Method for improving manufacture of laminated glass Technical Field

The present invention relates to a method to improve the manufacture of laminated glass by reducing air bubbles caused by wrinkles in the interlayer film. It is long known to produce laminated glass by providing heat and pressure to a stack with the general sequence of layers as glass/interlayer film/glass. Crucial for these lamination processes is the removal of air pockets from the stack either by removal or applying pressure and heat i.e. by physical solution of air in the polymer matrix of the interlayer film.

In any case, bubble-free laminates can only be obtained when the interlayer film is layered as flat as possible on the glass surface. Any wrinkle in the interlayer results in air bubbles which at usually cannot be removed during the lamination process and are visible in the final glass laminate. Glass laminates with visible air pockets will be rejected by the customer . The biggest sizes of glass commercially available is about 3 x 6 m. Accordingly, this is biggest size of laminated glass which can be produced at the time being, which requires an appropriate size of interlayer film. Interlayer film produced from plasticized polyvinyl butyral is therefore produced in a maximum width of 3.20 m and a length of up to 500 m coiled on a roll .

For producing the stack glass/interlayer film/glass, interlayer film layered on a first glass sheet. Any misplacement or wrinkle needs to be corrected manually before the second glass sheet is placed on the interlayer film. If the interlayer film has still wrinkles or air pockets, there is a considerable danger that these defects cannot be removed during lamination. Accordingly, it was the object of the invention to provide a process which improves the flatness of the interlayer film prior to lamination, thereby improving the yield of the lamination process by reducing the amount of defective laminated glazings.

It was found that the flatness of the interlayer film prior to lamination can be improved by providing vibrations either to the stack of interlayer film layered on a first glass sheet prior to the lamination process.

Object of the invention

The invention therefore relates to a method for producing laminated glass by providing an interlayer film on a first glass sheet to obtain a first stack, covering the interlayer film with a second glass sheet to obtain a second stack and laminate the second stack at a temperature above the Tg of the interlayer film to obtain the laminated glass, wherein the first stack is subjected to vibrational movement. In a variant of the invention, the second stack is subjected to vibrational movement.

Method

In the method of the invention, the first stack and optionally the second stack is subjected to vibrational movement in at least one dimension of the first/second stack to improve the flatness of the interlayer film thereby removing at least the major wrinkles of the interlayer film. Improving the flatness of the interlayer film improves the quality and/or the output yield of the lamination process.

The vibrational movement of the first and optionally the second stack may be provided in one or both dimensions of the stacks. For example, a rectangular stack may be vibrated in its longitudinal direction, which is usually in direction of the production line. In another variant of the method, a rectangular stack may be vibrated orthogonal to its longitudinal direction, which is usually orthogonal to the direction of the production line.

In another embodiment, the vibrational movement of the first and optionally the second stack is provided in both dimensions of the stacks. This may be simultaneously, i.e. resulting in a circular movement or alternatively, i.e. first in one dimension and then in the other. In this case, vibrational movement may be provided in direction of the production line and then orthogonal to the direction of the production line.

In yet another embodiment, the vibrational movement of the first and optionally the second stack is provided in (all) three dimension i.e. in and out of the plane of the stack. The vibrational movement of the first and optionally the second stack may be provided in these dimensions with an amplitude of 0,01 to 50 mm, preferable of 0,01 mm to 1 mm, more preferable between 0,01 and 0,5 mm. Independently to the amplitude, the vibrational movement of the first and optionally the second stack may be provided in these dimensions with a frequency between 50 KHz and 200 KHz or between 100 Hz to 100 KHz. duration of the movement depends on the number of wrinkles the interlayer film, the flatness of the interlayer film to achieved and the stickiness of interlayer film. The method may be manually controlled or automatically by an appropriate camera and computer system. The duration of the vibrational movement depends on the blockiness of the interlayer film and the temperature and humidity of the stack.

In order to reduce adhesion of the interlayer film to the glass, it is preferred that during to subjecting the vibrational movement, the first and optionally the second stack have a temperature of 0 to 20 °C. The temperature may be actively maintained and controlled during vibration of the stack or simply adjusted to an appropriate level prior to vibration. Optionally, humidity of the production lane is adjusted to 60-80%. Under such condition, 1 to 10 minutes of vibrational movement are sufficient.

In another embodiment, the second stack is subjected to vibrational movement too. In this variant, the same amplitude, frequency, direction of the vibrational movement and temperatures are used as already disclosed for the vibrational movement of the first stack.

The stacks are put in vibrational movement by appropriate means like an electrical, magnetic, pneumatic, hydraulic, piezoelectric or acoustic means like a motor, actor or transducer motor. Accordingly, another object of the invention is the use of a electrical, magnetic, pneumatic, hydraulic, piezoelectric or acoustic means for providing vibrational movement to a first stack comprising an interlayer film on a first glass sheet. All variants and embodiments of the method of the invention as disclosed apply to the use of such electrical, magnetic, pneumatic, hydraulic, piezoelectric or acoustic means.

Interlayer film The interlayer film used in accordance with the invention may be produced from plasticized polyvinyl acetal such as polyvinyl butyral (PVB) , Ionomer or ethylene vinyl acetate (EVA) . Preferably, the interlayer film is either smooth-surface or have a one- or both-sided surface structure with a roughness Rz from 0 to 100 ym, preferably Rz from 1 to 60 ym, particularly preferably Rz from 3 to 45 ym and in particular Rz from 4 to 20 ym.

In the method of the invention, more than one interlayer film may be used i.e. stacked on each other. The one interlayer film may have the same or a different chemical nature and/or composition. For example it is possible to embed an soft interlayer film between two harder interlayer films to achieve sound dampening. In such cases, the vibrational movements can be employed to the whole stack or layer-wise.

Polyvinyl Acetal

The preferred interlayer film used in accordance with the invention contains one or more polyvinyl acetals, with preferable each having a different polyvinyl alcohol content, degree of acetalisation, residual acetate content, ethylene proportion, molecular weight and/or different chain lengths of the aldehyde of the acetal groups.

The polyvinylacetal used in accordance with the invention results in particular from the reaction of at least one polyvinyl alcohol with one or more aliphatic unbranched keto- compounds containing 2 to 10 carbon atoms. To this end, n- butyraldehyde is preferably used to obtain polyvinylbytyral which is preferentially used in the invention. The polyvinyl acetals may have a content of polyvinyl acetate groups of 0.1 to 20 mol %, preferably 0.5 to 3 mol %, or 5 to 8 mol % . The polyvinyl alcohol content of the used polyvinyl acetals may be between 14 - 26 % by weight, 16 - 24 % by weight, 17 - 23 % by weight and preferably between 18 and 21 % by weight.

Additives

The interlayer film may contain alkali metal ion and/or earth alkali metal ion to adjust their adhesion level to glass (so called Anti-Adhesion Additives) .

As alkali metal ion, potassium or sodium or lithium are preferred. It is furthermore preferred to add the alkali metal ions. Bothe may be added in form of salts of carboxylic acids having 1 to 20 carbon atoms.

The total amount of alkali metal salts may be as low as 0.005 % by weight based on the weight of the interlayer film. Preferred ranges of alkali metal salt are 0.01 % - 0.1 %; 0.02 - 0.08 %; 0.03 - 0.06 %, each weight % based on the weight of the interlayer film. The interlayer film used in the laminates of the invention may additionally comprise alkaline earth ion. In a first embodiment of the invention, the film comprises 0 to 100 ppm alkaline earth ions, preferable 20 to 60 ppm. Plasticizer

Plasticiser-containing interlayer films used in accordance with the invention contain at least 24 % by weight, such as 24.0 - 36.0 % by weight, preferably 25.0 - 32.0 % by weight and in particular 26.0 - 30.0 % by weight plasticiser. Interlayer films used in accordance with the invention may contain, as plasticiser, one or more compounds selected from the following groups:

- esters of polyvalent aliphatic or aromatic acids, for example dialkyl adipates, such as dihexyl adipate, dioctyl adipate, hexyl cyclohexyl adipate, mixtures of heptyl adipates and nonyl adipates, diisononyl adipate, heptyl nonyl adipate, and esters of adipic acid with cycloaliphatic ester alcohols or ester alcohols containing ether compounds, dialkyl sebacates, such as dibutyl sebacate, and also esters of sebacic acid with cycloaliphatic ester alcohols or ester alcohols containing ether compounds, esters of phthalic acid, such as butyl benzyl phthalate or bis-2-butoxyethyl phthalate.

- esters or ethers of polyvalent aliphatic or aromatic alcohols or oligo ether glycols with one or more unbranched or branched aliphatic or aromatic substituents , for example esters of glycerol, diglycols, triglycols or tetraglycols with linear or branched aliphatic or cycloaliphatic carboxylic acids; Examples of the latter group include diethylene glycol-bis- (2-ethyl hexanoate) , triethylene glycol-bis- (2-ethyl hexanoate) , triethylene glycol-bis- (2- ethyl butanoate) , tetraethylene glycol-bis-n-heptanoate, triethylene glycol-bis-n-heptanoate, triethylene glycol-bis- n-hexanoate, tetraethylene glycol dimethyl ether and/or dipropylene glycol benzoate

- phosphates with aliphatic or aromatic ester alcohols, such as tris (2-ethylhexyl) phosphate (TOF) , triethyl phosphate, diphenyl-2-ethylhexyl phosphate, and/or tricresyl phosphate

- esters of citric acid, succinic acid and/or fumaric acid. Preferable, 1 , 2-cyclohexane dicarboxylic acid diisononyl ester (DINCH) or triethylene glycol-bis-2-ethyl hexanoate (3GO or 3G8) are used as plasticiser. In addition, the interlayer film may contain further additives, such as residual quantities of water, UV absorber, antioxidants, adhesion regulators, optical brighteners or fluorescent additives, stabilisers, colorants, processing aids, inorganic or organic nanoparticles , pyrogenic silicic acid and/or surface active substances.

Lamination Process

To laminate the second stack, any lamination method known to a person skilled in the art can be used.

For example, processes known as autoclave processes may be used. Autoclave processes are usually carried out at increased pressure of approximately 10 to 15 bar and temperatures from 100 to 150 °C during approximately 2 hours.

Vacuum bag or vacuum ring methods, for example according to EP 1 235 683 Bl, function at approximately 200 mbar and 130 to 145 °C. Vacuum laminators can also be used for the lamination process. These consist of a chamber that can be heated and evacuated, in which laminated glazings can be laminated within 30 - 60 minutes. Reduced pressures from 0.01 to 300 mbar and temperatures from 100 to 200 °C, in particular 130 - 160 °C, have proven their worth in practice.

The lamination step may comprise the prior production of a pre- laminate. In a pre-lamination step, excessive air is removed by gentle pressing of the stack at room temperature for example in nip-rollers .

Embedded objects

In a further embodiment of the invention, the interlayer film comprises at least two sub-layers of interlayer film which embed an object. The sub-layers of interlayer film have the composition as already disclosed. The object can be any flat- shaped object having not the properties of interlayer film. Objects which can be embedded between the sub-layers of the interlayer film with the method of the invention may be PET- film or solar modules.