JP3259254B2 - Blow molded product with little residual stress distortion - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a blow-molded article, and more particularly to a blow-molded article having a small residual stress distortion after window opening.

[0002]

2. Description of the Related Art Conventionally, blow molded articles have been widely used for various containers, cases, housings and the like. This blow-molded product is a container obtained by inserting a cylindrical molten resin extruded from a die into a mold, blow-molding with air, and cooling, or post-processing such as windowing if necessary for this container. Is obtained.

When such a blow molded article is manufactured in a mold, the outer surface 22 that contacts the mold 24 is rapidly cooled, but the inner surface 23 is gradually cooled. Thus, as shown schematically in FIG. 2, the inner side 23 tends to shrink more than the outer side 22. For this reason, internal stress is generated due to shrinkage. This stress acts on the outer surface 22 in the compression direction and acts on the inner surface 23 in the tensile direction, as indicated by the white arrow in the drawing.

[0004] When the blow molded article is used as a closed container, the residual stress is not particularly problematic because the entire container is balanced. However, when post-processing such as window opening processing is performed and used as a console box of an automobile or a case of home electric appliances, a problem of deformation due to residual stress occurs. For example, a box-shaped molded body 1 having a length (L), a width (W), and a height (H) as shown in FIG. A molded article 2 as shown in FIG. 1 (b) is obtained. In the molded article 2, the residual stress is released by forming the window 3. Therefore, as time passes, FIG.
As shown in (c), the molded article 2 is greatly distorted in the inward direction of the window 3, and particularly the width dimension is largely changed (WW). This is because when the closed box shape is maintained, the stress is balanced in the whole container, so that the deformation due to shrinkage does not occur, but the balance is lost due to the window opening processing, and the residual on the side surface having the window 3 is left. It is considered that the stress is released to cause deformation.

[0005] As a countermeasure, the cooling time during blow molding is lengthened, but not only does the productivity of blow molding decrease, but at present, it is not a sufficient solution. For this reason, a thick blow molded product having a large opening is not suitable for a product requiring dimensional accuracy.

Accordingly, an object of the present invention is to provide a blow-molded article having a small residual stress distortion after a window opening process.

[0007]

Means for Solving the Problems As a result of intensive studies in view of the above object, the present inventors have found that the residual stress of the blow molded article is such that the molding shrinkage on the inner surface side is larger than that on the outer surface side during blow molding. Due to this, distortion occurs when the residual stress is released by the window opening process, but the blow molded body has a multilayer structure, and the heat shrinkage of the material forming the inner layer is higher than that of the material forming the outer layer. It has been found that distortion can be greatly reduced by forming a small material and canceling out the difference in the molding shrinkage by the blow molding to some extent. Accordingly, the present inventors have studied the difference in the heat shrinkage of the inner and outer layers that effectively reduces the distortion of the blow molded article. As a result, the heat shrinkage of the material forming the inner layer is reduced by the heat shrinkage of the material forming the outer layer. It has been found that a case where the ratio is smaller than the ratio by 5/1000 or more is ideal. The present invention has been made based on the above findings.

That is, the blow molded article of the present invention having a small residual stress distortion is a molded article obtained by subjecting a part of a thermoplastic resin blow molded article to a window opening process, and the blow molded article has a multilayer structure. The inner layer is formed of a material having a heat shrinkage rate 5/1000 or more smaller than the material forming the outer layer, and the inner layer / outer layer has a thickness ratio of 10/90 to 90.
/ 10.

Hereinafter, the present invention will be described in detail. [1] Thermoplastic resin The thermoplastic resin used in the blow-molded article of the present invention is not particularly limited as long as blow molding is possible. Polyolefin, polyamide, polycarbonate, polyester (polyethylene terephthalate, polybutylene terephthalate, etc.), Olefin elastomers and the like can be mentioned. Among these, polyolefins, polyamides, and olefin elastomers are particularly preferred.

(1) Polyolefin Polyolefins include homopolymers of α-olefins such as ethylene, propylene, butene-1, pentene-1, hexene-1, and 4-methylpentene-1, ethylene and propylene or other α-olefins. Copolymers with olefins, or copolymers of two or more of these α-olefins. Among these, low-density polyethylene, linear low-density polyethylene, medium-density polyethylene, polyethylene such as high-density polyethylene, polypropylene, polybutene-
1, poly 4-methylpentene-1, ethylene-propylene block copolymer, ethylene-propylene random copolymer, ethylene-butene-1 copolymer, propylene-butene-1 copolymer, ethylene-vinyl acetate copolymer Coalescence and mixtures thereof. The polypropylene is not limited to a homopolymer, and a random or block copolymer with another α-olefin containing 50 mol% or more, preferably 80 mol% or more of a propylene component can also be used.
Comonomers copolymerized with propylene include ethylene and other α-olefins, with ethylene being particularly preferred. Thus, the term "polypropylene" as used herein is to be understood as not being limited to homopolymers of propylene but also including copolymers.

Further, a modified polyolefin obtained by modifying the above polyolefin with an unsaturated carboxylic acid or an anhydride thereof can also be used. Examples of the unsaturated carboxylic acid or its anhydride include acrylic acid, monocarboxylic acid such as methacrylic acid, maleic acid, fumaric acid, dicarboxylic acid such as itaconic acid, maleic anhydride, and dicarboxylic anhydride such as itaconic anhydride. And dicarboxylic acids and anhydrides thereof are particularly preferred.

The content of unsaturated carboxylic acid or its anhydride in the modified polyolefin is 0.01 to 15% by weight, especially 0.1 to 15% by weight.
It is preferably about 1% by weight. If the modification amount is less than 0.01% by weight, the effect of improving the compatibility with other resin components and inorganic fillers by addition of the modified polyolefin is not sufficient, and if it exceeds 15% by weight, the compatibility with the polyolefin is insufficient. descend.

The production of the modified polyolefin can be carried out by either a solution method or a melt kneading method. In the case of the solution method, a polyolefin, an unsaturated carboxylic acid (or acid anhydride) for modification and a catalyst are dissolved in an organic solvent such as xylene,
This is carried out with stirring at a temperature of 140 ° C. In the case of the melt-kneading method, the starting material is charged into an extruder, a twin-screw kneader, or the like,
Kneading while heating and melting at a temperature of 150-250 ° C.
In each case, a normal radical polymerization catalyst can be used as a catalyst, for example, benzoyl peroxide, lauroyl peroxide, ditertiary butyl peroxide, acetyl peroxide, tertiary butyl peroxybenzoic acid, dicumyl peroxide, Peroxides such as peroxybenzoic acid, peroxyacetic acid and tertiary butyl peroxypivalate, and diazo compounds such as azobisisobutyronitrile are preferred. The amount of the catalyst to be added is about 1 to 100 parts by weight based on 100 parts by weight of the unsaturated carboxylic acid for modification or its anhydride.

(2) Polyamide As the polyamide, hexamethylenediamine, decamethylenediamine, dodecamethylenediamine, 2,2,4- or 2,4,4, -trimethylhexamethylenediamine, 1,3- or 1,4 -Bis (aminomethyl) cyclohexane, bis (p-aminocyclohexylmethane), m- or p-
Aliphatic, alicyclic or aromatic diamines such as xylylenediamine, and adipic acid, suberic acid, sebacic acid,
Polyamides prepared from aliphatic, alicyclic or aromatic dicarboxylic acids such as cyclohexanedicarboxylic acid, terephthalic acid and isophthalic acid, 6-aminocaproic acid,
Polyamides produced from aminocarboxylic acids such as 11-aminoundecanoic acid and 12-aminododecanoic acid, polyamides produced from lactams such as ε-caprolactam and ω-dodecalactam, and copolymerized polyamides comprising these components Or mixtures of these polyamides. Specifically, nylon 6 (polyamide 6), nylon 66 (polyamide 66), nylon 610, nylon 9, nylon 6/66, nylon 66/610, nylon 6/11, nylon 6/12, nylon 12, nylon 46,
Amorphous nylon and the like can be mentioned. Of these, nylon 6 and nylon 66 are preferred in terms of good rigidity and heat resistance.

The molecular weight is not particularly limited, but usually a polyamide having a relative viscosity η _r (measured in JIS K6810, 98% sulfuric acid) of 0.5 or more is preferable, and a polyamide having a relative viscosity of 2.0 or more is preferable because of excellent mechanical strength.

(3) Olefin Elastomers The olefin elastomers include two or more α-olefins such as ethylene, propylene, butene-1, pentene-1, hexene-1, and 4-methylpentene-1. And copolymer rubber. Such olefin elastomers typically include ethylene-propylene copolymer rubber (EPR), ethylene-propylene-diene copolymer rubber (EPDM), and ethylene-butene copolymer rubber (EBR). Can be The diene component in the ethylene-propylene-diene copolymer rubber (EPDM) includes dicyclopentadiene, 1.4-hexadiene,
Non-conjugated dienes such as cyclooctadiene and methylene norbornene or conjugated dienes such as butadiene and isoprene can be used.

In the present invention, other heat stabilizers, light stabilizers, flame retardants, plasticizers, antistatic agents, mold release agents, nucleating agents, etc. are added to the above resin components for the purpose of modification. An agent can be appropriately added.

The blow molding resin is usually 0.2 / 1.
Those having a heat shrinkage in the range of 000 to 30/1000 are used. In the present invention, the heat shrinkage is
(Die size−dimension of molded product) × 1000 = value based on molding shrinkage (/ 1000).

[2] Composition of Inner Layer and Outer Layer (1) Difference in Heat Shrinkage In the present invention, the difference in shrinkage between the material forming the inner layer and the material forming the outer layer (outer layer material-inner layer material) is 5 / 10
00 or more, preferably 5/1000 to 20/1000. If the difference between the above values is less than 5/1000,
The effect of suppressing the amount of deformation due to residual strain is not sufficient.

(2) Component that gives difference in heat shrinkage rate In order to impart the above-mentioned difference in heat shrinkage rate between the inner layer material and the outer layer material, for example, the heat shrinkage of the inner layer material is added by adding an inorganic filler. The ratio may be reduced, or a method of forming the inner and outer layers using resins having different heat shrinkage ratios may be appropriately selected.

When heat shrinkage is reduced by adding an inorganic filler As the inorganic filler, talc, glass fiber, calcium carbonate, or the like can be used. The amount of the inorganic filler is from 1 to 4 with the resin component + the inorganic filler being 100% by weight.
It is preferably 0% by weight. When a polyolefin is used as the resin component, it is preferable to mix a modified polyolefin for the purpose of improving the adhesion between the polyolefin and the inorganic filler. Specifically, when using polypropylene as the outer layer material, it is preferable to use a composition comprising polypropylene, modified polypropylene and glass fiber as the inner layer material.

When the inner and outer layers are formed of resins having different heat shrinkage rates, the resin components are selected so that the difference in the heat shrinkage between the inner layer material and the outer layer material is within the above range. ,
It is preferable to use polyolefin and use polyamide as the inner layer material. In this case, a modified polyolefin layer is preferably interposed as an adhesive layer between the two layers.

(3) Thickness The thickness ratio of the outer layer to the inner layer of the blow molded article composed of the outer layer material and the inner layer material as described above is 10/90 to 90/10. Outside the above range, the effect of reducing the residual strain by the multilayering becomes insufficient.

[2] Manufacturing Method First, a resin component for the outer layer and a resin component for the inner layer are each melted, and if necessary, a filler such as glass fiber is blended. Extrude.
Subsequently, the parison is inserted into a mold, blown with air, and then cooled to obtain a blow molded body. The blow-molded article of the present invention can be obtained by subjecting the blow-molded article obtained in this way to window opening at a desired position.

[0025]

The blow-molded article of the present invention has a multilayer structure and has a heat shrinkage 5/10 that of the material forming the outer layer.
Since the inner layer is formed of a material smaller than 00 and the thickness ratio of the inner layer / outer layer is 10/90 to 90/10, deformation due to residual stress after window opening can be significantly reduced, and dimensional accuracy can be reduced. Can be improved.

Although the reason why such an effect can be obtained is not always clear, the difference in cooling conditions by forming a multilayer structure of the inner layer and the outer layer and forming the inner layer with a material having a smaller heat shrinkage than the outer layer is obtained. It is considered that this is because the stress based on the pressure is canceled.

[0027]

The present invention will be described in more detail with reference to the following examples. Reference Example Production of Resin Composition for Inner Layer and Outer Layer Material Polypropylene alone was designated as A, polypropylene, maleic anhydride-modified polypropylene, and glass fiber as a base resin composition, and the blending amount of polypropylene and glass fiber for this composition. The composition was varied and melt-kneaded to obtain compositions BG. The heat shrinkage of a molded article of the composition thus obtained was measured. The results are shown in Table 1.

[0028] Table 1 resin composition ^{No. A * B C D E F} G thermal shrinkage rate ⁽¹⁾ (/ 1000) 30 27 25 20 15 10 5 Note) (1) thermal shrinkage :( mold dimension - Molded product dimensions) x 100
0 was calculated. *: Polypropylene alone.

Examples 1 to 9 and Comparative Examples 1 and 2 The resin A was used as the outer layer material, and the resin compositions A to G as shown in Table 2 were used as the inner layer material. Thickness ratio (total thickness 3mm) and cooling time are second
By setting as shown in the table, a blow molded article (L200 mm × W40 mm × H26 mm) having the shape shown in FIG. 1 was produced. After leaving this blow molded body for 3 days,
180 mm x 20 mm window (leaving 10 mm from each side)
Was formed by cutting. After leaving the blow-molded article thus obtained for 24 hours, the width dimension deformation (W-
w (the dimension of the maximum deformation portion) was measured. The results are shown in Table 2.

Comparative Examples 3 to 6 The blow molded articles of the same shape prepared as a single layer of polypropylene (resin A) were similarly measured for the amount of deformation in the width dimension. The results are shown in Table 2.

COMPARATIVE EXAMPLES 7 AND 8 The blow-molded articles of the same shape produced in Example 3 with different thickness ratios were measured for the amount of deformation in the width dimension in the same manner. The results are shown in Table 2.

Table 2 Example 1 Example 2 Example 3 Example 4 Example 5 Type of Inner Layer Material C D FE E Type of Outer Layer Material A A A A A Difference in Thermal Shrinkage (Outer Layer Material-Inner Layer Material) ) (/ 1000) 5 10 15 20 15 Wall thickness ratio (inner layer / outer layer) 50/50 50/50 50/50 50/50 30/70 Cooling time (sec) ⁽¹⁾ 30 30 30 30 30 Deformation of width Amount (mm) ⁽²⁾ 0.9 0.7 0.5 0.1 0.5

Table 2 (continued) Example 6 Example 7 Example 8 Example 9 Comparative Example 1 Kind of inner layer material EEEGA Type of outer layer material A A A A A Difference in heat shrinkage (outer layer) Material-inner layer material) (/ 1000) 15 15 15 25 0 Thickness ratio (inner layer / outer layer) 70/30 10/90 90/10 50/50 50/50 Cooling time (sec) ⁽¹⁾ 30 30 30 30 30 Deformation of width (mm) ⁽²⁾ 0.3 0.8 0.7 − 0.5 1.5

Table 2 (Continued) Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 Comparative Example 6 Type of Inner Layer Material B − ^* − ^* − ^* − ^* Type of Outer Layer Material A A A A A Heat Shrinkage Difference (outer layer material-inner layer material) (/ 1000) 3----Wall thickness ratio (inner layer / outer layer) 50/50----Cooling time (seconds) ⁽¹⁾ 30 30 60 90 120 Width deformation Amount (mm) ⁽²⁾ 1.2 1.5 1.1 1.0 1.0

[0035]

Note) *: Monolayer product of polypropylene (1) Cooling time: Cooling time was set with the start of cooling at the start of air blow into the parison during blow molding. (2) Deformation amount of width dimension: Measure the width dimension (w) of the place where the largest deformation occurs 24 hours after the window opening processing, and determine the width dimension (W: 40 mm) of the molded body before window opening processing. Difference (Ww)
Is the amount of deformation.

As is clear from Table 2, the blow molded article of the present invention had a width dimension deformation of less than 1.0 mm. On the other hand, the multilayer blow-molded products of Comparative Examples 1 and 2 and Comparative Examples 7 and 8 had a large amount of deformation in the width dimension. From Comparative Examples 3 to 6, it can be seen that in the case of a single-layer blow-molded product, the amount of deformation in the width dimension can be reduced to some extent by increasing the cooling time, but cannot be reduced to less than 1.0 mm.

[0038]

As described in detail above, the blow-molded article of the present invention has a heat shrinkage 5/100 more than that of the material forming the outer layer.
The inner layer is formed from a material smaller than 0 or more, and the multi-layer blow-molded article having an inner layer / outer layer thickness ratio of 10/90 to 90/10 is subjected to window opening.

The blow molded article of the present invention has the following advantages. (1) Deformation due to residual stress after window opening has been significantly reduced. (2) The cooling time during blow molding in the manufacturing process can be reduced.

The blow molded product of the present invention is suitable for applications requiring dimensional accuracy, such as a console box or dashboard of an automobile, a case of a home electric appliance, and a housing of an OA device.

[Brief description of the drawings]

FIG. 1 shows a process of applying a window to a box-type blow-molded product, wherein (a) shows a state after blow-forming, (b) shows a state immediately after window-forming, and (c) shows a state after deformation. .

FIG. 2 is a cross-sectional view showing a stress in a wall portion of a blow molded product.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Blow molded body 2 ... Blow molded article 3 ... Window 21 ... Wall part 22 ... Outer side 23 ... Inner side 24 ... Die

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) B29C 49/22 B29D 22/00 B32B 7/02

Claims (1)

(57) [Claims] 1. A molded product obtained by subjecting a part of a thermoplastic resin blow-molded product to a window forming process, wherein the blow-molded product has a multilayer structure, and is 5 times smaller than a material forming an outer layer.
The inner layer is formed of a material having a heat shrinkage ratio smaller than / 1000 or more, and the thickness ratio of the inner layer / outer layer is 10/90 to 90 /
A blow-molded product with a small residual stress distortion, characterized in that it is 10.