JPH0338970B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a novel method for producing polymeric materials. British Patent Application No. 10746/73 describes molded articles,
Sometimes Young's modulus (dead load creep) is 3
×10 ¹⁰ N/m ² or more high-density polyethylene filaments, films, and fibers are described, and according to them, the weight average weight (w) is 200000 or less, the number average molecular weight (n) is 20000 or less, and n
is 10 ⁴ or more, w/n is 8 or less, n is 10 ⁴
In the following cases, a high modulus polyethylene molded article can be obtained by cooling a polymer with a w/n of 20 or less from a temperature near its melting point at a rate of 1 to 15°C per minute, and then stretching the cooled polymer. ing. We define crystalline polymers as having more than one (i.e., two or more) molecular chains of a given molecular chain.
A high modulus is obtained by subjecting the polymer to heat treatment under conditions that substantially reduce the possibility of its incorporation into crystalline lamellae, and by drawing the polymer at a speed and temperature such that the molecules become nearly perfectly linear. We discovered the fact that molecular substances can be obtained. That is, the present invention processes a crystalline polymer selected from high-density polyethylene, copolymers thereof, and polyoxymethylene having a weight average molecular weight of 300,000 or less from a temperature at or above its melting point to a temperature sufficiently lower than its crystallization temperature at least every time. minutes
Quenching the cooled polymer at a rate of 400° C. below its melting point so that its deformation ratio is greater than 20 in the case of high density polyethylene or greater than 15 in the case of copolymers of high density polyethylene or polyoxymethylene. The present invention relates to a method for producing a high modulus polymeric material having a Young's modulus of 3×10 ¹⁰ N/m ² or more, which is characterized by stretching the material so that it becomes . As used herein, a crystalline polymer refers to a polymer that can form a crystalline or semi-crystalline structure when its melt is cooled. The present invention can be applied to any crystalline polymer, preferably a vinyl polymer, and particularly preferably a vinyl polymer that crystallizes in a folded structure, such as polyethylene,
A linear birylic hydrocarbon polymer such as an ethylene/propylene block copolymer. The invention is also applicable to other substantially linear organic polymers, such as polyoxymethylene. Particularly good results have been obtained with high density polyethylene, which is herein defined as containing at least 95 weight percent ethylene and having a density of 0.91 to
Defined as a substantially linear ethylene homopolymer or copolymer having a weight of 1.0 g/cm ³ . The density is based on Appendix A of British Standard Specification No. 3412 (1966).
British Standard Specification No. 2782 (1970 ) method 509B
It was measured by. The crystalline polymer should have a suitably high weight average molecular weight so that the shaped article after stretching retains favorable physical properties in terms of strength and elongation at break. However, a high concentration of long chain moieties increases the chance that a given molecular chain will be introduced into more than one crystal lamella before stretching. Hereinafter, in this specification, such a molecular chain will be referred to as an interlamellar molecular chain. Although the present invention is not limited by any particular theory, it is believed that excess interlamellar molecular chains reduce the degree of molecular orientation and linearization obtained by stretching due to increased permanent morphological entanglement; It is thought that this prevents optimal physical properties from being obtained as a result. The preferred weight average molecular weight (w) of the polymer is
50,000 to 250,000, more preferably from 50,000
150000, and the number average molecular weight (n) is from 5000
25,000, more preferably 5,000 to 15,000. Normally, in order to make the deformation at the molecular level more uniform during the elongation process, w with respect to n is
It is advantageous to avoid increasing the ratio of
The preferred ratio of w to n is 30 or less. In particular, a relatively narrow molecular weight distribution, e.g.
10 When ⁴ or more, w/n is 10 or less (preferably 8 or less, most preferably 6 or less), and n is
Good results can be obtained by using a polymer with w/n of 25 or less (most preferably 15 or less) when the ratio is 10 ⁴ or less. Molecular weights quoted herein are determined by gel permeation chromatography. Heat treatment can, for example, cause a substantial portion of molecules with intermediate molecular weights to crystallize into discontinuous, highly ordered folded chain lamellae, while small amounts of very large and very small molecular weight molecules are separated. However, in rare cases where crystalline regions are interconnected, molecular weight fractionation has the effect of reducing the possibility of introducing excess molecular chains into more than one lamella. This effect can be obtained, for example, by the following three methods. (1) A method of cooling a polymer at a predetermined rate from a temperature at or above its melting point to an ambient temperature at which a desired crystal structure is obtained. In this case, the cooling rate depends on the molecular weight characteristics of the polymer. It is generally necessary to cool the polymer at a rate of less than 40°C per minute, preferably less than 20°C per minute. The most preferred cooling rate is 10°C per minute or less. (2) A method in which a polymer is cooled from its melting point or higher to a temperature below its crystallization temperature at a predetermined rate, and then rapidly cooled to ambient temperature. The cooling rate is preferably 1-15°C per minute, most preferably 2°C per minute.
~10℃. Preferably 5 to 20 degrees higher than the crystallization temperature
The polymer is quenched when the temperature below 0°C is reached. Quenching should preferably be at a rate of no more than 100,000°C per minute. (3) A method of rapidly cooling a polymer from a temperature at or above its melting point to near its crystallization temperature and holding the polymer at that temperature for a sufficient period of time to cause crystallization. Preferably the polymer is held at a temperature within 15°C of the crystallization temperature for 0.5 to 10 minutes. The polymer is then preferably rapidly cooled to ambient temperature. Optical micrographs of samples prepared by methods (1), (2), and (3), respectively, show that polymers with predetermined molecular weight characteristics contain chromatographic regions of uniform orientation of various sizes throughout the polymer. This shows that a structure is formed. In high density polyethylene these areas can reach up to 15μ. The conditions used in methods (1), (2) and (3) are selected based on the molecular weight characteristics of the polymer. However, in general, if the polymer has a particularly narrow molecular weight distribution, extremely slow cooling (at less than 1° C. per minute) will not produce a crystalline structure suitable for elongation. 40°C per minute in methods (1) and (2)
Making very fast cooling and methods of more than (3)
It has also been found that holding at the crystallization temperature for longer than necessary is also detrimental. Figures 1a, 1b and 1c show the methods (1) and (2) of the present invention in the case of high-density polyethylene, respectively.
and (3). As an alternative method of forming a crystalline structure that substantially reduces the possibility that a given molecular chain will be incorporated into more than one crystalline lamella, the polymer can be heated from a temperature at or above its melting point to a temperature well below its crystallization temperature. There is a method to obtain relatively low crystallinity by rapid cooling. This method, method (4), significantly reduces the size of spherulites and produces a crystal-containing structure surrounded by large amorphous regions, thereby reducing the number of interlamellar molecular chains. . Preferably the cooling rate is greater than or equal to 1000°C per minute, most preferably greater than or equal to 5000°C per minute throughout the crystallization temperature range, and the polymer is cooled to ambient temperature or below. Depending on the molecular weight characteristics of the polymer, it may be advantageous to reheat the cooled polymer to increase the size of the crystalline regions prior to attenuation. The optical micrograph of the sample produced by method (4) clearly shows that it has a spherulite structure connected in a string like the conventional method, but it can be distinguished from Tsuritsu in that the spherulites are small. be able to. Figure 1d shows the crystal structure produced by method (4) of the invention in the case of high density polyethylene. Structures formed with different heat treatment methods do not necessarily deform in the same way under a given condition. There will be an optimal elongation method for each manufacturing process. If there is obvious molecular orientation in the unstretched material,
Elongation may be subject to undesirable limitations. Polymer crystallization has been extensively studied;
Explanations can also be found in books such as Crystallization of Polymers (Chapter 8; Crystallization Kinetics and Mechanisms) by Elle Mandelkahn, published by McGraw-Hill in 1964. By observing changes in properties such as density and specific volume, it is understood that crystallization occurs in stages. There is a time lag until crystallization is observed, but as soon as it is observed, it progresses naturally and almost autocatalytically. Eventually, the crystallization reaches a state of pseudo-equilibrium, after which crystallization proceeds very slowly over a long period of time to a small but discernible amount. This crystallization process is continuous, and the rate of crystallization versus time is plotted in an S-shape, with no abrupt changes or discernible discontinuities. The rapid crystallization is called primary crystallization, and the slow crystallization stage is called secondary crystallization. It is believed that secondary crystallization is disadvantageous in obtaining high modulus, and while for some polymers some secondary crystallization can still provide favorable properties upon elongation; It has been found that the highest modulus is obtained when the process is not dominated by secondary crystallization. At least methods (1) and (2)
and (3), it has been found advantageous to allow the crystallization to proceed until the usually rapid initial crystals are substantially complete. The progress of crystallization can be tracked by measuring the density of the polymer. In methods (1), (2) and (3), the maximum elongation that can be achieved (maximum modulus obtained) for a given heat treatment and given polymer is determined by increasing the density until the polymer density reaches an optimum. increases with However, as the polymer density increases above the optimal degree, the maximum elongation obtained will decrease. By attenuating samples of different densities under the same conditions, it is possible to determine the optimal polymer density for a given attenuation condition. After heat treatment, the polymer is stretched at a temperature and at a rate such that the deformation is at least 15, preferably at least 20. It is believed that the high degree of elongation necessary to obtain high modulus is achieved by uniform stretching and consequent orientation of the polymer, which corresponds at the molecular level to the degree of unfolding of the molecules in the crystalline lamellae. A particularly preferred attenuation method is one in which the tensile force is less than or equal to the tensile strength of the polymer, but sufficient to cause linearization of the molecules by inducing a deformation in the plastic that exceeds the elongation that would occur by flow stretching. The polymer is drawn at high draw ratios at high speeds and temperatures. Preferably the stretch ratio is at least 20. Optimal stretching conditions depend to some extent on the nature of the polymer and its thermal history. In general, it is preferable to stretch the polymer relatively slowly, for example, at least 1 cm per minute between relatively possible clasps, usually about 10 to 20 cm per minute, at a temperature of at least 40°C below the melting point of the polymer. Stretch or 30-150cm/min at a temperature of 5-20℃ below the melting point on a stretching frame
Stretch at a speed of The physical properties of the polymeric material may be further improved by stepwise stretching, with pauses in the polymer between each step, and intermittent stretching. Preferably, polymers with relatively small cross-sections are subjected to a drawing process, and the invention is particularly suitable for the production of fibers and films. In particular, continuous filaments are produced by melt spinning or by drawing on drawing frames. For convenience, the fiber diameter or film thickness before stretching is preferably 1 mm or less. As used herein, the deformation ratio or stretching ratio is defined as the ratio of the length after treatment to the length before treatment or the ratio of the cross-sectional area after stretching to the cross-sectional area before stretching. In the method of the present invention, for example, the Young's modulus defined below is 3.
×10 ¹⁰ N/m ² or more, in some cases at least 6×
10 ¹⁰ N/m ² of polyethylene polymer can be produced. Since the Young's modulus of polymeric substances depends to a large extent on the measurement method, in this specification, the Young's modulus is determined by a dead-rotating creep test to 0.1.
It is defined as the measured modulus at 21°C when a tension of % is applied for 10 seconds. This test method was developed by Gupta and Ward; Journal of Macromolecular Science and Physics, B1;
373 (1967). It can be seen that the method of the invention results in polymer molecules that are substantially perfectly linearly arranged upon plastic deformation. This molecular orientation is often uniaxial, but by applying appropriate stretching, a biaxially oriented polymer can also be obtained. Substantially perfect orientation can be determined by physical measurements such as X-ray diffraction analysis and nuclear magnetic resonance analysis. According to the method of the invention, a polyethylene material having a Young's modulus of 5×10 ¹⁰ N/m ² or more is obtained. The theoretical Young's modulus of polyethylene is 24×10 ¹⁰ N/m ²
It can be seen that the polymers of the present invention are very close to this value. The polymeric material according to the invention is manufactured in a monolithic structure. The present invention will be explained below with reference to Examples. Example 1 High-density polyethylene (described later) was heated to 190°C with a diameter of 0.1
Melt-spun through a cm die, diameter 0.06~0.07cm
An isotropic filament is obtained. The filament is wound onto a 5.5 cm diameter cylinder rotating at 2.3 rpm. The cooling rate of the polymer is set at 5°C per minute, and the structure formed when the polymer temperature reaches 115°C is maintained by rapid cooling. Samples 3-4 cm long were tested at 72°C for 30-45 seconds using an Instron tensile tester at a crosshead speed of 20 cm/min.
Stretch under the following conditions. The stretching ratio is determined based on the change in the cross section of the filament. Two types of polymers selected from commercially available BP high-density polyethylene are used as samples. One is 075-60 grade, melt flow index 8.0, n: 14450, w: 69100 when measured at a temperature of 190°C and a load of 2.14 kg. Others are Rigidex 9, melt flow index 0.9, n: 6060, w: 126600
It is. Measure Young's modulus for 10 seconds at room temperature (21°C). The 075-60 grade has a narrow molecular weight distribution, that is, w/n = 4.8, and a stretched product with a stretching ratio of 20 and a Young's modulus of 4.0×10 ¹⁰ N/m ² can be obtained.
On the other hand, Rigidex 9 has a wide molecular weight distribution, that is, a high w value of w/n=20.9, and as a result, a stretched product having a considerably low Young's modulus can be obtained. Continuous filaments of the materials described above can be stretched on a stretching frame to give similar results. Example 2 By compression molding high-density polyethylene pellets between two copper plates at 160°C,
Obtain a 0.07cm thick sheet. Remove this sheet from the press and slowly press it at a rate of 7 to 9 degrees Celsius per minute.
Cool to 100°C (measured on the surface of the copper plate) and then quench in cold water. A rectangular sample with a length of 2 cm and a width of 0.5 cm was tested using an Instron tensile tester.
Stretch for 70-90 seconds at a crosshead speed of 10 cm/min. The stretching ratio is 0.2 on the surface of the sample before stretching.
Or make marks at 0.1 cm intervals and measure accordingly. Two grades of commercially available BP high-density polyethylene were used as samples. rigid index 50 is metreflow index 5.5, n: 6180, w: 101450, 140
−60 grade has a melt flow index of 12,
n: 13350, w: 67800. Rigidex 50
The maximum draw ratio for the 30140-60 grade is determined to be 37-38. The Young's modulus of representative samples was measured at room temperature for 10 seconds, and the results are shown in the table below. The following Examples 3 to 5 demonstrate that the maximum draw ratio obtainable occurs at the optimum density, and that the optimum density is a function of the heat treatment conditions. Example 3 High-density polyethylene (Rigidex 25, a product of BP Limited, w: 98800, n:
12950) is compression molded between two 0.5 mm thick copper plates at 160℃ to make a film. The plate is removed from the press, wrapped thickly in raw cotton, and the polymer is cooled at a rate of 5° C. per minute while being measured with a thermocouple. When the temperature reaches 120°C, place the plate in a glycerin bath maintained at 120°C and remove from 0 (do not enter the bath).
Hold for ~10 minutes. The density of the film is measured using a density column. A dumbbell-shaped film sample was tested at 75℃ for 60 seconds using an Instron tensile tester.
Stretch at a crosshead speed of 10 cm/min. Marks are placed on the sample before stretching at intervals of 0.2 or 0.1 cm, and the stretching ratio is determined based on the increase in length of the sample after stretching. Table 2 shows the influence of holding time at 120°C on density and maximum stretching ratio. Example 4 Immediately after removing the plate from the press, it was immersed in a glycerin bath and the polymer was heated at 40°C per minute.
The process is carried out in the same manner as in Example 3, except for cooling from 160°C to 120°C at a rate of . Table 2 shows the effect of density on drawing ratio. Example 5 A polymer is sandwiched between aluminum foils, and the whole is sandwiched between copper plates. Processing is carried out in the same manner as in Example 3, except that only the copper plate is removed immediately before placing the polymer and aluminum foil in the glycerin bath. The cooling rate is 400℃ per minute. Table 2 shows the effect of holding time at 120°C on density and maximum stretching ratio. [Table] Example 6 High-density polyethylene (Rigidex 140-60,
BP Limited products, w: 67800,
n: 13350) at 180° C. through an extrusion port with a 0.9 mm orifice, and the resulting filament is passed through a glycerin bath maintained at 120° C. before winding. The position of the bath below the extrusion port and the retention time of the filament in the bath are varied. The temperature of the filament entering the bath is approximately 135°C. Example 3
Stretch the filament under conditions similar to those described in . Table 3 shows the conditions for spinning and drawing and the properties of the drawn filament. In addition, for the modulus, Gupta and Ward are using the Synthesis of Macromolecular Science and Physics B.
1, 373 (1967) at 21°C. [Table] When the spun filament of Example 6 was cut and observed under a polarizing microscope, regularly oriented regions uniformly distributed throughout the filament were observed. This region represents the initial flux in spherulite growth. Example 7 The spun filament was wound at a speed of 150 cm per minute,
The same process as in Example 6 is carried out except that the room temperature is varied from 60 to 125°C. The temperature of the filament upon entering the bath is measured with an infrared pyrometer. The properties of the spun filament are shown in Table 4. Example 8 High density polyethylene (Rigidex 140-60)
is spun into single fibers and cooled using the same apparatus as in Example 6. The employment conditions are as follows. Extrusion rate: 0.3 g/min Extrusion temperature: 180°C Winding temperature: 5 feet/min Cooling distance from spinneret: 7.5cm Cooling temperature: 120°C Cooling length: 50cm Pin that maintained the resulting drawn yarn at 130°C Stretching ratio 23.8 with upper stretching frame, stretching speed 1 ft/
Stretch continuously in minutes. The drawn filament obtained has a strength of 6.7 gpd'tex, an elongation at break of 2.9%, and a creep modulus of 450×10 ⁸ N/m ² . [Table] [Table] Example 9 Rigidex 50 and 140-60 grade samples were sandwiched between metal plates at a temperature of 160°C, and after compression molding,
Cool to room temperature at a non-linear cooling temperature of less than 0.8°C per minute. A dumbbell-shaped sample with a length of 2 cm and a width of 0.5 cm is stretched using an Instron testing machine at 75°C. The test conditions and results are shown in Table-5. The significant difference in stretching behavior for samples with the same initial crystallinity is related to the broadening of the molecular weight distribution and therefore also to the molecular weight of the molecules in the amorphous phase. The optical micrograph of the isotropic sample of Rigidex 50 prepared by the method of this example shows regular orientation regions, but the isotropic sample of 140-60 shows a clear spherulite structure before stretching. It will be done. [Table] Example 10 Rigidex 50, 140-60 grade BXP10 (
n: 168000, w: 93800) and Rigidex 9 samples were sandwiched between metal plates and compression molded at 160°C.
Then cool with water to room temperature. A high stretching ratio can be obtained by stretching a dumbbell-shaped sample with a length of 2 cm and a width of 0.5 cm at 75° C. for different times using an Instron tensile sampler. The sample conditions and results are shown in Table 6. [Table] Example 11 Polypropylene samples of various molecular weights with a diameter of 0.2
Ram speed of 0.6 cm per minute and 110 cm per minute through the die
Stretch at 185° C. in air at a winding speed of cm. Place the spool about 3cm from the die. The filament is drawn on a drawing frame at a winding speed of about 130 cm per minute. The sample conditions (multi-stage process) are shown in Table-7. [Table] Table 8 shows the molecular weight characteristics, stretching ratio, and creep modulus of the two types of samples. [Table] Example 12 Polyoxymethylene (Delrin 500, a product of DuPont, n: 45000, w/n: slightly larger than 2) was heated at a ram speed of about 180°C or less in air.
0.6cm/min, winding speed approximately 36cm/min, diameter 0.2cm
diameter by melt spinning through a die of
Obtain an isotropic filament of 0.04-0.06 cm. The take-up spool was positioned at a distance of about 7 cm from the die. The obtained filament was drawn in two stages on a drawing frame at a winding speed of about 50 cm/min. The conditions at that time are shown in Table-9. [Table] [Table] [Table] Next, specific examples of technical aspects included within the scope of the present invention are listed. (1) subjecting a crystalline polymer having a weight average molecular weight of 300,000 or less, particularly 200,000 or less to a heat treatment under conditions that substantially reduce the possibility that a given molecular chain will be introduced into more than one crystal lamella; A method for producing a high modulus polymer material, characterized in that the polymer is stretched at a temperature and speed such that the deformation ratio is at least 15. (2) The method according to (1) above, wherein the crystalline polymer is a linear vinyl hydrocarbon polymer. (3) The method according to (1) or (2) above, wherein the crystalline polymer is high-density polyethylene. (4) The weight average molecular weight (w) of the polymer is 5000~
250,000, especially (1) to (3) above, which is between 50,000 and 150,000.
The method described in. (5) The number average molecular weight (n) of the polymer is 5000 or more
25,000, particularly 5,000 to 15,000, the method described in (1) to (4) above. (6) When the ratio of the weight average molecular weight to the number average molecular weight of the polymer is n> ¹⁰⁴ , w/n<10 (preferably <8), and when n< ¹⁰⁴ , w/n<
25 (preferably <15), the method described in (1) to (5) above. (7) The method described in (1) to (6) above, characterized in that the polymer is cooled from its melting point or higher to ambient temperature at a preset rate. (8) The method described in (7) above, wherein the polymer is cooled at a loading rate of 40°C or less per minute. (9) The above (7) or where the cooling rate is 20℃ per minute or less
(8) The method described. (10) Cooling the polymer from a temperature at or above its melting point to below its crystallization temperature at a preset rate, and then cooling it to ambient temperature.
The methods described in (1) to (6). (11) The method according to (10) above, wherein the polymer is cooled at a loading rate of 1 to 15°C per minute. (12) The method described in (10) or (11) above, wherein the polymer is cooled to a temperature 5 to 20°C lower than its crystallization temperature. (13) The above (1) to (6), wherein the polymer is rapidly cooled from a temperature at or above its melting point to a temperature near its crystallization temperature, and the polymer is held at that temperature for a sufficient time to cause crystallization. the method of. (14) 0.5 within 15℃ of the polymer's crystallization temperature.
The method described in (13) above, holding for ~10 minutes. (15) The method described in (13) or (14) above, wherein the polymer is then cooled to ambient temperature. (16) Rapidly cooling the polymer from a temperature at or above its melting point to a temperature below its crystallization temperature (1) above
(6) The method described. (17) The method described in (16) above, wherein the cooling rate is 1000°C or more per minute. (18) The method described in (16) or (17) above, wherein the polymer is cooled and then reheated to increase the crystalline region. (19) The method described in (1) to (15) above, wherein the method is subjected to heat treatment such that secondary crystallization is not a main crystallization step. (20) High draw ratios at speeds and temperatures sufficient to cause linearization of the polymer molecules by inducing plastic deformation in which the tensile force of the polymer is less than its tensile strength but greater than the elongation that would occur by flow drawing. Above (1) ~
(19) The method described. (21) The method according to (20) above, wherein the stretching ratio is at least 20. (22) The method according to (20) or (21) above, wherein the polymer is stretched between relatively movable clasps at a temperature of at least 40° C. or lower than the melting point of the polymer at a speed of 1 cm per minute or more. (23) The above (22) with a stretching speed of 10 to 20 cm per minute.
Method described. (24) The method according to (20) or (21) above, wherein the polymer is stretched on a stretching frame at a temperature of 5 to 20° C. below its melting point at a speed of 30 to 150 cm per minute. (25) Performing the stretching process in the enhancement stage while resting the polymer in the continuous stage (20) ~
(24) The method described. (26) The above for producing fibers or films.
The method described in (1) to (25). (27) The method according to (26) above, wherein the diameter of the fiber or the thickness of the film is 1 mm or less before stretching. (28) A high modulus polymeric substance produced by the method described in (1) to (27) above.

[Brief explanation of drawings]

Figures 1a to 1d show the method (1) of the present invention, respectively.
(4) This is a micrograph of the crystal structure of polyethylene produced by method (4).

Claims (1)

[Claims] 1 A crystalline polymer selected from high-density polyethylene, copolymers thereof, and polyoxymethylene having a weight average molecular weight of 300,000 or less is heated from its melting point or higher to a temperature sufficiently lower than its crystallization temperature at a rate of at least 400°C per minute. quench at high speed,
The cooled polymer is stretched at a temperature below its melting point such that its deformation ratio is greater than 20 for high density polyethylene or greater than 15 for copolymers of high density polyethylene or polyoxymethylene. The characteristic Young's modulus is 3×
10 A method for producing a high modulus polymer material of ¹⁰ N/m ² or more.