JPH02153944A - Resin composition for molding speaker box - Google Patents

Abstract

PURPOSE:To provide the subject lightweight composition having improved dissipation factor and rigidity (flexural modulus) by adding an inorganic filler and a chemical foaming agent in a specific ratio to a base material comprising a mixture of a PP copolymer and PP polymer. CONSTITUTION:(A) 100pts.wt. of a base material comprising a mixture of 25-50 pts.wt. of polypropylene-polyethylene block copolymer (preferably containing 20-30wt.% of the PE block) and 75-50pts.wt. of polypropylene homopolymer (preferably having a number-average mol.wt. of 20,000-35,000) is compounded with (B) 10-25pts.wt. of an inorganic filler (e.g. calcium carbonate) having a specific gravity of >=1 and (C) 0.1-0.5pt.wt. of a chemical foaming agent (e.g. asodicarbonamide) to provide the objective composition.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a resin composition for molding a speaker box, which is formed by blending an inorganic filler and a chemical foaming agent into a base material made of a resin mixture.

[Conventional technology]

Materials for manufacturing speaker boxes are required to have mechanical strength from the perspective of being used as a container for storing speakers, and are also required to have excellent acoustic properties from the perspective of being used as an audio device. In order to meet these conditions, various materials are used for producing speaker boxes, mainly depending on the intended use of the speaker. The main speaker box materials currently used in various fields are wood-based materials such as particle board and plywood, and resin-based materials such as acrylonitrile butadiene styrene, polystyrene, polymethyl methacrylate, etc.
These include those based on polycarbonate or polypropylene resins, and foams of these resins.

[Problem to be solved by the invention]

It is extremely difficult to manufacture conventionally used wood-based speaker box materials such as particle board and plywood into complex shapes. Therefore, if the space in which the speaker box is installed is limited and a speaker box that is suitable for the space must be manufactured, for example, in the case of a speaker box to be mounted on a vehicle, such wood-based materials are inappropriate.

Resin-based materials are generally easy to mold into speaker boxes of desired shapes, and are therefore widely used even in fields where it would be difficult to use wood-based materials. Further, since resin-based materials are generally lightweight, they are particularly suitable as materials for speaker boxes mounted on vehicles. However, since resins other than polypropylene are generally expensive, polypropylene resin is currently widely used as a manufacturing material for speaker boxes with complex shapes such as speaker boxes for vehicles. These are base materials, and they are generally used with fillers added to supplement their rigidity. The polypropylene resin currently used as a base material for speaker box molding materials is a polypropylene-polyethylene block copolymer. Polypropylene homopolymer itself lacks rigidity and has very low impact resistance, so the lack of rigidity cannot be compensated for by adding fillers, so it is not used as a base material for speaker box molding materials. Not yet.

The demand for improving the acoustic characteristics (loss coefficient) of speaker boxes continues to increase. In order to improve the loss factor in molding materials based on polypropylene-polyethylene block copolymers, the amount of filler blended must be reduced. However, this resulted in a decrease in rigidity, and thus could not satisfactorily meet the demand for improved acoustic characteristics.

In addition, speaker boxes installed in vehicles, etc.
The demand for weight reduction has been increasing in recent years.

In order to fully meet the above-mentioned needs for a speaker box, the present invention provides a speaker box with the following requirements as compared to a speaker box molded from a conventional filled polypropylene-polyethylene block copolymer based material. It is an object of the present invention to provide a molding composition that can improve the rigidity and loss coefficient, which are important among the performance characteristics, and improve the acoustic characteristics and reduce the weight of a molded speaker box.

[Means to solve the problem]

The speaker box molding resin composition of the present invention comprises a polypropylene-polyethylene block copolymer of 25 to 50%
10 to 25 parts by weight of an inorganic filler with a specific gravity of 1 or more and 0.1 to 0.1 to a chemical blowing agent to 100 parts by weight of a base material consisting of a mixture of 75 to 50 parts by weight of a polypropylene homopolymer and 75 to 50 parts by weight of a polypropylene homopolymer.
This is a resin composition formed by blending 0.5 parts by weight.

The polypropylene-polyethylene block copolymer used in the present invention preferably has a polyethylene content of 1
It is a copolymer of 0 to 30% by weight. If the polyethylene content is less than 10% by weight, sufficient impact resistance cannot be maintained, and if it is more than 30% by weight, the rigidity and strength will be significantly reduced, which is undesirable. Although any polyethylene content may be used as long as the polyethylene content is within the above-mentioned preferred range, products having a number average molecular weight of 20,000 to 35,000 are generally available. The blending amount of this copolymer in the composition of the present invention is 25 to 50
Parts by weight. If the amount of the copolymer exceeds 50 parts by weight, the impact strength of the molded speaker box will increase, but the rigidity and loss factor will decrease. If the amount of the copolymer is less than 25 parts by weight, the rigidity and loss factor are satisfactory, but the impact strength is reduced.

It is preferable to use a polypropylene homopolymer typically having a number average molecular weight of 20,000 to 35,000. The blending amount of the polypropylene homopolymer is 75 to 50 parts by weight, and the total amount with the polypropylene-polyethylene block copolymer is 100 parts by weight.

The inorganic filler having a specific gravity of 1 or more used in the present invention is a common inorganic filler used in molded speaker boxes, such as calcium carbonate, talc, mica, and the like. The amount of the inorganic filler in the composition of the present invention is 10 to 25 parts by weight per 100 parts of the base material made of a mixture of a polypropylene-polyethylene copolymer and a polypropylene homopolymer. If the amount of the inorganic filler is less than 10 parts by weight, the resulting molded article will lack rigidity. If the amount of the inorganic filler is more than 25 parts by weight, it is not preferable because the fluidity of the composition during molding will deteriorate.

The chemical foaming agent blended into the speaker box molding composition of the present invention may be any chemical foaming agent as long as it decomposes and foams at a molding temperature of 190 to 230°C.For example, azodicarbonamide Foaming agents such as are suitable. The chemical blowing agent is compatible with the composition comprising the above polymer base material and inorganic filler to which it is added, for example, in the form of a 10% by weight blend of polyethylene resin (mater batch). It may be added to the composition. If the amount of the chemical blowing agent is less than 0.1 part by weight, the expected effect will hardly be obtained;
If the amount is more than 1 part by weight, it is not preferable because it adversely affects the mechanical strength of the molded article.

When molding a speaker box using the composition of the present invention, a polypropylene-polyethylene copolymer, a polypropylene homopolymer, and an inorganic filler are prepared in advance using a -screw or twin-screw extruder, a Banbury mixer, etc. The mixture is kneaded, and then a chemical blowing agent is triblended with this mixture using a mixer such as a Henschel mixer, and the mixture is molded using, for example, an injection molding machine to produce a foamed speaker box.

Needless to say, the composition of the present invention may also contain conventional additives, such as pigments, which are added when manufacturing molded speaker boxes.

[For production]

In the composition of the present invention, the polypropylene-polyethylene block copolymer serves to ensure that the impact strength of the resulting molded speaker box is practically sufficient when foamed to reduce the weight of this product. do. Furthermore, the polypropylene homopolymer improves the loss factor, and the inorganic filler improves the rigidity. Therefore, the composition of the present invention formed by appropriately blending each of these components,
As a result, it is possible to provide a speaker box with improved rigidity and loss coefficient, improved acoustic characteristics, sufficient impact strength, and reduced weight.

A speaker box with a thickness of 0.4 cm was manufactured. About these speaker boxes Stiffness (flexural modulus)
, the loss factor was measured. The measurement results are shown in Table 1.

Chapter 1 Table 〔Example〕 Next, the present invention will be explained in more detail with reference to Examples.

The raw resin and talc were uniformly kneaded at a temperature of 210°C using a twin-screw extruder at the mixing ratio shown in Table 1, and then this mixture contained 10% by weight of azodicarbonamide. A composition was prepared by adding 2.0 parts by weight of polyethylene resin. The polypropylene-polyethylene block copolymer used had a polyethylene content of 20% and a number average molecular weight of 12
7,000, and the number average molecular weight of the polypropylene homopolymer was 21,000. These compositions were molded using a conventional injection molding machine, and the approximate size was 15x1.
5x 6 an.

Note) In this table, PP/PH represents a polypropylene-polyethylene block copolymer, and PR represents a polyethylene homopolymer (same as in Table 2).

Table 1 shows that the speaker box molded from the foaming agent-containing composition of the present invention has better rigidity (flexural modulus) and loss coefficient at the same talc content than the conventional speaker box of the comparative example. It can be seen that even when the talc content is small (-2/2), the rigidity (flexural modulus) is almost the same, and the loss factor is improved.

One Piece I In the same manner as in Example 1, a composition having the blending ratio shown in Table 2 was prepared, and a speaker box was molded from this composition. The blowing agent used was azodicarbonamide 0.25
The weight part was 0. The weight, thickness, and rigidity of the manufactured speaker box (flexural modulus (kg/cd)
(am')), the loss coefficient and the falling impact value as the second
In Table 2, the comparative examples that do not contain a blowing agent are conventional molding compositions.

Table 2 Table 2 shows that the speaker box molded from the composition of the present invention containing a foaming agent has a significantly reduced weight compared to conventional non-foamed products, and is also improved. It can be seen that the rigidity and number of #I failures are maintained.

〔Effect of the invention〕

A speaker box molded from the composition of the present invention is
Compared to conventional resin speaker boxes, the loss coefficient and rigidity (flexural modulus) are improved, resulting in improved acoustic properties, and since it is a foamed product, it is lightweight yet has sufficient impact strength. Therefore, the composition of the present invention can promote a lightweight speaker box while maintaining acoustic properties equivalent to or better than conventional non-foamed products.

Claims (1)

[Claims] 1. Polypropylene-polyethylene block copolymer 2
5 to 50 parts by weight and 75 to 50 parts by weight of polypropylene homopolymer
10 to 25 parts by weight of an inorganic filler with a specific gravity of 1 or more and 0.1 to 0.5 parts by weight of a chemical blowing agent are blended with 100 parts by weight of a base material consisting of a mixture with parts by weight. A resin composition for molding speaker boxes.