JPH0242650B2 - - Google Patents

Description

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

As used herein, the term "ultra-high molecular weight polyethylene" refers to
2 million or more when measured by 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., and also has a low coefficient of friction. It is expected to have a wide range of uses because of its good water resistance, non-toxicity, and sound-absorbing properties. However, this type of polyethylene
Due to its high viscosity when heated and melted, it is difficult to adapt to normal extrusion molding or injection molding methods, and large molded products, with the exception of round bars and small molded products, are manufactured by compression molding.

Recently, as a compression molding method for this kind of synthetic resin,
A two-stage compression molding method is carried out, which consists of a first step of producing a preform and a second step of producing a plate product from the preform. Conventionally, a compression molding machine for performing a two-stage compression molding method has a structure shown in FIG. First, as shown in FIG.
2 and a lower female mold 53, and a plurality of intermediate molds 54 provided between these, the intermediate mold 54 has a female-shaped recess 55 in the upper part and a male-shaped convex part in the lower part. It has a section 56.

In this compression molding machine 51, a required amount of resin compound powder is charged into the female mold 53 and each recess 55.
Then, the female mold 53 and the male mold 52 are held under pressure from above and below at a pressure of about 100 kg/cm ² for 5 to 10 minutes at room temperature using a pressure mechanism 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. As shown in FIG.
However, each peripheral wall of the recess 65 of the female mold 63 and the intermediate mold 64, and the male mold 62 and the intermediate mold 64
A plurality of heat medium passages 67 and 68 through which steam or cold water passes are provided independently in the convex portion 66, so that heating or cooling can be carried out in a timely manner. In this compression molding machine 61, the female mold 6
3. Preheat the male mold 62 and intermediate mold 64 to 200 to 220°C.
The preformed product is inserted into the female mold 63 and the recess 65, and heated and pressurized at a pressure of 20 to 50 kg/cm ² to melt it completely. The pressurizing time is about 1 hour when the plate pressure is 20 mm. Next, cooling water is passed through the heating medium passage 68 to cool both the front and back surfaces to solidify the molten material and obtain a plate-shaped molded product. At this time, increase the pressure to 100Kg/cm ² . In addition, the sides of the molded product need to be cooled more slowly than the front and back surfaces, so when cooled to 150℃,
Steam is passed through the heat medium passage 67 to heat the side, and the rate of descent is slowed until the temperature reaches 120°C. 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 A plurality of intermediate heating plates 74 provided in between and a number of molds 7 arranged between each heating plate.
5 and more. 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 the cost of the mold, but as the number of molding increases, the mold warps, so it is necessary to renew the mold earlier. Further, since the mold is equipped with a heat medium passage, etc., it is difficult to remove the molded product.

Problems to be Solved by the Invention In the case of these conventional two-stage compression molding methods, when the crystalline resin melts and then solidifies, 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. 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 is therefore difficult to handle, and the molded product obtained in the second step is not easily removed from the mold.

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

Means for Solving the Problems The mold according to the present invention is used in the second step of the method for molding ultra-high molecular weight polyethylene, which will be described later.
a base plate 22 with a frame, a bottom plate 23 disposed on the base plate 22, a surrounding frame 24 for regulating molding thickness disposed on the peripheral edge of the bottom plate 23, and a frame 24 disposed above the surrounding frame 24. The surrounding frame 24 consists of a top plate 25 for pressing the preformed product, and the surrounding frame 24 has linear rods 29 and 30 each having at least an inner surface made of a heat insulating material and arranged independently on each side of the bottom plate 23. It is.

First, a method for molding ultra-high molecular weight polyethylene will be explained.

This molding method involves heating a compound powder made of ultra-high molecular weight polyethylene or ultra-high molecular weight polyethylene containing a filler at a temperature of 140°C or higher under a pressure of 5 kg/cm ² or higher, so that the surface portion is baked. The first step is to obtain a preformed product and then cool it to room temperature under pressure.The first step is to heat the preform under pressure at a temperature of 5 kg/cm ² or more at a temperature that plasticizes the preform. This is a method for molding ultra-high molecular weight polyethylene, which comprises a second step of obtaining a molded product of the required thickness and then cooling it to room temperature under pressure.

Further, as a modification of the first step, a preformed product having a sintered surface portion can also be obtained by heating the same compound powder at a temperature of 180° C. or higher at room temperature.

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 to a very high pressure, for example 100 kg/cm ² , particularly good preforms are not 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 above the surrounding frame. , and a cushion material 6 disposed on the top plate 5.

The substrate 2 has an upright frame 7 around its periphery, 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, which is higher than the bulk of the compound powder charged within 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 180
~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.

Embodiment Next, as an embodiment of the present invention, a typical example of a 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 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. In addition to the above-mentioned rubbers, the material of the heat insulating layer 32 may be fluororubber, silicone rubber, urethane rubber, asbestos, or the like. 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 board product in the second step having such a structure is also heated and pressed by the multistage hot press machine 8. The press machine 8 consists of upper and lower heating plates 9, 10 equipped with a pressurizing mechanism, and a plurality of intermediate heating plates 11 provided between these.
0 and 11 each have a plurality of heat medium passages 12 representing a heat medium such as steam or cold water, and are configured to be able to heat or cool at the appropriate time.

Example of use 1 In the molding equipment shown in Fig. 1, 1000mm x 2000
When obtaining a molded product of mm x 20 mm, the effective area is 1000 mm x
In a frame 4 with a distance of 2000 mm and a height of 60 mm, ultra-high molecular weight polyethylene (trade name: Hostalen manufactured by Hoechst) is placed.
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 4 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 inside was examined, no air bubbles or nests were observed, and 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 firing was observed.

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

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

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

(a) The mold according to the present invention includes a frame-equipped substrate 22 having an upright stopper frame 27 on the periphery, and the substrate 22.
2, a surrounding frame 24 for regulating molding thickness arranged on the peripheral edge of the bottom plate 23, and a top plate 25 for pressing the preformed product arranged above the surrounding frame 24. Since the molded product is made of 100%, it can be made compact, and the productivity of molded products can be improved by using a multi-stage hot press.

(b) Since the mold according to the present invention is a split mold having no heat medium passage, etc., it is advantageous in terms of mold cost, and the molded product can be easily removed from the mold.

(c) Further, in the surrounding frame 24 of the mold, at least the inner surface of the straight rods 29 and 30 are made of a heat insulating material, and the bottom plate 23
Since they are arranged independently on each side of the molded article, it is possible to keep the peripheral edge of the molded product warm after heating. Therefore, there is no need to provide a separate heating device for keeping the peripheral edge warm, and in this respect only equipment costs can be reduced.

[Brief explanation of the drawing]

Fig. 1 is a plan view showing the main parts of the molding device used in the first step of the present invention, and Fig. 2 A and B are vertical cross-sections showing a typical example of a typical molding device used in the second step of the same figure. Figure, C in the same figure is B-B on A in the same figure.
A view taken along the line, and FIGS. 3A, 3B, and 3C are longitudinal cross-sectional views showing a conventional molding apparatus. 22... Board, 23... Bottom plate, 24... Surrounding frame,
25... Top plate, 27... Stopping frame, 29, 30... Straight bar body, 32... Heat insulation layer.

Claims (1)

[Claims] 1. A frame board 22 having a raised stopper frame 27 around it, a bottom plate 23 disposed on the board 22,
It consists of a surrounding frame 24 for regulating the molding thickness arranged on the peripheral edge of the bottom plate 23 and a top plate 25 for pressing the preformed product arranged above the surrounding frame 24.
2 is a mold made of ultra-high molecular weight polyethylene, in which linear rods 29 and 30, at least the inner surfaces of which are made of a heat insulating material, are arranged independently on each side of the bottom plate 23.