FR2557498A1 - INJECTION PROCESS IN TWO PHASES - Google Patents

Abstract

THIS PROCESS FOR OBTAINING BY INJECTION IN TWO PHASES OF A COMPOSITE BRUSH HAVING A SERIES OF RUBBER BRUSHES 44 MODIFIED "KRATON" AND A HANDLE 28 OF RELATIVELY RIGID AND HARDENING PLASTIC MATERIAL, SUCH AS POLYETHYLENE OR POLYSTYSTYSTYSTYSTYLENE. HANDLE 28 IN A MOLD CAVITY AND TO USE IT AS A CLOSURE OF ANOTHER MOLD CAVITY IN WHICH THE SILKS ARE SHAPED AT THE SAME TIME AS A SUPPORT LAYER 43 WHICH BETS BY FUSION TO THE HANDLE 28. THE SEPARATION OF THE PARTS OF MOLD DEFINING THIS LAST CAVITY IS CARRIED OUT SLOWLY (PREFERABLY AT A SPEED LESS THAN 1MMSEC.) IN AN INITIAL PHASE AND QUICKLY (AT A SPEED OF AT LEAST 10CMSEC.) IN A TERMINAL PHASE.

Description

INJECTION PROCESS IN TWO PHASES

  The present invention relates to a method of

  two-phase injection molding in a two-phase injection molding machine for the molding of composite brushes consisting, in part, of a flexible plastic material which tends to cling to a mold cavity during the formation of the article. The invention more particularly relates to the manufacture of a brush with modified rubber bristles known by the name Kraton (registered trademark by Shell Chemical Company), and with a handle made of a relatively rigid plastic material and hardening faster

  such as polyethylene or polystyrene. -

  The elasticity and flexibility of the Kraton makes it an excellent material for the bristles of the brush but

  is cause of great difficulties during its molding.

  Thus, if one uses the Kraton to make an integral brush in the handle of which are provided recesses or lateral nuclei to shoot on it and release the bristles coming from the cells of

  their cavity, the bonding ability of the bristles

  It should remain stuck in the cells and forcefully detach the handle from the mold part on which it is expected to remain during the opening stroke of the mold. The invention relates to a method for operating a machine for molding brushes

  two-component plastics, of the type indicated, which makes it possible

  to use for making silk, a modified rubber

  Kraton type, while ensuring that the bristles are

  suitably cells of the cavity in the-

which they are formed.

  This problem is solved, according to the invention, on the one hand, by a separate molding of the handle and bristles at the same time as a common support layer and on the other hand, by different stages of the process starting respectively

  rigid material and modified rubber with

  the handle to the support layer to form a two-component integral brush. The extraction of the bristles from the mold cells used for their formation takes place, during an initial phase of the opening stroke of the mold, at a controlled speed which is slow enough to maintain the continuity of the brush thus molded, and

  a much faster speed during the final phase

of the said race.

  According to a preferred embodiment, the rubber

  Kraton modified rubber is injected into a first cavity formed at a station of the machine between a mold primary part and a juxtaposed mold abutment.

  to one another, the first cavity comprising a

  elongated cells in the primary part of the mold and a contiguous space in the

  mold to produce a series of bristles

  integument of the common support layer. The bristles being

  held in their cells on the primary part of the

  on, remove the abutment to expose an over-

  important face of the support layer while leaving it

  cool with the bristles. Then we juxtapose to the first

  first mold part a third mold part, to another machine position, to form a second cavity closed by the large surface of the layer

  support. A plastic material is then injected

  stiffness in the second cavity in order to obtain a man-

  che adhering to the support layer along the surface

  important exposed. Once the handle has hardened,

  during a period of time during which the bristles and

  have been subjected to cooling, the first

  re and third mold parts are separated from each other while the handle is progressively removed from the primary part of the mold at controlled speed

  adapted, then at a faster separation speed.

  Through this process, the bristles and their support layer can cool longer than the handle, so as to reduce the Kraton's adhesion to the walls of the cavity. In order to obtain an efficient operation of the machine, it is nevertheless indicated that the injection and hardening of the handle, at the second station, coincides with

  the molding of a new set of bristles and a layer of

  port associated with the first item. This naturally requires

  duplication of the primary part of the mold.

  the bristles so that one of these parts can be

  juxtaposed to the mold abutment at the first pos-

  you while the other co-acts with the third part in

the second position.

  A machine adapted for this purpose may comprise a turret with four faces, each of them carrying

a primary part of the mold.

  Since the manufacture of the part of the mold forming the bristles, with its multiplicity of cells

  narrow, is much more expensive than the third par-

  relatively simple tie used to make the handle, the need to have at least two mold parts of

  type forming the bristles for each mold part

  the handle is a disadvantage; another inconvenience

  is the installation of an intermediate position in which the support layer which is an integral part of

  bristles is exposed to the atmosphere in order to cool

  to serve as a limit to the neck cavity in

the next post.

  A preferred embodiment of the invention is based on the discovery that it is possible to properly extract the modified rubber bristles such as Kraton from the cells of the cavity, even after a reduced cooling time provided that has already formed practically solidified handle of a more rigid plastic material to which the support layer can adhere

integrated into the bristles.

  The initial phase of the mold opening stroke during which the portions of the mold defining the bristle cavities are slowly separated at a controlled rate, as mentioned above, may be equal to or slightly greater than the bristle length so that the latter are detached from the walls of the cells before the complete opening of the mold, to allow ejection of the brush, which has just been achieved. The exact point of detachment depends, among other things, on the conicity of the cell walls; wider cone thus allows a decrease in the slow displacement phase of

the race.

  An advantageous succession of transactions

  the following steps: injection of the plastic material

  relatively rigid tick in a first cavity, formed

  at a station between a primary mold part and a

  secondary mold section which is juxtaposed

  hold the handle; during the hardening of the handle and the separation of these two mold parts, one juxtaposes

  at another post, a third part of the mold at the

  primary mold portion that further contains the handle, wherein the third portion has a multiplicity of elongate cells and an adjoining gap that faces the primary mold portion, the cells and the gap thereby forming a mold-bound secondary cavity; . Modified rubber, which relates to a material essentially the same as Kraton, is then injected into the second cavity to obtain a series of bristles integral with their common support layer, fused with the handle, followed by a separation of the third mold part and the primary part of the mold, at the speeds mentioned above. The composite brush thus molded is maintained in the part

  primary of the mold from where it is ejected later.

  It has been found that to obtain the best results

  As a result, the controlled rate of separation of mold parts should be less than one millimeter per second. Cells smaller than two centimeters, for example, will thus be released in about 18 seconds, after which the opening stroke of the mold can be terminated at a much higher speed, preferably of the order

2557498:

at least 10 cm per second.

  This is how a total race of 20 to 30 cm

  can be completed in 20 seconds or less.

  As stated by the manufacturer, Kraton is a block copolymer of the SBS type (styrene-butadiene-styrene),

  SEBS (styrene-ethylene-butadiene-styrene) or SIS (styrene

  isoprene-styrene). The first two types are particularly

  adapted to the present invention since they

  bind well, respectively, to polystyrene and poly-

  ethylene. We facilitate the combination of a handle

  polystyrene with a bristle body in SEBS in melange

  Kraton a small amount of polystyrene, for example, up to 5% by weight. Similarly, a small amount of polyethylene can be mixed with SBS-type Kraton.

if the handle is polyethylene.

  It must therefore be understood that the term

  modified "cane" used in this application may

  include a small proportion of some other

  plastic material mixed with the base block copolymer.

  All of the above - and other features

  of the invention will now be described in detail with reference to the accompanying diagrammatic drawing, in which:

  FIG. 1 is a plan view, in sectional view of

  a set of molds on the table of an injection molding machine, which is also

  that is operated according to the method of the invention

  tion; - Figure 2 is an enlarged sectional view of a detail of Part II of Figure 1; 3 is a view similar to FIG.

  a somewhat smaller scale, and showing

  additional tails; - Figure 4 is a view similar to Figure 3 showing a modification; - Figure 5 is a series of curves relating to the separation of mold parts forming cavities

bristles.

  The injection molding machine shown partially in FIG. 1 is similar to that described

  in U.S. Patent No. 3,482,284 to Herbert Rees.

  This machine comprises a frame (10) supporting a fixed plate (11) and a conventional clamping control of which only two reciprocating jacks (14 ') and (14' ') have been shown. These cylinders are rigid, a movable plate (13) sliding on a

  series of tie rods (12).

  A central shaft (15) is fixedly connected to a support plate (16) rotatable by 180

around its axis.

  The tray (16) supports two identical mold primary portions (20) and (20 ') which, in the illustrated closure position, are contiguous with a mold abutment (26) and a third mold portion (27) respectively. ) supported on the plate (11) by

  through a fixed support and distribution plate

  tion (50). The latter has a recess (51) which

  closing a flow divider (52) through which a

  A fast curing thermoplastic web, eg polyethylene, from the injection unit (53 ') is transmitted to a set of first cavities (54) defined between the mold parts (20') and (26). Concurently the mold portions (20 ") and (27) define a set of second cavities (55), each of which, as

  as seen in Figure 2, includes a space (55a) communicating

  as with a multiplicity of narrow cells, conver-

  outwardly (55b). The space (55a) is connected on the opposite side of the cells (55b) to a handle (28) of

  plastic material previously molded into a cavity cor-

  respondent (54). A modified rubber stream (Kraton) is introduced into the cavities (55) to form the bristles

  (44) in the conical cells (55b), forming part of

  coating of a common support layer (43) filling

  space (55a) as shown in FIG.

  che binding to the preformed handle (28). The ends of

  cells (55b) of each cavity, narrow enough to

  fishing for Kraton penetration, open up to a

this aeration (55c).

  The width of each cavity (55) in the region of the space (55a) is slightly greater than that of the

  cavities (54) so as to maintain a small annular space

  (29) to the preformed handle (28), wherein the Kraton, introduced through an orifice (58) can pass to form a bead surrounding the handle. This gap, and the contiguous beveled surface of the mold portion (27) defining a wedge-shaped gap (30) around the periphery of the handle, ensures that the handle is not

damaged when the mold closes.

  The pivoting plate (16) has two cutouts

  (59 ') and (59 ") enclosing the respective ejection plates

  (24 '), (24 ") with axes (124'), (124") passing through

  the mold parts (20 ') and (20 ") terminate in the retracted position contiguous to the spaces occupied by the handles (28), the ejection plates are urged in this retracted position by suitable means such as springs captive coil (60 ') (60 "). A

  push rod (23) passes through the plate (13) in the surface

  from the station served by the injection unit (53 ");

  hydraulic liner (22) moves it forward at the end of each

  molding cycle, removing the plate (13) from the

  than (12) in an opening stroke of the mold, to pull out a set of finished brushes with the sleeves (28), the

  support layers (43) and bristles (44) of cavities (55).

  The new sleeves formed concurrently in the post served by the injection unit (53 ') remain in position on the mold part (20') or (20 "), coagulating with the mold part (26) since this post is not equipped with a push rod such as that shown in (23), it being understood that, after each ejection of sets of finished brushes, and before the next mold closing stroke, the plate is rotated by 180 pivoting member (16) (as more particularly described in the Rees patent cited above) for interchanging the positions of the mold parts (20 ')

  and (20 '') before a new injection in both pos-

  your. The fluidized Kraton is fed from the uni-

  tee (53 ") in the two cavities (55) by a central tube (32) provided with heating channels (61) and a collar

  ring (62) closing a peripheral gap (63)

  2), in which part of the Kraton passes as it is

  see in Figure 3, during the injection step. Kra-

  your penetrates through the central hole (64) of the tube (32) that it leaves by a transverse slot (65) at the free end

  of it on its way to the orifices (58) of the two

  ities. The material remaining outside the cavities forms

  a hot moving element, generally similarly

  to that described in US Pat. No. 4,184,836 in the name of

Herbert Rees.

  Figure 4 illustrates a modular injection system

  for cavities (55) according to which the central part

  the mold part (27), which is otherwise unchanged, is equipped with a feed duct (40) terminating in an opening (41) from which the molten Kraton flows into a passage (42) similar to the slot (65) of Figure 2, leading to the two injection ports (58)

  (only one of which is shown in Figure 4). Not-

  wise (42) open towards the mold part (20 ") (or (20 ')

  in the other position of the pivoting plate (16)

  / with, nique a frustoconical clearance (46) being provided in this

  part of the mold to form a buffer which is an integral part

  of a cold moving element which is detached from the

  naked cavities (55) at orifices (58) at separation

  one of the other of the two mold parts. The branches

  sloping sections (42a of the passage (42), completely inte-

  the mold part (27) are thus freed from the

  tremities of the cold moving member which thus remains attached to the recessed mold portion (20 ") (or 20 ') until

  that a rod (45) supported by the associated ejection plate

  (24 ") (or 24 ') dislodges it.

  the duct (40) is maintained in a fluid state by means of

  heaters (61) surrounding it, thereby acting as

hot moving element.

  Each mold part (20 ') and (20 "), as especially illustrated, for the latter, in FIGS. 2 to 4, is provided with similar frustoconical releases,

  each being contiguous at the end of an ejector axis associated with

  cie (124 ') or (124 ") to form a buffer (28a) forming an integral part of the handle (28), which holds the handle in this mold part during the opening stroke, the buffers (28a) remaining on the handle of

  the finished article are not inconvenient and, in fact, are advan-

  tagging in the next operation during which one

  can stick a sponge on this surface of the handle.

  There are also other ways to maintain the

  on the core, such as recesses on the

  inner side faces of the handle.

  We will now describe, with reference to FIG.

  re 5, the unfolding of the opening race

  of the mold that has proved necessary to combine an ex-

  traction on bristles (44) of the cells (55b) with the cy-

  working key as short as possible. The graph in Figure 5 is based on a length of cells around

  16 mm for bristles of about the same length

  LATIONS. The opening of the mold occurs in two phases: an initial phase on 2 cm and a terminal phase of 28 cm. Curve A represents a mode of operation with Kraton as injected material and in which the initial phase, made ideally linear, lasts slightly

  less than 3 seconds while the terminal phase takes

  Viron a second. These times are perfectly satisfactory.

  for conventional thermoplastics such as polyethylene or polystyrene but are not suitable

  for the Kraton since the bristles can not be removed

  of their cavities. On curve B, the initial phase

  lengthened to 10 seconds (without significant change

  terminal phase); we arrive at a detachment

  bristles, but some of them are deformed.

  misfortune. Only when the duration of the

  at the initial phase close to 18 seconds, as

  on curve C, that we obtain perfect bristles

  straight; this corresponds to an average speed of

  separation slightly less than 1 mm / sec.

  The closing stroke of the mold can be effected

  killed at about the same speed as the phase

  terminal of the opening race. With a period of

  jection and cooling on the order of 10 seconds, the total duration of the cycle, in the conditions given, will be

about 30 seconds.

S749S he

Claims (7)

- CLAIMS -   1- Two-phase injection process for manufacturing   composite brushes, each of which is provided with a relatively flexible modified rubber set of bristles which tends to catch in the cavity of a mold   during a prolonged period of hardening and com-   further comprising, together with said bristles a handle of a relatively rigid plastic material and hardening more quickly, characterized in that on the one hand the handle and on the other hand bristles and a common support layers are molded separately at different stages operating, to   from the rigid material and the rubber   modified rubber, with adhesion of the handle to the support layer to form a two-component integral brush, and   in that the extraction of the bristles from the mold cells used   for their formation is performed, during an initial phase of the opening stroke of the mold, at a controlled speed sufficiently slow to maintain the continuity of the brush thus molded, and at a much higher speed   fast during the terminal phase of the said race.   2- injection method according to claim 1,   characterized in that the initial phase of the running of   mold's width does not nearly exceed the length bristles.   3- injection method according to claim 1 or claim 2, characterized in that it comprises the following steps:   (a) injection of the relative plastic material   rigidly in a first cavity (54) formed at a machine station between a primary mold portion (20) and a mold abutment (26), juxtaposed with each other, to obtain the handle (.28);   (b) After the hardening of the handle and the separation   the primary and secondary parts of the mold, juxtaposed / (27)   position of a third part of the mold to a primary part   mayor of mold, at another machine station, said   primary holding still in the neck /, 2a third par-   mold with a multiplicity of cells allon-   (55b) and a contiguous gap (55a) facing the primary portion of the mold, said cells and said gap thereby forming a second cavity (55) closed by the handle (28); - (c) injecting the modified rubber into the second cavity to produce the set of bristles (44) integral with the common support layer fused to the handle (28); (d) separating the third mold portion and the primary portion of the mold to disengage the molded bristles while retaining the molded brush on the primary portion of the mold and (e) ejecting the molded brush from the portion primary of the mold.   4- Method according to claim 3, characterized in that said controlled speed is less than one millimeter per second.   - Method according to claim 4, characterized in that said faster speed is of the order of at less than 10 centimeters per second.   6. Process according to any one of the claims   1 to 3, characterized in that the plastic material   latively rigid is polystyrene or polyethylene.   7. The process according to claim 3, characterized   in that during step (b), one juxtaposes to the part   secondary mold a duplicate of the primary part of the mold   the to reform the first cavity and we repeat the step   (a) at the same time as step (c).   8- Method according to claim 3, characterized in that during step (c) the modified rubber is injected after an edge of the mold in said interval then   from there into the cells forming the bristles.