JPS63199624A - Manufacture of thermoplastic resin sheet - Google Patents

Abstract

PURPOSE:To manufacture a resin sheet having a transparency wherein surface haze is especially low, at favorable stability through a high-speed extrusion, by a method wherein thermoplastic resin is extruded as a filmy material by making use of a resin extruding device and then introduced into a slit, into which cooling water flows down, for cooling. CONSTITUTION:An extruding device 1 includes a cylinder 3 provided with a hopper 2 for supply of a resin pellet and a screw 4 provided within the cylinder 3. The screw 4 is provided with a supply part 11, a compression part 12, a measuring part 13, a mixing part 14, a shearing part 15 and a stress mitigation part 16 in the order from a resin supply part side. Residual shearing stress of the resin which has passed through the shearing part 15 is mitigated by a stress mitigation part 16 and then extruded through a die 30. A resin filmy material 38 extruded through the extrusion die 30 is introduced into slits 31, 35 of an upper and lower stage water tanks 33, 36 into which cooling water flows down. The filmy resin material 38 is passed through the cooling water on the inside of a water tank 37 through pinching and pressing rolls 39, 40, taken off by take-off rolls 41, 42, then predetermined heat treatment is performed thereon by a roll group 43 and molding of a resin sheet is completed.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides a resin sheet using a thermoplastic resin as a molding material.
The present invention relates to a method of manufacturing films, etc., and relates to a method of manufacturing thermoplastic resin sheets that can be used for various packaging purposes.

[Background technology and its problems]

BACKGROUND ART Crystalline thermoplastic resins such as polypropylene and polyethylene have been used in various packaging fields as sheets and containers because of their thermoplasticity and ease of molding.

By the way, in the production of crystalline thermoplastic resin sheets such as polypropylene, the crystal form is controlled by cooling the sheets in order to improve the transparency of the sheets. Water cooling is the most efficient method for such rapid cooling, but there is a problem in that it is difficult to uniformly cool the resin film extruded from the extrusion die. As a method for uniformly cooling a shaped body with water, a method using "multistage slits" through which cooling water flows has already been proposed (Japanese Patent Application No. 86475/1982).

However, even if the cooling conditions and the like are controlled by the method described above, there is a limit to the cooling effect, and the transparency, surface uniformity, etc. of the resin sheet)tll[ as a molded article are not necessarily satisfactory.

Therefore, as a result of various studies conducted by the present inventors, we found that the influence of extrusion conditions at the stage of the molten resin before the extruded resin film comes into contact with cooling water, that is, the stage from material supply to the resin extrusion device to extrusion. We found that the extrusion conditions were large, and proposed a method using a combination of these extrusion conditions and the slit water cooling method (Japanese Patent Application No. 60-287512, No. 61-20).
2146) 0 As a result of a rough study of extrusion conditions, the present invention
We have discovered better extrusion conditions.

[Purpose of the invention]

The purpose of the present invention is to produce resin sheets with good transparency, especially low surface haze, by extrusion molding using an extrusion device set to specific conditions and specific water cooling conditions with good stability and high speed extrusion. The goal is to provide a way to do so.

[Means and effects for solving the problems] The present invention has the following features:
A thermoplastic resin is extruded as a film using a resin extrusion device having a supply section, a compression section, a measuring section, a mixing section, a shearing section, and a stress relaxation section sequentially from the resin supply side to the resin extrusion side. The film-like body is introduced into a slit through which cooling water flows, and is further cooled by running in the direction of the cooling water.

In short, the present invention focuses on the point that the limit of the water cooling effect is closely related to the extrusion conditions at the resin extrusion molding stage, and employs, for example, a specific screw structure in the resin extrusion device, while in the water cooling device, The above object is achieved by sufficiently cooling the resin by introducing the resin into a predetermined slit, and dramatically improving the transparency, etc. of the resulting resin sheets.

〔Example〕

Hereinafter, an example of the present invention will be explained based on the accompanying drawings.

First, as the thermoplastic resin used in the present invention, polypropylene resins, such as polypropylene homopolymers, random copolymers of propylene and 20% or less of other α-olefins, and blends thereof are suitable. However, this blend also includes a blend obtained by a multi-stage polymerization method. There are other crystalline resins such as polyethylene, polyester, and polyamide. Furthermore, resins similar to these, adhesive resins such as polyolefin resins graft-modified with maleic anhydride, easily weldable resins such as ethylene-vinyl acetate copolymers, ethylene-vinyl alcohol copolymers, polyamides, polyethylene terephants, etc. It is also applicable to coextruded multilayer sheets with gas barrier resins such as crates. In the case of a coextruded multilayer sheet, the extrusion apparatus of the present invention is used to extrude the main constituent components of the multilayer sheet, such as polypropylene.

FIG. 1 shows an extrusion device 1 used in this embodiment. This extrusion amount at is comprised of a cylinder 3 equipped with a hopper 2 for supplying resin pellets, and a screw 4 installed inside this cylinder 3.

The screw 4 is provided with a supply section 11, a compression section 12, a measuring section 13, a mixing section 14, a shearing section 15, and a stress relaxation section 16 in this order from the resin supply side to the resin extrusion side.

In the supply section 11, the resin pellets supplied from the hopper 2 are heated and pumped to the compression section 12 by the hexadecimal force of the screw. The supply section 11 normally has a compression ratio of 1
The groove depth is constant.

Note that the inner wall of the cylinder in the lower part of the hopper of the supply section 11 may be grooved, thereby increasing the amount of resin extruded. Moreover, the compression part 12 is usually compressed while being melted and plasticized, with the groove depth of the screw becoming gradually shallower, and the compression ratio is 2 to 4, preferably 2 to 3.

If the compression ratio exceeds 4, the shear stress at the end of the compression section 12 becomes large (which causes an increase in resin temperature, Mm of shear stress, breakup phenomenon, etc.), which is undesirable.
3. Normally, the groove depth is constant, and if melting in the compression part is incomplete, melting and plasticization is promoted. is deep (,3～
It is 15mm.

The mixing section 14 mixes the plasticized resin sent from the measuring section 13, and has the function of dividing and destroying the unmelted resin layer f layer <solid bed, especially in the case of high-speed extrusion molding. Here, the mixing part 14 is not particularly limited, and may be a gear type, a dalmage, a reverse thread with cuts, a multi-pin type, etc., and is mainly used to divide and destroy the unmelted resin layer, and is used for kneading action due to high shear. is relatively small, and abnormal heating of the resin due to shearing force does not occur. Among these, the gear type mixing part is preferred because it has many features such as simple structure, easy processing, solid bed separation and destruction action, and low shearing action. As for the type of gear type in the mixing part, a spur gear type is sufficient, but mixing part 14 such as a helical table type etc.
A specific numerical example will be described in the case where the zero-order mixing section 14 is of a spur gear type, which is not particularly limited as long as it is divided when the resin passes through it. The number of gear ridges, thickness, clearance between the top of the ridge and cylinder 3, etc.
It varies depending on the type of thermoplastic resin, the type of molding in which the screw is used, molding conditions, the size of the screw (diameter - D), etc.

However, generally, the clearance between the top of the gear and the cylinder 3 is 0.1 to 3 seconds. Q: If it is less than 1 mm, the shearing action will be strong, and if it exceeds 3IIIl, the dividing and breaking action will be weak (which is not preferable. Also, the tooth thickness is (0,
1 to 1) D, and from the point of view of splitting action, it is 0.5D.
The following is sufficient. Further, the number of gears may be plural.

The resin mixed in the mixing section 14 may be mixed in the mixing section 14 as necessary.
A cylindrical pressure release part 1 provided between the shearing part 16 and the shearing part 16
7 and is sent to the shearing section 15.

The shearing section 15 has the function of uniformly melting the molten resin and making the resin temperature uniform by shearing in a relatively short period of time. Here, as the shearing part 15, there are a torpedo, a dam ring, a Murdock, a Trestar, etc., and due to the small clearance between the shearing part 15 and the cylinder 3,
There is no particular restriction as long as it causes flow obstruction of the resin and increases shearing. However, in general, a torpedo is preferably used because of its simple structure and workability. Here, the length of the torpedo is 0.05 to 2 times, preferably 0.1 to 1 time, the screw diameter (D), and the clearance between the torpedo and the cylinder 3 is 0.3
~6 koi, preferably 0.5 to 4ffi11. However, these values should be selected according to the size of the screw, the combination of torpedo length and clearance, the type of resin, etc., and are not necessarily limited to these values. 17
In addition to serving as a structural link between the mixing section 14 and the shearing section 15, if the resin that has passed through the mixing section 14 is immediately sent to the shearing section 15, it becomes difficult for the resin to pass through the shearing section 15. Since the shearing part 15 is easy to use, providing a release part such as the cylindrical part 17 has the role of making it easier for the resin to pass through the shearing part 15.

As detailed above, the extruded bag WII used in the present invention has the following features:
Particularly, by providing a low-shear mixing section 14 in front of the shearing section 15, the solid bed is divided and destroyed, thereby preventing a large amount of unmelted resin from being transferred to the shearing section 15. There is. Therefore, the lengths of the supply section 11, the compression section 12) and the measuring section 13 may be arbitrarily determined in consideration of the resin mm, etc. However, in the present invention,
By providing the mixing section 14, high-speed molding can be performed with good extrusion stability without making the scrie length to the measuring section 13 relatively long.

Next, the resin uniformly kneaded in the shearing section 15 has residual shear stress due to shearing, so if this resin is extruded as it is from a goo, the surface properties will deteriorate due to rapid stress relaxation at the goo exit. Therefore, in the extrusion device 1 used in the present invention, the resin passing through the shearing section 15 is
After the residual shear stress is relieved by the next stress relaxation section 16, the material is extruded from the die.

The compression ratio of the screw in the area of the stress relaxation section 16 is 2
~0.5, preferably 1.6 to 0.8, at which the molten resin is measured (adjustment of the discharge amount), the shear stress remaining in the molten resin is relaxed, and the molten resin is Uniform cooling is also achieved. Although the length of this stress relaxation part 16 varies depending on its structure, it is a length at which sufficient relaxation is achieved, and is usually 4 to 20 times the diameter of the screw. The main purpose of this stress relaxation section 16 is to remove residual shear stress, and the structure is such that high kneading and high shear do not occur.

The structure of the portion extending from the stress relaxation part 16 to the goo side may be, for example, the structure shown in FIGS. 2 and 3. The stress relaxation part shown in FIG. Furthermore, as shown in FIG. 3, quantitative extrusion can also be controlled by providing a gear pump 21 after or in the middle of the stress relief section. Also,
Compression 1゛hi in this specification (■) means "(groove depth at the resin inflow end)/(groove depth at the resin extrusion end)" when the pitch of the screw is constant in each structural part. do.

In the extrusion device 1, the ratio L/D between the total length and the diameter of the screw 4 is 15 to 40. Preferably 20-3
It is designed to be 4.

Further, the inner wall of the cylinder 3 of the supply section 11 (particularly a part of the liner) can be grooved in the axial direction, thereby making it possible to smoothly supply the resin pellets.

In such an extrusion device Tll, the resin supplied into the cylinder 3 is transferred to the supply section 11, the compression section 12) and the measuring section 1.
3. It is extruded from the extrusion die via the mixing section 14, shearing section 15, and stress relaxation section 16. In addition, in the extrusion apparatus T11 of the present invention, it is more preferable to provide a pressure release part 17.1[1 on each resin extrusion side of the mixing part 14 and the shearing part 15.

In the extrusion device 1 used in the present invention, the shearing portion 15 may not only be a torpedo provided on the screw 4 side, but also a so-called ring pulp whose shearing force can be adjusted in combination with the cylinder wall. .

In this case, the supplied resin pellets are heated in the supply section 11 and forced into the compression section 12, where they are melted and plasticized and then forced into the metering section 13. The measuring section 13 promotes melting and plasticization, and the mixing section 14 divides and destroys the unmelted resin N (solid bed) to prevent a large amount (30% or more) of unmelted material from being transferred to the shearing section 15. Then, the molten resin is further uniformly melted in the shearing section 15 and the resin temperature is made uniform.Then, the molten resin homogenized in the shearing section 15 is pumped to the stress relaxation section 16, where the remaining shear stress is relieved. At the same time, after the resin is cooled and homogenized, it is extruded from the goo as a resin film.

FIG. 4 shows a slit cooling device that cools the resin film extruded from the extrusion device 1. This slit cooling device is similar to the above-mentioned proposal (Japanese Patent Application No. 60-2875).
No. 12), and is located below the die 30 equipped with the extrusion device 1 for realizing the extrusion described above. This slit cooling device includes a slit 31 through which cooling water flows, and a porous fluid straightener 3 for straightening the cooling water.
2, a lower aquarium 36 provided with a slit 35 located on the lower side of the upper aquarium 33 and located directly below the slit 31, and an aquarium 37 disposed further below the lower aquarium 36. , pressure rolls 39 and 40 that pinch the extruded resin film 38 to keep the traveling speed of the resin film 38 constant, and a pressure roll 39 and 40 for taking up the resin film 38 that has passed through the water tank 37. rolls 41 and 42, a group of rolls 43 for subjecting the resin film-like body 38 to a predetermined heat treatment, and an upper water tank 33 for discharging cooling water that has been cooled by flowing down into the water tank 37;
It is configured to include a pump 45 that circulates the water to the lower water tank 36.

In the slit cooling device, the resin film 38 extruded from the extrusion die 30 is introduced into the slits 31 and 35 of the upper water tank 33 and the lower water tank 36 through which cooling water flows, and is passed through the pressure rolls 39 and 40. After being passed through cooling water in a water tank 37 and taken up by take-up rolls 41 and 42, a predetermined heat treatment is performed as necessary by a roll group 43, and the resin sheet molding is completed. At this time, the flow rate of the cooling water from the slits 31 and 35 is set higher than the running speed of the resin film-like body 38, and the amount of cooling water in contact with the resin film-like body 38 is increased, thereby improving the cooling effect. is being planned. Note that it is preferable that the cooling water flow into the upper slit 31 so that the cooling water does not stagnate at the slit entrance, and for this purpose it is necessary to keep the water level of the upper water tank 33 low. Here, if stagnation occurs, non-uniform cooling of the molten resin film donor body 38 occurs, making it impossible to obtain a sheet neck with low external haze.

Below, specific examples will be described using the method for producing thermoplastic resin sheets of the present invention.

The raw material resin is homopolypropylene (v! degree 0.91B
/c11, melt index M I 8g/10m1
n, melting point 170℃, Idemitsu Petrochemical Company! Idemitsu Polypro F-70ON (trade name: Idemitsu Polypro F-70ON), manufactured by Ill.
It was extruded into a film using a T-Gui under conditions of a resin temperature of 250°C and a Gui lip temperature of 280'C.

*Screw diameter D-65we L/D-28
Supply section Length - 325 m Groove depth - 1 Off II 11 Compression section Length - 520 mm Groove depth - 10 → 4.5 mm (gradual decrease) Measuring section Length - 345 mm Groove depth - 4.5 m Mixing section... ...(15 mountains, tooth depth 3, 7
mm spur gear, 70% open area due to tooth root and clearance in cross section perpendicular to the mixing part axis, closed area 30% due to tooth ridge) Length - 20 m Clearance with cylinder - 1.3 mm Pressure release part... (Cylinder) Length - 65 Clearance with cylinder = 5 cabinets Shearing part... (Torpedo) Length = 15+
ms Clearance with cylinder 2 mm Stress relaxation part Length - 530 + w Groove depth - 5 mm *Groove machining on the inner wall of the lower cylinder of the hopper Next, the slit cooling device shown in Fig. 4 (the height of the upper slit 31 is 50 mm)
mm, width 2.5 ms, water level of upper water tank 33 5 degrees, water temperature 5°C, 2 layers of 60 mesh wire mesh, 4 stages fluid regulator 32 used,
Lower slit 35 height 10mm, width 5mm, lower water tank 3
6 (water level 10M, water temperature 5°C) and quenched, molded using pressure rolls 39 and 40 to a thickness of 0.2 mm.
A polypropylene sheet was obtained. Further, this sheet was heat treated using a roll group 43 at 130°C.

In manufacturing this sheet, we determined the maximum extrusion amount at which the thickness accuracy in the machine direction of the obtained sheet was ±5%.
The rotation speed of the screw 4 is 10 Or, p, m.

It was 11 (ikg/h. Also, 8 0 r, p, +
w, it was 93°1 kg/h. In addition, the haze of the obtained sheet was 4.1 at each of the above-mentioned rotation speeds!
, 3.7χ, and the glossiness is 124′ &, 1, respectively.
It was 29χ.

Comparative Example-1 In the screw used in the example, no mixing section was provided,
A sheet was molded according to the example except that the length of the measuring part was 365+w. The maximum stable extrusion rate is 80 r,p,
+n, it was 84.5 kg/h.

Comparative Example-2 In the screw used in the example, no measuring part was provided,
A sheet was molded according to the example except that the length of the supply part was 500 m and the length of the compression part was 690 m. The maximum stable extrusion rate was 79.1 kg/h at 80 r, p, m.

When manufacturing a polypropylene sheet with excellent transparency from the above specific examples and comparative examples, when the extruder of the present invention is used, it can be molded at high speed, and even when compared at the same rotation speed, the extrusion amount is 10%. %, and is also excellent in terms of energy consumption.

〔Effect of the invention〕

As described above, according to the present invention, by employing an extrusion device that enables optimal extrusion and a specific water cooling method, it is possible to achieve transparency in crystalline thermoplastic resins such as polypropylene, which have traditionally been difficult to manufacture. We were able to manufacture a sheet with excellent properties.

Moreover, it is possible to produce sheets with good thickness accuracy in the machine direction even if the extrusion rate is increased by 3 to 40% compared to conventional methods, and with the reduction of extrusion power, productivity is improved and sheets can be manufactured at low cost. It has the effect of

[Brief explanation of the drawing]

FIG. 1 is a side cross-sectional view of a resin extrusion device applied to the method for producing a thermoplastic resin sheet according to the present invention, and FIGS. 2 and 3 are cross-sectional views showing modified examples of the stress relaxation part of the extrusion device. 4 are sectional views showing a slit cooling device applied to the present invention. l... Extrusion device, 3... Cylinder, 4... Screw, 11... Supply section, 12... Compression section, 13...
・Measuring part, 14... Mixing part, 15... Shearing part, 1G
...Stress relaxation part, 31.35...Slit, 3 days.
...Resin membrane.

Claims (5)

[Claims] (1) Thermoplastic resin is extruded as a film using a resin extrusion device that has a supply section, compression section, metering section, mixing section, shearing section, and stress relaxation section sequentially from the resin supply side to the resin extrusion side. A method for producing thermoplastic resin sheets, which comprises introducing this resin film into a slit through which cooling water flows, and further cooling it by running it in the direction in which the cooling water flows. (2) A method for producing thermoplastic resin sheets according to claim 1, characterized in that the cooling water flowing down the slit flows down so as not to substantially stagnate at the slit entrance. (3) A method for producing thermoplastic resin sheets according to claim 1 or 2, wherein the thermoplastic resin is a crystalline resin. (4) A method for manufacturing thermoplastic resin sheets according to any one of claims 1 to 3, wherein the slit is of a multistage type. (5) Production of thermoplastic resin sheets according to any one of claims 1 to 4, characterized in that the cooling water flow rate is higher than the running speed of the resin film-like body. Method.