JP4013031B2 - Method for producing recovered polyethylene terephthalate recycled product - Google Patents

Description

【００７５】
比較例１
実施例１とは別のソースから得た回収品を粗粉砕し、実施例１と同様に洗浄して得たものを、２つの真空ベントを有する造粒機（エレマ社製）でペレットに造粒した。得られたペレットは、径３．０×２．０ｍｍで、ＩＶ値０．６４、水分率０．５％であった。
【００７６】
こうして得られたＰＥＴペレットを、実施例１と同様の固相重合機で同様にして固相重合した。固得られたものは、ＩＶ値０．７９、水分２０ppmであり、固相重合工程は時間あたりのＩＶ値増加の割合からみて非能率なものであつた。
【００７７】
比較例２
比較例１で得られた、固相重合前のペレットの一部を用い、単に加熱乾燥空気を用い、１８０℃、３時間乾燥を行うのみで、固相重合を行うことなく、実施例１と同様の装置で同様にして、押出シート化した。得られたシートは厚み０．２ｍｍ、示差熱ピーク１１２℃、結晶化度１６％の透明ものであった。このシートを用い、実施例１と同様の装置を用い、同様にして熱成形を行った。このものは、形状としては辛うじて良好な成形はなされていたが、大部分が白濁し透明度が低下しており、又簡単に脆性破損するなど、製品としては好ましいものではなかった。この白濁部分の結晶化度は３４％であった。[0001]
[Technical field to which the invention belongs]
The present invention relates to a method for producing a polyethylene terephthalate recycled product using recovered polyethylene terephthalate.
[0002]
[Prior art]
Polyethylene terephthalate (PET) resin molded products have high strength and excellent durability such as chemical resistance, light resistance, and wear resistance, and are molded into sheets and various forms of containers, beverages, liquids Widely used as food containers and food trays. Among such PET products, methods for recycling the PET products collected as used are also being studied in various fields.
[0003]
However, in the collected PET product, the quality of the resin has been deteriorated. When the collected product is used as it is or as a pellet and used as a raw material for melt extrusion or injection molding, compared with the case where a new resin is used, it is molded. It is inevitable that the quality and quality of the resulting product will deteriorate. For this reason, recycled PET resin products may be used for some applications such as textiles, films, and sheets, but as a raw material for producing high-quality PET products that require a high degree of polymerization. It is inappropriate.
[0004]
  Conventionally, as a method for improving the quality of recovered PET resin, a method of improving the intrinsic viscosity by solid-phase polymerization in an inert gas atmosphere such as nitrogen after making the recovered PET resin into pellets, flakes, etc. is known. (Japanese Patent Laid-Open No. 7-316919)News, specialNo. 2000-219728).
[0005]
However, in the conventional recycling method, it takes a long time for solid-phase polymerization, and it is necessary to provide an extra inefficient step such as pelletization or drying. In addition, these methods cannot sufficiently remove contaminants that are attached to the recovered product and are brought in from the outside or undesirable substances that are generated in the recycling process. In addition, it is difficult to highly remove these pollutants by a method such as washing so as to have high safety and hygiene. For this reason, in the field of food packaging, the use of recycled products of recovered polyethylene terephthalate has been refrained.
[0006]
[Problems to be solved by the invention]
The main object of the present invention is to provide a method for reusing recovered polyethylene terephthalate, which can efficiently produce a product having high safety and health and excellent quality.
[0007]
[Means for Solving the Problems]
As a result of intensive studies to achieve the above-mentioned object, the present inventor made the recovered polyethylene terephthalate into thin flakes or fine pulverized particles, and then improved the IV value by solid-phase polymerization under reduced pressure. It has been found that a polyethylene terephthalate resin with few impurities and improved physical properties can be obtained in a relatively short time according to a method of forming into a sheet or film having specific characteristics by extrusion molding. When the sheet or film thus obtained is thermoformed into a predetermined shape, it has good thermoformability, excellent physical properties, and can be effectively used in the field of food packaging. It has been found that a polyethylene terephthalate product with high safety and hygiene can be obtained, and the present invention has been completed here.
[0008]
That is, the present invention provides the following method for producing a recycled polyethylene terephthalate recycled product.
1. A method for producing a recycled polyethylene terephthalate product comprising the following steps (1) and (2):
(1) Using a recovered polyethylene terephthalate containing 80% by weight or more of flakes having a minimum thickness of 1 mm or less in the form of flakes or crushed grains as a raw material, solid-phase polymerization is performed at a pressure of 7 kPa or less and a temperature of 200 ° C. or more, and an intrinsic viscosity (IV) Step of setting the value to 0.7-2:
(2) The recovered polyethylene terephthalate obtained after the solid phase polymerization obtained in the step (1) is extruded to obtain a sheet-like or film-like non-foamed material satisfying the following conditions (i) and (ii). Process,
(I) When the non-foamed material is heated at a rate of temperature increase of 10 ° C./min using a differential thermal scanning calorimeter, the temperature showing the peak of the heat radiation curve during the first heating is 115 ° C. or higher;
(Ii) The crystallinity of the non-foamed material is 20% or less.
2. The method for producing a polyethylene terephthalate recycled product according to claim 1, wherein the recovered polyethylene terephthalate contains 50% by weight or more of a beverage bottle recovered product.
3. The method according to claim 1 or 2, wherein after the solid-phase polymerization reaction, extrusion is performed using an extruder having no drying mechanism without passing through a drying step.
4). A method for producing a recycled polyethylene terephthalate product comprising the following steps (1) and (2):
(1) Using a recovered polyethylene terephthalate containing at least 80% by weight of polyethylene terephthalate in the form of flakes having a minimum thickness of 1 mm or less or pulverized grains as a raw material, solid-phase polymerization is performed at a pressure of 7 kPa or less and a temperature of 200 ° C. or more, and intrinsic viscosity (IV) Step of setting the value to 0.7-2:
(2) The recovered polyethylene terephthalate obtained after the solid phase polymerization obtained in the step (1) is extruded, and a layer satisfying the following conditions (i) and (ii) is formed into a sheet or film having a multilayer structure. Forming a non-foamed body as at least one layer,
(I) When heating at a rate of temperature increase of 10 ° C./min using a differential thermal scanning calorimeter, the temperature showing the peak of the heat release curve during the first heating is 115 ° C. or higher;
(Ii) The crystallinity of the non-foamed material is 20% or less.
5. A polyethylene terephthalate molded article obtained by thermoforming a sheet-like or film-like non-foamed material obtained by any one of the above items 1 to 4.
6). Item 6. The polyethylene terephthalate molded product according to Item 5, which is a food packaging container.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the manufacturing method of the present invention will be described in detail for each component.
Recovered polyethylene terephthalate
In the method of the present invention, recovered polyethylene terephthalate is used as a raw material. There are no particular limitations on the type of recovered polyethylene terephthalate that can be used, and in addition to used products of various polyethylene terephthalate products, defective products and molding waste generated during the production of polyethylene terephthalate products can also be used. Among such recovered polyethylene terephthalates, used products of polyethylene terephthalate products are usually contaminated and the quality of the resin is deteriorated. As a result, the molecular weight is relatively low, and the intrinsic viscosity (IV) is in the range of about 0.5 to 0.75. When used as a raw material for melt extrusion and injection molding, the resulting molded product has strength and heat resistance. The physical properties such as properties are inferior. Further, when the extruded sheet or film is thermoformed, drawdown, which is a phenomenon in which the sheet stretches and hangs down by its own weight at the preheating stage, tends to hinder the forming. Also, the thermoformed product often becomes clouded. For this reason, the condition width of thermoforming is also small, which is not preferable because the quality and production efficiency of the thermoformed product are inferior.
[0010]
The method of the present invention is a method capable of efficiently producing a product having high safety and hygiene and excellent quality using such recovered polyethylene terephthalate as a raw material.
[0011]
Among recovered polyethylene terephthalate, in particular, beverage bottles have resin properties aimed at improving strength, heat resistance, barrier properties against gases and liquids, etc. while maintaining high transparency with oriented crystals. It is suitable as a raw material for producing recycled products that require properties.
[0012]
There are two types of polyethylene terephthalate (PET) bottle production methods, the stretch blow method and the direct blow method, and most of them, including those for beverages, are produced by the stretch blow method.
[0013]
The PET bottle obtained by the stretch blow method is molded at a high temperature so that there is substantially no stretch orientation effect because the preform once injection-molded is blow molded at a temperature condition that exerts the stretch orientation effect. It has better physical properties such as transparency, gas barrier properties, rigidity, and impact strength than direct blow type. Furthermore, the resin used for the stretch blow method is manufactured through liquid polymerization followed by solid phase polymerization, and has a molecular configuration suitable for solid phase polymerization. As will be described later, the production method of the present invention is a method in which the recovered polyethylene terephthalate is solid-phase polymerized again, then formed into a sheet or film, and then subjected to thermoforming with stretching. It can be considered as a method similar to the method. Therefore, the polyethylene terephthalate recovered product produced by the stretch blow method can be particularly suitably used as a raw material in the method of the present invention. Of course, the recovered polyethylene terephthalate produced by the direct blow method can also be solid-phase polymerized, some of which are copolymerized, and can be used even if efficiency is reduced. .
[0014]
Therefore, in the present invention, a resin recovered from a beverage bottle can be particularly preferably used, and the recovered polyethylene terephthalate used as a raw material preferably contains 50% by weight or more of a recovered product of a beverage bottle. In this way, when using a large amount of beverage bottles recovered, it is easy to arbitrarily advance the oriented crystals during extrusion molding or thermoforming, which will be described later, and is excellent in transparency, toughness, heat resistance, barrier properties, etc. A polyethylene terephthalate product can be obtained, and in particular, a product suitable as a food packaging container is obtained. Further, it is easy to efficiently produce a sheet or film having a small draw-down property and a large range of thermoforming conditions, and therefore a good thermoformed product can be obtained efficiently.
[0015]
There are various types of polyethylene terephthalate products, and some of them have a small IV value from the beginning, such as fiber products. In the present invention, such fiber products can also be used as raw materials. In addition, there are copolymer resins that are difficult to solid-phase polymerize or resins that contain a crystallization accelerator, but these may be mixed within a range that does not cause a problem.
Raw material preparation
In the method of the present invention, the recovered polyethylene terephthalate is usually subjected to sorting, pulverization, washing, etc., as necessary, prior to solid phase polymerization. These steps are not necessarily in this order, and the order may be arbitrarily changed, repeated, or part of them may be omitted.
[0016]
Sorting is performed to remove components other than the polyethylene terephthalate resin from the recovered product, and the sorting method is not particularly limited. For example, in addition to visual hand sorting, wind sorting, sorting using specific gravity difference, etc., sorting may be performed using various analysis means such as infrared spectroscopic analysis, Raman spectroscopic analysis, and X-ray spectroscopic analysis. In general, a collected product such as a bottle is subjected to visual sorting or machine sorting using these analysis means, and after pulverization, wind sorting, specific gravity difference (floating) sorting, or the like is usually performed.
[0017]
In the method of the present invention, the recovered polyethylene terephthalate undergoes a solid phase polymerization reaction in the form of flakes or crushed grains. At this time, the thickness of the minimum thickness portion of the flakes or crushed grains is 1 mm or less, preferably 0.5 mm or less. In this case, the minimum thickness part of the pulverized grain means the diameter when the pulverized grain is spherical, the short diameter when it is spindle-shaped, and the minimum thickness when the pulverized grain is irregular. Say part.
[0018]
In the recovered polyethylene terephthalate used as a raw material, the recovered polyethylene terephthalate in the form of flakes or pulverized particles having a minimum thickness of 1 mm or less may be contained in an amount of about 80% by weight or more, preferably 90% by weight or more.
[0019]
There is no particular limitation on the means for making flakes or pulverized grains, and it may be not only pulverization but also cutting. Various known cutting devices, compression devices, pulverization devices, friction granulation devices, melting A granulator or the like may be used. The length of the long side of the flakes or pulverized grains may be of a size that can be charged into the extruder, but is generally about 20 mm or less, preferably about 10 mm or less. In addition, the impact pulverized product and the friction melt product are preferable to the melt granulated product and the like because they are less deteriorated due to thermal history, have a large specific surface area, and are efficient in solid phase polymerization.
[0020]
By using such flaky or pulverized particles, the solid-phase polymerization reaction rate can be improved, and a resin having a predetermined intrinsic viscosity can be obtained in a relatively short polymerization time. The removal rate and removal amount of water and moisture are increased.
[0021]
The recovered polyethylene terephthalate is preferably washed before performing the solid phase polymerization reaction. The cleaning method may be appropriately selected according to the use of the recycled product, but it is usually preferable to perform cleaning using an alkali and a surfactant.
[0022]
The sorting process and the washing process described above can be performed at any time before or after the recovered polyethylene terephthalate is formed into flakes or crushed grains having a predetermined shape.
Solid state polymerization
About the above-mentioned recovered polyethylene terephthalate, a solid phase polymerization reaction is performed under reduced pressure or under vacuum to increase the intrinsic viscosity (IV) value to 0.7-2. Usually, the solid-state polymerization may be carried out at a pressure in the reaction apparatus of about 7 kPa or less, preferably about 2 kPa or less.
[0023]
In the conventional method, generally, a solid-phase polymerization reaction is performed in an inert gas atmosphere such as nitrogen gas at normal pressure, and an IV value is improved and components such as cyclic oligomers and glycols are repolymerized. It was less.
[0024]
In the present invention, by performing a solid-phase polymerization reaction under a reduced pressure of about 7 kPa or less, in addition to the effects of the conventional method, it adheres to the resin surface, and moisture and low molecular weight impurities contained therein are more highly volatilized and removed. Thus, a high-quality recycled resin with few low molecular weight impurities can be obtained. These low molecular weight impurities include water, glycols, aldehydes, etc., and in addition to these, they may be included in the collection of used products and may be unexpected, but these are highly removed. It can be preferable in terms of safety and health. Further, it is also preferable in terms of improving productivity by reducing substances that contaminate the molding die such as cyclic oligomers.
[0025]
In addition, when solid-state polymerization is performed under the above-described reduced pressure or vacuum, the removal rate of water and free glycol is promoted, whereby the polymerization rate and degree of polymerization can be easily improved, and the IV value is reduced. A polyethylene terephthalate resin having a high IV value, which was difficult to achieve by a normal solid phase polymerization method of 1.5 or more, can be easily obtained.
[0026]
As the solid phase polymerization apparatus, either a batch type or a continuous type may be used.
[0027]
The polymerization temperature during solid-phase polymerization may vary depending on the type of raw material, the pressure during the reaction, etc., but it is necessary to be about 200 ° C. or higher. If solid phase polymerization is performed at a temperature lower than this, impurities cannot be sufficiently removed, and the polymerization rate is too slow, which is not preferable. The upper limit of the reaction temperature may be a temperature at which the recovered polyethylene terephthalate used as a raw material is not fused. Usually, the upper limit temperature may be about 250 ° C. In the present invention, in order to make the polymerization reaction, the removal of volatile components, and dehydration and drying as fast as possible, it is preferable to set the temperature within the above temperature range as high as possible and as high as possible as long as material fusion does not become a problem. However, if the reaction time is too short, the removal of volatile matter becomes insufficient or the polymerization becomes insufficient, which is not preferable. Usually, the solid phase polymerization time in the range of about 30 minutes to 100 hours may be used. What is necessary is just to set concrete heating conditions etc. suitably so that IV value of a polyethylene terephthalate resin may be about 0.7-2 in the polymerization time range of this grade.
[0028]
In the solid phase polymerization, a known cross-linking agent, polymerization catalyst, etc. may be appropriately added as necessary.
[0029]
In the present invention, since the solid-state polymerization reaction is performed under reduced pressure or under vacuum, the heating efficiency tends to deteriorate when the recovered polyethylene terephthalate is heated to a predetermined polymerization temperature. For this reason, it is preferable to devise measures such as increasing the vessel wall heat transfer area ratio of the reaction vessel to the input material as much as possible and sufficiently stirring so that the raw material can be rapidly heated to a predetermined polymerization reaction temperature. . Further, the raw material may be heated to a predetermined polymerization temperature using a liquid or gaseous heat medium, and then the heat medium may be discharged and the polymerization reaction may be performed by reducing the pressure to a predetermined pressure. May be used to heat the raw material. When the raw material is heated to a predetermined polymerization reaction temperature, each of the above treatments may be performed under pressure.
[0030]
In addition, prior to performing the solid-phase polymerization reaction at 200 ° C. or higher under reduced pressure or vacuum, the recovered polyethylene terephthalate is usually kept at about 110 to 200 ° C. in order to prevent fusion of raw materials during solid-phase polymerization. It is preferable to allow crystallization to proceed by heating. However, in this case as well, depending on the raw materials used, it may be necessary to gradually proceed with the temperature rising crystallization so as not to be fused. At this time, the heating time in this step may be appropriately set so that crystallization proceeds to such an extent that the fusion of raw materials does not become a problem in the solid phase polymerization step that is actually employed. Usually, the heating time may be about 1 to 4 hours. There is no particular limitation on the heating atmosphere, and an air atmosphere, an inert gas atmosphere, a vacuum atmosphere, or the like can be appropriately employed. The pressure at that time may be any of normal pressure, pressurization, and reduced pressure. Moreover, when using gas, it is preferable that it is a dry gas, but it does not necessarily need to be a dry gas.
Extrusion molding
After the completion of the solid phase polymerization reaction, a sheet-like or film-like non-foamed material is formed by extrusion. In the extrusion molding in this case, an appropriate section of the obtained sheet-like or film-like non-foamed material is collected and heated at a temperature rising rate of 10 ° C./min using a differential thermal scanning calorimeter (DSC). In this case, it is necessary to mold so that the temperature showing the peak of the heat release curve during the first heating (hereinafter sometimes referred to as “differential heat peak value”) is 115 ° C. or higher.
[0031]
Such a differential heat peak value is a concept newly introduced in the present invention as an index of whether a non-foamed product obtained by extrusion molding can be a molded product of good quality through thermoforming. Conventional polyethylene terephthalate This is not considered at all in the manufacturing method of the recycled product. The differential heat peak value employed in the present invention is a value measured in the initial temperature raising process, and after repeated temperature rise and temperature drop, the measured value is inappropriate as an index for evaluating thermoformability. is there.
[0032]
In the present invention, it is necessary to perform extrusion molding so that the differential heat peak value is 115 ° C. or higher, preferably 125 ° C. or higher. If the differential heat peak value is less than 115 ° C., so-called whitening phenomenon (white turbidity) that spheroidization progresses during thermoforming and transparency is lowered, and drawdown becomes large is avoided. If the thermoforming temperature is lowered a little, the material will be forcibly stretched and formed. That is, a molded product with small thickness variation cannot be obtained, or deep molding becomes difficult. For this reason, the temperature condition width which can be shape | molded is small, and the quality of a thermoformed product tends to be inferior. Furthermore, there are few or almost no appropriate condition widths for exerting the stretching effect, and it becomes difficult to obtain a material having excellent characteristics due to the stretching effect.
[0033]
In addition, the non-foamed sheet or film obtained by extrusion molding needs to have a crystallinity of 20% or less. The crystal of polyethylene terephthalate includes a spherulite with little orientation and a bar crystal called an orientation crystal with orientation. Among these, spherulites are not preferable because the crystal size is increased if the crystallization progresses excessively, the transparency of the sheet or film is lowered, and the spreadability is reduced during thermoforming. Further, with respect to oriented crystals (bar crystals), there is a preferable aspect in that drawdown is reduced when the degree of crystallization is increased, but there is a problem that extensibility is reduced during thermoforming when crystallization is excessively advanced.
[0034]
From such a viewpoint, the non-foamed sheet or film obtained by extrusion molding needs to have a crystallinity of 20% or less. In the present invention, the degree of crystallinity is a value calculated from the measured value of the density of the non-foamed sheet or film. Specifically, when the density of the sample is 1.3330 g / cc, the crystallinity is 0%, and when the density is 1.3913, the crystallinity is 50%, and the density is measured by proportional calculation based on the following formula. The crystallinity is obtained from the value.
[0035]
Crystallinity (%) = 50 × (density (g / cc) −1.3330) / (1.3913-1.3330)
In order to produce a non-foamed product having a differential heat peak value of 115 ° C. or higher, it is easier to obtain a resin having a higher differential heat peak value when the IV value of the resin is larger. IV) It is important to extrude with a value raised to 0.7-2.
[0036]
Furthermore, the orientation and crystallinity produced when a sheet-like or film-like non-foamed material is used also affect the differential heat peak value. That is, as the orientation increases, the differential thermal peak value tends to decrease. Also, within the range of 20% or less of crystallinity, which is a requirement of the present invention, the differential thermal peak value tends to decrease as the crystallinity increases.
[0037]
Various factors such as in-mold shear history, stretching rate, stretching time, resin temperature and retention time affect the orientation and crystallinity. Usually, the larger the shear history in a certain direction (usually the flow direction) inside the mold, the better the orientation. In a specific process, the orientation becomes larger when trying to obtain a thin product by reducing the gap between the outlets of the mold. Also, the larger the elongation after discharging the mold, the better the orientation.
[0038]
As for the degree of crystallinity, the crystallinity decreases if it is oriented and then rapidly cooled to solidify, and the degree of crystallinity increases if it is gradually cooled and solidified. Further, if the film is rapidly stretched and rapidly cooled, the crystallinity becomes small, and if it is slowly stretched and slowly cooled, the crystallinity becomes large. Furthermore, if the stretched and cooled product is reheated for a short time, the crystallinity increases. Even when there is little orientation, that is, when spherulites are formed, crystallization decreases if the resin discharged from the mold is rapidly cooled, and crystallization proceeds if it is slowly cooled or reheated. Furthermore, since the recovered polyethylene terephthalate may contain a crystal accelerator, this point needs to be taken into consideration.
[0039]
In consideration of the above points, the requirements of the differential heat peak value of 115 ° C. or more and the crystallinity of 20% or less are satisfied by appropriately adjusting the orientation and crystallinity of the non-foam during extrusion. A sheet-like or film-like non-foamed material can be obtained. In an actual manufacturing process, efficient production is possible by feeding back the measured values of the differential thermal peak value and the crystallinity and setting appropriate manufacturing conditions while continuing production.
[0040]
In general, when the orientation and crystallization are large, drawdown is reduced during thermoforming, which will be described later. Therefore, the orientation is within the range satisfying the above conditions of the differential heat peak value of 115 ° C. or more and the crystallinity of 20% or less. It is preferable that the crystallinity is large.
[0041]
When producing a sheet-like or film-like non-foamed material that satisfies the above-described conditions by extrusion molding, the extrusion molding machine is not particularly limited, and is a single screw extruder, a twin screw extruder, a multi-screw extruder, Any type such as a rotary type can be used.
[0042]
Polyethylene terephthalate resin is easily decomposed and deteriorated by being affected by a very small amount of water at the time of molding, and it is usually necessary for the water content to be about 50 ppm or less. For this reason, it is usually molded after being subjected to a high degree of drying treatment and then fed into an extruder or using an extruder having a high degree of drying function. Extrusion is performed by a twin screw extruder equipped with an air vent.
[0043]
In contrast, the resin subjected to solid phase polymerization by the above-described method has a very low water content because moisture and volatile components are removed at the same time as the solid phase polymerization reaction. It can be directly supplied to form a sheet or film. For this reason, a drying process can be skipped and processing time can be shortened.
[0044]
In addition, since an extruder having no drying mechanism such as a deaeration vent can be used, an expensive extruder is not required and the extrusion can be efficiently performed. A circular die may be connected to the extruder and molded by an inflation method, or a flat die may be connected and molded by a casting method. There is no limitation on the cooling or stretching of the film or sheet extruded from the mold or the conditions for stretching. Conditions for the progress of oriented crystals that exhibit a so-called stretching effect can also be set.
[0045]
In the actual process, it is desirable to supply the solid-state polymerization vessel directly to the extruder without bringing it into contact with the outside air, but it may be supplied while bringing a dry gas such as dry air or nitrogen into contact therewith. Moreover, even when it contacts temporarily with external air, you may supply to an extruder, carrying out simple drying continuously with dry gas.
[0046]
In addition to the polyethylene terephthalate resin, the extruder may be supplied with additives used for normal extrusion, such as a colorant, a crosslinking modifier, a lubricant, a crystal accelerator, and an antistatic agent. . There is no particular limitation on the method of supplying these additives, for example, a method of supplying a blended solid phase polymerized polyethylene terephthalate resin, a method of metering each material to the same port or different ports of an extruder, etc. Can be adopted.
[0047]
Note that the above-described conditions of the differential heat peak value of 115 ° C. or more and the crystallinity of 20% or less must be satisfied when a non-foamed material is used in thermoforming described later. Normally, the differential heat peak value is easily affected by moisture, and if it is stored or thermoformed in a humid place, the differential heat peak value will be lower when actually used for thermoforming than when it is extruded. Tend. For this reason, it is necessary to set a differential heat peak value at the time of extrusion molding in consideration of moisture absorption conditions and the like.
[0048]
The thickness of the non-foamed sheet or film obtained by extrusion is usually preferably in the range of about 0.05 to 5 mm. The sheet or film thus obtained has a low drawdown property, a wide range of thermoforming conditions and a good thermoformability in thermoforming, and even if used as it is, strength, toughness, heat resistance, etc. In addition, the amount of adhering contaminants and volatile matter is small, and the food hygiene is good. In particular, it is highly useful as a food packaging material. In particular, when the recovered polyethylene terephthalate used as a raw material contains 50% by weight or more of recovered beverage bottles, the formed sheet or film has particularly good transparency, toughness, thermal properties, and barrier properties. It is also excellent for thermoforming.
[0049]
Moreover, you may form the sheet-form or film-form non-foaming body which satisfy | fills above-described conditions as at least one layer of a multilayer body.
[0050]
For example, a plurality of extruders can be used to add a multilayer forming die to form a multilayer body. The multilayer die may be either a circular die or a flat die. A method of adding a joining part immediately before a commonly used die, a method of joining upstream of the die discharge slit, and a method of joining immediately after discharge from this slit. Either of these can be used. Further, instead of the method using a multilayer forming die, sheets or films produced individually may be laminated in a separate process to form a multilayer body.
[0051]
The number of layers of the multilayer body is not particularly limited, but can usually be about 2 to 6 layers. The configuration of each layer of the multilayer body is not particularly limited, and it is sufficient that at least one layer of the multilayer body is formed of a non-foamed body that satisfies the above-described conditions. In particular, since the recycled polyethylene terephthalate obtained by the above-described solid phase polymerization has few impurities and good food hygiene, it is preferable to form the surface in contact with food with this recycled polyethylene terephthalate. The other layers can be formed of, for example, unmodified recovered polyethylene terephthalate or a novel polyethylene terephthalate resin. Moreover, you may add additives, such as a coloring agent, to each layer as needed. Further, other types of resin layers, heat seal layers, gas barrier layers, and the like may be provided. In the case of such a multilayer molded body, the total thickness may be about 0.05 to 5 mm.
Thermoforming
Next, various polyethylene terephthalate products can be obtained by thermoforming the sheet-like or film-like non-foamed body obtained by the above-described extrusion molding.
[0052]
There is no particular limitation on the thermoforming method. For example, using a single-wafer molding machine, a continuous molding machine, etc., various molding methods such as vacuum molding, pressure molding, matched die molding, plug assist molding, etc. are arbitrarily used. The target product can be produced by setting conditions.
[0053]
When thermoforming using a non-foamed sheet or film that satisfies the above-mentioned conditions, the appropriate temperature condition range for thermoforming is large, the drawdown property is small, and the sheet is spread with a uniform thickness. Easily eliminates spherulite growth that causes a decrease in transparency, and can be made to have excellent mechanical properties due to the property of moderately oriented or easily oriented crystals, and efficiently produce excellent thermoformed products It becomes possible. In other words, due to the large appropriate condition width and small draw-down property, for example, a relatively thick sheet of about 1 to 2 mm allows a temperature difference between the surface and the inside, and the crystallization progresses on the surface to impair thermoforming. Heating can be performed without causing the temperature variation in the molding machine and the variation in heating time to increase the efficiency of non-defective product production. Furthermore, due to the property that the drawdown is small and it is easy to spread with a uniform thickness, it is possible to perform deep molding with a large so-called drawing ratio, or molding with high precision.
[0054]
Although the heating temperature time condition and the cooling rate are arbitrary within the range where molding is possible, in the present invention, by using a non-foamed material that satisfies the above-described conditions, the appropriate temperature condition width for thermoforming increases, and the orientation The range suitable for crystallization is also included. For this reason, it is possible to express the stretching effect well by thermoforming under the condition that oriented crystals occur, and in particular, the strength, toughness, impact resistance is high, the gas barrier property, the heat-resistant dimensional stability are good, and the transparent It becomes possible to obtain a molded product having excellent properties. In order to obtain a thermoformed product having high transparency and excellent mechanical properties, which is one of the objects of the present invention, the crystallinity of the thermoformed product is 20% or less when spherulites are generated. However, if only the oriented crystal grows, it may be much more than this, for example, it may reach 30% or 40%.
[0055]
In addition, the molded article obtained by the method of the present invention is free from harmful substances adsorbed on the resin, contaminants, impurities generated during the polymerization reaction, etc. by performing solid-phase polymerization under reduced pressure. The product is highly hygienic. For this reason, for example, it can be suitably used as a food packaging container such as a pack of eggs, vegetables, pickles, etc., or various trays used for vegetables, meat and the like.
[0056]
【The invention's effect】
According to the method of the present invention, a high-quality recycled polyethylene terephthalate product having excellent physical properties can be obtained by an efficient production method using recovered polyethylene terephthalate as a raw material. In particular, according to the method of the present invention, it is possible to efficiently produce a high-quality thermoformed product that has few impurities and is excellent in safety and hygiene, so that the recovered polyethylene terephthalate can be effectively used as a raw material for food packaging containers. It becomes possible.
[0057]
【Example】
Hereinafter, the present invention will be described in more detail with reference to examples.
[0058]
Example 1
The collected colorless beverage bottles made of polyethylene terephthalate (PET) were pulverized and sorted by a pulverizer having a punching metal screen having a hole diameter of 8 mm, and the screen-passed products were classified into winds by labels and polyolefins. Next, alkaline water washing and rinsing were performed, and the polyolefins were separated by specific gravity with a hydrocyclone. Thereafter, the PET component was drained with a dehydrator and then air-dried to obtain a PET flake. The moisture content was 0.4%. The average thickness of the flakes was 0.47 mm, and the IV value was 0.743.
[0059]
The PET flakes thus obtained (500 kg) were put into a double-cone solid-phase polymerization machine having a capacity of 1500 liters without re-drying. The solid phase polymerization machine used has a heat medium jacket and has a structure that enables heating and cooling by circulation of heat medium oil (Barrel Therm # 200). While stirring the fed PET flakes at a rotation speed of 5 revolutions per minute, the temperature is raised to 130 ° C. at a rate of about 2 ° C. per minute with vessel wall heating and heated dry air, and held for 2 hours, followed by drying and crystallization. Made progress. Next, the temperature was switched to a high temperature setting (230 ° C.) so as to increase the temperature at the same speed. The final ultimate pressure was 133 Pa. During this time, the wall heating and rotation were maintained. In addition, the processing time setting of 200 degreeC or more was 10 hours. After completion of the reaction, the pressure was returned to normal pressure with nitrogen, and the contents were taken out after cooling.
[0060]
The PET flakes taken out had no fused mass, and there was no fused mass in the apparatus. The IV value was 0.99, and the water content was 20 ppm.
[0061]
The resin modified by the above method is supplied to a twin-screw extruder rotating in the same direction without venting with a diameter of 100 mm and L / D = 40 without making contact with substantially outside air while flowing a nitrogen air flow. Then, it was extruded from a T die having an effective width of 1200 mm connected to this extruder at a rate of 550 kg per hour and cast. The opening gap of the mold was 0.4 mm.
[0062]
The obtained sheet was colorless and very transparent with a width of 1160 mm, a thickness of 0.2 mm, a differential heat peak value of 130 ° C., and a crystallinity of 1%. Moreover, it was clean, suitable for a laminated material or a food packaging material as it was, and suitable for a thermoforming material.
[0063]
About this material, using a continuous thermoforming machine by a plug-assist vacuum forming method, thermoforming was performed by taking 16 shots of egg pack containers containing 10 folds each having an outer shape of about 220 × 245 mm and a depth of 40 mm. .
[0064]
In thermoforming, there was little drawdown, there was no generation of defective products such as wrinkles, and such deep-drawn molded products could be produced efficiently without precise temperature setting. In addition, the resulting molded product was precisely molded in detail, with high uniformity in thickness of each part, transparency and cleanliness, and high safety and hygiene, making it suitable for food packaging. . Further, the molded product had high rigidity and strength, low brittleness, and was comparable to a commercially available similar product using virgin resin. The crystallinity of the thermoformed product was 1 to 6%, depending on the site.
[0065]
Example 2
Except for using a solid-phase polymerized material in the same manner as in Example 1 and expanding the mold gap to lower the take-up speed, extrusion is performed in the same manner as in Example 1, and the thickness is 0.4 mm, the effective width is 950 mm, A sheet having a differential heat peak value of 131 ° C. and a crystallinity of 0% was molded.
[0066]
About this sheet | seat, the food container with a pattern with an external diameter of 130 mm and a drawing depth of 60 mm was thermoformed per shot 36 pieces by plug assist vacuum forming.
[0067]
The obtained molded product was excellent as in Example 1, and the deep drawing with a pattern was particularly precisely molded.
[0068]
Example 3
A used collection of egg packs molded with A-PET sheets is pulverized and classified by a pulverizer having a punching metal screen with a hole diameter of 8 mm. The screen-passed product is washed with alkaline water, then rinsed and air-dried. went. The thickness of the pulverized product was 0.19 mm, and the IV value was 0.69.
[0069]
500 kg of the PET flakes thus obtained were put into the same solid phase polymerization machine as in Example 1, and solid phase polymerization was performed under the same conditions as in Example 1.
[0070]
The obtained product had an IV value of 1.05 and a water content of 20 ppm, and the solid phase polymerization process was highly efficient in terms of the rate of increase in IV value per hour.
[0071]
By using the obtained solid phase polymerization resin and extruding in the same manner using the same apparatus as in Example 1, a highly transparent sheet with a differential heat peak of 132 ° C. and a crystallinity of 0% can be easily obtained. I was able to.
[0072]
Experimental example 1
The same processing was performed except that the same pulverized particles as in Example 3 were used and the solid phase polymerization time was changed. As a comparative experiment, solid phase polymerization was performed under a nitrogen atmosphere at normal pressure instead of performing solid phase polymerization under reduced pressure.
[0073]
The change in intrinsic viscosity (IV) with respect to the polymerization time is shown in Table 1 below. From this result, it was confirmed that the polymerization rate was increased when solid phase polymerization was performed under reduced pressure.
[0074]
[Table 1]

[0075]
Comparative Example 1
A product obtained from a source different from that in Example 1 is roughly pulverized and washed in the same manner as in Example 1 to produce pellets using a granulator (made by Elema) having two vacuum vents. Grained. The obtained pellet had a diameter of 3.0 × 2.0 mm, an IV value of 0.64, and a moisture content of 0.5%.
[0076]
The PET pellets thus obtained were subjected to solid phase polymerization in the same manner as in the solid phase polymerization machine similar to Example 1. The solid product obtained had an IV value of 0.79 and a water content of 20 ppm, and the solid phase polymerization process was inefficient in terms of the rate of increase in IV value per hour.
[0077]
Comparative Example 2
Using a part of the pellets obtained in Comparative Example 1 before solid phase polymerization, simply using heated and dry air, and drying at 180 ° C. for 3 hours, without performing solid phase polymerization, Example 1 and Extrusion sheets were formed in the same manner using the same apparatus. The obtained sheet was transparent with a thickness of 0.2 mm, a differential heat peak of 112 ° C., and a crystallinity of 16%. Using this sheet, thermoforming was performed in the same manner using the same apparatus as in Example 1. Although this product was barely well formed as a shape, most of the product was cloudy, its transparency was lowered, and it was not preferable as a product because it easily brittlely broken. The crystallinity of this cloudy portion was 34%.

Claims (4)

A method for producing a polyethylene terephthalate recycled product for producing food packaging containers by thermoforming, comprising the following steps (1) and (2):
(1) Using a recovered polyethylene terephthalate containing 80% by weight or more of flakes having a minimum thickness of 1 mm or less in the form of flakes or crushed grains as a raw material, solid-phase polymerization is performed at a pressure of 7 kPa or less and a temperature of 200 ° C. or more, and an intrinsic viscosity (IV) Step of setting the value to 0.7-2:
(2) The recovered polyethylene terephthalate obtained after the solid phase polymerization obtained in the step (1) is extruded to obtain a sheet-like or film-like non-foamed material satisfying the following conditions (i) and (ii). Process,
(I) When the non-foamed material is heated at a rate of temperature increase of 10 ° C./min using a differential thermal scanning calorimeter, the temperature at which the peak of the heat dissipation curve during the first heating is 115 ° C. to 132 ° C. ;
(Ii) The crystallinity of the non-foamed material is 20% or less. The method for producing a polyethylene terephthalate recycled product for producing food packaging containers by thermoforming according to claim 1, wherein the recovered polyethylene terephthalate contains at least 50% by weight of a beverage bottle recovered product. 3. Production of a polyethylene terephthalate recycled product for food packaging container production by thermoforming according to claim 1 or 2, wherein after the solid-state polymerization reaction, extrusion is performed using an extruder having no drying mechanism without passing through a drying step. Method. A method for producing a polyethylene terephthalate recycled product for producing food packaging containers by thermoforming, comprising the following steps (1) and (2):
(1) Using a recovered polyethylene terephthalate containing 80% by weight or more of flakes having a minimum thickness of 1 mm or less in the form of flakes or crushed grains as a raw material, solid-phase polymerization is performed at a pressure of 7 kPa or less and a temperature of 200 ° C. or more, and an intrinsic viscosity (IV) Step of setting the value to 0.7-2:
(2) The recovered polyethylene terephthalate obtained after the solid phase polymerization obtained in the step (1) is extruded, and a layer satisfying the following conditions (i) and (ii) is formed into a sheet or film having a multilayer structure. Forming a non-foamed body of at least one layer,
(I) When heating at a rate of temperature increase of 10 ° C./min using a differential thermal scanning calorimeter, the temperature showing the peak of the heat dissipation curve during the first heating is 115 ° C. to 132 ° C . ;
(Ii) Crystallinity is 20% or less.