EP0925165A1

EP0925165A1 - A method of manufacturing a microwaveable flatware article made of synthetic material, the article produced thereby and an ink-imprinted film component for use in making the flatware article

Info

Publication number: EP0925165A1
Application number: EP97939904A
Authority: EP
Inventors: Ching Chong Wu; Pierre Tardif
Original assignee: Genin Trudeau and Co Ltd
Current assignee: Genin Trudeau and Co Ltd
Priority date: 1996-09-05
Filing date: 1997-09-04
Publication date: 1999-06-30
Also published as: AU4195297A; WO1998009790A1; CA2184851A1

Abstract

A method of manufacturing a flatware article, such as a dish or cup that is decorated with a multi-colour design embedded in a food contacting surface of the article. The flatware article can be used in a microwave oven without causing deterioration of the multi-colour design, such as fading, bubbling or emission of harmful toxic fumes. The method comprises injecting molten polycarbonate material into a mould where is positioned a transparent film imprinted with the design. The film bonds with the polycarbonate material to form a laminated structure. The ink impression is applied on a surface of the film that bonds with the polycarbonate so the ink is embedded in the laminated structure and it is thus protected from scratches and contact by foods. The invention also extends to a novel flatware article.

Description

TITLE: A METHOD OF MANUFACTURING A MICROWAVEABLE

FLATWARE ARTICLE MADE OF SYNTHETIC MATERIAL, THE

ARTICLE PRODUCED THEREBY AND AN INK-IMPRINTED

FILM COMPONENT FOR USE IN MAKING THE FLATWARE

5 ARTICLE .

FIELD OF THE INVENTION

The present invention relates to a process for manufacturing articles made of synthetic materials such as polycarbonate, that are decorated with a design element embedded under the surface of the article. The invention is particularly well suited for manufacturing flatware such as dishes or cups that can be safely used m a microwave oven since the design element is encapsulated in the 5 surrounding material and thus it is unlikely to release harmful fumes when subjected to intense electromagnetic radiation. The invention also extends to such novel microwaveable article with an embedded design element and to a film component bearing a design element for use in 0 manufacturing the microwaveable article.

BACKGROUND OF THE INVENTION

Children in particular enjoy eating from flatware articles that are imprinted with colourful decorations such 5 as carton caracters. It is known to manufacture such flatware articles from melamine resin by embedding in the base melamine resin material a paper film bearing the colourful decoration.

ø Melamine resin however, releases harmful vapours when subject to intense electromagnetic radiation and it is therefore not suitable for manufacturing flatware that can be used to heat food in a microwave oven. Moreover, the embedded paper film may react with the electromagnetic 5 energy in the microwave oven, releasing fumes that may contaminate the contents being heated. Furthermore the paper film which surfaces the article, provides a poor surface finish that is prone to scratches and deterioration.

Many flatware articles, as realized In the prior art are made from polycarbonate, a material whose molecules do not react with the activity of a microwave oven. Accordingly those articles can safely be used in a microwave oven without risk of food contamination by toxic fumes. To decorate such polycarbonate articles, a decorative indicia is printed on their surface, such indicia however is prone to scratches and when subjected to Intense electromagnetic energy in a microwave oven, may bubble, or cause the ink- imprinted decoration to fade and release toxic fumes. Thus the article can not be safely used in a microwave oven even though the body material is inherently suitable for a microwave environment.

Although attempts have been made to improve the already existent microwaveable flatware articles with a decorative indicia, none of them are satisfactory. Thus there is a need to provide a flatware article with a surface decorated with an aesthetic design element that is resistant to scratches and when used in a microwave oven will not fade, bubble nor emit harmful toxic fumes.

OBJECTIVES AND STATEMENT OF THE INVENTION

It is an object of the present invention to provide a process for manufacturing a flatware article with a surface provided with an aesthetic design element that when used in a microwave oven will not fade, bubble nor emit harmful toxic umes. It is another object of the invention to provide a process for manufacturing a flatware article with a surface provided with an aesthetic design element which has a glossy surface finish that is highly resistant to scratches.

It is a further object of the invention to provide a flatware article with a surface provided with an aesthetic design element that when used in a microwave will not fade, bubble nor emit harmful toxic fumes.

Yet it is another object of the invention to provide an ink- imprinted film component for providing the aesthetic design element on the surface of the flatware article that when used in a microwave will not fade, bubble nor emit harmful toxic fumes.

As embodied and broadly described herein, the invention provides a microwaveable article for holding food products, said microwaveable article comprising:

- a main body including a first synthetic material;

- a decorative indicia placed on a surface of said main body; a film including a second synthetic material overlaying said decorative indicia; said film having a thickness and transparency selected to allow said decorative indicia to be visible to the human eye through the film; said film being bonded to said body along an area of juncture whereby said decorative indicia is encapsulated between said main body and said film;

- said first and second materials being compatible with one another whereby said area of juncture Is resistant to delaminatlon when said article Is used in a microwave oven; and - said first and second materials being selected to substan ially prevent degradation and release of toxic vapours when used in a microwave oven.

As embodied and broadly described herein, the invention also provides a process for manufacturing a microwaveable article for holding food products, said process comprising the steps of:

- placing in a mould a film carrying on an inner surface thereof a decorative indicia, said film being substantially transparent and made of a first synthetic material, said inner surface facing a cavity of said mould to contact material Injected therein

- injecting in said mould a second synthetic material, said second synthetic material being in a molten state to at least partially fill said mould and bond with said film along a line of juncture that at least partially surrounds said decorative indicia, whereby said decorative indicia is encapsulated between said film and said second synthetic material when the second synthetic material solidifies;

- said first and second materials being compatible with one another whereby said area of juncture when the second material solidifies is resistant to delaminatlon when, said article is used m a microwave oven,- and - said first and second materials being selected to substantially prevent degradation and release of toxic vapours when used in a microwave oven.

In a preferred embodiment, the microwaveable article is manufactured by Injection moulding. A film with a printed indicia on one side Is placed inside the mould with the printed Indicia facing the mould cavity. Polycarbonate that forms the main body of the article is then injected into the mould to bond with the film and thus encapsulate the decorative indicia. Polycarbonate is the material of choose for manufacturing the mam body of the article because is has a high impact strength, is dimensionally stable, and can be used in a microwave oven with no risks of distorting, softening or releasing toxic fumes. Polycarbonate is also characterised as having good resistance to chemicals and ultraviolet light and it is crack resistant .

In a most preferred embodiment, the film is a cast type clear polycarbonate film, more particular, a polycarbonate Acrylonit rile-Butadiene-Styrene (hereinafter referred to as ABS) coated material with low shrinkage and glossy surface finish. The ABS coating allows to provide a surface with high impact resistance, excellent surface finish, high dimensional stability at high temperatures, good chemical resistance and good stress cracking resistance.

The film has a low flow index and a molecular weight between 27 000 and 30 000 g/mol. The film has a thickness in the range from about 0.02mm to about 0.08mm and the surface of the film is treated to obtain a surface texture in the range from about 25 to 55 Dynes on which the decorative indicia is printed. The surface roughness allows the ink of the decorative indicia to adhere better to the surface.

After the injection process Is completed, the formed piece is subjected to a heat treatment process to relieve stresses that may have developed at the interface between the film and the main body. Most preferably, the heat treatment process is an annealing process that consists of heating the piece to a constant elevated temperature for a period of time and then allowing It to cool at a slow rate. DESCRIPTION OF THE DRAWINGS

Figure 1 is a perspective view of a flatware article well suited for use in a microwave oven, that is constructed in accordance to the invention;

Figure 2 is a perspective view of a clear polycarbonate film coated on the underside with an ink impression providing a decorative Indicia for use in manufacturing the flatware article in figure 1;

Figure 3 is a cross sectional view taken along lines 3-3 in figure 2;

Figure 4a is a cross sectional view of an injection mould, for manufacturing the flatware article shown in figure 1;

Figure 4b is an enlarged cross sectional view of the mould cavity shown at figure 4a, the mould being closed and the injection process initiated; and

Figure 5 is a further enlarged view of the mould cavity showing the distribution of the injected polymer and the clear polycarbonate film therein.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to the drawings, figure 1 illustrates a novel flatware article in the form of the dish 10 that is characterized by an aesthetic design indicia on the recessed food contacting surface of the dish. The dish 10 is constructed such that it can be safely used in a microwave oven. In other words, the material of the dish 10 will not release toxic fumes that can contaminate the food under the effect of electromagnetic radiation and heat . More specifically, the dish 10 includes a cup-shaped main body 12 including a downwardly sloping side wall and a flat bottom wall 16. The decorative indicia is applied to the flat bottom wall 16. Contrary to conventional processes where the indicia is simply printed on the surface of the dish, in the present case the indicia is embedded in the material of the dish so it is shielded from contact with the food.

As best shown in figures 2 and 3 the decorative Indicia which is an ink- impression 17 is shielded by a clear polycarbonate film 18 that is bonded with the base material of the dish 10. The film 18 includes a thin clear cast type layer of polycarbonate (commercial designation Merlon Lexan) 20, one surface thereof being printed with the indicia and the other surface coated with a ABS layer 22 that is very thin by comparison to the polycarbonate layer 20. The ABS layer provides a strong long lasting surface coating, resistant to stains, scratches, stress cracking and chemicals. The film 20 possess a low flow index with a molecular weight between 27 øøø and 3ø 000 g/mol. The thickness of the film (excluding the thickness of the Ink Impression) is in the range from about ø.02mm to about 0.08mm. Most preferably the thickness of the film is of 0.03mm.

The surface of the film on which the ink- impression 17 is made is treated in a manner well known to those skilled in the art to obtain a surface texture between 25 to 55 Dynes. Most preferably, the surface of the film has a texture of 42 Dynes. The surface roughness allows to retain well the ink-impression which has a typical thickness in the range from about 0.002mm and about 0.010mm. If the ink Impression is substantially less than 0.002mm it will be virtually transparent, while if it is too thick ie., substantially greater than 0.010mm, it will spread and botch the design on the film upon injection of the synthetic material forming the main body.

The manufacture of the dish 10 is accomplished in two stages, the first is the injection moulding process, depicted at figures 4, a and 6B and the final stage is an annealing step to release Internal stresses that may develop at the interface of the film 18 and the base material of the dish 10.

When the old is opened as in figure 4a, the film 18 which has previously been printed with the decorative indicia and die-cut to size is electrostatically charged ( in a manner well known to those skilled m the art) is placed in the injection old. The film is placed such that the ABS coated side, la is attracted due to its charge against the old plunger 24 and the or Inked side faces the old cavity. At this point, the old plunger is displaced in to close the mould cavity.

The injection process begins by heating (above 230 C) polycarbonate material and melting it into a polycarbonate resin. An in-line feed screw injects the molten polycarbonate material through a passage 2B into the enclosed cavity as shown in figure 6B.

Polycarbonate is an amorphous polymer which when heated to a temperature above its glass transition point 150 degrees C and then subjected to shearing stress, the molecules will tend to align themselves in the general direction of the stress. If the mass is then cooled below its transition temperature while the molecules are still under stress, the molecules remain in an oriented state. Such an orientation can have significant effects on the properties of the polymer mass. Thus in injection moulding, the shear stress action during the flow of the polycarbonate causes molecular orientation upon cooling. In order to avoid the undesirable built-in stress due to 5 such orientation of molecules before the plastic mass sets, the mould cavities are kept warm ie between 100 and 120 degrees C and the injection rates are fast.

After the injection of the polycarbonate has been lø completed the material gradually cools down and solidifies. During such cooling process the polycarbonate shrinks. The film 18 that has been heated by the molten polycarbonate also cools down and shrinks. Since the film 18 and the polycarbonate forming the remaining part of the dish lø are

15 unlikely to be of the same density, both components shrink at different rates which induces stresses at the zone of juncture film 18/maln body 14. To reduce such internal stresses, annealing is carried out to relieve stresses that developed during the phase transformation of the two

20 similar polycarbonate materials of different densities. Distortion and cracking may result if these stresses are not reduced, causing a poor weak bound between the film and the main body. The term annealing refers to a heat treatment m which a material is exposed to an elevated

25 temperature for an extended length of time and thereafter slowly cooled. Generally speaking, temperatures could range between 8øC to 150 C and the treatment time between 0.5 hour to 4 hours. Most preferably the dish 10 is treated at 110 C for 2 hours and then allowed to slowly

30 cool.

The above descriptions of a preferred embodiment should not be interpreted in any limiting manner since variations and refinements are possible which are within

35 the spirit and scope of the present invention. The scope of the invention is defined in the appended claims and their equivalents.

Claims

I claim:

1. A microwavable article for holding food products, said microwavable article comprising: - a main body including a first synthetic material;

- said first and second materials being compatible with one another whereby said area of juncture is resistant to delaminatlon when said article is subjected to electromagnetic radiation in a microwave oven; and - said first and second materials being selected to substantially prevent degradation and release of toxic vapours when subjected to electromagnetic radiation In a microwave oven.

2. A microwavable article as defined in claim 1, wherein said first and second materials are substantially free of stresses at said area of juncture that are capable of inducing delaminatlon of said film from said main body.

3. A microwavable article as defined in claim 2, wherein said first material includes polycarbonate.

4. A microwavable article as defined in claim 3, wherein said second material includes polycarbonate.

5. A microwavable article as defined in claim 4, wherein said film includes a inner layer made of polycarbonate and an outer protective layer.

6. A microwavable article as defined in claim 5, wherein said outer protective layer Is scratch resistant.

7. A microwavable article as defined in claim 6, wherein said protective layer is transparent.

8. A microwavable article as defined in claim 7, wherein said protective layer includes Acrylonltrlle-Butadlene- Styrene polymer.

9. A microwavable article as defined in claim 4 wherein said main body is substantially opaque.

10. A microwavable article as defined In claim 1, wherein said first and second materials have different densities.

11. A microwavable article as defined in claim 4, wherein said decorative indicia is an ink impression.

12. A microwavable article for holding food products including a recessed food contacting surface, said article comprising:

- a main body made of polycarbonate;

- a decorative indicia applied on said main body at said food contacting surface; - a film of substantially transparent polycarbonate material overlaying said decorative indicia, said film being bonded to said main body along an area of juncture to encapsulate said decorative Indicia between said main body and said film and thus prevent contact between said decorative indicia and food products placed on said food contacting surface;

- said film and said main body are substantially free of stresses at said area of juncture that are capable of inducing delaminatlon of said film from said main body.

13. A process for manufacturing a microwavable article of holding food products, said process comprising the steps

Of: - placing in a mould a film carrying on an inner surface a decorative indicia, said film being substantially transparent and made of a first synthetic material, said inner surface facing a cavity of said old to contact material injected therein - injecting in said mould a second synthetic material, said second synthetic material being in a molten state to at least partially fill said old and bond with said film along a line of juncture that surrounds said decorative indicia, whereby said decorative indicia is encapsulated between said film and said second synthetic material when the second synthetic material solidifies;

- said first and second materials being compatible with one another whereby said area of Juncture when the second synthetic material solidifies is resistant to delaminatlon when said article is subjected to electromagnetic radiation in a microwave oven; and

- said first and second materials being selected to substantially prevent degradation and release of toxic vapours when subjected to electromagnetic radiation in a microwave oven.

14. A process for manufacturing a microwavable article as defined in claim 13, comprising the step of subjecting said article once said second synthetic material has solidified to a heat-treatment to at least partially release stresses developed at said area of juncture.

15. A process for manufacturing a microwavable article as 5 defined In claim 14, wherein said heat treatment Includes a step of annealing said article.

16. A process for manufacturing a microwavable article as defined in claim 14, comprising the step of releasably 0 retaining said film to an inner surface of said mould while said second synthetic material is introduced In said mould.

17. A process for manufacturing a microwavable article as defined in claim 16, comprising the step of 5 electrostatically charging said film to releasably retain said film to an inner surface of said mould.

18. A process for manufacturing a microwavable article as defined in claim 14, comprising the step of depositing an ø ink impression on said film to create said decorative indicia.

19. A process for manufacturing a microwavable article as defined in claim 18, wherein said film Includes a roughened 5 surface on which said ink impression is applied.

20. A process for manufacturing a microwavable article as defined in claim 19, wherein the surface of said film on which said ink impression is applied has a surface 0 roughness In the range from about 22 to about 55 Dynes.

21. A process for manufacturing a microwavable article as defined in claim 20, wherein the surface of said film on which said ink Impression is applied has a surface 5 roughness of 45 Dynes.

22. A process for manufacturing a microwavable article as defined in claim 14, wherein said first synthetic material is polycarbonate.

23. A process for manufacturing a microwavable article as defined in claim 22, wherein said second synthetic material is polycarbonate.

24. A process for manufacturing a microwavable article as defined in claim 14, wherein said film has a thickness in the range from about ø.øø2 mm to about 0.010 mm.

25. A process for manufacturing a microwavable article as defined In claim 14, wherein said film has an outer protective layer that includes Acrylonltrile-Butadiene- Styrene polymer.

26. A process for manufacturing a microwavable article as defined in claim 23, wherein said first synthetic material and said second synthetic material when said second synthetic material is solidifies have different densities.

27. A microwavable article manufactured according to the process defined in claim 13.

28. A film for use In manufacturing a microwavable article for holding food products, said film being made of synthetic material and carrying on a main surface thereof a decorative indicia, said film having a thickness and transparency selected to allow said decorative indicia to be visible to the human eye through the film, said synthetic materials being selected to substantially prevent degradation and release of toxic vapours when exposed to elect omagnetic radiation in a microwave oven.

29. A film for use in manufacturing microwavable article for holding food products as defined in claim 28, wherein said synthetic material is polycarbonate.

5 30. A film as defined In claim 29, wherein said decorative Indicia is an ink impression.

31. A film as defined in claim 30, wherein said ink impression is applied on a surface of said film that is lø roughened.

32. A film as defined in claim 31, wherein the surface of said film on which said ink impression is applied has a surface roughness in the range from about 22 to about 55

15 Dynes.

33. A film as defined in claim 29, wherein said film has a thickness in the range from about ø.øø2 mm to about ø.ølømm.

20

34. A film as defined in claim 29 wherein said film has protective layer comprising Acrylonitrlle-Butadlene-Styrene polymer.