JPS6337122B2 - - Google Patents

Description

[Detailed description of the invention]

This invention relates to the production of polyvinyl butyral, and in particular to a method for producing polyvinyl butyral having desired controlled properties suitable for use in the production of laminated glass. Polyvinyl butyral is commonly used, for example, as a spacer (interlayer) in laminated safety glass used in the manufacture of vehicle windshields. Generally, polyvinyl butyral is obtained by a condensation reaction of polyvinyl alcohol (obtained by hydrolysis of polyvinyl acetate) and butyraldehyde. By varying the reaction conditions, the quantitative ratio of the starting materials and the molecular weight of the polyvinyl alcohol used, and by adding various additives and plasticizers, it is possible to vary the properties of the final product over a very wide range. It is. Therefore, a large number of methods for producing polyvinyl butyral have been proposed in order to modify the physicochemical properties of the final product depending on the intended use. When manufacturing laminated glass is intended, the following properties (methods for evaluating these properties will be described later) are considered important. Namely, (1) flow during compression of polyvinyl butyral sheet, (2) impact resistance of laminated glass containing polyvinyl butyral sheet as a spacer (interlayer film) (by falling ball test method), (3)
Adhesion of polyvinyl butyral to glass sheets of laminated glass (according to Pummel test method),
(4) Transparency of laminated glass (according to turbidity measurement method of laminated glass), and (5) Water resistance of laminated glass. However, to the best of the inventor's knowledge, methods for synthesizing polyvinyl butyral that satisfy some of the properties (1) to (4) in the above list are known, but these properties and/or moisture resistance are No satisfactory synthetic method is known. Furthermore, the plasticizers used in the production of conventional polyvinyl butyral are generally expensive, and the production cost of laminated glass obtained from polyvinyl butyral into which such plasticizers are mixed is high. The object of the present invention is to overcome the drawbacks of the known techniques as described above, to produce polyvinyl butyral which has properties suitable for the production of laminated glass and which allows the use of plasticizers that are much cheaper than those commonly used. is to provide. The method for producing polyvinyl butyral according to the present invention is a method of reacting polyvinyl alcohol in an aqueous solution with butyraldehyde, in which 8-15% by weight of polyvinyl alcohol, 2.5-10% by weight of an inorganic strong acid catalyst based on the polyvinyl alcohol, and polyvinyl While stirring an aqueous solution containing 0.15-0.40% by weight based on the alcohol of an emulsifier selected from alkylaryl sulfonates, alkyl sulfonates and mixtures thereof and maintained at 5-12°C, polyvinyl alcohol in this solution is added. An amount of butyraldehyde sufficient to react with 75-88% of the polyvinyl butyral is gradually added to the above solution such that the resulting polyvinyl butyral precipitates out 10-90 minutes after the start of the addition, and the resulting mixture is heated while stirring to the temperature. 8-15°C for over 30 minutes, then the temperature of the mixture was increased to 60°C for 1.5-4 hours.
and 80°C, then a base was added to the mixture to bring its pH to 9-11, and the temperature of the mixture was raised to 60°C for more than 15 minutes.
It is characterized by maintaining a temperature between 80° C. and then separating the precipitated polyvinyl butyral from the reaction mixture. Polyvinyl butyral is herein referred to as pv
It will be abbreviated as b. The polyvinyl alcohol used as starting material preferably has an acetate content of less than 5%. Hydrochloric acid, sulfuric acid, etc. are used as the inorganic strong acid catalyst, but it is preferable to use hydrochloric acid because it is inexpensive. Hydrochloric acid can be used as a solution with a density of 1.18. The amount of this solution used is 2.5-10% by weight of polyvinyl alcohol. Precipitation occurs when the amount of acid catalyst is too small (often less than 2.5% by weight)
PVB tends to form blocks, which complicates the separation operation and makes cleaning difficult. Conversely, if it is excessive (often over 10% by weight), the pvb
The precipitation of PVB occurs rapidly, and lumps of PVB are formed during the precipitation process.
There is a risk that this will occur. Furthermore, using excessive amounts of hydrochloric acid increases the cost of producing PVB. As emulsifiers, alkylaryl sulfonates such as dodecylbenzene sulfonate, alkyl sulfonates such as lauryl sulfonate and mixtures thereof are used, but dodecylbenzene sulfonate is preferably used, this compound being within acceptable limits in conventional manufacturing methods. Generates PVB with turbidity. The amount of emulsifier such as dodecylbenzene sulfonate used is 0.15-0.40% by weight of the polyvinyl alcohol. actually,
If the amount used is too small (often less than 0.15% by weight), PVB lumps are likely to form inside the reactor during heating. This mass is similar to that which forms at the end of the precipitation process when no emulsifier is used. Excessive amount of dodecylbenzene sulfonate is used (often relative to the weight of polyvinyl alcohol).
(more than 0.40% by weight), it becomes difficult to remove dodecylbenzenesulfonate when washing the resulting PVB, resulting in unsatisfactory turbidity of the final product. In order to obtain a PVB with good flow properties, the amount of butyraldehyde used should be sufficient to react with only 75-88% by weight of the polyvinyl alcohol present in the starting mixture. Butyraldehyde is preferably used at a temperature of 5-12°C.
gradually added to the solution of polyvinyl alcohol held at . The addition time is preferably 15-60 minutes, more preferably around 30 minutes. actually,
It was found that the precipitation rate of PVB depends on the addition rate of butyraldehyde, and that if the addition time is less than 15 minutes, the PVB precipitation rate is too high and there is a risk that lumpy PVB will be produced. On the other hand, if the time exceeds 60 minutes, the precipitation rate is too slow and pellet-like p.
VB is produced, which is difficult to clean. Addition times of about 30 minutes are best, as they result in a good-looking PVB powder with a particle size particularly suitable for post-processing. The condensation reaction that produces pvb is exothermic and
During the addition of butyraldehyde, the temperature of the reaction mixture rises to a temperature between 8°C and 15°C. The addition ratio of butyraldehyde is determined depending on the reaction conditions and butyraldehyde addition time.
should complete precipitation within about 10 to 90 minutes from the start of the butyraldehyde addition. After polymer precipitation, the reaction mixture is preferably maintained at a temperature between 8°C and 15°C during the reaction for more than 30 minutes with stirring. The reaction mixture was then gradually heated to 60 °C and 80 °C.
The temperature is raised between 0.degree. and preferably about 70.degree. The heating time is 1.5-4 hours, preferably 2.5 hours, and this preferred heating time is at a heating rate of 22
Corresponds to °C/hour. If the final temperature is below 60°C, the resulting PVB tends to give a diffusive laminated glass. The same thing is observed when the temperature exceeds 80°C, which also produces a block of PVB in the reactor. In order to obtain a PVB with a good appearance and a particle size most suitable for subsequent processing, it is best to use a final temperature of 70°C and a heating rate of 22°C/hour. Advantageously, sodium hydroxide is used to neutralize the acid catalyst and bring the pH of the reaction mixture to 9-11 at the temperatures employed. Sodium hydroxide is not only inexpensive, but also has mechanical properties, especially impact resistance, that are at least as good as with other bases such as potassium hydroxide or calcium oxide.
Generate pvb. After neutralization, the reaction mixture is kept at the adopted temperature between 60°C and 80°C for about 0.25-4 hours and then returned to room temperature. The precipitated PVB can be separated by simple filtration, washing with deionized water, moisture extraction, and drying. If the collected precipitate is washed only once, the final product will have a high degree of turbidity, so it is desirable to wash the product at least twice and pass it twice in succession. Even if washing is performed more than three times, the improvement in turbidity will be negligible. Hereinafter, the present invention will be described in more detail with reference to Examples. Before the examples, methods for evaluating some properties of PVB will be explained. Compression flow test A sheet-like PVB sample with a thickness of 0.76 mm (±0.01 mm) is cut into a disk shape with a diameter of 26 mm. This disk is sandwiched between two 60 x 60 mm glass plates. Heatable 2
A press equipped with two plates is used, and the plates are heated to 120° C., during which the sample sandwiched between the glass plates described above is inserted. After heating for 5 minutes without applying pressure, a pressure of 10 bar is applied for 5 minutes. If the diameter of the pushed PVB disk is D, the compressed flow is expressed by the following equation. F=D-26/26×100 Generally, the above measurements are performed twice for each sample. It is believed that the compression flow should be at least 60% for PVB to be used in the production of laminated glass. Pummel test (adhesion strength to glass plates) A PVB sheet with a thickness of 760 microns was stored in a humid atmosphere beforehand, sandwiched between two glass plates 30.5 x 30.5 cm, and then the obtained The laminated glass was heated at a temperature of 138℃ and a pressure of 10Kg/ ^cm2 for 20 minutes.
Compress for minutes. A sample with a size of 150 x 300 mm is cut out from the laminated glass sample thus obtained. The cut samples are stored at -18°C for 8 hours. The sample is then placed on a support tilted at 45° and struck with a 0.450 kg flat head hammer until the glass breaks. The area to be pounded is approximately 100 x 150 mm, and the entire surface is to be pounded. The amount of residual glass adhering to the polyvinyl butyral sheet is compared to a standard Pummel scale value expressed as a number from 0 to 10. This test is carried out on each side of the laminated glass and the results are expressed as two Pummel scale values. Standard Pummel scale values are as follows.

[Table] Laminated glasses tested in this manner are considered acceptable if their two Pummel values are greater than 5. Drop ball test (impact resistance) A flat laminated glass sample is placed horizontally on a wooden frame, and a steel ball weighing 2270 kg is dropped onto the center of the sample. The size of the laminated glass sample is 305mm x 305mm
The thickness of the glass plate used was 3 mm. The temperature of the sample is controlled to 21℃ (±2℃), and the test is carried out by gradually increasing the height at which the steel ball is dropped. Number of samples: 90
% indicates the approximate height in feet at which a steel ball will withstand penetrating laminated glass. It is considered satisfactory if this approximate height is 17 feet (5.18 m) or more. Turbidity Test The turbidity of a transparent sheet is defined as the percentage of the luminous flux that is transmitted through the transparent sheet with a deflection greater than 2.5°. Turbidity measurement is based on NF standard 54-111 (ASTM
D1003-61 method A). For PVB sheets to be suitable for the production of transparent laminated glass, the acceptable turbidity value is considered to be 0.3% or less. Water resistance test Thickness between two glass plates 30.5 x 30.5 x 0.30 cm
Prepare laminated glass with 762 micron plasticized spacers. The laminated glass sample is placed in boiling water for 2 hours, and the formation of bubbles or a white translucent zone at the sample periphery is examined. If there is no formation of bubbles or white translucent bands, the laminated glass can be said to have satisfactory water resistance. The examples below show various polyvinyl butyral syntheses; in these examples, laminated glass refers to
A 760 micron plasticized PVB spacer was sandwiched between two glass plates 30.5 x 30.5 x 0.30 cm at a temperature of 138°C.
means a laminated glass prepared by compression for about 20 minutes at a pressure of 10 Kg/cm ² . Example 1 67.5 g of sodium dodecylbenzenesulfonate and 2.65 kg of hydrochloric acid with a density of 1.18 are dissolved in an aqueous solution at a temperature of 10°C, in which 30 kg of polyvinyl alcohol is dissolved in 300 kg of water.
was added and mixed. The mixture was maintained at a temperature of 10° C. and 17.1 Kg of butyraldehyde was added gradually and regularly over a period of 30 minutes. A temperature increase of several degrees was observed. The reaction solution became white and its viscosity increased.
Twenty-eight minutes after the start of butyraldehyde addition and chlorination, polymer precipitation and viscosity reduction were observed. Then the mixture
It was held at 13°C for 90 minutes. Then the temperature
The temperature was gradually raised to 70°C over 150 minutes. 1.35Kg of sodium hydroxide was added to the reaction mixture. It was further held at 70°C for 240 minutes. It was then cooled and filtered. The recovered polymer powder is 2
It was washed twice, subjected to moisture extraction, and further dried. Laminated glasses obtained from this polymer showed good optical and mechanical properties and excellent water resistance.
During the water resistance test, this laminated glass showed no whitening or clouding at any point on its surface, including its periphery. Other properties of the PVB sheet prepared from this polymer were as follows. Compressed flow: 76%, Turbidity: 0.3, Falling impact strength: 20 feet (6.1 m) Example 2 To an aqueous solution of 30 kg of polyvinyl alcohol dissolved in 300 g of water, 135 g of sodium dodecylbenzenesulfonate and 2.65 kg of hydrochloric acid with a density of 1.18 are added. Mixed. Polymerization was carried out under the same conditions as in Example 1 to produce a polymer. The obtained polymer had poor optical properties, and the turbidity of the laminated glass was 0.6. This example shows that it is undesirable to use an emulsifier in excess of 0.40% by weight of polyvinyl alcohol. Example 3 The method of Example 1 was repeated. However, the amount of sodium dodecylbenzenesulfonate used is 67.5g.
Instead, it was 33.75g. Countless spherical lumps are generated in the reactor, and the resulting polymer has various properties,
In particular, the degree of turbidity was poor, and the laminated glass was slightly cloudy and opaque. In this example, the amount of emulsifier used is 0.15% by weight of polyvinyl alcohol.
It shows that it is unfavorable if it is less than. Example 4 The procedure of Example 1 was repeated until a precipitate was formed. After holding at 13°C, the temperature of the reaction mixture was increased to 90°C.
The temperature rose to A large block was formed in the reactor, and the polymer was recovered and formed into sheets with a flow rate of 58%. The laminated glass was opaque. This example shows that the reaction mixture is 80 ml after polymer precipitation.
Indicates that heating to temperatures exceeding ℃ is undesirable. Example 5 67.5 g of sodium dodecylbenzenesulfonate and 1.5 kg of hydrochloric acid having a density of 1.18 were added to an aqueous solution in which 30 kg of polyvinyl alcohol was dissolved in 300 g of water and mixed. 16.5 kg of butyraldehyde at a temperature of 10℃
Added over 30 minutes. After polymer precipitation, the reaction mixture was held at 13°C for 90 minutes. Next, the temperature was raised to 70°C, and the catalyst was further neutralized. Bring the reaction mixture to 70℃
After holding for 240 minutes, it was cooled and filtered. The precipitate was then washed, filtered three times and then dried. The turbidity of the obtained polymer was 0.3, and the falling ball impact strength of laminated glass prepared from this polymer was
It was 19 feet, the pummel was 9+9, and the flow was 64%. This laminated glass did not show whitening or clouding at any point on its surface during the water resistance test. Example 6 16.5 kg of butyraldehyde was added to the same mixture of polyvinyl alcohol aqueous solution as in Example 5, hydrochloric acid and sodium dodecylbenzenesulfonate at a temperature of 15°C. After the polymer was precipitated, the reaction mixture was kept at a low temperature and then raised at a rate of 22° C./hour. Large blocks were formed in the reactor, and the laminated glass prepared from the resulting polymer was highly turbid. This example shows that it is undesirable for the reaction initiation temperature to be higher than 12°C. Example 7 The procedure of Example 5 was repeated. However, the amount of hydrochloric acid used is
0.5Kg instead of 1.5Kg The resulting polymer was treated with plasticizer Flexol.
(trade name) and the polymer sheet showed oozing. In this example, the amount of catalyst used is polyvinyl alcohol.
A content of less than 2.5% by weight is undesirable. Example 8 The procedure of Example 5 was repeated. However, the maximum temperature increase was set at 50°C instead of 70°C. The laminated glass prepared from the obtained polymer was cloudy. This example shows that it is undesirable to reheat the reaction mixture after polymer precipitation below 60°C. Examples 9 and 10 The procedure in Example 5 was repeated up to the first pass of the reaction mixture. The recovered polymer was then washed once, subjected to moisture extraction, and further dried (Example 9).
The turbidity of the laminated glass was 0.7. This indicates that cleaning is insufficient. When the polymer was washed and filtered twice (Example 10), the turbidity was 0.4. Example 11 to 13 30 kg of polyvinyl alcohol with a molecular weight of 106,000 is added to water.
Hydrochloric acid 0.75 in an aqueous solution at a temperature of 10℃ to be dissolved in 300
Kg and sodium dodecylbenzenesulfonate
Added 67.5g and further added 17.1Kg of butyraldehyde.
Add gradually over 30 minutes. After polymer precipitation, the reaction mixture is kept at the same temperature.
Hold for 30 minutes. Then, it was heated to 65°C and 0.405Kg of sodium hydroxide was added. Heat this mixture at 65℃
After holding for 30 minutes, it was cooled and further filtered. The polymer was then washed, filtered, extracted and dried. The flow rate of the sheet prepared from this polymer was 61%. The laminated glass prepared from this sheet had a turbidity of 0.2, a drop impact strength of 23 feet, and excellent water resistance. It did not show any change during the water resistance test. The above procedure was repeated using 27.5 kg of polyvinyl alcohol with a molecular weight of 106,000 and 2.6 kg of polyvinyl alcohol with a molecular weight of 32,000 (Example 12). The flow rate of the sheet prepared from the resulting polymer was 68%. The above procedure was repeated using a mixture of 24 kg of polyvinyl alcohol with a molecular weight of 106,000 and 6 kg of polyvinyl alcohol with a molecular weight of 32,000 (Example 13). The flow rate of the sheet prepared from the resulting polymer was 71%. Examples 14 to 25 These examples discuss the effects of precipitation time (depending on butyraldehyde addition time), starting material temperature, and acid catalyst concentration. In the first example (Example 14), polyvinyl alcohol
An aqueous solution in which 39 kg was dissolved in 390 kg of water was cooled to a temperature of 10°C. To this were added 90 g of sodium dodecylbenzenesulfonate and 3 ml of hydrochloric acid having a density of 1.18. At a temperature of 10° C., 21 Kg of butyraldehyde was added gradually and regularly over a period of 30 minutes. The precipitation time was 28 minutes. After precipitation, the reaction mixture is kept at that temperature.
Stirred for 1.5 hours. 70 for 2 hours and 50 minutes.
Raise the temperature to 18°C and add a 10% by weight solution of sodium hydroxide.
added. After being kept at 70°C, the reaction mixture was cooled, filtered, and washed further. After extracting and drying the obtained polymer, a laminated glass was prepared using this polymer, and its optical and mechanical properties were good. Various plasticizers were added to the above polymers. These include Flexol (di-2-ethyl butyrate of triethylene glycol), Plastolein 90-83 (a mixture of C6-C9 ethylene glycol esters) and n-hexyl adipate (these are inexpensive plasticizers). However, when plasticized using PVB (which is not commonly used in this field), the compatibility was good and no oozing was observed in the plasticized PVB sheet. When a laminated glass was prepared using a sheet obtained from the above-mentioned polymer and a water resistance test was conducted, no whitening or clouding was observed at any point on the surface, including the periphery of the sample.
Shows complete water resistance. For examples 15 to 25, the temperature of the polyvinyl alcohol starting solution was 5°C or 10°C, the amount of acid catalyst was 1.5, 3 or 6 (i.e. 4.5, 9 and 18% by weight relative to the polyvinyl alcohol), and the addition of butyraldehyde. The above procedure was repeated using 10 or 30 minutes. The modified manufacturing conditions and the properties of the obtained PVB are shown in the table below.

[Table] +: Slightly grainy
: Many particles It was found that the appearance and properties of polyvinyl butyral changed depending on the polymer precipitation temperature. The product of very slow precipitation contains numerous particles that are not removed by washing and appear as poorly plasticized particles in the sheet. Sheets obtained from slowly precipitated polymers are less flexible than sheets obtained from rapidly precipitated powdered polymers. When the precipitation time is about 30 minutes, a powdered polymer with a very good appearance and excellent properties can be obtained. On the contrary, polymers precipitated too rapidly are not homogeneous and contain large blocks, and the laminated glass obtained therefrom tends to be cloudy. This is true for the majority of examples using acid catalyst 6 (18% by weight based on polyvinyl alcohol). Examples 26-34 These examples examine the effect of neutralization temperature on flow properties. Neutralization temperature 70, 80 and 90℃, low temperature holding time
The procedure of Example 1 was repeated with varying settings for 1.5 hours, 4 hours and 6 hours, and holding times at 70°C of 1.2 and 4 hours, respectively. The flow properties of sheets prepared from the obtained PVB were evaluated. The results were as shown in the table below.

[Table] It can be seen that the flow of the polymer sheet is small at a neutralization temperature of 90°C, but is a good value at a neutralization temperature of 70°C. Examples 35-42 These examples examine the effect of neutralization temperature on the properties of polymers and polymer sheets. Neutralization temperature is 55, 60, 65 and 70℃, low temperature holding time after polymer precipitation is 30 minutes to 90 minutes, high temperature holding time after neutralization is 15 minutes to 120 minutes, and amount of hydrochloric acid added with density 1.18. The procedure of Example 1 was repeated with each setting ranging from 2.5% to 5% by weight based on polyvinyl alcohol. These changed setting conditions and the results obtained are as shown in the table below.

【table】

[Table] (3) +: Examples with slight granules 43 to 50 In these examples, the influence of the time maintained at the neutralization temperature after neutralization will be examined. The neutralization temperature holding time after neutralization is 15, 30, 60 and
120 minutes, the amount of hydrochloric acid with a density of 1.18 is set to 2.5 to 5% by weight based on polyvinyl alcohol, the low temperature holding time after polymer precipitation is set to 30 to 90 minutes, and the neutralization temperature is set to 60 to 70°C. Repeated method 1. These setting conditions and the results obtained are as shown in the following table.

[Table] The moisture content of the obtained PVB sheet was approximately 0.7. It can be seen that the longer the temperature retention time after neutralization, the greater the falling ball impact strength. Example 51 Dissolve 30 kg of polyvinyl alcohol in 300 kg of water,
2.65 kg of hydrochloric acid having a density of 1.18 and 67.5 g of sodium dodecylbenzenesulfonate were added. The temperature of the mixture was 10℃, and the butyraldehyde
16.5Kg was added regularly over 30 minutes. After precipitation of the polymer, the reaction mixture was maintained at a temperature of 13° C. for 90 minutes with stirring. The temperature was then raised to 70°C over 2 hours and 15 minutes. After holding at 70℃ for 2 hours, sodium hydroxide
1.35Kg was added and the mixture was further maintained at 70°C for 4 hours. It was then cooled, filtered, washed, extracted and dried. When the obtained polymer was plasticized with triethylene glycol di(2-ethylbutyrate) (Flexol), Blastrain 90-83 (a mixture of C6-C9 ethylene glycol esters), and n-hexyl adipate, The resulting sheet showed no oozing. The compatibility with these three plasticizers was good. Example 52 The method of Example 14 was repeated. However, the amount of butyraldehyde used was 22Kg instead of 21Kg. The –OH group content of the obtained polymer was 20.6% (e.g.
14, it was 22.3%). The compression flow of the PVB sheet prepared from this polymer was 76% (67% for the polymer sheet in Example 14). It can be seen that as the amount of butyraldehyde relative to polyvinyl alcohol increases, the flow properties increase. Example 53 The method of Example 1 was repeated. However, the density is 1.18
The amount of hydrochloric acid used is 0.75Kg, and the low temperature holding time is 30
The temperature was maintained at high temperature for 30 minutes after neutralization, and the neutralization temperature was 65°C. Sheets prepared from the resulting polymer were particle-free and had a compressed flow of 65%. The laminated glass prepared from this sheet had a turbidity of 0.3, a drop impact strength of 24 feet, and a pummel bond strength of 8+9. Example 54 The same method as in Example 1 was repeated, except that 1.174 kg of sulfuric acid was used instead of hydrochloric acid. The properties of the obtained PVB sheet were the same as in Example 1. Example 55 The same procedure as in Example 1 was repeated, except that 50 g of sodium lauryl sulfonate was used instead of sodium dodecylbenzenesulfonate. The obtained p.
The characteristics of the VB sheet were as follows. Compressed flow: 67% Turbidity: 0.35 Falling ball impact strength: 19 feet (6 m) Example 56 1.174 kg of sulfuric acid was used instead of hydrochloric acid, and 50 g of sodium lauryl sulfonate was used instead of sodium dodecylbenzenesulfonate. Others are
The same method as in Example 1 was repeated. obtained pvb
The properties of the sheet were as follows. Compressed flow: 63% Turbidity: 0.25 Falling ball impact strength: 18 feet (5.9 m)

Claims (1)

[Claims] 1. A method of reacting polyvinyl alcohol in an aqueous solution with butyraldehyde, comprising 8-15% by weight of polyvinyl alcohol, 2.5-10% by weight of an inorganic strong acid catalyst based on the polyvinyl alcohol, and 0.15% by weight based on the polyvinyl alcohol. While stirring an aqueous solution containing ~0.40% by weight of an emulsifier selected from alkylaryl sulfonates, alkyl sulfonates or mixtures thereof and maintained at 5-12°C, 75-88% of the polyvinyl alcohol in this solution is added. % butyraldehyde is gradually added to the above solution such that the polyvinyl butyral formed precipitates out 10 to 90 minutes after the start of the addition, and the resulting mixture is heated at a temperature of 8-15°C with stirring. for more than 30 minutes and then bring the temperature of the mixture to 60°C for 1.5-4 hours.
The temperature of the mixture was increased to between 60°C and 80°C for more than 15 minutes by adding base to the mixture to bring its pH to 9-11.
A process for the production of polyvinyl butyral, characterized in that the temperature is maintained at a temperature between °C and then the precipitated polyvinyl butyral is separated from the reaction mixture. 2. The method according to claim 1, wherein the acid catalyst comprises hydrochloric acid. 3. The method of claim 2, wherein the density of the hydrochloric acid is 1.18 and the amount used is at least 2.5% by weight of the polyvinyl alcohol. 4. The method according to any one of claims 1 to 3, wherein the emulsifier is dodecylbenzene sulfonate. 5. The method according to any one of claims 1 to 4, wherein the time for adding butyraldehyde is 30 minutes. 6 After precipitation of polyvinyl butyral, the reaction mixture was
The method according to any one of claims 1 to 5, wherein the temperature is increased to 70°C. 7. The method according to any one of claims 1 to 6, wherein the reaction mixture is heated for 2.5 hours after precipitating the polyvinyl butyral and maintaining the temperature at the precipitation temperature. 8. The method according to any one of claims 1 to 7, wherein the produced polyvinyl butyral is washed at least twice after separation. 9. The method according to any one of claims 1 to 8, wherein the acetate content in the polyvinyl alcohol is less than 5%.