JPS6011611B2 - Deep drawing thermoforming of thermoplastic sheets - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an apparatus and method for manufacturing hollow articles from thermoplastic sheet material.

More particularly, the present invention relates to an apparatus and method for deep drawing hollow articles from thermoplastic sheet material. According to the invention, hollow articles made of thermoplastic sheet material deep drawn and having a large L'D (length to diameter) ratio by using Applicant's apparatus and method described in detail below. can be obtained.

In forming hollow articles such as parisodes, preforms, liners, etc. by deep drawing of thermoplastic sheet material, the thermoplastic sheet material is usually first heated to a temperature above the heat strain temperature, and then the thermoplastic material is placed on a mandrel. Stretch or vacuum the disconcerted thermoplastic material deep into the female mold using a vacuum.

In either case, the thermoplastic material in question becomes thinner as it is stretched to conform to the shape of the mold or mold, or the thermoplastic material becomes thinner as the softened sheet is stretched to conform to the shape of the mold. The material becomes very susceptible to the formation of wrinkles (especially on its top surface).

Applicant has invented an apparatus and method for ripening hollow articles requiring L/D ratios of up to 20/1.

By forming a heated thermoplastic sheet around a tapered heated mandrel, which can be equipped with a dome-shaped guide (a type of plugassist) of larger diameter than the mandrel and a branch tube leading to a vacuum device. , wrinkle-free deep-drawn hollow articles with uniform ID and wall thickness can be produced.

In the apparatus and method, a heated mandrel as described above is inserted into a mold cavity and a heated sheet material is stretched between the mold cavity and the mandrel. In the present apparatus and method, a dome-shaped guide or a tapered cavity guide (smooth cavity) having an inner diameter larger than the outer diameter (OD) of the mandrel and located directly above the mold cavity, A heated plastic sheet is uniformly stretched externally over the mandrel and into the mold cavity. The domed cavity guide portion of the mold cavity has two primary functions. First, the drawing ratio of the hollow article can be varied by changing the inner diameter of the domed cavity guide. The inner diameter of the guide defines the area of plastic material that is stretched from the plastic sheet onto the mandrel. Second, the guide prevents uneven stretching and wrinkle formation in large L/D hollow articles. Careful selection of guide diameter and cavity shape allows for very small draft angles (30'
The following hollow articles can be manufactured. Typically, a mandrel equipped with a vacuum device passes through a domed caviar guide and into a mold cavity to draw the thermoplastic sheet between the guide, mold cavity, and mandrel. The apparatus of the invention is further illustrated in the accompanying drawings.

The device consists of a mandrel or insertion aid 1, a holder 2 for the plastic sheet material and a mold cavity 3 with a cooling device 4, which fits over the cavity 3 and has a dome with a top and smooth sides. A mold cavity guide 5 is installed. This dome-shaped cavity guide 5 can have a tapered inner wall with an inner diameter larger than the inner diameter of the mold cavity 3 and is typically made of a plastic material, such as polypropylene, high density polyethylene, polytetrafluoroethylene, ylon, etc. or other materials that resist heat transfer from the heated plastic sheet material to the inner walls of the domed cavity guide. The dome-shaped guide 5 normally includes a hardened metal cutter 6 inserted at its bottom surface and near the entrance to the mold cavity 3. The holder 2 located directly above the domed cavity guide 5 is larger than the domed cavity guide 5 and is used to clamp the plastic sheet material in question. The center of the mandrel 1 is usually equipped with a vacuum line 7 through which air can be evacuated or blown (in order to form the hollow article and remove it after cooling). This line communicates with the outer wall of the mandrel 1 by holes 8 arranged along the marring direction of the mandrel 1. A heater 9 for heating the mandrel 1 is attached to the vacuum line 7 in the mandrel 1 . 0 to 3 for mandrel 1 shown in Figure 3.
Although a draft angle as low as 0' is shown, it should be understood that mandrels with larger draft angles are also within the scope of the invention. When the apparatus is operated and the plastic material to be patterned is fully extended from the area within the holder 2 and the mold is completely closed, as shown in the upper part of FIG. The plastic material from is cut with a cutter 6. The thermoplastic deep-drawn hollow articles with uniform wall thickness produced in the apparatus of the present invention are useful as containers in their own right, or can be further molded and blown to form preforms in the manufacture of plastic pins. It can be used as a parison or liner.

Thermoplastic sheets useful in making the hollow articles of this invention include polyolefins, polyvinyl halides including polyvinyl chloride, vinyl chloride copolymers, polyacrylates and copolymers, polymethacrylates and copolymers, polystyrene and copolymer, acrylonitrile copolymer, A
It can be any of the well-known thermoplastic materials such as matrix resins, polycarbonates, polyesters, and the like.

[Brief explanation of the drawing]

FIG. 1 is a partially cutaway sketch of a completed thermoplastic hollow article manufactured according to the present invention. FIG. 2 is a cross-sectional view taken along line 2--2 in FIG. FIG. 3 is a partially cutaway side view of the device. Figure 4 is the third
4 is a view taken along line 4-4 of the figure. FIG. 5 is a partially cutaway side view showing the drawing of the thermoplastic material between the mandrel and the cavity wall. Figure 6 is the 5th
6 is a view taken along line 6-6 of the figure; FIG. FIG. l FIG. 2 FIG. 3 FIG. 4 FIG. 5 FIG. 6

Claims (1)

[Claims] 1. A heating mandrel, a mold cavity, a device for holding a heated thermoplastic sheet between the mandrel and the mold cavity, and a device for heating the heating thermoplastic sheet by pushing the heating thermoplastic sheet and moving the mandrel. an apparatus for deep drawing hollow articles from a heated thermoplastic sheet, the apparatus comprising: an apparatus for extending the thermoplastic sheet onto the walls of a mandrel and into the mold cavity; and install a dome-shaped guide, the dome-shaped guide having an inner wall having a diameter larger than the inner diameter of the mold cavity, and the dome-shaped guide being located near the entrance of the mold cavity to accommodate the inserted hardened metal. An improved device consisting of installing the above dome-shaped guide equipped with a cutter. 2. The device of claim 1, wherein the device for holding the heated thermoplastic sheet is a holder located above the dome-shaped guide, and the holder is larger than the dome-shaped guide. 3. The device according to claim 2, wherein the mandrel and the mold cavity are tapered so as to come into close contact with each other. 4. The apparatus of claim 3, wherein the mandrel is provided with an internal vacuum line leading to holes in the mandrel wall through which air can be evacuated or blown.