BACKGROUND OF THE INVENTION

The present invention generally pertains to injection molding of plastic products and is particularly directed to a method and a system for producing cross-laminated products with greatly improved flexure and impact strength.

SUMMARY OF THE INVENTION

The present invention provides a method of injection molding a plastic product, that has a cross-laminated section including a first plastic layer and a second plastic layer, in a mold system comprising a first mold cavity with a first- layer-defining-mold-cavity-section and a second mold cavity with a second-layer- defining-mold-cavity-section that has a second-cavity-section-wall, the method comprising the steps of:

(a) injecting a quantity of first plastic into the first mold cavity so that first plastic flows in the first-layer-defining-mold-cavity-section in a first predetermined general direction;

(b) solidifying at least partly the flowed first plastic in the first-layer- defining-mold-cavity-section to thereby form said first plastic layer having a first- direction-flow-record;

(c) adjusting the mold system to thereby provide the second mold cavity with the second-cavity-section-wall including said first plastic layer;

(d) Injecting a quantity of second plastic into the second mold cavity so that second plastic flows in the second-layer-defining-mold-cavity-section in a second predetermined general direction, whereby second plastic in the second- layer-definϊng-mold-cavity-sectioπ fuses with said first plastic layer;

(e) solidifying the flowed second plastic in the second- layer-defining- mold-cavity-section to thereby form said second plastic layer, so that the second plastic layer has a second-direction-flow-record, which is positively different from said first-direction-flow-record, to thereby form said plastic product with said cross-laminated section that includes both the first plastic layer and the second plastic layer; and

(f) adjusting the mold system to thereby eject the product, and prepare for the next production cycle.

For high efficiency production, it is an advantage to operate two sets of mold systems concurrently in the same injection molding machine, but displaced in time so that the first injection, first solidifying and first adjusting step of one mold system set takes place generally simultaneously with the second injection, second solidifying and second adjusting step of the other system set.

The above mentioned method may be generalized for the production of products with three or more layers, therefore the present invention also provides a method of injection molding a plastic product, with a cross-laminated section that includes a primary layer, a secondary plastic layer and a tertiary plastic layer, in a mold system comprising a primary-layer-defining-mold-cavity-section a secondary mold cavity with a secondary-layer-defining-mold-cavity-section with a secondary-cavity-section-wall, and a tertiary mold cavity with a tertiary-layer- defirting-mold-cavity-section with a tertiary-cavity-section-wall, the method com¬ prising the steps of:

(a) injecting a quantity of primary plastic into the primary mold cavity so that the primary plastic flows in the primary-layer-defining-mold-cavity-section in a primary predetermined general direction;

(b) solidifying at least partly the flowed primary plastic in the primary- layer-defining-mold-cavity-section to thereby form said primary plastic layer having a primary-direction-flow-record;

(c) adjusting the mold system to thereby provide the secondary mol cavity with the secondary-cavity-section-wall including said secondary plasti layer;

(d) injecting a quantity of secondary plastic into the secondary mol cavity so that secondary plastic flows in the secondary-layer-defining-mold cavity-section in a secondary predetermined general direction, and fusing th secondary plastic in the secondary-layer-defining-mold-cavity-section with sai primary plastic layer;

(e) solidifying at least partly the flowed secondary plastic in th secondary-layer-defining mold-cavity-section to thereby form said secondar plastic layer having a secondary-direction-flow-record, and so that the secondar plastic layer has a secondary-direction-flow-record which is positively differen from said primary-direction-flow-record;

(f) Adjusting the mold system to thereby provide the tertiary mold cavit with the tertiary-cavity-section-wall including said secondary plastic layer;

(g) injecting a quantity of tertiary plastic into the tertiary mold cavity so that tertiary plastic flows in the tertiary-layer-defining-mold-cavity-section in a tertiary predetermined general direction, whereby tertiary plastic in the tertiary- layer-defining-mold-cavity-section fuses with said secondary plastic layer; (h) solidifying the flowed tertiary plastic in the tertiary-layer-defining- mold-cavity-section to thereby form said tertiary plastic layer, so that the tertiar plastic layer has a tertiary-direction-flow-record which is positively different from said secondary-direction-flow-record, to thereby form said plastic product with said cross-laminated section that includes all of the primary plastic layer, the secondary plastic layer and the tertiary plastic layer; and

(i) adjusting the mold system to thereby eject the product, and prepare for the next production cycle;

For high efficiency production, it is an advantage to operate three sets of mold systems concurrently in the same injection molding machine, but displaced in time so that the first injection, first solidifying and first adjusting step of one mold system set takes place generally simultaneously with the second injection, second solidifying and second adjusting step of an other mold system set, which takes place generally simultaneously with the third injection, third solidifying and third adjusting step of the remaining mold system set.

The present invention also provides a molding system for practicing the invented process, and a product made in accordance with the invented process as mentioned above.

Additional features of the present invention are described in relation to the description of the preferred embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a partial sectional view of a first mold cavity encasing a first plastic layer of a first preferred embodiment in accordance with the invention.

Figure 2 is a partial sectional view of a second mold cavity encasing a second plastic layer of the first preferred embodiment in accordance with the in¬ vention. Also shown is a sectional view of a cross-laminated product section taken along line 2-2 in figure 3. Figure 3 is a transparent partial view of a cross-laminated product which has been molded by the first and second mold cavities shown in figure 1 and figure 2.

Figure 4 is a partial sectional view of a first mold cavity encasing a first plastic layer of a second preferred embodiment in accordance with the invention. Figure 5 is a partial sectional view of a second mold cavity encasing a second plastic layer of the second preferred embodiment in accordance with the

invention. Also shown is a sectional view of a cross-laminated product sectio taken along line 5-5 in figure 6.

Figure 6 is a transparent partial view of a cross-laminated product whic has been molded by the first and second mold cavities shown in figure 5 and 6. Figure 7 is a partial sectional view of a first mold cavity encasing a firs plastic layer of a third preferred embodiment in accordance with the invention.

Figure 8 is a partial sectional view of a second mold cavity encasing a second plastic layer of the third preferred embodiment in accordance with the in¬ vention. Also shown is a sectional view of a cross-laminated product section taken along line 8-8 in figure 9.

Figure 9 is a transparent view of a cross-laminated product which has been molded by the first and second mold cavities shown in figure 7 and figure 8. .

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The first preferred embodiment is illustrated in figures 1-3. Shown is a mold system comprising a first mold cavity 1 with a first- layer-defining-mold-cavity-section 2 and a second mold cavity 3 with a second- layer-defining-mold-cavity-section 4 with a second-cavity-section-wall 5.

The first mold cavity 1 comprises a first-cavity-flow-channel 6 which is locate adjacent the first-layer-defining-mold-cavity-section 2, the second-layer- defining-mold-cavity-section 4 with thickness C is at least as thick as the first- cavity-flow-channel 6 with thickness F, whereby it is possible to mold the product without a ribbed surface.

The mold system includes a first mold 7 having a first mold part 8, which includes a gate, and a complementary mold part 9. The mold system further in- eludes a second mold 10 having a second mold part 11, which also includes a gate, and the same complementary mold part 9.

The system is operated by injecting a quantity of first plastic into the first mold cavity 1 so that first plastic flows in the first-layer-mold-cavity-section 2 in a first predetermined general direction, as indicated by a first arrow 12.

The flowed first plastic is then at least partly solidified in the first-layer- defining-mold-cavity-section 2 to thereby form a first plastic layer 13 having a first-direction-flow-record, similarly indicated by arrow 12.

The mold system is then adjusted to thereby provide the second mold cavity 3 with the second-cavity-section-wall 5 including the first plastic layer 13.

A quantity of second plastic is then injected into the second mold cavity 3 so that second plastic flows in the second-layer-defining-mold-cavity-section 4 in a second predetermined general direction, indicated by a second arrow 14, whereby second plastic in the second-layer-defining-mold-cavity-section fuses with the first plastic layer 13.

The flowed second plastic is then solidified in the second-layer-defining- mold-cavity-section 4, to thereby form a second plastic layer 15, so that the second plastic layer 15 has a second-direction-flow-record, similarly indicated by the second arrow 14, which is approximately at right angle to the first-direction- flow-record and therefore is positively different from the first-direction-flow- record, indicated by the first arrow 12, to thereby form a plastic product 16 with a cross-laminated section 17 that includes both the first plastic layer 13 and the second plastic layer 15. Arrows showing the flow direction of the second plastic are dotted.

The mold system is then adjusted to eject the plastic product 16. The plastic product 16 has gate marks 20 formed by gate means, not shown, of the first gate part 8, for injecting the first plastic.

When injecting the quantity of first plastic into the first mold cavity 1 so that first plastic flows in the first-layer-defining-mold-cavity-section 2 in a first

predetermined general direction, as indicated by the first arrow 12, the first plasti is directed into the first-layer-defining-mold-cavity-section 2 via the first-cavity flow-channel 6, so that the first plastic flows in the first-cavity-flow-channel 6 i a direction, which is indicated by a third arrow 13, which is positively differe from the first predetermined general direction, which was indicated by the first ar row 12. The angle between the flow directions depend mostly on relative cavit thicknesses within the first mold cavity. The second plastic layer 15 is molde with a wall thickness which is much thicker than the first plastic layer 13.

When the mold system is adjusted to provide the second mold cavity with the second-cavity-section-wall 5 including the first plastic layer 13, the mol system is adjusted by separating the first gate part 8 from the complementary pa 9 and combining the second gate part 11 with the complementary part 9 whil retaining the first plastic layer 13 with the complementary part 9, thereby transfer ring the first plastic layer 13 from the first mold 7 to the second mold 10 in orde to compose the second mold cavity 3 subsequent to the second-cavity-section wall 5 including the first plastic layer 13.

When the mold system is adjusted to provide the second mold cavity with the second-cavity-section-wall 5 including the first plastic layer 13, a sub stance 19 is added to the surface of the first plastic layer 13, before the first pias tic 13 layer fuses with the second plastic layer 15, in order to seal the substanc between the first plastic layer 13 and the second plastic layer 15. The substanc may for example be deposited as a result of a printing process, a fluorinatio process or an aluminizing process or for other reasons.

The first plastic of this first embodiment is a polystyrene plastic resin i a red colour and the second plastic is a clear transparent polystyrene.

It is also possible to mold the first plastic layer 13 and the second plasti layer 15 in the reverse order. Then the second plastic layer 15 is molded with

wall thickness which is much thinner than the first plastic layer 13, and the second plastic layer 15 is still molded with a second-direction-flow-record which is ap¬ proximately at a right angle to the first-direction-flow-record.

Since the flow of molten plastic in a mold is slightly improved when one of the mold walls is made of an other plastic material with a heat conductivity which is much lower than that of steel, the flow directions of the injected plastic may very slightly when the order of injection is reversed.

It is usually an advantage to inject the thinnest layer last, since the thin¬ nest layer require the highest injection pressure, this pressure may be reduced when injecting into a mold where one side wall of a cavity is made up of another plastic material.

The second preferred embodiment is illustrated in figures 4-6.

Shown is a mold system comprising a first mold cavity 21 with a first- layer-defining-mold-cavity-section 22 and a second mold cavity 23 with a second-layer-defining-mold-cavity-section 24 with a second-cavity-section-wall

25.

The first mold cavity 21 comprises a first-cavity-flow channel 26 which is located adjacent the first-layer-defining-mold-cavity-section 22, the second-layer- defining-mold-cavity-section 24 with thickness G is as least as thick as the first- cavity-flow-channel 26 with thickness H, whereby it is possible to mold the plastic product 36 without a ribbed surface.

The second mold cavity 23 comprises a second-cavity-fiow-channel 39 which is located adjacent the second-layer-defining-mold-cavity-section 24, the first- layer-defining-mold-cavity-section 22 with thickness K is at least as thick as the second-cavity-flow-channel 39 with thickness L, whereby it is possible to mold the plastic product 36 without a ribbed surface.

The mold system includes a first mold 27 with a first mold cavity 21, an a separate second mold 30 with a second mold cavity 23, each mold has its ow gate means, not shown.

The system is operated by injecting a quantity of first plastic into the firs mold cavity 21 so that first plastic flows in the first-layer-defining-mold-cavity section 22 in a first predetermined general direction, as indicated by a first arro 32.

The flowed first plastic is then at least partly solidified in the first-layer defining-mold-cavity-section 22 to thereby form a first plastic layer 33 having first-direction-flow-record, similarly indicated by arrow 32.

The mold system is then adjusted to provide the second mold cavity 2 with the second-cavity-section-wall 25 including the first plastic layer 33.

A quantity of second plastic is then injected into the second mold cavit

23 so that second plastic flows in the second-layer-defining-mold-cavity-sectio 24 in a second predetermined general direction, indicated by a second arrow 3 whereby second plastic in the second-layer-defining-mold-cavity-section fuse with the first plastic layer 33.

The flowed second plastic is then solidified in the second-layer-defining mold-cavity-section 24, to thereby form a second plastic layer 35, so that th second plastic layer 35 has a second-direction-flow-rβcord, similarly indicated b the second arrow 34, which is approximately at right angle to the first-direction flow-record and therefore is positively different from the first-direction-flow record, indicated by the first arrow 32, to thereby form a plastic product 36 with cross-laminated section 37 that includes both the first plastic layer 33 and th second plastic layer 35. Arrows showing the flow direction of the second plasti are dotted.

The mold system is then adjusted to eject the plastic product 36. The plastic product 36 has gate marks 29 formed by gate means, not shown, of the first mold cavity 21, for injecting the first plastic and other gate marks 28 formed by gate means, not shown, of the second mold cavity 23, for injecting the second plastic.

When injecting the quantity of first plastic into the first mold cavity 21 so that first plastic flows in the first-layer-defining-mold-cavity-section 22 in a first predetermined general direction, as indicated by the first arrow 32, the first plastic is directed into the first-layer-defining-mold-cavity-section 22 via the first-cavity- flow-channel 26, so that the first plastic flows in the first-cavity-flow-channel 26 in a direction, which is indicated by a third arrow 33, which is positively different from the first predetermined general direction, which was indicated by the first ar¬ row 32. The angle between the flow directions depend mostly on relative cavity thicknesses within the first mold cavity. When injecting the quantity of second plastic into the second mold cavity

23 so that second plastic flows in the second-layer-defining-mold-cavity-section

24 in a second predetermined general direction, as indicated by a second arrow 34, the second plastic is directed into the second-layer-defining-mold-cavity-section 24 via the second-cavity-flow-channel 39, so that the second plastic flows in the second-cavity-flow-channel 39 in a direction, which is indicated by a fourth arrow

40, which is positively different from the second predetermined general direction, which was indicated by the second arrow 34. The angle between the flow direc¬ tions depend mostly on relative cavity thicknesses within the second mold cavity.

The first plastic layer 33 is molded with a wall thickness which is ap- proximately the same as the wall thickness of the second plastic layer 35.

When the mold system is adjusted thereby providing the second mold cavity 23 with the second-cavity-section-wall 25 including the first plastic layer

33, the mold system is adjusted by transferring the first plastic layer 33 from t first mold 27 to the second mold 30, for example with the help of a robot, in ord to compose the second moid cavity 23 subsequent to the second-cavity-secti wall 25 including the first plastic layer 33. When the mold system is adjusted thereby providing the second mo cavity 23 with the second-cavity-section-wall 25 including the first plastic lay 33, a substance 31 is added to the surface of the first plastic layer 33, before t first plastic 33 layer fuses with the second plastic layer 35, in order to seal t substance between the first plastic layer 33 and the second plastic layer 35. The substance may for example be deposited as a result of a printi process, a fluoridation process or an aluminizing process or for other reasons.

The first plastic is an ABS plastic resin and the second plastic is a P plastic resin.

The third preferred embodiment is illustrated in figures 7-9. Shown is a mold system comprising a first mold cavity 41 with a firs layer-defining-mold-cavity-section 42 and a second mold cavity 43 with second-layer-defining-mold-cavity-section 44 with a second-cavity-section-w 45.

The system is operated by injecting a quantity of first plastic into the fir mold cavity 41 so that first plastic flows in the first-layer-defining-mold-cavit section 42 in the first predetermined general direction, as indicated by a first arro 52.

The flowed first plastic is then at least partly solidified in the first-laye defining-mold-cavity-section 42 to thereby form a first plastic layer 53 having first-direction-flow-record, similarly indicated by arrow 52.

The mold system is then adjusted to thereby provide the second mold cavity 43 with the second-cavity-section-wall 45 including the first plastic layer 53.

A quantity of second plastic is then injected into the second mold cavity 43 so that second plastic flows in the second-layer-defining-mold-cavity-section

44 in a second predetermined general direction, indicated by a second arrow 54, whereby second plastic in the second-layer-defining-mold-cavity-section fuses with the first plastic layer 53.

The flowed second plastic is then solidified in the second-layer-defining- mold-cavity-section 44, to thereby form a second plastic layer 55, so that the second plastic layer 55 has a second-direction-flow-record, similarly indicated by the second arrow 54, which is approximately at a right angle to the first-direction- flow-record, and therefore is positively different from the first-direction-flow- record, indicated by the first arrow 52, to thereby form a plastic product 56 with a cross-laminated section 57 that includes both the first plastic layer 53 and the second plastic layer 55. Arrows showing the flow direction of the second plastic are dotted.

The mold system is then adjusted to eject the plastic product 56.

The first plastic layer 53 is molded with a wall thickness which is ap- proximately the same as the wall thickness of the second plastic layer 55.

The first mold cavity 41 comprises a retractable wall section 46 and be¬ comes the second mold cavity 43 subsequent to the retractable wall section being retracted and the second-cavity-section-wall 45 becoming inclusive of the first plastic layer 53. When the mold system is adjusted thereby providing the second mold cavity 43 with the second-cavity-section-wall 45 including the first plastic layer 53, the mold system is adjusted by retracting the retractable wall section 46, so that the second mold cavity 43 retains the first plastic layer 53.

The first plastic and the second plastic is injected through a shared gat 59.

The first plastic is a clear transparent polystyrene plastic resin and th second plastic is also a clear transparent polystyrene plastic resin. While the above description contains many specificities, these should no be construed as limitations on the scope of the invention, but rather as ex emplification of the preferred embodiments thereof. Many other variations ar possible. All embodiments have for simplification been shown applied to flat plas tic products, but the invention is equally applicable to products which have no flat surfaces, particularly hollow cup-shaped products.

The shown embodiments also all have a non ribbed surface, but in man cases a ribbed surface is advantageous, and the invention applies equally well t products with ribbed surfaces.

The various particulars shown in a specific preferred embodiment als applies to the other preferred embodiments, it is for example quite possible t cover the surface of the first plastic layer of the third preferred embodiment with substance as is shown in the first and second preferred embodiments.

When the first and second plastic material is the same material it is no necessary to use an injection molding machine with more than one injection unit.