Method for internally coating a hollow glass body

Abstract

The present invention regards a method for internally coating a hollow glass body comprising the steps of: (a) applying on at least one internal surface of said hollow body at least one coating composition in form of liquid dispersion comprising at least one glass frit and at least one polymeric dispersing agent; (b) subjecting said internal surface comprising said coating composition to a thermal treatment, so as to obtain a vitrified coating layer.

Claims

1. Method for internally coating a hollow glass body comprising, in the following order: (a) applying by a spraying device, onto at least an internal surface of said hollow body, at least one coating composition, to obtain a coated glass body, wherein the coating composition is in the form of aqueous dispersion comprising at least one glass frit and at least one polymeric dispersing agent, said agent being present in such an amount that said composition has a thixotropic index lower than 200 second; said hollow body and said spraying device being in movement with respect to each other, said movement comprising keeping said hollow body rotating on itself during the application of said coating composition; and (b) subjecting said internal surface comprising said coating composition to a thermal treatment at a temperature in the range of 450-800 C., so as to obtain a vitrified coating layer, wherein said frit is present in the composition in a quantity comprised in the range 50-80% by weight with respect to the weight of the coating composition, wherein said polymeric dispersing agent is present in the composition in a quantity comprised in the range 1-20% by weight with respect to the weight of the liquid phase of said dispersion, and wherein said frit comprises, based on a total weight of said frit: SiO.sub.2 30-45%; Na.sub.2O 1-4%; P.sub.2O.sub.5 0-1%; CaO 2-6%; K.sub.2O 2-6%; TiO.sub.2 4-9%; ZnO 8-18%; BaO 0-2%; Bi.sub.2O.sub.3 2-6%; and B.sub.2O.sub.3 10-20%.

2. Method according to claim 1, wherein said at least one dispersing agent is a polycarboxylic thermoplastic resin.

3. Method according to claim 1, wherein said at least one dispersing agent is selected from among: a polyester resin, an acrylic resin, an amide resin and a vinyl resin.

4. Method according to claim 1 wherein said at least one dispersing agent is a cellulose resin.

5. Method according to claim 1, wherein said thixotropic index is lower than or equal to 100 seconds.

6. Method according to claim 1, wherein said thixotropic index is greater than or equal to 10 seconds.

7. Method according to claim 1, wherein said frit comprises at least one pigment.

8. Method according to claim 1, wherein said coating composition comprises at least one pigment dispersed in the liquid phase of said dispersion.

9. Method according to claim 1, wherein said coating composition has a linear thermal expansion coefficient (measured on the solid fraction) in the range 50-90.Math.10.sup.7 K.sup.1.

10. Method according to claim 1, wherein said coating composition has a viscosity in the range 1-50 Pa.Math.s.

11. Method according to claim 4, wherein said cellulose resin is a cellulose ether, a cellulose ester, or a mixture thereof.

12. Method according to claim 11, wherein said cellulose ether or ester has a degree of substitution in the range between 1-2.

13. Method according to claim 11, wherein said cellulose either or ester has a degree of substitution in the range between 0.5-2.2.

14. Method according to claim 1, wherein said thixotropic index is lower than or equal to 60 seconds.

15. Method according to claim 1, wherein said thixotropic index is greater than or equal to 30 seconds.

16. Method according to claim 1, wherein said coating composition has a linear thermal expansion coefficient (measured on the solid fraction) in the range 60-80.Math.10.sup.7 K.sup.1.

17. Method according to claim 1, wherein said coating composition has a linear thermal expansion coefficient (measured on the solid fraction) in the range 65-75.Math.10.sup.7 K.sup.1.

18. Method according to claim 1, wherein said coating composition has a viscosity in the range 5-30 Pa.Math.s.

19. Method according to claim 1, wherein said coating composition has a viscosity in the range 8-20 Pa.Math.s.

20. Method according to claim 1, wherein said frit is present in the composition in a quantity comprised in the range 55-70% by weight with respect to the weight of the coating composition.

21. Method according to claim 1, wherein said polymeric dispersing agent is present in the composition in a quantity comprised in the range 5-15% by weight with respect to the weight of the liquid phase of said dispersion.

22. Method according to claim 1, wherein said thermal treatment is carried out at a temperature in the range of 500-700 C.

Description

EXAMPLE 1

(1) There was prepared a coating composition according to the present invention having the following chemical composition (percentages by weight referred to the overall weight of the coating composition):

(2) TABLE-US-00002 glass frit (borosilicate) 65% pigment (CuO) 15% polycarboxylic resin 10% water 10%.

(3) The aforementioned components were mixed at room temperature up to obtaining a homogeneous coating composition with viscosity of about 6 Pa.Math.s (DIN 53013) corresponding to about 120 seconds DIN4 cup according to the UNI EN ISO 2431 standard. The coefficient of linear thermal dilation of the coating composition is equivalent to 72.Math.10.sup.7 K.sup.1 (ISO 7991:1987 standard).

(4) The thixotropic index of the coating composition was equivalent to 44 seconds.

(5) The composition was applied on the internal surface of a set of 30 bottles (with volume equivalent to 50 or 100 ml) made of soda lime both on the bottom and on the lateral walls through a spraying nozzle.

(6) The coated bottles were subjected to a thermal treatment at the temperature of about 600 C. for 40 min.

(7) For comparison purposes, the coatings obtained through the method of the present invention were compared with other glass bottles or containers having an inner coating applied using the method according to the prior art, as indicated in Table 1.

(8) The bottles coated with the method according to the present invention and the comparison items were subjected to a test for evaluating the mechanical and heat resistance of the coating, as well as the suitability to contact with food products and to prolonged contact with potentially aggressive substances. The results of the test are indicated in Table 1.

(9) TABLE-US-00003 TABLE 1 TOTAL CHEMICAL HEAT MIGRATION RESISTANCE WASHING SHOCK MECHANICAL DM 21/03/1973 IMMERSION DISHWASHER UNI EN COATING RESISTANCE (Autoclave test G1 (24 h, Room RESISTANCE 1183 COMPOSITION ISO 2409 at 121 C., 1 bar) temp.) EN 12875-2 (T = 50 C.) Glass flint High Transfers = Resistance to 1500 Breakage = (not coated) resistance; 1.85 mg/dm.sup.2 nail abrasion: washing 0% classification: 0 >100 times cycles: occurrence of visible aesthetic damaging marks Based on Insufficient Total No aesthetic 1-5 washing Breakage = organic resistance; detachment of alteration. cycles: 0% resins (liquid) classification: the coating Resistance to total loss of 3-4 from the glass nail abrasion = adhesion of 0 times the coating Based on Insufficient Total No aesthetic 5-10 washing Breakage = organic resistance. detachment of alteration cycles: 0% resins classification: the coating Resistance to loss of (powder) 3-4 from the glass nail abrasion = adhesion of 0 times the coating with partial decolouration sol-gel Good Total No aesthetic 5-10 washing Breakage = resistance; detachment of alteration. cycles: 10% classification: the coating Resistance to loss of 0-1 from the glass nail abrasion = adhesion of 20-50 times the coating with partial decolouration Powder High No aesthetic No aesthetic 100 washing Breakage = polish resistance; damage; alteration. cycles: 100% classification: 0 transfers = Resistance to breakage due 20.0-50.0 mg/dm.sup.2 nail abrasion = to heat and Caused by 70-80 times mechanical incomplete stresses. vitrification Surface decolouration Cased or High No aesthetic Resistance to 100 washing Breakage = manual glass resistance; damage; nail abrasion >100 cycles: 0% (glass on classification: 0 transfers = 8-10 mg/dm.sup.2 times occurrence of glass) defects, such as very visible marks present High No aesthetic No aesthetic 500 washing Breakage = invention resistance; damage; alteration cycles: 0% classification 0 transfers = 0.5-5.0 mg/dm.sup.2 After initial fading (variability due immersion. of the to the Resistance to outermost concentration nail abrasion >100 layer of the of pigments) times coating

(10) The tests show the high performance of the coating obtained according to the present invention. In particular, the experimental results show how, besides being easy to obtain, this coating is suitable to be used for the decoration and/or for the protective coating of hollow glass bodies intended to be used in various fields.

EXAMPLE 2

(11) A second coating composition according to the present invention was prepared having the following chemical composition (percentages by weight referred to the overall weight of the coating composition):

(12) TABLE-US-00004 glass frit (borosilicate) 65% pigment (TiO.sub.2) 15% cellulose ester 10% water 10%.

(13) The aforementioned components were mixed at room temperature until a homogeneous coating composition with viscosity of about 14 Pa.Math.s (DIN 53013) is obtained. The thixotropic index of the coating composition was of 36 seconds.

(14) The second coating composition was applied on a set of glass bottles according to the description of example 1, obtaining final coatings having the same performance in terms of mechanical and heat resistance, as well as suitability to contact with food products and prolonged contact with potentially aggressive substances of the coated bottles of example 1.