JPH05269754A - Purging agent - Google Patents

Abstract

PURPOSE:To rapidly discharge a thermoplastic resin remaining in a melt resin path in a device for melting and molding the thermoplastic resin to improve a product loss caused by a remaining purging agent to a great extent by a method wherein the purging agent is made of a thermoplastic resin meeting specific two formulas. CONSTITUTION:A perging agent is made of a thermoplastic resin meeting formulas I, II, where MI (15) is a melt index (g/10min) after heating for 15min at 220 deg.C (in nitrogen) (in a melt index determination at 190 deg.C under a load of 2160g), and MI (300) is a melt index (g/10min) after heating for 300min at 220 deg.C (in nitrogen) (in a melt index determination at 190 deg.C under a load of 2160g). The melt index of a purging agent of ethylene-vinyl alcohol copolymer (EVOH) at the time of purging is lower than that of an EVOH to be substituted. Therefore, the purging agent can discharge the EVOH in a flow path silimilarly to a conventional purging agent. Since the melt index of the purging agent is increased with time, the purging agent per se is easily discharged from the flow path.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is capable of promptly discharging EVOH remaining in a melting channel in an apparatus for melt molding a thermoplastic resin, particularly an ethylene-vinyl alcohol copolymer (hereinafter referred to as EVOH), and The present invention relates to a purging agent in which, when EVOH is introduced again into a flow channel, product defect loss due to the remaining purging agent is significantly improved.

[0002]

2. Description of the Related Art EVOH is today a packaging film for foods, containers, especially foods that require a barrier property against oxygen,
It has been found to be effective in fields where it is intended to be used for products requiring aroma retention.

However, when the EVOH is melt-extruded and molded, if the EVOH is run for a long time, the EVOH is gelated or decomposed in a stagnation portion in the resin flow path, so that the product may be mixed with lumps and gel-like substances. Alternatively, appearance defects may occur due to uneven thickness, streaks, and the like. Also, after stopping the operation, when restarting the operation, gelation in the resin flow path,
Alternatively, effervescent decomposition occurs and EVOH that has turned yellow is discharged for a long period of time, resulting in a great amount of time and a loss of extraordinary product for collecting a normal product. In the worst case, it is necessary to disassemble and clean the inside of the device flow path.

In order to solve these problems, when an abnormality such as a gel or a streak occurs during long-term operation, or when the operation is stopped, the EVOH resin flow path is filled with, for example, high density polyethylene (HDPE), A method of purging with linear low-density polyethylene (LLDPE), polystyrene (PS), polypropylene (PP) or the like is adopted. In particular, in order to increase the efficiency of purging, the melt viscosity index of the purging agent (the melt index measured at 190 ° C. under a load of 2160 g, 0.05 to 10 g / 10
A resin with a low content) is used, or depending on the case, a resin with a low melt index is gradually changed to lower the extrusion temperature and / or increase the discharge amount.

However, the purging operation is complicated and requires a lot of time and a purging agent, and, worse, when the purging is completed and EVOH is introduced into the flow path to restart the purging, A large amount of time is required for the purging agent to remain in the product for a long time and a normal product can be collected. In particular, PS, polyethylene terephthalate (PET), polycarbonate (P
In the case of a multilayer product such as C) or a structure to which a stretching operation is applied, there is a problem that a gel or a hump-like substance is mixed with a purging agent or a pinhole is broken in the EVOH layer at the time of stretching due to a gel or a hump-like substance. To make matters worse, the lower the melt index of the purging agent is, the more effective it is to remove the retained gel substance in the EVOH channel.
When restarted with, the purging agent is not easily discharged and remains in the product for a long time and is mixed. As a countermeasure against this, a method of gradually increasing the melt index of the purging agent at the time of restarting with EVOH is also adopted, but the operation is complicated, and the time and the amount of the purging agent become very large. It wasn't effective.

It is also described in JP-A-1-178545 that when a resin obtained by blending a polyamide-polyether elastomer with EVOH is used as a purging agent, it takes a short time to obtain a product after restarting with EVOH. ing. However, while this method has excellent effects, it is still insufficient.

From these points, it is easy to remove the retained gel-like substance in the EVOH flow path, and it is easy to discharge the purging agent by EVOH, that is, when the EVOH is restarted, it is commercialized in a short time. The development of possible purging agents is one of the important issues.

[0008]

EVOH has various excellent properties as described above, but when melt extrusion molding, coextrusion molding or coinjection molding is restarted for a long time or stopped, gel, There is a case that lumps, streaks, etc. are mixed in the product. Therefore, an object of the present invention is to easily remove the gel-like substance staying in the EVOH channel, and
The purpose is to provide a purging agent that can be discharged in a short time when restarting.

[0009]

The above object is achieved by providing a purging agent comprising a thermoplastic resin satisfying the following formulas (I) and (II). 20 ≧ MI (15) ≧ 0.01 (I) 0.05 ≧ MI (15) / MI (300) ≧ 10 ^-4 ... (II) MI (15) ... 220 ° C. (in nitrogen) Melt index after heating for 15 minutes (g / 10 minutes) (190 ° C., 2160)
Melt index (g / 10 minutes) after heating MI (300) ... 220 ° C. (in nitrogen) 300 minutes (190 ° C., 216
(Measured under 0g load)

According to the purging agent of the present invention, in a device for melt-molding a thermoplastic resin, the thermoplastic resin remaining in the melting channel can be promptly discharged, and the thermoplastic resin is reintroduced into the channel. In this case, since the purging agent itself can be discharged in a short time, the product loss due to the remaining purging agent can be greatly improved. Further, as the thermoplastic resin of the purging agent, when using a thermoplastic resin having a lower melt index than that of the thermoplastic resin to be replaced and higher than that of the thermoplastic resin to be replaced with the passage of time, the above effect is further enhanced. When the thermoplastic resin of the purging agent is of the same type as the thermoplastic resin to be replaced, for example, EVOHs, the effect is further promoted.

By satisfying the above formulas (I) and (II), the excellent effects as described above can be obtained as shown in the examples of the postoperative method, but the formulas (I) and (II) are more preferable. The conditions are as follows. 5 ≧ MI (15) ≧ 0.5 ... (I) ′ 0.01 ≧ MI (15) / MI (300) ≧ 10 ⁻⁴ ··· (II) ′

EVOH is suitable as the thermoplastic resin used in the purging agent in the present invention. This point will be described below. EVOH is also suitable as a resin to be substituted, to which this purging agent is applied, and this point will also be described.

EVOH used as a purging agent and a thermoplastic resin to be substituted in the present invention has an ethylene content of 15 to 70 mol%, preferably 20 to 60 mol%, and a saponification degree of a vinyl acetate component of 90% or more. It is preferably a saponified product of ethylene-vinyl acetate copolymer of 95% or more. This EVOH may be modified with a small amount of a copolymerization monomer, and as the modifying monomer, propylene,
1-butene, 1-hexene, 4-methyl-1-pentene, acrylic acid ester, methacrylic acid ester, maleic acid, phthalic acid, itaconic acid, alkyl vinyl ether, N-vinylpyrrolidone, N-normal butoxymethyl acrylamide, N- (2-dimethylaminoethyl)
Methacrylamides or quaternized products thereof, N-vinylimidazole or quaternized products thereof, and olefinically unsaturated monomers containing silicon (vinyltrimethoxysilane, vinyltriethoxysilane, vinylmethyldimethoxysilane, vinyltriacetoxysilane, etc.) Can be illustrated.

EVOH is generally saponified by adding a caustic alkali or an alkali metal alcoholate to an alcohol solution of an ethylene-vinyl acetate copolymer and then removing sodium acetate by-produced at the time of saponification by washing with water. Further, it can be obtained by adding an acid thereto, or immersing it in an acid solution, or adding a metal salt of a certain kind and an acid in combination.

EVOH used as a purging agent can be obtained by using a method described in, for example, JP-A-64-66262 in order to impart "a special viscosity change with time". This method will be described below. That is, EVOH contains (A) one or more metal salts of metals belonging to Group II of the Periodic Table, (B) pka
(Acidity index at 25 ° C) 3.5 or more, boiling point under normal pressure is 1
It can be obtained by treating with an acidic substance having a temperature of 80 ° C. or higher and an acidic substance having a boiling point of 120 ° C. or lower under atmospheric pressure at (C) pka 3.5 or higher. Here, the periodic table of the metal salt of (A) II
Metals belonging to the group include beryllium (Be), magnesium (Mg), calcium (Ca), zinc (Zn),
Barium (Ba) can be mentioned, as its salt, carbonate,
Examples thereof include acetate, sulfate and phosphate. Of these, calcium acetate and magnesium acetate are preferable from the viewpoint of controlling the change in viscosity of EVOH with time and the hue of EVOH. When used, one or more of these metal salts can be used.

The acidic substance having a pka (acidity index at 25 ° C.) of 3.5 or more and a boiling point of 180 ° C. or more under normal pressure of (B) is succinic acid, adipic acid, benzoic acid, capric acid or citric acid. , Organic acids such as lauric acid, boric acid, potassium dihydrogen phosphate, inorganic acid substances such as sodium dihydrogen phosphate, aspartic acid, aminobenzoic acid, amino acids such as glutamic acid, but not necessarily limited to these. Not done. An acidic substance having a boiling point of 250 ° C. or higher is preferable. When used, one or more of these may be used.

Examples of the acidic substance (C) having a pka of 3.5 or more and a boiling point of 120 ° C. or less under normal pressure include acetoacetic acid, formic acid and acetic acid, with acetic acid being more preferred.
As a method for adding EVOH to these substances, these substances may be directly added to EVOH and mixed, or EVOH may be added to an aqueous solution prepared by dissolving these substances in water.
You may take the operation of immersing OH.

After the addition of these substances to EVOH, the content of each substance in EVOH is 0.0005 to 0.50 in terms of the metal salt of (A).
0.5% by weight, preferably 0.001 to 0.3% by weight,
0.002 to 2.0% by weight, preferably 0.005 to 1.0% by weight, of an acidic substance having a pka of 3.5 or more in (B) and a boiling point of 180 ° C. or more under normal pressure, and a pka in (C).
For an acidic substance having a boiling point of 120 ° C. or less under normal pressure of 3.5 or more, 0.01 to 2.0% by weight, preferably 0.02 to 1.
It is 0% by weight. It is preferable that EVOH does not contain sodium acetate, which is a by-product during saponification, but even if it contains about 0.05% by weight, the above characteristics are not impaired.

Further, the EVOH composition is described in JP-A-60
-Periodic Table I as described in 199040
At least one salt or oxide containing at least one element selected from Group III, Group III and Group III, such as hydrotalcite compounds, metal salts of ethylenediaminetetraacetic acid, palmitic acid, stearic acid, oleic acid, linoleic acid , A higher fatty acid metal salt such as linoleic acid may be contained.

Furthermore, when EVOH in which a small amount of the above-mentioned olefinic unsaturated monomer containing silicon is copolymerized is used, it is easy to remove the gel-like substance staying in the EVOH channel, and the restart time is short with EVOH. It may be possible to discharge in time.

Next, a comparison will be made between the conventionally used purging agent and the purging agent of the present invention. Polyethylene (PE) and polystyrene (PS) are typically used as the conventional purging agent, but as the usual purging method, one having a melt index of the purging agent lower than that of EVOH is used. .. Therefore, when restarting with EVOH after purging, the purging agent is not discharged from the flow channel for a long period of time due to the difference in melt index, so that a large amount of extraordinary product is produced.

On the other hand, in the EVOH purging agent of the present invention, the melt index at the time of purging is replaced by E
Since it is lower than that of VOH, EVOH in the flow path is discharged similarly to the conventional purging agents such as PE and PS, and the melt index rises over time and becomes higher than that of EVOH. The purging agent itself is also easily discharged from the flow path. Moreover, since the molding resin and the purging agent are the same resin, there is an advantage that even if the purging agent that was not completely discharged during molding is discharged, it does not become an extraordinary product.

The melt extrusion apparatus in which the purging agent is used is not particularly limited. For example, a single layer film extruder, a single layer inflation extruder, a coextrusion sheet film forming machine, a coextrusion film forming machine, Used in extrusion blow molding machines, co-injection molding machines, etc.

Regarding the method of using the purging agent, usually, after the resin in the EVOH-side extruder hopper is exhausted, the purging agent is added about 6 to 20 times the resin retention amount of the extruder.
In this case, increasing the screw rotation speed is effective. There are three methods for restarting with EVOH after purging is completed. EV immediately after purging is completed
Reboot with OH. After the purging is completed, the extruder temperature is kept as it is and only the screw rotation is stopped to wait for the melt index of the purging agent to rise, and then the EVOH is restarted. After the purging is completed, the temperature is stopped (the melt index of the purging agent is increased during the temperature lowering), and the temperature is raised again to EV.
Reboot with OH. EVOH immediately after purging
When re-starting with, it is more effective to raise the extruder temperature slightly (the melt index rises faster).

As described above, EVOH is suitable as the thermoplastic resin used in the purging agent in the present invention, but in addition to this, polyolefin (ethylene (co) polymer, propylene (co) polymer, etc.), Polystyrene, polyamide, polyester, polyvinyl chloride, polyvinylidene chloride, etc. can also be used, and these resins can also be blended and used.

Further, EVOH resin is suitable as a resin to be subjected to melt molding (a resin to be substituted) to which the purging agent of the present invention is applied, but in addition to this, the above-mentioned polyolefin, polystyrene, polyamide, polyester, Polyvinyl chloride, polyvinylidene chloride, etc. can also be used. It is effective that the resin used for melt molding is of the same type as the thermoplastic resin used for the purging agent. The present invention will be further described below with reference to examples, but the present invention is not limited thereto.

[0027]

【Example】

Example 1 Feed block type three-kind five-layer coextrusion device (extrusion temperature of EVOH side extruder: 220 ° C., adhesive resin extruder extrusion temperature of 230 ° C., PET side extruder extrusion temperature of 280 ° C., feed block and die temperature 270 ° C.), the outermost polyester layer is 800 μm, the intermediate adhesive resin (maleic anhydride graft-modified ethylene-vinyl acetate copolymer) layer is 50 μm, and the innermost EVOH (ethylene content 44 mol). %, Saponification degree 99.5%, melt index 5.5 g / 10 min) A sheet having a layer of 50 μ was formed, and after 3 days, streaks and gels became visible in the EVOH layer. Therefore, the purging agent {EVO was added to the EVOH side extruder (discharge amount 5 kg / hr) under the above operating conditions.
H: ethylene content 31 mol%, saponification degree 99.4%,
Melt index MI (15) = 1.0, MI (30
0) = 1000} at a discharge rate of 5 kg / H for about 30 minutes (2.
5kg), after switching to EVOH again,
After 50 minutes, a good product sheet having no streaks and no spots was obtained. After a further 5 days, streaks and gels were generated in the EVOH layer, and thus the same purging agent was used again to perform purging under the above conditions, and then the screw rotation was stopped for 60 minutes while the temperature remained the same.
After 30 minutes, a good product sheet free of streaks and spots was obtained. After 4 more days, the same state as described above was reached, so after purging with the same purging agent under the same conditions, the operation was stopped. The next day, when the temperature was raised again and the mode was changed to EVOH, a good product sheet with no streaks and lumps was obtained after 15 minutes.

Examples 2 to 3 The brands of EVOH and purging agent were changed as shown in Table 1, the purging time was 30 minutes (Example 2) and 60 minutes (Example 3), and the others were carried out. The procedure was as in Example 1. Good results were obtained in each case.

Comparative Examples 1 to 3 When a blend of EVOH and a polyamide-polyether copolymer was used as a purging agent, some effects were observed, but the effects of the present invention were not reached (Tables 1 and 2).
(See also), and because the compatibility of polyamide and EVOH is relatively good, it may be difficult to find it despite the presence of EVOH gels, and the present invention is considered to be superior.

Comparative Examples 4 to 5 When PE was used as a purging agent, none of PE was suitable as a purging agent as shown in Tables 1 and 2.

[0031]

[Table 1]

[0032]

[Table 2]

[0033]

According to the purging agent of the present invention, in an apparatus for melt-molding a thermoplastic resin, the thermoplastic resin remaining in the melting channel can be promptly discharged, and the thermoplastic resin can be re-introduced into the channel. When introduced, the purging agent itself can be discharged in a short time, so that the product loss due to the remaining purging agent can be significantly reduced.

Claims (1)

[Claims] 1. A purging agent comprising a thermoplastic resin satisfying the following formulas (I) and (II). 20 ≧ MI (15) ≧ 0.01 (I) 0.05 ≧ MI (15) / MI (300) ≧ 10 ^-4 ... (II) MI (15) ... 220 ° C. (in nitrogen) Melt index after heating for 15 minutes (g / 10 minutes) (190 ° C., 2160)
Melt index (g / 10 minutes) after heating MI (300) ... 220 ° C. (in nitrogen) 300 minutes (190 ° C., 216
(Measured under 0g load)