JP2002096348A - Molded article using crystalline resin composition and injection molding method thereof - Google Patents

Abstract

(57) [Abstract] [Problem] Excellent long-term dimensional accuracy and dimensional stability of molded products,
To supply a molded product in which the occurrence of defects mainly occurring after molding such as warpage and sink is suppressed, so that it can be applied to a thick molded product. SOLUTION: The molded article has a foamed part inside, and
A non-foamed layer having a thickness of 500 μm or more in the surface layer portion,
A molded article obtained from the crystalline resin composition, wherein the apparent specific gravity of the molded article is in the range of 95 to 99.5% of the specific gravity of the crystalline resin composition.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a molded article made of a crystalline resin composition and an injection molding method thereof.

[0002]

2. Description of the Related Art Conventionally, polyacetal (hereinafter referred to as "POM")
Injection molded products made of crystalline resins, such as resins and polyamide (hereinafter abbreviated as “PA”) resins, have a higher molding shrinkage than amorphous resins, and are molded as the crystallization proceeds after molding. Restriction on product design, mold design and molding conditions due to characteristics such as gradually decreasing the volume of the product, low viscosity at melting, large volume shrinkage due to crystallization, and extreme change in fluidity at the melting point Was often seen.

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. In the injection molding of crystalline resin, as a method of suppressing the molding shrinkage rate, the flow rate is improved by using a resin having a small molecular weight, the number of gates is increased, the flow distance to the flow end is shortened, the resin temperature is reduced. In addition, it is often observed that the resin in the mold is easily subjected to pressure by devising, for example, increasing the mold temperature to decrease the speed at which the viscosity of the resin increases in the mold cavity.

In general, a crystalline resin having a low molecular weight has higher rigidity, lower toughness and impact resistance, and a shorter life to fatigue due to repeated loading, etc., as compared with a crystalline resin having a high molecular weight. Tend to be. Also,
Increasing the number of gates means increasing the volume of the sprue and runner parts.As a result, in addition to increasing the number of parts that do not become products for each molding cycle, there will be problems such as complicated mold structures. It can be said that it is not preferable from the viewpoint of manufacturing. In addition, the method of increasing the resin temperature causes the decomposition of the resin to be promoted, and the method of increasing the mold temperature causes a problem that the molding cycle becomes longer.

On the other hand, in the injection molding of a crystalline resin, as a method for securing dimensional stability after molding, a copolymer is used in POM, and the amount of shrinkage immediately after molding is increased by increasing the mold temperature to increase the shrinkage immediately after molding. Techniques such as reducing the dimensional change, taking a long cooling time, taking out after shrinking sufficiently in the mold, and performing annealing after molding to promote crystallization in a short time and shrink the volume. Has been adopted. Compared to POM homopolymers, POM / copolymers have higher tensile elongation at break and are superior in heat aging resistance, but have low rigidity, low solidification rate, and low heat deformation temperature. Some parts are considered problematic.

[0006] The method of increasing the mold temperature and increasing the cooling time causes problems such as a long molding cycle.
Since the annealing treatment is a post-processing after the molding, the number of molding steps is increased, and when the annealing treatment itself varies, it is feared that it may cause a variation in the dimension of the molded product. On the other hand, when a thick molded product is obtained, the surface of the molded product is liable to sink due to volume shrinkage after molding. Therefore, the product is formed into a shape in which the back side of the design surface (the opposite side of the design surface) is hollowed out. In many cases, a design method such as reducing the average thickness of the sample was selected.

However, ribs and the like provided to compensate for the decrease in strength while reducing the thickness of the molded product cause linear sink marks on the design surface, which complicates the mold structure. Depending on the shrinkage of the resin and the magnitude and direction of the load applied to the molded product, stress concentrates on the rib itself, which may cause destruction, and there are cases where it is difficult to obtain a product having a desired shape. On the other hand, in the conventional injection molding method, the injection pressure and the filling pressure change in proportion to the melt viscosity of the resin used. A resin having a high melt viscosity requires a high injection pressure at the time of resin injection, which results in a large amount of distortion remaining in a molded product. The molding distortion remaining in the molded article is also called “residual distortion”. This residual strain is gradually relaxed after molding, but this is often due to deformation and shrinkage of the molded product. This is also seen when the mold structure, molding conditions, etc., are not appropriate.

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, it can be said that when filling the resin cavity into the mold cavity, it is preferable that an appropriate pressure that hardly causes residual strain to remain is transmitted uniformly to the entire cavity.

As an injection molding method for improving the dimensional accuracy with less distortion of the molded article, it is conceivable to increase the resin temperature 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 crystalline resin. Usually 5 to 3 from melting point
It is carried out in the range 0 ° C. higher, often in the range 10-20 ° C. above the melting point. This can be said to be a temperature range in which the viscosity of the resin is high up to a temperature range higher by about 5 ° C. than the melting point, so that the filling is difficult and the melting of the resin is not sufficient, and the melted portion and the unmelted portion are easily mixed. When the unmelted portion is mixed in the molded product, there is a concern that a problem such as a decrease in strength may occur.

On the other hand, the resin temperature during molding is 30 ° C. below the melting point.
In the above high temperature range, the decomposition of resin is promoted, and the appearance of the molded product surface is called silver (or “silver streak”),
Discoloration of the molded product itself may occur, and the generated decomposition gas may easily 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.

[0011] In addition, when the resin temperature is set high, the volume change of the resin itself during cooling and solidification becomes large, which is likely to cause sink marks, voids, etc., and it takes time to cool the resin. 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 molded product at the time of taking out becomes smaller.

In addition, in the case of 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 temperature of the molded product at the time of removal is high. For this reason, after the molded article 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 article itself gradually decreases to the ambient temperature. This causes the dimensional accuracy to deteriorate, which is not preferable. Japanese Patent Application Laid-Open No. Sho 62-58287 discloses an injection molding method in which the surface temperature of the mold is extremely increased only when the resin is filled into the mold cavity.
No. "Injection molding method of rubber reinforced polystyrene resin",
Each is disclosed in JP-A-62-58288, "ABS resin injection molding method". Injection molding to obtain a crystalline resin molded product that has a smooth surface and good mold transferability by inserting an inductor between the molds and heating the mold surface with both molds open. Is the law.

In these injection molding methods, a step of inserting an inductor or a high-frequency induction heating coil between the molds during a molding cycle, heating the mold surface, and pulling out the inductor or the high-frequency induction heating coil from between the molds. is necessary. When this injection molding method is applied to a polyacetal resin, the mold temperature is set to a heat deformation temperature (P) under a load of 1.82 MPa.
About 110 ° C. for OM copolymer, about 130 ° C. for POM homopolymer), preferably above melting point (about 168 ° C. for POM copolymer, about 17 ° C. for POM homopolymer)
5 ° C).

In addition, since the molding cycle is extended due to the step of heating the mold surface, there is a problem in productivity, and in the case of high-frequency induction heating, the amount of electricity consumed is excessive, which is not preferable from the viewpoint of energy saving. . In addition, the injection molding method involving high-frequency induction heating is not preferable because it is limited to a molded product having a relatively flat shape because it limits the degree of freedom in product design of the molded product. 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, by injecting a crystalline resin at a high speed, the melt viscosity is prevented from rising due to cooling from a mold, the melt viscosity is reduced by a high shear force, and the pressure difference in the cavity is reduced. 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 product by injecting a compressed gas into a resin. The compressed gas has a pressure-holding effect from the inside of the molded article, and has the effect of suppressing the occurrence of sink marks on the molded article. 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, the residual distortion is small, the deformation of the molded product such as warpage can be reduced, and the dimensional accuracy can be expected to be improved. However, depending on the shape of the molded product, there are cases where the installation location of the gas injection port is limited, and the effect may not be sufficiently exhibited.

On the other hand, 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 article 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.

Further, 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, after filling the mold cavity with the resin and holding the resin under pressure as described in the examples of the publication, the pressure at this time (hereinafter referred to as “holding pressure”)
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.

[0019]

SUMMARY OF THE INVENTION The present invention has a foamed portion inside without limiting the resin composition of a crystalline resin represented by a polyacetal resin or a polyamide resin and without impairing the degree of freedom in product design. It is another object of the present invention to improve the precision of a molded product required for a crystalline resin by adjusting the apparent specific gravity of the molded product to be smaller than the specific gravity of the crystalline resin composition to be used.

Specifically, according to the present invention, the mold cavity can be easily filled, the molded product has excellent long-term dimensional accuracy and dimensional stability, and defects such as warpage and sink are mainly generated after molding. An object of the present invention is to obtain a suppressed molded product, and to enable application to a thick molded product.

[0021]

Means for Solving the Problems The present inventors did not limit the resin composition of crystalline resins typified by polyacetal resins and polyamide resins, and did not impair the degree of freedom in product design. An object of the present invention is to improve the precision of a molded product required for a crystalline resin by adjusting the apparent specific gravity of the molded product to be smaller than the specific gravity of the crystalline resin composition to be used.

Specifically, the present inventors have found that the mold cavity is easy to fill, that the molded product has excellent long-term dimensional accuracy and dimensional stability, and that the molded product is mainly formed by warping or sink mark. In order to obtain a molded product in which the occurrence of defects that occur later is suppressed, and to enable application to a thick molded product, the present inventors have studied. As a result, the molded article made of the crystalline resin composition has a foamed portion inside, and the apparent specific gravity of the molded article is smaller than the specific gravity of the crystalline resin composition. However, it has been found that it improves long-term dimensional accuracy and dimensional stability of molded products, facilitates filling in mold cavities, and solves problems that mainly occur after molding, such as warpage and sink marks that occur in molded products. The present invention has been completed.

That is, the present invention provides: The molded article has a foamed portion inside and 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 article is 95 to 99 of the specific gravity of the crystalline resin composition. A molded product obtained from the crystalline resin composition, wherein the content is within a range of 0.5%; The molded article obtained from the crystalline resin composition according to the above item 1, wherein the foamed portion inside the molded article is formed by dissolving or absorbing carbon dioxide in the crystalline resin composition. . After dissolving or absorbing 0.2% by weight or more of carbon dioxide in the crystalline resin composition and filling the mold cavity, the filling pressure is 30 to 85%.
3. A molded product obtained from the crystalline resin composition as described in 1 or 2 above, wherein the molded product is obtained by pressurizing and holding the resin at a pressure corresponding to%. 4. A molded article obtained from the crystalline resin composition according to any one of the above items 1 to 3, wherein the crystalline resin composition is a polyacetal resin containing at least a polyacetal component. 5. A molded article 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. In the crystalline resin composition, 0.
2. The molding according to the above item 1, wherein after dissolving or absorbing 2% by weight or more of carbon dioxide and filling the mold cavity, the resin is pressurized and held at a pressure corresponding to 30 to 85% of the filling pressure. 6. Injection molding method for product 6. The above-mentioned (6), wherein the crystalline resin composition in a molten state is filled in a mold cavity adjusted or maintained at or above atmospheric pressure.
And a method for injection-molding a molded article according to (1).

[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.

Specifically, polyacetal or polyoxymethylene (hereinafter abbreviated as “POM”) resin, polyamide (hereinafter abbreviated as “PA”) resin, polyethylene terephthalate (hereinafter abbreviated as “PET”) resin, polybutylene terephthalate (hereinafter abbreviated as “PET”) Hereinafter, the resin is abbreviated as “PBT”, a high-density polyethylene (hereinafter, abbreviated as “HDPE”) resin, a low-density polyethylene (hereinafter, abbreviated as “LDPE”) resin, a linear low-density polyethylene (hereinafter, abbreviated as “LLDPE”) resin. ,
A polyether ether ketone (hereinafter abbreviated as “PEEK”) resin, a polypropylene (hereinafter abbreviated as “PP”) resin, and the like are conceivable.

As the crystalline resin composition used in the present invention, a POM resin containing a POM component and a PA resin containing a PA component are preferable from the viewpoint that a molded article having excellent mechanical strength and high heat resistance is easily obtained. It can be said that. Where POM
There is no distinction between a POM homopolymer and a POM copolymer, and a POM in which another component such as a lubricating polymer or silicon is chemically bonded to the terminal portion of the POM molecule.
It may be an M 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, PET, PBT, various polyethylenes, PEEK, PP, polystyrene, ABS resin, polyvinyl chloride, polycarbonate, modified polyphenylene ether, polyphenylene sulfide, polyimide, polyamide imide, polyether imide, polyarylate,
Examples thereof include polysulfone, polyethersulfone, polyetheretherketone, liquid crystal polymer, polytetrafluoroethylene, thermoplastic elastomer, polytetrafluoroethylene, and polyvinyl alcohol.

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 a small powder such as dust can be prevented from being attached to a molded article made of the crystalline resin composition by static electricity.

In the present invention, the molded article made of the crystalline resin composition is characterized by having a foamed portion inside, and the foamed section has a cross section of the molded article magnified 10 to 20 times by an optical microscope or the like. When observed, it indicates a portion where a void due to foaming or a whitening phenomenon is confirmed.
The molded article made of the crystalline resin composition according to the present invention has a foamed portion inside, whereby the substantial thickness of the resin portion is reduced with respect to the product thickness, and the volume shrinkage is reduced. It is considered that the product has excellent long-term dimensional accuracy and dimensional stability.

Further, since the volume shrinkage of the crystalline resin composition is supplemented from the inside of the molded article by forming a foamed portion inside the molded article, sink marks are generated on the surface of the molded article. Seems to be suppressed. In the present invention, the molded article made of the crystalline resin composition has a foamed portion inside and a non-foamed layer having a thickness of 500 μm or more on the surface layer of the molded article. If the thickness of the layer is less than 500 μm, the surface of the molded article may be swollen, and 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. But,
If the holding pressure is too high or if the holding time is too long,
When the crystalline resin composition cools and solidifies in the mold cavity, the carbon dioxide dissolved in the crystalline resin composition hardly forms a foamed portion inside the molded product, and the surface of the molded product has a sink mark. This is not preferred because it may cause

In the present invention, the apparent specific gravity of a molded article refers to the specific gravity of an arbitrary part cut out from the molded article, and the specific gravity of the resin composition refers to the specific gravity of a resin pellet. The apparent specific gravity of a molded article of the crystalline resin composition according to the present invention is 95 to 90% of the specific gravity of the crystalline resin.
It is preferably in the range of 99.5%, and 96 to 99.
More preferably, it is in the range of 5% to 98-99.
Most preferably, it is in the range of 5%.

This means that the apparent specific gravity of the molded article is not more than 95% of the specific gravity of the crystalline resin, which means that the proportion occupied by the foamed portion inside the molded article is too large. Is not preferable because the decrease in strength 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 product, and the surface of the molded product has sink marks. It seems that the internal foamed portion does not exist effectively.

The fact that the apparent specific gravity of the molded article 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 article has an appropriately foamed portion. It is considered to be in the range of apparent specific gravity present. The method for forming a foamed part in a molded article made of the crystalline resin composition according to the present invention is not limited, but it is possible to dissolve or absorb carbon dioxide in the crystalline resin composition and then fill the mold cavity. It is preferable to form with.

This is because, after dissolving or absorbing carbon dioxide in the crystalline resin composition, the crystalline resin composition is cooled and solidified in the mold cavity by filling the mold cavity, thereby reducing the volume shrinkage. This is because, when it occurs, carbon dioxide dissolved or absorbed in the crystalline resin composition is formed by appropriately foaming. By having a foamed part inside the molded article made of the crystalline resin composition, it becomes possible to apply the molded article made of the thermoplastic resin composition to a thicker molded article, and the degree of freedom in product design is increased. Can be expected.

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 resin cavity 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.

Further, since the filling pressure at the time of filling the crystalline resin composition into the mold cavity is reduced, deformation of the molded article such as warpage after molding is less than that of the conventional molding method. This is considered to be due to the fact that the filling pressure during filling into the mold cavity is lower than that of the conventional molding method, so that residual strain hardly remains in the molded product. This facilitates injection molding with a crystalline resin composition having a high viscosity at the time of melting, and improves the quality of a molded product.
It is expected that a resin composition, which has not been realized until now because of increased flexibility in product design and high viscosity at the time of melting, can be realized.

The present invention is characterized in that 0.2% by weight or more of carbon dioxide is dissolved or absorbed in the crystalline resin composition. The method is as follows: in a heating cylinder of an injection molding machine. A method for mixing with the crystalline resin in a molten state, a method for mixing with the crystalline resin in a molten state from a nozzle of a molding machine, and a facility for supplying carbon dioxide between a mold and a nozzle of the molding machine is provided. A method of mixing the crystalline resin in a molten state, a method of granulating resin pellets in a state where carbon dioxide is mixed with a crystalline resin in a molten state in advance, and performing injection molding using the same, or a hopper of a molding machine in advance For example, a method of absorbing carbon dioxide into resin pellets in a closed container such as the above can be considered.

The carbon dioxide is easily dispersed uniformly in the crystalline resin composition of the present invention, and 0.2% by weight in a short time.
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) Measure the weight of the molded article immediately after molding (M1). 2) Put the molded product in a hot air dryer kept at 100 ° C for 48 hours.
After leaving for more than an hour to allow carbon dioxide to evaporate, the weight of the molded product taken out of the hot air drier is measured (M2). 3) The amount of dissolved or absorbed carbon dioxide (% by weight)
1−M2) ÷ Calculated from ÷ M2 × 100.

Normally, the injection molding method has a step of filling the mold cavity with the resin and then 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 In order to have an appropriate foamed portion, a preferable range of the holding pressure in the injection molding process is a range of 30 to 85%, more preferably a range of 30 to 80% with respect to the filling pressure. 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 the mold cavity expands. This is not preferable because a swelling phenomenon may occur in the molded product. Specifically, the dwell time is preferably 3 seconds or more, more preferably 5 seconds or more, and most preferably 7 seconds or more.

The molded article made of the crystalline resin composition of the present invention is a molded article, part, or product in the minimum unit constituted by the crystalline resin composition, and is used for automobiles, electronic products, containers, and household goods. , Electrical equipment, general machinery, plumbing parts, precision machinery, tools, industrial parts, the smallest unit of molded resin, parts and products made of crystalline resin used in transportation equipment, etc. Molded products that require processing,
Including products. In the present invention, the injection molding method of the crystalline resin composition is a molding and processing method of a thermoplastic resin that is usually performed, in addition to a commonly used injection molding method, a hollow injection molding method, a gas assist molding method, Blow molding, injection / compression molding, etc. are included.

In the injection molding method of a molded article 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,
If the amount of carbon dioxide dissolved or absorbed is not less than a certain value, a foamed pattern may be formed on the surface of the molded product. In order to suppress the occurrence of a foaming pattern on the surface of the molded product, the inside of the mold cavity must be adjusted or maintained by a pressurized gas at a pressure higher than the pressure at which foaming does not occur at the flow front of the crystalline resin composition. is necessary.

The pressure of the pressurized gas may be a minimum pressure at which the foaming pattern on the surface of the molded product disappears. The amount of gas used during the molding cycle is minimized, and the sealing of the mold cavity and the gas supply device are performed. In order to simplify the structure of the above, it is preferable that the gas pressure is low. 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, it can be said that the pressure of the gas for pressurizing the mold cavity is preferably not lower than atmospheric pressure and not higher than 15 MPa.

At this time, as the gas for adjusting or maintaining the inside of the mold cavity at 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 in detail with reference to examples, but the present invention is not limited to the examples.

The resin used for the injection molding was a POM resin homopolymer (“Tenac 401” manufactured by Asahi Kasei Corporation).
0 "), POM resin copolymer (" Tenac-C 4520 "manufactured by Asahi Kasei Kogyo Co., Ltd.), PA resin (" Leona 1702 "manufactured by Asahi Kasei Kogyo Co., Ltd.), glass fiber reinforced P
A resin (Leona 1300G manufactured by Asahi Kasei Kogyo Co., Ltd.)
(Glass fiber 33% added product) "). Both are in the form of pellets before molding. As a molding machine, "TUPARL TR50S2" manufactured by Sodick Plustech Co., Ltd. was used.

The φ30 gear has the shape shown in FIG. Module 1, number of teeth 30, tooth width 5 mm, diameter φ1.
Two gates, which are 2, are provided. The mold cavity has a seal structure so as to hold a pressurized gas.
The ISO dumbbell has the shape shown in FIG. The ISO dumbbell mold has a structure conforming to the ISO standard. Also, at the flow end of the mold cavity, 1 mm thick x 8 m
A tab having a width of m and a length of 10 mm is provided, and a seal structure is provided so as to hold a pressurized gas.

Unless otherwise specified, the cylinder temperature during injection molding was 280 ° C. for molding PA resin and 195 ° C. for molding POM resin. The mold temperature was 80 ° C. unless otherwise specified. For the same resin, the setting of the cylinder temperature and the mold temperature was the same for the GF reinforced grade and the non-reinforced grade. Also, unless otherwise noted
The injection speed is 15mm / sec during ISO dumbbell molding.
c, 30 mm / sec during φ30 gear molding. The filling pressure during molding was a value obtained by reading the filling pressure during injection on a monitor screen of a molding machine. The holding pressure was a value corresponding to 70% of the filling pressure, the holding time was 7 seconds, and the cooling time was 15 seconds.

The dimensional accuracy of the molded product is injection-molded φ30.
The diameter of the addendum circle of the gear molded product was measured using a micrometer. The sink amount of the molded product is the flow end portion of the injection-molded ISO dumbbell molded product, and the surface roughness is the molded I dumbbell molded product.
The central part of the SO dumbbell molded product was measured using a “surface roughness shape measuring device (“ Surfcom 570A ”manufactured by Tokyo Seimitsu Co., Ltd.)” which is a contact type surface roughness meter. The specific gravity of the resin is measured using an automatic hydrometer (“SG” manufactured by Shimadzu Corporation).
M-220G-60 ").

[0059]

Embodiments 1 to 4 Using Tenac 4010, TR5
Carbon dioxide is dissolved from the gas injection part provided in the center of the heating cylinder of the molding machine OSS2, and the apparent specific gravity of the molded product is 99.3%, 98.6%, 9 of the specific gravity of Tenac 4010.
Φ3 shown in FIG. 1 which is 7.9% and 96.5%
A 0 gear molded product was obtained. The presence or absence of the foamed portion was confirmed, and the thickness of the non-foamed layer was measured. The diameter of the tooth tip circle was measured at 2 hours, 1 day, 2 days, 4 days, 7 days, and 10 days after molding. Table 1 shows the results.

[0060]

Comparative Example 1 Tenac 401 as in Examples 1-4
The carbon dioxide is dissolved from the gas injection part provided at the center of the heating tube of the TR50S2 molding machine using 0, and the apparent specific gravity of the molded product is 94.3% of the specific gravity of Tenac 4010.
Thus, a φ30 gear molded product shown in FIG. 1 was obtained.
In the same manner as in Examples 1 to 4, the presence or absence of the foamed portion was confirmed, and the thickness of the non-foamed layer was measured. In addition, the tip circle diameter was measured.
Table 1 shows the results.

[0061]

[Comparative Example 2] TR50S using Tenac 4010
2 In such a manner that the apparent specific gravity of the molded product is equal to the specific gravity of Tenac 4010 by the same process as ordinary injection molding without dissolving carbon dioxide by the molding machine, the φ shown in FIG.
A 30-gear molded product was obtained. As in Examples 1 to 4, the presence or absence of a foamed portion was confirmed, but the presence of a foamed portion could not be confirmed. For this reason, the thickness of the non-foamed layer was not measured. In addition, the tip circle diameter was measured. Table 1 shows the results.

[0062]

[Table 1]

[0063]

Examples 5 to 7 Using a Leona 1702, TR50
Carbon dioxide is dissolved from the gas injection part provided at the center of the heating cylinder of the S2 molding machine, and the apparent specific gravity of the molded product is 99.1%, 98.2%, 97.4% of the specific gravity of Leona 1702.
% Of the ISO dumbbell molded article shown in FIG. The presence or absence of the foamed portion was confirmed, and the thickness of the non-foamed portion was measured. In addition, the amount of sink in the flow end portion was measured. Table 2 shows the results.

[0064]

Comparative Example 3 As in Examples 5-7, Leona 1702
The carbon dioxide is dissolved from the gas injection part provided in the center of the heating cylinder of the TR50S2 molding machine by using, and the apparent specific gravity of the molded product is 94.7% of the specific gravity of Leona 1702 in FIG. The indicated ISO dumbbell molded product was obtained.
As in Examples 5 to 7, the presence or absence of the foamed portion was confirmed, and the thickness of the non-foamed portion was measured. In addition, the amount of sink in the flow end portion was measured. Table 2 shows the results.

[0065]

Comparative Example 4 TR50S2 was prepared using Leona 1702.
Without dissolving carbon dioxide from the gas injection part provided in the center of the heating cylinder of the molding machine, by the same process as ordinary injection molding, the apparent specific gravity of the molded product is equivalent to the specific gravity of Leona 1702, An ISO dumbbell molded product shown in FIG. 2 was obtained. The presence or absence of a foamed portion was confirmed in the same manner as in Examples 5 to 7, but the presence of a foamed portion could not be confirmed. For this reason, the thickness of the non-foamed portion was not measured. In addition, the amount of sink in the flow end portion was measured. Table 2 shows the results.

[0066]

[Table 2]

[0067]

Embodiments 8 to 10 Using Leona 1300G, TR
After dissolving carbon dioxide gas in the molten resin in the heating cylinder from a gas injection part provided in the center of the heating cylinder of the 50S2 molding machine so that the dissolved amount of carbon dioxide becomes 0.32% by weight, Injection molding was performed to obtain a molded product having an ISO dumbbell shape shown in FIG. The holding pressure was set to a value corresponding to 35%, 50%, and 85% of the filling pressure when filling the mold cavity. The center part of the obtained ISO dumbbell molded product was cut, the presence or absence of a foamed portion in the molded product was checked, and the thickness of the non-foamed layer was measured. In addition, the apparent specific gravity of the molded article and the amount of sink in the flow end portion were measured. Table 3 shows the results.

[0068]

Comparative Example 5 As in Examples 8 to 10, Leona 130
Using 0G, the dissolved amount of carbon dioxide was 0.3 from the gas injection part 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 be 2% by weight, injection molding was performed to obtain a molded product having an ISO dumbbell shape shown in FIG. The holding pressure was set to a value corresponding to 10% of the filling pressure when filling the mold cavity. The center part of the obtained ISO dumbbell molded product was cut, the presence or absence of a foamed portion in the molded product was checked, and the thickness of the non-foamed layer was measured. Also, the apparent specific gravity of the molded product,
The amount of sink at the end of the flow was measured. Table 3 shows the results.

[0069]

[Comparative Example 6] TR50S using Leona 1300G
2 From the gas injection part provided in the center of the heating cylinder of the molding machine,
After dissolving carbon dioxide gas in the molten resin in the heating cylinder so that the dissolved amount of carbon dioxide becomes 0.32% by weight,
Injection molding was performed to obtain a molded product having an ISO dumbbell shape shown in FIG. The holding pressure was set to a value corresponding to 90% of the filling pressure when filling the mold cavity. The center portion of the obtained ISO dumbbell molded product was cut, and the presence or absence of a foamed portion in the molded product was confirmed. However, no foamed portion was confirmed. For this reason, the thickness of the non-foamed layer was not measured. The amount of sink at the end of the flow was measured. Table 3 shows the results.

[0070]

[Comparative Example 7] Same as normal injection molding without dissolving carbon dioxide gas in the molten resin in the heating cylinder from the gas injection part provided in the heating cylinder of the molded product at the center of the heating cylinder of the TR50S2 molding machine. To obtain a molded product having an ISO dumbbell shape shown in FIG. The holding pressure was a value corresponding to 70% of the filling pressure. The obtained ISO dumbbell molded product was cut at the center and checked for the presence of a foamed portion in the molded product. However, the presence of the foamed portion could not be confirmed. For this reason, the thickness of the non-foamed layer was not measured. The amount of sink at the end of the flow was measured.
Table 3 shows the results.

[0071]

[Table 3]

[0072]

Embodiments 11 to 13 Using a Tenac-C 4520, a heating tube was set so that the dissolved amount of carbon dioxide became 0.45% by weight from a gas injection portion provided at the center of the heating tube of the TR50S2 molding machine. After dissolving carbon dioxide gas in the molten resin in the inside, the mold is adjusted to 2.0, 3.0, and 5.0 MPa, and then filled into a mold cavity, whereby the ISO dumbbell molded product shown in FIG. Obtained. The holding pressure was set at 70% of the filling pressure. The filling pressure at the time of injection molding was read, and the apparent specific gravity and surface roughness of the molded product were measured.
The change in the total length of the ISO dumbbell molded article was measured at 2 hours, 1 day, 2 days, 4 days, 7 days, and 10 days after molding. Table 4 shows the results.

[0073]

Comparative Example 8 Tenac-C was used in the same manner as in Examples 11 to 13.
Using 4520, carbon dioxide gas was introduced into the molten resin in the heating cylinder from the gas injection part provided in the center of the heating cylinder of the TR50S2 molding machine so that the dissolved amount of carbon dioxide became 0.45% by weight. After melting, the mold cavity, which has not been pressure-adjusted, is filled to obtain the I shown in FIG.
An SO dumbbell molded product was obtained. The set value of the holding pressure is
It was 70% of the filling pressure. The filling pressure at the time of injection molding was read, and the apparent specific gravity and surface roughness of the molded product were measured. Also,
The change in the total length of the ISO dumbbell molded product was measured. Table 4 shows the results.

[0074]

Comparative Example 9 Tenac-C was used in the same manner as in Examples 11 to 13.
Using 4520, normal injection molding was performed without supplying carbon dioxide gas from the heating cylinder of the molding machine to obtain an ISO dumbbell-shaped molded article shown in FIG. The holding pressure was set at 70% of the filling pressure. The filling pressure at the time of injection molding was read, and the apparent specific gravity and surface roughness of the molded product were measured. Further, the change in the overall length of the ISO dumbbell molded product was measured. Table 4 shows the results.

[0075]

[Table 4]

[0076]

The molded article of the present invention is mainly used for molding such as warpage and sink without restricting the resin composition of crystalline resin represented by polyacetal resin and polyamide resin and without impairing the flexibility of product design. This is a molded product in which the occurrence of defects that occur later is suppressed, and can be applied to thicker molded products.

[Brief description of the drawings]

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

FIG. 2 shows an ISO dumbbell shape of the present invention.

[Explanation of symbols]

 1 φ30 gear 2 Gate 3 ISO dumbbell 4 Tab

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) B29K 105: 04 B29K 105: 04 C08L 59:00 C08L 59:00 77:00 77:00

Claims (7)

[Claims] 1. The molded article has a foamed part inside, and
A non-foamed layer having a thickness of 500 μm or more in the surface layer portion,
A molded article obtained from the crystalline resin composition, wherein the apparent specific gravity of the molded article is in the range of 95 to 99.5% of the specific gravity of the crystalline resin composition. 2. The crystalline resin composition according to claim 1, wherein the foamed portion inside the molded article is formed by dissolving or absorbing carbon dioxide in the crystalline resin composition. The resulting molded product. 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 article obtained from the crystalline resin composition according to claim 1 or 2, which is obtained by holding under pressure. 4. A molded article 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 article 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 product according to claim 1, wherein the injection molding is performed under pressure. 7. The injection molding of a molded article 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 atmospheric pressure and not more than 15 MPa. Method.