JP4265366B2 - Method for producing flexible polyurethane foam - Google Patents

Description

  The present invention relates to a method for producing a flexible polyurethane foam, and more particularly to a method for producing a low-density, low-hardness flexible polyurethane foam by a mechanical floss method.

  Flexible polyurethane foam by the mechanical floss method is used in rolls for copying machines, cosmetic puffs, carpets, packing, sealing materials, and the like. Various manufacturing methods, such as the method described in patent document 1 and the method described in patent document 2, are proposed as a manufacturing method of the flexible polyurethane foam by the mechanical floss method.

JP 2001-89547 A Japanese Patent Laid-Open No. 10-258437

  Since the production method of Patent Document 1 does not use a foam stabilizer, there are few problems of bleeding in the obtained polyurethane foam. However, the cell state of the obtained polyurethane foam is uneven in cell size, and the hardness varies depending on the part. When such a form is used for a paper feed roll, it is difficult to accurately feed paper. On the other hand, since the production method of Patent Document 2 uses alcohol-modified silicone oil and is centrifugally molded, a foam with few pinholes can be obtained. However, because of the centrifugal molding, the molded product is thin and is not suitable for molding a block shape or a thick product.

  TECHNICAL FIELD The present invention relates to a method for producing a flexible polyurethane foam by a mechanical floss method, and has a low hardness and low density in which fine cells are uniformly dispersed as compared with a conventional flexible polyurethane foam by a mechanical floss method. Is obtained.

  An object of the present invention is to provide a method for producing a flexible polyurethane foam having a low hardness and a low density as compared with the conventional mechanical floss method.

The present invention has been found as a result of intensive studies to solve the above-mentioned problems, that is, an organic polyisocyanate (A), a polyol (B), a catalyst (C), and a foam stabilizer (D). In the method for producing polyurethane foam, the polyurethane foam-forming composition dispersed and mixed is further foamed and cured after mixing and dispersing an inert gas by mechanical stirring.
The foam stabilizer (D) is a dimethylpolysiloxane-polyether polyol block copolymer,
Silicon content is 10-30% by mass,
The molecular weight distribution in the weight average molecular weight is 1,000 or more and less than 2,000: 30 to 40%, 2,000 or more and less than 4,000: 40 to 50%, 4,000 or more: 20 to 30%,
The mass ratio of a dimethylpolysiloxane part and a polyether polyol part is dimethylpolysiloxane part: polyether polyol part = 46 : 54 , It is a manufacturing method of a polyurethane foam characterized by the above-mentioned.

  The organic polyisocyanate (A) used in the present invention is diphenylmethane diisocyanate (hereinafter abbreviated as “MDI”), polyphenylene polymethylene polyisocyanate (hereinafter abbreviated as “MDI polynuclear condensate”), tolylene diisocyanate. Xylylene diisocyanate, tetramethyl xylylene diisocyanate, isophorone diisocyanate, hexamethylene diisocyanate, naphthalene diisocyanate, hydrogenated diphenylmethane diisocyanate, hydrogenated xylylene diisocyanate, etc. , Biuret, allophanate, carbodiimide, uretonimine, oxazolidone, amide, imide, isocyanurate, uretdione Those obtained by modifying the like. These may be used alone or in combination of two or more as required.

  In the present invention, the organic polyisocyanate (A) preferably has an isocyanate content of 5 to 35% by mass and a viscosity at 25 ° C. of 2,000 mPa · s or less, particularly in view of workability and moldability. The content is preferably 10 to 30% by mass, and the viscosity at 25 ° C. is preferably 1000 to 8000 mPa · s.

MDI and polymeric MDI will be described in more detail.
MDI is 4,4'-diphenylmethane diisocyanate (hereinafter abbreviated as 4,4'-MDI), 2,4'-diphenylmethane diisocyanate (hereinafter abbreviated as 2,4'-MDI), 2,2'- It exists in the form of a mixture (sometimes any single item) of three isomers of diphenylmethane diisocyanate (hereinafter abbreviated as 2,2'-MDI).

  The MDI polynuclear mixture exists in the form of a mixture of compounds having three or more benzene rings having an isocyanate group bonded in one molecule and having different degrees of condensation. Usually, it is not supplied in the form of the MDI-based multinuclear mixture alone, but is supplied in the form of a mixture with MDI (a mixture of MDI and MDI-based multinuclear mixture is abbreviated as “polymeric MDI”).

  In the first place, polymeric MDI is obtained by converting an amino group to an isocyanate group by phosgenation or the like of a condensation mixture (polyamine) obtained by the condensation reaction of aniline and formalin, and the product has a different degree of condensation from MDI. It is an MDI-based multinuclear mixture. The composition of MDI and polymeric MDI can be changed by changing the raw material composition ratio and reaction conditions during condensation, or by removing a portion of MDI by distillation. The MDI content of polymeric MDI and the isomer composition ratio of MDI can be determined from a calibration curve based on the area percentage of each peak obtained by gel permeation chromatography or gas chromatography.

  In the present invention, considering the working environment at the time of foam production, foam moldability, physical properties of the resulting polyurethane foam, etc., the MDI having a 4,4′-MDI content of 50 to 100% by mass, 4,4 ′ -Polymeric MDI containing MDI having an MDI content of 50 to 100% by mass, and these isocyanate group-terminated urethane prepolymers are preferred.

  The polyol (B) used in the present invention comprises a polymer polyol and a chain extender. Examples of the polymer polyol include polyether polyol, polyester polyol, polycarbonate polyol, and hydrophobic polyol. Here, as the polyether polyol, for example, those obtained by addition polymerization of alkylene oxide using propylene glycol, ethylene glycol, glycerin, trimethylolpropane, hexanetriol or the like as a starting material are preferable. Particularly, ethylene oxide or ethylene oxide and propylene oxide are added to glycerin. Those obtained by addition polymerization are preferred. Polyester polyols include condensed polyester polyols obtained by condensation of dicarboxylic acids with diols and triols, lactone polyester polyols obtained by ring-opening polymerization of lactones based on diols and triols, and polyether polyols with lactones at the ends. A polyol such as an ester-modified polyol modified with an ester is preferably used. Examples of the polycarbonate polyol include those obtained by a transesterification reaction between a low molecular polyol such as butanediol or hexanediol and a low molecular carbonate such as propylene carbonate or diethyl carbonate. As the hydrophobic polyol, polyisoprene polyol, polybutadiene polyol, hydrogenated polybutadiene polyol, or the like is used. These polymer polyol components may be used alone or in combination of two or more.

  The above-described polymer polyol is preferably hydrophobic. This is because the water absorption of the resulting foam is small, and the change in the conductive environment is small. A more preferred polyol has a substantial average functional group number of 2 to 4, a number average molecular weight of 1,000 to 10,000 (particularly preferably 2,000 to 5,000) and an oxyethylene group content of 50% by mass or less. Poly (oxypropylene) polyol or poly (oxyethylene-oxypropylene) polyol. The poly (oxyethylene-oxypropylene) polyol includes, for example, a block copolymer type, a random copolymer type, or a polymer obtained by adding ethylene oxide to the terminal of the poly (oxypropylene) polyol. When the substantial average functional group number is too small or the number average molecular weight is too large, the hardness of the foam tends to be too low. When the substantial average functional group number is too large or the number average molecular weight is too small, the foam hardness tends to be too high.

  Examples of the chain extender include ethylene glycol, propylene glycol, 1,4-butanediol, trimethylolpropane, tetramethylene ether glycol, polyethylene glycol and the like. These chain extenders may be used alone or in combination of two or more. In the present invention, 1,4-butanediol is preferred. This is because 1,4-butanediol has a primary hydroxyl group and thus has good reactivity, is liquid at room temperature, has excellent workability, and has an appropriate molecular weight, and thus has excellent mechanical strength. Is obtained.

  Examples of the catalyst (C) used in the present invention include monoamines such as triethylamine and dimethylcyclohexylamine, diamines such as tetramethylethylenediamine, tetramethylpropanediamine and tetramethylhexanediamine, pentamethyldiethylenetriamine and pentamethyldipropylenetriamine. , Triamines such as tetramethylguanidine, triethylenediamine, dimethylpiperazine, methylethylpiperazine, cyclic amines such as methylmorpholine, dimethylaminoethylmorpholine, dimethylimidazole, dimethylaminoethanol, dimethylaminoethoxyethanol, trimethylaminoethylethanolamine, Alcohol amines such as methylhydroxyethylpiperazine, hydroxyethylmorpholine, bis ( Methylaminoethyl) ether, ether amines such as ethylene glycol bis (dimethyl) aminopropyl ether, stannous octoate, dibutyltin diacetate, dibutyltin dilaurate, dibutyltin marker peptide, dibutyltin thiocarboxylate, dibutyltin dimaleate, dioctyl Known catalysts such as tin metal peptide, dioctyl tin thiocarboxylate, phenylmercuric propionate, and organometallic compounds such as octenoate can be used alone or in combination of two or more.

The foam stabilizer (D) used in the present invention is a dimethylpolysiloxane-polyether polyol block copolymer having a silicon content of 10 to 30% by mass and a molecular weight distribution in a weight average molecular weight of 1,000 or more. Less than 2,000: 30 to 40%, 2,000 or more and less than 4,000: 40 to 50%, 4,000 or more: 20 to 30%, and the mass ratio between the dimethylpolysiloxane part and the polyether polyol part is dimethylpolysiloxane. Part: Polyether polyol part = 46:54 .

  When the silicon content of the foam stabilizer (D) is out of the above range or when the mass ratio between the dimethylpolysiloxane part and the polyether polyol part is dimethylsiloxane rich, the resulting foam is difficult to take a fine cell structure. When the mass ratio of the dimethylpolysiloxane part and the polyether polyol part is rich in the polyether polyol, or when the molecular weight distribution is out of the above range, it is difficult to obtain a foam in which fine cells are uniformly dispersed or a low density foam.

The silicon content is measured by an ashing method, and specifically measured by the following procedure.
"Method for measuring silicon content"
1. Weigh sample accurately into crucible.
2. Heat the crucible and burn the contents.
3. Weigh the residue (ash) remaining in the crucible.
4). The silicon content is calculated according to the following formula.
Silicon content (%)
= (Mass of remaining ash / mass of sample weighed first)
× (32/64) × 100

The molecular weight distribution is measured by a gel permeation chromatography (GPC) method, and the measurement conditions are as follows.
"Molecular weight distribution measurement method"
Molecular weight distribution is evaluated by calculating the area% of each peak in the GPC chart. Apparatus: HLC-8220 manufactured by Tosoh Corporation
Column: TSKgel G3000H _XL x 2 + TSKgel G2000H _XL x 2 Fluid medium: THF (tetrahydrofuran)
Flow rate: 1 ml / min
Measurement temperature: 40 ° C
Detector: RI detector Injection volume: 100 μl
Weight average molecular weight: Calculated as a relative molecular weight with polystyrene Baseline: A line connecting the rising edge of the first peak and the end of the last peak in the GPC chart, not a line connecting the valleys and valleys of the peaks.

The mass ratio between the dimethylpolysiloxane part and the polyether polyol part can be determined by calculating by ¹ H-NMR measurement. The ¹ H-NMR measurement conditions in the present invention are as follows.
Model: Varian Unity 500 (FT-NMR)
Measurement frequency: 500 MHz

  The foam stabilizer (D) consists of oxyethylene groups and oxypropylene groups as repeating units in the polyether polyol portion, and the mass ratio of oxyethylene groups to oxypropylene groups is oxyethylene groups / oxypropylene groups. = 50 / 50-80 / 20 is preferable. This ratio is considered to be a ratio that imparts appropriate lipophilicity and hydrophilicity to the foam stabilizer (D) and exhibits the foam regulating action, that is, the performance as a surfactant to the maximum.

The ratio of the oxyethylene group to the oxypropylene group can be obtained by subjecting the foam stabilizer to Corish decomposition and calculating the recovered product by ¹ H-NMR measurement.

  The present invention can also use other conventionally known additives as required, for example, antioxidants, ultraviolet absorbers, flame retardants, colorants, conductive agents, insulating agents, luminescent agents, antibacterial agents, and fragrances. Etc.

  In order to produce the flexible polyurethane foam of the present invention using these raw materials, the polyisocyanate component, polyol component, catalyst, and other additives stored or prepared in separate containers are combined into one mixing head. Add while mixing inert gas, mix to homogeneity, flow the mixture onto a conveyor with a formwork and bottom paper, heat cure, or cast the mixture into a predetermined mold, etc. And heat curing. The foam obtained by such a method is a polyurethane foam having uniform fine cells and appropriate hardness. When a so-called foaming agent is used, the cells are not uniform.

  In this case, the isocyanate index (isocyanate group / active hydrogen group × 100) is preferably from 60 to 120, particularly preferably from 80 to 110. If the index is too low, the foam surface tends to be sticky. Moreover, when an index is too high, it may not harden | cure or it may become a foam with insufficient flexibility.

The flexible polyurethane foam thus obtained has a density of 0.2 to 0.9 g / cm ³ and an Asker hardness C of 80 or less, and becomes a uniform foam having fine cells.

  The flexible polyurethane foam obtained by the present invention includes various rolls such as toner conveying rolls, transfer rolls, charging rolls and developing rolls of electrophotographic apparatuses, bedclothes such as pillows and mattresses, cosmetic puffs, packing, sealing materials, carpet backings, etc. Used in the field of

  EXAMPLES Hereinafter, although an Example demonstrates this invention in more detail, this invention is not limited to these. In Examples and Comparative Examples, unless otherwise specified, the ratio is a mass ratio, and “%” is “mass%”.

[Analysis of foam stabilizer]
Results of measuring the hydroxyl value, silicon content, mass ratio of polysiloxane part / polyether part, and mass ratio of oxyethylene group (EO) / oxypropylene group (PO) in the polyether part for foam stabilizers 1 to 4 Is shown in Table 1.

In Table 1, the end groups:
^This was confirmed by ¹ H-NMR.
Silicon content:
It was measured by the ashing method described above.
Mass ratio of polysiloxane part / polyether part:
^It was measured by ¹ H-NMR.
EO / PO mass ratio of the polyether part:
After the Corish decomposition, the recovered material was measured by ¹ H-NMR.
* EO: Ethylene oxide PO: Propylene oxide foam stabilizer Molecular weight distribution:
It was measured by the GPC method described above.
Molecular weight distribution of the polyether part:
After the Corish decomposition, the recovered material was measured by the GPC method described above.

[Synthesis of isocyanate group-terminated urethane prepolymer]
Synthesis example Capacity equipped with stirrer, cooling pipe, nitrogen introduction pipe, thermometer: A 100 L reactor was charged with 350 g of MDI-1 and 650 g of polyol-1 and reacted at 80 ° C. for 4 hours with stirring. An isocyanate group-terminated urethane prepolymer NCO-1 was obtained. The isocyanate content of NCO-1 was 9.0%.

In the synthesis example, MDI-1:
Diphenylmethane diisocyanate (MDI) containing 50% MDI isomer mixture
Polyol-1:
Nominal average functional group number = 3, number average molecular weight = 3,000, oxyethylene group content = 11% terminal oxyethylene-capped poly (oxypropylene) polyol * MDI isomer mixture:
Mixtures of isomers other than 4,4'-MDI (2,2'-MDI and 2,4'-MDI)

[Preparation of polyol premix]
Formulation Examples 1-18
Volume: Polyol premixes OH-1 to -18 were prepared in a 2 L reactor by charging shown in Tables 2 and 3.

In Formulation Examples 1-18 and Tables 2 and 3, Polyol-1:
Nominal average functional group = 3, number average molecular weight = 3,000, oxyethylene group content = 11% terminal oxyethylene-capped poly (oxypropylene) polyol 1,4-BD:
1,4-butanediol TEDA-L33:
Amine catalyst (manufactured by Tosoh)

[Manufacture of polyurethane foam]
Example 1
Liquid temperature blended at a ratio shown in Table 4: 25 ° C. polyol premix OH-1 and liquid temperature: 25 ° C. polyisocyanate NCO-1 were mixed, stirred for 1 minute and mixed with dry air Was poured into a mold (10 cm × 10 cm × 10 cm, upper open), and then the mold into which the mixed liquid had been poured was left in a hot air oven adjusted to 80 ° C. for 2 hours to cure the polyurethane foam raw material. . The cured polyurethane foam was removed from the mold to produce a polyurethane foam.

Examples 2-8, Comparative Examples 1-10
Using the raw materials shown in Tables 4 and 5, polyurethane foam was produced in the same procedure as in Example 1.

[Evaluation of polyurethane foam]
Evaluation items and measurement methods of polyurethane foam are as follows.
density:
It calculated | required according to JISK6401.
The density measurement sample is a liquid two minutes after mixing the polyisocyanate and the polyol and a foam after the curing reaction.
hardness:
State of measurement cell by Asker hardness tester C type:
The flexible polyurethane foam is cut, and the number of cells per unit area of the cross section and the radius of the cells are measured. There were 5 cut points.

  From Tables 2 to 5, when the foam stabilizer defined in the present invention is used, the standard deviation of the cell radius in the example is about 0.04 mm, whereas the standard deviation of the cell radius in the comparative example is From 0.05 to 0.06 mm, it can be said that the example is a more uniform foam. Moreover, it was confirmed that the examples had a sufficiently low density.

Claims (1)

The polyurethane foam-forming composition in which the organic polyisocyanate (A), polyol (B), catalyst (C), and foam stabilizer (D) were dispersed and mixed was further mixed and dispersed with an inert gas by mechanical stirring. Thereafter, in a method for producing a flexible polyurethane foam obtained by foam curing,
The foam stabilizer (D) is a dimethylpolysiloxane-polyether polyol block copolymer,
Silicon content is 10-30% by mass,
The molecular weight distribution in the weight average molecular weight is 1,000 or more and less than 2,000: 30 to 40%, 2,000 or more and less than 4,000: 40 to 50%, 4,000 or more: 20 to 30%,
A method for producing a polyurethane foam, wherein the mass ratio of the dimethylpolysiloxane part to the polyether polyol part is dimethylpolysiloxane part: polyether polyol part = 46 : 54 .