JPH09141759A - Tubular member - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the shrink quantity of a pipe end generated at a time of cutting without performing long-time annealing by forming a molded product so that the tensile stress shown by the distribution of the internal stress in the axial direction of the molded product toward the wall thickness direction thereof shows the max. value on an outer surface and the distribution of a degree of crystallization in the wall thickness direction is min. on the outer surface and max. on an inner surface. SOLUTION: The tensile stress shown by the distribution of axial internal stress σ (z1) calculated by formula in a wall thickness direction shows the max. value on an outer surface and the distribution of the degree of crystallization of a molded product in the wall thickness direction is min. on the outer surface and max. on an inner surface. Herein, E is the longitudinal modulus, ν is a Poisson's ratio, z0 is the distance from the center 0 of the wall body of a tubular member to the surface of the wall body and quantity shown by ± on inner and outer surfaces, z1 is the distance between the surface obtained by removing the wall body of the tubular member from the surface over arbitrary depth in a laminar state and the center 0 of the wall body of the tubular ember and ϕ (Z1) is a curvature after the deformation of the wall body calculated by ϕ (Z1)=8f/L<2> when the warpage quantity of the wall body developed by removing the wall body of the tubular member from the surface by (Z0-z1) in a laminar state is set to (f) and the length of the wall body is set to L.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a tubular body made of a crystalline thermoplastic resin.

[0002]

2. Description of the Related Art Conventionally, a method of molding a crystalline thermoplastic resin such as polyethylene into a tubular molded article has hitherto been carried out by extruding a crystalline thermoplastic resin composition from a mold and then regulating the outer surface with a sizing die. However, it is common to perform cooling shaping mainly from the outer surface. According to such a molding method, in the obtained tubular molded product, a compressive axial stress is generated on the outer surface thereof, and a tensile axial stress is generated on the inner surface thereof. It remains as stress. When a tubular body having such a stress distribution is cut in a radial direction by a cutting machine, internal stress is released and rearranged, so that the end portion of the tubular body contracts, so-called tube end contraction phenomenon occurs. .

As a method of reducing the internal stress of the tubular molded product as described above, a method of annealing the obtained molded product at an appropriate temperature for a predetermined time is known (A. Bhatnagar).
et al. "Effect Annealing and Heat Fusion on Residu
al Stress in PolyethylenePipe. "ANTEC '85 pp 545-
549).

Further, as a method for specifically carrying out such annealing in the manufacturing process of the tubular body, Japanese Patent Publication No.
Nos. 4-7860 and 3-286843 are proposed.

In Japanese Patent Publication No. 64-7860, when a thermoplastic resin is extruded into a tube, the surface of the tube once solidified through a sizing step is heated to melt only the surface layer, and only the surface layer is formed. The melted tube is cooled and solidified again.

Further, in Japanese Patent Application Laid-Open No. 3-286843, heating of a thermoplastic resin molded product is performed by using far infrared rays, whereby residual stress can be removed in a short time.

[0007]

By the way, in the method of simply annealing in order to reduce the internal stress of the tubular molded article,
There is a problem in terms of productivity because the annealing time required for effectively removing the internal stress is long.

When the surface layer of the tube is melted and then cooled as in JP-B-64-7860, a portion having a higher degree of crystallinity than before the melting occurs in the vicinity of the outer surface of the molded product, resulting in a product. As a result, there is a problem that the tensile elongation of the tubular body decreases. Further, since the surface of the tubular body that has been cooled and solidified after sizing is melted, there is a problem that the surface property of the product is impaired.

Further, in Japanese Patent Laid-Open No. 3-7860, although the heating step can be shortened, if it is gradually cooled thereafter, the crystallinity of the outer surface of the molded product will increase, and the tensile elongation of the molded product will decrease. There is a problem.

An object of the present invention is to have a structure that is relatively easy to obtain without performing annealing for a long time, and to reduce the amount of contraction of the tube end that occurs during cutting, and
It is intended to provide a tubular body made of a crystalline thermoplastic resin capable of exhibiting a relatively large tensile elongation.

[0011]

In order to achieve the above object, the tubular body of the present invention has a distribution in the thickness direction of the axial internal stress σ (z1) calculated by the following equation (1). , The outer surface and the inner surface shows tensile stress, and the tensile stress shows the maximum value on the outer surface, the distribution of the crystallinity of the molded product in the thickness direction is the lowest on the outer surface, and , Characterized by being highest on the inner surface.

[0012]

(Equation 2)

Where E is the longitudinal elastic modulus ν is Poisson's ratio Z0 is the distance from the center 0 of the wall of the tubular body to the surface of the wall,
Amount represented by ± for outer surface and inner surface (see FIG. 1 (A)) Z1; between the surface after removing the wall of the tubular body in layers from the surface to an arbitrary depth and the center 0 of the wall of the tubular body Estimated distance (see Fig. 1 (A)) φ (Z1); The warp amount of the wall that appears by removing the wall of the tubular body in layers from the surface by (Z0-Z1) is f, and the length of the wall is Where L is (see FIG. 1 (B)), the curvature after deformation of the wall calculated by φ (Z1) = 8f / L ² ··· (2) where the axial internal stress is calculated by the above method. As the test piece for obtaining the value, a tubular body having a length L is cut in a strip shape along the axial direction.

The crystallinity can be measured by the following method. That is, JIS
It can be calculated by obtaining the density of the plastic using the method specified in K7112 and substituting it in the following equation (3).

[0015]

(Equation 3)

Where d is the density actually obtained from the resin sampled from the test piece, dc is the density of the resin used in the completely crystallized state, da is the density of the resin used is in the completely amorphous state, and the stress distribution and crystallization are as described above. As a method for obtaining the tubular body of the present invention having a distribution of degrees, the method exemplified below can be adopted.

First, the outer surface temperature of a tubular molded article molded by an arbitrary molding method as described below is set in a short time.
Below the melting point of the resin composition forming the tubular body, and
Raise to a temperature near the melting point. As for this heating method,
A method using far infrared rays, a method using high-frequency induction heating, a method of heating by direct flame, a method of heating by hot air, or the like can be adopted. Such heating is preferably continued for a certain period of time, provided that the temperature of the inner surface of the tubular body is kept within a temperature range of [melting point of resin composition constituting tubular body-50 ° C] or lower. .

Next, after the above heating process is completed, the outer surface of the tubular body is rapidly cooled. As a result, a tubular body having the above-mentioned internal stress distribution and crystallinity distribution can be obtained. As a cooling method, a liquid such as water may be applied from the outer surface of the tubular body, or the tubular body may be introduced into the liquid tank. Alternatively, the outer surface of the tubular body may be slid with respect to the cooling mold, and further cooling gas may be blown onto the outer surface of the tubular body.

As a method for molding the tubular molded product before the above-mentioned treatment, extrusion molding is most preferable because it is difficult to cool the hollow portion, but injection molding or compression molding is also possible. Good.

Examples of the crystalline thermoplastic resin used in the present invention include polyolefin resins represented by polyethylene, polypropylene and polybutene, fluorine resins such as polytetrafluoroethylene and polyvinyl difluorite, polyethylene terephthalate and nylon. And crystalline engineering plastics such as polyphenylene sulfide and polyether ether ketone.

Further, the above resin may contain additives such as a filler, a flame retardant, an ultraviolet absorber, a coloring material and a plasticizer. To specifically describe such an additive, the filler has an effect of improving the elastic modulus, lowering the cost, or lowering the specific gravity. For example, glass chop strands, calcium carbonate powder, balloon-shaped blast furnace ash. Etc. can be used. In addition, various halogen-based flame retardants,
Non-halogen type and inorganic type flame retardants can be used.
As the ultraviolet absorber, hindered amine type, benzophenone type, etc., and as the coloring material, organic type material,
Organic color formers, inorganic pigments and the like can be used, and as the plasticizer, phthalic acid ester, aliphatic dibasic acid ester type, glycol ester type and the like can be used.

The resin composition used for the tubular body of the present invention as described above has a Young's modulus at 23 ° C. of 40.
It is desirable that the pressure is at least 00 kg / cm ² . Further, the wall thickness of the tubular body of the present invention can be any thickness as long as the temperature of the outer surface and the inner surface can be maintained in the above-mentioned temperature range by heating from the outer surface.

[0023]

According to the stress distribution of the tubular body of the present invention in which the axial internal stresses on the inner and outer surfaces are both tensile stresses, and the tensile stresses on the outer surface are maximum values, the tube end contraction amount during cutting is extremely high. Low, and the crystallinity is the lowest on the outer surface,
It was confirmed that the distribution with the highest value on the inner surface does not impair the tensile elongation of the tubular body in the axial direction and shows the same size as the molded product without stress relaxation treatment. .

Further, since the tubular body having the internal stress distribution and crystallinity distribution of the present invention as described above can be obtained without raising the outer surface to the melting point, there is no fear of impairing the surface property of the product.

[0025]

EXAMPLES Next, the results of actually manufacturing and evaluating a tubular body having the structure of the present invention will be described together with comparative examples.

The measurement items were distribution of axial internal stress in the wall thickness direction of the tube wall (radial direction), distribution of crystallinity in the same direction, tube end shrinkage, and tensile elongation. Here, the distribution of the internal stress in the axial direction and the distribution of crystallinity are those measured by the method described above, and the contraction amount of the tube end is the outer diameter of the tube end when the tubular body is cut in the direction perpendicular to the axis. Fig. 2 shows the measurement site, which is the amount of shrinkage. Further, the tensile elongation is obtained by performing a tensile test using a test piece cut out from a tubular body in a dumbbell shape, and its specific test method is JIS K677.
I went according to 4. The measurement results of these various items
It shows in [Table 1]. In addition, in this [Table 1], the internal stress in the axial direction is indicated by positive tensile stress and negative compressive stress.

The method for molding the tubular body and the resin used were the same for the examples and the comparative examples, and a single screw extruder with a diameter of 90 mm was used to extrude Mitsui Petrochemical's medium density polyethylene NZ4004M (trade name) into a pipe shape. . For shaping into a tubular body, it was extruded from an extrusion die in a molten state, cooled while controlling the outer diameter with a sizing die, and cooled from the outer surface with a cooling water tank. Then, after the inner and outer surfaces were sufficiently cooled in the line, an annealing treatment specific to each of the following examples was subsequently performed on the production line to obtain each tubular body. The size of the tubular body is JIS K
It was a 150A1 U tube based on the regulations of 6774. The take-up speed of the production line was 0.3 m / min. The annealing treatment conditions of the example and each comparative example are shown below.

<Example> The outer surface of the tubular body was heated to 110 ° C by a 10 kW far-infrared heater having a length of 600 mm, and immediately thereafter, the outer surface was cooled in a spray water tank having a length of 600 mm.

<Comparative Example 1> 150 ° with a length of 300 mm
The outer surface of the tubular body is melted in a high temperature liquid bath of C (the treatment liquid is Torek liquid manufactured by Tokyo Kako), and immediately after that, a length of 600
Cooling was performed from the outer surface by means of a spray liquid tank of mm.

Comparative Example 2 The outer surface of the tubular body was heated to 110 ° C. with a far infrared heater having a length of 600 mm and allowed to cool in the line. <Comparative Example 3> The conditions were set such that after the shaping by the sizing die and the cooling in the line, no annealing was performed.

[0031]

[Table 1]

[0032]

As described above, according to the present invention, it has been found that the amount of shrinkage of the tube end generated at the time of cutting is small and the tensile elongation is almost the same as that of the case where no annealing is performed. Moreover, since the tubular body having the internal stress distribution and the crystallinity distribution of the present invention can be obtained without annealing for a particularly long time and without melting the outer surface, it is possible to obtain good productivity. Moreover, it can be manufactured without impairing the surface property of the product.

Further, in the present invention, since the internal stress (tensile stress) on the inner surface is smaller than those shown in Comparative Examples 2 and 3, the strength against the pressure acting inside the tubular body is high and the pressure resistance is high. It becomes a tall tubular body.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of how to determine an axial internal stress in the present invention.

FIG. 2 is an explanatory view of a method for measuring a pipe end contraction amount in Examples of the present invention and Comparative Examples.

Claims (1)

[Claims] 1. A hollow molded article made of a crystalline thermoplastic resin composition, wherein the axial internal stress σ (Z1) of the molded article calculated by the following formula is The surface and the inner surface show tensile stress, and the tensile stress shows the maximum value on the outer surface, and the distribution of the crystallinity of the molded product in the thickness direction is the lowest on the outer surface, and Tubular body characterized by being highest on the surface. (Equation 1) However, E: longitudinal elastic modulus ν; Poisson's ratio Z0; amount representing the distance from the center of the wall of the tubular body to the surface of the tubular body, with one of the outer and inner surfaces being +, Z1; The distance between the surface of the wall after removing the wall in layers at an arbitrary depth and the center of the wall of the tubular body φ (Z1); The wall of the tubular body is removed from the surface in layers (Z0-Z1) Where f is the amount of warp of the wall body and L is the length of the wall body, the curvature after deformation of the wall body calculated by φ (Z1) = 8f / L ^2.