A method for reducing the grammage of polyhydroxyalkanoate aqueous coating while maintaining barrier properties and applications thereof

Abstract

The application provides a method for reducing the grammage of a polyhydroxyaliphatic ester water-based coating while maintaining the barrier property and application thereof. The method for reducing the grammage of the polyhydroxyaliphatic ester water-based coating while maintaining the barrier property comprises the step of heat pressing the polyhydroxyaliphatic ester water-based coating after coating and drying, wherein in the heat pressing step, the polyhydroxyaliphatic ester water-based coating is heated to a temperature of 10-30 DEG C higher than the melting point of the polyhydroxyaliphatic ester, and a pressure of 300-600 kPa is applied, and the heat pressing time is controlled to 1-2 s. The application can reduce the coating grammage and improve the barrier property of the coating by heat pressing the polyhydroxyaliphatic ester water-based coating after coating and drying under specific conditions. The application has a simple production process and wide application prospect.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of water-based coating products, in particular to a method for reducing the grammage of polyhydroxyaliphatic ester water-based coating while maintaining the barrier property and application thereof. BACKGROUND

[0002] Various waterproof and impermeable products are needed in people's life, such as paper cups and the like. With the enhancement of people's awareness of health and environmental protection, products coated with polyhydroxyaliphatic ester water-based coating are becoming more and more popular.

[0003] At present, the process for preparing paper coated with polyhydroxyaliphatic ester water-based coating is as follows: polyhydroxyaliphatic ester water-based coating is applied to the surface of base paper, then flat treatment is performed by means of a doctor blade or an air knife, and then rapid (linear speed 60-80 m / min) drying and film forming treatment is performed by passing through a drying channel at 110-150℃, and finally winding is performed.

[0004] The polyhydroxyaliphatic ester coated paper prepared according to the above method has good film forming property, but the barrier property is general, and a higher coating grammage is required to increase the impermeability, and the coating grammage needs to reach 12-20 g / m 2 At this time, the coating amount is relatively high, the cost is increased, and sometimes there is still point penetration. SUMMARY

[0005] In view of the problems existing in the prior art, the present application provides a method for reducing the grammage of polyhydroxyaliphatic ester water-based coating while maintaining the barrier property and application thereof, which realizes the reduction of cost while achieving good barrier effect.

[0006] In a first aspect, the present application provides a method for reducing the grammage of polyhydroxyaliphatic ester water-based coating while maintaining the barrier property, which comprises the step of heat pressing the polyhydroxyaliphatic ester water-based coating after coating and drying, wherein in the step of heat pressing, the polyhydroxyaliphatic ester water-based coating is heated to a temperature higher than the melting point of polyhydroxyaliphatic ester by 10-30℃, while a pressure of 300-600 kPa is applied, and the heat pressing time is controlled to be 1-2 s.

[0007] According to the method provided by the present application, the grammage of the polyhydroxyaliphatic ester water-based coating after coating and drying is controlled to be 6-8 g / m 2 .

[0008] It should be noted that in the hot-pressing process of this invention, the heating temperature is 10-30°C higher than the melting point of polyhydroxyalkanoates (PHA), and this heating temperature is related to the applied pressure. That is, because this invention applies a pressure of 300-600 kPa, heating the coating to 10-30°C above the melting point of PHA softens it. Under pressure, the particles deform, thereby improving the barrier properties of the coating. If only at normal pressure, the aqueous PHA coating needs to be heated to 30-50°C above the melting point of PHA to soften. However, if softening is actually performed at normal pressure, the heating temperature is usually around 180°C. This temperature is too high, not only increasing energy consumption but also making processing difficult or affecting product quality (e.g., paper yellowing) for heat-sensitive substrates such as paper.

[0009] In summary, this invention involves subjecting the dried polyhydroxyalkanoate (PHA) waterborne coating to a second hot-pressing process. The temperature, pressure, and time of this hot-pressing process are controlled under specific conditions, causing the PHA waterborne coating to soften upon heating and undergo particle deformation under pressure, becoming more even and enhancing the adhesion between the internal particle surfaces. This significantly improves the barrier properties of the coating, while maintaining a very low coating weight of 6-8 g / m³. 2 A weight of 10 g / m² can achieve excellent barrier properties, which is significantly better than the 12-20 g / m² of existing technologies. 2 Coating effect. The method of this invention has low energy consumption and can achieve both good barrier properties and low basis weight of polyhydroxyalkanoate waterborne coatings at relatively low processing temperatures, providing technical support for the large-scale production of waterproof and impermeable products such as paper cups. In this invention, if the heating temperature is too high, the pressure is too great, or the hot pressing time is too long, the coating film will be overheated and completely melted, leading to film rupture. Furthermore, the molten film, due to its high viscosity, is prone to sticking to the rollers and will be peeled off from the coating substrate.

[0010] If the heating temperature is too low, the coating layer will not be heated enough and will not be softened. If the pressure is too low and the hot pressing time is too short, the coating layer will not produce a calendering effect and will not be able to improve its barrier properties.

[0011] In some embodiments of the present invention, the hot pressing process uses two metal rollers that rotate in the same or opposite directions, one of which is a smooth roller and the other is a soft roller with an elastic material wrapped around its surface, preferably rubber.

[0012] In the heat-pressing process, the dried polyhydroxyalkanoate aqueous coating is brought into contact with the light roller, and the light roller is heated so that the polyhydroxyalkanoate aqueous coating reaches a preset temperature. The soft roller and the light roller are pressed together to apply a target pressure to the polyhydroxyalkanoate aqueous coating. In this process, one of the metal rollers needs to be a soft roller made of elastic material. If both rollers are light rollers, the paper is likely to be crushed. The soft roller can provide a buffer effect and make the coating layer in close contact with the light roller.

[0013] It can be understood that other devices capable of providing the heat-pressing conditions for the polyhydroxyalkanoate aqueous coating can also be used.

[0014] In some embodiments of the present application, the coating substrate of the polyhydroxyalkanoate aqueous coating is paper. The parameters of the heat-pressing process of the present application are more suitable for the case where the coating substrate is paper. In the heat-pressing process, the substrate is also subjected to heat-pressing because the polyhydroxyalkanoate aqueous coating has been dried into a film and integrated with the substrate at this time.

[0015] The paper in the present application is a conventional paper understood by those skilled in the art, such as white card paper, gray board, copper plate paper, offset paper, corrugated paper, writing paper, kraft paper, newsprint paper, etc. In some embodiments of the present application, the paper used is white card paper.

[0016] In the present application, the polyhydroxyalkanoate aqueous coating used for coating is composed of a polyhydroxyalkanoate suspension and optional additives, and the solid content of the polyhydroxyalkanoate suspension is 25-50%.

[0017] In some embodiments of the present application, the polyhydroxyalkanoate suspension is obtained by dispersing polyhydroxyalkanoate powder into water. The polyhydroxyalkanoate powder can be obtained by microbial fermentation or by synthetic methods.

[0018] In other embodiments of the present application, the polyhydroxyalkanoate suspension is obtained by centrifugal extraction of a polyhydroxyalkanoate fermentation broth. Preferably, the centrifugal extraction includes cell wall breaking treatment. Directly using the polyhydroxyalkanoate solution obtained by centrifugal extraction of the polyhydroxyalkanoate fermentation broth as the raw material for preparing the polyhydroxyalkanoate aqueous coating has better dispersion effect and avoids agglomeration.

[0019] Preferably, the particle size D50 of the polyhydroxyalkanoate suspension is in the range of 0.1-5 μm. Within this range, the smaller the particle size, the more conducive to low grammage coating, while achieving better coating effect.

[0020] In some embodiments of the present application, the additives include one or more of film-forming agents, emulsifiers, leveling agents, and thickening agents.

[0021] Preferably, the amount of the film forming agent added is 0.1-1%, the amount of the emulsifier added is 0.1-1%, the amount of the leveling agent added is 0.1-1%, and the amount of the thickening agent added is 0.1-1%, based on the mass of the polyhydroxyaliphatic acid ester suspension.

[0022] In some embodiments of the present application, to obtain a polyhydroxyaliphatic acid ester aqueous coating with good performance, all of the four additives, i.e., the film forming agent, the emulsifier, the leveling agent, and the thickening agent, are added, but the amount of each of them is small, not more than 1%.

[0023] In some embodiments of the present application, the film forming agent is selected from one or more of diethylene glycol ether, propylene glycol ether, and N-methyl pyrrolidone.

[0024] In some embodiments of the present application, the emulsifier is selected from one or more of alkyl nonyl phenol ethoxyl ether, potassium dodecyl phosphate, sodium dodecyl polyoxyethylene ether sulfate, sodium lauroyl acid, and sodium alpha-alkenyl sulfonate.

[0025] In some embodiments of the present application, the leveling agent is selected from one or more of Digo 432, modified polysiloxane, and cellulose.

[0026] In some embodiments of the present application, the thickening agent is selected from one or more of gelatinized starch, polyacrylonitrile, sodium dodecyl benzene sulfonate, sodium polyacrylate, sodium alginate, and polypyrrolidone; preferably, the gelatinized starch is selected from one or more of corn starch, potato starch, sweet potato starch, and cassava starch.

[0027] In the present application, the preparation method of the polyhydroxyaliphatic acid ester aqueous coating is to mix the components uniformly, which can be specifically achieved by conventional means such as mechanical stirring or ultrasonic dispersion, and further de-bubbling operation can be performed.

[0028] In a second aspect, the present application provides a polyhydroxyaliphatic acid ester aqueous coating with low grammage and good barrier property.

[0029] The polyhydroxyaliphatic acid ester aqueous coating provided by the present application has a grammage of 6-8 g / m 2 The polyhydroxyaliphatic acid ester aqueous coating does not permeate in the dyne liquid penetration test, the hot coffee test, and the hot water test, respectively, and has good barrier property.

[0030] In a third aspect, the present application provides a barrier product, which comprises a substrate and the polyhydroxyaliphatic acid ester aqueous coating with low grammage and good barrier property.

[0031] In some embodiments of the present application, the substrate is paper.

[0032] The application provides a method for reducing the grammage of a polyhydroxyaliphatic ester aqueous coating while maintaining the barrier property and application thereof. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 SEM image of the polyhydroxyaliphatic ester aqueous coating after heat pressing treatment in Example 1;

[0034] Figure 2 SEM image of the polyhydroxyaliphatic ester aqueous coating directly coated in Comparative Example 1. DETAILED DESCRIPTION

[0035] The term "comprising" or "including" or "containing" in the present application is an open description, which contains the specified components or steps described, and other specified components or steps that do not materially affect.

[0036] The endpoints of the ranges and any values in the ranges disclosed herein are not limited to the precise values stated. The ranges and values should be construed to be approximations that allow for significant variation. Within the range and values, endpoints are not required to be separately and independently combinable to achieve a new range or value, unless otherwise stated herein.

[0037] In the description of the specification, the description of the terms "one embodiment", "some embodiments", "specific embodiments", or "some specific embodiments" means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the embodiments of the application. In the specification, the illustrative description of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any appropriate manner in any one or more embodiments or examples. In addition, the person skilled in the art can combine and combine the different embodiments or examples described in the specification and the features of the different embodiments or examples without contradiction.

[0038] In order to make the purpose, technical scheme and advantages of the present application clearer, the technical scheme in the present application will be described clearly and completely below. Obviously, the described embodiments are part of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by the person skilled in the art without creative labor are within the scope of protection of the present application.

[0039] Unless otherwise specified in the examples, the techniques or conditions were performed according to the techniques or conditions described in the literature in the field, or according to the product instructions. Unless otherwise specified, the reagents or instruments used were conventional products that can be purchased through regular channels.

[0040] The English abbreviations appearing in this text correspond to the following Chinese full names:

[0041] PHA: polyhydroxyalkanoate

[0042] P34HB: poly(3-hydroxybutyrate-co-4-hydroxybutyrate)

[0043] PHBV: poly(3-hydroxybutyrate-co-3-hydroxyvalerate).

[0044] The parts in the following examples are parts by weight unless otherwise specified.

[0045] In the following examples, the emulsifier is sodium lauroylate, the thickening agent is sodium alginate, the film-forming agent is diethanol ether, and the leveling agent is cellulose.

[0046] In the following examples, the dyne liquid penetration test: select 34# dyne liquid, add a drop to the paper coating layer with a smearing pen, stay for 60s, then wipe off the dyne liquid drop with water-absorbing paper, and observe whether there is any penetration phenomenon.

[0047] Hot coffee test: prepare a container to hold ≥95℃ hot coffee for 2h, and observe whether there is any penetration phenomenon.

[0048] Hot water test: prepare a container to hold 100℃ hot water for 2h, and observe whether there is any penetration phenomenon.

[0049] Example 1

[0050] This example provides a low grammage and good barrier polyhydroxyalkanoate aqueous coating, and its preparation method is as follows:

[0051] The aqueous coating composition is as follows: P34HB-10% 4HB (melting point 140℃) suspension 100 parts (with solid content 25 parts, water 75 parts), emulsifier 0.1 part, thickening agent 0.2 part, film-forming agent 0.1 part, leveling agent 0.1 part.

[0052] Aqueous coating preparation: weigh each component according to the mass ratio, mix, and then the viscosity is 380 mPa.s, the polyhydroxyalkanoate particle size D50 = 0.8μm, mechanical stirring for 30min, and ultrasonic for 20min to remove bubbles.

[0053] Coating: use a doctor blade to coat the aqueous coating on the surface of the paper, and then perform drying treatment, the drying temperature is 120℃, and the drying time is 25s. Single-sided single-layer coating, coating grammage 8g / m2 .

[0054] Heat press treatment: the paper with formed coating film layer was passed through a light roller, the temperature of the light roller was heated to 150℃, and at the same time, a pressure of 300kPa was applied to the paper, and the heat press time lasted for 2s.

[0055] The SEM image of the polyhydroxyaliphatic acid ester aqueous coating prepared in the example is shown in Figure 1 From the figure, it can be seen that after calendering treatment, the needle-shaped hole defects of the coating disappear, the coating is more compact, the interface between the coating particles disappears, and the barrier property is improved, and even when the coating weight is low, the barrier effect is good.

[0056] The polyhydroxyaliphatic acid ester aqueous coating obtained in the example was subjected to dyne liquid penetration test, no penetration; hot coffee test, no penetration; hot water test, no penetration.

[0057] Comparative Example 1

[0058] The comparative example provides a polyhydroxyaliphatic acid ester aqueous coating, and the preparation method is as follows:

[0059] Among them, the composition of the aqueous coating is: P34HB-10% 4HB (melting point 140℃) suspension 100 parts (in which the solid content is 25 parts, water 75 parts), emulsifier 0.1 part, thickening agent 0.2 part, film forming aid 0.1 part, leveling agent 0.1 part.

[0060] The aqueous coating is configured: each component is weighed according to the mass ratio, and after mixing, the viscosity is 380mPa.s, the polyhydroxyaliphatic acid ester particle size D50=0.8μm, mechanical stirring for 30min, ultrasonic for 20min to remove bubbles.

[0061] Coating: the aqueous coating is applied to the surface of the paper by using a doctor blade coating method, and then dried, the drying temperature is 120℃, and the drying time is 25s. Single-sided single-layer coating, coating weight 8g / m 2 .

[0062] No heat press treatment.

[0063] The SEM image of the polyhydroxyaliphatic acid ester aqueous coating prepared in the comparative example is shown in Figure 2 From the figure, it can be seen that the coating has needle-shaped hole defects, and the interface between the coating particles is clearly separated, and at this time, if the coating weight is low, it will have an adverse effect on the barrier effect.

[0064] The polyhydroxyaliphatic acid ester aqueous coating obtained in the comparative example was subjected to dyne liquid penetration test, penetration; hot coffee test, penetration; hot water test, penetration.

[0065] Comparative Example 2

[0066] The comparative example provides a polyhydroxyaliphatic ester aqueous coating, and a preparation method thereof is as follows:

[0067] The aqueous coating is prepared by mixing the following components: P34HB-10% 4HB (melting point 140 DEG C) suspension 100 parts (25 parts of solid content and 75 parts of water), emulsifier 0.1 part, thickening agent 0.2 part, film forming aid 0.1 part, and leveling agent 0.1 part.

[0068] The aqueous coating is prepared by mixing the following components: P34HB-10% 4HB (melting point 140 DEG C) suspension 100 parts (25 parts of solid content and 75 parts of water), emulsifier 0.1 part, thickening agent 0.2 part, film forming aid 0.1 part, and leveling agent 0.1 part.

[0069] Coating: the aqueous coating is applied to the surface of the paper by using a doctor blade coating method, and then drying treatment is performed, the drying temperature is 120 DEG C, and the drying time is 25 s. The coating is single-layer and single-sided, and the coating weight is 12 g / m 2 .

[0070] No hot pressing treatment is performed.

[0071] The polyhydroxyaliphatic ester aqueous coating obtained in the comparative example is subjected to dyne liquid penetration test, and there is point penetration; the hot coffee test, and there is point penetration; and the hot water test, and there is point penetration.

[0072] Comparative Example 3

[0073] The comparative example provides a polyhydroxyaliphatic ester aqueous coating, and a preparation method thereof is as follows:

[0074] The aqueous coating is prepared by mixing the following components: P34HB-10% 4HB (melting point 140 DEG C) suspension 100 parts (25 parts of solid content and 75 parts of water), emulsifier 0.1 part, thickening agent 0.2 part, film forming aid 0.1 part, and leveling agent 0.1 part.

[0075] The aqueous coating is prepared by mixing the following components: P34HB-10% 4HB (melting point 140 DEG C) suspension 100 parts (25 parts of solid content and 75 parts of water), emulsifier 0.1 part, thickening agent 0.2 part, film forming aid 0.1 part, and leveling agent 0.1 part.

[0076] Coating: the aqueous coating is applied to the surface of the paper by using a doctor blade coating method, and then drying treatment is performed, the drying temperature is 120 DEG C, and the drying time is 25 s. The coating is single-layer and single-sided, and the coating weight is 20 g / m 2 .

[0077] No hot pressing treatment is performed.

[0078] The polyhydroxyaliphatic ester aqueous coating obtained in the comparative example is subjected to dyne liquid penetration test, and there is no penetration; the hot coffee test, and there is no penetration; and the hot water test, and there is no penetration. However, the coating weight is high, and the cost is high.

[0079] Comparative Example 4

[0080] This comparative example provides a polyhydroxyalkanoate water-based coating, which is prepared as follows:

[0081] The water-based coating is composed of: P34HB-10% 4HB (melting point 140°C) suspension 100 parts (with solid content 25 parts, water 75 parts), emulsifier 0.1 part, thickening agent 0.2 part, film-forming aid 0.1 part, leveling agent 0.1 part.

[0082] Water-based coating configuration: each component is weighed according to the mass ratio, the viscosity after mixing is 380 mPa.s, the particle size D50 of polyhydroxyalkanoate is 0.8 μm, mechanical stirring for 30 min, ultrasonic for 20 min to remove bubbles.

[0083] Coating: the water-based coating is applied to the surface of the paper using a doctor blade coating method, and then dried at a drying temperature of 120°C for 25s. Single-sided single-layer coating, coating weight 8g / m 2 .

[0084] Hot pressing treatment: the paper with formed coating film layer is passed through a light roller, the temperature of the light roller is heated to 140°C, and at the same time, a pressure of 100kPa is applied to the paper, and the hot pressing time lasts for 0.3s.

[0085] The polyhydroxyalkanoate water-based coating obtained in this comparative example is subjected to dyne liquid penetration test, penetration; hot coffee test, penetration; hot water test, penetration.

[0086] Comparative Example 5

[0087] This comparative example provides a polyhydroxyalkanoate water-based coating, which is prepared as follows:

[0088] The water-based coating is composed of: P34HB-10% 4HB (melting point 140°C) suspension 100 parts (with solid content 25 parts, water 75 parts), emulsifier 0.1 part, thickening agent 0.2 part, film-forming aid 0.1 part, leveling agent 0.1 part.

[0089] Water-based coating configuration: each component is weighed according to the mass ratio, the viscosity after mixing is 380 mPa.s, the particle size D50 of polyhydroxyalkanoate is 0.8 μm, mechanical stirring for 30 min, ultrasonic for 20 min to remove bubbles.

[0090] Coating: the water-based coating is applied to the surface of the paper using a doctor blade coating method, and then dried at a drying temperature of 120°C for 25s. Single-sided single-layer coating, coating weight 8g / m 2 .

[0091] Hot-pressing treatment: the paper with formed coating film layer was passed through a light roller, the temperature of the light roller was heated to 170℃, and at the same time, a pressure of 700 kPa was applied to the paper, and the hot-pressing time lasted for 5 s.

[0092] The polyhydroxyalkanoate aqueous coating obtained in the present comparative example was subjected to dyne liquid penetration test, no penetration; hot coffee test, no penetration; hot water test, no penetration. However, yellowing of the paper and the coating and paper crushing deformation occurred.

[0093] Example 2

[0094] The present example provides a polyhydroxyalkanoate aqueous coating with low grammage and good barrier property, and the preparation method is as follows:

[0095] The aqueous coating composition is as follows: P34HB-15% 4HB (melting point 120℃) suspension 100 parts (solid content 30 parts, water 70 parts), emulsifier 0.5 parts, thickening agent 1 part, film forming agent 0.3 parts, leveling agent 0.2 parts.

[0096] The aqueous coating is configured by weighing each component according to the mass ratio, and after mixing, the viscosity is 420 mPa.s, the polyhydroxyalkanoate particle size D50 = 0.8 μm, mechanical stirring for 30 min, and ultrasonic for 20 min to remove air bubbles.

[0097] Coating: the aqueous coating is applied to the surface of the paper by using a doctor blade coating method, and then dried at a drying temperature of 120℃ for 25 s. Single-sided single-layer coating, coating grammage 8 g / m 2 .

[0098] Hot-pressing treatment: the paper with formed coating film layer was passed through a light roller, the temperature of the light roller was heated to 150℃, and at the same time, a pressure of 300 kPa was applied to the paper, and the hot-pressing time lasted for 2 s.

[0099] The polyhydroxyalkanoate aqueous coating obtained in the present example was subjected to dyne liquid penetration test, no penetration; hot coffee test, no penetration; hot water test, no penetration.

[0100] Example 3

[0101] The present example provides a polyhydroxyalkanoate aqueous coating with low grammage and good barrier property, and the preparation method is as follows:

[0102] The aqueous coating composition is as follows: PHBV-10% HV (melting point 140℃) suspension 100 parts (solid content 40 parts, water 60 parts), emulsifier 0.1 parts, thickening agent 0.5 parts, film forming agent 0.5 parts, leveling agent 0.5 parts.

[0103] Water-based paint configuration: each component is weighed according to the mass ratio, the viscosity is 320 mPa.s after mixing, the polyhydroxy aliphatic acid ester particle size D50 = 0.8 μm, mechanical stirring for 30 min, ultrasonic for 20 min to remove bubbles.

[0104] Coating: the water-based paint is applied to the surface of the paper by using a doctor blade coating method, and then dried at a drying temperature of 120℃ for 25s. The paper is coated on one side with a single layer, and the coating weight is 6g / m 2 .

[0105] Hot pressing treatment: the paper with the formed coating film layer is passed through a light roller, the temperature of the light roller is heated to 150℃, and the paper is subjected to a pressure of 500kPa at the same time, and the hot pressing time lasts for 1s.

[0106] The polyhydroxy aliphatic acid ester water-based coating obtained in the embodiment is subjected to daoyin liquid penetration test, no penetration; hot coffee test, no penetration; hot water test, no penetration.

[0107] Finally, it should be noted that: the above examples are only used to illustrate the technical solutions of the present application, but not to limit it; although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing examples, or make equivalent replacement for part of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A method of reducing the coat weight of a polyhydroxyalkanoate aqueous coating while maintaining barrier properties, characterized in that, The method comprises a hot-pressing step for the polyhydroxyalkanoate aqueous coating after drying and coating, and the coating substrate is paper; the polyhydroxyalkanoate aqueous coating for coating comprises a polyhydroxyalkanoate suspension and optional additives; the particle size D50 of the polyhydroxyalkanoate suspension is in the range of 0.1-5 μm; In the hot-pressing step, the polyhydroxyalkanoate aqueous coating is heated to a temperature 10-30 ℃ higher than the melting point of polyhydroxyalkanoate, and a pressure of 300-600 kPa is applied, and the hot-pressing time is controlled in the range of 1-2 s; The coating weight of the polyhydroxyalkanoate aqueous coating after drying is controlled at 6-8 g / m 2 ; The polyhydroxyalkanoate aqueous coating is subjected to the dyne liquid penetration test, hot coffee test and hot water test, and none of them is penetrated.

2. The method of reducing the coat weight of a polyhydroxyalkanoate aqueous coating while maintaining barrier properties according to claim 1, characterized in that, In the hot-pressing step, the device used is two metal rollers rotating in the same direction or in the opposite direction, one of which is a smooth roller, and the other is a soft roller with an elastic material wrapped on the surface, and the elastic material is rubber.

3. The method of reducing the coat weight of a polyhydroxyalkanoate aqueous coating while maintaining barrier properties according to claim 1 or 2, characterized in that, The solid content of the polyhydroxyalkanoate suspension is 25-50%.

4. The method of reducing the coat weight of a polyhydroxyalkanoate aqueous coating while maintaining barrier properties according to claim 3, characterized in that, The polyhydroxyalkanoate suspension is obtained by dispersing polyhydroxyalkanoate powder into water, or the polyhydroxyalkanoate suspension is obtained by centrifugal extraction of polyhydroxyalkanoate fermentation broth.

5. The method of reducing the coat weight of a polyhydroxyalkanoate aqueous coating while maintaining barrier properties according to claim 3, wherein, The additives include one or more of film-forming agents, emulsifiers, leveling agents, and thickening agents.

6. The method of reducing the coat weight of a polyhydroxyalkanoate aqueous coating while maintaining barrier properties according to claim 5, characterized in that, The addition amount of the film-forming agent is 0.1-1%, the addition amount of the emulsifier is 0.1-1%, the addition amount of the leveling agent is 0.1-1%, and the addition amount of the thickening agent is 0.1-1%, based on the mass of the polyhydroxyalkanoate suspension.

7. A low basis weight and high barrier polyhydroxyalkanoate aqueous coating prepared by the method of any one of claims 1 to 6, wherein the polyhydroxyalkanoate aqueous coating has a basis weight of 5 to 20 g / m2 and a barrier property of 0.5 to 2 g / m2 / day. The polyhydroxyalkanoate aqueous coating has a grammage of 6-8 g / m 2 The polyhydroxyalkanoate aqueous coating respectively carries out daime liquid penetration test, hot coffee test, hot water test, and none of them penetrates.

8. A barrier product, characterized in that The method comprises a substrate and the low-grammage and good-barrier polyhydroxyalkanoate aqueous coating of claim 7.

9. The barrier product according to claim 8, characterized in that The substrate is paper.

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