JP4236227B2 - Method and apparatus for producing thermoplastic resin sheet - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a thermoplastic resin sheet having a smooth and smooth surface appearance, specifically, an ethylene-vinyl acetate copolymer saponified product (that is, an ethylene-vinyl alcohol copolymer, hereinafter abbreviated as “EVOH” if necessary). The present invention relates to a method and an apparatus for manufacturing.
[0002]
[Prior art]
As a method for producing a thermoplastic resin sheet, a method is known in which a molten resin sheet melt-extruded from a die is brought into close contact with a cooling roll surface by an electrostatic pinning method to obtain a resin sheet. For example, JP-B-37-6142, JP-B-48-14784, JP-B-48-29311, JP-B-59-23270, JP-A-61-95925, JP-B-62-41095 JP-A-56-105930, JP-A-9-193231, JP-A-9-141728, and the like. In addition, the following applications have been filed.
[0003]
(1) In JP-A-7-186243, a thermoplastic resin such as a polyamide resin or a polyester resin is melt-extruded into a film, and the melt-extruded film is rapidly cooled and solidified by being brought into close contact with a rotary cooling roll by static electricity. However, when picking up, use an electrode with at least one tip having a specific resistance of 5 μΩ · cm or less and one or more protrusions capable of corona discharge, and applying a DC high voltage to the electrode to charge the molten film. A method for producing a thermoplastic resin film to be applied is shown.
[0004]
Here, as the electrode, “the electrode having one or more corona dischargeable projections such as a needle shape, a multi-needle shape in which needles are arranged, and a saw blade shape is used”. In this example, a 280 mm long electrode in which a needle (projection) made of copper (or silver-tungsten alloy) having a tip diameter of 0.10 mm, a thickness of 1.0 mmφ, and a length of 12 mm is embedded in a brass plate at a pitch of 2 mm is rotated. Arranged close to the cooling roll.
[0005]
(2) In Japanese Patent Publication No. 6-98672 (JP-A-2-48922), a molten thermoplastic resin (polyamide-based resin, EVOH-based resin, etc.) is extruded into a sheet form from a molding die and the extruded thermoplastic resin is extruded. An electrostatic charge is applied to the sheet surface from the first electrode, and then the charged EVOH sheet is adhered to the electrically insulating film of the cooling roller having an electrically insulating film on the surface of the substrate roller that is electrically grounded. The sheet is cooled and peeled off from the back surface of the cooling roller, and the surface of the cooling roller exposed by peeling off the sheet is imparted with an electrostatic charge having a polarity opposite to that of the first electrode from the second electrode. There is a description that a sheet having a smooth surface appearance can be produced.
[0006]
Here, as the first electrode, those having various shapes such as a wire electrode, a needle electrode, a knife edge electrode, a saw blade electrode, and a tape electrode are used. In the embodiment, tungsten wires are used as the first electrode and the second electrode.
[0007]
[Problems to be solved by the invention]
However, it was not easy to obtain a thermoplastic resin sheet having a good surface appearance over the entire width of the sheet even by the methods described in the literature listed above.
[0008]
For example, as described in the above document (1), even if an electrode in which needles are embedded in a metal plate at a pitch of 2 mm is arranged close to the rotary cooling roll, the surface appearance of the region on both ear ends of the sheet is There was a tendency to be inferior. Such a tendency was particularly conspicuous when the thermoplastic resin was EVOH. Therefore, when a high-quality sheet is required, it is necessary to trim and remove both ends of the obtained sheet by a considerable width, but this is disadvantageous in terms of manufacturing cost, and it is not used. Also, even if the trimming residue is crushed again and subjected to melt molding, the quality of the sheet is greatly reduced, so that the trimming residue can only be reused for limited applications that do not have another stringency. It will be.
[0009]
In view of such a situation, the present invention provides a method for obtaining a target sheet by bringing the molten resin sheet into close contact with a cooling roll while applying an electrostatic charge from an electrode to the molten resin sheet melt-extruded from a die. An object of the present invention is to provide a method capable of producing a thermoplastic resin (specifically, EVOH) sheet having a smooth and smooth surface appearance over the entire width region, and to provide an apparatus therefor.
[0010]
[Means for Solving the Problems]
The method for producing the thermoplastic resin sheet of the present invention comprises:
While giving an electrostatic charge from the electrode to the molten resin sheet of thermoplastic resin extruded from the die, in order to obtain a target sheet by closely contacting the molten resin sheet to the cooling roll,
The thermoplastic resin is a saponified ethylene-vinyl acetate copolymer having an ethylene content of 10 to 60 mol% and a saponification degree of the vinyl acetate component of 90 mol% or more, and the saponified ethylene-vinyl acetate copolymer Na and sum 0.1 to 30 ppm der Rukoto the metal content of K contained in and,
Needle-like electrodes with using the electrode disposed in the sheet width direction as the electrode, a needle-shaped electrodes in the region of the sheet binaural end needle density D ₂ of the needle-like electrodes in the region of the sheet center side The needle density is set to be larger than D ₁ .
[0011]
The apparatus for producing the thermoplastic resin sheet of the present invention comprises:
A device comprising an electrode for imparting an electrostatic charge to the molten resin sheet when a target sheet is obtained by closely adhering a molten resin sheet of a thermoplastic resin extruded from a die to a cooling roll,
The thermoplastic resin is a saponified ethylene-vinyl acetate copolymer having an ethylene content of 10 to 60 mol% and a saponification degree of the vinyl acetate component of 90 mol% or more, and the saponified ethylene-vinyl acetate copolymer The sum of the metal contents of Na and K contained therein is 0.1 to 30 ppm , and
The electrode has a needle-like electrodes are arranged in the sheet width direction structure, and needle-shaped needle density D ₂ of the needle-like electrodes in the region of the sheet binaural end in the region of the sheet center side It is characterized by being set to be larger than the needle density D ₁ of the electrode.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
The present invention will be described in detail below.
[0013]
<Thermoplastic resin , EVOH>
Oite the present invention, as the thermoplastic resin, ethylene, such as described below - vinyl acetate copolymer saponified (i.e. ethylene - vinyl alcohol copolymer, hereinafter abbreviated as "EVOH") is used.
[0014]
EVOH has an ethylene content of 10 to 60 mol% (preferably 20 to 60 mol%, more preferably 25 to 55 mol%), and a saponification degree of the vinyl acetate component of 90 mol% or more (preferably 95 mol% or more). And more preferably 98 mol% or more). When the ethylene content is too low, the water resistance of the film is insufficient and the gas barrier property at high humidity is insufficient. On the other hand, when the ethylene content is too high, the gas barrier property is insufficient. When the saponification degree is too low, the water resistance of the film is insufficient and the gas barrier property is also insufficient.
[0015]
EVOH may be a mixture of two or more types of EVOH having different ethylene contents and different saponification degrees. Further, it may be modified EVOH by copolymerization or graft polymerization for obtaining an ethylene-vinyl acetate copolymer (EVA) before saponification, or an addition reaction utilizing a functional group of EVOH. Furthermore, it may be a blended product by blending with another polymer during or after the EVOH production process.
[0016]
Examples of modification by copolymerization or graft polymerization of EVOH are α-olefins such as propylene, isobutylene, α-octene, α-dodecene, α-octadecene; acrylic acid, methacrylic acid, crotonic acid, maleic acid, maleic anhydride, Ethylenically unsaturated carboxylic acids such as itaconic acid or salts, anhydrides, mono- or dialkyl esters thereof; nitriles such as acrylonitrile and methacrylonitrile; amides such as acrylamide and methacrylamide; alkyl vinyl ethers; polyoxyethylene (meth) Polyoxyalkylene (meth) allyl ethers such as allyl ether and polyoxypropylene (meth) allyl ether; polyoxyalkylene (meth) acrylates such as polyoxyethylene (meth) acrylate and polyoxypropylene (meth) acrylate Relate; polyoxyethylene (meth) acrylamide, polyoxyalkylene (meth) acrylamide such as polyoxypropylene (meth) acrylamide, polyoxyethylene (1- (meth) acrylamide-1,1-dimethylpropyl) ester; polyoxyethylene Vinyl ether, polyoxypropylene vinyl ether; polyoxyethylene allylamine, polyoxypropylene allylamine, polyoxyethylene vinylamine, polyoxypropylene vinylamine; olefin sulfonic acid such as ethylene sulfonic acid, allyl sulfonic acid, methallyl sulfonic acid or salts thereof; N-acrylamidomethyltrimethylammonium chloride, allyltrimethylammonium chloride; dimethylallyl vinyl ketone; N-vinyl pyro This is a case where it is modified with a monomer such as pyrrolidone ring-containing monomer such as lidone; vinyl chloride, vinylidene chloride; silicon-containing monomer; allyl acetate; isopropenyl acetate.
[0017]
Examples of modification by addition reaction using the functional group of EVOH include modification by cyanoethyl group, modification by addition of alkylene oxide (addition of polyether component), and the like.
[0018]
Examples of blends by blending with other polymers during or after EVOH production include blending polyolefin, polyamide, polyester, polystyrene, polyvinyl alcohol, polyurethane, polymethylmethacrylate and their modifications as other polymers Is the case. In this case, other resins can be blended in an amount of about 0.1 to 150 parts by weight (particularly 0.1 to 100 parts by weight, more preferably 0.1 to 80 parts by weight) with respect to 100 parts by weight of EVOH (including a modified product). .
[0019]
The EVOH is required to have a sum of metal contents of Na and K contained therein of 0.1 to 30 ppm . When the sum of the metal contents of Na and K is too small , coloring (yellowing) may occur during extrusion. On the other hand, when the sum is too large, the occurrence frequency of the gel is increased, and the film tends to break during stretching, and the molten resin sheet is difficult to be charged. Acts negatively on sex.
[0020]
The content of metals other than Na and K is not particularly limited, but the sum of the metal contents of Ca and Mg is 1 to 200 ppm (preferably 2 to 150 ppm), of which the metal content of Ca is 100 ppm or less, Mg The content of Ca and / or Mg having a content of 100 ppm or less is effective in suppressing the generation of gel.
[0021]
<Molding into sheets>
In the present invention, a thermoplastic resin (EVOH) extruded from a die into a sheet is applied with an electrostatic charge from an electrode (that is, by an electrostatic pinning method), and the molten resin sheet is adhered to a cooling roll. To obtain the target sheet. The molten resin sheet may be not only a single-layer molten resin sheet but also a multilayer molten resin sheet. An electrically insulating coating such as a ceramic coating may be formed on the surface of the cooling roll. Further, an electrostatic charge having a polarity opposite to that of the second electrode can be imparted to the bare cooling roll surface from which the cooled sheet has been peeled off.
[0022]
As an extruder for extruding a thermoplastic resin (EVOH) , a general screw type extruder such as a single screw extruder or a twin screw extruder is used. The melting temperature is appropriately 10 to 80 ° C. (preferably 20 to 60 ° C.) higher than the melting point of EVOH. However, as long as the resin is sufficiently kneaded , the melting temperature is set as low as possible in order to suppress the generation of gel. It is preferable to do.
[0023]
If only a screw type extruder is used, quantitative extrudability may be lacking, and film thickness accuracy in the flow direction (MD direction) of the unstretched sheet may deteriorate. When such a trouble occurs, it is desirable to provide a gear pump between the extruder and the die (T die). The main structure of the gear pump is an inline type, a block mount type, etc., the number of gears is 2 gears, 3 gears, etc., and the gear shape is spar, helical or the like.
[0024]
The molten resin sheet comes into contact with the cooling roll and is cooled to become the target sheet. At this time, the temperature of the cooling roll is usually 60 ° C. or lower, preferably 40 ° C. or lower in many cases.
[0025]
In the present invention, an electrode in which needle-like electrodes are arranged in the sheet width direction is used as the electrode, and the needle density D ₂ of the needle-like electrodes in the region on the both ear ends of the sheet is determined as the region on the sheet center side. Is set to be larger than the needle density D ₁ of the needle-like electrode. Thus, by setting the needle density D ₂ to be larger than the needle density D _1, it is possible to obtain an EVOH sheet having a smooth and beautiful surface appearance in a region extending over the entire width of the sheet.
[0026]
More quantitatively speaking, the ratio of the needle density D ₁ of the needle-shaped electrode at 70% of the area of the needle density D ₂ and the seat center side of the needle-like electrodes in each 15% of the area of the sheet binaural end It is desirable to set D ₂ / D ₁ within a range of 1.01 to 5, preferably 1.1 to 4, and more preferably 1.2 to 3.
[0027]
In this case, the needles may be arranged uniformly or in close proximity in each of the area on the both ear ends of the sheet and the area on the center side of the sheet. FIG. 3 to be described later is an explanatory view showing an arrangement state of electrode needles. In Embodiments 1 and 2 of FIG. 3, needles are arranged at equal intervals over the entire width of the sheet as in the prior art. In the embodiment 3 of FIG. 3, are the needle density D ₂ of the needle-like electrodes in the region of the sheet binaural end side larger than the needle density D ₁ of the needle-shaped electrodes in the region of the sheet center side, but the sheet-Car In each of the ear end side region and the sheet center side region, the needle density is made uniform. In the aspect 4 of FIG. 3, the needle density D ₂ of the needle-like electrode in the region on the both ear ends of the sheet is made larger than the needle density D ₁ of the needle-like electrode in the region on the center side of the sheet. In the ear end side region, the needle density is increased toward the ear end, and in the intermediate region between the sheet both ear end region and the sheet center side region, the needle is closer to the center side region. The density is small. Various other variations are possible.
[0028]
<Secondary processing after sheet forming>
The sheet (unstretched sheet) obtained as described above can be used for various purposes as a single sheet. Moreover, this unstretched sheet can be used for a stretching process to form a uniaxially stretched film or a biaxially stretched film. Alternatively, the unstretched film or stretched film can be laminated with a base material to form a laminate film, or another substance can be coated to form a composite film. The unstretched film or stretched film may be subjected to vapor deposition of metal or inorganic oxide, sputtering, or ion plating to form a film.
[0029]
<Application>
The obtained sheet and its secondary processed products are excellent not only in appearance characteristics but also in properties such as gas barrier properties, fragrance retention properties, solvent resistance properties, and oil resistance properties. It is particularly useful as a film, sheet, tube, bag, container, etc. for packaging oils, etc., and can also be used for applications such as agricultural materials.
[0030]
【Example】
The following examples further illustrate the present invention.
[0031]
<Raw material EVOH>
As shown in Table 1 described later, EVOH resins having different copolymer compositions and alkali metal or alkaline earth metal contents were prepared. The alkali metal and alkaline earth metal were quantified by atomic absorption analysis.
[0032]
<Manufacturing equipment, electrodes>
FIG. 1 is a side view showing an example of the manufacturing apparatus of the present invention. FIG. 2 is a front view of the main part of the apparatus of FIG. FIG. 3 is an explanatory view showing an arrangement state of the needle (7a) of the electrode (7). 1-2, (1) is a single screw extruder, (2) is a gear pump, (3) is a die (T-die), (4) is a cooling roll (casting roll), (5) is a peeling roll, (6) is a DC high-voltage power supply, and (7) is an electrode. The needle (7a) of the electrode (7) is shown in FIG. (S ₁ ) is a molten resin sheet, and (S ₂ ) is a sheet after cooling.
[0033]
<Film forming conditions>
Using the above apparatus, a sheet was formed under the following conditions. That is, the above EVOH is supplied to a single-screw extruder (1), melt-extruded from a T-die (3) through a gear pump (2), and cooled to a temperature of 20 ° C., which is a 600 mm diameter cooling roll (casting roll) ( 4) Quenched above. An electrostatic charge was imparted to the molten resin sheet (S ₁ ) from the outside by a needle-like electrode (7). As a result, an EVOH sheet (unstretched film) (S ₂ ) having a thickness of 150 μm was obtained. Fine adjustment of the thickness was performed by adjusting the rotation speed of the cooling roll (4).
[0034]
1. Extrusion conditions with a single screw extruder ・ Screw inner diameter: 65 mm
・ L / D: 28
・ Screw compression ratio: 3.8
Extrusion temperature: C ₁ 210 ° C, C ₂ 220 ° C, C ₃ 230 ° C, C ₄ 230 ° C, C ₅ 220 ° C
[0035]
2. Gear pump ・ Number of gears: 2
・ Gear shape: Spar ・ Model: Inline type ・ Gear pump temperature: 220 ℃
[0036]
3. T die ・ Coat hanger type manifold type ・ Die width: 450 mm (430 mm in molten resin sheet width)
-Die temperature: 220 ° C
[0037]
4). Electrode ・ Electrode: Needle-shaped electrode (polytetrafluoroethylene resin plate with stainless needles implanted)
・ Applied voltage: 20 kV
・ Applied current: 3 mA
[0038]
5. Aspect of arrangement of electrode needles Aspect 1
Tip diameter: 0.08mm
Needle density D _{1 in} the 70% area on the center side of the sheet: 4 / cm
Needle density D ₂ in each 15% area on both ends of the sheet: 4 / cm (equally spaced)
Needle density ratio D ₂ / D ₁ = 1.0
Aspect 2
Tip diameter: 0.08mm
Needle density D _{1 in} the area of 70% on the center side of the sheet: 6 / cm
Needle density D ₂ in each 15% area on both ends of the sheet sheet: 6 / cm (equally spaced)
Needle density ratio D ₂ / D ₁ = 1.0
Aspect 3
Tip diameter: 0.08mm
Needle density D _{1 in} the 70% area on the center side of the sheet: 4 / cm
Needle density D ₂ in each 15% area on both ends of the sheet sheet: 6 / cm (equally spaced)
Needle density ratio D ₂ / D ₁ = 1.5
Aspect 4
Tip diameter: 0.08mm
Needle density D _{1 in} the 70% area on the center side of the sheet: 4 on average per cm
The needle density in the 40% area on the center is 4 / cm (equally spaced)
Each adjacent 15% area has a needle density of 5.5 to 4 / cm
(Gradation arrangement that becomes denser toward the outside)
Needle density D ₂ in each 15% area on both ends of the sheet: 6 needles / cm on average
6.5-5.5 / cm (gradient arrangement that becomes denser toward the ear end)
Needle density ratio D ₂ / D ₁ = 1.5
[0039]
<Appearance evaluation method>
The film appearance was evaluated visually. Evaluation was made into the following five stages of A, A ′, B, C, and D.
A: Smooth and beautiful A ': Smooth, beautiful but slightly inferior to A B: Slightly textured (uneven size less than 0.5mm)
C: Pear texture (unevenness size 0.5mm or more)
D: Air is entrained vertically in the MD direction. [0040]
<Summary of conditions and results>
Conditions and results are summarized in Table 1. In Table 1, “Region X” is a 15% region on each ear end side of the sheet, “Region Y ₂ ” is a 40% region on the center side of the sheet, and “Region Y ₁ ” is region X and region Y _2. And 15% of the area between the two. “Et” in the EVOH column is the ethylene content (mol%), and “SV” is the degree of saponification (mol%).
[0041]
[Table 1]

EVOH Appearance evaluation of metal content (ppm) electrode sheet
Et SV Na + K Ca Mg needle placement area X area Y ₁ area Y ₂
Comparative Example 1 32 99.8 20 10 1 Aspect 1 C B to A ′ A ′
Comparative Example 2 32 99.8 20 10 1 Aspect 2 C to B B to A ′ A
Example 1 32 99.8 20 10 1 Aspect 3 A A A
Example 2 32 99.8 20 Ten 1 embodiment 4 A A A
Comparative Example 3 44 99.8 100 10 1 Aspect 1 C B to A ′ A ′
Reference Example 1 44 99.8 100 Ten 1 embodiment 3 A 'A' A '
Comparative Example 4 32 99.8 1 0 25 Aspect 1 C B to A A
Example 3 32 99.8 1 0 25 Aspect 3 A A A
Comparative Example 5 44 99.8 80 10 1 Aspect 1 D B to A ′ A ′
Reference Example 2 44 99.8 80 Ten 1 embodiment 3 A 'A' A '
[0042]
From Table 1, when EVOH having the same composition and the same metal content is used, the surface appearance of the area over the entire width of the sheet is smooth and beautiful, while the comparative example is the area on the both ears side of the sheet and its area. It can be seen that the surface appearance of the region adjacent to the ear end side is inferior. Further, reference example in the case of using a different EVOH metal content is the better of Examples 1 to 3 in which the sum of the metal content of Na and K in the range of 0.1 to 30 ppm is out of that range 1. It can be seen that a more preferable surface appearance can be obtained as compared with Reference Example 2 .
[0043]
【The invention's effect】
The present invention therefore, as the sum of the metal content of Na and K to the thermoplastic resin contained in a specific ethylene content and using EVOH having a saponification degree and the EVOH is a specific range (0.1 to 30 ppm) In addition, only by devising the arrangement of the electrode needles, a smooth and beautiful EVOH sheet having an excellent surface appearance over the entire width of the sheet can be obtained. Therefore, the industrial value of the present invention is great.
[Brief description of the drawings]
FIG. 1 is a side view showing an example of a manufacturing apparatus of the present invention.
FIG. 2 is a front view of a main part of the apparatus shown in FIG.
FIG. 3 is an explanatory view showing an arrangement state of a needle (7a) of an electrode (7).
[Explanation of symbols]
(1)… Single screw extruder,
(2)… gear pump,
(3) Die (T-die),
(4)… cooling roll,
(5)… peeling roll,
(6)… DC high-voltage power supply,
(7)… electrode,
(7a) ... Needle of electrode (7),
(S ₁ ) ... Molten resin sheet,
(S ₂ )… (After cooling) sheet

Claims (3)

While giving an electrostatic charge from the electrode to the molten resin sheet of thermoplastic resin extruded from the die, in order to obtain a target sheet by closely contacting the molten resin sheet to the cooling roll,

The thermoplastic resin is a saponified ethylene-vinyl acetate copolymer having an ethylene content of 10 to 60 mol% and a saponification degree of the vinyl acetate component of 90 mol% or more, and the saponified ethylene-vinyl acetate copolymer The sum of the metal contents of Na and K contained therein is 0.1 to 30 ppm , and
Needle-like electrodes with using the electrode disposed in the sheet width direction as the electrode, a needle-shaped electrodes in the region of the sheet binaural end needle density D ₂ of the needle-like electrodes in the region of the sheet center side A method for producing a thermoplastic resin sheet, wherein the needle density is set to be larger than D ₁ . The ratio D ₂ / D ₁ between the needle density D ₂ of the needle-like electrode in each 15% region on the sheet ear end side and the needle density D ₁ of the needle-like electrode in the 70% region on the sheet center side is 1.01. The production method according to claim 1, wherein the production method is set within a range of ˜5. A device comprising an electrode for imparting an electrostatic charge to the molten resin sheet when a target sheet is obtained by closely adhering a molten resin sheet of a thermoplastic resin extruded from a die to a cooling roll,
The thermoplastic resin is a saponified ethylene-vinyl acetate copolymer having an ethylene content of 10 to 60 mol% and a saponification degree of the vinyl acetate component of 90 mol% or more, and the saponified ethylene-vinyl acetate copolymer The sum of the metal contents of Na and K contained therein is 0.1 to 30 ppm , and
The electrode has a needle-like electrodes are arranged in the sheet width direction structure, and needle-shaped needle density D ₂ of the needle-like electrodes in the region of the sheet binaural end in the region of the sheet center side An apparatus for producing a thermoplastic resin sheet, characterized in that it is set to be larger than the needle density D ₁ of the electrode.

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