JPH035297B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing a transparent crystalline polymer sheet with a smooth surface, high strength, and high modulus of elasticity by a pultrusion method. Generally, when molding a polymer material, a method is used in which the material is poured into a mold in a molten state or extruded from a die. Polymer materials molded using these methods have low molecular chain orientation and a small number of tie molecules connecting crystals, so they do not have high strength or elastic modulus. Therefore, in order to produce a sheet with high strength and high modulus of elasticity, it is necessary to deform the sheet in a specific direction by a method such as stretching or rolling to orient the molecular chains. In particular, rolling may be applicable to thick polymer sheets, but because the elastic recovery of amorphous chains causes the thickness to return immediately after passing through the rollers, so-called spring back, it is difficult to process with high precision. Moreover, a large deformation ratio cannot be obtained. On the other hand, in pultrusion molding, there is a restriction that the pultrusion stress must be smaller than the breaking strength of the material, and pultrusion molding of polymer sheets has not been attempted. In view of these circumstances, the present inventors formed a crystalline polymer sheet by pultrusion molding, and achieved high strength and
As a result of various research efforts to develop a method for manufacturing crystalline polymer sheets that exhibit high elastic modulus, we found that strain hardening occurs during the process of pulling out a crystalline polymer sheet, making it difficult for the sheet to break. We have discovered that it is possible to deform a sheet to a high deformation ratio by pultrusion under temperature conditions of I arrived at the eggplant. That is, in the present invention, a crystalline polymer raw sheet is loaded with a load of 10 MPa, and
Drawing at a draw ratio of at least 2.5 times through a pair of freely rotating rollers heated to a temperature above the onset of deformation when heated at a rate of °C/min and not exceeding the rising point of the differential scanning calorimetry melting curve. The present invention provides a method for producing a crystalline polymer sheet characterized by the following. The resins used in the method of the present invention include polyethylene, polypropylene, polyacetal resin, nylon,
Other crystalline polymers. Furthermore, there are no particular limitations on the molecular weight or molecular weight distribution of the resin used, as long as it is generally used for fibers, films, and molded products. In the method of the present invention, it is necessary to use a pair of freely rotating rollers, which, unlike a pair of rolling rollers that are forcibly driven, are simply supported so that they can rotate freely. This is a pair of rollers with no rolling action. In the method of the present invention, a crystalline polymer is formed into a sheet and cut into a certain width. Next, the sheet is drawn through a pair of freely rotating rollers maintained at a predetermined temperature, but in this case the distance between the rollers must be adjusted so that the stretching ratio of the sheet is at least 2.5 times. The stretching ratio here means the ratio of the length of the sheet after being drawn to the length of the sheet before being drawn. The method of the present invention needs to be carried out under predetermined temperature conditions. In other words, the temperature of the free rotating roller is set to a temperature that is higher than the deformation start temperature when the temperature is increased at a rate of 1°C/min with a load of 10 MPa, but does not exceed the rising temperature of the differential scanning calorimetry melting curve. There is a need. The deformation start temperature here refers to the temperature at which the strain-temperature curve deviates from the linear portion on the low-temperature side when the temperature is increased at a rate of 1° C./min with a load of 10 MPa applied. Figure 1 shows the strain-temperature curves of major crystalline polymers and how to determine the deformation onset temperature _T1 . Further, the rising temperature of the differential scanning calorimetry melting curve refers to the temperature at the intersection of the tangent at the inflection point on the low temperature side of the melting curve and the extension of the baseline. Figure 2 shows the differential scanning calorimetry melting curves of major crystalline polymers and how to determine their rise temperature _T2 . Differential Scanning Calorimetry Melting curves were measured using a Perkin Elmer DSC-2 differential scanning calorimeter at a heating rate of 5°C/min. If the temperature of the free rotating roller is lower than T ₁ , the pultrusion stress will be large and pultrusion will be difficult. Furthermore, at temperatures above T ₂ , the sheet melts and orientation of the molecular chains in the drawing direction cannot be imparted. Therefore, it is necessary to set the temperature of the freely rotating roller to a temperature that is greater than or equal to T ₁ and does not exceed T ₂ . The T ₁ and T ₂ values of major crystalline polymers are shown in the table below.

[Table] Next, the method of the present invention will be explained with reference to the accompanying drawings. FIG. 3 is a sectional view showing an embodiment of the present invention, in which a material sheet 1 is pulled out from between a pair of freely rotating rollers 22 heated to a predetermined temperature while applying tension to obtain a desired sheet. It is desirable that the material sheet be preheated in the preheating section 3. The spacing of the free-rotating rollers 22 can be adjusted to obtain drawn sheets of various thicknesses. The temperature of each roller is set to a temperature that is higher than the deformation start temperature when a load of 10 MPa is applied and the temperature is increased at a rate of 1° C./min, and does not exceed the rising temperature of the differential scanning calorimetry melting curve. The preferred drawing speed varies depending on the type and molecular weight of the resin, but if it is too fast, the temperature will easily break between the rollers, so the drawing speed should be
It is desirable to keep the speed below 500mm/min. It is necessary to select the spacing between the rollers in order to obtain a predetermined stretching ratio, but it is preferable that the spacing between the rollers be approximately 7 to 40% of the thickness of the material sheet.If the spacing between the rollers is too narrow, the sheet may If it is too wide, a sufficient deformation ratio cannot be obtained. Further, unlike in the case of general rolling, driving power for the roller section is not required, and the roller does not necessarily need to be forcibly driven to rotate during drawing. In the case of drawing or rolling metal, it is necessary to reach the desired rolling ratio or drawing ratio in multiple stages, whereas the method of the present invention has the advantage that metal can be drawn in one stage through a pair of heated rollers. It has characteristics. Of course, it is also possible to perform the process in multiple stages if desired. In the method of the present invention, since tension is applied to the sheet, the return of the thickness (spring back) immediately after passing through the rollers, which is seen in rolling, is suppressed.In fact, the sheet is stretched even after passing through the rollers, so that a high The deformation ratio is obtained. In the material sheet, the molecular chains are in a non-oriented state, but by pultrusion, the molecular chains become highly oriented in the drawing direction, and the number of tie molecules that connect the microcrystals increases. These structural changes are
It has a great influence on the mechanical properties of the sheet. In the stress-strain curve in a tensile test, most of the material sheets show a yield point, but sheets that have been deformed to a high deformation ratio by pultrusion do not yield to the breaking point. In addition, as the drawing ratio increases, the elongation decreases,
Tensile strength and elastic modulus increase. The strength and elastic modulus of the sheet deformed to the maximum stretch ratio by pultrusion are 5 to 30 times the values of the raw material sheet.
It was discovered for many crystalline polymers. Also,
The material sheet is opaque due to the presence of a spherulite structure, but since the spherulite structure is destroyed during the drawing process, the transparency of the drawn sheet is extremely good. If the method of the present invention is carried out in combination with sheet melt extrusion molding, a sheet with high strength and high modulus of elasticity can be obtained continuously, so it is suitable as an industrial method for producing crystalline polymer sheets. Next, the present invention will be explained in more detail with reference to Examples. In each example, a pair of freely rotating rollers made of stainless steel and having an outer diameter of 50 mm and a width of 70 mm were used. Elongation, tensile strength, and elastic modulus were measured according to JISK7113-1980 using an Instron type tensile tester {manufactured by Toyo Baudouin Co., Ltd., Tensilon UTM-100}. The meaning of each measurement value is as follows. Elongation at break: Strain value at tensile break. Yield elongation: Strain value at yield. Tensile strength: The value obtained by dividing the load at tensile break by the original cross-sectional area of the test piece. Modulus of elasticity: the ratio of tensile stress to strain at the starting point of deformation Example 1 Advanced polyethylene with a viscosity average molecular weight of 40,000 {manufactured by Mitsui Petrochemical Industries, Ltd., registered trademark name ``HIZEX''
2200J''} and a sheet of high-density polyethylene with a viscosity average molecular weight of 63,000 {manufactured by Mitsui Petrochemical Industries, Ltd., registered trademark name ``HIZEX 5000B''} was pultruded. The thickness of the material sheet is 1
mm, width is 20mm for 2200J and 30mm for 5000B
It is. The material sheet was pulled through rollers heated to 75°C, 100°C, or 120°C. The ratio of the roller spacing (tr) to the material sheet thickness (to) (tr/
to) and pulling stress (pulling tension/material sheet cross-sectional area),
The relationship between the drawing ratio and the ratio of the thickness (t) of the drawn sheet to the thickness of the material sheet (t/to) is shown as a graph in FIG. In the figure, 〇 is 2200J and the drawing speed is 50
mm/min, □ is 5000B and drawing speed is 50mm/min, ▽ is
These are the measured values at a drawing speed of 10 mm/min at 5000B. As is clear from the figure, in the case of 2200J, t/to
≪tr/to, the thickness of the drawn sheet is thinner than the roll interval, and a high drawing ratio of up to about 25 times can be obtained. On the other hand, in the case of 5000B, it is t/totr/to,
The thickness of the drawn sheet and the roll spacing are approximately equal, and a maximum drawing ratio of about 14 times can be achieved. In the case of 2200J, considerable deformation occurs in the post-stretching section, but in the case of 5000B, the deformation region is limited between the rolls. The relationship between the mechanical properties of the drawn sheet and the stretching ratio is shown in FIG. In the diagram, 〇 is 2200J and the roller temperature
100℃, △ is 2200J, roller temperature is 75℃,
2000J material sheet, □ is 5000B and roller temperature
100℃ is the measurement result for a 5000B material sheet. Further, in the figure, black symbols indicate yield strength and yield elongation, and white symbols indicate tensile strength, elongation at break, and elastic modulus. Material sheets and sheets drawn with a small stretching ratio (less than 5 for 5000B, less than 9 times for 2200J) show a yield point in the stress-strain curve in a tensile test, but sheets drawn to a higher drawing ratio show a yield point. It broke without yielding in the tensile test. As the stretching ratio increases, the elongation at break decreases;
Tensile strength, yield strength and elastic modulus increase. In the case of 2200J, a sheet was obtained that exhibited a tensile strength of 0.6-0.7 GPa and an elastic modulus of about 40 GPa at roller temperatures of 75°C and 100°C. Furthermore, in the case of 5000B, the tensile strength and elastic modulus reached 0.43 GPa and 14 GPa, respectively, at a roller temperature of 100°C. Example 2 Polypropylene with a viscosity average molecular weight of 2.17×10 ⁵ {manufactured by Mitsui Toatsu Chemical Co., Ltd., trade name Noblen FL-100}
A sheet with a thickness of 1 mm was cut into 30 mm width sheets, and pultrusion molding was performed at roller temperatures of 110°C and 135°C. Ratio between roller spacing and material sheet thickness (tr/to)
The relationship between
Shown in the figure. In the figure, ○ is the measurement result at a roller temperature of 135°C and a drawing speed of 50 mm/min, □ is a roller temperature of 135°C and a drawing speed of 500 mm/min, and △ is a measurement result at a roller temperature of 110°C and a drawing speed of 50 mm/min. As is clear from the figure, when the roller spacing is the same, the higher the roller temperature and the faster the drawing speed, the higher the stretching ratio, that is, the more deformation occurs in the post-stretching region. Further, the lower the roller temperature and the larger the deformation ratio, the greater the pull-out stress becomes. FIG. 7 shows the relationship between the mechanical properties of a drawn polypropylene sheet and the stretching ratio. In the figure, ○ indicates a roller temperature of 135°C, △ indicates a roller temperature of 110°C, and values measured for the material sheet. Black symbols represent yield elongation and yield strength, and white symbols represent elongation at break, tensile strength, and elastic modulus. A sheet drawn at a stretching ratio of 5 times or more breaks without yielding in a tensile test. However, low draw ratio (8
2 times or less), there is a tendency that the lower the roller temperature, the higher the tensile strength and elastic modulus.
The maximum stretching ratio obtained at each temperature was greater when the roller temperature was higher, and at a roller temperature of 135°C, a drawn sheet with an elastic modulus of 11 GPa was obtained. Example 3 A sheet of polyoxymethylene (a copolymer with a melt index of 2.5, manufactured by Polyplastics Co., Ltd., registered trademark name "Dyuracon M-25") with a thickness of 1 mm and a width of 15 mm was heated at a roller temperature of 140°C. Then, pultrusion molding was performed. The ratio between the roller spacing and the thickness of the material sheet (tr/to), the drawing stress, the stretching ratio, and the ratio between the thickness of the drawing sheet and the thickness of the material sheet (t/to)
to) is shown in Figure 8 with symbols 〇 and ●. 〇 and ● are drawing speeds of 500 mm/min and 10 mm/min, respectively.
Measured in minutes. It is possible to draw the sheet to a drawing ratio of up to 13.5 times, and at a drawing ratio of 5 times or more, the ratio is t/totr/to, and the roller interval and sheet thickness are approximately equal. The relationship between the stretching ratio and the mechanical properties of the polyoxymethylene drawn sheet is shown by the symbol ○ in FIG. Further, the symbol ● in the figure represents the yield elongation and yield strength of the polyoxymethylene material sheet. In a tensile test, the material sheet shows a yield point, but the drawn sheet breaks without yielding. A drawn sheet with a tensile strength of 1 GPa and an elastic modulus of 11 GPa was obtained. Example 4 Nylon-6 {manufactured by Toray Industries, Inc.} thickness 1 mm, width 30 mm
The sheet was pultruded at a roller temperature of 150°C. The relationship between the ratio of the roller interval to the material sheet thickness (tr/to), the drawing stress, the stretching ratio, and the ratio of the drawing sheet thickness to the material sheet thickness (t/to) is shown by △ in Figure 8. Ta. When tr/to≦0.3, t/to>tr/to,
Spring back occurs, and the maximum draw ratio that can be obtained is about 4.5 times. Compared to other crystalline polymers, it has higher pullout stress and deformation resistance. The relationship between the stretching ratio and mechanical properties of a drawn sheet of nylon-6 is shown by △ in FIG. Although the maximum draw ratio obtained was small at 4.5 times, the tensile strength was relatively high, and a drawn sheet with a maximum tensile strength of 0.5 GPa was obtained.

[Brief explanation of the drawing]

Figure 1 shows the strain-temperature curve and how to determine the deformation onset temperature when a constant load of 10 MPa is applied and the temperature is raised at a rate of 1°C/min. Figure 2 shows differential scanning calorimetry of major crystalline polymers. How to determine the melting curve and its rise temperature; Figure 3 is a cross-sectional view showing an example of an embodiment of the method of the present invention; Figures 4, 6, and 8 are for polyethylene, polypropylene, and polyoxymethylene, respectively. 5 and 7 are graphs showing the relationship between roller spacing, drawing stress, stretching ratio, and drawing sheet thickness for nylon-6 and nylon-6.
Figures 9 and 9 show the relationship between stretch ratio and mechanical properties for polyethylene, polypropylene, nylon-6 and polyoxymethylene, respectively.

Claims (1)

[Claims] 1. Put the crystalline polymer raw sheet into the sheet.
Through a pair of freely rotating rollers heated to a temperature above the deformation onset temperature when a load of 10 MPa is applied and the temperature is increased at a rate of 1 ° C / min, but not exceeding the rising point of the differential scanning calorimetry melting curve, A method for producing a crystalline polymer sheet, comprising drawing at a drawing ratio of at least 2.5 times.