IL37696A - Composite plastic articles and method and apparatus for making the same - Google Patents

Description

G This invention relates to improvements in the manuracture of plastic containers or the like wherein such containers are formed in a "blow mold from a pressure molded, closed-end parison that has been made on a core.

In the method of blow molding plastic hollow articles from parisons made by pressure molding, such as by injection molding or compression molding, the parison is molded in a parison mold around a core. The core may be a blow core and may then be removed together with the parison from the parison mold to a blow mold while the latter is still deformable and the parison is expanded into conformance with the blow mold by applying fluid pressure through the blow core to the inside of the parison, such procedure being known as injection blow molding.

Alternatively, the parison may be removed from the core, stored, if so desired, then heated to a temperature sufficient to render it deformable and expanded by fluid pressure into conformance with the blow mold.

Injection blow molding has many advantages compared to other processes for the production of hollow plastic .articles, such as the high dimensional accuracy of the product, the versatility of the process as to the variety of materials processed and its ability to make finished articles without the need for subsequent operations and without waste. It also exhibits difficulties that are related to the production of the parisons, as for example " It has been recognized that the quality of blown hollow articles made from pressure-molded parisons depends in large measure upon the dimensional accuracy of the parison immediately preceding the blowing step and upon the predetermined distribution of its temperature. Such dimensional accuracy and temperature distribution are difficult to control, particularly when the parisons to be molded are long in relation to their diameters. The dimensions and the temperature of the parison are largely determined by the mold in which it is made and particularly by the blow core. The blow core may be subject to rapid movement over appreciable distances in the course of each molding cycle. Its size is frequently not sufficient to accommodate efficient means for the control of its temperature and to- resist the pressure of the plastic during injection without deflecting. The choice of materials from which blow cores may be made is limited by the need to withstand the erosive action of the plastic during repeated molding cycles tc tool steels and the like hich do not have sufficient heat conductivity to facilitate temperature control. In addition, the fluid orifice of the blow core must be prevented from clogging and thereby adversely influencing the expansion of the parisons.

It has been attempted in the past to overcome these difficulties caused by blow cores. Thus, my U. S. Patent No. .3, 526, 687 Is directed to the prevention of clogging of the blow orifice. U. S. Patent 2, 305, 892 describes a procedure for molding parisons while stabilizing the blow In accordance with the present invention, the blow core is protected from the influence of the hot plastic that is brought into contact with it at high pressure in the course of the parison molding step by covering the blow core with a closely fitting preformed plastic sleeve that is compatible with the plastic from which the parison is to be made and forms a layer within the parison and within the article which is blown therefrom. The sleeve insulates the blow core from the heat of the plastic which would otherwise come into direct contact with the blow core and also protects the blow orifice from clogging by molten plastic. The blow core, surrounded by the sleeve, may be supported by holding it in pressure contact with selected aread of the parison mold. The hole or holes thereby produced in the injected parts of the parison do not result in discontinuities in the composite parison, because they are closed by the corresponding areas of the sleeve. Thus, the blow core may be supported without damaging the parison. The sleeve thus formed constitutes a lining within the parison and, after having been expanded with the parison into the blow mold, constitutes an inner lining within the blown article.

Such composite articles have the advantage that the lining and the remainder of the article walls may be composed of plastics having different characteristics and are particularly desirable when it is difficult to satisfy all of the requirements and specifications by means of 37696 ^> , Fig. ,7 is a partial elevation showing a web carrying a plurality juxtaposition with a sleeve mold 21, vacuum is applied in the mold cavity of the sleeve mold through connection 22 and the sheet converted into the desired shape by vacuum forming, i.e. by a drawing process that intrinsically produces attenuation of the sheet. Several sleeves so formed may now be stacked and placed into a holding fixture 2 5, shown in Pig. 6, which may be brought into alignment with a blow core 5 of an injection blow molding apparatus. The forming of the sleeve 1 may be one at a time or continuous, both methods being well known in the art. If it is continuous, the product of the forming operation may correspond to the formed web shown in Pig. 7 in which portions 25 that are shaped to correspond to the forming mold 21 of Pig. 5 are joined by parts of -the undeformed web 26. As an alternate to -placing the sleeves into a holding fixture 2 >, as in Pig. 6, such a web 2β may be fed over the blow core 5 in a manner such that one formed portion 25 after another is brought into juxtaposition with blow core 5· Obviously, the formed sleeves must be severed from web 26; however, this may be done before or after placing the sleeves 1 over the blow core 5 · As a further alternate, an undeformed web may be brought into juxtaposition with the blow core and the blow core itself used to form the sleeve in the web.

If the sleeves 1 are applied to the blow core from a holding fixture 2 as shown in Pig. 6, one procedure to cause them to adhere firmly to the blow core may consist of the following: After the fixture 23 and the blow core 5 are aligned, the blow core is inserted relatively loosely into the first sleeve in the stack. The sleeves in the fixture are not firmly stacked and may, if necessary, be kept slightly separated one from the other by jets of air acting between the sleeves. Once the blow core 5 is thus inserted, vacuum may be applied through the blow slot 15 with which the core is equipped to blow the parison into final shape and the sleeve thereby caused to De pressed against the blow core so that it will then remain attached thereto. Thereafter the blow, core 5, with the sleeve adhering, is removed from the fixture 23 which may be shifted to the side. Holding fixture 23 may of course be arranged to carry only a single sleeve 1 which, in that case, would be inserted into the fixture at a storage station alongside the assembly, for transfer onto the blow core.

Pig. 2 shows a parison mold which consists of blow core 5 carrying the sleeve 1 and a parison mold 6 and a tool for the forming of the open end of the. hollow article, shown as a neck ring 7. A passage 8 connects the parison mold 6 with a supply of hot plastic contained within cylinder 9 from which the molten plastic may be pressed into parison mold 6 by piston 10 under sufficient pressure to effect rapid filling of the space between the blow core 5 and the parison mold β and the space within neck ring 7 communicating with the parison mold.

The parison 11, being a composite containing the sleeve 1, as molded in the apparatus shown in Fig. 2, may not shown may be admitted through fluid passages 1 communicating with blow slots 15 to the interior of parison 11. The blow mold 12 has a mold cavity 14 corresponding to the shape of the hollow article to be made and it may be made of two halves which are separable when necessary for the removal of the finished article to be made therein.

The above indicated movements of the blow core may for example be carried out by apparatus shown in U.S.

Patents Nos. 2, 298, 716, 3, 100, 913; , 183, 552 and in my U.S. patent No. 3, 029,468. In any such apparatus, one or more blow cores may be used simultaneously and they may be moved from one operating position to another individually or in groups of several blow cores.

In operation of this method, sleeves according to Pig. 1 may be produced by any of the procedures referred to before, independently of the injection blow molding operation here described. Alternatively, sleeves may also be fashioned in place, as for example by applying plastic film stock tightly to the core 5. The sleeve material must have deformation characteristics that equal or exceed those of the parison material, at the temperature normally maintained for expanding the parison into the blow mold cavity 14.

Composite parisons that have been made as above described may, if desired, be stored before being expanded in the blow mold. In such a procedure the parisons are produced on a core which is not a blow core, removed from such core to storage, and reheated before blowing, all as known in the art.

The material of the sleeve may be capable of bonding the material of the parison at the temperature normally used for injection molding the latter material. To facilitate such bonding, the outside surface of the sleeve 1 that is to come into contact with the injected plastic, of the parison 11 may be treated by procedures that are known in the art to promote the adhesion of plastic surfaces.

For example, if the sleeve is to be made of polyethylene, its outside surface may be flame treated; in other instances it may be rendered tacky by application of a solvent prior to parison injection. Alternatively, the sleeve may be formed from laminated stock in such a way that the surface of the sleeve to come into contact in the injected plastic is capable of bonding thereto.

Sleeve 1 need not be made of a single material.

For example, the sleeve side walls 2 may be made of a material that is different from the material in the sleeve bottom which may, at times, be provided with a reinforcement for better support of the parison.

Although the sleeves will in most instances be made of plastics, it is also possible to make them partly or wholly of other materials, such as for example of extensible metal foil, or of elastomers.

When in place within the parison mold, the tip of the blow core, surrounded by the bottom of the sleeve mold, whenever it is desired to stabilize the blow core.

After the blow core is in place, hot plastic is injected into the parison mold through orifice 8 under action of piston 10 operating in pressure cylinder 9.

After injection, the hot plastic surrounds the sleeve 1 under pressure. Due to the intimate contact established thereby between the hot plastic and the exposed, surface of the sleeve, the sleeve is rapidly heated until its temperature approaches that of the injected plastic. At that temperature, adhesion of the two materials is usually facilitated and the material of the sleeve is moreover heated sufficiently to render the sleeve deformable at the same rate as the injected plastic. Accordingly, the sleeve combines with the injected plastic to form the composite parison 11.

After it is placed over the blow core 5> the sleeve 1 may cover the fluid passages 13 which are accordingly protected from the entry of plastic injected in the course of parison molding. Therefore, construction of the blow core is simplified and its operation rendered more reliable.

During the injection step, the blow core 5 is insulated from the hot plastic and protected from the friction of the plastic flowing at high velocity and pressure around the blow core.

It is at times beneficial to heat the sleeve prior to expansion by blowing, from the inside as well as from the outside as by the freshly injected plastic of the parison. This may be readily accomplished by constructing the blow it does not have to withstand the erosive effect of the plastic during injection and by heating the blow core electrically instead of by fluid circulation, as is common in injection blow molding to offset the temperature gradient •otherwise caused by repeated injection of plastic.

In order to prevent deflection of the blow core by the injected plastic and thereby to prevent undesirable variation of the parlson wall thickness, the blow core 5 may be firmly pressed against the bottom of the parlson mold, as shown in Fig. 2. Due to the sleeve that surrounds the blow core, only the sleeve will in fact be in contact with the parlson mold. Since no plastic can flow into the area of such contact, a discontinuity is produced in that area, which corresponds to the bottom j5 of the sleeve.

The sleeve may be made to have a thickness at bottom 3 corresponding to the desired thickness of the finished hollow article at that location. In the region immediately adjacent the area of contact between the sleeve and the parlson mold, the sleeve is firmly attached or fused to the parison. Thereby an opening in the wall of the. composite parison is avoided.

After forming of the parison by injection and the joining of the sleeve to the injected plastic, the blow core 5 is removed from the parison mold together with the neck ring 7 and with the parison 11 thereon, as shown i Fig. 3. It is next inserted into the blow mold 12, shown in Fig. 4.

For accurate location of the blow core 5 in the blow mold 12, the blow core may be pressed against the bottom of the blow mold, with the composite parison bottom or the sleeve bottom therebetween, as the case may be. Thus, the blow core .is maintained in alignment in the blow mold, the same as it was in the parison mold.

As the next step, pressure fluid, usually compressed air, is admitted into the composite parison through fluid passage 13 and blow slot 15 and the parison is expanded into the blow mold 12, to assume the shape of. the blow mold cavity 14, as indicated by dotted lines in Fig. 4.

Fluid pressure is maintained until the blown article cools sufficiently in contact with the walls of the blow mold 12, to be removed therefrom.

An important advantage of incorporating a sleeve 1 on the inside of a parison and. to form a composite article therefrom is to impart properties to the finished article 10 single plastic alone does not possess. For example, polyvinyl idine chloride, acrylo-nitrile polymers and certain other plastics provide excellent oxygen barrier properties, however only at appreciable expense; on the other hand, polystyrene is relatively inexpensive, has desirable mechanical properties but is at the same time very pervious to oxygen. In order to produce comparatively inexpensive containers having good resistance to oxygen permeation, a thin sleeve of the expensive plastic which is impervious may be employed in conjunction with polystyrene which is to constitute the Certain plastics, for example, polyvinylidine chloride, are difficult to handle in some of the operations described because of their tendency to collapse or to stick together. In order to facilitate the handling of such materials, the sleeves themselves may be made as composites from laminated film in which such difficult-to-handle material is carried by or between another plastic which is readily handled or which protects from collapse as the case may be.

Another important reason for the use of laminated sleeves is to provide additional combinations of properties, such as solvent resistance, resistance to gas transmission and the ability to adhere to the plastic molded around the sleeve. Such a combination may be obtained, for example, by making the sleeve from a laminated film composed of layers of polyethylene, polyvinyl chloride, polyvinylidene chloride and polystyrene and surrounding the sleeve with polystyrene in the course of parison- injection. Many of the plastics that have good gas barrier or solvent resistance properties are too expensive for the production of rigid walled commercial containers, such as for example, acetal polymers, ionomer resins, polyallomer copolymers, polycarbonates, polypropylene, polyvinylidene chloride, acrylonitrile and methacrylnitrile polymers, nylon and others, while other plastics, such as polystyrene and polyethylene are inexpensive, but do not have sufficient barrier or solvent resistance properties. In many instances the material having the properties desired for a given purpose, may not be directly compatible with the material from which the bulk of the container is to be made and therefore requires a further layer between itself and the bulk of the container, which layer is compatible with both.

It is thus seen that the sleeves may be designed as laminates or multi-layered structures to satisfy a multiplicity of requirements determined by the process of manufacture of the finished article or by the finished article itself.

Pig. 7a shows, as an example of such a laminated film from which a multi-layered sleeve may be made a cross section composed of layers a, b, c, each of which may be made of different materials having different properties from which to form sleeves that are, for example, readily handled .and that have the desired predetermined combination of properties.

Of course, any required number of layers may be employed according to the result desired, not only the three layers shown in Fig. 7a.

Whenever the material of the sleeve is to be relied upon to provide a gas transmission o solubility barrier inside the finished container, it is important to know whether the material so relied upon is indeed present throughout the area to be protected. In order to inspect the finished article in keeping with this requirement, the sleeve may be made of a material that the sleeve, whereby the latter Is also made transparent or translucent. In this manner, any discontinuity in the protective sleeve material may be readily discovered in the finished article, by optical inspection.

Alternatively, the two materials may be made to differ as to their radiation transmission properties, such as for example, ultraviolet radiation and the corresponding inspection effected by known means to detect the respective radiation intensity.

The sleeves may be inspected prior to the molding operation shown in Fig. 2 by conventional means.

It is also possible to produce finished articles having desirable appearance by providing different colors and degrees of transparency in the sleeve and in the material that is injected around it.

Usually, the container to be made is provided with a continuous, layer over its entire inside surface.

Occasionally, however, some portions of the container should remain without such a layer. In such instances, the sleeve is made with the corresponding wall area omitted.

In other cases, it is desired to have the inner layer cover areas in which there is an opening in the container, for example, at a dispensing opening, so as to keep the contents sealed until the container is first used, such as for example, under a closure of a powder container with a sifter top.

Such containers may be made as indicated in Pig. 8 plastic only over selected portions of the core and then blowing the composite parison into the desired shape to produce the finished article 17> having a discontinuity l8 covered with the film 19.

Claims (18)

Claims:

1. . The method of making a composite plastic article wherein a . multilayered plastic is formed in a parison mold by molding plastic around and in conformity with a core, confining the parison in a blow mold and expanding the parison therein by means of a pressure medium characterized by placing a preformed sleeve over the core prior to forming the pacison and molding the plastic ©round said preformed sleeve in the parison mold.

2· The method set forth in claim 1 further characterized in that the sleeve is formed from a plastic sheet. . Ί

3«H The method set forth in claim 2 further characterized in that the plastic sheet is laminated.

4. The method set forth in claim 1 further characterized in that the sleeve is formed from plastic powder.-

5. The method set forth in claim 1 further characterized in that the sleeve is preformed from a material that is different than said plastic.

6. The method set forth in claim 1 further characterized in that the material of said sleeve and the material of the plastic surrounding said sleeve are of different colors.'

7. The method set forth in claim 1 further characterized in that the core is a blow core.

8. The method set forth in claim 1 further characterized in that the parison is formed at a temperature sufficient to bond said parison to said sleeve.

9. The method set forth in claim 1 further characterized in that the parison is fprmed at a pressure sufficient to bond the parison to said sleeve.

10. The method set forth in claim 7 further characterized in that the sleeve is applied to the blow core by applying suction through the blow core.

11. The method set forth in claim 7 further characterized in that a series of such sleeves are placed over the blow, core in successive cycles.

12. The method set forth in claim 1 further characterized in that said material of the sleeve is selected from the group consisting of polyvinyl chloride, polyvinylidine chloride, polyacetal, nylon, polycarbonate, polyolefins, ionomer resins, polyallomer copolymers and of polymers of acrylonitrile and/methacrylnitrile.

The method set forth in claim 1 further characterized in that said plastic is selected from the group consisting of polymers of styrene and polymers of an olefin.

14. The method set forth in claim further characterized in tha at least one layer of the sleeve is composed of polyvinylidine chloride.

15. Apparatus for making composite plastic articles in an injection blow molding system which comprises a parison mold, a blow mold and a blow core on which the parison is to be formed characterized by a sleeve storage station adapted to contain a plurality of sleeves and a sleeve positioning station, means positioning said blow core in said sleeve positioning station, means transferring a sleeve from said storage station to said positioning station, and means positioning said sleeve on said blow core in said positioning station, means placing the blow core with said sleeve thereon in said parison mold, means injectin a plastic in said parison mold around said sleeve to form a composite parison and means positioning said blow core with said composite parison. thereon in said blow mold for blowing.

l6. Apparatus as set forth in claim 15 further characterized by holding means for said sleeve in said positioning station and means bringing said holding means and said blow core into alignment with said last station

17· Apparatus as set forth in claim 15 further characterized by means for selectively positioning said blow moid and said . positioning means in alignment with said blow core.

18. A composite plastic article whenever prepared by the methods set forth in claims.1 to 14·