GB2197881A

GB2197881A - Heat resistant vessel and process for manufacturing same

Info

Publication number: GB2197881A
Application number: GB08723143A
Authority: GB
Inventors: Nobuo Kanazawa; Hisamitsu Kakiyama; Hiroshi Sugimoto
Original assignee: Denki Kagaku Kogyo KK
Current assignee: Denka Co Ltd
Priority date: 1986-10-03
Filing date: 1987-10-02
Publication date: 1988-06-02
Anticipated expiration: 2007-10-02
Also published as: GB8723143D0; GB2197881B; AU7932787A; AU587913B2

Abstract

A heat resistant vessel having an improved colorant contamination resistance is made of a thermoplastic polyester resin having a crystallinity of 20% or more by forming an inorganic coating layer comprising a silicon compound or a metal oxide-containing silicon compound of at least one of an oxide and hydroxide of mainly silicon on a surface of the polyester resin. Formation of the inorganic coating layer may be from a metal alcoholate of mainly silicon or colloidal polysiloxane compounds having an acyloxy group and does not lower the heat resistance of the polyester resin having such a crystallinity. The applied materials may be heated at 70-220 DEG C. The metal of said metal oxide-containing silicon compound may be zirconium or titanium. The coating layer may be applied to a pre-formed vessel or to a sheet of thermoplastic polyester resin which is subsequently formed into a vessel prior to forming the final inorganic coating. The applied coating solution may contain an inorganic filler such as titanium oxide, zirconium silicate, nickel, copper oxide, chromium oxide manganese oxide or alumina.

Description

HEAT RESISTANT VESSEL AND PROCESS FOR tANUFACTURING SAME The present invention relates to a heat resistant vessel and a process for manufacturing the same. More specifically, the present invention relates to a heat resistant.asscel.havin^. > n excellent cnntamina- tion resistance when containing, for example, food, in which the heat resistant vessel comprises a thermoplastic polyester resin body and an inorganic coating layer on at least the inner surface of the body, the inorganic coating layer comprising a silicon compound or a metal oxide-containing silicon compound of oxide and/or hydroxide of mainly silicon.

Heretofore, methods for manufacturing a heat resistant article have involved the thermoforming of a sheet of a thermoplastic polyester resin and giving the resin a high crystallinity (for example, Japanese Examined Patent Publication (Kokoku) No. 44-5108, Japanese Unexamined Patent Publication (Kokai) No. 50-72950, and U.S. Patent No. 3,960,807).

However, vessels of a thermoplastic polyester resin having a high crystallinity have a drawback in that, if certain food, such as curry, having a color, is contained in the vessel and heated in an oven or microwave oven, a colorant in the food is transferred to the material of the vessel and adhered on the inner surface of the vessel, and this color is difficult to remove by cleaning or washing. Therefore, because of this difficulty in removing the contamination from the vessel, there is a reluctance to repeatedly use the vessel.

U.S. Patent No. 3,986,997 issued on October 19, 1976, discloses a coating composition comprising colloidal silica and a partial condensate of a silanol, to provide a transparent abrasion-resistant coating.

The composition of U.S. Patent No. 3,986,997 is different from the composition of a starting coating material used in the process of the present invention, in that it provides a coating including an organic group, and thus having a low resistance to both heat and contamination.

The present invention is intended to solve the above problem and provide a heat resistant vessel having an excellent heat and contamination resistance, by forming an inorganic coating layer of a silicon compound or a metal oxide-containing silicon compound of oxide and/or hydroxide of mainly silicon on at least the inner surface of a thermoplastic polyester resin vessel without changing the properties of the polyester resin having a high crystallinity.

Thus, the present invention provides a heat resistant vessel comprising: a body of the vessel made of a thermoplastic polyester resin having a crystallinity of 20% or more, the vessel body having inner and outer surfaces; and an inorganic coating layer on at least the inner surface of the vessel body, the inorganic coating layer comprising one of a silicon compound and a metal oxide-containing silicon compound of at least one of oxide and hydroxide of mainly silicon The present invention also provides a process for producing a heat resistant vessel, comprising the steps of: preparing a body of the vessel made of a thermoplastic polyester resin, the vessel body having inner and outer surfaces; applying, at least on the inner surface of the vessel body, a solution of at least one of a metal alcoholate of mainly silicon and colloidal polysiloxane compounds having an alcoxyl group; and heating the resultant coating of the solution to form an inorganic coating layer comprising one of a silicon compound and a metal oxide-containing silicon compound of at least one of oxide and hydroxide of mainly silicon; wherein the resultant heat resistant vessel comprises the vessel body of a thermoplastic polyester resin having a crystallinity of 20% or more and the inorganic coating layer on at least the inner surface of the vessel body.

Figures 1 and 2 are sectional views of heat resistant vessels according to the present invention.

Figure 1 illustrates a heat resistant vessel in which an inorganic silicon compound coating layer 1 is formed on only the inner surface of a thermoplastic polyester resin body 2 having a high crystallinity.

Figure 2 illustrates a heat resistant vessel in which inorganic silicon compound coating layers 1 are formed on both inner and outer surfaces of a thermoplastic polyester resin body 2 having a high crystallinity.

The resin used for the thermoplastic polyester resin body 2 has a crystallinity of 20% or more, preferably in a range of 20% to 50%, since in this preferable range, the shock resistance of the resin is not remarkably decreased. The crystallinity can be represented by a value of a hundred times the value X obtained from the formula: + = A + play , wherein 3 P Pc Pa Pc = 1.47 g/cm3, Pa = 1.331/cm , and P is a density of a thermoplastic polyester resin used.

The thermoplastic polyester resin is a synthetic resin having an ester bond of a reaction product from a saturated polybasic acid such as phthalic acid, isophthalic acid, terephthalic acid, maleic acid or succinic acid, and a polyhydric alcohol such as ethylene glycol, diethylene glycol, glycerol, trimethyl propane, or l-4-cyclohexanedimethanol.

The thermoplastic polyester resin may contain other synthetic resins and additives such as a nucleating agent, a stabilizer, a lubricant, and a pigment. When the resin contains such other synthetic resins or additives, the crystallinity of the resin calculated from the above formula should be corrected to allow for the density of the resin which is changed by addition of the other resins or additives.

The layer thickness of the vessel body of the polyester resin is not limited, depending on usage, but is preferably in a range such that the vessel body is not easily deformed, for example, in a range of 100 um to 2000 vm.

The inorganic coating layer formed on the vessel body of the polyester resin according to the present invention comprises one of a silicon compound and a metal oxide-containing silicon compound of at least one of oxide and hydroxide of mainly silicon (hereinafter simply referred as "a silicon compound"). The inorganic coating layer is obtainable from at least one of a metal alcoholate as represented by the following formulae, and colloidal polysiloxane compounds, by a reaction thereof as exemplified by the following specific example.

M(OR) (1) MloR) (OR) (2) n m RM(OR')n-l (3) wherein M is silicon, M' is a metal other than silicon such as titanium or zirconium, R is independently one of hydrogen and an alkyl group having 1 to 8 carbon atoms, R' is independently an alkyl group having 1 to 8 carbon atoms, the metal alcoholate represented by the formula (1), (2) or (3) having at least one alcoxyl group, n is an integer corresponding to a valence of M, and m is an integer corresponding to a valence of M'.

Specific example of the reaction: SiÒ(CH3)2CHj4 + 4H2O Si (OH)4 + 4(CH3)2CHOH Si (OH)4 + six2 + 2H2O The amount of metal t5' such as titanium or zirconium is not particularly limited, but less than 50 moles of the metal M' is preferable since a higher amount of the metal M' makes the cost increased.

The colloidal polysiloxane compounds as a starting material of the inorganic coating layer are colloidal particles which have been activated by treating well-known colloidal silica to produce alcoxyl and/or hydroxyl groups at the ends of polysiloxane, in such a manner that the activated colloidal polysiloxane compounds react in the same way as the metal alcoholates represented by the formulae (1), (2) and (3). The particle size of the colloidal particles ranges from 0.1 um to 1.0 um. The thus-obtainable colloidal polysiloxane compounds can be represented, for example, by the following formula:

wherein R is'independently one of hydrogen and an alkyl group having 1 to 8 carbon atoms, and at least a part of R is an alcoxyl group.Although the skeleton of the polysiloxane compound in the box in formula (4) represented schematically in two-dimensional form, it can be linear or in three dimensions.

In the starting material of the inorganic coating layer, the ratio of the metal alcoholate to the colloidal polysiloxane compounds is not limited, but is preferably in a range from 82:18 to 50:50 by weight. Too small an amount of colloidal polysiloxane compounds will generally make it difficult to obtain a thicker inorganic coating layer, and too high an amount of colloidal polysiloxane compounds may cause pores or cracks in the inorganic coating layer.

The starting coating material of the inorganic coating layer used in the present invention is a water-containing alcohol solution of a metal alcoholate and/or colloidal polysiloxane compounds.

The coating material used in the present invention may further contain additives such as an inorganic filler of, e.g., titanium oxide, zirconium silicate, nickel, copper oxide, chromium oxide, manganese oxide, alumina, etc., a colorant, a diluent, an accelerator and the like. The diluent may be isopropyl alcohol, ethyl cellosolve, etc. The accelerator is not particularly limited as long as it accelerates the hydrolysis of the metal alcoholate or polysiloxane compounds, and various organic acids are suitable in the present invention.

The inorganic coating layer can be formed on the thermoplastic polyester resin as shown below: After the polyester resin is cleaned by an alkali cleaning solution, etc., a starting solution of the inorganic coating layer is applied on a surface of the polyester resin by, e.g., brushing, spraying, dipping, etc., and then heated in an oven or a furnace at a temperature of 700C to 2200C, preferably 1200C to 2000C, more preferably 160"C to 1800C, for 5 to 30 minutes. This heating causes the reaction described above, and thus an inorganic coating layer of a silicon compound is formed on the resin If the above heating or drying temperature is lower than 700C, the time required for drying is undesirably long.

If the temperature is higher than 2200C, the speed of drying of the coating is increased such that bubbling may occur in the coating layer to form pin holes and, further, the crystallization of the resin is undesirably increased, to render the vessel useless. Thus, the heating condition of 160"C to 1800C for 5 to 30 minutes used in the present invention is used specifically for a heat resistant article of a thermoplastic polyester resin having a crystallinity of 20% or more, and gives a high productivity of the inorganic coating layer in cooperation with the selection of specific starting material of the coating.

The layer thickness of the silicon compound coating layer is not particularly limited, as long as the formation of pin holes does not occur, but a layer thickness of 2 to 20 um preferable from the viewpoint of economy. In the process according to the present invention, a relative thick inorganic coating layer is easily formed. One reason for this is that the substrate of the thermoplastic resin having a crystallinity of 20% or more and the volumetric change of the inorganic coating layer during the formation thereof are extremely compatible, and thus easily cooperate to form a thick coating layer.

The present invention is further characterized in that, by adding an inorganic filler such as titanium oxide, a further thicker coating layer is easily formed.

The manufacture of the heat resistant vessel according to the present invention can be carried out as follows: A thermoplastic polyester resin sheet previously containing a nucleating agent, etc., is thermoformed in a mold previously kept at a raised temperature in a vacuum forming, air-pressure forming or vacuum and air-pressure forming machine, to obtain a vessel body of a thermoplastic polyester resin having a crystallinity of 20% or more. On at least the inner surface of the vessel body, which will be in contact with the contained food, an inorganic coating layer of a silicon compound is formed. Thus, a heat resistant vessel having a good contamination resistance is obtained. Alternatively, a raw material of an inorganic silicon compound is first coated on a raw sheet of a thermoplastic polyester resin.The resultant resin sheet with the coating layer is heated and then formed by a vacuum forming, airpressure forming or vacuum and air-pressure forming machine to obtain a heat resistant vessel. Further alternatively, a raw material of an inorganic silicon compound is first coated on a raw sheet of a thermoplastic polyester resin, which is then formed by a vacuum, air-pressure, or vacuum and air-pressure forming machine, followed by heating to obtain a heat resistant vessel.

The thus obtained coating layer comprising oxide and/or hydroxide of mainly silicon, formed on a thermoplastic polyester resin body according to the present invention, is an inorganic layer and does not substantially contain organic groups. As a result, the coating layer has a high hardness or abrasion resistance and a high heat resistance, and does not have an affinity with colorants in food, etc., and thus is particularly suitable for the purpose of the present invention, i.e., the provision of a heat resistant vessel having an excellent resistance to heat and to contamination from food.

In Figure 17 the heat resistant vessel has an inorganic silicon compound coating layer 1 on only the inner surface of the vessel body 2 of the resin. On the outside of the vessel body 2 of the resin, another different heat resistant resin layer, etc., may be laminated by adhesion, etc., optionally or if necessary.

Figure 2 illustrates 2 heat resistant vessel in which inorganic silicon compound coating layers 1 are formed on both the inner and outer surfaces of the vessel body 2 of the resin.

The heat resistant vessel is used mainly for food and for cooking in an oven or a microwave oven, and is particularly effective for heating food containing colorant.

In the following examples, the estimations of the heat resistance and the food colorant contamination resistance of a vessel are carried out as shown below: Heat resistance: A vessel is placed in an oven at 180"C for 10 minutes, the vessel is then removed from the oven and deformation of the vessel is observed by the naked eye.

Excellent: No deformation No good: Deformation Food colorant contamination resistance: A vessel containing curry roux is heated in a microwave oven for 3 minutes. The content, i.e., the curry roux is then removed and the vessel is washed with water, and the coloration of the vessel is observed by the naked eye.

Excellent: No transfer of colorant No good: Transfer of colorant Examples 1 to 3 A thermoplastic polyester resin PET 5132 (by Eastman Chemical) was extruded to form a sheet having a thickness of 500 um. This sheet was thermoformed by a vacuum and air-pressure forming machine to obtain a vessel body having the dimensions 120 x 60 x 20 mm (depth of 20 mm), the vessel body having a high crystallinity. The vessel body was cleaned by dipping the vessel body in a 5% aqueous solution of an alkali cleaning agent for aluminum PS-500A (by Shoei Kogyo K.K.) at room temperature for 1 hour, followed by washing with water and heat drying. Then, a metal alcoholate compound solution Glasca G90 (by K.K.Nippon Kenkyusho, having a solid content of 18%, which provides a coating layer mainly comprised of SiO2) was coated on the inner surface of the polyester resin vessel body by air spraying, followed by drying the coating at 1800C for 20 minutes to form an inorganic coating layer of a silicon compound having a thickness of 10 um.

The heat resistance and the food colorant contamination resistance of the vessels were estimated and good results were obtained. The results are shown in the following Table.

Example 4 A thermoplastic polyester resin similar to that in Example 1 was extruded to form a sheet having a thickness of 700 um, which was then formed into a vessel body having the dimensions 120 x 60 x 20 mm by a vacuum and air-pressure forming machine.

The procedures of Example 1 were then repeated, except that a metal alcoholate solution Glasca Gll0OA (by K.K. Nippon Kenkyusho having a solid content of 518 and a white color, which provides a coating layer mainly comprised of SiO2 and TiO2) was coated by air spraying with an Iwata W-71-type spray gun (by Iwata, nozzle 3 diameter 1.0 mm, pressure 200 kg/cm3).

The heat resistance and food colorant contamination resistance of the vessel were tested and good results were obtained. The results are shown in the following Table.

Example 5 The procedures of Example 1 were repeated except that a metal alcoholate compound solution Glasca G90 (K.K. Nippon Kenkyusho) was coated on the inner surface of a vessel body of a thermoplastic resin by a brush in 2 an amount of about 50 g/m2.

The results of the heat resistance and food colorant contamination resistance tests of the vessel were good.

The results are shown in the Table.

Example 6 The procedures of Example 1 were repeatea. The cleaned thermoplastic polyester resin vessel body was dipped in a solution of a metal alcoholate compound Glasca G90 (K.K. Nippon Kenkyusho), followed by drying at normal temperature for 6 hours. Then, the vessel body was dipped again in the same solution, followed by heating at 1800C for 30 minutes in an oven to form an inorganic silicon compound coating layer having a thickness of about 20 pm on the entire surfaces of the polyester resin vessel body.

The results are shown in Table.

Examples 7 and 8~(Comparative) A thermoplastic polyester resin of Example 1 was extruded to form a sheet having a thickness of 500 um.

From this sheet a vessel having a shape similar to that of Example 1 but without a coating layer was formed.

The heat resistance and food colorant contamination resistance of thus-obtained vessels were estimated and were found to be poor. The results are shown in the following Table.

Table Food Food colorant Crystallinity Heat contamination Example of polyester resistance resistance resin (%) 1 25 Excellent Excellent 2 32 Excellent Excellent 3 22 Excellent Excellent 4 26 Excellent Excellent 5 32 Excellent Excellent 6 42 Excellent Excellent 7* 16 No good No good 8* 21 Excellent No godd * Comparative examples As seen in the Table, according to the present invention, a heat resistant vessel having an improved food colorant contamination resistance can be obtained while retaining the heat resistance of the vessel of a thermoplastic polyester resin having a high crystallinity.

Claims

1. A heat resistant vessel comprising: a body of the vessel made of a thermoplastic polyester resin having a crystallinity of 20% or more, the vessel body having inner and outer surfaces; and an inorganic coating layer on at least the inner surface of the vessel body, the inorganic coating layer comprising a silicon compound or a metal oxidecontaining silicon compound of at least one of an oxide and hydroxide of mainly silicon.

2. A heat resistant vessel according to claim ii wherein the vessel body has a layer of thickness of 100 pm to 2000 pm.

3. A heat resistant vessel according to claim 1 or claim 2 wherein saidwpolyester resin has a crystallinity of 20% to 50%.

4. A heat resistant vessel according to any one of the preceding claims wherein said polyester resin further comprises additives such as a nucleating agent, a stabilizer, a lubricant and a pigment.

5. A heat resistant vessel according to any one of the preceding claims wherein said polyester resin further comprises a thermoplastic resin other than polyester resin.

6. A heat resistant vessel according to any one of the preceding claims wherein said metal oxide-containing silicon compound of the inorganic coating layer contains at least 50 mole% of silicon based on the total weight of the metal including silicon.

7. A heat resistant vessel according to any one of the preceding claims wherein said inorganic coating layer has a thickness of 2 pm to 20 pm.

8. A heat resistant vessel according to any one of the preceding claims wherein the metal of said metal oxidecontaining silicon compound is one of zirconium and titanium.

9. A heat resistant vessel according to any one of the preceding claims wherein said inorganic coating layer further includes an inorganic filler such as titanium oxide, zirconium silicate, nickel, copper oxide, chromium oxide, manganese oxide, and alumina.

10. A heat resistant vessel according to any one of the preceding claims wherein said inorganic coating layer further contains additives such as a colorant, a diluent and an accelerator.

11. A heat resistant vessel comprising: a body of the vessel made of a thermoplastic polyester resin having a crystallinity of 20% to 50%, the vessel body having inner and outer surfaces and a thickness of 100 pm to 2000 pm; and an inorganic coating layer on at least the inner surface of the vessel body, the inorganic coating layer comprising a silicon compound of at least one of oxide and hydroxide, the inorganic coating layer having a thickness of 2 pm to 20 pm.

12. A heat resistant vessel according to claim 1, for containing food and to be repeatedly used in a microwave oven without contamination from food.

13. A process for producing a heat resistant vessel, comprising the steps of: preparing a body of the vessel made of a thermoplastic polyester resin, the vessel body having inner and outer surfaces; applying, at least on the inner surface of the vessel body, a solution of at least one of a metal alcoholate of mainly silicon and colloidal polysiloxane compounds having an alcoxyl group; and heating the resultant coating of the solution to form an inorganic coating layer comprising a silicon compound or a metal oxide-containing silicon compound of at least one of an oxide and hydroxide of mainly silicon; wherein the resultant heat resistant vessel comprises the vessel body of a thermoplastic polyester resin having a crystallinity of 20% or more and the inorganic coating layer on at least the inner surface of the vessel body.

14. A process according to claim 13, wherein said metal alcoholate has one of the following formulae: M(OR)n (1) M(OR)n-M (OR)m (2) RM(OR'),-1 (3) wherein M is silicon, M' is a metal such as titanium and zirconium, R is independently one of hydrogen and an alkyl group having 1 to 8 carbon atoms, R' is independently an alkyl group having 1 to 8 carbon atoms, the metal alcoholates represented by the formulae 1, 2 and 3 having at least one alcoxyl group, nazis an integer corresponding to a valence of M , and m is an integer corresponding to a valence of M'.

15. A process according to claim 13, wherein said colloidal polysiloxane compounds are colloidal particles obtained by treating colloidal silica to have an alcoxyl group so that the colloid particles are activated.

16. A process according to any one of claims 13-15, wherein a ratio of said metal alcoholate to said colloidal polysiloxane compounds is in a range of 82:18 to 50:50 by weight.

17. A process according to any one of claims 13-16, wherein said solution of at least one of the metal alcoholate and the colloidal polysiloxane compound further includes an inorganic filler such as titanium oxide, zirconium silicate, nickel, copper oxide, chromium oxide, manganese oxide, and alumina.

18. A process according to any one of claims 13-17, wherein said solution of at least one of the metal alcoholate and the colloidal polysiloxane compounds further contains additives such as a colorant, a diluent and an accelerator.

19. A process according to any one of claims 13-18, wherein said coating of said solution of at least one of the metal alcoholate and the colloidal polysiloxane compounds is heated at a temperature of 700C to 220 C to form the inorganic coating layer.

20. A process according to any one of claims 13-19, wherein a thermoplastic polyester resin is thermoformed to obtain the vessel body of the polyester resin having a crystallinity of 20% or more, followed by application of the soultion of at least one of the metal alcoholate and the colloidal polysiloxane compound.

21. A process for producing a heat resistant vessel, comprising the steps of: preparing a thermoplastic polyester resin sheet; applying on at least one surface of the polyester resin sheet a solution of at least one of a metal alcoholate of mainly silicon and colloidal polysiloxane compounds having an alcoxyl group; forming a vessel of the polyester resin sheet with a coating of said at least one of the metal alcoholate and the colloidal polysiloxane compound; heating the vessel of the polyester resin sheet with the coating to form a vessel of the polyester resin sheet having a crystallinity of 20% or more with an inorganic coating layer on at least one surface of the polyester resin sheet, the inorganic coating layer comprising a silicon compound or a metal oxide-containing silicon compound of at least one of an oxide and hydroxide of mainly silicon.

22. A heat resistant vessel substantially as herein described and illustrated with reference to the accompanying drawings.

23. A process for producing a heat resistant vessel substantially as herein described and exemplified.