The present invention relates to a synthetic resin composite for molding, and specifically relates to a synthetic resin composite that has a low mold shrinkage during molding and is suitable for producing complex, elaborate, and highly precise products molded from synthetic resin such as electrical appliances, auto parts, office automation equipment components, and precision equipment components. The present invention also relates to a method of molding and a molded product using the synthetic resin.
In general, synthetic resin is suitable for mass production due to its favorable moldability and it has been widely utilized in recent years as a molding material because it can be produced at low cost in a short time period, and it is possible to manufacture products with it that have a variety of properties. The molding methods of synthetic resin include extrusion molding, blow molding, and reaction molding; however, the most common method is injection molding, and the components produced by this method include electrical appliances, auto parts, office automation equipment components, and precision equipment components and the like.
In recent years there has been increasing demand for synthetic resin as a molding material in various fields; however, it is known that mold shrinkage occurs due to phase changes, crystallization, and thermal shrinkage with lowering temperature during the molding of synthetic resin. For that reason, the minimization of mold shrinkage by the blending of synthetic resin with various low shrinkage agents such as thermoplastic resin has been studied. When a thermoplastic resin, serving as a low shrinkage agent, is blended with a synthetic resin composite, low shrinkage can be achieved to a certain extent in the molded product; however, there is a problem in that the resulting heat resistance is not sufficient. Patent Document 1 discloses a low-shrinkage unsaturated polyester resin as a synthetic resin composite for molding with low shrinkage and good heat resistance. A molded product with low shrinkage during hardening and with high heat resistance can be produced from the resin in Patent Document 1 by blending an unsaturated polyester resin with A-B block copolymer.
Patent Document 1: Japanese Patent Application Publication No. H3-37257
The unsaturated polyester resin that is currently used for producing the above conventional resin mixture has problems such as its relatively low productivity, poor environment in the molding scene, and the difficulty in recycling the resin after use. Another problem is that the A-B block copolymer, an additive agent that serves as a low shrinkage agent, requires time and effort for preparation since it is produced from a raw material monomer through the processes of polymerization and purification.
The present invention is made in view of the above problems, and it is an object of the present invention to provide a synthetic resin composite for molding that is easy to produce, has a low mold shrinkage during molding, and is suitable for the manufacture of complex, elaborate, and highly precise products molded from synthetic resin.
In order to achieve the above object, it is preferable that the synthetic resin composite for the molding of the present invention be a blending of any synthetic resin with a substance that has an elasticity with a volume recovery of 15% or higher when the volume compaction due to pressure is 30% or higher (hereinafter described as an elastic substance).
It is also preferable that the elastic substance be an elastic graphite and that in the elastic graphite, the inner diameter of many porosities (hereinafter referred to as pores) formed by the carbon layer surface wall be substantially smaller than the molecules of the polymer compound of the synthetic resin.
In addition, it is preferable that the elastic substance constitute 5-70 weight percent of the synthetic resin composite.
The synthetic resin composite to be used for molding of the present invention can be easily produced by only kneading a particular fraction of synthetic resin and an elastic substance with a commercial kneader or the like, wherein the elastic substance has a volume recovery of 15% or more when the volume compaction by pressure is 30% or more. An example of a preferable substance with this property is elastic graphite, which has pores inside formed on the carbon layer surface wall whose inner diameter is substantially smaller than the molecules of the polymer compound of the above synthetic resin. By adding a certain pressure at molding, the elastic substance blends to the synthetic resin composite, providing a molded product with a low mold shrinkage factor and a high dimensional accuracy.
In the following description, details of the present invention are set forth with reference to the drawings.
<Synthetic Resin>
Both thermoplastic synthetic resin and thermosetting synthetic resin can be used in the present invention. For example, the thermoplastic synthetic resin includes polypropylene resin, polycarbonate resin, polyacetal resin, and others, and the thermosetting synthetic resin includes phenol resin, epoxy resin, urea resin, melamine resin, and others.
<Filler>
The filler to be used can be an elastic substance in which, when a load that has compressed the filler volume under pressure by 30% or more is removed, the filler recovers 15% or more of its volume.
Elastic graphite has its inside composed of a number of circular spaces divided by walls of carbon layer surface; in other words, it has a sponge-like structure. For that reason, elastic graphite is known to have a high compaction/recovery and elasticity limit. Therefore, it is preferable that the above elastic substance be elastic graphite and that the inner diameter of the pores formed by the carbon layer surface wall in the elastic graphite be substantially smaller than the molecules of polymer compound of the above synthetic resin. The elastic graphite that best satisfies the above conditions is the elastic graphite manufactured by SUPERIOR GRAPHITE Co. under the product name “DESULCO”. The inner diameter of the pores of DESULCO is approximately 19.2 nm.
When producing a synthetic resin composite for molding using synthetic resin with extremely large molecules, 5000 nm for example, Koa Sekiyu Kabushiki Kaisha, Mitsui Mining Company, Limited joint development elastic graphite (product name “ELFITE”) can be used as an elastic graphite satisfying the above conditions. The inner diameter of the pores in “ELFITE” is approximately 1000-5000 nm.
In addition, the synthetic resin composite may contain a known additive agent as needed. The additive agent may include, for example, an antioxidant, a fire retardant, an antistatic agent, a curing agent, a colorant, various anti-degradation agents, and/or a reinforcement, among other things.
It should be noted that the method of generating the synthetic resin composite (the method for adding the above filler and additive agents to the synthetic resin) is not limited to a particular method. For example, if the quantity of the above filler and additive agent to be blended is small, a method such as dry blending may be selected, whereas if the quantity of the filler and additive agent to be blended is large, a method such as melt kneading may be selected. It is also possible to use a filler and additive agent that have been dispersed and blended to a high concentration and then diluted before molding.
In the following description, further details of the present invention are set forth with reference to the embodiment described herein and comparative examples are given; however, these examples should not be construed in any way as limiting the invention.
[Measurement of Filler Volume Compaction/Recovery]
The measurement methods of the filler volume compaction/recovery used in the present examples are explained and comparative examples are given below with reference to
Used fillers; 1. elastic graphite (product name “DESULCO”) manufactured by SUPERIOR GRAPHITE Co.
2. graphite powder (product name “CPB”) manufactured by Nippon Graphite Industry Co., Ltd.
3. heavy calcium carbonate
4. Koa Sekiyu Kabushiki Kaisha, Mitsui Mining Company, Limited joint development elastic graphite (product name “ELFITE”)
Note that in the present example, the synthetic resin composite produced by mixing filler with synthetic resin was molded by using injection molding equipment (product name “IS45P” manufactured by Toshiba Machine CO., Ltd.). The measured load needed to be from 15.289 MPa to 196.1 MPa, which was the upper limit of the injection pressure of the injection molding equipment, or higher, and therefore, the measurement was performed by applying a load of 203.857 MPa, as shown in Tables 1-4, so that results were obtained that simulated the molding pressure conditions, which were able to be set by the injection molding equipment used in the examples subsequent to Example 1.
The results of the above Tables 1-4 are shown in
In the present example, the following synthetic resin and filler were used.
(1) Production of Synthetic Resin Composite for Molding
synthetic resin; polypropylene resin (product name “J-allomer EG110” manufactured by Japan Polyolefin Co., Ltd.)
filler; elastic graphite (product name “DESULCO”) manufactured by SUPERIOR GRAPHITE Co.
After crushing the filler so as to have a particle size of 0.1 mm or less and dry blending the synthetic resin and the filler, a kneader (product name “S-1 KRC” manufactured by Kurimoto, Ltd.) was used for kneading (with a barrel temperature of 240° C.) and the obtained composition was used after it had been crushed.
(2) Molding of Synthetic Resin for Molding
<Molding Conditions>
Using an injection molding machine (product name “IS45P” manufactured by Toshiba Machine Co., Ltd.), the produced composition was supplied to a mold via a nozzle under the above conditions and was molded by pressure molding, and then a tabular molded product (test specimen) was obtained. The mold used for the molding was tabular with a vertical length of 40.00 mm, a horizontal length of 25.00 mm, a thickness of 2.50 mm, and rounding portion at the four corners of 3.0 mm, and it had a filling inlet for filling one side face of the minor axis of the mold with the above produced resin. The size of the filling inlet was 4.00 mm×2.00 mm.
(3) Calculation of Mold Shrinkage Factor
After leaving the molded product (test specimen) for 24 hours or longer, its dimensions were measured, and the mold shrinkage factor was calculated using equation (3).
From the results shown in Table 5, it can be seen that the mold shrinkage factor varied depending on the injection pressure. Further, in the present example, when the ratio of the filler in the composition was 20 weight percent, the mold shrinkage factor became 0 when the injection pressure was 140.1 MPa, and when the injection pressure was further increased, the mold shrinkage factor became negative; in other words, a molded product larger than the inner dimension of the mold was obtained.
synthetic resin; the same resin as the polypropylene resin used in Example 1 was used
The production of the above synthetic resin composite for molding and the molding of the obtained composition were performed in the same manner as in Example 1, and the results are shown in Table 6.
synthetic resin; the same resin as the polypropylene resin used in Example 1 was used.
The production of the synthetic resin composite for molding using the above synthetic resin and filler and the molding of the obtained composite resin were performed in the same manner as in Example 1, and the results are shown in Table 7.
synthetic resin; the same resin as the polypropylene resin used in Example 1 was used.
The production of the synthetic resin composite for molding using the above synthetic resin and filler and the molding of the obtained composite resin were performed in the same manner as in Example 1, and the results are shown in Table 8.
synthetic resin; the same resin as the polypropylene resin used in Example 1 was used.
The production of the synthetic resin composite for molding using the above synthetic resin and filler and the molding of the obtained composite resin were performed in the same manner as in Example 1, and the results are shown in Table 9.
As is obvious from Tables 6-9, the mold shrinkage factor was lowered by increasing the injection pressure; however, the mold shrinkage factor was still higher than the result in Example 1, and a molded product with a high dimensional accuracy could not be obtained.
This was because if “CPB” or the heavy calcium carbonate powder was used as the filler, as is clear from Table 2, Table 3, and
On the other hand, the minimum molecular size of the polymer compound used as the synthetic resin was 100-200 nm in the case of polyethylene resin. In addition, as described above, the inner diameter of the pores formed by the carbon layer surface wall in “ELFITE” was 1000-5000 nm. Therefore, it is probable that since the inner diameter of the pores in “ELFITE” was larger than the molecules of the polymer compound of the synthetic resin used in the present example, the synthetic resin moved into the pores of the “ELFITE” when they were blended and the “ELFITE” thus lost its volume compaction/recovery function and a molded product with a high dimensional accuracy could not be obtained.
As described above, since it is preferable that the filler blended in the synthetic resin be elastic graphite and that in the elastic graphite the inner diameter of the pores formed by the carbon layer surface wall be substantially smaller than the molecules of the polymer compound of the above synthetic resin, the present example employed “DESULCO”. However, when manufacturing synthetic resin composite for molding using a synthetic resin made from a polymer compound with extremely large molecules (5000 nm for example), it is possible to use “ELFITE” etc. as the elastic graphite with elasticity so as to satisfy the above conditions.
In this example, the following synthetic resin and filler were employed.
(1) Production of Synthetic Resin Composite for Molding
synthetic resin; polycarbonate resin (product name “Iupilon S3000” manufactured by Mitsubishi Engineering-Plastics Corporation)
filler; elastic graphite (product name “DESULCO” manufactured by SUPERIOR GRAPHITE Co.)
The same method as is shown in Example 1 was employed for producing the synthetic resin composite with the exception that the barrel temperature in the kneader was changed to 280° C.
(2) Molding of Synthetic Resin Composite for Molding
<Molding Conditions>
The mold shrinkage factor of the produced molded product (test specimen) was calculated by using equation (3) above, and the result is shown in Table 10.
synthetic resin; the same polycarbonate resin used in Example 2 was used.
filler; not used
Production of the synthetic resin composite for molding using the above synthetic resin and filler and the molding of the obtained composition were performed in the same manner as in Example 2. As is clear from Table 11, the mold shrinkage factor was lowered by increasing the injection pressure; however, the mold shrinkage factor was still higher than the result in Example 1, and a molded product with a higher dimensional accuracy could not be obtained.
In this example, the following synthetic resin and filler were employed.
(1) Production of Synthetic Resin Composite for Molding
synthetic resin; polyacetal resin (product name “Duracon TD-25” manufactured by Polyplastics Co., Ltd.)
filler; elastic graphite (product name “DESULCO” manufactured by SUPERIOR GRAPHITE Co.)
The same method shown in Example 1 was employed for producing the synthetic resin composite, with the exception that the barrel temperature in the kneader was changed to 200° C.
(2) Molding of Synthetic Resin Composite for Molding
<Molding Conditions>
The mold shrinkage factor of the molded product (test specimen) was calculated by using the above equation (3), and the result is shown in Table 12.
synthetic resin; the same polyacetal resin used in Example 3 is used
Production of the synthetic resin composite for molding using the above synthetic resin and filler and the molding of the obtained composition were performed in the same manner as in Example 3. As is clear from Table 13, the mold shrinkage factor was lowered by increasing the injection pressure; however compared with the result of Example 3, the mold shrinkage factor was still higher, and a molded product with a higher dimensional accuracy could not be obtained.
As described above, the synthetic resin composite for molding of the present invention can be easily produced by only kneading a particular fraction of the synthetic resin with an elastic substance by a commercial kneader or the like, wherein the elastic substance has a volume recovery of 15% or more when the volume compaction by pressure is 30% or more. The elastic substance would preferably be elastic graphite, which has pores inside of it and formed by a carbon layer surface wall and their inner diameter is substantially smaller than the molecules of the polymer compound of the above synthetic resin. By adding a certain pressure at molding, the elastic substance blended with the synthetic resin provides a molded product with a low mold shrinkage factor and a high dimensional accuracy. In addition, it is also possible to change the dimensions of the molded product freely within a certain range by adjusting the pressure added in the molding process.
The synthetic resin for molding of the present invention is molded to become mechanical components in computers and office automation equipment, the bodies of precision instruments (such as cameras), lens barrels, and other sliding components/mechanical components such as gears, bearings, cams etc., and can be used as a part of products including machines, equipment and devices.
Number | Date | Country | Kind |
---|---|---|---|
2005-008411 | Jan 2005 | JP | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/JP05/17416 | 9/21/2005 | WO | 11/9/2006 |