A method for coating paper cups with a glass layer

Abstract

The invention relates to a method for coating disposable paper cups with a glass layer to enhance their durability while ensuring they do not pose any harm to human health or the environment.

Description

[0001] A METHOD FOR COATING PAPER CUPS WITH A GLASS LAYER

[0002] TECHNICAL FIELD

[0003] The invention relates to a method for coating disposable paper cups with a glass layer to enhance their durability while ensuring they do not pose any harm to human health or the environment.

[0004] BACKGROUND

[0005] Currently, containers such as cups, mugs, and bowls, which appear to be made of paper, are commonly used for holding liquids like tea, soup, and lemonade. However, the paperboard used in manufacturing these containers is coated with a layer of plastic on one side, which is positioned on the inner surface of the container. As a result, beverages come into direct contact with this plastic layer. In reality, what is referred to as a "paper cup" is actually a plastic cup that uses paper merely as an external support. The paper layer on the outside of the cup serves only as reinforcement for the plastic structure. While this may be considered relatively harmless for cold beverages, it is entirely unacceptable for hot beverages.

[0006] Additionally, after use, these cups, mugs, and bowls are often discarded indiscriminately and are non-recyclable, contributing significantly to plastic pollution. Furthermore, since the plastic layer on these containers is extremely thin, it breaks apart along with the attached paper fragments, disintegrating into tiny microplastic particles that contaminate the air, water, and soil. These microplastics enter our bodies not only through digestion but, more dangerously, through the respiratory system. Currently, no solution has been proposed in the prior art to address this issue. Alternatives such as glass, ceramic, or stainless-steel containers are considered the safest materials. However, these alternatives require collection and washing after use, making them unsuitable for the "use-and-dispose" approach.

[0007] In the known state of the art, Doganay Gida has introduced CAMPET, a glass- coated PET bottle used for beverages such as lemonade. This technology utilizes SCHOTT, the German glass industry's SiOx (pure glass) coating technology, and requires a significant investment in KHS Plasmax machines. The process involves coating the inner surface of PET bottles with an ultra-thin glass layer (less than 100 nanometers thick) using high electrical fields, pulsed microwaves, and glass vapor deposition (https: / / www.muhendisbeyinler.net / campet-nedir-ve-nasil-uretilir / ). In the known state of the art, Doganay Gida has introduced CAMPET, a glass-coated PET bottle used for beverages such as lemonade. This technology utilizes SCHOTT, a leading German glass manufacturer’s SiOx (pure glass) coating technology, and requires a significant investment in KHS Plasmax machines. The process involves coating the inner surface of PET bottles with an ultra-thin glass layer (less than 100 nanometers thick) using high electrical fields, pulsed microwaves, and glass vapor deposition.

[0008] AIM OF THE INVENTION

[0009] The objective of the invention is to completely eliminate the plastic layer, thereby preventing beverages from coming into contact with plastic coatings while also contributing to the reduction of plastic waste, particularly microplastic pollution.

[0010] DETAILED DESCRIPTION OF THE INVENTION

[0011] The invention comprises various embodiments for forming the glass surface coating on paper cups, all of which are covered within the scope of this application. The alternative embodiments for the coating process are as follows:

[0012] Concentrated Sodium Silicate Solution: Density 1.41 g / mL, Weight percentage 49%, Solution pH 13

[0013] Concentrated Hydrochloric Acid Solution: Weight percentage 30-32%, Density 1.15- 1.16 g / mL

[0014] Concentrated Sulfuric Acid Solution: Weight percentage 95-98%, Density 1.83-1.84 g / mL

[0015] Calcium Chloride (CaCI22H2O): Purity 99.9%

[0016] Magnesium Sulfate (MgSO47H2O): Purity 99.5%

[0017] Iron(lll) Chloride (FeCI3): Purity 95%

[0018] In the first embodiment of the invention, following a process similar to the SiOx (pure glass) coating technology known in the literature, a chemical method is applied to coat paper cups with pure SiO2. Initially, the paper cup is impregnated with a sodium silicate solution. Then, to convert the silicate anion in the absorbed sodium silicate solution into silicic acid, a sulfuric acid solution is added. Na2SiC>3 + H2SO4 Na2SC>4 + H2S1O3 (silicic acid) n H2SiC>3 + Isi — n H2O + (-SiC>2 -)n (pure glass)

[0019] Since concentrated sulfuric acid carbonizes cellulosic paperboard, it had to be used in a diluted form. However, it was observed that the precipitation of silicic acid as solid crystals was very slow and minimal when using diluted sulfuric acid. In the method, a 10% (w / v) diluted sulfuric acid solution was determined to be suitable (10 g of concentrated sulfuric acid diluted with water to make 100 mL). Nevertheless, during the conversion of silicic acid into crystalline SiO2by heating in an oven at 100-110°C, it was noted that, depending on the oven temperature and duration of heating, even cellulosic filter paper exhibited browning.

[0020] In another embodiment of the invention, paper cups were filled with concentrated silicate solution or diluted twofold (prepared by mixing 50 mL of concentrated solution with water to make 100 mL). The absorption time by the paper cup was varied between 180-200 minutes. After the absorption period, the cups were heated in an oven at 70-80°C for 1-3 hours to facilitate the process. The dried cups were then filled with 10% (w / v) diluted sulfuric acid and left for 10-30 minutes. Afterward, the acid was drained, the cups were rinsed with clean water and dried in an oven at 110°C for two hours. It was observed that uncoated cups weighing 2.684- 2.840 g had a glass coating of approximately 0.358-0.366 g after the process. However, despite modifying factors such as the concentrations of the chemicals, absorption times, drying temperatures, and drying durations, the light brown scorching and partial degradation observed on the cups could not be eliminated.

[0021] In another embodiment of the invention, hydrochloric acid solution was used. For this process, 25 mL of concentrated hydrochloric acid was diluted with water to a total volume of 100 mL, preparing a 25% (v / v) diluted hydrochloric acid solution. The same procedures as those applied with sulfuric acid were then conducted in the experiments. In these hydrochloric acid applications, the darkening on the cups was eliminated; however, degradation and loss of structural resistance in the cups persisted. Additionally, beyond the observed reduction in the grayish color, it became evident that the acid was causing the deterioration of the paper material. To understand the cause of these changes, three equal pieces were cut from a paper cup and immersed separately in water, 1 M sodium hydroxide (NaOH) solution, and 1 M sulfuric acid (H2SO4) solution for 2 hours. After immersion, the samples were removed, rinsed, and dried at 100°C for 2 hours. The piece left in water showed no color change, while the piece immersed in the basic solution (NaOH) turned yellow, and the piece immersed in the acidic solution (H2SO4) turned black. Based on these findings, the process was adjusted to focus on glassification using calcium and magnesium salts.

[0022] Pure glass consists of interconnected SiO2units, as seen in the formulas above. Ordinary window glass, on the other hand, typically contains about 75% silica (sand), 15% soda, and 10% lime. In many cases, lime is used together with dolomite (CaCO3MgCO3), which is an important component in glass manufacturing. To avoid the damage caused by acids to the paper material, the process was modified. Instead of pure glass, it was decided to apply an ordinary glass coating by first impregnating the paper cups with silicate, followed by a gradual treatment with concentrated calcium chloride and magnesium sulfate solutions.

[0023] After the cups were coated, hot water leakage tests were conducted, leading to adjustments in both concentration levels and solution absorption durations. The silicate impregnation time was increased from 1 minute to 180 minutes. After this step, saturated calcium chloride solution at room temperature was added to the dried cups. After the impregnation and drying of calcium chloride, a saturated magnesium sulfate solution was initially applied. However, due to the formation of crystals adhering to the edges of the paper cup caused by evaporation during prolonged absorption, the solution was partially diluted (90 g saturated solution + 10 g water) to prepare a concentrated magnesium sulfate solution. This adjusted solution was then used for impregnation, effectively preventing crystallization. Although calcium chloride solution precipitates as calcium silicate within the cellulose fibers when combined with silicate solution, it was unable to neutralize the alkalinity from the silicate solution. To address this, magnesium sulfate solution was used to precipitate the remaining silicate as magnesium silicate while also neutralizing the alkalinity by forming magnesium hydroxide. This approach eliminated the need for excessive washing with water to remove alkalinity. In trials where glassification was carried out using hydrochloric acid, the graying effect caused by basic silicate disappeared after acid treatment. However, in calcium-magnesium-based trials, the graying did not disappear. Nevertheless, as detailed below, drying the silicate at 40°C, followed by calcium-magnesium drying at 70°C, significantly reduced the graying effect. In another embodiment of the invention, concentrated sodium silicate solution was fully filled into the paper cup and allowed to absorb for 180-200 minutes without leakage. After draining and filtering, the cup was dried at 40°C for 10-15 hours. Next, the cup was completely filled with saturated calcium chloride solution and left to absorb for 23 hours. After draining and filtering, it was dried at 70°C for 3 hours. The dried cup was filled with concentrated magnesium sulfate solution and allowed to absorb for 24 hours. After draining and filtering the excess solution, it was dried at 70°C for 3 hours. In the hot water leakage test, no leakage was observed, but condensation of 0.013 g was recorded at the bottom of the cup in the first 30 minutes, and 0.002 g in the second 30 minutes. After immersion in hot water, the sodium chloride and sodium sulfate salts formed during the coating process dissolved and were removed. Following rinsing and drying again at 70°C for 3 hours, it was observed that the uncoated paper cup, initially weighing 3.7328 g, increased to a coated weight of 5.9202 g, resulting in a net coating weight of 2.1874 g of salt-free, clean, dry calcium magnesium silicate with some magnesium hydroxide. This corresponds to a 58 percent increase relative to the uncoated weight and a 37 percent proportion of glass coating relative to the total coated weight.

[0024] In another embodiment of the invention, to cover the gray-brown layer formed on the glass-coated paper cup, the cup was immersed in a diluted iron(lll) chloride solution, prepared by diluting a saturated FeCI3solution with water at a ratio of 1 :20 (by completing 25 mL of saturated solution to a total volume of 500 mL with water). After being immersed for one minute, the cup was dried at 100°C for two hours, resulting in a light terracotta-colored cup.

Claims

CLAIMS1 . A method for coating paper cups with a glass layer, characterized by comprising the steps of:- impregnating the paper cup with a sodium silicate solution,- adding a sulfuric acid solution to convert the silicate anion in the absorbed sodium silicate solution into silicic acid,- heating the paper cup containing silicic acid in an oven to convert the silicic acid into crystalline SiO2.

2. The step of adding the sulfuric acid solution according to claim 1 , characterized in that the sulfuric acid solution is a 10% dilution, prepared by mixing 10 g of concentrated sulfuric acid with water to make a total volume of 100 mL.

3. A method for coating paper cups with a glass layer, characterized by comprising the steps of:- filling the paper cup with a diluted silicate solution, prepared by mixing 50 mL of concentrated silicate solution with water to make a total volume of 100 mL,- allowing the solution to be absorbed by the paper cup, followed by drying,- subsequently filling the cup with saturated calcium chloride solution, allowing absorption, and drying,- then filling the cup with concentrated magnesium sulfate solution and allowing absorption,- drying in an oven,- in acid-based glass coating applications, filling the dried cups with either a 10% (w / v) diluted sulfuric acid solution or a 25% (v / v) diluted hydrochloric acid solution and allowing them to stand,- subsequently draining the acid, rinsing with clean water, and drying in an oven.

4. The step of allowing absorption by the paper cup according to claim 3, characterized in that the silicate absorption time ranges between 180 and 200 minutes at room temperature.

5.

5. The step of allowing absorption by the paper cup according to claim 3, characterized in that the absorption time for the calcium and magnesium solutions ranges between 23 and 25 hours.

6. The step of drying in an oven according to claim 3, characterized in that the drying temperature ranges between 70 and 80°C and the drying duration ranges between 1 and 3 hours.

7. The step of filling the dried cups with diluted sulfuric acid and allowing them to stand according to claim 3, characterized in that the standing time ranges between 10 and 30 minutes.

8. A method for coating paper cups with a glass layer, characterized by comprising the steps of:- impregnating the paper cup with a sodium silicate solution,- adding a hydrochloric acid solution to convert the silicate anion in the absorbed sodium silicate solution into silicic acid,- heating the paper cup containing silicic acid in an oven to convert the hydrochloric acid-treated silicic acid into crystalline SiO2.

9. The step of adding the hydrochloric acid solution according to claim 8, characterized in that the hydrochloric acid solution is a 25% (v / v) dilution, prepared by diluting 25 mL of concentrated hydrochloric acid with water to make a total volume of 100 mL.

10. A method for coating paper cups with a glass layer, characterized by comprising the steps of:- fully impregnating the paper cup with concentrated sodium silicate solution without leakage,- draining, filtering, and drying the cup,- fully filling the dried cup with saturated calcium chloride solution and allowing absorption,- draining, filtering, and drying the cup,- filling the dried cup with concentrated magnesium sulfate solution and allowing absorption,- draining, filtering the excess solution, and drying the cup.11 . The step of fully impregnating the paper cup with sodium silicate solution without leakage according to claim 10, characterized in that the impregnation time ranges between 180 and 200 minutes.

12. The step of draining, filtering, and drying after fully impregnating the paper cup with sodium silicate solution without leakage according to claim 10, characterized in that the drying is carried out at 40°C for a duration of 10 to 15 hours.

13. The step of filling the dried cup with concentrated magnesium sulfate solution and allowing absorption according to claim 10, characterized in that the absorption time ranges between 23 and 25 hours.

14. The step of draining, filtering, and drying after filling the dried cup with concentrated magnesium sulfate solution and allowing absorption according to claim 10, characterized in that the drying is carried out at 70°C for a duration of 3 hours.

15. The method for giving a light tea color to the surface of the paper cup after coating with a glass layer as described in any of the preceding claims, characterized in that the paper cup is immersed in a diluted Iron(lll) chloride solution, prepared by diluting a saturated FeCI3solution with water at a ratio of 1 :20 (by completing 25 mL of the saturated solution to a total volume of 500 mL), allowed to stand for 1 minute, and then dried at 100°C.