JP2002106683A - Molded gear of crystalline resin composition and injection molding method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the gear accuracy of a molded gear made of the crystalline synthetic resin without limiting the molecular weight and composition of the crystalline resin represented by the POM resin and the PA resin, and without hindering a degree of freedom in gear design. SOLUTION: This molded gear has a foaming part inside thereof, and has a non-foaming layer a 500 μm or more of thickness in a surface layer thereof. Apparent specific gravity of a molding exists in a range at 95-99.5% of the specific gravity of a crystalline resin composition (polyamide resin, polyacetal resin), and CO2 at 0.2% by weight or more is dissolved or absorbed in the crystalline resin composition, and this crystalline resin composition is filled in a mold cavity adjusted at a pressure value in a range from the atmospheric pressure to 1.5 MPa. Thereafter, the resin is pressurized by the pressure at 30-85% of the filling pressure and maintained in this condition.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a molded gear made of a crystalline resin composition and a method of injection molding the same.

[0002]

2. Description of the Related Art Conventionally, polyacetal (hereinafter referred to as "PO
M ") resin, polyamide (hereinafter abbreviated as" PA ")
Injection molded gears made of crystalline resin, such as resin, have a large molding shrinkage compared to amorphous resin, the volume of the molded gear gradually decreases with the progress of crystallization after molding, and the viscosity during melting decreases. Due to the features such as low temperature, large volumetric shrinkage due to crystallization, and extreme change in fluidity at the melting point, the product design, mold design, and molding conditions were often restricted.

For example, POM has a molding shrinkage of 1.8 to
It is relatively large at about 2.2%, which is one of the reasons why injection molding is difficult. However, it is typical for gears and the like because the molding shrinkage varies greatly depending on the molding conditions and it takes a long time until the dimensions are stabilized after molding. It can be said that there are many parts that are regarded as problematic when applied to precision parts to be manufactured. On the other hand, gears are widely used as mechanical components in various fields such as automobiles, general machines, precision machines, and electric and electronic devices. As a recent tendency, the range of use of gears made of crystalline resin is expanding because of excellent productivity, light weight, and rust resistance. Furthermore, the demands for dimensional accuracy for crystalline resin gears have become more sophisticated due to the high technology in each field, especially the spread and generalization of OA equipment, and responding to this has been a technical issue.

[0004] In order to further promote material substitution from metal to crystalline resin, it is difficult to ensure the precision, strength, product life, and the like of a crystalline resin gear at the same level as a metal gear. Becomes Therefore, solving this problem and approaching the level of metal gears can be said to be an issue in promoting material replacement from metal gears to those made of crystalline resin. In order to improve the accuracy of the gear made of crystalline resin, increase the number of gates, make the thickness as thin as possible, and make it uniform to suppress the deformation of the molded gear and make the shrinkage uniform Product design and mold design are generally performed.

Improvements have also been made to the crystalline resins used. Recently, there have been cases in which high flowability is ensured by reducing the molecular weight of the resin, and consideration has been given to facilitate transmission of uniform pressure to the end of the flow.
However, in general, a crystalline resin having a small molecular weight improves rigidity, but decreases toughness and impact resistance, and also tends to have a shorter life for fatigue due to repeated loading and the like. As described above, there are many examples of molded gears that are manufactured while sacrificing the characteristics of the resin.

In order to secure the gear strength, it is conceivable to increase the thickness of the product. Specifically, design changes such as increasing the tooth width and increasing the thickness of the web can be considered. However, thick molded gears tend to have sinks on the molded gear surface due to an increase in the absolute amount of volume shrinkage after molding, and are likely to be deformed due to uneven filling pressure during injection molding. There is a concern that this will occur. On the other hand, in order to extend the product life of gears made of crystalline resin, it is necessary to increase the molecular weight of the crystalline resin used. However, in a crystalline resin, the viscosity of the resin increases in proportion to the molecular weight, and in the conventional injection molding method, the injection pressure and the filling pressure change in proportion to the melt viscosity of the resin used.

[0007] A resin having a high melt viscosity requires a high injection pressure during resin injection, which results in a large amount of distortion remaining in the molded gear. The molding distortion remaining in the molded gear is also called “residual distortion”. This residual strain is gradually relaxed after forming, but this is often due to deformation and shrinkage of the formed gear. This is also seen when the mold structure, molding conditions, etc. are not appropriate. Further, the pressure applied to the resin filled in the mold cavity is preferably uniform, but the pressure distribution may be uneven near the gate and at the end of the flow. This means that it is difficult to transmit a sufficient pressure to the end portion of the flow, which causes poor appearance of the end portion of the flow, generation of voids, sink marks, expansion of molding shrinkage and unevenness.

Therefore, when filling the mold cavity with the resin, it can be said that it is preferable that an appropriate pressure, which hardly causes residual strain to remain, is uniformly transmitted to the entire cavity. As an injection molding method for improving the dimensional accuracy with less distortion of the molded gear, it is conceivable to increase the resin temperature setting during injection molding to lower the melt viscosity of the resin. Usually, the setting range of the resin temperature when molding the crystalline resin is narrower than that of the non-crystalline resin. Usually, it is carried out in the range of 5 to 30C higher than the melting point, and most often in the range of 10 to 20C higher than the melting point.

This is because the viscosity of the resin is high up to a temperature range of about 5 ° C. higher than the melting point, so that it is difficult to fill the resin, the resin is not sufficiently melted, and the melted portion and the unmelted portion are likely to coexist. It can be said that. When the unmelted portion is mixed in the formed gear, there is a concern about a problem such as a decrease in strength. On the other hand, in the temperature range where the resin temperature during molding is higher than the melting point by 30 ° C. or more, the decomposition of the resin is promoted, and a poor appearance called silver (or “silver streak”) on the surface of the molded gear and discoloration of the molded gear itself occur. In addition to the risk of decomposition, the generated decomposition gas tends to cause stains on the mold. This is not preferable because it may cause deterioration of the resin, may deteriorate the working environment, and may cause the mold to be disassembled and cleaned. Therefore, it can be said that there is a limit to the method of increasing the resin temperature in order to improve the fluidity of a crystalline resin having a high viscosity.

In addition, when the temperature of the resin is set high, the amount of change in the volume of the resin itself during cooling and solidification becomes large, which tends to cause sink marks, voids, and the like. However, there is a concern that productivity may decrease. On the other hand, by increasing the mold temperature, a decrease in resin temperature and an increase in viscosity in the mold cavity can be suppressed. However, when the mold temperature is increased,
Since the cooling time of the resin filled in the mold becomes longer, the molding cycle time inevitably becomes longer, and the size of the molding gear at the time of taking out becomes smaller.

In addition, in the injection molding in which the temperature of the mold is increased, if the cooling time is not sufficient and the cooling of the resin is insufficient, the molding gear temperature at the time of removal is in a high state. For this reason, after the molded gear is taken out from the mold, there is a possibility that volume shrinkage or deformation due to its own weight may occur before the temperature of the molded gear itself gradually decreases to the ambient temperature. This causes the dimensional accuracy to deteriorate, which is not preferable. On the other hand, new molding methods such as a high-speed injection molding method and a gas assist molding method have been proposed as injection molding methods for crystalline resins with improved dimensional accuracy and dimensional stability.

In the high-speed injection molding method, the crystalline resin is injected at a high speed to prevent the melt viscosity from rising due to cooling from the mold, and to reduce the melt viscosity by a high shear force to reduce the pressure difference in the cavity. Has the effect of doing Further, the effect of reducing the injection time is obtained, and the productivity is also improved. However, it is necessary to pay attention to the deterioration of the resin due to the heat generated by shearing, the generation of burrs due to high-speed injection, and the occurrence of resin burn due to adiabatic compression in the gas reservoir at the end of the mold cavity.

The gas assist molding method generally forms a hollow portion in a molded gear by injecting a compressed gas into a resin. This compressed gas has a pressure-holding effect from inside the formed gear, and has an effect of suppressing the occurrence of sink marks on the formed gear. The pressure-holding effect of the compressed gas is lower than the pressure-holding effect in the ordinary injection molding method, and the pressure-holding effect can be expected up to the end of the flow. For this reason, it is expected that deformation of the formed gear such as warpage can be reduced with little residual distortion and dimensional accuracy can be improved. However, depending on the shape of the molded gear, the location of the gas inlet may be limited, and the effect may not be sufficiently exhibited.

[0014] Japanese Patent Laid-Open No. 4-299113 and the like disclose the technology of resin gears by the gas assist molding method and the hollow injection molding method together with the manufacturing method. However, the resin back gear formed by the gas assist molding method and the hollow injection molding method described above can improve the accuracy because it is difficult to form the hollow portion uniformly or effectively over the entire circumference of the gear. In addition to difficulty in controlling the wall thickness, it can be said that it is difficult to secure strength.

On the other hand, in J.I. Appl. Polym. Sc
i. , Vol. 30, 2633 (1985), it is known that when carbon dioxide is absorbed by a resin, it acts as a plasticizer for the resin and lowers the glass transition temperature. It has not been widely applied to processing. Japanese Unexamined Patent Publication No. Hei 5-318541 discloses a method in which a gas such as carbon dioxide or nitrogen is contained in a thermoplastic resin, and the resin is filled in the cavity while removing the gas in the cavity. To obtain a molded gear without deterioration in strength and appearance. However, in this method, when carbon dioxide is used as the gas, the amount of the gas contained in the resin is small at a maximum of about 0.18% by weight, and it is difficult to obtain a sufficient fluidity improving effect. It can be said that it is difficult to obtain accuracy and dimensional stability.

[0016] Also, WO 98/52734 discloses that
In injection molding of thermoplastic resin,
Shows a method of filling molten resin whose viscosity has been reduced by dissolving more than 1% by weight into a mold cavity that has been kept pressurized with a gas such as carbon dioxide at a pressure higher than the pressure at which foaming does not occur at the flow front of the molten resin. The mold surface reproducibility, glossiness, and weld lines are less noticeable.
It is described that the method is effective for reproducibility of a sharp edge on a mold surface, reproducibility of fine irregularities on a mold surface, and the like.

However, the method includes a step of filling the mold cavity with the resin and holding the resin under pressure, which is described in the examples of the publication and the like.
Is in the range of 89-93% of the filling pressure. However, the holding pressure equivalent to 89% to 93% of the filling pressure may cause burrs and hardly form a foamed portion inside the molded product, and may cause defects such as sink marks and warpage which mainly occur after molding. Difficult to solve. Further, a specific method for improving the accuracy and strength of a molded gear formed of a crystalline resin molded gear having a large molding shrinkage has not been disclosed.

[0018]

DISCLOSURE OF THE INVENTION The present invention relates to a crystalline resin, such as a POM resin and a PA resin, which does not limit the molecular weight and the resin composition of the crystalline resin, without impairing the degree of freedom of the gear design. An object of the present invention is to improve the gear accuracy required for a molded gear made of a conductive resin. Specifically, the present invention makes it possible to easily fill a mold cavity, secure long-term stability of dimensions, improve gear accuracy, and enable application to thicker formed gears. It is in.

[0019]

Specifically, the present inventors have made it possible to freely design gears without limiting the fluidity and resin composition of crystalline resin compositions represented by POM resins and PA resins. 95 to 9 of a crystalline resin having a foamed portion inside and the apparent specific gravity of a molded gear is used without impairing the degree.
It is an object of the present invention to improve the gear accuracy required for a molded gear made of crystalline resin by using a molded gear of 9.5%.

Therefore, the present inventors aimed to obtain a molded gear which is easy to fill into a mold cavity, improves gear accuracy, and has a small amount of dimensional change due to heating or cooling / heating cycling. We studied to make it applicable to thick formed gears. As a result, the crystalline resin 9 has a foamed portion inside and uses the apparent specific gravity of the molded gear.
The inventors have found that a molded gear of 5 to 99.5% improves the gear accuracy required for a molded gear made of a crystalline resin, and has completed the present invention.

That is, the present invention provides: The molded gear has a foamed portion inside, and has a non-foamed layer having a thickness of 500 μm or more in the surface layer portion, and the apparent specific gravity of the molded product is 95 to 90% of the specific gravity of the crystalline resin composition. 1. a molded gear obtained from the crystalline resin composition, which is in a range of 99.5%; The molded gear obtained by the crystalline resin composition according to the above 1, wherein the foamed portion having the inside of the molded gear is formed by dissolving or absorbing carbon dioxide in the crystalline resin composition.

3. By dissolving or absorbing 0.2% by weight or more of carbon dioxide in the crystalline resin composition and filling the mold cavity, the resin is pressurized and held at a pressure corresponding to 30 to 85% of the filling pressure. 3. A molded gear obtained from the crystalline resin composition according to the above 1 or 2, which is obtained. A molded gear obtained from the crystalline resin composition according to any one of the above 1 to 3, wherein the crystalline resin composition is a polyacetal resin, containing at least a polyacetal component.

5. 5. A molded gear obtained from the crystalline resin composition according to any one of the above items 1 to 3, wherein the crystalline resin composition is obtained from a polyamide resin containing at least a polyamide component. After dissolving or absorbing 0.2% by weight or more of carbon dioxide in the crystalline resin composition and filling the mold cavity, the resin is pressurized and held at a pressure corresponding to 30 to 85% of the filling pressure. 6. The injection molding method of the molded gear according to the above 1, which is characterized by: The crystalline resin composition in a molten state, above atmospheric pressure,
7. The injection molding method of a molded gear according to the above item 6, wherein the mold cavity is filled or adjusted to 15 MPa or less.

[0024]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be specifically described below. In the present invention, the crystalline resin composition is a composition having a three-dimensional structure in which molecular chains are regularly arranged and mainly composed of a thermoplastic resin having a unique melting point. A composition containing a thermoplastic resin as a main component, which has a crystalline state at a temperature higher than the melting point but loses its crystallinity.

More specifically, polyacetal or polyoxymethylene (hereinafter abbreviated as “POM”) resin, PA resin, polyethylene terephthalate (hereinafter abbreviated as “PET”) resin, polybutylene terephthalate (hereinafter “PB”)
T ”), high-density polyethylene (hereinafter“ HDP ”)
E ”), low-density polyethylene (hereinafter“ LDP ”)
E), linear low-density polyethylene (hereinafter abbreviated as “LLDPE”) resin, polyetheretherketone (hereinafter abbreviated as “PEEK”) resin, polypropylene (hereinafter abbreviated as “PP”) resin, etc. Can be

As the crystalline resin composition used in the present invention, a POM resin containing a POM component, PA
It can be said that a PA resin containing a component is preferable. Where PO
There is no distinction between M and POM homopolymer or POM copolymer, and P is obtained by chemically bonding other components such as a lubricating polymer and silicon to the terminal portion of the POM molecule.
It may be an OM / block copolymer.

PA means PA6, PA66, PA
610, PA11, PA12, and other high molecular compounds having an acid amide bond. The crystalline resin composition in the present invention may be a polymer alloy obtained by mixing one or more resins having the above-mentioned crystalline resins as main components and having different properties. Resins having different properties that can be used in combination with the crystalline resin as the main component are
A resin component having the same molecular structure as the crystalline resin serving as the main component may be a resin component having a different molecular weight and molecular weight distribution, or may be another resin component having a different molecular structure.

There are no particular restrictions on the resins having different properties that can be used as a mixture with the crystalline resin as the main component as long as they are compatible with the crystalline resin as the main component. PA, PP, PET, PBT, PEEK,
Various polyethylene, polystyrene, ABS resin, polyvinyl chloride, polycarbonate, modified polyphenylene ether, polyphenylene sulfide, polyimide, polyamideimide, polyetherimide, polyarylate, polysulfone, polyethersulfone, liquid crystal polymer, polytetrafluoroethylene, thermoplastic Elastomers, polytetrafluoroethylene, polyvinyl alcohol and the like can be mentioned.

As an example of a mixture of a crystalline resin as a main component and resins having different properties, a polymer alloy of a PA resin and a polyphenylene ether (hereinafter abbreviated as “PPE”) resin (hereinafter referred to as “PA / PPE ”),
A polymer alloy such as a polymer alloy of a PP-based resin and a PPE-based resin (hereinafter abbreviated as “PP / PPE”) is conceivable. The crystalline resin composition used in the present invention includes:
For the purpose of imparting specific gravity and strength, an inorganic or organic filler can be added.

Examples of specific gravity imparting agents include inorganic salts, oxides, such as barium sulfate, red iron oxide, and tungsten powder.
Metal powder and the like can be considered. Further, as a strength imparting agent,
Glass fiber, carbon fiber, metal fiber, aramid fiber, potassium titanate, asbestos, silicon carbide, ceramic,
Silicon nitride, barium sulfate, calcium sulfate, kaolin, clay, pyrophyllite, bentonite, sericite, zeolite, mica, mica, nepheline sinite, talc, atalpargite, wollastonite,
Slag fiber, ferrite, silicon, calcium, calcium carbonate, magnesium carbonate, dolomite, zinc oxide,
Gypsum, glass beads, glass powder, glass balloon, quartz, quartz glass, alumina and the like can be considered.

The shape of the inorganic or organic filler is not limited, and a fibrous, plate-like, spherical or the like can be arbitrarily selected. In addition, two or more of the above-mentioned inorganic or organic fillers can be used in combination. Further, if necessary, it can be used after being pre-treated with a silane-based or titanium-based coupling agent. The amount of the inorganic or organic filler added to the crystalline resin composition of the present invention is not limited, but the specific gravity of the crystalline resin composition is adjusted, the rigidity is improved, In order to sufficiently obtain the effect of adding an additive, such as securing accuracy and suppressing deformation such as warpage, 5
The addition amount is preferably at least 10% by weight, more preferably at least 10% by weight. When the amount is less than 5% by weight, the effect of adding the above-mentioned filler is small.

Here, the added amount of the filler means a ratio when the total amount of the crystalline resin composition is 100% by weight,
When two or more fillers are used, the total amount of the fillers is referred to. In the present invention, the added amount of the inorganic or organic filler refers to the amount added when one kind of inorganic filler is added, and refers to the total added amount when two or more kinds of inorganic fillers are added. Further, the amount of the inorganic or organic filler added indicates a ratio when the total amount of the resin component, the inorganic or organic filler, and other additives is 100% by weight.

In the crystalline resin composition of the present invention, commonly used additives such as antioxidants, flame retardants, release agents, lubricants, heat stabilizers, weather resistance stabilizers, rust inhibitors, Filler, colorant, antibacterial agent, fungicide, etc.
More than one kind can be added. Further, by selecting one or more of carbon fiber, metal fiber, and graphite as other additives, the electric resistance value of the crystalline resin can be reduced. This is preferable because it is possible to prevent small powder such as dust from attaching to the gear formed of the crystalline resin composition due to static electricity.

In the present invention, the gear formed of the crystalline resin composition has a foamed portion inside and a substantially non-foamed non-foamed layer having a thickness of 500 μm or more on the surface layer. It is characterized by the following. The foamed portion refers to a portion where a void or whitening phenomenon due to foaming is observed when an arbitrary cross section of the molded gear is magnified and observed 10 to 20 times by an optical microscope or the like.

Since the molded gear made of the crystalline resin composition of the present invention has a foamed portion inside, the substantial thickness of the resin portion becomes smaller than the product thickness, and the volume shrinkage decreases. In addition, it is considered that the long-term dimensional accuracy and dimensional stability of the molded product are excellent. Further, when the crystalline resin filled in the mold cavity is cooled and solidified, a foamed portion is formed inside the molded gear, so that the volume shrinkage of the crystalline resin composition is reduced from the inside of the molded gear. It seems that the generation of sink marks on the surface of the formed gear is suppressed.

In the present invention, the molded gear made of the crystalline resin composition has a substantially non-foamed non-foamed layer having a thickness of 500 μm or more in the surface layer portion. If the thickness is less than 500 μm, there is a possibility that a swelling phenomenon may occur on the surface of the molded product,
It is not preferable because the mechanical strength may be reduced.
The thickness of the non-foamed layer can be adjusted by the holding pressure and the holding time. The higher the holding pressure and the longer the holding time, the thicker the non-foamed layer tends to be. However, if the holding pressure is too high or if the holding time is too long, when the crystalline resin composition is cooled and solidified in the mold cavity, the carbon dioxide dissolved in the crystalline resin composition Carbon is not preferred because it is difficult to form a foamed portion inside the molded article, and there is a fear that sink may occur on the surface of the molded article.

In the present invention, the apparent specific gravity is the specific gravity of the molded gear, and is the specific gravity of the entire molded gear or the specific gravity of an arbitrary portion of the molded gear in which the foamed portion and the substantially non-foamed portion are mixed. Point to. Further, the specific gravity of the crystalline resin composition indicates the specific gravity of the resin pellet. Since the molded gear made of the crystalline resin composition according to the present invention has a foamed portion inside, the apparent specific gravity of the molded gear is 95 to 99.5 of the specific gravity of the crystalline resin composition.
%.

The fact that the apparent specific gravity of the molded gear is 95% or less of the specific gravity of the crystalline resin means that the proportion of the foamed portion in the molded gear is too large, and the strength of the molded gear is reduced. Is not preferable because it cannot be ignored. When the apparent specific gravity exceeds 99.5% of the specific gravity of the crystalline resin, it means that the foamed portion is not sufficiently formed inside the molded gear, and the sink occurs on the molded gear surface. It seems that the internal foamed portion does not exist effectively.

The fact that the apparent specific gravity of the molded gear made of the crystalline resin composition of the present invention is in the range of 95 to 99.5% of the specific gravity of the crystalline resin used means that the inside of the molded gear has an appropriately foamed portion. It is considered to be in the range of apparent specific gravity present, more preferably in the range of 96 to 99.5%, most preferably in the range of 98 to 99.5%. In the present invention, the shape of the gear is not limited. It can be applied to rack gears, pinion gears, and the like, in addition to gears based on a generally used disk shape.

Normally, a resin molded gear is provided with a resin for improving the strength and a flow supporting effect at the time of filling the resin.
Although ribs are radially provided from the center of the gear to the root of the gear, in a molded gear obtained by ordinary injection molding, the boundary between the web and the rib becomes relatively thick, so that heat is generated. Is likely to accumulate, it takes time to solidify the resin, and shrinkage does not proceed uniformly, which may lead to a total pitch error of the gear and a decrease in roundness.

As a method of preventing a reduction in gear accuracy due to contraction of the ribs, there is also an example in which concentric ribs are provided, and ribs are alternately provided radially as connecting ribs to diffuse the contraction. Was done. Further, in the conventional formed gear, the cross-sectional shapes of the web portion and the rib portion are suppressed to a range that does not decrease the gear accuracy, and it can be said that there is a limit to the improvement of the gear strength due to the enlargement of the dimensions of the web portion and the rib portion.

The method of forming a foamed part in a molded gear made of the crystalline resin composition according to the present invention is not limited. However, after dissolving or absorbing carbon dioxide in the crystalline resin composition, the method is applied to a mold cavity. It is preferable to form by filling. This is because, after dissolving or absorbing carbon dioxide in the crystalline resin composition, by filling the mold cavity, the crystalline resin composition cools and solidifies in the mold cavity, causing volume shrinkage. This is because carbon dioxide dissolved or absorbed in the crystalline resin composition is formed by appropriately foaming.

The amount of carbon dioxide dissolved or absorbed in the crystalline resin composition is not limited. However, by dissolving or absorbing carbon dioxide in the crystalline resin composition, Is improved when filling into the mold cavity, and an increase in filling pressure can be suppressed. Therefore, the amount of dissolution or absorption is preferably 0.2% by weight or more, and 0.4% by weight or more. % Is more preferable. If the amount of carbon dioxide dissolved or absorbed is less than 0.2% by weight, it is difficult to obtain the effect of improving the fluidity by dissolving or absorbing carbon dioxide, and sufficient dimensional accuracy and dimensional stability are obtained. It is not preferable because it becomes difficult to obtain.

By dissolving or absorbing carbon dioxide in the crystalline resin composition, the fluidity when filling the mold with the crystalline resin composition is improved.
It is supposed that carbon dioxide is efficiently dispersed as a plasticizer when carbon dioxide is dissolved or absorbed in the crystalline resin composition in a molten state. As a result, there is no need to raise the resin temperature, so there is no need to worry about thermal decomposition and deterioration of the resin, and the mold temperature does not need to be raised more than necessary.

On the other hand, when the amount of carbon dioxide dissolved or absorbed is less than 0.2% by weight, it is difficult to obtain the effect of improving the fluidity by dissolving or absorbing carbon dioxide, and sufficient dimensional accuracy is obtained. It is not preferable because it becomes difficult to obtain dimensional stability. Further, since the filling pressure at the time of filling the mold resin cavity with the crystalline resin composition is reduced, deformation of the molded product such as warpage after molding is smaller than that of the conventional molding method. This is because the filling pressure when filling into the mold cavity is lower than the conventional molding method,
It is considered that the residual strain hardly remains in the molded product. This facilitates injection molding with a crystalline resin composition that has a high viscosity at the time of melting, improves the quality of molded products, increases the degree of freedom in product design, and has a high viscosity at the time of melting. The realization of an injection molded product using a resin composition that could not be realized can be expected.

The molded gear according to the present invention fills the mold cavity after dissolving or absorbing carbon dioxide in the crystalline resin composition, so that the crystalline resin composition is cooled and solidified in the mold cavity to obtain a volume. When shrinking, carbon dioxide dissolved or absorbed in the crystalline resin composition,
It is supposed that the molded gear is formed by appropriately foaming a thick portion such as a web portion and a rib portion of the formed gear. as a result,
It is considered that the amount of shrinkage is reduced by the foamed portion, and the shrinkage of the resin proceeds uniformly. For this reason, it is considered that the degree of freedom of the dimensions of the web portion and the rib portion is increased.

Since the molded gear made of the crystalline resin composition has a foamed portion inside, it can be applied to a molded gear having a thicker thickness, and can be applied to a molded gear made of the thermoplastic resin composition. Can be expected to increase. In the present invention, 0.
The method is characterized by dissolving or absorbing 2% by weight or more of carbon dioxide. The method includes mixing a crystalline resin in a molten state in a heating cylinder of an injection molding machine, and a method of mixing the molten resin from a nozzle portion of the molding machine. A method of mixing with the crystalline resin in a molten state, a method of providing equipment for supplying carbon dioxide between a mold and a nozzle of a molding machine, a method of mixing with the crystalline resin in a molten state, and a method of mixing crystals in a molten state in advance. A method in which resin pellets are granulated in a state in which carbon dioxide is mixed with the reactive resin and injection molding is performed using the pellets, or a method in which carbon dioxide is absorbed in the resin pellets in a closed container such as a hopper of a molding machine in advance. Can be

It is easy for carbon dioxide to be uniformly dispersed in the crystalline resin composition of the present invention.
Considering that it is easy to dissolve or absorb, it is easy to adjust the absorption or dissolution amount, the setup before molding is not complicated, and it is not necessary to make the molding machine hopper etc. pressure resistant structure, injection molding The crystalline resin composition in a molten state is provided by providing a facility for supplying carbon dioxide in a heating cylinder of the machine, at a nozzle of the molding machine, or at any position between the nozzle of the molding machine and the mold. It is preferable to dissolve or absorb carbon dioxide in the carbon dioxide.

In the present invention, the amount of carbon dioxide dissolved or absorbed is measured by the following method. (1) Immediately after molding, the weight of the molded gear is measured (M1). (2) The molded gear was left in a hot air drier kept at 100 ° C. for 48 hours or more to disperse carbon dioxide, and then the weight of the molded gear removed from the hot air drier was measured (M2).
And). (3) The amount of carbon dioxide dissolved or absorbed (% by weight)
It is calculated from (M1−M2) ÷ M2 × 100.

In the present invention, the injection molding method of the crystalline resin composition is a usual molding and processing method of a thermoplastic resin. In addition to a commonly used injection molding method, a hollow injection molding method and a gas assist Molding methods, blow molding methods, injection / compression molding methods and the like are included. On the other hand, in the present invention, the filling pressure refers to a resin pressure generated when filling a molten resin into a mold cavity. Specifically, the screw pressure in the in-line type injection molding machine and the plunger position in the pre-plasticization type injection molding machine indicate the resin pressure generated when moving from the measurement position to the PV switching position.

In a usual injection molding method, after filling the resin into the mold cavity, there is a step of further holding the resin in the cavity under pressure. This step is referred to as a "holding step", and the degree of the pressure is referred to as "holding pressure". In the injection molding method of the crystalline resin composition according to the present invention, after filling the crystalline resin composition into the mold cavity, , Filling pressure 30-85
%, The resin in the mold cavity is preferably held under pressure.

In the present invention, the holding pressure is 30% of the filling pressure.
If it is less than 1, the thickness of the non-foamed layer formed on the surface layer of the molded article becomes thin, and the proportion of the foamed portion in an arbitrary cross section becomes large. On the other hand, when the holding pressure exceeds 85% of the filling pressure, burrs may be generated, and a foamed portion may not be easily formed inside the molded product, and sink and warpage may easily occur after molding.

An injection-molded article made of a crystalline resin in which 0.2% by weight or more of carbon dioxide is dissolved or absorbed forms a non-foamed layer having an appropriate thickness on the surface layer of the molded article, and is formed inside the molded article. In order to have an appropriate foaming portion, the preferable range of the holding pressure in the injection molding process is in the range of 30 to 85% with respect to the filling pressure, and more preferably in the range of 30 to 80%. And most preferably in the range of 30-75%.

The holding time is not limited, but if the holding time is extremely short, the carbon dioxide dissolved or absorbed in the crystalline resin before filling into the mold cavity expands. This is not preferable because a swelling phenomenon may occur in the molded product. In the injection molding method of a molded gear using the crystalline resin composition of the present invention, when filling the mold cavity with the crystalline resin composition in which carbon dioxide is dissolved or absorbed, the amount of dissolved or absorbed carbon dioxide is constant. In the case described above, a foaming pattern may be generated on the surface of the formed gear.

In order to suppress the occurrence of a foaming pattern on the surface of the molded product, the inside of the mold cavity is pressurized by a pressurized gas.
It is preferable that the pressure is adjusted or maintained at or above a pressure at which foaming does not occur at the flow front of the crystalline resin composition. The pressure of the pressurized gas may be a minimum pressure at which the foaming pattern on the surface of the formed gear disappears. A lower gas pressure is preferred to minimize the amount of gas used during the molding cycle and to simplify the mold cavity seal and gas supply system structure. If the gas pressure exceeds 15 MPa, the mold may open due to the gas pressure, and problems such as difficulty in sealing the mold cavity may easily occur. Therefore, the pressure of the gas for pressurizing the mold cavity is higher than atmospheric pressure,
MPa or less, and more preferably 1 MPa or less.
It is not less than MPa and not more than 10 MPa.

In the present invention, when the crystalline resin in which carbon dioxide is dissolved or absorbed is filled in the mold cavity, the mold cavity is preferably adjusted or maintained at a pressure of not less than atmospheric pressure and not more than 15 MPa. However, from the start of resin filling, at least until the completion of the cooling step, preferably until the completion of the pressure-holding step, more preferably before the start of the pressure-holding step, it is preferable to release the pressure in the mold cavity. . At this time, as the gas for adjusting or holding the inside of the mold cavity to a constant pressure, a single substance or a mixture of various gases inert to the crystalline resin composition can be used.
Carbon dioxide and hydrocarbons having high solubility in the crystalline resin composition, and gases in which hydrogen has been partially replaced with fluorine are preferred.

Hereinafter, the present invention will be described specifically with reference to examples, but the present invention is not limited to the examples. The resins used for the injection molding were POM homopolymer (“Tenak 4010” manufactured by Asahi Kasei Corporation), POM
Block copolymer (“Tenak LA541” manufactured by Asahi Kasei Kogyo Co., Ltd.), POM copolymer (“Tenak-C 4520” manufactured by Asahi Kasei Kogyo Co., Ltd.), PA (“Leona 1300S” manufactured by Asahi Kasei Kogyo Co., Ltd.) is there. Both are in the form of pellets before molding. The molding machine is “TUPARL TR50S” manufactured by Sodick Plustech Co., Ltd.
2 "was used. The φ30 gear has the shape shown in FIG. The φ60 gear has the shape shown in FIGS. Cylinder temperature during injection molding is PO
195 ° C when molding M resin, 2 when molding PA resin
80 ° C. Mold temperature is 80 ° C unless otherwise specified
And

Unless otherwise specified, the injection speed was
When forming a φ30 gear, the speed was 30 mm / sec, and when forming a φ60 gear, the speed was 50 mm / sec. The filling pressure during molding is
The filling pressure at the time of injection was taken as the value read on the monitor screen of the molding machine. The holding pressure is a value equivalent to 70% of this filling pressure,
The holding time was 7 seconds, and the cooling time was 15 seconds. The heat treatment was performed by preparing a hot-air dryer whose temperature was adjusted to 80 ° C. The molded gear was stored for 24 hours in an environment of a temperature of 23 ° C. and a humidity of 50% RH for 24 hours after molding, and then left for 4 hours in an environment of 80 ° C. The dimensions were measured immediately before the heat treatment and 20 hours after the completion of the heat treatment.

The cooling / heating cycle treatment was performed by preparing a hot-air dryer whose temperature was controlled at 70 ° C. and a thermo-hygrostat whose temperature was controlled at −30 ° C. The humidity of the thermo-hygrostat was not adjusted. 23 hours after forming the formed gear, temperature 23
It was stored in an environment of 50 ° C. and a relative humidity of 50%. One cycle of the treatment was left in a 70 ° C. environment for 30 minutes and left in a −30 ° C. environment for 30 minutes, and 10 cycles were performed. The dimensions were measured immediately before the cooling / heating cycle treatment and 20 hours after the completion of the cooling / heating cycle treatment.

Unless otherwise specified, the dimensions of the molded gears were measured by measuring the diameter of the addendum circle with a micrometer. The specific gravity of the resin was measured using an automatic hydrometer (“SGM-220G-60” manufactured by Shimadzu Corporation). The tooth profile error and the tooth trace error were measured using a gear measuring machine ("GC-1HP type" manufactured by Osaka Seimitsu Kikai Co., Ltd.) according to a measurement program.

When measuring a single pitch error and a cumulative pitch error, a meshing tester (manufactured by Osaka Seiki Kikai Co., Ltd.)
Was carried out using Gear accuracy measurement method and rating,
"The Precision Standard for Injection-Molded Plastic Gears (JSPE-MPG 0201-1997)" described in the "Injection-Molded Plastic Gear Standards", 2000, published by the Japan Society of Precision Engineering.
Was carried out according to The roundness of the gear is measured by a roundness cylindrical shape measuring machine (Mitutoyo Co., Ltd. "Round Test RA-
400 "), the probe was brought into contact with the circularity measurement position (3) of the φ60 gear shown in FIG.

[0062]

Embodiments 1 to 3 Using Tenac-C 4520, T
After dissolving carbon dioxide in the molten resin in the heating cylinder from the gas injection part provided in the center of the heating cylinder of the R50S2 molding machine so that the dissolved amount of carbon dioxide becomes 0.92% by weight, 2 and 3 by filling the mold cavity.
Φ60 gears shown in Table 1 were obtained. The molded gear has a foamed portion inside, and the thickness of the non-foamed layer on the gear surface is 500 μm.
m, 30%, 50% of the filling pressure,
The values respectively corresponded to 70%. The cross section of the injection-molded gear was observed, the presence or absence of a foamed portion was confirmed, and the thickness of the non-foamed layer was measured. The cumulative pitch error was measured before and after the thermal cycle processing, and the amount of change in the cumulative pitch error was determined from the difference. Table 1 shows the results.

[0063]

[Comparative Example 1] As in Examples 1 to 3, Tenac-C 45
20 and the gas injection part provided at the center of the heating cylinder of the TR50S2 molding machine was used to reduce the amount of dissolved carbon dioxide to 0.9.
After dissolving carbon dioxide in the molten resin in the heating cylinder so as to have a concentration of 2% by weight, the mixture was filled in a mold cavity to obtain a φ60 gear shown in FIGS. The holding pressure is set to a filling pressure of 1 so that the molded gear has a foamed layer inside, and the thickness of the non-foamed layer on the surface of the gear is 500 μm or less.
It was set to a value corresponding to 0%. The cross section of the injection-molded gear was observed, the presence or absence of a foamed portion was confirmed, and the thickness of the non-foamed layer was measured. The cumulative pitch error was measured before and after the thermal cycle processing, and the amount of change in the cumulative pitch error was determined from the difference. Table 1 shows the results.

[0064]

Comparative Example 2 Using Tenac-C 4520, TR5
From the gas injection part provided in the heating cylinder of the molding gear at the center of the heating cylinder of the OS2 molding machine, do not dissolve the carbon dioxide gas in the molten resin in the heating cylinder, and perform the same as normal injection molding.
The φ60 gear shown in FIGS. 2 and 3 was obtained. The cross section of the injection-molded gear was observed, and the presence or absence of a foamed portion was confirmed. However, the presence of the foamed portion was not confirmed. For this reason, the thickness of the non-foamed layer was not measured. The cumulative pitch error was measured before and after the thermal cycle processing, and the amount of change in the cumulative pitch error was determined from the difference. Table 1 shows the results.

[0065]

[Table 1]

[0066]

Embodiments 4 to 7 Using Tenac 4010, TR5
The apparent specific gravity of the molding gear is 99.3 of the specific gravity of the resin from the gas injection part provided at the center of the heating cylinder of the molding machine.
%, 98.6%, 97.9%, and 96.5%, after dissolving carbon dioxide gas in the molten resin in the heating cylinder, injection molding was performed, and φ30 shown in FIG. A gear formed gear was obtained. Before and after the heat treatment, the tip diameter of the formed gear was measured, and the difference in the tip diameter was determined from the difference. Table 1 shows the results.

[0067]

Comparative Example 3 Tenac 401 as in Examples 1-4
0, from the gas injection portion provided at the center of the heating cylinder of the TR50S2 molding machine, into the molten resin in the heating cylinder so that the apparent specific gravity of the molding gear becomes 94.3% of the specific gravity of the resin. After dissolving the carbon dioxide gas, injection molding was performed to obtain a φ30 gear molded gear shown in FIG. Before and after the heat treatment, the tip diameter of the formed gear was measured, and the difference in the tip diameter was determined from the difference. Table 2 shows the results.

[0068]

Comparative Example 4 In the same manner as in Examples 4 to 7 and Comparative Example 3, by using Tenac 4010, carbon dioxide was introduced into the molten resin in the heating cylinder from the gas injection section provided at the center of the heating cylinder of the TR50S2 molding machine. Without dissolving the carbon gas, a φ30 gear molded gear shown in FIG. 1 was obtained by the same process as ordinary injection molding. Before and after the heat treatment, the tip diameter of the formed gear was measured, and the difference in the tip diameter was determined from the difference. Table 2 shows the results.

[0069]

[Table 2]

[0070]

Embodiments 8 to 10 Using Tenac LA541, T
From the gas injection portion provided at the center of the heating cylinder of the R50S2 molding machine, the dissolved amount of carbon dioxide was 0.42% by weight, 0.6%
After dissolving carbon dioxide gas in the molten resin in the heating cylinder so as to be 8% by weight and 1.52% by weight, a φ60 gear shown in FIGS. 2 and 3 is obtained by filling the mold cavity. Was. The filling pressure during injection molding was read from the measured resin pressure of the molding machine, and after molding, the apparent specific gravity of the molded gear was measured. Tooth mold errors were measured before and after the heat treatment, and the difference in tooth mold error was determined from the difference. Table 3 shows the results.

[0071]

Comparative Example 5 Tenac LA5 was prepared in the same manner as in Examples 5 to 7.
41, the amount of dissolved carbon dioxide was 0.1% from the gas injection portion provided at the center of the heating cylinder of the TR50S2 molding machine.
After dissolving carbon dioxide gas in the molten resin in the heating cylinder so as to have a concentration of 4% by weight, the mixture was filled into a mold cavity to obtain a φ60 gear shown in FIGS. The filling pressure during injection molding was read from the measured resin pressure of the molding machine, and after molding, the apparent specific gravity of the molded gear was measured. Before heat treatment,
After the treatment, the tooth mold error was measured, and the amount of change in the tooth mold error was determined from the difference. Table 3 shows the results.

[0072]

Comparative Example 6 In the same manner as in Examples 5 to 7 and Comparative Example 3, a tenac LA541 was used to dissolve carbon dioxide from a gas injection part provided in the center of a heating cylinder of a TR50S2 molding machine without dissolving carbon dioxide. By the same process as the injection molding of FIG.
The φ60 gear shown in FIG. 3 was obtained. The filling pressure during injection molding was read from the measured resin pressure of the molding machine, and after molding, the apparent specific gravity of the molded gear was measured. Tooth mold errors were measured before and after the heat treatment, and the difference in tooth mold error was determined from the difference. Table 3 shows the results.

[0073]

[Table 3]

[0074]

Examples 11 to 13 Using Leona 1300S, T
After dissolving carbon dioxide in the molten resin in the heating cylinder from the gas injection part provided at the center of the heating cylinder of the R50S2 molding machine so that the dissolved amount of carbon dioxide becomes 0.32% by weight, 2.2, 3.1, 5.3MP depending on carbon gas
By filling the mold cavity adjusted to the pressure a in FIG. a, the φ60 gear shown in FIGS. 2 and 3 was obtained. The tooth profile error and tooth streak error of the obtained gear were measured. Table 4 shows the results.

[0075]

Comparative Example 7 As in Examples 11 to 13, Leona 130
Using 0S, the dissolved amount of carbon dioxide was 0.0% from the gas injection part provided at the center of the heating cylinder of the TR50S2 molding machine.
Carbon dioxide is dissolved in the molten resin in the heating cylinder so as to be 8% by weight, and then filled into a mold cavity pressure-adjusted to 3.1 MPa, whereby φ60 shown in FIGS. Got the gear. The tooth profile error and tooth streak error of the obtained gear were measured. Table 4 shows the results.

[0076]

Comparative Example 8 As in Examples 11 to 13, Leona 130
Using 0S, the dissolved amount of carbon dioxide was 0.0% from the gas injection part provided at the center of the heating cylinder of the TR50S2 molding machine.
After dissolving carbon dioxide in the molten resin in the heating cylinder so as to be 8% by weight, the mixture is filled into a mold cavity whose pressure has not been adjusted.
Got the gear. The tooth profile error and tooth streak error of the obtained gear were measured. Table 4 shows the results.

[0077]

[Table 4]

[0078]

According to the present invention, the mold is improved by improving the molding method without limiting the resin composition of the crystalline resin represented by the polyacetal resin and the polyamide resin, without impairing the degree of freedom of the product design. The present invention provides a molded gear that can be easily filled into a cavity, improves gear accuracy, and has a small amount of dimensional change due to heat treatment and cooling / heat cycle treatment, and enables application to a thicker molded gear.

[Brief description of the drawings]

FIG. 1 shows the shape of a φ30 gear of the present invention.

FIG. 2 shows the shape of a φ60 gear of the present invention.

FIG. 3 shows a cross section of a φ60 gear of the present invention.

[Explanation of symbols]

 1 Gear 2 Web 3 Roundness measurement position

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Claims (7)

[Claims] 1. A molded gear has a foamed portion inside and a non-foamed layer having a thickness of 500 μm or more in a surface layer portion, and the apparent specific gravity of the molded product is such that the crystalline resin composition is A molded gear obtained from the crystalline resin composition, which has a specific gravity in the range of 95 to 99.5%. 2. The crystalline resin composition according to claim 1, wherein the foamed portion inside the molded gear is formed by dissolving or absorbing carbon dioxide in the crystalline resin composition. The resulting molded gear. 3. After dissolving or absorbing 0.2% by weight or more of carbon dioxide in the crystalline resin composition and filling the mold cavity, the resin is applied by a pressure corresponding to 30 to 85% of the filling pressure. A molded gear obtained by using the crystalline resin composition according to claim 1, wherein the molded gear is obtained by holding under pressure. 4. A molded gear obtained from the crystalline resin composition according to claim 1, wherein the crystalline resin composition is a polyacetal resin containing at least a polyacetal component. 5. A molded gear obtained from the crystalline resin composition according to claim 1, wherein the crystalline resin composition is obtained from a polyamide resin containing at least a polyamide component. 6. After dissolving or absorbing 0.2% by weight or more of carbon dioxide in the crystalline resin composition and filling the mold cavity, the resin is applied with a pressure corresponding to 30 to 85% of the filling pressure. The injection molding method for a molded gear according to claim 1, wherein the pressure is maintained. 7. The injection molding of a molded gear according to claim 6, wherein the crystalline resin composition in a molten state is filled into a mold cavity adjusted or maintained at a pressure of not less than the atmospheric pressure and not more than 15 MPa. Method.