JP2000301587A - Casting method for polyamide sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high speed casting method for a polyamide resin. SOLUTION: At a point where a molten polyamide resin sheet comes into contact with two moving cooling media, this polyamide resin sheet is held between two cooling media to be mechanically brought into close contact with cooling media and a water films or waterdrops are formed on the surfaces of the cooling media to form close contact force on both surfaces of the molten polyamide resin sheets by the surface tension due to the meniscuses between both surfaces of the sheets and the cooling media to cool the polyamide resin sheet in close contact state by surface tension and mechanical nip pressure.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for high-speed casting of a polyamide sheet. More specifically, the present invention provides an excellent cast sheet for biaxial stretching, and also provides a casting method which enables production of a cast sheet having excellent thickness uniformity, surface properties, transparency, and the like. Is what you do.

[0002]

2. Description of the Related Art Conventionally, as a method for obtaining a sheet having low crystallization by bringing a polyamide molten sheet into close contact with a cooling medium, an air knife method, an air chamber method, an electrostatic contact method, a press roll method, and a surface tension of water are used. Methods such as a close contact method, a rough surface roll method, and a high-temperature drum method have been used.

[0003]

However, any of such casting methods has the following major problems. (1) Adhesive force between the sheet and the cooling medium is insufficient by using any method such as a press roll method for obtaining a sheet having low crystallinity, an air knife method, an electrostatic adhesion method, and an adhesion method using surface tension of water. The casting speed was as low as 35 m / min at most. (2) For this purpose, the stretching ratio in the longitudinal direction (for example, 3
Times), the film winding speed is only about 100 m / min at most, which is slower than the normal film forming speed of 250 m / min of the biaxially stretched polyester sheet, and the production cost is high. I didn't get it. (3) In a method of casting while interposing an air layer between a cooling medium and a molten sheet, such as an air chamber method, a rough surface roll method, and a high-temperature drum method, 100 m is used.
Although high-speed casting at a rate of about / min is possible, the sheet thus obtained cannot be uniformly stretched in the next stretching step.

[0004] Thus, the following biaxial stretching is possible,
Moreover, a casting method capable of forming a film at a high speed of 300 m / min or more, that is, a high-speed casting method of 100 m / min or more has not been known.

[0005]

Means for Solving the Problems Accordingly, the present inventors have:
After extensively studying a method for improving the mutual adhesion between the polyamide melt sheet and the moving cooling medium,
In order to increase the adhesion, the molten polyamide sheet is sandwiched between two cooling media at a point where the molten polyamide sheet comes into contact with the moving cooling medium, and a water film or a droplet is formed on the surface of the cooling medium. By forming a meniscus between the cooling medium on both sides of the polyamide sheet and performing close contact cooling, excellent close contact cooling is realized by the surface tension of water and mechanical nip force, the casting method of the present invention. It was found.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below.

In the present invention, the polyamide resin is a polymer compound having an amide bond in the main chain, and typical examples thereof include nylon 6, nylon 66, nylon 610, nylon 12, nylon 11, and nylon 7. , Polymeta / paraxylylene adipamide (MXD6), polyhexamethylene terephthalamide / isophthalamide (6T
/ 6I), bisaminomethylcyclohexylmethane (B
AC) and adipic acid-containing polyamide (BA)
C6) and polyamide compounds selected from copolymers and mixtures thereof. The amount of the monomer or oligomer (MO) usually contained in the polyamide resin is preferably as small as possible in order to excel in the stability in the film forming process and the handleability in the post-process, etc. % By weight, more preferably 0.8% by weight or less.

In the case of the present invention, the polyamide resin particularly preferably used is nylon 6 and a copolymer thereof. The relative viscosity of the polyamide resin depends on various properties expected after molding, but is preferably in the range of 1 to 5, preferably 2 to 4 in ηr. Polyamide ethers obtained by copolymerizing polyether compounds such as polyethylene glycol, polypropylene glycol, and polytetramethylene glycol, and polyesteramide compounds obtained by copolymerizing with polyester may be used. May be modified to an amorphous polyamide resin having a long chain or a large substituent.

Of course, these polyamide resins include:
Various additives, for example, a slipping agent, an antiblocking agent, a bulking agent, a stabilizer, an antioxidant, a viscosity modifier such as a thickener / thickener, an antistatic agent, a colorant, a pigment, and a liquid crystal polyester amide Such resins can be used in combination.

When the surface of the molten polyamide sheet comes into direct contact with water, the surface of the polyamide sheet is crystallized and roughened by absorbing water, and the surface of the obtained sheet is roughened. In order to avoid this, it is preferable to laminate a resin layer having less water absorption than the polyamide resin, for example, a layer such as a polyester resin layer and a polyolefin resin layer on the polyamide layer. The resin to be laminated is preferably a resin having good compatibility and adhesion with polyamide and having relatively low water absorption.

Particularly preferred as the polyolefin resin used in the present invention are olefinic ionomers, especially ionomers such as ethylene zinc acrylate. As the polyester resin, a polyester resin obtained by copolymerizing polyethylene terephthalate (PET) or an ionic compound such as sodium sulfonate of isophthalic acid (SSIA) is preferably used.

The present invention relates to a casting method for cooling a molten polyamide sheet in close contact with a moving cooling medium, wherein the molten polyamide sheet sheet is in close contact with two moving cooling media at a point where the sheet is in contact with the moving cooling medium. In addition, a water film or a water droplet is formed on the surface of each cooling medium, and a meniscus is formed between both surfaces of the molten polyamide sheet and the cooling medium so that they are brought into close contact with each other.

[0013] With this configuration, the close contact cooling operation can be effectively performed by the surface tension of water and the mechanical nip force. That is, by doing so, it is possible to prevent the accompanying airflow above the cooling medium from entering between the molten polyamide sheet and the cooling medium and causing a crater-like surface defect on the cooling sheet surface. You can. That is, in a method of mechanically nipping, as in a simple calendering device, the accompanying airflow cannot be eliminated with a relatively small nip force.
m / min or higher speed cannot be expected at all, but even if the nip force is increased to form a bank in the molten sheet, at most 30 to
High speed casting is possible only at about 40m / min. Further, only by the method of forming a meniscus, the speed can be increased to about 40 to 50 m / min. However, at a speed higher than that, the accompanying airflow becomes large and the molten sheet rises greatly from the cooling medium and becomes cloudy due to crystallization. In addition to the drawback, the surface is roughened by water and only a sheet with poor transparency can be obtained.

As described above, high-speed casting at a speed of 100 m / min or more cannot be performed by a mere mechanical nip or a meniscus forming method alone.

Therefore, high-speed casting can be achieved for the first time by using both mechanical nip and meniscus formation as in the present invention.

In the present invention, the cooling medium is a medium having an action of cooling the molten polyamide sheet, and its form is not particularly limited, but a roll-shaped medium can be used. When the cooling medium is such a roll, a water film or a water droplet is formed on the surface of the cooling roll, and a meniscus is formed between the cooling roll and both sides of the molten sheet to be closely cooled. This is very important. As the cooling medium, a belt-shaped or plate-shaped cooling medium can be used.

In order to form a cooling roll having such a water film or water droplets on the surface, the roll surface temperature must be 2 to 20
Cooling to below the dew point with a refrigerant cooled to about ° C. to cause dew point to form naturally on the roll surface, or spraying steam, water mist, preferably charged water mist onto the roll, and / or sponge roll It is possible to use a method of transferring water by contacting with a water leaching roll such as a commercially available water absorbing and retaining roll, gravure roll, etc., in which fibers are laminated at a high density, such as a gravure roll. it can.

Of course, it is sometimes preferable to charge the cooling roll because the mist can be uniformly dispersed. In the present invention, the "water seepage roll" refers to the above-mentioned sponge roll, a water-absorbing and retaining roll in which fibers are laminated at a high density, a gravure roll, and the like, and, if desired, exudes water by pressing. It refers to a roll that can be used.

Further, in order to improve the uniform wettability of the surface of the cooling medium such as a cooling roll with water, it is also preferable to use a hydrophilic cooling medium such as a micro crack. The surface roughness of the cooling medium is preferably 0.6 μm or less, more preferably 0.2 μm or less, and the smoothness is effective for improving the adhesion and the smoothness of the obtained sheet. It is something.

At this time, by applying an electrostatic charge until the molten sheet comes into contact with the cooling medium, the speed can be further increased, which is often preferable.

Next, a method for producing a polyamide sheet using the casting method of the present invention will be described.

Polyamide raw materials used for melt extrusion, and inorganic additives such as silicon oxide, magnesium oxide, calcium carbonate, titanium oxide, aluminum oxide, mica, talc, kaolin, etc.
Raw materials to which organic compounds such as cross-linked polystyrene, ethylenebisstearylamide, stearic acid amide, calcium stearate, ionic polymer compound ionomers, etc. are added, raw materials once melted, and raw materials for the film obtained by the method of the present invention After mixing and drying the raw materials, they are dried and dehydrated, and then supplied to a melt extruder such as a single-screw extruder, twin-screw extruder, vent extruder, or tandem extruder so that the molecular weight is not reduced as much as possible. Under a nitrogen stream or under vacuum. At this time, it is preferable to use an appropriate filter, for example, a sintered metal, a porous ceramic, a sand, a wire mesh, or the like in order to remove foreign matter.

Further, in order to thinly laminate an ionomer layer which is a partial zinc salt of ethylene acrylic acid on both sides of the polyamide resin layer, the ionomer is melted from another extruder, and then supplied in a fixed amount to the polyamide layer in a molten state. To be laminated.

As described above, the polyamide / ionomer laminated molten sheet is cooled and solidified in contact with the moving cooling medium. A water film and water droplets are formed on the moving cooling medium, and the molten sheet and the cooling medium are interposed between the molten sheet and the cooling medium. A meniscus of water is formed and adhered by the surface tension of water.

Further, a cooling medium such as a water film or another roll having water droplets is also brought into contact with the sheet surface of the laminated molten polyamide sheet opposite to the sheet surface in contact with the cooling medium.
The speed can be increased by nipping.

In order to use a cooling medium such as a roll having such a water film or water droplets, the surface of the roll is cooled to a temperature lower than the dew point, or a steam or charged water mist is added to the cooling medium such as the roll. It is good to spray. It is also possible to apply an electrostatic charge to the melted thermoplastic resin sheet, bring it into close contact with a drum of a cooling medium such as a roll, rapidly cool it, and cast it.

The positional relationship between the die and the casting drum is not particularly limited, but a method of casting in the tangential direction of the cooling medium is advantageous. For this reason, it is preferable to use a crow mouth shape with a sharp tip.

The thus obtained cast film can be stretched as required to produce a polyamide sheet. Specific examples include, for example, longitudinal uniaxial stretching, horizontal uniaxial stretching, sequential biaxial stretching, and simultaneous biaxial stretching. Stretching can be performed according to a stretching method such as axial stretching. The stretching temperature is not particularly limited, but may be any temperature as long as it is equal to or higher than the glass transition temperature Tg of the resin, and an arbitrary temperature can be selected as needed. The stretching ratio in one direction is specifically about 3 times. After stretching, heat setting may be performed at a temperature equal to or lower than the melting point, if necessary.

The thus obtained polyamide resin sheet according to the present invention not only enables high-speed film formation, but also has excellent properties such as thickness uniformity, transparency, adhesiveness, slipperiness, moldability and toughness. Therefore, it becomes an excellent packaging film.

[Method for Measuring Physical Properties] Next, the method for measuring physical properties used in the present invention will be described below. 1. Relative viscosity ηr: Measured according to JIS-K1860. 2. Unevenness of film thickness: Using a film thick nest tester “KG601A” and an electronic micrometer “K306C” manufactured by Anritsu Corporation, 30
The thickness of a film sampled in mm width and 10 m length is continuously measured. The transport speed of the film was 3 m / min. Thickness maximum value Tmax (μm) and minimum value T at 10 m length
R = Tmax-Tmin was determined from min (μm), and the thickness unevenness (%) was determined as R / Tave × 100 from R and the average thickness Tave (μm) having a length of 10 m. 3. Thermal characteristics (Tm, Tg, Tmc) Using a DSC-II type measuring device manufactured by PerkinElmer, a sample weight of 10 mg, a temperature rising rate of 20 ° C. /
The temperature at which the deviation of the baseline started was Tg, the exothermic peak when the temperature was further increased was Tcc, and the endothermic peak temperature accompanying crystal melting was the melting point Tm.
After holding at Tm + 20 ° C. for 1 minute, the melt was cooled at a cooling rate of 20 ° C./min.
mc.

[0031]

EXAMPLES Examples and comparative examples will be shown below for better understanding of the present invention.

Example 1 Polyamide resin B (relative viscosity ηr 2.6, MO content 0.9 WT%, glass transition temperature 40 ° C., 0.1 wt% of spherical silica having an average particle size of 0.2 μm was added as an additive. ), The raw material was dried and supplied to a 125 mm melt extruder, melted at 280 ° C., and passed through a filter for removing foreign substances of 10 μm or less according to a conventional method. On the other hand, the ionomer "Surlyn" A (manufactured by DuPont) laminated on both surfaces of the polyamide resin B layer was 45 mm in thickness.
And melted at 265 ° C., and three layers of these molten resin A layers were laminated by a composite adapter which laminated three layers of A / B / A. A drum having water droplets on a 1800 mm diameter surface rotated at 130 m / min and kept at 15 ° C. (The drum surface is a chrome plating roll mirror-finished to a maximum roughness Rt = 0.1 μm. Saturated water vapor is sprayed to condense water droplets on the surface, and a nip roll having water droplets of 150 mm in diameter in contact with the drum (the surface is a micro-cracked chromium-plated hydrophilizing roll. Saturated water vapor is sprayed on the surface to form dew drops) and the melt is landed, adhered, and cooled so that it is tangent to each drum or roll. It was.

The cast film thus obtained has a thickness of 150 μm, and the thickness unevenness is as small as 1% or less in both the longitudinal direction and the width direction.
Even if the frequency analysis of the thickness unevenness is performed, there is no vibration at 0.5 to 10 Hz which is considered to be caused by the vibration at the landing point, and the crater has excellent thickness uniformity and excellent flatness. It is a sheet with low crystallinity without surface defects such as, etc.It can be clearly confirmed that it is transparent and completely amorphous and has excellent castability without edge width fluctuation. Was.

Subsequently, the cast film was stretched three times at a stretching temperature of 55 ° C. using a simultaneous biaxial stretching machine, cooled once to Tg or lower, and then heated again to 210 ° C. for fixed-length heat fixing, and 3% relaxed heat fixing in the longitudinal direction and the width direction at 150 ° C., respectively, and the edge end is cut to obtain a 15 μm-thick biaxially oriented laminated polyamide film of about 380 m / min in a stable state without breaking. The film was formed by winding and edge-treating at high speed.

The polyamide film thus obtained had a thickness uniformity of 2% in the longitudinal direction and 3% in the width direction, and was excellent in flatness without surface defects. .

Example 2 Polyamide resin (relative viscosity η)
r3.2, MO content 0.8WT%, glass transition temperature 4
0 ° C., 0.1 wt% of wet-agglomerated silica, 0.05 wt% of calcium stearate, and 0.03 wt% of ethylenebisstearylamide were added as additives.
According to a conventional method, the raw material is dried with hot air, and then supplied to a melt extruder having a 125 mm screw to be melted at 280 ° C.
Pass the following filter to remove foreign substances,
A drum in which water droplets are condensed on a 2500 mm diameter surface rotating at 100 m / min maintained at a surface temperature of 5 ° C. from a 100 mm wide T-die die (the drum surface has a maximum roughness Rt =
A chrome-plated roll having a 0.6 μm microcrack) and a nip roll having a water film with a diameter of 150 mm in contact with the drum (the surface is a chromium-plated hydrophilized roll in a microcrack state, and the roll surface is Saturated water vapor sprayed onto the surface to form dew drops
The melt was landed, adhered, and cooled so as to be tangent to each drum or roll at the point of contact.

The cast film thus obtained has a thickness of 150 μm, and the thickness unevenness is as small as 2% or less in both the longitudinal direction and the width direction. There is no vibration of 0.5 to 10 Hz, which is considered to be caused by the above, and the sheet has excellent thickness uniformity, low flatness and transparency, and low crystallinity. Without change,
The castability was excellent.

Subsequently, the cast film was stretched three times at a stretching temperature of 45 ° C. by a roll stretching machine, and then stretched three times by a tenter at a stretching temperature of 55 ° C. in a width direction. After cooling to 30 ° C. and clipping it off, it is again gripped by a tenter that can be relaxed in the longitudinal direction, heat-fixed while relaxing 5% in the longitudinal direction at 210 ° C., and further 3% in the width direction at 150 ° C. Heat-fixed, cut edge edge, thickness 1
A 5 μm biaxially oriented laminated polyamide film was wound at a high speed of about 380 m / min in a stable state without breaking, and edge-treated to form a film. Of course, there is almost no film breakage during film formation, and it is stable at about 300 m / min.
Rolled up.

The thickness unevenness of the polyamide film thus obtained is a film having excellent thickness uniformity of 5% in the longitudinal direction and 7% in the width direction, and is a transparent film having excellent flatness without surface defects. there were.

(Comparative Example 1) Except that the water droplets formed on the cooling drum and the nip roll used in Example 1 were not supplied, and thus no meniscus was formed, the rest was exactly the same as in Example 1. Cast. As a result, 1
At a high speed of 30 m / min, it was impossible to cast without entraining the accompanying airflow, and there were poor transparency and many surface defects. For this reason, the casting speed was reduced, and the upper limit speed at which the air layer of the accompanying airflow was not caught was determined. The upper limit speed was 33 m / min.
The speed was very slow, far from the speed of 0 m / min or more.

Comparative Example 2 In Example 1, without using a nip roll having water droplets, water droplets were supplied only to the cooling drum and a meniscus was formed only between the cooling drum and the molten polyamide sheet and cast. As a result, 50m /
At a high speed of more than one minute, the accompanying air flow pushed the molten polyamide sheet away and caught between the sheet and the drum, so that only a sheet with poor transparency and surface properties was obtained. The stretchability was poor, and uniform stretching was impossible.

[0042]

According to the method of the present invention, high-speed casting at a speed of 100 m / min or more is possible, and the transparency and surface smoothness of the obtained cast film are good. Thickness unevenness of 0.1 to 10 Hz, which is considered to be caused by vibration, is completely eliminated, and a polyamide film having good thickness uniformity is obtained.

As a result, not only the stretchability and the moldability are dramatically improved, but also the obtained polyamide film is excellent in toughness and exhibits excellent properties for various packaging applications.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI theme coat ゛ (reference) B29L 9:00 F term (reference) 4F071 AA54 AF27 AF30 BB02 BB08 BC01 4F207 AA22 AA24 AA29 AG01 AG03 AK02 KA01 KA17 KB22 KK55 KK63 KK66 KK74 KL65 KL84 KW23 KW26 4J002 CL011 CL031 FD030 FD070 FD100 FD330 GF00

Claims (7)

[Claims] 1. A method for cooling and solidifying a molten polyamide sheet by sandwiching the same between two cooling media, wherein a water film or water droplet is formed on the surface of the cooling medium, and a meniscus is formed between both surfaces of the molten polyamide sheet and the cooling medium. A method for casting a polyamide sheet, comprising forming and cooling closely. 2. The method for casting a polyamide sheet according to claim 1, wherein the formation of the water film or the water droplets is performed by spraying saturated steam, water mist, or charged water mist. . 3. The method for casting a polyamide sheet according to claim 1, wherein the formation of the water film or the water droplet is carried out by bringing a water seeping roll into contact with a cooling medium. 4. The method for casting a polyamide sheet according to claim 1, wherein the cooling medium is a roll. 5. The polyamide sheet according to claim 1, wherein the polyamide sheet is a laminate with a thin resin layer selected from ethylene ionomer, polyester, and hydrophobic polymer. Casting method. 6. The method for casting a polyamide sheet according to claim 1, wherein the polyamide sheet is stretched. 7. A method for producing a polyamide sheet, comprising using the method for casting a polyamide sheet according to claim 1 and stretching the obtained cast sheet.