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Development and evaluation of non-fog silicone sealant for automotive luminaire assembly

  • Categories:企业新闻
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  • Time of issue:2019-08-15 10:04
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(Summary description)The function and quality of automotive lamps are related to the performance and safety of the vehicle. The stable operation and function of the lamps depend not only on the design of the lamps, but also on the assembly process and supporting materials of the lamps. With the development of the automobile industry,

Development and evaluation of non-fog silicone sealant for automotive luminaire assembly

(Summary description)The function and quality of automotive lamps are related to the performance and safety of the vehicle. The stable operation and function of the lamps depend not only on the design of the lamps, but also on the assembly process and supporting materials of the lamps. With the development of the automobile industry,

  • Categories:企业新闻
  • Author:
  • Origin:
  • Time of issue:2019-08-15 10:04
  • Views:
Information

1 Introduction

 

The function and quality of automotive lamps are related to the performance and safety of the vehicle. The stable operation and function of the lamps depend not only on the design of the lamps, but also on the assembly process and supporting materials of the lamps. With the development of the automobile industry, the technology of automobile lamps is also constantly updated. At present, the design of automobile lamps, more components are installed in the lamp room, the reflection chamber is enlarged, the heat release is higher, the lamp design and function are improved, and the materials for the lamp are proposed. Higher technical requirements.

 

There are four general-purpose headlight sealants: butyl hot melt adhesive, polyurethane hot melt adhesive (PUR), one-component room temperature vulcanized silicone rubber (RTV-1), and two-component room temperature vulcanized silicone rubber (RTV-2). Among them, butyl hot melt adhesives have been basically eliminated due to poor heat resistance and weak adhesion; polyurethane hot melt adhesives have good bonding strength and have been recognized and applied by the industry, but they are currently paying attention to labor protection and environmental protection. Under the condition, due to its material toxicity, it is increasingly questioned. Silicone rubber sealant has gradually replaced silicone rubber sealant because of its excellent weather resistance, high and low temperature resistance, moisture resistance and excellent electrical insulation properties. Other rubber types have become the material of choice for headlight sealants.

 

Since 2013, Zhejiang Kesida New Materials Co., Ltd. has cooperated closely with Zhejiang Tianhao Auto Lamp Group Co., Ltd. to research and develop high-performance silicone sealant according to the requirements of automobile lamp assembly process and lamp use, and to establish sealant acceleration. The aging performance and sensitive fogging performance evaluation device can perform a number of in-depth test evaluations on the lamp sealant. Through the test and evaluation of the commercially available sealant, the causes of the commercially available sealed silicone rubber defects are analyzed item by item, especially Clearly analyze the mechanism of fogging of some commercial brand car light glues. On this basis, determine the optimal process and formula for the production of lamp sealant, and strictly monitor to ensure the stable and reliable performance of the sealed silicone rubber products. , to provide a solid technical guarantee for improving the quality of automotive lighting.

 

 

2 Development and evaluation of high performance sealing silicone rubber for lamp assembly

 

2.1 Lamp sealing silicone rubber use requirements and corresponding technical measures

 

In order to meet the assembly process and use requirements of automotive lamps, silicone rubber for lamp sealing requires proper and rapid curing. The cured sealant maintains stable bonding strength to the polypropylene substrate (PP) and polycarbonate (PC) of the lamp substrate. Long-term tolerance to environmental temperature change and high temperature of lamp work, anti-aging, for the installation of anti-fog coating film, it is also required that the sealant and anti-fog coating are compatible with fog.

 

For the assembly of headlights with large headlights, the production line occupies a large space. In order to improve production efficiency, a two-component condensation type room temperature vulcanized silicone rubber with relatively fast curing speed should be used as the sealant. The material, the fast cross-linking vulcanizing agent, the silicone high-efficiency thickening aid, and the kneading and kneading to obtain the lamp sealing silicone rubber which fully satisfies the above requirements.

 

For the assembly of small lights, one-component room temperature vulcanized silicone rubber with larger packaging specifications should be used as the sealant. In addition to the conventional mature technology of single-component room temperature vulcanized silicone rubber, the system also requires a faster curing speed and a higher initial bond strength.

 

2.2 The fogging mechanism and preventive measures of the headlight sealant

 

Anti-fog of automobile lamps is an important technical requirement. To improve the anti-fog performance of the lamps, it is one of the practical measures to apply anti-fog coating inside the lamps. If the lamp bonding and sealing material is not compatible with the anti-fog coating, fogging may occur. Commercially available brands do have some serious drawbacks to certain silicone rubbers, which are used to seal the headlights with anti-fog coatings, and some have fogging. The reason for the fog is that the brand product itself has technical defects.

 

The direct cause of fogging on the surface of the transparent material is related to the state of coagulation and aggregation of the surface material of the substrate, and the substance adsorbs and aggregates on the surface of the substrate, such as discontinuous uneven distribution of the formed droplets, due to different light transmittance or refractive index of different materials. Differences that cause fog or haze. The state of adsorption and spread of the substance on the surface of the substrate is related to the polarity or surface tension of the two materials. The liquid adsorption spread state on the solid surface can be characterized by the contact angle size, and the liquid contact angle is small, indicating that the liquid is similar in polarity to the solid substrate, and the liquid can be uniformly spread into a uniform liquid film on the surface of the solid substrate; The contact angle is large, the liquid and the solid substrate have different polarities, and the liquid is distributed in the form of droplets on the surface of the solid substrate. When the droplets are finely dispersed into a non-uniform film, the fogging state is displayed; if it is concentrated in the anti-fog The substance on the coating reacts with the anti-fog coating to form a new solid film, which will form an irreversible film.

 

(1) Contact angle test

 

In order to analyze the various factors related to the fogging phenomenon of the base material and the sealant component of the lamp assembly, the contact angle of the volatile component of the current common lamp sealant on the material of the lamp component was tested. The measured images of the contact angles are listed in the following atlas, and the relevant contact angle test data is listed in Table 1.

 

The components that may be volatilized in the lamp sealant are denoted by codes A and B respectively, and the luminaire material polycarbonate (PC) and the anti-fog coating film polycarbonate (C-PC) are applied.

 

The contact angles of the fine water droplets and the fine droplets of the volatile condensation component on the uncoated anti-fog coating film (PC) and the coated anti-fog coating film (C-PC) are as follows:

 

  

H2O/PC  θ=76.25°  H2O/C-PC  θ=13.34      B/PC  θ=16.58°      B/C-PC  θ=38.47°

 

 

 

In the above figure (left), the contact angle of water on the surface of the PC substrate is 76.25°, and the contact angle of water on the surface of the coated anti-fog coating C-PC substrate is reduced to 13.34°, and the strengthening of the anti-fog coating film can be seen. The water effect, that is, water (fog) can be adsorbed by the anti-fog coating film, and based on this, the lamp coated with the anti-fog coating film is less prone to water mist.

 

The above figure (right) is the contact angle image of the volatile B of the sealant. If the amount of accumulation is large enough to form a liquid film, the surface B of the ordinary PC can be uniformly dispersed without affecting the transparency of the PC, but B is coated. It is difficult to uniformly disperse on the surface of the C-PC over the anti-fog coating, and the result will be slightly misty.

 

Table 1 Contact angle of silicone rubber-related organic materials on polycarbonate substrates

 

Base material

PC

C-PC

Contact angle

water

76.25

13.34

VolatileA

8.86

37.87

VolatileB

16.58

38.47

 

(2) Some volatiles are condensed on the surface of the lampshade

In addition to the fogging phenomenon caused by the large contact angle of the volatile matter, there is also a reaction coagulation property of the volatile matter itself, which is hydrolyzed and precipitated on the surface of the lampshade after volatilization, and fogging may also occur. We conducted a lampshade condensation fogging test on possible volatile substances in the lamp-sealed silicone rubber. The experimental results are as follows:

 

 

Proactive use of high concentrations of volatiles experimental verification can cause fogging. It can be seen that some volatiles form an opaque film on the surface of the lampshade when the concentration is large enough, causing another type of fogging.

 

(3) Analysis of internal fogging mechanism of vehicle lights

 

In the normal state, the formation of fogging requires two factors at the same time: there are "fog source" substances that can be coagulated and aggregated, and environmental conditions that cause coagulation to coagulate. There are two types of condensable substances that may be fogged inside: one is the moisture that is common in the natural environment, mainly from the moisture in the air, and the other is the escape of materials such as lamp sealant. Condensable volatiles, residual volatiles in the sealant and volatile by-products released during the curing of the sealant.

 

Usually there is always more or less moisture in the natural ambient air. The ventilating hole of the lamp is connected to the atmosphere. The operation of the lamp makes the internal temperature of the lamp rise. When the lamp is turned off, the lamp cools down. The air cooling contraction in the cavity of the lamp will cause the outside air to carry moisture into the interior of the lamp. If the dew point is reached, The car lights will show fog. Due to the fogging caused by moisture entering the interior of the lamp, the environment may become repetitive due to environmental dampness; after the lamp is operated for a period of time, the water mist is vaporized and eliminated due to the increase in temperature. Improve the design of the lamp, the light inlet and outlet of the lamp facilitates the elimination of moisture in the lamp cavity, the airflow without dead space in the lamp cavity, and the application of a hydrophilic anti-fog coating can alleviate or avoid the fog caused by moisture.

 

The fog caused by the volatiles released by the sealant is caused by the condensation of volatiles on the lamp member into discrete droplets that are not wetted by the substrate. For example, if a sealant containing more volatile components is used, it may be in the lamp. Short fogging occurs shortly after assembly. After the first time the lamp is warmed up, the power is turned off. When the lamp is cooled down, the fogging phenomenon will be aggravated. For the fog caused by volatile matter, the inner part of the lamp is coated with hydrophilic anti-fog. The fogging after the film coating is often more serious than the fogging of the lamp without the anti-fog coating film. This is because the volatiles of the sealant are not wetted on the hydrophilic anti-fog coating film, so it is easier to agglomerate and show fogging. . In addition, due to the accumulation of the sealant volatiles on the hydrophilic anti-fog coating film, it may be followed by hydrolysis and precipitation reaction to form a solid mist film, and the fog film cannot be eliminated during the subsequent operation of the lamp.

 

(4) Evaluation of silicone lamp glues from different manufacturers

 

At present, a variety of brand lamp sealants are sold on the market, and the quality of the products is uneven. Tianzhu Lantern Co., Ltd. is the preferred applicable lamp sealant. It has been evaluated and analyzed by sealants sold by different manufacturers since 2016. It mainly detects the volatile content of the sealant and analyzes and evaluates the fogging condition and working stability of the corresponding sealant packaged lamp.

 

The performance evaluation of the sealant includes three items: 1 according to the glue supply and curing conditions provided by the rubber supplier, the weight reduction of the curing reaction process (24 hours) at room temperature; 2 the weight of the sealant heated at 120 ° C for 2 hours after curing Reduced amount; weight loss and appearance change at 3200 ° C for 2 hours. The test results of selling sealant samples to different manufacturers are listed in Table 2.

 

Table 2 Comparison of volatile content determination, heat aging and fogging of silicone rubber

 

 

Sealant sample

RTV-2

RTV-1

G company

Z company

9521

9622

T company

X company

D company

9611

Room temperature loss at room temperature for 24h

1.98

.96

1.06

0.85

4.99<

5.19

1.06

2.26

120℃×2h weightlessness

2.69

1.32

1.53

1.29

5.94

5.60

1.63

2.73

200℃×2h weightlessness

3.39

1.80

1.95

1.80

6.60

5.76

2.01

1.99

200℃×2h Variety

Brittle fracture

 

No change

No change

Become brittle

Turn soft

Turn soft

Slightly soft

Lamp fogging

Severe fog

 

Normal without fog

Normal without fog

Fog

Fog

 

Normal without fog

 

*G, Z, T are domestic company products; X and D are foreign company products; 9521, 9622, and 9611 are Costar's sealant.

 

 

 

The test results of the volatile content of the sealant further verify the positive correlation between the fogging of the lamp and the volatiles of the sealant. It is confirmed that the application of sealant with high volatile matter content will cause fogging of the lamp, especially the lamp with anti-fog coating. The sealing of the sealant with high volatile content is more obvious. .

 

Silicone rubber with inherent quality defects is subjected to brittle fracture after 200 ° C × 2 h accelerated heat aging test, thus losing the adhesive sealing performance, thereby causing serious damage such as water leakage or moisture leakage and fogging of the lamp.

 

The fogging of the lamp sealed with silicone rubber is not a common problem of silicone rubber materials. This is just a mistake of some brands of silicone rubber. The silicone rubber assembly lamp produced by the scientific and rigorous technology not only does not fog, but also the silicone rubber sealed lamp operation is more stable and reliable.

 

(5) Evaluation of polyurethane sealant

 

Individual automakers are concerned that silicone rubber assembly lights will fog, and Zhejiang Tianyi Company was required to switch to reactive polyurethane (PUR) for lamp sealing. Operators who have long used silicone rubber assembly lights have experienced discomfort such as nausea and headache after switching to polyurethane glue. To verify the safety information provided by the polyurethane manufacturer, it is also confirmed that the polyurethane sealant product contains harmful substances such as diphenylmethane diisocyanate. To confirm whether the polyurethane adhesive is indeed more stable and less foggy than silicone rubber. We use a special device for intensive detection of sealant fogging to conduct parallel evaluation tests on polyurethane rubber and silicone rubber.

 

Application evaluation to evaluate the same test device for sealing silicone rubber. The polyurethane hot melt adhesive sample of H Company and the KSD9622 car light glue sample of Costar Company were tested together for enhanced condition fogging. The test results of polyurethane hot melt adhesive are shown in Table 3 below:

 

Table 3 Polyurethane hot melt adhesive heating weight loss and fogging test

 

 

Test Conditions

Thermal weight loss%

Fog condition

90℃×2h

0.59

--

120℃×2h

0.87

Fog

140℃×2h

1.44

 

150℃×2h

 

Fog

 

Under the same conditions (120 °C × 2h, 150 °C × 2h), the same vehicle lamp PC translucent cover was used to compare the fogging status of H company polyurethane glue and Costar KSD-9622 silicone rubber. The test results are as follows: Shown as follows:

 

 

Test results: The PC corresponding to the polyurethane hot melt adhesive sample showed a clear translucent white mist film; the PC corresponding to the Costar Silicone sealant sample site showed no significant change.

 

4. High performance lamp sealing silicone rubber application

 

Zhejiang Kesida Company has developed a rigorous research and development program based on scientific theory, based on the working conditions and application requirements of automotive lamp sealants, and uses a number of effective new technologies to produce silicone sealants that meet the requirements of vehicle lamp assembly. Costar's headlight sealing silicone rubber compound has low volatile content, and the two-component silicone rubber material has a fast curing speed after mixing. The cured silicone rubber has high bonding strength, good resistance to high and low temperature impact and weathering resistance; The one-component sealing silicone rubber has a fast curing speed and a firm and reliable bonding. The product is used for the bonding and sealing of various types of lamps. It has been tested for more than five years in long-term operation, which proves that the quality of Cosida silicone rubber products is stable, especially suitable for the application of anti-fog coatings. The excellent reliability of assembling the lights without fog.

 

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