Interlayer for laminated glass and laminated glass Number:7,074,487 from the United States Patent and Trademark Office (PTO) owispatent The present invention has it for its object to provide an interlayer film for laminated glass and a laminated glass which shows a much decreased extent of blushing of the peripheral region thereof even when placed in a high-humidity atmosphere, without compromise in those fundamental performance characteristics which are required of laminated glass, such as transparency, weather resistance, adhesion and penetration resistance.The present invention is related to an interlayer film for laminated glass comprising a plasticized poly(vinyl acetal) resin and having the haze after 24 hours of immersion is not more than 50% when said interlayer film with a thickness of 0.3 to 0.8 mm is immersed in water at 23.degree. C.<H Interlayer, laminated, Interlayer, for, , 7074487.html, Patent, pto, 7074487

Title: Interlayer for laminated glass and laminated glass

Abstract: The present invention has it for its object to provide an interlayer film for laminated glass and a laminated glass which shows a much decreased extent of blushing of the peripheral region thereof even when placed in a high-humidity atmosphere, without compromise in those fundamental performance characteristics which are required of laminated glass, such as transparency, weather resistance, adhesion and penetration resistance.The present invention is related to an interlayer film for laminated glass comprising a plasticized poly(vinyl acetal) resin and having the haze after 24 hours of immersion is not more than 50% when said interlayer film with a thickness of 0.3 to 0.8 mm is immersed in water at 23.degree. C.

Patent Number: 7,074,487 Issued on 07/11/2006 to Shichiri, et al.

Inventors: Shichiri; Tokushige (Suita, JP); Miyai; Jiro (Koka-gun, JP); Bando; Akihiko (Koka-gun, JP); Toyama; Kiyofumi (Takatsuki, JP); Aoshima; Yoshio (Kusatsu, JP); Sannomiya; Isei (Koka-gun, JP); Nakajima; Minoru (Koka-gun, JP)
Assignee: Sekisui Chemical Co., Ltd. (Osaka, JP)

Appl. No.: 107774

Filed: March 28, 2002

Related U.S. Patent Documents


Application Number	Filing Date	Patent Number	Issue Date
09269412		6387516
PCT/JP98/01341	Mar., 1998

Foreign Application Priority Data


Jul 17, 1997 [JP]			HEI-9-192474
Aug 07, 1997 [JP]			HEI-9-213284
Aug 20, 1997 [JP]			HEI-9-223613
Sep 11, 1997 [JP]			HEI-9-247015
Sep 18, 1997 [JP]			HEI-9-253216
Jan 06, 1998 [JP]			HEI-10-000983
Feb 03, 1998 [JP]			HEI-10-022137

Current U.S. Class: 428/436 ; 428/332; 428/339; 428/437; 524/239; 524/284; 524/287; 524/322; 524/394; 524/400

Current International Class: B32B 17/10 (20060101)

Field of Search: 428/332,339,436,437 524/239,284,287,322,394,400

References Cited [Referenced By]

U.S. Patent Documents


3262835	July 1966	Lavin et al.
3402099	September 1968	Christensen
4020217	April 1977	Karasudani et al.
4292372	September 1981	Moynihan
4952457	August 1990	Cartier et al.
5340654	August 1994	Ueda et al.
5349014	September 1994	Degeilh
5427861	June 1995	D'Emico
5478412	December 1995	Simon et al.

Foreign Patent Documents


677788	Sep., 1966	BE
1201235	Feb., 1986	CA
2004482	Jun., 1990	CA
1926958	Feb., 1970	DE
2510118	Jan., 1976	DE
2838025	Mar., 1979	DE
0373139	Jun., 1990	EP
2007677	May., 1979	GB
44-32185	Dec., 1969	JP
45-4270	Feb., 1971	JP
48005772	Feb., 1973	JP
241547	Feb., 1982	JP
60210551	Oct., 1985	JP
4-55404	Feb., 1992	JP
5186250	Jul., 1993	JP
6502594	Mar., 1994	JP
7411340	Feb., 1995	JP

Other References

Patent Abstracts of Japan, vol. 15, No. 115, Mar. 19, 1991 & JP 03 005772 A, Jan. 11, 1991. cited by other .
Technical specifications concerning the NDH 300A turbidmeter of Nippon Denshoku Industries Co, Ltd. Jan. 10, 2003. cited by other.

Primary Examiner: Nakarani; D. S.
Attorney, Agent or Firm: Connolly, Bove, Lodge & Hutz, LLP

Claims

The invention claimed is:

1. An interlayer film for laminated glass comprising a plasticized poly(vinyl acetal) resin and at least one member selected from the group consisting of sodium salts and potassium salts and having the haze after 24 hours of immersion of not more than 50% when said interlayer film with a thickness of 0.3 to 0.8 mm is immersed in water at 23.degree. C.

2. The interlayer film for laminated glass according to claim 1 wherein the concentration of sodium in the interlayer film is not great than 50 ppm.

3. The interlayer film for laminated glass according to claim 2, which comprises a compound capable of forming a complex with sodium and potassium salts.

4. The interlayer film for laminated glass according to claim 2, which comprises an organic acid compatible with the resin and plasticizer and an amine compatible with the resin and plasticizer.

5. The interlayer film for laminated glass according to claim 2, which comprises at least one member selected from the group consisting of sodium salt, potassium salt and alkaline earth metal salt.

6. The interlayer film for laminated glass according to claim 1 wherein the concentration of potassium in the interlayer film is not greater than 100 ppm.

7. The interlayer film for laminated glass according to claim 6, which comprises a compound capable of forming a complex with sodium and potassium salts.

8. The interlayer film for laminated glass according to claim 6, which comprises an organic acid compatible with the resin and plasticizer and an amine compatible with the resin and plasticizer.

9. The interlayer film for laminated glass according to claim 6, which comprises at least one member selected from the group consisting of sodium salt, potassium salt and alkaline earth metal salt.

10. The interlayer film for laminated glass according to claim 1 which further comprises a compound capable of forming a complex with sodium and potassium salts.

11. The interlayer film for laminated glass according to claim 10, which comprises at least one member selected from the group consisting of sodium salt, potassium salt and alkaline earth metal salt.

12. The interlayer film for laminated glass according to claim 1 which further comprises an organic acid compatible with the resin and plasticizer and an amine compatible with the resin and plasticizer.

13. The interlayer film for laminated glass according to claim 12, which comprises at least one member selected from the group consisting of sodium salt, potassium salt and alkaline earth metal salt.

14. The interlayer film for laminated glass according to claim 1 which further comprises at least one member selected from the group consisting of sodium salt, potassium salt and alkaline earth metal salt.

15. The interlayer film for laminated glass according to claim 14 wherein the sodium salt and/or potassium salt is a salt of an organic acid containing 5 to 16 carbon atoms and the alkaline earth metal salt is a salt of an organic acid containing 5 to 16 carbon atoms.

16. A laminated glass comprising at least one pair of glass sheets and, as interposed therebetween, the interlayer film according to claim 1.

Description

TECHNICAL FIELD

The present invention relates to an interlayer film for laminated glass and to a laminated glass in which said interlayer film for laminated glass is used.

BACKGROUND ART

Laminated glass comprising at least two glass sheets and a plasticized poly(vinyl butyral) interlayer film sandwiched therebetween has fundamental characteristics required of laminated glass. For example, it has good transparency, weather resistance, bond strength, and penetration resistance. It hardly allows its fragments to scatter. Thus, it has so far been widely used as the windshields of automobiles or buildings, for instance.

While laminated glass of this kind is excellent in fundamental characteristics such as mentioned above and in safety, it is poor in moisture resistance. Thus, when the above-mentioned laminated glass is used in a high humidity environment, a problem may arise; namely, the interlayer film in the peripheral region of the laminate may whiten, since the peripheral edges of laminated glass are in direct contact with the environmental air.

This phenomenon of blushing is associated with the additive used for adjusting the bond strength between the interlayer film and the glass, as mentioned below.

In order that the laminated glass will sufficiently discharge the functions mentioned above, it is necessary to adjust the bond strength between interlayer film and glass so that it may fall within an adequate range. Thus, if the bond strength between interlayer film and glass is too weak, glass fragments formed upon breakage due to an external shock may peel off from the interlayer film and scatter to increase the risk for injuring the human bodies and other objects. If, conversely, the bond strength between interlayer film and glass is excessively high, the glass and interlayer film tend to break simultaneously upon receiving a shock load whereupon glass fragments accompanying fragments of the interlayer film will scatter, thus increasing the risks for injuring the human bodies and other objects.

On the contrary, when the bond strength between interlayer film and glass is within an adequate range, breakage of glass occurs over a wide area and results in concurrent partial interfacial peeling of the interlayer film and glass from each other and elongation of the interlayer film, and these phenomena are effective in increasing the resistance against shock and penetration.

Thus, in order to insure that, taking a traffic accident involving an automobile as an example, the shock to the driver and/or passenger may be absorbed, the risk for their being hauled through the broken windshield may be prevented or, in the case of an accident related to a building, the penetration of flying objects against the window pane or scattering of broken glass fragments may be prevented, the bond strength between interlayer film and glass must be judiciously controlled within said suitable range.

In view of the foregoing, various bond strength control agents for the interlayer film have so far been investigated in order to adjust the bond strength between interlayer film and glass to a level within an adequate range.

Thus, for example, Japanese Kokoku Publication Sho-46-4270 proposes an interlayer film for laminated glass which comprises a poly(vinyl acetal) resin composition containing 0.2 to 0.8% by weight of water and a specific amount of a specific metal alkylcarboxylate as a bond strength control agent. The bond strength between the interlayer film and glass according to the above proposal is adjusted to an adequate range by varying the proportions of the metal alkylcarboxylate distributed in the superficial layer of the interlayer film and in the inside layer of the interlayer film or varying the water content of the interlayer film.

The metal alkylcarboxylate-containing interlayer film such as proposed in the above publication, however, is low in moisture resistance, and the laminated glass manufactured by using said interlayer film has a problem in that when allowed to stand in a high-humidity atmosphere, it tends to undergo severe blushing due to moisture absorption by the interlayer film as the metal alkylcarboxylate content increases since the interlayer film is in direct contact with air in the peripheral region of the laminated glass. The phenomenon of blushing of the interlayer film may be prevented by decreasing the amount of the metal alkylcarboxylate as far as possible or avoiding the use thereof but, in that case, there occurs a problem crucial for the laminated glass that the bond strength between interlayer film and glass exceeds the proper range and is ready to allow simultaneous breakage or penetration of the glass and interlayer film upon receiving to an external shock load or the like.

In Japanese Kokoku Publication Sho-44-32185, there is proposed an interlayer film for laminated glass which comprises a molded poly(vinyl acetal) resin having a water content of 0.1 to 0.8% and containing 0.01 to 3 parts by weight, per 100 parts by weight of the resin, of at least one organic acid selected from among monocarboxylic acids containing 6 to 22 carbon atoms, dicarboxylic acids containing 4 to 12 carbon atoms, aliphatic monoaminomonocarboxylic acids containing 2 to 6 carbon atoms, aliphatic monoaminodicarboxylic acids containing 4 or 5 carbon atoms, citric acid, and mixtures thereof.

However, this interlayer film has the drawback that the addition of such a carboxylic acid causes the bond strength to change with the lapse of time. Moreover, another problem may arise; the acid may adversely affect the heat resistance and weather resistance of the interlayer film.

Japanese Kokoku Publication Sho-48-5772 discloses a laminate glass comprising at least two glass sheets glued together by means of a plasticized poly(vinyl acetal) resin composition, said plasticized poly(vinyl acetal) resin composition contains the sodium metal salt of an aliphatic carboxylic acid containing 10 to 22 carbon atoms.

Furthermore, in Japanese Kokoku Publication Sho-53-18207, the use is proposed of an alkali metal or alkaline earth metal salt of a monocarboxylic or dicarboxylic acid as a bond strength control agent in the plasticized poly(vinyl acetal) resin interlayer film.

In either of the above two proposals, a metal salt of a carboxylic acid containing a relatively large number of carbon atoms is used as the bond strength control agent, since such salt is readily soluble in the plasticizer contained in the interlayer film.

However, when a metal salt of a carboxylic acid containing a large number of carbon atoms is used as the bond strength control agent, there occurs a problem that the bond strength between interlayer film and glass changes with the lapse of time. Thus, even when the bond strength is adequate initially, the bond strength will gradually decrease with the lapse of time and the glass will readily undergo peeling when it receives a shock. For preventing this decrease in bond strength, it is necessary to mature the interlayer film by storing the same in an atmosphere of 40 to 50.degree. C. for 1 to 2 months, for instance. However, since the interlayer film has tackiness and a tendency toward self-adhesion, it is as a matter of fact difficult to store the interlayer film in such an atmosphere as mentioned above for a long period of time. Even if the maturing is performed, the decrease in bond strength with the lapse of time can be retarded but cannot be made nil, and the problem mentioned above still remains.

Japanese Kokai Publication Sho-60-210551 discloses a laminated glass comprising at least two glass sheets glued together by means of an interlayer film composed of a plasticized poly(vinyl acetal) resin containing, or carrying as adhered thereto, 0.02 to 0.40 part by weight of the potassium salt of a monocarboxylic acid containing 1 to 6 carbon atoms and 0.01 to 0.26 part by weight of a modified silicone oil per 100 parts by weight of said resin. Certain metal salts, however, may cause blushing of the laminated glass due to their coagulation in the form of particles within the interlayer film. Therefore, from the viewpoint of long-term prevention of blushing resulting from moisture absorption, said laminated glass cannot be said to be a perfect one.

In Japanese Kokoku Publication Hei-02-41547, there is proposed a poly(vinyl butyral) sheet in which an alkali or alkaline earth metal salt of formic acid is used as the bond strength control agent. Furthermore, in Japanese Kohyo Publication Hei-06-502594, an interlayer film containing potassium acetate added as a bond strength control agent is used in the examples of its specification.

In the three proposals mentioned above, a metal salt of a carboxylic acid containing a relatively small number of carbon atoms is used to overcome the problems mentioned above in relation to the use of a metal salt of a carboxylic acid containing a large number of carbon atoms.

When a metal salt of a carboxylic acid containing a small number of carbon atoms is used as the bond strength control agent, the problem of the decrease in bond strength between interlayer film and glass with lapse of time can indeed be solved but the moisture resistance of the interlayer film becomes insufficient and, as a result, another problem arises, namely the peripheral (edge) region of the laminated glass tends to undergo blushing due to absorption of moisture.

More specifically, the interlayer film is generally capable of absorbing moisture under ordinary atmospheric (humidity) conditions and, therefore, in using it in the manufacture of a laminated glass, it is common practice to submit the interlayer film to the lamination process after adjusting its water content to not more than about 0.5% by weight in an atmosphere of 25% RH, for instance. Since, however, the peripheral region of laminated glass are generally exposed, the interlayer film absorbs moisture in a high-humidity environment, whereby the water content increases to about 2 to 3% by weight. On that occasion, water gathers around minute crystals of said metal salt of a carboxylic acid containing a small number of carbon atoms, such as potassium acetate, magnesium acetate or potassium formate, as occurring in the interlayer film, to cause blushing. If the addition amount of the carboxylic acid containing a small number of carbon atoms or a salt thereof is decreased to prevent blushing, the bond strength between interlayer film and glass will deviate from the proper range, hence the shock absorbing potential, penetration resistance and other properties of the laminated glass will become insufficient.

In Japanese Kokai Publication Hei-05-186250, an attempt is made to improve the carboxylic acid salt-containing interlayer film in respect of blushing by using an interlayer film for laminated glass which is composed of a resin composition comprising a poly(vinyl acetal) resin, a plasticizer, an alkali or alkaline earth metal salt of a mono- or dicarboxylic acid containing not more than 12 carbon atoms and an organic acid.

Furthermore, in Japanese Kokai Publication Hei-07-41340, an interlayer film for laminated glass is proposed which is formed from a resin composition comprising a poly(vinyl acetal) resin, a plasticizer, a carboxylic acid metal salt and a straight-chain fatty acid.

The laminated glass including the interlayer film for laminated glasses according to the above proposals show reduced degrees of blushing in the peripheral region in moisture resistance testing but the extent of reduction in blushing is yet unsatisfactory. Moreover, if the content of the straight-chain fatty acid is increased for further reducing the degree of blushing, foaming and/or discoloration may possibly occur when the laminated glass is exposed to a relatively high temperature.

While the interlayer films proposed in the above-cited publications are results of attempts to solve the blushing problem by improving the bond strength control agent, those interlayer films which contain no bond strength control agent also whiten as a result of moisture absorption. Our recent research works have revealed that those impurities mentioned below in the resin are involved in the blushing phenomenon as one of the causes thereof.

The interlayer film for laminated glass of the present invention comprises a poly(vinyl acetal) resin as the main component thereof. The process for producing poly(vinyl acetal) resins comprises a step of neutralization. In this neutralization process, an aqueous solution of sodium hydroxide, sodium hydrogen carbonate or the like sodium salt is used. When the sodium salt is used in excess or when another sodium salt is formed as a result of neutralization, the sodium salt may remain in the product poly(vinyl acetal) resin. This residual sodium salt forms particles during polymerization and/or drying, and those particles promote the aggregation of water on the occasion of water absorption by the poly(vinyl acetal) resin, hence serve as a major cause of blushing of the product interlayer film for laminated glass due to moisture absorption. Furthermore, a sodium salt may remain even in poly(vinyl alcohol) in some instances, and this sodium salt may also serve as a cause of blushing of the interlayer film for laminated glass due to moisture absorption in certain instances.

In recent years, the trend toward the use of laminated glass as the automobile side glass screen or in buildings has been increasing and, in these applications, laminated glass is often used with the peripheral portions thereof being exposed. The need for preventing the blushing phenomenon is becoming more and more increased.

SUMMARY OF THE INVENTION

The present invention which solves the above problems has it for its object to provide an interlayer film for laminated glass and a laminated glass in which said interlayer film is used and which shows a much decreased extent of blushing of the peripheral region thereof even when placed in a high-humidity atmosphere, without compromise in those fundamental performance characteristics which are required of laminated glass, such as transparency, weather resistance, adhesion and penetration resistance.

The present invention consists in an interlayer film for laminated glass comprising a plasticized poly(vinyl acetal) resin and having the haze after 24 hours of immersion of not more than 50% when said interlayer film with a thickness of 0.3 to 0.8 mm is immersed in water at 23.degree. C.

DETAILED DESCRIPTION OF THE INVENTION

In the following, the present invention is described in detail.

The interlayer film for laminated glass of the present invention is such that when said interlayer film with a thickness of 0.3 to 0.8 mm is immersed in water at 23.degree. C., the haze value after 24 hours of immersion is not more than 50%.

The inventors of the present invention found that an interlayer film for laminated glass showing a haze of not more than 50% when said interlayer film with a thickness of 0.3 to 0.8 mm is immersed in water at 23.degree. C. for 24 hours is excellent in moisture resistance, showing little blushing in the peripheral region of the laminated glass even when placed in a high-humidity atmosphere. Based on this finding, the present invention has been completed.

When the haze mentioned above exceeds 50%, the blushing under high-humidity conditions cannot be fully prevented and poor moisture resistance may result, hence the above range is critical. In the present specification, said haze means a value measured by using an integrating turbidimeter after 24 hours of immersion of a sample interlayer film with a thickness of 0.3 to 0.8 mm in water at 23.degree. C.

The interlayer film for laminated glass of the present invention comprises a plasticized poly(vinyl acetal) resin film, and said plasticized poly(vinyl acetal) sheet contains a poly(vinyl acetal) resin as a main component.

Said poly(vinyl acetal) resin preferably has an average degree of acetalization of 40 to 75 mole percent. When said degree is less than 40 mole percent, the compatibility with the plasticizer will be low, making it difficult, in some instances, to incorporate the plasticizer in an amount necessary for securing penetration resistance. When said degree is over 75 mole percent, the resulting interlayer film for laminated glass will have a low mechanical strength and, in addition, a prolonged reaction time will be required for resin preparation, which is often undesirable from the process viewpoint. A more preferred range is 60 to 75 mole percent. When said degree is less than 60 mole percent, the hygroscopicity will be high and, therefore, blushing may readily occur in some instances. A still more preferred range is 64 to 71 mole percent.

In the above plasticized polyvinyl acetal) resin, the vinyl acetate content is preferably not more than 30 mole percent. When it is over 30 mole percent, blocking will readily occur in the process of resin production, making the resin production difficult. It is preferred that said content be not more than 19 mole percent.

Said plasticized poly(vinyl acetal) resin comprises a vinyl acetal component, a vinyl alcohol component and a vinyl acetate component. These components can be quantitated according to JIS K 6728 "Methods of testing poly(vinyl butyral)" or by the nuclear magnetic resonance (NMR) method, for instance.

In cases where the poly(vinyl acetal) resin comprises other than a poly(vinyl butyral) resin, the vinyl alcohol component and vinyl acetate component are first quantitated. The amount of the remaining vinyl acetal component can then be calculated by subtracting the amounts of the above both components from 100.

The poly(vinyl acetal) resin mentioned above can be produced by per se known methods. Thus, for example, poly(vinyl alcohol) is dissolved in warm water and, while maintaining the resulting aqueous solution at a specific temperature, for example 0 to 95.degree. C., preferably 10 to 20.degree. C., a necessary acid catalyst and a necessary aldehyde are added, and the acetalization reaction is allowed to proceed with stirring. The reaction temperature is then raised to 70.degree. C. for carrying the reaction to completion, followed by neutralization, washing with water and drying, to give a poly(vinyl acetal) resin powder.

The above poly(vinyl alcohol) to serve as the starting material preferably has an average degree of polymerization of 500 to 5,000, more preferably 1,000 to 2,500. When it is less than 500, the product laminated glass may have only a low penetration resistance. When it exceeds 5,000, resin film forming may become difficult and, in addition, the strength of the resin film may become excessively high.

It is preferred that the vinyl acetate component in the poly(vinyl acetal) resin obtained account for not more than 30 mole percent. Therefore, it is preferred that the degree of saponification of the above poly(vinyl alcohol) be not less than 70 mole percent. When said degree is less than 70 mole percent, the transparency and/or heat resistance of the resin may be low and the reactivity may also be low. More preferably, said degree is not less than 95 mole percent.

The average polymerization degree and saponification degree of the poly(vinyl alcohol) can be determined according to JIS K 6726 "Methods of testing poly(vinyl alcohol)", for instance.

The aldehyde mentioned above is preferably an aldehyde containing 3 to 10 carbon atoms. When the number of carbon atoms is less than 3, sufficient resin film moldability may not be obtained in some instances. When it exceeds 10, the reactivity for acetalization will be low and, in addition, resin blocking may readily occur and cause difficulties in resin synthesis.

The aldehyde mentioned above is not limited to any particular species but includes aliphatic, aromatic, alicyclic and other aldehydes, such as propionaldehyde, n-butyraldehyde, isobutyraldehyde, valeraldehyde, n-hexylaldehyde, 2-ethylbutyraldehyde, n-heptylaldehyde, n-octylaldehyde, n-nonylaldehyde, n-decylaldehyde, benzaldehyde and cinnamaldehyde. Preferred are aldehydes containing 4 to 8 carbon atoms, such as n-butyraldehyde, n-hexylaldehyde, 2-ethylbutyraldehyde and n-octylaldehyde. Among them, n-butyraldehyde, which contains 4 carbon atoms, is more preferred, since the use of the resulting poly(vinyl acetal) resin contributes to an increased bond strength of the resin film as well as excellent weather resistance and to easy production of the resin. The aldehydes may be used either singly or in a combination of two or more species.

In the interlayer film of the present invention, the particle diameter of a sodium salt therein is preferably not more than 10 .mu.m, more preferably not more than 5 .mu.m. The particle diameter of potassium salt in the interlayer film is preferably not more than 5 .mu.m.

When the sodium salt has a particle diameter greater than 10 .mu.m or the potassium salt has a particle diameter greater than 5 .mu.m, the salt particles may promote water aggregation and become a primary cause of blushing of the obtained interlayer film due to moisture absorption.

The sodium salt or potassium salt particle diameter referred to above is the particle diameter in the interlayer film. While the particle diameters of the sodium salt and potassium salt in the poly(vinyl acetal) resin, which are the primary raw material, are decreased in the process of sheet forming in some instances, said particle diameters are retained in other instances. Therefore, it is preferred that the particle diameters of sodium salt and potassium salt in the poly(vinyl acetal) resin be also within the above-specified range.

The particle diameters of sodium salt and potassium salt in the interlayer film can be determined by secondary ion imaging using a time-of-flight secondary ion mass spectrometer (TOF-SIMS).

In the interlayer film of the present invention, the sodium concentration is preferably not more than 50 ppm, and the potassium concentration in the interlayer film is preferably not more than 100 ppm. More preferably, the sodium concentration should be not less than 0.5 ppm and not more than 15 ppm, and the potassium concentration should be not less than 0.5 ppm and not more than 100 ppm.

When the sodium content of the interlayer film is over 50 ppm and/or the potassium content is over 100 ppm, water molecules gather around the sodium element and potassium element and grow to macroscopic sizes, whereupon blushing may become prominent. To prepare an interlayer film having a sodium content of less than 0.5 ppm and a potassium content of less than 0.5 ppm is not preferred from practical points of view in some instances, since the step of washing for eliminating the remaining sodium element or potassium element coming from the resin preparation step must be excessively prolonged and/or the degree of purification of water and other raw materials must be raised, among other measures, hence much time and expenses are required.

The concentration of sodium and that of potassium in the interlayer film can be determined by elemental analysis using an ICP emission spectrometer. The elemental analysis by ICP emission spectrometry is a technique comprising heating and decomposing the sample with sulfuric acid and nitric acid, making the decomposition product to volume with ultrapure water and then performing assaying by the ICP-AES method.

The inclusion of said sodium and/or potassium results from the use, for example in the preparation of poly(vinyl acetal) resin, of a sodium or potassium element-containing neutralizing agent, such as sodium carbonate, sodium hydrogen carbonate, sodium acetate, sodium hydroxide, potassium carbonate, potassium hydrogen carbonate, potassium acetate or potassium hydroxide, for neutralization of the acid catalyst used for the reaction, such as sulfuric acid or hydrochloric acid.

The neutralization procedure in the above poly(vinyl acetal) resin production process is effective in preventing the acid catalyst such as hydrochloric acid (HCl), which is essential for the poly(vinyl acetal) resin formation reaction in the preceding step, from remaining in the resin and deteriorate the very resin.

Usable as said neutralizing agent are alkali metal salts and alkaline earth metal salts. Unlike alkali metals, alkaline earth metals, when remaining in the interlayer film in fairly large amounts, can prevent blushing under high-humidity conditions, hence are preferred.

As said alkaline earth metal salts, there may be mentioned, among others, magnesium salts such as magnesium hydrogencarbonate, magnesium hydroxide, basic magnesium carbonate, barium salts such as barium hydroxide, and calcium salts such as calcium hydroxide.

The inclusion of said sodium and/or potassium also results from the sodium or potassium salt of a carboxylic acid and octylic acid, etc., added as a bond strength control agent, which is remaining in the interlayer film, or from the sodium element or potassium element contained in water and other raw materials used, in particular in poly(vinyl alcohol), and remaining in the interlayer film.

The amount of such alkali metals contained in pure water can be reduced to 1 ppm or less through the use of deionized water, for instance. On the other hand, the alkali metal content of the poly(vinyl alcohol) comes from the sodium acetate formed in the course of saponification of poly(vinyl acetate) in the process for producing the raw material poly(vinyl alcohol), and it is generally 0.4 to 1.5% by weight.

Therefore, by using a poly(vinyl alcohol) material having a sodium acetate content of not more than 0.4% by weight, the sodium element in the resin, which is hardly removable by washing, can be reduced and, by intensified washing or like measures, the sodium element can be consistently reduced to 50 ppm or below.

In the above process for poly(vinyl acetal) resin production, it is also possible to reduce the alkali metal content by washing the poly(vinyl acetal) resin with water until a pH of 5 or above is attained, followed by drying at a temperature not higher than 60.degree. C., without resort to the neutralization procedure mentioned above. By sufficient washing with water until a pH of 5 or above is attained, the content of the alkali metal, which is causative of blushing of the resulting resin film, can be reduced to a amount not over a required amount. Further, by drying at a relatively low temperature not higher than 60.degree. C., the resin can be protected against deterioration due to the inclusion of alkali metal and the remaining acid catalyst and, at the same time, the drying equipment can be protected from being corroded by the acid. Although the drying procedure may be carried out by any ordinary method, the vacuum drying method, in particular, is efficient and superior.

In the above step of washing with water, washing is preferably carried out with water at a temperature of not lower than 40.degree. C. Taking into consideration the fact that the resin in the slurry swells at 40.degree. C. or above, the temperature of water to be used for washing is raised to 40.degree. C. or above so that the efficiency of washing can be improved and resin deterioration due to the inclusion of alkali metal and/or acid catalyst residues can be prevented. By using washing water at 40.degree. C. or above, preferably 40 to 60.degree. C., in the step of washing, the resin in the slurry swells and the acid (HCl) and the neutralization product (alkali metal-containing product) contained in the resin can be readily washed away, whereby the washing efficiency can be improved. If the washing water temperature is below 40.degree. C., the resin cannot swell to a satisfactory extent, hence the efficiency can hardly be improved. If the washing water temperature is higher than 60.degree. C., the resin softens and resin particles stick together, forming blocks, hence the resin cannot have a stable particle size; in addition, any marked improvement in efficiency cannot be expected as compared with water at 60.degree. C. and, thus, a waste of energy results.

An alternative method may also be mentioned for preventing the above-mentioned inclusion of sodium and potassium. This method comprises using, in synthesizing a poly(vinyl acetal) resin by reacting poly(vinyl alcohol) with an aldehyde in the presence of hydrochloric acid catalyst, an epoxide as both a reaction terminator and a hydrochloric acid eliminator and subjecting the resulting poly(vinyl acetal) resin to sheet formation.

Said epoxide includes, among others, 1,2-epoxides of the general formula (I):

##STR00001## (wherein R.sup.1 and R.sup.2 each represents a hydrogen atom or an alkyl group and n represents an integer of 0 to 3), as well as 1,3-epoxides such as trimethylene oxide, tetrahydrofuran and tetrahydropyran, 1,4-epoxides, 1,5-epoxides and the like. These may be used singly or two or more of them may be used combinedly. Particularly preferred as the epoxide are ethylene oxide, propylene oxide and the like.

The above epoxide can be used in an effective amount sufficient to terminate the reaction and eliminate the hydrochloric acid.

As regards the mode of use of the above epoxide, the epoxide is used in lieu of the hydrochloric acid catalyst neutralizing agent to terminate the acetalization reaction and further to eliminate the hydrochloric acid, whereby the resin can be prevented from deterioration due to the inclusion of alkali metal and/or retention of acid catalyst.

In the present invention, it is preferred that a dispersant be incorporated in the interlayer film for laminated glass so that blushing under high-humidity conditions can be prevented more effectively.

As said dispersant, there may be mentioned compounds capable of forming complexes with sodium salts and potassium salts, organic acids compatible with the resin and plasticizer, and amines compatible with the resin and plasticizer.

Said compounds capable of forming complexes with sodium salts and potassium salts render the surroundings of metal salts such as sodium salts and potassium salts hydrophobic and thereby render it difficult for water to approach said surroundings, with the result that even upon moisture absorption by the poly(vinyl acetal) resin, the interlayer film for laminated glass as obtained can be prevented from undergoing blushing.

The above-mentioned compound capable of forming complexes with sodium salts and potassium salts includes but is not limited to ethylenediaminetetraacetic acid, salicylaldehyde, salicylic acid, salicylanilide, oxalic acid, 1,10-phenanthroline, acetylacetone, 8-hydroxyquinoline, dimethylglyoxime, 1,1-cyclohexanediacetic acid, salicylaldoxime and glycine. These may be used either singly or two or more of them may be used in combination.

The addition amount of the compound capable of forming complexes with sodium salts and potassium salts depends on the amount of the metal salt remaining in the poly(vinyl acetal) resin but is preferably within the range of 0.02 to 2 parts by weight per 100 parts by weight of the poly(vinyl acetal) resin. At an addition amount below 0.02 part by weight, the preventive effect on the blushing due to moisture absorption may be insufficient. At an addition amount exceeding 2 parts by weight, the compatibility with the poly(vinyl acetal) resin will be poor and a transparency problem may arise in some instances. A more preferred range is 0.05 to 1 part by weight.

Organic acids compatible with the resin and plasticizer and amines compatible with the resin and plasticizer can also be used as the dispersant mentioned above.

Among said organic acids compatible with the resin and plasticizer, at least one member selected from the group consisting of sulfonic acids containing 2 to 21 carbon atoms, carboxylic acids containing 2 to 20 carbon atoms, and phosphoric acids of the general formula (II) given below is used.

##STR00002## (In the above formula, R.sup.3 represents an aliphatic hydrocarbon group containing 1 to 18 carbon atoms or an aromatic hydrocarbon group containing 1 to 18 carbon atoms, and R.sup.4 represents a hydrogen atom, an aliphatic hydrocarbon group containing 1 to 18 carbon atoms, or an aromatic hydrocarbon group containing 1 to 18 carbon atoms.)

Referring to the sulfonic acids containing 2 to 21 carbon atoms, if the number of carbon atoms is less than 2, the hydrophilicity will be high, hence the compatibility with the poly(vinyl acetal) resin will be poor and insufficient dispersion will result. If the number of carbon atoms is over 21, the sulfonic acid will be hydrophobic, hence the compatibility with the poly(vinyl acetal) resin will be poor and phase separation may possibly occur. More preferred are those containing 7 to 18 carbon atoms.

The sulfonic acids containing 2 to 21 carbon atoms may be aliphatic or aromatic, for instance. The sulfonic acids containing 2 to 21 carbon atoms thus include, but are not limited to, benzenesulfonic acid, naphthalenesulfonic acid, alkylsulfonic acids with the alkyl moiety thereof containing 2 to 21 carbon atoms, alkylbenzenesulfonic acids with the alkyl moiety thereof containing 2 to 15 carbon atoms, and alkylnaphthalenesulfonic acids with the alkyl moiety thereof containing 2 to 11 carbon atoms, among others. More specifically, there may be mentioned p-toluenesulfonic acid, dodecylbenzenesulfonic acid, camphorsulfonic acid, hydroxypropanesulfonic acid, mesitylenesulfonic acid, and the like. These may be used singly or two or more of them may be used in combination.

The addition amount of the sulfonic acids containing 2 to 21 carbon atoms is preferably 0.01 to 2 parts by weight per 100 parts by weight of the poly(vinyl acetal) resin. At an addition amount less than 0.01 part by weight, the preventive effect on the blushing due to moisture absorption will be insufficient in some instances. At an addition amount exceeding 2 parts by weight, the resin deterioration may be promoted or the sulfonic acids themselves may cause the blushing. A more preferred addition amount is within the range of 0.03 to 1 part by weight.

Referring to the carboxylic acids containing 2 to 20 carbon atoms, if the number of carbon atoms is less than 2, the hydrophilicity will be high, hence the compatibility with the poly(vinyl acetal) resin will be poor and insufficient dispersion will result. If the number of carbon atoms is over 20, the carboxylic acid will be hydrophobic, hence the compatibility with the poly(vinyl acetal) resin will be poor and phase separation may possibly occur. More preferred are those containing 6 to 14 carbon atoms.

The carboxylic acids containing 2 to 20 carbon atoms may be aliphatic or aromatic, for instance. They may be dicarboxylic acids. Said carboxylic acids containing 2 to 20 carbons atoms thus include, but are not limited to, acetic acid, propionic acid, butyric acid, isobutyric acid, 2-ethylbutyric acid, octanoic acid, 2-ethylhexylic acid, lauric acid, myristic acid, stearic acid, oxalic acid, malonic acid, succinic acid, adipic acid, pimelic acid, sebacic acid, oleic acid, benzoic acid, toluic acid, naphthoic acid, 1,1-cyclohexanediacetic acid, salicylic acid and the like. These may be used singly or two or more of them may be used in combination.

The addition amount of the carboxylic acids containing 2 to 20 carbon atoms is preferably 0.01 to 3 parts by weight per 100 parts by weight of the poly(vinyl acetal) resin. At an addition amount less than 0.01 part by weight, the preventive effect on the blushing due to moisture absorption will be insufficient in some instances. At an amount exceeding 3 parts by weight, the compatibility with the resin will be poor and a transparency problem may arise or resin deterioration may be promoted. A more preferred range is 0.05 to 1 part by weight.

Referring to R.sup.3 and R.sup.4 in the phosphoric acids represented by the above general formula (II), if the number of carbon atoms in the aliphatic hydrocarbon group or aromatic hydrocarbon group exceeds 18, the phosphoric acid will be hydropholic, hence the compatibility with the poly(vinyl acetal) resin will be poor. A more preferred range of the number of carbon atoms is 6 to 12.

The phosphoric acids of general formula (II) include but are not limited to methylphosphoric acid, ethylphosphoric acid, propylphosphoric acid, isopropylphosphoric acid, butylphosphoric acid, laurylphosphoric acid, stearylphosphoric acid, 2-ethylhexylphosphoric acid, di(2-ethylhexyl)phosphoric acid, isodecylphosphoric acid, phenylphosphoric acid, dimethylphosphoric acid, diethylphosphoric acid, diisopropylphosphoric acid, dioctylphosphoric acid, diphenylphosphoric acid and dibenzylphosphoric acid. These may be used singly or two or more of them may be used in combination.

The addition amount of the phosphoric acid of general formula (II) is preferably 0.01 to 2 parts by weight per 100 parts by weight of the poly(vinyl acetal) resin. At an addition amount below 0.01 part by weight, the preventive effect on the blushing due to moisture absorption will be insufficient in some instances. At an amount exceeding 2 parts by weight, resin deterioration may be rather promoted or the phosphoric acid itself may cause the blushing. A more preferred range is 0.03 to 1 part by weight.

The organic acid compatible with the resin and plasticizer is used in combination with the amine compatible with the resin and plasticizer. Suited for use as the amine compatible with the resin and plasticizer are amines of the general formula (III):

##STR00003## (wherein R.sup.5, R.sup.6 and R.sup.7 may be the same or different and each represents a hydrogen atom, an aliphatic hydrocarbon group containing 1 to 20 carbon atoms or an aromatic hydrocarbon group containing 1 to 20 carbon atoms).

When the number of carbon atoms in the aliphatic hydrocarbon group or aromatic hydrocarbon group mentioned above exceeds 20, the amine becomes hydrophobic, hence the compatibility with the poly(vinyl acetal) resin may be poor in some instances. It is preferred that one of R.sup.5, R.sup.6 and R.sup.7 be a long-chain one. More preferably, R.sup.5 and R.sup.6 each independently is a hydrogen atom or a hydrocarbon group containing 1 or 2 carbon atoms, and R.sup.7 is a hydrocarbon group containing 6 to 16 carbon atoms.

The amine of general formula (III) includes but is not limited to primary amines such as methylamine, ethylamine, propylamine, hexylamine, octylamine, decylamine, dodecylamine, tetradecylamine, aniline, toluidine, naphthylamine, etc.; secondary amines such as dimethylamine, diethylamine, dipropylamine, dihexylamine, dioctylamine, N-methylaniline, etc.; tertiary amines such as trimethylamine, triethylamine, N,N-dimethylhexylamine, N,N-dimethyloctylamine, N,N-dimethyldecylamine, N,N-dimethyldodecylamine, N,N-dimethylaniline, pyridine, etc., among others. These may be used singly or two or more of them may be used in combination.

When a sulfonic acid containing 2 to 21 carbon atoms is used as the organic acid compatible with the resin and plasticizer, the addition amount of the amine of general formula (III) is preferably 0.01 to 2 parts by weight per 100 parts by weight of the poly(vinyl acetal) resin. At an addition amount less than 0.01 part by weight, the preventive effect on the blushing due to moisture absorption may be insufficient. At an addition amount exceeding 2 parts by weight, the compatibility with the resin will be poor, and a transparency problem may arise or the interlayer film may be discolored. A more preferred range is 0.02 to 1 part by weight.

When a carboxylic acid containing 2 to 20 carbon atoms is used as the organic acid compatible with the resin and plasticizer, the addition amount of the amine of general formula (III) is preferably 0.01 to 3 parts by weight per 100 parts by weight of the poly(vinyl acetal) resin. At an addition amount below 0.01 part by weight, the preventive effect on the blushing due to moisture absorption may be insufficient. At an addition amount exceeding 3 parts by weight, the compatibility with the resin will be poor, and a transparency problem may arise or the interlayer film may be discolored. A more preferred range is 0.05 to 1 part by weight.

When a phosphoric acid of the above general formula (II) is used as the organic acid compatible with the resin and plasticizer, the addition amount of the amine of general formula (III) is preferably 0.01 to 2 parts by weight per 100 parts by weight of the poly(vinyl acetal) resin. At an addition amount below 0.01 part by weight, the preventive effect on the blushing due to moisture absorption may be insufficient. At an addition amount exceeding 2 parts by weight, the compatibility with the resin will be poor, and a transparency problem may arise or the interlayer film may be discolored. A more preferred range is 0.05 to 1 part by weight.

The organic acid compatible with the resin and plasticizer and the amine compatible with the resin and plasticizer used as a dispersant as mentioned above respectively take the form of ions, for example sulfonyl ion, carboxyl ion, phosphoryl ion, and ammonium ion. These ions act on the surface of the particulate metal salt in the poly(vinyl acetal) resin and bind the metal ion and counter ion constituting said metal salt. When the resin is kneaded prior to sheet formation, the metal salt carrying these ions are dispersed in the resin and, as a result, the metal salt in particulate form becomes smaller or disappear. Therefore, local aggregation of water molecules is prevented and, even when the poly(vinyl acetal) resin absorbs moisture, the interlayer film of the laminated glass can be prevented from blushing.

In the present invention, it is preferred that the interlayer film for laminated glass contain at least one salt selected from the group consisting of alkali metal salts and alkaline earth metal salts as a bond strength control agent.

Said alkali metal salts and alkaline earth metal salts include but are not limited to potassium salts, sodium salts, magnesium salts and so forth. As the salt-forming acid, there may be mentioned organic acids, for example carboxylic acids such as octylic acid, hexylic acid, butyric acid, acetic acid and formic acid; and inorganic acids such as hydrochloric acid and nitric acid.

Among the alkali metal salts and alkaline earth metal salts mentioned above, alkali metal salts of organic acids containing 5 to 16 carbon atoms and alkaline earth metal salts of organic acids containing 5 to 16 carbon atoms are preferred. More preferred are the magnesium salts of carboxylic acids or dicarboxylic acids containing 6 to 10 carbon atoms.

Said magnesium salts of carboxylic acids or dicarboxylic acids include but are not limited to magnesium 2-ethylbutyrate, magnesium valerate, magnesium hexanoate, magnesium heptanoate, magnesium octanoate, magnesium nonanoate, magnesium decanoate, magnesium glutarate and magnesium adipate, among others.

It is supposed that the magnesium salts of carboxylic acids or dicarboxylic acids containing 6 to 10 carbon atoms occur in the form of salts in the sheet without electrolytic dissociation, and attract water molecules, making it possible to suppress the bond strength between the interlayer film and glass, with the result that the penetration resistance of the product laminated glass can be improved. Furthermore, since they are distributed in high concentrations on the sheet surface without aggregation in the sheet, they show a bond strength modifying effect even in small amounts, without causing excessive blushing upon moisture absorption, therefore they are preferable.

Said alkali metal salts and alkaline earth metal salts preferably have a particle diameter of not more than 3 .mu.m, more preferably not more than 1 .mu.m. When said diameter exceeds 3 .mu.m, water molecules around the alkali metal salt and/or alkaline earth metal salt particles grow to a macroscopic size, with the result that the blushing becomes unfavorably remarkable in some instances.

The means for reducing the particle size of 3 .mu.m or less is not limited to any particular method. Thus, for example, there may be mentioned the method comprising using a compound readily soluble in the poly(vinyl acetal) resin and plasticizer as a bond strength control agent, the method comprising using a compound which is hardly soluble in the poly(vinyl acetal) resin and plasticizer but hardly aggregate in the poly(vinyl acetal) resin and plasticizer, and the method comprising combinedly using a dispersant or compatibilizing agent capable of dispersing said compounds.

When a poly(vinyl butyral) resin is used as the poly(vinyl acetal) resin and triethylene glycol 2-ethylbutyrate is used as the plasticizer, the compound readily soluble in the above formulation is, for example, an organic acid salt, such as magnesium octanoate, magnesium neodecanoate and magnesium adipate. These are suitably used either singly or in a combination of two or more species.

As the compound hardly soluble in the above formulation but hardly aggregating in the formulation, there may be mentioned inorganic acid magnesium salts such as magnesium chloride and magnesium nitrate. These are suitably used either singly or in a combination of two or more species.

The dispersant or compatibilizing agent capable of dispersing the compound hardly soluble in the formulation is not limited to any particular species but includes alcohols such as ethanol and octyl alcohol, and long-chain organic acids such as octanoic acid and nonanoic acid, among others. These are suitably used either singly or in a combination of two or more species.

Among the various methods mentioned above, the method comprising using a compound which is by itself readily soluble in the poly(vinyl acetal) resin and plasticizer is most preferred. The method comprising using a compound hardly aggregating in the poly(vinyl acetal) resin and plasticizer is next preferred.

When a diester compound is used as the plasticizer, it is preferred that the alkali metal salt and alkaline earth metal salt mentioned above have the same acid component structure as that of the diester compound. Owing to their having an acid component structure identical or similar to that of the diester compound used as the plasticizer, they can be present stably and uniformly dispersed in the sheet, hence will not undergo changes with the lapse of time.

When triethylene glycol di-2-ethylbutyrate (hereinafter referred to sometimes as "3GH") or dihexyl adipate (hereinafter referred to sometimes as "DHA") is used as the plasticizer, a metal salt of a carboxylic acid containing 5 or 6 carbon atoms is preferably used as a bond strength control agent, since, in that case, the decrease in the bond strength with the lapse of time between the interlayer film and glass can be prevented and the prevention of blushing and prevention of the decrease in the bond strength with the lapse of time can be simultaneously accomplished. When triethylene glycol di-2-ethylhexanoate (hereinafter referred to sometimes as "3GO") is used as the plasticizer, it is preferred, for the same reasons, that a metal salt of a carboxylic acid containing 6 to 8 carbon atoms be contained in the formulation. When tetraethylene glycol di-2-ethylhexanoate (hereinafter referred to sometimes as "4GO") is used as the plasticizer, it is preferred that a metal salt of a carboxylic acid containing 6 or 7 carbon atoms be contained in the formulation.

For preventing the above plasticized poly(vinyl acetal) resin as far as possible from undergoing heat-induced hydrolysis in the sheet forming step, the use of plasticizers less susceptible to hydrolysis such as plasticizers of the side chain type, such as 3GH, 3GO and 4GO, or of the adipate type, such as DHA, is preferred to the use of such plasticizers as triethylene glycol diheptanoate (3G7) and tetraethylene glycol diheptanoate (4G7).

Said 3GH has long been in use as a plasticizer in interlayer films with practically acceptable results and the organic acid constituent thereof is of the side chain type. Therefore, 3GH is more advantageous than 3G7, 4G7 and the like, which are of the straight chain type, in that it is less hydrolyzable. The above-mentioned 3GO and 4GO are advantageous in that they are higher in boiling point than 3GH, for instance, and therefore are less volatile in the sheet forming step or in the lamination step.

Said 3GH, 3GO, 4GO and DHA may be used singly or in combination with another plasticizer such as mentioned hereinafter. The mixing ratio of said 3GH, 3GO, 4GO and/or DHA to said other plasticizer is preferred that the amount of said other plasticizer be less than 50% by weight of the amount of said plasticizer(s) 3GH, 3GO, 4GO and DHA. When this ratio is over 50% by weight, the characteristic features of 3GH, 3GO, 4GO and DHA are sacrificed by said other plasticizer and, therefore, the effect of the bond strength control agent used in combination with them may not be expressed to a satisfactory extent.

The carboxylic acid metal salt to be used as the bond strength control agent, when the plasticizer in the interlayer film is specified as mentioned above, includes but is not limited to pentanoic acid (of 5 carbon atoms) metal salts, hexanoic acid (2-ethylbutanoic acid) (of 6 carbon atoms) metal salts, heptanoic acid (of 7 carbon atoms) metal salts, octanoic acid (of 8 carbon atoms) metal salts, and so forth. According to the plasticizer mentioned above, one, two or more of these are suitably used. The carboxylic acid may be of the straight chain type or of the side chain type.

When a metal salt of a carboxylic acid containing too small a number of carbon atoms is used, the interlayer film obtained will have an insufficient moisture resistance, which may allow the blushing phenomenon to occur widely. Conversely, if a metal salt of a carboxylic acid containing an excessively large number of carbon atoms is used, the decrease in the bond strength with the lapse of time between the interlayer film and glass may be insufficient.

The above-mentioned carboxylic acid metal salt as the bond strength control agent may be used independently or in combination with another bond strength control agent, for example a bond strength control agent of met