JPH11348111A - Manufacturing method of sheet molded container made of synthetic resin - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To establish a method for manufacturing a synthetic resin sheet molded container capable of improving gas barrier properties, coloring properties, and printability, and further capable of collecting and reusing synthetic resin. SOLUTION: A sheet made of a synthetic resin is coated with a polyvinyl alcohol-based resin, and then thermoformed to form a container. After use, the polyvinyl alcohol-based resin coating layer on the surface of the container is subjected to post-treatment such as steam or hot water. This is a method for producing a synthetic resin sheet molded container that can be removed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a synthetic resin sheet molded container capable of improving gas barrier properties, coloring properties and printability, and recovering and reusing synthetic resin.

[0002]

2. Description of the Related Art A synthetic resin sheet molded container is generally manufactured by a method called vacuum forming. In addition, a method called pressure forming or vacuum pressure forming is also employed. The sheet is heated and softened in advance by non-contact heating such as an infrared heater or hot air or contact heating by a hot plate, and then compression-molded into a concave or convex mold by the force of vacuum or pressurized air, and then die-cut in the subsequent step. Container manufacturing methods are commonly employed.

[0003] Containers manufactured from synthetic resin sheets are frequently used mainly for packaging foods. Above all, miso is significantly discolored by oxygen, and a container is required to have high gas barrier properties. For this reason, for example, polyethylene terephthalate
(PET) sheet with ethylene-vinyl alcohol copolymer
(EVOH) laminating film, polypropylene
(PP) Use a sheet in which an EVOH resin is sandwiched in the middle layer of a sheet by co-extrusion, or use polyacrylonitrile (P
AN) A container formed of a resin sheet or the like and having excellent gas barrier properties is employed.

[0004] Upon collection of packaging waste, a PET bottle recycling system is gradually being constructed and is expected to become the largest flow in the near future. However, PET
Other than PP, polyethylene (PE), polystyrene (P
At present, the assembly of a recycling system for general-purpose resins such as S) has not been embodied yet. In particular, there is no recycling system for other composite resin products or resins containing chlorine such as polyvinyl chloride (PVC) and polyvinylidene chloride (PVDC), and many problems have been encountered in incineration, the last remaining treatment method. I have.

Conventionally, PVC sheet containers, which have been frequently used because of their good moldability and low cost, are sparse due to generation of chlorine gas during incineration, and their use has been refrained, particularly in the field of food packaging. On the other hand, foamed or unfoamed PS sheet containers are also used for a wide range of applications. Containers formed from foamed sheets are widely used for tray packaging of vegetables and fruits from fresh foods such as raw meat and fish, instant noodles, instant soups and hot drinks. Containers formed from unfoamed sheets are often used for ice cream, dairy products and dessert containers. Because foamed sheet molding trays are bulky, collection systems centered on mass retailers are gradually being constructed, but volume reduction is an urgent need. PP sheet molded containers are widely used in take-out lunch containers that are being sold at convenience stores due to the microwave-compatible function of improving heat resistance by kneading an inorganic filler in a resin. In addition, containers for retort sterilization made by molding a sheet in which an EVOH resin is sandwiched in the middle layer of the sheet by co-extrusion are widely used for packaging rice and curry that can be stored at room temperature. Leaves the problem.

[0006] PET sheet molded containers are transparent, lightweight and strong,
It is chemically stable and hardly eluted by other chemicals.
For this reason, PET sheet molded containers are expanding their share in the field of synthetic resin sheet molded containers, just as glass bottles that are advantageous for recycling and repeated use have been rapidly replaced by PET bottles. PP sheet molded containers and PS sheet molded containers have heat resistance but poor gas barrier properties. Also, PE
The T-sheet molded container is not a container having a sufficient gas barrier property in packaging of foods such as miso and sliced ham which are easily discolored by oxygen.

As a means for imparting gas barrier properties to a sheet-formed container, a method of bonding a film material having excellent gas barrier properties such as EVOH or coextruding an EVOH resin to the surface layer or the intermediate layer of the sheet has been adopted. . However, it is very difficult to separate and separate it when it is to be recycled after being collected as a used container.

[0008] PET bottles have been accepted by consumers for their excellent simplicity, similar to PET sheet molded containers, and rationalization by high-speed mass production hastened production, while lightweight and toughness has facilitated distribution. Increasing adoption. However, the large amount of used PET bottles has spurred the increase of urban garbage, and this collection and reuse (recycling)
Is a serious social problem that requires a technical solution.

When a PET bottle is used, for example, as a beverage container, it is completed by filling the beverage, sealing with a cap, and attaching a label. Conventionally, caps made of aluminum or PP are replaced with PET, and labels on paper, biaxially oriented polypropylene (OPP) film, shrinkable PS film, and PVC film are replaced with shrinkable PET film. There is also a trend to integrate them into the same material to facilitate collection and reuse.
However, some PET bottles for carbonated beverages are of an old type in which the bottom is formed into a hemispherical shape and are fitted with a PE hak called a base cup, which is an obstacle to collection.

[0010] The consumer opens the cap, drinks the beverage and discards the container. Upon recovery, the beverage, aluminum and PP caps remaining in these discarded containers must be removed, and labels made of paper, OPP, PS, PVC, etc. must be peeled off. Recycling of PET bottles involves thorough washing and separation, and the purest possible PE
To collect T flakes (flakes).

The process of turning used PET bottles into flakes involves various sorts and washings. First, the remaining bottles and glass bottles are removed by a weight separator, and then a vinyl chloride bottle is detected and removed by an X-ray detector. The sorted bottles are placed in a device called a rotary drum separator. By rotating and rubbing in a perforated drum, caps, hakama and a part of the label are removed. In the subsequent washing step, pre-washing with an alkaline detergent, main washing, and final washing are carefully performed in this order. After the washing, it is put into the separator again to remove foreign substances such as labels. Further, the colored bottle is removed by hand and crushed into flakes of about 8 mm square by a crusher. After washing, the flakes are removed through a specific gravity separator to remove PE and PP, and dried with hot air. The labels and fine powder in the dried flakes are removed by air separation, and the aluminum and other metals of the cap are removed by a separator using static electricity. Then, the adhesive and the like are removed by washing with a rinsing agent.

[0012]

As in the case of PET bottles, the recycling of PET sheet containers involves the application of many steps and advanced techniques, and the costs are accordingly high. Recycled raw materials that are expensive and inferior in quality compared to PET resin pellets synthesized in large quantities by petrochemicals are not materials that are actively used for development. In order to effectively use limited resources, it is necessary to reduce the cost of recycling used PET sheet containers. It is important to minimize the amount of resin used per PET sheet container.
The thickness of the container will be further reduced in the future. Accordingly, the gas barrier properties of the container deteriorate.

In order to improve the gas barrier property (barrier property) of a container made of a synthetic resin sheet, a method of laminating the container into layers and laminating various barrier resins, for example, EVOH, or a barrier resin directly on PET resin, for example, There is a method of kneading polyethylene naphthalate (PEN). These methods also make sorting difficult at the stage of collecting and recycling used containers.

Colored bottles complicate the sorting process in a PET bottle recycling system. In addition, many kinds of colored bottles that have been selected are difficult to recycle, and are often incinerated. Similarly, colored or printed containers made of synthetic resin sheets also have problems.

[0015]

DISCLOSURE OF THE INVENTION In view of the above situation, the present inventors have developed a method for obtaining a container made of a synthetic resin sheet which has a high barrier property, is easy to collect and reuse, and is freely colored and printed. As a result of intensive studies, PV
A method for thermoforming after coating with the A-based resin was found, and the present invention was achieved. That is, the present invention provides that a sheet made of a synthetic resin is coated with a PVA-based resin, and then thermoformed to form a container. After use, the PVA-based resin coating layer on the surface of the container can be removed by post-treatment. A method for producing a synthetic resin sheet molded container characterized by the following.

As the means for coating the PVA-based resin, an aqueous solution may be applied, sprayed, dried after dipping, a method of laminating a film, or other known methods. Further, the post-treatment as a means for removing the PVA-based resin coating layer means that the PVA-based resin is removed from the main body of the synthetic resin sheet by elution or swelling and peeling with steam, hot water, or alkaline water using the properties of the PVA-based resin. I do. Here, in the case of a colored container, PVA containing a dye or a pigment is used.
The synthetic resin solution is applied to a sheet made of a synthetic resin to cover the sheet, and in the case of a printing container, printing is performed on the outer surface of the coated PVA resin.

The PVA resin used has a degree of polymerization of 200 to
8000, a saponification degree of 90 to 100 mol% by PVA or
P having an α-olefin unit content of 1 to 20 mol%, a degree of polymerization of 200 to 5,000, and a degree of saponification of 90 to 100 mol%.
VA is suitable for removal by the above post-treatment.

As described above, PVA is applied to the synthetic resin sheet.
After coating and drying the base resin, thermoforming (vacuum forming, pressure forming, vacuum pressure forming, etc.) can be used to obtain a container with high barrier properties. The present invention provides a method by which a PVA-based resin is easily peeled off, and a colored film and a printing ink are also peeled off, whereby a recycled resin flake having the same quality as that of a virgin resin is obtained.

As a method for producing a container made of a synthetic resin sheet having a high barrier property, a method of the present invention in which a PVA-based resin is applied to a synthetic resin sheet and dried is applied to a surface or an intermediate layer of a conventional synthetic resin sheet. Compared with the method of co-extrusion of a cohesive resin, the installation cost of a high-speed coating / drying machine and one step increase, but the recycled resin flakes can be efficiently collected without the necessity of sorting, which is indispensable to prevent the incorporation of different types of resin when collecting bottles. Bring the benefits you get.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION The PVA-based resin used in the present invention is insoluble in cold water and has high water resistance and needs to be dissolved in hot water. Modified PVA is preferred. The unmodified PVA preferably has a polymerization degree of 200 to 8000, a saponification degree of 90 to 100 mol%, and more preferably 95 to 100 mol%. When the degree of polymerization is less than 200, the film strength is insufficient, and when it is 8000 or more, the viscosity becomes high and the workability is deteriorated. If the saponification degree is less than 90 mol%, the water resistance of the film is insufficient.

As the hydrophobic group-modified PVA, for example, 0.1 to 20 mol% of an α-olefin unit having 20 or less carbon atoms is used.
PVA-based resins are preferred. This hydrophobic group-modified PV
A is a polymerization degree of 200 to 5000 and a saponification degree of 90 to 100.
Mol%, more preferably 95 to 100 mol%. If the degree of polymerization is less than 200, the film strength is insufficient, and if it is more than 5000, the viscosity becomes high and the workability deteriorates. 90 mol% saponification degree
If the amount is less than the above range, the film has insufficient water resistance.

As the α-olefin having 20 or less carbon atoms, ethylene, propylene and isobutylene are preferable in terms of productivity. As the content of α-olefin units,
0.1 to 20 mol% is applied, preferably 3 to 1 mol%.
5 mol%. When the α-olefin unit is less than 0.1 mol%, the effect of modification is not exhibited, and when it exceeds 20 mol%, the solubility in water is impaired depending on the degree of polymerization.

The PVA resin used in the present invention is obtained by saponifying a vinyl ester polymer by a conventional method. Examples of the vinyl ester include vinyl formate, vinyl acetate, vinyl propionate, vinyl pivalate, and vinyl versatate, with vinyl acetate being preferred.

In the present invention, the above-mentioned PVA-based resin is coated on a synthetic resin sheet, dried, and then formed into a container by thermoforming. A solution of a PVA-based resin dissolved in a solvent, preferably water, is applied to a synthetic resin sheet and dried. The application method is not particularly limited, but an application method such as gravure coating or roll coating is employed. In this case, an undercoat agent may be used for the synthetic resin sheet, but is limited to a range that does not affect the recoverability. In addition, P
The VA resin may be laminated to a synthetic resin sheet with water, a solvent or water containing an undercoat agent, or a solvent, dried, and then formed into a container by thermoforming.

A coloring container is obtained by adding a coloring pigment or a dye to the PVA-based resin solution. Conventionally known pigments and dyes can be used. Food containers and seasoning containers are transported, sold and stored in various environments. that time,
It is discolored and deteriorated by strong ultraviolet rays such as sunlight and nearby fluorescent lights. In order to reduce the influence of ultraviolet rays, there is a strong demand to use a pigment to color brown, green, or blue and take measures to prevent ultraviolet rays. However, when the production number is small, adopting the means for directly coloring the container requires adjustment of many colored resin raw materials, which leads to an increase in cost and is actually difficult,
The method of the present invention in which a PVA-based resin solution to be coated is colored with a pigment or dye and applied and dried is employed relatively easily without being restricted by such restrictions.

In the method of the present invention, a coloring pigment or a dye is added to a PVA-based resin solution or is applied to a synthetic resin sheet without addition, and after drying, gravure printing, flexographic printing, offset printing is performed on the outer surface of the PVA-based resin. And printing such as screen printing. If gravure printing is applied directly to the synthetic resin sheet and molded, the production cost will be significantly reduced compared to attaching expensive adhesive labels etc. to the container, but when collecting the container, the printing ink will be dissolved and removed with an organic solvent etc. This method has not been adopted. By using the method of the present invention, gravure printing or the like is performed on the surface of the PVA-based resin film applied in advance without being restricted by such restrictions, and the printing ink of the formed container is easily recovered by hot water or steam at the time of collection. In the treatment, the coloring pigment and the printing ink are easily removed together with the PVA-based resin film. Here, "removable by steam or hot water" means that the PVA-based resin on the surface of the container is almost completely eluted under the measurement condition of immersing the container in hot water of 85 ° C. for 1 minute. The temperature of the steam or hot water used for removing the PVA-based resin is preferably 80 ° C. or higher, more preferably 90 ° C. or higher, but there is no particular limitation on the removing method, and a conventionally known method, for example, high crystallinity Of PVA resin
A method of dissolving or swelling and peeling by treatment with a 2% alkaline aqueous solution is used.

The PVA resin of the present invention may contain additives such as fillers, plasticizers, fragrances, lubricants, release agents, and ultraviolet absorbers as long as the effects of the present invention are not impaired.

For the recovery and reuse of the synthetic resin sheet molded container, the above-mentioned step of recycling the used PET bottle into flakes can be used as it is.

[0029]

EXAMPLES The present invention will be described in more detail with reference to the following Examples, which should not be construed as limiting the invention thereto. In the examples, unless otherwise specified, “%”
And "part" represents a basis of weight.

The method of measuring and evaluating the characteristic value is as follows. (1) Method of measuring characteristic values (1-1) Degree of polymerization and degree of saponification Measured according to JIS K6726.

(2) Evaluation Method (2-1) Gas Barrier Property MODERN CONTROLS, INC. Using an oxygen permeability measuring device MOCONOX-TRAN10 / 50A, a nitrogen carrier gas is flowed into the inside of the molding container, and the outside of the molding container is kept at 20 ° C. and 65% R under an oxygen atmosphere.
Under the condition of H, the amount of oxygen permeation was determined according to JIS K7126 (isobaric method). (2-2) Water resistance The container was immersed in water at 20 ° C. for 1 minute, and the outer surface of the container was rubbed with a finger to determine whether PVA was eluted. (2-3) Ease of recovery The container is immersed in a water bath containing hot water of 85 ° C,
One minute later, the iodine solution was sprinkled on the outer surface of the container, and the elution of PVA was determined based on the presence or absence of iodine coloring, and the ease of PET recovery was evaluated.

Example 1 PVA having a polymerization degree of 1700 and a saponification degree of 99.5 mol% (PV
A-1), and prepare a 1 mm thick P
The ET sheet is applied and dried by a roll coating method. The length of the dryer is 5m, the temperature is 85 ° C, and the sheet passing speed is 20m
/ Min. This sheet is passed through an oven having an infrared heater of 4 m in length, and is vacuum-formed to a size of 1 mm.
An about 980 cc miso container having a size of 20 mm × 150 mm × 55 mm was obtained. The thickness of the side surface of the obtained container is PET250μ.
m, and PVA-based resin was 1.0 μm. Table 1 shows the measurement results of gas barrier properties, water resistance, and ease of recovery. From the results in Table 1, it can be seen that all of the above properties are good.

[0033]

[Table 1]

Example 2 An ethylene content of 9 was used in place of PVA-1 used in Example 1.
Mol%, polymerization degree 900, saponification degree 99.0 mol% Except for using ethylene-modified PVA (referred to as PVA-2), the PVA was applied to a PET sheet and dried in the same manner as in Example 1, and the container was vacuum-formed. Obtained. The thickness of the side of the obtained container is P
ET was 250 μm and PVA resin was 1.0 μm. Table 1 shows the measurement results of gas barrier properties, water resistance, and ease of recovery. As in Example 1, all properties were good.

Example 3 To a 10% aqueous solution of PVA-2 used in Example 2, 1% of a blue pigment aqueous ink (Dick Safe CP507 primary color indigo blue manufactured by Dainippon Ink and Chemicals, Inc.) was added. In the same manner as in Example 1, the PVA aqueous solution was applied to a PET sheet and dried, and then a beautiful blue container was obtained by vacuum forming. The thickness of the side surface of the obtained container is PET 250 μm, PVA resin 1.0 μm.
Met. Table 1 shows the measurement results of gas barrier properties, water resistance, and ease of recovery. At a water temperature of 20 ° C, the blue color did not change and was 8
At 5 ° C., the container became colorless and transparent, PVA was completely eluted together with the ink, and PET could be easily recovered.

Example 4 In the same manner as in Example 1, a 10% aqueous solution of PVA-1 used in Example 1 was applied to a preformed PET sheet and dried.
Gravure printing machine manufactured by Orient Sogyo Co., Ltd.
(OSG-1000 type), a reduced deformation design assuming the final bottle shape was printed. A beautiful printing container was obtained by vacuum forming. The thickness of the obtained container is PET 250 μm, PVA
The resin was 1.0 μm. Table 1 shows the measurement results of gas barrier properties, water resistance, and ease of recovery. Even if the container was immersed in water at 20 ° C. and rubbed by hand, neither peeling of the printing ink nor elution or falling off of PVA was observed. When the obtained container was immersed in hot water at 85 ° C. for 1 minute, the container became colorless and transparent, the printing ink was detached, PVA was completely eluted, and PET could be easily recovered.

Example 5 PVA having a polymerization degree of 1700 and a saponification degree of 99.5 mol% (PV
A-1) A film (20 μm) heat-treated at 180 ° C. for 20 seconds is coated with a heat sealant. 1mm thick
Rolls heated to 200 ° C on PET sheet
The PVA film is pressure-bonded and laminated at a speed of 0 m / min. According to the vacuum forming method used in Example 1, the dimensions are 120 mm long × 1 mm wide.
An about 1000 cc miso container of 20 mm × 90 mm in height was obtained.
The thickness of the side surface of the obtained container is PET 250 μm, PVA
The system resin was 5 μm. Table 1 shows the measurement results of gas barrier properties, water resistance, and ease of recovery. From the results in Table 1, all of the above properties were good.

Comparative Example 1 A 1 mm thick PET sheet without PVA was passed through an oven having an infrared heater having a length of 4 m, and was vacuum-formed to form a sheet having a size of 120 mm × 150 mm × 55 mm.
A 0 cc miso container was obtained. The thickness of the side of the obtained container is P
ET was 250 μm. The measurement results of gas barrier properties, water resistance, and ease of recovery are shown in Table 1. The gas barrier properties were poor because there was no PVA coating.

Comparative Example 2 In place of PVA-1 used in Example 1, the polymerization degree was 900
Except for using PVA having a saponification degree of 88.0 mol% (referred to as PVA-3), a container was obtained by applying a PVA to a pre-formed PET sheet and drying it, followed by vacuum forming, in the same manner as in Example 1.
The thickness of the obtained container side surface was PET 250 μm and PVA-based resin 1.0 μm. Table 1 shows the measurement results of gas barrier properties, water resistance, and ease of recovery. When the container was immersed in water at 20 ° C. and rubbed by hand, PVA was easily eluted and dropped off. As described above, PVA having a low degree of saponification easily falls off only by being immersed in room temperature water, and the gas barrier property is not sufficient.

[0040]

According to the method for producing a synthetic resin sheet molded container according to the present invention, since it is coated with a PVA-based resin having excellent gas barrier properties, deterioration of the contents is prevented, and a dye or pigment of the PVA-based resin film is prevented. A container with beautiful colors can be obtained from the good stain. Moreover, after use, the PVA-based resin film can be removed by a simple post-treatment using steam or hot water, and the high-purity recovery of the synthetic resin can be easily performed, contributing to a recycling system for various synthetic resin containers. it can.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI B29K 67:00 105: 26 (72) Inventor Yoshiumi Umemura 1621 Sazu, Kurashiki-shi, Okayama Prefecture Kuraray Co., Ltd. (72) Inventor Sadahiko Shirakami 1621 Sazu, Kurashiki City, Okayama Prefecture Kuraray Co., Ltd.

Claims (5)

[Claims] 1. A sheet made of a synthetic resin is coated with a polyvinyl alcohol-based resin, and then thermoformed to form a container. After use, the polyvinyl alcohol-based resin coating layer on the surface of the container can be removed by post-treatment. A method for producing a synthetic resin sheet molded container, characterized in that: 2. The method for producing a synthetic resin sheet molded container according to claim 1, wherein a polyvinyl alcohol-based resin solution containing a dye or a pigment is coated on a sheet made of a synthetic resin. 3. The method for producing a synthetic resin sheet molded container according to claim 1, wherein printing is performed on the outer surface of the coated polyvinyl alcohol-based resin. 4. The method for producing a synthetic resin sheet molded container according to claim 1, wherein polyvinyl alcohol having a polymerization degree of 200 to 8000 and a saponification degree of 90 to 100 mol% is used as the polyvinyl alcohol resin. 5. The polyvinyl alcohol resin contains 1 to 20 mol% of an α-olefin unit and has a degree of polymerization of 20.
4. The method for producing a synthetic resin sheet molded container according to claim 1, wherein polyvinyl alcohol having a saponification degree of 90 to 100 mol% is used.