JPH02196808A - Terpolymer having excellent optical property - Google Patents

Abstract

PURPOSE:To obtain the subject copolymer useful as intermediate layer of laminated glass or laminated transparent plastics having excellent optical properties such as transparency in wide temperature range by subjecting specific ethylene/ vinyl acetate binary copolymer to uniform partial saponification. CONSTITUTION:An ethylene/vinyl acetate binary copolymer prescribed by (A) 46-53wt.% content of unit derived from vinyl acetate, (B) 1-20 g/10min MFI (MFI is melt flow index measured at 190 deg.C), (C) polydispersity Mw/Mn <=4.0 (Mw is weight-average molecular weight; Mn is number-average molecular weight) and (D) comonomer distribution of <=50mol% fraction of ethylene chain in triad measured by nucllar magnetic resonance of isotope carbon <13>C is uniformly subjected to partial saponification to afford the aimed ethylene/vinyl acetate/vinyl alcohol terpolymer prescribed by 12.4-15.2wt.% unit derived from vinyl alcohol and amorphous character having <=0.5cal/g enthalpy of crystal melting ( Hm).

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a terpolymer with excellent optical properties, and more specifically, a terpolymer with excellent optical properties consisting of ethylene/vinyl acetate/vinyl alcohol with a very limited composition. The present invention relates to a crosslinked copolymer with excellent optical properties and strength, and a crosslinked sheet obtained by crosslinking the terpolymer.

These terpolymers, crosslinked products, and crosslinked sheets exhibit extremely high performance as intermediate layers of laminated glass (laminated glass) and the like.

[Problems to be solved by conventional techniques and inventions] In recent years,
As the safety level of automobiles improves, windshield safety measures have become an absolute must to ensure the safety of passengers. In response to the demands of the times, the use of resin-reinforced double-layer safety glass for windshields is becoming a legal requirement in many countries around the world.

Currently, there are extremely strict standards for safety glass used in automobile windshields, such as the JASO standards in Japan.

Satisfying this standard while also satisfying cost requirements is an extremely difficult proposition.

However, there is a demand for materials that can be provided with superior economy and productivity while ensuring the safety of passengers.
It is not only limited to Japan, but now extends to the entire world.

To date, polyvinyl butyral has been used almost exclusively as the material for the interlayer of laminated automotive glass. Its major characteristics are its excellent transparency and high penetration resistance near room temperature, but its performance is not necessarily satisfactory. This polyvinyl butyral is
Although it exhibits high penetration resistance near room temperature, the penetration resistance is not necessarily satisfactory in a temperature range of 0°C or lower or in a temperature range of 80°C or higher. Furthermore, since softening is achieved by adding a large amount of plasticizer, there are considerable disadvantages associated with this.

By the way, ethylene/vinyl acetate/vinyl alcohol terpolymer (EVAVAL) is known to be excellent as a laminate material that can be used for glass and/or transparent synthetic resins, especially in terms of low-temperature properties.

US Pat. No. 3,923,757 discloses peroxide crosslinked EVAVAL. Also, US Pat. No. 3,378,515 describes EVAVAL crosslinked with aromatic diisocyanates.

Furthermore, U.S. Pat.
An adhesive film is disclosed in which EVAVAL is crosslinked by heating with electron beam irradiation or in the presence of a specific crosslinking agent. Further, although it is stated that the material has excellent properties over a wide temperature range, data that fully supports this is not disclosed.

According to the descriptions in these US patent specifications, the EVAVAL crosslinked material is said to be an attractive material because it has excellent low-temperature properties and a wide usable temperature range with plenty of room on the high-temperature side. However, this EVAVAL crosslinked product has not yet been widely used as a laminate material for safety glass in the industrial world. The reason for this is thought to be that when considering laminated glass having glass as layers on both sides, it is impossible to satisfy sufficiently high penetration resistance and sufficient transparency with this material.

On the other hand, regarding the physical properties of ethylene/vinyl acetate copolymers and their completely saponified products, see, for example, Journal of Polymer Science, Part A-1, Vol. 9, 3038-
3103 pages (Journal of Polymer
5science, Part A-1, Vol.
9P3083-3103), the relationship between the copolymer composition and the corresponding physical properties of binary copolymers of ethylene and vinyl acetate or vinyl alcohol is reported in detail.

However, it is almost impossible to infer the physical properties of a terpolymer such as EVAVAL from this report, and the reality is that there is relatively little knowledge regarding the relationship between the structure and physical properties of EVAVAL.

As mentioned above, the present inventors discovered a glass/glass intermediate layer (
Although there is a strong demand for materials with excellent performance as laminated safety glass, especially materials with penetration resistance, transparency, and appropriate adhesion, there are various broad points of view. In view of the fact that there is no material in practical use that satisfies sufficient performance, we conducted intensive research on EVAVAL, which is a material that is relatively easy to obtain in the industrial world. In particular, we deeply investigated the relationship between EVAVAL's manufacturing method, structure, and physical properties.

In the case of safety glass with glass layers on both sides, a polymeric material as an intermediate layer between the two glasses will play an extremely important role in order for the safety glass to exhibit high penetration resistance. Although it is easy to infer that this is the case, the details are not very clear.

The present inventors conducted repeated studies focusing on the properties of EVAVAL, particularly the fact that the tensile strength at break increases as the vinyl alcohol unit content increases, and found that an increase in the tensile strength at break leads to an increase in the energy for breaking the material. It was discovered that this also led to improved penetration resistance as a multi-layered laminated glass.

However, it has been found that such an improvement in penetration resistance also brings about an unfavorable peculiar optical behavior in EVAVAL when viewed as an intermediate layer for a windshield that requires high transparency.

For example, for EVAvAL, when the temperature was repeatedly raised and lowered between 20 and 130°C and the transparency was observed during that time, it was found that for a copolymer with a certain composition, there was a significant increase in temperature during the heating process. Although no optical changes were observed, a phenomenon was observed in which the haze suddenly increased in a specific narrow temperature range during the cooling process, and the material became transparent again upon further cooling. The unique haze increase behavior found here is hardly known so far, and is not mentioned at all in, for example, US Pat. No. 4,137,364.

Such unique haze behavior imparts strength to EVAVAL, even though it is not observed in ethylene/vinyl acetate copolymer (EVA) before hydrolysis or in EVA VA L, which has a relatively low hydrolysis rate. It has been found that this is possible in the area of relatively high vinyl alcohol content required for this purpose. On the other hand, the EVAVAL region with high interlayer suitability, which is necessary to improve the penetration resistance of laminated glass,
It was found to be in the area of high vinyl alcohol content.

U.S. Pat. No. 4,137,364 describes EVAV
It is noted that the electron beam crosslinked product of AL has a wider usable temperature range and superior properties compared to conventional materials. However, the examples disclosed herein are only examples of EVAVAL having a relatively low vinyl alcohol content, and there is no mention of the above-mentioned unique optical behavior. In other words, this unique optical behavior is explained in U.S. Pat.
This is a completely new phenomenon that could not have been predicted at the time of the invention of No. 137.364.

Taking advantage of this unexpected discovery, the present inventors conducted further research and investigated the properties of EVAVAL from every perspective in order to develop a material that can satisfy extremely high required characteristics, such as the interlayer of laminated glass for automobile windshields. Consideration was added from

As a result, EVAVAL with a limited structural range obtained by partially saponifying an ethylene/vinyl acetate copolymer with a very limited structural range as a starting material, or crosslinked products thereof, have been used to produce glass plates and synthetic materials. It has been found that it has extremely excellent properties as an intermediate layer (intermediate film) between a plurality of transparent plates made of resin plates. The present invention was completed based on this knowledge.

[Means to solve the problem]

That is, the present invention provides ethylene/vinyl acetate/
A vinyl alcohol terpolymer, wherein: i) the binary copolymer has a content of units derived from vinyl acetate of 46 to 53-t;
% ■ MFI is 1 to 20 g/10 minutes (However, MFI
is the melt flow index measured at 190''C.) ■'Polydispersity value M w / M n is 4.0 or less (However,
Mw represents a weight average molecular weight, and Mn represents a number average molecular weight. ) ■ It is defined by a comonomer distribution in which the ratio of ethylene chains in triads measured by nuclear magnetic resonance method of carbon-13c isotope is 50 mol % or less, and ii) the terpolymer is: ■ Vinyl The content of units derived from alcohol is 12.4
~15.2 wt% ■ Crystal fusion enthalpy (ΔHm) is 0.5 cal/
The object of the present invention is to provide a terpolymer with excellent optical properties characterized by being substantially amorphous and having a molecular weight of less than 100 g.

The present invention also provides a crosslinked copolymer and a crosslinked sheet obtained by crosslinking the above terpolymer.

The structure and composition of the ethylene/vinyl acetate binary copolymer used in the present invention are as described above. It can be characterized by the dispersion value (Mw/Mn) and the comonomer distribution determined by the nuclear magnetic resonance (C3C-NMR) method using the C13C isotope.

Here, (2) the content of units derived from vinyl acetate (vinyl acetate units) in the copolymer is 46 to 53 wt%, preferably 48 to 52 wt%. When an ungrooved copolymer with a vinyl acetate unit content of 46 wt% is used as a starting material,
The resulting terpolymer cannot achieve the objectives of the present invention from two points of view. One such case is that, although the transparency is sufficient, the strength is insufficient and the penetration resistance is insufficient when laminated with glass or synthetic resin. The other type is a case where the strength is sufficient but the transparency cannot be satisfied over a wide temperature range.

In any case, both strength and transparency cannot be sufficiently satisfied over a wide temperature range.

On the other hand, in the case of a copolymer having a vinyl acetate unit content exceeding 53-t%, a terpolymer which satisfies the haze properties of 1a can be obtained, but it is difficult to achieve both penetration resistance.

Next, this ethylene/vinyl acetate binary copolymer [2]
The MFI (measured at 190°C) is between 1 and 20 g/10 minutes, preferably between 2 and 12/10 minutes. MFI
If it exceeds 20 g/10 minutes, it is difficult to satisfy the penetration resistance while satisfying the haze characteristics of the terpolymer (EVAVAL) obtained by partially saponifying the terpolymer (EVAVAL) or its crosslinked product. The MFI of the binary copolymer as a starting material has a very large effect on the impact strength of the terpolymer obtained from the binary copolymer or its crosslinked product.

Moreover, M w / M n, which is the polydispersity value of the ethylene/vinyl acetate binary copolymer, is 4.0 or less, preferably 2.5 to 3.0. Mw/Mn is 4
．． If it exceeds 0, it is extremely difficult to strike a balance between penetration resistance and haze properties.

Furthermore, ■I3C- of the ethylene/vinyl acetate binary copolymer
In the comonomer distribution determined by the NMR method, it is important that the ratio of ethylene chains in the triad (i.e., the fraction of ethylene-ethylene-ethylene (EEE)) is 50 mol% or less, preferably 45 mol% or less. ，
When the ratio of EEE chains exceeds 50 mol%, it becomes extremely difficult to satisfy haze properties when a terpolymer or a crosslinked product thereof that satisfies penetration resistance is produced.

Ethylene/vinyl acetate binary copolymers that satisfy the extremely limited conditions described above can be produced by high-pressure copolymerization or solution copolymerization; Preferably 1 5 Q
Particularly preferred is production under a pressure of 0 to 3000 kg/cJ.

The terpolymer of the present invention can be obtained by uniformly partially saponifying the ethylene/vinyl acetate binary copolymer having the properties (1) to (4) above. The degree of saponification is as follows: (1) The content of units derived from vinyl alcohol is 12.4 to 15.
It should be within a range of 2 wt%. Vinyl alcohol unit content is 1 5. If it exceeds 2 ht%, the strength is satisfactory, but in many cases the haze characteristics cannot be satisfied.

That is, if the vinyl alcohol unit content becomes too high,
When a terpolymer or a crosslinked product thereof is heated to about 130° C. and the temperature is gradually lowered, there will be a temperature range where the haze increases rapidly during the temperature drop process. In addition, with an ungrooved copolymer having a vinyl alcohol unit content of 12.4 wt%, a crosslinked sheet with excellent haze properties can be obtained, but a crosslinked sheet that provides a laminate with high penetration resistance when laminated on glass is As a result of various studies, it has become clear that this is not the case. A more objective index for determining the lower limit of the vinyl alcohol content is the vinyl alcohol unit content that allows the terpolymer to maintain a tensile strength at break of at least 200 kg/cd.

Furthermore, the terpolymer of the present invention is substantially amorphous, and its objective standard is differential scanning calorimetry (DS).
C) (Differential Scanning
The enthalpy of crystal fusion (Δ) 1 m) of the terpolymer measured by Caloris + eter) is 0.5 cal/
Indicates a value of g or less.

The terpolymer of the present invention has the above-mentioned properties, and there are various methods for producing it, but preferably the above-mentioned binary copolymer is partially saponified in a homogeneous solution state in the presence of a solvent. You can get it by doing this. Representative examples of these methods include hydrolysis or transesterification in the presence of an acid or alkali catalyst. For example, a transesterification reaction is carried out using an acid or an alkali as a catalyst in a mixed solvent consisting of alcohol and a good solvent for both the starting material, the binary copolymer, and the EVAVAL to be produced, and which dissolves both copolymers. By doing so, uniform partial saponification can be achieved relatively easily.

In order to obtain the terpolymer having excellent optical properties of the present invention, both the ethylene/vinyl acetate binary copolymer used for saponification and the terpolymer produced by partial saponification must undergo a saponification reaction. When performing this, it is important to maintain a homogeneous solution state. If the saponification reaction is carried out in a non-uniform state, the resulting terpolymer will be structurally non-uniform, making it difficult to achieve both optical properties and strength, especially when crosslinked.

The reason why the terpolymer of the present invention cannot be obtained due to the non-uniform saponification reaction is not necessarily clear, but it is speculated as follows.

That is, for example, if pellets of ethylene/vinyl acetate binary copolymer are dispersed in a solvent such as methanol and alkaline saponification is carried out, even if the overall degree of saponification reaches the target value, the surface of the pellets In some areas, saponification progresses too much, and in the center of the pellet, saponification does not progress, resulting in insufficient saponification.

The thus obtained terpolymer (EVAVAL)
As a result, EVAVAL has an extremely wide composition distribution, and is not only inferior in terms of temperature dependence of haze, but also not very high in strength.

The terpolymer thus obtained (EVAVAL)
Although it is flexible, it has a high breaking strength of 200
Exhibits high breaking strength of kg/c+j or more.

It is also characterized by little variation in optical properties over a wide temperature range, with a haze value of 1 in the temperature range of 20 to 130°C.
It is as follows. The characteristics of such terpolymers are that they not only have excellent strength and optical properties even though they are not crosslinked, but also contain a high amount of units derived from vinyl alcohol, so they can be used for glass and/or Intermediate layer for transparent laminates sandwiched between multiple transparent plates made of synthetic resin plates (
It is extremely useful as an interlayer film material. In particular, it is useful as an intermediate layer material for a laminate made of glass and synthetic resin, or synthetic resin and synthetic resin, which are not required to have very strict heat resistance.

If the terpolymer (EVAVAL) of the present invention is further crosslinked if necessary, it not only has excellent optical properties but also has even better strength. This crosslinking causes the terpolymer to be exposed to ionizing radiation (electron beam, T-ray,
The process proceeds by irradiation with X-rays (such as X-rays) or by adding a crosslinking agent and causing a reaction. Among these, it is particularly preferable to crosslink the terpolymer by irradiation with ionizing radiation such as electron beams, and the degree of crosslinking is not particularly limited and may vary depending on the purpose of use and the shape of the crosslinked product. It may be selected as appropriate depending on the situation. For example, when a crosslinked sheet of a terpolymer is applied to an intermediate layer of laminated glass for automobiles, it is preferably crosslinked so that the gel fraction is J5wt% or more. Here, the gel fraction is a value obtained by performing Soxhlet extraction with boiling toluene for 5 hours.

In addition, the terpolymer crosslinked sheet obtained in this way has excellent optical properties, but specifically, the terpolymer crosslinked sheet has excellent optical properties.
The haze value measured in a temperature range of ~130'C is at most 1, preferably 0.7 or less. Considering that a cross-linked sheet with a haze value exceeding 1 is laminated with glass and used as safety glass for automobile windshields, it may cause eyestrain due to the reflection of light from the outside, especially when driving at night. Undesirable. Further, in order to obtain a crosslinked sheet with excellent penetration resistance, it is desirable that the tensile strength at break is 250 kg/cn1 or more, and particularly preferably 300 kg/c4 or more.

When producing such a crosslinked sheet, the terpolymer is processed by conventional extrusion molding means prior to crosslinking.
It is preferable to process it into a sheet. The molding temperature here is usually 80 to 200°C, but 100 to 150°C.
C is preferred.

Such a crosslinked sheet can be produced by crosslinking the terpolymer by irradiating it with ionizing radiation such as an electron beam after forming the terpolymer into a sheet using normal extrusion means or simultaneously with sheet forming. Obtainable. The thickness of the sheet is typically 0.2 to 1.0++ ua.

The irradiation dose of ionizing radiation is expressed as a function of irradiation time, and the required irradiation dose here is 15 to 25 Mrad.
The most suitable value is around 20 Mrad. The objective standard for determining the irradiation dose of ionizing radiation is that when the cross-linked sheet is subjected to a high-speed impact tester to determine the absorbed energy during penetration, the absorbed energy value is near the maximum value, The preferred range is the irradiation amount ±3 Mrad.

Equipment used for crosslinking, such as electron beam irradiation equipment, is mostly characterized by the acceleration voltage of the electron beam, and the acceleration voltage is 2.
00 to 1.000 kV, and preferably 300 to 900 kV in order to uniformly proceed with crosslinking to the inside of the sheet.

〔Example〕

Next, the present invention will be explained in more detail with reference to Examples and Comparative Examples.

Examples 1 to 3 Ethylene/vinyl acetate copolymer (EVA) with a vinyl acetate unit content of 52 wt% (Mw/Mn = 2.7 comonomer distribution (triad EEE fraction) = 42.0 mol%, M
After uniformly dissolving FI = 2.8 g/10 min] in a toluene/methanol mixed solvent (volume ratio = 1/1), this homogeneous solution was held at 60 °C and a predetermined amount of sodium hydroxide was added at 70°C. The methanol solution was gradually added at a rate that did not cause precipitation of the copolymer.

The reaction was continued for 3 hours at the boiling point of the mixed solvent, and after the reaction was completed, acetic acid in an amount of 1.1 times the mole of sodium hydroxide used was added to the reaction mixture, and stirring was continued for 10 minutes. A small amount of water was added to the reaction solution, and the reaction solution was cooled to 40° C., and then, while stirring the reaction solution well, acetone in the same volume as the solution was added to precipitate the polymer. After filtering out the precipitated powdery polymer, an acetone/water mixed solvent (volume ratio = 6
/1) and dried under reduced pressure under heat to obtain a solvent-free ethylene/vinyl acetate/vinyl alcohol 39 copolymer (EVAVAL).

Analysis and physical property measurements of the obtained terpolymer revealed the following properties.

(a) Weight ratio of each unit of ethylene/vinyl acetate/vinyl alcohol -54,6/31.1/14.3 (measured by infrared absorption analysis) (b) Enthalpy of crystal fusion (ΔHm) = 0.27c
al/g (measured by differential scanning calorimetry (DSC); heating rate 10'C/min) (C) Tensile breaking strength = 259 kg/c11! The EVAVAL obtained as described above was compression molded using a mold whose surface was coated with Teflon in a hot compression press at 120°C under a pressure of 20 kg/c+fl to a thickness of 0.76 mm. A terpolymer sheet was created.

Next, an electron beam irradiation device (manufactured by Nissin High Voltage ■, scanning type, EP) with an accelerating voltage of 750 kV was applied to the sheet.
A crosslinked terpolymer sheet was prepared by irradiating the sample with an electron beam in the air to a predetermined irradiation dose.

Table 1 shows the analysis results and physical property measurement results of the terpolymer sheet and crosslinked terpolymer sheet.

As is clear from Table 1, the terpolymer of the present invention and its electron beam crosslinked product exhibit high breaking strength and stably maintain high transparency over a wide temperature range.

Application Examples 1 to 4 Ternary copolymer sheet produced in Example 1 and Example 1
A laminated glass (laminated glass) using the crosslinked sheet as an intermediate layer was prepared using the crosslinked sheet manufactured in 3 to 3, and its physical properties were measured.

That is, the terpolymer sheet produced in the above example or its crosslinked sheet was sandwiched between two sheets of glass with a thickness of 2M, and the terpolymer sheet or its crosslinked sheet was sandwiched between two sheets of glass having a thickness of 2M, and the terpolymer sheet or the crosslinked sheet thereof was heated to 20K using a pressure press set at a surface temperature of 120°C.
The laminated glass was created by heating and bonding at a pressure of g/cffl for 10 minutes. The laminated glass thus produced was subjected to a penetration resistance test in accordance with JISR3212. As a result, all of these laminated glasses passed the 4m penetration test. Moreover, the amount of glass peeled at that time was 8 g for each laminated glass using the crosslinked sheets manufactured in Examples 1 to 3.

They were 12g and 11g. The physical properties of these laminated glasses are shown in Table 2.

Examples 4 to 7 Examples 1 to 3 above except for the conditions shown in Table 1.
A terpolymer sheet and a crosslinked sheet thereof were prepared in the same manner as above. The analysis results of this product are shown in Table 1.

Application Examples 5 to 12 Using the terpolymer sheets and crosslinked sheets thereof produced in Examples 4 to 7 above, laminated glasses having these as intermediate layers were created in the same manner as Application Examples 1 to 4 above. Its physical properties were measured. The results are shown in Table 2.

Comparative Examples 1 to 8 Ethylene/
A sheet of vinyl acetate/vinyl alcohol terpolymer and an electron beam crosslinked sheet thereof were prepared in the same manner as in the above example, and a laminated glass was made using the same in the same manner as in the above application example. These physical properties are shown in Table 3.

(The following is a blank space) (Effects of the invention) The terpolymer of the present invention has excellent optical properties such as transparency over a wide temperature range, and can be used as an intermediate layer in laminated glass and laminated transparent plastics (acrylic resin, polycarbonate resin, etc.). The crosslinked product or sheet of this terpolymer has excellent optical properties over a wide temperature range as well as mechanical strength. It is particularly effective as an intermediate layer in laminated glass.

Patent applicant: Showa Denko Co., Ltd.

Claims (4)

[Claims] (1) An ethylene/vinyl acetate/vinyl alcohol ternary copolymer obtained by uniformly partially saponifying an ethylene/vinyl acetate binary copolymer, the binary copolymer comprising: [1] The content of units derived from vinyl acetate is 46-53w
t% [2] MFI is 1 to 20 g/10 min (However, MFI is the melt flow index measured at 190°C.) [3] Polydispersity value Mw/Mn is 4.0 or less (However, Mw is the weight (Mn indicates the average molecular weight, and Mn indicates the number average molecular weight.) [4] Specified by a comonomer distribution in which the ratio of ethylene chains in the triad is 50 mol% or less, as measured by the nuclear magnetic resonance method of the isotopic carbon^1^3C. and ii) the terpolymer has a content of units derived from [5] vinyl alcohol of 12.
4 to 15.2 wt% [6] Crystal melting enthalpy (ΔHm) is 0.5 cal
1. A terpolymer with excellent optical properties, characterized in that it is substantially amorphous and has a molecular weight of less than /g. (2) A crosslinked copolymer having excellent optical properties and strength, obtained by crosslinking the terpolymer according to claim 1. (3) A crosslinked copolymer sheet with excellent optical properties and strength, obtained by irradiating the terpolymer according to claim 1 with ionizing radiation to crosslink it to a gel fraction of 55% or more. (4) The crosslinked copolymer sheet according to claim 3, wherein the ionizing radiation is an electron beam.