JP2011201991A - Polyamide resin composition for gas injection - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a molding material for gas injection, which realizes lightweight and production strength by gas injection and has good molding appearance and favorable texture.SOLUTION: The polyamide resin composition for gas injection is a polyamide resin composition comprising 8-60 pts.mass glass fiber reinforcement and 0.01-5 pts.mass channel carbon blackbased on 100 pts.mass total of 85-96 pts.mass polyamide 6 resin having a relative viscosity (RV) within the range of 1.8-2.6 when measured at 25°C, 1 g/dl using 96% concentrated sulfuric acid as a solvent and 4-15 pts.mass amorphous polyamide resin. Here, TC2 measured by a differential scanning calorimeter (DSC) is 183-190°C.

Description

  The present invention provides a polyamide resin composition having a wide range of gas injection molding conditions, a good molded appearance, a uniform thickness of the hollow portion inside the molded product, and a high strength molded product. Related to things.

Conventionally, glass fiber reinforced polyamide resins have been widely used as molding materials for machine parts and the like because of their excellent mechanical properties and heat resistance. In recent years, particularly in the automobile field, consideration is being given to reducing the weight in consideration of environmental considerations. Gas injection molding has been known as one of the methods for reducing the weight of resin materials (for example, Patent Document 1). Gas injection molding is a technique in which a high-pressure gas is injected immediately after a resin is injected into a mold in injection molding, and the mold surface is transferred by the pressure of the gas instead of holding pressure to obtain a hollow molded product. However, it is a technique that can be expected to reduce the amount of resin used by hollow molding and reduce weight, and to reduce warping and burrs.
However, when glass fiber reinforced resin is used for gas injection molding, the hollow wall thickness is biased due to poor fluidity, and the strength decreases at the thin wall part. The problem is likely to occur. Furthermore, since the pressure holding process is performed with gas pressure, there is a problem that the absolute pressure is insufficient and the transferability of the mold surface is lowered, and the appearance after molding becomes glass fiber floating and the quality is lowered. It was. In particular, when the mold surface is textured, the resin does not spread deeply into the texture, resulting in insufficient texture transfer, or even the same molded product has a difference in texture transfer depending on the location. There was a problem that appeared as a spot.

JP 11-99533 A

  An object of the present invention is to provide a polyamide having a wide range of gas injection molding conditions, a good molding appearance, a uniform thickness of a hollow portion inside the molded product, and a high strength molded product. It is to provide a resin composition.

As a result of intensive studies to solve the above problems, the present inventors have determined that the relative viscosity value of the polyamide 6 resin is within a specific range, the amorphous polyamide resin and the glass fiber are within a certain range, and carbon By specifying black, it has been found that a wide range of gas injection molding conditions can be obtained, and at the same time, the thickness of the hollow part of the molded product is uniform, the molded product has excellent appearance, and a high strength molded product can be obtained. The present invention employs the following configuration.
(1) 85% to 96 parts by mass of polyamide 6 resin having a relative viscosity value (RV) measured at 25 ° C. and 1 g / dl in the range of 1.8 to 2.6 using 96% concentrated sulfuric acid as a solvent, A polyamide resin composition comprising 8 to 60 parts by mass of a glass fiber reinforcement and 0.01 to 5 parts by mass of channel type carbon black with respect to a total of 100 parts by mass of 4 to 15 parts by mass of a crystalline polyamide resin. Thus, a polyamide resin composition for gas injection, wherein TC2 measured by a differential scanning calorimeter (DSC) is 183 ° C. or higher and 190 ° C. or lower.
(2) The polyamide resin composition for gas injection according to (1), which is used for a door handle for an automobile.

  By using the resin composition of the present invention for gas injection molding, the wall thickness is uniform, the strength as a machine part represented by an adult car door handle is sufficient, the appearance after molding is not spotted on the whole, glass It is possible to obtain a molded article having a good appearance with no fiber floating. In addition, a wide range of gas injection molding conditions can be taken.

The present invention will be specifically described below.
The polyamide 6 resin of the present invention has a relative viscosity of 1.8 to 2.6 measured at 25 ° C. and 1 g / dl using 96 mass% concentrated sulfuric acid as a solvent.
In order to obtain a polyamide 6 resin having a relative viscosity of 1.8 to 2.6, a polyamide 6 resin having a relative viscosity of 1.8 to 2.6 is polymerized, or a relative viscosity of more than 2.6 is obtained. There is a method of cleaving a polyamide molecular chain using a thinning agent with a polyamide 6 resin having a viscosity. As the viscosity reducer, aliphatic dicarboxylic acid, aromatic dicarboxylic acid, etc. are effective. Specifically, oxalic acid, malonic acid, succinic acid, adipic acid, azelaic acid, sebacic acid, phthalic acid, terephthalic acid, etc. Can be mentioned. The amount of addition is about 0.1 to 3 parts by mass with respect to 100 parts by mass of polyamide 6 resin and melt kneading is within the relative viscosity range of the present invention, but the value of relative viscosity varies depending on the type of polyamide 6 resin. Therefore, it is necessary to conduct a preliminary experiment in advance to determine the amount of addition of the thinning agent.

If a polyamide 6 resin having a relative viscosity of greater than 2.6 is used, the resin fluidity becomes low, so it becomes difficult to obtain a uniform hollow wall thickness by the gas pressure of the gas injection. The mold transferability is also lowered, making it difficult to obtain a good molded appearance. In particular, in the case of a textured mold surface, if the fluidity is low, the resin does not travel deep into the texture, and the texture transfer becomes insufficient. If the wrinkle transfer is insufficient, the light reflectivity of the surface of the molded article is increased, resulting in an appearance with poor texture. The grain transferability can be generally expressed by a gloss value. However, when a polyamide 6 resin having a relative viscosity of more than 2.6 is used, the gloss value becomes large.
When a polyamide 6 resin having a relative viscosity of less than 1.8 is used, the fluidity becomes too high, causing problems in handling such as the resin flowing out from the nozzle of the molding machine before injection. Further, the mechanical strength and impact strength of the molded product are also lowered.

The amorphous polyamide resin in the present invention does not show a clear melting point when measured with a differential scanning calorimeter (DSC) according to JIS K7121. Specifically, 4,4′-diamino-3,3′-dimethyl-dicyclo-hexylenemethane (CA), 4,4′-diaminodicyclo-hexylenemethane (PACM), metaxylylenediamine (MXD) ), Trimethyl-hexamethylenediamine (TMD), isophoronediamine (IA), 4,4′-diamine-dicyclo-hexylenepropane (PACP), diamines such as hexamethylenediamine, terftal acid, isophthalic acid, adipic acid, Examples include, but are not limited to, polymers or copolymers or blends obtained by polycondensation from dicarboxylic acids such as sebacic acid and dodecanedioic acid, and lactams such as caprolactam and lauryl lactam. It is not a thing.
Among these amorphous polyamide polymers, hexamethylene terephthalate / hexamethylene isophthalate copolymer (6T / 6I), 4,4'-diamino-3,3'-dimethyl-dicyclo-he is particularly preferable. Xylene methane (CA) / isophthalic acid (I) / lauryl lactam (LL) copolymer (I / CA / LL), terephthalic acid (T) / trimethyl-hexamethylenediamine (TMD) polymer (T / TMD), etc. It is.

The compounding amount of the amorphous polyamide resin is 4 to 15 parts by mass with respect to 100 parts by mass in total of the polyamide 6 resin and the amorphous polyamide resin. When the amount of the amorphous polyamide resin is less than part by mass, the cooling and solidification rate in the mold becomes faster, the thickness after the gas injection molding is uneven, the glass fiber floats after molding, Transferability becomes insufficient.
On the other hand, when the blending amount of the amorphous polyamide resin exceeds 15 parts by mass, the cooling and solidification rate becomes too slow and the releasability becomes worse, and the mold cannot be released due to close contact with the mold, or the surface of the molded product is separated. Type wrinkles appear. Furthermore, since crystallinity deteriorates, it leads to a decrease in mechanical strength and impact strength.
In the present invention, the cooling and solidification rate in the mold can be expressed by a temperature-falling crystallization temperature (Tc2) measured by a differential scanning calorimeter (DSC) according to JIS K7121. That is, when the blending amount of the amorphous polyamide is less than 4 parts by mass, Tc2 is 190 ° C. or higher and cooling solidification is accelerated, and when it exceeds 15 parts by mass, Tc2 is 183 ° C. or lower and the cooling solidification rate is slow. Become.

As the glass fiber reinforcing material of the present invention, all commercially available materials such as E-glass, S-glass and C-glass can be used. The thickness of the glass fiber is not particularly limited, and a glass fiber having a diameter of about 5 to 15 μm can be used if the cross section is circular. Moreover, it is preferable to use the glass fiber surface-treated with the coupling agent for polyamide resins, or a sizing agent.
In this invention, the compounding quantity of glass fiber is 8-60 mass parts with respect to a total of 100 mass parts of polyamide 6 resin and an amorphous polyamide resin, Preferably it is 10-40 mass parts.
When the blending amount is less than 8 parts by mass, the reinforcing effect by the glass fiber is small, and the mechanical strength and impact strength are insufficient. On the other hand, when the compounding quantity of glass fiber exceeds 60 mass parts, the fluidity | liquidity at the time of a fusion | melting will worsen, and the thickness after gas injection molding will become non-uniform | heterogenous. In addition, appearance defects such as glass fiber floating easily occur.

In the present invention, in addition to glass fibers, organic, inorganic, fiber reinforcing materials, and non-fibrous reinforcing materials can be used in combination. Examples of the fiber reinforcing material include carbon fiber, potassium titanate whisker, zinc oxide whisker, aluminum borate whisker, aramid fiber, alumina fiber, silicon carbide fiber, ceramic fiber, stone koji fiber, and metal fiber. Examples of non-fiber reinforcing materials include silicates such as wollastonite, zeolite, sericite, talc, kaolin, mica, clay, pyrophyllite, bentonite, and alumina silicate, alumina, silicon oxide, magnesium oxide, zirconium oxide, and titanium oxide. , Metal oxides such as iron oxide, carbonates such as calcium carbonate, magnesium carbonate and dolomite, sulfates such as calcium sulfate and barium sulfate, hydroxides such as magnesium hydroxide, calcium hydroxide and aluminum hydroxide, milled glass Examples thereof include fibers, glass flakes, glass beads, ceramic beads, boron nitride, and silicon carbide. These reinforcing materials may be hollow, and a plurality of types may be used in combination. In addition, these reinforcing materials are combined with a coupling agent such as an isocyanate compound, an organic silane compound, an organic titanate compound, an organic borane compound, and an epoxy compound at the same time as the compounding with the polyamide resin, or processed into a reinforcing material in advance. Is preferable in terms of obtaining better mechanical properties and appearance.
The compounding amount of these reinforcing materials other than glass fibers is a range that does not exceed 60 parts by mass of the glass fibers with respect to 100 parts by mass in total of the polyamide 6 resin and the amorphous polyamide resin.

The channel type carbon black used in the present invention is for coloring the composition of the present invention black. By using the channel type carbon black, it is possible to obtain a molded product having a much better surface gloss than carbon black produced by the furnace method or other methods. That is, in the case of carbon black other than channel-type carbon black, the surface appearance of the molded product changes abruptly even if it is blended in a small amount of 0.1 part by mass with respect to 100 parts by mass of the total of polyamide 6 resin and amorphous polyamide resin. Specifically, the glass fiber is in a raised state, the mold transferability of the molded product is uneven, or the texture transferability becomes insufficient.
This is presumably because the channel-type channel-type carbon black has a fine particle size and the surface properties have a high affinity for the polyamide resin.
In the present invention, the compounding amount of the channel type carbon black is 0.01 to 5 parts by mass, preferably 0.05 to 3 parts by mass with respect to 100 parts by mass in total of the polyamide 6 resin and the amorphous polyamide resin. It is. When the blending amount is less than 0.01 parts by mass, the blackness is lowered, and when it exceeds 5 parts by mass, the mechanical strength is lowered.

In order to adjust the blackness, the polyamide resin composition of the present invention can be used in combination with an organic dye typified by a nigrosine type. The compounding amount of the organic dye is in a range not exceeding 1 part by mass with respect to 100 parts by mass in total of the polyamide resin and the amorphous polyamide resin. When the amount exceeds 1 part by mass, the chemical resistance decreases.
Furthermore, as a pigment other than carbon black, zinc sulfide, zinc oxide, iron oxide, chromium compound, nickel compound, cobalt, cobalt compound, titanium compound and the like can be used in combination.
The amount of the pigment other than carbon black is in a range not exceeding 3 parts by mass with respect to 100 parts by mass in total of the polyamide 6 resin and the amorphous polyamide resin. When it exceeds 3 parts by mass, the mechanical strength and impact strength are lowered.

  In addition, the polymyad resin composition of the present invention includes an antioxidant, an ultraviolet absorber, a plasticizer, a lubricant, an antistatic agent, a difficult-to-use agent, which are generally used for polyamide resins within a range that does not impair the object of the present invention. Additives such as a flame retardant and a release agent can be blended depending on the purpose.

The method for producing the polyamide resin composition of the present invention is not particularly limited, and a general single-screw extruder, twin-screw extruder, pressure kneader, or the like can be used as a kneading apparatus. A twin screw extruder is particularly preferred.
As an embodiment, polyamide 6 resin, amorphous polyamide resin, glass fiber, channel type carbon black and other reinforcing materials, pigments, dyes, additives, etc. are mixed as necessary and put into a twin screw extruder. The polyamide resin composition can be produced by uniformly kneading and kneading. The kneading temperature is preferably 230 ° C. to 320 ° C., and the kneading time is preferably about 0.3 to 10 minutes.

In the present invention, the gas injection molding is performed by injecting a high-pressure gas such as nitrogen gas immediately after the resin is injected into the mold in the injection molding, and transferring the mold surface by the gas pressure to obtain a hollow molded product. It is a technique. The cylinder temperature at the time of molding is 220 to 320 ° C, preferably 230 to 290 ° C.
The degree of hollowness of the gas injection molding obtained in the present invention can be expressed by the uneven thickness that can be observed when the gas injection molded product is cut at the center. Specifically, the ratio of the thickness of the thickest portion of the cross section to the thickness of the thinnest portion can be made uneven. For example, if the thickness of the thickest part is 4.0 mm and the thickness of the thinnest part is 2.0 mm, the uneven thickness is 2.0 (= 4.0 mm / 2.0 mm). It is. The preferred thickness unevenness in the present invention is 1.0 to 8.0, more preferably 1.0 to 5.0. When the uneven thickness is 8.0 or more, the thickness of the thinnest part is too thin, and the hollow burst during molding or the strength of the molded product is reduced.

When gas injection molding is performed with the resin composition obtained in the present invention, it is possible to obtain a molded product having a uniform thickness, a high strength of the molded product, and a uniform appearance after molding. In addition, since a wide range of molding conditions can be taken, a good product can be obtained stably.
The molded product obtained by the present invention is suitable for the exterior parts of electrical and mechanical parts, and is most suitable for thick molded products. In particular, automobile door handles have a molded product with a large thickness and are designed parts, so an excellent molded appearance is required. By using the resin composition of the present invention for gas injection molding, product strength is high and lightweight. In addition, it is possible to stably mass-produce door handles with excellent molded appearance.

  The present invention will be described in more detail with reference to the following examples and comparative examples, but the present invention is not limited to these examples.

The raw materials used in Examples and Comparative Examples of the present invention are as follows.
-As the polyamide 6 resin, four types of relative viscosities of 3.1, 2.5, 2.2, and 1.9 were prepared.
The relative viscosity was calculated from the following formula by dissolving 0.25 g of polyamide resin in 25 ml of 96% by mass sulfuric acid, placing 10 ml of this solution in an Ostwald viscosity tube, measuring at 25 ° C.
RV = t / t0
RV: Relative viscosity t: Dropping time of sample solution t0: Falling time of solvent • A hexamethylene terephthalate / hexamethylene isophthalate copolymer (6T / 6I) was prepared as an amorphous polyamide resin.
-The glass fiber prepared the chopped type with a single fiber diameter of 13 micrometers.
Two types of carbon black, channel type carbon black (hereinafter abbreviated as channel CB) and furnace type carbon black (hereinafter abbreviated as furnace CB), were prepared.

Kneading was performed using a twin screw extruder. After premixing all the components except the glass fiber in each composition of Examples and Comparative Examples, the mixture was put into a hopper of a twin screw extruder and melt kneaded. Glass fiber was separately fed from the vent port of the twin screw extruder. The setting conditions of the twin screw extruder are a cylinder temperature of 240 to 280 ° C. and a kneading time of 0.5 to 3 minutes.
The temperature-falling crystallization temperature (Tc2) of the obtained polyamide resin composition was measured with a differential scanning calorimeter (DSC) according to JIS K7121.

  The pellets of Examples and Comparative Examples were subjected to gas injection molding of automobile door handles with an injection molding machine. The mold used was that whose surface was textured (TH-112). The cylinder temperature was 260 ° C., the mold temperature was 80 ° C., and nitrogen was used as the gas injection gas.

The door handle molded products of Examples and Comparative Examples were evaluated by the following methods.
(1) Uneven Wall Thickness Ratio of the thickness of the thickest part and the thinnest part of the cross section when the gas injection molded product is cut at the center.
(2) Releasability It was evaluated whether the gas injection molded product could be released smoothly. The case where it was possible to release the mold smoothly was judged as ◯, the case where mold release wrinkles appeared on the surface of the molded product was judged as △, and the case where the mold could not be released was rated as x.
(3) Molding appearance It was visually confirmed whether the surface appearance of the gas injection molded product was free of abnormalities such as glass fiber floating or the like, and whether the texture transferability was uneven.
(4) Gloss value The gloss value of the embossed surface near the gate of the gas injection molded product was measured. The measurement used BYK-Gardner Gmbh's micro-TRI-gloss in a 60 ° field of view.
(5) Drop test A gas injection molded product was dropped from a height of 1 m to evaluate whether cracking occurred.

  Examples and Comparative Examples were carried out with the compositions described in Tables 1 to 4, and each evaluation was performed.

  Even when the gas injection molding was performed on the pellets of each example, no problem was found in the uneven thickness property and releasability. Also, there is no problem of glass fiber floating, mold release wrinkles, etc. in the molded appearance, and the gloss value is 1.0 or less, and a molded product with a high texture and satisfactory strength can be obtained by sufficiently transferring the texture on the mold surface. It was.

On the other hand, in Comparative Example 1 and Comparative Example 6 in which the amorphous polymiad resin was not blended, the cooling and solidifying speed in the mold was increased, the uneven thickness was high, and the glass fiber was floated even in the molded appearance, and the gloss was increased. The value was as high as 1.5 or more, and the texture was low. In Comparative Example 2 in which the amorphous polyamide was excessively blended, there was no problem in uneven thickness, gloss value, and product strength, but the releasability deteriorated and release wrinkles were observed in the molded appearance. . Furthermore, in Comparative Example 3 in which an amorphous polyamide resin was added in excess of Comparative Example 2, the mold itself was in close contact with the mold, and the molded product could not be taken out.
In Comparative Example 4 in which the relative viscosity of the polyamide 6 resin is excessively increased and in Comparative Example 5 in which the amount of the glass fiber is excessively increased, the texture transferability is insufficient, the gloss value is increased, and the texture is lacking. Glass fiber floating was also observed.
In Comparative Example 7 in which the blending amount of the glass fiber was lowered and in Comparative Example 8 in which the blending amount of the channel CB was excessively high, there was no problem in uneven thickness, release property, molded appearance, and gloss value, but the strength was The result was insufficient and the result was broken in the drop test.
On the other hand, in Comparative Examples 9 and 10 using the furnace CB, glass fiber floating was observed in the molded appearance, and a satisfactory one was not obtained.

  The resin composition obtained in the present invention has a wide range of molding conditions in gas injection molding, high product strength, good molding appearance, and sufficient transfer of the mold surface, resulting in low gloss and texture. It will be expensive. Therefore, it is necessary to achieve both strength and weight reduction of the product, and is highly suitable for exterior members in the fields of electric and electronic fields and automobiles, particularly automobile door handles.

Claims (2)

85 to 96 parts by mass of a polyamide 6 resin having a relative viscosity value (RV) measured at 25 ° C. of 1 g / dl in the range of 1.8 to 2.6, using 96% concentrated sulfuric acid as a solvent, amorphous polyamide The resin composition is a polyamide resin composition comprising 8 to 60 parts by mass of a glass fiber reinforcement and 0.01 to 5 parts by mass of a channel type carbon black with respect to a total of 100 parts by mass of 4 to 15 parts by mass. A polyamide resin composition for gas injection, wherein TC2 measured with a scanning calorimeter (DSC) is 183 ° C. or higher and 190 ° C. or lower. 2. The polyamide resin composition for gas injection according to claim 1, which is used for a door handle for an automobile.