JPH0543490B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a high-strength thermoplastic resin body that exhibits high shape stability and rigidity at room temperature. One of the drawbacks of plastics, which have been widely used mainly in industry in recent years, is that their strength is considerably lower than that of other industrial materials, especially metals. The present invention relates to a method for producing resin bodies which significantly improves this drawback, particularly with regard to thermoplastic resins.

In general, many thermoplastic resin bodies are made by melting pellets and extrusion molding, injection molding, etc. at high temperatures near the melting point.
It is made by calender molding, compression molding, etc. At this time, even if it is cold deformed like metal, the shape will not be stable due to large spring back immediately after and strain recovery due to heat and the passage of time, so the cold working method is not usually adopted. do not have.

The strength of the plastic body obtained in this way, for example, the tensile strength of polyethylene, is approximately 1 kg.
f/mm ² , about 6 Kgf/mm ² for polyacetal, and about 7 Kgf/mm ² for polycarbonate. When comparing the strength per weight (specific strength), plastic is lighter, so it can be said that it is comparable, but when comparing the same dimensions, for example, mild steel, which is the most widely used in industry, is about 35Kgf. /mm ² , which is extremely low compared to that, and therefore its uses are inevitably limited.

In order to solve this problem, conventional measures have been taken to strengthen plastics by incorporating fibers into them. Many fibers, including glass fiber, have been developed to achieve the purpose of reinforcing the so-called fiber-reinforced plastics (sometimes abbreviated as FRP). However, this strengthening method is not necessarily easy and (1) is costly. (2) Cutting, pretreatment, and handling of fibers are complicated. (3) It is difficult to uniformly contain even short fibers (generally 1 to 2 mm or less). (4) It also tends to cause wear and damage to molding machine tools. There were many shortcomings.

This invention improves the strength of thermoplastic resin bodies without relying on such compositing, and provides new possibilities for the usefulness of thermoplastic resin bodies.

This invention consists of two steps. One is to process the thermoplastic resin under conditions that cause strain recovery as described above, that is, at temperatures up to warm temperatures including room temperature (hereinafter referred to as cold working), and the other is to process the processed body immediately after cold working. , rapid annealing (hereinafter referred to as incomplete annealing) is carried out while the shape is restrained by an external force using a member surrounding the periphery.

This incomplete annealing is desirably performed under conditions consisting of a combination of temperature and time that does not produce a relaxation effect. If annealing is performed at high temperature or for a long time to completely eliminate distortion,
In other words, if we allow the relaxation effect to occur completely,
Since there is no residual stress, the strength does not increase.

The principle was discovered by the present inventor in 1979, and was published in "Plasticity and Processing" Vol. 20, No. 222 (1979).
The phenomenon called thermally induced deformation of plastics, which was published on pages 610-617, is that thermoplastics extruded in a molten or semi-molten state and cooled have shape memory, and above a certain temperature, For example, when heated to a temperature that allows it to flow,
This is based on the phenomenon that even if no force is applied at that time, the material undergoes sudden large flow or deformation depending on the direction and degree of force applied during the previous molding process. Experiments have shown that it is possible to consciously create plastics that have the ability to undergo thermally induced deformation. That is, by heating (incomplete annealing) under appropriate conditions while restraining and holding the cold strain by external force, the nature of the strain changes and thermally induced deformability is formed. The thermally induced deformability obtained in this way is also completely hidden below the normal temperature, but becomes visible only when heated above a certain temperature. This heat-induced deformability can be used as is as a temperature-sensitive deformation function element, but if the deformation that appears when heated is suppressed by an external force, residual stress corresponding to that stress will be applied to the plastic. It will be totally immanent. If this residual stress is large, the plastic will be strengthened. Plastics treated in this way are, of course, stable in shape under normal circumstances, but their strength is improved by residual stress.

During heating, if the workpiece is held by a member having a surrounding surface to prevent deformation due to heating, the member will apply a force to the workpiece to counter deformation. As a result of this action, the workpiece is restrained by an external force, and the above-mentioned residual stress can be imparted to the plastic.

The method of incorporating residual stress by cold working and incomplete annealing and thereby strengthening it can be applied to all thermoplastic resins. For example, materials such as acrylic, which are hard and brittle at room temperature, can be deformed at temperatures of 100 to 150°C, so the same effect can be expected. Furthermore, the shape of the final product is not particularly limited. For example, for plates and strips, rolling methods can be used, for wires and rods, methods such as hole-meter rolling, drawing, and extrusion can be used, and for other shapes, metal processing methods can be used almost as is, and imperfections can be used. As long as the jig is devised to maintain its shape only during annealing, residual stress can be incorporated and a strengthening effect can be obtained.

The jig (member) should be in close contact with the workpiece so that it can sufficiently receive the external force caused by thermal deformation of the workpiece, and in some cases it is preferable to press it from the outside.

FIG. 1 is a schematic diagram showing step-by-step a method for making a reinforced plastic plate as an example of the method of the present invention, in which FIG. 1a shows cold rolling, and FIG. The incomplete annealing process is shown respectively.

In FIG. 1a, a plastic plate 1 of thickness T is shown.
The figure shows the process of forming a plate 1' with a thickness t using cold rolling rolls 2. In FIG. 1b, 3 and 4 are holders for holding the plate 1' having a thickness of t, and 5 and 6 are heating and cooling means.

FIG. 2 shows the incomplete annealing of a plastic rod and corresponds to the view in FIG. 1b for a plate. Bars of plastic formed by pultrusion, extrusion, or groove rolling are used. Second
In the figure, holders 3' and 4' are placed over the plastic rod-shaped body 1'' from above and below to hold the rod in place.Although not shown, heating means and cooling means may be provided on the holder in the case of FIG. 1b. It is similar to
In the case of a rod-shaped body, as shown in the figure, whenever it is held down from above and below, it is actually held down from the periphery.

In an actual production line, a long die with a predetermined gap connected to the outlet of a rolling mill is set, and the plastic immediately after cold rolling is passed through it. At this time, the material of the die does not matter, but it must have sufficient structural strength to suppress the deformation of the plastic as it tries to recover from the strain when it is heated. In addition to electric resistance heating, high frequency induction heating can also be used for heating the dice, and there are no particular limitations on the method. Further, the cooling may be water cooling or air cooling.

The method of this invention is as described above,
It is applicable not to things like films, but to things with high rigidity such as thin plates and rod-shaped objects, and in the case of plates, it is possible to manufacture objects with a sufficiently wide width.

Example 1 Commercially available polyacetal with a thickness of 6.3 mm (melting point 178
As shown in Figure 1a, a 60% reduction is applied to a thin plate with a glass transition point of 93°C (glass transition point: 93°C), with spring back subtracted, using a roll with a diameter of 70 mm, and immediately restrained in a holder (made of aluminum) in an electric resistance furnace. Then, incomplete annealing was performed at the following predetermined electric furnace temperature for a predetermined time. The strength of the prototype plate was determined using a Tensilon tensile tester at a parallel part width of 10 mm, GL of 20 mm, and a speed of 30 mm/min. The experimental results showed that the initial tensile strength was 7.35Kgf/ ^mm2 , but after incomplete annealing, the tensile strength was 10.5Kgf/mm2 in the rolling direction as shown in Figure 3.
~11.4Kgf/ ^mm2 , an improvement of about 50%. In Figure 2, () is the strength of the conventional board, () is 150
Strength when annealed at ℃ for 40 minutes, () at 170℃
Each shows the strength when annealed for 30 minutes.

Note that if the gap between the plate and the holder is large, this reinforcing effect will be diminished, so deformation during incomplete annealing must be suppressed as much as possible. The obtained board was kept at 30 to 35 degrees Celsius in midsummer for two months, and then in hot water at 100 degrees Celsius.
Even after holding for 30 minutes, no change in size or shape was observed. However, at high temperatures of 160 to 170°C, deformation occurs such as shrinkage in the rolling direction and increase in plate thickness, and the shape and strength of the plate were found to return to almost their original values.

Example 2 In order to strengthen the polyacetal in two directions, the polyacetal original sheet of Example 1 was cross-rolled, that is, rolled alternately in orthogonal directions (75% in total), then held at 150°C for 40 minutes, and then heated at 170°C to further increase the effect. An incomplete annealing process was carried out for 20 minutes. The tensile strength of this plate was 9.8 Kgf/mm ² in both directions. This is about a 30% improvement over the original.

Example 3 The above-mentioned polyacetal was cold rolled by 75% and
An incomplete annealing process was carried out at ℃ for 20 minutes. The tensile strength of this plate reached 24 kgf/mm ² , approximately 3.5 times that of the original plate. This shows that the higher the cold rolling rate, the greater the strengthening effect.

Example 4 A polycarbonate plate with a thickness of 6.1 mm was cold rolled by 60% and incompletely annealed at 120°C for 50 minutes. Its rolling strength reached 14 Kgf/mm ² , which was approximately 100% improved over the original sheet (7 Kgf/mm ^{2 )} .An improvement of about the same radius was observed after annealing at 150°C for 50 minutes.

The strength of plastics is usually improved by incorporating or combining them with fibers and other materials, but this naturally comes with limitations, so it is also necessary to modify the plastics themselves. The method of this invention is simple and can be incorporated into a continuous line that combines cold working and heating, and it can improve the strength by up to 250%, and is expected to be put to practical use. Of course, the effect will be even greater if it is applied to fiber-reinforced materials. Although a rolled plate is shown in the above embodiment, it goes without saying that compression, tension, deep drawing, drawing, extrusion, bending, and other processing methods can also have similar effects.

Furthermore, the plastic plate modified and strengthened by the method of the present invention has a remarkable improvement effect in terms of punching (drilling) workability. Plastic is soft and elastic, making it difficult to separate, so the punched edge usually takes on a wedge shape, making it impossible to obtain a straight cut surface like metal. However, the plate obtained by this invention has a high punching load or shear resistance due to improved strength, and at the same time, the excessive softness is suppressed, resulting in a smooth cut surface, and it can be put to practical use as it is.

Example 5 A plate made of polyacetal and polycarbonate obtained according to the present invention was punched using a punch diameter of 20 mm and a die diameter of 20.5 mm, and compared with a commercially available plate having a similar thickness.

Figure 4 shows the relationship between punch stroke and punching force (shear stress), where a is polyacetal, b is
1 and 2 respectively indicate polycarbonate, and in the figure, , indicates a commercially available product, and , indicates a product produced according to the present invention, respectively. As shown in the figure, it can be seen that in the case where the reinforcement according to the present invention is sufficient, the rise of the curve is more rapid and the maximum point is quickly reached, and the load decreases thereafter is also more rapid and the shearing is smoother.

Figure 5 shows the cut surface of the punched product.
1.a shows the case of polyacetal, b shows the case of polycarbonate, . shows the case of the conventional product, and . In the strengthened board, the main material separation is changed from a tension-first type to a shear-first type, and the cut surface has less gouge and is smooth, resulting in an excellent cut. The cut surface of the drilled product was similarly improved.

[Brief explanation of the drawing]

Figures 1a and b are diagrams showing each step of the method of the present invention, Figure 2 is a diagram showing the annealing state in the case of a rod-shaped body, and Figure 3 is a diagram showing the improvement in the strength of polyacetal according to the present invention. Figures 4a and 4b are diagrams showing the relationship between the punch stroke and shear stress of the reinforced plastic plate according to the present invention, and Figures 5a and 5b are cross-sectional views of the reinforced plastic plate according to the present invention and the conventional plate. It is a figure which compares a state. Explanation of symbols: 1...Plastic plate, 2...Rolling roll, 3, 4...Holder, 5, 6...Heating and cooling means.

Claims (1)

[Claims] 1 Deformation processing is performed on the thermoplastic resin body under conditions that cause strain recovery, and then the processed body is immediately annealed by rapid annealing while its shape is restrained by external force using a member having a surrounding surface. A method for producing a high-strength thermoplastic resin body having high shape stability and rigidity at room temperature, which is characterized by incorporating stress.