JPH0562067B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a heat-resistant container that can be heated together with cooking materials in a heating device such as an oven or a microwave oven.

Conventionally, ovens and microwave ovens each use separate containers, and cooking ingredients are placed inside the containers for cooking. Among these, ovens mainly use rolled metal products, and the container is heated together with the cooking ingredients, so for example, cakes have a temperature of 150 -
Heating is done at 180°C, and for gratin at 210-230°C. Therefore, extremely high heat resistance is required.
Moreover, heat-resistant glass containers are mainly used in microwave ovens. This is because metal may cause burnout in a microwave oven, so not only metal containers, but also containers with metal designs cannot be used. Containers such as those described above are heavy, and as containers for household heating equipment, which are often used by women, lighter and more heat-resistant containers are required.

However, while plastic has the advantage of being lightweight, it also has the disadvantage of poor heat resistance.
However, although there are heat-resistant plastics such as polymethylpentene and polysulfone, they are very expensive, and there has been a need for a marketable, low-cost, heat-resistant container. Focusing on the crystallinity of the resin, the amorphous portion melts at low temperatures, but the crystalline portion does not melt at very high temperatures. Therefore, this objective should be achieved if the crystal has high crystallinity and is heat resistant.

However, for example, if a molded product is formed by mixing a nucleating material into polyethylene terephthalate resin and crystallizing the molded product, the heat resistance will certainly improve, but on the other hand, it will become brittle and easily crack or chip. Furthermore, if heating and cooling are continued repeatedly, crystallization progresses even further.

The present invention aims to solve the above problems. That is, it includes an outer surface layer mainly composed of a homopolymer of polyethylene terephthalate, and at least one intermediate layer mainly composed of a copolymer of polyethylene terephthalate,
It is a multilayer heat-resistant container whose inner surface layer is made of polyethylene terephthalate homopolymer.

In addition, embodiments include those in which a nucleating agent is mixed into the inner and outer surface layers mainly composed of the homopolymer of polyethylene terephthalate, and those in which the crystallinity of the inner and outer surface layers is 40% or more,
The container is made of polyethylene terephthalate homopolymer, which is a multilayer heat-resistant container that accounts for 60 to 90 percent of the container's total volume. I will explain in more detail. Polyethylene terephthalate is a condensation product of ethylene glycol and terephthalic acid, and ester bonds are generated during polymerization. Both glycol and basic acid are 2
Each has a reactive group, so they react one after another,
Create polymers with a high degree of polymerization. As described above, a polyethylene terephthalate homopolymer is a polyethylene terephthalate homopolymer that is polymerized using only two components: ethylene glycol as a glycol and terephthalic acid as a dibasic acid, and has high crystallinity and a high melting point. Among the above two components, the glycol can be changed to a glycol other than ethylene glycol, such as neopentyl glycol, or the dibasic acid can be changed to a dibasic acid other than terephthalic acid, such as isophthalic acid. If a copolymer is prepared by containing 5 to 40 percent of a component that can be replaced with another material, a resin with low crystallinity and strong adhesion to homopolymers can be obtained.

In order to form multiple layers of the above homopolymer and copolymer of polyethylene terephthalate, there are methods such as injection molding and extrusion followed by air pressure molding. For example, using an injection molding machine with two injection cylinders, first filling the mold cavity with insufficient homopolymer to fill the mold cavity;
Next, by injection molding the copolymer before the resin solidifies in the gate area or cavity, we are considering obtaining a multilayer sandwich injection molded container in which the surface of the copolymer layer is covered with a homopolymer. It will be done. In addition, there is a method in which a copolymer injection molded product is placed in a mold with a larger cavity, and then a homopolymer is injected, fused and solidified, and a coextruded sheet is pressure molded. Possible methods include vacuum forming.

Copolymerized polymers are elastic, and even under thermal conditions where homopolymers undergo crystallization and become brittle, they hardly crystallize and do not crack easily. Furthermore, crystallization of homopolymers progresses by applying a temperature of 150 to 200°C. Preferably, when an inorganic substance of 0.01 to 1 micrometer is added to the homopolymer as a nucleating material and heated, crystallization proceeds. Originally, it would be heated at a temperature above the secondary dislocation point and below the melting point, but of course it is heated at a temperature lower than the melting point of the copolymer to promote crystallization of the homopolymer. Therefore, it is preferable that the copolymer has as high a melting point as possible. From this point of view, it is necessary to select a dibasic acid containing an aromatic nucleus with good symmetry or a glycol with good symmetry as the third component of the copolymer, and at the same time, keep the amount of contamination low and keep it at 5 to 10%. It is necessary to keep it.

That is, if it is less than 5%, crystallization will progress and the product will become brittle.

Moreover, if it is more than 10%, the melting point will be lowered so much that it will not be possible to improve the heat resistance of the homopolymer, so it is preferable to keep it in the range of 5 to 10%.

Dibasic acids containing aromatic nuclei with good symmetry and glycols with good symmetry as copolymerization components with polyethylene terephthalate are, for example, dicarboxylic acids such as (4,4')-biphenyldicarboxylic acid, (3,7)-naphthalene dicarboxylic acid etc. can be used, and as the diol, (4,
4')-biphenyl diol, (3,7)-naphthalene diol, bisphenol A type diol, etc. can be used.

In addition, when the inner and outer surface layers, that is, homopolymers, are crystallized, the internal molecular chains are strongly bonded and show improved heat resistance. Heat-resistant,
Heat resistance of about 220-230°C requires crystallinity of about 40 percent or more. Crystallinity levels below 40 percent create problems with deformation when subjected to such heat. Therefore, a degree of crystallinity of 40% or more is required, but a degree of crystallinity of 40 to 95% is mainly preferred.

However, even if the above conditions are satisfied, even if the skin layer is too thin or the core layer is too thick,
Even if the core layer is too thin, good effects cannot be obtained. In order to fully exhibit the characteristics of the heat-resistant container of the present invention, the homopolymer with higher heat resistance must account for at least 60 to 90%. That is, if it is less than 60%, it will easily undergo thermal deformation, and if it is more than 90%, it will become brittle and prone to cracking or chipping.

The above is the heat-resistant container of the present invention, but the purpose of the product of the present invention is to make it a heat-resistant container whose contents can be directly heated using an oven or microwave. In addition to so-called trays, containers such as lunch boxes and containers for infants can also be molded and used in the same way.

The feature of the product of the present invention is not only that it is heat resistant, but also that it can be used many times. In other words, if the material only needs to withstand heating once, it is not necessarily necessary to use multiple layers, but if it is heated many times, crystallization will progress to a considerably high point, and this will cause it to become brittle. It will break. One of the purposes of multi-layering is to prevent this. Next, since the crystallinity of the surface layer can be increased, the resistance to contamination by contents is increased, and the surface hardness is increased, making it less likely to be scratched.

As described above, the heat-resistant containers of the present invention can be easily molded using conventional molding machines, and their physical properties are significantly improved.

Examples of the present invention will be described below. Injection molding machine Co., Ltd.
A sandwich molding machine M-200A manufactured by Meiki Seisakusho was used. This molding machine has two injection devices with 50 mm diameter screws, and the resin on the skin side is Tenite, a polyethylene terephthalate homopolymer containing a crystallization accelerator.
PET Thermoplastic Polyester 5132 (manufactured by Eastman Kodak Co., Ltd.) is used, and the core resin is Unipet RN-133 (manufactured by Nippon Unipet Co., Ltd.), a copolymer of polyethylene terephthalate.
(The structure of RN-133 is 90 mol% terephthalic acid, 10 mol% isophthalic acid, and ethylene glycol.
100 mol% copolymer) was used. The mold is
It is a two-cavity mold with a center gate (pinpoint gate), and the cavity has a shallow tray shape with a thickness
It was 1.5mm.

First, add 45% of the resin on the skin side to the cavity capacity.
The amount equivalent to the percentage was injected.

At the same time as the injection of the skin resin was completed, the resin on the core side was injected in an amount equivalent to 50% of the capacity of the cavity, and then the skin resin was injected to completely fill the cavity. After holding pressure and cooling, the mold was opened and the molded product was taken out. The mold temperature during injection molding was 120°C. In the molded article, the skin layer was a homopolymer and the core layer was a copolymer, and the skin layer had a crystallinity of 50% and the core layer had a crystallinity of 20%. When the resulting molded product, a tray, was filled with gratin and baked at 220°C in an electric oven, the crystallinity of the tray increased, but the container did not deform. Even when I hit it against concrete, it didn't break.

As Comparative Example 1, the above Tenite PET
A tray was molded from Thermoplastic Polyester 5132 alone using the above mold. That is, injection molding was performed only with the skin injection machine without driving the core injection machine. The mold temperature was 120°C, the same as in the example.

The crystallinity of the obtained tray was 55%.
When gratin was baked in the same manner as in the example using an electric oven at 220℃, the crystallinity of the tray was 95.
%, and when I dropped it from 1 meter onto concrete, it cracked.

Comparative Example 2 uses only the core side resin, that is, the copolymer Unipet R-133 (RN-133 has a structure of 90 mol% terephthalic acid and 10 mol% isophthalic acid).
% and 100 mol % of ethylene glycol) was injected to obtain a tray having the same shape as the example. The crystallinity of the tray was 15%. When the gratin was baked in the same manner as in the example, the peripheral edge of the container was deformed. For this reason, it was determined that it could not be reused. As described above, the present invention is a highly heat-resistant container that can be used to reheat infant meals, and the container cools quickly and is easy to hold. The effect is very large, as it does not break even if dropped.

Claims (1)

[Claims] 1. An outer surface layer mainly composed of a homopolymer of polyethylene terephthalate, and a heat-resistant intermediate layer containing a dibasic acid containing an aromatic nucleus with good symmetry or a glycol with good symmetry as a third component. A multilayer heat-resistant container comprising at least one intermediate layer mainly composed of a copolymer of polyethylene terephthalate, and an inner surface layer comprising a homopolymer of polyethylene terephthalate. 2. The heat-resistant container according to claim 1, wherein a nucleating agent is mixed into the inner and outer surface layers. 3. The heat-resistant container according to claim 1 or 2, characterized in that the crystallinity of the inner and outer surface layers is 40% or more. 4. The heat-resistant container according to any one of claims 1 to 3, wherein the homopolymer of polyethylene terephthalate occupies 60 to 90 percent of the total volume of the container.