PRODUCTION

DESCRIPTION

Field of the Invention

The present invention relates to a molding machine and molding method developed in order to produce a thin-walled, lightweight pet preform.

Background of the Invention

Pet preform is the state of the material before being subjected to blowing process in plastic bottle production. After the pet preform is obtained, blowing process is applied on the pet preforms according to the product which is desired.

Pet preform is manufactured with two known methods. One of these is injection method, and the other one is pressure method which is not very common and used generally in bottle cap production. The wall thicknesses of the pet preforms produced with both methods should be in certain thicknesses in certain areas. Otherwise, it is not possible to produce in wall thickness under a certain value.

In the state of the art, there are several studies on base geometries of the pet preforms. The application defined as "conical base" by Husky Company, base designs made by Corvaglia or thinning the plastic amount formed on the base during production with Mintec technology can be shown as example. However, all these studies are for decreasing the excessive use of plastic on the base of the bottle after the pet preforms are blown and the bottle is formed.

Since the melt plastic is injected into the gap between the cavity and core parts present in the molding machine in preform production with the current injection methods, the wall thickness of the preform that can be obtained can be decreased to a certain level. Due to the viscosity characteristic of the material, it is not possible to mold in an area with thin walls with injection. Especially, the wall thickness in base and shoulder parts of the preforms in preform production cannot be thinned as much as it is desired. If it is thinned, it can cause deficient injection (short shot) or other drawbacks in the produced part. In addition to this, machines that can inject the melt under high pressure and at high speed are required for the production of thin walled pet preforms. Injection at high pressure causes wearing in parts of the molding machine and problems in the hydraulic system in time. Furthermore, it requires higher mold clamping forces. In addition to all these, excessive friction caused by the high pressure and speed harms the structure of the plastic and causes the generation of acetaldehyde which is an unwanted material in pet preform production. Summary of the Invention

The objective of the present invention is to provide a molding machine which enables to produce a thin walled, lightweight pet preform.

Another objective of the present invention is to provide a molding method which enables to produce a thin walled, lightweight pet preform.

A further objective of the present invention is to provide a molding machine wherein injection and compression methods enabling to produce a thin walled, lightweight pet preform are used in combination.

Detailed Description of the Invention

A "molding machine" and "molding method" developed to fulfill the objectives of the present invention is illustrated in the accompanying figures, in which: Figure 1 is the lateral cross sectional schematic view of an inventive exemplary molding machine in closed state.

Figure 2 is the steps of the molding method in which the inventive exemplary molding machine is used The components shown in Figure -1 are each given reference numerals as follows: 1. Molding machine

2. Cavity

3. Neck-ring

4. Core

5. Lock ring

6. Channel part

7. Cylinder part

8. Sealing member

9. Follower

10. Pin

11. Screw

The steps of the method shown in Figure -2 are each given reference numerals as follows:

100. Molding method

101. Closing the molding machine (1) such that there will be an opening between the lock ring (5) and the core piece (4) with the effect of oil pressure

102. Locking the molding machine (1)

103. Starting the injection of the plastic melt material

104. Applying holding pressure in order to fully fill the mold gap towards the end of the injection process

105. Ending the injection process

106. Moving the lock ring (5) as much as the amount of the opening between the core piece (4) and itself by decreasing the oil pressure with a control valve, and crushing the plastic melt material with compression method 107. Cooling

108. Removing the preforms by means of eject system of the molding machine (1)

A molding machine (1) which is developed in order to produce a thin walled and lightweight pet preform essentially comprises at least one cavity piece (2) which forms the body part during the plastic injection of the pet preform,

at least one neck-ring (3) which forms the mouth of preform during the plastic injection of the pet preform,

at least one core piece (4) which forms the internal part during the plastic injection of the pet preform,

at least one lock ring (5) which is mounted on the core piece (4) and enables the neck ring (3) and the core piece (4) to be locked in the same axis.

In a preferred embodiment of the invention, the core piece (4) forming the inner part during the plastic injection of the pet preform has at least one channel part (6) to which the hydraulic oil is transferred and at least one cylinder part (7) in which the hydraulic oil is filled in its structure.

In a preferred embodiment of the invention, at least one sealing member (8) is mounted on the lock ring (5), which prevents the hydraulic oil from leaking.

In the preferred embodiment of the invention, at least one follower (9) enabling the lock ring (5) to be attached to the cylinder (7) part in which the hydraulic oil is filled is mounted on the lock ring (5).

In the preferred embodiment of the invention, at least one pin (10) and at least one screw (11) preventing the lock ring (5) from detaching from the core piece (4) are mounted on the lock ring (5).

A molding method (100) developed to fulfill the objective of the present invention essentially comprises the steps of

Closing the molding machine (1) such that there will be an opening between the lock ring (5) and the core piece (4) due to the hydraulic pressure (101), - Locking the molding machine (1) (102),

Starting the injection process (103),

Applying holding pressure in order to fully fill the mold gap towards the end of the injection process (104),

Ending the injection process (105),

- Moving the lock ring (5) as much as the amount of the opening between the core piece (4) and itself by decreasing the oil pressure with a control valve, and crushing the plastic melt material with compression method (106),

- Cooling (107),

- Removing the preforms by means of eject system of the molding machine

(1) (108).

In first step (101) of the inventive molding method (100), the amount of the opening formed due to the hydraulic pressure between the lock ring (5) and the core piece (4) is determined according to the desired wall thickness of the preform to be produced.

In the inventive molding method (100), after the plastic material is injected into the mold, it is cooled by the cooling fluid circulating in the molds. As a result of cooling, the plastic melt filled into the mold is separated from the outer surfaces of the mold by shrinking. As a result of separation, the contact between the melt plastic and the mold inner surface is cut and this situation causes an improper cooling, and consequently it causes quality problem in the final product. In order to prevent this situation and fully fill the plastic in the mold gap, holding process is applied towards the end of the injection process. Therefore, an effective cooling process is performed without cutting the contact of the mold surface with the melt in first cooling stage.

In the inventive molding method (100) by means of the opening between the lock ring (5) and the core piece (4) formed due to the hydraulic pressure, injection can be performed with even less pressure. As a result, friction force decreases, the failures that can occur in the machine hydraulic system are avoided, the life of the molding parts increases and less force is required in order to lock (102) the molding machine (1). Furthermore, by means of lower injection pressure, the problems occurring in the core piece (4) and the thickness distribution difference in the wall of final products are decreased. In addition to all these advantages, acetaldehyde formation which is unwanted in pet preform production can be prevented significantly.

When the bases of the plastic bottles in the markets are cut and examined, it is seen that excessive amounts of plastic are used in these areas. In preforms produced with the inventive molding method (100), it is possible to thin the plastic thicknesses in the base and shoulder areas in an amount not only be thinned by injection method, therefore the unnecessary plastic consumption especially in the base is decreased, and raw material is saved. For example, a saving in a value of approximately 4.6% is provided in basis weight of 10.8 gr preform for a bottle of 0.5 1. When the daily production of this product around the country is considered, it is seen that the saving creates a significant amount. In addition to these, the requirement for heating the mouth (neck) section of the preforms more, which is a problem during blowing process in bottle production, is also eliminated. Furthermore, by means of thin wall provided in base and shoulder parts, the cooling of the melt plastic is faster and therefore a faster production is performed.