聚氨酯真空隔热板芯材的研制

聚氨酯真空隔热板芯材的研制

王娟 石芳录 朱贤 白品贤

（兰州华宇创新科技有限公司 甘肃兰州 730000）

摘 要：制备了用于聚氨酯真空隔热板的开孔硬泡芯材，该泡沫芯材的开孔率达95％。讨论了聚醚多元醇、开孔剂及泡沫稳定剂等组分对芯材性能的影响。并介绍了封装成真空隔热板的工艺。用该芯材制成的聚氨酯真空隔热板具有优良的隔热性能，其导热系数低于10 mW/(m·K)。

关键词：真空隔热板；开孔泡沫；聚氨酯；硬质泡沫；导热系数

硬质聚氨酯(PU)泡沫塑料由于具有优良的隔热性能，一直被广泛应用于家电、石化和建筑等行业。为了更好地节约能源，进一步提高其隔热性能是大家关注和研究的焦点。多年来在国内外业内人士的共同努力下，PU硬泡的隔热性能逐步提高，但是，硬质PU泡沫体闭孔中气体的存在，决定了PU硬泡的表观导热系数不可能低于该气体自身的导热系数。这样，从根本上阻碍了PU硬泡隔热性能的彻底优化。

聚氨酯真空隔热板(PU-VIP)是将开孔聚氨酯硬泡芯材真空封装在镀铝聚酯/聚乙烯薄膜内而成。由于抽真空脱除了开孔结构泡沫中的气体，使板材具有优良的隔热性能。将PU-VIP与浇注PU硬泡结合形成复合隔热结构，可用于冰箱隔热。当PU-VIP替代35%的普通浇注PU硬泡时，可使冰箱能耗降低25%[1]。可见，PU-VIP是一种高效、节能、环保型隔热材料，由于其不含任何CFC物质，对环境无污染，因此具有极好的发展和应用前景。

1 PU-VIP的隔热机理

一般用于隔热的PU硬泡是由大量的蜂窝状的微孔构成，这些微孔各自，互不相通，构成所谓“闭孔结构”，泡孔内充满了导热系数极低的CFC气体。PU硬泡的表观导热系数由下式表示： ＝g＋s＋r

式中：＝表观导热系数； g＝泡孔内气体的热传导；s＝泡沫骨架的热传导；r＝辐射热传导。

以CFC-11为发泡剂，常温下三种热传导在PU硬泡表观导热系数中所占大致比例见表1[2]。

表1 三种热传导占PU硬泡表观导热系数的比例

传热方式

比例/% 50～65 35～50 100

g r，s 

由表1可见，常温下气体的热传导g占PU硬泡表观导热系数的45%左右，接近一半。

显然，PU-VIP开孔硬泡芯材，采用抽真空的工艺，可使g0，其表观导热系数由下式表示：

＝s ＋ r

这样，由于PU-VIP芯材的气体导热系数g0，理论上其导热系数仅约为普通硬泡的一半左右，而实际应用中，通过优化泡孔结构、提高真空度等方法，可以进一步提高板材的隔热性能。实验证明，当PU-VIP内压降至0.5 Pa时，其导热系数可低达7 mW/(m·K)[1]。

2 实验

2.1 芯材配方

本实验的核心就是研制出开孔型微孔泡沫芯材，采用一步法工艺发泡成型，表2为本实验配方。

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表2 开孔型微孔泡沫芯材配方

原料 质量份

聚醚多元醇1)

100

泡沫稳定剂2)

0.5～1.0

开孔剂2) 0.5～1.0

复合催化剂3)

3～6

发泡剂4) 7～10

注: 1) 选用两种以上国产聚醚多元醇组合，组合聚醚的羟值450 mgKOH/g； 2)均选用德国高施米特公司聚氨酯助剂； 3)

选用德国高施米特公司催化剂与国产普通催化剂复合。4) 发泡剂为HCFC-141b，另含水0.5~2.0份。

2.2 芯材制作工艺

采用手工发泡或高压发泡机浇注将料液在室温下混合，在1500 r/min下搅拌8～10 s，注入40℃的不锈钢模具中，使泡沫自由上升（采用浮动式顶盖，与软泡模塑工艺相同），5 min后脱模，并在70℃下熟化24 h。

2.3 测试方法

用扫描电镜SEM测定孔径微观形态结构； 开孔率 按GB10799－方法测试； 密度 按GB/T6343－95方法测试； 导热系数 按GB3399－82方法测试； 压缩强度 按GB8813－88方法测试。

3 结果与讨论

3.1 芯材的三个技术要求

PU-VIP芯材的制备是真空板研制的关键技术之一，其配方实验及制作工艺与普通PU硬泡均有根本不同。PU-VIP芯材制备关键在于开孔率高、泡孔结构好、抗压性能强三点。 3.1.1 高开孔率

与普通闭孔结构的PU硬泡 (一般闭孔率大于95%)不同，作为PU-VIP真空板芯材，要求泡沫开孔率愈高愈好，以便于抽空，从而保持真空板内的真空度。因为真空板芯材中少量闭孔泡沫内的气体会缓慢逸出。本实验对平均孔径为200m的PU-VIP芯材在66.5Pa真空条件下的表观导热系数与泡沫开孔率的关系进行了分析，结果如图1所示。

图1 开孔泡沫表观导热系数与泡沫开孔率的关系

由图1可见，在一定真空条件下PU-VIP表观导热系数随泡沫开孔率的提高明显下降。实验结果表明，要使PU-VIP真正具有优良的隔热性能，芯材的开孔率应大于95％以上。 3.1.2 泡孔结构

真空板封装临界真空度依赖于真空板芯材泡孔结构[3]。泡孔尺寸小，结构均匀，其封装临界真空度可相应降低。普通PU硬泡的平均孔径在300～1000 m之间，而PU-VIP芯材孔径若为300～1000 m，要使制成的真空板达到隔热要求，真空度需保持在0.133 Pa水平。这样的真空度在实际生产中很难达到，因此要求用于真空隔热板的开孔泡沫具有更小的孔径。表3为本实验在真空度为13.3 Pa，开孔率95%时的不同孔径芯材的导热系数。

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表3 同样真空度下不同孔径芯材导热系数的对比

孔径/m 140 190 250 290 330

/mW·（m·K）

8.2 9.5 13 16 22

－1

从表3中可以看出，真空度为13.3 Pa时，平均孔径为140～250 m的开孔聚氨酯硬泡，可满足隔热

要求。

3.1.3 抗压性能

PU-VIP 抽空后，要使芯材与外界大气压力保持平衡而泡沫又不变形，则需要开孔泡沫具有一定的抗压性能。本实验制成的开孔硬泡的密度为50～60 kg/m3，压缩强度为0.5～0.6 MPa，可满足要求。由表4可知，同样真空水平(1.33 Pa)下，与其它真空板芯材（如硅粉、珍珠岩、玻璃纤维、硅酸钙粉末等）相比，要达到同样的压缩强度要求，PU-VIP的重量只需它们的1/3，而且相比之下，PU-VIP具有更低的导热系数[4]。

表4 PU-VIP及其它芯材的导热系数对比

芯材种类 硅粉 珍珠岩 硅酸钙粉末 开孔PU硬泡

密度/kg·m3

－

λ/W·（m·K）1

－

200～300

200～300 200～300 50～60

0.005～0.008 0.006～0.010 0.012～0.015 0.004～0.018

3.2 配方实验的主要影响因素 3.2.1 聚醚多元醇的选择

聚醚多元醇的种类对芯材抗压强度影响很大。实验发现采用高活性聚醚多元醇（羟值小于50mgKOH/g），虽很容易得到高开孔率、细孔的理想泡沫，但泡沫强度差，难以达到要求，真空封装后泡沫易变形；反之，选用硬质PU硬泡常用的高羟值低分子量的聚醚多元醇，虽解决了强度问题，但泡沫不易开孔，孔径也不理想。本实验选用两种国产高羟值聚醚多元醇为主，羟值分别为400和500 mgKOH/g，另加入一定量羟值小于50 mgKOH/g低羟值的高活性聚醚多元醇。再通过调整开孔剂、稳定剂等助剂的用量，保证了芯材的强度达到要求，得到满意的产品。 3.2.2 开孔剂和泡沫稳定剂的相对含量

开孔剂用量高有助于泡沫开孔，却使孔径变大；反之，稳定剂虽有利于孔径优化，但却抑制泡沫开孔，因此，如何协调二者的关系是研究的又一难点。表5列出了开孔剂质量分数为1时不同质量分数的稳定剂对PU-VIP泡沫开孔率和孔径的影响。

表5 稳定剂对芯材泡沫开孔率和孔径的影响

泡沫稳定剂用量 1)

0.50 0.75 1.00

开孔率/%

92 90 86

孔径/m 290 250 150

注: 1) 相对于100质量份聚醚多元醇的用量。

由表5可见，开孔剂和泡沫稳定剂在配方体系中虽用量很小，但其相对用量对泡沫开孔率及孔径大小的影响却十分显著。

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3.2.3 凝胶时间与孔径、开孔率的关系

对于用于VIP用途的PU硬泡，为了得到高开孔率的细泡孔，要求泡沫生长过程中在泡孔破裂的同时发生凝胶，若凝胶快则泡孔会产生闭孔结构，凝胶慢则泡孔变粗。在此，催化剂的种类和用量尤为关键。本实验选用了几种催化剂复合使用，研制出的PU-VIP硬泡芯材，密度为50～60 kg/m3，开孔率大于95%、平均孔径约140～250 m，其压缩强度大于0.5MPa。图2为同样放大倍数下研制的开孔芯材样品(a)与德国Bayer的环戊烷发泡同类泡沫样品(b)的扫描电镜(SEM)显微照片。

a b 图2 同样放大倍数下(×30)两种样品的显微照片（SEM）

3.3 芯材封装预处理

维持PU-VIP内部真空度的长期稳定是保证PU-VIP达到预期优异隔热性能的前提，而未经预处理的PU-VIP在使用过程中真空度很快下降，其原因如下： (1) 芯材及封装材料本身逸出气体

由于泡沫芯材实际开孔率为95%左右，还存在少量闭孔。在真空环境中，闭孔泡沫中的气体会慢慢释放，并且泡沫壁中溶解的极少量发泡剂以及胺催化剂等挥发成分的逸出以及封装材料释放出的气体等会导致真空度下降。另外在箱体发泡过程中，箱体的预热(约50℃)使PU-VIP表面温度达80～100℃，高温会加快上述气体的逸出，而使箱体壁的隔热性能恶化。 (2) 外部气体的渗透

由于压差，有可能造成气体（N2、O2、CO2和H2O等）通过封装材料隔离膜渗入，而使真空度下降。因此，针对以上可能发生的问题，封装前必须对芯材进行预处理。国外文献中提到的将芯材在封装前进行预处理及在真空板中封入吸气剂等解决VIP出气问题的方法都比较有效。本实验采取的方法是将预处理及封装工艺结合起来进行，即将芯材在120℃下烘烤30 min后，立刻在1.33～13.3 Pa的真空度下去气抽空，同时封入一定量的吸气剂。经过处理封装的板材与芯材未经处理的板材相比，导热系数随时间的变化很小。当芯材孔径150 m、开孔率为95%时，导热系数随时间的变化关系如图3所示。由图3可见，预处理及加入吸气剂对维持真空板使用所需的静态真空至关重要。

1－未处理泡沫塑料 2－经处理的泡沫

图3 导热系数随时间的变化关系

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3.4 PU-VIP芯材性能

本实验研制的PU-VIP芯材的主要技术指标，如表6所示，可见，PU-VIP芯材隔热性能达到了使用的要求。

表6 PU-VIP主要技术指标

项 目

开孔率/% 孔径/m 密度kg·m3

－

指标 ≥95 150～200 55～65

－

导热系数/W·(m·K)1 压缩强度/MPa

≤0.010 ≥0.5

注: PU-VIP内部真空度为13.3～66.5 Pa。

4 结束语

以国产聚醚为原料、选择合适的助剂配比，可以研制出具有良好性能的PU-VIP芯材，该芯材经有效的预处理封装工艺，制成的PU-VIP真空板材隔热性能优良，具有广阔的应用前景。

参考文献

1 胡忠伟. 国内外聚氨酯工业发展近况. 聚氨酯工业,1999,14(1):6

2 King J A, Latham D D, Ackley J C. Relationship of k-Factor versus Density for Various Appliance Foam Formulations Containing Next Generation. Journal of Cellular Plastics, 1996, 32 :356

3 Devos R, Rosbotham D, Deschaght J. Open-Celled Polyurethane Foam Based Vacuum Panel Technology :A fully Polyurethane Based Composite Technology for Vacuum Insulated Appliances. Journal of Cellular Plastics, 1996, 32 :471

4 Kodama K, Yuge K, Masuda Y T, et al. Development of Micro Cellular Open Cell Rigid PU Foams. Journal of Cellular Plastics, 1995, 31 : 27

Preparation of Open-Celled Rigid Polyurethane Foam for Vacuum Insulation Panels

Wang Juan Shi Fanglu Zhu Xian Bai Pinxian

(Lanzhou Huayu Innovation Technologies Co. Ltd, Gansu Lanzhou 730000)

Abstract: An open-celled polyurethane rigid foam for vacuum panel core material was prepared. The open-cell percent of the core material is about 95%. The effects of polyols, open-celled agents, stabilizers and other additives on properties of the core material were simply discussed, and the encapsulating technology of the vacuum insulation panel was introduced. The vacuum insulation panel has excellent insulating performance and

－

its thermal conductivity is less than 0.010 W/(m·K)1.

Keywords: vacuum insulation panel; open-celled foam; polyurethane; rigid foam; thermal conductivity

作者简介：

王娟 女，工程师，1971年出生，1994年四川联合大学高分子材料专业本科毕业，现从事聚氨酯硬泡的研究、生产及测试工作。

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Preparation of Open-Celled Rigid Polyurethane Foam for Vacuum

Insulation Panels

Wang Juan Shi Fanglu Zhu Xian Bai Pinxian

(Lanzhou Huayu Innovation Technologies Co.,Ltd , Lanzhou 730000)

Abstract: A opencelled polyurethane rigid foam for vacuum panel core material was prepared. The open-cell percent of the core material is about 95%. The effects of polyols, open-celled agents, stabilizers and other additives on properties of the core material were simply discussed, and the encapsulating technology of the vacuum insulation panel was introduced. The vacuum insulation panel has excellent insulating performance and

－

its thermal conductivity is less than 0.010 W/(m·K)1.

Keywords: vacuum insulation panel; opencelled foam; polyurethane; rigid foam; thermal conductivity

Polyurethane foam as an insulation material has so far been considered to be the most excellent, but the thermal conductivity of the foam cannot be reduced to less than the thermal conductivity of the blowing agent itself. It will be difficult to further improve its insulating performances.

Polyurethane vacuum panels (PU-VIP) are obtained by packing metal-plastic film laminated containers with the open cell foam and then sealing in a appropriate vacuum level, and its insulating performances is excellent . Used in the refrigerator or freezer compound with polyurethane rigid foam, when 35% polyurethane rigid foam was substituted, 25% of the energy consumption of the refrigerator or freezer would be decrease [1].

1 THE INSULATION METHANISM OF PU-VIP

The main thermal conductivity of PU rigid foam was expressed by formula below: =g+s +r

where:  is apparent thermal conductivity; g is thermal conductivity contributed through gas; s is thermal conductivity contributed through cell material; r is thermal conductivity contributed through radiation.

Table 1 shows the proportion of the three thermal conductivity of polyurethane rigid foam blown by CFC-11 in room temperature1[2].The ratio of g is almost 45%,and close to a half.。

Table 1. The proportion of the three thermal conductivity of polyurethane rigid foam blown by CFC-11

Thermal conductivity proportion /%

50-65 g

r，s 35-50

100 

Obviously, the main thermal conductivity of PU-VIP is expressed by formula below. Its thermal conductivity is only about a half of the generic rigid foam in theory .: =s +r

The result of experimentation shows that thermal conductivity will be 0.007 W/(m·K)[1 when the pressure in the panel has to be kept below the 0.5 Pa.

2 EXPERIMENTAL

2.1 Formulation

The formulation is shows in table 2.

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Formulations

Pbw

Table 2. Formulation of the micro cellular open cell foam

Multiple catalyzer 1) 2) 2)

Polyether polyolSurfactantOpen-cell agent 3)

100

0.5～1.0

0.5～1.0

3～6

Blowing

agent4) 7～10

*1) Multiple of two type homemade polyethers,, OH value, 450 mgKOH/g; 2)Silicone surfactant(Degussa Chemicals Co. Ltd);

3) Multiple of the homemade and Degussa(Degussa Chemicals Co. Ltd) catalyzer ; 4) HCFC-141b and water (0.5~2.0%)。

2.2 Preparing of the core materials

Foams mixture was poured directly into stainless steel boxes (40℃) and allowed to rise freely. The mixing speed and time was 1500 r/min,8～10 s .

The properties of the foams were measured after aging over 24h at 70℃. 2.3 Test methods

Micro cellular structure SEM；

Open cell content GB10799-； Density GB/T6343-95； Thermal conductivity GB3399-82； Compressive strength GB8813-88.

3 RESULTS AND DISCUSSION

3.1 Physical properties required for the core material 3.1.1 Full open cell content

The closed-cell content is detrimental to the long term performance of the evacuated panel because of the diffusion of gases, remaining in the closed cells , into the panel.

Figure 1 shows the relationship between the open cell content and the thermal conductivity of PU-VIP. A lower thermal conductivity resulted in a higher open cell content in a stated vacuum level. The resulting open cell content was 95%.

0.020

0.015

0.010

0.00520406080100 open cell content（%）Figure 1. The relationship between the open cell content and the thermal conductivity

(The cell size of foam was 200m, the vacuum level of PU-VIP was 66.5Pa)

3.1.2 Cell structure

A fine cell structure is important since the critical pressure of the panel composite is increased. The variations of the thermal radiation with various cell size was shown in table 3. The resulting average cell size of the core material was in the range of 140～250 m .

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Table 3. The thermal conductivity of various cell size foams at same vacuum level

(the vacuum level was 66.5Pa)

－

/W·（m·K）1 Cell size/m

140 0.0082 190 0.0095 250 0.013 290 0.016 330 0.022

3.1.3 Foam strength

The presence of a vacuum inside the facer material creates a high force per unit area on the foam., equivalent to atmospheric pressure.. Withstanding the forces of atmospheric pressure, requiring a level of compressive strength of foam was around 0.5～0.6 MPa ,which can be achieved by foams with densities around 50～60 kg/m3..This density was lower than any other vacuum panel core materials currently available as shown in table 44]。

Table 4. The thermal conductivity of different vacuum panel core materials

－－

core materials Density/kg·m3 λ/W·（m·K）1 Silica powder 200～300 0.005～0.008 Pearlite powder 200～300 0.006～0.010 Calcium silicate powder 200～300 0.012～0.015 Open cell foam 50～60 0.004～0.018

3.2 Experiment

3.2.1 Polyether employed

The blend polyol was prepared by two types of homemade polyethers (OH value was around 500 mgKOH/g ), mixed with a small quantity of high active polyether (OH value was around 50 mgKOH/g ). 3.2.2 Proportion of the open-cell agent and surfactant

Table 5 shows the effect of the surfactant on the open cell content and cell size. It was obvious.

Table 5. The effect of the surfactant on the open cell content

and cell size(the open cell agent level was 1 pbw) Surfactant 1)

0.50 0.75 1.00

Open cell content/%

92 90 86

Cell size/m

290 250 150

*1) pbw of surfactant level with blend polyol。

3.2.3 Relationship between the gel time, cell size and open cell content

In order to get the micro cellular and high open cell content foam , the gel time should be controlled by using appropriate catalyzers. We chose the multiple system of two or three catalyzers.

So, we developed the micro cellular (140～250 m) and high open cell content(around 95%)core material with adequate Compressive strength (0.5～0.6MPa).

The metallographes (SEM ) of the our foam (sample a)and Bayer cyclopentane-blown foam (sample b)were shown in figure 2 .The cell size of ours is more tenuous.

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a b

Figure 2. The metallographes ( SEM )of the our foam and Bayer cyclopentane blown foam (×30)

3.3 Encapsulation

After fired at 120℃for 30 min, the foam was treated immediately at 1.33～13.3 Pa 8 hours at room temperature and then encapsulated with suitable getters.

Figure3 depicts the change of thermal conductivity of PU-VIP as a function of time. It can be seen that the pretreatment of foam before encapsulation was very important.

0.0150.014 (w/mk) treated untreated0.0130.0120.0110.0100.009020406080100120time(days)Figure 3. The change of thermal conductivity of PU-VIP as a function of time

3.4 Performance of core material

The performance of the core material was shown in table 6.

Table 6. The performance of the core material

property

Open cell content/% Cell size /m

－

Density/kg·m3

－

Thermal conductivity/W·(m·K)1 Compressive strength /MPa

value 95 150～200 55～65 0.010  0.5

*:The internal vacuum level of PU-VIP was13.3～66.5 Pa。

4 CONCLUSION

The excellent insulating material--PU-VIP was studied by choosing appropriate polyether polyols, activator systems, surfactants and encapsulating method.

REFERENCES

1 胡忠伟. 国内外聚氨酯工业发展近况. 聚氨酯工业，1999，14（1）：6

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2 J.A.King,D.D.Latham,J.C.Ackley. Relationship of k-Factor versus Density for Various Appliance Foam

Formulations Containing Next Generation. Journal of Cellular Plastics, 1996, 32 :356

3 Devos R., Rosbotham D, Deschaght J. Open-Celled Polyurethane Foam Based Vacuum Panel

Technology :A fully Polyurethane Based Composite Technolngy for Vacuum Insulated Appliances. Journal of Cellular Plastics, 1996, 32 :471

4 K.Kodama,K.Yuge,Y.Masuda,T.Tanimoto. Development of Micro Cellular Open Cell Rigid PU Foams.

Journal of Cellular Plastics, 1995, 31 : 27

BIOGRAPHY:

Wang Juan , engineer, was born in 1971，is about study of polyurethane rigid foam now .

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