JPH08281775A - Thermoplastic resin molded object reduced in offensive taste and smell - Google Patents

Abstract

PURPOSE: To reduce offensive taste and smell by supplying a thermoplastic resin, inert gas and a specific ratio of water to an extruder to melt and knead the resin and discharging the lightweight substance formed at this time from the place immediately before the resin emitting orifice of the extruder along with the inert gas and water through a discharge device. CONSTITUTION: A thermoplastic resin is supplied to an extruder along with inert gas and water of which amt. is below 1% by wt. of the resin to be melted and kneaded and the lightweight substance formed by this kneading is discharged from the place immediately before the resin emitting orifice of the extruder along with the inert gas and water through a discharge device. As the thermoplastic resin, a polyolefin resin is especially desirable and, as the inert gas, nitrogen gas is especially desirable. The inert gas is blown into the hopper to the extruder of the thermoplastic resin to hold the interior of the hopper and the interior of the extruder to a low oxygen or oxygen free state and, by this method, oxidizing reaction is suppressed to the utmost and the discharge of the lightweight substance is accelerated. As the discharge device, a vacuum pump is desirable.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermoplastic resin molded product with reduced off-taste and off-flavor.

[0002]

2. Description of the Related Art Thermoplastic resins such as polyolefin resins are widely used as packaging materials for beverages and foods.
One of the properties required of the material is that it does not impair the aroma and taste of the contents such as drinks and foods. One of the causes of impairing the scent and taste of the contents is the migration and invasion of the taste and odor components from the packaging material into the contents. In order to prevent the migration and invasion of the components from the packaging material, the inner surface of the material that is in direct contact with the contents is covered with metal or the like, but when the materials become expensive and special contents are packed. Can only be used for

Molding of thermoplastic resin into packaging products such as drinks and foods is usually carried out by melting and softening the resin, but this melting causes the resin to oxidize and thermally decompose, resulting in off-taste and off-flavor. The component that causes is generated.

Conventionally, many molding processes of this packaging product are carried out through an extruder, but an inert gas such as nitrogen gas is sent to the extruder together with the resin so that no off-taste or offensive odor is generated during the molding process. Supply method, method that suppresses thermal decomposition of resin by performing molding process at low temperature, method that discharges off taste and odor components with vacuum pump, oxidation of resin by adding antioxidant (heat deterioration), heat Further, methods such as a method of preventing deterioration and a method of using a resin subjected to a low taste odor treatment as a raw material resin are performed. By these methods, the generation of off-taste and off-flavor in the molding process is suppressed, and by extension, the migration and invasion into the contents are prevented.

However, the effects of the above-mentioned and the above methods are small, and the productivity of the molding process is greatly reduced by the above-mentioned method. In the above-mentioned method, the inhibitor itself is decomposed and deteriorated to give a new taste. The above-mentioned method, in which an offensive odor component is generated, is most effective, but again in the extruder,
There is a problem that the resin is oxidized and decomposed, and a new off-taste or off-flavor component is newly generated.

[0006]

DISCLOSURE OF THE INVENTION It is an object of the present invention to provide a thermoplastic resin molded article in which the occurrence of off-taste or off-flavor, which occurs during the molding of a thermoplastic resin container for food or drink which is disliked by off-taste or off-flavor, is reduced. To aim.

[0007]

As a result of intensive studies, the inventors of the present invention have found that when molding a thermoplastic resin through an extruder, the resin is treated with an inert gas and a trace amount of water in the extruder. The present invention has been completed by finding that the object of the present invention can be achieved by supplying and forcibly discharging the light-weight substance generated therein.

That is, according to the present invention, a thermoplastic resin is melt-kneaded by supplying it to an extruder together with an inert gas and water of less than 1% by weight with respect to the resin, and a lightweight substance produced by this kneading is A gist of a thermoplastic resin molded body having a reduced off-flavor is formed by molding a resin obtained by discharging the resin together with an active gas and water vapor through a discharger from a position immediately before a resin discharge port of an extruder.

The thermoplastic resin used in the present invention is a polyolefin resin, polyvinyl chloride resin, polyester resin, polystyrene resin, polyvinylidene chloride resin,
Examples thereof include polyamide resins and ethylene-vinyl acetate copolymers. Among these, polyolefin resin is particularly desirable.

As the polyolefin resin which can be used,
Ethylene homopolymer, propylene, 1-butene, 1-
Hexene, 4-methyl-1-pentene, homopolymer of α-olefin such as 1-octene, copolymer of ethylene and one or more α-olefins, α-olefin and one or two or more Examples thereof include copolymers with other α-olefins.

Among these, ethylene homopolymers,
A copolymer (hereinafter referred to as a polyethylene resin), a homopolymer of propylene, and a copolymer (hereinafter referred to as a polypropylene resin) are particularly desirable.

As the polyethylene resin, low density polyethylene (LDPE) produced by a high pressure method and linear low density polyethylene (LLD) which is a copolymer with α-olefin are used.
PE), medium density polyethylene (MDPE) produced using Phillips catalyst, Ziegler-Natta type catalyst, etc.
Alternatively, high density polyethylene (HDPE), ultra low density polyethylene (VLDPE) and the like can be used.

These polyethylene resins have a melt index (MI; JIS K7210; load 2.16 k).
g, measured at 190 ° C.) of 0.1 to 100 g / 10 minutes is preferable.

As the polypropylene resin, a homopolymer of propylene, a random copolymer of propylene and ethylene or α-olefin, and a block copolymer can be used. These are mainly produced by using a Ziegler-Natta type catalyst. These polypropylene resins are melt flow rate (MFR; JIS K721
0; load 2.16 kg, measured at 230 ° C) is 0.3 to 50
It is preferably g / 10 min.

As the polyester resin, polyethylene terephthalate, polybutylene terephthalate, etc. may be used.
As the polystyrene resin, polystyrene, acrylonitrile-styrene copolymer, acrylonitrile-butadiene-styrene copolymer, and the like, and as the polyvinylidene chloride resin, polyvinylidene chloride, vinylidene chloride-vinyl chloride copolymer, vinylidene chloride-acrylonitrile. Examples of polyamide resins such as copolymers include nylon 6, nylon 66, nylon 11 and nylon 12.

According to the present invention, when a thermoplastic resin is molded and processed through an extruder to produce a molded article, an inert gas and a small amount of water are supplied to the extruder together with the thermoplastic resin, melted and kneaded, and then extruded. A lightweight substance consisting of many foreign substances generated in the aircraft, together with the supplied inert gas and generated steam,
It consists of forcibly discharging from a place just before the resin discharge port via a discharge machine.

In the present invention, examples of the inert gas supplied to the extruder together with the thermoplastic resin include nitrogen gas, carbon dioxide gas, helium gas and argon gas, and nitrogen gas is particularly desirable.

The inert gas is supplied by blowing the thermoplastic resin into a hopper which is a supply part of the extruder to keep the inside of the hopper and the inside of the extruder in a low oxygen or anoxic state. In order to suppress the oxidation reaction of the resin at the time of melt-kneading in the extruder as much as possible.

Further, the supply of the inert gas acts to suppress the entrainment of the lightweight material produced by the melt-kneading in the thermoplastic resin and to promote the discharge of the lightweight material from the extruder in the subsequent stage. The water supply to the extruder is introduced into the hopper of the extruder as well as the thermoplastic resin and the inert gas,
The supply amount is less than 1% by weight with respect to the raw material thermoplastic resin,
Preferably 100 weight PPm to 10,000 weight PPm
Less, more preferably 1,000 to 5,000 weight pp
m. When the supply amount is 1% by weight or more, the thermoplastic resin is decomposed and foreign matters such as wax-like substances are generated, which is not desirable. To supply such a trace amount of water to the extruder,
This is the main feature of the present invention, and when it is lacking, the object of the present invention is not achieved at all.

In the presence of an inert gas and water (steam), the thermoplastic resin is heated at a temperature above the melting temperature of the polyolefin resin in the extruder, for example, 150 to 300 ° C. in the case of polyethylene resin and polypropylene resin. Melt kneaded. As the extruder, any extruder can be used as long as it can be used for molding a molded product.

In addition, the raw material thermoplastic resin contains usual additives such as an antioxidant, a heat stabilizer, a neutralizing agent, an ultraviolet absorber, a light stabilizer, a lubricant, an antiblocking agent, an antistatic agent and a colorant. It is desirable that the additives are not blended, but those blending these additives can be used as long as they do not adversely affect the present invention.

According to the present invention, the light weight substance produced by the above-mentioned melt-kneading is then passed from a position just before the resin discharge port of the extruder through a suitable discharger together with the supplied inert gas and water vaporized water vapor. And discharge it outside the extruder.

As the ejector, any model can be used, but a model that can reduce the suction portion of the ejector to 1 atm or less, such as a vacuum pump, is desirable.

The thermoplastic resin treated as described above greatly reduces the content of substances which are considered to be the causative substances of off-taste and off-flavor, as compared with the resin obtained by simply passing through an extruder. , The offensive odor is also greatly improved.

The present invention is a molded product obtained by molding the thermoplastic resin obtained by the above method, and the molding also includes laminating with another member. Therefore, in the molded product, the resin By a normal molding machine, powder, pellets, containers, films, sheets, plates, molded articles formed into the required shape such as pipes, those molded articles, particularly films, sheets,
Laminated article formed by laminating other members such as paper, plastic film, plastic sheet, metal box, etc. by ordinary laminating means such as dry lamination, and the thermoplastic resin by ordinary laminating means such as direct lamination. For example, a laminated molded body obtained by directly laminating the above-mentioned other member is included. It is desirable that the molding and laminating processes are performed at a height and a temperature lower than the temperature at the time of melt-kneading in order to prevent the thermoplastic resin from being again oxidized or thermally decomposed.

[0026]

EXAMPLES The present invention will be described in detail with reference to Examples. In addition,
The test method in the examples was carried out by the following method.

Sensory test Pellets obtained in Examples and Comparative Examples were sealed in glass containers and stored for 5 days, and then subjected to the following tests. In each test, 5 panelists were good (5). -Evaluated in 5 grades of bad (1).

Odd taste test 10 g of pellets were put in 90 ml of distilled water and allowed to stand at room temperature for 2 days to evaluate the taste of the water.

Odor test 50 g of pellets were directly evaluated for odor.

2 g of GC (gas chromatographic) analysis pellets were heated at 100 ° C. for 10 minutes, the generated gas was collected in a trap tube at −130 ° C. while blowing helium gas, and then the trap tube was rapidly heated to 250 ° C. It was introduced into the GC analyzer. The area of all peaks of the obtained gas chromatogram was evaluated.

MI (melt index) Measured at 190 ° C. under a load of 2.16 kg according to JIS K7210.

MFR (melt flow rate) JIS K7210 conformity Measured at a load of 2.16 kg and 230 ° C.

SR (Swelling Ratio) The size of the strand obtained at the time of MI measurement is measured at two positions 5 mm below the strand, and the average thickness of the strand is divided by the inner diameter of the orifice of the tester to obtain the value.

[0034] Density JIS K7112 compliant (Example 1) extruder (30mmφ, L / D = 30 ) of the hopper - low density polyethylene (LDPE; MI7.8g /
10 minutes, SR1.57, density 0.916g / cm ^3),
Water and nitrogen gas of 3,000 ppm by weight are supplied to LDPE, melted and kneaded at 220 ° C., and a lightweight substance generated inside the extruder is supplied from the vent portion immediately before the resin discharge port, to which nitrogen gas is supplied. After the water was discharged with a vacuum pump together with the changed steam, the resin was extruded from a die attached to the extruder and molded into pellets.

As a result of measuring the physical properties of the obtained pellets,
MI 7.2 g / 10 minutes, SR 1.65, density 0.916
It was g / cm ³ . It was found that the deterioration of the resin was slight.

(Comparative Example 1) Pellets were obtained in the same manner as in Example 1 except that water and nitrogen gas were not used and the gas was not discharged by a vacuum pump. As a result of measuring the physical properties of this pellet, MI 5.9 g / 10 minutes, SR
It was 1.84 and the density was 0.916 g / cm ³ . It was found that the resin was more deteriorated than in Example 1.

Example 2 Pellets were obtained in the same manner as in Example 1 except that polypropylene (PP; MFR 0.5 g / 10 min) was used instead of LDPE and the melt-kneading temperature was 250 ° C. (Comparative Example 2) Example 2 is the same as Example 2 except that water and nitrogen gas are not used and the gas is not discharged by a vacuum pump.
Pellets were obtained in the same manner as in.

Pellets obtained in Example 1, Comparative Example 1, Example 2 and Comparative Example 2 and LDPE used as a raw material
A sensory test was conducted on PP and PP, and the following results were obtained in both the off-taste test and the off-flavor test.

Raw Material LDPE ≧ Example 1 >> Comparative Example 1 Raw Material PP ≧ Example 2 >> Comparative Example 2 Further, GC analysis was performed on the raw material LDPE pellets and the pellets obtained in Example 1 and Comparative Example 1. As a result, the area of all peaks was 8.0 times that of Example 1 and 36.9 times that of Comparative Example 1 with respect to that of the pellets of the raw material LDPE, confirming the relationship with off taste and odor. Was given.

[0040]

INDUSTRIAL APPLICABILITY In the thermoplastic resin molding of the present invention, the causative substances of off-taste and off-flavor are greatly reduced. Therefore, the molded product of the present invention, particularly the package of drinks and foods, has the effect of not impairing the scent and taste of the contents.

Further, the present invention is effective not only for beverages and food packaging products that are extremely disliked by taste and smell, but also as containers for cosmetics and the like that are disliked of off-flavors, interior and exterior products for daily necessities and home appliances, interior parts for automobiles, etc. Is.

Claims (3)

[Claims] 1. A thermoplastic resin is supplied to an extruder together with an inert gas and water in an amount of less than 1% by weight with respect to the resin, melt-kneaded, and a lightweight substance produced by this kneading is mixed with an inert gas and steam. At the same time, a thermoplastic resin molded body having a reduced off-flavor is formed by molding a resin obtained by discharging the resin through a discharger from a position immediately before a resin discharge port of an extruder. 2. The molded product according to claim 1, wherein the thermoplastic resin is a polyolefin resin. 3. The molded product according to claim 2, wherein the polyolefin resin is a polyethylene resin or a polypropylene resin.