicarboxylic acid, diol or hydroxydicarboxylic acid containing the above-mentioned rigid aromatic nucleus. Due to its inclusion, the crystallinity is lower than that of polyethylene terephthalate, and the glass transition point (Tg) is higher than that of polyethylene terephthalate. Examples of dicarboxylic acids containing aromatic nuclei include terephthalic acid, naphthalene dicarboxylic acid, diphenylene dicarboxylic acid, and diphenyl ether dicarboxylic acid. Examples of diols containing aromatic nuclei include xylylene glycol, hydroquinone, resorcinol, dihydroxydiphenyl, and bisphenol A.
, alkylene oxide adducts of bisphenol A, etc. Examples of hydroxycarboxylic acids containing aromatic nuclei include hydroxybenzoic acid, hydroxyalkoxybenzoic acid, hydroxyalkoxyphenylacetic acid, and hydroxynaphthoic acid.

[0021] In invention 1, the above polyester resins (a) and (b) are used, and in invention 2,
When the polyester resins (c) and (b) are used in combination, the crystallinity decreases and the heat shrinkage rate at low temperatures increases, and the T of these two resins decreases.
Due to the difference in g, there is no sudden increase in the shrinkage rate due to temperature rise, and the shrinkage is gradual, so that uniform heat shrinkage without shrinkage unevenness can be achieved.

[0022] The above polyester resins (a) and (b)
) and the blending ratio of the polyester resin (c) and (
The blending ratio with b) is as described above, and if the content of each resin is less than 5% by weight, the properties of the other resin will strongly appear and uneven shrinkage will become large, which is not preferable.

In addition, in invention 3, the above polyester resins (a) and (b) or the above polyester resin (c
) and (b), 5 to 3 polyethylene terephthalate
By mixing 0% by weight, the shrinkage rate at low temperatures increases, and due to the difference in the shrinkage rates of the three types of resins, the change in shrinkage rate due to heating becomes more gradual, which reduces uneven shrinkage. It is possible to achieve uniform heat shrinkage without any heat loss, and it also has the effect of improving heat resistance.

[0024] The above polyester resins (a) and (b)
) Alternatively, the blending ratio of polyethylene terephthalate to the polyester resins (c) and (b) is as described above; if it is less than 5% by weight, the effect of improving heat resistance is small, and if it exceeds 30% by weight, crystallinity increases, This is not preferable because the thermal shrinkage rate decreases and the unevenness of shrinkage increases.

[0025] The polyester resin composition as described above is melt-extruded into a sheet form by a conventional method such as the T-die method or the tubular method to obtain an unstretched film. Next, the heat-shrinkable polyester film of the present invention is obtained by stretching this unstretched film by about 1.5 to 6 times in at least one axis using a roll, tenter, tubular method, or the like.

Note that the thickness of the heat-shrinkable polyester film is 10 to 120 μm, preferably 30 to 70 μm, which is suitable for use as a shrinkable label in view of appearance and shrinkage speed.

[0027]

[Function] In Invention 1 and Invention 2, when the polyester resins (a) and (b) or (c) and (b) are used in combination, the crystallinity decreases and the heat resistance at low temperatures is reduced. The shrinkage rate increases, and the Tg of these two types of resins increases.
Due to the difference in temperature, the shrinkage rate does not suddenly increase due to temperature rise and shrinks gradually, achieving uniform heat shrinkage without uneven shrinkage. It has low temperature shrinkability.

Moreover, as the temperature rises from the temperature at which heat shrinkage begins, the heat shrinkability tends to gradually increase. In addition, in invention 3, the above polyester resin (a) and (
b) Alternatively, by mixing 5 to 30% by weight of polyethylene terephthalate in addition to the above polyester resins (c) and (b), the shrinkage rate at low temperature increases, and due to the difference in the shrinkage rate of the three types of resins, As the shrinkage rate changes due to heating, the shrinkage becomes more gradual, so uniform heat shrinkage without uneven shrinkage can be achieved, and heat resistance is also improved.

[0029]

[Examples] The present invention will be specifically explained below by giving Examples and Comparative Examples. Note that hereinafter, parts by weight are simply referred to as parts. (1) Examples of invention 1 (Examples 1 to 14) Table 1 regarding each component of polyester resin (a) and polyester resin (b) and their blending ratio
Each of these compositions was melt-extruded to obtain an unstretched film having a thickness of 120 μm.

[0030]

[Table 1]

For each unstretched film, 80
The film was stretched 3.0 times in the transverse direction at °C to obtain a heat-shrinkable film with a thickness of 40 μm. About this heat-shrinkable film,
Each shrinkage rate in the lateral direction was measured at every 10°C in the temperature range of 60°C to 110°C.

To measure the shrinkage rate, the sample was cut in the transverse direction to a length of 100 mm and a width of 10 mm, and the sample was shrunk for 5 minutes in hot air set at the measurement temperature, and the shrinkage rate was measured. Furthermore,
A lattice pattern was printed on this heat-shrinkable film, which was then rolled horizontally and heat-sealed to form a tubular heat-shrinkable label. This label was placed on a PET bottle, and after being shrunk in an oven at 120° C., the appearance of the label was observed and evaluated for the presence or absence of distortion and wrinkles in the printing.

Table 2 shows the results regarding the heat shrinkage rate and appearance after use.

[0034]

[Table 2]

(2) Examples of Invention 2 (Examples 15 to 21) The components of polyester resin (a) and polyester resin (b) and their blending ratios were as shown in Table 3, and each of these compositions was melt extrusion,
Unstretched films each having a thickness of 120 μm were obtained.

[0036]

[Table 3]

[0037] This heat-shrinkable film was evaluated in the same manner as in the above examples regarding the heat-shrinkage rate and the appearance after use. Table 4 shows the results regarding the heat shrinkage rate and appearance after use.

[0038]

[Table 4]

(3) Examples of Invention 3 (Examples 22 to 37) Blending ratio of each component of polyester resin (a) and polyester resin (b), and polyester resins (a), (b) and polyethylene terephthalate The compositions were as shown in Table 5, and each of these compositions was melt-extruded to obtain unstretched films each having a thickness of 120 μm.

[0040]

[Table 5]

[0041] This heat-shrinkable film was evaluated in the same manner as in the above-mentioned Examples in terms of heat-shrinkage rate and appearance evaluation after use. Further, a PET bottle equipped with the above label was filled with water and sealed and retorted at 124° C. for 45 minutes to observe deformation and discoloration of the label.

Table 6 shows the results regarding the heat shrinkage rate, the appearance after use, and the appearance of the label after retorting.

[0043]

[Table 6]

(4) Comparative Example The polyester resin compositions shown in Table 7 were melt-extruded to obtain unstretched films each having a thickness of 120 μm.

[0045]

[Table 7]

[0046] This heat-shrinkable film was evaluated in the same manner as in the above-mentioned Examples in terms of heat-shrinkage rate and appearance evaluation after use. Furthermore, deformation and discoloration of the labels were observed in the same manner as in Examples 22 to 37 for PET bottles equipped with the above labels, which were filled with water and sealed tightly.

The results regarding the heat shrinkage rate, the appearance after use, and the appearance of the label after retorting are shown in Table 8.

[0048]

[Table 8]

As is clear from the above results, the heat-shrinkable polyester film of the present invention can undergo low-temperature shrinkage at around 70°C, which is the heat-shrinkage start temperature of a heat-shrinkable vinyl chloride resin film. . Furthermore, what is important is that the shrinkage rate tends to gradually increase as the shrinkage temperature increases. Therefore, it is possible to overcome the uneven shrinkage phenomenon caused by a sudden increase in shrinkage rate.

Furthermore, as is clear from Examples 22 to 37, in the invention in which a small amount of polyethylene terephthalate was used in combination, in addition to the above characteristics, heat resistance was improved, and it was found that it was suitable as a label for retort containers. did .

On the other hand, the heat-shrinkable polyester films of Comparative Examples 1 to 5 all had a heat-shrinkage start temperature of 8.
The shrinkage rate was as high as 0°C and showed a rapid increase at 80°C.

[0052]

Effects of the Invention As described above, the heat-shrinkable polyester film of the present invention shrinks at a lower temperature than conventional heat-shrinkable polyester films, improving productivity. Since the shrinkage rate gradually increases as the product rises, it exhibits excellent shrinkage characteristics such as no uneven shrinkage. Therefore, it is suitable for the field of shrink labels for various containers such as PET containers, and is particularly suitable for shrink labels for containers that have a narrow part such as the neck part of a bottle and a thick part such as the body part. When used as a printing press, the shrinkage rate increases gradually so that the shrinkage does not become uneven, the adhesion is good, and there is no distortion in printing, so it is suitably used.

In addition, in invention 3, in which a small amount of polyethylene terephthalate is used, in addition to the above properties, heat resistance is improved, making it suitable as a label for retort containers. Furthermore, the heat-shrinkable polyester films of any of the inventions do not generate hydrogen chloride when incinerated unlike vinyl chloride resins. Since this heat-shrinkable polyester film is made of the same raw material as the PET container, the PET container can be recovered and reused with the label still attached.

Claims (3)

[Claims] Claim 1: The dicarboxylic acid component consists of terephthalic acid, and the diol component consists of ethylene glycol and 1,
95 to 5% by weight of a polyester resin (a) consisting of 4-cyclohexanedimethanol and two or more dicarboxylic acid components selected from terephthalic acid, isophthalic acid, phthalic acid, phenylene diacetic acid, and aliphatic dicarboxylic acids. Polyester resin (b) consisting of dicarboxylic acid and having a diol component of one or more diols selected from ethylene glycol, propylene glycol, butanediol, neopentyl glycol, diethylene glycol, and polyalkylene glycol (b) 5 to 95 weight A heat-shrinkable polyester film characterized by being formed by film-forming and stretching a resin composition consisting of %. [Claim 2] One or more selected from naphthalene dicarboxylic acid, diphenylene dicarboxylic acid, diphenyl ether dicarboxylic acid, diol containing an aromatic nucleus, and hydroxycarboxylic acid containing an aromatic nucleus as well as having terephthalic acid and ethylene glycol as main components. 95 to 5% by weight of a polyester resin (c) containing two or more components, and two or more dicarboxylic acid components selected from terephthalic acid, isophthalic acid, phthalic acid, phenylene diacetic acid, and aliphatic dicarboxylic acid. polyester resin (b) consisting of a dicarboxylic acid and a diol component consisting of one or more diols selected from ethylene glycol, propylene glycol, butanediol, neopentyl glycol, diethylene glycol, and polyalkylene glycol (b) 5 to 95 weight A heat-shrinkable polyester film characterized by being formed by film-forming and stretching a resin composition consisting of %. 3. A thermoplastic resin composition comprising a resin composition comprising 95 to 70% by weight of the resin composition according to claim 1 or 2 and 5 to 30% by weight of polyethylene terephthalate. Shrinkable polyester film.