JPH01284371A - Production of gas-shielding formed polystyrene vessel - Google Patents

Abstract

PURPOSE:To form a uniform gas-shielding coating film on the inside of a foamed polystyrene vessel by rotating the vessel at a relatively low speed and spraying polyvinylidene chloride latex on the inside of the vessel to be coated with airless spray nozzles. CONSTITUTION:A vessel 1 obtd. by foam-molding foamable polystyrene resin beads is rotated at a low speed of 300-2,000r.p.m. Polyvinylidene chloride latex contg. 40-60wt.% co- or terpolymer of 70-90% polyvinylidene chloride with 10-30% methyl acrylate and/or acrylonitrile is sprayed on the inside of the vessel 1 to be coated for 50-500msec with airless spray nozzles 2, 3 positioned toward the inside to form a film shielding moisture, preventing the permeation of oxygen and ensuring improved flavor retentivity.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application This invention relates to a method for manufacturing a gas-barrier expanded polystyrene container. More specifically, it is a food container made of foam-molded expandable polystyrene resin particles, which has improved moisture barrier and retention properties, oxygen permeation prevention, aroma retention, flavor retention, etc. in order to preserve food products. The present invention relates to a method for producing a gas-barrier container.

(b) Prior Art Containers having side walls and bottom walls made of expanded polystyrene fat particles are used as food packaging containers such as cup-shaped containers for instant noodles. This expanded polystyrene container is widely used as a container that has good insulation properties when hot water is poured into it, is lightweight, is easy to mass produce, is inexpensive, and is disposable. However, in the case of the above-mentioned expanded polystyrene containers, the permeability of water vapor and oxygen is high, and the food inside may contain moisture, solidifying the powdered soup, or oxidizing fats and oils due to oxygen intrusion, promoting deterioration of the quality of the food. However, there were drawbacks such as loss of taste.

Therefore, the inner surface of a container made of expanded polystyrene is coated with a layer of vinylidene chloride resin, which is known as a material with high gas barrier properties. In this method, the foamed polystyrene container is heated at 2,000 to 3.00 Orpm.
This method avoids the formation of a corrugated film by spraying vinylidene chloride latex on the inside of the rubber plate by regular air spray, spreading it using the rotational force, and shaking off the excess latex. (Special Publication No. 54-35531).

(c) Problems to be Solved by the Invention However, the above method is limited to coating only the inside of the container, and furthermore, since the latex is spread and spread by centrifugal force due to high-speed rotation, the bottom of the container is inevitably thin.
The lip of the side wall tends to become thicker, making it impossible to obtain a uniform coating thickness. Further, it is difficult to keep the amount of each coating resin constant.

This invention was developed in view of the above circumstances, and it is an object of the present invention to provide a method for producing a polystyrene foam container that has excellent gas barrier properties, which are important for food packaging containers, and also has excellent properties such as heat insulation, strength, and shape accuracy. That is.

(d) Means for Solving the Problems Thus, according to the present invention, when forming a coating film of vinylidene chloride latex over at least the entire inner surface of a container foam-molded with expandable polystyrene resin particles, Using an airless spray nozzle with the spray nozzle positioned at the desired coating surface while rotating at 300 to 2.00 rpm,
Spray vinylidene chloride latex containing 40 to 60% by weight of a binary or tertiary copolymer resin of 90% and methyl acrylate and/or acrylonitrile IO to 30% with a discharge time of 50 to 500 m5ec. Provided is a method for manufacturing a gas-barrier expanded polystyrene container characterized by forming a uniform gas-barrier coating film.

The method of the present invention is characterized in that vinylidene chloride latex is applied to a foam molded product of expandable polystyrene-based Mit resin particles using an airless spray nozzle while rotating the product at a relatively low speed.

In this invention, the container to be coated is obtained by foam molding expandable polystyrene resin particles,
Furthermore, one having an opening is preferable. The expandable polystyrene resin particles include styrene polymer, methylstyrene polymer, styrene-acrylonitrile copolymer,
One type of resin selected from copolymerization of styrene and acrylic ester or methacrylic ester contains 1 to 10% by weight of a blowing agent consisting of a hydrocarbon having a boiling point lower than the softening point of the resin. is preferred.

In this invention, the coating on the container is performed using an airless spray nozzle. Here, airless spray is usually used not only for general metal coatings, but also for plastic, leather, etc.
It is used for painting decorative items, etc., and the coating liquid is directly pressurized and discharged from a nozzle, and the energy is used to atomize it, which is then delayed to the object and adheres to it. In other words, when it is released from a nozzle at high speed under relatively high pressure (40 to 100 kg/cm'), it collides violently with the atmosphere and becomes atomized, and the ejection speed is several times faster than normal air spray. It has the advantage that it can penetrate into the recesses between the foamable resin particles on the surface of the molded article to a large extent, and that the coating adhesion efficiency is about 30% higher. A further advantage of this airless spray is that the amount of coating resin can be adjusted with high precision by setting the discharge time.

In the present invention, the coating liquid used in the airless spray nozzle has good usability, such as being easy to wet the container of the object, hard to cause waving of the coating liquid, and having good film forming properties. , Gas 1! ! breakage properties, adhesion between the coating film and the foamed molded product made of polystyrene particles, strength of the coating film, flexibility that can follow the foamed molded product, probing resistance, heat sealability, weather resistance, or R coating fluid. From stability during use,
Any desired vinylidene chloride latex is used. The vinylidene chloride latex is made of a binary or ternary copolymer of acrylate, methacrylate, acrylonitrile, and vinyl chloride. That is, a copolymer of polyvinylidene chloride 70 to 901 ft, %/methacrylate lO to 30% by weight, or polyvinylidene chloride 70 to 80
Copolymer of wt%/methacrylate lO~20wt%/acrylonitrile 10~20wt%, or polyvinylidene chloride TO~90wt%/acrylonitrile 10~3
0% by weight of copolymer is suitable. Latex has good wettability with foamed molded products during coating, has no cracks or cracks in the coating film, is less likely to drip (striped pattern), and is easy to form (solidify and dry moisture). It is necessary to conduct the process at an appropriate speed, and from this point of view, it is preferable to have a concentration hole for the resin content of the latex, but the storage stability of the latex and stability during use are also required, and the resin content is 4.
0 to 60% by weight or appropriate, and further 45 to 55% by weight
is preferred. Occurrence of latex repelling and coating film bubbles during coating is due to local wetting defects, but this can be improved by lowering the surface tension by appropriately selecting a surfactant. These surfactants are also essential as emulsifiers during polymerization or emulsion stabilizers during latex storage. Therefore, the surfactants and anionic surfactants used in the latex in this invention include sodium alkylaryl sulfonate, sodium alkyl sulfonate, sodium alkyl sulfate, alkylnaphthalene sulfonate, etc.
Examples of nonionic surfactants include polyoxyethylene alkyl ether, polyoxyethylene alkylphenol ether, polyethylene glycol higher fatty acid ester, and sorbitan higher fatty acid ester. The above-mentioned anionic and nonionic surfactants can be used together, and these surfactants contain 0.0% in the latex.
Preferably, it is used in an amount of 5 to 1.0% by weight. In this case, the latex resin particle diameter is 0.1 to 0.2 μm,
Latex surface tension is 30 to 60 dyne/cm (a
t20°C).

In this invention, when applying the above-mentioned coating liquid to the above-mentioned container using the above-mentioned airless spray nozzle, the above-mentioned container is rotated at a low speed and the coating is applied evenly over at least the entire inner surface of the container. It will be done. The above-mentioned low speed is a speed lower than that when coating is normally performed using an air spray nozzle, and is 300 to 2. OOOrpm.

During this coating, the airless spray nozzle is installed with its spray port positioned so that the desired coating surface can be coated evenly. When using one airless spray nozzle, it is preferable to repeat the coating process a predetermined number of times for each desired coating surface, for example, the side surface and the bottom surface. The coating may be simultaneously applied using a sufficient number of airless spray nozzles to position the spray nozzle and apply the coating uniformly. Furthermore, in the case of a container having an opening, the outer surface thereof may be coated. The time required for one discharge from the airless spray nozzles, which are installed in a predetermined number as described above, is adjusted so that the aforementioned latex can be accurately applied in the minimum necessary amount and a film can be formed with little variation in coating thickness. Ru. As an example of this, we set a limit of 40 g/l to prevent the latex applied to the container from running and forming stripes.
m", the rotation speed of the container is 300 to 2.00
When adjusted to the range of Orpm, the discharge time is 50~
It is preferable to set it within a range of 500 m5ec. Further, it is preferable to discharge the above-mentioned limit amount in two or more doses, since a coating film that is more uniform and has good gas barrier performance is formed. For the above details, refer to the description of the embodiments described later.

In the present invention, it is preferable to preheat the target foam molded product before coating by the above-mentioned spray method in order to prevent pinholes, cracks, etc. from being included during film formation after coating. Further, when forming a film after the above-mentioned coating, it is preferable to dry the foam molded product with hot air while rotating it at a lower speed (for example, 10 to 20 rpm) than at the time of coating.

The conditions for this hot air drying are limited to a temperature range in which the foamed molded product of the base material does not expand and expand, for example, 90 to 100°C. Further, the heating time varies depending on the area of the hot air outlet and the air volume, but approximately 60 to 120 seconds is appropriate. In addition, in coating when mass producing foam molded products,
A cooking method is used in which the cups are stacked, and it is necessary to prevent blocking (adhesion) due to the coating film. This blocking occurs due to insufficient drying of the coating film, so it is necessary to ensure sufficient drying. Further, after drying, it is preferable to complete the crystallization of polyvinylidene chloride from the viewpoint of gas barrier properties, and it is preferable to perform curing at 40 to 60° C. for 10 to 40 hours.

Note that conventional products can be applied as they are to the above-mentioned expandable polystyrene resin particles and foam molded products thereof. Further, a foam molded product having an expansion ratio of about 5 to 65 times is preferable. Further, the foamed molded product to be subjected to the method of the present invention may have any container shape, such as a cup shape, a box shape, a piece shape, a plate shape, etc.

(e) Effect According to the present invention, 70 to 90% polyvinylidene chloride and 10 to 10% of methyl acrylate and/or acrylonitrile are added to a foam molded container of expandable polystyrene resin particles that is rotated at a low speed of 300 to 2,000 rpm. 30%
Binary or tertiary copolymer resin content with 40 to 60% by weight
By spraying the vinylidene chloride latex contained in the above with an airless spray nozzle for a discharge time of 50 to 500 m5ec, at least the inner surface of the container is uniformly coated, and the applied coating liquid is free from non-uniformity due to centrifugal force. A gas barrier coating film with a uniform thickness is formed without any distribution.

The present invention will be described in detail below with reference to Examples, but the present invention is not limited thereby.

(f) Example Expandable polystyrene particles, Eslen beads HK (containing pentane S, O wt %) with an average particle diameter of 0.4 mm, are pre-foamed to a bulk density of 90 g/(l) while stirring in normal pressure saturated steam, The foamed beads were filled into a 450 m (cup-shaped mold cavity) and indirectly heated at a water vapor pressure of 2.2 kg/cm.
Molding was performed with direct heating for 0 sec and 2.0 sec, cooling water was passed for 3.5 sec, and the mold cavity was removed to obtain a cup-shaped molded product in which the foam particles were fused and integrated.

A latex with a resin content of 50% was prepared by emulsifying and dispersing a copolymer containing 80% by weight of vinylidene chloride and 20% by weight of methyl acrylate with sodium alkyl sulfonate and polyethylene glycol higher fatty acid.

When applying the vinylidene chloride latex to the outer surface of the cup-shaped molded product, two tubes were installed toward the side and bottom of the cup-shaped molded product (1) as shown in the schematic diagram in FIG. airless spray nozzle (2X
3) (both Nordson, type 713-201W)
/RES) and a two-stage piston pump with a hydraulic pressure of 40 kg.
/am”, and the above molded product (1) is i, ooorpm,
The discharge time of each nozzle was set to 320 msec for nozzle (2) and 150 msec for nozzle (3) for coating.

After spray coating, blow out 90℃ hot air with an outlet area of 15cm.
It was sprayed onto a coating cup rotating at a wind speed of 5 m/sea and lOrpm, and dried for 120 seconds.

The above coating process was repeated twice to form a substantially uniform coating film having a thickness of 20 to 25 μm and adhering 1.0=1.1 gr of polyvinylidene chloride resin per cup. Furthermore, in order to complete the crystallization of the coating resin, curing was performed at 40° C. for 40 hours to obtain a gas-barrier foamed polystyrene cup.

The cup manufactured through the above process has a good integration of the foamed polystyrene molded product and the polyvinylidene chloride coating, and there is no blocking when stacking the cups together.
There was no problem in terms of manufacturing or usage.

In a water vapor permeation test, the permeation rate of this gas barrier cup was 1.3gr/+"24HR5 at 30℃ and 75% R)I.
It was demonstrated that the water vapor barrier property was significantly higher than that of a conventional cup not coated with polyvinylidene chloride, which had a permeation amount of 45 to 50 g/Ill''.

(G) Effects of the Invention According to this invention, polyvinylidene chloride latex is spray-coated to form a film on a container that has conventionally been foam-molded from ordinary expandable polystyrene resin particles, resulting in a double-layered structure that is tightly integrated. By manufacturing the container, a container with good gas barrier properties can be obtained.

Therefore, the polyvinylidene chloride coating film provides excellent gas barrier properties necessary for containers for foods such as instant noodles, while the foam molding also provides excellent heat insulation and shape retention properties, creating containers with extremely high commercial value. It will be possible to manufacture it.

Furthermore, by applying the method of the present invention to a polystyrene foam sheet, it is possible to improve the stretching during processing of conventional acid-form sheets laminated with polyvinylidene chloride film. Therefore, it is possible to eliminate the disadvantages of weakening the strength in a certain direction and making it easy to tear.

It is also a method that can be easily applied to deeper containers or containers with complicated shapes.

As described above, the method of the present invention provides a foam container that is excellent in preventing moisture absorption, dehumidification, weight loss, aroma dissipation, deterioration of flavor due to air oxidation, etc. for foam molded products obtained by foam molding of expandable polystyrene resin particles. can be provided.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing the arrangement of airless spray nozzles in the coating process of one embodiment of the method of the present invention. (1)...Cup-shaped foam molded product, (2), (3
)...Airless spray nozzle. 21 Figure

Claims (1)

[Claims] 1. When forming a coating film of vinylidene chloride latex over at least the entire inner surface of a container foam-molded with expandable polystyrene resin particles,
0-2,000rpm. Using an airless spray nozzle with the spray nozzle positioned against the desired coating surface while rotating at 50 to 500 m of vinylidene chloride latex containing 40 to 60% by weight of polymer resin.
A method for producing a gas-barrier expanded polystyrene container, characterized in that a uniform gas-barrier coating film is formed by spraying with a discharge time of sec.