A new noise absorbing, vibration dampening PU.

In a moving automobile, the noise of the engine and outside goes into the passenger compartment, through the vehicle center and other pillars, cubicles that have a hollow cavity. Therefore in new cars the cavity is filled with plastic foam to prevent wind noise and to absorb vibration for the purpose of reducing the noise of the passenger compartment.

There are different methods to fill the cavity. For example, flexible polyurethane foam previously shaped to the cavity shape is inserted into the cavity through an access opening. Another way has raw materials, polyols, an isocyanate etc., which foam polyurethane foam, poured and foamed in the cavity.

The former method has the problem that the cavity is filled to a varying extent partially because of insertion through an access opening. It is difficult to completely fill the cavity along its configuration from comer to comer. Even if the shaped polyurethane foams can be filled there, the foam may move from a suitable place during the automobile's running, because the foam cannot be fixed on the oiled iron plate.

The latter method of pouring a polyol and an isocyanate directly, etc., has disadvantage because a new investment is necessary. Recently, rubber material, capable of foaming and expanding by heat encountered in the furnace for baking electrodeposited paint coating, was developed. This article reports on the developing of these polyurethane materials which foam and expand by heat as opposed to the aforementioned rubber materials. This material is the polyurethane sealing which is prepared by furnishing a liquid composition comprising polyols, an isocyanate, a silicon surfactant, a blowing agent, uniformly dispersing an inert gas or air in the liquid composition shape, and heat curing the bubbled shape at a temperature below the decomposition temperature of the blowing agent.

The composition is shaped into a sheet by sheeting process on a release paper. The scaling polyurethane frothed material before expanding by heat has a density of less them 1.0 g/[cm.sup.3]. The polyurethane sealing and expanding foam by heat is lighter than rubber foam and is better at absorbing the noise and vibration.

Materials

The foaming method of mechanical froth Generally, flexible polyurethane slab stock is foamed by blending blowing agent, for example water and methylene chloride, etc. The foaming method of mechanical froth is prepared by mechanically agitating an inert gas or air into the liquid by high shearing means such as a Hobart mixer or Oakes mixer, whereby the inert gas is uniformly dispersed as bubbles in the liquid phase comprising polyols and isocyanate, etc. At this point, the silicon surfactant serves to maintain the bubble stability.

The foaming gel from the mixing head is spouted on paper coated with a separating agent such as silicone which is poured on a belt conveyer and leveled by a doctor knife. The foam is cured by passing in an oven.

Blowing agent

There are some blowing agents which decompose by heat causing [CO.sub.2] and [N.sub.2] gas to occur, as shown in table 1. These blowing agents are used for foaming rubber, vinyl chloride and polyolefin.

[TABULAR DATA 1 OMITTED]

For this study, we used an organic blowing agent, OBSH, for these reasons:

* Decomposition temperature of OBSH is near the temperature of a furnace for baking electrodeposited paint coating.

* Decomposition temperature is stable.

* OBSH has little influence on urethane reaction.

* OBSH has no poisons. OBSH structure formula is shown in figure 1.

Poly BD R-45HT and R-15HT

Poly BD resins are polyols based on a polybutadiene skeleton. Two grades- R-45HT and R-15HT are listed in table 2.

Table 2 - physicochemical properties of poly
                BD resins

Grade                            R-45HT          R-15HT
Viscosity (poise/10[degrees]C)    160              80
          (poise/30[degrees]C)     50              15
          (poise/50[degrees]C)     20               4
Mn (GPC)                        2,800           1,200
1 OH (meq/g)                     0.83            1.80
OHv (mgKOH/g)                    46.6           105.5
Moisture content (%)             0.05            0.03
Density                         0.901           0.908Some characteristics are:

* Has high reactivity because Poly BD is a telechelic liquid rubber that has primary allylic-type hydroxyl groups;

* has good rubber elasticity, because the polydiene backbone has a predominant 1,4 microstructure;

* can be reinforced by carbon black, white carbon, and added process oil, asphalt, etc.;

* the glass transition temperature of Poly BD is under -70[degrees]C. Consequently, Poly BD has high levels of endurance against cold.

* has high levels of endurance against water, because Poly BD skeleton is polybutadiene that is hydrophobic.

* Poly BD has good insulation and high levels of dielectric properties.

Structure formula of Poly BD is shown in figure 2.

Other materials used include:

* #3000 - standard 3000 Mn polyether polyol;

* #4000 - standard 4000 Mn polyether polyol;

* Polyol A - 8000 Mn polyether polyol;

* Polyol B - difunctional 5000 Mn polyether polyol;

* EPOL - polyol based on a polyolefinic skeleton;

* Poly IP - polyol based on a polyisobutyrene skeleton;

* isocyanate - modified polymeric MDI (NCO% = 48.3%);

* surfactant - silicone;

* catalyst - nickel octylacid or dibutyltin dilaurate;

* plasticizer - dipropylene glycol mono methylether.

Experimental

The method of hand mixing in laboratory

Each material was put in a cup and mixed by a hand whip mixer for cooking. Amount of air was adjusted by mixing times. The mixed materials were poured on a release paper and leveled by a doctor knife. It was cured in an oven which was set on 70~100[degrees]C. The sheet was heated at 180[degrees]C for 15 minutes to foam.

Formulation

Usually, the polyol that was used on the foaming method of mechanical froth was polyether polyol based PPG. Further, in advance mixing OBSH into polyether polyol, they were agitated by a hand whip mixer and the sheet was produced. We investigated whether the hand based frothed foams were expanded by heat.

Every formulation did not form the foam because the sheet melted at about 150[degrees]C and did not stiffen and could not keep gas in resin. There was a problem of heat-resistance on the urethane resins based PPG, so we investigated about other type polyols.

To form the foam by the gas occurring later, urethane resins must have superior elongation and plasticity, and keep plastic strain after heat. We thought there was a possibility that the urethane resin had a character like unvulcanized rubber by using polydienic polyols.

Appearance after heat (table 4, formulations) is as follows:

* The foam is almost as big as the sheet before heat. Small bubbles have occurred on the surface of the foam.

Table 4 - formulation used polydienic polyols
Material phw        1      2     3     4
EPOL               100
Poly IP                   100
Poly BD R-45HT                   100
Poly BD R-15HT                          100
Isocyanate         35.9   34.5   34.1   55.6
(Index)            (110)  (110)  (110)  (110)
OBSH                 15     15     15    15
Surfactant           1.5    1.5    1.5   1.5
Catalyst             1.0    1.0    1.0   1.0

* The foam extended two times volume before heat.

* The foam had the same appearance.

* The foam extended four times volume before heat.

The sheet that was made by the foaming method of mechanical frorth to use polydienic polyols had high hardness possibly because there were many points by urethane bond. In case the hardness of resin before heat was stronger than a pressure of decomposing gas, the resin extended a level direction and did not foam to three dimensions. So we thought it was necessary to reduce crosslinking points to demand plasticity for the resin and it was possible to make a condition like an unvulcanized rubber due to lower isocyanate index and experiments. Also we thought it was connected with improvement of self adhesion.

According to lowering isocyanate index, gradually the sheet extended like a mountain. After heat though to lower too much, the bubbled composition would not be coagulative enough to shape, as shown in table 5. The sheet extended during heat once but it contracted little by little because the resin was weak. We discovered that it was different due to a change in the isocyanate index.

[TABULAR DATA 5 OMITTED]

We made experiments about four types of polydienic polyols. The sheet using R-15HT showed the highest blowing magnification. Also the coefficient of viscosity at R-15HT was the lowest. We decided the formulation on production line which R-15HT was main polyol.

The experiments at a production line

The method of the estimation

We tested in accordance with the method of an estimation about filled foam material by automobile makers. The standard condition on this test is that temperature is 20 [+ or -]2[degrees]C and relative humidity is 65 [+ or -]5%.

The iron plate for the estimation

The iron plate expanded by cold pressing process is washed in white gasoline and is dipped in oil protecting rust for 10 seconds or more. Later it is kept perpendicularly for 24 hrs.

The physical properties of the sheet

Sample size of the sheet is 30 x 85 x 1.5~2.0 mm cube. We mark a 40 mm line on the sample and measure tensile strength and elongation at a speed of 200 mm/min.

The blowing magnification

The iron plate size is 200 x 300 x 0.8 mm cube; the sample size is 100 x 100 x 1.5 nun cube. Temperature is: standard bake - 180[degrees] [+ or -] 2[degrees]C; overbake - 215[degrees] [+ or -]2[degrees]C and underbake - 160[degrees] [+ or -]2[degrees]C. The set time is 2 [+ or -]2 minutes.

We measure a thickness of the sample before and after heat and calculate the blowing magnification:

Blowing magnification = X/Y where X is a thickness of the sample before heat and Y is the maximum thickness of the sample after heat.

Fixing to the iron plate coating oil

The iron plate size is 70 x 150 x 0.8 mm cube, the sample size is 40 x 100 x 3.5 mm cube. We fix the sample to the iron plate at a speed of 300 mm/min by a roller of 200 g in weight. After one minute, we drop the plate perpendicularly from 10 cm high to a concrete floor. We check slip or not and peeling off. In case of nothing, we increase falling position by 10 cm and examine the height at which slip and peeling off occur.

Melting and dripping on the iron plate during heat

The iron plate size is 120 x 400 x 1.5 mm cube with an angle of 60 degrees. The sample size is 80 x 200 x 1.5 mm cube. We stick the sample to the plate at one side 50 mm (A) and another side 150 mm (B). After heat on standard bake, we measure the length of material melting and dripping on the plate both sides.

The physical properties of the foam

The iron plate size is 200 x 200 x 0.8 mm cube, sample size is 150 x 150 x 1.5 mm cube. The spacer, in case blowing magnification is over eight times, spacer thickness is 10 mm. In case blowing magnification is over 10 times, spacer thickness is 20 mm.

Standard condition

We put the sample between iron plate through spacers and it is heated on standard bake. We make a 30 x 85 mm square sample piece. After we measure a thickness and mark 40 mm line, we measure tensile strength and elongation. The sample pieces are aged in an oven setting on 80[degrees] [+ or -]2[degrees]C for 30 days. We take them out of the oven and after setting alone on standard condition we measure tensile strength and elongation. The sample pieces aged in an oven setting on 50[degrees] [+ or -]2[degrees]C and 95[+or -]RH% for 30 days.

Intensity of fixing

The iron plate size is 25 x 100 x 1.0 mm cube, the sample size is 25 x 25 x 1.5 mm cube. The sample is fixed on the iron plate at a speed of 300 nm/min by a roller of 200 g in weight. It is put between the plates through a spacer which is 5 nim in thickness and set by clips. It is heated at standard bake and set alone over an hour. We cut protruding parts from the iron plate and measure a fixing area by vernier calipers and tear structure at a speed of 50 mm/min.

Stability after stock

The iron plate size is 200 x 300 x 0.8 mm cube, the sample size is 100 x 100 x 1.5 mm cube. The sample is kept in an oven setting on 40[degrees] [+ or -]2[degrees]C 95[+ or -]5RH% for a week. We take it out of the oven and wipe off a drop of water. At once, it is heated at standard bake and set alone over an hour. We measure the maximum thickness of the foam and calculate the blowing magnification.

The production line

Generally, the coefficient of the polyether polyols using mechanical froth was about 700 (poise/30[degrees]C). But the viscosity of R-15HT was 1,500 (poise/30[degrees]C) and increased the viscosity because of adding the powder of the blowing agent. So we used a plasticizer. It was possible to use general plasticizers, for example aromatic oil and liquid paraffin. Although this scaling material is dipped in the liquid of electrodeposition before passing in a furnace for baking, electrodeposited paint coating, as an element which influences the liquid of electrodeposition doesn't have to soak out. Therefore, a plasticizer that has active hydrogen at the end is desirable to protect soaking out the liquid of electrodeposition. But in case of using short length diol, the sheet becomes hard and only extends a level direction, so low molecular weight monohydric alcohol is suitable. The sheet is produced on the line at the formulation (table 6).

Table 6 - formulation on the
production line

Material phw
Poly BD R-15HT      100
Isocyanate         42.6
(Index)             (75)
OBSH                 25
Surfactant          1.5
Catalyst            1.0
Plasticizer         5.0

Characteristic

The result of the estimation is in table 7. The amount of gas occurring from OBSH was different by temperature. Consequently, the blowing magnification was different too. We showed the difference of the magnification at each temperature in figure 3. Also the blowing magnification was different by the sheet area. We showed the difference of the magnification by a sheet area in figure 4. Figure 5 is the normal incident absorption coefficient at 20 mm thickness.

Table 7 - result of the estimation

Property
Physical properties before heat
Density (g/[cm.sup.3])              0.789
Tensile strength (kgf/[cm.sub.2])   4.71
Elongation (%)                        60

Physical properties afte heat
Density (g/[cm.sub.3]                 0.055
Tensile strength (kgf/[cm.sub.2]      0.47
Elongation (%)                          70

Blowing magnification
On standard bake                         13.3
On under bake                            12.3
On over bake                             13.9
Stability after stock                    12.9
                                    (no problem)
Fixing to the iron plate coating oil (cm)  70

Melting and dripping on the iron plate
during heat
A (mm)                                       29.3
B (mm)                                       32.3
Intensity of fixing (fgf/[cm.sup.2]           0.38

Conclusion

Bridgestone Corporation has developed a new noise absorbing and vibration damping polyurethane material. This material could be extended by heat in case of necessity. The best characteristic of this material was easily to fill a complicated shape or a point sealing completely by heat. We discovered that it extended like a mountain using a polydienic polyol and adjusting isocyanate index. Since a polydienic polyol is hydrophobic, it was suitable for a packing material to seal against water and air.

Raw materials were liquid, so it was easy to change a kind or amount of the blowing agent. Therefore, industrial uses of this material aren't restricted. Owing to make this material by the method of mechanical froth, it was light weight and produced to the sheet easily to manufacture. But we succeeded in having a high blowing magnification.

As reducing weight is demanded at many industrial fields recently, there are some problems to suppress noise and vibration. We expect various applications of this material to settle those problems.

Figure 1 - structural formula of OBSH

[ILLUSTRATION OMITTED]

Figure 2 - structure formula of poly BD

[ILLUSTRATION OMITTED]

Figure 3 - difference of the blowing magnification at each temperature

[ILLUSTRATION OMITTED]

Figure 4 - difference of the blowing magnification by a sheet area

[ILLUSTRATION OMITTED]

Figure 5 - normal absorption coefficient

[ILLUSTRATION OMITTED]

Reference

[1] Yves Malotel, Y.D. Nicolescu and J.J. Flat. 1994, "New polvol system based on Poly BD resins for integral skin foams," Utech '94, p. 57.