Preparation method of heat-insulating PLA (polylactic acid) foaming coated paper cup

Abstract

The invention belongs to the technical field of coated paper cups, and relates to a preparation method of a heat-insulating PLA (polylactic acid) foamed coated paper cup, which comprises the following steps: (1) preparing PLA coated paper from coated base paper and a coated raw material PLA through a coating process of a coating machine; (2) after the PLA coated paper is cut into paper samples, the PLA coated paper cup is prepared through a paper cup forming machine; (3) performing carbon dioxide soaking treatment on the PLA coated paper cup to prepare a PLA foamed coated paper cup; in the step (3), the mode of carbon dioxide soaking is that the PLA coated paper cup is placed in a high-temperature-resistant and high-pressure-resistant closed container, carbon dioxide is injected, constant-temperature and pressure-maintaining soaking is carried out, and pressure is rapidly relieved after soaking is completed. The carbon dioxide is subcritical or supercritical carbon dioxide fluid. According to the preparation method of the foaming coated paper cup, the prepared foaming coated paper cup has a heat insulation function, the method has the advantages of being simple and rapid, and a large number of raw materials and corresponding processing and manufacturing cost can be saved.

Description

Technical Field

[0001] The invention belongs to the technical field of laminated paper cups and relates to a method for preparing a heat-insulating PLA foamed laminated paper cup. Background Art

[0002] Hot drinks are an indispensable dietary habit in people's daily lives. Whether Westerners drink coffee or Orientals drink tea, everyone uses hot drink cups. Usually, disposable hot drink cups must be both heat-resistant and heat-insulated, so that you won't feel hot when holding the cup. The disposable EPS cup invented in the 1970s just meets this requirement, because the temperature resistance of PS is just above 100℃, and the material is given heat insulation after PS foaming. Therefore, the EPS cup is both heat-resistant and heat-insulating, which is a rare product. However, EPS causes white pollution and has been banned by the United Nations for production and sale. At present, except for the United States, where EPS plates and cups can still be seen, it is almost completely banned in other countries.

[0003] In order to meet people's hot drink habits and the development needs of industries such as fast food, take-out and outdoor gatherings, the following types of disposable hot drink cups are currently on the market:

[0004] PP cups, PP temperature resistance exceeds 130℃, the raw material price is cheap, and it is easy to process and shape. It is the main product of disposable hot drink cups at present. Common ones are blister PP cups (thin transparent cups) and thicker wall injection PP cups (transparent cups, frosted cups). These PP cups are heat-resistant but not heat-insulated. After pouring hot drinks, you must be careful to hold the cup port, or use a paper corrugated sleeve (or plastic sleeve) to cover the outside of the cup to avoid scalding. In recent years, due to the continuous development of PP foaming technology, some people prepare PP foam sheets through extrusion foaming production process, and then use paper cup making machine process to make EPP sheets into EPP cups. However, because this process route requires high melt strength polypropylene (HMSPP) raw materials and special extrusion foaming equipment, it requires large investment and high production cost, and it is difficult to make low cup prices, so there are no EPP cup products on the market.

[0005] PE coated paper cups are another main product of disposable hot drink cups. PE is water-resistant, oil-resistant, and heat-sealed. A very thin layer of PE coated film is applied on the paper sheet to prevent water leakage and prevent the softening of the paper cup. Ordinary PE coated paper cups are heat-resistant but not heat-insulating. There are currently two ways to change their heat insulation. One is to put a corrugated paper sleeve on the coated paper cup (low quality, inconvenient to use, and poor user experience), or to directly make the product into a double-layer paper structure coated paper cup (high quality, convenient to use, but high price); the other is to add a layer of foam film to the coated paper cup for heat insulation, such as the PerfecTouch product launched by Dixie in the United States, which makes good use of the heat insulation properties of foam. The preparation method of its foam insulation film layer is original and is still under patent protection. In addition to this, no other foam paper cup products have been seen. Recently, Dixie in the United States has launched the Insulair Hot Cup product. The paper cup is a single-layer paper cup. After the hot drink enters, the PE film on the inner wall of the cup shrinks to form a thin air insulation isolation layer. The higher the temperature of the hot drink, the better the insulation effect. No external insulation sleeve is required to achieve internal heat preservation and external insulation. The advantage of this cup is that it is a single-layer paper cup, which greatly reduces the consumption of raw materials and product storage space.

[0006] PLA coated paper cups are a completely biodegradable product. There are single-layer coated hot drink paper cups and double-layer paper structure heat-insulated coated paper cups on the market, but there are no PLA foam film heat-insulated paper cups. In recent years, as the country issued a "plastic ban" and began to control the impact of non-degradable plastics on the environment and ecology, PLA coated paper cups have developed rapidly. At present, PLA coated paper cups are gradually replacing PE coated paper cups. In the milk tea cup market, it has replaced some PP milk tea cups.

[0007] There are few studies on foamed coated paper. CN101198469A (published on June 11, 2008) discloses a foam-paperboard laminate, a product containing it and a preparation method, i.e., a preparation method of the foamed coated paper in the Dixie hot drink cup product. The method uses water in the base paper as a foaming agent, LDPE as the outer coating layer of the base paper, and HDPE blend as the inner coating layer for waterproof penetration. The double coated paper is subjected to a high temperature heat treatment to convert the water in the paper into water vapor, which dissolves and penetrates into the outer coating of the coated paper to expand and foam, thereby obtaining a heat-insulating foamed coating. CN107738490A (publication date: 2018-02-27) adopts LDPE / HDPE / LDPE three-layer co-extruded coating to replace the inner coating of HDPE blend, and selects LDPE / POE blend to replace LDPE outer coating, so as to obtain a heat-insulating foaming paper with good and soft hand feeling and strong velvety feeling, easy adhesion in post-processing and molding, and suitable for industrial production. It is worth mentioning that the preparation method of this foaming PE coating uses water in base paper as a foaming agent, which is only suitable for LDPE material foaming. If a polymer material is changed, it may not be possible to make a foaming coating in the same way. At present, there is no research report on the foaming of PLA coated paper. Summary of the invention

[0008] In view of the difference from the prior art, the present invention provides a method for preparing a foamed coated paper cup. The prepared foamed coated paper cup has a heat insulation function. The method has the advantages of being simple and quick, and can also save a large amount of raw materials and corresponding processing and production costs.

[0009] In order to solve the above technical problems, the purpose of the present invention is achieved through the following technical solutions:

[0010] A method for preparing a heat-insulating PLA foam coated paper cup, the method comprising the following steps:

[0011] (1) The laminated base paper and the laminated raw material PLA are prepared into PLA laminated paper through a coating process of a laminating machine;

[0012] (2) After the PLA coated paper is cut into paper samples, the PLA coated paper cups are prepared by a paper cup forming machine;

[0013] (3) The PLA coated paper cups are treated by immersion in carbon dioxide to prepare PLA foam coated paper cups;

[0014] In the step (3), the carbon dioxide soaking method is: the PLA coated paper cup is placed in a sealed container resistant to high temperature and high pressure, carbon dioxide is injected, and soaked at a constant temperature and pressure, and the pressure is quickly released after the soaking is completed;

[0015] The carbon dioxide is a subcritical or supercritical carbon dioxide fluid.

[0016] In the above-mentioned method for preparing a heat-insulating PLA foam coated paper cup, the coating weight of the PLA coated paper in step (1) is 25-100 g / m 2 , preferably 50-60g / m 2 ; The PLA coated paper is single-layer coated paper or double-layer coated paper. When the PLA coated paper is double-layer coated paper, at least one side of the PLA coated paper cup is a foaming structure. Therefore, in the PLA coated paper cup, the PLA foaming structure can be the inner coating surface of the paper cup, the outer coating surface of the paper cup, or the double coating surface of the paper cup. Furthermore, in the step (1), the coated paper is prepared by a coating machine, which is a single-coating coating machine for preparing single-layer coated paper or a double-coating coating machine for preparing double-layer coated paper. The coating process of the coating machine is a processing condition that matches the coating raw material used. Before the base paper is coated, the surface of the coating surface must be corona treated to ensure the coating fastness.

[0017] In the above-mentioned method for preparing a heat-insulating PLA foam coated paper cup, the coated base paper in step (1) is selected from any one of sulfate paper, ultra-high bulk paper cup base paper (FK0), high-grade paper cup base paper (FK1), paper cup base paper (FK2), foamed paper cup base paper (FKK), ultra-high bulk noodle bowl base paper (FMO), ultra-high bulk lunch box base paper (FCO), kraft paper, and silicone oil paper.

[0018] In the above-mentioned method for preparing a heat-insulating PLA foam coated paper cup, the paper cup forming machine in step (2) is any one of a low-speed, medium-speed or high-speed paper cup forming machine.

[0019] In the above-mentioned method for preparing an insulating PLA foam coated paper cup, in the step (1), the coating raw material PLA is a PLA resin or a PLA blend, the melt index of the PLA resin is 2-10g / 10min, and the detection conditions of the melt index are 190°C and 2.16kg. The PLA blend is a blend of different PLAs or a blend of PLA with other biodegradable materials. The other biodegradable materials are selected from any one or more combinations of PBS, PBAT, PBST, PHA and starch. When PLA is blended with other biodegradable materials, the content of PLA is not less than 60%.

[0020] In the above-mentioned method for preparing an insulating PLA foam coated paper cup, the coating raw material PLA contains a modifier, and the modifier is any one or more combinations of chain extenders, cross-linking agents, antioxidants, nucleating agents, compatibilizers, etc., and the content of the modifier is not higher than 10%.

[0021] In the above-mentioned method for preparing an insulated PLA foam coated paper cup, the high temperature and high pressure resistant container in step (3) is any temperature-controllable and pressure-resistant sealed container; after the PLA coated paper cup is quickly depressurized, the container is opened, the sample is taken out, and cooled at room temperature to obtain a PLA foam coated paper cup product.

[0022] In the above-mentioned method for preparing an insulating PLA foam coated paper cup, in the step (3), during carbon dioxide immersion, the holding temperature is 110-130° C., the holding pressure is 5-12 MPa, the holding time is 2-30 min, and the pressure release rate is 15-41 MPa / s.

[0023] In the above-mentioned method for preparing a heat-insulating PLA foam coated paper cup, the foaming condition of the foam film layer of the PLA foam coated paper cup can be controlled by controlling the carbon dioxide immersion conditions to meet the different needs of different products.

[0024] In the above-mentioned method for preparing a heat-insulating PLA foamed coated paper cup, the PLA coated paper cups in step (3) are stacked in piles, and the gaps between the cups are matched when stacked. By leaving sufficient gaps between the cups, the cups can be prevented from sticking to each other after the PLA is foamed.

[0025] In the above-mentioned method for preparing a heat-insulating PLA foam coated paper cup, the PLA foam coated paper cup also includes heat-insulating products similar to paper cups, such as instant noodle paper bowls, hot food lunch boxes, etc.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] 1. The present invention provides a method for preparing an insulating PLA foam coated paper cup. Under a certain temperature and pressure, a formed PLA coated paper cup is soaked with a carbon dioxide fluid, and the carbon dioxide is dissolved and penetrated into the PLA coating to reach a saturated state. The pressure is quickly released and the coating is foamed to obtain a PLA foam coated paper cup. Compared with ordinary coated hot drink cups, the hot drink cup of the present invention can use a PLA microporous foam film as the inner coating of the paper cup, giving the paper cup both heat-resistant and heat-insulating functions. Although the appearance of the paper cup is the same as that of an ordinary single-coated paper cup, after pouring hot drinks, the cup can be held by hand without being hot, which provides a completely different user experience. Compared with existing insulating coated paper cups, whether it is a double-layer paper structure or a paper cup with an external PE foam film, the preparation method of the present invention is simple and quick, and can save a large amount of raw materials and corresponding processing and production costs.

[0028] 2. The present invention uses carbon dioxide as a foaming agent and realizes solid-state foaming of the coating by precisely adjusting the processing parameters. Therefore, the product of the present invention is a brand-new foaming coating product. The thickness, pore size and appearance of the foaming coating can be adjusted according to the application requirements and user experience requirements.

[0029] 3. The process technology route for preparing heat-insulating PLA foamed coated paper cups of the present invention is constructed according to the existing technology route and equipment design for producing paper tableware. The added step of carbon dioxide immersion treatment for processing coated paper cups can be seamlessly linked with the existing mechanical equipment for preparing paper tableware products. Therefore, the present invention can be directly used for the production of heat-insulating PLA foamed coated tableware products, and has low production costs, rich product varieties, and controllable and adjustable product quality.

[0030] 4. The PLA foamed coated paper cup product of the present invention is a completely biodegradable product. Traditional PE foamed coated paper cups and the latest insulated air paper cups both use PE coating. Since PE is not degradable, its paper cup waste will produce microplastic particles, polluting the ecological environment. Therefore, the present invention replaces PE with PLA, and makes PLA into a microporous foamed coated paper cup, completely eradicating the non-degradable polymers in the coated paper cup product, creating a precedent for completely biodegradable insulated coated paper cup products, and will play a positive role in promoting ecological environmental protection and eliminating microplastic particle pollution. DETAILED DESCRIPTION

[0031] The present invention is further illustrated below through the description of specific implementation methods, but this is not a limitation of the present invention. Those skilled in the art can make various modifications or improvements based on the basic idea of ​​the present invention, but as long as they do not deviate from the basic idea of ​​the present invention, they are all within the scope of the present invention.

[0032] The determination method of each test data in this embodiment is as follows:

[0033] (1) Testing method for coating weight of laminated paper in the embodiment

[0034] Take a piece of coated paper and put it in the paper quantitative sampler to get a sheet with an area of ​​100cm 2 Weigh the disc with an electronic weigher and calculate the weight of the coated base paper (g / m 2 ), repeat the sampling and get the average value.

[0035] Test of coating weight

[0036] Before the formal coating, turn off the corona to obtain a coating sample in which the coating layer and paper are easily separated. In the same way as above, punch out the disc and slowly peel off the coating layer along the edge. If it still cannot be peeled off, soak it in alcohol and slowly rub it to peel it off. Weigh it with an electronic weighing device and calculate the weight of the coating layer (g / m 2 ), repeat sampling vertically and horizontally to get the average value.

[0037] (2) Testing methods for the thickness of laminated base paper, coating thickness of laminated paper and thickness of foamed film of laminated paper in the examples

[0038] Coated paper thickness

[0039] Take a die-cut coated base paper and use a vernier caliper to measure along the four edges of the paper. Select at least 10 points on each edge to measure the thickness of the base paper, record the measured values, and take the average value. Take 4 rolls of the same coated base paper, repeat the above measurement, and take the average value of the 4 measurements, which is the average thickness of the roll of coated base paper.

[0040] Laminated paper coating thickness

[0041] Take a die-cut laminated paper sample and measure the average thickness of the laminated paper (laminated base paper + coating film) in the same way as the laminated base paper above. Take 4 samples of the same laminated paper coating and repeat the above measurement. Then take the average of the 4 measured values, which is the average thickness of the laminated paper for this test. Then deduct the thickness of the laminated base paper to get the coating thickness of the laminated paper for this sample.

[0042] Laminated paper foam film thickness

[0043] Take a laminated paper cup foam sample, cut off the laminated paper cup body, the sticky part of the bottom of the cup, and the curled part of the cup mouth, and cut out a curved rectangular laminated foam paper. Measure the average thickness of the laminated foam paper (laminated base paper + foam film) in the same way as the laminated base paper above. Take 4 identical laminated paper cup foam samples, repeat the above measurement, and take the average of the 4 measured values, which is the average thickness of the laminated paper cup foam film in this test. Then deduct the thickness of the laminated base paper to get the laminated paper cup foam film thickness of the sample.

[0044] Deviation of thickness measurement

[0045] The average thickness measurement deviation of the same batch of foamed coated paper cups is ≤±0.02mm; the thickness measurement deviation of the same foamed coated paper cup sample at different measurement positions is ≤±0.2mm.

[0046] (3) Calculation method of the foam film density and the change of the film density of the laminated paper in the embodiment

[0047] Since the foaming of laminated paper is a process in which the thickness increases in the vertical direction of the film surface, while the area does not change in the horizontal direction of the film surface, the foaming film density of laminated paper can be calculated using the following formula:

[0048] D f =D0*T0*S0 / (T f *S f )=D0*T0 / T f

[0049] T0, S0, and D0 are the coating thickness, coating area, and coating material density of the coated paper, respectively. f , S f , D f They are the thickness, area and density of the foam film of the laminated paper. The area of ​​the laminated paper remains unchanged before and after foaming, S0 = S f .

[0050] After foaming, the density of the laminated paper decreases by X (%):

[0051] X(%)=(D0-D f ) / D0*100

[0052] The preparation method of each test sample in this embodiment is as follows:

[0053] (1) Preparation method of coated paper sample in the embodiment

[0054] 1.1. Preparation: Ensure that all equipment and components of the laminating machine are in normal working condition. Clean and calibrate necessary components to ensure that the material supply, laminating head, roller pressing and other parts are operating normally.

[0055] 1.2. Settings: According to the used laminating base paper, laminating resin raw materials and coating requirements, set the machine (such as laminating head temperature, laminating weight, etc.). According to the size and characteristics of the laminating base paper, adjust the parameters such as roller pressure, laminating head position, speed and pressure.

[0056] 1.3. Paper loading and material loading: Place the coated base paper to be coated on the roll rack, and guide the paper to the coating part, ensuring the paper tension and other alignment requirements. Suck the coating resin raw material into the barrel.

[0057] 1.4. Coating and winding: Start the laminating machine and start the coating process. The laminating head coats the film material from the top to the surface of the material and evenly distributes it on it. At the same time, the flatness and thickness control of the film material are ensured by roller pressing and other components. Always observe the machine speed, coating uniformity, coating weight deviation, etc. to ensure normal operation. While coating and winding, a roll of suitable laminated paper sample is obtained.

[0058] (2) Preparation method of coated paper sample in the embodiment

[0059] Place the above-mentioned coated paper roll samples on a fully automatic high-speed roll punching and cutting machine, select the paper cup (or other product) size molds such as the conventional 16OZ paper cup mold (155mm×269mm), the conventional 22OZ double-layer paper cup mold inner cup (188mm×270mm) and outer cup (159mm×268mm), start the machine, and automatically collect the punched and neatly stacked coated paper sheets.

[0060] The above-mentioned coated paper samples are placed in the fixture of the cup wallpaper of the fully automatic cup making machine, the base paper is installed, the process parameters are adjusted, and a batch of coated paper cup samples that meet the quality standards are obtained through continuous processes such as automatic paper feeding, sealing (bonding the cup wall), oiling, bottom punching, heating, knurling, curling, convex rolling, and cup unloading.

[0061] (3) Preparation method of foam coated paper cup sample in the embodiment

[0062] Take a laminated paper cup sample, place it in a carbon dioxide sealed container (mold) at constant temperature and pressure for a predetermined time, then quickly release the pressure, open the mold to take out the sample, and cool it at room temperature to obtain a laminated paper cup foam sample.

[0063] The sources of the coating materials in the embodiments of the present invention are shown in Table 1-1:

[0064] Table 1-1 Raw materials and sources

[0065] Compound Brand or specification source PLA 101 Zhejiang Hisun Biomaterials PLA Green Label SE2001 Zhejiang Hisun Biomaterials PLA LX175 TotalEnergiesCorbion

[0066] PLA101 (density 1.246g / cm 3 ) is the coating raw material, and according to the preparation method of the above-mentioned coated paper sample, coating is performed on different base papers to obtain single-sided PLA coated paper with different coating weights and different base papers. According to the preparation method of the above-mentioned coated paper cup sample, the single-sided PLA coated paper is prepared into a single-layer coated paper cup. The paper wall paper slurry layer of the label A paper cup is the Golden Palm high-grade paper cup base paper FK2, and the paper wall paper slurry layer of the label B paper cup is the Wuzhou natural color paper cup paper. The basic information of all single-layer coated paper cup samples is shown in Table 1-2.

[0067] In the present invention, two double-layer coated paper cup products are selected as experimental samples, wherein the label C is made of PLALX175 (density 1.223g / cm 3 ) as the coating material, while the label D is the green label SE2001 (density 1.247g / cm 3 ) is the laminating raw material, which is a blend of Hisun raw material brand PLA110 and PLA161, with a blending ratio of 70:30; the paper wall pulp layer of paper cup samples C and D are both Golden Palm high-grade paper cup base paper FK2. The basic information of the double-layer laminating paper cup samples can be found in Table 1-3.

[0068] Table 1-2 Basic information of single-layer paper cup samples

[0069]

[0070] Table 1-3 Basic information of double-layer paper cup samples

[0071]

[0072] The carbon dioxide treatment processing conditions of the coated paper cups are shown in Table 2.

[0073] Example 1

[0074] Randomly select 5 single-coated paper cups with sample number A1. The paper cups are placed flat in a 120℃ mold container without touching each other. 10MPa of carbon dioxide is injected. The samples are immersed at constant temperature and pressure for 2 minutes. The pressure is quickly released. The mold is opened to take out the samples. The samples are cooled at room temperature to obtain foamed coated paper cup samples. The appearance of the sample film surface is checked and the film thickness of the sample is tested. The results are shown in Table 2. After carbon dioxide treatment, the sample thickness increases by 0.13mm, the film density decreases by 92.9%, the film surface appearance is smooth, and the same paper cup feels both smooth and rough.

[0075] One thing that needs to be explained is that the paper cups made by the paper cup machine are of uniform size, and samples can be randomly selected for experiments; the sample cup mouth can be placed upward or downward in the mold container; the cups do not touch each other, mainly to prevent the PLA film surface from sticking to the paper surface.

[0076] Example 2

[0077] Randomly select 5 single-coated paper cups of sample numbers A2, A3, A4, A5, and A6, and place them flat in a 120°C mold container without touching each other. Inject 10MPa of carbon dioxide, soak at constant temperature and pressure for 8 minutes, quickly release the pressure, open the mold to take out the sample, and cool it at room temperature to obtain the foamed coated paper cup sample. Check the appearance of the sample film surface and test the film thickness of each sample number. The results are shown in Table 2. After carbon dioxide treatment, the thickness of samples with different numbers increased by 0.41-0.62mm, the film density decreased to 93.2-95.4%, and the film surface appearance was flat. Except for A2 and A3, which felt smooth and had an airy feel when pressed, all other samples felt rough and had horizontal lines.

[0078] Example 3

[0079] Randomly select 5 single-coated paper cups with sample number A2. The paper cups are not in contact with each other and are placed flat in a 120℃ mold container. 10MPa of carbon dioxide is injected and the samples are soaked at constant temperature and pressure for 2min, 10min and 30min respectively. The pressure is quickly released, the mold is opened to take out the samples, and they are cooled at room temperature to obtain foamed coated paper cup samples. Check the appearance of the sample film surface and test the thickness of the sample film layer. The results are shown in Table 2. After being treated with carbon dioxide, the thickness of the samples soaked for 2min, 10min and 30min increased by 0.27mm, 0.40mm and 0.17mm respectively, and the density of the film layer decreased by 90.0%, 93.0% and 85.0% respectively. The appearance of all sample films is flat, smooth to the touch, and has a sense of air when pressed.

[0080] Example 4

[0081] Randomly select 5 single-coated paper cups with sample number A2. The paper cups are not in contact with each other and are placed flat in a 120℃ mold container. 5MPa, 9MPa and 11MPa of carbon dioxide are injected respectively. The samples are soaked at constant temperature and pressure for 5min, and the pressure is quickly released. The samples are taken out of the mold and cooled at room temperature to obtain foamed coated paper cup samples. Check the appearance of the sample film surface and test the film thickness of the sample. The results are shown in Table 2. After carbon dioxide treatment, the thickness of the samples with pressures of 5MPa, 9MPa and 11MPa increased by 0.30mm, 0.36mm and 0.28mm respectively, and the film density decreased by 90.9%, 92.3% and 90.3% respectively. The appearance of the film surface of all samples is flat. Except for the sample with pressure of 9MPa, which feels smooth and has an air feeling when pressed, the other two samples with pressures of 5MPa and 11MPa feel rough.

[0082] Example 5

[0083] Randomly select 5 single-coated paper cups with sample number A2. The paper cups are not in contact with each other. They are placed flat in mold containers at 110℃, 120℃ and 130℃, respectively. 10MPa of carbon dioxide is injected, and the samples are soaked at constant temperature and pressure for 5min. The pressure is quickly released, the mold is opened to take out the samples, and they are cooled at room temperature to obtain foamed coated paper cup samples. Check the appearance of the sample film surface and test the thickness of the sample film layer. The results are shown in Table 2. After carbon dioxide treatment, the thickness of the samples at temperatures of 110℃, 120℃ and 130℃ increased by 0.22mm, 0.27mm and 0.17mm, respectively, and the density of the film layer decreased by 88.0%, 90.0% and 85.0%, respectively. The appearance of the film surface of all samples is flat, the sample at a temperature of 110℃ feels rough, the sample at a temperature of 120℃ feels smooth, and there is a sense of air when pressed. The sample at a temperature of 130℃ feels uneven.

[0084] Example 6

[0085] Sample heat resistance and insulation performance evaluation:

[0086] The double-layer paper cups commonly seen on the market were used as reference samples, and the paper cup samples of the above embodiments 1-5 were used as test samples to conduct comparative tests on their heat-resistant and heat-insulating properties. The specific method is to select a sufficient number of experimenters, pour hot water (boiling water) into the foamed coated paper cup sample and the double-layer paper cup sample respectively, and the same experimenter holds the sample paper cup and the double-layer paper cup filled with hot water with the same hand, and records the bearing time of the two paper cups filled with hot water respectively. If the bearing time of the sample paper cup filled with hot water is longer than or close to the bearing time of the double-layer paper cup filled with hot water, the judgment is "yes", otherwise it is judged "no". The test results of all the above samples are shown in Table 2. It can be seen that when the film surface is rough, the thickness of the foamed coated paper cup must be greater than 1.0mm to be better than or close to the heat insulation effect of the double-layer paper cup; when the film surface is smooth, the thickness of the foamed coated paper cup must be greater than 0.80mm to achieve the same or better heat insulation effect as the double-layer paper cup.

[0087] The appearance and feel of the foam coating reflect the internal pore structure and distribution of the foam coating to a certain extent. When the surface of the coating feels rough, most of the pores may be closed-cell structures. When the surface of the coating feels smooth and has a gas feeling when pressed, most of the pores may be open-cell structures. Therefore, samples with different appearances and feels may produce different thermal insulation effects. The relationship between the internal pore structure of the foam coating and the thermal insulation effect can be considered as a speculation of the inventor. However, it does not affect the implementation of the preparation method of the present invention and the results of the above-mentioned embodiments.

[0088] Example 7

[0089] Randomly select 6 single-coated paper cups of sample numbers B1 and B2, and place them flat in a 120℃ mold container without touching each other. Inject 10MPa of carbon dioxide, soak at constant temperature and pressure for 8min, quickly release the pressure, open the mold to take out the sample, and cool it at room temperature to obtain the foamed coated paper cup sample. Check the appearance of the sample film surface and test the film thickness of each sample number. The results are shown in Table 2. After carbon dioxide treatment, the thickness of sample numbers B1 and B2 increased by 0.36 and 0.33mm, and the film density decreased to 90.0 and 86.8%. The sample film surface became white, flat as a whole, smooth to the touch, and airy when pressed.

[0090] Table 2 Carbon dioxide treatment processing conditions, film thickness and expansion changes of coated paper cups

[0091]

[0092]

[0093] Example 8

[0094] Six double-layer coated paper cups of sample numbers C and D were randomly selected. The paper cups were not in contact with each other and were placed flat in a 120°C mold container. 10MPa of carbon dioxide was injected, and the samples were soaked at constant temperature and pressure for 8 minutes. The pressure was quickly released, the mold was opened to take out the samples, and they were cooled at room temperature to obtain foamed double-layer coated paper cup samples. The appearance of the film surface inside and outside the sample cup was checked respectively, and the thickness of the inner and outer film layers of each sample cup was tested. The results are shown in Table 3. After carbon dioxide treatment, the inner and outer thickness of sample number C increased by 0.11 and 0.07 mm, respectively, and the film layer density decreased to 91.7 and 87.5%, respectively; while the inner and outer thickness of sample number D increased by 0.07 and 0.13 mm, respectively, and the film layer density decreased to 87.5 and 92.9%, respectively; the inner and outer film surfaces of samples C and D were smooth in appearance and rough in feel.

[0095] Table 3 Carbon dioxide treatment processing conditions, film thickness and expansion changes of double-layer coated paper cups

[0096]

Claims

1. A method for preparing a heat-insulating PLA foam coated paper cup, characterized in that: The method comprises the following steps: (1) The laminated base paper and the laminated raw material PLA are prepared into PLA laminated paper through a coating process of a laminating machine; (2) After the PLA coated paper is cut into paper samples, the PLA coated paper cups are prepared by a paper cup forming machine; (3) The PLA coated paper cups are treated by immersion in carbon dioxide to prepare PLA foam coated paper cups; In the step (3), the carbon dioxide soaking method is: the PLA coated paper cup is placed in a sealed container resistant to high temperature and high pressure, carbon dioxide is injected, and soaked at a constant temperature and pressure, and the pressure is quickly released after the soaking is completed; The carbon dioxide is a subcritical or supercritical carbon dioxide fluid.

2. The method for preparing a heat-insulating PLA foam coated paper cup according to claim 1, characterized in that: The coating weight of the PLA coated paper in step (1) is 25-100 g / m 2 The PLA coated paper is single-coated paper or double-coated paper. When the PLA coated paper is double-coated paper, at least one side of the produced PLA coated paper cup is a foaming structure.

3. The method for preparing a heat-insulating PLA foam coated paper cup according to claim 2, characterized in that: The coating weight of the coated paper in step (1) is preferably 50-60 g / m 2 .

4. The method for preparing a heat-insulating PLA foam coated paper cup according to claim 1, characterized in that: In the step (1), the coated base paper is selected from any one of sulfate paper, ultra-high bulk paper cup base paper, high-grade paper cup base paper, paper cup base paper, foamed paper cup base paper, ultra-high bulk noodle bowl base paper, ultra-high bulk lunch box base paper, kraft paper, and silicone oil paper.

5. The method for preparing a heat-insulating PLA foamed coated paper cup according to claim 1, characterized in that: In the step (1), the coating raw material PLA is a PLA resin or a PLA blend, the melt index of the PLA resin is 2-10 g / 10 min, and the detection conditions of the melt index are 190° C. and 2.16 kg. The PLA blend is a blend of different PLAs or a blend of PLA and other biodegradable materials, and the other biodegradable materials are selected from any one or more combinations of PBS, PBAT, PBST, PHA and starch.

6. The method for preparing a heat-insulating PLA foamed coated paper cup according to claim 5, characterized in that: The coating raw material PLA contains a modifier, and the modifier is any one or more combinations of a chain extender, a cross-linking agent, an antioxidant, a nucleating agent, a compatibilizer, and the like.

7. The method for preparing a heat-insulating PLA foamed coated paper cup according to claim 1, characterized in that: In the step (3), during the carbon dioxide immersion, the holding temperature is 110-130° C., the holding pressure is 5-12 MPa, the holding time is 2-30 min, and the pressure release rate is 15-41 MPa / s.

8. The method for preparing a heat-insulating PLA foamed coated paper cup according to claim 1, characterized in that: The PLA coated paper cups in step (3) are stacked in piles, and the gaps between the cups are matched when stacking.

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