JP2003301060A - Thermoplastic resin for injection foam molding - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thermoplastic resin for injection foam molding to be used in producing an injection foam molded product which is improved in the failure of sink marks and sliver streaks. <P>SOLUTION: The thermoplastic resin for injection foam molding has a melting point of 150-180°C, and a resin temperature T(°C), a wall surface shear rate γ(1/sec), and a melt viscosity η (Pas) on molding which meet the formula 1: ημγ<SP>2</SP>×10<SP>-6</SP>+2T≥560, and the thermoplastic resin for injection foam molding is a propylene resin. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a thermoplastic resin used for injection foam molding.

[0002]

2. Description of the Related Art When a rib is attached to a molded product made of a thermoplastic resin for the purpose of reinforcing the strength, there is a problem that a dent (sink) occurs on the top plate and the appearance is deteriorated. . It is considered that this is because during molding, cooling of the top plate and the root of the rib is delayed compared to other general parts, and a difference in volume shrinkage occurs. As a countermeasure against this, conventionally, there has been an improvement in the molding method that optimizes the injection speed and pressure-holding conditions, an improvement in the process in which ribs are separately molded and then bonded to the design surface, and there are wrinkles on the surface where sink marks occur. Improvement of the design surface to hide the sink mark by giving it, improvement of the product design surface to reduce the volume shrinkage speed amount of the sink portion by making the plate thickness of the rib thinner than the general plate thickness, the volume with filler added Ingenuity has been made in terms of materials for selecting thermoplastic resins with low shrinkage. However, these methods not only reduce the flexibility of material selection, product design and mold design, but also increase the manufacturing cost and the original role of the rib (for example, impact energy related to automobile safety regulations). Function to absorb)
This sometimes led to the selection of a shape with insufficient performance in obtaining.

On the other hand, attempts have been made from a long time ago to compensate for shrinkage by supplementing volume contraction with volume expansion due to foaming. However, when injection foam molding is carried out under general molding conditions, a defective appearance called silver streak appears on the surface. Therefore, it was not suitable for applications requiring high-grade appearance such as automobile interior parts. A method of lowering the cylinder temperature in order to avoid silver streak failure is also known, but with this method, the volume expansion force due to foaming is weak and a sufficient effect cannot be obtained in terms of measures against core sink.

[0004]

Under such circumstances, an object of the present invention is to provide a thermoplastic resin for injection foam molding which is used for producing an injection foam molded article having improved sink marks and silver streak defects. .

[0005]

The present invention has a melting point of 150.
℃ ~ 180 ℃, and the resin temperature T (℃) at the time of molding
, Wall shear rate γ (1 / sec), and melt viscosity η (Pa
Sec) refers to a thermoplastic resin for injection foam molding satisfying the formula 1. η × γ ² × 10 ⁻⁶ + 2T ≧ 560 [Formula 1] Hereinafter, a detailed description will be given.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION Although it is not certain whether it is right or wrong, according to the study by the present inventors, in the silver streak, bubbles generated near the tip of the resin flow flowing in the cavity rub against the mold wall surface. If the temperature of the resin in contact with the mold wall surface when the bubbles reach the mold wall surface is sufficiently high, the silver streak once generated is considered to be eventually inconspicuous. Therefore, in the present invention, it is considered that the temperature of the resin in contact with the wall surface of the mold is increased by selecting the resin that generates a large amount of heat due to shearing, and the silver streak defect is improved. Whether this theory is right or wrong, according to the present invention, an injection-molded article with improved sink marks and silver streak defects can be obtained.

The thermoplastic resin for injection foam molding of the present invention comprises:
Melting point is 150 ° C. to 180 ° C., and resin temperature T (° C.) during molding, wall surface shear rate γ (1 / sec), and melt viscosity η (Pa · sec) satisfy Expression 1. It is a resin that generates a large amount of shear heat during molding. η × γ ² × 10 ^-6 + 2T ≧ 560 [Equation 1]

Here, T (° C.) is the resin temperature during molding.
The resin with the cylinder unit separated from the mold.
The temperature of the molten resin immediately after injection is measured by a thermocouple thermometer.
To measure. In addition, γ (1 / sec) is the wall shear rate during molding
Degree (shear rate at the part closest to the wall surface of the resin),
If the wall shear rate differs depending on the part,
Of the wall shear rate when the tip of the resin flow passes through the section
The lowest value shall be adopted. The wall shear rate is known
It may be obtained by a method such as Avraam I. Isayev,
 "Injection and Compression Molding Fundamentals",
 Finite elements described in Marcel Dekker, Inc., 44-61, 1987.
It is calculated by the method simulation. Also of the mold
The cavity has a rectangular cross section perpendicular to the resin flow direction.
If the flow direction of the resin is uniform, the melt viscosity of the resin
Under the approximation that is constant regardless of the shear rate
Cross-sectional dimensions (width W (cm) and thickness H (cm)) and injection
Rate Q (cm ³/ Sec) and
It γ = 6Q ÷ (W × H²) η (Pa · sec) is the melt viscosity of the resin during molding,
Capillary rheometer under the conditions of temperature T and γ
Therefore, it measures.

The left side of the above equation (1) is an image expression showing the index of the temperature at which shear heat is generated in the vicinity of the surface layer immediately after the inflow of the resin. The larger this value, the higher the surface layer temperature, and the value is 560 or more. It is preferably 600 or more and particularly preferably.

The thermoplastic resin for injection foam molding of the present invention comprises:
It is not particularly limited as long as it satisfies the above formula 1, and examples thereof include a styrene resin, an acrylic resin, an amide resin, and the like, and an olefin resin is preferably used. Examples of the olefin resin include ethylene, propylene, butene-1, pentene-1, hexene-1,
Homopolymers of α-olefins such as 3-methylbutene-1 and 4-methylpentene-1, copolymers obtained by copolymerizing at least two kinds of monomers selected from these, and copolymerizable with these And a copolymer with an unsaturated monomer of the above. Among the above, propylene resin is preferably used. The propylene-based resin here is a polymer obtained by polymerizing propylene and has isotactic crystallinity. Examples of the propylene-based resin include a propylene homopolymer and a copolymer of propylene and ethylene and / or an α-olefin having 4 to 12 carbon atoms. The propylene-based resin preferably has a melt flow rate measured according to JIS K6758 of 1 to 60 g / 10 minutes, more preferably 1 to 35 g / 10 minutes.

As the thermoplastic resin for injection foam molding of the present invention, these thermoplastic resins may be used alone or in combination of two or more kinds. When the present invention is applied to a composition containing two or more thermoplastic resins, the composition is preferably:
A composition containing 50% by weight or more of a propylene-based resin (expressed as 100% by weight of total resin components) is used.

Further, the foaming agent used in the injection foam molding is not particularly limited, and examples thereof include physical foaming agents represented by nitrogen gas and carbon dioxide, and organic or inorganic chemical foaming agents. Are known. When the gas known as the physical foaming agent is used in a supercritical state, it is easy to dissolve and diffuse in the molten resin, which is preferable.

The chemical foaming agent is not particularly limited as long as it is a chemical foaming agent used for injection foam molding of a thermoplastic resin, and an organic chemical foaming agent represented by an ADCA chemical foaming agent; baking soda or citric acid. Inorganic chemical foaming agents represented by The latter is preferable from the viewpoint of preventing mold contamination.

Since the amount of gas generated by these chemical foaming agents differs depending on the resin temperature during molding, it is difficult to unconditionally exemplify the amount used. The amount may be appropriately added according to the amount of gas suitable for the expansion ratio of the final product.

In producing an injection foam molding using the thermoplastic resin for injection foam molding of the present invention, molding conditions such as molding temperature are not particularly limited, and the viscosity of the thermoplastic resin used and the foaming agent It may be set appropriately according to the gas generation amount. The production is preferably carried out at a sufficiently high molding temperature (resin temperature at the time of molding) from the viewpoint of sink measures, and the molding temperature is more preferably 200 to 280 ° C.,
More preferably, it is 220 to 260 ° C. The molding temperature is controlled by setting the temperature of the cylinder and adjusting the screw rotation speed and back pressure in the plasticizing step. If the molding temperature is too high, foaming tends to occur, which is not preferable.

In producing an injection foam molding using the thermoplastic resin for injection foam molding of the present invention, no new equipment or additional mechanism is required for the mold or the injection molding apparatus, but further molding of the molded product is required. To reduce the weight, it is preferable that the thickness of the product is 2 mm or more if necessary. The plate thickness at this time refers to the thickness of a surface that is orthogonal to the mold clamping direction and that occupies most of the product. In order to further improve the foaming ratio, a method of increasing the cavity volume by operating the mold after filling the resin may be used. In this case, the plate thickness means the thickness before the mold operation is started.

The amount of resin injected when an injection foam molded article is manufactured using the thermoplastic resin for injection foam molding of the present invention is such that the entire cavity volume is filled with resin immediately after the end of resin injection. Is preferred.

The production of the injection foam molded article using the thermoplastic resin for injection foam molding of the present invention is not limited to the injection molded article having the ribs attached thereto, but also various injection molded articles having the same sink mark. Are suitable. INDUSTRIAL APPLICABILITY In the present invention, it is preferably applied to an injection molded body provided with ribs.

[0019]

EXAMPLES The present invention will be described below with reference to examples.
It is not limited to this. The evaluation methods in Examples and Comparative Examples are as follows.

(1) Melt flow rate According to JIS K6758, temperature 230 ° C., load 21.
It was measured at 18N.

(2) Melt viscosity A capillary having a length of 40 mm, a diameter of 1 mm, and a capillary inflow angle (the smaller value of the angles between the wall surfaces in the cross section of the capillary inflow part) of 90 degrees is used as a capillary in the Toyo Seiki Seisakusho Capillograph 1B. And measured. When it was not possible to directly measure the melt viscosity at the required wall shear rate, the measured values of the melt viscosity at a plurality of shear rates were plotted in a logarithmic log to obtain a quadratic approximation curve, which was obtained by interpolation.

(3) Product Appearance (Judgment of Silver Streak) The degree of silver streak was visually sensory evaluated. ◯: No silver streak is observed at all parts of the surface of the molded product. X: Silver streak is recognized on at least one part of the surface of the molded product.

(4) Sinking The degree of sinking was visually evaluated by sensory evaluation. ◯: No sink mark is observed for all ribs. Δ: A sink mark is recognized on at least one rib. X: A large sink mark is recognized in at least one rib.

Materials used in Examples and Comparative Examples are as follows.

(1) Blowing Agent Masterbatch An inorganic chemical blowing agent (MB3062 manufactured by Sankyo Kasei Co., Ltd.) was used.

(2) Pigment master batch Black SPEM-8H102HC manufactured by Sumika Color Co., Ltd.
AN was used.

In the examples and comparative examples, IS650E (manufactured by Toshiba Machine Co., Ltd., using a shut-off nozzle) is used as an injection molding machine, and the injection molding product (350 m) shown in FIG. 1 is used.
m × 90 mm × 25 mm) was obtained. The plate thickness of the part excluding the rib is 3.0 mm, and the wall thickness of the rib part is 1.4 m at the base.
m, the tip portion was 1.0 mm, and the height of the rib portion was 25 mm. The distance between the ribs was 20 mm. The product width is 12.5 cm and the plate thickness is 0.3 when the mold cavity is cut along a plane perpendicular to the flow direction, excluding the ribs.
cm and the injection rate is Q (cm ³ / sec), the wall shear rate is 6 × Q ÷ (12.5 × 0.3 ² ) = 5.3.
It becomes 3 × Q (1 / second).

Example 1 A propylene-ethylene block copolymer (AZ161C manufactured by Sumitomo Chemical Co., Ltd., melt flow rate = 30 g / 10 minutes), a foaming agent masterbatch, and a pigment masterbatch were used as 100 / 2.0. /0.5
Dry blending was performed at a compounding ratio of (wt part / wt part / wt part), and this mixed material was injection molded. The molding conditions and resin parameters were as follows. Resin temperature 230 ℃ Mold temperature 54 ℃ Cooling time 30 seconds Injection rate 390 cm ³ / second (Thus wall shear rate γ is 2
It was 080 (1 / second). ) Melt viscosity of resin (temperature 230 ° C, wall shear rate 2080
(1 / sec)) 29.9 (Pa · sec) Table 1 shows the value on the left side of Expression 1 and the evaluation result at this time.

Example 2 A propylene-ethylene block copolymer of another grade (specifically, AH561 manufactured by Sumitomo Chemical Co., Ltd., melt flow rate = 3 g /
It operated like Example 1 except having changed to 10 minutes).
The melt viscosity of the resin was 58.9 (Pa · sec). Table 1 shows the values on the left side of Expression 1 and the evaluation results at this time.

Comparative Example 1 A propylene-ethylene block copolymer (AU561E1 manufactured by Sumitomo Chemical Co., Ltd., melt flow rate = 60 g / 10 minutes), a foaming agent masterbatch, and a pigment masterbatch were mixed with 100 / 2.0. / 0.
Dry blending was carried out at a compounding ratio of 5 (wt part / wt part / wt part), and this mixed material was injection molded. The molding conditions and resin parameters were as follows. Resin temperature 180 ° C Mold temperature 54 ° C Cooling time 30 seconds Injection rate 195 cm ³ / sec (Thus wall shear rate γ is 1
It was 040 (1 / second). ) Melt viscosity of resin (temperature 180 ° C., wall shear rate 1040
(1 / sec)) 57.7 (Pa · sec) Table 1 shows the value on the left side of Expression 1 and the evaluation result at this time.

[0031]

[Table 1]

[0032]

INDUSTRIAL APPLICABILITY As described above in detail, according to the present invention, there is provided a thermoplastic resin for injection foam molding which is used for producing an injection foam molded article having improved sink marks and silver streak defects.

[Brief description of drawings]

FIG. 1 is a drawing showing the shape of an injection-molded article manufactured in an example.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁷ Identification code FI Theme Coat (reference) C08L 101: 00 C08L 101: 00 (72) Inventor Masaaki Tsutsubuchi 1-5 Anezaki Kaigan, Ichihara, Chiba Sumitomo Chemical In-house F-term (reference) 4F074 AA24 AA25 AA97 AB03 AB05 AG06 CA26 4F206 AA11 AG20 AM34 AM36 JA04 JM04 JN11

Claims (3)

[Claims] 1. A melting point of 150 ° C. to 180 ° C., and
Molding resin temperature T (° C) and wall shear rate γ (1 /
Sec) and the melt viscosity η (Pa · sec) satisfy the formula 1. A thermoplastic resin for injection foam molding. η × γ ² × 10 ^-6 + 2T ≧ 560 [Equation 1] 2. The thermoplastic resin for injection foam molding according to claim 1, wherein the thermoplastic resin is a propylene resin. 3. A melt flow rate of 1 to 60 (g / 10
The thermoplastic resin for injection foam molding according to claim 1 or 2.