JPH05185498A - Blow mold and manufacture of blow mold as well as blow molding method - Google Patents

Abstract

PURPOSE:To put out the marks of air bubble from the surface of a blow molding and thus improve the surface luster by spraying sand on the wall surface of molds to be rendered coarse and subsequently spaying glass beads thereon. CONSTITUTION:In order to put out the marks of air bubble from the surface of a molding, sand blast is executed in which sand is sprayed on the cavity surfaces 3a, 4a of molds 1, 2 to thereby make the wall surfaces 3a, 4a rough. The top ends of the fine projections forming the coarse surface are sharp. The surface is sprayed with glass beads so that the top ends of the projections are made round abrasively. By effecting the surface treatment, the surface luster of the blow molding is considerably improved in comparison with ones subjected to only sand blast by the use of sand having the same particle diameter and, moreover, marks of air bubbles are removed therefrom whereupon moldings with excellent surface appearance can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a blow molding die having an improved cavity wall surface, a method for producing the same, and a blow molding method using this die.

[0002]

2. Description of the Related Art Generally, in a blow molding die, a parison or preform held in the die is blown with compressed air to form a molded article. However, if the cavity wall surface of the molded article is smooth, Air is enclosed between the expanding molten resin and the wall surface of the cavity, and a trap of the enclosed air is generated on the surface of the molded product.

Therefore, conventionally, sand is blown onto the cavity wall surface of the mold to make the cavity wall surface a matte rough surface, thereby forming a gap between the stretched resin and the cavity wall surface, and allowing air to escape. I am trying.

[0004]

However, according to the conventional blow molding die, since the apexes of the minute protrusions forming the rough surface of the cavity wall surface are sharp, the protrusions of the protrusions are expanded during expansion of the resin. There was a problem that the gloss of the surface of the molded product was poor, such as the apex piercing the surface of the resin and traces of minute projections were deeply transferred to the surface when the resin was stretched.

[0005]

In order to solve the above-mentioned problems, a blow molding die according to the present invention blows sand onto a cavity wall surface of a die for forming a molded product, from a projection having a sharp apex. Is formed, and glass beads are sprayed on the rough surface to round the apexes of the protrusions. Further, the method for producing a blow molding die according to the present invention comprises a step of spraying sand on a cavity wall surface of a die forming a molded product to form a rough surface consisting of protrusions having sharp apexes, and the rough surface. And a step of rounding the apexes of the projections by spraying glass beads on the surface. The blow molding method according to the present invention is a blow molding method having a step of forming a rough surface by blowing sand onto a cavity wall surface of a blow molding die before performing molding of a molded product, in the step of forming the rough surface. It is characterized in that a step of spraying glass beads on the rough surface to round the apexes of the projections forming the rough surface is provided afterward, before molding the molded product.

[0006]

According to the blow molding die and the method for manufacturing the same according to the present invention, since a rough surface is formed on the cavity wall surface by blowing sand, a passage for releasing air to the boundary between the cavity wall surface and the resin to be stretch-molded. Is formed and air is not trapped between the resin and the cavity wall surface even if blow molding is performed. Therefore, no trace of air remains on the surface of the molded product. Further, since the apexes of the projections forming the rough surface are rounded by the blowing of the glass beads, the apexes of the satin-like projections do not stick to the surface of the resin stretched in the blowing step. Therefore, the resin that contacts the wall surface of the cavity smoothly extends, and even if unevenness occurs on the surface due to contact with the projection, the unevenness is shallow and the inclination of the inclined surface is small, so that the amount of reflected light on the surface of the molded product increases.

According to the blow molding method of the present invention, a step of making the cavity wall surface of the mold a rough matte surface is performed before the blow step of the molded product. By the process including the step of spraying the glass beads to the rough surface of the satin finish, the tips of the minute projections forming the rough surface of the satin finish are rounded and worn. If the blow step is performed in the subsequent step, the tip of the protrusion does not stick into the surface of the molded product to be stretched, so the round shape is shallowly transferred to the surface of the stretched resin. The gloss of the product is increased and the quality of appearance is improved.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A blow molding die according to an embodiment of the present invention, a method for producing the same, and a blow molding method using the die will be described with reference to the drawings.

FIG. 2 shows a blow molding die according to this embodiment, in which a movable die 2 moves so as to move toward and away from a fixed die 1. Recesses 3 and 4 that form a cavity are formed on the parting surfaces of the molds 1 and 2. Sandblast and sandblasting of glass beads are performed on the wall surfaces 3a and 4a of the recesses 3 and 4, respectively. Walls 3a, 4 of the recesses 3, 4 by sandblasting
a is a rough surface, and the vertices of the minute projections 5 forming the rough surface are sharp at the time of sandblasting as shown by the dotted line in the partial cross-sectional view of FIG. The tip of the is worn round.
In addition, 7 is a cutter part for cutting the lower part of the parison 6.

In this embodiment, the particle diameter of the sand sprayed on the wall surfaces 3a and 4a is 120 mesh, and the particle diameter of the glass beads sprayed is 80 mesh. By thus performing the surface treatment on the wall surfaces 3a and 4a of the molds 1 and 2, the molds 1 and 2 according to the present embodiment are completed.

In the blow molding method of the present invention, the surface treatment process of the wall surfaces 3a, 4a of the molds 1 and 2 is a part of the blow molding process. It is not necessary for the subsequent parison extrusion process.

After the surface treatment of the molds 1 and 2 is completed, the molds 1 and 2 are arranged facing each other on the fixed side and the movable side, and the extruder for the parison 6 (not shown) is provided above the molds 1 and 2. ) Is provided. The parison 6 has a liquidity index M in this embodiment.
PP (polypropylene) with I (melt index) = 3 is used. Parison 6 extruded from extruder
The extrusion temperature of is 210 ° C. When the parison 6 is positioned between the opened molds 1 and 2 and pushed out, and after the mold is closed and compressed air is blown into the parison 6, the parison 6 is stretched in the cavities of the molds 1 and 2. The parison 6 in the cavity is stretched, and the parison 6 becomes the wall surface 3.
When attached to a and 4a, the tips of the minute projections 5 forming the wall surfaces 3a and 4a are rounded, so that the force of the parison 6 pushing the wall surfaces 3a and 4a is the entire tip of the minute projections 5. Received and dispersed. Therefore, the portion 6a located between the protrusions 5 and 5 of the parison 6 is the groove portion 5a between the protrusions 5 and 5.
Never goes deep inside. Therefore, even if air is present between the parison 6 and the wall surfaces 3a, 4a, this air can move freely, and the air is sealed between the wall surfaces 3a, 4a and the parison 6 and accumulates in one place. Since there is no such thing, there is no trace of air accumulation on the surface of the molded product. Also, even if the marks of the protrusions 5 are transferred to the surface of the molded product,
The unevenness of this trace is shallow, and the inclination angle C of the uneven surface 6b of the unevenness with respect to the average surface 6c of the unevenness is small. Lessens the gloss and improves the gloss.

According to the blow molding die and the blow molding method of this embodiment, the glossiness becomes 65%,
Compared with the conventional gloss of a molded product made by sandblasting 120 mesh sand was 30%,
The gloss is remarkably improved, and the surface appearance of the molded product is good without any air traps.

The particle size of sand used for sandblasting is 8
When the mesh size was set to 0 mesh, the particle size of the glass beads was set to 80 mesh, and the material of the parison 6 and the extrusion temperature and the extrusion rate were set to the same as those in the above examples, the glossiness was 60%, but compared with the conventional one. It is possible to obtain almost twice the glossiness. Also, the appearance surface of the molded product molded under these conditions was good with no trace of air.

Further, the grain size of sand used for sandblasting is 120 mesh, the grain size of glass beads is 80 mesh, and the material of the parison 6 is low density polyethylene (L-
LDPE), the extrusion speed (MI) of the parison 6 is 2, and the extrusion temperature is 200 ° C. Blow molding improves the gloss of the molded product to 70%, and at the same time, the appearance surface of the molded product has air traps. Since there are no traces, the appearance quality of the molded product is good.

[0016]

[Effects] According to the blow molding die and the manufacturing method thereof according to the present invention, since sand is blown to form a rough surface on the cavity wall surface, a passage for allowing air to escape to the boundary between the cavity wall surface and the resin to be stretch-molded. Is formed and air is not trapped between the resin and the cavity wall surface even if blow molding is performed. Therefore, no trace of air pockets remains on the surface of the molded product.

Moreover, since the apex of the protrusion is rounded and worn by the spraying of the glass beads, the apex of the protrusion does not stick to the surface of the resin. Therefore, even if the resin is stretched in the blowing step, the resin that comes into contact with the cavity wall surface smoothly extends. As a result, there are no air pockets on the surface of the molded product, and even if unevenness occurs on the surface of the molded product due to contact with the protrusions, the unevenness is shallow and the slope of the inclined surface is small, so the surface of the molded product will not The amount of light increases.

Further, according to the blow molding method of the present invention, before the blow step of the molded product, there is first performed a step of making the cavity wall surface of the die rough with a satin finish. When the step of spraying the glass beads onto the rough surface of the satin finish is included between the steps, the tips of the minute projections forming the rough surface are worn roundly. As a result, even if stretch blow is performed in the subsequent step, the tip of the protrusion does not stick to the surface of the stretched resin, so that even if the trace of the protrusion is transferred to the surface of the stretched resin, it is transferred. The unevenness is shallow, and the angle of inclination of the uneven surface is small.
The gloss of the surface of the molded product is increased, and the appearance quality is improved.

[Brief description of drawings]

FIG. 1 is a partial cross-sectional view showing a contact state between a stretched resin and a cavity wall surface when stretched by a blow molding die according to an embodiment of the present invention.

FIG. 2 is a sectional view of a blow molding die according to the present embodiment.

[Explanation of symbols]

 1, 2 Molds 3a, 4a Wall surface (cavity wall surface) 5 Micro projection 6 Parison 6b Ridge surface of unevenness of parison surface 6c Average surface of unevenness of parison surface C Inclined angle of inclined surface with respect to average surface

Claims (3)

[Claims] 1. A sand mold is blown onto a cavity wall of a mold for forming a molded product to form a rough surface composed of projections having sharp apexes, and glass beads are sprayed on the rough surface to round the apexes of the projections. A blow molding die characterized in that 2. A step of spraying sand on a cavity wall surface of a mold for forming a molded article to form a rough surface composed of projections having sharp apexes, and glass beads are sprayed on the rough surface to apexe the projections. And a step of rounding the blow mold. 3. A blow molding method comprising a step of spraying sand onto a cavity wall surface of a blow molding die to form a rough surface before molding a molded product, which is performed after the step of forming the rough surface. A blow molding method comprising a step of spraying glass beads onto the rough surface to round the apexes of the projections forming the rough surface before molding the molded product.