JP2006232317A - Container showing superior recyclability, and its recycling method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a container which has a laminated structure including a fine gas barrier polyglycolic acid resin layer in addition to a main material resin layer but showing superior recyclability, and to provide an efficient recycling method for the container. <P>SOLUTION: The container has the laminated structure including at least one polyglycolic acid resin layer of 2 to 200 μm in thickness in addition to the main material resin layer of 120 to 600 μm in thickness. After crushing the container, the crushed matter is cleaned with alkaline water to remove the polyglycolic acid resin layer from the crushed material and recover the main material resin. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a highly recyclable container including a polyglycolic acid resin layer in addition to a main raw material resin layer, and a method for recycling the same. In the present specification, the term “container” means the meaning of a hollow molded container widely used to contain contents in addition to a “bottle” in a narrow sense or a normal usage having a relatively small diameter compared to the internal volume. Used for. It will be readily understood from the following description that the effects of the present invention are not limited to the exact shape of the container.

  Resin containers are widely used in large quantities as liquid containers such as drinking water, seasonings, edible oils, alcoholic beverages, fuels, and detergents because of their light weight, transparency, and good appearance. ing. This is especially true for so-called PET bottles (ie, polyester resin bottles), especially PET (polyethylene terephthalate) bottles.

  However, due to the recent urban problems such as reduction of environmental burden and reduction of garbage, resin containers used in large quantities are required to be recycled. Recycling includes a thermal energy recovery type by incineration, a chemical recycling type that returns to the monomer, a raw material type that returns to the resin raw material through pulverization and refining processes, and a returnable type that can be reused again as a container. In addition, a raw material mold that returns to a resin raw material through a refining process is employed, and the recovered resin raw material is often reused for fibers and the like.

  On the other hand, recently, in order to improve the preservation of the contents of hollow containers, it has been required to suppress the permeability of carbon dioxide gas and oxygen gas. As techniques for improving these, a gas barrier coating or a multilayer structure in which a gas barrier resin layer is disposed in an intermediate layer has been proposed.

  In the case of such a PET container having a gas barrier coating or a multi-layered structure in which a gas barrier resin layer is disposed in an intermediate layer, it is difficult to sufficiently separate the PET resin raw material from other resin components. And there is a possibility that the quality and safety as a recycled resin raw material may be hindered.

  In addition, for the purpose of preventing the photodegradation of contents such as beer, or for the purpose of producing a design effect, the use of colored PET bottles has been attempted, but recycling due to color mixing or the like has been attempted. Usage has been limited due to difficulties.

  An object of the present invention is to provide a container having a laminated structure including an additional resin layer in addition to a main raw material resin layer and having excellent recyclability, and an efficient recycling method thereof.

  According to the studies by the present inventors, in addition to the main raw material resin layer with a limited thickness, it is possible to provide a polyglycolic acid resin layer having a specific thickness as an additional resin layer. Has been found to be extremely effective.

  That is, the highly recyclable container of the present invention has a laminated structure including at least one polyglycolic acid resin in addition to the main raw material resin layer, the main raw material resin layer has a thickness of 120 to 600 μm, The glycolic acid resin has a thickness of 2 to 200 μm.

  The container recycling method of the present invention is a container having a laminated structure including at least one polyglycolic acid resin layer having a thickness of 2 to 200 μm in addition to the main raw material resin layer having a thickness of 120 to 600 μm. After crushing, the crushed material is washed with alkaline water to remove the polyglycolic acid-based resin layer as much as possible and recover the main raw material resin.

  The reason why the polyglycolic acid resin used in the present invention is particularly excellent as a constituent resin of the additional resin layer of the recycling container is as follows. That is, the polyglycolic acid resin is about 3 times or more (about 1/3 or less as an oxygen transmission coefficient) of EVOH (ethylene-vinyl alcohol copolymer) which is a typical gas barrier resin conventionally used. By including the thin layer in addition to the main raw material resin layer, an extremely improved gas barrier property can be obtained. Therefore, deterioration due to oxidation of the contents and quality deterioration due to the escape of carbon dioxide gas from the contents can be effectively prevented. Further, in the raw material type recycling generally adopted for PET containers and the like, a method of recovering resin raw materials through a step of alkali-washing the crushed material for the purpose of protein degradation after the container is crushed is employed. Here, the polyglycolic acid-based resin used in the present invention can be easily separated from the main raw material resin to be collected because of its high hydrolyzability with an alkaline cleaning liquid. In addition, glycolic acid as a hydrolyzate of polyglycolic acid resin in washing waste liquid is easily biodegraded into carbon dioxide and water by neutralizing the washing waste liquid and treating it with activated sludge. Don't be. In contrast, a polylactic acid polymer, which is a typical biodegradable resin known so far, does not exhibit gas barrier properties like a polyglycolic acid resin, and the hydrolysis rate due to alkali is also polyglycol. Slower than acid resins.

(Polyglycolic acid resin)
The polyglycolic acid resin is a hydrolyzable polyester having a repeating unit represented by the following formula (1):
_{- (OCH 2 CO) - (} 1)
A glycolic acid homopolymer (PGA) consisting only of the above repeating units is preferably used, and other repeating units can be included, but a structure in which the main chain is cleaved by hydrolysis is preferable. An ester structure including a carboxylic acid ester and a carbonic acid ester, an amide structure, and the like are preferable, and an aliphatic ester structure is particularly preferable because of easy hydrolysis. Examples include the following:
_{- (OCHCH 3 CO) - (} 2)
_{- (OCH 2 CH 2 CH 2} OCO) - (3)
_{- (OCH 2 CH 2 CH 2} CH 2 CO) - (4)
The proportion of other repeating unit structures is less than 50% by weight, preferably less than 30% by weight, more preferably less than 15% by weight. It is preferable in terms of strength to use a polyglycolic acid resin having a weight average molecular weight (measured in terms of polymethyl methacrylate by GPC) of 50,000 to 600,000.

(Main resin)
In addition, the polyglycolic acid-based resin can contain a crystal nucleating agent, a crystal retarding agent, and further an auxiliary agent such as a plasticizer, a heat stabilizer, a heat absorber, an ultraviolet absorber, a lubricant, and a pigment.

  The main raw material resin that forms a container together with a layer of polyglycolic acid resin is polyester (polyethylene terephthalate), polyethylene naphthalate (PEN), polyvinyl chloride (PVC), polyethylene (PE), polypropylene ( A wide variety of thermoplastic resins such as PP), polycarbonate (PC), polystyrene (PS), and polylactic acid (PLA) can be used. As described above, the polyglycolic acid resin has a gas barrier property that is remarkably larger than those of these general-purpose resins, and even when laminated with any resin, a container with improved gas barrier property is used. Can be formed. In particular, PET containers currently occupy the mainstream, and containers using PET as the main raw material are preferable from the viewpoint of economy and energy consumption when performing recovery and recycling. The thickness of the main raw material resin, particularly the PET layer, is set to a thickness of 120 to 600 μm.

  A plurality of resins can be mixed and used, but it is preferable to use a single raw material because quality is likely to deteriorate during recycling. Although it can be colored, it is preferable to use a single raw material because quality is likely to deteriorate due to color mixing during recycling.

  A small amount of polyglycolic acid resin may be contained in the main raw material resin layer, but the amount is preferably 10% by weight or less, more preferably 3% by weight or less, and most preferably 1% by weight or less. Thus, the main raw material resin layer containing the polyglycolic acid resin may be formed as a resin in which the main raw resin is mixed with a polyglycolic acid resin or the like. In this case, the recovered resin for forming the main raw material resin layer is the main raw material resin that is recycled and recovered (sometimes containing a small amount of polyglycolic acid-based resin) or the so-called virgin resin that is commercially available. It is more preferable from the viewpoint of workability that the raw material resin is mixed, and in particular, the ratio of the main raw material resin of the latter virgin exceeds 90% of the whole.

(Laminated structure)
The polyglycolic acid-based resin layer is preferably formed as an intermediate layer sandwiched between an outer layer and an inner layer mainly composed of a main raw material resin layer that forms a container. The intermediate layer may be a single layer or two or more layers. The composition ratio between the inner and outer layer resins and the polyglycolic acid resin can be arbitrarily determined depending on the performance and quality required for the container. In order to efficiently recycle the main raw material resin while providing good gas barrier properties, the weight ratio of the main raw material resin to the glycolic acid polymer (corresponding to the thickness ratio) is 99/1 to 55 / It is preferably in the range of 45, particularly 98/2 to 60/40. The polyglycolic acid-based resin layer preferably has a thickness of at least 2 μm and exhibits good gas barrier properties. In the case of a bottle, it is preferable that this thickness is maintained at the trunk occupying the main area, and there may be no polyglycolic acid resin layer at the bottom or neck. In addition, a mixed resin of the main raw material resin and the polyglycolic acid resin may be used as the recovered resin layer, but the amount of the polyglycolic acid resin in the recovered resin layer in that case is preferably 50% by weight or less, More preferably, it is 30 weight% or less, Most preferably, it is 10 weight% or less. The laminated structure includes a main raw material resin layer made of virgin main raw material resin (S1), a main raw material resin layer made of recycled main raw material resin and a main raw material resin of virgin (S2), and a recovered resin layer (R ), When the polyglycolic acid resin layer is indicated by (PGA), for example, (S1) / (R) / (PGA) / (S1), (S1) / (PGA) / (R), ( (S2) / (PGA) / (S2), (S2) / (PGA) / (S1), (S2) / (PGA) / (S2) / (PGA) / (S2), (S1) / (PGA) / (S2) / (PGA) / (S1), and so on.

  The container of the present invention includes, in addition to the container body, a label layer having a thickness of 50 to 100 μm (usually part of the container but may be provided on the entire circumference) and a cap as necessary. The label material is made of polystyrene resin, polypropylene resin, etc., and preferably has heat shrinkability, and the cap material is often used with a specific gravity of less than 1.

  For example, an adhesive resin layer can be appropriately inserted between the main raw material resin layer and the polyglycolic acid resin layer or between the surface of the container and the label, and may be used within a range that does not hinder recyclability. .

(Recycling method)
Recycling of containers is actually performed in PET containers, and the recycling process includes processes such as container crushing, sorting and removing containers other than PET, labels, caps, etc., washing, alkali washing, and drying. . When the container of the present invention is recycled, it is preferable that the same recycling process as that for the above PET container is performed.

  The label remaining in the collected container is generally removed by specific gravity separation or wind separation. PET usually has a specific gravity of about 1.3, and a label having a specific gravity of less than 1.3 is usually used, so that the specific gravity is easily separated in the cleaning liquid. Further, the label is usually 50 to 100 μm thick, and since PET is usually about 120 to 600 μm thick, it is easy to be separated by wind.

  If the cap has a specific gravity of less than 1.0, the specific gravity is easily separated in a cleaning liquid such as water. On the other hand, polyglycolic acid-based resins are usually used with a specific gravity of 1.4 or higher, most often 1.5 or higher in order to exhibit gas barrier properties.

  In a multilayer PET container, it is desirable to separate it from an easy PET layer or the like when the container is cut into flakes. Separation by cutting facilitates wind separation.

  The polyglycolic acid resin may form one or more layers, but the thickness is preferably equal to or less than the label used. In general, since the label is usually 40 to 200 μm, and most often 50 to 100 μm, the polyglycolic acid resin layer is also 200 μm or less, preferably 100 μm or less, more preferably 50 μm or less. Furthermore, since the specific gravity of the polyglycolic acid resin is higher than that of the label, it is particularly preferably less than 40 μm, particularly preferably less than 30 μm.

  In a multi-layer PET container including a polyglycolic acid resin layer, the polyglycolic acid resin layer may have a thickness distribution in order to optimize gas barrier properties and processability. The thickest part is preferably 200 μm or less, more preferably 100 μm or less. More preferably, it is 80 μm or less.

  The thickness distribution of the polyglycolic acid-based resin layer is preferably in the range of 10 times at the maximum and 1/10 of the minimum with respect to the thickness of the polyglycolic acid-based resin layer in the container body, which shows the average thickness. If it exceeds 10 times, the polyglycolic acid resin layer tends to remain after the recycling step, and if it is less than 1/10, it is difficult to exhibit gas barrier properties.

  In the container recycling cleaning step, an alkaline aqueous solution is preferably used. Usually, a 1 to 1.5% sodium hydroxide aqueous solution heated to 80 to 98 ° C is used. The washing time is often about 10 to 20 minutes.

  Polyglycolic acid-based resins are usually subjected to hydrolysis at random, gradually decreasing the molecular weight, and finally hydrolyzing to glycolic acid, showing water solubility. When the recyclability of the polyglycolic acid-based resin was examined, it was found that the polyglycolic acid-based resin was easily dissolved in a high-temperature alkaline cleaning solution from the surface.

  That is, the polyglycolic acid-based resin layer is preferably thinner in the recycling step using an alkaline cleaning liquid, and the resin layer is thinner in a short cleaning time. The preferred thickness is 2 to 200 μm, more preferably 3 to 100 μm, still more preferably 5 to 50 μm, particularly preferably 7 to 40 μm, and most preferably 10 to 30 μm. If it is too thin, it will be difficult to exhibit the original gas barrier properties. If it is thick, not only the air separation property is deteriorated, but also the polyglycolic acid resin layer is likely to remain even in the washing step.

  In the washing process, it is necessary to prepare an apparatus and conditions such that the polyglycolic acid resin layer comes into contact with the washing liquid, particularly alkali, and stirring and fluidization are performed to such an extent that the polyglycolic acid resin having a high specific gravity does not settle. It is preferable. In order to remove the polyglycolic acid-based resin layer in the washing step, the higher the temperature, the better. The longer the time, the better. However, in order to suppress the decomposition of PET, 5-30 minutes in the range of 60-100 ° C, preferably Is performed in the range of 10 to 20 minutes. The higher the alkali concentration of the alkaline cleaning liquid, the better the removal of the polyglycolic acid-based resin layer. However, from the original purpose of the alkaline cleaning, economy, influence on PET, etc., 0.1 to 2.0%, preferably 1 to 1.5% is used and may be used with a surfactant such as TRITONX-100.

(Waste liquid treatment)
Alkaline washing waste liquid containing glycolic acid generated by hydrolysis of polyglycolic acid resin is an organic acid that is naturally present in glycolic acid. It is preferable to biodegrade glycolic acid into H ₂ O and CO ₂ by sludge treatment to further reduce the burden on the ecosystem. The activated sludge treatment is also included in the conventional PET container recycling treatment, and the container recycling method of the present invention can be carried out essentially without any new capital investment. There is only a slight increase in the activated sludge treatment load.

(Coloring)
According to a preferred embodiment of the present invention, the polyglycolic acid resin layer is preferably colored. In this case, the obtained container is a color container, and light deterioration of the contents can be suppressed by suppressing light transmission. The polyglycolic acid-based resin layer is uniformly colored, but the design effect can be increased by adding a colored layer of an arbitrary form thereon. Various known colorants can be used to produce a desired color. Considering the environmental burden after recycling, for example, a red color is preferably a biodegradable colorant or pigment such as food red.

  Another advantage of coloring the polyglycolic acid resin layer is that it is possible to visually determine the number of times of washing, time, etc. during recycling. That is, when the polyglycolic acid resin remains, a solid colored resin remains, so that the imperfection of separation can be easily determined. Thereby, quality control of the recovered raw material resin after recycling can be greatly saved.

  Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples. In the following examples, “parts” means “parts by weight”.

Example 1
A polyglycolic acid resin (240 ° C., melt viscosity of 1800 Pa · s at 100 / s) is heated and melt-molded at 260 ° C., the plane dimensions are 200 mm × 200 mm, and the thicknesses are 5, 45, 90, 130, and 220 μm, respectively. A seed press sheet was formed. A square piece obtained by cutting each obtained press sheet into a 10 mm × 10 mm square was poured into an aqueous solution of 1.5 mass% NaOH at 90 ° C., and the shape change of the square piece was visually observed while gently stirring so as not to settle. The time at which PGA was dissolved in the washing solution and the presence of the PGA could not be visually confirmed was read to determine the disappearance time. The results are shown in the table below.

(Example 2)
PET (IV = 0.8) and PGA (240 ° C., melt viscosity of 1500 Pa · s at 100 / s) are fed into an injection molding machine having two cylinders, respectively, and PET / PGA / PET (thickness ratio = 45). / 10/45) three-layer preforms were molded, and bottles (internal volume = 500 cc, thickness 800 μm, weight 40 g) were produced using a blow molding machine.

  The obtained bottle was cut into a 2 cm square and washed in a 1N aqueous sodium hydroxide solution at 80 ° C. for 5 hours. The washed cut product was separated by filtration, washed with water, and dried to obtain 36 g of a recovered resin. When the infrared absorption spectrum of the obtained recovered resin was measured, only the PET-derived absorption was observed, and it was confirmed that PGA was completely removed.

(Example 3)
A bottle was produced in the same manner as in Example 2 except that PGA colored with 0.1 part of carbon black was used for 100 parts thereof.

  The obtained bottle was cut into a 2 cm square and washed in a 1N aqueous sodium hydroxide solution at 80 ° C. for 5 hours. The cut product was separated by filtration, washed with water, and dried to obtain a colorless recovered resin. When the infrared absorption spectrum of the obtained recovered resin was measured, only absorption derived from PET was observed, and it was confirmed that carbon black and PGA were completely removed.

Example 4
A bottle produced in the same manner as in Example 3 was cut into a 2 cm square and washed in 1N aqueous sodium hydroxide solution at 80 ° C. for 3 minutes. The washed cut product was separated by filtration. As a result, there was still a solid matter colored in black, and the product was again washed in a 1N aqueous sodium hydroxide solution at 80 ° C. for 3 hours. The cut product after rewashing was filtered, washed with water, and dried to obtain a colorless recovered resin. When the infrared absorption spectrum of the obtained recovered resin was measured, only absorption derived from PET was observed, and it was confirmed that carbon black and PGA were completely removed.

(Example 5)
The PET resin recovered in Example 3 was melt-pressed at 270 ° C., and cooled with a cooling press at room temperature to obtain a colorless and transparent PET sheet. Thereby, the recovered resin could be molded, and the recyclability of the main raw material resin PET could be confirmed.

(Example 6)
When the aqueous alkaline solution used for the washing treatment in Example 2 was analyzed by liquid chromatography, glycolic acid was detected. This solution was neutralized, diluted 100 times with water, poured into activated sludge aged by aeration, and cultured in an aerobic atmosphere at room temperature for one month. One month later, the reaction solution was analyzed again by liquid chromatography, and no glycolic acid was detected. Dissolved organic carbon was analyzed with a total organic carbon meter (Shimadzu Corporation TOC-5000A), but organic carbon was not detected and was discarded as it was.

  As described above, according to the present invention, in addition to the main raw material resin layer having a thickness of 120 to 600 μm, a laminated structure including a polyglycolic acid resin layer having a good gas barrier property of 2 to 200 μm is provided. A container having excellent recyclability while having a container and an efficient recycling method for the container are provided.

Claims (7)

In addition to the main raw material resin layer, it has a laminated structure including at least one polyglycolic acid resin, the main raw resin layer has a thickness of 120 to 600 μm, and the polyglycolic acid resin layer has a thickness of 2 to 200 μm. A highly recyclable container. The container according to claim 1, wherein the main raw material resin is polyester. The container according to claim 1 or 2, further comprising a label layer having a thickness of 50 to 100 µm. The container according to any one of claims 1 to 3, wherein the polyglycolic acid resin layer is colored. In addition to the main raw material resin layer having a thickness of 120 to 600 μm, a container having a laminated structure including at least one polyglycolic acid resin layer having a thickness of 2 to 200 μm is crushed, and then the crushed material is treated with alkaline water. The container is recycled by removing the polyglycolic acid-based resin layer by washing with a water and recovering the main raw material resin. The recycling method according to claim 5, wherein the polyglycolic acid resin layer is colored and the removal of the coloring from the crushed material is confirmed and the washing step is terminated. The recycling method according to claim 5 or 6, comprising a step of biodegrading the waste liquid from the washing step with activated sludge after neutralization.