JP2018039187A - Molding method of ethylene-vinyl ester copolymer saponification product - Google Patents

Abstract

Disclosed is a method for molding an ethylene-vinyl ester copolymer saponified product (EVOH resin) which has excellent extrusion stability when melt extrusion molding is carried out by lowering the set temperature of a barrel. A molding material composed of EVOH resin pellets is supplied to an extruder, melted while being conveyed by a screw in a barrel having a set temperature of 170 ° C. or less in a screw supply unit, and from the tip of the barrel. The molten material is extruded to form a molded product. Each pellet constituting the EVOH resin pellet group in the molding material is a pellet having an oval cross section, the maximum outer diameter of the pellet is the long diameter, and the minimum diameter in the cross section of the maximum area among the cross sections perpendicular to the long diameter is short. When the diameter is taken, the average value of the major axis / minor axis ratio is 1.6 or more. [Selection figure] None

Description

  The present invention relates to a method for molding an EVOH resin suitably used for producing a molded article such as a film by melt extrusion molding an ethylene-vinyl ester copolymer saponified product (hereinafter referred to as “EVOH resin”). More particularly, the present invention relates to a method for molding an EVOH resin having excellent extrusion stability during melt extrusion molding.

  The EVOH resin is a thermoplastic resin having high crystallinity due to hydrogen bonding between hydroxyl groups present in the polymer side chain, and also having high intermolecular force even in an amorphous part. Based on such a structure, a film using EVOH resin exhibits excellent gas barrier properties and is used for various applications by melt extrusion molding.

  EVOH resin used as a molding material is generally distributed as cylindrical or granular pellets having a length of about 1 to 10 mm. EVOH resin pellets are generally manufactured by a strand cut method. The strand cut method is a resin obtained by extruding a solution obtained by dissolving EVOH resin (or its composition) in an appropriate solvent into a coagulation liquid from a metal plate having a hole having a diameter of about 1 to 5 mm, or by heating and melting the resin. This is a method for producing EVOH resin pellets by cutting a rod-like strand obtained by extruding a die into a die and cooling and solidifying the rod-like strand into a certain size using a cutter.

In such a melt extrusion molding method using EVOH resin pellets, a molding material consisting of EVOH resin pellets is supplied to an extruder and melted while being transported by a screw in a heated barrel, and the molten material is fed from the tip of the barrel. To form a molded article, for example, a film.
In such a melt extrusion molding method, there is a problem that a so-called feed property is not good, in particular, when the molten resin flows in the barrel, the screw vibrates, or a sound is generated due to torque fluctuation during the extrusion of the resin. Since the state where such a sound is generated is a state in which a load is applied to the screw, in a severe case, there is a possibility of causing wear of the screw and mixing of wear powder into the molten resin. And mixing of the wear powder into the molten resin causes quality deterioration of a molded product such as a film.

  As a technique for improving the feed property at the time of melt extrusion molding, it has been proposed to use a molding material in which two types of EVOH resin pellets having different ethylene contents are mixed (see, for example, Patent Document 1). The molding material described in Patent Document 1 is a molding material composed of EVOH resin pellet groups, and each pellet constituting the EVOH resin pellet group is a pellet having a substantially circular or elliptical cross section. The group is a pellet mixture comprising a first EVOH resin pellet having an ethylene unit content of 20-34 mol% and a second EVOH resin pellet having an ethylene unit content of 35-60 mol%, and The difference in ethylene unit content between the first EVOH resin pellet and the second EVOH resin pellet is 10 to 30 mol% (see paragraph [0024]).

  By using a molding material in which two types of EVOH resin pellets having different compositions are mixed, the flowability (feedability) in the screw flow path constituting the melt plasticized portion is improved (paragraph [0079]. ]), The generation of abnormal noise is reduced as compared with the abnormal noise generated when the pellet obtained by the strand cut method is used. Further, this molding material can be suitably used as a material for melt molding, particularly a melt extrusion molding material such as a film or sheet fiber (see paragraph [0080]).

  Further, as another technique for improving the feed property at the time of melt extrusion molding, it has been proposed to use a molding material in which two types of EVOH resin pellets having different shapes are mixed (see, for example, Patent Document 2). The molding material described in Patent Document 2 is a molding material composed of EVOH resin pellet groups, and the pellet group includes a first EVOH resin pellet having a substantially circular or elliptical cross section, and a cylindrical second material. The mixing weight ratio of the first EVOH resin pellet and the second EVOH resin pellet is 99/1 to 20/80 (see paragraph [0013]).

  By using a molding material in which two types of EVOH resin pellets having different shapes are mixed, the feed property is improved (see paragraph [0081]). The occurrence of abnormal noise is reduced compared to the abnormal noise that occurs. Moreover, since this molding material is excellent in feed property, it is preferably used as a melt molding material for producing an EVOH resin molded product. In particular, it can be suitably used as a material for melt extrusion molding of films, sheets, fibers and the like (see paragraph [0082]). Furthermore, since this molding material is excellent in film moldability, that is, fluctuations in the width of the film to be melt-extruded are suppressed, production of a multilayer structure applied to melt-extrusion with other thermoplastic resins (See paragraph [0087]).

Japanese Patent Laying-Open No. 2015-143349 Japanese Patent Laying-Open No. 2015-155194

  When melt-extrusion of a film using the EVOH resin pellets described above is desired, for example, to suppress as much as possible fish eyes caused by thermally deteriorated gel, the temperature set in the barrel is lowered to the extent that extrusion is possible, and melt extrusion molding is performed. There is a case. However, in such a case, there is a problem that the obtained film width and resin pressure vary, and there is a demand for improvement in order to perform stable production.

  Patent Document 1 only describes that it can be suitably used as a material for melt extrusion molding of a film, and particularly mentions the case of melt extrusion molding by lowering the set temperature of the barrel. Absent. Moreover, although the film is shape | molded in the Example, evaluation about a film width or a resin pressure is not performed.

  In addition, Patent Document 2 only describes that fluctuations in the width of the melt-extruded film are suppressed, and the case where melt-extrusion molding is performed by lowering the set temperature of the barrel is particularly touched. Not. Moreover, although the film is shape | molded in the Example, evaluation about a film width or a resin pressure is not performed.

  The present invention has been made in view of the above problems, and an object of the present invention is to saponify an ethylene-vinyl ester copolymer (EVOH) which has excellent extrusion stability when melt extrusion molding is performed by lowering the set temperature of the barrel. Resin) molding method.

  When EVOH resin is melt-extruded and cut with a cutter before it is cooled and solidified, the edge part produced by cutting hangs down while it is cooled and solidified, and it acts to become spherical due to surface tension. , A pellet composed entirely of a curved surface is obtained. Specifically, although it depends on the shape at the time of melt extrusion (usually a quadrangular prism or cylinder), the cross section has a shape such as an oval spherical shape, a disc shape, or a rugby ball shape, and rarely a true spherical shape. Can exist.

  In order to obtain an optimum molding method in the case of melt extrusion molding by lowering the set temperature of the barrel within a range in which extrusion molding is possible, the present inventors paid attention to the shape of EVOH resin pellets and the relationship with extrusion stability. As a result, the present invention has been reached.

  That is, the present invention supplies a molding material comprising a saponified ethylene-vinyl ester copolymer saponification pellet group to an extruder and melts it while being transported by a screw in a heated barrel, from the tip of the barrel. A method for molding a saponified ethylene-vinyl ester copolymer saponified product by extruding a molten material to form a molded article, wherein each pellet constituting the saponified pellet group of ethylene-vinyl ester copolymer saponified has an oval cross section. When the maximum outer diameter of the pellet is the major axis and the smallest diameter in the cross section of the largest area among the sections perpendicular to the major axis is the minor axis, the average value of the major axis / minor axis ratio is 1.6 or more The set temperature of the barrel in the screw supply section is 170 ° C. or less, and is a method for molding an ethylene-vinyl ester copolymer saponified product. .

  In the present invention, the moisture content of the pellets is preferably 0.5% by weight or less.

  In the present invention, the average value of the major axis is preferably 1.6 to 10 mm, and the average value of the minor axis is preferably 1 to 10 mm.

  Moreover, it is preferable that the rotation speed of the said screw is 10-100 rpm.

  In a pellet without corners, the shape of the pellet approaches a true sphere when the major axis / minor axis ratio is close to 1, and conversely, when it is away from 1, the shape of the pellet becomes elongated. Since the average value of the major axis / minor axis ratio is 1.6 or more, the pellet used in the present invention has an oval shape that is relatively elongated compared to a true sphere. Therefore, a person skilled in the art normally considers that a molding material composed of EVOH resin pellets having a large major axis / minor axis ratio has poor fluidity, and such a molding material is avoided. However, unexpectedly good results were obtained when such a molding material was used intentionally in the case of melt extrusion molding with the set temperature lowered within the range where extrusion molding is possible.

  The molding method of the present invention is excellent in extrusion stability even when melt extrusion molding is carried out by lowering the set temperature of the barrel. As a result, for example, it is possible to stably obtain a molded article of good quality in which fish eyes are suppressed.

FIG. 1 is a schematic diagram for explaining a major axis and a minor axis in a pellet P that is an ellipsoid.

  The present invention supplies a molding material composed of saponified ethylene-vinyl ester copolymer pellets to an extruder and melts it while being transported with a screw in a heated barrel. Is a method for forming a saponified ethylene-vinyl ester copolymer saponified product, wherein each pellet constituting the saponified ethylene-vinyl ester copolymer saponified pellet group has an oval cross section. When the maximum outer diameter of the pellet is the major axis and the smallest diameter in the cross section of the largest area among the sections perpendicular to the major axis is the minor axis, the average value of the major axis / minor axis ratio is 1.6 or more The preset temperature of the barrel in the screw supply section is 170 ° C. or lower.

<Pellet with oval cross section>
Each pellet constituting the EVOH resin pellet group used in the molding method of the present invention is a pellet having a cross section in an oval shape. The oval shape includes an oval shape, an oval shape, an elliptical shape, and a curved shape close to these shapes. The cross section is a cross section of the pellet that is not particularly limited, and means that any cross section is oval, that is, there are no so-called corners.

<Long diameter and short diameter of pellet>
Each pellet constituting the EVOH resin pellet group used in the molding method of the present invention has an average value of the major axis / minor axis ratio of 1.6 or more.
Here, the major axis of the pellet is the maximum diameter when the pellet is observed three-dimensionally. Moreover, the short diameter of a pellet is the minimum diameter in the cross section which becomes the largest area among the cross sections perpendicular | vertical to this long diameter. For example, when the cross section is circular, it is the length of the diameter, and when it is elliptical, it is the length of the short axis.

Here, it demonstrates concretely, referring FIG. FIG. 1 shows a case where the pellet P is an ellipsoid for easy understanding. Since the maximum outer diameter when the pellet P is observed three-dimensionally is “a”, the major diameter is “a”. Next, the cross section having the maximum area among the cross sections perpendicular to the long diameter is the cross section F located at the midpoint of the long diameter. Since the cross section F is elliptical, the major axis is “b” and the minor axis is “c”, the minimum diameter of the section F is “c”. "
From the above, the pellet P shown in FIG. 1 has the major axis “a” and the minor axis “c”, and the major axis / minor axis ratio is “a / c”.

  In the present embodiment, the average value of 20 pellets is adopted for both the major axis and the minor axis.

<Measurement method of major axis and minor axis>
Each pellet constituting the EVOH resin pellet group used in the molding method of the present invention has an average value of the major axis / minor axis ratio of 1.6 or more, preferably 1.7 to 3, particularly preferably 2 to 2. 2.5. When such a value is too small, the extrusion stability in the case of melt extrusion molding by lowering the set temperature of the barrel within the extrudable range tends to be insufficient, and when it is within the above range, the effect of the present invention is There is a tendency to be obtained more efficiently.

The pellets constituting the EVOH resin pellet group used in the molding method of the present invention preferably have an average value of the major axis of 1.6 to 30 mm and an average value of the minor axis of 1 to 10 mm, particularly preferably the major axis. The average value is 3 to 20 mm, the average value of the minor axis is 2 to 6 mm, more preferably the average value of the major axis is 3.5 to 10 mm, and the average value of the minor axis is 2.5 to 5.5 mm. When this value is within the above range, the effect of the present invention tends to be obtained more efficiently.
In addition, the method of measuring the major axis and minor axis is, for example, taking a pellet and observing it, measuring the major axis using a measuring instrument such as a caliper, and then the cross-sectional position that becomes the maximum area among the cross sections perpendicular to the major axis Can be obtained by visual and tactile sensation, and the short diameter when such a cross section is assumed is similarly measured.

<Calculation method of standard deviation of major axis / minor axis ratio>
In this embodiment, the major axis and minor axis of the 20 pellets are measured to determine the major axis / minor axis ratio, so the standard deviation is determined for the 20 pellets.
When the major axis / minor axis ratio of 20 pellets is Xi (i = 1 to 20) and the average value of the major axis / minor axis ratio is Xave, the standard deviation S is obtained by the following mathematical formula (1).

Standard deviation S = √ [{(X1−Xave) ² + (X2−Xave) ² +... + (Xi−Xave) ² +... + (X19−Xave) ² + (X20−Xave) ² } / 20] (1)

  Each pellet constituting the EVOH resin pellet group used in the molding method of the present invention preferably has a major axis / minor axis ratio standard deviation of 0.13 or more, particularly preferably 0.13 to 0.18. . When this value is within the above range, the effect of the present invention tends to be obtained more efficiently.

<Method for measuring moisture content>
Each pellet constituting the EVOH resin pellet group used in the molding method of the present invention preferably has a moisture content of 0.5% by weight or less, particularly preferably 0.3% by weight or less, and more preferably 0%. .25% by weight or less.

The moisture content of the pellet is measured by the following method.
First, 10 g of pellets are taken in an aluminum cup, and the weight (C1 + P1) of the aluminum cup containing the aluminum cup alone (weight: C1) and the pellet (weight: P1) is measured. Then, the aluminum cup containing the pellets is subjected to heat treatment at 150 ° C. for 5 hours in a commercially available dryer (“SAFETY OVEN SPH-100” manufactured by Tabai Espec Co., Ltd.) which is not purged with nitrogen and is not evacuated. After the heat treatment, take out the aluminum cup containing the pellets from the dryer, leave it in a desiccator containing desiccant for 30 minutes to return the temperature of the pellets to room temperature, and remove the heat-treated pellets (weight: P2). The weight (C1 + P2) of the put aluminum cup is measured, and the moisture content (% by weight) is calculated by the following mathematical formula (2).

Water content (% by weight) = [{(C1 + P1) − (C1 + P2)} / {(C1 + P1) −C1}] × 100
= {(P1-P2) / P1} × 100 (2)

<Saponified ethylene-vinyl ester copolymer (EVOH resin) pellet>
(1) EVOH resin An ethylene-vinyl ester copolymer saponified product (EVOH resin) used as a molding material in the molding method of the present invention is obtained by saponifying ethylene and a vinyl ester monomer after copolymerization. The obtained ethylene-vinyl ester copolymer saponified product is a water-insoluble thermoplastic resin.
Generally, vinyl acetate is generally used as the vinyl ester monomer from the economical aspect. The polymerization method may be any known polymerization method, for example, solution polymerization, suspension polymerization, emulsion polymerization, or bulk polymerization. Generally, solution polymerization using methanol as a solvent is used. Moreover, any of a continuous type and a batch type may be sufficient.
As a method for introducing ethylene into the copolymer, ordinary ethylene pressure polymerization may be carried out. The content of the ethylene unit can be controlled by the pressure of ethylene, and is usually selected from the range of 25 to 80 kg / cm ^{2 according} to the intended ethylene content.

Saponification of the obtained ethylene-vinyl ester copolymer can also be performed by a known method. Such saponification can be performed using an alkali catalyst or an acid catalyst in a state where the copolymer obtained above is dissolved in an alcohol or a hydrous alcohol.
The EVOH resin synthesized as described above mainly contains ethylene units and vinyl alcohol structural units, and contains a slight amount of vinyl ester structural units remaining without being saponified.

  The EVOH resin used as the material for the EVOH resin pellets may further contain structural units derived from the comonomer shown below. Examples of the comonomer include propylene, isobutene, α-octene, α-dodecene, α-olefin such as α-octadecene, 3-buten-1-ol, 4-penten-1-ol, 3-butene-1, 2- Hydroxyl group-containing α-olefins such as diols, esterified products thereof, hydroxy group-containing α-olefin derivatives such as acylated products, unsaturated carboxylic acids or salts thereof, partial alkyl esters, complete alkyl esters, nitriles, amides, anhydrides, Examples thereof include comonomers such as unsaturated sulfonic acids or salts thereof, vinylsilane compounds, vinyl chloride, and styrene.

Furthermore, “post-modified” EVOH-based resins such as urethanization, acetalization, cyanoethylation, oxyalkylenation and the like may be used as the EVOH resin.
Among the above modified products, EVOH resins in which primary hydroxyl groups have been introduced into the side chains by copolymerization are preferred in that secondary moldability such as stretching and vacuum / pressure forming is improved. -EVOH resin having a diol structure in the side chain is preferred.

  As for the content (ethylene unit content rate) of the ethylene unit of EVOH resin which comprises the EVOH resin pellet group used for a molding material, 20-60 mol% is preferable. If the ethylene unit content is too low, the resulting molded article, particularly the stretched film, tends to have a reduced gas barrier property and appearance at high humidity, whereas if it is too high, the stretched film tends to have a reduced gas barrier property. .

  The saponification degree of the vinyl ester component in the EVOH resin used for the molding material is preferably 90 mol% or more, particularly preferably 93 to 99.99 mol%, further preferably 98 to 99.99 mol%. If the saponification degree is too low, the stretched film has a tendency to deteriorate gas barrier properties, moisture resistance, and the like.

  The melt flow rate (MFR) (210 ° C., load 2160 g) of the EVOH resin constituting the EVOH resin pellet group used for the molding material is preferably 1 to 100 g / 10 minutes, particularly preferably 2 to 50 g / 10 minutes. More preferably, it is 3-30 g / 10min. If the MFR is too large, the mechanical strength of the molded product tends to deteriorate, and if it is too small, the extrusion processability during molding tends to deteriorate.

The copolymerization conditions for synthesizing the EVOH resin as described above are not particularly limited, but the following conditions are preferably used.
Examples of the solvent used for such copolymerization include usually lower alcohols such as methanol, ethanol, propanol and butanol, ketones such as acetone and methyl ethyl ketone, and methanol is preferably used industrially.
The amount of the solvent used may be appropriately selected in consideration of the chain transfer constant of the solvent in accordance with the degree of polymerization of the target copolymer. For example, when the solvent is methanol, S (solvent) / M ( Monomer) = 0.01 to 10 (weight ratio) is preferable, and particularly preferably selected from the range of about 0.05 to 7 (weight ratio).

Examples of the polymerization catalyst used in the copolymerization include known radical polymerization catalysts such as azobisisobutyronitrile, acetyl peroxide, benzoyl peroxide, lauryl peroxide, t-butylperoxyneodecanoate, and t-butyl. Peroxypivalate, α, α′bis (neodecanoylperoxy) diisopropylbenzene, cumylperoxyneodecanoate, 1,1,3,3-tetramethylbutylperoxyneodecanoate, 1-cyclohexyl- Peroxyesters such as 1-methylethylperoxyneodecanoate, t-hexylperoxyneodecanoate, t-hexylperoxypivalate, di-n-propylperoxydicarbonate, di-iso-propyl Peroxydicarbonate], di-sec-butylperoxydicarbonate Bis (4-t-butylcyclohexyl) peroxydicarbonate, di-2-ethoxyethylperoxydicarbonate, di (2-ethylhexyl) peroxydicarbonate, dimethoxybutylperoxydicarbonate, di (3-methyl Low temperature active radical polymerization of peroxydicarbonates such as (-3-methoxybutylperoxy) dicarbonate, diacyl peroxides such as 3,3,5-trimethylhexanoyl peroxide, diisobutyryl peroxide, lauroyl peroxide A catalyst etc. are mentioned.
The amount of the polymerization catalyst used varies depending on the type of catalyst and cannot be determined unconditionally, but is arbitrarily selected according to the polymerization rate. For example, when azobisisobutyronitrile or acetyl peroxide is used, the concentration is preferably 10 to 2000 ppm, particularly preferably 50 to 1000 ppm, based on the vinyl ester monomer.

  It is preferable that a hydroxylactone compound or a hydroxycarboxylic acid coexist with the catalyst. Thereby, coloring of a pellet can be suppressed. The hydroxylactone compound is not particularly limited as long as it has a lactone ring and a hydroxyl group in the molecule, and examples thereof include L-ascorbic acid, erythorbic acid, glucono delta lactone, etc. L-ascorbic acid and erythorbic acid are used, and examples of the hydroxycarboxylic acid include glycolic acid, lactic acid, glyceric acid, malic acid, tartaric acid, citric acid, salicylic acid and the like, and preferably citric acid is used. It is done.

  The amount of the hydroxylactone compound or hydroxycarboxylic acid used is preferably 0.0001 to 0.1 parts by weight, particularly preferably 0, based on 100 parts by weight of the vinyl ester monomer in both batch and continuous systems. .0005 to 0.05 parts by weight, more preferably 0.001 to 0.03 parts by weight. If the amount used is too small, the coexistence effect tends not to be sufficiently obtained. Conversely, if the amount used is too large, polymerization of the vinyl ester monomer tends to be inhibited. In preparing such a compound in a polymerization system, there is no particular limitation, but usually an aliphatic ester (methyl acetate, ethyl acetate) containing a lower aliphatic alcohol (methanol, ethanol, propanol, tert-butanol, etc.) or a vinyl ester monomer. Etc.), a solvent such as water, or a mixed solvent thereof, and then charged into the polymerization reaction system.

  The copolymerization reaction cannot be generally specified depending on the solvent and pressure to be used, but is usually carried out below the boiling point of the solvent, preferably 40 to 80 ° C., particularly preferably 55 to 80 ° C. If the temperature is too low, a long time is required for the polymerization, and if the polymerization time is to be shortened, a large amount of catalyst is required. On the other hand, if the temperature is too high, the polymerization control becomes difficult.

  In the case of a batch system, the polymerization time is preferably 4 to 10 hours (particularly 6 to 9 hours). If the polymerization time is too short, the polymerization temperature must be increased or the amount of catalyst must be set large. Conversely, if the polymerization time is too long, it is not preferable from the viewpoint of productivity. In the case of a continuous type, the average residence time in the polymerization can is preferably 2 to 8 hours (particularly 2 to 6 hours). If the residence time is too short, the polymerization temperature must be increased or the amount of catalyst must be set large. Conversely, if the polymerization time is too long, there is a problem in terms of productivity, which is not preferable.

  The polymerization rate (vinyl ester monomer) is set as high as possible within the range in which polymerization can be controlled from the viewpoint of productivity, and is preferably 20 to 90%. If the polymerization rate is too low, there are problems such as productivity and the presence of a large amount of unpolymerized vinyl acetate monomer. Conversely, if the polymerization rate is too high, polymerization control becomes difficult, which is not preferable.

After polymerization for a predetermined time, after reaching a predetermined polymerization rate, a polymerization inhibitor is added if necessary, and unreacted ethylene gas is removed by evaporation, and then unreacted vinyl ester is driven out.
As a method of removing unreacted vinyl ester from the ethylene-vinyl ester copolymer from which ethylene has been removed by evaporation, for example, the copolymer solution is continuously added at a constant rate from the top of a column packed with Raschig ring. The mixed vapor of methanol and other organic solvent and unreacted vinyl ester was distilled from the top of the tower while blowing an organic solvent vapor such as methanol from the bottom of the tower, and the unreacted vinyl ester was removed from the bottom of the tower. A method of taking out the polymer solution is employed.

An alkali catalyst is added to the copolymer solution from which unreacted vinyl ester has been removed to saponify the vinyl ester component in the copolymer.
The saponification is performed using an alkali catalyst or an acid catalyst in a state where the copolymer obtained above is dissolved in an alcohol or a hydrous alcohol. Examples of the alcohol include methanol, ethanol, propanol, tert-butanol and the like, and methanol is particularly preferably used. The concentration of the copolymer in the alcohol is appropriately selected depending on the viscosity of the system, but is usually selected from the range of 10 to 60% by weight. Catalysts used for saponification include alkali catalysts such as alkali metal hydroxides and alcoholates such as sodium hydroxide, potassium hydroxide, sodium methylate, sodium ethylate, potassium methylate and lithium methylate; sulfuric acid, Examples include acid catalysts such as hydrochloric acid, nitric acid, metasulfonic acid, zeolite, and cation exchange resin.

The amount of the saponification catalyst used is appropriately selected depending on the saponification method, the target degree of saponification, etc. When using an alkali catalyst, it is usually based on the total amount of monomers such as vinyl ester monomers. 0.001-0.1 equivalent is preferable, Most preferably, it is 0.005-0.05 equivalent. With respect to such a saponification method, batch saponification, continuous saponification on a belt, and continuous saponification of a tower type are possible depending on the target degree of saponification, etc. For example, column saponification under constant pressure is preferably used because the crystallization reaction is highly efficient and easy to proceed.
The pressure during saponification cannot be generally stated depending on the ethylene unit content of the target EVOH resin, but is selected from the range of ^{2 to} 7 kg / cm ² , and the saponification temperature is preferably 80 to 150 ° C, particularly preferably. Is 100 to 130 ° C., and the saponification time is selected from 0.5 to 3 hours. In addition, it is preferable to neutralize EVOH resin after reaction as needed.

  As the EVOH resin used as the pellet raw material, the EVOH resin synthesized as described above is generally added to the EVOH resin within a range that does not impair the effects of the present invention, for example, a heat stabilizer, an antioxidant, a charging agent. Inhibitors, colorants, ultraviolet absorbers, plasticizers, light stabilizers, surfactants, antibacterial agents, desiccants, antiblocking agents, flame retardants, crosslinking agents, curing agents, foaming agents, crystal nucleating agents, antifogging agents An EVOH resin composition containing an additive for biodegradation, a silane coupling agent, an oxygen absorbent and the like may also be used.

(2) Manufacture of pellets Each pellet constituting the EVOH resin pellet group used in the molding method of the present invention is a pellet having a cross section in an oval shape. The cross section is a cross section of the pellet that is not particularly limited, and means that any cross section is oval, that is, there are no so-called corners. Such pellets are usually obtained by melt extrusion and cutting the EVOH resin in a molten state.
When EVOH resin is melt-extruded and cut with a cutter before it is cooled and solidified, the edge part produced by cutting hangs down while it is cooled and solidified, and it acts to become spherical due to surface tension. , A pellet composed entirely of a curved surface is obtained. Specifically, although it depends on the shape at the time of melt extrusion (usually, quadrangular prism, cylinder), the cross section has a shape such as an oval spherical shape, a disc shape, or a camel ball shape. Can exist.

The molding method of the present invention is characterized in that, for a pellet having a known cross-sectional shape such as an oval spherical shape, a disc shape, or a camel ball shape, an oval-shaped pellet group that is relatively elongated compared to a true sphere is used as a molding material. There is.
In order to obtain the pellet group used for the shaping | molding method of this invention, the following method is mentioned, for example.
1. 1. A method of obtaining the above-mentioned pellet group by screening pellets having a known cross-sectional shape such as an oval spherical shape, a disc shape, or a camel ball shape, and selecting pellets having a desired major axis / minor axis ratio. 2. Method of increasing the peripheral speed of the cutter blade when cutting EVOH resin in a molten state 3. Method for increasing the rotational speed of the cutter blade when cutting EVOH resin in a molten state 4. Method for increasing the discharge linear velocity of the resin when cutting the EVOH resin in a molten state Method of solid-liquid separation of highly flexible pellets immediately after EVOH resin is cut in a molten state using a centrifuge These can be used alone or in combination of a plurality of methods. Is possible.
Among them, the above methods 2, 3, and 4 are preferable because the degree of decrease in production efficiency is small. Further, when the methods 2, 3, 4 and the method 5 are used in combination, the productivity of the pellet group tends to increase.

A specific method for producing the pellet will be described in detail below.
As the EVOH resin raw material to be charged into a melt extruder for pellet production, (i) in the EVOH resin synthesis method, the EVOH resin solution or slurry obtained by saponification is used as it is or in the solution or slurry. The EVOH resin water-containing composition after adjusting the water content as appropriate may be used, or (ii) EVOH resin pellets obtained by the strand cut method (dried EVOH resin pellets) are melted and the EVOH resin in such a molten state is used. (Dry EVOH resin) may be used.

(2-1) When using EVOH resin water-containing composition (paste) as a raw material When using EVOH resin water-containing composition (paste) as a pellet raw material charged into an extruder, alcohol is used with respect to 100 parts by weight of EVOH resin. An EVOH resin-containing composition containing 0 to 10 parts by weight and 10 to 500 parts by weight of water is preferable.

When the EVOH resin hydrous composition having a high alcohol content is used, it is not possible to prevent the alcohol from being volatilized in a subsequent process, and it becomes difficult to maintain the work environment or the surrounding environment. Further, when the temperature of the pellet washing water is increased for alcohol removal, the pellets are easily stuck together, and conversely, washing at a low temperature increases the washing time and causes a reduction in production efficiency.
On the other hand, when an EVOH resin water-containing composition having a high water content is used, when cutting in a molten state, the pellets after cutting tend to be fused to each other or the pellet shape tends to be inhomogeneous. If the water content is too small, the fluidity of the EVOH resin water-containing composition tends to be insufficient, and the productivity of pellets tends to decrease.

  The method for adjusting the moisture content of the EVOH resin hydrous composition for pellet production is not particularly limited, but in order to increase the moisture content, a method of spraying water on the resin, a method of immersing the resin in water, The method of making it contact can be adopted. In order to lower the water content, drying may be performed as appropriate, and for example, drying may be performed using a fluid hot air dryer and / or a stationary hot air dryer. It is preferable to use a fluid hot air dryer from the viewpoint of reducing dry spots. Furthermore, it is preferable that the drying temperature is 120 ° C. or less from the viewpoint of suppressing thermal degradation.

  The EVOH resin solution after saponification is usually obtained as a solution containing a large amount of alcohol. By bringing the EVOH resin solution after saponification into contact with water vapor, an EVOH water-containing composition having a low alcohol content is derived from the container. And can be used as a raw material for pellet production.

  When the EVOH resin hydrous composition is charged into the extruder as a pellet raw material, the temperature of the EVOH resin hydrous composition in the extruder is preferably 70 to 170 ° C, particularly preferably 80 ° C or higher, more preferably 90 ° C or higher. It is 170 degrees C or less. When the temperature of the EVOH resin hydrous composition is less than 70 ° C., the EVOH resin may not be completely melted, and when it exceeds 170 ° C., the EVOH may be susceptible to thermal degradation. The temperature of the resin composition refers to the temperature detected in the vicinity of the discharge port at the tip of the extruder by a temperature sensor installed in the extruder cylinder.

Although the extruder to be used is not particularly limited, the diameter (diameter) of the nozzle is preferably 1 to 10 mm, particularly preferably 2 to 5 mm, from the viewpoint of easy handling of the pellets.
The number of cutter blades is preferably 2-8, and particularly preferably 3-6.
The cutter blade is preferably attached so as to be in contact with the discharge port of the die of the extruder. Therefore, the distance between the die and the cutter is 0 mm, but there may be a distance of about 0.01 to 0.2 mm.
As for the rotation speed of a cutter blade, 500-2500 rpm is preferable, Especially preferably, it is 1200-2000 rpm, More preferably, it is 1500-1900 rpm. When such a numerical value is within the above range, the molding material used in the molding method of the present invention tends to be obtained more efficiently.
The peripheral speed of the cutter blade is preferably 1 to 10 m / second, particularly preferably 3.5 to 8 m / second. When such a numerical value is within the above range, the molding material used in the molding method of the present invention tends to be obtained more efficiently.
The discharge linear velocity from the resin die is preferably 10 to 200 m / second, particularly preferably 50 to 200 m / second, and further preferably 100 to 180 m / second. When such a numerical value is within the above range, the molding material used in the molding method of the present invention tends to be obtained more efficiently.
The size and shape of the pellet can be adjusted by appropriately adjusting the nozzle diameter, the number of cutter blades, the number of rotations of the cutter blade, and the like.

  The EVOH resin hydrous composition extruded from a die, that is, the EVOH resin in a molten state, is cut before being cooled and solidified (hot cut method). The hot cut method may be cut in the atmosphere (air cut method) or extruded into a cutter installation container filled with cooling water and cut in cooling water (under water cut method), but the underwater cut method is preferred. The underwater cutting method can be performed using, for example, an underwater pelletizing apparatus.

  The cooling water is not limited to water. Water / alcohol mixtures; aromatic hydrocarbons such as benzene; ketones such as acetone and methyl ethyl ketone; ethers such as dipropyl ether; organic esters such as methyl acetate, ethyl acetate, and methyl propionate it can. Of these, water or a water / alcohol mixed solution is used because it is easy to handle. In the water / alcohol mixed solution, the water / alcohol (weight ratio) is usually 90/10 to 99/1. In addition, as said alcohol, alcohol, such as methanol, ethanol, propanol, can be used, and methanol is used preferably industrially.

  The temperature of the cooling water in the underwater cutting method is a temperature at which the EVOH resin extruded in the molten state does not solidify (solidify) instantaneously. When the cooling water comes into contact with the cooling water before cutting, the temperature of the cooling water is − It is preferable to set it as 20-50 degreeC, Most preferably, it is -5-30 degreeC.

(2-2) When using dry EVOH resin pellets as raw materials As raw materials for EVOH resin pellets constituting the molding material used in the molding method of the present invention, dry EVOH resin pellets (usually a moisture content of 0.5% by weight or less) ), The dried EVOH resin pellets are put into an extrusion kneader and melt extruded.
The size and shape of the dry EVOH resin pellet used as a raw material are not particularly limited.
The temperature of the EVOH resin in the extrusion kneader needs to be set higher than in the case of the EVOH resin water-containing composition. Specifically, 150-300 degreeC is preferable, Especially preferably, it is 200-285 degreeC, More preferably, it is 240-270 degreeC. When the set temperature is less than 150 ° C., the EVOH resin pellets tend not to melt completely. Conversely, when the EVOH resin temperature exceeds 300 ° C., the EVOH resin tends to be susceptible to thermal degradation. The resin temperature refers to the temperature detected in the vicinity of the discharge port at the tip of the extruder by a temperature sensor installed in the extruder cylinder.

The extruder to be used is not particularly limited, but from the viewpoint of easy handling of the pellet, the nozzle diameter (diameter) is preferably 1.0 to 5.0 mm, particularly preferably 2.0 to 3.5 mmφ. .
The number of cutter blades is preferably 2-8, and particularly preferably 3-6.
The cutter blade is preferably attached so as to be in contact with the discharge port of the die of the extruder. Therefore, the distance between the die and the cutter is 0 mm, but there may be a distance of about 0.01 to 0.2 mm.
The rotation speed of the cutter blade is preferably 50 to 2500 rpm, particularly preferably 1000 to 2300 rpm, further preferably 1200 to 2000 rpm, and still more preferably 1500 to 1900 rpm. When such a numerical value is within the above range, the molding material used in the molding method of the present invention tends to be obtained more efficiently.
The peripheral speed of the cutter blade is preferably 1 to 10 m / second, particularly preferably 3.5 to 8 m / second. When such a numerical value is within the above range, the molding material used in the molding method of the present invention tends to be obtained more efficiently.
The discharge linear velocity from the resin die is preferably 10 to 200 m / second, particularly preferably 50 to 200 m / second, and further preferably 100 to 180 m / second. When such a numerical value is within the above range, the molding material used in the molding method of the present invention tends to be obtained more efficiently.
The shape of the pellet can be adjusted by appropriately adjusting the nozzle diameter, the number of cutter blades, the number of rotations of the cutter blade, and the like.

  As in the case of using the EVOH resin hydrous composition as a raw material, the cut in the molten state may employ either an air cut method or an underwater cut method, but an underwater cut method is preferred. As the cooling water in the underwater cutting method, the cooling waters listed when using the EVOH resin water-containing composition as a raw material can be used. However, when dry EVOH resin pellets are used as raw materials, the temperature of the cooling water in the underwater cut method is when EVOH resin water-containing compositions are used as raw materials because it is easier to solidify than when EVOH resin water-containing compositions are used as raw materials. It is higher, 0-90 degreeC is preferable, Most preferably, it is 20-70 degreeC. In the molding material used in the molding method of the present invention, when a highly flexible pellet immediately after cutting is subjected to solid-liquid separation with a centrifuge, production efficiency tends to be improved.

  The pellet obtained as described above is preferably washed with water. In particular, pellets obtained using EVOH resin water-containing composition as a raw material usually contain an alkali metal salt that is a residue of a catalyst used during saponification, so in the case of such pellets, finally obtained molding In order to prevent quality deterioration such as coloring of the product, it is usually washed with water.

  Washing with water is carried out in a water bath at 10 to 60 ° C. For example, it is 200 to 1000 parts by weight (particularly preferably 300 to 600 parts by weight) of water with respect to 100 parts by weight of EVOH resin pellets, and 20 to 50 ° C. (particularly preferably 25 to 35 ° C.) and 0.5 to 5 It is preferable to carry out for 1 to 5 times (particularly preferably once) for a time. By such washing with water, the content of alcohol, acetic acid and sodium acetate having 5 or less carbon atoms in the EVOH resin is adjusted, and oligomers and impurities can also be removed.

  By washing with water, 0.0001 to 1 part by weight of alcohol having 5 or less carbon atoms, 0.01 to 1 part by weight of acetic acid, and 0.01 to 1 part by weight of sodium acetate with respect to 100 parts by weight of EVOH resin pellets Part can be adjusted.

After washing with water, if necessary, the EVOH resin pellets are brought into contact with an aqueous solution of the additive.
Examples of the additive include organic acids such as acetic acid, propionic acid, butyric acid, lauric acid, stearic acid, oleic acid, and behenic acid, or alkali metal salts thereof (sodium, potassium, etc.), alkaline earth metal salts (calcium, Magnesium), zinc salts and the like; or inorganic acids such as sulfuric acid, sulfurous acid, carbonic acid, phosphoric acid, boric acid, or alkali metal salts thereof (sodium, potassium, etc.), alkaline earth metal salts (calcium, magnesium) Etc.), and heat stabilizers such as salts such as zinc salts.
Of these, it is particularly preferable to add boron compounds, acetates and phosphates including acetic acid, boric acid and salts thereof.
By making it contact with the aqueous solution of this additive, an additive can be contained in the said EVOH resin pellet, and various physical properties, such as thermal stability at the time of melt molding, can be improved.
As a method of bringing the aqueous solution into contact with the additive aqueous solution, 3% or less (particularly preferably 0.3 to 1.5%) of the additive aqueous solution is 200 to 1000 parts by weight (particularly with respect to 100 parts by weight of EVOH resin pellets). Preferably 300 to 600 parts by weight), 10 to 80 ° C. (particularly preferably 20 to 60 ° C., more preferably 30 to 40 ° C.), 0.5 to 5 hours, 1 to 3 times (particularly preferably) Once)

  By the operation of contacting with an aqueous solution of the additive, 0.001 to 1 part by weight of acetic acid and boron compound are usually converted into boron with respect to 100 parts by weight of EVOH resin pellet (analyzed by ICP emission spectrometry after ashing). ) 0.001 to 1 part by weight, acetate or phosphate (including hydrogen phosphate) converted to metal (after ashing and analyzed by ICP emission analysis) 0.0005 to 0.1 weight It is preferable to adjust to the part.

As described above, the water-containing EVOH resin pellets in which the concentration of each component is adjusted are dried. The moisture content of the dried EVOH resin pellets is preferably 1% by weight or less, particularly preferably 0.5% by weight or less.
As such a drying method, various drying methods can be adopted. Examples include a method using a centrifugal dehydrator, a method of draining water during air transportation, a stationary drying method, a fluidized drying method, and the like. It is also possible to employ a multistage drying process that combines these drying methods.

  In the EVOH resin pellets thus obtained, if necessary, a compounding agent generally incorporated into the EVOH resin within a range not inhibiting the effects of the present invention, such as an antioxidant, an antistatic agent, a colorant, an ultraviolet ray Absorber, lubricant, plasticizer, light stabilizer, surfactant, antibacterial agent, desiccant, antiblocking agent, flame retardant, crosslinking agent, curing agent, foaming agent, crystal nucleating agent, antifogging agent, biodegradation additive An agent, a silane coupling agent, an oxygen absorbent and the like may be blended.

<Uses of molding materials>
Since the molding material having the above-described configuration is excellent in extrusion stability, it is preferably used as a melt molding material for producing an EVOH resin molded product.
Further, the molding material can be suitably used as a material for melt extrusion, particularly melt extrusion molding of films, sheets, fibers and the like. As such melt molding methods, extrusion molding methods (T-die extrusion, inflation extrusion, blow molding, melt spinning, profile extrusion, etc.) and injection molding methods are mainly employed.

The conditions and type of the molding machine to be used are not particularly limited, but an extruder is usually used. The melt plasticizing part of the extruder can be either a screw type or a plunger type, but is preferably a screw type. The extruder may be either a vertical type or a horizontal type, and may be either a single screw type or a twin screw type. The screw L / D (screw length / screw diameter) and the compression ratio (C) are not particularly limited, but L / D is preferably 20 to 35, particularly preferably 25 to 30, and C is 1. 5-8 are preferable, Most preferably, it selects from the range of 2-5.
The melt molding temperature is usually selected from the range of 150 to 300 ° C.
In addition, it is preferable that the preset temperature of the barrel in the supply part of the screw of an extruder is 170 degrees C or less, Especially preferably, it is 110-150 degreeC, More preferably, it is 110-130 degreeC. When there are a plurality of barrels corresponding to the screw supply unit, the minimum value of the set temperatures of the plurality of barrels corresponding to the screw supply unit may be the above temperature.
In the molding method of the present invention, for example, even when the screw rotation speed of the extruder is low and the friction between the screw and the molding material is likely to occur, the feed property is good. Therefore, the screw rotation speed of the extruder is preferably 10 to 100 rpm, particularly preferably 20 to 90 rpm, and further preferably 30 to 60 rpm.

  The film and sheet can be used for various applications as they are by molding, but are usually used as a laminate by laminating with other base materials in order to further increase the strength or impart other functions. The EVOH resin film, sheet or laminate thereof obtained by using the molding method of the present invention is used as a packaging material for food packaging materials, industrial chemical packaging materials, agricultural chemical packaging materials, and the like based on excellent gas barrier properties. In addition, the EVOH resin film, sheet or laminate thereof may be further formed into a cup or bottle.

  A thermoplastic resin is useful as another substrate used in the laminate. Examples of thermoplastic resins include linear low-density polyethylene, low-density polyethylene, ultra-low-density polyethylene, medium-density polyethylene, high-density polyethylene, and the like, polypropylene, ethylene-propylene (block and random) copolymers, propylene -Α-olefin (α-olefin having 4 to 20 carbon atoms) copolymer, polyolefins such as polybutene and polypentene, grafted polyolefins obtained by graft-modifying these polyolefins with unsaturated carboxylic acids or esters thereof, ionomers, ethylene -Vinyl acetate copolymer, ethylene-acrylic acid copolymer, ethylene-acrylic acid ester copolymer, polyester resin, polyamide resin (including copolymer polyamide), polyvinyl chloride, polyvinylidene chloride, acrylic Resins, polystyrene, vinyl ester resins, polyester elastomers, polyurethane elastomers, halogenated polyolefins such as chlorinated polyethylene and chlorinated polypropylene, aromatic or aliphatic polyketones, and polyalcohols obtained by reducing them. However, from the viewpoint of practicality such as physical properties (particularly strength) of the laminate, polyolefin resins and polyamide resins are preferable, and polyethylene and polypropylene are particularly preferably used.

  These base resins contain an antioxidant, an antistatic agent, a lubricant, a core material, an antiblocking agent, an ultraviolet absorber, a wax and the like as conventionally known within a range not impairing the gist of the present invention. May be.

The lamination method for laminating the resin composition by the molding method of the present invention with another substrate can be performed by a known method. For example, a method of melt-extrusion laminating another substrate on a film or sheet of a resin composition, a method of melt-extrusion laminating the resin on another substrate, and a co-extrusion of the resin and another substrate Method, a method of dry laminating the resin (layer) and another substrate (layer) using a known adhesive such as an organic titanium compound, an isocyanate compound, a polyester compound, a polyurethane compound, or the like on another substrate For example, a method of removing the solvent after applying the resin solution may be used.
Among these, the co-extrusion method is preferable from the viewpoint of cost and environment. Even when the molding method of the present invention is used, it can be applied to extrusion molding with other thermoplastic resins. Since the molding method of the present invention is excellent in film moldability, that is, fluctuations in the width of the film to be melt-extruded are suppressed, production of a multilayer structure applied to melt co-extrusion with other thermoplastic resins Can be suitably used.

  When the EVOH resin layer derived from the molding method of the present invention is A (A1, A2,...) And the thermoplastic resin layer is B (B1, B2,...), The layer structure of the laminate is A / B. Not only the layer structure but also B / A / B, A / B / A, A1 / A2 / B, A / B1 / B2, B2 / B1 / A / B1 / B2, B2 / B1 / A / B1 / A / Arbitrary combinations such as B1 / B2 are possible. In addition, when R represents a recycling layer containing a mixture of the EVOH resin and the thermoplastic resin, which is obtained by re-melt molding an end portion or a defective product generated in the process of manufacturing the laminate, B / R / A, B / R / A / B, B / R / A / R / B, B / A / R / A / B, B / R / A / R / A / R / B, etc. It is.

The laminate as described above is preferably subjected to a heat stretching treatment for further improvement of physical properties. A known stretching method can be employed for the heat stretching process and the like.
As the stretching method, in addition to a roll stretching method, a tenter stretching method, a tubular stretching method, a stretching blow method, and the like, a deep drawing method, a vacuum forming method, or the like having a high stretching ratio can be employed. In the case of biaxial stretching, both a simultaneous biaxial stretching method and a sequential biaxial stretching method can be employed. The stretching temperature is preferably 80 to 170 ° C, and particularly preferably selected from the range of about 100 to 160 ° C.

  It is preferable to perform heat setting after the stretching treatment. The heat setting can be performed by a known means, and the stretched film is heat-treated at 80 to 170 ° C. (particularly preferably 100 to 160 ° C.) for about 2 to 600 seconds while maintaining a tension state.

  When the laminated film is used for heat shrink packaging of raw meat, processed meat, cheese, etc., it is used as a product film without heat setting after stretching, and the raw meat, processed meat, cheese, etc. are stored in the film, The film is heat-shrinked at 50 to 130 ° C. (particularly preferably 70 to 120 ° C.) for about 2 to 300 seconds, and the film is heat-shrinked and closely packed.

  It does not specifically limit as a shape of a laminated body, A film, a sheet | seat, a tape, a bottle, a pipe, a filament, a profile cross-section extrudate, etc. are illustrated. The laminated body can be subjected to heat treatment, cooling treatment, rolling treatment, printing treatment, dry lamination treatment, solution or melt coating treatment, bag making processing, deep drawing processing, box processing, tube processing, split processing, etc. .

  EXAMPLES Hereinafter, although this invention is demonstrated further in detail based on an Example, this invention is not limited only to this Example.

<Manufacture of EVOH resin pellets>
(1) EVOH resin pellets of Examples EVOH resin water / methanol mixed solution (water / methanol = 40/60 (weight ratio)) having an ethylene content of 29 mol% and a saponification degree of 99.7 mol%, EVOH resin concentration of 45% ) Was used as a raw material. The water-containing EVOH resin was put into an extruder and melt-kneaded, the melt was extruded from a die having three holes (hole diameter 2.5 mm), and cut with a hot cutter having five blades. The resin temperature at this time was 60 degreeC. The flow rate of the circulating water of the cutter was 42 liters / minute. At this time, the discharge linear velocity from the die was 56.9 m / min, the rotation speed of the cutter blade was 1800 rpm, and the peripheral speed was 4.1 m / sec.

  The obtained pellets were dried in a fluid dryer at 122 ° C. for 16 hours to obtain a molding material comprising the EVOH resin pellet group of the example. The moisture content of such pellets was 0.14% by weight. 20 pellets were taken out from the obtained pellet group, the major axis and the minor axis were measured by the method described above, and the average value was calculated. Further, for the 20 pellets, the major axis / minor axis ratio was determined, and the average value and standard deviation were calculated. That is, the EVOH resin pellets of the examples have an average value of the major axis of 4.6 mm, an average value of the minor axis of 2.8 mm, an average value of the major axis / minor axis ratio of 1.67, and a standard deviation of the major axis / minor axis ratio of 0.15. Met.

(2) EVOH resin pellet of comparative example Water / methanol mixed solution of EVOH resin having an ethylene content of 29 mol% and a saponification degree of 99.7 mol% (water / methanol = 40/60 (weight ratio), EVOH resin concentration of 45% ) Was used as a raw material. The hydrated EVOH resin was put into an extruder and melt-kneaded, the melt was extruded from a die having three holes (hole diameter 2.5 mm), and cut with a hot cutter having three blades. The resin temperature at this time was 60 degreeC. The flow rate of the circulating water of the cutter was 42 liters / minute. At this time, the discharge linear velocity from the die was 32.9 m / min, the rotation speed of the cutter blade was 900 rpm, and the peripheral speed was 2.0 m / sec.

  The obtained pellets were dried in a fluid dryer at 122 ° C. for 16 hours to obtain a molding material composed of EVOH resin pellets of Comparative Example. The moisture content of such pellets was 0.22% by weight. 20 pellets were taken out from the obtained pellet group, the major axis and the minor axis were measured by the method described above, and the average value was calculated. Further, for the 20 pellets, the major axis / minor axis ratio was determined, and the average value and standard deviation were calculated. That is, the EVOH resin pellet of the comparative example has an average value of the major axis of 3.9 mm, an average value of the minor axis of 3.0 mm, an average value of the major axis / minor axis ratio of 1.29, and a standard deviation of the major axis / minor axis ratio of 0.11. Met.

<Molding method>
Each molding material of the example and the comparative example was put into an extruder and formed into a film under the following conditions to form an EVOH resin film having a thickness of 50 μm. In addition, the temperature conditions were respectively performed under the three conditions described in Table 1 below.
Screw inner diameter: 40mm
L / D: 28
Screw compression ratio: 3.0
T die: Coat hanger type Die width: 450mm
Screw speed of extruder: 40rpm
Extrusion temperature (° C.): Set temperature of barrel in C1 / C2 / C3 / C4 / H (head) / AD (adapter) / D (die)

かかる成形方法において、スクリュの供給部におけるバレルはＣ１である。

In such a molding method, the barrel in the screw supply section is C1.

<Evaluation method>
(Variation in film width)
Using each molding material (EVOH resin pellet group) of Examples and Comparative Examples, a film was formed according to the above molding method, and about 60 minutes after the start of molding, a total of 10 points was measured every 50 mm, and the film width was measured. In the measurement data, (a) the difference between the maximum value and the minimum value and (b) the standard deviation were calculated.

(Resin pressure fluctuation)
Films were molded according to the above molding method using each molding material (EVOH resin pellet group) of Examples and Comparative Examples, and the resin pressure in each part of the extruder after 40 minutes from the start of molding was measured at intervals of 1 second. The standard deviation in the measurement data was calculated. The larger the standard deviation value of the resin pressure, the greater the resin pressure fluctuation.
The resin pressure in the extruder was measured at each of the ten first to tenth measurement positions advanced by distances L1 to L10 from the screw end toward the traveling direction.
First measurement position: distance L1 = 10 × D (screw diameter)
Second measurement position: distance L2 = 12 × D
Third measurement position: distance L3 = 14 × D
Fourth measurement position: distance L4 = 16 × D
5th measurement position: distance L5 = 18 × D
Sixth measurement position: distance L6 = 20 × D
Seventh measurement position: distance L7 = 22 × D
Eighth measurement position: distance L8 = 24 × D
Ninth measurement position: distance L9 = 26 × D
10th measurement position: distance L10 = 28 × D
Then, standard deviations PS1 to PS10 of the resin pressure measured at the first to tenth measurement positions were calculated, respectively.

<Evaluation results>
(Variation in film width)

  In Reference Examples 1 and 2, melt extrusion molding was performed at a barrel set temperature of 180 ° C. in the screw supply section. In Reference Examples 1 and 2, the maximum value-minimum value of the film width was a low value, and the standard deviation was small and good results were obtained. Thus, it can be seen that, in melt extrusion molding at a set temperature that is normally performed, stable molding is possible regardless of the average value of the ratio of the major axis / minor axis.

  On the other hand, in Example 1 in which melt extrusion molding was performed at a barrel set temperature of 120 ° C. in the screw supply unit and in Example 2 in which melt extrusion molding was performed at a set temperature of 150 ° C., Comparative Examples 1 and 2 In contrast, the maximum value-minimum value of the film width is small, and the standard deviation of the film width is also small. Therefore, Examples 1 and 2 using oval pellets that are relatively elongated compared to true spheres as molding materials are compared with Comparative Examples 1 and 2 using pellets close to true spheres as molding materials. It can be seen that the variation in film width is small.

(Resin pressure fluctuation)

  In Reference Examples 1 and 2, a relatively low value is obtained at any measurement position. In melt extrusion molding at a set temperature that is normally performed, stable molding is performed regardless of the average value of the major axis / minor axis ratio. It is understood that is possible.

On the other hand, in Example 1 in which melt extrusion molding was performed at a set temperature of a barrel of 120 ° C. in the screw supply unit and in Example 2 in which melt extrusion molding was performed at a set temperature of 150 ° C., Comparative Example 1 and Compared to 2, the standard deviations PS1 to PS10 of the resin pressure are small at all measurement positions. Therefore, Examples 1 and 2 using oval pellets that are relatively elongated compared to true spheres as molding materials are compared with Comparative Examples 1 and 2 using pellets close to true spheres as molding materials. It can be seen that the fluctuation of the resin pressure is small in comparison.
From the above, Examples 1 and 2 are superior in extrusion stability at the time of melt extrusion molding by lowering the set temperature of the barrel as compared with Comparative Examples 1 and 2, so that fish eyes are suppressed and quality is improved. A high molded article can be obtained.

  Since the molding method of the present invention is excellent in extrusion stability when melt extrusion molding is performed by lowering the set temperature of the barrel, it is preferably used when molding a high-quality molded product while suppressing fish eyes.

a Long diameter (maximum outer diameter of pellet)
b Cross section maximum diameter c Short diameter (cross section minimum diameter)
F cross section P pellet

Claims (4)

A molding material composed of saponified pellets of ethylene-vinyl ester copolymer is supplied to an extruder and melted while being conveyed by a screw in a heated barrel, and the molten material is extruded from the tip of the barrel and molded. A method for molding a saponified ethylene-vinyl ester copolymer for molding a product,
Each of the pellets constituting the ethylene-vinyl ester copolymer saponified pellet group is a pellet having an oval cross section, the maximum outer diameter of the pellet being the long diameter, and the cross section having the maximum area among the cross sections perpendicular to the long diameter When the minimum diameter is a minor axis, the average value of the major axis / minor axis ratio is 1.6 or more,
The setting temperature of the barrel in the supply part of the said screw is 170 degrees C or less, The shaping | molding method of the ethylene-vinyl ester copolymer saponified material characterized by the above-mentioned.   The method for molding a saponified ethylene-vinyl ester copolymer according to claim 1, wherein the moisture content of the pellet is 0.5% by weight or less.   3. The saponified ethylene-vinyl ester copolymer according to claim 1, wherein an average value of the major axis is 1.6 to 10 mm and an average value of the minor axis is 1 to 10 mm. Molding method. The method for forming a saponified ethylene-vinyl ester copolymer according to any one of claims 1 to 3, wherein the screw has a rotation speed of 10 to 100 rpm.

Images