JPH07124996A - Insert molded article - Google Patents

Abstract

PURPOSE:To prevent for a long time cracks and breakages from occurring on a molded article by using a polyacetal copolymer resin with a crystallization time of at least a specified time when insert molding of a premolded part is performed. CONSTITUTION:As a polyacetal copolymer resin, a polyacetal copolymer resin with a crystallization time of at least 5min. is used. This copolymer resin is pref. a polymer wherein 3-30wt.% oxyalkylene unit with the carbon number of at least 2 are incorporated in a polymer wherein oxyalkylene unit is a main constitutional unit and the melt index is pref. 1.0-60g/10min.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an insert-molded product, and more particularly to an insert-molded product suitable for use in applications requiring precision and excellent dimensional stability.

[0002]

2. Description of the Related Art Various home appliances such as tape recorders and video tape recorders (VTRs) and automobile parts are
A so-called insert that holds a member such as metal or ceramics with a plastic located on the outer periphery of the insert because of its advantages such as a great degree of freedom in design, reduction of post-processing, weight reduction, and low cost. Molded products manufactured by the molding method are often used. As these thermoplastic resins for insert molding, various resins such as polyolefin resins such as polyethylene and polypropylene as well as engineering plastics such as polyester resin, polyacetal resin, polyamide resin and polycarbonate resin are used. The above-mentioned engineering plastics are used particularly for applications requiring precision and dimensional stability, and polyacetal resins excellent in rigidity, creep characteristics and sliding characteristics are heavily used.

[0003]

However, in general, resin molding is performed at a high temperature and then cooled to room temperature, and the insert parts and the insert parts are fixed due to the difference in thermal expansion coefficient between the insert parts and the resin. A stress is generated between the boss and the resin boss. In particular, the polyacetal resin has a large shrinkage after molding as compared with other thermoplastic resins, so that the stress thereof is large. This stress has a function of fixing the insert part to the resin boss portion, but sometimes the boss portion is cracked due to the strain generated by this stress, or the molded product is sometimes broken. Further, there is a problem that even if there are no cracks or cracks at the beginning of molding, creep fracture occurs after a long time. As measures against these, many measures have been taken in terms of shape such as increasing the thickness of the resin part and providing slits in the resin part, but it is not satisfactory because the manufacturing process becomes complicated. .

[0004]

DISCLOSURE OF THE INVENTION The inventors of the present invention have solved the problems of the prior art by reducing the stress between the insert part made of metal or ceramics and the resin boss portion and making the insert molded product long-term. As a result of diligently studying for the purpose of providing cracks and cracks and providing a good molded product, it was found that it is extremely effective to use a specific polyacetal copolymer resin, and the present invention is completed. Came to. That is, the present invention is an insert-molded product obtained by insert-molding a polyacetal copolymer resin having a crystallization time of 5 minutes or more into a preformed part.

The crystallization time referred to in the present invention means that the polyacetal resin is held at 200 ° C. for 5 minutes using a differential scanning calorimeter (hereinafter referred to as DSC), and then the temperature is lowered to 152 ° C. at 10 ° C./minute. It means the time from the start of holding when kept at ℃ to the exothermic peak due to crystallization, and the shorter the time, the faster the crystallization rate. In the present invention, the polyacetal copolymer resin having the crystallization time of 5 minutes or more is selectively used. To obtain an excellent insert-molded product, the crystallization time of the resin material used is important. If the crystallization time is shorter than 5 minutes, the shrinkage during molding and the post-shrinkage when the molded product is heated are large. However, the intended effect of the present invention cannot be obtained. On the contrary, if the crystallization time is too long, not only the solidification time of the injected resin becomes long and the productivity is lowered, but also the mechanical strength of the obtained molded article is lowered, which is not preferable and practically 5 A range of up to 500 minutes is preferred.

The polyacetal resin of the present invention is a copolymer containing a oxymethylene unit (--OCH _2- ) as a main constituent unit and a copolymer or terpolymer obtained by copolymerizing the following cyclic ether or cyclic formal. It is united. Further, the skeleton of the polymer is not particularly limited, and there is no problem even if it has not only a linear structure but also a branched structure or a crosslinked structure. In addition, the melt index of such polyacetal resin (hereinafter referred to as MI)
Is not particularly limited, but 1.0 from the viewpoint of formability.
It is desirable to be ~ 60g / 10min. When the MI is less than 1.0, the resin does not flow well during injection molding, and it becomes difficult to obtain a molded product having a desired shape. On the other hand, if the MI is too large, the molded product becomes brittle, which is not preferable. The melt index as used in the present invention is 190 ° C, 21 ° C, according to ASTM-D1238.
The value measured with a load of 60 g is expressed in units of g / 10 minutes.

The comonomer component used for producing the polyacetal copolymer is not particularly limited, but it is generally preferable to be at least one selected from those having a structure of the following general formula.

[0008]

[Chemical 1]

(Wherein R ₁ , R ₂ , R ₃ and R ₄ are the same or different substituents, and are a hydrogen atom and an alkyl group (having 1 to 5 carbons and 0 to 3 hydrogens being halogens). Atom-substituted, the same shall apply hereinafter) or a halogen-substituted alkyl group, and R ₅ represents a methylene group, an oxymethylene group, a methylene group or an oxymethylene group substituted by an alkyl group or an alkyl halide, respectively. Group (in this case p =
Integer of 0 to _{3), - (CH 2) q} -OCH 2 - (q = 1~4 integer)
Or - a divalent group represented by (q = 1 to 4 integer) (in this case p = 1) - (O- CH 2 -CH 2) q -OCH 2. ) Further, in order to obtain a copolymer having a crystallization time of 5 minutes or more as described above, 3 oxyalkylene units having 2 or more carbon atoms are added to a polymer having an oxymethylene unit as a main constituent unit.
To 30% by weight, preferably 3 to 15% by weight, particularly, the monomer component constituting the oxyalkylene unit having 2 or more carbon atoms is 1,3-dioxolane, diethylene glycol formal, 1,3-propanediol formal, 1 It is desirable to be any one or more of 1,4-butanediol formal, 1,5-pentanediol formal and 1,6-hexanediol formal.

The present invention is based on conventionally known additives such as various stabilizers including antioxidants, nucleating agents, pigments, antistatic agents, light stabilizers and reinforcing materials such as
Glass fiber, glass flakes, talc, mica,
Potassium titanate whiskers can be added and blended. In addition, polymer blends with polyurethane resins, acrylic resins, polyolefin resins, etc., and polymer alloys are also possible.

[0011]

[Function] The polyacetal copolymer resin having a crystallization time of 5 minutes or more has not only excellent mechanical strength, heat resistance and slidability, but also small shrinkage during molding and shrinkage due to post-heating and excellent dimensional stability. Since it exhibits excellent properties, it can be used as an optimum resin material for parts that require particularly high precision and dimensional stability, and it is possible to obtain an insert-molded product with extremely few cracks and cracks over a long period of time. Further, since the stress applied to the molded product is reduced, it is possible to reduce the wall thickness.

[0012]

EXAMPLES The present invention will now be described in detail with reference to Examples, but it goes without saying that the present invention is not limited to these. Example 1 As a copolymer component, a polyacetal copolymer resin containing 3% by weight of an oxyalkylene unit composed of 1,3-dioxolane was used to mold a molded product shown in FIG. 1 with an injection molding machine. The molded product obtained is at a temperature of 23 ° C and a relative humidity of 50.
After being left for 24 hours in a room adjusted to 100%, the degree of sticking (the degree of rattling) between the inserted metal member and the resin boss and the presence or absence of cracks in the resin were examined.
Further, after performing a heat shock test on this molded product, the degree of fixation (the degree of rattling) between the metal part and the resin boss portion and the presence or absence of cracks or cracks in the resin portion were examined. The results are shown in Table 1. The heat shock test is a test in which a molded product is heated at 120 ° C for 1 hour, then immediately moved to an atmosphere of -40 ° C and cooled for 1 hour. 100 cycles of heating-cooling as one cycle I went. Example 2 A polymer having 5% by weight of oxyethylene units was produced by the same procedure as in Example 1 except that the mixing ratio of trioxane and 1,3-dioxolane was changed. The same test as in Example 1 was carried out also when this polymer was used. The results are shown in Table 1. Example 3 The procedure of Example 1 was repeated except that 1,3-dioxolane was changed to 1,4-butanediol formal to prepare a polymer having an oxybutylene unit of 4% by weight. The same test as in Example 1 was carried out also when this polymer was used. The results are shown in Table 1. Comparative Example 1 A polymer having 2.5% by weight of oxyethylene units was obtained by the same procedure as in Example 1 except that trioxane and ethylene oxide were mixed at a constant mixing ratio. The same test as in Example 1 was carried out also when this polymer was used. The results are shown in Table 1.

The degree of adhesion between the insert part (metal part) and the resin part was evaluated according to the following criteria. ○: There is almost no gap between the metal part and the resin part, and there is no rattling of the resin part. ×: There is a gap between the metal substrate and the resin part, and there is rattling of the resin part. The warpage, deformation, cracks, and the presence of cracks were evaluated according to the following criteria. ○: No warpage, deformation, cracks, or cracks in resin parts ×: Significant warpage, deformation, or cracks, cracks in resin parts

[0014]

[Table 1]

[0015]

The polyacetal resin of the present invention not only has excellent mechanical strength, heat resistance, and slidability, but also exhibits excellent dimensional stability with little shrinkage during molding and shrinkage due to post-heating. It is used for insert molding parts that require precision and dimensional stability. Furthermore, by using this polyacetal resin, it is possible to obtain an insert-molded product which is excellent in fixing the insert parts and the resin parts, has no rattling, and has very few cracks or breaks in the resin parts.

[Brief description of drawings]

FIG. 1 is a schematic view of an insert-molded product produced in an example.

[Explanation of symbols]

 1 Insert parts (metal parts) 2 Polyacetal copolymer resin 3 Boss part

Claims (4)

[Claims] 1. An insert-molded article obtained by insert-molding a polyacetal copolymer resin having a crystallization time of 5 minutes or more into a preformed part. 2. A polyacetal copolymer resin having a crystallization time of 5 minutes or more containing 3 to 30% by weight of an oxyalkylene unit having 2 or more carbon atoms in a polymer having an oxymethylene unit as a main constituent unit. The insert-molded article according to claim 1. 3. The monomer component constituting the oxyalkylene unit having 2 or more carbon atoms is ethylene oxide, 1,3
-Dioxolane, diethylene glycol formal, 1,
3-propanediol formal, 1,4-butanediol formal, 1,5-pentanediol formal and
The insert-molded article according to claim 2, which is one or more of 1,6-hexanediol formal. 4. The insert-molded article according to claim 1, wherein the polyacetal copolymer resin has a melt index of 1.0 to 60 g / 10 minutes.