JPS6329907B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a water-resistant adhesive, and in particular to an adhesive comprising a synthetic rubber latex and an isocyanate compound system having excellent weight increase stability and viscosity stability. More specifically, the present invention relates to an adhesive for plywood or wood for secondary processing of plywood, which does not contain formaldehyde (hereinafter abbreviated as formalin), and which requires particularly high water resistance. Currently, urea resins, melamine-urea cocondensation resins, phenolic resins, and the like are mainly used as adhesives for plywood or secondary processing of plywood, for example. These adhesives are widely used because they are inexpensive and have good water resistance, but recently the formalin that remains in these adhesives has caused a poor environment for plywood manufacturing work, and the plywood made using these adhesives has become Formalin is released from manufactured furniture and houses, and it has become a problem all over the world. Recently, various attempts have been made to reduce the release of formalin from urea resins, etc., and considerable results have been achieved. Due to variations in the rate and heat and pressure conditions, there is a high possibility that the adhesive will not be cured completely, which may cause formalin release from the product. On the other hand, there are adhesives for plywood that do not contain formalin at all, such as protein-based and vinyl acetate resin-based adhesives, but these are not generally used because of their poor water resistance. In addition, non-formalin-based synthetic rubber latex (hereinafter referred to as latex) is used as an adhesive for plywood.
Or polyvinyl alcohol (hereinafter referred to as PVA)
Examples of using isocyanate-based adhesives are, for example, Japanese Patent Publication No. 55-18759 and Japanese Patent Publication No. 1875-1875.
69137, JP-A-50-69138, JP-A-50-69139, etc. However, the latex used in these methods is mainly used as coated paper, and is also used in other products such as fiber processing and carpet backing agents. In particular, latex for coated paper, which accounts for most of its uses, must satisfy physical properties such as gloss, ink receptivity, and blister properties, as well as coating properties and flowability during coating. From the viewpoint that the properties must be satisfied, the average particle diameter of the latex should be 0.01~
Most of them have a particle size of 0.23μ, and no study has been conducted at least from the viewpoint of particle size. Therefore, it is not compatible with PVA, and adhesive reinforcement,
Adding extenders and fillers, which are used to increase viscosity, adjust fluidity, and reduce costs, may result in excessive viscosity or loss of fluidity, resulting in restrictions on the amount of fillers added. It was often. In addition, the stability of the product as an adhesive may be impaired, and if the isocyanate compound used as a crosslinking agent is distributed, the pot life may be extremely shortened.
It had drawbacks such as being impractical. Therefore, it is often necessary to add surfactants, wetting agents, and dispersants, resulting in a decrease in the water resistance of the adhesive and at the same time, a foaming phenomenon occurs, making it impractical. The present invention provides that the latex used in an adhesive system consisting of a main ingredient consisting of latex, polyvinyl alcohol, an extender and a filler, and a crosslinking agent which is an isocyanate compound has excellent miscibility with the extender and filler. In addition, it has excellent compounding and bulking properties that allow these to be freely blended, and furthermore, it has excellent product stability, and is also excellent in pot life and stability in terms of thickening over time after the isocyanate compound, which is a crosslinking agent, is added and blended. Furthermore, the object of the present invention is to provide an adhesive having excellent adhesive performance, particularly water resistance. As a result of intensive research to achieve this, the inventors of the present invention have found that the miscibility of latex with extenders and fillers, compounding and increasing properties, product stability, water resistance, etc. are determined by the average particle diameter of latex. When the average particle size is 0.25μ or more,
We have discovered that the above-mentioned drawbacks can be eliminated and completed the present invention. That is, the present invention comprises a base material consisting of a modified or unmodified synthetic rubber latex, polyvinyl alcohol, an extender and a filler, an isocyanate compound,
Alternatively, the present invention is a water-resistant adhesive comprising a crosslinking agent which is an isocyanate-based polymer, characterized in that the average particle diameter of the synthetic rubber latex is 0.25μ or more. When using the above-mentioned adhesive of the present invention, the above-mentioned expansion properties of the extender and filler, pot life after addition and blending of the isocyanate compound,
It is an adhesive of extremely high practical value, with excellent stability such as thickening over time, and excellent adhesive performance, especially water resistance. The average particle diameter of the synthetic rubber latex employed in the present invention will be explained in detail below. The average particle diameter of the synthetic rubber latex referred to in the present invention can be measured by measurement methods such as electron micrograph method, light scattering method, centrifugal sedimentation method, and soap titration method. A combination of two methods was used: photography and light scattering. Next, the miscibility and compounding capacity of extenders and fillers as used in the present invention means that extenders and fillers such as wheat flour, calcium carbonate, talc, clay, and kaolin are added to an adhesive system at a certain ratio. When blended, if the initial viscosity of the resulting adhesive is on the low viscosity side, it is considered good, meaning that there is room for increase in volume, and it also means that the initial viscosity of the adhesive does not change over time and is stable. do. The initial viscosity of the finished product is generally in the range of 50 to 1000 poise, and in practice, the range of 80 to 300 poise is targeted. After the isocyanate compound, which is a crosslinking agent, is blended, there must be little change in viscosity over time, and the pot life must be stable. From this point of view, according to the findings of the present inventors, changes in the miscibility of extenders, fillers, etc., as well as compounding increaseability, occur when the average particle diameter of the synthetic rubber latex used reaches 0.25μ. noticeable.
If the average particle size is 0.25μ or less, the initial viscosity of the adhesive mixture will be several hundred poise or more, and the viscosity will change over time for less than a month. It loses its fluidity over time. Furthermore, in terms of adhesive performance, the water-resistant adhesive performance in particular deteriorates significantly. On the other hand, if the average particle size is 0.25μ or more,
As the average particle size increases, the interfacial free energy of the entire synthetic rubber latex particle decreases, resulting in increased stability.Also, the amount of emulsifier adsorbed per unit number of latex particles increases, resulting in stability. It is thought that the miscibility of the above-mentioned extenders and fillers and the ability to increase the amount by blending are increased by increasing the properties, and the larger the average particle diameter is, the more preferable it is. However, general methods for enlarging the particles of synthetic rubber latex include reducing the amount of emulsifier used during production, or adding inorganic salts such as potassium phosphate, potassium sulfate, and sodium phosphate. However, the polymerization reaction time is generally long and, for example, the average particle diameter is
Several days of reaction time are required to obtain a synthetic rubber latex having a particle diameter of 0.5μ or more. Therefore, from a practical standpoint such as industrial productivity, the average particle diameter of the synthetic rubber latex referred to in the present invention is 0.25 to 0.25.
A range of 0.45μ is preferred. The solid content concentration in the synthetic rubber latex is usually 40 to 60% by weight. The modified or unmodified type latex with an average particle diameter of 0.25μ or more used in the present invention is:
The main components are typified by open-chain aliphatic conjugated dienes, vinyl aromatic compounds, and ethylenically unsaturated carboxylic acid esters. Specifically, the open chain aliphatic conjugated diene includes butadiene, isoprene, 2-chlorobutadiene, etc., but butadiene is particularly preferred. Usually, this butadiene is used in a range of 25 to 60% by weight of the total monomers. In addition, examples of vinyl aromatic compounds include styrene,
Examples include α-methylstyrene and vinyltoluene, with styrene being particularly preferred. Typically, the vinyl aromatic compound is used in an amount ranging from 40 to 75% by weight of the total monomers. In addition, examples of ethylenically unsaturated carboxylic acids include methyl methacrylate, acrylonitrile,
Examples include methacrylic esters, and methyl methacrylate is particularly preferred. Usually, this ethylenically unsaturated carboxylic acid is used in an amount of 40 to 75% by weight of the total monomers. In particular, this monomer may be used in place of the open-chain aliphatic conjugated diene, or mixtures thereof may also be used. The above-mentioned monomers constitute the main components of latex, but other functional group monomers include acrylic acid, methacrylic acid, crotonic acid, itaconic acid, fumaric acid, maleic acid, and the like. Furthermore, examples of monomers having an amide group include acrylamide and methacrylamide. Furthermore, examples of monomers having a hydroxyl group include hydroxyethyl acrylate, hydroxymethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, and hydroxypropyl methacrylate. Furthermore, as a monomer having a glycidyl group,
These include glycidyl acrylate, glycidyl methacrylate, and acrylic glycidyl ether.
In addition, acrolein, p-styrene sulfonic acid, etc. are also used. These functional group-imparting monomers are usually used in an amount of 0.1 to 10% by weight of the total monomers. Incidentally, the concentration of the latex is usually in the range of 40 to 60% by weight. The polymerization method of the latex for use in the present invention will be described in detail in Reference Examples and Examples described later. The polyvinyl alcohol used in the present invention refers to ordinary partially or completely saponified PVA or PVA derivatives, and the degree of polymerization and saponification of these are not particularly limited, but in particular, the degree of polymerization is 300 to 2500. , one with a saponification degree of 80 to 100 mol% is preferable. The concentration of PVA in the adhesive is arbitrary, but is in the range of 1 to 15% by weight, preferably 3 to 8% by weight. The extender used in the present invention basically not only functions to increase the volume, but also reacts with other components of the adhesive, especially isocyanate compounds, and
It also functions to impart water resistance and initial adhesiveness to the adhesive. Wheat flour, starches, defatted soybean flour, blood meal, etc. can be used as bulking agents, but among these, wheat flour and starches are imparted with water resistance by isocyanate compounds, and are gelatinized in cold water. This is preferable because it becomes gelatinized and viscous by heating during adhesion. Inorganic fillers such as clay, kaolin, talc, and calcium carbonate are used as fillers, but organic fillers such as wood flour and walnut shell powder can also be used. The blending method and blending ratio of these extenders and fillers vary depending on the purpose of use of the adhesive.
Basically latex or latex
The appropriate proportion of the PVA aqueous solution is 10 to 70% by weight, especially the range of 20 to 40% by weight of the plywood adhesive. Further, these extenders and fillers may be used alone or in combination, but it is preferable to use the extenders and fillers at the same time. On the other hand, the isocyanate compound or polymer thereof used in the present invention may be any compound as long as it yields polyurethane, such as tolylene diisocyanate (hereinafter abbreviated as TDI), hydrogenated TDI, Typical polyisocyanates that can be used include methylolpropane (TMP)-TDI adduct, triphenylmethane triisocyanate (TTI), diphenylmethane diisocyanate (MDI), hydrogenated MDI, and hexamethylene diisocyanate addition condensate. It is also possible to use a method of mixing polyisocyanate and polyol, that is, using a polyol such as polyester mixed with an excessive amount of the above-mentioned isocyanate compound. It is also possible to use a prepolymer system, i.e., an NCO-terminated prepolymer prepolymerized with a polyol and an excess of polyisocyanate, or an OH-terminated prepolymer prepolymerized with an excess of polyol when using an excess of polyisocyanate as described above. It may be used by adding it to. Particularly preferred among these isocyanate compounds and polymers are TMP-TDI adducts,
It is MDI. The blending ratio of the isocyanate compound or its polymer is in the range of 5 to 50% by weight based on the solid content in the adhesive. The adhesive of the present invention can be used for bonding materials where at least one of the materials to be bonded is ordinary wood, as well as baseboards for plywood, precious wood for veneer plywood, single wood for parquet plywood, wood for overlay plywood, and the like. Other adherends that can be bonded to wood include paper, textile products, synthetic resins, inorganic boards, and metals. When using the adhesive of the present invention, it is possible to achieve sufficient adhesion with just room-temperature adhesion (cold press); however,
Furthermore, if a short-term rise in absolute adhesive performance is expected, thermopressure bonding is of course possible. Next, the present invention will be further explained by reference examples and examples. In the following, parts and percentages are by weight unless otherwise specified. Reference Example 1 Manufacture of latex: 85 parts of water, 0.9 parts of potassium persulfate, 0.5 parts of potassium phosphate, and ethylenediaminetetraacetic acid were placed in a pressurized reactor (hereinafter simply referred to as the reactor) equipped with a nitrogen-substituted stirrer. 0.06 part of sodium and 0.06 part of sodium alkylbenzenesulfonate were charged, and the mixture was stirred and heated. Meanwhile, 35 parts of butadiene and 65 parts of styrene were charged into a monomer preparation tank, and an aqueous solution of 0.45 parts of sodium alkylbenzenesulfonate dissolved in 45 parts of water was charged into an emulsifier aqueous solution tank, and both were sent to an emulsifier to emulsify and emulsify the monomer. adjusted. When the temperature inside the reactor reached 65°C, the emulsifying monomer was continuously introduced into the reactor, and the introduction was completed in 7 hours while maintaining the temperature inside the reactor at 70°C. . Thereafter, the reaction was continued for an additional 6 hours. The polymerization rate was 99%. The polymer obtained by the above manufacturing method (hereinafter referred to as latex) was neutralized with 8% ammonia water to reduce the pH.
Adjusted to 9.0. Next, unreacted monomers were removed from this latex by a conventional steam distillation method, and the latex was further concentrated under reduced pressure to adjust the solid content to 48%. The average particle diameter of the latex obtained here was 0.25 μm as measured by electron microphotography. Reference Example 2 A latex was obtained using the same polymerization method as in Reference Example 1, except that the amount of sodium alkylbenzenesulfonate initially charged into the reactor was changed to 0.04 parts. The average particle diameter of the obtained latex was 0.32μ as measured by electron microscopy. Reference Example 3 A latex was obtained using the same polymerization method as in Reference Example 1, except that the amount of sodium alkylbenzenesulfonate initially charged into the reactor was changed to 0.03 parts. The average particle diameter of the obtained latex was 0.41 μm as measured by electron microscopy. Reference Example 4 A latex was obtained using the same polymerization method as in Reference Example 1, except that 0.05 part of sodium alkylbenzenesulfonate was initially charged into the reactor. The average particle diameter of the obtained latex was 0.21 μm as measured by electron microscopy. Reference Example 5 A latex was obtained using the same polymerization method as in Reference Example 1, except that 0.3 parts of potassium phosphate was initially charged into the reactor. The average particle diameter of the obtained latex was 0.21 μm as measured by electron microscopy. Reference Example 6 A latex was obtained using the same polymerization method as in Reference Example 1, except that 1.0 part of potassium phosphate was initially charged into the reactor.
The average particle size of this product was 0.27μ. Reference Example 7 A latex was obtained using the same polymerization method as in Reference Example 1, except that 1.5 parts of potassium phosphate was initially charged into the reactor.
The average particle size of this product was 0.35μ. Reference Example 8 In the same polymerization method as in Reference Example 1, the monomer charges were 34 parts of butadiene and 65 parts of styrene.
A latex was obtained in exactly the same manner except that 1 part and 1 part of methacrylic acid were used. The average particle diameter was 0.26μ. Reference Example 9 Using the same polymerization method as in Reference Example 1, the monomer charges were changed to 33 parts of butadiene, 65 parts of styrene, 0.5 parts of methacrylic acid, 0.5 parts of acrylic acid, and 1 part of 2-hydroxyethyl acrylate. A latex was obtained using the same procedure except for the following. The average particle size was 0.25μ. Example 1 (1) Polyvinyl alcohol aqueous solution (Kuraray KK
(product name, 217, solid content adjusted to 15.4% by weight)
100 parts, calcium carbonate (manufactured by Maruo Calcium,
Product name: Super SS) 60 parts, sodium hexametaphosphate 0.5 parts, antifoaming agent (dibutyl phthalate)
0.3 part was blended and stirred to obtain a blend for evaluating the physical properties of the water-resistant adhesive of the present invention. (below,
This mixture is abbreviated as masterbatch). The viscosity of this masterbatch at 25°C measured by a Bruckfield rotational viscometer (Model BH) was 300 poise using an NO6 rotor and 10 rpm. (2) Masterbatch obtained in Example 1-(1) above
To 100 parts, 50 parts of latex having various average particle diameters shown in Table 1 below are blended and stirred to form a compound ( (hereinafter abbreviated as main agent) was obtained. Changes in viscosity of the base agent thus obtained were monitored after 5 minutes, 7 days, and 30 days. In this case, the conditions for leaving for 7 days and 30 days are as follows. The base ingredients obtained under each condition were placed in a polyethylene bottle (No. 5) with a stopper and allowed to stand at a temperature of 40°C, and the viscosity was measured again under the above-mentioned conditions. The results are shown in Table-1. (3) Furthermore, a diphenylmethane-4,4'-diisocyanate-based compound (manufactured by Mitsui Nisso Urethane KK, product name: MDI-CR-200)
15 parts were added and mixed by stirring to obtain a water-resistant adhesive of the present invention. a The viscosity change of the adhesive obtained in Example 1-(3) above was tracked after 5 minutes and 60 minutes. The results are shown in Table-2. b Next, the adhesive obtained in Example 1-(3)-b above was subjected to an adhesive performance test under the following adhesive working conditions based on JIS-K-6802. (1) Bonding work conditions Material type: Hemlock 200×80×15m/m Moisture content: 12
~16% Coating amount 300g/ ^m2 Apply with two spatulas Open assembly time 1 minute or less Closed assembly time 15 minutes or less Clamping pressure 12.3Kg/ ^cm2 Clamp with a press at room temperature, and after 5 minutes, clamp by hand Tighten,
It was left to stand at a temperature of 20°C for 23 hours. Curing After the above-mentioned clamping, the clamp was released and the sample was cured at a temperature of 20°C for 7 days. (2) Adhesive Performance Test (Compression Shear Adhesive Strength) As mentioned above, the performance was evaluated based on JIS.K-6802 under normal conditions (abbreviated as T-) and repeated boiling (abbreviated as T-). The above performance evaluation results are shown in Table 3.

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Claims (1)

[Claims] 1. In an adhesive consisting of a main ingredient consisting of modified or unmodified synthetic rubber latex, polyvinyl alcohol, an extender and a filler, and a crosslinking agent which is an isocyanate compound or an isocyanate polymer, the average particle diameter of the synthetic rubber latex is
A water-resistant adhesive characterized by a thickness of 0.25μ or more.