JPH03124443A - Laminated film - Google Patents

Abstract

PURPOSE:To obtain high-sealing strength at a low heat-sealing temperature, by a method wherein a heat-sealing layer is formed of a polybutylene terephthalate copolymer having a specific melting point, in a film obtained by laminating a polybutylene terephthalate layer and the heat-sealing layer to each other. CONSTITUTION:A heat-sealing layer is formed of a polybutylene terephthalate copolymer having the molding point of 140-215 deg.C. An ingredient which is a copolymer polyester obtained by replacing at least a part of one side ingredient out of a terephthalic acid ingredient and 1,4-butandiol ingredient constituting polybutylene terephthalate with the other ingredient and a component replaceable with the former one is bivalent carboxylic acid or its acid anhydride. Ethylene glycol and diethylene glycol are mentioned as diol replaceable with the 1,4-butandiol. Since this film is heat-sealed by heating on a polybutylene terephthalate layer side at a temperature lower than the molding point, high heat-sealing strength is obtained and breakage of the film is not generated at the time of heat-sealing.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a laminated film suitable as a packaging material etc. which is subjected to heat treatment in a microwave oven or retort treatment.

[Prior Art and Problems to be Solved by the Invention] Conventionally, various synthetic resin films such as polyethylene and polypropylene have been used as packaging materials. however,
These films generally do not have sufficient heat resistance, oil resistance, fragrance retention, etc.

On the other hand, polybutylene terephthalate film is known as a film having excellent heat resistance and mechanical strength. Like polyethylene terephthalate film, this polybutylene terephthalate film has excellent gas barrier properties, chemical stability such as oil resistance, and hygiene, and also has higher elongation, tear strength, and impact strength than polyethylene terephthalate film. It has many advantages. In particular, polybutylene terephthalate film is non-stretched and has excellent heat resistance, so it has a characteristic that the shrinkage rate of the film at high temperatures is extremely small. Therefore, polybutylene terephthalate, which has such excellent properties, is useful as a packaging material that has excellent protection properties for contents and requires heat resistance, such as packaging materials for foods that are heated in a microwave or retort. be.

However, heat-sealing a highly heat-resistant film generally requires a high heat-sealing temperature.

That is, in the case of polybutylene terephthalate film, heat sealing can only be performed at a temperature of about 225° C. or higher.

Furthermore, polybutylene terephthalate has a low heat sealing strength even when heat sealing a polybutylene terephthalate film at a high temperature, probably because it has a high crystallization rate. Furthermore, since the appropriate heat-sealing temperature range is narrow, there is a problem in that when a polybutylene terephthalate film is heat-sealed at high temperatures, the strength of the boundary area between the sealed portion and the non-sealed portion is significantly reduced, leading to breakage. As described above, although polybutylene terephthalate has excellent properties, its uses are severely limited.

Therefore, the object of the present invention is to obtain high heat-sealing strength at a low heat-sealing temperature while using a polybutylene terephthalate layer as a constituent element, and to have high heat resistance and oil resistance so that the film does not break during heat sealing. It is also an object of the present invention to provide a laminated film having excellent fragrance retention and the like.

[Structure of the Invention] The present invention is a film in which a polybutylene terephthalate layer and a heat-sealing layer are laminated, and the heat-sealing layer is formed of a polybutylene terephthalate copolymer having a melting point of 140 to 215°C. The above-mentioned problems are solved by the laminated film.

In addition, in this specification, melting point is JIS K712
This is a value measured using a differential scanning calorimeter (D SC) under the conditions of a heating rate of 10° C./min in accordance with 1.

Polybutylene terephthalate, which is a constituent material of the laminated film of the present invention, has a melting point of about 225° C. and is excellent in heat resistance, aroma retention, oil resistance, etc.

Moreover, polybutylene terephthalate film usually exhibits a crystal-like luster and has a good appearance. It also has excellent heat resistance, mechanical strength, and gas barrier properties against oxygen gas and water vapor, so when used as a packaging film, it provides excellent protection for contents.

The thickness of the polybutylene terephthalate layer can be set as appropriate, but is usually 10 to 1000 μm, preferably 15 to 50 μm.
It is about 0 μm. If the film thickness of the polybutylene terephthalate layer is less than 10 μm, it is difficult to form a uniform layer by extrusion molding, etc., and if it exceeds 1000 μm,
The film becomes excessively thick and is not economical.

A heat seal layer is laminated on the polybutylene terephthalate layer made of polybutylene terephthalate. The polybutylene terephthalate copolymer constituting this heat-sealing layer has the same or similar constitutional units to those of polybutylene terephthalate, so it has excellent adhesion to the polybutylene terephthalate layer, and
Shows properties similar to polybutylene terephthalate. Therefore, the properties of the laminated film containing the polybutylene terephthalate layer are not significantly degraded.

In addition, polybutylene terephthalate-based copolymer is a copolymerized polyester in which at least a part of at least one of the terephthalic acid component and 1,4-butanediol component that constitutes polybutylene terephthalate is replaced with another component. means.

In the polybutylene terephthalate copolymer, components that can partially replace the terephthalic acid component include divalent carboxylic acids or their acid anhydrides, such as maleic acid, maleic anhydride, succinic acid, adipic acid, and pimeline. aliphatic dicarboxylic acids such as speric acid, azelaic acid, sebacic acid, dodecanoic acid; alicyclic dicarboxylic acids such as 1,4-cyclohexanedicarboxylic acid; phthalic acid, phthalic anhydride, isophthalic acid, naphthalene-2,6 -dicarboxylic acid,
Examples include aromatic dicarboxylic acids such as diphenyl-4,4'-dicarboxylic acid and 3-sulfoisophthalic acid. At least one of these divalent carboxylic acids or acid anhydrides can be used.

Examples of diols that can replace a part of the 1,4-butanediol component include ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, polypropylene glycol, and triethylene glycol. , 1,3-butylene glycol, neopentyl glycol, 1.5-bentanediol, 1.6-hexanediol, aliphatic diols such as polymethylene glycol; 1,4-cyclohexyl glycol, 1,4-cyclohexanediol Alicyclic diols such as metatool, 2,2-bis(4-hydroxycyclohexyl)bronokun, etc., and adducts of hydrogenated bisphenol A and alkylene oxides such as ethylene oxide and propylene oxide; resorcinol, 2
．． 2-bis(4-hydroxyphenyl)pronodone, an adduct of bisphenol A and an alkylene oxide such as ethylene oxide or propylene oxide, such as 2,2'-bis(4-hydroxyethoxyphenyl)
Pronosun, 2,2'-bis(4-hydroxyjethoxyphenyl)pro! Man, 2.2'-bis(4-hydroxypolyethoxyphenyl)propane, 2.2'-bis(4-hydroxypropoxyphenyl)pronokun,
2.2'bis(4-hydroxydipropoxyphenyl)
Aromatic diols such as propane and 2,2'-bis(4-hydroxypolypropoxyphenyl)propane are exemplified. At least one of these diols can be used.

A portion of the terephthalic acid component and the 1,4-butanediol component may be substituted with hydroxycarboxylic acid. Examples of hydroxycarboxylic acids include aliphatic hydroxycarboxylic acids such as glycolic acid and oxypropionic acid; aromatic hydroxycarboxylic acids such as hydroxybenzoic acid, and at least one of them can be used.

At least one of the substituent components consisting of divalent carboxylic acid or its acid anhydride, diol, and hydroxycarboxylic acid
It is preferable that this component substitutes 5 to 75 mol%, particularly 10 to 50 mol%, of at least one of the terephthalic acid component and the 1,4-butanediol component corresponding to the above-mentioned substituted component. If the amount of substitution component is less than 5 mol %, it is difficult to lower the heat sealing temperature, and if it exceeds 75 mol %, the properties of the polybutylene terephthalate copolymer itself deteriorate.

The weight average molecular weight of the polybutylene terephthalate copolymer is usually about 5,000 to 1,000,000, preferably about 10,000 to 500,000.

The polybutylene terephthalate copolymer has a melting point of 140 to 215°C, preferably 160 to 195°C.
°C copolymer is used. That is, the melting point of the polybutylene terephthalate copolymer is 140°C or higher, preferably 160°C or higher, and about 10°C or lower, preferably about 30°C or lower, than the polybutylene terephthalate.

The melting point of polybutylene terephthalate copolymer is 140℃
If it is less than 215° C., it will not be able to withstand heating in a microwave oven or retort treatment, and if it exceeds 215° C., it will be difficult to obtain high heat sealing strength at a low heat sealing temperature. Note that as the difference in melting point between polybutylene terephthalate and polybutylene terephthalate copolymer increases, the temperature range in which heat sealing can be performed expands, and greater heat sealing strength can be obtained.

The intrinsic viscosity of the polybutylene phthalate copolymer is at least about 0.5 dJ/g, preferably 0 when using the solvent 0-chlorophenol at a temperature of 25 ± 1°C.
．． It is about 75~2°5 dl.

The thickness of the heat-sealing layer can be set appropriately depending on the use of the film, but it is usually 5 to 250 μs, preferably 10 μs.
It is about 100 μm. The thickness of the heat seal layer is 51
If it is less than #, the heat sealing strength will be low and 250μ
If it exceeds m, the film becomes excessively thick and is not economical.

This type of laminated film can be heat-sealed by heating from the polybutylene terephthalate layer side at a heat-sealing temperature lower than the melting point of the polybutylene terephthalate that makes up the polybutylene terephthalate layer. Strength can be obtained, and the film does not break during heat sealing.

The heat sealing temperature is not particularly limited as long as it is below the melting point of polybutylene terephthalate and above the melting point of the polybutylene terephthalate copolymer, but is usually about 150 to 210°C, preferably 175 to 20°C.
The temperature is about 0°C. When heat sealed in this way,
Although it uses a polybutylene terephthalate layer as a component, it can be heat-sealed smoothly and reliably.

The polybutylene terephthalate layer and/or heat-sealing layer constituting the laminated film of the present invention may contain other polymers and additives as long as the properties, heat-sealability, etc. of each layer are not impaired.

Other polymers include, for example, polyethylene, polypropylene, ethylene-vinyl acetate copolymer, ethylene-vinyl acetate copolymer,
Olefin polymers such as ethyl acrylate copolymers and ionomers; acrylic polymers; styrenic polymers such as polystyrene and styrene-acrylic copolymers; other polyesters such as polyethylene terephthalate; polyacetals; polyvinyl acetate; polyvinyl chloride; Polyvinylidene chloride, vinylidene chloride-acrylonitrile copolymer, vinylidene chloride-vinyl chloride copolymer, vinylidene chloride-vinyl acetate copolymer, vinylidene chloride-acrylic acid copolymer, vinylidene chloride-methacrylic acid copolymer, vinylidene chloride - Vinylidene chloride polymers such as acrylic acid ester copolymers and vinylidene chloride-methacrylic acid ester copolymers; Chlorinated polyolefins such as chlorinated polypropylene; Cellulose polymers; Vinyl chloride-
Examples include vinyl acetate copolymers. These polymers may be used alone or in combination of two or more.

Examples of additives include antioxidants, ultraviolet absorbers, heat stabilizers, plasticizers, antistatic agents, tackifiers, plasticizers, fillers, waxes, lubricants, dyes and pigments, and the like.

The laminated form of the laminated film of the present invention is not particularly limited as long as the heat seal layer is located on at least one surface of the laminated film.

The laminated film of the present invention can be laminated by a conventional method, for example, by coextrusion, by extruding a molten resin composition to form a heat-sealing layer onto a polybutylene terephthalate film, or by laminating with an adhesive layer interposed therebetween. It can be manufactured by laminating a polybutylene terephthalate layer and a heat seal layer.

The laminated film of the present invention exhibits high mechanical strength even in an unstretched state, so stretching treatment is not necessarily necessary.
Uniaxial or biaxial stretching treatment may be performed as necessary. Examples of stretching methods include roll stretching, rolling stretching, belt stretching,
Conventional stretching methods such as tenter stretching, tube stretching, and a combination thereof can be applied. The stretching ratio can be set as appropriate depending on the desired properties of the film, for example from 1.5 to
It is about 20 times, preferably about 2 to 15 times. If the stretching ratio is less than 1.5 times, the stretching effect will be small, and if it exceeds 20 times, it will be excessively stretched and productivity will decrease.

The stretching process is carried out at a temperature below the melting point of the polymer constituting the film and above the secondary transition point. Further, after stretching the film, it may be heat-set by heating in order to fix the molecular orientation.

Further, the surface of the laminated film may be subjected to surface treatment such as corona discharge treatment, high frequency treatment, flame treatment, chromic acid treatment, solvent treatment, etc.

Furthermore, a coating layer, such as a gas barrier layer, an antistatic layer, a slippery layer, etc., may be formed on the surface of the laminated film, particularly on the surface of the polybutylene terephthalate layer, depending on the application.

The laminated film of the present invention can be used in a wide range of applications, such as individual packaging for foods, interior and exterior packaging films, etc., but it can also be used in applications that require heat resistance, such as heating in a microwave oven. It is suitable as a film for sealing the opening of a cooking container, a packaging film for retort food, and the like.

[Effects of the Invention] As described above, according to the laminated film of the present invention, the heat seal layer laminated on the polybutylene terephthalate layer is formed of a polybutylene terephthalate copolymer having a specific melting point. Even though the polybutylene terephthalate layer is used as a component, high heat-sealing strength can be obtained at a low heat-sealing temperature, and the film does not break during heat-sealing. It also has excellent heat resistance, oil resistance, fragrance retention, etc.

[Examples] The present invention will be described in more detail below based on Examples.

Example 1 Polybutylene terephthalate (made by Polyplastic ■,
A polybutylene terephthalate copolymer (trade name: DURANEDUX 500FP) and a polybutylene terephthalate copolymer (melting point 205°C) were mixed using a normal coextrusion molding machine to form a polybutylene terephthalate layer with a thickness of 15 μm. A laminated film having a heat seal layer thickness of 10 μm was obtained.

In addition, as a polybutylene terephthalate copolymer,
50 mol% of dicarboxylic acid consisting of a ratio of terephthalic acid/isophthalic acid-87.5/12.5 (molar ratio);
A polyester copolymerized with 50 mol% of 4-butanediol was used.

Example 2 In place of the polybutylene terephthalate copolymer of Example 1, 50 mol% of terephthalic acid and 1°4-butanediol/2,2-bis(4-hydroxyethoxyphenyl)propane-90/10 ( molar ratio)
Polybutylene terephthalate copolymer with 0 mol% (
Melting point: 206° C.), and in the same manner as in Example 1, a laminated film having a polybutylene terephthalate layer with a thickness of 15 μm and a heat seal layer with a thickness of 10 μm was obtained.

Comparative Example A film having a thickness of 25#ffi was obtained from the polybutylene terephthalate of Example 1 using a conventional T-die extruder.

The films obtained in each example were heated to a temperature of 2
Heat sealing was performed under the conditions of 10°C, pressure of 1 k'3/crA, and pressurization time of 1 second, and the peel strength of the heat-sealed portion was determined at a peel rate of 100 mm/min. In addition,
The film obtained in the comparative example could not be heat-sealed under the above heat-sealing conditions, so
Under the conditions of 40°C, pressure 1 kg/aJ, and pressurization time 1 second,
Heat seal and test the heat seal strength (
r/15mm) was measured.

The results are shown in the table.

As is clear from the table, the films of the comparative examples require high temperatures for heat sealing and have low heat seal strength. In addition, the film of the comparative example had a breaking force (produced) during heat sealing, making it difficult to heat seal it smoothly.

On the other hand, it was found that the laminated films of Examples 1 and 2 exhibited large heat-sealing strength even at low heat-sealing temperatures, and the film did not exhibit any breaking force.

Claims (1)

[Claims] A film in which a polybutylene terephthalate layer and a heat-sealing layer are laminated, the heat-sealing layer comprising:
A laminated film formed of a polybutylene terephthalate copolymer having a melting point of 40 to 215°C.