FR2781715A1 - Mold producing and coating plastic objects with paint, includes secondary cavity forming peripheral bead joined by thin web to main molding, to resist paint leakage in parting plane - Google Patents

Abstract

Around the main cavity, between the two mold sections, there is a secondary cavity (12). An intermediate passage (14), up to 1 mm thick, connects the two cavities. Independent claims are also included for the method of coating a plastic molding, and the plastic molding so produced. Plastic (22) is first introduced into the main cavity. Coating material (24) is then injected under pressure, contacting the part-solidified plastic surface. During initial injection, plastic enters a peripheral secondary cavity (12) through the intermediate passage.

Description

The invention relates to a method and a mold for producing a

  coating on a plastic part, as well as the part obtained.

  It aims to produce a plastic part covered with a coating in order to improve its appearance. This coating generally constitutes a layer of paint. This technique is generally called "In Mold Coating" (IMC) - in French, coating in the mold -. It has the advantage of reducing the number of operations, the loss of coating material and the costs of obtaining the part compared to a painting operation in the

gun.

  A mold is already known, described in particular in US-A-4 668 460, comprising: - two parts reserving between them a main mold cavity, - means for introducing plastic material into the main mold cavity, - means pressure injection of a material of

  coating in the main mold cavity.

  However, the injection pressure of the coating material being high, leakage of coating material from the mold cavity occurs.

  frequently occur by the joint plane of the mold.

  These leaks then no longer allow a satisfactory distribution - almost constant over the entire part - of the pressure for the coating material. The coating material is then not present on the entire desired surface of the part and the quality - at least in appearance - of the

coating is perfectible.

  The present invention aims to solve these problems. To do this, it proposes that the mold further comprises a secondary cavity disposed at the periphery of the main mold cavity, between the two parts of the mold, this secondary cavity communicating with the main cavity by an intermediate passage having a thickness less than or equal to 1 millimeter. This secondary cavity reduces leakage of coating material from the mold cavity and pressure disparities in the material.

  coating inside the main cavity.

  To further improve the effect of the secondary cavity (ies) on the absorption of the problems mentioned, the invention proposes that: - the secondary cavity (s) comprises (include) a bulged part and a space connecting the bulged part and the main cavity, via said passage, - the bulged part has at least locally a thickness greater than that of the intermediate passage and greater than or equal to 0.5 millimeters, and - the space includes a thickness between that of the

  intermediate passage and said thickness of the swollen part.

  The bulged part favors the filling of the secondary cavity with the plastic material, in particular by creating an expansion chamber

for the accumulated air.

  This swollen part also causes a pressure drop of the coating material inside the secondary cavity, in the case o

  the coating material would have escaped somewhat through the passage.

  In order to improve the appearance qualities of the finished part, the invention proposes that the main cavity also comprises a drop zone,

  of reduced thickness, near the intermediate passage.

  This reduced thickness zone extends the main cavity. It defines a drop zone arranged near the intermediate passage, that is to say on the periphery of the main cavity and makes it possible to cut the part perpendicular to the surface of the part covered with the material.

coating, after demolding.

  This solution improves the quality of appearance of the finished part compared to the solution consisting in cutting the part in the zone corresponding to the intermediate passage since then the material of

  coating would cover only part of the surface of the room.

  The invention also relates to a method. There is already known a process described in particular in FR-A-2 729 886, in which: a) plastic material is introduced inside a main mold-molding cavity, b) a pressure material is injected coating in the main cavity, in contact with a partially solidified surface of the

plastic material.

  However, this solution has the aforementioned drawbacks. To resolve them, the invention proposes that during step a), the plastic material is introduced into at least one secondary cavity disposed on the periphery of the main cavity, this introduction being carried out through an intermediate passage connecting the main and secondary cavities and whose thickness in section is such that the coating material cannot penetrate there during step b) after having

  introduced plastic during step a).

  The presence of a sheet of thin plastic in the secondary cavity, all around the main cavity, plays the role of

seal.

  The invention also relates to a part comprising: - a main part of which a surface is covered with a coating material, and - a secondary part surrounding the main part to which it is connected by a sheet of material whose thickness is less or

equal to 1 millimeter.

  The invention will appear even more clearly in the

  description which follows, made with reference to the drawings attached in

  which: - Figure 1 is a schematic sectional view of a mold according to the invention, during a first step of the process, - Figure 2 is an enlarged view of the detail marked II in Figure 1, - Figure 3 shows on an enlarged scale the detail marked II in Figure 1, during a second step of the process, - Figure 4 shows on an enlarged scale the detail marked II in Figure 1, during a third step of the process,

  - Figure 5 illustrates a variant of Figure 4.

  Figures 1 to 5 illustrate a mold 2 comprising a first part 2a, concave, usually called a matrix and a second part

  2b, convex, usually called a punch.

  The die 2a and the punch 2b reserve between them a main cavity 4 for molding and a secondary cavity 12 for molding present at the periphery of the main cavity 4. They come into contact with one another

  along a joint plane 3 disposed on the periphery of the main cavity.

  The main cavity 4 is delimited by a surface 4a of the

  die and a surface 4b of the punch.

  The matrix 2a contains means 6 for injecting plastic material 22 into the main cavity 4 and an injection head 8 for material

  coating opening into the main cavity 4 via an injection channel 9.

  The secondary cavity 12 extends along the joint plane 3 of the mold, over the entire periphery of the main cavity 4. It communicates with the main cavity 4 via a narrow passage 14. It comprises a bulged part 18 and a peripherally extending conduit to form

  a space 16 connecting the bulged part 18 and the main cavity 4.

  The passage 14 has a thickness ú less than or equal to 1 millimeter. This thickness is advantageously greater than or equal to 0.5 millimeters to allow the passage of the plastic. A thickness of less than 0.5 millimeters may however be suitable for certain plastics. The space 16 has a width 1 advantageously between 1 and 5 millimeters, preferably substantially 2 millimeters. Here it has a substantially constant thickness equal to that of the passage 14. It

  might be slightly beveled.

  The swollen part 18 has a thickness E greater than that of the passage 14 and advantageously between 0.5 and 3 millimeters, preferably substantially equal to 1 millimeter. Its width L is advantageously between 0.5 and 5 millimeters, preferably

  substantially equal to 3 millimeters.

  To obtain a plastic part covered with a coating, plastic material 22 is first introduced into the main cavity 4, here by

injection via the means 6.

  The thickness ú of the passage 14 is such that it allows the passage of the

plastic 22.

  When the introduction of the plastic material 22 is complete, the plastic material 22 then completely fills the main cavity 4 and fully or partially the secondary cavity 12 and defines the body of the

finished piece.

  The plastic is allowed to cool and then waits until at least the surface layer 22a of the material 22 coming into contact with the surface 4a is at least partially solidified to inject a coating material 24 in the fluid state between the plastic material 22 and the surface 4a. In fact, otherwise the coating material 24 may not

  stay on the surface of the body 22 and mix with the plastic.

  The cooling of the plastic material 22 causes its withdrawal, which consequently generates the presence of a space 20 between the body 22

and the surface 4a.

  The coating material is then injected under high pressure into the space 20. Preferably, the body 22 is not yet completely solidified, so that it can be slightly compressed under pressure

  coating material injection.

  It should be noted that the thickness of the coating layer which then forms on the surface of the body 22 has a thickness generally between 0.06 millimeter and 0.25 millimeter for a body whose thickness is

  between approximately 2 and 3.5 millimeters.

  The coating material 24 is then distributed over the entire surface 4a. Given the small thickness ú of the passage 14, the withdrawal of the plastic material 22 does not release sufficient space to allow the passage of the coating material 24, which cannot then enter the secondary cavity 12. In addition, the passage 14 being of small thickness compared to the average thickness of the body 22, the plastic material is completely hardened and therefore incompressible at this location when the coating material

24 arrives in this passage.

  If, however, the coating material 24 were to enter the secondary cavity 12 through the passage 24, given its small thickness, the space 16 would create such a pressure drop by friction in the coating material that in all event the bead should not be

  covered with coating material.

  In addition, the swollen part 18 having a relatively large thickness E, that is to say of the order of the average thickness of the body 22, a space 26 is released in this part by the withdrawal of the plastic. Thus, if a small amount of the coating material 24 reaches this swollen part, it will be trapped there, since it would be decompressed. The part 1 obtained after demolding, here an automotive shield, has a main part and a secondary part. The main part comprises the body 22, the face 22a of which is entirely covered with coating material 24. The secondary part comprises a peripheral bead corresponding to the bulged part 18 of the secondary cavity and a ply 32 corresponding to the space 16. The bead 30 is therefore connected to the main part of the part 1 by the ply whose thickness is substantially equal to that of the space 16, that is to say generally between 0.5 and 1 millimeter. The secondary part of the part can then either be camouflaged or separated from the main part, in particular by cutting at the junction of the

  two parts, substantially parallel to the surface 22a of the body.

  The variant presented in FIG. 5 differs from the solution presented in the preceding figures in that the main cavity 4 is extended by a drop zone 34 added at its periphery, near the intermediate passage 14. The thickness e of the zone drop 34 is reduced compared to that of the main cavity 4 by the presence of a boss 28 on the surface

  4b near the joint plane 3.

  Thus, the cutting of the part, perpendicular to its surface 22a, in the drop zone 34 will be facilitated. Preferably, as illustrated by the dashed line 36, the cutting will be carried out at the edge of this drop zone 34, so that only a small part of this drop zone remains on the finished part. The entire surface 22a of the finished part will then be covered with

coating material.

  It will be understood that for the solution of the invention to be fully satisfactory, the secondary cavity and / or the passage must be present over the entire periphery of the main cavity 4, in the manner

a seal.

  Of course, the invention is in no way limited to the embodiments

  which have just been described and which are given only by way of example.

  In particular, the injection means 6 and / or

  the injection head 8 inside the punch.

Claims (10)

Claims   1. Mold (2) for producing a coating (24) on a plastic part (1) (22), the mold comprising: - two parts (2a, 2b) reserving between them a main cavity (4) for molding, - means (6) for introducing plastic material into the main molding cavity, - means (8) for pressure injection of a coating material (24), into the main molding cavity, characterized in that that it further comprises a secondary cavity (12) disposed at the periphery of the main mold cavity, between the two parts of the mold, this secondary cavity communicating with the main cavity by an intermediate passage (14) having a thickness (ú) lower or equal to 1 millimeter.   2. Mold according to claim 1, characterized in that: - the (the) cavity (s) secondary (s) comprises (include) a bulged part (18) and a space (16) connecting the bulged part and the main cavity, via said passage, - the swollen part has at least locally a thickness (E) greater than that of the intermediate passage and greater than or equal to 0.5 millimeter, and - the space (16) comprises a thickness between that of   intermediate passage (14) and said thickness (E) of the bulged part.   3. Mold according to claim 1 or 2, characterized in that the mold having a joint plane (3), the (the) cavity (s) secondary (s)   extends along the joint plane of the mold.   4. Mold according to any one of the preceding claims,   characterized in that the main cavity further comprises a zone of   fall, of reduced thickness, near the intermediate passage.   5. Method for producing in a mold (2), a coating (24) on a plastic part (1) (22), in which: a) plastic material (22) is introduced inside a main mold cavity (4) of the mold, b) a coating material (24) is injected under pressure into the main cavity, in contact with a partially solidified surface (22a) of the plastic material, characterized in that during from step a), the plastic is introduced into at least one secondary cavity (12) disposed at the periphery of the main cavity, this introduction being effected through an intermediate passage (14) putting the main and secondary cavities into communication and whose thickness (e) is such that the coating material cannot enter it during step b), after plastic has been introduced into it during step a).   6. Method according to claim 5, characterized in that after step b), the part obtained is removed from the mold, then the part (30, 32) is separated from the part corresponding to the secondary cavity of the part (22, 24) of the room   corresponding to the main cavity.   7. Method according to claim 6, characterized in that: - the main cavity is extended by a drop zone of reduced thickness (e), near the intermediate passage, and - the part is cut out in the part corresponding to the zone of   reduced thickness drop, perpendicular to said surface.   8. Part obtained by implementing the method according to one   any of claims 5 to 7.   9. Plastic part (1) comprising: - a main part (22,24) of which a surface (22a) is covered with a coating material (24), and - a secondary part (30, 32) surrounding the main part to which it is connected by a sheet (32) whose thickness (e) is less than or equal to 1 millimeter. 10. Part according to claim 9, characterized in that the secondary part comprises a peripheral bead (30) not covered with coating material.