JPH0681700B2 - Biaxially stretched plastic bottle manufacturing method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a biaxially stretched plastic bottle having excellent appearance characteristics such as smoothness, glossiness and shape reproducibility.

(Conventional technology) Polypropylene and polyethylene terephthalate (PET)
Bottles made by melt blow molding or stretch blow molding of plastics like these are lightweight and have excellent impact resistance and transparency.Especially, PET is used and stretch blow molded. Since it is also excellent in permeability to some extent, it has been widely used as a container for storing various beverages, particularly beer and carbonated beverages.

When manufacturing a biaxially stretched plastic bottle, a thermoplastic plastic preform is placed in a blow mold consisting of a split mold and a bottom mold, and a stretching rod is inserted into the preform to stretch and stretch the preform in the axial direction. The method of expanding and stretching the preform in the circumferential direction is generally adopted. However, in the case of this method, the preform bottom portion against which the stretching rod hits hardly undergoes the stretching operation, and therefore the bottom portion is inferior in pressure resistance and heat resistance.Therefore, there is also a proposal for strengthening this bottom portion. Many have already been done.

For example, in JP-A-63-78728, it is described that after preform is stretch blow-molded, the center part of the bottom part is depressed and deformed inward by a bottom pin, and then this is blow-molded without being stretch-deformed. Has been done. Also, Japanese Patent Laid-Open No. 1-
Japanese Unexamined Patent Publication No. 124546 describes that a partially thermally crystallized thermal crystallization part is provided at the bottom of the container body, and a region other than the thermal crystallization part is stretched to a high draw ratio.

(Problems to be Solved by the Invention) However, the biaxially stretched plastic bottle according to the conventional method is satisfactory in the strength of the bottom portion,
It has not been fully satisfactory in terms of appearance characteristics such as smoothness, glossiness and shape reproducibility.

That is, in the case of a biaxially stretched plastic bottle, the unstretched bottom center part remains unstretched and remains relatively thick, but since the expansion and stretching of the body part tends to be biased, the unstretched thickness The center part of the bottom of the container is offset in any direction from the axis of the bottle, which may give the purchaser of the package an impression that the bottle is distorted.

In addition, in the case of polycondensation type resin such as PET, the resin always contains monomers and oligomers with a certain probability, and these monomers and oligomers are volatilized from the preform surface during stretch blow molding. The problem of depositing on the blow mold surface occurs. That is, the blow mold surface becomes satin-finished due to the deposition of monomers and oligomers, and this is transferred to the bottle surface to be molded, and the bottle surface also becomes satin-finished, and the flatness and glossiness of the surface are lost. .
In order to prevent this, the blow mold surface must be cleaned frequently, and the operation for that purpose causes the productivity to decrease, and the effect of improving the appearance characteristics of the bottle by cleaning can still be sufficiently satisfied. is not.

Therefore, an object of the present invention is to provide a method for producing a biaxially stretched plastic bottle which solves the above-mentioned drawbacks in the conventional method for producing a biaxially stretched plastic bottle and is excellent in appearance characteristics such as smoothness, glossiness or shape reproducibility. There is.

(Means for Solving the Problems) According to the present invention, a thermoplastic plastic preform is placed in a blow mold composed of a split mold and a bottom mold, and a drawing rod is inserted into the preform to insert a drawing rod. In a method for producing a biaxially stretched plastic bottle, which comprises stretching and stretching a reform in the axial direction and expanding and stretching the preform in the circumferential direction, a bottom die, or a part of the bottom die is split into a split die. While movably arranged in the moving direction, a gap is formed between the bottom mold and the split mold to allow free flow of gas, and during biaxial stretching of the preform, the bottom mold and the preform are brought into close contact with each other and stretched. A method for manufacturing a biaxially stretched plastic bottle is provided, which comprises moving the rod and rapidly exhausting air in the blow mold through the gap.

(Function) Also in the method for producing the biaxially stretched plastic bottle of the present invention, the preform of the thermoplastic is positioned in the blow mold including the split mold and the bottom mold, and the stretch rod is inserted into the preform to form the preform. While stretching and stretching in the axial direction and expanding and stretching the preform in the circumferential direction, the bottom mold or a part of the bottom mold is arranged in the split mold so as to be movable in the moving direction of the stretching rod, and the bottom mold and the split mold. A remarkable feature is that a gap is formed between the mold and the gas so that the gas can flow freely.

That is, in the present invention, by arranging the bottom mold and the split mold so as to satisfy the above conditions, during biaxial stretching of the preform, the bottom mold and the preform are brought into close contact at the start of stretching or during the longitudinal stretching. It is possible to perform the stretching movement of the stretching rod and the expansion and stretching by blowing the fluid, and to quickly exhaust the air in the blow mold through the gap. Therefore, the center of the bottom part that is held in an unstretched state by the abutting stretch bar, even if the expansion and stretching of the body part tends to occur unbalanced, the center of the bottom part is properly held in the center of the bottle, Irregular molding is prevented. Thus, according to the present invention, by preventing the center shift of the bottle bottom, it is possible to enhance the appearance characteristics of the bottle, the commercial value, and the thickness distribution of the bottle bottom is centered in the strict sense of the center. Since the thickness can be distributed from the center toward the periphery, the required thickness of the entire bottle bottom can be reduced and the material cost of the bottle can be saved.

Further, according to the present invention, since the air in the cabty during the preform expansion / expansion is rapidly discharged to the outside of the split mold,
Even if the monomer or oligomer is volatilized in the air inside the cavity, this air does not tend to be compressed, and the air inside the cavity is rapidly discharged outside the cavity during stretch blow molding into a bottle. It is possible to prevent the monomers and oligomers from depositing on the surface of the blow mold, and as a result, the surface of the blow mold can be maintained in the original smooth state of the blow mold. That is, the factors that cause the monomers and oligomers contained in the plastic forming the preform to deposit on the surface of the blow mold are the direct transfer that occurs when the plastic that is being molded comes into contact with the mold surface and the volatilization in the air as the atmosphere. It is considered that the above-mentioned monomer and oligomer are indirectly transferred by depositing on the blow mold surface, but in the former case, the cooling of the plastic starts immediately, and therefore the latter effect is considered to be large.

In the conventional technique, during stretch blow molding, the air in the mold is gradually discharged out of the mold through the parting gap of the split mold, so that the monomers and oligomers volatilized from the preform are deposited on the blow mold surface. Then it becomes a satin finish, which is transferred to the surface of the bottle to be molded,
The surface of the bottle also becomes matte and loses its smoothness and gloss, and in order to prevent this, the blow mold surface must be frequently cleaned. However, the present invention eliminates all of these drawbacks.

(Examples) The present invention will be described in detail below based on specific examples shown in the accompanying drawings.

1 to 6 of the accompanying drawings show the sequence of the stretch blow molding process of the present invention. FIG. 1 shows the preform insertion process,
FIG. 2 shows the bottom mold lowering process, FIG. 3 shows the split mold closing process, FIG. 4 shows the stretching rod raising process, FIG. 5 shows the stretching blow process, and FIG. 6 shows the mold opening product take-out process.

The apparatus used in the present invention roughly comprises a pair of blow molds 1a and 1b, a bottom mold 2, and a drawing rod 3. Blow mold 1a,
Inside 1b is a cavity 4 for molding a bottle, and a cavity surface 5 regulates the shoulder and body of the bottle. The bottom mold 2 regulates the bottom of the bottle, and the inner surface of the bottom mold has a protrusion 7 at the center and a recess 8 at the periphery. Further, the bottom mold 2 is provided with an elevating shaft 9. The blow molds 1a and 1b have a preform supporting core mold (not shown) on the lower side in a closed state.
Alternatively, it has an opening 10 that engages with the preform supported by the core mold, and an opening 11 that engages with the bottom mold 2 on the upper side thereof. The stretch rod 3 can be moved in and out of the cavity through the preform supporting core mold in a state where the blow molds 1a and 1b are closed. Bottom mold 2
Engages exactly with the opening 11 when the bottom mold 2 is in the raised position when the blow molds 1a, 1b are closed, but when the bottom mold 2 is in the lowered position, the bottom mold lifting shaft 9 and the opening 11 are A gap 17 (3rd
(See the figure) is formed. The bottom portion 2 is biased downward by means such as a weight or a spring, but can be moved upward by driving an air cylinder or by raising the stretching rod 3.

The preform 13 used in the molding method of the present invention is a bottomed preform having a cap fastening neck portion 14, a body portion 15 and a bottom portion 16. The preform 13 is formed by injection molding of plastic as will be described later, and is substantially amorphous so as to enable molecular orientation by biaxial stretching.

First, in FIG. 1, the blow molds 1a and 1b are in an open state, while the bottom mold 2 is in a raised position. In this state,
The preform 13 is supported by the core mold and inserted into the cavity position of the split mold.

Then, in FIG. 2, the bottom mold 2 is lowered into close engagement with the preform bottom 16. In this state, the bottom type lifting shaft 9
A gap 17 is formed between the opening 11 and the opening 11 to allow free flow of air.

When the support of the preform 13 is completed, as shown in FIG. 3, the blow molds 1a and 1b are closed and the preparation stage is completed.

In FIG. 4, the stretching rod 3 is inserted into the preform 13 through the core mold, and the stretching and stretching of the preform is started. During this stretching and stretching, it is general to perform pre-blowing in the preform to smoothly perform stretching. At this time, the bottom mold 2 is lifted as the stretching rod 3 is lifted while the bottom mold 2 is tightly engaged with the preform bottom 16.

Then, in FIG. 5, a fluid is blown into the preform which is being extended through a passage in the stretching rod or a passage between the stretching rod and the core mold to expand and stretch the preform in the circumferential direction. That is, by this, the bottom mold 2 and the preform 13
While the and are always in close contact with each other, the stretching and stretching by the stretching rod and the expansion and stretching by the fluid blowing are performed, and as a result, the center of the bottom is properly held in the center of the bottle, and irregular molding is prevented, and the center of the bottle bottom is prevented. The shift will be prevented. During the stretch blow molding, the bottom die lifting shaft 9
Since a gap 17 (see FIG. 4) is formed between the opening 11 and the opening 11 to allow free flow of air, this gap
It is possible to rapidly exhaust the air in the cavity 4 through 17. Therefore, the monomers and oligomers in the air are prevented from depositing on the blow mold surface 5,
As a result, the blow mold surface 5 can be maintained in the original smooth condition of the blow mold.

Thus, the biaxially stretched plastic bottle 20 is formed,
This plastic bottle is composed of a tubular body portion 21 that is integrally molded, a bottom portion 22 that closes the lower end of the body portion, and a mouth portion 24 that is connected to the upper end of the body portion via a shoulder portion 23. The outer surface shape of each part of the bottle corresponds to the cavity surface 5 and the bottom mold inner surface shape.

The molded bottle is cooled by heat transfer from the mold to a temperature at which it is not deformed even when taken out, and then the split molds 1a and 1b are opened and taken out to the outside as shown in FIG.

The biaxially stretched bottle manufacturing method of the present invention can be modified in many ways without departing from the spirit of the present invention.

In the present invention, as the resin forming the preform, that is, the container body, any thermoplastic resin can be used as long as it is a stretch-blow-moldable thermoplastic resin having a molecular orientation. As such resin, polypropylene,
Olefin resins such as polybutene-1, poly-4-methylpentene-1, propylene-ethylene copolymer, propylene-butene-1 copolymer and ionomer; thermoplastic polyesters such as polyethylene terephthalate (PET) and polybutylene terephthalate; Polycarbonates; Acrylic-butadiene-styrene copolymer (ABS resin);
Polyacetal resin; nylon 6, nylon 66, xylylene adipamide resin, nylons such as copolymerized nylon thereof; acrylic resin such as polymethylmethacrylate;
Examples thereof include polyarylate and polysulfone. These resins These resins can be used alone or in combination of two or more kinds, and can be used, for example, in the form of a blend of two or more kinds of resins or in the form of a multilayer laminate of two or more kinds. .

Also, when it is desired to have a high degree of gas barrier properties, a multilayer laminate with a gas barrier resin such as an ethylene-vinyl alcohol copolymer, a nylon resin, a vinylene chloride resin, or a high nitrile resin is used. It is good to use in the form of.

Of these resins, the present invention is preferably applied to thermoplastic polyesters, particularly polyethylene terephthalate (PET) and thermoplastic copolyesters mainly composed of ethylene terephthalate. This is because the polyester container has excellent transparency, but contains a relatively large amount of monomers and oligomers inside the resin, and also has a large effect of molecular orientation effect or thinning due to stretching,
Defects such as a decrease in surface gloss due to adhesion of a monomer or an oligomer to the mold surface and a defective appearance due to a center shift are rather conspicuous. By applying the present invention, however, such defects are effectively eliminated.

Blow molding parison can be injection molded PET to make a substantially amorphous bottomed preform, or extruding resin into a pipe shape through a ring die, cooling it and cutting it to a predetermined size, Close one end to make a bottomed preform. The drawing temperature of this preform,
For example, after preheating to a temperature of 85 to 125 ° C., particularly 95 to 120 ° C., while stretching in the axial direction in a blow mold,
It is expanded and stretched in the circumferential direction to form a bottle. The draw ratio in the axial direction is generally 1.2 to 3.0 times, particularly preferably in the range of 1.8 to 2.5 times, and the draw ratio in the circumferential direction is generally 2.0.
It is preferably in the range of 7.0 to 7.0 times, particularly 3.5 to 5.0 times.
The bottle after stretch blow molding can be used as a packaging container without post-treatment, or can be heat-treated by a means known per se to be used as a heat-resistant packaging container. The heat setting is preferably performed at 120 to 180 ° C. The heat setting may be performed simultaneously with the stretch blow molding or may be performed separately from the molding.

In the present invention, the contact between the bottom mold and the preform bottom is
It should be understood that it is enough to prevent center shift during expansion and stretching, and that excessive pressing is not necessary. The contact area between the bottom mold and the bottom of the preform is 50
It is good to be in the range of to 300 mm ² , and the pressing force is 5 to
It should be in the 50kg range. The air distribution gap formed between the bottom mold and the split mold during stretch blow molding is such that free flow of air is possible. Cross section of 40
It should be in the range of 85% to 85%.

According to the present invention, it is possible to prevent the deposition of a monomer or an oligomer on the surface of a mold and manufacture a biaxially stretched plastic bottle having a surface in which the surface of the mold is faithfully reproduced. Thus, if the mold surface is mirror-finished, a bottle with a smooth surface and gloss can be manufactured,
In addition, when the surface of the mold is matted, it is possible to manufacture a bottle in which the matte pattern is faithfully reproduced.

Example 1 and Comparative Example 1. Polyethylene terephthalate having an intrinsic viscosity (IV) of 0.79 was melt-injection-molded to produce a preform having a weight of 59 g and having the shape shown in FIG. This preform was preheated to a temperature of 110 ° C. in an infrared heating furnace and stretch blow molded.

As blow type, height 305mm, barrel diameter 95mm, internal volume 150ml
The dimensions shown in FIGS. 1 to 6 were used. Blow molding was performed by the following two methods.

Method A: Stretch blow molding was performed with the bottom mold being fixed to the upper opening of the split mold.

Method B: The bottom mold is movable in the vertical direction as shown in FIGS. 1 to 6 so that air can freely flow through the gap formed between the bottom mold and the split mold during blow molding. Then, blow molding was performed.

In the stretch blow molding, the blow mold temperature was set to 150 ° C., and after the molding was completed, heat setting was performed by holding the bottle in the mold for about 10 seconds.

The surface states of the obtained products were compared. Since the state of mold stains, and hence the bottle surface state, depends on the number of times of molding, the relationship between the time from the start of molding and the bottle surface state (surface stain state) was investigated. For the surface condition of the bottle, cut the columnar body of the bottle and use the direct reading haze meter manufactured by Toyo Seiki Seisakusho Co., Ltd. to measure the haze value (JIS K6714).
Compared with.

The results are shown in Table 1.

From the results in Table 1 above, it can be seen that according to the present invention, stains on the bottle surface can be significantly prevented.

Example 2 and Comparative Example 2. In Example 1 and Comparative Example 1, a preform having a basis weight of 48 g was used, and a blow mold had a height of 250 mm, a side of 65 mm, a diagonal line of 85 mm, and an internal volume of 900 ml. In the same manner as in Example 1 and Comparative Example 1 except that was used, a heat-resistant bottle having a thin bottom portion was manufactured.

For the obtained bottles, the bottom weight of the bottle (the weight of the portion whose height from the bottom is 15 mm or less) and the wall thickness distribution were compared. The wall thickness distribution is centered on the bottom (dome-shaped recess).
B, the ground contact area B, the bottom outer circumference C whose height from the ground contact area is 10 mm, and the trunk wall area D which is 100 mm from the ground contact area
I followed the dots. The results are shown in Table 2.

According to the results of Table 2 above, according to the present invention, it is possible to reduce the thickness of the bottom portion without causing center deviation.

(Effect of the Invention) According to the present invention, a thermoplastic plastic preform is placed in a blow mold consisting of a split mold and a bottom mold, and a stretching rod is inserted into the preform to stretch and stretch the preform in the axial direction. Along with, by expanding and stretching the preform in the circumferential direction, when manufacturing a biaxially stretched plastic bottle,
The bottom mold, or a part of the bottom mold is arranged in the split mold so as to be movable in the moving direction of the stretching rod, and a gap in which gas is freely flown is formed between the bottom mold and the split mold. When the preform is biaxially stretched, the bottom die and the preform are brought into close contact with each other to move the stretching rod, and the air in the blow die can be rapidly exhausted through the gap, resulting in smoothness, glossiness or shape. It was possible to manufacture a biaxially stretched plastic bottle having excellent appearance characteristics such as reproducibility.

[Brief description of drawings]

1 to 6 show the sequence of the stretch blow molding process of the present invention. FIG. 1 is a preform inserting process, FIG. 2 is a bottom mold lowering process, FIG. 3 is a split mold closing process, and FIG. Is a drawing rod raising step, FIG. 5 is a drawing blow step, and FIG. 6 is a partial sectional side view showing a mold opening product taking out step. 1a and 1b are blow molds, 2 is bottom molds, 3 is a drawing rod, 4 is a cavity for bottle molding, 5 is a cavity surface, 9 is a lifting shaft, 10 is a lower opening, 11 is an upper opening, and 13 is The preform, 16 is the bottom, 17 is the gap.

Claims (1)

[Claims] 1. A thermoplastic preform is placed in a blow mold consisting of a split mold and a bottom mold, and a stretching rod is inserted into the preform to stretch and stretch the preform in the axial direction. In a method for producing a biaxially stretched plastic bottle, which comprises expanding and stretching a preform in the circumferential direction, a bottom mold or a part of the bottom mold is arranged in a split mold so as to be movable in a moving direction of a stretching rod, and A gap allowing free passage of gas is formed between the mold and the split mold, and when the preform is biaxially stretched, the bottom mold and the preform are brought into close contact with each other to move the stretching rod and blown through the gap. A method for producing a biaxially stretched plastic bottle, which comprises rapidly exhausting air in a mold.