JPS63118229A - Preparation of thermoplastic resin sheets - Google Patents

Abstract

PURPOSE:To stably prepare resin sheets excellent in characteristics such as transparency at a high speed using an apparatus having a wide selection range, by a method wherein a thermoplastic resin is kneaded by a high kneading type extruder to be extruded in a molten state and supplied to a low kneading type extruder to be extruded from a die as a resin film-like body which is, in turn, introduced into a slit wherein cooling water flows down at the inlet thereof without stagnation and runs therethrough to be cooled. CONSTITUTION:The second low kneading type single screw extruder 20 is connected to the first high kneading type single screw or twin-screw extruder 10 equipped with a resin supplying hopper 11 through a connection pipe 19 and a die 30 is connected to the second extruder 20 through a gear pump 29 for quantitative extrusion and a resin film body is extruded from said die 30. The resin film body 38 extruded from the extrusion die 30 is introduced into the slits 31, 35, where cooling water flows down without stagnation, of both of an upper stage water tank 33 and a lower stage water tank 36 to pass through the cooling water in a water tank 37 through pressure rolls 39, 40 and taken over by take-over rolls 41, 42 and subsequently subjected to predetermined heat-treatment if necessary by a roll group 43 to complete the molding of a resin sheet.

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 for producing thermoplastic resin sheets for producing films and the like.

[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 the polypropylene mentioned above, in order to improve the transparency of the sheets, rapid cooling is performed to control the crystal form. 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 membrane-like body with water, a method using multistage slits through which cooling water flows has already been proposed (Japanese Unexamined Patent Publication No. 58-203018).

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 resin sheets as molded products are not always 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 molten resin before the extruded resin film comes into contact with cooling water, that is, the stage from material supply to the resin extruder to extrusion. We discovered that there is a large stress on the tip of the extruder as an extrusion condition! ! He devised a method using an extruder equipped with a Japanese section, and proposed a method using this extrusion condition in combination with a slit water cooling method (Japanese patent application No. 60-287).
512, Japanese Patent Application No. 61-202146), these methods are excellent methods, but the selection of equipment is limited, and it is difficult to satisfy kneading properties, relaxation properties, and extrusion stability. There are also problems such as difficulty in manufacturing, and a better manufacturing method has been desired.

(Objective of the Invention) An object of the present invention is to provide a method for producing resin sheets with excellent characteristics such as transparency at high speed and with good stability using equipment with a wide range of equipment selection. .

(Means and effects for solving the problems) The present invention has the following features:
This method was developed based on the fact that the transparency of resin sheets varies depending on the water-cooling state of the molten resin film, and the limit of the water-cooling effect is closely related to the extrusion conditions at the resin extrusion forming stage. Water cooling of the resin membrane was carried out by running the cooling water through a flowing slit so as not to substantially stagnate at the inlet, while extrusion conditions were such that sufficient kneading and stress relaxation were carried out. However, if we try to achieve sufficient kneading and stress relaxation with one extruder, a special screw structure is required, which limits the range of equipment selection. By separating the extruder for the purpose of producing a thermoplastic resin and the extruder for the purpose of sufficient stress relaxation, it is possible to obtain a thermoplastic resin sheet (1) with good optical properties without limiting the range of equipment selection. .

Therefore, in the present invention, in order to perform sufficient melt-kneading, for example, a high-kneading type first extruder with a compression ratio of 2 or more, preferably 3 or more is used, and in order to perform sufficient stress relaxation, For example, a low kneading type second extruder having a steady extrusion function with a compression ratio of less than 2, preferably 1.5 or less, usually about 1, is used, and the first extruder is used to extrude the thermoplastic resin. The kneaded and molten resin is extruded through a connecting pipe into a second extruder, and the second extruder extrudes it from a die as a resin film with excellent surface properties while sufficiently relaxing stress. As mentioned above, the shaped body is introduced into the slit flowing downward so that the cooling water does not stagnate, and is cooled to improve optical properties such as transparency.

〔Example〕

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an apparatus for carrying out the manufacturing method of the present invention will be described below with reference to the accompanying drawings.

First, the thermoplastic resin used in the present invention is a polypropylene resin, such as a homopolymer of polypropylene, or a random copolymer of propylene and 20% or less of other α-olefin, and one or more of these polymers. However, this blend also includes blends obtained by multi-stage polymerization. In addition, polyethylene resins, mixtures of polypropylene resins and polyethylene resins or elastomers, polyesters, polyamides, and the like can also be used. Furthermore, similar resins to these, adhesive resins such as polyolefin resins graft-modified with maleic anhydride, easily weldable resins such as ethylene-vinyl acetate copolymer, ethylene-vinyl alcohol copolymer, polyamide, polyethylene It can also be applied to coextruded multilayer sheets with gas barrier resins such as terephthalate.

FIG. 1 shows the overall configuration of this embodiment, and shows an axle or two-axis high-kneading type first hopper equipped with a resin supply hopper 11.
A single-screw, low-kneading type second extruder 4t is connected to the extruder 10 via a connecting pipe 19. 20 is connected and this second extrusion 81
A die 30 is connected to the die 20 via a gear pump 29 for quantitative extrusion, and the resin film is extruded from the die 30. A slit cooling device for cooling the resin film extruded from the die 30 is provided below the die 30. This pickpocket 7) cooling device corresponds to the device previously proposed (Japanese Patent Application No. 60-287512).

The slit cooling device includes an upper water tank 33 equipped with a slit 31 through which cooling water flows and a porous fluid regulating fluid 32 for straightening the cooling water, and a slit cooling device arranged on the lower side of this upper water tank 33 and directly below the slit 31. A lower water tank 36 with a slit 35 located therein, a water tank 37 located further below the lower water tank 36, and an extruded resin strip 38 are compressed to keep the running speed of the resin membrane 38 constant. pressure rolls 39, 40 for maintaining the resin film 38 in the water tank 37, rolls 41, 42 for taking over the resin film 38 passed through the water tank 37, roll group 43 for subjecting the resin film 38 to a predetermined heat treatment, and the water tank 37. 37 and is cooled by a cooler 44, the pump 45 circulates the cooling water to the upper water tank 33 and the lower water tank 36 as necessary.

In the slit cooling device, the resin film 38 extruded from the extrusion die 3 is placed in the upper water tank 3 through which cooling water flows.
3 and into the slits 31 and 35 of the lower water tank 36, passes through the cooling water in the water tank 37 via the pressure rolls 39 and 40, is taken up by the take-up rolls 41 and 42, and is then transferred to the roll group 43. A predetermined heat treatment is performed, and the resin sheet molding is completed. At this time, the slit 31
The cooling water flow rate from the resin film body 38 and 35 is
The traveling speed 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 to improve the cooling effect. 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. If stagnation occurs here, non-uniform cooling of the molten resin film occurs, making it impossible to obtain a sheet with low external haze.

Although FIG. 1 shows a preferable case of two-stage slit cooling, depending on the thickness of the sheet m, molding speed, etc., only the upper slit 31 may be sufficient.

FIG. 2 shows an example of a single-screw first extruder 10 used in this example. The extruder 10 includes a cylinder 13 equipped with a hopper 11 and a filter 12 for supplying resin pellets, and a screw 14 installed inside the cylinder 13.

At this time, the screw 14 of the first extrusion i10 is as follows:
There is no particular restriction on the shape etc., for example, resin supply part,
A mm-sized high-kneading type screw having a compression part and a lightening part can be used, and if necessary, the tip of the screw may have a part to promote kneading and mixing, such as a torpedo or dalmage.

That is, in the first extruder IO, it is not necessary to particularly reduce the residual stress of the resin, and it is sufficient to be able to perform high-speed, uniform kneading and extrusion, and a high-compression, high-shear screw is generally used.

The screw 14 shown in FIG. 2 is equipped with a uniform kneading improving part 15 made of a torpedo at its tip, and this screw 14 is rotationally driven by a motor 17 via a reducer 16, and as the screw 14 rotates, the hopper 1
The resin berent supplied from 1 is sufficiently kneaded while being melted and plasticized, and is forced to pass through the filter I2 and into the connecting pipe 19 by the driving force of the screw 14.

, this high kneading type first extruder 10 has a screw 14
The compression ratio is increased by increasing the groove depth from the resin supply side to the resin extrusion side, and this compression ratio is 2 or more,
Preferably, the number is 3 or more, and the molten resin is sufficiently kneaded by this first extrusion [10]. On this occasion,
A compression ratio of less than 2 is not preferable because it causes unnecessary retention of the resin and insufficient initial kneading. Further, the screw 14 may be of any type,
A type in which the groove depth changes at a constant pitch, or a type in which the groove depth is constant and the pitch changes may be used. The uniform kneading improving section 15 is, for example, the torpedo or a modified torpedo such as a dalmage with grooves in the axial direction on the circumferential surface, where resistance is given to the flow of the resin and uniform melting of the resin is achieved by shearing. Kneading is done. This uniform kneading improving section 15,
The gap between cylinder I3 and the inner wall is made small to increase shear. In addition, the uniform crosstalk improving section 15
For example, when a torpedo is used, the length is usually 0.1 to 2 times the screw diameter, preferably 0.2 to 1.
The average void cross-sectional area between the uniform kneading improving portion 15 and the cylinder 13 is, for example, 1/2 to 1/20, preferably 1/3 to 1/1, of the average void cross-sectional area of the screw 14.
is within the range of Specifically, although it depends on the length of the torpedo part, the gap with the cylinder wall is 1/150 = 1/20 of the screw diameter, preferably 1/20.
100 to 1/30. However, these values need to be optimally selected depending on the type of resin, section length, etc. At this time, the structure is the simplest if the uniform kneading improving section 15 is a torpedo.

FIG. 3 shows an example of the second extruder 20 used in this example. This extruder 20 includes the connecting pipe 1
9 is connected to the cylinder 22 equipped with the filter 21, and the screw 2 installed in this cylinder 22.
3.

The screw 23 has a relatively deep groove depth.
Low) compression, low shear screws are used. This screw 23 is rotationally driven by a motor 25 via a reducer 24, and as the screw 23 rotates, the connecting pipe 19
The sufficiently kneaded molten resin supplied from the molten resin is sent to the gear pump 29 through the filter 21 by the driving force of the screw 23 while being stress-relaxed.
At step 9, the amount of extrusion is set to a fixed amount, and the resin is extruded through the die 30 to form a resin film 38.

The screw 2 in this low kneading type second extrusion 820
The compression ratio of 3 is less than 2, preferably 1.5 or less. Usually, a straight screenie with a compression ratio of 1 is used, but a straight screenie with a compression ratio of 0.5 may be used.

Here, 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 evenly cooled. For this cooling, forced cooling of the cylinder 22) and screw 23 is performed as necessary. The main purpose of this second extruder 20 is to remove residual shear stress, and the structure is such that high kneading and high shear do not occur.

The second extrusion a20 may have the structure shown in FIG. 4, for example. The second extrusion a20 shown in FIG. A non-kneading portion 27 without a screw is formed on the tip end side of the screw 23, and this also makes it possible to sufficiently relieve the shear stress of the resin to a greater extent than in the case described above. In addition, the compression ratio 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 first and second extruders 10.20, each motor 17.25 is controlled by a speed controller (not shown) to maintain an appropriate operational balance. 10.20 is detected, and the rotational speed of the motor 17 of the first extrusion [920 is controlled so that the difference between these pressures is constant. Further, the ratio L/D between the total length and the diameter of the screw in the first and second extruders 10120 is not particularly limited, and in the first extruder 10 it is lO ~ 30, and in the second extruder 1120 5~
It is designed to be 40. In addition, in the first and second extruders 10 and 20, the screw diameter is relatively small in the first extruder 10 and relatively large in the second extruder 20, and the screw rotation speed is Machine 10 is large,
The second extruder 20 is made smaller, and the molding temperature is
Including shear heat generation, the first extruder 10 has a high temperature, and the second extrusion t! 120 is lowered and this second extruder 20 is optionally cooled as described above.

According to this embodiment, when extruding the molten resin film for three days, the extruder is used for the first extrusion 610 of the high kneading type for the purpose of uniform melting and kneading, and for the low kneading type for the purpose of stress relaxation. Since the mold is separated from the second extrusion 8120, extrusion stability can be improved without using an extruder with a specially shaped screw, and each extrusion filo, 20 can be designed in the best way according to its purpose. From the device i! It is possible to widen the flow characteristics and also to widen the selection range of operating conditions. Further, the contradictory problems of kneading properties and stress relaxation, high-speed moldability and low 1-chang extrusion can be simultaneously satisfied, and high-speed stable molding becomes possible, resulting in low manufacturing costs and energy savings.

Furthermore, due to good kneading properties and sufficient stress relaxation, it is possible to extrude sheets with excellent surface properties.Coupled with rapid and sufficient cooling using a slit cooling device, optical properties such as transparency and gloss can be achieved. A sheet with good properties can be obtained.

In addition, in carrying out the present invention, the first and second extruders 10
．． 20 is not limited to the structures shown in FIGS. 2 to 4 described above, but may have other structures that can achieve the purpose of the present invention.
In addition, extrusion devices other than 10 and 20 are not limited to the configuration shown in FIG. 1. For example, the gear pump 29 is not necessarily required, and the first extruder 10
It is also possible to install a static mixer on the outlet side.

〔Effect of the invention〕

According to the present invention as described above, an apparatus with a wide range of selectivity can be used, and by using optimal extrusion conditions and water cooling conditions, a thermoplastic resin sheet [manufacturing method] with improved transparency and gloss compared to conventional methods can be achieved. It has the effect of being able to provide

[Brief explanation of the drawing]

FIG. 1 is an overall configuration diagram of an apparatus used in the method for manufacturing thermoplastic resin sheets according to the present invention, FIG. 2 is a sectional view showing an example of a first extruder used in the apparatus, and FIG. 3 is a sectional view showing an example of a second extruder used in the device,
FIG. 4 is a sectional view showing a part of a modified example of the second extruder. 10... First extruder, 19... Connection pipe, 20...
- Second extruder, 30... Gui, 31.35... Slit, 38... Resin film-like body. Agent: Patent attorney Minoru Kinoshita (and 1 other person) Figure 2 23:, T7"-Figure 4 25 = 7-ta procedure chief Hosho Seisho yakusho) November 2, 1986 Information Record 61-265263 No. 2) Name of the invention Method for manufacturing thermoplastic resin sheets 3. Person making the amendment 1. rm with timber cattle 100, address of Guyou, Horowan Bay
3-1-1 Marunouchi, Chiyoda-ku, Tokyo Name: Idemitsu Petrochemical Co., Ltd. Representative: Mutsumi Hongo 4, Agent address: 4F Takagi Building, 1-7 Okubo-chome, Shinjuku-ku, Tokyo Telephone (03) 205-84718 , Contents of the amendment (1) On page 15, line 18 of the specification, after “...possible.”, “Furthermore, the static mixer is installed at the outlet side of the second extruder 20 or at the outlet side of the gear pump 29.” It is also possible to install it on the side. Add J.

Claims (2)

[Claims] (1) A thermoplastic resin is kneaded by a first extruder of high kneading type and extruded as a molten resin, and this molten resin is supplied via a connecting pipe to a second extruder of low kneading type. ,
The second extruder extrudes the resin film from the die, and the resin film is cooled by running it into a slit that flows down so that cooling water does not substantially stagnate at the inlet. A method for producing thermoplastic resin sheets. (2) In claim 1, the high-kneading type first extruder has a compression ratio of 2 or more, and the low-kneading second extruder has a compression ratio of less than 2. A method for producing thermoplastic resin sheets characterized by the following.