JP2627947B2 - Heat shrinkable polyester film - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a heat-shrinkable polyester film formed from a specific polyester.

<Prior art> A large number of polyester-based heat-shrinkable films have been commercially available. For example, as disclosed in JP-A-55-100118, a polyester copolymer having an acid component of terephthalic acid and isophthalic acid is used. Films formed by blending with polyethylene terephthalate, and films formed from polyester containing 1.4 cyclohexane dimethanol as a diol component as shown in JP-A-57-42726 are well known. In any case, since the shrinkage starting temperature is not another low, the low-temperature heat shrinkage is insufficient.For example, when used as a shrink label for a polyester-based container, the container may be deformed in the shrinking process. Was concerned.

Further, the conventionally used polystyrene-based heat-shrinkable film has a large natural shrinkage rate, and as described above, for example, when used as a shrink label, due to this natural shrinkage, it is difficult to coat the sleeve-shaped label on the container. However, there is a problem that trouble is easily caused. Furthermore, the conventionally used polyvinyl chloride-based heat-shrinkable film may damage the furnace when incinerated as waste, and there has been a problem in using polyvinyl chloride as a raw material in such a point.

<Problems to be Solved by the Invention> As described above, for example, a shrink label for a polyester-based container is desired to have a low-temperature heat shrinkage and not have a natural shrinkage rate. Along the way, we have had a need to explore heat shrinkable films that have low temperature heat shrinkage and no natural shrinkage.
Under these circumstances, it has been found that a polyester-based heat-shrinkable film generally does not have a natural shrinkage rate and does not damage a furnace during waste incineration.

<Means for Solving the Problems> The present invention focuses on the fact that the polyester-based heat-shrinkable film has a low natural shrinkage rate and does not damage the incinerator in the waste treatment as described above, and further pursued the results. The heat-shrinkable film made of a specific polyester into which adipic acid is introduced in a specific amount as a dicarboxylic acid component has no spontaneous shrinkage and low shrinkage initiation temperature. The invention has been reached. That is, a feature of the present invention is that the heat-shrinkable polyester film comprises a dicarboxylic acid component containing 60 to 90 mol% of terephthalic acid, 5 to 20 mol% of isophthalic acid and 5 to 20 mol% of adipic acid, and a diol component. Glass transition temperature obtained from
The point is that the film is formed using polyester at 70 ° C.

Next, means for solving the problem will be described in more detail.

The polyester according to the present invention is synthesized with a dicarboxylic acid component containing terephthalic acid, isophthalic acid, and adipic acid and a diol component, and has a glass transition temperature in a specific range.
90 mol%, isophthalic acid and adipic acid are 5
2020 mol%, and the glass transition temperature must be in the range of 40-70 ° C.

In the polyester film according to the present invention, the action of apidic acid is one large point, and if the content of adipic acid as a dicarboxylic acid component is less than 5 mol%, the shrinkage onset temperature is unlikely to be low. %, The shrinkage onset temperature decreases too much,
There is a concern that spontaneous shrinkage may occur.
If it is less than mol%, the heat shrinkage rate is not expected to improve as much as expected.
If it exceeds mol%, the heat shrinkage rate becomes too large and shows a sudden shrinkage at a certain temperature or at a certain temperature. The content of terephthalic acid in the dicarboxylic acid component is derived from the results of the contents of isophthalic acid and adipic acid. If the content is less than 60 mol%, the initial effect cannot be obtained. It is close to homopolyethylene terephthalate, and an appropriate heat shrinkage cannot be expected.

Furthermore, the polyester film according to the present invention must have a glass transition temperature in the range of 40 to 70 ° C.
When the temperature is lower than 70 ° C., the temperature at which the shrinkage starts becomes too large, which may cause spontaneous shrinkage. On the other hand, when the temperature exceeds 70 ° C., the temperature at which the shrinkage starts becomes too high, and the desired effect is hardly obtained. As described above, the polyester according to the present invention uses terephthalic acid, isophthalic acid, and adipic acid as the dicarboxylic acid components in a specific amount, and is required to have a specific glass transition temperature. However, a preferable heat-shrinkable film cannot be obtained for the above reasons.

In general, polyethylene phthalate and the like are also synthesized using not only terephthalic acid but also dimethyl terephthalate and terephthalic acid derivatives such as diethyl terephthalate as a dicarboxylic acid component. Of course, the terephthalic acid, isophthalic acid and adipic acid used as the dicarboxylic acid component include the so-called derivatives in which the H atom in the carboxyl group is replaced by a methyl group, an ethyl group or the like.

Examples of the diol component used for synthesizing the polyester according to the present invention include ethylene glycol, diethylene glycol, and propylene glycol, but are not particularly limited, and any dihydric alcohol or the like can be appropriately used. At this time, in the dicarboxylic acid component according to the present invention, the diol component and the synthesized polyester, if necessary, as long as the properties are not impaired, even if other monomers are appropriately introduced, it is no problem. These are all within the scope of the present invention.

A known method may be applied to form a film of the polyester according to the present invention, and there is no particular limitation.

When a heat-shrinkable film is formed, it is necessary to pass through a stretching step. Usually, a method of stretching the film uniaxially or biaxially in a longitudinal and / or transverse manner after film formation is adopted. For application to shrink labels and the like, uniaxial stretching is desirable (there is no particular limitation). For example, uniaxial stretching in a direction perpendicular to the machine direction (transverse direction) by a tenter or the like can be mentioned as a preferred embodiment. For example, the film may be subjected to uniaxial stretching in a machine direction (longitudinal direction) by a hot roll or the like. When used as a shrink film for general packaging, biaxial stretching is desirable, but there is no particular limitation. Of course, uniaxial or biaxial stretching by a tubular method may be performed, and the stretching method is not particularly limited. The stretching temperature is usually from 60 to 90 ° C., preferably from 70 to 80 ° C., but is not particularly limited, and the stretching ratio is 3 to 5 in the case of uniaxial stretching.
The ratio can be exemplified by about 3.5 times, preferably about 3.5 to 4.5 times, and there is no particular limitation. In forming the film, it is inevitable to blend necessary amounts of other thermoplastic resins, additives such as antistatic agents, lubricants, inorganic fine particles, fillers and the like into the polyester according to the present invention.

The heat shrinkage of the heat shrinkable polyester film of the present invention is not particularly limited, and may be appropriately determined depending on the application.
Usually, the heat shrinkage in the stretching direction when immersed in a glycerin bath for 30 seconds is 25 to 45% at 70 ° C, 40 to 60% at 80 ° C, and 50 at 100 ° C.
About 65% is desirable. For example, when used as a shrink label for a polyester-based container, it is desirable to have the above-mentioned heat shrinkage ratio, and when it is out of this range, it is possible to use it, but if anything, various troubles are likely to occur.

As the use of the heat-shrinkable polyester film according to the present invention, in addition to the shrink labels for polyester-based containers as described above, glass bottles, appropriate plastic containers, various containers, suitably used as shrink labels for metal cans, etc. For use in labels, generally uniaxially stretched is preferred. Other applications include lid materials for containers, general heat-shrinkable packaging materials, and the like, and biaxially stretched materials are generally preferred. As described above, applications are wide and there is no particular limitation.

<Example 1> An extruded film was formed from a polyester obtained using 96 mol% of ethylene glycol and 4 mol% of diethylene glycol as diol components as raw materials, using a dicarboxylic acid component described in Table 1 as a raw material. An unstretched flat film was obtained. The film was uniaxially stretched four times by a tenter at a stretching temperature of 75 ° C. in a direction (lateral direction) perpendicular to the machine direction.
Table 1 shows the thermal shrinkage in the transverse direction at 60, 65, 70, 80, 90 and 100 ° C. during the second immersion.

Experiments Nos. 1 and 2 show the ones of the present invention, and Nos. 3 to 5 show the ones of the comparative examples. Is rapidly accelerated from 70 to 80 ° C., so that contraction spots and the like easily occur. In the case of No. 5, the shrinkage rate is increased, and the shrinkage at 60 to 70 ° C. is rapidly promoted.

<Example 2> A polyester in which the dicarboxylic acid component was composed of 79 mol% of terephthalic acid, 10 mol% of isophthalic acid and 11 mol% of adipic acid, and the diol component was composed of 96 mol% of ethylene glycol and 4 mol% of diethylene glycol was prepared. 1
Extrusion film formation and stretching were performed in the same manner as described above to obtain a heat-shrinkable film.

<Comparative Example 1> A styrene-based film composed of 100 parts by weight of a styrene-butadiene block copolymer having a styrene content of 85% by weight and 10 parts by weight of polyethylene was prepared, and was horizontally uniaxially stretched four times by a tenter at 85 ° C. A heat-shrinkable polystyrene yarn film having a thickness of 60 μm was obtained.

<Comparative Example 2> A film made of polyvinyl chloride was prepared and 2.8 at 85 ° C.
Twenty times uniaxial stretching with a tenter, 60μ thick PVC
A heat shrinkable film was obtained.

The physical properties of Example 2 and Comparative Examples 1 and 2 are shown in Table 2.

Judging from these results, the product of Example 2 has a particularly excellent natural shrinkage as compared with that of the conventionally used polyvinyl chloride shown in Comparative Example 1, and also has excellent tensile strength. Furthermore, the effect of the present invention can be seen from this point because the incinerator is less corrosive. By the way, high tensile strength means that there are few flaws, cracks, etc.,
It shows high durability when used for applications such as shrink labels, lid materials, and other general packaging materials. Further, the general-purpose polystyrene-based heat-shrinkable film shown in Comparative Example 2 is significantly inferior to the data of the examples in data such as low-temperature heat shrinkage, natural shrinkage, and tensile strength.

<Example 3> A predetermined printing was applied to the heat-shrinkable polyester film obtained in Example 2, and a center seal having a diameter of 93.6 mm and a height of 83 mm was made so that the stretching direction coincided with the circumferential direction of the bottle described later. A shrink label was obtained by forming a cylinder by the method.
Such a shrink label, the maximum diameter of the trunk is 93 mm
A 1.5-inch polyethylene terephthalate biaxially-stretched bottle was covered and passed through a heat shrinkage step to obtain a shrink label-coated polyester bottle. Here, a shrink tunnel was used as the heat shrinking step, and the temperature in the tunnel was set at three locations: the inlet, the center, and the outlet, and the label covering state was observed. Table 3 shows the results.

<Comparative Example 3> A mixture of 60% by weight of a polyester using 50% by mole of terephthalic acid and 50% by mole of isophthalic acid as a dicarboxylic acid component and 40% by weight of polyethylene terephthalate using ethylene glycol as a diol component was formed into an extrusion film. Then, a heat-shrinkable film was obtained in the same manner as in Example 2, and a shrink label-coated polyester bottle was obtained in the same manner as in Example 3. Table 3 shows the covering state of the label.

From the results in Table 3, it can be seen from the results of Example 3 that the coating of Example 3 had good gloss and no avatar was generated, and that the coated state was good, whereas the coating of Comparative Example 3 was poor in gloss and generated avatars. Was seen. In addition, the product of Example 3 can be reused as a bottle or the like by pulverizing the powder while keeping the label coated when using the waste, which is advantageous in this respect.

<Effects of the Invention> The present invention is as described above, and the heat-shrinkable polyester film according to the present invention has a low shrinkage onset temperature, and thus has excellent low-temperature heat shrinkability and extremely low natural shrinkage. It has characteristics and is particularly suitable as, for example, a shrink label for a container made of polyester, and can be expected to have a wide variety of other uses. Furthermore, because of its excellent tensile strength,
There are few cracks and the like, and there are advantages such as not damaging the furnace when incinerating waste, and it is expected to be used in the future.

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Claims (4)

(57) [Claims] 1. A polyester having a glass transition temperature of 40 to 70 ° C. obtained from a diol component and a dicarboxylic acid component containing 60 to 90 mol% of terephthalic acid, 5 to 20 mol% of isophthalic acid and 5 to 20 mol% of adipic acid. A heat-shrinkable polyester film formed by using as a material. 2. The heat-shrinkable polyester film according to claim 1, which is uniaxially stretched in a direction perpendicular to the machine direction after forming the film. 3. The heat shrinkage in the stretching direction when immersed in a glycerin bath for 30 seconds is 25 to 45% at 70 ° C., 40 to 60% at 80 ° C. and 10%.
The heat-shrinkable polyester film according to claim 2, which has a content of 50 to 65% at 0 ° C. 4. The heat-shrinkable polyester film according to claim 3, which is suitable as a shrink label for a polyester container.