JPH0126325B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to a method for molding ultra-high molecular weight polyethylene.

As used herein, the term "ultra-high molecular weight polyethylene" refers to
This refers to polyethylene that exhibits a molecular weight of 2,000,000 or more, or 2,000,000 or more when measured using a light scattering method.

Conventional technology Ultra high molecular weight polyethylene is superior to general polyethylene and other plastics in terms of abrasion resistance, impact resistance, stress cracking resistance, cold resistance, etc. In addition, it has a low coefficient of friction, It is expected to have a wide range of applications because of its water resistance, non-toxicity, and good sound-absorbing properties. However, this type of polyethylene has a high viscosity when heated and melted, so it is difficult to adapt to normal extrusion molding or injection molding methods.Except for round bars and small molded products, large molded products are manufactured using compression molding. has been done.

Recently, as a compression molding method for this type of synthetic resin, a two-stage compression molding method has been adopted, which consists of a first step of manufacturing a preformed product and a second step of manufacturing a plate product from the preformed product. ing. Conventionally, a compression molding machine for performing a two-stage compression molding method has a structure shown in FIG. First, the compression molding machine 51 in the first step is
As shown in FIG.
4 has a female-shaped recess 55 at the upper part and a male-shaped convex part 56 at the lower part.

In this compression molding machine 51, resin compound powder is charged into the female mold 53 and each recess 55. Then, the female die 53 and the male die 52 are kept under pressure from above and below at a pressure of about 100 kg/cm ² for 5 to 10 minutes to obtain a preformed product. This preformed product is then removed from the mold and transferred to the second step. In this case, the preformed product is easily disintegrated and must be handled with great care.
The compression molding machine 61 for the second step is of the same type as the compression molding machine 51 for the first step, as shown in FIG. The mold 62 and the convex portion 66 of the intermediate mold 64 are each independently provided with a plurality of heat medium passages 67 and 68 through which steam or cold water passes, so that heating or cooling can be carried out in a timely manner. In this compression molding machine 61, a female mold 63, a male mold 62, and an intermediate mold 64 are heated in advance to 200 to 220°C, and the preformed product is inserted into the female mold 63 and the recess 65, and a pressure of 20° C.
Heat and pressurize at ~50Kg/cm ² to melt completely. The pressing time is about 1 hour for a plate thickness of 20 mm. Next, cooling water is passed through the heat medium passage 68 to cool both the front and back surfaces of the resin to solidify the molten material, thereby obtaining a plate-shaped molded product. At this time, increase the pressure to 100Kg/cm ² .
In addition, since the side portions need to be cooled more slowly than the front and back surfaces, when the side portions are cooled to 150°C, the heating medium passage 6
Pass steam through 7 to heat the side and slow down the rate of descent until the temperature reaches 120℃. Then, the molded product is cooled to room temperature and the pressure is maintained at 100 kg/cm ² . FIG. 3C shows a modification of the molding machine in the second step. In this case, the pressure molding machine 71 has a hot press mechanism, and upper and lower heating plates 72 and 73 equipped with a pressure mechanism, and these It consists of a plurality of intermediate heating plates 74 provided in between and a number of molds 75 arranged between each heating plate. The mold 75 is composed of an upper mold 76, a lower mold 77, and a pair of side frames 78, and is also configured to be able to be heated or cooled. The molding conditions were the same as in the previous case. In the case of this deformation, it is economical in terms of mold cost, but as the number of molding increases, the mold warps, so it is necessary to renew the mold earlier. Moreover, since the mold is equipped with a heat medium passage, etc., it is difficult to remove the mold.

Problems to be Solved by the Invention In the case of these conventional two-stage compression molding methods, when the crystalline resin solidifies after melting, an extremely large volume change occurs mainly due to crystallization, and heat conductivity is extremely low. In order to give the molded product the desired physical properties, the mold for the second step must be capable of heating and cooling, and in order to increase the density of the molded product, high-temperature heating such as 200 to 220°C is required. and about 100
Molding equipment with a complex mechanism and high durability that can withstand high pressures of kg/cm ² is required. Furthermore, the preformed product obtained in the first step is easily disintegrated and difficult to handle, and the molded product obtained in the second step is not easy to remove from the mold.

This invention was made with the intention of solving all of the problems mentioned above.

Means for Solving the Problems The first molding method according to the present invention is to form a preformed product made of ultra-high molecular weight polyethylene with a sintered surface portion or ultra-high molecular weight polyethylene containing a filler. The method is characterized in that a preformed product is pressurized and heated at a temperature that plasticizes the preformed product under a pressure of cm ² or higher to obtain a molded product of a required thickness, and then this is cooled to room temperature under pressure.

Further, in the molding method according to the second invention, a compound powder made of ultra-high-density polyethylene is pressurized and heated at a temperature of 140° C. or higher under a pressure of 5 kg/cm ² or higher to form a preform in which the surface portion is sintered. The first step is to obtain the product and then cool it to room temperature under pressure, and the preformed product is
Under a pressure of Kg/cm ² or more, the preformed product is heated under pressure at a temperature that plasticizes it to obtain a molded product of the required thickness.
This is a method for molding ultra-high molecular weight polyethylene, which comprises a second step of cooling the polyethylene to room temperature under pressure.

Furthermore, in the molding method according to the third invention, as a modified method of the first step, the same compound powder is heated at 180°C under normal pressure.
By heating at the above temperature, a preformed product whose surface portion is sintered is obtained.

In the first step, the formulation made of ultra-high molecular weight polyethylene may contain inorganic fillers such as glass fibers, carbon fibers, glass beads, graphite, molybdenum powder, and carbon black. The formulation also includes conventional antioxidants, as appropriate.

In the pressure heating method of the first step, in order to obtain a preformed product with a sintered surface portion, the pressure must be 5 Kg/cm ² or higher and the temperature must be 140° C. or higher. If the pressure is less than 5 Kg/cm ² , the density of the preformed product will be too low, resulting in poor heat transfer, and there is a risk that the preformed product will break.
However, even if the pressure is increased significantly, for example to 100 kg/cm ² , a particularly excellent preformed product cannot be obtained. Considering equipment costs, etc., 5 to 50 kg/cm ² is suitable. Furthermore, if the temperature is less than 140°C, sintering does not occur. However, if the temperature is too high, the resin will have a low molecular weight, so a temperature of 140 to 160°C is preferable. The pressure heating time and cooling time are determined by the thickness of the preform, the structure of the molding device, the pressure, and the temperature.

In this way, in the first step, a preformed product whose surface portion is sintered is obtained. This material does not have cracks or cracks and does not easily disintegrate, and is extremely easy to handle, transport, stack, etc.

A typical example of the molding apparatus used in the first step is shown in FIG.

The mold 1 includes a substrate 2, a bottom plate 3 placed on the substrate 2, a surrounding frame 4 placed around the bottom plate 3, and a top plate 5 for pressing resin powder placed on the upper part of the surrounding frame 4. and,
It consists of a cushion material 6 arranged on a top plate 5.

The substrate 2 has an upright frame 7 around it, which prevents resin powder leaking from the mold from scattering. In the case of a molded product of 1000 mm x 2000 mm x 20 mm, the bottom plate 3 and top plate 5 are both 4 mm thick.
It has a mirror finish. The effective area of the surrounding frame 4 is 1000 mm x 2000 mm, and the height is 60 mm. It is higher than the bulk of the compound powder charged in the surrounding frame 4. The top plate 5 and cushion material 6 are sized to fit inside the surrounding frame 4. The cushion material 6 has a thick plate shape, is made of heat-resistant rubber reinforced with glass fiber, and has a thickness of 18 mm.

The mold 1 of the preformed product in the first step having such a structure is heated and pressurized by a multistage hot press machine 8. The press machine 8 consists of upper and lower heating plates 9 and 10 equipped with a pressurizing mechanism, and a plurality of intermediate heating plates 11 provided between these. It has a plurality of heat medium passages 12 through which the heat medium passes, and is configured to be able to heat or cool at the appropriate time.

A variant of the first step, atmospheric heating, is usually carried out in an oven. In this case, the temperature is limited to 180° C. or higher in order to obtain a preformed product whose surface portion is sintered. If the temperature is too high, the resin will become lower in molecular weight, so
200°C is preferred. The heating time is again determined by the thickness of the preform, the construction of the forming equipment, pressure and temperature. The preformed product after heating is allowed to cool to room temperature.

The reason why the pressure is limited to 5 kg/cm ² or more in the second step is that if it is less than 5 kg/cm ² , the density of the preformed product will be increased to improve heat conductivity, and the existing air will be expelled, resulting in a plastic preform. This is because the product cannot be compressed to a specified thickness. However, even if the pressure is increased significantly, for example to 100 kg/cm ² , a particularly excellent preformed product cannot be obtained. Considering equipment costs, etc., 5 to 20 kg/cm ² is suitable. Although the temperature varies in relation to the pressure, it is the temperature that plasticizes the preform under a certain pressure, and is usually 160°C or higher. However, if the temperature is too high, the resin will have a low molecular weight, so 160 to 220°C is preferable. The pressure during cooling is
In order to follow the volume change of the resin, the amount is increased from that during heating, and is usually 10 to 40 kg/cm ² . The pressure heating time and cooling time are also determined by the thickness of the preform, the structure of the molding equipment, pressure and temperature.

By pressurizing and heating the preformed product in this way,
The remaining air is expelled and the desired molded article is obtained.

A typical example of the molding apparatus used in the second step is shown in FIG.

The mold 21 includes a frame substrate 22 having an upright stopper frame 27 on the periphery, a bottom plate 23 placed on the substrate 22, and a molding thickness regulating enclosure placed on the periphery of the bottom plate 23. It consists of a frame 24 and a top plate 25 for pressing the preformed product placed above the surrounding frame 24.

Thin cushion materials 26 and 28 made of heat-resistant rubber reinforced with glass fibers are disposed below the bottom plate 23 and above the top plate 25, respectively. However, these cushion materials 26 and 28 are not necessarily essential. Both the bottom plate 23 and the top plate 25 have a thickness of 4 mm, and also have a mirror finish. The area of the preformed product is 1000mm×
When the thickness of the molded product is 2000 mm, the height of the surrounding frame 24 for regulating the molded thickness is 20 mm. Same frame 2
4 consists of a pair of long straight rods 29 and a pair of short straight rods 30 that are independent of each other, and each straight rod has an aluminum main body 31 with a square cross section (20 mm x 20 mm).
And a 10mm thick insulation layer 3 attached to the inner surface of this
It consists of 2. The heat insulating layer 32 is made of ethylene propylene terpolymer rubber reinforced with glass fibers. The material of the heat insulating layer 32 may be fluororubber, silicone rubber, urethane rubber, asbestos, etc. in addition to the above-mentioned rubbers. The four straight rods constituting the surrounding frame 24 are in contact with each side of the preformed product, and have a small gap of 5 to 10 mm between them and the stopper frame 27, so that the preformed product can be pressurized and heated. Due to the outward bulge caused by this, it can be moved up to the stop frame 27 and stopped there. In addition, each straight bar body may have a required small gap between it and the preformed product, and may be arranged so as to be in contact with the inner surface of the stop frame 27.

The mold 21 for the synthetic resin plate product in the second step having such a structure is also heated and pressed by the multistage hot press machine 8. The structure of this press machine 8 is as described above.

Effects of the invention Since this invention is configured as described above,
The following effects are produced.

a In the first step, the pressure is 5Kg/cm2 ^or more and the temperature is 140
Since the blended powder is heated under pressure at temperatures above can be extremely low compared to the conventional method explained at the beginning, and therefore has a great advantage in terms of equipment costs. Therefore, the mold for the first step can be made compact, and the productivity of preformed products can be improved by using a multi-stage hot press.

b As a modification of the first step, when heating the compound at 180°C or higher at normal pressure, a pressurizing mechanism is not required, so a heating device such as an ordinary oven can be used as is, reducing equipment costs. It has great advantages in terms of.

c In the second step, the preformed product is heated under pressure at a pressure of 5 kg/cm ² or more and at a temperature that plasticizes the preformed product, so both the pressure and temperature can be lower than in the conventional method. It has great advantages in terms of heat costs and equipment costs.

Example Next, embodiments of the invention will be described.

Example 1 In the molding apparatus shown in Fig. 1, 1000 mm x 2000
When obtaining a molded product of mm x 20 mm, the effective area is 1000 mm x
Inside the frame 4, which is 2000 mm long and 60 mm high, ultra-high molecular weight polyethylene (Hoechst product name Hostalen) is used.
GUR412) and a commercially available antioxidant, 0.1 PHR, to a height of 47 mm. Pressure 10
Kg/cm ² and a temperature of 160° C. for 30 minutes, followed by cooling at the same pressure for 30 minutes. In this way, a preformed product with a thickness of 34 mm with a sintered surface portion was obtained.

Then, the preformed product is taken out from the mold 1 and placed in the second mold.
Transfer to the molding equipment shown in the figure, and heat at a pressure of 5Kg/ ^cm2 .
It was heated under pressure at 180°C for 55 minutes. In this state, the molded product protruded 1 to 2 mm from the surrounding frame 24 having a height of 20 mm. The pressure is then reduced while the temperature drops to 150-120°C.
The weight was gradually increased to 20Kg/ ^cm2 . In this state, the height of the molded product was the same as that of the surrounding frame 24. The molded product was then cooled to room temperature under a pressure of 20 kg/cm ² . In this way, a plate-shaped molded product with a thickness of 20 mm was obtained. When this molded product was cut vertically and horizontally and the interior was examined, no air bubbles or nests were found. The molding was uniform throughout.
Furthermore, there were no spot-like sink marks or warpage due to depression on the surface, and no discoloration due to burning was observed.

Examples 2-7 The operation of Example 1 was repeated using a formulation in which glass fibers, carbon fibers, glass beads, graphite, molybdenum powder, and carbon black were each added separately at 10% by weight based on the resin. .

The obtained molded article had almost the same physical properties as those obtained in Example 1.

[Brief explanation of drawings]

1A and 1B are vertical cross-sectional views showing a typical example of a molding apparatus used in the first step of the present invention, FIG. B is a vertical sectional view showing a typical example of a typical molding device used in the second step, C is a view taken along line B-B on A in the same figure, and FIG. FIG. 2 is a longitudinal sectional view showing a conventional molding device. 22... Board, 23... Bottom plate, 24... Surrounding frame, 25...
Top plate, 27... Stop frame, 29, 30... Straight bar body, 32...
insulation layer.

Claims (1)

[Claims] 1. A preformed product made of ultrahigh molecular weight polyethylene with a sintered surface portion or ultrahigh molecular weight polyethylene containing a filler is plasticized under a pressure of 5 kg/cm ² or more. A method for molding ultra-high molecular weight polyethylene, which is characterized by heating under pressure to obtain a molded product of a required thickness at a temperature that causes it to oxidize, and then cooling the molded product under pressure to room temperature. 2 A blend powder made of ultra-high molecular weight polyethylene or ultra-high molecular weight polyethylene containing filler,
The first step is to pressurize and heat at a temperature of 140°C or higher under a pressure of 5 kg/cm ² or higher to obtain a preformed product with a sintered surface, and then cool it to room temperature under pressure, and preforming. The second step is to heat the product under pressure of 5 kg/cm ² or more at a temperature that plasticizes the preformed product to obtain a molded product of the required thickness, and then cool it to room temperature under pressure. A method for molding ultra-high molecular weight polyethylene. 3 A blend powder made of ultra-high molecular weight polyethylene or ultra-high molecular weight polyethylene containing filler,
The first step is to obtain a preformed product with a sintered surface portion by heating at a temperature of 180°C or higher under normal pressure, and the preformed product is plasticized under a pressure of 5Kg/cm ² or higher. A second step is to heat the product under pressure and heat to obtain a molded product of the required thickness, and then cool it to room temperature under pressure.
A method of molding ultra-high molecular weight polyethylene consisting of steps.