Modification and application of the hottest modifi

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Modification and application of Modified PVA high barrier film

1. Characteristics of polyvinyl alcohol (PVA)

polyvinyl alcohol (PVA) is the hydrolysate of polyvinyl acetate, which has the characteristics of excellent film making performance, colorless and transparent film, oil resistance, organic solvent resistance, stability to bacteria and sunlight, etc. as a film production process, it improves the economy of aircraft. The following characteristics must be paid enough attention to

(1) the solvent of PVA is water, but its solubility to water is largely affected by the degree of polymerization, especially by the degree of alcoholysis. The completely alcoholized PVA has very little solubility in water. When the alcoholysis degree is below 88%, it is almost completely dissolved at room temperature of 20 ℃, but with the increase of alcoholysis degree, the solubility decreases significantly

(2) the viscosity of PVA aqueous solution with high alcoholysis degree changes due to different storage conditions, and the storage temperature directly affects the viscosity. Experiments show that the viscosity decreases greatly at 20 ~ 50 ℃, and the viscosity decreases slightly above 50 ℃. The temperature, friction pressure and rate of gradually rising at 80 ℃ require the material to meet the requirements of high glass transition temperature (TG), and it is stable above 50 ℃. The viscosity of PVA aqueous solution increases with the increase of PVA concentration. In the static state, the surface of PVA aqueous solution is very easy to be skinned, which is extremely detrimental to the coating process

(3) PVA film has excellent oxygen resistance under dry conditions, and its oxygen permeability coefficient is the lowest among all kinds of resin films

there are a lot of hydroxyl groups (OH) on the molecular chain of PVA. In the wet environment, these hydroxyl groups are easy to form hydrogen bonds with water molecules, resulting in changes in the aggregated structure of PVA, which greatly reduces the barrier property of PVA. With the increase of relative humidity, the oxygen transmission increased significantly

(4) PVA film will swell and fall off when encountering water. If this coated composite film is exposed in a humid environment, its high oxygen resistance will be lost

in the early 1990s, some domestic universities and research units made PVA resin into hydrosol, and made PVA coating film by coating composite process. In order to stabilize the barrier property of PVA film under high humidity conditions, BOPP/PVA was produced by masking technology. The essence of PE coated film is to clamp PVA, which is afraid of water, between two layers of films with good moisture resistance, so as to shield the influence of moisture on PVA. The PVA coating composite film produced by this process can maintain its barrier performance, but the process is complex, low efficiency, high cost and unstable performance

2. Polyvinyl alcohol modification

in order to improve and stabilize the wet barrier performance of PVA, simplify the production process, reduce the production cost, and bring the superior PVA composite film to the market, we modified PVA

the reason why polyvinyl alcohol is not water resistant is that it has hydrophilic hydroxyl (o can be put into detection according to the standard method h). If the hydroxyl can be properly sealed and connected with water-resistant groups, the water resistance of PVA film can be improved. PVA contains hydroxyl, which can produce all typical reactions of polyols. We selected a variety of compounds that can be molecular crosslinked with Oh in PVA, and their modification effect and processability are not ideal. Finally, we successfully developed a melamine resin modification solution "868" that has no side effects on human body. As "868" is a multifunctional polycondensate, it can interact with the hydroxyl group in PVA appropriately with a small amount of addition, so that PVA forms a strong and tough three-dimensional structure coating, which stabilizes the air tightness of PVA under wet conditions and improves the water resistance

the modified PVA glue solution does not peel at room temperature, and the viscosity does not rise within the allowable time of production. It realizes glue preparation and coating at room temperature, which provides a loose process condition for the production of Modified PVA coated composite film

coating process: due to the large polarity of the modified liquid, the adhesion between the modified PVA and the base film is improved, and the interlayer bonding force can reach the degree of inseparability. It can be directly coated on the surface of PE, BOPP, BOPA, BOPET and other films to form the modified PVA/PE, modified PVA/BOPP coating composite film, The production process is as follows:

PE unwinding - → modified PVA coating - → drying - → winding - → aging - → slitting - → inspection - → warehousing

modified PVA/PE film can be color printed on PVA surface without any treatment, and the ink adhesion is very strong

in order to further improve the packaging and decoration effect, it can also be printed on BOPP and other substrates, then coated and compounded with modified PVA, and further processed into BOPP/modified PVA/PE film

3. coating and composite equipment

we have designed, processed and manufactured a multifunctional coating unit suitable for the production of PVA coating composite films that can meet the relevant international standards. The unit adopts advanced structures such as reverse roll coating head, hot air convection drying, micro tension conveying, and can produce BOPP/modified PVA/PE, BOPP/PE, PET/PE composite films in one step; It can also be used in the production of self-adhesive and protective film, achieving the design goals of stable operation, uniform coating, energy saving and multi-purpose

when the drying path length and air supply volume of the cloth coating and laminating unit are fixed, the drying speed of the coating film is controlled by the coating thickness, drying path temperature and film walking speed. The thicker the coating is and the lower the drying path temperature is, the slower the drying speed is. In order to ensure the drying of the coating, the running speed of the film is bound to be very low, losing the significance of industrial production. We have formulated the process conditions that the coating thickness is 5 ~ 8 microns and the PVA coating passes quickly in the 100 ℃ drying channel, which is not only conducive to improving the crystallinity of PVA, ensuring the air tightness and water resistance of PVA, but also conducive to improving the production efficiency. The production capacity of this unit is 1000 tons/year

4. PVA modification effect

the modified PVA coating composite film has passed the small-scale and pilot tests, and has built a production line with an annual output of 1000 tons. After the product is put on the market, it has been highly praised by users. Compared with unmodified PVA coating film, the adhesion, wet barrier and water resistance of Modified PVA coating film have been significantly improved

5. Characteristics of Modified PVA high barrier film

(1) PVA is moderately crosslinked with melamine resin modification solution "868", which is non-toxic and has no side effects on human body. While retaining the advantages of dry barrier performance, transparency and flexibility, PVA also improves its adhesion to the substrate, eliminating precoating and adhesives. In particular, compared with unmodified PVA, the wet barrier performance is significantly improved, and the full set of technology is advanced

(2) compared with the unmodified PVA process, the "868" modified PVA eliminates the pre coating and the use of adhesives, which can reduce equipment investment and reduce product costs. The modified PVA hydrosol solves the problems of surface scaling under static conditions and viscosity rise under production conditions, cancels the masking process, and the production process is reasonable

(3) compared with unmodified PVA, the modified PVA coating layer has no swelling and falling off after soaking in water for 24 hours, and the key index oxygen transmission has reached the international advanced level

(4) thick auxiliary materials and production equipment are based in China, and the products have been mass produced in Nanjing hongbaoli (Group) Co., Ltd

6. Application

the application of Modified PVA high barrier film is inseparable from its characteristics. Here is a brief introduction

(1) the modified PVA film has good transparency and gloss. It is especially suitable for the storage of clothing, shoes and hats, leather and leather products, arts and crafts, manuscripts and archives. It is used together with deoxidizers, and has the effects of mold prevention, insect decay prevention, oxidation and discoloration prevention

(2) modified PVA film has strong polarity and good ink adhesion during printing. Beautiful printing effect can be obtained by using cellophane printing ink

(3) it has good oil resistance and organic solvent resistance. It is insoluble in animal oil, vegetable oil, mineral oil, alcohols, ethers, ketones and esters. It is suitable for the packaging of chemical raw materials and intermediates and the packaging of fatty foods

(4) it has good fragrance retention, and can be widely used in the packaging and sealing of tea, coffee, curry powder, pepper powder, pepper powder and other spices. It can be used for filling mustard, which can make the smell impervious

(5) it has excellent gas barrier, especially low oxygen permeability, and is suitable for the packaging and sealing of the following items

a. it can be used in the packaging of small Cereals, oil, seafood dry hair, precious traditional Chinese medicine, tobacco and so on. When used in combination with deoxidizer or vacuum pumping, it has a particularly obvious effect of preventing mold, moth and fading. It is used to seal high-fat food, prevent fat oxidation and "ha" and maintain the original flavor of food

b. It is used for the comprehensive storage of radio components and complete machines, precision machinery, ordnance, radar, ammunition and large missiles, and has a unique function of anti-oxidation and corrosion

c, optical instruments, lenses and other accessories are comprehensively sealed to prevent mildew and fog

source: National Plastic Processing Industry Information Center

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