KR101695921B1 - Biaxyally oriented polyester thermal adhesive film - Google Patents

Abstract

The biaxially stretched polyester thermoadhesive film comprising crystalline polyester and amorphous copolymerized polyester is superior in transparency, heat resistance, adhesive strength and the like to conventional ones, and thus can be utilized as a sealant for a retort food packaging material for a microwave oven.

Polyester, sealant, adhesive, retort

Description

Biaxially oriented polyester thermoadhesive film {BIAXYALLY ORIENTED POLYESTER THERMAL ADHESIVE FILM}

The present invention relates to a biaxially stretched polyester thermal adhesive film which can be used as a sealant of a food pouch requiring heat resistance.

Recently, as convenience is emphasized, processed foods of Zhejiang Province, called retort foods, are greatly developed. Among retort foods, in the case of foods using microwave ovens, the temperature of the food often rises above the melting point of the polyolefin used as the packaging material.

However, since the melting point of conventional unleaded polypropylene (CPP) is below 160 ° C, the heat resistance is insufficient when used in foods cooked in a microwave oven. In particular, when the content of fat is high, the viscosity is high, the fry is large, or the spicy taste is strong, the temperature at the interface between the food and the packaging material rises to 180 ° C or more. When CPP is used in the sealant, And there is a tendency that the food is infiltrated into the sealant due to the lack of oil resistance.

In addition, in the case of a packaging material for a microwave oven in which aluminum foil or vapor deposition can not be used as an oxygen barrier film as a component of a food packaging material for retort, a transparent vapor deposition film is used. In this case, Due to the haze, it is difficult to manufacture the transparent packaging material with the contents visible, and it is difficult to recycle even when the different materials are stacked.

As a conventional polyolefin-based thermal adhesive film, Korean Patent Laid-Open Publication No. 2007-0089820 discloses a polyolefin-based adhesive film for packaging retort. However, since the heat shrinkage rate and adhesive strength of the film are superior in terms of heat shrinkage and adhesive strength, however, as described above, since the heat resistance is lower than 160 캜, there is a problem that the film melts when heated in a microwave oven.

Polyesters have higher heat resistance than polyolefins in terms of the properties of materials, but conventionally have been applied only to applications where metal lamination or easy-peel films are not strongly required for self-adhesive strength. Korean Patent Laid-Open Publication No. 1999-0065023 discloses a thermoadhesive copolymerized polyester film for metal lamination, and Korean Patent Laid-Open No. 2001-0002729 discloses a coextruded two-layer polyester adhesive film. However, the metal lamination film has insufficient self-adhesive strength at the pouch manufacturing process temperature, and the coextruded film has a problem that the coextruded layer is separated after the retort sterilization treatment, and the low adhesion start of the amorphous adhesive layer It is difficult to be used as a sealant such as adhesion occurs during retort sterilization treatment due to temperature.

Accordingly, an object of the present invention is to provide a self-adhesive biaxially stretched polyester thermoadhesive film which is improved in heat resistance and transparency, and can be peelable and permanently bonded according to composition and bonding conditions.

According to this object, the present invention relates to a thermoplastic resin composition comprising a crystalline polyester and an amorphous copolymerized polyester and having a haze of 10% or less, a melting temperature exceeding 200 DEG C, self-bonding at 200 to 250 DEG C for 1 second after lamination with the base layer Wherein the adhesive strength of the biaxially oriented polyester thermally adhesive film is 1.5 to 5.0 kgf / 15 mm.

The biaxially stretched polyester thermally adhesive film of the present invention is superior in heat resistance and transparency to the conventional polyolefin thermally adhesive film and has a higher adhesive strength than the conventional polyester thermally adhesive film and can be used as a sealant for a microwave- As shown in FIG.

Hereinafter, the present invention will be described in more detail.

In order to produce a thermally adhesive film having a sufficient adhesive strength at a high temperature, it is advantageous to increase the copolymerization ratio of the amorphous component so as to be amorphous. However, the amorphous copolymerized polyester has a strong tendency to shrink even when heat-set during biaxial stretching. On the other hand, in the case of the crystalline polyester, even if biaxial stretching is carried out, the heat shrinkage ratio can be reduced through heat fixation, but adhesion is lost due to thermal hardening. As described above, the amorphous copolyester improves the adhesiveness and the crystalline polyester improves the dimensional stability and flexibility. Therefore, in order to satisfy both adhesiveness and thermal stability and impact strength, amorphous copolyester and crystalline polyester They should be mixed in an appropriate ratio.

For example, the crystalline polyester may be contained in an amount of 10 to 60% by weight based on the weight of the entire film, and the amorphous copolymerized polyester may be contained in an amount of 40 to 90% by weight.

The crystalline polyester used in the film of the present invention preferably has polybutylene terephthalate (PBT), polytrimethylene terephthalate (PTT), or a mixed resin thereof to lower the melting point and increase the flexibility.

The amorphous copolymerizable polyester used in the film of the present invention is a polyester obtained by copolymerizing at least one polyester selected from the group consisting of polyethylene terephthalate (PET), polybutylene terephthalate (PBT), and polytrimethylene terephthalate (PTT) Or a bifunctional acid-amorphous amorphous resin. At this time, the copolymerization ratio of the dihydric alcohol or the dicarboxylic acid is preferably 10 to 25 mol% based on the total amorphous copolymerized polyester resin.

As the divalent alcohol or divalent acid to be copolymerized, at least one selected from the group consisting of neopentyl glycol, 1, 4-cyclohexane dimethanol, isophthalic acid, and dimethyl isophthalic acid may be used, A dicarboxylic acid may be used, and particularly, it is preferably dimethyl isophthalate.

At this time, the crystalline polyester and the amorphous copolymerized polyester are preferably polymerized using a food-compatible catalyst, and for example, Ti or Ge is preferably used.

The heat-sealable film of the present invention preferably has a specific gravity after heat setting in the range of 1.30 to 1.36, and the adhesiveness and dimensional stability can be further improved within the above range.

The heat-adhesive film of the present invention is preferably stretched 2.5 to 3.5 times in the longitudinal direction and 2.5 to 4.5 times in the transverse direction. The heat setting can be carried out at 190 to 250 ° C, and it is preferable to provide 3 to 5% relaxation after heat fixing in the tenter in order to provide dimensional stability in the transverse direction.

The thermal adhesive film of the present invention may have a single layer structure basically, and preferably has a thickness of 20 to 80 탆 for use in a sealant application.

The film of the present invention is suitable for use as a sealant of a retort food packaging material having a heat resistance of 200 ° C or higher because of being made of a polyester resin as a raw material and thus having excellent heat resistance, It can be used as a sealant for a rapidly growing microwave oven retort food packaging material.

Further, since the adhesive strength when self-adhering at 200 to 250 ° C for one second after lamination with the base film is 1.5 to 5.0 kgf / 15 mm, it is not harmful to use as a thermally adhesive film, and depending on the compounding ratio of the starting resin and the bonding condition Both easy-peel adhesion and permanent adhesion can be achieved. The higher the content of the crystalline polyester, the lower the bonding temperature, the more the peelable adhesion becomes. The lower the content of the crystalline polyester, the more the bonding temperature becomes.

In addition, the film of the present invention has a haze of 10% or less, which is particularly suitable for use as a packaging material in comparison with a conventional opaque polyolefin-based thermal adhesive film.

The film of the present invention preferably has a heat shrinkage ratio of less than 5% in each of the longitudinal and transverse directions at a temperature of 120 to 150 캜 and a time of 20 to 40 minutes.

When the heat-sealable film of the present invention is used as the sealant of the packaging material, it can be located on the innermost side of the packaging material laminate structure. For example, when used as a general retort food packaging material, it may be composed of polyester // aluminum foil // nylon // sealant layer, and when used as a food packaging material for a microwave oven, a transparent deposition polyester // nylon Or a layer of polyester / sealant, and other various layer composition combinations are possible. In the case of food packaging for microwave ovens, the entire layer of the laminated structure can be combined with polyester, which can also be environmentally beneficial in terms of recycling.

Hereinafter, the present invention will be described in more detail with reference to Examples. However, the following Examples are intended to illustrate the present invention, but the present invention is not limited to the following Examples.

Production of heat-sealable film

Comparative Example 1

ZK99S having a thickness of 70 mu m among the CPP film (TORAYFAN * NO) manufactured by Toray Co. was used.

Comparative Example 2

A coextruded two-layer polyester thermal adhesive film having a thickness of 50 탆 was prepared under the conditions of Example 2 disclosed in Korean Patent Laid-Open No. 2001-0002729.

Example 1

Polybutylene terephthalate (LG Chem, product name: LUPOX HV1010) polymerized with a Ti catalyst was used as the crystalline polyester. As the amorphous copolymerized polyester, a polyester polymerized with a Ti catalyst and having a main component of ethylene terephthalate and a copolymer of dimethyl isophthalate at 18 mol% was used. The crystalline polyester and the amorphous copolymerized polyester were blended at a weight ratio of 40/60 and extruded at a temperature of 280 ° C on a T-die, stretched 3.0 times at 70 ° C in the machine direction, Was stretched 4.2 times at 95 to 110 DEG C to prepare a 50 mu m film. This was heat-set at 200 ° C and 4.5% relaxed to improve lateral dimension stability. Thus, a biaxially oriented polyester thermally adhesive film having a specific gravity of 1.34 was obtained.

Application as a sealant

(12 m) // nylon (15 m) // sealant (50 m) using the thermal adhesive films prepared in Comparative Examples 1 to 2 and Example 1 as a sealant, followed by dry lamination dry lamination method to form a urethane adhesive.

Test Example

The properties of the heat-adhesive films of the comparative examples and the examples were evaluated as follows and summarized in Table 1 below.

All properties except adhesion strength were measured with a thermo-adhesive film alone, and the bonding strength was measured after lamination of PET and nylon.

a. Hayes

The haze of the heat adhesive films prepared in the above Comparative Examples and Examples was measured according to JIS K7136.

b. Breaking strength, breaking elongation, Young's modulus

The thermal adhesive films prepared in the above Comparative Examples and Examples were measured according to ASTM D 882, and each film was measured using a universal tester (UTM, model name 4206-001) manufactured by INSTRON Co., After cutting to a width of 15 mm, the distance between the chucks was set to 50 mm, and the tensile speed was measured at a speed of 200 mm / min.

c. Adhesive strength

The urethane-based adhesive prepared by laminating PET and nylon using the thermal adhesive films of the above Comparative Examples and Examples as a sealant was bonded at 230 캜 at 0.2 MPa for 1 second in a heat seal bar, And measured in the direction of 180 degrees at a speed of 300 m / min.

d. Contraction ratio

The 10 x 10 cm specimens of the heat-bondable films prepared in the above Comparative Examples and Examples were left in an autoclave under the retort treatment conditions (120 ° C, 30 minutes), and the longitudinal and transverse lengths were measured.

e. Melting temperature (heat-resistant temperature)

The peel point of the endothermic curve measured at a heating rate of 20 ° C / minute using a differential scanning calorimeter (DSC) manufactured by Perkin-Elmer Co., Ltd. was measured for the heat adhesive films prepared in the above Comparative Examples and Examples Respectively.

From the above Table 1, it can be seen that the melting temperature of the film of Example 1 is about 220 캜, which is superior to that of the conventional thermal adhesive films according to Comparative Examples 1 and 2. In addition, it is excellent in terms of haze and is therefore suitable as a packaging film. The results of thermal shrinkage evaluation for longitudinal and transverse directions under the retort conditions (120 ° C and 30 minutes) show that the heat shrinkage of the sealant should be less than 5% and sufficient adhesive strength of 3.5kgf / 15mm or more, Respectively. As a result, the adhesive strength is higher than that of the conventional polyester-based thermal adhesive film and is superior to the polyolefin-based thermal adhesive film in heat resistance and transparency, and thus it is considered to be suitable for a retort food pouch for a microwave oven.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, It is to be understood that the invention may be practiced within the scope of the appended claims.

Claims (11)

A biaxially oriented polyester heat bonding film comprising a mixed resin of a crystalline polyester and an amorphous copolymerized polyester, The amorphous copolymerizable polyester is a polyester in which dimethyl isophthalate is copolymerized with a polyester selected from the group consisting of polyethylene terephthalate (PET), polybutylene terephthalate (PBT) and polytrimethylene terephthalate (PTT) The biaxially stretched polyester thermal adhesive film has a haze of 10% or less, a melting temperature of more than 200 ° C, an adhesive strength of 1.5 to 5.0 kgf / 15 mm when self-adhered at 200 to 250 ° C for 1 second after lamination with the base layer , And a heat shrinkage ratio in the longitudinal direction and the transverse direction at a temperature of 120 to 150 캜 and a time of 20 to 40 minutes, respectively, of less than 5%. The method according to claim 1, Characterized in that the crystalline polyester is contained in an amount of 10 to 60% by weight and the amorphous copolymerized polyester is contained in an amount of 40 to 90% by weight, based on the total weight of the biaxially stretched polyester thermoadhesive film. Polyester thermal adhesive film. The method according to claim 1, Wherein the crystalline polyester comprises a polybutylene terephthalate (PBT), a polytrimethylene terephthalate (PTT), or a mixed resin thereof. The method according to claim 1, Wherein the amorphous copolymerizable polyester is a polyester selected from the group consisting of polyethylene terephthalate (PET), polybutylene terephthalate (PBT) and polytrimethylene terephthalate (PTT), wherein the content of dimethyl isophthalate is 10 to 25 mol% Lt; RTI ID = 0.0 >%, < / RTI > The method according to claim 1, Wherein the amorphous copolymerizable polyester is a polyester further copolymerized with at least one selected from the group consisting of neopentyl glycol, 1-4-cyclohexanedimethanol and isophthalic acid. . The method according to claim 1, Characterized in that the crystalline polyester is contained in an amount of 10 to 40% by weight and the amorphous copolymerized polyester is contained in an amount of 60 to 90% by weight, based on the total weight of the biaxially stretched polyester thermally adhesive film. Polyester thermal adhesive film. The method according to claim 1, The biaxially oriented polyester heat bonding film is characterized in that it has a single layer structure. The method according to claim 1, Wherein the crystalline polyester and the amorphous copolymerized polyester are polymerized using at least one of Ti and Ge. The method according to claim 1, Wherein the crystalline polyester is contained in an amount of 10 to 40% by weight based on the total weight of the biaxially stretched polyester thermally adhesive film, the amorphous copolymerized polyester is contained in an amount of 60 to 90% by weight, The crystalline polyester and the amorphous copolymerized polyester are polymerized using at least one of Ti and Ge, The biaxially stretched polyester thermally adhesive film has a single layer structure, Characterized in that the biaxially stretched polyester thermoadhesive film is used as a sealant in a retort food packaging material. The method according to claim 1, Wherein the specific gravity of the biaxially stretched polyester thermoadhesive film is from 1.30 to 1.36. The method according to claim 1, Characterized in that the biaxially stretched polyester thermally adhesive film is used as a sealant of a retort food packaging material.