HK1185368B - Heat-curable polyorganosiloxane composition and use thereof - Google Patents

Description

Heat-curable polyorganosiloxane composition and use thereof

Technical Field

The present invention relates to a heat-curable polyorganosiloxane composition, and more particularly to a heat-curable polyorganosiloxane composition used for bonding a base portion having an image display portion and a light-transmissive protective portion of an image display device.

Background

In general, an image display device such as a braun tube, a liquid crystal, a plasma, or an organic EL device is configured by using, as a polarization separation element, a polarization separation type diffractive optical element (hologram color filter) which diffracts and splits an incident light beam and selectively collects the diffracted and split light beams of respective wavelength bands toward positions corresponding to respective color pixels of R (red), G (green), and B (blue) formed on a polarization modulation element. Among these, a panel-type image display device generally includes a display region (image display portion) in which a plurality of pixels including a semiconductor layer or a phosphor layer or a light-emitting layer constituting an active element are arranged in a matrix between a pair of substrates at least one of which has light permeability, such as glass, and a gap between the display region (image display portion) and a protective portion formed of an optical plastic such as glass or acrylic is tightly sealed with an adhesive.

As the adhesive used here, a thermosetting resin composition is generally used instead of an ultraviolet curable resin composition for structural reasons such as applying a light-shielding coating material to the outer frame portion of the protective portion of the image display device, and among these, an acrylic adhesive is widely used. However, since the acrylic adhesive has low wettability with a member, productivity is poor, and shrinkage rate during curing is high, which may affect the member by strain or the like. In addition, there is a problem that yellowing, cracking and the like occur at high temperature after curing. Therefore, development of alternative materials is desired.

Patent document 1 discloses a transparent impact-absorbing member for an optical display body, which is a plate-like body obtained by curing a silicone composition.

Patent document 2 discloses the following technique: in electronic components such as transistors, diodes, capacitors, coils, LSIs, and ICs, which are sealed with a sealing resin such as an epoxy resin or a polyphenylene sulfide resin, a liquid specific thermosetting silicone resin composition is impregnated into gaps that are often formed at the interface between the sealing resin and leads of the electronic component, and into gaps that the electronic component itself has in its structure, and the sealing state is restored by thermosetting the composition.

Documents of the prior art

Patent document

Patent document 1: japanese patent laid-open No. 2004117831

Patent document 2: japanese laid-open patent publication No. H9169908

Disclosure of Invention

Problems to be solved by the invention

The transparent impact-absorbing member disclosed in patent document 1 is a plate-like body obtained by curing a silicone composition. When the base portion having the image display portion of the image display device is bonded to the translucent protective portion using the transparent impact-absorbing member of the plate-like body, bubbles are likely to enter during bonding, and also peeling occurs at a high temperature or bubbles are likely to enter after bonding, so visibility is likely to be lowered.

The heat-curable silicone resin composition disclosed in patent document 2 has the following problems: a chain polyorganohydrogensiloxane in which 3 or more hydrogen atoms bonded to silicon atoms are present in a molecular side chain in one molecule is used, but since reactivity is low, curing at low temperature is delayed or curing is not performed for a predetermined time.

As described above, a heat-curable polyorganosiloxane composition has a small cure shrinkage rate, is excellent in impact resistance after curing, and has good reliability at high temperatures, and particularly, when used for bonding a base portion having an image display portion and a light-transmitting protective portion of an image display device, a composition having good wettability with the base portion and the protective portion has not been sufficiently produced in the prior art, and in recent years in which the image display device has high brightness, high definition, and diversified sizes, the demand for such a composition has been further increased.

The present invention aims to provide a heat-curable polyorganosiloxane composition which has good wettability with a base and a protective portion, a small cure shrinkage, excellent impact resistance after curing, and good reliability at high temperatures, and particularly, when used for bonding a base having an image display portion and a light-transmitting protective portion of an image display device, has good wettability with the base and the protective portion.

Means for solving the problems

The invention relates to a heat-curable polyorganosiloxane composition, which contains:

(A) a linear polyorganosiloxane represented by the formula (I),

(in the formula (I), R^aIndependently is C₂-C₆An alkenyl group, which is a radical of an alkenyl group,

R^bindependently is C₁-C₆An alkyl group or a phenyl group, or a substituted or unsubstituted alkyl group,

n1 is a value at which the viscosity of (A) at 23 ℃ is 2000cP or less);

(B1) a linear polyorganosiloxane represented by the formula (II),

(in the formula, R^cIs a hydrogen atom, and is a hydrogen atom,

R^dindependently is C₁-C₆An alkyl group or a phenyl group, or a substituted or unsubstituted alkyl group,

n2 is a value such that the viscosity of (B1) at 23 ℃ is 0.1 to 300 cP;

(B2) is a cyclic polyorganohydrogensiloxane containing R^e ₂HSiO_1/2Unit (in the formula, R^eRepresents a hydrogen atom or C₁-C₆Alkyl) and SiO_4/2A unit having 3 or more hydrogen atoms bonded to a silicon atom in one molecule;

(C) a platinum-based catalyst; and

(D) a tackifier;

(B1) number of hydrogen atoms bonded to silicon atom of (2) H_B1Number H of hydrogen atoms bonded to silicon atom in (B2)_B2Number of sums (H)_B1+H_B2) Number Vi of alkenyl groups relative to (A)_AThe ratio of the first to the second is 0.2 to 1.0,

H_B1relative to H_B1+H_B2And 0.5 to 0.8.

Effects of the invention

According to the present invention, there is provided a heat-curable polyorganosiloxane composition which has a small cure shrinkage, has excellent impact resistance after curing, and has good reliability at high temperatures, and which has good wettability with a base portion and a protective portion when used for bonding the base portion having an image display portion and the light-transmissive protective portion of an image display device.

Detailed Description

The component (A) in the present invention is a linear polyorganosiloxane containing an alkenyl group represented by the formula (I),

(in the formula, R^aIndependently is C₂-C₆Alkenyl groups (e.g.vinyl, allyl, 3-butenyl or 5-hexenyl),

R^bindependently is C₁-C₆Alkyl (e.g., methyl, ethyl, propyl, butyl, pentyl, hexyl) or phenyl,

n1 is a value such that the viscosity of (A) at 23 ℃ is 2000cP or less).

By blending (a), a stable three-dimensional structure due to a crosslinking reaction at the time of curing can be ensured, curing shrinkage is suppressed, and good visibility can be ensured.

As R^aThe vinyl group is more preferable from the viewpoint of easy synthesis and no deterioration in the fluidity of the composition before curing and the heat resistance of the cured product.

As R^bFrom the viewpoint of ease of synthesis, and an excellent balance between the fluidity of the composition and the mechanical strength after curing, the methyl group is preferred.

The (a) is preferably polymethylvinylsiloxane having both ends capped with dimethylvinylsiloxane units and having dimethylsiloxane units as an intermediate unit.

The viscosity of (A) is set to be not more than 2000cP at 23 ℃, preferably 100 to 2000cP, from the viewpoint of ensuring stable liquid properties of the composition. In order to achieve the above viscosity range, the weight average molecular weight of (a) is preferably adjusted. The viscosity in the present invention is a value measured at 23 ℃ at 60rpm using a rotational viscometer.

The component (B1) in the present invention is a linear polyorganohydrogensiloxane represented by the formula (II),

(in the formula, R^cIs a hydrogen atom, and is a hydrogen atom,

R^dindependently is C₁-C₆Alkyl (e.g., methyl, ethyl, propyl, butyl, pentyl, hexyl) or phenyl,

n2 is a value such that the viscosity of (B1) at 23 ℃ is 0.1 to 300cP or less.

As R^dFrom the viewpoint of ease of synthesis, and an excellent balance of properties such as mechanical strength and fluidity before curing, a methyl group is preferable.

The (B1) is preferably a polymethylhydrosiloxane having both terminal ends capped with dimethylhydrosiloxane units and having dimethylsiloxane units as an intermediate unit.

(B1) The viscosity of (b) is 0.1 to 300cP, preferably 1 to 200cP, at 23 ℃.

(B2) according to the invention is a cyclic polyorganohydrogensiloxane comprising R^e ₂HSiO_1/2Unit (in the formula, R^eRepresents a hydrogen atom or C₁-C₆Alkyl (e.g., methyl, ethyl, propyl, butyl, pentyl, hexyl)) and SiO_4/2The unit having 3 or more hydrogen atoms bonded to silicon atoms in one molecule is a component contributing to the adjustment of hardness by forming a cured product into a network. R as a hydrogen atom^ePreferably 3 to 100, more preferably 3 to 50 molecules. As C₁-C₆R of alkyl^eFrom the viewpoint of ease of synthesis and the like, a methyl group is preferable.

As (B2), R^e ₂HSiO_1/2Units and SiO_4/2The ratio of units, preferably to SiO_4/2 units 1 mol, R^e ₂HSiO_1/2The unit is 1.5 to 2.2 mol, and more preferably 1.8 to 2.1 mol. Typically, e.g. [ R ]^e ₂HSiO_1/2]₈[SiO_4/2]₄Or [ R ]^e ₂HSiO_1/2]₁₀[SiO_4/2]₅Thus, it is preferable that 3 to 5 SiO atoms are contained_4/2The units form a cyclic siloxane skeleton and each SiO_4/2Unit bonded with 2R^e ₂HSiO_1/2Cyclic polyorganohydrogensiloxanes of units, particularly preferably SiO each_4/2Unit is bonded with 2 (CH)₃)₂HSiO_1/2Cyclic polyorganohydrogensiloxanes of units.

(B2) The viscosity of (b) is preferably 1 to 100cP, and more preferably 1 to 50 cP.

The number H of hydrogen atoms bonded to silicon atoms of (B1) is set to give a cured product an appropriate hardness_B1Number H of hydrogen atoms bonded to silicon atom of (B2)_B2The total amount of (A) with respect to the number Vi of silicon atom-bonded alkenyl groups_ARatio of (H)_B1+H_B2)/Vi_AIs 0.2 to 1.0, preferably 0.5 to 1.0.

In addition, from the viewpoint of ensuring impact resistance of the cured product and reliability at high temperature, H_B1Relative to H_B1+H_B2The amount of the surfactant is 0.5 to 0.8, preferably 0.6 to 0.8.

The catalyst (C) of the present invention is a catalyst for promoting an addition reaction between the alkenyl group of (A) and the hydrosilyl groups of (B1) and (B2). From the viewpoint of good catalytic activity, it is preferable to use a compound of a platinum group metal atom such as platinum, rhodium, palladium, preferably platinic chloride, a reaction product of platinic chloride and an alcohol, a platinum compound such as a platinum-olefin complex, a platinum-vinylsiloxane complex, a platinum-ketone complex, a platinum-phosphine complex, a rhodium compound such as a rhodium-phosphine complex, a rhodium-sulfide complex, a palladium compound such as a palladium-phosphine complex, more preferably a platinum compound, and still more preferably a platinum-vinylsiloxane complex.

From the viewpoint of ensuring an appropriate curing rate, the content of (C) is preferably 0.1 to 1000 ppm by weight, more preferably 0.5 to 200 ppm by weight, in terms of platinum group metal atoms, based on the weight of (A).

Examples of the thickener (D) in the present invention include alkoxysilanes. For example, the reaction product of 1, 1, 3, 5, 7-pentamethylcyclotetrasiloxane and 3-methacryloxypropyltrimethoxysilane can be used.

Specifically, preferred are alkoxysilanes having a side chain represented by the following formula,

(in the formula, Q¹And Q²Independently of one another, an alkylene group, preferably C₁-C₄Alkylene radical, R³Is represented by C₁-C₄Alkyl groups).

Examples of the alkoxysilane include the following compounds.

From the viewpoint of ensuring appropriate adhesiveness, (D) is preferably 0.1 to 2 parts by weight, more preferably 0.5 to 1 part by weight, based on 100 parts by weight of (a).

The composition of the present invention may contain a curing retarder, an inorganic filler, and the like, within a range not impairing the effects of the present invention. As the curing retarder, there may be mentioned: acetylene compounds such as 3-methyl-1-butyn-3-ol, 3-methyl-1-pentyn-3-ol, 3, 5-dimethyl-1-hexyn-3-ol and 1-ethynyl-1-cyclohexanol, and vinyl group-containing cyclic siloxanes having a vinyl group bonded to a ring silicon atom such as 1, 3, 5, 7-tetravinyl-1, 3, 5, 7-tetramethylcyclotetrasiloxane. Examples of the inorganic filler include: dry fine powder silica such as fumed silica and arc silica is preferably fumed silica. Further, the surface of the silica may be treated with a silazane compound such as hexamethyldisilazane, 1, 3-divinyl-1, 1, 3, 3-tetramethyldisilazane, a polyorganosiloxane such as octamethylcyclotetrasiloxane, or the like.

The composition of the present invention can be prepared by uniformly kneading the components (a), (B1), (B2), (C) and (D) and, if necessary, other components, with a mixing apparatus such as a universal kneader or kneader.

The viscosity of the composition of the present invention at 23 ℃ is preferably 2000cP or less, and may be set to 50 to 2000cP, from the viewpoint of ductility at the time of coating. More preferably 80 to 1500cP, and still more preferably 300 to 1000 cP.

The composition of the present invention can be used for bonding a base part having an image display part of an image display device and a light-transmitting protective part, but when the image display device is large (50 to 100 inches), the viscosity of the composition is preferably 50 to 300cP from the viewpoint of ductility at the time of application. From the viewpoint of obtaining a composition having such a viscosity, (A) having a viscosity of 50 to 300cP is preferably used. On the other hand, in the case of a small-sized image display device (less than 50 inches) such as a mobile phone, the viscosity of the composition is preferably 300 to 2000cP from the viewpoint of workability. From the viewpoint of obtaining a composition having such a viscosity, (A) having a viscosity of 300 to 2000cP is preferably used.

The composition of the present invention may have a transmittance after curing of 80 to 100%, preferably 90 to 100%. Since the composition has a good transmittance, the composition is good in visibility after thermosetting between the base portion having the image display portion and the light-transmitting protective portion of the image display device.

The composition of the present invention can be cured at a heating temperature of 50 to 80 ℃. The heating time may be set to 0.1 to 3 hours, for example.

According to the composition of the present invention, the E hardness after curing can be 1 to 40. When the E hardness is within this range, after the composition is thermally set between the base portion having the image display portion of the image display device and the translucent protective portion, the stress from the outside is appropriately relaxed, and the deformation resistance is ensured, whereby the visibility can be ensured. The E hardness can be adjusted by the ratio of (B1) to (B2). The E hardness in the present invention is a value measured in accordance with JIS K6253E. When the image display device is large, the E hardness is preferably 1 to 30. On the other hand, in a small-sized image display device such as a mobile phone, since it is assumed that the device is carried, the E hardness after curing is 10 to 40, preferably 15 to 40, from the viewpoint of durability.

The base portion of the image display device and the light-transmitting protective portion can be bonded to each other by applying the composition of the present invention to the base portion of the image display portion, bonding the protective portion to the base portion, and curing the composition by heating with a dryer or the like. The base portion of the image display portion may be provided with a step for preventing the composition from flowing out at the peripheral edge portion as necessary. The composition of the present invention has a small cure shrinkage rate, and therefore, the image display unit (panel) can be suitably used for manufacturing a large-screen image display device preferably having a size of 5 to 100 inches, but is not limited thereto.

Examples

The present invention will be described in more detail below with reference to examples and comparative examples. However, the present invention is not limited to these examples.

The compositions of examples and comparative examples were prepared by manually kneading the components with the compositions shown in table 1.

The components used are as follows.

A-1: polymethylvinylsiloxane having both ends capped with dimethylvinylsiloxane units and having dimethylsiloxane units as the intermediate unit (viscosity 870cP at 23 ℃ C.)

A-2: polymethylvinylsiloxane having both terminals capped with dimethylvinylsiloxane units and having dimethylsiloxane units as an intermediate unit (viscosity 350cP at 23 ℃ C.)

A-3: polymethylvinylsiloxane having both terminals capped with dimethylvinylsiloxane units and having dimethylsiloxane units as an intermediate unit (viscosity 100cP at 23 ℃ C.)

A-4: polymethylvinylsiloxane having both terminals capped with dimethylvinylsiloxane units and having dimethylsiloxane units as an intermediate unit (viscosity 2000cP at 23 ℃ C.)

A-5: polymethylvinylsiloxane having both terminals capped with dimethylvinylsiloxane units and having dimethylsiloxane units as an intermediate unit (viscosity 110cP at 23 ℃ C.)

B1: polymethylhydrosiloxane having both ends capped with dimethylhydrosiloxane units and having dimethylsiloxane units as the intermediate unit (viscosity 20cP at 23 ℃ C.)

B2: the average unit formula is [ H (CH)₃)₂SiO_1/2]₈[SiO_4/2]₄(effective hydrogen amount 1%)

B3: polymethylhydrosiloxane having both ends end-capped with trimethylsiloxane units and having dimethylsiloxane units and methylhydrogensiloxane units as intermediate units

C: a complex obtained by heating chloroplatinic acid and 1, 3, 5, 7-tetravinyl-1, 3, 5, 7-tetramethylcyclotetrasiloxane in a molar ratio of 1: 2 and having a platinum content of 2% by weight.

D: reaction product of 1, 1, 3, 5, 7-pentamethylcyclotetrasiloxane and 3-methacryloxypropyltrimethoxysilane

E: 3, 5-dimethyl-1-hexyn-3-ol

The physical properties were evaluated as follows. The results are shown in Table 1.

(1) Viscosity of the oil

The viscosity at 23 ℃ was measured using a rotational viscometer (Vismetron VDA-L) (manufactured by Zhipu System Co., Ltd.) at 60rpm with a spindle No. 3.

(2) E hardness after curing

The compositions of examples and comparative examples were coated on a mold coated with Teflon (registered trademark) to a thickness of 6mm, and then, cured by heating at 70 ℃ for 1 hour.

The E hardness of a cured product at 23 ℃ was measured by DUROMETER HARDNESS TYPE E (manufactured by ASKER) in accordance with JIS K6253E.

(3) Wettability with structural member

2g of the composition was dropped from a 10ml container onto the center of a 5cm square clean glass plate washed with a neutral detergent and dried, and the composition was evaluated for the time required for spreading to the edge of the glass. The evaluation was carried out at a temperature of 23 ℃ and a humidity of 50%.

(4) Discoloration at elevated temperatures

The compositions of examples and comparative examples were applied between 2 glass plates 1mm thick to a thickness of 200 μm, and samples cured by heating at 70 ℃ for 1 hour were allowed to stand on a constant temperature and humidity layer set at a high temperature of 85 ℃ for 500 hours and then returned to a state of 23 ℃ and the Yellow Index (Yellow Index) as an Index of the degree of discoloration was evaluated by a spectrophotometer (CM-3500 d, Minolta, Co., Ltd.).

(5) Change at high humidity

The compositions of examples and comparative examples were coated between a 3-inch glass panel having a thickness of 0.6mm and a 3-inch PMMA panel having a thickness of 0.5mm to a thickness of 0.2mm, and heat-cured at 70 ℃ for 1 hour. The sample was allowed to stand on a constant temperature and humidity layer set to a high temperature and humidity condition of 85 ℃ and 85% RH for 500 hours, and then returned to a state of 23 ℃ and 50% RH, and then the state of the sample was observed. The case where peeling and resin cracking occurred in the cured product was x, and the case where peeling and resin cracking were not observed at all was O.

(6) Thermal shock

The compositions of examples and comparative examples were coated between a 3-inch glass panel having a thickness of 0.6mm and a 3-inch PMMA panel having a thickness of 0.5mm to a thickness of 0.2mm, and heat-cured at 70 ℃ for 1 hour. The samples were subjected to an environmental test (equipment name: TSA-71S-A manufactured by ESPEC K.K.) by subjecting the samples to temperature cycles of-50 ℃ to 125 ℃ for 300 times (each temperature was maintained for 30 minutes).

After that, the temperature was returned to 23 ℃ and the state of the cured product was observed. X represents the case where a crack of 0.02mm or more and/or an air layer of 0.02mm or more in maximum diameter is generated in the cured product, and O represents the case where no crack, air layer, or damage is observed at all.

(7) Curing shrinkage

The specific gravity of the composition before curing was measured by a gravity cup, the specific gravity after curing was measured by an electronic densitometer (SD-120L manufactured by MIRAGE corporation), and the difference between the specific gravities was calculated from the following equation.

Cure shrinkage (%) ((specific gravity after curing-specific gravity before curing)/specific gravity after curing) × 100

(8) Point pressure test

The compositions of examples and comparative examples were coated between a 3.5-inch glass panel having a thickness of 0.6mm and a 3.5-inch PMMA panel having a thickness of 0.5mm to a thickness of 0.2mm, and cured by heating at 70 ℃ for 1 hour.

The sample was pressed to 10kgf at a predetermined load of 7.5 mm/min by a metal rod having a semicircular head end portion with a diameter of 10mm on the PMMA plate side of the sample as the upper side.

For 1 sample, approximately equal 5 sites were pressurized within 3.5 inches under the above conditions.

By this pressing, fine cracks are generated in the cured product at the pressed portion, and peeling occurs between the glass plate or the PMMA plate and the cured product. The appearance of the pressed portion is changed from the appearance of the non-pressed portion because the portion becomes white due to the presence of cracks or peeling. This change in appearance was visually confirmed, and for 1 sample, if no change in appearance was observed in 1 part or more, it was assumed to be O, and for 1 sample, if no change in appearance was observed in 1 part or more, it was assumed to be x.

(9) Transmittance of light

The compositions of examples and comparative examples were applied between 2 glass plates 1mm thick to a thickness of 200 μm, and the samples after heat curing at 70 ℃ for 1 hour were allowed to stand on a constant temperature and humidity layer set at a high temperature of 85 ℃ for 500 hours and then returned to a state of 23 ℃, and then the transmittance as an index of the degree of transparency was evaluated by a spectrophotometer (CM-3500 d, Minolta, Inc.).

TABLE 1

The compositions of the examples have good wettability with members, small cure shrinkage, excellent impact resistance after curing, and good reliability at high temperatures. From this, it was found that the composition of the present invention is suitable for the production of an image display device. The comparative example using the linear polyorganohydrogensiloxane did not cure under heating at 70 ℃ for 1 hour.

Industrial applicability

The heat-curable polyorganosiloxane composition of the present invention is useful for bonding a base portion having an image display portion and a light-transmitting protective portion of an image display device such as a braun tube, a liquid crystal, a plasma, or an organic EL device.

Claims (7)

1. A heat-curable polyorganosiloxane composition containing

A: an alkenyl group-containing linear polyorganosiloxane represented by the formula (I),

in the formula (I), R^aIndependently is C₂-C₆An alkenyl group, which is a radical of an alkenyl group,

R^bindependently is C₁-C₆Alkyl or benzeneThe base group is a group of a compound,

n1 is a value such that the viscosity of A at 23 ℃ is 2000cP or less;

b1: a linear polyorganohydrogensiloxane represented by formula (II),

in the formula (II), R^cIs a hydrogen atom, and is a hydrogen atom,

R^dindependently is C₁-C₆An alkyl group or a phenyl group, or a substituted or unsubstituted alkyl group,

n2 is a value at which the viscosity of B1 at 23 ℃ is 0.1 to 300 cP;

b2: cyclic polyorganohydrogensiloxanes comprising R^e ₂HSiO_1/2Unit and SiO_4/2Unit having 3 or more hydrogen atoms bonded to silicon atoms in one molecule, wherein R^eRepresents a hydrogen atom or C₁-C₆An alkyl group;

c: a platinum-based catalyst; and

d: a tackifier;

wherein the content of the first and second substances,

number H of hydrogen atoms bonded to silicon atom of B1_B1Number H of silicon atom-bonded hydrogen atoms to B2_B2The number of sums, i.e. H_B1+H_B2Number of alkenyl groups Vi relative to A_AThe ratio of the first to the second is 0.2 to 1.0,

H_B1relative to H_B1+H_B2And 0.51 to 0.8.

2. The heat-curable polyorganosiloxane composition according to claim 1, wherein B2 is a cyclic polyorganohydrogensiloxane in which R is the same as R^e ₂HSiO_1/2Unit and SiO_4/2Ratio of units to 1 mol of SiO₂In the case of units, R^e ₂HSiO_1/2The unit is 1.5-2.2 mol.

3. According to the rightThe heat-curable polyorganosiloxane composition according to claim 2, wherein B2 is a cyclic polyorganohydrogensiloxane containing 3 to 5 SiO atoms_4/2The units form a cyclic siloxane skeleton and each SiO_4/2Unit bonded with 2R^e ₂HSiO_1/2Cyclic polyorganohydrogensiloxanes of units.

4. The heat-curable polyorganosiloxane composition according to any of claims 1 to 3, wherein D is an alkoxysilane.

5. The heat-curable polyorganosiloxane composition according to any one of claims 1 to 3, which is used for bonding a base having an image display portion and a light-transmissive protective portion of an image display device.

6. The heat-curable polyorganosiloxane composition according to claim 4, which is used for bonding a base having an image display portion of an image display device to a light-transmitting protective portion.

7. An image display device, which is obtained by bonding a base part having an image display part and a light-transmitting protective part of the image display device using the heat-curable polyorganosiloxane composition according to any one of claims 1 to 4.