A method of producing a mould suitable for providing a surface finish to a plastic item

Abstract

A method of producing a mould for use in a rotational moulding process comprises the step of ablating at least one distinct area of the surface of the mould. An ink is applied to the surface of the mo

Description

FIELD OF THE INVENTION

[0001] The present invention relates to a method of producing a mould suitablefor providing a surface finish to a plastic item. More especially, the mould provides a wood effect surface finish to the item. Moreover, the invention relates to a mould for use in a rotational moulding machine which provides an artificial wood finish to the item produced. BACKGROUND TO THE INVENTION

[0002] Plastic is a favoured choice of material for most products. In clinical environments for example, it is the material choice for furniture due to plastic furniture being hardwearing, lightweight and easy to clean, needing very little day-to-day maintenance.

[0003] However, the appearance of plastic furniture tends to lack the ability to nurture a warm and welcoming environment, due to its basic appearance with solid, plain colours. Without commercial constraints, natural materials such as wood would be preferred to foster rehabilitation and reflection in patients.

[0004] It has proven difficult to provide a realistic natural wood appearance to plastic products.

[0005] There has been attempts to provide a natural appearance to plastic. One known method involves applying a vinyl sheet with an artificial wood grain. While this is a cost-effective method, it is not suitable for custodial or clinical environments as the vinyl sheet can be peeled and vandalised easily by users.

[0006] Another known method is to apply a wood veneer to the top surface of the plastic. This method involves applying a very thin sheet of natural wood to the base material. It provides the natural look and feel of typical wood furniture, but it can be easily vandalised to damage the wood layer or to separate the two layers.

[0007] The present invention seeks to alleviate the aforementioned problems by providing a method for manufacturing plastic furniture that has a realistic wood effect finish by creating or adapting a mould prior to its use in a rotationally moulding process. STATEMENT OF THE INVENTION

[0008] According to a first aspect of the invention, there is provided a method of producing a mould for use in a rotationally moulding process, the method comprising the steps of: ablating at least one distinct area of the surface of the mould; applying an ink to the surface of the mould and cleaning the ink from the un-ablated areas of the mould surface to only leave ink within the distinct ablated areas.

[0009] By “ablating” it is meant removing material, for example without limitation, by chemical etching, mechanical engraving.

[0010] Preferably, the surface of the mould is ablated using laser engraving.

[0011] Preferably, at one least one area of the surface of the mould is ablated with a first pattern at a first depth, and at least one other area of the surface of the mould is ablated with a second pattern at a second depth.

[0012] Preferably, the first depth is approximately 0.06mm.

[0013] Preferably, the second ablation depth is approximately 0.03mm.

[0014] Preferably, the ink comprises a liquid polymer with a colour pigment.

[0015] Preferably, the liquid polymer is a polyolefin.

[0016] According to a second aspect of the invention, there is provided a method of manufacturing a plastic item using the mould of the first aspect, wherein the method comprises: selecting a base polymer and adding a colour pigment complimentary the colour of the ink; injecting the base polymer into the mould; and utilising the mould in a rotational moulding process. BRIEF DESCRIPTION OF DRAWINGS

[0017] Preferred embodiments of the invention will now be described by way of example only and with reference to the figures, in which:

[0018] Figure 1 is a close up view of a mould surface ablated in accordance with the invention;

[0019] Figure 2 is a close-up view of the mould surface of figure 1 with ink applied in accordance with the invention; and

[0020] Figure 3 us a close-up view of the surfacer of a plastic item produced from the mould of the invention. DETAILED DESCRIPTION OF THE INVENTION

[0021] The present invention relates to a method of creating or adapting a mould for use in a rotational moulding process to produce plastic item, for example, an item of furniture.

[0022] The invention also relates to a method of producing plastic items, for example, furniture, using the mould and the rotational moulding process.

[0023] The mould is adapted or created to produce a surface finish to the plastic item. Specifically, the described embodiment teaches how to make a wood effect surface finish. Preferably, the surface finish is textured so to feel like the product is made from wood as well as looking like it is made from wood.

[0024] Primarily, the method consists of creating a suitable mould prior to undergoing the manufacturing process for producing the plastic item. The mould created is suitable for use in a rotational moulding process. It may though be suitable for use in other manufacturing processes involving plastic, for example as a mould in plastic injection manufacturing processes, where a surface finish to the item manufactured is desired.

[0025] The first step of the method is to create ablations in the surface of the mould through laser engraving. The engraving provides distinct patterned areas to imitate vein and grain effects of wood.

[0026] The second step of the method is to apply an ink to the surface of the mould to fill the ablations.

[0027] Agranulated polymer is then placed in the mould and the mould is then used in a rotational moulding process.

[0028] The Applicant found that the depth of the ablations had a direct correlation to the depth of colour of the surface finish of the product formed.

[0029] In order to imitate the wood effect as closely and realistically as possible, the Applicant conducted a series of detailed experiments to establish the optimal depths of the ablations. The results of which are shown in the table below: ABLATION DETAIL FEEDBACK 0.06mm veins + 0.03mm grain Wood effect with the most realistic appearance 0.03mm veins + 0.03mm grain Not enough colour variation 0.05mm veins + 0.05mm grain Deeper colour but not enough variation 0.04mm veins + 0.03mm grain Veins too shallow 0.025mm veins + 0.025mm grain Did not hold ink well, faint appearance, ink became difficult to remove with repeated tool use wherein the millimetre value refers to laser engrave depth.

[0030] The Applicant concluded that two engraving depths, being 0.06mm for the vein appearance and 0.03mm for the grain appearance produced the most realistic finish. It is though appreciated that the perceived realism of the effect is subjective and so other depths and depth variations may be selected.

[0031] The Applicant also concluded that the variation in depth between the veins and the grain created a subtle tonal effect, where deeper engravings appeared richer and colour, whilst shallower engravings provided a lighter tone. The contrast enhanced the overall realism, resulting in a wood-like appearance and texture that appeared and felt both natural and visually appealing.

[0032] Further, the depth of the engraving was carefully selected to ensure that cleaning of the surface for infection control was not compromised which is particularly important if the items are to be used in a mental health environment.

[0033] An example of the mould surface being engraved at first and second depths imitating wood veining and wood graining respectively is shown in figure 1.

[0034] Having established the optimal depths of the ablations of in the mould surface, the Applicant turned to colour combinations that provided the most realistic wood effect appearance.

[0035] Avariety of trials were conducted to explore colour variations. It was found that a wood appearance, imitating for example oak, walnut or grey wood are not achieved using a single block colour but a rather a combination of colour tones.

[0036] To this end, the Applicant achieved multiple colour tones by selecting an ink of a first colour and a base polymer with a pigment of a second colourwhich compliments the ink colour. The base polymer is one suitable for producing items such as furniture using rotational moulding methods and could be, for example polyethylene. Alternative suitable polymeric materials may include, without limitation, polypropylene, polyamide, polycarbonate or polyvinyl chloride.

[0037] It was found that the ink interacts with the base polymer to provide a multi-tone colour finish. The Applicant conducted a series of detailed experiments to establish different colour combinations. The results of which are shown in the table below: BASE POLYMER COLOUR INK COLOUR Greywood (Pantone 406C) Pantones 409C, 7530U, 409C Walnut (Pantone 18-1112 TPX)) Pantones 161C, 8007, 8011 Beige (Pantone 14-1118 TPX) Pantones 7505C, 7507C Birch (Pantone 7506C or Pantone 2309C) Pantone 726C

[0038] The method of creating a mould will now be explained. Whilst reference is to “creating” a mould, it could also be the case that a pre-made mould maybe adapted for the purposes of the invention if the mould surface of the mould has not already been engraved or etched or is otherwise uneven.

[0039] Firstly, the surface of the mould is laser engraved to the provide the wood effect patterns. As described above, to provide an optimal wood effect, the surface is first engraved with a vein pattern, at a depth of approximately 0.06mm, and then engraved with a second grain pattern at a depth of approximately 0.03mm.

[0040] The selected ink is then applied evenly over the surface using a suitable applicator such as, for example a squeegee. Preferably, the ink is applied in a single fluid motion.

[0041] Excess ink is then scraped off the surface, also with the squeegee, in a single fluid motion so that ink remains only within the engraved pits.

[0042] The surface of the tool may be further cleaned using a cloth or rag.

[0043] An example of the mould surface with the ablations filled with ink is shown in figure 2.

[0044] Once the surface is cleaned and ink is only within the engraved pits of the surface, the mould is closed and the appropriate shot weight of the base polymer with selected colour pigment is added.

[0045] The mould is then placed into a rotational moulding tool to produce the product. As ink encapsulation is achieved at surface temperatures above the melting temperature of polyolefin the ink becomes integral to the product and cannot be removed.

[0046] An example of the surface finish of the product is shown in figure 3.

[0047] The mould is designed to be compatible with electrically heated tooling, ensuring consistent flat surfaces to the product.

Claims

1. A method of producing a mould for use in a rotational moulding process, the method comprising the steps of:ablating at least one distinct area of the surface of the mould;applying an ink to the surface of the mould and cleaning the ink from the un-ablated areas of the mould surface to only leave ink within the distinct ablated areas.

2. A method according to claim 1, wherein the surface of the mould is ablated using laser engraving.

3. A method according to claim 2, wherein at one least one area of the surface of the mould is ablated with a first pattern at a first depth, and at least one other area of the surface of the mould is ablated with a second pattern at a second depth.

4. A method according to claim 3, wherein the first depth is approximately 0.06mm.

5. A method according to claim 4, wherein the second ablation depth is approximately 0.03mm.

6. A method accordingtoany preceding claim, wherein the ink comprises a liquid polymer with a colour pigment.

7. A method according to claim 6, wherein the liquid polymer is a polyolefin.

8. A method of manufacturing a plastic item using the mould of any one of claims 1 to 7, wherein the method comprises:selecting a base polymer and adding a colour pigment complimentary the colour of the ink;injecting the base polymer into the mould; andutilising the mould in a rotational moulding process.

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