JP2002331537A - Centrifugal molding machine and centrifugal molding method - Google Patents

Abstract

(57) [Problem] To improve the efficiency of production work by facilitating attachment and detachment of a drive shaft and a mold and shortening the occupation time of a centrifugal molding machine per molded product. SOLUTION: An outlet 2 provided in a joining member 16 is provided with a mold 13 having an inner diameter R2 smaller than an outer diameter R1 of a mold fitting portion 17 of a cylindrical joining member 16 provided at an end of a drive shaft 12.
After inserting the gas into the mold fitting portion 17 while allowing the gas to flow from the inner side toward the outer peripheral surface side, the outflow of the gas is stopped,
The mold 13 is fitted in the mold fitting portion 17 and attached to the drive shaft 12. The resin material is injected into the mold 13 rotated by the drive shaft 12, and subjected to centrifugal molding while heating. Then, the gas is caused to flow out to the outlet 22 and the mold 13 is moved to the drive shaft 12.
, And heat-treat the resin molded product in the removed mold 13 in a separate process.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a centrifugal molding machine and a centrifugal molding method, and more particularly to a centrifugal molding machine and a centrifugal molding method which facilitate the attachment and detachment of a mold and a drive shaft, improve work efficiency, and improve centrifugal molding productivity. It is.

[0002]

2. Description of the Related Art With the development of color printers and the like at higher speeds, transfer belts having a high elastic modulus with little change in belt speed are required. In order to meet these required performances, a seamless belt manufactured by a centrifugal molding method is mainly used as a belt for the above application, and various manufacturing methods and manufacturing apparatuses have been proposed.

For example, in JP-A-10-58469,
For molding resin products that require heat treatment after centrifugal molding,
After the centrifugal molding, the mold can be easily removed from the shaft (drive shaft) and heat-treated in a separate oven. Therefore, a centrifugal molding machine and a centrifugal molding method capable of shortening the molding cycle have been proposed.

[0004]

However, according to the centrifugal molding machine and the centrifugal molding method disclosed in Japanese Patent Application Laid-Open No. H10-58469,
The mechanism for centering the shaft is complicated, and it is difficult to secure the run-out accuracy of the inner surface of the mold, and it is difficult to manufacture the device with high accuracy. Further, since the weight of the mold is heavy, it is not suitable for high-speed rotation, and it takes time to replace the mold. Further, there is a problem that the cost required for manufacturing the device is significantly increased in order to maintain the accuracy, and as a result, the product cannot be manufactured at low cost.

Further, the conventional seamless belt is manufactured by centrifugal molding using a polyimide resin or the like, and has a problem that the production cost is high although the performance is excellent. With the recent reduction in the price of electrophotographic equipment,
Cost reduction of the transfer belt is desired, and development of more efficient manufacturing methods and manufacturing apparatuses is required.

One of the major factors that increase the manufacturing cost by centrifugal molding is that the occupation time of the centrifugal molding machine per molded product is long. Therefore, in order to mass-produce the belt, a large number of centrifugal molding machines are required, and the equipment cost increases. That is, in order to reduce the cost of the seamless belt by centrifugal molding, it is necessary to shorten the occupation time of the centrifugal molding machine per molded product.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and it has been made easy to attach and detach a mold to and from a shaft (drive shaft) and to shorten the occupation time of a centrifugal molding machine per molded product. The task is to improve the efficiency of production work.

[0008]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a drive shaft provided with rotation by a motor, and a cylindrical mold into which a resin material is injected and which rotates through the drive shaft. In the centrifugal molding machine provided with, at the tip of the drive shaft, provided a cylindrical joining member having a mold fitting portion for fitting and holding the mold, the outer diameter of the mold fitting portion, The joint member is set to be larger than the inner diameter of the mold, and the joining member is provided with a blowout port for allowing gas to flow from the inside of the joining member toward the outer peripheral surface, and the drive shaft and the mold are attached and detached. A centrifugal molding machine having a flexible configuration is provided.

With the above configuration, when the mold is fitted,
Alternatively, when the mold is detached, the inner diameter of the mold can be temporarily increased from the outer diameter of the mold fitting portion simply by letting a gas such as air flow from the outlet toward the outer peripheral surface side of the joining member. The attachment and detachment of the drive shaft and the mold can be facilitated. Also, after the mold is inserted into the predetermined position, the inner diameter of the mold can be returned to the original state only by a simple operation of stopping the outflow of air, and the drive shaft and the mold are positioned at the predetermined position. It can be firmly fitted. In this manner, the easy expansion and contraction and the elasticity of the mold material make it possible to obtain easy detachability and strong bonding force. Therefore, since the attaching / detaching operation of the mold is very simple and can be performed in a short time, the occupation time of the centrifugal molding machine per one seamless molded article to be molded can be shortened, and the molding cycle can be shortened. it can.

The drive shaft and the mold are centered on the drive shaft only by fitting the cylindrical mold into the mold fitting portion of the cylindrical joining member provided at the tip of the drive shaft. It is good to make it the structure which is easily connected in the state where it was set. Thereby, the centering mechanism is easy, and the workability can be improved,
Even when rotated, the shaft does not run out with respect to the axis of the drive shaft.

The thickness of the mold is 0.01 mm or more and 3 mm
The thickness is preferably 0.05 mm or more and 1 mm or less. The mold can be significantly lighter than the mold of the conventional centrifugal molding machine, and the attachment and detachment of the mold can be further facilitated. Further, since the thickness is small, the material cost can be reduced, and the manufacturing cost can be reduced. The reason for the above range is that the thickness of the mold is 0.01 m
When the thickness is smaller than m, there is a problem that distortion occurs during rotation of the mold and the thickness of the obtained seamless belt becomes large. On the other hand, when the thickness of the mold is larger than 3 mm, the mold is driven by the drive shaft. This is because it is difficult to join the mold and the mold becomes heavy, and the joining method of the present invention cannot hold the mold when the mold is rotated.

The elastic modulus of the mold material is 50 × 10¹⁰dyn
・ Cm^-2More than 300 × 10¹⁰dyn · cm^-2Less than
It is preferred that The above range is for mold
The elastic modulus of the material is 50 × 10¹⁰dyn · cm ^-2Than
If it is small, distortion will occur when the mold rotates, resulting in a seam
The problem that the variation of the thickness of the wrestling belt increases
On the other hand, the elastic modulus is 300 × 10¹⁰dy
ncm^-2If it is larger, it is difficult to join the mold to the drive shaft.
It is because it becomes. Preferred materials include Fe, Cu,
Al, Ni, Mg, Ti, brass, duralumin, stainless steel
And the like. The material of the mold is flexible.
Is preferred.

The outer diameter R1 of the mold fitting portion is set to be larger than the inner diameter R2 of the mold and varies depending on the material, but preferably satisfies the following formula. 0.001 ≦
100 × (R1-R2) /R1≦2.0, preferably 0.01 ≦ 100 × (R1-R2) /
It is preferred that R1 ≦ 1.0, and more preferably, R1 ≦ 1.0.
It is preferable that the relation of 05 ≦ 100 × (R1−R2) /R1≦0.5 is satisfied. The above range is defined as the above 100 × (R1
If the value of -R2) / R1 is less than 0.001, a sufficient joining force between the drive shaft and the mold cannot be obtained, while
If it is larger than 2.0, it becomes difficult to insert the mold.

[0014] It is preferable that the outlet be provided uniformly in both the circumferential direction and the axial direction of the drive shaft over the outer periphery of the joining member. By arranging the outlets in a well-balanced and uniform manner, the inner diameter of the mold can be evenly expanded at the time of gas outflow, and the attachment and detachment of the mold can be further facilitated. The number of outlets is not particularly limited, but is preferably 4 or more, and more preferably 8 or more, from the viewpoint of detachability. Further, the size and shape of the outlet are not particularly limited as long as the mold can be easily attached and detached.

[0015] The pressure of the gas flowing out of the outlet is preferably 0.5 kgf / cm ² or more 6.0 kgf / cm ² or less. The reason for the above range is that if the pressure is smaller than 0.5 kgf / cm ² , the inner diameter of the mold cannot be sufficiently expanded. On the other hand, if the pressure is larger than 6.0 kgf / cm ² , the mold strength is reduced. This is because there is a possibility that it will have an effect.

According to the present invention, there is provided a centrifugal molding method for performing centrifugal molding while rotating a cylindrical mold into which a resin material is injected by using a drive shaft rotated by a motor. A mold having an inner diameter smaller than the outer diameter of the mold fitting portion of the cylindrical joining member provided at the tip of the drive shaft, using a mold detachably attached to the drive shaft, and an outlet provided in the joining member. After the gas is inserted into the mold fitting portion while allowing the gas to flow from the inner side toward the outer peripheral surface side, the outflow of the gas is stopped, and the mold is fitted to the mold fitting portion and attached to the drive shaft. A resin material is poured into a mold rotated by a drive shaft, and centrifugal molding is performed while heating. After the centrifugal molding, gas is discharged to the outlet, and the mold is removed from the drive shaft. Heat treatment of the resin molded product in the mold in a separate process It provides a centrifugal molding method characterized.

As described above, the mold can be detached simply by taking gas in and out from the outlet provided in the joining member, so that the mold can be easily replaced in a short time, and the molded product can be formed. The occupation time of one centrifugal molding machine can be shortened. In addition, since the mold after centrifugal molding can be removed together with the resin molded product and subjected to heat treatment in a separate step, after molding one belt, another mold is attached to the drive shaft, so that the next A belt can be formed. Therefore, the efficiency of the production operation can be improved.

As the resin material, it is preferable to use a thermosetting resin having a glass transition temperature of 150 ° C. or more and 280 ° C. or less. Thereby, a resin molded product having a high elastic modulus can be obtained. When the glass transition temperature is lower than 150 ° C., there is a problem that the tensile elastic modulus of the obtained resin molded product such as a seamless belt becomes low,
On the other hand, if the glass transition temperature is higher than 280, non-uniform peeling from the mold occurs at the time of heat treatment, and there is a problem that dimensional accuracy of a resin molded product such as a seamless belt is deteriorated. Among the thermosetting resins, a polyamideimide resin is particularly preferable in terms of high elastic modulus and workability.
In addition, a polyimide resin, a polyurethane (urea) resin, an epoxy resin, or the like can be used.

Preferably, the mold is made of a thin, flexible material. By making it thin, the weight of the mold can be reduced, and the mold can be easily handled.
Workability is further improved. Furthermore, since it is lightweight, the mold can be rotated at a high speed, and the moldability of the resin molded product can be improved.

The resin material is injected into the mold rotated by the drive shaft, and centrifugal molding is performed while heating. The heating temperature during centrifugal molding is preferably 100 ° C. or more and 140 ° C. or less. Is preferably from 5 minutes to 60 minutes. The reason why the heating temperature is set in the above range is that if the heating temperature is lower than 100 ° C., the molding is insufficient depending on the resin material. On the other hand, if the heating temperature is higher than 140 ° C., it becomes higher than the boiling point of the solvent contained in the resin. Therefore, there is a problem that the solvent boils and bubbles are generated in the resin molded product. The heating time is set in the above range because if the heating time is shorter than 5 minutes, the resin cannot be rotated until the fluidity of the resin is lost, and the moldability of the resin deteriorates. When the mold is removed from the centrifugal molding machine, the resin may be partially peeled off from the mold, and this peeled part causes uneven shrinkage during the subsequent heat treatment process, which significantly deteriorates the dimensional accuracy of the product. Because there is.

The temperature of the mold is preferably controlled by a far-infrared heater or a hot air generator, and the temperature is preferably controlled by measuring the surface of the mold with a non-contact thermometer.

After the above-mentioned centrifugal molding, a gas is caused to flow out to the above-mentioned outlet, the mold is removed from the drive shaft, and the resin molded product in the removed mold is subjected to heat treatment in another step. The heat treatment is preferably performed in an oven or the like together with the mold. The heat treatment temperature is preferably set to 100 ° C. or more and 300 ° C. or less. Specifically, in order to prevent the generation of bubbles due to the solvent during heating and to obtain good surface smoothness, it is usually preferable to raise the temperature slowly, for example, to raise the temperature from 100 ° C. to 250 ° over 3 hours. It is preferable to heat or increase the temperature stepwise at 150 ° C. for 60 minutes, 200 ° C. for 60 minutes, and 250 ° C. for 60 minutes.

After the heat treatment, the mold is preferably cooled together with the resin molded product, and after cooling, the resin molded product is preferably removed from the mold. As a result, the resin molded product can be easily separated from the mold, and the molded product can be taken out in a good state without affecting the dimensional accuracy and performance of the resin molded product.

It is preferable that the inner surface of the mold is subjected to a release treatment. Thereby, the molded product can be easily peeled off from the mold. As the release agent used for the release treatment, a fluorine-based or silicone-based release agent is preferable, and a baking type is particularly preferable.

The rotational speed of the mold is not less than 1000 rpm and 30
It is preferably at most 00 rpm. The reason for setting the above range is that if the rotational speed is less than 1000 rpm, a molded product may not be produced with high accuracy depending on the resin material. On the other hand, if the rotational speed is greater than 3000 rpm, mechanical accuracy and vibration may be reduced. This is because it may be difficult in some cases.

In the centrifugal molding method of the present invention, the centrifugal molding machine of the present invention can be suitably used, and the mounting and dismounting of the mold can be performed extremely smoothly, so that the working time is reduced and the production efficiency is improved. And a seamless belt can be manufactured at low cost.

[0027]

Embodiments of the present invention will be described below with reference to the drawings. 1 and 2 show a centrifugal molding machine of the present invention. The centrifugal molding machine 10 includes a drive shaft 12 to which rotation is given by a motor 11, and a cylindrical mold 13 into which a resin material is injected and which rotates through the drive shaft 12. Cover 14 and frame 1
5 is provided.

The distal end 12a of the drive shaft 12 arranged in the frame 15 is made to enter the heat insulating cover 14, and the mold fitting portion of the cylindrical joining member 16 provided at the distal end 12a of the drive shaft 12 that has entered. At 17, the mold 13 is fitted and held. The thickness t of the mold 13 is 0.12 mm.
Is made of Ni and the elastic modulus is 201 × 10 ¹⁰ dyn.
Cm- ² .

In the heat insulating cover 14, a far infrared heater 18 for heating a mold is provided. In addition, an intake port 19 for sending hot air from the hot air generator to the mold 13 in the heat insulating cover 14 and an exhaust port 20 for discharging air in the heat insulating cover 14 are provided on opposing surfaces. Mold 13
Is controlled by measuring the surface of the mold with a non-contact thermometer 21.

As shown in FIGS. 2A and 2B, the outer diameter R1 of the mold fitting section 17 is 168.54 mm, the inner diameter R2 of the mold 13 is 168.39 mm, and the mold fitting section 17 is formed. Is set to be larger than the inner diameter R2 of the mold 13, and 100 × (R1−R2) /R1=0.089.

The joining member 16 is provided with an outlet 22 for allowing gas to flow from the inside of the joining member 16 toward the outer peripheral surface. The outlet 22 is connected to the joining member 1.
6 are provided at equal intervals in the circumferential direction over the outer peripheral surface 16a of the nozzle 6 and the cross-sectional shape of the outlet 22 is circular. When the mold 13 is attached / detached, air is blown in / out from the outlet 22 to adjust the fitting state between the mold fitting portion 17 and the mold 13 so that the drive shaft 12 and the mold 13 can be freely attached / detached. And Further, the distal end portion 16 of the joining member 16
b has a configuration in which the diameter is reduced toward the mold 13 and the insertion of the cylinder 13 is easy.

Hereinafter, the centrifugal molding method of the present invention using the centrifugal molding machine 10 will be described. As shown in FIGS. 3A, 3B, and 3C, first, an inner diameter R2 having a diameter smaller than the outer diameter R1 of the mold fitting portion 17 of the cylindrical joining member 16 provided at the tip of the drive shaft 12. The inner diameter of the mold 13 is adjusted by moving the inner diameter of the mold 13 into the mold fitting portion 17 while allowing the gas to flow from the inside of the outlet 22 provided in the joining member 16 toward the outer peripheral surface side (in the direction of the arrow in the figure). Is temporarily expanded from the outer diameter of the mold and inserted into the mold fitting portion 17.

After inserting the mold 13 into the mold fitting portion 17,
Stop the outflow of gas, return the inner diameter of the mold 13 to the original state,
The mold 13 is fitted in the mold fitting portion 17 by the tightening force, and the mold 13 and the drive shaft 12 are connected.

Next, a resin material is injected into the mold 13 which has been subjected to a surface release treatment in advance on the inner peripheral surface 13a of the mold with a silicone-based release agent, and a far-infrared heater 18 and hot air generated from hot air are generated. While heating the mold 13 by the
The centrifugal molding is performed while rotating the mold 13 through 2.
The temperature of the mold 13 is controlled by measuring the surface temperature of the mold 13 with a non-contact thermometer 21.

After the centrifugal molding, the gas is allowed to flow out again from the inside of the outlet 22 toward the outer peripheral surface, and the inner diameter R2 of the mold 13 is temporarily expanded from the outer diameter R1 of the mold fitting portion 17, and When the mold 13 and the mold fitting portion 17 are disengaged, the mold 13
Is removed from the drive shaft 12.

The resin molded product in the removed mold 13 is subjected to a heat treatment in another step. After the heat treatment, the mold 13 is cooled together with the resin molded product, and after cooling, the resin molded product is removed from the mold 13.

According to the above-mentioned method, since the mold and the drive shaft can be easily attached and detached, the exchange of the mold becomes smooth, and after molding the resin molded product, the process can immediately proceed to the next centrifugal molding.
The production efficiency of centrifugal molding can be improved.

In the above embodiment, the number of outlets provided in the joining member 16 is circular and eight in number. However, as shown in FIG. Sixteen outlets 22 'can be provided evenly in the axial direction. In addition, as shown in FIG. 4B, the cross-sectional shape of the outlet 22 ″ may be elliptical. Further, as shown in FIG. The outlet 22 "'can be provided in a reduced diameter portion reduced in diameter toward the mold side.
The shape, size, and number of the outlets are not limited to the above-described embodiments, but may be various shapes, sizes, and numbers, and may be various combinations according to a mold to be fitted. Can be.

Hereinafter, examples of the seamless belt produced by the centrifugal molding method of the present invention using the centrifugal molding machine of the first embodiment will be described in detail.

(Example 1) A polyamideimide resin (glass transition temperature: 206 ° C) in which carbon black was dispersed as a resin material was poured into a mold (width: 450 mm) and centrifuged at 1500 rpm and 130 ° C for 30 minutes.
After stopping the rotation of the centrifugal molding machine and removing the mold from the drive shaft of the centrifugal molding machine, the mold is put into an oven and heated at 150 ° C. for 60 minutes.
60 minutes at 200 ° C and then 60 minutes at 250 ° C.
Heated for a minute. The mold was taken out of the oven, the mold was cooled, and the molded product was removed from the mold. The belt contracted due to cooling, so that the belt was released from the mold and could be easily removed. The air pressure was 3.0 kgf / cm ² .

The carbon black-dispersed polyamide-imide resin was prepared by a conventionally known method. Carbon black can be obtained by using a solvent (N
-Methyl-2-pyrrolidrin) and the polyamide imide resin were mixed and dispersed again with a bead mill.

As a production example of a seamless belt produced by a conventional centrifugal molding machine, a belt was produced under the following conditions of Comparative Example 1.

Comparative Example 1 A centrifugal molding machine having a structure different from that of a mold and a drive shaft was used. The thickness of the mold is 2 cm, and as shown in FIG. 5, the mold 1 and the drive shaft 2 are joined by connecting the tapered projection 1 a provided on the mold 1 to the tapered groove 2 a of the drive shaft 2. By being pulled toward, the protrusion 1a and the groove 2a were joined. After centrifugal molding under the same conditions as in Example 1, the rotation speed was set to 500 rpm,
Heating was performed in a centrifugal molding machine at 200 ° C. for 60 minutes and 250 ° C. for 60 minutes. After cooling, the belt was released from the mold. The other conditions such as the resin material are the same as those in Example 1.
The same as above.

Regarding the occupation time of the centrifugal molding machines of Example 1 and Comparative Example 1, the manufacturing cost of the apparatus, and the manufacturing cost of the mold,
It is shown in Table 1 below. In addition, about the cost, the comparative example 1
Represents the cost of the first embodiment as an index when is set to 100.

[0045]

[Table 1]

In the first embodiment, since the thickness of the mold is small and the weight of the mold is light, a person can hold the mold in his / her hand and can attach and detach the mold and the mold fitting portion. The exchange operation was very smooth, and the occupation time of the centrifugal molding machine required for producing one belt could be extremely reduced to 30 minutes. Further, since the thickness of the mold is thin, the material cost of the mold can be reduced, and the manufacturing cost of the entire centrifugal molding machine can be reduced. On the other hand, in Comparative Example 1, since the weight of the mold was large, it took time and labor to replace the mold.
Since the heat treatment step is performed in the centrifugal molding machine, the occupation time of the centrifugal molding machine required for producing one belt is very long, and the working efficiency is poor. Due to the material cost of the mold and the difference in the mounting structure between the mold and the drive shaft, the cost of the mold and the device was also higher than in Example 1.

[0047]

As is apparent from the above description, according to the present invention, the mold and the drive shaft can be easily attached and detached only by taking in and out of air. The occupation time can be shortened, and the efficiency of the production operation can be improved. It is only necessary to provide a blow-out port for taking in and out of air, and only to let out air. No complicated joining structure is required. In addition, since the thickness of the mold is reduced, the mold and the centrifugal molding machine can be manufactured at low cost. Therefore, a resin molded product such as a seamless belt can be produced at low cost.

[Brief description of the drawings]

FIG. 1 is a schematic view showing a centrifugal molding machine of the present invention.

FIGS. 2A and 2B are diagrams showing details of a mold and a mold fitting portion.

FIGS. 3A, 3B, and 3C are diagrams illustrating a method of fitting a mold to a mold fitting portion.

FIGS. 4A, 4B, and 4C are diagrams showing other forms of the outlet provided in the joining member.

FIG. 5 is a diagram showing a state in which a mold and a drive shaft of a conventional centrifugal molding machine are attached.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Centrifugal molding machine 11 Motor 12 Drive shaft 13 Die 16 Joining member 17 Die fitting part 22 Outlet

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Jun Nishibayashi 3-6-9, Wakihama-cho, Chuo-ku, Kobe-shi, Hyogo Sumitomo Rubber Industries, Ltd. F-term (reference) 4F205 AA36 AA40 AG16 AJ01 GA02 GB01 GF01 GN01 GN13 GN28 GW05

Claims (5)

[Claims] 1. A centrifugal molding machine having a drive shaft rotated by a motor and a cylindrical mold into which a resin material is injected and rotated via the drive shaft. Providing a cylindrical joining member having a mold fitting portion for fitting and holding the mold, wherein the outer diameter of the mold fitting portion is set to be larger than the inner diameter of the mold, and the joining member A centrifugal molding machine characterized in that an outlet for discharging gas from the inside of the joining member toward the outer peripheral surface is provided, and the drive shaft and the mold are detachable. 2. The thickness of the mold is not less than 0.01 mm and not more than 3 m.
m or less, and the elastic modulus of the mold material is 50 × 10 ¹⁰ dy
The centrifugal molding machine according to claim 1, wherein the density is not less than n · cm ^{−2 and not} more than 300 × 10 ¹⁰ dyn · cm ⁻² . 3. A centrifugal molding method for performing centrifugal molding while rotating a cylindrical mold into which a resin material is injected by a drive shaft rotated by a motor. Using a mold, a mold having an inner diameter smaller than the outer diameter of the mold fitting portion of the cylindrical joining member provided at the tip of the drive shaft is taken from the inside of the outlet provided in the joining member. After the gas is inserted into the mold fitting portion while allowing the gas to flow toward the outer peripheral surface side, the outflow of the gas is stopped, the mold is fitted to the mold fitting portion, attached to the drive shaft, and rotated by the drive shaft. Inject the resin material into the mold that is
Centrifugal molding is performed while heating.After the centrifugal molding, gas is discharged to the outlet, the mold is removed from the drive shaft, and the resin molded product in the removed mold is subjected to heat treatment in a separate process. Centrifugal molding method. 4. The centrifugal molding method according to claim 3, wherein a thermosetting resin having a glass transition temperature of 150 ° C. or more and 280 ° C. or less is used as the resin material. 5. The centrifugal molding method according to claim 3, wherein the mold is made of a thin, flexible material.