JP4222462B2 - Preform for heat-resistant PET bottle - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a preform (parison) used for the production of polyethylene terephthalate resin bottles (hereinafter referred to as PET bottles), and in particular, a large-capacity heat-resistant PET bottle is biaxially stretched by a single-stage method (single blow) using a cold parison method. The present invention relates to a preform for a heat-resistant PET bottle that enables blow molding.
[0002]
[Prior art]
PET bottles are widely used as bottles of drinking water and the like.
The basic manufacturing process of this PET bottle is to melt pellets such as granules and use an injection molding machine to have a cylindrical body part via a shoulder part below the stopper part and the stopper part, and the bottom part. A so-called test tubular preform made of a cylindrical body having the above is formed, and then this preform is heated to a glass transition temperature or higher and formed into a bottle shape by biaxial stretch blow molding.
The blow molding can be roughly divided into a one-step method (single blow) and a two-step method (double blow). The one-step method is adapted to the final shape of the PET bottle as shown in FIG. This is a method of blow molding directly into the product shape of a PET bottle in one step directly from a preform using a mold with a designed cavity. The two-step method is first a primary larger than the final product shape as shown in FIG. The bottle is blow-molded using a mold, heated in a hot-air oven, etc., and spontaneously shrunk to form a secondary bottle. The secondary bottle is blow-molded again using the mold, and the final product It is a method to make a shape.
Therefore, the two-stage method (double blow) is more complicated and requires more equipment than the one-stage method (single blow), and uses a lot of energy, but for the reasons explained below, Conventionally, heat-resistant PET bottles are often blow-molded by a two-stage method.
PET resin has the characteristics that tensile yield strength is improved by orientation crystallization by stretching, oxygen permeability coefficient to prevent quality deterioration of drinking water is reduced, and heat resistance is achieved by heat crystallization. However, when heated to a temperature higher than the glass transition temperature (about 70 ° C.), it has the property of rapidly shrinking in size and deforming.
On the other hand, there are two types of PET bottles, non-heat-resistant (general) bottles and heat-resistant bottles, depending on the purpose of use, and since general bottles are filled with drinking water below the glass transition temperature of PET, heat resistance is not required. Manufactured by single blow molding.
[0003]
Recently, drinking water heated to 85 ° C or higher is filled for the purpose of heating and sterilizing the air reservoir inside the spout that occurs when filling PET bottles with drinking water, and the bottle is turned downward and held for a certain period of time. However, in conventional bottles (non-heat-resistant bottles), it becomes soft and deforms when filled with high-temperature drinking water having a glass transition temperature of 70 ° C. or higher due to the properties of the PET resin. The need for heat-resistant PET bottles that have been heat-treated in advance has increased.
Here, as a method for producing a heat-resistant PET bottle, a plug portion of a preform formed by melt injection molding of a pellet by a cold parison method is heated and whitened and crystallized to improve heat resistance. If the molding is performed by blowing, the heat resistance of the barrel portion is improved by reheating, and thus, conventionally, double blow molding has been a common method for producing a heat resistant PET bottle.
[0004]
However, as a result of various investigations to make single blow molding of heat-resistant PET bottles for reasons such as single blow molding being shorter than double blow molding and less equipment costs, etc. Is adopted.
After forming a preform by injection molding of PET resin pellets, the plug portion of the preform is heated and whitened and crystallized, and the preform is heated to a glass transition temperature or higher in a heating zone such as a hot air furnace. As shown in 4 (a), it is set in a mold heated to a predetermined temperature of about 140 to 150 ° C., blown into a product shape, and heat set for a certain time.
Here, heat setting is also referred to as heat fixation, and means that the surface density of PET is increased and the heat resistance is improved by contacting the surface of a heated mold for a certain time (about 3 seconds).
Thereafter, as shown in FIG. 4C, the mold is cooled and the mold is opened to take out the product.
[0005]
However, the double blow molding can be expanded to a size larger than that of the product to obtain a primary bottle, so that the substantial draw ratio of the PET resin can be increased. Since the draw ratio is determined by the ratio of the product shape, the product may have insufficient strength due to insufficient draw ratio, the oxygen transmission coefficient may increase, and the outer shape is heated because it is heated above the glass transition temperature during heat setting. Since it may be easily deformed, it has been practically used only for bottles with relatively small capacities of 350, 500, and 750 ml, and close to a cylindrical shape. The bottle is difficult to ensure the strength and oxygen permeation resistance of the PET bottle, especially the shape of the bottle is almost square, so the shape stability is difficult Ku, has been considered can not single blow molding up to now.
[0006]
Moreover, in order to ensure the strength and heat resistance of the stopper part of the PET bottle, only the stopper part of the preform is subjected to the heating whitening crystallization treatment. In this case, generally, the conventional stopper shown in FIG. Explained based on the enlarged cross-sectional view of the plug portion of the preform 101 for double blow molding (a portion enlarged view), the preform is connected to the heating furnace in an inverted state with the plug portion a down. However, only the part of the plug part a is heated, and the outer diameter of the plug part shrinks due to this heating, and the heating is performed by the weight of the preform body located above the plug part of the preform. However, it tends to deform so that the thickness of the softened plug portion becomes thick.
However, it is important for the plug part to be fitted and sealed with the cap of the PET bottle, so that it is necessary to minimize variations in the dimensions of the thread part of the preform plug part and the coupler part during heating. When blowing high pressure air of about 35 atmospheres into the reform, it is necessary to form the plug inner diameter equivalent part straight so that it can be stably fitted to the blowing mandle, but the conventional preform is straight Since the length of the portion is long, the thickness of the coupler portion 111 is reduced, and there is a drawback that the dimensional change of the threaded portion and the coupler outer diameter during heating tends to be large.
[0007]
[Problems to be solved by the invention]
In view of the above circumstances, an object of the present invention is to provide a preform capable of stably performing biaxial stretch blow molding of a large-capacity heat-resistant PET bottle by single blow molding using a cold parison method.
[0008]
[Means for Solving the Problems]
In the double blow molding method, as described above, the primary bottle shown in FIG. 5 (b) is made larger than the final product bottle shape shown in FIG. In the blow molding method, since the final product bottle shape is obtained by only one blow, the substantial stretch ratio is determined by the ratio between the bottle shape and the preform.
However, due to the characteristics of the PET resin, it is necessary to ensure a substantial draw ratio greater than a predetermined value in order to ensure a predetermined strength and oxygen permeability, and the product shape of a large-capacity PET bottle of 2000 ml or the like is generally square. Therefore, a higher tensile yield strength is required, and it is necessary to reduce the oxygen permeability coefficient in order to prevent the quality deterioration of the drinking water as the filling.
[0009]
Therefore, as a result of detailed examinations this time, while considering the shape of the preform in which PET resin is uniformly stretched into a substantially square bottle shape at the time of biaxial stretch blow molding, and particularly, abnormal deformation of the shape hardly occurs at the time of blow molding. The length under the neck of the preform can be made shorter than the length under the neck of the conventional preform for double blow molding, so that the stretch ratio at the time of single blow molding can be increased.
Specifically, a biaxially stretched blow molded container having a large capacity using polyethylene terephthalate resin is provided when a single blow molding is performed by the cold parison method. In a preform comprising a bottomed cylindrical body having a cylindrical body portion, the neck length under the spout is set so that the longitudinal stretch ratio is 1.85 or more, and the lateral stretch ratio is 3 The outer diameter of the body was set to be 5 or more.
Desirably, the longitudinal stretching ratio is 1.85 or more, the transverse stretching ratio is 3.5 or more, and the area stretching ratio (longitudinal stretching ratio × transverse stretching ratio) is set to 7.0 or more. It is good.
Further, it is desirable that the transverse direction draw ratio of the short body portion is 3.5 or more in the case of a substantially square bottle having a capacity of 2000 ml or the like in the transverse direction.
Here, the longer the draw ratio in the machine direction and the transverse direction, the more the strength and oxygen permeation resistance are improved. However, in order to maintain the stability of the bottle product shape during blow molding, the draw ratio in the machine direction is 2. 3 or less and the transverse draw ratio is preferably 4.0 or less.
[0010]
Also, in the case of a substantially square PET bottle with a large capacity of 2000 ml, in order to further improve the strength and prevent shape deformation due to the heat effect during heat setting, it is heavier than the conventional preform weight per unit of 67 g. It is better to set and thicken the barrel of the product. Set the weight of 6 liters to 70.5 g of 2 liter heat resistant PET bottle preform, and the barrel thickness is 4.0 mm. The shape was set to be as described above.
Here, the thickness of the body portion of the preform is a relative value to the draw ratio, but it is desirable to secure a thickness of 4.2 mm or more, and 5.0 mm to stably maintain the bottle product shape. The following is desirable.
[0011]
When the preform is turned upside down and the plug part is heated and whitened, by providing a thick part inside the coupler part, the variation in the dimensional change of the thread part and coupler outer diameter part during heating of the preform is suppressed, And, in order to improve the mounting stability to the blowing mandle and stabilize the quality, it is used when single blow molding a biaxially stretched blow molded container having a large capacity using polyethylene terephthalate resin by the cold parison method. In the preform consisting of a bottomed tubular body with a cylindrical body part via a shoulder part below the plug part and the plug part, a thick part is provided inside the plug part corresponding to the position of the coupler part. The plug portion inner straight portion length is set in the range of 8 to 12 mm.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
An embodiment in which the present invention is applied to a substantially square PET bottle having a capacity of 2000 ml shown in FIG. 3 will be described below, but is not limited thereto, and is set according to various bottle product shapes of 1000 ml or more. Can change.
The product shape of the PET bottle is 2 g in total length: 305 mm, under neck length 2 b: 282.57 mm, plug part neck ring outer diameter 2 h: 33 mm, plug part screw thread outer diameter 2 i: 27.56 mm, plug part length 2 a : The shape of the preform according to the present invention with respect to 22.43 mm, short body width 2e: 88.5 mm, and long body width 21e: 106 mm is shown in FIG. 1, total length 1 g: 170.43 mm, under neck length 1 b: 148 mm, plug part neck ring outer diameter 1 h: 33 mm, plug part thread outer diameter 1 i: 27.56 mm, plug part length 1 a: 22.43 mm, trunk outer diameter 1 e: 28.9 mm, wall thickness 1 f: The thickness was set to 4.4 mm, shoulder length 1c: 19 mm, and weight per unit weight 69 g.
For the sake of clarity, the size of the preform 1 is indicated by a two-dot chain line in the product shape of FIG.
[0013]
Thus, the longitudinal draw ratio 2b ÷ 1b = 282.5 ÷ 148 = 1.91 , and the transverse draw ratio 2e ÷ (1e-1f) = 88.5 ÷ (28. 9-4.4) = 3.61 , and as a result, an area stretch ratio of 7.12 is secured.
In addition, since the weight per unit weight is set to 69 g, which is heavier than the conventional double blow molding preform weight per unit of 67 g, the tensile yield strength of the product bottle is improved and the shape change at the time of heat setting is suppressed. It became possible to produce a PET bottle with a large capacity of 2000 ml stably.
[0014]
The process will be described with reference to FIG. 4. As shown in FIG. 4 (a), the preform 1 according to the present invention is set in the mold 3 heated to 140 to 150 [deg.] C. As shown in FIG. The air is blown from the blow port 5 while being stretched upward by the stretching rod 4.
Then, it hold | maintains for several seconds in order to heat-set with a metal mold | die, and cools by blowing in air from the cooling air supply port 6 as shown in FIG.
The exhaust 6a is exhausted from the blow port at this time.
Next, as shown in FIG. 4D, the mold is opened and the PET bottle product 2 is taken out.
[0015]
For reference, the shape of a conventional double blow molding preform 101 is shown in FIG. 6, and the neck length b of the preform is as long as 155.93 mm, and the thickness of the body portion is reduced to 4.0 mm accordingly. ing.
The substantial draw ratio is the ratio between the preform and the primary bottle shown in FIG. 5 (b), but the apparent value between the preform and the final product bottle shape is a longitudinal draw ratio of 1.81, The transverse draw ratio is 3.64 and the area draw ratio is 6.59.
Further, the shoulder length 1c of the preform according to the present invention is set to 19 mm, which is slightly longer than the shoulder length c18 mm of the conventional preform, so that the stretching of the shoulder is adjusted.
[0016]
Next, the shape of the plug portion of the preform will be described based on an enlarged cross-sectional view of the plug portion of the preform shown in FIG.
In order to ensure the sealing performance with the cap, the plug part coupler diameter 1j: 27.97 mm, the plug part coupler height 1d: 14.1 mm, the plug part screw thread outer diameter 1i: 27.56 mm, and the plug The inner diameter 1k: 20.6 mm is standardized.
Therefore, the feature of the shape of the plug portion in the present invention is that the thick portion 11 is provided inside the plug portion where the inner diameter 1p of the plug is 19 mm, and the plug portion has a height of 14.1 mm. The length of the straight portion 1n is in the range of 8 to 12 mm.
While maintaining the strength of the plug portion by providing a thick portion inside the plug portion of the coupler portion, the dimensional change during the heat treatment was suppressed, and the length of the plug portion straight portion was set within a predetermined range. As a result, it was possible to stably fit the blowing mandle when the preform was blown.
[0017]
【The invention's effect】
When the preform according to the present invention is used, even in a large-capacity heat-resistant PET bottle, a predetermined stretch ratio can be ensured by shortening the length under the neck, while considering the shape of the entire preform, Since the thickness of the part is thicker than before, the strength of the product bottle can be secured and the heat effect during heat setting can be suppressed, and the thick part is provided inside the plug part and the straight part is kept within the specified range. Since it was set, it became possible to perform single blow molding stably and continuously by the cold parison method.
As a result, in conventional double blow molding, blow molding is performed twice, so two sets of blow molding machines and blow molds are required, and a heating furnace for the primary bottle is also required, but single blow is possible. As a result, only one set of blow molding machine and blow mold is required, the process is simplified, running costs such as equipment costs and energy costs can be greatly reduced, and there is no need to reblow in double blow molding. Quality trouble is eliminated and product quality is improved.
In addition, the simplified equipment can be expected to reduce equipment failures and improve equipment availability.
Furthermore, the area occupied by the facilities is less than half, and the building area is small.
[Brief description of the drawings]
FIG. 1 shows an example of a 2000 ml PET bottle preform according to the present invention.
2 shows an enlarged cross-sectional view of the plug portion of FIG. 1. FIG.
FIGS. 3A and 3B show an example of a product shape of a single blow molded PET bottle using the preform according to the present invention, and are (a) a front view and (b) a side view.
FIG. 4 shows a process diagram of single blow molding.
FIG. 5 shows a change in bottle shape in double blow molding.
FIG. 6 shows a cross-sectional view of an example of a conventional 2000 ml PET bottle preform for double blow molding.
[Explanation of symbols]
1 Preform 1a Preform Plug Port Length 1b Preform Neck Length 1c Preform Shoulder Length 1d Preform Coupler Height 1e Preform Body Outer Diameter 1f Preform Body Thickness of 1g Preform total length 1h Preform plug neck neckring outer diameter 1i Preform screw thread outer diameter 1j Preform coupler diameter 1k Preform plug inner diameter 1n Preform mouth Plug part straight part length 1p Pre-plug mouth part thick part inner diameter 11 Pre-plug mouth part thick part 2 Example of a PET bottle formed by single blow molding using the preform according to the present invention is shown.
2a PET bottle cap length 2b PET bottle neck length 2e PET bottle short barrel width 21e PET bottle long barrel width 2g PET bottle full length 2h PET bottle plug neck neck ring outer diameter 2i PET Bottle thread outer diameter

Claims (1)

Cylindrical body through a shoulder part below the spout part and the spigot part provided when single-blow molding a biaxially stretched blow molded container using polyethylene terephthalate resin with a capacity of 2000 ml by the cold parison method In a preform comprising a bottomed cylindrical body with a portion, the neck portion under the mouthpiece portion is subjected to heat whitening crystallization treatment, and the longitudinal stretch ratio is 1.85 or more. A preform for a heat-resistant PET bottle, wherein the body diameter is set so that the transverse stretch ratio is 3.5 or more.

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