JPH0424377B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention uses low concentrations of water-soluble polyglycols and certain polyvinyl alcohols, hereinafter referred to as PVA.
The present invention relates to suppressing the inherent dustiness of the polyvinyl alcohol by contacting with the polyvinyl alcohol. Usually high dusting substances (dusting
Various methods are known for controlling dust in materials. For example, it is known to mix high dusting powders such as antimony oxide with less than about 1% by weight polytetrafluoroethylene to form a dry, dust-free mixture. Additionally, methods are known for controlling the dustiness of water-insoluble alkali metal carboxylate salts, whereby the salts are mixed with pyrogenic silica or pyrogenic alumina particles. It is known to produce substantially dust-free powder compositions of spray-dried acrylic resins, according to which one or more selected from the group consisting of 2-hexadecyl alcohol and isotridecanol. A dedusting amount of organic alcohol is added. It is also known to reduce the dissemination of fugitive dust particles into the atmosphere by treating the particles with octylphenoxyethanol and an aqueous solution of a copolymer of ethylene oxide and propylene oxide.
Satisfactory methods for de-dusting PVA still have to be disclosed. The present invention relates to a process for producing substantially dust-free PVA powder, comprising contacting PVA with about 0.5% to about 4.0% polyglycol and products therefrom. All percentages stated herein are by weight unless otherwise specified. The PVA to be treated by the method of the invention is
Hoeppler falling ball method
It has a viscosity of 2 to 125 Pa·s, measured on a 4% by weight aqueous solution at 20° C., according to the method (ASTM-D1343), and a degree of hydrolysis or alcoholysis of at least 80 mol %. PVA is a copolymer of 90-98% by weight vinyl alcohol and 10-2% by weight of other monomers (e.g. methacrylic acid, acrylic acid, fumaric acid, maleic acid or copolymers of itaconic acid with _C1 - _C4 -alkyl esters, etc.). The dustiness of PVA is caused by fine particles formed when dissolved polyvinyl acetate is hydrolyzed or alcoholyzed to PVA or when PVA is milled into particulate form. The advantages of certain highly finely divided polyvinyl alcohols with respect to water slurry and solvation properties are well established. However, highly fine PVA is inherently dusty which can be unpleasant for workers. Previous attempts to improve end-use performance by mixing various additives with polyvinyl alcohol have limited the amount of additives and PVA.
Difficulties were encountered due to the limited compatibility of This compatibility is typically illustrated by loss of aqueous solution or film clarity, film forming ability, and tensile strength. The aim of the invention is to maintain the advantageous water solubility properties of small particle size (highly fine) products while
The objective is to reduce the dustiness of PVA and accomplish this without adverse modification to the physical film or solution properties of the original polyvinyl alcohol. The present invention agglomerates these fines during or after PVA production by adding polyglycols to the PVA production stream. Polyglycols can be used as solids dissolved or dispersed in fluids or as liquids. small
By agglomerating the PVA fines, the overall particle size distribution is shifted towards larger and heavier particle sizes, thereby reducing the amount of fines that can remain suspended in the atmosphere during operation, thus reducing the overall particle size distribution. Increase PVA yield. This mixing of PVA and polyglycol can be carried out in any conventional manner as long as the mixing results in intimate contact between the polyglycol and PVA, such as by blast mixing, fluidized bed mixing, mill mixing or solvent based mixing. Dust removal additive, polyglycol is about 200~
Defined as polyethylene glycol or methoxypolyethylene glycol with a molecular weight of 14,000, said polyethylene glycol has the general formula
HOCH ₂ (CH ₂ OCH ₂ ) _o has CH ₂ OH. A preferred polyglycol is polyethylene glycol having a molecular weight of about 600 due to its excellent dust suppression properties after extreme temperature recycling. Block copolymers containing polyethylene glycol components with a predominant ethoxy content (greater than 50%) of propylene oxide are preferred, albeit to a lesser extent, insofar as the end use of the PVA is adversely affected. It is. The molecular weight of these copolymers ranges from about 1,000 to 14,000. Polyglycol's physical properties make it particularly suitable to act as a dust suppressant for PVA. The easy cold water solubility of polyglycols allows aggregated fines to retain PVA water solubility. Pologlycols do not reduce the tensile strength of films conventionally made from PVA. Furthermore, although the polyglycols remain on the surface of the PVA particles, they do not introduce adverse surfactant activity to the PVA end use. Surprisingly, as explained below, other compounds commonly placed in the polyglycol group as plasticizer additives to PVA include glycerin, water, diethylene glycol, and dibutyl phosphate, as dust suppressants for PVA. It has been found to be relatively ineffective. The dustiness of PVA is determined by one of two tests. In the first test, an amount of the PVA/polyglycol mixture is added to a cylindrical glass jar so that the jar is half full. After capping the jar tightly, invert the sample and immediately return it to its upward position.
The time required for the PVA fines to settle from the upper half of the jar (referred to as suspension time) is measured in seconds. For the purposes of the present invention, dust-free PVA is achieved when the suspension time is 3 seconds or less. In the second test, a ^fritted funnel was used for ⁵ minutes ^at 150
Determine the weight percentage of free dust fines of PVA that can be removed from the gram PVA sample. For purposes of the present invention, a 50% reduction in dust weight percentage is desired to provide a significant improvement at manufacturing scale. Both tests are more fully explained in the Examples below. The dust remover contains about 0.5% to 4.0% polyglycol, more preferably about 0.5% to 2.0% polyglycol.
% of polyglycol with PVA, these ranges are derived according to the method of the fully explained examples. The mixing is carried out at a temperature where the polyglycol is in a liquid state but not so high that the PVA undergoes degradation, i.e. from about -15°C to 150°C.
It is carried out in the range of °C. Polyglycol and PVA
The contact time required to achieve uniform mixing between the two is generally at least 5 minutes, with that time sufficient to achieve a dust reduction of at least 50%. Examples Various polyglycol dust suppression additives
PVA [Elvanol (Elvanol 71−30, E,
I, fully hydrolyzed PVA containing 100% polyvinyl alcohol units, manufactured by DuPont de Nemois & Co.
and Gelvatol, sold by Monsanto Chemical Company (86-89% hydrolyzed PVA) to aggregate PVA fines.
All samples were purchased from Read Co., York,
The granulated PVA was heated above the melting point of the additive (approximately 65°C) in a Readco Sigma Blade mixer manufactured by Pa., and the additive was then mixed for approximately 30 minutes to ensure uniformity. The degree of dustiness of the mixture was prepared by obtaining a 150gm sample of 9.46
The fines suspension time was determined by placing in a 1 quart x10 ^-4 m ³ cylindrical jar and inverting the jar with fines suspension time measured in seconds. new PVA
The suspension time for was measured as a control. The results are shown in the table below.

EXAMPLE This example is to illustrate that a polyglycol having a molecular weight of about 600 is preferred due to its retention of dust suppression properties after extreme temperature cycling. PVA〔Elvanol (Elvanol 71−30, EI
du Pont de Nemours and Company) was mixed in a sealed jar with a polyglycol having the molecular weight specified below. After mixing on a roll mill for 20 minutes, the samples were exposed to a temperature of 90°C for 1 hour and then at -7°C for 4 hours. Suspension time was measured at ambient temperature.

【table】

EXAMPLE This example is to illustrate that compounds generally placed in the polyglycol group as plasticizer additives to PVA are not effective as dust control additives to PVA. Quantitative data is also included to show that polyglycols with a molecular weight of 600 are preferred over polyglycols with a molecular weight of 6000. Several 150g samples of PVA (Elvanol
71-30, E, I, du Pont de Nemours and
Company) were prepared by mixing the various additives described below on a roll mill for approximately 20 minutes and tested for dustiness. A control sample of PVA was also tested. The dustiness of the sample is an open “ACE”
Place the sample on the filter plate of a B (70-100 micron) porous fritted funnel for 5 minutes from the bottom opening of the funnel.
PVA can be removed from PVA by blowing up 4.7 x 10 ^-4 m ³ /sec (1.0 ft ³ /min) of air and then measuring the weight of the sample remaining on the filter plate. It was determined quantitatively as the weight percentage of free dust fines. The results are shown in the table below. Additives percentage without dust 8.3 Polyethylene glycol 2.0% according to the invention with a molecular weight of 600 2.0 Polyethylene glycol 2.0% according to the invention with a molecular weight of 6000 3.2 2.0% Glycerin 6.7 2.0% Diethylene glycol 6.2 2.0% Dibutyl phosphate 5.2 2.0% Alkylaryl Polyether Alcohols 5.1 Example This example shows that adding less than about 0.5% polyglycol does not adequately remove dust from PVA and that adding more than about 4.0% polyglycol to PVA increases dust removal from PVA. This is to explain what not to do. The same method used in the examples was used in this case. Two samples of PVA are used, sample A shows 8.3% dust and sample B shows 11.5% dust according to the method of the example before polyglycol treatment. These samples were chosen to determine the lower and upper limits of percentage polyglycol needed to control PVA dustiness. Samples with more than about 12% dust after addition of about 3% more polyglycol will display particle agglomeration and therefore cannot be fluidized during the plant manufacturing process.
Control the handling of PVA. Samples were treated with increasing amounts of polyethylene glycol of molecular weight 600.
The results are shown in the table below and graphically shown in the figure.
This figure shows that less than about 0.5% polyglycol
Not removing enough dust from PVA, ie not removing 50% of the dust. Additionally, the maximum amount of polyglycol required to completely suppress dustiness in PVA samples was 11.5% before polyglycol treatment.
This was evidenced by sample B, which was designated as dust. In that case, add 3% to 4% polyglycol to PVA.
was added before it completely lost liquidity. The shaded areas of the diagram therefore represent the lower and upper limits of the percentage polyglycol required to practice the invention, i.e.
It is useful to specify 0.5% to 4.0% based on the weight of PVA. Sample A is the most commonly found commercial PVA
shows the fines content. As can be seen with reference to the figure, more than about 2.0% polyglycol does not further reduce the percentage dust of PVA. Therefore, it takes
The preferred amount of polyglycol needed to remove dust in PVA is 0.5% to 2.0%. Sample A Polyethylene glycol (600 molecular weight) Percentage dust 0.0 8.3 0.8 2.9 2.0 2.0 3.0 1.9 5.0 1.9 6.0 1.9 Sample B Polyethylene glycol (600 molecular weight) Percentage dust 0.0 11.5 1.0 7.5 2.0 4.5 3.0 2. 5 3.5 2.0 (Liquidity loss) Example Although this example does not affect the end-use properties of PVA when the polyglycol is cast from an aqueous solution into film form, other compounds commonly placed in the polyglycol group as plasticizer additives to PVA may improve the tensile strength of such films. This is to explain that . PVA (Elvanol 71-30, E, I, du Pont de
Nemours and Company) aqueous solution was cast from the aqueous solution onto a glass plate, air dried for 24 hours and tested at 21°C and 50% before Instron testing.
Conditioned for 48 hours at relative humidity. Tensile strength at break was determined according to the following method: A 2.5 cm wide, 22 mil thick sample was first separated by a 2.5 cm jyo and pulled through the jyo in an Instron tester at a speed of 5 cm/min. The tensile strength exhibited at break was an average of 5 samples. Untreated PVA
The tensile strength of the film made from is 77× ¹⁰³
It is KPa. The results are shown in the table below. Additives Tensile strength 0.8% polyglycol (molecular weight 600) 77×10 ³ KPa 2.0% polyglycol (molecular weight 600) 77×10 ³ KPa 2.0% glycerin 77×10 ³ KPa 2.0% diethylene glycol 70×10 ³ KPa 2.0% dibutyl phosph No film is obtained due to loss of wetting properties

[Brief explanation of drawings]

The accompanying drawing is a graphical representation of the effect of polyglycol concentration on the dustiness of PVA.

Claims (1)

[Claims] 1. According to the Hepler falling ball method (ASTM-D1343)
2 to 2 measured for a 4% aqueous solution at 20°C.
A method for producing a substantially dust-free polyvinyl alcohol powder having a viscosity of 125 mPa·s and a degree of hydrolysis of at least 80 mol %, the polyvinyl alcohol powder having a viscosity of 0.5% to 4.0% by weight based on its weight. , polyethylene glycol with a molecular weight of 200 to 14,000, an ethylene oxide/propylene oxide copolymer with an ethylene oxide content of at least 50% by weight and a molecular weight of 1,000 to 14,000, and a methoxypolyethylene glycol with a molecular weight of 200 to 14,000. a dedusting additive selected from the group consisting of mixing with a dedusting additive selected from the group, said mixing being carried out at a temperature where said polyglycol is liquid and said PVA does not undergo deterioration. 2. The method of claim 1, wherein the dust removal additive is added to the PVA at a concentration of 0.5% to 2.0% by weight. 3. The method according to claim 1 or 2, wherein the dust removal additive is polyethylene glycol having a molecular weight of 600.