JPH02258237A - Continuous manufacture of high-strength/high-stiffness polyolefin material - Google Patents

Abstract

PURPOSE:To constitute the above method so that a high-strength/high-stiffness material is obtained continuously by a method wherein polyolefin powder is compression-molded with a specific pressurizing device at a temperature of lower than the melting point and rolling and stretching are performed. CONSTITUTION:Polyolefin powder loaded within a hopper 14 is dropped onto a lower end running endless belt through an outlet of the hopper, to begin with. After preheating of the same up to a fixed temperature by a preheater 12 at need, the same is moved to a pinching and pressing part with a top and bottom endless belts 5, 6 and then transferred to a compressing part where a roller group 8 and pressurizing plate 7 are arranged. Hereupon, compressive force is applied to a compressed matter by passing through the roller group 8 and endless belts 5, 6. In this instance, also heat through a heating unit is transferred similarly to the compressed matter through the roller group 8 and endless belts 5, 6, a temperature of the compressed matter is held at the fixed temperature and a precompression-molded sheet is molded continuously. Thus the title material is obtained by rolling the obtained precompression-molded sheet and then stretching the same.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention involves continuous compression molding of polyolefin powder at a temperature below the melting point of the powder, followed by rolling and stretching to obtain high strength and high elasticity. The present invention relates to a method for continuously producing polyolefin materials.

[Conventional technology]

So-called ultra-high molecular weight polyolefins, which have extremely high molecular weights, are used in various fields as engineering plastics with characteristics such as excellent impact resistance, abrasion resistance, and self-lubricating properties. This ultra-high molecular weight polyolefin has a much higher molecular weight than general-purpose polyolefins, so if it can be highly oriented, it is expected that molded products with high strength and high elasticity can be obtained. Various orientation studies have been conducted.

However, ultra-high molecular weight polyolefins have a higher melt viscosity than general-purpose polyolefins, have extremely poor moldability using normal methods, and currently cannot be highly oriented by stretching.

Ball-Smith, Beeter-Jahn-Lemstra, and others proposed a method for producing polyolefin materials with high strength and high modulus by stretching a gel obtained from a decalin solution (dope) of ultra-high molecular weight polyolefin to a high magnification. (Japanese Unexamined Patent Publication No. 15408/1983).

The polymer concentration in the dope has a weight average molecular weight of 150
It has only been carried out at extremely low concentrations of 3% by weight for 1,000,000 and 1% by weight for 4,000,000.
It is extremely disadvantageous in terms of economics such as handling.

Furthermore, there are various proposals regarding methods for highly stretching and highly oriented single crystal mats of ultra-high molecular weight polyolefins [JP-A-59-187614, JP-A-60-15].
No. 120, JP-A No. 60-97836, Proceedings of the Society of Polymer Science, No. 34@4, p. 873 (1985), etc.].

However, these methods require that ultra-high molecular weight polyolefin be prepared in advance as a dilute solution in a solvent such as xylene, decalin, or kerosene, and then subjected to cooling and isothermal crystallization to obtain a single crystal mat, which is then subjected to solid-phase extrusion, stretching, etc. It is something to do. Therefore, even with this method, the problem of having to use a large amount of solvent when producing a single crystal mat remains unsolved.

In order to solve the above-mentioned problems, the present inventors compression molded an ultra-high molecular weight polyolefin powder at a temperature below the melting point of the powder without melting or melting it, and then rolled and stretched it. proposed a method for producing high-strength, high-modulus polyolefin materials (Japanese Patent Application Laid-Open No. 63-4151).
No. 2 and Japanese Unexamined Patent Publication No. 63-66207).

(Problems to be Solved by the Invention) However, in the compression molding process in the methods disclosed in these publications, polyolefin powder is sandwiched between heated upper and lower pressure plates, heated and pressurized for a predetermined period of time, and then preformed. It is a batch method to obtain sheets, which is inferior in productivity, and in order to obtain a material with sufficient high strength and high elastic modulus, the pressure usually exceeds several hundred g/crs'. There were problems such as the need for

(Means for Solving the Problems) Based on the above, the present inventors have made extensive studies to solve these problems, and have found that polyolefin powder is heated to a temperature below the melting point of the polyolefin powder using a specific pressurizing means. It has been discovered that a polyolefin material with high strength and high modulus of elasticity can be continuously obtained by compression molding under the following conditions, followed by rolling and stretching.

That is, the present invention supplies polyolefin powder between a pair of vertically opposed endless belts, moves the polyolefin powder while being sandwiched between the endless belts, and also provides a pressure plate and a pressure plate provided inside the endless belts. Compression molding the polyolefin powder at a temperature below the melting point of the powder by means of a pressing means consisting of a group of mutually connected rotatable rollers between the pressing plate and the endless belt, and then rolling and stretching. The present invention relates to a method for continuously producing a high-strength, high-modulus polyolefin material characterized by:

(Preferred mode for carrying out the invention) The method of the present invention includes polymerization and molding steps (compression molding,
During solid-phase extrusion and stretching, polyolefins do not undergo complicated operations such as melting or dissolving in a solvent, and by using a specific pressure means, compression molding can be performed at lower pressures than in the past, making it an excellent product. This method has an excellent feature that allows continuous and easy production of a high-strength, high-modulus polyolefin material having excellent physical properties.

The polyolefin used in the continuous production method of the high-strength/high-modulus polyolefin material of the present invention has a carbon number of 2 to
8, preferably a homopolymer of 2 to 6 α-olefins,
For example, low density polyethylene, medium density polyethylene, high density polyethylene, polypropylene, polybutene-1,
Poly-4-methylbenterne-1, etc., or a copolymer with an α-olefin having a different number of carbon atoms, such as a copolymer of ethylene and an α-olefin having 3 to 12 carbon atoms, preferably 3 to 8 carbon atoms. , a copolymer of propylene and an α-olefin having 4 to 12 carbon atoms, preferably 4 to 8 carbon atoms.

In addition, it is generally desirable for these polyolefins used in the present invention to have a higher molecular weight, since this makes it possible to obtain a material having higher strength and higher modulus of elasticity.

For example, in the case of polyethylene, the viscosity average molecular weight is 500,000 to 12 million, preferably 900,000 to 9 million, more preferably 1.2 million to 6 million, and the intrinsic viscosity in decalin at 135°C is 5 to 50 dl/ g,
Preferably 8-40 dl/g, preferably 10-3 od
A so-called ultra-high molecular weight polyethylene having a molecular weight of 1/g is preferable, and even in the case of polypropylene, it is preferable that the molecular weight is 1 million or more.

Further, the shape of these polyolefins is not particularly limited, but granule-like or powder-like ones are usually preferably used. For example, in the case of polyethylene, the particle size is 2000μ
Below, preferably 1000μ or less is desirable. Further, the narrower the particle size distribution, the better the sheet can be obtained.

In the continuous method for producing a high-strength, high-modulus polyolefin material of the present invention, polyolefin powder is first continuously compression-molded to form a pre-compression-molded sheet.

The apparatus used to form this pre-compression molded sheet will be briefly explained based on FIG. 1, which is a specific example.

This device essentially consists of a pair of endless belts 5.
A pressure plate 7 for pressurizing the powder sample via this endless belt, and a roller group 8 rotatably connected to each other between the pressure plate and the endless belt.
It has a pressurizing means consisting of. - Three or more rolls may be provided for one endless belt, and the outer diameter of the rolls is not limited at all as long as the endless belt operates well.

Endless belts usually have a wall thickness of 0.1 to 1.
An endless belt with a diameter of about 5 mm and a mirror-polished surface in contact with the object to be compressed can be suitably used. If the wall thickness of the endless belt is too thin, it will be easily deformed or damaged, and if it is too thick, the diameter of the rolls that apply tension to the endless belt will become large, which is undesirable because the entire device will become larger. Stainless steel is a typical material for the endless belt, but other suitable metal belts or belts coated with a resin such as fluororesin may also be used.

The pressure means in the present invention includes a pressure plate provided inside the endless belt and a group of rotatable rollers connected to each other between the pressure plate and the endless belt. The rotatable, mutually connected roller group interposed between the pressure plate and the endless belt is such that the rotating axes of the rollers in the roller group are arranged substantially perpendicular to the traveling direction of the endless belt, and do not contact each other. It is appropriate to arrange a large number of them in close proximity.

The outer diameter of this roller is preferably small, specifically about 5 to 30 mm. If the outer diameter of the roller is too small, the local linear pressure applied to the endless belt becomes too large, and the endless belt is likely to be left with marks from the small diameter roller, and the endless belt is likely to be deformed. Furthermore, if the outer diameter of the roller is too large, it is necessary to lengthen the pressure section (pressure plate). If the pressure section is short, the number of rollers in the pressure section will be insufficient, making it impossible to obtain a good pre-compression molded sheet.

The central axes of these rollers are fixed by chains 9 at both ends, and by meshing these chains with sprockets 10 arranged at the front and rear of the pressure plate, the roller group can be moved at about 1/2 the running speed of the endless belt. It is best to run at a speed of Note that there may be no problem even if there are three or more sprockets. This roller group may be fixedly interposed between the endless belt and the pressure plate, but in this case, frictional force due to slip is generated between the roller group, the endless belt, and the pressure plate, respectively. , problems arise in the durability of the device.

The pressure plate is not particularly limited as long as the surface in contact with the roller group is smooth and can transmit pressure uniformly.

The length of the pressure plate in the running direction of the endless belt is usually 30 to 40.0 cm, preferably about 50 to 20,000 cm. The average pressure that the pressure plate applies to the endless belt is usually between 0.1 and 20 g/cm2
A pressure of preferably 0.5 to 1 (1 kg/cm2) and more preferably 1.0 to 8.0 g/cm2 is sufficient.The pressure plate can press the polyolefin powder through an endless belt. Although it is a secondary role,
At the same time, it can also be used as a means for heating the object to be compressed. In the method of the present invention, the compression process is carried out at a temperature below the melting point of the polyolefin powder to be compressed, and the subsequent rolling and stretching processes produce a high-strength, high-modulus polyolefin material. It is extremely important to obtain However, in order to obtain a good pre-compression molded sheet, it is desirable that the temperature be within an acceptable range even if it is below the melting point. For example, for polyethylene, the temperature is usually 50°C or higher, preferably 90°C or higher, and for polypropylene, the temperature is usually 90°C or higher, preferably 130°C or higher, and below the melting point of each.

As a heating means for the material to be compressed (polyolefin powder), it is best to directly heat the endless belt in the pressurizing section, but as shown in Fig. 2, there is a heating means inside the pressurizing plate. ], and the material to be compressed is heated from the pressure plate through the roller group and the endless belt, or a preheater 12 is provided close to the endless belt as shown in FIG. is actually convenient.

The heating means 11 may be arranged in the pressure plate by providing a heat insulating part 13 and then embedding an electric heater in the pressure plate, or by providing a heat medium circulation flow path in the pressure plate. It may also be heated using a heat medium.

To carry out the continuous production method of the high strength/high modulus polyolefin material of the present invention using this exemplified apparatus,
First, the polyolefin powder charged into the hopper 14 is dropped from the hopper outlet having a predetermined cross-sectional shape onto an endless belt running downward. The running speed of the endless belt depends on the length of the pressure plate and the compression conditions, but is normally about 50 to 200 cm/win.

The polyolefin powder placed on the endless belt is preheated to a predetermined temperature using a preheater if necessary, and then moved to a clamping section between the upper and lower endless belts, and then a group of rollers and a pressure plate are arranged. The compressor is then moved to the compression section. Here, pressure from a hydraulic cylinder (not shown) is transmitted from the hydraulic piston 15 to the pressure plate, and a compression force is applied to the object to be compressed via a group of rollers and an endless belt. At this time, the heat from the heating body is similarly transferred to the object to be compressed via the roller group and the endless belt, and the temperature of the object to be compressed is maintained at a predetermined temperature.

The pre-compression molded sheet compression molded in this way is
After passing through the roll section, it leaves the endless belt.

In this way, the pre-compression molded sheet is continuously molded.

In the present invention, a high-strength, high-modulus polyolefin material is obtained by rolling and then stretching the pre-compression molded sheet thus obtained.

As the rolling method, a known method can be used, but
A rolled sheet or film is obtained by holding the polyolefin in the same phase state without melting it and compressing it with rolling rolls having different rotational speeds. At this time, the deformation ratio of the material due to the rolling operation can be selected from a wide range, and is usually 1.2 to 20, preferably 1.5 to 20 in terms of rolling efficiency (length after rolling/length before rolling). Preferably g 1.5-1
It is desirable to set it to 0. At this time, it is desirable to carry out the rolling operation at a temperature of 20° C. or higher and lower than the melting point, preferably 90° C. or higher and lower than the melting point. Of course, the above rolling operation can be performed multiple times or more.

There are various methods for tensile stretching performed after rolling. Depending on the heating means, there are hot air stretching, cylinder stretching, roll stretching, hot plate stretching, etc.

In either case, stretching is performed with a speed difference between a pair of nip rolls or a clover roll. The temperature is 20-150℃,
Preferably it is carried out at 50-140°C. Further, the stretching process can be performed not only in one stage but also in multiple stages. in this case,
- It is preferable to carry out the second stage at a higher temperature than the second stage.

The stretching speed can be selected as appropriate, and is usually 0.1 to 200c+s/
However, in consideration of economical efficiency, a high speed is preferable, and it is usually desirable to carry out the speed within a range of 5 to 200 cm/sin.

The higher the stretching ratio, the higher the strength and the higher the elastic modulus, so it is desirable to increase the stretching ratio as much as possible. However, in the production method of the present invention, for example, when ultra-high molecular weight polyethylene is used, A total stretching ratio (stretching ratio of the total of rolling and tensile stretching) of 60 times or more, preferably 80 to 200 times is possible, and stretching at an extremely high stretching ratio is possible.

Thus, a high strength, high modulus polyolefin material is produced. According to the method of the present invention, for example, when polyethylene is used as the polyolefin, the tensile modulus is 120
As represented by the fact that a polyethylene material having a tensile strength of GPa or more and a tensile strength of 2 GPa or more can be obtained, a polyolefin material with extremely high strength and high elastic modulus can be obtained.

(Effect of the invention) According to the present invention, from ultra-high molecular weight polyolefin powder,
A method for continuously producing a polyolefin sheet having high strength and high elastic modulus using a simple method has been provided.

〔Example〕

Example 1 Equipment specifications: 1. Roll diameter 500n++++ Surface length 300mm2, Steel belt wall thickness 0.6mm
Width 200mm3, small roller diameter 12ffi
I+1 Surface length 250mm4, Pressure plate length 11000III Width 200mm5, Hydraulic cylinder diameter 125+nm Ultra-high molecular weight polyethylene powder with a viscosity average molecular weight of about 2 million was heated to 130°C using a compression molding device with the above specifications, and the material was The average pressure is approximately 6 to 870 m2, the wall thickness is 1.1 mm, and the width is 10 mm.
A sheet of 011In+ was continuously pre-compression molded at a speed of 1 m/win.

Next, this sheet was heated for 1 m with a surface temperature adjusted to 140°C.
Diameter 150 rotating in opposite directions at the same circumferential speed up and down / min.
The film was supplied between a pair of rolls having a surface length of 300 mm and a distance of 30 μm, and was rolled to obtain a film with a stretching ratio of 5 times. The obtained rolled film was slit to a width of 1 m1+, and then, using a heated roll type stretching device with a roll diameter of 250 mm, the temperature was 135°C and the peripheral speed of the roll was as follows.
Stretching was performed at a magnification of 20 times at a low speed of 1.5 cra for 1 minute and a high speed of 30 cm/min. The obtained fiber had a tensile modulus of 130 GPa and a tensile strength of 3.4 GPa.

Comparative Example 1 Using the press molding machine in Example 1, the temperature was 130°C.
Example 1 was carried out in the same manner as in Example 1 except that a molded sheet with a wall thickness of 11 mm was used under the conditions of 870 m2 at a pressure of 5 and a pressurizing time of 10 minutes, but the resulting fiber could only be stretched 9.5 times. The tensile modulus of elasticity was 85 GPa, and the tensile strength was 2.6 GPa.

(Measurement method of tensile modulus and strength) Elastic modulus and strength were measured using Strograph R at a temperature of 23°C.
Measured at The sample length between the clamps is 150m■
The tensile speed was set at 100 mm/min. The elastic modulus was calculated using the stress at O,tX strain. The cross-sectional area of the sample required for calculation was determined by measuring the weight and length of the sample, assuming the density of polyethylene as tg/CI+3.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing an outline of an apparatus used in the manufacturing method of the present invention, and FIG. 2 is an enlarged view of the vicinity of the pressurizing part of the apparatus of FIG. 1. 1-4: Roll 5.6: Endless belt: Pressure plate 8: Roller group 9: Chain
lO: Sprocket l: Heating means
12: Preheater 13: Heat insulation part 14: Hopper 15: Hydraulic piston Patent applicant Nippon Oil Co., Ltd.

Claims (1)

[Claims] 1) A polyolefin powder is supplied between a pair of endless belts facing each other vertically, and the polyolefin powder is moved while being sandwiched between the endless belts, and a pressure plate provided inside the endless belt and the pressure plate are provided. and an endless belt, the polyolefin powder is compression-molded at a temperature below the melting point of the powder by means of a pressurizing means consisting of a group of mutually connected rotatable rollers, and then rolled and stretched. Continuous manufacturing method for high strength, high modulus polyolefin materials.