White latex resistant to low-temperature freezing and thawing and preparation method thereof

Abstract

The invention discloses a low temperature freeze thawing resistant white latex and a preparation method thereof, and relates to the technical field of polymer emulsion polymerization, the low temperature freeze thawing resistant white latex comprises the following raw materials by weight: 80-100 parts of polyvinyl alcohol, 90-110 parts of vinyl acetate, 40-60 parts of small molecular alcohol, 1-5 parts of acrylic acid, 1-5 parts of an initiator, 0-5 parts of a pH regulator, and 0-5 parts of a preservative. The polyvinyl alcohol is divided into two parts to be added in the preparation process, the first part is added during the polymerization reaction and is used as a protective colloid of the polymerization reaction, and the second part is added after the polymerization reaction and is used for improving the performance of the white latex. The white latex prepared by the invention has excellent low-temperature resistance, can still maintain the original performance of the white latex after 5 cycles of freeze thawing test at-17 DEG C to 25 DEG C, and has wide application prospects.

Description

Technical Field

[0001] The invention relates to the technical field of polymer emulsion polymerization, and in particular to a white latex resistant to low-temperature freezing and thawing and a preparation method thereof. Background Art

[0002] White latex (polyvinyl acetate emulsion) is one of the most widely used, largest-volume, and oldest water-soluble adhesives. It is widely used in furniture assembly, packaging materials, wood processing, leather and paper, construction and decoration, the cigarette industry, foam plastics, fiberboard, porous materials, and other fields because of its advantages such as ease of use, low raw material cost, simple production process and equipment, low environmental pollution, and high bonding strength.

[0003] The traditional method of synthesizing white latex mainly uses polyvinyl alcohol as a protective colloid and is obtained by polymerization of vinyl acetate through free radical reaction. The white latex synthesized by this method is difficult to withstand low temperature environments. When the ambient temperature is below 0°C, the water in the glue is easy to freeze, causing the emulsion structure to be destroyed and the adhesive performance to drop significantly, which seriously limits its application in cold areas or outdoor scenes in winter. Especially when it needs to undergo multiple freeze-thaw cycles (such as temperature fluctuations during transportation or storage), the stability and durability of conventional white latex face severe challenges. Therefore, providing a white latex that is resistant to low temperature freeze-thaw is a problem that the existing technology urgently needs to solve. Summary of the Invention

[0004] The purpose of the present invention is to provide a white latex resistant to low-temperature freeze-thaw and a preparation method thereof, so as to solve the problems of poor low-temperature freeze-thaw resistance and the like in the prior art.

[0005] The purpose of the present invention can be achieved through the following technical solutions:

[0006] A white latex resistant to low-temperature freeze-thaw, comprising the following raw materials in parts by weight:

[0007]

[0008]

[0009] Furthermore, the degree of polymerization of the polyvinyl alcohol is 1200-2400, and the degree of alcoholysis is 86-90%;

[0010] Furthermore, the small molecule alcohol is a monoalcohol or polyol having 3 or less carbon atoms;

[0011] Furthermore, the initiator is at least one of ammonium persulfate, hydrogen peroxide and potassium persulfate;

[0012] Furthermore, the pH regulator is at least one of sodium acetate, sodium bicarbonate and sodium hydroxide;

[0013] Furthermore, the preservative is phenoxyethanol;

[0014] A method for preparing a low-temperature freeze-thaw resistant white latex specifically comprises the following steps:

[0015] S1. Preparation of polyvinyl alcohol aqueous solution: Deionized water was added to two containers, and polyvinyl alcohol was added while stirring continuously. The mixture was heated to 89-91°C and kept warm for 1-2 hours. After stirring until completely dissolved, the mixture was cooled to 60-70°C to obtain polyvinyl alcohol aqueous solution 1 and polyvinyl alcohol aqueous solution 2.

[0016] Furthermore, the weight ratio of the deionized water to the polyvinyl alcohol is (1:0.06-0.16);

[0017] Furthermore, the weight ratio of the polyvinyl alcohol aqueous solution 1 to the polyvinyl alcohol aqueous solution 2 is (1:0.5-1.5);

[0018] S2. Preparation of initiator aqueous solution: Weigh the formulated amount of initiator and dissolve it in 20-30 parts of deionized water with stirring;

[0019] S3. Preparation of monomer mixture: Weigh the formulated amount of vinyl acetate and acrylic acid and mix them evenly;

[0020] S4, polymerization reaction: heat the polyvinyl alcohol aqueous solution 1 in S1 to 80-85°C, add part of the initiator aqueous solution and part of the monomer mixture, and react at 75-85°C for 25-35 minutes; then dropwise add the remaining initiator aqueous solution and the remaining monomer mixture to the container over 4-6 hours. After the addition is complete, heat to 83-87°C and maintain at this temperature for one hour;

[0021] Furthermore, the weight portion of the initiator aqueous solution is 3-7 parts, and the weight portion of the monomer mixture is 9-11 parts;

[0022] S5. After the heat preservation is completed, add the polyvinyl alcohol aqueous solution 2, cool to 35-45° C., add a pH regulator to adjust the pH of the emulsion to 5-6, then add the remaining amount of deionized water and the formulated amount of small molecule alcohol and preservative, and stir evenly.

[0023] Beneficial effects of the present invention:

[0024] 1. The present invention innovates the production process of white latex, namely, by adding polyvinyl alcohol in steps to prepare white latex with low-temperature freeze-thaw resistance. The polyvinyl alcohol added in the first step is mainly used as a protective colloid in the polymerization reaction, forming a stable emulsion system, preventing monomer droplets from agglomerating and stratifying, and ensuring that the polymerization reaction proceeds evenly and stably. The second step is used to improve performance, mainly utilizing the steric hindrance stabilization mechanism of polyvinyl alcohol. As polyvinyl alcohol molecules adsorb on the surface of latex particles, they form a thick hydration layer. When particles approach, they generate strong osmotic repulsion and entropic repulsion, preventing aggregation. In addition, it also plays a role in thickening, repairing or strengthening the original protective layer, improving freeze-thaw stability, and improving rheological properties.

[0025] 2. The present invention improves the low-temperature stability of white latex by introducing small molecule alcohol. Since small molecule alcohol can lower the freezing point of water in white latex, it can be inserted between the white latex polymer molecular chains, increasing the flexibility and mobility of the molecular chains, so that the molecular chains can still maintain a certain flexibility at low temperatures and are not easy to harden and become brittle. In addition, the small molecule alcohol has good compatibility with other components in the white latex and can be evenly dispersed in the system, which helps to stabilize the colloidal structure of the emulsion, so that the prepared white latex can still maintain stable performance after undergoing 5 cycles in a freeze-thaw test at -17°C to 25°C. DETAILED DESCRIPTION

[0026] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0027] Unless otherwise specified, the experimental methods in the following examples are conventional methods and were performed according to the techniques or conditions described in the literature in the field or according to the product instructions. The materials and reagents used in the following examples, unless otherwise specified, were all commercially available.

[0028] Example 1

[0029] This embodiment discloses a white latex that is resistant to freezing and thawing at low temperatures, comprising the following raw materials in parts by weight (weighed by weight based on 1 kg): 90 parts of polyvinyl alcohol, 100 parts of vinyl acetate, 50 parts of small molecule alcohol, 3 parts of acrylic acid, 3 parts of initiator, 3 parts of pH regulator, 3 parts of preservative, and 786 parts of deionized water. Specifically, the degree of polymerization of polyvinyl alcohol is 1700, and the degree of alcoholysis is 88%; the small molecule alcohol is glycerol; the initiator is ammonium persulfate; the pH regulator is sodium acetate, and the preservative is phenoxyethanol. Prepare the raw materials according to the above raw materials and weight ratios, and prepare the white latex, comprising the following steps:

[0030] S1. Preparation of polyvinyl alcohol aqueous solution: 350 parts of deionized water were added to each of two three-necked flasks. 45 parts of polyvinyl alcohol were added to each of the two three-necked flasks while continuously stirring. The mixture was heated to 91° C. and kept warm for 2 hours. After stirring until completely dissolved, the mixture was cooled to 60° C. to obtain polyvinyl alcohol aqueous solution 1 and polyvinyl alcohol aqueous solution 2.

[0031] S2. Preparation of initiator aqueous solution: Weigh 3 parts of initiator and dissolve them in 20 parts of deionized water with stirring;

[0032] S3. Preparation of monomer mixture: Weigh 100 parts of vinyl acetate and 3 parts of acrylic acid and mix them evenly;

[0033] S4, polymerization reaction: Heat the polyvinyl alcohol aqueous solution 1 in S1 to 80°C, add 3 parts of initiator aqueous solution and 9 parts of monomer mixture, and react at 82°C for 30 minutes; then gradually add the remaining initiator aqueous solution and the remaining monomer mixture dropwise to the three-necked flask over 4 hours. After the addition is complete, heat to 85°C and keep warm for one hour;

[0034] S5. After the heat preservation is completed, add 2 parts of polyvinyl alcohol aqueous solution, cool to 35°C, add 3 parts of pH regulator to adjust the pH of the emulsion to 5, then add 50 parts of small molecule alcohol, 3 parts of preservative and the remaining formula amount of water, stir evenly, and obtain the white latex product of the present invention.

[0035] Example 2

[0036] The method of Example 1 was followed, except that the small molecule alcohol was glycerol in equal parts by weight.

[0037] Example 3

[0038] The method of Example 1 was followed, except that the small molecule alcohol was ethylene glycol in equal parts by weight.

[0039] Example 4

[0040] The method of Example 1 was followed, except that the degree of polymerization of the polyvinyl alcohol was 1200 and the degree of alcoholysis was 88%.

[0041] Example 5

[0042] The method of Example 1 was followed, except that the degree of polymerization of the polyvinyl alcohol was 2400 and the degree of alcoholysis was 88%.

[0043] Example 6

[0044] The method of Example 1 was followed, except that the degree of polymerization of the polyvinyl alcohol was 1700 and the degree of alcoholysis was 86%.

[0045] Example 7

[0046] The method of Example 1 was followed, except that the degree of polymerization of the polyvinyl alcohol was 2400 and the degree of alcoholysis was 90%.

[0047] Example 8

[0048] This embodiment discloses a white latex that is resistant to freezing and thawing at low temperatures, comprising the following raw materials in parts by weight (weighed by weight based on 1 kg): 90 parts of polyvinyl alcohol, 100 parts of vinyl acetate, 50 parts of small molecule alcohol, 3 parts of acrylic acid, 3 parts of initiator, 3 parts of pH regulator, 3 parts of preservative, and 786 parts of deionized water. Specifically, the degree of polymerization of polyvinyl alcohol is 1700, and the degree of alcoholysis is 88%; the small molecule alcohol is glycerol; the initiator is ammonium persulfate; the pH regulator is sodium acetate, and the preservative is phenoxyethanol. Prepare the raw materials according to the above raw materials and weight ratios, and prepare the white latex, comprising the following steps:

[0049] S1. Preparation of polyvinyl alcohol aqueous solution: 467 parts and 233 parts of deionized water were added to two three-necked flasks, respectively. 60 parts and 30 parts of polyvinyl alcohol were added to the two three-necked flasks, respectively, under continuous stirring. The mixture was heated to 91° C. and kept warm for 2 hours. After stirring until completely dissolved, the mixture was cooled to 60° C. to obtain polyvinyl alcohol aqueous solution 1 and polyvinyl alcohol aqueous solution 2.

[0050] S2. Preparation of initiator aqueous solution: Weigh 3 parts of initiator and dissolve them in 20 parts of deionized water with stirring;

[0051] S3. Preparation of monomer mixture: Weigh 100 parts of vinyl acetate and 3 parts of acrylic acid and mix them evenly;

[0052] S4, polymerization reaction: Heat the polyvinyl alcohol aqueous solution 1 in S1 to 80°C, add 3 parts of initiator aqueous solution and 9 parts of monomer mixture, and react at 82°C for 30 minutes; then gradually add the remaining initiator aqueous solution and the remaining monomer mixture dropwise to the three-necked flask over 4 hours. After the addition is complete, heat to 85°C and keep warm for one hour;

[0053] S5. After the heat preservation is completed, add 2 parts of polyvinyl alcohol aqueous solution, cool to 35°C, add 3 parts of pH regulator to adjust the pH of the emulsion to 5, then add 50 parts of small molecule alcohol, 3 parts of preservative and the remaining formula amount of water, stir evenly, and obtain the white latex product of the present invention.

[0054] Example 9

[0055] This embodiment discloses a white latex that is resistant to freezing and thawing at low temperatures, comprising the following raw materials in parts by weight (weighed by weight based on 1 kg): 90 parts of polyvinyl alcohol, 100 parts of vinyl acetate, 50 parts of small molecule alcohol, 3 parts of acrylic acid, 3 parts of initiator, 3 parts of pH regulator, 3 parts of preservative, and 786 parts of deionized water. Specifically, the degree of polymerization of polyvinyl alcohol is 1700, and the degree of alcoholysis is 88%; the small molecule alcohol is glycerol; the initiator is ammonium persulfate; the pH regulator is sodium acetate, and the preservative is phenoxyethanol. Prepare the raw materials according to the above raw materials and weight ratios, and prepare the white latex, comprising the following steps:

[0056] S1. Preparation of polyvinyl alcohol aqueous solution: 420 parts and 280 parts of deionized water were added to two three-necked flasks, respectively. 36 parts and 54 parts of polyvinyl alcohol were added to the two three-necked flasks, respectively, under continuous stirring. The mixture was heated to 91° C. and kept warm for 2 hours. After stirring until completely dissolved, the mixture was cooled to 60° C. to obtain polyvinyl alcohol aqueous solution 1 and polyvinyl alcohol aqueous solution 2.

[0057] S2. Preparation of initiator aqueous solution: Weigh 3 parts of initiator and dissolve them in 20 parts of deionized water with stirring;

[0058] S3. Preparation of monomer mixture: Weigh 100 parts of vinyl acetate and 3 parts of acrylic acid and mix them evenly;

[0059] S4, polymerization reaction: Heat the polyvinyl alcohol aqueous solution 1 in S1 to 80°C, add 3 parts of initiator aqueous solution and 9 parts of monomer mixture, and react at 82°C for 30 minutes; then gradually add the remaining initiator aqueous solution and the remaining monomer mixture dropwise to the three-necked flask over 4 hours. After the addition is complete, heat to 85°C and keep warm for one hour;

[0060] S5. After the heat preservation is completed, add 2 parts of polyvinyl alcohol aqueous solution, cool to 35°C, add 3 parts of pH regulator to adjust the pH of the emulsion to 5, then add 50 parts of small molecule alcohol, 3 parts of preservative and the remaining formula amount of water, stir evenly, and obtain the white latex product of the present invention.

[0061] Comparative Example 1

[0062] The method of Example 1 was followed, except that the mass ratio of the polyvinyl alcohol aqueous solution 1 to the polyvinyl alcohol aqueous solution 2 was 1:0.

[0063] Comparative Example 2

[0064] The method of Example 1 was followed, except that the mass ratio of the polyvinyl alcohol aqueous solution 1 to the polyvinyl alcohol aqueous solution 2 was 1:2.

[0065] Comparative Example 3

[0066] The method of Example 1 was followed, except that 80 parts by weight of glycerol was added.

[0067] Comparative Example 4

[0068] The method of Example 1 was followed, except that 20 parts by weight of glycerol was added.

[0069] Comparative Example 5

[0070] The method of Example 1 was followed, except that no glycerol was added.

[0071] In order to more intuitively and clearly demonstrate the differences between the embodiments of the present invention and the comparative examples in terms of various key performance indicators, and to facilitate understanding of the significant advantages of the technical solutions of the present invention, the formulations and test results of the key materials of Examples 1-9 and Comparative Examples 1-5 are listed in Tables 1 and 2. The test items include appearance, viscosity, solid content, adhesive strength, and freeze-thaw testing. The specific test methods are as follows:

[0072] Appearance: According to GB / T11178-2001, place the white latex sample in a colorless and transparent container under natural light or fluorescent light and observe its color and state.

[0073] Viscosity test: using a Brookfield viscometer, the test conditions are: 3#sp, 12RPM, 25℃, LVDV.

[0074] Solids content test: Accurately weigh 1g of emulsion and evenly apply it to the bottom of a bottle or onto tin foil. Place in a drying oven at 105°C for 3 hours. Remove and place in a desiccator, cool to room temperature, and weigh. Calculate solids content using the following formula: Solids content = Weight after drying / Weight before drying × 100%.

[0075] Bond Strength: Take two 2.5cm x 2.5cm birch boards, clean their surfaces, and draw a line 0.5cm from one end of the boards. Weigh 0.0500-0.0520g of adhesive and evenly apply it to the other 2.5cm x 2.0cm flat front board, leaving one end uncoated. Overlap the two boards and place them in a fixed pressure fixture at room temperature for 24 hours. Remove the pressure, place the bonded boards on a press, and press them apart. Measure and record the readings. Repeat the experiment four times and take the average value.

[0076] Freeze-thaw test: After the samples are packaged according to the product export packaging requirements (sealed plastic bottles of different volumes), they are placed in a low-temperature refrigerator and stored at -17°C for 2 weeks. After being taken out, they are placed in a forced air drying oven at 25°C for 1 week. After 5 cycles, the samples are compared with the untreated white latex to observe the colloidal state, adhesion and other properties, and visually check for stratification or separation.

[0077] Table 1

[0078]

[0079]

[0080] Table 2

[0081]

[0082]

[0083] It can be seen from Table 1 and Table 2 that in Examples 1-9, the viscosity of the prepared white latex is 2600-10050, the solid content is 21.1-23.5%, the bonding strength is 12.5-14.7 MPa, and the appearance is a white viscous liquid after 5 freeze-thaw test cycles, without stratification or separation, and the bonding strength has no obvious change, indicating that the white latex prepared by the present invention has excellent low-temperature freeze-thaw resistance; by contrast, in combination with Comparative Examples 1-2, when the mass ratio of polyvinyl alcohol aqueous solution 1 and polyvinyl alcohol aqueous solution 2 is higher than the preferred ratio, the prepared white latex has no obvious change in appearance, viscosity, solid content, and bonding strength, but after 3 low-temperature freeze-thaw cycle tests, it is found that there are lumps in appearance, no adhesion and cannot be restored. This is due to the lack of polyvinyl alcohol modification, which causes the white latex to easily break or demulsify at low temperatures. Coagulation, decreased bonding strength; when the mass ratio is lower than the preferred ratio, the prepared white latex has no obvious changes in viscosity, solid content, bonding strength and low-temperature freeze-thaw test, but the appearance is poor, which will affect the market; Combined with Comparative Example 3, when the addition amount of small molecule alcohol is higher than the preferred ratio, the viscosity and solid content of the prepared white latex have no obvious changes, the bonding strength is reduced, and the bonding strength decreases significantly after 5 low-temperature freeze-thaw cycle tests, which may be due to excessive plasticization effect; Combined with Comparative Examples 4-5, when the addition amount of small molecule alcohol is lower than the preferred ratio or is zero, the viscosity and bonding strength of the prepared white latex have no obvious changes, the solid content shows a downward trend, and after 3 or 1 low-temperature freeze-thaw cycle tests, it is found that there are lumps in appearance, no bonding strength and cannot be restored, which may be due to the lack of plasticization effect, resulting in the lack of plastic deformation ability of the film at low temperatures, and it is easy to become hard and brittle.

[0084] The above is a detailed description of an embodiment of the present invention. However, the content described is only a preferred embodiment of the present invention and should not be considered to limit the scope of the present invention. All equivalent changes and improvements made within the scope of the present invention should still fall within the scope of the patent coverage of the present invention.

Claims

1. A white latex resistant to low temperature freeze-thaw, characterized in that: The invention comprises the following raw materials in parts by weight:

2. The low-temperature freeze-thaw resistant white latex according to claim 1, characterized in that: The polymerization degree of the polyvinyl alcohol is 1200-2400, and the alcoholysis degree is 86-90%.

3. The low-temperature freeze-thaw resistant white latex according to claim 1 or 2, characterized in that: The small molecule alcohol is a monoalcohol or polyol having 3 or less carbon atoms.

4. The low-temperature freeze-thaw resistant white latex according to claim 1, characterized in that: The initiator is at least one of ammonium persulfate, hydrogen peroxide and potassium persulfate.

5. The low-temperature freeze-thaw resistant white latex according to claim 1, characterized in that: The pH regulator is at least one of sodium acetate, sodium bicarbonate and sodium hydroxide.

6. The low-temperature freeze-thaw resistant white latex according to claim 1, characterized in that: The preservative is phenoxyethanol.

7. A method for preparing a low-temperature freeze-thaw resistant white latex according to any one of claims 1 to 6, characterized in that: The steps include: S1. Preparation of polyvinyl alcohol aqueous solution: Deionized water was added to two containers, and polyvinyl alcohol was added to each container while stirring continuously. The mixture was heated to 89-91°C, kept warm for 1-2 hours, stirred until completely dissolved, and then cooled to 60-70°C to obtain polyvinyl alcohol aqueous solution 1 and polyvinyl alcohol aqueous solution 2. S2. Preparation of initiator aqueous solution: Weigh the formulated amount of initiator and dissolve it in 20-30 parts of deionized water with stirring; S3. Preparation of monomer mixture: Weigh the formulated amount of vinyl acetate and acrylic acid and mix them evenly; S4, polymerization reaction: heat the polyvinyl alcohol aqueous solution 1 in S1 to 80-85°C, add part of the initiator aqueous solution and part of the monomer mixture, and react at 75-85°C for 25-35 minutes; then dropwise add the remaining initiator aqueous solution and the remaining monomer mixture to the container over 4-6 hours. After the addition is complete, heat to 83-87°C and keep warm for one hour; S5. After the heat preservation is completed, add the polyvinyl alcohol aqueous solution 2, cool to 35-45° C., add a pH regulator to adjust the pH of the emulsion to 5-6, then add the remaining amount of deionized water and the formulated amount of small molecule alcohol and preservative, and stir evenly.

8. The method for preparing the low-temperature freeze-thaw resistant white latex according to claim 7, wherein: In step S1, the weight ratio of the deionized water to the polyvinyl alcohol is 1:(0.06-0.16).

9. The method for preparing the low-temperature freeze-thaw-resistant white latex according to claim 7, wherein: In step S1, the weight ratio of the polyvinyl alcohol aqueous solution 1 to the polyvinyl alcohol aqueous solution 2 is (1:0.5-1.5).

10. The method for preparing the low-temperature freeze-thaw resistant white latex according to claim 7, wherein: In step S4, the weight portion of the partial initiator aqueous solution is 3-7 parts, and the weight portion of the partial monomer mixed solution is 9-11 parts.

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