JPS6360694B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing a plastic molded article, and more specifically, the present invention relates to a method for producing a plastic molded article, and more specifically, it is possible to obtain gas barrier properties by regrinding a multilayer molded article having an ethylene-vinyl alcohol copolymer layer and a low water absorption thermoplastic resin layer. The present invention relates to a method for producing plastic molded articles having excellent mechanical properties, flavor properties, and appearance properties. Ethylene-vinyl alcohol copolymer is one of the resins with the best permeability to gases such as oxygen among various resins, and this property is used to make packaging containers such as bottles and cups. It is widely used in fields such as film and film. This ethylene-
Vinyl alcohol copolymers are sensitive to humidity, and have the disadvantage that under high humidity conditions such as 100% RH, the oxygen permeability coefficient increases by about an order of magnitude. In order to improve this shortcoming,
The gas barrier layer containing ethylene-vinyl alcohol copolymer has a layered structure in which the inner and outer surface layers of low water absorption resin such as polyethylene and polypropylene are sandwiched together to reduce the influence of humidity on the ethylene-vinyl alcohol copolymer. This method has been widely adopted. When manufacturing packaging containers from this laminate, burrs due to pinch-off occur in blow molding of bottles, etc., and regrinding of punching scraps, etc. occurs in cup molding, so reusing them is a resource saving perspective. It is necessary from This regrind is based on the laminated structure mentioned above, and uses low water absorption resin and ethylene.
It is made of a blend with a vinyl alcohol copolymer, but when it is reused to mold containers, films, or sheets, the properties of the molded product are extremely poor, such as gas barrier properties, strength, etc. It was observed that mechanical properties such as elongation and impact resistance, flavor properties, and appearance properties were significantly reduced. Therefore, an object of the present invention is to provide a method for effectively utilizing regrinding of a multilayer molded product containing a low water absorbency resin and an ethylene-vinyl alcohol copolymer in the production of a molded product. Another object of the present invention is to obtain from the above regrind,
The object of the present invention is to provide a method for manufacturing molded articles such as containers, films, and sheets that have excellent gas barrier properties, mechanical properties, flavor properties, and appearance properties. According to the present invention, a plastic molded article is produced by melt extrusion molding a blend containing an ethylene-vinyl alcohol copolymer and a low water absorption thermoplastic resin alone or in combination with other resins. In the method, the blend is regrinding of a multilayer molded article having an ethylene-vinyl alcohol copolymer layer and a low water absorption thermoplastic resin layer, and the regrinding includes forced ventilation with heated gas prior to melt extrusion. and drying the regrind until the water content per vinyl alcohol unit of the ethylene-vinyl alcohol copolymer is less than 1.3% by weight, and then melt extrusion molding. be done. The present invention reuses regrinding of a multilayer molded product having an ethylene-vinyl alcohol copolymer layer and a low water absorption thermoplastic resin layer in the production of the molded product, and this regrind is performed prior to melt extrusion. It is characterized in that it is dried by forced ventilation of heated gas, and the degree of drying is such that the water content per unit of vinyl alcohol in the ethylene-vinyl alcohol copolymer is less than 1.3% by weight. be. According to the present invention, the gas barrier properties, mechanical properties, flavor properties, and appearance properties of the molded product formed from this regrind are significantly improved, and the molded product can be reused for molding into containers, films, or sheets. becomes possible. The present inventors have made the following findings as a result of extensive research into the causes of deterioration of various properties that occur during the regrind melt extrusion molding. Ethylene-
As is known per se, vinyl alcohol copolymers are water-absorbing, and therefore, regrind (hereinafter simply referred to as regrind or blend), which is a blend of an ethylene-vinyl alcohol copolymer and a low water-absorbing resin, is known as a vinyl alcohol copolymer. ) are always placed in the atmosphere, so they absorb some amount of water. Moreover, in melt extrusion of a blend of ethylene-vinyl alcohol copolymer and low water absorption resin, unlike in the case of single extrusion of ethylene-vinyl alcohol copolymer, the ethylene-vinyl alcohol copolymer in the blend is placed under very special conditions. That is, in the molten resin stream of this blend, the copolymer takes the form of a sea-island dispersed state in a continuous phase in a low water absorption resin such as polyolefin, or the copolymer takes the form of a sea-island dispersion in a continuous phase in a low water absorption resin such as polyolefin, or As proposed, it has a structure distributed in thin layers,
Moreover, the water in the blend is adsorbed by the ethylene-vinyl alcohol copolymer with the above distribution structure,
Moreover, the surrounding environment is surrounded by a hydrophobic resin medium. Furthermore, even though ethylene-vinyl alcohol copolymer can be melt-molded, it is a resin that is more susceptible to thermal deterioration than other resins such as polyolefin, so regrinding that has a history of melt-molding Thermal deterioration of the resin has already progressed. When heat acts on this ethylene-vinyl alcohol copolymer, which tends to undergo thermal deterioration, in the presence of water, the thermal deterioration of the resin progresses at an accelerated pace. In other words, it has been found that the presence of water acts as a catalyst for thermal deterioration when remelting an ethylene-vinyl alcohol copolymer that has a history of melting. Moreover, when melting the blend, the water-containing ethylene-vinyl alcohol copolymer is exposed to the melting temperature in the form of fine particles or layers confined by the hydrophobic resin, so the copolymer appears to be ,
Affected by heat under conditions such as autoclaving, resulting in gelation, rubberization, foaming, etc., resulting in reduced gas barrier properties; reduced strength, elongation, and impact resistance; resin decomposition This causes problems such as deterioration of flavor due to the inclination of the product; poor appearance due to coloring, foaming, etc. As already pointed out, in the regrind used in the present invention, since the ethylene-vinyl alcohol copolymer layer has a structure in which the ethylene-vinyl alcohol copolymer layer is sandwiched with a low water-absorbing resin layer, once the ethylene-vinyl alcohol copolymer absorbs moisture, it dries. The problem is that it is quite difficult. In the present invention, it has been discovered that when this regrind is dried by forced ventilation of heated gas, the drying can surprisingly be carried out efficiently without deterioration of the resin. That is, JP-A-55-150316 describes that when a vinyl alcohol polymer is dried by hot air drying means, the polymer becomes colored and generates a strange odor, but this is not the subject of the present invention. The reason drying is possible without these drawbacks with regrind is that a low water absorption resin layer exists on the regrind surface, preventing direct contact between the ethylene-vinyl alcohol copolymer and hot air. On the other hand, the water permeability of the low water absorption resin layer increases at high temperatures, and this is thought to be due to the fact that the water in the copolymer evaporates effectively and rapidly into the hot air through the low water absorption resin layer. . In the present invention, it should be noted that the moisture content is not the moisture content per whole regrind, but the moisture content per vinyl alcohol unit of the ethylene-vinyl alcohol copolymer. The water content during this regrind is per vinyl alcohol unit.
It is clear from the results of Examples described below that a content of less than 1.3% is extremely critical for preventing foaming and coloring of regrind molded products. As the ethylene-vinyl alcohol copolymer, an ethylene-vinyl acetate copolymer having an ethylene content of 20 to 60 mol%, especially 25 to 50 mol%, and a saponification degree of 96 mol% or more, especially 99 mol% A saponified copolymer obtained by saponification as described above is used. The saponified ethylene vinyl alcohol copolymer should have a molecular weight sufficient to form a film, and is generally 0.01 dl measured at 30°C in a mixed solvent of 85:15 weight ratio of phenol:water. It is desirable to have a viscosity of at least 0.05 dl/g, particularly at least 0.05 dl/g. Thermoplastic resins with a water absorption rate of 0.5% or less, especially 0.1% or less, as measured by ASTM D570, are used as low water absorbency resins. Typical examples thereof include low-, medium-, or high-density polyethylene, isotactyl Polypropylene, ethylene-propylene copolymer, polybutene-1, ethylene-butene-1
Olefins such as copolymers, propylene-butene-1 copolymers, ethylene-propylene-butene-1 copolymers, ethylene-vinyl acetate copolymers, ionically crosslinked olefin copolymers (ionomers), or blends thereof. Examples include thermoplastic polyesters such as polyethylene terephthalate and polytetramethylene terephthalate, and polycarbonates. In the blend used in the present invention, ethylene-
Vinyl alcohol copolymer (EVOH) and low water absorption thermoplastic resin (LMR) can be present in any ratio, but in regrind, compared to EVOH,
The amount of LMR is large, generally EVOH:LMR = 1:2 to 1:1000, especially = 1:3 to 1:500. The blend may contain thermoplastic resins other than those exemplified above. For example, since ethylene-vinyl alcohol copolymer and low water absorption resin usually do not have thermal adhesive properties, an adhesive resin may be added to one or both of these resin layers, or an adhesive resin may be added between the two resin layers. An adhesive resin layer is provided. Naturally, these adhesive resins will also be mixed into the regrind blend. Such adhesive resins include carboxylic acid,
Carbonyl based on carboxylic anhydrides, carboxylates, carboxylic amides, carboxylic esters, etc.

[Formula] groups in the main chain or side chain, 1 to 700 milli-equivalent (m・eq)/100g resin, especially 10
Examples include thermoplastic resins containing a concentration of 500 meq/100 g resin. Suitable examples of adhesive resins include ethylene-acrylic acid copolymers, ionically crosslinked olefin copolymers, maleic anhydride grafted polyethylene, maleic anhydride grafted polypropylene, acrylic acid grafted polyolefins, ethylene-vinyl acetate copolymers, Polymerized polyester, copolymerized polyamide, etc. These carbonyl-containing thermoplastic resins are generally
It is present in an amount of 200 to 0.01 parts by weight, in particular 100 to 0.1 parts by weight, per 100 parts by weight of the total amount of EVOH and LMR. In the present invention, the blend in the form of regrind is dried so that the moisture content falls within the above-mentioned range. The drying operation is performed by forcing heated gas through the regrind, using heated air or nitrogen. The temperature is such that the moisture permeability of the low hygroscopic resin is high and the moisture is effectively evaporated into the heated gas, and a temperature of 50 to 150° C. is suitable. Of course, drying may be performed in one stage or in multiple stages. Furthermore, in combination with the drying method described above,
Drying using a desiccant, for example, a drying method using a desiccant such as activated alumina, silica gel, zeolite, anhydrone, or dehydrite can be applied. A suitable example of a drying method using a desiccant is a drying method using a heated inert dry gas. For example, a double tower is filled with a desiccant, and the dry gas from one tower is heating and passing through the blend to dry the blend;
The wet gas from the blend is brought into contact with the desiccant in the tower and regenerated into dry gas, and the used desiccant in the other tower is regenerated, and these operations are performed alternately. . Strictly speaking, the moisture content in a blend can be determined by the Karl Fischer method, but it can also be easily determined by the weight reduction method using a thermobalance. The content of combined vinyl alcohol units can be determined by infrared molecular absorption spectrometry. In this specification, the water content is defined based on the amount of vinyl alcohol units in the ethylene vinyl alcohol copolymer, since the influence of water may vary depending on the vinyl alcohol unit content of the copolymer. This is because it changes. The degree of thermal deterioration of the ethylene-vinyl alcohol units in this blend is determined by measuring the blend using a differential scanning calorimeter and determining the half-width of the melting peak characteristic of ethylene-vinyl alcohol copolymers. It can be evaluated by That is, when the degree of thermal deterioration of the ethylene vinyl alcohol copolymer is low, this half-width is narrow, and when this degree is large, the half-width is large. In the present invention, it is desirable to carry out the drying treatment so that the half width (ΔT) is within 20°C, particularly within 15°C. The regrind that has been dried by the method described above can be used as it is, or if necessary, mixed with a low water absorption resin or an ethylene-vinyl alcohol copolymer to make a blend, which can then be melt-extruded and made into containers and films. It is formed into the shape of a sheet or the like. At this time, the molded product may be formed from a single layer of the blend, or it may be coextruded with other resins or resin compositions to form a molded product with a laminated structure. Other resins used for coextrusion with the blend include low water absorbency resins, ethylene vinyl alcohol copolymers, adhesive resins, and blends of two or more of these. Some suitable examples of the layer structure are BL blend, low water absorption resin.
LMR, ethylene-vinyl alcohol copolymer
EVOH and adhesive resin are expressed as AD as follows, but of course the present invention is not limited thereto. Single layer structure BL Double layer structure BL/LMR, BL/EVOH Three layer structure BL/EVOH/BL, BL/EVOH+AD/BL,
BL/EVOH+AD+LMR/BL, EVOH/AD/
BL, EVOH/BL/LMR Four-layer structure LMR/BL/EVOH/LMR+AD, LMR/
BL/EVOH+AD/LMR Five-layer structure BL/AD/EVOH/AD/BL, LMR/AD/
EVOH/AD/BL, BL/EVOH/BL/
EVOH/BL 6-layer structure LMR/AD/EVOH/AD/BL/LMR 7-layer structure LMR/BL/AD/EVOH/AD/BL/LMR 8-layer structure LMR/BL/LMR/AD/EVOH/AD/
BL/LMR Nine-layer structure LMR/BL/LMR/AD/EVOH/AD/
LMR/BL/LMR. The aforementioned blend is melt-kneaded in an extruder and then extruded into a predetermined shape through a die such as a T-die or a circular die. In the case of multilayer coextrusion, each resin layer is melt-kneaded in an extruder corresponding to the resin layer, and then extruded through a multilayer die. According to the present invention, in any of these cases, thermal deterioration of the copolymer components in the blend is prevented, so the extrusion properties are also good, and the extrudate is free from defects such as surging, hard eyes, and taring. is obtained. The molded product is
It can take the form of a film, a sheet, a parison for forming a bottle or a tube, a preform for forming a pipe, a bottle or a tube, and the like. Forming bottles from parisons, pipes or preforms
This is easily accomplished by pinching off the extrudate with a pair of split dies and blowing fluid into the interior of the pinch-off. Also,
After the pipe or preform is cooled, it is heated to a stretching temperature, stretched in the axial direction, and blow-stretched in the circumferential direction using fluid pressure to obtain a stretched blown bottle or the like. Moreover, packaging containers such as cup-shaped, tray-shaped, etc. can be obtained by subjecting the film or sheet to vacuum forming, pressure forming, stretch forming, plug-assist forming, and the like. The invention is illustrated by the following example. Example Inner and outer layers are made of low density polyethylene (Yukalon ZE)
-41, manufactured by Mitsubishi Yuka Co., Ltd.), ethylene-vinyl alcohol copolymer in the middle layer (EVAL-F, manufactured by Kuraray Co., Ltd.)
manufactured by Showa Denko Co., Ltd.), and modified polyethylene (Shorex ER-403, Showa Denko K.K.) is used for the adhesive layer, and the layer composition ratio is outer layer: adhesive layer: middle layer: inner layer = 10:0.5:
An elliptical bottle having a symmetrical five-layer laminated structure with a ratio of 1:0.5:10 was molded. The average wall thickness of the bottle was approximately 600μ, and the internal volume was approximately 280c.c. This bottle was shredded using a crusher (Daiko Seiki Co., Ltd.) to produce regrind. This regrind was stored under various conditions to maintain the moisture content described below, and then the regrind was used as the inner and outer layers. A bottle with a similar layer structure was created. The extruder has a diameter of 65 mm for the inner and outer layers, and L/D.
22, a similar one with a diameter of 40 mm and L/D of 20 for the intermediate layer, and a similar one with a diameter of 32 mm and L/D of 20 for the adhesive layer, and the die temperature was formed under conditions of 200℃. During extrusion, a hopper dryer (manufactured by Matsui Seisakusho) capable of injecting nitrogen gas was used to supply regrind while injecting dry nitrogen gas. The hot air temperature was 100°C, and the drying time was about 1.5 hours. For materials other than regrind, please
The resins were dried in a circulation oven at 100°C for 10 hours, and the moisture content of each resin was 0.1% by weight or less, and it was confirmed that no foaming or yellowing occurred during extrusion. The observation results of the molded bottle are shown below. By the way,
The regrind storage period is one day. In addition, a comparison is shown between cases in which heating is not performed using a hopper dryer, and cases in which heating is performed but no nitrogen gas is injected.

[Table] It can be seen that regrind with a large moisture content causes a lot of foaming and yellowing. Furthermore, drying is facilitated by heating and forced ventilation using a hopper dryer. Among the molded bottles, the appearance is the worst (storage conditions
90%RH, without heating with hopper dryer) Bottle (A)
A bottle (B) with the best appearance (storage conditions: 45% RH, heating with a hopper dryer) was filled with 3% saline solution, tightly stoppered, and then cooled and stored at -4°C in a refrigerator. One day later, the bottle was dropped vertically onto a concrete surface 10 times from a height of 1.2 m in a refrigerator to evaluate its impact resistance. In (A), 3 out of 10 bottles broke, while in (B), none of the 10 bottles broke. Therefore, it has been found that when molding is performed by regrinding with a high moisture content, the impact resistance also decreases. Furthermore, among the molded bottles, distilled water was added to the bottle (C) that received a rating of △ for both foaming and yellowing (storage conditions: 65% RH, heated by a hopper dryer) and the above (A) and (B). After filling and sealing, the container was stored at 37° C. for 3 days, and then the distilled water was subjected to a flavor test in the same manner as in Example 1. The results are shown below.

[Table] From the above results, it was found that products molded by regrind with a high moisture content were not good in terms of flavor. Comparative Example 1 In order to observe the extrusion behavior of the ethylene vinyl alcohol copolymer depending on the water content, a bottle was molded as in the example. Materials other than ethylene vinyl alcohol copolymer are virgin and have a low moisture content.
It is dried to less than 0.1% by weight.

[Table] When the moisture content after drying is compared with the regrind of the example, it is clearly lower, and it can be seen that the ethylene vinyl alcohol copolymer can be easily dried. However, bottle observation results show that although foaming is improved by reducing the amount of water, yellowing is not improved at all. As for regrind, clearly, foaming and yellowing disappear as the moisture content decreases. Therefore, in drying with hot air, the ethylene vinyl alcohol copolymer is directly exposed to the hot air, which seems to cause severe thermal deterioration of the ethylene vinyl alcohol copolymer, resulting in yellowing. On the other hand, in the case of regrinding, since the low water absorption resin layer serves as a protective layer, it is thought that thermal deterioration of the ethylene-vinyl alcohol copolymer can be suppressed. Comparative Example 2 The materials used in the example, low-density polyethylene, ethylene vinyl alcohol copolymer, and modified polyethylene were blended at a ratio of 20:1:1, and pellets with the same composition ratio as the regrind of the example were extruded. . Using these as the inner and outer layers, a bottle was molded and evaluated in the same manner as in the examples. During extrusion, hot air drying using a hopper dryer was carried out for 1.5 and 3.0 hours. Furthermore, regrind in the example was also evaluated.

[Table] When comparing the moisture content after drying between blend and regrind, blend tends to be lower. In regrind, the ethylene vinyl alcohol copolymer is completely sandwiched in the low water absorption resin layer, and the diffusion of water from the ethylene vinyl alcohol copolymer is excluded, whereas in blending, both are in a dispersed state. This seems to be because the diffusion of moisture is not so affected. Therefore, it is necessary to quickly dry the regrind using forced ventilation. However, from bottle observation results, although foaming is improved by reducing the water content, yellowing is not improved by hot air drying. Therefore, even in the case of a blend system, it is thought that thermal deterioration of the ethylene vinyl alcohol copolymer occurs due to hot air. Comparative Example 3 In Example and Comparative Example 1, ordinary air was used instead of nitrogen, hot air drying was performed using a hopper dryer, and a bottle was molded and evaluated in the same manner.

[Table] The amount of moisture after drying was somewhat higher than when nitrogen was used in an absolutely dry state. The yellowing of the ethylene vinyl alcohol copolymer is more severe than in Comparative Example 1, and it is expected that oxidative deterioration has also occurred. On the other hand, it can be seen that in regrind, the low water absorption resin serves as a protective layer, and oxidative deterioration can be prevented to some extent. However, hot air drying using nitrogen gas injection is more effective in preventing yellowing of the ethylene vinyl alcohol copolymer during regrinding.

Claims (1)

[Claims] 1. A method for producing a plastic molded article comprising melt extrusion molding a blend containing an ethylene-vinyl alcohol copolymer and a low water absorption thermoplastic resin alone or in combination with other resins, wherein the blend The product is regrinding of a multilayer molded product having an ethylene-vinyl alcohol copolymer layer and a low water absorption thermoplastic resin layer, and prior to melt extrusion, heated gas is forced through the regrind. 1. A method for producing a plastic molded article, which comprises drying an ethylene-vinyl alcohol copolymer until the water content per vinyl alcohol unit becomes less than 1.3% by weight, and then melt-extruding it.