GB1561067A - Manufacture of biaxially oriented plastics containers - Google Patents

Description

(54) THE MANUFACTURE OF BIAXIALLY ORIENTATED PLASTICS CONTAINERS (71) We, THE STANDARD OIL COMPANY of Midland Building, Cleveland, Ohio 44115, United States of America a corporation organised under the state of Ohio, United States of America do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to an apparatus for controlling the distribution of plastics material in the manufacture of biaxially orientated plastics containers, and more particularly relates to a blow moulding apparatus which allows for uniform stretch rate and careful temperature control which permits the production of biaxially orientated plastics containers having uniform wall thickness and good clarity.

It is an object of this invention to pro vide an apparatus which produces plastics containers having a high degree of orien tation.

It is also an object to provide biaxially orientated plastics containers having im proved performance properties by utiliz ation of lower orientation temperatures.

Another object is the provision of plastics containers having improved plastics material distribution in the base thereof.

Another object is the provision of a plastics moulding apparatus which gives higher axial stretch ratios because of care fully controlled stretch rates.

According to the invention there is provided a plastics moulding apparatus suitable for the manufacture of biaxially orientated hollow plastics containers from a plastics preform; the apparatus comprising a hollow mould; means for positioning the plastics preform within the cavity of the mould and for expanding and urging the walls of the preform into contact with the walls of the mould cavity, the said means comprising a movable blow pin equipped with a contacting tip, the said blow pin having means responsive to fluid pressure to cause it to move axially to stretch the preform and spring means for controlling the rate of axial movement of the blow pin so that the blow pin tip cannot force the walls of the said preform against the wall of the cavity of the mould, the said blow pin tip being of an insulating material which reduces the heat loss from the thermoplastic preform through the blow pin tip; and mould heat ing means for preventing the thermoplastic preform material from dropping below orientation temperatures.

In the accompanying drawings, an em bodiment of this invention appears wherein: Figure 1 is a side sectional elevational view of a mould apparatus. The mould in this particular embodiment is for a bottle in inverted position.

Figure 2 is another side elevation in section of the mould apparatus showing the plastics material partially inflated within the mould.

Figure 3 is a view taken along line 3-3 in Figure 1.

Figure 4 is a view taken along line 4-4 in Figure 1.

The mould I is composed of two hollow mould halves 2 and 2' which are equipped with cartridge heaters 3 which can be located at intervals of from 6 to 60 degrees apart around the circumference of the mould 1. Within the mould there is positioned a plastics parison or preform 4 which has been preheated to the orientation temperature. The blow pin 5 has an enlarged lower end 5' which functions as a piston and is movable in a vertical direction, having a tip 6 which is made of a low heat-transfer coefficient material such as Teflon , nylon, polyester or Transite (Transite is a trade mark for a composite of asbestos and Portland cement), and as the blow pin moves up it forces the preform 4 towards the upper limit of the cavity of the mould 1. There is also provided a blowing mandrel 7 through which is passed a fluid, usually a gas, which enters under positive pressure through port 8 which forces the blow pin to move upwardly to a position as shown in Figure 2 and is in communication with annular orifices 8' and 8", which in turn inflates the preform 4 as shown in Figure 2. As the preform 4 is inflated by the gas flowing through the blowing mandrel 7, the blow pin 5 by virtue of force of the gas on the piston 5' moves upward forcing the preform 4 in an upward direction. The upward travel of the blow pin 5 is somewhat restricted by spring 9 which becomes compressed as the blow pin 5 moves upwardly to allow the blow pin tip 6 to approach the top of the inside of the cavity of the mould I but not to push the upper centre part of the expanded preform 4 against the top portion of the cavity of the mouldl.

The apparatus of the present invention is useful in the manufacture of biaxially orientated containers from orientatable thermoplastic materials such as polypropylene, polystyrene, polyvinyl chlorides, polyesters, and particularly thermoplastic nitrile gas barrier resins including those described in U.S. Patents Nos.3,426,102, 3,451,538, 3,586,737, 3,763,278 and 3,821,348. The production of clear, biaxially orientated bottles from nitrile gas barrier resins which have rather narrow orientation ranges is readily accomplished in the apparatus of this invention.

By means of the apparatus of this invention, biaxially orientated plastics containers can be produced with improved control of plastics material distribution throughout the walls of the containers, and a high degree of orientation is obtained in the base of the container by employing materials which have low heat-transfer coefficients in construction of the tip 6 of the orientation blow-stretch pin 5. Materials such as Teflon, nylon, polyester and Transite, can be used for the tip 6 to reduce the heat loss from the preform 4 to the tip 6 and blow pin 5, thus allowing more and better stretch of the preform 4 in the area of the tip 6 before the thermoplastic material in the expanded preform 4 drops below the orientation temperature of the thermoplastic material. Use of this apparatus allows for use of lower orientation temperatures and better utilization of the thermoplastic material in the base of the preform and higher performance of the base portion of the finished orientated container in terms of creep resistance and drop-impact resistance, and requires less plastics material than normal in this area of the container which results in a reduction in the weight of thermoplastic material needed for the container.

In controlling the rate of axial stretch of the preform 4, better control over thermoplastic material distribution in the vertical walls of the orientated container can be obtained at lower temperatures with the apparatus of this invention. Control of the longitudinal stretch of a thermoplastic preform is obtained by the spring loading of the longitudinal stretch device or blow pin 5. By varying the spring 9 constant and length of spring 9 or using a spring 9 which has a variable spring constant, different rates of stretch can be obtained for a given stretch distance. This improvement combines with the insulated mandrel tip 6 to markedly improve the orientation and thermoplastic material distribution in the base of the container. The spring 9 will slow or stop the blow pin 5 before it reaches the bottom of the cavity of the finished container mould 1, keeping the thermoplastic material from dropping below orientation temperature by contacting the wall of the cool mould at this point before the preform has been fully inflated. This allows the blowing fluid pressure to stretch the thermoplastic material in the preform near the base of the container over the entire area of the base giving improved distribution of plastics material and increased orientation in the base of the container.

Because the heated thermoplastic preform is not instantaneously expanded into the form of the interior of the container mould 1, orientation stress whitening can occur when thermoplastics having narrow orientation temperature ranges (5 - 15"F) are used in the manufacture of biaxially orientated plastics containers. Orientation stress whitening can be eliminated using the apparatus of the present invention by an increase in the surface temperature of the mould cavity in the areas where either high stretch is experienced or in areas where the thermoplastic material fills the mould cavity last. The careful control of the temperature of selected areas on the surface of the mould cavity is accomplished using electric low-watt density cartridge heaters or zoned temperature-controlled fluid in the mould areas where stress whitening ordinarily occurs. By eliminating stress whitening, a container of uniform clarity is obtained, and improved thermoplastic material distribution is obtained in the areas of the mould cavity surface where stress whitening normally occurs.

EXAMPLE In an apparatus like that described in the drawings and specification above, a biaxially orientated bottle was prepared from a nitrile rubber-modified copolymer of about 75(to acrylonitrile and 25% methyl acrylate (Barex 210 resin marketed by Vistron Corporation) (Barex is a Registered Trade Mark). The mould halves each contained 3 electric cartridge heaters. The heaters were equally spaced radially about the mould and each was of a 50-watt capacity and 4 inch by 1 inch long. The heaters were located 1 inch from the top of the blow-moulded cavity as shown in the drawings (bottom of the bottle).

An injection moulded plastics preform was installed on the blowing mandrel. The preform was heated by radiant heat to about 220"F on the mandrel before it was placed in the mould cavity and blow moulded. The preform had the following dimensions: neck finish 28 mm neck finish, I.D. .730 inch body, O.D. .982 inch wall thickness .120 inch overall length 6.5 inches Body of preform had a degree draft angle.

The blowing mandrel had an O.D. in the neck finish which provided a push fit between the preform and the mandrel. The relaxed length of the blowing mandrel was designed so that the tip did not quite contact the inside of the preform. The mould halves (blow cavity for a 32-ounce round bottle with screw neck having a body diameter of 3.14 inches and an overall height of 10.75 inches with a 28-mm neck finish) were closed around the mandrel and preform and the blow-air supply was connected to the port 8, and the biaxial orientation process was started. the pressure of the blow air was programmed so that it was at 200 psig for 2 second and at 180 psig for 9 seconds. When the blow air was thus applied to the port, both axial stretching and radial blowing as shown in Figure 2 occurred simultaneously. Air through orifices 8' and 8" was used to adjust or fine tune the radial flow. The upward stroke of the blow pin was somewhat retarded by the stretch-control spring. The blow pin had the following characteristics: blow pin-piston diameter.547 inch mandrel inside diameter .551 inch orifice area (8") .003 inch2 orifice area (8') .0005 inch control spring (9) 10 coil, 1.45 inches long spring constant 2.838 pounds per inch tip (6) Teflon A highly orientated bottle having excellent clarity was produced.

WHAT WE CLAIM IS: 1. A plastics moulding apparatus suitable for the manufacture of biaxially orientated hollow plastics containers from a plastics preform; the apparatus comprising a hollow mould; means for positioning the plastics preform within the cavity of the mould and for expanding and urging the walls of the preform into contact with the walls of the mould cavity, the said means comprising a movable blow pin equipped with a contacting tip, the said blow pin having means responsive to fluid pressure to cause it to move axially to stretch the preform and spring means for controlling the rate of axial movement of the blow pin and for limiting the axial movement of the blow pin so that the blow pin tip cannot force the walls of the said preform against the wall of the cavity of the mould, the said blow pin tip being of an insulating material which reduces the heat loss from the thermoplastic preform through the blow pin tip; and mould heating means for preventing the thermoplastic preform material from dropping below orientation temperatures.

2. An apparatus as claimed in claim 1, wherein the tip of the blow pin is made of polytetrafluorethylene, nylon, polyester, or a composite of asbestos and Portland cement.

3. An apparatus as claimed in claim 1 or 2, wherein the mould is of a cylindrical shape and equipped with zone-controlled heaters located at intervals of from 6 to 60 degrees around the circumference of the mould.

4. A plastics moulding apparatus substantially as herein described with reference to the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (4)

**WARNING** start of CLMS field may overlap end of DESC **. stretch is experienced or in areas where the thermoplastic material fills the mould cavity last. The careful control of the temperature of selected areas on the surface of the mould cavity is accomplished using electric low-watt density cartridge heaters or zoned temperature-controlled fluid in the mould areas where stress whitening ordinarily occurs. By eliminating stress whitening, a container of uniform clarity is obtained, and improved thermoplastic material distribution is obtained in the areas of the mould cavity surface where stress whitening normally occurs. EXAMPLE In an apparatus like that described in the drawings and specification above, a biaxially orientated bottle was prepared from a nitrile rubber-modified copolymer of about 75(to acrylonitrile and 25% methyl acrylate (Barex 210 resin marketed by Vistron Corporation) (Barex is a Registered Trade Mark). The mould halves each contained 3 electric cartridge heaters. The heaters were equally spaced radially about the mould and each was of a 50-watt capacity and 4 inch by 1 inch long. The heaters were located 1 inch from the top of the blow-moulded cavity as shown in the drawings (bottom of the bottle). An injection moulded plastics preform was installed on the blowing mandrel. The preform was heated by radiant heat to about 220"F on the mandrel before it was placed in the mould cavity and blow moulded. The preform had the following dimensions: neck finish 28 mm neck finish, I.D. .730 inch body, O.D. .982 inch wall thickness .120 inch overall length 6.5 inches Body of preform had a degree draft angle. The blowing mandrel had an O.D. in the neck finish which provided a push fit between the preform and the mandrel. The relaxed length of the blowing mandrel was designed so that the tip did not quite contact the inside of the preform. The mould halves (blow cavity for a 32-ounce round bottle with screw neck having a body diameter of 3.14 inches and an overall height of 10.75 inches with a 28-mm neck finish) were closed around the mandrel and preform and the blow-air supply was connected to the port 8, and the biaxial orientation process was started. the pressure of the blow air was programmed so that it was at 200 psig for 2 second and at 180 psig for 9 seconds. When the blow air was thus applied to the port, both axial stretching and radial blowing as shown in Figure 2 occurred simultaneously. Air through orifices 8' and 8" was used to adjust or fine tune the radial flow. The upward stroke of the blow pin was somewhat retarded by the stretch-control spring. The blow pin had the following characteristics: blow pin-piston diameter.547 inch mandrel inside diameter .551 inch orifice area (8") .003 inch2 orifice area (8') .0005 inch control spring (9) 10 coil, 1.45 inches long spring constant 2.838 pounds per inch tip (6) Teflon A highly orientated bottle having excellent clarity was produced. WHAT WE CLAIM IS:

1. A plastics moulding apparatus suitable for the manufacture of biaxially orientated hollow plastics containers from a plastics preform; the apparatus comprising a hollow mould; means for positioning the plastics preform within the cavity of the mould and for expanding and urging the walls of the preform into contact with the walls of the mould cavity, the said means comprising a movable blow pin equipped with a contacting tip, the said blow pin having means responsive to fluid pressure to cause it to move axially to stretch the preform and spring means for controlling the rate of axial movement of the blow pin and for limiting the axial movement of the blow pin so that the blow pin tip cannot force the walls of the said preform against the wall of the cavity of the mould, the said blow pin tip being of an insulating material which reduces the heat loss from the thermoplastic preform through the blow pin tip; and mould heating means for preventing the thermoplastic preform material from dropping below orientation temperatures.

2. An apparatus as claimed in claim 1, wherein the tip of the blow pin is made of polytetrafluorethylene, nylon, polyester, or a composite of asbestos and Portland cement.

3. An apparatus as claimed in claim 1 or 2, wherein the mould is of a cylindrical shape and equipped with zone-controlled heaters located at intervals of from 6 to 60 degrees around the circumference of the mould.

4. A plastics moulding apparatus substantially as herein described with reference to the accompanying drawings.