WO1997034755A1

WO1997034755A1 - In-mold decorated plastic articles

Info

Publication number: WO1997034755A1
Application number: PCT/IL1997/000070
Authority: WO
Inventors: Rimon Ben Dor
Original assignee: Lotemplast Plastic Products Company Ltd.
Priority date: 1996-03-18
Filing date: 1997-02-24
Publication date: 1997-09-25
Also published as: IL117538A; AU1732297A; IL117538A0; EP0889777A1

Abstract

In-mold decoration process for the production of molded plastic articles covered at least in part with a skin material, comprises the steps of: (a) providing an injection mold having a male and a female half; (b) cutting the skin material to the appropriate dimensions to provide individual skin pieces; (c) suspending a skin piece between said two halves of the mold by holding it from about its upper edge, the rest of the skin piece being free; (d) closing the mold; (e) injecting a stream of a molten plastic material centrally of the mold, whereby the plastic stream will apply the skin piece to the second half of the mold without causing wrinkles and form a plastic frame around at least all sides but one of the skin piece; (f) allowing the plastic to solidify; and (g) opening the mold and extracting the resulting molded piece.

Description

In-Mold Decorated Plastic Articles

Field of the Invention

This invention relates to a process for in-mold decoration of plastic articles, viz. for the production of plastic articles which are partly covered for decorative purposes, usually on one side thereof, with a sheet-like material, preferably a fabric; to a mold for the production of such articles and to decorated plastic articles which have not been trimmed at their periphery.

Background of the Invention

Plastic articles which have been laminated with decorative materials, are known in the art. Thus woven or non-woven fabrics can be applied to plastics by lamination and the resulting laminated article may be formed, e.g. by compression or vacuum molding or by other processes, to desired shapes. These processes, however, require several manufacturing steps and are labor-intensive and expensive. The art has understood the desirability of in-mold lamination, viz. of processes which would permit to produce a plastic article, having a skin or covering, by a single injection molding operation. However, a fully satisfactory process for this purpose has not been developed so far.

EP 629487 describes a process for the production of a laminated plastic component comprising a thermoplastic body and a covering layer. The body is injection molded in a tube, one half of which is then moved to a second position where a complementary press tool presses and laminates the covering layer onto the body.

EP 80153 describes the production of a plastic molding by plasticating the material used and introducing heat into the cavity between top and bottom mold tools, between which there is placed one decorative sheet of material, which is preferably a foam backed laminate plastic film, fabric, and the like. DE 4132413 describes a molded article which consists of an injection molding with, at least on one side, a fabric decorative layer, which has a plastic film between the molding and the fabric and this is bonded to both.

Japanese apphcation 24807/1988 describes the production of a multilayer molded article by clamping edges of a skin material between a female mold and a skin material fixing frame, preform the skin material, supplying a melt of a thermoplastic resin as a cover material and then molding the resin.

All the aforesaid processes are relatively complex and expensive and do not permit time saving and intensive production, nor do they permit to achieve the most desired decorated plastic products.

EP 500033 contains a discussion of several prior art processes, which is incorporated herein by reference. Said EP discloses a process for producing multilayered molded articles, which comprises attaching a skin material to a frame, pressing the frame between two molds, injecting an amount of thermoplastic resin melt between the skin material and one of the molds, while this is not fully closed, and finally closing the molds to compress said resin melt to form a layer between the skin material and the other mold. This process, however, has several disadvantages. Firstly, it permits to manufacture only articles which are completely covered with skin material and have to be trimmed along their periphery, since the frame to which the skin material is attached is held between the two molds. Secondly, the flow of resin melt by compression creates stresses in the skin material. And thirdly, the process is slow and does not permit time saving and intensive production.

It is therefore the object of this invention to provide a process for making decorated plastic articles, particularly such articles decorated with fabrics, which is free of the disadvantage of a prior art. It is another object of this invention to provide such a process that is a single step process and is time as well as labor saving and adapted to intensive production.

It is a further object of this invention to provide such a process for producing a molded plastic article covered with a textile fabric, wherein the fabric does not cover the entire surface of one side of the article, but is surrounded by a frame of exposed plastic material, at least on all its sides but one and preferably on all its sides.

It is a still further object of this invention to provide such a process which permits to produce signs or decorative shapes or printing of plastic material in relief on the surface of the textile fabric covering, in a single, injection molding step.

It is a still further object of this invention to provide such a process that is extremely fast and adapted for high production, besides being completely labor saving.

It is a still further object of this invention to provide such a process which can be fully automated.

It is a still further object of this invention to provide plastic articles having a textile covering which does not cover the entire surface of the article, but is encased in a frame of plastic material.

It is a still further object of this invention to provide a mold for carrying out a process fulfilling the aforesaid objects.

It is a still further object of this invention to provide such a process which eliminates the necessity of a trimming operation of the finished product. It is a still further object of this invention to provide an injection mold which can produce plastic articles decorated with textile fabrics, wherein the textile fabric is spaced from the periphery of the article on all its sides but one and preferably on all its sides.

Other objects of the invention will appear as the description proceeds.

Summary of the invention

The in-mold decoration process for the production of molded plastic articles covered at least in part with a skin material, according to the invention, comprises the steps of: providing an injection mold having a male and a female half; cutting the skin material to the appropriate dimensions to provide individual skin pieces; suspending a skin piece between said two halves of the mold by holding it from about its upper edge, the rest of the skin piece being free; closing the mold; injecting a stream of a molten plastic material centrally of the mold, whereby the plastic stream will apply the skin piece to the second half of the mold without causing wrinkles and form a plastic frame around at least all sides but one of the skin piece; allowing the plastic to solidify; and opening the mold and extracting the resulting molded piece.

The expression "skin material" designates the material that is intended to cover at least part of one surface of the plastic article, usually to achieve a decorative effect, but optionally for other purposes. A portion of skin material, cut to size for a single article, is called "skin piece". Woven and non-woven fabrics, including coated fabrics, can be used as skin materials. By the expression "plastic frame" is meant a narrow portion of exposed plastic material that surrounds the skin piece in the finished article. The plastic frame may be complete, viz. extend on all sides of the article, completely to surround the skin piece, or it may be incomplete, viz. extend on all sides minus one of the article. Along the sides on which a frame extends, the skin piece is spaced from the periphery of the article by a distance equal to the width of the frame. "Decorated article" means herein an article of manufacture having a body that is made of a thermoplastic material, practically a thermoplastic synthetic polymer that can be formed by injection molding, and having a skin covering, usually of film -like material, applied to at least part of at least one surface of said body and permanently bound thereto. A finished article may comprise other parts or elements besides such a body. The part of the article that is obtained by the injection molding process, as it is extracted from the mold, will be called "the molded piece". The molded piece may be then folded or bent or otherwise modified and/or assembled with other parts to constitute the finished article.

According to a first form of the invention, by which a molded piece is produced in which the skin covering is spaced from all sides of the piece but one, a skin piece projects beyond the mold on its uppermost side, once it is closed, and is held vertically by it. Therefore, after the resulting decorated molded piece has been extracted from the mold, it must be trimmed on said uppermost side, to remove the portion thereof which extends beyond the plastic body generated in the injection.

According to a second, preferred form of the invention, by which a decorated molded piece is produced in which the skin covering is spaced from its periphery from all sides, a skin piece is placed between the halves of the open mold in a vertical position, is seized close to its uppermost edge by suitable holding means provided in the mold while this latter is still open, while leaving it free on its other edges whereby to suspend it between the halves of said open mold, the mold is then closed and plastic matter is injected, the said vertical position being such that the uppermost edge of said skin piece is lower than the uppermost edge of the mold cavity defined by the closed mold. The plane of symmetry of the skin piece, when it is suspended between the halves of the open mold may be called "the central plane of the mold". It is not a plane of symmetry of the mold, but it is the central plane between the tips of the skin piece holding means, when these have been actuated to engage and retain said skin piece.

For carrying out the process of the invention in the said second, preferred form, a special mold is provided, which constitutes a part of the invention. Said mold is provided with extendable and retractable skin piece holding means projecting from the upper portion of at least one of the mold halves, and retractable within said mold half as the mold is closed. When said holding means are provided only in one of the mold half, they cooperate, to engage and retain the skin piece in the desired vertical position, with a surface of the other half, or, preferably, with components of said other half, more preferably with the ejector pins, that have the function of extracting the molded piece from the mold as in conventional injection molds, and more precisely, with the uppermost of said . Since it is desirable that said holding means contact the skin piece over a small area thereof, and they are displaceable towards and away from the skin piece, preferably by having a portion thereof slide within a corresponding housing, they will be generally called "pins", but this term is used briefly to designate any and all means for holding a skin piece vertically, and its use should not be construed as involving any limitation as to the structure of said means.

The mold for carrying out the invention in said second, preferred form thereof, is combined with provisional holding means separate from the mold, which serve to hold the skin piece temporarily in the appropriate position between the two halves of the open mold, until it is firmly engaged by the holding means or pins of the mold and may also be part of a mechanism conveying the skin pieces to the mold or molds. When such a combination of a mold, provided with holding means, and provisional holding means, and optionally a conveyor mechanism, is provided, the process of the invention may be carried out in a completely automatic manner and with a particularly high production rate, since a production line may be provided which comprises means for seizing the skin pieces one by one and carrying them to one mold or to a plurality of molds and for inserting them between the two halves of the mold and retaining them there, to release them once they are seized by the holding means of the mold itself. The production line may optionally include means for cutting skin material into skin pieces. The cycle of the mold can also be entirely automatic, comprising the stages of closing, injecting the plastic material, allowing the same to sohdify, opening the mold, extracting the molded piece and conveying it to an appropriate destination. All the operations of the mold and of the entire production hne can be controlled by control and synchronizing means, easily designed by persons skilled in the art.

In the process of the invention, the skin pieces bend and conform to the mold about essentially horizontal axes, they may also be bent to some extent about other axes, including vertical axes, thereby producing convex edges and other portions. The skin piece, being freely suspended in the mold, will bend and loosely conform to it while it closes, and when the plastic material is injected through one of the mold halves, said skin piece is pushed towards and pressed against the other one of the mold halves and may be stretched to some extent, due to its inherent elasticity. A degree of stretch will assure that the skin piece, in the finished mold-decorated article, will be smooth and free of wrinkles.

According to another aspect of the invention, an ornamental relief is obtained in the molded piece thanks to the permeability of practically all fabrics to the plastic matter, when it is sufficiently flowable to be injection molded. In that case, the mold half against which the skin piece is applied and pressed by the plastic stream, is provided with recesses corresponding to the desired reliefs. While the plastic material will not seep through the fabric as long as this latter is free to move, it will do so once the fabric has contacted said mold half and has been pressed against it.

In the aforesaid second, preferred form of the invention, the holding pins, provided in the mold, will slightly retract and disengage from the skin piece a short time before the injection has been completed. This will permit the injected plastic to flow between said pins and the skin piece and to form a plastic layer opposite said pins, to avoid the formation of holes in the plastic body of the molded piece and of corresponding skin piece portions not supported by plastic. It has been found that, during and after said retraction of the holding pins, the skin piece is adequately supported by the injected plastic. The holding pins will leave no appreciable mark on the outer face of the molded piece, viz. on the exposed face of the skin piece, and will leave a noticeable mark on the plastic side of the molded piece, but since this latter is not intended to be the decorative side, this mark will have no relevance.

In a preferred form of the invention, the holding means are in the form of round pins having a diameter of a few millimeters at the point at which they contact the skin piece. However, they may have a larger diameter at a point at which they are spaced from the skin piece, whereby the plastic stream will exert a pressure on them and tend to push them back into the mold half in which they are provided. While the motion of the holding pins is controlled by actuating means, preferably pneumatically, the pressure of the plastic material guarantees that the pins will withdraw as they should, even if the pneumatic control should be inefficient or fail altogether.

Since the molded piece comprises a skin or fabric covering on one of its surfaces - which is the outer surface of the finished article, if the molded piece is bent in such a way that the finished article which comprises it (optionally in combination with other parts) forms a hollow body, such as a box or purse or the like - and further comprises a plastic body underlying said skin or covering, the molten plastic is injected through one of the mold halves and applies and presses the skin piece against the other half. The mold half through which the molten plastic is injected will be called "the male half or "the male mold" and the other half will be called "the female half or "the female mold". This does not necessarily mean that the male half or mold comprises a core portion projecting into a corresponding cavity of the female half or mold, though this will often be the case. The distinction between the mold halves or molds, in this specification and claims, is based essentially on the fact that at the end of the injection the skin piece contacts and conforms to one of them (the female half), while a plastic layer has formed in contact with the other one (the male half), through which the injection has been effected.

For optimal results of the process according to the invention, a number of conditions should preferably be observed.

The thickness of the plastic body of the molded piece should exceed 2 mm.

The plastic matter used should have a Melt Flow Index (MFI) from 5 to 25. Suitable plastics are, for example but not exclusively, polyolefins, such as polyethylene or polypropylene, and soft PVC. The injection should be carried out at a sufficiently moderate speed so as not to generate shear stresses between the fabric and the mold.

The inner surfaces of the mold, with which the fabric comes into contact, should not be such as to facihtate the fabric's sliding over them, whereby to create folds and wrinkles. Therefore said surfaces should be so shaped and finished as to oppose such sliding, and may have, for that purposes, ridges and/or grooves, or have a rough surface finish.

The fabrics used, whether woven or non-woven - knitted fabrics are generally unsatisfactory - may be made of natural, artificial or synthetic fibers. Natural or artificial fibers generally provide a better and stronger coupling to the plastic matter. Synthetic fibers, if thermoplastic, may be cut by the apphcation of heat, e.g. at temperatures of 450-550°C, whereby neater and more stable cuts are produced by the fibers' melting or softening and becoming welded to one another along the cut lines, provided that at least 25% of the fibers included in the fabric thermoplastic. On the other hand, in order to obtain a good coupling of a woven fabric to the plastic matter, it is desirable that the fabric should not comprise more than 70% of synthetic fibers. Non-woven fabrics may be made entirely of synthetic fibers and yet provide a good coupling. The coupling properties of the fabric can also be improved by a suitable coating. It should be understood that the coupling between fabric and plastic is a complex phenomenon. It involves on the one hand adhesive forces and on the other hand the penetration of the plastic into the structure of the fabric itself. It is therefore influenced by the surface properties of both the fibers that compose the fabric and the plastic, by the physical structure of the fibers, by the kind and dimensional parameters of the weave or of the disposition of the individual fibers in the non-woven structure, and so on. Expert persons, however, will have no difficulty in selecting the appropriate fabric-plastic pairs for each specific decorated article to be produced.

Brief Description of the Drawings

In the drawings:

Fig. 1 is a block diagram illustrating the stages of a process according to an embodiment of the invention;

Fig. 2 is a schematic cross-section of a mold, according to an embodiment of the invention, in its open condition;

Fig. 3 shows the same cross-section of Fig. 2, but with the addition of the skin piece;

Fig. 4 is a schematic cross-section of the mold shown in Fig. 2, in an almost closed condition, a detail of which is illustrated in Fig. 4a at an enlarged scale;

Fig. 5 is a schematic cross-section of the same mold, in its closed condition, details of which are illustrated in Figs. 5a, 5b and 5c at an enlarged scale;

Fig. 6 is a front view of the inside of the female mold;

Fig. 7 is similar to Fig. 6, but with the addition of the skin piece;

Fig. 8 is a view of a molded piece made by the mold of Figs. 2 to 7;

Fig. 9 is a cross-section of said piece taken on plane IX-IX of Fig. 8;

Fig. 10 is another view of said piece, seen from the side opposite to Fig. 8;

Fig. 11 is a schematic, enlarged cross-section of a portion of a mold according to another embodiment of the invention; and

Fig. 12 is a front view of a portion of the outer face of a decorated article obtained from the mold of Fig. 11. Detailed Description of Preferred Embodiments

An embodiment of the process in its aforesaid second, preferred form will now be described. The succession of the process stages is schematically set forth in the block diagram of Fig. 1. In Fig. 1, the following numerals correspond to the following steps-materials or operations:

BLOCK NO. STEP

70 SKIN STOCK

71 CUTTING

72 SKIN PIECE

73 HOLDING AND CONVEYOR MEANS

74 OPEN MOLD

75 POSITIONING SKIN PIECE IN OPEN MOLD

76 CLOSING MOLD

80 EXTRACTING MOLDED PIECE

81 DECORATED MOLDED PIECE

82 FINISHING

83 DECORATED ARTICLE

At the beginning of the operations, the mold is open. The skin stock - usually a fabric strip stock (70), formed directly as such or obtained by cutting a fabric stock into strips, and generally having a weight of e.g. 100-250 grams per square meter - is cut into pieces (71), having dimensions corresponding to the outer dimensions of the article to be produced minus the strip of exposed plastic which constitutes the plastic frame about the skin piece in the molded piece. A skin piece (72) is seized by convenient holding means and conveyed by conveyor means (73) to a position over the mold, and is then positioned within the mold (75), or, more properly, between the two halves of the open mold (74), by lowering it as far as necessary. The mold is closed (76), the plastic melt (78) is injected thereinto (77), allowed to solidify and then extracted (79-80). The molded piece thus obtained (81) is subjected to any required finishing operations (82), to obtain any specific, finished, decorated article (83). While the block diagram relates to one mold and to the production of one molded piece, the production line will generally include a number of molds and the aforementioned operations will be repeated for each one of them.

Figs. 8 to 10 illustrate a molded piece according to an embodiment of the mvention. It comprises a hollow portion 51 and two hds 52, joined to portion 51 by thinner joint lines 53, which function as pivots about which the hds can rotate until their edges 54 contact each other and the hds 52 and hollow portion 51 together form a box-like structure, held closed by clasp 55. During the rotation of said hds, the wings 56, which have the shape of arcs of circle, slide over the edges 57 of hollow portion 51. As seen in Fig. 10, a fabric skin 58 covers most of outer surface of hollow portion 51 and of hds 52 - and therefore of the box-like structure which results when the hds are rotated into mutual contact - but does not reach the edges of the hds 52, thus creating a frame 59 of exposed plastic. .

Fig. 2 illustrates a mold for making the molded piece of Figs. 8 and 9, in its open condition after a previously made molded piece has been extracted from it. Said mold comprises or is composed of two mold halves. The mold half through which the molten plastic is injected is indicated at 11 and will be called briefly the "male mold". It is shown in axial cross-section, viz. in cross-section on a vertical plane passing through the axis of the male mold core 16, hereinafter described. The other mold half injected is indicated at 12 and will be called briefly the "female mold". It is shown in staggered cross-section on vertical planes the traces of which are indicated at II-II is Fig. 6, hereinafter described. The molten plastic material is injected through the male mold from feed port 15 and through channel 13 having an outlet port at 14.

It is to be noted that the plastic melt, which is to constitute the molded piece or at least the part thereof to be covered by the fabric, should preferably be introduced into the mold cavity through a single inlet. Thus the fabric is always tensioned outwardly and there are no points at which different streams of injected melt meet and wherein folds and creases may be created in the fabric.

In view of the particular shape of the piece to be cut and molded, the male mold comprises a projecting core generally indicated at 16 and has curved profiles 17 for generating corresponding edges 57 in the molded piece, while profiles 17a generate the wings 56 (see also Fig. 4a). It will be understood that these details relate to the specific piece that is being exemplified, and different details and shapes will be provided in the various portions of the mold when a different piece is to be molded. Male mold 11 is also provided in its upper portion with holding means, specifically pins 20, which in this embodiment are in the number of two, but might be in a different number. Pins 20 are provided at their rear with a piston portion 21, through which they are pneumatically actuated axially to slide within cylinder 22. Further, each pin 20 is provided with a foremost portion or tip 23, better seen in the enlarged details of Figs. 4a and 5c, which is also circular in shape. Rearwardly of the tip 23, each pin 20 has a shoulder 24 having the diameter of the pin body.

Correspondingly, female mold 12 has a cavity 30 which matches the projection or core 16. The female mold too can be provided with skin piece holding means, but since, anyway, it comprises ejector pins 31, 32 and 33, which are conventional in the injection molding art, no separate holding means need be provided, because the upper ejector pins 31 can operate as such holding means. Ejector pins 31, 32 and 33 are mounted on a slide or piston generally indicated at 34, which operates as two-stage piston. One stage - the extraction stage - is actuated by hydraulic means. The hydraulic actuation of the extraction stage is conventional in the injection molding art and need not be described in greater detail. In Fig. 2, piston 34 is shown at the end of the extraction stage. The second stage - the skin piece holding stage, to be described hereinafter - is actuated by pneumatic means. Further, the male and female molds comprise structural details that are not connected to the invention, and are conventional, or at least well known in the injection molding art.

Fig. 3 shows the mold in the same open condition as Fig. 2, the same parts being indicated by the same numerals, with the addition, however, of the fabric skin piece 40, which has been brought to the place it must occupy in the mold by a conveyor - not illustrated, as it may be conventional - which holds the fabric piece by means of clips 41. A chp 41 is shown in the open condition at 41a in the drawing. It will be noted that piston 34 (and with it the ejector pins 31, 32 and 33) is shown at the end of its second actuation stage, viz. has been displaced, by pneumatic means, to its foremost position towards the male mold. Concurrently, the pins 20 have been displaced towards the female mold by pneumatic means acting on piston 21, and the skin piece 40 is held, shghtly below its uppermost edge, between the ejector pins 31 and the pins 20 or, more precisely, their narrow tips 23, although these latter are not clearly visible in the drawings, in view of their small dimension. Central ejector pins 33 are spaced from skin piece 40, while bottom ejector pins 32 touch said skin piece, but do not deviate it from the vertical, straight position which it occupies by its own weight when it is suspended from chps 41 or is held near its upper edge by ejector pins 31 and pins 20. It is seen in Fig. 3, and better in the details of Figs. 4a and 5c, that pins 20 are shghtly axially displaced with respect to ejector pins 31 and, more precisely, their axis is shghtly higher than the axes of the ejector pins. If one does not take into account the thickness of the skin piece, numeral 40 also indicates what has been called the central plane of the mold. The tips of ejector pins 31 and of pins 20 practically meet on said central plane.

Fig. 6 is a front view of the inside of the female mold, when the mold is open, as in Fig. 2.

The ejector pins 31, 32 and 33, in this embodiment, are each in the number of two. The injection orifice 14 is shown in broken hnes. The tips 23 of pins 20 are also indicated, and it is seen that they are eccentric not only vertically, as hereinbefore noted, but also horizontally, with respect to ejector pin 31. The upper and bottom profiles 42 and 43 of the female mold cavity are particularly shaped for the production of the article exemplified in this embodiment, but they have no particular significance with regard to the invention, as they will determined in each case by the shape of the piece to be injection molded.

Fig. 7 is similar to Fig. 6, but it shows the fabric skin piece 40 in position, held by clips 41. For dimensional reasons, the skin piece 40 is shown as interrupted. The portions of the mold which are behind the fabric skin piece are illustrated in broken hnes.

Fig. 4 shows the mold in an intermediate stage of its closure. It is seen that the ejector pins have been partially withdrawn, and so have the pins 20. Core 16 of the male mold has begun to enter the corresponding recess 30 of the female mold, and in so doing, has bent the skin piece 40, which has acquired a curved shape determined by said core 16 and cavity 30, by the upper edge which is between ejector pins 31 and pins 20, and by ejector pins 32, over which the skin piece shdes as it retracts into the mold due to the curved shape which it has acquired. It is seen that there is a gap between the core 16 and more precisely, the skin piece which is folded over said core, and the inner surface of the cavity 30. Fig. 4a shows the central portion of Fig. 4 at an enlarged scale. The mold should be closed at a moderate speed. Its closure should generally take about 3 to 8 seconds.

Fig. 5, finally, shows the mold in its completely closed condition. The ejector pins have retracted completely within the female mold. There is of course a gap between the matching surfaces of the male and female mold, which corresponds to the thickness of the molded piece. The skin piece 40 is loosely held in this gap. When the molten plastic is injected through the core of the male mold, it apphes pressure to its side of the skin piece and apphes it against the surface of the female mold cavity and fills the gap that thus remains between the skin piece and the outer surface of the male mold. These phenomena are better illustrated in the details at an enlarged scale of portions of Fig. 5. Fig. 5a shows at enlarged scale the core 16 of the male mold 11 and the cavity 30 of the female mold 12, in a closed mold condition and before the injection. It is seen how the skin piece 40 is loosely contained within the gap 39 between said core and said cavity. Fig. 5b shows the same detail after the injection. The skin piece 40 has been firmly applied against the surface of the female cavity 30, and the plastic occupies the entire space between the skin piece and the core 16, constituting a layer 51 of plastic which, after solidification, will be part of the molded piece plastic body. Fig. 5c shows a detail of the upper portion of the mold cavity, where the skin piece 40 is held between the ejector pins 31 and tips 23 of pins 20. When the mold has closed and the injection has not yet taken place, the shoulders 24 of pins 20 are flush with the surface of the male mold, while tips 23 protrude from the male mold and cooperate with the ejector pins 31, which have fully retreated within the female mold, to retain the skin piece 40.

When the injection takes place, pins 20 are gradually retreated so that tips 23 of pins 20 become spaced by a few tenths of millimeter from the surface of the ejector pins 31. This does not cause the skin piece to become displaced, as it is held in place by the stream of molten plastic. The molten plastic therefore can become inserted between said tips 23 and said ejector pins 31, and create there a thin layer of plastic, to establish continuity of the plastic body of the finished article and avoid the formation of a hole therein.

A variant of the invention is schematically illustrated in Fig. 11, which is an enlarged cross-section of a portion of the mold, having male portion 63 and female portion 60, in the closed condition, as in Fig. 5. In said portion, the female mold 60 has recesses 61, which together define a decorated pattern or a writing or any desired figure. When the mold is closed, the skin piece 62, shown in broken hnes, has been apphed or/and pressed against the surface of the female mold, but its elasticity is not sufficient for it extend and penetrate into recesses 61. The continued pressure of the injected plastic material causes this latter to seep through the skin piece, if this is a fabric or other porous material, and fill the recesses 61, thus creating a corresponding rehef representing decorative design or writing, as shown by way of example in Fig. 12, which is a front view of a portion of the outer face of the molded piece, bearing such rehefs, indicated at 64.

The creation of such rehefs can have another purpose, besides the decorative purpose set forth above, viz. it can serve to strengthen the fabric, especially near its borders, to avoid their unraveling and in general their detachment from the plastic body. The rehefs serve as anchors against such phenomena.

In any case, in order that the plastic rehefs should have a clean and attractive appearance, certain conditions should preferably be observed. The height of the rehefs should be at least three times their width. The roots of the rehefs, viz. the points at which they project from the fabric, should be sharp, so that they should emerge cleanly from the fabric surface. In some cases, it may be desirable that the fabric should cover at least a part of the rehefs, once again for decorative purposes and this can be obtained by modification of the aforesaid conditions: e.g., the ratio of the width of the rehefs to their height can be suitably changed to allow the fabric to appear in some areas over the rehefs. It is important to note that, when planning the structure of the article and of the mold, care must be taken to avoid that the recesses of the mold which form the rehefs become independent channels for the flow of the plastic matter. In other words, the volume ratio of the cross-section of the plastic body (which is located under the fabric) to the cross-section of the rehefs must be such that said recesses, which form the rehefs, be fed with plastic melt through the layer of said melt which flows under the fabric. This means that the flow of the plastic melt should always be from the direction of the plastic body of the molded piece, through the fabric, into the rehefs. The structure of the molded piece must be so planned that there be no possibility that the flow of the plastic melt begin through said recesses, which form the rehefs, and that said recesses become channels through which the plastic melt is fed to the other parts ofthe molded piece. If this should occur, a situation may be created in which the plastic melt passes through the fabric and stains of plastic appear over the surface of the fabric.

After the completion of the injection, the mold cycle is completed in the conventional manner of injection molding, by allowing sufficient time for the plastic matter to sohdify, by reopening the mold and extracting the resulting molded piece by means of ejector pins 31, 32 and 33. The molded piece is then finished, as by folding it in box or other form, assembling it with auxiliary elements, applying to it further decorative matter, and so no. The finishing operations, which are not part of the invention and therefore are not described or illustrated, will depend on what finished, decorated plastic article it is desired to produce.

When the invention is carried into practice in its first, less preferred form, the mold is not provided with retaining pins, but is otherwise as illustrated in the preceding embodiment. The skin piece is positioned between the mold halves when the mold is open and held by means, such as chps, located above the mold, or even by hand, until the mold is closed. The mold is closed over the upper edge of the skin piece, which hangs therefrom and is otherwise free, and the molten plastic matter is injected. The molding operation occurs in the same way described with reference to the preferred embodiment and the results are the same, except that the laminated article thus obtained has an upper edge which extends above the upper edge of the article, and therefore the article must be trimmed, after its extraction, along said upper edge. Therefore the skin piece is spaced from the periphery of the article on all sides except the upper one where no plastic frame has been created.

While embodiments of the invention have been described by way of illustration, it will be apparent that many variations, modifications and adaptations can be made therein by skilled persons, without departing from the spirit of the invention or exceeding the scope of the claims.

Claims

1. In-mold decoration process for the production of molded plastic articles covered at least in part with a skin material, comprising the steps of: providing an injection mold having a male and a female half; cutting the skin material to the appropriate dimensions to provide individual skin pieces; suspending a skin piece between said two halves of the mold by holding it from about its upper edge, the rest of the skin piece being free; closing the mold; injecting a stream of a molten plastic material centrally of the mold, whereby the plastic stream will apply the skin piece to the second half of the mold without causing wrinkles and form a plastic frame around at least all sides but one of the skin piece; allowing the plastic to sohdify; and opening the mold and extracting the resulting molded piece.

2. In-mold decoration process according to claim 1, by which an article is produced in which the skin covering is spaced from all sides of the plastic article but one, comprising closing the mold to cause its halves to engage and retain a skin piece vertically from about its upper edge, beginning the injection of the plastic material when the mold has been closed, and, after the resulting decorated molded piece has been extracted from the mold, trimming the same on the side on which the skin piece extends beyond the plastic.

3. In-mold decoration process according to claim 1, by which a decorated article is produced in which the skin covering is spaced from its periphery on all sides, comprising placing a skin piece between the halves of the open mold in a vertical position, seizing the same close to its uppermost edge by holding means while the mold is still open, then closing the mold, and injecting the plastic matter, the said vertical position being such that said uppermost edge of said skin piece is lower than the uppermost edge of the mold cavity defined by the closed mold.

4. In-mold decoration process according to claim 2 or 3, wherein the plastic material is injected into the mold from a centrally located position of the male half of the mold.

5. In-mold decoration process according to claim 3, comprising disengaging the holding means from the skin piece, on the side of the male mold half, before the injection is completed.

6. In-mold decoration process according to claim 2 or 3, wherein the skin piece is allowed to hang freely from about its upper edge during the injection.

7. In-mold decoration process according to claim 1, further comprising producing an ornamental rehef in the finished article by providing in the female mold half recesses corresponding to said rehef, applying the skin piece against said female mold half, and causing the injected plastic material to seep through skin piece into said recesses due to the injection pressure.

8. In-mold decoration process according to claim 1, wherein the plastic material has an MFI between 5 and 25.

9. In-mold decoration process according to claim 1, wherein the plastic material is chosen from among polyolefins and soft PVC.

10. In-mold decoration process according to claim 1, wherein the skin material is a woven or non-woven fabric.

11. In-mold decoration process according to claim 1, wherein the skin material is a fabric made of thermoplastic yarns.

12. In-mold decoration process according to claim 1, wherein the skin material is a fabric made of natural yarns.

13. In-mold decoration process according to claim 1, wherein the skin material is a fabric made of a mixture of thermoplastic and natural yarns

14. Mold for the production of in-mold decorated plastic pieces, comprising a male and a female mold half, extendable and retractable skin piece holding means being provided in the upper portion of at least one of the mold halves for engaging and retaining a skin piece in a suspended position between the mold halves, when the mold is open.

15. Mold according to claim 14, wherein skin piece holding means are provided at least in the male mold half.

16. Mold according to claim 15, wherein the holding means are round pins having a diameter of a few millimeters at the point at which they contact the skin piece.

17. Mold according to claim 16, wherein the holding pins have a larger diameter at a point at which they are spaced from the skin piece.

18. Mold according to claim 14, further comprising pneumatic means for actuating the holding pins to engage the skin piece and to retract from it.

19. Mold according to claim 14, which comprises ejector pins for extracting the molded pieces from the mold and means for actuating said ejector pins from an inactive position and an active, extracting position, further comprising means for actuating the uppermost of said ejector pins to function as skin piece holding means.

20. Mold according to claim 19, wherein skin piece holding means are provided in the male mold half and are so positioned and actuated as to cooperate with the uppermost ejector pins to engage and retain a skin piece in a suspended position between the mold halves, when the mold is open .

21. Apparatus for the production of decorated plastic pieces, comprising molds according to claim 14 and provisional holding means separate from the mold.

22 Apparatus according to claim 21, further comprising a conveyor mechanism for conveying the skin pieces to the mold or molds.

23. Apparatus according to claim 22, further comprising synchronizing and control means.

24. Decorated molded pieces, having a plastic body and a fabric covering on one face thereof, characterized in that the fabric covering is spaced from periphery of the article on all its sides.

25. Decorated plastic articles, comprising a molded piece according to claim 24.

26. In-mold decoration process for the production of decorated plastic pieces, substantially as described and illustrated.

27. Mold for the production of in-mold decorated plastic pieces, substantially as described and illustrated.

28. Decorated molded pieces, substantially as described and illustrated.

29. Decorated plastic articles, substantially as described and illustrated.