JP3062966B2 - Method of manufacturing blow molded product with little residual distortion - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for obtaining a symmetrical product by halving a synthetic resin blow-molded product by post-processing.
The present invention relates to a method for producing a blow molded product from which a molded product with little residual distortion can be obtained.

[0002]

2. Description of the Related Art As is well known, a blow molding method is a method in which a molten resin (parison) extruded from a die is sandwiched in a mold, air is blown into the inside, and after cooling, a molded product is taken out as a product. . At this time, the outside of the molded article is rapidly cooled by the mold, and the inside is gradually cooled by heat transfer from the film to the air, so that the cooling conditions are different between the inner and outer surfaces of the molded article.

Generally, a crystalline resin such as polyolefin is used as a material for blow molding, and the difference in cooling conditions as described above causes a difference in crystallinity, and a difference in the degree of crystallization during molding on the inner and outer surfaces of the molded product. Since the shrinkage ratios are different, residual stress acts between the inner and outer surfaces of the molded product.

[0004] Blow-molded articles are used for automobile parts such as seat backs, door trims, console boxes, bumpers, etc., cases for home electric parts, housings for OA equipment, and the like. However, the problem of residual stress as described above did not appear.

[0005]

However, when a molded article is divided in half and a plurality of symmetrical parts are to be molded at once, the residual stress is released at the cut end after the half, and the molded article is deformed. . This deformation can hardly be improved even if the molding conditions such as the cooling time during blow molding are changed. As a result, a blow-molded product by such half-split is unsuitable for a product requiring dimensional accuracy.

[0006]

SUMMARY OF THE INVENTION However, the present inventors have solved the inconvenience of the above-mentioned conventional example, and can obtain a product with little residual distortion even in a blow-molded product by half-split, and can manufacture a product requiring dimensional accuracy. The present inventors have found a method for producing a blow molded article, and have accomplished the present invention. That is, in a method of manufacturing a blow molded product to obtain a symmetrical product by halving a synthetic resin blow molded product by post-processing, the blow molded product has a multi-layered structure, and the inner surface material has a smaller shrinkage than the outer surface material. Use small materials
In this case, the difference in shrinkage between the inner surface material and the outer surface material is 5 / 1,00
The gist is that the thickness is set to 0 to 20 / 1,000 and the thickness ratio is set to 10/90 to 90/10.

In the present invention, examples of the outer surface material include thermoplastic resins such as polyolefin, polyamide, and thermoplastic elastomer. As the polyamide, a polymer compound having an acid amide (-CONH-) as a repeating unit is used in a polymerization manner, (1) by ring-opening polymerization of lactam, (2) by polycondensation of aminocarboxylic acid,
(3) Those obtained by polycondensation of diamine and dibasic acid. These include nylon 6, nylon 12, nylon 9, nylon 11, nylon 66, nylon 610, and the like. Of these, nylon 6 and nylon 66 are preferred.

[0008] Polyolefins include low density polyethylene, linear low density polyethylene, medium density polyethylene,
High density polyethylene, polypropylene, poly-1-butene, poly-4-methyl-1-pentene, ethylene-propylene block or random copolymer, ethylene-1
-Butene copolymer, propylene-1-butene copolymer,
Examples thereof include an ethylene-vinyl acetate copolymer and a mixture thereof.

[0009] The thermoplastic elastomer is a crystalline polyolefin, preferably a polypropylene or propylene-ethylene copolymer, and a olefin copolymer rubber, preferably an ethylene-propylene rubber or an ethylene-propylene-diene copolymer rubber. Dynamically heat-treated plastic elastomers may be used. Among the thermoplastic resins, polypropylene is most preferred.
The inner surface material is a mixture of the thermoplastic resin and a filler. As the thermoplastic resin, the same polyolefin as the outer surface material, polyamide, thermoplastic elastomer,
can give. Examples of the filler include talc, glass fiber, calcium carbonate and the like. It is preferable to use a modified polyolefin for compatibility of the mixture of the thermoplastic resin and the filler and for stabilizing other physical properties.

The modified polyolefin is obtained by reacting the above-mentioned polyolefin with an unsaturated carboxylic acid or a derivative thereof. Examples of the unsaturated carboxylic acid include maleic acid and endobicyclo- [2.2.1] -5-. Heptene-2.3 dicarboxylic acid, acrylic acid, methacrylic acid,
Examples thereof include itaconic acid and fumaric acid, and derivatives thereof include acid anhydrides, acid amides and esters. Various known methods can be adopted as a method for reacting the unsaturated carboxylic acid or its derivative with the polyolefin.
For example, it is obtained by adding a reaction initiator such as an organic peroxide to each of polyolefin or olefin-based copolymer rubber or a mixture thereof and an unsaturated carboxylic acid or a derivative thereof, mixing them in advance, and then melt-kneading them. . As the modified polyolefin, maleic anhydride-modified polypropylene is preferable. Further, an adhesive layer can be used to increase the adhesive strength between the outer surface material and the inner surface material. As the adhesive layer, the above-mentioned modified polyolefin is desirable, and maleic anhydride-modified polypropylene is particularly preferred.

Normally, in blow molding, it is necessary to take a long cooling time in order to suppress the amount of deformation. However, in the case of a half-split product by single-layer blow, the amount of deformation is small even if the cooling time is lengthened.
Does not change much. Therefore, it is necessary to divide the blow molded product in half by post-processing and use a material having a small shrinkage rate as the inner surface material in the method of manufacturing a blow molded product to obtain a symmetrical product, thereby forming a multi-layer structure. Usually, in the blow molding, it is necessary to increase the cooling time in order to suppress the deformation amount. However, in the case of a half-split product by single-layer blow, the deformation amount does not change much even if the cooling time is increased.

In the case of a multilayer structure, if the difference in shrinkage between the inner surface material and the outer surface material is less than 5/1000, the amount of deformation due to residual strain cannot be suppressed so much. 20/1000 difference in shrinkage between inner and outer materials
Above, a reverse warpage deformation of the molded product occurs. Therefore, the difference in shrinkage between the inner surface material and the outer surface material is 5/1000 to 20/1000.
In a range other than the above range, the deformation of the molded product becomes conspicuous, so that the range of the difference in shrinkage ratio is preferably 5/1000 to 20/1000. The thickness ratio between the inner surface material and the outer surface material is preferably 10/90 to 90/10. If the thickness ratio is out of this range, the deformation of the molded product is conspicuous, which is not preferable. Here, the shrinkage ratio refers to the ratio of the length in the long direction immediately after molding of a molded article obtained by blow molding the used material, the inner surface material and the outer surface material alone, and the amount of deformation in the long direction after 24 hours. It was done.

The present invention uses the above-mentioned materials for a multi-layer blow molding machine and uses a wide variety of materials, for example, two kinds of two layers of an inner surface material and an outer surface material, or an inner surface material, an adhesive layer, and an outer surface material. After forming three types and three layers of parison and blow molding,
The product is obtained by splitting the cooling time in half.

[0014]

The present invention relates to a blow-molded article obtained by using a material having a small shrinkage rate as an inner face material in a multilayer blow-molded article, and setting a difference in the shrinkage rate and a thickness ratio between the inner face material and the outer face material to a specific range. The amount of deformation can be reduced, and the dimensional accuracy can be improved.

Hereinafter, embodiments of the present invention will be described. Polypropylene (MFR 0.5 g / 10 min) is used as the outer surface material, and 30 parts by weight of glass fiber and 5 parts by weight of maleic anhydride-modified polypropylene are mixed with 100 parts by weight of the polypropylene as the inner surface material. And a two-layer, two-layer blow molded product [40 mmW
× 26mmH × 200mm Lt = 3mm] and made 40mmW × 26mm
A test piece of H × 20 mm L before being cut in half is cut out and cut in half after 3 days, and a U-shaped test piece [40 mmW × 13
mmH × 20 mmL].

In addition, a cooling time is provided with the start of cooling when the air blow into the parison is started during blow molding. The width of the test piece before the half-cut and the width 24 hours after the half-cut were measured, and the difference was defined as the deformation amount. Table 1 shows the results. In Table 1, Comparative Examples 1 to 3 show that the deformation amount of the single-layer blow molded product cannot be suppressed even when the cooling time is changed. From Examples 1 to 4 and Comparative Examples 4 to 6, it can be seen that the deformation amount is small within the range of the difference in the shrinkage ratio of the present invention. From Examples 5 to 8 and Comparative Examples 7 to 8, it is understood that the deformation of the molded product is small when the thickness ratio between the inner surface material and the outer surface material is within the range of the present invention.

[0017]

The method of determining the shrinkage ratio between the inner and outer members is as follows. Test criteria: MSTO226-03 Injection mold shrinkage test method Outline: Molded using an injection molding machine under specified molding conditions using a prescribed mold, and a measure of the degree of change from the mold dimensions to the product dimensions. I do. Mold: 120 mm square sheet mold (thickness: 2 mm) Measurement position: Marks are placed on the mold at 100 mm intervals, and the dimension between marks of the molded product is read. Molding shrinkage = (100-dimension between molded product markings) / 100

[0019]

As described above, according to the method for producing a blow-molded article having a small residual strain of the present invention, a resin having a small shrinkage is used for the inner surface of the laminate, and the difference in shrinkage from the outer material and the inner surface are determined. By setting the thickness ratio between the material and the outer surface material to a specific range, a half-split blow-molded product with less distortion can be obtained. As a result, not only a plurality of left-right symmetric molded products such as an automobile door trim having good dimensional accuracy can be produced, but also other resin molded products can be efficiently and accurately manufactured.

────────────────────────────────────────────────── (5) References JP-A-5-31800 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B29C 49/00-49/80 B32B 1 / 00-35/00

Claims (1)

(57) [Claims] 1. A method for producing a blow molded article in the halved by post-processing the synthetic resin blow-molded article obtained products symmetric, the blow-molded article and various multi-layer structure, the inner surface material
Use a material with a smaller shrinkage than the outer surface material, in which case,
The difference in shrinkage between the inner and outer materials is 5 / 1,000 to 20 / 1,000
And a wall thickness ratio of 10/90 to 90/10.