This invention relates to the field of hot dip molding and specifically relates to a process for making a composite dip molded article having a first part of a solid plastisol and a second integral skin of a chemically blown plastisol.

We are aware of U.S. Patent No. 4,344,303 which discloses a laminated plastic cooling device in which a flexible insulating layer, which may be of a cellular structure, is provided with cavities filled with a freezable gel and a flexible plastic liner is attached by adhesive bonding, heat welding or sonic welding. The foam rubber layer is described as being extruded, cast or molded in a conventional manner.

In the present invention we utilized a conventional dip molding process to form an integral article having one layer of solid plastic and an attached integral layer of foamed polymer. Conventionally, when using a hot dipping process, a heated mandrel is dipped into a plastisol so that the heat from the mandrel causes the surrounding plastisol to gel on the mandrel. The mandrel is then withdrawn from the plastisol at a slow steady rate to prevent runs and dips. The mandrel with the gelled plastisol thereon is then post-baked in a forced air oven or in a bath of molten salt or other noncompatible oils to fuse the plastisol. After a predetermined time the mandrel is taken out of the post-baked medium and either air cooled or water cooled after which the plastisol part is stripped from the mandrel. The foregoing process is very satisfactory for a solid polymer article but when this process is utilized with a chemically blown plastisol foam, the finished article is unacceptable from an esthetic and functional standpoint. An article made in this fashion from a chemically blown plastisol has craters and blister marks on the inside, that is, the side touching the mold, and

similar defects on the outside surface. These defects are caused by excess heating or uneven heating caused by the foam development, dirty mandrel, etc., and is not a commercially feasible process. In addition, an article made this way is very flimsy and soft and has very little "body".

Accordingly, one of the principal features of th present invention is the provision of an integral plastisol article having a solid layer and a fused or physically bonded foamed skin.

The present invention therefore provides a hot dip molded composite foamed plastic article including a fused solid plastisol body portion which does not contain a blowing agent, and having a thickness of at least 15 mils (0.38 mm), and a fused foamed plastisol layer of uniform composition expanded from a thickness of at least 20 mils (0.5 mm) bonded thereto and covering substantially all of said body portion, said fused, foamed plastisol layer having uniform non-blistered outer surface. A further feature of the invention is the provision of a process of dip molding using two types of plastisol, the first of which is a solid type and the second of which is a chemically blown foam type.

The present further provides a process for makin a composite foamed plastic article with a non-foamed inner layer and a foamed outer layer which includes the steps of heating a dip mold to a mold temperature in the range of about 340-380°F (171-193°C), immersing the heated dip mold into a first plastisol bath containing no blowing agent for a time sufficient to form a gel coating of the first plastisol thereon having a thickness of at least about 15 mils (0.38 mm), and then removing the heated dip mold with the plastisol gel coating thereon from the first plastisol bath, and partially fusing the solid plastisol coating, immersing the hot dip mold with partially fused hot solid plastisol coating thereon into a second

plastisol bath containing a chemical blowing agent for a time sufficient to form a layer of the second plastisol, having a thickness of at least about 10 mils (0.25 mm), on the partially fused solid plastisol coating and then removing the dip mold from the second plastisol bath, heating the layer of the second plastisol and the partially fused plastisol coating at a temperature and for a time sufficient to fuse, foam and expand the layer of the second plastisol and bond the coating and layer, and then cooling and recovering the article.

Further features and advantages of the invention will be apparent from the following description of a preferred embodiment of the invention together with the accompanying drawings, wherein: Fig. 1 is a representation of a mandrel;

Fig. 2 is a side elevational view of an object formed from the mandrel shown in Fig. 1;

Fig. 3 is a fragmentary sectional view taken along line 3-3 of Fig. 2; and Fig. 4 is a schematic flow diagram of the proces embodied in the present invention.

Fig. 1 shows a mold mandrel 10 which contains a body portion 11 and a series of mandrels 12 attached thereto. The mandrels 12 have the shape of the articles to be molded, and Figs. 2 and 3 show a typical article formed according to the present invention. The article 20 shown is an insulating receptacle for a beer or soda can and comprises an inner layer 21 of solid plastisol and an outer layer 22 of chemically blown foam plastisol. The layers are generally similar and are fused or physically bonded together into an integral unit.

In the process of this invention as illustrated in the flow diagram shown in Fig. 4, the mold mandrel 10 first is heated preferably to a temperature of about 340°F to about 380°F (171-193°C), and then dipped into a vat of plastisol which does not contain a blowing

agent. A typical such plastisol is polyvinylchloride which is commercially available from many sources.

The heated mandrel is allowed to remain in the plastisol for about 5 to about 15 seconds, whereby the plastisol gels on the mandrel to a thickness of about .015 to about 0.060 inches (0.38-1.5 mm). The mandrel then is slowly and carefully withdrawn from the plastisol so as to minimize dripping and running of the plastisol which could form an imperfect outer surface which would not fuse at a uniform rate. The plastisol covered mandrel then is partially fused at a temperature of about 350°F to about 450°F (177-232°C) for about 0 to about 180 seconds. The hot plastisol covered mandrel then is inserted into a second vat containing plastisol having a chemical blowing agent incorporated therein. A typical such plastisol is polyvinylchloride with chemical blowing agent. Suitable blowing agents include ABFA (1,1'-azo bisformamide) , and OBSH (P,P' oxybis (benzenesulfonyl hydrazine)). The blowing agent preferably is heat activated. These plastisols with blowing agent incorporated are available commercially from many sources, or the product can be fabricated at the plant site from plastisol and blowing agen .

The mandrel is retained in the second plastisol vat for about 2 to about 30 seconds until a layer of plastisol of about .010 to about 0.080 inches (0.25-1.8 mm) in thickness is coated thereon.

The mandrel then is withdrawn from the second plastisol vat and post-baked at a temperature of about 430°F to about 480°F (221-249°C) for a time of about

30 to about 1200 seconds. This causes the plastisol to partially gel and foam and expand to a thickness from about 0.125 to about 0.350 inches (3.2-8.9 mm). It also fuses or unites physically with the solid plastisol layer into an integral unit. This physical bonding occurs because the solid plastisol is only partially gelled and

reacts with the plastisol containing foaming agent to fuse and form a unitary article. Since the solid plastisol unit has a uniformly clean surface, the second foaming layer containing plastisol gels uniformly without hot or cold spots and forms a smooth uniform outer surface after the gelation is completed and the two layers are fused together.

The final step is to cool the plastisol article in air or water and then strip the finished article from the mandrel for storage or packing.

In addition to the indicated use as an insulator for beverage cans, this invention is useful for making soft grips for tool handles, bicycle handles, thermos bottle jackets, etc.