JPH0753423B2 - Continuous production method of high strength and high modulus polyolefin material - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to continuous compression molding of a polyolefin powder at a temperature below the melting point of the powder, followed by rolling and stretching to obtain high strength and high elasticity. Index continuous polyolefin material.

[Conventional technology]

So-called ultra-high molecular weight polyolefin having a remarkably high molecular weight is used in various fields as an engineering plastic characterized by having excellent impact resistance, abrasion resistance, and self-lubricating property. This ultra-high molecular weight polyolefin has a much higher molecular weight than general-purpose polyolefins, so if it is possible to achieve high orientation, it is expected that a molded product with high strength and high elasticity will be obtained. Various studies have been made.

However, the ultra-high molecular weight polyolefin has a higher melt viscosity than a general-purpose polyolefin, the molding processability is extremely poor by a usual method, and it cannot be stretched to be highly oriented at present.

Paul Smith, Peter Yarn, Remstra et al. Proposed a method for producing a polyolefin material having high strength and high elastic modulus by stretching a gel obtained from a decalin solution (dope) of an ultrahigh molecular weight polyolefin at a high ratio. (JP-A-56-15408). The polymer concentration in the dope is
The weight average molecular weight of 1.5 million is 3% by weight and that of 4 million is 1% by weight, which is extremely low concentration. In practical use, a large amount of solvent is used and a highly viscous solution is prepared. It is extremely disadvantageous in terms of economics such as method and handling.

There are also various proposals for a method of highly stretching and highly orienting a single crystal mat of an ultrahigh molecular weight polyolefin [JP-A-59-187614, JP-A-60-15120, and JP-A-6-16015].
0-97836, Proceedings of the Polymer Society of Japan, Vol. 34, No. 4, page 873 (1985
Year) etc.].

However, in these methods, an ultrahigh molecular weight polyolefin is previously made into a dilute solution of a solvent such as xylene, decalin, or kerosene, and then solid phase extrusion or stretching is performed using a single crystal mat obtained by cooling or isothermal crystallization. It is something to do. Therefore, even with this method, the problem that a large amount of solvent has to be used at the time of producing the single crystal mat has not yet been solved.

In order to solve the above mentioned problems, the inventors have carried out compression molding of ultra high molecular weight polyolefin powder without melting or melting below the melting point of the powder and then rolling and stretching. , A method for producing a high-strength, high-modulus polyolefin material has been proposed (JP-A-63-41512 and JP-A-63-66207).

[Problems to be Solved by the Invention]

However, the compression molding step in the methods disclosed in these is a batch method in which a polyolefin powder is sandwiched between heated upper and lower pressure plates and heated for a predetermined time and pressed to obtain a preformed sheet. It is inferior in properties, and there is a problem that a pressure of several hundred kg / cm ² or more is usually required as a pressurizing pressure in order to obtain a material having sufficiently high strength and high elastic modulus. .

[Means for Solving the Problems]

From the above, the present inventors, as a result of intensive studies to solve these problems, by a specific pressurizing means, the polyolefin powder is compression molded below the melting point of the polyolefin powder, and then rolled. It was discovered that a polyolefin material having high strength and high elastic modulus can be continuously obtained by stretching.

That is, the present invention is to supply a polyolefin powder between a pair of endless belts that are vertically opposed to each other, move the polyolefin powder while sandwiched by the endless belt, and a pressure plate provided inside the endless belt. And the polyolefin powder is compression-molded at a temperature below the melting point of the powder by a pressing means consisting of a group of rollers connected to each other and rotatable between the pressing plate and the endless belt, and then rolled and drawn. The present invention relates to a continuous production method of a high-strength, high-modulus polyolefin material characterized by the above.

[Preferable Embodiments for Carrying Out the Invention]

The method of the present invention comprises polymerization and molding steps (compression molding,
In solid phase extrusion and stretching), the polyolefin does not undergo complicated operations such as melting or dissolution in a solvent even once, and by using a specific pressurizing means, compression molding under low pressure becomes possible compared to the conventional method, which is excellent. It has an excellent characteristic that a high-strength, high-modulus polyolefin material having excellent physical properties can be continuously and easily manufactured.

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

In addition, it is desirable that these polyolefins used in the present invention generally have a higher molecular weight because a material having higher strength and higher elastic modulus can be obtained. For example, in the case of polyethylene, the viscosity average molecular weight is 500,000 to 12,000,000, preferably 900,000 to 9,000,000, more preferably 1.2,000,000 to 6,000,000, 135 ° C, and if expressed by the intrinsic viscosity in decalin, 5 to 50 dl / The so-called ultra-high molecular weight polyethylene having g, preferably 8 to 40 dl / g, preferably 10 to 30 dl / g is desirable, and in the case of polypropylene, the molecular weight is preferably 1,000,000 or more.

Further, the shape of these polyolefins is not particularly limited, but normally, a granular or powdery one is preferably used. For example, in the case of polyethylene, the particle size is 2000 μm or less, preferably 1000 μm or less. Further, a narrower particle size distribution will give a better sheet.

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

An apparatus used for forming this pre-compression molded sheet will be briefly described with reference to FIG. 1 which is a specific example.

This device basically comprises a pair of endless belts 5 and 6 which are vertically opposed to each other and are tensioned by rolls 1 to 4.
A pressure plate 7 for pressing the powder sample through the endless belt, and a roller group 8 rotatably connected to each other between the pressure plate and the endless belt.
And a pressurizing means consisting of. Three or more rolls may be provided for one endless belt, and the outer diameter of the roll is not limited as long as the endless belt operates well.

As the endless belt, one having a wall thickness of about 0.1 to 1.5 mm and a surface of the endless belt which comes into contact with the object to be compressed and which is mirror-finished can be preferably used. If the thickness of the endless belt is too thin, the endless belt is likely to be deformed or damaged, and if it is thick, the diameter of the roll that applies tension to the endless belt becomes large, which undesirably increases the size of the entire apparatus. A typical example of the material of the endless belt is stainless steel, but it is also possible to use a suitable single body of another metal belt, or a material obtained by coating these belts with a resin such as a fluororesin.

The pressure means in the present invention comprises a pressure plate provided inside the endless belt and a group of rollers which are rotatably connected to each other between the pressure plate and the endless belt. As a group of rotatable rollers connected to each other interposed between the pressure plate and the endless belt, the rotation 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 suitable to arrange a large number of them in close contact with each other.

The outer diameter of the 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, the trace of the small diameter roller is likely to be left on the endless belt, and the endless belt is likely to be deformed. In addition, when the outer diameter of the roller is too large, it is necessary to lengthen the pressure unit (pressure plate). When the pressing part is short, the number of rollers in the pressing part is insufficient, and a good preliminary compression-molded sheet cannot be obtained.

The center axis of both ends of each of these rollers is fixed by a chain 9, and by engaging this chain with a sprocket 10 arranged in front of and behind the pressure plate, the roller group is about half the traveling speed of the endless belt. It is good to drive at the speed of. This sprocket has 3
It does not matter if there is more than one. This roller group may be fixedly interposed between the endless belt and the pressure plate, but in this case, a frictional force due to slip occurs between the roller group and the endless belt and the pressure plate, respectively. However, a problem occurs 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 the pressure can be transmitted uniformly.

The length of the pressure plate in the running direction of the endless belt is usually 30 to 400 cm, preferably about 50 to 200 cm.
The average pressure that the pressure plate exerts on the endless belt is
Usually, a pressure of about 0.1 to 20 kg / cm ^2, preferably 0.5 to 10 kg / cm ^{2, and} more preferably 1.0 to 8.0 kg / cm ² is sufficient. The pressing plate has a primary role of pressing the polyolefin powder through the endless belt, but can also be used as a heating means for the object to be compressed at the same time.
In the method of the present invention, the compression step is performed at a temperature lower than the melting point of the polyolefin powder that is the object to be compressed, and the rolling and stretching steps that are subsequently performed provide high strength and high elastic modulus polyolefin material. Is extremely important in obtaining However, in order to obtain a good pre-compression molded sheet, it is desirable that the temperature is below the melting point but is within an allowable range. For example, for polyethylene, a temperature of usually 50 ° C. or higher, preferably 90 ° C. or higher, and for polypropylene, usually 90 ° C. or higher, preferably 130 ° C. or higher, and a temperature below the respective melting points are desirable.

As a heating means for the object to be compressed (polyolefin powder) for that purpose, it is optimal to directly heat the endless belt in the pressing portion, but as shown in FIG. 2, the heating means 11 is provided in the pressing plate. It is actually arranged to heat the object to be compressed from the pressure plate through the roller group and the endless belt, or to dispose the preheater 12 close to the endless belt as shown in FIG. It is convenient.

As a mode of arranging the heating means 11 on the pressure plate, an electric heater may be embedded in the pressure plate after providing the heat insulating portion 13, or a circulation channel of the heat medium is arranged in the pressure plate. Then, you may heat using a heat medium.

To carry out the continuous production method of the high-strength and high-modulus polyolefin material of the present invention by using this exemplified apparatus,
First, the polyolefin powder charged in the hopper 14 is dropped onto the lower endless belt running from the hopper outlet having a predetermined cross-sectional shape. The traveling speed of the endless belt depends on the length of the pressure plate and the compression conditions, but is usually about 50 to 200 cm / min. The polyolefin powder on the endless belt is, if necessary, preheated to a predetermined temperature by a preheater, and then moved to the pressure part of the upper and lower endless belts, and then a roller group and a pressure plate are arranged. It is transferred to the compression unit. Here, the 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 the roller group and the endless belt. At this time, heat from the heating body is also transferred to the object to be compressed through the roller group and the endless belt, and the temperature of the object to be compressed is maintained at a predetermined temperature.

The precompression-molded sheet compression-molded in this way is
After passing the roll section, leave the endless belt.
In this way, the pre-compression molded sheet is continuously molded.

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

A known method can be used as the rolling method,
A rolled sheet or film is obtained by pressing the polyolefin in a solid state without melting it with rolling rolls having different rotation directions. At this time, the deformation ratio of the material due to the rolling operation can be widely selected, and usually, the rolling efficiency (length after rolling / length before rolling) is 1.2 to 20, preferably 1.5 to 20 and more preferably 1.5 to 10 is preferable. 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 rolling operation described above can be carried out once or more in multiple stages.

There are various methods of tensile stretching performed after rolling. There are hot air drawing, cylinder drawing, roll drawing, hot plate drawing and the like depending on the heating means and the like. In both cases, stretching is performed with a speed difference between a pair of nip rolls or clover rolls. The temperature is 20-150 ° C, preferably 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 step at a higher temperature than the first step.

The stretching speed can be appropriately selected and is usually in the range of 0.1 to 200 cm / min, but a higher speed is preferable in consideration of economic efficiency,
Usually, it is desirable to carry out in the range of 5 to 200 cm / min.

The higher the draw ratio, the higher the strength and the high elastic modulus that can be achieved, so it is desirable to increase the draw ratio as much as possible, but in the production method of the present invention, for example, when ultrahigh molecular weight polyethylene is used, A total draw ratio of 60 times or more, preferably 80 to 200 times (a total draw ratio of rolling and tensile drawing) is possible, and an extremely high draw 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 elastic modulus is 120 GPa.
As described above, a polyolefin material having an extremely high strength and a high elastic modulus can be obtained, as typified by obtaining a polyethylene material having a tensile strength of 2 GPa or more.

〔The invention's effect〕

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 by a simple method is provided.

〔Example〕

Example 1 Equipment specifications: 1. Roll diameter 500 mm Face length 300 mm 2. Steel belt wall thickness 0.6 mm Width 200 mm 3. Small diameter roller diameter 12 mm Face length 250 mm 4. Pressurizing plate length 1000 mm Width 200 mm 5. Hydraulic pressure Cylinder diameter 125 mm Viscosity average molecular weight of about 20
100,000 ultra high molecular weight polyethylene powder is heated to 130 ℃, the average pressure on the material is about 6 Kg / cm ² and the wall thickness is 1.1 mm and width.
A 100 mm sheet was continuously precompressed at a speed of 1 m / min.

Next, rotate this sheet in the opposite direction at the same peripheral speed of 1 m / min with the surface temperature adjusted to 140 ° C. Diameter 150 mm, face length 3
Supplied between a pair of rolls with a distance of 00 mm and a roll distance of 30 μm
Rolling was performed to obtain a film having a draw ratio of 5 times. The obtained rolled film was slit into a width of 1 mm, and then the roll diameter was 250 mm using a hot roll type stretching device, the temperature was 135 ° C., the peripheral speed of the roll was 1.5 cm / min on the low speed side, and 30 cm / min on the high speed side. Minutes and stretched at a draw ratio of 20 times. The obtained fiber had a tensile elastic modulus of 130 GPa and a tensile strength of 3.4 GPa.

Comparative Example 1 Using the press molding machine in Example 1, a temperature of 130 ° C.,
Molded wall thickness 1.1 under conditions of pressure 5Kg / cm ² and pressurization time 10 minutes
The same procedure as in Example 1 was carried out except that a mm sheet was used.
Only 5 times stretch is possible and the tensile modulus of the fiber obtained is 85Gp
The tensile strength was 2.6 GPa.

(Measurement Method of Tensile Elastic Modulus and Strength) The elastic modulus and strength were measured at a temperature of 23 ° C. using Strograph R. The sample length sandwiched between the clamps was 150 mm, and the tensile speed was 100 mm / min. The elastic modulus was calculated using the stress at 0.1% strain. The cross-sectional area of the sample required for the calculation was obtained by measuring the weight and length of the sample with the density of polyethylene being 1 g / cm ³ .

[Brief description of drawings]

FIG. 1 is a schematic view showing the 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 section of the apparatus of FIG. 1 to 4: Roll 5,6: Endless belt 7: Pressure plate, 8: Roller group 9: Chain, 10: Sprocket 11: Heating means, 12: Preheater 13: Insulation part, 14: Hopper 15: Hydraulic piston

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Claims (1)

[Claims] 1. A polyolefin powder is supplied between a pair of endless belts which are vertically opposed to each other, and the polyolefin powder is moved while being sandwiched by the endless belt, and a pressure plate provided inside the endless belt and Compressing and molding the polyolefin powder below a temperature below the melting point of the powder by pressing means consisting of a group of rollers connected to each other between the pressing plate and the endless belt so as to be rotatable, and then rolling and stretching. A method for continuously producing a high-strength, high-modulus polyolefin material characterized by: