JPH11291244A - Method for drying saponified ethylene/vinyl acetate copolymer pellets - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for drying saponified ethylene/vinyl acetate copolymer pellets reduced in the fluctuations of torque or change in injection amt. at a time of melt molding and capable of obtaining a molded article such as a film or a sheet excellent in thickness uniformity. SOLUTION: An alcohol soln. of a saponified ethylene/vinyl acetate copolymer or an alcohol/water mixed soln. thereof is molded into a strand and this strand is cut to obtain pellets and, when these pellets are dried, static drying and fluidizing drying are combined to be used.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for drying EVOH pellets for obtaining saponified ethylene-vinyl acetate copolymer pellets having excellent melt moldability.

[0002]

2. Description of the Related Art Generally, saponified ethylene-vinyl acetate copolymer (hereinafter abbreviated as EVOH) is excellent in transparency, gas barrier property, fragrance retention, solvent resistance, oil resistance, and the like. Utilized to a great extent, they are used by being formed into films and sheets of food packaging materials, pharmaceutical packaging materials, industrial chemical packaging materials, agricultural chemical packaging materials, and the like, or containers such as bottles. EVOH is obtained by copolymerizing ethylene and vinyl acetate to obtain an ethylene-vinyl acetate copolymer and further saponifying it. Usually, an alcohol solution of EVOH or a mixed solution of alcohol / water is formed into a strand, The strands are cut into pellets and then dried to produce product pellets.
For example, JP-B-46-37665 discloses EVOH.
At 95 ° C. in an atmosphere of an inert gas with an oxygen content of 5% or less.
It is disclosed below that fluidized drying with stirring is performed.

[0003]

However, the fluid drying alone has an effect on the reduction of the fish eye of EVOH, but the torque fluctuation at the time of melt molding,
It has been clarified that the change in the discharge amount is large and that there is a defect in the uniformity of the thickness of the molded product. At present, there is a demand from the market for a drying method capable of obtaining EVOH pellets having excellent melt moldability.

[0004]

The inventor of the present invention has conducted intensive studies to solve the above-mentioned problems, and as a result, the EV dissolved in an alcohol solution or a mixed solution of alcohol / water.
When the OH paste is formed into a strand, and the pellet obtained by cutting the strand is dried, the target EVOH pellet can be obtained by using a combination of standing drying and fluidized drying. The invention has been completed.

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail.
The EVOH used in the present invention is not particularly limited, but has an ethylene content of 20 to 60 mol% (more preferably 25 to 60 mol%).
55 mol%), and the degree of saponification is 90 mol% or more (furthermore, 95 mol%).
Mol% or more) is preferable, and the ethylene content is
If it is less than 20 mol%, the gas barrier properties of the molten molded article at high humidity are greatly reduced. Conversely, if it exceeds 60 mol%, or if the saponification degree is less than 90 mol%, the gas barrier properties and the resistance to heat are reduced. It is not preferable because chemical properties are lowered.

[0006] The EVOH used in the present invention contains a small amount of a modifying component such as unsaturated carboxylic acid, anhydride thereof,
Any modified polymerization component such as salts, esters, α-olefins, vinyl ethers, vinyl silanes, nitriles, and amides may be contained. In the present invention,
EVO having an ethylene content and a saponification degree in the above ranges
If it is H, it may be used alone or two or more EVOHs having different compositions may be used in combination.

[0007] EVOH used for drying in the present invention is E
It is not particularly limited as long as an alcohol solution of VOH such as methanol or a mixed solution of alcohol / water is formed into a strand, and the strand is cut and pelletized, but the water content is 20 to 80% by weight (furthermore, 30-7
(0% by weight). In the above, when the water content is less than 20% by weight, the effect of the present invention is not obtained. On the contrary, when the water content is more than 80% by weight, the pellets may be fused at the stage of standing drying or fluid drying, which is not preferable.

The most characteristic feature of the present invention is that, when drying the pellets, the combination of standing drying and fluidized drying is used. The term “static drying” means that the EVOH pellets are substantially stirred, dispersed and dispersed. Such drying means that drying is performed without being given a dynamic action, and the drying apparatus for performing the drying is not particularly limited. Examples of the mold include a band dryer, a tunnel dryer, and a vertical dryer.

[0009] Fluid drying means drying in which EVOH pellets are substantially stirred or dispersed by mechanical or hot air, and a cylindrical / groove type stirring dryer is used as the dryer for performing the drying. , Cylindrical dryer, (tower type, box type) rotary dryer, (semi-continuous two-stage, continuous horizontal multi-chamber type, continuous perforated plate multi-stage) fluidized bed dryer, vibrating fluidized bed dryer, conical rotary dryer And the like.

Either static drying or fluid drying may be performed first, and after static drying, fluid drying may be performed, or fluid drying may be performed, and then static drying may be performed. First, a method of performing fluidized drying after performing stationary drying will be described.

Air or an inert gas (nitrogen gas, helium gas, argon gas, etc.) is used as a heating gas used for standing drying.
0 ° C. or less, more preferably 40 to 95 ° C., and particularly preferably 60 to 95 ° C.
９０90 ° C.

At this time, the passing speed of the heating gas in the dryer is preferably less than 1.0 m / sec, and more preferably 0.01 to 0.6 m / sec. If the passage speed exceeds 1.0 m / sec, it is difficult to keep the pellets stationary, which is not preferable.

[0013] The still drying time is 10 minutes to 4 minutes.
8 hours is preferred, and more preferably 30 minutes to 36 hours. The EVOH is dried so as to have a water content of 10 to 70% by weight (more preferably 15 to 60% by weight) by the above-mentioned standing drying, and is at least 3.0% by weight (more than the water content before the standing drying). Is preferably from 5.0 to 30% by weight). EV
If the above water content of OH is less than 10% by weight, fish eyes may be generated when the product after fluid drying described below is melt-molded. Conversely, if it exceeds 70% by weight, the product after fluid drying is melt molded. In such a case, there is a case where discharge fluctuation or the like easily occurs and stable molding cannot be performed, which is not preferable. Further, if the water content is lower than 3.0% by weight than the water content before standing and drying, it tends to be difficult to obtain the effects of the present invention.

After the stationary drying, fluidized drying is performed. The fluidized drying is not particularly limited as long as the fluidized drying is carried out while the EVOH pellets are stirred or dispersed by mechanical or hot air. The heating gas used for the fluidized drying is an inert gas (nitrogen gas, helium gas, helium gas). Gas, argon gas, etc.), and the temperature of the heating gas is preferably 80 ° C. or more, and more preferably 90 to 15 ° C.
0 ° C.

[0015] Further, the passing speed of the heating gas in the dryer is preferably 0.7 to 10 m / sec, more preferably 0.7 to 5.0 m / sec, particularly 1.0 to 3.0 m / sec.
If the passing speed is less than 0.7 m / sec, uniform moisture control between the pellets is difficult and the fusion of the pellets may occur. On the other hand, if it exceeds 10 m / sec, fine powder or chipping may occur. It is not preferable because it is easy to do.

The time for fluidized drying is from 10 minutes to 4 minutes.
8 hours is preferred, and more preferably 30 minutes to 24 hours.

It is preferable to adjust the water content of EVOH to be 0.001 to 2.0% by weight (more preferably 0.01 to 1.0% by weight) by the above-mentioned fluidized drying. If the water content is less than 0.001% by weight, the long-run moldability tends to decrease. On the other hand, if it exceeds 2.0% by weight, water foaming tends to occur in the molded product, which is not preferable.

Next, a method of carrying out fluidized drying and then drying by standing will be described. First, air or an inert gas (nitrogen gas, helium gas, argon gas, or the like) is used as a heating gas used for fluidized drying, and the temperature of the heating gas is preferably 95 ° C. or less, and more preferably 40 to 90 ° C.
° C, especially 55-90 ° C.

At this time, the passage speed of the heating gas in the dryer is preferably 0.7 to 10 m / sec, more preferably 0.7 to 5.0 m / sec, particularly 1.0 to 3.0 m / sec.
If the passing speed is less than 0.7 m / sec, fusion of the pellets is likely to occur, and conversely, 10 m / sec.
Exceeding the range is not preferred because chipping of fine powder and pellets is likely to occur. The fluidized drying time is 5 minutes to 3 minutes.
6 hours is preferred, and more preferably 10 minutes to 24 hours.

Drying is performed so that the water content of EVOH becomes 5.0 to 60% by weight (furthermore, 10 to 55% by weight) by the above-mentioned fluidized drying, and the water content before the fluidized drying is 5.0.
It is preferable to lower the weight by at least 10% by weight (more preferably 10 to 45% by weight). When the water content is less than 5.0% by weight, discharge fluctuation is likely to occur when the product after standing drying described below is melt-molded, and when it exceeds 60% by weight, fusion of pellets is likely to occur during standing drying. When the product after standing and drying is melt-molded, fish eyes may be generated, which is not preferable. On the other hand, if the water content is less than 5.0% by weight lower than the water content before fluid drying, it tends to be difficult to obtain the effects of the present invention.

After the above-mentioned fluidized drying, static drying is performed. As a heating gas used for stationary drying, an inert gas (nitrogen gas, helium gas, argon gas, or the like) is used, and the temperature of the heating gas is preferably 75 ° C. or higher, and more preferably 85 to 150 ° C.

At this time, the gas passage speed in the dryer is preferably less than 1.0 m / sec, and more preferably 0.01 to 0.5 m / sec. When the passage speed exceeds 1 m / sec, it is difficult to keep the pellets in a stationary state, which is not preferable.

[0023] The time for the stationary drying is from 10 minutes to 7 minutes.
It is preferably 2 hours, more preferably 1.0 to 48 hours. By the above-mentioned stationary drying, the water content of EVOH is 0.001 to 0.001.
Preferably, the content is 2.0% by weight (further, 0.01 to 1.0% by weight). If the water content is less than 0.001% by weight, the long-run formability tends to decrease, and
Exceeding the weight percent is not preferred because water foaming is likely to occur in the molded article.

The EVOH pellets thus obtained are frequently used for molded articles, and are formed into pellets, films, sheets, containers, fibers, rods, pipes, various molded articles, etc. by melt molding or the like, and these are pulverized. In many cases, the product is used for melt molding again using a product (such as when a recovered product is reused) or a pellet.

As a melt molding method, an extrusion molding method (T-
Die extrusion, inflation extrusion, blow molding, melt spinning, profile extrusion, etc.) and injection molding are mainly employed.
The melt molding temperature is often selected from the range of 150 to 300 ° C. The EVOH pellets are also frequently used for laminates, and are particularly used as a laminate in which a thermoplastic resin layer is laminated on at least one surface of a layer made of EVOH.

In manufacturing the laminate, EVO
The other substrate is laminated on one or both sides of the layer of H. As a lamination method, for example, the EVOH film,
A method of melt-extruding a thermoplastic resin into a sheet, a method of melt-extruding the EVOH to a substrate such as a thermoplastic resin,
A method of co-extruding VOH and another thermoplastic resin, and further forming an EVOH film, sheet and other base film or sheet obtained by the present invention on an organic titanium compound, an isocyanate compound, a polyester-based compound, polyurethane A dry lamination method using a known adhesive such as a compound may be used.

In the case of coextrusion, the mating resin may be a linear low density polyethylene, low density polyethylene, medium density polyethylene, high density polyethylene, ethylene-vinyl acetate copolymer, ionomer, ethylene-propylene copolymer, ethylene -Acrylate copolymer, polypropylene, propylene-α-olefin (having 4 to 20 carbon atoms)
Α-olefins) copolymers, polyolefins such as polybutenes and polypentenes, or polyolefins in a broad sense, such as homo- or copolymers of these olefins, or graft-modified homo- or copolymers of these olefins with unsaturated carboxylic acids or esters thereof Resin, polyester, polyamide, copolymerized polyamide, polyvinyl chloride, polyvinylidene chloride, acrylic resin, polystyrene, vinyl ester resin,
Examples thereof include polyester elastomer, polyurethane elastomer, chlorinated polyethylene, and chlorinated polypropylene. EVOH can also be co-extruded. Among these, polypropylene, polyamide, polyethylene, ethylene-vinyl acetate copolymer, polystyrene, and PET are preferably used from the viewpoint of ease of coextrusion film formation and practicality of film physical properties (particularly strength).

Further, a molded product such as a film or a sheet is once obtained from the EVOH pellets obtained by the present invention, and another substrate is extrusion-coated thereon, or the film or sheet of the other substrate is formed by using an adhesive. In the case of lamination, any substrate (paper, metal foil, uniaxially or biaxially stretched plastic film or sheet, woven fabric, nonwoven fabric, metal flocculent, woody, etc.) other than the above-mentioned thermoplastic resin can be used.

The layer structure of the laminate is such that the EVOH layer is a (a
₁ , a ₂ ,...) And other base materials, for example, a thermoplastic resin layer b (b ₁ , b ₂ ,. Not only the two-layer structure of
b / a / b, a / b / a, a 1 / a 2 / b, a / b 1 /
Any combination such as b ₂ , b ₂ / b ₁ / a / b ₁ / b ₂ is possible. In the filament form, a and b are bimetallic,
Any combination such as a core (a) -sheath (b) type, a core (b) -sheath (a) type, or an eccentric core-sheath type is possible.

The laminate is used as it is in various shapes, but it is preferable to perform a stretching treatment in order to further improve the physical properties of the laminate.
Either uniaxial stretching or biaxial stretching may be used. Stretching at the highest possible magnification is preferable in terms of physical properties, such as a stretched film or a stretched sheet which does not generate pinholes, cracks, stretch unevenness, delamination, etc. during stretching. Is obtained.

Examples of the stretching method include a roll stretching method, a tenter stretching method, a tubular stretching method, a stretching blow method, and the like.
Of the deep drawing, vacuum forming and the like, those having a high stretching ratio can be employed. In the case of biaxial stretching, any of a simultaneous biaxial stretching method and a sequential biaxial stretching method can be adopted. Stretching temperature is 80
To 170 ° C, preferably 100 to 160 ° C.

After completion of the stretching, heat setting is performed. The heat setting can be performed by a well-known means, and heat treatment is performed at 80 to 170 ° C., preferably 100 to 160 ° C. for about 2 to 600 seconds while keeping the stretched film in a tensioned state. When the raw meat, processed meat, cheese or the like is used for heat shrink packaging, the product is not heat-set after stretching, but is used as a product film, and the raw meat, processed meat, cheese, and the like are stored in the film. ~ 130 ° C, preferably 70 ~ 120
The film is subjected to a heat treatment at a temperature of about 2 to 300 seconds to thermally shrink the film and tightly package it.

The shape of the thus obtained laminate may be any shape, and examples thereof include a film, a sheet, a tape, a bottle, a pipe, a filament, and an extrudate having a modified cross section. Further, the obtained laminate is heat-treated, cooled, rolled, printed, dry-laminated,
Solution or melt coating processing, bag making processing, deep drawing processing, box processing, tube processing, split processing, and the like can be performed. The films, sheets, containers and the like obtained as described above are useful as various packaging materials for foods, pharmaceuticals, industrial chemicals, agricultural chemicals and the like.

[0034]

The present invention will be specifically described below with reference to examples. In the examples, “parts” and “%” mean on a weight basis unless otherwise specified. Example 1 Methanol / water [5] of EVOH [ethylene content 35 mol%, saponification degree 99.5 mol%] adjusted to a liquid temperature of 50 ° C.
0/50 (weight ratio)] was extruded in a strand form from a nozzle having a hole diameter of 4 mm into a water tank maintained at 5 ° C. After the coagulation is completed, the strand is cut with a cutter through a take-off roller attached to the end of the water tank to obtain a pellet (1) having a diameter of 4 mm and a length of 4 mm. After washing with warm water, the mixture was poured into an aqueous acetic acid solution and stirred for 4 hours to obtain EVOH pellets (2) having a water content of 50%. Obtained. <Standing drying step> The obtained pellet (2) was passed through a batch-type aeration-flow box-type dryer through a nitrogen gas at 80 ° C at a speed of 0.5 m.
/ Sec and dried for 12 hours to obtain a water content of 30
% Pellet (3) was obtained. The difference in water content between before and after standing and drying was 20%. <Fluidized drying step> Next, the above pellet (3) was passed through a nitrogen gas at 120 ° C in a batch type fluidized bed dryer at a flow rate of 2.
The mixture was passed at 5 m / sec and dried for 12 hours to obtain dried pellets having a moisture content of 0.2%. The obtained dried pellets were formed into a film under the following conditions to obtain a film. In addition, a continuous operation for 96 hours was performed, and the torque fluctuation, discharge amount change, and film thickness change at that time were evaluated.

(Film forming conditions by single screw extruder) Screw inner diameter 40 mm L / D 28 Screw compression ratio 3.2 T die Coat hanger type Die width 450 mm Extrusion temperature C1: 190 ° C, H: 210 ° C C2: 210 ° C, D: 210 ° C C3: 220 ° C, C4: 220 ° C

(Torque Fluctuation) The fluctuation of the screw torque A (ampere) under the motor load of the extruder (screw rotation speed 40 rpm) during continuous film formation was evaluated as follows. ○: Fluctuation of less than ± 5% △: Fluctuation of ± 5 to less than ± 10% ×: Fluctuation of ± 10% or more

(Change in Discharge Amount) The extruder (40
(rpm) was evaluated as follows. ○: Fluctuation of less than ± 5% △: Fluctuation of less than ± 5 ± 10% ×: Fluctuation of ± 10% or more (Change in film thickness) Measure the thickness of the film in the MD direction every hour. , 40 μm as a center value, and a fluctuation ratio was obtained and evaluated as follows.・ ・ ・: Fluctuation ratio of less than ± 5% Δ: Fluctuation ratio of ± 5 to less than ± 10% ×: Fluctuation ratio of ± 10% or more Table 1 shows the evaluation results of the above items.

Example 2 Pellets (2) were obtained in the same manner as in Example 1, and dried in the following order of the fluidized drying step and the stationary drying step to obtain dried pellets. <Flow drying step> Pellets (2) obtained in Example 1
Was passed through a batch-type fluidized bed dryer at 75 ° C. at a passage speed of 2.0 m / sec, and dried for 3 hours to obtain pellets (3) having a water content of 20%. The difference in water content before and after fluid drying was 30%. <Standing drying step> Next, the obtained pellets (3) were passed through a batch-type ventilation flow box dryer at 125 ° C. at a passage speed of 0.3 m / sec, and dried for 18 hours. A dry pellet having a moisture content of 0.3% was obtained. The obtained dried pellets were formed into a film and evaluated in the same manner as in Example 1.
It was shown to.

Comparative Example 1 In Example 1, the fluidized drying step was omitted, and the stationary drying step was performed under the following conditions to obtain dried pellets. <Standing drying step> The pellet (2) obtained in Example 1 was passed through a batch-type aeration-flow box dryer at 105 ° C at a passage speed of 0.8 m / sec, and dried for 48 hours. Thus, dried pellets having a moisture content of 0.3% were obtained. The obtained product pellets were formed into a film in the same manner as in Example 1, and evaluated in the same manner as in Example 1. The evaluation results are shown in Table 1.

Comparative Example 2 In Example 2, the standing drying step was omitted, and the fluidized drying step was performed under the following conditions to obtain dried pellets. <Flow drying step> Pellets (2) obtained in Example 1
Was passed through a batch type fluidized bed dryer at 110 ° C. at a passage speed of 3.0 m / sec, and dried for 20 hours to obtain dried pellets having a water content of 0.2%. The obtained dried pellets were formed into a film and evaluated in the same manner as in Example 1, and the evaluation results are shown in Table 1.

[0041]

[Table 1] Torque fluctuation Discharge amount change Film thickness change Example 1 ○ ○ ○ 〃 2 ○ ○ ○ Comparative example 1 × × × 〃 2 × × ×

[0042]

According to the present invention, when an alcohol solution of EVOH or a mixed solution of alcohol / water is formed into a strand, and the pellet obtained by cutting the strand is dried, static drying and fluidized drying are performed. Since it is used in combination, the EVOH obtained can be formed into a film or a sheet having excellent uniformity in thickness with little change in torque and change in discharge amount at the time of melt molding, and can be used for food and medicine, It is very useful for applications such as films, sheets, tubes, bags, containers and the like for packaging agricultural and industrial chemicals.

Claims (8)

[Claims] 1. An alcohol solution of a saponified ethylene-vinyl acetate copolymer or a mixed solution of alcohol / water is formed into a strand, and the strand obtained by cutting the strand is dried while standing. A method for drying pellets of a saponified ethylene-vinyl acetate copolymer, characterized by using a combination of drying and fluidized drying. 2. The method for drying saponified ethylene-vinyl acetate copolymer pellets according to claim 1, wherein fluidized drying is performed after static drying. 3. The method for drying saponified ethylene-vinyl acetate copolymer pellets according to claim 1, wherein static drying is carried out after fluidized drying. 4. A saponified ethylene-vinyl acetate copolymer pellet having a moisture content of 20 to 80% by weight before standing drying, 10 to 70% by weight after standing drying, and ethylene before and after standing drying. 3. The method for drying saponified ethylene-vinyl acetate copolymer pellets according to claim 1 or 2, wherein the difference in water content between the saponified vinyl acetate copolymer pellets is 3.0% by weight or more. 5. The water content of the saponified ethylene-vinyl acetate copolymer pellets is 20 to 80% by weight before fluidized drying, 5.0 to 60% by weight after fluidized drying, and the ethylene content before and after fluidized drying. The method for drying saponified ethylene-vinyl acetate copolymer pellets according to claim 1 or 3, wherein the difference in water content of the saponified vinyl acetate copolymer pellets is 5.0% by weight or more. 6. The method according to claim 1, wherein the stationary drying is performed by contacting with a heated gas of 100 ° C. or less, and the fluidized drying is performed by contacting with a heated gas of 80 ° C. or more. A method for drying saponified ethylene-vinyl acetate copolymer pellets according to the above. 7. The method according to claim 1, wherein fluidized drying is performed by contacting with a heated gas of 95 ° C. or less, and static drying is performed by contacting with a heated gas of 75 ° C. or more. A method for drying saponified ethylene-vinyl acetate copolymer pellets according to the above. 8. The ethylene according to claim 1, which is a saponified ethylene-vinyl acetate copolymer having an ethylene content of 20 to 60 mol% and a saponification degree of 90 mol% or more. -A method for drying saponified vinyl acetate copolymer pellets.