WO2015123812A1

WO2015123812A1 - An apparatus comprising injection molded thermoplastic and a method

Info

Publication number: WO2015123812A1
Application number: PCT/CN2014/072206
Authority: WO
Inventors: Rob THOMPSON; Nigel DUNLEA; Kairong LIAO; Yi Yang; Chuanhua CHIANG
Original assignee: Nokia Technologies Oy; Nokia (China) Investment Co., Ltd.
Priority date: 2014-02-18
Filing date: 2014-02-18
Publication date: 2015-08-27
Also published as: EP3108724A1; EP3108724A4

Abstract

An apparatus comprising: a body comprising injection molded semi-crystalline thermoplastic comprising a first amorphous portion that defines at least an exterior surface of the body and a second crystalline portion that defines at least an interior of the body; wherein the first amorphous portion comprises interstitial spaces and wherein a surface texture of the exterior surface of the body is determined by exposed interstitial spaces.

Description

AN APPARATUS COMPRISING INJECTION MOLDED THERMOPLASTIC

AND A METHOD TECHNOLOGICAL FIELD

Embodiments of the present invention relate to an apparatus comprising injection molded thermoplastic and a method. BACKGROUND

Engineering plastics are often used for forming injection molded apparatus such as housing components for electronic devices. The molded engineering plastic may not, however, provide a desired surface texture to a user.

A solution to this problem has been to apply an elastomer coating to a rigid substrate of molded engineering plastic. The elastomer coating provides a 'soft-touch' exterior.

BRIEF SUMMARY

According to various, but not necessarily all, embodiments of the invention there is provided an apparatus comprising: a body comprising injection molded semi-crystalline thermoplastic comprising a first amorphous portion that defines at least an exterior surface of the body and a second crystalline portion that defines at least an interior of the body; wherein the first amorphous portion comprises interstitial spaces and wherein a surface texture of the exterior surface of the body is determined by exposed interstitial spaces. According to various, but not necessarily all, embodiments of the invention there is provided a method comprising: enabling slower solidification of injected plastic within a mold to produce a core of crystalline plastic; enabling faster solidification of injected plastic adjacent the mold to produce a skin of amorphous plastic; ejecting the molded plastic;

and polishing an exterior surface of the molded plastic to create a surface texture determined by exposed interstitial spaces of the amorphous plastic. According to various, but not necessarily all, embodiments of the invention there is provided examples as claimed in the appended claims.

BRIEF DESCRIPTION For a better understanding of various examples that are useful for understanding the brief description, reference will now be made by way of example only to the accompanying drawings in which:

Fig 1 illustrates an example of an apparatus that has a body comprising injection molded semi-crystalline thermoplastic;

Fig 2 illustrates an example of an apparatus that has a body comprising injection molded semi-crystalline thermoplastic that has an exterior amorphous portion comprising exposed interstitial spaces;

Fig 3 illustrates an example of an apparatus that has a body comprising injection molded semi-crystalline thermoplastic that has an exterior amorphous portion comprising cross-linked polymer chains;

Fig 4 illustrates an example of an injection molding system;

Fig 5 illustrates an example of a method for manufacturing the apparatus previously described in relation to Figs 1 , 2 or 3;

Fig 6 illustrates operational parameters of the injection molding system; and

Fig 7 illustrates an example of an exterior housing for an electronic device that has a body comprising injection molded semi-crystalline thermoplastic that has an exposed exterior amorphous portion comprising exposed interstitial spaces and which is used without an over- coating. DETAILED DESCRIPTION

The following description describe some examples of an apparatus 2 and also an example of a method 200 for manufacturing an apparatus 2. The apparatus 2 at least in some examples has a rigid 'soft-touch' exterior provided by a polished exterior surface 22 of a first amorphous portion 12 rather than by application of an elastomer coating to a rigid substrate. Such a rigid 'soft-touch' apparatus 2 is a single component that has, as technical effect, both an exterior texture similar to an elastomer and has the rigidity of an engineering plastic.

Fig 1 illustrates an example of an apparatus 2. The apparatus 2 has a body 20 comprising injection molded semi-crystalline thermoplastic 10. The injection molded semi-crystalline thermoplastic 10 comprises a first amorphous portion 12 that defines at least an exterior surface 22 of the body 20 and a second crystalline portion 14 that defines at least an interior 24 of the body 20.

Fig 2 illustrates a schematic illustration of injection molded semi-crystalline thermoplastic 10 comprising a first amorphous portion 12 that defines at least an exterior surface 22 of the body 20 and a second crystalline portion 14 that defines at least an interior 24 of the body 20.

The first amorphous portion 12 comprises interstitial spaces 30. A surface texture of the exterior surface 22 of the body 20 is determined by exposed interstitial spaces 32 at a polished exterior surface 22 of first amorphous portion 12. Fig 3 illustrates a schematic illustration of injection molded semi-crystalline thermoplastic 10 comprising a first amorphous portion 12 that defines at least an exterior surface 22 of the body 20 and a second crystalline portion 14 that defines at least an interior 24 of the body 20.

In some but not necessarily all examples, the injection molded semi- crystalline thermoplastic 10 comprises polarized polymer chains 40 that can cross-link via Van der Waals forces. The first amorphous portion 12 may be a non-annealed 'frozen' amorphous state of the thermoplastic 10. The polymer chains 30 may be randomly arranged and cross-linked. This results in a high configurational entropy. Voids formed between the cross-linking polymer chains 30 form the interstitial spaces 30. A surface texture of the exterior surface 22 of the body 20 is determined by exposed interstitial spaces 32 at a polished exterior surface 22 of first amorphous portion 12.

The interstitial spaces 32 are distributed throughout the first amorphous portion 12 which may consequentially be described as micro-porous.

The second crystalline portion 14 may be an annealed 'frozen' crystalline state of the thermoplastic 10. The polymer chains 30 are ordered and may be aligned. This results in a low configurational entropy. Voids are not formed between the polymer chains 30 and there are none or fewer/smaller interstitial spaces 30.

The first amorphous portion 12 may therefore have a higher proportion of cross-linking polymer chains 40 and a lower proportion of aligned polymer chains 40 than the second crystalline portion 14. The second crystalline portion 14 forms a core of the injection molded semi-crystalline thermoplastic 10 being entirely surrounded by a skin of the first amorphous portion 12. In the preceding examples illustrated in Figs 1 , 2 and 3, the injection molded semi-crystalline thermoplastic 10 may be an engineering thermoplastic.

The thermoplastic 10 may be selected to have a low-rate of cystallinity.

The injection molded semi-crystalline thermoplastic 10 may have a Vicat softening point greater than 100°C.

The first amorphous portion 12 may have an acceptable hardness according to IS0518. For example, it may have no visible scratches at a load of 3N using a 0.75mm tip diameter hardness test pencil.

The body 29 may have a stiffness in the range 50-70MPa. The injection molded semi-crystalline thermoplastic 10 may be homopolymer.

The injection molded semi-crystalline thermoplastic may comprise or consist of acetal polymer. For example, the injection molded semi- crystalline thermoplastic may comprise or consist of polyoxymethylene (POM).

The second crystalline portion 14 will typically have a greater density than the first amorphous portion 12 and will become flexible at a higher temperature than the first amorphous portion 12. The second crystalline portion 14 may become liquid over a narrow temperature band at its melting temperature.

Fig 4 illustrates an example of an injection molding system 100. The system 100 comprises a cylinder 102 narrowing to a nozzle 104, an Archimedes screw 106 for injecting the thermoplastic 10 (not illustrated), a mold 1 10 configured to receive the injected thermoplastic 10 and a pressure system 120 for applying pressure to the mold 1 10 during the cooling of the thermoplastic 10.

The cylinder 102 has a cylinder temperature T1 . The nozzle 104 has a nozzle temperature T2. The mold 1 10 has a mold contact temperature T3. The pressure system 120 applies a molding pressure P. Fig 5 illustrates an example of a method 200 for manufacturing the apparatus 2 previously described in relation to Figs 1 , 2 or 3.

The method comprises: slow solidification 202 of injected plastic 10 within a mold 1 10 to produce a core 24 of crystalline plastic 14 and fast solidification of injected plastic 10 adjacent the mold 1 10 to produce a skin of amorphous plastic 12;

ejecting 206 the molded plastic 10 from the mold 1 10;

and polishing 208 an exterior surface 22 of the molded plastic 10 to create a surface texture determined by exposed interstitial spaces 32 of the amorphous plastic 12.

Slow solidification 202 of injected plastic 10 within a mold 1 10 to produce a core 24 of crystalline plastic 14 and fast solidification of injected plastic adjacent the mold to produce a skin of amorphous plastic, are enabled by using non-standard operating parameters of the injection molding system 100. In the method 200, as schematically illustrated in Fig 6, the cylinder temperature T1 and nozzle temperature T2 are unusually high compared to conventional operation of an injection molding system 100, and the mold contact temperature T3 and the applied molding pressure P are unusually low compared to conventional operation of an injection molding system 100.

The thermoplastic 10 is injected as a molten liquid, it may be at a temperature at least 10% above its melting point temperature.

A large temperature difference between the molten plastic 10 and the mold 1 10 results in rapid solidification of the liquid plastic 10 adjacent the mold 1 10 forming the first amorphous portion 12, whereas the higher plastic temperature results in slower solidification at the mold core forming the second crystalline portion 14.

In some but not necessarily all examples, the injected thermoplastic 10 may comprise or consist of polyoxymethylene (POM).

The melting temperature of polyoxymethylene (POM) Tm is around 180°C.

In the method 200, as schematically illustrated in Fig 6, the cylinder temperature T1 and nozzle temperature T2 are unusually high compared to conventional operation of an injection molding system 100. They may, for example be, 210°C. This is over 30°C (~ 1 8%) above the melting temperature of polyoxymethylene (POM) Tm. The mold contact temperature T3 and the applied molding pressure P are unusually low compared to conventional operation of an injection molding system 100. The mold contact temperature T3 may be 80°C. The applied molding pressure P may be 80MPa.

There is a large temperature difference of over 120°C between the temperature (210 °C) of the molten plastic 10 and the temperature (80 °C) of the mold 1 10. This results in rapid solidification of the liquid plastic 10 adjacent the mold 1 10 forming the first amorphous portion 12.

Referring back to Fig 5, polishing an exterior surface 22 of the molded plastic 10 to create a surface texture determined by exposed interstitial spaces 32 of the amorphous plastic 12 may comprise mechanical polishing.

For example, the ejected molded plastic body 20 may be tumbled in a barrel with plastic grinding stones comprising, for example, unsaturated polymer resin with 600 mesh sand and calcium carbonate particles for 1 hour at 30 revolutions per minute. The plastic grinding stones may be cone-shaped or frustoconically shaped plastic media.

The resulting direct product of the method 200 is the apparatus 2 which has a 'soft-touch' finish without having any additional coatings applied.

As illustrated in Fig 7, the apparatus 2 may be an exterior housing 302 for an electronic device 300 which is used without the addition of an additional coating.

Examples of suitable electronic device 300 include but are not limited to personal, mobile electronic devices and accessories for such devices. Such devices may, in some example, be hand-portable that is, sized to be carried within the palm of a user's hand.

Examples of suitable electronic device 300 include but are not limited laptop computers, tablet computers, computer peripheral devices, mobile cellular telephones, personal media players.

Where a structural feature has been described, it may be replaced by means for performing one or more of the functions of the structural feature whether that function or those functions are explicitly or implicitly described.

As used here 'module' refers to a unit or apparatus that excludes certain parts/components that would be added by an end manufacturer or a user. The apparatus 2 may be a module.

The term 'comprise' is used in this document with an inclusive not an exclusive meaning. That is any reference to X comprising Y indicates that X may comprise only one Y or may comprise more than one Y. If it is intended to use 'comprise' with an exclusive meaning then it will be made clear in the context by referring to "comprising only one.." or by using "consisting".

In this brief description, reference has been made to various examples. The description of features or functions in relation to an example indicates that those features or functions are present in that example. The use of the term 'example' or 'for example' or 'may' in the text denotes, whether explicitly stated or not, that such features or functions are present in at least the described example, whether described as an example or not, and that they can be, but are not necessarily, present in some of or all other examples. Thus 'example', 'for example' or 'may' refers to a particular instance in a class of examples. A property of the instance can be a property of only that instance or a property of the class or a property of a sub-class of the class that includes some but not all of the instances in the class. Although embodiments of the present invention have been described in the preceding paragraphs with reference to various examples, it should be appreciated that modifications to the examples given can be made without departing from the scope of the invention as claimed.

Features described in the preceding description may be used in combinations other than the combinations explicitly described.

Although functions have been described with reference to certain features, those functions may be performable by other features whether described or not.

Although features have been described with reference to certain

embodiments, those features may also be present in other embodiments whether described or not.

Whilst endeavoring in the foregoing specification to draw attention to those features of the invention believed to be of particular importance it should be understood that the Applicant claims protection in respect of any patentable feature or combination of features hereinbefore referred to and/or shown in the drawings whether or not particular emphasis has been placed thereon.

Claims

WHAT IS CLAIMED IS:

1. An apparatus comprising:

a body comprising injection molded semi-crystalline thermoplastic comprising a first amorphous portion that defines at least an exterior surface of the body and a second crystalline portion that defines at least an interior of the body;

wherein the first amorphous portion comprises interstitial spaces and wherein a surface texture of the exterior surface of the body is determined by exposed interstitial spaces.

2. An apparatus as claimed in claim 1 , wherein the second crystalline portion has a greater density than the first amorphous portion.

3. An apparatus as claimed in claim 1 or 2, wherein the second crystalline portion becomes flexible at a higher temperature than the first amorphous portion.

4. An apparatus as claimed in any preceding claim, wherein the second crystalline portion becomes liquid over a narrow temperature band comprising a melting temperature.

5. An apparatus as claimed in any preceding claim wherein the second crystalline portion has a lower configuration entropy than the first amorphous portion.

6. An apparatus as claimed in any preceding claim, wherein the first amorphous portion has a higher proportion of cross-linking polymer chains and a lower proportion of aligned polymer chains than the second crystalline portion.

7. An apparatus as claimed in any preceding claim, wherein the injection molded semi-crystalline thermoplastic is an engineering thermoplastic.

8. An apparatus as claimed in any preceding claim, wherein the injection molded semi-crystalline thermoplastic is homopolymer.

9. An apparatus as claimed in any preceding claim, wherein the injection molded semi-crystalline thermoplastic has a Vicat softening point greater than 100°C.

10. An apparatus as claimed in any preceding claim, wherein the injection molded semi-crystalline thermoplastic comprises acetal polymer.

1 1 . An apparatus as claimed in any preceding claim, wherein the injection molded semi-crystalline thermoplastic comprises polyoxymethylene.

12. An apparatus as claimed in any preceding claim, wherein the first amorphous portion is porous.

13. An apparatus as claimed in any preceding claim, wherein the first amorphous portion is polished.

14. An apparatus as claimed in any preceding claim, wherein the first amorphous portion has no visible scratches at a load of 3N using a 0.75mm tip diameter hardness test pencil.

15. An apparatus as claimed in any preceding claim, wherein the body has a stiffness in the range 50-70MPa.

16. A housing of an electronic device comprising the apparatus as claimed in any preceding claim.

17. A method comprising:

enabling slower solidification of injected plastic within a mold to produce a core of crystalline plastic;

enabling faster solidification of injected plastic adjacent the mold to produce a skin of amorphous plastic;

ejecting the molded plastic;

and polishing an exterior surface of the molded plastic to create a surface texture determined by exposed interstitial spaces of the amorphous plastic.

18. A method as claimed in claim 17, wherein the plastic is selected to have a low-rate of cystallinity.

19. A method as claimed in claim 17 or 18 wherein the plastic is injected at a temperature at least 30°C above its melting point.

20. A method as claimed in any of claims 17 to 19, wherein the plastic is injected as a molten liquid at a temperature at least 10% above its melting point temperature.

21 . A method as claimed in any of claims 17 to 20, wherein faster solidification of injected plastic is enabled by maintaining a mold temperature of less than 90°C.

22. A method as claimed in any of claims 16 to 21 , wherein enabling slower solidification of injected plastic within a mold and enabling faster solidification of injected plastic adjacent the mold is achieved by establishing a temperature gradient between the mold and the injected plastic of greater than 100°C.

23. A method as claimed in any of claims 17 to 22, wherein slower solidification of injected plastic is enabled by exerting a reduced pressure of 80MPA on the injected plastic.

24. A method as claimed in any of claims 17 to 23, wherein polishing an external surface of the molded plastic comprises mechanical polishing.

25. A method as claimed in claim 24, wherein mechanical polishing comprises tumbling the apparatus with sand and calcium carbonate.

26. A method as claimed in any of claims 17 to 25, comprising producing as a direct product an exterior housing for an electronic device which is used without the addition of an additional coating.

27. A system comprising means for performing the method of any of claims 17 to 26.