Method for processing food container having pattern

Abstract

The present invention relates to a method for processing a food container having a pattern. The method comprises the following content: performing injection molding on a thermoplastic material to form a flat product; treating the flat product to improve the adhesive force of the surface of the flat product; attaching a pattern to the surface of the treated flat product; performing a heating treatment on the flat product attached with the pattern, so as to soften the flat product; and processing the softened flat product to form a desired shape of a food container. In the present method, by means of the characteristic of a thermoplastic material being able to be softened by heating and repeatedly shaped, the material is initially processed into a flat product, and then a pattern is attached to the surface of the flat product, such that it is more convenient to process the pattern on the flat product, and the method is also conducive to achieving multi-colored, detailed and embossed pattern effects; and compared with pattern processing methods for a thermosetting material, the method is more conducive to manufacturing a product fully covered with a pattern on the surface.

Description

Method for processing food container with pattern Technical Field

[0001] The present invention relates to a method for processing a food container with a pattern, in particular to a food container made of a thermoplastic material. Background Art

[0002] Existing food containers are often made of ceramic. While ceramic is very beautiful, its fragility leads to high storage and transportation costs. This has led to the emergence of porcelain-like food containers on the market. For example, dinner plates made of the thermosetting material melamine are processed with various patterns to create the effect of ceramic tableware. However, with the improvement of living standards, the substances released by improper use of melamine tableware have attracted consumer attention, negatively affecting its market acceptance. The industry has begun to use thermoplastic materials to produce porcelain-like tableware. However, the pattern processing methods that can be achieved on thermosetting materials are not applicable to thermoplastic materials. The pattern processing effect is poor, and it is difficult to produce tableware with a fully patterned surface. Therefore, there is room for improvement in the processing methods of thermoplastic food containers with patterns. Technical issues

[0003] The technical problem solved by the present disclosure is to provide a processing method suitable for thermoplastic food containers with patterns, which is conducive to making exquisite patterns on such containers. Technical Solutions

[0004] The technical solution adopted by the present invention to solve the technical problem is: a method for processing a food container with a pattern, the method comprising the following contents:

[0005] Take thermoplastic materials and process them into flat products through injection molding;

[0006] Treating flat products to improve surface adhesion;

[0007] Attaching the pattern to the processed flat product surface;

[0008] The flat product with the pattern is heated to soften it;

[0009] The softened flat product is processed and formed into the shape required for food containers.

[0010] As described above, the method for processing a food container with a pattern further includes spraying a transparent protective film, wherein the transparent protective film is sprayed after the pattern is attached to a flat product, or after the flat product with the pattern is processed into a food container shape.

[0011] As described above, in the method for processing a food container with a pattern, the transparent protective film is one of a UV protective film, a water-based protective film, and an oily protective film.

[0012] As described above, in the method for processing a food container with a pattern, the thermoplastic material is PET, which contains 75-88% polyethylene terephthalate, 10-20% mineral powder filler, and 1-3% nucleating agent.

[0013] As described above, in a method for processing a food container with a pattern, the selected PET material is first dried using a drying device at a drying temperature of 80-150 degrees Celsius for 2-6 hours, and then injection molded using an injection molding machine at a molding temperature of 220-320 degrees Celsius.

[0014] As described above, a method for processing a food container with a pattern improves the adhesion of the flat product surface by applying an adhesion treatment agent or using a plasma surface treatment process.

[0015] In the aforementioned method for processing a food container with a pattern, the flat product with the pattern is heated to 90-180 degrees Celsius to soften it.

[0016] As described above, in the method for processing a food container with a pattern, the softened product is processed into the desired shape through a stamping or oil pressure process.

[0017] As described above, a method for processing a food container with a pattern is provided. When a flat product is processed into a food container, the shape change caused by the shape change is analyzed in advance to determine the effect of the shape change on the surface pattern of the flat product. A pattern prototype is designed based on this, and the pattern prototype is attached to the surface of the flat product.

[0018] As described above, in the method for processing a food container with a pattern, the food container is a dinner plate. Beneficial effects

[0019] The beneficial effects of the present disclosure are as follows: first, a thermoplastic material is processed into a flat product, the surface of the flat product is flat and has no curvature, which facilitates processing of patterns on the surface; then, the flat product with the pattern is processed into a food container. Compared with the pattern processing method of thermosetting materials, the pattern effect is more refined and is more conducive to the production of products with a fully covered surface pattern. Best Mode for Carrying Out the Invention

[0020] To make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them.

[0021] Based on the described embodiments of the present invention, all other embodiments derived by persons of ordinary skill in the art without inventive effort are within the scope of protection of the present invention. Unless otherwise defined, technical or scientific terms used in this disclosure shall have the same ordinary meaning as understood by persons of ordinary skill in the art to which the present invention belongs.

[0022] As used in this disclosure, "first," "second," and similar terms do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Similarly, "a," "an," or "the" and similar terms do not indicate a quantitative limitation, but rather indicate the presence of at least one. "Include" or "comprising" and similar terms mean that the elements or objects preceding the term include the elements or objects listed after the term and their equivalents, without excluding other elements or objects. "Connected" or "connected" and similar terms are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. "Up," "down," "left," "right," and the like are only used to indicate relative positional relationships. When the absolute position of the object being described changes, the relative positional relationship may also change accordingly.

[0023] Melamine, a thermosetting material, is commonly used to make porcelain-like tableware. The main raw material for melamine tableware is high-purity melamine resin, a polymer compound formed by the polymerization of melamine and formaldehyde. Some consumers are not very accepting of this, and improper use of melamine tableware may release toxic substances, causing harm to the body. The industry uses thermoplastic materials to make tableware, but the pattern processing methods used for melamine tableware are not suitable for thermoplastic tableware. This is because melamine tableware cannot be repeatedly formed by heat. The pattern is applied to the tableware that has already been formed. Since tableware often has curved parts, the processing precision of the pattern is negatively affected, and it is not conducive to producing tableware with a fully covered pattern.

[0024] Therefore, a method for processing a food container with a pattern is provided, the method comprising the following contents:

[0025] Take thermoplastic materials and process them into flat products through injection molding;

[0026] Treating flat products to improve surface adhesion;

[0027] Attaching the pattern to the processed flat product surface;

[0028] The flat product with the pattern is heated to soften it;

[0029] The softened flat product is processed and formed into the shape required for food containers.

[0030] Thermoplastic materials are substances that can flow and deform when heated and retain a specific shape after cooling. They are made mainly of thermoplastic resins with various additives. Under certain temperature conditions, the plastic can soften or melt into any shape, and the shape remains unchanged after cooling. This state can be repeated many times and remains plastic. This repetition is simply a physical change, known as thermoplasticity. Taking advantage of the repeated deformation of thermoplastic materials by heating, they are first processed into flat products, and then their surface adhesion is improved, allowing the pattern to better adhere to the surface of the flat product. Because the surface of the product is flat and has no bends, the pattern adheres better and the reproduction of its details is optimized. The flat product with the pattern is then heated and softened again, allowing it to be processed and formed into the desired food container.

[0031] Thermoplastic materials can be modified polyethylene terephthalate (PET), which contains 75-88% polyethylene terephthalate, 10-20% mineral powder filler, and 1-3% nucleating agent. The material is dried in a drying equipment at a temperature range of 80-150 degrees Celsius for 2-6 hours, and then processed into flat products using a horizontal or vertical injection molding machine with a molding temperature of 220-320 degrees. The processing parameters are adjusted according to the size and shape of the finished product. After completing the injection molding process, the sprue and flash are trimmed.

[0032] The PET with the aforementioned ingredients has properties such as high temperature resistance (140 degrees Celsius) and chemical corrosion resistance, but during the painting process for pattern processing, the paint film often has poor adhesion problems, which will affect the appearance quality of the product and also reduce its performance.

[0033] The reasons for poor paint film adhesion when spraying PET are probably as follows:

[0034] Low plastic surface energy: The surface energy of PET material is small, making it difficult for the paint to wet and adhere to its surface, thereby reducing adhesion; Improper surface pretreatment: Before spraying, if the PET surface is not effectively cleaned and there are oil stains, impurities, etc., it will directly affect the adhesion of the paint; Improper paint selection: Different types of paint have different effects on the adhesion of the PET surface. Choosing unsuitable paint will significantly reduce the adhesion; Spraying process problems: During spraying, the paint is not evenly distributed on the PET surface, or the coating thickness is insufficient, which may lead to a decrease in adhesion.

[0035] Chemical and physical methods can be used to treat the problems of PET itself, so as to effectively solve the problem of poor paint film adhesion of PET material during the painting process and improve the appearance quality and performance of the product. The specific methods are as follows:

[0036] Improve the surface energy of plastics: By using some special adhesion treatment agents, the surface energy of PET is increased, thereby increasing the adhesion of the coating to the PET surface. For example, when using PET adhesion treatment agents, apply the PET adhesion treatment agent to the surface of the PET substrate through the primer construction method. The functional groups contained in the PET adhesion treatment agent can form a close bond with the PET material, thereby improving the adhesion of the coating on the PET surface.

[0037] The PET treating agent adopts a modified polyurethane emulsion and is prepared according to the following process: a prepolymer is prepared by using 12 parts by weight of toluene 2,6-diisocyanate, 5.5 parts of polyether diol, 4 parts of 1,4-butanediol, 5.5 parts of dimethylol propionic acid, and 6.5 parts of cyanuric acid epoxy resin as raw materials; 3 parts of hydroxyethyl acrylate is added to cap the prepolymer and the reaction is carried out for 30 minutes; the temperature is lowered to 45°C, 4 parts of triethylamine is added for neutralization reaction to form a salt, and the reaction is carried out for 6 minutes; 6 parts of deionized water are added for emulsification for 60 minutes, and the prepolymer is cooled to room temperature to obtain a modified polyurethane.

[0038] When using, the treatment agent can be diluted with benzene solvent: the ratio is 1-5 times. After dilution, the treatment agent is sprayed on the surface of the product and left to stand at room temperature for 30-120 minutes or put into baking equipment, the baking temperature is 40-120 degrees, the time is 2-10 minutes, and the film thickness is 3-50um.

[0039] Optimize surface pretreatment: Use effective methods such as frosting and solvent cleaning to remove oil and impurities on the PET surface, increase surface roughness, and increase the contact area between the coating and the substrate, thereby improving adhesion.

[0040] Choose the right coating: According to the characteristics of PET material, choose a suitable coating, such as a coating containing polar groups, to improve the bonding strength between the coating and the PET surface.

[0041] Optimize the spraying process: By adjusting the spraying equipment parameters such as pressure, distance, speed, etc., the coating can be distributed more evenly on the PET surface, and the coating thickness can be ensured to be moderate to improve adhesion.

[0042] Physical surface treatment: Plasma treatment modifies the chemical properties of a material's surface, thereby improving its surface properties. Surface reactions involve excited molecules, free radicals, and ions, as well as the effects of ultraviolet radiation from the plasma. Plasma energy can act on the material surface through light radiation, neutral molecular flux, and ion flow. The dissipation of this energy is the process by which the surface is modified.

[0043] Low-temperature plasma emits visible, ultraviolet, and infrared light. Ultraviolet light is not only strongly absorbed by the material but also generates free radicals on the surface. These active sites then undergo chemical reactions with the gas components in the plasma, leading to a series of surface modifications. Neutral particles, through their own free radical dissociation, can trigger various chemical reactions on the material surface (dehydrogenation, oxidation, and addition). Ion flux impacting the surface causes surface etching and heating, which also triggers reactions similar to those caused by neutral flux. These three effects together underlie the principle of low-temperature plasma surface modification. Low-temperature plasma's effect on the material occurs only within a thickness of tens to thousands of angstroms, significantly improving the surface properties of the material while leaving the bulk properties unaffected. This is achieved while offering the advantages of high efficiency, low cost, and environmental friendliness.

[0044] Specifically, corona oxidation treatment is used to enhance adhesion on flat PET surfaces. This process utilizes high-frequency, high-voltage (up to 5,000-15,000 V / m²) corona discharges on the surface of the treated PET plastic, generating a low-temperature plasma. This generates free radicals on the plastic surface, causing crosslinking of the polymers, roughening the surface and increasing its receptivity to polar solutions. These ions penetrate the surface of the printed material through electrical shock and penetration, disrupting its molecular structure. This in turn oxidizes and polarizes the surface molecules, eroding the surface through ion shock and increasing adhesion.

[0045] The operation is as follows:

[0046] Place the PET flat product in the corona discharge equipment, connect high-voltage direct current to make the corona equipment discharge, and the surface of the PET material will come into contact with high-energy ions to form an oxide film. The performance of the film can then be improved through treatments such as cleaning and drying.

[0047] The pattern can be attached to the processed flat product by silk screen printing, pad printing, hot stamping, flatbed printing, water transfer printing, heat transfer printing, sublimation and other processes.

[0048] Silk screen printing is a printing method in which a squeegee squeezes a screen, elastically deforming it and depositing a slurry onto the material to be printed. Pad printing etches the desired pattern onto a steel plate (sheet). The pad printer's oil reel returns oil, causing the blade assembly to descend, collecting the remaining ink from the etched pattern into the ink basin. The adhesive properties of the pad then transfer the pattern to the substrate. Hot stamping uses metal foil to add a decorative effect by transferring it to printed materials or other surfaces through heat and pressure. Cold stamping uses pressure, adhesion, and peeling to transfer metal foil to printed materials or other surfaces without heat. Flatbed printing, also known as universal UV printing, replaces silk screen printing and produces full-color images in one pass. Water transfer printing uses water as a medium to transfer a color pattern printed on paper or specialty PVA to the substrate. Heat transfer printing involves sublimating the heat transfer ink at high temperatures, penetrating the surface, and forming a vibrant image.

[0049] The flat product with the pattern enters the heating equipment, such as hot air circulation oven, tunnel furnace and other equipment. The heating tube can also be used to locally heat the part of the flat product that needs to be bent, and the surface of the product can be heated to 90-180 degrees Celsius to achieve the desired softening effect.

[0050] The softened product is processed into the required shape through stamping or hydraulic pressure. The required shape mold is installed on the stamping or hydraulic equipment. The softened flat product is placed in the mold and pressed to obtain the required shape.

[0051] To prevent the pattern from coming into direct contact with food and to prevent it from being easily worn, a transparent protective film is generally placed on the pattern surface. The transparent protective film can be processed after the pattern is attached to the flat product, or after the flat product with the pattern is processed into a food container.

[0052] Transparent protective films can be made from UV, water-based, or oil-based materials. Commonly used UV protective films include urethane acrylates (polyurethane acrylates), epoxy acrylates, polyester acrylates, polyether acrylates, and vinyl ether oligomers that do not contain acrylates. Under UV radiation of medium- and short-wavelength ultraviolet light (300-800 nanometers), the photoinitiator in the liquid UV material is stimulated to become free radicals or cations, which triggers the polymerization of the polymer material (resin) containing active functional groups into an insoluble and infusible solid coating.

[0053] UV paint process flow:

[0054] Spraying: Filter with 400 mesh filter cloth before use, control the spraying pressure at 0.4-0.5Mpa, and the paint viscosity at 10-20s / 25℃.

[0055] Leveling: After spraying, infrared leveling must be ensured for more than 3 minutes, and the temperature must be around 40°C. If the leveling time is too short or the temperature is too low, bubbles, pinholes, gloss loss, fogging, etc. may easily appear on the surface. For single-component topcoat finishing, the leveling time should not exceed 4 minutes, otherwise, the topcoat may be corroded.

[0056] Curing: The design curing speed of UV high gloss paint is 4m / min (lamp distance 150mm). For specific work, the transmission chain speed, UV lamp power or lamp distance can be adjusted according to needs.

[0057] Water-based protective films include rosin-modified maleic acid resin, water-soluble acrylic resin, styrene-modified maleic acid resin, water-based amino resin and polyvinyl alcohol.

[0058] The following process can be used to spray water-based protective film:

[0059] Weigh the required spray paint according to the mixing ratio, stir the paint until it is evenly distributed, and dilute it according to the following ratio: 3 parts varnish, 1 part curing agent, and 3 parts boiling water. Before spraying, remove oil stains and contaminants from the substrate to be sprayed. Spraying can only be carried out after the substrate is completely dry. Do not mix other types of paints or solvents during spraying. Pay attention to the cleanliness of the spraying environment. Choose a spray gun with a caliber of 1.0-2.0mm and a spray gun pressure of 3-4kg / cm2. The optimal spraying temperature is approximately 25℃, with humidity below 80%. Adjust the mist amplitude to medium pressure and calibrate to 3-4kg / cm2. Try to wet the surface of the workpiece as much as possible and control the oil amount evenly. After spraying, bake at a constant temperature of 70℃ for 30 minutes and fully dry for 48 hours.

[0060] Taking a common dinner plate as an example, the edge of the plate has a certain width and is horizontal or has a certain inclination angle. The middle of the plate is a concave storage space for placing food. The pattern can be set on the edge of the plate or in the middle of the plate. When this type of dinner plate is processed, the pattern attached to the flat product will not be deformed due to stamping.

[0061] In some embodiments, a pattern is attached to the position where the flat product is deformed by punching. For example, when a flat product with a full pattern is punched into tableware, part of the position with the pattern will inevitably be bent. In order to obtain a better pattern effect, the impact of product deformation on the pattern can be reduced by designing a suitable pattern, such as using a single color block, landscape, etc.

[0062] Furthermore, the shape changes caused by processing a flat product into a food container can be pre-analyzed, and the deformation effects of these changes on the surface pattern of the flat product can be calculated. Based on this deformation, a pattern prototype can be designed and attached to the surface of the flat product. In this way, when the flat product is stamped into a food container, the pattern prototype will also change accordingly, presenting the desired effect. For example, a 0.9cm line attached to a dinner plate will be stretched to 1cm during stamping. If the designer requires a 1cm line on the plate, the pattern prototype attached to the flat product only needs to be a 0.9cm line.

[0063] In summary, this method uses the property of thermoplastic materials that can be softened by heating and repeatedly molded to initially process the material into a flat product, and then attach the pattern to the surface of the flat product. It is more convenient to process patterns on flat products, and is also conducive to achieving multi-color, delicate, and embossed pattern effects. Compared with the pattern processing method of thermosetting materials, it is more conducive to producing patterns that fully cover the product surface, because the tableware made of thermosetting materials needs to be molded first, and the tableware after molding has a curved structure, making the full coverage pattern design difficult to achieve.

[0064] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that the present invention is susceptible to various modifications, combinations, and variations. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of the claims.

Claims

1. A processing method for a food container with a pattern, characterized in that, The method includes the following steps: Take a thermoplastic material and injection mold it into a flat product; Treat the flat product to improve the adhesion of its surface; Attach a pattern to the surface of the treated flat product; Subject the flat product with the attached pattern to a heating treatment to soften it; Process the softened flat product into the shape required for a food container.

2. A processing method for a food container with a pattern as claimed in claim 1, wherein: The method further includes spraying a transparent protective film, which is sprayed after the pattern is attached to the flat product, or after the flat product with the attached pattern is processed into the shape of a food container.

3. A processing method for a food container with a pattern as claimed in claim 2, wherein: The transparent protective film is one of a UV protective film, a water-based protective film, and an oil-based protective film.

4. A processing method for a food container with a pattern as claimed in claim 1, wherein: The thermoplastic material is PET, which contains 75 - 88% of polyethylene terephthalate, 10 - 20% of mineral powder filler, and 1 - 3% of nucleating agent.

5. A processing method for a food container with a pattern as claimed in claim 4, wherein: The selected PET material is first dried using a drying device at a drying temperature of 80 - 150 °C for a drying duration of 2 - 6 hours, and then injection molded using an injection molding machine at a molding temperature of 220 - 320 °C.

6. A processing method for a food container with a pattern as claimed in claim 5, wherein: Improve the adhesion of the surface of the flat product by applying an adhesion treatment agent or using a plasma surface treatment process.

7. A processing method for a food container with a pattern as claimed in claim 1, wherein: The flat product with the attached pattern is heated to 90 - 180 °C to soften it.

8. A processing method for a food container with a pattern as claimed in claim 1, wherein: The softened product is processed into the required shape by stamping or hydraulic pressing processes.

9. A processing method for a food container with a pattern as claimed in claim 1, wherein: For the shape change generated when the flat product is processed into a food container, pre-analyze the influence of this shape change on the surface pattern of the flat product, and thus design a pattern prototype, and attach this pattern prototype to the surface of the flat product.

10. A processing method for a food container with a pattern as claimed in claim 1, wherein: The food container is a dinner plate.