KR102271966B1 - Polyester sheet of multi-layer structure with excellent thermal resistance and food container thereby - Google Patents

Abstract

The present invention relates to a polyester sheet having a multilayer structure having excellent heat resistance and a food container manufactured therefrom. The polyester sheet having a multilayer structure having excellent heat resistance according to the present invention has PET (Polyethylene terephthalate) and PBT (Polybutylene terephthalate) in an upper layer and a lower layer. ) by adding an adhesive resin to the mixed resin containing It is integrally molded by the co-extrusion process and has the effect of heat sealing, and the food container manufactured therefrom has the advantage that it can be cooked in a microwave oven.

Description

Polyester sheet of multi-layer structure with excellent thermal resistance and food container prepared therefrom

The present invention relates to a polyester sheet having a multilayer structure with excellent heat resistance and a food container manufactured therefrom, and more particularly, to supplement the heat resistance of polyester sheets that are useful in real life because of their good transparency, strength and processability. Polyethylene terephthalate (PET) and polybutylene terephthalate (PBT) are mixed to provide a polyester sheet with excellent heat resistance that can be usefully used for cooking in a microwave oven, such as a lunch box, and a food container manufactured therefrom.

In order to maintain the freshness of the food and prevent deterioration in the distribution process of the food, the food is sealed with a packaging material such as a packaging container or a packaging film. However, if the food packaging material is not suitable, the food deteriorates under the influence of moisture, oxygen, light, etc. during distribution, and various microorganisms grow, and the fat and major vitamins are oxidized and the nutrition deteriorates. will do

In particular, it is important to select an appropriate packaging material because freshness is important for processed meat foods such as sausages and hams, and foods that are easily perishable such as lunch boxes or various meats, and the characteristics of these packaging materials require functionality in various areas. Among them, the gas barrier property is a property that determines the preservation of food, and the demand for such functionality is increasing according to the diversification of packaging technology, the distribution period and form, and regulations on packaging materials in the environmental aspect.

In the food packaging field, long-term preservation is the most important function required for packaging materials according to recent changes in dietary habits and distribution patterns. Factors that accelerate the deterioration of food include oxygen, light, heat, and moisture. Among them, oxygen permeation is the most influential factor in inducing oxidation, which is the most common form of food deterioration. There are always points that are unsuitable for microwave and oven cooking.

Various packaging containers have been developed for this purpose, but conventional food packaging containers are made of a polypropylene layer, an oxygen barrier layer, an adhesive layer, and the like, and thus have poor heat resistance and impact resistance, which is disadvantageous for food packaging. Considering this point, the food container can be manufactured in consideration of its thickness, but there is a problem in that the production cost increases as the cost of molding and manufacturing the container increases.

Polyethylene (PE), polypropylene (PP), and polyvinyl chloride (PVC) are the most widely used general-purpose materials for product packaging. Currently, convenience store lunch boxes are mostly manufactured using PP with good heat resistance. . However, although PP has good heat resistance, it has disadvantages in terms of strength, transparency, and processability. In recent years, PET resin, a type of engineering plastic, is being used a lot as a packaging material in order to show the appearance of the product more clearly and to express the packaged contents in a luxurious way. to be.

These PET containers are not distorted or corroded inside, and there is no risk of contents leaking due to easy tearing or abrasion like cartons. is increasing Furthermore, in order to solve the conventional problems, a sheet of a multi-layer structure is molded through a lamination process to manufacture a food container, but there is a problem in that the sheets are peeled from each other due to lamination between different materials, and there are still many problems in heat resistance for microwave and oven cooking. is holding

In order to solve the conventional problems as described above, the peelable polyester film having an oxygen film of Korean Patent Application Laid-Open No. 10-2005-0045865 (Mitsubishi Polyester Film GMBH, Germany) is a base layer (B) and APET /Contains a heat-sealable outer layer (A) that is peelable from /CPET and CPET, wherein the sealable outer layer (A) comprises: a) 80 to 99% by weight of polyester; and b) 1 to 10 wt% of organic particles and/or inorganic particles having an average particle diameter d50 of 2.5 to 12 μm, c) 12 to 89 wt% of a unit derived from at least one aromatic dicarboxylic acid of the polyester and 11 to 88% by weight of a unit derived from at least one aliphatic dicarboxylic acid, the sum of the dicarboxylic acids is configured to constitute 100 mol%, d) the d50 and the layer thickness dA of the outer layer (A) The ratio of is greater than or equal to 1, and the base layer (B) describes a coextruded biaxially oriented polyester film comprising poly(m-xyleneadipamide) (MXD6).

In addition, the same Patent Publication No. 10-1200241 (Dongseo Co., Ltd.) discloses an aluminum foil layer 200 and a gravure printing layer 300 on the upper surface of the protective layer 100 for preventing wrinkling and maintaining the shape of food packaging. ) and the base film layer 400, in the multilayer film for food packaging formed by sequentially laminating and laminating, the protective layer 100 is a core layer 110 having a predetermined thickness and an upper / A multilayer film for food packaging, characterized in that it is integrally formed by laminating and laminating LLDPE layers 120 each having a predetermined thickness on the lower surface, and can simultaneously improve the strength, moisture permeability, and breakability of the packaging material. It is said that it can be safely stored for a long period of time and that anyone can easily open the packaging to improve the convenience of use.

In addition, in the same Patent Publication No. 10-1459275 (Toray Chemical Co., Ltd.), (A) a first base film layer and (B) a second blend film layer on the other side of the (A) first base film layer A molded article for food packaging comprising a laminated multi-layer sheet, wherein (A) the thickness of the first base film layer is 600-700 μm; (B) the thickness of the second blend film layer is 40-60 ㎛; The (A) first base film layer is selected from among polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyethylene terephthalate glycol (PETG), and polycyclohexylenedimethylene terephthalate glycol (PCTG). at least a first polymer resin film layer; The (B) second blend film layer comprises 90-98% by weight of the second polymer resin and 2-10% by weight of the third polymer resin; the second polymer resin is at least one selected from polyethylene terephthalate glycol (PETG) and polycyclohexylenedimethylene terephthalate glycol (PCTG); The third polymer resin is a molded article for food packaging using a co-extrusion method, characterized in that at least one selected from linear low-density polyethylene (LLDPE), low-density polyethylene (LDPE), high-density polyethylene (HPDE), and polypropylene (PP). has been

In addition, the same Patent Publication No. 10-1539711 (DuPont Teijin Films U.S. Limited Partnership, USA) discloses a container and a thermoformable composite polymer film cover that can be heat-sealed thereto for storing and cooking food comprising a cover. An oven heatable vacuum skin package comprising: (i) a thermoformable substrate comprising a first copolyester material comprising units of terephthalic acid, azelaic acid, ethylene glycol and diethylene glycol; layer; and (ii) a heat-sealable layer on the surface of the base layer comprising a second copolyester material different from the first copolyester material, i. the bowl comprising on the surface of the bowl a sealing region comprising a flat flange and in contact with the heat sealable layer to form a seal; ii. 0.02mg per soluble extract of food contact surface exposed to the solvent 1in ² (- bowl and thermoforming the composite polymeric film cover both the food contact surface when exposed to chloroform, distilled water for 2 hours at 250 ℉ (121 ℃) 0.0031 mg/cm ² ) should not be exceeded; When in 150 ℉ exposed to n- heptane for 2 hours, the food contact surface The chloroform-requirements that must not be soluble extract exceeds 0.02mg (0.0031mg / cm ²⁾ per a 1in ² of food contact surface exposed to the solvent follow; wherein the first copolyester material has a crystallinity of less than 50% and the thermoformable composite polymer film cover can be vacuum thermoformed to conform to the surface of a food product.

And in the same Laid-Open Patent Publication No. 10-2017-0081370 (Dongwoo Fine Chem Co., Ltd.), it includes an inner layer, a gas barrier layer and an outer layer sequentially stacked, and the gas barrier layer is made of an ethylene-vinyl acetate copolymer, and the As a multilayer film for food packaging containers having a vinyl acetate content of 21 to 40% by weight in the ethylene-vinyl acetate copolymer, it is possible to prepare a multilayer film having excellent inter-film adhesion without using a separate adhesive for adhesion between the film and the film. It is described that it is possible to simplify the manufacturing process of the multilayer film as well as to have excellent gas shielding properties.

On the other hand, in the present invention, in the polyester sheet of a multilayer structure made of PET (Polyethylene terephthalate), in order to compensate for the shortcomings of the heat resistance and moldability of the PET sheet, the upper layer and the lower layer are mixed with PET and PBT, and the middle layer is composed of PET, The present invention was completed by developing a polyester sheet having a multi-layered structure with excellent heat resistance that can be usefully used for microwave cooking by integrally molding by an extrusion process and a food container manufactured therefrom.

Laid-open Patent Publication No. 10-2005-0045865 (published on May 17, 2005) Registered Patent Publication No. 10-1200241 (Announcement date: November 12, 2012) Registered Patent Publication No. 10-1459275 (Announcement date November 07, 2014) Registered Patent Publication No. 10-1539711 (Announcement Date July 27, 2015) Publication No. 10-2017-0081370 (published on July 12, 2017)

An object of the present invention is to improve the problem of a food container made of a polyester sheet that cannot be used because of its low heat resistance and cannot maintain its original shape when cooked in a microwave oven, and has a multilayer structure made of PET (Polyethylene terephthalate). of polyester sheet, by mixing PBT (Polybutylene terephthalate) in the upper and lower layers, the formability is good and the heat resistance is improved to 110°C or higher (130°C), and the sheets are peeled from each other due to lamination between different materials It is an object to provide a polyester sheet having a multilayer structure that is integrally molded by a triple co-extrusion process, heat sealing is possible, and has excellent heat resistance, and a food container manufactured therefrom as well as to prevent the problem of being formed.

The polyester sheet having a multilayer structure having excellent heat resistance of the present invention is a polyester sheet having a multilayer structure formed by a co-extrusion process, wherein the upper and lower layers are PET (Polyethylene terephthalate) and PBT (Polybutylene terephthalate) 20 to 70:30 It is constituted by adding an adhesive resin in a range of 0.1 to 5% by weight to a mixed resin containing a weight ratio of ~ 80, and the intermediate layer between the upper and lower layers is made of PET (Polyethylene terephthalate), and the upper layer, the middle layer, and the lower layer are 3 It is characterized in that it is integrally molded by a hollow co-extrusion process.

According to a preferred embodiment of the present invention, the adhesive resin uses any one selected from rubber, acryl, and urethane, and the polyester sheet of the multilayer structure has a total thickness of 0.2 ~ As 2 mm, the thickness of the middle layer compared to the upper or lower layer is characterized in that it is molded in a ratio of 1:1 to 2.5.

The polyester sheet having a multi-layer structure with excellent heat resistance according to the present invention is formed by adding an adhesive resin to a mixed resin containing PET (Polyethylene terephthalate) and PBT (Polybutylene terephthalate) in the upper and lower layers, so that the sheet is formed without using a separate adhesive. It not only simplifies the manufacturing process by solving the problem of peeling from each other, but also improves the heat resistance of the sheet to 110°C or higher, and is integrally molded by the triple co-extrusion process, thereby enabling heat sealing. The manufactured food container has the advantage that it can be cooked in a microwave oven.

BRIEF DESCRIPTION OF THE DRAWINGS It is sectional drawing which shows the polyester sheet of the three-layer structure by this invention.

Hereinafter, with reference to the drawings, it will be described in detail with respect to the polyester sheet having a multilayer structure excellent in heat resistance of the present invention and a food container prepared therefrom, which will be described in detail by those of ordinary skill in the art to which the present invention belongs (hereinafter ' It is intended to illustrate the extent to which those skilled in the art can easily carry out the invention), and this does not mean that the technical spirit and scope of the present invention are limited thereto.

As shown in FIG. 1, in the polyester sheet having a multilayer structure having excellent heat resistance according to the present invention, the upper layer 100 and the lower layer 300 are PET (Polyethylene terephthalate) and PBT (Polybutylene terephthalate) 20 ~ 70: 30 ~ It is composed by adding an adhesive resin in the range of 0.1 to 5% by weight to the mixed resin containing 80 in a weight ratio, and the intermediate layer 200 between the upper layer 100 and the lower layer 300 is made of PET (Polyethylene terephthalate), The upper layer 100 , the middle layer 200 , and the lower layer 300 are integrally formed by a triple co-extrusion process.

The saturated polyester used in the present invention refers to a linear thermoplastic polymer having an ester bond in the main chain, and unlike unsaturated polyester, does not include an unsaturated bond involved in curing in the molecule. In principle, since it can be synthesized by polycondensation of dibasic acid and glycol, various kinds of saturated polyesters can be manufactured, but they are mainly consumed as synthetic fibers and films made of polyterephthalate. As a saturated polyester other than polyethylene terephthalate (PET) so far, polybutylene terephthalate (PBT) is in demand as an engineering plastic excellent in moldability.

The properties of the saturated polyester vary depending on its structure, but it has excellent surface smoothness and a glossy appearance. PET and PBT both have high melting point and crystallinity, and show excellent dimensional stability because they have low water absorption and thermal expansion coefficient. However, PET has problems such as impact resistance and heat resistance due to its crystallization properties, but other mechanical properties are very excellent like other saturated polyesters. In addition, it can be said that it is a well-balanced resin with good electrical properties and weather resistance.

PET, a kind of saturated polyester, is a kind of engineering plastic. It has good transparency and strength and good processability, so it is useful in real life. However, its heat resistance is somewhat weak, so it cannot maintain its original shape when used for microwave cooking. There is a problem that it cannot be used due to deformation. On the other hand, PBT is a crystalline resin like PET, but it has a lower crystallization region than PET, crystallization is quicker, and has excellent properties as a molding material because of its low viscosity when bonding and good fluidity in the mold. .

In addition, since PBT has small deformation in the molding step, heat resistance up to 150° C. and flame retardancy, and maintains transparency even during rapid cooling to maintain the same transparency as PET, in the present invention, the heat resistance and moldability of PET In order to improve the , the upper layer 100 and the lower layer 300 contain polyethylene terephthalate (PET) and polybutylene terephthalate (PBT) in a weight ratio of 20 to 70: 30 to 80 in a weight ratio of 80 to a mixed resin containing an adhesive resin in the range of 0.1 to 5% by weight. is added, and the intermediate layer 200 is made of PET (Polyethylene terephthalate).

The properties of these saturated polyesters vary depending on their structure, but they generally have a rich surface smoothness and a glossy appearance. PET and PBT both have a high melting point and crystallinity, and show excellent dimensional stability because of their low water absorption and thermal expansion coefficient. However, PET and PBT have different properties due to ethylene and butylene polymers, respectively, and thus have disadvantages in bonding properties. Among the mixed resins, rubber, acryl, or urethane When the adhesive strength with the intermediate layer 200 composed of PET is increased by adding any one selected adhesive resin in the range of 0.1 to 5% by weight, it is manufactured by solving the problem of sheets peeling from each other without using a separate adhesive. The process is not only simple, but the heat resistance of the sheet is improved to 110° C. or higher, and the upper layer 100, the middle layer 200, and the lower layer 300 are integrally formed by the triple co-extrusion process to block heat (heat). sealing) is possible.

Since the polyester sheet as described above cannot be heat sealed by a single-layer structure, it can be made into a three-layered sheet for heat sealing and at the same time to manufacture food containers with excellent moldability and heat resistance. The polyester sheet of the multi-layer structure has a total thickness of 0.2 to 2 mm, and the thickness of the middle layer 200 compared to the upper layer 100 or the lower layer 300 is preferably molded in a ratio of 1:1 to 2.5, the intermediate layer By forming the thickness of 200 to be slightly thicker than the upper layer 100 or the lower layer 300, the performance of the product due to excellent strength can be more firmly guaranteed, and from this, a polyester sheet with a multi-layer structure that can be cooked in a microwave oven. It is possible to obtain a food container to be manufactured.

Hereinafter, an example in which a food container made of a polyester sheet having a multilayer structure according to the present invention is tested will be described, but the present invention will be described through a preferred embodiment that can be easily understood and practiced by those skilled in the art. Explain.

[Example 1]

1. A molded article obtained by vacuum-forming a polyester sheet with a multilayer structure formed of an upper layer (PET+PBT, 0.2mm)/intermediate layer (PET, 0.36mm)/lower skin layer (PET+PBT, 0.2mm) by a triple co-extrusion process (tray, lid part) is prepared.

2. Boil water in an electric kettle.

3. Put 1/2 of boiling water in the tray and check the condition by attaching the lid.

4. Based on our own test: Is there any deformation of the molded product after 3 minutes

division plain PET invention


before use

after 3 minutes

As shown in Table 1, the conventional container made of general PET does not maintain the shape of the molded article as it is after 3 minutes, whereas the molded article manufactured by the present invention has no external deformation of the molded article even after 3 minutes. It has been confirmed that the gas shielding property is excellent and there is no generation of harmful substances harmful to the human body.

[Example 2]

1. Prepare a vacuum-formed general PET molded product and a PET molded product (0.7t) according to the present invention.

2. Put food in the trays of both molded products and fix the lid with a stapler.

3. Put it in a microwave of 700W and check the condition by operating it by time.

4. Based on our own test: No deformation of the molded product after 2 minutes and 30 seconds of microwave operation

before the test After 2 minutes and 30 seconds of operation

General PET (left) and the present invention (right)

As a result of the microwave test as in Example 2, it was confirmed that the general PET molded article was deformed to the extent that both the tray and the lid could not maintain the original shape in 1 minute and 30 seconds after starting from 30 seconds of operation. It was confirmed that PET molded products can maintain good condition for more than 2 minutes and 30 seconds (about 4 minutes), so that they can sufficiently function as a food container such as a microwave-cooked lunch box.

Therefore, the polyester sheet of the multilayer structure according to the present invention can be substituted, modified and changed in various forms within the scope of the present invention without departing from the technical spirit of the present invention. As a functional material for sheet products, it can be used in various uses and forms.

100: upper layer (PET + PBT)
200: intermediate layer (PET)
300: lower layer (PET + PBT)

Claims (4)

In the polyester sheet of a multilayer structure molded by a co-extrusion process,
The upper layer 100 and the lower layer 300 are mixed resin containing PET (Polyethylene terephthalate) and PBT (Polybutylene terephthalate) in a weight ratio of 20 to 70: 30 to 80, rubber, acrylic, or urethane ( Urethane) by adding any one type of adhesive resin selected from 0.1 to 5% by weight,
The intermediate layer 200 between the upper layer 100 and the lower layer 300 is made of PET (Polyethylene terephthalate),
The upper layer 100, the middle layer 200, and the lower layer 300 have a total thickness of 0.2 to 2 mm by a triple coextrusion process, and the thickness of the middle layer 200 compared to the upper layer 100 or the lower layer 300 is 1: A polyester sheet having a multilayer structure with excellent heat resistance, characterized in that it is integrally molded at a ratio of 1 to 2.5. delete delete A food container manufactured from the polyester sheet of claim 1 having a multi-layered structure having excellent heat resistance.

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