JP2836003B2 - Molded product for plated product and molding method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a molded product of an acetal-based resin composition for use in a plated product, for example, as an outside door handle of an automobile, and a method of molding the same.

[0002]

2. Description of the Related Art Conventionally, for a plated product which is used in place of a metal product and is made of a synthetic resin molded product as a base material, in order to obtain necessary strength and a texture close to that of the metal product, the molded product as a base material is used. A molded article of an acetal-based resin composition is used. As the acetal-based resin composition, for example, an acetal-based resin composition containing finely divided calcium carbonate as described in JP-B-58-4936 is used. This molded body is subjected to plating after the surface of the molded body is subjected to etching treatment, and can obtain high plating peel strength.

[0003] By the way, the above-mentioned molded product is obtained by using an acetal resin containing fine powdered calcium carbonate as a molding material.
Although it is formed by injection molding, it is required to be as thin as possible and as thin as possible in order to prevent so-called sink marks.

It is known that the injection speed needs to be as high as possible as a point to be noted in molding ("Industrial Materials", Vol. 31, No. 3, p. 54). This is required to improve the surface gloss and plating peel strength of the plated product. If the injection speed is high, the shear rate of the molding material near the surface of the molded body is increased, and this is the surface gloss and plating peel strength. It is presumed that this leads to a uniform surface structure and a distribution state of calcium carbonate particles, which leads to an improvement in surface roughness. Therefore, from the viewpoint of uniformly increasing the shear rate of the molding material near the surface of the molded body, the molded body is required to be uniform and thin.

[0005]

However, in order to realize a uniform high shearing rate of the molding material near the surface of the molded article based on the high injection speed, the molded article must be as thin and as uniform as possible. Because of this, the design constraints are large and the resulting plated product design
There is a problem that the use and the function are also limited, and the range of applicable plating products is limited.

Incidentally, the plating peel strength is practically 600.
g / 5 mm width is required. In order to realize this, conventionally, after uniformly reducing the thickness, a further 160 cc / mm is required.
Injection is performed at a speed as fast as seconds, and there is a problem that the selection range of the injection molding machine is narrow.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and relates to a molded product for an acetal-based resin composition containing finely divided calcium carbonate, for a molded product for a plated product, the surface gloss of the obtained plated product, and Based on the high injection speed, which is required for improving the peel strength, the design constraint for achieving a uniform high shear rate of the molding material near the surface of the molded body is reduced, and various applications and It is an object of the present invention to be able to apply to a plated product having a function.

[0008]

According to the first aspect of the present invention, there is provided an acetal-based resin composition containing finely divided calcium carbonate, wherein the hollow ratio of the hollow resin is 12% or more by a hollow injection molding method. The hollow molded body having a portion is used for a plated product.

Further, in the invention of claim 2, the molten molding material is injected into the mold cavity using the acetal-based resin composition containing fine powdered calcium carbonate as the molding material, and the molten molding material is further melted in the mold cavity. A pressurized fluid is injected into the molding material, and after the molding material is cooled, the pressurized fluid is discharged to form the hollow molded body having a hollow ratio of 12 or more.

The present invention will be further described.

First, the acetal-based resin composition used in the present invention contains finely powdered calcium carbonate, as in the case of a conventionally used molded product for a plated product, and is preferably 100 parts by weight of the acetal resin. , 3 to 30 parts by weight of finely powdered calcium carbonate, 0.1% of unsaturated polyester.
1 to 10 parts by weight.

The molded product for a plated product according to the present invention has a hollow portion. This hollow portion is formed by a hollow injection molding method. It is different.

In the hollow injection molding method, in the injection molding method, a pressurized fluid is injected into a molten molding material injected into a mold cavity, and after the necessary cooling, the injected pressurized fluid is discharged. This is a molding method for molding a molded article.

As the pressurized fluid, a fluid which is gaseous or liquid at normal temperature and normal pressure and which does not react with or be compatible with the molding material at the temperature and pressure of injection molding is used. For example, nitrogen,
Carbon dioxide, air, helium, glycerin, liquid paraffin and the like are used, but usually a gas is used, and an inert gas such as nitrogen, helium, neon and argon is particularly preferable.

Hereinafter, the hollow injection molding method will be further described by taking as an example the case where a gas is used as the pressurized fluid.

[0016] Hollow injection molding using gas as a pressurized fluid is performed by a combination of a usual injection molding machine and a gas injection device.

First, an acetal-based resin composition containing fine powdered calcium carbonate is used as a molding material, and the molten molding material is injected into a mold cavity by a usual injection molding machine. At this time, the mold preferably has a mold cavity surface temperature of 100 to 150 ° C, more preferably 110 to 140 ° C. Further, the injection speed is preferably 50 cc / sec or more.

The reason why the mold cavity surface temperature and the injection speed are preferable is not necessarily clear, but the mold cavity surface temperature is controlled by pressurizing a pressurized gas described later by relieving rapid cooling of the molding material. It is presumed that the molding material is sometimes easily pressed against the surface of the mold cavity, and this is beneficial for improving the surface gloss and plating peel strength of the plated product obtained. As for the injection speed, as described in the section of the prior art, it is assumed that the shearing rate acting on the molding material near the surface of the molded body provides similar benefits.

Next, a pressurized gas is injected into the molten molding material in the mold cavity by a gas injection device.

The gas press-in device is a device for pressurizing a pressurized gas into a molten molding material in a mold cavity through a pipe and maintaining (pressurizing) the gas pressure for a required time.

The gas press-fitting device may be of a type in which pressurized gas compressed in advance to a high pressure and stored in an accumulator is supplied to the molten molding material in the mold cavity at the time of pressurized gas press-fitting. At times, a method in which a gas is fed into a molten molding material in a mold cavity by a pump and pressurized may be used.

The pressurized gas can be injected through a gas nozzle built in the injection nozzle or a gas nozzle provided in a mold. The pressurized gas may be injected directly into the mold cavity, or may be injected into a sprue or runner. The pressurized gas pressed into the sprue or the runner is pressed into the molten molding material in the mold cavity via the gate.

The injection timing of the pressurized gas may be after injection of a sufficient amount of molten molding material to fill the mold cavity (full shot) or by injection of an insufficient amount of molten molding material to fill the mold cavity. (short shot)
It may be any one after. However, in the present invention, a relatively large hollow portion needs to be formed because the hollow ratio is required to be 12% or more, as described later, and from this point, a short shot is usually obtained.

In the case of full shot, as the molding material shrinks due to cooling, a pressurized gas is injected according to the amount of shrinkage. In the case of a short shot, a pressurized gas corresponding to the unfilled amount of the molten molding material and the contraction amount of the molding material is injected.

In the case of a full shot, it is preferable to perform a suck-back after injection of the molten molding material and then press-in a pressurized gas because the press-in is facilitated. In the case of a short shot, it is preferable to start press-in of the pressurized fluid before the movement of the flow end of the molten molding material in the mold cavity stops. When the flow is restarted by pressurizing the pressurized gas after the flow end of the molten molding material has once stopped, a flow mark is easily generated in this portion, and the surface gloss of the obtained plated product tends to be uneven.

In the case of a short shot, after injection of a part of the molten molding material, the injection of the pressurized gas can be performed together with the injection of the remaining molten molding material.

When the pressurized gas is injected as described above, the shrinkage due to the cooling of the molding material is compensated for by the pressurized gas, so that even a molded article having an apparently thick or variable thickness can be shrunk. Is suppressed. Further, the pressurized gas having extremely high fluidity propagates the pressure to every corner of the molded body, and the state of close contact between the molding material and the mold cavity surface is improved.

[0028] It is not clear why this leads to a good surface gloss of the plated product and an improvement in the peel strength of the plated product, but in addition to the above-mentioned shear rate acting on the molding material near the surface of the molded product, It is presumed that the good adhesion of the molding material to the mold cavity surface also leads to a uniform surface state and a distribution state of calcium carbonate particles, which leads to an improvement in surface gloss and plating peel strength.

After the pressurized gas is injected, an appropriate pressure holding time for maintaining the pressure of the pressurized gas is taken as needed.
After the molding material is cooled to such an extent that it does not deform, the pressurized gas is discharged and the molded body is taken out.

As described above, the molded article according to the present invention has a hollow portion formed by press-in of a pressurized gas, and the hollow ratio needs to be 12% or more. Generally up to 50%. If the hollow ratio is too low, it becomes difficult to sufficiently press the molding material against the mold cavity surface, and the surface gloss and plating peel strength of the obtained plated product are reduced. In addition, those having a high hollow ratio are formed by short shots. The higher this is, the greater the amount of spread of the molten molding material due to pressurized gas injection and the more likely it is to cause poor appearance due to flow marks and the like.

The hollow ratio is defined by the following equation.

Hollow ratio (%) = ｛(V × ρ−M) / (V ×
ρ)｝ × 100

In the above formula, V is the apparent volume of the obtained hollow molded body, ρ is the specific gravity of the molding material used, M
Is the mass of the obtained hollow molded body.

The molded article according to the present invention is subjected to plating after its surface is subjected to etching treatment.

The above-mentioned surface etching treatment can be performed in the same manner as in the prior art. For example, sulfuric acid aqueous solution or sulfuric acid
It can be carried out, for example, by immersing the molded body in a phosphoric acid-containing aqueous solution.

The surface of the molded body having an etched surface has a rough surface for improving the adhesion of the plating layer, and has micropores as elution or falling off of calcium carbonate particles. It is considered that high plating peeling strength is obtained by the anchor effect obtained by partial penetration of the layer. And it is presumed that the molded article according to the present invention has a distribution of calcium carbonate particles in which the roughness of the surface is appropriately formed and micropores in a state where an anchor effect is easily obtained are left. .

In general, chemical plating and electroplating are used as plating for finishing.

[0038]

【Example】

Example 1 A molded body (maximum thickness 30 mm, minimum thickness 1 mm) for an outside door handle for automobiles was molded using the following acetal-based resin composition as a molding material.

Acetal resin (“Tenac PT300” manufactured by Asahi Kasei Corporation): 100 parts by weight Calcium carbonate: 8 parts by weight Unsaturated polyester: 1.2 parts by weight

The molten molding material at 200 ° C. is injected at an injection speed of 440 cc / sec into a mold cavity whose surface temperature is adjusted to 120 ° C., and a nitrogen gas is further opened into the mold cavity. From 30kgf /
It was injected for 5 seconds at a pressure of cm ^2. Thereafter, the compact was held for 30 seconds as it was, and after the pressurized nitrogen gas was discharged, the molded body was taken out from the mold.

The hollow ratio of the obtained molded product was 25.4%.

The obtained molded body was degreased with trichloroethane, and 96% sulfuric acid / 85% phosphoric acid / water = 40/25/3.
After being immersed in a solution of 5 (weight ratio) at 40 ° C. for 8 minutes to perform an etching treatment, it was immersed in warm water of 80 ° C. for 10 minutes to be washed.

After the molded body after the etching treatment is immersed in a pretreatment liquid for plastic plating (“Catalyst” manufactured by Okuno Pharmaceutical Co., Ltd.) and an accelerator, a chemical plating solution (“MTP chemical nickel plating liquid” manufactured by Okuno Pharmaceutical Co., Ltd.) is used. ), And immediately subjected to electroplating.

Table 1 shows the measurement results of the plating peel strength of the obtained plated product.

The plating peel strength was 5 mm on the plating surface.
This refers to the force required for peeling when a parallel cut is made in the width and the plated layer between the cuts is pulled in a direction perpendicular to the plating surface, thereby peeling the plated layer.

Example 2 The results of measuring the plating peel strength in the same manner as in Example 1 except that the hollow ratio was 12.5% are shown in Table 1.

Example 3 The results of measuring the plating peeling strength in the same manner as in Example 1 except that the injection speed was 110 cc / sec are shown in Table 1.

Example 4 Table 1 shows the results of measuring the plating peeling strength in the same manner as in Example 1 except that the injection speed was changed to 50 cc / sec.

Comparative Example 1 The results of measuring the plating peeling strength in the same manner as in Example 1 except that the hollow ratio was changed to 11.6% are shown in Table 1.

Comparative Example 2 Table 1 shows the results of measuring the plating peeling strength in the same manner as in Example 1 except that the injection speed was set to 100 cc / sec by ordinary injection molding without injection of nitrogen gas.

[0051]

[Table 1]

[0052]

The present invention is as described above, and it is possible to apply a plating having a sufficient peel strength to a molded product having a large thickness and a variable thickness. Is largely eliminated, and applicable plating products are significantly expanded. Further, since the plated product is a hollow body, the weight can be reduced and the total cost can be reduced. Further, since the injection at a low injection speed is sufficient, the range of choice of the molding machine is widened.

Claims (2)

(57) [Claims] 1. A molded article made of an acetal resin composition containing finely divided calcium carbonate and having a hollow portion having a hollow ratio of 12% or more by a hollow injection molding method, for a plated product. Molded body. 2. A molten molding material is injected into a mold cavity using an acetal-based resin composition containing finely divided calcium carbonate as a molding material, and a pressurized fluid is injected into the molten molding material in the mold cavity. A pressurized fluid is discharged, and then the pressurized fluid is discharged to form a hollow molded body having a hollow ratio of 12% or more, thereby forming a molded product for a plated product.