COMPOSITION SCREEN-PRINTABLE ON POLYVINYL BUTYRAL

[0001] The invention relates to the field of laminated glazing units, commonly constituted of two sheets of glass bonded to one another by means of a sheet of polyvinyl butyral for example.

[0002] Laminated glazing units have many uses: a layer that reflects solar radiation, making it possible to lower the temperature of the instrument panel and the ambient temperature in the passenger compartment, a support for the interior rearview mirror, electric current feed busbars especially for an ITO layer or a network of heating wires, an upper strip that filters solar radiation of optionally graduated coloration, a rain detector, etc. Laminated glazing units are thus printed for various purposes: edge of the glazing unit opacified over its entire periphery in order to protect the underlying adhesive and hide the body components or seals from the view of an observer outside of the vehicle, markings relating to the manufacture, or to various standards, opacified surface in order to hide the base of the interior rear-view mirror from the view of an observer outside of the vehicle.

[0003] The printing of laminated glazing units may aim to opacify a portion of the surface thereof, with black or any other color. It may moreover have the objective of tinting, while preserving a certain transparency, or even a high light transmission, compatible with the current standards for a windshield.

[0004] Finally, the result of printing laminated glazing units may not be visible in the absence of ultraviolet radiation, for example emitted from the inside of the vehicle: this is the case for printing of the interior face of the glazing unit with a varnish that contains phosphors (the interlay adhesive of the glazing unit does not allow the ultraviolet rays from solar radiation through).

[0005] It is customary to produce such printing on sheets of flat glass, that is to say, where appropriate, before bending operations (this is because it is much more difficult to print onto curved surfaces). One preferred process is screen printing: it is able to provide the required optical qualities: good coverage, opacity and resolution, and can be easily industrialized. The printing composition must however have short drying times, compatible with an in-line process. Drying times that are too long would not make it possible to carry out an in-line process, but would require intermediate storage and finally an unacceptable cost premium.

[0006] Furthermore, in the case of an industrial in-line process, it is sought to carry out the screen printing in a single pass.

[0007] Screen printing onto sheets of flat glass is not without drawbacks. In particular, the sheets of glass, during the bending thereof, in pairs, come into physical contact with one another or with the mechanical components of the bending equipment. This physical contact requires the prior use of an additional furnace for the annealing of the printing composition, in order to prevent the printed surfaces that are insufficiently hardened and dried from being adversely affected.

[0008] This problem could be solved by carrying out the screen printing on the interlayer adhesive sheets and no longer on the glass sheets. Until now, it was still not known how to carry out printing, via screen printing in a single pass and with relatively short drying times on substrates made of sheets of flexible plastic such as polyvinyl butyral, of opaque or transparent colored designs, or else of designs containing any particles (metallic particles, SnO₂:In particles, SnO₂:F particles, etc.) or phosphors, etc.

[0009] In any case, printing is sought that has clear outlines, with no blurring, and with a required definition as a function of the application.

[0010] In the case of opaque coloration, the following are furthermore sought:

• • [0011] good coverage, which is expressed by the complete absence of transparency in the form of pinholes; and
  • [0012] a required opacity corresponding to an optical density at least equal to 3, preferably to 4.

[0013] In the case of transparent coloration, an absence of agglomeration and of diffusion and a haze that doesn't exceed 1% are sought.

[0014] The objective of the invention is therefore the provision of a process of screen printing onto an interlayer polyvinyl butyral sheet of a laminated glazing unit, having the combination of the aforementioned advantages, in particular that can be carried out in a single pass with “touch-dry” times that do not exceed 10 minutes, preferably 5 minutes and in particular 2 minutes.

[0015] This objective is achieved by the invention, one subject of which is a composition suitable for printing, via screen printing, a sheet of polyvinyl butyral intended to be part of a laminated glazing unit, characterized in that it comprises at least one polyvinyl butyral resin having a molecular weight at most equal to 50 000 and at least one solvent.

[0016] This composition may comprise a mixture of several different polyvinyl butyral resins having molecular weights at most equal to 50 000.

[0017] Thus, the invention makes it possible to achieve the high quality required defined above with a single screen-printing pass and short touch-dry times.

[0018] Preferably, the polyvinyl butyral resin has a molecular weight at most equal to 40 000, preferably 30 000. This feature is even necessary in the case of black opaque printing or opaque printing of any color. (It is also advantageous for phosphor and transparent colored printing, for which a polyvinyl butyral resin having a molecular weight up to 50 000 may however also be used).

[0019] Advantageously, the polyvinyl butyral resin has a molecular weight at least equal to 10 000, preferably to 15 000.

[0020] It is moreover preferred that the [OH] content of the polyvinyl butyral resin corresponds to a maximum weight percentage of polyvinyl alcohol of 22%, preferably 20% and in particular 18% and a minimum weight percentage of 9%, preferably 11% and in particular 13%.

[0021] Preferably, the glass transition temperature T_g of the polyvinyl butyral resin is at most equal to 70° C.

[0022] According to other advantageous features of the composition of the invention:

• • [0023] it comprises 2 to 35% by weight of polyvinyl butyral resin;
  • [0024] it comprises 1 to 50% by weight of at least one pigment and/or one other particle and/or a dye and/or a phosphor; it may therefore be the mixture of several of the latter; in this regard, it must be pointed out that the invention allows the use of remarkably high proportions of pigments, hence remarkable opacities, indicated by optical densities which may reach values of at least 4, or even 5, are obtained without furthermore impeding the implementation of the screen printing.

[0025] The dimensions of the particles of pigments, others and phosphors are from 0 to 5 μm.

[0026] Furthermore, 40 to 65% by weight of the pigments are advantageously coated.

[0027] The pigments, defined in particular by their CAS (Chemical Abstracts Service, American Chemical Society) No. and their CI (Color Index) No., may be chosen from those from the table below.

	Pigments	CAS No.	CI No.
	Yellow 13	13515-40-7	Yellow 13
	Monoazo yellow	6486-23-3	Yellow 3
	Benzimidazolone yellow	31837-42-0	Yellow 151
	Monoazo yellow	12225-18-2	Yellow 97
	Quinacridone pink	980-26-7	Red 122
	Quinacridone violet	1047-16-1	Violet 19
	Dioxazine violet	6358-30-1	Violet 23
	Carbon black	1333-86-4	Black 7
	Black iron oxide	1317-61-9
	Phthalocyanine blue	147-14-8	Blue 15.3
	Phthalocyanine green	2786-76-7	Green 7
	Titanium dioxide	13463-67-7

[0028] As another particle, mention may be made of the particles of ITO (SnO₂:In), or of SnO₂:F in view of forming, for example, athermic coatings, that absorb infrared rays.

[0029] Dyes which may be used within the context of the invention, defined by their type and the CI No., are the following.

	Dyes	Type	CI No.
	Yellow	Cr complex	Yellow 88
	Yellow	Co complex	Yellow 25
	Orange	Co complex	Orange 11
	Brown	Cr complex	Brown 43
	Red	Cr complex	Red 130
	Red	Cr complex	Red 122
	Blue	Cu-phthalocyanine	Blue 136
	Blue	Cu-phthalocyanine	Blue 70
	Black	Cr complex	Black 29

[0030] As examples of phorphors, use may be made of the following, defined by their formula.

	Phosphors	Formula
	Green	Zn2SiO4:Mn
	Blue	BaMgAl10O17:Eu
	Yellow	Y202S:Eu, Sm + BaMgAl10O17
	Yellow	Beta-Quinophthalone
	Red	Y2O3:Eu
	Red	Y2O2S:Eu

[0031] Moreover, it is appreciated that the solvent solubilizes the polyvinyl butyral resin and does not deform the sheet of polyvinyl butyral at the surface.

[0032] The solvent is opportunely chosen from the following.

	Solvents	CAS No.
	Diacetone alcohol	123-42-2
	Benzyl alcohol	100-51-6
	1-Methoxy-2-propanol	107-98-2
	Butyl glycol	111-76-2
	Dipropylene glycol monomethyl	34590-94-8
	ether (DPM)
	Methoxy propanol acetate	108-65-6
	Acetic acid, 3-methoxy-n-butyl	4435-53-4
	ester (butoxyl)
	Glycolic acid, n-butyl ester	7397-62-8
	(Polysolvant O)
	Dibasic esters (DBE)	1119-40-0/106-65-0/
		627-93-0
	Cyclohexanone	108-94-1

[0033] According to other preferred features of the composition:

• • [0034] it comprises 30 to 75% by weight of solvent;
  • [0035] 0.2 to 3% by weight of a thixotropic agent consisting of a silica or several silicas as a mixture.

[0036] Another subject of the invention is a process for printing, via screen printing, a sheet of polyvinyl butyral intended to be part of a laminated glazing unit, characterized in that a composition as described above is applied to the sheet, through a screen-printing screen and in that the thickness of the wet layer of composition applied compensates for the roughness of the sheet, being in particular at least equal to 14 μm. During the drying of the composition, certain surface irregularities of the sheet of polyvinyl butyral may reappear, even more when a portion of the composition may then be absorbed by the sheet. These irregularities are favorable to the degassing during the assembly of the laminate.

[0037] This process provides the desired high quality in a single pass. According to one particularly advantageous feature, it does not require any heating means, but may be carried out at low temperature.

[0038] Another subject of the invention is a sheet of polyvinyl butyral intended to be part of a laminated glazing unit and printed, via screen printing, using a composition described above. In one particular embodiment, at least one portion of the surface of the sheet (the printed portion) has an optical density at least equal to 4, preferably to 5.

[0039] Other subjects of the invention consist of

• • [0040] a laminated glazing unit comprising such a sheet of polyvinyl butyral; and
  • [0041] the application of such a laminated glazing unit, for instance motor vehicle glazing, at least one portion of the periphery of which is opacified, in particular darkened.

[0042] The application of this glazing unit in the construction industry is however also part of the invention.

[0043] The invention is illustrated by the following examples, in which all the amounts under columns entitled “Formula” are percentages by weight.

[0044] Screen printing is carried out in a single pass on an interlayer polyvinyl butyral sheet of a laminated glazing unit. The temperature is stabilized at 14-16° C. in order to guarantee a better surface flatness of the support and prevent it from being tacky.

[0045] The opaque black printing composition below is used.

Opaque black	Formula/100	Formula min/max
PVB resin CAS No. 63148-65-2,	12	11/13
68648-78-2 MW 15 000 to
30 000/OH 14/18
Carbon black	10	8/12
Black iron oxide	30	28/32
Wetting agent and dispersant	3	2/4
of modified polyester type in
solution in white spirit
Hydrophilic fumed silica CAS	1	0.5/1.5
7631-86-9 Specific surface
area (BET): 350/410
Cyclohexanone	38	37/39
Dipropylene glycol monomethyl	5	4/7
ether (DPM)
Tension additive: polydimethyl	1	0.5/1.5
siloxane

[0046] The desired high quality of coverage—lack of pin holes, opacity, sharpness of the contours, definition, lack of blurring, is achieved.

[0047] The touch-dry time is around two minutes.

[0048] The preceding example is reproduced with the following composition.

Opaque black	Formula/100	Formula min/max
PVB resin CAS No. 63148-65-2,	7.5	7/8
68648-78-2 MW 50 000 to
60 000/OH 18/20
Carbon black	7	6/8
Black iron oxide	28	27/29
Wetting agent and dispersant	3	2/4
of modified polyester type in
solution in white spirit
Hydrophilic fumed silica CAS	1	0.5/1.5
7631-86-9 Specific surface
area (BET): 350/410
Cyclohexanone	47.5	46/50
Dipropylene glycol monomethyl	5	4/7
ether (DPM)
Tension additive: polydimethyl	1	0.5/1.5
siloxane

[0049] With this composition, characterized by a relatively high molecular weight, a low opacity (presence of pin holes) is obtained, the passage in the screen-printing screen is more difficult.

[0050] Opaque color printing is carried out by reproducing example 1 with the composition below.

Opaque colors	Formula/100	Formula min/max
PVB resin CAS No. 63148-65-2,	20	19/21
68648-78-2 MW 15 000 to
30 000/OH 14/18
Yellow 151 pigment	15	14/16
Wetting agent and dispersant	3	2/4
of modified polyester type in
solution in white spirit
Hydrophilic fumed silica CAS	1	0.5/1.5
7631-86-9 Specific surface
area (BET): 350/410
Cyclohexanone	55	54/56
Dipropylene glycol monomethyl	5	4/7
ether (DPM)
Tension additive: polydimethyl	1	0.5/1.5
siloxane

[0051] The same high quality is obtained as in example 1.

[0052] EXAMPLE 3

[0053] Transparent color printing is carried out by reproducing example 1 with the composition below.

Transparent colors	Formula/100	Formula min/max
PVB resin CAS No. 63148-65-2,	20	19/21
68648-78-2 MW 15 000 to
30 000/OH 14/18
Red 122 dye	10	9/11
Wetting agent and dispersant	3	2/4
of modified polyester type in
solution in white spirit
Hydrophilic fumed silica CAS	1	0.5/1.5
7631-86-9 Specific surface
area (BET): 350/410
Cyclohexanone	60	59/61
Dipropylene glycol monomethyl	5	4/7
ether (DPM)
Tension additive: polydimethyl	1	0.5/1.5
siloxane

[0054] The same high quality is obtained as in example 1.

[0055] In addition, in terms of transparency an excellent optical quality, an absence of agglomeration and of diffusion and a haze that does not exceed 1% are observed.

[0056] EXAMPLE 4

[0057] Phosphor pigment printing is carried out by reproducing example 1 with the composition below.

Phosphors	Formula/100	Formula min/max
PVB resin CAS No. 63148-65-2,	22	21/22
68648-78-2 MW 15 000 to
30 000/OH 14/18
Blue BaMgAl10O17:Eu phosphor	3	1/4
pigment
Wetting agent and dispersant	3	2/4
of modified polyester type in
solution in white spirit
Hydrophilic fumed silica CAS	1	0.5/1.5
7631-86-9 Specific surface
area (BET): 350/410
Cyclohexanone	65	63/66
Dipropylene glycol monomethyl	5	4/7
ether (DPM)
Tension additive: polydimethyl	1	0.5/1.5
siloxane

[0058] The same high quality is obtained as in examples 1, 2 and 3.